75 / 2023-06-08 15:08:47

Study on the Thermal Characteristics of Coal Spontaneous Combustion under Variable Oxygen Conditions

Metamorphic degree; Coal spontaneous combustion; Variable oxygen conditions; Thermogravimetric analysis; activation energy

Mine fires are the most frequent disasters that occur during coal mining. Nearly 60% of mines in China have experienced fires, and the most severely affected areas are mined-out area that cause coal spontaneous combustion fires. The division of the "three zones" in goaf not only reduces the phenomenon of coal spontaneous combustion, but also provides rapid prevention and remedial measures for the dangerous areas of spontaneous combustion . However, the reaction process of coal spontaneous combustion under variable oxygen conditions is complex and difficult to control, so mine fires caused by coal spontaneous combustion under different oxygen concentrations are still frequent. The reason for this situation is that coal with different degrees of metamorphism exhibits differences in spontaneous combustion reaction characteristics due to changes in oxygen concentration. Therefore, exploring the characteristics of coal spontaneous combustion under variable oxygen conditions will provide guidance for the division of the "three zones" in goaf and the prevention and control of coal spontaneous combustion. At present, Thermogravimetric analysis experiment has been widely used. This technology can accurately calculate and analyze the change of middling coal quality, heat release and kinetic parameters in the process of coal oxygen reaction, which has been used by many scholars to explore coal spontaneous combustion. At the same time After studying the kinetic parameters of different coal ranks using the Coats Redfern integration method, it was found that activation energy can identify the tendency of coal spontaneous combustion. Therefore, studying the activation energy of coal through functional methods is of great significance for the prevention and control of coal spontaneous combustion. In response to the fact that coal still has the ability to oxidize and self ignite under different oxygen concentrations, three types of coal with different degrees of metamorphism, namely brown coal, gas coal, and fat coal, were selected as experimental samples for synchronous thermal analysis experiments. The results showed that coal with different degrees of metamorphism has the ability to oxidize and self ignite under oxygen concentrations of 3%, 5%, 10%, and 14% The thermogravimetric curve under 18% conditions and the Coats Redfren integration method were used to integrate the oxygen absorption and weight increase stages and thermal decomposition stages of coal, in order to analyze the spontaneous combustion of coal and study the spontaneous combustion characteristics and critical oxygen concentration of coal with different metamorphic degrees. The result analysis shows that the lower the degree of deterioration of the coal, the more likely it is to undergo oxidation reactions and the higher the propensity for spontaneous combustion. As the degree of coal densification increases, the weight loss rate of the coal at different oxygen concentrations gradually decreases. The exothermic heat of spontaneous combustion of lignite, gas coal and fatty coal at oxygen concentrations of 3%-5%, 10%-14% and 14%-18% respectively are greater than the other oxygen concentration stages while the apparent activation energy gradually decreases. The results of this research can provide a theoretical basis for the delineation of three zones of coal spontaneous combustion in coal mining areas with similar degrees of metamorphism.