Coal fire prevention in large areas over long term with a composite inert gas-a case study in Tangkou coal mine, China

In order to effectively control the serious spontaneous combustion of residual coal in large areas over long term, and reduce the cost of fire prevention process, ensure the safety of fire prevention process, we injected a composite inert gas (1:1 v/v CO2 and N-2) into the goaf at the 5306 working face of the Tangkou coal mine. Thanks to its special properties, the composite inert gas overcame some shortcomings of using only N-2 or CO2 as the inert gas and showed some unique features. Field test results at the 5306 working face showed that 9 days after the injection of the composite inert gas, the CO concentration rapidly decreased from 14.9 ppm to 0.1 ppm and from 4821 ppm to 21 ppm in the return airflow and in the corner of the return air at the working face, respectively. Meanwhile, the concentration of CO2 in the return airflow never exceeded 1500 ppm (Maximum allowable concentration) after the injection of composite inert gas into the goaf. Therefore, the composite inert gas, which is also cheaper than CO2, could effectively reduce fire risk in goaf over an extended time without compromising the safety of underground workers.