Set Point Identification and Robustness Testing of Electrostatic Separation Processes

Identification of the optimal operating conditions and evaluation of their robustness are critical issues for the industrial application of electrostatic separation techniques. In spite of extensive investigations performed in recent years, no standard procedure is available for guiding the research of the set point and for minimizing the process sensibility to changes in certain critical factors. The aim of this paper is to formulate a set of recommendations regarding the choice of high-voltage, roll-speed, and feed-rate values for an important class of electrostatic separation applications: the selective sorting of conductive and nonconductive constituents of granular industrial wastes. The experiments were carried out on a laboratory separator, built by one of the authors, with various samples of chopped wire wastes furnished by l'Entreprise des Industries des Cacircbles, Biskra, Algeria. Several one-factor-at-a-time experiments, followed by two factorial designs (one composite, the other fractional), were performed based on the following three-step strategy: 1) identifying the domain of variation of the controlled variables; 2) finding the best choice of the set point; and 3) assessing the robustness of the process, i.e., testing whether the performance of the system remains satisfactory even when the factors vary slightly around that point. The results presented in this paper are strictly valid only for a well-defined category of processed materials, but a similar approach could be adopted for a wider range of electrostatic separation applications