Supercritical carbon dioxide (sCO2) power cycles have garnered significant research and application momentum in recent years in the United States, Europe, Japan, South Korea, and other regions, owing to their compact overall power generation systems, rapid power response, high thermodynamic cycle efficiency, and broad applicability across various heat source temperatures. Looking ahead, beyond playing a pivotal role in terrestrial power generation, sCO2 power cycles are poised to provide compact, highly efficient, clean, and cost-effective thermodynamic conversion solutions for defense and military equipment, including space power systems, aero-engines, and nuclear-powered submarines.
Thermodynamic cycles utilizing supercritical CO2 as the working fluid are termed sCO2 power cycles. These encompass three primary categories: various closed Brayton cycles, Rankine cycles designed for highly efficient waste heat recovery, and semi-closed Brayton cycles centered on direct oxy-fuel combustion (such as the Allam cycle). An sCO2 power cycle primarily consists of a compressor, heat source, turbine, heat exchangers, control systems, and sealing systems. The compressor operates near the critical point of CO2, where the working fluid exhibits high density, low viscosity, and low isentropic compression work. Consequently, the compressor's work accounts for only 30% of the turbine's output, compared to 45% in helium turbine cycles and 50%–60% in gas turbine cycles. This confers a distinct advantage in high power density, making sCO2 cycles highly suitable for efficient power generation in industrial waste heat recovery, medium- and small-sized marine propulsion, and distributed combined heat and power (CHP) systems. Furthermore, sCO2 possesses excellent heat transfer characteristics. Because the working fluid undergoes no phase change in the supercritical state, there is no "pinch point" during heat exchange with the heat source, resulting in high heat transfer efficiency. Studies have demonstrated that the sCO2 closed power cycle features a more compact structure and may partially replace helium power cycles in the future to meet the more efficient pre-cooling demands of aerospace aircraft.
A fluid whose pressure and temperature both exceed their respective critical values is defined as a supercritical fluid. In this state, the working fluid no longer exhibits distinct phase changes. The critical point of pure CO2 is 7.38 MPa and 31.1°C. Utilizing supercritical CO2 as a working fluid most intuitively yields a highly compact core engine. Figure 2 illustrates a comparison by GE Aerospace of the primary application areas and thermodynamic cycle efficiencies of sCO2 power cycles versus current mainstream power cycles. It is evident that within a heat source temperature range of 400–800°C, sCO2 power cycles not only offer advantages in high cycle efficiency, cleanliness, safety, and low cost for the conversion and utilization of traditional fossil fuels like natural gas and coal, but also hold immense potential in the thermodynamic conversion of new energy sources such as nuclear, concentrated solar, and biomass gasification.
The concept of the sCO2 power cycle was first proposed in the 1960s, with the United States taking the lead in preliminary conceptualization and feasibility studies for its application in nuclear reactors. However, several technological factors constrained its development at the time. First, the manufacturing processes then could not meet the requirements for one-piece machining of impellers and blades. It was not until the mid-1990s, with the widespread adoption of five-axis machining, that impeller manufacturing breakthroughs were achieved, paving the way for commercial product development. Second, sCO2 power cycles rely on recuperators to enhance cycle efficiency. When the reactor core outlet temperature exceeds 500°C, the recuperated heat is approximately twice the core's heat release, a task beyond the capabilities of conventional recuperator technology. The advent of ultra-compact recuperator technology over the past decade has made the realization of sCO2 power cycles possible. Third, the development of dry gas seals provided an appropriate solution for the high-pressure, high-speed sealing challenges in sCO2 power cycles. Additionally, nickel-based alloys resolved the issue of carbon atom replacement reactions between ordinary carbon steel and the carbon in CO2, while high-speed gas foil bearings and high-speed motors offered highly efficient structural solutions for megawatt-class small-scale sCO2 power cycles.
Suzhou Pharma Machinery Co.,Ltd.
2026/07/06
Gino
