Influence of coal properties on the CO2 adsorption capacity of coal gasification residues

Post-underground coal gasification (UCG) sites hold attractive prospects for geological storage of carbon dioxide. For the successful commercial implementation of UCG with carbon capture and storage (CCS), site-selection is crucial, and a careful techno-economic feasibility analysis is essential to systematically assess the site related parameters aside from evaluating the environmental risk. This study is related to one of the important aspects of site selection- the coal type. Specifically, this work investigates the influence of coal properties and gasification conditions on the adsorption capacities of CO2 on gasified coal chars. For this purpose, four coals of diverse ranks varying from lignite to bituminous were selected and subjected to CO2 gasification at atmospheric pressure for 10 min at 800, 900, and 1000 degrees C under a low heating rate of 5 degrees C/min. Subsequently, the gasified chars, as well as the raw coals, were tested for their adsorption capacity in a purpose built volumetric adsorption apparatus at 45.5 degrees C and pressures up to 90 bar. Also, complementary coal and char analysis were carried out for determining the surface area, pore size distribution, and surface morphology. The CO2 storage capacity was observed to be a strong function of the coal properties and gasification conditions. Among the samples examined, the highest adsorption capacity was observed for chars of the sub-bituminous coals. The CO2 adsorption capacity at 80 bar and 45.5 degrees C on the sub-bituminous char samples was 2.08, 2.43, and 1.95 mmole/g that were prepared at 800, 900, and 1000 degrees C, respectively. The experimental adsorption isotherms were fitted to the Dubinin-Radushkevic (DR) and the Dubinin-Astakhov (DA) models.