CCC負荷分配介紹

負荷分配控制在壓縮機網絡中，壓縮機通常并聯(lián)運行，有時也有串聯(lián)運行形成網絡運行的目的包括：備份靈活操作增加額外的能力通常注重單元機組的運行而忽略網絡的優(yōu)化控制壓縮機制造商通常集中于單元機組的控制。從“網絡”的觀點來看，應實現優(yōu)良的喘振保護和網絡的負荷分配優(yōu)化控制。壓縮機網絡

并聯(lián)機組控制系統(tǒng)的目標是：保持主性能變量穩(wěn)定（壓力或流量）將負荷優(yōu)化分配到網絡中的各臺機組上，同時：發(fā)生喘振的機率最低。最低的能耗在啟動或停開單一機組時將所帶來的工藝擾動降到最低。壓縮機網絡ProcessPIC11UICVSDSCompressor12UICVSDSCompressor2HIC1Suctionheader用于調節(jié)負荷的壓縮機滿負荷運轉的壓縮機注：所有控制系統(tǒng)均為獨立運行變送器未標明?；矩摵煞≧c,1qr,12Rc,2qr,22Compressor1Compressor2MachinesoperateatsameRcsincesuctionanddischargeofbothmachinesaretiedtogetherPIC-SPBaseloadoneormorecompressorsandlettheother(s)absorbtheloadswingsSwingmachineBasemachineBasemachineisfullyloadedandrunswithoutrecycleQC,2=

QP,2SwingmachinecanberunningwithrecycleQC,1QP,1where:QP=FlowtoprocessQC=TotalcompressorflowQC-QP=RecycleflowLoadcouldbere-dividedtoeliminaterecycleQP,1QP,1+

QP,2

=

QP,1+

QP,2注：基本負荷法效率較低。基本負荷法增加了#1壓縮機組發(fā)生喘振的危險性，這是由于#1壓縮機將獨立承擔調整任何擾動?；矩摵煞ㄐ枰僮魅藛T的經常干預?；矩摵煞ú⒉皇峭扑]的方式基本負荷法控制QP,2ProcessPIC11UICCompressor1VSDSCompressor2SuctionheaderNotesPerformancecontrollersactindependentofantisurgecontrolHighercapitalcostduetoextraFlowMeasurementDevices(FMD)HigherenergycostsduetopermanentpressurelossacrossFMD’s1FIC2FIC2UICoutoutRSPRSPRSPoutRSPEqualFlowDivisionLoadsharing

FlowDiagramforControlProcessVSDSMachine2operateswithrecyclewhilemachine1stillhasturndownMachinesoperateatsameRcsincesuctionanddischargeofbothmachinesaretiedtogetherEqualflowdivisionmightworkifbothmachinesareidenticalMachinesareneveridenticalexceptbycoincidenceBiasrelayonremotesetpointwouldonlyworkifcurveshavesamesteepnessNotes:RequiresadditionalcapitalinvestmentinFMD’sRequiresadditionalenergyduetopermanentpressurelossacrossFMD’sPoorpressurecontrolduetopositivefeedbackincontrolsystem(seenext)EqualflowdivisionisNOTrecommendedRc,1qr,12Rc,2qr,22PIC-SPQP,1QP,2QC,2EqualflowEqualflowQP,1=

QP,2EqualFlowDivisionLoadsharing

ParallelCompressorControlCompressor1Compressor2where:QP=FlowtoprocessQC=TotalcompressorflowQC-QP=RecycleflowQ2RcN1N3N2Inatypicalmaster-slavecontrolschemetheslaveneedstobeapprox.5timesfasterthanthemasterAThemachineisoperatinginpointAThisistheintersectionof4lines:ResistancelineR1PerformancecurveN1PIC-SPFIC-SP=OutputofPICR1PIC-SPFIC-SPProcessdisturbancecausestheresistancetochangefromR1toR2R2AsaresultthemachinemovestopointBBSincethePICisslowitdoesnotmoveitsoutputyetwhichistheFIC-SPTheFICreactsfastandwilltrytomaintainitsSPTheFICwillspeedupthemachinetopointCatspeedN3CThedisturbanceisamplifiedPositivefeedbacksystemOnlyasthePICstartstoreduceitsoutputtocontrolpressuretheFIC-SPcomesdownandthepressureisrestoredDNotesCausesinstabilitynearsurgePoorpressurecontrolduetopositivefeedbackincontrolsystemPIC1OUTRSPFIC1OUTRSPMasterSlaveSIC1DynamicResponse/

