Maximum thermal efficiencies of supercritical CO2 power cycle at various power capacities

Herein, we investigate the relationships between efficiencies ηth, main vapor parameters (P5 and T5) and power capacities (Wnet) on coal-fired supercritical carbon dioxide cycle (sCO2). We developed a model to couple the cycle and the components. The overlap energy strategy and boiler module design reduce the efficiency penalty. The multi-stages axial turbines and compressors were modeled to explore their performance as Wnet changes. For given Wnet, ηth increases as T5 increases. However, ηth displays parabolic distribution versus P5, due to the tradeoff between the decreased pressure drop of sCO2 boilers and the increased compression power, as P5 raises. Then, for fixed T5 given by the tolerance limit of materials, the monotonous increase of the optimal P5 with increase of Wnet is found, due to the decreased pressure drops of sCO2 boiler as positive effect suppressing the increased compression power as negative effect. Finally, with Wnet in the range of (100–1000) MWe, the system efficiency is found to increase as Wnet increases, matching the scale law regarding efficiencies with respect to system sizes. Our work concludes important roles of boiler pressure drops and compression work on system, providing the guidance to select the “optimal” power capacity that has the “best” system performance.