Atmospheric Chemistry
Unit _ - Control of Air Pollution
FABRIC FILTER – It consists of a tabular bag which is closed at the upper end and has a happer attached at the lower end to collect particles when they are dislodged from the fabric. Many such bags are hanged in a bag house. The filter bags are cleaned occasionally by a mechanical shaker for efficient filtration. It has high efficiency and can filter 0.5 µm size particles.
ELECTROSTATIC PRECIPITATOR – It works on the principle of electrostatic precipitation i.e. electrically charged particles are separated from the air by electrical field. It consists of –
1 Electrically charged (positive) collecting surface.
2 High voltage discharge electrodes.
3 Weight at bottom of electrode wire to keep the wire in position.
Working – The polluted air enters from the bottom and flows upwards. The high voltage in the wire (50KV) ionizes the air. The negative ions move towards the ground surface and pass on their charge (negative) to the particles also. Then those negatively charged particles are electrostatically drawn towards the positively charged collector surface where they are finally deposited. The collecting surface is occasionally vibrated to remove deposited particles so that the thickness of the dust collector does not exceed 6mm otherwise electrical attraction becomes weak and efficiency of the precipitator is reduced. The precipitator has 99% efficiency and can be operated at high temperature (600° C). It is more economical and simple to use.
WET COLLECTORS OR SCRUBBERS – Wet collectors remove particulates from gas stream by incorporating the particles into liquid droplets directly on contact. The collection efficiency of a wet collector is a function of the energy consumed in the air to water contact process. The energy consumed is directly proportional to the pressure drop. Generally, collectors operating at very low pressure drop will remove only medium to coarse size particles while those operating at
FABRIC FILTER – It consists of a tabular bag which is closed at the upper end and has a happer attached at the lower end to collect particles when they are dislodged from the fabric. Many such bags are hanged in a bag house. The filter bags are cleaned occasionally by a mechanical shaker for efficient filtration. It has high efficiency and can filter 0.5 µm size particles.
ELECTROSTATIC PRECIPITATOR – It works on the principle of electrostatic precipitation i.e. electrically charged particles are separated from the air by electrical field. It consists of –
1 Electrically charged (positive) collecting surface.
2 High voltage discharge electrodes.
3 Weight at bottom of electrode wire to keep the wire in position.
Working – The polluted air enters from the bottom and flows upwards. The high voltage in the wire (50KV) ionizes the air. The negative ions move towards the ground surface and pass on their charge (negative) to the particles also. Then those negatively charged particles are electrostatically drawn towards the positively charged collector surface where they are finally deposited. The collecting surface is occasionally vibrated to remove deposited particles so that the thickness of the dust collector does not exceed 6mm otherwise electrical attraction becomes weak and efficiency of the precipitator is reduced. The precipitator has 99% efficiency and can be operated at high temperature (600° C). It is more economical and simple to use.
WET COLLECTORS OR SCRUBBERS – Wet collectors remove particulates from gas stream by incorporating the particles into liquid droplets directly on contact. The collection efficiency of a wet collector is a function of the energy consumed in the air to water contact process. The energy consumed is directly proportional to the pressure drop. Generally, collectors operating at very low pressure drop will remove only medium to coarse size particles while those operating at