Fluidized Bed Tribocharging Research Articles

Electrostatic Separation of Tribocharged Granular Mixtures of Two or More Plastics Originating From WEEE

Electrostatic separation is able to process mixtures of plastics from waste electrical and electronic equipment. The efficiency of the electrostatic separation depends on the electric charge acquired by the particles in the appropriate tribocharging devices. The aim of this work is to validate the possibility of using a roll-type electrostatic separator to sort mixtures of particles that are difficult to process by other means. In this type of separator, the plastic particles are charged by triboelectric effect. Two types of charging devices have been used: fluidized bed and rotating multicylinder. Two series of experiments were performed with samples composed in equal proportions of: first, acrylonitrile butadiene styrene (ABS) and polystyrene (PS); second, polypropylene (PP) and polyethylene (PE). A third series of experiments were carried out with a mixture of three plastics: PP, PE, and ABS, and the last series of experiments were carried out with a mixture of four plastics of (PE/PP/ABS/PS), with an average particle diameter ranging between 3 and 6 mm. The efficiency of the electrostatic separation was evaluated by measuring the charge, purity, and recovery of the granules collected at the outlet of the electrostatic separation. The results confirm that the separation of ABS/PS and PP/PE mixtures is feasible and the best separation results were obtained using the fluidized bed tribocharger.

Electrostatic separation of HIPS/ABS and HIPS/ABS-PC plastic mixtures from IT equipment using fluidized bed tribocharging

The paper presents an experimental study of the triboelectrostatic separation feasibility of two plastic mixtures, high-impact polystyrene (HIPS)/acrylonitrile butadiene styrene (ABS) and high-impact polystyrene (HIPS)/acrylonitrile butadiene styrene-polycarbonate (ABS-PC). To mirror real-world material recovery situations, the mixtures of 1-2 mm granular samples were sourced from Information Technology (IT) waste. In addition to balanced composition mixtures of 50% component A and 50% component B, heavily unbalanced compositions such as 10% A/90% B and 90% A/10% B were used in this study. The laboratory set-up consists in a free fall electrostatic separator equipped with a fluidized bed tribocharging device, characterized by interchangeable tribocharging chambers. Preliminary tests established the optimal material for the tribocharging chamber and the duration of the charging process. Samples of granular mixture were tribocharged, then introduced into the free-fall electrostatic separator. The analysis of the seven collecting boxes contents shows a recovery rate of approximately 90% and a purity of about 99% for both components. These results demonstrate the feasibility and the high efficiency of the triboelectrostatic separation of balanced and as well as heavily unbalanced composition mixtures of HIPS/ABS and HIPS/ABS-PC, using the fluidized bed for the tribocharging device.

Triboelectric Charging and Electrostatic Separation of Granular Polymers Containing Brominated Flame Retardants

The general purpose of the present article is to study the feasibility of removing brominated flame retardant (BFR) polymers from mixed granular wastes using triboelectric charging and electrostatic separation techniques. The study was carried out on mixtures consisting of equal quantities of plastic particles either BFR-free or containing 4.8% of hexabromobenzene (i.e., 40 000 ppm of bromine). Three triboelectric charging devices were used-a vibrating tribocharger [a container made of stainless steel, polystyrene (PS), or polypropylene (PP), and fixed on a vibrating table], a rotating cylinder tribocharger made of polyvinyl chloride, or a fluidized bed tribocharger, the walls of which were made of either poly methyl methacrylate, PS, PP, or polyethylene (PE). The experiments were carried out on three granular mixtures [BFR high impact PS (HIPS)/BFR-free HIPS, BFR PP/BFR-free PP, BFR PE/BFR-free PE]. The selective sorting of the granular mixtures was performed using a roll-type electrostatic separator. The results confirm that separating BFR plastics from BFR-free plastics is feasible. Best separation results were obtained for the mixtures tribocharged in the fluidized bed tribocharger.

