廢水設(shè)計：排泥設(shè)備簡介及污泥的深度處理(英文)

ProcessingandTreatmentofSludge目錄SLUDGEPROCESSINGFLOWDIAGRAMSASLUDGEANDSCUMPUMPINGBPRELIMINARYSLUDGEPROCESSINGOPERATIONSCPartASLUDGEPROCESSINGFLOWDIAGRAMSGeneralizedsludgeprocessingflowdiagramPartBSLUDGEANDSCUMPUMPINGSLUDGEANDSCUMPUMPINGSludgeproducedinwastewatertreatmentplantsmustbeconveyedfrompointtopointintheplantinconditionsrangingfromawaterysludgeorscumtoathicksludge.Sludgemayalsobepumpedoff-siteforlongdistancesfortreatmentanddisposition.Foreachtypeofsludgeandpumpingapplication,adifferenttypeofpumpmaybeneeded.PumpsPumpsusedmostfrequentlytoconveysludgeincludetheplunger,progressivecavity,hose,solidshandlingcentrifugal(screwcentrifugalsandtraditional“non-clogdesigns),recessedimpeller,diaphragm,high-pressurepistondiaphragm,androtarylobetypes.Othertypesofpumpssuchashydraulicpistonslurrypumpshavealsobeenusedtopumpsludge.Chopperpumpsareusedextensivelyforpumpingscumcontainingrags,plastics,andotherfibrousmaterialsthatrequireshredding.TheadvantagesanddisadvantagesofeachtypeofpumparesummarizedinTable13–14.PlungerPumpsPlungerpumpshavebeenusedfrequentlyforsludgeapplications,especiallyprimarysludges,andhaveprovedtobequitesatisfactory.Theadvantagesofplungerpumpsareasfollows:1.Pulsatingactionofsimplexandalsoduplexpumpstendstoconcentratethesludgeinthehoppersaheadofthepumpsandresuspendsolidsinpipelineswhenpumpingatlowvelocities.2.Theyaresuitableforsuctionliftsupto3m(10ft)andareself-priming.3.Lowpumpingratescanbeusedwithlargeportopenings.4.Positivedeliveryisprovidedunlesssomeobjectpreventstheballchecksvalvesfromseating.5.Theyhaveconstantbutadjustablecapacity,regardlessoflargevariationsinpumpinghead.6.Dischargepressurelimitationsareapproximately10to11bar(150to165lbf/in.2).(1bar=100kPa）7.Heavysludgeconcentrationsmaybepumpediftheequipmentisdesignedfortheloadconditions.Plungerpumpscomewithone,two,orthreeplungers(calledsimplex,duplex,ortriplexunits)withcapacitiesof2.5to3.8L/s(40to60gal/min)perplunger,andlargermodelsareavailable.Pumpspeedsshouldbebetween40and50strokespermin.Becausegreaseaccumulationsinsludgelinescauseaprogressiveincreaseinheadwithuse,heavierdutypumpsshouldbedesignedforaminimumheadof6.9bar(100lbf/in.2).Capacityisdecreasedinconstantspeedpumpsbyshorteningthestrokeoftheplunger;however,thepumpsseemtooperatemoresatisfactorilyatornearfullstroke.Forthisreason,manypumpsareprovidedwithvariable-speeddrivesforspeedcontrolofcapacity.Aplungerpumpdiffersfromacentrifugalorrecessedimpellerpumpinthatitsdischargeispulsingduetotheactionofapiston;consequently,theactualflowwhilesludgeismovinginthepipelineisgreaterthanaveragepumpingcapacity.Theheadlosscalculations,therefore,mustbebasedonthepeakpulsatingflowratherthanthedesignflow.ThefactorsgiveninTable13–15canbeusedtoaccountfortheactualpeakpulsatingorinstantaneousflow.ProgressiveCavityPumpsTheprogressivecavitypumphasbeenusedsuccessfullyonalmostalltypesofsludges.Thepumpiscomposedofasingle-threadedrotorthatoperateswithaminimumofclearanceinadouble-threadedhelixelastomerstator.Avolumeor“cavity”movesprogressivelyfromsuctiontodischargewhentherotorturns.Thepumpisself-primingatsuctionliftsupto8.5m(28ft),butitmustnotbeoperateddryoritwillburnouttheelastomerstator.Progressivecavitypumpsareavailableincapacitiesupto126L/s(2000gal/min)andmaybeoperatedatdischargeheadsof48bar(720lbf/in.2)withsludge.Thistypeofpumprequiresoversizingtomeetsystemconditionsoverthelifeoftheofequipment.Forexample,ifa9.5L/s(150gal/min)pumpisrequiredthepumpselectionshouldbesizedforanadditional50percentorapumpsizedfor14.25L/s(225gal/min).Speedforsludgeapplicationsshouldbelimitedtoapproximately250rev/min.Forsludgesandforsystemsfeedingdewateringequipment,agrindernormallyprecedesthesepumps.Thepumpsareexpensivetomaintainbecauseofwearoftherotorsandstators,particularlyinprimarysludgepumpingapplicationswheregritispresent.

