Babcock Amp Wilcox Co Steam Its Generation and Use

Steam, Its Generationand Use

Babcock & Wilcox Co.

Release date: 2007-09-18Source: Bebook

STEAM

ITS GENERATION AND USE

[Illustration]

THE BABCOCK & WILCOX CO. NEW YORK

Thirty-fifth Edition

4th Issue

Copyright, 1919, by The Babcock & WilcoxCo.

* * * * *

Bartlett Orr Press

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[Illustration: Wrought-steel VerticalHeader Longitudinal Drum Babcock &Wilcox Boiler, Equipped with Babcock &Wilcox Superheater and Babcock & WilcoxChain Grate Stoker]

THE EARLY HISTORY OF THEGENERATION AND USE OF STEAM

While the time of man's first knowledgeand use of the expansive force of the vaporof water is unknown, records show thatsuch knowledge existed earlier than 150 B.C. In a treatise of about that time entitled"Pneumatica", Hero, of Alexander,described not only existing devices of hispredecessors and contemporaries but alsoan invention of his own which utilized theexpansive force of steam for raising waterabove its natural level. He clearlydescribes three methods in which steammight be used directly as a motive ofpower; raising water by its elasticity,elevating a weight by its expansive powerand producing a rotary motion by itsreaction on the atmosphere. The thirdmethod, which is known as "Hero's

engine", is described as a hollow spheresupported over a caldron or boiler by twotrunnions, one of which was hollow, andconnected the interior of the sphere withthe steam space of the caldron. Two pipes,open at the ends and bent at right angles,were inserted at opposite poles of thesphere, forming a connection between thecaldron and the atmosphere. Heat beingapplied to the caldron, the steamgenerated passed through the hollowtrunnion to the sphere and thence into theatmosphere through the two pipes. By thereaction incidental to its escape throughthese pipes, the sphere was caused torotate and here is the primitive steamreaction turbine.

Hero makes no suggestions as toapplication of any of the devices hedescribes to a useful purpose. From thetime of Hero until the late sixteenth and

early seventeenth centuries, there is norecord of progress, though evidence isfound that such devices as were describedby Hero were sometimes used for trivialpurposes, the blowing of an organ or theturning of a skillet.

Mathesius, the German author, in 1571;Besson, a philosopher and mathematicianat Orleans; Ramelli, in 1588; Battista DeliaPorta, a Neapolitan mathematician andphilosopher, in 1601; Decause, the Frenchengineer and architect, in 1615; andBranca, an Italian architect, in 1629, allpublished treatises bearing on the subjectof the generation of steam.

To the next contributor, Edward Somerset,second Marquis of Worcester, isapparently due the credit of proposing, ifnot of making, the first useful steamengine. In the "Century of Scantlings and

Inventions", published in London in 1663,he describes devices showing that he hadin mind the raising of water not only byforcing it from two receivers by directsteam pressure but also for some sort ofreciprocating piston actuating one end of alever, the other operating a pump. Hisdescriptions are rather obscure and nodrawings are extant so that it is difficult tosay whether there were any distinctlynovel features to his devices aside fromthe double action. While there is no directauthentic record that any of the devices hedescribed were actually constructed, it isclaimed by many that he really built andoperated a steam engine containingpistons.

In 1675, Sir Samuel Moreland wasdecorated by King Charles II, for ademonstration of "a certain powerfulmachine to raise water." Though there

appears to be no record of the design ofthis machine, the mathematical dictionary,published in 1822, credits Moreland withthe first account of a steam engine, onwhich subject he wrote a treatise that isstill preserved in the British Museum.

[Illustration: 397 Horse-power Babcock &Wilcox Boiler in Course of Erection at thePlant of the Crocker Wheeler Co.,Ampere, N. J.]

Dr. Denys Papin, an ingenious Frenchman,invented in 1680 "a steam digester forextracting marrowy, nourishing juicesfrom bones by enclosing them in a boilerunder heavy pressure," and findingdanger from explosion, added acontrivance which is the first safety valveon record.

The steam engine first became

commercially successful with ThomasSavery. In 1699, Savery exhibited beforethe Royal Society of England (Sir IsaacNewton was President at the time), amodel engine which consisted of twocopper receivers alternately connected bya three-way hand-operated valve, with aboiler and a source of water supply. Whenthe water in one receiver had been drivenout by the steam, cold water was pouredover its outside surface, creating a vacuumthrough condensation and causing it to fillagain while the water in the otherreservoir was being forced out. A numberof machines were built on this principleand placed in actual use as mine pumps.

The serious difficulty encountered in theuse of Savery's engine was the fact that theheight to which it could lift water waslimited by the pressure the boiler andvessels could bear. Before Savery's engine

was entirely displaced by its successor,Newcomen's, it was considerablyimproved by Desaguliers, who applied thePapin safety valve to the boiler andsubstituted condensation by a jet withinthe vessel for Savery's surfacecondensation.

In 1690, Papin suggested that thecondensation of steam should beemployed to make a vacuum beneath acylinder which had previously been raisedby the expansion of steam. This was theearliest cylinder and piston steam engineand his plan took practical shape inNewcomen's atmospheric engine. Papin'sfirst engine was unworkable owing to thefact that he used the same vessel for bothboiler and cylinder. A small quantity ofwater was placed in the bottom of thevessel and heat was applied. When steamformed and raised the piston, the heat was

withdrawn and the piston did work on itsdown stroke under pressure of theatmosphere. After hearing of Savery'sengine, Papin developed an improvedform. Papin's engine of 1705 consisted of adisplacement chamber in which a floatingdiaphragm or piston on top of the waterkept the steam and water from directcontact. The water delivered by thedownward movement of the piston underpressure, to a closed tank, flowed in acontinuous stream against the vanes of awater wheel. When the steam in thedisplacement chamber had expanded, itwas exhausted to the atmosphere througha valve instead of being condensed. Theengine was, in fact, a non-condensing,single action steam pump with the steamand pump cylinders in one. A curiousfeature of this engine was a heater placedin the diaphragm. This was a mass ofheated metal for the purpose of keeping

the steam dry or preventing condensationduring expansion. This device might becalled the first superheater.

Among the various inventions attributed toPapin was a boiler with an internal firebox, the earliest record of suchconstruction.

While Papin had neglected his earliersuggestion of a steam and piston engine towork on Savery's ideas, ThomasNewcomen, with his assistant, JohnCawley, put into practical form Papin'ssuggestion of 1690. Steam admitted fromthe boiler to a cylinder raised a piston byits expansion, assisted by a counter-weighton the other end of a beam actuated by thepiston. The steam valve was then shut andthe steam condensed by a jet of coldwater. The piston was then forceddownward by atmospheric pressure and

did work on the pump. The condensedwater in the cylinder was expelled throughan escapement valve by the next entry ofsteam. This engine used steam havingpressure but little, if any, above that of theatmosphere.

[Illustration: Two Units of 8128 HorsePower of Babcock & Wilcox Boilers andSuperheaters at the Fisk Street Station ofthe Commonwealth Edison Co., Chicago,Ill., 50,400 Horse Power being Installed inthis Station. The Commonwealth EdisonCo. Operates in its Various Stations a Totalof 86,000 Horse Power of Babcock &Wilcox Boilers, all Fitted with Babcock &Wilcox Superheaters and Equipped withBabcock & Wilcox Chain Grate Stokers]

In 1711, this engine was introduced intomines for pumping purposes. Whether itsaction was originally automatic or whether

dependent upon the hand operation of thevalves is a question of doubt. The storycommonly believed is that a boy,Humphrey Potter, in 1713, whose duty itwas to open and shut such valves of anengine he attended, by suitable cords andcatches attached to the beam, caused theengine to automatically manipulate thesevalves. This device was simplified in 1718by Henry Beighton, who suspended fromthe bottom, a rod called the plug-tree,which actuated the valve by tappets. By1725, this engine was in common use in thecollieries and was changed but little for amatter of sixty or seventy years.Compared with Savery's engine, from theaspect of a pumping engine, Newcomen'swas a distinct advance, in that the pressurein the pumps was in no manner dependentupon the steam pressure. In common withSavery's engine, the losses from thealternate heating and cooling of the steam

cylinder were enormous. Thoughobviously this engine might have beenmodified to serve many purposes, its useseems to have been limited almost entirelyto the pumping of water.

The rivalry between Savery and Papinappears to have stimulated attention to thequestion of fuel saving. Dr. John Allen, in1730, called attention to the fact that owingto the short length of time of the contactbetween the gases and the heatingsurfaces of the boiler, nearly half of theheat of the fire was lost. With a view toovercoming this loss at least partially, heused an internal furnace with a smoke fluewinding through the water in the form of aworm in a still. In order that the length ofpassage of the gases might not act as adamper on the fire, Dr. Allenrecommended the use of a pair of bellowsfor forcing the sluggish vapor through the

flue. This is probably the first suggesteduse of forced draft. In forming an estimateof the quantity of fuel lost up the stack, Dr.Allen probably made the first boiler test.

Toward the end of the period of use ofNewcomen's atmospheric engine, JohnSmeaton, who, about 1770, built andinstalled a number of large engines of thistype, greatly improved the design in itsmechanical details.

[Illustration: Erie County Electric Co., Erie,Pa., Operating 3082 Horse Power ofBabcock & Wilcox Boilers andSuperheaters, Equipped with Babcock &Wilcox Chain Grate Stokers]

The improvement in boiler and enginedesign of Smeaton, Newcomen and theircontemporaries, were followed by those ofthe great engineer, James Watt, an

instrument maker of Glasgow. In 1763,while repairing a model of Newcomen'sengine, he was impressed by the greatwaste of steam to which the alternatingcooling and heating of the engine gaverise. His remedy was the maintaining ofthe cylinder as hot as the entering steamand with this in view he added a vesselseparate from the cylinder, into which thesteam should pass from the cylinder andbe there condensed either by theapplication of cold water outside or by ajet from within. To preserve a vacuum inhis condenser, he added an air pumpwhich should serve to remove the water ofcondensation and air brought in with theinjection water or due to leakage. As thecylinder no longer acted as a condenser,he could maintain it at a high temperatureby covering it with non-conductingmaterial and, in particular, by the use of asteam jacket. Further and with the same

object in view, he covered the top of thecylinder and introduced steam above thepiston to do the work previouslyaccomplished by atmospheric pressure.After several trials with an experimentalapparatus based on these ideas, Wattpatented his improvements in 1769. Asidefrom their historical importance, Watt'simprovements, as described in hisspecification, are to this day a statement ofthe principles which guide the scientificdevelopment of the steam engine. Hiswords are:

"My method of lessening theconsumption of steam, and consequentlyfuel, in fire engines, consists of thefollowing principles:

"First, That vessel in which the powers ofsteam are to be employed to work theengine, which is called the cylinder in

common fire engines, and which I call thesteam vessel, must, during the wholetime the engine is at work, be kept as hotas the steam that enters it; first, byenclosing it in a case of wood, or anyother materials that transmit heat slowly;secondly, by surrounding it with steam orother heated bodies; and, thirdly, bysuffering neither water nor any othersubstance colder than the steam to enteror touch it during that time.

"Secondly, In engines that are to beworked wholly or partially bycondensation of steam, the steam is to becondensed in vessels distinct from thesteam vessels or cylinders, althoughoccasionally communicating with them;these vessels I call condensers; and,whilst the engines are working, thesecondensers ought at least to be kept ascold as the air in the neighborhood of

the engines, by application of water orother cold bodies.

"Thirdly, Whatever air or other elasticvapor is not condensed by the cold ofthe condenser, and may impede theworking of the engine, is to be drawnout of the steam vessels or condensers by

means of pumps, wrought by the enginesthemselves, or otherwise.

"Fourthly, I intend in many cases toemploy the expansive force of steam topress on the pistons, or whatever may beused instead of them, in the samemanner in which the pressure of theatmosphere is now employed in commonfire engines. In cases where cold watercannot be had in plenty, the engines maybe wrought by this force of steam only,by discharging the steam into the airafter it has done its office....

"Sixthly, I intend in some cases to applya degree of cold not capable of reducingthe steam to water, but of contracting itconsiderably, so that the engines shall beworked by the alternate expansion andcontraction of the steam.

"Lastly, Instead of using water to renderthe pistons and other parts of the engineair and steam tight, I employ oils, wax,resinous bodies, fat of animals,quick-silver and other metals in theirfluid state."

The fifth claim was for a rotary engine, andneed not be quoted here.

The early efforts of Watt are typical ofthose of the poor inventor struggling withinsufficient resources to gain recognitionand it was not until he became associated

with the wealthy manufacturer, MattheuBoulton of Birmingham, that he met withthe success upon which his present fame isbased. In partnership with Boulton, thebusiness of the manufacture and the sale ofhis engines were highly successful in spiteof vigorous attacks on the validity of hispatents.

Though the fourth claim of Watt's patentdescribes a non-condensing engine whichwould require high pressures, his aversionto such practice was strong.Notwithstanding his entire knowledge ofthe advantages through added expansionunder high pressure, he continued to usepressures not above 7 pounds per squareinch above the atmosphere. To overcomesuch pressures, his boilers were fedthrough a stand-pipe of sufficient height tohave the column of water offset thepressure within the boiler. Watt's attitude

toward high pressure made his influencefelt long after his patents had expired.

[Illustration: Portion of 9600 Horse-powerInstallation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock& Wilcox Chain Grate Stokers at the BlueIsland, Ill., Plant of the Public Service Co.of Northern Illinois. This CompanyOperates 14,580 Horse Power of Babcock& Wilcox Boilers and Superheaters in itsVarious Stations]

In 1782, Watt patented two other featureswhich he had invented as early as 1769.These were the double acting engine, thatis, the use of steam on both sides of thepiston and the use of steam expansively,that is, the shutting off of steam from thecylinder when the piston had made but aportion of its stroke, the power for thecompletion of the stroke being supplied

by the expansive force of the steamalready admitted.

He further added a throttle valve for theregulation of steam admission, inventedthe automatic governor and the steamindicator, a mercury steam gauge and aglass water column.

It has been the object of this brief historyof the early developments in the use ofsteam to cover such developments onlythrough the time of James Watt. Theprogress of the steam engine from thistime through the stages of higherpressures, combining of cylinders, theapplication of steam vehicles andsteamboats, the adding of third and fourthcylinders, to the invention of the turbinewith its development and theaccompanying development of thereciprocating engine to hold its place, is

one long attribute to the inventive geniusof man.

While little is said in the biographies ofWatt as to the improvement of steamboilers, all the evidence indicates thatBoulton and Watt introduced the first"wagon boiler", so called because of itsshape. In 1785, Watt took out a number ofpatents for variations in furnaceconstruction, many of which contain thebasic principles of some of the modernsmoke preventing furnaces. Until the earlypart of the nineteenth century, the lowsteam pressures used caused but littleattention to be given to the form of theboiler operated in connection with theengines above described. About 1800,Richard Trevithick, in England, and OliverEvans, in America, introducednon-condensing, and for that time, highpressure steam engines. To the initiative of

Evans may be attributed the general use ofhigh pressure steam in the United States, afeature which for many yearsdistinguished American from Europeanpractice. The demand for light weight andeconomy of space following the beginningof steam navigation and the invention ofthe locomotive required boilers designedand constructed to withstand heavierpressures and forced the adoption of thecylindrical form of boiler. There are in useto-day many examples of every step in thedevelopment of steam boilers from the firstplain cylindrical boiler to the most moderntype of multi-tubular locomotive boiler,which stands as the highest type offire-tube boiler construction.

The early attempts to utilize water-tubeboilers were few. A brief history of thedevelopment of the boilers, in which thisprinciple was employed, is given in the

following chapter. From this history it willbe clearly indicated that the firstcommercially successful utilization ofwater tubes in a steam generator isproperly attributed to George H. Babcockand Stephen Wilcox.

[Illustration: Copyright by Underwood &Underwood

Woolworth Building, New York City,Operating 2454 Horse Power of Babcock &Wilcox Boilers]

BRIEF HISTORY OF WATER-TUBEBOILERS[1]

As stated in the previous chapter, the firstwater-tube boiler was built by John Blakeyand was patented by him in 1766. Severaltubes alternately inclined at oppositeangles were arranged in the furnaces, theadjacent tube ends being connected bysmall pipes. The first successful user ofwater-tube boilers, however, was JamesRumsey, an American inventor, celebratedfor his early experiments in steamnavigation, and it is he who may be trulyclassed as the originator of the water-tubeboiler. In 1788 he patented, in England,several forms of boilers, some of whichwere of the water-tube type. One had a firebox with flat top and sides, with horizontaltubes across the fire box connecting thewater spaces. Another had a cylindrical

fire box surrounded by an annular waterspace and a coiled tube was placed withinthe box connecting at its two ends with thewater space. This was the first of the "coilboilers". Another form in the same patentwas the vertical tubular boiler, practicallyas made at the present time.

[Illustration: Blakey, 1766]

The first boiler made of a combination ofsmall tubes, connected at one end to areservoir, was the invention of anotherAmerican, John Stevens, in 1804. Thisboiler was actually employed to generatesteam for running a steamboat on theHudson River, but like all the "porcupine"boilers, of which type it was the first, it didnot have the elements of a continuedsuccess.

[Illustration: John Stevens, 1804]

Another form of water tube was patentedin 1805 by John Cox Stevens, a son of JohnStevens. This boiler consisted of twentyvertical tubes, 1� inches internal diameterand 40� inches long, arranged in a circle,the outside diameter of which wasapproximately 12 inches, connecting awater chamber at the bottom with a steamchamber at the top. The steam and waterchambers were annular spaces of smallcross section and contained approximately33 cubic inches. The illustration shows thecap of the steam chamber secured bybolts. The steam outlet pipe "A" is a pipe ofone inch diameter, the water enteringthrough a similar aperture at the bottom.One of these boilers was for a long time atthe Stevens Institute of Technology atHoboken, and is now in the SmithsonianInstitute at Washington.

[Illustration: John Cox Stevens, 1805]

About the same time, Jacob Woolf built aboiler of large horizontal tubes, extendingacross the furnace and connected at theends to a longitudinal drum above. Thefirst purely sectional water-tube boiler wasbuilt by Julius Griffith, in 1821. In thisboiler, a number of horizontal water tubeswere connected to vertical side pipes, theside pipes were connected to horizontalgathering pipes, and these latter in turn toa steam drum.

In 1822, Jacob Perkins constructed a flashboiler for carrying what was thenconsidered a high pressure. A number ofcast-iron bars having 1� inches annularholes through them and connected at theirouter ends by a series of bent pipes,outside of the furnace walls, werearranged in three tiers over the fire. The

water was fed slowly to the upper tier by aforce pump and steam in the superheatedstate was discharged to the lower tiers intoa chamber from which it was taken to theengine.

[Illustration: Joseph Eve, 1825]

The first sectional water-tube boiler, with awell-defined circulation, was built byJoseph Eve, in 1825. The sections werecomposed of small tubes with a slightdouble curve, but being practicallyvertical, fixed in horizontal headers, whichheaders were in turn connected to a steamspace above and a water space belowformed of larger pipes. The steam andwater spaces were connected by outsidepipes to secure a circulation of the waterup through the sections and down throughthe external pipes. In the same year, JohnM'Curdy of New York, built a "Duplex

Steam Generator" of "tubes of wrought orcast iron or other material" arranged inseveral horizontal rows, connectedtogether alternately at the front and rearby return bends. In the tubes below thewater line were placed interior circularvessels closed at the ends in order toexpose a thin sheet of water to the action ofthe fire.

[Illustration: Gurney, 1826]

In 1826, Goldsworthy Gurney built anumber of boilers, which he used on hissteam carriages. A number of small tubeswere bent into the shape of a "U" laidsidewise and the ends were connectedwith larger horizontal pipes. These wereconnected by vertical pipes to permit ofcirculation and also to a vertical cylinderwhich served as a steam and waterreservoir. In 1828, Paul Steenstrup made

the first shell boiler with vertical watertubes in the large flues, similar to theboiler known as the "Martin" andsuggesting the "Galloway".

The first water-tube boiler having firetubes within water tubes was built in 1830,by Summers & Ogle. Horizontalconnections at the top and bottom wereconnected by a series of vertical watertubes, through which were fire tubesextending through the horizontalconnections, the fire tubes being held inplace by nuts, which also served to makethe joint.

[Illustration: Stephen Wilcox, 1856]

Stephen Wilcox, in 1856, was the first touse inclined water tubes connecting waterspaces at the front and rear with a steamspace above. The first to make such

inclined tubes into a sectional form wasTwibill, in 1865. He used wrought-irontubes connected at the front and rear withstandpipes through intermediateconnections. These standpipes carried thesystem to a horizontal cross drum at thetop, the entrained water being carried tothe rear.

Clarke, Moore, McDowell, Alban andothers worked on the problem ofconstructing water-tube boilers, butbecause of difficulties of constructioninvolved, met with no practical success.

[Illustration: Twibill, 1865]

It may be asked why water-tube boilersdid not come into more general use at anearly date, that is, why the number ofwater-tube boilers built was so small incomparison to the number of shell boilers.

The reason for this is found in thedifficulties involved in the design andconstruction of water-tube boilers, whichdesign and construction required a highclass of engineering and workmanship,while the plain cylindrical boiler iscomparatively easy to build. The greaterskill required to make a water-tube boilersuccessful is readily shown in the greatnumber of failures in the attempts to makethem.

[Illustration: Partial View of 7000Horse-power Installation of Babcock &Wilcox Boilers at the Philadelphia, Pa.,Plant of the Baldwin Locomotive Works.This Company Operates in its VariousPlants a Total of 9280 Horse Power ofBabcock & Wilcox Boilers]

REQUIREMENTS OF STEAM BOILERS

Since the first appearance in "Steam" of thefollowing "Requirements of a Perfect SteamBoiler", the list has been copied manytimes either word for word or clothed indifferent language and applied to somespecific type of boiler design orconstruction. In most cases, although fullcompliance with one or more of therequirements was structurally impossible,the reader was left to infer that the boilerunder consideration possessed all thedesirable features. It is noteworthy thatthis list of requirements, as prepared byGeorge H. Babcock and Stephen Wilcox,in 1875, represents the best practice ofto-day. Moreover, coupled with the boileritself, which is used in the largest and mostimportant steam generating plantsthroughout the world, the list forms a

fitting monument to the foresight andgenius of the inventors.

REQUIREMENTS OF A PERFECT STEAMBOILER

1st. Proper workmanship and simpleconstruction, using materials whichexperience has shown to be the best, thusavoiding the necessity of early repairs.

2nd. A mud drum to receive all impuritiesdeposited from the water, and so placed asto be removed from the action of the fire.

3rd. A steam and water capacity sufficientto prevent any fluctuation in steampressure or water level.

4th. A water surface for the disengagementof the steam from the water, of sufficient

extent to prevent foaming.

5th. A constant and thorough circulation ofwater throughout the boiler, so as tomaintain all parts at the same temperature.

6th. The water space divided into sectionsso arranged that, should any section fail,no general explosion can occur and thedestructive effects will be confined to theescape of the contents. Large and freepassages between the different sections toequalize the water line and pressure in all.

7th. A great excess of strength over anylegitimate strain, the boiler being soconstructed as to be free from strains dueto unequal expansion, and, if possible, toavoid joints exposed to the direct action of

the fire.

8th. A combustion chamber so arrangedthat the combustion of the gases started inthe furnace may be completed before thegases escape to the chimney.

9th. The heating surface as nearly aspossible at right angles to the currents ofheated gases, so as to break up thecurrents and extract the entire availableheat from the gases.

10th. All parts readily accessible forcleaning and repairs. This is a point of thegreatest importance as regards safety andeconomy.

11th. Proportioned for the work to bedone, and capable of working to its fullrated capacity with the highest economy.

12th. Equipped with the very best gauges,safety valves and other fixtures.

The exhaustive study made of each one ofthese requirements is shown by thefollowing extract from a lecture deliveredby Mr. Geo. H. Babcock at CornellUniversity in 1890 upon the subject:

THE CIRCULATION OF WATER IN STEAMBOILERS

You have all noticed a kettle of waterboiling over the fire, the fluid risingsomewhat tumultuously around the edgesof the vessel, and tumbling toward thecenter, where it descends. Similar currentsare in action while the water is simplybeing heated, but they are not perceptibleunless there are floating particles in theliquid. These currents are caused by thejoint action of the added temperature andtwo or more qualities which the waterpossesses.

1st. Water, in common with most othersubstances, expands when heated; astatement, however, strictly true onlywhen referred to a temperature above 39degrees F. or 4 degrees C., but as in the

making of steam we rarely have to do withtemperatures so low as that, we may, forour present purposes, ignore thatexception.

2nd. Water is practically a non-conductorof heat, though not entirely so. If ice-coldwater was kept boiling at the surface theheat would not penetrate sufficiently tobegin melting ice at a depth of 3 inches inless than about two hours. As, therefore,the heated water cannot impart its heat toits neighboring particles, it remainsexpanded and rises by its levity, whilecolder portions come to be heated in turn,thus setting up currents in the fluid.

Now, when all the water has been heatedto the boiling point corresponding to thepressure to which it is subjected, eachadded unit of heat converts a portion,about 7 grains in weight, into vapor,

greatly increasing its volume; and themingled steam and water rises morerapidly still, producing ebullition such aswe have noticed in the kettle. So long asthe quantity of heat added to the contentsof the kettle continues practically constant,the conditions remain similar to those wenoticed at first, a tumultuous lifting of thewater around the edges, flowing towardthe center and thence downward; if,however, the fire be quickened, theupward currents interfere with thedownward and the kettle boils over (Fig.1).

[Illustration: Fig. 1]

If now we put in the kettle a vesselsomewhat smaller (Fig. 2) with a hole inthe bottom and supported at a properdistance from the side so as to separate theupward from the downward currents, we

can force the fires to a very much greaterextent without causing the kettle to boilover, and when we place a deflecting plateso as to guide the rising column toward thecenter it will be almost impossible toproduce that effect. This is the invention ofPerkins in 1831 and forms the basis of verymany of the arrangements for producingfree circulation of the water in boilerswhich have been made since that time. Itconsists in dividing the currents so thatthey will not interfere each with the other.


But what is the object of facilitating thecirculation of water in boilers? Why maywe not safely leave this to the unassistedaction of nature as we do in culinaryoperations? We may, if we do not care forthe three most important aims insteam-boiler construction, namely,

efficiency, durability, and safety, each ofwhich is more or less dependent upon aproper circulation of the water. As forefficiency, we have seen one proof in ourkettle. When we provided means topreserve the circulation, we found that wecould carry a hotter fire and boil away thewater much more rapidly than before. It isthe same in a steam boiler. And we alsonoticed that when there was nothing butthe unassisted circulation, the rising steamcarried away so much water in the form offoam that the kettle boiled over, but whenthe currents were separated and anunimpeded circuit was established, thisceased, and a much larger supply of steamwas delivered in a comparatively drystate. Thus, circulation increases theefficiency in two ways: it adds to the abilityto take up the heat, and decreases theliability to waste that heat by what istechnically known as priming. There is yet

another way in which, incidentally,circulation increases efficiency of surface,and that is by preventing in a greater orless degree the formation of depositsthereon. Most waters contain someimpurity which, when the water isevaporated, remains to incrust the surfaceof the vessel. This incrustation becomesvery serious sometimes, so much so as toalmost entirely prevent the transmission ofheat from the metal to the water. It is saidthat an incrustation of only one-eighth inchwill cause a loss of 25 per cent inefficiency, and this is probably within thetruth in many cases. Circulation of waterwill not prevent incrustation altogether,but it lessens the amount in all waters, andalmost entirely so in some, thus addinggreatly to the efficiency of the surface.


A second advantage to be obtainedthrough circulation is durability of theboiler. This it secures mainly by keepingall parts at a nearly uniform temperature.The way to secure the greatest freedomfrom unequal strains in a boiler is toprovide for such a circulation of the wateras will insure the same temperature in allparts.

3rd. Safety follows in the wake ofdurability, because a boiler which is notsubject to unequal strains of expansion andcontraction is not only less liable toordinary repairs, but also to rupture anddisastrous explosion. By far the mostprolific cause of explosions is this samestrain from unequal expansions.


[Illustration: 386 Horse-power Installation

of Babcock & Wilcox Boilers at B. F. Keith'sTheatre, Boston, Mass.]

Having thus briefly looked at theadvantages of circulation of water in steamboilers, let us see what are the best meansof securing it under the most efficientconditions We have seen in our kettle thatone essential point was that the currentsshould be kept from interfering with eachother. If we could look into an ordinaryreturn tubular boiler when steaming, weshould see a curious commotion ofcurrents rushing hither and thither, andshifting continually as one or the othercontending force gained a momentarymastery. The principal upward currentswould be found at the two ends, one overthe fire and the other over the first foot orso of the tubes. Between these, thedownward currents struggle against therising currents of steam and water. At a

sudden demand for steam, or on the liftingof the safety valve, the pressure beingslightly reduced, the water jumps up injets at every portion of the surface, beinglifted by the sudden generation of steamthroughout the body of water. You haveseen the effect of this sudden generation ofsteam in the well-known experiment with aFlorence flask, to which a cold applicationis made while boiling water underpressure is within. You have alsowitnessed the geyser-like action whenwater is boiled in a test tube heldvertically over a lamp (Fig. 3).


If now we take a U-tube depending from avessel of water (Fig. 4) and apply the lampto one leg a circulation is at once set upwithin it, and no such spasmodic action canbe produced. Thus U-tube is the

representative of the true method ofcirculation within a water-tube boilerproperly constructed. We can, for thepurpose of securing more heating surface,extend the heated leg into a long incline(Fig. 5), when we have the well-knowninclined-tube generator. Now, by addingother tubes, we may further increase theheating surface (Fig. 6), while it will still bethe U-tube in effect and action. In such aconstruction the circulation is a function ofthe difference in density of the twocolumns. Its velocity is measured by thewell-known Torricellian formula, V =(2gh)^{�}, or, approximately V = 8(h)^{�}, hbeing measured in terms of the lighterfluid. This velocity will increase until therising column becomes all steam, but thequantity or weight circulated will attain amaximum when the density of the mingledsteam and water in the rising columnbecomes one-half that of the solid water in

the descending column which is nearlycoincident with the condition of half steamand half water, the weight of the steambeing very slight compared to that of thewater.


It becomes easy by this rule to determinethe circulation in any given boiler built onthis principle, provided the construction issuch as to permit a free flow of the water.Of course, every bend detracts a little andsomething is lost in getting up the velocity,but when the boiler is well arranged andproportioned these retardations are slight.

Let us take for example one of the 240horse-power Babcock & Wilcox boilershere in the University. The height of thecolumns may be taken as 4� feet,measuring from the surface of the water to

about the center of the bundle of tubesover the fire, and the head would be equalto this height at the maximum ofcirculation. We should, therefore, have avelocity of 8(4�)^{�} = 16.97, say 17 feetper second. There are in this boilerfourteen sections, each having a 4-inchtube opening into the drum, the area ofwhich (inside) is 11 square inches, thefourteen aggregating 154 square inches,or 1.07 square feet. This multiplied by thevelocity, 16.97 feet, gives 18.16 cubic feetmingled steam and water discharged persecond, one-half of which, or 9.08 cubicfeet, is steam. Assuming this steam to be at100 pounds gauge pressure, it will weigh0.258 pound per cubic foot. Hence, 2.34pounds of steam will be discharged persecond, and 8,433 pounds per hour.Dividing this by 30, the number of poundsrepresenting a boiler horse power, we get281.1 horse power, about 17 per cent, in

excess of the rated power of the boiler.The water at the temperature of steam at100 pounds pressure weighs 56 poundsper cubic foot, and the steam 0.258 pound,so that the steam forms but 1/218 part ofthe mixture by weight, and consequentlyeach particle of water will make 218circuits before being evaporated whenworking at this capacity, and circulatingthe maximum weight of water through thetubes.

[Illustration: A Portion of 9600Horse-power Installation of Babcock &Wilcox Boilers and Superheaters BeingErected at the South Boston, Mass., Stationof the Boston Elevated Railway Co. ThisCompany Operates in its Various Stationsa Total of 46,400 Horse Power of Babcock &Wilcox Boilers]


It is evident that at the highest possiblevelocity of exit from the generating tubes,nothing but steam will be delivered andthere will be no circulation of water exceptto supply the place of that evaporated. Letus see at what rate of steaming this wouldoccur with the boiler under consideration.We shall have a column of steam, say 4feet high on one side and an equal columnof water on the other. Assuming, as before,the steam at 100 pounds and the water atsame temperature, we will have a head of866 feet of steam and an issuing velocity of235.5 feet per second. This multiplied by1.07 square feet of opening by 3,600seconds in an hour, and by 0.258 gives234,043 pounds of steam, which, thoughonly one-eighth the weight of mingledsteam and water delivered at themaximum, gives us 7,801 horse power, or32 times the rated power of the boiler. Of

course, this is far beyond any possibility ofattainment, so that it may be set down ascertain that this boiler cannot be forced toa point where there will not be an efficientcirculation of the water. By the samemethod of calculation it may be shown thatwhen forced to double its rated power, apoint rarely expected to be reached inpractice, about two-thirds the volume ofmixture of steam and water delivered intothe drum will be steam, and that the waterwill make 110 circuits while beingevaporated. Also that when worked at onlyabout one-quarter its rated capacity,one-fifth of the volume will be steam andthe water will make the rounds 870 timesbefore it becomes steam. You will thus seethat in the proportions adopted in thisboiler there is provision for perfectcirculation under all the possibleconditions of practice.

[Illustration: Fig. 8 [Developed to showCirculation]]

In designing boilers of this style it isnecessary to guard against having theuptake at the upper end of the tubes toolarge, for if sufficiently large to allowdownward currents therein, the wholeeffect of the rising column in increasingthe circulation in the tubes is nullified (Fig.7). This will readily be seen if we considerthe uptake very large when the only headproducing circulation in the tubes will bethat due to the inclination of each tubetaken by itself. This objection is onlyovercome when the uptake is so small asto be entirely filled with the ascendingcurrent of mingled steam and water. It isalso necessary that this uptake should bepractically direct, and it should not becomposed of frequent enlargements andcontractions. Take, for instance, a boiler

well known in Europe, copied and soldhere under another name. It is made up ofinclined tubes secured by pairs into boxesat the ends, which boxes are made tocommunicate with each other by returnbends opposite the ends of the tubes.These boxes and return bends form anirregular uptake, whereby the steam isexpected to rise to a reservoir above. Youwill notice (Fig. 8) that the upward currentof steam and water in the return bendmeets and directly antagonizes the upwardcurrent in the adjoining tube. Only oneresult can follow. If their velocities areequal, the momentum of both will beneutralized and all circulation stopped, or,if one be stronger, it will cause a back flowin the other by the amount of difference inforce, with practically the same result.

[Illustration: 4880 Horse-power Installationof Babcock & Wilcox Boilers at the Open

Hearth Plant of the Cambria Steel Co.,Johnstown, Pa. This Company Operates aTotal of 52,000 Horse Power of Babcock &Wilcox Boilers]


In a well-known boiler, many of whichwere sold, but of which none are nowmade and a very few are still in use, theinventor claimed that the return bends andsmall openings against the tubes were forthe purpose of "restricting the circulation"and no doubt they performed well thatoffice; but excepting for the smallness ofthe openings they were not as efficient forthat purpose as the arrangement shown inFig. 8.


Another form of boiler, first invented by

Clarke or Crawford, and lately revived,has the uptake made of boxes into which anumber, generally from two to four tubes,are expanded, the boxes being connectedtogether by nipples (Fig. 9). It is awell-known fact that where a fluid flowsthrough a conduit which enlarges and thencontracts, the velocity is lost to a greater orless extent at the enlargements, and has tobe gotten up again at the contractions eachtime, with a corresponding loss of head.The same thing occurs in the constructionshown in Fig. 9. The enlargements andcontractions quite destroy the head andpractically overcome the tendency of thewater to circulate.

A horizontal tube stopped at one end, asshown in Fig. 10, can have no propercirculation within it. If moderately driven,the water may struggle in against theissuing steam sufficiently to keep the

surface covered, but a slight degree offorcing will cause it to act like the test tubein Fig. 3, and the more there are of them ina given boiler the more spasmodic will beits working.

The experiment with our kettle (Fig. 2)gives the clue to the best means ofpromoting circulation in ordinary shellboilers. Steenstrup or "Martin" and"Galloway" water tubes placed in suchboilers also assist in directing thecirculation therein, but it is almostimpossible to produce in shell boilers, byany means the circulation of all the waterin one continuous round, such as marks thewell-constructed water-tube boiler.

As I have before remarked, provision for aproper circulation of water has beenalmost universally ignored in designingsteam boilers, sometimes to the great

damage of the owner, but oftener to thejeopardy of the lives of those who areemployed to run them. The noted case ofthe Montana and her sister ship, wheresome $300,000 was thrown away in tryingan experiment which a properconsideration of this subject would haveavoided, is a case in point; but who shallcount the cost of life and treasure not,perhaps, directly traceable to, but,nevertheless, due entirely to such neglectin design and construction of thethousands of boilers in which thisnecessary element has been ignored?

In the light of the performance of theexacting conditions of present daypower-plant practice, a review of thislecture and of the foregoing list ofrequirements reveals the insight of theinventors of the Babcock & Wilcox boiler

into the fundamental principles of steamgenerator design and construction.

Since the Babcock & Wilcox boiler becamethoroughly established as a durable andefficient steam generator, many types ofwater-tube boilers have appeared on themarket. Most of them, failing to meetenough of the requirements of a perfectboiler, have fallen by the wayside, while afew failing to meet all of the requirements,have only a limited field of usefulness.None have been superior, and in the mostcases the most ardent admirers of otherboilers have been satisfied in looking upto the Babcock & Wilcox boiler as astandard and in claiming that the newerboilers were "just as good."

Records of recent performances under themost severe conditions of services on landand sea, show that the Babcock & Wilcox

boiler can be run continually and regularlyat higher overloads, with higher efficiency,and lower upkeep cost than any otherboiler on the market. It is especiallyadapted for power-plant work where it isnecessary to use a boiler in which steamcan be raised quickly and the boilerplaced on the line either from a cold stateor from a banked fire in the shortestpossible time, and with which the capacity,with clean feed water, will be largelylimited by the amount of coal that can beburned in the furnace.

The distribution of the circulation throughthe separate headers and sections and theaction of the headers in forcing amaximum and continuous circulation in thelower tubes, permit the operation of theBabcock & Wilcox boiler withoutobjectionable priming, with a higherdegree of concentration of salts in the

water than is possible in any other type ofboiler.

Repeated daily performances at overloadshave demonstrated beyond a doubt thecorrectness of Mr. Babcock's computationregarding the circulating tube and headerarea required for most efficient circulation.They also have proved that enlargement ofthe area of headers and circulating tubesbeyond a certain point diminishes thehead available for causing circulation andconsequently limits the ability of the boilerto respond to demands for overloads.

In this lecture Mr. Babcock made theprediction that with the circulating tubearea proportioned in accordance with theprinciples laid down, the Babcock &Wilcox boiler could be continuously run atdouble its nominal rating, which at thattime was based on 12 square feet of

heating surface per horse power. Thisprediction is being fulfilled daily in all thelarge and prominent power plants in thiscountry and abroad, and it has beenrepeatedly demonstrated that with cleanwater and clean tube surfaces it is possibleto safely operate at over 300 per cent ofthe nominal rating.

In the development of electrical powerstations it becomes more and moreapparent that it is economical to run aboiler at high ratings during the times ofpeak loads, as by so doing the lay-overlosses are diminished and the economy ofthe plant as a whole is increased.

The number and importance of the largeelectric lighting and power stationsconstructed during the last ten years thatare equipped with Babcock & Wilcoxboilers, is a most gratifying demonstration

of the merit of the apparatus, especially inview of their satisfactory operation underconditions which are perhaps moreexacting than those of any other service.

Time, the test of all, results with boilers aswith other things, in the survival of thefittest. When judged on this basis theBabcock & Wilcox boiler standspre-eminent in its ability to cover thewhole field of steam generation with thehighest commercial efficiency obtainable.Year after year the Babcock & Wilcoxboiler has become more firmlyestablished as the standard of excellencein the boiler making art.

[Illustration: South Boston Station of theBoston Elevated Ry. Co., Boston, Mass.9600 Horse Power of Babcock & WilcoxBoilers and Superheaters Installed in thisStation]

[Illustration: 3600 Horse-power Installationof Babcock & Wilcox Boilers at the PhippsPower House of the Duquesne LightCompany, Pittsburgh, Pa.]

EVOLUTION OF THE BABCOCK & WILCOXWATER-TUBE BOILER

Quite as much may be learned from therecords of failures as from those ofsuccess. Where a device has been oncefairly tried and found to be imperfect orimpracticable, the knowledge of that trialis of advantage in further investigation.Regardless of the lesson taught by failure,however, it is an almost every-dayoccurrence that some device orconstruction which has been tried andfound wanting, if not worthless, is againintroduced as a great improvement upon adevice which has shown by its survival tobe the fittest.

The success of the Babcock & Wilcoxboiler is due to many years of constantadherence to one line of research, in

which an endeavor has been made tointroduce improvements with the view toproducing a boiler which would mosteffectively meet the demands of the times.During the periods that this boiler hasbeen built, other companies have placedon the market more than thirty water-tubeor sectional water-tube boilers, most ofwhich, though they may have attainedsome distinction and sale, have nowentirely disappeared. The followingincomplete list will serve to recall thenames of some of the boilers that have hada vogue at various times, but which arenow practically unknown: Dimpfel,Howard, Griffith & Wundrum, Dinsmore,Miller "Fire Box", Miller "American", Miller"Internal Tube", Miller "Inclined Tube",Phleger, Weigant, the Lady Verner, theAllen, the Kelly, the Anderson, the Rogers& Black, the Eclipse or Kilgore, the Moore,the Baker & Smith, the Renshaw, the

Shackleton, the "Duplex", the Pond &Bradford, the Whittingham, the Bee, theHazleton or "Common Sense", theReynolds, the Suplee or Luder, the Babbit,the Reed, the Smith, the Standard, etc., etc.

It is with the object of protecting ourcustomers and friends from loss throughpurchasing discarded ideas that there isgiven on the following pages a briefhistory of the development of the Babcock& Wilcox boiler as it is built to-day. Theillustrations and brief descriptions indicateclearly the various designs andconstructions that have been used and thathave been replaced, as experience hasshown in what way improvement might bemade. They serve as a history of theexperimental steps in the development ofthe present Babcock & Wilcox boiler, thevalue and success of which, as a steamgenerator, is evidenced by the fact that the

largest and most discriminating userscontinue to purchase them after years ofexperience in their operation.

[Illustration: No. 1]

No. 1. The original Babcock & Wilcoxboiler was patented in 1867. The main ideain its design was safety, to which all otherfeatures were sacrificed wherever theyconflicted. The boiler consisted of a nest ofhorizontal tubes, serving as a steam andwater reservoir, placed above andconnected at each end by bolted joints to asecond nest of inclined heating tubes filledwith water. The tubes were placed oneabove the other in vertical rows, each rowand its connecting end forming a singlecasting. Hand-holes were placed at eachend for cleaning. Internal tubes wereplaced within the inclined tubes with aview to aiding circulation.

No. 2. This boiler was the same as No. 1,except that the internal circulating tubeswere omitted as they were found to hinderrather than help the circulation.

Nos. 1 and 2 were found to be faulty inboth material and design, cast metalproving unfit for heating surfaces placeddirectly over the fire, as it cracked as soonas any scale formed.

No. 3. Wrought-iron tubes weresubstituted for the cast-iron heating tubes,the ends being brightened, laid in moulds,and the headers cast on.

The steam and water capacity in thisdesign were insufficient to secureregularity of action, there being noreserve upon which to draw during firingor when the water was fed intermittently.

The attempt to dry the steam bysuperheating it in the nest of tubes formingthe steam space was found to beimpracticable. The steam delivered waseither wet, dry or superheated, accordingto the rate at which it was being drawnfrom the boiler. Sediment was found tolodge in the lowermost point of the boilerat the rear end and the exposed portionscracked off at this point when subjected tothe furnace heat.


No. 4. A plain cylinder, carrying the waterline at its center and leaving the upper halffor steam space, was substituted for thenest of tubes forming the steam and waterspace in Nos. 1, 2 and 3. The sections weremade as in No. 3 and a mud drum added tothe rear end of the sections at the pointthat was lowest and farthest removed from

the fire. The gases were made to pass off atone side and did not come into contactwith the mud drum. Dry steam wasobtained through the increase ofseparating surface and steam space andthe added water capacity furnished astorage for heat to tide over irregularitiesof firing and feeding. By the addition of thedrum, the boiler became a serviceableand practical design, retaining all of thefeatures of safety. As the drum wasremoved from the direct action of the fire,it was not subjected to excessive straindue to unequal expansion, and itsdiameter, if large in comparison with thatof the tubes formerly used, was small whencompared with that of cylindrical boilers.Difficulties were encountered in this boilerin securing reliable joints between thewrought-iron tubes and the cast-ironheaders.


No. 5. In this design, wrought-iron waterlegs were substituted for the cast-ironheaders, the tubes being expanded intothe inside sheets and a large cover placedopposite the front end of the tubes forcleaning. The tubes were staggered oneabove the other, an arrangement found tobe more efficient in the absorption of heatthan where they were placed in verticalrows. In other respects, the boiler wassimilar to No. 4, except that it had lost theimportant element of safety through theintroduction of the very objectionablefeature of flat stayed surfaces. The largedoors for access to the tubes were also acause of weakness.

An installation of these boilers was made atthe plant of the Calvert Sugar Refinery inBaltimore, and while they were satisfactory

in their operation, were never duplicated.


No. 6. This was a modification of No. 5 inwhich longer tubes were used and overwhich the gases were caused to makethree passes with a view of bettereconomy. In addition, some of the stayedsurfaces were omitted and handholessubstituted for the large access doors. Anumber of boilers of this design were builtbut their excessive first cost, the lack ofadjustability of the structure under varyingtemperatures, and the inconvenience oftransportation, led to No. 7.


No. 7. In this boiler, the headers and waterlegs were replaced by T-heads screwed tothe ends of the inclined tubes. The faces of

these Ts were milled and the tubes placedone above the other with the milled facesmetal to metal. Long bolts passed througheach vertical section of the T-heads andthrough connecting boxes on the heads ofthe drums holding the whole together. Alarge number of boilers of this designwere built and many were in successfuloperation for over twenty years. In mostinstances, however, they were altered tolater types.



Nos. 8 and 9. These boilers were known asthe Griffith & Wundrum type, the concernwhich built them being later merged inThe Babcock & Wilcox Co. Experimentswere made with this design with fourpassages of the gases across the tubes and

the downward circulation of the water atthe rear of the boiler was carried to thebottom row of tubes. In No. 9 an attemptwas made to increase the safety andreduce the cost by reducing the amount ofsteam and water capacity. A drum at rightangles to the line of tubes was used but asthere was no provision made to secure drysteam, the results were not satisfactory.The next move in the direction of safetywas the employment of several drums ofsmall diameter instead of a single drum.


This is shown in No. 10. A nest of smallhorizontal drums, 15 inches in diameter,was used in place of the single drum oflarger diameter. A set of circulation tubeswas placed at an intermediate anglebetween the main bank of heating tubesand the horizontal drums forming the

steam reservoir. These circulators were toreturn to the rear end of the circulatingtubes the water carried up by thecirculation, and in this way were to allowonly steam to be delivered to the smalldrums above. There was no improvementin the action of this boiler over that of No.9.

The four passages of the gas over thetubes tried in Nos. 8, 9 and 10 were notfound to add to the economy of the boiler.


No. 11. A trial was next made of a box coilsystem, in which the water was made totransverse the furnace several timesbefore being delivered to the drum above.The tendency here, as in all similarboilers, was to form steam in the middle ofthe coil and blow the water from each end,

leaving the tubes practically dry until thesteam found an outlet and the waterreturned. This boiler had, in addition to adefective circulation, a decidedlygeyser-like action and produced wetsteam.


All of the types mentioned, with theexception of Nos. 5 and 6, had betweentheir several parts a large number ofbolted joints which were subjected to theaction of the fire. When these boilers wereplaced in operation it was demonstratedthat as soon as any scale formed on theheating surfaces, leaks were caused due tounequal expansion.

No. 12. With this boiler, an attempt wasmade to remove the joints from the fireand to increase the heating surface in a

given space. Water tubes were expandedinto both sides of wrought-iron boxes,openings being made for the admission ofwater and the exit of steam. Fire tubeswere placed inside the water tubes toincrease the heating surface. This designwas abandoned because of the rapidstopping up of the tubes by scale and theimpossibility of cleaning them.


No. 13. Vertical straight line headers ofcast iron, each containing two rows oftubes, were bolted to a connection leadingto the steam and water drum above.


No. 14. A wrought-iron box was substitutedfor the double cast-iron headers. In thisdesign, stays were necessary and were

found, as always, to be an element to beavoided wherever possible. The boilerwas an improvement on No. 6, however. Aslanting bridge wall was introducedunderneath the drum to throw a largerportion of its heating surface into thecombustion chamber under the bank oftubes.

This bridge wall was found to be difficult tokeep in repair and was of no particularbenefit.


No. 15. Each row of tubes was expanded ateach end into a continuous header, cast ofcar wheel metal. The headers had asinuous form so that they would lie closetogether and admit of a staggered positionof the tubes when assembled. While otherdesigns of header form were tried later,

experience with Nos. 14 and 15 showedthat the style here adopted was the best forall purposes and it has not been changedmaterially since. The drum in this designwas supported by girders resting on thebrickwork. Bolted joints were discarded,with the exception of those connecting theheaders to the front and rear ends of thedrums and the bottom of the rear headersto the mud drum. Even such joints,however, were found objectionable andwere superseded in subsequentconstruction by short lengths of tubesexpanded into bored holes.


No. 16. In this design, headers were triedwhich were made in the form of triangularboxes, in each of which there were threetubes expanded. These boxes werealternately reversed and connected by

short lengths of expanded tubes, beingconnected to the drum by tubes bent in amanner to allow them to enter the shellnormally. The joints between headersintroduced an element of weakness andthe connections to the drum wereinsufficient to give adequate circulation.


No. 17. Straight horizontal headers werenext tried, alternately shifted right and leftto allow a staggering of tubes. Theseheaders were connected to each other andto the drums by expanded nipples. Theobjections to this boiler were almost thesame as those to No. 16.



Nos. 18 and 19. These boilers weredesigned primarily for fire protectionpurposes, the requirements demanding asmall, compact boiler with ability to raisesteam quickly. These both served thepurpose admirably but, as in No. 9, theonly provision made for the securing ofdry steam was the use of the steam dome,shown in the illustration. This dome wasfound inadequate and has since beenabandoned in nearly all forms of boilerconstruction. No other remedy beingsuggested at the time, these boilers werenot considered as desirable for generaluse as Nos. 21 and 22. In Europe, however,where small size units were more indemand, No. 18 was modified somewhatand used largely with excellent results.These experiments, as they may now becalled, although many boilers of some ofthe designs were built, clearlydemonstrated that the best construction

and efficiency required adherence to thefollowing elements of design:

1st. Sinuous headers for each vertical rowof tubes.

2nd. A separate and independentconnection with the drum, both front andrear, for each vertical row of tubes.

[Illustration: No. 20A]

[Illustration: No. 20B]

3rd. All joints between parts of the boilerproper to be made without bolts or screwplates.

4th. No surfaces to be used whichnecessitate the use of stays.

5th. The boiler supported independentlyof the brickwork so as to allow freedom forexpansion and contraction as it is heatedor cooled.

6th. Ample diameter of steam and waterdrums, these not to be less than 30 inchesexcept for small size units.

7th. Every part accessible for cleaning andrepairs.

With these points having beendetermined, No. 20 was designed. Thisboiler had all the desirable features just

enumerated, together with a number ofimprovements as to detail of construction.The general form of No. 15 was adhered tobut the bolted connections betweensections and drum and sections and muddrum were discarded in favor ofconnections made by short lengths ofboiler tubes expanded into the adjacentparts. This boiler was suspended fromgirders, like No. 15, but these in turn werecarried on vertical supports, leaving thepressure parts entirely free from thebrickwork, the mutually deterioratingstrains present where one was supportedby the other being in this way overcome.Hundreds of thousands of horse power ofthis design were built, giving greatsatisfaction. The boiler was known as the"C. I. F." (cast-iron front) style, anornamental cast-iron front having beenusually furnished.


The next step, and the one which connectsthe boilers as described above to theboiler as it is built to-day, was the designillustrated in No. 21. These boilers wereknown as the "W. I. F." style, the frontsfurnished as part of the equipment beingconstructed largely of wrought iron. Thecast-iron drumheads used in No. 20 werereplaced by wrought-steel flanged and"bumped" heads. The drums were madelonger and the sections connected towrought-steel cross boxes riveted to thebottom of the drums. The boilers weresupported by girders and columns as inNo. 20.


No. 22. This boiler, which is designated asthe "Vertical Header" type, has the same

general features of construction as No. 21,except that the tube sheet side of theheaders is "stepped" to allow the headersto be placed vertically and at right anglesto the drum and still maintain the tubes atthe angle used in Nos. 20 and 21.


No. 23, or the cross drum design of boiler,is a development of the Babcock & Wilcoxmarine boiler, in which the cross drum isused exclusively. The experience of theGlasgow Works of The Babcock & Wilcox,Ltd., with No. 18 proved that properattention to details of construction wouldmake it a most desirable form of boilerwhere headroom was limited. A largenumber of this design have beensuccessfully installed and are givingsatisfactory results under widely varyingconditions. The cross drum boiler is also

built in a vertical header design.

Boilers Nos. 21, 22 and 23, with a fewmodifications, are now the standard forms.These designs are illustrated, as they areconstructed to-day, on pages 48, 52, 54, 58and 60.

The last step in the development of thewater-tube boiler, beyond which it seemsalmost impossible for science and skill toadvance, consists in the making of allpressure parts of the boiler of wroughtsteel, including sinuous headers, crossboxes, nozzles, and the like. Thisconstruction was the result of the demandsof certain Continental laws that are cominginto general vogue in this country. TheBabcock & Wilcox Co. have at the presenttime a plant producing steel forgings thathave been pronounced by the _LondonEngineer_ to be "a perfect triumph of the

forgers' art".

The various designs of this allwrought-steel boiler are fully illustrated inthe following pages.

[Illustration: Wrought-steel VerticalHeader Longitudinal Drum Babcock &Wilcox Boiler, Equipped with Babcock &Wilcox Superheater and Babcock & WilcoxChain Grate Stoker]

THE BABCOCK & WILCOX BOILER

The following brief description of theBabcock & Wilcox boiler will clearlyindicate the manner in which it fulfills therequirements of the perfect steam boileralready enumerated.

The Babcock & Wilcox boiler is built in twogeneral classes, the longitudinal drumtype and the cross drum type. Either ofthese designs may be constructed withvertical or inclined headers, and theheaders in turn may be of wrought steel orcast iron dependent upon the workingpressure for which the boiler isconstructed. The headers may be ofdifferent lengths, that is, may connectdifferent numbers of tubes, and it is by achange in the number of tubes in heightper section and the number of sections in

width that the size of the boiler is varied.

The longitudinal drum boiler is thegenerally accepted standard of Babcock &Wilcox construction. The cross drumboiler, though originally designed to meetcertain conditions of headroom, hasbecome popular for numerous classes ofwork where low headroom is not arequirement which must be met.

LONGITUDINAL DRUMCONSTRUCTION--The heating surface ofthis type of boiler is made up of a drum ordrums, depending upon the width of theboiler extending longitudinally over theother pressure parts. To the drum ordrums there are connected through crossboxes at either end the sections, which aremade up of headers and tubes. At thelower end of the sections there is a muddrum extending entirely across the setting

and connected to all sections. Theconnections between all parts are by shortlengths of tubes expanded into boredseats.

[Illustration: Forged-steel Drumhead withManhole Plate in Position]

The drums are of three sheets, of suchthickness as to give the required factor ofsafety under the maximum pressure forwhich the boiler is constructed. Thecircular seams are ordinarily single lapriveted though these may be double lapriveted to meet certain requirements ofpressure or of specifications. Thelongitudinal seams are properlyproportioned butt and strap or lap rivetedjoints dependent upon the pressure forwhich the boilers are built. Where buttstrap joints are used the straps are bent tothe proper radius in an hydraulic press.

The courses are built independently totemplate and are assembled by anhydraulic forcing press. All riveted holesare punched one-quarter inch smaller thanthe size of rivets as driven and are reamedto full size after the plates are assembled.All rivets are driven by hydraulic pressureand held until black.

[Illustration: Forged-steel DrumheadInterior]

The drumheads are hydraulic forged at asingle heat, the manhole opening andstiffening ring being forged in position.Flat raised seats for water column and feedconnections are formed in the forging.

All heads are provided with manholes, theedges of which are turned true. Themanhole plates are of forged steel andturned to fit manhole opening. These

plates are held in position by forged-steelguards and bolts.

The drum nozzles are of forged steel,faced, and fitted with taper thread studbolts.

[Illustration: Forged-steel Drum Nozzle]

Cross boxes by means of which thesections are attached to the drums, are offorged steel, made from a single sheet.

Where two or more drums are used in oneboiler they are connected by a cross pipehaving a flanged outlet for the steamconnection.

[Illustration: Forged-steel Cross Box]

The sections are built of 4-inch hot finishedseamless open-hearth steel tubes of No. 10

B. W. G. where the boilers are built forworking pressures up to 210 pounds.Where the working pressure is to beabove this and below 260 pounds, No. 9 B.W. G. tubes are supplied.

[Illustration: Inside Handhole FittingsWrought-steel Vertical Header]

The tubes are expanded into headers ofserpentine or sinuous form, which disposethe tubes in a staggered position whenassembled as a complete boiler. Theseheaders are of wrought steel or of castiron, the latter being ordinarily suppliedwhere the working pressure is not toexceed 160 pounds. The headers may beeither vertical or inclined as shown in thevarious illustrations of assembled boilers.

[Illustration: Wrought-steel VerticalHeader]

Opposite each tube end in the headersthere is placed a handhole of sufficient sizeto permit the cleaning, removal or renewalof a tube. These openings in the wroughtsteel vertical headers are elliptical inshape, machine faced, and milled to a trueplane back from the edge a sufficientdistance to make a seat. The openings areclosed by inside fitting forged plates,shouldered to center in the opening, theirflanged seats milled to a true plane. Theseplates are held in position by studs andforged-steel binders and nuts. The jointsbetween plates and headers are madewith a thin gasket.

[Illustration: Inside Handhole FittingWrought-steel Inclined Header]

In the wrought-steel inclined headers thehandhole openings are either circular or

elliptical, the former being ordinarilysupplied. The circular openings have araised seat milled to a true plane. Theopenings are closed on the outside byforged-steel caps, milled and ground true,held in position by forged-steel safetyclamps and secured by ball-headed boltsto assure correct alignment. With this styleof fitting, joints are made tight, metal tometal, without packing of any kind.

[Illustration: Wrought-steel InclinedHeader]

Where elliptical handholes are furnishedthey are faced inside, closed by insidefitting forged-steel plates, held to theirseats by studs and secured by forged-steelbinders and nuts.

The joints between plates and header aremade with a thin gasket.

[Illustration: Cast-iron Vertical Header]

The vertical cast-iron headers haveelliptical handholes with raised seatsmilled to a true plane. These are closed onthe outside by cast-iron caps milled true,held in position by forged-steel safetyclamps, which close the openings from theinside and which are secured byball-headed bolts to assure properalignment. All joints are made tight, metalto metal, without packing of any kind.

The mud drum to which the sections areattached at the lower end of the rearheaders, is a forged-steel box 7� inchessquare, and of such length as to beconnected to all headers by means ofwrought nipples expanded intocounterbored seats. The mud drum isfurnished with handholes for cleaning,

these being closed from the inside byforged-steel plates with studs, and securedon a faced seat in the mud drum byforged-steel binders and nuts. The jointsbetween the plates and the drum are madewith thin gaskets. The mud drum is tappedfor blow-off connection.

All connections between drums andsections and between sections and muddrum are of hot finished seamlessopen-hearth steel tubes of No. 9 B. W. G.

Boilers of the longitudinal drum type aresuspended front and rear fromwrought-steel supporting frames entirelyindependent of the brickwork. This allowsfor expansion and contraction of thepressure parts without straining either theboiler or the brickwork, and also allows ofbrickwork repair or renewal without in anyway disturbing the boiler or its

connections.

[Illustration: Babcock & WilcoxWrought-steel Vertical Header CrossDrum Boiler]

CROSS DRUM CONSTRUCTION--The crossdrum type of boilers differs from thelongitudinal only in drum construction andmethod of support. The drum in this type isplaced transversely across the rear of theboiler and is connected to the sections bymeans of circulating tubes expanded intobored seats.

The drums for all pressures are of twosheets of sufficient thickness to give therequired factor of safety. The longitudinalseams are double riveted butt strapped,the straps being bent to the proper radiusin an hydraulic press. The circulatingtubes are expanded into the drums at the

seams, the butt straps serving as tubeseats.

The drumheads, drum fittings and featuresof riveting are the same in the cross drumas in the longitudinal types. The sectionsand mud drum are also the same for thetwo types.

Cross drum boilers are supported at therear on the mud drum which rests oncast-iron foundation plates. They aresuspended at the front from a wrought-ironsupporting frame, each section beingsuspended independently from the crossmembers by hook suspension bolts. Thismethod of support is such as to allow forexpansion and contraction withoutstraining either the boiler or the brickworkand permits of repair or renewal of thelatter without in any way disturbing theboiler or its connections.

The following features of design and ofattachments supplied are the same for alltypes.

FRONTS--Ornamental fronts are fitted tothe front supporting frame. These havelarge doors for access to the front headersand panels above the fire fronts. The firefronts where furnished have independentframes for fire doors which are bolted on,and ashpit doors fitted with blast catches.The lugs on door frames and on doors arecast solid. The faces of doors and of framesare planed and the lugs milled. The doorsand frames are placed in their finalrelative position, clamped, and the holesfor hinge pins drilled while thus held. Aperfect alignment of door and frame is thusassured and the method is representativeof the care taken in small details ofmanufacture.

The front as a whole is so arranged thatany stoker may be applied with but slightmodification wherever boilers are set withsufficient furnace height.

[Illustration: Cross Drum Boiler Front]

In the vertical header boilers largewrought-iron doors, which give access tothe rear headers, are attached to the rearsupporting frame.

[Illustration: Wrought-steel InclinedHeader Longitudinal Drum Babcock &Wilcox Boiler, Equipped with Babcock &Wilcox Superheater]

[Illustration: Automatic Drumhead Stopand Check Valve]

FITTINGS--Each boiler is provided with the

following fittings as part of the standardequipment:

Blow-off connections and valves attachedto the mud drum.

Safety valves placed on nozzles on thesteam drums.

A water column connected to the front ofthe drum.

A steam gauge attached to the boiler front.

Feed water connection and valves. Aflanged stop and check valve of heavypattern is attached directly to eachdrumhead, closing automatically in case ofa rupture in the feed line.

All valves and fittings are substantiallybuilt and are of designs which by their

successful service for many years havebecome standard with The Babcock &Wilcox Co.

The fixtures that are supplied with theboilers consist of:

Dead plates and supports, the platesarranged for a fire brick lining.

A full set of grate bars and bearers, thelatter fitted with expansion sockets for sidewalls.

Flame bridge plates with necessaryfastenings, and special fire brick for liningsame.

Bridge wall girder for hanging bridge wallwith expansion sockets for side walls.

A full set of access and cleaning doors

through which all portions of the pressureparts may be reached.

A swing damper and frame with damperoperating rig.

There are also supplied with each boiler awrench for handhole nuts, a water-driventurbine tube cleaner, a set of fire tools anda metal steam hose and cleaning pipeequipped with a special nozzle for blowingdust and soot from the tubes.

Aside from the details of design andconstruction as covered in the foregoingdescription, a study of the illustrations willmake clear the features of the boiler as awhole which have led to its success.

The method of supporting the boiler hasbeen described. This allows it to be hungat any height that may be necessary to

properly handle the fuel to be burned or toaccommodate the stoker to be installed.The height of the nest of tubes which formsthe roof of the furnace is thus thecontrolling feature in determining thefurnace height, or the distance from thefront headers to the floor line. The sidesand front of the furnace are formed by theside and front boiler walls. The rear wall ofthe furnace consists of a bridge wall builtfrom the bottom of the ashpit to the lowerrow of tubes. The location of this wall maybe adjusted within limits to give the depthof furnace demanded by the fuel used.Ordinarily the bridge wall is thedetermining feature in the locating of thefront baffle. Where a great depth offurnace is necessary, in which case, if thefront baffle were placed at the bridge wallthe front pass of the boiler would berelatively too long, a patented constructionis used which maintains the baffle in what

may be considered its normal position,and a connection made between the baffleand the bridge wall by means of a tile roof.Such furnace construction is known as a"Webster" furnace.

[Illustration: Longitudinal DrumBoiler--Front View]

A consideration of this furnace will clearlyindicate its adaptability, by reason of itsflexibility, for any fuel and any design ofstoker. The boiler lends itself readily toinstallation with an extension or Dutchoven furnace if this be demanded by thefuel to be used, and in general it may bestated that a satisfactory furnacearrangement may be made in connectionwith a Babcock & Wilcox boiler forburning any fuel, solid, liquid or gaseous.

The gases of combustion evolved in the

furnace above described are led over theheating surfaces by two baffles. These areformed of cast-iron baffle plates lined withspecial fire brick and held in position bytube clamps. The front baffle leads thegases through the forward portion of thetubes to a chamber beneath the drum ordrums. It is in this chamber that asuperheater is installed where such anapparatus is desired. The gases make aturn over the front baffle, are leddownward through the central portion ofthe tubes, called the second pass, bymeans of a hanging bridge wall of brickand the second baffle, around which theymake a second turn upward, pass throughthe rear portion of the tubes and are led tothe stack or flue through a damper box inthe rear wall, or around the drums to adamper box placed overhead.

The space beneath the tubes between the

bridge wall and the rear boiler wall formsa pocket into which much of the soot fromthe gases in their downward passagethrough the second pass will be depositedand from which it may be readily cleanedthrough doors furnished for the purpose.

The gas passages are ample and are soproportioned that the resistance offered tothe gases is only such as will assure theproper abstraction of heat from the gaseswithout causing undue friction, requiringexcessive draft.

[Illustration: Partial Vertical SectionShowing Method of Introducing FeedWater]

The method in which the feed water isintroduced through the front drumhead ofthe boiler is clearly seen by reference tothe illustration. From this point of

introduction the water passes to the rear ofthe drum, downward through the rearcirculating tubes to the sections, upwardthrough the tubes of the sections to thefront headers and through these headersand front circulating tubes again to thedrum where such water as has not beenformed into steam retraces its course. Thesteam formed in the passage through thetubes is liberated as the water reaches thefront of the drum. The steam so formed isstored in the steam space above the waterline, from which it is drawn through aso-called "dry pipe." The dry pipe in theBabcock & Wilcox boiler is misnamed, asin reality it fulfills none of the functionsordinarily attributed to such a device. Thisfunction is usually to restrict the flow ofsteam from a boiler with a view to avoidpriming. In the Babcock & Wilcox boiler itsfunction is simply that of a collecting pipe,and as the aggregate area of the holes in it

is greatly in excess of the area of the steamoutlet from the drum, it is plain that therecan be no restriction through thiscollecting pipe. It extends nearly thelength of the drum, and draws steamevenly from the whole length of the steamspace.

[Illustration: Cast-iron Vertical HeaderLongitudinal Drum Babcock & WilcoxBoiler]

[Illustration: Closed Open

Patented Side Dusting Doors]

The large tube doors through which accessis had to the front headers and the doorsgiving such access to the rear headers inboilers of the vertical header type havealready been described and are shownclearly by the illustrations on pages 56 and

74. In boilers of the inclined header type,access to the rear headers is securedthrough the chamber formed by theheaders and the rear boiler wall. Largedoors in the sides of the setting give fullaccess to all parts for inspection and forremoval of accumulations of soot. Smalldusting doors are supplied for the sidewalls through which all of the heatingsurfaces may be cleaned by means of asteam dusting lance. These side dustingdoors are a patented feature and theshutters are self closing. In wide boilersadditional cleaning doors are supplied atthe top of the setting to insure ease inreaching all portions of the heatingsurface.

The drums are accessible for inspectionthrough the manhole openings. Theremoval of the handhole plates makespossible the inspection of each tube for its

full length and gives the assurance that nodefect can exist that cannot be actuallyseen. This is particularly advantageouswhen inspecting for the presence of scale.

The materials entering into theconstruction of the Babcock & Wilcoxboiler are the best obtainable for thespecial purpose for which they are usedand are subjected to rigid inspection andtests.

The boilers are manufactured by means ofthe most modern shop equipment andappliances in the hands of an old andwell-tried organization of skilledmechanics under the supervision ofexperienced engineers.

[Illustration: Cast-iron Vertical HeaderCross Drum Babcock & Wilcox Boiler]

ADVANTAGES OF THE BABCOCK &WILCOX BOILER

The advantages of the Babcock & Wilcoxboiler may perhaps be most clearly setforth by a consideration, 1st, of water-tubeboilers as a class as compared with shelland fire-tube boilers; and 2nd, of theBabcock & Wilcox boiler specifically ascompared with other designs ofwater-tube boilers.

WATER-TUBE _VERSUS_ FIRE-TUBEBOILERS

Safety--The most important requirement ofa steam boiler is that it shall be safe in sofar as danger from explosion is concerned.If the energy in a large shell boiler underpressure is considered, the thought of thedestruction possible in the case of anexplosion is appalling. The late Dr. RobertH. Thurston, Dean of Sibley College,Cornell University, and past president ofthe American Society of MechanicalEngineers, estimated that there issufficient energy stored in a plain cylinderboiler under 100 pounds steam pressure toproject it in case of an explosion to aheight of over 3� miles; a locomotiveboiler at 125 pounds pressure fromone-half to one-third of a mile; and a 60horse-power return tubular boiler under

75 pounds pressure somewhat over a mile.To quote: "A cubic foot of heated waterunder a pressure of from 60 to 70 poundsper square inch has about the sameenergy as one pound of gunpowder." Fromsuch a consideration, it may be readilyappreciated how the advent of highpressure steam was one of the strongestfactors in forcing the adoption ofwater-tube boilers. A consideration of thethickness of material necessary forcylinders of various diameters under asteam pressure of 200 pounds andassuming an allowable stress of 12,000pounds per square inch, will perhaps bestillustrate this point. Table 1 gives suchthicknesses for various diameters ofcylinders not taking into consideration theweakening effect of any joints which maybe necessary. The rapidity with which theplate thickness increases with thediameter is apparent and in practice, due

to the fact that riveted joints must be used,the thicknesses as given in the table, withthe exception of the first, must beincreased from 30 to 40 per cent.

In a water-tube boiler the drums seldomexceed 48 inches in diameter and thethickness of plate required, therefore, isnever excessive. The thinner metal can berolled to a more uniform quality, the seamsadmit of better proportioning, and thejoints can be more easily and perfectlyfitted than is the case where thicker platesare necessary. All of these pointscontribute toward making the drums ofwater-tube boilers better able to withstandthe stress which they will be called upon toendure.

The essential constructive differencebetween water-tube and fire-tube boilerslies in the fact that the former is composed

of parts of relatively small diameter asagainst the large diameters necessary inthe latter.

The factor of safety of the boiler partswhich come in contact with the mostintense heat in water-tube boilers can bemade much higher than would bepracticable in a shell boiler. Under theassumptions considered above inconnection with the thickness of platesrequired, a number 10 gauge tube (0.134inch), which is standard in Babcock &Wilcox boilers for pressures up to 210pounds under the same allowable stress aswas used in computing Table 1, the safeworking pressure for the tubes is 870pounds per square inch, indicating thevery large margin of safety of such tubesas compared with that possible with theshell of a boiler.

TABLE 1

PLATE THICKNESS REQUIRED FORVARIOUS CYLINDER DIAMETERS

ALLOWABLE STRESS, 12000 POUNDSPER SQUARE INCH, 200 POUNDSGAUGE PRESSURE, NO JOINTS

+---------+-----------+ |Diameter | Thickness| |Inches | Inches | +---------+-----------+| 4 | 0.033 | | 36 | 0.300 | | 48| 0.400 | | 60 | 0.500 | | 72 |

0.600 | | 108 | 0.900 | | 120 |1.000 | | 144 | 1.200 |+---------+-----------+

A further advantage in the water-tubeboiler as a class is the elimination of allcompressive stresses. Cylinders subjectedto external pressures, such as fire tubes orthe internally fired furnaces of certain

types of boilers, will collapse under apressure much lower than that which theycould withstand if it were appliedinternally. This is due to the fact that ifthere exists any initial distortion from itstrue shape, the external pressure will tendto increase such distortion and collapsethe cylinder, while an internal pressuretends to restore the cylinder to its originalshape.

Stresses due to unequal expansion havebeen a fruitful source of trouble infire-tube boilers.

In boilers of the shell type, the rivetedjoints of the shell, with their consequentdouble thickness of metal exposed to thefire, gives rise to serious difficulties. Uponthese points are concentrated all strains ofunequal expansion, giving rise to frequentleaks and oftentimes to actual ruptures.

Moreover, in the case of such rupture, thewhole body of contained water is liberatedinstantaneously and a disastrous andusually fatal explosion results.

Further, unequal strains result in shell orfire-tube boilers due to the difference intemperature of the various parts. Thisdifference in temperature results from thelack of positive well defined circulation.While such a circulation does notnecessarily accompany all water-tubedesigns, in general, the circulation inwater-tube boilers is much more definedthan in fire-tube or shell boilers.

A positive and efficient circulation assuresthat all portions of the pressure parts willbe at approximately the same temperatureand in this way strains resulting fromunequal temperatures are obviated.

If a shell or fire-tubular boiler explodes,the apparatus as a whole is destroyed. Inthe case of water-tube boilers, the drumsare ordinarily so located that they areprotected from intense heat and anyrupture is usually in the case of a tube.Tube failures, resulting from blisters orburning, are not serious in their nature.Where a tube ruptures because of a flaw inthe metal, the result may be more severe,but there cannot be the disastrousexplosion such as would occur in the caseof the explosion of a shell boiler.

To quote Dr. Thurston, relative to thegreater safety of the water-tube boiler:"The stored available energy is usuallyless than that of any of the other stationaryboilers and not very far from the amountstored, pound for pound, in the plaintubular boiler. It is evident that theiradmitted safety from destructive explosion

does not come from this relation, however,but from the division of the contents intosmall portions and especially from thosedetails of construction which make ittolerably certain that any rupture shall belocal. A violent explosion can only comefrom the general disruption of a boiler andthe liberation at once of large masses ofsteam and water."

Economy--The requirement probably nextin importance to safety in a steam boiler iseconomy in the use of fuel. To fulfill such arequirement, the three items, of propergrate for the class of fuel to be burned, acombustion chamber permitting completecombustion of gases before their escape tothe stack, and the heating surface of such acharacter and arrangement that themaximum amount of available heat may beextracted, must be co-ordinated.

Fire-tube boilers from the nature of theirdesign do not permit the variety ofcombinations of grate surface, heatingsurface, and combustion space possible inpractically any water-tube boiler.

In securing the best results in fueleconomy, the draft area in a boiler is animportant consideration. In fire-tubeboilers this area is limited to the crosssectional area of the fire tubes, a conditionfurther aggravated in a horizontal boilerby the tendency of the hot gases to passthrough the upper rows of tubes instead ofthrough all of the tubes alike. In water-tubeboilers the draft area is that of the spaceoutside of the tubes and is hence muchgreater than the cross sectional area of thetubes.

Capacity--Due to the generally moreefficient circulation found in water-tube

than in fire-tube boilers, rates ofevaporation are possible with water-tubeboilers that cannot be approached wherefire-tube boilers are employed.

Quick Steaming--Another important resultof the better circulation ordinarily found inwater-tube boilers is in their ability toraise steam rapidly in starting and to meetthe sudden demands that may be thrownon them.

In a properly designed water-tube boilersteam may be raised from a cold boiler to200 pounds pressure in less than one-halfhour.

For the sake of comparison with the figureabove, it may be stated that in the U. S.Government Service the shortest timeallowed for getting up steam in Scotchmarine boilers is 6 hours and the time

ordinarily allowed is 12 hours. In largedouble-ended Scotch boilers, such as aregenerally used in Trans-Atlantic service,the fires are usually started 24 hoursbefore the time set for getting under way.This length of time is necessary for suchboilers in order to eliminate as far aspossible excessive strains resulting fromthe sudden application of heat to thesurfaces.

Accessibility--In the "Requirements of aPerfect Steam Boiler", as stated by Mr.Babcock, he demonstrates the necessityfor complete accessibility to all portions ofthe boiler for cleaning, inspection andrepair.

Cleaning--When the great difference isrealized in performance, both as toeconomy and capacity of a clean boilerand one in which the heating surfaces have

been allowed to become fouled, it may beappreciated that the ability to keepheating surfaces clean internally andexternally is a factor of the highestimportance.

Such results can be accomplished only bythe use of a design in boiler constructionwhich gives complete accessibility to allportions. In fire-tube boilers the tubes arefrequently nested together with a spacebetween them often less than 1� inchesand, as a consequence, nearly the entiretube surface is inaccessible. When scaleforms upon such tubes it is impossible toremove it completely from the inside of theboiler and if it is removed by a turbinehammer, there is no way of knowing howthorough a job has been done. With theformation of such scale there is dangerthrough overheating and frequent tuberenewals are necessary.

[Illustration: Portion of 29,000 Horse-powerInstallation of Babcock & Wilcox Boilers inthe L Street Station of the Edison ElectricIlluminating Co. of Boston, Mass. ThisCompany Operates in its Various Stationsa Total of 39,000 Horse Power of Babcock &Wilcox Boilers]

In Scotch marine boilers, even with theengines operating condensing, completetube renewals at intervals of six or sevenyears are required, while largereplacements are often necessary in lessthan one year. In return tubular boilersoperated with bad feed water, completetube renewals annually are not uncommon.In this type of boiler much sediment fallson the bottom sheets where the intenseheat to which they are subjected bakes itto such an excessive hardness that the onlymethod of removing it is to chisel it out.

This can be done only by omitting tubesenough to leave a space into which a mancan crawl and the discomforts under whichhe must work are apparent. Unless such adeposit is removed, a burned and buckledplate will invariably result, and ifneglected too long an explosion willfollow.

In vertical fire-tube boilers using a waterleg construction, a deposit of mud in suchlegs is an active agent in causing corrosionand the difficulty of removing such depositthrough handholes is well known. Acomplete removal is practicallyimpossible and as a last resort to obviatecorrosion in certain designs, the bottom ofthe water legs in some cases have beenmade of copper. A thick layer of mud andscale is also liable to accumulate on thecrown sheet of such boilers and may causethe sheet to crack and lead to an

explosion.

The soot and fine coal swept along with thegases by the draft will settle in fire tubesand unless removed promptly, must be cutout with a special form of scraper. It is notunusual where soft coal is used to findtubes half filled with soot, which rendersuseless a large portion of the heatingsurface and so restricts the draft as tomake it difficult to burn sufficient coal todevelop the required power from suchheating surface as is not covered by soot.

Water-tube boilers in general are from thenature of their design more readilyaccessible for cleaning than are fire-tubeboilers.

Inspection--The objections given above inthe consideration of the inability toproperly clean fire-tube boilers hold as

well for the inspection of such boilers.

Repairs--The lack of accessibility infire-tube boilers further leads to difficultieswhere repairs are required.

In fire-tube boilers tube renewals are aserious undertaking. The accumulation ofhard deposit on the exterior of the surfacesso enlarges the tubes that it is oftentimesdifficult, if not impossible, to draw themthrough the tube sheets and it is usuallynecessary to cut out such tubes as willallow access to the one which has failedand remove them through the manhole.

When a tube sheet blisters, the defectivepart must be cut out by hand-tapped holesdrilled by ratchets and as it is frequentlyimpossible to get space in which to driverivets, a "soft patch" is necessary. This isbut a makeshift at best and usually results

in either a reduction of the safe workingpressure or in the necessity for a newplate. If the latter course is followed, theold plate must be cut out, a new onescribed to place to locate rivet holes and inorder to obtain room for driving rivets, theboiler will have to be re-tubed.

The setting must, of course, be at leastpartially torn out and replaced.

In case of repairs, of such nature infire-tube boilers, the working pressure ofsuch repaired boilers will frequently belowered by the insurance companies whenthe boiler is again placed in service.

In the case of a rupture in a water-tubeboiler, the loss will ordinarily be limited toone or two tubes which can be readilyreplaced. The fire-tube boiler will be socompletely demolished that the question

of repairs will be shifted from the boiler tothe surrounding property, the damage towhich will usually exceed many times thecost of a boiler of a type which would haveeliminated the possibility of a disastrousexplosion. In considering the properrepair cost of the two types of boilers, thefact should not be overlooked that it ispoor economy to invest large sums inequipment that, through a possibleaccident to the boiler may be whollydestroyed or so damaged that the cost ofrepairs, together with the loss of timewhile such repairs are being made, wouldpurchase boilers of absolute safety andleave a large margin beside. Thepossibility of loss of human life should alsobe considered, though this may seem a farcry from the question of repair costs.

Space Occupied--The space required forthe boilers in a plant often exceeds the

requirements for the remainder of theplant equipment. Any saving of space in aboiler room will be a large factor inreducing the cost of real estate and of thebuilding. Even when the boiler plant iscomparatively small, the saving in spacefrequently will amount to a considerablepercentage of the cost of the boilers. Table2 shows the difference in floor spaceoccupied by fire-tube boilers and Babcock& Wilcox boilers of the same capacity, thelatter being taken as representing thewater-tube class. This saving in space willincrease with the size of the plant for thereason that large size boiler units whilecommon in water-tube practice areimpracticable in fire-tube practice.

TABLE 2

COMPARATIVE APPROXIMATEFLOOR SPACE OCCUPIED BY

BABCOCK & WILCOX AND H. R. T.BOILERS

+------------+----------------+---------------+|Size of unit|Babcock & Wilcox| H. R. T.| |Horse Power |Feet and Inches |Feetand Inches|+------------+----------------+---------------+ |100 | 7 3 �19 9 | 10 0 �20 0 | | 150| 7 10 �19 9 | 10 0 �22 6 | | 200 | 90 �19 9 | 11 6 �23 10 | | 250 | 9 0

�19 9 | 11 6 �23 10 | | 300 | 10 2 �199 | 12 0 �25 0 |+------------+----------------+---------------+

BABCOCK & WILCOX BOILERS ASCOMPARED WITH OTHER WATER-TUBEDESIGNS

It must be borne in mind that the simplefact that a boiler is of the water-tubedesign does not as a necessity indicatethat it is a good or safe boiler.

Safety--Many of the water-tube boilers onthe market are as lacking as are fire-tubeboilers in the positive circulation which, ashas been demonstrated by Mr. Babcock'slecture, is so necessary in therequirements of the perfect steam boiler.In boilers using water-leg construction,there is danger of defective circulation,leaks are common, and unsuspectedcorrosion may be going on in portions ofthe boiler that cannot be inspected.Stresses due to unequal expansion of the

metal cannot be well avoided but they maybe minimized by maintaining at the sametemperature all pressure parts of theboiler. The result is to be secured only bymeans of a well defined circulation.

The main feature to which the Babcock &Wilcox boiler owes its safety is theconstruction made possible by the use ofheaders, by which the water in eachvertical row of tubes is separated from thatin the adjacent rows. This constructionresults in the very efficient circulationproduced through the breaking up of thesteam and water in the front headers, theeffect of these headers in producing such apositive circulation having been clearlydemonstrated in Mr. Babcock's lecture.The use of a number of sections, thuscomposed of headers and tubes, has adistinct advantage over the use of acommon chamber at the outlet ends of the

tubes. In the former case the circulation ofwater in one vertical row of tubes cannotinterfere with that in the other rows, whilein the latter construction there will bedownward as well as upward currents andsuch downward currents tend to neutralizeany good effect there might be through thediminution of the density of the watercolumn by the steam.

Further, the circulation results directlyfrom the design of the boiler and requiresno assistance from "retarders", checkvalves and the like, within the boiler. Allsuch mechanical devices in the interior ofa boiler serve only to complicate thedesign and should not be used.

This positive and efficient circulationassures that all portions of the pressureparts of the Babcock & Wilcox boiler willbe at approximately the same temperature

and in this way strains resulting fromunequal temperatures are obviated.

Where the water throughout the boiler is atthe temperature of the steam contained, acondition to be secured only by propercirculation, danger from internal pitting isminimized, or at least limited only toeffects of the water fed the boiler. Wherethe water in any portion of the boiler islower than the temperature of the steamcorresponding to the pressure carried,whether the fact that such lowertemperatures exist as a result of lack ofcirculation, or because of intentionaldesign, internal pitting or corrosion willalmost invariably result.

Dr. Thurston has already been quoted tothe effect that the admitted safety of awater-tube boiler is the result of thedivision of its contents into small portions.

In boilers using a water-leg construction,while the danger from explosion will belargely limited to the tubes, there is thedanger, however, that such legs mayexplode due to the deterioration of theirstays, and such an explosion might bealmost as disastrous as that of a shellboiler. The headers in a Babcock & Wilcoxboiler are practically free from any dangerof explosion. Were such an explosion tooccur, it would still be localized to a muchlarger extent than in the case of awater-leg boiler and the headerconstruction thus almost absolutelylocalizes any danger from such a cause.

Staybolts are admittedly an undesirableelement of construction in any boiler. Theyare wholly objectionable and the onlyreason for the presence of staybolts in aboiler is to enable a cheaper form ofconstruction to be used than if they were

eliminated.

In boilers utilizing in their designflat-stayed surfaces, or stayboltconstruction under pressure, corrosionand wear and tear in service tends toweaken some single part subject tocontinual strain, the result being anincreased strain on other parts greatly inexcess of that for which an allowance canbe made by any reasonable factor ofsafety. Where the construction is such thatthe weakening of a single part willproduce a marked decrease in the safetyand reliability of the whole, it follows ofnecessity, that there will be acorresponding decrease in the workingpressure which may be safely carried.

In water-leg boilers, the use of suchflat-stayed surfaces under pressurepresents difficulties that are practically

unsurmountable. Such surfaces exposed tothe heat of the fire are subject to unequalexpansion, distortion, leakage andcorrosion, or in general, to many of theobjections that have already beenadvanced against the fire-tube boilers inthe consideration of water-tube boilers asa class in comparison with fire-tubeboilers.

[Illustration: McAlpin Hotel, New YorkCity, Operating 2360 Horse Power ofBabcock & Wilcox Boilers]

Aside from the difficulties that may arise inactual service due to the failure ofstaybolts, or in general, due to the use offlat-stayed surfaces, constructionalfeatures are encountered in the actualmanufacture of such boilers that make itdifficult if not impossible to produce afirst-class mechanical job. It is practically

impossible in the building of such a boilerto so design and place the staybolts that allwill be under equal strain. Such unequalstrains, resulting from constructionaldifficulties, will be greatly multiplied whensuch a boiler is placed in service. Much ofthe riveting in boilers of this design mustof necessity be hand work, which is neverthe equal of machine riveting. The use ofwater-leg construction ordinarily requiresthe flanging of large plates, which isdifficult, and because of the number ofheats necessary and the continual workingof the material, may lead to the weakeningof such plates.

In vertical or semi-vertical water-tubeboilers utilizing flat-stayed surfaces underpressure, these surfaces are ordinarily solocated as to offer a convenient lodgingplace for flue dust, which fuses into a hardmass, is difficult of removal and under

which corrosion may be going on with nopossibility of detection.

Where stayed surfaces or water legs arefeatures in the design of a water-tubeboiler, the factor of safety of such partsmust be most carefully considered. In suchparts too, is the determination of the factormost difficult, and because of the"rule-of-thumb" determination frequentlynecessary, the factor of safety becomes inreality a factor of ignorance. As opposed tosuch indeterminate factors of safety, in theBabcock & Wilcox boiler, when the factorof safety for the drum or drums has beendetermined, and such a factor may bedetermined accurately, the factors for allother portions of the pressure parts aregreatly in excess of that of the drum. AllBabcock & Wilcox boilers are built with afactor of safety of at least five, andinasmuch as the factor of the safety of the

tubes and headers is greatly in excess ofthis figure, it applies specifically to thedrum or drums. This factor represents agreater degree of safety than aconsiderably higher factor applied to aboiler in which the shell or any rivetedportion is acted upon directly by the fire,or the same factor applied to a boilerutilizing flat-stayed surface construction,where the accurate determination of thelimiting factor of safety is difficult, if notimpossible.

That the factor of safety of stayed surfacesis questionable may perhaps be bestrealized from a consideration of the severerequirements as to such factor called forby the rules and regulations of the Board ofSupervising Inspectors, U. S. Government.

In view of the above, the absence of anystayed surfaces in the Babcock & Wilcox

boiler is obviously a distinguishingadvantage where safety is a factor. It is ofinterest to note, in the article on theevolution of the Babcock & Wilcox boiler,that staybolt construction was used inseveral designs, found unsatisfactory andunsafe, and discarded.

Another feature in the design of theBabcock & Wilcox boiler tending towardadded safety is its manner of suspension.This has been indicated in the previouschapter and is of such nature that all of thepressure parts are free to expand orcontract under variations of temperaturewithout in any way interfering with anypart of the boiler setting. The sectionalnature of the boiler allows a flexibilityunder varying temperature changes thatpractically obviates internal strain.

In boilers utilizing water-leg construction,

on the other hand, the construction is rigid,giving rise to serious internal strains andthe method of support ordinarily madenecessary by the boiler design is not onlyunmechanical but frequently dangerous,due to the fact that proper provision is notmade for expansion and contraction undertemperature variations.

Boilers utilizing water-leg construction arenot ordinarily provided with mud drums.This is a serious defect in that it allowsimpurities and sediment to collect in aportion of the boiler not easily inspected,and corrosion may result.

Economy--That the water-tube boiler as aclass lends itself more readily than doesthe fire-tube boiler to a variation in therelation of grate surface, heating surfaceand combustion space has been alreadypointed out. In economy again, the

construction made possible by the use ofheaders in Babcock & Wilcox boilersappears as a distinct advantage. Becauseof this construction, there is a flexibilitypossible, in an unlimited variety of heightsand widths that will satisfactorily meet thespecial requirements of the fuel to beburned in individual cases.

An extended experience in the design offurnaces best suited for a wide variety offuels has made The Babcock & Wilcox Co.leaders in the field of economy. Furnaceshave been built and are in successfuloperation for burning anthracite andbituminous coals, lignite, crude oil,gas-house tar, wood, sawdust andshavings, bagasse, tan bark, natural gas,blast furnace gas, by-product coke ovengas and for the utilization of waste heatfrom commercial processes. The greatnumber of Babcock & Wilcox boilers now

in satisfactory operation under such a widerange of fuel conditions constitutes anunimpeachable testimonial to the ability tomeet all of the many conditions of service.

The limitations in the draft area of fire-tubeboilers as affecting economy have beenpointed out. That a greater draft area ispossible in water-tube boilers does not ofnecessity indicate that proper advantageof this fact is taken in all boilers of thewater-tube class. In the Babcock & Wilcoxboiler, the large draft area taken inconnection with the effective bafflingallows the gases to be brought intointimate contact with all portions of theheating surfaces and renders suchsurfaces highly efficient.

In certain designs of water-tube boilers thebaffling is such as to render ineffectivecertain portions of the heating surface, due

to the tendency of soot and dirt to collecton or behind baffles, in this way causingthe interposition of a layer ofnon-conducting material between the hotgases and the heating surfaces.

In Babcock & Wilcox boilers the standardbaffle arrangement is such as to allow theinstallation of a superheater without in anyway altering the path of the gases fromfurnace to stack, or requiring a change inthe boiler design. In certain water-tubeboilers the baffle arrangement is such thatif a superheater is to be installed acomplete change in the ordinary baffledesign is necessary. Frequently to insuresufficiently hot gas striking the heatingsurfaces, a portion is by-passed directlyfrom the furnace to the superheaterchamber without passing over any of theboiler heating surfaces. Any sucharrangement will lead to a decrease in

economy and the use of boilers requiringit should be avoided.

Capacity--Babcock & Wilcox boilers arerun successfully in every-day practice athigher ratings than any other boilers inpractical service. The capacities thusobtainable are due directly to the efficientcirculation already pointed out. Inasmuchas the construction utilizing headers has adirect bearing in producing suchcirculation, it is also connected with thehigh capacities obtainable with thisapparatus.

Where intelligently handled and keptproperly cleaned, Babcock & Wilcoxboilers are operated in many plants atfrom 200 to 225 per cent of their ratedevaporative capacity and it is not unusualfor them to be operated at 300 per cent ofsuch rated capacity during periods of peak

load.

Dry Steam--In the list of the requirementsof the perfect steam boiler, the necessitythat dry steam be generated has beenpointed out. The Babcock & Wilcox boilerwill deliver dry steam under highercapacities and poorer conditions of feedwater than any other boiler nowmanufactured. Certain boilers will, whenoperated at ordinary ratings, handle poorfeed water and deliver steam in which themoisture content is not objectionable.When these same boilers are driven athigh overloads, there will be a directtendency to prime and the percentage ofmoisture in the steam delivered will behigh. This tendency is the result of the lackof proper circulation and once more thereis seen the advantage of the headers of theBabcock & Wilcox boiler, resulting as itdoes in the securing of a positive

circulation.

In the design of the Babcock & Wilcoxboiler sufficient space is providedbetween the steam outlet and thedisengaging point to insure the steampassing from the boiler in a dry statewithout entraining or again picking up anyparticles of water in its passage even athigh rates of evaporation. Ample time isgiven for a complete separation of steamfrom the water at the disengaging surfacebefore the steam is carried from the boiler.These two features, which are additionalcauses for the ability of the Babcock &Wilcox boiler to deliver dry steam, resultfrom the proper proportioning of thesteam and water space of the boiler. Fromthe history of the development of theboiler, it is evident that the cubicalcapacity per horse power of the steam andwater space has been adopted after

numerous experiments.

That the "dry pipe" serves in no way thegenerally understood function of suchdevice has been pointed out. As stated, thefunction of the "dry pipe" in a Babcock &Wilcox boiler is simply that of a collectingpipe and this statement holds trueregardless of the rate of operation of theboiler.

In certain boilers, "superheating surface"is provided to "dry the steam," or toremove the moisture due to priming orfoaming. Such surface is invariably asource of trouble unless the steam isinitially dry and a boiler which will deliverdry steam is obviously to be preferred toone in which surface must be suppliedespecially for such purpose. Wheresuperheaters are installed with Babcock &Wilcox boilers, they are in every sense of

the word superheaters and not driers, thesteam being delivered to them in a drystate.

The question has been raised inconnection with the cross drum design ofthe Babcock & Wilcox boiler as to itsability to deliver dry steam. Experiencehas shown the absolute lack of basis forany such objection. The Babcock & WilcoxCompany at its Bayonne Works some timeago made a series of experiments to see inwhat manner the steam generated wasseparated from the water either in thedrum or in its passage to the drum. Glasspeepholes were installed in each end of adrum in a boiler of the marine design, atthe point midway between that at whichthe horizontal circulating tubes enteredthe drum and the drum baffle plate. Byholding a light at one of these peepholesthe action in the drum was clearly seen

through the other. It was found that withthe boiler operated under three-quarterinch ashpit pressure, which, with the fuelused would be equivalent toapproximately 185 per cent of rating forstationary boiler practice, that each tubewas delivering with great velocity a streamof solid water, which filled the tube for halfits cross sectional area. There was nospray or mist accompanying suchdelivery, clearly indicating that the steamhad entirely separated from the water in itspassage through the horizontal circulatingtubes, which in the boiler in question werebut 50 inches long.

[Illustration: Northwest Station of theCommonwealth Edison Co., Chicago, Ill.This Installation Consists of 11,360 HorsePower of Babcock & Wilcox Boilers andSuperheaters, Equipped with Babcock &Wilcox Chain Grate Stokers]

These experiments proved conclusivelythat the size of the steam drums in thecross drum design has no appreciableeffect in determining the amount ofliberating surface, and that sufficientliberating surface is provided in thecirculating tubes alone. If further proof ofthe ability of this design of boiler todeliver dry steam is required, such proofis perhaps best seen in the continued useof the Babcock & Wilcox marine boiler, inwhich the cross drum is used exclusively,and with which rates of evaporation areobtained far in excess of those secured inordinary practice.

Quick Steaming--The advantages ofwater-tube boilers as a class over fire-tubeboilers in ability to raise steam quicklyhave been indicated.

Due to the constant and thoroughcirculation resulting from the sectionalnature of the Babcock & Wilcox boiler,steam may be raised more rapidly than inpractically any other water-tube design.

In starting up a cold Babcock & Wilcoxboiler with either coal or oil fuel, where aproper furnace arrangement is supplied,steam may be raised to a pressure of 200pounds in less than half an hour. With aBabcock & Wilcox boiler in a test whereforced draft was available, steam wasraised from an initial temperature of theboiler and its contained water of 72degrees to a pressure of 200 pounds, in12� minutes after lighting the fire. Theboiler also responds quickly in startingfrom banked fires, especially whereforced draft is available.

In Babcock & Wilcox boilers the water is

divided into many small streams whichcirculate without undue frictionalresistance in thin envelopes passingthrough the hottest part of the furnace, thesteam being carried rapidly to thedisengaging surface. There is no part ofthe boiler exposed to the heat of the firethat is not in contact with water internally,and as a result there is no danger ofoverheating on starting up quickly nor canleaks occur from unequal expansion suchas might be the case where an attempt ismade to raise steam rapidly in boilersusing water leg construction.

Storage Capacity for Steam andWater--Where sufficient steam and watercapacity are not provided in a boiler, itsaction will be irregular, the steampressure varying over wide limits and thewater level being subject to frequent andrapid fluctuation.

Owing to the small relative weight ofsteam, water capacity is of greaterimportance in this respect than steamspace. With a gauge pressure of 180pounds per square inch, 8 cubic feet ofsteam, which is equivalent to one-halfcubic foot of water space, are required tosupply one boiler horse power for oneminute and if no heat be supplied to theboiler during such an interval, thepressure will drop to 150 pounds persquare inch. The volume of steam space,therefore, may be over rated, but if this betoo small, the steam passing off will carrywater with it in the form of spray. Too greata water space results in slow steaming andwaste of fuel in starting up; while too muchsteam space adds to the radiating surfaceand increases the losses from that cause.

That the steam and water space of the

Babcock & Wilcox boiler are the result ofnumerous experiments has previouslybeen pointed out.

Accessibility--Cleaning. That water-tubeboilers are more accessible as a class thanare fire-tube boilers has been indicated.All water-tube boilers, however, are notequally accessible. In certain designs, dueto the arrangement of baffling used it ispractically impossible to remove alldeposits of soot and dirt. Frequently, inorder to cheapen the product, sufficientcleaning and access doors are notsupplied as part of the boiler equipment.The tendency of soot to collect on thecrown sheets of certain vertical water-tubeboilers has been noted. Such deposits aredifficult to remove and if corrosion goes onbeneath such a covering the sheet maycrack and an explosion result.

[Illustration: Rear View--LongitudinalDrum Vertical Header Boiler, ShowingAccess Doors to Rear Headers]

It is almost impossible to thoroughly cleanwater legs internally, and in such placesalso is there a tendency to unsuspectedcorrosion under deposits that cannot beremoved.

