Process control design and analysis for wastewater disinfection, stream neutralization, and run-to-run strategies PDF
Preview Process control design and analysis for wastewater disinfection, stream neutralization, and run-to-run strategies
PROCESSCONTROLDESIGNANDANALYSISFORWASTEWATER DISINFECTION,STREAMNEUTRALIZATION,ANDRUN-TO-RUNSTRATEGIES By CHRISTOPHEREDWARDMEREDITH ADISSERTATIONPRESENTEDTOTHEGRADUATESCHOOL OFTHEUNIVERSITYOFFLORIDAINPARTIALFULFILLMENT OFTHEREQUIREMENTSFORTHEDEGREEOF DOCTOROFPHILOSOPHY UNIVERSITYOFFLORIDA 2003 Copyright2003 by ChristopherEdwardMeredith ToBeckyandRuby ACKNOWLEDGMENTS Iwouldliketoexpressmysincereappreciationtomyadvisor,OscarCrisalle, withoutwhosesupportthisdissertationwouldnothavebeenpossible. Iamalsograteful fortheopportunityhehasgivenmetoobtainaminorinelectricalengineering. IwishtothankProfessorsHaniphLatchman,SpyrosSvoronos,andJasonWeaver forservingonmysupervisorycommittee. Dr.Svoronoswasparticularlyhelpfulinthe developmentofthewastewaterchlorinationproject,aswereChuckFenderandProfs. PaulChadikandRobertThieke. IthankH.MikeMahon,VaradharajanBasker,GiovaniNunes,JonEngelstad, SerkanKincal,andChuckBaab,whocamebeforeandBrianRemarkwhowillfollow. Theyallhavenotonlycontributedgreatlytomyresearchbuthavebeengoodfriends. Finally,Iwishtothankmymother,Sheila,andmybrother,Doug,fortheir unendingsupport. IV 11 TABLEOFCONTENTS page ACKNOWLEDGMENTS iv ABSTRACT viii CHAPTER INTRODUCTION 1 1 2 WASTEWATERCHLORINATIONUSINGANOVELCONTROL 6 2.1 Introduction 6 2.2 ProcessModelofaTypicalWastewaterDisinfectionPlant 7 2.2.1 KineticModelofChlorineReactioninaWastewaterTreatmentPlant 10 2.2.2 DosageAreaModel 13 2.2.3 ContactAreaModel 17 2.2.4 SimplifiedModelofaPlugFlowReactor 18 2.2.5 LinearizedState-SpaceModelofaPlugFlowReactor 2 2.3 PlantDataFittingandParameterEstimation 22 2.4 ControlDesignandAssessmentofPerformance 27 2.4.1 DescriptionandTuningoftheSlavePIController 3 2.4.2 DescriptionandTuningoftheMasterPIController 37 2.4.3 DescriptionandTuningoftheMasterPIControllerandSmithPredictor....44 2.4.4 DescriptionandTuningoftheMasterPIControllerandAdaptiveSmith Predictor — 48 2.5 NovelProcessModification DynamicWeir 52 2.5.1 DynamicWeirControllerDesign 55 2.5.2 Closed-LoopResponseoftheEntireModelforStepChangesinFlowrate UsingaDynamicWeir 60 2.5.3 Closed-LoopResponseoftheEntireModelforVaryingFlowrateUsinga DynamicWeir 64 2.5.4 RobustnessAnalysisfortheModel-BasedResidenceTimeController 66 2.5.5 PropagationofErrorAnalysisforthePIFeedback-ControlledSystem 69 2.5.6 AdditionalBenefitsoftheDynamicWeirDesign 72 2.6 Conclusions 75 3 STABILITYOFPI-CONTROLLEDRUN-TO-RUNSTATICSYSTEMSWITH SIGNIFICANTDELAY 79 v 1 3.1 Introduction 79 3.2 DerivationofaPIRun-to-RunController 80 3.3 PlantStabilityunderFeedbackControl 82 3.3.1 NominalStabilityRegion 83 3.3.2 RobustnessAnalysis 87 3.3.3 TuningCorrelations 91 3.4 PlantStabilityunderPIControlwithaSmithPredictor 94 3.4.1 Closed-loopdynamicsunderPIcontrolwithaSmithPredictor 95 3.4.2 StabilityRegionasaFunctionofModelUncertainty 96 3.5 Conclusions 99 4 CONTROLOFPHUSINGANOVELOPTICALSENSOR 101 4.1 Introduction 101 4.2 ModelingandSimulationofapHControlSystem 104 4.2.1 ProcessModelofpHControlinaCSTR 106 4.2.2 TraditionalElectrodes 11 4.2.3 NovelOpticalSensors 116 4.3 Closed-LoopSimulations 122 4.3.1 Noise-FreeClosed-LoopPerformance 127 4.3.2 Closed-LoopPerformancewithRealisticNoise 135 4.4 DesignofanExperimentalSystem 141 4.4.1 Apparatus 142 4.4.2 MeasurementNoiseAnalysis 145 4.5 Conclusions 150 5 CONCLUSIONSANDFUTUREWORK 152 APPENDIX A DISTRIBUTEDPARAMETEREQUATIONDERIVATION 157 B PERFORMANCEASSESSMENTOFTHESTANDARDFEEDBACK CONTROLCONFIGURATION 160 C REVIEWOFTHEOPERATIONOFADISCRETECONTROLLER APPLIEDTOACONTINUOUSSYSTEM 164 DCONDITIONSFORWHICHTHETRANSFERFUNCTION(3-8)HAS UNSTABLEPOLE-ZEROCANCELLATIONS 165 E VALUESOFaANDpFORTHE2-PARAMETERCURVEFITSOFTHE FUNCTIONSGENERATEDBYTHEJURYTEST 167 F CONDITIONSFORWHICHTHETRANSFERFUNCTION(3-38)HAS UNSTABLEPOLE-ZEROCANCELLATIONS 168 GREVIEWOFWEAKACID-STRONGBASECHEMISTRY 170 vi HAPPLICATIONOFDESCARTES'RULEOFSIGNS 