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Research Papers

Thermodynamic Optimization of Supercritical CO2 Brayton Power Cycles Coupled to Line-Focusing Solar Fields

[+] Author and Article Information
Luis Coco Enríquez, Javier Muñoz-Antón

Energy Engineering Department,
Technical University of Madrid UPM,
Madrid 28040, Spain

José María Martínez-Val Peñalosa

Professor
Energy Engineering Department,
Technical University of Madrid UPM,
Madrid 28040, Spain

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 February 17, 2017; final manuscript received June 11, 2017; published online September 12, 2017. Assoc. Editor: Marc Röger.

J. Sol. Energy Eng 139(6), 061005 (Sep 12, 2017) (8 pages) Paper No: SOL-17-1063; doi: 10.1115/1.4037381 History: Received February 17, 2017; Revised June 11, 2017

An opportunity for increasing the parabolic solar power plant efficiency is substituting the actual subcritical Rankine power cycles with the innovative s-CO2 Brayton cycles. In this paper, three configurations are assessed: the recompression cycle (RC), the partial cooling with recompression cycle (PCRC), and the recompression with main compression intercooling cycle (RCMCI), with one reheating stage. The thermodynamic parameters are optimized with three algorithms: SUBPLEX, UOBYQA, and NEWUOA, and the results validated with thermoflow Software. The parabolic troughs and linear Fresnel solar collectors are studied with different heat transfer fluids (HTFs): Solar Salt, HITEC XL, Therminol-VP1, Syltherm 800, and Therminol 75. The dual-loop solar field (SF), combining thermal oil and molten salt (MS) in the same solar plant, is also analyzed. The plant power output and plant energy efficiency are translated into SF aperture area and cost at design point. From the point of view of the plant efficiency and SF cost, the PTC and LF solar collector with Solar Salt as HTF coupled to a s-CO2 Brayton RCMCI cycle is selected as the optimum design solution and compared with the actual PTC Rankine solar plant performance at design point. The total recuperator conductance (UA) plays an important role in optimizing the plant performance, limited by the minimum heat exchangers (HX) pinch point. The UA increment could compensate the HX pressure drop and the compressor inlet temperature (CIT) increment, both impacting very negatively in the s-CO2 plant performance.

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References

Figures

Grahic Jump Location
Fig. 1

Line-Focusing (PTC or LF collectors) solar power plant coupled with RCMCI s-CO2 Brayton cycle with ReHeating. The dual-loop SF configuration is studied in detail in Ref. [51]. The combination of two HTFs in the same solar plant optimizes the SF cost, gaining synergies operating at different temperature range in dual-loop SF. The thermal oils is a mature highly validated technology not requiring heat tracing. The MS provides the possibility of increasing the TIT up to 550 °C.

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Fig. 2

PTC SF cost estimation versus TIT. s-CO2 Brayton RCMCI, CIT = 32 °C. Ideal performance (see Table 4).

Grahic Jump Location
Fig. 3

LF SF cost estimation versus TIT. s-CO2 Brayton RCMCI, CIT = 32 °C. Ideal performance (see Table 4).

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