研究煤自燃过程中孔隙结构的演变规律,对于进一步认识煤自燃(CSC)机理及其防治具有重要价值。在这项研究中,我们选择了三种低阶煤,并使用核磁共振(NMR)可视化了热处理后煤的孔隙结构的宏观演变,并分析了温度(25-500°C)对煤的孔隙结构的影响,包括孔隙度,渗透性,和分形维数。得到的结果表明,煤中的整体NMR信号随着温度的升高而增加,表明热处理可以引起增大,打开,以及煤中孔隙和裂缝的相互连接。煤的等效平均孔隙半径(rm)与温度呈正相关,随着RM的大幅增加,尤其是在温度超过200°C之后。在加热过程中,三种煤的孔隙度和渗透率均有随温度升高的趋势。在300°C以上的温度下,煤的渗透性急剧增加,预测更高的流体输送能力。此外,提出了核磁共振多重分形理论用于定量孔隙空间维度表征。结果表明,在加热过程中,煤孔隙吸附空间的分形维数随温度的升高而增大,渗流空间的分形维数与温度呈负相关。此外,吸附空间的尺寸变化比渗透空间的尺寸变化更大,这意味着低阶煤的吸附能力受温度的影响更大。
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 (rm) of coal shows a positive correlation with temperature, with a substantial increase in rm, 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.