Early Warning and System Construction for Coal Spontaneous Combustion Based on Multiple Indicator Gases – A Case Study of Wuhai Mining Area

Over 90% of the coal seams mined in China are prone to spontaneous combustion or self-ignition. During the exploitation and utilization of coal, the risk of spontaneous combustion is quite high. In order to achieve the prediction and early warning of coal spontaneous combustion, the four representative coal-bearing strata of the Wuhai mining area were used as research objects. Through the program temperature rise experiment, the variation laws of gas‑generation concentration rate, oxygen‑consumption rate and Graham Fire Coefficient of the coal sample during the oxidation process with the increase of temperature were obtained. The analysis of the experimental results determined that CO, O2, R2(△CO/△O2), C2H4, C2H6, and C2H4/C2H6 could be used as indicators for the early warning of coal seam spontaneous combustion. The temperature range for coal spontaneous combustion early warning was divided into <50°C, 50–100°C, 100–130°C, 130–150°C, 150–250°C, and >250°C. The warning levels were classified as “green, blue, yellow, orange, red, and black.” The seven characteristic stages (latent, oxidation, self-heating, critical, pyrolysis, fission, and combustion) are matched with the evolution of functional groups, and the corresponding reaction types for each stage are clearly defined. This matching enables the early warning signals not only to indicate the degree of danger, but also to indicate the current molecular reaction process of the coal body. Based on this, the identification and prevention of coal spontaneous combustion hazards in the Wuhai mining area were achieved, which is of great significance for ensuring efficient mining of the working face.