Characterization of pore structure and the gas diffusion properties of tectonic and intact coal: Implications for lost gas calculation

Accurate calculation of the amounts of lost gas from coal are of great importance in underground mining. In this study, the effects of pore structure and the gas diffusion properties on the lost gas from tectonic and intact coals were investigated by the mercury intrusion porosimetry method (MIP), N-2 (77 K) and CO2 (273 K) adsorption methods, and gas adsorption equilibrium/desorption tests. The results indicated that mesopore and macropore volumes increased after tectonic damage, as did the specific surface areas (SSA) and porosities. However, there was little change for the micropore volumes. Additionally, the desorption experiments indicated that the initial desorption and gas flow capacities of tectonic coal were greater than those of intact coal. Both laboratory and field results demonstrate that there is more higher lost gas for tectonic coal, which is directly influenced by the developed mesopore and macropore structure and by the initial gas desorption capacity. The logarithmic function method is a relatively better choice. When the gas content is determined in coal mines, the sampling exposure times should be kept as short as possible. From the perspective of engineering, this study provides a reference for the calculation of lost gas in tectonic coals. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.