Multicomponent Competitive Adsorption of CH ₄ with Injected Superheated CO ₂ , N ₂ , and H ₂ O in Lignite

High Resolution Image Download MS PowerPoint Slide Investigating competitive adsorption between injected gases and CH 4 is crucial for enhancing coalbed methane recovery. Two research gaps remain: the competitive adsorption of H 2 O with CH 4 and the behavior of superheated gases with CH 4 have not been systematically studied. Here, a lignite supercell model was constructed, and grand canonical Monte Carlo and molecular dynamics simulations were performed at 473.15 K and 0–10 MPa. In the CH 4 /H 2 O binary system, the selectivity coefficient increases with pressure, indicating that low-pressure H 2 O injection (<3 MPa) offers the strongest selectivity advantage, while the marginal benefit above 7 MPa approaches zero. At 90% injected gas ratio, the maximum atomic density (H 2 O:0.01, CO 2:0.07, N 2:0.10) and potential energy peak (H 2 O: −5.95, CO 2: −3.75, N 2: −3.35 kcal/mol) of CH 4 evaluate the displacement limits from “quantity” and “quality” perspectives, respectively. In the N 2 /CH 4 /CO 2 ternary system, a CH 4 molar fraction of 30% is identified as the competitive adsorption turning point: below 30%, N 2 and CO 2 jointly suppress CH 4 (favorable for displacement); above 30%, CH 4 gradually dominates. This critical composition is verified by both maximum atomic density and potential energy peaks, providing a quantitative basis for optimizing gas injection ratios. This study fills the knowledge gap in superheated gas–CH 4 competitive adsorption and supports enhanced CBM recovery.