Will Thermal oil replace Steam as a Heat ?

Thermal oils as a heat transfer media is gaining acceptance replacing steam in many applications. This article is a brief on its advantages over steam , specifications and applications.

What is Thermal Oil?

Thermal oils are heat transfer fluids that transfer the heat from one hot source to another process. This could be from a combustion chamber or from any exothermic process. The main application is in fluid phase heat transfer.

They are available in chemically different forms as:


•Synthetic Oil, which are aromatic compounds.

•Petroleum based oils, which are paraffin’s.

•Synthetic glycol based fluids.

Thermal oils are available in a wide range of specifications to suit the needs of various processes. Currently available thermal oils have a maximum temperature limit of around 400 °C. There are Thermal oils that are in use in Cryogenic fields up to -100 °C.



Steam vs. Thermal Oil

A heat transfer medium is required where direct heating of a process is not practically possible.
Steam was the prime choice as a heat transfer medium. The advantages of steam were the availability, low cost of water, with no environmental issues.

Effective Heat transfer by steam uses the latent heat. The saturation pressure dictates the temperature at which heat transfer takes place. To obtain higher temperatures the pressures have to be higher. For 350 °C, you will require a pressure of 180 bar. This will require higher thickness for the heat exchangers tubes. This increases the weight and thermal stresses and will require special manufacturing techniques. All this leads to higher cost.

Thermal oil scores on this point. Even at temperatures of 350 °C, the pressure requirements are just sufficient to overcome the system pressure drops. This also decreases the pumping cost.

The system is simple in that it requires only a pump, an expansion and storage tank and the heat exchangers. A steam system on the other hand requires demineralized makeup water supply, drains, traps, safety valves, chemical additions and blow downs.

Using thermal oils eliminates all these complications along with issues of corrosion, scaling, fouling, and deposits in the heat transfer areas. This is why thermal oil finds many uses in the process industry. All this leads to considerable reduction in cost. Unlike steam, thermal oils also find use in applications where the temperatures are below zero °C.

Thermal Oil Heaters

Thermal oil heaters functionally are similar to steam boilers. The combustion chamber that burns fuel oil, bio fuel, coal or any other fuel with all necessary safety devices is the same. Since there is, no evaporation the oil passes through simple heater coils placed in the radiant or convection zones. The oil pumped through these coils heats up and flows to the process heat exchanger. The cooler oil returns to a tank and then back to the pump. An expansion tank takes care of the thermal expansion. The tanks have provisions to prevent the oxidation and vaporization of the oil.
Marine applications use very compact heaters with helical coils.

Heaters downstream of gas turbines or diesel engines can function as heat recovery systems for use in suitable downstream process.