废水处理工艺设计的光解,除垢,管道与控制 39页

废水处理工艺设计及计算第6章9-11节n目录『CONTENT』▷6-9PHOTOLYSIS光解▷6-10CHEMICALNEUTRALIZATIONSCALECONTROL&STABILIZATION化学中和水垢控制稳定性▷6-11CHEMICALSTORAGE,FEEDING,PIPING,&CONTROLSYSTEMS化学贮藏、供给、管道及控制系统n6-9PHOTOLYSISn6-91Photolysisisaprocessbywhichconstituentsarebrokendownbyexposureandabsorptionofphotonsfromalightsource.AswithAOPs,theprimaryuseofphotolysisisfortheremovaloftraceorganiccompoundsinwaterreuseapplications.Innaturalsystems,sunlightisthelightsourceforphotolysisreactions,however,inengineeredsystems,ultraviolet(UV)lampsareusedtoproducethephotonicenergy.Theeffectivenessofthephotolysisprocessdepends,inpart,onthecharacteristicsofthereclaimedwater,structureofthecompounds,designofthephotolysisreactor,anddoseandwavelengthoftheappliedlight.Thephotolysisratecanbeestimatedfromtherateatwhichthecompoundabsorbslightandthephotonicefficiencyofthereaction(quantumyield).定义n6-91光解工艺PhotolysisProcessesEngineeredphotolysisreactionsareconductedinspeciallydesignedreactorsoptimizedwithrespecttoUVdose.PhotolysisreactorsaretypicallycomprisedofastainlesssteelcolumnorpipecontainingUVlampsarrangedparalleltotheflow,perpendiculartotheflow,orinacrisscrossingpatternperpendiculartothedirectionofflow.原理Thephotonsthatareabsorbedcausetheelectronsintheouterorbitalofsomecompoundsformsanunstablecompoundthatsplitsapartorbecomesreactive.UV与O3、H2O2、Fenton联用。UV会促进H2O2产生OH·但加入H2O2会抑制某些有机物的分解n6-91FoulingthatmayoccurontheoutsideoftheUVlampprotectivequartzsleevemaybemanagedusinganautomaticcleaningsystemconsistingofacollarthatperiodicallymovesalongthelamptoremoveprecipitatesandinterceptedmatter.Whenusedinconjunctionwithreverseosmosispretreatment,thechemicalsaddedtoreducethepHforscalecontrolinthemembraneswillalsoreducethepotentialforprecipitationontheUVlamps.Photolysisreactionsarecausedbylightemissionintheultravioletrange(200to400nm).TherearethreetypesofUVlampsusedforphotolysisprocesses:(1)low-pressurelow-intensity,(2)low-pressurehigh-intensity,and(3)medium-pressurehigh-intensitylamps.Low-pressurelampsemitmuchoftheirenergyatawavelengthof254nmwhilemediumpressurelampsemitenergyatmultiple.Thetypeoflampusedandreactorconfigurationwilldependontheconstituenttoberemovedaswellasthewatermatrixandsite-specificconditions.n6-91光解所涉及基本概念:(1)紫外光吸收(2)入射能量(3)光解速率(4)电效率TheabsorptionoflightbyacompoundinwaterorotheraqueoussolutioncanbedescribedusingtheBeer-LambertLaw.Theabsorbanceofasolutionisameasureoftheamountoflightabsorbedbyconstituentsinthesolutionusingaspectrophotometerataspecifiedwavelengthandoverafixedpathlength.1紫外光吸收AbsorptionofUVLightA=absorbance,dimensionlessL=lightintensityafterpassingthroughsolutionL=lightintensityafterpassingthroughablanksoluteε=extinctioncoefficientC=concentrationoflightabsorbingsolutex=lengthoflightpathK=absorptivityTheextinctioncoefficientisafunctionofwavelengthbecauseasthewavelengthdecreasesmoreenergeticphotonsareabsorbedandtheabsorptivityofalightabsorbingcompoundincreases.n6-91不同物质的消光系数n6-91溶液中存在多种化合物的情形：使用多重波长光源的情形：canbedeterminedusingasimilarapproachsummingadsorptionofeachcompoundforeachwavelength.2入射能量EnergyInputforPhotolysisThelampoutputandreactorsizecanbeusedtoestimatetheenergyinputforthephotolysisreaction.