ReactionperformanceofFCCslurrycatalyticcracking.pdf
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1、Reactionperformanceof FCC slurrycatalyticcracking XingyingLan, ChunmingXu, Gang Wang,Jinsen Gao * State Key Laboratoryof HeavyOil Processing,China Universityof Petroleum,Beijing102249,PR China 1.Introduction The ?uidizedcatalyticcrackingof hydrocarbonsis the mainstay processfortheproductionofgasolin
2、eandlighthydrocarbon productsfromheavyhydrocarbonssuchas vacuumgas oils.The resourceof thecrudeoilforcesthe re?nersto processmoreand morevacuumresidinFCC units1 . Withtheuseofheavier feedstocks,increasingamountsofcokearefoundinside?uid catalyticcracking(FCC) disengagervessel2 . Coke is commonly obse
3、rvedon the surfaceof the cyclonebarrels,disengagerdome, and walls3,4 . Coke depositionin the disengagervesselreduces theoperatingreliabilityof FCC unit,dueto theconstantriskof problemslinkedto hamperedcatalystcirculationcausedby pieces of cokebreakingloose5,6 . Cokeformationhasbeenobservedwhereconde
4、nsationof hydrocarbonvaporsoccurs3 . Heavierboilingcomponentsin the crackedproductsmaybe verycloseto theirdewpoint,and they willeasilycondenseandformcokenucleationsitesoneven slightlycoolersurfaces.Thereare moreheavyhydrocarbonsin the FCC feedstockswiththe increaseof the residblendingpercentage. Iti
5、s hardtoatomizecompletelythefeedstocks,andtheheavy componentscannotbe fullyvaporizedand adhereto the surfaceof the catalyst.The unvaporizedheavyhydrocarbonsare strippedin the strippingsection,and enterthe disengager.Passage of stripped hydrocarbonsthroughthecoolerareaof thedisengagervessel, alongwit
6、htheirextendedresidencetimeinsidethevessel, enhancesthe chanceof condensationof the heaviestcomponents of strippedhydrocarbons,whichcausescoke formationinsidethe disengagervessel. In the commercialoperation,thereare the twobasic methodsto minimizecoking:avoiddeadspotsandpreventheatlosses.An exampleo
7、f the ?rstmethodis using domesteamor purgesteamto sweep out stagnantareas in the disengager7,8 . An exampleof the secondmethodis usingproperinsulationin the disengagervessels 9 . In fact,theessentialmethodtosolvecokingproblemsis to preventheavyhydrocarbonsfromenteringthe disengager.In other words,he
8、avyhydrocarbonsshouldbeconvertedtolighter hydrocarbonsas completelyas possiblebeforetheyenterthe disengager.Therefore,if regeneratedcatalystis introducedintothe strippingzoneand mixedwithspentcatalyst,the mixtureof spent and regeneratedcatalysts?owdownwardthroughthestripper, wherethe countercurrents
9、treamstripsthe entrainedhydrocarbon fromthe catalystmixture.This admixingof spentand regenerated catalystnotonlyraisesthespentcatalysttemperaturetoeffect desorptionofentrainedhydrocarbon,butalsoimprovesthe catalystactivitytoenhancecatalyticcrackingoftheentrained hydrocarbon,thusconvertingmoreentrain
10、edheavyhydrocarbons to lighterhydrocarbonproducts.Consequently,the quantityof the heavyhydrocarbonspronetocokeis decreased,whichreduces subsequentcokeformationin thedisengagervessel. SlurryoilistheheaviestcomponentofFCChydrocarbon products,anditismostlikelytobe condensedtoformcoke. Therefore,itshoul
11、dbeconvertedtolighterhydrocarbonsas completelyas possible.Ingeneral,FCC Slurryis mainlyusedas blendingcompositefor heavyfuel oil 10 .In some commercialFCC unit,theslurryoilcan be recycledand crackedalongwithfresh CatalysisToday140 (2009)174178 A R T I C L EI N F O Article history: Availableonline4 D
12、ecember2008 Keywords: FCC slurry Catalyticcracking Coke A B S T R A C T The condensationof heavyhydrocarboncauses the coke formationinsidethe disengagervessel.Slurryoil is the heaviestcomponentof FCC hydrocarbonproductsandmostlikelyto be condensedto formcoke. Convertingslurryto lighterhydrocarbonsca
