Penetration mechanisms in periodically-cleaned woven fabric filters

The two objectives of this study were to (1) investigate the penetration mechanisms of a periodically-cleaned woven fabric filter typical of fabrics used to collect fly ash from coal-fired power plants, and (2) examine the effects of filtration velocity and inlet particle size on the penetration levels of this fabric. The results of five different test methods indicated that the dominant source of penetration was from pinhole leaks in the dust cake and supporting fabric. These tests were performed under a variety of operating conditions, with filtration velocities from 0.64 to 2.91 m/min and inlet particle sizes from 3.3 to 8.5 μm mass mean diameter (MMD). Using a bench scale test facility and sections of previously conditioned filter bags, it was found that there was a critical mass mean diameter between 5.5 μm and 7.5 μm, where fly ashes less than this value penetrated the fabric at a relatively constant rate independent of the dust loading added to the fabric. Penetration, Pn, of a 7.5 μm MMD fly ash decreased exponentially as the dust loading added to the filter increased. These test results differ from previously reported bench scale data where a rapid decrease in penetration early in the filtration cycle changed to a constant or steady-state emission. The initial fabric penetration (Pn_O) was found to be exponentially increasing with increasing filtration velocity (V). This relationship between Pn_O and V was observed for 3.3, 5.5 and 7.5 pm mass mean diameter fly ashes.

With a pilot scale facility, it was determined that the initial penetration exponentially increased as the inlet fly ash mass mean diameter decreased.