Numerical analysis of separation performance of an axial-flow cyclone for supercritical CO2-water separation in CO2 plume geothermal systems

Abstract

Supercritical CO2 produced by CO2 plume geothermal systems can be used in Brayton cycles if entrained water is removed. A physical parameter analysis indicated that the supercritical CO2-water mixture presented a gas-liquid phase, and an improved axial-flow cyclone was designed to realize the separation. This study was conducted using computational fluid dynamics to simulate three parts of the flow, including continuous supercritical CO2, discrete water droplets and the water film. A Reynolds stress model was adopted to calculate turbulence, the Eulerian-Lagrangian method was applied to simulate the coupled gas-liquid two-phase flow, and the Surface Film Model was employed to predict the liquid film. The effects of the number of guide vanes on separation performance were investigated. The results of the simulations demonstrate that the increase in the number of guide vanes strengthens the tangential velocity of the continuous phase and expands the static pressure. Furthermore, it is easier for particles to move towards the wall surface and then transform into water film when the increased vane number shortens the pitch of the helical trajectories. This also contributes to the thickening of the water film, along with an increment in film velocity. It is obtained that more guide vanes could improve the removal efficiency of the water droplets while increasing the pressure drop. Erosion analysis indicates the separator with 6 vanes suffers the most severe erosion. A comprehensive economic assessment shows that the design of 8 vanes is the most economically friendly option.