Spontaneous combustion characteristics of hydrothermal eroded coal in deep mining

Abstract

In the process of deep mining, the temperature of mine water is significantly higher than that of shallow coal seams. The erosion of high-temperature hydrothermal fluids affects the physical and chemical characteristics of coal, which in turn affects its spontaneous combustion process. To study the spontaneous combustion characteristics and influencing mechanisms of coal under the influence of hydrothermal erosion in deep mining, through low-field nuclear magnetic resonance, molecular dynamics simulation, mechanical test and C600 trace heat experiment, the influence of hydrothermal erosion on coal porosity, pore size distribution, mechanical strength and oxidation heat characteristic parameters was analyzed. Combined with correlation analysis, the correlation between various parameters was quantitatively described. The study results show that under the dual influence of thermal stress and swelling, the internal pore structure of hydrothermal eroded coal changes significantly. There is a significant positive correlation between hydrothermal temperature and total porosity of coal, and the correlation coefficient is 0.97. With the increase of hydrothermal temperature, the total porosity of coal increases from 0.24% to 1.35%, the proportion of micropores decreases from more than 69% to less than 60%, and the proportion of mesopores and macropores increases. Coal body pore size significantly affects the oxygen diffusion coefficient, which increases exponentially with a linear increase in coal body pore size. Under the influence of hydrothermal erosion, the development of coal pores and the dissolution of some organic matter significantly reduce the mechanical strength of coal. From raw coal to 80 ℃ hydrothermal eroded coal, the average compressive strength decreases from 23 MPa to 11.6 MPa, which is reduced by 50%. Compared with raw coal, the heat release intensity of hydrothermal erosion coal is higher and the heat release is greater. The heat release of TH40, TH50, TH60, TH70 and TH80 increase by 12.61%, 16.63%, 17.32%, 19.36% and 25.02%, respectively. The correlation coefficient between hydrothermal temperature and coal oxidation heat release is 0.92. Hydrothermal erosion significantly affects the porosity and oxidation process of coal. As the hydrothermal temperature increases, the porosity of the coal body increases, the mechanical strength weakens, the oxygen consumption and oxidation rate of the oxidation process accelerate, and the heat release increases. Hydrothermal erosion coal has a higher risk of spontaneous combustion, and the higher the hydrothermal temperature is, the greater the risk is.

Keywords

• coal spontaneous combustion
• deep mining
• hydrothermal erosion
• pores
• oxidation