Thermal oil systems typically consist of a primary system and one or more secondary systems.

The primary system consists of a boiler, pump(s), piping, storage tank, expansion tank, possibly a heat exchanger, etc., which are arranged as a circuit and, of course, equipped with the necessary pressure and temperature safety devices. The boiler heats the thermal oil, and the pump circulates the oil through the primary circuit.

Thermal oil systems can be equipped with so-called economizers. These are units installed in the boiler’s exhaust gas system that can improve efficiency by a few percent.

In the secondary circuits—that is, those parts of the thermal system connected to the users (which could be a reactor vessel, a drying tunnel, or anything else)—the heat required there will be released via controlled valves. The cooled oil is then pumped back into the primary circuit to be reheated by the boiler.

It should be clear that the capacity of the boiler depends on the size of the secondary circuits and the heat demand per circuit. In thermal oil systems, all circuits are protected against overpressure, excessively high or low temperatures, and the flow rate is constantly monitored. If the pump(s) fail, the boiler is automatically shut down to prevent overheating and/or combustion of the thermal oil.

By far the majority of thermal oil systems operating at temperatures up to 350°C are virtually pressureless and operate in the liquid phase of the thermal oil. At temperatures above 350°C, the pressure can rise to as high as 10 bar. Thermal oil systems operating around 400°C can operate not only in the liquid phase but also in the gas phase of the thermal fluid, depending on the customer’s requirements.