Worldwide Engineering Corporation

Electrostatic Precipitator

An electrostatic precipitator is a large, industrial emission-control unit. It is designed to trap and remove dust particles from the exhaust gas stream of an industrial process. Precipitators are used in these industries:

  • Power/Electric

  • Cement

  • Chemicals

  • Metals

  • Paper

In many industrial plants, particulate matter created in the industrial process is carried as dust in the hot exhaust gases. These dust-laden gases pass through an electrostatic precipitator that collects most of the dust. Cleaned gas then passes out of the precipitator and through a stack to the atmosphere. Precipitators typically collect 99.9% or more of the dust from the gas stream.

Precipitators function by electrostatically charging the dust particles in the gas stream. The charged particles are then attracted to and deposited on plates or other collection devices. When enough dust has accumulated, the collectors are shaken to dislodge the dust, causing it to fall with the force of gravity to hoppers below. The dust is then removed by a conveyor system for disposal or recycling.

Depending upon dust characteristics and the gas volume to be treated, there are many different sizes, types and designs of electrostatic precipitators. Very large power plants may actually have multiple precipitators for each unit.

 

Basic Principles 

Electrostatic precipitation removes particles from the exhaust gas stream of an industrial process. Often the process involves combustion, but it can be any industrial process that would otherwise emit particles to the atmosphere. Six activities typically take place:

  • Ionization - Charging of particles

  • Migration - Transporting the charged particles to the collecting surfaces

  • Collection - Precipitation of the charged particles onto the collecting surfaces

  • Charge Dissipation - Neutralizing the charged particles on the collecting surfaces

  • Particle Dislodging - Removing the particles from the collecting surface to the hopper

  • Particle Removal - Conveying the particles from the hopper to a disposal point

The major precipitator components that accomplish these activities are as follows:

  • Discharge Electrodes

  • Power Components

  • Precipitator Controls

  • Rapping Systems

  • Purge Air Systems

  • Flue Gas Conditioning

 

Design & Performance Requirements 

Designing a precipitator for optimum performance requires proper sizing of the precipitator in addition to optimizing precipitator efficiency. While some users rely on the precipitator manufacturer to determine proper sizing and design parameters, others choose to either take a more active role in this process or hire outside engineering firms.

Precipitator performance depends on its size and collecting efficiency. Important parameters include the collecting area and the gas volume to be treated. Other key factors in precipitator performance include the electrical power input and dust chemistry.

  • Precipitator sizing
    The sizing process is complex as each precipitator manufacturer has a unique method of sizing, often involving the use of computer models and always involving a good dose of judgment. No computer model on its own can assess all the variables that affect precipitator performance.

  • Collecting Efficiency
    Based on specific gas volume and dust load, calculations are used to predict the required size of a precipitator to achieve a desired collecting efficiency.

  • Power Input
    Power input is comprised of the voltage and current in an electrical field. Increasing the power input improves precipitator collecting efficiency under normal conditions.