外文翻译-甲醇精馏采用高效塔板和工艺路线的改进

外文翻译1、英文原文MethanoldistillationtrayswithhighefficiencyandprocessimprovementsinlineAbstractBriefdescriptionofthemethanoldistillationtowerinternalsrehabilitationprograms:micro-holewidthefficientcompositeplate,moresuitablethantheregularpacking,superior;analysisofthreetowersofmethanoldistillationtowerprocessthantheadvantagesoftechnologyandeconomicbenefits.KeywordsTrayefficiencyProcessRouteImproveFormanychemicalelements,theenergyconsumptionofthetechnologyisalwaysanimportantfactorineconomicindicators.Saveenergy,reduceconsumptionandspeedupthepaceoftechnologicaltransformation,theimplementationofproductstructureadjustment,thesurvivalofeverybusinessdispute,anddevelopmentofimportantmeasures.Nowaftermyfactorytechnicaltransformationdescribedbymethanoldistillationtraysandimprovedhightechnologyroutetoreducingenergyconsumptionplayanimportantrole.Practiceshows,forthemethanoldistillationseparation,notjustrelyonhighlyefficientdistillationcolumninternalsusedinordertoachievesignificantreductioninenergyconsumptionofalcoholdistillation,andmethanoldistillationprocessimprovementscanbemadetothesystemconsumptiondecreasedsignificantly.1AmethanoldistillationtowerprocessCurrently,mostofthetwintowersofmethanoldistillationseparationprocessesareused.Myfactoryhasasetof3104t/amethanoltowerdistillationunit,inDecember2002tobeexpandedto8104t/amethanoltowerdistillationunit,theprocessshowninFigure1.Thisprocessconstitutedbythetwodistillationcolumns:pre-towerandthemaintower.Comefromthemethanolsynthesissectioninthecrudemethanolcontaining86%methanol,thefirstintothepre-tower,isactuallyapre-columnextractivedistillationcolumn,inthetopofthetowerbyaddingtheequivalentof20%crudemethanolfeed.30%ofthewater,waterasextractantthecrudemethanolintodimethyletherandothercompoundcontainedintheseparatelightcomponents,thuspre-columnbasedproductsmainlylightcomponentssuchasdimethylether,andthetowerbottomproductmainlyamixtureofmethanolandwater.Pre-columnconditionsaregenerallyoperatedundernormalpressure,thetoptemperatureof65.75orso,bottomofthecolumntemperatureisabout80.Pre-towertraysusuallyinstalled45.60,canachieveatheoreticalseparationstep25-35.Sincethetowerwasextractedbymethanolandwatertowertotowerbottom,socrudemethanolfeedopeningpositionisrelativelyhigh,generallyupfromthebottomofthecolumnnumberofthefirst36-40blockboardfeed.Pre-Tatabottomoutflowofmethanolandwatermixtureimmediatelyintothemaintower,inthemaintowerofmethanolandfuselachievewaterseparation.Usuallyinstalledinthemaintowerblocktray65-85,needs36,050atheoreticalseries(asthebackflowofsize).Manyplantproductsareoftenstressedthetowerofmethanolconcentration,whiletheoutflowofwateronthebottomofthecolumnwithmethanolcontentlessimportance