Mohamed Miloudi

Experimental Comparative Study of Different Tribocharging Devices for Triboelectric Separation of Insulating Particles

Several tribocharging devices are commonly used for charging insulating particles in order to separate granular plastic mixtures using a vertical triboelectric separator. However, there is no comparative analysis of these devices when tribocharging is achieved using identical samples of insulating particles. The objective of this paper is to carry out an experimental study that compares several tribocharging devices built up in the laboratory: a rotating cylinder, a tribo-cyclone, a static tribocharger, a propeller-type unit, and a fluidized bed. The study was performed using two granular samples of polyvinyl chloride (PVC) and high-density polyethylene (HDPE), for two different particle sizes: 1 and 2 mm. Experimental results showed that, when tribocharging pure samples of either PVC or HDPE, tribo-cyclone is the most efficient. However, when mixed samples are processed, the fluidized bed device gives the best results in terms of electric charge and separation efficiency.

Experimental investigation of a new tribo-electrostatic separation process for mixed fine granular plastics

Triboelectrostatic separation of millimeter-size particles is a well-known process, which is widely used in the recycling industry. However, when processing fine particles with an average diameter of 0.1 mm or less, this technique is still inefficient. The aim of this paper is the experimental investigation of a patent-pending triboelectrostatic separation process based on a fluidized bed tribocharging system where the fine granules to be sorted are exposed to the electric field generated between a pair of rotating metallic disks connected to two high-voltage supplies of opposite polarities. The lower parts of the disk electrodes are immersed in the fluidized bed. The experiments were carried out on a granular mixture composed of fine white and gray PVC particles of average size 20 μm. The particles to be separated are positively and negatively tribocharged using the fluidization air provided by a variable-speed blower, and then they are pinned to the disk electrodes of opposite polarities. The separation outcome, in terms of recovery and purity, is highly efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the interelectrode gap, the thickness of the fluidized bed, and the fluidization rate.

Optimization of Belt-Type Electrostatic Separation of Triboaerodynamically Charged Granular Plastic Mixtures

Electrostatic separation is frequently employed for the selective sorting of conducting and insulating materials for waste electric and electronic equipment. In a series of recent papers, the authors have presented several novel triboelectrostatic separation installations for the recycling of the main categories of plastics contained in information technology wastes. The aim of the present work is to optimize the design and the operation of such an installation, composed of a belt-type electrostatic separator associated to a propeller-type tribocharging device. The experimental design method is employed for modeling and optimizing the separation of a mixture of high-impact polystyrene and acrylonitrile butadiene styrene granules originating from shredded out-of-use computer cases. A distinct experiment is carried out on three synthetic mixtures of virgin plastic granules: 75% polyamide (PA)+ 25% polycarbonate (PC), 50% PA+ 50% PC, and 25% PA + 75% PC. The best results are obtained for the mixtures containing equal quantities of the two constituents.

Optimisation of belt-type electrostatic separation of granular plastic mixtures tribocharged in a propeller-type device

Electrostatic separation has already proven its efficiency as a method to recover metals and plastics from granular waste electrical and electronic equipment (WEEE). Nevertheless, there still is some work to do regarding the sorting of the various sorts of plastics (ABS, ABS-PC, HIPS, PC) contained in information technology wastes. The main objective of this paper is to optimize the electrode configuration and the operation of a belt-type electrostatic separator employed in conjunction with a new tribo-aerodynamic charging device. This application is particularly designed for the recovery of granular materials issued from shredding of computer cases, which contain large quantities of ABS. The following control variables were considered for the optimization: (i) distance between the axis of the high-voltage electrode and the surface of the grounded belt electrode; (ii) angular position of the high-voltage electrode with respect to the horizontal plane; (iii) high-voltage level. Experimental design methodology was employed for determining the optimum value of each variable, using commercial software (MODDE, Umetrics, Sweden).

Experimental Investigation of Electrostatic Separators of Plastic Particles using Different Charging Devices

Tribo-electrostatic separation is a clean technology that enables the recycling of plastics contained in granular waste of electric and electronic equipment (WEEE). The granules are first charged using a tribocharging device and then separated in a horizontal intense electric field generated between two vertical electrodes energized with two high-voltage supplies of opposite polarities. The aim of this paper is to perform a comparison between three different tribocharging devices commonly used: the fluidized bed, the static charger, and the tribo-cyclone. The study was carried out using the same granular sample comprising 50% PVC (Polyvinyl chloride) and 50% HDPE (High-density polyethylene) particles of 1–2 mm average granulometric size. In spite that particles acquire higher electric charge using the cyclone device, separation efficiency is better with the fluidized bed device.

