What is the principle behind electrostatic precipitator (ESP) operation for fly ash collection?

The principle behind electrostatic precipitator (ESP) operation for fly ash collection is to use electrical forces to separate fly ash particles from the flue gas stream. ESPs work by first charging the fly ash particles with a negative electrical charge. This is accomplished by passing the flue gas through a high-voltage electrical field created between electrodes. The electrodes consist of discharge electrodes (wires or rigid frames) and collecting plates (large, flat surfaces). A high negative voltage (typically -20 to -70 kV) is applied to the discharge electrodes, creating a corona discharge – an ionization zone around the electrodes. As fly ash particles pass through this corona, they collide with ionized gas molecules (electrons and ions) and become negatively charged. Once charged, the fly ash particles are attracted to the positively charged collecting plates due to electrostatic attraction. The charged particles migrate towards the collecting plates, where they deposit and accumulate. Periodically, the collecting plates are cleaned by rapping or vibrating them. This dislodges the accumulated fly ash, which falls into collection hoppers located below the plates. The collected fly ash is then removed from the hoppers for disposal or reuse. The efficiency of an ESP depends on factors such as the voltage applied, the size and electrical properties of the fly ash particles, the gas flow rate, and the design of the electrodes and collecting plates. ESPs are highly effective at removing fine particles from flue gas, making them a crucial component of air pollution control systems in power plants.