Simulation study on coal pyrolysis in deep coal underground gasification process

The study of coal seam temperature fields traditionally focuses on establishing the overall heat conduction equation of the coal seam and the gasification reaction of coal char, often ignoring the relationship with coal pyrolysis and the influence of heat absorption. In the complete gasification process, however, it is necessary to study the detailed pyrolysis and gasification characteristics of the coal seam. In this paper, the gasification process parameters of coal and rock are obtained by analyzing samples from a depth of more than 900 m. By considering the influence of coal pyrolysis and heat absorption on the evolution of the temperature field, a modified chemical percolation devolatilization (CPD) model is established based on the target coal samples. The results demonstrate that coal pyrolysis endothermy significantly suppresses the temperature rise rate and reduces the peak coal seam temperature by 35–45 °C compared with scenarios ignoring pyrolysis, verifying the strong coupling among pyrolysis, heat absorption, and temperature field evolution. The composition of the product gas and corresponding kinetic parameters are highly dependent on the coal molecular structure. Quantitative analysis shows that the semi-coke yield reaches its maximum at 550 °C, tar yield ranges from 11.2 to 13.1%, and the average carbon conversion rate during coal gasification is approximately 97.32%.