TM 5-810-15
mechanical cyclone type and U beam. Cyclone
temperature of no more than 700 degrees F, boiler
separators are more common. Cyclones can be
manufacturers will normally use a single section
either water or steam cooled to reduce refractory
style superheater. Superheaters on coal fired units
thickness.
are of the pendant type and hence are not drainable.
d. Solids reinjection device. Solids that have
Further, superheaters are either exposed to the
been removed in the separator are reintroduced into
radiation of the fire in the furnace, or are located
the combustor for additional carbon burnout and
above a "nose" usually on the rear furnace wall that
increased combustion efficiency. This recirculating
provides for a radiant-convection superheater
loop is sometimes referred to as the "thermal fly
surface. The design and construction of
wheel." Solids reinjection devices consist of a
superheaters is in accordance with the ASME
refractory lined pipe with fluidizing air nozzles.
Boiler and Pressure Vessel Code that applies to the
This device is frequently called either a J-valve, L-
boiler. Normally, superheaters for boilers covered
valve or loop seal. Sorbent for sulfur capture enters
by this manual, will have tubes made of carbon
the boiler either through the reinjection device or
steel, either SA-210 or SA-192, whereas the
through separate feeders into the lower combustor
saturated or water carrying tubes of the boiler and
section.
furnace will be made of carbon steel type SA-178.
(1) For proper operation, particularly of pen-
includes the use of an EHE to recover heat from
dant, nondrainable type superheaters, fluid pressure
recycled solids. Most manufacturers do not use an
drop is needed to provide proper distribution of the
EHE due to problems encountered.
steam through the tubes. It is desirable to locate the
steam outlet connection at the center of the
superheater outlet header for proper steam
3-16.
Boiler components.
distribution, but end outlets are acceptable if proper
a. Superheaters. Superheaters receive saturated
design consideration is given to the flow
steam from the boiler steam drum after having gone
distribution imbalances caused by the header con-
through the steam and water separating
figuration.
components within the steam drum. This steam
(2) A factor to be considered about super-
should have a purity of 1 part per million (ppm) or
heater pressure drop is the power cost required for
better depending on the quality of the boiler water.
the boiler feed pump. The higher the pressure drop,
The superheater is sized so as to add sufficient heat
the more pump power required.
to the steam to obtain the desired final steam
temperature. For units with a final steam
3-20
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