Lect 7 2022industry and environment pollution -.pdf

Mes528 industry and environment pollution

1. ME528-2
Industry and Environment
Pollution
Dr. Ali Mahmoud Ali Attia
7
th
Lecture: Particulate matter control
College of Engineering
Department of Mechanical Engineering

2. Contents
•Know particle description, sources, composition, and impact on human health
•Describe the interaction of Particles with flue gas and its separation
•Define terminal settling velocity
•Identify basic control devices for particulate emissions
•Describe fundamental, operation, and performance for particle control devices
(scrubbers, electrostatic precipitator, filters, settling chambers, and cyclones).

3. PM; Definition, sources, and impact
➢Particulatematter(PM)isanyfinelydividedliquidorsolidsubstanceentrainedin
effluentgasstreamsorsuspendedinambientairsuchassmoke,dust,andfinemist.
PMlessthan10μmisdefinedasPM10andisregulatedasacriteriapollutant.
➢PM(solidparticlesordust)iseitherdirectly
emittedintoatmosphere(primaryparticles)
orformedinatmospherebychemical
reactions(secondaryparticles).
➢Forexample,inareaswherewoodburningis
mainheatingfuelduringwintertime,mostof
atmosphericPMareprimary.However,during
summertimephotochemicaloccurrences,a
substantialambientPMfractioncanbe
attributedtosecondaryreactionsinthe
atmosphere.

4. PM; Definition, sources, and impact;Cont.
➢Particlesizeisexpressedasaerodynamicdiameter,Da,definedasthediameterof
spherehavingunitdensity(1g/cm-3)whichhasthesameterminalsettlingvelocityin
airastheparticleunderconsideration.
➢AtmosphericPM(eithersolidorliquid)haveaerodynamicdiametersbetween0.002
μm(smallestdetectablesizebynucleicondensation)and100μm(veryfinesand
particlesthatislargeenoughandcanremainsuspendedforsignificanttimesbut
quicklyfalloutofinquiescentatmosphere).
➢Mostimportantparticlesizewithrespecttoatmosphericchemistry,physics,and
healtheffectsissmallerthan10-μmindiameter.
➢Totalsuspendedparticulate(TSP)representsallparticlesinsizefrom0to≈40μm.
➢PM10fractionrangesfrom0to10μm,andPM2.5sizefractionrangesfrom0to2.5
μminaerodynamicdiameter.
➢ImportanceofprimaryandsecondaryPMdependsongeographicallocation(or
specificmixofemissions),andonthepredominantatmosphericchemistry.

5. PM; Definition, sources, and impact;Primary
➢Primaryparticlesareemittedinseveralsizeranges,themostcommonbeinglessthan
1μminaerodynamicdiameterfromgasfiredcombustionsourcesandlargerthan1μm
inaerodynamicdiameterfromdustsources.PrimaryPMaredispersedandtransported
inatmosphereandmaybesubjectedvariousphysicalandchemicalprocesses.
➢Keysourcesofprimaryparticlesinclude:
➢Stationarysources(e.g.,boilers,processheaters,incinerators,andsteamgenerators),
➢Areasources(e.g.,fires,wind-blowndust,andresidentialfuelcombustion),
➢Mobilesources(e.g.,automobiles,buses,trucks,trains,andaircraft),
➢Agriculturalactivities(e.g.,fertilizers,herbicides,andlandoperations,and
➢Biogenicsources(aspollenfragmentsandparticulateproductsfromleafsurfaces).
➢PMcategoriesasperparticlesizeinclude:
➢Nucleationrange(<0.08μm)asfromcombustionorsooncondensationin
atmosphere.
➢Accumulationrangeupto2.5μm;includecondensedanddropletsize.
➢Coarserange(>2.5μm)duetogrindingactivitiesandmaterialgeologicalorigin