Advantagesofthepumpsare(1)theflowratesarecontrolledeasilyusingvariablespeeddrives;

(2)pulsationisminimal;(3)operationisrelativelysimple.CentrifugalPumpsCentrifugalpumpsofsolidshandlingor“non-clog”designarecommonlyusedtopumpactivatedsludge.Incentrifugalpumpingapplications,theproblemischoosingthepropernumberandcapacitytoaccommodatethetypicalwiderangeofflowratesrequired.Atanygivenspeed,centrifugalpumpsoperatewellonlyifthepumpingheadiswithinarelativelynarrowrange;thevariablenatureofsludge,however,causespumpingheadstochange.Theselectedpumpsmusthavesufficientclearancetopassthesolidswithoutcloggingandhaveasmallenoughcapacitytoavoidpumpingasludgedilutedbylargequantitiesofwastewateroverlyingthesludgeblanket.立式無堵塞自吸離心泵Throttlingthedischargetoreducethecapacityisimpracticalbecauseoffrequentstoppages;henceitisabsolutelyessentialthatthesepumpsbeequippedwithvariablespeeddrives.Centrifugalpumpsofspecialdesign:recessedimpellerand“chopper”typepumpshavebeenusedforpumpingprimarysludge.Recessedimpellerpumpshaveimpellersthatarefullyrecessedandareveryeffectiveinconveyingsludgeandhighersludgeconcentrationsthanthesolidshandlingcentrifugalpumps.Thesizeofparticlesthatcanbehandledislimitedonlybythediameterofthesuctionordischargeopenings.Therotatingimpellerdevelopsavortexinthesludgesothatthemainpropulsiveforceistheliquiditself.Mostofthefluiddoesnotactuallypassthroughthevanesoftheimpeller,therebyminimizingabrasivecontact;however,pumpsusedinsludgeservicearerecommendedtohavenickelorchromeabrasion-resistantvoluteandimpellers.Thepumpscanoperateonlyoveranarrowheadrangeatagivenspeed,sothesystemoperatingconditionsmustbeevaluatedcarefully.Variablespeedcontrolisrecommendedwherethepumpsareexpectedtooperateoverawiderangeofheadconditions.Forhigh-pressureapplications,multiplepumpsmaybeused,connectedtogetherinseries.Chopper-typepumpshaveacutterknifeattachedtoanon-clogimpellerthatagitatesandbreaksuplargesolidsthattendtoblockthepumpsuction.Incomingsludgeischoppedbysharpenedimpellerbladesthatturnacrossthecutterbar.Slow-speedcentrifugalandmixed-flowpumpsarecommonlyusedforreturningactivatedsludgetotheaerationtanks.Screwpumpsarealsobeingusedforthisserviceespeciallywherepumpsarerequiredtohavealargeturndown.Screwcentrifugalpumpstendtohavelesscloggingissuesfortheseapplications.DiaphragmPumpsDiaphragmpumpsuseaflexiblemembranethatispushedandpulledtocontractandenlargeanenclosedcavity.Flowisdirectedthroughthiscavitybycheckvalves,whichmaybeeitherballorflaptype.Thecapacityofadiaphragmpumpisalteredbychangingeitherthelengthofthediaphragmstrokeorthenumberofstrokesperminute.Pumpcapacitycanbeincreasedandflowpulsationssmoothedoutbyprovidingtwopumpchambersandusingbothstrokesofthediaphragmforpumping.Diaphragmpumpsarerelativelylowcapacityandlowhead;thelargestavailableairdiaphragmpumpdelivers14L/s(220gal/min)against15m(50ft)ofhead.High-PressurePistonPumpsHigh-pressurepistonpumpsareusedinhigh-pressureapplicationssuchaspumpingsludgelongdistances.Severaltypesofpistonpumpshavebeendevelopedforhigh-pressureapplicationsandaresimilarinactiontoplungerpumps.Thehigh-pressurepistonpumpsuseseparatepowerpistonsormembranesordiaphragmstoseparatethedrivemechanismsfromcontactingthesludge.Advantagesofthesetypesofpumpsare(1)theycanpumprelativelysmallflowratesathighpressures,upto13.8bar(note1bar5100kPa)(200lbf/in.2),(2)largesolidsuptothedischargepipediametercanbepassed,(3)arangeofsludgeconcentrationscanbehandled,(4)thepumpingcanbeaccomplishedinasinglestage.Thepumps,however,areveryexpensive.柱塞泵和活塞泵有什么區(qū)別？1.活塞泵活塞不會伸出缸體，而柱塞要伸出缸體；2.活塞靠改變缸體內(nèi)的容積產(chǎn)生吸排力，柱塞靠改變缸套外的容積產(chǎn)生吸排力；3.活塞會與缸體圓柱內(nèi)表面直接接觸，而柱塞不會，一般會隔著一個密封件。

