Abstract:
The method of sensing coal spontaneous combustion temperature based on acoustic wave technology has the advantages of wide application scenarios and real-time continuity, but the precursor characteristics of acoustic wave signals in the process of coal spontaneous combustion have not yet been revealed. The study of acoustic effects and precursor characteristics in the process of coal spontaneous combustion provides a theoretical basis for the detection and warning of coal spontaneous combustion by acoustic wave method. The article firstly theoretically analyses the thermal damage rupture evolution process and acoustic wave transmission characteristics of coal rock. Three sizes of coal spontaneous combustion acoustic wave information testing systems were established to test the infrasound, acoustic emission and acoustic sound velocity information during coal heating and combustion. Using linear fitting, multiple fractal theory, Fourier transform and other methods, the paper analyse the temporal characteristics, temperature correlation, spatial characteristics, nonlinear characteristics and spectra of acoustic signals to reveal the precursor characteristics of acoustic signals in the process of spontaneous combustion of coal. The results show that with the increase of coal temperature, the infrasound sound pressure value increases paroxysmally, and the ringing counts, energy value and acoustic sound velocity of acoustic emission signals are positively correlated with the temperature. The infrasound signals and acoustic time changes were more obvious in the pre-coal spontaneous combustion period. The acoustic emission signal increases and changes more significantly after 100 ℃. The acoustic signal has spatial characteristics. With the increase of the distance from the heat source, the ringing count and energy change by decreasing. The speed of sound at different distances increases with increasing temperature, and the
R2 of the speed-temperature fitting equation exceeds 0.9. The infrasound and acoustic emission signals have multiple fractal characteristics during coal heating and correspond well with the thermal rupture of spontaneous coal combustion. In addition, the main frequency of infrasound waves migrated and the amplitude of the main frequency increased during the process of coal warming. Finally, the acoustic emission test was carried out in the high-temperature anomaly area of the coal field. The acoustic emission signals in the temperature anomalies change significantly.