6. Particle size
distribution in
ambient air
Calculated residence time of particles in
atmosphere depending on their size, based
on gravitational settling in stilled and stirred
chambers
Particle size distribution
from the Combustion of
Several Organics and from
Automobiles and a Candle

7. PM; Definition, sources, and impact;Secondary
➢AccumulationrangeofPMresultsfromcoagulationofsmallerparticlesemitted
from:combustionsources;condensationofvolatilespecies;gas-to-particle
conversion;andfromfinelygrounddustparticles.
➢Thepeakofcoarseragefallsbetween6and25μmwithabilitytoget50%(cut-point)
atPM10.
➢Secondaryaerosols;Sulfatesandnitratesarethemostcommon
➢Secondaryparticles;thoughafractionoforganiccarbonareformedviaatmospheric
reactionsinvolvingvolatileorganiccompounds(VOC)orduetoconversionof
atmosphericgasescantosuspendedparticlesbyabsorption(intocharcoal),solution
(assolubleinwater),orcondensation(incooledambient).
➢GaseousprecursorsofsulfatesandnitratesPMareSO
2,SO
3,NO
xandammonia.
➢Majorityofsecondarysulfatesarefoundduetocombinationofsulfuricacid(H
2SO
4),
ammoniumbisulfate(NH
4HSO
4),andammoniumsulfate((NH
4)
2SO
4).Whilemajority
ofsecondarynitratesareammoniumnitrate(NH
4NO
3).

8. PM; Definition, sources, and impact;Composition
➢TherearesixmajorcomponentsofthePM10massinmosturbanareas:
➢Geologicalmaterial(oxidesofaluminum,silicon,calcium,titanium,andiron)-less
than10%ofPM2.5massconcentrations,butitisthemostelementincoarsePM;
➢Organiccarbon(consistingofhundredsofcompounds)(OC)–includingn-alkanes,
n-alkanoicacid,onen-alkenoicacid,onen-alkanal,aliphaticdi-carboxylicacids,
aromaticpolycarboxylicacids,polycyclicaromatichydrocarbons(PAH),polycyclic
aromaticketones(PAK),polycyclicaromaticquinones(PAQ),diterpenoidacidsand
somenitrogen-containingcompounds;
➢Elementalcarbon(EC);
➢Sulfate
➢Nitrate;and
➢Ammonium
➢Majorityofsulfuricacid,ammoniumbisulfate,ammoniumsulfate,ammonium
nitrate,andbothOCandECarefoundin"fineparticlesizefraction“;PM2.5sizerange
whereOCandECareimportantconstituentsofmostoftheiremissionsources

9. Mass
Balance
based on
Chemical
Composition
of Annual
Mean Fine
Particle, for
(a) West Los
Angeles and
(b)
Rubidoux
(Riverside),
California

10. PM; Definition, sources, and impact
➢HealthImpact:
➢IncreaseinPM10resultedinincreaseinrespiratorymortality,cardiovascular
mortality,respiratoryhospitaladmissions,andgrade-schoolabsences.
➢TheultrafinePMisthemostpathogenicforhumanandanimals;eventheyrepresent
smallportioninautopsiedhumanlungsofthetotalexposure.
➢USEPAhasstudiedtherelative
contributionofdifferentemission
sourcestoambientPM10andPM2.5.
Resultsindicatethatindustrial
processesandfuelcombustion
accountsfor5%and4%ofPM10,
respectively.However,forPM2.5
thesetwosourcecategories
contribute12%and10%ofthetotal.

