Triboelectrostatic separation of granular plastics mixtures from waste electric and electronic equipment

The efficiency of the electrostatic separation of insulating granular mixtures depends on the electric charge carried by the particles. The first objective of this work was to characterize the tribocharging properties of various plastic materials in the composition of waste electric and electronic equipment: polyvinyl chloride (PVC), “high-impact” polystyrene (HIPS), acrylonitrile butadiene styrene (ABS), “high-density” polyethylene (HDPE), polycarbonate (PC), polyamide (PA). Thus, in a first series of experiments, 15 samples composed of binary mixtures of above plastics were initially charged in a fluidized bed device, then separated using a free-fall electrostatic separator. The six plastics could be ordered in a specific triboelectric series: PVC, HIPS, ABS, PEHD, PC, PA. The second objective was to evaluate the efficiency of three tribocharging devices: a static charger, a fluidized bed, and a fan-type device. The triboelectrostatic separation experiments performed with four different binary mixtures (PVC/PA, PC/PA, HIPS/PA, and HIPS/ABS) showed that the fluidized bed is the most effective.     

Tribo-electrostatic separation of a quaternary granular mixture of plastics

Many tribo-electrostatic separation studies of binary mixtures of millimeter-sized plastic particles have been performed. The objective of this work is an experimental investigation for separating a quaternary mixture comprising four different plastic types issued from waste electrical and electronic equipment. The feasibility of the separation of such quaternary mixtures by the sliding mode tribocharging with a metal wall was demonstrated. The separation of a mixture comprising PA, PC, high impact polystyrene, and polyvinyl chloride granules is better in terms of both purity and recovery when charging the particles by sliding contact with the metal wall, then in the case of a fluidized bed device.     

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.     

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.     

Gas flow influences on bubbling and flow characteristics of fluidized bed with immersed tube under electrostatic effects

Industrial bubbling fluidized beds are used to fluidize particles. When particles are fluidized, electrostatic effects will cause the particles to form obvious agglomerates, thus reducing fluidization performance. For better fluidization performance, internal component immersed tubes are usually placed in fluidized bed to limit the bubble size and reduce particle agglomerates. Meanwhile, pulsed gas flow can increase particle disturbance, which is also an effective method to reduce particle agglomerates. In this paper, the CFD-DEM model under electrostatic effects is constructed to research the bubbling and flow characteristics in fluidized beds. Firstly, particle mixing qualities with and without the immersed tube are compared. Then, the effects of different superficial gas velocities are investigated with an immersed tube. Finally, different frequencies are applied to study the energy loss and flow characteristics around the immersed tube. The results show that the addition of the immersed tube can reduce bubble size to facilitate particle mixing. Due to the obstruction of the immersed tube, the bubbles are generated near the wall. As the superficial gas velocity increases, the larger bubbles are generated. Moreover, the electrostatic force applied to the particles varies periodically with the frequency of incoming pulsed gas flow, with fluctuations maximal at 2.5 Hz.     

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.     

Interaction effect of various factors and sulfur migration for pyrite recovery by vibrated fluidized bed

ABSTRACT

Gangue is a hazardous solid waste with high yield in the world. Due to higher proportion of pyrite in the gangue, pyrite recovery from gangue is significant for environmental protection. As effective recovery methods, dry separation methods have been received amount of attentions in the mineral processing field. In this study, vibrated fluidized bed was attempted to use for pyrite recovery. Vibration energy was introduced to strengthen the density segregation in the fluidized bed. The study also investigated the interaction effect of gas velocity, vibration intensity, and bed height in the vibrated fluidized bed. Moreover, sulfur migration has been studied by several advanced analytical techniques. The results showed that separation efficiency was directly related to the interaction effect among various factors. After the separation, the sulfur content of concentrates were increased to 37.31, 35.43, and 28.62% for ?6?+?3, ?3?+?1, and ?1?+?0.5?mm size fractions. The sulfur segregation’s standard deviation (S_sulfur) was beyond 0.70. In addition, elements of S and Fe accounted for higher proportion in the concentrates after the separation. The study indicated that pyrite could be effectively enriched by the vibrated fluidized bed.     

