Gasholders and their Tanks - EUGRIS and their tanks - Readin… · Gasholders and their Tanks 2...

Gasholders and their Tanks 1 Written by Dr Russell Thomas (28/2/2014)

Photograph 1. The world’s oldest remaining gasholder at Fulham, attributed to Samuel Clegg.

Gasholders and their Tanks

A profile of the construction of differenttypes of gasholders, their associated tanksand their occurrence on former gasworksand gasholder station sites.

Prepared by Dr Russell Thomas, TechnicalDirector, Parsons Brinckerhoff, Redland, Bristol,UK, 0117-933-9262, [email protected] [email protected]. The author isgrateful to fellow members of the Institution ofGas Engineers and Managers Panel for theHistory of the Industry and the staff of theNational Grid Gas Archive for their kindassistance.

IntroductionThis profile aims to give an insight into theconstruction and operation of gasholders andtheir tanks, for those who investigate formergasworks sites or have a general interest in thegas industry. All images courtesy of the NationalGas Archive, unless stated.

Although gasholders seem simple, the complexityand ingenuity of these structures should not beunderestimated; they are the result of complexengineering design which was gradually refinedand improved. This profile is limited to a briefdescription of the different designs of gasholders,their operation and, importantly, their tanks.

Gasholders are the only remaining distinctivefeature of a gasworks to still be visible. Thesestructures are characterised by a series of largeinterconnected (telescopic) cylindrical vessels(lifts) which would rise and fall, depending on thevolume of gas stored. The number of operationalgasholders has gradually decreased over thepast 10 years, and now no gasholders remain in

active service within the gas industry. This isbecause low-pressure gas storage is no longerrequired, as improved storage capacity has beencreated elsewhere in the gas network.

A few hundred gasholders still remain today.These are mothballed and awaiting demolition,unless protected by listed status. The gasholdershown in photograph 1, situated in Fulham,London, is a listed structure and the world’soldest surviving gasholder.

The tanks of former gasholders are often stillpresent on many former gasworks sites, infilledand hidden beneath the ground. Duringdemolition, the tank void formed a ready-maderepository for rubble and waste; as such, it canbe a potential source of pollution, posing a risk tohuman health and the water environment.

mailto:[email protected]

mailto:[email protected]


Contents

Section page

Introduction 1

Gasholders in a Historical Context 3

The Housing of Gasholders 7

Column-Guided Gasholders 7

Guide-Framed Gasholders 8

Cable-Guided Gasholders 8

Flying Lifts 9

Spiral-Guided Gasholders 9

Waterless or Dry Gasholders 10

Crowns, Cups and Dips 10

Gasholder Tanks 11

Gasholder Site or Gasworks 13

Demolition of Gasholders 15

Single-Lift holders 17

Multiple-Lift Gasholders 19

Methods for Estimating the Volume of theGasholder Tank with a Dumpling Present19

Selected Bibliography 20

Photograph 2. Evolution of gasholders on a former gasworks. Bottom right: cast iron columnguided. Bottom left: steel guide framed. Top: spiral guided. Source IGEM PHI.


Figure 2. The gasworks built by Clegg for Ackerman, a famous Londonprinter, indicating the retort setting (Fig. 1), tar receiver (Fig. 2), limepurifier (Fig. 3) and gasholder (Fig. 4). From the Journal of Gas Lighting.

Figure 1. A drawing of the gasholderdeveloped by Antoine Lavoisier, whichappeared in his work ‘Opuscules physiques etchimiques’. From King’s Treatise Vol. II, 1879.

Gasholders in a Historical Context

The word ‘gasometer’ is commonly found onhistorical Ordnance Survey maps dating back totheir first editions. The term can even be foundon older tithe maps. It was a term used by the layperson, never the gas engineer. It originatedfrom the instrument that Antoine Lavoisierdeveloped to store and supply a uniform streamof oxygen for his experiments and is shown in

Figure 1. This had manyof the later features of agasholder for storing coalgas.

In terms of coal gasstorage and supply,gasometer was anincorrect term. They werenot used to measure gas,as that was the role of thegas meter, although theydid give a crude visualindication. They weredesigned to fulfil the roleof a gas storage vessel(gasholder). The termgasometer was used inearly gas texts, such asSamuel Clegg Junior’sPractical Treatise on theManufacture andDistribution of Coal Gas,but not in later gasengineering texts.

Many old structuresmarked as gasometers onmaps were adjacent tomills, factories, hospitalsand country houses andwere associated withsmall gasworks (Figure 2). The gasworksthemselves were often not specifically marked onmaps. Where a gasometer site is shown, it islikely to be a small gasworks, with the productionplant located in a nearby building or complex ofoutbuildings. A detailed review of the history andoperation of gasworks can be found in theaccompanying profile on ‘The History andOperation of Gasworks (Manufactured GasPlants) in Britain’.

Many of the factory and mill gasworks date backto 1805-1830 when the gas industry was in itsinfancy. At this time, William Murdoch, SamuelClegg and their gas engineer contemporarieswere overseeing the construction of smallgasworks for factory owners. These followed thesuccess of gas installations at the mills of Philipsand Lee (Salford, by Murdoch) and Henry Lodge(Sowerby Bridge, by Clegg) in 1805.


