Planning for Successful Transients and Trips in a 1 MWe-Scale High-Temperature sCO2 Test Loop

Supercritical CO2 power cycles incorporate a unique combination of high fluid pressure, temperature, and density as well as limited component availability (e.g., high-temperature trip valves) that can result in operational challenges, particularly during off-design and transient operation. These conditions and various failure scenarios must be considered and addressed during the facility, component, and control system design phase in order to ensure machinery health and safety during operation. This paper discusses significant findings and resulting design/control requirements from a detailed failure modes and effects analysis that was performed for the 1 MWe-scale supercritical CO2 test loop at Southwest Research Institute, providing insight into design and control requirements for future test facilities and applications. The test loop incorporates a centrifugal pump, axial turboexpander, gas-fired primary heat exchanger, and micro-channel recuperator for testing in a simple recuperated cycle configuration at pressures and temperatures up to 255 bara and 715°C, respectively. The analysis considered offdesign operation as well as high-impact failures of turbomachinery and loop components that may require fast shutdowns and blowdowns. The balance between fast shutdowns/blowdowns and the need to manage thermal stresses in the turbomachinery resulted in staged shutdown sequences and impacted the design/control strategies for major loop components and ancillary systems including the fill, vent, and seal supply systems.