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Research Papers

High Temperature Thermochemical Heat Storage for Concentrated Solar Power Using Gas–Solid Reactions

[+] Author and Article Information
Franziska Schaube

Antje Wörner, Rainer Tamme

 German Aerospace Center (DLR e.V.), Pfaffenwaldring 38–40, 70569 Stuttgart, Germany

1

Corresponding author.

J. Sol. Energy Eng 133(3), 031006 (Jul 25, 2011) (7 pages) doi:10.1115/1.4004245 History: Received January 15, 2011; Accepted April 20, 2011; Published July 25, 2011; Online July 25, 2011

High temperature thermal storage technologies that can be easily integrated into future concentrated solar power plants are a key factor for increasing the market potential of solar power production. Storing thermal energy by reversible gas–solid reactions has the potential of achieving high storage densities while being adjustable to various plant configurations. In this paper the Ca(OH)2 /CaO reaction system is investigated theoretically. It can achieve storage densities above 300 kWh/m3 while operating in a temperature range between 400 and 600°C. Reactor concepts with indirect and direct heat transfer are being evaluated. The low thermal conductivity of the fixed bed of solid reactants turned out to considerably limit the performance of a storage tank with indirect heat input through the reactor walls. A one-dimensional model for the storage reactor is established and solved with the Finite Element Method. The reactor concept with direct heat transfer by flowing the gaseous reactant plus additional inert gas through the solid reactants did not show any limitation due to heat transfer. If reaction kinetics are fast enough, the reactor performance in case of the Ca(OH)2 /CaO reaction system is limited by the thermal capacity of the gaseous stream to take-up heat of reaction. However, to limit pressure drop and the according losses for compression of the gas stream, the size of the storage system is restricted in a fixed bed configuration.

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Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 6

Length of the reaction zone

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Figure 7

Conversion and temperature depending on particle diameter during discharge of the storage: CaO + H2 O → Ca(OH)2

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Figure 8

Temperature distribution in the reactor at t = 5 h

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Figure 9

Conversion and temperature depending on reaction rate during discharge of the storage: CaO + H2 O → Ca(OH)2

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Figure 10

Conversion in the reactor at t = 5 h

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Figure 1

Equilibrium of Ca(OH)2 ⇌CaO + H2 O

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Figure 2

Thermal conductivity of calcium hydroxide

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Figure 3

Moving reaction zone

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Figure 4

Length of the reaction zone and the reactor

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Figure 5

Compression work

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