Performance Test Results of the Supercritical CO₂ Compressor for a New Gas Turbine Generating System

Supercritical carbon dioxide (S-CO₂) gas turbines can generate power at high cycle thermal efficiency, even at modest temperatures of 500–550°C, because of their markedly reduced compressor work near the critical point. Furthermore, the reaction between Na and CO₂ is milder than that between H₂O and Na. A more reliable and economically advantageous power generation system could be achieved by coupling with a sodium-cooled fast reactor. At Tokyo Institute of Technology, numerous development projects have been conducted for development of this system in cooperation with JAEA. Supercritical CO₂ compressor performance test results are given as described herein. A centrifugal compressor is chosen for the performance test. Main compressor parts are stored in a pressure vessel. Maximum design conditions of the supercritical CO₂ test apparatus are pressure of 11 MPa, temperature of 150°C, the flow rate of 6 kg/s and rotational speed of 24,000 rpm. The centrifugal compressor has an electric motor with permanent magnets on the rotor surface, with speed control by an inverter up to 24,000 rpm, a rotor shaft for the impeller, and a motor supported by gas bearings. Different compressor design points are examined using impellers of three kinds; test data are obtained using those impellers under steady state conditions with changing pressure, temperature, flow rate, and compressor rotor speed. The pressure ratio (compressor outlet pressure/inlet pressure) is obtained with the function of compressor rotational speed and the fluid flow rate. The data cover a broad region from sub-critical to supercritical pressure. Such data were obtained for the first time. No unstable phenomenon was observed in the area where the CO₂ properties change sharply. Data of the pressure ratio vs. flow rate were coincident with the fundamental compressor theory.