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 degrees 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 degrees 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 degrees 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.