In Babcock & Wilcox boilers every portionof the interior of the heating surfaces canbe reached and kept clean, while any sootdeposited on the exterior surfaces can beblown off while the boiler is underpressure.

Inspection--The accessibility which makespossible the thorough cleaning of allportions of the Babcock & Wilcox boileralso provides a means for a thoroughinspection.

Drums are accessible for internalinspection by the removal of the manholeplates. Front headers may be inspectedthrough large doors furnished for thepurpose. Rear headers in the inclinedheader designs may be inspected from thechamber formed by such headers and therear wall of the boiler. In the verticalheader designs rear tube doors arefurnished, as has been stated. In certaindesigns of water-tube boilers in order toassure accessibility for inspection of therear ends of the tubes, the rear portion ofthe boiler is exposed to the atmospherewith resulting excessive radiation losses.In other designs the means of access to therear ends of the tubes are of a makeshiftand unworkmanlike character.

By the removal of handhole plates, alltubes in a Babcock & Wilcox boiler may be

inspected for their full length either for thepresence of scale or for suspectedcorrosion.

Repairs--In Babcock & Wilcox boilers thepossession of great strength, theelimination of stresses due to uneventemperatures and of the resulting dangerof leaks and corrosion, the protection ofthe drums from the intense heat of the fire,and the decreased liability of the scaleforming matter to lodge on the hottest tubesurfaces, all tend to minimize the necessityfor repairs. The tubes of the Babcock &Wilcox boiler are practically the only partwhich may need renewal and these only atinfrequent intervals When necessary, suchrenewals may be made cheaply andquickly. A small stock of tubes, 4 inches indiameter, of sufficient length for the boilerused, is all that need be carried to makerenewals.

Repairs in water-leg boilers are difficult atbest and frequently unsatisfactory whencompleted. When staybolt replacementsare necessary, in order to get at the innersheet of the water leg, several tubes mustin some cases be cut out. Not infrequentlya replacement of an entire water leg isnecessary and this is difficult and requiresa lengthy shutdown. With the Babcock &Wilcox boiler, on the other hand, even if itis necessary to replace a section, this maybe done in a few hours after the boiler iscool.

In the case of certain staybolt failures theworking pressure of a repaired boilerutilizing such construction will frequentlybe lowered by the insurance companieswhen the boiler is again placed in service.The sectional nature of the Babcock &Wilcox boiler enables it to maintain its

original working pressure over longperiods of time, almost regardless of thenature of any repair that may be required.

[Illustration: 1456 Horse-power Installationof Babcock & Wilcox Boilers at the RaritanWoolen Mills, Raritan, N. J. The First ofThese Boilers were Installed in 1878 and1881 and are still Operated at 80 PoundsPressure]

Durability--Babcock & Wilcox boilers arebeing operated in every-day service withentirely satisfactory results and under thesame steam pressure as that for which theywere originally sold that have beenoperated from thirty to thirty-five years. Itis interesting to note in considering the lifeof a boiler that the length of life of aBabcock & Wilcox boiler must be taken asthe criterion of what length of life ispossible. This is due to the fact that there

are Babcock & Wilcox boilers in operationto-day that have been in service from atime that antedates by a considerablemargin that at which the manufacturer ofany other water-tube boiler now on themarket was started.

Probably the very best evidence of thevalue of the Babcock & Wilcox boiler as asteam generator and of the reliability ofthe apparatus, is seen in the sales of thecompany. Since the company was formed,there have been sold throughout the worldover 9,900,000 horse power.

A feature that cannot be overlooked in theconsideration of the advantages of theBabcock & Wilcox boiler is the fact that asa part of the organization back of theboiler, there is a body of engineers ofrecognized ability, ready at all times toassist its customers in every possible way.

[Illustration: 2400 Horse-power Installationof Babcock & Wilcox Boilers in the UnionStation Power House of the PennsylvaniaRailroad Co., Pittsburgh, Pa. ThisCompany has a Total of 28,500 HorsePower of Babcock & Wilcox BoilersInstalled]

HEAT AND ITS MEASUREMENT

The usual conception of heat is that it is aform of energy produced by the vibratorymotion of the minute particles ormolecules of a body. All bodies areassumed to be composed of thesemolecules, which are held together bymutual cohesion and yet are in a state ofcontinual vibration. The hotter a body orthe more heat added to it, the morevigorous will be the vibrations of themolecules.

As is well known, the effect of heat on abody may be to change its temperature, itsvolume, or its state, that is, from solid toliquid or from liquid to gaseous. Wherewater is melted from ice and evaporatedinto steam, the various changes areadmirably described in the lecture by Mr.

Babcock on "The Theory of SteamMaking", given in the next chapter.

The change in temperature of a body isordinarily measured by thermometers,though for very high temperaturesso-called pyrometers are used. The latterare dealt with under the heading "HighTemperature Measurements" at the end ofthis chapter.


By reason of the uniform expansion ofmercury and its great sensitiveness toheat, it is the fluid most commonly used inthe construction of thermometers. In allthermometers the freezing point and theboiling point of water, under mean oraverage atmospheric pressure at sea level,are assumed as two fixed points, but thedivision of the scale between these two

points varies in different countries. Thefreezing point is determined by the use ofmelting ice and for this reason is oftencalled the melting point. There are in usethree thermometer scales known as theFahrenheit, the Centigrade or Celsius, andthe R�umur. As shown in Fig. 11, in theFahrenheit scale, the space between thetwo fixed points is divided into 180 parts;the boiling point is marked 212, and thefreezing point is marked 32, and zero is atemperature which, at the time thisthermometer was invented, wasincorrectly imagined to be the lowesttemperature attainable. In the centigradeand the R�umur scales, the distancebetween the two fixed points is dividedinto 100 and 80 parts, respectively. In eachof these two scales the freezing point ismarked zero, and the boiling point ismarked 100 in the centigrade and 80 in theR�umur. Each of the 180, 100 or 80

divisions in the respective thermometers iscalled a degree.

Table 3 and appended formulae are usefulfor converting from one scale to another.

In the United States the bulbs ofhigh-grade thermometers are usuallymade of either Jena 58^{III} borosilicatethermometer glass or Jena 16^{III} glass,the stems being made of ordinary glass.The Jena 16^{III} glass is not suitable foruse at temperatures much above 850degrees Fahrenheit and the harder Jena59^{III} should be used in thermometers fortemperatures higher than this.

Below the boiling point, the hydrogen-gasthermometer is the almost universalstandard with which mercurialthermometers may be compared, whileabove this point the nitrogen-gas

thermometer is used. In both of thesestandards the change in temperature ismeasured by the change in pressure of aconstant volume of the gas.

In graduating a mercurial thermometer forthe Fahrenheit scale, ordinarily a degree isrepresented as 1/180 part of the volume ofthe stem between the readings at themelting point of ice and the boiling pointof water. For temperatures above thelatter, the scale is extended in degrees ofthe same volume. For very accurate work,however, the thermometer may begraduated to read true-gas-scaletemperatures by comparing it with the gasthermometer and marking thetemperatures at 25 or 50 degree intervals.Each degree is then 1/25 or 1/50 of thevolume of the stem in each interval.

Every thermometer, especially if intended

for use above the boiling point, should besuitably annealed before it is used. If thisis not done, the true melting point and alsothe "fundamental interval", that is, theinterval between the melting and theboiling points, may change considerably.After continued use at the highertemperatures also, the melting point willchange, so that the thermometer must becalibrated occasionally to insure accuratereadings.

TABLE 3

COMPARISON OF THERMOMETERSCALES

+---------------+----------+----------+----------+| |Fahrenheit|Centigrade|R�umur |+---------------+----------+----------+----------+|Absolute Zero | -459.64 | -273.13 |

-218.50 | | | 0 | -17.78 |-14.22 | | | 10 | -12.22 |-9.78 | | | 20 | -6.67 | -5.33| | | 30 | -1.11 | -0.89 ||Freezing Point | 32 | 0 | 0 ||Maximum Density| | | | |of Water | 39.1 | 3.94 | 3.15 | |

| 50 | 10 | 8 | | |75 | 23.89 | 19.11 | | | 100| 37.78 | 30.22 | | | 200 |93.33 | 74.67 | |Boiling Point | 212 |100 | 80 | | | 250 | 121.11| 96.89 | | | 300 | 148.89 |119.11 | | | 350 | 176.67 |141.33 |+---------------+----------+----------+----------+

F = 9/5C+32� = 9/4R+32�

C = 5/9(F-32�) = 5/4R

R = 4/9(F-32�) = 4/5C

As a general rule thermometers aregraduated to read correctly for totalimmersion, that is, with bulb and stem ofthe thermometer at the same temperature,and they should be used in this way whencompared with a standard thermometer. Ifthe stem emerges into space either hotteror colder than that in which the bulb isplaced, a "stem correction" must beapplied to the observed temperature inaddition to any correction that may befound in the comparison with the standard.For instance, for a particular thermometer,comparison with the standard with bothfully immersed made necessary thefollowing corrections:

_Temperature_ _Correction_ 40�F0.0 100 0.0 200 0.0 300 +2.5 400 -0.5 500 -2.5

When the sign of the correction is positive(+) it must be added to the observedreading, and when the sign is a negative(-) the correction must be subtracted. Theformula for the stem correction is asfollows:

Stem correction = 0.000085 �n (T-t)

in which T is the observed temperature, tis the mean temperature of the emergentcolumn, n is the number of degrees ofmercury column emergent, and 0.000085is the difference between the coefficient ofexpansion of the mercury and that in theglass in the stem.

Suppose the observed temperature is 400degrees and the thermometer is immersedto the 200 degrees mark, so that 200degrees of the mercury column projectinto the air. The mean temperature of the

emergent column may be found by tyinganother thermometer on the stem with thebulb at the middle of the emergentmercury column as in Fig. 12. Suppose thismean temperature is 85 degrees, then

Stem correction = 0.000085 �200 �(400 -85) = 5.3 degrees.

As the stem is at a lower temperature thanthe bulb, the thermometer will evidentlyread too low, so that this correction mustbe added to the observed reading to findthe reading corresponding to totalimmersion. The corrected reading willtherefore be 405.3 degrees. If thisthermometer is to be corrected inaccordance with the calibrated correctionsgiven above, we note that a furthercorrection of 0.5 must be applied to theobserved reading at this temperature, sothat the correct temperature is 405.3 - 0.5

= 404.8 degrees or 405 degrees.



Fig. 12 shows how a stem correction canbe obtained for the case just described.

Fig. 13 affords an opportunity forcomparing the scale of a thermometercorrect for total immersion with one whichwill read correctly when submerged to the300 degrees mark, the stem beingexposed at a mean temperature of 110degrees Fahrenheit, a temperature oftenprevailing when thermometers are usedfor measuring temperatures in steammains.

Absolute Zero--Experiments show that at32 degrees Fahrenheit a perfect gas

expands 1/491.64 part of its volume if itspressure remains constant and itstemperature is increased one degree.Thus if gas at 32 degrees Fahrenheitoccupies 100 cubic feet and itstemperature is increased one degree, itsvolume will be increased to 100 +100/491.64 = 100.203 cubic feet. For a riseof two degrees the volume would be 100 +(100 �2) / 491.64 = 100.406 cubic feet. Ifthis rate of expansion per one degree heldgood at all temperatures, and experimentshows that it does above the freezingpoint, the gas, if its pressure remained thesame, would double its volume, if raised toa temperature of 32 + 491.64 = 523.64degrees Fahrenheit, while under adiminution of temperature it would shrinkand finally disappear at a temperature of491.64 - 32 = 459.64 degrees below zeroFahrenheit. While undoubtedly somechange in the law would take place before

the lower temperature could be reached,there is no reason why the law may not beused within the range of temperaturewhere it is known to hold good. From thisexplanation it is evident that under aconstant pressure the volume of a gas willvary as the number of degrees between itstemperature and the temperature of-459.64 degrees Fahrenheit. To simplifythe application of the law, a newthermometric scale is constructed asfollows: the point corresponding to -460degrees Fahrenheit, is taken as the zeropoint on the new scale, and the degreesare identical in magnitude with those onthe Fahrenheit scale. Temperaturesreferred to this new scale are calledabsolute temperatures and the point -460degrees Fahrenheit (= -273 degreescentigrade) is called the absolute zero. Toconvert any temperature Fahrenheit toabsolute temperature, add 460 degrees to

the temperature on the Fahrenheit scale:thus 54 degrees Fahrenheit will be 54 +460 = 514 degrees absolute temperature;113 degrees Fahrenheit will likewise beequal to 113 + 460 = 573 degrees absolutetemperature. If one pound of gas is at atemperature of 54 degrees Fahrenheit andanother pound is at a temperature of 114degrees Fahrenheit the respectivevolumes at a given pressure would be inthe ratio of 514 to 573.

[Illustration: Ninety-sixth Street Station ofthe New York Railways Co., New YorkCity, Operating 20,000 Horse Power ofBabcock & Wilcox Boilers. This Companyand its Allied Companies Operate a Totalof 100,000 Horse Power of Babcock &Wilcox Boilers]

British Thermal Unit--The quantitativemeasure of heat is the British thermal unit,

ordinarily written B. t. u. This is thequantity of heat required to raise thetemperature of one pound of pure waterone degree at 62 degrees Fahrenheit; thatis, from 62 degrees to 63 degrees. In themetric system this unit is the _calorie_ andis the heat necessary to raise thetemperature of one kilogram of pure waterfrom 15 degrees to 16 degrees centigrade.These two definitions lead to adiscrepancy of 0.03 of 1 per cent, which isinsignificant for engineering purposes,and in the following the B. t. u. is takenwith this discrepancy ignored. Thediscrepancy is due to the fact that there isa slight difference in the specific heat ofwater at 15 degrees centigrade and 62degrees Fahrenheit. The two units may becompared thus:

1 Calorie = 3.968 B. t. u. 1 B. t. u. =0.252 Calories.

_Unit_ _Water_ _Temperature Rise_1 B. t. u. 1 Pound 1 Degree Fahrenheit1 Calorie 1 Kilogram 1 Degreecentigrade

But 1 kilogram = 2.2046 pounds and 1degree centigrade = 9/5 degreeFahrenheit.

Hence 1 calorie = (2.2046 �9/5) = 3.968 B.t. u.

The heat values in B. t. u. are ordinarilygiven per pound, and the heat values incalories per kilogram, in which case the B.t. u. per pound are approximatelyequivalent to 9/5 the calories perkilogram.

As determined by Joule, heat energy has a

certain definite relation to work, oneBritish thermal unit being equivalent fromhis determinations to 772 foot pounds.Rowland, a later investigator, found that778 foot pounds were a more exactequivalent. Still later investigationsindicate that the correct value for a B. t. u.is 777.52 foot pounds or approximately778. The relation of heat energy to work asdetermined is a demonstration of the firstlaw of thermo-dynamics, namely, that heatand mechanical energy are mutuallyconvertible in the ratio of 778 foot poundsfor one British thermal unit. This law,algebraically expressed, is W = JH; Wbeing the work done in foot pounds, Hbeing the heat in B. t. u., and J being Joulesequivalent. Thus 1000 B. t. u.'s would becapable of doing 1000 �778 = 778000 footpounds of work.

Specific Heat--The specific heat of a

substance is the quantity of heat expressedin thermal units required to raise or lowerthe temperature of a unit weight of anysubstance at a given temperature onedegree. This quantity will vary for differentsubstances For example, it requires about16 B. t. u. to raise the temperature of onepound of ice 32 degrees or 0.5 B. t. u. toraise it one degree, while it requiresapproximately 180 B. t. u. to raise thetemperature of one pound of water 180degrees or one B. t. u. for one degree.

If then, a pound of water be considered asa standard, the ratio of the amount of heatrequired to raise a similar unit of any othersubstance one degree, to the amountrequired to raise a pound of water onedegree is known as the specific heat of thatsubstance. Thus since one pound of waterrequired one B. t. u. to raise itstemperature one degree, and one pound

of ice requires about 0.5 degrees to raiseits temperature one degree, the ratio is 0.5which is the specific heat of ice. To beexact, the specific heat of ice is 0.504,hence 32 degrees �0.504 = 16.128 B. t. u.would be required to raise thetemperature of one pound of ice from 0 to32 degrees. For solids, at ordinarytemperatures, the specific heat may beconsidered a constant for each individualsubstance, although it is variable for hightemperatures. In the case of gases adistinction must be made between specificheat at constant volume, and at constantpressure.

Where specific heat is stated alone,specific heat at ordinary temperature isimplied, and _mean_ specific heat refers tothe average value of this quantity betweenthe temperatures named.

The specific heat of a mixture of gases isobtained by multiplying the specific heatof each constituent gas by the percentageby weight of that gas in the mixture, anddividing the sum of the products by 100.The specific heat of a gas whosecomposition by weight is CO_{2}, 13 percent; CO, 0.4 per cent; O, 8 per cent; N,78.6 per cent, is found as follows:

CO_{2} : 13 �0.217 = 2.821 CO : 0.4�0.2479 = 0.09916 O : 8 �0.2175 =1.74000 N : 78.6 �0.2438 = 19.16268 -------- 100.0 23.82284

and 23.8228 �100 = 0.238 = specific heat ofthe gas.

The specific heats of various solids, liquidsand gases are given in Table 4.

Sensible Heat--The heat utilized in raisingthe temperature of a body, as that inraising the temperature of water from 32degrees up to the boiling point, is termedsensible heat. In the case of water, thesensible heat required to raise itstemperature from the freezing point to theboiling point corresponding to thepressure under which ebullition occurs, istermed the heat of the liquid.

Latent Heat--Latent heat is the heat whichapparently disappears in producing somechange in the condition of a body withoutincreasing its temperature If heat beadded to ice at freezing temperature, theice will melt but its temperature will not beraised. The heat so utilized in changing thecondition of the ice is the latent heat and inthis particular case is known as the latentheat of fusion. If heat be added to water at212 degrees under atmospheric pressure,

the water will not become hotter but willbe evaporated into steam, the temperatureof which will also be 212 degrees. The heatso utilized is called the latent heat ofevaporation and is the heat whichapparently disappears in causing thesubstance to pass from a liquid to agaseous state.

TABLE 4

SPECIFIC HEATS OF VARIOUSSUBSTANCES+--------------------------------------------------------------------+ | SOLIDS

|+-------------------------------+----------------+-------------------+ | |Temperature[2]| | |

| Degrees | Specific | || Fahrenheit | Heat |

+-------------------------------+----------------+---

----------------+ | Copper |59-460 | .0951 | | Gold

| 32-212 | .0316 | | WroughtIron | 59-212 | .1152 || Cast Iron | 68-212 |.1189 | | Steel (soft) |68-208 | .1175 | | Steel (hard)

| 68-208 | .1165 | | Zinc| 32-212 | .0935 | |

Brass (yellow) | 32 |.0883 | | Glass (normal ther. 16^{III}) |

66-212 | .1988 | | Lead| 59 | .0299 | | Platinum

| 32-212 | .0323 | |Silver | 32-212 | .0559

| | Tin | -105-64 |.0518 | | Ice | |

.5040 | | Sulphur (newly fused) || .2025 |

+-------------------------------+----------------+-------------------+ | LIQUIDS

|

+-------------------------------+----------------+-------------------+ | |Temperature[2]| | |

| Degrees | Specific | || Fahrenheit | Heat |

+-------------------------------+----------------+-------------------+ | Water[3] |59 | 1.0000 | | Alcohol

| 32 | .5475 | || 176 | .7694 | | Mercury

| 32 | .03346 | |Benzol | 50 | .4066

| | | 122 |.4502 | | Glycerine |59-102 | .576 | | Lead (Melted)

| to 360 | .0410 | |Sulphur (melted) | 246-297 |.2350 | | Tin (melted) |

| .0637 | | Sea Water (sp. gr.1.0043) | 64 | .980 | | SeaWater (sp. gr. 1.0463) | 64 |.903 | | Oil of Turpentine | 32

| .411 | | Petroleum| 64-210 | .498 | | SulphuricAcid | 68-133 | .3363 |+-------------------------------+----------------+-------------------+ | GASES

|+--------------------------+---------------+--------------+----------+ | | |Specific | Specific | | |Temperature[2]| Heat at | Heat at | |

| Degrees | Constant |Constant | | | Fahrenheit |

Pressure | Volume |+--------------------------+---------------+--------------+----------+ | Air | 32-392

| .2375 | .1693 | | Oxygen| 44-405 | .2175 | .1553 | |Nitrogen | 32-392 | .2438| .1729 | | Hydrogen | 54-388

| 3.4090 | 2.4141 | | SuperheatedSteam | | See table 25 | || Carbon Monoxide | 41-208 |

.2425 | .1728 | | Carbon Dioxide| 52-417 | .2169 | .1535 | |Methane | 64-406 | .5929| .4505 | | Blast Fur. Gas (approx.) | ...

| .2277 | ... | | Flue gas(approx.) | ... | .2400 | ... |+--------------------------+---------------+--------------+----------+

Latent heat is not lost, but reappearswhenever the substances pass through areverse cycle, from a gaseous to a liquid,or from a liquid to a solid state. It may,therefore, be defined as stated, as the heatwhich apparently disappears, or is lost tothermometric measurement, when themolecular constitution of a body is beingchanged. Latent heat is expended inperforming the work of overcoming themolecular cohesion of the particles of thesubstance and in overcoming theresistance of external pressure to change

of volume of the heated body. Latent heatof evaporation, therefore, may be said toconsist of internal and external heat, theformer being utilized in overcoming themolecular resistance of the water inchanging to steam, while the latter isexpended in overcoming any resistance tothe increase of its volume duringformation. In evaporating a pound of waterat 212 degrees to steam at 212 degrees,897.6 B. t. u. are expended as internallatent heat and 72.8 B. t. u. as externallatent heat. For a more detaileddescription of the changes brought aboutin water by sensible and latent heat, thereader is again referred to the chapter on"The Theory of Steam Making".

Ebullition--The temperature of ebullition ofany liquid, or its boiling point, may bedefined as the temperature which existswhere the addition of heat to the liquid no

longer increases its temperature, the heatadded being absorbed or utilized inconverting the liquid into vapor. Thistemperature is dependent upon thepressure under which the liquid isevaporated, being higher as the pressureis greater.

TABLE 5

BOILING POINTS AT ATMOSPHERICPRESSURE

+---------------------+--------------+ || Degrees | | | Fahrenheit

| +---------------------+--------------+ |Ammonia | 140 | | Bromine

| 145 | | Alcohol | 173 || Benzine | 212 | | Water

| 212 | | Average Sea Water |213.2 | | Saturated Brine | 226 | |Mercury | 680 |

+---------------------+--------------+

Total Heat of Evaporation--The quantity ofheat required to raise a unit of any liquidfrom the freezing point to any giventemperature, and to entirely evaporate it atthat temperature, is the total heat ofevaporation of the liquid for thattemperature. It is the sum of the heat of theliquid and the latent heat of evaporation.

To recapitulate, the heat added to a bodyis divided as follows:

Total heat = Heat to change thetemperature + heat to overcome themolecular cohesion + heat to overcome

the external pressure resisting anincrease of volume of the body.

Where water is converted into steam, thistotal heat is divided as follows:

Total heat = Heat to change thetemperature of the water + heat toseparate the molecules of the water + heatto overcome resistance to increasein volume of the steam, = Heat of theliquid + internal latent heat + external

latent heat, = Heat of the liquid +total latent heat of steam, = Totalheat of evaporation.

The steam tables given on pages 122 to127 give the heat of the liquid and the totallatent heat through a wide range oftemperatures.

Gases--When heat is added to gases thereis no internal work done; hence the totalheat is that required to change thetemperature plus that required to do theexternal work. If the gas is not allowed toexpand but is preserved at constant

volume, the entire heat added is thatrequired to change the temperature only.

Linear Expansion of Substances byHeat--To find the increase in the length of abar of any material due to an increase oftemperature, multiply the number ofdegrees of increase in temperature by thecoefficient of expansion for one degreeand by the length of the bar. Where thecoefficient of expansion is given for 100degrees, as in Table 6, the result should bedivided by 100. The expansion of metalsper one degree rise of temperatureincreases slightly as high temperatures arereached, but for all practical purposes itmay be assumed to be constant for a givenmetal.

TABLE 6

LINEAL EXPANSION OF SOLIDS AT

ORDINARY TEMPERATURES

(Tabular values represent increase perfoot per 100 degrees increase intemperature, Fahrenheit or centigrade)

+-------------------+--------------+----------------+----------------+ | | Temperature| | | | |Conditions[4]|Coefficient per |Coefficientper | | Substance | Degrees | 100Degrees | 100 Degrees | | |Fahrenheit | Fahrenheit | Centigrade|+-------------------+--------------+----------------+----------------+ |Brass (cast) | 32 to212 | .001042 | .001875 | |Brass(wire) | 32 to 212 | .001072 |.001930 | |Copper | 32 to 212 |.000926 | .001666 | |Glass (English| | | | |flint)| 32 to 212 | .000451 | .000812 |

|Glass (French | | || |flint) | 32 to 212 | .000484

| .000872 | |Gold | 32 to 212| .000816 | .001470 | |Granite(average) | 32 to 212 | .000482 |.000868 | |Iron (cast) | 104 |.000589 | .001061 | |Iron (softforged) | 0 to 212 | .000634 |.001141 | |Iron (wire) | 32 to 212 |

.000800 | .001440 | |Lead |32 to 212 | .001505 | .002709 ||Mercury | 32 to 212 | .009984[5]| .017971 | |Platinum | 104

| .000499 | .000899 | |Limestone| 32 to 212 | .000139 | .000251

| |Silver | 104 | .001067 |.001921 | |Steel (Bessemer | |

| | |rolled, hard) | 0 to212 | .00056 | .00101 | |Steel(Bessemer | | | ||rolled, soft) | 0 to 212 | .00063 |

.00117 | |Steel (cast, | |

| | |French) | 104 |.000734 | .001322 | |Steel (cast

| | | | |annealed,English) | 104 | .000608 |.001095 |+-------------------+--------------+----------------+----------------+

High Temperature Measurements--Thetemperatures to be dealt with insteam-boiler practice range from those ofordinary air and steam to the temperaturesof burning fuel. The gases of combustion,originally at the temperature of thefurnace, cool as they pass through eachsuccessive bank of tubes in the boiler, tonearly the temperature of the steam,resulting in a wide range of temperaturesthrough which definite measurements aresometimes required.

Of the different methods devised for

ascertaining these temperatures, some ofthe most important are as follows:

1st. Mercurial pyrometers fortemperatures up to 1000 degreesFahrenheit.

2nd. Expansion pyrometers fortemperatures up to 1500 degreesFahrenheit.

3rd. Calorimetry for temperatures up to2000 degrees Fahrenheit.

4th. Thermo-electric pyrometers fortemperatures up to 2900 degreesFahrenheit.

5th. Melting points of metal which flow atvarious temperatures up to the meltingpoint of platinum 3227 degrees Fahrenheit.

6th. Radiation pyrometers fortemperatures up to 3600 degreesFahrenheit.

7th. Optical pyrometers capable ofmeasuring temperatures up to 12,600degrees Fahrenheit.[6] For ordinary boilerpractice however, their range is 1600 to3600 degrees Fahrenheit.

[Illustration: 228 Horse-power Babcock &Wilcox Boiler, Installed at the WentworthInstitute, Boston, Mass.]

Table 7 gives the degree of accuracy ofhigh temperature measurements.

TABLE 7

ACCURACY OF HIGH TEMPERATUREMEASUREMENTS[7]

+------------------------+------------------------+ |Centigrade | Fahrenheit |

+-------------+----------+-------------+----------+| | Accuracy | | Accuracy | |Temperature | Plus or | Temperature |Plus or | | Range | Minus | Range| Minus | | | Degrees | |Degrees |+-------------+----------+-------------+----------+| 200- 500 | 0.5 | 392- 932 | 0.9 || 500- 800 | 2 | 932-1472 | 3.6 || 800-1100 | 3 | 1472-2012 | 5.4 || 1100-1600 | 15 | 2012-2912 | 27| | 1600-2000 | 25 | 2912-3632 | 45

|+-------------+----------+-------------+----------+

Mercurial Pyrometers--At atmosphericpressure mercury boils at 676 degreesFahrenheit and even at lowertemperatures the mercury in

thermometers will be distilled and willcollect in the upper part of the stem.Therefore, for temperatures much above400 degrees Fahrenheit, some inert gas,such as nitrogen or carbon dioxide, mustbe forced under pressure into the upperpart of the thermometer stem. Thepressure at 600 degrees Fahrenheit isabout 15 pounds, or slightly above that ofthe atmosphere, at 850 degrees about 70pounds, and at 1000 degrees about 300pounds.

Flue-gas temperatures are nearly alwaystaken with mercurial thermometers as theyare the most accurate and are easy to readand manipulate. Care must be taken thatthe bulb of the instrument projects into thepath of the moving gases in order that thetemperature may truly represent the fluegas temperature. No readings should beconsidered until the thermometer has

been in place long enough to heat it up tothe full temperature of the gases.

Expansion Pyrometers--Brass expandsabout 50 per cent more than iron and inboth brass and iron the expansion isnearly proportional to the increase intemperature. This phenomenon is utilizedin expansion pyrometers by enclosing abrass rod in an iron pipe, one end of therod being rigidly attached to a cap at theend of the pipe, while the other isconnected by a multiplying gear to apointer moving around a graduated dial.The whole length of the expansion piecemust be at a uniform temperature before acorrect reading can be obtained. This fact,together with the lost motion which islikely to exist in the mechanism connectedto the pointer, makes the expansionpyrometer unreliable; it should be used

only when its limitations are thoroughlyunderstood and it should be carefullycalibrated. Unless the brass and iron areknown to be of the same temperature, itsaction will be anomalous: for instance, if itbe allowed to cool after being exposed toa high temperature, the needle will risebefore it begins to fall. Similarly, a rise intemperature is first shown by theinstrument as a fall. The explanation is thatthe iron, being on the outside, heats orcools more quickly than the brass.

Calorimetry--This method derives its namefrom the fact that the process is the sameas the determination of the specific heat ofa substance by the water calorimeter,except that in one case the temperature isknown and the specific heat is required,while in the other the specific heat isknown and the temperature is required.

The temperature is found as follows:

A given weight of some substance such asiron, nickel or fire brick, is heated to theunknown temperature and then plungedinto water and the rise in temperaturenoted.

If X = temperature to be measured, w =weight of heated body in pounds, W =weight of water in pounds, T = finaltemperature of water, t = differencebetween initial and final temperatures ofwater, s = known specific heat of body.Then X = T + Wt �ws

Any temperatures secured by this methodare affected by so many sources of errorthat the results are very approximate.

Thermo-electric Pyrometers--When wiresof two different metals are joined at one

end and heated, an electromotive forcewill be set up between the free ends of thewires. Its amount will depend upon thecomposition of the wires and thedifference in temperature between thetwo. If a delicate galvanometer of highresistance be connected to the "thermalcouple", as it is called, the deflection of theneedle, after a careful calibration, willindicate the temperature very accurately.

In the thermo-electric pyrometer of LeChatelier, the wires used are platinum anda 10 per cent alloy of platinum andrhodium, enclosed in porcelain tubes toprotect them from the oxidizing influenceof the furnace gases. The couple with itsprotecting tubes is called an "element".The elements are made in different lengthsto suit conditions.

It is not necessary for accuracy to expose

the whole length of the element to thetemperature to be measured, as theelectromotive force depends only uponthe temperature of the juncture at theclosed end of the protecting tube and thatof the cold end of the element. Thegalvanometer can be located at anyconvenient point, since the length of thewires leading to it simply alter theresistance of the circuit, for whichallowance may be made.

The advantages of the thermo-electricpyrometer are accuracy over a wide rangeof temperatures, continuity of readings,and the ease with which observations canbe taken. Its disadvantages are high firstcost and, in some cases, extreme delicacy.

Melting Points of Metals--The approximatetemperature of a furnace or flue may bedetermined, if so desired, by introducing

certain metals of which the melting pointsare known. The more common metals forma series in which the respective meltingpoints differ by 100 to 200 degreesFahrenheit, and by using these in order,the temperature can be fixed between themelting points of some two of them. Thismethod lacks accuracy, but it suffices fordeterminations where approximatereadings are satisfactory.

The approximate melting points of certainmetals that may be used fordeterminations of this nature are given inTable 8.

Radiation Pyrometers--These are similar tothermo-electric pyrometers in that athermo-couple is employed. The heat raysgiven out by the hot body fall on a concavemirror and are brought to a focus at a pointat which is placed the junction of a

thermo-couple. The temperature readingsare obtained from an indicator similar tothat used with thermo-electric pyrometers.

Optical Pyrometers--Of the opticalpyrometers the Wanner is perhaps themost reliable. The principle on which thisinstrument is constructed is that ofcomparing the quantity of light emanatingfrom the heated body with a constantsource of light, in this case a two-voltosmium lamp. The lamp is placed at oneend of an optical tube, while at the otheran eyepiece is provided and a scale. Abattery of cells furnishes the current forthe lamp. On looking through thepyrometer, a circle of red light appears,divided into distinct halves of differentintensities. Adjustment may be made sothat the two halves appear alike and areading is then taken from the scale. Thetemperatures are obtained from a table of

temperatures corresponding to scalereadings. For standardizing the osmiumlamp, an amylacetate lamp, is providedwith a stand for holding the optical tube.

TABLE 8

APPROXIMATE MELTING POINTS OFMETALS[8]

+-----------------+------------------+ | Metal| Temperature | | |Degrees

Fahrenheit|+-----------------+------------------+ |WroughtIron | 2737 | |Pig Iron (gray) |2190-2327 | |Cast Iron (white)| 2075

| |Steel | 2460-2550 | |Steel(cast) | 2500 | |Copper |1981 | |Zinc | 786 ||Antimony | 1166 | |Lead| 621 | |Bismuth | 498

| |Tin | 449 | |Platinum

| 3191 | |Gold | 1946 ||Silver | 1762 | |Aluminum

| 1216 |+-----------------+------------------+

Determination of Temperature fromCharacter of Emitted Light--As a furthermeans of determining approximately thetemperature of a furnace, Table 9,compiled by Messrs. White & Taylor, maybe of service. The color at a giventemperature is approximately the same forall kinds of combustibles under similarconditions.

TABLE 9

CHARACTER OF EMITTED LIGHT ANDCORRESPONDING APPROXIMATETEMPERATURE[9]

+--------------------------------------+-----------+| Character of Emitted Light|Temperature| | |Degrees | | |Fahrenheit|+--------------------------------------+-----------+|Dark red, blood red, low red | 1050

| |Dark cherry red | 1175| |Cherry, full red | 1375 ||Light cherry, bright cherry, light red|1550 | |Orange | 1650

| |Light orange | 1725 ||Yellow | 1825 | |Lightyellow | 1975 | |White

| 2200 |+--------------------------------------+-----------+

THE THEORY OF STEAM MAKING

[Extracts from a Lecture delivered byGeorge H. Babcock, at Cornell University,1887[10]]

The chemical compound known as H_{2}Oexists in three states or conditions--ice,water and steam; the only differencebetween these states or conditions is in thepresence or absence of a quantity ofenergy exhibited partly in the form of heatand partly in molecular activity, which, forwant of a better name, we are accustomedto call "latent heat"; and to transform itfrom one state to another we have only tosupply or extract heat. For instance, if wetake a quantity of ice, say one pound, atabsolute zero[11] and supply heat, the firsteffect is to raise its temperature until itarrives at a point 492 Fahrenheit degrees

above the starting point. Here it stopsgrowing warmer, though we keep onadding heat. It, however, changes from iceto water, and when we have addedsufficient heat to have made it, had itremained ice, 283 degrees hotter or atemperature of 315 degrees Fahrenheit'sthermometer, it has all become water, atthe same temperature at which itcommenced to change, namely, 492degrees above absolute zero, or 32degrees by Fahrenheit's scale. Let us stillcontinue to add heat, and it will now growwarmer again, though at a slower rate--thatis, it now takes about double the quantityof heat to raise the pound one degree thatit did before--until it reaches atemperature of 212 degrees Fahrenheit, or672 degrees absolute (assuming that weare at the level of the sea). Here we findanother critical point. However much moreheat we may apply, the water, as water, at

that pressure, cannot be heated any hotter,but changes on the addition of heat tosteam; and it is not until we have addedheat enough to have raised thetemperature of the water 966 degrees, orto 1,178 degrees by Fahrenheit'sthermometer (presuming for the momentthat its specific heat has not changed sinceit became water), that it has all becomesteam, which steam, nevertheless, is at thetemperature of 212 degrees, at which thewater began to change. Thus overfour-fifths of the heat which has beenadded to the water has disappeared, orbecome insensible in the steam to any ofour instruments.

It follows that if we could reduce steam atatmospheric pressure to water, withoutloss of heat, the heat stored within it wouldcause the water to be red hot; and if wecould further change it to a solid, like ice,

without loss of heat, the solid would bewhite hot, or hotter than melted steel--itbeing assumed, of course, that the specificheat of the water and ice remain normal, orthe same as they respectively are at thefreezing point.

After steam has been formed, a furtheraddition of heat increases the temperatureagain at a much faster ratio to the quantityof heat added, which ratio also variesaccording as we maintain a constantpressure or a constant volume; and I amnot aware that any other critical pointexists where this will cease to be the factuntil we arrive at that very hightemperature, known as the point ofdissociation, at which it becomes resolvedinto its original gases.

The heat which has been absorbed by onepound of water to convert it into a pound of

steam at atmospheric pressure is sufficientto have melted 3 pounds of steel or 13pounds of gold. This has been transformedinto something besides heat; stored up toreappear as heat when the process isreversed. That condition is what we arepleased to call latent heat, and in it residesmainly the ability of the steam to do work.

[Graph: Temperature in FahrenheitDegrees (from Absolute Zero) againstQuantity of Heat in British Thermal Units]

The diagram shows graphically therelation of heat to temperature, thehorizontal scale being quantity of heat inBritish thermal units, and the verticaltemperature in Fahrenheit degrees, bothreckoned from absolute zero and by theusual scale. The dotted lines for ice andwater show the temperature which wouldhave been obtained if the conditions had

not changed. The lines marked "gold" and"steel" show the relation to heat andtemperature and the melting points ofthese metals. All the inclined lines wouldbe slightly curved if attention had beenpaid to the changing specific heat, but thecurvature would be small. It is worthnoting that, with one or two exceptions, thecurves of all substances lie between thevertical and that for water. That is to say,that water has a greater capacity for heatthan all other substances except two,hydrogen and bromine.

In order to generate steam, then, only twosteps are required: 1st, procure the heat,and 2nd, transfer it to the water. Now, youhave it laid down as an axiom that when abody has been transferred or transformedfrom one place or state into another, thesame work has been done and the sameenergy expended, whatever may have

been the intermediate steps or conditions,or whatever the apparatus. Therefore,when a given quantity of water at a giventemperature has been made into steam ata given temperature, a certain definitework has been done, and a certain amountof energy expended, from whatever theheat may have been obtained, or whateverboiler may have been employed for thepurpose.

A pound of coal or any other fuel has adefinite heat producing capacity, and iscapable of evaporating a definite quantityof water under given conditions. That is thelimit beyond which even perfection cannotgo, and yet I have known, and doubtlessyou have heard of, cases where inventorshave claimed, and so-called engineershave certified to, much higher results.

The first step in generating steam is in

burning the fuel to the best advantage. Apound of carbon will generate 14,500British thermal units, during combustioninto carbonic dioxide, and this will be thesame, whatever the temperature or therapidity at which the combustion may takeplace. If possible, we might oxidize it at asslow a rate as that with which iron rusts orwood rots in the open air, or we mightburn it with the rapidity of gunpowder, aton in a second, yet the total heatgenerated would be precisely the same.Again, we may keep the temperaturedown to the lowest point at whichcombustion can take place, by bringinglarge bodies of air in contact with it, orotherwise, or we may supply it with justthe right quantity of pure oxygen, andburn it at a temperature approaching thatof dissociation, and still the heat unitsgiven off will be neither more nor less. Itfollows, therefore, that great latitude in the

manner or rapidity of combustion may betaken without affecting the quantity of heatgenerated.

But in practice it is found that otherconsiderations limit this latitude, and thatthere are certain conditions necessary inorder to get the most available heat from apound of coal. There are three ways, andonly three, in which the heat developed bythe combustion of coal in a steam boilerfurnace may be expended.

1st, and principally. It should be conveyedto the water in the boiler, and be utilized inthe production of steam. To be perfect, aboiler should so utilize all the heat ofcombustion, but there are no perfectboilers.

2nd. A portion of the heat of combustion isconveyed up the chimney in the waste

gases. This is in proportion to the weight ofthe gases, and the difference betweentheir temperature and that of the air andcoal before they entered the fire.

3rd. Another portion is dissipated byradiation from the sides of the furnace. In astove the heat is all used in these latter twoways, either it goes off through thechimney or is radiated into thesurrounding space. It is one of theprincipal problems of boiler engineeringto render the amount of heat thus lost assmall as possible.

The loss from radiation is in proportion tothe amount of surface, its nature, itstemperature, and the time it is exposed.This loss can be almost entirely eliminatedby thick walls and a smooth white orpolished surface, but its amount isordinarily so small that these

extraordinary precautions do not pay inpractice.

It is evident that the temperature of theescaping gases cannot be brought belowthat of the absorbing surfaces, while it maybe much greater even to that of the fire.This is supposing that all of the escapinggases have passed through the fire. In caseair is allowed to leak into the flues, andmingle with the gases after they have leftthe heating surfaces, the temperature maybe brought down to almost any pointabove that of the atmosphere, but withoutany reduction in the amount of heatwasted. It is in this way that those lowchimney temperatures are sometimesattained which pass for proof of economywith the unobserving. All surplus airadmitted to the fire, or to the gases beforethey leave the heating surfaces, increasesthe losses.

We are now prepared to see why and howthe temperature and the rapidity ofcombustion in the boiler furnace affect theeconomy, and that though the amount ofheat developed may be the same, the heatavailable for the generation of steam maybe much less with one rate or temperatureof combustion than another.

Assuming that there is no air passing upthe chimney other than that which haspassed through the fire, the higher thetemperature of the fire and the lower thatof the escaping gases the better theeconomy, for the losses by the chimneygases will bear the same proportion to theheat generated by the combustion as thetemperature of those gases bears to thetemperature of the fire. That is to say, if thetemperature of the fire is 2500 degreesand that of the chimney gases 500 degrees

above that of the atmosphere, the loss bythe chimney will be 500/2500 = 20 percent. Therefore, as the escaping gasescannot be brought below the temperatureof the absorbing surface, which ispractically a fixed quantity, thetemperature of the fire must be high inorder to secure good economy.

The losses by radiation being practicallyproportioned to the time occupied, themore coal burned in a given furnace in agiven time, the less will be theproportionate loss from that cause.

It therefore follows that we should burn ourcoal rapidly and at a high temperature tosecure the best available economy.

[Illustration: Portion of 9880 Horse-powerInstallation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock

& Wilcox Chain Grate Stokers at the SouthSide Elevated Ry. Co., Chicago, Ill.]

PROPERTIES OF WATER

Pure water is a chemical compound of onevolume of oxygen and two volumes ofhydrogen, its chemical symbol beingH_{2}O.

The weight of water depends upon itstemperature. Its weight at fourtemperatures, much used in physicalcalculations, is given in Table 10.

TABLE 10

WEIGHT OF WATER ATTEMPERATURES USED IN PHYSICALCALCULATIONS

+---------------------------+----------+----------+| Temperature Degrees |Weightper|Weight per| | Fahrenheit

|Cubic Foot|Cubic Inch| | |Pounds | Pounds |

+---------------------------+----------+----------+|At 32 degrees or freezing | | || point at sea level | 62.418 | 0.03612| |At 39.2 degrees or point of| || | maximum density | 62.427 |0.03613 | |At 62 degrees or standard |

| | | temperature | 62.355| 0.03608 | |At 212 degrees or boiling |

| | | point at sea level |59.846 | 0.03469 |+---------------------------+----------+----------+

While authorities differ as to the weight ofwater, the range of values given for 62degrees Fahrenheit (the standardtemperature ordinarily taken) being from62.291 pounds to 62.360 pounds per cubicfoot, the value 62.355 is generallyaccepted as the most accurate.

A United States standard gallon holds 231cubic inches and weighs, at 62 degreesFahrenheit, approximately 8-1/3 pounds.

A British Imperial gallon holds 277.42cubic inches and weighs, at 62 degreesFahrenheit, 10 pounds.

The above are the true weights correctedfor the effect of the buoyancy of the air, orthe weight in vacuo. If water is weighed inair in the ordinary way, there is acorrection of about one-eighth of one percent which is usually negligible.

TABLE 11

VOLUME AND WEIGHT OF DISTILLEDWATER AT VARIOUSTEMPERATURES[12]

+-----------+---------------+----------+

|Temperature|Relative Volume|Weightper| | Degrees | Water at 39.2 |CubicFoot| | Fahrenheit| Degrees = 1 |Pounds |+-----------+---------------+----------+ | 32| 1.000176 | 62.42 | | 39.2 |1.000000 | 62.43 | | 40 | 1.000004

| 62.43 | | 50 | 1.00027 | 62.42| | 60 | 1.00096 | 62.37 | | 70| 1.00201 | 62.30 | | 80 | 1.00338

| 62.22 | | 90 | 1.00504 | 62.11| | 100 | 1.00698 | 62.00 | | 110| 1.00915 | 61.86 | | 120 |

1.01157 | 61.71 | | 130 | 1.01420| 61.55 | | 140 | 1.01705 | 61.38| | 150 | 1.02011 | 61.20 | | 160| 1.02337 | 61.00 | | 170 |

1.02682 | 60.80 | | 180 | 1.03047| 60.58 | | 190 | 1.03431 | 60.36| | 200 | 1.03835 | 60.12 | | 210| 1.04256 | 59.88 | | 212 |

1.04343 | 59.83 | | 220 | 1.0469

| 59.63 | | 230 | 1.0515 | 59.37 || 240 | 1.0562 | 59.11 | | 250 |

1.0611 | 58.83 | | 260 | 1.0662| 58.55 | | 270 | 1.0715 | 58.26 || 280 | 1.0771 | 57.96 | | 290 |

1.0830 | 57.65 | | 300 | 1.0890| 57.33 | | 310 | 1.0953 | 57.00 || 320 | 1.1019 | 56.66 | | 330 |

1.1088 | 56.30 | | 340 | 1.1160| 55.94 | | 350 | 1.1235 | 55.57 || 360 | 1.1313 | 55.18 | | 370 |

1.1396 | 54.78 | | 380 | 1.1483| 54.36 | | 390 | 1.1573 | 53.94 || 400 | 1.167 | 53.5 | | 410 |1.177 | 53.0 | | 420 | 1.187 |52.6 | | 430 | 1.197 | 52.2 | |440 | 1.208 | 51.7 | | 450 |1.220 | 51.2 | | 460 | 1.232 |50.7 | | 470 | 1.244 | 50.2 | |480 | 1.256 | 49.7 | | 490 |1.269 | 49.2 | | 500 | 1.283 |48.7 | | 510 | 1.297 | 48.1 | |

520 | 1.312 | 47.6 | | 530 |1.329 | 47.0 | | 540 | 1.35 |46.3 | | 550 | 1.37 | 45.6 | |560 | 1.39 | 44.9 |+-----------+---------------+----------+

Water is but slightly compressible and forall practical purposes may be considerednon-compressible. The coefficient ofcompressibility ranges from 0.000040 to0.000051 per atmosphere at ordinarytemperatures, this coefficient decreasingas the temperature increases.

Table 11 gives the weight in vacuo and therelative volume of a cubic foot of distilledwater at various temperatures.

The weight of water at the standardtemperature being taken as 62.355 poundsper cubic foot, the pressure exerted by thecolumn of water of any stated height, and

conversely the height of any columnrequired to produce a stated pressure,may be computed as follows:

The pressure in pounds per square foot =62.355 �height of column in feet.

The pressure in pounds per square inch =0.433 �height of column in feet.

Height of column in feet = pressure inpounds per square foot �62.355.

Height of column in feet = pressure inpounds per square inch �0.433.

Height of column in inches = pressure inpounds per square inch �27.71.

Height of column in inches = pressure inounces per square inch �1.73.

By a change in the weights given above,the pressure exerted and height of columnmay be computed for temperatures otherthan 62 degrees.

A pressure of one pound per square inch isexerted by a column of water 2.3093 feetor 27.71 inches high at 62 degreesFahrenheit.

Water in its natural state is never foundabsolutely pure. In solvent power waterhas a greater range than any other liquid.For common salt, this is approximately aconstant at all temperatures, while withsuch impurities as magnesium and sodiumsulphates, this solvent power increaseswith an increase in temperature.

TABLE 12

BOILING POINT OF WATER AT

VARIOUS ALTITUDES

+--------------+----------------+-------------+---------------+ |Boiling Point | Altitude Above |Atmospheric | Barometer | | Degrees| Sea Level | Pressure | Reduced || Fahrenheit | Feet | Pounds per |to 32 Degrees | | | |Square Inch | Inches |+--------------+----------------+-------------+---------------+ | 184 | 15221 | 8.20| 16.70 | | 185 | 14649 |8.38 | 17.06 | | 186 | 14075| 8.57 | 17.45 | | 187 |

13498 | 8.76 | 17.83 | | 188| 12934 | 8.95 | 18.22 | |189 | 12367 | 9.14 | 18.61 || 190 | 11799 | 9.34 | 19.02

| | 191 | 11243 | 9.54 |19.43 | | 192 | 10685 | 9.74| 19.85 | | 193 | 10127 |9.95 | 20.27 | | 194 | 9579

| 10.17 | 20.71 | | 195 |9031 | 10.39 | 21.15 | | 196| 8481 | 10.61 | 21.60 | |197 | 7932 | 10.83 | 22.05 || 198 | 7381 | 11.06 | 22.52

| | 199 | 6843 | 11.29 |22.99 | | 200 | 6304 | 11.52| 23.47 | | 201 | 5764 |11.76 | 23.95 | | 202 | 5225

| 12.01 | 24.45 | | 203 |4697 | 12.26 | 24.96 | | 204| 4169 | 12.51 | 25.48 | |205 | 3642 | 12.77 | 26.00 || 206 | 3115 | 13.03 | 26.53

| | 207 | 2589 | 13.30 |27.08 | | 208 | 2063 | 13.57| 27.63 | | 209 | 1539 |13.85 | 28.19 | | 210 | 1025

| 14.13 | 28.76 | | 211 |512 | 14.41 | 29.33 | | 212 |

Sea Level | 14.70 | 29.92 |+--------------+----------------+-------------+-----

----------+

Sea water contains on an averageapproximately 3.125 per cent of its weightof solid matter or a thirty-second part ofthe weight of the water and salt held insolution. The approximate composition ofthis solid matter will be: sodium chloride76 per cent, magnesium chloride 10 percent, magnesium sulphate 6 per cent,calcium sulphate 5 per cent, calciumcarbonate 0.5 per cent, other substances2.5 per cent.

[Illustration: 7200 Horse-power Installationof Babcock & Wilcox Boilers andSuperheaters at the Capital Traction Co.,Washington, D. C.]

The boiling point of water decreases as thealtitude above sea level increases. Table12 gives the variation in the boiling point

with the altitude.

Water has a greater specific heat orheat-absorbing capacity than any otherknown substance (bromine and hydrogenexcepted) and its specific heat is the basisfor measurement of the capacity of heatabsorption of all other substances. Fromthe definition, the specific heat of water isthe number of British thermal unitsrequired to raise one pound of water onedegree. This specific heat varies with thetemperature of the water. The generallyaccepted values are given in Table 13,which indicates the values as determinedby Messrs. Marks and Davis and Mr.Peabody.

TABLE 13

SPECIFIC HEAT OF WATER ATVARIOUS TEMPERATURES

+----------------------+--------------------------------+ | MARKS AND DAVIS |PEABODY | | From Values of |

From Values of | | Barnes andDieterici | Barnes and Regnault |+-----------+----------+---------------------+----------+ |Temperature| Specific |Temperature | Specific | +-----------+Heat +----------+----------+ Heat | |Degrees | | Degrees | Degrees |

| |Fahrenheit ||Centigrade|Fahrenheit| |+-----------+----------+----------+----------+----------+ | 30 | 1.0098 | 0 | 32 |1.0094 | | 40 | 1.0045 | 5 | 41| 1.0053 | | 50 | 1.0012 | 10 |50 | 1.0023 | | 55 | 1.0000 | 15| 59 | 1.0003 | | 60 | 0.9990 |16.11 | 61 | 1.0000 | | 70 | 0.9977| 20 | 68 | 0.9990 | | 80 |

0.9970 | 25 | 77 | 0.9981 | | 90

| 0.9967 | 30 | 86 | 0.9976 | |100 | 0.9967 | 35 | 95 | 0.9974 || 110 | 0.9970 | 40 | 104 |0.9974 | | 120 | 0.9974 | 45 | 113

| 0.9976 | | 130 | 0.9979 | 50 |122 | 0.9980 | | 140 | 0.9986 | 55| 131 | 0.9985 | | 150 | 0.9994 |

60 | 140 | 0.9994 | | 160 | 1.0002| 65 | 149 | 1.0004 | | 170 |

1.0010 | 70 | 158 | 1.0015 | | 180| 1.0019 | 75 | 167 | 1.0028 | |

190 | 1.0029 | 80 | 176 | 1.0042 || 200 | 1.0039 | 85 | 185 |1.0056 | | 210 | 1.0052 | 90 | 194

| 1.0071 | | 220 | 1.007 | 95 |203 | 1.0086 | | 230 | 1.009 | 100

| 212 | 1.0101 |+-----------+----------+----------+----------+----------+

In consequence of this variation in specificheat, the variation in the heat of the liquid

of the water at different temperatures isnot a constant. Table 22[13] gives the heatof the liquid in a pound of water attemperatures ranging from 32 to 340degrees Fahrenheit.

The specific heat of ice at 32 degrees is0.463. The specific heat of saturated steam(ice and saturated steam representing theother forms in which water may exist), issomething that is difficult to define in anyway which will not be misleading. Whenno liquid is present the specific heat ofsaturated steam is negative.[14] The use ofthe value of the specific heat of steam ispractically limited to instances wheresuperheat is present, and the specific heatof superheated steam is covered later inthe book.

BOILER FEED WATER

All natural waters contain some impuritieswhich, when introduced into a boiler, mayappear as solids. In view of the apparentpresent-day tendency toward large sizeboiler units and high overloads, theimportance of the use of pure water forboiler feed purposes cannot beover-estimated.

Ordinarily, when water of sufficient purityfor such use is not at hand, the supplyavailable may be rendered suitable bysome process of treatment. Against thecost of such treatment, there are manyfactors to be considered. With water inwhich there is a marked tendency towardscale formation, the interest anddepreciation on the added boiler unitsnecessary to allow for the systematic

cleaning of certain units must be taken intoconsideration. Again there is aconsiderable loss in taking boilers off forcleaning and replacing them on the line.On the other hand, the decrease incapacity and efficiency accompanying anincreased incrustation of boilers in use hasbeen too generally discussed to needrepetition here. Many experiments havebeen made and actual figures reported asto this decrease, but in general, suchfigures apply only to the particular set ofconditions found in the plant where theboiler in question was tested. So manyfactors enter into the effect of scale oncapacity and economy that it is impossibleto give any accurate figures on suchdecrease that will serve all cases, but thatit is large has been thoroughly proven.

While it is almost invariably true thatpractically any cost of treatment will pay a

return on the investment of the apparatus,the fact must not be overlooked that thereare certain waters which should never beused for boiler feed purposes and whichno treatment can render suitable for suchpurpose. In such cases, the only remedy isthe securing of other feed supply or theemployment of evaporators for distillingthe feed water as in marine service.

TABLE 14

APPROXIMATE CLASSIFICATION OFIMPURITIES FOUND IN FEED WATERS

THEIR EFFECT AND ORDINARYMETHODS OF RELIEF

+-----------------------+--------------+-----------------------------+ | Difficulty Resulting |Nature of | Ordinary Method of | |from Presence of | Difficulty |Overcoming or Relieving |

+-----------------------+--------------+-----------------------------+ | Sediment, Mud, etc. |Incrustation | Settling tanks, filtration, | |

| | blowing down.| | | | |

| Readily Soluble Salts | Incrustation |Blowing down. | | |

| | | Bicarbonates ofLime, | Incrustation | Heating feed.Treatment by | | Magnesia, etc. |

| addition of lime or of lime | || | and soda. Barium carbonate. |

| | | | |Sulphate of Lime | Incrustation |Treatment by addition of | || | soda. Barium carbonate. | |

| | | |Chloride and Sulphate | Corrosion |Treatment by addition of | | ofMagnesium | | carbonate ofsoda. | | | |

| | Acid | Corrosion |

Alkali. | | || | | Dissolved Carbonic| Corrosion | Heating feed. Keeping air| | Acid and Oxygen | | fromfeed. Addition of | | || caustic soda or slacked | |

| | lime. | || | | | Grease

| Corrosion | Filter. Iron alum as || | | coagulent.Neutralization | | | |by carbonate of soda. Use | || | of best hydrocarbon oils. | |

| | | |Organic Matter | Corrosion | Filter.Use of coagulent. | | || | | Organic Matter |Priming | Settling tanks. Filter in | |(Sewage) | | connectionwith coagulent. | | | |

| | Carbonate of Soda in |Priming | Barium carbonate. New feed

| | large quantities | | supply. Iffrom treatment, | | | |change. |+-----------------------+--------------+-----------------------------+

It is evident that the whole subject of boilerfeed waters and their treatment is one forthe chemist rather than for the engineer. Abrief outline of the difficulties that may beexperienced from the use of poor feedwater and a suggestion as to a method ofovercoming certain of these difficulties isall that will be attempted here. Such a briefoutline of the subject, however, willindicate the necessity for a chemicalanalysis of any water before a treatment istried and the necessity of adapting thetreatment in each case to the nature of thedifficulties that may be experienced.

Table 14 gives a list of impurities which

may be found in boiler feed water,grouped according to their effect on boileroperation and giving the customarymethod used for overcoming difficulty towhich they lead.

Scale--Scale is formed on boiler heatingsurfaces by the depositing of impurities inthe feed water in the form of a more or lesshard adherent crust. Such deposits are dueto the fact that water loses its solublepower at high temperatures or becausethe concentration becomes so high, due toevaporation, that the impurities crystallizeand adhere to the boiler surfaces. Theopportunity for formation of scale in aboiler will be apparent when it is realizedthat during a month's operation of a 100horse-power boiler, 300 pounds of solidmatter may be deposited from watercontaining only 7 grains per gallon, while

some spring and well waters containsufficient to cause a deposit of as high as2000 pounds.

The salts usually responsible for suchincrustation are the carbonates andsulphates of lime and magnesia, and boilerfeed treatment in general deals with thegetting rid of these salts more or lesscompletely.

TABLE 15

SOLUBILITY OF MINERAL SALTS INWATER (SPARKS) IN GRAINS PER U. S.GALLON (58,381 GRAINS), EXCEPT ASNOTED

+------------------------------+------------+-------------+ |Temperature Degrees Fahrenheit|60 Degrees | 212 Degrees |+------------------------------+------------+--------

-----+ |Calcium Carbonate | 2.5| 1.5 | |Calcium Sulphate |140.0 | 125.0 | |MagnesiumCarbonate | 1.0 | 1.8 ||Magnesium Sulphate | 3.0 pounds |12.0 pounds | |Sodium Chloride |3.5 pounds | 4.0 pounds | |SodiumSulphate | 1.1 pounds | 5.0pounds |+------------------------------+------------+-------------+

CALCIUM SULPHATE ATTEMPERATURE ABOVE 212DEGREES (CHRISTIE)

+------------------------------+----+----+-------+----+---+ |Temperature degreesFahrenheit|284 |329 |347-365| 464|482||Corresponding gauge pressure | 38 | 87|115-149| 469|561| |Grains per gallon

|45.5|32.7| 15.7 |10.5|9.3|

+------------------------------+----+----+-------+----+---+

Table 15 gives the solubility of thesemineral salts in water at varioustemperatures in grains per U. S. gallon(58,381 grains). It will be seen from thistable that the carbonates of lime andmagnesium are not soluble above 212degrees, and calcium sulphate whilesomewhat insoluble above 212 degreesbecomes more greatly so as thetemperature increases.

Scale is also formed by the settling of mudand sediment carried in suspension inwater. This may bake or be cemented to ahard scale when mixed with otherscale-forming ingredients.

Corrosion--Corrosion, or a chemical action

leading to the actual destruction of theboiler metal, is due to the solvent oroxidizing properties of the feed water. Itresults from the presence of acid, eitherfree or developed[15] in the feed, theadmixture of air with the feed water, or asa result of a galvanic action. In boilers ittakes several forms:

1st. Pitting, which consists of isolated spotsof active corrosion which does not attackthe boiler as a whole.

2nd. General corrosion, produced bynaturally acid waters and where theamount is so even and continuous that noaccurate estimate of the metal eaten awaymay be made.

3rd. Grooving, which, while largely amechanical action which may occur inneutral waters, is intensified by acidity.

Foaming--This phenomenon, whichordinarily occurs with waterscontaminated with sewage or organicgrowths, is due to the fact that thesuspended particles collect on the surfaceof the water in the boiler and renderdifficult the liberation of steam bubblesarising to that surface. It sometimes occurswith water containing carbonates insolution in which a light flocculentprecipitate will be formed on the surfaceof the water. Again, it is the result of anexcess of sodium carbonate used intreatment for some other difficulty whereanimal or vegetable oil finds its way intothe boiler.

Priming--Priming, or the passing off ofsteam from a boiler in belches, is causedby the concentration of sodium carbonate,sodium sulphate or sodium chloride in

solution. Sodium sulphate is found in manysouthern waters and also where calcium ormagnesium sulphate is precipitated withsoda ash.

Treatment of Feed Water--For scaleformation. The treatment of feed water,carrying scale-forming ingredients, isalong two main lines: 1st, by chemicalmeans by which such impurities as arecarried by the water are caused toprecipitate; and 2nd, by the means of heat,which results in the reduction of the powerof water to hold certain salts in solution.The latter method alone is sufficient in thecase of certain temporarily hard waters,but the heat treatment, in general, is usedin connection with a chemical treatment toassist the latter.

Before going further into detail as to thetreatment of water, it may be well to define

certain terms used.

_Hardness_, which is the most widelyknown evidence of the presence in waterof scale-forming matter, is that quality, thevariation of which makes it more difficult toobtain a lather or suds from soap in onewater than in another. This action is madeuse of in the soap test for hardnessdescribed later. Hardness is ordinarilyclassed as either temporary or permanent.Temporarily hard waters are thosecontaining carbonates of lime andmagnesium, which may be precipitated byboiling at 212 degrees and which, if theycontain no other scale-formingingredients, become "soft" under suchtreatment. Permanently hard waters arethose containing mainly calcium sulphate,which is only precipitated at the hightemperatures found in the boiler itself, 300degrees Fahrenheit or more. The scale of

hardness is an arbitrary one, based on thenumber of grains of solids per gallon andwaters may be classed on such a basis asfollows: 1-10 grain per gallon, soft water;10-20 grain per gallon, moderately hardwater; above 25 grains per gallon, veryhard water.

_Alkalinity_ is a general term used forwaters containing compounds with thepower of neutralizing acids.

_Causticity_, as used in water treatment, isa term coined by A. McGill, indicating thepresence of an excess of lime addedduring treatment. Though such presencewould also indicate alkalinity, the term isarbitrarily used to apply to those hydrateswhose presence is indicated byphenolphthalein.

Of the chemical methods of water

treatment, there are three generalprocesses:

1st. Lime Process. The lime process is usedfor waters containing bicarbonates of limeand magnesia. Slacked lime in solution, aslime water, is the reagent used. Thiscombines with the carbonic acid which ispresent, either free or as carbonates, toform an insoluble monocarbonate of lime.The soluble bicarbonates of lime andmagnesia, losing their carbonic acid,thereby become insoluble and precipitate.

2nd. Soda Process. The soda process isused for waters containing sulphates oflime and magnesia. Carbonate of soda andhydrate of soda (caustic soda) are usedeither alone or together as the reagents.Carbonate of soda, added to watercontaining little or no carbonic acid orbicarbonates, decomposes the sulphates

to form insoluble carbonate of lime ormagnesia which precipitate, the neutralsoda remaining in solution. If free carbonicacid or bicarbonates are present,bicarbonate of lime is formed and remainsin solution, though under the action ofheat, the carbon dioxide will be driven offand insoluble monocarbonates will beformed. Caustic soda used in this processcauses a more energetic action, it beingpresumed that the caustic soda absorbsthe carbonic acid, becomes carbonate ofsoda and acts as above.

3rd. Lime and Soda Process. This process,which is the combination of the first two, isby far the most generally used in waterpurification. Such a method is used wheresulphates of lime and magnesia arecontained in the water, together with suchquantity of carbonic acid or bicarbonatesas to impair the action of the soda.

Sufficient soda is used to break down thesulphates of lime and magnesia and asmuch lime added as is required to absorbthe carbonic acid not taken up in the sodareaction.

All of the apparatus for effecting suchtreatment of feed waters is approximatelythe same in its chemical action, thenumerous systems differing in the methodsof introduction and handling of thereagents.

The methods of testing water treated by anapparatus of this description follow.

When properly treated, alkalinity,hardness and causticity should be in theapproximate relation of 6, 5 and 4. Whentoo much lime is used in the treatment, thecausticity in the purified water, asindicated by the acid test, will be nearly

equal to the alkalinity. If too little lime isused, the causticity will fall toapproximately half the alkalinity. Thehardness should not be in excess of twopoints less than the alkalinity. Where toogreat a quantity of soda is used, thehardness is lowered and the alkalinityraised. If too little soda, the hardness israised and the alkalinity lowered.

Alkalinity and causticity are tested with astandard solution of sulphuric acid. Astandard soap solution is used for testingfor hardness and a silver nitrate solutionmay also be used for determining whetheran excess of lime has been used in thetreatment.

Alkalinity: To 50 cubic centimeters oftreated water, to which there has beenadded sufficient methylorange to color it,add the acid solution, drop by drop, until

the mixture is on the point of turning red.As the acid solution is first added, the redcolor, which shows quickly, disappears onshaking the mixture, and this colordisappears more slowly as the criticalpoint is approached. One-tenth cubiccentimeter of the standard acid solutioncorresponds to one degree of alkalinity.

[Illustration: 2640 Horse-power Installationof Babcock & Wilcox Boilers at the BotanyWorsted Mills, Passaic, N. J.]

Causticity: To 50 cubic centimeters oftreated water, to which there has beenadded one drop of phenolphthaleindissolved in alcohol to give the water apinkish color, add the acid solution, dropby drop, shaking after each addition, untilthe color entirely disappears. One-tenthcubic centimeter of acid solutioncorresponds to one degree of causticity.

The alkalinity may be determined from thesame sample tested for causticity by thecoloring with methylorange and addingthe acid until the sample is on the point ofturning red. The total acid added indetermining both causticity and alkalinityin this case is the measure of the alkalinity.

Hardness: 100 cubic centimeters of thetreated water is used for this test, onecubic centimeter of the soap solutioncorresponding to one degree of hardness.The soap solution is added a very little at atime and the whole violently shaken.Enough of the solution must be added tomake a permanent lather or foam, that is,the soap bubbles must not disappear afterthe shaking is stopped.

Excess of lime as determined by nitrate ofsilver: If there is an excess of lime used in

the treatment, a sample will become adark brown by the addition of a smallquantity of silver nitrate, otherwise a milkywhite solution will be formed.

Combined Heat and Chemical Treatment:Heat is used in many systems of feedtreatment apparatus as an adjunct to thechemical process. Heat alone will removetemporary hardness by the precipitation ofcarbonates of lime and magnesia and,when used in connection with the chemicalprocess, leaves only the permanenthardness or the sulphates of lime to betaken care of by chemical treatment.

TABLE 16

REAGENTS REQUIRED IN LIME ANDSODA PROCESS FOR TREATING 1000 U.S. GALLONS OF WATER PER GRAIN PERGALLON OF CONTAINED IMPURITIES[16]

+-----------------------+-----------+-----------+ || Lime[17] | Soda[18] | |

| Pounds | Pounds |+-----------------------+-----------+-----------+ |Calcium Carbonate | 0.098 | ... | |Calcium Sulphate | ... | 0.124 | |Calcium Chloride | ... | 0.151 | |Calcium Nitrate | ... | 0.104 | |Magnesium Carbonate | 0.234 | ... || Magnesium Sulphate | 0.079 | 0.141

| | Magnesium Chloride | 0.103 |0.177 | | Magnesium Nitrate | 0.067 |

0.115 | | Ferrous Carbonate | 0.169| ... | | Ferrous Sulphate | 0.070 |0.110 | | Ferric Sulphate | 0.074 |0.126 | | Aluminum Sulphate | 0.087| 0.147 | | Free Sulphuric Acid | 0.100

| 0.171 | | Sodium Carbonate |0.093 | ... | | Free Carbon Dioxide |0.223 | ... | | Hydrogen Sulphite |0.288 | ... |

+-----------------------+-----------+-----------+

The chemicals used in the ordinary limeand soda process of feed water treatmentare common lime and soda. The efficiencyof such apparatus will depend wholly uponthe amount and character of the impuritiesin the water to be treated. Table 16 givesthe amount of lime and soda required per1000 gallons for each grain per gallon ofthe various impurities found in the water.This table is based on lime containing 90per cent calcium oxide and sodacontaining 58 per cent sodium oxide,which correspond to the commercialquality ordinarily purchasable. From thistable and the cost of the lime and soda, thecost of treating any water per 1000 gallonsmay be readily computed.

Less Usual Reagents--Barium hydrate issometimes used to reduce permanent

hardness or the calcium sulphatecomponent. Until recently, the high cost ofbarium hydrate has rendered its useprohibitive but at the present it is obtainedas a by-product in cement manufactureand it may be purchased at a morereasonable figure than heretofore. It actsdirectly on the soluble sulphates to formbarium sulphate which is insoluble andmay be precipitated. Where this reagent isused, it is desirable that the reaction beallowed to take place outside of the boiler,though there are certain cases where itsinternal use is permissible.

Barium carbonate is sometimes used inremoving calcium sulphate, the productsof the reaction being barium sulphate andcalcium carbonate, both of which areinsoluble and may be precipitated. Asbarium carbonate in itself is insoluble, itcannot be added to water as a solution and

its use should, therefore, be confined totreatment outside of the boiler.

Silicate of soda will precipitate calciumcarbonate with the formation of agelatinous silicate of lime and carbonate ofsoda. If calcium sulphate is also present,carbonate of soda is formed in the abovereaction, which in turn will break down thesulphate.

Oxalate of soda is an expensive butefficient reagent which forms a precipitateof calcium oxalate of a particularlyinsoluble nature.

Alum and iron alum will act as efficientcoagulents where organic matter ispresent in the water. Iron alum has notonly this property but also that of reducingoil discharged from surface condensers toa condition in which it may be readily

removed by filtration.

Corrosion--Where there is a corrosiveaction because of the presence of acid inthe water or of oil containing fatty acidswhich will decompose and cause pittingwherever the sludge can find a restingplace, it may be overcome by theneutralization of the water by carbonate ofsoda. Such neutralization should becarried to the point where the water willjust turn red litmus paper blue. As apreventative of such action arising fromthe presence of the oil, only the highestgrades of hydrocarbon oils should beused.

Acidity will occur where sea water ispresent in a boiler. There is the possibilityof such an occurrence in marine practiceand in stationary plants using sea water forcondensing, due to leaky condenser tubes,

priming in the evaporators, etc. Suchacidity is caused through the dissociationof magnesium chloride into hydrochlorideacid and magnesia under hightemperatures. The acid in contact with themetal forms an iron salt which immediatelyupon its formation is neutralized by thefree magnesia in the water, therebyprecipitating iron oxide and reformingmagnesium chloride. The preventive forcorrosion arising from such acidity is thekeeping tight of the condenser. Where it isunavoidable that some sea water shouldfind its way into a boiler, the acidityresulting should be neutralized by sodaash. This will convert the magnesiumchloride into magnesium carbonate andsodium chloride, neither of which iscorrosive but both of which arescale-forming.

The presence of air in the feed water

which is sucked in by the feed pump is awell recognized cause of corrosion. Airbubbles form below the water line andattack the metal of the boiler, the oxygenof the air causing oxidization of the boilermetal and the formation of rust. Theparticle of rust thus formed is swept awayby the circulation or is dislodged byexpansion and the minute pit thus leftforms an ideal resting place for other airbubbles and the continuation of theoxidization process. The prevention is, ofcourse, the removing of the air from thefeed water. In marine practice, wherethere has been experienced the mostdifficulty from this source, it has beenfound to be advantageous to pump thewater from the hot well to a filter tankplaced above the feed pump suctionvalves. In this way the air is liberated fromthe surface of the tank and a head isassured for the suction end of the pump. In

this same class of work, the corrosiveaction of air is reduced by introducing thefeed through a spray nozzle into the steamspace above the water line.

Galvanic action, resulting in the eatingaway of the boiler metal throughelectrolysis was formerly consideredpractically the sole cause of corrosion. Butlittle is known of such action aside from thefact that it does take place in certaininstances. The means adopted as a remedyis usually the installation of zinc plateswithin the boiler, which must have positivemetallic contact with the boiler metal. Inthis way, local electrolytic effects areovercome by a still greater electrolyticaction at the expense of the more positivezinc. The positive contact necessary isdifficult to maintain and it is questionablejust what efficacy such plates have exceptfor a short period after their installation

when the contact is known to be positive.Aside from protection from suchelectrolytic action, however, the zincplates have a distinct use where there isthe liability of air in the feed, as they offera substance much more readily oxidizedby such air than the metal of the boiler.

Foaming--Where foaming is caused byorganic matter in suspension, it may belargely overcome by filtration or by theuse of a coagulent in connection withfiltration, the latter combination havingcome recently into considerable favor.Alum, or potash alum, and iron alum,which in reality contains no alumina andshould rather be called potassia-ferric, arethe coagulents generally used inconnection with filtration. Such matter as isnot removed by filtration may, undercertain conditions, be handled by surfaceblowing. In some instances, settling tanks

are used for the removal of matter insuspension, but where large quantities ofwater are required, filtration is ordinarilysubstituted on account of the time elementand the large area necessary in settlingtanks.

Where foaming occurs as the result ofovertreatment of the feed water, theobvious remedy is a change in suchtreatment.

Priming--Where priming is caused byexcessive concentration of salts within aboiler, it may be overcome largely byfrequent blowing down. The degree ofconcentration allowable before primingwill take place varies widely withconditions of operation and may bedefinitely determined only by experiencewith each individual set of conditions. It isthe presence of the salts that cause

priming that may result in the absoluteunfitness of water for boiler feed purposes.Where these salts exist in such quantitiesthat the amount of blowing downnecessary to keep the degree ofconcentration below the priming pointresults in excessive losses, the onlyremedy is the securing of another supplyof feed, and the results will warrant thechange almost regardless of the expense.In some few instances, the impurities maybe taken care of by some method of watertreatment but such water should besubmitted to an authority on the subjectbefore any treatment apparatus isinstalled.

[Illustration: 3000 Horse-power Installationof Cross Drum Babcock & Wilcox Boilersand Superheaters Equipped with Babcock& Wilcox Chain Grate Stokers at theWashington Terminal Co., Washington, D.

C.]

Boiler Compounds--The method oftreatment of feed water by far the mostgenerally used is by the use of some of theso-called boiler compounds. There aremany reliable concerns handling suchcompounds who unquestionably securethe promised results, but there is a greattendency toward looking on the compoundas a "cure all" for any water difficulties andcare should be taken to deal only withreputable concerns.

The composition of these compounds isalmost invariably based on soda withcertain tannic substances and in someinstances a gelatinous substance which ispresumed to encircle scale particles andprevent their adhering to the boilersurfaces. The action of these compounds isordinarily to reduce the calcium sulphate

in the water by means of carbonate of sodaand to precipitate it as a muddy form ofcalcium carbonate which may be blownoff. The tannic compounds are used inconnection with the soda with the idea ofintroducing organic matter into any scalealready formed. When it has penetrated tothe boiler metal, decomposition of thescale sets in, causing a disruptive effectwhich breaks the scale from the metalsometimes in large slabs. It is this effect ofboiler compounds that is to be mostcarefully guarded against or inevitabletrouble will result from the presence ofloose scale with the consequent danger oftube losses through burning.

When proper care is taken to suit thecompound to the water in use, the resultssecured are fairly effective. In general,however, the use of compounds may onlybe recommended for the prevention of

scale rather than with the view to removingscale which has already formed, that is, thecompounds should be introduced with thefeed water only when the boiler has beenthoroughly cleaned.

FEED WATER HEATING AND METHODSOF FEEDING

Before water fed into a boiler can beconverted into steam, it must be firstheated to a temperature corresponding tothe pressure within the boiler. Steam at160 pounds gauge pressure has atemperature of approximately 371 degreesFahrenheit. If water is fed to the boiler at60 degrees Fahrenheit, each pound musthave 311 B. t. u. added to it to increase itstemperature 371 degrees, which increasemust take place before the water can beconverted into steam. As it requires 1167.8B. t. u. to raise one pound of water from 60to 371 degrees and to convert it into steamat 160 pounds gauge pressure, the 311degrees required simply to raise thetemperature of the water from 60 to 371degrees will be approximately 27 per cent

of the total. If, therefore, the temperatureof the water can be increased from 60 to371 degrees before it is introduced into aboiler by the utilization of heat from somesource that would otherwise be wasted,there will be a saving in the fuel requiredof 311 �1167.8 = 27 per cent, and there willbe a net saving, provided the cost ofmaintaining and operating the apparatusfor securing this saving is less than thevalue of the heat thus saved.

The saving in the fuel due to the heating offeed water by means of heat that wouldotherwise be wasted may be computedfrom the formula:

100 (t - t_{i}) Fuel saving percent = --------------- (1) H +32 - t_{i}

where, t = temperature of feed water after

heating, t_{i} = temperature of feed waterbefore heating, and H = total heat above32 degrees per pound of steam at theboiler pressure. Values of H may be foundin Table 23. Table 17 has been computedfrom this formula to show the fuel savingunder the conditions assumed with theboiler operating at 180 pounds gaugepressure.

TABLE 17

SAVING IN FUEL, IN PER CENT, BYHEATING FEED WATER GAUGEPRESSURE 180 POUNDS

+-----------+-----------------------------------------+ | Initial | Final Temperature--DegreesFahrenheit ||Temperature|-----+-----+-----+-----+-----+-----+-----| | Fahrenheit| 120 | 140 | 160 |180 | 200 | 250 | 300 |

+-----------+-----+-----+-----+-----+-----+-----+-----+ | 32 | 7.35|9.02|10.69|12.36|14.04|18.20|22.38| |35 | 7.12|8.79|10.46|12.14|13.82|18.00|22.18| |40 | 6.72|8.41|10.09|11.77|13.45|17.65|21.86| |45 | 6.33| 8.02|9.71|11.40|13.08|17.30|21.52| | 50 |5.93| 7.63| 9.32|11.02|12.72|16.95|21.19|| 55 | 5.53| 7.24|8.94|10.64|12.34|16.60|20.86| | 60 |5.13| 6.84| 8.55|10.27|11.97|16.24|20.52|| 65 | 4.72| 6.44| 8.16|9.87|11.59|15.88|20.18| | 70 | 4.31|6.04| 7.77| 9.48|11.21|15.52|19.83| |75 | 3.90| 5.64| 7.36|9.09|10.82|15.16|19.48| | 80 | 3.48|5.22| 6.96| 8.70|10.44|14.79|19.13| |85 | 3.06| 4.80| 6.55|8.30|10.05|14.41|18.78| | 90 | 2.63|4.39| 6.14| 7.89| 9.65|14.04|18.43| | 95

| 2.20| 3.97| 5.73| 7.49|9.25|13.66|18.07| | 100 | 1.77| 3.54|5.31| 7.08| 8.85|13.28|17.70| | 110 |.89| 2.68| 4.47| 6.25| 8.04|12.50|16.97| |

120 | .00| 1.80| 3.61| 5.41|7.21|11.71|16.22| | 130 | | .91|2.73| 4.55| 6.37|10.91|15.46| | 140 || .00| 1.84| 3.67| 5.51|10.09|14.68| |150 | | | .93| 2.78| 4.63|9.26|13.89| | 160 | | | .00| 1.87|3.74| 8.41|13.09| | 170 | | | |.94| 2.83| 7.55|12.27| | 180 | | || .00| 1.91| 6.67|11.43| | 190 | | |

| | .96| 5.77|10.58| | 200 | || | | .00| 4.86| 9.71| | 210 | || | | | 3.92| 8.82|+-----------+-----+-----+-----+-----+-----+-----+-----+

Besides the saving in fuel effected by theuse of feed water heaters, otheradvantages are secured. The time

required for the conversion of water intosteam is diminished and the steamcapacity of the boiler thereby increased.Further, the feeding of cold water into aboiler has a tendency toward the settingup of temperature strains, which arediminished in proportion as thetemperature of the feed approaches that ofthe steam. An important additionaladvantage of heating feed water is that incertain types of heaters a large portion ofthe scale forming ingredients areprecipitated before entering the boiler,with a consequent saving in cleaning andlosses through decreased efficiency andcapacity.

In general, feed water heaters may bedivided into closed heaters, open heatersand economizers; the first two depend fortheir heat upon exhaust, or in some caseslive steam, while the last class utilizes the

heat of the waste flue gases to secure thesame result. The question of the type ofapparatus to be installed is dependentupon the conditions attached to eachindividual case.

In closed heaters the feed water and theexhaust steam do not come into actualcontact with each other. Either the steamor the water passes through tubessurrounded by the other medium, as theheater is of the steam-tube or water-tubetype. A closed heater is best suited forwater free from scale-forming matter, assuch matter soon clogs the passages.Cleaning such heaters is costly and theefficiency drops off rapidly as scale forms.A closed heater is not advisable where theengines work intermittently, as is the casewith mine hoisting engines. In this class ofwork the frequent coolings betweenoperating periods and the sudden

heatings when operation commences willtend to loosen the tubes or even pull themapart. For this reason, an open heater, oreconomizer, will give more satisfactoryservice with intermittently operatingapparatus.

Open heaters are best suited for waterscontaining scale-forming matter. Much ofthe temporary hardness may beprecipitated in the heater and thesediment easily removed. Such heaters arefrequently used with a reagent forprecipitating permanent hardness in thecombined heat and chemical treatment offeed water. The so-called live steampurifiers are open heaters, the water beingraised to the boiling temperature and thecarbonates and a portion of the sulphatesbeing precipitated. The disadvantage ofthis class of apparatus is that some of thesulphates remain in solution to be

precipitated as scale when concentrated inthe boiler. Sufficient concentration to havesuch an effect, however, may often beprevented by frequent blowing down.

Economizers find their largest field wherethe design of the boiler is such that themaximum possible amount of heat is notextracted from the gases of combustion.The more wasteful the boiler, the greaterthe saving effected by the use of theeconomizer, and it is sometimes possibleto raise the temperature of the feed waterto that of high pressure steam by theinstallation of such an apparatus, thesaving amounting in some cases to asmuch as 20 per cent. The fuel used bearsdirectly on the question of the advisabilityof an economizer installation, for when oilis the fuel a boiler efficiency of 80 per centor over is frequently realized, an efficiencywhich would leave a small opportunity for

a commercial gain through the addition ofan economizer.

From the standpoint of spacerequirements, economizers are at adisadvantage in that they are bulky andrequire a considerable increase overspace occupied by a heater of the exhausttype. They also require additionalbrickwork or a metal casing, whichincreases the cost. Sometimes, too, thefrictional resistance of the gases throughan economizer make its adaptabilityquestionable because of the draftconditions. When figuring the net returnon economizer investment, all of thesefactors must be considered.

When the feed water is such that scale willquickly encrust the economizer and throwit out of service for cleaning during anexcessive portion of the time, it will be

necessary to purify water beforeintroducing it into an economizer to makeit earn a profit on the investment.

From the foregoing, it is clearly indicatedthat it is impossible to make a definitestatement as to the relative saving byheating feed water in any of the threetypes. Each case must be worked outindependently and a decision can bereached only after an exhaustive study ofall the conditions affecting the case,including the time the plant will be inservice and probable growth of the plant.When, as a result of such study, thepossible methods for handling theproblem have been determined, thesolution of the best apparatus can be madeeasily by the balancing of the savingpossible by each method against its firstcost, depreciation, maintenance and costof operation.

Feeding of Water--The choice of methodsto be used in introducing feed water into aboiler lies between an injector and apump. In most plants, an injector would notbe economical, as the water fed by suchmeans must be cold, a fact which makesimpossible the use of a heater before thewater enters the injector. Such a heatermight be installed between the injectorand the boiler but as heat is added to thewater in the injector, the heater could notproperly fulfill its function.

TABLE 18

COMPARISON OF PUMPS ANDINJECTORS_________________________________________________________________________ |

| | | |Method of Supplying | |

| | Feed-water to Boiler |Relative amount of | Saving of fuel over| |Temperature of feed-water as | coalrequired per | the amount required| |delivered to the pump or to | unit of time,the | when the boiler is | | injector, 60degrees Fahren- | amount for a direct-|fed by a direct- | | heit. Rate ofevaporation of | acting pump, feeding|acting pump without| | boiler, to poundsof water | water at 60 degrees | heater

| | per pound of coal from and |without a heater, | Per Cent | | at212 degrees Fahrenheit | being taken asunity| ||______________________________|_____________________|____________________| |

| | | |Direct-acting Pump feeding | |

| | water at 60 degrees without| | | | a heater

| 1.000 | .0 | |

| | | |Injector feeding water at | |

| | 150 degrees without a heater |.985 | 1.5 | | Injector

feeding through a | || | heater in which the water is || | | heated from 150 to 200

| | | | degrees| .938 | 6.2 | |

| | | |Direct-acting Pump feeding | |

| | water through a heater in || | | which it is

heated from 60 | | || to 200 degrees | .879 |

12.1 | | | || | Geared Pump run from the

| | | | engine,feeding water | || | through a heater in which it || | | is heated from 60 to 200

| | | | degrees

| .868 | 13.2 ||______________________________|_____________________|____________________|

The injector, considered only in the light ofa combined heater and pump, is claimedto have a thermal efficiency of 100 percent, since all of the heat in the steam usedis returned to the boiler with the water.This claim leads to an erroneous idea. If apump is used in feeding the water to aboiler and the heat in the exhaust from thepump is imparted to the feed water, thepump has as high a thermal efficiency asthe injector. The pump has the furtheradvantage that it uses so much less steamfor the forcing of a given quantity of waterinto the boiler that it makes possible agreater saving through the use of theexhaust from other auxiliaries for heatingthe feed, which exhaust, if an injector wereused, would be wasted, as has been

pointed out.

In locomotive practice, injectors are usedbecause there is no exhaust steamavailable for heating the feed, this beingutilized in producing a forced draft, andbecause of space requirements. In powerplant work, however, pumps areuniversally used for regular operation,though injectors are sometimes installedas an auxiliary method of feeding.

Table 18 shows the relative value ofinjectors, direct-acting steam pumps andpumps driven from the engine, the datahaving been obtained from actualexperiment. It will be noted that whenfeeding cold water direct to the boilers,the injector has a slightly greater economybut when feeding through a heater, thepump is by far the more economical.

Auxiliaries--It is the general impressionthat auxiliaries will take less steam if theexhaust is turned into the condensers, inthis way reducing the back pressure. As amatter of fact, vacuum is rarely registeredon an indicator card taken from thecylinders of certain types of auxiliariesunless the exhaust connection is short andwithout bends, as long pipes and manyangles offset the effect of the condenser.On the other hand, if the exhaust steamfrom the auxiliaries can be used forheating the feed water, all of the latentheat less only the loss due to radiation isreturned to the boiler and is saved insteadof being lost in the condensing water orwasted with the free exhaust. Taking intoconsideration the plant as a whole, itwould appear that the auxiliary machinery,under such conditions, is more efficientthan the main engines.

[Illustration: Portion of 4160 Horse-powerInstallation of Babcock & Wilcox Boilers atthe Prudential Life Insurance Co. Building,Newark, N. J.]

STEAM

When a given weight of a perfect gas iscompressed or expanded at a constanttemperature, the product of the pressureand volume is a constant. Vapors, whichare liquids in aeriform condition, on theother hand, can exist only at a definitepressure corresponding to eachtemperature if in the saturated state, thatis, the pressure is a function of thetemperature only. Steam is water vapor,and at a pressure of, say, 150 poundsabsolute per square inch saturated steamcan exist only at a temperature 358degrees Fahrenheit. Hence if the pressureof saturated steam be fixed, itstemperature is also fixed, and _viceversa_.

Saturated steam is water vapor in the

condition in which it is generated fromwater with which it is in contact. Or it issteam which is at the maximum pressureand density possible at its temperature. Ifany change be made in the temperature orpressure of steam, there will be acorresponding change in its condition. Ifthe pressure be increased or thetemperature decreased, a portion of thesteam will be condensed. If thetemperature be increased or the pressuredecreased, a portion of the water withwhich the steam is in contact will beevaporated into steam. Steam will remainsaturated just so long as it is of the samepressure and temperature as the waterwith which it can remain in contact withouta gain or loss of heat. Moreover, saturatedsteam cannot have its temperaturelowered without a lowering of its pressure,any loss of heat being made up by thelatent heat of such portion as will be

condensed. Nor can the temperature ofsaturated steam be increased except whenaccompanied by a corresponding increasein pressure, any added heat beingexpended in the evaporation into steam ofa portion of the water with which it is incontact.

Dry saturated steam contains no water. Insome cases, saturated steam isaccompanied by water which is carriedalong with it, either in the form of a sprayor is blown along the surface of the piping,and the steam is then said to be wet. Thepercentage weight of the steam in amixture of steam and water is called thequality of the steam. Thus, if in a mixture of100 pounds of steam and water there isthree-quarters of a pound of water, thequality of the steam will be 99.25.

Heat may be added to steam not in contact

with water, such an addition of heatresulting in an increase of temperatureand pressure if the volume be keptconstant, or an increase in temperatureand volume if the pressure remainconstant. Steam whose temperature thusexceeds that of saturated steam at acorresponding pressure is said to besuperheated and its propertiesapproximate those of a perfect gas.

As pointed out in the chapter on heat, theheat necessary to raise one pound of waterfrom 32 degrees Fahrenheit to the point ofebullition is called the _heat of the liquid_.The heat absorbed during ebullitionconsists of that necessary to dissociate themolecules, or the _inner latent heat_, andthat necessary to overcome the resistanceto the increase in volume, or the _outerlatent heat_. These two make up the _latentheat of evaporation_ and the sum of this

latent heat of evaporation and the heat ofthe liquid make the _total heat_ of thesteam. These values for various pressuresare given in the steam tables, pages 122 to127.

The specific volume of saturated steam atany pressure is the volume in cubic feet ofone pound of steam at that pressure.

The density of saturated steam, that is, itsweight per cubic foot, is obviously thereciprocal of the specific volume. Thisdensity varies as the 16/17 power over theordinary range of pressures used in steamboiler work and may be found by theformula, D = .003027p^{.941}, which iscorrect within 0.15 per cent up to 250pounds pressure.

The relative volume of steam is the ratio ofthe volume of a given weight to the volume

of the same weight of water at 39.2degrees Fahrenheit and is equal to thespecific volume times 62.427.

As vapors are liquids in their gaseous formand the boiling point is the point of changein this condition, it is clear that this point isdependent upon the pressure under whichthe liquid exists. This fact is of greatpractical importance in steam condenserwork and in many operations involvingboiling in an open vessel, since in thelatter case its altitude will haveconsiderable influence. The relationbetween altitude and boiling point ofwater is shown in Table 12.

The conditions of feed temperature andsteam pressure in boiler tests, fuelperformances and the like, will be found tovary widely in different trials. In order tosecure a means for comparison of different

trials, it is necessary to reduce all results tosome common basis. The method whichhas been adopted for the reduction to acomparable basis is to transform theevaporation under actual conditions ofsteam pressure and feed temperaturewhich exist in the trial to an equivalentevaporation under a set of standardconditions. These standard conditionspresuppose a feed water temperature of212 degrees Fahrenheit and a steampressure equal to the normal atmosphericpressure at sea level, 14.7 poundsabsolute. Under such conditions steamwould be generated _at_ a temperature of212 degrees, the temperaturecorresponding to atmospheric pressure atsea level, _from_ water at 212 degrees.The weight of water which _would_ beevaporated under the assumed standardconditions by exactly the amount of heatabsorbed by the boiler under actual

conditions existing in the trial, is,therefore, called the equivalentevaporation "from and at 212 degrees."

The factor for reducing the weight of wateractually converted into steam from thetemperature of the feed, at the steampressure existing in the trial, to theequivalent evaporation under standardconditions is called the _factor ofevaporation._ This factor is the ratio of thetotal heat added to one pound of steamunder the standard conditions to the heatadded to each pound of steam in heatingthe water from the temperature of the feedin the trial to the temperaturecorresponding to the pressure existing inthe trial. This heat added is obviously thedifference between the total heat ofevaporation of the steam at the pressureexisting in the trial and the heat of theliquid in the water at the temperature at

which it was fed in the trial. To illustrate byan example:

In a boiler trial the temperature of the feedwater is 60 degrees Fahrenheit and thepressure under which steam is delivered is160.3 pounds gauge pressure or 175pounds absolute pressure. The total heat ofone pound of steam at 175 poundspressure is 1195.9 B. t. u. measured abovethe standard temperature of 32 degreesFahrenheit. But the water fed to the boilercontained 28.08 B. t. u. as the heat of theliquid measured above 32 degreesFahrenheit. Therefore, to each pound ofsteam there has been added 1167.82 B. t.u. To evaporate one pound of water understandard conditions would, on the otherhand, have required but 970.4 B. t. u.,which, as described, is the latent heat ofevaporation at 212 degrees Fahrenheit.Expressed differently, the total heat of one

pound of steam at the pressurecorresponding to a temperature of 212degrees is 1150.4 B. t. u. One pound ofwater at 212 degrees contains 180 B. t. u. ofsensible heat above 32 degreesFahrenheit. Hence, under standardconditions, 1150.4 - 180 = 970.4 B. t. u. isadded in the changing of one pound ofwater into steam at atmospheric pressureand a temperature of 212 degrees. This isin effect the definition of the latent heat ofevaporation.

Hence, if conditions of the trial had beenstandard, only 970.4 B. t. u. would berequired and the ratio of 1167.82 to 970.4B. t. u. is the ratio determining the factor ofevaporation. The factor in the assumedcase is 1167.82 �970.4 = 1.2034 and if thesame amount of heat had been absorbedunder standard conditions as wasabsorbed in the trial condition, 1.2034

times the amount of steam would havebeen generated. Expressed as a formulafor use with any set of conditions, thefactor is,

H - h F = ----- (2) 970.4

Where H = the total heat of steam above 32degrees Fahrenheit from steamtables, h = sensible heat of feed waterabove 32 degrees Fahrenheit fromTable 22.

In the form above, the factor may bedetermined with either saturated orsuperheated steam, provided that in thelatter case values of H are available forvarying degrees of superheat andpressures.

Where such values are not available, theform becomes,

H - h + s(t_{sup} - t_{sat}) F =---------------------------- (3) 970.4

Where s = mean specific heat ofsuperheated steam at thepressure existing in the trial fromsaturated steam to thetemperature existing in the trial,t_{sup} = final temperature of steam,t_{sat} = temperature of saturated steam,corresponding to pressureexisting, (t_{sup} - t_{sat}) = degrees ofsuperheat.

The specific heat of superheated steamwill be taken up later.

Table 19 gives factors of evaporation forsaturated steam boiler trials to cover alarge range of conditions. Except for themost refined work, intermediate values

may be determined by interpolation.

Steam gauges indicate the pressure abovethe atmosphere. As has been pointed out,the atmospheric pressure changesaccording to the altitude and the variationin the barometer. Hence, calculationsinvolving the properties of steam arebased on _absolute_ pressures, which areequal to the gauge pressure plus theatmospheric pressure in pounds to thesquare inch. This latter is generallyassumed to be 14.7 pounds per squareinch at sea level, but for other levels itmust be determined from the barometricreading at that place.

Vacuum gauges indicate the difference,expressed in inches of mercury, betweenatmospheric pressure and the pressurewithin the vessel to which the gauge isattached. For approximate purposes, 2.04

inches height of mercury may beconsidered equal to a pressure of onepound per square inch at the ordinarytemperatures at which mercury gaugesare used. Hence for any reading of thevacuum gauge in inches, G, the absolutepressure for any barometer reading ininches, B, will be (B - G) �2.04. If thebarometer is 30 inches measured atordinary temperatures and not correctedto 32 degrees Fahrenheit and the vacuumgauge 24 inches, the absolute pressurewill be (30 - 24) �2.04 = 2.9 pounds persquare inch.

