To continuously protect downstream components, it is important that any electrostatic precipitator or other filter provide low maintenance and high availability. Tar in the waste gas complicates the maintenance of the electrostatic precipitator, plugging in-line process equipment and hampering the operation of prime movers that use the gas (e.g., a gas engine). In this situation, it is critical that any gas-cleaning system be able to remove the tar from the waste gas.

A wet electrostatic precipitator can perform this function. The basic principle of a wet electrostatic precipitator is as follows: The process gas enters the electrostatic precipitator either horizontally or vertically. The gas is spread to a uniform flow profile across the entire filter cross-section by means of a gas distribution system. The gas flow direction through the electric field is always opposite to the direction of gravity. The process gas and the dust particles are electrically charged by means of the high voltage (75 to 135 kilovolts) applied between the corona discharge electrodes and the honeycomb-type collecting electrodes. The charged ions are produced in the corona discharge and then attach themselves to dust
particles or droplets of tar and water. These particles and droplets are negatively charged and are attracted to the positively charged electrode.

The precipitated dust and liquid flows downward (pulled by gravity) to the bottom of the electrostatic precipitator for removal. The purified gas leaves the filter through the gas outlet hood. The wet electrostatic precipitator captures tar aerosols and dust particles, thereby protecting downstream equipment from potential damage. Wet-gas cleaning has successfully been applied in electricity generation with gas engines in applications such as updraft and downdraft gasifiers, and with circulating fluidized bed gasifiers.

Unlike many forms of gas-cleaning technology, both types of electrostatic precipitators can be custom designed to achieve any required efficiency while operating at most emission levels. Burning biomass can present a special environmental challenge well suited to the use of a custom-designed electrostatic precipitator. Picking a knowledgeable electrostatic precipitator vendor with extensive experience in a wide range of industries will ensure a successful design for your facility.

Petru Sangeorzan is the national sales manager for Weis Environmental LLC. Reach him at p.sangeorzan@weisenvironmental.com or (901) 531-6081.

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