美国炼油协会年会论文2中英文对照.docx
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美国炼油协会年会论文2中英文对照.docx
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美国炼油协会年会论文2中英文对照
CostEffectiveSolutionsforReductionofBenzeneinGasoline
MaartenJ.Almering,KerryL.Rock,ArvidsJudzis–CDTECH
Introduction
Inthecurrentglobalquestfortheproductionofcleanerfuels,benzenehasbeenidentifiedasagasolinecomponent
thatshouldbereduced.Asaresult,theEnvironmentalProtectionAgencyplacedalimitof1volumepercentof
benzeneinreformulatedgasoline(RFG)in1995.TherecentlyissuedMSATIIregulationsfurtherreducebenzene
tolessthan0.62percentinallU.S.gasolineby2011.Europe,Canada,Australia,Japanandothershavealso
adoptedlimitsonbenzene.Manyothercountriesarecurrentlyintheprocessofreducingbenzeneingasoline.
Formostrefiners,thereductionofbenzeneinRFGwaseasilyaccomplishedusingexistingoptions.Manyrefiners
simplyadjustedtheC6contentofthenaphthafeedtotheirreformerbyprefractionationandproducedreformatewith
reducedbenzenecontent.Refinerswithintegratedchemicaloperationswereabletosendtheirlightreformateto
extractionfacilitiesandmovebenzeneintothepetrochemicalmarket.Otherswerealsoabletotakeadvantageof
thisoptionbyexportingthelightreformatefractionoverthefenceforoutsideprocessing.Severalrefineriesinstalled
facilitiesforhydrogenationofbenzene.Anotherpossibilityisreactionofpropylenewithbenzenetoproduce
cumene.However,thisapproachrequiressignificantcleanupoftheimpuritiesinrefinerypropyleneconsiderably
increasingthetotalcapitalcost.
Theremovalofbenzenefromthegasolinepoolrepresentsthelossofoneofthehighestoctanecomponents.The
currentprogramofaddingethanoltothegasolinepoolwilleventuallymakemostrefinerslongonoctane.Asa
result,thebenzene/octaneissueisnotasignificantfactor.
ThebenzenereductionrequiredbyMSATIIisclearlyamuchlargerquantitytodealwithandrefinersmaybeforced
tomakemoresubstantialchangesinrefineryoperationstoachievetheselevels.Formanyrefiners,prefractionation
ofthereformerfeedwillnotprovideasufficientbenzenereduction.Thehighcapitalcostofbenzeneextraction
expansionsornewfacilitieswillalsonotprovideanattractiveanswerforallrefiners,especiallysmallerrefineriesor
thoseinlocationsremotefromthepetrochemicalbenzeneusers.Assuminghydrogenavailabilityisnotaproblem,
benzenehydrogenationmayprovidetheanswer.Evenifhydrogensupplyisaproblem,itmaywellhavetobe
addressedbytheneedtoremovesulfurfromFCCgasolineaswellasotherrefineryproducts,asincreased
pressuretoreducesulfuremissionscomesintoplayinthenearfuture.Therefinerwhoislookingdowntheroad
andmakingplansprobablyhasahydrogenplantincreasinginpriority.
BenzeneSources
Inthetypicalrefinerybenzenecomesfromseveralsourcesincluding;
1)Lightstraightrungasoline
2)Reformate
2)Hydrocrackate
4)FCCgasoline
5)Cokergasoline
Howeverthebenzenefromthereformerusually
represents50-80%ofthetotal(Figure1).Asa
result,thereformateisthenaturalplacetofocus
benzenereduction.Inmostcasesthedesulfurized
lightstraightruncanbeco-processedwiththe
reformateforbenzenereduction.
ReformateIsPrimaryBenzene
Source
50to80%
LightStraightRun
Reformate
FCC
Hydrocrackate
Coker
Figure1ConventionalBenzene
Saturation
Theconventionalapproachto
removingbenzenefrom
reformateisshowninFigure
2.Reformateisfractionatedin
areformatesplittertotake
benzeneandlighter
componentsoverhead.The
toluenecontentofthelight
reformatefractionislimitedto
minimizeitslossdueto
hydrogenation.Thisbenzene
containingfractionissenttoa
hydrogenationreactorwhere
benzeneisconvertedto
cyclohexaneinahighly
exothermic,highpressure,
fixedbedcatalyticreactor.Acooledrecyclestreamisnormallyrequiredtomodulatereactortemperature.The
reactoreffluentissenttoastripperwherelightendsareremovedbyfractionation.Thisapproachrequiresmany
equipmentitems(highcapitalcost)andissusceptibletoupsetsinoperation.
TheCDHydroProcess
In1994,anewprocessforhydrogenationwas
commercialized.ThepatentedCDHydro
processcombinesfractionationwith
hydrogenation.Proprietarydistillationdevices
(CDModules)containingcatalystareinstalled
inthetopsectionofthefractionationcolumn
(Figure3).Hydrogenisintroducedbeneaththe
catalystzone.Fractionationcarrieslight
componentsintothecatalystzonewherethe
reactionwithhydrogenoccurs.Fractionation
alsosendsheavymaterialstothebottom.In
addition,cleanhydrogenatedreflux
continuouslywashesthecatalystzone.These
factorscombinetoprovidealongcatalystlife.
