In a double-stage unit electrostatic precipitator, the charging and collection steps take place within two different regions. They have been used primarily for control of finely divided liquid particles and controlling solid or sticky materials is usually difficult. Therefore, double-stage electrostatic precipitators have limited use for particulate emission control.
The ionizing stage consists of a series of small positively charged wires equally spaced from parallel ground tubes that charges the particles suspended in the air flow through the ionizer. The second stage consists of parallel metal plates less than 1 in apart.
The liquid particles receive a positive charge in the ionizer stage and are collected at the negative plates in the second stage. Collected liquids drain by gravity to a pan located bellow the plates.