Figure 3. Design of an early gas holder taken from ‘A practical Treatise on the Manufacture andDistribution of Coal Gas’ by Samuel Clegg Junior. This simple design shows many of the featurescommon in later gasholders. Note the basic guiding of the gasholder vessel by metal brackets witheyelets running on cylindrical metal bars; these were later replaced by guided rollers.

The philosophy of building small gasworks for asingle establishment was initially successful, butthese small gasworks gradually lost favour to theconcept of centralised gasworks with distributionmains supplying a larger number of customers.This idea was principally promoted by theGerman Friedrich Winzer who, to gainacceptance in Britain, anglicised his name toFrederick Winsor. In 1812, Winsor helpedestablish the first gas company to provide apublic supply, the Gas Light and Coke Company.

Whilst many of the factory and mill gasworksappeared small, they often produced more gasthan many of the village and town gasworks,given the number of lights they needed to supply.This was because an adequately lit mill using thesimple burners available at the time could haverequired many hundreds of burners throughoutthe mill and associated properties, compared to avillage gasworks with 20-30 street lamps and 30-40 customers.

These mill and factory gasworks disappeared foreconomic rather than technical reasons. Thelarger gasworks established in industrial townscould supply many mills at a much lower pricethan the mill owners could achieve within theirown gasworks. The isolated mills, hospitals andcountry houses (away from a mains supply) kepttheir gasworks (and gasholders) much longer, butwould later transfer to mains gas when it reachedthem, or move to an alternative form of gas (egacetylene) or electricity. A few mill gasworks didevolve into the main town gasworks for their area,and many others provided a limited public supplythrough a limited local gas mains, which wasoften absorbed later by the local gas company.

Gasholders have been a feature of gasworksever since they were first constructed; examplesof such early gasholders can be seen in figures 2and 3 and photographs 1 and 3. The rectangular

gasholder design shown in Figure 2 was used byMurdoch and Clegg in early gas installations.

The gasholder consisted primarily of two parts: atank which contained water, and a vessel or liftwhich would contain the gas. The purpose of thegasholder was more than just to store the purifiedgas; it acted as a crude visible ‘meter’, a bufferbetween production rates and the more erraticconsumption rates, and until boosters wereintroduced it provided the pressure in the gasmains for the distribution of the gas. Thegasholder operated on the basic principle of agas-filled floating vessel, rising and falling in aseal of water.

The function of the water was primarily to providean elastic gas-tight seal in which the vessel couldrise or fall. The water also received the whole ofthe pressure exerted by the weight of the vesseland, in this way, the water formed the necessaryresistance to raise the vessel or expel the gas.

It was very important that the weight of thegasholder vessel was correctly calculated so thatit would provide sufficient pressure to the gas inthe mains with which it was connected.

It was not unusual for weights to be placed on thetop of a gasholder to increase pressure. Thereare even stories of the gas manager and his


family sitting on top of the gasholder at a smallgasworks in order to provide the extra pressure attimes of very high demand.

If the weight of the gasholder was too great, itwould put increased back-pressure on theexhauster. If an exhauster was not used, theweight thrown by the gasholder would restrict theflow of the gas leaving the retorts, and the tarreleased from the coal would be degraded to

carbon black in the retort.

The first gasholders were rectangular and over-engineered, being constructed of iron with aheavy wooden frame, and holding about 14 m3

(500 ft3) of gas. At this time, the gasholder tankwas used to condense the tar from the gas, andto purify sulphur from the gas by adding lime towater in the tank. This early use of lime wasineffective due to the settlement of the lime.

Rectangular gas holders continued to be builtuntil 1815 when they were replaced by thecylindrical design. These cylindrical gasholderswere bigger and had a greater capacity than therectangular tanks they replaced. The biggestproblem with the new gasholders was the buildingof suitable tanks. At this time, the tanks wereusually built above ground and constructed fromwood. However, they were not particularly robustand were prone to leaking and collapse. The lastof these wooden tanks was removed from theGas Light and Coke Company’s Brick Lanegasworks in 1843. The great gas engineerSamuel Clegg developed some alternatives formsof gasholder but none of these was an effectivereplacement.

By 1819, gasholders had reached capacities ofabout 566 m3 (20,000 ft3) using iron or woodentanks. John Malam, a gas engineer of thefamous Malam gas-engineering dynasty, didmuch to improve cylindrical gasholder design byreducing the weight of the internal framing andusing counterbalance weights and chains.Malam also developed a system where thegasholder was guided by a central rod and tube.This rod and tube system was used extensivelyon small gasholders, many such examplessurviving until at least the 1870s. Brick tankswere introduced in 1818, with stone and concretetanks coming later.

Their simple design and reliability saw thegasholder concept remain in use for over 200years. Almost all gasholders worked on the sameprinciple. The vessels or piston would rise andfall depending on the quantity of gas stored. Itwas the method employed to guide themovement of the vessel or piston that differed asthe gasholder technology developed.

Photograph 3. The primitive gasholder at the first small gasworks at the Soho factory of Boltonand Watt.


Figure 4. A schematic diagram of a guide-framed gasholder with a below-ground tank.

