Experimental and Numerical Investigation of In-Situ Pressurized Pyrolysis Characteristics of Tar-Rich Coal

In-situ pyrolysis represents a promising method for the clean and efficient utilization of tar-rich coal; however, the high-pressure underground environment presents substantial challenges for elucidating pyrolysis mechanisms. In this study, ReaxFF molecular dynamics simulations were combined with experimental validation to investigate the pyrolysis behavior of tar-rich coal under high-pressure conditions. Experimental findings indicate that, during the middle-temperature stage of pyrolysis, the activation energy required for char formation increases moderately as pressure increases. Under in-situ pyrolysis conditions, the maximum tar yield for high-tar coal reaches 9.14% at 873 K, while at 2 MPa, the maximum tar yield decreases to 6.97%. Furthermore, the polycyclic aromatic hydrocarbon content in the tar increases with the pressure. Molecular dynamics simulations reveal that the solid-phase pyrolysis process of tar-rich coal slows with increasing pressure. Although the total tar yield increases as the temperature rises to 2000 K, it plateaus at higher temperatures. Despite discrepancies between simulation and experimental results due to scale effects and the omission of heat and mass transfer processes, both approaches display similar pyrolysis trends, thereby reinforcing each other's validity. These findings provide atomic-scale insight into high-pressure in-situ pyrolysis of tar-rich coal and offer theoretical support for its in-situ development.