Modeling temperature distribution upon liquid-nitrogen injection into a self heating coal mine goaf

Abstract

Liquid N2 could be injected into goaf to decrease temperature and prevent spontaneous combustion during mining. A working face at Liangbaosi coal mine was adopted for study. Firstly, a mathematical model for calculating the temperature field in goaf was developed and field tests without injection of liquid N2 were conducted to validate the model. Comparable development trends and hot zones between the simulation and field measurements were found. The hot zones were located about 35–45 m behind the workface on the air-return and air-intake sides in the goaf. Then the model was employed to simulate the time development of temperature distribution in the goaf with injection of liquid N2 from different locations. It was observed that a low-temperature cooling zone (<300K) due to injection of liquid N2 gradually grew and became relatively stable 90 min after continuous injection. The size of the cooling zone depends on the injection location and flow rate. The cooling zone was smaller when the N2 was injected from the air-intake side than from the air-return side. The largest cooling zone was found when the N2 was injected 35m behind the workface from the air-return side. The cooling zone increases with increasing N2 perfusion rate. This study provides a quantitative assessment for preventing coal oxidation and spontaneous combustion using the liquid N2 technology.