# Review of Coal-Fired Electrification and Magnetic Separation Desulfurization Technology
## 4 Friction Electrostatic Separation Technology
### The Development of Friction Electrostatic Separation Technology  
Since the emergence of friction electrostatic separation technology, a series of related studies have been carried out both at home and abroad [19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35]. The research on friction electrostatic separation has been active in foreign countries. In the early years, the United States and other countries carried out friction electrostatic separation in the aspects of fly ash decarburization and mineral removal from micro-pulverized coal. However, the domestic start is relatively late, and the research on frictional electrification mainly focuses on the two aspects of pulverized coal treatment and fly ash decarburization. Figure 3: Motion trajectories of negatively charged particles with different particle sizes in an electric field [17; 18]. A, B, C and D represent 44 \(\upmu\)m, 106 \(\upmu\)m, 209 \(\upmu\)m, 400 \(\upmu\)m particles respectively. In the 1970s, the University of Western Ontario [19; 20; 21] designed a fluidized bed friction charge separator, the device consists of a fluidized bed, a metal screen electrode and a U-type (V-type) collecting tank. In order to overcome the problem that fine ore particles are difficult to fluidize, [PERSON] [20] has carried out an experimental study on the electroseparation of 15-45 \(\upmu\)m particles by means of vibratory fluidized bed friction charge method, and a vibratory fluidized bed friction charge separator was developed. The University of Cagliari in Italy has continuously improved the airflow electric separator [22] and redesigned a new type of turbine friction separator. The electrostatic separator overcomes the problem that the fine particles are insufficiently charged due to concentration in the center of the cyclone that they cannot be sorted normally, the low productivity and the high energy consumption. In Germany, [PERSON] and [PERSON] invented a method for improving the electrostatic separation of coal powder to remove pyrite [23], in this method, a fatty acid glycerol ester is used to regulate the treatment of pulverized coal and to control the temperature and humidity in the process of electroseparation, after the pulverized coal is treated by this method, a very good sorting effect can be obtained by multi-stage electric selection. After the 1980s, STI (Delaware High-tech Park, Newark, DE, USA), cooperated with NEP, a New England power plant, to install the first prototype of the STI separator with 18 t/h processing capacity at the Salem Port Power Plant of NEP Company [24]. In Canada, the application of rare-phase cyclotron separator in coal separation experiments at the University of Western Ontario, shows that the removal rate of pyrite is 47% [14]. After the 1990s, [PERSON] [25] developed a kind of rotary friction electric separator, which can charge the material particles by the rotating friction charging device. [PERSON] [26] also developed a novel rotary friction separator (RTS) with obvious particle size range. A friction electroseparator was invented by [PERSON] [27] to remove pyrite and ash minerals from pulverized coal. [PERSON] and [PERSON] studied the electrical properties and triboelectric charge of common associated minerals in coal and coal, the effects of temperature and humidity on the resistivity of coal and its associated minerals are analyzed. It is concluded that increasing the temperature and decreasing the humidity are beneficial to the separation effect [28]. In 2010, [PERSON] analyzed the X-ray fluorescence spectra of four associated minerals and coal sorting products, and concluded that they can be effectively separated by frictional electrification [29]. In 2012, [PERSON] and [PERSON] studied the flow of air and the motion characteristics of particles in the friction electric separator, and found that the air flow movement was greatly disturbed by the friction rod.