Overview of electrostatic devices for control of submicrometer particles

The electrostatic precipitator (ESP) is the most widely used of a family of air pollution control devices that primarily exploit electrical forces in the control of particulate emissions. Others are the space-charge precipitator (SCP) (where the electric precipitation field is generated by the particles being collected), the self-agglomerate (SAG) (where oppositely charged particles are induced to agglomerate by the mutual force of attraction), the charged-droplet scrubber (CDS-I) (where drops charged to one polarity collect pollutant particles charged to the opposite polarity), charged-droplet scrubber (CDS-II) (where bipolar drops collect oppositely-charged fine pollutant particles), and charged-drop precipitators (CDP) (where fields generated by charged drops are used to precipitate like-charged fine particles onto electrodes). Using gas-residence time for effective cleaning as a dominant criterion, a broad overview of the relative merits of each of these systems in the control of submicrometer particles is given. Experiments illustrate the SCP and SAG modes. The CDS and CDP configurations are modeled and tested in experiments designed to isolate the relevant collection processes. The characteristic-time approach to interrelating diverse systems identifies the electrofluidized bed (EFB) as yet another configuration, one that is especially attractive for obtaining high efficiency with extremely short residence times.