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David A. Bell, Brian F. Towler, Maohong Fan I-Coal Gasification and Its Applications -William Andrew (2010)

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david bell brian towler maohong fan coal gasification and its applications william andrew
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COALGASIFICATIONANDITSAPPLICATIONSDAVIDABELLBRIANFTOWLERMAOHONGFANAmsterdamBostonHeidelbergLondonNewYorkOxfordParisSanDiegoSanFranciscoSingaporeSydneyTokyoWilliamAndrewisanimprintofElsevierWilliamAndrewisanimprintofElsevierTheBoulevard,LangfordLane,Kidlington,OxfordOX51GB,UK30CorporateDrive,Suite400,Burlington,MA01803,USAFirstedition2011CopyrightC2112011ElsevierInc.Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystemortransmittedinanyformorbyanymeanselectronic,mechanical,photocopying,recordingorotherwisewithoutthepriorwrittenpermissionofthepublisherPermissionsmaybesoughtdirectlyfromElsevier’sScience&TechnologyRightsDepartmentinOxford,UK:phone(+44)(0)1865843830;fax(+44)(0)1865853333;email:permissions@elsevier.com.AlternativelyyoucansubmityourrequestonlinebyvisitingtheElsevierwebsiteathttp://elsevier.com/locate/permissions,andselectingObtainingpermissiontouseElseviermaterialNoticeNoresponsibilityisassumedbythepublisherforanyinjuryand/ordamagetopersonsorpropertyasamatterofproductsliability,negligenceorotherwise,orfromanyuseoroperationofanymethods,products,instructionsorideascontainedinthematerialherein.Becauseofrapidadvancesinthemedicalsciences,inparticular,independentverificationofdiagnosesanddrugdosagesshouldbemadeBritishLibraryCataloguinginPublicationDataAcataloguerecordforthisbookisavailablefromtheBritishLibraryLibraryofCongressCataloging-in-PublicationDataAcatalogrecordforthisbookisavailablefromtheLibraryofCongressISBN:978-0-8155-2049-8ForinformationonallWilliamAndrewpublicationsvisitourwebsiteatbooks.elsevier.comPrintedandboundinGreatBritain111213141510987654321INTRODUCTIONpartofthegasifierdesign.Ifthegasificationoccursatrelativelylowtemperatures,thentarwillbeproduced.Tarremovalisalsoanintegralpartofgasifierdesign.Higher-temperaturegasifiersdonotproducesignificanttar.ThesyngasalsocontainssulfurintheThisisabookaboutcoalgasificationanditsrelatedtechnologies.TherelationshipbetweenthesetechnologiesisshowninFigure0.1.Thegasificationprocessbeginswithaviablefeedstock.Inthisbook,wefocusononeofthosefeedstocksthatmustgothroughthegasificationprocess,coal.Thenatureofcoal,includingitspropertiesandavailability,aredescribedinChapter1.Petcoke,petroleumcoke,asolid,high-carbonbyproductofpetroleumrefining,canalsobegasified.Gasifiersdesignedforcoal,especiallyhightemperature,entrainedflowgasifiers,areusedforthisapplication.Biomassgasificationhasagreatdealincommonwithcoalgasification,butbiomassgasifiersareoptimizedforbiomassfeedstock.Theproductofgasificationissyngas,whichisprimarilyamixtureofcarbonmonoxideandhydrogen.Mostsyngas,however,isnotcurrentlymadebygasification,butratherbythesteamreformingofnaturalgas.Inthisprocess,steamandnaturalgasarefedtocatalyst-packedtubes,whichareheldinsideafurnacetoprovidetheendothermicheatofreaction.Figure0.1alsoshowsothergases,whichcanbeblendedwithsyngasforfurtherprocessing.Onesuchgasunderconsiderationishydrogen,whichcanbeproducedbyelectrolyzingwaterusingoff-peakpowerfromanuclearpowerplant.Inafewcases,carbondioxidefromanexternalsourcemaysupplementthecarbonmonoxideinsyngas.Justascoalisnottheonlyfeedstockforgasification,gasificationisnottheonlyuseofcoal.Mostcoalisburnedtoproduceelectricpower.Chapter2describesafewofthenon-gasificationusesofcoal.GasificationisdescribedinChapters3,4,and5.Chapter3describesgasificationasachemicalreactionsystem.Althoughthischaptermaylookcomplex,ourknowledgeofthechemistryofgasificationisfarfromcomplete.Chapter4coversseveralgasifierdesigns.Thesedesignswereselectedbecausetheyarenowincommercialuseordevelopment,orbecausetheyillustrateinterestingconcepts.Onegasificationapproachissufficientlydifferentthatitdeservesitsownchapter,undergroundcoalgasification,coveredinChapter5.Insteadofminingcoalandtransportingittoagasifier,thecoalisleftinplaceunderground,andthereactantgasesarebroughttothecoal.Deeplyburiedcoalseams,whichareuneconomictomine,maybeexploitedbyundergroundcoalgasification.Syngasleavingthegasifiercontainsnumerousimpurities.Theinorganicfractionofthefeedstockleavesassolidashormoltenslag.AshorslagremovalisusuallyanintegralixxIntroductionimpurityremovalwatergasshiftCO2removalsteamsequestrationSyngasprocessinghydrogen,electricpowerammonia,nitrogenfertilizersmethanol,dimethylether,hydrocarbonsProductssubstitutenaturalgas,Fischer-TropschhydrocarbonsformofH2S,withlesserquantitiesofCOS.SulfurmustberemovedfromsyngaseithertopreventemissionofSO2whensyngasisburned,ortopreventcatalystpoisoningindownstreamreactors.SulfurremovalisdescribedinChapter6.Carbondioxideremovalcanoccureitherasapartofimpurityremoval,orafterwatergasshift,asshowninFigure0.1.Thetraditionalcarbondioxideremovaltechniquesarecloselyrelatedtosulfurremoval,andaredescribedinChapter6.Theabilitytoremovecarbonfromsyngasandsequesteritinageologicalformationisoneofthemajorattractionsofcoalgasification.Thisallowscoaltobeusedwhileminimizinggreenhousegasemissions.Amajorobjectiontothisapproachisthatcarboncaptureandsequestrationareexpensive.Thispromptedagreatdealofresearchintonewcarbondioxideseparationtechnologies,andwhichisdescribedinChapter10.Syngascontainsanumberofminorimpurities,andoneofthemoresignificantismercury,aneurotoxin.RemovalofmercuryisdiscussedinChapter9.Forsomeapplications,anearlypurehydrogenstreamisdesired.Inothers,suchasmethanolsynthesis,aspecificratioofcarbonmonoxidetohydrogenisrequired.IneithercoalpetcokebiomassnaturalgasothergasFeedstocksgasificationsteamreformingGasificationFigure0.1Gasificationandrelatedtechnologies.case,thegasifierusuallyproducesahigherratioofcarbonmonoxidetohydrogenthandesired.Thisrationeedstobeshiftedtowardsagreaterhydrogencontent.Theusualwaytodothisisthroughthewatergasshiftreactioninwhichcarbonmonoxidereactswithsteamtoformhydrogenandcarbondioxide,asdescribedinChapter7.Hydrogencanthenbeburnedinaturbinetogenerateelectricpower,anapplicationknownasinte-gratedgasificationcombinedcycle.Thisisameansofproducingelectricpowerfromcoalwithminimalgreenhousegasemissions.IntroductionxiHydrogenisalsoapotentialtransportationfuel.Theusualapproachistoproduceelectricpowerfromhydrogeninafuelcell,andthenusethatpowerinanelectricmotor.Oneofthemaintechnicalobstaclesisapracticalmeansofstoringhydrogeninavehicle.Chapter9exploreshydrogenstorageforthisapplication.Nearlyallsyntheticnitrogenchemicalsstartasammonia,synthesizedfromhydrogenandnitrogengas.Nitrogenfertilizersare,byfar,thelargestvolumesyntheticnitrogenchemicals.Chapter11describesammoniasynthesisandsomeofthemorecommonnitrogenfertilizercompounds.Methanolisamajorcommoditychemicalmadefromsyngas,asdescribedinChapter12.Methanolisanintermediateusedtomakeawiderangeofproducts.Oneofthese,dimethylether(DME),isespeciallyinteresting.DMEcanbeusedasafuelorconvertedtohydrocarbons,includinggasolineandolefinsforpolymerproduction.Chapter13describesthedirectconversionofsyngastohydrocarbons,includingsubstitutenaturalgas(methane)andFischer-Tropschliquid,asyntheticcrudeoil.TheFischer-Tropschliquidisthenrefinedtomeetpetroleumproductspecifications.Coalisaninexpensivefeedstock,butgasification-basedplantstendtohaveveryhighcapitalconstructioncosts.Inconcept,onecouldbuildasingleplantthatwouldincorporatealloftheelementsshowninFigure0.1,butsuchacomplexplantwouldbeextraordinarilyexpensivetobuild.Instead,gasification-basedplantshaveamorelimitedsetoffeaturesdictatedbyeconomicsandtheregulatoryenvironment.Therearetwomajortrendsthatpromptcurrentinterestincoalgasification.Thefirstisthewidelyheldbeliefthatconventionalpetroleumsuppliesaredeclining,whiledemandfortransportationfuelscontinuestorise.Thishasledtoheightenedinterestinalternativeenergysupplies,includingcoal.Thesecondmajortrendisconcernaboutglobalwarming.Gasificationoffersarelativelycost-effectivemeansofusingcoalwhileminimizinggreenhousegasemissions.CHAPTER1TheNatureofCoalContentsTheGeologicOriginofCoal1CoalAnalysisandClassification2CoalRank4AshThermalProperties5CoalasaPorousMaterial9SpontaneousCombustion10(leastconverted)coalisknownaslignite,whichcanbefurtherconvertedtosub-bitu-minouscoal,bituminouscoal,andfinallyanthracite.ThesecoaltypesstronglyinfluencetheFigure1.1Coalification.CoalGasificationandItsApplications.C2112011ElsevierInc.1ISBNB978-0-8155-2049-8.10001-4,doi:10.1016/B978-0-8155-2049-8.10001-4Allrightsreserved.propertiesanduseofcoal,andwillbediscussedfurther.PeatLigniteSub-bituminousBituminousAnthraciteIncreasingage,conversionReserves,Resources,andProduction11References15THEGEOLOGICORIGINOFCOALCoalisfossilizedpeat.Apeatbogisamarshwithlushvegetation.Plantmatterdiesandfallsintothewater,wherepartialdecompositionoccurs.Aerobicbacteriadepletethewaterofoxygen,andbacterialmetabolicproductsinhibitfurtherdecompositionbyanaerobicbacteria.Plantmatteraccumulatesonthemarshbottomfasterthanitdecomposes,and,overaperiodofmanyyears,alayerofpeatforms.Thepeatthatbecametoday’scoalwaslaiddownmillionsofyearsago.Buriedpeatisconvertedtocoalwhenhighpressureandelevatedtemperatureisappliedtotheburiedlayer.Thisprocessisknownascoalification.Thephysicalandchemicalstructureofthecoalchangesovertime.AsshowninFigure1.1,theyoungestPetrographyisthevisualinspectionofarocksampletodeterminethemineraltypesinthesample.Whenappliedtocoal,thedifferentcoaltypesareknownasmacerals.Table1.1listscoalmacerals,andshowshowtheyarederivedfromplantmaterial.COALANALYSISANDCLASSIFICATIONCoalisusedprimarilyasafuel,soitsmostimportantpropertyisitsheatofcombustion.Grosscalorificvalue,alsoknownashigherheatingvalue(HHV),isdeterminedbymeasuringtheheatreleasedwhencoalisburnedinaconstant-volumecalorimeter,withanintitialoxygenpressureof2to4MPA,andwhenthecombustionproductsarecooledtoafinaltemperaturebetween20and35C14C(ASTMD5865-04).ThetestsmentionedinthisbookareprimarilybasedontheAmericanSocietyforTestingandMaterials(ASTM)specifications.1Coalisavariable,widelydistributedandwidelyusedmaterialsoawiderangeofstandardtestshavebeendevelopedbyavarietyofindividualsandorganizations.Coalisaporousmedium,andthesepores,especiallyinlowrankcoals,cancontainsubstantialquantitiesofwatereventhoughthecoalappearstobedry.Thewateriseitheradsorbedontohydrophilicsurfacesitesorheldinporesbycapillaryforces.Whenthismoistcoalisburnedorgasified,asubstantialfractionofthecombustionheatisrequiredTable1.1Coalmacerals,basedonASTMD121-05andASTMD2799-05a.1MaceralSecretiniteNoobviousplantstructure,sometimes2TheNatureofCoalcontainingfractures,slitsornotch.SemifusiniteLikefusinite,butwithlessdistinctevidenceofcellularstructure.groupMaceralOriginCommentsVitriniteVitriniteWoodytissueofplants(cellulose,lignin)MostcommonmaceralLiptiniteAlginiteBotryoccusalgaeWaxy,resinousmaterialsCutiniteWaxycoating(cuticle)ofleaves,rootsandstemsResinitePlantresinsSporiniteSporesandpollengrainsIntertiteFusiniteSomestructuresofplantcellwallstillvisibleDerivedfromstronglyalteredanddegradedpeatInertodentriniteFragmentsincorporatedwithinothermacerals.MacraniteNoplantcellwallstructure,largerthan10mmMicraniteNoplantcellwallstructure,lessthan10mm,andtypically1to5mmFunginiteFungiTheNatureofCoal3Fixedcarbon,whichismostlycarbonbutcancontainotherelementsrepresentsthecombustibleportionofthecoalcharthatremainsafterthevolatileshavebeenremoved.Proximateanalysisresultsaresometimesreportedonadrymineralmatter-freebasis.Mineralmatteriscalculatedusingthefollowingequation:Mm¼1:08