Temperature effects on thermal diffusivity of bituminous coal using different pre-oxidation levels in a nitrogenous atmosphere

•Arrangement of molecular chains for oxidised coal became more regular.•Variation of thermal diffusivity for oxidised coal was coherent with that of raw coal.•Change rate of Thermal diffusivity for oxidised coal was weaker comparing raw coal.•Main parameters effecting thermal diffusivity of oxidised coal was obtained. Thermal diffusivity is a prominent parameter affecting heat transfer in coal and thus has a significant effect on coal spontaneous combustion (CSC). Two bituminous coals were collected from the coal mines of Ewirgol and Sangshuping for conducting the experimental tests. The samples were heated to 80, 120, 150, and 200 °C in air using a temperature-programmed device. The parameters of the aromatic micro-crystalline structure were measured by X-ray diffraction, and thermal diffusivity data was obtained using a laser flash apparatus between the temperatures 30 and 300 °C in a nitrogenous atmosphere. The main parameters in the aromatic micro-crystalline structures that affect thermal diffusivity of oxidised coal at 30 °C were explored using the grey correlation method. Results indicated that as temperature increased, the thermal diffusivity of each sample decreased swiftly, then slowly. As oxidation temperature increased, the thermal diffusivity increased linearly. The interlayer spacing of the aromatic micro-crystalline structures decreased, while the other parameters such as interlayer spacing, stacking height of crystallite, extension length, effective number, average grain size, and crystallinity all increased. The main parameters affecting the thermal diffusivity of oxidation coal at 30 °C were derived from the grey correlation degree. These findings are helpful understanding the heat transfer process within oxidised coal.