Abstract
In this study, a direct recompression supercritical CO2 Brayton cycle, using parabolic trough solar concentrators (PTC), is developed and analyzed employing a new simulation model. The effects of variations in operating conditions and parameters on the performance of the s-CO2 Brayton cycle are investigated, also under varying weather conditions. The results indicate that the efficiency of the s-CO2 Brayton cycle is mainly affected by the compressor outlet pressure, turbine inlet temperature and cooling temperature: Increasing the turbine inlet pressure reduces the efficiency of the cycle and also requires changing the split fraction, where increasing the turbine inlet temperature increases the efficiency, but has a very small effect on the split fraction. At the critical cooling temperature point (31.25 °C), the cycle efficiency reaches a maximum value of 0.4, but drops after this point. In optimal conditions, a cycle efficiency well above 0.4 is possible. The maximum system efficiency with the PTCs remains slightly below this value as the performance of the whole system is also affected by the solar tracking method used, the season and the incidence angle of the solar beam radiation which directly affects the efficiency of the concentrator. The choice of the tracking mode causes major temporal variations in the output of the cycle, which emphasis the role of an integrated TES with the s-CO2 Brayton cycle to provide dispatchable power.
Highlights
The growing energy demand and the need for reducing global greenhouse gas emissions from fossil fuels have led to vigorous development of renewable energy [1,2,3]
Recent studies indicate that renewable energy, including concentrating solar power (CSP) technologies, could play a significant role in the forthcoming development [4,5,6]
The supercritical CO2 (s-CO2) cycle could be integrated into CSP systems in different ways, e.g., using parabolic troughs and synthetic oils as HTF, which could yield an energy efficiency of 33% [37], or molten salts with a solar power tower (SPT), having an optimum/maximum hot salt temperature at 565 ◦ C [38]
Summary
The growing energy demand and the need for reducing global greenhouse gas emissions from fossil fuels have led to vigorous development of renewable energy [1,2,3]. Some studies have proposed an innovative solar thermal power system based on the Rankine cycle, which employs screw expanders and direct steam generations with water as heat transfer and working fluid [26,27]. The s-CO2 cycle could be integrated into CSP systems in different ways, e.g., using parabolic troughs and synthetic oils as HTF, which could yield an energy efficiency of 33% [37], or molten salts with a solar power tower (SPT), having an optimum/maximum hot salt temperature at 565 ◦ C [38]. The direct-heated PTC refers to heat collection in the solar field through the cycle work fluid, which eliminates the need of an intermediate HTF, such as oil or molten salt This design may reduce the investment costs and increase the power production due to improved heat transfer. The novel design of this integrated CSP plant employs carbon dioxide both as a heat transfer fluid in the concentrators and as a working fluid in the Brayton cycle to reduce energy losses from intermediate heat exchangers
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