Study on the model experiment and numerical simulation for underground coal gasification

The gas production process in underground coal gasification is closely linked to the temperature distribution and seepage conditions of the gasifier. In this paper, mathematical models on the underground coal gasification in steep coal seams are established according to their storage conditions and features of gas production process. Additionally, the paper introduces ways to determine model parameters and the control volume method to solve the model. On the basis of the model experiment, the calculation results are analyzed. From the distribution of temperature field, the calculation value is slightly higher than measurement one. The relative errors of all measuring points are virtually within 10%. According to the simulated calculation results, with the increase of the length for the gasification channel, the heating value of the gas improves. However, behind the reduction zone, it increases with a smaller margin. The influence of the temperature field on the heating value for the gas is noticeable. Due to the effect of temperature, in high temperature zone, the change gradient of the measured value of the concentration field for the gas compositions is larger than that of calculated value. The simulated results of the pressure field in the gasification panel 22 and 75 h after the ignition indicate that the relative calculation errors are 5.00–14.29 and 9.68–17.24%, respectively, with a corresponding pressure drop rate of 9.5 and 11.97%. On the whole, the simulation value conforms with the experiment value, which supports the numerical simulation on the temperature field, concentration field and pressure field of underground coal gasification in the steep coal seams is correct. Thus, it lays a necessary and scientific theoretical foundation for further quantitatively studying the process of underground coal gasification and forecasting the change patterns.