Effects of particle properties on entrainment and electrostatics in gas-solid fluidized beds

The effects of particle properties on particle entrainment and electrostatic charges in fluidized beds of binary mixtures of fines (glass beads, polyethylene or alumina) with coarse particles (glass beads or polyethylene) were investigated in a column of 150 mm inner diameter and 2 m height. The degree of electrification in the bed was measured by collision ball probes of 53 mm O.D. at three levels, directly connected to electrometers. The charge density of entrained particles in the freeboard was measured by a freeboard sampler acting as a Faraday cup. The magnitude of electrostatic charges inside the fluidized bed increased slightly, whereas the entrainment flux decreased, as the size of the coarse particles decreased at constant superficial gas velocity. The electrostatic charges increased and entrainment flux decreased as the coarse particle density increased. The charge magnitude inside the fluidized bed increased and the entrainment flux decreased as the fine particle density increased. The electrostatic charges and entrainment flux also increased as the fines concentration increased. The fines concentration had little or no effect on fines charge densities. Bipolar charging was observed in all experiments, with fine particles charged positively and large ones negatively. (C) 2015 Elsevier B.V. All rights reserved.