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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

MULTI-OBJECTIVE OPTIMIZATION OF S-CO2 RECOMPRESSION BRAYTON CYCLE INTEGRATED INTO EXISTING DEVELOPED MOLTEN SALT SOLAR POWER TOWER

Kun Wang
Key Laboratory of Thermo-Fluid Science and Engineering of MOE, School of Energy and Power Engineering, Xi'an Jiaotong University

Ya-Ling He
Key Laboratory of Thermo-Fluid Science and Engineering of Ministry of Education, School of Energy and Power Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China

Zhang-Jing Zheng
Xi'an Jiaotong University, No.28 Xianning west Rd, Xi'an, Shaanxi 710049, China

Huan Xi
Xi'an Jiaotong University, No.28 Xianning west Rd, Xi'an, Shaanxi 710049, China

Abstract

In the present study, an indirect integration of a S-CO2 Brayton cycle with the existing mature molten salt solar power tower is modeled integrally. Based on the integrative model, the multi-objective optimization is performed by using non-dominated sorting genetic algorithm-II with the exergy efficiency and the specific work as the two objective functions, where the hot salt temperature, the cycle high pressure, the cycle low pressure, the cycle intermediate pressure, the split ratio and the conductance ratio are selected as decision variables. The trade-off between the exergy efficiency and the specific work in the form of Pareto-optimal solution curves are obtained. The results show that when using Solar Salt (60 wt% NaNO3 and 40 wt% KNO3) as heat transfer fluid, the optimal hot salt temperature, the cycle high pressure, the cycle low pressure, the intermediate pressure almost fall at fixed values (i.e. 565 °C, 28.9 MPa, 8.6 MPa and 16.0 MPa, respectively) under given conditions. The corresponding optimal exergy efficiency ranges from 30.0% to 32.2%, and the optimal specific work ranges from 127 kW·kg-1 to 142 kW·kg-1. Novel salts with higher maximum allowable temperature ranging from 696 °C to 794 °C as well as good heat transfer performance are recommended to be developed. When using such novel salts, the performance of the solar power tower system can be improved: the optimal exergy efficiency ranges from 30.4% to 33.2%, and the optimal specific work ranges from 158 kW·kg-1 to 198 kW·kg-1.

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