Application of Supercritical CO2 Brayton Cycle Integrated System Test (IST) TRACE Model to Initial Turbomachinery and Brayton Loop Testing

by Kevin D. Rahner & Michael J. Hexemer
Knolls Atomic Power Laboratory

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A 100kWe Integrated System Test (IST) is being built to demonstrate a closed loop Brayton power cycle with Supercritical CO2 (S-CO2) as the working fluid. Prior to delivery of the IST turbo-compressor (TC), testing was performed at Barber Nichols, Inc. (BNI) using the Sandia National Laboratory’s (SNL) GenIV test loop to operationally check a new thrust bearing and machine performance. Initial startup of the TC resulted in thrust bearing overload and damage. Test results and supporting TRACE modeling work identified that the initial startup was overly focused on avoiding compressor surge and resulted in zero or reverse turbine flow and high thrust loads. A new startup procedure was developed to balance the concerns for compressor surge and maintain forward turbine flow, by modifying valve lineups and initial fluid conditions. This paper reviews the development efforts for establishing the appropriate initial fluid conditions needed for a successful startup of the TC test and how they are being used to influence the startup procedures for the IST. In addition comparisons between model performance and this initial TC test data are provided and identify the level of agreement.