A Precipitator is a device that captures particulates from a gas stream.

In the simplest terms, a precipitator is a large box. The particulate laden gases are drawn into one side of the box using perforated plate and diffusers to evenly distribute the gas. Inside, high voltage electrodes impart a negative charge to the particles entrained in the gas. These negatively charged particles are then attracted to a grounded collecting surface, which is positively charged. The gas then leaves the box, up to 99.9% cleaner than when it entered.

Inside the box, the particles from the continuing flow of dust build up on the collection plates or tubes. At periodic intervals, the plates in a Dry ESP are rapped, and the tubes in a Wet ESP are flushed, causing the particles to fall into the collection hopper. In a Dry ESP the particles are usually removed from the hopper by a rotary screw arrangement. In a WET ESP the hoppers are designed to gravity drain or pump the flush water to designated treatment or disposal.