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'废水处理工艺设计及计算第6章9-11节
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
6-9PHOTOLYSIS
6-91Photolysisisaprocessbywhichconstituentsarebrokendownbyexposureandabsorptionofphotonsfromalightsource.AswithAOPs,theprimaryuseofphotolysisisfortheremovaloftraceorganiccompoundsinwaterreuseapplications.Innaturalsystems,sunlightisthelightsourceforphotolysisreactions,however,inengineeredsystems,ultraviolet(UV)lampsareusedtoproducethephotonicenergy.Theeffectivenessofthephotolysisprocessdepends,inpart,onthecharacteristicsofthereclaimedwater,structureofthecompounds,designofthephotolysisreactor,anddoseandwavelengthoftheappliedlight.Thephotolysisratecanbeestimatedfromtherateatwhichthecompoundabsorbslightandthephotonicefficiencyofthereaction(quantumyield).定义
6-91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
6-91FoulingthatmayoccurontheoutsideoftheUVlampprotectivequartzsleevemaybemanagedusinganautomaticcleaningsystemconsistingofacollarthatperiodicallymovesalongthelamptoremoveprecipitatesandinterceptedmatter.Whenusedinconjunctionwithreverseosmosispretreatment,thechemicalsaddedtoreducethepHforscalecontrolinthemembraneswillalsoreducethepotentialforprecipitationontheUVlamps.Photolysisreactionsarecausedbylightemissionintheultravioletrange(200to400nm).TherearethreetypesofUVlampsusedforphotolysisprocesses:(1)low-pressurelow-intensity,(2)low-pressurehigh-intensity,and(3)medium-pressurehigh-intensitylamps.Low-pressurelampsemitmuchoftheirenergyatawavelengthof254nmwhilemediumpressurelampsemitenergyatmultiple.Thetypeoflampusedandreactorconfigurationwilldependontheconstituenttoberemovedaswellasthewatermatrixandsite-specificconditions.
6-91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.
6-91不同物质的消光系数
6-91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.
6-913光解速率RateofPhotolysisTherateatwhichacompoundisphotolyzeddependsontherateandfrequencyofphotonabsorption.Thequantumyieldisaquantityusedtodescribethefrequencyatwhichphotonabsorptionresultsinaphotolysisreactionandisspecifictothetypeofcompoundandthewavelength.量子产率quantumyieldAsageneralrule,thequantumyieldincreasesaswavelengthdecreases(increasingphotonicenergy).
6-91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.
6-91electricalefficiencyperlogorder(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。
6-91局限性PhotolysisProcessLimitationsTheefficiencyofthephotolysisprocessdepends,inpart,onthecharacteristicsofthewatermatrixandcompoundstargetedfordegradation.theextinctioncoefficientforresidualorganicmattervariesoverawiderangeandmayinterferewiththephotolysisofothercompounds.thelightenergyinputmaybeabsorbedbytheotherconstituents,theremaybephotonlossesuponreflectionoffthereactorwall,andtheprecipitatethatbuildsupontheexteriorsurfaceofsleevesthatcoverthelampsduetotheelevatedtemperaturewillblocklighttransmission.解决方案:ToovercomethelimitationsassociatedwithphotolysisprocessesrelatedtoabsorbanceofUVenergybynon-targetconstituentsinwaterreuse,pretreatmentusingreverseosmosisshouldbeusedtoremovemostoftheinterferingcompoundsandimprovetheoverallprocessperformance.Pilotstudiesshouldbeconductedtocharacterizetheexpectedefficiencyofphotolysisandtherateandcharacteristicsoffoulingofthelampsleeve.
6-10化学中和&水垢控制&稳定性』
6-102Theremovalofexcessacidityoralkalinitybytreatmentwithachemicaloftheoppositecompositionistermedneutralization.Ingeneral,alltreatedwastewaterswithexcessivelyloworhighpHwillrequireneutralizationbeforetheycanbedispersedtotheenvironment.Scalingcontrolisrequiredfornanofiltrationandreverseosmosistreatmenttocontroltheformationofscale,whichcanseverelyimpactperformance.Chemicalstabilizationisoftenrequiredforhighlytreatedwastewaterstocontroltheiraggressivenesswithrespecttocorrosion.定义与概念1PH调节Inavarietyofwastewatertreatmentoperationsandprocesses,thereisoftenaneedforpHadjustment.Becauseanumberofchemicalsareavailablethatcanbeused,thechoicewilldependonthesuitabilityofagivenchemicalforaparticularapplicationandprevailingeconomics.
