CHEMISTRY OF THE ADSORPTION OF CARBON DIOXIDE BY ARGONNE PREMIUM COALS AND A MODEL TO SIMULATE CO2 SEQUESTRATION IN COAL SEAMS

摘要

The interactions of CO2 with coal were investigated under a set of conditions to determine the effects of the nature of the coal and the sequestration environment including parameters such as rank and moisture content of the coal, the temperature, pressure, and pH. A mathematical model was also developed to simulate the coal bed methane production and the CO2 sequestration processes. The excess adsorption and desorption isotherms of CO2 on eight Argonne Premium coal samples were measured using the volumetric method. The isotherms were found to be rectilinear and fit to the conventional adsorption model equations poorly due to the coal swelling. An adsorption isotherm equation was derived to account for the volumetric changes and significantly better fits were obtained. Upon drying, the volume of coals was determined to shrink, which was about 2% to 5% for medium and high rank coals, and up to 40% for the low rank coals. The swelling of coals during adsorption isotherm measurements in CO2 was estimated to be about the same as the shrinkage that occurred during the moisture loss. If the swelling was not included in the adsorption isotherm equation, the reported adsorption capacities and surface areas of the coals were overestimated by about 15%. The adsorption capacities of moisture-free Argonne coals were found to be about 2.2 ± 0.8 mmole/g-coal, daf basis and to be lower in wet coals. The isosteric heat of adsorption for CO2 on Argonne coals was estimated to be about 25±2 kJ/mole, regardless of the coal rank. The adsorption capacity of CO2 on the weak solutions of acid leached coals was higher than both the base leached and untreated coals, possibly due to the removal of ash content of the coals. The modeling results developed to simulate the CO2 injection process suggest that the CO2 can be injected at a rate of about 10*103 standard m3 per day. The injected CO2 will reach the production well, which is separated from the injection well by 826 m, in about 30 years. During this period, about 160*106 Sm3 of CO2 can be stored within a 2.14 (km)2 coal seam.