Experimental investigation on microstructure influence of high temperature on spontaneous combustion of coal with different ranks

Deep coal mining brings new challenges for prevention and control of spontaneous combustion in coal mines. For example, high geothermal environment caused by the increase of mining depth directly changes the initial conditions of coal oxidation and self-heating, then affects the micro-structure of coal, and increases the risk of fire. In order to study the influence of high geothermal environment on spontaneous combustion characteristics of coal in deep coal mining, eight coal samples with different coal rank were tested and compared. The coal samples were treated in simulated high ground temperature environment for 30 days and their pore structure changes were measured by static capacity method. The variation of main active groups of coal under the influence of ground temperature were analyzed by the Fourier infrared spectroscopy. The CO yield from the test was compared with the CO yield in the programmed temperature experiment at 180 ℃. The results show that the changes of —OH stretching (free hydroxyl group) and C—H structure (aliphatic hydrocarbons) in coal are the largest. The specific surface area of anthracite coal decreases to as low as 46.01% under the long term high geothermal environment. The pore of bituminous coal is mainly larger than 3 nm, with least structure change after treating. The pore size of lignite coal is more developed than that of bituminous coal. After treatment, the specific surface area of lignite and bituminous coal increases by 4.04% and 20.4% respectively, and the average pore size of lignite and bituminous coal decreases by 20.5% and 14.4% respectively. The influence of ground temperature on coal spontaneous combustion with different coal rank is significantly different. High ground temperature in-creases the CO production of anthracite, bituminous and lignite coal by 13.1%, 28.5% and 36.1%, respectively, which indicates that low-rank coal is more susceptible to high ground temperature environment. This research provides a reference for the prevention and control of fire hazards in underground mine gob in high geothermal environment.