存在问题：Theactualperformanceofaphotoreactorisexpectedtobelowerthancomputedduetolightbeingabsorbedbythereactorwallsorblockedbytheprecipitatethatformsonthelampsleeve.Whileasafetyfactorspecifictoaparticularsystemcouldbeappliedtocompensatefortheseinefficiencies,pilotstudiesareusedtoobtainmorereliabledesigncriteria.n6-913光解速率RateofPhotolysisTherateatwhichacompoundisphotolyzeddependsontherateandfrequencyofphotonabsorption.Thequantumyieldisaquantityusedtodescribethefrequencyatwhichphotonabsorptionresultsinaphotolysisreactionandisspecifictothetypeofcompoundandthewavelength.量子产率quantumyieldAsageneralrule,thequantumyieldincreasesaswavelengthdecreases(increasingphotonicenergy).n6-91伪一级动力学方程ThepseudofirstorderratelawTypically,thelightabsorptionbythecomponentthatistargetedforremovalisminorascomparedtothelightabsorptionbythebackgroundwatermatrix.（全局平均光解反应速率）4电效率ElectricalEfficiencyTheelectricalenergyrequirementforphotolyticreactionsissignificantduetotheprocessinefficiencies.Consequently,itisimportanttocompareprocessefficiencyonthebasisofelectricalusageperamountofcompounddestruction.Onesuchmeasureistheelectricalefficiencyperlogorder(EE/O)ofcompounddestruction.n6-91electricalefficiencyperlogorder（单位体积降低单位个数量级消耗的电能）通过测量EE/O可以对于特定反应可以计算流率。n6-91局限性PhotolysisProcessLimitationsTheefficiencyofthephotolysisprocessdepends,inpart,onthecharacteristicsofthewatermatrixandcompoundstargetedfordegradation.theextinctioncoefficientforresidualorganicmattervariesoverawiderangeandmayinterferewiththephotolysisofothercompounds.thelightenergyinputmaybeabsorbedbytheotherconstituents,theremaybephotonlossesuponreflectionoffthereactorwall,andtheprecipitatethatbuildsupontheexteriorsurfaceofsleevesthatcoverthelampsduetotheelevatedtemperaturewillblocklighttransmission.解决方案：ToovercomethelimitationsassociatedwithphotolysisprocessesrelatedtoabsorbanceofUVenergybynon-targetconstituentsinwaterreuse,pretreatmentusingreverseosmosisshouldbeusedtoremovemostoftheinterferingcompoundsandimprovetheoverallprocessperformance.Pilotstudiesshouldbeconductedtocharacterizetheexpectedefficiencyofphotolysisandtherateandcharacteristicsoffoulingofthelampsleeve.n6-10化学中和&水垢控制&稳定性』n6-102Theremovalofexcessacidityoralkalinitybytreatmentwithachemicaloftheoppositecompositionistermedneutralization.Ingeneral,alltreatedwastewaterswithexcessivelyloworhighpHwillrequireneutralizationbeforetheycanbedispersedtotheenvironment.Scalingcontrolisrequiredfornanofiltrationandreverseosmosistreatmenttocontroltheformationofscale,whichcanseverelyimpactperformance.Chemicalstabilizationisoftenrequiredforhighlytreatedwastewaterstocontroltheiraggressivenesswithrespecttocorrosion.