TABLE 19

FACTORS OF EVAPORATIONCALCULATED FROM MARKS AND

DAVIS TABLES

______________________________________________________________________ | |

| |Feed || |Temp- |

||erature|| |Degrees| Steam Pressure byGauge | |Fahren-|

| |heit ||

|_______|______________________________________________________________| | |

| | | | | | | || 50 | 60 | 70 | 80 | 90 | 100 |

110 ||_______|________|________|________|________|________|________|________| | |

| | | | | | | |32 | 1.2143 | 1.2170 | 1.2194 | 1.2215 |1.2233 | 1.2233 | 1.2265 | | 40 | 1.2060 |1.2087 | 1.2111 | 1.2131 | 1.2150 | 1.2168| 1.2181 | | 50 | 1.1957 | 1.1984 | 1.2008

| 1.2028 | 1.2047 | 1.2065 | 1.2079 | | 60| 1.1854 | 1.1881 | 1.1905 | 1.1925 |1.1944 | 1.1961 | 1.1976 | | 70 | 1.1750 |1.1778 | 1.1802 | 1.1822 | 1.1841 | 1.1859| 1.1873 | | 80 | 1.1649 | 1.1675 | 1.1699| 1.1720 | 1.1738 | 1.1756 | 1.1770 | | 90| 1.1545 | 1.1572 | 1.1596 | 1.1617 |1.1636 | 1.1653 | 1.1668 | | 100 | 1.1443 |1.1470 | 1.1493 | 1.1514 | 1.1533 | 1.1550| 1.1565 | | 110 | 1.1340 | 1.1367 | 1.1391| 1.1411 | 1.1430 | 1.1448 | 1.1462 | | 120| 1.1237 | 1.1264 | 1.1288 | 1.1309 |1.1327 | 1.1345 | 1.1359 | | 130 | 1.1134 |1.1161 | 1.1185 | 1.1206 | 1.1225 | 1.1242| 1.1257 | | 140 | 1.1031 | 1.1058 | 1.1082| 1.1103 | 1.1122 | 1.1139 | 1.1154 | | 150| 1.0928 | 1.0955 | 1.0979 | 1.1000 |1.1019 | 1.1036 | 1.1051 | | 160 | 1.0825 |1.0852 | 1.0876 | 1.0897 | 1.0916 | 1.0933| 1.0948 | | 170 | 1.0722 | 1.0749 | 1.0773| 1.0794 | 1.0813 | 1.0830 | 1.0845 | | 180| 1.0619 | 1.0646 | 1.0670 | 1.0691 |

1.0709 | 1.0727 | 1.0741 | | 190 | 1.0516 |1.0543 | 1.0567 | 1.0587 | 1.0606 | 1.0624| 1.0638 | | 200 | 1.0412 | 1.0439 | 1.0463| 1.0484 | 1.0503 | 1.0520 | 1.0535 | | 210| 1.0309 | 1.0336 | 1.0360 | 1.0380 |1.0399 | 1.0417 | 1.0432 ||_______|________|________|________|________|________|________|________|______________________________________________________________________ | |

| |Feed || |Temp- |

||erature|| |Degrees| Steam Pressure byGauge | |Fahren-|

| |heit ||

|_______|______________________________________________________________| | |

| | | | | | | || 120 | 130 | 140 | 150 | 160 |

170 | 180 ||_______|________|________|________|________|________|________|________| | |

| | | | | | | |32 | 1.2280 | 1.2292 | 1.2304 | 1.2314 |1.2323 | 1.2333 | 1.2342 | | 40 | 1.2196 |1.2209 | 1.2221 | 1.2231 | 1.2241 | 1.2250| 1.2259 | | 50 | 1.2093 | 1.2106 | 1.2117| 1.2128 | 1.2137 | 1.2147 | 1.2156 | | 60| 1.1990 | 1.2003 | 1.2014 | 1.2025 |1.2034 | 1.2044 | 1.2053 | | 70 | 1.1887 |1.1900 | 1.1911 | 1.1922 | 1.1931 | 1.1941| 1.1950 | | 80 | 1.1785 | 1.1797 | 1.1809| 1.1819 | 1.1828 | 1.1838 | 1.1847 | | 90| 1.1682 | 1.1695 | 1.1706 | 1.1717 |1.1725 | 1.1735 | 1.1744 | | 100 | 1.1579 |1.1592 | 1.1603 | 1.1614 | 1.1623 | 1.1633| 1.1642 | | 110 | 1.1477 | 1.1489 | 1.1500| 1.1511 | 1.1520 | 1.1530 | 1.1539 | | 120| 1.1374 | 1.1386 | 1.1398 | 1.1408 |1.1418 | 1.1427 | 1.1436 | | 130 | 1.1271 |1.1284 | 1.1295 | 1.1305 | 1.1315 | 1.1324

| 1.1333 | | 140 | 1.1168 | 1.1181 | 1.1192| 1.1203 | 1.1212 | 1.1221 | 1.1230 | | 150| 1.1065 | 1.1078 | 1.1089 | 1.1099 |1.1109 | 1.1118 | 1.1127 | | 160 | 1.0962 |1.0975 | 1.0986 | 1.0997 | 1.1006 | 1.1015| 1.1024 | | 170 | 1.0859 | 1.0872 | 1.0883| 1.0893 | 1.0903 | 1.0912 | 1.0921 | | 180| 1.0756 | 1.0768 | 1.0780 | 1.0790 |1.0800 | 1.0809 | 1.0818 | | 190 | 1.0653 |1.0665 | 1.0676 | 1.0687 | 1.0696 | 1.0706| 1.0715 | | 200 | 1.0549 | 1.0562 | 1.0573| 1.0584 | 1.0593 | 1.0602 | 1.0611 | | 210| 1.0446 | 1.0458 | 1.0469 | 1.0480 |1.0489 | 1.0499 | 1.0508 ||_______|________|________|________|________|________|________|________|______________________________________________________________________ | |

| |Feed || |Temp- |

||erature|

| |Degrees| Steam Pressure byGauge | |Fahren-|

| |heit ||

|_______|______________________________________________________________| | |

| | | | | | | || 190 | 200 | 210 | 220 | 230 |240 | 250 ||_______|________|________|________|________|________|________|________| | |

| | | | | | | |32 | 1.2350 | 1.2357 | 1.2364 | 1.2372 |1.2378 | 1.2384 | 1.2390 | | 40 | 1.2267 |1.2274 | 1.2282 | 1.2289 | 1.2295 | 1.2301| 1.2307 | | 50 | 1.2164 | 1.2171 | 1.2178| 1.2186 | 1.2192 | 1.2198 | 1.2204 | | 60| 1.2061 | 1.2068 | 1.2075 | 1.2083 |1.2089 | 1.2095 | 1.2101 | | 70 | 1.1958 |1.1965 | 1.1972 | 1.1980 | 1.1986 | 1.1992| 1.1998 | | 80 | 1.1855 | 1.1863 | 1.1869| 1.1877 | 1.1883 | 1.1889 | 1.1895 | | 90

| 1.1750 | 1.1760 | 1.1766 | 1.1774 |1.1780 | 1.1786 | 1.1792 | | 100 | 1.1650 |1.1657 | 1.1664 | 1.1671 | 1.1678 | 1.1684| 1.1690 | | 110 | 1.1547 | 1.1554 | 1.1562| 1.1569 | 1.1575 | 1.1581 | 1.1587 | | 120| 1.1444 | 1.1452 | 1.1459 | 1.1466 |1.1472 | 1.1478 | 1.1484 | | 130 | 1.1341 |1.1349 | 1.1356 | 1.1363 | 1.1369 | 1.1375| 1.1381 | | 140 | 1.1239 | 1.1246 | 1.1253| 1.1260 | 1.1266 | 1.1272 | 1.1278 | | 150| 1.1136 | 1.1143 | 1.1150 | 1.1157 |1.1163 | 1.1169 | 1.1176 | | 160 | 1.1033 |1.1040 | 1.1047 | 1.1054 | 1.1060 | 1.1066| 1.1073 | | 170 | 1.0930 | 1.0937 | 1.0944| 1.0951 | 1.0957 | 1.0963 | 1.0969 | | 180| 1.0826 | 1.0834 | 1.0841 | 1.0848 |1.0854 | 1.0860 | 1.0866 | | 190 | 1.0723 |1.0730 | 1.0737 | 1.0745 | 1.0751 | 1.0757| 1.0763 | | 200 | 1.0620 | 1.0627 | 1.0634| 1.0641 | 1.0647 | 1.0653 | 1.0660 | | 210| 1.0516 | 1.0523 | 1.0530 | 1.0538 |1.0544 | 1.0550 | 1.0556 |

|_______|________|________|________|________|________|________|________|

The temperature, pressure and otherproperties of steam for varying amounts ofvacuum and the pressure above vacuumcorresponding to each inch of reading ofthe vacuum gauge are given in Table 20.

TABLE 20

PROPERTIES OF SATURATED STEAMFOR VARYING AMOUNTS OF VACUUM

CALCULATED FROM MARKS ANDDAVIS TABLES______________________________________________________________________ | |

| | | | | | | || | Heat of | Latent | Total |

| | | | Temp- | the Liquid| Heat| Heat | | | | | erature |Above | Above | Above |Density or| |

| Absolute | Degrees | 32 De- | 32 De-| 32 De- |Weight per| | Vacuum |Pressure | Fahren- | grees | grees |grees |Cubic Foot| |Ins. Hg.| Pounds |heit | B. t. u. |B. t. u.|B. t. u.| Pounds ||________|__________|_________|___________|________|________|__________| || | | | | | | |29.5 | .207 | 54.1 | 22.18 | 1061.0 |1083.2 | 0.000678 | | 29 | .452 | 76.6| 44.64 | 1048.7 | 1093.3 | 0.001415 | |28.5 | .698 | 90.1 | 58.09 | 1041.1 |1099.2 | 0.002137 | | 28 | .944 | 99.9| 67.87 | 1035.6 | 1103.5 | 0.002843 | |27 | 1.44 | 112.5 | 80.4 | 1028.6 |1109.0 | 0.00421 | | 26 | 1.93 | 124.5| 92.3 | 1022.0 | 1114.3 | 0.00577 | |25 | 2.42 | 132.6 | 100.5 | 1017.3 |1117.8 | 0.00689 | | 24 | 2.91 | 140.1| 108.0 | 1013.1 | 1121.1 | 0.00821 | |22 | 3.89 | 151.7 | 119.6 | 1006.4 |1126.0 | 0.01078 | | 20 | 4.87 | 161.1

| 128.9 | 1001.0 | 1129.9 | 0.01331 | |18 | 5.86 | 168.9 | 136.8 | 996.4 |1133.2 | 0.01581 | | 16 | 6.84 | 175.8| 143.6 | 992.4 | 1136.0 | 0.01827 | |14 | 7.82 | 181.8 | 149.7 | 988.8 |1138.5 | 0.02070 | | 12 | 8.80 | 187.2| 155.1 | 985.6 | 1140.7 | 0.02312 | |10 | 9.79 | 192.2 | 160.1 | 982.6 |1142.7 | 0.02554 | | 5 | 12.24 | 202.9| 170.8 | 976.0 | 1146.8 | 0.03148 ||________|__________|_________|___________|________|________|__________|

From the steam tables, the condensedTable 21 of the properties of steam atdifferent pressures may be constructed.From such a table there may be drawn thefollowing conclusions.

TABLE 21

VARIATION IN PROPERTIES OF

SATURATED STEAM WITH PRESSURE___________________________________________________ | | | | |

| | Pressure |Temperature | Heat of |Latent | Total | | Pounds | Degrees |Liquid | Heat | Heat | | Absolute |Fahrenheit |B. t. u. |B. t. u.|B. t. u.||__________|____________|_________|________|________| | | | | |

| | 14.7 | 212.0 | 180.0 | 970.4 |1150.4 | | 20.0 | 228.0 | 196.1 |960.0 | 1156.2 | | 100.0 | 327.8 |298.3 | 888.0 | 1186.3 | | 300.0 | 417.5

| 392.7 | 811.3 | 1204.1 ||__________|____________|_________|________|________|

As the pressure and temperature increase,the latent heat decreases. This decrease,however, is less rapid than thecorresponding increase in the heat of theliquid and hence the total heat increases

with an increase in the pressure andtemperature. The percentage increase inthe total heat is small, being 0.5, 3.1, and4.7 per cent for 20, 100, and 300 poundsabsolute pressure respectively above thetotal heat in one pound of steam at 14.7pounds absolute. The temperatures, on theother hand, increase at the rates of 7.5,54.6, and 96.9 per cent. The efficiency of aperfect steam engine is proportional to theexpression (t - t_{1})/t in which t and t_{1}are the absolute temperatures of thesaturated steam at admission and exhaustrespectively. While actual engines onlyapproximate the ideal engine in efficiency,yet they follow the same general law.Since the exhaust temperature cannot belowered beyond present practice, itfollows that the only available method ofincreasing the efficiency is by an increasein the temperature of the steam atadmission. How this may be accomplished

by an increase of pressure is clearlyshown, for the increase of fuel necessary toincrease the pressure is negligible, asshown by the total heat, while the increasein economy, due to the higher pressure,will result directly from the rapid increaseof the corresponding temperature.

TABLE 22

HEAT UNITS PER POUND ANDWEIGHT PER CUBIC FOOT OF WATERBETWEEN 32 DEGREES FAHRENHEIT AND

340 DEGREES FAHRENHEIT_________________________________ || | | |Temperature|Heat Units|Weight | | Degrees | per | per | |Fahrenheit| Pound |Cubic Foot||___________|__________|__________| |

| | | | 32 | 0.00 | 62.42| | 33 | 1.01 | 62.42 | | 34 |

2.01 | 62.42 | | 35 | 3.02 | 62.43

| | 36 | 4.03 | 62.43 | | 37 |5.04 | 62.43 | | 38 | 6.04 | 62.43| | 39 | 7.05 | 62.43 | | 40 |8.05 | 62.43 | | 41 | 9.05 | 62.43| | 42 | 10.06 | 62.43 | | 43 |11.06 | 62.43 | | 44 | 12.06 | 62.43| | 45 | 13.07 | 62.42 | | 46 |

14.07 | 62.42 | | 47 | 15.07 | 62.42| | 48 | 16.07 | 62.42 | | 49 |

17.08 | 62.42 | | 50 | 18.08 | 62.42| | 51 | 19.08 | 62.41 | | 52 |

20.08 | 62.41 | | 53 | 21.08 | 62.41| | 54 | 22.08 | 62.40 | | 55 |

23.08 | 62.40 | | 56 | 24.08 | 62.39| | 57 | 25.08 | 62.39 | | 58 |

26.08 | 62.38 | | 59 | 27.08 | 62.37| | 60 | 28.08 | 62.37 | | 61 |

29.08 | 62.36 | | 62 | 30.08 | 62.36| | 63 | 31.07 | 62.35 | | 64 |

32.07 | 62.35 | | 65 | 33.07 | 62.34| | 66 | 34.07 | 62.33 | | 67 |

35.07 | 62.33 | | 68 | 36.07 | 62.32

| | 69 | 37.06 | 62.31 | | 70 |38.06 | 62.30 | | 71 | 39.06 | 62.30| | 72 | 40.05 | 62.29 | | 73 |

41.05 | 62.28 | | 74 | 42.05 | 62.27| | 75 | 42.05 | 62.26 | | 76 |

44.04 | 62.26 | | 77 | 45.04 | 62.25| | 78 | 46.04 | 62.24 | | 79 |

47.04 | 62.23 | | 80 | 48.03 | 62.22| | 81 | 49.03 | 62.21 | | 82 |

50.03 | 62.20 | | 83 | 51.02 | 62.19| | 84 | 52.02 | 62.18 | | 85 |

53.02 | 62.17 | | 86 | 54.01 | 62.16| | 87 | 55.01 | 62.15 | | 88 |

56.01 | 62.14 | | 89 | 57.00 | 62.13| | 90 | 58.00 | 62.12 | | 91 |

59.00 | 62.11 | | 92 | 60.00 | 62.09| | 93 | 60.99 | 62.08 | | 94 |

61.99 | 62.07 | | 95 | 62.99 | 62.06| | 96 | 63.98 | 62.05 | | 97 |

64.98 | 62.04 | | 98 | 65.98 | 62.03| | 99 | 66.97 | 62.02 | | 100 |

67.97 | 62.00 | | 101 | 68.97 |

61.99 | | 102 | 69.96 | 61.98 | |103 | 70.96 | 61.97 | | 104 | 71.96| 61.95 | | 105 | 72.95 | 61.94 | |106 | 73.95 | 61.93 | | 107 |

74.95 | 61.91 | | 108 | 75.95 |61.90 | | 109 | 76.94 | 61.88 | |110 | 77.94 | 61.86 | | 111 | 78.94| 61.85 | | 112 | 79.93 | 61.83 | |113 | 80.93 | 61.82 | | 114 |

81.93 | 61.80 | | 115 | 82.92 |61.79 | | 116 | 83.92 | 61.77 | |117 | 84.92 | 61.75 | | 118 | 85.92| 61.74 | | 119 | 86.91 | 61.72 | |120 | 87.91 | 61.71 | | 121 |

88.91 | 61.69 | | 122 | 89.91 |61.68 | | 123 | 90.90 | 61.66 | |124 | 91.90 | 61.65 | | 125 | 92.90| 61.63 | | 126 | 93.90 | 61.61 | |127 | 94.89 | 61.59 | | 128 |

95.89 | 61.58 | | 129 | 96.89 |61.56 | | 130 | 97.89 | 61.55 | |131 | 98.89 | 61.53 | | 132 | 99.88

| 61.52 | | 133 | 100.88 | 61.50 | |134 | 101.88 | 61.49 | | 135 |

102.88 | 61.47 | | 136 | 103.88 |61.45 | | 137 | 104.87 | 61.43 | |138 | 105.87 | 61.41 | | 139 |106.87 | 61.40 | | 140 | 107.87 |61.38 | | 141 | 108.87 | 61.36 | |142 | 109.87 | 61.34 | | 143 |110.87 | 61.33 | | 144 | 111.87 |61.31 | | 145 | 112.86 | 61.29 | |146 | 113.86 | 61.27 | | 147 |114.86 | 61.25 | | 148 | 115.86 |61.24 | | 149 | 116.86 | 61.22 | |150 | 117.86 | 61.20 | | 151 |118.86 | 61.18 | | 152 | 119.86 |61.16 | | 153 | 120.86 | 61.14 | |154 | 121.86 | 61.12 | | 155 |122.86 | 61.10 | | 156 | 123.86 |61.08 | | 157 | 124.86 | 61.06 | |158 | 125.86 | 61.04 | | 159 |126.86 | 61.02 | | 160 | 127.86 |61.00 | | 161 | 128.86 | 60.98 | |

162 | 129.86 | 60.96 | | 163 |130.86 | 60.94 | | 164 | 131.86 |60.92 | | 165 | 132.86 | 60.90 | |166 | 133.86 | 60.88 | | 167 |134.86 | 60.86 | | 168 | 135.86 |60.84 | | 169 | 136.86 | 60.82 | |170 | 137.87 | 60.80 | | 171 |138.87 | 60.78 | | 172 | 139.87 |60.76 | | 173 | 140.87 | 60.73 | |174 | 141.87 | 60.71 | | 175 |142.87 | 60.69 | | 176 | 143.87 |60.67 | | 177 | 144.88 | 60.65 | |178 | 145.88 | 60.62 | | 179 |146.88 | 60.60 | | 180 | 147.88 |60.58 | | 181 | 148.88 | 60.56 | |182 | 149.89 | 60.53 | | 183 |150.89 | 60.51 | | 184 | 151.89 |60.49 | | 185 | 152.89 | 60.47 | |186 | 153.89 | 60.45 | | 187 |154.90 | 60.42 | | 188 | 155.90 |60.40 | | 189 | 156.90 | 60.38 | |190 | 157,91 | 60.36 | | 191 |

158.91 | 60.33 | | 192 | 159.91 |60.31 | | 193 | 160.91 | 60.29 | |194 | 161.92 | 60.27 | | 195 |162.92 | 60.24 | | 196 | 163.92 |60.22 | | 197 | 164.93 | 60.19 | |198 | 165.93 | 60.17 | | 199 |166.94 | 60.15 | | 200 | 167.94 |60.12 | | 201 | 168.94 | 60.10 | |202 | 169.95 | 60.07 | | 203 |170.95 | 60.05 | | 204 | 171.96 |60.02 | | 205 | 172.96 | 60.00 | |206 | 173.97 | 59.98 | | 207 |174.97 | 59.95 | | 208 | 175.98 |59.93 | | 209 | 176.98 | 59.90 | |210 | 177.99 | 59.88 | | 211 |178.99 | 59.85 | | 212 | 180.00 |59.83 | | 213 | 181.0 | 59.80 | |214 | 182.0 | 59.78 | | 215 | 183.0| 59.75 | | 216 | 184.0 | 59.73 | |217 | 185.0 | 59.70 | | 218 | 186.1| 59.68 | | 219 | 187.1 | 59.65 | |220 | 188.1 | 59.63 | | 221 |

189.1 | 59.60 | | 222 | 190.1 |59.58 | | 223 | 191.1 | 59.55 | |224 | 192.1 | 59.53 | | 225 | 193.1| 59.50 | | 226 | 194.1 | 59.48 | |227 | 195.2 | 59.45 | | 228 | 196.2| 59.42 | | 229 | 197.2 | 59.40 | |230 | 198.2 | 59.37 | | 231 |

199.2 | 59.34 | | 232 | 200.2 |59.32 | | 233 | 201.2 | 59.29 | |234 | 202.2 | 59.27 | | 235 | 203.2| 59.24 | | 236 | 204.2 | 59.21 | |237 | 205.3 | 59.19 | | 238 | 206.3| 59.16 | | 239 | 207.3 | 59.14 | |240 | 208.3 | 59.11 | | 241 |

209.3 | 59.08 | | 242 | 210.3 |59.05 | | 243 | 211.4 | 59.03 | |244 | 212.4 | 59.00 | | 245 | 213.4| 58.97 | | 246 | 214.4 | 58.94 | |247 | 215.4 | 58.91 | | 248 | 216.4| 58.89 | | 249 | 217.4 | 58.86 | |250 | 218.5 | 58.83 | | 260 |

228.6 | 58.55 | | 270 | 238.8 |

58.26 | | 280 | 249.0 | 57.96 | |290 | 259.3 | 57.65 | | 300 | 269.6| 57.33 | | 310 | 279.9 | 57.00 | |320 | 290.2 | 56.66 | | 330 | 300.6| 56.30 | | 340 | 311.0 | 55.94 |

|___________|__________|__________|

The gain due to superheat cannot bepredicted from the formula for theefficiency of a perfect steam engine givenon page 119. This formula is not applicablein cases where superheat is present sinceonly a relatively small amount of the heatin the steam is imparted at the maximumor superheated temperature.

The advantage of the use of high pressuresteam may be also indicated byconsidering the question from the aspectof volume. With an increase of pressurecomes a decrease in volume, thus onepound of saturated steam at 100 pounds

absolute pressure occupies 4.43 cubicfeet, while at 200 pounds pressure itoccupies 2.29 cubic feet. If then, inseparate cylinders of the samedimensions, one pound of steam at 100pounds absolute pressure and one poundat 200 pounds absolute pressure enter andare allowed to expand to the full volume ofeach cylinder, the high-pressure steam,having more room and a greater range forexpansion than the low-pressure steam,will thus do more work. This increase inthe amount of work, as was the increase intemperature, is large relative to theadditional fuel required as indicated bythe total heat. In general, it may be statedthat the fuel required to impart a givenamount of heat to a boiler is practicallyindependent of the steam pressure, sincethe temperature of the fire is so high ascompared with the steam temperature thata variation in the steam temperature does

not produce an appreciable effect.

The formulae for the algebraic expressionof the relation between saturated steampressures, temperatures and steamvolumes have been up to the present timeempirical. These relations have, however,been determined by experiment and, fromthe experimental data, tables have beencomputed which render unnecessary theuse of empirical formulae. Such formulaemay be found in any standard work ofthermo-dynamics. The following tablescover all practical cases.

Table 22 gives the heat units contained inwater above 32 degrees Fahrenheit atdifferent temperatures.

Table 23 gives the properties of saturatedsteam for various pressures.

Table 24 gives the properties ofsuperheated steam at various pressuresand temperatures.

These tables are based on those computedby Lionel S. Marks and Harvey N. Davis,these being generally accepted as beingthe most correct.

TABLE 23

PROPERTIES OF SATURATEDSTEAM

REPRODUCED BY PERMISSIONFROM MARKS AND DAVIS "STEAMTABLES AND DIAGRAMS"(Copyright, 1909, by Longmans, Green &Co.)____________________________________________________________________|Pressure,| Temper- |Specific Vol-|Heat

of |Latent Heat|Total Heat| | Pounds|ature De-| ume Cu. Ft. |the Liquid,| ofEvap., |of Steam, | |Absolute |grees F. |per Pound | B. t. u. | B. t. u. | B. t. u. ||_________|_________|_____________|___________|___________|__________| | 1 |101.83 | 333.0 | 69.8 | 1034.6 |1104.4 | | 2 | 126.15 | 173.5 |94.0 | 1021.0 | 1115.0 | | 3 | 141.52| 118.5 | 109.4 | 1012.3 | 1121.6 |

| 4 | 153.01 | 90.5 | 120.9 |1005.7 | 1126.5 | | 5 | 162.28 |73.33 | 130.1 | 1000.3 | 1130.5 | |6 | 170.06 | 61.89 | 137.9 | 995.8| 1133.7 | | 7 | 176.85 | 53.56 |144.7 | 991.8 | 1136.5 | | 8 |182.86 | 47.27 | 150.8 | 988.2 |1139.0 | | 9 | 188.27 | 42.36 |156.2 | 985.0 | 1141.1 | | 10 |193.22 | 38.38 | 161.1 | 982.0 |1143.1 | | 11 | 197.75 | 35.10 |165.7 | 979.2 | 1144.9 | | 12 |

201.96 | 32.36 | 169.9 | 976.6 |1146.5 | | 13 | 205.87 | 30.03 |173.8 | 974.2 | 1148.0 | | 14 |209.55 | 28.02 | 177.5 | 971.9 |1149.4 | | 15 | 213.0 | 26.27 |181.0 | 969.7 | 1150.7 | | 16 | 216.3

| 24.79 | 184.4 | 967.6 | 1152.0 || 17 | 219.4 | 23.38 | 187.5 |965.6 | 1153.1 | | 18 | 222.4 |22.16 | 190.5 | 963.7 | 1154.2 | |19 | 225.2 | 21.07 | 193.4 | 961.8| 1155.2 | | 20 | 228.0 | 20.08 |

196.1 | 960.0 | 1156.2 | | 22 | 233.1| 18.37 | 201.3 | 956.7 | 1158.0 |

| 24 | 237.8 | 16.93 | 206.1 |953.5 | 1159.6 | | 26 | 242.2 |15.72 | 210.6 | 950.6 | 1161.2 | |28 | 246.4 | 14.67 | 214.8 | 947.8| 1162.6 | | 30 | 250.3 | 13.74 |

218.8 | 945.1 | 1163.9 | | 32 | 254.1| 12.93 | 222.6 | 942.5 | 1165.1 |

| 34 | 257.6 | 12.22 | 226.2 |

940.1 | 1166.3 | | 36 | 261.0 |11.58 | 229.6 | 937.7 | 1167.3 | |38 | 264.2 | 11.01 | 232.9 | 935.5| 1168.4 | | 40 | 267.3 | 10.49 |

236.1 | 933.3 | 1169.4 | | 42 | 270.2| 10.02 | 239.1 | 931.2 | 1170.3 |

| 44 | 273.1 | 9.59 | 242.0 |929.2 | 1171.2 | | 46 | 275.8 | 9.20

| 244.8 | 927.2 | 1172.0 | | 48 |278.5 | 8.84 | 247.5 | 925.3 |1172.8 | | 50 | 281.0 | 8.51 |250.1 | 923.5 | 1173.6 | | 52 | 283.5

| 8.20 | 252.6 | 921.7 | 1174.3 || 54 | 285.9 | 7.91 | 255.1 |919.9 | 1175.0 | | 56 | 288.2 | 7.65

| 257.5 | 918.2 | 1175.7 | | 58 |290.5 | 7.40 | 259.8 | 916.5 |1176.4 | | 60 | 292.7 | 7.17 |262.1 | 914.9 | 1177.0 | | 62 | 294.9

| 6.95 | 264.3 | 913.3 | 1177.6 || 64 | 297.0 | 6.75 | 266.4 |911.8 | 1178.2 | | 66 | 299.0 | 6.56

| 268.5 | 910.2 | 1178.8 | | 68 |301.0 | 6.38 | 270.6 | 908.7 |1179.3 | | 70 | 302.9 | 6.20 |272.6 | 907.2 | 1179.8 | | 72 | 304.8

| 6.04 | 274.5 | 905.8 | 1180.4 || 74 | 306.7 | 5.89 | 276.5 |904.4 | 1180.9 | | 76 | 308.5 | 5.74

| 278.3 | 903.0 | 1181.4 | | 78 |310.3 | 5.60 | 280.2 | 901.7 |1181.8 | | 80 | 312.0 | 5.47 |282.0 | 900.3 | 1182.3 | | 82 | 313.8

| 5.34 | 283.8 | 899.0 | 1182.8 || 84 | 315.4 | 5.22 | 285.5 |897.7 | 1183.2 | | 86 | 317.1 | 5.10

| 287.2 | 896.4 | 1183.6 | | 88 |318.7 | 5.00 | 288.9 | 895.2 |1184.0 | | 90 | 320.3 | 4.89 |290.5 | 893.9 | 1184.4 | | 92 | 321.8

| 4.79 | 292.1 | 892.7 | 1184.8 || 94 | 323.4 | 4.69 | 293.7 |891.5 | 1185.2 | | 96 | 324.9 | 4.60

| 295.3 | 890.3 | 1185.6 | | 98 |

326.4 | 4.51 | 296.8 | 889.2 |1186.0 | | 100 | 327.8 | 4.429 |298.3 | 888.0 | 1186.3 | | 105 |331.4 | 4.230 | 302.0 | 885.2 |1187.2 | | 110 | 334.8 | 4.047 |305.5 | 882.5 | 1188.0 | | 115 |338.1 | 3.880 | 309.0 | 879.8 |1188.8 | | 120 | 341.3 | 3.726 |312.3 | 877.2 | 1189.6 | | 125 |344.4 | 3.583 | 315.5 | 874.7 |1190.3 | | 130 | 347.4 | 3.452 |318.6 | 872.3 | 1191.0 | | 135 |350.3 | 3.331 | 321.7 | 869.9 |1191.6 | | 140 | 353.1 | 3.219 |324.6 | 867.6 | 1192.2 | | 145 |355.8 | 3.112 | 327.4 | 865.4 |1192.8 | | 150 | 358.5 | 3.012 |330.2 | 863.2 | 1193.4 | | 155 |361.0 | 2.920 | 332.9 | 861.0 |1194.0 | | 160 | 363.6 | 2.834 |335.6 | 858.8 | 1194.5 | | 165 |366.0 | 2.753 | 338.2 | 856.8 |

1195.0 | | 170 | 368.5 | 2.675 |340.7 | 854.7 | 1195.4 | | 175 |370.8 | 2.602 | 343.2 | 852.7 |1195.9 | | 180 | 373.1 | 2.533 |345.6 | 850.8 | 1196.4 | | 185 |375.4 | 2.468 | 348.0 | 848.8 |1196.8 | | 190 | 377.6 | 2.406 |350.4 | 846.9 | 1197.3 | | 195 |379.8 | 2.346 | 352.7 | 845.0 |1197.7 | | 200 | 381.9 | 2.290 |354.9 | 843.2 | 1198.1 | | 205 |384.0 | 2.237 | 357.1 | 841.4 |1198.5 | | 210 | 386.0 | 2.187 |359.2 | 839.6 | 1198.8 | | 215 |388.0 | 2.138 | 361.4 | 837.9 |1199.2 | | 220 | 389.9 | 2.091 |363.4 | 836.2 | 1199.6 | | 225 |391.9 | 2.046 | 365.5 | 834.4 |1199.9 | | 230 | 393.8 | 2.004 |367.5 | 832.8 | 1200.2 | | 235 |395.6 | 1.964 | 369.4 | 831.1 |1200.6 | | 240 | 397.4 | 1.924 |

371.4 | 829.5 | 1200.9 | | 245 |399.3 | 1.887 | 373.3 | 827.9 |1201.2 | | 250 | 401.1 | 1.850 |375.2 | 826.3 | 1201.5 ||_________|_________|_____________|___________|___________|__________|

[Illustration: Portion of 6100 Horse-powerInstallation of Babcock & Wilcox BoilersEquipped with Babcock & Wilcox ChainGrate Stokers at the Campbell Street Plantof the Louisville Railway Co., Louisville,Ky. This Company Operates a Total of14,000 Horse Power of Babcock & WilcoxBoilers]

TABLE 24

PROPERTIES OF SUPERHEATEDSTEAM

REPRODUCED BY PERMISSION

FROM MARKS AND DAVIS "STEAMTABLES AND DIAGRAMS"(Copyright, 1909, by Longmans, Green &Co.)__________________________________________________________________ | | |

| | | |Degrees of Superheat |

|Pressure||_______________________________________________| | Pounds |Saturated| | |

| | | | |Absolute| Steam |50 | 100 | 150 | 200 | 250 | 300 ||________|_________|_______|_______|_______|_______|_______|_______| | t|162.3 | 212.3 | 262.3 | 312.3 | 362.3 |412.3 | 462.3 | | 5 v| 73.3 | 79.7 |85.7 | 91.8 | 97.8 | 103.8 | 109.8 | | h|1130.5 |1153.5 |1176.4 |1199.5 |1222.5|1245.6 |1268.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|

193.2 | 243.2 | 293.2 | 343.2 | 393.2 |443.2 | 493.2 | | 10 v| 38.4 | 41.5 |44.6 | 47.7 | 50.7 | 53.7 | 56.7 | | h|1143.1 |1166.3 |1189.5 |1212.7 |1236.0|1259.3 |1282.5 ||________|_________|_______|_______|_______|_______|_______|_______| | t|213.0 | 263.0 | 313.0 | 363.0 | 413.0 |463.0 | 513.0 | | 15 v| 26.27 | 28.40|30.46| 32.50| 34.53| 36.56| 38.58| |h| 1150.7 |1174.2 |1197.6 |1221.0 |1244.4|1267.7 |1291.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|228.0 | 278.0 | 328.0 | 378.0 | 428.0 |478.0 | 528.0 | | 20 v| 20.08 | 21.69|23.25| 24.80| 26.33| 27.85| 29.37| |h| 1156.2 |1179.9 |1203.5 |1227.1 |1250.6|1274.1 |1297.6 ||________|_________|_______|_______|_______|_______|_______|_______| | t|240.1 | 290.1 | 340.1 | 390.1 | 440.1 |

490.1 | 540.1 | | 25 v| 16.30 | 17.60|18.86| 20.10| 21.32| 22.55| 23.77| |h| 1160.4 |1184.4 |1208.2 |1231.9 |1255.6|1279.2 |1302.8 ||________|_________|_______|_______|_______|_______|_______|_______| | t|250.4 | 300.4 | 350.4 | 400.4 | 450.4 |500.4 | 550.4 | | 30 v| 13.74 | 14.83|15.89| 16.93| 17.97| 18.99| 20.00| |h| 1163.9 |1188.1 |1212.1 |1236.0 |1259.7|1283.4 |1307.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|259.3 | 309.3 | 359.3 | 409.3 | 459.3 |509.3 | 559.3 | | 35 v| 11.89 | 12.85|13.75| 14.65| 15.54| 16.42| 17.30| |h| 1166.8 |1191.3 |1215.4 |1239.4 |1263.3|1287.1 |1310.8 ||________|_________|_______|_______|_______|_______|_______|_______| | t|267.3 | 317.3 | 367.3 | 417.3 | 467.3 |517.3 | 567.3 | | 40 v| 10.49 | 11.33|

12.13| 12.93| 13.70| 14.48| 15.25| |h| 1169.4 |1194.0 |1218.4 |1242.4 |1266.4|1290.3 |1314.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|274.5 | 324.5 | 374.5 | 424.5 | 474.5 |524.5 | 574.5 | | 45 v| 9.39 | 10.14|10.86| 11.57| 12.27| 12.96| 13.65| |h| 1171.6 |1196.6 |1221.0 |1245.2 |1269.3|1293.2 |1317.0 ||________|_________|_______|_______|_______|_______|_______|_______| | t|281.0 | 331.0 | 381.0 | 431.0 | 481.0 |531.0 | 581.0 | | 50 v| 8.51 | 9.19|9.84| 10.48| 11.11| 11.74| 12.36| |h| 1173.6 |1198.8 |1223.4 |1247.7 |1271.8|1295.8 |1319.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|287.1 | 337.1 | 387.1 | 437.1 | 487.1 |537.1 | 587.1 | | 55 v| 7.78 | 8.40|9.00| 9.59| 10.16| 10.73| 11.30| | h|

1175.4 |1200.8 |1225.6 |1250.0 |1274.2|1298.1 |1322.0 ||________|_________|_______|_______|_______|_______|_______|_______| | t|292.7 | 342.7 | 392.7 | 442.7 | 492.7 |542.7 | 592.7 | | 60 v| 7.17 | 7.75|8.30| 8.84| 9.36| 9.89| 10.41| | h|1177.0 |1202.6 |1227.6 |1252.1 |1276.4|1300.4 |1324.3 ||________|_________|_______|_______|_______|_______|_______|_______| | t|298.0 | 348.0 | 398.0 | 448.0 | 498.0 |548.0 | 598.0 | | 65 v| 6.65 | 7.20|7.70| 8.20| 8.69| 9.17| 9.65| | h|1178.5 |1204.4 |1229.5 |1254.0 |1278.4|1302.4 |1326.4 ||________|_________|_______|_______|_______|_______|_______|_______| | t|302.9 | 352.9 | 402.9 | 452.9 | 502.9 |552.9 | 602.9 | | 70 v| 6.20 | 6.71|7.18| 7.65| 8.11| 8.56| 9.01| | h|1179.8 |1205.9 |1231.2 |1255.8 |1280.2

|1304.3 |1328.3 ||________|_________|_______|_______|_______|_______|_______|_______| | t|307.6 | 357.6 | 407.6 | 457.6 | 507.6 |557.6 | 607.6 | | 75 v| 5.81 | 6.28|6.73| 7.17| 7.60| 8.02| 8.44| | h|1181.1 |1207.5 |1232.8 |1257.5 |1282.0|1306.1 |1330.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|312.0 | 362.0 | 412.0 | 462.0 | 512.0 |562.0 | 612.0 | | 80 v| 5.47 | 5.92|6.34| 6.75| 7.17| 7.56| 7.95| | h|1182.3 |1208.8 |1234.3 |1259.0 |1283.6|1307.8 |1331.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|316.3 | 366.3 | 416.3 | 466.3 | 516.3 |566.3 | 616.3 | | 85 v| 5.16 | 5.59|6.99| 6.38| 6.76| 7.14| 7.51| | h|1183.4 |1210.2 |1235.8 |1260.6 |1285.2|1309.4 |1333.5 |

|________|_________|_______|_______|_______|_______|_______|_______| | t|320.3 | 370.3 | 420.3 | 470.3 | 520.3 |570.3 | 620.3 | | 90 v| 4.89 | 5.29|5.67| 6.04| 6.40| 6.76| 7.11| | h|1184.4 |1211.4 |1237.2 |1262.0 |1286.6|1310.8 |1334.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|324.1 | 374.1 | 424.1 | 474.1 | 524.1 |574.1 | 624.1 | | 95 v| 4.65 | 5.03|5.39| 5.74| 6.09| 6.43| 6.76| | h|1185.4 |1212.6 |1238.4 |1263.4 |1288.1|1312.3 |1336.4 ||________|_________|_______|_______|_______|_______|_______|_______| | t|327.8 | 377.8 | 427.8 | 477.8 | 527.8 |577.8 | 627.8 | | 100 v| 4.43 | 4.79|5.14| 5.47| 5.80| 6.12| 6.44| | h|1186.3 |1213.8 |1239.7 |1264.7 |1289.4|1313.6 |1337.8 ||________|_________|_______|_______|___

____|_______|_______|_______| | t|331.4 | 381.4 | 431.4 | 481.4 | 531.4 |581.4 | 631.4 | | 105 v| 4.23 | 4.58|4.91| 5.23| 5.54| 5.85| 6.15| | h|1187.2 |1214.9 |1240.8 |1265.9 |1290.6|1314.9 |1339.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|334.8 | 384.8 | 434.8 | 484.8 | 534.8 |584.8 | 634.8 | | 110 v| 4.05 | 4.38|4.70| 5.01| 5.31| 5.61| 5.90| | h|1188.0 |1215.9 |1242.0 |1267.1 |1291.9|1316.2 |1340.4 ||________|_________|_______|_______|_______|_______|_______|_______| | t|338.1 | 388.1 | 438.1 | 488.1 | 538.1 |588.1 | 638.1 | | 115 v| 3.88 | 4.20|4.51| 4.81| 5.09| 5.38| 5.66| | h|1188.8 |1216.9 |1243.1 |1268.2 |1293.0|1317.3 |1341.5 ||________|_________|_______|_______|_______|_______|_______|_______| | t|

341.3 | 391.3 | 441.3 | 491.3 | 541.3 |591.3 | 641.3 | | 120 v| 3.73 | 4.04|4.33| 4.62| 4.89| 5.17| 5.44| | h|1189.6 |1217.9 |1244.1 |1269.3 |1294.1|1318.4 |1342.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|344.4 | 394.4 | 444.4 | 494.4 | 544.4 |594.4 | 644.4 | | 125 v| 3.58 | 3.88|4.17| 4.45| 4.71| 4.97| 5.23| | h|1190.3 |1218.8 |1245.1 |1270.4 |1295.2|1319.5 |1343.8 ||________|_________|_______|_______|_______|_______|_______|_______| | t|347.4 | 397.4 | 447.4 | 497.4 | 547.4 |597.4 | 647.4 | | 130 v| 3.45 | 3.74|4.02| 4.28| 4.54| 4.80| 5.05| | h|1191.0 |1219.7 |1246.1 |1271.4 |1296.2|1320.6 |1344.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|350.3 | 400.3 | 450.3 | 500.3 | 550.3 |

600.3 | 650.3 | | 135 v| 3.33 | 3.61|3.88| 4.14| 4.38| 4.63| 4.87| | h|1191.6 |1220.6 |1247.0 |1272.3 |1297.2|1321.6 |1345.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|353.1 | 403.1 | 453.1 | 503.1 | 553.1 |603.1 | 653.1 | | 140 v| 3.22 | 3.49|3.75| 4.00| 4.24| 4.48| 4.71| | h|1192.2 |1221.4 |1248.0 |1273.3 |1298.2|1322.6 |1346.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|355.8 | 405.8 | 455.8 | 505.8 | 555.8 |605.8 | 655.8 | | 145 v| 3.12 | 3.38|3.63| 3.87| 4.10| 4.33| 4.56| | h|1192.8 |1222.2 |1248.8 |1274.2 |1299.1|1323.6 |1347.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|358.5 | 408.5 | 458.5 | 508.5 | 558.5 |608.5 | 658.5 | | 150 v| 3.01 | 3.27|

3.50| 3.75| 3.97| 4.19| 4.41| | h|1193.4 |1223.0 |1249.6 |1275.1 |1300.0|1324.5 |1348.8 ||________|_________|_______|_______|_______|_______|_______|_______| | t|361.0 | 411.0 | 461.0 | 511.0 | 561.0 |611.0 | 661.0 | | 155 v| 2.92 | 3.17|3.41| 3.63| 3.85| 4.06| 4.28| | h|1194.0 |1223.6 |1250.5 |1276.0 |1300.8|1325.3 |1349.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|363.6 | 413.6 | 463.6 | 513.6 | 563.6 |613.6 | 663.6 | | 160 v| 2.83 | 3.07|3.30| 3.53| 3.74| 3.95| 4.15| | h|1194.5 |1224.5 |1251.3 |1276.8 |1301.7|1326.2 |1350.6 ||________|_________|_______|_______|_______|_______|_______|_______| | t|366.0 | 416.0 | 466.0 | 516.0 | 566.0 |616.0 | 666.0 | | 165 v| 2.75 | 2.99|3.21| 3.43| 3.64| 3.84| 4.04| | h|

1195.0 |1225.2 |1252.0 |1277.6 |1302.5|1327.1 |1351.5 ||________|_________|_______|_______|_______|_______|_______|_______| | t|368.5 | 418.5 | 468.5 | 518.5 | 568.5 |618.5 | 668.5 | | 170 v| 2.68 | 2.91|3.12| 3.34| 3.54| 3.73| 3.92| | h|1195.4 |1225.9 |1252.8 |1278.4 |1303.3|1327.9 |1352.3 ||________|_________|_______|_______|_______|_______|_______|_______| | t|370.8 | 420.8 | 470.8 | 520.8 | 570.8 |620.8 | 670.8 | | 175 v| 2.60 | 2.83|3.04| 3.24| 3.44| 3.63| 3.82| | h|1195.9 |1226.6 |1253.6 |1279.1 |1304.1|1328.7 |1353.2 ||________|_________|_______|_______|_______|_______|_______|_______| | t|373.1 | 423.1 | 473.1 | 523.1 | 573.1 |623.1 | 673.1 | | 180 v| 2.53 | 2.75|2.96| 3.16| 3.35| 3.54| 3.72| | h|1196.4 |1227.2 |1254.3 |1279.9 |1304.8

|1329.5 |1353.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|375.4 | 425.4 | 475.4 | 525.4 | 575.4 |625.4 | 675.4 | | 185 v| 2.47 | 2.68|2.89| 3.08| 3.27| 3.45| 3.63| | h|1196.8 |1227.9 |1255.0 |1280.6 |1305.6|1330.2 |1354.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|377.6 | 427.6 | 477.6 | 527.6 | 577.6 |627.6 | 677.6 | | 190 v| 2.41 | 2.62|2.81| 3.00| 3.19| 3.37| 3.55| | h|1197.3 |1228.6 |1255.7 |1281.3 |1306.3|1330.9 |1355.5 ||________|_________|_______|_______|_______|_______|_______|_______| | t|379.8 | 429.8 | 479.8 | 529.8 | 579.8 |629.8 | 679.8 | | 195 v| 2.35 | 2.55|2.75| 2.93| 3.11| 3.29| 3.46| | h|1197.7 |1229.2 |1256.4 |1282.0 |1307.0|1331.6 |1356.2 |

|________|_________|_______|_______|_______|_______|_______|_______| | t|381.9 | 431.9 | 481.9 | 531.9 | 581.9 |631.9 | 681.9 | | 200 v| 2.29 | 2.49|2.68| 2.86| 3.04| 3.21| 3.38| | h|1198.1 |1229.8 |1257.1 |1282.6 |1307.7|1332.4 |1357.0 ||________|_________|_______|_______|_______|_______|_______|_______| | t|384.0 | 434.0 | 484.0 | 534.0 | 584.0 |634.0 | 684.0 | | 205 v| 2.24 | 2.44|2.62| 2.80| 2.97| 3.14| 3.30| | h|1198.5 |1230.4 |1257.7 |1283.3 |1308.3|1333.0 |1357.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|386.0 | 436.0 | 486.0 | 536.0 | 586.0 |636.0 | 686.0 | | 210 v| 2.19 | 2.38|2.56| 2.74| 2.91| 3.07| 3.23| | h|1198.8 |1231.0 |1258.4 |1284.0 |1309.0|1333.7 |1358.4 ||________|_________|_______|_______|___

____|_______|_______|_______| | t|388.0 | 438.0 | 488.0 | 538.0 | 588.0 |638.0 | 688.0 | | 215 v| 2.14 | 2.33|2.51| 2.68| 2.84| 3.00| 3.16| | h|1199.2 |1231.6 |1259.0 |1284.6 |1309.7|1334.4 |1359.1 ||________|_________|_______|_______|_______|_______|_______|_______| | t|389.9 | 439.9 | 489.9 | 539.9 | 589.9 |639.9 | 689.9 | | 220 v| 2.09 | 2.28|2.45| 2.62| 2.78| 2.94| 3.10| | h|1199.6 |1232.2 |1259.6 |1285.2 |1310.3|1335.1 |1359.8 ||________|_________|_______|_______|_______|_______|_______|_______| | t|391.9 | 441.9 | 491.9 | 541.9 | 591.9 |641.9 | 691.9 | | 225 v| 2.05 | 2.23|2.40| 2.57| 2.72| 2.88| 3.03| | h|1199.9 |1232.7 |1260.2 |1285.9 |1310.9|1335.7 |1360.3 ||________|_________|_______|_______|_______|_______|_______|_______| | t|

393.8 | 443.8 | 493.8 | 543.8 | 593.8 |643.8 | 693.8 | | 230 v| 2.00 | 2.18|2.35| 2.51| 2.67| 2.82| 2.97| | h|1200.2 |1233.2 |1260.7 |1286.5 |1311.6|1336.3 |1361.0 ||________|_________|_______|_______|_______|_______|_______|_______| | t|395.6 | 445.6 | 495.6 | 545.6 | 595.6 |645.6 | 695.6 | | 235 v| 1.96 | 2.14|2.30| 2.46| 2.62| 2.77| 2.91| | h|1200.6 |1233.8 |1261.4 |1287.1 |1312.2|1337.0 |1361.7 ||________|_________|_______|_______|_______|_______|_______|_______| | t|397.4 | 447.4 | 497.4 | 547.4 | 597.4 |647.4 | 697.4 | | 240 v| 1.92 | 2.09|2.26| 2.42| 2.57| 2.71| 2.85| | h|1200.9 |1234.3 |1261.9 |1287.6 |1312.8|1337.6 |1362.3 ||________|_________|_______|_______|_______|_______|_______|_______| | t|399.3 | 449.3 | 499.3 | 549.3 | 599.3 |

649.3 | 699.3 | | 245 v| 1.89 | 2.05|2.22| 2.37| 2.52| 2.66| 2.80| | h|1201.2 |1234.8 |1262.5 |1288.2 |1313.3|1338.2 |1362.9 ||________|_________|_______|_______|_______|_______|_______|_______| | t|401.0 | 451.0 | 501.0 | 551.0 | 601.0 |651.0 | 701.0 | | 250 v| 1.85 | 2.02|2.17| 2.33| 2.47| 2.61| 2.75| | h|1201.5 |1235.4 |1263.0 |1288.8 |1313.9|1338.8 |1363.5 ||________|_________|_______|_______|_______|_______|_______|_______| | t|402.8 | 452.8 | 502.8 | 552.8 | 602.8 |652.8 | 702.8 | | 255 v| 1.81 | 1.98|2.14| 2.28| 2.43| 2.56| 2.70| | h|1201.8 |1235.9 |1263.6 |1289.3 |1314.5|1339.3 |1364.1 ||________|_________|_______|_______|_______|_______|_______|_______|

t = Temperature, degrees Fahrenheit. v =Specific volume, in cubic feet, per pound.h = Total heat from water at 32 degrees, B.t. u.

[Graph: Temperature of Steam--DegreesFahr. against Temperature inCalorimeter--Degrees Fahr.

Fig. 15. Graphic Method of DeterminingMoisture Contained in Steam fromCalorimeter Readings]

MOISTURE IN STEAM

The presence of moisture in steam causesa loss, not only in the practical waste of theheat utilized to raise this moisture from thetemperature of the feed water to thetemperature of the steam, but also throughthe increased initial condensation in anengine cylinder and through friction andother actions in a steam turbine. Thepresence of such moisture also interfereswith proper cylinder lubrication, causes aknocking in the engine and a waterhammer in the steam pipes. In steamturbines it will cause erosion of the blades.

The percentage by weight of steam in amixture of steam and water is called the_quality of the steam_.

The apparatus used to determine the

moisture content of steam is called acalorimeter though since it may notmeasure the heat in the steam, the name isnot descriptive of the function of theapparatus. The first form used was the"barrel calorimeter", but the liability oferror was so great that its use wasabandoned. Modern calorimeters are ingeneral of either the throttling or separatortype.

Throttling Calorimeter--Fig. 14 shows atypical form of throttling calorimeter.Steam is drawn from a vertical mainthrough the sampling nipple, passesaround the first thermometer cup, thenthrough a one-eighth inch orifice in a diskbetween two flanges, and lastly around thesecond thermometer cup and to theatmosphere. Thermometers are inserted inthe wells, which should be filled withmercury or heavy cylinder oil.

[Illustration: Fig. 14. ThrottlingCalorimeter and Sampling Nozzle]

The instrument and all pipes and fittingsleading to it should be thoroughlyinsulated to diminish radiation losses.Care must be taken to prevent the orificefrom becoming choked with dirt and to seethat no leaks occur. The exhaust pipeshould be short to prevent back pressurebelow the disk.

When steam passes through an orificefrom a higher to a lower pressure, as is thecase with the throttling calorimeter, noexternal work has to be done inovercoming a resistance. Hence, if there isno loss from radiation, the quantity of heatin the steam will be exactly the same afterpassing the orifice as before passing. If thehigher steam pressure is 160 pounds

gauge and the lower pressure that of theatmosphere, the total heat in a pound ofdry steam at the former pressure is 1195.9B. t. u. and at the latter pressure 1150.4 B. t.u., a difference of 45.4 B. t. u. As this heatwill still exist in the steam at the lowerpressure, since there is no external workdone, its effect must be to superheat thesteam. Assuming the specific heat ofsuperheated steam to be 0.47, each poundpassing through will be superheated45.4/0.47 = 96.6 degrees. If, however, thesteam had contained one per cent ofmoisture, it would have contained less heatunits per pound than if it were dry. Sincethe latent heat of steam at 160 poundsgauge pressure is 852.8 B. t. u., it followsthat the one per cent of moisture wouldhave required 8.5 B. t. u. to evaporate it,leaving only 45.4 - 8.5 = 36.9 B. t. u.available for superheating; hence, thesuperheat would be 36.9/0.47 = 78.5

degrees, as against 96.6 degrees for drysteam. In a similar manner, the degree ofsuperheat for other percentages ofmoisture may be determined. The action ofthe throttling calorimeter is based uponthe foregoing facts, as shown below.

Let H = total heat of one pound of steamat boiler pressure, L = latent heat ofsteam at boiler pressure, h = total heatof steam at reduced pressure after passing

orifice, t_{1} = temperature ofsaturated steam at the reduced pressure,

t_{2} = temperature of steam afterexpanding through the orifice in thedisc, 0.47 = the specific heat ofsaturated steam at atmospheric pressure,

x = proportion by weight of moisture insteam.

The difference in B. t. u. in a pound ofsteam at the boiler pressure and after

passing the orifice is the heat available forevaporating the moisture content andsuperheating the steam. Therefore,

H - h = xL + 0.47(t_{2} - t_{1})

H - h - 0.47(t_{2} - t_{1}) or x =--------------------------- (4) L

Almost invariably the lower pressure istaken as that of the atmosphere. Undersuch conditions, h = 1150.4 and t_{1} = 212degrees. The formula thus becomes:

H - 1150.4 - 0.47(t_{2} - 212) x =------------------------------ (5) L

For practical work it is more convenient todispense with the upper thermometer inthe calorimeter and to measure thepressure in the steam main by an accuratesteam pressure gauge.

A chart may be used for determining thevalue of x for approximate work withoutthe necessity for computation. Such a chartis shown in Fig. 15 and its use is as follows:Assume a gauge pressure of 180 poundsand a thermometer reading of 295degrees. The intersection of the verticalline from the scale of temperatures asshown by the calorimeter thermometerand the horizontal line from the scale ofgauge pressures will indicate directly theper cent of moisture in the steam as readfrom the diagonal scale. In the presentinstance, this per cent is 1.0.

Sources of Error in the Apparatus--A slighterror may arise from the value, 0.47, usedas the specific heat of superheated steamat atmospheric pressure. This value,however is very nearly correct and anyerror resulting from its use will be

negligible.

There is ordinarily a larger source of errordue to the fact that the stem of thethermometer is not heated to its full length,to an initial error in the thermometer andto radiation losses.

With an ordinary thermometer immersedin the well to the 100 degrees mark, theerror when registering 300 degrees wouldbe about 3 degrees and the truetemperature be 303 degrees.[19]

The steam is evidently losing heat throughradiation from the moment it enters thesampling nipple. The heat available forevaporating moisture and superheatingsteam after it has passed through theorifice into the lower pressure will bediminished by just the amount lost throughradiation and the value of t_{2}, as shown

by the calorimeter thermometer, will,therefore, be lower than if there were nosuch loss. The method of correcting for thethermometer and radiation errorrecommended by the Power TestCommittee of the American Society ofMechanical Engineers is by referring thereadings as found on the boiler trial to a"normal" reading of the thermometer. Thisnormal reading is the reading of the lowercalorimeter thermometer for dry saturatedsteam, and should be determined byattaching the instrument to a horizontalsteam pipe in such a way that the samplingnozzle projects upward to near the top ofthe pipe, there being no perforations inthe nozzle and the steam taken onlythrough its open upper end. The testshould be made with the steam in aquiescent state and with the steampressure maintained as nearly as possibleat the pressure observed in the main trial,

the calorimeter thermometer to be thesame as was used on the trial or oneexactly similar.

With a normal reading thus obtained for apressure approximately the same asexisted in the trial, the true percentage ofmoisture in the steam, that is, with theproper correction made for radiation, maybe calculated as follows:

Let T denote the normal reading for theconditions existing in the trial. The effect ofradiation from the instrument as pointedout will be to lower the temperature of thesteam at the lower pressure. Let x_{1}represent the proportion of water in thesteam which will lower its temperature anamount equal to the loss by radiation.Then,

H - h - 0.47(T - t_{1}) x_{1} =

----------------------- L

This amount of moisture, x_{1} was not inthe steam originally but is the result ofcondensation in the instrument throughradiation. Hence, the true amount ofmoisture in the steam represented by X isthe difference between the amount asdetermined in the trial and that resultingfrom condensation, or,

X = x - x_{1}

H - h - 0.47(t_{2} - t_{1}) H - h - 0.47(T -t_{1}) = --------------------------- ------------------------ L L

0.47(T - t_{2}) = --------------- (6)L

As T and t_{2} are taken with the samethermometer under the same set of

conditions, any error in the reading of thethermometers will be approximately thesame for the temperatures T and t_{2} andthe above method therefore corrects forboth the radiation and thermometererrors. The theoretical readings for drysteam, where there are no losses due toradiation, are obtainable from formula (5)by letting x = 0 and solving for t_{2}. Thedifference between the theoretical readingand the normal reading for no moisturewill be the thermometer and radiationcorrection to be applied in order that thecorrect reading of t_{2} may be obtained.

For any calorimeter within the range of itsordinary use, such a thermometer andradiation correction taken from one normalreading is approximately correct for anyconditions with the same or a duplicatethermometer.

The percentage of moisture in the steam,corrected for thermometer error andradiation and the correction to be appliedto the particular calorimeter used, wouldbe determined as follows: Assume a gaugepressure in the trial to be 180 pounds andthe thermometer reading to be 295degrees. A normal reading, taken in themanner described, gives a value of T = 303degrees; then, the percentage of moisturecorrected for thermometer error andradiation is,

0.47(303 - 295) x = ----------------845.0

= 0.45 per cent.

The theoretical reading for dry steam willbe,

1197.7 - 1150.4 - 0.47(t_{2} - 212) 0 =

------------------------------------845.0

t_{2} = 313 degrees.

The thermometer and radiation correctionto be applied to the instrument used,therefore over the ordinary range ofpressure is

Correction = 313 - 303 = 10 degrees

The chart may be used in thedetermination of the correct reading ofmoisture percentage and the permanentradiation correction for the instrumentused without computation as follows:Assume the same trial pressure, feedtemperature and normal reading as above.If the normal reading is found to be 303degrees, the correction for thermometerand radiation will be the theoretical

reading for dry steam as found from thechart, less this normal reading, or 10degrees correction. The correcttemperature for the trial in question is,therefore, 305 degrees. The moisturecorresponding to this temperature and 180pounds gauge pressure will be found fromthe chart to be 0.45 per cent.

[Illustration: Fig. 16. Compact ThrottlingCalorimeter]

There are many forms of throttlingcalorimeter, all of which work upon thesame principle. The simplest one isprobably that shown in Fig. 14. Anextremely convenient and compact designis shown in Fig. 16. This calorimeterconsists of two concentric metal cylindersscrewed to a cap containing athermometer well. The steam pressure ismeasured by a gauge placed in the supply

pipe or other convenient location. Steampasses through the orifice A and expandsto atmospheric pressure, its temperatureat this pressure being measured by athermometer placed in the cup C. Toprevent as far as possible radiation losses,the annular space between the twocylinders is used as a jacket, steam beingsupplied to this space through the hole B.

The limits of moisture within which thethrottling calorimeter will work are, at sealevel, from 2.88 per cent at 50 poundsgauge pressure and 7.17 per cent moistureat 250 pounds pressure.

Separating Calorimeter--The separatingcalorimeter mechanically separates theentrained water from the steam andcollects it in a reservoir, where its amountis either indicated by a gauge glass or isdrained off and weighed. Fig. 17 shows a

calorimeter of this type. The steam passesout of the calorimeter through an orifice ofknown size so that its total amount can becalculated or it can be weighed. A gaugeis ordinarily provided with this type ofcalorimeter, which shows the pressure inits inner chamber and the flow of steam fora given period, this latter scale beinggraduated by trial.

The instrument, like a throttlingcalorimeter, should be well insulated toprevent losses from radiation.

While theoretically the separatingcalorimeter is not limited in capacity, it iswell in cases where the percentage ofmoisture present in the steam is known tobe high, to attach a throttling calorimeterto its exhaust. This, in effect, is the using ofthe separating calorimeter as a smallseparator between the sampling nozzle

and the throttling instrument, and isnecessary to insure the determination ofthe full percentage of moisture in thesteam. The sum of the percentages shownby the two instruments is the moisturecontent of the steam.

The steam passing through a separatingcalorimeter may be calculated by Napier'sformula, the size of the orifice beingknown. There are objections to such acalculation, however, in that it is difficult toaccurately determine the areas of suchsmall orifices. Further, small orifices havea tendency to become partly closed bysediment that may be carried by thesteam. The more accurate method ofdetermining the amount of steam passingthrough the instrument is as follows:

[Illustration: Fig. 17. SeparatingCalorimeter]

A hose should be attached to the separatoroutlet leading to a vessel of water on aplatform scale graduated to 1/100 of apound. The steam outlet should beconnected to another vessel of waterresting on a second scale. In each case, theweight of each vessel and its contentsshould be noted. When ready for anobservation, the instrument should beblown out thoroughly so that there will beno water within the separator. Theseparator drip should then be closed andthe steam hose inserted into the vessel ofwater at the same instant. When theseparator has accumulated a sufficientquantity of water, the valve of theinstrument should be closed and the hoseremoved from the vessel of water. Theseparator should be emptied into thevessel on its scale. The final weight of eachvessel and its contents are to be noted and

the differences between the final andoriginal weights will represent the weightof moisture collected by the separator andthe weight of steam from which themoisture has been taken. The proportionof moisture can then be calculated fromthe following formula:

100 w x = ----- (7) W - w

Where x = per cent moisture in steam,W = weight of steam condensed, w =weight of moisture as taken out by theseparating calorimeter.

Sampling Nipple--The principle source oferror in steam calorimeter determinationsis the failure to obtain an average sampleof the steam delivered by the boiler and itis extremely doubtful whether such asample is ever obtained. The twogoverning features in the obtaining of such

a sample are the type of sampling nozzleused and its location.

The American Society of MechanicalEngineers recommends a sampling nozzlemade of one-half inch iron pipe closed atthe inner end and the interior portionperforated with not less than twentyone-eighth inch holes equally distributedfrom end to end and preferably drilled inirregular or spiral rows, with the first holenot less than one-half inch from the wall ofthe pipe. Many engineers object to the useof a perforated sampling nipple because itordinarily indicates a higher percentage ofmoisture than is actually present in thesteam. This is due to the fact that if theperforations come close to the innersurface of the pipe, the moisture, which inmany instances clings to this surface, willflow into the calorimeter and cause a largeerror. Where a perforated nipple is used,

in general it may be said that theperforations should be at least one inchfrom the inner pipe surface.

A sampling nipple, open at the inner endand unperforated, undoubtedly gives asaccurate a measure as can be obtained ofthe moisture in the steam passing that end.It would appear that a satisfactory methodof obtaining an average sample of thesteam would result from the use of an openend unperforated nipple passing through astuffing box which would allow the end tobe placed at any point across the diameterof the steam pipe.

Incidental to a test of a 15,000 K. W. steamengine turbine unit, Mr. H. G. Stott and Mr.R. G. S. Pigott, finding no experimentaldata bearing on the subject of lowpressure steam quality determinations,made a investigation of the subject and the

sampling nozzle illustrated in Fig. 18 wasdeveloped. In speaking of samplingnozzles in the determination of themoisture content of low pressure steam,Mr. Pigott says, "the ordinary standardperforated pipe sampler is absolutelyworthless in giving a true sample and it isvital that the sample be abstracted fromthe main without changing its direction orvelocity until it is safely within the samplepipe and entirely isolated from the rest ofthe steam."

[Illustration: Fig. 18. Stott and PigottSampling Nozzle]

It would appear that the nozzle illustratedis undoubtedly the best that has beendeveloped for use in the determination ofthe moisture content of steam, not only inthe case of low, but also in high pressuresteam.

Location of Sampling Nozzle--Thecalorimeter should be located as near aspossible to the point from which the steamis taken and the sampling nipple should beplaced in a section of the main pipe nearthe boiler and where there is no chance ofmoisture pocketing in the pipe. TheAmerican Society of Mechanical Engineersrecommends that a sampling nipple, ofwhich a description has been given,should be located in a vertical main, risingfrom the boiler with its closed endextending nearly across the pipe. Wherenon-return valves are used, or where thereare horizontal connections leading fromthe boiler to a vertical outlet, water maycollect at the lower end of the uptake pipeand be blown upward in a spray which willnot be carried away by the steam owing toa lack of velocity. A sample taken from thelower part of this pipe will show a greater

amount of moisture than a true sample.With goose-neck connections a smallamount of water may collect on the bottomof the pipe near the upper end where theinclination is such that the tendency to flowbackward is ordinarily counterbalancedby the flow of steam forward over itssurface; but when the velocitymomentarily decreases the water flowsback to the lower end of the goose-neckand increases the moisture at that point,making it an undesirable location forsampling. In any case, it should be bornein mind that with low velocities thetendency is for drops of entrained water tosettle to the bottom of the pipe, and to betemporarily broken up into spraywhenever an abrupt bend or otherdisturbance is met.

[Illustration: Fig. 19. Illustrating theManner in which Erroneous Calorimeter

Readings may be Obtained due toImproper Location of Sampling Nozzle

Case 1--Horizontal pipe. Water flows atbottom. If perforations in nozzle are toonear bottom of pipe, water piles againstnozzle, flows into calorimeter and givesfalse reading. Case 2--If nozzle locatedtoo near junction of two horizontal runs,as at a, condensation from vertical pipewhich collects at this point will bethrown against the nozzle by the velocity of

the steam, resulting in a false reading.Nozzle should be located far enoughabove junction to be removed from waterkept in motion by the steam velocity, asat b. Case 3--Condensation in bend willbe held by velocity of the steam as shown.When velocity is diminished duringfiring intervals and the like moistureflows back against nozzle, a, and falsereading is obtained. A true reading will

be obtained at b provided condensationis not blown over on nozzle. Case4--Where non-return valve is placedbefore a bend, condensation will collecton steam line side and water will be sweptby steam velocity against nozzle andfalse readings result.]

Fig. 19 indicates certain locations ofsampling nozzles from which erroneousresults will be obtained, the reasons beingobvious from a study of the cuts.

Before taking any calorimeter reading,steam should be allowed to flow throughthe instrument freely until it is thoroughlyheated. The method of using a throttlingcalorimeter is evident from the descriptionof the instrument given and the principleupon which it works.

[Illustration: Babcock & Wilcox

Superheater]

SUPERHEATED STEAM

Superheated steam, as already stated, issteam the temperature of which exceedsthat of saturated steam at the samepressure. It is produced by the addition ofheat to saturated steam which has beenremoved from contact with the water fromwhich it was generated. The properties ofsuperheated steam approximate those of aperfect gas rather than of a vapor.Saturated steam cannot be superheatedwhen it is in contact with water which isalso heated, neither can superheatedsteam condense without first beingreduced to the temperature of saturatedsteam. Just so long as its temperature isabove that of saturated steam at acorresponding pressure it is superheated,and before condensation can take placethat superheat must first be lost through

radiation or some other means. Table24[20] gives such properties ofsuperheated steam for varying pressuresas are necessary for use in ordinaryengineering practice.

Specific Heat of Superheated Steam--Thespecific heat of superheated steam atatmospheric pressure and near saturationpoint was determined by Regnault, in1862, who gives it the value of 0.48.Regnault's value was based on four seriesof experiments, all at atmosphericpressure and with about the sametemperature range, the maximum of whichwas 231.1 degrees centigrade. For fiftyyears after Regnault's determination, thisvalue was accepted and applied to higherpressures and temperatures as well as tothe range of his experiments. More recentinvestigations have shown that the specificheat is not a constant and varies with both

pressure and the temperature. A numberof experiments have been made byvarious investigators and, up to thepresent, the most reliable appear to bethose of Knoblauch and Jacob. Messrs.Marks and Davis have used the values asdetermined by Knoblauch and Jacob withslight modifications. The first consists in avarying of the curves at low pressuresclose to saturation because ofthermodynamic evidence and in view ofRegnault's determination at atmosphericpressure. The second modification is athigh degrees of superheat to followHolborn's and Henning's curve, which isaccepted as authentic.

For the sake of convenience, the meanspecific heat of superheated steam atvarious pressures and temperatures isgiven in tabulated form in Table 25. Thesevalues have been calculated from Marks

and Davis Steam Tables by deducting fromthe total heat of one pound of steam at anypressure for any degree of superheat thetotal heat of one pound of saturated steamat the same pressure and dividing thedifference by the number of degrees ofsuperheat and, therefore, represent theaverage specific heat starting from that atsaturation to the value at the particularpressure and temperature.[21] Expressedas a formula this calculation is representedby

H_{sup} - H_{sat} Sp. Ht. =----------------- (8) S_{sup} - S_{sat}

Where H_{sup} = total heat of one pound ofsuperheated steam at anypressure and temperature, H_{sat} =total heat of one pound of saturated steamat same pressure, S_{sup} =temperature of superheated steam taken,

S_{sat} = temperature of saturated steamcorresponding to the pressuretaken.

TABLE 25

MEAN SPECIFIC HEAT OFSUPERHEATED STEAMCALCULATED FROM MARKS AND DAVISTABLES_______________________________________________________________ |Gauge |

| |Pressure |Degree of Superheat | |

|_____________________________________________________| | | 50 | 60 | 70 |80 | 90 | 100 | 110 | 120 | 130 ||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| | 50 |.518| .517| .514| .513| .511| .510| .508|.507| .505| | 60 | .528| .525| .523|.521| .519| .517| .515| .513| .512| | 70

| .536| .534| .531| .529| .527| .524| .522|.520| .518| | 80 | .544| .542| .539|.535| .532| .530| .528| .526| .524| | 90| .553| .550| .546| .543| .539| .536| .534|.532| .529| | 100 | .562| .557| .553|.549| .544| .542| .539| .536| .533| | 110| .570| .565| .560| .556| .552| .548| .545|.542| .539| | 120 | .578| .573| .567|.561| .557| .554| .550| .546| .543| | 130| .586| .580| .574| .569| .564| .560| .555|.552| .548| | 140 | .594| .588| .581|.575| .570| .565| .561| .557| .553| | 150| .604| .595| .587| .581| .576| .570| .566|.561| .557| | 160 | .612| .603| .596|.589| .582| .576| .571| .566| .562| | 170| .620| .612| .603| .595| .588| .582| .576|.571| .566| | 180 | .628| .618| .610|.601| .593| .587| .581| .575| .570| | 190| .638| .627| .617| .608| .599| .592| .585|.579| .574| | 200 | .648| .635| .624|.614| .605| .597| .590| .584| .578| | 210| .656| .643| .631| .620| .611| .602| .595|

.588| .583| | 220 | .664| .650| .637|

.626| .616| .607| .600| .592| .586| | 230| .672| .658| .644| .633| .622| .613| .605|.597| .591| | 240 | .684| .668| .653|.640| .629| .619| .610| .602| .595| | 250| .692| .675| .659| .645| .633| .623| .614|.606| .599||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____| |Gauge |

| |Pressure |Degree of Superheat | |

|-----------------------------------------------------|| | 140 | 150 | 160 | 170 | 180 | 190 |200 | 225 | 250 ||---------+-----+-----+-----+-----+-----+-----+-----+-----+-----| | 50 | .504| .503| .502|.501| .500| .500| .499| .497| .496| | 60| .511| .509| .508| .507| .506| .504| .504|.502| .500| | 70 | .516| .515| .513|.512| .511| .510| .509| .506| .504| | 80| .522| .520| .518| .516| .515| .514| .513|.511| .508| | 90 | .527| .525| .523|

.521| .519| .518| .517| .514| .510| | 100| .531| .529| .527| .525| .523| .522| .521|.517| .513| | 110 | .536| .534| .532|.529| .528| .526| .525| .520| .517| | 120| .540| .537| .535| .533| .531| .529| .528|.523| .519| | 130 | .545| .542| .539|.537| .535| .533| .531| .527| .523| | 140| .550| .547| .544| .541| .539| .536| .534|.530| .526| | 150 | .554| .550| .547|.544| .542| .539| .537| .533| .529| | 160| .558| .554| .551| .548| .545| .543| .541|.536| .531| | 170 | .562| .558| .555|.552| .549| .546| .544| .538| .533| | 180| .566| .561| .558| .555| .552| .549| .546|.540| .536| | 190 | .569| .565| .562|.558| .555| .552| .549| .543| .538| | 200| .574| .569| .566| .562| .558| .555| .552|.546| .541| | 210 | .578| .573| .569|.565| .561| .558| .555| .549| .543| | 220| .581| .577| .572| .568| .564| .561| .558|.551| .545| | 230 | .585| .580| .575|.572| .567| .564| .561| .554| .548| | 240

| .589| .584| .579| .575| .571| .567| .564|.556| .550| | 250 | .593| .587| .582|.577| .574| .570| .567| .559| .553||_________|_____|_____|_____|_____|_____|_____|_____|_____|_____|

Factor of Evaporation with SuperheatedSteam--When superheat is present in thesteam during a boiler trial, wheresuperheated steam tables are available,the formula for determining the factor ofevaporation is that already given, (2),[22]namely,

H - h Factor of evaporation =----- L

Here H = total heat in one pound ofsuperheated steam from the table, h and Lhaving the same values as in (2).

Where no such tables are available but the

specific heat of superheat is known, theformula becomes:

H - h + Sp. Ht.(T - t) Factor ofevaporation = ---------------------- L

Where H = total heat in one pound ofsaturated steam at pressure existingin trial, h = sensible heat above 32degrees in one pound of water at thetemperature entering the boiler, T =temperature of superheated steam asdetermined in the trial, t = temperatureof saturated steam corresponding to theboiler pressure, Sp. Ht. = meanspecific heat of superheated steam at thepressure and temperature as found inthe trial, L = latent heat of one pound ofsaturated steam at atmosphericpressure.

Advantages of the Use of SuperheatedSteam--In considering the saving possibleby the use of superheated steam, it is toooften assumed that there is only a saving inthe prime movers, a saving which is atleast partially offset by an increase in thefuel consumption of the boilers generatingsteam. This misconception is due to thefact that the fuel consumption of the boileris only considered in connection with adefinite weight of steam. It is true thatwhere such a definite weight is to besuperheated, an added amount of fuelmust be burned. With a properly designedsuperheater where the combinedefficiency of the boiler and superheaterwill be at least as high as of a boiler alone,the approximate increase in coalconsumption for producing a given weightof steam will be as follows:

_Superheat_ _Added Fuel_ _Degrees_

_Per Cent_ 25 1.59 503.07 75 4.38 100 5.69

150 8.19 200 10.58

These figures represent the added fuelnecessary for superheating a definiteweight of steam to the number of degreesas given. The standard basis, however, ofboiler evaporation is one of heat units and,considered from such a standpoint, againproviding the efficiency of the boiler andsuperheater is as high, as of a boiler alone,there is no additional fuel required togenerate steam containing a definitenumber of heat units whether such units bedue to superheat or saturation. That is, if 6per cent more fuel is required to generateand superheat to 100 degrees, a definiteweight of steam, over what would berequired to produce the same weight ofsaturated steam, that steam whensuperheated, will contain 6 per cent more

heat units above the fuel watertemperature than if saturated. This holdstrue if the efficiency of the boiler andsuperheater combined is the same as ofthe boiler alone. As a matter of fact, theefficiency of a boiler and superheater,where the latter is properly designed andlocated, will be slightly higher for thesame set of furnace conditions than wouldthe efficiency of a boiler in which nosuperheater were installed. A superheater,properly placed within the boiler setting insuch way that products of combustion forgenerating saturated steam are utilized aswell for superheating that steam, will not inany way alter furnace conditions. With agiven set of such furnace conditions for agiven amount of coal burned, the fact thatadditional surface, whether as boilerheating or superheating surface, is placedin such a manner that the gases mustsweep over it, will tend to lower the

temperature of the exit gases. It is such alowering of exit gas temperatures that isthe ultimate indication of added efficiency.Though the amount of this added efficiencyis difficult to determine by test, that thereis an increase is unquestionable.

Where a properly designed superheater isinstalled in a boiler the heating surface ofthe boiler proper, in the generation of adefinite number of heat units, is relieved ofa portion of the work which would berequired were these heat units deliveredin saturated steam. Such a superheaterneeds practically no attention, is notsubject to a large upkeep cost ordepreciation, and performs its functionwithout in any way interfering with theoperation of the boiler. Its use, thereforefrom the standpoint of the boiler room,results in a saving in wear and tear due tothe lower ratings at which the boiler may

be run, or its use will lead to the possibilityof obtaining the same number of boilerhorse power from a smaller number ofboilers, with the boiler heating surfacedoing exactly the same amount of work asif the superheaters were not installed. Thesaving due to the added boiler efficiencythat will be obtained is obvious.

Following the course of the steam in aplant, the next advantage of the use ofsuperheated steam is the absence of waterin the steam pipes. The thermalconductivity of superheated steam, that is,its power to give up its heat to surroundingbodies, is much lower than that ofsaturated steam and its heat, therefore, willnot be transmitted so rapidly to the walls ofthe pipes as when saturated steam isflowing through the pipes. The loss of heatradiated from a steam pipe, assuming noloss in pressure, represents the equivalent

condensation when the pipe is carryingsaturated steam. In well-covered steammains, the heat lost by radiation whencarrying superheated steam isaccompanied only by a reduction of thesuperheat which, if it be sufficiently high atthe boiler, will enable a considerableamount of heat to be radiated and stilldeliver dry or superheated steam to theprime movers.

It is in the prime movers that theadvantages of the use of superheatedsteam are most clearly seen.

In an engine, steam is admitted into aspace that has been cooled by the steamexhausted during the previous stroke. Theheat necessary to warm the cylinder wallsfrom the temperature of the exhaust to thatof the entering steam can be supplied onlyby the entering steam. If this steam be

saturated, such an adding of heat to thewalls at the expense of the heat of theentering steam results in the condensationof a portion. This initial condensation isseldom less than from 20 to 30 per cent ofthe total weight of steam entering thecylinder. It is obvious that if the steamentering be superheated, it must bereduced to the temperature of saturatedsteam at the corresponding pressurebefore any condensation can take place. Ifthe steam be superheated sufficiently toallow a reduction in temperatureequivalent to the quantity of heat that mustbe imparted to the cylinder walls and stillremain superheated, it is clear that initialcondensation is avoided. For example:assume one pound of saturated steam at200 pounds gauge pressure to enter acylinder which has been cooled by theexhaust. Assume the initial condensation tobe 20 per cent. The latent heat of the steam

is given up in condensation; hence, .20�838 = 167.6 B. t. u. are given up by thesteam. If one pound of superheated steamenters the same cylinder, it would have tobe superheated to a point where its totalheat is 1199 + 168 = 1367 B. t. u. or, at 200pounds gauge pressure, superheatedapproximately 325 degrees if the heatgiven up to the cylinder walls were thesame as for the saturated steam. Assuperheated steam conducts heat lessrapidly than saturated steam, the amountof heat imparted will be less than for thesaturated steam and consequently theamount of superheat required to preventcondensation will be less than the abovefigure. This, of course, is the extreme caseof a simple engine with the range oftemperature change a maximum. Ascylinders are added, the range in each isdecreased and the condensation isproportionate.

The true economy of the use ofsuperheated steam is best shown in acomparison of the "heat consumption" ofan engine. This is the number of heat unitsrequired in developing one indicatedhorse power and the measure of therelative performance of two engines isbased on a comparison of their heatconsumption as the measure of a boiler isbased on its evaporation from and at 212degrees. The water consumption of anengine in pounds per indicated horsepower is in no sense a true indication of itsefficiency. The initial pressures andcorresponding temperatures may differwidely and thus make a difference in thetemperature of the exhaust and hence inthe temperature of the condensed steamreturned to the boiler. For example:suppose a certain weight of steam at 150pounds absolute pressure and 358

degrees be expanded to atmosphericpressure, the temperature then being 212degrees. If the same weight of steam beexpanded from an initial pressure of 125pounds absolute and 344 degrees, toenable it to do the same amount of work,that is, to give up the same amount of heat,expansion then must be carried to a pointbelow atmospheric pressure to, say, 13pounds absolute, the final temperature ofthe steam then being 206 degrees. Inactual practice, it has been observed thatthe water consumption of a compoundpiston engine running on 26-inch vacuumand returning the condensed steam at 140degrees was approximately the same aswhen running on 28-inch vacuum andreturning water at 90 degrees. With anequal water consumption for the two setsof conditions, the economy in the formercase would be greater than in the latter,since it would be necessary to add less

heat to the water returned to the boiler toraise it to the steam temperature.

The lower the heat consumption of anengine per indicated horse power, thehigher its economy and the less thenumber of heat units must be imparted tothe steam generated. This in turn leads tothe lowering of the amount of fuel that mustbe burned per indicated horse power.

With the saving in fuel by the reduction ofheat consumption of an engine indicated, itremains to be shown the effect of the use ofsuperheated steam on such heatconsumption. As already explained, theuse of superheated steam reducescondensation not only in the mains butespecially in the steam cylinder, leaving agreater quantity of steam available to dothe work. Furthermore, a portion of thesaturated steam introduced into a cylinder

will condense during adiabatic expansion,this condensation increasing as expansionprogresses. Since superheated steamcannot condense until it becomessaturated, not only is initial condensationprevented by its use but also suchcondensation as would occur duringexpansion. When superheated sufficiently,steam delivered by the exhaust will still bedry. In the avoidance of suchcondensation, there is a direct saving inthe heat consumption of an engine, theheat given up being utilized in thedeveloping of power and not in changingthe condition of the working fluid. That is,while the number of heat units lost inovercoming condensation effects would bethe same in either case, when saturatedsteam is condensed the water ofcondensation has no power to do workwhile the superheated steam, even after ithas lost a like number of heat units, still

has the power of expansion. The savingthrough the use of superheated steam inthe heat consumption of an enginedecreases demands on the boiler andhence the fuel consumption per unit ofpower.

Superheated Steam for SteamTurbines--Experience in usingsuperheated steam in connection withsteam turbines has shown that it leads toeconomy and that it undoubtedly pays touse superheated steam in place ofsaturated steam. This is so well establishedthat it is standard practice to usesuperheated steam in connection withsteam turbines. Aside from the economysecured through using superheated steam,there is an important advantage arisingthrough the fact that it materially reducesthe erosion of the turbine blades by theaction of water that would be carried by

saturated steam. In using saturated steamin a steam turbine or piston engine, thework done on expanding the steam causescondensation of a portion of the steam, sothat even were the steam dry on enteringthe turbine, it would contain water onleaving the turbine. By superheating thesteam the water that exists in the lowpressure stages of the turbine may bereduced to an amount that will not causetrouble.

Again, if saturated steam containsmoisture, the effect of this moisture on theeconomy of a steam turbine is to reducethe economy to a greater extent than theproportion by weight of water, one percent of water causing approximately afalling off of 2 per cent in the economy.

The water rate of a large economical steamturbine with superheated steam is reduced

about one per cent, for every 12 degreesof superheat up to 200 degrees Fahrenheitof superheat. To superheat one pound ofsteam 12 degrees requires about 7 B. t. u.and if 1050 B. t. u. are required at theboiler to evaporate one pound of thesaturated steam from the temperature ofthe feed water, the heat required for thesuperheated steam would be 1057degrees. One per cent of saving,therefore, in the water consumption wouldcorrespond to a net saving of aboutone-third of one per cent in the coalconsumption. On this basis 100 degrees ofsuperheat with an economical steamturbine would result in somewhat over 3per cent of saving in the coal for equalboiler efficiencies. As a boiler with aproperly designed superheater placedwithin the setting is more economical for agiven capacity than a boiler without asuperheater, the minimum gain in the coal

consumption would be, say, 4 or 5 per centas compared to a plant with the sameboilers without superheaters.

The above estimates are on the basis of athoroughly dry saturated steam or steamjust at the point of being superheated orcontaining a few degrees of superheat. Ifthe saturated steam is moist, the savingdue to superheat is more and ordinarilythe gain in economy due to superheatedsteam, for equal boiler efficiencies, ascompared with commercially dry steam is,say, 5 per cent for each 100 degrees ofsuperheat. Aside from this gain, as alreadystated, superheated steam preventserosion of the turbine buckets that wouldbe caused by water in the steam, and forthe reasons enumerated it is standardpractice to use superheated steam forturbine work. The less economical thesteam motor, the more the gain due to

superheated steam, and where there are anumber of auxiliaries that are run withsuperheated steam, the percentage of gainwill be greater than the figures givenabove, which are the minimum and are forthe most economical type of large steamturbines.

An example from actual practice willperhaps best illustrate and emphasize theforegoing facts. In October 1909, a seriesof comparable tests were conducted byThe Babcock & Wilcox Co. on the steamyacht "Idalia" to determine the steamconsumption both with saturated andsuperheated steam of the main engine onthat yacht, including as well the feedpump, circulating pump and air pump.These tests are more representative thanare most tests of like character in that thesaving in the steam consumption of theauxiliaries, which were much more

wasteful than the main engine, formed animportant factor. A r�um�of these tests waspublished in the Journal of the Society ofNaval Engineers, November 1909.

The main engines of the "Idalia" are fourcylinder, triple expansion, 11-1/2 �19inches by 22-11/16 �18 inches stroke.Steam is supplied by a Babcock & Wilcoxmarine boiler having 2500 square feet ofboiler heating surface, 340 square feet ofsuperheating surface and 65 square feet ofgrate surface.

The auxiliaries consist of a feed pump 6 �4�6 inches, an independent air pump 6 �12�8 inches, and a centrifugal pump drivenby a reciprocating engine 5-7/16 �5inches. Under ordinary operatingconditions the superheat existing is about100 degrees Fahrenheit.

Tests were made with various degrees ofsuperheat, the amount being varied byby-passing the gases and in the tests withthe lower amounts of superheat by passinga portion of the steam from the boiler tothe steam main without passing it throughthe superheater. Steam temperaturereadings were taken at the engine throttle.In the tests with saturated steam, thesuperheater was completely cut out of thesystem. Careful calorimeter measurementswere taken, showing that the saturatedsteam delivered to the superheater wasdry.

The weight of steam used was determinedfrom the weight of the condensed steamdischarge from the surface condenser, thewater being pumped from the hot well intoa tank mounted on platform scales. Thesame indicators, thermometers andgauges were used in all the tests, so that

the results are directly comparable. Theindicators used were of the outside springtype so that there was no effect of thetemperature of the steam. All tests were ofsufficient duration to show a uniformity ofresults by hours. A summary of the resultssecured is given in Table 26, which showsthe water rate per indicated horse powerand the heat consumption. The latterfigures are computed on the basis of theheat imparted to the steam above theactual temperature of the feed water and,as stated, these are the results that aredirectly comparable.

TABLE 26

RESULTS OF "IDALIA" TESTS_______________________________________________________________________ |

| | | | | | |Date1909 |Oct. 11|Oct. 14|Oct.

14|Oct. 12|Oct. 13||_______________________________|_______|_______|_______|_______|_______||Degrees of superheat Fahrenheit| 0 |57 | 88 | 96 | 105 | |Pressures,pounds per} Throttle| 190 | 196 | 201 |198 | 203 | |square inch above } First| | | | | | |AtmosphericPressure } Receiver| 68.4 | 66.0 | 64.3 |61.9 | 63.0 | | } Second | |

| | | | | } Receiver|9.7 | 9.2 | 8.7 | 7.8 | 8.4 | |Vacuum,

inches | 25.5 | 25.9 | 25.9 | 25.4| 25.2 | |Temperature, DegreesFahrenheit| | | | | | |

} Feed | 201 | 206 | 205 | 202| 200 | | } Hot Well | 116 |109.5 | 115 | 111.5 | 111 | |

| | | | | | |Revolutionsper minute | | | | | || {Air Pump | 57 | 56 | 53 |54 | 45 | | {Circulating Pump|

196 | 198 | 196 | 198 | 197 | |{Main Engine | 194.3 | 191.5 | 195.1 |191.5 | 193.1 | |Indicated Horse Power,

| | | | | | | MainEngine | 512.3 | 495.2 | 521.1 | 498.3| 502.2 | |Water per hour, total pounds|9397 |8430 |8234 |7902 |7790 ||Water per indicated | | || | | | Horse Power, pounds |18.3 | 17.0 | 15.8 | 15.8 | 15.5 | |B. t. u.per minute per | | | | || | indicated Horse Power | 314 |

300 | 284 | 286 | 283 | |Per centSaving of Steam | ... | 7.1 | 13.7 |13.7 | 15.3 | |Percent Saving of Fuel |

| | | | | |(computed) | ... | 4.4 | 9.5 | 8.9 |9.9 ||_______________________________|_______|_______|_______|_______|_______|

The table shows that the saving in steam

consumption with 105 degrees ofsuperheat was 15.3 per cent and in heatconsumption about 10 per cent. This maybe safely stated to be a conservativerepresentation of the saving that may beaccomplished by the use of superheatedsteam in a plant as a whole, wheresuperheated steam is furnished not only tothe main engine but also to the auxiliaries.The figures may be taken as conservativefor the reason that in addition to the savingas shown in the table, there would be in anordinary plant a saving much greater thanis generally realized in the drips, wherethe loss with saturated steam is greatly inexcess of that with superheated steam.

The most conclusive and most practicalevidence that a saving is possible throughthe use of superheated steam is in the factthat in the largest and most economicalplants it is used almost without exception.

Regardless of any such evidence,however, there is a deep rooted convictionin the minds of certain engineers that theuse of superheated steam will involveoperating difficulties which, withadditional first cost, will more than offsetany fuel saving. There are, of course,conditions under which the installation ofsuperheaters would in no way beadvisable. With a poorly designedsuperheater, no gain would result. Ingeneral, it may be stated that in a newplant, properly designed, with a boilerand superheater which will have anefficiency at least as high as a boilerwithout a superheater, a gain is certain.

Such a gain is dependent upon the class ofengine and the power plant equipment ingeneral. In determining the advisability ofmaking a superheater installation, all ofthe factors entering into each individual

case should be considered and balanced,with a view to determining the saving inrelation to cost, maintenance, depreciationetc.

In highly economical plants, where thewater consumption for an indicated horsepower is low, the gain will be less thanwould result from the use of superheatedsteam in less economical plants where thewater consumption is higher. It isimpossible to make an accurate statementas to the saving possible but, broadly, itmay vary from 3 to 5 per cent for 100degrees of superheat in the large andeconomical plants using turbines or steamengines, in which there is a large ratio ofexpansion, to from 10 to 25 per cent for100 degrees of superheat for the lesseconomical steam motors.

Though a properly designed superheater

will tend to raise rather than to decreasethe boiler efficiency, it does not follow thatall superheaters are efficient, for if thegases in passing over the superheater donot follow the path they would ordinarilytake in passing over the boiler heatingsurface, a loss may result. This isnoticeably true where part of the gases arepassed over the superheater and areallowed to pass over only a part or in somecases none of the boiler heating surface.

With moderate degrees of superheat, from100 to 200 degrees, where the piping isproperly installed, there will be no greateroperating difficulties than with saturatedsteam. Engine and turbine buildersguarantee satisfactory operation withsuperheated steam. With high degrees ofsuperheat, say, over 250 degrees,apparatus of a special nature must be usedand it is questionable whether the

additional care and liability to operatingdifficulties will offset any fuel savingaccomplished. It is well established,however, that the operating difficulties,with the degrees of superheat to which thisarticle is limited, have been entirelyovercome.

The use of cast-iron fittings withsuperheated steam has been widelydiscussed. It is an undoubted fact thatwhile in some instances superheatedsteam has caused deterioration of suchfittings, in others cast-iron fittings havebeen used with 150 degrees of superheatwithout the least difficulty. The quality ofthe cast iron used in such fittings hasdoubtless a large bearing on the life ofsuch fittings for this service. Thedifficulties that have been encountered arean increase in the size of the fittings andeventually a deterioration great enough to

lead to serious breakage, the developmentof cracks, and when flanges are drawn uptoo tightly, the breaking of a flange fromthe body of the fitting. The latter difficultyis undoubtedly due, in certain instances, tothe form of flange in which the strain of theconnecting bolts tended to distort themetal.

The Babcock & Wilcox Co. have used steelcastings in superheated steam work over along period and experience has shownthat this metal is suitable for the service.There seems to be a general tendencytoward the use of steel fittings. InEuropean practice, until recently, cast ironwas used with apparently satisfactoryresults. The claim of European engineerswas to the effect that their cast iron was ofbetter quality than that found in thiscountry and thus explained the resultssecured. Recently, however, certain

difficulties have been encountered withsuch fittings and European engineers areleaning toward the use of steel for thiswork.

The degree of superheat produced by asuperheater placed within the boilersetting will vary according to the class offuel used, the form of furnace, thecondition of the fire and the rate at whichthe boiler is being operated. This isnecessarily true of any superheater sweptby the main body of the products ofcombustion and is a fact that should beappreciated by the prospective user ofsuperheated steam. With a properlydesigned superheater, however, suchfluctuations would not be excessive,provided the boilers are properlyoperated. As a matter of fact the point tobe guarded against in the use ofsuperheated steam is that a maximum

should not be exceeded. While, as stated,there may be a considerable fluctuation inthe temperature of the steam as deliveredfrom individual superheaters, where thereare a number of boilers on a line thetemperature of the combined flow of steamin the main will be found to be practicallya constant, resulting from the offsetting ofvarious furnace conditions of one boiler byanother.

[Illustration: 8400 Horse-power Installationof Babcock & Wilcox Boilers andSuperheaters at the Butler Street Plant ofthe Georgia Railway and Power Co.,Atlanta, Ga. This Company Operates aTotal of 15,200 Horse Power of Babcock &Wilcox Boilers]

PROPERTIES OF AIR

Pure air is a mechanical mixture of oxygenand nitrogen. While different authoritiesgive slightly varying values for theproportion of oxygen and nitrogencontained, the generally accepted valuesare:

By volume, oxygen 20.91 per cent,nitrogen 79.09 per cent. By weight,oxygen 23.15 per cent, nitrogen 76.85 percent.

Air in nature always contains otherconstituents in varying amounts, such asdust, carbon dioxide, ozone and watervapor.

Being perfectly elastic, the density orweight per unit of volume decreases in

geometric progression with the altitude.This fact has a direct bearing in theproportioning of furnaces, flues and stacksat high altitudes, as will be shown later inthe discussion of these subjects. Theatmospheric pressures corresponding tovarious altitudes are given in Table 12.

The weight and volume of air depend uponthe pressure and the temperature, asexpressed by the formula:

Pv = 53.33 T (9)

Where P = the absolute pressure inpounds per square foot, v = the volumein cubic feet of one pound of air, T = theabsolute temperature of the air in degreesFahrenheit, 53.33 = a constant for airderived from the ratio of pressure, volume and temperature of a perfect gas.

The weight of one cubic foot of air willobviously be the reciprocal of its volume,that is, 1/v pounds.

TABLE 27

VOLUME AND WEIGHT OF AIRAT ATMOSPHERIC PRESSURE ATVARIOUS TEMPERATURES_______________________________________| | | | | |Volume | | | Temperature | OnePound | Weight One | | Degrees | in

| Cubic Foot | | Fahrenheit | Cubic Feet| in Pounds ||_____________|____________|____________| | | | | | 32 |12.390 | .080710 | | 50 | 12.843 |.077863 | | 55 | 12.969 | .077107

| | 60 | 13.095 | .076365 | | 65| 13.221 | .075637 | | 70 |

13.347 | .074923 | | 75 | 13.473 |

.074223 | | 80 | 13.599 | .073535| | 85 | 13.725 | .072860 | | 90

| 13.851 | .072197 | | 95 |13.977 | .071546 | | 100 | 14.103| .070907 | | 110 | 14.355 |.069662 | | 120 | 14.607 | .068460| | 130 | 14.859 | .067299 | |

140 | 15.111 | .066177 | | 150 |15.363 | .065092 | | 160 | 15.615| .064041 | | 170 | 15.867 |.063024 | | 180 | 16.119 | .062039| | 190 | 16.371 | .061084 | |

200 | 16.623 | .060158 | | 210 |16.875 | .059259 | | 212 | 16.925| .059084 | | 220 | 17.127 |.058388 | | 230 | 17.379 | .057541| | 240 | 17.631 | .056718 | |

250 | 17.883 | .055919 | | 260 |18.135 | .055142 | | 270 | 18.387| .054386 | | 280 | 18.639 |.053651 | | 290 | 18.891 | .052935| | 300 | 19.143 | .052238 | |

320 | 19.647 | .050898 | | 340 |20.151 | .049625 | | 360 | 20.655| .048414 | | 380 | 21.159 |.047261 | | 400 | 21.663 | .046162| | 425 | 22.293 | .044857 | |

450 | 22.923 | .043624 | | 475 |23.554 | .042456 | | 500 | 24.184| .041350 | | 525 | 24.814 |.040300 | | 550 | 25.444 | .039302| | 575 | 26.074 | .038352 | |

600 | 26.704 | .037448 | | 650 |27.964 | .035760 | | 700 | 29.224| .034219 | | 750 | 30.484 |.032804 | | 800 | 31.744 | .031502| | 850 | 33.004 | .030299 |

|_____________|____________|____________|

Example: Required the volume of air incubic feet under 60.3 pounds gaugepressure per square inch at 115 degreesFahrenheit.

P = 144 (14.7 + 60.3) = 10,800.

T = 115 + 460 = 575 degrees.

53.33 �575 Hence v = ----------- = 2.84cubic feet, and 10,800

1 1 Weight per cubic foot =- = ---- = 0.352 pounds. v2.84

Table 27 gives the weights and volumes ofair under atmospheric pressure at varyingtemperatures.

Formula (9) holds good for other gaseswith the change in the value of the constantas follows:

For oxygen 48.24, nitrogen 54.97,hydrogen 765.71.

The specific heat of air at constantpressure varies with its temperature. Anumber of determinations of this valuehave been made and certain of thoseordinarily accepted as most authentic aregiven in Table 28.

TABLE 28

SPECIFIC HEAT OF AIRAT CONSTANT PRESSURE AND VARIOUSTEMPERATURES______________________________________________________________ | |

| | | Temperature Range| | |

|_________________________|_______________|____________________| | || | | | Degrees |Degrees | Specific Heat | Authority| | Centigrade | Fahrenheit | |

||____________|____________|_______________|____________________| | || | | | -30- 10 | -22- 50

| 0.2377 | Regnault | | 0-100| 32- 212 | 0.2374 | Regnault | |

0-200 | 32- 392 | 0.2375 | Regnault| | 20-440 | 68- 824 | 0.2366 |

Holborn and Curtis | | 20-630 | 68-1166| 0.2429 | Holborn and Curtis | |

20-800 | 68-1472 | 0.2430 | Holbornand Curtis | | 0-200 | 32- 392 |0.2389 | Wiedemann ||____________|____________|_______________|____________________|

This value is of particular importance inwaste heat work and it is regrettable thatthere is such a variation in the differentexperiments. Mallard and Le Chatelierdetermined values considerably higherthan any given in Table 28. All things

considered in view of the discrepancy ofthe values given, there appears to be asmuch ground for the use of a constantvalue for the specific heat of air at anytemperature as for a variable value. Wherethis value is used throughout this book, ithas been taken as 0.24.

Air may carry a considerable quantity ofwater vapor, which is frequently 3 per centof the total weight. This fact is ofimportance in problems relating to heatingdrying and the compressing of air. Table29 gives the amount of vapor required tosaturate air at different temperatures, itsweight, expansive force, etc., and containssufficient information for solvingpractically all problems of this sort thatmay arise.

