One of the most dangerous situations in the operation of a boiler is
that of a fuel explosion in the furnace. The photo above shows the
complete devastation of a utility boiler.
Conditions have to be just right for an explosion to occur and when a
boiler is properly operated, it is not possible for such an event to
take place. The most common causes of a fuel explosion are:
hrsg boiler
Fuel-rich mixtures - The danger of a fuel-rich mixture is that high
concentrations of unburned fuel can build up. When this unburned fuel
ignites, it can do so in a very rapid or explosive manner. Fuel-rich
mixtures can occur any time that insufficient air is supplied for the
amount of fuel being burned. Never add air to a dark smoky furnace. Trip
the unit, purge thoroughly, then correct the problem. By adding air
with a fire in the unit, you may develop an explosive mixture. While it
is dangerous to have too rich a mixture, the reverse is not true. A lean
mixture which results in more air than necessary, while not efficient,
is not dangerous.
Poor atomization of oil - Just as fuel-rich mixtures could allow
accumulation of unburned combustibles, any inventory of a combustible
fuel in the furnace can result in an explosion. Boilers are blown up
every year as a result of poor atomization of oil which results in
incomplete combustion and can lead to unburned oil puddling on the floor
of the furnace. To prevent this, the oil tips must be clean, the oil
temperature must be correct, the oil viscosity must be in spec, and the
atomizing steam (or air) pressure and fuel oil pressure must be properly
adjusted.
Improper purge - Many of the explosions occur after a combustion problem
which has resulted in a burner trip. Consider the following example:
suppose that the oil tip becomes plugged, which disturbs the spray
pattern, causing an unstable flame that results in a flame failure. The
operator attempts to relight the burner without investigating the cause
and during successive attempts to relight the burner, oil is sprayed
into the furnace.
The oil on the hot furnace floor begins to volatize and release its
combustible gases when the operator initiates another trial for
ignition. The pilot then ignites the large inventory of unburned
combustible gases in the furnace, which produces the explosion.
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