Simulation of interfacial mass transfer process accompanied by Rayleigh convection in NaCl solution

Rayleigh convection caused by dissolved CO2 is critical for CO2 capture and storage technology in saline aquifers. However, the poor experimental measurements of theoretical model parameters limit a further analysis of the interfacial mass transfer process after the convection occurring. In this study, a two-dimensional lattice Boltz-maim method (LBM) including electrostatic and volume forces is used to simulate Rayleigh convection for CO2 in a NaCl solution at 293.15 K, 1.00 atm. Through calculating the key parameter of the simulated onset time, it indicates that the CO2 interfacial concentration is only 15-20% of the saturated concentration at the true gas-liquid mass transfer interface. Besides, the simulated convective onset time would be delayed by increasing the salt concentration. The average instantaneous mass transfer factor is also decreased with the increased concentration and when the concentration of the NaCl solution is less than 3 mol L-1 (M), the mass transfer rate can be accelerated by more than 3.2 times. We propose a new method to obtain surface renewal time which is determined according to the concentration and velocity field simulated by LBM and find that changes in mass transfer rate follow the penetration theory in the molecular diffusion stage while abiding by the surface renewal theory in the interfacial convection stage. Our results can provide a valuable guide for relevant economic evaluation and appropriate geological sequestrated sites.

Automated summary

Rayleigh convection of dissolved CO2 is crucial for CO2 capture and storage in saline aquifers. Simulation results show that the CO2 interfacial concentration is low and can be affected by salt concentration, with mass transfer rate being accelerated by increasing NaCl solution concentration.