Abstract
Improving energy efficiency and reducing carbon emissions are crucial for the technological advancement of power systems. Various carbon dioxide (CO2) power cycles have been proposed for various applications. For high-temperature heat sources, the CO2 power system is more efficient than the ultra-supercritical steam Rankine cycle. As a working fluid, CO2 exhibits environmentally friendly properties. CO2 can be used as an alternative to organic working fluids in small- and medium-sized power systems for low-grade heat sources. In this paper, the main configurations and performance characteristics of CO2 power systems are reviewed. Furthermore, recent system improvements of CO2 power cycles, including supercritical Brayton cycles and transcritical Rankine cycles, are presented. Applications of combined systems and their economic performance are discussed. Finally, the challenges and potential future developments of CO2 power cycles are discussed. CO2 power cycles have their advantages in various applications. As working fluids must exhibit environmentally-friendly properties, CO2 power cycles provide an alternative for power generation, especially for low-grade heat sources.
Highlights
Carbon dioxide (CO2) was first patented in 1850 as a refrigerant (Bodinus, 1999)
To recover the exhaust and cooling simultaneously, Song et al designed a supercritical CO2 (sCO2) cycle with two-stage regeneration, and the maximum output power of the engine was increased by 6.9% (Song et al, 2018)
The energy efficiency of the high-temperature sCO2 power cycle increases with an increase in the maximum working pressure
Summary
Carbon dioxide (CO2) was first patented in 1850 as a refrigerant (Bodinus, 1999). In the 1930s and 1940s, with the advent of chlorofluorocarbons (CFCs), CO2 was gradually replaced. The results for the thermal efficiency of the recompression cycle cover the range of the other layouts, indicating that the split-flow layouts are well suited for high-temperature applications with a single heat source. An investigation showed that the thermal efficiency of the system decreased slightly from 43.88 to 43.11% with a small increase in the heat transfer area, when the inlet temperature of the highpressure turbine was reduced to 390°C, and the inlet pressure decreased from 20 to 15 MPa (Guo et al, 2018). The cycle efficiency increased as the inlet temperature of the high-pressure turbine increased, the net power output decreased. Compared with the conventional steam Rankine cycle, the sCO2 cycle has low critical pressure, high density, high heat transfer rate, high specific power, and small size (Feng and Wang, 2019), thereby making it suitable for various heat sources.
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