Electric charge neutralization of granular materials using an air-assisted ionizer under different operational conditions

Abstract

An operation of electric charge neutralization is often integrated in complex electrostatic separation processes targeted at the selective sorting of the constituents of granular mixtures in a wide range of industrial applications. The aim of the present work is to prove the possibility of increasing the charge elimination efficiency of a commercial air-assisted neutralizer, under various dynamic conditions simulating realistic industrial scenarios. Three experimental setups were tested. In the first one, particles were charged by triboelectric effect and then transported by a grounded metallic conveyor belt before being subjected to ionic bombardment from the commercial neutralizer. The second configuration employed a custom-designed rotating-roll corona-electrostatic separator. Particles were charged by corona discharge and then transported on the rotating roll electrode before being neutralized by an air-assisted ionizer installed opposite the roll electrode. In the third experimental configuration, the neutralization system was installed downstream from the particle detachment step of the second configuration. After being dislodged from the grounded rotating drum by a mechanical brush, the charged insulating particles fell freely under gravity through the ionization zone. This zone comprised the commercial ionizing neutralizer positioned opposite a grounded rectangular metal plate. The factors investigated were the applied voltage (U_n) and the distance (d_n) between the neutralizing electrode and the grounded (belt, roll, the plate) electrode, as well as the air velocity (v). The findings highlight the substantial role of airflow in enhancing ion dispersion and promoting charge neutralization, particularly through its interaction with the electric field geometry and particle dynamics. For instance, residual charge-to-mass ratio dropped to as low as 1–2 nC/g in the first configuration at air velocity of 2 m/s. This study clearly demonstrates the critical importance of finely tuning geometry, electrical field strength, and air dynamics to optimize electrostatic neutralization. These findings provide valuable guidelines for designing more efficient electrostatic separation systems, particularly for industrial recycling processes involving insulating materials.