IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 40, NO. 1, JANUARY/FEBRUARY 2004 53 Optimization of Electrostatic Separation Processes Using Response Surface Modeling Lucian Dascalescu, Senior Member, IEEE, Amar Tilmatine, Florian Aman, and Michaela Mihailescu Abstract—The efficiency of electrostatic separation processes depends on a multitude of factors, including the characteristics of the granular mixtures to be sorted, the feed rate, the configu- ration of the electrode system, the applied high voltage, and the environmental conditions. The possibility of optimizing the op- eration of industrial electrostatic separators using rather simple computed-assisted experimental design techniques has already been demonstrated. The aim of the present work is to analyze the peculiarities of application of a more sophisticated group of response surface experimental design techniques that make use of quadratic functions for modeling the electrostatic separation process. One unique contribution to this work is to consider the economic value of the process in addition to the technical result. The 11 electrostatic separation tests, corresponding to a central composite design, were carried out on samples of chopped elec- tric wire wastes. The CARPCO laboratory roll-type electrostatic separator employed for this study enabled a rigorous control of two factors: the applied high-voltage level and the speed of the rotating roll electrode. The objective was to maximize the benefits from the recycling of both constituents of the binary copper–polyvinyl chloride granular mixture. The optimum op- erating conditions computed with the quadratic model derived from the experimental results were in good agreement with the data of pilot-plant tests. Thus, the highest extraction of useful materials was obtained at high voltage and low speed, while the optimum conditions for greatest economic value were found to be high voltage and high speed. The response surface methodology can be easily applied to most of the industrial applications of electrostatic separation technologies. Index Terms—Design of experiments, electrostatic separation, experimental modeling, response surface method. I. INTRODUCTION E XTENSIVE laboratory and pilot-plant experimentation is needed for the development of a new electrostatic separa- tion application (Fig. 1) [1]–[6]. The efficiency of the separation process depends on the characteristics of the granular mixtures to be sorted, the feed rate, the configuration of the electrode Paper MSDAD-A 03–14, presented at the 2001 Industry Applications So- ciety Annual Meeting, Chicago, IL, September 30–October 5, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Electrostatic Processes Committee of the IEEE Industry Applications Society. Manuscript submitted for review October 15, 2001 and released for publication October 9, 2003. L. Dascalescu is with the Electronics and Electrostatics Research Unit, LAII- ESIP, UPRES-EA 1219, University Institute of Technology, 16021 Angoulême Cedex, France (e-mail: ldascalescu@iutang.univ-poitiers.fr). A. Tilmatine was with the Electronics and Electrostatics Research Unit, LAII- ESIP, UPRES-EA 1219, University Institute of Technology, 16021 Angoulême Cedex, France. He is now with the Faculty of Electrical Engineering, University of Sidi-Bel-Abbes, 22000 Sidi-Bel-Abbes, Algeria. F. Aman is with HAMOS GmbH, 82377 Penzberg, Germany. M. Mihailescu is with the High-Intensity Electric Fields Laboratory, Tech- nical University of Cluj-Napoca, 3400 Cluj-Napoca, Romania. Digital Object Identifier 10.1109/TIA.2003.821812 Fig. 1. Constituents of the granular mixture subjected to separation: (a) polyvinyl chloride and (b) copper. system, the applied high voltage, and the environmental con- ditions [7], [8]. In some cases, mathematical models of the mul- tifactorial electrostatic separation process [9], [10] can be used for estimating the values of the input variables that are likely to optimize the response. Nevertheless, the optimum of the process is usually obtained only after an impressive number of tests (up to several hundreds, in the case of the electrostatic separation of complex minerals [3]). In spite of the fact that the electrostatic separation of polyvinyl chloride (PVC) wire insulation from copper con- ductor (Fig. 1) is an already classical application [8], each new type of electric cable waste necessitates the tuning of process parameters. The experimental design techniques [12]–[15] enable the choosing of the proper number of tests and the conditions of accomplishing them, in order to attain a well-defined objective. They contribute to reducing the costs, as well as the time consumed for experiments. With such techniques, all the relevant factors of a process are varied simultaneously over a set of planned experiments. The results are connected by a mathematical model that is subsequently used for interpretation, prediction, and optimization. Thus, the investigators can identify the input variables that have a real 0093-9994/04$20.00 © 2004 IEEE