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Research Papers

Development of a Thermal Energy Storage System for Parabolic Trough Power Plants With Direct Steam Generation

[+] Author and Article Information
Doerte Laing

German Aerospace Center (DLR ), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germanydoerte.laing@dlr.de

Thomas Bauer, Dorothea Lehmann

German Aerospace Center (DLR ), Institute of Technical Thermodynamics, Pfaffenwaldring 38-40, 70569 Stuttgart, Germany

Carsten Bahl

Technical Department, Ed. Züblin AG, Albstadtweg 3, 70567 Stuttgart, Germany

J. Sol. Energy Eng 132(2), 021011 (May 10, 2010) (8 pages) doi:10.1115/1.4001472 History: Received September 29, 2009; Revised March 18, 2010; Published May 10, 2010; Online May 10, 2010

For future parabolic trough plants direct steam generation in the absorber pipes is a promising option for reducing the costs of solar thermal power generation. These new solar thermal power plants require innovative storage concepts, where the two-phase heat transfer fluid poses a major challenge. A three-part storage system is proposed where a phase change material (PCM) storage will be deployed for the two-phase evaporation, while concrete storage will be used for storing sensible heat, i.e., for preheating of water and superheating of steam. A pinch analysis helps to recognize interface constraints imposed by the solar field and the power block and describes a way to dimension the latent and sensible components. Laboratory test results of a PCM test module with 140kgNaNO3, applying the sandwich concept for enhancement of heat transfer, are presented, proving the expected capacity and power density. The concrete storage material for sensible heat was improved to allow the operation up to 500°C for direct steam generation. A storage system with a total storage capacity of 1MWh is described, combining a PCM module and a concrete module, which will be tested in 2009 under real steam conditions around 100 bars.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Overview of a three-part thermal energy storage system for DSG combining sensible and latent heat storages

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Figure 2

Boundary conditions in a three-part thermal energy storage system for DSG combining sensible and latent heat storages

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Figure 3

Pie charts illustrating the division of the total amount of heat into the three parts of the storage system during charge at 107 bars (left) and discharge at 81 bars (right)

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Figure 4

Diagram of the water/steam temperature over the amount of heat stored/released, case A: storage system outlet temperature during charge equals the final feed water temperature of 260°C

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Figure 5

Diagram of the water/steam temperature over the amount of heat stored/released, case B: storage system outlet temperature raised

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Figure 6

NaNO3 PCM storage test module

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Figure 7

Experimental results of a typical charge/discharge cycle

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Figure 8

Superposition of reference cycle runs 2927 h, 3574 h, and 3867 h after start of operation

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Figure 9

Mass losses of aggregates in oven experiment

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Figure 10

Mass losses of concrete samples in oven experiment

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Figure 11

Compressive strength measurement of concrete

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Figure 12

Schematic layout of the test-loop

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Figure 13

PCM module of the pilot scale steam storage

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Figure 14

Concrete module of the pilot scale steam storage

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