化工專業(yè)英語

Unit8

CoalconversionprocessCoalconsistsprimarilyofcarbon,hydrogen,andoxygen,andcontainslesseramountsofnitrogenandsulfurandvaryingamountsofmoistureandmineralmatter.Themodeofformationofcoal,thevariationinplantcomposition,themicrostructure,andthevarietyofmineralmatterindicatethatthereisamixtureofmaterialsincoal.Thenatureoftheorganicspeciespresentdependsonthedegreeofbiochemicalchangeoftheoriginalplantmaterial,onthehistoricpressuresandtemperaturesaftertheinitialbiochemicaldegradation,andonthefinelydividedmineralmatterdepositedeitheratthesametimeastheplantmaterialorlater.煤主要由碳、氫、氧組成并含有少量的氮、硫及含量不一的水份和礦物質(zhì)。煤的構(gòu)成方式、成煤植物成分的變化、微觀結(jié)構(gòu)以及所含礦物質(zhì)的多樣性均說明煤是由多種物質(zhì)組成的混合體。各種有機物質(zhì)的性質(zhì)取決于最初植物成分生化變化的程度、最初生物降解后長期各種壓力和溫度的影響、與植物成分同期沉積或后期沉積的細微的礦物質(zhì)的作用。Deposition沉積物sedimentTheprincipaltypesoforganiccompoundshaveresultedfromtheformationandcondensationofpolynuclearandheterocyclicringcompoundscontainingcarbon,hydrogen,nitrogen,oxygen,andsulfur.Thefractionofcarboninaromaticringstructuresincreaseswithrank.主要類型的有機化合物是含碳、氫、氮、氧和硫的多核化合物與雜環(huán)化合物構(gòu)成與縮合的產(chǎn)物。芳環(huán)結(jié)構(gòu)中碳的含量隨著煤化程度的增加而增加。PolynuclearAromaticHydrocarbons（PAH）多環(huán)芳烴polycyclicaromatichydrocarbonsMonocyclicBicyclicNearlyallcoalisusedincombustionandcoking.Atleast80%isburneddirectlyinboilersforgenerationofelectricityorsteamforindustrialpurposes.Smallamountsareusedfortransportation,spaceheating,firingofceramicproducts,etc.Therestisessentiallypyrolyzedtoproducecoke,coalgas,ammonia,coaltar,andlightoilproductsfromwhichmanychemicalsareproduced.Combustiblegasesandchemicalintermediatesarealsoproducedbythegasificationofcoal,anddifferentcarbonproductsareproducedbyvariousheattreatments.Asmallamountofcoalisusedinmiscellaneous各種各樣的applicationssuchasfillers,pigments,foundrymaterial,andwaterfiltration.幾乎所有的煤都用于燃燒和煉焦。至少80%的煤直接在鍋爐中燃燒用于工業(yè)發(fā)電或產(chǎn)生蒸汽。少量的煤用于運輸、供熱和燒制陶器。其余基本通過熱裂解產(chǎn)生焦碳、煤氣、氨、煤焦油和輕油等產(chǎn)品由此可生成其他很多化工產(chǎn)品。煤氣化過程產(chǎn)生許多可燃氣體和化學(xué)中間體不同的熱處理會生成不同的含碳產(chǎn)品。也有少部分的煤被廣泛用作填料、顏料、鑄造材料和水過濾材料等方面。Thereisnodoubtabouttheswitchfromoiltocoalasasourceoforganicchemicals;theonlyuncertaintyconcernsthetime-scaleandrateatwhichithappens.Coal-conversionprocessesunderdevelopmentaredirectedtowardsproducingeithergaseousorliquidfeedstockswhichapproximateincompositiontopetroleum-derivedfeedstocks.Theycanthenbeutilizeddirectlyinexistingpetrochemicalplantsandprocesses.從以石油作為有機化學(xué)品的來源到以煤為有機化學(xué)品的來源這種轉(zhuǎn)變是無可置疑的。但是唯一無法確定的是這種轉(zhuǎn)變需要的時間與發(fā)生的速度。

