Study on filtering characteristics of aerosol particulates in a powder-grain dual-layer granular bed

Here we investigated the filtering characteristics of a powder-grain dual-layer granular bed filter to improve its filtration efficiency in an experimental granular bed filter apparatus (inner diameter, 100 mm) with aerosol particles generated by firing a smoke agent. The concentration and size distribution of the aerosol particles upstream and downstream of the granular bed filter were detected using a Welas 3000 aerosol particle size spectrometer. Filtration experiments were performed in a powder layer bed, an expanded perlite particle layer bed, and their combined layer bed consisting of a lower layer of heavy powder and an upper layer of expanded perlite particles, respectively. At the superficial filtration velocity of 0.1 m/s, the filtration efficiency of a 3.0-mm-thick, 0.074-0.10 mm powder layer bed was 96.240%, while that of a 150-mm-thick, 113-1.00-mm expanded perlite particle layer bed was 89.905%. At the same superficial filtration velocity of 0.1 m/s, the powder-grain dual-layer granular bed filter achieved a filtration efficiency of 99.835%, and the growth rate of the pressure drop with filtration time was similar to that of the single expanded perlite particle layer bed, and much lower than that of the single powder layer bed. These results fully demonstrate the filtering characteristics of high efficiency and low pressure drop increasing rate of cascade filtration in the powder-grain dual-layer granular bed filter. (C) 2014 Elsevier B.V. All rights reserved.