The development of exothermic surface reaction between coal and oxygen affected by methane during coal spontaneous combustion in gob

Abstract

Coal spontaneous combustion (CSC) derives from the exothermic coal-oxygen reaction occurring at coal's surface. However, methane's influence on this process is still unclear in gob environments. To this end, non-isothermal experiments were performed to elucidate methane's impact on the exothermic effect, pore structure evolvement, and surface composite variation in CSC. Our findings indicated that methane inhibited the exothermic effect; however, low methane (<42.9 %) did not significantly reduce the danger of CSC, but increased methane explosion risk. Methane's influence on pore structure can be elevated by a higher temperature, leading to larger pores, greater surface area, and higher pore volumes. X-ray photoelectron spectroscopic analysis revealed an increase in C1s, C-C and C-H bonds with rising methane and a decrease in O1s and oxygen-containing groups. C-O groups were the main structures affected by methane. O1s and oxygen-containing groups remained stable at low (<20 %) and high (>50 %) methane concentrations, because coal lay in oxygen-rich and fuel-rich oxidation states, respectively. Methane's influence on exothermic reaction originates from competitive adsorption. Methane competes with oxygen and other gases for adsorption sites. This changes the surface properties and affects the competitive adsorption between methane and other gases. This study can provide valuable insights for mitigating CSC risk.