A back analysis of the temperature field in the combustion volume space during underground coal gasification

Abstract

The exact shape and size of the gasification channel during underground coal gasification (UGC) are of vital importance for the safety and stability of the upper parts of the geological formation. In practice existing geological measurements are insufficient to obtain such information because the coal seam is typically deeply buried and the geological conditions are often complex. This paper introduces a cylindrical model for the gasification channel. The rock and soil masses are assumed to be homogeneous and isotropic and the effect of seepage on the temperature field was neglected. The theory of heat conduction was used to write the equation predicting the temperature field around the gasification channel. The idea of an excess temperature was introduced to solve the equations. Applying this model to UCG in the field for an influence radius, r, of 70 m gave the model parameters, u_1,2,3…, of 2.4, 5.5, 8.7… By adjusting the radius (2, 4, or 6 m) reasonable temperatures of the gasification channel were found for 4 m. The temperature distribution in the vertical direction, and the combustion volume, were also calculated. Comparison to field measurements shows that the results obtained from the proposed model are very close to practice.