Collection of fine particles in electrostatic precipitators : influence of EHD induced agitation and of particles disintegration

The paper focuses on two particular phenomena which contribute to the poor collection efficiency of fine particles (from ~ 0.1 μm to ~ 2 μm) by electrostatic precipitators (ESPs). After considerations on the influence of turbulence which tends to decrease the collection rate, a conjecture is recalled on the action of the charged fine particles which is expected to give the main contribution in the generation of small eddies in ESPs. Results are presented of an experimental study of the collection efficiency η of cigarette smoke. The efficiency is found to decrease as the dust concentration is increased and the efficiency decrease is attributed to the increase in eddy diffusivity. The second phenomenon observed in the study is the disintegration of agglomerates in the ESP. A marked agglomeration process occurs because the smoke is kept in a big balloon during a few minutes; this agglomeration is more and more marked as the smoke concentration is raised. When charged in the ESP, some of the agglomerates disintegrate under the Coulomb repulsion, which increases the apparent collection efficiency η of the bigger particles (> ~ 0.6 μm) but clearly decreases η for the smaller ones (< ~0.5 μm).