Plate-type Electrostatic Separator Research Articles

Experimental and numerical evaluation of two electrode systems for plate-type electrostatic separators

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and non-conductive granular materials. The separation generally takes place in the electric field generated between an elliptical electrode, which is connected to a high voltage supply, and a grounded S-shaped electrode. The aim of the present work is to evaluate the separation performances attainable with another electrode system, consisting of two metallic plates, a short one that is connected to the high-voltage and a long one that is grounded. The experiments are carried out with a mixture of mm-size granules of copper and PVC, originating from mechanically processed electric wire wastes. The results of the composite factorial experimental designs performed for each of the two electrode systems are quite similar. The numerical modelling and simulation of the electric field and of particle trajectories explain the experimental findings and support the practical recommendations regarding the industrial application of the two electrode systems.

Optimization of metals and plastics recovery from electric cable wastes using a plate-type electrostatic separator

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and non-conductive granular materials. The aim of this work is to identify the optimal operating conditions of such equipment, when employed for separating copper and plastics from either flexible or rigid electric wire wastes. The experiments are performed according to the response surface methodology, on samples composed of either “calibrated” particles, obtained by manually cutting of electric wires at a predefined length (4mm), or actual machine-grinded scraps, characterized by a relatively-wide size distribution (1–4mm). The results point out the effect of particle size and shape on the effectiveness of the electrostatic separation. Different optimal operating conditions are found for flexible and rigid wires. A separate processing of the two classes of wire wastes is recommended.

Optimal Operation of a Plate-Type Corona-Electrostatic Separator for the Recovery of Metals and Plastics from Granular Wastes

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and nonconductive granular materials. Unfortunately, the purity of the conductive products is often compromised by the fact that the trajectories of the nonconductive granules cannot be controlled. The aim of the present work is to validate a relative simple solution to this problem: subjecting the granules to a corona discharge during their sliding down the plate electrode. This discharge does not affect the conductive granules but charges the nonconductive ones, so that the electric force would tend to pin them to the surface of the grounded electrode. In this way, the friction forces between the granules and the plate increase and the inertia forces decrease. Design of experiments methodology is employed to identify the optimum high-voltage, relative position of the electrodes, and configuration of the collector. The conclusions of this study served at the optimum design of an industrial corona-assisted plate-type electrostatic separator for the recycling of metals and plastics from granular electric cable wastes.

Processes for sustainable development using high-intensity electric fields

Intense electric fields up to 107 V/m generate very interesting and useful applications for the environment. Several processes using high electrical voltage for environment preservation were developed in the laboratory. The purpose of this study was to review these applications, highlighting their economic and environmental benefits: (1) electrostatic separators of particles used in industrial wastes recycling; (a) role-type electrostatic separator for granular mixtures of plastic–metal particles; (b) free-fall and rotating belt triboelectric separators for mixtures of plastic–plastic particles; (c) plate-type electrostatic separator for mixtures of metal–metal particles, (2) electrostatic precipitators for gas cleaning and (3) ozone generators for air and water treatment.

Genetic algorithm‐optimised charge simulation method for electric field modelling of plate‐type electrostatic separators

A novel combination of genetic algorithms (GAs) and the charge simulation method (CSM) is proposed for enhancing the computation precision of electric fields associated with plate-type electrostatic separators; a new recycling technology of electrical and electronics waste. An algorithm is developed to, automatically, arrive at optimal arrangement of the simulating charges and their locations in order to eliminate dependency on user judgment and experience. Accurate results for electric field computation, compared with earlier published techniques, are realised for several design parameters of the separator. Experiments carried out for determination of detachment fields of small metallic particles (steel spheres of radius 0.501 mm) confirmed validity of the numerical simulation. The present work shows that the coupled GA-CSM algorithm can be an efficient and flexible design tool for accurate field computation of electrostatic separation equipment.

Enhancing selectivity of plate-type electrostatic separators using non-dominated sorting genetic algorithms (NSGA-II)

The paper presents a novel application of non-dominated sorting genetic algorithms NSGA-II to optimise the performance of plate-type electrostatic separator; an environmental friendly technique for selective sorting of conductive from nonconductive constituents of a granular mixture. As several decision variables control detachment of the particles from the plate; hence the separator's selectivity, NSGA-II is applied to determine their optimal values subject to simultaneous satisfaction of two proposed objective functions. These functions aim to maximise the separation distances, while maintaining the detachment fields, for different species. A GA-optimised charge simulation algorithm was developed to enable computations of detachment fields and positions of the particles. Two extreme solutions encompassing the other Pareto results are examined and analysed. The study illustrates the applicability of NSGA-II in solving the complex multiobjective optimisation problem of electrostatic separators in order to facilitate new development and designs of this environmental friendly technology.

