air pollution control devices.pptx
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EQUIPMENTS TO
CONTROL AIR
POLLUTION
ARUN. S
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COMMON CONTROLDEVICES
POLLUTANTS EXAMPLES WHERE USED
Packed towers, spray chambers, venturiscrubbers
Gases, vapours, sulphur oxides, solidparticles, liuid droplets
Asphalt and concrete batch plants, coalburnin! power plants
"arbon absorbers #apour phase #$"s, %a&ardous AirPollutants '%APs(
Soil remediation )acilities, oil re)ineries,steel mills, printers
*abric )ilters or ba!houses Particulate +atter 'P+( Asphalt batch plants, steel mills,)oundries, )ertili&er plants,
"atalytic reactors #$"s, Gases -and )ills, oil re)ineries, printin! or paintshops
"yclones -ar!e P+ ood shops, pharmaceuticalmanu),acture rock crushers, cementplants
/SPs P+ Power plants, steel 0 paper mills,smelters, cement plants, re)ineries
1ncinerators #$"s, !ases, )umes, %aps, P+ Soil contaminated with !asoline, ink andprintin!, ha&ardous waste disposal
2io)ilters #$"s, odours, %3S, marcaptans astewater treatment plants
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PARTICULATE CONTROLEQUIPMENT Basic Mechanisms
Gravitational settlin!
"entri)u!al impaction
1nertial impaction
4irect interception
4i))usion
/lectrostatic perception
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GRAVITATIONAL SETTLINGCHAMBERS
5o remove lar!e, abrasive particles )rom !as streams
Reuire simple maintenance
5he particulate matter is settled by its own wei!ht by
lowerin! the )lue !as velocity.
1t essentially consists o) a chamber in which the
velocity o) the carrier !as is decreased so that
particles in the !as settle down by !ravity.
#elocity o) a !as is reduced by expandin! the ductin!
into a chamber o) a suitable dimension so that a low!as velocity is obtained. 1ts e))iciency can be
increased by providin! plates or ba))les
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CYCLONE SEPARATOR
Used )or the separation o) solids )rom )luids
Separation based both on particle si&e and
particle density
1t uses centri)u!al )orce to e))ect the separation 1t consists essentially a short vertical cylinder
closed at the top and by a conical bottom. 5he air
with its load o) solid introduced tan!entially at the
top, solids particles drop into the hopper and outlet
air pass throu!h the top central portion.
idely used )or the collectin! o) wood chips
,heavy and coarse dusts
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FABRIC FILTERS OR BAGHOUSES
*abric collectors use )iltration to separate dust particulates
)rom dusty !ases.
5he most e))icient and cost e))ective types o) dust collectors
available and can achieve a collection e))iciency o) more
than 667 )or very )ine particulates. 4ust8laden !ases enter the ba! house and pass throu!h
)abric ba!s that act as )ilters. 5he ba!s can be o) woven or
)elted cotton, synthetic, or !lass8)iber material in either a
tube or envelope shape.
5heir advanta!es include retention o) )inest particles,collection o) particulates in dry )orm and low pressure drop
As classi)ied by cleanin! method, three common types o)
ba! houses are9
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Mechanical shaker
Reverse je
Reverse air
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ELECTROSTATIC PRECIPITATOR
Particulate collection device that removes
particles )rom a )lowin! !as 'such as air( usin!
the )orce o) an induced electrostatic char!e.
%i!hly e))icient )iltration devices that minimallyimpede the )low o) !ases throu!h the device,
and can easily remove )ine particulate matter
such as dust and smoke )rom the air stream.
/SP applies ener!y only to the particulatematter bein! collected and there)ore is very
e))icient in its consumption o) ener!y
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ACID GAS (SO2
CONTROL)
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FLUE GAS DESULPHURISATION
Used to remove S$3)rom the exhaust )lue !ases o) )ossil )uel power
plants.
+ost *G4 systems employ two sta!es9 one )or )ly ash removal and
the other )or S$3removal.
1n wet scrubbin! systems, the )lue !as normally passes )irst throu!h a
)ly ash removal device, either an electrostatic precipitator or a wetscrubber, and then into the S$3absorber.
1n dry in:ection or spray dryin! operations, the S$3is )irst reacted with
the sorbent and then the )lue !as passes throu!h a particulate control
device.
%ydrodesul)uri&ation o) )uel has been used )or treatin! )uel oils be)oreuse.
*luidi&ed bed combustion adds lime to the )uel durin! combustion.
5he lime reacts with the S$3to )orm sul)ates which become part o)
the ash.
