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…/‚/‘fddf‚Vƒjƒj VfRJTJjVVDj ƒ/„/5¢$6…/ #‚/iJjV`‚jJVƒjƒjV„TjJjŽ ‚/ƒ „/  $5 „/ „‚/  Tjl`VjGDjgVƒjƒjVƒdljdJjŽ‚/…ƒ/1ž$:ƒ/…#‚/  DlfVji]jYVƒjƒjTiV‚jRdljŽ"// †#ƒ/1œ$:„/#†‚/ jJYldjVVƒjJ‚jJiGjjTJ‚jJ‚/‡‚/2š$Aƒ/ˆ‚/ jG„VjYVƒjJ‚j Jdjl]fNjJf ‚/ˆ#ƒ/30–$09ƒ/ ˆ#‚/ ‘Gj]‚iljdJ‚jGJ‚j JdigYVV`‘‚/‰ƒ/;“$0Aƒ/ #‰‚/‘ `jjGTTDjGJ‚jJTƒj‚iR„jGi"//#‰‚/C<0Ž$0Ah‚/ #‰#//“Y„jGgD‚jJVƒj‚NjjGVTDjR‚/Š! ‚/ <0ˆ$210€Ô_ÔððmÔ_Ô€diameter)€absorb€many€times€more€ions€than€smallÏparticles€(>1€Ô_ÔððmÔ_Ô€diameter),€the€electrical€forces€are€much€stronger€on€the€large€particles€(EPA,€1996).ÌÌÔ_ÔDueÔ_Ô€to€necessary€clearances€needed€for€Ô_ÔnonelectrifiedÔ_Ô€internal€components€at€the€top€of€wire„plate€Ô_ÔESPsÔ_Ô,€partÏof€the€gas€is€able€to€flow€around€the€charging€zones.€€This€is€called€ð ðÔ_ÔsneakageÔ_Ôðð€and€places€an€upper€limit€onÏthe€collection€efficiency.€€Wire„pipe€Ô_ÔESPsÔ_Ô€provide€no€Ô_ÔsneakageÔ_Ô€paths€around€the€collecting€region,€but€fieldÏÔ_ÔnonuniformitiesÔ_Ô€may€allow€some€particles€to€avoid€charging€for€a€considerable€fraction€of€the€tube€length.€€DryÏwire„pipe€Ô_ÔESPsÔ_Ô€are,€however,€subject€to€Ô_ÔreentrainmentÔ_Ô€of€the€collected€material€after€cleaning€the€collectorsÏwith€a€rapping€or€acoustic€mechanism,€though€the€closed€nature€of€the€pipes€increases€chances€forÏrecollection€(Ô_ÔAWMAÔ_Ô,€1992).ÌÌÔ_ÔAnotherÔ_Ô€major€factor€in€the€performance€is€the€resistivity€of€the€collected€material.€€Because€the€particles€formÏa€continuous€layer€on€the€ESP€pipes,€all€the€ion€current€must€pass€through€the€layer€to€reach€the€ground.€€ThisÏcurrent€creates€an€electric€field€in€the€layer,€and€it€can€become€large€enough€to€cause€local€electricalÏbreakdown.€€When€this€occurs,€new€ions€of€the€wrong€polarity€are€injected€into€the€wire„pipe€gap€where€theyÏreduce€the€charge€on€the€particles€and€may€cause€sparking.€€This€breakdown€condition€is€called€ð ðbackÏcorona.ðð€€Back€corona€is€prevalent€when€the€resistivity€of€the€layer€is€high,€usually€above€2€x€10òò11óó€ohm„cm.€Ð zÊ ÐAbove€this€level,€the€collection€ability€of€the€unit€is€reduced€considerably€because€the€sever€back€coronaÏcauses€difficulties€in€charging€the€particles.€€Low€Ô_ÔresistivitiesÔ_Ô€will€also€cause€problems.€€At€Ô_ÔresistivitiesÔ_Ô€belowÏ10òò8óó€ohm„cm,€the€particles€are€held€on€the€collecting€surface€so€loosely€that€general€Ô_ÔreentrainmentÔ_Ô,€as€well€asÐ ð@  Ðthat€associated€with€collector€cleaning,€become€much€more€severe.