Lattice Boltzmann modeling for enhanced membrane separation of geothermal energy utilization

Abstract

Reducing carbon emissions and utilizing geothermal energy via supercritical carbon dioxide extraction from reservoirs for direct power generation necessitates the removal of mixed vapor. A shell-tube hollow fiber membrane contactor, utilizing differential pressure and absorption fluid, is devised for vapor absorption. This membrane-based separation process encompasses a multicomponent multiphase system of supercritical carbon dioxide and water, water-salt transport, and mass transfer across the porous membrane. To investigate pore-scale mass transfer, a multicomponent multiphase pseudopotential lattice Boltzmann model is established, simulating carbon dioxide-water two-phase flow, coupled with a continuous species transfer model for salt behavior in the absorbent. Flow direction analysis reveals countercurrent flow as superior to cocurrent for vapor absorption. Augmenting the original membrane with equal macropore counts enhances mass transfer, with increasing size amplifying the effect. Macropore arrangements at constant porosity suggest minimizing resistance in the propagation path as crucial for mass transport improvement. A left-small-right-large macropore size gradient distribution outperforms its reverse counterpart, enhancing performance by approximately 20%. This is attributed to larger macropores in high-concentration regions facilitating localized vapor transport.