Baghouses原文.docx

Baghouses原文.docx

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Baghouses原文

Baghouses

JohnD.McKenna

PresidentETS,Inc.

PollutionControlConsultants

Roanoke,Virginia

and

GaryP.Greiner

ExecutiveVicePresident,ETS,Inc.

PollutionControlConsultants

Roanoke,Virginia

1.DESCRIPTIONOFCONTROLDEVICE

Fabricfilterdustcollectors,commonlyreferredtoasbaghouses,areamongtheoldestandmostwidelyappliedparticulateemissioncontroldevices.Itisreportedthatthereareover200,000currently（1980）inoperationintheUnitedStates.Theuniversallyemployedprincipleofoperation,simplystated,istheremovalofdustfromdust-ladengasbypassingthegasthroughafiltrationmedium,normallyafabric.Thecleanedgasemergesfromonesideofthemediumwhilethedustiscollectedontheotherside.Subsequentlythecollecteddustisremovedfromthefabric.Differentcollectordesigns,fabrictypes,configurations,andavarietyofcleaningmethodsprovidenumeroushardwarecombinations.Anumberofthebasicdesignsemergeddominantinthemarketplace.Thesedesignsandtheirmaintenancefeatureswillbediscussedsubsequently.

Thereareroughly100U.S.fabric-filtermanufacturers.Thelargercompaniesusuallyoffermorethanonefabric-filterdesigntype.Themarketisextremelycompetitive,andthereforedesignsareconstantlychangedbythemoreaggressivecompanies.Withsomanymanufacturers,productdesignpossibilities,andadynamicmarket,onerealizesthathardandfastoperatingandmaintenancerulesaredifficulttocomeby,anditisimportantfortheusertoestablishwherethefabric-filterdustcollectorfitsintothedesignandapplicationpicture.

1.1CategorizingFabricFilters

Tobetterunderstandone’sfabric-filterdustcollector（baghouse）,itishelpfultodeterminewhereitfitsamongthevarioustypesoffabricfilters.Whenonetriestogroupfabricfiltersintoanumberofcategories,itsoonbecomesobviousthatthetaskisnotsimple.Thereappearstobeanexceptiontoeachoftherules.Thecreationofcertaincategories,thoughtheyarenotrigid,isyetveryhelpful.

Onesuchapproachistogroupfabric-filterdesignsbycleaningmethod,asshowninTable1-1.Therearethreemajorcleaningmethods:

shakers,reverse-air,andpulsejets.Inadditiontothesethreedominantcleaningmethods,thereexistalargenumberofothercleaningmethodswhicharelessoftenapplied.Recently,combinationsofthethreeprimarymethodshavebeenoccasionallyemployed.Forexample,reverse-airandshakehavebeenusedincombination,andreverse-airwithapulseassist.

TABLE1-1Designgroupingsforfabricfilterdustcollectors:

groupingbycleaningmethod.

CleaningMethod

GeneralCharacteristicsAssociatedwithDesignType

Shaker

Insidecollection

Manualandautomaticcleaning

Wovenfiltermedia

Cakefiltration

Generallyintermittent---smalloperation

Largeandsmallvolumes

Oftennocompartments

Reverse-air

Insidecollection

Automaticcleaning

Woven-filtermedia

Cakefiltration

Continuousoperation

Mediumandlargevolumes

Compartments

Pulse-jet

Outsidecollection

Automaticcleaning

Felt-filtermedia

Mediafiltration

Continuousoperation

Mediumandsmallvolumes

Oftennocompartments

Anotherapproachtogroupingfabricfilterisbycapacity（seeTable1-2）.Generally,thegroupingsaresmallvolumes（i.e.,below10,000acfm）,mediumvolumes（i.e.,10,000to100,000acfm）,andlargevolumes（i.e.,>100,000tothemultimillionacfmlevel）.

TABLE1-2Designgroupingsforfabric-filterdustcollectors:

groupingbycapacity.

CapacityRange

GeneralCharacteristicsAssociatedwithDesignType

Lowcapacity

Off-the-shelf,smallunits,handlinghundredstoafewthousandcfm;littleornoassembly;prebagged;manualcleaningsystemsavailablewithsometypes

Pulse-jet,shake,cartridge

Mediumcapacity

Modulardesigns:

afewthousandtolessthan100,000cfm;littlefieldassemblyrequired;generallyprebagged

Pulsejet;highG/C

Highcapacity

Shippablemodulardesign:

fiftythousandtoonemillionCFM;

moderatefieldassembly;fieldbagged

Reverse-airandshake

Structural:

100,000to1millioncfm;field-assembledandfield-bagged

Reverse-airandshake;lowG/C

Thefilter-mediatypeandtemperaturecapabilitiesprovidetwootherwaystocategorizeandviewfabricfilters.Wovenvs.feltedmediaarethemedia-typecategoriesandhigh-temperature（>400ºF）,medium-temperature（200to400ºF）,andlow-temperatureapplications（<200ºF）areusefultemperaturegroupings.Twoadditionalwaystogroupfiltersareintermittentvs.continuousserviceandinsidevs.outsidebagcollection.

Oneshouldbeawareofthesedistinctionsandattempttofindwherethecollectorinquestionfits;thus,whenconsideringoperatingortroubleshootingrecommendations,oneonlyappliesrecommendationsthataresuitedtothetypeofcollectorbeingused.

