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Copyright © May 1997, Pacific Gas and Electric Company, all rights reserved. Revised 4/25/97

APPLICATION NOTE

An In-Depth Examination of an EnergyEfficiency Technology

Energy Efficient

Operations and

Maintenance

Strategies for

Industrial Gas Boilers

Summary

Large, complex and widely used, indus-trial boilers are major consumers of fuel.

Proper operations and maintenance(O&M) procedures must be followed toensure safe and efficient operations.

It is often assumed that good O&M pro-vides no energy savings because it issimply “what should be done.” Actually,without proper O&M energy consump-tion can increase dramatically—asmuch as 10 to 20 percent as the systemslowly gets out of adjustment. Thus,

savings from energy-efficient O&Mstrategies can be thought of as avoidedconsumption.

Maintenance includes keeping physicalcomponents in good working order andwithin design specifications. This in-cludes cleaning heat transfer surfaces,controls tuning and maintaining insula-tion. Before boiler tune-ups, system di-agnostics should be performed and anydeficient equipment brought back tospecifications. Changes to designspecifications can be made, but all im-plications of the change must first beconsidered.

Operational practices include equipmentadjustments, handling and analysis ofboiler log information and identificationof boiler performance goals. Operationsand maintenance practices overlap andgreatly influence each other.

Due to the complexity and importance ofefficient operation of industrial boilers,specialists are often contracted to per-form some or all O&M functions.

Summary .............................................1

How Operations and Maintenance

Strategies Save Energy......................2Energy-Saving Operations andMaintenance Strategies .....................3

Applicability ........................................9

Field Observations to AssessFeasibility............................................9

Estimation of Energy Savings.........10

Factors That Influence Operations

and Maintenance Costs ...................11

Laws, Codes, and Regulations........11

Definitions of Key Terms .................12

References to More Information......12

Trade Organizations.........................13

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PG&E Energy Efficiency Information ©

“Industrial Gas Boiler O&M Strategies”

How Operations andMaintenance Strategies

Save Energy

Proper operation and maintenance ofboilers will help derive useful work fromas much of the fuel as practical, byavoiding unnecessary efficiency lossesand matching boilers to loads. It is im-portant to establish operational goals

and to maintain accurate logs for eachboiler so that variances can be quicklyidentified and remedied.

Efficiency losses are avoided by main-taining clean heat transfer surfaces, op-

timizing the air-to-fuel ratio 1 of the

burner, keeping steam vessels andpipes properly insulated, minimizingsteam and boiler gas leakage, followinggood blowdown procedures, and mini-mizing steam pressure in keeping withload requirements.

It is also important to match the boilersin use to the steam or hot water load.For facilities with multiple boilers andvariable loads, achieving the most effi-

cient combination of boilers may meanoccasionally shutting down some to al-low others to operate at a more efficientfiring rate. Controls must be properlyadjusted and coordinated for continuous

1Bold-Italic words are defined in the section

titled Definition of Key Terms.

Maintain StackGas Analyzers

Maintain Clean HeatTransfer Surfaces

Maintain Insulation on

Boiler and Piping

Minimize Blowdown whileMaintaining Water Quality

Minimize SteamPressure

OptimizeAir/Fuel

Rat io

MaintainControls

Figure 1: Boiler systems and components requiring operations and maintenance strategies for efficient performance. (Reprinted with permission from Boiler Operator’s Guide, 3

rd ed. By A. Kohan and H.

Spring. Copyright 1991 by McGraw-Hill Cos. All rights reserved)

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delivery of steam or hot water to proc-esses that are likely to be dynamic.

Energy-Saving Operations

and Maintenance Strategies

Boiler maintenance refers to keepingthe boiler itself in efficient working con-dition. Boiler operation refers to ad-

justments and procedures that ensurethe boiler meets its loads efficiently andsafely. This document addresses op-erations and maintenance (O&M)strategies as they apply to energy con-siderations, not safety issues. Addingenergy-saving equipment (e.g., econo-mizers, air pre-heaters and deaerators)is not considered.

