A one-dimensional design methodology for supercritical carbon dioxide Brayton cycles: Integration of cycle conceptual design and components preliminary design

Abstract

The state-of-the-art supercritical carbon dioxide Brayton cycles are complex integrated systems featured with strong coupling effects between the cycle and components. To reveal cycle characteristics precisely and conduct cycle design efficiently, integration of the cycle design and components design are required at the very beginning. In this paper, a one-dimensional design methodology for supercritical carbon dioxide Brayton cycles was proposed, based on the integration between cycle conceptual design and components preliminary design. Details of the preliminary design methodology for turbomachinery and heat exchangers were presented. A 500kWe and 5MWe recompression cycle were designed as demonstration examples, and comparative analysis of cycle performance and components performances were performed. Meanwhile, parametric analysis of some crucial parameters was carried out and some design considerations for recompression cycle were presented. Design results suggest that the 5MWe cycle could reach a higher thermal efficiency of 38.0% compared with 37.0% for the 500kWe cycle, which fundamentally results from the larger mass flow rate. The enhanced mass flow rate would lead to higher turbomachinery efficiency in the 5MWe cycle, and the stator loss reductions contribute to the turbomachinery efficiency improvements. As for the design of recompression cycle, selecting a flow split ratio smaller than its optimum value and a reasonably high effectiveness for each recuperator is recommended. Keeping the rotation speed of the re-compressor within its optimum region is also suggested, especially for low-power cycles. Besides, the main-compressor inlet temperature is a crucial parameter, and a compromise between cycle efficiency and system maintenance should be made.