A recent research paper published in Applied Thermal Engineering highlights the importance of defined protocols to effectively flush and clean newly built facilities, which is needed prior to filling the system with expensive fluids, such as solar thermal fluids.

Newly Built Concentrated Solar Power Plants – Time To Consider Flushing and Cleaning as an Industry Standard?

Chris Wright


Global Industry News recently reported that Europe became the largest market for heat transfer fluids in 2015 with a 33.6% share in terms of heat transfer fluid consumption. One of the key factors for this growth has been the expansion of concentrated solar power plants. This growth is an opportunity to standardise and establish best practices when new plants are built or when old fluids are replaced.

The most commonly used solar heat transfer fluid (HTF) is the eutectic mixture of biphenyl and diphenyl oxide with well-known and commercially available fluids being Dowtherm A, Globaltherm® Omnitech and Therminol VP-1. Such fluids offer the advantage that they can operate up to 400 degrees Celsius. The HTF sector, of which solar thermal fluids is a part was estimated to be worth $2,811 million in 2015 and projected to grow by 6.8% over the next 5 years [1]. Concentrated solar power (CSP) plants are an important factor in the growth of HTFs per se and more specifically in the growth of solar HTFs. Indeed, solar HTF is needed in both newly built CSP plants and when replacing an old, commonly referred to as thermally degraded, solar fluid.

A recent research paper published in Applied Thermal Engineering [2] highlights the importance of defined protocols to effectively flush and clean newly built facilities, which is needed prior to filling the system with expensive fluids, such as solar thermal fluids. The article highlights the following findings in relation to newly built plants that use thermal fluids:

“Heat transfer fluid (HTF) cleanliness is critical to the effectiveness and safety of a HTF system. Routine monitoring of HTF condition is a critical part of ongoing HTF system maintenance. However, the condition of any fluid introduced into a HTF system needs to be monitored closely to ensure that foreign contaminants are not introduced. Such contaminants act to accelerate the ageing of a HTF once in operation. The current research concerns the flushing and cleaning protocol that is used to remove foreign contaminants during the building of a new HTF system. The current study was performed in Scandinavia for a client building a new HTF system that had a capacity of 100 metric tons. The system was flushed with Globaltherm® C1 was used to flush and clean the system prior to filling with a synthetic HTF. The value of the protocol was assessed in terms of its ability to remove contaminants – water, environmental and system build contaminants.

The protocol involved the use of a fine filter (15 microns pores) and laboratory analysis to assess cleanliness of the fluid. The results from nineteen fluid samples are presented herein.

Results show the presence of water and particle contaminants (4, 6 and 14 microns in size) including silicon, aluminium, iron, calcium and zinc. The flushing and cleaning fluid works by suspending particles in solution and these are subsequently drained from the HTF system. The detection of particles in the fluid demonstrates that the flushing and cleaning fluid and the protocol are effective in removing finer particles from a system. Further analysis assessed the relationship between water and particle contaminants. Results showed a positive association between water and the presence of larger particles (i.e., 14 microns). No association was found between water and smaller particles (4 and 6 microns). This data highlight the value of monitoring both water and particle contamination, and that water may be a substitute method to measuring particles directly. The presence of water in a fluid can be observed and detected onsite, so this may be an early sign of other contaminants present in a newly build HTF system.

To conclude, the flushing and cleaning protocol described herein is effective in the removal of contaminants during a HTF system build. This protocol has been shown to be effective by subsequent laboratory analysis. The presence of water may be an early sign of environmental contamination and the formation of rust.”



The key take-home messages from this new research are: a) That flushing and cleaning a newly built facility (e.g., a CSP plant) is critical and needed prior to filling with a HTF such as biphenyl diphenyl oxide blends; b). Flushing and cleaning protocols are effective in removing foreign contaminants and water; and, c) That the detection of water in a newly built facility may be an early sign of environmental contamination.



The author would like to acknowledge the writing support provided by Red Pharm communications, which is part of the Red Pharm company (please see @RedPharmCo on Twitter).


Reference list

[1] Global Industry News published 18th March 2016. Source: http://globalindustrynews.org/2016/03/18/europe-became-largest-market-for-heat-transfer-fluids-in-2015-with-33-6-share-in-terms-of-htfs-consumption/

[2] Wright, C.I., The use of a flushing and cleaning protocol to remove foreign contaminants – a study from a newly built heat transfer plant with a capacity of 100 metric tonnes. Applied Thermal Engineering 2016 (In Press). Accessed: 20th March 2016. Source: http://www.sciencedirect.com/science/article/pii/S1359431116300916



About Christopher Wright
Christopher Wright is a research scientist, graduating from the University of Leeds in the UK with a BSc and PhD. His research focuses on the use and maintenance of heat transfer fluids in manufacturing and processing, which includes food, pharmaceutical, specialist chemicals and solar sectors.



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