High-Pressure CO2 Excess Sorption Measurements on Powdered and Core Samples of High-Rank Coals from Different Depths and Locations of the South Wales Coalfield

Abstract

The experimental analysis aimed at investigating the high-pressure (sub- and supercritical) CO2 sorption behavior on two high-rank coals of different sizes is presented in this paper. Coals from the same seam (9 ft seam) but from depths of 150 m [black diamond (BD) coal] and 550 m [Aberpergwm (AB) coal] and different locations of the South Wales (UK) coalfield, known to be strongly affected by tectonically developed fracture systems, are employed for that purpose. Hence, the sorption behavior of powdered (0.25–0.85, 2.36–4.0 mm) and core samples obtained from locations associated with the deformation-related changes is analyzed in this paper to assess the CO2 storage potential of such coals. The results show that the coals exhibit maximum adsorption capacities up to 1.93 mol/kg (BD coal) and 1.82 mol/kg (AB coal). No dependence of the CO2 maximum sorption capacity with respect to the sample size for the BD coal is observed, whereas for the AB coal the maximum sorption capacity is reduced by more than half between the powdered and core samples. The CO2 sorption rates on the BD coal decrease by a factor of more than 9 from 0.25–0.85 to 2.36–4.0 mm and then remain relatively constant with further increase in sample size. The opposite is observed for the AB coal where sorption rates decrease with increasing sample size, that is, reducing by a factor of more than 100 between the 0.25–0.85 mm and core samples. The differences in behavior are interpreted through the structure each coal exhibits associated with the burial depths and sampling locations as well as through the minor variations in ash contents. This study demonstrates that anthracite coals, having experienced sufficient deformation, resulting in changes in fracture frequency, can adsorb significant amounts of CO2, offering great prospect to be considered as a CO2 sequestration option.