090105009罗浩猛 外文文献原稿和译文.docx
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090105009罗浩猛外文文献原稿和译文
外文文献原稿和译文
原稿
MethanolDistillationSystem:
ProcessAnalysisandColumnDesign
Abstract:
Baseonindustrialresearchandexperience,theprocessofmethanoldistillationisanalyzed,andaboveall,anewconceptofhighpressureflowsheetandlowpressureflowsheetisdefined.ThenewconfigurationhelpstohandleproblemsencounteredinmanyfactoriesinChina.Theinterinfluencebetweenprocessandcolumninternalpatternisalsopointedout.Recommendationofnewcolumninternaldesignsisgiven.Finally,industrialexamplestellthehowthenewconceptworksandthepossibilityofcombiningprocesstogivemoreopenstosolveengineeringproblems.
Keywords:
methanoldistillation,two-effectdistillation,highpressureflowsheetandlowpressureflowsheet,flowsheetanalysis,simulationwithhydraulic,columninternaldesign
INTRODUCTION
Averyimportantmaterialinorganicchemicalindustry,methanoliswidelyinvolvedinthemanufactureofplasticmaterial,syntheticfiberandrubber,dyestuff,coveringmaterial,spice,medicalfield,pesticideandetc.Also,itisnotonlyafinesolventformanyorganiccompoundsbutasoundsubstituteforgasolineinmanycountriesasgreenenergy.Withthequickdevelopmentofthenationaleconomy,thedemand(actualorpotential)ofmethanolhassharplyincreased,whichacceleratesthedevelopmentofthemethanolindustryandincrementofthemethanoloutput.Presently,methanoldistillationtechnologyhasbeendevelopedtobelarge-scale,lowenergyconsumingandmoreenvironmental.Themainpatentdealersinthisindustryoftheworldhavetheequipmentsdesignedfor50007500t/dEz~.ButChina(mainland)hashardlynorunningunitswithcapabilityover200kt/aofhighquality(suchasO-M-232EUS).Recently,NationalEngineeringResearchCenterforDistillationTechnologyatTianjinUniversity
(NERCDT)hasdonemuchontechnicalandmarketresearch,includingthesimulationofallthefamiliarflowsheetsonindustrialandlabdata,especiallystudyingthe2-effectheatexchangebetweenthe2methanolrefiningcolumns.Asasummaryofourwork,thehighpressureprocessandthelowpressureprocessfor3+1–columnprocesswasputforward.
1.PROCESSDESCRIPTION
Methanolcanbesynthesizedfrommanymaterials,forinstance,naturalgas,gasoil,fueloil,coal,etc.Exceptforthedifferenceincatalysts,reactionmechanicsandtheconcentrationofmethanolinrawproduct,thesubsequentdistillationprocessandequipmentsaresimilar,fallingintothreemainassortments:
2–columnprocess,3-columnprocessand3+1–columnprocess.A2-columnprocessiscomposedoflightendscolumnandmethanolrefiningcolumnormaincolumnwhichisfoundinfactoriesunder100kt/a,offeringsimpleprocess,equipmentsandlowinvestment.3-columnprocessisbuiltupbylightendscolumn,pressuredmethanolrefiningcolumn(PMRC)andatmosphericmethanolrefiningcolumn(AMRC),forminga2-effectsdistillationwiththemixtureofthedistillatesfromthe2methanolrefiningcolumnsthemethanolproduct.Thecharacteristicofthisprocessisthe2–effectdistillationpatternbetweenPMRCandAMRC,meaningheatexchangebetweenthetopofPMRCandthebottomofAMRC.Thispatternsavestheenergy(by30%~40~)andtherecyclerateofcoolingwater.Ifamethanolrecoverycolumn,orstripper,orwatercolumninvolvesafterthelowpressuremethanolrefiningcolumntoimprovethequalityofthewastewater,theprocesswillturninto3+1-columnprocess.
1.1LightEndsColumn
Nomatterin2-columnprocess,3–columnprocessor3+1-columnprocess,theLightEndColumn(LEC)playsthesameRole.Someofthelightcomponentinrawmethanolfataltotheproductareremovedinthiscolumn,suchasmethylformate(MFOR),dimethylether(DME),C1~C6,aswellasacetoneandmethylethylketone(MEK).SomepublicationsdefineMFOR,
DMEandC1~C6asthealcoholic–solubleimpurities,whileDMEandMEKtheaquatic-solubleimpurities.ThestandardofthedivisioncanbefoundinTable1.
Industrialinvestigationshowsthatthebasicmeasuresoftheremovaloperationincludelargerefluxratioandprocesswaterinletorbothtaken.Theprinciplesrespectivelyemploythedifferenceofboilingpointorrelativevolatilityandsolubilityofthecomponents.
Asaroutinemethod,largerefluxratio;say0.7~0.9(refluxtocolumnfeed),requireshighcondensertemperaturetoremovelightimpuritiesofhighboilingpoint,forexampleacetone.Obviously,thismethodisaccompaniedbyhighenergyconsumption.Becausetheabovemethodcannotreducethelossofmethanol,processwaterisaddedtothecolumntochangetheconcentrationofmethanolandwaterinordertoweakenthesolubilityoftheliquidmixtureinthecolumntothealcoholic-solubleimpurities.Theprocesswaterisnormallyfedtothecolumnin3ways:
intothe2ndcondenser,atthetopofthecolumnandalongwiththerawmethanolfeed.