TABLE 29

WEIGHTS OF AIR, VAPOR OF WATER,AND SATURATED MIXTURES OF AIR ANDVAPOR AT DIFFERENTTEMPERATURES, UNDER THEORDINARY ATMOSPHERIC PRESSURE OF29.921 INCHES OF MERCURY

Column Headings: 1: TemperatureDegrees Fahrenheit 2: Volume of Dry Airat Different Temperatures, the Volume at32 Degrees being 1.000 3: Weight ofCubic Foot of Dry Air at the DifferentTemperatures Pounds 4: Elastic Force ofVapor in Inches of Mercury (Regnault) 5:Elastic Force of the Air in the Mixture of Airand Vapor in Inches of Mercury 6:Weight of the Air in Pounds 7: Weight ofthe Vapor in Pounds 8: Total Weight ofMixture in Pounds 9: Weight of VaporMixed with One Pound of Air, in Pounds10: Weight of Dry Air Mixed with OnePound of Vapor, in Pounds 11: Cubic Feet

of Vapor from One Pound of Water at itsown Pressure in Column 4____________________________________________________________________________ || | | | || | | | | | Mixtures of AirSaturated | | | | | | |

with Vapor | ||___|_____|_____|______|______________________________________________|______|| | | | | |Weight of Cubic Foot| | | | | | | | | | ofthe Mixture of | | | | | | || | | Air and Vapor | | |

| | | | | ||_____________________| | | | || | | | | | | | | |

| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8| 9 | 10 | 11 ||___|_____|_____|______|______|_____|_______|_______|________|________|______|| | | | | | | | | |

| | | 0| .935|.0864|.044|29.877|.0863|.000079|.086379|.00092|1092.4 | | | 12| .960|.0842|.074|29.849|.0840|.000130|.084130|.00155| 646.1 | | | 22| .980|.0824|.118|29.803|.0821|.000202|.082302|.00245| 406.4 | | | 32|1.000|.0807|.181|29.740|.0802|.000304|.080504|.00379| 263.81 |3289 | | 42|1.020|.0791|.267|29.654|.0784|.000440|.078840|.00561| 178.18 |2252 | | | | | || | | | | | | |52|1.041|.0776|.388|29.533|.0766|.000627|.077227|.00810| 122.17 |1595 | | 62|1.061|.0761|.556|29.365|.0747|.000881|.075581|.01179| 84.79 |1135 | | 72|1.082|.0747|.785|29.136|.0727|.001221|.073921|.01680| 59.54 | 819 | | 82|1.102|.0733|1.092|28.829|.0706|.001667|.072267|.02361| 42.35 | 600 | | 92|1.122|.0720|1.501|28.420|.0684|.002250|.070717|

.03289| 30.40 | 444 | | | | | || | | | | | ||102|1.143|.0707|2.036|27.885|.0659|.002997|.068897|.04547| 21.98 | 334 | |112|1.163|.0694|2.731|27.190|.0631|.003946|.067046|.06253| 15.99 | 253 | |122|1.184|.0682|3.621|26.300|.0599|.005142|.065042|.08584| 11.65 | 194 | |132|1.204|.0671|4.752|25.169|.0564|.006639|.063039|.11771| 8.49 | 151 | |142|1.224|.0660|6.165|23.756|.0524|.008473|.060873|.16170| 6.18 | 118 | | | | | | |

| | | | | ||152|1.245|.0649|7.930|21.991|.0477|.010716|.058416|.22465| 4.45 | 93.3||162|1.265|.0638|10.099|19.822|.0423|.013415|.055715| .31713| 3.15 | 74.5||172|1.285|.0628|12.758|17.163|.0360|.016682|.052682| .46338| 2.16 | 59.2||182|1.306|.0618|15.960|13.961|.0288|.0

20536|.049336| .71300| 1.402| 48.6||192|1.326|.0609|19.828|10.093|.0205|.025142|.045642| 1.22643| .815| 39.8| || | | | | | | | | |

| |202|1.347|.0600|24.450|5.471|.0109|.030545|.041445| 2.80230|.357| 32.7| |212|1.367|.0591|29.921|0.000|.0000|.036820|.036820|Infinite|.000| 27.1||___|_____|_____|______|______|_____|_______|_______|________|________|______|

Column 5 = barometer pressure of 29.921,minus the proportion of this due to vaporpressure from column 4.

COMBUSTION

Combustion may be defined as the rapidchemical combination of oxygen withcarbon, hydrogen and sulphur,accompanied by the diffusion of heat andlight. That portion of the substance thuscombined with the oxygen is calledcombustible. As used in steamengineering practice, however, the termcombustible is applied to that portion ofthe fuel which is dry and free from ash,thus including both oxygen and nitrogenwhich may be constituents of the fuel,though not in the true sense of the termcombustible.

Combustion is perfect when thecombustible unites with the greatestpossible amount of oxygen, as when oneatom of carbon unites with two atoms of

oxygen to form carbon dioxide, CO_{2}.The combustion is imperfect whencomplete oxidation of the combustibledoes not occur, or where the combustibledoes not unite with the maximum amountof oxygen, as when one atom of carbonunites with one atom of oxygen to formcarbon monoxide, CO, which may befurther burned to carbon dioxide.

Kindling Point--Before a combustible canunite with oxygen and combustion takesplace, its temperature must first be raisedto the ignition or kindling point, and asufficient time must be allowed for thecompletion of the combustion before thetemperature of the gases is lowered belowthat point. Table 30, by Stromeyer, givesthe approximate kindling temperatures ofdifferent fuels.

TABLE 30

KINDLING TEMPERATURE OF VARIOUSFUELS

____________________________________ || | | | Degrees

| | | Fahrenheit ||_________________|__________________|| | | | Lignite Dust |300 | | Dried Peat | 435 | |Sulphur | 470 | | AnthraciteDust | 570 | | Coal | 600

| | Coke | Red Heat | |Anthracite | Red Heat, 750 | | CarbonMonoxide | Red Heat, 1211 | | Hydrogen

| 1030 or 1290 ||_________________|__________________|

Combustibles--The principal combustiblesin coal and other fuels are carbon,hydrogen and sulphur, occurring in

varying proportions and combinations.

Carbon is by far the most abundant as isindicated in the chapters on fuels.

Hydrogen in a free state occurs in smallquantities in some fuels, but is usuallyfound in combination with carbon, in theform of hydrocarbons. The density ofhydrogen is 0.0696 (Air = 1) and its weightper cubic foot, at 32 degrees Fahrenheitand under atmospheric pressure, is0.005621 pounds.

Sulphur is found in most coals and someoils. It is usually present in combined form,either as sulphide of iron or sulphate oflime; in the latter form it has no heat value.Its presence in fuel is objectionablebecause of its tendency to aid in theformation of clinkers, and the gases fromits combustion, when in the presence of

moisture, may cause corrosion.

Nitrogen is drawn into the furnace with theair. Its density is 0.9673 (Air = 1); itsweight, at 32 degrees Fahrenheit andunder atmospheric pressure, is 0.07829pounds per cubic foot; each pound of air atatmospheric pressure contains 0.7685pounds of nitrogen, and one pound ofnitrogen is contained in 1.301 pounds ofair.

Nitrogen performs no useful office incombustion and passes through thefurnace without change. It dilutes the air,absorbs heat, reduces the temperature ofthe products of combustion, and is thechief source of heat losses in furnaces.

Calorific Value--Each combustibleelement of gas will combine with oxygenin certain definite proportions and will

generate a definite amount of heat,measured in B. t. u. This definite amount ofheat per pound liberated by perfectcombustion is termed the calorific value ofthat substance. Table 31, gives certain dataon the reactions and results of combustionfor elementary combustibles and severalcompounds.

TABLE 31

OXYGEN AND AIR REQUIREDFOR COMBUSTION

AT 32 DEGREES AND 29.92INCHES

Column headings:

1: Oxidizable Substance or Combustible2: Chemical Symbol 3: Atomic orCombining Weight 4: Chemical Reaction

5: Product of Combustion 6: Oxygen perPound of Column 1 Pounds 7: Nitrogenper Pound of Column 1. 3.32[23] �OPounds 8: Air per Pound of Column 1.4.32[24] �O Pounds 9: Gaseous Productper Pound of Column 1[25] + Column 8Pounds 10: Heat Value per Pound ofColumn 1 B. t. u. 11: Volumes of Column 1Entering Combination Volume 12:Volumes of Oxygen Combining withColumn 11 Volume 13: Volumes of ProductFormed Volume 14: Volume per Pound ofColumn 1 in Gaseous Form Cubic Feet 15:Volume of Oxygen per Pound of Column 1Cubic Feet 16: Volume of Products ofCombustion per Pound of Column 1 CubicFeet 17: Volume of Nitrogen per Pound ofColumn 1 3.782[26] �Column 15 CubicFeet 18: Volume of Gas per pound ofColumn 1 = Column 10 �Column 17 Cubic Feet

BY WEIGHT________________________________________________________________________ |

| | | | | | |1 | 2 | 3 | 4 | 5 | 6 ||________________|_______|____|________________|_________________|_______| |

| | | | | | |Carbon | C | 12 | C+2O = CO_{2} |Carbon Dioxide | 2.667 | | Carbon |C | 12 | C+O = CO | CarbonMonoxide | 1.333 | | Carbon Monoxide|CO | 28 | CO+O = CO_{2} | CarbonDioxide | .571 | | Hydrogen | H | 1| 2H+O = H_{2}O | Water | 8 | |

| | / CH_{4}+4O = | CarbonDioxide \ | | Methane | CH_{4}| 16| | | 4 | | || \ CO_{2}+2H_{2}O | and Water /| | Sulphur | S | 32 | S+2O = SO_{2}| Sulphur Dioxide | 1 ||________________|_______|____|________

________|_________________|_______|

________________________________________________________ | | | || | | | 1 | 2 | 7 | 8 |

9 | 10 ||________________|_______|_______|_______|_______|_______| | | | |

| | | | Carbon | C | 8.85 |11.52 | 12.52 | 14600 | | Carbon | C| 4.43 | 5.76 | 6.76 | 4450 | | CarbonMonoxide| CO | 1.90 | 2.47 | 3.47 |10150 | | Hydrogen | H | 26.56 |34.56 | 35.56 | 62000 | | | || | | | | Methane | CH_{4}|13.28 | 17.28 | 18.28 | 23550 | | |

| | | | | | Sulphur | S| 3.32 | 4.32 | 5.32 | 4050 ||________________|_______|_______|_______|_______|_______|

BY VOLUME

________________________________________________________________ | || | | | | | 1 | 2 |

11 | 12 | 13 | 14 ||_________________|________|______|____|________________|________| | |

| | | | | | Carbon| C | 1C | 2 | 2CO_{2} | 14.95 | |Carbon | C | 1C | 1 | 2CO| 14.95 | | Carbon Monoxide | CO |2CO | 1 | 2CO_{2} | 12.80 | |Hydrogen | H | 2H | 1 | 2H_{2}O

| 179.32 | | Methane | CH_{4} |1C4H | 4 | 1CO_{2} 2H_{2}O| 22.41 | |Sulphur | S | 1S | 2 | 1SO_{2}| 5.60 ||_________________|________|______|____|________________|________|

_____________________________________________________________ | | |

| | | | | 1 | 2 | 15| 16 | 17 | 18 |

|_________________|________|_______|________|________|________| | || | | | | | Carbon | C

| 29.89 | 29.89 | 112.98 | 142.87 | |Carbon | C | 14.95 | 29.89 | 56.49| 86.38 | | Carbon Monoxide | CO |6.40 | 12.80 | 24.20 | 37.00 | | Hydrogen

| H | 89.66 | 179.32 | 339.09 |518.41 | | Methane | CH_{4} | 44.83 |67.34 | 169.55 | 236.89 | | Sulphur | S

| 11.21 | 11.21 | 42.39 | 53.60 ||_________________|________|_______|________|________|________|

It will be seen from this table that a poundof carbon will unite with 2-2/3 pounds of

oxygen to form carbon dioxide, and willevolve 14,600 B. t. u. As an intermediatestep, a pound of carbon may unite with1-1/3 pounds of oxygen to form carbonmonoxide and evolve 4450 B. t. u., but inits further conversion to CO_{2} it wouldunite with an additional 1-1/3 times itsweight of oxygen and evolve theremaining 10,150 B. t. u. When a pound ofCO burns to CO_{2}, however, only 4350 B.t. u. are evolved since the pound of COcontains but 3/7 pound carbon.

Air Required for Combustion--It hasalready been shown that each combustibleelement in fuel will unite with a definiteamount of oxygen. With the ultimateanalysis of the fuel known, in connectionwith Table 31, the theoretical amount of airrequired for combustion may be readilycalculated.

Let the ultimate analysis be as follows:

_Per Cent_ Carbon 74.79Hydrogen 4.98 Oxygen 6.42Nitrogen 1.20 Sulphur 3.24 Water

1.55 Ash 7.82 ------ 100.00

When complete combustion takes place,as already pointed out, the carbon in thefuel unites with a definite amount ofoxygen to form CO_{2}. The hydrogen,either in a free or combined state, willunite with oxygen to form water vapor,H_{2}O. Not all of the hydrogen shown in afuel analysis, however, is available for theproduction of heat, as a portion of it isalready united with the oxygen shown bythe analysis in the form of water, H_{2}O.Since the atomic weights of H and O arerespectively 1 and 16, the weight of thecombined hydrogen will be 1/8 of the

weight of the oxygen, and the hydrogenavailable for combustion will be H - 1/8 O.In complete combustion of the sulphur,sulphur dioxide SO_{2} is formed, which insolution in water forms sulphuric acid.

Expressed numerically, the theoreticalamount of air for the above analysis is asfollows:

0.7479 C �2-2/3 = 1.9944 O needed (0.0642 ) ( 0.0498 - -------) H �8 =

0.3262 O needed ( 8 ) 0.0324 S �1= 0.0324 O needed

------ Total 2.3530 O needed

One pound of oxygen is contained in 4.32pounds of air.

The total air needed per pound of coal,therefore, will be 2.353 �4.32 = 10.165.

The weight of combustible per pound offuel is .7479 + .0418[27] + .0324 + .012 =.83 pounds, and the air theoreticallyrequired per pound of combustible is10.165 �.83 = 12.2 pounds.

The above is equivalent to computing thetheoretical amount of air required perpound of fuel by the formula:

( O) Weight perpound = 11.52 C + 34.56 (H - -) + 4.32 S(10) ( 8)

where C, H, O and S are proportional partsby weight of carbon, hydrogen, oxygenand sulphur by ultimate analysis.

In practice it is impossible to obtainperfect combustion with the theoreticalamount of air, and an excess may berequired, amounting to sometimes double

the theoretical supply, depending uponthe nature of the fuel to be burned and themethod of burning it. The reason for this isthat it is impossible to bring each particleof oxygen in the air into intimate contactwith the particles in the fuel that are to beoxidized, due not only to the dilution of theoxygen in the air by nitrogen, but becauseof such factors as the irregular thickness ofthe fire, the varying resistance to thepassage of the air through the fire inseparate parts on account of ash, clinker,etc. Where the difficulties of drawing airuniformly through a fuel bed areeliminated, as in the case of burning oilfuel or gas, the air supply may bematerially less than would be required forcoal. Experiment has shown that coal willusually require 50 per cent more than thetheoretical net calculated amount of air, orabout 18 pounds per pound of fuel eitherunder natural or forced draft, though this

amount may vary widely with the type offurnace, the nature of the coal, and themethod of firing. If less than this amount ofair is supplied, the carbon burns tomonoxide instead of dioxide and its fullheat value is not developed.

An excess of air is also a source of waste,as the products of combustion will bediluted and carry off an excessive amountof heat in the chimney gases, or the air willso lower the temperature of the furnacegases as to delay the combustion to anextent that will cause carbon monoxide topass off unburned from the furnace. Asufficient amount of carbon monoxide inthe gases may cause the action known assecondary combustion, by igniting ormingling with air after leaving the furnaceor in the flues or stack. Such secondarycombustion which takes place eitherwithin the setting after leaving the furnace

or in the flues or stack always leads to aloss of efficiency and, in some instances,leads to overheating of the flues and stack.

Table 32 gives the theoretical amount ofair required for various fuels calculatedfrom formula (10) assuming the analyses ofthe fuels given in the table.

The process of combustion of differentfuels and the effect of variation in the airsupply for their combustion is treated indetail in the chapters dealing with thevarious fuels.

TABLE 32

CALCULATED THEORETICALAMOUNT OF AIR REQUIRED PERPOUND OF VARIOUS FUELS

____________________________________________________________ | |Weightof Constituents in One |Air Required| |Fuel |Pound Dry Fuel |perPound | ||______________________________|of Fuel

| | | Carbon | Hydrogen|Oxygen |Pounds | | | PerCent| Per Cent| Per Cent | ||________________|_________|_________|__________|____________| |Coke |94.0 | . | . | 10.8 | |AnthraciteCoal | 91.5 | 3.5 | 2.6 | 11.7 ||Bituminous Coal | 87.0 | 5.0 | 4.0 |11.6 | |Lignite | 70.0 | 5.0 |20.0 | 8.9 | |Wood | 50.0 |6.0 | 43.5 | 6.0 | |Oil | 85.0| 13.0 | 1.0 | 14.3 ||________________|_________|_________|__________|____________|

[Illustration: 4064 HORSE-POWERInstallation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock& Wilcox Chain Grate Stokers, at theCosmopolitan Electric Co., Chicago, Ill.]

ANALYSIS OF FLUE GASES

The object of a flue gas analysis is thedetermination of the completeness of thecombustion of the carbon in the fuel, andthe amount and distribution of the heatlosses due to incomplete combustion. Thequantities actually determined by ananalysis are the relative proportions byvolume, of carbon dioxide (CO_{2}),oxygen (O), and carbon monoxide (CO),the determinations being made in thisorder.

The variations of the percentages of thesegases in an analysis is best illustrated inthe consideration of the completecombustion of pure carbon, a pound ofwhich requires 2.67 pounds of oxygen,[28]or 32 cubic feet at 60 degrees Fahrenheit.The gaseous product of such combustion

will occupy, when cooled, the samevolume as the oxygen, namely, 32 cubicfeet. The air supplied for the combustion ismade up of 20.91 per cent oxygen and79.09 per cent nitrogen by volume. Thecarbon united with the oxygen in the formof carbon dioxide will have the samevolume as the oxygen in the air originallysupplied. The volume of the nitrogen whencooled will be the same as in the airsupplied, as it undergoes no change.Hence for complete combustion of onepound of carbon, where no excess of air issupplied, an analysis of the products ofcombustion will show the followingpercentages by volume:

_Actual Volume__for One Pound Carbon_ _Per Cent_

_Cubic Feet_ _byVolume_ Carbon Dioxide 32

= 20.91 Oxygen 0

= 0.00 Nitrogen 121= 79.09 --------- Air required for one pound Carbon

153 = 100.00

For 50 per cent excess air the volume willbe as follows:

153 �1� = 229.5 cubic feet of air perpound of carbon.

_Actual Volume_ _for OnePound Carbon_ _Per Cent__Cubic Feet_ _by Volume_ CarbonDioxide 32 = 13.91 } Oxygen

16 = 7.00 } = 20.91 per centNitrogen 181.5 = 79.09

----- ------ 229.5= 100.00

For 100 per cent excess air the volume willbe as follows:

153 �2 = 306 cubic feet of air per poundof carbon.

_Actual Volume_ _for OnePound Carbon_ _Per Cent__Cubic Feet_ _by Volume_ CarbonDioxide 32 = 10.45 } Oxygen

32 = 10.45 } = 20.91 per centNitrogen 242 = 79.09

--- ------ 306= 100.00

In each case the volume of oxygen whichcombines with the carbon is equal to(cubic feet of air �20.91 per cent)--32 cubicfeet.

It will be seen that no matter what theexcess of air supplied, the actual amount ofcarbon dioxide per pound of carbonremains the same, while the percentage

by volume decreases as the excess of airincreases. The actual volume of oxygenand the percentage by volume increaseswith the excess of air, and the percentageof oxygen is, therefore, an indication of theamount of excess air. In each case the sumof the percentages of CO_{2} and O is thesame, 20.9. Although the volume ofnitrogen increases with the excess of air,its percentage by volume remains thesame as it undergoes no change whilecombustion takes place; its percentage forany amount of air excess, therefore, will bethe same after combustion as before, ifcooled to the same temperature. It must beborne in mind that the above conditionshold only for the perfect combustion of apound of pure carbon.

Carbon monoxide (CO) produced by theimperfect combustion of carbon, willoccupy twice the volume of the oxygen

entering into its composition and willincrease the volume of the flue gases overthat of the air supplied for combustion inthe proportion of

100 + � the per cent CO 1 to----------------------- 100

When pure carbon is the fuel, the sum ofthe percentages by volume of carbondioxide, oxygen and one-half of thecarbon monoxide, must be in the sameratio to the nitrogen in the flue gases as isthe oxygen to the nitrogen in the airsupplied, that is, 20.91 to 79.09. Whenburning coal, however, the percentage ofnitrogen is obtained by subtracting thesum of the percentages by volume of theother gases from 100. Thus if an analysisshows 12.5 per cent CO_{2}, 6.5 per centO, and 0.6 per cent CO, the percentage ofnitrogen which ordinarily is the only other

constituent of the gas which need beconsidered, is found as follows:

100 - (12.5 + 6.5 + 0.6) = 80.4 per cent.

The action of the hydrogen in the volatileconstituents of the fuel is to increase theapparent percentage of the nitrogen in theflue gases. This is due to the fact that thewater vapor formed by the combustion ofthe hydrogen will condense at atemperature at which the analysis is made,while the nitrogen which accompanied theoxygen with which the hydrogen originallycombined maintains its gaseous form andpasses into the sampling apparatus withthe other gases. For this reason coalscontaining high percentages of volatilematter will produce a larger quantity ofwater vapor, and thus increase theapparent percentage of nitrogen.

Air Required and Supplied--When theultimate analysis of a fuel is known, the airrequired for complete combustion with noexcess can be found as shown in thechapter on combustion, or from thefollowing approximate formula:

Pounds of air required per pound of fuel=

(C O S) 34.56 (- + (H - -) +-)[29] (11) (3 8 8)

where C, H and O equal the percentage byweight of carbon, hydrogen and oxygen inthe fuel divided by 100.

When the flue gas analysis is known, thetotal, amount of air supplied is:

Pounds of air supplied per pound of fuel

=

N 3.036 (-----------) �C[30](12) CO_{2} + CO

where N, CO_{2} and CO are thepercentages by volume of nitrogen,carbon dioxide and carbon monoxide inthe flue gases, and C the percentage byweight of carbon which is burned from thefuel and passes up the stack as flue gas.This percentage of C which is burned mustbe distinguished from the percentage of Cas found by an ultimate analysis of the fuel.To find the percentage of C which isburned, deduct from the total percentageof carbon as found in the ultimate analysis,the percentage of unconsumed carbonfound in the ash. This latter quantity is thedifference between the percentage of ashfound by an analysis and that asdetermined by a boiler test. It is usually

assumed that the entire combustibleelement in the ash is carbon, whichassumption is practically correct. Thus ifthe ash in a boiler test were 16 per centand by an analysis contained 25 per centof carbon, the percentage of unconsumedcarbon would be 16 �.25 = 4 per cent ofthe total coal burned. If the coal containedby ultimate analysis 80 per cent of carbonthe percentage burned, and of which theproducts of combustion pass up thechimney would be 80 - 4 = 76 per cent,which is the correct figure to use incalculating the total amount of air suppliedby formula (12).

The weight of flue gases resulting from thecombustion of a pound of dry coal will bethe sum of the weights of the air per poundof coal and the combustible per pound ofcoal, the latter being equal to one minusthe percentage of ash as found in the

boiler test. The weight of flue gases perpound of dry fuel may, however, becomputed directly from the analyses, asshown later, and the direct computation isthat ordinarily used.

The ratio of the air actually supplied perpound of fuel to that theoretically requiredto burn it is:

N 3.036(---------)� CO_{2}+CO------------------ (13) C O 34.56(- +H - -) 3 8

in which the letters have the samesignificance as in formulae (11) and (12).

The ratio of the air supplied per pound ofcombustible to the amount theoreticallyrequired is:

N ------------------ (14) N - 3.782(O -

�CO)

which is derived as follows:

The N in the flue gas is the content ofnitrogen in the whole amount of airsupplied. The oxygen in the flue gas is thatcontained in the air supplied and whichwas not utilized in combustion. Thisoxygen was accompanied by 3.782 timesits volume of nitrogen. The total amount ofexcess oxygen in the flue gases is (O -�CO); hence N - 3.782(O - �CO)represents the nitrogen content in the airactually required for combustion and N�(N - 3.782[O - �CO]) is the ratio of the airsupplied to that required. This ratio minusone will be the proportion of excess air.

The heat lost in the flue gases is L = 0.24 W(T - t) (15)

Where L = B. t. u. lost per pound of fuel,W = weight of flue gases in pounds perpound of dry coal, T = temperature offlue gases, t = temperature ofatmosphere, 0.24 = specific heat of theflue gases.

The weight of flue gases, W, per pound ofcarbon can be computed directly from theflue gas analysis from the formula:

11 CO_{2} + 8 O + 7 (CO + N)---------------------------- (16) 3 (CO_{2}+ CO)

where CO_{2}, O, CO, and N are thepercentages by volume as determined bythe flue gas analysis of carbon dioxide,oxygen, carbon monoxide and nitrogen.

The weight of flue gas per pound of drycoal will be the weight determined by this

formula multiplied by the percentage ofcarbon in the coal from an ultimateanalysis.

[Graph: Temperature of EscapingGases--Deg. Fahr. against Heat carriedaway by Chimney Gases--In B.t.u. perpound of Carbon burned.[31]

Fig. 20. Loss Due to Heat Carried Away byChimney Gases for Varying Percentagesof Carbon Dioxide. Based on Boiler RoomTemperature = 80 Degrees Fahrenheit.Nitrogen in Flue Gas = 80.5 Per Cent.Carbon Monoxide in Flue Gas = 0. PerCent]

Fig. 20 represents graphically the loss dueto heat carried away by dry chimney gasesfor varying percentages of CO_{2}, anddifferent temperatures of exit gases.

The heat lost, due to the fact that thecarbon in the fuel is not completely burnedand carbon monoxide is present in the fluegases, in B. t. u. per pound of fuel burnedis:

( CO ) L' = 10,150 �(-----------) (17) (CO + CO_{2})

where, as before, CO and CO_{2} are thepercentages by volume in the flue gasesand C is the proportion by weight ofcarbon which is burned and passes up thestack.

Fig. 21 represents graphically the loss dueto such carbon in the fuel as is notcompletely burned but escapes up thestack in the form of carbon monoxide.

[Graph: Loss in B.T.U. per Pound ofCarbon Burned[32] against Per Cent

CO_{2} in Flue Gas

Fig. 21. Loss Due to Unconsumed CarbonContained in the CO in the Flue Gases]

Apparatus for Flue Gas Analysis--TheOrsat apparatus, illustrated in Fig. 22, isgenerally used for analyzing flue gases.The burette A is graduated in cubiccentimeters up to 100, and is surroundedby a water jacket to prevent any change intemperature from affecting the density ofthe gas being analyzed.

For accurate work it is advisable to usefour pipettes, B, C, D, E, the first containinga solution of caustic potash for theabsorption of carbon dioxide, the secondan alkaline solution of pyrogallol for theabsorption of oxygen, and the remainingtwo an acid solution of cuprous chloridefor absorbing the carbon monoxide. Each

pipette contains a number of glass tubes,to which some of the solution clings, thusfacilitating the absorption of the gas. In thepipettes D and E, copper wire is placed inthese tubes to re-energize the solution as itbecomes weakened. The rear half of eachpipette is fitted with a rubber bag, one ofwhich is shown at K, to protect the solutionfrom the action of the air. The solution ineach pipette should be drawn up to themark on the capillary tube.

The gas is drawn into the burette throughthe U-tube H, which is filled with spunglass, or similar material, to clean the gas.To discharge any air or gas in theapparatus, the cock G is opened to the airand the bottle F is raised until the water inthe burette reaches the 100 cubiccentimeters mark. The cock G is thenturned so as to close the air opening andallow gas to be drawn through H, the

bottle F being lowered for this purpose.The gas is drawn into the burette to a pointbelow the zero mark, the cock G thenbeing opened to the air and the excess gasexpelled until the level of the water in Fand in A are at the zero mark. Thisoperation is necessary in order to obtainthe zero reading at atmospheric pressure.

The apparatus should be carefully testedfor leakage as well as all connectionsleading thereto. Simple tests can be made;for example: If after the cock G is closed,the bottle F is placed on top of the framefor a short time and again brought to thezero mark, the level of the water in A isabove the zero mark, a leak is indicated.

[Illustration: Fig. 22. Orsat Apparatus]

Before taking a final sample for analysis,the burette A should be filled with gas and

emptied once or twice, to make sure thatall the apparatus is filled with the new gas.The cock G is then closed and the cock I inthe pipette B is opened and the gas drivenover into B by raising the bottle F. The gasis drawn back into A by lowering F andwhen the solution in B has reached themark in the capillary tube, the cock I isclosed and a reading is taken on theburette, the level of the water in the bottleF being brought to the same level as thewater in A. The operation is repeated untila constant reading is obtained, the numberof cubic centimeters being the percentageof CO_{2} in the flue gases.

The gas is then driven over into the pipetteC and a similar operation is carried out.The difference between the resultingreading and the first reading gives thepercentage of oxygen in the flue gases.

The next operation is to drive the gas intothe pipette D, the gas being given a finalwash in E, and then passed into the pipetteC to neutralize any hydrochloric acidfumes which may have been given off bythe cuprous chloride solution, which,especially if it be old, may give off suchfumes, thus increasing the volume of thegases and making the reading on theburette less than the true amount.

The process must be carried out in theorder named, as the pyrogallol solutionwill also absorb carbon dioxide, while thecuprous chloride solution will also absorboxygen.

As the pressure of the gases in the flue isless than the atmospheric pressure, theywill not of themselves flow through thepipe connecting the flue to the apparatus.The gas may be drawn into the pipe in the

way already described for filling theapparatus, but this is a tedious method. Forrapid work a rubber bulb aspiratorconnected to the air outlet of the cock Gwill enable a new supply of gas to bedrawn into the pipe, the apparatus thenbeing filled as already described. Anotherform of aspirator draws the gas from theflue in a constant stream, thus insuring afresh supply for each sample.

The analysis made by the Orsat apparatusis volumetric; if the analysis by weight isrequired, it can be found from thevolumetric analysis as follows:

Multiply the percentages by volume byeither the densities or the molecularweight of each gas, and divide theproducts by the sum of all the products;the quotients will be the percentages byweight. For most work sufficient accuracy

is secured by using the even values of themolecular weights.

The even values of the molecular weightsof the gases appearing in an analysis by anOrsat are:

Carbon Dioxide 44 Carbon Monoxide 28Oxygen 32 Nitrogen 28

Table 33 indicates the method ofconverting a volumetric flue gas analysisinto an analysis by weight.

TABLE 33

CONVERSION OF A FLUE GASANALYSIS BY VOLUME TO ONE BYWEIGHT

Column Headings:

A: Analysis by Volume Per Cent B:Molecular Weight C: Volume timesMolecular Weight D: Analysis by WeightPer Cent_____________________________________________________________________ |

| | | | | | Gas| A | B | C | D |

|________________________|_______|___________|________|_______________| |

| | | | | || | | | | || | | | 536.8 | |

Carbon Dioxide CO_{2} | 12.2 | 12+(2�6)| 536.8 | ------ = 17.7 | | || | | 3022.8 | | |

| | | | | || | | 11.2 | | Carbon

Monoxide CO | .4 | 12+16 | 11.2 |------ = .4 | | | | || 3022.8 | | | | |

| | | | | |

| 220.8 | | Oxygen O | 6.9| 2�6 | 220.8 | ------ = 7.3 | |

| | | | 3022.8 | || | | | | || | | | 2254.0 | |

Nitrogen N | 80.5 | 2�4 | 2254.0| ------ = 74.6 | | | | |

| 3022.8 ||________________________|_______|___________|________|_______________| |

| | | | | | Total| 100.0 | | 3022.8 | 100.0

||________________________|_______|___________|________|_______________|

Application of Formulae andRules--Pocahontas coal is burned in thefurnace, a partial ultimate analysis being:

_Per Cent_ Carbon82.1 Hydrogen 4.25 Oxygen

2.6 Sulphur 1.6 Ash 6.0 B. t. u., per pound dry 14500

The flue gas analysis shows:

_Per Cent_

CO_{2} 10.7 O 9.0 CO 0.0 N (by difference) 80.3

Determine: The flue gas analysis by weight(see Table 33), the amount of air requiredfor perfect combustion, the actual weightof air per pound of fuel, the weight of fluegas per pound of coal, the heat lost in thechimney gases if the temperature of theseis 500 degrees Fahrenheit, and the ratio ofthe air supplied to that theoreticallyrequired.

Solution: The theoretical weight of airrequired for perfect combustion, per

pound of fuel, from formula (11) will be,

(.821 .026 .016) W = 34.56(---- + (.0425 - ----) + ----) = 10.88 pounds. ( 3 8 8 )

If the amount of carbon which is burnedand passes away as flue gas is 80 per cent,which would allow for 2.1 per cent ofunburned carbon in terms of the totalweight of dry fuel burned, the weight ofdry gas per pound of carbon burned willbe from formula (16):

11 �10.7 + 8 �9.0 + 7(0 + 80.3) W =--------------------------------- = 23.42 pounds 3(10.7 + 0)

and the weight of flue gas per pound ofcoal burned will be .80 �23.42 = 18.74pounds.

The heat lost in the flue gases per pound ofcoal burned will be from formula (15) andthe value 18.74 just determined.

Loss = .24 �18.74 �(500 - 60) = 1979 B. t. u.

The percentage of heat lost in the fluegases will be 1979 �14500 = 13.6 per cent.

The ratio of air supplied per pound of coalto that theoretically required will be 18.74�10.88 = 1.72 per cent.

The ratio of air supplied per pound ofcombustible to that required will be fromformula (14):

.803 ------------------------- = 1.73 .803 -3.782(.09 - � �0)

The ratio based on combustible will begreater than the ratio based on fuel if there

is unconsumed carbon in the ash.

Unreliability of CO_{2} Readings TakenAlone--It is generally assumed that highCO_{2} readings are indicative of goodcombustion and hence of high efficiency.This is true only in the sense that such highreadings do indicate the small amount ofexcess air that usually accompanies goodcombustion, and for this reason highCO_{2} readings alone are not consideredentirely reliable. Wherever an automaticCO_{2} recorder is used, it should bechecked from time to time and the analysiscarried further with a view to ascertainingwhether there is CO present. As thepercentage of CO_{2} in these gasesincreases, there is a tendency toward thepresence of CO, which, of course, cannotbe shown by a CO_{2} recorder, and whichis often difficult to detect with an Orsat

apparatus. The greatest care should betaken in preparing the cuprous chloridesolution in making analyses and it must beknown to be fresh and capable ofabsorbing CO. In one instance that cameto our attention, in using an Orsatapparatus where the cuprous chloridesolution was believed to be fresh, no COwas indicated in the flue gases but onpassing the same sample into a Hempelapparatus, a considerable percentage wasfound. It is not safe, therefore, to assumewithout question from a high CO_{2}reading that the combustion iscorrespondingly good, and the question ofexcess air alone should be distinguishedfrom that of good combustion. The effect ofa small quantity of CO, say one per cent,present in the flue gases will have anegligible influence on the quantity ofexcess air, but the presence of such anamount would mean a loss due to the

incomplete combustion of the carbon inthe fuel of possibly 4.5 per cent of the totalheat in the fuel burned. When this isconsidered, the importance of a completeflue gas analysis is apparent.

Table 34 gives the densities of variousgases together with other data that will beof service in gas analysis work.

TABLE 34

DENSITY OF GASES AT 32 DEGREESFAHRENHEIT AND ATMOSPHERICPRESSURE ADAPTED FROMSMITHSONIAN TABLES

+----------+----------+--------+---------+----------+---------------+ | | | | |

| Relative | | | | |Weight | | Density, | | || | of | Volume | Hydrogen = 1 | |

| |Specific|One Cubic| of+-------+-------+ | Gas | Chemical|Gravity | Foot |One Pound ||Approx-| | | Symbol | Air=1 |Pounds |Cubic Feet| Exact | imate |+----------+----------+--------+---------+----------+-------+-------+ |Oxygen | O | 1.053

| .08922 | 11.208 | 15.87 | 16 ||Nitrogen | N | 0.9673 | .07829 |12.773 | 13.92 | 14 | |Hydrogen | H| 0.0696 | .005621 | 177.90 | 1.00 | 1 ||Carbon | | | | | |

| | Dioxide | CO_{2} | 1.5291 | .12269| 8.151 | 21.83 | 22 | |Carbon || | | | | | | Monoxide| CO | 0.9672 | .07807 | 12.809 |13.89 | 14 | |Methane | CH_{4} |0.5576 | .04470 | 22.371 | 7.95 | 8 ||Ethane |C_{2}H_{6}| 1.075 | .08379 |11.935 | 14.91 | 15 | |Acetylene|C_{2}H_{2}| 0.920 | .07254 | 13.785 |12.91 | 13 | |Sulphur | | |

| | | | | Dioxide | SO_{2} |2.2639 | .17862 | 5.598 | 31.96 | 32 ||Air | ... | 1.0000 | .08071 | 12.390| ... | ... |+----------+----------+--------+---------+----------+-------+-------+

[Illustration: 1942 Horse-power Installationof Babcock & Wilcox Boilers andSuperheaters in the Singer Building, NewYork City]

CLASSIFICATION OF FUELS

(WITH PARTICULAR REFERENCE TOCOAL)

Fuels for steam boilers may be classifiedas solid, liquid or gaseous. Of the solidfuels, anthracite and bituminous coals arethe most common, but in this class mustalso be included lignite, peat, wood,bagasse and the refuse from certainindustrial processes such as sawdust,shavings, tan bark and the like. Straw, cornand coffee husks are utilized in isolatedcases.

The class of liquid fuels is representedchiefly by petroleum, though coal tar andwater-gas tar are used to a limited extent.

Gaseous fuels are limited to natural gas,

blast furnace gas and coke oven gas, thefirst being a natural product and the twolatter by-products from industrialprocesses. Though waste gases fromcertain processes may be considered asgaseous fuels, inasmuch as the question ofcombustion does not enter, the methods ofutilizing them differ from that forcombustible gaseous fuel, and thequestion will be dealt with separately.

Since coal is by far the most generallyused of all fuels, this chapter will bedevoted entirely to the formation,composition and distribution of the variousgrades, from anthracite to peat. The otherfuels will be discussed in succeedingchapters and their combustion dealt within connection with their composition.

Formation of Coal--All coals are ofvegetable origin and are the remains of

prehistoric forests. Destructive distillationdue to great pressures and temperatures,has resolved the organic matter into itsinvariable ultimate constituents, carbon,hydrogen, oxygen and other substances,in varying proportions. The factors of time,depth of beds, disturbance of beds and theintrusion of mineral matter resulting fromsuch disturbances have produced thevariation in the degree of evolution fromvegetable fiber to hard coal. This variationis shown chiefly in the content of carbon,and Table 35 shows the steps of suchvariation.

TABLE 35

APPROXIMATE CHEMICAL CHANGESFROM WOOD FIBER TOANTHRACITE COAL

+----------------------+-------+--------+-------+

|Substance |Carbon|Hydrogen|Oxygen |+----------------------+-------+--------+-------+|Wood Fiber | 52.65 | 5.25 | 42.10| |Peat | 59.57 | 5.96 | 34.47 ||Lignite | 66.04 | 5.27 | 28.69 ||Earthy Brown Coal | 73.18 | 5.68 |21.14 | |Bituminous Coal | 75.06 | 5.84| 19.10 | |Semi-bituminous Coal | 89.29 |5.05 | 5.66 | |Anthracite Coal | 91.58

| 3.96 | 4.46 |+----------------------+-------+--------+-------+

Composition of Coal--The uncombinedcarbon in coal is known as fixed carbon.Some of the carbon constituent iscombined with hydrogen and this,together with other gaseous substancesdriven off by the application of heat, formthat portion of the coal known as volatilematter. The fixed carbon and the volatilematter constitute the combustible. The

oxygen and nitrogen contained in thevolatile matter are not combustible, butcustom has applied this term to thatportion of the coal which is dry and freefrom ash, thus including the oxygen andnitrogen.

The other important substances enteringinto the composition of coal are moistureand the refractory earths which form theash. The ash varies in different coals from 3to 30 per cent and the moisture from 0.75to 45 per cent of the total weight of thecoal, depending upon the grade and thelocality in which it is mined. A largepercentage of ash is undesirable as it notonly reduces the calorific value of the fuel,but chokes up the air passages in thefurnace and through the fuel bed, thuspreventing the rapid combustionnecessary to high efficiency. If the coalcontains an excessive quantity of sulphur,

trouble will result from its harmful actionon the metal of the boiler where moistureis present, and because it unites with theash to form a fusible slag or clinker whichwill choke up the grate bars and form asolid mass in which large quantities ofunconsumed carbon may be imbedded.

Moisture in coal may be more detrimentalthan ash in reducing the temperature of afurnace, as it is non-combustible, absorbsheat both in being evaporated andsuperheated to the temperature of thefurnace gases. In some instances,however, a certain amount of moisture in abituminous coal produces a mechanicalaction that assists in the combustion andmakes it possible to develop highercapacities than with dry coal.

Classification of Coal--Custom hasclassified coals in accordance with the

varying content of carbon and volatilematter in the combustible. Table 36 givesthe approximate percentages of theseconstituents for the general classes ofcoals with the corresponding heat valuesper pound of combustible.

TABLE 36

APPROXIMATE COMPOSITION ANDCALORIFIC VALUE OF GENERALGRADES OF COAL ON BASIS OFCOMBUSTIBLE

+-------------------+----------------------------+--------------+ | Kind of Coal | Per Cent ofCombustible | B. t. u. | |+------------+---------------+ Per Pound of | |

|Fixed Carbon|Volatile Matter|Combustible |+-------------------+------------+---------------+--------------+ |Anthracite |97.0 to 92.5|

3.0 to 7.5 |14600 to 14800||Semi-anthracite |92.5 to 87.5| 7.5 to12.5 |14700 to 15500| |Semi-bituminous|87.5 to 75.0| 12.5 to 25.0 |15500 to16000| |Bituminous--Eastern|75.0 to 60.0|25.0 to 40.0 |14800 to 15300||Bituminous--Western|65.0 to 50.0| 35.0 to50.0 |13500 to 14800| |Lignite |Under 50 | Over 50 |11000 to 13500|+-------------------+------------+---------------+--------------+

Anthracite--The name anthracite, or hardcoal, is applied to those dry coalscontaining from 3 to 7 per cent volatilematter and which do not swell whenburned. True anthracite is hard, compact,lustrous and sometimes iridescent, and ischaracterized by few joints and clefts. Itsspecific gravity varies from 1.4 to 1.8. Inburning, it kindles slowly and with

difficulty, is hard to keep alight, and burnswith a short, almost colorless flame,without smoke.

Semi-anthracite coal has less density,hardness and luster than true anthracite,and can be distinguished from it by thefact that when newly fractured it will sootthe hands. Its specific gravity is ordinarilyabout 1.4. It kindles quite readily andburns more freely than the trueanthracites.

Semi-bituminous coal is softer thananthracite, contains more volatilehydrocarbons, kindles more easily andburns more rapidly. It is ordinarily freeburning, has a high calorific value and is ofthe highest order for steam generatingpurposes.

Bituminous coals are still softer than thosedescribed and contain still more volatilehydrocarbons. The difference between thesemi-bituminous and the bituminous coalsis an important one, economically. Theformer have an average heating value perpound of combustible about 6 per centhigher than the latter, and they burn withmuch less smoke in ordinary furnaces. Thedistinctive characteristic of the bituminouscoals is the emission of yellow flame andsmoke when burning. In color they rangefrom pitch black to dark brown, having aresinous luster in the most compactspecimens, and a silky luster in suchspecimens as show traces of vegetablefiber. The specific gravity is ordinarilyabout 1.3.

Bituminous coals are either of the caking

or non-caking class. The former, whenheated, fuse and swell in size; the latterburn freely, do not fuse, and arecommonly known as free burning coals.Caking coals are rich in volatilehydrocarbons and are valuable in gasmanufacture.

Bituminous coals absorb moisture from theatmosphere. The surface moisture can beremoved by ordinary drying, but a portionof the water can be removed only byheating the coal to a temperature of about250 degrees Fahrenheit.

Cannel coal is a variety of bituminous coal,rich in hydrogen and hydrocarbons, and isexceedingly valuable as a gas coal. It has adull resinous luster and burns with a brightflame without fusing. Cannel coal isseldom used for steam coal, though it issometimes mixed with semi-bituminous

coal where an increased economy at highrates of combustion is desired. Thecomposition of cannel coal isapproximately as follows: fixed carbon, 26to 55 per cent; volatile matter, 42 to 64 percent; earthy matter, 2 to 14 per cent. Itsspecific gravity is approximately 1.24.

Lignite is organic matter in the earlierstages of its conversion into coal, andincludes all varieties which areintermediate between peat and coal of theolder formation. Its specific gravity is low,being 1.2 to 1.23, and when freshly minedit may contain as high as 50 per cent ofmoisture. Its appearance varies from alight brown, showing a distinctly woodystructure, in the poorer varieties, to ablack, with a pitchy luster resembling hardcoal, in the best varieties. It is non-cakingand burns with a bright but slightly smokyflame with moderate heat. It is easily

broken, will not stand much handling intransportation, and if exposed to theweather will rapidly disintegrate, whichwill increase the difficulty of burning it.

Its composition varies over wide limits.The ash may run as low as one per centand as high as 50 per cent. Its high contentof moisture and the large quantity of airnecessary for its combustion cause largestack losses. It is distinctly a low-gradefuel and is used almost entirely in thedistricts where mined, due to itscheapness.

Peat is organic matter in the first stages ofits conversion into coal and is found inbogs and similar places. Its moisturecontent when cut is extremely high,averaging 75 or 80 per cent. It isunsuitable for fuel until dried and eventhen will contain as much as 30 per cent

moisture. Its ash content when dry variesfrom 3 to 12 per cent. In this country,though large deposits of peat have beenfound, it has not as yet been foundpracticable to utilize it for steamgenerating purposes in competition withcoal. In some European countries,however, the peat industry is common.

Distribution--The anthracite coals are, withsome unimportant exceptions, confined tofive small fields in Eastern Pennsylvania,as shown in the following list. These fieldsare given in the order of their hardness.

Lehigh or Eastern Middle Field GreenMountain District Black Creek DistrictHazelton District Beaver Meadow DistrictPanther Creek District[33]

Mahanoy or Western Field[34] EastMahanoy District West Mahanoy District

Wyoming or Northern Field CarbondaleDistrict Scranton District Pittston District Wilkesbarre District Plymouth District

Schuylkill or Southern Field EastSchuylkill District West Schuylkill District Louberry District

Lykens Valley or Southwestern FieldLykens Valley District ShamokinDistrict[35]

Anthracite is also found in Pulaski andWythe Counties, Virginia; along theborder of Little Walker Mountain, and inGunnison County, Colorado. The areas inVirginia are limited, however, while inColorado the quality varies greatly inneighboring beds and even in the samebed. An anthracite bed in New Mexico wasdescribed in 1870 by Dr. R. W. Raymond,

formerly United States MiningCommissioner.

Semi-anthracite coals are found in a fewsmall areas in the western part of theanthracite field. The largest of these bedsis the Bernice in Sullivan County,Pennsylvania. Mr. William Kent, in his"Steam Boiler Economy", describes this asfollows: "The Bernice semi-anthracite coalbasin lies between Beech Creek on thenorth and Loyalsock Creek on the south. Itis six miles long, east and west, and hardlya third of a mile across. An 8-foot vein ofcoal lies in a bed of 12 feet of coal andslate. The coal of this bed is the dividingline between anthracite andsemi-anthracite, and is similar to the coalof the Lykens Valley District. Mineanalyses give a range as follows: moisture,0.65 to 1.97; volatile matter, 3.56 to 9.40;fixed carbon, 82.52 to 89.39; ash, 3.27 to

9.34; sulphur, 0.24 to 1.04."

Semi-bituminous coals are found on theeastern edge of the great AppalachianField. Starting with Tioga and BradfordCounties of northern Pennsylvania, thebed runs southwest through Lycoming,Clearfield, Centre, Huntingdon, Cambria,Somerset and Fulton Counties,Pennsylvania; Allegheny County,Maryland; Buchannan, Dickinson, Lee,Russell, Scott, Tazewell and Wise Counties,Virginia; Mercer, McDowell, Fayette,Raleigh and Mineral Counties, WestVirginia; and ending in northeasternTennessee, where a small amount ofsemi-bituminous is mined.

The largest of the bituminous fields is theAppalachian. Beginning near the northernboundary of Pennsylvania, in the westernportion of the State, it extends

southwestward through West Virginia,touching Maryland and Virginia on theirwestern borders, passing throughsoutheastern Ohio, eastern Kentucky andcentral Tennessee, and ending in westernAlabama, 900 miles from its northernextremity.

The next bituminous coal producingregion to the west is the Northern Field, innorth central Michigan. Still further to thewest, and second in importance to theAppalachian Field, is the Eastern InteriorField. This covers, with the exception ofthe upper northern portion, nearly theentire State of Illinois, southwest Indianaand the western portion of Kentucky.

The Western Field extends through centraland southern Iowa, western Missouri,southwestern Kansas, eastern Oklahomaand the west central portion of Arkansas.

The Southwestern Field is confinedentirely to the north central portion ofTexas, in which State there are also twosmall isolated fields along the Rio GrandeRiver.

The remaining bituminous fields arescattered through what may be termed theRocky Mountain Region, extending fromMontana to New Orleans. A partial list ofthese fields and their location follows:

Judith Basin Central Montana BullMountain Field Central MontanaYellowstone Region SouthwesternMontana Big Horn Basin RegionSouthern Montana Big Horn Basin RegionNorthern Wyoming Black Hills Region

Northeastern Wyoming Hanna FieldSouthern Wyoming Green River Region

Southwestern Wyoming Yampa FieldNorthwestern Colorado North Park

Field Northern Colorado DenverRegion North Central ColoradoUinta Region Western ColoradoUinta Region Eastern UtahSouthwestern Region SouthwesternUtah Raton Mountain Region SouthernColorado Raton Mountain RegionNorthern New Mexico San Juan RiverRegion Northwestern New MexicoCapitan Field Southern New Mexico

Along the Pacific Coast a few small fieldsare scattered in western California,southwestern Oregon, western andnorthwestern Washington.

Most of the coals in the above fields are onthe border line between bituminous andlignite. They are really a low grade ofbituminous coal and are known assub-bituminous or black lignites.

Lignites--These resemble the brown coalsof Europe and are found in the westernstates, Wyoming, New Mexico, Arizona,Utah, Montana, North Dakota, Nevada,California, Oregon and Washington. Manyof the fields given as those containingbituminous coals in the western states alsocontain true lignite. Lignite is also found inthe eastern part of Texas and in Oklahoma.

Alaska Coals--Coal has been found inAlaska and undoubtedly is of great value,though the extent and character of thefields have probably been exaggerated.Great quantities of lignite are known toexist, and in quality the coal ranges incharacter from lignite to anthracite. Thereare at present, however, only two fields ofhigh-grade coals known, these being theBering River Field, near Controllers Bay,and the Matanuska Field, at the head ofCooks Inlet. Both of these fields are known

to contain both anthracite and high-gradebituminous coals, though as yet theycannot be said to have been opened up.

Weathering of Coal--The storage of coalhas become within the last few years to acertain extent a necessity due to marketconditions, danger of labor difficulties atthe mines and in the railroads, and thecrowding of transportation facilities. Thefirst cause is probably the most important,and this is particularly true of anthracitecoals where a sliding scale of prices isused according to the season of the year.While market conditions serve as one ofthe principal reasons for coal storage,most power plants and manufacturingplants feel compelled to protect their coalsupply from the danger of strikes, carshortages and the like, and it is customaryfor large power plants, railroads and coalcompanies themselves, to store

bituminous coal. Naval coaling stations arealso an example of what is done alongthese lines.

Anthracite is the nearest approach to theideal coal for storing. It is not subject tospontaneous ignition, and for this reason isunlimited in the amount that may be storedin one pile. With bituminous coals,however, the case is different. Mostbituminous coals will ignite if placed inlarge enough piles and all suffer more orless from disintegration. Coal producersonly store such coals as are least liable toignite, and which will stand rehandling forshipment.

The changes which take place in storedcoal are of two kinds: 1st, the oxidization ofthe inorganic matter such as pyrites; and2nd, the direct oxidization of the organicmatter of the actual coal.

The first change will result in an increasedvolume of the coal, and sometimes in anincreased weight, and a markeddisintegration. The changes due to directoxidization of the coal substances usuallycannot be detected by the eye, but as theyinvolve the oxidization of the carbon andavailable hydrogen and the absorption ofthe oxygen by unsaturated hydrocarbons,they are the chief cause of the weatheringlosses in heat value. Numerousexperiments have led to the conclusionthat this is also the cause for spontaneouscombustion.

Experiments to show loss in calorific heatvalues due to weathering indicate thatsuch loss may be as high as 10 per centwhen the coal is stored in the air, and 8.75per cent when stored under water. Itwould appear that the higher the volatile

content of the coal, the greater will be theloss in calorific value and the more subjectto spontaneous ignition.

Some experiments made by Messrs. S. W.Parr and W. F. Wheeler, published in 1909by the Experiment Station of the Universityof Illinois, indicate that coals of the naturefound in Illinois and neighboring states arenot affected seriously during storage fromthe standpoint of weight and heating value,the latter loss averaging about 3� per centfor the first year of storage. They foundthat the losses due to disintegration and tospontaneous ignition were of greaterimportance. Their conclusions agree withthose deduced from the otherexperiments, viz., that the storing of alarger size coal than that which is to beused, will overcome to a certain extent theobjection to disintegration, and that thelarger sizes, besides being advantageous

in respect to disintegration, are less liableto spontaneous ignition. Storage underwater will, of course, entirely prevent anyfire loss and, to a great extent, will stopdisintegration and reduce the calorificlosses to a minimum.

To minimize the danger of spontaneousignition in storing coal, the piles should bethoroughly ventilated.

Pulverized Fuels--Considerableexperimental work has been done withpulverized coal, utilizing either coal dustor pulverizing such coal as is too small tobe burned in other ways. If satisfactorilyfed to the furnace, it would appear to haveseveral advantages. The dust burned insuspension would be more completelyconsumed than is the case with the solidcoals, the production of smoke would beminimized, and the process would admit of

an adjustment of the air supply to a pointvery close to the amount theoreticallyrequired. This is due to the fact that inburning there is an intimate mixture of theair and fuel. The principal objections havebeen in the inability to introduce thepulverized fuel into the furnace uniformly,the difficulty of reducing the fuel to thesame degree of fineness, liability ofexplosion in the furnace due to impropermixture with the air, and the decreasedcapacity and efficiency resulting from thedifficulty of keeping tube surfaces clean.

Pressed Fuels--In this class are thosecomposed of the dust of some suitablecombustible, pressed and cementedtogether by a substance possessingbinding and in most cases inflammableproperties. Such fuels, known asbriquettes, are extensively used in foreigncountries and consist of carbon or soft

coal, too small to be burned in theordinary way, mixed usually with pitch orcoal tar. Much experimenting has beendone in this country in briquetting fuels,the government having taken an activeinterest in the question, but as yet thisclass of fuel has not come into common useas the cost and difficulty of manufactureand handling have made it impossible toplace it in the market at a price tosuccessfully compete with coal.

Coke is a porous product consisting almostentirely of carbon remaining after certainmanufacturing processes have distilled offthe hydrocarbon gases of the fuel used. Itis produced, first, from gas coal distilled ingas retorts; second, from gas or ordinarybituminous coals burned in specialfurnaces called coke ovens; and third,from petroleum by carrying the distillationof the residuum to a red heat.

Coke is a smokeless fuel. It readilyabsorbs moisture from the atmosphereand if not kept under cover its moisturecontent may be as much as 20 per cent ofits own weight.

Gas-house coke is generally softer andmore porous than oven coke, ignites morereadily, and requires less draft for itscombustion.

[Illustration: 16,000 Horse-powerInstallation of Babcock & Wilcox Boilersand Superheaters at the Brunot's IslandPlant of the Duquesne Light Co.,Pittsburgh, Pa.]

THE DETERMINATION OF HEATINGVALUES OF FUELS

The heating value of a fuel may bedetermined either by a calculation from achemical analysis or by burning a samplein a calorimeter.

In the former method the calculationshould be based on an ultimate analysis,which reduces the fuel to its elementaryconstituents of carbon, hydrogen, oxygen,nitrogen, sulphur, ash and moisture, tosecure a reasonable degree of accuracy. Aproximate analysis, which determines onlythe percentage of moisture, fixed carbon,volatile matter and ash, withoutdetermining the ultimate composition ofthe volatile matter, cannot be used forcomputing the heat of combustion with thesame degree of accuracy as an ultimate

analysis, but estimates may be based onthe ultimate analysis that are fairly correct.

An ultimate analysis requires the servicesof a competent chemist, and the methodsto be employed in such a determinationwill be found in any standard book onengineering chemistry. An ultimateanalysis, while resolving the fuel into itselementary constituents, does not revealhow these may have been combined in thefuel. The manner of their combinationundoubtedly has a direct effect upon theircalorific value, as fuels having almostidentical ultimate analyses show adifference in heating value when tested ina calorimeter. Such a difference, however,is slight, and very close approximationsmay be computed from the ultimateanalysis.

Ultimate analyses are given on both a

moist and a dry fuel basis. Inasmuch as thelatter is the basis generally accepted forthe comparison of data, it would appearthat it is the best basis on which to reportsuch an analysis. When an analysis isgiven on a moist fuel basis it may bereadily converted to a dry basis bydividing the percentages of the variousconstituents by one minus the percentageof moisture, reporting the moisture contentseparately.

_Moist Fuel_ _Dry Fuel_

C 83.95 84.45 H 4.234.25 O 3.02 3.04 N 1.271.28 S .91 .91 Ash 6.03

6.07 ------ 100.00

Moisture .59 .59 ------100.00

Calculations from an UltimateAnalysis--The first formula for thecalculation of heating values from thecomposition of a fuel as determined froman ultimate analysis is due to Dulong, andthis formula, slightly modified, is the mostcommonly used to-day. Other formulaehave been proposed, some of which aremore accurate for certain specific classesof fuel, but all have their basis in Dulong'sformula, the accepted modified form ofwhich is:

Heat units in B. t. u. per pound of dry fuel =

O 14,600 C + 62,000(H - -) +4000 S (18) 8

where C, H, O and S are the proportionateparts by weight of carbon, hydrogen,oxygen and sulphur.

Assume a coal of the composition given.Substituting in this formula (18),

Heating value per pound of dry coal

( .0304) = 14,600 �.8445+ 62,000 (.0425 - -----) + 4000 �.0091 =14,765 B. t. u. ( 8 )

This coal, by a calorimetric test, showed14,843 B. t. u., and from a comparison thedegree of accuracy of the formula will benoted.

The investigation of Lord and Haas in thiscountry, Mabler in France, and Bunte inGermany, all show that Dulong's formulagives results nearly identical with thoseobtained from calorimetric tests and maybe safely applied to all solid fuels exceptcannel coal, lignite, turf and wood,provided the ultimate analysis is correct.

This practically limits its use to coal. Thelimiting features are the presence ofhydrogen and carbon united in the form ofhydrocarbons. Such hydrocarbons arepresent in coals in small quantities, butthey have positive and negative heats ofcombination, and in coals these appear tooffset each other, certainly sufficiently toapply the formula to such fuels.

High and Low Heat Value of Fuels--In anyfuel containing hydrogen the calorificvalue as found by the calorimeter is higherthan that obtainable under most workingconditions in boiler practice by an amountequal to the latent heat of the volatilizationof water. This heat would reappear whenthe vapor was condensed, though inordinary practice the vapor passes awayuncondensed. This fact gives rise to adistinction in heat values into the so-called"higher" and "lower" calorific values. The

higher value, _i. e._, the one determinedby the calorimeter, is the only scientificunit, is the value which should be used inboiler testing work, and is the onerecommended by the American Society ofMechanical Engineers.

There is no absolute measure of the lowerheat of combustion, and in view of thewide difference in opinion amongphysicists as to the deductions to be madefrom the higher or absolute unit in thisdetermination, the lower value must beconsidered an artificial unit. The lowervalue entails the use of an ultimate analysisand involves assumptions that would makethe employment of such a unitimpracticable for commercial work. Theuse of the low value may also lead to errorand is in no way to be recommended forboiler practice.

An example of its illogical use may beshown by the consideration of a boileroperated in connection with a specialeconomizer where the vapor produced byhydrogen is partially condensed by theeconomizer. If the low value were used incomputing the boiler efficiency, it isobvious that the total efficiency of thecombined boiler and economizer must bein error through crediting the combinationwith the heat imparted in condensing thevapor and not charging such heat to theheat value of the coal.

Heating Value of Gaseous Fuels--Themethod of computing calorific values froman ultimate analysis is particularly adaptedto solid fuels, with the exceptions alreadynoted. The heating value of gaseous fuelsmay be calculated by Dulong's formulaprovided another term is added to providefor any carbon monoxide present. Such a

method, however, involves the separatingof the constituent gases into theirelementary gases, which is oftentimesdifficult and liable to simple arithmeticalerror. As the combustible portion ofgaseous fuels is ordinarily composed ofhydrogen, carbon monoxide and certainhydrocarbons, a determination of thecalorific value is much more readilyobtained by a separation into theirconstituent gases and a computation of thecalorific value from a table of such valuesof the constituents. Table 37 gives thecalorific value of the more commoncombustible gases, together with thetheoretical amount of air required for theircombustion.

TABLE 37

WEIGHT AND CALORIFIC VALUEOF VARIOUS GASES AT 32 DEGREES

FAHRENHEIT AND ATMOSPHERICPRESSURE WITH THEORETICALAMOUNT OF AIR REQUIRED FORCOMBUSTION

+---------------+----------+------+-----+------+----------+-----------+ | Gas | Symbol|Cubic |B.t.u|B.t.u.|Cubic Feet|CubicFeet | | | | Feet | per | per |of Air | of Air | | | |ofGas|Pound|Cubic | Required | Required| | | | per | | Foot |perPound | Per Cubic | | ||Pound | | | of Gas |Foot of Gas|+---------------+----------+------+-----+------+----------+-----------+ |Hydrogen | H|177.90|62000| 349 | 428.25 | 2.41 ||Carbon Monoxide| CO | 12.81| 4450|347 | 30.60 | 2.39 | |Methane

|CH_{4} | 22.37|23550| 1053 | 214.00 |9.57 | |Acetylene |C_{2}H_{2}|

13.79|21465| 1556 | 164.87 | 11.93 |

|Olefiant Gas |C_{2}H_{4}| 12.80|21440|1675 | 183.60 | 14.33 | |Ethane|C_{2}H_{6}| 11.94|22230| 1862 | 199.88| 16.74 |+---------------+----------+------+-----+------+----------+-----------+

In applying this table, as gas analyses maybe reported either by weight or volume,there is given in Table 33[36] a method ofchanging from volumetric analysis toanalysis by weight.

Examples:

1st. Assume a blast furnace gas, theanalysis of which in percentages by weightis, oxygen = 2.7, carbon monoxide = 19.5,carbon dioxide = 18.7, nitrogen = 59.1.Here the only combustible gas is the

carbon monoxide, and the heat value willbe,

0.195 �4450 = 867.75 B. t. u. per pound.

The _net_ volume of air required to burnone pound of this gas will be,

0.195 �30.6 = 5.967 cubic feet.

2nd. Assume a natural gas, the analysis ofwhich in percentages by volume is oxygen= 0.40, carbon monoxide = 0.95, carbondioxide = 0.34, olefiant gas (C_{2}H_{4}) =0.66, ethane (C_{2}H_{6}) = 3.55, marsh gas(CH_{4}) = 72.15 and hydrogen = 21.95. Allbut the oxygen and the carbon dioxide arecombustibles, and the heat per cubic footwill be,

From CO = 0.0095 � 347 = 3.30

C_{2}H_{4} = 0.0066 �1675 = 11.05C_{2}H_{6} = 0.0355 �1862 = 66.10CH_{4} = 0.7215 �1050 = 757.58 H= 0.2195 � 349 = 76.61

------ B. t. u. per cubic foot 914.64

The _net_ air required for combustion ofone cubic foot of the gas will be,

CO = 0.0095 � 2.39 = 0.02 C_{2}H_{4}= 0.0066 �14.33 = 0.09 C_{2}H_{6} = 0.0355�16.74 = 0.59 CH_{4} = 0.7215 � 9.57 =6.90 H = 0.2195 � 2.41 = 0.53

---- Total net air per cubic foot8.13

Proximate Analysis--The proximateanalysis of a fuel gives its proportions byweight of fixed carbon, volatilecombustible matter, moisture and ash. Amethod of making such an analysis whichhas been found to give eminently

satisfactory results is described below.

From the coal sample obtained on theboiler trial, an average sample ofapproximately 40 grams is broken up andweighed. A good means of reducing sucha sample is passing it through an ordinarycoffee mill. This sample should be placedin a double-walled air bath, which shouldbe kept at an approximately constanttemperature of 105 degrees centigrade,the sample being weighed at intervalsuntil a minimum is reached. Thepercentage of moisture can be calculatedfrom the loss in such a drying.

For the determination of the remainder ofthe analysis, and the heating value of thefuel, a portion of this dried sample shouldbe thoroughly pulverized, and if it is to bekept, should be placed in an air-tightreceptacle. One gram of the pulverized

sample should be weighed into aporcelain crucible equipped with a wellfitting lid. This crucible should besupported on a platinum triangle andheated for seven minutes over the fullflame of a Bunsen burner. At the end ofsuch time the sample should be placed in adesiccator containing calcium chloride,and when cooled should be weighed.From the loss the percentage of volatilecombustible matter may be readilycalculated.

The same sample from which the volatilematter has been driven should be used inthe determination of the percentage of ash.This percentage is obtained by burningthe fixed carbon over a Bunsen burner orin a muffle furnace. The burning should bekept up until a constant weight is secured,and it may be assisted by stirring with aplatinum rod. The weight of the residue

determines the percentage of ash, and thepercentage of fixed carbon is easilycalculated from the loss during thedetermination of ash after the volatilematter has been driven off.

Proximate analyses may be made andreported on a moist or dry basis. The drybasis is that ordinarily accepted, and thisis the basis adopted throughout this book.The method of converting from a moist to adry basis is the same as described in thecase of an ultimate analysis. A proximateanalysis is easily made, gives informationas to the general characteristics of a fueland of its _relative_ heating value.

Table 38 gives the proximate analysis andcalorific value of a number ofrepresentative coals found in the UnitedStates.

TABLE 38

APPROXIMATE COMPOSITION ANDCALORIFIC VALUE OF CERTAIN TYPICALAMERICAN COALS

____________________________________________________________________________| | | | || | | | | |

| No. | State | County | Field, Bed| Mine | Size | | | |or Vein | | | | |

| | | | | || | | |

____|_______|________________|________________|_______________|_____________|

| | || | | ANTHRACITES

| |____|_______|_________________________________________________|_____________|

| | | | || 1 | Pa. | Carbon | Lehigh |Beaver Meadow | | 2 | Pa. |Dauphin | Schuylkill | |Buckwheat | 3 | Pa. | Lackawanna |Wyoming | Belleview | No. 2 Buck. |

4 | Pa. | Lackawanna | Wyoming |Johnson | Culm. | 5 | Pa. |Luzerne | Wyoming | Pittston |No. 2 Buck. | 6 | Pa. | Luzerne |Wyoming | Mammoth | Large |7 | Pa. | Luzerne | Wyoming |

Exeter | Rice | 8 | Pa. |Northumberland | Schuylkill | Treverton

| | 9 | Pa. | Schuylkill |Schuylkill | Buck Mountain | | 10| Pa. | Schuylkill | | York Farm

| Buckwheat | 11 | Pa. | || Victoria | Buckwheat | 12 | Pa.

| Carbon | Lehigh | Lehigh & |Buck. & Pea | | | | |Wilkes C. Co. | | 13 | Pa. |

Carbon | Lehigh | |Buckwheat | 14 | Pa. | Lackawanna |

|Del. & Hud. Co.| No. 1 Buck. |____|_______|________________|________________|_______________|_____________|

| | || | | SEMI-ANTHRACITES

| |____|_______|_________________________________________________|_____________|| | | | |

| 15 | Pa. | Lycoming | Loyalsock || | 16 | Pa. | Sullivan || Lopez | | 17 | Pa. |

Sullivan | Bernice | ||____|_______|________________|________________|_______________|_____________|

| | || | | SEMI-BITUMINOUS

| |____|_______|__________________________

_______________________|_____________|| | | | |

| 18 | Md. | Alleghany | Big Vein, || | | | |

George's Crk. | | | 19 |Md. | Alleghany | George's Creek |

| | 20 | Md. | Alleghany |George's Creek | | | 21 |Md. | Alleghany | George's Creek |Ocean No. 7 | Mine run | 22 | Md. |Alleghany | Cumberland | |

| 23 | Md. | Garrett | |Washington | Mine run | | |

| | No. 3 | | 24 | Pa.| Bradford | | Long Valley |

| 25 | Pa. | Tioga | |Antrim | | 26 | Pa. | Cambria

| "B" or Miller | Soriman Shaft | || | | | C. Co. |

| 27 | Pa. | Cambria | "B" orMiller | Henrietta | | 28 | Pa. |Cambria | "B" or Miller | Penker |

| 29 | Pa. | Cambria | "B" orMiller | Lancashire | | 30 | Pa. |Cambria | Lower | Penn. C. & C.| Mine run | | | |Kittanning | Co. No. 3 | | 31 |Pa. | Cambria | Upper | Valley

| Mine run | | | |Kittanning | | | 32 | Pa. |Clearfield | Lower | Eureka |Mine run | | | | Kittanning

| | | 33 | Pa. | Clearfield| | Ghem | Mine run | 34

| Pa. | Clearfield | | Osceola| | 35 | Pa. | Clearfield |

Reynoldsville | | | 36 | Pa.| Clearfield | Atlantic- | |

Mine run | | | | Clearfield| | | 37 | Pa. | Huntington

| Barnet & Fulton| Carbon | Minerun | 38 | Pa. | Huntington || Rock Hill | Mine run | 39 | Pa. |Somerset | Lower | Kimmelton |

Mine run | | | | Kittanning| | | 40 | Pa. | Somerset| "C" Prime Vein | Jenner | Mine run

|____|_______|________________|________________|_______________|_____________|

_____________________________________________________________________ |

| | | |Proximate Analysis (Dry Coal) |B. t. u.|

| No.|________________________________________| Per | | | | | |

| Pound | Authority | | Moisture |Volatile | Fixed | Ash | Dry | |

| | Matter | Carbon | | Coal ||

____|__________|__________|________|_________|________|______________| || | | | | | || | | | | |

____|__________|__________|________|_________|________|______________| || | | | | | 1 |1.50 | 2.41 | 90.30 | 7.29 | | Gale

| 2 | 2.15 | 12.88 | 78.23 | 8.89| 13137 | Whitham | 3 | 8.29 | 7.81

| 77.19 | 15.00 | 12341 | Sadtler | 4| 13.90 | 11.16 | 65.96 | 22.88 |10591 | B. & W. Co. | 5 | 3.66 | 4.40| 78.96 | 16.64 | 12865 | B. & W. Co. |6 | 4.00 | 3.44 | 90.59 | 5.97 |13720 | Carpenter | 7 | 0.25 | 8.18| 79.61 | 12.21 | 12400 | B. & W. Co. |8 | 0.84 | 6.73 | 86.39 | 6.88 | |Isherwood | 9 | | 3.17 | 92.41 |4.42 | 14220 | Carpenter | 10 | 0.81 |

5.51 | 75.90 | 18.59 | 11430 | |11 | 4.30 | 0.55 | 86.73 | 12.72 |12642 | B. & W. Co. | 12 | 1.57 | 6.27| 66.53 | 27.20 | 12848 | B. & W. Co. || | | | | | |13 | | 5.00 | 81.00 | 14.00 | 11800

| Carpenter | 14 | 6.20 | | |11.60 | 12100 | Denton |____|__________|__________|________|_________|________|______________| || | | | | | || | | | | |____|__________|__________|________|_________|________|______________| || | | | | | 15 |1.30 | 8.72 | 84.44 | 6.84 | |

| 16 | 5.48 | 7.53 | 81.00 | 11.47 |13547 | B. & W. Co. | 17 | 1.29 | 8.21| 84.43 | 7.36 | | |____|__________|__________|________|_________|________|______________| || | | | | | || | | | | |____|__________|__________|________|_________|________|______________| || | | | | | 18 |3.50 | 21.33 | 72.47 | 6.20 | 14682 |B. & W. Co. | | | | | |

| | 19 | 3.63 | 16.27 | 76.93| 6.80 | 14695 | B. & W. Co. | 20 | 2.28

| 19.43 | 77.44 | 6.13 | 14793 | B. &W. Co. | 21 | 1.13 | | | |14451 | B. & W. Co. | 22 | 1.50 | 17.26| 76.65 | 6.09 | 14700 | | 23 |2.33 | 14.38 | 74.93 | 10.49 | 14033 |U. S. Geo. S.| | | | | |

| [37] | 24 | 1.55 | 20.33 |68.38 | 11.29 | 12965 | | 25 |2.19 | 18.43 | 71.87 | 9.70 | 13500 |

| 26 | 3.40 | 20.70 | 71.84 |7.46 | 14484 | N. Y. Ed. Co.| | |

| | | | | 27 | 1.23 |18.37 | 75.28 | 6.45 | 14770 | So. Eng.

Co. | 28 | 3.64 | 21.34 | 70.48 | 8.18| 14401 | B. & W. Co. | 29 | 4.38 |21.20 | 70.27 | 8.53 | 14453 | B. & W.Co. | 30 | 3.51 | 17.43 | 75.69 | 6.88| 14279 | U. S. Geo. S.| | | |

| | | | 31 | 3.40 |14.89 | 75.03 | 10.08 | 14152 | B. & W.

Co. | | | | | | || 32 | 5.90 | 16.71 | 77.22 | 6.07

| 14843 | U. S. Geo. S.| | | || | | | 33 | 3.43 |

17.53 | 69.67 | 12.80 | 13744 | B. & W.Co. | 34 | 1.24 | 25.43 | 68.56 | 6.01| 13589 | B. & W. Co. | 35 | 2.91 |

21.55 | 69.03 | 9.42 | 14685 | B. & W.Co. | 36 | 1.55 | 23.36 | 71.15 | 5.94| 13963 | Whitham | | | |

| | | | 37 | 4.50 |18.34 | 73.06 | 8.60 | 13770 | B. & W.Co. | 38 | 5.91 | 17.58 | 73.44 | 8.99| 14105 | B. & W. Co. | 39 | 3.09 |

17.84 | 70.47 | 11.69 | 13424 | U. S.Geo. S.| | | | | | |

| 40 | 9.37 | 16.47 | 75.76 |7.77 | 14507 | P. R. R. |____|__________|__________|________|_________|________|______________|

APPROXIMATE COMPOSITION AND

CALORIFIC VALUE OF CERTAIN TYPICALAMERICAN COALS--Continued

____________________________________________________________________________| | | | || | | | | |


| | | | | || | | |

____|_______|________________|________________|_______________|_____________|

| | | | || 41 | W. Va.| Fayette | New River| Rush Run | Mine run | 42 | W. Va.|Fayette | New River | Loup Creek| | 43 | W. Va.| Fayette | NewRiver | | Slack | 44 | W.Va.| Fayette | New River | |Mine run | 45 | W. Va.| Fayette |

New River | Rush Run | Mine run |46 | W. Va.| McDowell | Pocahontas| Zenith | Mine run | | || No. 3 | | | 47 | W.

Va.| McDowell | Tug River | BigSandy | Mine run | 48 | W. Va.|Mercer | Pocahontas | Mora |Lump | 49 | W. Va.| Mineral | ElkGarden | | | 50 | W. Va.|McDowell | Pocahontas | Flat Top| Mine run | 51 | W. Va.| McDowell |Pocahontas | Flat Top | Slack | 52| W. Va.| McDowell | Pocahontas |Flat Top | Lump |____|_______|________________|________________|_______________|_____________|

| | || | | BITUMINOUS

| |____|_______|_________________________________________________|_____________|| | | | |

| 53 | Ala. | Bibb | Cahaba |Hill Creek | Mine run | 54 | Ala. |Jefferson | Pratt | Pratt No. 13 |

| 55 | Ala. | Jefferson | Pratt |Warner | Mine run | 56 | Ala. |Jefferson | | Coalburg |Mine run | 57 | Ala. | Walker |Horse Creek | Ivy C. & I. | Nut | |

| | | Co. No. 8 || 58 | Ala. | Walker | Jagger |

Galloway C. | Mine run | | || | Co. No. 5 | | 59 |

Ark. | Franklin | Denning |Western No. 4 | Nut | 60 | Ark. |Sebastian | Jenny Lind | Mine No. 12| Lump | 61 | Ark. | Sebastian |Huntington | Cherokee | Mine run |62 | Col. | Boulder | South Platte |

Lafayette | Mine run | 63 | Col. |Boulder | Laramie | Simson |Mine run | 64 | Col. | Fremont |Canon City | Chandler | Nut and |

| | | | | Slack| 65 | Col. | Las Animas | Trinidad

| Hastings | Nut | 66 | Col. | LasAnimas | Trinidad | Moreley |Slack | 67 | Col. | Routt | Yampa

| Oak Creek | | 68 | Ill. |Christian | Pana | Penwell Col. |Lump | 69 | Ill. | Franklin | No. 6

| Benton | Egg | 70 | Ill. |Franklin | Big Muddy | Zeigler |� inch | 71 | Ill. | Jackson | BigMuddy | | | 72 | Ill. | LaSalle | Streator | | |73 | Ill. | La Salle | Streator |Marseilles | Mine run | 74 | Ill. |Macoupin | Nilwood | Mine No. 2| Screenings | 75 | Ill. | Macoupin |Mt. Olive | Mine No. 2 | Mine run |76 | Ill. | Madison | Belleville |Donk Bros. | Lump | 77 | Ill. |Madison | Glen Carbon | |Mine run | 78 | Ill. | Marion |

| Odin | Lump | 79 | Ill. |Mercer | Gilchrist | |Screenings | 80 | Ill. | Montgomery |Pana or No. 5 | Coffeen | Mine run |81 | Ill. | Peoria | No. 5 | Empire

| | 82 | Ill. | Perry | DuQuoin | Number 1 | Screenings |____|_______|________________|________________|_______________|_____________|

APPROXIMATE COMPOSITION ANDCALORIFIC VALUE OF CERTAIN TYPICALAMERICAN COALS--Continued

_____________________________________________________________________ |

| | | |Proximate Analysis (Dry Coal) |B. t.u.| | No.|________________________________________| Per | | | | | |

| Pound | Authority | | Moisture |

Volatile | Fixed | Ash | Dry | || | Matter | Carbon | | Coal |

|____|__________|__________|________|_________|________|______________| || | | | | | 41 |2.14 | 22.87 | 71.56 | 5.57 | 14959 |U. S. Geo. S.| 42 | 0.55 | 19.36 | 78.48| 2.16 | 14975 | Hill | 43 | 6.66 |20.94 | 73.16 | 5.90 | 14412 | B. & W.Co. | 44 | 2.16 | 17.82 | 75.66 | 6.52| 14786 | B. & W. Co. | 45 | 0.94 |

22.16 | 75.85 | 1.99 | 15007 | B. & W.Co. | 46 | 4.85 | 17.14 | 76.54 | 6.32| 14480 | U. S. Geo. S.| | | |

| | | | 47 | 1.58 |18.55 | 76.44 | 4.91 | 15170 | U. S.Geo. S.| 48 | 1.74 | 18.55 | 75.15 |6.30 | 15015 | U. S. Geo. S.| 49 | 2.10 |15.70 | 75.40 | 8.90 | 14195 | B. & W.

Co. | 50 | 0.52 | 24.02 | 74.59 | 1.39| 14490 | B. & W. Co. | 51 | 3.24 |

15.33 | 77.60 | 7.07 | 14653 | B. & W.Co. | 52 | 3.63 | 16.03 | 78.04 | 5.93

| 14956 | B. & W. Co. |____|__________|__________|________|_________|________|______________| || | | | | | || | | | | |____|__________|__________|________|_________|________|______________| || | | | | | 53 |6.19 | 28.58 | 55.60 | 15.82 | 12576 |B. & W. Co. | 54 | 4.29 | 25.78 | 67.68| 6.54 | 14482 | B. & W. Co. | 55 | 2.51

| 27.80 | 61.50 | 10.70 | 13628 | U. S.Geo. S.| 56 | 0.94 | 31.34 | 65.65 |3.01 | 14513 | B. & W. Co. | 57 | 2.56 |31.82 | 53.89 | 14.29 | 12937 | U. S.

Geo. S.| | | | | | || 58 | 4.83 | 34.65 | 51.12 |

14.03 | 12976 | U. S. Geo. S.| | || | | | | 59 | 2.22

| 12.83 | 75.35 | 11.82 | | U. S. Geo.

S.| 60 | 1.07 | 17.04 | 74.45 | 8.51 |14252 | U. S. Geo. S.| 61 | 0.97 | 19.87| 70.30 | 9.83 | 14159 | U. S. Geo. S.|62 | 19.48 | 38.80 | 49.00 | 12.20 |11939 | B. & W. Co. | 63 | 19.78 | 44.69| 48.62 | 6.69 | 12577 | U. S. Geo. S.|

64 | 9.37 | 38.10 | 51.75 | 10.15 |11850 | B. & W. Co. | | | || | | | 65 | 2.15 | 31.07| 53.40 | 15.53 | 12547 | B. & W. Co. |66 | 1.88 | 28.47 | 55.58 | 15.95 |12703 | B. & W. Co. | 67 | 6.67 | 42.91| 55.64 | 1.45 | | Hill | 68 |8.05 | 43.67 | 49.97 | 6.36 | 10900 |Jones | 69 | 8.31 | 34.52 | 54.05 |11.43 | 11727 | U. S. Geo. S.| 70 | 13.28| 31.97 | 57.37 | 10.66 | 12857 | U. S.Geo. S.| 71 | 4.85 | 31.55 | 62.19 |6.26 | 11466 | Breckenridge | 72 | 8.40| 41.76 | 51.42 | 6.82 | 11727 |

Breckenridge | 73 | 12.98 | 43.73 |49.13 | 7.14 | 10899 | B. & W. Co. | 74 |

13.34 | 34.75 | 44.55 | 20.70 | 10781| B. & W. Co. | 75 | 13.54 | 41.28 |46.30 | 12.42 | 10807 | U. S. Geo. S.| 76| 13.47 | 38.69 | 48.07 | 13.24 |12427 | U. S. Geo. S.| 77 | 9.78 | 38.18| 51.52 | 10.30 | 11672 | Bryan | 78| 6.20 | 42.91 | 49.06 | 8.03 | 11880| Breckenridge | 79 | 8.50 | 36.17 |41.64 | 22.19 | 10497 | Breckenridge |80 | 11.93 | 34.05 | 49.85 | 16.10 |10303 | U. S. Geo. S.| 81 | 17.64 | 31.91| 46.17 | 21.92 | 10705 | B. & W. Co. |

82 | 9.81 | 33.67 | 48.36 | 17.97 |11229 | B. & W. Co. |____|__________|__________|________|_________|________|______________|


_______________________________________

_____________________________________| | | | || | | | | |


| | | | | || | | |

|_______|________________|________________|_______________|_____________| |

| | | | |83 | Ill. | Perry | Du Quoin |Willis | Mine run | 84 | Ill. |Sangamon | | Pawnee |Slack | 85 | Ill. | St. Clair |Standard | Nigger Hollow | Mine run| 86 | Ill. | St. Clair | Standard |Maryville | Mine run | 87 | Ill. |Williamson | Big Muddy | Daws| Mine run | 88 | Ill. | Williamson |Carterville | Carterville | | |

| | or No. 7 | | |

Wapello | Wapello | |Lump | 103 | Kan. | Cherokee |Weir Pittsburgh| Southwestern | Lump| | | | | Dev. Co.

| | 104 | Kan. | Cherokee |Cherokee | | Screenings | 105| Kan. | Cherokee | Cherokee |

| Lump | 106 | Kan. | Linn |Boicourt | | Lump | 107 |Ky. | Bell | Straight Creek | Str. Ck.C. & | Mine run | | | |

| C. Co. | | 108 | Ky. |Hopkins | Bed No. 9 | Earlington |Lump | 109 | Ky. | Hopkins | BedNo. 9 | Barnsley | Mine run | 110 |Ky. | Hopkins | Vein No. 14 | Nebo

|Pea and Slack| 111 | Ky. | Johnson| Vein No. 1 | Miller's Creek| Mine run| 112 | Ky. | Mulenburg | Bed No. 9| Pierce |Pea and Slack| 113 | Ky. |

Pulaski | | Greensburg || 114 | Ky. | Webster | Bed No. 9

____|_______|________________|________________|_______________|_____________|

______________________________________________________________________ |


| No.|________________________________________| Per | | | | | |



____|__________|__________|________|_________|________|______________| || | | | | | 83 |7.22 | 33.06 | 53.97 | 12.97 | 11352 |U. S. Geo. S.| 84 | 4.81 | 41.53 | 39.62| 18.85 | 10220 | Jones | 85 | 14.39| 32.90 | 44.84 | 22.26 | 11059 | B. &W. Co. | 86 | 15.71 | 38.10 | 41.10 |

20.80 | 10999 | B. & W. Co. | 87 | 8.17| 34.33 | 52.50 | 13.17 | 12643 | U. S.Geo. S.| 88 | 4.66 | 35.65 | 56.86 |7.49 | 12286 | Univ. of Ill.| | || | | | | 89 | 11.91 |33.70 | 55.90 | 10.40 | 12932 | B. & W.Co. | | | | | | |

| 90 | 2.83 | 40.03 | 51.97 | 8.00| 13375 | Stillman | 91 | 0.83 | 39.70| 52.28 | 8.02 | 13248 | Jones | 92

| 6.17 | 35.42 | 53.55 | 11.03 | 11916| Dearborn | 93 | 10.73 | 35.75 |54.46 | 9.79 | 12911 | B. & W. Co. | 94 |10.72 | 44.02 | 46.33 | 9.65 | 11767 |

U. S. Geo. S.| 95 | 16.59 | 42.17 |48.44 | 9.59 | 13377 | U. S. Geo. S.| 96 |

2.28 | 34.95 | 50.50 | 14.55 | 11920 |Dearborn | 97 | 11.62 | 41.17 |46.76 | 12.07 | 12740 | U. S. Geo. S.| 98| 13.48 | 39.40 | 43.09 | 17.51 |11678 | U. S. Geo. S.| 99 | 16.01 | 37.82| 46.24 | 15.94 | 11963 | U. S. Geo. S.|

100 | 14.88 | 41.53 | 39.63 | 18.84 |11443 | U. S. Geo. S.| 101 | 12.44 | 41.27

| 40.86 | 17.87 | 11671 | U. S. Geo. S.|102 | 8.69 | 36.23 | 43.68 | 20.09 |11443 | U. S. Geo. S.| 103 | 4.31 | 33.88| 53.67 | 12.45 | 13144 | U. S. Geo. S.|| | | | | | |

104 | 6.16 | 35.56 | 46.90 | 17.54 |10175 | Jones | 105 | 1.81 | 34.77 |52.77 | 12.46 | 12557 | Jones | 106 |4.74 | 36.59 | 47.07 | 16.34 | 10392 |

Jones | 107 | 2.89 | 36.67 | 57.24 |6.09 | 14362 | U. S. Geo. S.| | |

| | | | | 108 | 6.89| 40.30 | 55.16 | 4.54 | 13381 | St. Col.Ky. | 109 | 7.92 | 40.53 | 48.70 | 10.77| 13036 | U. S. Geo. S.| 110 | 8.02 |

31.91 | 54.02 | 14.07 | 12448 | B. & W.Co. | 111 | 5.12 | 38.46 | 58.63 |2.91 | 13743 | U. S. Geo. S.| 112 | 9.22| 33.94 | 52.18 | 13.88 | 12229 | B. &W. Co. | 113 | 2.80 | 26.54 | 63.58 |

9.88 | 14095 | N. Y. Ed. Co.| 114 | 7.30| 31.08 | 60.72 | 8.20 | 13600 | B. & W.Co. | 115 | 3.82 | 31.82 | 58.78 |9.40 | 13175 | B. & W. Co. | 116 | 9.00| 30.55 | 46.26 | 23.19 | 9889 | B. & W.Co. | 117 | 7.28 | 37.62 | 43.83 |18.55 | 12109 | U. S. Geo. S.| 118 | 12.45| 39.39 | 48.47 | 12.14 | 12875 | Univ.

of Mo. | | | | | | || 119 | 8.58 | 41.78 | 45.99 |

12.23 | 12735 | Univ. of Mo. | 120 | 10.84| 31.72 | 55.29 | 12.99 | 12500 | Univ.

of Mo. | 121 | 9.45 | 36.72 | 52.20 |11.08 | 13180 | Univ. of Mo. | 122 | 13.09

| 37.83 | 42.95 | 19.22 | 11500 | U. S.Geo. S.| | | | | | |

| 123 | 12.24 | 45.69 | 47.98 |6.33 | 14197 | U. S. Geo. S.| | |

| | | | | 124 | 20.78| 39.36 | 50.00 | 10.64 | 12602 | U. S.Geo. S.| 125 | 12.17 | 36.31 | 51.17 |12.52 | 12126 | B. & W. Co. |

____|__________|__________|________|_________|________|______________|


____________________________________________________________________________| | | | || | | | | |


| | | | | || | | |

|_______|________________|________________|_______________|_____________| |

| | | | |126 | Ohio | Athens | Hocking Valley| Sunday Creek | Slack | 127 | Ohio |Belmont | Pittsburgh | Neff Coal Co.

| Mine run | | | | No. 8| | | 128 | Ohio |

Columbiana | Middle | Palestine| | | | | Kittanning |

| | 129 | Ohio | Coshocton| Middle | Morgan Run | Mine run

| | | | Kittanning || | 130 | Ohio | Guernsey |Vein No. 7 | Little Kate | | 131 |Ohio | Hocking | Hocking Valley |

| Lump | 132 | Ohio | Hocking| Hocking Valley | | | 133 |Ohio | Jackson | Brookville |Superior | Mine run | | || | Coal Co. | | 134 |Ohio | Jackson | Lower |Superior | Mine run | | || Kittanning | Coal Co. | | 135| Ohio | Jackson | Quakertown |Wellston | | 136 | Ohio |Jefferson | Pittsburgh | Crow Hollow| � inch | | | | or No. 8

| | | 137 | Ohio | Jefferson| Pittsburgh | Rush Run No. 1| � inch

| | | | or No. 8 | || 138 | Ohio | Perry | Hocking

| Congo | | 139 | Ohio |Stark | Massillon | | Slack

| 140 | Ohio | Vinton | Brookville| Clarion | Nut and | | || or No. 4 | | Slack | 141 |

Okla. | Choctaw | McAlester |Edwards No. 1 | Mine run | 142 | Okla. |Choctaw | McAlester | Adamson| Slack | 143 | Okla. | Creek |

| Henrietta | Lump and | | || | | Slack | 144

| Pa. | Allegheny | Pittsburgh || Slack | | | | 3rd Pool| | | 145 | Pa. |

Allegheny | Monongahela | TurtleCreek | | 146 | Pa. | Allegheny| Pittsburgh | Bertha | � inch |147 | Pa. | Cambria | | Beach

Creek | Slack | 148 | Pa. | Cambria| Miller | Lincoln | Mine run |

149 | Pa. | Clarion | Lower Freeport || | 150 | Pa. | Fayette |

Connellsville | | Slack | 151 |Pa. | Greene | Youghiogheny |

| Lump | 152 | Pa. | Greene |Westmoreland | | Screenings |153 | Pa. | Indiana | | Iselin

| Mine run | 154 | Pa. | Jefferson || Punxsutawney | Mine run | 155

| Pa. | Lawrence | Middle || | | | | Kittanning

| | | 156 | Pa. | Mercer| Taylor | | | 157 | Pa.| Washington | Pittsburgh | Ellsworth

| | 158 | Pa. | Washington |Youghiogheny | Anderson | � inch| 159 | Pa. | Westmoreland | Pittsburgh

| Scott Haven | Lump | 160 | Tenn.| Campbell | Jellico | |

| 161 | Tenn. | Claiborne | Mingo

| | | 162 | Tenn. | Marion| | Etna | | 163 |

Tenn. | Morgan | Brushy Mt. || | 164 | Tenn. | Scott | Glen

Mary No. 4| Glen Mary | | 165 |Tex. | Maverick | | Eagle Pass

| | 166 | Tex. | Paolo Pinto || Thurber | Mine run | 167 | Tex.

| Paolo Pinto | | Strawn |Mine run | 168 | Va. | Henrico |

| Gayton | |____|_______|________________|________________|_______________|_____________|

_____________________________________________________________________ |


| No.|________________________________________| Per | | | | | |

| Pound | Authority | | Moisture |

Volatile | Fixed | Ash | Dry | || | Matter | Carbon | | Coal |

|____|__________|__________|________|_________|________|______________| || | | | | | 126 |12.16 | 34.64 | 53.10 | 12.26 | 12214 |

| 127 | 5.31 | 38.78 | 52.22 |9.00 | 12843 | U. S. Geo. S.| | |

| | | | | 128 | 2.15 |37.57 | 51.80 | 10.63 | 13370 | Lord &

Haas | | | | | | || 129 | | 41.76 | 45.24 | 13.00

| 13239 | B. & W. Co. | | | || | | | 130 | 6.19 |

33.02 | 59.96 | 7.02 | 13634 | B. & W.Co. | 131 | 6.45 | 39.12 | 50.08 |10.80 | 12700 | Lord & Haas | 132 | 2.60

| 40.80 | 47.60 | 11.60 | 12175 | Jones| 133 | 7.59 | 38.45 | 43.99 | 17.56

| 11704 | U. S. Geo. S.| | | || | | | 134 | 8.99 |

41.43 | 50.06 | 8.51 | 13113 | U. S.Geo. S.| | | | | | |

| 135 | 3.38 | 35.26 | 54.18 |7.56 | 12506 | Hill | 136 | 4.04 |40.08 | 52.27 | 9.65 | 13374 | U. S.Geo. S.| | | | | | |

| 137 | 4.74 | 36.08 | 54.81 |9.11 | 13532 | U. S. Geo. S.| | |

| | | | | 138 | 6 41 |38.33 | 46.71 | 14.96 | 12284 | B. & W.

Co. | 139 | 6.67 | 40.02 | 46.46 |13.52 | 11860 | B. & W. Co. | 140 | 2.47| 42.38 | 50.39 | 6.23 | 13421 | U. S.Geo. S.| | | | | | |

| 141 | 4.79 | 39.18 | 49.97 |10.85 | 13005 | U. S. Geo. S.| 142 | 4.72| 28.54 | 58.17 | 13.29 | 12105 | B. &W. Co. | 143 | 7.65 | 36.77 | 50.14 |13.09 | 12834 | U. S. Geo. S.| | |

| | | | | 144 | 1.77| 32.06 | 57.11 | 10.83 | 13205 |Carpenter | | | | | |

| | 145 | 1.75 | 36.85 |53.94 | 9.21 | 13480 | Lord & Haas | 146| 2.61 | 35.86 | 57.81 | 6.33 | 13997| U. S. Geo. S.| 147 | 3.01 | 32.87 |55.86 | 11.27 | 13755 | B. & W. Co. | 148| 5.39 | 30.83 | 61.05 | 8.12 | 13600| B. & W. Co. | 149 | 0.54 | 35.93 |57.66 | 6.41 | 13547 | | 150 |1.85 | 28.73 | 63.22 | 7.95 | 13775 |Whitham | 151 | 1.25 | 32.60 |54.70 | 12.70 | 13100 | B. & W. Co. | 152| 11.12 | 31.67 | 55.61 | 12.72 |13100 | P. R. R. | 153 | 2.70 | 29.33 |63.56 | 7.11 | 14220 | B. & W. Co. | 154| 3.38 | 29.33 | 64.93 | 5.73 | 14781| B. & W. Co. | 155 | 0.70 | 37.06 |56.24 | 6.70 | 13840 | Lord & Haas | |

| | | | | | 156| 4.18 | 32.19 | 55.55 | 12.26 | 12820| B. & W. Co. | 157 | 2.46 | 35.35 |58.46 | 6.19 | 14013 | U. S. Geo. S.| 158| 1.00 | 39.29 | 54.80 | 5.91 | 13729

| Jones | 159 | 4.06 | 32.91 | 59.78| 7.31 | 13934 | B. & W. Co. | 160 |1.80 | 37.76 | 62.12 | 1.12 | 13846 |U. S. Navy | 161 | 4.40 | 34.31 | 59.22| 6.47 | | U. S. Geo. S.| 162 | 3.16 |32.98 | 56.59 | 10.43 | | |

163 | 1.77 | 33.46 | 54.73 | 11.87 |13824 | B. & W. Co. | 164 | 1.53 | 40.80| 56.78 | 2.42 | 14625 |Ky. State Col.|

165 | 5.42 | 33.73 | 44.89 | 21.38 |10945 | B. & W. Co. | 166 | 1.90 | 36.01| 49.09 | 14.90 | 12760 | B. & W. Co. |

167 | 4.19 | 35.40 | 52.98 | 11.62 |13202 | B. & W. Co. | 168 | 0.82 | 17.14| 74.92 | 7.94 | 14363 | B. & W. Co. |

____|__________|__________|________|_________|________|______________|


____________________________________________________________________________| | | | || | | | | |


| | | | | || | | |

|_______|________________|________________|_______________|_____________| |

| | | | |169 | Va. | Lee | Darby |Darby | 1� inch | 170 | Va. | Lee

| McConnel | Wilson | Minerun | 171 | Va. | Wise | UpperBanner | Coburn | 3� inch | 172 |Va. | Rockingham | | CloverHill | | 173 | Va. | Russel |Clinchfield | | | 174 | Va.| | Monongahela | Bernmont| | 175 | W. Va.| Harrison |

Pittsburgh | Ocean | Mine run |176 | W. Va.| Harrison | |Girard | Nut, Pea | | | |

| | and Slack | 177 | W.Va.| Kanawha | Winifrede |Winifrede | | 178 | W. Va.|Kanawha | Keystone | Keystone| Mine run | 179 | W. Va.| Logan |Island Creek | |Nut and Slack|180 | W. Va.| Marion | Fairmont |Kingmont | | 181 | W. Va.|Mingo | Thacker | Maritime |

| 182 | W. Va.| Mingo | GlenAlum | Glen Alum | Mine run | 183| W. Va.| Preston | Bakerstown |

| | 184 | W. Va.| Putnam |Pittsburgh | Black Betsy | Bug dust |185 | W. Va.| Randolph | UpperFreeport | Coalton | Lump and Nut|____|_______|________________|________________|_______________|_____________|

| | |

| | | LIGNITES AND LIGNITICCOALS | |____|_______|_________________________________________________|_____________|| | | | |

| 186 | Col. | Boulder | | Rex| | 187 | Col. | El Paso || Curtis | | 188 | Col. | El

Paso | | Pike View | |189 | Col. | Gunnison | South Platte |Mt. Carbon | | 190 | Col. | LasAnimas | | Acme | |191 | Col. | | Lehigh || | 192 |N. Dak.| McLean |

| Eckland | Mine run | 193 |N.Dak.| McLean | | Wilton |Lump | 194 |N. Dak.| McLean |

| Casino | | 195 |N. Dak.|Stark | Lehigh | Lehigh |Mine run | 196 |N. Dak.| William |Williston | | Mine run | 197|N. Dak.| William | Williston |

| Mine run | 198 | Tex. | Bastrop |Bastrop | Glenham | | 199 |Tex. | Houston | Crockett || | 200 | Tex. | Houston |

| Houston C. & | | | || | C. Co. | | 201 |

Tex. | Milam | Rockdale | Worley| | 202 | Tex. | Robertson |

Calvert | Coaling No. 1 | | 203 |Tex. | Wood | Hoyt |Consumer's | | | | |

| Lig. Co. | | 204 | Tex. |Wood | Hoyt | | |205 | Wash. | King | | BlackDiamond | | 206 | Wyo. | Carbon

| Hanna | | Mine run |207 | Wyo. | Crook | Black Hills |Stilwell Coal | | | | |

| Co. | | 208 | Wyo. |Sheridan | Sheridan | Monarch |

| 209 | Wyo. | Sweetwater | RockSpring | | Screenings | 210 |

Wyo. | Uinta | Adaville | Lazeart| |

____|_______|________________|________________|_______________|_____________|

_____________________________________________________________________ |

| | | |Proximate Analysis (Dry Coal) |B. t.u.| | No.|________________________________________| Per | | | | | |



____|__________|__________|________|_________|________|______________| || | | | | | 169 |4.35 | 38.46 | 56.91 | 4.63 | 13939 |U. S. Geo. S.| 170 | 3.35 | 36.35 |57.88 | 5.77 | 13931 | U. S. Geo. S.| 171

| 3.05 | 32.65 | 62.73 | 4.62 | 14470| U. S. Geo. S.| 172 | | 31.77 | 57.98| 10.25 | 13103 | | 173 | 2.00 |35.72 | 56.12 | 8.16 | 14200 | |174 | | 32.00 | 59.90 | 8.10 |13424 | Carpenter | 175 | 2.47 | 39.35

| 52.78 | 7.87 | 14202 | U. S. Geo. S.|176 | | 36.66 | 57.49 | 5.85 |14548 | B. & W. Co. | | | || | | | 177 | 1.05 | 32.74| 64.38 | 2.88 | 14111 | Hill | 178 |2.21 | 33.29 | 58.61 | 8.10 | 14202 |

U. S. Geo. S.| 179 | 1.12 | 38.61 |55.91 | 5.48 | 14273 | Hill | 180 |1.90 | 35.31 | 57.34 | 7.35 | 14198 |U. S. Geo. S.| 181 | 0.68 | 31.89 |63.48 | 4.63 | 14126 | Hill | 182 |3.02 | 33.81 | 59.45 | 6.74 | 14414 |U. S. Geo. S.| 183 | 4.14 | 29.09 |63.50 | 7.41 | 14546 | U. S. Geo. S.| 184| 7.41 | 32.84 | 53.96 | 13.20 | 12568| B. & W. Co. | 185 | 2.11 | 29.57 |

59.93 | 10.50 | 13854 | U. S. Geo. S.|____|__________|__________|________|_________|________|______________| || | | | | | || | | | | |____|__________|__________|________|_________|________|______________| || | | | | | 186 |16.05 | 42.12 | 47.97 | 9.91 | 10678 |B. & W. Co. | 187 | 23.25 | 42.11 |49.38 | 8.51 | 11090 | B. & W. Co. | 188| 23.77 | 48.70 | 41.47 | 9.83 | 10629| B. & W. Co. | 189 | 20.38 | 46.38 |47.50 | 6.12 | | | 190 | 16.74| 47.90 | 44.60 | 7.50 | |Col. Sc. ofM.| 191 | 18.30 | 45.29 | 44.67 | 10.04| | | 192 | 29.65 | 45.56 |47.05 | 7.39 | 10553 | Lord | 193 |35.96 | 49.84 | 38.05 | 12.11 | 11036 |U. S. Geo. S.| 194 | 29.65 | 46.56 |38.70 | 14.74 | | Lord | 195 |35.84 | 43.84 | 39.59 | 16.57 | 10121 |

U. S. Geo. S.| 196 | 41.76 | 39.37 |48.09 | 12.54 | 10121 | B. & W. Co. | 197| 42.74 | 40.83 | 47.79 | 11.38 |10271 | B. & W. Co. | 198 | 32.77 |42.76 | 36.88 | 20.36 | 8958 | B. & W.Co. | 199 | 23.27 | 40.95 | 38.37 |20.68 | 10886 | U. S. Geo. S.| 200 | 31.48| 46.93 | 34.40 | 18.87 | 10176 | B. &

W. Co. | | | | | || | 201 | 32.48 | 43.04 | 41.14 |15.82 | 10021 | B. & W. Co. | 202 | 32.01

| 43.70 | 43.08 | 13.22 | 10753 | B. &W. Co. | 203 | 33.98 | 46.97 | 41.40 |11.63 | 10600 | U. S. Geo. S.| | |

| | | | | 204 | 30.25| 43.27 | 41.46 | 15.27 | 10597 || 205 | 3.71 | 48.72 | 46.56 | 4.72 |

| Gale | 206 | 6.44 | 51.32 |43.00 | 5.68 | 11607 | B. & W. Co. | 207| 19.08 | 45.21 | 46.42 | 8.37 | 12641| U. S. Geo. S.| | | | || | | 208 | 21.18 | 51.87 |

40.43 | 7.70 | 12316 | U. S. Geo. S.| 209| 7.70 | 38.57 | 56.99 | 4.44 | 12534| B. & W. Co. | 210 | 19.15 | 45.50 |48.11 | 6.39 | 9868 | U. S. Geo. S.|____|__________|__________|________|_________|________|______________|

[Illustration: Portion of 12,080 Horse-powerInstallation of Babcock & Wilcox Boilersand Superheaters at the Potomac ElectricCo., Washington, D. C.]

