Thermophysical properties of coal during low temperature oxidation under different oxygen concentrations

Thermophysical properties govern the heat transfer during coal spontaneous combustion. Under different oxygen concentrations, the mass and heat intensity of three metamorphic levels of bituminous coal were investigated through synchronous thermal analysis, and their thermophysical parameters were tested using a laser-flash apparatus. The results indicated that as the oxygen concentration increased, the T-3 (the temperature at maximum mass) and exothermic initial temperature slowly decreased. The changes in T-1 (maximum adsorption temperature) and T-2 (initial temperature at the oxygen-absorption and mass-gain stage) were nonsignificant. The effect of oxygen concentration on mass, heat intensity, and thermophysical parameters was primarily concentrated in high-temperature regions. As the temperature increased, the thermal diffusivity first decreased and then increased. The specific heat capacity gradually increased, then plateaued until it began to decrease; meanwhile, the thermal conductivity increased, first slowly and then quickly. A calculation model for different temperatures and oxygen concentrations was established through curve fitting.