3manufactured gases.docx
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3manufactured gases.docx
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3manufacturedgases
3.ManufacturedGases
[1]Manufacturedgasisdefinedhereinasacombustiblegasproducedfromcoal,coke,oil,orbyreformingofnatural,liquefiedpetroleumgasesoranymixturesthereof,andincludinganynaturalorliquefiedpetroleumgasifusedforenriching.
[2]Themanufacturedgasesmaybedividedintoabout18groupsorclassificationsasfollows:
[3]1.Acetyleneisprimarilyusedforcuttingandweldingoperationsrequiringhighflametemperatureandithasbeenusedasanilluminant.It’smadefromcalciumcarbideandwater.
[4]2.Hydrogenasafuelislimitedtospecialindustrialpurposes.Suchascertaincuttingandweldingoperation.It’smadebyelectrolysisofwater,bythermalcrackingofnaturalgasandotherhydrocarbons,andbythewatergasreaction.
[5]3.Sewagegasisproducedfromsewagesludgeindigestingequipment.Itsheatingvalueaveragesbetween600and700Btupercuftandconsistsofabouttwo-thirdsmethaneandone-thirdcarbondioxide.
[6]4.Butane-airandpropane-airgasesconsistofmixturesofbutaneorpropaneandairtoprovidefuelgaseswithanydesiredheatingvaluesfrom450to2000Btu.Theyareusedasthegassupplyforsmallcommunitiesandaspeakloadgasbymanynaturalgascompanies.
[7]5.Thermallycrackedgasismadebydecompositionofnaturalgas,liquefiedpetroleumgases,orgasoline.It’shighinsaturatedandunsaturatedhydrocarbonswithsomehydrogen.
[8]6.Catalyticallycrackedgasismadebypassingthegasorlighthydrocarbonliquidtobecrackedovernickeloxidecatalystmaintainedataselectedtemperaturebyexternalheat.Regulatedamountsofsteammaybeintroduced.ThegasiscomposedofCOandH2withappreciableamountsofN2andCO2,someoftheuncrackedgasorliquidvapormaybemixedwiththecrackedgastoincreasetheheatingvalue.
[9]7.Oilgasesaremadebythemaldecompositionofoilswhichmayvaryfromnaphthatoheavyresiduumhighcarbonoils.Theirheatingvaluesvaryfrom300to400Btupercuftandtheirprimaryuseisforapeakloadsupplementbynaturalgascompanies.
[10]8.Refineryoilgasisproducedinoilrefineriesfromtwochiefsources,namelyevolutionofabsorbedgasesfromcrudesduringthedistillationprocessandasaby-productofrefinerycrackingoperations.Dependingupontheamountofhydrocarbonsremoved,theheatingvaluemaybefrom1400to2000Btupercuft.
[11]9.Reformedgasesareusuallymadebythermallycrackingnaturalgas,propane,butane,orrefineryoilgasinwatergasgeneratorsorsimilarspecialequipment.Theresultantgasvariesappreciablyincompositiondependingupontheequipmentusedandthepercentageofthegasbeingcracked.Reformedgascontainshydrogen,carbonmonoxide,andsaturatedandunsaturatedhydrocarbons.
[12]10.Coalgasismadeinretortbythedistillationofthevolatilematterfromcoal.It’shighinhydrogenandmethanewithlesseramountsofcarbonmonoxideandilluminants.
[13]11.Cokeovengasismadeasby-productofcokeovensbythedistillationofthevolatilematterfromthecoal.Cokeistheprimaryproduct.Thegasproducedisusuallyaround500Btupercuftwiththecombustibleconstituentsconsistingofhydrogen,methane,ethane,carbonmonoxide,andilluminantes.Attheendofacokingperiodthegasisprimarilyhydrogen,atthebeginningitishighinmethane.Alowtemperaturecokingprocesswillproduceahigh-Btugas,asthereislittlebreakdownofthesaturatedhydrocarbons.
[14]12.Producedgasisgeneratedwhenairoroxygenispassedthroughathickbedofhotcoalorcoke.TheproductsofthisprocessareCO,N2(fromtheuseofair),andsomeCO2.Inactualpractice,steamisaddedtotheairtoreduceclinkerformationandthesteamdecompositionformshydrogeninvaryingquantities.
[15]13.Blastfurnacegasisaby-productinthemanufactureofpigironinblastfurnaces.Foritsheatingvaluederivedmainlyfromcarbonmonoxideistoolow,it’susuallyusedforheatingpurposeswithintheplant.
[16]14.Bluegas,watergas,orbluewatergas,ismadebypassingsteamoverhotcoke,coal,orothercarbonaceousmaterial,andconsistsessentiallyofcarbonmonoxideandhydrogenwithvaryingamountsofcarbondioxideandnitrogen.Itburnswithablueflame.
[17]15.Carburetedwatergasconsistsofwatergasasabasewhichhasbeencarburetedorenrichedwiththermallycrackedoil,naturalgas,orliquefiedpetroleumgas.InadditiontoconsiderablepercentagesofCOandH2,therearevaryingamountsofunsaturatedhydrocarbons(illuminants)andsaturatedhydrocarbons.Nearlyanydesiredheatingvaluefrom300to1200Btumaybeattained,dependingupontheprocessemployed.
[18]16.Synthesisgasismadebyvariousprocessesfromcoal,coke,naphthaorotherhydrocarbons,andconsistsessentiallyofCOandH2intheratioof1to2.ThecrudegasalsocontainshighpercentagesofCO2.
