Molecular simulation of coal-fired plant flue gas competitive adsorption and diffusion on coal

Abstract Better understanding the microcosmic mechanism of CO 2 , O 2 , and N 2 competitive adsorption can benefit the effective CO 2 storage and fire prevention by injecting coal-fired flue gas into the goaf. Toward this aim, macromolecular coal model was established. Grand Canonical Monte Carlo and Molecular Dynamics simulation were carried out at single, binary, and ternary component systems under the conditions of 298.15–318.15 K and up to 10000 kPa. Simulation results demonstrate that the absolute adsorption amount decreases with the increase of temperature and water content in coal, and increases with the pressure increasing and corresponding bulk mole fraction. The competitiveness is CO 2  > O 2  > N 2 basing on the ternary adsorption selectivity of CO 2 /O 2 (5.6–24.2), CO 2 /N 2 (8.4–29.3), and O 2 /N 2 (1.2–1.5). The isosteric adsorption heat of CO 2 (about 29.1–30.9 kJ/mol) is nearly double of O 2 or N 2 (about 16.6–17.3 kJ/mol), and CO 2 occupies stronger adsorption sites without being affected by O 2 or N 2 . The interaction energy between CO 2 and coal is greater than O 2 or N 2 due to the electrostatic energy and much larger van der Waals energy. The adsorbed molecules swell the coal and the trend of self-diffusion coefficients with pressure is consistent with loading and volumes. So the flue gas injecting into the goaf is better than pure N 2 , and can store large amounts of CO 2 (0.406 mmol/g), meanwhile inhibit the coal spontaneous combustion, visually displayed by density distributions. The findings provide essential evidence for injection parameters such as temperature, pressure, gas concentration, injectivity, moisture, and so on.