Abstract It is necessary to study the thermophysical properties and heat transfer mechanism of coal for underground coal gasification (UCG). The long-flame coal from Ningtiaota coal mine was pyrolyzed and oxidized at different temperatures (200, 250, 300, 350 °C in nitrogen, and 100, 150, 200, 225, 250, 275, 300, 325 °C in air), respectively. The influence of pre-treatment temperature and real-time temperature on thermal diffusivity, specific heat capacity, and thermal conductivity of coal was studied by laser-flash method. The results show that there are strong correlations between temperatures and thermophysical properties. During the real-time testing, with the rise of real-time temperature, the thermal diffusivity of different pre-treated coal decreases and the change rate gradually decreases. Meanwhile, specific heat capacity and thermal conductivity increase, and obvious stage characteristics are shown around 210–240 °C. Pyrolysis and oxidation can significantly degrade the thermal diffusivity and thermal conductivity of coal samples, and the degradation degree of oxidized coal is higher. The specific heat capacities of pyrolyzed and oxidized coal are normally higher than raw coal, and the effect of oxidation on the specific heat capacity increases with real-time temperature. The results can provide an important reference for exploring coal’s thermophysical properties change mechanism during the process of UCG.
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