Experimental analysis of a vibrating tribocharging device of plastic particles for free-fall triboelectric separator

The selective sorting of mixed granular plastics can be achieved by tribocharging them in a vibrated parallelepiped chamber of variable height prior to introducing them in a free fall electrostatic separator. Although such vibrating tribochargers are currently used in industry, no experimental investigation of these devices has been carried out, yet. The objective of this work is to characterize this class of tribochargers by estimating both the electric charge imparted to the granules and the electrostatic separation efficiency. The granular product (a mixture of high-density poly-ethylene - HDPE - and poly-vinyl-chloride - PVC) is introduced through a funnel into the vibrating chamber, where the particles get triboelectrically charged by undergoing collisions between themselves and with the walls of the device. The obtained results showed that the efficiencies of both the charging and the separation depend on the geometry and the operating conditions of the tribocharger (height, length. inclination angle, motor speed). Charge per mass ratios beyond 3 nC/g have been easily attained and the efficiency of the separation was excellent: more than 90% of the HDPE and PVC in the feed are recovered at the outlet of the installation.