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Chapter 12Chapter 12
Air Pollut ion Cont rolAir Pollut ion Cont rol
A. Cont rol of Gaseous Pollu tant sA. Cont rol of Gaseous Pollu tant s
B. Cont rol of Part iculates Pollut antsB. Cont rol of Part iculates Pollut ants
A. Cont rol of Gaseous Pollu tant sA. Cont rol of Gaseous Pollu tant s
Absorption (Wet Scrubbing)Absorption (Wet Scrubbing)
AdsorptionAdsorption CombustionCombustion
FGDFGD
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AbsorptionAbsorption
Adsorption SystemsAdsorption Systems
consist of a bed of adsorbing materialconsist of a bed of adsorbing material
activated carbonactivated carbon adsorbing material is housed within aadsorbing material is housed within a
pressure vessel through which thepressure vessel through which the
contaminated air passescontaminated air passes
pollutants are transferred from air to adsorberpollutants are transferred from air to adsorber
AdsorptionAdsorption
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AdsorptionAdsorption
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Incineration or flaringIncineration or flaring
used to oxidize:used to oxidize:
carbon monoxidecarbon monoxide
organic air pollutantsorganic air pollutants
organics containing chlorine, sulfur, and nitrogenorganics containing chlorine, sulfur, and nitrogen
to carbon dioxide and waterto carbon dioxide and water direct flame combustion and catalyticdirect flame combustion and catalytic
combustioncombustion
IncinerationIncineration
IncinerationIncineration
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Vertical Venturi ScrubberVertical Venturi Scrubber
Packed Bed ScrubberPacked Bed Scrubber
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Control Technologies forControl Technologies forNitrogen OxidesNitrogen Oxides
PreventivePreventive
minimizing operatingminimizing operating
temperaturetemperature
fuel switchingfuel switching
low excess airlow excess air
flue gas recirculationflue gas recirculation staged combustionstaged combustion
secondary combustionsecondary combustion
Post combustionPost combustion
selective catalyticselective catalyticreductionreduction
selective nonselective non--catalyticcatalyticreductionreduction
B. Cont rol of Part iculate Pollut antsB. Cont rol of Part iculate Pollu tants
Settling chambersSettling chambers
based onbased on StokeStokess LawLaw
practical lower limit is 50practical lower limit is 50--100100 mm
CycloneCyclone lower limit = 10lower limit = 10 mm
Bag house filterBag house filter
removes very small particlesremoves very small particles
Liquid scrubbingLiquid scrubbing
Electrostatic precipitation (ESP)Electrostatic precipitation (ESP)
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based onbased on StokeStokess LawLaw
practical lower limit is 50practical lower limit is 50--100100 mm
Settling ChambersSettling Chambers
CyclonesCyclones
can be used for 50can be used for 50--100100 m size particlesm size particles
simple economical unitsimple economical unit
no moving partsno moving parts
relies on inertial effectsrelies on inertial effects
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Cyclones.Cyclones.
For particle sizes greater than about 10For particle sizes greater than about 10 m inm in
diameter, the collector of choice is the cyclonediameter, the collector of choice is the cyclone
(Figure 6(Figure 6--30). This is an inertial collector with no30). This is an inertial collector with no
moving parts.moving parts.
The particulateThe particulate--laden gas is accelerated throughladen gas is accelerated through
a spiral motion, which imparts a centrifugal forcea spiral motion, which imparts a centrifugal force
to the particles.to the particles.
The particles are hurled out of the spinning gasThe particles are hurled out of the spinning gas
and impact on the cylinder wall of the cyclone.and impact on the cylinder wall of the cyclone.
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CycloneCyclone
21
2
5.0
9
=
gpQ
HBd
( )212 LLH
+=
De
L3D2
L1
L2
Dd
H
B
d0.5 = cut diameter at 50% removal
= dynamic viscosity of gas, Pa-sB = width, m
H = height, m
p = particle density, kg/m3Qg = gas flow rate, m3/s = effective number of turns
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Ex. 6-9Given:
D2 = 0.5 m
Qg = 4 m3/s
T = 25 oC
p = 800 kg/m3
For standard Cyclone:
B = 0.25 D2 = 0.13 m
H = 0.5 D2 = 0.25 mL1 = L2 = 2 D2 = 1 m
Q = What is the removal efficiency
for particles with ave
diameter of 10 m?
( ) 7.371)1(225.0
=+=
)(41.2
1041.2)7.37)(4)(800(
)25.0()13.0)(105.18(9 65.0
26
5.0
m
xxd
=
=
=
@ d =10 m 15.441.2
10
5.0
==d
d
= 0.95
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Cyclone Installation at Wood Working Plant
http://www.fkinc.com/cyclones.htm
BaghouseBaghouse FilterFilter
similar to conventional homesimilar to conventional home
vacuum cleanervacuum cleaner
particle size smaller that 10particle size smaller that 10mm
High removal efficiency for < 5High removal efficiency for < 5 m particlesm particles cannot be used forcannot be used for
wet air systemswet air systems
corrosive gasescorrosive gases
gases above 260gases above 260ooCC
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Air FiltrationAir Filtration
Air FiltrationAir Filtration
ImpactionImpaction
DiffusionDiffusion
Straining (Interception)Straining (Interception)
ElectrostaticsElectrostatics
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Wet ScrubberWet Scrubber
can be used wherecan be used where
air is wetair is wet
corrosivecorrosive
hothot
wherewhere baghousesbaghouses can not be usedcan not be used
for even higher efficiencies, a combinationfor even higher efficiencies, a combination
of a venturi scrubber and cyclone and canof a venturi scrubber and cyclone and can
be usedbe used
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ScrubberScrubber
VenturiVenturi
Liquid ScrubberLiquid Scrubber
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ESPESP
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ESPESP
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Effectiveness of Air PollutionEffectiveness of Air Pollution
Control DevicesControl Devices
0.00001 0.0001 0.001 0.01 0.1 1 1 10 100 1000 10,000
Pollutant diameter (m)
Electrostatic precipitator
Bag filter
Adsorber
Scrubber
Incinerator
Cyclone
Settling chamber
Wet scrubber
Comparison of Air PollutionComparison of Air Pollution
Control DevicesControl Devices
A Setling Chamber
B Simple Cyclone
C H igh efficiency cyclone
D E le ctr osta tic P rec ipita to r
E Spray Tower Wet Scrubber
F Venturi Scrubber
G Bag Filter