Collection of Aerosol Particles by Electrostatic Droplet Spray Scrubbers

Abstract

Theoretical calculations and experimental measurements show that the collection of small aerosol particles (0.05 to 5 micron diameter range) by water droplets in spray scrubbers can be substantially increased by electrostatically charging the droplets and particles to opposite polarity. Measurements with a 140 acfm two chamber spray scrubber (7 seconds gas residence time) showed an increase in the overall particle collection efficiency from 68.8% tit uncharged conditions to 93.6% at charged conditions, with a dioctyl phthalate aerosol (1.05 μm particle mass mean diameter and 2.59 geometric standard deviation). The collection efficiency for 0.3 μm particles increased from 35 to 87% when charged. During 1973–1974 a 1000 acfm pilot plant electrostatic scrubber was constructed inside a 40 ft trailer for evaluation on controlling particu-late emissions from pulp mill operations (funded by Northwest Pulp and Paper Association). Field tests performed on the particle emissions exhausting from SO₂ absorption towers treating the gases from a magnesium based sulfite recovery boiler have shown particle collection efficiencies ranging from about 60 to 99% by weight, depending on the electrostatic scrubber operating conditions. Energy requirements for the University of Washington electrostatic scrubber are about 0.5 hp/1000 acfm (350 Watts/1000 acfm) including gas pressure drop, water pressure drop, and electrostatic charging of the water spray droplets and the particles.