Meitan xuebao (Apr 2024)
Gas injection methods and energy recovery efficiency in underground coal gasification
Abstract
The study of energy recovery from underground coal gasification (UCG) with different gas injection methods is conducive to the development of a more efficient UCG process. Various UCG modeling experiments were designed and implemented for fixed and mobile gas injection points, the total gasification coal consumption and rate were calculated based on stoichiometry and carbon balance method, and the effects of the two gas injection processes on the composition and calorific value of the gas were compared and analyzed. On this basis, the changes in gas production per unit of coal and effective gas composition under different gas injection methods were analyzed, and the energy recovery rates of the two gas injection process experiments were evaluated. The results show that increasing the net O2 injection flow rate can improve the gas calorific value decay in the fixed injection point experiment, but the promotion effect of increasing the net O2 injection flow rate on the gasification reaction decreased with the expansion of the gasification cavity. By increasing the net O2 injection flow rate three times, the calorific value of gas was increased by 2.01, 1.27 and 1.10 MJ/m3, respectively, and the gasification efficiency (the ratio of the calorific value of the gas to the heat of combustion of carbon) was increased by 14.64%, 9.45% and 7.73%, respectively. Moving the position of the gas injection point can achieve a short-time rapid recovery of the calorific value of the gas and the gasification efficiency. Moving the position of the gas injection point four times, each time the moving distance was 300 mm, the calorific value of the gas was increased by 2.95, 3.32, 3.37 and 2.54 MJ/m3, respectively, and the gasification efficiency was increased by 17.99%, 21.04%, 27.88%, and 13.92%. The two gas injection process experiments respectively gasified 72.49 kg and 91.47 kg of coal, and the average coal consumption rate was 0.97 and 1.27 kg/h. The gasification efficiency and coal consumption rate showed a synchronous mutation, and this phenomenon was more obvious after changing the injection conditions of the gasifier and moving the position of the gas injection point, which indicated that there was a certain relationship between the gasification efficiency and the coal consumption rate. Compared with the fixed gas injection point experiment, moving the location of the gas injection point can effectively improve the gasification effect, and the effective gas composition and gasification efficiency was increased by 12.5% and 23.23%, respectively, under the same gasifier injection conditions.
Keywords
