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 particle (diameter <0.1 μm) capture under controlled conditions. Corona currents were measured under various applied voltages for a one- and two-stage mode of operation. The corona current was observed to decrease at the higher gas velocities because fewer ions reached the collector surface. The presence of the particles (NaCl and Al₂O₃) in the ESP resulted in a decrease in the corona current due to a reduction in ion emissions. Collection efficiencies were measured under various operating conditions and it was found that lower electrical resistivity of particles resulted in the decrease of collection efficiency because of reduced attractive force at collector surfaces after deposition. A decrease in collection efficiency was observed (both in a one- and two-stage ESP for different kinds of particles, NaCl, Al₂O₃, and SiO₂) with the reduction in particle size below 0.1 μm. A statistical approach for particle-charging process, which assigns discrete charge levels to particles with the same size, in conjunction with the transport equation was used to support the experimental observations. This approach of fractional charging was more accurate than an assumption of uniform particle charging.