Boiler Maintenance

Boiler maintenance must be systematic.Applied properly, it minimizes energyconsumption and downtime due to un-anticipated failures. Responsibilityshould be assigned for performing andkeeping written records of daily, weekly,monthly and annual maintenance tasks.Checklists should be used. They ensurethe operator does not forget any tasks,serve as records of work done and are away to communicate the boilers’ status.Completed checklists should be postedfor all operators to review. Old checklistsshould be systematically filed for refer-ence. A list of specific energy-relatedmaintenance items follows.

Boiler System Diagnostics and Inspection

The tune-up of a fire-tube or smallerwater-tube industrial boiler can usuallybe performed with only minimal ad-vanced preparation, but large industrial

boilers warrant diagnostic testing beforeformal tune-up. The primary aim here isto identify off-design equipment per-formance or undesirable site-specificoperating practices/constraints. If

maintenance, adjustment, calibration ormodification of operating practices areneeded, they should be completed be-fore attempting to optimize boiler perfor-mance.

Before analyzing stack gas, negative- draft boilers should be checked for airleakage using smoke-generating sticks,the flame of a butane lighter or ultra-sonic equipment. Leaks need to besealed so the quantity of air supplied forcombustion can be controlled; suchcontrol is essential if stack gas tests areto be accurate. High oxygen readingscaused by air leaks can lead operatorsto reduce the air-to-fuel ratio, resultingin unburned combustibles (i.e., wastedfuel) in the stack. Note that air leakagefrom positive-draft boilers will be from the boiler to the surrounding area. Thisdoes not affect stack gas tests, butposes a potential hazard and should beremedied. Ultrasonic equipment can beused to detect such leaks.

The boiler should also be checked forsteam and water leaks. Ultrasonicprobes can be used to detect steamleaks in water-tube boilers. For anyboiler with a water storage tank leakagecan be checked by shutting off themake-up water supply and observingthe water level in the tank over a speci-

fied period of time. A decrease issymptomatic of a potential tube leak.Prior to testing, the operator must beabsolutely certain low-water cutoffcontrols are in place and functioningproperly.

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Large industrial boilers (100,000 -500,000 Ib/hr steam flow) tend to haveparticular design and operating charac-teristics that make diagnostics and tun-ing more complex. For example, they

are generally field-erected to custom-ized designs and component selection.Multiple burners are common. Combus-tion controls tend to be more complexand auxiliary equipment such aseconomizers and air preheaters is morelikely to be present. Older balanced-draft units may have significant airleakage. For these reasons it is oftendesirable to hire a specialist to performdiagnostic and tuning work.

Combustion non-uniformity should betested as part of the diagnosis. Identify-ing and eliminating non-uniform com-bustion requires a very disciplined ap-proach; methods are discussed in theBoiler Operations section.

Maintain Clean Heat Transfer Surfaces - Fire Side

Although it is unlikely to be significant

for gas boilers, soot can build up on thefire side of heat transfer surfaces, inhib-iting heat transfer. Less heat is trans-ferred to the water and more heat is car-ried out in the flue gases. Elevatedstack temperatures may indicate fouling of heat transfer surfaces. It is esti-mated that each 40°F rise in stack tem-perature cuts efficiency 1 percentagepoint. Before assuming stack tempera-ture increases are due to fouling,

changes to firing rates, exhaust gascomposition and combustion air tem-perature should be considered. As ageneral rule, stack gas temperatureshould not be more than 150°F abovethe temperature of saturated steam atthe boiler operating pressure.

Fire side fouling is not likely when natu-ral gas is being burned. The most likelycauses are low air-to-fuel ratios, im-proper fuel preparation or malfunction-ing burners. Gas-burning fire-tube boil-

ers should have their tubes inspected atleast once a year, more frequently forsystems with problematic combustion.The tubes should be cleaned (or“punched”) as needed. Many devicesare available to do this; they may in-clude a vacuum or water attachment toremove the loosened soot.

