2.3.3.1
Grates
Grates shall have individual sections constructed of heavy-duty,
heat-resisting cast-iron, shall be fitted or cored for proper air
distribution, and shall be designed for easy replacement of individual
sections. [Chain grates shall have staggered links connected by pins to
form a continuous flat chain the full width of the furnace.] [Traveling
grates shall have grate blocks mounted on carrier bars which, in turn,
shall be fastened to two or more drive chains to form a continuous flat
grate surface the full width of the furnace.] Continuous grates shall be
supported at the ends by suitable sprockets and at intermediate points on
suitable tracks or skids.
2.3.3.2
Conveyor Grate
Conveyor grate shall be driven by [electric motor connected through a
suitable speed-reduction unit] [hydraulically-operated variable speed
drive]. All gears and chains required for the drive shall be enclosed in a
dust-tight and oil-tight housing. Main shafts for the grates shall have a
forced system of lubrication with fittings located outside the casing or
have self-lubricating bearings. If the forced lubrication system is
supplied, bearings shall be fitted with dust seals and easily accessible
forced lubrication fittings. Stoker controls shall be suitable for
connection to the combustion control system to accurately regulate the coal
feed rate. Manual setting of the coal feed rate by varying stoker feed as
required to maintain any desired capacity between 25 to 125 percent of
boiler capacity shall be possible without disconnecting linkage. Feed rate
shall be changed by varying the speed of the grate. Air volume shall
automatically vary in direct proportion with the feed rate. Possible feed
rate shall vary in not less than 10 equal increments. Electric motor shall
be [totally enclosed fan-cooled type] [totally enclosed fan-cooled type
suitable for installation in a Class II, Division 1, Group F hazardous
location in accordance with NFPA 70]. [Motor starter shall be [manual]
[[magnetic] [across-the-line] [reduced voltage start]] type with
[general-purpose] [dust-tight] [explosion-proof] enclosure.]
2.3.3.3
Hoppers
Hoppers shall be constructed of steel plates not less than 6.4 mm 1/4 inch
thick, shall have a capacity of not less than [_____] kg pounds, and shall
be provided with suitable cleanout doors. Coal feed to the hoppers shall
be fitted with concave type transitions to insure the proper distribution
of coal and coal fines across the width of the hoppers. Stoker frame shall
be constructed of cast-iron, cast steel, or forgings, and all parts of the
stoker, except the grates, shall be properly cooled or otherwise protected
from the furnace heat to prevent damage by warping or undue expansion.
Furnace arrangement and shape shall be as recommended by the stoker
manufacturer to insure proper combustion of the fuel. Stoker front plate
shall form the front of the boiler for the full width of the boiler and
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 doors of refractory-lined cast
iron. Structural framing as required shall support the stoker and its
components from the boiler foundation or boiler room floor. At the end of
the grate, the ash shall be discharged into a bunker or pit as indicated.
The bunker shall have a dust-tight enclosure made of steel plates not less
than 6.4 mm l/4 inch thick, properly protected with firebrick where exposed
to the furnace, and shall be fitted with cast-iron, refractory-lined
SECTION 15555A
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