TM 5-810-15
(8) A static and dynamic structural analyses
the internal surfaces to drop below 250 degrees F.
must be made of the wind, earthquake, dead, and
This requirement does not apply when scrubbers
thermal loads. Vortex shedding of wind loads must
are used with low temperature discharge (150 to
be considered to be assured that destructive natural
180 degrees F) into the stack because the flue gas
is already below dew point temperature.
d. Stack construction. The stack height and di-
(3) A truncated cone at the top of the stack
ameter, support, corrosion resistance, and eco-
will decrease cold air downdrafts at the periphery
nomic factors dictate the type of construction to be
of the stack and will thus help maintain stack
utilized.
temperature, but stack draft will decrease consid-
(1) Stacks are generally made of concrete or
erably.
steel because of the high cost of radial brick
construction. If stack gases are positively pressur-
3-19.
Adjustable Speed Drives.
ized, or if flue gases will be at or below the dew
Significant electrical power savings can be realized
point of the gases, corrosion resistant linings must
at reduced boiler loads by installing adjustable
be provided; linings must be able to withstand
speed drives (ASD) on ID and FD fans. The
temperature excursions which may be experienced
economics of ASD*s depend on the boiler load
in the flue gas if flue gas scrubbers are bypassed.
profile (number of hours at different loads). The
(2) Stacks of steel or concrete construction
feasibility of ASD installation should be verified by
will be insulated to avoid condensation by not
an LCCA.
allowing
3-29
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