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.