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

Abstract

The use of supercritical carbon dioxide (sCO2) cycle has been proposed as a promising alternative toreplace conventional steam Rankine cycle. This study entails the development of a power cycle model toassess the impact of fluctuations on the heat source and environmental conditions on a recompressionsCO2 Brayton cycle during off-design operation. Two operational strategies are tested during off-designoperation, including fixed recompression fraction and adjusted recompression fraction. It is found that asuperior performance is obtained when the recompression fraction is adjusted according to heat additionand ambient temperature variations. The variations of the heat addition have a greater impact thanambient temperature on the cycle’s performance, showing up to 70% greater cycle efficiency when theheat addition ratio is reduced to 30%. In some conditions, the recompression cycle operates similarly to aregenerative cycle, hence no recompression fraction is required when the heat addition ratio is lowerthan 55%. The influence of the ambient temperature is more relevant when a dry cooler is used, and inthis case, it is important to include a detailed cooler’s model in order to account for the variability of thethermophysical properties of the carbon dioxide close to its critical point.