TABLE 39

SHOWING RELATION BETWEENPROXIMATE AND ULTIMATE ANALYSESOF COAL

========================================================================= | | |

| Common in | | |

| |Proximate &| || Proximate | | Ultimate

| | | Analysis | UltimateAnalysis | Analysis ||--------------------|-----------|--------------------------|-----------| | | | | V | | |H | | N | | | M | | | | | o| | | y | | i | S | | o | | | |

| l M | C | C | d | O | t | u | | i| | S | | | a a | F a | a | r | x | r| l | | s | | t | | | t t | i r | r | o| y | o | p | | t | | a | Field | | i t| x b | b | g | g | g | h | A | u | | t |or | | l e | e o | o | e | e | e | e |s | r | | e | Bed | Mine | e r | d n | n |n | n | n | r | h | e ||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | | |Icy Coal| || | | | | | | | | | | &

Iron | | | | | | | | | | || Horse | Co. | | | | | | | |

| | |Ala| Creek | No. 8

|31.81|53.90|72.02|4.78| 6.45|1.66|.80|14.29| 2.56||---|----------------|-----|-----|-----|----|-----|----|----|-----|-----| | | |Central | || | | | | | | | | | |C. &C. | | | | | | | | | | | |Hunt- | Co. | | | | | | | || | |Ark|ington | No. 3|18.99|67.71|76.37|3.90|3.71|1.49|1.23|13.30| 1.99||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | | Pana | Clover || | | | | | | | | | | or |Leaf, | | | | | | | | | ||Ill| No. 5 | No. 1|37.22|45.64|63.04|4.49|10.04|1.28|4.01|17.14|13.19||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | |No. 5, | | || | | | | | | | | |Warrick|

| | | | | | | | | | |Ind|Co. |Electric|41.85|44.45|68.08|4.78|

7.56|1.35|4.53|13.70| 9.11||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | |No. 11,| St. | || | | | | | | | |

|Hopkins|Bernard,| | | | | | || | | |Ky | Co. | No. 11

|41.10|49.60|72.22|5.06| 8.44|1.33|3.65|9.30| 7.76||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | |"B" or | | || | | | | | | | | |Lower || | | | | | | | | | |

|Kittan-| Eureka,| | | | | | || | | |Pa | ning | No. 31|16.71|77.22|84.45|4.25| 3.04|1.28| .91|6.07| .56||---|-------|--------|-----|-----|-----|----|-----|----|----|-----|-----| | |Indiana| | || | | | | | | | |Pa | Co. ||29.55|62.64|79.86|5.02| 4.27|1.86|1.18|7.81| 2.90||---|-------|--------|-----|-----|-----|----|-----|

----|----|-----|-----| |W. | Fire | Rush || | | | | | | | | |Va |Creek | Run |22.87|71.56|83.71|4.64|3.67|1.70| .71| 5.57| 2.14|=========================================================================

Table 39 gives for comparison the ultimateand proximate analyses of certain of thecoals with which tests were made in thecoal testing plant of the United StatesGeological Survey at the LouisianaPurchase Exposition at St. Louis.

The heating value of a fuel cannot bedirectly computed from a proximateanalysis, due to the fact that the volatilecontent varies widely in different fuels incomposition and in heating value.

Some methods have been advanced for

estimating the calorific value of coals fromthe proximate analysis. William Kent[38]deducted from Mahler's tests of Europeancoals the approximate heating valuedependent upon the content of fixedcarbon in the combustible. The relation asdeduced by Kent between the heat andvalue per pound of combustible and theper cent of fixed carbon referred tocombustible is represented graphically byFig. 23.

Goutal gives another method ofdetermining the heat value from aproximate analysis, in which the carbon isgiven a fixed value and the heating valueof the volatile matter is considered as afunction of its percentage referred tocombustible. Goutal's method checksclosely with Kent's determinations.

All the formulae, however, for computing

the calorific value of coals from aproximate analysis are ordinarily limitedto certain classes of fuels. Mr. Kent, forinstance, states that his deductions arecorrect within a close limit for fuelscontaining more than 60 per cent of fixedcarbon in the combustible, while for thosecontaining a lower percentage, the errormay be as great as 4 per cent, either highor low.

While the use of such computations willserve where approximate results only arerequired, that they are approximateshould be thoroughly understood.

Calorimetry--An ultimate or a proximateanalysis of a fuel is useful in determiningits general characteristics, and asdescribed on page 183, may be used inthe calculation of the approximate heatingvalue. Where the efficiency of a boiler is to

be computed, however, this heating valueshould in all instances be determinedaccurately by means of a fuel calorimeter.

[Graph: B.T.U. per Pound of Combustibleagainst Per Cent of Fixed Carbon inCombustible

Fig. 23. Graphic Representation of Relationbetween Heat Value Per Pound ofCombustible and Fixed Carbon inCombustible as Deduced by Wm. Kent.]

In such an apparatus the fuel is completelyburned and the heat generated by suchcombustion is absorbed by water, theamount of heat being calculated from theelevation in the temperature of the water.A calorimeter which has been accepted asthe best for such work is one in which thefuel is burned in a steel bomb filled withcompressed oxygen. The function of the

oxygen, which is ordinarily under apressure of about 25 atmospheres, is tocause the rapid and complete combustionof the fuel sample. The fuel is ignited bymeans of an electric current, allowancebeing made for the heat produced by suchcurrent, and by the burning of the fusewire.

A calorimeter of this type which will befound to give satisfactory results is that ofM. Pierre Mahler, illustrated in Fig. 24 andconsisting of the following parts:

A water jacket A, which maintains constantconditions outside of the calorimeterproper, and thus makes possible a moreaccurate computation of radiation losses.

The porcelain lined steel bomb B, in whichthe combustion of the fuel takes place incompressed oxygen.

[Illustration: Fig. 24. Mahler BombCalorimeter]

The platinum pan C, for holding the fuel.

The calorimeter proper D, surrounding thebomb and containing a definite weighedamount of water.

An electrode E, connecting with the fusewire F, for igniting the fuel placed in thepan C.

A support G, for a water agitator.

A thermometer I, for temperaturedetermination of the water in thecalorimeter. The thermometer is bestsupported by a stand independent of thecalorimeter, so that it may not be movedby tremors in the parts of the calorimeter,

which would render the making ofreadings difficult. To obtain accuracy ofreadings, they should be made through atelescope or eyeglass.

A spring and screw device for revolvingthe agitator.

A lever L, by the movement of which theagitator is revolved.

A pressure gauge M, for noting the amountof oxygen admitted to the bomb. Between20 and 25 atmospheres are ordinarilyemployed.

An oxygen tank O.

A battery or batteries P, the current fromwhich heats the fuse wire used to ignite thefuel.

This or a similar calorimeter is used in thedetermination of the heat of combustion ofsolid or liquid fuels. Whatever the fuel tobe tested, too much importance cannot begiven to the securing of an averagesample. Where coal is to be tested, testsshould be made from a portion of the driedand pulverized laboratory sample, themethods of obtaining which have beendescribed. In considering the methods ofcalorimeter determination, the remarksapplied to coal are equally applicable toany solid fuel, and such changes inmethods as are necessary for liquid fuelswill be self-evident from the samedescription.

Approximately one gram of the pulverizeddried coal sample should be placeddirectly in the pan of the calorimeter.There is some danger in the using of apulverized sample from the fact that some

of it may be blown out of the pan whenoxygen is admitted. This may be at leastpartially overcome by forming about twograms into a briquette by the use of acylinder equipped with a plunger and ascrew press. Such a briquette should bebroken and approximately one gram used.If a pulverized sample is used, care shouldbe taken to admit oxygen slowly toprevent blowing the coal out of the pan.The weight of the sample is limited toapproximately one gram since thecalorimeter is proportioned for thecombustion of about this weight whenunder an oxygen pressure of about 25atmospheres.

A piece of fine iron wire is connected tothe lower end of the plunger to form a fusefor igniting the sample. The weight of ironwire used is determined, and if aftercombustion a portion has not been burned,

the weight of such portion is determined.In placing the sample in the pan, and inadjusting the fuse, the top of thecalorimeter is removed. It is then replacedand carefully screwed into place on thebomb by means of a long handled wrenchfurnished for the purpose.

The bomb is then placed in thecalorimeter, which has been filled with adefinite amount of water. This weight is the"water equivalent" of the apparatus, _i. e._,the weight of water, the temperature ofwhich would be increased one degree foran equivalent increase in the temperatureof the combined apparatus. It may bedetermined by calculation from theweights and specific heats of the variousparts of the apparatus. Such adetermination is liable to error, however,as the weight of the bomb lining can onlybe approximated, and a considerable

portion of the apparatus is not submerged.Another method of making such adetermination is by the adding of definiteweights of warm water to definite amountsof cooler water in the calorimeter andtaking an average of a number ofexperiments. The best method for themaking of such a determination isprobably the burning of a definite amountof resublimed naphthaline whose heat ofcombustion is known.

The temperature of the water in the waterjacket of the calorimeter should beapproximately that of the surroundingatmosphere. The temperature of theweighed amount of water in thecalorimeter is made by someexperimenters slightly greater than that ofthe surrounding air in order that the initialcorrection for radiation will be in the samedirection as the final correction. Other

experimenters start from a temperaturethe same or slightly lower than thetemperature of the room, on the basis thatthe temperature after combustion will beslightly higher than the room temperatureand the radiation correction be either aminimum or entirely eliminated.

While no experiments have been made toshow conclusively which of these methodsis the better, the latter is generally used.

After the bomb has been placed in thecalorimeter, it is filled with oxygen from atank until the pressure reaches from 20 to25 atmospheres. The lower pressure willbe sufficient in all but exceptional cases.Connection is then made to a current fromthe dry batteries in series so arranged asto allow completion of the circuit with aswitch. The current from a lighting systemshould not be used for ignition, as there is

danger from sparking in burning the fuse,which may effect the results. Theapparatus is then ready for the test.

Unquestionably the best method of takingdata is by the use of co-ordinate paper anda plotting of the data with temperaturesand time intervals as ordinates andabscissae. Such a graphic representationis shown in Fig. 25.

[Graph: Temperature--� C. againstTime--Hours and Minutes

Fig. 25. Graphic Method of RecordingBomb Calorimeter Results]

After the bomb is placed in thecalorimeter, and before the coal is ignited,readings of the temperature of the watershould be taken at one minute intervals fora period long enough to insure a constant

rate of change, and in this way determinethe initial radiation. The coal is thenignited by completing the circuit, thetemperature at the instant the circuit isclosed being considered the temperatureat the beginning of the combustion. Afterignition the readings should be taken atone-half minute intervals, though becauseof the rapidity of the mercury's riseapproximate readings only may bepossible for at least a minute after thefiring, such readings, however, beingsufficiently accurate for this period. Theone-half minute readings should be takenafter ignition for five minutes, and for, say,five minutes longer at minute intervals todetermine accurately the final rate ofradiation.

Fig. 25 shows the results of such readings,plotted in accordance with the methodsuggested. It now remains to compute the

results from this plotted data.

The radiation correction is first applied.Probably the most accurate manner ofmaking such correction is by the use ofPfaundler's method, which is amodification of that of Regnault. Thisassumes that in starting with an initial rateof radiation, as represented by theinclination of the line AB, Fig. 25, andending with a final radiation representedby the inclination of the line CD, Fig. 25,that the rate of radiation for theintermediate temperatures between thepoints B and C are proportional to theinitial and final rates. That is, the rate ofradiation at a point midway between B andC will be the mean between the initial andfinal rates; the rate of radiation at a pointthree-quarters of the distance between Band C would be the rate at B plusthree-quarters of the difference in rates at

B and C, etc. This method differs fromRegnault's in that the radiation wasassumed by Regnault to be in each caseproportional to the difference intemperatures between the water of thecalorimeter and the surrounding air plus aconstant found for each experiment.Pfaundler's method is more simple thanthat of Regnault, and the results by the twomethods are in practical agreement.

Expressed as a formula, Pfaundler'smethod is, though not in form given byhim:

_ _ | R' - R | C = N|R +------ (T" - T)| (19) |_ T' - T _|

Where C = correction in degreecentigrade, N = number of intervalsover which correction is made, R =initial radiation in degrees per interval,

R' = final radiation in degrees per interval,T = average temperature for period

through which initial radiation iscomputed, T" = average temperatureover period of combustion[39], T' =average temperature over period throughwhich final radiation iscomputed.[39]

The application of this formula to Fig. 25 isas follows:

As already stated, the temperature at thebeginning of combustion is the readingjust before the current is turned on, or B inFig. 25. The point C or the temperature atwhich combustion is presumablycompleted, should be taken at a pointwhich falls well within the established finalrate of radiation, and not at the maximumtemperature that the thermometerindicates in the test, unless it lies on the

straight line determining the finalradiation. This is due to the fact that incertain instances local conditions willcause the thermometer to read higher thanit should during the time that the bomb istransmitting heat to the water rapidly, andat other times the maximum temperaturemight be lower than that which would beindicated were readings to be taken atintervals of less than one-half minute, _i.e._, the point of maximum temperature willfall below the line determined by the finalrate of radiation. With this understandingAB, Fig. 25, represents the time of initialradiation, BC the time of combustion, andCD the time of final radiation. Therefore toapply Pfaundler's correction, formula (19),to the data as represented by Fig. 25.

N = 6, R = 0, R' = .01, T = 20.29, T' = 22.83,

20.29 + 22.54 + 22.84 + 22.88 + 22.87 +

22.86 T" =--------------------------------------------- = 22.36 6

_ _ | .01 - 0| C = 6|0 + -------------(22.36 - 20.29)|

|_ 22.85 - 20.29 _|

= 6 �.008 = .048

Pfaundler's formula while simple is ratherlong. Mr. E. H. Peabody has devised asimpler formula with which, under properconditions, the variation from correction asfound by Pfaundler's method is negligible.

It was noted throughout an extendedseries of calorimeter tests that themaximum temperature was reached by thethermometer slightly over one minute afterthe time of firing. If this period betweenthe time of firing and the maximum

temperature reported was exactly oneminute, the radiation through this periodwould equal the radiation per one-halfminute _before firing_ plus the radiationper one-half minute _after the maximumtemperature is reached_; or, the radiationthrough the one minute interval would bethe average of the radiation per minutebefore firing and the radiation per minuteafter the maximum. A plotted chart oftemperatures would take the form of acurve of three straight lines (B, C', D) inFig. 25. Under such conditions, using thenotation as in formula (19) the correctionwould become,

2R + 2R' C = ------- + (N - 2)R', or R + (N -1)R' (20) 2

This formula may be generalized forconditions where the maximumtemperature is reached after a period of

more than one minute as follows:

Let M = the number of intervals betweenthe time of firing and the maximumtemperature. Then the radiation throughthis period will be an average of theradiation for M intervals before firing andfor M intervals after the maximum isrecorded, or

MR + MR' M M C = ------- +(N - M)R' = - R + (N - -)R' (21) 2 2 2

In the case of Mr. Peabody's deductions Mwas found to be approximately 2 andformula (21) becomes directly, C = R + (N- 1)R' or formula (20).

The corrections to be made, as secured bythe use of this formula, are very close tothose secured by Pfaundler's method,

where the point of maximum temperatureis not more than five intervals later thanthe point of firing. Where a longer periodthan this is indicated in the chart of plottedtemperatures, the approximate formulashould not be used. As the period betweenfiring and the maximum temperature isincreased, the plotted results are furtherand further away from the theoreticalstraight line curve. Where this period isnot over five intervals, or two and a halfminutes, an approximation of the straightline curve may be plotted by eye, andordinarily the radiation correction to beapplied may be determined very closelyfrom such an approximated curve.

Peabody's approximate formula has beenfound from a number of tests to giveresults within .003 degrees Fahrenheit forthe limits within which its application holdsgood as described. The value of M, which

is not necessarily a whole number, shouldbe determined for each test, though in allprobability such a value is a constant forany individual calorimeter which isproperly operated.

The correction for radiation as found onpage 188 is in all instances to be added tothe range of temperature between thefiring point and the point chosen fromwhich the final radiation is calculated. Thiscorrected range multiplied by the waterequivalent of the calorimeter gives theheat of combustion in calories of the coalburned in the calorimeter together withthat evolved by the burning of the fusewire. The heat evolved by the burning ofthe fuse wire is found from thedetermination of the actual weight of wireburned and the heat of combustion of onemilligram of the wire (1.7 calories), _i. e._,multiply the weight of wire used by 1.7,

the result being in gram calories or theheat required to raise one gram of waterone degree centigrade.

Other small corrections to be made arethose for the formation of nitric acid andfor the combustion of sulphur to sulphuricacid instead of sulphur dioxide, due to themore complete combustion in thepresence of oxygen than would bepossible in the atmosphere.

To make these corrections the bomb of thecalorimeter is carefully washed out withwater after each test and the amount ofacid determined from titrating this waterwith a standard solution of ammonia or ofcaustic soda, all of the acid being assumedto be nitric acid. Each cubic centimeter ofthe ammonia titrating solution used isequivalent to a correction of 2.65 calories.

As part of acidity is due to the formation ofsulphuric acid, a further correction isnecessary. In burning sulphuric acid theheat evolved per gram of sulphur is 2230calories in excess of the heat which wouldbe evolved if the sulphur burned tosulphur dioxide, or 22.3 calories for eachper cent of sulphur in the coal. One cubiccentimeter of the ammonia solution isequivalent to 0.00286 grams of sulphur assulphuric acid, or to 0.286 �22.3 = 6.38calories. It is evident therefore that aftermultiplying the number of cubiccentimeters used in titrating by the heatfactor for nitric acid (2.65) a furthercorrection of 6.38 - 2.65 = 3.73 is necessaryfor each cubic centimeter used in titratingsulphuric instead of nitric acid. Thiscorrection will be 3.73/0.297 = 13 units foreach 0.01 gram of sulphur in the coal.

The total correction therefore for the

aqueous nitric and sulphuric acid is foundby multiplying the ammonia by 2.65 andadding 13 calories for each 0.01 gram ofsulphur in the coal. This total correction isto be deducted from the heat value asfound from the corrected range and theamount equivalent to the calorimeter.

After each test the pan in which the coalhas been burned must be carefullyexamined to make sure that all of thesample has undergone completecombustion. The presence of black specksordinarily indicates unburned coal, andoften will be found where the coal containsbone or slate. Where such specks arefound the tests should be repeated. Intesting any fuel where it is found difficult tocompletely consume a sample, a weighedamount of naphthaline may be added, thetotal weight of fuel and naphthaline beingapproximately one gram. The naphthaline

has a known heat of combustion, samplesfor this purpose being obtainable from theUnited States Bureau of Standards, andfrom the combined heat of combustion ofthe fuel and naphthaline that of the formermay be readily computed.

The heat evolved in burning of a definiteweight of standard naphthaline may alsobe used as a means of calibrating thecalorimeter as a whole.

COMBUSTION OF COAL

The composition of coal varies over such awide range, and the methods of firing haveto be altered so greatly to suit the variouscoals and the innumerable types offurnaces in which they are burned, thatany instructions given for the handling ofdifferent fuels must of necessity be of themost general character. For each kind ofcoal there is some method of firing whichwill give the best results for eachindividual set of conditions. General rulescan be suggested, but the best results canbe obtained only by following suchmethods as experience and practice showto be the best suited to the specificconditions.

The question of draft is an all importantfactor. If this be insufficient, proper

combustion is impossible, as the suction inthe furnace will not be great enough todraw the necessary amount of air throughthe fuel bed, and the gases may pass offonly partially consumed. On the otherhand, an excessive draft may cause lossesdue to the excess quantities of air drawnthrough holes in the fire. Where coal isburned however, there are rarelycomplaints from excessive draft, as thiscan be and should be regulated by theboiler damper to give only the draftnecessary for the particular rate ofcombustion desired. The draft required forvarious kinds of fuel is treated in detail inthe chapter on "Chimneys and Draft". Inthis chapter it will be assumed that thedraft is at all times ample and that it isregulated to give the best results for eachkind of coal.

TABLE 40

ANTHRACITE COAL SIZES

_________________________________________________________________ |

| | | | || Testing Segments | |

| Round Mesh | Standard Square | || | Mesh | |

Trade Name|__________________|__________________|| | | | | | |

| Through | Over | Through| Over | | | Inches |Inches | Inches | Inches ||___________________________|_________|________|_________|________| |

| | | | | | Broken| 4-1/2 | 3-1/4 | 4 | 2-3/4 | |

Egg | 3-1/4 | 2-3/8 | 2-3/4 |

2 | | Stove | 2-3/8 | 1-5/8 |2 | 1-3/8 | | Chestnut | 1-5/8| 7/8 | 1-3/8 | 3/4 | | Pea| 7/8 | 5/8 | 3/4 | 1/2 | | No. 1Buckwheat | 5/8 | 3/8 | 1/2 |1/4 | | No. 2 Buckwheat or Rice | 3/8 |3/16 | 1/4 | 1/8 | | No. 3 Buckwheat orBarley | 3/16 | 3/32 | 1/8 | 1/16 ||___________________________|_________|________|_________|________|

Anthracite--Anthracite coal is ordinarilymarketed under the names and sizes givenin Table 40.

The larger sizes of anthracite are rarelyused for commercial steam generatingpurposes as the demand for domestic usenow limits the supply. In commercialplants the sizes generally found are Nos. 1,2 and 3 buckwheat. In some plants wherethe finer sizes are used, a small

percentage of bituminous coal, say, 10 percent, is sometimes mixed with theanthracite and beneficial results securedboth in economy and capacity.

Anthracite coal should be fired evenly, insmall quantities and at frequent intervals. Ifthis method is not followed, dead spots willappear in the fire, and if the fire gets tooirregular through burning in patches,nothing can be done to remedy it until thefire is cleaned as a whole. After this gradeof fuel has been fired it should be leftalone, and the fire tools used as little aspossible. Owing to the difficulty of ignitingthis fuel, care must be taken in cleaningfires. The intervals of cleaning will, ofcourse, depend upon the nature of the coaland the rate of combustion. With the smallsizes and moderately high combustionrates, fires will have to be cleaned twiceon each eight-hour shift. As the fires

become dirty the thickness of the fuel bedwill increase, until this depth may be 12 or14 inches just before a cleaning period. Incleaning, the following practice is usuallyfollowed: The good coal on the forwardhalf of the grate is pushed to the rear half,and the refuse on the front portion eitherpulled out or dumped. The good coal isthen pulled forward onto the front part ofthe grate and the refuse on the rear sectiondumped. The remaining good coal is thenspread evenly over the whole gratesurface and the fire built up with freshcoal.

A ratio of grate surface to heating surfaceof 1 to from 35 to 40 will under ordinaryconditions develop the rated capacity of aboiler when burning anthracitebuckwheat. Where the finer sizes areused, or where overloads are desirable,however, this ratio should preferably be 1

to 25 and a forced blast should be used.Grates 10 feet deep with a slope of 1�inches to the foot can be handledcomfortably with this class of fuel, andgrates 12 feet deep with the same slopecan be successfully handled. Where gratesover 8 feet in depth are necessary, shakinggrates or overlapping dumping gratesshould be used. Dumping grates may beapplied either for the whole grate surfaceor to the rear section. Air openings in thegrate bars should be made from 3/16 inchin width for No. 3 buckwheat to 5/16 inchfor No. 1 buckwheat. It is important thatthese air openings be uniformlydistributed over the whole surface to avoidblowing holes in the fire, and it is for thisreason that overlapping grates arerecommended.

No air should be admitted over the fire.Steam is sometimes introduced into the

ashpit to soften any clinker that may form,but the quantity of steam should be limitedto that required for this purpose. Thesteam that may be used in a steam jetblower for securing blast will in certaininstances assist in softening the clinker,but a much greater quantity may be usedby such an apparatus than is required forthis purpose. Combustion arches sprungabove the grates have proved ofadvantage in maintaining a high furnacetemperature and in assisting in the ignitionof fresh coal.

Stacks used with forced blast should be ofsuch size as to insure a slight suction in thefurnace under any conditions of operation.A blast up to 3 inches of water should beavailable for the finer sizes supplied byengine driven fans, automaticallycontrolled by the boiler pressure. Theblast required will increase as the depth of

the fuel bed increases, and the slightsuction should be maintained in thefurnace by damper regulation.

The use of blast with the finer sizes causesrapid fouling of the heating surfaces of theboiler, the dust often amounting to over 10per cent of the total fuel fired. Economicaldisposal of dust and ashes is of the utmostimportance in burning fuel of this nature.Provision should be made in the baffling ofthe boiler to accommodate and dispose ofthis dust. Whenever conditions permit, theashes can be economically disposed of byflushing them out with water.

Bituminous Coals--There is noclassification of bituminous coal as to sizethat holds good in all localities. TheAmerican Society of Mechanical Engineerssuggests the following grading:

_Eastern Bituminous Coals_--

(A) Run of mine coal; the unscreened coaltaken from the mine.

(B) Lump coal; that which passes over abar-screen with openings 1� incheswide.

(C) Nut coal; that which passes through abar-screen with 1�-inch openings andover one with �-inch openings.

(D) Slack coal; that which passes through abar-screen with �-inch openings.

_Western Bituminous Coals_--

(E) Run of mine coal; the unscreened coaltaken from the mine.

(F) Lump coal; divided into 6-inch, 3-inchand 1�-inch lump, according to thediameter of the circular openings overwhich the respective grades pass; also 6�3-inch lump and 3 �1�-inch lump,according as the coal passes through acircular opening having the diameter ofthe larger figure and over that of thesmaller diameter.

(G) Nut coal; divided into 3-inch steam nut,which passes through an opening 3inches diameter and over 1� inches; 1�inch nut, which passes through a 1�-inchdiameter opening and over a �-inchdiameter opening; �-inch nut, whichpasses through a �-inch diameteropening and over a 5/8-inch diameteropening.

(H) Screenings; that which passes through

a 1�-inch diameter opening.

As the variation in character of bituminouscoals is much greater than in theanthracites, any rules set down for theirhandling must be the more general. Thedifficulties in burning bituminous coalswith economy and with little or no smokeincreases as the content of fixed carbon inthe coal decreases. It is their volatilecontent which causes the difficulties and itis essential that the furnaces be designedto properly handle this portion of the coal.The fixed carbon will take care of itself,provided the volatile matter is properlyburned.

Mr. Kent, in his "Steam Boiler Economy",described the action of bituminous coalafter it is fired as follows: "The first thingthat the fine fresh coal does is to choke the

air spaces existing through the bed ofcoke, thus shutting off the air supply whichis needed to burn the gases producedfrom the fresh coal. The next thing is avery rapid evaporation of moisture fromthe coal, a chilling process, which robs thefurnace of heat. Next is the formation ofwater-gas by the chemical reaction, C +H_{2}O = CO + 2H, the steam beingdecomposed, its oxygen burning thecarbon of the coal to carbonic oxide, andthe hydrogen being liberated. Thisreaction takes place when steam isbrought in contact with highly heatedcarbon. This also is a chilling process,absorbing heat from the furnaces. The twovaluable fuel gases thus generated wouldgive back all the heat absorbed in theirformation if they could be burned, butthere is not enough air in the furnace toburn them. Admitting extra air through thefire door at this time will be of no service,

for the gases being comparatively coolcannot be burned unless the air is highlyheated. After all the moisture has beendriven off from the coal, the distillation ofhydrocarbons begins, and a considerableportion of them escapes unburned, owingto the deficiency of hot air, and to theirbeing chilled by the relatively coolheating surfaces of the boiler. During allthis time great volumes of smoke areescaping from the chimney, together withunburned hydrogen, hydrocarbons, andcarbonic oxide, all fuel gases, while at thesame time soot is being deposited on theheating surface, diminishing its efficiencyin transmitting heat to the water."

To burn these gases distilled from the coal,it is necessary that they be brought intocontact with air sufficiently heated to causethem to ignite, that sufficient space beallowed for their mixture with the air, and

that sufficient time be allowed for theircomplete combustion before they strikethe boiler heating surfaces, since thesesurfaces are comparatively cool and willlower the temperature of the gases belowtheir ignition point. The air drawn throughthe fire by the draft suction is heated in itspassage and heat is added by radiationfrom the hot brick surfaces of the furnace,the air and volatile gases mixing as thisincrease in temperature is taking place.Thus in most instances is the firstrequirement fulfilled. The element ofspace for the proper mixture of the gaseswith the air, and of time in whichcombustion is to take place, should betaken care of by sufficiently largecombustion chambers.

Certain bituminous coals, owing to theirhigh volatile content, require that the airbe heated to a higher temperature than it

is possible for it to attain simply in itspassage through the fire and byabsorption from the side walls of thefurnace. Such coals can be burned with thebest results under fire brick arches. Sucharches increase the temperature of thefurnace and in this way maintain the heatthat must be present for ignition andcomplete combustion of the fuels inquestion. These fuels too, sometimesrequire additional combustion space, andan extension furnace will give this inaddition to the required arches.

As stated, the difficulty of burningbituminous coals successfully will increasewith the increase in volatile matter. Thispercentage of volatile will affect directlythe depth of coal bed to be carried and theintervals of firing for the most satisfactoryresults. The variation in the fuel over suchwide ranges makes it impossible to

definitely state the thickness of fires for allclasses, and experiment with the class offuel in use is the best method ofdetermining how that particular fuelshould be handled. The followingsuggestions, which are not to beconsidered in any sense hard and fastrules, may be of service for generaloperating conditions for hand firing:

Semi-bituminous coals, such asPocahontas, New River, Clearfield, etc.,require fires from 10 to 14 inches thick;fresh coal should be fired at intervals of 10to 20 minutes and sufficient coal chargedat each firing to maintain a uniformthickness. Bituminous coals fromPittsburgh Region require fires from 4 to 6inches thick, and should be fired often incomparatively small charges. Kentucky,Tennessee, Ohio and Illinois coals requirea thickness from 4 to 6 inches. Free

burning coals from Rock Springs,Wyoming, require from 6 to 8 inches,while the poorer grades of Montana, Utahand Washington bituminous coals requirea depth of about 4 inches.

In general as thin fires are foundnecessary, the intervals of firing should bemade more frequent and the quantity ofcoal fired at each interval smaller. As thinfires become necessary due to thecharacter of the coal, the tendency toclinker will increase if the thickness beincreased over that found to give the bestresults.

There are two general methods of handfiring: 1st, the spreading method; and 2nd,the coking method.

[Illustration: Babcock & Wilcox ChainGrate Stoker]

In the spreading method but little fuel isfired at one time, and is spread evenlyover the fuel bed from front to rear. Wherethere is more than one firing door thedoors should be fired alternately. Theadvantage of alternate firing is the wholesurface of the fire is not blanketed withgreen coal, and steam is generated moreuniformly than if all doors were fired atone time. Again, a better combustionresults due to the burning of more of thevolatile matter directly after firing thanwhere all doors are fired at one time.

In the coking method, fresh coal is fired atconsiderable depth at the front of the grateand after it is partially coked it is pushedback into the furnace. The object of such amethod is the preserving of a bed ofcarbon at the rear of the grate, in passingover which the volatile gases driven off

from the green coal will be burned. Thismethod is particularly adaptable to a gratein which the gases are made to passhorizontally over the fire. Modern practicefor hand firing leans more and moretoward the spread firing method. Againthe tendency is to work bituminous coalfires less than formerly. A certain amountof slicing and raking may be necessarywith either method of firing, but ingeneral, the less the fire is worked thebetter the results.

Lignites--As the content of volatile matterand moisture in lignite is higher than inbituminous coal, the difficultiesencountered in burning them are greater.A large combustion space is required andthe best results are obtained where afurnace of the reverberatory type is used,giving the gases a long travel beforemeeting the tube surfaces. A fuel bed from

4 to 6 inches in depth can be maintained,and the coal should be fired in smallquantities by the alternate method. Abovecertain rates of combustion clinker formsrapidly, and a steam jet in the ashpit forsoftening this clinker is often desirable. Aconsiderable draft should be available,but it should be carefully regulated by theboiler damper to suit the condition of thefire. Smokelessness with hand firing withthis class of fuel is a practical impossibility.It has a strong tendency to foul the heatingsurfaces rapidly and these surfaces shouldbe cleaned frequently. Shaking grates,intelligently handled, aid in cleaning thefires, but their manipulation must becarefully watched to prevent good coalbeing lost in the ashpit.

Stokers--The term "automatic stoker"oftentimes conveys the erroneousimpression that such an apparatus takes

care of itself, and it must be thoroughlyunderstood that any stoker requires expertattention to as high if not higher degreethan do hand-fired furnaces.

Stoker-fired furnaces have manyadvantages over hand firing, but where astoker installation is contemplated thereare many factors to be considered. It istrue that stokers feed coal to the fireautomatically, but if the coal has first to befed to the stoker hopper by hand, itsautomatic advantage is lost. This is as trueof the removal of ash from a stoker. In ageneral way, it may be stated that a stokerinstallation is not advantageous exceptpossibly for diminishing smoke, unless theautomatic feature is carried to the handlingof the coal and ash, as where coal and ashhandling apparatus is not installed there isno saving in labor. In large plants,however, stokers used in conjunction with

the modern methods of coal storage andcoal and ash handling, make possible alarge labor saving. In small plants thelabor saving for stokers over hand-firedfurnaces is negligible, and the expense ofthe installation no less proportionatelythan in large plants. Stokers are, therefore,advisable in small plants only where thesaving in fuel will be large, or where thesmoke question is important.

Interest on investment, repairs,depreciation and steam required for blastand stoker drive must all be considered.The upkeep cost will, in general, be higherthan for hand-fired furnaces. Stokers,however, make possible the use ofcheaper fuels with as high or highereconomy than is obtainable underoperating conditions in hand-firedfurnaces with a better grade of fuel. Thebetter efficiency obtainable with a good

stoker is due to more even and continuousfiring as against the intermittent firing ofhand-fired furnaces; constant air supply asagainst a variation in this supply to meetvarying furnace conditions in hand-firedfurnaces; and the doing away to a greatextent with the necessity of working thefires.

Stokers under ordinary operatingconditions will give more nearlysmokeless combustion than will hand-firedfurnaces and for this reason must often beinstalled regardless of otherconsiderations. While a constant air supplyfor a given power is theoretically securedby the use of a stoker, and in manyinstances the draft is automaticallygoverned, the air supply should,nevertheless, be as carefully watched andchecked by flue gas analyses as in thecase of hand-fired furnaces.

There is a tendency in all stokers to causethe loss of some good fuel or siftings in theashpit, but suitable arrangements may bemade to reclaim this.

In respect to efficiency of combustion,other conditions being equal, there will beno appreciable difference with thedifferent types of stokers, provided thatthe proper type is used for the grade offuel to be burned and the conditions ofoperation to be fulfilled. No stoker willsatisfactorily handle all classes of fuel, andin making a selection, care should betaken that the type is suited to the fuel andthe operating conditions. A cheap stoker isa poor investment. Only the best stokersuited to the conditions which are to bemet should be adopted, for if there is to bea saving, it will more than cover the cost ofthe best over the cheaper stoker.

Mechanical Stokers are of three generaltypes: 1st, overfeed; 2nd, underfeed; and3rd, traveling grate. The traveling gratestokers are sometimes classed as overfeedbut properly should be classed bythemselves as under certain conditionsthey are of the underfeed rather than theoverfeed type.

Overfeed Stokers in general may bedivided into two classes, the distinctionbeing in the direction in which the coal isfed relative to the furnaces. In one classthe coal is fed into hoppers at the front endof the furnace onto grates with aninclination downward toward the rear ofabout 45 degrees. These grates arereciprocated, being made to takealternately level and inclined positions andthis motion gradually carries the fuel as itis burned toward the rear and bottom of

the furnace. At the bottom of the grates flatdumping sections are supplied forcompleting the combustion and forcleaning. The fuel is partly burned orcoked on the upper portion of the grates,the volatile gases driven off in this processfor a perfect action being ignited andburned in their passage over the bed ofburning carbon lower on the grates, or onbecoming mixed with the hot gases in thefurnace chamber. In the second class thefuel is fed from the sides of the furnace forits full depth from front to rear onto gratesinclined toward the center of the furnace. Itis moved by rocking bars and is graduallycarried to the bottom and center of thefurnace as combustion advances. Heresome type of a so-called clinker breakerremoves the refuse.

Underfeed Stokers are either horizontal orinclined. The fuel is fed from underneath,

either continuously by a screw, orintermittently by plungers. The principleupon which these stokers base their claimsfor efficiency and smokelessness is that thegreen fuel is fed under the coked andburning coal, the volatile gases from thisfresh fuel being heated and ignited in theirpassage through the hottest portion of thefire on the top. In the horizontal classes ofunderfeed stokers, the action of a screwcarries the fuel back through a retort fromwhich it passes upward, as the fuel aboveis consumed, the ash being finallydeposited on dead plates on either side ofthe retort, from which it can be removed.In the inclined class, the refuse is carrieddownward to the rear of the furnace wherethere are dumping plates, as in some ofthe overfeed types.

Underfeed stokers are ordinarily operatedwith a forced blast, this in some cases

being operated by the same mechanism asthe stoker drive, thus automaticallymeeting the requirements of variouscombustion rates.

Traveling Grates are of the class bestillustrated by chain grate stokers. Asimplied by the name these consist ofendless grates composed of short sectionsof bars, passing over sprockets at the frontand rear of the furnace. Coal is fed bygravity onto the forward end of the gratesthrough suitable hoppers, is ignited underignition arches and is carried with thegrate toward the rear of the furnace as itscombustion progresses. When operatedproperly, the combustion is completed asthe fire reaches the end of the grate andthe refuse is carried over this rear end bythe grate in making the turn over the rearsprocket. In some cases auxiliary dumpinggrates at the rear of the chain grates are

used with success.

Chain grate stokers in general produceless smoke than either overfeed orunderfeed types, due to the fact that thereare no cleaning periods necessary. Suchperiods occur with the latter types ofstokers at intervals depending upon thecharacter of the fuel used and the rate ofcombustion. With chain grate stokers thecleaning is continuous and automatic, andno periods occur when smoke willnecessarily be produced.

In the earlier forms, chain grates had anobjectionable feature in that the admissionof large amounts of excess air at the rear ofthe furnace through the grates waspossible. This objection has been largelyovercome in recent models by the use ofsome such device as the bridge wall waterbox and suitable dampers. A distinct

advantage of chain grates over other typesis that they can be withdrawn from thefurnace for inspection or repairs withoutinterfering in any way with the boilersetting.

This class of stoker is particularlysuccessful in burning low grades of coalrunning high in ash and volatile matterwhich can only be burned with difficultyon the other types. The cost of up-keep in achain grate, properly constructed andoperated, is low in comparison with thesame cost for other stokers.

The Babcock & Wilcox chain grate isrepresentative of this design of stoker.

Smoke--The question of smoke andsmokelessness in burning fuels hasrecently become a very important factor ofthe problem of combustion. Cities and

communities throughout the country havepassed ordinances relative to thequantities of smoke that may be emittedfrom a stack, and the failure of operators tolive up to the requirements of suchordinances, resulting as it does in finesand annoyance, has brought their attentionforcibly to the matter.

The whole question of smoke andsmokelessness is to a large extent acomparative one. There are any number ofplants burning a wide variety of fuels inordinary hand-fired furnaces, in extensionfurnaces and on automatic stokers that areoperating under service conditions,practically without smoke. It is safe to say,however, that no plant will operatesmokelessly under any and all conditionsof service, nor is there a plant in which thedegree of smokelessness does not dependlargely upon the intelligence of the

operating force.

[Illustration: Fig. 26. Babcock & WilcoxBoiler and Superheater Equipped withBabcock & Wilcox Chain Grate Stoker.This Setting has been ParticularlySuccessful in Minimizing Smoke]

When a condition arises in a boiler roomrequiring the fires to be brought upquickly, the operatives in handling certaintypes of stokers will use their slice barsfreely to break up the green portion of thefire over the bed of partially burned coal.In fact, when a load is suddenly thrown ona station the steam pressure can often bemaintained only in this way, and such useof the slice bar will cause smoke with thevery best type of stoker. In a certain plantusing a highly volatile coal and operatingboilers equipped with ordinary hand-firedfurnaces, extension hand-fired furnaces

and stokers, in which the boilers with thedifferent types of furnaces were onseparate stacks, a difference in smokefrom the different types of furnaces wasapparent at light loads, but when a heavyload was thrown on the plant, all threestacks would smoke to the same extent,and it was impossible to judge which typeof furnace was on one or the other of thestacks.

In hand-fired furnaces much can beaccomplished by proper firing. Acombination of the alternate andspreading methods should be used, thecoal being fired evenly, quickly, lightlyand often, and the fires worked as little aspossible. Smoke can be diminished bygiving the gases a long travel under theaction of heated brickwork before theystrike the boiler heating surfaces. Airintroduced over the fires and the use of

heated arches, etc., for mingling the airwith the gases distilled from the coal willalso diminish smoke. Extension furnaceswill undoubtedly lessen smoke wherehand firing is used, due to the increase inlength of gas travel and the fact that thistravel is partially under heated brickwork.Where hand-fired grates are immediatelyunder the boiler tubes, and a high volatilecoal is used, if sufficient combustion spaceis not provided the volatile gases, distilledas soon as the coal is thrown on the fire,strike the tube surfaces and are cooledbelow the burning point before they arewholly consumed and pass through assmoke. With an extension furnace, thesevolatile gases are acted upon by theradiant heat from the extension furnacearch and this heat, together with the addedlength of travel causes their morecomplete combustion before striking theheating surfaces than in the former case.

Smoke may be diminished by employing abaffle arrangement which gives the gasesa fairly long travel under heatedbrickwork and by introducing air abovethe fire. In many cases, however, specialfurnaces for smoke reduction are installedat the expense of capacity and economy.

From the standpoint of smokelessness,undoubtedly the best results are obtainedwith a good stoker, properly operated. Asstated above, the best stoker will causesmoke under certain conditions.Intelligently handled, however, underordinary operating conditions, stoker-firedfurnaces are much more nearly smokelessthan those which are hand fired, and are,to all intents and purposes, smokeless. Inpractically all stoker installations thereenters the element of time for combustion,the volatile gases as they are distilled

being acted upon by ignition or otherarches before they strike the heatingsurfaces. In many instances too, stokersare installed with an extension beyond theboiler front, which gives an added lengthof travel during which, the gases are actedupon by the radiant heat from the ignitionor supplementary arches, and here againwe see the long travel giving time for thevolatile gases to be properly consumed.

To repeat, it must be emphatically borne inmind that the question of smokelessness islargely one of degree, and dependent toan extent much greater than is ordinarilyappreciated upon the handling of the fueland the furnaces by the operators, bethese furnaces hand fired or automaticallyfired.

[Illustration: 3520 Horse-power Installationof Babcock & Wilcox Boilers at the

Portland Railway, Light and Power Co.,Portland, Ore. These Boilers are Equippedwith Wood Refuse Extension Furnaces atthe Front and Oil Burning Furnaces at theMud Drum End]

SOLID FUELS OTHER THAN COAL ANDTHEIR COMBUSTION

Wood--Wood is vegetable tissue whichhas undergone no geological change.Usually the term is used to designate thosecompact substances familiarly known astree trunks and limbs. When newly cut,wood contains moisture varying from 30per cent to 50 per cent. When dried for aperiod of about a year in the atmosphere,the moisture content will be reduced to 18or 20 per cent.

TABLE 41

ULTIMATE ANALYSES AND CALORIFICVALUES OF DRY WOOD (GOTTLIEB)

_______________________________________

________________ | | | | || | | | Kind | | | | || B. t. u.| | of | C | H | N | O |Ash | per | | Wood | | | || | Pound ||________|_______|______|______|_______|______|_________| | | | | |

| | | | Oak | 50.16 | 6.02 | 0.09 |43.36 | 0.37 | 8316 | | Ash | 49.18 |6.27 | 0.07 | 43.91 | 0.57 | 8480 | | Elm| 48.99 | 6.20 | 0.06 | 44.25 | 0.50 | 8510| | Beech | 49.06 | 6.11 | 0.09 | 44.17 |0.57 | 8391 | | Birch | 48.88 | 6.06 | 0.10| 44.67 | 0.29 | 8586 | | Fir | 50.36 |5.92 | 0.05 | 43.39 | 0.28 | 9063 | | Pine| 50.31 | 6.20 | 0.04 | 43.08 | 0.37 | 9153| | Poplar | 49.37 | 6.21 | 0.96 | 41.60 |1.86 | 7834[40]| | Willow | 49.96 | 5.96 |0.96 | 39.56 | 3.37 | 7926[40]||________|_______|______|______|_______|______|_________|

Wood is usually classified as hard wood,including oak, maple, hickory, birch,walnut and beech; and soft wood,including pine, fir, spruce, elm, chestnut,poplar and willow. Contrary to generalopinion, the heat value per pound of softwood is slightly greater than the samevalue per pound of hard wood. Table 41gives the chemical composition and theheat values of the common woods.Ordinarily the heating value of wood isconsidered equivalent to 0.4 that ofbituminous coal. In considering thecalorific value of wood as given in thistable, it is to be remembered that whilethis value is based on air-dried wood, themoisture content is still about 20 per centof the whole, and the heat produced inburning it will be diminished by thisamount and by the heat required toevaporate the moisture and superheat it tothe temperature of the gases. The heat so

absorbed may be calculated by theformula giving the loss due to moisture inthe fuel, and the net calorific valuedetermined.

In designing furnaces for burning wood,the question resolves itself into: 1st, theessential elements to give maximumcapacity and efficiency with this class offuel; and 2nd, the construction which willentail the least labor in handling andfeeding the fuel and removing the refuseafter combustion.

Wood, as used commercially for steamgenerating purposes, is usually a wasteproduct from some industrial process. Atthe present time refuse from lumber andsawmills forms by far the greater part ofthis class of fuel. In such refuse themoisture may run as high as 60 per centand the composition of the fuel may vary

over wide ranges during different portionsof the mill operation. The fuel consists ofsawdust, "hogged" wood and slabs, andthe percentage of each of theseconstituents may vary greatly. Hoggedwood is mill refuse and logs that havebeen passed through a "hogging machine"or macerator. This machine, through theaction of revolving knives, cuts or shredsthe wood into a state in which it mayreadily be handled as fuel.

Table 42 gives the moisture content andheat value of typical sawmill refuse fromvarious woods.

TABLE 42

MOISTURE AND CALORIFIC VALUEOF SAWMILL REFUSE_____________________________________________________________________ |

| | | | || | Per Cent | B. t. u. | |

Kind of Wood | Nature of Refuse |Moisture | per Pound | | |

| | Dry Fuel ||_____________________|_______________________|__________|____________| |

| | | | |Mexican White Pine | Sawdust and HogChips | 51.90 | 9020 | | YosemiteSugar Pine | Sawdust and Hog Chips |62.85 | 9010 | | Redwood 75%, |Sawdust, Box Mill | | | |Douglas Fir 25% | Refuse and Hog |42.20 | 8977[41] | | Redwood |Sawdust and Hog Chips | 52.98 |9040[41] | | Redwood | Sawdustand Hog Chips | 49.11 | 9204[41] | |Fir, Hemlock, | | |

| | Spruce and Cedar | Sawdust| 42.06 | 8949[41] ||_____________________|________________

_______|__________|____________|

It is essential in the burning of this class offuel that a large combustion space besupplied, and on account of the usuallyhigh moisture content there should bemuch heated brickwork to radiate heat tothe fuel bed and thus evaporate themoisture. Extension furnaces of the propersize are usually essential for good resultsand when this fuel is used alone, gratesdropped to the floor line with an ashpitbelow give additional volume forcombustion and space for maintaining athick fuel bed. A thick fuel bed isnecessary in order to avoid excessivequantities of air passing through theboiler. Where the fuel consists of hoggedwood and sawdust alone, it is best to feedit automatically into the furnace throughchutes on the top of the extension. Thebest results are secured when the fuel is

allowed to pile up in the furnace to aheight of 3 or 4 feet in the form of a coneunder each chute. The fuel burns bestwhen not disturbed in the furnace. Eachfuel chute, when a proper distance fromthe grates and with the piles maintained attheir proper height, will supply about 30or 35 square feet of grate surface. Whilelarge quantities of air are required forburning this fuel, excess air is as harmfulas with coal, and care must be taken thatsuch an excess is not admitted through firedoors or fuel chutes. A strong natural draftusually is preferable to a blast with thisfuel. The action of blast is to make theregulation of the furnace conditions moredifficult and to blow over unconsumed fuelon the heating surfaces and into the stack.This unconsumed fuel settling in portionsof the setting out of the direct path of thegases will have a tendency to igniteprovided any air reaches it, with results

harmful to the setting and breechingconnection. This action is particularlyobjectionable if these particles are carriedover into the base of a stack, where theywill settle below the point at which the flueenters and if ignited may cause the stack tobecome overheated and buckle.

Whether natural draft or blast is used,much of the fuel is carried onto the heatingsurfaces and these should be cleanedregularly to maintain a good efficiency.Collecting chambers in various portions ofthe setting should be provided for thisunconsumed fuel, and these should bekept clean.

With proper draft conditions, 150 poundsof this fuel containing about 30 to 40 percent of moisture can be burned per squarefoot of grate surface per hour, and in aproperly designed furnace one square foot

of grate surface can develop from 5 to 6boiler horse power. Where the woodcontains 50 per cent of moisture or over, itis not usually safe to figure on obtainingmore than 3 to 4 horse power per squarefoot of grate surface.

Dry sawdust, chips and blocks are alsoused as fuel in many wood-workingindustries. Here, as with the wet wood,ample combustion space should besupplied, but as this fuel is ordinarily kilndried, large brickwork surfaces in thefurnace are not necessary for theevaporation of moisture in the fuel. Thisfuel may be burned in extension furnacesthough these are not required unless theyare necessary to secure an added furnacevolume, to get in sufficient grate surface,or where such an arrangement must beused to allow for a fuel bed of sufficientthickness. Depth of fuel bed with the dry

fuel is as important as with the moist fuel. Ifextension furnaces are used with this drywood, care must be taken in their designthat there is no excessive throttling of thegases in the furnace, or brickwork troublewill result. In Babcock & Wilcox boilersthis fuel may be burned without extensionfurnaces, provided that the boilers are setat a sufficient height to provide amplecombustion space and to allow for properdepth of fuel bed. Sometimes this is gainedby lowering the grates to the floor line andexcavating for an ashpit. Where the fuel islargely sawdust, it may be introduced overthe fire doors through inclined chutes. Theold methods of handling and collectingsawdust by means of air suction and blastwere such that the amount of air admittedthrough such chutes was excessive, butwith improved methods the amount of airso admitted may be reduced to anegligible quantity. The blocks and refuse

which cannot be handled through chutesmay be fired through fire doors in the frontof the boiler, which should be madesufficiently large to accommodate thelarger sizes of fuel. As with wet fuel, therewill be a quantity of unconsumed woodcarried over and the heating surfaces mustbe kept clean.

In a few localities cord wood is burned.With this as with other classes of woodfuel, a large combustion space is anessential feature. The percentage ofmoisture in cord wood may make itnecessary to use an extension furnace, butordinarily this is not required. Amplecombustion space is in most cases securedby dropping the grates to the floor line,large double-deck fire doors beingsupplied at the usual fire door levelthrough which the wood is thrown byhand. Air is admitted under the grates

through an excavated ashpit. The side,front and rear walls of the furnace shouldbe corbelled out to cover about one-thirdof the total grate surface. This preventscold air from laneing up the sides of thefurnace and also reduces the gratesurface. Cord wood and slabs form anopen fire through which the frictional lossof the air is much less than in the case ofsawdust or hogged material. Thecombustion rate with cord wood is,therefore, higher and the grate surfacemay be considerably reduced. Such woodis usually cut in lengths of 4 feet or 4 feet 6inches, and the depth of the grates shouldbe kept approximately 5 feet to get thebest results.

Bagasse--Bagasse is the refuse of sugarcane from which the juice has beenextracted by pressure between the rolls ofthe mill. From the start of the sugar

industry bagasse has been considered thenatural fuel for sugar plantations, and inview of the importance of the industry aword of history relative to the use of thisfuel is not out of place.

When the manufacture of sugar was in itsinfancy the cane was passed through but asingle mill and the defecation andconcentration of the saccharine juice tookplace in a series of vessels mounted oneafter another over a common fire at oneend and connected to a stack at theopposite end. This primitive method wasknown in the English colonies as the"Open Wall" and in the Spanish-Americancountries as the "Jamaica Train".

The evaporation and concentration of thejuice in the open air and over a direct firerequired such quantities of fuel, and thebagasse, in fact, played such an important

part in the manufacture of sugar, thatoftentimes the degree of extraction, whichwas already low, would be sacrificed tothe necessity of obtaining a bagasse thatmight be readily burned.

The furnaces in use with these methodswere as primitive as the rest of theapparatus, and the bagasse could beburned in them only by first drying it. Thisnaturally required an enormous quantity ofhandling of the fuel in spreading andcollecting and frequently entailed ashutting down of the mill, because ashower would spoil the supply which hadbeen dried.

The difficulties arising from the necessityof drying this fuel caused a widespreadattempt on the part of inventors to theturning out of a furnace which wouldsuccessfully burn green bagasse. Some of

the designs were more or less clever, andabout the year 1880 several such greenbagasse furnaces were installed. Thesedid not come up to expectations, however,and almost invariably they wereabandoned and recourse had to be takento the old method of drying in the sun.

From 1880 the new era in the sugarindustry may be dated. Slavery was almostuniversally abolished and it becamenecessary to pay for labor. The cost ofproduction was thus increased, whilegrowing competition of European beetsugar lowered the prices. The onlyremedy for the new state of affairs was thecheapening of the production by theincrease of extraction and improvement inmanufacture. The double mill took theplace of the single, the open wall methodof extraction was replaced by vacuumevaporative apparatus and centrifugal

machines were introduced to do the workof the great curing houses. As opposed tothese improvements, however, the steamplants remained as they started, consistingof double flue boilers externally fired withdry bagasse.

On several of the plantations horizontalmultitubular boilers externally fired wereinstalled and at the time were consideredthe acme of perfection. Numerous attemptswere made to burn the bagasse green,among others the step grates importedfrom Louisiana and known as the LeonMarie furnaces, but satisfactory resultswere obtained in none of the appliancestried.

The Babcock & Wilcox Co. at this timeturned their attention to the problem withthe results which ultimately led to itssolution. Their New Orleans

representative, Mr. Frederick Cook,invented a hot forced blast bagassefurnace and conveyed the patent rights tothis company. This furnace while not asefficient as the standard of to-day, andexpensive in its construction, did,nevertheless, burn the bagasse green andenabled the boilers to develop theirnormal rated capacity. The first furnace ofthis type was installed at the Southwoodand Mt. Houmas plantations and on a smallplantation in Florida. About the year 1888two furnaces were erected in Cuba, one onthe plantation Senado and the other at theCentral Hormiguero. The results obtainedwith these furnaces were so remarkable incomparison with what had previously beenaccomplished that the company wasoverwhelmed with orders. The expense ofauxiliary fuel, usually wood, which wascostly and indispensable in rainy weather,was done away with and as the mill could

be operated on bagasse alone, the steamproduction and the factory work could beregulated with natural increase in dailyoutput.

Progress and improvement in themanufacture itself was going on at aremarkable rate, the single grinding hadbeen replaced by a double grinding, thisin turn by a third grinding, and finally themaceration and dilution of the bagasse wascarried to the extraction of practically thelast trace of sugar contained in it. Thequantity of juice to be treated wasincreased in this way 20 or 30 per cent butwas accompanied by the reduction to aminimum of the bagasse available as afuel, and led to demands upon the furnacebeyond its capacity.

With the improvements in themanufacture, planters had been

compelled to make enormous sacrifices tochange radically their systems, and theheavy disbursement necessary for millapparatus left few in a financial position tomake costly installations of good furnaces.The necessity of turning to somethingcheap in furnace construction but whichwas nevertheless better than the earlymethod of burning the fuel dry led to theinvention of numerous furnaces by allclasses of engineers regardless of theirknowledge of the subject and based uponno experience. None of the furnaces thusproduced were in any sense inventions butwere more or less barefacedinfringements of the patents of TheBabcock & Wilcox Co. As the companycould not protect its rights without hurtingits clients, who in many cases against theirown will were infringing upon thesepatents, and as on the other hand theywere anxious to do something to meet the

wants of the planters, a series ofexperiments were started, at their ownrather than at their customers' expense,with a view to developing a furnace which,without being as expensive, would stillfulfill all the requirements of themanufacturer. The result was the cold blastgreen bagasse furnace which is nowoffered, and it has been adopted asstandard for this class of work after yearsof study and observation in ourinstallations in the sugar countries of theworld. Such a furnace is described later inconsidering the combustion of bagasse.

Composition and Calorific Value ofBagasse--The proportion of fiber containedin the cane and density of the juice areimportant factors in the relation thebagasse fuel will have to the total fuelnecessary to generate the steam requiredin a mill's operation. A cane rich in wood

fiber produces more bagasse than a poorone and a thicker juice is subject to ahigher degree of dilution than one not sorich.

Besides the percentage of bagasse in thecane, its physical condition has a bearingon its calorific value. The factors hereentering are the age at which the canemust be cut, the locality in which it isgrown, etc. From the analysis of anysample of bagasse its approximatecalorific value may be calculated from theformula,

8550F + 7119S + 6750G -972W B. t. u. per pound bagasse =---------------------------- (22) 100

Where F = per cent of fiber in cane, S =per cent sucrose, G = per cent glucose, W

= per cent water.

This formula gives the total available heatper pound of bagasse, that is, the heatgenerated per pound less the heatrequired to evaporate its moisture andsuperheat the steam thus formed to thetemperature of the stack gases.

Three samples of bagasse in which the ashis assumed to be 3 per cent give from theformula:

F = 50 S and G = 4.5 W = 42.5 B. t. u. =4183 F = 40 S and G = 6.0 W = 51.0 B. t.u. = 3351 F = 33.3 S and G = 7.0 W = 56.7B. t. u. = 2797

A sample of Java bagasse having F = 46.5,S = 4.50, G = 0.5, W = 47.5 gives B. t. u.3868.

These figures show that the dryer thebagasse is crushed, the higher the calorificvalue, though this is accompanied by adecrease in sucrose. The explanation liesin the fact that the presence of sucrose inan analysis is accompanied by a definiteamount of water, and that the residual juicecontains sufficient organic substance toevaporate the water present when a fuel isburned in a furnace. For example, assumethe residual juice (100 per cent) to contain12 per cent organic matter. From theconstant in formula,

12�119 (100-12)�72 ------- = 854.3and ------------ = 855.4. 100 100

That is, the moisture in a juice containing12 per cent of sugar will be evaporated bythe heat developed by the combustion ofthe contained sugar. It would, therefore,appear that a bagasse containing such

juice has a calorific value due only to itsfiber content. This is, of course, true onlywhere the highest products of oxidizationare formed during the combustion of theorganic matter. This is not strictly the case,especially with a bagasse of a highmoisture content which will not burnproperly but which smoulders andproduces a large quantity of products ofdestructive distillation, chiefly heavyhydrocarbons, which escape unburnt. Thereasoning, however, is sufficient to explainthe steam making properties of bagasse ofa low sucrose content, such as are securedin Java, as when the sucrose content islower, the heat value is increased byextracting more juice, and hence moresugar from it. The sugar operations in Javaexemplify this and show that with a highdilution by maceration and heavy pressurethe bagasse meets all of the steamrequirements of the mills without auxiliary

fuel.

A high percentage of silica or salts inbagasse has sometimes been ascribed asthe reason for the tendency to smoulder incertain cases of soft fiber bagasse. This,however, is due to the large moisturecontent of the sample resulting directlyfrom the nature of the cane. Soluble salts inthe bagasse has also been given as theexplanation of such smouldering action ofthe fire, but here too the explanation liessolely in the high moisture content, thisresulting in the development of onlysufficient heat to evaporate the moisture.

TABLE 43

ANALYSES AND CALORIFICVALUES OF BAGASSE+---------------------------------------------------------------------+

|+----------+--------+-------+-------+-------+-------+-------+-------+| || | | || | | |B.t.u. || || | || | | | | per || || Source|Moisture| C | H | O | N | Ash |Pound || || | | | | || | Dry || || | | | || | |Bagasse|||+----------+--------+-------+-------+-------+-------+-------+-------+| ||Cuba | 51.50 |43.15 | 6.00 | 47.95 | | 2.90 | 7985 ||||Cuba | 49.10 | 43.74 | 6.08 | 48.61 |

| 1.57 | 8300 || ||Cuba | 42.50 |43.61 | 6.06 | 48.45 | | 1.88 | 8240 ||||Cuba | 51.61 | 46.80 | 5.34 | 46.35 |

| 1.51 | || ||Cuba | 52.80 |46.78 | 5.74 | 45.38 | | 2.10 | ||||Porto Rico| 41.60 | 44.28 | 6.66 | 47.10| 0.41 | 1.35 | 8359 || ||Porto Rico|43.50 | 44.21 | 6.31 | 47.72 | 0.41 | 1.35| 8386 || ||Porto Rico| 44.20 | 44.92 |6.27 | 46.50 | 0.41 | 1.90 | 8380 ||

||Louisiana | 52.10 | | | | |2.27 | 8230 || ||Louisiana | 54.00 | |

| | | | 8370 || ||Louisiana |51.80 | | | | | | 8371 ||||Java | | 46.03 | 6.56 | 45.55 |0.18 | 1.68 | 8681 |||+----------+--------+-------+-------+-------+-------+-------+-------+|+---------------------------------------------------------------------+

Table 43 gives the analyses and heatvalues of bagasse from various localities.Table 44 gives the value of mill bagasse atdifferent extractions, which data may be ofservice in making approximations as to itsfuel value as compared with that of otherfuels.

TABLE 44

VALUE OF ONE POUND OF MILL

BAGASSE AT DIFFERENT EXTRACTIONS

1: Per Cent Extraction of Weight of Cane2: Per Cent Moisture in Bagasse 3: PerCent in Bagasse 4: Fuel Value, B. t. u. 5:Per Cent in Bagasse 6: Fuel Value, B. t. u.7: Per Cent in Bagasse 8: Fuel Value, B. t.u. 9: Total Heat Developed per Pound ofBagasse 10: Heat Required to EvaporateMoisture[42] 11: Heat Available for SteamGeneration 12: Pounds of BagasseEquivalent to one Pound of Coal of 14,000B. t. u.

+----------------------------------------------------------------+|+---+-----+----------+---------+---------+----------------+----+| || | | | ||B.t.u. Value per| || || | | Fiber |Sugar |Molasses |Pound of Bagasse| |||| |+-----+----+----+----+----+----+-----+----+-----

+ || || | | | | | | | | | || || || 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |9 | 10 | 11 | 12 ||

|+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| || BASED UPON CANEOF 12 PER CENT FIBER AND JUICECONTAINING || ||18 PER CENT OFSOLID MATTER. REPRESENTINGTROPICAL CONDITIONS |||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ||75|42.64|48.00|3996|6.24|451 |3.12|217|4664 |525 |4139 |3.38|| ||77|39.22|52.17|4343|5.74|414 |2.87|200|4958 |483 |4475 |3.13|| ||79|35.15|57.14|4757|5.14|371 |2.57|179|5307 |433 |4874 |2.87|| ||81|30.21|63.16|5258|4.42|319 |2.21|154|5731 |372 |5359 |2.61|| ||83|24.12|70.59|5877|3.53|256 |1.76|122|6255 |297 |5958 |2.35|| ||85|16.20|80.00|6660|2.40|173 |1.20| 83

|6916 |200 |6716 |2.08|||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| || BASED UPON CANEOF 10 PER CENT FIBER AND JUICECONTAINING || ||15 PER CENT OFSOLID MATTER. REPRESENTINGLOUISIANA CONDITIONS|||+---+-----+-----+----+----+----+----+----+-----+----+-----+----+| ||75|51.00|40.00|3330|6.00|433 |3.00|209|3972 |678 |3294 |4.25|| ||77|48.07|43.45|3617|5.66|409 |2.82|196|4222 |592 |3630 |3.86|| ||79|44.52|47.62|3964|5.24|378 |2.62|182|4524 |548 |3976 |3.52|| ||81|40.18|52.63|4381|4.73|342 |2.36|164|4887 |495 |4392 |3.19|| ||83|35.00|58.82|4897|4.12|298 |2.06|143|5436 |431 |5005 |2.80|| ||85|28.33|66.67|5550|3.33|241 |1.67|116|5907 |349 |5558 |2.52|||+---+-----+-----+----+----+----+----+----+----

-+----+-----+----+|+----------------------------------------------------------------+

Furnace Design and the Combustion ofBagasse--With the advance in sugarmanufacture there came, as described, adecrease in the amount of bagasseavailable for fuel. As the general efficiencyof a plant of this description is measuredby the amount of auxiliary fuel requiredper ton of cane, the relative importance ofthe furnace design for the burning of thisfuel is apparent.

In modern practice, under certainconditions of mill operation, and withbagasse of certain physical properties, thebagasse available from the cane groundwill meet the total steam requirements ofthe plant as a whole; such conditionsprevail, as described, in Java. In the United

States, Cuba, Porto Rico and like countries,however, auxiliary fuel is almostuniversally a necessity. The amount willvary, depending to a great extent upon theproportion of fiber in the cane, whichvaries widely with the locality and with theage at which it is cut, and to a lesser extentupon the degree of purity of themanufactured sugar, the use of themaceration water and the efficiency of themill apparatus as a whole.

[Illustration: Fig. 27. Babcock & WilcoxBoiler Set with Green Bagasse Furnace]

Experience has shown that this fuel may beburned with the best results in largequantities. A given amount of bagasseburned in one furnace between twoboilers will give better results than thesame quantity burned in a number ofsmaller furnaces. An objection has been

raised against such practice on thegrounds that the necessity of shuttingdown two boiler units when it is necessaryfor any reason to take off a furnace,requires a larger combined boilercapacity to insure continuity of service. Asa matter of fact, several small furnaces willcost considerably more than one largefurnace, and the saving in original furnacecost by such an installation, taken inconjunction with the added efficiency ofthe larger furnace over the small, willprobably more than offset the cost ofadditional boiler units for spares.

The essential features in furnace design forthis class of fuel are ample combustionspace and a length of gas travel sufficientto enable the gases to be completelyburned before the boiler heating surfacesare encountered. Experience has shownthat better results are secured where the

fuel is burned on a hearth rather than ongrates, the objection to the latter methodbeing that the air for combustion enterslargely around the edges, where the fuelpile is thinnest. When burned on a hearththe air for combustion is introduced intothe furnace through several rows oftuyeres placed above and symmetricallyaround the hearth. An arrangement of suchtuyeres over a grate, and a propermanipulation of the ashpit doors, willovercome largely the objection to gratesand at the same time enable other fuel tobe burned in the furnace when necessary.This arrangement of grates and tuyeres isprobably the better from a commerciallyefficient standpoint. Where the air isadmitted through tuyeres over the grate orhearth line, it impinges on the fuel pile as awhole and causes a uniform combustion.Such tuyeres connect with an annularspace in which, where a blast is used, the

air pressure is controlled by a blower.

All experience with this class of fuelindicates that the best results are securedwith high combustion rates. With a naturaldraft in the furnace of, say, three-tenthsinch of water, a combustion rate of from250 to 300 pounds per square foot of gratesurface per hour may be obtained. With ablast of, say, five-tenths inch of water, thisrate can be increased to 450 pounds persquare foot of grate surface per hour.These rates apply to bagasse as firedcontaining approximately 50 per cent ofmoisture. It would appear that the mosteconomical results are secured with acombustion rate of approximately 300pounds per square foot per hour which, asstated, may be obtained with natural draft.Where a natural draft is available sufficientto give such a rate, it is in general to bepreferred to a blast.

Fig. 27 shows a typical bagasse furnacewith which very satisfactory results havebeen obtained. The design of this furnacemay be altered to suit the boilers to whichit is connected. It may be changed slightlyin its proportions and in certain instancesin its position relative to the boiler. Thefurnace as shown is essentially a bagassefurnace and may be modified somewhat toaccommodate auxiliary fuel.

The fuel is ignited in a pit A on a hearthwhich is ordinarily elliptical in shape. Airfor combustion is admitted through thetuyeres B connected to an annular space Cthrough which the amount of air iscontrolled. Above the pit the furnacewidens out to form a combustion space Dwhich has a cylindrical or spherical roofwith its top ordinarily from 11 to 13 feetabove the floor. The gases pass from this

space horizontally to a second combustionchamber E from which they are ledthrough arches F to the boiler. Thearrangement of such arches is modified tosuit the boiler or boilers with which thefurnace is operated. A furnace of suchdesign embodies the essential features ofample combustion space and long gastravel.

The fuel should be fed to the furnacethrough an opening in the roof above thepit by some mechanical means which willinsure a constant fuel feed and at the sametime prevent the inrush of cold air into thefurnace.

This class of fuel deposits a considerablequantity of dust, which if not removedpromptly will fuse into a hard glass-likeclinker. Ample provision should be madefor the removal of such dust from the

furnace, the gas ducts and the boilersetting, and these should be thoroughlycleaned once in 24 hours.

Table 45 gives the results of several testson Babcock & Wilcox boilers using fuel ofthis character.

TABLE 45

TESTS OF BABCOCK & WILCOXBOILERS WITH GREEN BAGASSE____________________________________________________________________ | Durationof Test | Hours | 12 | 10 | 10 |10 | | Rated Capacity of Boiler |HorsePower| 319 | 319 | 319 | 319 | | GrateSurface |Square Feet| 33 | 33 |16.5 | 16.5 | | Draft in Furnace |Inches | .30 | .28 | .29 | .27 | | Draft atDamper | Inches | .47 | .45 | .46| .48 | | Blast under Grates | Inches

| ... | ... | ... | .34 | | Temperature of ExitGases | Degrees F.| 536 | 541 | 522 |547 | | /CO_{2} | Per Cent |13.8 | 12.6 | 11.7 | 12.8 | | Flue GasAnalysis { O | Per Cent | 5.9 | 7.6 |8.2 | 6.9 | | \CO | Per Cent |0.0 | 0.0 | 0.0 | 0.0 | | Bagasse per Hour

as Fired | Pounds | 4980 | 4479 | 5040 |5586 | | Moisture in Bagasse | PerCent |52.39 |52.93 |51.84 |51.71 | | DryBagasse per Hour | Pounds | 2371 |2108 | 2427 | 2697 | | Dry Bagasse perSquare Foot| | | | | | | ofGrate Surface per Hour| Pounds | 71.9 |63.9 |147.1 |163.4 | | Water per Hour fromand at | | | | | | | 212Degrees | Pounds |10141 | 9850|10430 |11229 | | Per Cent of RatedCapacity | | | | | | |Developed | Per Cent | 92.1 |89.2 | 94.7 |102.0 ||____________________________|_________

__|______|______|______|______|

Tan Bark--Tan bark, or spent tan, is thefibrous portion of bark remaining after usein the tanning industry. It is usually veryhigh in its moisture content, a number ofsamples giving an average of 65 per centor about two-thirds of the total weight ofthe fuel. The weight of the spent tan isabout 2.13 times as great as the weight ofthe bark ground. In calorific value anaverage of 10 samples gives 9500 B. t. u.per pound dry.[43] The available heat perpound as fired, owing to the greatpercentage of moisture usually found, willbe approximately 2700 B. t. u. Since theweight of the spent tan as fired is 2.13 asgreat as the weight of the bark as groundat the mill, one pound of ground barkproduces an available heat ofapproximately 5700 B. t. u. Relative tobituminous coal, a ton of bark is equivalent

to 0.4 ton of coal. An average chemicalanalysis of the bark is, carbon 51.8 percent, hydrogen 6.04, oxygen 40.74, ash1.42.

Tan bark is burned in isolated cases and ingeneral the remarks on burning wet woodfuel apply to its combustion. The essentialfeatures are a large combustion space,large areas of heated brickwork radiatingto the fuel bed, and draft sufficient for highcombustion rates. The ratings obtainablewith this class of fuel will not be as high aswith wet wood fuel, because of the heatvalue and the excessive moisture content.Mr. D. M. Meyers found in a series ofexperiments that an average of from 1.5 to2.08 horse power could be developed persquare foot of grate surface with horizontalreturn tubular boilers. This horse powerwould vary considerably with the methodin which the spent tan was fired.

[Illustration: 686 Horse-power Babcock &Wilcox Boiler and Superheater in Courseof Erection at the Quincy, Mass., Station ofthe Bay State Street Railway Co.]

LIQUID FUELS AND THEIR COMBUSTION

Petroleum is practically the only liquid fuelsufficiently abundant and cheap to be usedfor the generation of steam. It possessesmany advantages over coal and isextensively used in many localities.

There are three kinds of petroleum in use,namely those yielding on distillation: 1st,paraffin; 2nd, asphalt; 3rd, olefine. To thefirst group belong the oils of theAppalachian Range and the Middle Westof the United States. These are a darkbrown in color with a greenish tinge. Upontheir distillation such a variety of valuablelight oils are obtained that their use as fuelis prohibitive because of price.

To the second group belong the oils foundin Texas and California. These vary in

color from a reddish brown to a jet blackand are used very largely as fuel.

The third group comprises the oils fromRussia, which, like the second, are usedlargely for fuel purposes.

The light and easily ignited constituents ofpetroleum, such as naphtha, gasolene andkerosene, are oftentimes driven off by apartial distillation, these products being ofgreater value for other purposes than foruse as fuel. This partial distillation does notdecrease the value of petroleum as a fuel;in fact, the residuum known in trade as"fuel oil" has a slightly higher calorificvalue than petroleum and because of itshigher flash point, it may be more safelyhandled. Statements made with referenceto petroleum apply as well to fuel oil.

In general crude oil consists of carbon and

hydrogen, though it also contains varyingquantities of moisture, sulphur, nitrogen,arsenic, phosphorus and silt. The moisturecontained may vary from less than 1 toover 30 per cent, depending upon the caretaken to separate the water from the oil inpumping from the well. As in any fuel, thismoisture affects the available heat of theoil, and in contracting for the purchase offuel of this nature it is well to limit the percent of moisture it may contain. A largeportion of any contained moisture can beseparated by settling and for this reasonsufficient storage capacity should besupplied to provide time for such action.

A method of obtaining approximately thepercentage of moisture in crude oil whichmay be used successfully, particularly withlighter oils, is as follows. A burettegraduated into 200 divisions is filled to the100 mark with gasolene, and the

remaining 100 divisions with the oil, whichshould be slightly warmed before mixing.The two are then shaken together and anyshrinkage below the 200 mark filled upwith oil. The mixture should then beallowed to stand in a warm place for 24hours, during which the water and silt willsettle to the bottom. Their percentage byvolume can then be correctly read on theburette divisions, and the percentage byweight calculated from the specificgravities. This method is exceedinglyapproximate and where accurate resultsare required it should not be used. Forsuch work, the distillation method shouldbe used as follows:

Gradually heat 100 cubic centimeters ofthe oil in a distillation flask to atemperature of 150 degrees centigrade;collect the distillate in a graduated tubeand measure the resulting water. Such a

method insures complete removal of waterand reduces the error arising from theslight solubility of the water in gasolene.Two samples checked by the two methodsfor the amount of moisture present gave,

_Distillation_ _Dilution_ _PerCent_ _Per Cent_ 8.716.25 8.82 6.26

TABLE 46

COMPOSITION ANDCALORIFIC VALUE OF VARIOUS OILS

+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+ | Kind of Oil | %C | %H | %S |%O |S.G.|FP | %H2O |Btu |Authority

|+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------

+ |California, Coaling | | | ||.927|134| |17117|Babcock & WilcoxCo. | |California, Bakersfield | | || |.975| | |17600|Wade| |California, Bakersfield | | |1.30|

|.992| | |18257|Wade ||California, Kern River | | | ||.950|140| |18845|Babcock & WilcoxCo. | |California, Los Angeles | ||2.56| | | | |18328|Babcock &Wilcox Co. | |California, Los Angeles |

| | | |.957|196||18855|Babcock & Wilcox Co. ||California, Los Angeles | | | ||.977| | .40 |18280|Babcock & WilcoxCo. | |California, Monte Christo| | |

| |.966|205| |18878|Babcock &Wilcox Co. | |California, Whittier | |

| .98| |.944| |1.06 |18507|Wade| |California, Whittier | |

| .72| |.936| |1.06 |18240|Wade| |California

|85.04|11.52|2.45| .99[44]| | |1.40|17871|Babcock & Wilcox Co. ||California |81.52|11.51|.55|6.92[44]| |230| |18667|U.S.N.Liquid Fuel Board| |California || | .87| | | | .95|18533|Blasdale | |California

| | | | |.891|257||18655|Babcock & Wilcox Co. ||California | | |2.45||.973| |1.50[45]|17976|O'Neill ||California | | |2.46||.975| |1.32 |18104|Shepherd| |Texas, Beaumont |84.6 |10.9|1.63|2.87 |.924|180| |19060|U.S.N.Liquid Fuel Board| |Texas, Beaumont|83.3 |12.4 | .50|3.83 |.926|216||19481|U.S.N. Liquid Fuel Board| |Texas,Beaumont |85.0 |12.3 |1.75| .92[44]|

| | |19060|Denton ||Texas, Beaumont |86.1 |12.3 |1.60|

|.942| | |20152|Sparkes |

|Texas, Beaumont | | | ||.903|222| |19349|Babcock & WilcoxCo. | |Texas, Sabine | | | |

|.937|143| |18662|Babcock &Wilcox Co. | |Texas|87.15|12.33|0.32| |.908|370||19338|U. S. N. | |Texas|87.29|12.32|0.43| |.910|375||19659|U. S. N. | |Ohio|83.4 |14.7 |0.6 |1.3 | | | |19580|

| |Pennsylvania |84.9|13.7 | |1.4 |.886| ||19210|Booth | |West Virginia

|84.3 |14.1 | |1.6 |.841| ||21240| | |Mexico |

| | | |.921|162||18840|Babcock & Wilcox Co. | |Russia,Baku |86.7 |12.9 | | |.884| |

|20691|Booth | |Russia,Novorossick |84.9 |11.6 | |3.46 | |

| |19452|Booth | |Russia,Caucasus |86.6 |12.3 | |1.10

|.938| | |20138| | |Java|87.1 |12.0 | | .9 |.923| |

|21163| | |Austria, Galicia|82.2 |12.1 |5.7 | |.870| |

|18416| | |Italy, Parma|84.0 |13.4 |1.8 | |.786| | | |

| |Borneo |85.7 |11.0| |3.31 | | | |19240|Orde

|+-------------------------+-----+-----+----+--------+----+---+--------+-----+------------------------+

%C = Per Cent Carbon %H = PerCent Hydrogen %S = Per Cent Sulphur%O = Per Cent Oxygen S.G. =Specific Gravity FP = Degrees FlashPoint %H_{2}O = Per Cent Moisture Btu= B. t. u. Per Pound

Calorific Value--A pound of petroleumusually has a calorific value of from 18,000

to 22,000 B. t. u. If an ultimate analysis of anaverage sample be, carbon 84 per cent,hydrogen 14 per cent, oxygen 2 per cent,and assuming that the oxygen is combinedwith its equivalent of hydrogen as water,the analysis would become, carbon 84 percent, hydrogen 13.75 per cent, water 2.25per cent, and the heat value per poundincluding its contained water would be,

Carbon .8400 �14,600 = 12,264 B. t. u.Hydrogen .1375 �62,100 = 8,625 B. t. u.

------[**Should be .1375 x62,000 = 8,525] Total 20,889B. t. u.[**Would be Total = 20,789]

The nitrogen in petroleum varies from0.008 to 1.0 per cent, while the sulphurvaries from 0.07 to 3.0 per cent.

Table 46, compiled from various sources,gives the composition, calorific value and

other data relative to oil from differentlocalities.

The flash point of crude oil is thetemperature at which it gives offinflammable gases. While information onthe actual flash points of the various oils ismeager, it is, nevertheless, a question ofimportance in determining theiravailability as fuels. In general it may bestated that the light oils have a low, and theheavy oils a much higher flash point. Adivision is sometimes made at oils having aspecific gravity of 0.85, with a statementthat where the specific gravity is belowthis point the flash point is below 60degrees Fahrenheit, and where it is above,the flash point is above 60 degreesFahrenheit. There are, however, manyexceptions to this rule. As the flash point islower the danger of ignition or explosionbecomes greater, and the utmost care

should be taken in handling the oils with alow flash point to avoid this danger. On theother hand, because the flash point is highis no justification for carelessness inhandling those fuels. With properprecautions taken, in general, the use ofoil as fuel is practically as safe as the use ofcoal.

Gravity of Oils--Oils are frequentlyclassified according to their gravity asindicated by the Beaume hydrometerscale. Such a classification is by no meansan accurate measure of their relativecalorific values.

Petroleum as Compared with Coal--Theadvantages of the use of oil fuel over coalmay be summarized as follows:

1st. The cost of handling is much lower, theoil being fed by simple mechanical means,

resulting in,

2nd. A general labor saving throughout theplant in the elimination of stokers, coalpassers, ash handlers, etc.

3rd. For equal heat value, oil occupiesvery much less space than coal. Thisstorage space may be at a distance fromthe boiler without detriment.

4th. Higher efficiencies and capacities areobtainable with oil than with coal. Thecombustion is more perfect as the excessair is reduced to a minimum; the furnacetemperature may be kept practicallyconstant as the furnace doors need not beopened for cleaning or working fires;smoke may be eliminated with theconsequent increased cleanliness of theheating surfaces.

5th. The intensity of the fire can be almostinstantaneously regulated to meet loadfluctuations.

6th. Oil when stored does not lose incalorific value as does coal, nor are thereany difficulties arising from disintegration,such as may be found when coal is stored.

7th. Cleanliness and freedom from dustand ashes in the boiler room with aconsequent saving in wear and tear onmachinery; little or no damage tosurrounding property due to such dust.

The disadvantages of oil are:

1st. The necessity that the oil have areasonably high flash point to minimize thedanger of explosions.

2nd. City or town ordinances may impose

burdensome conditions relative to locationand isolation of storage tanks, which in thecase of a plant situated in a congestedportion of the city, might make use of thisfuel prohibitive.

3rd. Unless the boilers and furnaces areespecially adapted for the use of this fuel,the boiler upkeep cost will be higher thanif coal were used. This objection can beentirely obviated, however, if theinstallation is entrusted to those who havehad experience in the work, and theoperation of a properly designed plant isplaced in the hands of intelligent labor.

TABLE 47

RELATIVE VALUE OF COALAND OIL FUEL

+------+--------+-------+---------------------------

--------------------+ |Gross | Net | Net |Water Evaporated from and at |

|Boiler| Boiler |Evap- | 212 DegreesFahrenheit per Pound of Coal ||Effic-|Effici-|oration+-----+-----+-----+-----+-----+-----+-----+-----+ | iency|ency[46]| from | | |

| | | | | | | with | with |andat | | | | | | | | | | Oil |Oil | 212 | 5 | 6 | 7 | 8 | 9 | 10 |11 | 12 | | Fuel | Fuel |Degrees| | |

| | | | | | | ||Fahren-| | | | | | | | | |

| | heit+-----+-----+-----+-----+-----+-----+-----+-----+ | | | per |

| | | | Pound | Pounds of OilEqual to One Pound of Coal | | ||of Oil | |+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ | 73 | 71 | 13.54|.3693|.4431|.5170|.5909|.6647|.7386|.8

124|.8863| | 74 | 72 | 13.73|.3642|.4370|.5099|.5827|.6556|.7283|.8011|.8740| | 75 | 73 | 13.92|.3592|.4310|.5029|.5747|.6466|.7184|.7903|.8621| | 76 | 74 | 14.11|.3544|.4253|.4961|.5670|.6378|.7087|.7796|.8505| | 77 | 75 | 14.30|.3497|.4196|.4895|.5594|.6294|.6993|.7692|.8392| | 78 | 76 | 14.49|.3451|.4141|.4831|.5521|.6211|.6901|.7591|.8281| | 79 | 77 | 14.68|.3406|.4087|.4768|.5450|.6131|.6812|.7493|.8174| | 80 | 78 | 14.87|.3363|.4035|.4708|.5380|.6053|.6725|.7398|.8070| | 81 | 79 | 15.06|.3320|.3984|.4648|.5312|.5976|.6640|.7304|.7968| | 82 | 80 | 15.25|.3279|.3934|.4590|.5246|.5902|.6557|.7213|.7869| | 83 | 81 | 15.44|.3238|.3886|.4534|.5181|.5829|.6447|.7125|.7772|+------+--------+-------+-----+-----+-----+-----

+-----+-----+-----+-----+ | | | Net || | | |Evap-

| | | ||oration| | | |

| from | | || |and at | | |

| | 212 | Barrels of Oil Equal toOne Ton of Coal | | | |Degrees|

| | ||Fahren-| | | |

| heit | | || | per | | |

| |Barrel | || | |of Oil |

|+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+ | 73 | 71 | 4549|2.198|2.638|3.077|3.516|3.955|4.395|4.835|5.275| | 74 | 72 | 4613|2.168|2.601|3.035|3.468|3.902|4.335|4.769|5.202| | 75 | 73 | 4677|2.138|2.565|2.993|3.420|3.848|4.275|4.

703|5.131| | 76 | 74 | 4741|2.110|2.532|2.954|3.376|3.798|4.220|4.642|5.063| | 77 | 75 | 4807|2.082|2.498|2.914|3.330|3.746|4.162|4.578|4.994| | 78 | 76 | 4869|2.054|2.465|2.876|3.286|3.697|4.108|4.518|4.929| | 79 | 77 | 4932|2.027|2.433|2.838|3.243|3.649|4.054|4.460|4.865| | 80 | 78 | 4996|2.002|2.402|2.802|3.202|3.602|4.003|4.403|4.803| | 81 | 79 | 5060|1.976|2.371|2.767|3.162|3.557|3.952|4.348|4.743| | 82 | 80 | 5124|1.952|2.342|2.732|3.122|3.513|3.903|4.293|4.683| | 83 | 81 | 5187|1.927|2.313|2.699|3.085|3.470|3.856|4.241|4.627|+------+--------+-------+-----+-----+-----+-----+-----+-----+-----+-----+

[Illustration: City of San Francisco, Cal.,Fire Fighting Station. No. 1. 2800 Horse

Power of Babcock & Wilcox Boilers,Equipped for Burning Oil Fuel]

Many tables have been published with aview to comparing the two fuels. Such ofthese as are based solely on the relativecalorific values of oil and coal are oflimited value, inasmuch as the efficienciesto be obtained with oil are higher than thatobtainable with coal. Table 47 takes intoconsideration the variation in efficiencywith the two fuels, but is based on aconstant calorific value for oil and coal.This table, like others of a similar nature,while useful as a rough guide, cannot beconsidered as an accurate basis forcomparison. This is due to the fact thatthere are numerous factors entering intothe problem which affect the savingpossible to a much greater extent than dothe relative calorific values of two fuels.Some of the features to be considered in

arriving at the true basis for comparisonare the labor saving possible, the spaceavailable for fuel storage, the facilities forconveying the oil by pipe lines, the hoursduring which a plant is in operation, theload factor, the quantity of coal requiredfor banking fires, etc., etc. The only exactmethod of estimating the relativeadvantages and costs of the two fuels is byconsidering the operating expenses of theplant with each in turn, including the costsof every item entering into the problem.

Burning Oil Fuel--The requirements forburning petroleum are as follows:

1st. Its atomization must be thorough.

2nd. When atomized it must be broughtinto contact with the requisite quantity ofair for its combustion, and this quantitymust be at the same time a minimum to

obviate loss in stack gases.

3rd. The mixture must be burned in afurnace where a refractory materialradiates heat to assist in the combustion,and the furnace must stand up under thehigh temperatures developed.

4th. The combustion must be completedbefore the gases come into contact withthe heating surfaces or otherwise the flamewill be extinguished, possibly to ignitelater in the flue connection or in the stack.

5th. There must be no localization of theheat on certain portions of the heatingsurfaces or trouble will result fromoverheating and blistering.

The first requirement is met by theselection of a proper burner.

The second requirement is fulfilled byproperly introducing the air into thefurnace, either through checkerworkunder the burners or through openingsaround them, and by controlling thequantity of air to meet variations in furnaceconditions.

The third requirement is provided for byinstalling a furnace so designed as to givea sufficient area of heated brickwork toradiate the heat required to maintain aproper furnace temperature.

The fourth requirement is provided for bygiving ample space for the combustion ofthe mixture of atomized oil and air, and agas travel of sufficient length to insure thatthis combustion be completed before thegases strike the heating surfaces.

The fifth requirement is fulfilled by the

adoption of a suitable burner in connectionwith the furnace meeting the otherrequirements. A burner must be used fromwhich the flame will not impinge directlyon the heating surface and must be locatedwhere such action cannot take place. Ifsuitable burners properly located are notused, not only is the heat localized withdisastrous results, but the efficiency islowered by the cooling of the gases beforecombustion is completed.

Oil Burners--The functions of an oil burneris to atomize or vaporize the fuel so that itmay be burned like a gas. All burners maybe classified under three general types:1st, spray burners, in which the oil isatomized by steam or compressed air;2nd, vapor burners, in which the oil isconverted into vapor and then passed intothe furnace; 3rd, mechanical burners, inwhich the oil is atomized by submitting it

to a high pressure and passing it through asmall orifice.

Vapor burners have never been in generaluse and will not be discussed.

Spray burners are almost universally usedfor land practice and the simplicity of thesteam atomizer and the excellent economyof the better types, together with the lowoil pressure and temperature requiredmakes this type a favorite for stationaryplants, where the loss of fresh water is nota vital consideration. In marine work, or inany case where it is advisable to save feedwater that otherwise would have to beadded in the form of "make-up", eithercompressed air or mechanical means areused for atomization. Spray burners usingcompressed air as the atomizing agent arein satisfactory operation in some plants,but their use is not general. Where there is

no necessity of saving raw feed water, thegreater simplicity and economy of thesteam spray atomizer is generally the mostsatisfactory. The air burners requireblowers, compressors or other apparatuswhich occupy space that might beotherwise utilized and require attentionthat is not necessary where steam is used.

Steam spray burners of the older typeshad disadvantages in that they were sodesigned that there was a tendency for thenozzle to clog with sludge or coke formedfrom the oil by the heat, without means ofbeing readily cleaned. This has beenovercome in the more modern types.

Steam spray burners, as now used, may bedivided into two classes: 1st, insidemixers; and 2nd, outside mixers. In theformer the steam and oil come into contactwithin the burner and the mixture is

atomized in passing through the orifice ofthe burner nozzle.

[Illustration: Fig. 28. Peabody Oil Burner]

In the outside mixing class the steam flowsthrough a narrow slot or horizontal row ofsmall holes in the burner nozzle; the oilflows through a similar slot or hole abovethe steam orifice, and is picked up by thesteam outside of the burner and isatomized. Fig. 28 shows a type of thePeabody burner of this class, which hasgiven eminent satisfaction. Theconstruction is evident from the cut. It willbe noted that the portions of the burnerforming the orifice may be readilyreplaced in case of wear, or if it is desiredto alter the form of the flame.

Where burners of the spray type are used,heating the oil is of advantage not only in

causing it to be atomized more easily, butin aiding economical combustion. Thetemperature is, of course, limited by theflash point of the oil used, but within thelimit of this temperature there is no dangerof decomposition or of carbon deposits onthe supply pipes. Such heating should bedone close to the boiler to minimizeradiation loss. If the temperature is raisedto a point where an appreciablevaporization occurs, the oil will flowirregularly from the burner and cause theflame to sputter.

On both steam and air atomizing types, aby-pass should be installed between thesteam or air and the oil pipes to providefor the blowing out of the oil duct. Strainersshould be provided for removing sludgefrom the fuel and should be so located asto allow for rapid removal, cleaning andreplacing.

Mechanical burners have been in use forsome time in European countries, but theirintroduction and use has been of onlyrecent occurrence in the United States.Here as already stated, the means foratomization are purely mechanical. Themost successful of the mechanicalatomizers up to the present have been ofthe round flame type, and only these willbe considered. Experiments have beenmade with flat flame mechanical burners,but their satisfactory action has beenconfined to instances where it is onlynecessary to burn a small quantity of oilthrough each individual burner.

This system of oil burning is especiallyadapted for marine work as the quantity ofsteam for putting pressure on the oil issmall and the condensed steam may bereturned to the system.

The only method by which successfulmechanical atomization has beenaccomplished is one by which the oil isgiven a whirling motion within the burnertip. This is done either by forcing the oilthrough a passage of helical form or bydelivering it tangentially to a circularchamber from which there is a centraloutlet. The oil is fed to these burners undera pressure which varies with the make ofthe burner and the rates at whichindividual burners are using oil. The oilparticles fly off from such a burner instraight lines in the form of a cone ratherthan in the form of a spiral spray, as mightbe supposed.

With burners of the mechanical atomizingdesign, the method of introducing air forcombustion and the velocity of this air areof the greatest importance in securing

good combustion and in the effects on thecharacter and shape of the flame. Suchburners are located at the front of thefurnace and various methods have beentried for introducing the air forcombustion. Where, in the spray burners,air is ordinarily admitted through acheckerwork under the burner proper,with the mechanical burner, it is almostuniversally admitted around the burner.Early experiments with these airdistributors were confined largely tosingle or duplicate cones used with theidea of directing the air to the axis of theburner. A highly successful method of suchair introduction, developed by Messrs.Peabody and Irish of The Babcock &Wilcox Co., is by means of what they terman "impeller plate". This consists of acircular metal disk with an opening at thecenter for the oil burner and with radialmetal strips from the center to the

periphery turned at an angle which in thelater designs may be altered to give the airsupply demanded by the rate ofcombustion.

The air so admitted does not necessarilyrequire a whirling motion, butexperiments show that where the air isbrought into contact with the oil spray withthe right "twist", better combustion issecured and lower air pressures and lessrefinement of adjustment of individualburners are required.

Mechanical burners have a distinctadvantage over those in which steam isused as the atomizing agent in that theylend themselves more readily toadjustment under wider variations of load.For a given horse power there willordinarily be installed a much greaternumber of mechanical than steam

atomizing burners. This in itself is a meansto better regulation, for with the steamatomizing burner, if one of a number isshut off, there is a marked decrease inefficiency. This is due to the fact that withthe air admitted under the burner, it isordinarily passing through thecheckerwork regardless of whether it isbeing utilized for combustion or not. Witha mechanical burner, on the other hand,where individual burners are shut off, airthat would be admitted for such burner,were it in operation, may also be shut offand there will be no undue loss fromexcess air.

