高炉上料变频调速系统设计Word文档格式.docx

高炉上料变频调速系统设计Word文档格式.docx

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controlstrategy

I.INTRODUCTION

TheworkingstateofIndustrialboilercombustionsystemiscloselyrelatedtoitsairsupplysystem,inducedventilationsystem,gratesystemanddrumwaterlevelandothers.Properregulation,controloftheseassociatedsystemsistosolvethattheboileroperatingefficiencyislowandaneffectivemeansofenvironmentalpollutionisserious.Atpresent,toimprovetheoperatingefficiencyofindustrialboilershasbecomethetechnologyofexistingcoal-firedindustrialboilerspressingissuestoberesolved,withfar-reachingsignificance.

II.ABOILERCOMBUSTIONPROCESS

Industrialboilersisamulti-input,multiple-output,nonlinearandstrongcouplingofdynamicobjects,theboiler'

scombustionprocessisastronginterference,nonlinear,time-varying,multi-variableandcomplexprocess.Boileroperationwillshowthefollowingtwostates:

Whentheboilerisrunningathighload,duetolargeload,amountofcoalgrateandairsupplyisalsogreat,hightemperaturefurnace,theburningintensity.Alowerexcessairratiocaneffectivelyreducethefluegastemperature,raisethetemperatureofthefurnaceandconvectiontubesandbeconducivetothecontinuationoftinyparticlesofcarboncombustion,therebyreducingthesmokedamageandmechanicallossofincompletecombustion.Whentheboilerareoperatingatlowload,duetoloadsmall,grateforcoalvolumeandacorrespondingreductioninairsupply,combustionintensitydecreased,Theuseofahighexcessaircoefficient,canrelativelyincreaseinairsupply,improvethecarbonparticlesandoxygeninthecollisionrateandtheosmoticpressureofoxygentocarbon,andbeconducivetoenhancedcombustion,raisingthefurnacetemperatureandconvectiveheattransfercoefficientsegment.

Boilersystemheatbalanceoftheexpression:

Q=Q1+Q2+Q3+Q4+Q5+Q6

（1）

TypeinQ-thetotalheatinputboilersystem;

Q1-effectiveuseofheat（forheatingwaterandproducingsteam）;

Q2-exhaustheatloss;

Q3-incompletecombustiongasheatloss;

Q4-incompletecombustionofsolidheatloss;

Q5-boilerheatloss;

Q6-ashphysicalheatloss.

Inpracticalapplications,Q2+Q3+Q4aremainlycomposedofheatloss.Thethermalefficiencyoftheboilerasfollows:

（2）

Therelationshipbetweenboilerheatlossandtheexcessairratio-

isshowninFig.1.

Figure1.Combustionprocessheatbalance

Astheexcessaircoefficient-

increases,theamountofairintothefurnaceincreases,coalandcombustiblegascompletelycombusts,reducingQ3andQ4,ButQ2increaseswiththeincreasingofairsupply,whileaccountingforthelargestproportionofheatloss.So,alongwiththeexcessaircoefficient-

increases,Q3andQ4decreaseFigure1.CombustionprocessheatbalanceandQ2increases,Q2+Q3+Q4isamajorpartoftheboilerheatloss.AsbeseenfromFig1thataboutthreeofQ2+Q3+Q4formtheconcavecurvehavingaminimumpoint-K,atthepointoftheboilerheatlossminimum,maximumthermalefficiency.Point-Kcorrespondstothebestexcessaircoefficient-

whichisthebestair-coalratio.Theboilerheatlossisinfluencedatthesametimebythecoal,furnaceairleakageandotherfactors.Whenthesefactorschange,theheatlosscurveextremepointswillalsotakeplacedriftchanges,soinpracticalapplications,wemustconstantlylookforthebestair-coalratiooperatingpoint.

III.THECONTROLSTRATEGYOFBOILERCOMBUSTION

A.ControlPrinciple

Inviewofthecharacteristicsintheprocessofindustrialboileroperation,thesystemadaptsideaofcombiningthecentralcontrolandsubsystemcontroltoensurethemostefficientcombustiononconditionthatthesystemmeetstheloaddemand.ControlblockdiagramshowsinFig2.Centralcontrollercarryoutoptimizecalculationaccordingtotheparameterstransmittedfromacquisitionsystem-theboileroutlettemperature,flowrate,airsupply,inducedairflow,waterflow,watertemperature,thedeliveryofcoalandsoon.Combinedwiththepreviousoperatingrules,centralcontrollergivesoptimizationoperatingparametersandpassesthemtovarioussubsystemsintherespective.Eachsub-optimaldoeslineartermsaccordingtotheresults,thenadjustsseveraldevicesthroughfrequencyconversion.