Originally, gasholders contained only a singlevessel (lift) suspended within the tank; later,multiple-lift (telescopic) gasholders weredeveloped. Telescopic gasholders allowed amuch greater volume of gas to be stored inroughly the same footprint of land, making themmore cost effective. When Samuel Clegg Juniorwrote his treatise in 1841, he commented thattelescopic gasholders were an expensiveexception to be used only in highly constrainedsites. They eventually became commonplace,with many earlier single-lift gasholders beingextended to multiple-lift.

Gasholders could generally be classified underfour main headings, namely:

gasholders with vertical columns or guide-framing (Figure 4), which could be single-liftor telescopic, with or without ‘flying lifts’

gasholders guided by wire ropes or cables(rope-based systems appeared circa 1885and were short lived)

spiral-guided holders (single- or multiple-lift);the guide rails could be left-hand, right-handor both, and either internal or external andattached to the lifts

waterless or ‘dry’ gasholders which storedgas beneath a floating piston

Another later form of gas storage were high-pressure static vessels, which had no tanks ormoving parts, and received and stored gas atmuch higher pressure than those listed above.These bullet-shaped or spherical tanks are shownin Photograph 4. In additon, in more recentyears, gas has been stored within high-pressuregas mains, as liquified natural gas (e.g., DynevorArms, Wales) and within depleted gas fields (e.g.,rough gas storage) or salt caverns (e.g., Holford,Cheshire).

Phtotograph 4. A high-pressure bullet-type gasholder (left, courtesy of the IGEM PHI) and highpressures sphere gasholder (right), behind which is a small LPG tank.

Dumpling

Ground level

Standard

Pier

Trellis cross girder

Rim of brick tank

DryWell

Crown

2nd Lift

1st Lift

Gasholder tank


The Housing of Gasholders

Early safety concerns over gasholders expressedby Sir Joseph Banks and members of the RoyalSociety, led to gasholders being limited in sizeand constructed in strengthened buildings.Known as a gasometer house, this was aseparate superstructure built around thegasholder to protect it from explosions and theweather, especially lightning. The logic behindthis was not entirely sound, as gas could leakfrom the gasholder into the air within thegasometer house, forming a potentially explosiveatmosphere. They were phased out in the UK,but in Europe and North America, where coldweather brought the risk of freezing and highsnowfall, ornate brick-built gasometer houses(Figure 5) were constructed. Examples inCopenhagen, Leipzig, Vienna and Warsaw arepreserved.

Figure 5. A gasometer house. From King’sTreatise Vol. II, 1879.

Column-Guided GasholdersColumn-guided gasholders (figures 6 and 7) weresimple and generally reliable systems. As thename suggests, the weight and movement of the

vessel lifts were supported by columns attachedto the top of the gasholder tank. On the inside ofthese columns (facing the lift), guide rails wereattached to ensure the rigid guiding of the lift.Guide wheels were attached to arms extendingfrom the rim of the top of the lifts. The wheelswould run up and down within the guide rail set inthe columns.

The column-guided method proved the mostsuccessful, until advancements in the later 19th

century.

Some very simple early gasholders were guidedby a single central rod and tube as devised byMalam.

Figure 6. Drawing of an early single-liftgasholder with counterweights and a brickbelow-ground tank. From ‘A PracticalTreatise on the manufacture and distributionof coal gas’ by William Richards, 1877.

Early examples of guided gasholders used cast-iron tripods as seen in Photograph 1 and Figure3. These tripods were isolated from each otherand used for small holders of 40-50ft (12-15m)diameter by gas engineers such as JohnKirkham. When larger gasholders were required,Kirkham connected the tripods using iron girders.The gasholder vessel moved up and down onbrackets with a pierced eyelet which ran oncylindrical metal bars (Figure 3).

Figure 7. A three-lift column-guidedgasholder at the City of London GasCompan’s works at Blackfriars, London.From King’s Treatise, Vol II, 1879.


Photograph 5. A two-lift frame-guided gasholder with below- groundtank, using Cutler’s patented system, Southern England. Imagecourtesy of the IGEM PHI.

These columns would be attached to each otherwith heavy cast-iron or wrought-iron trellis crossgirders, and bolted onto the piers of the gasholdertank. Given the considerable weight of the cast-iron columns, they were not suitable for very highgasholder frames (100ft/30m) as the piersrequired were large and costly. These cast-ironconstructions were later superseded by structurescomposed of comparatively light rolled mild steel.

Early gasholders used counterweights (figures 6and 7 and Photograph 3) but these were largelyphased out (apart from specialist situations).Whilst the counterbalances reduced the

resistance to gas enteringthe gasholder, they alsoreduced the pressure ofgas leaving the gasholder.

Guide-FramedGasholdersGuide-framed gasholderswere similar to thecolumn-guided design(the two terms were ofteninterchanged), except thata lighter and moreextensive framework wasbuilt around thegasholder, forming anouter cylinder of structuralsteel or ironwork. Theguide frame was attachedto the outside of theabove-ground tank or tothe top of a below-groundtank by bolts onto thepiers.

Vertical girders (known asstandards) wereintersected by horizontal

girders and braced diagonally for extra strength(Figure 7).

An important development was Cutler’s patentedguide framing, which consisted of verticalstandards braced by diagonal triangulatedframing rather than horizontal girders(Photograph 5).

