Numerical analysis of membrane–absorption separation for supercritical carbon dioxide and water mixture of plume geothermal power generation systems

Abstract

A plume geothermal system provides a viable option for simultaneously storing carbon dioxide and producing supercritical working fluid with geothermal energy. Its water content, however, may cause problems, such as water hammer and corrosion, when the geothermal energy is utilized. A membrane–absorption separation method is employed to remove water from the supercritical carbon dioxide–water mixture. A numerical solution procedure is thereafter employed to evaluate the separation performance with different design parameters. If it is assumed that each membrane is repeatable and independent, then it can be divided into regular hexagon structures. The results show that a lower mixture inlet velocity and a higher lithium bromide solution concentration lead to a better separation performance. Moreover, the membrane remains practically unchanged even when the mixture inlet temperature varies. A multi-objective genetic algorithm optimization is implemented with an optimal solution search method. For a 65% concentration lithium bromide solution, the optimization results indicate that the best separation efficiency can reach 93.53%, and the total mass transfer area is 1093.5 m2. The findings suggest that membrane–absorption separation is efficient and commercially viable for separating supercritical carbon dioxide–water mixtures. This separation technology can provide purified working fluids for power generation systems.