废水处理工艺设计的光解,除垢,管道与控制.ppt

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 Photolysisisaprocessbywhichconstituentsarebrokendownbyexposureandabsorptionofphotonsfromalightsource AswithAOPs theprimaryuseofphotolysisisfortheremovaloftraceorganiccompoundsinwaterreuseapplications Innaturalsystems sunlightisthelightsourceforphotolysisreactions however inengineeredsystems ultraviolet UV lampsareusedtoproducethephotonicenergy Theeffectivenessofthephotolysisprocessdepends inpart onthecharacteristicsofthereclaimedwater structureofthecompounds designofthephotolysisreactor anddoseandwavelengthoftheappliedlight Thephotolysisratecanbeestimatedfromtherateatwhichthecompoundabsorbslightandthephotonicefficiencyofthereaction quantumyield 定义 光解工艺PhotolysisProcesses EngineeredphotolysisreactionsareconductedinspeciallydesignedreactorsoptimizedwithrespecttoUVdose 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 FoulingthatmayoccurontheoutsideoftheUVlampprotectivequartzsleevemaybemanagedusinganautomaticcleaningsystemconsistingofacollarthatperiodicallymovesalongthelamptoremoveprecipitatesandinterceptedmatter Whenusedinconjunctionwithreverseosmosispretreatment thechemicalsaddedtoreducethepHforscalecontrolinthemembraneswillalsoreducethepotentialforprecipitationontheUVlamps Photolysisreactionsarecausedbylightemissionintheultravioletrange 200to400nm TherearethreetypesofUVlampsusedforphotolysisprocesses 1 low pressurelow intensity 2 low pressurehigh intensity and 3 medium pressurehigh intensitylamps Low pressurelampsemitmuchoftheirenergyatawavelengthof254nmwhilemediumpressurelampsemitenergyatmultiple Thetypeoflampusedandreactorconfigurationwilldependontheconstituenttoberemovedaswellasthewatermatrixandsite specificconditions 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AbsorptionofUVLight A absorbance dimensionlessL lightintensityafterpassingthroughsolutionL lightintensityafterpassingthroughablanksolute extinctioncoefficientC concentrationoflightabsorbingsolutex lengthoflightpathK absorptivity Theextinctioncoefficientisafunctionofwavelengthbecauseasthewavelengthdecreasesmoreenergeticphotonsareabsorbedandtheabsorptivityofalightabsorbingcompoundincreases 不同物质的消光系数 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EnergyInputforPhotolysis Thelampoutputandreactorsizecanbeusedtoestimatetheenergyinputforthephotolysisreaction 存在问题 Theactualperformanceofaphotoreactorisexpectedtobelowerthancomputedduetolightbeingabsorbedbythereactorwallsorblockedbytheprecipitatethatformsonthelampsleeve Whileasafetyfactorspecifictoaparticularsystemcouldbeappliedtocompensatefortheseinefficiencies pilotstudiesareusedtoobtainmorereliabledesigncriteria 3光解速率RateofPhotolysis Therateatwhichacompoundisphotolyzeddependsontherateandfrequencyofphotonabsorption Thequantumyieldisaquantityusedtodescribethefrequencyatwhichphotonabsorptionresultsinaphotolysisreactionandisspecifictothetypeofcompoundandthewavelength 量子产率quantumyield Asageneralrule thequantumyieldincreasesaswavelengthdecreases increasingphotonicenergy 伪一级动力学方程Thepseudofirstorderratelaw Typically thelightabsorptionbythecomponentthatistargetedforremovalisminorascomparedtothelightabsorptionbythebackgroundwatermatrix 全局平均光解反应速率 4电效率ElectricalEfficiency Theelectricalenergyrequirementforphotolyticreactionsissignificantduetotheprocessinefficiencies Consequently itisimportanttocompareprocessefficiencyonthebasisofelectricalusageperamountofcompounddestruction Onesuchmeasureistheelectricalefficiencyperlogorder EE O ofcompounddestruction electricalefficiencyperlogorder 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 局限性PhotolysisProcessLimitations Theefficiencyofthephotolysisprocessdepends inpart onthecharacteristicsofthewatermatrixandcompoundstargetedfordegradation theextinctioncoefficientforresidualorganicmattervariesoverawiderangeandmayinterferewiththephotolysisofothercompounds thelightenergyinputmaybeabsorbedbytheotherconstituents theremaybephotonlossesuponreflectionoffthereactorwall