In general, the more modern the gasholder, thelighter the material used to construct the guideframing. The gasholders moved up and down theguide rails on wheels in a similar fashion to thecolumn-guided gasholders, with the guide rails on

the standards rather than on the columns. Someearly examples were known to have beenconstructed using wooden frames.

Cable-Guided Gasholders

Wire-rope or cable-guided gasholders used acomplex arrangement of at least three separatecables for a single-lift gasholder which stretchedvia a series of pulleys from the top of thegasholder tank to the top of the gasholder vesseland back. This kept the cables taut and thefloating vessel in position. They were invented inthe 1880s by the Darlington engineer, EdwardPease. Figure 8 shows a two-lift example of acable-guided gasholder.

Their use was short-lived (circa 1890-1910) asalternative designs proved more effective andreliable. They were retrofitted on some column-guided tanks where ground instability had causedthe columns and tanks to move, and thegasholder to jam.

Figure 8. A cable-guided gasholder in anabove-ground steel tank. From an old advertcirca 1880.


Flying Lifts

Both column-guided and guide-framedgasholders could be extended by inserting aflying lift, often, but not always (as in the case ofPhotograph 6) by adding a spiral-guided lift.

A flying lift was an additional inner lift retrofittedinto the gasholder; instead of running within theset columns or rails, the flying lift could extendabove the columns or standards without beingdirectly attached to them.

Photograph 6. A gasholder fitted with a flyinglift.

This was a common practice for many years toquickly increase capacity on gasworks, but waslater phased out. This method benefited frombeing relatively easy and cheap to retrofit withoutinterfering with the existing guide frame or

columns. The gas engineer would need toensure the gasholder structure could withstandthe additional weight and shear forces exerted bystrong side winds.

Photograph 7. Spiral-guided gasholder withtwo lifts in a steel above-ground tank. Imagecourtesy of the IGEM PHI.

Spiral Guided GasholdersThe spiral-guided gasholder concept wasproposed by Mr W. Webber and invented by MrWilliam Gadd of Manchester. They wereintroduced into the UK in 1888. The UK’s firstspiral-guided gasholder was built in 1890 inNorthwich, Cheshire, by Clayton, Son and Co Ltd.of Leeds. The spiral-guided gasholder dispensedwith the external frame above the tank, with thelifts supported instead by spiral guiding rails fixedto the lifts.

This design generally employed spiral guide railsfixed to the side of the gasholder lifts as shown inPhotograph 7 and Figure 9. The spiral guide railsengaged with rollers (two above and two belowthe rail) on the edge of the tank in such a mannerthat the bell moved up and down in a screw-likefashion (Photograph 8). The guide rails could beall left-handed, all right-handed, or successivecombinations of both.

Figure 9. Schematic of a spiral-guidedgasholder with an above-ground tank,showing the internal detail and water level.The rails on the outer lift were always fixed to theexterior of the lift, but those on succeeding liftscould be either interior or exterior, although thelatter were used in preference.

Spiral-guided gasholders required more preciseengineering and, as a result, the rollers were atgreater risk of jamming than the other types ofgasholders, if damaged. They were particularlyat risk from the wheels freezing, which could leadto the catastrophic collapse of the lifts.

Gas inlet & outlet

Tank

Crown

1st lift

2nd lift

Spiralguide rail


Photograph 8. Multiple Roller Carriage whichguides the upwards and downwardsmovement of the spiral gasholder. FromModern Gasworks Practice by Alwyn Meade.

Waterless or Dry GasholdersThis design allowed for a simplified system,where the major moving part was the piston,dispensing with the need for the water seal andassociated water-filled tank. The piston was ableto rise and fall via the guide rollers. The outercylindrical shell was dissimilar in appearance toother gasholders. The outer shell remainedstatic, had the same diameter throughout, and theroof of the structure was permenantly fixed.

The MAN (Maschinenfabrik Augsburg-NürnbergAG) gasholder (Figure 10) was the first of the drygasholders and was developed in Germany in1915. The Klonne was another German drygasholder design. The MAN and Klonnewaterless gasholders had tar and oil/grease sealsrespectively; only the MAN required recirculationof the seal fluid.

Figure 10. A MAN waterless gas holder.

These gasholders allowed the heavy water tanksused on water-sealed gasholders to be dispensedwith, requiring less expenditure on foundations.Another benefit was that the gas remained dry.The MAN was polygonal in plan, and the Klonnewas circular. There was a third equally importantbut different design: the Wiggins dry gasholder(Photograph 9). This American design is stillpopular and is used for gas storage for the steel,iron, and coke-making industries. The largest lowpressure gasholders ever built were the Klonnegasholder built in 1938 in Gelsenkirchen(Germany) which was 80m in diameter and 136mhigh and had a capacity of 594k m3 (21m ft3) and

the MAN gasholder built in 1934 in Chicago(USA) which had a capacity of 566k m3 (20m ft3).

Photograph 9. Wiggins type gasholder atMillom, England. Image courtesy of Mr SydBennet.

Crowns, Cups and DipsDue to the relative weakness of the dome (crown)of the gasholder vessel, support was required toprevent it from buckling when all the lifts weredown and there was no gas pressure within thegasholder. In these cases, the crown requiredeither its own internal frame (akin to the supportsin an umbrella) to provide strength, or supportfrom underneath to maintain its shape (a crownrest). Where an internal frame was used, thiswas still supported on a central column or pier.Trussing was generally limited to gasholders witha diameter of 170ft (52m) or less, due to thetechnical limitations of the method.

