Thermal Oil Heaters             

Both water and steam are used as heat carriers in process heating systems. But at temperatures above 100°C, water and steam requires a corresponding higher operating pressure. In industrial heating this high temperature level is often a demand in order to achieve the necessary high output (intensity) of the process.

When establishing the heating system with water and steam, you must - at these high temperatures - deal with systems and components designed for very high pressures and consequently you must deal with requirements and special pressure vessel considerations in regards to strength and safety issues of the system in general and all the components.

This means large dimensions and weights, extensive safety procedures, approvals from authorities - and a lot of extra costs.

In thermal oil heaters, a special oil-based thermal fluid is used as the heat carrier - instead of water or steam. This thermal fluid - also called heat transfer fluid (HTF) - operates at atmospheric pressure all the way up to above 300°C. Comparing this to water and steam, this would require a corresponding steam or water pressure of above 85 bar to obtain the temperature of for instance 300°C.

At higher temperature than 320-340°C, the thermal fluid must also be pressurised (see below), however only moderate over-pressure compared to water and steam (which would then require 150 - 170 bar).

Basically the thermal fluid works as any other heating fluid, - it is heated and it is cooled while it is pumped through the system with consumers and heaters in a closed circuit, - just like low-temperature domestic water heating systems.
 

Understanding the basic logic of a thermal oil heating system is actually not that difficult. Only the operating temperature is much higher than water circulating system. However these high temperature and the nature of oil means that both the system and the components becomes quite different in design and special features.

In other words, the design of thermal oil heating systems and the parts hereof required not only special skilled designers and engineers - it also require these persons having many solid experiences in the many different challenges that always arise in such installations.

The thermal oil heating units and the systems must be designed for operating with the special thermal fluid developed for high temperature application. Still oil is being used, and oil is per definition potential flammable, dangerous  and  even  fatal  if  not  dealt  with the correct way - and this issue is very important to keep in mind throughout the design and installation of components and system.

Ensuring low thermal fluid film temperature (highest local temperature at the contact point to heating surface/element) is essential when designing the thermal oil boilers. A correct design of the boiler is a controlled film temperature and this prevents cracking of the fluid - and this detail makes thermal oil boilers fundamental quite different in design than steam boilers and other kind of boilers and heaters.

For instance, where water heaters and steam boilers can be heated using an internal pool of hot water, the thermal fluid must only be heated by forced circulation; ensuring at all time the important high velocity of the thermal fluid.

It is recommended that potential users of a thermal oil heating systems make special efforts in order to ensure that the chosen supplier of the thermal oil system is both skilled and experienced in these fields, and not only experienced in steam and hot water systems. If a thermal fluid heating systems can become both very costly and dangerous when not attended properly in choice of component and installation of system.