Research progress on numerical simulation methods and models for underground coal gasification

Coal underground gasification (UCG) transforms the physical extraction of coal into the chemical extraction of gas, which is effective for exploiting deep coal deposits. Numerical simulation technology for UCG is a crucial tool for studying the complex processes involved in coal gasification. This study was conducted to determine the direction in which UCG numerical simulation is developing, specifically by reviewing the research progress and achievements made in this area and identifying the existing problems and future research directions. The findings indicate the following: (1) Research has focused on the reaction issues of coal underground gasification, considering mass and heat transfer effects and gasification cavity expansion. Chemical equilibrium, gasification block, packed bed, and gasification channel models have been developed, which have certain advantages in solving gasification reaction problems influenced by cavity structure and reasonable simplifications capable of describing local issues. (2) The dynamic description of gasification cavity structures is a challenging problem that UCG numerical simulation needs to address. The cavity expansion mechanism includes thermochemical consumption, coal spalling, roof collapse, and debris accumulation. Thermochemical consumption causes the mechanical properties of coal and rock to change, leading to spalling under stress. (3) Process models emphasize dynamic simulations of the gasification process, including cavity evolution and gasification products. The reactor combination model, continuous medium equivalent model, and multimodule integration model are primarily used. (4) Future UCG numerical simulation technology development will prioritize modularity, systematization, and intelligence. There is an urgent need to facilitate the chemical reaction kinetics of large coal blocks, the coupling of discontinuous media, and the integration of multifunctional systems, including that of numerical simulation technology with artificial intelligence. With continuous improvements, numerical simulation technology will play a greater technical supporting role in UCG industrialization.