Experimental and theoretical studies of ultra-fine particle behavior in electrostatic precipitators

A cylindrical electrostatic precipitator (ESP) was used to investigate the applied voltage versus corona current characteristics and ultra-fine partic le(diameter < 0.1 mu m) capture under controlled conditions. Corona current s were measured under various applied voltages for a one- and two-stage mod e of operation. The corona current was observed to decrease at the higher g as velocities because fewer ions reached the collector surface, The presenc e of the particles (NaCl and Al2O3) in the ESP resulted in a decrease in th e corona current due to a reduction in ion emissions. Collection efficienci es were measured under various operating conditions and it was found that l ower electrical resistivity of particles resulted in the decrease of collec tion efficiency because of reduced attractive force at collector surfaces a fter deposition. A decrease in collection efficiency was observed (both in a one- and two-stage ESP for different kinds of particles, NaCl, Al-2 O-3, and SiO2) with the reduction in particle size below 0.1 mu m. A statistical approach for particle-charging process, which assigns discrete charge leve ls to particles with the same size, in conjunction with the transport equat ion was used to support the experimental observations. This approach of fra ctional charging was more accurate than an assumption of uniform particle c harging. (C) 2000 Elsevier Science B.V. All rights reserved.