Experimental Analysis of a Vibrating Tribocharging Device of Plastic Particles for a Free-Fall Electrostatic Separator

The selective sorting of mixed granular plastics can be achieved by tribocharging 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, which is a mixture of high-density polyethylene (HDPE) and polyvinyl 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 charging and separation depend on the geometry and the operating conditions of the tribocharger (height, length, inclination angle, and motor speed). Charge per mass ratios beyond 3 nC/g have been easily attained, and the efficiency of the separation is excellent: more than 90% of the HDPE and PVC in the feed have been recovered at the outlet of the installation.