Micronized plastic waste recycling using two-disc tribo-electrostatic separation process

Triboelectrostatic separation of millimeter-size granular mixtures is nowadays widely used in the recycling industry. However, the separation of micronized particles of an average granulometric size of 100 µm is still inefficient. This paper is aimed to carry out an experimental investigation of a triboelectrostatic separation process based on a fluidized bed tribocharging system produced between a pair of rotating aluminum disks supplied by two high-voltage DC supplies of opposite polarities. The granular mixture used in this work is composed of micronized white pure virgin PolyVinyl Chloride particles (WPVC) and gray PolyVinyl Chloride particles that contain a small percentage of carbon (GPVC) of average size 100 μm. Moreover, a homemade method was developed to estimate the purity of the separated products. It was deduced that the separation outcome, in terms of recovery and purity, is efficient and depends on several factors: the high-voltage level, the rotating speed of the disks, the fluidization rate, the total mass of the fluidized bed and the composition ratio of the granular mixture.

Experimental Modeling of a New Triboelectrostatic Separation Process for Micronized Plastics

Triboelectrostatic separation of millimeter-size granular plastic mixtures is widely used in recycling industry. However, electrostatic separation of micronized plastics is still inefficient since the adhesion and aerodynamic forces surpass the electric force. The aim of this paper is to optimize a new separation process for mixed fine granular plastics based on a fluidized bed tribocharging system. A pair of opposite high-voltage parallel plate electrodes are immersed in that bed and undergo a vertical alternating movement. The fine polyvinyl chloride particles of average size 0.1-mm particles to be separated are tribocharged using a fluidization air provided by a variable-speed blower. The charged particles are pinned to the electrodes of opposite polarities. The separation depends on several factors: the electric field, the speed of the electrode movement, the mass of the granular product, and the fluidization rate. The latter was the most significant factor, and the interval between the electrodes should not be less than 2 cm to avoid corona discharge.

Experimental Investigation of a New Triboelectrostatic 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.

Tribocharging of Mixed Granular Plastics in a Fluidized-Bed Device

The output of any electrostatic separation process is strongly dependent on the effectiveness of particle charging. The aim of the present paper is to evaluate the effects of several factors that might influence the efficiency of a fluidized bed tribocharger, in the presence of an electric field orthogonally oriented to the direction of the fluidization air. The experiments were carried out on several synthetic mixtures of binary granular mixtures. The velocity of the fluidization air, the duration of the tribocharging process, and the composition of the mixture were the three process variables investigated. Whenever possible, the effects of these variables on the output of the process (i.e., the mass and the charge of the granules collected at the electrodes), were evaluated using the experimental design methodology. The results of full- and composite-factorial experimental designs were analyzed with a commercial software (MODDE 5.0, Umetrics). The effectiveness of the charging process was found to depend significantly on each of these factors. The propitious aerodynamic design of the device is a prerequisite for the successful industry application of the technique.

Controlling Particle Trajectory in Free-Fall Electrostatic Separators

The purity and recovery of concentrates obtained in industrial free-fall electrostatic separators can be increased by preventing the impacts between the particles and the electrodes. The aim of this paper is to analyze the possibility to control particle trajectories in such separators by modifying the conditions of particle admission in the interelectrode space. The parametric equations of a charged particle trajectory in the electric field between the electrodes of a free-fall separator served for writing a numerical modeling program in MATLAB. The ten control factors of the free-fall electrostatic separation process were employed as input variables of this program: particle charge and dimension, trajectory start point coordinates, feed input angle and initial velocity, electrode length and inclination, interelectrode spacing, and applied high voltage. A custom-designed laboratory free-fall electrostatic separator (length of the electrodes: 1000 mm; standard interelectrode spacing: 300 mm; and nominal high voltage: 90 kV), provided with a fluidized-bed tribocharger, was employed for validating the conclusions of the numerical modeling. The geometrical data of this separator were taken into account for computing the initial velocity nu0 of the particles entering the electric field zone. Another important parameter of the numerical model, which is the granule charge q, was attributed the value measured at the exit of the fluidized-bed tribocharger. The numerical simulations were performed for the two values of the feed input angle: alpha = 4deg and alpha = 8deg, considering polyethylene therephtalate (PET) and polyvinyl chloride (PVC) particles of different sizes. A good agreement was found between the theoretical predictions and the results of the experiments carried out with two binary mixtures: 50% PET/50% PVC and 10% PET/90% PVC. Both the numerical modeling and the experimental study demonstrated that the feed input angle a influences the outcome of the electrostatic separation to a great extent.

