Loop Filling and Start Up With a Closed Loop sCO2 Brayton Cycle

Recent testing has been performed on a 1 MWe sCO2 closed loop recuperated cycle under funding from the US DOE Sunshot initiative and industry partners. Some of the goals of this funding included the development of a 1 MWe loop, a 10 MWe turbine, and performance and mechanical testing. One of the key challenges that presented itself was the filling, start-up, and shut down of the entire system. Understanding the loop transient performance is important when having to bring a turbine online, transitioning from peak to partial loading, and also managing routine and emergency shut downs. Due to large changes in density near the critical point for CO2 and its tendency to form dry ice when expanded to atmospheric pressure, managing loop filling and venting is critical in ensuring that components do not get damaged. Specific challenges were centered on protecting the dry gas seals, maintaining proper mass in the loop, and also thermal transients during trips. This paper will take a detailed look at the challenges encountered during start up and shut downs, and also the solutions that were implemented to successful transition between different phases of the testing.