(84f) Electrostatic Phenomenon in Gas-Liquid-Solid Fluidized Beds

One of the major problems in fluidized beds is particle agglomeration. A number of factors are involved in the formation of particle agglomerates, with electrostatic charges being one key factor. It has been observed that electrostatic forces induced by the charges carried by particles change the hydrodynamics of the fluidized bed system. This phenomenon is predominant when dielectric materials (e.g. polyethylene and polystyrene particles) are used.

Traditionally, the electrostatic phenomenon has been studied mostly in gas-solid fluidized beds, particularly in polymer reactors. In gas-solid systems, electrostatic charges are generated through various mechanisms such as triboelectrification, ion collection, thermionic emission, and frictional charging and can cause particle agglomeration and hazardous electrical discharges. However, little is known regarding the electrostatic phenomenon in fluidized bed systems with dielectric liquids. Industries have recently reported newly discovered problems of static control in liquid-hydrocarbon-polymer particle systems, particularly occurring during polyethylene production.

In this study, electrostatic charging in liquid-solid and gas-liquid-solid fluidized beds is investigated using an electrostatic detector, which can be directly inserted into the bed. A liquid with low dielectric constant and low viscosity is selected for the experiments. Various particles including glass beads, polyethylene resins, and porous alumina particles are used to investigate the effect of solid loading, liquid and gas velocity, and dielectric characteristics of particles on the electrostatic charging phenomenon in fluidized beds. It is found that the dielectric constants and viscosities of the liquids strongly influence the electrostatic phenomenon in liquid-solid or gas-liquid-solid fluidized beds. Both particle chain and cluster formations are observed during fluidization. From the controlled experimental studies, it is found that higher gas and liquid velocities, larger solid loading, and lower dielectric constants of particles result in a higher level of charge accumulation in fluidized beds. Several methods of static control including adding humidity and adding group C particles were investigated for its effectiveness in lowering charge accumulation in fluidized beds.