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.
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