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Research Papers: Gas Turbines: Controls, Diagnostics, and Instrumentation

Thermodynamic and Economic Analysis and Multi-objective Optimization of Supercritical CO2 Brayton Cycles

[+] Author and Article Information
Hang Zhao, Qinghua Deng, Wenting Huang, Dian Wang

Institute of Turbomachinery,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China

Zhenping Feng

Institute of Turbomachinery,
School of Energy and Power Engineering,
Xi'an Jiaotong University,
Xi'an 710049, China
e-mail: zpfeng@mail.xjtu.edu.cn

1Corresponding author.

Contributed by the Controls, Diagnostics and Instrumentation Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received December 30, 2015; final manuscript received January 7, 2016; published online March 15, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(8), 081602 (Mar 15, 2016) (9 pages) Paper No: GTP-15-1585; doi: 10.1115/1.4032666 History: Received December 30, 2015; Revised January 07, 2016

Supercritical CO2 Brayton cycles (SCO2BC) including the SCO2 single-recuperated Brayton cycle (RBC) and recompression recuperated Brayton cycle (RRBC) are considered, and flexible thermodynamic and economic modeling methodologies are presented. The influences of the key cycle parameters on thermodynamic performance of SCO2BC are studied, and the comparative analyses on RBC and RRBC are conducted. Nondominated Sorting Genetic Algorithm II (NSGA-II) is selected for the Pareto-based multi-objective optimization of the RRBC, with the maximum exergy efficiency and the lowest cost per power (k$/kW) as its objectives. Artificial neural network (ANN) is chosen to accelerate the parameters query process. It is shown that the cycle parameters such as heat source temperature, turbine inlet temperature, cycle pressure ratio, and pinch temperature difference of heat exchangers have significant effects on the cycle exergy efficiency. The exergy destruction of heat exchanger is the main reason why the exergy efficiency of RRBC is higher than that of the RBC under the same cycle conditions. RBC has a cost advantage from economic perspective, while RRBC has a much better thermodynamic performance, and could rectify the temperature pinching problem that exists in RBC. It is also shown that there is a conflicting relationship between the cycle cost/cycle power (CWR) and the cycle exergy efficiency. The optimization results could provide an optimum tradeoff curve enabling cycle designers to choose their desired combination between the efficiency and cost. ANN could help the users to find the SCO2BC parameters fast and accurately.

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References

Figures

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Fig. 1

Diagram of (a) RBC and (b) RRBC

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Fig. 5

Effect of cycle pressure ratio on the exergy destruction for the key components in RBC

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Fig. 4

Effect of cycle pressure ratio on the exergy destruction for the key components in RRBC (a) turbine and compressor and (b) heat exchanger

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Fig. 3

Effect of cycle pressure ratio on the exergy efficiency for a different pinch temperature difference of LTR and HTR in RBC and RRBC

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Fig. 2

Effect of cycle pressure ratio on the exergy efficiency for different turbine inlet temperatures in RBC and RRBC

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Fig. 6

Flow chart of NSGA-II

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Fig. 8

Pareto optimal relation curve between the CWR (k$/kW) and the cycle exergy efficiency

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