(425h) Investigation of Electrostatic Reduction in Gas-Solid Fluidized Bed By In-Situ Corona Charge Eliminator

When particles are fluidized, they acquire electrostatic charges due to impacts and frictions. The accumulation of excess electrostatic charges in fluidized bed reactors (FBRs) can cause problems such as particles agglomeration, wall sheets and even an unscheduled shutdown. Reduction of the electrostatic charge accumulation can prevent these issues. This study develops a technique called In-situ Corona Charge Eliminator (ICCE), based on the mechanisms of gas corona discharging and particle corona charging, for reducing electrostatic charge in FBRs. The experiment was carried out in a 420 mm internal diameter plexiglass fluidized bed, with LLDPE particles and dry air as the fluidized particles and gas respectively. The electrostatics in the fluidized bed at various superficial gas velocities (0.2~0.7 m/s) were first characterized in multiaspect, such as electrostatic potential, particle charge-to-mass ratio and electric field strength, by means of electrostatic probe, faraday cup and field meter respectively. The results show that the axial electrostatic potential in the bubble column, particle specific charge and electric field strength in the dilute phase increased with increasing gas velocity. At small gas velocities, the particles in the fluidized bed were bipolar charged, with negative charged particles at the bottom and positive charged particles at the top. However, polarity reversal was observed for the bottom particles at large gas velocities. Moreover, six corona electrodes were installed on the inner wall of fluidized bed and the electrostatic charge level was found to be significantly reduced by ICCE. The polarity of the particle charge reversed under the action of ICCE at low gas velocities due to limited charge accumulation on particles caused by impacts and frictions. With increasing gas velocity, the charge accumulation on particles increased obviously due to strengthened impacts and frictions. Therefore, electrostatic charge was partially reduced at large gas velocities by the same setting of ICCE as used at lower gas velocity. The results indicate that ICCE is an effective and promising technique for reducing electrostatic charges in FBRs.