Aþ0:55SEqn.1.3Where:Mm¼percentmineralmatterA¼percentashS¼percentsulfur(ASTMD3177orD4239)remainsassteamandthattheheatofcondensationisnotrecovered.Waterinthecoalreducesitsheatingvaluebyitsheatofvaporization,2.395MJ/kgwater(1055Btu/lbwater).Again,foratypicalPRBcoal:LHV;moist¼19:8MJkgcoalC02:395MJkgwaterC30:28kgwaterkgcoal¼19:1MJkgcoalC188;200BtulbcoalC19Eqn.1.2ProximateAnalysis(ASTMD3172-89)involvesaseriesofteststhatheatandburncoal.Moistureismeasured(ASTMD3173-03)bydeterminingtheweightlossaftercoalisdriedat104to110C14C.Volatilesarethenmeasured(ASTMD3175-02)bydeterminingadditionalweightlosswhencoalispyrolyzedat950C14C.Ashisdeter-mined(ASTMD3174-04)bytheweightofinorganicmaterialsremainingaftercoalisburned.Fixedcarbonisthefractionofcoalthatisnotmoisture,volatiles,orash.WaterintheHHVtestisprimarilyanon-combustiblediluent.Forexample,aWyomingPowderRiverBasincoaltypicallyhasanHHVof19.8MJ/kg(8500Btu/lb)anda28%moisturelevel.OnecanthencalculateanHHVvalueforthecoalifitisdried:HHV;dry¼19:8MJ=kg1C00:28¼27:5MJkgC1811;800BtulbC19Eqn.1.1Ifcoalisburnedorgasifiednearatmosphericpressure,thentheheatofcondensationforthewatermaynotberecovered.Forexample,inacoal-firedpowerplant,thewatercontainedinthecoalmaygoupthestackassteam.Inothersituations,theheatofcondensationisrecovered,butthevalueofthisheatisrelativelylowbecauseofitstemperature.Inthesecases,abetterestimateofcoalheatofcombustionisthenetcalorificvalue,alsoknownasLowerHeatingValue(LHV),whichassumesthatvaporizedwatertovaporizewater.Sincethefinaltemperatureinthegrosscalorificvaluetestis20to35C14C,mostofthewateriscondensed,therebyrecoveringtheheatofvaporization.The1.08factorpresumesthatmineralsinthecoalarehydrated.Thiswaterofhydrationislostwhenthecoalisburned.The0.55factorassumesthatsulfurispresentaspyrites,whichinmanyareasareconvertedtothecorrespondingoxidesduringcombustion.Ultimateanalysis(ASTMD3176)describescoalintermsofitselementalcomposi-tion.Foradriedcoal,weightpercentagesofcarbon,hydrogen,nitrogen,sulfur,andasharemeasured.Theremainderofthecoalsampleisassumedtobeoxygen.COALRANKInthecoalificationprocess,thecoalrankincreasesfromlignitetoanthracite,asshowninFigure1.1.Coalrankisusefulinthemarket,becauseitisaquickandconvenientwaytodescribecoalwithoutadetailedanalysissheet.AmoredetaileddescriptionofcoalrankisRankgreaterthanthanthanlessthan4TheNatureofCoalMeta-anthracite98n/an/a2Anthracite929828Semi-anthracite8692814Lowvolatilebituminouscoal78861422Mediumvolatilebituminouscoal69782231HighvolatileAbituminouscoaln/a6931n/ashowninTables1.2and1.3.Bituminousandsub-bitumouscoalsaretheprimarycommercialcoals.Arelativelysmallamountofanthraciteisavailable.IntheUSA,anthracitesareproducedonlyinnorth-easternPennsylvania.Lignitesareabundant.Buttheeconomicsofhaulingalow-gradefuellongdistancesareunfavorable;somostligniteisconsumedclosetowhereitismined.Peatisalsominedandgenerallyusedclosetowhereitismined.Peatmaybeeitherconsideredoldbiomassorveryyoungcoal.Innationsthatregulategreenhousegasemissions,thedifferencebetweenthetwoismorethanmeresemantics.Carbondioxideemissionsfrombiomasscombustionarenotconsideredacontributortoglobalwarming,becausetheseemissionsareoffsetbycarbondioxideuptakebygrowingbiomass.Ontheotherhand,thesameemissionsfromfossilfuels,arerestricted.Emissionsfrompeatcombustionarearegulatorygrayarea.Somecoal,particularlybituminouscoal,hasthetendencytocake.Withincreasingtemperature,coalparticlessimultaneouslypyrolizeandpartiallymelt,causingthecoalparticlestosticktooneanother.Somegasificationreactors,especiallymovingbedandfluidizedbedgasifiers,arelimitedtoprocessingcoalthatdoesnotcake.Table1.2Classificationofanthraciticandbituminouscoalsbyrank(ASTMD388-05).1Fixedcarbonlimits(drymineral-matter-freebasis),%Volatilematterlimits(drymineral-matter-freebasis),%EqualorLessGreaterEqualorTheNatureofC
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