(259d) Electrostatic Charging Phenomenon in Gas-Liquid-Solid Flow Systems

During the operation of multiphase systems such as fluidized beds, electrostatic charges are generated when the materials involved are dielectric in nature. The accumulation of electrostatic charges within the system can be operationally hazard. Work on understanding and hence preventing the electrostatic charging phenomena has mostly focused on the gas-solid media. Relatively little is performed on particulates and multiphase systems with non-conductive liquids as the medium. In this study, electrostatic charging in gas-liquid-solid fluidized beds with liquid as the continuum phase under different operating conditions is explored. Two different charge-reducing methods are also evaluated. Based on the experimental studies, it is found that the superficial gas and liquid velocities have a significant effect on the rate of the charge generation and transfer in a three-phase fluidized bed through varying the frequency and the intensity of the particle collisions. The local number density of the particles also affects the distribution of the electrostatic signal obtained. The methods of reducing electrostatic charge accumulation are also investigated by considering two approaches: adding fine powder and adding an anti-static agent such as Larostat 264A. When 15 wt% of fine glass powder is added to an air-Norpar15-HDPE (high density polyethylene) fluidized bed, the charge inside the fluidized bed is reduced by 71.4 %. The added fine powder can not only reduce the electrostatic charge but also affect interparticle forces, such as van der Waals forces, thereby altering the fluidization behavior. When, on the other hand, as little as 0.5 wt% of the anti-static agent, Larostat 264A in a liquid form, is added to the air-Norpar15-HDPE, the electrostatic level is very quickly reduced by 82.9 % and within one hour the electrostatics completely is vanished from the system.