Preliminary design of S-CO₂ Brayton cycle for APR-1400 with power generation and desalination process

This study was conducted to explore the capabilities of the S-CO₂ Brayton cycle for a cogeneration system for APR-1400 application. Three concepts of the S-CO₂ simple recuperated co-generation cycle were designed. A supercritical CO₂ (S-CO₂) Brayton cycle is recently receiving significant attention as a promising power conversion system in wide range of energy applications due to its high efficiency and compact footprint. The main reason why the S-CO₂ Brayton cycle has these advantages is that the compressor operates near the critical point of CO₂ (30.98 .deg. C, 7.38MPa) to reduce the compression work significantly compared to the other Brayton cycles. In this study, the concept of replacing the entire steam cycle of APR-1400 with the S-CO₂ Brayton cycle is evaluated. The power generation purpose S-CO₂ Brayton cycles are redesigned to generate power and provide heat to the desalination system at the same time. The performance of these newly suggested cycles are evaluated in this paper. The target was to deliver 147MW heat to the desalination process. The thermal efficiencies of the three concepts are not significantly different, but the 3^rd concept is relatively simpler than other cycles because only an additional heat exchanger is required. Although the 2^nd concept is relatively complicated in comparison to other concepts, the temperatures at the inlet and outlet of the DHX are higher than that of the others. As shown in the results, the S-CO₂ Brayton cycles are not easy to outperform the steam cycle with very simple layout and general design points under APR-1400 operating condition. However, this study shows that the S-CO₂ Brayton cycles can be designed as a co-generation cycle while producing the target desalination heat with a simple configuration. In addition, it was also found that the S-CO₂ Brayton cycle can achieve higher cycle thermal efficiency than the steam power cycle under APR-1400 condition through re-optimization. The re-optimization strategy deviated from the traditional S-CO₂ Brayton cycle design approach which fixes the compressor inlet condition to approach the critical point of CO₂ as near as possible for a simple cycle configuration