College of Mining Engineering, Taiyuan University of Technology, Taiyuan, 030024, Shanxi, China.
College of Safety and Emergency Management Engineering, Taiyuan University of Technology, Jinzhong, 030600, Shanxi, China.
J Environ Radioact. 2023 Dec;270:107284. doi: 10.1016/j.jenvrad.2023.107284. Epub 2023 Aug 25.
The surface isotope radon measurement method (SIRMM) is widely used in fire source detection in abandoned mines. However, studies on the long-distance migration of radon during coal spontaneous combustion are lacking, which hinders the further popularization of this technology in coal fire prevention and control. For this reason, the migration law of radon in overlying strata in fire areas was studied through experiments and numerical simulation. The radon exhalation concentration of coal was found to increase at first and then decrease in the range of 30-350 °C through experiments. The radon concentration reaches the maximum value (557.1 Bq/m) at 150 °C, which is 6.3 times higher than that at 30 °C. Based on the radon source term obtained by fitting the experimental data, the radon migration model of coal spontaneous combustion in abandoned goaf was constructed, and the dynamic distribution characteristics of the airflow, temperature, and radon concentration fields in the overlying strata area were analyzed. The internal relationship between surface radon and underground fire source was discussed. The simulation results revealed the sharp change in the porosity of the overlying rock causes radon concentration at the interface between the caving and fissure zones to increase continually with the process of spontaneous combustion, providing material and energy support for the long-distance radon migration. When the maximum temperature of the coal pile reaches 70 °C, the concentration of radon released from the coal pile increases rapidly to 13696 Bq/m, and the radon from the underground space appears on the surface at this temperature. In the range of 70-150 °C, with rapid increase in radon released from coal piles, the surface concentration of radon also increased rapidly to 225 Bq/m. At the high-temperature stage exceeding 150 °C, the concentration of radon released from coal piles exhibited a downward trend, resulting in a decrease in the rate of increase of radon concentration on the surface. A close relationship between the surface radon concentration and underground fire source temperature in the process of coal spontaneous combustion was observed. In the spatial position, the peak position of radon on the surface was highly consistent with that of the fire source longitudinally, which ensures the accuracy of the SIRMM to determine the location of the hidden fire source. This suggests that the SIRMM can accurately evaluate the fire source's temperature and fire area's development trend.
表面同位素氡测量方法（SIRMM）广泛应用于废弃矿井火源探测。然而，对于煤自燃过程中氡的长距离迁移的研究还比较缺乏，这阻碍了该技术在煤火灾害防治中的进一步推广。为此，通过实验和数值模拟研究了火区上覆岩层中氡的迁移规律。实验发现，煤的氡逸出浓度在 30-350°C 范围内先升高后降低。在 150°C 时，氡浓度达到最大值（557.1 Bq/m），是 30°C 时的 6.3 倍。基于拟合实验数据得到的氡源项，构建了废弃采空区煤自燃的氡迁移模型，分析了上覆岩层区域内风流、温度和氡浓度场的动态分布特征，探讨了地表氡与地下火源之间的内在关系。模拟结果揭示了上覆岩层的孔隙率急剧变化，导致冒落裂隙带界面处的氡浓度随着自燃过程的不断增加，为长距离氡迁移提供了物质和能量支持。当煤堆的最高温度达到 70°C 时，煤堆释放的氡浓度迅速增加到 13696 Bq/m，地下空间的氡在此温度下出现在地表。在 70-150°C 范围内，随着煤堆释放的氡迅速增加，地表氡浓度也迅速增加到 225 Bq/m。在超过 150°C 的高温阶段，煤堆释放的氡浓度呈下降趋势，导致地表氡浓度增加率下降。在煤自燃过程中，地表氡浓度与地下火源温度之间存在密切关系。在空间位置上，地表氡的峰值位置与纵向火源高度一致，这保证了 SIRMM 确定隐火源位置的准确性。这表明 SIRMM 可以准确评估火源温度和火区的发展趋势。