研制中的煤轉(zhuǎn)化工藝目的是為了生產(chǎn)出氣體原料或液體原料。這些原料與石油衍生物原料的成分近似可直接應(yīng)用于當(dāng)今的石化工廠及其工藝中。Gaseousproduct氣體產(chǎn)物Toachievethis,however,twoproblemsmustbeovercome,whichareaconsequenceofthedifferingnaturesofcoalandoil.Firstly,theH:Cratiosaredifferentforcoalandforpetroleum-derivedliquidfeedstocks.Secondly,significantamountsofheteroatomsarepresentincoal,particularlysulphurwhichmayreachlevelsashighas3%.Thesulphurhastoberemovedfortworeasons:(ⅰ)oncombustionitwillformtheatmospheric(大氣的)pollutantSO2,and(ⅱ)itisapotent（強烈的）catalystpoison,andmostofthedownstreampetrochemicalprocessesarecatalytic.However,itsremovalfromcoalisdifficultanditisthereforeremovedfromtheconversionproductsinstead.但由于煤和石油性質(zhì)不同，為達到這個目的有兩個問題必須解決。首先煤和從石油中提取的液態(tài)原料中的氫/碳比不同。其次煤包含眾多的雜環(huán)原子尤其是硫原子比例高達3%?；谝韵聝煞矫嬖蛎罕仨毭摿?1:燃燒時會生成大氣污染物SO2；2：它是一種很強的催化劑毒物而大部分下游石油化工工藝都需用催化劑。但從煤中脫硫很困難，因此需要從煤轉(zhuǎn)化產(chǎn)品中脫硫。CoalProcessingtoSyntheticFuelsandOtherProductsTheprimaryapproachestocoalprocessingorcoalconversionarethermaldecomposition,includingpyrolysisorcarbonization,gasification,andliquefactionbyhydrogenation.Thehydrogenationofcoalisnotcurrentlypracticedcommercially.HighTemperatureCarbonization.Hightemperaturesandlongprocessingtimesareusedincarbonizingcokingcoalsincokeovensorgasretorts.Besidesmetallurgical（冶金的）orgascoketheproductsincludefuelgas,crudetar,lightoils(benzene,tolueneandxylene,referredtoasBTX,andsolventnaphtha),andammoniagas.煤制備合成燃料及其它產(chǎn)品煤加工轉(zhuǎn)化的主要方法是熱分解，包括高溫分解或干餾、氣化及加氫液化。煤的加氫目前還沒有實現(xiàn)商業(yè)化。高溫碳化。在焦?fàn)t或干餾爐中在高溫下長時間進行煤的碳化和焦化。除了冶金焦炭和氣化焦之外，焦化的主要產(chǎn)品包括燃料氣、粗焦油、輕油（苯、甲苯、二甲苯，也就是BTX，和溶劑石腦油和氨氣）Metallurgy冶金Mostcoalchemicalsareobtainedfromhightemperaturetarwithanaverageyieldover5%ofthecoalwhichiscarbonized.Theyieldsincokingareabout70%oftheweightoffeedcoal.Tarsobtainedfromverticalgasretortshaveamuchmoreuniformchemicalcompositionthanthosefromcokeovens.Twoormorecoalsareusuallyblended（配煤）.Theconditionsofcarbonizationvarydependingonthecoalsusedandaffectthetarcomposition.Coal-tarchemicalsincludephenols,cresols,xylenes,benzene,toluene,naphthanlene,andanthracene.大部分煤基化學(xué)品是從高溫煤焦油中獲取，碳化過程中平均5%的煤生成焦油。焦的產(chǎn)率大約是進料煤的70%。從立式干餾爐制備的焦油比焦?fàn)t中的焦油有更均勻的化學(xué)成分。通常兩種或更多中的煤配合使用。碳化的條件因煤種而異，因此焦油的組成也不同。煤焦油化學(xué)品包括苯酚、甲酚、苯、甲苯、二甲苯、萘和蒽。vertical豎直的horizontal水平的

