Electrostatic Precipitator

Electrostatic Precipitator, an electrical device for removing suspended impurities such as dust, fumes, or mist, from air or other gases, developed around 1906. Although more expensive than mechanical collectors such as air filters, electrostatic precipitators are more efficient, and are particularly effective in removing very fine particles. The gas to be purified moves through passages that have a series of discharge electrodes suspended in the passage centres, insulated electrically from the rest of the precipitator. The electrodes are supplied with direct current at high voltages ranging from 30,000 to 75,000 volts. Beyond the discharge electrodes are large metal collector electrodes that are electrically charged.

The high-voltage current applied to the discharge electrodes ionizes the impurities; this ionization charges the suspended particles. The collector electrodes have a charge opposite of the ionized particles, so the suspended particles move towards the collector electrodes and become deposited on the electrode's surface. Periodically, the collector electrodes must be washed or scraped clean to remove the deposited impurities. Electrostatic precipitators are used extensively in eliminating atmospheric pollution from the exhausts of industrial devices such as steam boilers and cement kilns; they are also used for collecting sulphuric acid and phosphoric acid mists, and recovering sodium compounds in soda and sulphate pulp mills.

See also Air Pollution; Colloid.