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 thermic fluid heaters this high temperature level is often a demand in order to achieve the necessary high output of the process.
When establishing the thermic fluid heaters 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 thermic fluid 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 – operates at atmospheric pressure all the way up to 300°C. Comparing this to water and steam, it would require a corresponding steam or water pressure of above 85 bar to obtain the temperature of 300°C.
At higher temperature than 320-340°C, the thermal fluid too must be pressurised (see below), however only moderate overpressure compared to water and steam (which require 150 – 170 bar). In the principle this thermal fluid works as any other heating fluid, it is heated and it is cooled when passing through the system, – just like low-temperature domestic heating systems.