When flue gases get released through a chimney, it may consist of dust particles which need to be removed from the flue gases before these flue gases get discharged to the atmosphere. By removing the dust particles from flue gases, we can control the air pollution. Electrostatic precipitator installed in the thermal power plant does this work for boiler furnace system. This device is situated just before the entry of chimney so that the flue gases can be purified or filtered before the gases enter in the bottom of the chimney through which gases will get released in the atmosphere.
Working Principle of Electrostatic PrecipitatorThe working principle of the electrostatic precipitator is quite simple. It has two sets of electrodes one is positive and another is negative. The negative electrodes are in the form of rod or wire mesh. Positive electrodes are in the form of plates. The positive plates and negative electrodes are placed vertically in the electrostatic precipitator alternatively one after another. The negative electrodes are connected to a negative terminal of high voltage DC source, and positive plates are connected to the positive terminal of the DC source. The positive terminal of the DC source may be grounded to get stronger negativity in the negative electrodes. The distance between each negative electrode and positive plate and the DC voltage applied across them are so adjusted that the voltage gradient between each negative electrode and adjacent positive plate becomes quite high to ionize the medium between these.
The medium between the electrodes is air, and due to the high negativity of negative electrodes, there may be a corona discharge surround the negative electrode rods or wire mesh. The air molecules in the field between the electrodes become ionized, and hence there will be free electrons in the space. The entire system is enclosed by a metallic container on which one side is provided with an inlet of the flue gas, and the opposite side is provided with the outlet of the filtered gas to the chimney. As soon as the flue gases enter into the system of an electrostatic precipitator, dust particles in the gases collide with the free electrons available in the medium between the electrodes. As a result, the dust particles become negatively charged due to the collision with the free electrons in the medium. Then these negatively charged particles will be attracted due to electrostatic force of the positive plates.
Consequently, the charged dust particles move towards the positive plates and deposited on positive plates. Here, the extra electron of the dust particles will be removed at positive plates and the particles then fall down due to gravitational force. We call the positive plates as collecting plates. The flue gases after travelling through the electrostatic precipitator become free from ash particles and ultimately remove to the atmosphere through a chimney. An electrostatic precipitator does not contribute directly to the production of electricity in the thermal power plant but it helps to keep the atmosphere clean which is quite important for living beings. Hoppers are fitted below the electrostatic precipitator chamber for collecting dust particles. Water pray may be used on the top to accelerate the removal of the dust from the collecting plates.