Hydrogen monitoring and control in the heat transfer fluid of parabolic trough plants

Abstract

In this study hydrogen concentrations in the heat transfer fluid (HTF) of parabolic trough systems were analyzed and hydrogen control by venting was practically tested in several plants. Concentrations between 10 and 800 µmol/kg and decreases of hydrogen by venting between 10 - 75% were found. A model consideration is presented that clearly demonstrates the impact of equilibrating HTF from the solar field with the fluid in vessels on hydrogen concentration. Concentrations could be reduced more than 80% in the solar field if equilibrium of the gas with gas spaces in vessels was achieved. Hydrogen formation rates of used HTF with up to nine years of service life were checked with lab tests. These indicate increasing hydrogen formation of up to eightfold compared to unused fluid which gives rise to re-consider recommendations of maximum tolerable concentrations of low and high boilers in used eutectic mixtures of biphenyl and diphenyl oxide.