Wet electrostatic precipitators (ESPs) are used in some gasification plants. The gas is passed through a strong electric field with electrodes. High voltage charges the solid and liquid particles. As the flue gas passes through a chamber containing anode plates or rods with a potential of 30 to 75 kV, the particles in the flue gas pick up the charge and are collected downstream by positively charged cathode collector plates. Grounded plates or walls also attract the charged particles and are often used for design simplicity. Although collection efficiency does not decrease as particles build up on the plates, periodic mechanical wrapping is required to clean the plates to prevent the impediment of the gas flow or the short-circuiting of the electrodes through the built-up ash.

The collected solid particles are cleaned by mechanical means, but a liquid like tar needs cleaning by a thin film of water. Wet electrostatic precipitators have very high (> 90%) collection efficiency over the entire range of particle size down to about 0.5 micron, and they have very low pressure drop (few inches water gauge). Sparking due to high voltage is a concern with an ESP, especially when it is used to clean highly combustible syngas. Thus, the savings from lower fan power due to low pressure drop is offset by a higher safety cost. Additionally, the capital cost for ESP is three to four times higher than that for a wet scrubber.