Experimental and Numerical Modeling of a New Tribo-Electrostatic Separation Process for Granular Plastics Mixtures

Abstract

The paper aims at optimizing the operation of a free-fall electrostatic separator equipped with a novel tribo-charging device for the processing of granular plastic mixtures. Experiments were performed with a mixture of polycarbonate and polyamide granules (cylinders of 1.5 mm in diameter and 3 mm in length). The samples of granules to be charged were introduced in the gap between the two co-axial cylinders of the tribo-charging device, and were put into turbulent motion for 30 s by two oppositely oriented air jets (pressure: 2 bar). Then, the charged particles were left to fall freely between the vertical plate electrodes of an electrostatic separator. A composite experimental design enabled the modeling and optimization of the tribo-electrostatic separation process as a function of the following control factors: applied high voltage, inter-electrode distance, and the inclination angle of the feeding device. Under optimal conditions, the purity obtained is close to 99%. A numerical model of particle trajectories confirms the conclusions of the experimental study. The simulations point out the effect of each control variable on the outcome of the separation process.