Research Papers

Comparative System Performance Analysis of Direct Steam Generation Central Receiver Solar Thermal Power Plants in Megawatt Range

[+] Author and Article Information
Javier Sanz-Bermejo, Víctor Gallardo-Natividad, José Gonzalez-Aguilar

IMDEA Energy Institute,
Avda. Ramón de la Sagra, 3
Móstoles 28935, Spain

Manuel Romero

IMDEA Energy Institute,
Avda. Ramón de la Sagra, 3
Móstoles 28935, Spain
e-mail: manuel.romero@imdea.org

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING. Manuscript received September 3, 2013; final manuscript received December 4, 2013; published online January 9, 2014. Assoc. Editor: Aldo Steinfeld.

J. Sol. Energy Eng 136(1), 010908 (Jan 09, 2014) (9 pages) Paper No: SOL-13-1247; doi: 10.1115/1.4026279 History: Received September 03, 2013; Revised December 04, 2013

This work proposes and analyses several integration schemes specially conceived for direct steam generation (DSG) in megawatt (MW) range central receiver solar thermal power plants. It is focused on the optical performance related to the heliostat field and the arrangement of receiver absorbers, and the management of steam within a Rankine cycle in the range between 40–160 bar and 400–550 °C at design point. The solar receiver is composed of one single element for saturated steam systems or two vertically aligned separated units, which correspond to the boiler and the superheater (dual-receiver concept), for superheated steam solar thermal power plants. From a fixed heliostat field obtained after layout optimization for the saturated steam solar plant the heliostat field is divided in two concentric circular trapezoids where each of them independently supplies the solar energy required by the boiler and the superheater for the different steam conditions. It has been observed that the arrangement locating the boiler above the superheater provides a slightly higher optical efficiency of the collector system, formed by the solar field and the receiver, compared with the reverse option with superheater above boiler. Besides, two-zone solar fields provide lower performances than the entire heliostat layout aiming at one absorber (saturation systems). Optical efficiency of two-zone solar fields decreases almost linearly with the increment of superheater heat demand. Concerning the whole solar collector, heliostat field plus receiver, the performance decreases with temperature and almost linearly with the steam pressure. For the intervals of steam pressure and temperature under analysis, solar collector of saturated steam plant achieves an optical efficiency 3.2% points higher than the superheated steam system at 40 bar and 400 °C, and the difference increases up to 9.3% points when compared with superheated system at 160 bar and 550 °C. On the other hand, superheated steam systems at 550 °C and pressure between 60 and 80 bar provide the highest overall efficiency, and it is 2.3% points higher than performance of a saturated steam solar plant at 69 bar. However, if saturated steam cycle integrates an intermediate reheat process, both would provide similar performances. Finally, it has been observed that central receiver systems (CRS) producing saturated steam and superheated steam at 500 °C operating at 40 bar provide similar performances.

Copyright © 2014 by ASME
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Fig. 1

Sketch of the direct steam dual-receiver CRS plant

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Fig. 2

Schematic diagram of the 69 bar saturated steam solar power plant implemented in Ebsilon® Professional

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Fig. 3

Schematic diagram of the superheated steam generation solar power plant implemented in Ebsilon® Professional

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Fig. 4

Layout of the reference heliostat field

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Fig. 5

Two-zone distribution of the heliostat field assuming that (top) the boiler is above the superheater or (bottom) the superheater above the boiler. (a) and (d), 40 bar/400 °C; (b) and (e), 80 bar/500 °C; (c) and (f), 160 bar/550 °C. Empty squares and filled triangles indicate heliostats directing sunlight to the boiler and superheater, respectively.

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Fig. 6

Heliostat field performance depending on the two-zone solar field configuration (see Table 2)

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Fig. 7

Solar collector (heliostat field and receiver) overall performance as function of steam conditions

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Fig. 8

Flux distribution on (a) the boiler and (b) the superheater in configuration D (boiler flux peak, 650 kW/m2; boiler size, 11 m × 12.1 m; superheater flux peak, 300 kW/m2; and superheater size, 11 m × 7.8 m)

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Fig. 9

Rankine cycle efficiency as function of steam temperature and pressure conditions at high-pressure turbine inlet

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Fig. 10

Overall efficiency of 10-MWe steam tower concentrating solar power plants




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