RotaryLobePumpsRotarylobepumpsarepositivedisplacementpumpsinwhichtworotatingsynchronouslobespushthefluidthroughthepump.Rotationalspeedandshearingstressesarelow.Forsludgepumping,lobesaremadeofhardmetalorhardrubber.Thistypeofpumprequiresoversizingtomeetsystemconditionsoverthelifeoftheofequipment.Forexampleifa9.5L/s(150gal/min)pumpisrequiredthepumpselectionshouldbesizedforanadditional50percentorapumpsizedfor14.25L/s(225gal/min).Speedforsludgeapplicationsshouldbelimitedtoapproximately250to300rev/mindependingontheabrasivenessofthesludge.Anadvantagecitedfortherotarylobepumpisthatlobereplacementislesscostlythanrotor,andstatorreplacementforprogressivecavitypumpsandthespacerequiredforinstallationisless.Rotarylobepumps,likeotherpositive-displacementpumps,mustbeprotectedagainstpipelineobstructions.HosePumpsPeristaltichosepumpshavealsobeenusedforpumpingsludge.Thepumpworksbyalternatelycompressingandrelaxingaspeciallydesignedresilientbutreinforcedhose.Thehoseiscompressedbetweentheinnerwallofthepumphousingandthecompressionshoesontherotor.Alubricantisusedtoreduceheatandwearonthehose.Thepumpsareavailableincapacitiesrangingfrom36to1250L/min(10to330gal/min).Asapositive-displacementpump,thepumpoutputisdirectlyproportionaltospeedateitherhighorlowdischargepressures.Theprimarydisadvantagesofthehosepumparethepulsatingflow,hosewear,andtherelativelyhighcostofhosereplacement.Typicalsludgetreatmentflowdiagrams

ApplicationofpumpstotypesofsludgeandbiosolidsAdvantagesanddisadvantagesofvarioustypesofsludgepumpsHeadlossDeterminationTheheadlossencounteredinthepumpingofsludgedependsontheflowproperties(rheology)ofsludge,thepipediameter,andtheflowvelocity.Ithasbeenobservedthatheadlossesincreasewithincreasedsolidscontent,increasedvolatilecontent,andlowertemperatures.Whenthepercentvolatilemattermultipliedbythepercentsolidsexceeds600,difficultiesmaybeencounteredinpumpingsludge.Water,oil,andmostotherfluidsare“Newtonian,”whichmeansthatthepressuredropisproportionaltothevelocityandviscosityunderlaminarflowconditions.Asthevelocityincreasespastacriticalvalue,theflowbecomesturbulent.Theheadlossinpumpingunconcentratedactivatedandtrickling-filtersludgesmaybefrom10to25percentgreaterthanforwater.Primary,digested,andconcentratedsludgesatlowvelocitiesmayexhibitaplastic-flowphenomenoninwhichadefinitepressureisrequiredtoovercomeresistanceandstartflow.Theresistancethenincreasesapproximatelywiththefirstpowerofthevelocitythroughoutthelaminarrangeofflow,whichextendstoabout1.1m/s(3.5ft/s),thelowercriticalvelocity.Abovethehighercriticalvelocityatabout1.4m/s(4.5ft/s),theflowmaybeconsideredturbulent.Intheturbulentrange,thelossesforwell-digestedsludgemaybemorethantwotothreetimesthelossesforwater.Thelossesforprimaryandconcentratedsludges,especiallythoseconditionedwithpolymer,andscummaybeconsiderablygreater.Theriskofunderestimatingtheheadlossalsoincreasesasthepipingdistanceandsludgeconcentrationincreases.Wherepossible,particularlyinlong-distancesludgepumping,hydraulicstudiesshouldbeconductedtoconfirmtherangesofheadlosscharacteristics.SimplifiedHeadlossComputationsRelativelysimpleproceduresareusedtocomputeheadlossforshortsludgepipelines.Theaccuracyoftheseproceduresmaybeadequate,especiallyatsludgesolidsconcentrationslessthan3percentbyweight.Todeterminetheheadloss,thefactorkisobtainedfromFig.13–5(a)foragivensolidscontentandtypeofsludge.Theheadlosswhenpumpingsludgeiscomputedbymultiplyingtheheadlossofwater,determinedbyusingtheDarcy-Weisbach,Hazen-Williams,orManningequations,byk.ThevaluesgivenonFig.13–5(a)shouldbeusedonlywhen(1)velocitiesareatleast0.8m/s(2.5ft/s);(2)velocitiesdonotexceed2.4m/s(8ft/s);(3)thixotropicbehaviorisnotconsidered;

(4)thepipeisnotobstructedbygreaseorothermaterials.Anotherapproximatemethodmakesuseofempiricalmultiplicationfactorcharts[seeFig.13–5(b)].Theapproximatemethodinvolvesonlyvelocityandpercentsolidsconsideration.ApplicationofRheologytoHeadlossComputationsForpumpingsludgeoverlongdistances,analternativemethodofcomputingheadlosscharacteristicshasbeendevelopedbasedontheflowpropertiesofthesludge.AmethodofcomputingheadlossforlaminarflowconditionswasderivedoriginallybyBabbittandCaldwell(1939),basedontheresultsofexperimentalandtheoreticalstudies.Additionalstudieshavebeenperformedforthetransitionfromlaminartoturbulentflow(Mulbargeretal.,1981;U.S.EPA,1979)andaresummarizedinSanksetal.(1998).Long-distancepumpingofmixturesofuntreated(raw)primaryandsecondarysludgeisdiscussedbyCarthewetal.(1983).Theapproachusedinthosestudiesforturbulentflow,whichisofcriticalimportanceforlongpipelines,isdescribedbelow.Forlaminarandtransitionalflow,computationalproceduresdescribedinSanksetal.(1998)arerecommended.Asstatedpreviously,water,oil,andmostothercommonfluidsare“Newtonian,”whichmeansthepressuredropisdirectlyproportionaltothevelocityandviscosityunderlaminar-flowconditions.Asthevelocityincreasespastacriticalvalue,theflowbecomesturbulent.ThetransitionfromlaminartoturbulentflowdependsontheReynoldsnumber,whichisinverselyproportionaltothefluidviscosity.Wastewatersludge,however,isanon-Newtonianfluid.Thepressuredropunderlaminarconditionsisnotproportionaltoflow,sotheviscosityisnotaconstant.ThepreciseReynoldsnumberatwhichturbulentflowcharacteristicsareencounteredisuncertainforsludges.SludgehasbeenfoundtobehavemuchlikeaBinghamplastic,asubstancewithastraight-linerelationshipbetweenshearstressandflowonlyafterflowbegins.ABinghamplasticisdescribedbytwoconstants:theyieldstressSy

andthecoefficientofrigidityη.TypicalrangesofvaluesforyieldstressandcoefficientofrigidityareshownonFigs.13–6(a)and(b).Ifthetwoconstantscanbedetermined,thepressuredropoverawiderangeofvelocitiescanbeobtainedusingordinaryequationsforwaterandtheuseofFig.13–6(c).AsobservedonFigs.13–6(a)and(b),publisheddataquantifyingyieldstressandthecoefficientofrigidityvaluesforwastewatersludgesarehighlyvariable.Pilotstudiesshouldbeconductedtodeterminetherheologicaldataforspecificapplications.ProceduresfordevelopingyieldstressandthecoefficientofrigidityusingapipelineviscometerandrotationalviscometerarealsogivenbyCarthewetal.(1983).Twodimensionlessnumberscanbeusedtodeterminethepressuredropduetofrictionforsludge:ReynoldsnumberandHedstromnumber.Reynoldsnumberiscalculatedbyusingthefollowingexpression:Hedstromnumber,whichisreviewedbyHilletal.