11. PM Interaction with Gas and PM separation
➢GaseskinetictheoryisusedtounderstandtheinteractionofPMwithsurroundinggas
basedontemperature,pressure,meanfreepath,viscosity,anddiffusioninmovinggas.
➢Assumptionofkinetictheory:
➢Gasestravelinstraightlineshavingmoleculesasrigidspheres
➢Largenumberofsmallmoleculeswithrelevantdiscontinuousin-betweendistances
➢Airmoleculestravelwithaveragespeedof463m/secatstandardconditions;that
increaseswithdecreaseofmoleculeweightandincreaseoftemperaturesquareroot
➢Gasviscosityrepresentsthetransferofmomentumbyrandomlymovingmolecules
fromafastermovinglayerofgastoanadjacentslowermovinglayerofgas.
➢diffusionisthetransferofmolecularmasswithoutanyfluidflow.Diffusiontransfer
ofgasmoleculesisfromahighertoalowerconcentration
➢Reynoldsnumbercharacterizesgasflowisdimensionlessindexdescribingtheflow
regime;&#3627408453;
&#3627408466;=
&#3627409164;????????????
??????
;forlaminarflow,viscousforcespredominate,whileforturbulent
flow,inertialforcesdominatetheflowcausingthedisappearanceofstreamlines.

12. PM Interaction with Gas and PM separation; Cont.
➢Forparticlecarriedbymovinggasstreamtowardsatarget.
Ifparticletouchesthetarget,itlikelytosticktothetarget
duetointersurfaceforces.Thetargetmaybeliquiddroplet,
asinthecaseofwetscrubbers,orsolid,asinafabricfilter
baghouse.
➢Theparticlebeingcarriedbythegasstreammaybesmall,
medium,orlargeinsizemovingtowardthetarget.Thegas
flowstreamlinesareshownasdivergingastheyapproach
thetarget,thenmovingaroundthetarget.
➢Mechanismsbywhichparticletouchesthetarget:
➢Impaction;forlargeparticlehavinglargemomentumthat
tendstokeepthestraightmotionofparticletowardtarget
➢Interception;forintermediatesizefrom0.1to1µwith
insufficientinertiatoleavegasstreamline
➢Diffusion;forsmallparticles<0.1µwithBrownianmotion

13. PM Interaction with Gas and PM separation; Cont.
➢Aerodynamicdiameter,d
a,isthesphericaldiameterofaparticlehavingdensityof1
g/m
3
thatwouldhavethesamesettlingvelocityasthatofirregularformparticleor
aerosolinquestion.
➢Stokes’sequivalentdiameter,d
s,isthesphericaldiameterofequivalentparticle
havingthesamevolume(V)andthesameterminalsettlingvelocity;or??????
&#3627408480;
=
3
Τ6??????&#3627409163;.
➢Nonmovingparticlehasgravitationalforceactingon
it,butforuniformflowvelocitytherewillbeadrag
forceduetoflowviscosity.Particlewillstarttomove
orcarriedbymovingflowatvelocitybalancesthetwo
principalforcesactinguponit;dragforceandgravity.
➢Thisiscalledterminalsettlingvelocityofaspecified
particlesizethatdependsonparticlesize,densityand
shapeinadditiontopropertiesofthefluid.

14. PM Interaction with Gas and PM separation; Cont.
➢Dragforcedependsontheflowconditionsandempiricalfactorcalleddragcoefficient
andisobtainedbymultiplyingthevelocitypressureoftheflowingfluidbythe
projectedareaoftheparticle:??????
&#3627408465;=??????
&#3627408465;.
1
2
.&#3627409164;.??????
2
.??????
??????.Where:C
d:thedragcoefficient
dependingonReandcanbeestimatedgraphically&ρ:thedensityofthefluid&V:the
flowvelocity&A
p:theprojectedareaoftheparticleatrightanglestothedirectionof
themotion
➢ForsphericalparticleunderStokes’slaw,
whichisgenerallyvalidfortheaerosolinthe
ambientatmosphere,??????
&#3627408465;=3.&#3627409163;.??????.??????
??????.??????
??????(for
Re<1)considerthefollowingassumption:
➢rigidsphericalparticle
➢inertialforceis<<viscousforce
➢continuumfluid
➢freeflowwithneglectedwalleffects
➢constantairdensity

