中国石油大学化学反应工程课件14

《中国石油大学化学反应工程课件14》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、Chapter14ModelsforNonidealReactorsNotalltankreactorsareperfectlymixednordoalltubularreactorexhibitplug-flowbehavior.Inthesesituations,somemeansmustbeusedtoallowfordeviationsfromidealbehavior.Chapter13showedhowtheRTDwassufficientifthereactionwasfirst-orderorifthefluidwaseitherinstateofco

2、mpletesegregationormaximummixedness.Buttheothersituationscomposeagreatmajorityofreactoranalysisproblemandcannotbeignored.14.1One–ParameterModelUseasingleparametertoaccountforthenonidealityofarealreactor,suchasanonidealtubularreactor.FornonidealCSTR,theone-parametermodelsincludethereacto

3、rdeadvolumeVdorthefractionfoffluidbypassingthereactor.14.2Tanks-in-SeriesModelArealreactorcanbemodeledasanumberoftanks-in-series.Thenumberoftanksnecessary,n,isdeterminedfromtheE(t)curve.ForafirstorderreactionKnowingthevalueofn,wecandeterminetheconversionand/oreffluentconcentrationsforth

4、ereactor.ForreactionsotherthanfirstorderandformultiplereactionsThesequentialequationsmustbesolved:14.3DispersionmodelThismodelisalsousedtodescribenonidealtubularreactors.Inthismodel,thereisanaxialdispersionofthematerials,whichisgovernedbyananalogytoFick’slawofdiffusion,superimposedonthe

5、flow.Toillustratehowdispersionaffectstheconcentrationprofileinatubularreactor,weconsidertheinjectionofaperfecttracerpulse.Thefollowingfigureshowshowdispersioncausesthepulsetobroadenasitmovesdownthereactorandbecomeslessconcentrated.TheConcentrationProfileThemolarflowrateoftracer(FT)bybot

6、hconvectionanddispersionis:AmolebalanceontheinerttracerTgivesAxialDispersionModelSubstitutingforFTanddividingbythecross-sectionalareaAC,weobtaintheaxialdispersionmodelasfollows:DispersioninaTubularReactorwithLaminarFlowInalaminarflowreactorweknowthattheaxialvelocityvariesintheradialdire

7、ctionaccordingtotheHagen-Poiseuilleequation:whereUistheaveragevelocity.RTDFunctionForlaminarflowwesawthattheRTDfunctionE(t)wasgivenby:InarrivingatthisdistributionE(t)itwasassumedthattherewasnotransferofmoleculesintheradialdirectionbetweenstreamlines.ResidenceTimeCalculationWith