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HYDRODESULPHURIATION %4S is a catalytic chemical process widely used
5he industrial hydrodesulphuri&ation processes include
)acilities )or the capture and removal o) the resultin! %3S
!as which is converted into byproduct elemental sul)ur or
sul)uric acid "3%;S% < %3= "3%>< %3S
Reaction takes place in a )ixed8bed reactor at
elevated temperatures ran!in! )rom ?@@ to @@ B" and
elevated pressures ran!in! )rom ?@ to C?@ atmospheres
in the presence o) a catalyst consistin! o)
an alumina base impre!nated
with cobalt and molybdenum 'usually called a "o+o(
catalyst or nickel and molybdenum 'called Ni+o(
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DRY SCRUBBER
4ry scrubbin! systems are o)ten used )or the removal
o) odorous and corrosive !ases
4ry scrubbin! systems can be cate!ori&ed as dry
sorbent in:ectors '4S1s( or as spray dryer absorbers
'S4As( Dr! s"r#en injeci"ninvolves the addition o)
an alkaline material 'usually hydrated lime or soda
ash( into the !as stream to react with the acid !ases.
1n s$ra! %r!er a#s"r#ers, the )lue !ases areintroduced into an absorbin! tower 'dryer( where the
!ases are contacted with a )inely atomi&ed
alkaline slurry.
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!ET SCRUBBER
5he polluted !as stream is brou!ht into contact with the
scrubbin! liuid, by sprayin! it with the liuid or by
)orcin! it throu!h a pool o) liuid, so as to remove the
pollutants.
5he reaction takin! place in wet scrubbin! usin! a"a"$?'limestone( slurry can be expressed as9
CaCO&'s"li%( ) SO*'+as( , CaSO&'s"li%( )
CO*'+as(
hen wet scrubbin! with a +!'$%(3'ma!nesiumhydroxide( slurry
M+'OH(*'s"li%( ) SO*'+as( , M+SO&'s"li%( ) H*O
'li-.i%(
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VENTURI SCRUBBER
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A conver!in!Ddiver!in! section o) duct.
5he conver!in! section accelerates the !as stream to
hi!h velocity. hen the liuid stream is in:ected at the
throat, which is the point o) maximum velocity, the
turbulence caused by the hi!h !as velocity atomi&esthe liuid into small droplets, which creates the sur)ace
area necessary )or mass trans)er to take place.
5he hi!her the pressure drop in the venturi, the
smaller the droplets and the hi!her the sur)ace area. 5he penalty is in power consumption.
*or simultaneous removal o) S$3and )ly ash, venturi
scrubbers can be used.
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PAC"ED BED SCRUBBER
"onsists o) a tower with packin! material inside
in the shape o) saddles, rin!s, or some hi!hly
speciali&ed shapes desi!ned to maximi&e
contact area between the dirty !as and liuid.
Packed towers typically operate at much lower
pressure drops than venturi scrubbers and are
there)ore cheaper to operate. 5hey also typically
o))er hi!her S$3removal e))iciency.
5he drawback is that they have a !reater
tendency to plu! up i) particles are present in
excess in the exhaust air stream.
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SPRAY TO!ERS
5he simplest type o) scrubber.
1t consists o) a tower with spray no&&les,
which !enerate the droplets )or sur)ace
contact. Spray towers are typically used when
circulatin! a slurry .
5he hi!h speed o) a venturi would causeerosion problems, while a packed tower
would plu! up i) it tried to circulate a slurry.
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VOC ABATEMENT
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ADSORPTION SYSTEMS
1nvolves the molecular attraction o) !ases or
vapours onto the sur)ace o) adsorbent solids E
activated carbon or molecular sieves
5he attraction maybe physical or chemical
A)ter the activated carbon is saturated with #$"s,
it is treated to strip o)) the collected #$"s
#$"s E )urther treatment 0 "arbon E reused in
adsorption reactor
"ommonly used )or removin! !ases )rom
contaminated soil, oil re)ineries, industrial paint
shops and steel mills
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FLARE
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Also known as a /lare sack,it is an elevated
vertical conveyance )ound accompanyin! the
presence o) oil wells, !as
wells,ri!s, re)ineries, chemical plants, natural
!as plants, and land)ills.
5hey are used to eliminate waste !as which is
otherwise not )easible to use or transport. 5hey
also act as sa)ety systems )or non8waste !asand is released via pressure relie) valve when
needed to ease the strain on euipment.
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THERMAL O#IDIERS ORINCINERATORS
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A process unit )or air pollution control in many chemical plants that
decomposes ha&ardous !ases at a hi!h temperature and releases
them into the atmosphere.
Used to destroy %APs and #$"s )rom industrial air streams.