定义与概念1PH调节Inavarietyofwastewatertreatmentoperationsandprocesses,thereisoftenaneedforpHadjustment.Becauseanumberofchemicalsareavailablethatcanbeused,thechoicewilldependonthesuitabilityofagivenchemicalforaparticularapplicationandprevailingeconomics.n6-102Wastewaterthatisacidiccanbeneutralizedwithanynumberofbasicchemicals.Sodiumhydroxideandsodiumcarbonate,althoughsomewhatexpensive,areconvenientandareusedwidelybysmallplantsorfortreatmentwheresmallquantitiesareadequate.Lime,whichischeaper,butsomewhatlessconvenient,isthemostwidelyusedchemical.Limecanbepurchasedasquicklimeorslakedhydratedlime,high-calciumordolomiticlime,andinseveralphysicalforms.Limestoneanddolomiticlimestonearecheaper,butlessconvenienttouseandslowerinreactionrate.Becausetheycanbecomecoatedincertainwastetreatmentapplications,theiruseislimited.Calciumchemicalsoftenformsludgesthatrequiredisposal.酸性废水调节物及其优缺点碱性废水的调节Ifacidicwastestreamsarenotavailableorarenotadequatetoneutralizealkalinewastes,sulfuricacidiscommonlyemployed.Insometreatmentplants,carbondioxideintheformoffluegashasbeenusedtoneutralizealkalinewastewaters.n6-102调节pH常用化合物n6-1022成垢可能性分析Withtheincreasingusethatisbeingmadeofnanofiltration,reverseosmosis,andelectrodialysisinwastewaterreuseapplications,adjustmentofthescalingcharacteristicsoftheeffluenttobetreatedisimportanttoavoidcalciumcarbonateandsulfatescaleformation.Theformationofscalewithinthetreatmentmodulewillcausedeteriorationintheperformance,ultimatelyleadingtothefailureofthemembranemodule.Manytheorieshaveresultedintheformationofrelativeindexesthatareusedtoassesswhetherawaterisundersaturated,balanced,orsupersaturatedwithrespecttocalciumcarbonate.Anundersaturatedwaterwilltendtodissolveanexistingcalciumcarbonatefilm;abalancedwaterwillneitherdissolveorformafilm;asupersaturedwaterwilltendtoformafilm.相关的理论包括：Langeliersaturationindex，Ryznerstabilityindex，MINTEQA2，MINEQL+等。n6-102LangelierSaturationIndexThetendencytodevelopcalciumcarbonate(CaCO3)scaleduringtheadvancedtreatmentoftreatedeffluentcanbeapproximatedbycalculatingtheLangelierSaturationIndex(LSI).判别标准：LSI>0:可能结垢LSI<0:不结垢，反而去除处理单元上的水垢LSI=0:不结垢也不除垢LSI只用于碳酸钙水垢总溶固系数n6-102RyznerStabilityIndexAnalternativeindexknownasthestabilityindexwasproposedbyRyzner(1944)andisusedinanumberofindustrialapplications.判别标准：RSI<5.5：形成重垢5.58.5：水极容易除垢corrosiveAggressive指数的计算LSI常用于废水处理；RSI常用于工业生产。n6-102活度系数γ离子强度I对于CaCO3（pH6.5~9.0）n6-102水垢控制ScaleControlCaCO3水垢可以通过以下几种途径去除：酸化，降低pH和碱度；通过离子交换和石灰软化，减少钙浓度；添加阻垢剂，增加CaCO3溶解度；石灰软化法：使用石灰软化硬水的方法，在硬水中加入消石灰，与水中的硬度成分碳酸化合物反应、生成难溶的碱性物质。使其沉淀析出，达到软化的目的的方法，利用这种方法可使水中钙浓度降低到10~35ppm。稳定性StabilizationWastewatereffluentthatisdemineralizedwithreverseosmosiswillgenerallyrequirepHandcalciumcarbonateadjustmenttopreventmetalliccorrosion,duetothecontactofthedemineralizedwaterwithmetallicpipesandequipment.Corrosionoccursbecausematerialfromthesolidissolubilizedtosatisfythevarioussolubilityproducts.DemineralizedwatertypicallyisstabilizedbyaddinglimetoadjusttheLSI.n6-11贮存&进料系统n6-113Thedesignofchemicaltreatmentoperationsinvolvesnotonlythesizingofthevariousunitoperationsandprocessesbutalsothenecessaryappurtenances.Becauseofthecorrosivenatureofmanyofthechemicalsusedandthedifferentformsinwhichtheyareavailable,specialattentionmustbegiventothedesignofchemicalstorage,feeding,piping,andcontrolsystems.