Numerical Modeling of Insulating Particles Trajectories in Roll-type Corona-Electrostatic Separators

The trajectories of the insulating particles in roll-type corona-electrostatic separators depend on the configuration of the electrode system, the applied high voltage, the roll speed, the size of the particles and the relative humidity of the ambient air. The aim of this work was to point out how numerical modeling can be of use in the study of the effects of these factors. Particle charging is modeled using the Pauthenier's equation for spheres in uniform electric field. The equation of particle discharging was obtained after an experimental study of the surface potential decay of a granular layer of insulating material in contact with an electrode. The trajectories are computed based on the balance equation of the electrical and mechanical forces that act on such charged particles. The numerical results are in good agreement with the experimental findings.

I. Introduction

Electrostatic separation is an effective technology for recovering metallic and insulating materials from granular industrial wastes [1], [2], [3]. The particles to be sorted are deposited by a vibratory feeder on a grounded rotating roll electrode, which introduces them in a zone of an intense electric field created by one or several high voltage electrodes. One of the electrodes creates a corona discharge that charges all the particles by ion bombardment. The insulating particles adhere to the surface of the roll electrode under the effect of the electric image force, while the conducting ones are charged by electrostatic induction and projected towards the static electrode of opposite sign [4]–[9].