電界を印加した粒子充填層による帯電微粒子の捕集

抄録

Regulations for small dust particles in exhaust gases are getting more and more stringent because epidemiologic studies have revealed the hazards of suspended particulate materials (SPM) in ambient air. Dust particles were electrically charged with unipolar ion flow from a barrier discharging electrode and then collected in an electrified packed bed, i.e., a packed bed to which a strong electric field is applied. The collection efficiency of the electrified packed bed turned out very high, namely, the efficiency for submicron particles was higher than 99% for a bed of 8 cm high packed with 3 mm alumina spherical particles. The electric field across the bed was 3 kV/cm, the superficial velocity, 0.63 m/s with 0.43 kPa pressure drop.

To examine refreshment and regeneration of used packed beds, soil dust (Kanto loam, JIS No.11) and DEPM (diesel exhaust particulate matter) were collected continually in the electrified packed bed until the collection efficiency deteriorated appreciably. Then the bed was backwashed with fresh air blows, which blew three times for one second at a superficial velocity of 2.5 m/s. The backwashing was effective for soil dust, but wasn’t for DEPM (tar and soot) because the electric resistivity of the packed bed could not be recovered enough by the backwashing.

As is well known, DEPM is oxidizable by ozone and radicals generated from electric plasma. The suitable temperature for the chemical reaction is believed to be higher than 150℃, preferably 250℃. In this experiment, however, the temperature of the bed was kept below 70℃ because the bed container was made of transparent plastics. Nevertheless it was found that some chemically active species (probably OH radical) generated from the barrier discharging electrode helped to oxidize DEPM.