Study on electrical properties of coal at spontaneous combustion characteristic temperature

Abstract

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.