Gas inlet Gas outlet

Gas storage space belowpiston

Tar seal

Piston

Electric lift foraccess to

piston.

Ventilator

Elevation SectionTar circulatingpump


Figure 11. A cups and dips (grips)arrangement.The crown rest consisted of a series of radiatingrafters carried on columns erected in the tank andconnected by purlins to form a skeletonframework with the same shape as the crown.Earlier gasholders, especially very largeexamples, used a fixed timber framework(standing in the water tank) upon which the crowncould be seated (Photograph10).

The cups and the dips (otherwise known as grips)were the semi-circular or square features whichinterlocked to form the seals at the edges of eachlift (Figure 11). As the inner lift rose to itsmaximum, the cups and grips interlocked. Thecup was sufficiently deep to form a gas-tight sealwhen filled with water.

The cups and dips were of similar size andranged from 20-30cm wide and 40-60cm deep,depending on the size of the gasholder. Theywere in use prior to 1833, but it was in 1833 thatthe cup and dip system was patented by StephenHutchinson. Originally they were built of wrought

iron but were later replaced by mild steel, when itbecame available.

The outer lift of a column or frame-guidedgasholder had a different arrangement, having abottom curb carriage at its base. This wasoriginally referred to as a ‘wooden curb’, and itsrole was both simple and clever. It wasconstructed of Memel timber (pine), measured30cm x 30cm, and extended around the base ofthe outer lift. Whilst submerged in the gasholdertank, the timber would add buoyancy to the lift.Once partially out of the water, it would act as aweight to stop the lift leaving the water tank andblowing the seal, diverting gas to flow to othergasholders not yet filled with gas. The liftsgrounded on rest blocks of stone or concrete setin the annulus of the gasholder tank.

Photograph 10. A gasholder with the sheetingremoved from the crown, exposing the crownrest and water-filled tank.

Gasholder TanksThe gasholder tank was the part of the gasholderwhich would house the lifts when down (empty ofgas) and contain the water in which the lifts wouldrise and fall, depending on gas flow. The waterfunctioned primarily as an elastic gas-tight seal.

The tank was waterproofed to prevent waterleakage. The gasholder tank could be belowground level (Figure12), partially below groundlevel, or entirely above ground level, dependingon the type of gasholder employed and theground conditions.

The material from which a gasholder tank wasconstructed was dependent on the available localbuilding materials and the ground conditions atthe gasworks. Where a local source of goodquality building stone was available, then thiswould have been used to build the tank. Themost commonly used material for building below-ground gasholder tanks was brick (preferably low-porosity hard-burnt bricks). The full range ofbuilding materials for gasholder tanks comprised:

stone brick mass or reinforced concrete cast or wrought Iron steel bedrock combination of the above (composite)

Figure 12. Schematic of a gasholder tankwith a dumpling and annulus.

Cup plateDip plateCup skirtingplateDip skirtingplate

Water


50° 48° 45° 40° 37°

28°

21°

16°

WallPuddle

Angle ofrepose forexcavation

Concrete

Dumpling

Valve pit or dry well

Photograph 11. A brick gasholder tank withdumpling visible at the base.

As brick or stone tanks were porous, the outerfacing walls and base of the tanks were usuallybacked with puddle clay. The puddle could bepure clay, but it was thought preferable to mixclay with one-third sand, silt, or soil free fromplant matter; this was firmer in texture and lessliable to crack when dry. The puddle would beprepared outside of the trench and built up in thinlayers as the wall of the tank was built; it waskept moistened, punned well, and backed up withcarefully pounded earth.

An alternative method of waterproofing wasthrough the application of an inch (2.5cm) renderof Portland cement to the internal face of thetank. Applied successfully, this could make thepuddle redundant and on such tanks puddle wasnot always used. The use of 4 inch bricks witha cement lining could also serve this purpose.Tanks built from waterproof concrete did notrequire rendering or puddle.

The excavations required for the construction of agasholder tank were dependent on groundconditions. As can be seen in Figure 13, the safeangles of repose varied depending on the strata,with compact earth offering the steepest and wetclay the shallowest.

A few examples existed where gasholder tankswere hewn out of bedrock. Gasholder tanks atthe Chester gasworks were constructed this way,and still required waterproofing.

Where ground conditions were favourable, it wasmore economical to leave a conical moundknown as a cone or dumpling (Photograph 11),within the centre of the gasholder tank. In tankswhose diameters did not exceed circa 18m (59ft),it would be more economical to remove all thematerial if it required waterproofing leaving a flatbase, unless it was constructed in rock, stiff clayor chalk.

Strata Angle ofrepose

Compact earth 50°Earth 48°Rubble 45°Drained clay 45°Gravel 40°Shingle 39°Dry sand 37-38°Peat 28°Damp sand 21-22°Wet clay 16°

Figure 13. The effect of ground conditions on the angle of repose when constructing anunderground gasholder tank, showing angles of repose for different strata.


