Relevant parameters involved in tribocharging of powders during dilute phase pneumatic transport

This work presents the results of an experimental study carried out on the tribo-charging of fine glass particles during their pneumatic conveying. The effect of several parameters such as the chemical nature of the transport pipe, the particles mean size, the solids flow rate, the air velocity and the relative humidity (RH) was examined. Experiments were carried out using several batches of monodisperse glass particles with mean particle sizes ranging from 75 mu n to 500 mu m. Both spherical and angular particles were used. Powders were conveyed through two types of pipe materials (Teflon and Nylon) at dilute loadings and varying relative humidities of air (0-90%). The total charge of conveyed powder was measured using a terminal Faraday cage. Furthermore, a series of four Faraday cages was used to measure the charge transfer between the wall and particles along the flow path. Greater electrostatic effects were observed for larger particles, higher air velocities, higher solids flowrate and lower RH. A simple model of charge transfer was also established in order to describe the time evolution of charges on the particles and the wall. Results showed that the tribocharging rate can be conveniently represented by an exponential-deceleration model. (C) 2011 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.