Ion I. Inculet

ELECTROSTATIC SEPARATION OF PLASTICS FOR RECYCLING

Abstract The authors describe some successful experiments for electrostatic separation of various two-component mixtures of plastic waste. Two methods of triboelectric charging of plastics are described. One consists of a fluidized bed system with a central feeding tube. The second is a novel form of a rotating tube charger. Separation takes place in an electrostatic separation tower equipped with a set of nine sampling bins at the bottom for collection of the components. Numerous experiments have shown the feasibility of obtaining extract contents in excess of 99%. The rotating tube charger is preferred over the fluidized bed because of its simplicity and energy savings. The process has recently been adapted to an industrial scale capable of processing 1000 kg/hour and is currently being used to separate post-industrial plastic waste.

MINORITY CHARGE SEPARATION IN FALLING PARTICLES WITH BIPOLAR CHARGE

Abstract Fluidization of polymer powders is used extensively in the powder coating industry. During the fluidization process the paint particles become electrically charged due to particle–particle and particle–wall interactions. In the course of this tribocharging, or friction charging process, it has been observed that a bipolarity of charged powder exists. The smaller, or finer, particles tribocharge oppositely to the larger size particles; thus, there exist both positively and negatively charged particles within the fluidized bed. A simple technique for charge measurement and separation has been developed whereby a small sample of bipolar charged powder taken from the fluidized bed is poured from a height and a separation occurs between the majority and minority particles of opposite charge. The amount of separation is a function of charge on the individual particles and the height at which the sample is poured. A computational model, based on techniques of molecular dynamics, has been developed to simulate the trajectories of individual charged particles when a sample of bipolar charged powder is poured. The model takes into account electrical, drag and gravitational forces acting on each particle and confirms the statistically analyzed experimental results.

The measurement of bipolar charge in polydisperse powders using a vertical array of Faraday pail sensors

A vertical array of Faraday pail sensors was developed to partially separate bipolar charged polydisperse powder and measure the charge-to-mass ratio of the powder deposited in each Faraday pail. In our experiments, the system consisted of seven Faraday pails, six special Faraday pails, which were mounted vertically in cascade, and a normal Faraday pail located at the bottom. The inner and outer pails of the special Faraday pails had open holes on the upper and lower covers. The bipolar charged polydisperse powder was sampled from an earthed metallic fluidized bed with an earthed metallic vertical tube at the axis of the bed. As the powder falls, individual particles experience separation forces due to the gravity segregation and space charge repulsion. The particles thus deposit into different inner Faraday pails according to their charge, size and mass. Each powder sample was collected and the charge-to-mass ratio was measured. The size distribution of the particles sampled from each Faraday pail was analyzed to clarify the effect of this factor on contact charging between particles.

Ozone Generation in Positive Corona Electrostatic Precipitators

Ozone generation is one of the most important limitations in the design of an efficient electrostatic precipitator for use in air-conditioning systems.

Size distribution of particles entrained from fluidized beds: Electrostatic effects

Abstract Experimental results obtained with solids ranging from 69 μm cracking catalyst to 400 μm polyethylene showed that the smallest particles were not the most easily elutriated from fluidized beds of mixed size particles. This is in contradiction with the assumption made by existing models for the prediction of the flux and size distribution of particles elutriated from a fluidized bed. The smallest particles cannot be removed by elutriation from a mixture of particles of various sizes. The smallest particles may be agglomerated with larger particles. Reducing or eliminating particle electrostatic charges by injecting counteracting charges or increasing the gas humidity did not greatly affect the size distribution of the elutriated particles. Electrostatic forces were, thus, not responsible for particle agglomeration. Electrostatic effects, on the other hand, greatly reduced the flux of elutriated particles by creating an extra electrostatic pressure drop in the fluidized bed freeboard. They also changed the fluidization quality of the bed of polyethylene particles.

Charging of polymer powder inside a metallic fluidized bed

Abstract An experimental study concerning the charging phenomena involved in the fluidization of polymer powder paint shows that there are two main charging processes at work inside the bed. It is well known that tribocharging occurs in the fluidization of insulating particles but surprisingly induction charging also occurs. This paper presents the experimental charge-to-mass ratio distribution associated with the deposits that develop on the walls of the bed. This distribution correlates well with the electric field distribution close to the wall solved using Finite Element Method software.

IEEE-industry applications society annual meeting: September 29–October 1, 1975, Atlanta, Georgia, USA

Abstract Overall, the meteoric rise in the size of this conference in the last two years is an indication of the importance of electrostatics in many practical applications. It is unfortunate that the subject of electrostics has been comparatively neglected by the scientific, academic and industrial communities for many years. This conference is helping to stimulate interest and fill that void.

Co-generation of ozone and hydrogen peroxide by dielectric barrier AC discharge in humid oxygen

Abstract In situ ozonation by a parallel-plate dielectric barrier AC discharge through oxygen onto water surfaces (”electroozonation—) has been used to generate ozone in the gas phase and transport it across the gas-liquid interface in a single step, with simultaneous generation of hydrogen peroxide in the liquid phase. The latter may contribute to efficiency in terms of oxidative power production vs. electrical power consumption in that hydroxyl radicals are generated independently from ozone decomposition. The process is akin to glow-discharge electrolysis, in which OH radicals are produced from ionized or activated water molecules, rattier than by H2O2-induced ozone decomposition as in other advanced oxidations based upon O3/H2O2.

Bipolar charging in polydisperse polymer powders in industrial processes

The purpose of this paper is to review the previous published work and to describe some results showing bipolar charging using polymer powders in two common industrial processes: fluidized beds and pneumatic transport. A new measurement system is described for measuring the bipolar charge distribution. This consists of a vertical array of seven Faraday pail sensors, which can selectively detect different charge components based upon particle size (gravity segregation) and charge (space charge repulsion). For the experiments reported here the charge and mass values were measured for each sensor allowing the calculation of charge to mass ratio (Q/M). In addition, size distribution and surface analyses were carried out for representative samples of the powder components. Data are presented for several types of polymer powders (volume mean diameter <100 /spl mu/m), with and without extraparticulate additives. The results, in all but one of the cases reported, show that even though the net charge may be positive or negative the fine particles show a negative charge and the coarse particles positive. These results are compared under several possible hypotheses.

Tribo-electrification system for electrostatic separation of plastics

The authors describe a novel tribo-electrification system developed at the Applied Electrostatic Research Centre of the University of Western Ontario for various mixtures of waste plastics. The system consists of: a single (or a battery of) specially designed rotating (long tubes) cylinders made out of selected metals which have been shown to achieve excellent selective tribo-electrification of the individual components in the processed mixtures, a HV Separation tower, and collecting trays (or conveyors) for the separated fractions. To show the performance of the cylinder, results are presented for separation experiments involving feeding four chosen tribo-electrified mixtures of two components of waste plastics obtained from processing industries in the form of flakes or granules of: polystyrene, polypropylene, and high density polyethylene.<<ETX>>