Effects of Pressure, Temperature, and Gas Velocity on Electrostatics in Gas-Solid Fluidized Beds

The influences of operating pressure, temperature, and gas velocity on the degree of electrification in a fluidized bed of glass beads and different grades of polyethylene resin 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 in the bed. Faraday cups also measured the charge density in the bed by taking samples from three different online sampling ports at different levels. The degree of electrification increased as pressure increased from 1.0 to 8.0 bar, probably due to an increase in bubble rise velocity, frequency, and volume fraction. The maximum static charges were found at approximately two-thirds of the bed height and near the axis. As the pressure increased, particle-particle and particle-wall collisions near the distributor and wall contributed heavily to static charge generation. At higher temperatures (up to 75 degrees C),, the bed exhibited smoother fluidization. Temperature played a significant role in determining electrostatic charging. As the superficial gas velocity increased from 0.23 to 0.40 m/s, the degree of electrification increased. However, at higher gas velocities, the polarity in the freeboard region was opposite to that in the bed, indicating that fines entrained from the column carried charges, resulting in a net charge of polarity opposite to that inside the bed.