化工專業(yè)英語(yǔ)

Lesson4ChemicalReactionEngineering化學(xué)反應(yīng)工程A1Everyindustrialchemicalprocessisdesignedtoproduceeconomicallyadesiredproductfromavarietyofstartingmaterialsthroughasuccessionoftreatmentsteps.每一個(gè)工業(yè)化學(xué)過(guò)程的目的是從不同的原材料，經(jīng)過(guò)一系列的處理步驟生產(chǎn)經(jīng)濟(jì)所需的產(chǎn)品。2Fig.4-1showsatypicalsituation.圖4-1展示了一個(gè)典型的情況。3Therawmaterialsundergoanumberofphysicaltreatmentstepstoputthemintheforminwhichtheycanbereactedchemically.原料進(jìn)行了一些物理處理的步驟，使它們能夠發(fā)生化學(xué)反應(yīng)。4Theythenpassthroughthereactor.然后讓他們通過(guò)反應(yīng)器。5Theproductsofthereactionmustthenundergofurtherphysicaltreatment--separations,purifications,etc.-forthefinaldesiredproducttobeobtained.產(chǎn)物要經(jīng)歷進(jìn)一步的物理處理——分離，凈化提純等等，以獲得期望的最終產(chǎn)品。B1Designofequipmentforthephysicaltreatmentstepsisstudiedintheunitoperations.物理處理步驟設(shè)備的設(shè)計(jì)在單元操作中研究。2Hereweareconcernedwiththechemicaltreatmentstepofaprocess.在這里我們關(guān)心的是一個(gè)過(guò)程的化學(xué)處理步驟。3Economicallythismaybeininconsequentialunit,sayasimplemixingtank.從經(jīng)濟(jì)的角度說(shuō)，這可能是個(gè)不重要的單元，比如說(shuō)一個(gè)簡(jiǎn)單的攪拌槽。4Moreoftenthannot,however,thechemicaltreatmentstepistheheartoftheprocess,thethingthatmakesorbreakstheprocesseconomical.然而通常，化學(xué)處理步驟是一個(gè)過(guò)程的核心，它決定這個(gè)過(guò)程經(jīng)濟(jì)的成敗。C1Designofthereactorisnoroutinematter,andmanyalternativescanbeproposedforaprocess.反應(yīng)器的設(shè)計(jì)不是普通的事，對(duì)于一個(gè)過(guò)程有許多可供選擇的建議。2Insearchingfortheoptimumitisnotjustthecostofreactorthatmustbeminimized.尋找最佳的條件，不僅是反應(yīng)器成本的最小化。3Onedesignmayhavelowreactorcost,butthematerialsleavingtheunitmaybesuchthattheirtreatmentrequiresmuchhighercostthanalternativedesigns.一個(gè)設(shè)計(jì)可能反應(yīng)器的成本較低，但材料離開裝置可能比其他的設(shè)計(jì)需要更高的處理費(fèi)。4Hence,theeconomicsoftheover-allprocessmustbeconsidered.因此，必須要考慮整個(gè)過(guò)程的經(jīng)濟(jì)。D1Reactordesignusesinformation,knowledge,andexperiencefromavarietyofareasthermodynamics,chemicalkinetics,fluidmechanics,heattransfer,masstransfer,andeconomic.反應(yīng)器的設(shè)計(jì)使用了各個(gè)領(lǐng)域的信息，知識(shí)和經(jīng)驗(yàn)，比如熱力學(xué)，化學(xué)動(dòng)力學(xué)，流體力學(xué)，傳熱，傳質(zhì)，和經(jīng)濟(jì)學(xué)。2Chemicalreactionengineeringis,thesynthesisofallthesefactorswiththeaimofproperlydesigningachemicalreactor.化學(xué)反應(yīng)工程，是這些因素的綜合學(xué)科，旨在設(shè)計(jì)出正確的化學(xué)反應(yīng)器。E1Thedesignofchemicalreactorsisprobablytheoneactivitywhichisuniquetochemicalengineering,anditisprobablythisfunctionmorethananythingelsewhichjustifiestheexistenceofchemicalengineeringasadistinctbranchofengineering.化學(xué)反應(yīng)器的設(shè)計(jì)對(duì)于化學(xué)工程而言可能是一個(gè)獨(dú)特的活動(dòng)，它的這個(gè)功能可能比任何東西都更能證明化學(xué)工程作為一個(gè)獨(dú)特的分支工程的存在。F1Inchemicalreactordesigntherearetwoquestionswhichmustbeanswered:Whatchangecanweexpecttooccur？(ii)Howfastwilltheytakeplace？