Research Papers

Mechanism of Hydrogen Formation in Solar Parabolic Trough Receivers

[+] Author and Article Information
Luc Moens

 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401luc_moens@nrel.gov

Daniel M. Blake

 National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401

J. Sol. Energy Eng 132(3), 031006 (Jun 14, 2010) (5 pages) doi:10.1115/1.4001402 History: Received September 23, 2008; Revised May 05, 2009; Published June 14, 2010; Online June 14, 2010

Solar parabolic trough systems for electricity production are receiving renewed attention, and new solar plants are under construction to help meet the growing demands of the power market in the Western United States. The growing solar trough industry will rely on operating experience it has gained over the last two decades. Recently, researchers found that trough plants that use organic heat transfer fluids (HTFs) such as Therminol VP-1 are experiencing significant heat losses in the receiver tubes. The cause has been traced back to the accumulation of excess hydrogen gas in the vacuum annulus that surrounds the steel receiver tube, thus compromising the thermal insulation of the receiver. The hydrogen gas is formed during the thermal decomposition of the organic HTF that circulates inside the receiver loop, and the installation of hydrogen getters inside the annulus has proven to be insufficient for controlling the hydrogen buildup over the lifetime of the receivers. This paper will provide an overview of the chemical literature dealing with the thermal decomposition of diphenyl oxide and biphenyl, which are the two constituents of Therminol VP-1.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Components of Therminol VP-1 and Dowtherm A

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Figure 2

Cleavage of biphenyl by hydrogen atom

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Figure 3

Radical-induced formation of polyphenyls and hydrogen

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Figure 4

Cleavage reactions of DPO

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Figure 5

Aromatic compounds formed during thermal breakdown of Dowtherm A

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Figure 6

Proposed mechanism for thermal breakdown of DPO/biphenyl mixtures (Ph–O–Ph=DPO; Ph–Ph=biphenyl; Ph•=C6H5•=phenyl radical)

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Figure 7

Catalytic conversion of DPO into dibenzofuran



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