Hybrid electrostatic filtration systems for fly ash particles emission control. A review

The removal of submicron and nanoparticles from flue gases emitted by coal fired boilers is the subject of extensive studies in recent years. Electrostatic precipitators and fibrous filters are the most commonly used gas cleaning devices for the removal of these particles in power plants and industry. However, the collection efficiency of electrostatic precipitators decreases for particles smaller than 1 gm. Fibrous filters provide higher filtration efficiency for particles of this size, but the pressure drop is higher, and additional energy is needed to supply the outlet fan. Recently, special attention of engineers has been given to hybrid constructions, which apply electrostatic fields and forces in order to improve the performances of bag filters. There are three types of such solutions, which have been investigated in the literature: (1) electrically energized filter, in which fibres of the filter are energized by an electric field; (2) hybrid electrostatic filter, which applies electrostatic charging of particles before their filtration by bag filter; and (3) hybrid electrostatic precipitator, which uses a conventional electrostatic precipitator for the removal of coarse particles, and a subsequent bag filter for the removal of fine particles leaving the precipitator. All of these constructions allow the collection efficiency for PM2.5 particles to be increased and the pressure drop across the bag filter to be reduced. In this paper, various hybrid electrostatic filtration systems have been reviewed and their performances compared with respect to the collection efficiency, pressure drop and dust cake dislodging.