Improved Overall Performances of a Tribo-Aero-Electrostatic Separator for Granular Plastics From Waste Electric and Electronic Equipment

The two-conveyor-electrode tribo-aero-electrostatic separator patented in 2010 was designed to sort granular mixtures of insulating materials in a fluidized bed subjected to an electric field perpendicular to the direction of the fluidizing air. The prototype has proven its efficiency for the separation of insulating granules ≤ 2 mm, attaining excellent recovery rates. Its performances were less satisfactory for larger particles (2-5 mm). The objective of this work is to evaluate three modifications of the construction of this device, in order to increase the hourly throughput and improve the purity of the products, by controlling the charge acquired by the granules and the electric field intensity. Numerical simulations enabled the optimization of the electric field distribution in the active zone of the separator, and an experimental study was carried out, in order to identify the best conditions for granule charging by triboelectric effect. The tests were carried out for four configurations of the electrode system, by using a mixture of acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS) originated from grinding out-of-use computer cases. The typical granule size was 2-5 mm. The experimental approach validated a change in the position of the fluidized bed, with respect to the conveyor electrodes, to increase the residence time of the granular materials and hence the amount of electric charge acquired by each particle. In order to intensify the electrical field, two solutions were tested and validated: 1) add a grounding electrode in the proximity of the high-voltage electrodes; 2) dispose vertically the high-voltage electrodes. For the tested materials, the vertical arrangement of the electrodes gave the best hourly throughput rates and purity of the separated products.