Preliminary experimental study of a supercritical CO2 power cycle test loop with a high-speed turbo-generator using R134a under similarity conditions

Research on applying a supercritical carbon dioxide power cycle (S-CO2) to concentrating solar power (CSP) instead of a steam Rankine cycle or an air Brayton cycle has been recently conducted. An S-CO2 system is suitable for CSP owing to its compactness, higher efficiency, and dry-cooling capability. At the Korea Institute of Energy Research (KIER), to implement an S-CO2 system, a 10 kWe class test loop with a turbinealternator-compressor (TAC) using gas foil bearings was developed. A basic sub-kWe class test loop with a highspeed radial type turbo-generator and a test loop with a capability of tens of kWe with an axial type turbogenerator were then developed. To solve the technical bottleneck of S-CO2 turbomachinery, a partial admission nozzle and oil-lubrication bearings were used in the turbogenerators. To experience the closed-power cycle and develop an operational strategy of S-CO2 operated at high pressure, an organic Rankine cycle (ORC) operating test using a refrigerant as the working fluid was conducted owing to its operational capability at relatively low-pressure conditions of approximately 30 to 40 bar. By operating the sub-kWe class test loop using R134a as the working fluid instead of CO2, an average turbine power of 400 W was obtained.