[19]17.Undergroundproducedwatergasmadeinundergroundcoalseamsbypassingair,withorwithoutsupplementaloxygenorsteam,throughanignitedmassofcoal,hasbeenproducedexperimentallyinseveralcountries.
[20]18.UndergroundoilgaseshavebeenstudiedintheUnitedStatesfromtheviewpointofgeneratingthemviaundergroundatomaticbombexplosionsinoilshaleformationstobreakuptheshalerockandreleasethekerosenepresent.Thenbyretortinginplace,petroleumfractionssuchasafuelgascouldbeproducedandbroughttothesurface.
READINGMaterrialA
GaseousFuels
Althoughvariousgaseousfuelshavebeenusedasenergysourcesinthepast,heatingandcoolingapplicationsarepresentlylimitedtonaturalandliquefiedpetroleumgases.
TypesandProperties
Naturalgasisanearlyodorlessandcolorlessgasthataccumulatesintheupperpartsofoilandgaswells.Rawnaturalgasisamixtureofmethane(55to98%),higherhydrocarbons(primarilyethane)andnoncombustiblegases.Someconstituents,principallywatervapor,hydrogensulfide,helium,liquefiedpetroleumgasesandgasolineareremovedpriortodistribution.
Typicalcompositionsofnaturalgasdistributedforuseasfuelinclude:
methane,CH4(70to96%),ethane,C2H6(1to14%),propane,C3H8(0to4%),butane,C4H10(0to2%),pentane,C5H12(0to0.5%),hexane,C6H14(0to2%),carbondioxide,CO2(0to2%),oxygen,O2(0to1.2%),andnitrogen,N2(o.4to17%).Naturalgasesaresometimesdividedintothreetypes:
highinert,highmethaneandhighkj,definedinTable3.
Thecompositionofanaturalgasdependsonitsgeographicalsource.Thecompositionofgasdistributedinagivenlocationcanveryslightlysincethegasisdrawnfromvarioussources,butafairlyconstantheatingvalueisusuallymaintainedforcontrolandsafetypurposes.Thelocalgasutilityisthebestsourceofcurrentgascompositiondataforaparticulararea.
Heatingvaluesofnaturalgasesvaryfrom33500to44700KJ/M3,buttheusuallyrangeis37000to39000Kj/m3.Unknownheatingvaluesforparticulargasescanbecalculatedfromcompositiondata.
Odorants(suchasmercaptans)areaddedtonaturalgastogiveitacharacteristicodorforsafetypurpose.
Liquefiedpetroleumgasesconsistprimarilyofpropaneandbutane,normallyobtainedasabyproductofoilrefineryoperationsorbystrippingnaturalgas.Propaneandbutanearegaseousunderusualatmosphericconditions,butcanbeliquefiedbymoderatepressuresatnormaltemperatures.
Threeliquefiedpetroleumgasesarecommerciallyavailableasfuels;butane,propaneandamixtureofthetwo.
Commercialpropaneconsistsprimarilyofpropanebutgenerallycontainsabout5to10%propylene.Ithasaheatingvalueofabout50510KJ/Kgorabout120000KJ/M3ofgas.Atatmosphericpressure,commercialpropanehasaboilingpointofabout-40℃.ThelowboilingpointofpropanemakesitusableduringwinterinthenorthernUnitedStatesanditisavailableincylinders,bottles,tanktrucksortankcars.
Commercialbutaneconsistsprimarilyofbutanebutmayconstainupto5%butylene.Ithasaheatingvalueofabout49000kj/kgorabout120000kj/m3ofgas.Atatmosphericpressure,commercialbutanehasarelativelyhighboilingpointofabout0℃.Therefore,butanecannotbeusedincoldweatherunlessgastemperatureismaintainedabove0℃orbutanepartialpressureisdecreasedbydilutionwithlowerboilingpointgases.Butaneisusuallyavailableinbottles,tanktrucksortankcars,butnotincylinders.
Commercialpropane-butanemixtureswithvaryingratiosofpropaneandbutaneareavailable,Theirpropertiesgenerallyfallbetweenthoseoftheunmixedfuels.
Propane-airandbutane-airmixturesareusedinplaceofnaturalgasinsmallcommunitiesandatpeakloadsbynaturalgascompanies.
Manufacturedgasesarecombustiblegasesproducedfromcoal,coke,oil,liquefiedpetroleumgasesornaturalgas.Thesefuelsareusedprimarilyforindustrialin-plantoperationsorasspecialtyfuels(eg.,acetyleneforwelding)
ReadingMaterialB
Thefutureofplasticpipeathigherpressures
ParticipantsinanAGAmeetingpanelonplasticpipediscussedthepossibilityofusingpolyethylenegaspipeathigherpressures.Topicsincludedthedesignequation,includingworkbeingdonebyISOonanupdatedversion,andtheevaluationofrapidcrackpropagationinaPEpiperesin.Thisisofcriticalimportancebecauseaspipeisusedathigherpressuresandinlargerdiameters,thepossibilityofRCPincreases.
Severalyearsago,AGA’sPlasticPipeDesignEquationTaskGroupreviewedthedesignequationtodetermineifhigheroperatingpressurescouldbeusedinplasticpipingsystems.Membersfelttheperformanceofourpiperesinswasnottrulyreflectedbythedesignequation.Itwasgenerallyacceptedthatthelong-termpropertiesofmodernresinsfar
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