PressureToFlowCascadePressurecontroller(PIC)providesRemoteSetPoint(RSP)forFlowcontroller(FIC)TheFICprovidestheRSPforthespeedcontroller(SIC),suctionthrottlevalveorguidevanesThePICisthemasterandtheFICistheslaveMasterSlaveNotesAllcontrollersarecoordinating controlresponsesviaaserialnetworkMinimizesrecycleunderalloperatingconditionsProcess1UICVSDSCompressor1VSDSCompressor2Suctionheader1LSIC2UICoutRSPSerialnetworkoutRSP2LSIC1MPICSerialnetworkSerialnetworkEquidistantLoadsharing

FlowDiagramforControlProcessMachinesoperateatsameRcsincesuctionanddischargeofbothmachinesaretiedtogetherPIC-SPTheDEVisadimensionlessnumberrepresentingthedistancebetweentheoperatingpointandtheSurgeControlLineLinesofequalDEVcanbeplottedontheperformancecurvesasshown0.10.20.3DEV=00.10.20.3MachinesarekeptatthesamerelativedistancetotheSurgeControlLine(SCL)ThismeansinpracticethesameDEVforbothmachinesDEV1DEV2RecyclewillonlystartwhenallmachinesareontheirSCLSinceDEVisdimensionlessallsortsofmachinescanbemixed:small,big,axials,centrifugalsTheDEVwillbethesameforallmachinesbuttheywilloperateatdifferentspeedsandflowratesSCL=SurgeControlLineRc,1qr,12Rc,2qr,22Compressor1Compressor2Dev1=Dev2Q1=

Q2N1=N2Notes:Maximumturndown(energysavings)withoutrecycleorblow-offMinimizestheriskofsurgesinceallmachinesabsorbpartofthedisturbanceAutomaticallyadaptstodifferentsizemachinesCCCpatentedalgorithmEquidistantLoadsharing

ParallelCompressorControlLoadsharingControllerLoopDecouplingFAModePIRTLoop

Decoupling+Antisurge

ControllerAnalogInputs+DEVToantisurgevalveToperformancecontrolelementPrimaryresponseDEVDEVPrimaryresponseToperformancecontrolelementDEV>0Don’tchangeoutputxYesNoPrimaryresponsePrimaryresponseDon’tchangeoutputNoxYesApplyloadsharinggainToantisurgevalve