Thelargestconsumerofcokeistheironandsteelindustry.Cokeisalsousedtomakecalciumcarbide,fromwhichacetylene乙炔ismade.Synthesisgasformethanolandammoniaproductionisalsomadefromgasificationofcoke.LowTemperatureCarbonization.Lowertemperaturecarbonizationoflumpcoalatca700℃primarilyusedforproductionofsolidsmokelessfuel,givesaquantitativelyandqualitativelydifferentyieldofsolid,liquid,andgaseousproductsthandoesthehightemperatureprocesses.Althoughanumberoflowtemperatureprocesseshavebeenstudied,onlyafewhavebeenusedcommercially.Thesehavebeenlimitedinthetypesofcoalthatareacceptable,andtheby-productsarelessvaluablethanthoseobtainedfromhightemperatureprocessing.焦化的最大消費者是煉鐵和煉鋼工業(yè)。焦還沒用于制造電石用于制備乙炔。焦的氣化所得合成氣可用于制備甲醇和合成氨。低溫碳化在大約700度下低溫碳化塊煤主要用于制備固體無煙燃料，得到了與高溫加工量和性質(zhì)截然不同的固體、液體和氣體產(chǎn)物。雖然研究了很多低溫碳化過程，但是僅有很少的實現(xiàn)商業(yè)化。由于可接受的煤種很有限，同時副產(chǎn)物沒有高溫碳化產(chǎn)物的價值高。Liquefactionofcoal,viahydrogenation,isquiteanoldprocesswhichwasoperatedcommerciallyinGermanyduringWorldWarIIwhenexternalfuelsupplieswerecutoff.Tensofmillionsoftonnesofgasolinewereproducedinthiswayduringthisperiod.Interestingly,Germanyistodayplayingaleadingpartinthedevelopmentofmoreefficientprocesses.FortheresultingliquidstobesuitablechemicalfeedstocktheH:Cratiomustbeimprovedinfavorofmorehydrogen.Clearlythiscanbeachievedintwoways—eitherbyaddinghydrogenorbyremovingcarbon.液化。煤的加氫液化是一個非常古老的工藝，早在第二次世界大戰(zhàn)期間，德國由于缺乏外部的燃料供給，就已經(jīng)進行商業(yè)化操作了。在這個時期，約通過該法生產(chǎn)了幾千萬噸汽油。有趣的是現(xiàn)在德國在開發(fā)更有效的工藝上走在了前列。對于生成的液體可以作為合適的化學(xué)品原料的話，H：C比必須改善以有更多的氫。很明顯這個可以通過加氫或脫炭實現(xiàn)。LiquefactionAlthoughmanyofthenewprocessesareonlyatthepilot-plantstage（中試階段）ofdevelopment,theirsuperiorityovertheoldmethodsisduetoincreasedsophisticationofthechemicalengineeringemployedplusimprovementsinthecatalystsavailable.Thebasicproblems,however,remainthesame—poorselectivityinproducingthedesiredfractionsandarelativelyhighrateofconsumptionofhydrogen.雖然很多新工藝仍處于發(fā)展的初級階段，但是，同老方法相比，它們由于提高可用催化劑的性能和增加了所用化工工程的精確性，因而這種方法更具優(yōu)勢。但是基本問題仍然是一樣的——對生產(chǎn)目標(biāo)產(chǎn)品的選擇性較低，而氫的用量相對較高。Thefundamentalprocessesinvolvedarepyrolysis,solventextractionandhydrogenation.Differencesbetweenthetechniquesbeingdevelopedlieinhowthesefundamentalprocessesarecombined.Notethatintheaboveprocessesthemainproductisahighlycarbonaceous（含碳的）solidmaterialknownaschar.Thisiseitherburnttoprovideprocessheatorreactedwithwaterandoxygentoproducehydrogen.