Study on the propagation law of temperature field in surrounding rock of underground coal gasification (UCG) combustion cavity based on dynamic thermal parameters

Abstract

Abstract The high temperature generated during underground coal gasification will not only produce high-temperature thermal stress in the surrounding rock of the combustion area, but also change the physical and mechanical parameters of the surrounding rock. The change of thermal parameters affects the expansion of the temperature field inside the surrounding rock, causing the change of mechanical properties and internal thermal stress of surrounding rock in combustion zone, and then affects the stability of the gasifier. In the past, the research on the propagation law of temperature field in surrounding rock of combustion zone based on dynamic variation of thermal parameters with temperature was very limited, which severely limited the development of the strata control technology of underground coal gasification, so it is urgent to carry out this research. In this study, an explicit finite difference method is used to establish a numerical model for calculating the temperature field in materials under the thermal parameters varying with the temperature, which is applied to the study of the temperature field expansion in the surrounding rock of the combustion area of the underground coal gasification, obtaining the following results: With time, the influence range of temperature field in the strata gradually expands, and the temperature of each point in the strata increases first and then decreases, and the temperature extreme gradually expands to the inside of the strata. By extracting the temperature extremes of each point of surrounding rocks in the combustion cavity, it is found that the propagation range of temperature field is 11.4 m in the roof, 9.3 m in the floor and 9.6 m in the coal wall on both sides. The coal wall within 3.1 m on both sides of the combustion cavity loses its bearing capacity, and the bearing capacity of the coal wall within 1.7 m decreases, which has adverse effects on the coal wall within 4.8 m. This study can play an important role in promoting the progress of surrounding rock control technology of underground coal gasification.