andtheprecipitatethatbuildsupontheexteriorsurfaceofsleevesthatcoverthelampsduetotheelevatedtemperaturewillblocklighttransmission 解决方案 ToovercomethelimitationsassociatedwithphotolysisprocessesrelatedtoabsorbanceofUVenergybynon targetconstituentsinwaterreuse pretreatmentusingreverseosmosisshouldbeusedtoremovemostoftheinterferingcompoundsandimprovetheoverallprocessperformance Pilotstudiesshouldbeconductedtocharacterizetheexpectedefficiencyofphotolysisandtherateandcharacteristicsoffoulingofthelampsleeve Theremovalofexcessacidityoralkalinitybytreatmentwithachemicaloftheoppositecompositionistermedneutralization Ingeneral alltreatedwastewaterswithexcessivelyloworhighpHwillrequireneutralizationbeforetheycanbedispersedtotheenvironment Scalingcontrolisrequiredfornanofiltrationandreverseosmosistreatmenttocontroltheformationofscale whichcanseverelyimpactperformance Chemicalstabilizationisoftenrequiredforhighlytreatedwastewaterstocontroltheiraggressivenesswithrespecttocorrosion 定义与概念 1PH调节 Inavarietyofwastewatertreatmentoperationsandprocesses thereisoftenaneedforpHadjustment Becauseanumberofchemicalsareavailablethatcanbeused thechoicewilldependonthesuitabilityofagivenchemicalforaparticularapplicationandprevailingeconomics Wastewaterthatisacidiccanbeneutralizedwithanynumberofbasicchemicals 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 调节pH常用化合物 2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 LangelierSaturationIndex Thetendencytodevelopcalciumcarbonate 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 RyznerStabilityIndex AnalternativeindexknownasthestabilityindexwasproposedbyRyzner 1944 andisusedinanumberofindustrialapplications 判别标准 RSI8 5 水极容易除垢 corrosive Aggressive 指数的计算 LSI常用于废水处理 RSI常用于工业生产 活度系数 离子强度I 对于CaCO3 pH6 5 9 0 水垢控制ScaleControl CaCO3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Stabilization WastewatereffluentthatisdemineralizedwithreverseosmosiswillgenerallyrequirepHandcalciumcarbonateadjustmenttopreventmetalliccorrosion duetothecontactofthedemineralizedwaterwithmetallicpipesandequipment Corrosionoccursbecausematerialfromthesolidissolubilizedtosatisfythevarioussolubilityproducts DemineralizedwatertypicallyisstabilizedbyaddinglimetoadjusttheLSI Thedesignofchemicaltreatmentoperationsinvolvesnotonlythesizingofthevariousunitoperationsandprocessesbutalsothenecessaryappurtenances Becauseofthecorrosivenatureofmanyofthechemicalsusedandthedifferentformsinwhichtheyareavailable specialattentionmustbegiventothedesignofchemicalstorage feeding piping andcontrolsystems 化学贮存ScaleControl 进料系统 固体进料DryChemicalFeedSystems Adrychemicalfeedsystemtypicallyconsistsofastoragehopper drychemicalfeeder adissolvingtank andapumpedorgravitydistributionsystem Theunitsaresizedaccordingtothevolumeofwastewater treatmentrate andoptimumlengthoftimeforchemicalfeedinganddissolving Hoppersusedwithpowderedchemicalsthatarecompressibleandcanformanarchsuchaslimeareequippedwithpositiveagitatorsandadustcollectionsystem Drychemicalfeedersareeitherofthevolumetricorgravimetrictype Inthevolumetrictypethevolumeofthedrychemicalfedismeasured whereasinthegravimetrictypetheweightofchemicalfedismeasured Withadryfeedsystem thedissolvingoperationiscritical Thecapacityofthedissolvingtankisbasedonthedetentiontime whichisdirectlyrelatedtothewettabilityorrateof solutionofthechemical Whenthewatersupplyiscontrolledforthepurposeofformingaconstantstrengthsolution mechanicalmixersshouldbeused Dependingontheflowpatternwithinthemixingtank itmaybenecessarytoaddbafflesforeffectivemixing Insmallermixingtanks themixercanbesetatanangletoavoidtheuseofbaffles Solutionsorslurriesareoftenstoredafterdissolvinganddischargedtotheapplicationpointatmeteredratesbychemicalfeedpumps 进料器类型Typicalcharacteristicsofchemicalfeedersa 液体进料LiquidChemicalFeedSystems Liquidchemicalfeedsystemstypicallyincludeasolutionstoragetank transferpump daytankfordilutingtheconcentratedsolution andchemicalfeedpumpfordistribution totheapplicationpoint Ingeneral liquidfeedsystemsprovideforbetteri