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The influence of micro-morphology and micro-structure on fly ash triboelectrostatic beneficiation

Wang Wenping, Chen Yinghua, Haisheng Li, Dong Haoran, Wang Guanghui

Physicochemical Problems of Mineral Processing

2021

Vol. 57, iss. 1

53--63

Fly ash is a complex system with a variety of fine particles. The complex relationship between unburned carbon and ash particles has an important influence on the efficiency of fly ash triboelectrostatic beneficiation. The particles adhered to the two electrode plates are collected through the triboelectrostatic beneficiation experiment. The scanning electron microscopy and X-ray fluorescence are used to detect the microscopic differences between the particles of positive and negative plates. The results show that the flaky carbon particles in the raw ash and the ash particles larger than 4µm are more easily separated, while it is converse for the ash particles with particle size less than 4µm. With the particle size less than 4µm, it is gradually more obvious for the influence of adhesion caused by the roughness surface of spherical unburned carbon particles, and the surface pores structure of porous carbon particles. The binding structure between unburned carbon and ash particles is complex and changeable. It is not beneficial to improve the separation efficiency. Therefore, the micro-structure and micro-morphology have an important effect on fly ash triboelectrostatic beneficiation. Some suggestions were proposed from the microscopic point to improve the efficiency of fly ash triboelectrostatic beneficiation.

The role of electrical heating on tribocharging and triboelectrostatic beneficiation of fly ash

Haisheng Li, Yinghua Chen, Xinxi Zhang, Chaoyong Li

Physicochemical Problems of Mineral Processing

2019

Vol. 55, iss. 4

896--905

Triboelectrostatic beneficiation is an effective technique to remove unburned carbon from fly ash. The purpose of this study is to enhance the particles tribocharging, and improve the efficiency of removal unburned carbon from fly ash using electrical heating. An experimental system with electrical heating was established to realize the tribocharging measurement and fly ash triboelectrostatic beneficiation. The experimental material collected from a thermal power station was fly ash with an average loss on ignition of 20.76%. The operating conditions were electric field voltage of 40KV and air flow rate ranging from 1.7 to 4.25 m/s. The influence of heating temperature and heating position on tribocharging and triboelectrostatic beneficiation was discussed. The feasibility of electrical heating was evaluated by the charge-to-mass ratio (CMR), loss on ignition (LOI) and removal unburnt carbon rate (RCR). The results indicate that the increasing of collision probability for heated particles can improve the charging efficiency. The heating temperature related to gas moisture content and particles dielectric constant is inversely proportional to the LOI of ash, whereas it is opposite for the RCR. The heating position has an effect on the CMR and RCR because of changed contact time between charged particles and compressed air. The optimum conditions are the air flow rate of 4.25 m/s, heating temperature of 90℃. Heating tube III is suitable to install electrical heating system. The electrical heating is proved to be effective to improve the efficiency of fly ash triboelectrostatic beneficiation.

Experimental study on triboelectrostatic beneficiation of wet fly ash using Microwave Heating

Li H., Chen Y., Zhang X., Zhao Y., Tao Y., Li C., He X.

Physicochemical Problems of Mineral Processing

2016

Vol. 52, iss. 1

328--341

Triboelectrostatic beneficiation, as a physical method, of fly ash cannot only meet the technical requirements of fly ash application but also recycle of an unburned carbon as a useful energy source. The aim of this study was to investigate the feasibility of improving efficiency of triboelectrostatic beneficiation of wet fly ash using microwave heating. The wet fly ash with different moisture contents had an average loss-on-ignition of 12.56%. The fly ash samples were heated in a microwave oven before the experiments. The experimental conditions were electric field voltage of 40 kV and air flux ranging from 12 to 30 m3/h. The influence of the microwave heating on the wet fly ash triboelectrostatic beneficiation was discussed under the conditions of different microwave intensity and irradiation time. The results indicated that the removal rate and recycle rate of the unburned carbon showed a significant increase performance as the wet fly ash was processed by the microwave heating which was attributed to changes of moisture contents and dielectric constants caused by the microwave heating. The feasibility had been verified according to the experimental study on fly ash with different moisture contents. It can be concluded that the microwave heating process was efficiently applied for the wet fly ash triboelectrostatic beneficiation.