1.2CleaningMethods

ShakersSimplystated,ashakercleaningsystemremovesthecollecteddustfromthesurfaceofthebagbymechanicallyshakingthebag.Thiscanbedonemanuallyinthecaseofsmalldustcollectors.Generally,however,itisaccomplishedbytheuseofamotordrivinganeccentric（Figure1-1）,whichinturnhasarodconnectedtothebags.Itisprobablytheoldestbagcleaningtechniqueandiscurrentlyemployedoverthefullrangeofbaghousecapacitiesfromverysmalloff-the-shelfunitstotheextremelylargestructuraldesignunits（Figure8-2）.

FIGUER1-1AAF’ruggedshakermechanism-usedonAmertubeshaker-typefabriccollectors

FIGUER1-2AnAAFAmertubeshaker-typefabriccollector

Thebagisgenerallyopenatthebottomandclosedatthetop,beingfixedinthetubesheetatthebottomandattachedtotheshakingmechanismatthetop（Figure1-3）.Withthisconfigurationthedustiscollectedontheinsideofthebag.Thebagnormallycontainsnoringsorcages.Theflowofdirtygastothebagsisstoppedduringthecleaningprocess.

FIGUER1-1AAF'sshakersupportlogs

IntheUnitedStates,shakersnormallyemploywovenclothatgas/clothratiosbelow4:

1.Attemptsthusfartouseshakecleaningincollectionwithdomesticfelthaveledeithertoineffectivecleaningandthushighpressuredroportothefiltermediumbeingshakenapart.

Theimportantparametersaffectingtheefficiencyofcleaningarefrequency,oscillation,andamplitude.TheseareshowninTable1-3.

TABLE1-3Shakecleaning-parameters.

Frequency

Usuallyseveralcycles/second;adjustable

Motiontype

Simpleharmonicorsinusoidal

Peakacceleration

1-10g

Amplitude

Fractionofaninchtofewinches

Mode

Off-stream

Duration

10-100cycles,30sectofewminutes

Commonbagdiameters

5,8,12in.

Toachieveacontinuousshake-cleanbaghouse,theunitneedstobesubdividedintoanumberofisolatablecompartments,suchthatonecompartmentatatimemaybetakenoff-streamforcleaning.

Thenormalprocedurefortheintermittent-shakecleaningprocessistofirstdamperofftheinletflowand,ifnecessary,theoutletflowofdirtygas.Thisshouldalmostimmediatelyresultinzeropressuredropacrossthebags.Oncethisconditionisachieved,shakingofthebagscanbeinitiated.Shakingcontinuesforasmanyas100shakecycles.Thecleaningisthenstoppedandthecompartmentismomentarilykeptdormantuntilthedustsettles.Thedampersarethenopenedandthefiltrationprocessresumed.Ifreverse-airisemployedtoassistthecleaningprocess,thecleaningcyclemayconsistofaseriesofrepeatedshake,thenreverse-aircyclesbeforetheunitisbroughton-stream.

Reverse-flowcleaningReverse-aircleaningisperhapsthegentlestcleaningmethod.Inthismethodthedustisremovedfromthebagsbyback-flushingwithlow-pressure（afewincheswatergauge）reversedflow.Inthecaseofhigh-temperatureapplications,thejust-cleanedhotgasisemployedtoback-flushratherthanambient-temperatureair.Woven-filtermediaaregenerallyemployedinconjunctionwithreverse-aircleaning.Thecleaningismotivatedbyaseparatecleaningfanwhichisnormallymuchsmallerthanthemainsystemfansinceonlyafractionofthetotalsystemiscleanedatanyonetime.Inthecaseofanegativepressuresystem,oneoftencancleanwithoutareverseflowfan.Theflowrateofcleaninggasisnormallyaboutequaltothatofthedirtygas（seeTable1-4）.

TABLE1-4Reverse-aircleaning---parameters.

Frequency

Cleaningonecompartmentatatime,sequencingonecompartmentafteranother;canbecontinuousorinitiatedbyamaximum-pressure-dropswitch

Motion

Gentlecollapseofbag（concaveinward）upondeflation;slowlyre-pressurizeacompartmentaftercompletionofaback-flush

Mode

Off-stream

Duration

1-2min,includingvalveopeningandclosinganddustsettlingperiods;reverse-airflowitselfnormally10-30sec

Commonbagdiameter

8,12in:

length22,30ft

Bagtension

50-75lbstypical,optimumvaries;adjustedafteron-stream

Mostoften,reverse-flowsystemsarecomprisedofanumberofisolatablecompartments.Thegas/clothratiosusuallyemployedarelessthan4:

1.Normally,thedustiscollectedontheinsideofthebag,thebagbeingopenatthebottomandclosedatthetop.Thebagwillcontainringstokeepitfromcollapsingcompletelyduringflowreversal.Completecollapsewould,ofcourse,prohibitcleaningsincethedustparticleswouldbeunabletofalldownwithinthebagtothehopper.Cleaningisaccomplishedbothwithandwithoutflexing（partialcollapsing）ofthebag.Reverseflowwithoutflexingcanbeemployedwhenthedustisveryeasilydislodgedfromthebagsurface.Figure1-4showsatypicalcleaningcycle.Intheon-stream-gasfilteringmode,thecompartmentandoutletdampersareopenandthedirtygasentersthebagatthebottom.Thedustiscollectedontheinsid