Studies of Dust Cake Formation and Structure in Fabric Filtration

摘要

Measurements with composite fabrics in which the upstream layer had a very low packing density (i.e., low fiber volume fraction) support the hypothesis that pressure drop reduction by means of electrical stimulation is due to preferential formation of the dust cake in the region of low packing density. The interdependence of electrical stimulation of fabric filters and intensity of cleaning by reverse-air flow has been studied. While standard commercial felts and woven glass fabrics show only a moderate response to cleaning vigor, pressure drop across the napped felts exhibits a strong dependence on both applied voltage and reverse-air velocity. In order to determine whether effects of fiber cross-sectional shape on filtration performance were mainly mechanical or electrostatic in origin, filter felts were made with round or lobed cross-section fibers and were coated with gold. The hypothesis that effects due to fiber geometry have a large electrostic component is thus reinforced. The stability of the dust cake also appears to depend on electrostatic forces. Theoretical studies of capture on single fibers in an electric field have revealed the axial polarization effects, frequently ignored in similar studies, can overwhelm the effects of the more commonly studied radial polarization.