SUBMICRON PARTICLE AGGLOMERATION AND PRECIPITATION BY USING A BIPOLAR CHARGING METHOD

The collection efficiency of modern electrostatic precipitators (ESP) is very high except for that of submicron particles. To improve the collection efficiency of fine particles, it is considered to use an electrostatic agglomeration technique. This technique is to produce larger particles by collision of oppositely charged fine particles under Coulomb force. In this paper, a two-stage ESP with a bipolar charging section is proposed and the fundamental characteristics of agglomeration and precipitation of submicron particles are studied. The ESP consists of a bipolar charging section and an electric field section. Smoke particle trajectories are observed and particle size distributions are measured with the charging voltage and the electric field strength as parameters. Moreover, particle charges are calculated by using a corona field calculation method and theoretical particle trajectories are compared with experimental results. As a typical result, 0.3-1 mum particles decrease to only 18% (75% without bipolar charging), while 1-5 mum particles increase to about 82% (25% without bipolar charging). The mean diameter of smoke particles with electrostatic agglomeration increases two times compared to that of non-agglomerated particles. The collection efficiency for submicron particles is about 80% under an optimum condition.