Research Papers

Thermodynamic Study of Advanced Supercritical Carbon Dioxide Power Cycles for Concentrating Solar Power Systems

[+] Author and Article Information
Craig S. Turchi

e-mail: craig.turchi@nrel.gov

Zhiwen Ma

e-mail: zhiwen.ma@nrel.gov

Ty W. Neises

e-mail: ty.neises@nrel.gov

Michael J. Wagner

e-mail: michael.wagner@nrel.gov
National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80401

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received September 14, 2012; final manuscript received March 12, 2013; published online June 25, 2013. Assoc. Editor: Markus Eck.

J. Sol. Energy Eng 135(4), 041007 (Jun 25, 2013) (7 pages) Paper No: SOL-12-1230; doi: 10.1115/1.4024030 History: Received September 14, 2012; Revised March 12, 2013

Supercritical CO2 (s-CO2) operated in a closed-loop Brayton cycle offers the potential of higher cycle efficiency versus superheated or supercritical steam cycles at temperatures relevant for concentrating solar power (CSP) applications. Brayton-cycle systems using s-CO2 have a smaller weight and volume, lower thermal mass, and less complex power blocks versus Rankine cycles due to the higher density of the fluid and simpler cycle design. The simpler machinery and compact size of the s-CO2 process may also reduce the installation, maintenance, and operation cost of the system. In this work we explore s-CO2 Brayton cycle configurations that have attributes that are desirable from the perspective of a CSP application, such as the ability to accommodate dry cooling and achieve greater than 50% efficiency, as specified for the U.S. Department of Energy SunShot goal. Recompression cycles combined with intercooling and/or turbine reheat appear able to hit this efficiency target, even when combined with dry cooling. In addition, the intercooled cycles expand the temperature differential across the primary heat exchanger, which is favorable for CSP systems featuring sensible-heat thermal energy storage.

Copyright © 2013 by ASME
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Fig. 1

Simple Brayton cycle with reheat

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Fig. 2

Recompression Brayton cycle with reheat

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Fig. 3

Partial cooling cycle with recompression and reheat

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Fig. 4

Recompression with main-compression intercooling and reheat

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Fig. 5

Cycle comparison with Dostal [10]. In order to match [10], a 90% turbine efficiency is assumed for the recompression cycles, while all other cycles assume a 93% turbine efficiency.

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Fig. 6

Comparison of s-CO2 Brayton cycles

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Fig. 7

Performance of s-CO2 Brayton and steam cycles relative to CIT (or condenser temperature). All cycles, Brayton and Rankine, include single-stage reheat.




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