The design and demonstration of a fluidized bed incinerator for the destruction of hazardous organic materials in soils

Many types of thermal oxidation systems in existence today are suitable for the destruction of organic hazardous wastes. Few, however, offer the versatility of fluidized beds. Past research and commercial fluidized bed installations have demonstrated the ability of fluidized beds to successfully destroy organic constituents in a wide assortment of gas, liquid, sludge, and solid wastes. This article describes a further advance: the design and testing of a fluidized bed capable of destroying organic constituents in clay, silt, sands, and gravels. This advance makes fluidized beds suitable for on-site waste cleanup of breached lagoons, dump sites with leached liquids, or spills of liquid chemical wastes.The soil decontamination program was designed to evaluate the effectiveness of fluidized bed systems for total cleanup of sites contaminated with hazardous organic materials. This paper describes the research program conducted to optimize fluidized bed design for this application, and discusses the lessons learned on material handling. The conclusion is that fluidized bed incineration systems are an effective tool for the cleanup of hazardous organic materials in soil.     

Decrease of Cl contents in waste plastics using a gas–solid fluidized bed separator

In order to decrease Cl content in waste plastics, dry density float-sink separation of Cl-contained and Cl-free plastics was explored using a semi-continuous rotating-type gas–solid fluidized bed separator with silica sand. The separator has two distinctive features: (1) the plastics can be fed at a middle height of the sand bed, and (2) when the plastics are recovered with the sand from a container after the float-sink, the recovery height of the sand bed can be changed to designate the plastics as floaters or sinkers. The waste plastics of Cl content = 5.4 wt% were used in this study. The separation was investigated by changing the experimental conditions. As a result, the float-sink of the plastics was affected by the air velocity for fluidization, the float-sink time and the feed amount of plastics. The possible causes of the effects were discussed by focusing on the apparent density of fluidized bed, the fluidization intensity, the size segregation of fluidized particle, the shape of the plastics, and the interactions between the plastics during the float-sink. When the recovery height was changed at the adjusted conditions, the Cl content in the floaters was successfully decreased to be 0.4–0.85 wt%, at which the recovery of the Cl-free plastics was 40–60%.     

Fluctuations of the number of solid-phase particles in a fluidized bed

An analytic expression is obtained for calculating the relative fluctuation of the number of particles in a fluidized bed. The fluctuation of the number of particles in a bed consisting of glass pellets fluidized with water has been experimentally investigated. The relative fluctuations obtained in these experiments are compared with the theoretical values for a fluidized bed and an ideal gas.     

Recovery of metal fractions from waste printed circuit boards via the vibrated gas-solid fluidized bed

The vibrated gas-solid fluidized bed based on fluidized separation technology was used to recycle the metallic fraction of waste printed circuit boards (WPCBs). The size fraction composition and element distribution of the crushed products were analyzed by sieving and X-ray fluorescence, respectively. The contents of Cu, Zn, Fe and Ti in various size fractions had significant differences, resulting in preliminary enrichment. The performance of vibration on the fluidization characteristics of WPCBs powder was described. With fluidization number, vibration frequency and vibration amplitude as variables, the separation performance of WPCBs powder under various operational conditions was studied. With the optimum operated conditions, the optimal recovery rates of metallic fraction of the three size fractions of 1–0.5 mm, 0.5–0.25 mm and 0.25–0.125 mm were 88.53%, 95.61% and 82.28%, respectively. The vibrated gas-solid fluidized bed can effectively enrich and recover the metallic fraction of WPCBs, providing convenience for subsequent separation.     

Magnetite particle surface attrition model in dense phase gas–solid fluidized bed for dry coal beneficiation

Dense-phase high-density fluidized bed has received considerable attention worldwide due to the urgent need for an efficient dry separation technology. This study on magnetite particle attrition model and size distribution change rule in a dense-phase gas–solid fluidized bed for dry beneficiation analyzes the complex process of magnetite particle attrition and fine particle generation. A model of magnetite particle attrition rate is established, with the particle attrition rate leveling off gradually with the attrition time in the dense-phase gas–solid fluidized bed. Magnetite particle attrition in the dense-phase gas–solid fluidized bed is consistent with Rittinger’s surface theory, where the change in surface area of magnetite particles is proportional to the total excess kinetic energy consumed and the total attrition time. An attrition experiment of magnetite particles is conducted in a laboratory-scale dense-phase gas–solid fluidized bed for dry beneficiation.     

