碱金属 英文文献
Energy&Fuels2004,18,1625-16321625
EffectsofCalciumOxideontheCrackingofCoalTarin
theFreeboardofaFluidizedBed
JiaYongbin,*HuangJiejie,andWangYang
InstituteofCoalChemistry,ChineseAcademyofSciences,Taiyuan,Shanxi,030001,China
ReceivedOctober28,2003.RevisedManuscriptReceivedJune6,2004
Theeffectsofcalciumoxideontarcrackinginthefreeboardofafluidizedbedunderdifferentfreeboardconditionshavebeeninvestigatedinordertoreduceoreliminatethetarproducedincoalpyrolysisandsimultaneouslytomakecoalgasofhighqualities.Becausenobubblesareinthefreeboard,thetarwouldbecontactedwellwithcalciumoxide,andthetarcrackingisimproved.Theresultsshowthattarconversionincreasesapparentlywiththeadditionofcalciumoxide,buttheeffectofcalciumoxideonthetarconversiondecreasesgraduallywithfreeboardtemperatureandissmallabove700°C,especiallywhenthepercentageofcalciumoxideisincreasedfrom6%to12%.Atlowerfreeboardtemperatureof650°C,theeffectofcalciumoxideonthetarconversionincreaseswithresidencetime,apparently;however,at750°Ctheeffectofcalciumoxideonthetarconversionisonlyapparentatshortresidencetime.Therateoftarcrackingcanbeexpressedbyasimplefirst-orderreaction,andtheactivationenergyisdecreasedby30%or45%when6%or12%ofcalciumoxideisadded,whichisalmostequaltotheresultofLvandYue[Lv,J.F.;Yue,G.X.J.TsinghuaUniv.(Sci.Technol.)1997,37(2),6-10.]inafixedbedforbenzeneortoluene,respectively.
Introduction
Intheintegratedfuelgasandsteamcombinedcyclepowergenerationprocess,charispartlycombustedinacirculatedfluidizedbed,andhotchariscirculatedintoapyrolyzertoheatcoalfromafeeder.Incoalpyrolysis,charandcoalgasareproduced,andtheformeriscirculatedintothecirculatedfluidizedbedagainandthelatterisusuallyusedfortowngasandgeneratingpower.Becausetheconditionsofcoalpyrolysisarerelativelymild,theyieldofaliphatichydrocarbonsishigherandcoalgasisofhigherthermalvalue.However,atthesametimetarisproduced,whicheasyfoulsandblocksthepipeandcanmakeabigproblemfortheoperationofthetotalsystem.Furthermore,thesmallamountoftarisnoteconomictorecover.Waterscrub-bingisusuallyusedtoremovethetarinthegaseousproducts,butthewastewaterproducedisdifficulttodealwithandthethermalefficiencyofthewholeprocesswouldalsobereduced.1
Therefore,itisidealtoreduceoreliminatethetarinbed,whichnotonlycansolvethetarproblembutalsocanincreasetheyieldofcoalgas.Thetarcatalyticcrackingwaswellinvestigatedinthepast.Thefixedbedreactorandbubblefluidizedbedwereusedinmostresearch,butthecatalytictarconversioninthefree-boardoffluidizedbedislittlestudied.BakerandMudgeinvestigatedthecatalyticconversionofcoaltarinafixed-bedusingcatalystssuchasY-zeolite/SiO2-Al2O3,CoMo/LZ-Y82,Fe2O3;2theirresultsshowedthatthe
*Correspondingauthor.Tel:8133514078231.Fax:8133514041153.E-mail:jiayongbin@http://doc.xuehai.net.
(1)Aznar,M.P.;Caballero,M.A.;Gil,J.;Mart ´n,J.A.;Corella,J.Ind.Eng.Chem.Res.1998,37,2668-268.
cokeisamajorproductoftarcrackingwithallofthecatalysts,andallofthecatalystslostactivitywithtimeduetocokebuildup.Simelletal.alsoinvestigatedthecatalyticpurificationoftarryfuelgaswithcarbonaterocksandferrousmaterialsinatubereactor,3anditwasfoundthattheactivitiesofcarbonaterockswereaffectedstronglybytheirphysicalproperties,andthemineralmattermayhaveincreasedtheactivityofferrousmaterialsbyproducingabetterporematrixfortarcomposition.Forcoalpyrolysis,afluidizedbedhassomeadvantagesofsimpleoperation,largecapacity,anddirectuseofpulverizedcoal.4Corellaetal.5-7havedonein-depthandalmostall-sidedworksonbiomassgasificationforthecleaningofhotgasusingmanycatalysts,suchasCaO,MgO,CaO-MgO,andmanyimportantresultswereachieved.Theequipmenttheyusedincludedagasifierandacatalyticreactor,whichareconnectedinseries,andsometimesaguardbedwasinsertedbetweenthem.Forrawmaterialtheyusedbiomass,notcoal,sotheselectionofreactionconditionsandthenatureoftarswouldbedifferent.Thefreeboardoffluidizedbedplaysanimportantroleintarcracking,buttherearenotspecialinvestigationstobedone,
(2)Baker,E.G.;Mudge,L.K.Ind.Eng.Chem.Res.1987,26,1390-1395.
(3)Simell,P.A.;Leppa¨lahti,J.K.;Bredenberg,J.B.Fuels1992,71,211-217.
(4)Li,H.B.;Fang,Y.T.;Wang,Y.;Zhang,B.J.CoalConversion1997,20(4),9-13.
(5)Delgado,J.;Aznar,M.P.;Corella,J.Ind.Eng.Chem.Res.1997,36,1535-1543.
(6)Gil,J.;Caballero,M.A.;Mart ´n,J.A.;Aznar,M.P.;Corella,J.Ind.Eng.Chem.Res.1999,38,4226-4235.(7)Gil,J.;Caballero,M.A.;Mart ´n,J.A.;Aznar,M.P.;Corella,J.Ind.Eng.Chem.Res.1996,35,3637-3643.
10.1021/ef034077vCCC:$27.50©2004AmericanChemicalSociety
PublishedonWeb09/22/2004
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