DEV￡0CompressorsinParallel

theprimaryresponseMasterControllerPVSPPIDMastercontrollercontrolsthemainProcessVariable(PV)viaitsPIDcontrolblockTheoutputofthemastercontrollerPIDgoestotheprimaryresponseblockintheloadsharingcontrollerIntheprimaryresponseblockthecontrollerchecksifthemachineisclosetotheSCL:Yes:don’treducecapacity-keepoutputconstantNo:reducecapacityasnecessaryApplyloadsharinggainM0TheoutputofthemastercontrollergoesviatheprimaryresponseblockdirectlytotheperformancecontrolelementInordertocheckifthemachineisclosetotheSCLtheprimaryresponseblockneedstheDEVTheDEVisreportedbytheantisurgecontrollerWhenthemachineisclosetotheSCLthemastercontrollerwillnolongerreduceperformancetocontroltheprimaryvariableThemastercontrollerwillstarttoopentherecyclevalvetocontroltheprimaryvariableIfDEV<=0applyloadsharinggainOutputgoestoantisurgevalveLoopDecouplingFAModePILoopDecoupling+AnalogInputs+DEVToantisurgevalveToperformancecontrolelementPIDLoadbalancingPVPVSPPrimaryresponseDEVDEVDEVDEVfromotherloadsharingcontrollersPrimaryresponseAverageSPTheloadbalancingresponseLoadsharingControllerAntisurgeControllerMasterControllerThefastmastercontrollercontrolstheprimaryprocessvariablebydirectlymanipulatingthefinalcontrolelementsInordertobalancethemachinestheyneedtobekeptatthesameDEVTheantisurgecontrollerreportstheactualDEVtotheloadbalancingblockintheloadsharingcontrollerThisreportedDEVbecomestheProcessVariable(PV)fortheloadbalancingPIDloopTheloadsharingcontrollerreportsthisDEVPValsotothemastercontrollerOtherloadsharingcontrollersalsoreporttheirDEVPVtothemastercontrollerThemastercontrollercalculatestheaverageofallreportedDEVPV’sThisaverageDEVissentouttoallloadsharingcontrollerstobecometheSPforallloadbalancingblocksTheloadbalancingblockisaslowcontrollerthatwillequalizeallDEV’sforallparallelcompressorsItsoutputisaddedtothetotaloutputtotheperformancecontrolelementRTThePressureOverrideControl(POC)responseWhenalargedisturbanceoccursitcanhappenthattheperformancecontrolelement(e.g.speed)istooslowtokeepthepressureundercontrolTheoperatingpointridesthecurveandthepressurerisessharplyThereisahighchancetoexceedthereliefvalvesettingandtriptheprocessTheCCCmastercontrollerhasaPressureOverrideControl(POC)modethatwillopentheantisurgevalvetogetthedisturbanceundercontrolquicklyOpeningoftheantisurgevalveismuchfasterthanareductioninspeedAssoonastheoperatingpointdropsunderthePOC-SPlinetheantisurgevalvesstarttocloseagainTheprimaryPIDloopwillstabilizetheoperatingpointonthePIC-SPlineBenefitsFastresponseduringfastupsetsAvoidprocesstripsduetolackofresponseinperformancecontrolelementsAllowscloseroperationtoprocesslimitswithout takingriskLoopDecouplingFAModePILoopDecoupling+AnalogInputs+DEVToantisurgevalveToperformancecontrolelementPIDLoadbalancingPVPVSPPrimaryresponseDEVDEVDEVDEVfromotherloadsharingcontrollersPrimaryresponseAverageSPLoadsharingControllerAntisurgeControllerMasterControllerRTPI(One-Sided)SPPVPOC-SPRcqr2PIC-SPReliefvalvesettingProcess1AUICVSDSSection1VSDSSection1SuctionHeaderALSICoutRSPSerialnetworkRSPBLSIC1MPICSerialnetworkSerialnetworkSection2Section22AUIC1BUIC1BUICSerialnetworkSerialnetworkoutTrainBTrainAHowtooperateequidistantfromtheSurgeControlLine(SCL)whenthereismorethanonesectionpermachine???Selectpertrain--intheloadsharingcontroller--thesectionclosesttotheSCLByselectingthesectionclosesttotheSCLitisguaranteedthattheothersectiononthesametrainisnotinrecycleEquidistantLoadsharing

formulti-sectioncompressorsSharetheload--equalDEV’sforbothtrains--onthesectionclosesttotheSCLLoadsharingControllerLoopDecouplingLoadbalancingFAModePIRT+AntisurgeControllerAnalogInputsAverage+SPPVDEVfromotherloadsharingcontrollersDEV1Toantisurgevalve-1ToperformancecontrolelementPIDPVSPPrimaryresponseBothantisurgecontrollersreporttheirDEVtotheloadsharingcontrollerDEV1PI(One-Sided)SPPVPrimaryresponseFAModePIRTLoopDecoupling+AntisurgeControllerDEV2Toantisurgevalve-2DEV2PrimaryresponseThelowestDEVisselected:thesectionclosesttotheSCL<TheselectedDEVisreportedto:PrimarycontrolresponseblocksLoadbalancingblockMastercontrolleraveragingblockSelectingthesectionclosesttoSCLforparalleloperationMasterControllerLoopDecouplingMainselectioncriteriaforFMDinantisurgecontrolsystem:RepeatabilitySufficientsignal-to-noiseratioAccuracyoftheFMDisnotcriticalFMDdelaysmustbeabsolutelyminimalPresentstate-of-the-artlimitsthechoiceofFMDtoheadflowmetersortootherdevicesthatarebasedontheprincipleofvelocitymeasurement:OrificeplatesVenturi’sPitottubesetc.RecommendedflowrangeforFMDandtransmitterismaximumcompressorflowRecommended

