Methods of Controlling Gaseous Pollutants

Controlling gas pollutants can be done with the help of 3 different methods mentioned below:

1. Combustion: This technique is used when the pollutants are in the form of organic gases or vapors. During flame combustion or catalytic process, these organic pollutants are converted into water vapor and relatively less harmful products, such as CO₂.

2. Absorption: In this technique, the gaseous effluents are passed through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more of the pollutants present in the gaseous effluents.

3. Absorbent: The gaseous effluents are passed through porous solid absorbents kept in suitable container. The organic and inorganic constituents of the effluent gases are trapped at the interface of the solid absorbent by physical absorbent.

Methods of Control Particulate Emissions

Principally, two devices remove particulate air pollutants.

1. Arresters (used ideally to separate particulate matter from contaminated air).

2. Scrubbers (used to clean air for both dusts and gases by passing it through dry or wet packing materials).

Particulate matter arresters may be of different kinds.

1. Gravity: In this process, the particles settle down by gravitational force.

2. Sudden change in direction of the gas flow: This causes the particles to separate out due to greater momentum. Cyclonic separators and trajectory separators are commonly used to separate out particulate matters from industrial emissions with minimum moisture content. These separations work on the principle of dust separation by centrifugal force and are efficient for coarser dust particles.

3. Filters are usually used to collect extremely fine particulate matters. Different types of filter materials are available to suit different quality and size of the particulate matters. The gases containing dust are passed through a porous medium. These porous media may be woven or filled fabrics. The particles present in the gas are trapped and collected in the filters. The gases freed from the particles are discharged. Purification period setting period exit for gas.

4. Electrostatic precipitator (ESP) is the most effective device to remove particulate pollutants ESP works on the principle of electrical charging of the dust particles and collecting it on a differently charged platform. Both dry and wet type scrubbers are also used for dust separation. However, scrubber is the least used device for separating particulate matters from the emissions, as this device is best suited for the removal of gaseous pollutants.

5. Wet scrubbers: Wet scrubbers are used in chemical, mining, and metallurgical industries to trap SO₂, NH₂, metal fumes, etc.