Tribocharging of plastics granulates in a fluidized bed device

The paper presents a modular fluidized bed device for the study of plastics tribocharging and electrostatic separation, with application in the field of plastic recycling. Evaluation of the device in independent operation for charge-to-mass ratio measurements pointed out the different triboelectric behaviour of six tribocharging chambers made of plastic (PVC, PP, PET, PE, PMMA) and aluminium. The electrostatic separation tests carried out on PET and PVC granulates confirmed the effectiveness of the fluidized bed tribocharging device integrated in a free fall separator. They pointed out three charging mechanisms by particle/particle and particle/walls collisions.

Design and performance evaluation of triboelectrostatic separation system for the separation of PVC and PET materials using a fluidized bed tribocharger

A triboelectrostatic separation system using a fluidized-bed tribocharger for the removal of PVC material in the mixture of PVC/PET plastics was designed and evaluated as a function of tribocharger material, air flow rate, electric field strength, and the mixing ratio of two-component mixed plastics. The test system consists of the fluidized-bed tri- bocharger, a separation chamber, a collection chamber and a controller. PVC and PET particles can be imparted negative and positive surface charges, respectively, due to the difference in the work function values of plastics suspended in the fluidized-bed tribocharger, and can be separated by passing them through an external electric field. Experimental results show that separation efficiency is strongly dependent on the tribocharger material, electric field strength and particles mixing ratio. In the optimum conditions of 150 l/m air flow rate and 2.6 kV/cm electric field strength, highly concentrated PVC (99.1%) can be recovered with a yield of more than 95% from the mixture of PVC and PET materials for a single stage of processing.

Triboelectrostatic separation system for separation of PVC and PS materials using fluidized bed tribocharger

A triboelectrostatic separation system using a fluidized bed tribocharger for the removal of PVC material in the mixture of PVC/PS plastics is designed and evaluated as a function of electric field strength, air flow rate, and the mixing ratio of two- component mixed plastics. It consists of a fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. PVC and PS particles can be imparted negative and positive surface charges, respectively, due to the difference in the work function values of plastics suspended in the fluidized-bed tribocharger, and can be separated by passing them through an external electric field. Experimental results show that separation efficiency is strongly dependent on the electric field strength and particle mixing ratio. In the optimum conditions of 150 lpm air flow rate and 2.6 kV/cm electric field strength a highly concentrated PVC (99.1%) can be recovered with a yield of more than 99.2% from the mixture of PVC and PS materials for a single stage of processing.

PVC Separation and Flow Visualization of Triboeletrostatically Charged Plastic Particles Using Fluidized Bed Tribocharger

ABSTRACT A particle flow visualization and separation of triboelectrically charged particles in the external electric field by a fludized bed tribocharger are conducted for the removal of PVC particles from mixed waste plastics. The laboratory scale triboelectrostatic separation system consists of the fluidized bed tribocharger, a separation chamber, a collection chamber and a controller. PVC and PET particles can be imparted negative and positive surface charges, respectively due to the difference of triboelectric charging series between particles and particles in the fluidized bed tribocharger, and can be separated by passing them through an external electric field. To visualize these charged particles, He-Ne laser was used with cylindrical lenses to generate a sheet beam. The highly concentrated PVC (91.9%) can be recovered with a yield of about 96.1% from the mixture of PVC and PET materials for a single stage of processing. The triboelectrostatic separation system using the fluidized tribocharger shows the potential to be an effective method for removing PVC from mixed plastics for waste recycling.

Triboelectrostatic separation of pvc materials from mixed plastics for waste plastic recycling

This study covers the triboelectrostatic separation of Polyvinylchloride (PVC) materials from mixed plastics such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS). The PVC material generates hazardous hydrogen chloride gas resulting from the combustion in the incinerators. The laboratory scale triboelectrostatic separation system consists of a fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. Negative and positive surface charges can be imparted to the PVC and PET particles, respectively, due to the difference of triboelectric charging series between the particles in the fluidized-bed tribocharger. They can be separated by passing through an external electric field. A highly concentrated PVC (91.9%) can be recovered with a yield of about 96.1% from the mixture of PVC and PET materials in a single stage of processing. For the removal of PVC from the two-component mixed plastics such as PVC/PET, PVC/PP, PVC/PE or PVC/PS, separation results show the recovery of 96–99% with the pure extract content in excess of 90%. The triboelectrostatic separation system using the fluidized-bed tribocharger shows the potential to be an effective method for removing PVC from mixed plastics for waste plastic recycling.