Design and analysis of radial and axial turbomachinery of supercritical CO2 power cycles

Abstract

The most common application of the supercritical CO2 (S-CO2) power cycle is a Brayton cycle operating between two supercritical pressures. The key idea of this cycle is that the compression process occurs in the vicinity of the critical point, which results in a consumption power lower than in a classical Brayton cycle, which uses ideal gas as working fluid. This reduction in the compression work enables the S-CO2 power cycle to work with a medium temperature range in the thermal source, achieving good efficiencies in the range of 300ºC/500ºC. The design of the turbomachinery plays an important role in S-CO2 power cycles and it is outside the experience of the existing turbomachines. The size of the machines is very small compared to the size of turbines and compressors of classical cycles because of the high density of S-CO2. In this study, a compressor and a turbine for a high-power S-CO2 cycle from a fusion power plant are designed and different alternatives are explored. Radial versus axial configuration, number of stages and other relevant characteristics are investigated in order to maximize the efficiency of the machines. Two analysis tools, AXIAL and COMPAL from Concepts NREC, for multistage axial and radial turbomachinery, respectively, have been used to carry out the mean-line designs. In addition, NIST property database is used in the calculations, so real CO2 properties have been considered.