Study on multi field coupling numerical simulation of nitrogen injection in goaf and fire-fighting technology

In order to effectively prevent the spontaneous combustion of residual coal in goaf, taking the 10,101 fully mechanized top coal caving face of Baozigou coal mine as research object, the multi-field coupling numerical model of nitrogen injection in goaf is established. The FLUENT software is used to study the variation law of spontaneous combustion zone in goaf under dynamic mining of working face with different nitrogen injection parameters, determining the range of spontaneous combustion zone in stable stage. The fitting curve between nitrogen injection parameters and width of spontaneous combustion zone in goaf is obtained. Results show that with the increase of nitrogen injection depth from 10 to 60 m, the width of spontaneous combustion zone in goaf begins to decrease gradually, yet the width of spontaneous combustion zone tends to expand after more than 40 m. When the nitrogen injection location is 40 m, the spontaneous combustion zone width decreases from 49 to 22 m as the nitrogen injection volume increases from 500 to 1000 m(3)/h. Nitrogen injection continuously reduces the area of high temperature zone and temperature extreme value. When the nitrogen injection parameter is set to (40 m–1000 m(3)/h), temperature extreme value decreases by 308.85 K compared with that without nitrogen injection. When the nitrogen injection parameter is (40 m–690 m(3)/h), it can meet the inert cooling requirements of goaf. The width of spontaneous combustion zone is 31 m and the temperature extreme value is 309.95 K at the moment. Finally, engineering application of the fire prevention technology combining shot-off loss wind and nitrogen injection is used to test effect of spontaneous combustion prevention and verify accuracy of nitrogen injection simulation. CO concentration at the measuring point 1, 3 and 5 are reduced to 0 × 10(−3)‰, 2 × 10(−3)‰ and 1.2 × 10(−3)‰, and temperature are reduced to 295.15 K, 296.15 K and 295.65 K respectively. It shows that the spontaneous combustion of residual coal in goaf has been successfully controlled.