Laboratory studies, confirmed by field studies at both large and small scales, elucidated behavior of a granular panel bed for gas filtration with accumulation of filter cakes on gas-entry surfaces (filtering occurring by a sieving mechanism). Filtration is cyclic: intermittently, flow of dusty gas is interrupted, and the panel is subjected to a sharp "reverse" puff of gas (a "puffback"), producing a body movement of sand toward gas-entry faces, dumping both dust cake and a relatively small quantity of sand from each face. (c) 2005 Elsevier B.V. All rights reserved.