erensan°
“The Heating Engineer”
- 41 –
280111
Deposits
The solid deposits in the boiler are in the form of scales or mud
in pipes and other surfaces.
Deposits in the form of scales
The reason for scaling is lack of a chemical medium that will
turn deposits that form in many boilers into mud and such
deposits, normally forming mud, harden and stick to surfaces
under specific conditions.
Scaling leads to excessive heating in heating surfaces and
thereby to pipe perforations. To ensure prevention of scaling,
the boiler feedwater should be passed from processing to
provide the desired chemical conditions before being given to
the boiler. The water in the boiler should also be kept in
suitable chemical conditions. The correctness of the chemical
process to be applied should be checked with periodical boiler
water and boiler feedwater analyses.
Mud
Formation of mud on boiler surfaces should be prevented as it
will reduce heat transfer and lead to overheating of surfaces.
When the boiler is put out of operation, the water inside should
not be discharged until it has cooled down thoroughly and the
mud thus formed should be prevented from baking solid on hot
surfaces.
Corrosion
Corrosion may happen when the boiler is in operation or when
it is taken out of operation. If crusty deposits do not exist in the
boiler, the life of the metal parts and pipes of the boiler
depends on local blowholes or erosion of pipes or body due to
corrosion.
erensan
°
“The Heating Engineer”
- 42 –
280111
If red or black iron oxide stains exist in locations with
blowholes, these have formed due to neutral or alkaline
character of the boiler water.
If there is excessive heat in regions, the boiler water is in
contact with metal parts and water circulation is not sufficient,
they develop blowholes or pitting. Corrosion may similarly form
in water of neutral character, although more slowly. As a result
of this type of corrosion, iron oxide and hydrogen gas formed.
Sometimes, due to high metal temperatures that arise because
of bad heat transfer on surfaces covered with excessive
deposits, the deposited materials enter reaction with the metal
leading to corrosion.
Therefore, the necessary hardware should be used to purge
boiler feedwater from all kinds of gases, especially from
oxygen. (For this purpose a gas remover called de-aerator
should be utilized.) Furthermore, various gas removing
chemicals should be added to the boiler water.
The CO
2
concentration in the steam condenser should be kept
at minimum value.
Prevention of gas side corrosion
When liquid fuel and especially heavy fuel oil is used, sulphur
content reaches approximately 3%. During combustion, sulphur
collects on fire and smoke surfaces, especially in far corners.
During start stop operations of the boiler, the water vapor in
the chimney gas condenses and sulphur mixes with water to
form sulphuric acid.
To prevent this:
• Liquid fuel with low sulphur content should be used.
• Soot and smut gathering on boiler heating surfaces
(combustion chamber, smoke pipes, smoke chest)
should not be allowed, cleaning process should be
performed as frequently as possible.
• Panorin should be applied to heating surfaces. (The soot
on surfaces will disappear and boiler smoke side
cleaning will become easier).
• The burner should not be stopped very frequently.
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