Neutralization of Electrically Charged Insulating Materials Using Various AC Voltage Waveforms

During certain electrostatic process, insulating materials acquire large amounts of electric charge, and retain them longer than necessary. These static charges are accompanied by electrostatic nuisances that must be taken into account as early as during the design phase of a new process. The objective of this study was to investigate the various factors that can impact the performance of a commercial neutralizer in eliminating residual static charge on mm-size insulating granules originating from shredded waste electric cables. The study was carried out using a commercial charge neutralizer supplied from a sinusoidal, square or triangular alternating voltage generator. The granules were charged in a roll-type electrostatic separator equipped with a dual corona electrode system. The effectiveness of the neutralization was evaluated by calculating the ratio between the charge and the mass before and just after neutralization. The effectiveness of neutralization depends on the waveform, the frequency and the amplitude of the applied AC voltage, as well as on the inter-electrode distance. The results show that an excellent neutralization (up to 90%) can be obtained for each of the three AC voltage waveforms by appropriately adjusting the neutralization parameters.