Roman Morar

Corona and electrostatic electrodes for high-tension separators

Abstract A systematic reseach has been performed, aiming at the optimization of the corona and electrostatic electrodes of roll-type high-tension separators for mixed granular solids. The theoretical analysis of corona-charging and charge-neutralization processes has led to a crude evaluation of the electrical parameters (corona current per unit of length, power of the corona discharge) which should characterize the electrodes for a certain application. Computer modelling of the electric field has enabled the formulation of several design principles, which have been fully-verified by the experiments. Laboratory tests have been carried out in order to compare the various technical solutions and to state some criteria for electrode evaluation. The preliminary reports on the industrial application of the suggested electrode designs are extremely encouraging.

Charges and forces on conductive particles in roll-type corona-electrostatic separators

Mathematical modelling is a powerful tool in the optimization of electroseparation technologies and equipment. This paper proposes the use of a numerical method of field analysis to evaluate more accurately the charges and forces on millimeter-size conductive particles of virtually any shape in contact with an electrode. A program based on the boundary-element method was tested for this purpose, and provided the input data to an algorithm for the computation of particle trajectories. The results were in good agreement with the observations made on a laboratory electroseparator. The effect of space charge on the behavior of conductive particles was studied with a three-electrode system (a grounded grid, between a corona electrode and a metallic plate, energized by two high-voltage supplies of opposite polarities). The accuracy of numerical simulations of electroseparation processes is expected to increase when a mathematical model of particle motion in DC corona fields will be incorporated in the existing computer programs. >

Corona - electrostatic separators for recovery of waste non-ferrous metals

Abstract This paper presents a series of roll-type electroseparators conceived by High-Intensity Electric Fields Research Laboratory of the Polytechnic Institute of Cluj-Napoca in the last twelve years. The multifunctional ILES-1 and ELSEP corona-electrostatic laboratory separators have been used to study the electro-separability of metallics (copper and aluminium) from chopped wire and cable scrap and to optimize the operating conditions. A comparison is made between the current-voltage characteristics of wire-, needles-, and blade-type electrodes. The theoretically-established design criteria (the polarity of the d.c. high-voltage generator, the setting of the active electrodes, the speed and the radius of the roll) were experimentally confirmed and then used for developing ELSIM-series industrial electroseparators, fabricated by “ELECTROMURES” Company of Tirgu Mures.

Factors which influence the insulation-metal electroseparation

Abstract The experimental study of insulation-metal electroseparation as a multifactorial process has been performed by means of a console-type laboratory apparatus, with four high-voltage electrode carriers, interchangeable roll electrodes, and a set of collecting boxes. The paper illustrates how an electroseparator like this can be employed by research-, design- or application-engineers to investigate the role of each parameter or operating variable. It was revealed the influence exerted on the process by: (i) the homogeneity (composition, granulometric distribution) and the superfacial moisture of the feed material; (ii) the positioning of the corona electrodes and the type of their emitting elements. A special study, based on a charge simulation program, was devoted to the shape, size and location of the electrostatic electrode. The interdependence between the electrical and mechanical factors, such as roll speed and roll radius, are distinctively discussed, with reference to an experiment made with a sample of chopped electric wire and cable scrap, containing stranded and massive copper, polyethylene and polyvinyl chloride. Several technical solutions suggested by the authors (corona electrodes with radially-orientated emitting wire segments, non-circular electrostatic electrode) have been adopted by the recycling industry.

ELECTROSTATIC SEPARATION OF INSULATING AND CONDUCTIVE PARTICLES FROM GRANULAR MIXES

Abstract Electrostatic separation is extensively used for the selective sorting of granular mixtures, by means of the electric forces which act on charged or polarized bodies. The roll-type separator with combined corona-electrostatic field has been proved to be the most advantageous solution when the purpose is to isolate conductive particles from non-conductive ones. The paper presents the contributions of the High Intensity Electric Fields Laboratory of the Technical University of Cluj-Napoca to the development of this solution for various industrial applications. The first chapter is devoted to the theoretical analysis of the phenomena and points out the multitude of factors which influence the efficiency of the separation process. A special attention is paid to the study of the corona charging conditions of insulating particles. In the second and third cahpters, the authors show how the results of numerical modeling guided the design of new equipment and the optimization of their operating conditions...