A 1/32-inch layer of soot reduces boilerefficiency an estimated 2.5 percent, a1/8-inch layer an estimated 8.5 percent.To illustrate, consider a boiler generat-ing 200 psig/500°F steam at a rate of50,000 lb/hr and an 85 percent effi-ciency using $.50/therm natural gas.Generation costs would be approxi-mately $6.00 per 1,000 pounds ofsteam. Assuming 7,000 annual operat-ing hours and average annual sootbuildup of 1/16-inch, the annual cost ofthe resulting 4.5 percent efficiency losswould be approximately $84,000.

Maintain Clean Heat Transfer Surfaces - Water Side

Scale deposits on the water side ofboiler tubes present problems similar tothose described above. One differenceis that the fire side may still be clean,allowing the tubes to absorb heat with-out any means of dissipation. This canlead to tube failure, especially in water-

tube boilers.

The relationship between scale thick-ness and efficiency losses is similar tothose for soot buildup, although lossesmay be twice those for soot, dependingon the type of scale. The best way todeal with scale is not to let it form in the

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first place. This is accomplished by acombination of properly treating theboiler water in water softeners before itenters the boiler, by the injection ofchemicals into the boiler water and byblowing down the system. Table 1 pro-vides acceptable concentration limits of

common impurities. Scale formation islikely beyond these limits.

Removing scale that has already formedcan be accomplished by mechanicalmeans, water treatment or acid clean-ing. Mechanical and acid cleaning re-quire care to avoid damaging the tubes;water cleaning requires care not to re-move scale too quickly. Removing scaletoo quickly can result in large pieces of

removed scale restricting water flows,leading to localized overheating andpossible catastrophic failure.

Maintenance of Insulation

The primary mechanism for heat lossthrough the skin of an uninsulated boiler

is radiant heat loss. The higher thetemperature of the boiler skin (insulatedor not), the greater the radiant heat lossto the surroundings. Note that a boilerat partial load has a skin temperaturethe same as if it were at full load, aslong as the steam it is generating stays

at the same temperature; thus radiantlosses are the same at either load.However, the losses are a higher per-centage of the fuel consumed at thelower firing rate. Therefore, in boilersthat run at lower loads for significant pe-riods, good insulation is more important.

The first inch of insulation reduces heatloss by about 90 percent. Each addi-tional inch obviously will have much less

impact. One rule of thumb is that anysurface above 120°F should be insu-lated, including boiler surfaces, steam orcondensate piping and fittings. Remov-able insulating jackets are available forvalves, flanges, pressure-reducingvalves, steam traps and other fittings.Note that a 6-inch gate valve may have

BoilerPressure

Range (psig)

Total Solids(ppm)

Total Alka-linity (ppm)

SuspendedSolids(ppm)

Silica(ppm)

0 - 300 3,500 700 300 125

301 - 450 3,000 600 250 90

451 - 600 2,500 500 150 50

601 - 750 2,000 400 100 35

751 - 900 1,500 300 60 20

901 - 1,000 1,250 250 40 8

1,001 - 1,500 1,000 200 20 2.5

Table 1: Acceptable Concentration Limits of Boiler Water Solids

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more than 6 square feet of surface areaover which to radiate heat from thesystem.

Damaged, missing or wet insulation

should be repaired or replaced. The in-sulating value of wet insulation is vastlycompromised and what is making it wetneeds to be identified and removed be-fore replacing it. Common causes of wetinsulation are leaking valves, externalpiping leaks, tube leaks or leakage fromadjacent equipment.

Boiler Operations

Natural gas-fired boiler operationalproblems commonly fall into three majorcategories:

Operation at non-optimum air-to-fuelratios

Lack of combustion uniformity

Combustion controls/instrumentationplacement issues

These types of problems are discussedin this section to aid in their identifica-tion. Other operational issues are alsodiscussed.

