Study on the Gasification Mechanism and Kinetic Characteristics of Deep Underground Coal Gasification Based on Pressurized TG-FTIR

Underground coal gasification technology is a crucial supplementary method for coal mining and utilization, as well as a key in situ clean coal utilization technology. It plays a significant role in helping China achieve its strategic goals of "carbon neutrality" and "carbon peaking," holding important practical significance. Pyrolysis pressure is a key factor affecting the yield of deep underground coal gasification. This study employs combined pressurized thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) to investigate the pyrolysis characteristics of raw coal under pressurized conditions. The results indicate that when the pyrolysis pressure is increased to 2.0 MPa, the raw coal undergoes plastic deformation during the slow pyrolysis stage, which significantly inhibits the escape of CO₂ and CH₄. The mass-weighted average activation energy E-(m) of the raw coal pyrolysis process increases with increasing pyrolysis pressure, and the E-(m) rises from 7.108 to 21.414 kJ/mol. As pyrolysis pressure increases, the activation energy of the rapid polycondensation stage and rapid pyrolysis stage increases, while that of the slow pyrolysis stage decreases from 3.874 to 3.405 kJ/mol. This indicates that pressure primarily affects the decomposition and polycondensation of macromolecular structures during pyrolysis. The findings from this work provide new insights into the mechanism of gas separation in pressurized pyrolysis processes and inspire the future practical application of deep underground coal gasification.