Elastic wave response characteristics and mechanism of coal oxidation spontaneous combustion

doi:10.16265/j.cnki.issn1003-3033.2025.05.1689

Abstract

Abstract:

In order to accurately locate the hidden spontaneous combustion area inside the broken coal pillar using elastic wave detection, the response characteristics and mechanism of the elastic wave velocity of coal to temperature were experimentally studied. Firstly, coal samples were pretreated by temperature programmed furnace to obtain coal samples with different oxidation degrees. Then, elastic wave and low-field NMR tests were conducted to analyze the characteristics of elastic wave and pore cracks of coal with different oxidation degrees. Finally, combined with thermogravimetric(TG) analysis and single variable briquette experiments, the elastic wave response characteristics and mechanism of coal oxidation spontaneous combustion were revealed. The results show that the P-wave and S-wave velocities of raw coal gradually decrease with increasing temperature, and the P-wave velocity decreases 2.4 times that of the S-wave velocity after the maximum mass loss temperature of TG curve. The decreasing trend of P-wave velocity shows an obvious segmental characteristic. Before the maximum mass loss temperature of the TG curve in stage Ⅰ, the P-wave velocity decreases at a rate of approximately 1.27 m/s·℃^-1. from the maximum mass loss temperature to the final temperature, the decline rate of P-wave velocity increases to 4.51 m/s·℃^-1. The porosity of coal increases from 1.57% at 30 ℃ to 9.6% at 360 ℃. In particular, after the temperature exceeds the maximum mass loss temperature, the number and aperture of cracks increase significantly, which not only lengthens the propagation path of elastic waves, but also decreases the propagation speed of elastic waves. As the propagation medium of elastic waves, the coal matrix does not decompose obviously before the maximum mass loss temperature, and the corresponding P-wave velocity of briquette remains stable at about 900 m/s. After exceeding the maximum mass loss temperature, the coal matrix decomposes rapidly, and the corresponding P-wave velocity of briquette drops to 798 m/s at 360 ℃, which proves that the coal matrix gradually transitions from a "high wave velocity" medium to a"low wave velocity" medium.

Key words: coal oxidation spontaneous combustion, elastic wave, response characteristics, pore and fracture, longitudinal wave velocity, coal matrix

CLC Number:

X936

ZHU Shuangjiang, LU Yi, LI He, LI Min, GUO Xin, ZHAO Xin. Elastic wave response characteristics and mechanism of coal oxidation spontaneous combustion[J]. China Safety Science Journal, 2025, 35(5): 145-152.

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