Experimental Study on a New Dual-Layer Granular Bed Filter for Removing Particulates

A new dual-layer granular bed filter for hot gas cleanup was invented and studied experimentally. Fine sand, 0.5–1 mm grain size and about 1350 kg/m3 bulk density, was used as the lower layer of the filter. Expanded perlite particles, 2–5 mm grain size and about 70 kg/m3 bulk density, was used for the upper layer of the filter in this study. It was confirmed that the sizes and densities of these two media matched well; the binary media remained in complete segregation during regeneration by fluidization. Test results show that the filtration of the expanded perlite particle layer was characterized as “deep bed filtration.” Filtration of the fine sand layer was “surface cake filtration.” The expanded perlite particle layer contributed about 90% to the bed dust capacity, but only about 20% to the total bed pressure drop, which increased the bed dust capacity ten fold compared to a single-layer bed of the same sand and the same total bed pressure drop. The dust cake on the surface of the fine sand layer raised the collection efficiencies to over 99.99%.