Analysis of different Supercritical CO2 Brayton Cycles Integrated with Transcritical CO2 Cycle and Organic Rankine Cycle

Abstract

For concentrating solar power (CSP) applications, supercritical CO2 (S-CO2) has the potential to provide greater cycle efficiency than superheated or supercritical steam cycles. The transcritical CO2 cycle (TCO2 cycle) performs well in the domain of low-grade waste heat recovery. As an alternative to TCO2, the organic Rankine cycle (ORC) has been proposed for recovering waste heat. Studies have been carried out integrating SCO2 Cycle with either ORC or TCO2. Until now, simple, recompression and partial cooling configuration of SCO2 cycle has been focused on and a single cycle is used for waste heat. In this research, a thermodynamic study and optimization of combined power cycles having multiple bottoming cycles are being carried out with the objective of enhancing the total thermal efficiency of power cycles. Besides, along with recompression and partial cooling SCO2 layout, another additional configuration i.e main compression with intercooling is used. In order to examine the behaviour of combined cycles, parametric analysis is performed with respect to some key parameters. And also, comparison between the combined cycle models is done. Analysis is conducted at 25 MPa maximum and 7.5 MPa minimum pressure at 20°C ambient temperature. Results reveal that rise in S-CO2 cycle maximum temperature enhances combined cycle thermal efficiency. MCIT enhances efficiency up to 40–45°C owing to pseudocritical effects, then decreases. When the TCO2 cycle's turbine intake pressure increases, the combined cycle's energy efficiency improves, but only up to a point, then starts falling.However, bottoming cycle condensation temperature decreases efficiency. When compared to corresponding standalone cycle, combined cycle configurations demonstrate significantly improved performance. Furthermore, it is found that the main compression with intercooling models gives better performance than the other two proposed models.