Research on recompression supercritical CO2 power cycle system considering performance and stability of main compressor

Abstract

The supercritical carbon dioxide (sCO2) power cycle has good prospects for use in many energy applications. Ensuring the stable operation of the power cycle is an important issue. The inlet condition of the main compressor in the sCO2 recompression cycle is close to the critical point of CO2 and the physical properties of CO2 change drastically near the critical point, so the study of inlet parameter change behavior of the main compressor is of great significance to the stable operation of the equipment and the system. This paper investigates the performance of an sCO2 recompression power cycle system under off-design conditions with different cooling and heating conditions. Unlike previous studies, this paper uses more accurate compressor and heat exchanger models to simulate the system for off-designed performance. A 1-D optimization prediction model of the compressor and a density-based segmented heat exchanger model are introduced to predict the performance changes of the system. The operating conditions, performance, and stability of the compressor under different cooling and heating conditions were compared. The results show that variations in different cooling and heating conditions change the inlet temperature of the compressor, causing the sCO2 compressor to deviate from optimal operation. As the inlet temperature increases, the power consumption of the compressor increases. At an inlet temperature of 305 K, the power is 1.93 MW (main compressor, MC) and 2.17 MW (recompressor, RC). When the inlet temperature increases to 310 K, the power increases by more than 10 %. The largest change in system efficiency is 3.76 % for a change in cooling conditions, and the largest change in compressor speed is 14.23 % (MC) and 7.79 % (RC) for a change in heating conditions, respectively. The operating condition of the main compressor moves far away from the surge line when its inlet temperature increases, which means the operation of the main compressor is more stable in this situation. The results of this paper contribute to the stable operation of the sCO2 recompression cycle.