Coal–gas interaction: implications of changes in texture and porosity

Abstract

Transient sorption and desorption of helium and carbon dioxide in Upper Freeport coal powder and lumps were analyzed. Differences in texture and porosity between the powder and lumps may affect the transport and interaction of the penetrant and coal. In this work, we address macroscopic and mesoscopic structural differences between powdered and non-powdered coals that influence the rates of the gas transport kinetics and changes in coal texture (swelling, shrinkage, and changes in the pore structure and interconnectivity) and the reciprocal free-phase pressure decay (relaxation). Comparison of the multi-exponential relaxation time constants as a function of pressure, for CO₂ and inert gas (helium), allows us to postulate several mechanisms responsible for observed pressure decay patterns.