reactor

Introduction

Thereactorisakindofequipmentthatrealizesthereactionprocess,whichisusedtorealizetheliquid-phasesingle-phasereactionprocessandtheliquid-liquid,gas-liquid,liquid-solid,gas-liquid-solidandothermultiphasereactionprocess.Thereareoftenstirring(mechanicalstirring,airflowstirring,etc.)devicesinthevessel.Whentheheightdiameterisrelativelylarge,multi-layerstirringbladescanbeused.Whenthematerialsneedtobeheatedorcooledduringthereactionprocess,ajacketcanbesetonthewallofthereactor,oraheatexchangesurfacecanbesetinthereactor,orheatexchangecanbeperformedthroughexternalcirculation.

Type

Reactorappearancephotos(4photos)

Thetypesofcommonlyusedreactors(seetable)are:①TubereactionDevice.Itiscomposedofemptypipesorfilledpipeswithrelativelylargelengthanddiameter,whichcanbeusedtorealizegas-phasereactionandliquid-phasereaction.②Kettlereactor.Itiscomposedofacylindricalcontainerwithrelativelysmalllengthanddiameter,andisoftenequippedwithmechanicalstirringorairflowstirringdevices.Itcanbeusedforliquid-phasesingle-phasereactionprocessandliquid-liquidphase,gas-liquidphase,gas-liquid-solidphasereactionprocess.Thegas-liquidphasereactionprocessiscalledabubblingstirredtank(seebubblingreactor);thegas-liquidsolidphasereactionprocessiscalledastirredtankslurryreactor.③Reactorwithabedofsolidparticles.Gasor(and)liquidpassesthroughafixedormovingbedofsolidparticlestoachieveamultiphasereactionprocess,includingfixedbedreactors,fluidizedbedreactors,movingbedreactors,tricklebedreactors,etc.④Towerreactor.Towerequipmentusedtorealizegas-liquidorliquid-liquidreactionprocesses,includingpackedtowers,platetowers,bubbletowers,etc.(seecolorpictures).⑤Jetreactor.Itisadeviceformixingwithanejectortorealizeasingle-phasegasorliquidphasereactionprocessandamultiphasereactionprocesssuchasgas-liquidphaseandliquid-liquidphase.⑥Variousotheratypicalreactors.Suchasrotarykiln,aerationtank,etc.

Modeofoperation

Accordingtothemodeofoperation,thereactorcanbedividedinto:

①Batchtankreactor,orbatchtank.

Theoperationisflexible,easytoadapttodifferentoperatingconditionsandproductvarieties,andissuitablefortheproductionofsmallbatches,multiplevarietiesandlongreactiontimes.Thedisadvantagesofintermittentkettlesare:auxiliaryoperationssuchasloadingandunloadingarerequired,andtheproductqualityisnoteasytobestable.However,forsomereactionprocesses,suchassomefermentationreactionsandpolymerizationreactions,itisstilldifficulttoachievecontinuousproduction,andbatchtanksarestilluseduptonow.

Inabatch-operatedreactor,therawmaterialsareaddedtothereactoratacertainratioatatime,andthematerialsaredischargedatatimeafterthereactionreachesacertainrequirement.Continuousoperationofthereactoristocontinuouslyaddrawmaterialsandcontinuouslydischargethereactionproducts.Whentheoperationreachesasteadystate,thecomposition,temperatureandotherstateparametersofthematerialatanypositioninthereactorwillnotchangewithtime.Thesemi-continuousoperationreactorisalsocalledthesemi-batchoperationreactor.Itisbetweentheabovetwo.Usually,onereactantisaddedatonce,andthentheotherreactantiscontinuouslyadded.Afterthereactionreachesacertainrequirement,stoptheoperationanddischargethematerial.

Theadvantageofthebatchreactoristhattheequipmentissimple,thesameequipmentcanbeusedtoproduceavarietyofproducts,especiallysuitableforsmallbatch,multi-varietyproductioninindustrialsectorssuchasmedicineanddyes.Inaddition,thereisnobackmixingofmaterialsinthebatchreactor,whichisbeneficialtomostreactions.Thedisadvantageisthatauxiliaryprocessessuchasloadingandunloadingandcleaningarerequired,andtheproductqualityisnoteasytobestable.

②Continuoustankreactor,orcontinuoustank

).Theshortcomingsoftheintermittentkettlecanbeavoided,butthestirringeffectwillcausethebackmixingofthefluidinthekettle.Insituationswherethestirringisintense,theliquidviscosityislow,ortheaverageresidencetimeislong,theflowpatternofthematerialinthekettlecanberegardedasafullymixedflow,andthereactionkettleiscorrespondinglycalledafullymixedkettle.Wherehighconversionratesarerequiredorsidereactionsinseriesarerequired,theback-mixingphenomenoninthetankreactorisanunfavorablefactor.Atthistime,multi-tankreactorscanbeusedinseriestoreducetheadverseeffectsofbackmixing,andthereactionconditionscanbecontrolledinseparatetanks.

Continuousreactorsshouldbeusedasmuchaspossibleforlarge-scaleproduction.Theadvantagesofcontinuousreactorsarestableproductqualityandeasyoperationandcontrol.Thedisadvantageisthattherearedifferentdegreesofbackmixingincontinuousreactors,whichisanunfavorablefactorformostreactionsandshouldbesuppressedbyreasonablereactormodelselectionandstructuraldesign.

③Semi-continuoustankreactor.

Referstoareactorinwhichonerawmaterialisaddedatonceandanotherrawmaterialiscontinuouslyadded.Itscharacteristicsarebetweenbatchandcontinuoustanks.