,sothepre-columntoamixtureofmethanolandwaterareinthelowerhalfintothetowermaintower.Locationofthefeedusedbyseveralbottomofthecolumn20abouta26plate.Themainmethanoldistillationtowergenerallyoperateatatmosphericpressure.Toweroperatingtemperatureof65-66,bottomofthecolumnoperatingtemperatureof1051IO.C.Towerrefinedmethanolproductgenerallyrequiremoisture0.1%,methanolcontent99.5%,whilethebottomofthecolumnwithmethanolcontentinthedischargedwatermustbe0.5%.Topreventpre-towerwithalightcomponenttothemaintowerandmovedwithmethanolontopofthetowerwaspurifiedmethanolproductoutoftowers,themaintowerfromthetop,generallyinthefirst10orsosidedrawtraypurifiedmethanolproduct.Highenergyconsumptionofsuchprocesses,Iplantsteamconsumptionpertonofmethanolint2TransformationofmethanoldistillationlineThetransformationofmethanoldistillationsystem,canbeusedtwoways:First,highefficientdistillationcolumninternalstoimprovetheseparationefficiency,reducebackflow,therebyreducingenergyconsumption;Anotherwayistochangetheseparationline,andreduceenergyconsumption.Efficientuseofmethanoldistillationtowerinternalscanimproveyieldandreduceenergyconsumptionwiththerole,butthemagnitudedoesnotmeetexpectations.Atthesametimechangingthedistillationprocessroutetothegreatereffectofreducingenergyconsumption.Themostcommonlyusedpiecesofhigh-DistillationColumnwithstructuredpackingandefficientmaintraytwocategories.Accordingtotheactualsituationinourfactory,structuredpackingdoesnotapplytoourplantexpansiontransformationofmethanoldistillation.Reasonsareasfollows.(1)Thehighseparationefficiencyofstructuredpackingismainlyexpressedinthehydrocarbonclasssystem.Forthistypeofmaterialsystem,theliquidssurfacetensionisverylow,easy-to-thestructuredpackinghasalargenumberofsurfaceareaonthestretch,resultinginsignificantgas-liquidinterfacialsurfacearea,toachieveexcellentseparationefficiency.Inthemethanoldistillationsystemiscompletelydifferent.Theliquidinthetwotowerscontainalotofwater,somuchhigherthanthesurfacetensionofliquidorganichydrocarbonclass.Thustheliquidsurfaceinthefillerdispersionisseverelyreduced,gas-liquidmasstransferefficiencyisboundtofallsignificantly.Suchasmethanoldistillationtowerinthesecondhalf,closeto100%watercontent,surfacetensionisalsocloseto56dyn/cm(0.056N/m),asusedinthiscondition,thestructuredpacking,theseparationisnotsatisfactory.Iplant3104t/amethanoldistillationdevicebetransformedintoan8104t/amethanolproductioncapacity,regulatory(2)structuredpackingbed,thebedfloortothetopalwaysinstalltheappropriateliquiddistributor,sothatdownwardflowofliquidtoachieveuniformdistributionalongthetowersection.However,thegradualdownwardflowofliquid,theinitiallyuniformdistributionalongthetowersectionoftheliquidwillgraduallyaccumulatetothetowerwall.Thisphenomenonisknownaswallflow(wallflow).Whenthewallofflowoccurs,mostoftheliquidalongthecolumnwalltothedownstreamregion,whilemostofthegasinthecentralregionofupwardflowtower.Thishasresultedintheseparationofgas-liquidflow.Greatlyreducedthecontactbetweengasandliquid.OnecanimaginethatatthistimeThestructuredpackingdistillationcolumncannothaveagoodseparationefficiency.Toovercomethisproblem,generallywheninthedesignofstructuredpackingdistillationcolumn,apackedbedisonly6seektoachieveaseriesof10theory,ifatheoryofdistillationprocessrequiresfarmorethanthenumberofseries,theyshouldbestructuredpackingbedisdividedintoseveralsections,eachdistributorinstalledbetweentheliquidandthentoachieveuniformdistributionofliquidflowagain.However,thisarrangementwouldallowthecomplexstructureofthedistillationcolumn,expensive.Bythisanalysis,usingstructuredpackingfactorymethanoldistillationcolumntransformationisnotfeasible.CanIusethehighlyefficienttransformationofplanttraystomethanoldistillationcolumn,inordertosignificantlyreducetheenergyconsumptionofmethanoldistillationsystemdo?Avarietyofanalysisshowsthatthisapproachtoimprovethesystemcapacity,productpuritymethanolandmethanolyieldTheeffectisobvious,buttheeffectonreducingenergyconsumption,butalsonotverysatisfactory.DistillationTechnologyCo.,Ltd.NanjingCanningproductionefficiencyofcompositeholeminiaturevalvetrays,iscurrentlytheonlycompanyapprovedbytheU.S.researchcompanydistillationefficientindustrialscalepilottesttrays,thetowerisequippedwithacompositehole-boardmicro-valve,triangletopromoteandmultiplebubblehemdowncomer,seeFigure2.Withhighflux,highseparationefficiency,operatingflexibilityandsoon.Thetrayefficiencythanconventionaltraymorethan25%,usingtheplatetransformationoffactorypre-towersandmethanoldistillationtower,theoriginaldiameterofcolumnundertheconditionsofconstantexpansiontomeetthe8104t/amethanoldemandinvestmentthanthe50%reductioninuseofstructuredpacking,andcanreducethepre-towerwaterandbackflowofthemaintower.Whichcanreducetheenergyconsumptionofmethanoldistillationsystempurposes.Buttheprocesssimulationanalysisshowsthatundertheseconditionsmethanoldistillationsystem,loweringenergyconsumptionisonlyabout5%,thisrateisstillrelativelysmall,Istillcannotmeetthemethanolplanttoexpandoutputwithoutincreasingcoal-firedboilerrequirements.2Canningaffectedcompaniesaroundthethree-dimensionalmaptrayefficiencysignificantlyreduceenergyconsumptionfromthepointofview,onlythereplacementofhighefficiencyinternalsofthislineisnotenough,soitmustbefromthedistillationpointtofindabettersolutiontotheproblemMethods.33TaticansignificantlyreducetheenergyconsumptionofpurealcoholInmanydistillationsystem,peopletendtounityofthetwoorthreetowersandtwotowers,andstrivetoreduceenergyconsumption.Thismeansreducingenergyconsumptionofmachinesistoreducethenumberofevaporationandcondensationofmaterialstoreduceenergyconsumption.However,formethanoldistillation,thepeoplearetheoppositeofatowerwillbedividedintotwotowers,buttheycanmakealotoflowerenergyconsumption.Addressedbeforethemethanoldistillationtowerisapre-extractivedistillation.Inthetopofthetowerbyaddingextractant-water,methanolanddimethyletherandotherlightcomponentsseparately.Thetowersenergyconsumptiondependsonwaterandfeedcomposition,feedcompositionisasyntheticprocess(catalysttype.Synthesisofpressure,etc.)decisions,distillationsectioninnotatlibertytodemandforchanges.Thewaterisdeterminedbymethanol-dimethylether-watervapor-liquidequilibriumofthreesubstances.Toweroperatingatatmosphericpressureaslongasthepre-conditions,thevapor-liquidequilibriumisbasicallyfixed,basicallythesizeofwaterisfixed.Thus,themethanoldistillationcolumnatatmosphericpressureconditionsexpectedlittletochangetheprocessconditionstoreduceenergyconsumptionpossibilities.Onlybyadoptinghighefficiencyplate,increasetheseparationefficiency,reducereturnflowstoreduceenergyconsumption.However,themethanoldistillationtowerdistillationprocessisnotthecase.Methanoldistillationtowertowerfeedfromthebottomofpre-mixtureofmethanolandwater.Inthemethanoldistillationtowerfortheseparationprocessisactuallyheatingofmethanolevaporationfromthewateroutoftheprocess.Intheprocessofdistillationtowers,themaintoweroftheroleofdistillationtowerbottomisputinenoughcaloriestomakemethanoloutofthewatercompletelyevaporated,condensinginthetopofthetowerberefinedmethanolproduct.GermanLurgiCompanyinthedevelopmentofitslowpressuremethanolsynthesisprocess,theuseofthethreecolumnsofmethanolpurificationprocess.Thisprocesswillbemethanoldistillationtowerisdividedintotwotowers:thePressurizedandatmosphericdistillationcolumndistillation.TheprocessshowninFigure3.2、译文甲醇精馏采用高效塔板和工艺路线的改进摘要简要说明了甲醇精馏塔的内件改造方案：复合孔微型阔高效塔板，比规整填料更适宜、更优越；分析了甲醇精馏三塔工艺比双塔工艺的优越性和经济效益。关键词高效塔板工艺路线改进对许多化工单元来说，能耗总是其技术经济指标的一个重要因素。节约能源，降低消耗，加快技改步伐，实施产品结构调整，是每个企业争生存、求发展的重要措施。现就我厂技改后甲醇精馏阐述采用高效塔板和改进工艺路线，对降低能耗起到的重要作用。生产实践证明，对于甲醇精馏分离，不能仅依靠高效塔内件应用于精馏塔中，以达到明显地降低甲醇精馏能耗，而甲醇精馏工艺流程的改进也可以使该系统的能耗明显下降。1甲醇精馏双塔流程目前，大部分甲醇精馏过程均采用双塔分离流程。我厂现有一套3104ta甲醇双塔精馏装置，2002年12月拟扩建为8104ta甲醇双塔精馏装置，其流程见图1。这一流程主要由两个精馏塔构成：预塔和主塔。由甲醇合成工段来的粗甲醇含甲醇86左右，首先进入预塔，预塔实际上是一个萃取精馏塔，在塔顶加入相当于粗甲醇进料20。30左右的水，以水为萃取剂将粗甲醇进料中所含的二甲醚等轻组份分开，因而预塔塔顶产品主要是二甲醚等轻组分，而塔底产品中则主要是甲醇与水的混合物。预塔一般都在常压条件下操作，塔顶温度为65。75左右，塔底温度为80左右。预塔内一般安装有4560块塔板，能达到2535个理论分离级数。由于该塔是通过塔顶加水萃取甲醇至塔底，故粗甲醇进料口位置比较高，一般在由塔底向上数第3640块板上进料。预塔塔底流出的甲醇与水的混合物立即进入主塔，在主塔内实现甲醇与杂醇、水的分离。主塔一般安装有6585块塔板，需要36050个理论级数(视回流量大小而定)。许多生产装置往往强调塔顶甲醇产品浓度，而对塔底流出水中的甲醇含量不太重视，所以由预塔来的甲醇与水的混合物往往在主塔下半部分入塔。