化学反应工程Chapter 14

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1、化学反应工程Chapter14TheTanks-In-SeriesModelThismodelcanbeusedwheneverthedispersionmodelisused;andfornottoolargeadeviationfromplugflowbothmodelsgiveidenticalresults,forallpracticalpurposes.Whichmodelyouusedependsonyourmood(心情)andtaste.Thetanks-in-seriesmodelissimple,canbeusedwit

2、hanykinetics,anditcanbeextendedwithouttoomuchdifficultytoanyarrangementofcompartments,withorwithoutrecycle.化学反应工程Figure14.1Thetanks-in-seriesmodel化学反应工程14.1PULSERESPONSEEXPERIMENTSANDTHERTDFigure14.1showsthesystemweareconsidering.WealsodefineThenandatanyparticulartime,from

3、Eq.11inChapter11化学反应工程Forthefirsttank.Considerasteadyflowm3/soffluidintoandoutofthefirstoftheseidealmixedflowunitsofvolumeV1.Attimet=0injectapulseoftracerintothevesselwhichwhenevenly(均匀地)distributedinthevessel(anditis)hasaconcentrationC0(C0=M/V1).Atanytimetafterthetraceri

4、sintroducedmakeamaterialbalance,thus化学反应工程InsymbolsthisexpressionbecomeswhereC1istheconcentrationoftracerintank“1.”Separatingandintegratingthengivesor化学反应工程SincetheareaunderthisC/C0versustcurveis(checkthisifyouwish)itallowsyoutofindtheEcurve;soonemaywrite[－]N=1(1)Thatistos

5、ay,forasinglemixedflowreactor,itsEfunctionis化学反应工程Separatinggivesafirst-orderdifferentialequation,whichwhenintegratedgives[－]N=2(2)ForthesecondtankwhereC1enters,C2leaves,amaterialbalancegives化学反应工程FortheNthtank.Integrationforthe3rd,4th,Nthtankbecomesmorecomplicatedsoitis

6、simplertodoallofthisbyLaplacetransforms.TheRTD’s,meansandvariances,bothintimeanddimensionlesstimewerefirstderivedbyMacMulinandWeber(1935)andaresummarizedbyEq.3.化学反应工程GraphicallytheseequationsareshowninFig.14.2.ThepropertiesoftheRTDcurvesaresketchedinFig.14.3.(3)化学反应工程化学反应工

7、程Figure14.2RTDcurvesforthetanks-in-seriesmodel,Eq.3.化学反应工程Figure14.3PropertiesoftheRTDcurveforthetanks-in-seriesmodel.化学反应工程14.2CHEMICALCONVERSIONFirst-OrderReactionChapter6developstheconversionequation.Thusforfirst-orderreactionsinonetankforNtanksinseriesAcomparisonwithpl

8、ugflowperformanceisgiveninFig.6.5.化学反应工程Forsmalldeviationsfromplugflow(largeN)comparisonw