Experimental Study of Coal Pyrolysis under the Simulated High Temperature and High-Stress Conditions of Underground Coal Gasification

Coal pyrolysis under high-temperature and high-stress conditions was studied experimentally in this work. Which experimental table should be chosen was studied, and parameter settings such as the final pyrolysis temperature, heating rate, and stresses were investigated, Pyrolysis experiments of Xinglongzhuang gas coal and Huating long-flame coal were conducted using an improved Paterson gas-medium high-pressure and high-temperature testing (Paterson HPT) system at temperatures of up to 1000 degrees C and under different stresses conditions. The results were compared to those of coal pyrolysis experiments without any stress and using a GRTE80/11 tube furnace. The average heating rates used in these experiments were as low as 0.44 K/min. The produced gas and semicoke (coke) yields both increased with increasing stress, while the tar yield decreased. However, the variations in the yields of the pyrolysis products induced by the same increase in stress gradually decreased as the stress:increased and nearly reached a peak at approximately 750 degrees C. The concentrations of CH4 and CO2 in the pyrolysis gas gradually increased with increasing stress, while the H-2 and CO concentrations gradually decreased. Regarding the variations in H-2, CO, CH4, and CO2, the Huating coal displayed significantly more variations than the Xinglongzhuang coal for the same increase in, stress, indicating its higher sensitivity. The variation curve for each gas component under each stress state was similar to the corresponding curve in the stress-free state, indicating that temperature is a dominant factor in coal pyrolysis, and that the effects of stress-induced secondary reactions are relatively small.