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

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

doi:10.1016/j.apenergy.2013.01.060

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

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

Research output: Contribution to journal › Article › peer-review

61 Scopus citations

Abstract

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.

Original language	English
Pages (from-to)	243-253
Number of pages	11
Journal	Applied Energy
Volume	106
DOIs	https://doi.org/10.1016/j.apenergy.2013.01.060
State	Published - Jun 2013

Funding

This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. This work was performed for the project “Working Fluids and Their Effect on Geothermal Turbines” sponsored by the Geothermal Technologies Program, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy under Contract DE-AC05-00OR22725, Oak Ridge National Laboratory, managed and operated by UT-Battelle, LLC.

Funders	Funder number
U.S. Department of Energy	DE-AC05-00OR22725
Office of Energy Efficiency and Renewable Energy
Oak Ridge National Laboratory

Keywords

Cycle efficiency
Geothermal binary plant
Heat transfer coefficient
Working fluid

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

Access to Document

10.1016/j.apenergy.2013.01.060

Cite this

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title = "Mixtures of SF6-CO2 as working fluids for geothermal power plants",

abstract = "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.",

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author = "Hebi Yin and Sabau, {Adrian S.} and Conklin, {James C.} and Joanna McFarlane and Qualls, {A. Lou}",

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AU - Yin, Hebi

AU - Sabau, Adrian S.

AU - Conklin, James C.

AU - McFarlane, Joanna

AU - Qualls, A. Lou

PY - 2013/6

Y1 - 2013/6

N2 - 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.

AB - 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.

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