15. PM Interaction with Gas and PM separation; Cont.
➢Atterminalsettlingvelocity,thedragforcebalancesgravitational
forceand buoyancyforce:??????
&#3627408465;=3.&#3627409163;.??????.??????
??????.??????
??????=
&#3627409164;??????−&#3627409164;??????.&#3627409163;.&#3627408465;
??????
3
.??????
6
here??????
??????=??????
&#3627408480;&#3627408481;or??????
&#3627408480;&#3627408481;=
&#3627409164;??????−&#3627409164;??????.&#3627408465;??????
2
.??????
18.??????
.For&#3627409164;
??????≫&#3627409164;
??????,
then??????
&#3627408480;&#3627408481;=
&#3627409164;??????.&#3627408465;??????
2
.??????
18.??????
whereV
P:particlevelocity(m/s),ρ
P:particle
density(kg/m
3
),ρa:fluiddensity(kg/m
3
)asair,dp:particle
diameter(m),g:gravitationalacceleration(9.81m/s
2
)&μ:fluid
viscosity(kg/m·s)
➢Example:Determinesettlingvelocityfora0.5mmdiameter
particlewithadensityof2000kg/m
3
in20ºCwater.
➢Task:drawonlogscalethevariationofsettlingvelocityofdust
forparticlefrom0to10mmdiameterinairat21°Cand100kPa
pressure.Assumesphericalparticleswithρ=1280kgm
-3
,andthat
airviscosityμ=1.8x10
-5
N.s.m
-2
andρa=1.2kgm
-3( ) ( )( )
( )
m/s140
skg/m00101018
m/s81.9m00050kg/m9982000
223
.
.
.
V
sT =

−
=

16. PM Interaction with Gas and PM separation; Cont.
➢Thecharacteristictimeperiodforparticletotransferfromonestatetoanotheriscalled
theparticlerelaxationtimedeterminedby:??????
??????=
&#3627409164;??????.&#3627408465;??????
2
18.??????
.
➢Forflowinductscarryingdust,thehorizontaldistanceparticletraveleddependson
flowconditions,andparticleproperties.Themaximumtravelingdistanceorthestop
distanceSwillbe:&#3627408454;=??????
??????∗??????
??????,??????,where??????
??????,??????istheinitialparticlevelocity.
➢Incaseofcurvaturepathasflowinacircularmannerwithincylinder,theinertialforce
appliedinaspinninggasstreamisoftentermedcentrifugalforce.Theparticlevelocity
duetoinertialforcecanbeestimatedusingthesameproceduredescribedforterminal
settlingvelocityduetogravitationalforce.Herecentrifugalforcebalancesdragforce:
➢??????
&#3627408465;=3.&#3627409163;.??????.??????
??????.??????
??????&??????
&#3627408464;=??????
??????.
??????
??????
2
??????
=
&#3627409163;
6
.??????
??????
3
.&#3627409164;
??????.
??????
??????
2
??????
&??????
&#3627408465;=??????
&#3627408464;orgenerally:
➢??????
??????=
&#3627409164;??????−&#3627409164;??????.&#3627408465;??????
2
.??????
??????
2
18.??????.??????
➢whereV
t:tangentialvelocityofthegas&R:radialpositionoftheparticle
Particle separation depends on square of gas stream tangential
velocity and inversely on path radius

17. Control devices for particulate emissions
➢Toseparateparticlesfromgasstreamlines,itisnecessarytobreakthemomentum
relationbetweenparticlesandcarrier(fluegas).Thiscanbeattainedeitherbysudden
changeofcrosssectionalareaoftheflow(gravityforces),bysuddenchangeoftheflow
direction(centrifugalforces),orbyflowobstruction.
➢Commondevicesusedtocontrolparticulateemissionsinclude:
➢ElectrostaticPrecipitation(particleobstruction)
➢FabricFilters(particleobstruction)
➢VenturiScrubbers(particleobstructionandgravityforces)
➢Cyclones(enhancementofcentrifugalforces)
➢SettlingChambers(enhancementofgravityforces)
➢CurrentPMcontroldevicesfocusoncapturingparticulatematter≤10μmdependingon
dustsize,dustresistivity,exhaustflowrate,temperature,humidity,andexhaust
chemicalpropertiesasexplosiveness,acidity,alkalinity,andflammability.Usually,
combinationofmultipledevicesareusedtoachievetargetedcollectionefficiencyfor
specificparticlesize.

