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1、EffectofRadialTemperatureProfilesonYieldsinSteamCrackingK.M.VanGeem,G.J.Heynderickx,andG.B.MarinLaboratoriumvoorPetrochemischeTechniek,GhentUniversity,B-9000Gent,BelgiumRadialtemperatureprofilesduringsteamcrackingresultinradialnonuniformitiesintheproductyield
2、sduetoradialvariationsintheconcentrationoftheradicals.Theeffectofusinga1-Dora2-Dreactormodelonthecalculatedproductyieldsisevaluatedforthecrackingofethane.Witha2-Dreactormodelthesimulatedethyleneyielddecreases.Ethyleneformedatthehigh-temperaturezoneneartheho
3、twalldiffusestothecenterwheresecondaryreactionsarefavored,generatingC3andC4olefins.ThiseffectisconfirmedbythecalculationofareactorofaKelloggMillisecondFurnace.Inthissmall-diameterreactorthe1-Dbehaviorismorepronounced,resultinginhigherethyleneyieldsatcomparabl
4、econversions.Theeffectoftheradialgradientsonthecokingratecalculatedwithafundamentalkineticcokingmodelbasedonelementaryreactionstepsisevenmorepronounced.Onlywhenthecokemodeliscoupledtoa2-Dreactormodel,agoodagreementwiththereferencedataisobserved.Inordertoobt
5、ainaccuratesimu-lationresultsthemoredetailed2-Dreactormodelisrequired,evenifthisincreasesthecomputationaleffort.©2004AmericanInstituteofChemicalEngineersAIChEJ,50:173183,2004Keywords:thermalcracking,twodimensionalreactormodel,simulation,cokeformation,ethune
6、crackingIntroductionplug-flowmodelinsufficient(Froment,1992).Furthermore,aradialtemperaturegradientimpliesthattheconditionsprevail-Tubularreactorsareusedinindustryforimportantprocessesingattheprocessgascokeinterfaceontheonehand,andthesuchassteamcrackingandpol
7、ymerization.Theiranalysisandconditionsinthecenterofthereactorcoilontheotherhanddesignisfrequentlybasedon1-dimensionalmodels,thatis,maydifferappreciably(DeSaegher,1996).Cokeformationatconsideringgradientsonlyintheaxialdirection.Semiempiricaltheinterfacecondi
8、tions(Sundarametal.,1981)orataveragedcorrelationscanapproximatetheaverageofradialconcentra-conditionsascalculatedwitha1-dimensionalmodelwilldif-tionandtemperatureprofilesfrommore-dimensionalmodelsfer.It