Air pollution control

11. Introduction
 Environmental pollution
2. Air pollution
 Major air pollutants
 Sources of air pollution
 Effect of air pollution
3. Air pollution control
 Source control
 Controlling process and technology
 Particulate matter pollutants
 Gaseous pollutants
4. Conclusion
5. References

 The earth is the only planet known in the universe capable of
supporting life.
The life supporting properties are The Atmosphere and
Hydrosphere .
Environment pollution and efforts for the betterment of living
standards are the two sides of the same coin.
In the wake of industrialization, consequent urbanization and
ever increasing population, the basic amenities of life namely,
air, water and land are being polluted continuously.

Atmosphere is a thin layer of gas which
surrounds the Earth.
Three major layers : Troposphere, Stratosphere,
Mesosphere.
99% of the volume of clean air is in
Troposphere, which extends 17km above MSL.
Nitrogen (78%) and Oxygen (21%) and 1%
Argon, CO2 and water vapour.

As per the definition of the World Health
Organization (WHO), air pollution is a
“situation in which the outdoor atmosphere
contains materials in concentrations which
are harmful to people or their
environment”.

COx
SOx
NOx
Volatile Organic Compounds (VOCs)
Suspended particulate matter
Photochemical oxidants
Radioactive substances
Heat

1. Natural sources
Example: Volcanic eruption
releases poisonous gases.
2. Man-made sources
Example: Deforestation, burning
of fossil fuel, emission from vehicles,
smokes from industries.

Human health
Animals
Vegetation
Environment

1. Control at source
2. Controlling devices and technology
 Particulate pollution control
 Gaseous pollution control

1. Source relocation
2. Source shut down
3. Fuel or Energy substitution
4. Process changes
5. Good operating practices
6. Vehicular emission control

Particulate matter is the sum of all solid and liquid particles
suspended in air, many of which are hazardous. This complex
mixture contains for instance dust, pollen, soot, smoke, and liquid
droplets.
Temperature and chemical composition of gases to be cleaned from
particulants before the selection of proper control device.
Information on the physical form of the suspended material, its
abrasive properties, size and shape, chemical composition and
electrical sensitivity is required for this selection.
There Five major groups of processes.
a) Settling chambers
b) Inertial separator or Cyclone
c) Electrostatic precipitator
d) Bag houses and filters
e) Wet scrubbers

a) SETTLING CHAMBERS
 A simplest device, collecting dust of size
>10µm.
 Settling chambers use the force of gravity
to remove solid particles. The gas stream
enters a chamber where the velocity of
the gas is reduced. Large particles drop
out of the gas and are recollected in
hoppers. Because settling chambers are
effective in removing only larger
particles, they are used in conjunction
with a more efficient control device.
 The size, shape of particles and density
and viscosity are important parameters.

b) INERTIAL SEPERATOR
OR CYCLONE
This process is achieved by a sudden
change in the direction of gas flow.
The dust particle is spinning in a
circular path, it is subjected to an
outward force. As a result the
particles collect on the wall and fall
to the bottom of the vessel.

c)ELECTROSTATIC PRECIPITATORS
 Passing the particle laden gases
between high voltage discharge
electrodes.
 Majority of particles get charged
and collected on ground
electrodes.
 At intervals both discharge and
collecting electrodes are rapped to
dislodge collected particles from
the electrodes, which then fall into
hoppers at the bottom of the
precipitator.
 Ele. Precipitator is efficient for the
particle size below 0.01µm, can
tolorate operating temperature as
high as 7000k.

d) BAG HOUSE AND FILTERS
This method is most often used type of
device, which is required to meet
any future standards limiting the
emission of respirable particles.
The collection efficiency is very high
and even for particle of 0.01µm
diameter .
The Fabric filters, or bag houses ,
remove dust from a gas stream by
passing the stream through a porous
fabric.
The fabric filter is efficient at removing
fine particles and can exceed
efficiencies of 99% in most
applications.

E) WET SCRUBBERS
Objective of scrubber is to
entrain the particulate matter
in liquid droplets. Water
subsequently flows from the
bottom of the scrubber, the
particulate is allowed to settle
and clarified water is re-
circulated.

The removal methods for gaseous pollutants
are designed to concentrate the pollutants in a
liquid (absorption) or a solid (adsorption).
Sometimes direct conversion of gaseous
pollutants is possible by combustion.
The central pollution (prevention and control)
board, New Delhi has fixed standard for
ambient air quality in India under the Air Act,
1981 beyond which an ambient air can be
considered polluted in a legal sense.

Area
category
Suspended
particulate
matter
SO2 CO NO2
Industrial
and mixed
use
500 120 5000 120
Residential
and Rural
200 80 2000 50
Sensitive
area (tourist
resort, game
sanctuary)
100 30 1000 30
AMBIENT AIR QUALITY STANDARD IN INDIA
(concentration in µgm3)

Vehicle at manufacturing stage 60 Hatridge Smoke Units (HSU)
Vehicle on road 70 HSU
Category Vehicle on
road
Vehicle at
manufacturing
stage
2 or 3 wheeler
vehicles with
engine
displacement less
than 50cc
5.0 5.0
Other 2 or 3
wheelers
4.5 5.5
4 wheelers 4.0 3.5
STANDARD FOR VEHICULAR EMISSION
Petrol driven vehicles: (Limits of CO in percentage
volume)
Diesel driven vehicles: (Smoke density)

This processes is selected to remove
gaseous pollutants by dissolution into a
liquid solvent such as water or in a caustic or
acid solution. (most commonly water is
used as an absorbent).

As the gas stream passes through the
liquid, the liquid absorbs the gas.
Absorption is commonly used to recover
products or to purify gas streams that have
high concentrations of organic compounds.
Among several considerations in
absorption unit design, the most important
is the selection of a suitable liquid solvent,
determination of the limits of absorption
efficiency, selection of appropriate
equipment for liquid-gas contact and
capital cost of the unit.

b) ADSORTION
Adsorption is a process where gases,
vapours or liquids are concentrated
on a solid surface as a result of
surface or chemical force (physical
adsorption and chemisorptions
respectively). The amount of
adsorbed substances depends
directly on the internal surface area
of solid and the kinetics of the
process.
The most important adsorbents in
industrial use to-days are Bauxite,
activated carbon, activated alumina,
silica gel and molecular sieves.

This method for the removal of VOCs
since they can be decompose to CO2 and
H2O.
The Direct and indirect or catalytic
methods are used.
The catalytic method is preferred when
low temperature of the process is
desired.

The most commonly used catalysts are
the Cu, Ni, V and Zn compounds. IF the
concentrations of air pollutants are
high, a combination of sorption
methods and catalytic reaction is used.

Air pollution is a major environmental issue. It can
affect the health and life support systems as well.
Since clear air is an essential factor of life for
respiration, it is necessary to prevent the sources of air
pollution.
Due to air pollution destructive phenomena like acid
rain, global warming etc.
Using appropriate controlling devices and processes,
the pollutants in the air can be removed.
There are five processes for the removal of particulate
matters. Settling chambers, Cyclone, Electrostatic
precipitators, Bag houses and filters and Scrubbers.
For gaseous matters, Absorption, adsorption and
combustion processes are used.

G.N Pondey, Environmental management(1997), P. 150-
156
Mishra, Fundamentals of air and water pollution,
P. 51-56
R.M Harrison, Pollution: Control, Effects and Control, P.
201-203
Marquita. K. Hill, Understanding environmental
pollution, P. 80-136.
http/www.wikipedia.com.

Air pollution control

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