Effect of high temperature on the thermal properties of briquettes

Coal's thermal and physical properties are crucial for safe mining and fire prevention in coal mines. With the rise of underground coal gasification technology, studying coal seam thermal insulation has become vital. Thermal conductivity and thermal diffusivity impact the efficiency, stability, and safety of underground coal gasification. We evaluated the thermal properties of briquette from 30℃ to 300℃ using the hot disk method and differential scanning calorimetry. In a nitrogen atmosphere, we found that thermal diffusivity decreases and specific heat capacity increases with temperature. Thermal conductivity first increases, then decreases. The temperature sensitivity of these properties follows a consistent trend. Both longitudinal (Vp) and transverse (Vs) wave velocities of coal decrease linearly with temperature. Thermal conductivity increases with elastic wave speed, while thermal diffusivity shows an inverse relationship. This is due to the shift from phonon-like heat transfer to high-frequency diffusion as temperature rises, reducing the correlation between wave velocity and thermal properties. We established prediction models for thermal conductivity and thermal diffusivity based on elastic wave velocity. Our results provide a framework for selecting and evaluating the stability of underground coal gasification sites. They also offer insights for predicting coal and rock thermal properties from well logging data.