Proposal for a combined supercritical CO2 and organic Rankine Cycle: System design and exergoeconomic analysis

This study discusses a supercritical CO₂ recompression cycle (s-CO₂-RC) combined with a regenerative and recuperative organic Rankine cycle (RRORC) where the system components are designed using Flownex, a commercial software. Key geometrical parameters are taken into account to calculate pressure drop and other critical parameters, such as overall heat transfer coefficients, rather than relying on assumptions. Four working fluids—R123, R141b, R245ca and R601a—are considered for the RRORC. The mass and energy balances are applied, the geometric parameters are determined, and the results are further utilized to perform exergy and exergoeconomic evaluation. R601a performs best and hence is selected for further analyses. A parametric study is also conducted to determine the suitable RRORC vapor extraction pressure. This study found that the condenser in the RRORC is the largest among all the heat exchangers, followed by the intermediate heat exchanger-I (IHX-I) of the sCO₂ cycle. Although smaller in size, IHX-I has the highest heat duty among all exchangers. This highlights that heat exchanger size is not solely dictated by heat transfer rate, emphasizing the crucial role of component design. The combined system produces 11.01 MW of net power with an energy efficiency of 36.84 % and 42.79 % exergy efficiency. Exergoeconomic analysis reveals that the overall cost rate of the combined system is 558.49 $/h, with the s-CO₂ turbine and intermediate heat exchanger (IHX-I) as major contributors. The s-CO₂ turbine is the most capital-intensive component, attributing 70.7 % of the capital cost rate. The payback period of the combined system is 11.55 years.