Experimental study on the exogenous fire evolution and flue gas migration during the fire zone sealing period of the coal mining face

Fire zone sealing is an effective approach to suppress the spread of underground fire disasters. This study aims to investigate exogenous fire evolution characteristics during the fire zone sealing period of coal mining face. Firstly, the self-designed coal mining face model experimental platform was used to construct a goaf model with a high reduction degree, and then a series of model experiments on fire zone sealing was carried out. The temperature field distribution, the smoke concentration variation, and the exogenous fire source evolution characteristics in the sealed fire zone are analyzed. The results show that under the influence of flue gas and the thermal effect generated by external fire source, the wind speed on the air return side increases sharply from 1.2 m/s to 3.4 m/s, which seriously disturbs the ventilation status. During the sealing process, the temperature of the fire source rises first and reaches a peak of 940.1℃ when it is half-sealed and then decreases rapidly. Different sealing methods have significant influences on fire development characteristics. The SIFTR sealing method can rapidly cut off the airflow, slow down the outflow of the flue gas and significantly reduce the fire source temperature; The SIRS sealing method can steadily reduce the air supply in the fire zone, but its cooling effect on the fire source is not remarkable. The SRFTI sealing method causes airflow disorder in the later stage of fire zone sealing, which possibly leads to methane explosion accidents. The gob space significantly impacts the asphyxiation fire extinguishing effect of sealing. Compared with the single tunnel sealing case, after the mining face fire zone is sealed, the temperature of the fire source decreases more slowly, the smoke concentration in the fire zone reduces at a higher rate, and the oxygen concentration in the fire zone at the later sealing stage rises rapidly. At 120 min after the sealing, the oxygen concentration in all parts of the working face fire zone rebound to 20.07%, so more effective firefighting measures such as nitrogen injection should be adopted to enhance the impact of asphyxiating after the working face fire zone is sealed.