Pore Structure evolution and fractal analysis of Shenhua non-caking coal during low-temperature oxidation

Revealing the evolution of pore structure during low-temperature oxidation is important for the deep-going understanding of coal spontaneous combustion disasters. For this purpose, the pore structure parameters and fractal dimension of Shenhua bituminous coal during low-temperature oxidation were examined by low-temperature nitrogen adsorption and mercury intrusion porosimetry. With the enhancement of oxidation degree, the pore connectivity increased, but the pore volume decreased, especially micropores, which decrease by 79.08%. In the two fractal dimensions, D-1 increases from 2.684 to 2.924 while D-2 decreases from 2.686 to 2.481, indicating that the pores have a rougher surface and a less heterogenous structure after low-temperature oxidation. An exponential characteristic is observed between the comprehensive fractal dimension and the gas yield. At last, a pore structure evolution mechanism was proposed, dividing the evolution into two stages: collapse of micropores and merging of micropores and transition pores. The research findings in this paper will lay the foundation for understanding the mass transfer in the low-temperature oxidation process.