technologies for air pollution control-part-1
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TECHNOLOGYFORAIRPOLLUTION
CONTROLPART1
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TECHNIQUESWITHOUTUSINGEMISSIONS
CONTROLDEVICES
Process Change
Wind, Geothermal, Hydroelectric, or Solar Unit instead of Fossil fired
Unit.
Change in Fuel
e.g. Use of Low Sulfur Fuel, instead of High Sulfur fuel.
Good Operating Practices
Good Housekeeping
Maintenance
Plant Shutdown
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COMMONLYUSEDMETHODSFORAIRPOLLUTION
CONTROL
PARTICULATE
Cyclones
Electrostatic Precipitators
Fabric Filter
Wet Scrubbers
GASES
Adsorption Towers
Thermal Incernation
Catalytic Combustion
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SOXCONTROL
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GENERAL METHODS FOR CONTROL OF SO2
EMISSIONS
Change to Low Sulfur Fuel
Natural Gas
Liquefied Natural Gas
Low Sulfur Oil
Low Sulfur Coal
Use Desulfurized Coal and Oil Increase Effective Stack
Height
Build Tall Stacks
Redistribution of Stack Gas Velocity Profile
Modification of Plume Buoyancy
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GENERALMETHODSFORCONTROLOFSO2
EMISSIONS(CONTD.)
Use Flue Gas Desulfurization Systems
Use Alternative Energy Sources, such as Hydro-Power or
Nuclear-Power
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FLUEGASDESULFURIZATION
SO2scrubbing, or Flue Gas Desulfurization processes can be
classified as:
Throwaway or Regenerative, depending upon whether the recovered sulfur
is discarded or recycled.
Wet or Dry, depending upon whether the scrubber is a liquid or a solid.
Flue Gas Desulfurization Processes
The major flue gas desulfurization ( FGD ), processes are :
Limestone Scrubbing
Lime Scrubbing
Dual Alkali Processes
Lime Spray Drying
Wellman-Lord Process
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LIMESTONESCRUBBING
Limestone slurry is sprayed on the incoming flue gas.
The sulfur dioxide gets absorbed The limestone and the
sulfur dioxide react as follows :
CaCO3+ H2O + 2SO2----> Ca+2+ 2HSO3
-+ CO2
CaCO3+ 2HSO3-+ Ca+2----> 2CaSO3 + CO2 + H2O
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LIMESCRUBBING
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LIMESCRUBBING
The equipment and the processes are similar to those in
limestone scrubbing Lime Scrubbing offers better
utilization of the reagent. The operation is more flexible.
The major disadvantage is the high cost of lime
compared to limestone.
The reactions occurring during lime scrubbing are :
CaO + H2O -----> Ca(OH)2
SO2+ H2O H2SO3
H2SO3 + Ca(OH)2 -----> CaSO3.2 H2O
CaSO3.2 H2O + (1/2)O2 -----> CaSO4.2 H2O
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DUALALKALISYSTEM
Lime and Limestone scrubbing lead to deposits inside spray tower.
The deposits can lead to plugging of the nozzles through which thescrubbing slurry is sprayed.
The Dual Alkali system uses two regents to remove the sulfur
dioxide. Sodium sulfite / Sodium hydroxide are used for the absorption of
sulfur dioxide inside the spray chamber.
The resulting sodium salts are soluble in water,so no deposits areformed.
The spray water is treated with lime or limestone, along with make-up sodium hydroxide or sodium carbonate.
The sulfite / sulfate ions are precipitated, and the sodium hydroxideis regenerated.
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LIMESPRAYDRYING
Lime Slurry is sprayed into the chamber
The sulfur dioxide is absorbed by the slurry
The liquid-to-gas ratio is maintained such that the spray dries
before it reaches the bottom of the chamber
The dry solids are carried out with the gas, and are collectedin fabric filtration unit
This system needs lower maintenance, lower capital costs,
and lower energy usage
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GENERALMETHODSFORCONTROLOFNOX
EMISSIONS
NOx control can be achieved by:
Fuel Denitrogenation
Combustion Modification
Modification of operating conditions
Tail-end control equipment
Selective Catalytic Reduction
Selective Non - Catalytic Reduction
Electron Beam Radiation
Staged Combustion
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FUELDENITROGENATION
o One approach of fuel denitrogenation is to remove a large part of the nitrogen
contained in the fuels. Nitrogen is removed from liquid fuels by mixing the fuels
with hydrogen gas, heating the mixture and using a catalyst to cause nitrogen in
the fuel and gaseous hydrogen to unite. This produces ammonia and cleaner
fuel.
