(70bn) Control of Electrostatic Discharge by Using Feedback Control Type Ionizer for Powder Handling Process

To prevent dust explosions and fires, such as those that occur in large silos as a result of electrostatic discharges (ESD), we have developed a new feedback control-type ionizer (feedback control system) that controls and manages the electrostatic charge in powder. The feedback control system is composed mainly of an ionizer, an electrostatic field strength sensor, and computer control equipment. In this study, we evaluated experimentally the practical version of the feedback control system through several tests at a pneumatic powder transport facility. As powder, polypropylene (PP) pellets with a mean particle size of 3 mm were used in this experiment. The electric field strength in the loading pipe inside the silo was measured with an electrostatic field sensor, which was attached to the down side of the ionizer (flange type) at a distance of 0.01 m. The specific charges of the falling powders in the silo were also measured using a Faraday Cage. The results of the experiment revealed that the feedback control system had the following characteristics: (1) it was possible to control the performance of the ionizer with a supply current; (2) the electrostatic field strength in the loading pipe from the charge powder was reduced and maintained at near zero by using the feedback control system; and (3) the performance of the feedback control system was superior to that of others, such as AC- or DC-type ionizers. The details and results of the experiment are presented in this paper.