Electrostatically enhanced stainless steel filters: Effect of filter structure and pore size on particle removal

The goal of this study was to investigate the effect of using stainless steel fibrous and porous filters as the ground electrode of a point-to-plate electrostatic precipitator on particle penetration. The effect of filter medium structure and pore size on particle removal has been investigated as a function of particle size for particles in the range of 0.03 to 1 mum and filter face velocities in the range of 15 to 75 cm/s. Furthermore, the effect of filter thickness on penetration reduction was investigated in order to develop a better understanding of the relationship between the filtration depth, filter face velocity, and particle size for each filter. Seven different filters were tested. Four of the filters were made of 316L SS sintered metal fibers and three were made of 316L SS metal powders. The pore sizes of these filters ranged from 6 mum to 100 mum. The application of the electrical field decreased particle penetration by a factor of 6 to 54, depending on filter type and filtration velocity, with higher reductions achieved at lower filtration velocities (e.g., 15 cm/s). Particle penetration did not depend significantly on particle size. Our experiments also showed that submicrometer particles are captured in the first few layers of the filters by the action of electrostatic forces. The effect of particle loading on particle penetration was also investigated at a filter face velocity of 75 cm/s. Contrary to the electrically active fibrous filters (electret), the accumulation of particles up to 25 g/m(2) did not create "back corona," which would substantially decrease the collection efficiency of the grounded filter. By comparison, the performance of electrically active fibrous filters has been shown to rapidly degrade as particle loading exceeds 2-3 g/m(2).