Synergetics: The cooperative phenomenon in multi-compressions S-CO2 power cycles

Abstract

Abstract Mature power plant uses regenerative steam Rankine cycle to achieve excellent performance, but there is a lack of general approach for gas Brayton cycle. Here, synergetics is introduced to construct multi-compressions S-CO2 cycle for the first time. Our work starts from the analysis of recompression cycle (RC). RC is decoupled into two simple Brayton cycles (SCs). We show that at the optimal split ratio of flow rate, the mixing stream coming from the two subsystems does not generate exergy destruction, and the heat transfer induced exergy destruction is controlled to an acceptable level. Thus, the two subsystems are synergistic to have the efficiency reinforcing feedback. This finding inspires us to construct multi-compressions cycle. For example, the tri-compressions cycle (TC) is built by cooperation between RC and SC, and the four-compressions cycle (FC) is formed based on TC and SC. At the main vapor parameters 550 °C/20 MPa, thermal efficiencies are increased from 47.43% for RC to 49.47% for TC. A regime map is presented to select multi-compressions cycle based on main vapor parameters. We state that both of multi-compressions and reheating are effective. The combination of both approaches further improves system performance, but multi-compressions are preferable because the high temperature induced heat transfer issue can be avoided. This work fills the gap on how to reach excellent performance for gas Brayton cycle driven by various heat sources such as nuclear energy, solar energy and fossil energy etc.