Collection efficiency in a three-dimensional randomly arranged dual-layer granular bed filter

Abstract The dual-layer granular bed filter packed with randomly arranged granules was simulated to study the effects of bed depth of the lower layer of fine granules and the inlet gas velocity on the collection mechanism. The computational results show that the collection efficiency is much better from this granular bed than a single-layer granular bed, especially for particle diameters of 1–10 μm. The inlet gas velocity has less effect on the grade collection efficiency of the dual-layer granular bed than of the single-layer granular bed. The dual-layer granular bed provides a high collection efficiency and low pressure drop. The relationship between the grade collection efficiency and the Stokes number ( St ) based on the inlet gas velocity is obtained. If St is below a threshold, the grade collection efficiency remains stable; if St is in value above threshold, the grade collection efficiency increases linearly with lg( St ). As the bed depth of the lower layer of fine granules increases, the threshold for St shifts forward.