常用的进料位置在由塔底数起第20一26块塔板左右。甲醇精馏的主塔一般均在常压下操作。塔顶操作温度为6566，塔底操作温度为1051IO。C。塔顶的精甲醇产品一般要求含水量01，甲醇含量995，而塔底排放水中的甲醇含量必须05。为防止预塔中轻组份带至主塔并随甲醇上移至塔顶而被精甲醇产品带出塔，主塔一般均在距塔顶第10块塔板左右侧线采出精甲醇产品。此种流程能耗较高，我厂每吨甲醇耗蒸汽在21。25t。2甲醇精馏改造路线探讨甲醇精馏系统的改造可以采用两种方法：一是采用高效精馏塔内件来提高分离效率，降低回流量，从而降低能耗；另一种方法则是改变分离路线，以降低能耗。采用高效精馏塔内件可提高甲醇收率兼具有降低能耗的作用，但其幅度不能满足人们的期望。同时改变精馏工艺路线对降低能耗有更大的效果。目前常用的高效精馏塔内件主要有规整填料和高效塔板两大类。根据我厂实际情况，规整填料不适用于我厂甲醇精馏扩产改造。原因分析如下。(1)规整填料的高分离效率主要是表现在轻烃类系统中。对于这一类物料系统来说，液相的表面张力极低，易于在规整填料所具有的大量表面积上舒展开，从而造成极大的气液接触表面积，达到极佳的分离效率。而在甲醇精馏系统中则完全不一样。两塔的液相中均含有大量的水份，使得液相表面张力大大高于轻烃类有机物。因而液体在填料表面上的分散能力大大下降，气液传质效率也必然大幅度下降。如在甲醇精馏主塔的下半段，含水量接近100，表面张力也趋近于56dyncm(0056Nm)，如在此条件下采用规整填料，则分离效果并不理想。在我厂3104ta甲醇精馏装置上改造成为8104ta甲醇生产能力，规整填料很难完成此项任务。(2)在规整填料床层中，床层最上方总要安装适当的液体分布器，以使向下流动的液体达到沿塔截面均匀分布。然而在液体逐渐向下流动时，起先沿塔截面均匀分布的液体会逐渐地向塔壁积累。这种现象称为“壁流”(wallflow)。当壁流发生时，大部分液体沿塔壁区域向下流，而大部分气体则在塔中心区域向上流。这就造成了气液流动的分离。从而大大削弱了气液之间的接触。可想而知，此时的规整填料精馏塔不可能有很好的分离效率。为克服此问题，一般在设计规整填料精馏塔时，一段填料床层仅力求达到6一10个理论级数，如一精馏过程需要的理论级数远远超过此数，则应将规整填料床层分为若干段，每段之间安装液体再分布器，使液体流动再次达到均匀分布。但这种安排将使整个精馏塔的结构复杂，造价昂贵。通过以上分析，采用规整填料改造我厂甲醇精馏塔是不可行的。是否可以用高效塔板来改造我厂甲醇精馏塔，以大幅度降低甲醇精馏系统的能耗呢?各种分析表明，这一途径对提高系统处理能力、甲醇产品的纯度和甲醇收率的效果明显，但在降低能耗上的效果，还不能令人十分满意。南京凯宁精馏技术有限公司生产的复合孔微型阀高效塔板，是目前国内唯一一家经美国精馏研究公司工业规模试验测试的高效塔板，该塔板上装有复合孔微型阀、三角形鼓泡促进器和多折边降液管，见图2。具有通量高，分离效率高，操作弹性大等特点。该塔板比常规塔板效率高25以上，采用此塔板改造我厂甲醇精馏预塔和主塔，在原塔径不变的条件下能够满足扩产8104ta甲醇的要求，投资比采用规整填料降低50，并且能够降低预塔用水量和主塔回流量。从而达到降低甲醇精馏系统能耗之目的。但工艺模拟分析表明，在这种条件下甲醇精馏系统能耗的降低也只不过是5左右，这一幅度还是比较小的，仍然不能适应我厂扩大甲醇产量，而不增加燃煤锅炉的要求。围2凯宁公司商效塔板的立体图从大幅度降低能耗的角度考虑，仅更换高效塔内件这一路线还是不够的，所以还必须从精馏工艺的角度去寻找解决问题的更好方法。3三塔提纯甲醇可大幅降低能耗在许多精馏系统中，人们往往将两塔合一或三塔并二，力求达到能耗的降低。这一途径降低能耗的机在于减少物料蒸发与冷凝的次数，以减少能量消耗。然而，对于甲醇精馏提纯来说，人们反其道而行之，将一塔分为二塔，却可以使能耗大量的降低。前已述及，甲醇精馏的预塔是一萃取蒸馏塔。通过在塔顶加入萃取剂水，将甲醇与二甲醚等轻组份分开。该塔的能耗主要取决于用水量和进料组成，进料组成是由合成工艺(催化剂类型。合成压力等)决定的，精馏工段不能随意要求改变。而用水量则是取决于甲醇二甲醚水三种物质的气液平衡。只要预塔操作在常压条件下，这一气液平衡也是基本固定的，用水量的大小也基本被固定下来。因而，甲醇精馏预塔在常压条件下几乎没有改变工艺条件以降低能耗的可能性。只有采高效塔板，提高分离效率，减少回流量来降低能耗。然而，甲醇精馏主塔内的精馏过程却不是这样。甲醇精馏主塔的进料是来自预塔底部甲醇与水的混合物。在甲醇精馏主塔内进行的分离过程实际上是在加热条件下，甲醇从水中蒸发出来的过程。在双塔精馏过程中，精馏主塔内的作用就是在塔底施加足够的热量，使甲醇从水中完全蒸发出来，而在塔顶冷凝得到精甲醇产品。德国Lurgi公司在开发其低压合成甲醇的工艺时，采用了三塔精馏甲醇提纯流程。这一流程将甲醇精馏主塔分为两个塔：加压精馏塔和常压精馏塔。其工艺流程图见图3。从甲醇预精馏塔底部出来的甲醇与水的混合物先进入加压精馏塔，在此塔顶部采出约占总产量50的精甲醇。加压精馏塔底部物料必然浓度稍低的甲醇与水的混合物，该混合物再进入常压精馏塔进一步将剩余甲醇与水分开。这一流程的设计和操作的关键在于适当确定加压塔的操作压力，从而使得加压塔塔顶蒸出的精甲醇气为常压塔塔底再沸器的热源，使得整个甲醇与水分离过程只需要在加压塔底部从外部输入热量，而在常压塔底部不需要从外部引进热量。从设备的角度上看，加压塔塔顶的冷凝器即为常压塔塔底的再沸器。工艺分析表明，将甲醇精馏主塔一分为二，确实是可以节省相当的能量消耗。首先，对于常压精馏塔其塔底温度在105110。C左右。要使得加压塔塔顶的精甲醇气成为常压塔底再沸器的热源，加压塔塔顶温度应在120左右，塔顶压力约056MPa(G)，考虑到加压塔内精馏塔板所造成的压降，加压塔底部压力应为06MPa(G)左右，而塔底温度只有130左右。为对这种温度下的甲醇液体加热气化，使用一般的低压蒸汽即可。换句话说，三塔流程加压塔再沸器所需蒸汽和双塔流程常压塔再沸器所需蒸汽基本上是同等级的。其二，在采用三塔流程后，加压塔和常压塔顶分别采出约50的精甲醇。而这两塔回流比基本相同，因而，这两个塔内的蒸发量基本相同，从而塔底部再沸器所需的热量也相同。由于三塔流程中加压塔和常压塔的甲醇蒸发总量以及两塔的回流量之和均与双塔流程中精馏主塔基本一样，故三塔