The air pollutants are of two types. These are particulates and gaseous. Different methods are used to control their effects.

(A) Particulates:

The particulate matter consists of minute suspended particles. The size of such particles range between 0.1 µm to 100 µm. The control of the particulate matter of this size depends upon their (a) Physical and chemical characteristics, (b) Concentration, (c) Volume, (d) Temperature and humidity of the gaseous medium.

Depending on these factors the methods for removal of particulate matter have been classified in to five types, these are:


(I) Settling Chambers:

This method is used to remove large particles of size greater than 50 (im from gas stream. The efficiency of this method is less for low concentration, suspension and lesser size of the particles.

(II) Cyclone Seperator:

Cyclone separators utilize centrifugal force generated by a spinning gas stream to separate the particulate matter from the carrier gas. This method is effective for removal of much smaller particles as compared to settling chamber method. It separates particles of size range between 5-10.


(III) Wet Scrubber (Collectors):

Wet collectors have a number of advantages over dry collector such as simultaneous removal of particles and gaseous pollutants, but suffer from the problems of corrosion and liquid waste disposal. The basic function of the wet scrubber is to provide contact between the scrubbing liquid usually water and the particles to be removed. This method is suitable for particles from 0.2 to 10.

(IV) Bag Filters:

The removal of particles of size range less than 10 p is done using bag filters. This method is reliable and efficient and is capable for removal of high pressure drop and its maintenance is expensive.


(V) Electrostatic Precipitator:

This method is widely used for removal of particulate emissions of power plants, cement, paper mills and oil refineries. The particulates include dust, fibers and small particles such as acid mists.

The main disadvantages of this method are its high internal cost, sensitivity, to variable particulates, loadings, occurrence of ionization of a gas in a limited operating range. It requires large space.

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