Design and performance analysis of a supercritical CO2 (sCO2)-water separator for power generation systems using hot sCO2 from geothermal reservoirs

Abstract

CO2 has been believed a potential working fluid for geothermal heat mining. A novel hydrocyclone was designed to address the separation problem of sCO2 and water produced from geothermal reservoirs, preparing pure sCO2 for direct expansion through a turbine for power generation. The Reynolds stress model (RSM) and discrete particle model (DPM) were employed in numerical simulations to analyze the flow behavior and droplet separation process inside the hydrocyclone, as well as to determine the influence of operational and structural parameters on separator performance. The results show that the velocity distribution inside the separator has Rankine vortex characteristics, ensuring effective separation of water droplets. Four operational parameters (inlet velocity, droplet size, water mass fraction and split ratio) and three geometrical parameters (inlet equivalent diameter, cylinder chamber diameter and overflow outlet location/size) were found to have important impacts on separation efficiency. It has been found that droplet size is the most significant factor. Separation efficiency was modeled as reaching 100% when droplet size was greater than 7 μm. Inlet velocity, split ratio, inlet equivalent diameter, and overflow outlet diameter were also found to significantly impact the pressure drop of the separator. The split ratio is the most important adjustable operational parameter affecting the separation process. An optimal split ratio for each inlet water mass fraction was obtained. The insertion depth of the overflow pipe can also be optimized for separator performance. The analysis results in this paper can be used for design optimization and operation guidance of the sCO2-water separation system.