Temperature field distribution and parametric study in underground coal gasification stope

In order to study the distribution characteristics and related parameters of the temperature field in underground coal gasification stope, Laplace transform and inverse Laplace transform were used to determine the analytical solution to temperature propagation in the stope under type one boundary conditions. Additionally, Mathematic software was used to conduct numerical simulation. Results indicate that in an unsteady stage, the temperature field gradually propagated in the coal seam, and that the propagation rate became steady after a gradual increase. The time required for the temperature field in the coal seam undergoing gasification to transform from the unsteady to the steady state was inversely proportional to the advance rate of the flame working face. During the stages of temperature increase and decrease, the temperature field in the roof, floor, and surrounding coal seam gradually moved towards the interior. During the temperature increase stage, the peak of the temperature field occurred on the surface of the surrounding rock and gradually increased; it also moved inward from the surface and gradually decreased during the temperature decrease stage. The temperature decrease stage had greater influence on the temperature field in the roof, floor, and surrounding seam than the temperature increase stage. The influence of the temperature increase stage was related to the advance rate of the flame working face; this influence is negligible when the advance rate of the flame working face exceeded a threshold value. Finally, based on the features of the envelope curves of temperature curve families, the ranges of the surrounding coal seam with no load-bearing capacity and coking cycle were obtained, as were after determination of their respective criteria and temperature threshold values.