Study on the influence of different rock/coal mixture ratio on thermal storage and low temperature oxidation of coal

Coal mines in the goaf are formed by the collapse and accumulation of coal rock, and the process of oxidizing and heat storage of singular coal does not reflect the real environmental conditions within the airspace. In this study, coal and rock mixing on coal spontaneous combustion (CSC) is experimentally investigated, and the bituminous coals and typical siltstones, mudstones and shales in the overlying rock layers of the goaf are selected. The different rock/coal blending ratios and real low oxygen conditions in the goaf are considered. The results show that in addition to coal, shale also contains some substances such as graphite and fixed carbon, which would participate in oxidization and heat storage processes. The thermal conductivity and thermal diffusivity of the rock/coal mixtures increased with the increase of the rock blending ratio. The heat storage capacity of the three rocks is shale > mudstone > siltstone. After blending rocks in bituminous coal, the contents of functional groups –OH, –CH3, –CH2, CC, etc. is decreased, and the degree of decrease is greater with the increase of blending ratio, and the degree of decrease of shale/coal mixture is relatively small compared with the others. As the proportion of rock in the rock/coal mixture increases, all oxidized combustion stages are delayed to varying degrees. Under the same oxygen concentration, the activation energy of rock/coal mixtures is higher than bituminous coal, and the activation energy of siltstone/coal, mudstone/coal, and shale/coal increased by 25.28 %, 20.12 %, and 14.84 %, respectively. The degree of CSC inhibition by the three rock/coal mixtures is siltstone/coal > mudstone/coal > shale/coal. The research results are of great significance to the prevention and control of CSC in the real environment of goaf.