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Research Papers

Effect of Pressure Drop and Reheating on Thermal and Exergetic Performance of Supercritical Carbon Dioxide Brayton Cycles Integrated With a Solar Central Receiver

[+] Author and Article Information
Ricardo Vasquez Padilla

CSIRO Energy Centre,
PO Box 330,
Newcastle, NSW 2300
e-mail: Ricardo.Vasquezpadilla@csiro.au

Yen Chean Soo Too

CSIRO Energy Centre,
PO Box 330,
Newcastle, NSW 2300
e-mail: Yenchean@csiro.au

Andrew Beath

CSIRO Energy Centre,
PO Box 330,
Newcastle, NSW 2300
e-mail: Andrew.Beath@csiro.au

Robbie McNaughton

CSIRO Energy Centre,
PO Box 330,
Newcastle, NSW 2300
e-mail: Rob.Mcnaughton@csiro.au

Wes Stein

CSIRO Energy Centre,
PO Box 330,
Newcastle, NSW 2300
e-mail: Wes.Stein@csiro.au

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received March 3, 2015; final manuscript received July 26, 2015; published online August 18, 2015. Assoc. Editor: M. Keith Sharp.

J. Sol. Energy Eng 137(5), 051012 (Aug 18, 2015) (12 pages) Paper No: SOL-15-1049; doi: 10.1115/1.4031215 History: Received March 03, 2015; Revised July 26, 2015

Concentrated solar power using supercritical carbon dioxide (S-CO2) Brayton cycles offers advantages of similar or higher overall thermal efficiencies than conventional Rankine cycles using superheated or supercritical steam. The high efficiency and compactness of S-CO2, as compared with steam Rankine cycles operating at the same temperature, make this cycle attractive for solar central receiver applications. In this paper, S-CO2 Brayton cycle is integrated with a solar central receiver that provides heat input to the power cycle. Three configurations were analyzed: simple, recompression (RC), and recompression with main intercooling (MC). The effect of pressure drop in heat exchangers and solar receiver and solar receiver surface temperature on the thermal and exergetic performance of the CO2 Brayton cycle with and without reheat condition was studied. Energy, exergy, and mass balance were carried out for each component and the cycle first law and exergy efficiencies were calculated. In order to obtain optimal operating conditions, optimum pressure ratios were obtained by maximizing the cycle thermal efficiency under different pressure drops and solar receiver temperature conditions. Optimization of the cycle first law efficiency was carried out in python 2.7 by using sequential least squares programing (SLSQP). The results showed that under low pressure drops, adding reheat to the S-CO2 Brayton cycle has a favorable effect on the thermal and exergy efficiencies. Increasing pressure drop reduces the gap between efficiencies for reheat and no reheat configuration, and for pressure drop factors in the solar receiver above 2.5%, reheat has a negligible or detrimental effect on thermal and exergy performance of S-CO2 Brayton cycles. Additionally, the results showed that the overall exergy efficiency has a bell shape, reaching a maximum value between 18.3% and 25.1% at turbine inlet temperatures in the range of 666–827 °C for different configurations. This maximum value is highly dependent on the solar receiver surface temperature, the thermal performance of the solar receiver, and the solar field efficiency. As the solar receiver surface temperature increases, more exergy destruction associated with heat transfer losses to the environment takes place in the solar receiver and therefore the overall exergy efficiency decreases. Recompression with main intercooling (MC) showed the best thermal (ηI,cycle > 47% at Tin,turbine > 700 °C) and exergy performance followed by RC configuration.

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References

Figures

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Fig. 1

S-CO2 configurations: (a) simple, (b) RC, and (c) MC. Adapted from Ref. [2].

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Fig. 2

Temperature–entropy diagram for different S-CO2 Brayton cycle configurations. Tin,turbine = 600 °C and ζ = 1.0%.

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Fig. 3

Thermal validation of the proposed Model. Data taken from Kulhánek and Dostál [6] and Turchi et al. [2].

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Fig. 4

CFD. Location: Alice Springs, Australia.

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Fig. 5

Effect of pressure drop in the solar receiver on the cycle first law efficiency for different S-CO2 Brayton cycle configurations. Ref: steam (USC) plant, ηI ∼ 47% operating at 732/760 °C and 35 MPa [65].

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Fig. 6

Effect of turbine inlet temperature on optimum total pressure ratio, rp, for different S-CO2 Brayton cycle configurations. ζ = 2.5%.

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Fig. 7

Effect of solar receiver temperature approach in the solar receiver on the overall exergy efficiency for different S-CO2 Brayton cycle configurations. ζ = 1.0%.

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Fig. 8

Effect of solar receiver temperature approach in the solar receiver on the overall exergy efficiency for different S-CO2 Brayton cycle configurations. ζ = 2.5%.

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Fig. 9

Effect of surface temperature in the solar receiver on the overall exergy efficiency for different S-CO2 Brayton cycle configurations. ζ = 5.0%.

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Fig. 11

Effect of solar field efficiency and radiation view factor on the optimum turbine inlet temperature to maximize the overall exergy efficiency for different S-CO2 Brayton cycle configurations without reheat. ζ = 2.5%. (a) ΔTR = 100 °C and (b) ΔTR = 200 °C.

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Fig. 10

Effect of solar field efficiency and radiation view factor on the optimum overall exergy efficiency for different S-CO2 Brayton cycle configurations without reheat. ζ = 2.5%. (a) ΔTR = 100 °C and (b) ΔTR = 200 °C.

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