Air-to-Fuel Ratio

Efficient operation of any combustionequipment is highly dependent on aproper air-to-fuel ratio. Due to the me-chanics of combustion, it is necessary to

provide more air than would be requiredto provide exactly the right quantity ofoxygen (O2) to burn all the fuel without

any O2 left over. Because air is com-

prised of approximately 21 percent O2

and 79 percent nitrogen (N2), in deliver-

ing the right amount of O2, nearly four

times as much N2 is also delivered. Ni-

trogen absorbs heat and carries it outthe stack, resulting in a loss to the sys-tem. Minimizing excess air , consistentwith complete combustion, minimizes

this heat loss.

Complete carbon combustion formscarbon dioxide (CO2) and heat is re-

leased. Incomplete combustion formscarbon monoxide (CO) and less thanone-third as much heat is released, al-though CO does have the potential forcompleting combustion to form CO2 if

another oxygen atom can be found. COis an unburned combustible and, in the

stack gas, an efficiency loss to the sys-tem. Figure 2 shows the relationship ofexcess (or deficient) air to unburnedcombustibles, CO2 and O2 in the flue

gas.

Excess air is determined from the con-centration of either CO2 or O2 in the

stack gas, but O2 provides more accu-

rate results. Many stack gas analyzerscombine the measurement of either O2

or CO2 with the concentration of CO.Most systems will also display a calcu-lated combustion efficiency value.

Even with continuous monitoring of theflue gas, non-optimum air-to-fuel ratiosmay result due to air leaking in up-stream of the analyzer; infrequent or in-correct analyzer calibration; insufficientcombustion air supply at full load; or ananalyzer placed at a non-representative

location.

Air in-leakage in large industrial boilersis often a consequence of their bal-anced-draft design. Air that enters theboiler after the combustion zone willcause high O2 readings at the analyzer

and the operator may adjust the air-to-

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fuel ratio downward , resulting in oxy-gen-starved, inefficient combustion.

Another common cause of operation ata non-optimum O2 level is infrequent or

incorrect analyzer calibration. Routinescheduled analyzer calibration is critical.Note that even when following manu-facturer’s instructions, improperly la-beled calibration gas cylinders orplugged lines may bias the calibration.

Occasionally, boilers operate at belownormal excess air levels because thereis insufficient combustion air supply atfull load. High CO emissions can result.Partially plugged or leaking air preheat-ers can starve the burners for air.

Leaking air preheater seals can lead toerroneously high O2 readings if the inlet

combustion air leaks over into the fluegases. For these reasons, diagnostictesting prior to a boiler tune-up shouldinclude an air preheater leakage andefficiency test. For further information

on potential air-to-fuel ratio problemsand solutions, see Reference 4.

Combustion Uniformity

Complete combustion at efficient excessair levels requires the fuel and air to be

uniformly mixed throughout the primarycombustion zone. In multi-burner gasboilers, non-uniform combustion can re-sult if the fuel and air are not evenlydistributed. Just one misadjusted ormalfunctioning burner spoils the boilerefficiency effort. The natural tendencywhen encountering noticeable CO levelsis to raise excess air levels for the wholeboiler, causing the other burners to op-erate at unnecessarily high O2 levels.

Uniform combustion can quite often beachieved by simple adjustments (e.g ., tothe air register or damper settings). Inother cases, further diagnostic testing isrequired. Considerable insight intocombustion uniformity can be obtainedby mapping the O2 profile at the econo-

% BYV OL U M E R A N GE OF OP T IM U M

EXCESS AIR

O 2 I N F

L U E GA S

C O 2 I N F LU E G AS

C O M B U

S T I B L E S I N

F L U E G

A S

DEFICIENT AIR EXCESS AIR

THEORETICAL AIR

Figure 2: Generalized relationships of O2, CO2 and unburned combustibles in the flue gas as a function of combustion air supplied .

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mizer exit (or a duct location in closeproximity to the boiler O2 analyzer

probe, if one exists). Systems exist thatwill automatically measure and map O2

concentrations on a continuous basis.

A complete combustion uniformity as-sessment typically involves an evalua-tion of combustibles and oxides of nitro-gen (NOx) emissions. For further infor-

mation regarding combustion uniformity,see Reference 4.

