Two facts of life: you will die, and you will pay taxes. This also applies to heat transfer fluids, notes Dr. Chris I. Wright of Global Group. “Heat transfer fluids will thermally degrade over time and will need to be replaced at the end of their workable life. All the same, the working life of a fluid, and a thermal plant, can be — and should be — sustained for as long as possible.”
Managing the byproducts of thermal degradation is crucial. Heat transfer fluids thermally degrade to form long and short-chain hydrocarbons, which also are called light-ends. Fortunately, light-ends can be removed, Wright notes.
Why is flashpoint so important for an end user? To answer this, Wright notes, it is important to understand that a heat transfer fluid thermally degrades and forms a mixture of high-boiling polymeric materials (heavy-ends or long-chain hydrocarbons) and volatile low-boiling compounds (light-ends or short-chain hydrocarbons).
So why is it important to measure light-ends? This can be answered by referring to the work by T. Ennis on the “Safety in Design of Thermal Fluid Heat Transfer Systems,” where it was stated: “Low-boiling compounds are problematic because they can lead to vapor locking if the system is not properly vented.” Ennis went on to note that if low boilers accumulate in the heat transfer fluid, they can significantly reduce the fluid’s flashpoint and autoignition temperature.
Monitoring light-ends is therefore important to the safety of a heat transfer fluid system. Wright recommends that flashpoint temperature — which is inversely related to light-ends — is monitored routinely. This can be conducted as part of a condition monitoring program for a heat transfer fluid.
Is it possible to control the flashpoint temperature of a heat transfer fluid? The recent work by Wright and colleagues — published as a case history entitled “The long-term effectiveness of a light-ends removal kit in the management of heat transfer fluid plant safety: a case study to show its effectiveness 5 years after installation” — describes an effective approach to the continuous management of light-ends using a light-ends removal kit (LERK). The case relates to a customer of Global Heat Transfer that was using a mineral-based heat transfer fluid and routinely had closed flashpoint temperature issues with the flashpoint dropping below a defined threshold (and safe) value of 266°F (130°C). During this three-year period, closed flashpoint ranged between 410 and 180°F (210 and 82°C), a difference of 230°F (128°C).
After consultation, the customer agreed to the installation of a light-ends removal kit. Following its permanent installation, closed flashpoint temperature has remained above 266°F for the subsequent five years. During this period, closed flashpoint remained constant between 383 and 286°F (195 and 141°C,) a difference of 97°F (54°C). For the company in the study, the LERK therefore removed one liter per day, which would otherwise have remained in the heat transfer fluid system and led to a decrease in closed flashpoint temperature. (The full case study was published in Heat Transfer Engineering.)
Installation of a light-ends removal kit led to the continuous control of closed flashpoint temperature through removal of light-ends from the customer’s thermal fluid heating system, Wright notes. This is important in terms of the heat transfer fluid system’s long-term safety.