AIR POLLUTION CONTROL 

Cannot be fully prevented but can be controlled.

1.  Preventative measures 
2. Control measures using equipment's.

Preventative measures (source control)

  • Selection of suitable fuel. (Low sulphur coal in power plant, using of CNG) 
  • Modification in industrial process. 
  • Selection of suitable site and zoning for industrial unit.
How can we control the air pollution

Control measures

  • When source control not possible some measures taken to prevent pollution.
  • Collecting pollutants by using equipments.
  • Destroying the pollutants by thermal or catalytic combustion.
  • Changing the pollutants to less toxic form.
  • By releasing the pollutants through tall chimneys for greater dispersion.

PREVENTATION BYLAWS

  • Various laws has been established for the menace of air pollution. 
  • Air (Prevention & control of pollution ) Act,1981. 
  • Air (Prevention & control of pollution ) Amendment Act,1987. 
  • Motor vehicle Act, 1988. 
  • Air (Prevention & control of pollution) Union Territories Rules, 1983. 
  • Environment Protection Act, 1986.

The government is trying to

Gravitational settling chamber:

  • Used to remove particles with size greater than 50 μm.
  • Velocity of flue gas reduced in large chamber.
  • Particles settle under gravitational force.

Advantages 

  • Low initial cost. 
  • Easy to design. 
  • Low pressure drop. 
  • Low maintenance cost. 
  • Dry and continuous disposal of solid particulates.

Disadvantages 

  • Require large space. 
  • Less collection efficiency. 
  • Only larger size particles can be collected

Cyclone separator

  • Centrifugal force is utilized to separate the particulate matter. 
  • It can remove 10 to 50 μm particle size. 
  • Used mostly in industries.

Advantages

  • Low initial cost. 
  • Require less floor area. 
  • Simple construction and maintenance. 
  • Can handle large volume of gas at high temp.

Disadvantages

  • Requires large head room. 
  • Less efficiency for smaller particles (<10μm). 
  • Sensitive to variable dust load and flow rate.

Electrostatic precipitators

  • Works on the principle of electrical charging of particulate Matter (-ve) and collecting it in a +ve charged surface.
  • 99% efficiency.
  • Can remove particle size range of 0.1 μm to 1 μm.

Advantages

  • High collection efficiency. 
  • Particles may be collected dry or wet. 
  • Can be operated at high temp. (300-450˚c). 
  • Maintenance is normal. 
  • Few moving parts.

Disadvantages 

  • High initial cost. 
  • Require high voltage. 
  • Collection efficiency reduce with time. 
  • Space requirement is more. 
  • Possible of explosion during collection of combustible gases or particulates.


 Fabric filters

  • Flue gas is allowed to pass through a woven Fabric, which filters out Particulate matter. 
  • Small particles are retained on the fabric. 
  • Remove particles up to 1 μm. 
  • Its efficiency up to 99%.

Advantages 

  • Higher collection efficiency for smaller than 10 μm particle size. 
  • Performance decrease becomes visible, giving prewarning. 
  • Normal power consumption

Disadvantages 

  • High temp. gases need to be cooled. 
  • High maintenance and fabric replacement cost. 
  • Large size equipment. 
  • Fabric is liable to chemical attack.

Scrubbers

Particulate matters are incorporated into liquid droplets and removed from the gas stream.

Different types of scrubbers are- 

- Spray tower 
- Venturi scrubber 
- Cyclone scrubber

  • Flue gas made to push up against a down falling water current. 
  • Particulate matter mix up with water thus falls down and gets removed.

Advantages 

  • Simultaneously remove particulates and gaseous pollutants. 
  • Hot gases can be cooled down. 
  • Corrosive gases can be recovered and neutralize. 


Disadvantages 

  • Lot of waste waters produced. 
  • Poses freezing problem in cold countries. 
  • Maintenance cost is high when corrosive materials are collected.