Experiment on the programmed temperature rise in a spontaneous combustion of coal and its application in experimental teaching

As the main energy source in China, coal has an important strategic position in the country’s economic development. China’s coal-based energy structure model will not change in the short term, but coal mine accidents occur frequently. Mine fire is a major disaster that threatens safe coal mine production, which incurs huge economic losses and threatens the personal safety of miners and coal mine production. However, coal spontaneous combustion primarily causes mine fires. The occurrence mechanism of coal spontaneous combustion is highly complex and is affected by the inherent combustion characteristics of coal and external environmental factors. Therefore, it is necessary to comprehensively analyze various phenomena and characteristics in the process of coal spontaneous combustion and apply quantitative indicators to express to predict the risk and ensure the safe production of the mine.

Oxygen concentration is an important factor influencing coal oxidation reaction. In this paper, the temperature-programmed experimental system is used to conduct the spontaneous combustion experiment of coal samples with three oxygen concentrations of 20.9%, 10%, and 7% regarding the heat dissipation, oxidation, and asphyxiation zones in the goaf. The gas products at different temperature stages are collected, the effects of temperature and oxygen concentration on the concentration of gas products are analyzed, and the index gases are classified and evaluated in detail.

The results show the following: (1) The cross-point temperature (CPT) decreases with the increase in the oxygen concentration. The cross-point temperature under dry-air conditions is 144.6 ℃. The error between the CPT value calculated by the BM empirical relationship and the experimental data is only 6.08%. The higher the oxygen concentration, the smaller the critical temperature, and the higher the gas concentration. (2) The content of oxidation products increases with the oxygen concentration. When heating commences, minimal CO and CH₄ gases are generated, but with the increase in the temperature, C₂H₄ and C₂H₆ gases appear gradually. The oxidation reaction of coal samples is primarily affected by temperature and oxygen concentration. At a certain temperature, the higher the oxygen concentration, the more intense the coal-oxygen composite reaction, and more gas products appear. (3) For different oxygen concentration environments, the regularity of generating CO gas is highly significant, which can be used as an indicator gas to evaluate the spontaneous combustion of coal. In dry air, the temperature of C₂H₄ is earlier than that of C₃H₆, implying that the existence of C₂H₄ indicates that the coal oxidation process has entered an accelerated stage. The emergence of C₃H₆ gas marks the transformation of the coal oxidation into strong oxidation. Recently, the programmed temperature rise experiment has become an important research field.

Through indoor experiments, students can deeply understand the mechanism of coal spontaneous combustion and the process of establishing the prediction index system and introduce the experiment into the classroom. This practical teaching approach not only helps students to apply theoretical knowledge to practical problems but also broadens their horizons and improves their interest in scientific research, achieving better teaching results.