TM 5-810-15
the tubes through inspection or handhole access
engineering staff. In addition to the various math-
ports.
ematical approaches for sizing these components a
(3) The amount of heating surface in the
good deal of this design is based on years of
furnace and its configuration is generally arranged
experience with its empirical data as well as various
to suit the firing method, and to provide the
manufacturing considerations.
necessary time and space for complete combustion
of the fuel. Firing methods include gas, oil, pulver-
3-18.
Boiler stacks.
ized coal, stoker fired, and atmospheric circulating
a. General. In boiler operation applications, the
fluidized bed. The particular fuel(s) fired also
stack flue gas temperature will be below the dew
impacts design. The boiler bank is sized in con-
point a considerable amount of the time due to low
junction with the furnace and superheater to
loads, start-up and shutdown, plus normal weather
provide the steam capacity as well as to lower the
conditions. Drainage of water should be provided
exit gas temperature to the value required. The
due to operating conditions as well as rain and
economizer, if provided, is sized to lower the exit
snow. Some of the factors to consider in stack
gas temperature to the desired value without
design are:
getting into a (steaming) condition under normal
(1) Flue gas conditions. The erosive and
operating conditions. Generally this means the
corrosive constituents, dew point temperature, and
economizer is sized to permit a 25 to 50 degrees F
maximum temperature if bypassing the economizer
margin between the exit water temperature and
or air preheater.
saturation temperature at operating conditions. The
(2) Temperature restrictions which relate to
air heater, if provided, is sized to provide the
the methods of construction and the type of stack
desired air temperature to the pulverizers or stoker
lining material to be utilized.
as well as to lower the exit gas temperature to the
(3) Stack and lining material must be
desired value.
selected to withstand corrosive gases (related to
(4) Fitting the size of each component into
sulfur in the fuel).
the most efficient and least expensive unit is the
(4) Wind, earthquake and dead loads, which
function of the boiler manufacturer and their
includes the moment 1 load from deflection.
3-27
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