Monitoring the degradation of heat transfer fluids

    Solar thermal plants run at high temperatures for extended periods and over time heat transfer fluids will degrade through thermal cracking or oxidation or both. It is important that these processes are routinely monitored to ensure a plant continues to operate safely and efficiently. Laboratory analysis can be used to assess both the state of thermal cracking and oxidation. A model for assessing these is discussed in this article.

    Reports indicate that the global heat transfer fluid (HTF) market will increase in value from $1,684 million in 2011 to $2,557 million in 2017. This demand is dependent on Europe which was reported to account for one-third of the global HTF demand and be driven by growth in the Asia-Pacific region.

    There are a wide variety of HTFs with a wide range of uses including the production of energy, for example, in concentrated solar power (CSP) plants. The most commonly used solar HTF is the eutectic mixture of biphenyl and diphenyl oxide (e.g., Therminol VP-1, Globatherm Omnitech and Dowtherm A). The two most common types of thermal degradation are thermal cracking and oxidative stress. Thermal cracking comprises the breaking-up of larger hydrocarbon molecules into smaller molecules; oxidation is the gaining of oxygen. At high temperature, a HTF will degrade through thermal cracking or oxidation or both. During thermal cracking, carbon will accumulate and the flash point temperature will start to decline. During oxidation, carbon accumulates and the total acid number (TAN), an indicator of oxidative state, will start to increase. Read more…

    Christopher Wright
    Global Group of Companies

    Article published in: FuturENERGY March 2016