Engineering Chemistry S Datta

POLLUTION PREVENTION AND WASTE MINIMISATION 577
Highlights:
Pollution:
(i) “The excessive discharge or addition of undesirable substances or unwanted
foreign matter into the environment, thereby adversely altering the natural
quality of the environment, and causing damage to human, plants or animal
life”.
(ii) Major Air Pollutants:
• Gases like SO 2
, SO 3
, H 2
S, NO, NO 2
, CO, CO 2
, hydrocarbons.
• Particulates like dust, smoke, smog, lead, mercury, cadmium.
(iii) Control of Air Pollution:
• Using chimneys
• Using cyclone separator, electrostatic precipitator
• By cleaning the fuels like coal, petroleum
• By treating the exhaust gases
• By plantation of trees
(iv) Important effects of Air Pollution:
1. Acid rain
2. Green-house effect
3. Depletion of ozone layer
4. Photochemical smog formation
5. Heavy metal poisoning
Air pollution control
Air pollution can be controlled by preventing the formation of the pollutants at the
source. Some of the following remedies can be helpful:
1. (a) Pollution due to emissions from automobiles can be minimised by using catalysts
to aid the effective combustion.
(b) By purifying the fuel, removing sulfur by bio and normal methods of desulfurization
and also by reducing the emission of SO 2
in flue gases by treating
with liq. NH 3
, alk. KMnO 4
etc.
2. (a) The industrial process can be improved by modifying the old machineries so
that pollution due to imperfect conversions can be corrected.
(b) Installation of air treatment plants for the purification of vent gases containing
objectionable pollutants.
3. The use of “tall stacks or chimneys” reduces the concentration of air pollutants in
the ground level. The gases discharged through these get diluted and are dispersed
to a height that reduces pollution in ground level.
4. Alternative source of energy is to be tried instead of conventional fuels causing
pollution.
5. Installation of devices
(a) Cyclone collector. It is used for precleaning of air for removal of dry particulates
of size ranging from 5–20 µm. The air/gas is passed through a tight circular
spiral-fitted chamber. The centrifugal forces throw the particulates towards the
wall from where they settle down due to gravity. The collected particles are
periodically removed. The action of cyclone separator is as shown in Fig. 27.2.