18. Purposes for particulate/dust collection/removal/Control
➢Dustcollectionisconcernedwiththeremovalorcollectionofsoliddustsingasesfor
purposesof:
➢Air-pollutioncontrol,asashremovalfrompower-plantfluegases
➢Equipment-maintenancereduction,asinfiltrationofengine-intakeairorpyrites
furnace-gastreatmentpriortoitsentrytoacontactsulfuricacidplant
➢Safetyorhealth-hazardelimination,asincollectionofsiliceousandmetallicdusts
aroundgrindinganddrillingequipmentandinsomemetallurgicaloperationsand
flourdustsfrommilling
➢Product-qualityimprovement,asinaircleaningintheproductionofpharmaceutical
productsandphotographicfilm
➢Recoveryofvaluableproduct,asdustsfromdryersandsmelters
➢Powdered-productcollection,asinpneumaticconveying;thespraydryingofmilk,
eggs,andsoap;andthemanufactureofhigh-purityzincoxideandcarbonblack

19. Applicable dust control devices
as per emission source and
targeted particle sizes

20. Venturi Scrubbers
➢Venturiscrubbersuseanatomizedliquid
streamthrough/upstream/downstreamthe
throatsectiontoenvelopsolidparticles.Due
toturbulencethefineatomizedscrubbing
liquidinthroatinteractedwitharticle.After
throatsection,mixturedecelerates,and
furtherimpactsoccurcausingagglomeration
ofdropletsenoughtofalldown.
➢Onceparticlesarecapturedbyliquid,the
wettedPMandtheexcessliquiddropletsare
thenseparatedfromthegasstreambyan
entrainmentsection,whichusuallyconsistsof
acyclonicseparatorand/oramisteliminator.
➢Typicalflowratesforsingle-throatventuri
scrubberunitare0.2to28sm
3
/sec.
Venturi scrubber uses wet
impingement to trap gas-
laden particles in a liquid
form to remove coarse
particle, then cyclone used
for additional purification

21. Venturi Scrubbers;Cont.
➢Higherflowscanbeusedwithventuribyusingeithermultipleventurescrubbersin
paralleloramultiplethroatedventure.
➢VenturiscrubberstypicallyhavebeenappliedtocontrolPMemissionsfromutility,
industrial,commercial,andinstitutionalboilersfiredwithcoal,oil,wood,andliquid
waste.
➢Venturiscrubbersarecommonlyusedindifferentindustrialsectorswhereitis
necessarytoobtainhighcollectionefficienciesforfinePMwithhighconcentrations;
includingchemical,mineralproducts,wood,pulpandpaper,rockproducts,and
asphaltmanufacturingindustries,lead,aluminum,ironandsteel,andgrayiron
productionindustries;andtomunicipalsolidwasteincinerators
➢VenturiscrubbershavePMcollectionefficienciesofrange70-99%dependingon
applicationforPMwithaerodynamicdiametersofapproximately0.5to5μm.

