Study on the thermal behavior of coal during the spontaneous combustion latency

Although the spontaneous combustion latency provides the initial heat for coal self-heating, the thermal behavior of the process has been scarcely investigated in the literature. The temperature rise characteristics and heat production during the latency was studied using an isothermal flow reactor with a thermopile sensor. Results reveal that the plot of ln (dT/dt) against 1/T follows a second order polynomial function during the isothermal oxidation of coal. The starting temperature and particle size of the coal are fundamental parameters in terms of coal self-heating as it affects both the time taken to reach the peak temperature and the value of peak temperature. The heat generation of coal increased significantly above 50 °C, making coal more prone to spontaneous combustion. Besides, in situ electron spin resonance (ESR) experiments were also carried out to study changes in free radicals of coal during isothermal oxidation. The generating rate of free radicals in the first 10 min is significantly higher, and it gradually becomes slower in the subsequent oxidation. The results from this research will be helpful to inhibit the occurrence of coal spontaneous combustion by reducing the generation and oxidation of free radicals.