Hot Oil and Heat Transfer Fluids
Circulating systems of hot oil or specialized heat transfer fluids are often used as heat sources in
situations where fired heat or steam are not suitable. Heat transfer fluids and mineral oils can be
used over a temperature range from 50 ºC to 400 ºC. The upper temperature limit on use of hot
oils is usually set by thermal decomposition of the oil, fouling, or coking of heat-exchange tubes.
Some heat transfer fluids are designed to be vaporized and condensed in a similar manner to the
steam system, though at lower pressures; however, vaporization of mineral oils is usually avoided,
as less volatile components in the oil could accumulate and decompose, causing accelerated
fouling.
The most common situation where a hot oil system is used is in plants that have many relatively
small high-temperature heating requirements. Instead of building several small fired heaters, it can
be more economical to supply heat to the process from circulating hot oil streams and build a single
fired heater that heats the hot oil. Use of hot oil also reduces the risk of process streams being
exposed to high tube-wall temperatures that might be experienced in a fired heater. Hot oil systems
are often attractive when there is a high pressure differential between the process stream and HP
steam and use of steam would entail using thicker tubes. Hot oil systems can sometimes be justified
on safety grounds if the possibility of steam leakage into the process is very hazardous