22. Venturi Scrubbers;Advantages & Disadvantages of Venturi Scrubbers:
Advantages of Venturi Scrubbers include:
•Capable of handling flammable &
explosive dusts
•Can handle mists in process exhausts
•Relatively low maintenance
•Simple in design and easy to install
•Collection efficiency can be varied
•Provides cooling for hot gases
•Neutralizes corrosive gases and dusts
Their disadvantages include
•Effluent liquid can create water pollution
•Waste product collected wet
•High potential for corrosion problems
•Requires protection against freezing
•Final exhaust gas requires reheating to
avoid visible plume
•Collected PM may be contaminated, and
not recyclable
•Disposal of waste sludge may be very
expensive

23. Electrostatic precipitators (ESP)
➢ESPisPMcontroldeviceusingelectricalforcesto
moveparticlesentrainedwithinexhausttocollection
surface.
➢Entrainedparticlesaregivennegativelyelectrical
chargebyusingcentralelectrodes(longwiresorrigid
“masts”suspendedfromaframe)maintainedathigh
voltagethatabletogenerateelectricalfieldforcing
particlestothecollectorplates.
➢InESP,ACvoltage(220to480volts)isconvertedto
pulsatingDCvoltageintherangeof20to100KV.
➢Theappliedvoltagecauseselectricallybreakdownof
gasbetweenelectrodes;thisactionisknownas
“corona.”
➢Electrodesaregivennegativepolaritybecausea
negativecoronasupportsahighervoltagethandoesa
positivecoronabeforesparkingoccurs.

24. Electrostatic precipitators (ESP); Cont.
➢Aslargeparticles(>10μmdiameter)absorbmanytimesmoreionsthansmallparticles
(>1μmdiameter),soelectricalforcesaremuchstrongeronthelargeparticles.
➢Thecollectedparticulatematerialslidesdownwardintoahopperthatisevacuated
periodicallyviadust-handlingsystem(aspneumaticconveyor)thenproperlydisposed.
➢ESPcollectionefficiencyishigh(typicallymorethan99%forparticleslessthan10µm).
➢ESPcollectionefficiencyisaffectedbydustsize,dustresistivity,gastemperature,
chemicalcomposition(ofthedustandthegas),andparticlesizedistribution.
➢ESPsarenotsuitedforusein:
➢FluctuatingprocessesduetosensitivityofESPforfluctuationsinflowrates,
temperatures,particulateandgascomposition,andparticulateloadings.
➢Siteshavinglimitedspace,sinceESPsmustberelativelylargetoobtainthelowgas
velocitiesnecessaryforefficientPMcollection.
➢Veryhightemperatureofstream
➢Dustswithveryhighresistivities

25. Electrostatic precipitators (ESP); Cont.
➢TypesofESP:
➢WetESPs,wherecollectorsareeitherintermittentlyorcontinuouslywashedby
waterspray,whilehopperisreplacedbydrainagesystemthatistreatedon-site.
➢DryESPs.
➢Advantages:
➢Highefficiencyforsmallparticlesof99.5-99.9%.
➢Lowoperatingandmaintenancecosts.
➢Particlesmaybecollecteddryorwet.
➢Handlelargevolumeofhightemp.gas(300-450˚c).
➢Fewmovingparts.
➢DisadvantagesofESP:
➢Highinitialcostandneedlargespace
➢Requireshighcharges&highvoltagethatleadtoexplosionwithhazardpersonnel
safety.
➢Notsuitableforcombustibleparticlesorparticleswithhighresistivity.

26. Fabric filters
➢Inafabricfilter,fluegasispassedthroughatightlywovenorfeltedfabric,restricting
thepassingofPMthatcanbecollectedonfabricbysievingandothermechanisms.
Theformeddustcakebehindfiltersignificantlyincreasesthecollectionefficiency
➢Fabricfiltersformsinsheets,cartridges,orbags.Numberofindividualfabricfilter
unitscanbehousedtogetherinagroup.
➢Fabricfilters(namegivenasfabricisusuallyconfiguredincylindricalbags)havebags
of6-9mlongand10to30cmindiameter.Commonfabricsfrompolyolefins,nylons,
acrylics,andpolyestersareusefulonlyatrelativelylowtemperaturesof95to150ºC.
Forhightemperature,thermallystablefabricssuchasfiberglass,Teflon,orNomex
mustbeused.
➢Sizeandmaterialsofbagsdependon:
➢Volumetricairflowtoclotharearatio.
➢Particulateloadingandcharacteristics
➢Fluegasestemperature.

