Heat transfer fluid (HTF) systems used in the process industry can be considered the heart of the plant. However, the heat transfer fluids are frequently taken for granted. Commonly, incomplete knowledge about operation and maintenance of heat transfer fluid, or thermic fluid, may result in premature oxidation or thermal degradation. Thermal degradation can be quantified by the percentage of low boiling and high boiling content of the fluid. It is dependent upon the selected chemistry, system design and on-stream time as well as the fluid’s operating bulk and film temperatures within the heater.
In general, aromatic-based synthetic fluids are more resistant to thermal degradation than natural mineral oils, which are products of crude petroleum processing. This is apparent as no mineral oil heat transfer fluids are rated to bulk operating temperatures above 620°F (327°C). Normally, mineral oil heat transfer fluids’ suitable operating temperatures are limited to 540 to 575°F (282 to 302°C). Synthetic aromatic chemistries are rated up to 750°F (400°C). This permits synthetic aromatic fluids to be used at higher temperatures and for longer durations.