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Mixtures of SF6–CO2 as working fluids for geothermal power plants


  • Yin, Hebi
  • Sabau, Adrian S.
  • Conklin, James C.
  • McFarlane, Joanna
  • Qualls, A. Lou


In this paper, supercritical/transcritical thermodynamic cycles using mixtures of SF6–CO2 as working fluids were investigated for geothermal power plants. The system of equations that described the thermodynamic cycle was solved using a Newton–Raphson method. This approach allows a high computational efficiency even when thermophysical properties of the working fluid depend strongly on the temperature and pressure. The thermophysical properties of the mixtures were obtained from National Institute of Standards and Technology (NIST) REFPROP software and constituent cubic equations. The local heat transfer coefficients in the heat exchangers were calculated based on the local properties of the working fluid, geothermal brine, and cooling water. The heat exchanger areas required were calculated. Numerical simulation results presented for different cycle configurations were used to assess the effects of the SF6 fraction in CO2, brine temperature, and recuperator size on the cycle thermal efficiency, and size of heat exchangers for the evaporator and condenser. For working fluids with SF6, concentrations of 15 and 20mol% were found to yield the highest Brayton and Rankine cycle efficiencies, respectively.

Suggested Citation

  • Yin, Hebi & Sabau, Adrian S. & Conklin, James C. & McFarlane, Joanna & Qualls, A. Lou, 2013. "Mixtures of SF6–CO2 as working fluids for geothermal power plants," Applied Energy, Elsevier, vol. 106(C), pages 243-253.
  • Handle: RePEc:eee:appene:v:106:y:2013:i:c:p:243-253
    DOI: 10.1016/j.apenergy.2013.01.060

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    References listed on IDEAS

    1. Chen, Huijuan & Goswami, D. Yogi & Rahman, Muhammad M. & Stefanakos, Elias K., 2011. "A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power," Energy, Elsevier, vol. 36(1), pages 549-555.
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    Cited by:

    1. Rovira, Antonio & Rubbia, Carlo & Valdés, Manuel & Martínez-Val, José M., 2014. "Thermodynamic cycles optimised for medium enthalpy units of concentrating solar power," Energy, Elsevier, vol. 67(C), pages 176-185.
    2. Ayub, Mohammad & Mitsos, Alexander & Ghasemi, Hadi, 2015. "Thermo-economic analysis of a hybrid solar-binary geothermal power plant," Energy, Elsevier, vol. 87(C), pages 326-335.
    3. Liu, Qiang & Duan, Yuanyuan & Yang, Zhen, 2014. "Effect of condensation temperature glide on the performance of organic Rankine cycles with zeotropic mixture working fluids," Applied Energy, Elsevier, vol. 115(C), pages 394-404.
    4. Ghasemi, Hadi & Sheu, Elysia & Tizzanini, Alessio & Paci, Marco & Mitsos, Alexander, 2014. "Hybrid solar–geothermal power generation: Optimal retrofitting," Applied Energy, Elsevier, vol. 131(C), pages 158-170.
    5. Wang, Enhua & Yu, Zhibin, 2016. "A numerical analysis of a composition-adjustable Kalina cycle power plant for power generation from low-temperature geothermal sources," Applied Energy, Elsevier, vol. 180(C), pages 834-848.
    6. Li, Jian & Liu, Qiang & Duan, Yuanyuan & Yang, Zhen, 2017. "Performance analysis of organic Rankine cycles using R600/R601a mixtures with liquid-separated condensation," Applied Energy, Elsevier, vol. 190(C), pages 376-389.
    7. Adams, Benjamin M. & Kuehn, Thomas H. & Bielicki, Jeffrey M. & Randolph, Jimmy B. & Saar, Martin O., 2015. "A comparison of electric power output of CO2 Plume Geothermal (CPG) and brine geothermal systems for varying reservoir conditions," Applied Energy, Elsevier, vol. 140(C), pages 365-377.
    8. Sarkar, Jahar, 2015. "Review and future trends of supercritical CO2 Rankine cycle for low-grade heat conversion," Renewable and Sustainable Energy Reviews, Elsevier, vol. 48(C), pages 434-451.
    9. Liu, Qiang & Shen, Aijing & Duan, Yuanyuan, 2015. "Parametric optimization and performance analyses of geothermal organic Rankine cycles using R600a/R601a mixtures as working fluids," Applied Energy, Elsevier, vol. 148(C), pages 410-420.
    10. repec:eee:appene:v:198:y:2017:i:c:p:145-159 is not listed on IDEAS
    11. Habka, Muhsen & Ajib, Salman, 2015. "Evaluation of mixtures performances in Organic Rankine Cycle when utilizing the geothermal water with and without cogeneration," Applied Energy, Elsevier, vol. 154(C), pages 567-576.
    12. Cheng, Wen-Long & Li, Tong-Tong & Nian, Yong-Le & Xie, Kun, 2014. "Evaluation of working fluids for geothermal power generation from abandoned oil wells," Applied Energy, Elsevier, vol. 118(C), pages 238-245.
    13. Zhang, Xinxin & Kobayashi, Noriyuki & He, Maogang & Wang, Jingfu, 2016. "An organic group contribution approach to radiative efficiency estimation of organic working fluid," Applied Energy, Elsevier, vol. 162(C), pages 1205-1210.
    14. Zhao, Li & Bao, Junjiang, 2014. "Thermodynamic analysis of organic Rankine cycle using zeotropic mixtures," Applied Energy, Elsevier, vol. 130(C), pages 748-756.
    15. repec:eee:energy:v:140:y:2017:i:p1:p:818-836 is not listed on IDEAS
    16. Yu, Haoshui & Feng, Xiao & Wang, Yufei & Biegler, Lorenz T. & Eason, John, 2016. "A systematic method to customize an efficient organic Rankine cycle (ORC) to recover waste heat in refineries," Applied Energy, Elsevier, vol. 179(C), pages 302-315.


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