The most basic precipitator contains a row of thin vertical wires, and followed by a stack of large flat metal plates oriented vertically, with the plates typically spaced about 1 cm to 18 cm apart, depending on the application. The air stream flows horizontally through the spaces between the wires, and then passes through the stack of plates.

A negative voltage of several thousand volts is applied between wire and plate. If the applied voltage is high enough, an electric corona discharge ionizes the air around the electrodes, which then ionizes the particles in the air stream.

The ionized particles, due to the electrostatic force, are diverted towards the grounded plates. Particles build up on the collection plates and are removed from the air stream.

A two-stage design (separate charging section ahead of collecting section) has the benefit of minimizing ozone production,[citation needed] which would adversely affect health of personnel working in enclosed spaces. For shipboard engine rooms where gearboxes generate an oil mist, two-stage ESP's are used to clean the air, improving the operating environment and preventing buildup of flammable oil fog accumulations. Collected oil is returned to the gear lubricating system.


Precipitators function by electrostatically charging particles in the gas stream. The charged particles are attracted to and deposited on plates or other collection devices. The treated air then passes out of the precipitator and through a stack to the atmosphere. When enough particles have accumulated on the collection devices, they are shaken off the collectors by mechanical rappers. The particulates, which can be either wet or dry, fall into a hopper at the bottom of the unit, and a conveyor system transports them away for disposal or recycling. Precipitators are often deployed with denitrification units that remove nitrogen oxides and scrubbers or other devices that remove sulfur dioxide.

The most basic precipitator design consists of a row of thin vertical wires and a stack of large flat vertical metal plates. The plates are spaced from less than 0.5 inch (1.3 cm) to about 7 inches (about 17.8 cm) apart, depending on the application. The gas stream flows horizontally between the wires and through the stack of plates. A negative charge of several thousand volts is applied between the wires and plates to remove impurities from the gas stream.

Plate precipitators are often marketed to the public as air purifiers or as a permanent replacement for furnace filters. Unlike some other air purification technologies, they typically do not become breeding grounds for harmful forms of bacteria. Yet, the plates can be difficult to clean and can also produce ozone and nitrogen oxides. Some consumer precipitation filters are sold with special soak-off cleaners that allow the entire plate array to be removed and soaked for several hours, which loosens the particulates.