Influences of SO2, NO, and CO2 Exposure on Pore Morphology of Various Rank Coals: Implications for Coal-Fired Flue Gas Sequestration in Deep Coal Seams

摘要

Carbon dioxide (CO2) sequestration in deep coal seams with enhanced coal-bed methane recovery is a promising way to store the main anthropogenic greenhouse gas, CO2, in geologic time. Recently, injection of CO2 mixed with coal-fired flue gas components, i.e., SO2 and NOx, into coal seams has gained attention because it offers great advantages in reducing the cost of CO2 capture, flue gas desulfuration, and denitration. As a preliminary investigation on the feasibility of coal-fired flue gas sequestration in deep coal seams, the influences of SO2, NO, and CO2 exposures on the pore morphology of various rank coals are addressed in this work. Considering the optimum coal reservoir conditions for flue gas sequestration, the interaction of CO2 with coals was studied at a temperature of 45 degrees C and a pressure of 12 MPa. The results show that both CO2 exposure and SO2 exposure lead to decreases in both the specific surface area and pore volume of micropores of various rank coals. The micropore morphology of both Hulunbuir coal and Shenmu coal after NO exposure exhibits degradation, while the opposite trend is found for Erdos coal and Yangquan coal. The average micropore size of all the coals after contact with CO, NO, and SO2 decreases. The CO2, NO, and SO2 dependences of the meso- and macropore surface area and volume of coals are complex and strongly related to the coal rank. Fractal analyses show that the pore surfaces of coals after CO2, NO, and SO2 exposures become smooth, as indicated by the surface fractal dimension determined from the Neimark model, which is consistent with the increasing trend of the average meso- and macropore size. Generally, the influences of SO2, NO, and CO2 exposures on pore morphology of various rank coals may play an important role in the diffusion and adsorption performance of fluid within the target coal reservoir. Thus, comprehensive evaluation of the dependence of coal pore morphology on fluid exposure is needed for the practical coal-fired flue gas sequestration in deep coal seams.