27. Fabric filters; Cont.
➢Methodstocleanandremovedustcakeinclude:
➢Mechanicalshakingofthebags;commonforitssimplicityaswellasitseffectiveness.
➢Reverse-aircleaningisalsousedextensivelyandimproved,evenit’slesseffective
thanmechanicalshaking.Itisusedonlyifdustreleaseseasilyfromthefabric.
➢Sonichornsusecompressedairtovibrateametaldiaphragm,producingalow
frequencysoundwavefromthehornbelldependingonfabricareaandnumberof
baghouses.
➢Pulse-jetcleaningoffabricfiltersisarelativelynewconceptascomparedtoother
typesoffabricfiltersasitcantreathighdustloadings,operateatconstantpressure
drop,andoccupylessspacethanothertypesoffabricfilters.
➢Typicalequipmentdesignefficienciesover99%;dependingon:
➢Gasfiltrationvelocity,efficiencyincreaseswithincreasedfiltrationvelocity
➢Particlecharacteristics,efficiencyincreaseswithincreasedparticlesize
➢Fabriccharacteristics
➢Cleaningmechanism.

28. Fabric filters; Cont.
➢Advantages:
➢Highremovalyieldforcoarseandfinedust;
➢Varyingloaddoesnotinfluencepressuredropandefficiency;
➢Collecteddustcanpossiblybere-usedintheprocess;
➢CollectionefficiencynotaffectedbysulfurcontentofthecombustionfuelasinESPs.
➢Nohighvoltagerequirements;
➢Flammabledustmaybecollected;
➢Relativelyeasytouse.
➢Disadvantages:
➢Limitedforhighmoistureleveloradditionalheatingisneeded;
➢Riskofexplosion;Sparksandsootmustbeavoidedatleastbeextinguishedbefore
filter.
➢Certaindustsneedsspecialfabrictreatmentstoassistincakeremoval;
➢Fabricbagstendtoburnormeltreadilyattemperatureextremes;
➢Stickydustmustbeavoided.Eventually,extraauxiliarymaterialscanbeadded.

29. Settling (gravity collectors, expansion, or outfall) chambers
➢Gravitysettlingchambersarethesimplestandthe
oldestdustcollectorstoremoveeffectivelylarge
particles,sotheyareusedincombinationwithother
dustcontroldevicestocapturesmallerparticles.
➢Settlingchambersarebuiltinformoflong,horizontal,
rectangularchamberswithaninletatoneendandan
exitatthesideortopoftheoppositeend.Flowwithin
thechambermustbeuniform.
➢Hoppersareusedtocollectthesettled-outmaterialby
employingdragscrapersandscrewconveyers.
➢Thedustremovalsystemmustbesealedtopreventair
leakageintochamberwhichincreasesturbulence
causingdustre-entrainment,andpreventsdustfrom
beingproperlydischargedfromthedevice.

30. Settling chambers; Cont.
➢Typesofsettlingchambersinclude:
➢Expansionchamber,wherefluegasvelocityissignificantlyreducedasthegas
expandsinalargechamber.Thevelocityreductionallowslargerparticlestosettle
outofgasstream.
➢Multiple-traysettlingchamberisanexpansionchamberwithanumberofthintrays
causinggastoflowhorizontallybetweenthemresultinginimprovingcollection
efficiency.Multiple-traysettlingchambershavelowervolumerequirementsthan
expansion-typeforthecollectionofsmallparticles(<15μm).
➢Efficiencyofsettlingchambersincreaseswiththeresidencetimeofuncleangas
throughchamber,sogasvelocitymustbelowenoughtopreventdustfromre-
entrainment;gasvelocityshouldbe<3m/sandrecommendedtobe<0.3m/s.
➢Collectionefficiencydependsonparticlesizeandsettlingchamberdimensions.
Settlingchambersaremosteffectiveforlargeand/ordenseparticles.
➢Settlingchambersareeffectiveforremovingparticles>50μmforlowparticledensity,
downto10μmwithhighmaterialdensity.

