inspection and access doors, and shall have provisions for ash removal.
2.3.4
Vibrating Grate Stokers
Vibrating grate stokers shall be the grate level feed, forced draft type
with the vibrating action of the grate used to feed the coal from the
hopper through the furnace and to discharge the ashes into the ash pit.
Stokers shall be provided complete with hopper, feed gate, grate, drive
mechanism, and all necessary auxiliary equipment. Stoker shall be capable
of handling the specified coal. Coal shall be automatically fed from the
hopper onto the grate and shall be evenly distributed across the full width
of the grate. A manual adjustment shall be provided to regulate the fuel
bed thickness. Ashes shall be automatically and continuously discharged to
the ash pit. The area under the grates shall be divided into not less than
four air-tight zones for forced draft supply and shall have suitable zone
control dampers with external indicating, operating, and locking devices.
2.3.4.1
Grates
Grates shall be either air-cooled or water-cooled with grate bars in
intimate contact with the water tubes. Grates shall have individually
replaceable sections of iron or steel suitable for the temperatures
encountered. All pressure parts including water tubes, headers, and valves
shall be suitable for boiler pressure specified and shall be constructed in
accordance with ASME BPVC SEC I. Grate sections shall be properly designed
for even air distribution over the entire grate area.
2.3.4.2
Controls
Stoker controls shall be designed for connection to the combustion control
system to accurately regulate the coal feed rate and shall be arranged for
manual operation, independent of the combustion control system. Variation
of coal feed rate shall be accomplished by changing the length of time of
the vibrations. Vibration generator shall be belt-connected or
gear-connected to the electric motor. Unit shall be free of any vibration
that may damage other parts of the boiler or the building structure.
Bearing requiring lubrication shall be provided with easily accessible
lubrication fittings. Combustion air volume shall automatically vary in
direct proportion with the coal feed rate. Stoker shall be driven by
electric motor. Motor shall be high starting torque [totally enclosed,
nonventilated] [totally enclosed, fan-cooled] totally enclosed, fan-cooled
suitable for installation in a Class II, Division 1, Group F hazardous
location in accordance with NFPA 70. Motor starter shall be magnetic,
reversing [across-the-line] [reduced voltage start] type with
[general-purpose] [dust-tight] [explosion-proof] enclosure.
2.3.4.3
Hoppers
Hoppers shall be constructed of steel plates not less than 6.4 mm 1/4 inch
thick, shall have a capacity not less than [_____] kg pounds, and shall be
provided with a suitable method of cleanout. Furnace arches of a design
suitable for the intended use and a type that will insure proper combustion
of the fuel shall be provided. Lower furnace sidewall headers in a
waterwall boiler shall be inclined to accommodate the inclined grate
arrangement. Stoker front shall form the front of the boiler for the full
width of the boiler and shall extend from the firing floor to some point
above the stoker where it shall connect to the boiler structural framing.
Front shall be cast-iron or steel plate refractory lined with cleanout and
access doors of refractory-lined cast-iron. Structural framing as required
SECTION 15555A
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