Increasing concerns over growing CO 2 levels in the atmosphere have led to a worldwide demand for efficient, cost-effective, and clean carbon capture technologies. One of these technologies is the Carbonation-Calcination Reaction (CCR) process, which utilizes a calcium-based sorbent in a high-temperature reaction (carbonation) to capture the CO 2 from the flue gas stream and releases a pure stream of CO 2 in the subsequent calcination reaction that can be sequestered. A 120 KWth subpilot-scale combustion plant utilizing coal at 20 pph along with natural gas has been established at The Ohio State University to test the CCR process. Experimental studies on CO 2 capture using calcium-based sorbents have been performed at this facility. Greater than 99% CO 2 and SO 2 capture has been achieved at the subpilot-scale facility on a once-through basis at a Ca:C mole ratio of 1.6. In addition, the sorbent reactivity is maintained over multiple cycles by the incorporation of a sorbent reactivation hydration step in the carbonation-calcination cycle.

Carbon dioxide sequestration in coal seams with enhanced coal-bed methane recovery (CO2-ECBM) is considered as a promising option for permanent carbon dioxide storage. As one of the most important factors to the success of the CO2-ECBM process, adsorption of methane and CO2 on coal helps to assess the amount of recoverable methane as well as the storage capacity of CO2 of the targeted coal seam. In this work, the methane and CO2 adsorption isotherms were measured with a volumetric technique at temperatures of 35, 50, and 65 °C and pressures up to 16 and 12 MPa (CO2 adsorption at 35 °C is limited below 6 MPa), respectively. Four coals of various rank exploited from four main coal seams in China were tested. The isotherms fit well to the Ono-Kondo lattice model, which confirms the applicability of this model in describing the adsorption behaviors of methane and CO2 on coal under the supercritical conditions. In addition, the experimental results show that the excess adsorption of CO2 reaches the maximum level between 7 and 9 MPa, while the excess adsorption of methane exhibits a less pronounced maximum. The maximum adsorption capacities of the coals for methane and CO2 decrease slightly with temperature increase. Additionally, the maximum adsorption capacities of methane and CO2 are also dependent on coal rank (indicated by vitrinite reflectance coefficient, R o max) and present a U-shaped trend with coal rank. The preferential adsorption ratio of CO2 to methane on a basis of absolute adsorption obtained from Ono-Kondo lattice model is in the range of 1.13−3.52 under test conditions. This ratio of bituminous coals (R o max ranging from 0.47% to 1.35%) decreases significantly with increasing pressure; however, the pressure dependence of the preferential adsorption ratio is less pronounced for the anthracite (R o max = 4.06%). The preferential adsorption ratio decreases with an increase in coal rank with the only exception of anthracite.

Carbon dioxide sequestration on coal with enhanced coalbed methane recovery (CO 2 -ECBM) is acknowledged as a promising way to mitigate CO 2 emissions. For successfully understanding and implementing CO 2 -ECBM process, the potential interactions of CO 2 with coal during CO 2 sequestration in coal seams were investigated. Research methods consisting of lowtemperature nitrogen adsorption−desorption and chromatographic analysis were used to address the transformation of coal pore morphology and the capability of supercritical CO 2 extraction when coal contacts with high pressure CO 2 . According to the test results, interaction of coal with high pressure CO 2 does not create a significant influence on pore shape and mesoporous volume distribution of any rank of coal. However, this causes the coal surface fractal dimension and specific surface area to be changed, which implies that the coal's pore morphology change due to CO 2 sorption is irreversible. The results also indicate that the injection of high-pressure CO 2 does not only change the pore morphology of coal but also has the ability to extract the hydrocarbons present in the coal matrix. The extracted hydrocarbons are of biological toxicity and can be mobilized with gas or water to other geologic structures and aquifers. Thus, the potential environmental safety and health issues (ES&H issues) related to CO 2 sequestration in deep coal seams require thorough assessment.

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