Oxygen Analyzer Location

Occasionally, boilers with O2 analyzers

have them placed at a

non-representative location in the fluegas duct. This can be identified by diag-nostic tests where the O2 analyzer sam-

ple plane is traversed with a probe con-nected to a portable O2 analyzer. An-

other approach is to install a grid ofsample probes in the duct to obtain acomposite average gas sample. Eitherapproach can be valuable in evaluatingcombustion uniformity in a large multi-ple-burner unit.

Reduce Steam Pressure

To the extent practical, steam should begenerated at the lowest pressure thatwill meet the highest-pressure demand.Less fuel is required and lower stacktemperatures result, improving effi-ciency. Savings may be as much as 1 or2 percent, but actual savings depend onthe starting pressure and the pressurereduction that is realized. For example,a 50 psi drop from 150 psig saturatedsteam will reduce the steam (and stack)temperature by 28°F, saving approxi-mately 0.7 percent. A 50 psi drop from400 psig saturated steam, however, willresult in only a 12°F drop for an ap-

proximate 0.3 percent saving.

Blowdown Management

Blowdown is essential for maintaininglow concentrations of dissolved solids inthe water (skimming blowdown) or re-

moving solids that have settled out ofthe water (bottom blowdown). Bothpractices result in unavoidable energylosses as hot water is wasted to thedrain, and a balance must be main-tained between acceptable results andenergy losses. Skimming blowdown isbest used as a continuous process,bottom blowdown is best done periodi-cally as several short blowdowns. Con-tinuous blowdown makes the use ofheat recovery devices more feasible.

Load Management

In many industrial facilities, loads varywith production schedules or seasons.When multiple boilers serve manyloads, it is important to manage them asefficiently as possible.

Individual boilers achieve maximum effi-ciency over a specific firing range. Units

with high excess air requirements orsignificant radiation losses at low loadswill have peak efficiency at a high load.Boilers with constant excess air levelsand small radiation losses over the loadrange will exhibit peak efficiency at alower load. Efficiencies should be de-termined over the full range of firingrates. More efficient boilers should bebrought on line first as loads increase,and less efficient units should be taken

off-line first as loads drop. Where possi-ble, scheduling of loads can helpachieve optimum system performance.

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Applicability

All strategies presented in this Applica-tion Note are applicable to all boilers,

although the method of implementationwill vary: Large installations will benefitfrom automated systems; smaller or fire-tube systems may employ manualmethods.

Field Observations toAssess Feasibility

This section discusses field observa-tions and checks that will ensure thatO&M procedures are allowing efficientsystem operation.

Related to Applicability

O&M needs to be performed on allboiler systems. The strategies in thisApplication Note can enhance the per-formance of any system not already

practicing them. The following generalobservations apply:

For boilers over 100,000 lbs/hrsteam capacity, check to see if auto-mated systems to achieve operationalobjectives (e.g., O2-trim controls, blow-

down systems) are installed. It is proba-bly easiest to just ask the operator.

Review of boiler maintenance logs

will quickly reveal the frequency withwhich critical functions are carried out.If some are seldom or never performed,they should be added to the list ofregular maintenance items.

Related to Energy Savings

Too much excess air will show upas elevated stack temperatures, be-cause the hot gases are being forcedthrough the boiler too quickly, withouttime for adequate heat transfer. Gener-

ally, stack temperature should not bemore than 150°F above the temperatureof saturated steam at the boiler operat-ing pressure.

Boiler operation logs should indi-cate whether excess air is too far out oflimits of good practice. Gas-fired boilersshould be able to operate at 5 to 10percent excess air. This range corre-sponds to 1 to 2 percent O2, 11.9 to

12.3 percent CO2, and, depending onstack temperature, efficiencies of 85.2to 85.4 percent.

On balanced-draft boilers, normalO2 readings coupled with high combus-

tibles and/or low stack temperaturesmay indicate air leakage into the systemor air preheater seal leakage, situationsthat need to be remedied. Air leakagemay also be indicated if high O2 read-

ings are coupled with normal or evenlow stack temperatures.

Missing or degraded insulation onboiler, steam and condensate lines andfittings.