Figure2.Controlblockdiagram

B.CombustionControlSystem

Boilercombustioncontrolsystemincludes:

loadcontrolsystem,thefurnacenegativepressurecontrolsystem.Asthereareanumberofcouplingbetweensubsystems,itdecouplessolvedthroughacentralcontrolleroptimizedcalculationofthemutualcouplingbetweensubsystems.Inordertolettheboileradapttothechanges,theamountofairsupplyandfuelmustbechangedatthesametime.

Asthedeliveryofcoalismoredifficulttomeasure,moreoverconsideringalag,thesystemusestheairsupplyasthemainadjustmentparameter.Optimalcontrolofairsupplyingcanbecarriedoutfirstlywhentheloadchange.Airsupplycontrolsystemtaskistoensurefullcombustionoffuelputintothefurnace,sothattheboilerscangethighestcombustionefficiency.Theoptimumefficiencyofboileroperation-

mustcorrespondtothebestofoxyacetyleneratio-

.Whentheamountoftimetheamountofcoalissure,thatcorrespondstothebestairsupply.Therefore,theboilercombustionsystemofSelf-OptimizingControlinessenceistofindthebestairsupplyinessence.ItscontrolflowshowsinFig.3.

ThenusingDEalgorithmrealizesself-optimizingcontrolofboilercombustionsystem.Specificmethodsasfollows:

inacertainperiodoftime,assumingthesameamountofcoalandairsupplyasthecontrolobject,wetakethewindvalueasthechromosomecodingandtheefficiencyoffunctionasfitnessfunctiontofindtheefficiencyofoptimizationuntilfindthemaximum,whichistheboilerreachingoptimumcombustionconditions.Atthispoint,theratiooftheamountofcoalandtheairflowisthebestair-coalratio.AccordingtoDEalgorithmbasicflow,firstofall,takeanapproximationoftheamountofairtheboilercombustionsystemrequiredastheinitialpopulation.Doinitialize（chromosomeencoded）,calculateoffitnessandthencarryonthreekindsofbasic-sub-operationsselection,crossover,andmutationgeneticoperatorstogenerateanewindividual.Finallycalculatethefitness,repeattheabovestepsuntilyoufindthemaximumefficiency.

Figure3.Combustioncontrolsystemflow

（1）AirSupplyVolumeControl

First,basedonexperiencetosetagoodvalue

themostoptimalvalueisfoundwhentheboilertoreachsteadyoperatingconditionsbychangingtheoxy-acetylene-

.Takingintoaccountthelagcharacteristicsofcombustionsystem,wegenerallyneedtodelayacertaintimeafterthechange

（availableon-siteadjustment）,thenmeasured

untilobtainthebestvalue.Atthispoint,thecontrolsystemautomaticallystopsoptimization,thedefaultcurrentvalueasthebestair-coalratio,andthenstarttheself-optimizingtimer,andbereadyforthenextoptimization.Generaloptimizationshouldnotbetooshortinterval,whichcanbesetbasedontheactualworkingconditions.Inthetimetakentoreachthenextself-optimizing,thecontroldeviceswillfirstlydeterminewhetherthesystemcomeintoastablestate,waittogointoastablestateandthenstartanewroundofoptimization.

（2）FurnaceNegativePressureControl

Inthefurnaceofboiler,ithasacertainnegativepressuretoavoidexcessiveheatwithexhaustoftailgasandcanalsopreventtheboilerfurnaceflameoutbecauseofpressure.Negativepressurecontrolisbyregulatingtheamountofboilerblower.Therelationshipbetweenblastvolumeandairflowvolumecitedaspecificrelationshiptheformationoffurnacenegativepressure.Blastfurnacechangesarethemainfactorsresultinnegativepressuredisturbances.Thecontrolsystemcontrolairvolumeregulatorthroughthefrequencycontrolsystem.Atthesametimefurnacepressurechangeisafastlink.Wheninthedesignofnegativepressurecontroller,itadaptfeedforwardPIDcontroller.Thus,oncetheamountofblowingchange,thecontrollercanquicklyadjustthespeedinduceddraftfan,whichwillcontrolthefurnacenegativepressurerequiredrange.Throughon-sitecommissioning,wefoundthatusingblastfeedforwardcontrolallowstherapidnatureofthecontrolsystemgreatlyimproved.

（3）TheControlofGrateGivingCoal

Throughthegratespeedcontrollingtheamountofcoal,itisanimportantguaranteeforeconomicandsafeoperationofboiler.Accordingtoon-siteoperationalexperience,themotorspeedisnothigherthan70%ofitsratedspeed.Whenthemotorspeedlimitisreached,theactuatorisnolongertheimplementationofthedirectivespeedup.Therefore,wemustsetareasonablespeedupperlimitonthegratetopreventthattheburningoffuelisnotsufficient,resultinginenergywasteandenvironmentalpollution.Chainboilerisatypicalmulti-variabletime-varyingcouplingdelaysystem;

itisdifficultthatusingtraditionalmeansofcontrolcontrolsthesystemmoreeffectively.

Thisisalsothereasonthatalotofmediumandsmallsized