化學(xué)反應(yīng)器的設(shè)計(jì)有兩個(gè)必須回答的問(wèn)題：（1）我們預(yù)期發(fā)生什么變化？（2）他們發(fā)生的有多快？2Thefirstquestionconcernsthermodynamics,thesecondthevariousrateprocesses--chemicalkinetics,heattransfer,etc.第一個(gè)問(wèn)題涉及熱力學(xué)，第二個(gè)問(wèn)題涉及各種速率過(guò)程——化學(xué)動(dòng)力學(xué)，傳熱等。3Puttingthesealltogetherandtryingtodeterminehowtheseprocessesareinterrelatedcanbeanextremelydifficultproblem;hencewestartwiththesimplestofsituationsandbuildupouranalysisbyconsideringadditionalfactorsuntilwearcabletohandlethemoredifficultproblems.把這些放在一起，試圖確定這些過(guò)程是怎樣相關(guān)聯(lián)的，是一個(gè)非常困難的問(wèn)題；因此，我們從最簡(jiǎn)單的情況著手，考慮附加因素，建立我們的分析，直到我們能處理更難的問(wèn)題。GThermodynamics熱力學(xué)1Thermodynamicsgivestwoimportantpiecesofinformationneededindesign,theheatliberatedorabsorbedduringreactionandthemaximumpossibleextentofreaction.熱力學(xué)給出設(shè)計(jì)中需要的兩條重要的信息，在反應(yīng)中會(huì)放出和吸收熱量，而且最大值可能表示反應(yīng)的程度。2Chemicalreactionsareinvariablyaccompaniedbytheliberationorabsorptionofheat,themagnitudeofwhichmustbeknownforproperdesign.ConsiderthereactionaA→rR+sS,ΔHrpositive,endothermic;negative,exothermic化學(xué)反應(yīng)總是伴隨著熱量的釋放或吸收，為了合理的設(shè)計(jì)，必須知道它的大小，考慮下面的反應(yīng)：aA→rR+sS,ΔHr,正反應(yīng)，吸熱；逆反應(yīng)，放熱。H1TheheatofreactionattemperatureTistheheattransferredfromsurroundingstothereactingsystemwhenamolesofAdisappeartoformrmolesofRandsmolesofS,withthesystemmeasuredatthesametemperatureandpressurebeforeandafterreaction.溫度為T時(shí)，amol的A消失生成了rmol的R和smol的S，反應(yīng)的熱量是環(huán)境傳遞給反應(yīng)體系的，這是在反應(yīng)前后相同的溫度和壓力下對(duì)體系測(cè)量的結(jié)果。2Withheatsofreactionknownorestimablefromthermochemicaldata,themagnitudeoftheheateffectsduringreactioncanbecalculated.從熱化學(xué)數(shù)據(jù)中可以得到或估算反應(yīng)的熱量，反應(yīng)中產(chǎn)生的熱量大小可以計(jì)算。I1ThermodynamicsalsoallowscalculationoftheequilibriumconstantKfromthestandardfreeenergiesofthereactingmaterials.熱力學(xué)也可以從反應(yīng)物的標(biāo)準(zhǔn)自由能來(lái)計(jì)算平衡常數(shù)。2Withtheequilibriumconstantknown,theexpectedmaximumattainableyieldoftheproductsofreactioncanbeestimated.由于平衡常數(shù)已知，可以估算出反應(yīng)中可以得到的預(yù)期產(chǎn)品的最大產(chǎn)量。JChemicalKinetics化學(xué)動(dòng)力學(xué)1Underappropriateconditionsfeedmaterialsmaybetransformedintonewanddifferentmaterialswhichconstitutedifferentchemicalspecies.適當(dāng)?shù)臈l件下，供給的材料可能轉(zhuǎn)變?yōu)樾碌牟煌牟牧?，形成不同的化學(xué)物質(zhì)。2Ifthisoccursonlybyrearrangementorredistributionoftheconstituentatomstoformnewmolecules,wesaythatachemicalreactionhasoccurred.如果發(fā)生這種情況只是由于構(gòu)成原子的重排或再分配，形成新的分子，我們就說(shuō)一個(gè)化學(xué)反應(yīng)已經(jīng)發(fā)生了。3Chemistryisconcernedwiththestudyofsuchreactions.化學(xué)關(guān)注的是這種反應(yīng)的研究。4Itstudiesthemodeandmechanismofreactions,thephysicalandenergychangesinvolvedandtherateofformationofproduces.用于高溫反應(yīng)，管可能布置在爐子里。