115 / 2023-06-15 22:56:27

Study on spontaneous combustion characters of magmatic erosion coal based on active sites

Magmatic erosion; Thermal decomposition; Active sites; Free radical;

In recent years, as mining depth has increased, an increasing number of mines have experienced the phenomenon of magma intrusion into coal. With the occurrence of magma-eroded coal spontaneous combustion during mining, there has been an increasing focus on the influence of geological conditions on the characteristics of coal spontaneous combustion. Magma intrusion created a high-temperature environment within the coal, which led to a sealing effect. High temperature facilitated several significant effects, including the secondary hydrocarbon generation of coal, an increase in vitrinite reflectivity, the development of pore structure, and the removal of volatiles. Following magma erosion, the coal would undergo low-temperature oxidation during mining. The difference was that the low-temperature oxidation process of magma-eroded coal occurred after the thermal decomposition of coal. Extensive production practices have revealed that coal affected by magmatic erosion exhibits a tendency for a significant rise in CO concentration and spontaneous combustion, even when the degree of coal metamorphism is high. Several scholars have conducted temperature-programmed experiments on magma-eroded coal, revealing that oxygen consumption increased, the cross-point temperature decreased, and the spontaneous combustion tendency was heightened. The assessment of the spontaneous combustion propensity of silicified coal in contacted metamorphism with magma suggests that silicified coal exhibited a reduced likelihood of spontaneous combustion. As a result, the existing findings regarding the impact of magma erosion on the coal spontaneous combustion characteristics presented divergent results. These results indicated significant variations in the coal spontaneous combustion characteristics within different zones of magma influence. Furthermore, the current understanding of the magma intrusion spontaneous combustion characteristics primarily focuses on physical structural changes, such as pores and water. The impact of the functional groups thermal decomposition on the coal spontaneous combustion characteristics has received limited attention and is seldom discussed in current research. This paper primarily investigated the influence of the thermal decomposition process on the subsequent coal spontaneous combustion process. In this paper, the oxidation experiment of thermal decomposition coal was carried out at room temperature. The changes in functional groups and free radicals before and after thermal decomposition were studied using FTIR and EPR. The results indicated that the core temperature rose rapidly when the coal sample was oxidized at room temperature. This phenomenon is due to the generation and accumulation of several active sites within the thermally decomposed coal. These active sites underwent rapid oxidation at room temperature, leading to an increase in the coal temperature. The chemical structure changes revealed that the decomposition process of coal resulted in the breakdown of oxygen-containing functional groups and an increase in active alkyl radicals. The study revealed that the thermal decomposition of oxygen-containing functional groups in coal generated a significant amount of active alkyl radicals. The oxidation of these radicals served as the underlying cause for the high activity and self-heating observed in thermally decomposed coal. This study is of great significance to reveal the spontaneous combustion mechanism of magma-eroded coal and develop efficient flame retardants through the influence on the thermal decomposition process and spontaneous combustion characteristics of coal.