grate shall hold air leakage to a minimum. Moving grates shall be
furnished complete with supporting steel, shafts, sprockets, chain, gears,
skid bars, and bearings as required. The front end of the grates where the
ash is discharged shall be enclosed with a dust-tight enclosure made of
heavy cast-iron plates not less than 16 mm 5/8 inch thick and properly
protected with firebrick where exposed to the furnace or shall be of
refractory lined steel plate. The vertical fronts of the enclosure shall
be fitted with refractory lined inspection and access doors, one for each
feeder. The roof of the enclosure shall be sealed with refractory to
protect the metal parts from the furnace temperature. The underside of the
grates shall be enclosed to form a chamber. Hopper for receiving the ashes
shall be constructed as indicated or as recommended by the manufacturer.
Over-fire air jets shall be provided as required for proper turbulence and
2.3.1.3
Vibrating Grate
Vibrating grate of high air resistant type shall be especially designed for
spreader stoker firing and for continuous ash discharge. Grates shall be
either air- or water-cooled with openings to provide proper distribution of
air under the fuel bed. Grates shall be heavy-duty, heat-resisting
cast-iron, and individual sections shall be replaceable. A manual
adjustment shall be provided to regulate the ash bed thickness and ashes
shall be automatically discharged to the ash pit. The front of the grates
where the ash is discharged shall be enclosed with a dust-tight enclosure
of heavy cast-iron plates not less than 16 mm 5/8 inch thick and properly
protected with firebrick where exposed to the furnace, or shall be of
refractory-lined steel plate. The vertical fronts of this enclosure shall
be fitted with refractory-lined inspection and access doors, one to each
feeder. The roof of this enclosure shall be sealed with refractory for
protecting the metal parts from the furnace temperature. The underside of
the grates shall be enclosed to form a chamber with a hopper for receiving
the ashes. Over-fire air jets shall be provided for turbulence and
2.3.1.4
Controls
Stoker controls that accurately regulate the coal feed rate shall be the
type required for connection to the combustion control system. Manual
setting of the coal feed rate with variation of stoker feed as required to
maintain any desired capacity between 50 and 110 percent of boiler capacity
shall be possible without disconnecting linkage. Separate feeder and grate
drives shall be provided. Grate shall be driven through a variable speed
transmission with devices for changing speed interlocked with fuel feed
regulation. Manual adjustment of grate speed shall be only for allowing
synchronization with fuel feed. All gears and chains of the variable speed
transmission and gear reduction units, as required, shall run in a bath of
oil and be enclosed in a dust-tight and oil-tight case.
Front and rear shafts of the grates shall be fitted with a forced
lubrication system with fittings located outside the setting. All bearings
shall be antifriction type with hardened inner and outer races fitted with
dust seals and easily accessible forced lubrication fittings. Stoker and
grate shall be provided with safety release devices to protect the
mechanism from foreign materials or obstructions. Stoker shall be driven
by electric motor. Electric motor shall be [totally enclosed, fan-cooled]
[totally enclosed fan-cooled for installation in Class II, Division 1,
Group F hazardous location in accordance with NFPA 70]. Motor starter
shall be magnetic [across-the-line] [reduced voltage start] type with
SECTION 15555A
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