• Energy Research

The movement of the powdery material occurs in a multi-phase non-uniform electrostatic field at determined values of the voltage and the frequency, using travelling wave technique. This technique was applied for very small particles such as bacteria and other similar particle size. The objective of this work is to analyze the movement of PVC micronized particles and the feasibility of the separation of PVC/copper granular mixture of average size 100 μm. Two-phase and three-phase conveyors, which are supplied by high voltage amplifiers controlled by digital function generators, have been the subject of a parametric experimental investigation. Several factors were analyzed such as the voltage level up to 1400 V, the frequency, the phase shift and the number of phases of the conveyor. The obtained results showed that depending on the values of the above factors: i) the micronized particles can move instantly right after switching the conveyor, ii) the particles move towards one direction or the other of the conveyor iii) the separation of a granular mixture of plastic and copper micronized particles is possible.

Electrostatic charge generated by friction is well known but poorly understood. The aim of this study is to evaluate the effects of various factors involved in the frictional conformal-contact. The study focused on the tribocharging process between two polymer slabs. As it is a multi-factorial process with several interacting variables, the experimental design methodology was employed for its modeling. Three factors were taken into consideration and their domains of variation established as follows; contact force, from 2 to 10 N; charging time, from 10 to 290 s and the frequency of back-and-forth sliding motion, from 0.5 to 1.5 Hz. The distribution of the electric charge at the surface of polymers was measured by the auto-compensated inductive probe connected to an electrostatic voltmeter. A mathematical model allowing the evaluation of the effects of the various factors and of their interactions was obtained. A comparison between the triboelectic behavior of PTFE, PVC and ABS was made. It was found that electric potential increases with the contact force and the charging time, but decreases with the frequency of the back-and-forth sliding motion.

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and nonconductive granular materials. Unfortunately, the purity of the conductive products is often compromised by the fact that the trajectories of the nonconductive granules cannot be controlled. The aim of the present work is to validate a relative simple solution to this problem: subjecting the granules to a corona discharge during their sliding down the plate electrode. This discharge does not affect the conductive granules but charges the nonconductive ones, so that the electric force would tend to pin them to the surface of the grounded electrode. In this way, the friction forces between the granules and the plate increase and the inertia forces decrease. Design of experiments methodology is employed to identify the optimum high-voltage, relative position of the electrodes, and configuration of the collector. The conclusions of this study served at the optimum design of an industrial corona-assisted plate-type electrostatic separator for the recycling of metals and plastics from granular electric cable wastes.