The multi-scale pore structure of superfine pulverized coal. Part 1. Macropore morphology

The accurate description of the complex multi-scale pore structure plays a crucial role in efficient coal utilization. However, there are few studies about the macroporosity in pulverized coals, which is important for understanding the migration paths and mechanisms. In this work, both macropore geometry and topology of superfine pulverized coal were characterized through mercury intrusion porosimetry (MIP). Furthermore, the permeability of coal with different sizes was addressed based on the percolation theory, and the compressibility was discussed. Finally, the macropore morphology was comprehensively evaluated based on three different fractal models. The results show the pore geometry in superfine pulverized coal can be depicted as the isolated large pore clusters occurring in continuous small pore networks. With the decline in particle size, the compressibility drops by 2.7 x 10-11 Pa-1 and 1.2 x 10-11 Pa-1 for NMG and HN samples. In addition, the fractal analyses confirm that with decreasing particle sizes, the surface fractal dimensions increase for both NMG and HN, whilst the structure fractal dimensions show the opposite. The pore geometry and topology have a combined effect on the permeability, which is correlated to both surface and structure fractal dimension, leading to the maximum permeability around 20 mu m for studied coals (954.87 mD for NMG_18.7 and 482.08 mD for HN_23.9). The macropore morphology obtained here is useful for constructing a more comprehensive coal pore network, and better understanding the mass and heat transfer in coal particles, which sheds lights on further exploring the reaction mechanisms of new clean coal utilization technologies.