Pollutants are destroyed via thermal combustion where they are
chemically chan!ed to )orm "$3and %3$. /ner!y recovery e))iciency can reach 6;7
4i))erent types include 9
Re!enerative thermal oxidi&er 'R5$(
Re!enerative catalytic oxidi&er 'R"$(
#entilation air methane thermal oxidi&er '#A+5$F(
5hermal recuperative oxidi&er
"atalytic oxidi&er
4irect )ired thermal oxidi&er 8 a)terburner
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CRYOGENICCONDENSERS "ryo!enic condensation is a process that allows
recovery o) volatile or!anic compounds '#$"s( )or
reuse.
5he condensation process reuires very low
temperatures so that #$"s can be condensed andhence liuid nitro!en has emer!ed as a viable substance
)or use in the extremely low8temperature or cryo!enic
'less than 8C>@ de!rees "( condensation process.
"ryo!enic condensation is best suited to exhaust
streams with low )lowrates 'below 3@@@ standard )t?Dmin(andDor vapor concentrations above C@@ parts per million
on a volumetric basis 'ppmv(.
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NOXCONTROL
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SELECTIVE CATALYTIC REDUCTION
A means o) convertin! nitro!en oxides, also re)erred to
as N$xwith the aid o) a catalyst 'ceramic as carrier, and
oxides o) base metals like # 0 ( into N3, and %3$ usin!
a !aseous reductant 8 anhydrous N%?, aueous N%?
or urea, at a temp between >?@ and 3@ H. Application8 lar!e utility 0 industrial boilers
'reduce N$xby @86;7(. 4iesel en!ines 0 !as turbines.
Reactions
N$ < N%?< $3= N3< >%3$
3N$3< N%?< $3= ?N3< >%3$
N$ < N$3< 3N%?= 3N3< ?%3$
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Se$ec%i&e n'n(ca%a$)%ic *e+,c%i'n
A method to lessen N$x emissions in conventional
power plants that burn biomass, waste and coal by
in:ectin! N%? or urea into the boiler at a location
where the )lue !as is betweenC,@@ 0 3,@@@ B*
producin! N3, "$30 %3$. N%3"$N%3< %3$ 8I 3N%?< "$3
N$ < N%?< $38I N3< > %3$
1t can achieve the same e))iciency o) about 6@ 7
as S"R, but practical constraints o) temperature, time,and mixin! exist.
SN"R has an economical advanta!e as the cost o)
the catalyst isnt there.
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E#HAUST GAS RECIRCULATION
1t is a N$x emissions reduction techniue used in petrol
and diesel en!ines.
Recirculates a portion o) the en!ines exhaust !as back to
the en!ine cylinders. 1n a !asoline en!ine, this inert
exhaust displaces the amount o) combustible matter in thecylinder. 1n a diesel en!ine, the exhaust !as replaces
some o) the excess oxy!en in the pre8combustion mixture.
5he exhaust !as, added to the )uel, oxy!en, and
combustion products, increases the speci)ic heat
capacity o) the cylinder contents, which lowersthe adiabatic )lame temperature. 2ecause N$x )ormation
pro!resses much )aster at hi!h temperatures, /GR
reduces the amount o) N$x the combustion !enerates
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CATALYTIC CONVERTER
A device used to reduce the toxicity o) emissions )rom an 1" en!ine.
orks by usin! a catalyst to stimulate a chemical reaction in which
toxic by8products o) combustion are converted to less8toxic
substances.
6@7 conversion o) carbon monoxide, hydrocarbons, and nitro!en
oxides into less harm)ul !ases in automobiles. Pt8Rh E reduction catalyst 0 Pt8Pd E oxidation catalyst
5wo way 9 3"$ < $3= 3"$3
"x%3x
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MERCURY
CONTROL
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DIOXIN AND
FURAN CONTROL
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Sources o) dioxins and )urans include
waste incinerators, cement production,
)ossil8)uel8)ired combustors,
and )orest )ires.
4ioxin and )uran compound emissions
are calculated in
two di))erent ways9
As the total dioxin and )uran compound concentrations
As the T"0ic E-.ivalenc! 1."ien'5/L(
concentration
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CONTROL TECHNIQUES
2oth dioxin and )uran compounds are destroyed when
the !as temperatures exceeds approximately C@@B*
5hese temperatures usually exist in the combustion
&ones o) incinerators and )ossil8)uel8)ired boilers.
5he )ormation mechanisms decrease to ne!li!ible rateswhen the !as stream temperature decreases below
@@B*. 5he !as stream should be su))iciently cooled prior
to the air pollution control system can eliminate this
)ormation mechanism.
5he best way to control dioxin and )uran emissions ispreventin! their )ormation by reducin! or eliminatin! the
chlorine in the )uel and waste material bein! burned.
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