2205 kW per square meter 700,000 Btu per square
foot per hour when coal meeting the criteria set out
in the Stoker Selection Criteria shown in NAVFAC
Design Manual DM-3.6, Table 12 is used. When coal
is specified which does not meet this criteria then
the grate heat release will have to be lowered
accordingly.
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The active grate area shall be such that the heat release at the maximum
continuous rating shall not exceed [_____] kW per square meter Btu per hour
per square foot. At minimum boiler rating the stoker grate heat release
shall be a minimum of [2280] [2850] MJ per square meter [200,000] [250,000]
Btu per square foot; this results in a guaranteed turndown ratio of [_____]
to 1. Grate area shall be the product of the width between the inside
faces of the sidewall heaters at the grate line and the length of the
air-supplied grate area. The grate shape shall be designed so that the
heat release per front meter foot of stoker width does not exceed 2930 kW
10,000,000 Btu/hour at the maximum continuous boiler rating.
2.4.2.2
Construction
a.
Fuel Feed Control: Coal shall be fed to and distributed in the
furnace by not less than three overfeed type spreader stoker
feeders for each boiler. Feeders shall be operated simultaneously
and at synchronized speeds so that any one feeder may be taken out
of service without affecting the operation of the others. Each
feeder shall be readily adjustable to ensure proper fuel
distribution within the furnace. Design and size the total
combined width of the feeder openings for proper distribution of
the fuel over the width of the stoker grate. Design shall be such
that the combined width of the feeders shall not be less than 40
percent of the width of the stoker grate. The feeders shall be
capable of handling and uniformly distributing coal varying in
size from 6 to 32 mm 1/4 to 1 1/4 inches with no more than 40
percent passing a 6 mm 1/4 inch round mesh over the entire grate
area. The feeder shall be capable of properly performing with
moisture in the fuel as high as 15 percent by weight.
Materials
of construction shall be such that coal with high sulfur content
can be satisfactorily used without extensive corrosion over the
lifetime of the parts. Provide moving parts of the feeders with
anti-friction type bearings and with a forced system of
lubrication. Bearings subject to high temperatures shall be water
cooled. Gear teeth shall be machine cut.
b.
Coal Hopper: Provide a metal hopper for each spreader stoker
feeder. Hoppers shall be not less than 6 mm 1/4 inch thick 304
stainless steel plate, rigidly reinforced and connected to the
coal grates. Support hoppers from the floor or boiler columns to
eliminate weight on the feeders. Provide hoppers with suitable
cleanout doors located in the front.
c.
Air Plenum (Siftings Hopper) and Ducts: The traveling
grate/stoker shall be complete with under grate air plenum,
manually operated blast gates and operating handles, and siftings
hopper. Plenum and air ducts shall be not less than 10 gage steel
plate. Locate and protect structural supports so that they will
not be overheated or damaged by heat from either the furnace or
ash pit. Provide unit with necessary observation doors or ports
SECTION 15502N
Page 66
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