液化所涉及的基本過程有熱解，溶劑萃取和加氫。研發(fā)的各種工藝間的差異在于這些基本過程的結(jié)合方式。請注意，在上述過程中的主要產(chǎn)品是一種高含碳的固體材料，即焦炭。焦炭可以用于燃燒來提供熱量，或與水和氧反應(yīng)產(chǎn)生氫氣。Theliquidsproducedbycoalliquefactionaresimilartofractionsobtainedbydistillationofcrudeoil(althoughtheyaremuchricherinaromatics),andthereforerequirefurthertreatment,e.g.cracking,beforebeingusedforsynthesis.煤液化的液相產(chǎn)品與粗油蒸餾獲得的產(chǎn)品組分相似（盡管其芳香族化合物的含量更高），因此，在其用于合成前，必須經(jīng)過進一步處理，即裂解。Anumberofgasifiersareeitheravailablecommerciallyorinvariousstagesofdevelopment.Thesearedescribedasfixedbed,fluidizedbed,andentrainedorrotatingbed.氣化。氣化爐較多，有的已經(jīng)商業(yè)化，有的還處于研發(fā)的不同階段。這些氣化爐可分為固定床、流化床和夾帶床或旋轉(zhuǎn)床。Thefixedbedinvolvesanupwardflowofreactiongasthrougharelativelystationarybedofhotcoal.Thegasvelocityisslowenoughtoavoidblowingthecoaloutofthebed.Thefluidizedbedoperateathighergasvelocitiesthanthefixedbedandutilizessomewhatsmallerparticles.固定床是讓一股向上流動的反應(yīng)氣流經(jīng)一個相對固定的熱煤床層。氣體流速很慢從而避免將煤帶出床層。流化床則在一個氣速比固定床高的操作條件下進行，并且使用較細顆粒的物料。Gasification.Theentrainedbedoperateswithparallelflowsofreactiongasandfinelypulverizedcoalparticlestominimizereactiontimeandmaximizethroughputofproduct.夾帶床采用反應(yīng)氣和細粉煤顆粒并行流動的操作方式，從而獲得最小的反應(yīng)時間和最大的產(chǎn)品吞吐量。Therotatingbedissimilartoakiln,whichoperateswiththecoalenteringattheupperpartoftheinclinedkiln.Rotationavoidsclinkingandexposesfreshsurfacestoenhancecompletionofthereaction.旋轉(zhuǎn)床則類似于一個窯，煤從這個傾斜的窯的上部進入。旋轉(zhuǎn)避免了碎裂和新鮮表面的暴露，從而強化了熱解反應(yīng)的完成。SurfaceGasificationtechnology.Gasificationofcoalforfuelgasandchemicalintermediateproductionhasbeendevelopedcommerciallyandimprovementsintechnologyarebeingstudiedinanumberoffacilities.IntheUnitedStates,thepurposeofanumberofprogramshasshiftedfromproductionofasubstitutenaturalgas(methane)toelectricpowergenerationthroughtheintegratedgasification-combined-cycle(IGCC)plants.Theinterestinthisuseofcoalresultsfromthelowemissionlevelsthatcanbeachievedandthepotentialforhigherpowergenerationefficiency.表面氣化技術(shù)。煤氣化用于燃料氣和化學(xué)品中間體的生產(chǎn)已經(jīng)商業(yè)化，且很多機構(gòu)正在進行技術(shù)改進的研究。在美國，一些項目的目標(biāo)從代用天然氣（甲烷）的生產(chǎn)向利用整體煤氣化聯(lián)合循環(huán)（IGCC）技術(shù)發(fā)電轉(zhuǎn)移。人們之所以對這種煤炭利用技術(shù)感興趣，是因為它存在低排放水平和高發(fā)電效率的潛力。Futurelargegasificationplants,intendedtoproduceca7X106m3standardofmethaneperdayareexpectedtobesitednearacoalfieldhavinganadequatewatersupply.Itischeapertotransportenergyintheformofgasthroughapipelinethancoalbyeitherrailorpipeline.Theprocesschosenisexpectedtoutilizeavailablecoalinthemosteconomicalmanner.