6-102Wastewaterthatisacidiccanbeneutralizedwithanynumberofbasicchemicals.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.
6-102调节pH常用化合物
6-1022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。
6-102LangelierSaturationIndexThetendencytodevelopcalciumcarbonate(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
6-102RyznerStabilityIndexAnalternativeindexknownasthestabilityindexwasproposedbyRyzner(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。
6-102活度系数γ离子强度I对于CaCO3(pH6.5~9.0)
6-102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.
6-11贮存&进料系统
6-113Thedesignofchemicaltreatmentoperationsinvolvesnotonlythesizingofthevariousunitoperationsandprocessesbutalsothenecessaryappurtenances.Becauseofthecorrosivenatureofmanyofthechemicalsusedandthedifferentformsinwhichtheyareavailable,specialattentionmustbegiventothedesignofchemicalstorage,feeding,piping,andcontrolsystems.化学贮存ScaleControl
6-113
6-113进料系统
6-113固体进料DryChemicalFeedSystemsAdrychemicalfeedsystemtypicallyconsistsofastoragehopper,drychemicalfeeder,adissolvingtank,andapumpedorgravitydistributionsystem.Theunitsaresizedaccordingtothevolumeofwastewater,treatmentrate,andoptimumlengthoftimeforchemicalfeedinganddissolving.Hoppersusedwithpowderedchemicalsthatarecompressibleandcanformanarchsuchaslimeareequippedwithpositiveagitatorsandadustcollectionsystem.Drychemicalfeedersareeitherofthevolumetricorgravimetrictype.Inthevolumetrictypethevolumeofthedrychemicalfedismeasured,whereasinthegravimetrictypetheweightofchemicalfedismeasured.
6-113Withadryfeedsystem,thedissolvingoperationiscritical.Thecapacityofthedissolvingtankisbasedonthedetentiontime,whichisdirectlyrelatedtothewettabilityorrateofsolutionofthechemical.Whenthewatersupplyiscontrolledforthepurposeofformingaconstantstrengthsolution,mechanicalmixersshouldbeused.Dependingontheflowpatternwithinthemixingtank,itmaybenecessarytoaddbafflesforeffectivemixing.Insmallermixingtanks,themixercanbesetatanangletoavoidtheuseofbaffles.Solutionsorslurriesareoftenstoredafterdissolvinganddischargedtotheapplicationpointatmeteredratesbychemicalfeedpumps.
6-113
6-113进料器类型Typicalcharacteristicsofchemicalfeedersa
6-113
6-113
6-113
6-113液体进料LiquidChemicalFeedSystemsLiquidchemicalfeedsystemstypicallyincludeasolutionstoragetank,transferpump,daytankfordilutingtheconcentratedsolution,andchemicalfeedpumpfordistributiontotheapplicationpoint.Ingeneral,liquidfeedsystemsprovideforbetterinitialcontactanddispersionofthechemicalandthewastewater.Thestoragetankissizedbaseduponthestabilityofthechemical,feedraterequirements,regulatoryrequirements,deliveryconstraints,andavailabilityofthesupply.Spillorsecondarycontainmentisusuallyrequiredaroundthestoragetanks;chemicalsthatarehighlyreactiveshouldnotbestorednexttoeachother.
6-113液体进料示意图
6-113典型液体进料装置
6-113气体进料GasChemicalFeedSystemsChemicalsthatareusedasagasincludeammonia,chlorine,oxygen,ozone,andsulfurdioxide.Gasfeedsystemsareusedmostlyforfeedingchemicalsusedfordisinfectionanddechlorination.Chlorine,acommonlyusedchemicalfordisinfection,isoftensuppliedinaliquidformwithinthestoragecontainerandevaporatescontinuouslyasthegasisdrawnfromtheheadspaceabovetheliquidinthestoragecontainer.
6-113Theoptimaltimeformixingcanvaryfromafractionofasecondtoseveralsecondsormore.Becauseofthedifficultiesinachievingrapidmixinginlargetreatmentplantswithasinglemixingdevice,theuseofmultiplemixingdevicesisrecommended.Theparticularmixingdeviceselectedforagivenapplicationmustbebasedonaconsiderationofthereactiontimesandoperativemechanismsforthechemicalsthatarebeingused.原料混合InitialChemicalMixing
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'
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