CCC负荷分配介绍

负荷分配控制在压缩机网络中，压缩机通常并联运行，有时也有串联运行形成网络运行的目的包括：备份灵活操作增加额外的能力通常注重单元机组的运行而忽略网络的优化控制压缩机制造商通常集中于单元机组的控制。从“网络”的观点来看，应实现优良的喘振保护和网络的负荷分配优化控制。压缩机网络

并联机组控制系统的目标是：保持主性能变量稳定（压力或流量）将负荷优化分配到网络中的各台机组上，同时：发生喘振的机率最低。最低的能耗在启动或停开单一机组时将所带来的工艺扰动降到最低。压缩机网络ProcessPIC11UICVSDSCompressor12UICVSDSCompressor2HIC1Suctionheader用于调节负荷的压缩机满负荷运转的压缩机注：所有控制系统均为独立运行变送器未标明。基本负荷法Rc,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：基本负荷法效率较低。基本负荷法增加了#1压缩机组发生喘振的危险性，这是由于#1压缩机将独立承担调整任何扰动。基本负荷法需要操作人员的经常干预。基本负荷法并不是推荐的方式基本负荷法控制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