化学贮存ScaleControln6-113n6-113进料系统n6-113固体进料DryChemicalFeedSystemsAdrychemicalfeedsystemtypicallyconsistsofastoragehopper,drychemicalfeeder,adissolvingtank,andapumpedorgravitydistributionsystem.Theunitsaresizedaccordingtothevolumeofwastewater,treatmentrate,andoptimumlengthoftimeforchemicalfeedinganddissolving.Hoppersusedwithpowderedchemicalsthatarecompressibleandcanformanarchsuchaslimeareequippedwithpositiveagitatorsandadustcollectionsystem.Drychemicalfeedersareeitherofthevolumetricorgravimetrictype.Inthevolumetrictypethevolumeofthedrychemicalfedismeasured,whereasinthegravimetrictypetheweightofchemicalfedismeasured.n6-113Withadryfeedsystem,thedissolvingoperationiscritical.Thecapacityofthedissolvingtankisbasedonthedetentiontime,whichisdirectlyrelatedtothewettabilityorrateofsolutionofthechemical.Whenthewatersupplyiscontrolledforthepurposeofformingaconstantstrengthsolution,mechanicalmixersshouldbeused.Dependingontheflowpatternwithinthemixingtank,itmaybenecessarytoaddbafflesforeffectivemixing.Insmallermixingtanks,themixercanbesetatanangletoavoidtheuseofbaffles.Solutionsorslurriesareoftenstoredafterdissolvinganddischargedtotheapplicationpointatmeteredratesbychemicalfeedpumps.n6-113n6-113进料器类型Typicalcharacteristicsofchemicalfeedersan6-113n6-113n6-113n6-113液体进料LiquidChemicalFeedSystemsLiquidchemicalfeedsystemstypicallyincludeasolutionstoragetank,transferpump,daytankfordilutingtheconcentratedsolution,andchemicalfeedpumpfordistributiontotheapplicationpoint.Ingeneral,liquidfeedsystemsprovideforbetterinitialcontactanddispersionofthechemicalandthewastewater.Thestoragetankissizedbaseduponthestabilityofthechemical,feedraterequirements,regulatoryrequirements,deliveryconstraints,andavailabilityofthesupply.Spillorsecondarycontainmentisusuallyrequiredaroundthestoragetanks;chemicalsthatarehighlyreactiveshouldnotbestorednexttoeachother.n6-113液体进料示意图n6-113典型液体进料装置n6-113气体进料GasChemicalFeedSystemsChemicalsthatareusedasagasincludeammonia,chlorine,oxygen,ozone,andsulfurdioxide.Gasfeedsystemsareusedmostlyforfeedingchemicalsusedfordisinfectionanddechlorination.Chlorine,acommonlyusedchemicalfordisinfection,isoftensuppliedinaliquidformwithinthestoragecontainerandevaporatescontinuouslyasthegasisdrawnfromtheheadspaceabovetheliquidinthestoragecontainer.n6-113Theoptimaltimeformixingcanvaryfromafractionofasecondtoseveralsecondsormore.Becauseofthedifficultiesinachievingrapidmixinginlargetreatmentplantswithasinglemixingdevice,theuseofmultiplemixingdevicesisrecommended.Theparticularmixingdeviceselectedforagivenapplicationmustbebasedonaconsiderationofthereactiontimesandoperativemechanismsforthechemicalsthatarebeingused.原料混合InitialChemicalMixingn废水处理工艺设计及计算感谢各位老师评判指导南京理工大学