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 [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 ensure 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 ensure 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 15.9 mm 5/8 inch thick, properly protected with firebrick where
exposed to the furnace; shall be fitted with cast-iron, refractory lined
inspection and access doors; and shall have provisions for ash removal.
2.3.4
Vibrating Grate Stokers
**************************************************************************
NOTE: Any paragraphs describing stoker equipment
not necessary for the system specified will be
deleted.
**************************************************************************
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 discharge the ashes into the ash pit.
Stokers shall be complete with hopper, feed gate, grate, drive mechanism,
and all necessary auxiliary equipment. 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 airtight zones for forced draft supply and shall have
suitable zone control dampers with external indicating, operating, and
2.3.4.1
Grates
Grates shall be either air cooled or water cooled with grate bars in
intimate contact with the watertubes. Grates shall have individually
replaceable sections of iron or steel suitable for the temperatures
SECTION 15559A
Page 35
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