Thermodynamic performance analysis of different supercritical Brayton cycles using CO₂-based binary mixtures in the molten salt solar power tower systems

The potential to improve the performance of molten salt solar power tower system (SPT) is explored through the proposal of CO₂-based binary mixture cycle in the present study. The feasibility of using xenon and butane as the additives to the S-CO₂ cycle are discussed from the perspective of thermodynamic analysis. The detail parametric study is performed to reveal the effects of crucial parameters on the performance of 4 system configurations. Furthermore, the systematic comparison is conducted for 4 cycle layouts adopting CO₂/xenon, CO₂ and CO₂/butane separately to illustrate the mechanism of performance improvement of SPT system coupled to CO₂-based binary mixture cycle. The optimal performance of the SPT system is also demonstrated. Finally, the best performance system layout and suitable additives are recommended. The results indicate the following issues. Adding xenon into S-CO₂ cycle can obviously improve the overall thermal efficiency and exergy efficiency. While the effects of butane as an additive are converse. The inter-cooling CO₂/xenon cycle is recommended as the most suitable layout coupled to the SPT system, and the exergy efficiency is 1.18%∼1.32% higher than that of the SPT system with S-CO₂ inter-cooling cycle. Detail exergy loss fraction distribution illustrates that the receiver is the highest exergy loss part and followed by the heliostat field, and butane as an additive is beneficial to reduce the receiver exergy loss for its smaller temperature difference. The study can provide a novel way to improve the SPT system performance and give a clue to the addition of CO₂-based binary mixture in power cycles particularly for the application of SPT system.