4E analysis of supercritical carbon dioxide (sCO2) cycles: evaluating energy, exergy, environmental sustainability, and economic impacts in combined systems

Supercritical carbon dioxide (sCO₂) emerges as an effective working fluid in closed-loop energy conversion cycles, offering significant advantages over traditional steam-based Rankine cycles. This research focuses on optimizing combined cycle systems utilizing sCO₂ to enhance energy efficiency, improve exergy performance, increase stability, reduce emissions, and lower costs. Various configurations of the sCO₂ cycle are analyzed, with an emphasis on their impact on efficiency as dictated by the first and second laws of thermodynamics. Key parameters include a gas turbine outlet temperature of 489 °C, a smoke flow rate of 89 kg/s, and a maximum cycle pressure of 230 bar, alongside turbine pinch temperatures of 30 °C and condenser pinch temperatures of 20 °C. The study evaluates three configurations: simple cycle, recuperator cycle, and split cycle, achieving first law efficiencies of 17.73%, 19.26%, and 23.56%, respectively. By minimizing exergy losses, this research enhances environmental sustainability and system stability, leading to reduced pollutant emissions. Economic analyses further compare the electricity generation costs of sCO₂ cycles to those of steam cycles, revealing cost ratios of 0.80, 0.92, and 0.98 for the simple, recuperator, and split cycles, respectively. Additionally, sustainability indices for the simple, recuperator, and split cycles are calculated at 1.92, 2.09, and 2.76, respectively. The findings underscore that advancements in sCO₂ cycles not only improve power output, energy efficiency, and environmental sustainability but also reduce cycle costs and environmental pollution.