13、n alleviatecoke formation.The slurrycrackingexperiments werecarriedout in a con?ned?uidizedbed reactor.The resultsshowedthat the crackabilityof slurrywas lowerthanthatof FCC feedstock,dueto thedifferenceof theirproperties.About30 wt.%heavyoil remainedintheproductaftertheslurrywascracked,butitsendpoi
14、ntdeclinedandtheheavier componentdecreased.The comparisonof slurrycrackingresultsat differentreactiontemperaturesand regeneratedcatalystcontentsindicatedthatthe appropriateoperatingconditionsfor slurryconversion werethereactiontemperatureof 500 8C and theregeneratedcatalystcontentwithin2550 wt.%. Cr
15、ownCopyright? 2008Publishedby ElsevierB.V. All rightsreserved. * Correspondingauthor.Tel.:+86 10 89733993. E-mailaddress:(J. Gao). Contentslistsavailableat ScienceDirect CatalysisToday j o u r n a l h o m e p a g e : w w w. e l s ev i e r. co m/ l o ca t e/ ca tt o d 0920-5861/$see frontmatter.Crown
16、Copyright?2008Publishedby ElsevierB.V. All rightsreserved. doi: 10.1016/j.cattod.2008.10.013 feed. Thereis, however,limitedinformationin the openliterature on the crackingbehaviorof FCC slurry.So, this studywas designed toinvestigatethecatalyticcrackingbehaviorof FCC slurry,and thento determinethe a
17、ppropriateoperatingconditionsto convert slurryin FCC strippingsection. 2.Experimental 2.1.Feedstocksand catalysts TheslurrywassampledfromthecommercialFCC unitof PetrochinaHuabeiPetrochemicalCorporation.Thephysical propertiesof slurryoil analyzedweredensity,molecularweight, carbonresidue,andhydrocarb
18、ontype.Theseanalyseswere tabulatedin Table1. The catalystwas equilibriumLBO-16sample fromthe same commercialFCC unit,and its majorpropertieswere presentedinTable2. Thecatalystsusedinourexperiments includedspentcatalystsandregeneratedcatalysts.Thecokeon spentcatalystswas1.12 wt.%,whilethecokeonregene
19、rated catalystswas0.02 wt.%. 2.2.Apparatus Crackingexperimentswerecarriedout in a con?ned?uidizedbed reactorsystem,showninFig. 1.It is comprisedof ?ve sections:oil and steaminputmechanisms,reactionzone,temperaturecontrolsystem, productsseparationandcollectionsystem.A variableamountof distilledwaterw
20、as pumpedintoa furnaceto formsteam,and then mixedwiththe feedstockpumpedsimultaneouslyby anotherpump attheoutletofaconstanttemperaturebox.Themixturewasheatedin a pre-heater,andthenenteredintothereactor,wherecatalytic crackingreactionstookplace. Afterreaction,the oilgas was cooled and separatedintoli
21、quidsampleand gas sample. 2.3. Analyticalmethods Catalyticcrackingproductsincludegas, liquidandcoke.An Agilent6890gas chromatographwithChemStationsoftwarewas usedto measurethe volumepercentageof componentsin the gas product.The equationof statefor idealgases convertsthe volume datato mass percentage
22、s.The liquidproductwas analyzedwitha simulateddistillationgaschromatogramtogettheweight percentageofgasoline,dieseloilandheavyoil.Cokecontenton catalystswasmeasuredwitha cokeanalyzer. 2.4. Operatingconditions Thecrackingexperimentsof slurryoilwerecarriedoutover regeneratedcatalystssampledfroma comme
23、rcialFCC unit.The Table1 Propertiesof FCC slurry. ItemData Density(g/cm 3 , 20 8C)0.9668 API14.3 Carbonresidue(wt.%)5.70 Molecularweight425 H/Cratio1.48 Groupanalysis(wt.%) Saturates50.46 Aromatics34.85 Resins9.40 Asphaltenes5.29 Table2 Propertiesof catalystLBO-16. ItemData Micro-activityindex67 Sur
24、facearea (m 2/g) 102 Pore volume(cm 3 /g)0.28 Packingdensity(g/cm 3 )0.90 Component(wt.%) Al2O344.30 Re2O34.01 Metalscontent Na (wt.%)0.24 Fe (wt.%)0.41 Cu (mg/g)24 Ni (mg/g)12465 V (mg/g)431 Particlesize distribution(wt.%) 020mm0 2040mm5 4080mm51 80mm44 Fig. 1. Schematicdiagramof con?ned?uidizedbed
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