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1、10.450ProcessDynamics,Operations,andControlLectureNotes-1Lesson1.Designofasurgetanktosmoothoutfluctuationsinflow.Definitionofimportantprocesscontrolterms.1.0ContextMuchofthechemicalengineeringcurriculumconcernscontinuousprocessesoperatingatsteadystate.Wellandgood,butthere'smoretoit:continuous
2、processesmaybedisturbedinavarietyofways,andtheeffectspropagatethroughtheprocessasafunctionoftime–throughouttheprocess,temperature,pressure,flow,andcompositionmayriseorfall.ProcessControlisaboutmanagingdisturbances,forproductquality,foreconomics,forsafety.Webeginwithasimpleexample:1.1Surgetank
3、Envisiontwocontinuousprocessesoperatinginseries.Process1feedsastreamwitoprocess2.fromotherprocesseswiprocess1process2tootherprocessesStreamwihassomesteadydesignflowrate,butinpracticeitvaries,causingproblemsinprocess2.Wemightattacktheproblembyreducingthecauseofvariationinprocess1;wemightalsoat
4、tempttomitigatetheeffectofthevariationonprocess2.Propagationofdisturbancesbetweenprocessesisacommonproblem,andacommonsolutionisthesurgetank;itsjobistodampoutchangesinwifromtheupstreamprocessandthusdeliverasteadierwotothedownstreamprocess.fromprocess1wihtoprocess2wo110.450ProcessDynamics,Opera
5、tions,andControlLectureNotes-1Noticethattheinletflowisunconstrained,andtheoutletflowispumped.Becausethesurgetankitselfisnotasteady-stateprocess,INdoesnotequalOUT,andthustheliquidlevelwillvarywithtime.1.2DesigningthetankWemightapproachthedesignby(1)characterizingtheinletstream(2)specifyinglimi
6、tsontheoutletstream(3)makingasuitableprocessmodeltoconnectinletwithoutletStatedinthisway,it'snotsodifferentfromapproachingasteadystateprocessdesign.Inlet:supposethattheflowswingsby±40%overa20-minuteperiod.2πtw=10,000+4000sin(1.2.1)i20-1whereflowisinkghandtimeinminutes.Ofcourse,realdatawouldbe
7、moremessy,butthat'sjustamatterofdetail.Onecanlearnalotaboutthesystembysimplifyingtotheessentialfeatures.-1Outlet:thedesiredflowwois10,000kgh.Let'sbehard-nosedandinsistonnovariation.Processmodel:byinstinctachemicalengineerwritesamaterialbalanc
