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外文翻译--麦秸燃烧和二氧化碳气化的加压热重分析反应研究 英文版.pdf

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外文翻译--麦秸燃烧和二氧化碳气化的加压热重分析反应研究 英文版.pdf

JfPRESSURIZEDTHERMOGRAVIMETRICREACTIVITYSTUDYOFWHEATSTRAWCOMBUSTIONANDC02GASIFICATION.OleRathmannandJytteB.IllerupDepartmentofCombustionResearchRiseNationalLaboratoryDK4000Roskilde,DENMARKKeywordsWheatstrawbiomass,Pressurized,Gasificationreactivity.Abstract.Biomassfuelreactivityisinterestingsincebiomass,ase.g.wheatstraw,isarelevantfuelforadvancedpressurizedpowerplantsduetotheCO,neutrality.InthisstudycombustionandC0,gasificationreactivitiesofpulverizedwheatstrawcharupto40barwereinvestigatedbyisothermalthermogravimetricanalysis,andtheresultswerecomparedtoatypicalsubbituminouscoal.Arecentlybuiltpressurizedthermogravimetricanalyzerofthehorizontaltype,withoperatingconditionsatleastupto1200C,45bar,wasused.InthestudytheeffectsoftemperatureandpartialpressureofthereactantsO2andC02,respectively,wereseen,forgasificationalsotheinhibitioneffectofCO,whereasadistincttotalpressureeffectcouldnotbeobserved.Alsotheeffectofusingnonpulverizedstrawpieceswasinvestigated.INTRODUCTIONTheuseofbiomassfuelsforpowergenerationandheatproductionhasanumberofadvantageswiththeC02neutralityandsavingofdepletablefossilfuelsamongthemostobvious.Inaddition,nationallegislationinDenmarkurgetouselocallyavailablebiomassase.g.woodwasteandstraw.Consideringthefuture,characterizationofbiomassfuelwillthusberelevantinrelationtocombustionandgasificationforhighefficiencypressurizedpowerplanttypesasIGCC.Asaresult,researchgroupsinScandinaviaandelsewherehavebeenactiveincharacterizingthebiomassfuelsrelevantintheirrespectivecountries,andmainissueshavebeeninfluenceofpressure,temperatureandgascompositiononthereactionrate.Especiallywood,strawandblackliquorchargasificationreactivitiesatmoderatereactionrateshavebeenstudiedusinglargesampleverticalPressurizedThermoGravimetricAnalyzerPTGAinstruments.BlackadderRensfelt1985studiedpyrolysisofwood,celluloseandlignineupto800Cat1to40bar.Moilanenetal.1993investigatedatmosphericsteamgasificationofcharsofwood,peatandblackliquorincomparisonwithcoalandbrowncoal,whileWhittyetal.1993binvestigatedpyrolysisandcharC02gasificationofcoarselypulverizedwoodandpeatat850°Cat120bar.StoltzeetaL1993studiedatmosphericsteamgasificationoflargesamplesofbarleystrawcharat75OoC950C.BlackliquorcharwasinvestigatedbyBackmanetal.1993andbyWhitty1993regardingpressurizedC02andsteamgasificationinpresenceofCOat650800°Cand130bar.ThefollowingoverallpictureisseenInpyrolysis,woodcharyieldincreasesclearlywithincreasingpyrolysispressure,whilethereactivitydisplaysaweakdecrease.Woodcharreactivityissimilartothatofpeatandbrowncoalandabout1orderofmagnitudefasterthanforcoal,blackliquordisplaysareactivity2ordersofmagnitudefasterthanwood,andgasificationwithsteamhasareactivityabout4timesfasterthanwithCO,.Thereactvityincreasesstronglywithincreasingtemperatureandasseenforcoal.Increaseintotalpressureatconstantgaspercentagecompositionhasaweak,enhancingeffectforwoodwhileforblackliquortheeffectisdirectlyreducing,attributedtoinhibitionbyCOorH,insidethecharpores.InthisworkwehaveinvestigatedcombustionandCO,gasificationreactionratesofstrawasthisfuelisexpectedtobeoneoftheimportantbiomassfuelsinfutureadvancedDanishpowerheatingstations.