Electrostatic charging phenomenon in gas–liquid–solid flow systems

Abstract

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 hazardous. Work on understanding and, hence, preventing the electrostatic charging phenomena has mostly focused on gas–solid media. Relatively little study has been 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 was explored. Two different charge-reducing methods were also evaluated. Based on experimental studies, it was found that the superficial gas and liquid velocities have a significant effect on the rate of charge generation and transfer in a three-phase fluidized bed because of variation in the frequency and the intensity of the particle collisions. The local number density of the particles also affected the distribution of the electrostatic signal obtained. Two methods of reducing electrostatic charge accumulation were also investigated: adding fine powder and adding an anti-static agent such as Larostat 264A. When 15 wt% of fine glass powder was added to an air-Norpar15-HDPE (high density polyethylene) fluidized bed, the charge inside the fluidized bed was reduced by 72%. When, on the other hand, as little as 0.5 wt% of the anti-static agent, Larostat 264A in a liquid form, was added to the air-Norpar15-HDPE, the electrostatic level was quickly reduced by 83% and within 1 h the electrostatic charge was completely eliminated from the system.