CCC負荷分配介紹

負荷分配控制在壓縮機網(wǎng)絡中，壓縮機通常并聯(lián)運行，有時也有串聯(lián)運行形成網(wǎng)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(wǎng)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(wǎng)絡”的觀點來看，應實現(xiàn)優(yōu)良的喘振保護和網(wǎng)絡的負荷分配優(yōu)化控制。壓縮機網(wǎng)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(wǎng)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(wǎng)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(jīng)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