Thermodynamic Analysis of a SCO₂ Part-Flow Cycle Combined With an Organic Rankine Cycle With Liquefied Natural Gas as Heat Sink

The supercritical carbon dioxide (SCO₂) part-flow cycle can achieve higher efficiency compared with conventional Brayton cycle as it can avoid the pinch point problem inside the regenerative heat exchanger. To recover the waste heat from the pre-cooler in the cycle and improve the overall cycle efficiency, a new integrated power system driven by nuclear reactor is proposed to achieve the energy cascade utilization. This system combines a SCO₂ part-flow cycle with an organic Rankine cycle (ORC) using liquefied natural gas (LNG) as heat sink to utilize the cold energy of LNG. In this paper a mathematical model is established to simulate the SCO₂ part-flow cycle coupled with an ORC under steady state condition, and a thermodynamic parametric analysis is conducted to investigate the effects of some key parameters, including the turbine inlet pressure, the turbine and compressor isentropic efficiency and pressure drop ratio, on the system performance. The results indicate that the integrated power system is effective to recover the waste heat and may achieve the overall cycle thermal efficiency of 52.12% under the operating conditions of 20MPa, 800K and part-flow ratio 0.68, which can be further improved with parametric optimization of the system.