未來可日產(chǎn)7X106m3標(biāo)準(zhǔn)甲烷的大型氣化廠，其理想的位置是在具有充足水源的煤田附近。能源通過管道以氣相形式輸送要比通過鐵路或管線輸送煤要便宜。選擇的工藝最好是采用最經(jīng)濟的方式利用不同的煤。UndergroundCoalGasification(UCG).Undergroundcoalgasificationisintendedtogasifyacoalseaminsitu,convertingthecoalintogasandleavingtheashunderground.Thisapproachavoidstheneedforminingandreactorsgasification.UCGispresentlyconsideredmostinterestingfordeepcoalorsteeplyslopingseams.Thisapproachinvolvesdrillingholestoprovideairoroxygenforgasificationandremovalofproductgasesandliquids.地下煤氣化（UCG）。地下煤氣化是為了在原位將煤層氣化，使煤轉(zhuǎn)化為氣，同時將灰留于地下。這種方法無需開采和反應(yīng)器氣化。對深層煤和極度傾斜煤層，UCG是目前人們最感興趣的技術(shù)。這種方法需要鉆孔以輸入氣化所需的空氣或氧氣并輸出生成的氣體和液體產(chǎn)品。Alowcalorificvaluegas,whichincludesnitrogenfromair,couldbeproducedforboilerorturbineuseinelectricpowerproduction,oranintermediatecalorificvaluegascontainingnonitrogenforanindustrialfuelgas,orsynthesesgasforchemicalandmethaneproductioncouldbeprovided.Thisapproachisstillnoncommercialinpartbecauseitisnoteconomicallycompetitive.地下煤氣化可以產(chǎn)出供鍋爐和發(fā)電的汽輪機所用的含有氮氣的（源自空氣）低熱值氣體，也可以生產(chǎn)供工業(yè)燃料氣所需的不含氮的中等熱值的氣體，或是供化學(xué)品和甲烷生產(chǎn)所需的合成氣。由于在經(jīng)濟上不具備競爭力，這種方法目前仍沒有實現(xiàn)商業(yè)化。AlthoughmanyenvironmentalandsafetyproblemscanbeavoidedusingUCG.thereissomeconcernaboutgroundwatercontaminationasaresultoftheprocess.Thechemistryofundergroundgasificationhasmuchincommonwithsurfacegasification,however,manyoftheparameters參數(shù)cannotbecontrolledbecausethereactionoccursinaremotesite.HeatenergytodrivethegasificationcomesprimarilyfromcarboncombustiontoproduceCOandthenCO2.雖然UCG技術(shù)可以避免許多環(huán)境和安全問題，但是該工藝對地下水的污染還是需要注意的。雖然地下氣化化學(xué)和地表氣化有許多相同之處，然而，由于其反應(yīng)發(fā)生在遠程地點，因而許多參數(shù)無法控制。氣化反應(yīng)所需的熱能主要來自于碳燃燒生成CO和CO2的反應(yīng)。Becausemanycoalseamsarealsoaquifers含水層thereisaconsiderableamountofwaterintrusion,whichleadstosteamgenerationattheexpenseofthereactionenergy.Asaresulttherateofairoroxygenpassagethroughtheinjectionwellsandseamareadjustedtomaintainalowlevelofmoistureintheproductgas.ThesteamisbeneficialforchargasificationandsomeisconsumedinthewatergasshiftreactiontoproduceH2andCO,fromH20andCO2.SomeH2reactswithCtoproduceCH4,whichenhancesthecalorificvalueofthegas.由于許多煤層同時也是含水層，因此有大量水入侵，從而導(dǎo)致反應(yīng)熱的消耗和蒸汽的生成。因此，必須調(diào)整空氣或氧氣通過注入井和煤層的速率，以維持產(chǎn)品氣中的水分在一個較低的水平。蒸汽對于焦炭的氣化是有好處的，其中部分蒸汽用于從H20和CO2向H2和CO轉(zhuǎn)變的水煤氣變換反應(yīng)。