Filtration of electrified solid particles

The filtration of electrified solid particles in a fixed bed of sand was carried out. The particles were electrified by impacting them against an obstacle. This was done in a controlled way, so that several levels of charging could be attained. The collection of the charged particles took place in a cylindrical filter 0.15 m in diameter and three bed heights (0.01, 0.02, and 0.04 m) tall. Phosphatic concentrate particles with a mean diameter of 5.2 μm were utilized as the test powder. The results have shown that the presence of electrostatic charges can alter significantly the filtering behavior of the granular bed. The measured penetration of particles through the bed in the initial stages of the filtration was compared to the theoretical prediction, and the discrepancies suggest that the effect of electrostatic charges is stronger in the larger particles (>3 μm). As filtration progresses, the effect of charges is strongly felt, as the increase in the pressure drop caused by the deposited particles becomes less pronounced with increasing particle charge. In some cases, an increase in the penetration of particles is observed. The relation between particle charge and filtering behavior was not linear: the bed penetration increased, passed through a maximum, and then decreased with increasing particle charge, and the pressure drop behaved accordingly. The measurement of charge distribution between the particles revealed the presence of both positively and negatively charged particles, with the predominance of the former, which resulted in a positive mean charge for the aerosol. This distribution was affected by the level of charging and seems to be responsible for the nonlinear behavior of the filter.