Optimal Part-Load Performance of Supercritical Carbon Dioxide Brayton Cycles During Inventory Control

Supercritical carbon dioxide (sCO2) cycles are gaining attention for their efficiency and low carbon footprint in power plants. This study focuses on optimizing the performance of a 5 MW simple recuperated sCO2 Brayton loop during inventory control, a recommended strategy for maximum part-load efficiencies. Variable speed operation of turbomachines is explored to enhance part-load efficiency across the operating range, contrasting with the baseline case of constant turbine and compressor speeds. The analysis, which is based on an analytical formulation and validated component models, reveals that part-load efficiency can be improved by variable speed operation of the turbomachines. Additionally, decoupled shaft systems are found to outperform coupled or single shaft systems. Further, part-load efficiency deterioration in case of constant speeds has been discussed in detail. A unique feature of this study is the modeling methodology; model for the compressor is derived by modifying an ideal gas compressor model to account for the behavior of a real gas compressor. Component matching is performed systematically to accurately estimate sCO2 cycle conditions. The results predicted by the model provide valuable insights on design of control strategy including inventory management for better response and improved efficiency while operating under part-load conditions.