The report published in the Journal of Heat Transfer Engineering (HTE) says one of the biggest issues with such plants is the time taken to build them, increasing the risk of contamination including water, dirt, dust and welding slag.
contaminants need to be removed prior to filling
It says contaminants need to be removed prior to filling with a relatively more expensive synthetic HTF which is estimated to be 10 times more expensive than a mineral-based HTF.
According to Chris Wright, research scientist, co-author of the report, it is important to remove foreign contaminants prior to filling with a virgin HTF because contaminants accelerate the aging of a HTF and shorten its life.
He believes past research has shown more frequent SACA (sampled and chemically analysed) is associated with better overall fluid condition and filtering a fluid does not necessarily remove all foreign contaminants.
If these are not removed, they remain in the fluid, especially if their particle size is smaller than the filter pore size.
“In normal practice, flushing and cleaning fluids and HTFs are sampled and chemically analyzed (SACA) as part of an ongoing program to manage fluid condition,” he said.
“This case study demonstrates using a flushing and cleaning fluid, Globaltherm TMC1 specifically, is important to remove foreign contaminants that accumulate during a system build and that a flushing and cleaning fluid does this effectively by suspending particulates in the fluid itself.
“This is especially important as in the current case a mobile filtration unit was used in addition to the flushing and cleaning fluid to maximize the cleaning of the HTF system. However, the mobile unit was only available during the flushing phase, so extra care was taken to avoid contamination of the subsequent fill with a virgin HTF.”
Flushing and cleaning fluid
A flushing and cleaning fluid works by physically suspending built debris and insoluble materials and pushing these through the HTF system. Whilst in circulation, the flushing and cleaning fluid is filtered (15 micron pores) by mobile filter units to remove particulates.
The effectiveness of filtering can be seen from the debris that accumulates in the filters as well as visually inspecting the appearance of the HTF over time.
“The objective of flushing is to remove particulates before the HTF system is filled with a virgin HTF,” added Wright.
“The process of flushing a HTF system is conducted according to a standardized operating procedure, with care being taken to manage and handle the HTF in accordance with the safety data sheet.
“How to conduct flushing prior to flushing the low, high and dump lines of the HTF system header tank need to be identified. Once identified these lines need to be checked to ensure they are clear and once filling of the HTF system has been started, the flushing and cleaning fluid that is flowing through them should be clear.
“The flushing procedure is initiated by attaching a suction pump and hose to the dump valve on the header tank of the HTF system and the HTF system is filled with flushing and cleaning fluid. This allows the flushing and cleaning fluid to be drained from the HTF system as well as to assist with the removal of air from the HTF system.
“The valve from the header tank is closed. The flushing and cleaning fluid is then pumped from the lowest point in the HTF system. Flushing and cleaning fluid is pumped through the heater coils, the production line and to the header tank, where it is drained through the dump.
“Material that collected in the filters was analyzed and the main elements detected were silicon (a minor constituent), iron (a major constituent) and aluminum (trace constituent). Calcium and zinc were not detected.”
In conclusion, Wright and his partner, Eole Picot, found minor quantities of iron were found in flushing and cleaning fluid and larger quantities were detected in the HTF system filters.
The presence of iron is indicative of ferrous debris and is typically found following the cutting and/or oxidation of pipework.
“The lesson here is the virgin HTF would have been contaminated by these particulates if the flushing phase had not been performed,” said Wright.
“The recommendation is to use the flush to suspend these particulates and then to drain this from the HTF system prior to filling with a virgin HTF, helping to reduce contamination and prolong the potential life of the HTF and HTF system.
“In addition to routine SACA, customers should consider employing cleanliness scoring as part of their maintenance program. SACA is an industry standard that needs to be considered at the start of every project and maintained. This can be complemented by measures of fluid cleanliness which defines the size and distribution of foreign contaminates in a flushing and cleaning fluid/ HTF.
“The condition of a HTF is important to the long-term safety and reliability of new, and old, HTF systems and fluid management needs to be included at the beginning of projects and continued throughout the life of a HTF plant.”
Source: Journal of Heat Transfer Engineering (HTE).
Author(s): Christopher Ian Wright of Global Group of Companies, Cold Meece Estate, Cold Meece, Staffordshire, UK and Eole Picot of Pole Etudes Locomotive et TGV Optimisation de la maintenance TGV chez SNCF, Paris, France.
Date: July 7, 2015