Feedingmethod

Forcontinuousreactorswithmorethantworawmaterials,theflowdirectionofthematerialscanbeco-currentorcounter-current.Forequipmentinwhichseveralreactorsformacascade,cross-flowfeedingcanalsobeused,thatis,onerawmaterialpassesthrougheachreactorinturn,andtheotherrawmaterialisaddedtoeachreactorseparately.Inadditiontoflowoutwards,therearealsorawmaterialsthatareaddedfromoneend(orbothends)ofthereactoranddividedintosections.Stagedadditionmeansthatonekindofrawmaterialisaddedfromoneend,andtheotherkindofrawmaterialisdividedintoseveralstagestobeaddedfromdifferentpositionsinthereactor.Cross-flowcanalsoberegardedasakindofstagedfeedingmethod.Whatfeedingmethodshouldbeuseddependsonthecharacteristicsofthereactionprocess.

Heatexchangemethod

Mostreactionshaveobviousthermaleffects.Inordertomakethereactionproceedundersuitabletemperatureconditions,itisoftennecessarytoexchangeheatonthereactantsystem.Theheatexchangemethodsincludeindirectheatexchangeanddirectheatexchange.Indirectheatexchangereferstotheheatexchangebetweenthereactionmaterialandtheheatingmediumthroughthepartitionwall,anddirectheatexchangereferstothedirectheatexchangebetweenthereactionmaterialandtheheatingmedium.Forexothermicreactions,thereactionheatcarriedbythereactionproductcanbeusedtoheatthereactionrawmaterialstoreachtherequiredreactiontemperature.Thiskindofreactoriscalledanautothermalreactor.

Accordingtotheheatexchangeconditionsduringthereactionprocess,thereactorcanbedividedinto:

①"Isothermalreactor"Anidealreactorwherethetemperatureofthereactantsystemisequaleverywhere.Areactorwithextremelysmallreactionheateffect,orfullheatexchangebetweenthereactionmaterialandtheheatcarrier,oralargeheatfeedbackinthereactor(suchasavigorouslystirredtankreactor),canbeapproximatedasanisothermalreactor.

②"Adiabaticreactor"Anidealreactorwithoutheatexchangebetweenthereactionzoneandtheenvironment.Alarge-scaleindustrialreactorwithoutaheatexchangedeviceinthereactionzonecanberegardedasanadiabaticreactorwhentheheatexchangewiththeoutsideisnegligible.

③"Non-isothermalnon-adiabaticreactor"hasheatexchangewiththeoutside,andthereisalsoheatfeedbackinthereactor,butthereactorthatcannotreachisothermalconditions,suchasthetubularfixed-bedreactor.

Theheatexchangecanbecarriedoutinthereactionzone,suchasastirredtankwithajacketforheatexchange,orinthereactionzone,suchasamulti-stagereactorwithheatexchangebetweenstages.

Operatingconditions

Mainlyreferstotheoperatingtemperatureandoperatingpressureofthereactor.Temperatureisasensitivefactorthataffectsthereactionprocess,andanappropriateoperatingtemperatureortemperaturesequencemustbeselectedtomakethereactionprocessproceedunderoptimizedconditions.Forexample,forreversibleexothermicreactions,atemperaturesequenceofhighfirstandlowtemperatureshouldbeusedtobalancethereactionrateandequilibriumconversionrate(seechemicalequilibrium).

Thereactorcanbeoperatedundernormalpressure,pressureornegativepressure(vacuum).Pressure-operatedreactorsaremainlyusedforreactionprocessesinvolvinggas.Increasingtheoperatingpressureishelpfultoacceleratethegasphasereaction.Forgas-phasereversiblereactionswithreducedtotalmoles,itcanincreasetheequilibriumconversionrate,suchassyntheticammoniaandsyntheticmethanol.Increasingtheoperatingpressurecanalsoincreasethesolubilityofthegasintheliquid,somanygas-liquidreactionprocessesandgas-liquidsolid-phasereactionprocessesadoptpressureoperationtoincreasethereactionrate,suchastheoxidationofp-xylene.

Selection

Foraspecificreactionprocess,theselectionofthereactorrequirescomprehensiveconsiderationofvariousfactorssuchastechnology,economyandsafety.

Thebasiccharacteristicsofthereactionprocessdeterminetheappropriatereactorform.Forexample,thegas-solidphasereactionprocessgenerallyusesafixedbedreactor,afluidizedbedreactororamovingbedreactor.However,theappropriateselectionneedstoconsiderthethermaleffectofthereaction,therequirementsforthereactionconversionrateandselectivity,thephysicalandchemicalpropertiesofthecatalystandthedeactivation,etc.,andeventheconceptualdesignofdifferentreactorsisrequiredtocarryouttechnicaldevelopment.Andeconomicanalysiscanbedeterminedlater.

Inadditiontotheformofthereactor,theoperatingmodeandfeedingmodeofthereactoralsoneedtobeconsidered.Forexample,forprocesseswithserialorparallelsidereactions,stagedfeedmaybebetterthanone-timefeed.Thetemperaturesequenceisalsoanimportantfactorinreactorselection.Forexample,foranexothermicreversiblereaction,atemperaturesequenceofhighfirstandthenlowshouldbeused.Multi-stage,inter-stageheatexchangereactorscanmakethetemperaturesequenceofthereactormorereasonable.Reactoroccupiesanimportantpositioninprocessindustrialproduction.Asfarastheconstructioninvestmentandoperatingcostsofthewholeprocessareconcerned,theproportionofreactorsmaynotbeverylarge.However,itsperformanceandoperationperformanceaffectstheoutputandqualityofthepre-andpost-processingandproducts,andalsohasanimportantimpactontheconsumptionofrawmaterials,energyconsumptionandproductcosts.Therefore,theresearchanddevelopmentofthereactorisofgreatsignificanceforthedevelopmentofvariousprocessindustries.

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