Tribocharging of Granular Plastic Mixtures in View of Electrostatic Separation

The output of any electrostatic separation process is strongly dependent on the effectiveness of particle charging. A novel laboratory-scale fluidized-bed tribo-charging device has been described in a previous paper. The aim of the present work is to asses the effectiveness of two materials, aluminium and polypropylene, that could be employed for the manufacturing of the tribo-charging chamber of that device. The electrostatic separation experiments designed in this purpose were carried out on three samples of a granular polyethylene/polyvinyl chloride mixture, characterized by different compositions. Aluminium and polypropylene were found to be equally effective for the tribo-electrostatic separation of the 50% PVC, 50% PE sample. For the other two samples (10% PVC, 90% PE; 90% PVC110% PE), the best results were obtained with the polypropylene tribo-charging chamber.

Optimal high-voltage energization of corona-electrostatic separators

The selection of the high-voltage supply can play an important role in the optimization of electrostatic separation processes. This paper aims to evaluate the influence of the main high-voltage parameters (waveform, polarity, level) on the efficiency of electrostatic separation, in the case of insulation-metal granular mixtures. A roll-type laboratory high-tension separator was employed for the experimental study, and the tests were carried out with samples of granular materials taken from the technological flowsheet of a recycling plant for electric wire scraps. The oscillograms of the voltage and of the current across the separator proved to be of great use for studying the transition from corona to spark discharges. The experiments, performed under various operating conditions (roll speed, roll radius, high-voltage level, interelectrode distance), show the existence of a strong interdependence between these parameters, the frequency of spark discharges, and the efficiency of the separation process. The reported results suggest that monitoring the frequency of the spark discharges could be of use for controlling the optimum operating voltage for a given electrostatic separation application. Although the full-wave rectifier allows for lower operating voltages than the half-wave rectifier, its general effectiveness in electrostatic separation processes is superior. Good insulation-metal electrostatic separation can be achieved at either positive or negative polarity of the high-voltage supply, but negative electrode energization is recommended for most industrial applications.

Corona–Electrostatic Separation: An Efficient Technique for the Recovery of Metals and Plastics From Industrial Wastes

Better management of secondary resources, such as copper, aluminium and plastics from electric wire and cable waste requires improved methods of processing of reusable materials. This paper presents three typical examples of recycling technologies, each of them using the capability of electric fields to sort metallic and insulating materials from granular mixture. The efficiency of corona–electrostatic separation as a basic operation of a recycling flowsheet has been demonstrated for feedrates not exceeding 200 kg/hour. At the same time, it has been proved that electroseparation can represent a complement to conventional air–gravity separation of metals and insulators from industrial wastes. The in–plant tests provided useful information for a customs–design of corona–electrostatic separators.

High-voltage supplies for corona-electrostatic separators

The selection of the high-voltage supply can play an important role In the optimisation of electrostatic separation processes. The present work aimed to evaluate the influence of the main high-voltage parameters (waveform, polarity, level) on the efficiency of electroseparation, in the case of insulation-metal granular mixtures. A roll-type laboratory electroseparator was employed for the experimental study and the tests were carried out with granular materials prelevated from the technological flowsheet of a recycling plant for electric wire scraps. The experiments shown the existence of a strong interdependence between the level of the operating voltage and the other electrical parameters, Although the full-wave rectifier allows for lower operating voltages than the half-wave rectifier, its general effectiveness in electroseparation processes is superior. The optimum operating voltage of an electroseparator seems to be slightly lower than the level at which the frequency of the spark discharges tends to exceed 60 min/sup -1/. The oscillograms of the voltage and of the current across the separator proved to be of great use for studying the transition from corona to spark discharges. Good insulation-metal electroseparation can be achieved at either positive or negative polarity of the high-voltage supply, but negative electrode energization is recommended for most industry applications.

Influence of material superficial moisture on insulation-metal electroseparation

The efficiency of separating by electrostatic means the constituents of a polyvinyl chloride (PVC)-metal granular mixture depends on the moisture content of the materials. Laboratory research has been carried out to determine the acceptable superficial humidity of the granules to be separated. The experimental study has been implemented on a roll-type laboratory separator with a corona electrostatic field. Ten samples of 50% PVC and 50% aluminum or copper, with a moisture content in the range W=0-0.9%, have been identically processed. Several diagrams show the influence of the humidity on PVC and metal recovery from the granular mixture. It is found that efficient PVC-metal separation can be obtained for a moisture content of less than 0.3%. Experimental results are qualitatively discussed on the basis of the electrical charge of the PVC grain, the time constant of the discharge process, and the electric image force.<<ETX>>