TheworkwasperformedundercontractwithandtheDanishutilityassociationsElsaandElkraftwithintheEuropeanUnionAPASprogramme,andwassupportedbytheDanishMinistryofEnergy.EXPERIMENTALThefuelsampleswerepreparedfromwheatstrawnormallyusedinDanishelectricalpoweddistrictheatingstations.Entirestrawsweregroundtopulverized,averagestmwsampleswithaparticlediametersmallerthan200fim.Charofpulverizedstraw,strawinternodepieces,strawnodesandgrainswereproducedinafurnacebya7minutes900Cpyrolysisheattreatmentatatmosphericpressurewithoutoxygenaccess.Therawfuelcompositionsgivenintable1indicaterathersimilarproximatecompositionswhileashcompositionsdiffer,especiallywithrespecttoK20andP,O,.704ThePTGAinstrumentusedforthestudyfig.1isamodifiedDuPontthermogravimetricanalyzerofthehorizontaltype,recentlybuiltatRISQ.ThefuelsampleisplacedonasmallIcmdiameterPlatinumtrayhangingonahorizontalbalancearm,situatedinareactiontubetogetherwiththermocouples.Thereactiontubeisheatedfromoutsidebyaheaterelement,andtheentirethermobalancearrangementisplacedinsidea35Ipressurevessel.Pressureandflowcontrolareperformedbyanumberofvalvesandgasmassflowcontrollers.Thetestgas,selectablefromeitheraninertgasN,sourceorapremixedreactivegassource,issuppliedtotherearendofthereactiontubewithafillerelementtoheatthetestgastooperatingtemperature.Atestgasratecorrespondingtoalinearvelocityinthereactiontubeofabout1cm/sat1000Cisusedgivingaswitchingtimeforthegascompositionatthesamplepositionofabout100s.ThebalancesytemistheoriginalDuPontcomponent,whilereactiontube,ovenandallexternalsystemsarenew.ThePTGAcanoperateupto45barand1200°Csimultaneously.Samplesuptoabout150mgcanbeinvestigated,butforlowdensityfuelsthepracticallimitissetbythefuelvolumeandmaybe5toIOmg.Dataloggingisperformedonceper2seconds.Pyrolysisexperimcntswereperformedinaninerttestgaswitharampedtemperature.ThecombustionandgasificationreactivityexperimentswereperformedisothermallywiththeoperatingtemperatureestablishedininerttestgasafterwhichthereactivetestgasN2/02orN,/C02/C0mixturewasselected.Themaximumconversionratethatcouldbemeasuredwassetbythetestgasswitchingtimeandthemaximumdiffusionrateofreactanttothesampleandwithinthesample.Theexperimentalweightsignalswerecompensatedforbouyancyandbalancearmlengthexpansion,basedoncalibrationtests.ForthereactivityexperimentsatransformationthenfollowedofthecompensatedweighttoaconversiondegreeXandareactivityRreactionrateperremainingcharxmcomchRdmJdt/m,dX/dt/1X12wherem,andmCoaretheinstantaneousandinitialcharmassondryandashfreebasis,respectively.Eachreactivityexperimentwascharacterizedbythereactivityat50conversion,b,,andthevariationofRwithconversionXwas,asanapproximation,describedbyasinglenormalizedreactivityprofilefXnormalizedto1.0atX0.5foreachofthereactiontypes,i.e.RXR,sf.AncstimateofthereactiontimetoacertainconversiondegreecouldthenbecalculatedasrxtxIfX/IXdX3JoRESULTSAminornumberofpyrolysisexperimentswereperformedonraw,pulverizedstrawsamplestoseetheinfluenceofheatingrateandpressureinthetemperaturerange1501000°C.At20bar,heatingratesof10,30or5OWminhadnoeffectoncharyield.Withaheatingrateof30C/minthecharyieldseemedtoincreaseweaklywithpressure15,20and22charyield2.5uncertaintyfor1.5,20barand40bar,andthemaximumpyrolysisrateoccurredinanarrowrangefrom342°Cto355°C.Moreaccurateexperimentalresultsarenecessarytoquantifythepressureeffectonthecharyield.Astheseresultsshowedlittleeffectofpyrolysispressureitwasassumedthattheatmosphericpyrolysispressurewasofnoimportancefortheresultingchar.Combustionreactivitywasmeasuredattemperaturesfrom300°Cto410C,pressuresfrom1.5.barto40barand0,pressuresfrom0.08barto0.8bar.Theresultsfor,5areshowninfig.2.Thereactivityincreasedwithincreasingconversiondegree,withvaluesatX0.2andX0.8about0.6and1.7timesthevalueatX0.5,respectively.Whileresultsatsuchlowtemperaturesarenotdirectlyapplicabletopracticalconditionstheypermitcomparisontocorrespondinreferencecoaldata.At400°Cand0.26bar02,thereactivitywasfoundtobeabout0.002s,about30timeshigherthanthereactivityforthereferencecoal.ThedependenceontemperatureandO2partialpressurecorrespondstoanactivationenergyof110kJ/moleandareactionorderof0.61.Theactivationenergyissimilartothatofthereferencecoalbutthereactionorderisalittlelower.Nosignificanteffectofthetotalpressurewasobserved.P705LIco2gasificationreactivitywasmeasuredinthefluidizedbedrelevanttemperaturerange850ClO5O0Cat20barandwith3differentgascompositions,includingonewiththeinhibitorcomponentCO,asshowninfig.3.Afewoftheseexperimentswererepeatedat4and40bartotalpressurewithunchangedC02/C0partialpressures.At1000°Cthereactivityb,swasfoundtobeabout0.006sin0.7barCo2andnoCO.Thereactivityincreasedwithconversiondegree,withValuesatXO.2andX4.8about0.6and2timesthevalueatX4.5,respectively.ThepresentStrawreactivityisabout16timesfasterthanforthereferencecoaland1.52timesfasterthanforthewoodreactivityasmeasuredbyWhittyetal.1993a.Theresultsforb.5couldbeinterpretedintermsofLangmuirHinshelwoodkineticsseee.g.Laurendeau1978.skPco,/laPcobPcoz,wherek,,a,andbhaveArrheniustemperaturedependence,foraandb,however,withnegativeactivationenergies.Inspiteofsomeunsystematicvariationintheexperimentaldata,saturationdescribedbythebparameterwasclearlyobservedasthereactivityincreasedlessthanproportionallytotheincreaseinC02pressurefrom0.7to2.2barinabsenceofCO.Also,thecleardecreaseinreactivityfrom1.5to5times,whenchangingfroma2/0bartoa2/2barCO,/COtestgas,indicatesclearlyinhibitiondescribedbytheaparameteratthetesttemperatures.Boththesaturationandinhibitioneffectsshowedanexpectedreductionwithincreasingtemperature.Thepresentresultsaretooscarcetopermitanunambiguousdeterminationofkineticparameters,butasshowninfig.3,aLangmuirHinshelwoodrepresentationcouldbeobtainedusingaandbparametersfromthereferencecoalincombinationwithafittedklparameter.However,thevalueofthisk,parameterindependenceoftemperatureisstronglydependentontheappliedvaluesoftheaandbparameters.Themeasurementssuggestamoderatereactivityreductionwithincreasingtotalpressure,maybeupto2timeswhenthepressureisincreasedfrom4to40baratconstantC02andCOpartialpressures.Incontrasttoblackliquorreactivity,thepresentdatasuggestanincreasingreactivitywhenincreasingthepressureatconstantgaspercentagecomposition.Thereactivityofcharofnonpulverizedstrawparticleswasmeasuredat9001000°Cwith20barpressureand2/2barC02/C0partialpressure.Relativetothecharofaverage,pulverizedstrawtheinternodeparticlesshowedareactivitymorethan2.5timesfaster,nodeparticlesshowedareactivity2timesslowerat900°Cwhileat950°Cand1000°Citwasmorethan3timesfasterthanforpulverizedstraw.Grainsshowedareactivityabout2.5timesslowerthanpulverizedstraw.Thesurprisingfasterreactionsofinternodeandnodeparticlesmaybeduetothenonpackedstructureofthesample,butforthenodesthisbehaviormayalsobeduetothehigherconcentrationofthecatalystK20intheashseetable1.DISCUSSIONANDCONCLUSIONThepresentPTGAinstrumenthasprovedtobeavaluableinstrumentforbiomassfuelreactivityanalysisatmoderatereactionrates,inthepresentstudyofwheatstraw.Pyrolysisofpulverizedstrawsuggestedasmallincreaseincharyieldwithincreasingpressure.Pressurizedcombustionandgasificationreactivityofstrawcharsamples,pyrolyzedatlowheatingrate,wasinvestigatedupto40barbutwiththemainpartoftheinvestigationsat20bar.Thecombustionreactivityatlowtemperaturearound350°Cwith0.08to0.8bar02wassomewhatmorethanoneorderofmagnitudehigherthanforareferencecoalandwiththesamerelativetemperaturedependence.Thedependenceon0,partialpressurewasweaker,andnosignificantdependenceontotalpressureatconstantpartialpressurecouldbeobserved.COiGasificationreactivitywasinvestigatedaround950°Catco,andcopressuresaround1bar,Theresults.displayingbothCO,saturationandCoinhibition,couldbeunderstoodi,,ofhmuhHhshelwoodkinetics,butmoreaccuratemeasurementsarenecessarytoactuallydeterminethekineticParameters.InabsolutemagnitudethemawcharreactivitywasfoundtobeanorderofmagnitudehigherthanfortheWferenCecoalandalsoalittlehigherthanforwoodbiomass.Charofnonpulverizedsuawparticles,includinggrains,displayedreactionratesmoderatelyscatteringabove3timesandkhw2timesthatOfthepulverizedsamples,presumablyasaofsizeeffect,compactnessandcompositionofthenonpulverizedparticles.nefuelreactivityresultsdisplayedamxkratedecreasewithtotalpressure,butmoreaccurateareneededtotellwhetherthisisasignificanteffectAlso,experimentswithcharspyrolyzedathighheatingratesatvariouspressureswouldberelevanttodistinguishbetweentheeffectsoftotalpressurethroughPyrolysisandthroughchargasification,706IREFERENCESBacunan,R.,Frederick,W.J.andHupa,M.,BasicStudiesonBlackLiquorPyrolysisandCharGasification.BioresourceTechnology461993pp153158.Blackadder,W.,Rensfelt,E.I985.Apressurizedthermobalanceforpyrolysisandgasifcationstudiesofbiomass,woodandpeat,inFundamentalsofThermochemicalBiomassConversion,editedbyR.P.Overendet.al.,Elsevier1985.Laurendeau,N.M.1978.HeterogeneousKineticsofCoalCharGasificationandCombustion.Prog.EnergyCombust.Sci.41978,pp221270.Moilanen,A.,SaviharjqK.andHarju,T.1993.Steamgasifcationreactivitiesofvariousfuelchars,inAdvancesinThermochemicalBiomassConversion,pp.131141,editedbyBridgwater,A.V.,BlackieAcademicProfessional1993.Stoltze,S.,Henriksen,U.,Lyngbech,T.andChristensen,O.1993.GasifcationofstrawinalargesampleTGA.Nordicseminaronsolidfuelreactivity,Gothenburg,Nov.24th1993.Whitty,K.J.1993a.GasifcationofblackliquorwithH20underpressurizedconditions.MSci.thesis.Report934,Dept.Chem.Engin.AboAkademi,Finland.Whitty,K.J.,Sorvari,V.,Backman,R.,andHupa,M.1993b.Pressurizedpyrolysisandgasifcationstudiesofbiomasses.AboAkademi,DepartmentofChemicalEngineering,Report937,IFRFSwedishFinnishFlameDays1993.TABLESANDFIGURESTableI.Fuelproximateultimateanalysis.MostrelevantspeciesandcompoundsareincludedpyrolyzedfuelaverageVolatiles77.375.183.2Hydrogen5.86.8Carbon47.244.6winashISiO,Na,OKZOP2052.42.045YFig.1.RecentlybuiltPressurizedThermogravimetricAnalyzerinstrumentusedinthisstudy.ANelectricalconnectionjitthroughsareplacedintherearflangele3sideofthepressurevessel707

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