Viscosity and separation performance of a gas-solid separation fluidized beds

A theoretical model of viscosity in gas-solid separation fluidized beds is established according to the two-phase flow theory of fluidized beds. After comparing theoretical and measured values, the correlation coefficient between the two is as high as 0.99, showing that the model has good predictability for the viscosity of fluidized beds. Meanwhile, the viscosity and its influencing factors were studied using a Brookfield viscometer. The study shows that smaller medium particles (0.074–0.15?mm) can reduce the viscosity of fluidized beds, but they will aggravate the viscosity fluctuation at more than 5?wt% addition, which is unfavorable to the stability of fluidized beds. In addition, in the actual separation process, the external factors (such as moisture and coal powder content) also affect the viscosity of the fluidized beds. Increasing the moisture increases the viscosity of the fluidized bed, whereas coal dust has the opposite effect. In order to ensure the stability of the fluidized bed, the bed moisture content should be controlled below 1?wt%, while the content of coal powder should be limited below 5?wt%. Based on separation tests, reducing the viscosity will improve the separation performance of a fluidized bed at the proper fluidized gas velocity, with the lowest possible error E_p of 0.085.     

Effect of particle size composition on the separation of waste printed circuit boards by vibrated gas–solid fluidized bed

The mechanism of fine particles on the separation of waste printed circuit boards by vibrated fluidized bed is not clear. In this paper, the influence of particle composition on fluidization behavior and separation characteristics of waste printed circuit boards particles was studied. The separation results showed that the increase of fine particles significantly reduced the metal recovery. When the content of fine particles was 20 %, the concentrate yield decreased by 11.26 % and the metal recovery declined by 15.93 %. The analysis of fluidization characteristics proved that the stability of the bed was reduced at higher fine particle content. When the content of fine particles was 20 %, the standard deviation of bed pressure drop was 34.15 Pa higher than that without fine particles. And the microscopic and X-ray fluorescence analysis confirmed that the adhesion behavior of fine particles prevented them from being separated by density. In addition, it was found that the pre-removal of iron and aluminum could effectively improve the separation performance with a fine particle content of 20 %, and the metal recovery increased by 6.29 %. Based on this, our findings will provide important guidance for efficient recovery of valuable metals from waste printed circuit boards.     

多流程循环流化床技术在综合能源服务中的应用

园区级的清洁供热是目前综合能源服务中需要迫切解决的问题。多流程循环流化床技术采用"三床两返多流程"的结构设计,解决了传统的循环流化床锅炉小型化的问题。工业实践证明,多流程循环流化床锅炉可以选用生物质、工业固体废弃物、煤炭等作为燃料,针对多种燃料的热效率达到88%~92%,且污染物排放均达到了国家和地方标准中对排放浓度限值的要求。多流程循环流化床技术具有分散能源分散利用、多种燃料同时适用的优势,可以有效地为园区级的综合能源服务提供帮助。     

A novel approach to recycling of glass fibers from nonmetal materials of waste printed circuit boards

The printed circuit boards (PCBs) contain nearly 70% nonmetal materials, which usually are abandoned as an industrial solid-waste byproduct during the recycling of waste PCBs. However those materials have abundant high-value glass fibers. In this study, a novel fluidized bed process technology for recycling glass fibers from nonmetal materials of waste PCBs is studied. The recycled glass fibers (RGF) are analyzed by determination of their purity, morphology and surface chemical composition. This process technology is shown to be effective and robust in treating with nonmetal materials of waste PCBs. The thermoset resins in the nonmetal materials are decomposed in the temperature range from 400 °C to 600 °C. And the glass fibers are collected at high purity and recovery rate by the cyclone separators without violating the environmental regulation. This novel fluidized bed technology for recycling high-value glass fibers from nonmetal materials of waste PCBs represents a promising way for recycling resources and resolving the environmental pollutions during recycling of waste PCBs.     