171 I DEVELOPMENTOFTHEEXHAUSTIVENUMERICALSEARCHUSEDTO OPTIMIZECONTROLPERFORMANCE 174 J MOVINGAVERAGEANDEXPONENTIALFILTERS 177 LISTOFREFERENCES 180 BIOGRAPHICALSKETCH 185 AbstractofDissertationPresentedtotheGraduateSchool oftheUniversityofFloridainPartialFulfillmentofthe RequirementsfortheDegreeofDoctorofPhilosophy PROCESSCONTROLDESIGNANDANALYSISFORWASTEWATER DISINFECTION,STREAMNEUTRALIZATION,ANDRUN-TO-RUNSTRATEGIES By ChristopherEdwardMeredith December2003 Chairman: OscarD.Crisalle MajorDepartment: ChemicalEngineering Thewastewaterchlorinationprocessinfixed-sizeopen-channelreactorsisa challengingcontrolproblembecauseofthepresenceofavariabledeadtimecausedby changesintheinletflowrate. Theapproachproposedhereinvolvestheutilizationofa movingweirasanactuatorinanovelresidencetimecontrolscheme,designedtoensure thatfluidpassingthroughthereactorexperiencesaconstantresidencetimeindependent offlowrate. Thedynamicweircontrolloopisconceivedtosupplementexistingcontrol structuresthatarechargedwithmanipulatingthedosageofchlorine. Simulationsstudies showthatbothfeedforwardandfeedbackmanifestationsoftheresidencetimecontroller arehighlyeffectiveatimprovingchlorinedosagecontrolandarehighlyrobustwith respecttoweir-flowmodelingandmeasurementerrors. Infact,thesecontrollershavethe potentialtoimprovethecontrolperformancedramaticallywhilesavingasmuchas45% ofthechlorineusedfortreatment. viii Anautomaticcontrolsystemdescribedasrun-to-runisoneinwhichadiscrete controllerisappliedtoaninherentlydiscreteprocess,andwheretheperformance measurementsaremadeonlyafterallprocessingiscompleted. Acompletetheoretical analysisisdevelopedforthecaseofastaticplantunderproportional-integralcontrol, resultinginquantitativedescriptionsofthenominalandrobuststabilityregions,and recommendedtuningheuristics. TheanalysisforthecaseofaSmithPredictordesign showsthatverysmallmodelingerrorsintheestimatedmeasurementdelaymaycause closed-loopinstability. Therefore,theuseofaSmithPredictorforrun-to-runsystems sufferingfromuncertaintyinthedelayisnotrecommended. Aweak-acid/strong-baseneutralizationcontrolsystemutilizingtwoalternative pHsensorsismodeledandanalyzed. ThefirstsensorisatraditionalpHelectrodewhose outputsignalisproportionaltopH,andthesecondsensorisafiber-opticoptrodethat producesasignalthatisproportionaltohydrogenionconcentration. Systematic simulationstudiesshowthatnoinherentperformanceimprovementisobservedwhen usingtheoptrodeinsteadoftheelectrodesensorinthefeedbackloop. IX CHAPTER 1 INTRODUCTION Therearethreetypesofprocesscontrolstudiesaddressedinthisdissertation, namely,adesignproject,atheoreticalproject,andanexperimentalproject.Thedesign projectexamineswastewaterchlorinationcontrol,adistributed-parametersystemthatis typicallydifficulttocontrolwithstandardstrategiesduetothepresenceofhigh variationsinflowrate. Itisshownthatanoveldesignmodificationbasedonan automaticallyadjustedmovingweircanleadtodramaticallyimprovedperformance.In thetheoreticalstudy,single-inputsingle-outputrun-to-rununitoperationsare investigatedforthecaseofastaticplant. Therun-to-runcontrollerformiscontrasted withastandarddiscretecontrollerform,exposingsubtledifferencesinbehavioral characteristicsunderclosed-loopcontrol. Finally,theexperimentalprojectseeksto improvetheperformanceofpHcontrolsystemsthatusetraditionalpHelectrodes. Knowntobehighlynon-linear,theelectrodemayhavelimitedperformancepotentialasa result. Anovellinearopticalsensorisintroducedasanalternative. Chapter2presentsadesignstudyinvolvingastandardwastewaterchlorination basin. Itisshownthattraditionalcontrolschemeshavedifficultymaintainingtheoutlet concentrationataspecifiedvalue. Thedifficultyiscausedbytheeffectthatthevarying flowrateofwastewaterhasonthedeadtime(residencetime)ofthesystem. Becausethe volumeofthereactorisconstant,residencetimeisinverselyproportionaltoflowrate, andthelattercanvarybyasmuchasanorderofmagnitude. Specifically,thevariable residencetimecausespoorclosed-loopperformance. Thesystemismodifiedby 1
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