Theheatofreactionevaporatesliquidandthe
resultingvaporiscondensedintheoverhead
condensertoprovideadditionalreflux.The
naturaltemperatureprofileinthefractionation
columnresultsinavirtuallyisothermalcatalyst
bedratherthanthetemperatureincreasetypical
ofconventionalfixedbedreactors.
Lightendscontrolcanbeachievedbyaddition
ofapasteurizationsectionatthetopofthefractionationcolumn.Theoverheadproductistakenasasidedrawwith
reducedcontentofhydrogenandotherlightends.
TheCDHydroprocesscanoperateatmuchlowerpressurethanconventionalprocesses.Pressuresforthe
CDHydroprocessaretypicallysetbythefractionationrequirements.Additionally,theeliminationofaseparate
hydrogenationreactorandhydrogenstripperoffersignificantcapitalcostreductionrelativetoconventional
technologies.Theresultingprocesssimplificationcanalsoreducemanpowerrequirements.
Anotherfactorthatisimportantinthedesignofrefiningunitsissafety.Thecombinationofintegralreactionheat
removal,lowoperatingpressureandfewerequipmentitemsenhancesthesafetyoftheCDHydroprocessrelativeto
conventionaltechnologies.
TheBenzeneCDHydroProcess
TheCDHydroprocessofferssignificantadvantageswhenappliedtothehydrogenationofbenzene.Thetypical
processschemeispresentedinFigure4.RequirementsofMSATIIcanbemetinafractionationcolumnwhichis
similartothatrequiredtoproducethelightreformatefortheconventionalfixedbedbenzenehydrogenationprocess.
Noadditionalreactorsystemorhydrogenstrippingcolumnisrequired.TheBenzeneCDHydrocolumnisoperated
tominimizethetolueneinthecatalystzone.Hydrogenisaddedbelowthecatalystzoneandsaturationofbenzene
tocyclohexaneintheoverheadproductisvirtuallycomplete.Conversionofbenzeneinreformateexceeding95%
hasbeendemonstratedat35psigoperatingpressure.MostapplicationsoftheBenzeneCDHydroprocesswillbe
designedtoachieve70to99+%benzenehydrogenationatlessthan100psigoperatingpressure.Conventional
processesrequire350to500psig.TheBenzeneCDHydroprocessmayprovidemuchhigherlevelsofbenzene
removalthanrequiredbyMSATIIinspecific
circumstances.Inthesecasesrefinersmaywant
toconsiderusingthehighefficiencyofthe
BenzeneCDHydroprocessratherthanreduce
benzeneinotherstreamsorotherlocations.
Tradingofbenzenereductioncreditscouldalso
makethisoptioninteresting.
Thisfirstcommercialinstallationforhydrogenation
ofbenzeneinreformateviatheBenzeneCDHydro
processwasstartedupinDecember1995by
TexacoatitsBakersfield,Californiarefinery.This
unitwasdesignedforabenzeneconversionof
80%.Benzeneconversioniscontrolledbythe
amountofhydrogenfedtothecolumn.The
columnoperatesatarefluxdrumpressureof75
psigsothattheoffgasmaybeventedtothe
refineryfuelgassystem.Thecapacityofthisunit
wasrecentlyincreasedbymorethan30%by
installinganadvancedCDModuledesignwith
increasedcatalystactivity.ThereweresixcommercialBenzeneCDHydrounitsinoperationattheendof2005.Thesefacilitiesarelistedin
Table1.OnemoreBenzeneCDHydrounitisscheduledforstartupin2010.
Table1
BenzeneCDHydroOperatingUnits
ClientLocationReformerFeedBenzene%Start-up
TexacoBakersfield,CASemiRegen2.521995
NanseiSekiyuOkinawa,JapanSemiRegen5.751999
BPRotterdamEuroport,NetherlandsSemiRegen3.291999
ShellHarburg,GermanyCCR4.411999
ExxonMobilAltona,AustraliaSemiRegen8.932005
CaltexLytton,AustraliaCCR10.182005
AlternateConfiguration
Insomecasestherefinermayneedtoremovemorebenzenethancanbeaccomplishedbytreatingthereformate
alone.ThissituationcouldoccuriftheLightStraightRun(LSR)hasahighbenzenecontentoriftherearenoother
lowbenzenestreamstodilutethepoolbenzenetotherequiredlevel.Seasonalblendingconsiderationsorthe
periodiclossofproductionfromkeyrefineryunitsmayrequirefurtherbenzenereductioncapabilitytoprovide
operatingflexibilityandensureyearlyaveragebenzenelimitsarenotexceeded.Figure5presentsdataforsucha
situation.Thisrefinerneedstoreducebenzenefrom1.9%inthereformateplusdesulfurizedLSRdownto0.4%in
ordertomeetaverageannualpoolspecifications.Evenif100%ofthebenzenewasremovedfromthereformate,
theLSRbenzenecontentwouldkeeptheblendedaverageabove0.4%.Therefore,therefinermusttreatboth
streamsforbenzeneremoval.
OriginalBenzeneBalance
Thefollowingconfiguration(Figure6)showshowthisrefinerwouldreducethebenzeneusingaconventional
approach.InordertohydrogenatethebenzeneintheLSR,itmustfirstbedesulfurized.Itmaybepossibletomake
useoftheexistinghydrotreatingfacilitiesfordesulfurizationofboththenaphthaandtheLSR.Thisalsooffersthe
opportunitytoreducethebenzeneprecursorsintheReformerfeedby
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