Impact of cold source temperature on transcritical CO2 power cycle: Design point optimization and off-design performance analysis

Abstract

The transcritical CO₂ (T-CO₂) power cycle is regarded as one of the most promising alternatives to the steam power cycle in nuclear power plants. However, these plants often operate with transient cold source conditions, leading to deviations from the optimal design point and performance degradation. Therefore, this study examines a double recompression T-CO₂ power cycle to optimize the design point pump inlet temperature and investigate part-load performance under cold source fluctuations. Results indicate that the lowest design point pump inlet temperature is optimal for low temperature cold sources and high load conditions to maximize thermal efficiency. When the system operates at 80 % load with a cold source temperature of 5 °C, the thermal efficiencies at the design point pump inlet temperature of 15 °C and 25 °C are 58 % and 56.93 %, respectively. In contrast, a moderate design point pump inlet temperature is better suited for accommodating wide fluctuations in operating conditions. A lower cold source temperature helps mitigate the reduction in thermal efficiency caused by load decreases. Furthermore, reducing the split ratio of low-temperature compressor can enhance thermal efficiency as the cold source temperature increases. These findings provide an effective approach to minimizing performance degradation in the T-CO₂ power cycle under off-design conditions.