Further adjustment to meet load conditionsis possible by a change in the oil pressureacting on all burners at once. A goodburner will atomize moderately heavy oilwith an oil pressure as low as 30 poundsper square inch and from that point up to

200 pounds or above. The heating of theoil also has an effect on the capacity ofindividual burners and in this way a thirdmethod of adjustment is given. Underworking conditions, the oil pressureremaining constant, the capacity of eachburner will decrease as the temperature ofthe oil is increased though at lowtemperatures the reverse is the case. Someexperiments with a Texas crude oil havinga flash point of 210 degrees showed thatthe capacity of a mechanical atomizingburner of the Peabody type increasedfrom 80 degrees Fahrenheit to 110degrees Fahrenheit, from which point itfell off rapidly to 140 degrees and thenmore slowly to the flash point.

The above methods, together with theregulation possible through manipulationof the boiler dampers, indicate the widerange of load conditions that may be

handled with an installation of this class ofburners.

As has already been stated, results withmechanical atomizing burners that may beconsidered very successful have beenlimited almost entirely to cases whereforced blast of some description has beenused, the high velocity of the air enteringbeing of material assistance in securingthe proper mixture of air with the oil spray.Much has been done and is being done inthe way of experiment with this class ofapparatus toward developing a successfulmechanical atomizing burner for use withnatural draft, and there appears to be noreason why such experiments should noteventually produce satisfactory results.

Steam Consumption of Burners--TheBureau of Steam Engineering, U. S. Navy,made in 1901 an exhaustive series of tests

of various oil burners that may beconsidered as representing, in so far asthe performance of the burnersthemselves is concerned, the practice ofthat time. These tests showed that a burnerutilizing air as an atomizing agent,required for compressing the air from 1.06to 7.45 per cent of the total steamgenerated, the average being 3.18 percent. Four tests of steam atomizing burnersshowed a consumption of 3.98 to 5.77 percent of the total steam, the average being4.8 per cent.

Improvement in burner design has largelyreduced the steam consumption, though toa greater degree in steam than in airatomizing burners. Recent experimentsshow that a good steam atomizing burnerwill require approximately 2 per cent ofthe total steam generated by the boileroperated at or about its rated capacity.

This figure will decrease as the capacity isincreased and is so low as to be practicallynegligible, except in cases where thequestion of loss of feed water is allimportant. There are no figures availableas to the actual steam consumption ofmechanical atomizing burners butapparently this is small if the requirementis understood to be entirely apart from thesteam consumption of the apparatusproducing the forced blast.

Capacity of Burners--A good steamatomizing burner properly located in awell-designed oil furnace has a capacity ofsomewhat over 400 horse power. Thisquestion of capacity of individual burnersis largely one of the proper relationbetween the number of burners used andthe furnace volume. In some recent testswith a Babcock & Wilcox boiler of 640rated horse power, equipped with three

burners, approximately 1350 horse powerwas developed with an available draft of.55 inch at the damper or 450 horse powerper burner. Four burners were also triedin the same furnace but the total steamgenerated did not exceed 1350 horsepower or in this instance 338 horse powerper burner.

From the nature of mechanical atomizingburners, individual burners have not aslarge a capacity as the steam atomizingclass. In some tests on a Babcock & Wilcoxmarine boiler, equipped with mechanicalatomizing burners, the maximum horsepower developed per burner wasapproximately 105. Here again the burnercapacity is largely one of proper relationbetween furnace volume and number ofburners.

Furnace Design--Too much stress cannot

be laid on the importance of furnacedesign for the use of this class of fuel.Provided a good type of burner is adoptedthe furnace arrangement and the methodof introducing air for combustion into thefurnace are the all important factors. Nomatter what the type of burner, satisfactoryresults cannot be secured in a furnace notsuited to the fuel.

The Babcock & Wilcox Co. has had muchexperience with the burning of oil as fueland an extended series of experiments byMr. E. H. Peabody led to the developmentand adoption of the Peabody furnace asbeing most eminently suited for this classof work. Fig. 29 shows such a furnaceapplied to a Babcock & Wilcox boiler, andwith slight modification it can be as readilyapplied to any boiler of The Babcock &Wilcox Co. manufacture. In the descriptionof this furnace, its points of advantage

cover the requirements of oil-burningfurnaces in general.

The atomized oil is introduced into thefurnace in the direction in which itincreases in height. This increase infurnace volume in the direction of theflame insures free expansion and athorough mixture of the oil with the air,and the consequent complete combustionof the gases before they come into contactwith the tube heating surfaces. In such afurnace flat flame burners should be used,preferably of the Peabody type, in whichthe flame spreads outward toward thesides in the form of a fan. There is notendency of the flames to impinge directlyon the heating surfaces, and the furnacecan handle any quantity of flame withoutdanger of tube difficulties. The burnersshould be so located that the flames fromindividual burners do not interfere nor

impinge to any extent on the side walls ofthe furnace, an even distribution of heatbeing secured in this manner. The burnersare operated from the boiler front andpeepholes are supplied through which theoperator may watch the flame whileregulating the burners. The burners canbe removed, inspected, or cleaned andreplaced in a few minutes. Air is admittedthrough a checkerwork of fire bricksupported on the furnace floor, theopenings in the checkerwork being soarranged as to give the best economicresults in combustion.

[Illustration: Fig. 29. Babcock & WilcoxBoiler, Equipped with a Peabody OilFurnace]

With steam atomizing burners introducedthrough the front of the boiler in stationarypractice, it is usually in the direction in

which the furnace decreases in height andit is with such an arrangement thatdifficulties through the loss of tubes maybe expected. With such an arrangement,the flame may impinge directly upon thetube surfaces and tube troubles from thissource may arise, particularly where thefeed water has a tendency toward rapidscale formation. Such difficulties may bethe result of a blowpipe action on the partof the burner, the over heating of the tubedue to oil or scale within, or the actualerosion of the metal by particles of oilimproperly atomized. Such action need notbe anticipated, provided the oil is burnedwith a short flame. The flames frommechanical atomizing burners have a lessvelocity of projection than those fromsteam atomizing burners and if introducedinto the higher end of the furnace, shouldnot lead to tube difficulties provided theyare properly located and operated. This

class of burner also will give the mostsatisfactory results if introduced so that theflames travel in the direction of increase infurnace volume. This is perhaps bestexemplified by the very good resultssecured with mechanical atomizingburners and Babcock & Wilcox marineboilers in which, due to the fact that theboilers are fired from the low end, theflames from burners introduced throughthe front are in this direction.

Operation of Burners--When burners arenot in use, or when they are being startedup, care must be taken to prevent oil fromflowing and collecting on the floor of thefurnace before it is ignited. In starting aburner, the atomized fuel may be ignitedby a burning wad of oil-soaked waste heldbefore it on an iron rod. To insure quickignition, the steam supply should be cutdown. But little practice is required to

become an adept at lighting an oil fire.When ignition has taken place and thefurnace brought to an even heat, the steamshould be cut down to the minimumamount required for atomization. Thisamount can be determined from theappearance of the flame. If sufficient steamis not supplied, particles of burning oil willdrop to the furnace floor, giving ascintillating appearance to the flame. Thesteam valves should be opened justsufficiently to overcome this scintillatingaction.

Air Supply--From the nature of the fuel andthe method of burning, the quantity of airfor combustion may be minimized. As withother fuels, when the amount of airadmitted is the minimum which willcompletely consume the oil, the results arethe best. The excess or deficiency of aircan be judged by the appearance of the

stack or by observing the gases passingthrough the boiler settings. A perfectlyclear stack indicates excess air, whereassmoke indicates a deficiency. Withproperly designed furnaces the bestresults are secured by running near thesmoking point with a slight haze in thegases. A slight variation in the air supplywill affect the furnace conditions in an oilburning boiler more than the samevariation where coal is used, and for thisreason it is of the utmost importance thatflue gas analysis be made frequently onoil-burning boilers. With the air forcombustion properly regulated byadjustment of any checkerwork or anyother device which may be used, and thedampers carefully set, the flue gas analysisshould show, for good furnace conditions,a percentage of CO_{2} between 13 and 14per cent, with either no CO or but a trace.

In boiler plant operation it is difficult toregulate the steam supply to the burnersand the damper position to meet suddenand repeated variations in the load. Adevice has been patented whichautomatically regulates by means of theboiler pressure the pressure of the steamto the burners, the oil to the burners andthe position of the boiler damper. Such adevice has been shown to give goodresults in plant operation where handregulation is difficult at best, and in manyinstances is unfortunately not evenattempted.

Efficiency with Oil--As pointed out inenumerating the advantages of oil fuelover coal, higher efficiencies areobtainable with the former. With boilers ofapproximately 500 horse power equippedwith properly designed furnaces andburners, an efficiency of 83 per cent is

possible or making an allowance of 2 percent for steam used by burners, a netefficiency of 81 per cent. The conditionsunder which such efficiencies are to besecured are distinctly test conditions inwhich careful operation is a primerequisite. With furnace conditions that arenot conductive to the best combustion, thisfigure may be decreased by from 5 to 10per cent. In large properly designedplants, however, the first named efficiencymay be approached for uniform runningconditions, the nearness to which it isreached depending on the intelligence ofthe operating crew. It must beremembered that the use of oil fuelpresents to the careless operatorpossibilities for wastefulness much greaterthan in plants where coal is fired, and ittherefore pays to go carefully into thisfeature.

Table 48 gives some representative testswith oil fuel.

TABLE 48

TESTS OF BABCOCK AND WILCOXBOILERS WITH OIL FUEL

_______________________________________________________________________ |

| | | | ||Pacific Light|Pacific Light|Miami

Copper | | | and Power |and Power | Company | | Plant

| Company | Company | | ||Los Angeles, | |

Miami, | | | Cal.|Redondo, Cal.| Arizona ||_____________________________|_____________|_____________|_____________| |

| | | | | |

Rated Capacity | Horse | || | | of Boiler | Power | 467

| 604 | 600 ||__________________|__________|_____________|_____________|_____________| |

| | | | | | | | |Duration of Test | Hours | 10 | 10 | 7| 7 | 10 | 4 | | | | || | | | | | Steam Pressure |

| | | | | | | | by Gauge| Pounds | 156.4| 156.9| 184.7| 184.9|

183.4| 189.5| | | | | || | | | | Temperature of |

Degrees | | | | | | | |Feed Water | F. | 62.6| 61.1| 93.4|101.2| 157.7| 156.6| | | || | | | | | | Degrees of |Degrees | | | | | | | |Superheat | F. | | | 83.7|144.3| 103.4| 139.6| | | || | | | | | | Factor of |

| | | | | | | |

Evaporation ||1.2004|1.2020|1.2227|1.2475|1.1676|1.1886| | | | | | | |

| | | Draft in Furnace | Inches | .02 |.05 | .014| .19 | .12 | .22 | | |

| | | | | | | | Draft atDamper | Inches | .08 | .15 | .046| .47| .19 | .67 | | | | | || | | | | Temperature of |

Degrees | | | | | | | |Exit Gases | F. | 438 | 525 | 406 |537 | 430 | 612 | | _ | | |

| | | | | | Flue | CO_{2} |Per Cent | | | 14.3 | 12.1 | | | |Gas | O | Per Cent | | | 3.8 |6.8 | | | | Analysis|_CO | Per Cent| | | 0.0 | 0.0 | | | | |

| | | | | | | | OilBurned | | | | | | || | per Hour | Pounds | 1147 | 1837

| 1439 | 2869 | 1404 | 3214 | | || | | | | | | | Water

Evaporated | | | | | | || | per Hour from | | | | || | | | from and at | Pounds |

18310| 27855| 22639| 40375| 21720|42863| | 212 Degrees | | | |

| | | | | | | || | | | | | Evaporation from |

| | | | | | | | and at212 | | | | | | | | |Degrees per | Pounds | 15.96| 15.16|

15.73| 14.07| 15.47| 13.34| | Pound ofOil | | | | | | | | |

| | | | | | | | |Per Cent of | | | | | || | | Rated Capacity | Pounds |113.6| 172.9| 108.6| 193.8| 104.9| 207.1|| Developed | | | | | |

| | | | | | | || | | | B. t. u. per | | | |

| | | | | Pound of Oil | B. t. u. |18626| 18518| 18326| 18096| 18600|18600| | | | | | |

| | | | Efficiency | Per Cent |83.15| 79.46| 83.29| 76.02| 80.70| 69.6 ||__________________|__________|______|______|______|______|______|______|

Burning Oil in Connection with OtherFuels--Considerable attention has beenrecently given to the burning of oil inconnection with other fuels, and acombination of this sort may be advisableeither with the view to increasing theboiler capacity to assist over peak loads,or to keep the boiler in operation wherethere is the possibility of a temporaryfailure of the primary fuel. It would appearfrom experiments that such a combinationgives satisfactory results from thestandpoint of both capacity and efficiency,if the two fuels are burned in separatefurnaces. Satisfactory results cannotordinarily be obtained when it isattempted to burn oil fuel in the same

furnace as the primary fuel, as it ispractically impossible to admit the properamount of air for combustion for each ofthe two fuels simultaneously. The Babcock& Wilcox boiler lends itself readily to adouble furnace arrangement and Fig. 30shows an installation where oil fuel isburned as an auxiliary to wood.

[Illustration: Fig. 30. Babcock & WilcoxBoiler Set with Combination Oil andWood-burning Furnace]

Water-gas Tar--Water-gas tar, orgas-house tar, is a by-product of the coalused in the manufacture of water gas. It isslightly heavier than crude oil and has acomparatively low flash point. In burning,it should be heated only to a temperaturewhich makes it sufficiently fluid, and anyfurnace suitable for crude oil is in generalsuitable for water-gas tar. Care should be

taken where this fuel is used to install asuitable apparatus for straining it before itis fed to the burner.

[Illustration: Babcock & Wilcox BoilersFired with Blast Furnace Gas at theBethlehem Steel Co., Bethlehem, Pa. ThisCompany Operates 12,900 Horse Power ofBabcock & Wilcox Boilers]

GASEOUS FUELS AND THEIRCOMBUSTION

Of the gaseous fuels available for steamgenerating purposes, the most commonare blast furnace gas, natural gas andby-product coke oven gas.

Blast furnace gas, as implied by its name,is a by-product from the blast furnace ofthe iron industry. This gasification of thesolid fuel in a blast furnace results, 1st,through combustion by the oxygen of theblast; 2nd, through contact with theincandescent ore (Fe_{2}O_{3} + C = 2 FeO+ CO and FeO + C = Fe + CO); and 3rd,through the agency of CO_{2} eitherformed in the process of reduction ordriven from the carbonates charged eitheras ore or flux.

Approximately 90 per cent of the fuelconsumed in all of the blast furnaces of theUnited States is coke. The consumption ofcoke per ton of iron made varies from 1600to 3600 pounds per ton of 2240 pounds ofiron. This consumption depends upon thequality of the coal, the nature of the ore,the quality of the pig iron produced andthe equipment and management of theplant. The average consumption, and onewhich is approximately correct forordinary conditions, is 2000 pounds ofcoke per gross ton (2240 pounds) of pigiron. The gas produced in a gas furnaceper ton of pig iron is obtained from theweight of fixed carbon gasified, the weightof the oxygen combined with the materialof charge reduced, the weight of thegaseous constituents of the flux and theweight of air delivered by the blowingengine and the weight of volatilecombustible contained in the coke.

Ordinarily, this weight of gas will be foundto be approximately five times the weightof the coke burned, or 10,000 pounds perton of pig iron produced.

With the exception of the small amount ofcarbon in combination with hydrogen asmethane, and a very small percentage offree hydrogen, ordinarily less than 0.1 percent, the calorific value of blast furnacegas is due to the CO content which whenunited with sufficient oxygen when burnedunder a boiler, burns further to CO_{2}.The heat value of such gas will vary in mostcases from 85 to 100 B. t. u. per cubic footunder standard conditions. In modernpractice, where the blast is heated by hotblast stoves, approximately 15 per cent ofthe total amount of gas is used for thispurpose, leaving 85 per cent of the total foruse under boilers or in gas engines, that is,approximately 8500 pounds of gas per ton

of pig iron produced. In a modern blastfurnace plant, the gas serves ordinarily asthe only fuel required. Table 49 gives theanalyses of several samples of blastfurnace gas.

TABLE 49

TYPICAL ANALYSES OF BLASTFURNACE GAS

+----------------------------------------------------------------+|+-----------------------+------+----+-----+----+------+--------+| || |CO_{2}| O| CO | H |CH_{4}| N |||+-----------------------+------+----+-----+----+------+--------+| ||Bessemer Furnace |9.85|0.36|32.73|3.14| .. |53.92 ||||Bessemer Furnace | 11.4 | .. |27.7|1.9 | 0.3 |58.7 || ||Bessemer Furnace

| 10.0 | .. |26.2 |3.1 | 0.2 |60.5 ||

||Bessemer Furnace | 9.1 | .. |28.7|2.7 | 0.2 |59.3 || ||Bessemer Furnace

| 13.5 | .. |25.2 |1.43| .. |59.87 ||||Bessemer Furnace[47] | 10.9 | .. |27.8|2.8 | 0.2 |58.3 || ||Ferro ManganeseFurnace| 7.1 | .. |30.1 | .. | .. |62.8[48]||||Basic Ore Furnace | 16.0 |0.2 |23.6 |.. | .. |60.2[48]|||+-----------------------+------+----+-----+----+------+--------+|+----------------------------------------------------------------+

Until recently, the important considerationin the burning of blast furnace gas hasbeen the capacity that can be developedwith practically no attention given to theaspect of efficiency. This phase of thequestion is now drawing attention andfurnaces especially designed for goodefficiency with this class of fuel aredemanded. The essential feature is ample

combustion space, in which thecombustion of gases may be practicallycompleted before striking the heatingsurfaces. The gases have the power ofburning out completely after striking theheating surfaces, provided the initialtemperature is sufficiently high, but wherethe combustion is completed before suchtime, the results secured are moresatisfactory. A furnace volume ofapproximately 1 to 1.5 cubic feet per ratedboiler horse power will give a combustionspace that is ample.

Where there is the possibility of a failure ofthe gas supply, or where steam is requiredwhen the blast furnace is shut down, coalfired grates of sufficient size to get therequired capacity should be installed.Where grates of full size are not required,ignition grates should be installed, whichneed be only large enough to carry a fire

for igniting the gas or for generating asmall quantity of steam when the blastfurnace is shut down. The area of suchgrates has no direct bearing on the size ofthe boiler. The grates may be placeddirectly under the gas burners in astandard position or may be placedbetween two bridge walls back of the gasfurnace and fired from the side of theboiler. An advantage is claimed for thestandard grate position that it minimizesthe danger of explosion on the re-ignitionof gas after a temporary stoppage of thesupply and also that a considerableamount of dirt, of which there is a gooddeal with this class of fuel and which isdifficult to remove, deposits on the fire andis taken out when the fires are cleaned. Inany event, regardless of the location of thegrates, ample provision should be madefor removing this dust, not only from thefurnace but from the setting as a whole.

Blast furnace gas burners are of twogeneral types: Those in which the air forcombustion is admitted around the burnerproper, and those in which this air isadmitted through the burner. Whateverthe design of burner, provision should bemade for the regulation of both the air andthe gas supply independently. A gasopening of .8 square inch per rated horsepower will enable a boiler to develop itsnominal rating with a gas pressure in themain of about 2 inches. This pressure isordinarily from 6 to 8 inches and in thisway openings of the above size will begood for ordinary overloads. The airopenings should be from .75 to .85 squareinch per rated horse power. Good resultsare secured by inclining the gas burnersslightly downward toward the rear of thefurnace. Where the burners areintroduced over coal fired grates, they

should be set high enough to giveheadroom for hand firing.

Ordinarily, individual stacks of 130 feethigh with diameters as given in Kent'stable for corresponding horse power arelarge enough for this class of work. Such astack will give a draft sufficient to allow aboiler to be operated at 175 per cent of itsrated capacity, and beyond this point thecapacity will not increase proportionatelywith the draft. When more than one boileris connected with a stack, the draftavailable at the damper should beequivalent to that which an individual stackof 130 feet high would give. The draft fromsuch a stack is necessary to maintain asuction under all conditions throughout allparts of the setting. If the draft is increasedabove that which such a stack will give,difficulties arise from excess air forcombustion with consequent loss in

efficiency.

A poor mixing or laneing action in thefurnace may result in a pulsating effect ofthe gases in the setting. This action may attimes be remedied by admitting more airto the furnace. On account of thepossibility of a pulsating action of thegases under certain conditions and thepuffs or explosions, settings for this classof work should be carefully constructedand thoroughly buckstayed and tied.

Natural Gas--Natural gas from differentlocalities varies considerably incomposition and heating value. In Table 50there is given a number of analyses andheat values for natural gas from variouslocalities.

This fuel is used for steam generatingpurposes to a considerable extent in some

localities, though such use is apparentlydecreasing. It is best burned byemploying a large number of smallburners, each being capable of handling30 nominal rated horse power. The use of alarge number of burners obviates thedanger of any laneing or blowpipe action,which might be present where largeburners are used. Ordinarily, such a gas,as it enters the burners, is under apressure of about 8 ounces. For thepurpose of comparison, all observationsshould be based on gas reduced to thestandard conditions of temperature andpressure, namely 32 degrees Fahrenheitand 14.7 pounds per square inch. Whenthe temperature and pressurecorresponding to meter readings areknown, the volume of gas under standardconditions may be obtained by multiplyingthe meter readings in cubic feet by 33.54P/T, in which P equals the absolute

pressure in pounds per square inch and Tequals the absolute temperature of the gasat the meter. In boiler testing work, theevaporation should always be reduced tothat per cubic foot of gas under standardconditions.

TABLE 50

TYPICAL ANALYSES (BY VOLUME)AND CALORIFIC VALUES OF NATURAL

GAS FROM VARIOUSLOCALITIES

+----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ |Locality of Well|H |CH_{4}| CO |CO_{2}| N | O | Heavy

|H_{2}S|B. t. u.| | | | | | || |Hydro- | | per | | | || | | | |carbons| | Cubic | |

| | | | | | | | |Foot | | | | | | | | |

| |Calcul- | | | | | | || | | |ated[49]|

|----------------+-----+-----+-----+-----+-----+----+-------+------+--------+ |Anderson, Ind. |1.86|93.07| 0.73| 0.26| 3.02|0.42| 0.47 |0.15 | 1017 | |Marion, Ind. |1.20|93.16| 0.60| 0.30| 3.43|0.55| 0.15 |0.20 | 1009 | |Muncie, Ind. |2.35|92.67| 0.45| 0.25| 3.53|0.35| 0.25 |0.15 | 1004 | |Olean, N. Y. | |96.50|0.50| | |2.00| 1.00 | | 1018 ||Findlay, O. | 1.64|93.35| 0.41| 0.25|3.41|0.39| 0.35 | 0.20 | 1011 | |St. Ive,Pa. | 6.10|75.54|Trace| 0.34| | |18.12 | | 1117 | |Cherry Tree,Pa.|22.50|60.27| | 2.28| 7.32|0.83|6.80 | | 842 | |Grapeville, Pa.|24.56|14.93|Trace|Trace|18.69|1.22|40.60 | | 925 | |Harvey Well, | || | | | | | | | | ButlerCo., Pa.|13.50|80.00|Trace| 0.66| | |5.72 | | 998 | |Pittsburgh, Pa. |

9.64|57.85| 1.00| |23.41|2.10| 6.00 || 748 | |Pittsburgh, Pa. |20.02|72.18|1.00| 0.80| |1.10| 4.30 | | 917 ||Pittsburgh, Pa. |26.16|65.25| 0.80| 0.60|

|0.80| 6.30 | | 899 |+----------------+-----+-----+-----+-----+-----+----+-------+------+--------+

[Illustration: 1600 Horse-power Installationof Babcock & Wilcox Boilers andSuperheaters at the Carnegie Natural GasCo., Underwood, W. Va. Natural Gas is theFuel Burned under these Boilers]

When natural gas is the only fuel, theburners should be evenly distributed overthe lower portion of the boiler front. If thefuel is used as an auxiliary to coal, theburners may be placed through the firefront. A large combustion space isessential and a volume of .75 cubic feetper rated horse power will be found to

give good results. The burners should beof a design which give the gas and air arotary motion to insure a proper mixture. Acheckerwork wall is sometimes placed inthe furnace about 3 feet from the burnersto break up the flame, but with a gooddesign of burner this is unnecessary.Where the gas is burned alone and nogrates are furnished, good results aresecured by inclining the burner downwardto the rear at a slight angle.

By-product Coke Oven Gas--By-productcoke oven gas is a product of thedestructive distillation of coal in a distillingor by-product coke oven. In this class ofapparatus the gases, instead of beingburned at the point of their origin, as in abeehive or retort coke oven, are takenfrom the oven through an uptake pipe,cooled and yield as by-products tar,ammonia, illuminating and fuel gas. A

certain portion of the gas product isburned in the ovens and the remainderused or sold for illuminating or fuelpurposes, the methods of utilizing the gasvarying with plant operation and locality.

Table 51 gives the analyses and heat valueof certain samples of by-product cokeoven gas utilized for fuel purposes.

This gas is nearer to natural gas in its heatvalue than is blast furnace gas, and ingeneral the remarks as to the propermethods of burning natural gas and thefeatures to be followed in furnace designhold as well for by-product coke oven gas.

TABLE 51

TYPICAL ANALYSES OF BY-PRODUCT COKE OVEN GAS

+----------------------------------------------+|+------+-------------------------------------+|||CO_{2}| O |CO |CH_{4}| H | N |B.t.u.per|| || | | | | | |CubicFoot|||+------+-----+---+------+----+----+----------+| || 0.75 |Trace|6.0|28.15 |53.0|12.1|505 || || 2.00 |Trace|3.2|18.80|57.2|18.0| 399 || || 3.20 | 0.4|6.3|29.60 |41.6|16.1| 551 || || 0.80 |1.6 |4.9|28.40 |54.2|10.1| 460 |||+------+-----+---+------+----+----+----------+| +----------------------------------------------+

The essential difference in burning the twofuels is the pressure under which itreaches the gas burner. Where this isordinarily from 4 to 8 ounces in the case ofnatural gas, it is approximately 4 inches ofwater in the case of by-product coke ovengas. This necessitates the use of larger gasopenings in the burners for the latter class

of fuel than for the former.

By-product coke oven gas comes to theburners saturated with moisture andprovision should be made for the blowingout of water of condensation. This gas too,carries a large proportion of tar andhydrocarbons which form a deposit in theburners and provision should be made forcleaning this out. This is bestaccomplished by an attachment whichpermits the blowing out of the burners bysteam.

UTILIZATION OF WASTE HEAT

While it has been long recognized that thereclamation of heat from the waste gases ofvarious industrial processes would lead toa great saving in fuel and labor, theproblem has, until recently, never beengiven the attention that its importancemerits. It is true that installations havebeen made for the utilization of such gases,but in general they have consisted simplyin the placing of a given amount of boilerheating surface in the path of the gasesand those making the installations havebeen satisfied with whatever power hasbeen generated, no attention being givento the proportioning of either the heatingsurface or the gas passages to meet thepeculiar characteristics of the particularclass of waste gas available. The Babcock& Wilcox Co. has recently gone into the

question of the utilization of what has beenknown as waste heat with greatthoroughness, and the results secured bytheir installations with practically alloperations yielding such gases areeminently successful.

TABLE 52

TEMPERATURE OF WASTE GASESFROM VARIOUS INDUSTRIALPROCESSES

+-----------------------------------------------------+|+-----------------------------------+---------------+| ||Waste Heat From|Temperature[50]|| ||| Degrees |||+-----------------------------------+---------------+| ||Brick Kilns | 2000-2300|| ||Zinc Furnaces |

2000-2300 || ||Copper MatteReverberatory Furnaces| 2000-2200 ||||Beehive Coke Ovens |1800-2000 || ||Cement Kilns| 1200-1600[51]|| ||Nickel RefiningFurnaces | 1500-1750 || ||OpenHearth Steel Furnaces | 1100-1400|||+-----------------------------------+---------------+|+-----------------------------------------------------+

The power that can be obtained fromwaste gases depends upon theirtemperature and weight, and both of thesefactors vary widely in different commercialoperations. Table 52 gives a list of certainprocesses yielding waste gases the heat ofwhich is available for the generation ofsteam and the approximate temperature ofsuch gases. It should be understood that

the temperatures in the table are theaverage of the range of a complete cycleof the operation and that the minimum andmaximum temperatures may vary largelyfrom the figures given.

The maximum available horse power thatmay be secured from such gases isrepresented by the formula:

W(T-t)s H. P. = ------- (23)33,479

Where W = the weight of gases passingper hour, T = temperature of gasesentering heating surface, t =temperature leaving heating surface, s= specific heat of gases.

The initial temperature and the weight orvolume of gas will depend, as stated, upon

the process involved. The exit temperaturewill depend, to a certain extent, upon thetemperature of the entering gases, but willbe governed mainly by the efficiency ofthe heating surfaces installed for theabsorption of the heat.

Where the temperature of the gasavailable is high, approaching that foundin direct fired boiler practice, the problemis simple and the question of design ofboiler becomes one of adapting theproper amount of heating surface to thevolume of gas to be handled. With suchtemperatures, and a volume of gasavailable approximately in accordancewith that found in direct fired boilerpractice, a standard boiler or one butslightly modified from the standard willserve the purpose satisfactorily. As thetemperatures become lower, however, theproblem is more difficult and the

departure from standard practice moreradical. With low temperature gases, toobtain a heat transfer rate at allcomparable with that found in ordinaryboiler practice, the lack of temperaturemust be offset by an added velocity of thegases in their passage over the heatingsurfaces. In securing the velocitynecessary to give a heat transfer rate withlow temperature gases sufficient to makethe installation of waste heat boilers showa reasonable return on the investment, thefrictional resistance to the gases throughthe boiler becomes greatly in excess ofwhat would be considered good practicein direct fired boilers. Practically alloperations yielding waste gases requirethat nothing be done in the way ofimpairing the draft at the furnace outlet, asthis might interfere with the operation ofthe primary furnace. The installation of awaste heat boiler, therefore, very

frequently necessitates providingsufficient mechanical draft to overcome thefrictional resistance of the gases throughthe heating surfaces and still leave ampledraft available to meet the maximumrequirements of the primary furnace.

Where the temperature and volume of thegases are in line with what are found inordinary direct fired practice, the area ofthe gas passages may be practicallystandard. With the volume of gas known,the draft loss through the heating surfacesmay be obtained from experimental dataand this additional draft requirement metby the installation of a stack sufficient totake care of this draft loss and still leavedraft enough for operating the furnace atits maximum capacity.

Where the temperatures are low, theadded frictional resistance will ordinarily

be too great to allow the draft required tobe secured by additional stack height andthe installation of a fan is necessary. Such afan should be capable of handling themaximum volume of gas that the furnacemay produce, and of maintaining a suctionequivalent to the maximum frictionalresistance of such volume through theboiler plus the maximum draftrequirement at the furnace outlet. Stacksand fans for this class of work should befigured on the safe side. Where a faninstallation is necessary, the loss of draft inthe fan connections should be considered,and in figuring conservatively it should beremembered that a fan of ample size maybe run as economically as a smaller fan,whereas the smaller fan, if overloaded, isoperated with a large loss in efficiency. Inpractically any installation where lowtemperature gas requires a fan to give theproper heat transfer from the gases, the

cost of the fan and of the energy to drive itwill be more than offset by the addedpower from the boiler secured by its use.Furthermore, the installation of such a fanwill frequently increase the capacity of theindustrial furnace, in connection withwhich the waste heat boilers are installed.

In proportioning heating surfaces and gaspassages for waste heat work there are somany factors bearing directly on whatconstitutes the proper installation that it isimpossible to set any fixed rules. Eachindividual installation must be consideredby itself as well as the particularcharacteristics of the gases available, suchas their temperature and volume, and thepresence of dust or tar-like substances,and all must be given the proper weight inthe determination of the design of theheating surfaces and gas passages for thespecific set of conditions.

[Graph: Per Cent of Water Heating Surfacepassed over by Gases/Per Cent of theTotal Amount of Steam Generated in theBoiler against Temperature in DegreesFahrenheit of Hot Gases Sweeping HeatingSurface

Fig. 31. Curve Showing Relation BetweenGas Temperature, Heating Surface passedover, and Amount of Steam Generated.Ten Square Feet of Heating Surface areAssumed as Equivalent to One BoilerHorse Power]

Fig. 31 shows the relation of gastemperatures, heating surface passed overand work done by such surface for use incases where the temperatures approachthose found in direct fired practice andwhere the volume of gas available isapproximately that with which one horse

power may be developed on 10 squarefeet of heating surface. The curve assumeswhat may be considered standard gaspassage areas, and further, that there is noheat absorbed by direct radiation from thefire.

Experiments have shown that this curve isvery nearly correct for the conditionsassumed. Such being the case, itsapplication in waste heat work is clear.Decreasing or increasing the velocity ofthe gases over the heating surfaces fromwhat might be considered normal directfired practice, that is, decreasing orincreasing the frictional loss through theboiler will increase or decrease theamount of heating surface necessary todevelop one boiler horse power. Theapplication of Fig. 31 to such use may bestbe seen by an example:

Assume the entering gas temperatures tobe 1470 degrees and that the gases arecooled to 570 degrees. From the curve,under what are assumed to be standardconditions, the gases have passed over 19per cent of the heating surface by the timethey have been cooled 1470 degrees.When cooled to 570 degrees, 78 per centof the heating surface has been passedover. The work done in relation to thestandard of the curve is represented by(1470 - 570) �(2500 - 500) = 45 per cent.(These figures may also be read from thecurve in terms of the per cent of the workdone by different parts of the heatingsurfaces.) That is, 78 per cent - 19 per cent= 59 per cent of the standard heatingsurface has done 45 per cent of thestandard amount of work. 59 �45 = 1.31,which is the ratio of surface of the assumedcase to the standard case of the curve.Expressed differently, there will be

required 13.1 square feet of heatingsurface in the assumed case to develop ahorse power as against 10 square feet inthe standard case.

The gases available for this class of workare almost invariably very dirty. It isessential for the successful operation ofwaste-heat boilers that ample provision bemade for cleaning by the installation ofaccess doors through which all parts of thesetting may be reached. In manyinstances, such as waste-heat boilers set inconnection with cement kilns, settlingchambers are provided for the dust beforethe gases reach the boiler.

By-passes for the gases should in all casesbe provided to enable the boiler to be shutdown for cleaning and repairs withoutinterfering with the operation of theprimary furnace. All connections from

furnace to boilers should be kept tight toprevent the infiltration of air, with theconsequent lowering of gas temperatures.

Auxiliary gas or coal fired grates must beinstalled to insure continuity in theoperation of the boiler where theoperation of the furnace is intermittent orwhere it may be desired to run the boilerwith the primary furnace not in operation.Such grates are sometimes usedcontinuously where the gases availableare not sufficient to develop the requiredhorse power from a given amount ofheating surface.

Fear has at times been expressed thatcertain waste gases, such as thosecontaining sulphur fumes, will have adeleterious action on the heating surface ofthe boiler. This feature has been carefullywatched, however, and from plants in

operation it would appear that in theabsence of water or steam leaks within thesetting, there is no such harmful action.

[Illustration: Fig. 32. Babcock & WilcoxBoiler Arranged for Utilizing Waste Heatfrom Open Hearth Furnace. This Settingmay be Modified to Take Care ofPractically any Kind of Waste Gas]

CHIMNEYS AND DRAFT

The height and diameter of a properlydesigned chimney depend upon theamount of fuel to be burned, its nature, thedesign of the flue, with its arrangementrelative to the boiler or boilers, and thealtitude of the plant above sea level. Thereare so many factors involved that as yetthere has been produced no formula whichis satisfactory in taking them all intoconsideration, and the methods used fordetermining stack sizes are largelyempirical. In this chapter a methodsufficiently comprehensive and accurate tocover all practical cases will be developedand illustrated.

Draft is the difference in pressureavailable for producing a flow of the gases.If the gases within a stack be heated, each

cubic foot will expand, and the weight ofthe expanded gas per cubic foot will beless than that of a cubic foot of the cold airoutside the chimney. Therefore, the unitpressure at the stack base due to theweight of the column of heated gas will beless than that due to a column of cold air.This difference in pressure, like thedifference in head of water, will cause aflow of the gases into the base of the stack.In its passage to the stack the cold air mustpass through the furnace or furnaces of theboilers connected to it, and it in turnbecomes heated. This newly heated gaswill also rise in the stack and the action willbe continuous.

The intensity of the draft, or difference inpressure, is usually measured in inches ofwater. Assuming an atmospherictemperature of 62 degrees Fahrenheit andthe temperature of the gases in the

chimney as 500 degrees Fahrenheit, and,neglecting for the moment the differencein density between the chimney gases andthe air, the difference between the weightsof the external air and the internal fluegases per cubic foot is .0347 pound,obtained as follows:

Weight of a cubic foot of air at 62 degreesFahrenheit = .0761 pound Weight of acubic foot of air at 500 degrees Fahrenheit= .0414 pound------------------------Difference = .0347 pound

Therefore, a chimney 100 feet high,assumed for the purpose of illustration tobe suspended in the air, would have apressure exerted on each square foot of itscross sectional area at its base of .0347�100 = 3.47 pounds. As a cubic foot ofwater at 62 degrees Fahrenheit weighs

62.32 pounds, an inch of water would exerta pressure of 62.32 �12 = 5.193 pounds persquare foot. The 100-foot stack would,therefore, under the above temperatureconditions, show a draft of 3.47 �5.193 orapproximately 0.67 inches of water.

The method best suited for determiningthe proper proportion of stacks and flues isdependent upon the principle that if thecross sectional area of the stack issufficiently large for the volume of gases tobe handled, the intensity of the draft willdepend directly upon the height;therefore, the method of procedure is asfollows:

1st. Select a stack of such height as willproduce the draft required by theparticular character of the fuel and theamount to be burned per square foot of

grate surface.

2nd. Determine the cross sectional areanecessary to handle the gases withoutundue frictional losses.

The application of these rules follows:

Draft Formula--The force or intensity of thedraft, not allowing for the difference in thedensity of the air and of the flue gases, isgiven by the formula:

/ 1 1 \ D = 0.52 H �P |--- - -----| (24) \ T T_{1}/

in which

D = draft produced, measured ininches of water, H = height of top of

stack above grate bars in feet, P =atmospheric pressure in pounds persquare inch, T = absolute atmospherictemperature, T_{1} = absolutetemperature of stack gases.

In this formula no account is taken of thedensity of the flue gases, it being assumedthat it is the same as that of air. Any errorarising from this assumption is negligiblein practice as a factor of correction isapplied in using the formula to cover thedifference between the theoretical figuresand those corresponding to actualoperating conditions.

The force of draft at sea level (whichcorresponds to an atmospheric pressure of14.7 pounds per square inch) produced bya chimney 100 feet high with thetemperature of the air at 60 degreesFahrenheit and that of the flue gases at 500

degrees Fahrenheit is,

/ 1 1 \ D = 0.52 �100 �14.7 |--- - --- | = 0.67 \ 521 961 /

Under the same temperature conditionsthis chimney at an atmospheric pressure of10 pounds per square inch (whichcorresponds to an altitude of about 10,000feet above sea level) would produce adraft of,

/ 1 1 \ D = 0.52 �100 �10 | ---- --- | = 0.45 \ 521 961 /

For use in applying this formula it isconvenient to tabulate values of theproduct

/ 1 1 \ 0.52 �14.7|--- ------| \ T T_{1}/

which we will call K, for various values ofT_{1}. With these values calculated forassumed atmospheric temperature andpressure (24) becomes

D = KH. (25)

For average conditions the atmosphericpressure may be considered 14.7 poundsper square inch, and the temperature 60degrees Fahrenheit. For these values andvarious stack temperatures K becomes:

_Temperature Stack Gases_ _ConstantK_ 750 .0084 700

.0081 650 .0078600 .0075 550

.0071 500 .0067450 .0063 400.0058 350 .0053

Draft Losses--The intensity of the draft as

determined by the above formula istheoretical and can never be observedwith a draft gauge or any recordingdevice. However, if the ashpit doors of theboiler are closed and there is noperceptible leakage of air through theboiler setting or flue, the draft measured atthe stack base will be approximately thesame as the theoretical draft. Thedifference existing at other timesrepresents the pressure necessary to forcethe gases through the stack against theirown inertia and the friction against thesides. This difference will increase with thevelocity of the gases. With the ashpit doorsclosed the volume of gases passing to thestack are a minimum and the maximumforce of draft will be shown by a gauge.

As draft measurements are taken along thepath of the gases, the readings grow lessas the points at which they are taken are

farther from the stack, until in the boilerashpit, with the ashpit doors open forfreely admitting the air, there is little or noperceptible rise in the water of the gauge.The breeching, the boiler damper, thebaffles and the tubes, and the coal on thegrates all retard the passage of the gases,and the draft from the chimney is requiredto overcome the resistance offered by thevarious factors. The draft at the rear of theboiler setting where connection is made tothe stack or flue may be 0.5 inch, while inthe furnace directly over the fire it may notbe over, say, 0.15 inch, the differencebeing the draft required to overcome theresistance offered in forcing the gasesthrough the tubes and around the baffling.

One of the most important factors to beconsidered in designing a stack is thepressure required to force the air forcombustion through the bed of fuel on the

grates. This pressure will vary with thenature of the fuel used, and in manyinstances will be a large percentage of thetotal draft. In the case of natural draft, itsmeasure is found directly by noting thedraft in the furnace, for with properlydesigned ashpit doors it is evident that thepressure under the grates will not differsensibly from atmospheric pressure.

Loss in Stack--The difference between thetheoretical draft as determined by formula(24) and the amount lost by friction in thestack proper is the available draft, or thatwhich the draft gauge indicates whenconnected to the base of the stack. Thesum of the losses of draft in the flue, boilerand furnace must be equivalent to theavailable draft, and as these quantities canbe determined from record ofexperiments, the problem of designing astack becomes one of proportioning it to

produce a certain available draft.

The loss in the stack due to friction of thegases can be calculated from the followingformula:

f W� C H [Delta]D = -------- (26) A�

in which

[Delta]D = draft loss in inches of water,W = weight of gas in pounds passing persecond, C = perimeter of stack in feet,

H = height of stack in feet, f = aconstant with the following values at sealevel: .0015 for steel stacks,temperature of gases 600 degreesFahrenheit. .0011 for steel stacks,temperature of gases 350 degreesFahrenheit. .0020 for brick orbrick-lined stacks, temperature of gases

600 degrees Fahrenheit. .0015for brick or brick-lined stacks,temperature of gases 350 degreesFahrenheit. A = Area of stack in squarefeet.

[Illustration: 24,420 Horse-powerInstallation of Babcock & Wilcox Boilersand Superheaters, Equipped with Babcock& Wilcox Chain Grate Stokers in theQuarry Street Station of theCommonwealth Edison Co., Chicago, Ill.]

This formula can also be used forcalculating the frictional losses for flues, inwhich case, C = the perimeter of the flue infeet, H = the length of the flue in feet, theother values being the same as for stacks.

The available draft is equal to thedifference between the theoretical draftfrom formula (25) and the loss from

formula (26), hence:

f W� C H d^{1} = availabledraft = KH - -------- (27) A�

Table 53 gives the available draft in inchesthat a stack 100 feet high will producewhen serving different horse powers ofboilers with the methods of calculation forother heights.

TABLE 53

AVAILABLE DRAFT

CALCULATED FOR 100-FOOT STACK OFDIFFERENT DIAMETERS ASSUMINGSTACK TEMPERATURE OF 500 DEGREESFAHRENHEIT AND 100 POUNDS OF GASPER HORSE POWER

FOR OTHER HEIGHTS OF STACKMULTIPLY DRAFT BY HEIGHT �100

+-----+-------------------------------------------------------------------+ |Horse|

| |Power|Diameter of Stack in Inches |+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | |36 |42|48 |54 |60 |66 |72 |78 |84 |90 |96|102|108|114|120|132|144|+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+ | 100 |.64| || | | | | | | | | | | | | | | |

200 |.55|.62| | | | | | | | | | || | | | | | 300 |.41|.55|.61| | | || | | | | | | | | | | | 400|.21|.46|.56|.61| | | | | | | | | |

| | | | | 500 | |.34|.50|.57|.61| | || | | | | | | | | | | 600 |

|.19|.42|.53|.59| | | | | | | | | || | | | 700 | | |.34|.48|.56|.60|.63|

| | | | | | | | | | | 800 | ||.23|.43|.52|.58|.61|.63| | | | | | |

| | | | 900 | | ||.36|.49|.56|.60|.62|.64| | | | | | |

| | |1000 | | ||.29|.45|.53|.58|.61|.63|.64| | | | || | | |1100 | | | ||.40|.50|.56|.60|.62|.63|.64| | | | || | |1200 | | | ||.35|.47|.54|.58|.61|.63|.64|.65| | | |

| | |1300 | | | ||.29|.44|.52|.57|.60|.62|.63|.64|.65| || | | |1400 | | | | ||.40|.49|.55|.59|.61|.63|.64|.65|.65| || | |1500 | | | | ||.36|.47|.53|.58|.60|.62|.63|.64|.65|.65|

| | |1600 | | | | ||.31|.43|.52|.56|.59|.62|.63|.64|.65|.65|

| | |1700 | | | | | ||.41|.50|.55|.58|.61|.62|.64|.64|.65| || |1800 | | | | | ||.37|.47|.54|.57|.60|.62|.63|.64|.65| |

| |1900 | | | | | ||.34|.45|.52|.56|.59|.61|.63|.64|.64| || |2000 | | | | | | ||.43|.50|.55|.59|.61|.62|.63|.64| | ||2100 | | | | | | ||.40|.49|.54|.58|.60|.62|.63|.64| | ||2200 | | | | | | ||.38|.47|.53|.57|.59|.61|.62|.64| | ||2300 | | | | | | ||.35|.45|.52|.56|.59|.61|.62|.63| | ||2400 | | | | | | ||.32|.43|.50|.55|.58|.60|.62|.63| | ||2500 | | | | | | | ||.41|.49|.54|.57|.60|.61|.63| | | |2600| | | | | | | | ||.47|.53|.56|.59|.61|.62|.64|.65| |2700 |

| | | | | | | ||.45|.52|.55|.58|.60|.62|.64|.65| |2800 |

| | | | | | | ||.44|.59|.55|.58|.60|.61|.64|.65| |2900 |

| | | | | | | ||.42|.49|.54|.57|.59|.61|.63|.65| |3000 |

| | | | | | | ||.40|.48|.53|.56|.59|.61|.63|.64| |3100 |

| | | | | | | ||.38|.47|.52|.56|.58|.60|.63|.64| |3200 |

| | | | | | | | ||.45|.51|.55|.58|.60|.63|.64| |3300 | || | | | | | | ||.44|.50|.54|.57|.59|.62|.64| |3400 | || | | | | | | ||.42|.49|.53|.56|.59|.62|.64| |3500 | || | | | | | | ||.40|.48|.52|.56|.58|.62|.64| |3600 | || | | | | | | | ||.47|.52|.55|.58|.61|.63| |3700 | | | |

| | | | | | ||.45|.51|.55|.57|.61|.63| |3800 | | | |

| | | | | | ||.44|.50|.54|.57|.61|.63| |3900 | | | |

| | | | | | ||.43|.49|.53|.56|.60|.63| |4000 | | | |

| | | | | | ||.42|.48|.52|.56|.60|.62| |4100 | | | |

| | | | | | ||.40|.47|.52|.55|.60|.62| |4200 | | | |

| | | | | | ||.39|.46|.51|.55|.59|.62| |4300 | | | |

| | | | | | | ||.45|.50|.54|.59|.62| |4400 | | | | || | | | | | | |.44|.49|.53|.59|.62||4500 | | | | | | | | | | | ||.43|.49|.53|.58|.61| |4600 | | | | || | | | | | | |.42|.48|.52|.58|.61||4700 | | | | | | | | | | | ||.41|.47|.51|.57|.61| |4800 | | | | || | | | | | | |.40|.46|.51|.57|.60||4900 | | | | | | | | | | | | ||.45|.50|.57|.60| |5000 | | | | | | || | | | | | |.44|.49|.56|.60|

+-----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

FOR OTHER STACK TEMPERATURES ADDOR DEDUCT BEFORE MULTIPLYING BYHEIGHT �100 AS FOLLOWS[52]

For 750 Degrees F. Add .17 inch. For 700Degrees F. Add .14 inch. For 650 DegreesF. Add .11 inch. For 600 Degrees F. Add.08 inch. For 550 Degrees F. Add .04 inch.For 450 Degrees F. Deduct .04 inch. For400 Degrees F. Deduct .09 inch. For 350Degrees F. Deduct .14 inch.

[Graph: Horse Power of Boilers againstDiameter of Stack in Inches

Fig. 33. Diameter of Stacks and HorsePower they will Serve

Computed from Formula (28). For brick orbrick-lined stacks, increase the diameter 6per cent]

Height and Diameter of Stacks--From thisformula (27) it becomes evident that astack of certain diameter, if it be increased

in height, will produce the same availabledraft as one of larger diameter, theadditional height being required toovercome the added frictional loss. Itfollows that among the various stacks thatwould meet the requirements of aparticular case there must be one whichcan be constructed more cheaply than theothers. It has been determined from therelation of the cost of stacks to theirdiameters and heights, in connection withthe formula for available draft, that theminimum cost stack has a diameterdependent solely upon the horse power ofthe boilers it serves, and a heightproportional to the available draftrequired.

Assuming 120 pounds of flue gas per hourfor each boiler horse power, whichprovides for ordinary overloads and theuse of poor coal, the method above stated

gives:

For an unlined steel stack--

diameter in inches = 4.68 (H. P.)^{2/5}(28)

For a stack lined with masonry--

diameter in inches = 4.92 (H. P.)^{2/5}(29)

In both of these formulae H. P. = the ratedhorse power of the boiler.

From this formula the curve, Fig. 33, hasbeen calculated and from it the stackdiameter for any boiler horse power canbe selected.

For stoker practice where a large stackserves a number of boilers, the area is

usually made about one-third more thanthe above rules call for, which allows forleakage of air through the setting of anyidle boilers, irregularities in operatingconditions, etc.

Stacks with diameters determined asabove will give an available draft whichbears a constant ratio of the theoreticaldraft, and allowing for the cooling of thegases in their passage upward through thestack, this ratio is 8. Using this factor informula (25), and transposing, the heightof the chimney becomes,

d^{1} H = ----- (30) .8 K

Where H = height of stack in feet abovethe level of the grates, d^{1} = availabledraft required, K = constant as informula.

Losses in Flues--The loss of draft in straightflues due to friction and inertia can becalculated approximately from formula(26), which was given for loss in stacks. Itis to be borne in mind that C in thisformula is the actual perimeter of the flueand is least, relative to the cross sectionalarea, when the section is a circle, isgreater for a square section, and greatestfor a rectangular section. The retardingeffect of a square flue is 12 per centgreater than that of a circular flue of thesame area and that of a rectangular withsides as 1 and 1�, 15 per cent greater. Thegreater resistance of the more or lessuneven brick or concrete flue is providedfor in the value of the constants given forformula (26). Both steel and brick fluesshould be short and should have as near acircular or square cross section aspossible. Abrupt turns are to be avoided,

but as long easy sweeps require valuablespace, it is often desirable to increase theheight of the stack rather than to take upadded space in the boiler room. Shortright-angle turns reduce the draft by anamount which can be roughlyapproximated as equal to 0.05 inch foreach turn. The turns which the gases makein leaving the damper box of a boiler, inentering a horizontal flue and in turning upinto a stack should always be considered.The cross sectional areas of the passagesleading from the boilers to the stackshould be of ample size to provide againstundue frictional loss. It is poor economy torestrict the size of the flue and thus makeadditional stack height necessary toovercome the added friction. The generalpractice is to make flue areas the same orslightly larger than that of the stack; theseshould be, preferably, at least 20 per centgreater, and a safe rule to follow in

figuring flue areas is to allow 35 squarefeet per 1000 horse power. It isunnecessary to maintain the same size offlue the entire distance behind a row ofboilers, and the areas at any point may bemade proportional to the volume of gasesthat will pass that point. That is, the areasmay be reduced as connections to variousboilers are passed.

[Illustration: 6000 Horse-power Installationof Babcock & Wilcox Boilers at the UnitedStates Navy Yard, Washington, D. C.]

With circular steel flues of approximatelythe same size as the stacks, or reducedproportionally to the volume of gases theywill handle, a convenient rule is to allow0.1 inch draft loss per 100 feet of fluelength and 0.05 inch for each right-angleturn. These figures are also good forsquare or rectangular steel flues with areas

sufficiently large to provide againstexcessive frictional loss. For losses inbrick or concrete flues, these figuresshould be doubled.

Underground flues are less desirable thanoverhead or rear flues for the reason thatin most instances the gases will have tomake more turns where underground fluesare used and because the cross sectionalarea of such flues will oftentimes bedecreased on account of an accumulationof dirt or water which it may be impossibleto remove.

In tall buildings, such as office buildings, itis frequently necessary in order to carryspent gases above the roofs, to install astack the height of which is out of allproportion to the requirements of theboilers. In such cases it is permissible todecrease the diameter of a stack, but care

must be taken that this decrease is notsufficient to cause a frictional loss in thestack as great as the added draft intensitydue to the increase in height, which localconditions make necessary.

In such cases also the fact that the stackdiameter is permissibly decreased is noreason why flue sizes connecting to thestack should be decreased. These shouldstill be figured in proportion to the area ofthe stack that would be furnished underordinary conditions or with an allowanceof 35 square feet per 1000 horse power,even though the cross sectional areaappears out of proportion to the stackarea.

Loss in Boiler--In calculating the availabledraft of a chimney 120 pounds per hourhas been used as the weight of the gasesper boiler horse power. This covers an

overload of the boiler to an extent of 50per cent and provides for the use of poorcoal. The loss in draft through a boilerproper will depend upon its type andbaffling and will increase with the per centof rating at which it is run. No figures canbe given which will cover all conditions,but for approximate use in figuring theavailable draft necessary it may beassumed that the loss through a boiler willbe 0.25 inch where the boiler is run atrating, 0.40 inch where it is run at 150 percent of its rated capacity, and 0.70 inchwhere it is run at 200 per cent of its ratedcapacity.

Loss in Furnace--The draft loss in thefurnace or through the fuel bed variesbetween wide limits. The air necessary forcombustion must pass through theinterstices of the coal on the grate. Wherethese are large, as is the case with broken

coal, but little pressure is required to forcethe air through the bed; but if they aresmall, as with bituminous slack or smallsizes of anthracite, a much greaterpressure is needed. If the draft isinsufficient the coal will accumulate on thegrates and a dead smoky fire will resultwith the accompanying poor combustion;if the draft is too great, the coal may berapidly consumed on certain portions ofthe grate, leaving the fire thin in spots anda portion of the grates uncovered with theresulting losses due to an excessiveamount of air.

[Graph: Force of Draft between Furnaceand Ash Pit--Inches of Water againstPounds of Coal burned per Square Foot ofGrate Surface per Hour

Fig. 34. Draft Required at DifferentCombustion Rates for Various Kinds of

Coal]

Draft Required for Different Fuels--Forevery kind of fuel and rate of combustionthere is a certain draft with which the bestgeneral results are obtained. Acomparatively light draft is best with thefree burning bituminous coals and theamount to use increases as the percentageof volatile matter diminishes and the fixedcarbon increases, being highest for thesmall sizes of anthracites. Numerous otherfactors such as the thickness of fires, thepercentage of ash and the air spaces in thegrates bear directly on this question of thedraft best suited to a given combustionrate. The effect of these factors can only befound by experiment. It is almostimpossible to show by one set of curvesthe furnace draft required at various ratesof combustion for all of the differentconditions of fuel, etc., that may be met.

The curves in Fig. 34, however, give thefurnace draft necessary to burn variouskinds of coal at the combustion ratesindicated by the abscissae, for a generalset of conditions. These curves have beenplotted from the records of numerous testsand allow a safe margin for economicallyburning coals of the kinds noted.

Rate of Combustion--The amount of coalwhich can be burned per hour per squarefoot of grate surface is governed by thecharacter of the coal and the draftavailable. When the boiler and grate areproperly proportioned, the efficiency willbe practically the same, within reasonablelimits, for different rates of combustion.The area of the grate, and the ratio of thisarea to the boiler heating surface willdepend upon the nature of the fuel to beburned, and the stack should be sodesigned as to give a draft sufficient to

burn the maximum amount of fuel persquare foot of grate surface correspondingto the maximum evaporative requirementsof the boiler.

Solution of a Problem--The stack diametercan be determined from the curve, Fig. 33.The height can be determined by addingthe draft losses in the furnace, through theboiler and flues, and computing fromformula (30) the height necessary to givethis draft.

Example: Proportion a stack for boilersrated at 2000 horse power, equipped withstokers, and burning bituminous coal thatwill evaporate 8 pounds of water from andat 212 degrees Fahrenheit per pound offuel; the ratio of boiler heating surface tograte surface being 50:1; the flues being100 feet long and containing tworight-angle turns; the stack to be able to

handle overloads of 50 per cent; and therated horse power of the boilers based on10 square feet of heating surface per horsepower.

The atmospheric temperature may beassumed as 60 degrees Fahrenheit and theflue temperatures at the maximumoverload as 550 degrees Fahrenheit. Thegrate surface equals 400 square feet.

2000 �34� The total coalburned at rating = ---------- = 8624 pounds. 8

The coal per square foot of grate surfaceper hour at rating =

8624 ---- = 22 pounds. 400

For 50 per cent overload the combustionrate will be approximately 60 per cent

greater than this or 1.60 �22 = 35 poundsper square foot of grate surface per hour.The furnace draft required for thecombustion rate, from the curve, Fig. 34, is0.6 inch. The loss in the boiler will be 0.4inch, in the flue 0.1 inch, and in the turns 2�0.05 = 0.1 inch. The available draftrequired at the base of the stack is,therefore,

_Inches_ Boiler 0.4 Furnace 0.6 Flues 0.1 Turns 0.1 --- Total 1.2

Since the available draft is 80 per cent ofthe theoretical draft, this draft due to theheight required is 1.2 �.8 = 1.5 inch.

The chimney constant for temperatures of60 degrees Fahrenheit and 550 degreesFahrenheit is .0071 and from formula (30),

1.5 H = ----- = 211 feet. .0071

Its diameter from curve in Fig. 33 is 96inches if unlined, and 102 inches inside iflined with masonry. The cross sectionalarea of the flue should be approximately70 square feet at the point where the totalamount of gas is to be handled, tapering tothe boiler farthest from the stack to a sizewhich will depend upon the size of theboiler units used.

Correction in Stack Sizes for Altitudes--Ithas ordinarily been assumed that a stackheight for altitude will be increasedinversely as the ratio of the barometricpressure at the altitude to that at sea level,and that the stack diameter will increaseinversely as the two-fifths power of thisratio. Such a relation has been based onthe assumption of constant draft measuredin inches of water at the base of the stackfor a given rate of operation of the boilers,

regardless of altitude.

If the assumption be made that boilers,flues and furnace remain the same, andfurther that the increased velocity of agiven weight of air passing through thefurnace at a higher altitude would have noeffect on the combustion, the theory hasbeen advanced[53] that a different lawapplies.

Under the above assumptions, whenever astack is working at its maximum capacityat any altitude, the entire draft is utilized inovercoming the various resistances, eachof which is proportional to the square ofthe velocity of the gases. Since boilerareas are fixed, all velocities may berelated to a common velocity, say, thatwithin the stack, and all resistances may,therefore, be expressed as proportional tothe square of the chimney velocity. The

total resistance to flow, in terms of velocityhead, may be expressed in terms ofweight of a column of external air, thenumerical value of such head beingindependent of the barometric pressure.Likewise the draft of a stack, expressed inheight of column of external air, will benumerically independent of thebarometric pressure. It is evident,therefore, that if a given boiler plant, withits stack operated with a fixed fuel, betransplanted from sea level to an altitude,assuming the temperatures remainconstant, the total draft head measured inheight of column of external air will benumerically constant. The velocity ofchimney gases will, therefore, remain thesame at altitude as at sea level and theweight of gases flowing per second with afixed velocity will be proportional to theatmospheric density or inverselyproportional to the normal barometric

pressure.

To develop a given horse power requiresa constant weight of chimney gas and airfor combustion. Hence, as the altitude isincreased, the density is decreased and,for the assumptions given above, thevelocity through the furnace, the boilerpasses, breeching and flues must becorrespondingly greater at altitude than atsea level. The mean velocity, therefore, fora given boiler horse power and constantweight of gases will be inverselyproportional to the barometric pressureand the velocity head measured in columnof external air will be inverselyproportional to the square of thebarometric pressure.

For stacks operating at altitude it isnecessary not only to increase the heightbut also the diameter, as there is an added

resistance within the stack due to theadded friction from the additional height.This frictional loss can be compensated bya suitable increase in the diameter andwhen so compensated, it is evident that onthe assumptions as given, the chimneyheight would have to be increased at aratio inversely proportional to the squareof the normal barometric pressure.

In designing a boiler for high altitudes, asalready stated, the assumption is usuallymade that a given grade of fuel willrequire the same draft measured in inchesof water at the boiler damper as at sealevel, and this leads to making the stackheight inversely as the barometricpressures, instead of inversely as thesquare of the barometric pressures. Thecorrect height, no doubt, falls somewherebetween the two values as larger flues areusually used at the higher altitudes,

whereas to obtain the ratio of the squares,the flues must be the same size in eachcase, and again the effect of an increasedvelocity of a given weight of air throughthe fire at a high altitude, on thecombustion, must be neglected. In makingcapacity tests with coal fuel, no differencehas been noted in the rates of combustionfor a given draft suction measured by awater column at high and low altitudes,and this would make it appear that thecorrect height to use is more nearly thatobtained by the inverse ratio of thebarometric readings than by the inverseratio of the squares of the barometricreadings. If the assumption is made thatthe value falls midway between the twoformulae, the error in using a stack figuredin the ordinary way by making the heightinversely proportional to the barometricreadings would differ about 10 per cent incapacity at an altitude of 10,000 feet, which

difference is well within the probablevariation of the size determined bydifferent methods. It would, therefore,appear that ample accuracy is obtained inall cases by simply making the heightinversely proportional to the barometricreadings and increasing the diameter sothat the stacks used at high altitudes havethe same frictional resistance as thoseused at low altitudes, although, if desired,the stack may be made somewhat higherat high altitudes than this rule calls for inorder to be on the safe side.

The increase of stack diameter necessaryto maintain the same friction loss isinversely as the two-fifths power of thebarometric pressure.

Table 54 gives the ratio of barometricreadings of various altitudes to sea level,values for the square of this ratio and

values of the two-fifths power of this ratio.

TABLE 54

STACK CAPACITIES,CORRECTION FACTORS FOR ALTITUDES

_______________________________________________________________________ |

| | | | | |Altitude | | R | |R^{2/5} | | Height in Feet | Normal |Ratio Barometer | | Ratio Increase | |Above | Barometer | Reading | R�| in Stack | | Sea Level | | Sea

Level to | | Diameter | | || Altitude | | |

|________________|___________|_________________|_______|________________| |

| | | | | |

0 | 30.00 | 1.000 | 1.000 |1.000 | | 1000 | 28.88 | 1.039

| 1.079 | 1.015 | | 2000 |27.80 | 1.079 | 1.064 | 1.030 | |

3000 | 26.76 | 1.121 | 1.257 |1.047 | | 4000 | 25.76 |

1.165 | 1.356 | 1.063 | | 5000| 24.79 | 1.210 | 1.464 | 1.079| | 6000 | 23.87 | 1.257 |1.580 | 1.096 | | 7000 | 22.97| 1.306 | 1.706 | 1.113 | |8000 | 22.11 | 1.357 | 1.841 |1.130 | | 9000 | 21.28 | 1.410

| 1.988 | 1.147 | | 10000 |20.49 | 1.464 | 2.144 | 1.165 ||________________|___________|_________________|_______|________________|

These figures show that the altitude affectsthe height to a much greater extent thanthe diameter and that practically noincrease in diameter is necessary for

altitudes up to 3000 feet.

For high altitudes the increase in stackheight necessary is, in some cases, such asto make the proportion of height todiameter impracticable. The method to berecommended in overcoming, at leastpartially, the great increase in heightnecessary at high altitudes is an increasein the grate surface of the boilers whichthe stack serves, in this way reducing thecombustion rate necessary to develop agiven power and hence the draft requiredfor such combustion rate.

TABLE 55

STACK SIZES BY KENT'SFORMULA

ASSUMING 5 POUNDS OF COALPER HORSE POWER

____________________________________________________________________ | | |

| | | | |Height of Stack in Feet |Side of| |

||______________________________________________|Equiva-| | Dia- | Area | | | |

| | | | | | | lent | |meter|Square| 50| 60| 70| 80 | 90 | 100|110| 125| 150| 175|Square | |Inches|Feet|___|___|___|____|____|____|____|____|____|____| Stack | | | |

|Inches | | | |Commercial Horse Power | ||______|______|______________________________________________|_______| | || | | | | | | | | | | | | 33| 5.94|106|115|125| 133| 141| 149| |

| | | 30 | | 36 | 7.07|129|141|152|163| 173| 182| | | | | 32 | | 39 |8.30|155|169|183| 196| 208| 219| 229|245| | | 35 | | 42 |9.62|183|200|216| 231| 245| 258| 271|289| 316| | 38 | | 48 |12.57|246|269|290| 311| 330| 348| 365|389| 426| 460| 43 | | 54 |15.90|318|348|376| 402| 427| 449| 472|503| 551| 595| 48 | | 60 |19.64|400|437|473| 505| 536| 565| 593|632| 692| 748| 54 | | 66 |23.76|490|537|580| 620| 658| 694| 728|776| 849| 918| 59 | | 72 |28.27|591|646|698| 747| 792| 835| 876|934|1023|1105| 64 | | 78 |33.18|700|766|828| 885| 939|990|1038|1107|1212|1310| 70 | | 84 |38.48|818|896|968|1035|1098|1157|1214|1294|1418|1531| 75 ||______|______|___|___|___|____|____|____|____|____|____|____|_______| | |

| | | | | |Height of Stack in Feet |Side

of| | ||______________________________________________|Equiva-| | Dia- | Area | | || | | | | | lent | |

meter|Square| 100| 110 | 125 | 150 | 175| 200 | 225 | 250 |Square | |Inches| Feet|____|_____|_____|_____|_____|_____|_____|_____| Stack | | | |

|Inches | | | |Commercial Horse Power | ||______|______|______________________________________________|_______| | || | | | | | | | | | | 90| 44.18|1338| 1403| 1496| 1639| 1770|1893| 2008| 2116| 80 | | 96 |50.27|1532| 1606| 1713| 1876| 2027|2167| 2298| 2423| 86 | | 102 |56.75|1739| 1824| 1944| 2130| 2300|2459| 2609| 2750| 91 | | 108 |63.62|1959| 2054| 2190| 2392| 2592|

2770| 2939| 3098| 98 | | 114 |70.88|2192| 2299| 2451| 2685| 2900|3100| 3288| 3466| 101 | | 120 |78.54|2438| 2557| 2726| 2986| 3226|3448| 3657| 3855| 107 | | 126 |86.59|2697| 2829| 3016| 3303| 3568|3814| 4046| 4265| 112 | | 132 |95.03|2970| 3114| 3321| 3637| 3929|4200| 4455| 4696| 117 | | 144|113.10|3554| 3726| 3973| 4352| 4701|5026| 5331| 5618| 128 | | 156|132.73|4190| 4393| 4684| 5131| 5542|5925| 6285| 6624| 138 | | 168|153.94|4878| 5115| 5454| 5974| 6454|6899| 7318| 7713| 150 ||______|______|____|_____|_____|_____|_____|_____|_____|_____|_______|

Kent's Stack Tables--Table 55 gives, inconvenient form for approximate work, thesizes of stacks and the horse power ofboilers which they will serve. This table is

a modification of Mr. William Kent's stacktable and is calculated from his formula.Provided no unusual conditions areencountered, it is reliable for the ordinaryrates of combustion with bituminous coals.It is figured on a consumption of 5 poundsof coal burned per hour per boiler horsepower developed, this figure giving afairly liberal allowance for the use of poorcoal and for a reasonable overload. Whenthe coal used is a low grade bituminous ofthe Middle or Western States, it is stronglyrecommended that these sizes beincreased materially, such an increasebeing from 25 to 60 per cent, dependingupon the nature of the coal and thecapacity desired. For the coal burned perhour for any size stack given in the table,the values should be multiplied by 5.

A convenient rule for large stacks, 200 feethigh and over, is to provide 30 square feet

of cross sectional area per 1000 ratedhorse power.

Stacks for Oil Fuel--The requirements ofstacks connected to boilers under whichoil fuel is burned are entirely differentfrom those where coal is used. While moreattention has been paid to the matter ofstack sizes for oil fuel in recent years,there has not as yet been gathered thelarge amount of experimental dataavailable for use in designing coal stacks.

In the case of oil-fired boilers the loss ofdraft through the fuel bed is partiallyeliminated. While there may be practicallyno loss through any checkerworkadmitting air to the furnace when a boileris new, the areas for the air passage in thischeckerwork will in a short time bedecreased, due to the silt which is presentin practically all fuel oil. The loss in draft

through the boiler proper at a given ratingwill be less than in the case of coal-firedboilers, this being due to a decrease in thevolume of the gases. Further, the action ofthe oil burner itself is to a certain extentthat of a forced draft. To offset thisdecrease in draft requirement, thetemperature of the gases entering thestack will be somewhat lower where oil isused than where coal is used, and the draftthat a stack of a given height would give,therefore, decreases. The factors as givenabove, affecting as they do the intensity ofthe draft, affect directly the height of thestack to be used.

As already stated, the volume of gasesfrom oil-fired boilers being less than in thecase of coal, makes it evident that the areaof stacks for oil fuel will be less than forcoal. It is assumed that these areas willvary directly as the volume of the gases to

be handled, and this volume for oil may betaken as approximately 60 per cent of thatfor coal.

In designing stacks for oil fuel there aretwo features which must not beoverlooked. In coal-firing practice there israrely danger of too much draft. In theburning of oil, however, this may play animportant part in the reduction of planteconomy, the influence of excessive draftbeing more apparent where the load onthe plant may be reduced at intervals. Thereason for this is that, aside from a slightdecrease in temperature at reduced loads,the tendency, due to careless firing, istoward a constant gas flow through theboiler regardless of the rate of operation,with the corresponding increase of excessair at light loads. With excessive stackheight, economical operation at varyingloads is almost impossible with hand

control. With automatic control, however,where stacks are necessarily high to takecare of known peaks, under lighter loadsthis economical operation becomes lessdifficult. For this reason the question ofdesigning a stack for a plant where theload is known to be nearly a constant iseasier than for a plant where the load willvary over a wide range. While great caremust be taken to avoid excessive draft, stillmore care must be taken to assure a draftsuction within all parts of the setting underany and all conditions of operation. It isvery easily possible to more than offset theeconomy gained through low draft, by thelosses due to setting deterioration,resulting from such lack of suction. Underconditions where the suction is notsufficient to carry off the products ofcombustion, the action of the heat on thesetting brickwork will cause its rapidfailure.

[Illustration: 7800 Horse-power Installationof Babcock & Wilcox Boilers, Equippedwith Babcock & Wilcox Chain GrateStokers at the Metropolitan West SideElevated Ry. Co., Chicago, Ill.]

It becomes evident, therefore, that thequestion of stack height for oil-firedboilers is one which must be consideredwith the greatest of care. The designer, onthe one hand, must guard against the evilsof excessive draft with the view to planteconomy, and, on the other, against theevils of lack of draft from the viewpoint ofupkeep cost. Stacks for this work shouldbe proportioned to give ample draft forthe maximum overload that a plant will becalled upon to carry, all conditions ofoverload carefully considered. At the sametime, where this maximum overload isfigured liberally enough to insure a draft

suction within the setting under allconditions, care must be taken against theinstallation of a stack which would givemore than this maximum draft.

TABLE 56

STACK SIZES FOR OIL FUEL

ADAPTED FROM C. R. WEYMOUTH'STABLE (TRANS. A. S. M. E. VOL.34)

+----------------------------------------------------+|+--------+-----------------------------------------+| || | Height in Feet Above BoilerRoom Floor ||||Diameter+------+------+------+-----+--------------+| || Inches | 80 | 90 | 100 | 120 |

140 | 160 |||+--------+------+------+------+------+------+------+| || 33 | 161 | 206 | 233 | 270 |

306 | 315 || || 36 | 208 | 253 | 295 |331 | 363 | 387 || || 39 | 251 | 303 |343 | 399 | 488 | 467 || || 42 | 295 |359 | 403 | 474 | 521 | 557 || || 48 |399 | 486 | 551 | 645 | 713 | 760 || ||54 | 519 | 634 | 720 | 847 | 933 | 1000|| || 60 | 657 | 800 | 913 | 1073 | 1193| 1280 || || 66 | 813 | 993 | 1133 |1333 | 1480 | 1593 || || 72 | 980 | 1206| 1373 | 1620 | 1807 | 1940 || || 84 |1373 | 1587 | 1933 | 2293 | 2560 | 2767 |||| 96 | 1833 | 2260 | 2587 | 3087 | 3453| 3740 || || 108 | 2367 | 2920 | 3347 |4000 | 4483 | 4867 || || 120 | 3060 |3660 | 4207 | 5040 | 5660 | 6160 |||+--------+------+------+------+------+------+------+|+----------------------------------------------------+

Figures represent nominal rated horsepower. Sizes as given good for 50 per centoverloads.

Based on centrally located stacks, shortdirect flues and ordinary operatingefficiencies.

Table 56 gives the sizes of stacks, andhorse power which they will serve for oilfuel. This table is, in modified form, onecalculated by Mr. C. R. Weymouth after anexhaustive study of data pertaining to thesubject, and will ordinarily givesatisfactory results.

Stacks for Blast Furnace Gas Work--Forboilers burning blast furnace gas, as in thecase of oil-fired boilers, stack sizes assuited for coal firing will have to bemodified. The diameter of stacks for thiswork should be approximately the same asfor coal-fired boilers. The volume of gaseswould be slightly greater than from a coalfire and would decrease the draft with a

given stack, but such a decrease due tovolume is about offset by an increase dueto somewhat higher temperatures in thecase of the blast furnace gases.

Records show that with this class of fuel175 per cent of the rated capacity of aboiler can be developed with a draft at theboiler damper of from 0.75 inch to 1.0 inch,and it is well to limit the height of stacks toone which will give this draft as amaximum. A stack of proper diameter, 130feet high above the ground, will producesuch a draft and this height shouldordinarily not be exceeded. Until recentlythe question of economy in boilers firedwith blast furnace gas has not beenconsidered, but, aside from theeconomical standpoint, excessive draftshould be guarded against in order tolower the upkeep cost.

Stacks should be made of sufficient heightto produce a draft that will develop themaximum capacity required, and this draftdecreased proportionately for loads underthe maximum by damper regulation. Theamount of gas fed to a boiler for any givenrating is a fixed quantity and if a draft inexcess of that required for that particularrate of operation is supplied, economy isdecreased and the wear and tear on thesetting is materially increased. Excess airwhich is drawn in, either through oraround the gas burners by an excessivedraft, will decrease economy, as in anyother class of work. Again, as in oil-firedpractice, it is essential on the other handthat a suction be maintained within allparts of the setting, in this case not only toprovide against setting deterioration but toprotect the operators from leakage of gaswhich is disagreeable and may bedangerous. Aside from the intensity of the

draft, a poor mixture of the gas and air or a"laneing" action may lead to secondarycombustion with the possibility ofdangerous explosions within the setting,may cause a pulsating action within thesetting, may increase the exittemperatures to a point where there isdanger of burning out damper boxes, and,in general, is hard on the setting. It ishighly essential, therefore, that the furnacebe properly constructed to meet the draftwhich will be available.

Stacks for Wood-fired Boilers--For boilersusing wood as fuel, there is but little dataupon which to base stack sizes. The loss ofdraft through the bed of fuel will vary overlimits even wider than in the case of coal,for in this class of fuel the moisture mayrun from practically 0.0 per cent to over 60per cent, and the methods of handling andfiring are radically different for the

different classes of wood (see chapter onWood-burning Furnaces). As economy isordinarily of little importance, high stacktemperatures may be expected, and oftenunavoidably large quantities of excess airare supplied due to the method of firing. Ingeneral, it may be stated that for this classof fuel the diameter of stacks should be atleast as great as for coal-fired boilers,while the height may be slightlydecreased. It is far the best plan indesigning a stack for boilers using woodfuel to consider each individual set ofconditions that exist, rather than try tofollow any general rule.

One factor not to be overlooked in stacksfor wood burning is their location. The fineparticles of this fuel are often carriedunconsumed through the boiler, andwhere the stack is not on top of the boiler,these particles may accumulate in the base

of the stack below the point at which theflue enters. Where there is any air leakagethrough the base of such a stack, this fuelmay become ignited and the stack burned.Where there is a possibility of such actiontaking place, it is well to line the stack withfire brick for a portion of its height.

Draft Gauges--The ordinary form of draftgauge, Fig. 35, which consists of a U-tube,containing water, lacks sensitiveness inmeasuring such slight pressuredifferences as usually exist, and for thatreason gauges which multiply the draftindications are more convenient and aremuch used.

[Illustration: Fig. 35. U-tube Draft Gauge]

[Illustration: Fig. 36. Barrus Draft Gauge]

An instrument which has given excellent

results is one introduced by Mr. G. H.Barrus, which multiplies the ordinaryindications as many times as desired. Thisis illustrated in Fig. 36, and consists of aU-tube made of one-half inch glass,surmounted by two larger tubes, orchambers, each having a diameter of 2�inches. Two different liquids which will notmix, and which are of different color, areused, usually alcohol colored red and acertain grade of lubricating oil. Themovement of the line of demarcation isproportional to the difference in the areasof the chambers and the U-tube connectingthem. The instrument is calibrated bycomparison with the ordinary U-tubegauge.

In the Ellison form of gauge the lowerportion of the ordinary U-tube has beenreplaced by a tube slightly inclined to thehorizontal, as shown in Fig. 37. By this

arrangement any vertical motion in theright-hand upright tube causes a verymuch greater travel of the liquid in theinclined tube, thus permitting extremelysmall variation in the intensity of the draftto be read with facility.

[Illustration: Fig. 37. Ellison Draft Gauge]

The gauge is first leveled by means of thesmall level attached to it, both legs beingopen to the atmosphere. The liquid is thenadjusted until its meniscus rests at the zeropoint on the left. The right-hand leg is thenconnected to the source of draft by meansof a piece of rubber tubing. Under thesecircumstances, a rise of level of one inch inthe right-hand vertical tube causes themeniscus in the inclined tube to pass fromthe point 0 to 1.0. The scale is divided intotenths of an inch, and the sub-divisions arehundredths of an inch.

The makers furnish a non-drying oil for theliquid, usually a 300 degrees test refinedpetroleum.

A very convenient form of the ordinaryU-tube gauge is known as the Peabodygauge, and it is shown in Fig. 38. This is asmall modified U-tube with a sliding scalebetween the two legs of the U and withconnections such that either a draft suctionor a draft pressure may be taken. The topsof the sliding pieces extending across thetubes are placed at the bottom of themeniscus and accurate readings inhundredths of an inch are obtained by avernier.

[Illustration: Fig. 38. Peabody Draft Gauge]

EFFICIENCY AND CAPACITY OF BOILERS

Two of the most important operatingfactors entering into the consideration ofwhat constitutes a satisfactory boiler are itsefficiency and capacity. The relation ofthese factors to one another will beconsidered later under the selection ofboilers with reference to the work they areto accomplish. The present chapter dealswith the efficiency and capacity only with aview to making clear exactly what is meantby these terms as applied to steamgenerating apparatus, together with themethods of determining these factors bytests.

Efficiency--The term "efficiency",specifically applied to a steam boiler, isthe ratio of heat absorbed by the boiler inthe generation of steam to the total amount

of heat available in the medium utilized insecuring such generation. When thismedium is a solid fuel, such as coal, it isimpossible to secure the completecombustion of the total amount fed to theboiler. A portion is bound to drop throughthe grates where it becomes mixed withthe ash and, remaining unburned,produces no heat. Obviously, it is unfair tocharge the boiler with the failure to absorbthe portion of available heat in the fuel thatis wasted in this way. On the other hand,the boiler user must pay for such wasteand is justified in charging it against thecombined boiler and furnace. Due to thisfact, the efficiency of a boiler, as ordinarilystated, is in reality the combined efficiencyof the boiler, furnace and grate, and

Efficiency of boiler,} Heat absorbed perpound of fuel furnace and grate } =------------------------------- (31)

Heat value per pound of fuel

The efficiency will be the same whetherbased on dry fuel or on fuel as fired,including its content of moisture. Forexample: If the coal contained 3 per centof moisture, the efficiency would be

Heat absorbed per pound of dry coal�0.97 ------------------------------------------

Heat value per pound of dry coal�0.97

where 0.97 cancels and the formulabecomes (31).

The heat supplied to the boiler is due tothe combustible portion of fuel which isactually burned, irrespective of whatproportion of the total combustible firedmay be.[54] This fact has led to the use of a

second efficiency basis on combustibleand which is called the efficiency of boilerand furnace[55], namely,

Efficiency of boiler and furnace[55]

Heat absorbed per pound ofcombustible[56] =-------------------------------------- (32)Heat value per pound of combustible

The efficiency so determined is used incomparing the relative performance ofboilers, irrespective of the type of gratesused under them. If the loss of fuel throughthe grates could be entirely overcome, theefficiencies obtained by (31) and (32)would obviously be the same. Hence, inthe case of liquid and gaseous fuels, wherethere is practically no waste, theseefficiencies are almost identical.

As a matter of fact, it is extremely difficult,if not impossible, to determine the actualefficiency of a boiler alone, asdistinguished from the combinedefficiency of boiler, grate and furnace. Thisis due to the fact that the losses due toexcess air cannot be correctly attributed toeither the boiler or the furnace, but only toa combination of the complete apparatus.Attempts have been made to devisemethods for dividing the lossesproportionately between the furnace andthe boiler, but such attempts areunsatisfactory and it is impossible todetermine the efficiency of a boiler apartfrom that of a furnace in such a way as tomake such determination of any practicalvalue or in a way that might not lead toendless dispute, were the question to arisein the case of a guaranteed efficiency.From the boiler manufacturer's standpoint,

the only way of establishing an efficiencythat has any value when guarantees are tobe met, is to require the grate or stokermanufacturer to make certain guaranteesas to minimum CO_{2}, maximum CO, andthat the amount of combustible in the ashand blown away with the flue gases doesnot exceed a certain percentage. Withsuch a guarantee, the efficiency should bebased on the combined furnace andboiler.

General practice, however, hasestablished the use of the efficiency basedupon combustible as representing theefficiency of the boiler alone. When suchan efficiency is used, its exact meaning, aspointed out on opposite page, should berealized.

The computation of the efficienciesdescribed on opposite page is best

illustrated by example.

Assume the following data to bedetermined from an actual boiler trial.

Steam pressure by gauge, 200 pounds.Feed temperature, 180 degrees. Totalweight of coal fired, 17,500 pounds.Percentage of moisture in coal, 3 per cent.Total ash and refuse, 2396 pounds. Totalwater evaporated, 153,543 pounds. Percent of moisture in steam, 0.5 per cent.Heat value per pound of dry coal, 13,516.Heat value per pound of combustible,15,359.

The factor of evaporation for such a set ofconditions is 1.0834. The actualevaporation corrected for moisture in thesteam is 152,775 and the equivalentevaporation from and at 212 degrees is,therefore, 165,516 pounds.

The total dry fuel will be 17,500 �.97 =16,975, and the evaporation per pound ofdry fuel from and at 212 degrees will be165,516 �16,975 = 9.75 pounds. The heatabsorbed per pound of dry fuel will,therefore, be 9.75 �970.4 = 9461 B. t. u.Hence, the efficiency by (31) will be 9461�13,516 = 70.0 per cent. The totalcombustible burned will be 16,975 - 2396= 14,579, and the evaporation from and at212 degrees per pound of combustible willbe 165,516 �14,579 = 11.35 pounds.Hence, the efficiency based oncombustible from (32) will be (11.35�97.04) �15,359 = 71.79.[**should be71.71]

For approximate results, a chart may beused to take the place of a computation ofefficiency. Fig. 39 shows such a chartbased on the evaporation per pound of dry

fuel and the heat value per pound of dryfuel, from which efficiencies may be readdirectly to within one-half of one per cent.It is used as follows: From the intersectionof the horizontal line, representing theevaporation per pound of fuel, with thevertical line, representing the heat valueper pound, the efficiency is read directlyfrom the diagonal scale of efficiencies. Thischart may also be used for efficiencybased upon combustible when theevaporation from and at 212 degrees andthe heat values are both given in terms ofcombustible.

[Graph: Evaporation from and at 212� perPound of Dry Fuel against B.T.U. per Poundof Dry Fuel

Fig. 39. Efficiency Chart. Calculated fromMarks and Davis Tables

Diagonal Lines Represent Per CentEfficiency]

Boiler efficiencies will vary over a widerange, depending on a great variety offactors and conditions. The highestefficiencies that have been secured withcoal are in the neighborhood of 82 percent and from that point efficiencies arefound all the way down to below 50 percent. Table 59[57] of tests of Babcock &Wilcox boilers under varying conditions offuel and operation will give an idea of whatmay be obtained with proper operatingconditions.

The difference between the efficiencysecured in any boiler trial and the perfectefficiency, 100 per cent, includes thelosses, some of which are unavoidable inthe present state of the art, arising in theconversion of the heat energy of the coal to

the heat energy in the steam. These lossesmay be classified as follows:

1st. Loss due to fuel dropped through thegrate.

2nd. Loss due to unburned fuel which iscarried by the draft, as small particles,beyond the bridge wall into the setting orup the stack.

3rd. Loss due to the utilization of a portionof the heat in heating the moisturecontained in the fuel from the temperatureof the atmosphere to 212 degrees; toevaporate it at that temperature and tosuperheat the steam thus formed to thetemperature of the flue gases. This steam,of course, is first heated to the temperatureof the furnace but as it gives up a portion ofthis heat in passing through the boiler, thesuperheating to the temperature of the exit

gases is the correct degree to beconsidered.

4th. Loss due to the water formed and bythe burning of the hydrogen in the fuelwhich must be evaporated andsuperheated as in item 3.

5th. Loss due to the superheating of themoisture in the air supplied from theatmospheric temperature to thetemperature of the flue gases.

6th. Loss due to the heating of the dryproducts of combustion to the temperatureof the flue gases.

7th. Loss due to the incompletecombustion of the fuel when the carbon isnot completely consumed but burns to COinstead of CO_{2}. The CO passes out ofthe stack unburned as a volatile gas

capable of further combustion.

8th. Loss due to radiation of heat from theboiler and furnace settings.

Obviously a very elaborate test wouldhave to be made were all of the aboveitems to be determined accurately. Inordinary practice it has become customaryto summarize these losses as follows, themethods of computing the losses beinggiven in each instance by a typicalexample:

(A) Loss due to the heating of moisture inthe fuel from the atmospheric temperatureto 212 degrees, evaporate it at thattemperature and superheat it to thetemperature of the flue gases. This inreality is the total heat above thetemperature of the air in the boiler room,in one pound of superheated steam at

atmospheric pressure at the temperatureof the flue gases, multiplied by thepercentage of moisture in the fuel. As thetotal heat above the temperature of the airwould have to be computed in eachinstance, this loss is best expressed by:

Loss in B. t. u. per pound =W(212-t+970.4+.47(T-212)) (33)

Where W = per cent of moisture in coal,t = the temperature of air in the boiler

room, T = temperature of the fluegases, .47 = the specific heat ofsuperheated steam at the atmospheric

pressure and at the flue gastemperature, (212-t) = B. t. u. necessaryto heat one pound of water from thetemperature of the boiler room to 212degrees, 970.4 = B. t. u. necessary toevaporate one pound of water at 212

degrees to steam at atmospheric

pressure, .47(T-212) = B. t. u. necessary tosuperheat one pound of steam atatmospheric pressure from 212 degrees totemperature T.

[Illustration: Portion of 15,000 Horse-powerInstallation of Babcock & Wilcox Boilers,Equipped with Babcock & Wilcox ChainGrate Stokers at the Northumberland, Pa.,Plant of the Atlas Portland Cement Co. ThisCompany Operates a Total of 24,000 HorsePower of Babcock & Wilcox Boilers in itsVarious Plants]

(B) Loss due to heat carried away in thesteam produced by the burning of thehydrogen component of the fuel. Inburning, one pound of hydrogen uniteswith 8 pounds of oxygen to form 9 poundsof steam. Following the reasoning of item(A), therefore, this loss will be:

Loss in B. t. u. per pound =9H((212-t)+970.4+.47(T-212)) (34)

where H = the percentage by weight ofhydrogen.

This item is frequently considered as a partof the unaccounted for loss, where anultimate analysis of the fuel is not given.

(C) Loss due to heat carried away by drychimney gases. This is dependent uponthe weight of gas per pound of coal whichmay be determined by formula (16), page158.

Loss in B. t. u. per pound = (T-t)�24�.

Where T and t have values as in (33),

.24 = specific heat of chimney gases,

W = weight of dry chimney gas perpound of coal.

(D) Loss due to incomplete combustion ofthe carbon content of the fuel, that is, theburning of the carbon to CO instead ofCO_{2}.

10,150 CO Loss in B. t. u.per pound = C�-------- (35) CO_{2}+CO

C = per cent of carbon in coal by ultimateanalysis,

CO and CO_{2} = per cent of CO andCO_{2} by volume from flue gas analysis.

10,150 = the number of heat unitsgenerated by burning to CO_{2} onepound of carbon contained in carbonmonoxide.

(E) Loss due to unconsumed carbon in theash (it being usually assumed that all thecombustible in the ash is carbon).

Loss in B. t. u. per pound = per cent C �percent ash �B. t. u. per pound of combustiblein the ash (usually taken as 14,600 B. t. u.) (36)

The loss incurred in this way is, directly,the carbon in the ash in percentage termsof the total dry coal fired, multiplied by theheat value of carbon.

To compute this item, which is of greatimportance in comparing the relativeperformances of different designs ofgrates, an analysis of the ash must beavailable.

The other losses, namely, items 2, 5 and 8

of the first classification, are ordinarilygrouped under one item, as unaccountedfor losses, and are obviously the differencebetween 100 per cent and the sum of theheat utilized and the losses accounted foras given above. Item 5, or the loss due tothe moisture in the air, may be readilycomputed, the moisture being determinedfrom wet and dry bulb thermometerreadings, but it is usually disregarded as itis relatively small, averaging, say, one-fifthto one-half of one per cent. Lack of datamay, of course, make it necessary toinclude certain items of the second andordinary classification in this unaccountedfor group.

TABLE 57

DATA FROM WHICH HEATBALANCE (TABLE 58) ISCOMPUTED

+------------------------------------------------------+|+----------------------------------------------------+| ||Steam Pressure by Gauge, Pounds

| 192 || ||Temperature of Feed,Degrees Fahrenheit | 180 ||||Degrees of Superheat, DegreesFahrenheit |115.2|| ||Temperature ofBoiler Room, Degrees Fahrenheit| 81 ||||Temperature of Exit Gases, DegreesFahrenheit | 480 || ||Weight of Coal Usedper Hour, Pounds | 5714||||Moisture, Per Cent |1.83|| ||Dry Coal Per Hour, Pounds

| 5609|| ||Ash and Refuse per Hour,Pounds | 561|| ||Ash and Refuse(of Dry Coal), Per Cent |10.00||||Actual Evaporation per Hour, Pounds

|57036|| || .- C, Per Cent|78.57|| || | H, Per Cent

| 5.60|| ||Ultimate | O, Per Cent

| 7.02|| ||Analysis -+ N, Per Cent| 1.11|| ||Dry Coal | Ash, Per

Cent | 6.52|| || '- Sulphur,Per Cent | 1.18|| ||Heat Value perPound Dry Coal, B. t. u. |14225||||Heat Value per Pound Combustible, B. t.u. |15217|| ||Combustible in Ash byAnalysis, Per Cent | 17.9|| || .-CO_{2}, Per Cent |14.33|| ||FlueGas -+ O, Per Cent | 4.54||||Analysis | CO, Per Cent |0.11|| || '- N, Per Cent|81.02|||+----------------------------------------------+-----+|+------------------------------------------------------+

A schedule of the losses as outlined,requires an evaporative test of the boiler,an analysis of the flue gases, an ultimateanalysis of the fuel, and either an ultimate

or proximate analysis of the ash. As theamount of unaccounted for losses forms abasis on which to judge the accuracy of atest, such a schedule is called a "heatbalance".

A heat balance is best illustrated by anexample: Assume the data as given inTable 57 to be secured in an actual boilertest.

From this data the factor of evaporation is1.1514 and the evaporation per hour fromand at 212 degrees is 65,671 pounds.Hence the evaporation from and at 212degrees per pound of dry coal is65,671�609 = 11.71 pounds. The efficiencyof boiler, furnace and grate is:

(11.71�70.4)�4,225 = 79.88 per cent.

The heat losses are:

(A) Loss due to moisture in coal,

= .01831 ((212-81)+970.4+.47(480-212)) =22. B. t. u., = 0.15 per cent.

(B) The loss due to the burning ofhydrogen:

= 9�0560((212-81)+970.4+.47(480-212)) =618 B. t. u., = 4.34 per cent.

(C) To compute the loss in the heat carriedaway by dry chimney gases per pound ofcoal the weight of such gases must be firstdetermined. This weight per pound of coalis:

(11CO_{2}+8O+7(CO+N))(-------------------)C ( 3(CO_{2}+CO) )

where CO_{2}, O, CO and H are the

percentage by volume as determined bythe flue gas analysis and C is thepercentage by weight of carbon in the dryfuel. Hence the weight of gas per pound ofcoal will be,

(11�4.33+8�.54+7(0.11+81.02))(-----------------------------)�8.57 = 13.7pounds. ( 3(14.33+0.11) )

Therefore the loss of heat in the dry gasescarried up the chimney =

13.7�.24(480-81) = 1311 B. t. u., =9.22 per cent.

(D) The loss due to incomplete combustionas evidenced by the presence of CO in theflue gas analysis is:

0.11 ----------�7857�0,150 = 61. B. t. u.,14.33+0.11 = .43 per cent.

(E) The loss due to unconsumed carbon inthe ash:

The analysis of the ash showed 17.9 percent to be combustible matter, all of whichis assumed to be carbon. The test showed10.00 of the total dry fuel fired to be ash.Hence 10.00�179 = 1.79 per cent of thetotal fuel represents the proportion of thistotal unconsumed in the ash and the lossdue to this cause is

1.79 per cent �14,600 = 261 B. t. u., = 1.83 per cent.

The heat absorbed by the boilers perpound of dry fuel is 11.71�70.4 = 11,363 B.t. u. This quantity plus losses (A), (B), (C),(D) and (E), or11,363+22+618+1311+61+261 = 13,636 B.t. u. accounted for. The heat value of the

coal, 14,225 B. t. u., less 13,636 B. t. u.,leaves 589 B. t. u., unaccounted for losses,or 4.15 per cent.

The heat balance should be arranged inthe form indicated by Table 58.

TABLE 58

HEAT BALANCE

B. T. U. PER POUND DRY COAL14,225

+----------------------------------------------------------------------+|+--------------------------------------------------------------------+| ||

|B. t. u.|Per Cent|||+--------------------------------------------------+--------+--------+| ||Heat absorbed byBoiler | 11,363 | 79.88 ||

||Loss due to Evaporation of Moisture inFuel | 22 | 0.15 || ||Loss due toMoisture formed by Burning of Hydrogen|

618 | 4.34 || ||Loss due to Heat carriedaway in Dry Chimney Gases| 1311 |9.22 || ||Loss due to IncompleteCombustion of Carbon | 61 | 0.43|| ||Loss due to Unconsumed Carbon inthe Ash | 261 | 1.83 || ||Loss dueto Radiation and Unaccounted Losses |589 | 4.15 |||+--------------------------------------------------+--------+--------+| ||Total

| 14,225 | 100.00 |||+--------------------------------------------------+--------+--------+|+----------------------------------------------------------------------+

Application of Heat Balance--A heatbalance should be made in connectionwith any boiler trial on which sufficient

data for its computation has beenobtained. This is particularly true wherethe boiler performance has beenconsidered unsatisfactory. The distributionof the heat is thus determined and anyextraordinary loss may be detected.Where accurate data for computing such aheat balance is not available, such acalculation based on certain assumptionsis sometimes sufficient to indicate unusuallosses.

The largest loss is ordinarily due to thechimney gases, which depends directlyupon the weight of the gas and itstemperature leaving the boiler. As pointedout in the chapter on flue gas analysis, thelower limit of the weight of gas is fixed bythe minimum air supplied with whichcomplete combustion may be obtained. Asshown, where this supply is unduly small,the loss caused by burning the carbon to

CO instead of to CO_{2} more than offsetsthe gain in decreasing the weight of gas.

The lower limit of the stack temperature,as has been shown in the chapter on draft,is more or less fixed by the temperaturenecessary to create sufficient draft suctionfor good combustion. With natural draft,this lower limit is probably between 400and 450 degrees.

Capacity--Before the capacity of a boiler isconsidered, it is necessary to define thebasis to which such a term may bereferred. Such a basis is the so-calledboiler horse power.

The unit of motive power in general useamong steam engineers is the "horsepower" which is equivalent to 33,000 footpounds per minute. Stationary boilers areat the present time rated in horse power,

though such a basis of rating may lead andhas often led to a misunderstanding._Work_, as the term is used in mechanics,is the overcoming of resistance throughspace, while _power_ is the _rate_ of workor the amount done per unit of time. As theoperation of a boiler in service implies nomotion, it can produce no power in thesense of the term as understood inmechanics. Its operation is the generationof steam, which acts as a medium toconvey the energy of the fuel which is inthe form of heat to a prime mover in whichthat heat energy is converted into energyof motion or work, and power isdeveloped.

If all engines developed the same amountof power from an equal amount of heat, aboiler might be designated as one havinga definite horse power, dependent uponthe amount of engine horse power its

steam would develop. Such a statement ofthe rating of boilers, though it would stillbe inaccurate, if the term is considered inits mechanical sense, could, throughcustom, be interpreted to indicate that aboiler was of the exact capacity requiredto generate the steam necessary todevelop a definite amount of horse powerin an engine. Such a basis of rating,however, is obviously impossible whenthe fact is considered that the amount ofsteam necessary to produce the samepower in prime movers of different typesand sizes varies over very wide limits.

To do away with the confusion resultingfrom an indefinite meaning of the termboiler horse power, the Committee ofJudges in charge of the boiler trials at theCentennial Exposition, 1876, atPhiladelphia, ascertained that a goodengine of the type prevailing at the time

required approximately 30 pounds ofsteam per hour per horse powerdeveloped. In order to establish a relationbetween the engine power and the size ofa boiler required to develop that power,they recommended that an evaporation of30 pounds of water from an initialtemperature of 100 degrees Fahrenheit tosteam at 70 pounds gauge pressure beconsidered as _one boiler horse power_.This recommendation has been generallyaccepted by American engineers as astandard, and when the term boiler horsepower is used in connection withstationary boilers[58] throughout thiscountry,[59] without special definition, it isunderstood to have this meaning.

Inasmuch as an equivalent evaporationfrom and at 212 degrees Fahrenheit is thegenerally accepted basis ofcomparison[60], it is now customary to

consider the standard boiler horse poweras recommended by the CentennialExposition Committee, in terms ofequivalent evaporation from and at 212degrees. This will be 30 pounds multipliedby the factor of evaporation for 70 poundsgauge pressure and 100 degrees feedtemperature, or 1.1494. 30 �1.1494 =34.482, or approximately 34.5 pounds.Hence, _one boiler horse power is equal toan evaporation of 34.5 pounds of water perhour from and at 212 degrees Fahrenheit_.The term boiler horse power, therefore, isclearly a measure of evaporation and notof power.