Development and combustion characteristics of microwave plasma-assisted fluidized bed combustor

A novel waste treatment method that can efficiently decompose waste, suppress by-product generation, and operate at a low cost is urgently required. Herein, a microwave plasma-assisted combustor was developed and its combustion characteristics were investigated for application in solid waste treatment. The experimental conditions for obtaining good states of fluidization, mixing, and plasma formation were examined prior to the combustion experiments. Subsequently, the optimal experimental conditions, such as the filling amount of bed particles, bed particle diameter, microwave irradiation position, and microwave output, required for good combustion were achieved. Combustion experiments based on these conditions revealed that a good fluidization state is required to obtain a good combustion state in this device, although the combustion condition does not necessarily depend on the system pressure at each O₂ flow rate. Comparison of the conditions with similar fluidization states at O₂ flow rates of 1–4 L/min revealed a maximum fuel conversion ratio at 4 L/min owing to the combustion promotion caused by increased O₂ partial pressure. The fuel did not remain in the fluidized bed combustor after the combustion experiments.     

Electrostatic Separation of Peeling and Gluten from Finely Ground Wheat Grains

Sieving and air classification are not efficient enough for the extraction of the high-nutritional-value constituents of wheat. The aim of this article is to validate a simple electrostatic separation method of peeling and gluten, which are two such nutriments contained in finely ground wheat grains. The electrostatic separator is composed of metallic grounded belt conveyer and a rotating roll electrode connected to a high voltage supply. The electrostatic behavior of peeling and gluten powders was characterized using surface potential decay and direct charge measurements. These first set of experiments pointed out the conductive behavior of these powders: in contact with a grounded electrode, they lose their charge in less than 10 s. In a second set of experiments, mixtures of 50% peeling and 50% gluten powders were processed by electrostatic separation. Experimental design methodology was used to model the outcome of the separation process as function of two control variables: the high-voltage applied to the roll electrode and the speed of the belt conveyor electrode. In this way, it was possible to determine the optimal operational conditions for the recovery of high-purity peeling and gluten fractions.     

MEASUREMENTS OF IN-BED TUBE BUNDLE EROSION AND PARTICLE-TUBE COLLISION FREQUENCY IN A GAS FLUIDIZED BED

Erosion of an in-bed tube bundle by bed materials (ash, coal, and sorbents) impingement has caused serious problems to many fluidized bed combustion (FBC) boilers. Experimental investigation of the tube erosion processes was made by placing the erosion-prone wax cylinders in a bench-scale, cold fluidized bed to simulate the long term erosion effect. This paper discusses the results of systematic measurements of weight losses of an in-bed tube bundle under various test conditions. The specific erosion rate of immersed wax specimens ranges from 25 to 175 µg/ (cm² hr) when impacted by 0.55 mm glass beads at a superficial velocity of 75 cm/s. The tube bundle height and configuration were found to have a prominent influence on the mean solid flow pattern and hence the tube erosion. A comparison of the erosion rates of narrow-pitch and wide-pitch staggered bundles, as well as the in-line bundle are presented. Electrostatic impact probes based on the triboelectric effect of moving particles were developed as the primary standard for measuring the particle-surface collision frequency, which is one of the major parameters characterizing the tube erosion. The peripheral distribution of collision frequency around an embedded tube was measured and correlated with the results from weight loss measurement.     

Dynamic forces on an immersed cylindrical tube and analysis of particle interaction in 2D-gas fluidized beds

The interactions of bubbles and particles with fixed cylindrical tubes in two-dimensional fluidized beds were investigated by experiments and by simulations, based on results for single bubbles impinging on a tube. The experimental results based on PIV analysis support our previous force origin model and indicate that the model is able to successfully model bubble behavior and particle motion around fixed objects. The simulation results give useful predictions, dynamic force induced on a tube consists of the force from pressure gradient, fluid viscous force and particle contact force. The predominant force component is from the pressure gradient. As bubbles directly interact with a tube, the particle contact force contribution briefly becomes predominant.Bubble behavior and particle motion are greatly affected by the state of the emulsion phase as the medium of the fluidized bed into which gas is injected. Hence the dynamic forces on immersed objects are directly affected by the state of the emulsion phase.