Togetthesamemethanolandwaterconcentrationattheinletposition,processwaterinthefirstwayamountsapproximately5%thatofthefeed,whiletheothers,10%~20%.
Inmanyunits,analkalinesolution(~15%NaOH)isaddedtotheexhaustionsectionofthecolumntobalancetheacidsforamoderatepHvalueoftherefinedrawmethanol.
1.2RefiningColumn/MainColumnFlowsheet
Thiscolumn,packedortrayed,havetheproductmethanolbysidedrawnearthetopofthecolumninthedistillationsection,takingup85%effectivelengthofthecolumn.Atthemiddleoftheexhaustionsection,asidedrawremovesmethanol,ethanol,isopropanolandpropanol,etc.Toassurehighpurityofthewastewater(<100PPMmethanol).Whenhighqualitymethanolproductrequired,anothersidedraw,calledethanolsidedrawinfactories,isopenedatthebottomofthedistillationsectionandjustalittlehigherthanthefeedinlet,tohelpreducetheconcentrationofethanolinmethanolproduct.
1.3RefiningColumnsin3-columnFlowsheet
Inthe3multiple-effectdistillationtypes,feedsplitting(FS),lightspilt/forward(LSF)and1igh(split/reverse(LSR),theLSF2-effect
patternbyLurgiisthemostpopularinChina.AsshowedinFigure2theentirefeedstream(refinedrawmethanol)ispumpedtoPMRC.Abouthalfofthe1ightkeycomponent(methanol)isremovedin
thedistillateatrelativelyhighpurity.Thebottomproduct,containingremainderofthekeylightcomponentisfedtoAMRCandispurifiedinthiscolumn.OneortwoSidelinesWillbedrawntohelpthepurificationofwastewaterandthedistillate.Inthiscasetheheatintegrationisinthedirectionofmassflow.
Athighpressure,therelativevolatilityisdecreased.ThiscontributestoexplainthereasonwhyinmanyfactoriesthemethanolfromthePMRC
ContainsmoreimpuritiesthanthatfromAMRC,thoughtherefluxratioinPMPCis1argerthanthatoftheAMRC.Theotherreasonsarebobblepointrefluxtemperatureandtheexistenceofremainderlightends.Thetwoproductscanbesoldatdifferentpricesorinmixture.Besidesthis,theshortageincludestheincreasedpumpingcoststoincreasethefeedpressure,thepurchasecostforthickercolumnwallneededforhighpressureandoperationcostforthemorecomplicatedflowsheet.Butinmanycases,theseincreasesaresmallwhencomparedwiththelargesavingsintheutilitiesinboilingandcondensing.
Sincein3-columnflowsheet,purityofboththemethanolatthetopandwastewateratthebottomisrequired,aminimumTbetweentheflowsinthereboilierofAMRCandcondenserofPMRCtogiveenoughheatdutyfortheseservices.This,usually20,isdeterminedbytheoperationpressureofPMRC,andthepressuredropoftheAMRC,whilethelatterisdeterminedbytheinternalsofthecolumnatacertaincolumnI.D..
1.4TheHighPressureFlowsheet(HPF)
Inmethanoldistillationunitsoflargescale(say,300kt/a,usuallyin3-columnflowsheet),methanollostwithinthesidedraw(s)oftheAMRC,aswellashighpressureitimposesonthewastewatertreatment,cannotbeomitted.ThesolutionisfeedingthesidedrawfromexhaustionsectionoftheAMRCtoamethanolrecoverycolumn(orstripper)onthebasisof3-columnprocess.Mostofthepurifiedwastewater,inthiscase,drainsfromtheAMRCbottom,anotherlittleportionofitfromthatoftheforthcolumn.Thisrequiresmuchhigherbottomtemperatureinordertoripeoffmethanolandotherlightorganicimpuritiesinwastewater.BecausethethermalresourceofreboilerforthiscolumnistheoverheadmethanolvaporinthePMRC,tomaintainnormaloperation,theoperationpressureofthehighpressuremethanolrefiningcolumnmustbehighenoughtoofferthetemperaturegradientinheatexchange(condenser/reboiler).
1.5TheLowPressureFlowsheet(LPF)
Theconfigurationoflowpressureprocesscomesfromthecomparisonwiththehighpressureflowsheet,differinginthefeedpatternofthemethanolrecoverycolumn.ThisdefinesaflowsheetwithAMRCtoabandonitsrequirementtothebottomwastewaterandthebottomproduct(with5%~10%wtmethanolinit)asthefeedoftheforthcolumn.ThevariationsavesthesidedrawsformtheexhaustionsectionofAMRC,makingthecolumnstructuresimpler,and,ofthemostimportance,obtainsalowerreboilingtemperaturebecauseofthechangeinbottomcomposition.Thissituation,asthelogicofthehighpressureflowsheet,callsforaloweroperationtemperatureofthetopvaporflowatPMRCandaloweroperationpressureaccordingly.
1.6ComparisonoftheHPFandLPF
TheoperationpressureofPMRCinHPFisaround850~900kPa(A),whilethatofLPF640~700kPa(A).Obviouslyriseupatthefirstglancethedifferencesincostsforfeedpumpingandrequirementfortheconditionofheatingmedium.And,toobtainb