This technology can reduce the nitrogen contained in both naturally
occurring and synthetic fuels.
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COMBUSTIONMODIFICATION
Combustion control uses one of the following strategies:
Reduce peak temperatures of the flame zone. The methods are :
increase the rate of flame cooling
decrease the adiabatic flame temperature by dilution
Reduce residence time in the flame zone. For this we change the
shape of the flame zone
Reduce Oxygen concentration in the flame one. This can be
accomplished by:
decreasing the excess air controlled mixing of fuel and air
using a fuel rich primary flame zone
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CATALYTICCOMBUSTION
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CATALYTICEMISSIONCONTROL
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MODIFICATIONOFOPERATINGCONDITIONS
The operating conditions can be modified to achieve
significant reductions in the rate of thermal NOx
production. the various methods are:
Low-excess firing
Off-stoichiometric combustion ( staged combustion )
Flue gas recirculation
Reduced air preheat
Reduced firing rates
Water Injection
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SELECTIVECATALYTICREDUCTION(SCR)
Schematic process flow diagram NOXcontrol
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CARBON MONOXIDE CONTROL
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FORMATIONOFCARBONMONOXIDE
Due to insufficient oxygen
Factors affecting Carbon monoxide formation:
Fuel-air ratio
Degree of mixing
Temperature
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GENERALMETHODSFORCONTROLOFCO
EMISSIONS
Control carbon monoxide formation.
Note : CO & NOx control strategies are in conflict.
Stationary Sources
Proper Design
Installation
Operation
Maintenance
Process Industries
Burn in furnaces or waste heat boilers.
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CARBON DIOXIDE CONTROL
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CO2EMISSIONSFROMFOSSILFUEL
COMBUSTIONBYSECTORANDFUELTYPE
Source: USEPA(y-axis units are teragrams of CO
2equivalent)
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GENERALMETHODSFORCONTROLOFCO2
EMISSIONS
Reducing energy consumption, increasing the efficiency
of energy conversion
Switching to less carbon intensive fuels
Increasing the use of renewable sources
Sequestering CO2through biological, chemical, orphysical processes
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Types of Sources
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Source: Seingeur, 2004 and Mason and Sheu, 2002.
Source: Presentation by J. Pacyna and J. Munthe at mercury workshop in Brussels,
March 29-30, 2004
Types of Sources
Worldwide Distribution of Emissions
C T M
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CONTROLTECHNOLOGIESFORMERCURY
EMISSIONS
Currently installed control devices for SO2, NOX,and particulates, in a
power plant, remove some of the mercury before releasing from the
stack
Activated Carbon Injection:Particles of activated carbon are injected into the exit gas flow, downstream
of the boiler. The mercury attaches to the carbon particles and is removed in
a particle control device
Thief process for the removal of mercury from flue gas:
It is a process which extracts partially burned coal from a pulverized coal-
fired combustor using a suction pipe, or "thief," and injects the resulting
sorbent into the flue gas to capture the mercury.
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PARTICULATE MATTER CONTROL
Range: 20 to 40000 mg/m**3
First step: Process controlSecond step: Use of collection device
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INDUSTRIALSOURCESOFPARTICULATEEMISSIONS
Iron & Steel Mills, the blast furnaces, steel making furnaces.
Petroleum Refineries, the catalyst regenerators, air-blown asphalt
stills, and sludge burners.
Portland cement industry
Asphalt batching plants
Production of sulfuric acid
Production of phosphoric acid
Soap and Synthetic detergent manufacturing
Glass & glass fiber industry
Instant coffee plants
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EFFECTS OF PARTICULATE EMISSIONS
Primary Effects
Reduction of visibility
size distribution and refractive index of the particles
direct absorption of light by particles
direct light scattering by particles
150 micro g / m3concentration ~ average visibility of 5 miles
( satisfactory for air and ground transportation )
Soiling of nuisance increase cost of building maintenance, cleaning of furnishings,
and households
threshold limit is 200 - 250 micro g / m3( dust )
levels of 400 - 500 micro g / m3considered as nuisance
G M F C O
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GENERALMETHODSFORCONTROLOF
PARTICULATEEMISSIONS
Five Basic Types of Dust Collectors :
Gravity and Momentum collectors
Settling chambers, louvers, baffle chambers
Centrifugal Collectors
Cyclones
Mechanical centrifugal collectors
Fabric Filters
Baghouses
Fabric collectors
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Tubular Dust Collector Arrangement for an
ESP
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