DpcorrespondingtoQmax,compressoris10”WC(250mmH2O)ormoreFlowMeasuringDevice

(FMD)selectioncriteriaThepreferredlocationoftheFMD:SuctionofcompressorAsclosetotheinletflangeaspossibleVSDSCompressorDischargeSuctionminimumpossibleLesspreferablelocationoftheFMD:DischargeofcompressorAsclosetothedischargeflangeaspossibleminimumpossibleSelectionofthelocationshouldbebasedon:NecessityofsurgedetectionOftenmoredifficultwithflowmeasuredindischargeCapitalcostofflowmeasuringdeviceOperatingcostoftheFMD(permanentpressureloss)FlowMeasuringDevice

(FMD)locationThespeedofapproachingsurgeishighThetransmittertypeandbrandshouldbeselectedbasedontwomajorfactors:ReliabilitySpeedofresponseDesiredrisetimefor

Dp(flow)transmittersis200msorlessPressurestepis100%Thefirstorderresponse(63%)islessthan200msDesiredrisetimeforpressuretransmittersis500msorlessResponsetimeofthe

FMDtransmitter

Inonly400ms,DPOdroppedby14%,witha2%changein

DPc100%0100%0100%01SEC.DPoACDBPdACDBDPcACDBTimeActualpressureTransmitteroutput63%response1-(1/e)t1islessthan200msKnowingtheflowisessentialtodeterminethedistancebetweentheoperatingpointandtheSCLDampingthe

Dpo

(flow)transmitterdestroysessentialinformationDampingthe

Dpo

(flow)transmittercanparalyzethecompleteantisurgecontrolsystem!!!Theeffectofdamping

theDpo

(flow)transmitter500-5001.252.503.755Time(seconds)FlowStartofSurgeActualFlowt=16.0st=1.70st=0.20st=0.03sCriteriaforantisurgevalvesizingbasedonCCC’sexperienceProvideadequateantisurgeprotectionforworstpossibledisturbancesProvideadequateantisurgeprotectioninalloperatingregimesSizedtoprovideflowpeaksgreaterthanwhatisrequiredinsteadystatetooperateontheSurgeControlLineSizedtoavoidchokezoneNotbeoversizedfromcontrollabilitypointofviewTakepointAattheintersectionofthemaximumspeedperformancecurveandtheSurgeLimitLine(SLL)Calculate

Cv,calc(orequivalent)forpointASelectstandardvalvesizeusingthefollowingcriteria:1.8.Cv,calc<Cv,selected<2.2.Cv,calcRcQvolASizingtheantisurgecontrolvalveARc

Analternativemethodyieldingexcellentresultsis:TakedesignpointofthecompressorpointADrawahorizontallinethroughthedesignpointTakepointBatintersectionofmaximumspeedperformancecurveandthehorizontallineBCalculateCv,calcinpointBSelectstandardvalvesizeusingthefollowingcriteria: 0.9.Cv,calc<Cv,selected<1.1.Cv,calcSizingtheantisurge

controlvalve-alternativemethodQvolAntisurgevalvestrokespeedAntisurgevalvemusthavespeedofresponseadequateforantisurgeprotectionforalldisturbancesRecommendedfullstroketimes:Size

