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(471d) Design and Operation of a 10 MWe Supercritical CO2 Recompression Brayton Power Cycle

Zitney, S. E., National Energy Technology Laboratory
Liese, E. A., National Energy Technology Laboratory
Supercritical carbon dioxide (sCO2)Brayton power cycles are gaining increasing attention as an attractive alternative to conventional Brayton and Rankine cycles using steam.   Brayton cycles with sCO2 as the working fluid have the potential for more compact design, higher thermal efficiencies, and lower cost of electricity.  In view of these promising advantages, the U.S. Department of Energy under its Supercritical Transformational Electric Power Program is in the process of designing, with the intent to build, a nominal 10 MWe (net) sCO2 Brayton cycle test facility to accelerate scale-up, development, and commercial deployment.  In this work, steady-state and dynamic process models of a 10 MWe indirect recuperated sCO2 recompression Brayton cycle have been developed to analyze cycle design and operation for use with power generation applications.  The process models are capable of predicting the nominal design point, off-design, and part-load performance. 

In this presentation, the 10 MWe sCO2 recompression Brayton process model, assumptions, and design parameters will be described and the key results for the nominal steady-state operating point will be presented.  The additional specifications and methods applied to provide increased model fidelity for generating the rigorous pressure-driven dynamic model will also be discussed, including the use of performance curves for the turbomachinery and flow-dependent pressure drop correlations, volume specifications, and heat capacity calculations for the heat exchangers.  The dynamic model predicts time-dependent profiles of key outputs such as power generated and thermal efficiency as a function of compressor inlet temperature and pressure, turbine inlet temperature, bypass recompression fraction, and other key variables for the purpose of designing effective control strategies.

From the dynamic perspective, this presentation will highlight the transient responses of the sCO2 cycle to reductions in heat input, representing typical off-design and part-load scenarios arising from integration with a load-following energy plant.   Based on the open-loop cycle results without controllers, several operational strategies will be analyzed for maximizing cycle efficiency by maintaining turbine inlet temperature during heat input turndown subject to process constraints.