Multiple boilers running at low firesimultaneously may indicate potentialimprovements through load manage-ment. Low-fire conditions can be deter-mined by asking the operator or com-paring steam flow rates, as indicated bygauges or readouts at a control panel,to boiler ratings.

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Related to Implementation Cost

The size of the boiler and thenumber of burners will influence thecosts of maintaining proper air-to-fuel

ratios and fuel pretreatment. Not onlydo multi-burner systems have moreunits to maintain, they must also be co-ordinated to achieve optimum efficien-cies.

Stack gas characteristics may in-fluence the type of stack gas analyzerpurchased. If the analyzer requiresextractive stack gas samples, systemsmay need to be installed to remove

moisture or particulates before analysisis performed.

Estimation of EnergySavings

Unlike adding energy conservingequipment like economizers or oxygentrim control, no energy savings will be

reflected in a facility’s utility bills whenongoing O&M is practiced. The value ofongoing O&M is in the avoidance of un-necessary fuel consumption. It is diffi-cult, if not impossible, to quantify thisavoided consumption as there is not agood baseline (i.e., how the systemwould consume fuel without O&M) forcomparison.

Whether the strategies employed result

in combustion improvements, reductionsin radiant losses or better load man-agement, all can be measured in termsof improved efficiencies. The fuel sav-ings (or fuel consumption avoidance)realized are determined from a ratio ofthe change in efficiency to the original

efficiency.

( )Fractional Savings

E E

E

N O

O

_ =

−

where E N = New Efficiency obtained by implementing the strategy

E O = Pre-Implementation (Old) Ef-

ficiency

Note that savings are greater than justthe number of efficiency percentagepoints gained, because the starting effi-ciency will be less than one. For exam-ple, if a boiler’s efficiency is improved

from 75 to 80 percent, the operatingefficiency point gain will be 5 percent,but the savings will be 5 percent dividedby 0.75— 6.7 percent savings.

In general, properly applied boiler O&Mcan be expected to save 5 to 10 percentof the energy that would otherwise beconsumed. This reduction is difficult toquantify as it is an avoided, rather thana reduced, consumption. The only way

to determine savings would be to estab-lish a baseline by stopping O&M func-tions— clearly unacceptable.

In a typical gas boiler plant, maintainingproper air-to-fuel ratios and water qualityare probably the two most importantO&M procedures. They are both essen-tial and are generally well attended to,although opportunities for improvementoften exist. Closely related to the air-to-fuel ratio are air leakage, O2 analyzerlocation and combustion uniformity is-sues.

Depending on conditions at the site, re-duced steam pressure, blowdown andload management may offer opportuni-ties for significant savings. In most

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situations, insulation improvements offerfew opportunities for large savings.

Factors That Influence

Operations andMaintenance Costs

As mentioned earlier, boiler size andcomplexity dictate the level of O&M foroptimum performance. Besides thoseitems, this section provides other con-siderations that will influence the cost ofan O&M program aimed at energy re-duction.

The availability of labor is a primeconsideration. It is necessary to de-termine whether existing staff have theability or the time to perform additionalO&M duties, and if not whether to hirethose abilities or to contract for them.

The frequency with which the newtasks are to be performed bears di-rectly on whether existing staff has time

available. Contractors will definitely fig-ure frequency of site visits into any costestimates.

Another labor-related issue is thetime required to analyze informationfrom O&M logs and any measurementsthat are taken. This becomes more im-portant as the cost of energy increasesas a percentage of the cost of produc-tion. That is, in an industry where en-

ergy accounts for 1 percent of the costof production, the incentive to reduceenergy costs will be less than at one inwhich energy costs are 10 percent. Inthe latter case, it is more likely time fordata analysis will be found.

Depending on the strategies in-

volved, consumables may be re-quired. Many of these costs are inci-dental and are not generally a majorcontributor to strategy costs. Items forconsideration are chemical cells used in

gas analyzers, hardcopy charts andcalibration gases. Cost of maintenancefor the analyzers themselves shouldalso be considered.