Removal of Metallic Particles From Acrylonitrile Butadiene Styrene Wastes Using Electrostatic Separation Methods

Electrostatic separation techniques have been widely used in the recycling industry. The aim of this paper is to assess the possibility of employing them for the beneficiation of the newest and fastest growing category of wastes: the “end-of-life” information technology equipment. The study was performed on samples extracted from a granular acrylonitrile butadiene styrene (ABS) product obtained after the disassembling and shredding of information technology wastes. The samples that typically contained less than 0.1% metals in weight were processed in a laboratory electrostatic separator that enabled the reproduction of the two most important electrode configurations employed in the industry. The design-of-experiments methodology was employed for evaluating the effects of the various electrical and mechanical control variables on the outcome of the separation process. The reported data demonstrate that, by the appropriate adjustment of the input variables of either a plate-type electrostatic separator or a roll-type corona-electrostatic installation, it is possible to remove all the metallic particles from the ABS product, while keeping at a minimum the quantity of plastics lost in the rejected conductive fraction.

Statistical Control of Electrostatic Separation Processes

The aim of this article is to point out the characteristics of Shewhart and CUSUM charts when applied to electrostatic separation processes and validate their ability to detect special events that may be indicators of out-of-control situations. This article also shows how the effectiveness of statistical process control (SPC) can be improved by using the cumulative sum (CUSUM) chart. Experiments were carried out with a mixture of bronze and aluminum particles (size range: 1-2 mm) by using a plate-type electrostatic separator. The mobile-average Shewhart and CUSUM charts were established based on 20 electrostatic separation tests performed under optimal operating conditions. An out-of-control situation was simulated, and the response of the process was analyzed with both types of charts. The small-shift process response was detected only on the CUSUM chart. See “Nomenclature” for the nomenclature used in this article.

Séparateurs électrostatiques des particules. Application à la récupération des déchets industriels

Electrostatic separation is a generic term given to a significant class of technologies of industrial waste processing, widely used for the sorting of granular mixtures due to electric forces acting on particles whose average size is approximately 5 mm. The paper describes three electrostatic processes of separation depending on the granular mixture: 1) role-type electrostatic separator: used to sort mixtures of metal/plastic particles (copper/PVC for example); 2) plate-type electrostatic separator: used to sort mixtures of metal/metal particles (copperllead for example); 3) free fall electrostatic separator: used to sort mixtures of plastic/plastic particles (PVC/PE for example).

Behavior of Conducting Particles in a New Electrostatic Separator with Two High-Voltage Electrodes

The objective of this work was to analyze the behavior of good conducting granules in a newly designed plate-type electrostatic separator. Commercial software was employed for the numerical analysis of the electric field generated by an original electrode configuration. This enabled the evaluation of the electric charge and forces on conducting particles. The trajectory of a single particle was calculated over a set of 1300 points. The simulated results show that the trajectories depend on the applied voltage, the radius, and the mass density of the granules. They were found in good agreement with the experiments carried out on a laboratory electrostatic separator.

Electrostatic separators of particles: Application to plastic/metal, metal/metal and plastic/plastic mixtures

Electrostatic separation is a generic term given to a significant class of technologies of industrial waste processing, widely used for the sorting of granular mixtures due to electric forces acting on particles whose average size is approximately 5mm. The focus of this paper is on three electrostatic processes of separation used for processing of different types of mixtures: (i) role-type electrostatic separator, used to sort mixtures containing metal/plastic particles (copper/PVC for example); (ii) plate-type electrostatic separator, used to sort mixtures containing metal/metal particles (copper/lead for example) and (iii) free-fall electrostatic separator, used to sort mixtures of plastic/plastic particles (PVC/PE for example). Experiments carried out on industrial samples using laboratory electrostatic separators confirm the efficiency of these processes and show that the processes can improve the recovery and purity of products resulting from industrial wastes.

