Electrostatics in gas-solid fluidized beds for different particle properties

Electrostatics in fluidized beds of glass beads and polyethylene resins of different physical and chemical properties were investigated in a fluidization column of 150 mm inner diameter and 2.0 m height. Eight collision ball probes at different levels and radial positions measured the degree of electrification. For Geldart group B particles, the degree of electrification increased slightly with decreasing particle size. Charging for group A particles was significantly greater than for group B particles. For binary mixtures, the degree of electrification increased as the proportion of small (65 mu m) particles increased. Bipolar charging was observed in all experiments where polyethylene resin particles constituted the bed materials, with large particles charging negatively, and fine particles positively. The effect of adding fine (<30 mu m) glass beads on electrostatics in a fluidized bed of relatively large (574 mu m) glass beads was also studied. As the proportion of fines increased from 0.0 to 2.0 wt%, the degree of electrification decreased, charge fluctuations decreased and the bed exhibited smoother fluidization. Particles entrained in the freeboard were charged oppositely to those in the bed. The degree of electrification decreased as the proportion of Larostat 519 increased from 0.0 to 0.5 wt%, but increased when the wt% of Larostat reached 1.5%, probably due to the tendency of Larostat particles to adsorb water and agglomerate. Entrained Larostat particles carried the same charge polarity as the large particles in the bed. (c) 2012 Elsevier Ltd. All rights reserved.