Hot, wet, dirty stack gases mayrequire special treatment before be-ing analyzed; additional equipmentmay have to be added to a stack gasanalysis system.

Laws, Codes, andRegulations

It is assumed that ASME Pressure Ves-sel and Piping Codes were followed atthe time of boiler installation. Energy-saving O&M procedures should not af-fect any periodic inspections requiredunder existing regulations.

While the Clean Air Act Amendments of1990 apply in California, the state’s own37 air quality control districts each havetheir own regulations, generally amongthe most restrictive in the country. Ofspecial concern are stringent NOx emis-

sion requirements; burner manufactur-ers have developed special low-NOx

burners to address them. Other strate-gies include modifications to the com-

bustion equipment, flue gas recirculationand downstream treatment of the fluegas to convert NOx to nitrogen and wa-

ter.

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Definitions of Key Terms

Air Register: A device surroundinga burner used to direct the combustion

air flow.

Air-to-Fuel Ratio: The weight (solidor liquid fuels) or volume (gaseous fu-els) ratio of air to fuel delivered to thecombustion process.

Balanced-Draft: The operation of aforced draft fan and an induced draftfan, balanced to create a slight negativepressure in the furnace.

Blowdown: The act of releasingsome of the water from an operatingboiler to maintain a low level of sus-pended solids in the water. Since solidsare not carried away by the steam, theywill build up in the water if action is nottaken. Blowdown can also refer to thewater thus released.

Excess Air: That amount of air in-troduced to the combustion process thatis in addition to the exact amount re-quired for all the fuel to burn with nooxygen left over.

Fouling: The accumulation of de-posits on the surface of heat exchangesurfaces.

Negative Draft Boiler: A boiler inwhich the combustion chamber and hotgas passages are maintained at a pres-sure less than the air pressure sur-rounding the boiler. This is accom-plished by means of a downstream fan(i.e., and induced-draft fan) that pullsthe hot gases through the passages.

Positive Draft Boiler: A boiler inwhich the combustion chamber and hotgas passages are maintained at a pres-sure higher than the air pressure sur-rounding the boiler. This is accom-

plished by means of an upstream fan(i.e., and forced-draft fan) that pushesthe hot gases through the passages.

Scale: A deposit of medium to ex-treme hardness occurring on waterheating surfaces of a boiler because ofan undesirable condition in the boilerwater.

Tune-up: The adjustment of air-to-

fuel ratios, reduction of stack losses andadjustment of forced and induced draftfans to optimize boiler energy perform-ance.

References to MoreInformation

1. Culp, A., “Principles of Energy Con-

version,” McGraw-Hill, 1st Edition,1979.

2. Dukelow, S.G., “Improving Boiler Ef-ficiency,” Instrument Society ofAmerica, 2nd Edition, 1985.

3. Kohan, A., Spring, H., “Boiler Op-erator’s Guide,” McGraw-Hill, 3rdEdition, 1991.

4. Payne, W.F., Thompson, R.E.,“Efficient Boiler Operations Source-book,” Fairmont Press, 4th Edition,1996.

5. PG&E Engineering Dept., “Boiler Ef-ficiency,” Workshop Handbook, 1991

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6. PG&E Engineering Dept., “CustomerEnergy Use Guidebook,” 1991.

7. PG&E Engineering Dept., “BasicBoilers - Improving Energy Effi-

ciency,” Workshop Handbook, 1994.8. Yaverbaum, L., “Energy Saving by

Increasing Boiler Efficiency,” EnergyTechnology Review Series, No. 40,Noyes Data Corporation, 1979.

Trade Organizations

Further information may be obtained

from:

The Combustion Institute5001 Baum Blvd #635Pittsburgh, PA 15238Tel (412) 687-1366Fax (412) 687-0340

Amer. Boiler Mfrs. Assoc.950 N. Glebe Rd. #160Arlington, VA 22203

Tel (412) 687-1366Fax (412) 687-0340ASTM100 Barr Harbor Dr.W. Conshohoeken, PA 19428Tel (412) 687-1366Fax (412) 687-0340

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