Speaker
Description
Deep, unminable coal seams are promising targets for carbon capture, utilization, and storage (CCUS). When supercritical CO2 (ScCO2) is injected in the presence of water, coupled physicochemical interactions and thermal effects can simultaneously modify coal microstructure and subsequently alter CO2 transport. Although ScCO2-induced structural changes and pressure effects have been widely studied, reported trends are not always consistent. In particular, how treatment pressure and desorption thermal effect jointly regulate post-treatment CO2 diffusivity remains insufficiently understood.
In this study, we investigate the impacts of ScCO2-H2O treatment on the microstructure and CO2 diffusion behavior of bituminous coal by integrating experiments with numerical simulation. Coal samples were exposed to ScCO2-H2O at 308 K for 20 days in high-pressure reactors under two representative pressures (8 MPa and 12 MPa). Pore structure evolution was quantified using low-temperature gas adsorption (CO2 and N2), surface functional groups were semi-quantified by Fourier-transform infrared spectroscopy (FTIR), and CO2 diffusion experiments were conducted to obtain diffusion kinetics. To represent the non-isothermal diffusion process, we developed a coupled diffusion-temperature model that incorporates the desorption thermal effect and a convective thermal boundary condition. The model was used to simulate transient desorption-diffusion and to back-calculate diffusion coefficients, enabling quantitative evaluation of pressure-dependent diffusion behavior after ScCO2-H2O treatment.
ScCO2–H2O treatment primarily promotes the development of micropores and mesopores, while leaving the macropore distribution largely unchanged. As a result, micropore specific surface area (SSA) and pore volume (PV) increase substantially and become the dominant contributors to total SSA and PV. The treatment also induces pore-size-dependent changes in surface roughness and structural complexity across micro-, meso-, and macropores, with these responses intensifying as ScCO2 pressure increases. Chemically, the overall abundance of functional groups decreases, with oxygen-containing groups showing the most pronounced depletion. Structural parameters indicate longer aliphatic chains, higher structural complexity and coal maturity, and reduced aromatic ordering, consistent with a looser structure and enhanced aromatic-ring vibrational intensities. With increasing ScCO2 pressure, aliphatic chain length continues to increase, whereas other chemical changes become less pronounced. Simulations indicate that the convective boundary condition more accurately captures the initial decreases in temperature and diffusion content driven by desorption thermal effect, compared to isothermal condition. Combined with diffusion experiments, the results demonstrate that ScCO2-H2O treatment effectively enhances CO2 diffusion performance in bituminous coal, as evidenced by increases in cumulative diffusion content, the diffusion rate at 5 min, the reference diffusion coefficient, and the effective diffusion coefficient, these improvements strengthen with ScCO2 pressure.
| Country | UK |
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