When replacing fluid that has reached the end of its life, it is essential to consider how much time and money to spend performing this task. Important considerations include process down time (including cooling, draining and filling), labour (including personal protection equipment) and disposal costs, as well as the cost of the new fluid. Many fluids are compatible enough that a simple drain and fill is all that is necessary, but one should check with the new fluid supplier to be sure.
A system cleaner should be considered if there are cold spots in the system. Completely plugged lines will probably have to be replaced or purged using very high pressure. If there is any flow through the affected area, non-aqueous cleaners will generally work. There are two types of cleaners. Additive cleaners are added to the existing fluid and clean while the system continues to operate. Once all of the lines are hot again, the system is drained and recharged. Other cleaners are designed for faster ‘off-line’ cleaning but require an additional flushing step to remove the cleaner. It is essential to ensure that the cleaner is compatible with the fluid.
If drains are not located at all low points of the piping so that the fluid can be easily drained or pumped out, then one should be prepared to break flanges, open pressure taps or remove valves, flex hoses, or other components from the piping to ensure complete fluid removal. Using compressed nitrogen to force the fluid out one end of an open loop is tricky to implement but effective.
Draining the system warm/hot will leave less fluid and solids in the lines than draining it cold. The heater should be shut down while the pump continues to run until the fluid has cooled to between 150°F and 180°F. At that point, the systems should be drained as quickly as possible.
Flushing fluids are typically high-solvent-content liquids whose only real purpose is to dilute existing fluid that is too viscous at ambient temperature to completely drain from the system. Unlike a cleaner, a flushing fluid will not remove system deposits. It also adds two additional steps because the flushing fluid must be flushed out of the system to prevent premature degradation of the new heat transfer fluid. Fluid suppliers should...
Written by Ed Cass, Paratherm, USA.
This article was originally published in the Winter 2020 issue of Tanks & Terminals. To read the full article, and other great technical articles in this issue, view the full issue here. You can also register to receive a free regular copy of the magazine here.
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