一些氫氣和C發(fā)生反應(yīng)產(chǎn)生甲烷，從而增加氣體的熱值。GasificationofcoalusingsteamandoxygenindifferentgasifiersprovidesvaryingproportionsofCOandH2.Operationsatincreasingpressuresincreasetheformationofmethane.BecausemixturesofCOandH2areusedasthestartofchemicalsynthesisandmethaneisnotwantedorneededforchemicalprocesses,theconditionsfavoringitsformationareavoided.Theproductgasesmaythenbepassedovercatalyststoobtainspecificproducts.Iron-basedcatalystsareusedtoproducehydrocarbonsintheFischer-Tropschprocess,orzineorcoppercatalystsareusedtomakemethylalcohol.煤氣化制備液體燃料和化學(xué)品。在不同的氣化爐中采用蒸汽和氧氣進行煤氣化所產(chǎn)生的一氧化碳和氫氣的比值是不同的。操作壓力的增大可以促進甲烷的形成。由于一氧化碳和氫氣的混合物才是化學(xué)合成的初始底物，而甲烷是該化學(xué)過程不需要的，因此，需要避開有利于甲烷形成的條件。產(chǎn)品氣將被通過催化劑以生產(chǎn)特定的產(chǎn)品。在FT工藝中用鐵基催化劑可生產(chǎn)烴類，鋅或銅催化劑則用于甲醇的生產(chǎn)。LiquidFuelsandChemicalsfromGasificationofCoal.TheFischer-Tropschprocesshasnotbeeneconomicalincompetitivemarkets.TheSouthAfricanSasolplanthasoperatedsuccessfullyusingthemodificationoftheFischer-Tropschprocess.Theoriginalplantwasdesignedtoproduce227,000t/yofgasoline,dieseloil,solvents,andchemicalsfrom907,000metrictonsofnoncakinghighashsub-bituminouscoal.ThesuccessoftheSasolprojectisattributedtotheavailabilityofcheapcoalandthereliabilityoftheselectedcomponents.Fischer-Tropsch工藝在競爭市場中不具備經(jīng)濟優(yōu)勢。南非Sasol廠應(yīng)用改良的Fischer-Tropsch工藝卻取得了成功。該廠的設(shè)計生產(chǎn)能力是：每年利用907,000噸不粘高灰次煙煤來生產(chǎn)227,000t汽油、柴油、溶劑和化學(xué)品。Sasol項目的成功歸功于便宜煤的使用以及所選組分的可靠性。Avarietyofpilotplantsusingfluid-bedgasifiershavebeenbuiltintheUnitedStates,Germanyandelsewhere.TheWinklerprocessistheonlyonethathasbeenusedonalargescale.ItwasdevelopedinGermanyinthe1920stomakesynthesisgasatatmosphericpressure.Planswerebeingmadetodevelopapressurizedversion.在美國、德國以及其他地方建立了各種應(yīng)用流化床氣化爐的工廠。Winkler工藝是唯一以大規(guī)模進行運作的工藝。在常壓下進行合成氣生產(chǎn)的工藝始于1920s的德國。并制訂了加壓工藝的發(fā)展計劃。Pressurized加壓的AtmosphericpressureTheuseofbiotechnologytoprocesscoaltomakegaseousandliquidfuelsisanemergingfield.Bacteriaandenzymeshavebeenstudiedtoestablishthetechnicalfeasibilityofconversion.TheearliestworkwasdoneonmicrobialdecompositionofGermanhardcoals.Reactorshavebeendesignedtouseavarietyofbacteriaandfungitobreakdownthelargemolecularstructureintosmallerunitsthatmaybeusefulasintermediates(solubilization)orasliquidandgaseousfuels(conversion).煤的生物處理。利用生物技術(shù)處理煤來生產(chǎn)氣體和液體燃料是一個新興的領(lǐng)域。人們對細菌和酶進行研究以建立這種轉(zhuǎn)化的技術(shù)可行性。最早的工作是對德國的硬煤進行微生物