31. Settling chambers; Cont.
Advantages of Settling Chambers Disadvantages of Settling Chambers
➢Lowcapitalcostwithlowoperating
costs
➢Verylowenergycost
➢Nomovingparts
➢Fewmaintenancerequirements
➢Excellentreliability
➢Lowpressuredropthroughdevice
➢Devicenotsubjecttoabrasiondueto
lowgasvelocity
➢Provideincidentalcoolingofgasstream
➢Drycollectionanddisposal
➢RelativelylowPMcollection
efficiencies
➢Unabletohandlestickyortacky
materials
➢Effectiveonlyforlargephysicalsize
➢Traysinmultiple-traysettling
chambermaywarp
➢Needsmorespace
➢Laminarflowmaynotexist
practically.

32. Cyclones (centrifugal separators or inertial separators)
➢CyclonesarePMcollectiondevicestoremovelargeand
abrasiveparticlesdependingoninertiaofparticles.Many
smallcyclonesareoperatinginparallel;calledmulticyclone,or
multiclone.
➢Cyclonesoperatebycreatingadoublevortexinsidecylindrical
andconebody.Theincominggasisforcedintoacircular
motiondownward,forcingPMtotheinnersurfaceofthe
cyclonewalls.Atthebottomofthecyclone,thegasturnsand
thenspiralsupthroughthecenterofthecycloneandexitsout
ofthetopoutlet.
➢Hereparticlesareforcedcentrifugallytowardthewallswith
differentmomentumofthatofgastravelingthroughandout
ofthecyclone.Soparticles-gasinteractionisbroken,and
particlescansettlebygravity.
➢Singlecycloneshaveacontrolefficiencybetween80to99%
fortotalPM,60to95%forPM10,and20to70%forPM2.5.

33. Cyclones; cont.
➢Typesofcyclones(dependingonwayofintroducinggasstreamand
waysofdischargingthecollecteddust):
➢tangentialinlet,axialdischarge
➢axialinlet,axialdischarge
➢tangentialinlet,peripheraldischarge
➢axialinlet,peripheraldischarge
➢Typesofcyclones(accordingtocycloneefficiencybasedoncyclone
dimensionsrelativetoitscylindricaldiameter-D
c):
➢Highefficiencycyclone,
➢Mediumefficiencycyclone,and
➢conventional(low)efficiencycyclone
➢Pressuredropandsizearekeyparametersaffectingcycloneoperationcost&efficiency
➢Highefficienciescanbeobtainedbyincreasinginletvelocities,butthisalsoincreases
pressuredrop.Valuesofvelocityof18m/Sec&pressuredrop≈2.5kPaarecommon.

34. Cyclones; cont.
➢Multipleparallelcyclonesareusedifpredictedcollectionefficiencyisinadequatefora
singleunitwhilemulti-cyclonesinseriesareusedtoimprovecyclonecollection
efficiency.
➢Cycloneefficiencyincreaseswithincreaseof:
➢particlesizeand/ordensity,
➢inletductvelocity,
➢cyclonebodylength,
➢numberofgasrevolutionsinthecyclone,
➢ratioofbodydiametertogasexitdiameter,
➢dustloading,and
➢smoothnessofthecycloneinnerwall
Disadvantages of Cyclones
➢RelativelylowPMcollectionefficienciesforsmallsize
➢Unabletohandlestickyortackymaterials
➢Highefficiencyunitsexperienceshigh-pressuredrops
Advantages of Cyclones
➢Lowcapitalcost
➢Nomovingpart
➢Fewmaintenancerequirements
➢Lowoperatingcosts
➢Relativelylow-pressuredrop
➢Drycollectionanddisposal
➢Relativelysmallspacerequirements

35. Thank you
Now Your Questions.