A study on the thermal behavior of coal gangue mountains under airflow influence based on MD and CFD simulations

• Published in: International journal of hydrogen energy Vol. 93; pp. 788 - 804
• Main Authors: Wang, Peng, Yang, Shaochen, Wang, Wencai, Cao, Zhao, Cao, Yongdan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 03-12-2024
• Subjects: Coal gangue mountains; Computational fluid dynamics; Molecular dynamics; Oxidation spontaneous combustion; Thermal behavior; Molecular dynamics; Computational fluid dynamics; Oxidation spontaneous combustion; Coal gangue mountains; Thermal behavior
• ISSN: 0360-3199
• DOI: 10.1016/j.ijhydene.2024.10.341

The long-term accumulation of coal gangue can lead to an increase in internal temperature. If the temperature becomes excessive, it can cause spontaneous combustion, posing serious environmental risks. The process is significantly influenced by external airflow. This study analyzes the thermodynamic properties and oxidation heat release rate of coal gangue samples through laboratory experiments. Subsequently, molecular dynamics (MD) simulations are used to investigate the mechanism of oxidation heat release during the heating process of coal gangue under varying oxygen supply conditions. Based on these findings, a coupled three-field model for the heating process of coal gangue mountains is developed. Using computational fluid dynamics (CFD) methods, transient simulations are conducted to analyze the internal thermal behavior of coal gangue mountains under the influence of external airflow, clarifying the risks of spontaneous combustion. The results indicate that after reaching T2 (295.16 °C), coal gangue enters an accelerated oxidation phase, with an increased heat release rate, heightening the risk of spontaneous combustion. The oxidation heat release rate of coal gangue accelerates with rising temperature and oxygen concentration, entering a rapid reaction phase after 300 °C, with a sharp increase in reaction rate. Compared to N2, coal gangue surfaces exhibit stronger adsorption of O2, and temperature changes affect N2 diffusion more sensitively (O2 diffusion coefficient increases by 0.312 Å2/ps, N2 diffusion coefficient increases by 0.334 Å2/ps). The isosteric heat of O2 adsorption in coal gangue decreases significantly with increasing adsorption amount, and higher temperatures hinder competitive adsorption of O2. The temperature in the deep and foot areas of the coal gangue mountains is lower, while the middle and upper areas near the slope surface exhibit higher temperatures, indicating a higher risk of spontaneous combustion in these regions. When environmental wind speed is too high or too low, both the internal temperature of the coal gangue mountains and the area of spontaneous combustion risk zones decrease. At a wind speed of 3 m/s, the spontaneous combustion risk zone reaches its maximum area of 73.47 m2, but when the wind speed increases to 7 m/s, the risk area decreases to 65.72 m2.
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•The mechanism of exothermic reaction of coal gangue oxidation was described by thermodynamic experiment and MD simulation.•The coupled three-field model of spontaneous combustion of coal gangue mountain was established.•The internal thermal behavior of coal gangue mountain is analyzed by using CFD method.•According to the numerical simulation results, soil mulch method is used to cool down the coal gangue mountain.