Closetoopen

Opentoclose1”to4” 1second <3seconds6”to12” 2seconds <5seconds16”andup 3seconds <10secondsClosingtimeneedstobethesameorderofmagnitudetoassurethesameloopgaininbothdirectionsAntisurgevalvecharacteristicNormallycontrolvalvesareselectedtobeopen80%to90%fordesignconditionsAntisurgevalvescanoperateanywherebetween0%and100%Inordertohaveanequalloop-gainoverthewholeoperatingrangealinearvalveisrequiredThiswillallowforthefastesttuningleadingtosmallersurgemarginsStrokespeedandcharacteristicoftheantisurgevalveMostnormalcontrolvalvescanbemadetoperformasrequiredforantisurgecontrolThefollowingstepshelpimprovetheperformanceofthevalveInstallpositionerMinimizetubinglengthbetweenI/PandvalvepositionerInstallvolumeboosterMinimizevolumeandresistancebetweenvolumeboosterandactuatorIncreaseairsupplylineto3/4”ormoreIncreasesizeofairconnectionintotheactuatorDrilladditionalholesinactuator-avoidspullingavacuumImprovingtheperformanceoftheantisurgevalvePipinglay-outinfluencesthecontrollabilityofthethetotalsystemTheprimaryobjectiveoftheantisurgecontrolleristoprotectthecompressoragainstsurgeThisisachievedbyloweringtheresistancethecompressorisfeelingTheresistanceisloweredbyopeningtheantisurgevalveDead-timeandtime-laginthesystemneedstobeminimizedThisisachievedby minimizingthe volumebetween threeflangesDischargeflangeof thecompressorRecyclevalveflangeCheckvalveflangeVSDSCompressor1volumetobeminimizedPipinglay-outconsiderationwhendesigninganantisurgecontrolsystemSection1Section2Inordertoprotectsection1theantisurgevalveneedstobeopenedThevolumebetweencompressordischarge,checkvalveandantisurgevalvedeterminesthedeadtimeandlagtimeinthesystemLargevolumeLargevolumesignificantlydecreasestheeffectivenessoftheantisurgeprotectionResultPoorsurgeprotectionLargesurgemarginsEnergywasteProcesstripsbecauseofsurgeNote:ThisspecificpipinglayoutisfoundonmanywetgascompressorsinFCCU’sUsingasingleantisurgevalveincreasesrecyclelagtimeSection1Section2Thepipinglay-outforsection2isexcellentforsurgeprotectionMinimumvolumebetweenthethreeflangesSmallvolumeThepipinglay-outforsection1isnotidealLargevolumetobede-pressurizeddecreasesabilityofthecontrolsystemtoprotectthemachineagainstsurgeResultPoorsurgeprotectionLargesurgemarginsEnergywasteProcesstripsbecauseofsurgeSharingrecyclecoolers

degradessurgeprotectionCompressor1Compressor1hasidealpipinglay-outforsurgeprotectionMinimumvolumebetweenthethreeflangesCompressor2MinimumvolumeThepipinglay-outforcompressor2iscommonlyfoundintheindustryThecoolercreatesadditionalvolumeanddecreasestheeffectivenessoftheantisurgecontrolsystemIncreasedvolumeduetocoolerThepipinglay-outforcompressor2canbeacceptableiftheadditionalvolumedoesnotcreateexcessivedeadtimeandlaginthemResultIncreasedsurgemarginsEnergywasteInstallingrecyclevalveupstreamfrom

coolerimprovescontrolresponseCompressorhasidealpipinglay-outforsurgeprotectionMinimumvolumebetweenthethreeflangesforallsectionsRecyclelinesconfiguredforoptimumsurgeprotectionMinimumvolumeSection2Section3Section1ProcessSuctionLay-out#1hasminimumvolumebetweentheflangesandisthebestlay-outforantisurgecontrolpurposesSection2Section3Section1ProcessSuctionSection1Section2Section3SuctionProcessLay-out#1:CompressorwithrecyclelinesoptimallyconfiguredforantisurgecontrolLay-out#2:Compressorwithcoolersupstreamofrecycletake-offWhenselectinglay-out#2theresidencetimeofthegasinthe“surge”volumeshouldbeverifiedtocheckacceptabletimedelaysarenotexceededThesetwopipinglay-outsaremostcommonforantisurgecontrolLay-out#2requiresonecoolerlessandthusthecapitalinvestmentislowerLay-out#2willrequirebiggersurgecontrolmarginsWhichantisurgepipingconfigurationdoyouchoose???AnalogcontrollerSLLSCL100%0%Controlleroutput100%0%LeadingengineeringcontractorperformedevaluationofexecutiontimeinfluenceonabilitytoprotectcompressorfromsurgeDynamicsimulationofcompressorwasbuiltDigitalcontrollersarecomparedagainstanalogcontrolleronsimulationAnalogcontrollerhasnoexecutiontimeandisimmediateAnalogcontrollertunedforminimumovershootDigitalcontrollersgetexactsametuningparametersDigitalcontrollersgetexactsamedisturbanceOperatingpointTimeTimeInfluenceofcontroller

executiontimeAnalogcontrollerSLLSCL100%0%100%0%100%ControlleroutputOperatingpointDigitalcontroller(2exec