Air Pollution Control Devices...

Air Pollution Control Devices Air pollution control devices (APCD) are a series of devices which are used to prevent a variety of different pollutants, both gaseous and solid, from entering the atmosphere mainly out of the industrial stacks. These control devices can be separated into two broad categories namely (i) devices which control the amount of particulate matter escaping into the environment, and (ii) devices which controls the acidic gas emissions into the atmosphere. By and large the air pollutants are generated due to the combustion of fuels in the furnaces. The major combustion-generated pollutants are the oxides of nitrogen (NOx), sulphur dioxide (SO2), carbon monoxide (CO), unburned hydrocarbons, and particulate matter. The generated pollutants are carried by the exhaust gases produced during the combustion of the fuel. These exhaust gases are then normally passed through the APCDs before releasing them to the atmosphere.  The pollutants are removed, destroyed, or transformed in the control devices before the discharge of the exhaust gas into the atmospheric air. Common methods for removing the pollutants from the exhaust gases work on the following principles. Destroying pollutants by thermal or catalytic combustion, such as by use of a flare stack, a high temperature incinerator, or a catalytic combustion reactor. This technique is used when the pollutants are in the form of organic gases or vapours. During flame combustion or catalytic process, these organic pollutants are converted into water vapour and relatively less harmful products, such as carbon dioxide (CO2). Changing pollutants to less harmful forms through chemical reactions, such as converting nitrogen oxides (NOx) to nitrogen and water through the addition of ammonia to the exhaust gas in front of a selective catalytic reactor. In the technique known as ‘absorption’, the gaseous effluents are passed through scrubbers or absorbers. These contain a suitable liquid absorbent, which removes or modifies one or more...