(1986),iscalculatedasfollows:UsingthecalculatedReynoldsnumberandtheHedstromnumber,thefrictionfactorfcanbedeterminedfromFig.13–6(c).Thepressuredropforturbulentconditionscanthenbecalculatedfromthefollowingrelationship:SludgePipingInwastewatertreatmentplants,conventionalsludgepipingshouldnotbesmallerthan150mm(6in.)indiameteralthoughsmaller-diameterglass-linedpipehasbeenusedsuccessfully.Sludgepipingmaynotneedtobelargerthan200mm(8in.),unlessthevelocityexceeds1.5to1.8m/s(5to6ft/s),inwhichcasethepipeissizedtomaintainthatvelocity.Gravitysludgewithdrawallinesshouldnotbelessthan200mm(8in.)indiameter.Itiscommonpracticetoinstallanumberofcleanoutsintheformofpluggedteesorcrossesinsteadofelbowssothatthelinescanberoddedifnecessary.Pumpconnectionsshouldnotbesmallerthan100mm(4in.)indiameter.Inthedesignoflongsludgelines,however,specialdesignfeaturesshouldbeconsideredincluding:(1)providingtwopipesunlessasinglepipecanbeshutdownforseveraldayswithoutcausingproblems;(2)providingforexternalcorrosionandpipeloads;(3)addingfacilitiesforapplyingdilutionwaterforflushingtheline;(4)providingmeanstoinsertapipecleaner;(5)includingprovisionsforsteaminjection,especiallyincoldclimatesandwhereexcessivegreaseaccumulationoccurs;(6)providingairreliefandblowoffvalvesforthehighandlowpoints;(7)consideringthepotentialeffectsofwaterhammer.PartCPRELIMINARYSLUDGEPROCESSINGOPERATIONSGrinding,degritting,blending,andstorageofsludgeisnecessarytoprovidearelativelyconstant,homogeneousfeedtosubsequentprocessingfacilities.Blendingandstoragecanbeaccomplishedeitherinasingleunitdesignedtodobothorseparatelyinotherplantcomponents.Screeningofrawsludgeordigestedbiosolidsissometimesrequiredinreuseapplicationsfortheremovalofplastics,rags,andothermaterial.Eachofthesepreliminaryoperationsisdiscussedinthissection.PRELIMINARYSLUDGEPROCESSINGOPERATIONSGrindingSludgegrindingisaprocessinwhichlargeandstringymaterialcontainedinsludgeiscutorshearedintosmallparticlestopreventcloggingorwrappingaroundrotatingequipment.Grindershistoricallyhaverequiredhighmaintenance,butnewerdesignsofslow-speedgrindershavebeenmoredurableandreliable.Thesedesignsincludeimprovedbearingsandseals,hardenedsteelcutters,overloadsensors,andmechanismsthatreversethecutterrotationtoclearobstructionsorshutdowntheunitiftheobstructioncannotbecleared.ScreeningBecauserawwastewaterscreenscanallowsignificantquantitiesofsolidmaterialtopassthrough,sludgescreeningisanalternativetogrinding.Screeningisadvantageousinthatnuisancematerialisremovedfromthesludgestream.Stepscreens,shownonFig.5–4(c)inChap.5,canbeusedfortheremovaloffinesolidsfromseptageandprimarysludge.Screenopeningsnormallyrangefrom3to6mm(0.12to0.24in.),althoughopeningsupto10mm(0.4in.)canbeused.Anothertypeofsludgescreenisaninlinescreenthatcanbeinstalledinapipeline(seeFig.13–8).Thescreenremovesmaterialbypassingtheflowstreamthroughascreenwith3to10-mm(0.12to0.4-in.)openingsalthough5mm(0.2in.)isthetypicalsizeforwastewatersludges.Materialcapturedbythescreenmovesbyascrewconveyorintoapressorcompactionzonewhereitisdewateredandcompacted.Materialisejectedfromthepresszonewhensufficientsolidsbuilduptoovercometheforceontheunit’sdischargecone.Screeningsolidsconcentrationsrangefrom30to50percent.Allowableoperatingpressureisreportedtobe100kPa(14lbf/in.2).Thescreenedsludgeisdilutedandmayrequirethickening.DegrittingInsomeplantswhereseparategritremovalfacilitiesarenotusedaheadoftheprimarysedimentationtanks,orwherethegritremovalfacilitiesarenotadequatetohandlepeakflowsandpeakgritloads,itmaybenecessarytoremovethegritbeforefurtherprocessingofthesludge.Wherefurtherthickeningoftheprimarysludgeisdesired,apracticalcons