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Summary: Supercritical CO2 (sCO2) has been proven to be a promising working fluid for geothermal heat mining, and the produced hot sCO2 can be directly used for power generation. However, the sCO2 produced from a brine‐based reservoir may contain a certain amount of water, preventing direct power‐cycle utilization. In this paper, an axial vane separator was designed to address the separation problem of sCO2 and water produced from geothermal reservoirs. First, the influences of operational and structural parameters on the separation performance were analyzed through numerical simulations. Five factors were selected to develop separation performance regression models by the response‐surface method (RSM). Finally, geometrical parameter optimization was applied to these RSM models. The results show that the guide vane area and the exhaust inlet are the main locations impacting the system pressure drop. The separation performance can be affected by many factors, including the guide blade outlet angle, number of vanes, hub diameter, length of the vortex tube, droplet size, and inlet velocity. The water‐droplet size and the number of vanes are the most critical factors affecting the separation efficiency. The inlet velocity, the number of vanes, and the hub diameter have a larger influence on the pressure drop of the separator. The optimization results indicate that the separation efficiency can reach 100% under certain operating conditions with a pressure drop no greater than 100 kPa. [ABSTRACT FROM AUTHOR]

• A hydrocyclone separator was designed to separate water from sCO 2 for CPG. • RSM and DPM were used to study flow characteristics of sCO 2 and water. • Rankine vortex distribution was advantageous for the separation process. • Effects of parameters on separation efficiency and pressure drop were studied. CO 2 has been believed a potential working fluid for geothermal heat mining. A novel hydrocyclone was designed to address the separation problem of sCO 2 and water produced from geothermal reservoirs, preparing pure sCO 2 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 sCO 2 -water separation system. [ABSTRACT FROM AUTHOR]