Combination of heat energy extraction and fire control in underground high-temperature zones of coal fire areas

Coal fires are global disasters. Large quantities of coal resources are burned worldwide, and enormous quantities of heat energy are generated as a result. To realize the combination of heat energy extraction and fire control in coal fire areas, a forced convective heat extraction and cooling (FCHEC) method was proposed. Numerical simulations, experiments, and field tests were conducted to analyze the borehole layout, heat transfer medium (HTM), and applicability of this method. The results revealed that when HTM injection and extraction boreholes reached the high-temperature area in the residual coal zone, the proposed method yielded the greatest decrease in temperature. An HTM containing a mixture of water mist and nitrogen was developed and applied for FCHEC in field tests. The coal fire in the test area was effectively controlled, and the heat energy was extracted. At the center of the test area, the maximum temperature decreased by 56.6%, and the heat extraction rate reached 12.4 kW. This study provides a feasible method that promotes the utilization of coal fire as a resource and achieves an effective combination of heat energy extraction and coal fire management.