Wang Haiyan, Li Jinglei, Zhang Yanwei, Wu Yaling, Wang Zhuo
School of Emergency Management and Safety Engineering, China University of Mining and Technology, Beijing, 100083, People's Republic of China.
Environ Sci Pollut Res Int. 2023 Mar;30(14):39932-39945. doi: 10.1007/s11356-022-25069-z. Epub 2023 Jan 5.
Studying the evolution of the pore structure of coal during spontaneous combustion is of great value in further understanding the mechanism of coal spontaneous combustion (CSC) and its prevention. In this study, we selected three low-rank coals and used nuclear magnetic resonance (NMR) to visualize the macroscopic evolution of the pore structure of coal after heat treatment and to analyze the effect of temperature (25-500 °C) on the pore structure of coal, including porosity, permeability, and fractal dimensions. The obtained results show that the overall NMR signal in coal increases with increasing temperature, indicating that heat treatment can induce the enlargement, opening, and interconnection of pores and fractures in coal. The equivalent average pore radius (r) of coal shows a positive correlation with temperature, with a substantial increase in r, especially after temperatures above 200 °C. During heating, the porosity and permeability of all three coals tended to increase with temperature. At temperatures above 300 °C, the permeability of coal dramatically increases, predicting a higher fluid transport capacity. Furthermore, NMR multifractal theory was proposed for quantitative pore space dimensional characterization. The obtained results show that the fractal dimensions of the adsorption space of coal pores increase and then decrease with temperature during heating, while the fractal dimensions of percolation space are negatively correlated with temperature. In addition, the dimensions of adsorption space vary more strongly than those of percolation space, meaning that the adsorption capacity of low-rank coals is more significantly influenced by temperature.
研究煤在自燃过程中孔隙结构的演化对于进一步理解煤自燃（CSC）机理及其防治具有重要价值。在本研究中，我们选取了三种低阶煤，利用核磁共振（NMR）技术可视化热处理后煤孔隙结构的宏观演化，并分析温度（25 - 500℃）对煤孔隙结构的影响，包括孔隙率、渗透率和分形维数。所得结果表明，煤中的NMR总体信号随温度升高而增加，这表明热处理可促使煤中孔隙和裂隙的扩大、开启及相互连通。煤的等效平均孔径（r）与温度呈正相关，r显著增大，尤其是在温度高于200℃之后。在加热过程中，三种煤的孔隙率和渗透率均随温度升高而增大。在温度高于300℃时，煤的渗透率急剧增加，预示着更高的流体传输能力。此外，提出了NMR多重分形理论用于定量表征孔隙空间维度。所得结果表明，加热过程中煤孔隙吸附空间的分形维数随温度升高先增大后减小，而渗流空间的分形维数与温度呈负相关。此外，吸附空间的维度变化比渗流空间更为强烈，这意味着低阶煤的吸附能力受温度的影响更为显著。