€€Hence,€care€must€be€taken€in€measuringÏor€estimating€resistivity€because€it€is€strongly€affected€by€such€variables€as€temperature,€moisture,€gasÏcomposition,€particle€composition,€and€surface€characteristics€(Ô_ÔAWMAÔ_Ô,€1992).ÌÌÔ_Ôò òAdvantages:ó óÔ_ÔÐ  #Z% ÐÌÔ_ÔÔ_ÔÔ_ÔDry€wire„Ô_Ôpipe€Ô_ÔESPsÔ_Ô€and€other€Ô_ÔESPsÔ_Ô€in€general,€because€they€act€only€on€the€particulate€to€be€removed,€andÏonly€minimally€hinder€flue€gas€flow,€have€very€low€pressure€drops€(typically€less€than€13€millimeters€(mm)€(0.5Ïin.)€water€column).€€As€a€result,€energy€requirements€and€operating€costs€tend€to€be€low.€€They€are€capableÏof€very€high€efficiencies,€even€for€very€small€particles.€€They€can€be€designed€for€a€wide€range€of€gasÏtemperatures,€and€can€handle€high€temperatures,€up€to€700òòoóóC€(1300òòoóóF).€€Dry€collection€and€disposal€allowsÐ ù'I#+ Ðfor€easier€handling.€€Operating€costs€are€relatively€low.€€Ô_ÔESPsÔ_Ô€are€capable€of€operating€under€high€pressureÏ(to€1,030€Ô_ÔkPaÔ_Ô€(150€psi))€or€vacuum€conditions.€€Relatively€large€gas€flow€rates€can€be€effectively€handled,Ïthough€are€uncommon€in€wire„pipe€Ô_ÔESPsÔ_Ô€(Ô_ÔAWMAÔ_Ô,€Ô_Ô1992).ñXñÌñXñÔ_ÔÔ_ÔñXñÐ A+‘&/ ÐñXññ_ññ]ñÌñ]ññ]ñÌñ]ññ_ññ^ññ]ñÌñ]ññ^ññ`ññYñÐ A+‘&/ ÐñYññ`ññañÐ o*¿%. ÐÑ*Ñâ âÑÑÑ  Ñâ âÑ  ÑñañÔ_ÔÔ_ÔÔ  Ôò òDisadvantages:ó óÔ_ÔÐ ° ÐÌÔ_ÔÔ_ÔÔ_ÔESPsÔ_Ô€generally€have€high€capital€costs.€€Wire€discharge€electrodes€(approximately€2.5€mm€(0.01€in.)€inÏdiameter)€are€high„maintenance€items.€€Corrosion€can€occur€near€the€top€of€the€wires€because€of€air€leakageÏand€acid€condensation.€€Also,€long€weighted€wires€tend€to€oscillate€„€the€middle€of€the€wire€can€approach€theÏpipe,€causing€increased€sparking€and€wear.€€Newer€ESP€designs€are€tending€toward€rigid€electrodes,€orÏð ðmastsðð€which€largely€eliminate€the€drawbacks€of€using€wire€electrodes€(Cooper€and€Alley,€1994;€Flynn,€1999).ÌÌÔ_ÔÔ_ÔÔ_ÔESPsÔ_Ô€in€general€are€not€suited€for€use€in€processes€which€are€highly€variable€because€they€are€very€sensitiveÏto€fluctuations€in€gas€stream€conditions€(flow€rates,€temperatures,€particulate€and€gas€composition,€andÏparticulate€loadings).€Ô_ÔESPsÔ_Ô€are€also€difficult€to€install€in€sites€which€have€limited€space€since€Ô_ÔESPsÔ_Ô€must€beÏrelatively€large€to€obtain€the€low€gas€velocities€necessary€for€efficient€PM€collection€(Cooper€and€Alley,€1994).€ÏCertain€Ô_ÔparticulatesÔ_Ô€are€difficult€to€collect€due€to€extremely€high€or€low€resistivity€characteristics.€€There€canÏbe€an€explosion€hazard€when€treating€combustible€gases€and/or€collecting€combustible€Ô_ÔparticulatesÔ_Ô.