甲醇精馏文献英文.docx

甲醇精馏文献英文.docx

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甲醇精馏文献英文

MethanolDistillationSystem:

ProcessAnalysisandColumnDesign

SunJinsheng,TianYufeng,XuShimin,DingHui,WangTao,LiXingang,ZhengYanmei

（1ShoolofChemicalEngineeringandTechnology,TianjinUniversity,Tianjin300072;

2NationalEngineeringResearchCenterforDistillationTechnology,Tianjin300072）

AbstractBaseonindustrialresearchandexperience,theprocessofmethanoldistillationisanalyzed,andaboveall,anewconceptofhighpressureflowsheetandlowpressureflowsheetisdefined.ThenewconfigurationhelpstohandleproblemsencounteredinmanyfactoriesinChina.Theinterinfluencebetweenprocessandcolumninternalpatternisalsopointedout.Recommendationofnewcolumninternaldesignsisgiven.Finally,industrialexamplestellthehowthenewconceptworksandthepossibilityofcombiningprocesstogivemoreopenstosolveengineeringproblems.

Keywordsmethanoldistillation,two-effectdistillation,highpressureflowsheetandlowpressureflowsheet,flowsheetanalysis,simulationwithhydraulic,columninternaldesign

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.

1PROCESSDESCRIPTION

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

Theoperationpressureof