Occasionally, tanks were built by making acircular cutting in the ground and constructing aniron or brick annular channel to contain the water,with the intervening central space also beingcovered with a shallow layer of water (Figure 14).These were termed annular tanks. Sandstoneversions of these tanks, made watertight withpitch of asphalt, have been found in variouslocations, including Liverpool and Chester whichhad suitably shallow and solid bedrock.

Figure 14. A schematic representation of anannular gasholder tank.The weakest point on a circular masonry tankwas always the point at which the gas pipesentered and exited the gasholder. These pipeswere used to transfer the gas to and from the gasmains to the gasholder, through the water seal.The gas pipes were generally situated within arecess in the tank walls; however, by passingthrough the wall, the wall circle was broken andthe tank was weakened, making it more likely tofail. A recess was only used on small gasholdertanks in modern times, a dry well being preferred(as shown in figures 3, 5 and 9). Methods usedto minimise stress on the circular tank wallincluded the installation of iron struts or the use ofsquare pipes built into the wall.

Large gasholder tanks required wall-strengthening methods which included layers ofthick Portland cement, at 60-90cm intervals, intowhich the brick or stone was placed. As analternative, hooped-iron or flat-iron rings werebuilt at intervals into the wall.

If ground conditions made it very expensive toconstruct good foundations to build a tank, orthere was a high water table in a porous strata(e.g., sand), then an above-ground tank would beused. Above-ground tanks were generallyconstructed of flanged cast iron (later, wroughtiron or steel plates), bolted or riveted togetherand built on a reinforced concrete slab(Photograph 12). These tanks could be easilydismantled and reused elsewhere. Buriedremains of these tanks are uncommon, except fortank bottoms and the first row of plates. If groundconditions were too unstable even for an above-ground tank, then the concrete slab would requirepiled foundations. These above-ground tanksplaced the gasholder in a more elevated position

than an underground tank, putting it at greaterrisk from wind damage. They were thereforesometimes seen as an option of last resort. Aftercirca 1920 it was unusual for below-ground tanksto be chosen; however, all gasholders were builton the most suitable design for the conditionsencountered on that specific site.

Gasholder Site or GasworksNot all sites containing gasholders were activegasworks. During the expansion anddevelopment of the gas industry and itsdistribution network, some new sites weredeveloped purely for the storage of gas; thesewere referred to as gasholder stations. Thesegasholder stations were developed either

Photograph 12. Concrete foundation slab of an above-ground gasholder.


Photograph 13. The famous Kennington Gasholder, backdrop to the Oval Cricket Ground

because there was insufficient room for theconstruction of new gasholders on the gasworkssite, or new areas of supply had been developedand a new remote gasholder was required tostore and distribute (via pressure of thegasholder) to this area. In larger cities, thegasworks sometimes expanded to fill the entirefootprint of the site, making it necessary for someor all of the associated gasholders to be placedelsewhere. Thus the Nine Elms gasworks hadgasholders at Battersea, while Vauxhall gasworks

had gasholders at the Kennington Oval(Photograph 13).

These gasholders would have been supplied withgas under a greater pressure (medium orintermediate pressure) than used for localdistribution (low pressure) from large centralisedgasworks on the distribution network. From theearly origins of the gas industry until about 1920,gas would have only existed in the mains at a lowpressure of up to 40 mbar. Prior to theintroduction of booster pumps, the only pressure

to the gas mains was provided by the weight ofthe gasholder. Descriptions of gas pressure inthe gas distribution networks have graduallychanged over time as gas networks becamemore integrated at a local, regional and finallynational level.

The gasholders were connected to the low-pressure gas mains, which are used for localdistribution to domestic properties andbusinesses. The intermediate-pressure andmedium-pressure gas distribution systems aresupplied from the high-pressure gas transmissionsystem through Pressure Reduction Stations(PRS). PRSs also reduce the gas pressure fromthe intermediate- and medium-pressure mainsinto the low-pressure distribution system. ThePRS is designed to ensure that the pressure in agas main or gas service pipe does not exceed itsmaximum design pressure.

Table 1. different types of gas mains and theirpressures

Type of Mains Pressure of Mains

Low 0-75 mbar

Medium 75 mbar - 2 bar

Intermediate 2-7 bar

High Above 7 bar

National TransmissionSystem

85 bar

In addition to the gas distribution networks, thereis a national gas transmission system (NTS)which operates at 85 bar. This transports gasaround Britain at a speed of approximately 25miles per hour from North Sea gas fields,continental gas interconnectors, gas storagefacilities and LNG importation sites. The NTSsupplies major industrial customers as well as thegas distribution networks.


Photograph 14. The decommissioning of a gasholder at Croydon in the 1970s. Removal of the guide-frame standards (left) and the partiallyinfilled gasholder tank.

Demolition of Gasholders

As the demand for gas increased, so did therequirements placed on gasholders, whose sizeand capacity increased over time. Many earlygasholders were replaced by larger models.These redundant gasholders would have beendecommissioned and filled in, decommissioned,removed and replaced by a larger gasholder, or

the gasholder removed and the tank retained andmodified for use as a tar tank.Gas infrastructure developments in Britain meantthe gradual disappearance of the requirement forlow-pressure gasholders. From the 1950sonwards, many small gasholders (retained onsmall former gasworks sites to maintain localdistribution) became redundant and weredecommissioned. The local gas network wasinstead supplied from a larger centralisedgasholder station elsewhere. More recent

developments in improving the gas networksacross Britain have led to alternative storagecapacity being developed in the gas mains, atstorage sites such as depleted gas fields, saltcaverns and LNG storage facilities. Coupled withthe faster transmission of gas across the country,this has made low-pressure gas storage ingasholders redundant, leading to thedecommissioning of gasholders across Britain.


