Lucian Dascalescu

NO/sub x/ removal process using pulsed discharge plasma

Nonequilibrium plasma can be used to promote chemical reactions that reduce the emission of gaseous pollutants, such as NO/sub x/, produced by coal-burning power plants or by diesel engines. Laboratory experiments were carried out to study the decrease of NO/sub x/ in simulated flue gases (initial concentration of NO: 200 to 800 ppms, O/sub 2/: 10%; N/sub 2/ was the balance gas) by means of a pulsed-discharge plasma generated in a cylinder-type reactor (outer electrode; 20 mm diameter). A rotary spark gap provided square-wave high voltages up to 25 kV, at a frequency of 250 Hz, to corona electrodes of 0.1, 3.3, and 6.4 mm diameter. The tests were performed at various temperatures (ambient to 220 degrees C) and constant residence time (0.6 s). The removal performance depended on the size of the discharge electrode and was better at room temperature. The addition of C/sub 2/H/sub 4/ significantly enhanced the removal performance; the concentration of NO/sub x/ decreased from 800 ppm to 300 ppm in the discharge. The by-products of this process were analyzed using infrared spectroscopy. No traces of toxic gases could be detected. >

Charging of particulates in the corona field of roll-type electroseparators

The physics of corona charging phenomena is of paramount importance for the development of such electrotechnologies as precipitation of dust, spraying of powders and selective sorting of particulate mixtures. This study focused on the use of corona discharge in electroseparation processes. Crude theoretical evaluations pointed out that the required corona current density and high-voltage level in this application depend on various factors, such as material characteristics, feed rate and configuration of the electrode system. Experiments carried out on a laboratory roll-type electroseparator demonstrated the capability of a new corona electrode design to generate an extended and quasi-uniform corona field. Stable corona discharges were obtained when energizing that electrode at both positive and negative polarities from a reversible non-filtered full-bridge high-voltage rectifier. The voltage-current characteristics of the corona discharge from the new electrode were determined under various operating conditions: (i) without material in the inter-electrode gap; (ii) with a monolayer of a 50% aluminium-50% polyvinyl chloride particulate mixture on the surface of the grounded electrode; (iii) with a similar monolayer of metallic particles (99% aluminium); and (iv) with a layer of insulating particles (99% polyvinyl chloride). In each case, attention was paid to the upper acceptable limit of operating voltage, as well as to some side effects of corona discharges, such as audible noise and ozone generation. The efficacy of corona charging was assessed by electroseparation tests involving two groups of particulate materials: (i) barley grains, impurified with weeds and soil particulates; and (ii) granular mixtures of metals and plastics, yielded by chopping electric wire and cable scrap. Several practical considerations were formulated, based on a critical evaluation of the experimental results.

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. >

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.

Numerical analysis of the electric field of roll-type electrostatic separators☆

Abstract 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. Levins “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.

Tribocharging and electrostatic separation of mixed granular solids in fluidized bed devices

Granular materials, when fluidized by air or other gaseous medium, acquire electrostatic charge by inter-particle and particle-wall collisions. The effectiveness of particle tribocharging achieved with such fluidization process is crucial for establishing the feasibility of electrostatic separation of mixed granular solid wastes in the recycling industry. The present paper aims at a crude evaluation of the effects of the main factors that influence the efficiency of such a tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on binary mixtures taking combinations of two of the three polymeric materials in different tests: (a) virgin polyamide, (b) polycarbonate and (c) polyacetal granules. The variables investigated were the duration of the tribocharging process, the level of the high-voltage applied to the electrode and the composition of the mixture. The analysis of the experimental data revealed the effects of each variable on the mass and the charge of the granules collected at the electrodes.

Fluidized Bed Device for Plastic Granules Triboelectrification

The study of the triboelectrification process is the key factor to the successful industrial application of electrostatic separation in the field of plastics recycling. Therefore, the aim of the present work is to evaluate an original device for the laboratory study of this process. The original design of the fluidized bed type triboelectrification device has the following distinctive features: (i) transparent walls to observe the fluidization process and the particles moving in the triboelectrification module; (ii) air distributors with different mesh apertures correlated with granule size; (iii) quick replacement of the triboelectrification Plexiglas chamber with other metallic (aluminium, copper) or nonmetallic chambers (polyvinyl chloride—PVC, polyethylene—PE, and polyethylene terephthalate—PET); (iv) possibility of independent operation, for granule charge measurement or integrated operation, for the electrostatic separation experiments using a free-fall electrostatic separator. The results of charge measurement experiments pointed out the different triboelectric behaviour of two types of granules (polystyrene and low-density polyethylene) in contact with the walls of the device. The electrostatic separation experiments carried out on a binary mixture of mm-size polystyrene/polyethylene granules confirmed the effectiveness of the triboelectrification device.