油气储运毕业设计文献翻译.docx

油气储运毕业设计文献翻译.docx

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油气储运毕业设计文献翻译

PetroleumRefiningProcesses

Desulphurisation

Sulphuroccursincrudeoilscombinedinavarietyofways,fromthesimplestcompoundH2Stocomplexringstructures.H2SisproducedduringdistillationofthecrudeoilbydecompositionofhigherboilingsulphurcompoundsandappearsintheLPGfromwhichitmustberemovedbecauseofitspoisonousandcorrosivenature.Thisisdonebycountercurrentwashingwithanamine（e.g.diethanolamine）,theH2Sbeingremovedforsulphurrecoverybyheatingtheaminesolutioninaseparatevesselthusregeneratingtheamineforrecycletothewashingstage.MercaptanscanbeconsideredderivativesofH2S,inwhichonehydrogenatomisreplacebyacarbon/hydrogengroup,andsharesomeofitsunpleasantpropertiesofbadsmellandcorrosivity.Thosemercaptansboilingbelowabout80℃arereadilydissolvedinalkalinesolutionsbutthesolubilitydecreasesrapidlyabovethattemperature.ForLPGandlightgasolinesthereforethemercaptanscanberemovedbycountercurrentwashingwithcausticsodasolution.

TheUOPMeroxprocessusescausticsodatoextractthemercaptanswhicharethenoxidisedwithairtodisulphidesandthecausticsodaregeneratedforfurtheruse.Theoxidationstepisassistedbyametalcomplexcatalystdissolvedinthecausticsoda.

Theprocesscanberepresentedasfollow:

4C2H5SH+4NaOH=4C2H5SNa+2H2O+2H2O

+O2

2C2H5S—SC2H5+4NaOH

Thedisulphidesarenotsolubleincausticsodaandformanoillayerwhichcanberemoved.

Mercaptansinfractionboilingbetween80℃and250℃cannotbeoxidisedtodisulphidesintheMeroxsolutionwithair.Thedisulphides,whicharenon-corrosiveandhavelittlesmell,remaindissolvedintheoilsothatnoactualdesulphurisationhasbeenachivedbuttheproductshavebeen“sweetened”.Anotherprocessfortheoxidationofmercaptansusescopperchlorideasacatalyst.Bothprocessescanbeusedintheproductionofaviationjetfuels.

Asthecutstakenfromcrudeoilincreaseinboilingpointitisfoundthatthesulphurincreases.Inthe250-350℃rangewhichisusedforbothdieselfuelanddomesticcentral-heatingfuelthesulphurcontentisabout1percentweightfrommostMiddleEastcrudes.WhenthismaterialisburntthesulphurisoxidisedtoSO2which,beingeasilyoxidisedtosulphuricacid,causesatmosphericpollutionandcorrosionofmetals.Thesulphurcannotbetreatedbythemethodspreviouslyoutlinedasitismainlycombinedwithcarbonandhydrogeninformsmuchmorecomplicatedthanthesimplemercaptans.Thesecomplexcompoundshavetobebrokendowntogetatthesulphurwhichisdonebypassingtheoiltogetherwithhydrogenathightemperature（320-420℃）andhighpressure（25-70bar）,overacatalystcontainingcobaltandmolybdenumoxidesonanaluminabase,madeintheformofsmallpelletsorextrudates.Thereactioniseasierandthecatalystlifebetterwhentheratioofhydrogentofeedisseveraltimeshigherthanthatnecessarytocompletethereactionchemically.UndertheseconditionsthesulphurcompoundsdecomposeandthesulphurcombineswiththehydrogentogiveH2S.Almostallofthesulphurcompoundscanbedecomposedinthiswaywithoutsignificantlyaffectingtheremaininghydrocarbons.

Thisprocessofdesulphurisation,alsocalled“hydrofining”,iseffectiveinattackingallformsofsulphurcompounds,andcanbeusedtotreatanypartofcrudeoil.

Inprincipletheequipmentusedforallfeedsisbasicallysimlarandwillcontainmeansforcarryingoutthefollowingsteps:

1Supplythefeedandhydrogentothereactoratthecorrecttemperatureandpressure.

2Coolthereactorproducttocondensetheoilandallowtheseparationoftheexcesshydrogensothatitcanberecycledtothereactor.

3RemovetheH2Sandsmallquantity（2-3percent）oflow-boilinghydrocarbonsproductedinthereaction.

Apumptakesthefeedandraisesittotherepuiredpressureandpassesitthroughtubesinafurnacewhereitisheatedtotherequiredtemperaturebeforebeingmixedwiththehydrogenandpassingintothereactor.Thereactorproductiscooled,partiallybythefreshfeedinaheatexchangertosavefuel,andpartiallybywaterinanotherheatexchanger.Excesshydrogenisseparatedfromthecondensedoilinadrumandrecirculatedbacktothereactorbyacompressortogetherwithfreshhydrogentoreplacetheamountconsumedinthereaction.TheliquidfromthedrumispassedintoadistillationcolumnwheretheH2Sandlow-boilingbreakdownproductsareremovedandthedesulphurisedoiltakenfromthebottomofthecolumn.