Separation of Fine Granular Mixtures in S-Plate-Type Electrostatic Separators

Plate-type electrostatic separators are commonly used for the selective sorting of conductive from nonconductive constituents of a granular mixture. This paper addresses the more delicate issue of granular materials that are characterized by finite nonzero resistivities. The study was conducted with three materials having similar granule size range and specific weight but slightly different electrical properties. Two sets of experiments were performed for evaluating the effect of electrode geometry on the behavior of each of the materials. These results were then employed for predicting the outcome of the electrostatic separation of binary mixtures of good and poor conductors. A third set of experiments validated the predictions and pointed out a couple of nonelectric factors that might deteriorate the performance of a plate-type electrostatic separator in an industrial environment.

Numerical computation of conducting particle trajectories in plate-type electrostatic separators

Development of new applications of plate-type electrostatic separators need increased controllability of particle trajectories. The aim of this paper is to model the particle behavior after lift-off from the plate electrode. A superficial charge simulation program was employed for the computation of the electric field in the active zone of the separator. This enabled the evaluation of the charge acquired by a conducting particle in contact with the plate electrode and the electric force exerted on it before and after detachment. Based on a previously derived mathematical model, the particle trajectories were calculated for various electrode configurations. The data of such numerical simulations can guide the experimental studies needed for the assessment of new industry applications of electrostatic sorting or classifying techniques.

Premises for the numerical computation of conducting particle trajectories in plate-type electrostatic separators

Increasing the controllability of particle trajectories is a crucial issue in the development of new industrial applications of plate-type electrostatic separators. The relative position of the electrodes and the applied high-voltage are the two factors that influence the magnitude of the electric force exerted on the particles composing a given granular mixture. The aim of the paper is to model the particle behaviour after lift-off from the plate electrode. A program based on the boundary element method was employed for the computation of the electric field in the active zone of the separator. This enabled the evaluation of the charge acquired by a conducting particle in contact with the plate electrode and the electric force exerted on it before and after detachment. An algorithm is proposed for the computation of particle trajectories for various electrode configurations, as a step towards complete feasibility studies concerning new industry applications of electrostatic sorting or classifying techniques.

Numerical analysis of the electric field in plate-type electrostatic separators

The high intensity of the electric field of a plate-type electrostatic separator depends on the shape, size and relative position of the electrodes. An extended zone of quasi-uniform intense electric field may contribute to a significant improvement of the eletrostatic separation efficiency. In this paper, the analysis of the electric field was carried out using Prof. Levin's “Charge Simulation Program”, which is based on the boundary element method and is provided with advanced pre- and post-processing capabilites. Several electric field configurations were studied. The circular profile tubular high-voltage (“active”) electrode was shown to generate an intense electric field on only 2/3 of the grounded (“passive”) electrode. Two cylindrical “active” electrodes might improve the situation. By using an ellipse profile tubular “active” electrode the resulted electric field was more uniform and the separation efficiency could be expected to increase. A good agreement was found between the theoretical predictions and the results of a simple experiment. A laboratory plate-type electrostatic separator was built in conformity with the design suggested by the results of this work.

Modelling of conducting particle behaviour in plate-type electrostatic separators

The charging of conductive particles in contact with an electrode affected by a non-uniform electric field is a physical mechanism of paramount importance for various electrostatic technologies, including the separation of particulate mixtures. The aim of this paper is to model the behaviour of such charged particles in plate-type electrostatic separators. A computer program based on the boundary element method enabled the evaluation of the electric field strength at the surface of the plate electrode of these installations. The results of field computation were then employed for estimating the charge of perfectly-conducting spherical particles, as well as their position on the plate electrode, at the moment of detachment under the action of the electric force acting on them. The data reported in the paper point out the following factors which affect particle detachment and hence the efficiency of the electrostatic separation: the size and specific mass of the particles; the slope of the plate electrode; the dimensions and relative position of the high-voltage electrode; and the level of the high voltage applied to the electrode system. Experiments carried out with two kinds of particles (silver-plated polyamide spheres of radius 1.5 mm and mass 0.0192 g; and steel balls of radius 0.2-0.25 mm and average mass 0.000 45 g) confirmed the conclusions of numerical simulations. The modelling of particle behaviour in contact with plate electrodes facilitates the feasibility studies and can guide the experimental tests, which are needed for the development of any new application of the electrostatic separation method.