Electrical Properties Of Coal Research Articles

Breakage features of coal treated by cyclic single pulse electrical disintegration

AbstractHigh‐voltage electrical pulse (HVEP) technology, a potential method for degassing coal seam in the future, has made great progress in field application. However, the previous studies mainly concentrated on the coal‐crushing effect of the action of single pulse, ignoring the influence of cyclic single pulse on the fracture structure of coal. In this paper, Huaibei anthracite coal and Inner Mongolia bituminous coal were taken as the experimental objects to study the effect of cyclic single pulse on the fracture structure of coal. The results show that the uneven distribution of electric field in the coal causes the crack to break along the interface between the mineral and the coal. Besides, the characteristics of cracks and functional groups of coal before and after electrical breakdown were investigated through scanning electron microscope and Fourier transform infrared spectroscopy. The results suggest that the relative contents of oxygen‐containing functional groups are reduced after electrical breakdown, which promotes the gas desorption from the surfaces of coal samples. Moreover, changes in CH4 adsorption capacity of HVEP‐treated coal were studied through a high‐pressure adsorption instrument, with the adsorption temperature set from 40 to 120°C. The results show that the adsorption amount of electrically broken coal is smaller than that of raw coal, which proves that temperature and current exert similar influences on the adsorption capacity of coal sample. Additionally, current waveforms indicate that the peak current increases with the number of cycle, whereas the breakdown time decreases with it. However, the peak current and breakdown time will eventually become stable as the number of cycles grows, demonstrating that electrical properties of coal are changed in the process of breakdown, which thus affects the next discharge.

Study on electrical properties of coal at spontaneous combustion characteristic temperature

ABSTRACT In order to study the variation of electrical parameters in the process of spontaneous combustion of coal, first, 9 characteristic temperature points of 5 kinds of coal samples at low temperature oxidation stage and high temperature spontaneous combustion stage were obtained based on temperature programmed experiment and thermogravimetric experiment. According to these experiments samples at characteristic temperature points were prepared. Then, the complex impedance parameters of each coal sample are measured at the alternating current of 20 Hz to n × 106 Hz, and the volume resistivity and the complex permittivity of the coal sample are obtained by calculation. Finally, the volume resistivity temperature model and the complex dielectric constant temperature model of coal samples are obtained by fitting the electrical parameters at 100 kHz test frequency. The results showed that the volume resistivity of coal samples decreased rapidly in the mid-low frequency and slowly in the mid-high frequency. Under the fixed test frequency, the volume resistivity of coal samples rises first and then decreases with the increase of temperature. Both the real and imaginary parts of the complex relative permittivity of coal samples decrease with the increase of temperature, and the slope of the curve decreases gradually.

Electromagnetic Techniques in the Development of Coal-Derived Energy Sources – A Review

AbstractThis paper reviews work performed in applying advanced electromagnetics techniques in the development of coal-derived energy sources and associated conversion processes. Attention is focused in the investigations related to the electrical properties of coal at radio frequencies, and in the modeling and design of electromagnetic systems (both reflection and transmission type) for the remote detection, monitoring, and mapping of coal conversion processes. Specific applications include underground coal gasification (UCG) processes and fluidized-bed combustors (FBC). Recommendations are made of applications where electromagnetic methods should play a prominent role in the future.