Muchofthecrudeoilboilingabove350℃isusedtomakeheavyfueloilforpower-stations,shipsandlargeindustrialplantsandcanhaveasulphurcontentof2.5-4percentweightfrommostMiddleEastcrudes.BuringthismaterialreleasesSO2andveryhighchimneyshavetobeused（anumberinthe500-600footrangehavebeenbuilt,oneof800feetintheUSA）sothattheSO2canbedisperedwidelyintheatmospherethusavoidinglocalisedpollution.Theidealsolutionwouldbetodesulphuriseallpartsofthecrudeoil.Unfortunately,althoughthedesulphurisationofdistillatesboilinguptoabout550℃cabberelativelyeasilyaccomplished,thetreatmentofheavycrude-oilresiduesposesmanydifficultproblems.Withincreasingboiling-pointthedifficultyofdesulphurisationincreasesandalsotheproportionofmoleculescontainingsulphurbecomeshigh（possiblyupto50percent）whichmeansthatahighproportionofthemoleculespresentmustbedecomposed.Tracemetalsintheoiltendtodeactivatethemosteffectivedesulphurisationcatalystsandhighpressures（upto170bar）mustbsused.Allthesefactorsresultinhighcostsforfuel-oildesulphurisation.Alsorecentdevelopmentsinthecrude-oilsopplysituationworldwidehaveplacedastongemphasisonenergyconservation.Consequently,fuelintensiveprocesseswouldbeemployedonlyasalastresortwhenalternativemeansofminimingpollutionarenotviable.

InarefinerywheredesulphurisationisusedextensivelytheproductionofH2Scaneasilyreach100tonnesperday.AlthoughtheH2ScouldbeburnttoSO2andventedfromallstacks,itisveryundesirablebecauseoftheatmosphericpollutioncausedandadditionalplantisinstslledtorecoverthesulphur.TheH2SisburnttoSO2withtheoxygensupplylimitedsothataboutone-thirtoftheH2Sburns.Thisgivesamixtureoftwo-thirdsH2Sandone-thirdSO2whichwillcombinetoformsulphurandwater:

2H2S+SO2=3S+2H2O

Thesulphuriscollectedandisusuallysoldtochemicalcompaniesmainlyforthemanufactureofsulphuricacid.

ThermalCracking

Whenhydrocarbonsareheatedtotemperaturesexceedingabout450℃theybegintodecompose.Thelargemoleculesbreakingor“cracking”intosmallerones.Paraffinsarethemosteasilycrackedfollowedbynaphthenes,aromaticsbeingextremelyrefractory.Atonetimethermal-crackingprocesseswerewidelyusedtoimprovetheoctanenumberofnaphthasortoproducegasolineandgasoilfromheavyfractions.Thequalityofthegasolinefromthethermalcrackingofnaphthaisnothighenoughforpresentmotorgasolinesandtheprocesshasfallenoutofuse.Theproductsfromheavyoilcrackingrequirementsandwhileatpresenttheprocessislittleuseditcouldbeofinterestshouldconversionofheavydistillates（upto550℃）togasoilsberequired.Onethermalcrackingprocesspresentlyincommonuseisvisbreakingwhichisthethermalcrackingofviscouscrude-oilresiduestoreducetheirviscousitybybreakingdownthelargecomplexmoleculestosmallerones.Asatisfactoryfueloilcanthembemadewithoutthenecessityofusinggasoilsorkerosinetoblendwiththeviscousresidue.

Anotherthermal-crackingprocesspresentlyemployedisDelayedCoking,whichisnormallyappliedtoatmosphericorvacuumresiduesfromlowsulphurcrudesfortheproductionofelectrodegradecoke（usedmostlyinaluminiumproduction）.Theresidueisheatedtoabout500℃andpassedtothebottomofalargedrumwherethecrackingreactionproceedswhichbreaksdownthehigh-boilingmaterials,Thelowerboilingmaterialsformedvaporiseatthehightemperatureinthedrumandpassoutofthetoptothefractionationsystemwheretheyareseparatedintogas,gasolineandgasoilandleavebehindinthedrumaporousmassofcoke.Whenthedrumisfullofcokethefeedisswitchedtoanotherdrumwhichisfilledwhilethefulloneissteamedoutandthecokeremoved.Asinthethermal-crackingprocesstheliquidproductsrequirehydrogenationforuseasnaphthaorgasoil.

CatalyticCracking

Thermalcrackingofheavydistillatesforgasolineproductionisnotselectiveandproducessubstantialquantitiesofgasandfueloiltogetherwiththegasoline,whichisalsonotofverygoodquality.Aboutthirtyyearsagoitwasfoundthatfuller’searthandsimillarmaterialscouldactascrackingcatalystsandgiveagoodyieldofhighoctanenumbergasline（catalyticcracking）.Unfortunately,thefuller’searthbecamequicklycoveredincarbonandnolongeractedasacatalystwasreturnedtoitspreviousactivityandthustooperatetheprocesscontinuouslyitwasnecessarytodevisemethodsofalternativelyusingandregeneratingthecatalystcontinuouslyonalargescale.

Oneofthemostsuccessfulmethodsofachievingthisdependsontheuseoffluidisation.Whenagasispassedupthroughabedoffinepowerthebehaviourofthepowerdependsonthevelocityofthegas.Ifitishigh（about1m/sec.）theparticlesaremovedaboutbythegasandthebedofpoweractslikeafluidandcanbetransported,finditsownlevel,ect.justlikealiquid.Byusingthisproperty,thecatalyst,inpowerform,canbecirculatedcontinuouslybetweenareactionstageandaregenerat