Low-high temperature flue gas direct injection in south African bituminous and anthracite coals: Sorption capacity assessment

Numerous studies have been carried out recently on the sequestration of carbon dioxide (CO₂), a greenhouse gas, produced due to human activities. Consequently, storage of CO₂ in storage sites, such as unmineable coal seams, has been identified as one of the promising options with the advantage of recovering coal-bed methane (CH4). However, CO₂ injected into coal seams contains additional gases that may reduce storage capacity, cause changes in sorption behaviour and physicochemical properties of coal. This research was aimed at investigating the sorption behaviour of three South African coals (sorbents) upon pure CO₂ and flue gas (sorbates) sorption. Measurements were conducted on 10 g samples with a grain size < 2 mm. A synthetic industrial flue gas containing 12% CO₂, 5.5% O₂, 82% N₂, 0.38% SO₂ and 0.12% NO₂ was used in the study. Sorption isotherms were measured at a temperature ranging from 30 to 60°C and pressures up to 9 MPa using a high-pressure CO₂ volumetric adsorption system (HPCVAS). Sorption of CO₂ by coal was highly reduced in the presence of additional gases due to competition for sorption sites. The reduction in CO₂ (in flue gas) sorption capacity of coal was up to 63% compared to sorption of pure CO₂.