Technologies for Air Pollution Control-Part-1

8/11/2019 Technologies for Air Pollution Control-Part-1

1/54

TECHNOLOGYFORAIRPOLLUTION

CONTROLPART1


2/54

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


3/54

COMMONLYUSEDMETHODSFORAIRPOLLUTION

CONTROL

PARTICULATE

Cyclones

Electrostatic Precipitators

Fabric Filter

Wet Scrubbers

GASES

Adsorption Towers

Thermal Incernation

Catalytic Combustion


4/54

SOXCONTROL


5/54

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


6/54

GENERALMETHODSFORCONTROLOFSO2

EMISSIONS(CONTD.)

Use Flue Gas Desulfurization Systems

Use Alternative Energy Sources, such as Hydro-Power or

Nuclear-Power


7/54

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


8/54


9/54

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


10/54

LIMESCRUBBING


11/54

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


12/54

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.


13/54

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


14/54


15/54


16/54


17/54


18/54


19/54

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


20/54

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.


21/54

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


22/54

CATALYTICCOMBUSTION


23/54

CATALYTICEMISSIONCONTROL


24/54

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


25/54


26/54

SELECTIVECATALYTICREDUCTION(SCR)

Schematic process flow diagram NOXcontrol


27/54


28/54


29/54


30/54


31/54


32/54

CARBON MONOXIDE CONTROL


33/54

FORMATIONOFCARBONMONOXIDE

Due to insufficient oxygen

Factors affecting Carbon monoxide formation:

Fuel-air ratio

Degree of mixing

Temperature


34/54

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.


35/54

CARBON DIOXIDE CONTROL


36/54


37/54


38/54

CO2EMISSIONSFROMFOSSILFUEL

COMBUSTIONBYSECTORANDFUELTYPE

Source: USEPA(y-axis units are teragrams of CO

2equivalent)


39/54

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


40/54


41/54

Types of Sources


42/54

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


43/54

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.


44/54

PARTICULATE MATTER CONTROL

Range: 20 to 40000 mg/m**3

First step: Process controlSecond step: Use of collection device


45/54

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


46/54

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


47/54

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


48/54


49/54


50/54


51/54

Tubular Dust Collector Arrangement for an

ESP


52/54


53/54


54/54

Technologies for Air Pollution Control-Part-1

Documents

Transcript of Technologies for Air Pollution Control-Part-1