Experimental study on the thermal properties of coal during pyrolysis, oxidation, and re-oxidation

During heat transfer in coal, the thermal properties parameters (thermal diffusivity, specific heat capacity, and thermal conductivity) play a key role. The thermal properties of coal during pyrolysis, oxidation, and re-oxidation were investigated by laser-flash apparatus LFA457 from 30 to 300 °C. Thermogravimetric (TG) experiments were conducted to analyze the variation of coal mass. The results showed that during oxidation, the thermal properties of coal presented stage characteristics. As temperature increased, the thermal diffusivity decreased first and then increased; the specific heat capacity rose first and then performed steadily; the thermal conductivity presented a slow increment first and then rapidly grew. During pyrolysis and re-oxidation, the thermal diffusivity decreased as temperature increased, while the specific heat capacity and thermal conductivity increased. The thermal diffusivity and thermal conductivity during re-oxidation were higher than those during primary oxidation, while the specific heat capacity was lower. Meanwhile, the sensitivity of thermal diffusivity to temperature during re-oxidation decreased, while the sensitivity of thermal conductivity increased compared with that during pyrolysis and oxidation. The results are meaningful for an understanding of heat transfer in coal seam during spontaneous combustion of coal and fire spread.