UPackedbedreactors填充床反應(yīng)器1Therearetwobasictypesofpacked-bedreactor:thoseinwhichthesolidisareactant,andthoseinwhichthesolidisacatalyst.填充床反應(yīng)器有兩種基本類型：一種是固體是反應(yīng)物，一種是固體是催化劑。2Manyexamplesofthefirsttypecanbefoundintheextractivemetallurgicalindustries.可以在濕法冶金工業(yè)中發(fā)現(xiàn)第一種類型的很多例子。V1Inthechemicalprocessindustriesthedesignerwillnormallybeconcernedwiththesecondtype:catalyticreactors.在化學(xué)過(guò)程工業(yè)中，設(shè)計(jì)師通常會(huì)關(guān)注第二類：催化反應(yīng)器。2Industrialpacked-bedcatalyticreactorsrangeinsizefromsmalltubes,afewcentimetersdiameterlolargediameterpackedbeds.工業(yè)上的填充床催化反應(yīng)器的大小由直徑是幾厘米的小試劑瓶到大直徑的填充床。3Packed-bedreactorsareusedforgasandgas-liquidreactions.填充床反應(yīng)器適用于氣體反應(yīng)和氣—液反應(yīng)。4Heat-transferratesinlargediameterpackedbedsarepoorandwherehighheat-transferratesarerequiredfluidizedbedsshouldbeconsidered.在大直徑填充床中，傳熱率是很低的，如果需要高的傳熱率，應(yīng)該考慮流化床。WFluidizedbedreactors流化床反應(yīng)器1Theessentialfeaturesofafluidizedbedreactorarethatthesolidsareheldinsuspensionbytheupwardflowofthereactingfluid;thispromoteshighmassandheat-transferratesandgoodmixing.流化床反應(yīng)器的基本特征是，利用反應(yīng)流體向上的流動(dòng)來(lái)保持固體的懸浮；這促進(jìn)了高的傳質(zhì)、傳熱率和良好的混合。2Thesolidsmaybeacatalyst;areactantinfluidizedcombustionprocesses;oraninertpowder,addedtopromoteheattransfer.固體可能是一個(gè)催化劑；可能是流化床燃燒過(guò)程中的反應(yīng)物；或著是促進(jìn)傳熱的惰性粉末。3Thoughtheprincipaladvantageofafluidizedbedoverafixedbedisthehigherheat-transferrate,fluidizedbedsarealsousefulwhereitisnecessarytotransportlargequantitiesofsolidsaspartofthereactionprocesses,suchaswherecatalystsaretransferredtoanothervesselforregeneration.雖然，流化床超過(guò)固定床的主要優(yōu)勢(shì)是更高的傳熱率，對(duì)于反應(yīng)過(guò)程中必須傳輸大量的固體，流化床也是有用的，如催化劑被轉(zhuǎn)移到另一個(gè)容器中再次使用。X1Fluidizationcanonlybeusedwithrelativelysmallsizedparticles,<300nmwithgases.流化作用只適用于尺寸相對(duì)較小的顆粒，小于300nm的氣體。2Agreatdealofresearchanddevelopmentworkhasbeendoneonfluidizedbedreactorsinrecentyears,butthedesignandscaleupoflargediameterreactorsisstillanuncertainprocessanddesignmethodsarelargelyempirical.近年來(lái)，對(duì)于流化床反應(yīng)器，大量的研究和開發(fā)工作已經(jīng)完成，但是，大規(guī)模反應(yīng)器的設(shè)計(jì)和規(guī)模仍是一個(gè)不確定的過(guò)程，設(shè)計(jì)方法主要憑經(jīng)驗(yàn)。YBatchorcontinuousprocessing間歇和連續(xù)加工1Inabatchprocessallthereagentsareaddedatthecommencement;thereactionproceedsthecompositionschangingwithtime,andthereactionisstoppedandtheproductwithdrawnwhentherequiredconversionhasbeenreached.在間歇過(guò)程中，一開始加入所有的試劑；反應(yīng)成分隨時(shí)間變化，當(dāng)達(dá)到需要的轉(zhuǎn)化時(shí)，反應(yīng)停止，取出產(chǎn)物。2Batchprocessesaresuitableforsmall-scaleproductionandforprocesseswherearangeofdifferentproducts,orgradesistobeproducedinthesameequipment;forinstance,pigments,dyestuffsandpolymers.間歇過(guò)程適合小規(guī)模生產(chǎn)和加工一系列不同的產(chǎn)品，或是在相同的設(shè)備中生產(chǎn)不同等級(jí)的產(chǎn)品；例如，顏料，染料和聚合物。Z1Incontinuousprocessesthereactantsarefed