Compressor Design for the Supercritical CO2 Brayton Cycle

C, with a cycle efficiency of 45%. Turbomachinery used in the cycle is composed of two compressors (a main compressor and a recompressing compressor) and a turbine, which work on a single shaft. In fact the high cycle efficiency is realized by having the main compressor operate near the critical point of CO2 to benefit from reduced compression work. Introduction of the recompressing compressor which operates at a temperature higher than critical is to avoid the pinch-point problem which otherwise occurs in the subsequent recuperator. Because the perfect gas law does not apply near the saturation line, CO2 was treated as a real gas and the NIST property database was used for the purpose of CO2 thermodynamics and transport property evaluation. The preliminary design process for the supercritical CO2 compressors is mainly discussed in this paper. Steady-state design as well as off-design analysis was performed using the AXIAL TM program modified for real gas properties. The results show that the supercritical CO2 compressors are more compact than helium compressors, with equivalent adiabatic efficiency.