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Research Papers: Gas Turbines: Cycle Innovations

Second Law Analysis of Integrated Solar Combined Cycle Power Plants

[+] Author and Article Information
S. Can Gülen

Engineering Technology Group,
Bechtel Power,
Frederick, MD 21703
e-mail: scgulen@bechtel.com

Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 19, 2014; final manuscript received September 30, 2014; published online December 2, 2014. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(5), 051701 (May 01, 2015) (9 pages) Paper No: GTP-14-1493; doi: 10.1115/1.4028741 History: Received August 19, 2014; Revised September 30, 2014; Online December 02, 2014

Integrated solar combined cycle (ISCC) is an operationally simple, clean electric power generation system that is economically more attractive vis-à-vis stand-alone concentrating solar power (CSP) technology. The ISCC can be designed to achieve two primary goals: (1) replace natural gas combustion with solar thermal power at the same output rating to reduce fuel consumption and stack emissions and/or (2) replace supplementary (duct) firing in the heat recovery steam generator (HRSG) with “solar firing” to boost power generation on hot days. Optimal ISCC design requires a seamless integration of the solar thermal and fossil-thermal technologies to maximize the solar contribution to the overall system performance at the lowest possible size and cost. The current paper uses the exergy concept of the second law of thermodynamics to distill the quite complex optimization problem to its bare essentials. The goal is to provide the practitioners with physics-based, user-friendly guidelines to understand the key drivers and the interaction among them. Ultimately, such understanding is expected to help direct studies involving heavy use of time consuming system models in a focused manner and evaluate the results critically to arrive at feasible ISCC designs.

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Figures

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Fig. 1

Schematic description of a generic ISCC with a GTCC and CSP plant comprising a solar field and solar steam generator

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Fig. 2

Solar collector thermal efficiency for three major CSP technologies as a function of Trec, CR, and DNI

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Fig. 3

Conceptual HRSG section layout (HP, IP, or LP) for external heat addition via additional steam generation

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Fig. 4

External GTCC bottoming cycle heat addition via additional HP steam generation with feed water take-off from A in Fig. 3 (1 in. of Hg ∼ 34 mbar)

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Fig. 5

Impact of switching feed water take-off location from A to C in Fig. 3 (100 pps ∼ 45 kg/s, to convert from °F to °C, subtract 32 and divide by 1.8)

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Fig. 6

Key performance-cost trade-off drivers for ISCC based on HP steam generation in a CRS-based solar plant

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Fig. 7

Exergy loss in the HRSG, ST, and condenser as a fraction of GT exhaust gas exergy at the HRSG inlet. The dashed-line curves are for the large-sized bottoming cycle.

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Fig. 8

HRSG heat release diagram (the inset shows the decrease in main and reheat steam temperatures)

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Fig. 9

Conceptual HRSG-ST layout for external heat addition via reheat superheating

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Fig. 10

Impact of HRSG steam level on additional ST power output via external heat addition. (The plots can be used for generic 3PRH GTCC bottoming cycle studies using the fractional information on x- and y-axes.)

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Fig. 11

Impact of HRSG steam level on GTCC net (thermal) efficiency output via external heat addition (constant GT heat consumption)

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