It is of great significance to study the characteristics of low-temperature oxidation of coal in an adiabatic environment for the prediction and control of coal spontaneous combustion. Coal spontaneous combustion experimentation can better simulate the field conditions and reflect and test the actual process underlying the spontaneous combustion of coal. Numerical simulation methods can provide a systematic solution for research on the dynamic evolution process of coal spontaneous combustion. In this study, a large-scale coal spontaneous combustion test bench was employed to test the oxidation heating characteristics and gas generation laws of Huangling coal samples from 303–443 K, revealing the spatiotemporal evolution characteristics of the gas concentration and temperature fields. Based on the theory of computational fluid dynamics (CFD), a mathematical model of the spontaneous combustion of coal in the adiabatic state is therefore constructed. The evolution law and distribution characteristics of the temperature and gas concentration fields of coal in the experimental furnace are simulated by Fluent. The results indicate that the position of the highest coal temperature in the experimental furnace mainly changed along the central axis and gradually moved down toward the air inlet as the coal temperature continued to rise. Above the critical temperature (353 K), the high-temperature point mobility was high, and only one-tenth of the ignition period could be utilized to travel along with more than one-third of the original distance from the intake side. In the furnace, O₂, CO, and CO₂ were distributed in the upper and lower layers at different concentration values. The concentration of O₂ gradually decreased from the inlet side along the gas flow direction, but the concentrations of CO and CO2 demonstrated the opposite behavior. When the temperature exceeded 120°C, the consumption of O₂ and the production of CO and CO₂ gases were mainly distributed in the furnace body below 0.65 m. The simulation results are in line satisfactorily with the experimental results. This study provides theoretical support for field index gas and three zone division. The development of the model can improve the existing theory of coal spontaneous combustion and find a more systematic and reasonable criterion for judging coal spontaneous combustion.

Ammonium polyphosphate (APP) is a type of fire-fighting material that has excellent performance; however, it also has the disadvantage of facile deliquescence. Microcapsule technology is therefore employed in this study to use melamine resin as encasing material in the preparation of melamine–formaldehyde resin-microencapsulated APP. The performance of prepared microcapsules is characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric experiments. The experimental results show that the same APP characteristic peaks (e.g., N-H stretching vibration peaks) and characteristic absorption peaks of melamine-formaldehyde (MF) resin (e.g., vibration peak of MF ring) are exhibited by the microcapsules. Furthermore, the coated microcapsule surface is rough because of the adsorption of solid particles, indicating that the wall material successfully covers the core material. Thermogravimetric analysis shows that the microcapsules can effectively increase and decrease the maximum weight loss rate temperature and maximum weight loss rate, respectively. When the microcapsule content constitutes 15% of the total sample mass, the maximum weight loss rate and coal temperature decrease and increase by 0.58%/min and 13°C, respectively. This significantly inhibits the composite coal-oxygen process, indicating the improved fire-fighting performance afforded by microcapsules. The Research provides a new direction for the development of fire-fighting materials.

To investigate the influence of moisture on the exothermic properties of coal oxidation, this study investigated the variation in thermal effect and radical parameters in the oxidation process of coal under different moisture content. This was achieved through thermogravimetric–differential thermal experiments and electron spin resonance experiments. Additionally, the study analyzed the impact of free radicals on the characteristics of the thermal effect of coal at different oxidation stages using the product–moment correlation method. The results indicate that the moisture content of 8% is a critical point for promoting or inhibiting the oxidation reaction of coal. Below this threshold, it promotes the oxidation reaction, while above it, it plays an inhibitory role. The most significant promotional effect was observed at 8% moisture content, which increased both the weight loss and heat release by 8.61% and 1567.04 J/g, respectively, while also significantly enhancing free radical species and complexity. Conversely, when the moisture content of coal reached 20%, there was a notable inhibition effect, with a reduced weight loss and exothermic capacity by 4.94% and 2705.03 J/g, respectively, along with decreased free radical species and complexity. The free radical species and heat effect parameters in coal showed a strong correlation at all stages of low-temperature oxidation, thus indicating that g-factor can characterize the coal oxidation process to some extent.