Lucien Dascalescu

Plastic wastes recovery using free‐fall triboelectric separator

Among the separation techniques used in industry, the triboelectric separation of insulating particles using rotary tube is an efficient technology employed in waste recovery and mineral industries. This process, also called free‐fall triboelectric separation, is widely used for the sorting and the purification of granular materials resulting from industrial plastic wastes. This paper offers a comprehensive description of a laboratory triboelectric separator build by the authors, and its use for an experimental study carried out on granular samples containing particles of PVC (Polyvinyl chloride) and PE (Polyethylene). Thus, among the variable factors of the process, we analysed the influence of the most important ones, that is, the rotational speed of the cylinder n(rpm), the applied high voltage U(kV), the charging time of the particles t(s), the mass of the sample m(g) and the composition percentage of the sample Cp (%).

Surface potential decay dynamic characteristics of negative-corona-charged fibrous dielectric materials

The dielectric behavior of an insulating material is commonly characterized by exposing its surface to a DC corona discharge for relatively short duration and then recording the decay of the electric potential Vs at its surface, Vs = f(t). The representation of the surface potential decay (SPD) by using tdVs/dt = f(log t) plots has already been used to perform a finer analysis of the dielectric response of film insulators. The present paper takes advantage of this peculiar way of representing the SPD in view of characterizing the dielectric behavior of fibrous electrets negatively-charged from a triode-type (wire-gridplate) electrode system. The experiments were performed in ambient air (temperature: 20 ± 1 °C), at various values of the relative humidity (range 25 % to 65%). This paper reports experimental data collected on a polypropylene (PP) film (sheet thickness: 250 μm) and two types of PP non-woven media (fabric thickness: 300 μm), characterized by different fiber diameters (20 μm and 4 μm). The initial surface potential and the dynamics of SPD of fibrous dielectric materials were found to be affected by the corona charging conditions (relative humidity of the ambient air, grid voltage and grid current), as well as by the properties of the fibers and the structure of the non-woven media. An appropriate model of SPD should take into account charge injection from the media-electrode interface, charge transport controlled by bulk mechanisms and local high electric field effects due to the porous structure of the media.

Experimental analysis and optimisation of a free-fall triboelectric separator of granular plastic particles

Among the separation techniques used in industry, the triboelectric separation of insulating particles using rotary tube is an efficient technology employed in waste recovery and mineral industries. This process, also called free-fall triboelectric separation, is widely used for the sorting and the purification of granular materials resulting from industrial plastic wastes. This paper aims to achieve a comprehensive description of the laboratory triboelectric separator built up by the authors, and its utilisation for an experimental study carried out on granular samples containing particles of polyvinyl chloride and polyethylene. Thus, among the variable factors of the process, we analysed the influence of the most important ones, i.e. the rotational speed of the cylinder n (rpm), the applied high voltage U (kV), the charging time of the particles t (s), the mass of the sample m (g) and the composition percentage of the sample C p (%). Furthermore, the output process was optimised using the methodology of experimental designs. The obtained results are very instructive and confirmed the efficiency of this separation method for the processing of industrial plastic wastes.

Surface potential decay characterization of non-woven electret filter media

Electric charging of the non-woven electret filter media leads to increased particle collection efficiency. Estimation of the charge state of the media can be done by measuring its surface potential. The aim of this paper is to evaluate the effects of the factors that influence the surface potential decay characteristics of these media: the grid potential of the triode-type corona electrode system employed for the electric charging, the active carbon, the ambient relative humidity and the temperature at which the media are thermally pre-conditioned. The experiments were carried out on two types of samples, one of which includes an active carbon layer between two 400 μm thick layers of non - woven polypropylene fibers, the diameter of each fiber being approximately 20 μm. The results show that the surface potential values increase with the increasing of the electric potential of the grid. Thus, if the grid potential Vg increases from 3 to 10 kV, the surface potential value increases over 3 times. A 20% increase of the surface potential values is also recorded in the case of thermally conditioned samples. The surface potential decreases by roughly 10% in the case of the samples with carbon layer, and by about 20%, and in the case of relative humidity increase from 21% to 80%.

Numerical Analysis of the Induced Corona Vibrations on High-Voltage Transmission Lines Affected by Rainfall

Droplets formation on high-voltage transmission lines affected by rainfall amplifies the corona discharges from the conductors. The induced corona vibrations intensify the fatigue of high-voltage conductors and supporting elements. The alternating presence of space charge and the ionic wind associated with the corona discharge are the main causes of this phenomenon. The objective of this paper is to validate a numerical simulation method to investigate the effects of different parameters (electric field strength and polarity, rain intensity, transverse wind velocity) on the amplitude of the induced corona vibrations. The finite element method was used to develop the numerical model of the conductor movement under the action of mechanical and electrical forces, while time discretization was made with the finite difference method. The numerical simulation results were in good agreement with the experimental data available in the literature. The model enables better comprehension of the induced corona vibration mechanism.

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.

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).

Collection efficiency of submicrometre particles using single and double DBD in a wire-to-square tube ESP

The aim of this work is to study the collection of submicrometre particles charged by a dielectric barrier discharge (DBD) in two types of wire-to-square glass tube electrostatic precipitators (ESPs). They are, respectively, designated as single DBD-ESP and double DBD-ESP, depending on the absence or presence of a dielectric layer around the high-voltage wire electrode. The experiments are performed with incense smoke particles having a mean size of about 0.32 µm. An aerosol spectrometer is employed for characterizing the size distribution of these particles at the outlet of the ESPs. The collection efficiency is estimated for various applied voltages and frequencies (ranges: 8–28 kV, 0.3–1000 Hz) at a fixed air flow rate (5.1 L min−1). The electrical measurements show that in the case of the single DBD-ESP, the discharge mode is rather homogeneous. In contrast, the discharge has a filamentary behaviour in the case of the double DBD-ESP. Results show that the particle collection efficiency of both ESPs is higher at high applied voltages and within a certain frequency range. However, corroborating the collection efficiency results with the power consumption measurements reveals that the double DBD-ESP offers better performances for a larger frequency range.

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.

Experimental study of the tribocharging process of plastic granular materials on a vibratory feeder device

Triboelectrostatic separation of granular plastics wastes is a technology that is more and more employed in the recycling industry. The paper is aimed at characterizing the tribocharging of Polyvinyl Chloride (PVC), Polyamide (PA) and High Density Polyethylene (HDPE) granules on a vibratory feeder tray covered by a Polyethylene Terephthalate (PET) sheet, in order to evaluate the possibility of using this device in a continuous tribo-electrostatic separation process. A capacitive probe was used to evaluate the surface charge density on the PET sheet. When the tray of the vibratory feeder was grounded, the charge density at the surface of the PET sheet was found to increase slightly after every tribocharging experiment, while the charge of PA granules saturated at 2.6 nC/g. In the case of an isolated PET sheet, its surface charge density is rapidly increasing and tends to saturate, limiting the charge/mass ratio of PA granules at 1.4 nC/g. Similar results were recorded for other tested materials, proving the efficiency of the tribocharging on the PET tray of the vibratory feeder.