Surface characteristics and re-ignition law of water-soaked coal in a coal mine closed fire area

There are different degrees of oxidized coal samples in the gobs of coal mines, and there will be hidden dangers of re-ignition of water-soaked coal after the fire zone is closed. Using an atomic force microscope (AFM) and a simultaneous thermal analyzer, the re-ignition properties of coal samples and the pore dynamic evolution in different water-immersed areas of the goaf were studied. The results show that the IO (oxidation after water immersion) coal sample has a more microporous structure and larger fractal dimension when oxidized at 300 °C. The roughness of OI (water immersion after oxidation) coal samples decreases as the oxidation temperature increases. The re-ignition temperature points of the IO300 and O200I coal samples are lower, and the combustion heat release is greater. Before reaching 311 °C, the oxidation kinetics curve conforms to the cubic polynomial ln[-ln(1-a))/T2] =A(1/T)3-B(1/T)2 + C(1/T)-D. After reaching 311 °C, the activation energy of IO300 and O200I coal samples is smaller and more prone to oxidation and re-ignition, which conforms to ln [- ln (1-a))/T2] =A (1/T) – B. Different control measures can be taken in different areas and points based on the oxidized degree and different immersion methods to prevent coal spontaneous combustion (CSC) in closed fire areas.