In simple terms, decommissioning would includethe gas connections to the gasholder beingdisconnected and blanked off, and the gasholderpurged of explosive gases. The outer horizontaltrellises and each standard or column would becut, then demolished individually as shown inPhotograph 13.

The lifts would then be removed, with the crownbeing removed before the columns or standards.The iron or steel work would be taken as scrapfor recycling and the money obtained used tooffset the cost of the project. If below-groundtanks were present, these were often infilled withdemolition rubble and any residual site wastessuch as ash or spent oxide, a waste material fromthe purification of town gas. Gasholder tankswere ready-made landfills given their oftenwatertight bases and side walls and were capableof being capped.

Tanks which contained a dumpling also containedan annular trench or annulus; this was locatedjust inside the tank wall. The annulus wouldprovide a flattened circular trench for the lifts torest when the gasholder was empty of gas. Itvaried in size, but reviewing numerous records itappears that it was generally between 0.91m (3ft)and 1.82m (6ft) wide. Where encountered ininfilled gasholders, they are generally found tocontain a depth of 200-300mm of gasholdersludge as well as the rest blocks.

Recent gasholder demolitions have beenundertaken to much higher environmentalstandards, with the gasholder tanks backfilledwith a suitably clean aggregate or site-wonmaterials with the appropriate geotechnicalproperties. .

Figure 15. Examples of details of gasholders tanks found on gasholder plans.


Calculating the Size of Gasholder Tanks

The first task is to establish whether thegasholder tank was above ground (Photograph15), partially below ground, or below ground.

This can be worked out from the informationavailable for the gasholder, including plans,photographs and records. Records may showwhether the tank was above or below ground andgive the depth of the tank, its capacity and thenumber of lifts. If this information is not available,then the construction material provides anindication. Brick, stone and concrete tanks werenormally used to construct tanks which weretotally or predominantly below ground. Iron andsteel were generally used for tanks which wereabove or predominantly above ground; however,they were, on occasion, also used for below-ground tanks.

Photographs provide a vital source of information,revealing the type of gasholder and the positionof the tank. All types of gasholder (with theexception of waterless types) could have anabove-ground (figures 2, 8, 9 and photographs 2,6, 7, 13, 15, 16) or below-ground gasholder tank(figures 3, 4, 6, 7 and photographs 2, 6, 7, 13, 15,16). If a tank is not visible on the photograph, itcan be assumed the gasholder had a below-ground tank.

An important point to remember is that evenabove-ground tanks had concrete slabs whichcould be buried significantly below ground level(approximately 1-1.5 mbgl) due to ground-raisingactivities on redeveloped sites. Waterless-typegasholders only had above-ground tanks (Figure10 and Pphotograph 9).

Methods for Estimating the Depth of theGasholder Tank with Limited Information

Single-Lift Gasholders

Simple Ratio for Single-Lift Gasholders

For single-lift holders the height of the vesselvaried from 0.3 to 0.4 of the diameter of the tank.The height of the vessel was usually about 0.30m(1ft) shorter than the depth of the tank.

For example, a 20m diameter gasholder wouldhave a tank depth of between 6 and 8m.

Calculation for Single-,Lift Gasholders Based onDiameter and Capacity

If the capacity of the gasholder and the diameterof the tank are known then the approximate depthof the tank can be calculated using the followingequation (valid for metric or imperial units).

(Capacity /( x (radius)2)) = depth of tank(approximately)

This rough estimation for tank depth works betterwith single-lift tanks, but it can also be applied tomultiple-lift tanks. It should be used along withother measures to calculate the potential tankdepth. An assumption can also be made basedon the graph inFfigure 16.

Photograph 15. Construction of an above ground steel tank


Photograph 16. Construction of two above-ground spiral-guided gasholders at a former gasworks in South-West England. Images courtesy of IGEM PHI.


Multiple-Lift Gasholders

Each lift would have been of a similar depth; i.e.,the depth of each lift is approximately equal to thetotal height of the inflated gasholder divided bythe proposed number of lifts, due allowance beingmade for the depth of cups and grips. The depthof the tank would have been roughly equal to thedepth of the average lift height.

Simple Ratio for Multiple-Lift Gasholders

For telescopic gasholders, the normal proportionfor the depth of the tank varied between 0.5 and1.0 of the mean diameter. Modern GasworksPractice suggested that 0.64 could be used as aratio between total height and diameter of a four-lift gasholder. It also suggested that 0.5 could beused as a ratio between total height and diameterof a three-lift gasholder. On this basis it could be

assumed that for a two-lift gasholder the ratiowould have been about 0.4. The depth of thetank was usually slightly longer than each of theindividual lifts of the gasholder (they were roughlythe same length, inner vessels being slightly tallerthan the outer vessel).

Calculation for Multiple-Lift Gasholders Based onDiameter and Capacity

The same equation could be used as highlightedabove, but the number of lifts must be factored in.An assumption could also be made based on thedata in the graph in Figure 16.

