废水处理工艺设计的光解,除垢,管道与控制

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6-9PHOTOLYSIS6-91Photolysisisaprocessbywhichconstituentsarebrokendownbyexposureandabsorptionofphotonsfromalightsource.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。1.UV会促进H2O2产生OH·2.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.1.theextinctioncoefficientforresidualorganicmattervariesoverawiderangeandmayinterferewiththephotolysisofothercompounds.2.thelightenergyinputmaybeabsorbedbytheotherconstituents,theremaybephotonlossesuponreflectionoffthereactorwall,andtheprecipitatethatbuildsupontheexteriorsurfaceofsleevesthatcoverthelampsduetotheelevatedtemperaturewillblocklighttransmission.解决方案：ToovercomethelimitationsassociatedwithphotolysisprocessesrelatedtoabsorbanceofUVenergybynon-targetconstituentsinwaterreuse,pretr