NATURAL
CIRCULATION
* A monotube once-through boiler consists of
a single tube running from feed water inlet to
discharge. Parallel tube once-through boilers
have two or more tubes running along side
one another from inlet to discharge.
* Cool feed water enters the economizing
section where the water is warmed by
exhaust gasses departing the boiler.
* The warmed water passes into the
generating zone and the burner heated
generating tubes fully evaporate the water
into steam.
* The steam is raised above saturation
temperature in the superheater zone. A
thermostat at the steam outlet causes a valve
to divert from a cooler region of the boiler
into the superheater. This “normalizer”
regulates the degree of superheat, allowing
the boiler to produce steam of adequate
temperature without overheating.
FORCED
CIRCULATION
MONOTUBE,
ONCE-THROUGH
BOILER
CIRCULATION REVIEW
* Cold feed water enters the steam drum by way
of the economizer where it is warmed by
exhaust gasses leaving the boiler.
* Warmed feed water entering the steam drum is
still cooler than the saturated temperature water
in the drum and therefore sinks downwards
towards the lower water drum by way of the
unheated downcomers.
* Water entering the lower drum through the
downcomers displaces water in the drum up
into the generating tubes. The tubes are heated
by the burner, converting part of the water into
steam. This less dense steam/water mix rises
rapidly through the tubes to the steam drum.
* The steam/water mix separates in the steam
drum, the steam rising to the upper side of the
drum where it is collected and distributed to the
engine and other uses; often first passing
through a superheater to raise the temperature
to a more efficient level. The water is cooled by
feed entering the boiler and descends through
the downcomers to repeat the cycle.
* Cold feed water enters the drum by way of
the economizer where it is warmed by exhaust
gasses leaving the boiler.
* The circulating pump draws water from the
drum and forces it through generator coils
heated by the burner. Part of the water is
vaporized to steam.
* The steam and water separate in the drum,
the steam component rising to the top of the
drum where it is collected and flows to the
engine by way of the illustrated superheater.
The circulating pump sends the water
component back through the generating coils.
CIRCULATION REVIEW
* Cold feed water enters the steam drum by way
of the economizer where it is warmed by
exhaust gasses leaving the boiler.
* Warmed feed water entering the steam drum is
still cooler than the saturated temperature water
in the drum and therefore sinks downwards
towards the lower water drum by way of the
unheated downcomers.
* Water entering the lower drum through the
downcomers displaces water in the drum up
into the generating tubes. The tubes are heated
by the burner, converting part of the water into
steam. This less dense steam/water mix rises
rapidly through the tubes to the steam drum.
* The steam/water mix separates in the steam
drum, the steam rising to the upper side of the
drum where it is collected and distributed to the
engine and other uses; often first passing
through a superheater to raise the temperature
to a more efficient level. The water is cooled by
feed entering the boiler and descends through
the downcomers to repeat the cycle.