Steam Boiler Safety Interlock
A boiler could be potential bomb if you do not take care of
it sufficiently! Because it is a fired pressure vessel, it
has the potential to be pressurized beyond its designed
strength if something goes wrong with the operating equipment.
Water treatment has to be done carefully to prevent corrosion
and scaling that can lead to deformation, overheating, and
carry over of the water.
That is on the waterside of the boiler. What about the fire
side? A strong fire is burning inside the boiler. The
combustion equipment of a boiler must be maintained in a
tip-top condition all the time.
Bad combustion will give rise not only to reduction in
combustion efficiency, but it will also result in deposits
of soot. The soot tends to cover the pipes, and the steel
plates. The heat transfer will be reduced, or worst still,
the soot may catch fire inside the boiler.
This is especially a concern in oil fired boiler. If the
atomization of the fuel is not good, or the nozzle itself
leaks, an imperfect combustion will be the result. Very
often, oil may drip inside the combustion chamber or may be
sprayed on the boiler tubes.
Automatic boiler burners are often started using an electric
spark over a fine mist of light fuel oil. If the flame does
not start, the oil must not be allowed to continue to spray
inside the combustion chamber, otherwise a dangerous
explosive mixture of fuel and air will develop inside.
So one of the boiler safety interlocks is to cut out the
boiler burner when the flame fails to ignite.
Another interlock is low burner air pressure. If the forced
draft fan does not develop enough pressure, combustible gases
will not be able to be driven away. This is dangerous.
The above two safety interlocks work during the starting up
of the boiler. How about the times when the boiler is already
in operation?
The water level interlock is one of the most important safety
features. If the water level in the boiler becomes too low,
perhaps due to feed water pump failure, or other reasons,
some parts of the tubes, or shell that are exposed to the
heat from the flame will not be cooled by the water. The
temperature will rise up and the steel parts will eventually
lose their strength due to the intense heat from the flame of
the burner.
The safety interlocks will shut off the burners of the boiler
and prevent further damage.
The steam pressure will continue to rise as long as the
burners continue to burn. How do boilers maintain the steam
pressure?
Think safety!
Until next time....
Thomas Yoon
Editor, Facworld Ezine More information can be obtained at
Facworld Ezine
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