Experimental Modeling of a New Triboelectrostatic Separation Process for Mixed Granular Polymers

Recycling of plastics from industrial wastes requires appropriate sorting technologies, such as the free-fall electrostatic separation of tribocharged granular materials. This paper introduces a novel electrostatic separation process characterized by the fact that the granules to be separated are charged in a fluidized bed affected by an electric field generated by two rotating roll electrodes. The experimental design methodology was employed for the modeling and optimization of the separation of a mixture composed of acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS), originating from shredded obsolete computer cases. After processing the experimental data using the MODDE 5.0 software, the masses of ABS, HIPS, and middling collected after separation were expressed as quadratic functions of three of the control variables of the process: 1) duration; 2) speed of the fluidization air; and 3) high voltage applied to the electrode system. The obtained results demonstrate the effectiveness of this method for the separation of plastics from granular wastes.

Improved Overall Performances of a Tribo-Aero-Electrostatic Separator for Granular Plastics From Waste Electric and Electronic Equipment

The two-conveyor-electrode tribo-aero-electrostatic separator patented in 2010 was designed to sort granular mixtures of insulating materials in a fluidized bed subjected to an electric field perpendicular to the direction of the fluidizing air. The prototype has proven its efficiency for the separation of insulating granules ≤ 2 mm, attaining excellent recovery rates. Its performances were less satisfactory for larger particles (2-5 mm). The objective of this work is to evaluate three modifications of the construction of this device, in order to increase the hourly throughput and improve the purity of the products, by controlling the charge acquired by the granules and the electric field intensity. Numerical simulations enabled the optimization of the electric field distribution in the active zone of the separator, and an experimental study was carried out, in order to identify the best conditions for granule charging by triboelectric effect. The tests were carried out for four configurations of the electrode system, by using a mixture of acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS) originated from grinding out-of-use computer cases. The typical granule size was 2-5 mm. The experimental approach validated a change in the position of the fluidized bed, with respect to the conveyor electrodes, to increase the residence time of the granular materials and hence the amount of electric charge acquired by each particle. In order to intensify the electrical field, two solutions were tested and validated: 1) add a grounding electrode in the proximity of the high-voltage electrodes; 2) dispose vertically the high-voltage electrodes. For the tested materials, the vertical arrangement of the electrodes gave the best hourly throughput rates and purity of the separated products.

Corona-assisted plate-type electrostatic separation process for granular plastic wastes

Plate-type electrostatic separators are commonly employed for the selective sorting of conductive and non-conductive granular materials. Unfortunately, the purity of the conductive products is often compromised by the fact that the trajectories of the non-conductive 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 non-conductive 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.

Robustness testing of a free-fall triboelectric separation process for plastic waste recovery

Among the separation techniques used in industries, the triboelectric separation of insulating particles using a rotary tube is an effective way employed in the waste recovery of plastic and mineral products. This process, also called free-fall triboelectric separation, is widely used for the sorting of granular mixtures resulting from industrial plastic wastes. Given that the robustness of such a separation process is an important issue, a standard procedure is used for determining the set point and for minimising the process sensitivity of sorting mixed particles of different polymers to changes in the values of some critical factors. The aim of this paper was to analyse the efficiency of the triboelectric separation process of polymers with respect to any slight variation in the values of the most significant factors. Experiments with a sample of high-density polyethylene and polyvinyl chloride plastic granules were carried out on a laboratory experimental bench. Several one-factor-at-a-time experiments, followed by two factorial designs (one composite and the other fractional), were performed based on the following experimental procedure: (1) determination of the variation limits of the input variables; (2) identification of the set point and (3) robustness testing of the process, i.e. testing whether the performance of the system remains high even when the factors vary slightly around the set point.

Analysis and reduction of common-mode and differential-mode EMI noise in a Flyback switch-mode power supply (SMPS)

In the design of power electronics systems, electromagnetic compatibility (EMC) should be well attended. This paper provides a characterization approach for conducted electromagnetic interference (EMI) in a Flyback switch-mode power supplies. However, when such equipment is poorly designed and/or constructed then considerable levels of EMI are generated, and problems are caused both within the network and to the other electronic equipment nearby. Advances in computer aided design software and device models have enabled the waveforms within a switch-mode power supply to be accurately simulated. As a result of this, simulation techniques can be used to predict conducted interference levels generated by a Flyback. This paper introduces an efficient method to predict by simulation the conducted EMI of Flyback, accordingly mitigation is incorporated to reduce these electromagnetic emissions and susceptibility of SMPS.