€€RelativelyÏsophisticated€maintenance€personnel€are€required,€as€well€as€special€precautions€to€safeguard€personnel€fromÏthe€high€voltage.€€Dry€Ô_ÔESPsÔ_Ô€are€not€recommended€for€removing€sticky€or€moist€particles.€€Ozone€is€producedÏby€the€negatively€charged€electrode€during€gas€ionization€(Ô_ÔAWMAÔ_Ô,€1992).ÌÌò òOther€Considerations:ó óÐ wÇ ÐÌÔ_ÔDustsÔ_Ô€with€very€high€Ô_ÔresistivitiesÔ_Ô€(greater€than€10òò10óó€ohm-cm)€are€also€not€well„suited€for€collection€in€dry€Ô_ÔESPsÔ_Ô.€Ð n ÐThese€particles€are€not€easily€charged,€and€thus€are€not€easily€collected.€€High-resistivity€particles€also€formÏash€layers€with€very€high€voltage€gradients€on€the€collecting€electrodes.€€Electrical€breakdowns€in€these€ashÏlayers€lead€to€injection€of€positively€charged€ions€into€the€space€between€the€discharge€and€collectingÏelectrodes€(back€corona),€thus€reducing€the€charge€on€particles€in€this€space€and€lowering€collection€efficiency.€ÏFly€ash€from€the€combustion€of€low-sulfur€coal€typically€has€a€high€resistivity,€and€thus€is€difficult€to€collectÏ(Ô_ÔICACÔ_Ô,€1999).ÌÓU#ÓÌò òReferences:ó óÐ ®þ ÐÌÔ_ÔAWMAÔ_Ô,€1992.€€Air€&€Waste€Management€Association,€€òòAir€Pollution€Engineering€Manualóó,€Van€Ô_ÔNostrandÔ_ÔÐ U¥ ÐReinhold,€New€York.€ÌÌCooper€&€Alley,€1994.€€C.€D.€Cooper€and€F.€C.€Alley,€òòAir€Pollution€Control:€A€Design€Approachóó,€SecondÐ Ë! ÐEdition,€Ô_ÔWavelandÔ_Ô€Press,€Inc.€IL.ÌÔ_ÔÌEPA,€1996.€€U.S.€EPA,€Office€of€Air€Quality€Planning€and€Standards,€ð ðOAQPS€Control€Cost€Manual,ðð€FifthÏEdition,€EPA€453/B„96„001,€Research€Triangle€Park,€NC.€February.€ÌÌEPA,€1997.€€U.S.€EPA,€Office€of€Air€Quality€Planning€and€Standards,€ð ðCompilation€of€Air€PollutantÏEmission€Factors,€Volume€I,€Fifth€Edition,€Research€Triangle€Park,€NC.,€October.ÌÌEPA,€1998.€€U.S.€EPA,€Office€of€Air€Quality€Planning€and€Standards,€ð ðStationary€Source€ControlÏTechniques€Document€for€Fine€Particulate€Matter,ðð€EPA„452/R„97„001,€Research€Triangle€Park,€NC.,ÏOctober.Ìâ âÐ £)ó$- ÐFlynn,€1999.€€Brian€Flynn,€Beltran€Associates,€Inc.,€(718)€338„3311,€personal€communication€with€EricÏâ âAlbright,€February€5,€1999.ÌÌICAC,€1999.€€Institute€of€Clean€Air€Companies€internet€web€page€www.icac.com,€Control€TechnologyÏInformation€„€Electrostatic€Precipitator,€page€last€updated€January€11,€1999.ÌÌSTAPPA/ALAPCO,€1996.€€State€and€Territorial€Air€Pollution€Program€Administrators€and€Association€ofÏLocal€Air€Pollution€Control€Officials,€ð ðControlling€Particulate€Matter€Under€the€Clean€Air€Act:€A€Menu€ofÏOptions,ðð€July.€