A thermal-mechanical coupled numerical model for simulation of coal gasification trial at Wieczorek, Poland

摘要

Underground coal gasification (UCG) is a combination of mining, exploitation and gasification that eliminates the need for conventional mining techniques in areas where coal is difficult to access.UCG also has potential environmental benefits compared to conventional coal mining and processing methods.The focus of this paper is the numerical simulation of the UCG field trial at Wieczorek,Poland.In the field trial,a continuous reaction injection point process was adopted (CRIP) within a 6m thick coal layer located at a depth of 452m.A coupled thermal-mechanical numerical model was created in which temperature dependant mechanical properties were assigned based on laboratory data.Three temperature ranges within which the mechanical properties change significantly were identified from laboratory experimentation, and material behaviour was assigned within the numerical models based on these temperature ranges.The CRIP process was simulated by moving the front head of an injection well with a velocity of 1m/day, based on field trial specifications.The coal burning process was simulated by modifying the energy balance equation with an additional term as a source that relates to the calorific value of coal.The source term was modified with a time decay function to account for the gradual decrease of energy from the coal over time as it burns.The mechanical degradation of coal due to burning was simulated by removing the burnt zones from the calculation after a specific time.In this study, it was found that maximum temperature was always less than 1100oC, which agrees with available literature.Results will be presented which illustrate the rate and magnitude of burning as well as effects on ground movements.The results have implications to engineers working in the design and operation of UCG.