Mechanism and control of electrification in pneumatic conveying of powders

This paper describes the mechanism and control of electrification in pneumatic conveying of powders by both numerical and experimental approaches. A three-dimensional discrete element method (DEM) was used to analyze the particle movement (collision velocity, number of collision, etc.) in a pneumatic conveying process under various operating conditions. A simplified model that assumed the electrification of a single particle to be proportional to the vertical collision velocity and the number of collision against the pipe wall was proposed and the electrification during conveying of powders was numerically computed. The electrification of particles during the pneumatic conveying was also measured and then compared with the calculated results to confirm the validity of the proposed model. A novel electrostatic charge control system comprised corona discharge neutralizer, electrostatic filed strength sensor, and computer control system was developed and applied to the powder pneumatic conveying process. Dynamic characteristics of electrostatic charge and its elimination process through the corona discharge neutralizer were analyzed. Based on these characteristics, a simplified transfer function composed of first-order lag element including dead time was proposed and optimal control parameters for digital PID (proportional-integral-differential) control was determined. Performance of the control system was also investigated experimentally. It was found that the electrostatic charge in the pneumatic conveying process was completely self-controlled. (c) 2005 Elsevier Ltd. All rights reserved.