Methods for Estimating the Volume of theGasholder Tank with a Dumpling Present

It should be remembered that while only below-ground tanks had a dumpling, many undergroundtanks did not have them. Tanks less than 16-18m in diameter and requiring waterproofing didnot generally have dumplings unless built in rock,stiff clay or chalk. Some smaller tanks of brick orstone had floors paved with flagstones.

The dumpling was a mound of earth left within thegasholder tanks for economical reasons (i.e., itwas cheaper to leave the material in-situ thanexcavate it. It was often covered in a layer ofcement, or consisted of puddle covered withstone or brick.

The dumpling was not a uniform structure and itsshape as highlighted in Figure 23 would be highlydependent on the strata in which the tank wasconstructed. An annular channel was builtbetween the edge of the tank wall and the start ofthe dumpling, measuring roughly 3ft (0.91m) and6ft (1.82m) wide.

The dumpling was generally cone shaped with aflat top (e.g., Figure 13) although dumplingswhich were more dome shaped were alsoconstructed. On this basis, calculating thevolume of a dumpling cannot be easily presented


here, and it must be made on a case-by-casebasis.

The simple calculation for working out the volumeof a cone can be used to roughly estimate itssize. This calculation is the volume of a cone =(1/3) x x Radius2 x height. This calculation doesnot take into account that the dumpling was oftena wide short cone with a flat top (a frustum of acone), with the angles dependent on the strata. Amore accurate approach would therefore be towork out the area of a frustum of a cone asbelow.

( x h)V = 3 (R2+r2+Rr)v= volumeh = heightR = radius of the base of cone,r = radius of the top of the cone

Ideally, the height of the dumpling needs to beknown. This can be worked out from previousinvestigations, if boreholes were correctly placed.This information is generally not available fromsite plans or gasholder records for infilled tanks.

Old gasholder records did provide a lot of detailrelating to the gasholders tanks, but theserecords are rare, as they were generally disposedof when the gasholder was decommissioned.Where this information is not available fromrecords or site investigation details, previousexperience of investigating gasholder tanks orreference texts must be brought to bear.

Alternatively, assumptions can be made based ona standard rule of thumb, which is the volume ofthe dumpling is 30% of the tank. However, this

does not take into account the significantvariation encountered based on groundconditions. It would be more accurate tocalculate the size of the dumpling based on theangle of repose used in the strata in which thetank was built, and use this to guide the size ofthe upper flat surface of the cone.

Despite these problems, the presence of adumpling is very important and it should be takeninto account when investigating former gasholdertanks. The volume of the dumpling is veryimportant when working out the volume of infilledmaterial present within the tank and remediationvolumes. Subtracting the volume of the dumplingfrom the cylindrical volume of the tank will providethe volume of potentially infilled material withinthe tank.

Selected Bibliography

Below is a selected bibliography of books whichmay be of interest to the reader:

Accum, F.C., Practical Treatise on Gas Light, R.Ackerman, London, 1816

Clegg Jnr S., A Treatise on Gas Works and thePractice of Manufacturing and Distributing CoalGas, 1841 (other later editions), John Weale,London

Chandler, D. and Lacey, A.D., The rise of the gasindustry in Britain, 1949, British Gas Council

Cripps, F.S., The Guide-Framing of Gasholdersand Strains in Structures Connected with Gas-Works. Walter King, London

Francis, A., Stepney Gasworks, Museum ofLondon Archaeology Study Series 22, Museum ofLondon Archaeology, London, 2010

Hunt, C., A History of the Introduction of GasLighting, 1907, Walter King, London

King C. Editor, King’s Manual of GasManufacture, 1948

Meade, A.,, Modern Gas Works Practice, 1916,1921, 1934, Benn Brothers, London

Morgan, J. J., A Textbook of American GasPractice, 1931, published by the Author

Newbigging, T., and Fewtrell, Wm., threevolumes published between 1878-1913 King’sTreatise on the Science & Practice of theManufacture & Distribution of Gas, Walter King,London

Stewart E.G., Town Gas – Its Manufacture andDistribution, Science Museum/HMSO, 1958

Terrace, J., Terrace’s Notebook for GasEngineers & Students, 1948, Ernest Benn Ltd.,London

The Institution of Gas Engineers and Managers,Variable volume gasholders storing lighter thanair gases, 2011, IGEM/SR/4 Edition 3,Communication 1752

Disclaimer: The purpose of this document is toact as a pointer to the activities carried out onformer gasworks. The author will not beresponsible for any loss, however arising, fromthe use of, or reliance on, this information. Thisdocument (‘this publication’) is provided ‘as is’,without warranty of any kind, either expressed orimplied. You should not assume that thispublication is error-free or that it will be suitablefor the particular purpose which you have in mind.We assume no responsibility or liability for errorsor omissions in this publication. Readers areadvised to use the information contained hereinpurely as a guide and to take appropriateprofessional advice where necessary.

R h

r

Gasholders and their Tanks - EUGRIS and their tanks - Readin… · Gasholders and their Tanks 2...

Documents

Transcript of Gasholders and their Tanks - EUGRIS and their tanks - Readin… · Gasholders and their Tanks 2...