Optimized operation of recompression sCO2 Brayton cycle based on adjustable recompression fraction under variable conditions

• Published in: Energy (Oxford) 2021-07, Vol.227, p.120334, Article 120334
• Main Authors: Correa, Faustino, Barraza, Rodrigo, Soo Too, Yen Chean, Vasquez Padilla, Ricardo, Cardemil, José M.
• Format: Article
• Language: English
• Subjects: Ambient temperature; Brayton cycle; Carbon cycle; Carbon dioxide; Compressing; Critical point; Environmental conditions; Heat; Heat exchangers; Rankine cycle; Recompression Brayton cycle; Recompression fraction; Steam; Supercritical carbon dioxide; Thermal efficiency optimization; Thermophysical models; Thermophysical properties
• ISSN: 0360-5442; 1873-6785
• DOI: 10.1016/j.energy.2021.120334

The use of supercritical carbon dioxide (sCO2) cycle has been proposed as a promising alternative to replace conventional steam Rankine cycle. This study entails the development of a power cycle model to assess the impact of fluctuations on the heat source and environmental conditions on a recompression sCO2 Brayton cycle during off-design operation. Two operational strategies are tested during off-design operation, including fixed recompression fraction and adjusted recompression fraction. It is found that a superior performance is obtained when the recompression fraction is adjusted according to heat addition and ambient temperature variations. The variations of the heat addition have a greater impact than ambient temperature on the cycle’s performance, showing up to 70% greater cycle efficiency when the heat addition ratio is reduced to 30%. In some conditions, the recompression cycle operates similarly to a regenerative cycle, hence no recompression fraction is required when the heat addition ratio is lower than 55%. The influence of the ambient temperature is more relevant when a dry cooler is used, and in this case, it is important to include a detailed cooler’s model in order to account for the variability of the thermophysical properties of the carbon dioxide close to its critical point. •A recompression sCO2 Brayton model is created for nominal and off-design operation.•Variable boundary conditions affect a recompression sCO2 Brayton performance.•Adjustable recompression fraction optimizes the thermal efficiency of the cycle.