Off-design performance of the supercritical carbon dioxide recompression Brayton cycle with NDDCT cooling for concentrating solar power

The aim of this study is to investigate the off-design performance of an air-cooled supercritical carbon dioxide recompression Brayton cycle for concentrating solar thermal power generation. Off-design component models were developed in a system modelling framework. The components were designed for 25 MWe net power generation at ambient temperature 30 degrees C, with design point cycle thermal efficiency of 46.2%. The off-design performance was investigated for a range of heat source temperatures, ambient temperatures and cycle mass flow rates. Key elements of the off-design control scheme used are independent compressor shaft speeds, fixed low side pressure (assuming inventory control), and fixed turbine speed (for synchronous operation). The cycle can maintain nominal net power generation at 50 degrees C ambient temperature with increased cycle mass flow rate and turbine inlet temperature. At design point turbine inlet temperature and mass flow rate, net power generation decreases by approximately 10% for each 10 degrees C increase above the design point ambient temperature. The high design point ambient temperature limits the beneficial effect low ambient temperature. The effect of decreasing the design point ambient temperature was investigated. While this allows higher peak cycle efficiency, it also leads to much greater deterioration of cycle efficiency with increasing ambient temperature. (C) 2019 Elsevier Ltd. All rights reserved.