Time-varying characteristics of electromagnetic radiation during the coal-heating process

- Time-varying characteristics of electromagnetic radiation during coal-heating process were studied.
- The R/S statistical laws of electromagnetic radiation signals in the time series were analyzed.
- The generation mechanism of electromagnetic radiation in coal-heating process was studied.
- A conceptual design of the electromagnetic radiation detection method to conceal fire was presented.

Forecasting and predicting coalfield fire and coal concealed fire are difficult components of coal fire control, and there is currently a lack of widely applicable effective methods for these processes. Electromagnetic radiation (EMR) has the advantage of multi-direction cross-locating and has been widely used to monitor and provide early warnings for coal and rock dynamic disasters. In this paper, the time-varying characteristics of EMR during 3 metamorphic grades of the coal-heating process were studied. EMR signals were clearly generated in different metamorphic grades of the coal-heating process. The variation trend of the EMR signals was different for 3 metamorphic grades of coal. According to R/S statistical analysis of the EMR signal time series, all Hurst values were greater than 0.5 and the correlation coefficient was above 0.9. There is a positive correlation between the EMR signals and coal temperature. In the coal-heating process, the EMR signal intensity varied if the EMR test frequency was 1 kHz, 15 kHz and 50 kHz. Thermal deformation and thermal cracking of the coal body occurred in the coal-heating process. The free electrons and electric dipole in coal migrate and generate EMR. Based on the changing characteristics of the EMR in the coal-heating process, we present the conceptual design of a method to detect concealed fire in underground mines.