A method of basing the horse power ratingof a boiler adopted by boilermanufacturers is that of heating surfaces.Such a method is absolutely arbitrary andchanges in no way the definition of a boilerhorse power just given. It is simply a

statement by the manufacturer that hisproduct, under ordinary operatingconditions or conditions which may bespecified, will evaporate 34.5 pounds ofwater from and at 212 degrees per definiteamount of heating surface provided. Theamount of heating surface that has beenconsidered by manufacturers capable ofevaporating 34.5 pounds from and at 212degrees per hour has changed from timeto time as the art has progressed. At thepresent time 10 square feet of heatingsurface is ordinarily considered theequivalent of one boiler horse poweramong manufacturers of stationary boilers.In view of the arbitrary nature of suchrating and of the widely varying rates ofevaporation possible per square foot ofheating surface with different boilers anddifferent operating conditions, such a basisof rating has in reality no particularbearing on the question of horse power

and should be considered merely as aconvenience.

The whole question of a unit of boilercapacity has been widely discussed with aview to the adoption of a standard to whichthere would appear to be a more rationaland definite basis. Many suggestions havebeen offered as to such a basis but up tothe present time there has been nonewhich has met with universal approval orwhich would appear likely to be generallyadopted.

With the meaning of boiler horse power asgiven above, that is, a measure ofevaporation, it is evident that the capacityof a boiler is a measure of the power it candevelop expressed in boiler horse power.Since it is necessary, as stated, for boilermanufacturers to adopt a standard forreasons of convenience in selling, the

horse power for which a boiler is sold isknown as its normal rated capacity.

The efficiency of a boiler and themaximum capacity it will develop can bedetermined accurately only by a boilertest. The standard methods of conductingsuch tests are given on the followingpages, these methods being therecommendations of the Power TestCommittee of the American Society ofMechanical Engineers brought out in1913.[61] Certain changes have beenmade to incorporate in the boiler codesuch portions of the "InstructionsRegarding Tests in General" as apply toboiler testing. Methods of calculation andsuch matter as are treated in other portionsof the book have been omitted from thecode as noted.

[Illustration: Portion of 2600 Horse-power

Installation of Babcock & Wilcox Boilers,Equipped with Babcock & Wilcox ChainGrate Stokers at the Peter SchoenhofenBrewing Co., Chicago, Ill.]

1. OBJECT

Ascertain the specific object of the test,and keep this in view not only in the workof preparation, but also during theprogress of the test, and do not let it beobscured by devoting too close attentionto matters of minor importance. Whateverthe object of the test may be, accuracy andreliability must underlie the work frombeginning to end.

If questions of fulfillment of contract areinvolved, there should be a clearunderstanding between all the parties,preferably in writing, as to the operatingconditions which should obtain during thetrial, and as to the methods of testing to befollowed, unless these are alreadyexpressed in the contract itself.

Among the many objects of performancetests, the following may be noted:

Determination of capacity andefficiency, and how these compare withstandard or guaranteed results.

Comparison of different conditions ormethods of operation.

Determination of the cause of eitherinferior or superior results.

Comparison of different kinds of fuel.

Determination of the effect of changes ofdesign or proportion upon capacity orefficiency, etc.

2. PREPARATIONS

_(A) Dimensions:_

Measure the dimensions of the principalparts of the apparatus to be tested, so faras they bear on the objects in view, ordetermine these from correct workingdrawings. Notice the general features ofthe same, both exterior and interior, andmake sketches, if needed, to show unusualpoints of design.

The dimensions of the heating surfacesof boilers and superheaters to be foundare those of surfaces in contact with thefire or hot gases. The submerged surfacesin boilers at the mean water level shouldbe considered as water-heating surfaces,and other surfaces which are exposed to

the gases as superheating surfaces.

_(B) Examination of Plant:_

Make a thorough examination of thephysical condition of all parts of the plantor apparatus which concern the object inview, and record the conditions found,together with any points in the matter ofoperation which bear thereon.

In boilers, examine for leakage of tubesand riveted or other metal joints. Notethe condition of brick furnaces, grates and

baffles. Examine brick walls andcleaning doors for air leaks, either byshutting the damper and observing theescaping smoke or by candle-flame test.Determine the condition of heatingsurfaces with reference to exteriordeposits of soot and interior deposits ofmud or scale.

See that the steam main is so arrangedthat condensed and entrained watercannot flow back into the boiler.

If the object of the test is to determine thehighest efficiency or capacity obtainable,any physical defects, or defects ofoperation, tending to make the resultunfavorable should first be remedied; allfoul parts being cleaned, and the wholeput in first-class condition. If, on the otherhand, the object is to ascertain theperformance under existing conditions, nosuch preparation is either required ordesired.

_(C) General Precautions againstLeakage:_

In steam tests make sure that there is no

leakage through blow-offs, drips, etc., orany steam or water connections of theplant or apparatus undergoing test, whichwould in any way affect the results. Allsuch connections should be blanked off, orsatisfactory assurance should be obtainedthat there is leakage neither out nor in.This is a most important matter, and noassurance should be consideredsatisfactory unless it is susceptible ofabsolute demonstration.

3. FUEL

Determine the character of fuel to beused.[62] For tests of maximum efficiencyor capacity of the boiler to compare withother boilers, the coal should be of somekind which is commercially regarded as astandard for the locality where the test ismade.

In the Eastern States the standards thusregarded for semi-bituminous coals arePocahontas (Va. and W. Va.) and NewRiver (W. Va.); for anthracite coals those ofthe No. 1 buckwheat size, fresh-mined,containing not over 13 per cent ash byanalysis; and for bituminous coals,Youghiogheny and Pittsburgh coals. Insome sections east of the AlleghenyMountains the semi-bituminous Clearfield(Pa.) and Cumberland (Md.) are also

considered as standards. These coalswhen of good quality possess theessentials of excellence, adaptability tovarious kinds of furnaces, grates, boilers,and methods of firing required, besidesbeing widely distributed and generallyaccessible in the Eastern market. Thereare no special grades of coal mined inthe Western States which are widely andgenerally considered as standards fortesting purposes; the best coalobtainable in any particular locality beingregarded as the standard of comparison.

A coal selected for maximum efficiencyand capacity tests, should be the best of itsclass, and especially free from slaggingand unusual clinker-forming impurities.

For guarantee and other tests with aspecified coal containing not more than acertain amount of ash and moisture, the

coal selected should not be higher in ashand in moisture than the stated amounts,because any increase is liable to reducethe efficiency and capacity more than theequivalent proportion of such increase.

The size of the coal, especially where it isof the anthracite class, should bedetermined by screening a suitablesample.

4. APPARATUS AND INSTRUMENTS[63]

The apparatus and instruments requiredfor boiler tests are:

(A) Platform scales for weighing coaland ashes.

(B) Graduated scales attached to thewater glasses.

(C) Tanks and platform scales forweighing water (or water meterscalibrated in place). Wherever practicablethe feed water should be weighed,especially for guarantee tests. The mostsatisfactory and reliable apparatus for thispurpose consists of one or more tankseach placed on platform scales, thesebeing elevated a sufficient distanceabove the floor to empty into a receiving

tank placed below, the latter beingconnected to the feed pump. Whereonly one weighing tank is used thereceiving tank should be of larger sizethan the weighing tank, to affordsufficient reserve supply to the pumpwhile the upper tank is filling. If a singleweighing tank is used it should preferably

be of such capacity as to requireemptying not oftener than every 5minutes. If two or more are used theintervals between successive emptyingsshould not be less than 3 minutes.

(D) Pressure gauges, thermometers, anddraft gauges.

(E) Calorimeters for determining thecalorific value of fuel and the quality ofsteam.

(F) Furnaces pyrometers.

(G) Gas analyzing apparatus.

5. OPERATING CONDITIONS

Determine what the operating conditionsand method of firing should be to conformto the object in view, and see that theyprevail throughout the trial, as nearly aspossible.

Where uniformity in the rate ofevaporation is required, arrangementcan be usually made to dispose of thesteam so that this result can be attained.In a single boiler it may beaccomplished by discharging steamthrough a waste pipe and regulating theamount by means of a valve. In a battery of

boilers, in which only one is tested, thedraft may be regulated on the remainingboilers to meet the varying demands forsteam, leaving the test boiler to workunder a steady rate of evaporation.

6. DURATION

The duration of tests to determine theefficiency of a hand-fired boiler, should be10 hours of continuous running, or suchtime as may be required to burn a total of250 pounds of coal per square foot ofgrate.

In the case of a boiler using a mechanicalstoker, the duration, where practicable,should be at least 24 hours. If the stoker isof a type that permits the quantity andcondition of the fuel bed at beginning andend of the test to be accurately estimated,the duration may be reduced to 10 hours,or such time as may be required to burnthe above noted total of 250 pounds persquare foot.

In commercial tests where the service

requires continuous operation night andday, with frequent shifts of firemen, theduration of the test, whether the boilersare hand fired or stoker fired, should beat least 24 hours. Likewise in commercialtests, either of a single boiler or of a plantof several boilers, which operateregularly a certain number of hours andduring the balance of the day the fires arebanked, the duration should not be lessthan 24 hours.

The duration of tests to determine themaximum evaporative capacity of aboiler, without determining the efficiency,should not be less than 3 hours.

7. STARTING AND STOPPING

The conditions regarding the temperatureof the furnace and boiler, the quantity andquality of the live coal and ash on thegrates, the water level, and the steampressure, should be as nearly as possiblethe same at the end as at the beginning ofthe test.

To secure the desired equality ofconditions with hand-fired boilers, thefollowing method should be employed:

The furnace being well heated by apreliminary run, burn the fire low, andthoroughly clean it, leaving enough livecoal spread evenly over the grate (say 2to 4 inches),[64] to serve as a foundationfor the new fire. Note quickly the thicknessof the coal bed as nearly as it can be

estimated or measured; also the waterlevel,[65] the steam pressure, and thetime, and record the latter as the startingtime. Fresh coal should then be firedfrom that weighed for the test, the ashpitthroughly cleaned, and the regular workof the test proceeded with. Before theend of the test the fire should again beburned low and cleaned in such amanner as to leave the same amount of live

coal on the grate as at the start. Whenthis condition is reached, observequickly the water level,[65] the steampressure, and the time, and record thelatter as the stopping time. If the waterlevel is not the same as at the beginning a

correction should be made bycomputation, rather than by feedingadditional water after the final readingsare taken. Finally remove the ashes andrefuse from the ashpit. In a plantcontaining several boilers where it is not

practicable to clean themsimultaneously, the fires should becleaned one after the other as rapidly asmay be, and each one after cleaningcharged with enough coal to maintain athin fire in good working condition. Afterthe last fire is cleaned and in workingcondition, burn all the fires low (say 4 to 6inches), note quickly the thickness ofeach, also the water levels, steampressure, and time, which last is taken asthe starting time. Likewise when the timearrives for closing the test, the firesshould be quickly cleaned one by one,and when this work is completed theyshould all be burned low the same as thestart, and the various observations madeas noted. In the case of a large boilerhaving several furnace doors requiring thefire to be cleaned in sections one afterthe other, the above directionspertaining to starting and stopping in a

plant of several boilers may be followed.

To obtain the desired equality ofconditions of the fire when a mechanicalstoker other than a chain grate is used, theprocedure should be modified wherepracticable as follows:

Regulate the coal feed so as to burn thefire to the low condition required forcleaning. Shut off the coal-feedingmechanism and fill the hoppers level full.Clean the ash or dump plate, notequickly the depth and condition of the coalon the grate, the water level,[66] thesteam pressure, and the time, andrecord the latter as the starting time. Thenstart the coal-feeding mechanism, cleanthe ashpit, and proceed with the regularwork of the test.

When the time arrives for the close of

the test, shut off the coal-feedingmechanism, fill the hoppers and burn thefire to the same low point as at thebeginning. When this condition isreached, note the water level, the steampressure, and the time, and record thelatter as the stopping time. Finally cleanthe ashplate and haul the ashes.

In the case of chain grate stokers, thedesired operating conditions should bemaintained for half an hour before starting

a test and for a like period before itsclose, the height of the throat plate andthe speed of the grate being the sameduring both of these periods.

8. RECORDS

A log of the data should be entered innotebooks or on blank sheets suitablyprepared in advance. This should be donein such manner that the test may bedivided into hourly periods, or ifnecessary, periods of less duration, andthe leading data obtained for any one ormore periods as desired, thereby showingthe degree of uniformity obtained.

Half-hourly readings of the instruments areusually sufficient. If there are sudden andwide fluctuations, the readings in suchcases should be taken every 15 minutes,and in some instances oftener.

The coal should be weighed anddelivered to the firemen in portionssufficient for one hour's run, thereby

ascertaining the degree of uniformity offiring. An ample supply of coal shouldbe maintained at all times, but the quantityon the floor at the end of each hourshould be as small as practicable, so thatthe same may be readily estimated anddeducted from the total weight.

The records should be such as toascertain also the consumption of feedwater each hour and thereby determinethe degree of uniformity of evaporation.

9. QUALITY OF STEAM[67]

If the boiler does not produce superheatedsteam the percentage of moisture in thesteam should be determined by the use ofa throttling or separating calorimeter. Ifthe boiler has superheating surface, thetemperature of the steam should bedetermined by the use of a thermometerinserted in a thermometer well.

For saturated steam construct a samplingpipe or nozzle made of one-half inch ironpipe and insert it in the steam main at apoint where the entrained moisture islikely to be most thoroughly mixed. Theinner end of the pipe, which should extendnearly across to the opposite side of themain, should be closed and interiorportion perforated with not less thantwenty one-eighth inch holes equally

distributed from end to end and preferablydrilled in irregular or spiral rows, with thefirst hole not less than half an inch from thewall of the pipe.

The sampling pipe should not be placednear a point where water may pocket orwhere such water may effect the amount ofmoisture contained in the sample.Where non-return valves are used, orthere are horizontal connections leadingfrom the boiler to a vertical outlet, watermay collect at the lower end of theuptake pipe and be blown upward in aspray which will not be carried away bythe steam owing to a lack of velocity. Asample taken from the lower part of thispipe will show a greater amount ofmoisture than a true sample. Withgoose-neck connections a small amountof water may collect on the bottom of thepipe near the upper end where the

inclination is such that the tendency toflow backward is ordinarilycounterbalanced by the flow of steamforward over its surface; but when thevelocity momentarily decreases the waterflows back to the lower end of thegoose-neck and increases the moisture atthat point, making it an undesirablelocation for sampling. In any case it mustbe borne in mind that with low velocitiesthe tendency is for drops of entrainedwater to settle to the bottom of the pipe,and to be temporarily broken up intospray whenever an abrupt bend or otherdisturbance is met.

If it is necessary to attach the samplingnozzle at a point near the end of a longhorizontal run, a drip pipe should beprovided a short distance in front of thenozzle, preferably at a pocket formed bysome fitting and the water running along

the bottom of the main drawn off, weighed,and added to the moisture shown by thecalorimeter; or, better, a steam separatorshould be installed at the point noted.

In testing a stationary boiler the samplingpipe should be located as near aspracticable to the boiler, and the same istrue as regards the thermometer wellwhen the steam is superheated. In anengine or turbine test these locationsshould be as near as practicable to throttlevalve. In the test of a plant where it isdesired to get complete information,especially where the steam main isunusually long, sampling nozzles orthermometer wells should be provided atboth points, so as to obtain data at eitherpoint as may be required.

10. SAMPLING AND DRYING COAL

During the progress of test the coal shouldbe regularly sampled for the purpose ofanalysis and determination of moisture.

Select a representative shovelful fromeach barrow-load as it is drawn from thecoal pile or other source of supply, andstore the samples in a cool place in acovered metal receptacle. When all thecoal has thus been sampled, break up thelumps, thoroughly mix the whole quantity,and finally reduce it by the process ofrepeated quartering and crushing to asample weighing about 5 pounds, thelargest pieces being about the size of apea. From this sample two one-quartair-tight glass fruit jars, or other air-tightvessels, are to be promptly filled andpreserved for subsequent determinations

of moisture, calorific value, and chemicalcomposition. These operations should beconducted where the air is cool and freefrom drafts.

[Illustration: 3460 Horse-power Installationof Babcock & Wilcox Boilers at theChicago, Ill., Shops of the Chicago andNorthwestern Ry. Co.]

When the sample lot of coal has beenreduced by quartering to, say, 100pounds, a portion weighing, say, 15 to 20pounds should be withdrawn for thepurpose of immediate moisturedetermination. This is placed in a shallowiron pan and dried on the hot iron boilerflue for at least 12 hours, being weighedbefore and after drying on scales readingto quarter ounces.

The moisture thus determined is

approximately reliable for anthracite andsemi-bituminous coals, but not for coalscontaining much inherent moisture. Forsuch coals, and for all absolutely reliabledeterminations the method to be pursuedis as follows:

Take one of the samples contained in theglass jars, and subject it to a thoroughair drying, by spreading it in a thin layerand exposing it for several hours to theatmosphere of a warm room, weighing itbefore and after, thereby determining thequantity of surface moisture itcontains.[68] Then crush the whole of itby running it through an ordinary coffeemill or other suitable crusher adjustedso as to produce somewhat coarse grains(less than 1/16 inch), thoroughly mix thecrushed sample, select from it a portionof from 10 to 50 grams,[69] weigh it in abalance which will easily show a

variation as small as 1 part in 1000, anddry it for one hour in an air or sand bath ata temperature between 240 and 280degrees Fahrenheit. Weigh it and recordthe loss, then heat and weigh again untilthe minimum weight has been reached.The difference between the original andthe minimum weight is the moisture inthe air-dried coal. The sum of themoisture thus found and that of the surfacemoisture is the total moisture.

11. ASHES AND REFUSE

The ashes and refuse withdrawn from thefurnace and ashpit during the progress ofthe test and at its close should be weighedso far as possible in a dry state. If wet theamount of moisture should be ascertainedand allowed for, a sample being taken anddried for this purpose. This sample mayserve also for analysis and thedetermination of unburned carbon andfusing temperature.

The method above described for samplingcoal may also be followed for obtaining asample of the ashes and refuse.

12. CALORIFIC TESTS AND ANALYSES OFCOAL

The quality of the fuel should bedetermined by calorific tests and analysisof the coal sample above referred to.[70]

13. ANALYSES OF FLUE GASES

For approximate determinations of thecomposition of the flue gases, the Orsatapparatus, or some modification thereof,should be employed. If momentarysamples are obtained the analyses shouldbe made as frequently as possible, say,every 15 to 30 minutes, depending on theskill of the operator, noting at the time thesample is drawn the furnace and firingconditions. If the sample drawn is acontinuous one, the intervals may be madelonger.

14. SMOKE OBSERVATIONS[71]

In tests of bituminous coals requiring adetermination of the amount of smokeproduced, observations should be maderegularly throughout the trial at intervals of5 minutes (or if necessary every minute),noting at the same time the furnace andfiring conditions.

15. CALCULATION OF RESULTS

The methods to be followed in expressingand calculating those results which are notself-evident are explained as follows:

(A) _Efficiency._ The "efficiency ofboiler, furnace and grate" is the relationbetween the heat absorbed per pound ofcoal fired, and the calorific value of one

pound of coal.

The "efficiency of boiler and furnace" isthe relation between the heat absorbedper pound of combustible burned, and the

calorific value of one pound ofcombustible. This expression ofefficiency furnishes a means for comparingone boiler and furnace with another,when the losses of unburned coal due togrates, cleanings, etc., are eliminated.

The "combustible burned" isdetermined by subtracting from theweight of coal supplied to the boiler, themoisture in the coal, the weight of ashand unburned coal withdrawn from thefurnace and ashpit, and the weight ofdust, soot, and refuse, if any, withdrawnfrom the tubes, flues, and combustionchambers, including ash carried away inthe gases, if any, determined from theanalysis of coal and ash. The"combustible" used for determining thecalorific value is the weight of coal less the moisture and ash found by analysis.

The "heat absorbed" per pound of coal,or combustible, is calculated bymultiplying the equivalent evaporationfrom and at 212 degrees per pound ofcoal or combustible by 970.4.

Other items in this section which havebeen treated elsewhere are:

(B) Corrections for moisture in steam.

(C) Correction for live steam used.

(D) Equivalent evaporation.

(E) Heat balance.

(F) Total heat of combustion of coal.

(G) Air for combustion and the methodsrecommended for calculating theseresults are in accordance with thosedescribed in different portions of thisbook.

16. DATA AND RESULTS

The data and results should be reported inaccordance with either the short form orthe complete form, adding lines for datanot provided for, or omitting those notrequired, as may conform to the object inview.

17. CHART

In trials having for an object thedetermination and exposition of thecomplete boiler performance, the entirelog of readings and data should be plottedon a chart and represented graphically.

18. TESTS WITH OIL AND GAS FUELS

Tests of boilers using oil or gas for fuelshould accord with the rules here given,excepting as they are varied to conform tothe particular characteristics of the fuel.The duration in such cases may bereduced, and the "flying" method ofstarting and stopping employed.

The table of data and results shouldcontain items stating character offurnace and burner, quality andcomposition of oil or gas, temperature ofoil, pressure of steam used forvaporizing and quantity of steam used forboth vaporizing and for heating.

TABLE DATA AND RESULTS OFEVAPORATIVE TEST SHORTFORM, CODE OF 1912

1 Test of.................boiler locatedat................................ todetermine...............conductedby.............................. 2 Kind offurnace.......................................................... 3 Gratesurface.................................................square feet 4 Water-heatingsurface.........................................squarefeet 5 Superheatingsurface..........................................squarefeet 6Date..................................................................... 7Duration............................................................hours 8 Kind and size ofcoal....................................................

AVERAGE PRESSURES, TEMPERATURES,ETC.

9 Steam pressure bygauge............................................pounds10 Temperature of feed water enteringboiler.........................degrees 11Temperature of escaping gases leavingboiler......................degrees 12 Force ofdraft between damper andboiler...........................inches 13Percentage of moisture in steam, ornumber degrees ofsuperheating..................per cent ordegrees

TOTAL QUANTITIES

14 Weight of coal asfired[72]........................................pounds15 Percentage of moisture incoal...................................per cent 16Total weight of dry coalconsumed..................................pounds 17Total ash and

refuse...............................................pounds 18 Percentage of ash and refuse in drycoal.........................per cent 19 Totalweight of water fed to theboiler[73]........................pounds 20 Totalwater evaporated, corrected for moisturein steam............pounds 21 Total equivalentevaporation from and at 212degrees...............pounds

HOURLY QUANTITIES AND RATES

22 Dry coal consumed perhour.........................................pounds 23Dry coal per square feet of grate surfaceper hour.................pounds 24 Waterevaporated per hour corrected for qualityof steam...........pounds 25 Equivalentevaporation per hour from and at 212degrees............pounds 26 Equivalentevaporation per hour from and at 212degrees per square foot of

water-heatingsurface........................pounds

CAPACITY

27 Evaporation per hour from and at 212degrees (same as Line 25).....pounds 28Boiler horse power developed (Item27�4�).............boiler horse power 29Rated capacity, in evaporation from and at212 degrees per hour....pounds 30 Ratedboiler horsepower...............................boiler horsepower 31 Percentage of rated capacitydeveloped...........................per cent

ECONOMY RESULTS

32 Water fed per pound of coal fired (Item19�tem 14)................pounds 33 Waterevaporated per pound of dry coal (Item20�tem 16)...........pounds 34 Equivalent

evaporation from and at 212 degrees perpound of dry coal (Item 21�tem16)...................................pounds 35Equivalent evaporation from and at 212degrees per pound of combustible[Item 21�Item 16-Item17)]......................pounds

EFFICIENCY

36 Calorific value of one pound of drycoal.........................B. t. u. 37 Calorificvalue of one pound ofcombustible......................B. t. u.

( Item 34�70.4)38 Efficiency of boiler, furnace and grate(100 �-------------)....per cent ( Item 36 )

( Item 35�70.4) 39Efficiency of boiler and furnace (100

�-------------)...........per cent ( Item 37 )

COST OF EVAPORATION

40 Cost of coal per ton of......poundsdelivered in boiler room......dollars 41Cost of coal required for evaporating 1000pounds of water from and at 212degrees........................................dollars

[Illustration: Portion of 3600 Horse-powerInstallation of Babcock & Wilcox Boilers,Equipped with Babcock & Wilcox ChainGrate Stokers at the Loomis Street Plant ofthe Peoples Gas Light & Coke Co.,Chicago, Ill. This Company has Installed7780 Horse Power of Babcock & WilcoxBoilers]

THE SELECTION OF BOILERS WITH ACONSIDERATION OF THE FACTORSDETERMINING SUCH SELECTION

The selection of steam boilers is a matterto which the most careful thought andattention may be well given. Within thelast twenty years, radical changes havetaken place in the methods and appliancesfor the generation and distribution ofpower. These changes have been madelargely in the prime movers, both as totype and size, and are best illustrated bythe changes in central station power-plantpractice. It is hardly within the scope ofthis work to treat of power-plant designand the discussion will be limited to aconsideration of the boiler end of thepower plant.

As stated, the changes have been largely

in prime movers, the steam generatingequipment having been considered moreor less of a standard piece of apparatuswhose sole function is the transfer of theheat liberated from the fuel by combustionto the steam stored or circulated in suchapparatus. When the fact is consideredthat the cost of steam generation is roughlyfrom 65 to 80 per cent of the total cost ofpower production, it may be readilyunderstood that the most fruitful field forimprovement exists in the boiler end of thepower plant. The efficiency of the plant asa whole will vary with the load it carriesand it is in the boiler room where suchvariation is largest and most subject tocontrol.

The improvements to be secured in theboiler room results are not simply a matterof dictation of operating methods. Thesecuring of perfect combustion, with the

accompanying efficiency of heat transfer,while comparatively simple in theory, isdifficult to obtain in practical operation.This fact is perhaps best exemplified bythe difference between test results andthose obtained in daily operation evenunder the most careful supervision. Thisdifference makes it necessary to establisha standard by which operating results maybe judged, a standard not necessarily thatwhich might be possible under testconditions but one which experimentshows can be secured under the very bestoperating conditions.

The study of the theory of combustion,draft, etc., as already given, will indicatethat the question of efficiency is largely amatter of proper relation between fuel,furnace and generator. While thepossibility of a substantial saving throughadded efficiency cannot be overlooked,

the boiler design of the future must, evenmore than in the past, be consideredparticularly from the aspect of reliabilityand simplicity. A flexibility of operation isnecessary as a guarantee of continuity ofservice.

In view of the above, before the questionof the selection of boilers can be taken upintelligently, it is necessary to consider thesubjects of boiler efficiency and boilercapacity, together with their relation toeach other.

The criterion by which the efficiency of aboiler plant is to be judged is the cost ofthe production of a definite amount ofsteam. Considered in this sense, theremust be included in the efficiency of aboiler plant the simplicity of operation,flexibility and reliability of the boiler used.The items of repair and upkeep cost are

often high because of the nature of theservice. The governing factor in theseitems is unquestionably the type of boilerselected.

The features entering into the plantefficiency are so numerous that it isimpossible to make a statement as to ameans of securing the highest efficiencywhich will apply to all cases. Suchefficiency is to be secured by the properrelation of fuel, furnace and boiler heatingsurface, actual operating conditions, whichallow the approaching of the potentialefficiencies made possible by therefinement of design, and a systematicsupervision of the operation assisted by adetailed record of performances andconditions. The question of supervisionwill be taken up later in the chapter on"Operation and Care of Boilers".

The efficiencies that may be expectedfrom the combination of well-designedboilers and furnaces are indicated in Table59 in which are given a number of testswith various fuels and under widelydifferent operating conditions.

It is to be appreciated that the resultsobtained as given in this table arepractically all under test conditions. Thenearness with which practical operatingconditions can approach these figures willdepend upon the character of thesupervision of the boiler room and theintelligence of the operating crew. Thesize of the plant will ordinarily govern theexpense warranted in securing the rightsort of supervision.

The bearing that the type of boiler has onthe efficiency to be expected can only berealized from a study of the foregoing

chapters.

Capacity--Capacity, as already defined, isthe ability of a definite amount ofboiler-heating surface to generate steam.Boilers are ordinarily purchased under amanufacturer's specification, which rates aboiler at a nominal rated horse power,usually based on 10 square feet of heatingsurface per horse power. Such a builders'rating is absolutely arbitrary and impliesnothing as to the limiting amount of waterthat this amount of heating surface willevaporate. It does not imply that theevaporation of 34.5 pounds of water fromand at 212 degrees with 10 square feet ofheating surface is the limit of the capacityof the boiler. Further, from a statement thata boiler is of a certain horse power on themanufacturer's basis, it is not to beunderstood that the boiler is in any state ofstrain when developing more than its rated

capacity.

Broadly stated, the evaporative capacity ofa certain amount of heating surface in awell-designed boiler, that is, the boilerhorse power it is capable of producing, islimited only by the amount of fuel that canbe burned under the boiler. While such astatement would imply that the question ofcapacity to be secured was simply one ofmaking an arrangement by whichsufficient fuel could be burned under adefinite amount of heating surface togenerate the required amount of steam,there are limiting features that must beweighed against the advantages of highcapacity developed from small heatingsurfaces. Briefly stated, these factors are asfollows:

1st. Efficiency. As the capacity increases,there will in general be a decrease in

efficiency, this loss above a certain pointmaking it inadvisable to try to secure morethan a definite horse power from a givenboiler. This loss of efficiency withincreased capacity is treated below indetail, in considering the relation ofefficiency to capacity.

2nd. Grate Ratio Possible or Practicable.All fuels have a maximum rate ofcombustion, beyond which satisfactoryresults cannot be obtained, regardless ofdraft available or which may be securedby mechanical means. Such being thecase, it is evident that with this maximumcombustion rate secured, the only methodof obtaining added capacity will bethrough the addition of grate surface.There is obviously a point beyond whichthe grate surface for a given boiler cannotbe increased. This is due to theimpracticability of handling grates above a

certain maximum size, to the enormousloss in draft pressure through a boilerresulting from an attempt to force anabnormal quantity of gas through theheating surface and to innumerable detailsof design and maintenance that wouldmake such an arrangement whollyunfeasible.

3rd. Feed Water. The difficulties that mayarise through the use of poor feed water orthat are liable to happen through the use ofpractically any feed water have alreadybeen pointed out. This question of feed isfrequently the limiting factor in thecapacity obtainable, for with an increase insuch capacity comes an addedconcentration of such ingredients in thefeed water as will cause priming, foamingor rapid scale formation. Certain waterswhich will give no trouble that cannot bereadily overcome with the boiler run at

ordinary ratings will cause difficulties athigher ratings entirely out of proportion toany advantage secured by an increase inthe power that a definite amount of heatingsurface may be made to produce.

Where capacity in the sense of overload isdesired, the type of boiler selected willplay a large part in the successfuloperation through such periods. A boilermust be selected with which there ispossible a furnace arrangement that willgive flexibility without undue loss inefficiency over the range of capacitydesired. The heating surface must be soarranged that it will be possible to installin a practical manner, sufficient gratesurface at or below the maximumcombustion rate to develop the amount ofpower required. The design of boiler mustbe such that there will be no priming orfoaming at high overloads and that any

added scale formation due to suchoverloads may be easily removed. Certainboilers which deliver commercially drysteam when operated at about their normalrated capacity will prime badly when runat overloads and this action may take placewith a water that should be easily handledby a properly designed boiler at anyreasonable load. Such action is ordinarilyproduced by the lack of a well defined,positive circulation.

Relation of Efficiency and Capacity--Thestatement has been made that in generalthe efficiency of a boiler will decrease asthe capacity is increased. Considering theboiler alone, apart from the furnace, thisstatement may be readily explained.

Presupposing a constant furnacetemperature, regardless of the capacity atwhich a given boiler is run; to assure equal

efficiencies at low and high ratings, theexit temperature in the two instanceswould necessarily be the same. For thistemperature at the high rating, to beidentical with that at the low rating, therate of heat transfer from the gases to theheating surfaces would have to varydirectly as the weight or volume of suchgases. Experiment has shown, however,that this is not true but that this rate oftransfer varies as some power of thevolume of gas less than one. As the heattransfer does not, therefore, increaseproportionately with the volume of gases,the exit temperature for a given furnacetemperature will be increased as thevolume of gases increases. As this is themeasure of the efficiency of the heatingsurface, the boiler efficiency will,therefore, decrease as the volume of gasesincreases or the capacity at which theboiler is operated increases.

Further, a certain portion of the heatabsorbed by the heating surface isthrough direct radiation from the fire.Again, presupposing a constant furnacetemperature; the heat absorbed throughradiation is solely a function of the amountof surface exposed to such radiation.Hence, for the conditions assumed, theamount of heat absorbed by radiation atthe higher ratings will be the same as atthe lower ratings but in proportion to thetotal absorption will be less. As the addedvolume of gas does not increase the rate ofheat transfer, there are therefore twofactors acting toward the decrease in theefficiency of a boiler with an increase inthe capacity.

TABLE 59

TESTS OF BABCOCK & WILCOX

BOILERS WITH VARIOUS FUELS

______________________________________________________________________|Number| | | |Rated | | of | Name and Location |Kind of Coal | Kind of | Horse | | Test |

of Plant | | Furnace |Powerof| | | | | |Boiler | | | | |

| ||______|___________________________|________________|_________|________| ||Susquehanna Coal Co., |No. 1Anthracite|Hand | | | 1|Shenandoah, Pa. |Buckwheat|Fired | 300 ||______|___________________________|________________|_________|________| ||Balbach Smelting & |No. 2Buckwheat |Wilkenson| | | 2

|Refining Co., Newark, N. J.|andBird's-eye | Stoker | 218 ||______|___________________________|________________|_________|________| ||H. R. Worthington, |No. 2Anthracite|Hand | | | 3 |HarrisonN. J. |Buckwheat |Fired | 300||______|___________________________|________________|_________|________| ||Raymond Street Jail, |Anthracite Pea|Hand | | | 4 |Brooklyn, N. Y.

| |Fired | 155 ||______|___________________________|________________|_________|________| ||R. H. Macy & Co., |No. 3Anthracite|Hand | | | 5 |NewYork, N. Y. |Buckwheat |Fired |

293 ||______|___________________________|________________|_________|________| ||National Bureau of |Anthracite Egg

|Hand | | | 6 |Standards,Washington, D.C.| |Fired | 119||______|___________________________|________________|_________|________| ||Fred. Loeser & Co., |No. 1Anthracite|Hand | | | 7 |Brooklyn,N. Y. |Buckwheat |Fired | 300||______|___________________________|________________|_________|________| ||New York Edison Co., |No. 2Anthracite|Hand | | | 8 |New YorkCity |Buckwheat |Fired | 374

||______|___________________________|________________|_________|________| ||Sewage Pumping Station, |HockingValley |Hand | | | 9 |Cleveland,O. |Lump, O. |Fired | 150 ||______|___________________________|________________|_________|________| |

|Scioto River Pumping Sta., |HockingValley, |Hand | | | 10 |Cleveland,O. |O. |Fired | 300 ||______|___________________________|________________|_________|________| ||Consolidated Gas & Electric|Somerset,Pa. |Hand | | | 11 |Co., Baltimore,Md. | |Fired | 640 ||______|___________________________|________________|_________|________| ||Consolidated Gas & Electric|Somerset,Pa. |Hand | | | 12 |Co., Baltimore,Md. | |Fired | 640 ||______|___________________________|________________|_________|________| ||Merrimac Mfg. Co., |Georges Creek,|Hand | | | 13 |Lowell, Mass.

|Md. |Fired | 321 ||______|___________________________|________________|_________|________| ||Great West'n Sugar Co., |Lafayette,Col.,|HandFired| | | 14 |Ft. Collins,

Col. |Mine Run |Extension| 351||______|___________________________|________________|_________|________| ||Baltimore Sewage Pumping |New River

|Hand | | | 15 | Station| |Fired | 266 ||______|___________________________|________________|_________|________| ||Tennessee State Prison, |BrushyMountain,|Hand | | | 16 |Nashville,Tenn. |Tenn. |Fired | 300 ||______|___________________________|________________|_________|________| ||Pine Bluff Corporation, |Arkansas Slack|Hand | | | 17 |Pine Bluff, Ark.

| |Fired | 298 ||______|___________________________|________________|_________|________| ||Pub. Serv. Corporation |Valley, Pa.,|Roney | | | 18 |of N. J., Hoboken

|Mine Run |Stoker | 520 |

|______|___________________________|________________|_________|________| ||Pub. Serv. Corporation |Valley, Pa.,|Roney | | | 19 |of N. J., Hoboken

|Mine Run |Stoker | 520 ||______|___________________________|________________|_________|________| ||Frick Building, |Pittsburgh Nut|American | | | 20 |Pittsburgh, Pa.

|and Slack |Stoker | 300 ||______|___________________________|________________|_________|________| ||New York Edison Co., |Loyal Hanna,Pa.|Taylor | | | 21 |New York City

| |Stoker | 604 ||______|___________________________|________________|_________|________| ||City of Columbus, O., |HockingValley, |Detroit | | | 22 |Dept.Lighting |O. |Stoker | 300||______|___________________________|___

_____________|_________|________| ||Edison Elec. Illum. Co., |New River|Murphy | | | 23 |Boston, Mass.

| |Stoker | 508 ||______|___________________________|________________|_________|________| ||Colorado Springs & |Pike View,Col.,|Green Chn| | | 24 |InterurbanRy., Col. |Mine Run |Grate | 400||______|___________________________|________________|_________|________| ||Pub. Serv. Corporation |Lancashire, Pa.|B&W.Chain| | | 25 |of N. J., Marion

| |Grate | 600 ||______|___________________________|________________|_________|________| ||Pub. Serv. Corporation |Lancashire, Pa.|B&W.Chain| | | 26 |of N. J., Marion

| |Grate | 600 ||______|___________________________|________________|_________|________| |

|Erie County Electric Co., |MercerCounty, |B&W.Chain| | | 27 |Erie,Pa. |Pa. |Grate | 508 ||______|___________________________|________________|_________|________| ||Union Elec. Lt. & Pr. Co., |Mascouth, Ill.|B&W.Chain| | | 28 |St. Louis, Mo.

| |Grate | 508 ||______|___________________________|________________|_________|________| ||Union Elec. Lt. & Pr. Co., |St. Clair|B&W.Chain| | | 29 |St. Louis, Mo.

|County, Ill. |Grate | 508 ||______|___________________________|________________|_________|________| ||Commonwealth Edison Co.,|Carterville, |B&W.Chain| | | 30|Chicago, Ill. |Ill.,Screenings|Grate | 508 ||______|___________________________|________________|_________|________|

________________________________________________________________|Number|Grate |Dura-|Steam|Temper-|Degrees|Factor| Draft | |of |Surf. | tion|Pres. | ature | Super | of| In | At | | Test |Square|Test | By |Water | -heat |Evapo-|Furnace|Boiler| |

| Feet |Hours|Gauge|Degrees|Degrees|ration|Inches|Damper| | | | |Pounds| Fahr. |Fahr. | |Upr/Lwr|Inches||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 1 | 84 |8 | 68 | 53.9 | |1.1965| +.41 | .21 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | +.65 | | | 2 | 51.6| 7 | 136.3| 203 | 150 |1.1480| .47 |.56 ||______|______|_____|______|_______|___

____|______|_______|______| | | || | | | | | | | 3 | 67.6 |8 | 139 | 139.6 | 139 |1.1984| .70 | .96||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 4 | 40 |8 | 110.2| 137 | |1.1185| .33 | .43 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 5 | 59.5 |10 | 133.2| 75.2 | |1.1849| .19 | .40||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 6 | 26.5 |18 | 132.1| 70.5 | |1.1897| .33 | ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | +.51 | | | 7 | 48.9| 7 | 101. | 121.3 | |1.1333| -.20 | .30|

|______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 8 | 59.5 |6 | 191.8| 88.3 | |1.1771| .50 | ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 9 | 27 |24 | 156.3| 58 | |1.2051| .10 | .24 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 10 | |24 | 145 | 75 | |1.1866| .26 | .46 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 11 | 118 |8 | 170 | 186.1 | 66.7 |1.1162| .34 | .42

||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 12 | 118 |7.92| 173 | 180.2 | 75.2 |1.1276| .44 |.58 |

|______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 13 | 52 |24 | 75 | 53.3 | |1.1987| .25 | .35 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 14 | 59.5 |8 | 105 | 35.8 | |1.2219| .17 | .38 |

|______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 15 | 59.5 |24 | 170.1| 133 | |1.1293| .12 | .43||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 16 | 51.3 |10 | 105 | 75.1 | |1.1814| .21 | .42 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 17 | 59.5 |8 | 149.2| 71 | |1.1910| .35 | .59 |

|______|______|_____|______|_______|___

____|______|_______|______| | | || | | | | | | | 18 |103.2| 10 | 133.2| 65.3 | 65.9 |1.2346|.05 | .49 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 19 |103.2| 9 | 139 | 64 | 80.2 |1.2358| .18| .57 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 20 | 53 |9 | 125 | 76.6 | |1.1826| +1.64 | .64 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 21 | 75 |8 | 198.5| 165.1 | 104 |1.1662| +3.05 |.60 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 22 | |9 | 140 | 67 | 180 |1.2942| .22 | .35 |

|______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 23 | 90|16.25| 199 | 48.4 | 136.5 |1.2996| .23 |1.27 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 24 | 103 |8 | 129 | 56 | |1.2002| .23 | .30 |

|______|______|_____|______|_______|_______|______|_______|______| | | || | | | | +.52 | | | 25 | 132| 8 | 200 | 57.2 | 280.4 |1.3909| +.19 |

.52 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | +.15 | | | 26 | 132| 8 | 199 | 60.7 | 171.0 |1.3191| .04 |

.52 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 27 | 90 |

8 | 120 | 69.9 | |1.1888| .31 | .58 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 28 |103.5| 8 | 180 | 46 | 113 |1.2871| .62| 1.24 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 29 |103.5| 8 | 183 | 53.1 | 104 |1.2725| .60

| 1.26 ||______|______|_____|______|_______|_______|______|_______|______| | | || | | | | | | | 30 | 90 |7 | 184 | 127.1 | 180 |1.2393| .68 | 1.15||______|______|_____|______|_______|_______|______|_______|______|______________________________________________________________|Number|Temper-| Coal

| | of | ature | Total | Moist-| Total

|Ash and| Total |DryCoal| | Test|FlueGas|Weight:| ure | dry |Refuse|Combus-|/sq.ft.| | |Degrees|Fired | Per | Coal | Per | tible | Grate || | Fahr. |Pounds | Cent | Pounds|Cent | Pounds|/Hr.Lb.||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 1 | |11670 | 4.45 | 11151 | 26.05 | 8248 | 16.6||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 2 | 487 |8800 | 7.62 | 8129 | 29.82 | 5705 | 19.71||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 3 | 559 |10799 | 6.42 | 10106 | 20.02 | 8081 |21.77 ||______|_______|_______|_______|_______

|_______|_______|_______| | | || | | | | | | 4 | 427 |5088 | 4.00 | 4884 | 19.35 | 3939 | 15.26||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 5 | 414 |9440 | 2.14 | 9238 | 11.19 | 8204 | 15.52||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 6 | 410 |8555 | 3.62 | 8245 | 15.73 | 6948 | 17.28||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 7 | 480 |7130 | 7.38 | 6604 | 18.35 | 5392 | 19.29||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 8 | 449 |

7500 | 2.70 | 7298 | 27.94 | 5259 | 14.73||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 9 | 410 |15087 | 7.50 | 13956 | 11.30 | 12379 | 21.5

||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 10 | 503 |29528 | 7.72 | 27248 | | | 24.7 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 11 | 487 |20400 | 2.84 | 19821 | 7.83 | 18269 |21.00 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 12 | 494 |21332 | 2.29 | 20843 | 8.23 | 19127 |22.31 ||______|_______|_______|_______|_______

|_______|_______|_______| | | || | | | | | | 13 | 516 |24584 | 4.29 | 23529 | 7.63 | 21883 |18.85 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 14 | 523 |15540 | 18.64 | 12643 | | | 28.59 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 15 | 474 |18330 | 2.03 | 17958 | 16.36 | 16096 |12.57 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 16 | 536 |12243 | 2.14 | 11981 | | | 23.40 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 17 | 534 |10500 | 3.04 | 10181 | | | 21.40 ||______|_______|_______|_______|_______

|_______|_______|_______| | | || | | | | | | 18 | 458 |18600 | 3.40 | 17968 | 18.38 | 14665 |17.41 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 19 | 609 |23400 | 2.56 | 22801 | 16.89 | 18951 |24.55 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 20 | 518 |10500 | 1.83 | 10308 | 12.22 | 9048 |21.56 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 21 | 536 |25296 | 2.20 | 24736 | | | 41.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 22 | 511 |14263 | 8.63 | 13032 | | | |

|______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 23 | 560 |39670 | 4.22 | 37996 | 4.32 | 36355 |25.98 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 24 | 538 |23000 | 23.73 | 17542 | | | 21.36 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 25 | 590 |32205 | 4.03 | 30907 | 15.65 | 26070 |29.26 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 26 | 529 |24243 | 4.09 | 23251 | 12.33 | 20385 |22.01 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 27 | 533 |

22328 | 4.42 | 21341 | 16.88 | 17739 |29.64 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 28 | 523 |32163 | 13.74 | 27744 | | | 33.50 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 29 | 567 |36150 | 14.62 | 30865 | | | 37.28 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 30 | |30610 | 11.12 | 27206 | 14.70 | 23198 |43.20 ||______|_______|_______|_______|_______|_______|_______|_______|

______________________________________________________________ |Number|Water | | Flue Gas Analysis | |

of |Actual | Equiv.|ditto /|%Rated|CO_{2} | O | CO | | Test|Evapor-|Evap. @|sq.ft. |Cap'ty.| Per |Per | Per | | | ation |>=212�|Heating|Develpd| Cent | Cent | Cent || |/Hr.Lb.|/Hr.Lb.|Surface|PerCent|

| | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 1 | 10268 |12286 | 4.10 | 118.7 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 2 | 8246 |9466 | 4.34 | 125.7 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 3 | 9145 |10959 | 3.65 | 105.9 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 4 | 5006 |

5599 | 3.61 | 104.7 | 12.26 | 7.88 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 5 | 7434 |8809 | 3.06 | 87.2 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 6 | 2903 |3454 | 2.91 | 84.4 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 7 | 7464 |8459 | 2.82 | 81.7 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 8 | 9164 |10787 | 2.88 | 83.5 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 9 | 4374 |5271 | 3.51 | 101.8 | 11.7 | 7.3 | 0.07 ||______|_______|_______|_______|_______

|_______|_______|_______| | | || | | | | | | 10 | 8688 |10309 | 3.44 | 99.6 | 12.9 | 5.0 | 0.2 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 11 | 24036 |26829 | 4.19 | 121.5 | 12.5 | 6.4 | 0.5 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 12 | 25313 |28544 | 4.46 | 129.3 | 13.3 | 5.1 | 0.5 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 13 | 9168 |10990 | 3.42 | 99.3 | 9.6 | 8.8 | 0.4 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 14 | 11202 |13689 | 3.91 | 113.5 | 9.1 | 9.9 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 15 | 7565 |

8543 | 3.21 | 93.1 | 10.71 | 9.10 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 16 | 9512 |11237 | 3.74 | 108.6 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 17 | 9257 |11025 | 3.70 | 107.2 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 18 | 15887 |19614 | 3.77 | 108.7 | 11.7 | 7.7 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 19 | 21320 |26347 | 5.06 | 146.7 | 11.9 | 7.8 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 20 | 9976 |11978 | 3.93 | 112.0 | 11.3 | 7.5 | 0.0 ||______|_______|_______|_______|_______

|_______|_______|_______| | | || | | | | | | 21 | 28451 |33066 | 5.47 | 158.6 | 12.3 | 6.4 | 0.7 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 22 | 10467 |13526 | 4.51 | 130.7 | 11.9 | 7.2 | 0.04 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 23 | 20700 |26902 | 5.30 | 153.5 | 11.1 | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 24 | 14650 |17583 | 4.40 | 127.4 | | | ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 25 | 28906 |40205 | 6.70 | 194.2 | 10.5 | 8.3 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 26 | 23074 |

30437 | 5.07 | 147.0 | 10.1 | 9.0 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 27 | 20759 |24678 | 4.85 | 140.8 | 10.1 | 9.1 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 28 | 21998 |28314 | 5.67 | 161.5 | 8.7 | 10.6 | 0.0 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 29 | 24386 |31031 | 6.11 | 177.1 | 8.9 | 10.7 | 0.2 ||______|_______|_______|_______|_______|_______|_______|_______| | | || | | | | | | 30 | 30505 |37805 | 7.43 | 215.7 | 10.4 | 9.4 | 0.2 ||______|_______|_______|_______|_______|_______|_______|_______|

_______________________________________________________ |Number| Proximate

Analysis Dry Coal | Equiv.|Combnd.| |of |Volatl.| Fixed | Ash |B.t.u./|Evap.@|Efficy.| | Test |Matter |Carbon | Per |Pound |>=212�/|Boiler | | | Per | Per| Cent | Dry | Pound |& Grate| | |

Cent | Cent | | Coal|DryCoal|PerCent||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 1 | | | 26.05 | 11913| 8.81 | 71.8 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 2 | | | | 11104 |8.15 | 72.1 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 3 | 5.55 | 80.60 | 13.87 |12300 | 8.67 | 68.4 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 4 | 7.74 | 77.48 | 14.78 |

12851 | 9.17 | 69.2 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 5 | | | | 13138 |9.53 | 69.6 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 6 | 6.13 | 84.86 | 9.01 |13454 | 9.57 | 69.0 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 7 | | | | 12224 |8.97 | 71.2 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 8 | 0.55 | 86.73 | 12.72 |12642 | 8.87 | 68.1 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 9 | 39.01 | 48.08 | 12.91 |12292 | 9.06 | 71.5 ||______|_______|_______|_______|_______

|_______|_______| | | | | || | | | 10 | 38.33 | 46.71 | 14.96 |12284 | 9.08 | 71.7 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 11 | 19.86 | 73.02 | 7.12 |14602 | 10.83 | 72.0 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 12 | 20.24 | 72.26 | 7.50 |14381 | 10.84 | 73.2 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 13 | | | | 14955 |11.21 | 72.7 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 14 | 39.60 | 54.46 | 5.94 |11585 | 8.66 | 72.5 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 15 | 17.44 | 76.42 | 5.84 |

15379 | 11.42 | 72.1 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 16 | 33.40 | 54.73 | 11.87 |12751 | 9.38 | 71.4 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 17 | 15.42 | 62.48 | 22.10 |12060 | 8.66 | 69.6 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 18 | 14.99 | 75.13 | 9.88 |14152 | 10.92 | 74.88 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 19 | 14.40 | 74.33 | 11.27 |14022 | 10.40 | 71.97 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 20 | 32.44 | 56.71 | 10.85 |13510 | 10.30 | 74.6 ||______|_______|_______|_______|_______

|_______|_______| | | | | || | | | 21 | 19.02 | 72.09 | 8.89 |14105 | 10.69 | 73.5 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 22 | 32.11 | 53.93 | 13.96 |12435 | 9.41 | 73.4 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 23 | 19.66 | 75.41 | 4.93 |14910 | 11.51 | 74.9 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 24 | 43.57 | 46.22 | 10.21 |11160 | 8.02 | 69.7 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 25 | 22.84 | 69.91 | 7.25 |13840 | 10.41 | 72.6 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 26 | 32.36 | 60.67 | 6.97 |

14027 | 10.47 | 72.1 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 27 | 33.26 | 54.03 | 12.71 |12742 | 9.25 | 70.4 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 28 | 28.96 | 46.88 | 24.16 |10576 | 8.16 | 74.9 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 29 | 36.50 | 41.20 | 22.30 |10849 | 8.04 | 71.9 ||______|_______|_______|_______|_______|_______|_______| | | | | || | | | 30 | | | 10.24 | 13126| 9.73 | 71.9 ||______|_______|_______|_______|_______|_______|_______|

[Illustration: 15400 Horse-powerInstallation of Babcock & Wilcox Boilers

and Superheaters, Equipped with Babcock& Wilcox Chain Grate Stokers at the Plantof the Twin City Rapid Transit Co.,Minneapolis, Minn.]

This increase in the efficiency of the boileralone with the decrease in the rate atwhich it is operated, will hold to a pointwhere the radiation of heat from the boilersetting is proportionately large enough tobe a governing factor in the total amount ofheat absorbed.

The second reason given above for adecrease of boiler efficiency with increaseof capacity, viz., the effect of radiant heat,is to a greater extent than the first reasondependent upon a constant furnacetemperature. Any increase in thistemperature will affect enormously theamount of heat absorbed by radiation, asthis absorption will vary as the fourth

power of the temperature of the radiatingbody. In this way it is seen that but a slightincrease in furnace temperature will benecessary to bring the proportional part,due to absorption by radiation, of the totalheat absorbed, up to its proper proportionat the higher ratings. This factor of furnacetemperature more properly belongs to theconsideration of furnace efficiency than ofboiler efficiency. There is a point,however, in any furnace above which thecombustion will be so poor as to actuallyreduce the furnace temperature and,therefore, the proportion of heat absorbedthrough radiation by a given amount ofexposed heating surface.

Since it is thus true that the efficiency of theboiler considered alone will increase witha decreased capacity, it is evident that ifthe furnace conditions are constantregardless of the load, that the combined

efficiency of boiler and furnace will alsodecrease with increasing loads. This factwas clearly proven in the tests of theboilers at the Detroit Edison Company.[74]The furnace arrangement of these boilersand the great care with which the testswere run made it possible to secureuniformly good furnace conditionsirrespective of load, and here themaximum efficiency was obtained at apoint somewhat less than the ratedcapacity of the boilers.

In some cases, however, and especially inthe ordinary operation of the plant, thefurnace efficiency will, up to a certainpoint, increase with an increase in power.This increase in furnace efficiency isordinarily at a greater rate as the capacityincreases than is the decrease in boilerefficiency, with the result that thecombined efficiency of boiler and furnace

will to a certain point increase with anincrease in capacity. This makes theordinary point of maximum combinedefficiency somewhat above the ratedcapacity of the boiler and in many casesthe combined efficiency will be practicallya constant over a considerable range ofratings. The features limiting theestablishing of the point of maximumefficiency at a high rating are the same asthose limiting the amount of grate surfacethat can be installed under a boiler. Therelative efficiency of differentcombinations of boilers and furnaces atdifferent ratings depends so largely uponthe furnace conditions that what might holdfor one combination would not for another.

In view of the above, it is impossible tomake a statement of the efficiency atdifferent capacities of a boiler and furnacewhich will hold for any and all conditions.

Fig. 40 shows in a general form the relationof efficiency to capacity. This curve hasbeen plotted from a great number of tests,all of which were corrected to bring themto approximately the same conditions. Thecurve represents test conditions. Theefficiencies represented are those whichmay be secured only under suchconditions. The general direction of thecurve, however, will be found to holdapproximately correct for operatingconditions when used only as a guide towhat may be expected.

[Graph: Combined Efficiency of Boiler andFurnace Per Cent against Per Cent ofBoiler's Rated Capacity Developed

Fig. 40. Approximate Variation ofEfficiency with Capacity under TestConditions]

Economical Loads--With the effect ofcapacity on economy in mind, the questionarises as to what constitutes theeconomical load to be carried. In figuringon the economical load for an individualplant, the broader economy is to beconsidered, that in which, against theboiler efficiency, there is to be weighedthe plant first cost, returns on suchinvestment, fuel cost, labor, capacity, etc.,etc. This matter has been widelydiscussed, but unfortunately suchdiscussion has been largely limited tocentral power station practice. The powergenerated in such stations, whilerepresenting an enormous total, is by nomeans the larger proportion of the totalpower generated throughout the country.The factors determining the economic loadfor the small plant, however, are the sameas in a large, and in general the statementsmade relative to the question are equally

applicable.

The economical rating at which a boilerplant should be run is dependent solelyupon the load to be carried by thatindividual plant and the nature of suchload. The economical load for eachindividual plant can be determined onlyfrom the careful study of each individualset of conditions or by actual trial.

The controlling factor in the cost of theplant, regardless of the nature of the load,is the capacity to carry the maximum peakload that may be thrown on the plant underany conditions.

While load conditions, do, as stated, varyin every individual plant, in a broad senseall loads may be grouped in three classes:1st, the approximately constant 24-hourload; 2nd, the steady 10 or 12-hour load

usually with a noonday period of no load;3rd, the 24-hour variable load, found incentral station practice. The economicalload at which the boiler may be run willvary with these groups:

1st. For a constant load, 24 hours in theday, it will be found in most cases that,when all features are considered, the mosteconomical load or that at which a givenamount of steam can be produced the mostcheaply will be considerably over therated horse power of the boiler. How muchabove the rated capacity this mosteconomic load will be, is dependentlargely upon the cost of coal at the plant,but under ordinary conditions, the point ofmaximum economy will probably be foundto be somewhere between 25 and 50 percent above the rated capacity of theboilers. The capital investment must beweighed against the coal saving through

increased thermal efficiency and the laboraccount, which increases with the numberof units, must be given properconsideration. When the question isconsidered in connection with a plantalready installed, the conditions aredifferent from where a new plant iscontemplated. In an old plant, where thereare enough boilers to operate at low ratesof capacity, the capital investment leads toa fixed charge, and it will be found that themost economical load at which boilers maybe operated will be lower than where anew plant is under consideration.

2nd. For a load of 10 or 12 hours a day,either an approximately steady load orone in which there is a peak, where theboilers have been banked over night, thecapacity at which they may be run with thebest economy will be found to be higherthan for uniform 24-hour load conditions.

This is obviously due to originalinvestment, that is, a given amount ofinvested capital can be made to earn alarger return through the higher overload,and this will hold true to a point where theadded return more than offsets thedecrease in actual boiler efficiency. Hereagain the determining factors of what is theeconomical load are the fuel and labor costbalanced against the thermal efficiency.With a load of this character, there isanother factor which may affect theeconomical plant operating load. This isfrom the viewpoint of spare boilers. Thatsuch added capacity in the way of sparesis necessary is unquestionable. Since theymust be installed, therefore, theirpresence leads to a fixed charge and it isprobable that for the plant, as a whole, theeconomical load will be somewhat lowerthan if the boilers were considered only asspares. That is, it may be found best to

operate these spares as a part of theregular equipment at all times exceptwhen other boilers are off for cleaning andrepairs, thus reducing the load on theindividual boilers and increasing theefficiency. Under such conditions, theadded boiler units can be considered asspares only during such time as some ofthe boilers are not in operation.

Due to the operating difficulties that maybe encountered at the higher overloads, itwill ordinarily be found that the mosteconomical ratings at which to run boilersfor such load conditions will be between150 and 175 per cent of rating. Here againthe maximum capacity at which the boilersmay be run for the best plant economy islimited by the point at which the efficiencydrops below what is warranted in view ofthe first cost of the apparatus.

3rd. The 24-hour variable load. This is aclass of load carried by the central powerstation, a load constant only in the sensethat there are no periods of no load andwhich varies widely with different portionsof the 24 hours. With such a load it isparticularly difficult to make any assertionas to the point of maximum economy thatwill hold for any station, as this point ismore than with any other class of loaddependent upon the factors entering intothe operation of each individual plant.

The methods of handling a load of thisdescription vary probably more than withany other kind of load, dependent uponfuel, labor, type of stoker, flexibility ofcombined furnace and boiler etc., etc.

In general, under ordinary conditions suchas appear in city central power stationwork where the maximum peaks occur but

a few times a year, the plant should bemade of such size as to enable it to carrythese peaks at the maximum possibleoverload on the boilers, sufficient marginof course being allowed for insuranceagainst interruption of service. With theboilers operating at this maximumoverload through the peaks a largesacrifice in boiler efficiency is allowable,provided that by such sacrifice theoverload expected is secured.

[Illustration: Portion of 4890 Horse-powerInstallation of Babcock & Wilcox Boilers atthe Billings Sugar Co., Billings, Mont. 694Horse Power of these Boilers are Equippedwith Babcock and Wilcox Chain GrateStokers]

Some methods of handling a load of thisnature are given below:

Certain plant operating conditions make itadvisable, from the standpoint of planteconomy, to carry whatever load is on theplant at any time on only such boilers aswill furnish the power required whenoperating at ratings of, say, 150 to 200 percent. That is, all boilers which are inservice are operated at such ratings at alltimes, the variation in load being takencare of by the number of boilers on theline. Banked boilers are cut in to take careof increasing loads and peaks and placedagain on bank when the peak periods havepassed. It is probable that this method ofhandling central station load is to-day themost generally used.

Other conditions of operation make itadvisable to carry the load on a definitenumber of boiler units, operating these atslightly below their rated capacity duringperiods of light or low loads and securing

the overload capacity during peaks byoperating the same boilers at high ratings.In this method there are no boilers kept onbanked fires, the spares being spares inevery sense of the word.

A third method of handling widely varyingloads which is coming somewhat intovogue is that of considering the plant asdivided, one part to take care of what maybe considered the constant plant load, theother to take care of the floating orvariable load. With such a method thatportion of the plant carrying the steadyload is so proportioned that the boilersmay be operated at the point of maximumefficiency, this point being raised to amaximum through the use of economizersand the general installation of anyapparatus leading to such results. Thevariable load will be carried on theremaining boilers of the plant under either

of the methods just given, that is, at thehigh ratings of all boilers in service andbanking others, or a variable capacityfrom all boilers in service.

The opportunity is again taken to indicatethe very general character of anystatements made relative to theeconomical load for any plant and toemphasize the fact that each individualcase must be considered independently,with the conditions of operationsapplicable thereto.

With a thorough understanding of themeaning of boiler efficiency and capacityand their relation to each other, it ispossible to consider more specifically theselection of boilers.

The foremost consideration is, withoutquestion, the adaptability of the design

selected to the nature of the work to bedone. An installation which is onlytemporary in its nature would obviouslynot warrant the first cost that a permanentplant would. If boilers are to carry anintermittent and suddenly fluctuating load,such as a hoisting load or a reversing millload, a design would have to be selectedthat would not tend to prime with thefluctuations and sudden demand for steam.A boiler that would give the highestpossible efficiency with fuel of onedescription, would not of necessity givesuch efficiency with a different fuel. Aboiler of a certain design which might begood for small plant practice would not,because of the limitations in practicablesize of units, be suitable for largeinstallations. A discussion of the relativevalue of designs can be carried on almostindefinitely but enough has been said toindicate that a given design will not serve

satisfactorily under all conditions and thatthe adaptability to the service requiredwill be dependent upon the fuel available,the class of labor procurable, the feedwater that must be used, the nature of theplant's load, the size of the plant and thefirst cost warranted by the service theboiler is to fulfill.

TABLE60

ACTUALEVAPORATION FOR DIFFERENTPRESSURES AND TEMPERATURES OFFEED WATERCORRESPONDING TO ONE HORSEPOWER (34� POUNDS PER HOUR FROMAND AT 212 DEGREES FAHRENHEIT)

--------------------------------------------------------------------------------------------------------------

--------------------------- Temperature|

| of |Pressure by Gauge--Pounds per

Square Inch | Feed|

| Degrees |

| Fahrenheit | 50 |60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 |140 | 150 | 160 | 170 | 180 | 190 | 200 |210 | 220 | 230 | 240 | 250 |-----------+-----------------------------------------------------------------------------------------------------------------------------| 32|28.41|28.36|28.29|28.24|28.20|28.16|28.13|28.09|28.07|28.04|28.02|27.99|27.97|27.95|27.94|27.92|27.90|27.89|27.87|27.86|27.83| 40|28.61|28.54|28.49|28.44|28.40|28.35|28.32|28.29|28.26|28.23|28.21|28.18|28.16|28.14|28.12|28.11|28.09|28.07|28.06|28

.05|28.03| 50|28.85|28.79|28.73|28.68|28.64|28.60|28.56|28.53|28.50|28.47|28.45|28.43|28.40|28.38|28.36|28.35|28.33|28.31|28.30|28.28|28.27| 60|29.10|29.04|28.98|28.93|28.88|28.84|28.81|28.77|28.74|28.72|28.69|28.67|28.65|28.62|28.60|28.59|28.57|28.55|28.54|28.52|28.51| 70|29.36|29.29|29.23|29.18|29.14|29.09|29.06|29.02|28.99|28.96|28.94|28.92|28.89|28.87|28.85|28.83|28.82|28.80|28.78|28.77|28.76| 80|29.62|29.55|29.49|29.44|29.39|29.35|29.31|29.27|29.24|29.22|29.19|29.17|29.14|29.12|29.10|29.08|29.07|29.05|29.03|29.02|29.00| 90|29.88|29.81|29.75|29.70|29.65|29.61|29.57|29.53|29.50|29.47|29.45|29.42|29.40|29.38|29.36|29.34|29.32|29.30|29.29|29.27|29.25| 100|30.15|30.08|30.02|29.96|29.91|29.87|29

.83|29.80|29.76|29.73|29.71|29.68|29.66|29.63|29.61|29.60|29.58|29.56|29.54|29.53|29.51| 110|30.42|30.35|30.29|30.23|30.18|30.14|30.10|30.06|30.03|30.00|29.97|29.95|29.92|29.90|29.88|29.86|29.84|29.82|29.81|29.79|29.77| 120|30.70|30.63|30.56|30.51|30.46|30.41|30.37|30.33|30.30|30.27|30.24|30.22|30.19|30.17|30.15|30.13|30.11|30.09|30.07|30.06|30.04| 130|30.99|30.91|30.84|30.79|30.73|30.69|30.65|30.61|30.57|30.54|30.52|30.49|30.47|30.44|30.42|30.40|30.38|30.36|30.35|30.33|30.31| 140|31.28|31.20|31.13|31.07|31.02|30.97|30.93|30.89|30.86|30.83|30.80|30.77|30.75|30.72|30.70|30.68|30.66|30.64|30.62|30.61|30.59| 150|31.58|31.49|31.42|31.36|31.31|31.26|31.22|31.18|31.14|31.11|31.08|31.06|31.03|31.01|30.98|30.96|30.94|30.92|30.91|30

.89|30.87| 160|31.87|31.79|31.72|31.66|31.61|31.56|31.51|31.47|31.44|31.40|31.37|31.35|31.32|31.29|31.27|31.25|31.23|31.21|31.19|31.18|31.16| 170|32.18|32.10|32.02|31.96|31.91|31.86|31.81|31.77|31.73|31.70|31.67|31.64|31.62|31.59|31.57|31.54|31.52|31.50|31.49|31.47|31.46| 180|32.49|32.41|32.33|32.27|32.22|32.16|32.12|32.08|32.04|32.00|31.97|31.95|31.92|31.89|31.87|31.84|31.82|31.80|31.79|31.77|31.75| 190|32.81|32.72|32.65|32.59|32.53|32.47|32.43|32.38|32.35|32.32|32.29|32.26|32.23|32.20|32.17|32.15|32.13|32.11|32.09|32.07|32.05| 200|33.13|33.05|32.97|32.91|32.85|32.79|32.75|32.70|32.66|32.63|32.60|32.57|32.54|32.51|32.49|32.46|32.44|32.42|32.40|32.38|32.36| 210|33.47|33.38|33.30|33.24|33.18|33.13|33

.08|33.03|32.99|32.95|32.92|32.89|32.86|32.83|32.81|32.79|32.76|32.74|32.72|32.70|32.68|-----------------------------------------------------------------------------------------------------------------------------------------

The proper consideration can be given tothe adaptability of any boiler for theservice in view only after a thoroughunderstanding of the requirements of agood steam boiler, with the application ofwhat has been said on the properoperation to the special requirements ofeach case. Of almost equal importance tothe factors mentioned are the experience,the skill and responsibility of themanufacturer.

With the design of boiler selected that isbest adapted to the service required, thenext step is the determination of the boiler

power requirements.

The amount of steam that must begenerated is determined from the steamconsumption of the prime movers. It hasalready been indicated that suchconsumption can vary over wide limitswith the size and type of the apparatusused, but fortunately all types have beenso tested that manufacturers are enabledto state within very close limits the actualconsumption under any given set ofconditions. It is obvious that conditions ofoperation will have a bearing on the steamconsumption that is as important as thetype and size of the apparatus itself. Thisbeing the case, any tabular informationthat can be given on such steamconsumption, unless it be extended to animpracticable size, is only of use for themost approximate work and more definitefigures on this consumption should in all

cases be obtained from the manufacturerof the apparatus to be used for theconditions under which it will operate.

To the steam consumption of the mainprime movers, there is to be added that ofthe auxiliaries. Again it is impossible tomake a definite statement of what thisallowance should be, the figure dependingwholly upon the type and the number ofsuch auxiliaries. For approximate work, itis perhaps best to allow 15 or 20 per centof the steam requirements of the mainengines, for that of auxiliaries. Whateverfigure is used should be taken highenough to be on the conservative side.

When any such figures are based on theactual weight of steam required, Table 60,which gives the actual evaporation forvarious pressures and temperatures offeed corresponding to one boiler horse

power (34.5 pounds of water per hour fromand at 212 degrees), may be of service.

With the steam requirements known, thenext step is the determination of thenumber and size of boiler units to beinstalled. This is directly affected by thecapacity at which a consideration of theeconomical load indicates is the best forthe operating conditions which will exist.The other factors entering into suchdetermination are the size of the plant andthe character of the feed water.

The size of the plant has its bearing on thequestion from the fact that higherefficiencies are in general obtained fromlarge units, that labor cost decreases withthe number of units, the first cost ofbrickwork is lower for large than for smallsize units, a general decrease in thecomplication of piping, etc., and in general

the cost per horse power of any design ofboiler decreases with the size of units. Toillustrate this, it is only necessary toconsider a plant of, say, 10,000 boilerhorse power, consisting of 40-250horse-power units or 17-600 horse-powerunits.

The feed water available has its bearing onthe subject from the other side, for it hasalready been shown that very large unitsare not advisable where the feed water isnot of the best.

The character of an installment is also afactor. Where, say, 1000 horse power isinstalled in a plant where it is known whatthe ultimate capacity is to be, the size ofunits should be selected with the idea ofthis ultimate capacity in mind rather thanthe amount of the first installation.

Boiler service, from its nature, is severe.All boilers have to be cleaned from time totime and certain repairs to settings, etc.,are a necessity. This makes it necessary, indetermining the number of boilers to beinstalled, to allow a certain number of unitsor spares to be operated when any of theregular boilers must be taken off the line.With the steam requirements determinedfor a plant of moderate size and areasonably constant load, it is highlyadvisable to install at least two spareboilers where a continuity of service isessential. This permits the taking off of oneboiler for cleaning or repairs and stillallows a spare boiler in the event of someunforeseen occurrence, such as theblowing out of a tube or the like.Investment in such spare apparatus isnothing more nor less than insurance onthe necessary continuity of service. Insmall plants of, say, 500 or 600 horse

power, two spares are not usuallywarranted in view of the cost of suchinsurance. A large plant is ordinarily laidout in a number of sections or panels andeach section should have its spare boileror boilers even though the sections arecross connected. In central station work,where the peaks are carried on the boilersbrought up from the bank, such sparesare, of course, in addition to these bankedboilers. From the aspect of cleaningboilers alone, the number of spare boilersis determined by the nature of any scalethat may be formed. If scale is formed sorapidly that the boilers cannot be keptclean enough for good operating results,by cleaning in rotation, one at a time, thenumber of spares to take care of suchproper cleaning will naturally increase.

In view of the above, it is evident that onlya suggestion can be made as to the

number and size of units, as norecommendation will hold for all cases. Ingeneral, it will be found best to install unitsof the largest possible size compatiblewith the size of the plant and operatingconditions, with the total powerrequirements divided among such anumber of units as will give properflexibility of load, with such additionalunits for spares as conditions of cleaningand insurance against interruption ofservice warrant.

In closing the subject of the selection ofboilers, it may not be out of place to referto the effect of the builder's guaranteeupon the determination of design to beused. Here in one of its most importantaspects appears the responsibility of themanufacturer. Emphasis has been laid onthe difference between test results andthose secured in ordinary operating

practice. That such a difference exists iswell known and it is now pretty generallyrealized that it is the responsiblemanufacturer who, where guarantees arenecessary, submits the conservativefigures, figures which may readily beexceeded under test conditions and whichmay be closely approached under theordinary plant conditions that will be metin daily operation.

OPERATION AND CARE OF BOILERS

The general subject of boiler roompractice may be considered from twoaspects. The first is that of the broad planteconomy, with a suggestion as to themethods to be followed in securing thebest economical results with the apparatusat hand and procurable. The second dealsrather with specific recommendationswhich should be followed in plant practice,recommendations leading not only toeconomy but also to safety and continuityof service. Such recommendations aredictated from an understanding of thenature of steam generating apparatus andits operation, as covered previously in thisbook.

It has already been pointed out that theattention given in recent years to steam

generating practice has come with arealization of the wide difference existingbetween the results being obtained inevery-day operation and thosetheoretically possible. The amount of suchattention and regulation given to the steamgenerating end of a power plant, however,is comparatively small in relation to thatgiven to the balance of the plant, but itmay be safely stated that it is here thatthere is the greatest assurance of a returnfor the attention given.

In the endeavor to increase boiler roomefficiency, it is of the utmost importancethat a standard basis be set by whichaverage results are to be judged. With thetheoretical efficiency obtainable varyingso widely, this standard cannot be placedat the highest efficiency that has beenobtained regardless of operatingconditions. It is better set at the best

obtainable results for each individual plantunder its conditions of installation anddaily operation.

With an individual standard so set, presentpractice can only be improved by asystematic effort to approach this standard.The degree with which operating resultswill approximate such a standard will befound to be directly proportional to theamount of intelligent supervision given theoperation. For such supervision to begiven, it is necessary to have not only a fullrealization of what the plant can do underthe best operating conditions but also a fulland complete knowledge of what it isdoing under all of the different conditionsthat may arise. What the plant is doingshould be made a matter of continuousrecord so arranged that the results may bedirectly compared for any period or set ofconditions, and where such results vary

from the standard set, steps must be takenimmediately to remedy the causes of suchfailings. Such a record is an importantcheck in the losses in the plant.

As the size of the plant and the fuelconsumption increase, such a check oflosses and recording of results becomes anecessity. In the larger plants, the savingof but a fraction of one per cent in the fuelbill represents an amount running intothousands of dollars annually, while theexpense of the proper supervision tosecure such saving is small. The methodsof supervision followed in the large plantsare necessarily elaborate and complete. Inthe smaller plants the same methods maybe followed on a more moderate scalewith a corresponding saving in fuel and aninappreciable increase in either plantorganization or expense.

There has been within the last few years agreat increase in the practicability andreliability of the various types of apparatusby which the records of plant operationmay be secured. Much of this apparatus isingenious and, considering the work to bedone, is remarkably accurate. From thedelicate nature of some of the apparatus,the liability to error necessitates frequentcalibration but even where the accuracy isknown to be only within limits of, say, 5per cent either way, the records obtainedare of the greatest service in consideringrelative results. Some of the recordsdesirable and the apparatus for securingthem are given below.

[Illustration: 2400 Horse-power Installationof Cross Drum Babcock & Wilcox Boilersand Superheaters at the WestinghouseElectric and Manufacturing Co., EastPittsburgh, Pa.]

Inasmuch as the ultimate measure of theefficiency of the boiler plant is the cost ofsteam generation, the important recordsare those of steam generated and fuelconsumed Records of temperature,analyses, draft and the like, serve as acheck on this consumption, indicating thedistribution of the losses and affording ameans of remedying conditions whereimprovement is possible.

Coal Records--There are many devices onthe market for conveniently weighing thecoal used. These are ordinarily accuratewithin close limits, and where the size ornature of the plant warrants the investmentin such a device, its use is to berecommended. The coal consumptionshould be recorded by some other methodthan from the weights of coal purchased.The total weight gives no way of dividing

the consumption into periods and it willunquestionably be found to be profitableto put into operation some scheme bywhich the coal is weighed as it is used. Inthis way, the coal consumption, during anyspecific period of the plant's operation,can be readily seen. The simplest of suchmethods which may be used in smallplants is the actual weighing on scales ofthe fuel as it is brought into the fire roomand the recording of such weights.

Aside from the actual weight of the fuelused, it is often advisable to keep othercoal records, coal and ash analyses andthe like, for the evaporation to beexpected will be dependent upon thegrade of fuel used and its calorific value,fusibility of its ash, and like factors.

The highest calorific value for unit cost isnot necessarily the indication of the best

commercial results. The cost of fuel isgoverned by this calorific value only whensuch value is modified by local conditionsof capacity, labor and commercialefficiency. One of the important factorsentering into fuel cost is the considerationof the cost of ash handling and themaintenance of ash handling apparatus ifsuch be installed. The value of a fuel,regardless of its calorific value, is to bebased only on the results obtained inevery-day plant operation.

Coal and ash analyses used in connectionwith the amount of fuel consumed, are adirect indication of the relation betweenthe results being secured and the standardof results which has been set for the plant.The methods of such analyses havealready been described. The apparatus issimple and the degree of scientificknowledge necessary is only such as may

be readily mastered by plant operatives.

The ash content of a fuel, as indicated froma coal analysis checked against ashweights as actually found in plantoperation, acts as a check on grateefficiency. The effect of any saving in theashes, that is, the permissible ash to beallowed in the fuel purchased, isdetermined by the point at which the costof handling, combined with the falling offin the evaporation, exceeds the saving offuel cost through the use of poorer coal.

Water Records--Water records with thecoal consumption, form the basis forjudging the economic production of steam.The methods of securing such records areof later introduction than for coal, but greatadvances have been made in theapparatus to be used. Here possibly, to agreater extent than in any recording

device, are the records of value indetermining relative evaporation, that is,an error is rather allowable provided suchan error be reasonably constant.

The apparatus for recording suchevaporation is of two general classes:Those measuring water before it is fed tothe boiler and those measuring the steamas it leaves. Of the first, the venturi meteris perhaps the best known, thoughrecently there has come into considerablevogue an apparatus utilizing a weir notchfor the measuring of such water. Bothmethods are reasonably accurate andapparatus of this description has anadvantage over one measuring steam inthat it may be calibrated much morereadily. Of the steam measuring devices,the one in most common use is the steamflow meter. Provided the instruments areselected for a proper flow, etc., they are of

inestimable value in indicating the steamconsumption. Where such instruments areplaced on the various engine room lines,they will immediately indicate anexcessive consumption for any one of theunits. With a steam flow meter placed oneach boiler, it is possible to fix relativelythe amount produced by each boiler and,considered in connection with some of the"check" records described below, clearlyindicate whether its portion of the totalsteam produced is up to the standard setfor the over-all boiler room efficiency.

Flue Gas Analysis--The value of a flue gasanalysis as a measure of furnace efficiencyhas already been indicated. There are onthe market a number of instruments bywhich a continuous record of the carbondioxide in the flue gases may be securedand in general the results so recorded areaccurate. The limitations of an analysis

showing only CO_{2} and the necessity ofcompleting such an analysis with an Orsat,or like apparatus, and in this way checkingthe automatic device, have already beenpointed out, but where such records areproperly checked from time to time andare used in conjunction with a record offlue temperatures, the losses due to excessair or incomplete combustion and the likemay be directly compared for any period.Such records act as a means for controllingexcess air and also as a check onindividual firemen.

Where the size of a plant will not warrantthe purchase of an expensive continuousCO_{2} recorder, it is advisable to makeanalyses of samples for various conditionsof firing and to install an apparatuswhereby a sample of flue gas covering aperiod of, say, eight hours, may beobtained and such a sample afterwards

analyzed.

Temperature Records--Flue gastemperatures, feed water temperaturesand steam temperatures are all taken withrecording thermometers, any number ofwhich will, when properly calibrated, giveaccurate results.

A record of flue temperatures isserviceable in checking stack losses and,in general, the cleanliness of the boiler. Arecord of steam temperatures, wheresuperheaters are used, will indicateexcessive fluctuations and lead to aninvestigation of their cause. Feedtemperatures are valuable in showing thatthe full benefit of the exhaust steam isbeing derived.

Draft Regulation--As the capacity of aboiler varies with the combustion rate and

this rate with the draft, an automaticapparatus satisfactorily varying this draftwith the capacity demands on the boilerwill obviously be advantageous.

As has been pointed out, any fuel has somerate of combustion at which the bestresults will be obtained. In a properlydesigned plant where the load isreasonably steady, the draft necessary tosecure such a rate may be regulatedautomatically.

Automatic apparatus for the regulation ofdraft has recently reached a stage ofperfection which in the larger plants at anyrate makes its installation advisable. Theinstallation of a draft gauge or gauges isstrongly to be recommended and a recordof such drafts should be kept as being acheck on the combustion rates.

An important feature to be considered inthe installing of all recording apparatus isits location. Thermometers, draft gaugesand flue gas sampling pipes should be solocated as to give as nearly as possible anaverage of the conditions, the gasesflowing freely over the ends of thethermometers, couples and samplingpipes. With the location permanent, thereis no security that the samples may beconsidered an average but in any eventcomparative results will be secured whichwill be useful in plant operation. The bestpermanent location of apparatus will varyconsiderably with the design of the boiler.

It may not be out of place to refer briefly tosome of the shortcomings found in boilerroom practice, with a suggestion as to ameans of overcoming them.

1st. It is sometimes found that the

operating force is not fully acquainted withthe boilers and apparatus. Probably themost general of such shortcomings is thefixed idea in the heads of the operativesthat boilers run above their rated capacityare operating under a state of strain andthat by operating at less than their ratedcapacity the most economical service isassured, whereas, by determining what aboiler will do, it may be found that themost economical rating under theconditions of the plant will beconsiderably in excess of the builder'srating. Such ideas can be dislodged onlyby demonstrating to the operatives whatmaximum load the boilers can carry,showing how the economy will vary withthe load and the determining of theeconomical load for the individual plant inquestion.

2nd. Stokers. With stoker-fired boilers, it is

essential that the operators know thelimitations of their stokers as determinedby their individual installation. A thoroughunderstanding of the requirements ofefficient handling must be insisted upon.The operatives must realize that smokelessstacks are not necessarily the indication ofgood combustion for, as has been pointedout, absolute smokelessness is oftentimessecured at an enormous loss in efficiencythrough excess air.

Another feature in stoker-fired plants is inthe cleaning of fires. It must be impressedupon the operatives that before the firesare cleaned they should be put intocondition for such cleaning. If this cleaningis done at a definite time, regardless ofwhether the fires are in the best conditionfor cleaning, there will be a great loss ofgood fuel with the ashes.

3rd. It is necessary that in each individualplant there be a basis on which to judgethe cleanliness of a boiler. From theoperative's standpoint, it is probably morenecessary that there be a thoroughunderstanding of the relation betweenscale and tube difficulties than betweenscale and efficiency. It is, of course,impossible to keep boilers absolutely freefrom scale at all times, but experience ineach individual plant determines the limitto which scale can be allowed to formbefore tube difficulties will begin or aperceptible falling off in efficiency willtake place. With such a limit of scaleformation fixed, the operatives should beimpressed with the danger of allowing it tobe exceeded.

4th. The operatives should be instructed asto the losses resulting from excess air dueto leaks in the setting and as to losses in

efficiency and capacity due to theby-passing of gases through the setting,that is, not following the path of the bafflesas originally installed. In replacing tubesand in cleaning the heating surfaces, caremust be taken not to dislodge baffle brickor tile.

[Illustration: 2000 Horse-power Installationof Babcock & Wilcox Boilers, Equippedwith Babcock & Wilcox Chain GrateStokers at the Sunnyside Plant of thePennsylvania Tunnel and TerminalRailroad Co., Long Island City, N. Y.]

5th. That an increase in the temperature ofthe feed reduces the amount of workdemanded from the boiler has beenshown. The necessity of keeping the feedtemperature as high as the quantity ofexhaust steam will allow should bethoroughly understood. As an example of

this, there was a case brought to ourattention where a large amount of exhauststeam was wasted simply because the feedpump showed a tendency to leak if thetemperature of feed water was increasedabove 140 degrees. The amount wastedwas sufficient to increase the temperatureto 180 degrees but was not utilized simplybecause of the slight expense necessary tooverhaul the feed pump.

The highest return will be obtained whenthe speed of the feed pumps is maintainedreasonably constant for should the pumpsrun very slowly at times, there may be aloss of the steam from other auxiliaries byblowing off from the heaters.

6th. With a view to checking steam lossesthrough the useless blowing of safetyvalves, the operative should be made torealize the great amount of steam that it is

possible to get through a pipe of a givensize. Oftentimes the fireman feels a senseof security from objections to a drop insteam simply because of the blowing ofsafety valves, not considering the lossesdue to such a cause and makes no effort tocheck this flow either by manipulation ofdampers or regulation of fires.

The few of the numerous shortcomingsoutlined above, which may be found inmany plants, are almost entirely due tolack of knowledge on the part of theoperating crew as to the conditionsexisting in their own plants and the betterperformances being secured in others.Such shortcomings can be overcome onlyby the education of the operatives, theshowing of the defects of present methods,and instruction in better methods. Wheresuch instruction is necessary, the value ofrecords is obvious. There is fortunately a

tendency toward the employment of abetter class of labor in the boiler room, atendency which is becoming more andmore marked as the realization of thepossible saving in this end of the plantincreases.

The second aspect of boiler roommanagement, dealing with specificrecommendations as to the care andoperation of the boilers, is dictated largelyby the nature of the apparatus. Some of thefeatures to be watched in considering thisaspect follow.

Before placing a new boiler in service, acareful and thorough examination shouldbe made of the pressure parts and thesetting. The boiler as erected shouldcorrespond in its baffle openings, wherebaffles are adjustable, with the printsfurnished for its erection, and such baffles

should be tight. The setting should be soconstructed that the boiler is free toexpand without interfering with thebrickwork. This ability to expand appliesalso to blow-off and other piping. Aftererection all mortar and chips of brickshould be cleaned from the pressure parts.The tie rods should be set up snug andthen slacked slightly until the setting hasbecome thoroughly warm after the firstfiring. The boiler should be examinedinternally before starting to insure theabsence of dirt, any foreign material suchas waste, and tools. Oil and paint aresometimes found in the interior of a newboiler and where such is the case, aquantity of soda ash should be placedwithin it, the boiler filled with water to itsnormal level and a slow fire started. Aftertwelve hours of slow simmering, the fireshould be allowed to die out, the boilercooled slowly and then opened and

washed out thoroughly. Such a proceedingwill remove all oil and grease from theinterior and prevent the possibility offoaming and tube difficulties when theboiler is placed in service.

The water column piping should beexamined and known to be free and clear.The water level, as indicated by the gaugeglass, should be checked by opening thegauge cocks.

The method of drying out a brick settingbefore placing a boiler in operation isdescribed later in the discussion of boilersettings.

A boiler should not be cut into the line withother boilers until the pressure within it isapproximately that in the steam main. Theboiler stop valve should be opened veryslowly until it is fully opened. The

arrangement of piping should be such thatthere can be no possibility of watercollecting in a pocket between the boilerand the main, from which it can be carriedover into the steam line when a boiler iscut in.

In regular operation the safety valve andsteam gauge should be checked daily. Insmall plants the steam pressure should beraised sufficiently to cause the safetyvalves to blow, at which time the steamgauge should indicate the pressure atwhich the valve is known to be set. If itdoes not, one is in error and the gaugeshould be compared with one of knownaccuracy and any error at once rectified.

In large plants such a method of checkingwould result in losses too great to beallowed. Here the gauges and valves areordinarily checked at the time a boiler is

cut out, the valves being assured of notsticking by daily instantaneous openingthrough manipulation by hand of the valvelever. The daily blowing of the safety valveacts not only as a check on the gauge butinsures the valve against sticking.

The water column should be blown downthoroughly at least once on every shift andthe height of water indicated by the glasschecked by the gauge cocks. The bottomblow-offs should be kept tight. Theseshould be opened at least once daily toblow from the mud drum any sediment thatmay have collected and to reduce theconcentration. The amount of blowingdown and the frequency is, of course,determined by the nature of the feed waterused.

In case of low water, resulting either fromcarelessness or from some unforeseen

condition of operation, the essential objectto be obtained is the extinguishing of thefire in the quickest possible manner.Where practicable, this is bestaccomplished by the playing of a heavystream of water from a hose on the fire.Another method, perhaps not so efficient,but more generally recommended, is thecovering of the fire with wet ashes or freshfuel. A boiler so treated should be cut outof line after such an occurrence and athorough inspection made to ascertainwhat damage, if any, has been donebefore it is again placed in service.

The efficiency and capacity depend to anextent very much greater than is ordinarilyrealized upon the cleanliness of theheating surfaces, both externally andinternally, and too much stress cannot beput upon the necessity for systematiccleaning as a regular feature in the plant

operation.

The outer surfaces of the tubes should beblown free from soot at regular intervals,the frequency of such cleaning periodsbeing dependent upon the class of fuelused. The most efficient way of blowingsoot from the tubes is by means of a steamlance with which all parts of the surfacesare reached and swept clean. There arenumerous soot blowing devices on themarket which are designed to bepermanently fixed within the boilersetting. Where such devices are installed,there are certain features that must bewatched to avoid trouble. If there is anyleakage of water of condensation withinthe setting coming into contact with theboiler tubes, it will tend toward corrosion,or if in contact with the heated brickworkwill cause rapid disintegration of thesetting. If the steam jets are so placed that

they impinge directly against the tubes,erosion may take place. Where suchpermanent soot blowers are installed, toomuch care cannot be taken to guardagainst these possibilities.

Internally, the tubes must be kept freefrom scale, the ingredients of which astudy of the chapter on the impurities ofwater indicates are present in varyingquantities in all feed waters. Not only hasthe presence of scale a direct bearing onthe efficiency and capacity to be obtainedfrom a boiler but its absence is anassurance against the burning out of tubes.

In the absence of a blow-pipe action of theflames, it is impossible to burn a metalsurface where water is in intimate contactwith that surface.

In stoker-fired plants where a blast is used,

and the furnace is not properly designed,there is a danger of a blow-pipe action ifthe fires are allowed to get too thin. Therapid formation of steam at such points oflocalized heat may lead to the burning ofthe metal of the tubes.

Any formation of scale on the interiorsurface of a boiler keeps the water fromsuch a surface and increases its tendencyto burn. Particles of loose scale that maybecome detached will lodge at certainpoints in the tubes and localize thistendency at such points. It is because ofthe danger of detaching scale and causingloose flakes to be present that the use of aboiler compound is not recommended forthe removal of scale that has alreadyformed in a boiler. This question iscovered in the treatment of feed waters. Ifoil is allowed to enter a boiler, its action isthe same as that of scale in keeping the

water away from the metal surfaces.


It has been proven beyond a doubt that avery large percentage of tube losses isdue directly to the presence of scalewhich, in many instances, has been so thinas to be considered of no moment, and theimportance of maintaining the boilerheating surfaces in a clean conditioncannot be emphasized too strongly.

The internal cleaning can best beaccomplished by means of an air orwater-driven turbine, the cutter heads ofwhich may be changed to handle variousthicknesses of scale. Fig. 41 shows aturbine cleaner with various cutting heads,which has been found to give satisfactoryservice.

Where a water-driven turbine is used, itshould be connected to a pump which willdeliver at least 120 gallons per minute percleaner at 150 pounds pressure. Thispressure should never be less than 90pounds if satisfactory results are desired.Where an air-driven turbine is used, thepressure should be at least 100 pounds,though 150 pounds is preferable, andsufficient water should be introduced intothe tube to keep the cutting head cool andassist in washing down the scale as it ischipped off.

Where scale has been allowed toaccumulate to an excessive thickness, thework of removal is difficult and tedious.Where such a heavy scale is of sulphateformation, its removal may be assisted byfilling the boiler with water to which therehas been added a quantity of soda ash, abucketful to each drum, starting a low fire

and allowing the water to boil fortwenty-four hours with no pressure on theboiler. It should be cooled slowly,drained, and the turbine cleaner usedimmediately, as the scale will tend toharden rapidly under the action of the air.

Where oil has been allowed to get into aboiler, it should be removed beforeplacing the boiler in service, as describedpreviously where reference is made to itsremoval by boiling out with soda ash.

Where pitting or corrosion is noted, theparts affected should be carefully cleanedand the interior of the drums should bepainted with white zinc if the boiler is toremain idle. The cause of such actionshould be immediately ascertained andsteps taken to apply the proper remedy.

When making an internal inspection of a

boiler or when cleaning the interiorheating surfaces, great care must be takento guard against the possibility of steamentering the boiler in question from otherboilers on the same line either through thecareless opening of the boiler stop valveor some auxiliary valve or from an openblow-off. Bad accidents through scaldinghave resulted from the neglect of thisprecaution.

Boiler brickwork should be kept pointedup and all cracks filled. The boiler bafflesshould be kept tight to prevent by-passingof any gases through the heating surfaces.

Boilers should be taken out of service atregular intervals for cleaning and repairs.When this is done, the boiler should becooled slowly, and when possible, beallowed to stand for twenty-four hours afterthe fire is drawn before opening. The

cooling process should not be hurried byallowing cold air to rush through thesetting as this will invariably cause troublewith the brickwork. When a boiler is off forcleaning, a careful examination should bemade of its condition, both external andinternal, and all leaks of steam, water andair through the setting stopped. If water isallowed to come into contact withbrickwork that is heated, rapiddisintegration will take place. If water isallowed to come into contact with themetal of the boiler when out of service,there is a likelihood of corrosion.

If a boiler is to remain idle for some time,its deterioration may be much more rapidthan when in service. If the period forwhich it is to be laid off is not to exceedthree months, it may be filled with waterwhile out of service. The boiler should firstbe cleaned thoroughly, internally and

externally, all soot and ashes beingremoved from the exterior of the pressureparts and any accumulation of scaleremoved from the interior surfaces. Itshould then be filled with water, to whichfive or six pails of soda ash have beenadded, a slow fire started to drive the airfrom the boiler, the fire drawn and theboiler pumped full. In this condition it maybe kept for some time without bad effects.

If the boiler is to be out of service for morethan three months, it should be emptied,drained and thoroughly dried after beingcleaned. A tray of quick lime should beplaced in each drum, the boiler closed, thegrates covered and a quantity of quicklime placed on top of the covering. Specialcare should be taken to prevent air, steamor water leaks into the boiler or onto thepressure parts to obviate danger ofcorrosion.

[Illustration: 3000 Horse-power Installationof Babcock & Wilcox Boilers in the MainPower Plant, Chicago & Northwestern Ry.Depot, Chicago, Ill.]

BRICKWORK BOILER SETTINGS

A consideration of the losses in boilerefficiency, due to the effects of excess air,clearly indicates the necessity ofmaintaining the brick setting of a boilertight and free from air leaks. In view of thetemperatures to which certain portions ofsuch a setting are subjected, the materialto be used in its construction must be ofthe best procurable.

Boiler settings to-day consist almostuniversally of brickwork--two kinds beingused, namely, red brick and fire brick.

The red brick should only be used in suchportions of the setting as are wellprotected from the heat. In such location,their service is not so severe as that of firebrick and ordinarily, if such red brick are

sound, hard, well burned and uniform,they will serve their purpose.

The fire brick should be selected with thegreatest care, as it is this portion of thesetting that has to endure the hightemperatures now developed in boilerpractice. To a great extent, the life of aboiler setting is dependent upon thequality of the fire brick used and the careexercised in its laying.

The best fire brick are manufactured fromthe fire clays of Pennsylvania. South andwest from this locality the quality of fireclay becomes poorer as the distanceincreases, some of the southern fire clayscontaining a considerable percentage ofiron oxide.

Until very recently, the importantcharacteristic on which to base a judgment

of the suitability of fire brick for use inconnection with boiler settings has beenconsidered the melting point, or thetemperature at which the brick will liquifyand run. Experience has shown, however,that this point is only important withincertain limits and that the real basis onwhich to judge material of this descriptionis, from the boiler man's standpoint, thequality of plasticity under a given load.This tendency of a brick to become plasticoccurs at a temperature much below themelting point and to a degree that maycause the brick to become deformedunder the stress to which it is subjected.The allowable plastic or softeningtemperature will naturally be relative anddependent upon the stress to be endured.

With the plasticity the determining factor,the perfect fire brick is one whose criticalpoint of plasticity lies well above the

working temperature of the fire. It isprobable that there are but few brick onthe market which would not show, iftested, this critical temperature at thestress met with in arch construction at apoint less than 2400 degrees. The fact thatan arch will stand for a long period underfurnace temperatures considerably abovethis point is due entirely to the fact that itstemperature as a whole is far below thefurnace temperature and only about 10 percent of its cross section nearest the fireapproaches the furnace temperature. Thisis borne out by the fact that arches whichare heated on both sides to the fulltemperature of an ordinary furnace willfirst bow down in the middle andeventually fall.

A method of testing brick for thischaracteristic is given in the TechnologicPaper No. 7 of the Bureau of Standards

dealing with "The testing of clayrefractories with special reference to theirload carrying capacity at furnacetemperatures." Referring to the test for thisspecific characteristic, this publicationrecommends the following: "Whensubjected to the load test in a mannersubstantially as described in this bulletin,at 1350 degrees centigrade (2462 degreesFahrenheit), and under a load of 50 poundsper square inch, a standard fire bricktested on end should show no seriousdeformation and should not becompressed more than one inch, referredto the standard length of nine inches."

In the Bureau of Standards test forsoftening temperature, or criticaltemperature of plasticity under thespecified load, the brick are tested on end.In testing fire brick for boiler purposessuch a method might be criticised,

because such a test is a compression testand subject to errors from unequalbearing surfaces causing shear.Furthermore, a series of samples,presumably duplicates, will not fail in thesame way, due to the mechanical variationin the manufacture of the brick. Arches thatfail through plasticity show that the tensilestrength of the brick is important, thisbeing evidenced by the fact that thebottom of a wedge brick in an arch that hasfailed is usually found to be wider than thetop and the adjacent bricks are firmlycemented together.

A better method of testing is that of testingthe brick as a beam subjected to its ownweight and not on end. This method hasbeen used for years in Germany and isrecommended by the highest authoritiesin ceramics. It takes into account thefailure by tension in the brick as well as by

compression and thus covers the tensionelement which is important in archconstruction.

The plastic point under a unit stress of 100pounds per square inch, which may betaken as the average maximum arch stress,should be above 2800 degrees to giveperfect results and should be above 2400degrees to enable the brick to be usedwith any degree of satisfaction.

The other characteristics by which thequality of a fire brick is to be judged are:

Fusion point. In view of the fact that thecritical temperature of plasticity is belowthe fusion point, this is only important as anindication from high fusion point of a hightemperature of plasticity.

Hardness. This is a relative quality based

on an arbitrary scale of 10 and is anindication of probable cracking andspalling.

Expansion. The lineal expansion per brickin inches. This characteristic in conjunctionwith hardness is a measure of the physicalmovement of the brick as affecting a massof brickwork, such movement resulting incracked walls, etc. The expansion will varybetween wide limits in different brick andprovided such expansion is not in excessof, say, .05 inch in a 9-inch brick, whenmeasured at 2600 degrees, it is notparticularly important in a properlydesigned furnace, though in general thesmaller the expansion the better.

Compression. The strength necessary tocause crushing of the brick at the center ofthe 4� inch face by a steel block one inchsquare. The compression should ordinarily

be low, a suggested standard being that abrick show signs of crushing at 7500pounds.

Size of Nodules. The average size of flintgrains when the brick is carefully crushed.The scale of these sizes may beconsidered: Small, size of anthracite rice;large, size of anthracite pea.

