Wang Zhijun, Zhu Zhiguan
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo 454000, Henan, PR China.
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, Henan, PR China.
ACS Omega. 2021 Dec 8;6(50):34889-34903. doi: 10.1021/acsomega.1c05562. eCollection 2021 Dec 21.
Heat injection is an effective way to enhance coalbed methane (CBM) extraction. However, at present, the best way to inject that heat is not clear. To determine how the heating rate affects methane desorption, desorption tests at constant high (95 °C) and low (20 °C) temperatures and at three different heating rates (0.3, 0.6, and 0.9 °C/min to 95 °C) were conducted. The desorption content (the volume of gas desorbed per mass of coal) and the desorption rate under the constant 95 °C temperature were greater than those under the constant 20 °C temperature. For the heating rate tests, the total desorption contents under heating rates of 0.3, 0.6, and 0.9 °C/min were 1.322 times, 1.115 times, and 1.095 times that from the constant 95 °C temperature tests, respectively. The final desorption contents from the entire desorption process under heating rates of 0.3, 0.6, and 0.9 °C/min were 1.42 times, 1.30 times, and 1.20 times that from the constant 95 °C temperature tests, respectively. In the early parts of the heating stages, the desorption rates under the three heating rate tests were lower than those under the constant 95 °C temperature tests. When the heating stages ended, the desorption rates under the three heating rates were greater than those under the constant 95 °C temperature tests. After the heating ended, the desorption rates decreased rapidly. A higher heating rate was correlated with a faster decrease in the desorption rate. Kinetic analysis showed that heating coal to a high temperature before methane is desorbed did not suppress the diffusion coefficient decrease. Heating during desorption prevented the diffusion coefficient decrease. A lower heating rate is correlated with a slower diffusion coefficient decrease. Low heating rates were more effective for desorbing methane. The heat injection in the later stage of desorption had a more significant effect on promoting methane desorption than did the early desorption stage heat injection. An equation for calculating the optimal heat injection rate was proposed. These findings will offer significant references for the selection of a suitable way to inject heat to enhance CBM extraction.
热注入是提高煤层气（CBM）开采效率的有效方法。然而，目前最佳的热注入方式尚不清楚。为了确定加热速率如何影响甲烷解吸，进行了在恒定高温（95℃）和低温（20℃）以及三种不同加热速率（0.3、0.6和0.9℃/min至95℃）下的解吸试验。在95℃恒定温度下的解吸量（单位质量煤解吸出的气体体积）和解吸速率大于20℃恒定温度下的解吸量和解吸速率。对于加热速率试验，加热速率为0.3、0.6和0.9℃/min时的总解吸量分别是95℃恒定温度试验解吸量的1.322倍、1.115倍和1.095倍。加热速率为0.3、0.6和0.9℃/min时整个解吸过程的最终解吸量分别是95℃恒定温度试验解吸量的1.42倍、1.30倍和1.20倍。在加热阶段的早期，三种加热速率试验下的解吸速率低于95℃恒定温度试验下的解吸速率。当加热阶段结束时，三种加热速率下的解吸速率大于95℃恒定温度试验下的解吸速率。加热结束后，解吸速率迅速下降。加热速率越高，解吸速率下降越快。动力学分析表明，在甲烷解吸前将煤加热到高温不会抑制扩散系数的降低。解吸过程中加热可防止扩散系数降低。较低的加热速率与较慢的扩散系数降低相关。低加热速率对甲烷解吸更有效。解吸后期的热注入比解吸早期的热注入对促进甲烷解吸的影响更显著。提出了计算最佳热注入速率的方程。这些研究结果将为选择合适的热注入方式以提高煤层气开采效率提供重要参考。