Ratio of Nodules. The percentage of agiven volume occupied by the flint grains.This scale may be considered: High, 90 to100 per cent; medium, 50 to 90 per cent;low, 10 to 50 per cent.

The statement of characteristics suggestedas desirable, are for arch purposes wherethe hardest service is met. For side wallpurposes the compression and hardnesslimit may be raised considerably and theplastic point lowered.

Aside from the physical properties bywhich a fire brick is judged, it issometimes customary to require achemical analysis of the brick. Such ananalysis is only necessary as determiningthe amount of total basic fluxes (K_{2}O,Na_{2}O, CaO, MgO and FeO). Thesefluxes are ordinarily combined into oneexpression, indicated by the symbol RO.This total becomes important only above0.2 molecular equivalent as expressed inceramic empirical formulae, and this limitshould not be exceeded.[75]

From the nature of fire brick, their valuecan only be considered from a relativestandpoint. Generally speaking, what areknown as first-grade fire brick may bedivided into three classes, suitable forvarious conditions of operation, as follows:

Class A. For stoker-fired furnaces wherehigh overloads are to be expected orwhere other extreme conditions of serviceare apt to occur.

Class B. For ordinary stoker settings wherethere will be no excessive overloadsrequired from the boiler or any hand-firedfurnaces where the rates of driving will behigh for such practice.

Class C. For ordinary hand-fired settingswhere the presumption is that the boilerswill not be overloaded except at rareintervals and for short periods only.

Table 61 gives the characteristics of thesethree classes according to the featuresdetermining the quality. This tableindicates that the hardness of the brick ingeneral increases with the poorerqualities. Provided the hardness is

sufficient to enable the brick to withstandits load, additional hardness is a detrimentrather than an advantage.

TABLE 61

APPROXIMATE CLASSIFICATIONOF FIRE BRICK

________________________________________________________________________ |

| | | | |Characteristics | Class A | Class B

| Class C ||_____________________|________________|________________|________________| |

| | | | |Fuse Point, Degrees | Safe at Degrees|Safe at Degrees| Safe at Degrees| |Fahrenheit | 3200-3300 |2900-3200 | 2900-3000 | | |

| | | |Compression Pounds | 6500-7500 |7500-11,000 | 8500-15,000 | || | | | | HardnessRelative | 1-2 | 2-4 | 4-6| | | | || | Size of Nodules | Medium |

Medium to |Medium to Large | || | Medium Large | |

| | | || | Ratio of Nodules | High |Medium to High | Medium Low | |

| | | to Medium ||_____________________|________________|________________|________________|

An approximate determination of thequality of a fire brick may be made fromthe appearance of a fracture. Where such afracture is open, clean, white and flinty,the brick in all probability is of a goodquality. If this fracture has the fine uniform

texture of bread, the brick is probablypoor.

In considering the heavy duty of brick inboiler furnaces, experience shows thatarches are the only part that ordinarilygive trouble. These fail from the followingcauses:

Bad workmanship in laying up of brick.This feature is treated below.

The tendency of a brick to become plasticat a temperature below the fusing point.The limits of allowable plastic temperaturehave already been pointed out.

Spalling. This action occurs on the innerends of combustion arches where they areswept by gases at a high velocity at the fullfurnace temperature. The mosttroublesome spalling arises through cold

air striking the heated brickwork. Failurefrom this cause is becoming rare, due tothe large increase in number of stokerinstallations in which rapid temperaturechanges are to a great degree eliminated.Furthermore, there are a number of brickon the market practically free from suchdefects and where a new brick isconsidered, it can be tried out and if thedefect exists, can be readily detected andthe brick discarded.

Failures of arches from the expansivepower of brick are also rare, due to thefact that there are a number of brick inwhich the expansion is well within theallowable limits and the ease with whichsuch defects may be determined before abrick is used.

Failures through chemical disintegration.Failure through this cause is found only

occasionally in brick containing a highpercentage of iron oxide.

With the grade of brick selected bestsuited to the service of the boiler to be set,the other factor affecting the life of thesetting is the laying. It is probable thatmore setting difficulties arise from theimproper workmanship in the laying up ofbrick than from poor material, and toinsure a setting which will remain tight it isnecessary that the masonry work be donemost carefully. This is particularly truewhere the boiler is of such a type as torequire combustion arches in the furnace.

Red brick should be laid in a thoroughlymixed mortar composed of one volume ofPortland cement, 3 volumes of unslackedlime and 16 volumes of clear sharp sand.Not less than 2� bushels of lime should beused in the laying up of 1000 brick. Each

brick should be thoroughly embeddedand all joints filled. Where red brick andfire brick are both used in the same wall,they should be carried up at the same timeand thoroughly bonded to each other.

All fire brick should be dry when used andprotected from moisture until used. Eachbrick should be dipped in a thin fire claywash, "rubbed and shoved" into place, andtapped with a wooden mallet until ittouches the brick next below it. It must berecognized that fire clay is not a cementand that it has little or no holding power.Its action is that of a filler rather than abinder and no fire-clay wash should beused which has a consistency sufficient topermit the use of a trowel.

All fire-brick linings should be laid up fourcourses of headers and one stretcher.Furnace center walls should be entirely of

fire brick. If the center of such walls arebuilt of red brick, they will melt down andcause the failure of the wall as a whole.

Fire-brick arches should be constructed ofselected brick which are smooth, straightand uniform. The frames on which sucharches are built, called arch centers,should be constructed of batten strips notover 2 inches wide. The brick should belaid on these centers in courses, not inrings, each joint being broken with a bondequal to the length of half a brick. Eachcourse should be first tried in place dry,and checked with a straight edge to insurea uniform thickness of joint betweencourses. Each brick should be dipped onone side and two edges only and tappedinto place with a mallet. Wedge brickcourses should be used only wherenecessary to keep the bottom faces of thestraight brick course in even contact with

the centers. When such contact cannot beexactly secured by the use of wedgebrick, the straight brick should lean awayfrom the center of the arch rather thantoward it. When the arch is approximatelytwo-thirds completed, a trial ring shouldbe laid to determine whether the keycourse will fit. When some cutting isnecessary to secure such a fit, it should bedone on the two adjacent courses on theside of the brick away from the key. It isnecessary that the keying course be a truefit from top to bottom, and after it has beendipped and driven it should not extendbelow the surface of the arch, butpreferably should have its lower ledgeone-quarter inch above this surface. Afterfitting, the keys should be dipped,replaced loosely, and the whole coursedriven uniformly into place by means of aheavy hammer and a piece of woodextending the full length of the keying

course. Such a driving in of this courseshould raise the arch as a whole from thecenter. The center should be soconstructed that it may be dropped free ofthe arch when the key course is in placeand removed from the furnace withoutbeing burned out.

[Illustration: A Typical Steel Casing for aBabcock & Wilcox Boiler Built by TheBabcock & Wilcox Co.]

Care of Brickwork--Before a boiler isplaced in service, it is essential that thebrickwork setting be thoroughly andproperly dried, or otherwise the settingwill invariably crack. The best method ofstarting such a process is to block open theboiler damper and the ashpit doors assoon as the brickwork is completed and inthis way maintain a free circulation of airthrough the setting. If possible, such

preliminary drying should be continuedfor several days before any fire is placedin the furnace. When ready for the dryingout fire, wood should be used at the start ina light fire which may be gradually built upas the walls become warm. After the wallshave become thoroughly heated, coal maybe fired and the boiler placed in service.

As already stated, the life of a boilersetting is dependent to a large extent uponthe material entering into its constructionand the care with which such material islaid. A third and equally important factorin the determining of such life is the caregiven to the maintaining of the setting ingood condition after the boiler is placed inoperation. This feature is discussed morefully in the chapter dealing with generalboiler room management.

Steel Casings--In the chapter dealing with

the losses operating against highefficiencies as indicated by the heatbalance, it has been shown that aconsiderable portion of such losses is dueto radiation and to air infiltration into theboiler setting. These losses have beenvariously estimated from 2 to 10 per cent,depending upon the condition of thesetting and the amount of radiationsurface, the latter in turn being dependentupon the size of the boiler used. In themodern efforts after the highest obtainableplant efficiencies much has been done toreduce such losses by the use of aninsulated steel casing covering thebrickwork. In an average size boiler unitthe use of such casing, when properlyinstalled, will reduce radiation losses fromone to two per cent., over what can beaccomplished with the best brick settingwithout such casing and, in addition,prevent the loss due to the infiltration of

air, which may amount to an additional fiveper cent., as compared with brick settingsthat are not maintained in good order.Steel plate, or steel plate backed byasbestos mill-board, while acting as apreventative against the infiltration of airthrough the boiler setting, is not aseffective from the standpoint of decreasingradiation losses as a casing properlyinsulated from the brick portion of thesetting by magnesia block and asbestosmill-board. A casing which has been foundto give excellent results in eliminating airleakage and in the reduction of radiationlosses is clearly illustrated on page 306.

Many attempts have been made to usesome material other than brick for boilersettings but up to the present nothing hasbeen found that may be consideredsuccessful or which will give assatisfactory service under severe

conditions as properly laid brickwork.

BOILER ROOM PIPING

In the design of a steam plant, the pipingsystem should receive the most carefulconsideration. Aside from the constructivedetails, good practice in which is fairlywell established, the important factors arethe size of the piping to be employed andthe methods utilized in avoiding difficultiesfrom the presence in the system of water ofcondensation and the means employedtoward reducing radiation losses.

Engineering opinion varies considerablyon the question of material of pipes andfittings for different classes of work, andthe following is offered simply as asuggestion of what constitutes goodrepresentative practice.

All pipe should be of wrought iron or soft

steel. Pipe at present is made in"standard", "extra strong"[76] and "doubleextra strong" weights. Until recently, afourth weight approximately 10 per centlighter than standard and known as"Merchants" was built but the use of thispipe has largely gone out of practice. Pipesizes, unless otherwise stated, are given interms of nominal internal diameter. Table62 gives the dimensions and some generaldata on standard and extra strongwrought-iron pipe.

TABLE 62

DIMENSIONS OF STANDARD ANDEXTRA STRONG[76]WROUGHT-IRON AND STEEL PIPE

_______________________________________________________________ | |

| | | | Diameter| Circumference | |

|__________________________|__________________________| | | | |

| | | |External| Internal|External| Internal | |

|Standard|_________________|Standard|_________________| | | and | || and | | | | Nominal | Extra

|Standard| Extra | Extra |Standard|Extra | | Size | Strong | | Strong |Strong | | Strong ||_________|________|________|________|________|________|________| | | |

| | | | | | 1/8 | .405 |.269 | .215 | 1.272 | .848 | .675 | |

1/4 | .540 | .364 | .302 | 1.696 | 1.144| .949 | | 3/8 | .675 | .493 | .423 |2.121 | 1.552 | 1.329 | | 1/2 | .840 |.622 | .546 | 2.639 | 1.957 | 1.715 | |3/4 | 1.050 | .824 | .742 | 3.299 | 2.589| 2.331 | | 1 | 1.315 | 1.049 | .957 |

4.131 | 3.292 | 3.007 | | 1-1/4 | 1.660 |1.380 | 1.278 | 5.215 | 4.335 | 4.015 | |1-1/2 | 1.900 | 1.610 | 1.500 | 5.969 |5.061 | 4.712 | | 2 | 2.375 | 2.067 |1.939 | 7.461 | 6.494 | 6.092 | | 2-1/2 |2.875 | 2.469 | 2.323 | 9.032 | 7.753 |7.298 | | 3 | 3.500 | 3.068 | 2.900 |10.996 | 9.636 | 9.111 | | 3-1/2 | 4.000 |3.548 | 3.364 | 12.566 | 11.146 | 10.568 |

| 4 | 4.500 | 4.026 | 3.826 | 14.137 |12.648 | 12.020 | | 4-1/2 | 5.000 | 4.506| 4.290 | 15.708 | 14.162 | 13.477 | | 5| 5.563 | 5.047 | 4.813 | 17.477 | 15.849 |15.121 | | 6 | 6.625 | 6.065 | 5.761 |20.813 | 19.054 | 18.099 | | 7 | 7.625 |7.023 | 6.625 | 23.955 | 22.063 | 20.813 || 8 | 8.625 | 7.981 | 7.625 | 27.096 |25.076 | 23.955 | | 9 | 9.625 | 8.941 |8.625 | 30.238 | 28.089 | 27.096 | | 10 |10.750 | 10.020 | 9.750 | 33.772 | 31.477 |30.631 | | 11 | 11.750 | 11.000 | 10.750| 36.914 | 34.558 | 33.772 | | 12 |

12.750 | 12.000 | 11.750 | 40.055 | 37.700| 36.914 ||_________|________|________|________|________|________|________|

__________________________________________________________ | | |

| | | | | Length| | | | Internal | of |Nominal Weight | | | Transverse|Pipe in | Pounds per | | |Area |Feet per| Foot | ||_____________________| Square|_________________| | | ||Foot of | | | | Nominal | Standard| Extra |External|Standard| Extra | |Size | | Strong |Surface | |Strong ||_________|__________|__________|________|________|________| | | |

| | | | | 1/8 | .0573 |.0363 | 9.440 | .244 | .314 | | 1/4 |.1041 | .0716 | 7.075 | .424 | .535 | |3/8 | .1917 | .1405 | 5.657 | .567 |

.738 | | 1/2 | .3048 | .2341 | 4.547 |

.850 | 1.087 | | 3/4 | .5333 | .4324 |3.637 | 1.130 | 1.473 | | 1 | .8626 |.7193 | 2.904 | 1.678 | 2.171 | | 1-1/4 |1.496 | 1.287 | 2.301 | 2.272 | 2.996 | |

1-1/2 | 2.038 | 1.767 | 2.010 | 2.717 |3.631 | | 2 | 3.356 | 2.953 | 1.608 |

3.652 | 5.022 | | 2-1/2 | 4.784 | 4.238| 1.328 | 5.793 | 7.661 | | 3 | 7.388 |

6.605 | 1.091 | 7.575 | 10.252 | | 3-1/2| 9.887 | 8.888 | .955 | 9.109 | 12.505| | 4 | 12.730 | 11.497 | .849 |10.790 | 14.983 | | 4-1/2 | 15.961 |14.454 | .764 | 12.538 | 17.611 | | 5 |19.990 | 18.194 | .687 | 14.617 | 20.778| | 6 | 28.888 | 26.067 | .577 |18.974 | 28.573 | | 7 | 38.738 | 34.472| .501 | 23.544 | 38.048 | | 8 | 50.040

| 45.664 | .443 | 28.544 | 43.388 | | 9| 62.776 | 58.426 | .397 | 33.907 |

48.728 | | 10 | 78.839 | 74.662 | .355| 40.483 | 54.735 | | 11 | 95.033 |90.763 | .325 | 45.557 | 60.075 | | 12 |113.098 | 108.43 | .299 | 49.562 |65.415 ||_________|__________|__________|________|________|________|

Dimensions are nominal and except wherenoted are in inches.

In connection with pipe sizes, Table 63,giving certain tube data may be found tobe of service.

TABLE 63

TUBE DATA, STANDARD OPENHEARTH OR LAP WELDED STEEL TUBES

+-----+--+----+-----+------+------+------+------+-------+-------+-------+ |S E D|B | T | I D|Circumference| Transverse |Square|Length |Nominal| |i x i|. | h | n i || Area | Feet |in Feet|Weight | |z t

a|W | i | t a | |Square Inches| of| per |Pounds | |e e m|. | c | e m+------+------+------+------+ Exter |Square |per | | r e| | k | r e|Exter-|Inter-|Exter-|Inter-| -nal |Footof| Foot | | n t|G | n | n t | nal | nal |nal | nal |Surface| Exter | | | a e|a |e | a e | | | | | per | -nal || | l r|u | s | l r | | | | |Footof|Surface| | | |g | s | | | |

| |Length | | | | |e | | || | | | | | |

+-----+--+----+-----+------+------+------+------+-------+-------+-------+|1-1/2|10|.134|1.232| 4.712|3.870|1.7671|1.1921| .392 | 2.546 | 1.955| |1-1/2| 9|.148|1.204| 4.712|

3.782|1.7671|1.1385| .392 | 2.546 | 2.137| |1-1/2| 8|.165|1.170| 4.712|3.676|1.7671|1.0751| .392 | 2.546 | 2.353| | 2 |10|.134|1.732| 6.283|5.441|3.1416|2.3560| .523 | 1.909 | 2.670| | 2 | 9|.148|1.704| 6.283|5.353|3.1416|2.2778| .523 | 1.909 | 2.927| | 2 | 8|.165|1.670| 6.283|5.246|3.1416|2.1904| .523 | 1.909 | 3.234| |3-1/4|11|.120|3.010|10.210|9.456|8.2958|7.1157| .850 | 1.175 | 4.011| |3-1/4|10|.134|2.982|10.210|9.368|8.2958|6.9840| .850 | 1.175 | 4.459| |3-1/4| 9|.148|2.954|10.210|9.280|8.2958|6.8535| .850 | 1.175 | 4.903| | 4|10|.134|3.732|12.566|11.724|12.566|10.939| 1.047 | .954 | 5.532 | | 4 |9|.148|3.704|12.566|11.636|12.566|10.775| 1.047 | .954 | 6.000 | | 4 |8|.165|3.670|12.566|11.530|12.566|10.578| 1.047 | .954 | 6.758 |

+-----+--+----+-----+------+------+------+------+-------+-------+-------+

Dimensions are nominal and except wherenoted are in inches.

Pipe Material and Thickness--For saturatedsteam pressures not exceeding 160pounds, all pipe over 14 inches should be3/8 inch thick O. D. pipe. All other pipeshould be standard full weight, excepthigh pressure feed[77] and blow-off lines,which should be extra strong.

For pressures above 150 pounds up to 200pounds with superheated steam, all highpressure feed and blow-off lines, highpressure steam lines having threadedflanges, and straight runs and bends ofhigh pressure steam lines 6 inches andunder having Van Stone joints should beextra strong. All piping 7 inches and over

having Van Stone joints should be fullweight soft flanging pipe of special quality.Pipe 14 inches and over should be 3/8 inchthick O. D. pipe. All pipes for thesepressures not specified above should befull weight pipe.

Flanges--For saturated steam, 160 poundsworking pressure, all flanges forwrought-iron pipe should be cast-ironthreaded. All high pressure threadedflanges should have the diameterthickness and drilling in accordance withthe "manufacturer's standard" for "extraheavy" flanges. All low pressure flangesshould have diameter, thickness anddrilling in accordance with "manufacturer'sstandard" for "standard flanges."

The flanges on high pressure lines shouldbe counterbored to receive pipe andprevent the threads from shouldering. The

pipe should be screwed through the flangeat least 1/16 inch, placed in machine andafter facing off the end one smooth cutshould be taken over the face of the flangeto make it square with the axis of the pipe.

[Illustration: 2000 Horse-power Installationof Babcock & Wilcox Boilers andSuperheaters, Equipped with Babcock &Wilcox Chain Grate Stokers at theKentucky Electric Co., Louisville, Ky.]

For pressures above 160 pounds, wheresuperheated steam is used, all highpressure steam lines 4 inches and overshould have solid rolled steel flanges andspecial upset lapped joints. In themanufacture of such joints, the ends of thepipe are heated and upset against the faceof a holding mandrel conforming to theshape of the flange, the lapped portion ofthe pipe being flattened out against the

face of the mandrel, the upsetting actionmaintaining the desired thickness of thelap. When cool, both sides of the lap arefaced to form a uniform thickness and aneven bearing against flange and gasket.The joint, therefore, is a strictly metal tometal joint, the flanges merely holding thelapped ends of the pipe against the gasket.

A special grade of soft flanging pipe isselected to prevent breaking. The bendingaction is a severe test of the pipe and if itwithstands the bending process and thepressure tests, the reliability of the joint isassured. Such a joint is called a Van Stonejoint, though many modifications andimprovements have been made since thejoint was originally introduced.

The diameter and thickness of such flangesshould be special extra heavy. Suchflanges should be turned to diameter, their

fronts faced and the backs machined inlieu of spot facing.

In lines other than given for pressures over150 pounds, all flanges for wrought-ironpipe should be threaded. All threadedflanges for high pressure superheatedlines 3� inches and under should be"semi-steel" extra heavy. Flanges for otherthan steam lines should be manufacturer'sstandard extra heavy.

Welded flanges are frequently used inplace of those described with satisfactoryresults.

Fittings--For saturated steam underpressures up to 160 pounds, all fittings 3�inches and under should be screwed.Fittings 4 inches and over should haveflanged ends. Fittings for this pressureshould be of cast iron and should have

heavy leads and full taper threads.Flanged fittings in high pressure linesshould be extra heavy, and in low pressurelines standard weight. Where possible inhigh pressure flanges and fittings, boltsurfaces should be spot faced to providesuitable bearing for bolt heads and nuts.

Fittings for superheated steam up to 70degrees at pressures above 160 poundsare sometimes of cast iron.[78] Forsuperheat above 70 degrees such fittingsshould be "steel castings" and in generalthese fittings are recommended for anydegree of superheat. Fittings for other thanhigh pressure work may be of cast iron,except where superheated steam iscarried, where they should be of "wroughtsteel" or "hard metal". Fittings 3� inchesand under should be screwed, 4 inchesand over flanged.

Flanges for pressures up to 160 pounds inpipes and fittings for low pressure lines,and any fittings for high pressure linesshould have plain faces, smooth tool finish,scored with V-shaped grooves for rubbergaskets. High pressure line flanges shouldhave raised faces, projecting the fullavailable diameter inside the bolt holes.These faces should be similarly scored.

All pipe � inch and under should haveground joint unions suitable for thepressure required. Pipe � inch and overshould have cast-iron flanged unions.Unions are to be preferred to wrought-ironcouplings wherever possible to facilitatedismantling.

Valves--For 150 pounds working pressure,saturated steam, all valves 2 inches andunder may have screwed ends; 2� inchesand over should be flanged. All high

pressure steam valves 6 inches and overshould have suitable by-passes. All valvesfor use with superheated steam should beof special construction. For pressuresabove 160 pounds, where the superheatdoes not exceed 70 degrees, valve bodies,caps and yokes are sometimes made ofcast iron, though ordinarily semi-steel willgive better satisfaction. The spindles ofsuch valves should be of bronze and thereshould be special necks with condensingchambers to prevent the superheatedsteam from blowing through the packing.For pressures over 160 pounds anddegrees of superheat above 70, all valves3 inches and over should have valvebodies, caps and yokes of steel castings.Spindles should be of some non-corrosivemetal, such as "monel metal". Seat ringsshould be removable of the samenon-corrosive metal as should the spindleseats and plug faces.

All salt water valves should have bronzespindles, sleeves and packing seats.

The suggestions as to flanges for differentclasses of service made on page 311 holdas well for valve flanges, except that suchflanges are not scored.

Automatic stop and check valves arecoming into general use with boilers andsuch use is compulsory under the boilerregulations of certain communities. Whereused, they should be preferably placeddirectly on the boiler nozzle. Where two ormore boilers are on one line, in addition tothe valve at the boiler, whether this be anautomatic valve or a gate valve, thereshould be an additional gate valve on eachboiler branch at the main steam header.

Relief valves should be furnished at the

discharge side of each feed pump and onthe discharge side of each feed heater ofthe closed type.

Feed Lines--Feed lines should in allinstances be made of extra strong pipedue to the corrosive action of hot feedwater. While it has been suggested abovethat cast-iron threaded flanges should beused in such lines, due to the suddenexpansion of such pipe in certain instancescast-iron threaded flanges crack beforethey become thoroughly heated andexpand, and for this reason cast-steelthreaded flanges will give moresatisfactory results. In some instances,wrought-steel and Van Stone joints havebeen used in feed lines and thisundoubtedly is better practice than the useof cast-steel threaded work, though theadditional cost is not warranted in allstations.

Feed valves should always be of the globepattern. A gate valve cannot be closelyregulated and often clatters owing to thepulsations of the feed pump.

Gaskets--For steam and water lines wherethe pressure does not exceed 160 pounds,wire insertion rubber gaskets 1/16 inchthick will be found to give good service.For low pressure lines, canvas insertionblack rubber gaskets are ordinarily used.For oil lines special gaskets are necessary.

For pressure above 160 pounds carryingsuperheated steam, corrugated steelgaskets extending the full availablediameter inside of the bolt holes give goodsatisfaction. For high pressure water lineswire inserted rubber gaskets are used,and for low pressure flanged joints canvasinserted rubber gaskets.

Size of Steam Lines--The factors affectingthe proper size of steam lines are theradiation from such lines and the velocityof steam within them. As the size of thesteam line increases, there will be anincrease in the radiation.[79] As the sizedecreases, the steam velocity and thepressure drop for a given quantity ofsteam naturally increases.

There is a marked tendency in modernpractice toward higher steam velocities,particularly in the case of superheatedsteam. It was formerly considered goodpractice to limit this velocity to 6000 feetper minute but this figure is to-dayconsidered low.

In practice the limiting factor in thevelocity advisable is the allowablepressure drop. In the description of the

action of the throttling calorimeter, it hasbeen demonstrated that there is no lossaccompanying a drop in pressure, thedifference in energy between the higherand lower pressures appearing as heat,which, in the case of steam flowing througha pipe, may evaporate any condensationpresent or may be radiated from the pipe.A decrease in pipe area decreases theradiating surface of the pipe and thus thepossible condensation. As the heatliberated by the pressure drop is utilizedin overcoming or diminishing thetendency toward condensation and theheat loss through radiation, the steam as itenters the prime mover will be drier ormore highly superheated where highsteam velocities are used than where theyare lower, and if enough excess pressureis carried at the boilers to maintain thedesired pressure at the prime mover, thepressure drop results in an actual saving

rather than a loss. The whole is analogousto standard practice in electricaldistributing systems where generatorvoltage is adjusted to suit the loss in thefeeder lines.

In modern practice, with superheatedsteam, velocities of 15,000 feet per minuteare not unusual and this figure is veryfrequently exceeded.

Piping System Design--With the propersize of pipe to be used determined, themost important factor is the provision forthe removal of water of condensation thatwill occur in any system. Suchcondensation cannot be wholly overcomeand if the water of condensation is carriedto the prime mover, difficulties willinvariably result. Water is practicallyincompressible and its effect whentraveling at high velocities differs little

from that of a solid body of equal weight,hence impact against elbows, valves orother obstructions, is the equivalent of aheavy hammer blow that may result in thefracture of the pipe. If there is not sufficientwater in the system to produce this result,it will certainly cause knocking andvibration in the pipe, resulting eventuallyin leaky joints. Where the water reachesthe prime mover, its effect will vary fromdisagreeable knocking to disruption. Toofrequently when there are disastrousresults from such a cause the boilers areblamed for delivering wet steam when, asa matter of fact, the evil is purely a result ofpoor piping design, the most commoncause of such an action being thepocketing of the water in certain parts ofthe piping from whence it is carried alongin slugs by the steam. The action isparticularly severe if steam is admitted to acold pipe containing water, as the water

may then form a partial vacuum bycondensing the steam and be projected ata very high velocity through the pipesproducing a characteristic sharp metallicknock which often causes bursting of thepipe or fittings. The amount of waterpresent through condensation may beappreciated when it is considered thatuncovered 6-inch pipe 150 feet longcarrying 3600 pounds of high pressuresteam per hour will condenseapproximately 6 per cent of the total steamcarried through radiation. It follows thatefficient means of removing condensationwater are absolutely imperative and thefollowing suggestions as to such meansmay be of service:

The pitch of all pipe should be in thedirection of the flow of steam. Wherever arise is necessary, a drain should beinstalled. All main headers and important

branches should end in a drop leg andeach such drop leg and any low points inthe system should be connected to thedrainage pump. A similar connectionshould be made to every fitting wherethere is danger of a water pocket.

Branch lines should never be taken fromthe bottom of a main header but wherepossible should be taken from the top.Each engine supply pipe should have itsown separator placed as near the throttleas possible. Such separators should bedrained to the drainage system.

Check valves are frequently placed indrain pipes to prevent steam from enteringany portion of the system that may be shutoff.

Valves should be so located that theycannot form water pockets when either

open or closed. Globe valves will form awater pocket in the piping to which theyare connected unless set with the stemhorizontal, while gate valves may be setwith the spindle vertical or at an angle.Where valves are placed directly on theboiler nozzle, a drain should be providedabove them.

High pressure drains should be trapped toboth feed heaters and waste headers.Traps and meters should be provided withby-passes. Cylinder drains, heaterblow-offs and drains, boiler blow-offs andsimilar lines should be led to waste. Theends of cylinder drains should not extendbelow the surface of water, for on startingup or on closing the throttle valve with thedrains open, water may be drawn backinto the cylinders.

TABLE 64

RADIATION FROM COVERED ANDUNCOVERED STEAM PIPES

CALCULATED FOR 160 POUNDSPRESSURE AND 60 DEGREESTEMPERATURE

+---------------------------------------------------------------------+|+------+---------------------------+----+----+----+-----+-----+-----+| || | || | | | | || || Pipe |

|1/2 |3/4 | 1 |1-1/4|1-1/2| ||||Inches| Thickness of Covering|inch|inch|inch|inch |inch |Bare |||+------+---------------------------+----+----+----+-----+-----+-----+| || |B. t. u. per linealfoot | | | | | | || || | perhour |149 |118 | 99 | 86 | 79 |597 || || |B. t. u. per square foot | || | | | || || | per hour

|240 |190 |161 | 138 | 127 | 959 || || 2|B. t. u. per square foot | | | | || || || | per hour per one degree || | | | | || || | difference in

temperature|.770|.613|.519|.445 |.410|3.198|||+------+---------------------------+----+----+----+-----+-----+-----+| || |B. t. u. per linealfoot | | | | | | || || | perhour |247 |193 |160 | 139 | 123|1085 || || |B. t. u. per square foot || | | | | || || | per hour

|210 |164 |136 | 118 | 104 | 921 || ||4 |B. t. u. per square foot | | | | |

| || || | per hour per one degree || | | | | || || | difference

in temperature|.677|.592|.439|.381 |.335|2.970|||+------+---------------------------+----+----+----+-----+-----+-----+| || |B. t. u. per linealfoot | | | | | | || || | perhour |352 |269 |221 | 190 | 167

|1555 || || |B. t. u. per square foot || | | | | || || | per hour



in temperature|.655|.500|.410|.355 |.310|2.89 |||+------+---------------------------+----+----+----+-----+-----+-----+| || |B. t. u. per linealfoot | | | | | | || || | perhour |443 |337 |276 | 235 | 207|1994 || || |B. t. u. per square foot || | | | | || || | per hour



in temperature|.632|.481|.394|.335 |.297|2.85 |||+------+---------------------------+----+----+----+-----+-----+-----+| || |B. t. u. per lineal

foot | | | | | | || || | perhour |549 |416 |337 | 287 | 250|2468 || || |B. t. u. per square foot || | | | | || || | per hour

|195 |148 |120 | 102 | 89 | 877 || ||10 |B. t. u. per square foot | | | || | || || | per hour per onedegree | | | | | | || || |difference intemperature|.629|.477|.387|.329 |.287|2.83 |||+------+---------------------------+----+----+----+-----+-----+-----+|+---------------------------------------------------------------------+

Covering--Magnesia, canvas covered.

For calculating radiation for pressure andtemperature other than 160 pounds, and 60degrees, use B. t. u. figures for one degreedifference.

Radiation from Pipes--The evils of thepresence of condensed steam in pipingsystems have been thoroughly discussedabove and in some of the previous articles.Condensation resulting from radiation,while it cannot be wholly obviated, can, byproper installation, be greatly reduced.

Bare pipe will radiate approximately 3 B. t.u. per hour per square foot of exposedsurface per one degree of difference intemperature between the steam containedand the external air. This figure may bereduced to from 0.3 to 0.4 B. t. u. for thesame conditions by a 1� inch insulatingcovering. Table 64 gives the radiationlosses for bare and covered pipes withdifferent thicknesses of magnesiacovering.

Many experiments have been made as to

the relative efficiencies of different kindsof covering. Table 65 gives someapproximately relative figures based onone inch covering from experiments byPaulding, Jacobus, Brill and others.

TABLE 65

APPROXIMATE EFFICIENCIESOF VARIOUS COVERINGS REFERREDTO BARE PIPES+--------------------------------+|+-------------------+----------+| ||Covering |Efficiency|||+-------------------+----------+| ||Asbestocel

| 76.8 || ||Gast's Air Cell | 74.4|| ||Asbesto Sponge Felt| 85.0 ||||Magnesia | 83.5 || ||AsbestosNavy Brand| 82.0 || ||Asbesto SpongeHair| 86.0 || ||Asbestos Fire Felt |73.5 || |+-------------------+----------+|+--------------------------------+

Based on one-inch covering.

The following suggestions may be ofservice:

Exposed radiating surfaces of all pipes, allhigh pressure steam flanges, valve bodiesand fittings, heaters and separators,should be covered with non-conductingmaterial wherever such covering willimprove plant economy. All main steamlines, engine and boiler branches, shouldbe covered with 2 inches of 85 per centcarbonate of magnesia or the equivalent.Other lines may be covered with one inchof the same material. All covering shouldbe sectional in form and large surfacesshould be covered with blocks, exceptwhere such material would be difficult toinstall, in which case plastic materialshould be used. In the case of flanges the

covering should be tapered back from theflange in order that the bolts may beremoved.

All surfaces should be painted before thecovering is applied. Canvas is ordinarilyplaced over the covering, held in place bywrought-iron or brass bands.

Expansion and Support of Pipe--It is highlyimportant that the piping be so run thatthere will be no undue strains through theaction of expansion. Certain points areusually securely anchored and theexpansion of the piping at other pointstaken care of by providing supports alongwhich the piping will slide or by means offlexible hangers. Where pipe is supportedor anchored, it should be from the buildingstructure and not from boilers or primemovers. Where supports are furnished,they should in general be of any of the

numerous sliding supports that areavailable. Expansion is taken care of bysuch a method of support and by theproviding of large radius bends wherenecessary.

It was formerly believed that piping wouldactually expand under steam temperaturesabout one-half the theoretical amount dueto the fact that the exterior of the pipewould not reach the full temperature of thesteam contained. It would appear,however from recent experiments thatsuch actual expansion will in the case ofwell-covered pipe be very nearly thetheoretical amount. In one case noted, asteam header 293 feet long when heatedunder a working pressure of 190 pounds,the steam superheated approximately 125degrees, expanded 8� inches; thetheoretical amount of expansion under theconditions would be approximately

9-35/64 inches.

[Illustration: Bankers Trust Building, NewYork City, Operation 900 Horse Power ofBabcock & Wilcox Boilers]

FLOW OF STEAM THROUGH PIPES ANDORIFICES

Various formulae for the flow of steamthrough pipes have been advanced, allhaving their basis upon Bernoulli'stheorem of the flow of water throughcircular pipes with the propermodifications made for the variation inconstants between steam and water. Theloss of energy due to friction in a pipe isgiven by Unwin (based upon Weisbach) as

f 2 v� W L E_{f} = ----------(37) gd

where E is the energy loss in foot poundsdue to the friction of W units of weight ofsteam passing with a velocity of v feet persecond through a pipe d feet in diameterand L feet long; g represents the

acceleration due to gravity (32.2) and f thecoefficient of friction.

Numerous values have been given for thiscoefficient of friction, f, which, fromexperiment, apparently varies with boththe diameter of pipe and the velocity of thepassing steam. There is no authentic dataon the rate of this variation with velocityand, as in all experiments, the effect ofchange of velocity has seemed less thanthe unavoidable errors of observation, thecoefficient is assumed to vary only with thesize of the pipe.

Unwin established a relation for thiscoefficient for steam at a velocity of 100feet per second,

/ 3 \ f = K| 1 + --- | (38) \ 10d /

where K is a constant experimentallydetermined, and d the internal diameter ofthe pipe in feet.

If h represents the loss of head in feet, then

f 2 v� W L E_{f} = Wh =---------- (39) gd

f 2 v� L and h = -------- (40) gd

If D represents the density of the steam orweight per cubic foot, and p the loss ofpressure due to friction in pounds persquare inch, then

hD p = --- (41) 144

and from equations (38), (40) and (41),

D v� L / 3 \ p =-------- �K | 1 + --- | (42) 72 gd \ 10d /

To convert the velocity term and to reduceto units ordinarily used, let d_{1} thediameter of pipe in inches = 12d, and w =the flow in pounds per minute; then

[pi] / d_{1}\ w = 60v �--- |---- |^{2} D 4 \ 12 /

9.6 w and v = -------------- [pi] d_{1}^2 D

Substituting this value and that of d informula (42)

/ 3.6 \ w^{2} L p = 0.04839K | 1 + ----- | ----------- (43) \

d_{1} / D d_{1}^{5}

Some of the experimental determinationsfor the value of K are: K = .005 for water(Unwin). K = .005 for air (Arson). K =.0028 for air (St. Gothard tunnelexperiments). K = .0026 for steam(Carpenter at Oriskany). K = .0027 forsteam (G. H. Babcock).

The value .0027 is apparently the mostnearly correct, and substituting in formula(43) gives,

/ 3.6 \ w^{2} L p =0.000131 | 1 + ---- | ----------- (44) \ d_{1}/ D d_{1}^{5}

/ pDd_{1}^{5} \ w = 87 |-------------- |^{�} (45) | / 3.6 \| | | 1 + ---- | L | \ \

d_{1}/ /

Where w = the weight of steam passing inpounds per minute, p = the differencein pressure between the two ends of thepipe in pounds per square inch, D= density of steam or weight per cubicfoot,[80] d_{1} = internal diameter of pipein inches, L = length of pipe in feet.

TABLE 66

FLOW OF STEAMTHROUGH PIPES+---------------------------------------------------------------------------------------+|Initl|Diameter[81] of Pipe in Inches,Length of Pipe = 240 Diameters ||Gauge|---------------------------------------------------------------------------------+ |Press| � |1 | 1� | 2 | 2� | 3 | 4 | 5 | 6 | 8 |10 | 12 | 15 | 18 |

|Pound|---------------------------------------------------------------------------------+ |/SqIn|Weight of Steam per Minute, in Pounds,With One Pound Loss of Pressure |+-----+---------------------------------------------------------------------------------+ | 1|1.16|2.07| 5.7|10.27|15.45|25.38| 46.85|77.3|115.9|211.4| 341.1| 502.4|804|1177| | 10 |1.44|2.57|7.1|12.72|19.15|31.45| 58.05|95.8|143.6|262.0| 422.7| 622.5|996|1458| | 20 |1.70|3.02|8.3|14.94|22.49|36.94|68.20|112.6|168.7|307.8| 496.5|731.3|1170|1713| | 30 |1.91|3.40|9.4|16.84|25.35|41.63|76.84|126.9|190.1|346.8| 559.5|824.1|1318|1930| | 40|2.10|3.74|10.3|18.51|27.87|45.77|84.49|139.5|209.0|381.3| 615.3|906.0|1450|2122| | 50|2.27|4.04|11.2|20.01|30.13|49.48|

91.34|150.8|226.0|412.2| 665.0|979.5|1567|2294| | 60|2.43|4.32|11.9|21.38|32.19|52.87|97.60|161.1|241.5|440.5|710.6|1046.7|1675|2451| | 70|2.57|4.58|12.6|22.65|34.10|56.00|103.37|170.7|255.8|466.5|752.7|1108.5|1774|2596| | 80|2.71|4.82|13.3|23.82|35.87|58.91|108.74|179.5|269.0|490.7|791.7|1166.1|1866|2731| | 90|2.83|5.04|13.9|24.92|37.52|61.62|113.74|187.8|281.4|513.3|828.1|1219.8|1951|2856| | 100|2.95|5.25|14.5|25.96|39.07|64.18|118.47|195.6|293.1|534.6|862.6|1270.1|2032|2975| | 120|3.16|5.63|15.5|27.85|41.93|68.87|127.12|209.9|314.5|573.7|925.6|1363.3|2181|3193| | 150|3.45|6.14|17.0|30.37|45.72|75.09|138.61|228.8|343.0|625.5|1009.2|1486.5|2378|

3481|+---------------------------------------------------------------------------------------+

This formula is the most generallyaccepted for the flow of steam in pipes.Table 66 is calculated from this formulaand gives the amount of steam passing perminute that will flow through straightsmooth pipes having a length of 240diameters from various initial pressureswith one pound difference between theinitial and final pressures.

To apply this table for other lengths ofpipe and pressure losses other than thoseassumed, let L = the length and d thediameter of the pipe, both in inches; l, theloss in pounds; Q, the weight under theconditions assumed in the table, andQ_{1}, the weight for the changedconditions.

For any length of pipe, if the weight ofsteam passing is the same as given in thetable, the loss will be,

L l = ---- (46) 240d

If the pipe length is the same as assumedin the table but the loss is different, thequantity of steam passing per minute willbe,

Q_{1} = Ql^{�} (47)

For any assumed pipe length and loss ofpressure, the weight will be,

/240dl\ Q_{1} = Q|-----|^{�} (48) \ L /

TABLE 67

FLOW OF STEAMTHROUGH PIPESLENGTH OF PIPE 1000 FEET

+--------------------------------------------------++----------------------------------------+ |Discharge in Pounds per Minutecorresponding to || Drop in Pressurein | | Drop in Pressure on Right forPipe Diameters || Pounds per SquareInch corresponding | | in Inchesin Top Line || to Discharge onLeft: Densities | |

|| and corresponding AbsolutePressures | ||| per Square Inch in First Two Lines |+--------------------------------------------------++----------------------------------------+ |Diameter[82]--Discharge ||Density--Pressure--Drop |+--------------------------------------------------++----------------------------------------+ | 12 | 10

| 8 | 6 | 4 | 3 | 2�| 2 | 1�| 1 ||.208|.230|.284|.328|.401|.443|.506|.548| | In| In | In | In | In | In | In | In | In | In ||90 | 100| 125| 150| 180| 200| 230| 250|+--------------------------------------------------++-------+--------------------------------+|2328|1443| 799| 371|123.|55.9|28.8|18.1|6.81|2.52||18.10|16.4|13.3|11.1|9.39|8.50|7.44|6.87| |2165|1341|742|344|114.6|51.9|27.6|16.8|6.52|2.34||15.60|14.1|11.4|9.60|8.09|7.33|6.41|5.92||1996|1237| 685|318|106.0|47.9|26.4|15.5|6.24|2.16||13.3|12.0|9.74|8.18|6.90|6.24|5.47|5.05||1830|1134| 628| 292|97.0|43.9|25.2|14.2|5.95|1.98||11.1|10.0|8.13|6.83|5.76|5.21|4.56|4.21||1663|1031| 571| 265|88.2|39.9|24.0|12.9|5.67|1.80||9.25|8.36|6.78|5.69|4.80|4.34|3.80|3.51||1580| 979| 542| 252|

83.8|37.9|22.8|12.3|5.29|1.71||8.33|7.53|6.10|5.13|4.32|3.91|3.42|3.16||1497| 928| 514| 239|79.4|35.9|21.6|11.6|5.00|1.62||7.48|6.76|5.48|4.60|3.88|3.51|3.07|2.84||1414| 876| 485| 226|75.0|33.9|20.4|10.9|4.72|1.53||6.67|6.03|4.88|4.10|3.46|3.13|2.74|2.53||1331| 825| 457| 212|70.6|31.9|19.2|10.3|4.43|1.44||5.91|5.35|4.33|3.64|3.07|2.78|2.43|2.24||1248| 873| 428| 199|66.2|23.9|18.0|9.68|4.15|1.35||5.19|4.69|3.80|3.19|2.69|2.44|2.13|1.97||1164| 722| 400| 186|61.7|27.9|16.8|9.03|3.86|1.26||4.52|4.09|3.31|2.78|2.34|2.12|1.86|1.72||1081| 670| 371| 172|57.3|25.9|15.6|8.38|3.68|1.17||3.90|3.53|2.86|2.40|2.02|1.83|1.60|1.48|| 998| 619| 343| 159|52.9|23.9|14.4|7.74|3.40|1.08||

3.32|3.00|2.43|2.04|1.72|1.56|1.36|1.26|| 915| 567| 314| 146|48.5|21.9|13.2|7.10|3.11|0.99||2.79|2.52|2.04|1.72|1.45|1.31|1.15|1.06|| 832| 516| 286| 132|44.1|20.0|12.0|6.45|2.83|0.90||2.31|2.09|1.69|1.42|1.20|1.08|.949|.877|| 748| 464| 257| 119|39.7|18.0|10.8|5.81|2.55|0.81||1.87|1.69|1.37|1.15| .97|.878|.769|.710|| 665| 412| 228| 106| 35.3|16.0|9.6|5.16|2.26|0.72||1.47|1.33|1.08|.905|.762|.690|.604|.558|| 582| 361| 200|92.8| 30.9|14.0|8.4|4.52|1.98|0.63||1.13|1.02|.828|.695|.586|.531|.456|.429|+--------------------------------------------------++----------------------------------------+

To get the pressure drop for lengths otherthan 1000 feet, multiply by lengths in feet�1000.

Example: Find the weight of steam at 100pounds initial gauge pressure, which willpass through a 6-inch pipe 720 feet longwith a pressure drop of 4 pounds. Underthe conditions assumed in the table, 293.1pounds would flow per minute; hence, Q =293.1, and

_ _ | 240�� | Q_{1} =293.1 | ------- |^{�} = 239.9 pounds |_ 720�2_|

Table 67 may be frequently found to be ofservice in problems involving the flow ofsteam. This table was calculated by Mr. E.C. Sickles for a pipe 1000 feet long fromformula (45), except that from the use of avalue of the constant K = .0026 instead of.0027, the constant in the formula becomes87.45 instead of 87.

In using this table, the pressures anddensities to be considered, as given at thetop of the right-hand portion, are the meanof the initial and final pressures anddensities. Its use is as follows: Assume anallowable drop of pressure through agiven length of pipe. From the value asfound in the right-hand column under thecolumn of mean pressure, as determinedby the initial and final pressures, pass tothe left-hand portion of the table along thesame line until the quantity is foundcorresponding to the flow required. Thesize of the pipe at the head of this columnis that which will carry the requiredamount of steam with the assumedpressure drop.

The table may be used conversely todetermine the pressure drop through apipe of a given diameter delivering aspecified amount of steam by passing from

the known figure in the left to the columnon the right headed by the pressure whichis the mean of the initial and finalpressures corresponding to the dropfound and the actual initial pressurepresent.

For a given flow of steam and diameter ofpipe, the drop in pressure is proportionalto the length and if discharge quantities forother lengths of pipe than 1000 feet arerequired, they may be found byproportion.

TABLE 68

FLOW OF STEAM INTO THEATMOSPHERE__________________________________________________________________ | |

| | | | | Absolute |Velocity | Actual | Discharge | Horse

Power | | Initial | of Outflow | Velocity| per Square | per Square | | Pressure |at Constant | of Outflow | Inch of | Inchof | | per Square | Density | Expanded| Orifice | Orifice if | | Inch | Feet

per | Feet per | per Minute | HorsePower | | Pounds | Second | Second

| Pounds | = 30 Pounds | | || | | per Hour |

|____________|_____________|____________|____________|_____________| | |

| | | | | 25.37 |863 | 1401 | 22.81 | 45.6 | |

30. | 867 | 1408 | 26.84 |53.7 | | 40. | 874 | 1419 |35.18 | 70.4 | | 50. | 880 |1429 | 44.06 | 88.1 | | 60. |885 | 1437 | 52.59 | 105.2 | |70. | 889 | 1444 | 61.07 |122.1 | | 75. | 891 | 1447 |65.30 | 130.6 | | 90. | 895 |1454 | 77.94 | 155.9 | | 100. |

898 | 1459 | 86.34 | 172.7 | |115. | 902 | 1466 | 98.76 |197.5 | | 135. | 906 | 1472 |115.61 | 231.2 | | 155. | 910 |1478 | 132.21 | 264.4 | | 165. |912 | 1481 | 140.46 | 280.9 | |215. | 919 | 1493 | 181.58 |

363.2 ||____________|_____________|____________|____________|_____________|

Elbows, globe valves and a square-endedentrance to pipes all offer resistance to thepassage of steam. It is customary tomeasure the resistance offered by suchconstruction in terms of the diameter of thepipe. Many formulae have been advancedfor computing the length of pipe indiameters equivalent to such fittings orvalves which offer resistance. Theseformulae, however vary widely and for

ordinary purposes it will be sufficientlyaccurate to allow for resistance at theentrance of a pipe a length equal to 60times the diameter; for a right angleelbow, a length equal to 40 diameters, andfor a globe valve a length equal to 60diameters.

The flow of steam of a higher toward alower pressure increases as the differencein pressure increases to a point where theexternal pressure becomes 58 per cent ofthe absolute initial pressure. Below thispoint the flow is neither increased nordecreased by a reduction of the externalpressure, even to the extent of a perfectvacuum. The lowest pressure for which thisstatement holds when steam is dischargedinto the atmosphere is 25.37 pounds. Forany pressure below this figure, theatmospheric pressure, 14.7 pounds, isgreater than 58 per cent of the initial

pressure. Table 68, by D. K. Clark, givesthe velocity of outflow at constant density,the actual velocity of outflow expanded(the atmospheric pressure being taken as14.7 pounds absolute, and the ratio ofexpansion in the nozzle being 1.624), andthe corresponding discharge per squareinch of orifice per minute.

Napier deduced an approximate formulafor the outflow of steam into theatmosphere which checks closely with thefigures just given. This formula is:

pa W = ---- (49) 70

Where W = the pounds of steam flowingper second, p = the absolute pressurein pounds per square inch, and a = thearea of the orifice in square inches.

In some experiments made by Professor

C. H. Peabody, in the flow of steamthrough pipes from � inch to 1� incheslong and � inch in diameter, with roundedentrances, the greatest difference fromNapier's formula was 3.2 per cent excess ofthe experimental over the calculatedresults.

For steam flowing through an orifice from ahigher to a lower pressure where thelower pressure is greater than 58 per centof the higher, the flow per minute may becalculated from the formula:

W = 1.9AK ((P - d)d)^{�} (50)

Where W = the weight of steamdischarged in pounds per minute, A =area of orifice in square inches, P = theabsolute initial pressure in pounds persquare inch, d = the difference inpressure between the two sides in pounds

per square inch, K = a constant =.93 for a short pipe, and .63 for a hole in a thin plate or a safety valve.

[Illustration: Vesta Coal Co., California,Pa., Operating at this Plant 3160 HorsePower of Babcock & Wilcox Boilers]

HEAT TRANSFER

The rate at which heat is transmitted from ahot gas to a cooler metal surface overwhich the gas is flowing has been thesubject of a great deal of investigationboth from the experimental and theoreticalside. A more or less complete explanationof this process is necessary for a detailedanalysis of the performance of steamboilers. Such information at the present isalmost entirely lacking and for this reasona boiler, as a physical piece of apparatus,is not as well understood as it might be.This, however, has had little effect in itspractical development and it is hardlypossible that a more completeunderstanding of the phenomenadiscussed will have any radical effect onthe present design.

The amount of heat that is transferredacross any surface is usually expressed asa product, of which one factor is the slopeor linear rate of change in temperatureand the other is the amount of heattransferred per unit's difference intemperature in unit's length. In Fourier'sanalytical theory of the conduction of heat,this second factor is taken as a constantand is called the "conductivity" of thesubstance. Following this practice, theamount of heat absorbed by any surfacefrom a hot gas is usually expressed as aproduct of the difference in temperaturebetween the gas and the absorbingsurface into a factor which is commonlydesignated the "transfer rate". There hasbeen considerable looseness in thewritings of even the best authors as to theway in which the gas temperaturedifference is to be measured. If the gasvaries in temperature across the section of

the channel through which it is assumed toflow, and most of them seem to considerthat this would be the case, there are twomean gas temperatures, one the mean ofthe actual temperatures at any time acrossthe section, and the other the meantemperature of the entire volume of thegas passing such a section in any giventime. Since the velocity of flow will of acertainty vary across the section, thissecond mean temperature, which is onetacitly assumed in most instances, mayvary materially from the first. The twomean temperatures are onlyapproximately equal when the actualtemperature measured across the sectionis very nearly a constant. In what follows itwill be assumed that the meantemperature measured in the second wayis referred to. In English units thetemperature difference is expressed inFahrenheit degrees and the transfer rate in

B. t. u.'s per hour per square foot ofsurface. Pecla, who seems to have beenone of the first to consider this subjectanalytically, assumed that the transfer ratewas constant and independent both of thetemperature differences and the velocityof the gas over the surface. Rankine, on theother hand, assumed that the transfer rate,while independent of the velocity of thegas, was proportional to the temperaturedifference, and expressed the total amountof heat absorbed as proportional to thesquare of the difference in temperature.Neither of these assumptions has anywarrant in either theory or experiment andthey are only valuable in so far as their usedetermine formulae that fit experimentalresults. Of the two, Rankine's assumptionseems to lead to formulae that more nearlyrepresent actual conditions. It has beenquite fully developed by William Kent inhis "Steam Boiler Economy". Professor

Osborne Reynolds, in a short paperreprinted in Volume I of his "ScientificPapers", suggests that the transfer rate isproportional to the product of the densityand velocity of the gas and it is to beassumed that he had in mind the meanvelocity, density and temperature over thesection of the channel through which thegas was assumed to flow. Contrary toprevalent opinion, Professor Reynoldsgave neither a valid experimental nor atheoretical explanation of his formula andthe attempts that have been made since itsfirst publication to establish it on anytheoretical basis can hardly be consideredof scientific value. Nevertheless, Reynolds'suggestion was really the starting point ofthe scientific investigation of this subjectand while his formula cannot in any sensebe held as completely expressing thefacts, it is undoubtedly correct to a firstapproximation for small temperature

differences if the additive constant, whichin his paper he assumed as negligible, isgiven a value.[83]

Experimental determinations have beenmade during the last few years of the heattransfer rate in cylindrical tubes atcomparatively low temperatures and smalltemperature differences. The results atdifferent velocities have been plotted andan empirical formula determinedexpressing the transfer rate with thevelocity as a factor. The exponent of thepower of the velocity appearing in theformula, according to Reynolds, would beunity. The most probable value, however,deduced from most of the experimentsmakes it less than unity. After consideringexperiments of his own, as well asexperiments of others, Dr. WilhelmNusselt[84] concludes that the evidencesupports the following formulae:

_ _ [lambda]_{w} | wc_{p} [delta] | a = b ------------ |--------------- |^{u} d^{1-u} |_[lambda] _|

Where a is the transfer rate in caloriesper hour per square meter ofsurface per degree centigrade differencein temperature, u is a physicalconstant equal to .786 from Dr. Nusselt's

experiments, b is a constantwhich, for the units given below, is 15.90,

w is the mean velocity of the gas inmeters per second, c_{p} is thespecific heat of the gas at its meantemperature and pressure incalories per kilogram, [delta] is thedensity in kilograms per cubic meter,[lambda] is the conductivity at the meantemperature and pressure incalories per hour per square meter per

degree centigrade temperaturedrop per meter, [lambda]_{w} is theconductivity of the steam at thetemperature of the tube wall,d is the diameter of the tube in meters.

If the unit of time for the velocity is madethe hour, and in the place of the product ofthe velocity and density is written itsequivalent, the weight of gas flowing perhour divided by the area of the tube, thisequation becomes:

_ _ [lambda]_{w} |Wc_{p} | a = .0255 ------------ | ---------

|^{.786} d^{.214} |_ A[lambda] _|

where the quantities are in the unitsmentioned, or, since the constants areabsolute constants, in English units,

a is the transfer rate in B. t. u. per

hour per square foot of surface perdegree difference in temperature, Wis the weight in pounds of the gas flowing

through the tube per hour, Ais the area of the tube in square feet,d is the diameter of the tube in feet,c_{p} is the specific heat of the gas atconstant pressure, [lambda] is theconductivity of the gas at the meantemperature and pressure in B. t. u.per hour per square foot of surfaceper degree Fahrenheit drop intemperature per foot, [lambda]_{w} is theconductivity of the steam at thetemperature of the wall of the tube.

The conductivities of air, carbonic acid gasand superheated steam, as affected by thetemperature, in English units, are:

Conductivity of air .0122 (1 +.00132 T) Conductivity of carbonic acid

gas .0076 (1 + .00229 T) Conductivity ofsuperheated steam .0119 (1 + .00261 T)

where T is the temperature in degreesFahrenheit.

Nusselt's formulae can be taken as typicalof the number of other formulae proposedby German, French and Englishwriters.[85] Physical properties, inaddition to the density, are introduced inthe form of coefficients from aconsideration of the physical dimensionsof the various units and of the theoreticalformulae that are supposed to govern theflow of the gas and the transfer of heat. Allassume that the correct method ofrepresenting the heat transfer rate is bythe use of one term, which seems to beunwarranted and probably has beenadopted on account of the convenience inworking up the results by plotting them

logarithmically. This was the methodProfessor Reynolds used in determininghis equation for the loss in head in fluidsflowing through cylindrical pipes and it isnow known that the derived equationcannot be considered as anything morethan an empirical formula. It, therefore, iswell for anyone considering this subject tounderstand at the outset that the formulaediscussed are only of an empirical natureand applicable to limited ranges oftemperature under the conditionsapproximately the same as thosesurrounding the experiments from whichthe constants of the formula weredetermined.

It is not probable that the subject of heattransfer in boilers will ever be on anyother than an experimental basis until themathematical expression connecting thequantity of fluid which will flow through a

channel of any section under a given headhas been found and some explanation ofits derivation obtained. Taking thesimplest possible section, namely, a circle,it is found that at low velocities the loss ofhead is directly proportional to thevelocity and the fluid flows in straightstream lines or the motion is direct. Thismotion is in exact accordance with thetheoretical equations of the motion of aviscous fluid and constitutes almost adirect proof that the fundamentalassumptions on which these equations arebased are correct. When, however, thevelocity exceeds a value which isdeterminable for any size of tube, thedirect or stream line motion breaks downand is replaced by an eddy or mixing flow.In this flow the head loss by friction isapproximately, although not exactly,proportional to the square of the velocity.No explanation of this has ever been found

in spite of the fact that the subject has beentreated by the best mathematicians andphysicists for years back. It is to beassumed that the heat transferred duringthe mixing flow would be at a much higherrate than with the direct or stream lineflow, and Professors Croker andClement[86] have demonstrated that this istrue, the increase in the transfer being somarked as to enable them to determine thepoint of critical velocity from observingthe rise in temperature of water flowingthrough a tube surrounded by a steamjacket.

The formulae given apply only to a mixingflow and inasmuch as, from what has justbeen stated, this form of motion does notexist from zero velocity upward, it followsthat any expression for the heat transferrate that would make its value zero whenthe velocity is zero, can hardly be correct.

Below the critical velocity, the transfer rateseems to be little affected by change invelocity and Nusselt,[87] in another paperwhich mathematically treats the direct orstream line flow, concludes that, while it isapproximately constant as far as thevelocity is concerned in a straightcylindrical tube, it would vary from pointto point of the tube, growing less as thesurface passed over increased.

It should further be noted that no accountin any of this experimental work has beentaken of radiation of heat from the gas.Since the common gases absorb very littleradiant heat at ordinary temperatures, ithas been assumed that they radiate verylittle at any temperature. This may or maynot be true, but certainly a visible flamemust radiate as well as absorb heat.However this radiation may occur, since itwould be a volume phenomenon rather

than a surface phenomenon it would beconsidered somewhat differently fromordinary radiation. It might apply asincreasing the conductivity of the gaswhich, however independent of radiation,is known to increase with the temperature.It is, therefore, to be expected that at hightemperatures the rate of transfer will begreater than at low temperatures. Theexperimental determinations of transferrates at high temperatures are lacking.

Although comparatively nothing is knownconcerning the heat radiation from gasesat high temperatures, there is no questionbut what a large proportion of the heatabsorbed by a boiler is received direct asradiation from the furnace. Experimentsshow that the lower row of tubes of aBabcock & Wilcox boiler absorb heat at anaverage rate per square foot of surfacebetween the first baffle and the front

headers equivalent to the evaporation offrom 50 to 75 pounds of water from and at212 degrees Fahrenheit per hour.Inasmuch as in these experiments noseparation could be made between theheat absorbed by the bottom of the tubeand that absorbed by the top, the averageincludes both maximum and minimumrates for those particular tubes and it is fairto assume that the portion of the tubesactually exposed to the furnace radiationsabsorb heat at a higher rate. Part of thisheat was, of course absorbed by actualcontact between the hot gases and theboiler heating surface. A large portion ofit, however, must have been due toradiation. Whether this radiant heat camefrom the fire surface and the brickworkand passed through the gases in thefurnace with little or no absorption, orwhether, on the other hand, the radiationwere absorbed by the furnace gases and

the heat received by the boiler was asecondary radiation from the gasesthemselves and at a rate corresponding tothe actual gas temperature, is a question. Ifthe radiations are direct, then the term"furnace temperature", as usually used hasno scientific meaning, for obviously thetemperature of the gas in the furnacewould be entirely different from theradiation temperature, even were itpossible to attach any significance to theterm "radiation temperature", and it is notpossible to do this unless the radiationsare what are known as "full radiations"from a so-called "black body". If furnaceradiation takes place in this manner, theindications of a pyrometer placed in afurnace are hard to interpret and suchtemperature measurements can be of littlevalue. If the furnace gases absorb theradiations from the fire and from thebrickwork of the side walls and in their

turn radiate heat to the boiler surface, it isscientifically correct to assume that theactual or sensible temperature of the gaswould be measured by a pyrometer andthe amount of radiation could becalculated from this temperature byStefan's law, which is to the effect that therate of radiation is proportional to thefourth power of the absolute temperature,using the constant with the resultingformula that has been determined fromdirect experiment and other phenomena.With this understanding of the matter, theradiations absorbed by a boiler can betaken as equal to that absorbed by a flatsurface, covering the portion of the boilertubes exposed to the furnace and at thetemperature of the tube surface, whencompletely exposed on one side to theradiations from an atmosphere at thetemperature in the furnace. With thisassumption, if S^{1} is the area of the

surface, T the absolute temperature of thefurnace gases, t the absolute temperatureof the tube surface of the boiler, the heatabsorbed per hour measured in B. t. u.'s isequal to

_ _ | / T \ / t \ |1600 | |----|^{4} - |----|^{4}| S^{1}|_\1000/ \1000/ _|

In using this formula, or in any workconnected with heat transfer, the externaltemperature of the boiler heating surfacecan be taken as that of saturated steam atthe pressure under which the boiler isworking, with an almost negligible error,since experiments have shown that with asurface clean internally, the externalsurface is only a few degrees hotter thanthe water in contact with the inner surface,even at the highest rates of evaporation.Further than this, it is not conceivable that

in a modern boiler there can be muchdifference in the temperature of the boilerin the different parts, or much differencebetween the temperature of the water andthe temperature of the steam in the drumswhich is in contact with it.

If the total evaporation of a boilermeasured in B. t. u.'s per hour isrepresented by E, the furnace temperatureby T_{1}, the temperature of the gasleaving the boiler by T_{2}, the weight ofgas leaving the furnace and passingthrough the setting per hour by W, thespecific heat of the gas by C, it followsfrom the fact that the total amount of heatabsorbed is equal to the heat receivedfrom radiation plus the heat removed fromthe gases by cooling from the temperatureT_{1} to the temperature T_{2}, that

_ _ | / T \ / t \ |

E = 1600 | |----|^{4} - |----|^{4}| S^{1} +WC(T_{1} - T_{2}) |_\1000/ \1000/_|

This formula can be used for calculatingthe furnace temperature when E, t andT_{2} are known but it must beremembered that an assumption which isprobably, in part at least, incorrect isimplied in using it or in using any similarformula. Expressed in this way, however, itseems more rational than the oneproposed a few years ago by Dr.Nicholson[88] where, in place of thesurface exposed to radiation, he uses thegrate surface and assumes the furnace gastemperature as equal to the firetemperature.

If the heat transfer rate is taken asindependent of the gas temperature andthe heat absorbed by an element of the

surface in a given time is equated to theheat given out from the gas passing overthis surface in the same time, a singleintegration gives

Rs (T - t) = (T_{1} - t) e^{- --} WC

where s is the area of surface passed overby the gases from the furnace to any pointwhere the gas temperature T is measured,and the rate of heat transfer is R. Aswritten, this formula could be used forcalculating the temperature of the gas atany point in the boiler setting. Gastemperatures, however, calculated in thisway are not to be depended upon as it isknown that the transfer rate is notindependent of the temperature. Again, ifthe transfer rate is assumed as varyingdirectly with the weight of the gasespassing, which is Reynolds' suggestion, it

is seen that the weight of the gases entirelydisappears from the formula and as aconsequence if the formula was correct, aslong as the temperature of the gasentering the surface from the furnace wasthe same, the temperatures throughout thesetting would be the same. This is knownalso to be incorrect. If, however, in placeof T is written T_{2} and in place of s iswritten S, the entire surface of the boiler,and the formula is re-arranged, itbecomes:

_ _ WC | T_{1} - t | R= --- Log[89]| --------- | S |_ T_{2} -t _|

This formula can be considered as giving away of calculating an average transferrate. It has been used in this way forcalculating the average transfer rate fromboiler tests in which the capacity has

varied from an evaporation of a little over3 pounds per square foot of surface up to15 pounds. When plotted against the gasweights, it was found that the points werealmost exactly on a line. This line,however, did not pass through the zeropoint but started at a point correspondingto approximately a transfer rate of 2.Checked out against many other tests, thestraight line law seems to hold generallyand this is true even though materialchanges are made in the method ofcalculating the furnace temperature. Theinclination of the line, however, variedinversely as the average area for thepassage of the gas through the boiler. If Ais the average area between all the passesof the boiler, the heat transfer rate inBabcock & Wilcox type boilers withordinary clean surfaces can be determinedto a rather close approximation from theformula:

W R = 2.00 + .0014 - A

The manner in which A appears in thisformula is the same as it would appear inany formula in which the heat transfer ratewas taken as depending upon the productof the velocity and the density of the gasjointly, since this product, as pointed outabove, is equivalent to W/A. Nusselt'sexperiments, as well as those of others,indicate that the ratio appears in theproper way.

While the underlying principles fromwhich the formula for this average transferrate was determined are questionable andat best only approximately correct, itnevertheless follows that assuming thetransfer rate as determinedexperimentally, the formula can be used inan inverse way for calculating the amount

of surface required in a boiler for coolingthe gases through a range of temperaturecovered by the experiments and it hasbeen found that the results bear out thisassumption. The practical application ofthe theory of heat transfer, as developed atpresent, seems consequently to rest onthese last two formulae, which from theirnature are more or less empirical.

Through the range in the production ofsteam met with in boilers now in servicewhich in the marine type extends to theaverage evaporation of 12 to 15 pounds ofwater from and at 212 degrees Fahrenheitper square foot of surface, the constant 2 inthe approximate formula for the averageheat transfer rate constitutes quite a largeproportion of the total. The comparativeincrease in the transfer rate due to achange in weight of the gases is not asgreat consequently as it would be if this

constant were zero. For this reason, withthe same temperature of the gasesentering the boiler surface, there will be agradual increase in the temperature of thegases leaving the surface as the velocity orweight of flow increases and theproportion of the heat contained in thegases entering the boiler which isabsorbed by it is gradually reduced. It is,of course, possible that the weight of thegases could be increased to such anamount or the area for their passagethrough the boiler reduced by additionalbaffles until the constant term in the heattransfer formula would be relativelyunimportant. Under such conditions, aspointed out previously, the final gastemperature would be unaffected by afurther increase in the velocity of the flowand the fraction of the heat carried by thegases removed by the boiler would beconstant. Actual tests of waste heat boilers

in which the weight of gas per square footof sectional area for its passage is manytimes more than in ordinary installationsshow, however, that this condition has notbeen attained and it will probably neverbe attained in any practical installation. Itis for this reason that the conclusions of Dr.Nicholson in the paper referred to and ofMessrs. Kreisinger and Ray in thepamphlet "The Transmission of Heat intoSteam Boilers", published by theDepartment of the Interior in 1912, are notapplicable without modification to boilerdesign.

In superheaters the heat transfer iseffected in two different stages; the firsttransfer is from the hot gas to the metal ofthe superheater tube and the secondtransfer is from the metal of the tube to thesteam on the inside. There is, theoretically,an intermediate stage in the transfer of the

heat from the outside to the inside surfaceof the tube. The conductivity of steel issufficient, however, to keep thetemperatures of the two sides of the tubevery nearly equal to each other so that theeffect of the transfer in the tube itself canbe neglected. The transfer from the hotgas to the metal of the tube takes place inthe same way as with the boiler tubesproper, regard being paid to thetemperature of the tube which increases asthe steam is heated. The transfer from theinside surface of the tube to the steam isthe inverse of the process of the transfer ofthe heat on the outside and seems to followthe same laws. The transfer rate, therefore,will increase with the velocity of the steamthrough the tube. For this reason, internalcores are quite often used in superheatersand actually result in an increase in theamount of superheat obtained from a givensurface. The average transfer rate in

superheaters based on a difference inmean temperature between the gas on theoutside of the tubes and the steam on theinside of the tubes is if R is the transfer ratefrom the gas to the tube and r the rate fromthe tube to the steam:

Rr ----- R + r

and is always less than either R or r. Thisrate is usually greater than the averagetransfer rate for the boiler as computed inthe way outlined in the precedingparagraphs. Since, however, steam cannot,under any imagined set of conditions, takeup more heat from a tube than would waterat the same average temperature, this factsupports the contention made that theactual transfer rate in a boiler mustincrease quite rapidly with thetemperatures. The actual transfer rates insuperheaters are affected by so many

conditions that it has not so far beenpossible to evolve any formula of practicalvalue.

[Illustration: Iron City Brewery of thePittsburgh Brewing Co., Pittsburgh, Pa,Operating in this Plant 2000 Horse Powerof Babcock & Wilcox Boilers]

INDEX

PAGE

Absolute pressure117 Absolute zero

80 Accessibility of Babcock & Wilcoxboiler 59 Acidity in boilerfeed water 106 Actualevap. corresponding to boiler horsepower 288 Advantages of Babcock& Wilcox boilers 61 Stokerfiring 195Water tube over fire tube boilers

61 Air, composition of147 In boiler feed water

106 Properties of147 Required for

combustion 152, 156Specific heat of148 Supplied for combustion

157 Vapor in

149 Volume of147 Weight of147 Alkalinity in boiler feed water

103 Testing feed for103 Altitude, boiling

point of water at 97Chimney sizes corrected for

248 Alum in feed water treatment106 A. S. M. E. code for boiler

testing 267 Analyses,comparison of proximate and ultimate

183 Proximate coal, and heatingvalues 177 Analysis, coal,proximate, methods of 176Coal, ultimate173 Determination of heating value from

173 Analysis, Flue gas155 Flue gas, methods of

160 Flue gas, objectof 155 Anthracitecoal 166Combustion rates with

246 Distribution of167 Draft required for

246 Firing190 Grate ratio for

191 Semi166 Sizes of

190 Steam as aid to burning191 Thickness of fires with

191 Arches, fire brick, asaid to combustion 190 Firebrick, for 304Fire brick, laying305 Automatic stokers, advantages of

195 Overfeed196 Traveling grate

197 Traveling grate,Babcock & Wilcox 194Underfeed 196Auxiliaries, exhaust from, in heating feedwater 113 Superheated steamwith 142 Auxiliarygrates, with blast furnace gas

228 With oil fuel225 With waste heat

235 Babcock, G. H., lecture oncirculation of water in Boilers 28Lecture on theory of steam making

92 Babcock & Wilcox Co., Works atBarberton, Ohio 7 Works atBayonne, N. J. 6Babcock & Wilcox boiler, accessibility of

59 Advantages of61 Circulation of water in

57, 66 Construction of49 Cross boxes

50 Cross drum53 Cross drum, dry

steam with 71Drumheads49 Drums49 Durability75 Evolution of39 Fittings55 Fixtures

55 Fronts53 Handhole fittings50, 51 Headers

50, 51 Inclined header, wrought steel54 Inspection75 Life of

76 Materials entering into theconstruction of 59 Mud drums

51 Path ofgases in 57 Pathof water in 57Rear tube doors of53, 74 Repairs

75 Safety of66 Sections

50 Set for utilizing waste heat236 Set with Babcock & Wilcox chain

grate stoker 12 Set withbagasse furnace 208Set with Peabody oil furnace

222 Supports, cross drum53 Supports, longitudinal drum

52 Tube doors53 Vertical header,

cast iron 58 Verticalheader, wrought steel 48Babcock & Wilcox chain grate stoker

194 Babcock & Wilcoxsuperheater 136Bagasse, composition of

206 Furnace209 Heat, value of

206 Tests of Babcock & Wilcoxboilers with 210 Value ofdiffusion 207Barium carbonate in feed water treatment

106 Barium hydrate in feedwater treatment 106 Barrusdraft gauge 254Bituminous coal, classification of

167 Combustion rates with246 Composition of

177 Distribution of168 Firing methods

193 Semi166 Sizes of

191 Thickness of fire with193 Blast furnace gas,

burners for 228Combustion of228 Composition of

227 Stacks for228 Boiler, Blakey's

23 Brickwork, care of307 Circulation of water in steam

28 Compounds109 Development of

water tube 23 Eve's24 Evolution

of Babcock & Wilcox 39Fire tube, compared with water tube

61 Guerney's24 Horse power

263 Loads, economical283 Perkins'24 Room piping

108 Room practice297 Rumsey's

23 Stevens', John23 Stevens', John Cox

23 Units, numberof 289 Units, sizeof 289 Wilcox's

25 Woolf's23 Boilers,

capacity of 278Care of 291Efficiency of 256Horse power of

265 Operation of291 Requirements of steam

27 Testing267 Boiling point

86 Of various substances86 Of water as affected by

altitude 97 Brick, fire304 Arches305 Classification of

304 Compressionof 303Expansion of303 Hardness of

303 Laying up305 Nodules, ratio of

303 Nodules, size of303 Plasticity of302 Brick, red302 Brickwork, care of

307 British thermal unit83 Burners, blast furnace

gas 228 By-productcoke oven gas 231Natural gas 231

Oil 217Oil, capacity of221 Oil, mechanical atomizing

219 Oil, operation of223 Oil, steam atomizing

218 Oil, steamconsumption of 220

Burning hydrogen, loss due to moistureformed in 261 By-product cokeoven gas burners 231By-product coke oven gas, combustion of

231 By-product coke oven gas,composition and heat value of 231Calorie 83Calorific value (see Heat value).Calorimeter, coal, Mahler bomb

184 Mahler bomb, method ofcorrection 187 Mahlerbomb, method of operation of

185 Calorimeter, steam, compact type ofthrottling 132 Correction for

131 Location ofnozzles for 134Normal reading131 Nozzles134 Separating

133 Throttling129 Capacity of boilers

264, 278 As affecting economy

276 Economical loads283 With bagasse

210 With blastfurnace gas 228With coal 280With oil fuel 224Capacity of natural gas burners

229 Capacity of oil burners221 Carbon dioxide in flue

gases 154 Unreliabilityof readings taken alone 162Carbon, fixed165 Incomplete combustion of, loss due to

158 Monoxide, heat value of151 Monoxide, in flue

gases 155Unconsumed in ash, loss due to

261 Care of boilers when out ofservice 300 Casings,boilers 307Causticity of feed water

103 Testing for

105 Celsius thermometer scale79 Centigrade thermometer

scale 79 Chain gratestoker, Babcock & Wilcox194 Chemicals required in feed watertreatment 105 Chimney gases,losses in 158, 159Chimneys (see Draft). Correction indimensions for altitude 248Diameter of 243

Draft available from241 Draft loss in239 For blast furnace gas

253 For oil fuel251 For wood fuel

254 Height of243 Horse power they will serve

250 Circulation of water inBabcock & Wilcox boilers 57, 66 Ofwater in steam boilers28 Results of defective62, 66, 67 Classification of coals

166 Fire brick304 Feed water difficulties

100 Fuels165 Cleaners, turbine tube

299 Cleaning, ease of,Babcock & Wilcox boilers 73Closed feed water heaters

111 Coal, Alaska169 Analyses and heat value

177 Analysis, proximate176 Analysis, ultimate

173 Anthracite166 Bituminous

167 Cannel167 Classification

of 165, 166Combustion of190 Comparison with oil

214 Consumption, increase due tosuperheat 139 Distribution of

167 Formation of165 Lignite

167 Records293

Semi-anthracite166 Semi-bituminous

166 Sizes of anthracite190 Sizes of bituminous

191 Code of A. S. M. E. forboiler testing 267 Coefficientof expansion of various substances

87 Coke171 Oven gas, by-product, burners

231 Oven gas, by-product,combustion of 231 Ovengas, by-product, composition and heatvalue of 231 Coking method of firing

195 Color asindication of temperature91 Combination furnaces

224 Combustible in fuels150 Combustion

150 Air required for152, 156 Air supplied for

157 Combustion ofcoal 190 Ofgaseous fuels 227Of liquid fuels

212 Of solid fuels other than coal201 Composition of bagasse

205 Blast furnace gas227 By-product coke

oven gas 231 Coals177 Natural

gas 229 Oil213 Wood

201Compounds, boiler

109 Compressibility of water97 Compression of fire brick

303 Condensation, effect ofsuperheated steam on 140 Insteam pipes 313Consumption, heat, of engines

141 Correction, stem, forthermometers 80 For

normal reading in steam calorimeter131 For radiation, bomb

calorimeter 187 Corrosion101, 106

Coverings, pipe315 Cross drum, Babcock & Wilcox boiler

52, 53, 60 Dry steam with71 Draft area as

affecting economy in Babcock & Wilcoxboilers 70 Available from chimneys

241 Draft loss in chimneys239 Loss in boilers

245 Loss in flues243 Loss in

furnaces 245 Draftrequired for anthracite246 Required for various fuels

246 Drums, Babcock & Wilcox,cross 53 Cross, boxes

50 Heads49 Longitudinal49 Manholes

49 Nozzles on50 Dry steam in

Babcock & Wilcox boilers71 Density of gases

147 Steam115 Dulong's formula for heating value

173 Ebullition, point of86 Economizers

111 Efficiency of boilers,chart of 258Combustible basis256 Dry coal basis

256 Increase in, due to superheaters139 Losses in (see Heat

balance) 259 Testing267 Test _vs._

operating 278Variation in, with capacity

284 With coal288 With oil

224 Ellison draft gauge254 Engine, Hero's

13 Engines, superheated steamwith 141 Equivalentevaporation from and at 212 degrees

116 Eve's boiler24 Evolution of Babcock & Wilcox

boiler 39 Exhaust steamfrom auxiliaries 113Expansion, coefficient of

87 Of fire brick303 Of pipe

315 Pyrometer89 Factor of evaporation

117 Fahrenheit thermometer scale79 Fans, use of, in waste

heat work 233 Feedwater, air in 106As affecting capacity279 Boiler100 Feed water heaters, closed

111 Economizers111 Open

111 Feed water heating, methods

of 111 Saving by110 Feed water,

impurities in 100Lines 312Method of feeding110 Feed water treatment

102 Chemical102 Chemical, lime and soda

process 102 Chemical,lime process 102Chemical, soda process

102 Chemicals used in lime and sodaprocess 105 Combined heatand chemical 105 Heat

102 Lessusual reagents 106Firing, advantages of stoker

195 Methods for anthracite190 Bituminous193 Lignite

195 Fittings, handhole inBabcock & Wilcox boilers 50, 51

Pipe 311Superheated steam145 With Babcock & Wilcox boilers

55 Fixtures with Babcock &Wilcox boilers 55 Flanges,pipe 309 Flowof steam into pressure above atmosphere

317 Into the atmosphere328 Through orifices

317 Through pipes317 Flue gas analysis

155 Conversionof volumetric to weight 161Methods of making160 Object of155 Orsat apparatus

159 Flue gas, composition of155 Losses in158, 159 Weight per pound of

carbon in fuel 158 Weightper pound of fuel 158Weight resulting from combustion

157 Foaming102, 107 Fuel analysis, proximate

176 Ultimate173 Fuel calorimeter,

Mabler bomb 184 Tests,method of making186 Fuels, classification of

165 Gaseous, and their combustion227 Fuels, liquid, and their

combustion 212 Solid, coal190 Solid,

other than coal 201Furnace, bagasse209 Blast furnace gas

228 By-product coke oven gas231 Combination wood and

oil 225 Efficiency of283 Natural gas229 Peabody oil

222 Webster55 Wood

burning 201, 202

Galvanic action107 Gas, blast furnace, burners

228 Combustion of228 Composition of

227 Gas, by-product cokeoven, burners 231Combustion of231 Composition of and heat value

231 Gas, natural, burners229 Combustion of

229 Composition andheat value of 229 Gases,chimney, losses in 158,159 Density of163 Flue (see Flue gases). Path of inBabcock & Wilcox boilers57 Waste (see Waste heat)

232 Gaskets312 Gauges, draft, Barrus

254 Ellison255 Peabody255 U-tube

254 Gauges, vacuum117 Grate ratio for anthracite

191 Gravity of oils214 Grooving102 Guerney's boiler

24 Handholefittings for Babcock & Wilcox boilers50, 51 Handholes in Babcock & Wilcox

boilers 50, 51 Hardness ofboiler feed water 102Permanent102 Temporary

102 Testing for105 Hardness of fire brick

303 Heat and chemical methods oftreating feed water 105 And itsmeasurement 79Balance 262Consumption of engines

141 Latent84 Of liquid

120 Sensible

84 Specific (see Specific heat)83 Total

86 Transfer323 Heat value of bagasse

205 By-product coke oven gas231 Coal

177 Heat value of fuels,determination of 173Determination of Kent's approximatemethod 183 High and low

174 Heat value ofnatural gas 229 Oil

215 Wood201 Heat

waste (see Waste heat)232 Heaters, feed water, closed

111 Economizers111 Open

111 Heating feed water, savingby 110 Hero's engine

13 High and lowheat value of fuels 174

High pressure steam, advantages of use of119 High temperature

measurements, accuracy of 89Horse power, boiler

265 Evaporation (actual) correspondingto 288 Rated boiler

265 Stacks for various, ofboilers 250 Hydrogen influe gases 156 Ice,specific heat of 99"Idalia", tests with superheated steam onyacht 143 Impurities in boiler feedwater 100 Incompletecombustion of carbon, loss due to

158 Injectors, efficiency of112 Relative efficiency of, and

pumps 112 Iron alum infeed water treatment 106Kent, Wm., determination of heat valuefrom analysis 183 Stack table

250 Kindling point150 Latent heat

84, 115 Laying of firebrick 305 Redbrick 305Lignite, analyses of181 Combustion of

195 Lime and soda treatment of boilerfeed 102 Used in chemicaltreatment of feed 105 Limetreatment of boiler feed water

102 Liquid fuels and their combustion212 Loads, economical boiler

283 Losses due toexcess air 158 Dueto unburned carbon158 Due to unconsumed carbon in the ash

261 Losses in efficiency (seeHeat balance). In flue gases

158, 159 Low water in boilers298 Melting points of

metals 91 Mercurialpyrometers 89Moisture in coal, determination of

176 In fuels, losses due to259 In steam, determination of

129 Mud drum ofBabcock & Wilcox boiler51 Napier's formula for flow of steam

321 Natural gas, burners for229 Combustion of

229 Composition andheat value of 229 Nitrateof silver in testing feed water105 Nitrogen, as indication of excess air

157 In air147 In flue gases157 Nodules, fire brick, ratio of

303 Size of303 Normal reading,

throttling calorimeter 131Nozzles, steam sampling for calorimeter

134 Location of134 Oil fuel, burners (see

Burners). Capacity with224 Combustion of

217 Comparison with coal214 Composition and

heat value of 213Efficiency with224 Furnaces for

221 Gravity of214 In combination with other fuels

224 Stacks for251 Tests with

224 Open hearth furnace,Babcock & Wilcox boiler set for utilizingwaste heat from 236Open heaters, feed water

111 Operation of boilers291 Optical pyrometers

91 Orsat apparatus160 Oxalate of soda in

feed water treatment 106Oxygen in air147 Flue gases155 Peabody draft gauge

255 Formulae for coal calorimeter

correction 188 Furnace for oilfuel 221, 222 Oilburner 218Peat 167Perkins' boiler24 Pfaundler's method of coal calorimeterradiation correction 187 Pipe coverings

315 Data308 Expansion of

315 Pipe fittings311 Flanges

309 Flow ofsteam through 317Radiation from bare and covered

314 Sizes312 Supports for

315 Piping, boiler room308 Pitting

102 Plant records, coal293 Draft

294 Temperature294 Water

293 Plasticity of fire brick302 Pressed fuels

171 Priming in boilers102 Methods of

treating for 107Properties of water96 Proximate analyses of coal

177 Proximate analysis173 Method of making

176 Pulverized fuels170 Pump, efficiency of

feed 112 Pyrometers,expansion 89Mercurial 89Optical 91Radiation 90Thermo-electric90 Quality of steam

129 Radiation correction for coalcalorimeter 187, 188 Correctionfor steam calorimeter 131Effect of superheated steam on

140 From pipes314 Losses in efficiency due to

307 Pyrometers90 Ratio of air supplied to

that required for combustion 157Reagents, less usual in feed treatment

106 Records, plant, coal293 Draft

294 Temperature294 Water

293 Requirements of steamboilers 27 Asindicated by evolution of Babcock &Wilcox 45 Rumsey's boiler

23 Safety of Babcock &Wilcox boilers 66 Saltsresponsible for scale101 Solubility of101 Sampling coal

271 Nozzles for steam134 Nozzles for steam, location of

134 Steam

134 Steam, errors in135 Saturated air

149 Saving by heatingfeed 110 Withsuperheat in "Idalia" tests143 With superheat in prime movers

140, 142 Scale (seeThermometers) 101Sea water, composition of

97 Sections, Babcock & Wilcox boiler50 Selection of boilers

277 Sensible heat84 Separating steam

calorimeter 132 Sizes ofanthracite coal 190Bituminous coal191 Smoke, methods of eliminating

197 Smokelessness, relativenature of 197 Withhand-fired furnaces199 With stoker-fired furnaces

199 Soda, lime and, treatment of

feed 103 Oxalate of, intreatment of feed 106Removal of scale aided by

300 Silicate of, in treatment of feed106 Treatment of boiler feed

103 Space occupied byBabcock & Wilcox boilers 66Specific heat83 Specific heat of air

148 Ice99 Saturated steam

99 Specific heat of superheated steam137 Various solids, liquids

and gases 85 Water99 Spreading

method of firing 193Stacks and draft (see Chimneys)

237 Stacks for blast furnace gas228 Oil fuel

251 Wood202, 254 Stayed surfaces,

absence of, in Babcock & Wilcox boilers

69 Difficulties arising from use of67 Steam

115 As aid to combustion ofanthracite 191 As aid tocombustion of lignite 195Consumption of prime movers

289 Density of115 Flow of, into atmosphere

320 Flow of, into pressureabove atmosphere 318 Flowof, through pipes 317High pressure, advantage of

119 History of generation and use of13 Making, theory of

92 Moisture in129 Properties of, for

vacuum 119Properties of saturated122 Properties of superheated

125 Quality of129 Saturated115 Specific heat of saturated

99 Specific heat ofsuperheated 137Specific volume of115 Superheated

137 Superheaters (see Superheatedsteam). Steaming, quick, with Babcock &Wilcox boilers 73 StemCorrection, thermometer

80 Stevens, John, boiler23 Stevens, John Cox, boiler

23 Stokers, automatic,advantages of 195Babcock & Wilcox chain grate

194 Overfeed196 Smokelessness with

199 Traveling grate197 Underfeed

196 Superheated steam137 Additional fuel

for 139 Effect oncondensation 140Effect on radiation

140 Fittings for use with145 "Idalia" tests with

143 Specific heat of137 Variation in temperature of

145 With turbines142 Superheater,

Babcock & Wilcox 136Effect of on boiler efficiency

139 Supports, Babcock & Wilcox boiler52, 53 Tan bark

210 Tar, water gas225 Temperature,

accuracy of high, measurements89 As indicated by color

91 Of waste gases232 Records294 Test conditions _vs._ operating

conditions 278 Testing, boiler,A. S. M. E. code for 267 Testsof Babcock & Wilcox boilers with bagasse

210 Coal280 Oil

224 Theory of steam making92 Thermo-electric pyrometers

90 Thermometer scale,celsius 79Thermometer scale, centigrade

76 Fahrenheit79 R�umur

79 Thermometer scales, comparisonof 80 Conversion of

80 Thermometerstem correction for 80Thermometers, glass for

79 Throttling calorimeter129 Total heat

86, 115 Treatment of boiler feedwater (see Feed water) 102Chemicals used in105 Less usual reagents in

106 Tube data309 Doors in Babcock & Wilcox

boilers 53 Tubes inBabcock & Wilcox boilers

50 Ultimate analyses of coal183 Analysis of fuels

173 Unaccounted losses inefficiency 261Unconsumed carbon in ash

261 Units, boiler, number of289 Size of

289 Units, British thermal83 Unreliability of CO_{2}

readings alone 162 Vacuumgauges 117Properties of steam for119 Valves used with superheated steam

312 Variation in propertiesof saturated steam 119Superheat from boilers

145 Volume of air147 Water96 Volume, specific, of steam

115 Waste heat, auxiliary grateswith boilers for 235 Babcock &Wilcox boilers set for use with

236 Boiler design for233 Curve of temperature, heat

absorption, and heating surface 235Draft for 233Fans for use with233 Power obtainable from

232 Temperature of, from variousprocesses 232 Utilization of

232 Water, air inboiler feed 106Boiling points of97 Compressibility of

97 Water feed, impurities in100 Methods of feeding to boiler

132 Saving by heating110 Treatment (see

Feed water). Water-gas tar225 Heat of the liquid

120 Path of, in Babcock &Wilcox boilers 57Properties of 96Records 293

Specific heat of99 Volume of96 Weight of96, 120 Watt, James

17 Weathering of coal169 Webster furnace

55 Weight of air147 Wilcox boiler

25 Wood, combustion ofdry 202 Wet

203 Compositionand heat value of 201Furnace design for201 Moisture in201 Sawmill refuse

202 Woolf s boiler24 Zero, absolute

81

FOOTNOTES

[Footnote 1: See discussion by George H.Babcock, of Stirling's paper on"Water-tube and Shell Boilers", inTransactions, American Society ofMechanical Engineers, Volume VI., Page601.]

[Footnote 2: When one temperature aloneis given the "true" specific heat is given;otherwise the value is the "mean" specificheat for the range of temperature given.]

[Footnote 3: For variation, see Table 13.]

[Footnote 4: Where range of temperatureis given, coefficient is mean over range.]

[Footnote 5: Coefficient of cubicalexpansion.]

[Footnote 6: Le Chatelier's Investigations.]

[Footnote 7: Burgess-Le Chatelier.]

[Footnote 8: For accuracy of hightemperature measurements, see Table 7.]

[Footnote 9: Messrs. White & Taylor Trans.A. S. M. E., Vol. XXI, 1900.]

[Footnote 10: See Scientific AmericanSupplement, 624, 625, December, 1887.]

[Footnote 11: 460 degrees below the zeroof Fahrenheit. This is the nearestapproximation in whole degrees to thelatest determinations of the absolute zeroof temperature]

[Footnote 12: Marks and Davis]

[Footnote 13: See page 120.]

[Footnote 14: See Trans., A. S. M. E., Vol.XIV., Page 79.]

[Footnote 15: Some waters, not naturallyacid, become so at high temperatures, aswhen chloride of magnesia decomposeswith the formation of free hydrochlorideacid; such phenomena become moreserious with an increase in pressure andtemperature.]

[Footnote 16: L. M. Booth Company.]

[Footnote 17: Based on lime containing 90per cent calcium oxide.]

[Footnote 18: Based on soda containing 58per cent sodium oxide.]

[Footnote 19: See Stem Correction, page

80.]

[Footnote 20: See pages 125 to 127.]

[Footnote 21: The actual specific heat at aparticular temperature and pressure is thatcorresponding to a change of one degreeone way or the other and differsconsiderably from the average value forthe particular temperature and pressuregiven in the table. The mean values givenin the table give correct results whenemployed to determine the factor ofevaporation whereas the actual values atthe particular temperatures and pressureswould not.]


[Footnote 23: Ratio by weight of O to N inair.]

[Footnote 24: 4.32 pounds of air containsone pound of O.]

[Footnote 25: Per pound of C in the CO.]

[Footnote 26: Ratio by volume of O to N inair.]

[Footnote 27: Available hydrogen.]

[Footnote 28: See Table 31, page 151.]

[Footnote 29: This formula is equivalent to(10) given in chapter on combustion. 34.56= theoretical air required for combustionof one pound of H (see Table 31).]

[Footnote 30: For degree of accuracy ofthis formula, see Transactions, A. S. M. E.,Volume XXI, 1900, page 94.]

[Footnote 31: For loss per pound of coal

multiply by per cent of carbon in coal byultimate analysis.]

[Footnote 32: For loss per pound of coalmultiply by per cent of carbon in coal byultimate analysis.]

[Footnote 33: The Panther Creek Districtforms a part of what is known as theSouthern Field; in the matter of hardness,however, these coals are more nearly akinto Lehigh coals.]

[Footnote 34: Sometimes called WesternMiddle or Northern Schuylkill Field.]

[Footnote 35: Geographically, theShamokin District is part of the WesternMiddle Mahanoy Field, but the coals foundin this section resemble more closelythose of the Wyoming Field.]


[Footnote 37: U. S. Geological Survey.]

[Footnote 38: See "Steam Boiler Economy",page 47, First Edition.]

[Footnote 39: To agree with Pfaundler'sformula the end ordinates should be givenhalf values in determining T", _i. e._, T" =((Temp. at B + Temp. at C) �2 + Temp. allother ordinates) �N]

[Footnote 40: B. t. u. calculated.]

[Footnote 41: Average of two samples.]

[Footnote 42: Assuming bagassetemperature = 80 degrees Fahrenheit andexit gas temperature = 500 degreesFahrenheit.]

[Footnote 43: Dr. Henry C. Sherman.Columbia University.]

[Footnote 44: Includes N.]

[Footnote 45: Includes silt.]

[Footnote 46: Net efficiency = grossefficiency less 2 per cent for steam used inatomizing oil.

Heat value of oil = 18500 B. t. u.

One ton of coal weighs 2000 pounds. Onebarrel of oil weighs 336 pounds. Onegallon of oil weighs 8 pounds.]

[Footnote 47: Average of 20 samples.]

[Footnote 48: Includes H and CH_{4}.]

[Footnote 49: B. t. u. approximate. For

method of calculation, see page 175.]

[Footnote 50: Temperatures are averageover one cycle of operation and may varywidely as to maximum and minimum.]

[Footnote 51: Dependant upon length ofkiln.]

[Footnote 52: Results secured by thismethod will be approximately correct.]

[Footnote 53: See "Chimneys for CrudeOil", C. R. Weymouth, Trans. A. S. M. E.,Dec. 1912.]

[Footnote 54: To determine the portion ofthe fuel which is actually burned, theweight of ashes should be computed fromthe total weight of coal burned and thecoal and ash analyses in order to allow forany ash that may be blown away with the

flue gases. In many cases the ash socomputed is considerably higher than thatfound in the test.]

[Footnote 55: As distinguished from theefficiency of boiler, furnace and grate.]

[Footnote 56: To obtain the efficiency ofthe boiler as an absorber of the heatcontained in the hot gases, this should bethe heat generated per pound ofcombustible corrected so that any heat lostthrough incomplete combustion will not becharged to the boiler. This, however, doesnot eliminate the furnace as the presenceof excess air in the gases lowers theefficiency and the ability to run withoutexcess air depends on the design andoperation of the furnace. The efficiencybased on the total heat value per pound ofcombustible is, however, ordinarily takenas the efficiency of the boiler

notwithstanding the fact that it necessarilyinvolves the furnace.]

[Footnote 57: See pages 280 and 281.]

[Footnote 58: Where the horse power ofmarine boilers is stated, it generally refersto and is synonymous with the horse powerdeveloped by the engines which theyserve.]

[Footnote 59: In other countries, boilersare ordinarily rated not in horse power butby specifying the quantity of water theyare capable of evaporating from and at 212degrees or under other conditions.]

[Footnote 60: See equivalent evaporationfrom and at 212 degrees, page 116.]

[Footnote 61: The recommendations arethose made in the preliminary report of the

Committee on Power Tests and at the timeof going to press have not been finallyaccepted by the Society as a whole.]

[Footnote 62: This code relates primarily totests made with coal.]

[Footnote 63: The necessary apparatus andinstruments are described elsewhere. Nodefinite rules can be given for location ofinstruments. For suggestions on location,see A. S. M. E. Code of 1912, Appendix 24.For calibration of instruments, see Code,Vol. XXXIV, Trans., A. S. M. E., pages1691-1702 and 1713-14.]

[Footnote 64: One to two inches for smallanthracite coals.]

[Footnote 65: Do not blow down thewater-glass column for at least one hourbefore these readings are taken. An

erroneous indication may otherwise becaused by a change of temperature anddensity of the water within the column andconnecting pipe.]

[Footnote 66: Do not blow down thewater-glass column for at least one hourbefore these readings are taken. Anerroneous indication may otherwise becaused by a change of temperature anddensity of the water within the column andconnecting pipe.]

[Footnote 67: For calculations relating toquality of steam, see page 129.]

[Footnote 68: Where the coal is very moist,a portion of the moisture will cling to thewalls of the jar, and in such case the jarand fuel together should be dried out indetermining the total moisture.]

[Footnote 69: Say � ounce to 2 ounces.]

[Footnote 70: For methods of analysis, seepage 176.]

[Footnote 71: For suggestions relative toSmoke Observations, see A. S. M. E. Codeof 1912, Appendix 16 and 17.]

[Footnote 72: The term "as fired" meansactual condition including moisture,corrected for estimated difference inweight of coal on the grate at beginningand end.]

[Footnote 73: Corrected for inequality ofwater level and steam pressure atbeginning and end.]

[Footnote 74: See Transactions, A. S. M. E.,Volume XXXIII, 1912.]

[Footnote 75: For methods of determining,see Technologic Paper No. 7, Bureau ofStandards, page 44.]

[Footnote 76: Often called extra heavypipe.]

[Footnote 77: See Feed Piping, page 312.]

[Footnote 78: See Superheat Chapter, page145.]

[Footnote 79: See Radiation from SteamLines, page 314.]

[Footnote 80: D, the density, is taken as themean of the density at the initial and finalpressures.]

[Footnote 81: Diameters up to 5 inches,inclusive, are _actual_ diameters ofstandard pipe, see Table 62, page 308.]

[Footnote 82: Diameters up to 4 inches,inclusive, are _actual_ internal diameters,see Table 62, page 308.]

[Footnote 83: H. P. Jordan, "Proceedings ofthe Institute of Mechanical Engineers",1909.]

[Footnote 84: "Zeitschrift des VereinesDeutscher Ingenieur", 1909, page 1750.]

[Footnote 85: Heinrich Gr�er--Zeit. d. Ver.Ing., March 1912, December 1912.Leprince-Ringuet--Revue de Mecanique.July 1911. John Perry--"The Steam Engine".T. E. Stanton--Philosophical Transactions,1897. Dr. J. T. Nicholson--ProceedingsInstitute of Engineers & Shipbuilders inScotland, 1910. W. E. Dally--ProceedingsInstitute of Mechanical Engineers, 1909.]

[Footnote 86: Proceedings Royal Society,Vol. LXXI.]

[Footnote 87: Zeitschrift des VereinesDeutscher Ingenieur, 1910, page 1154.]

[Footnote 88: Proceedings Institute ofEngineers and Shipbuilders, 1910.]

[Footnote 89: Natural or HyperbolicLogarithm.]

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