Division 1, Group F hazardous location in accordance with NFPA 70
]]. [Motor starter shall be magnetic [across-the-line] [reduced
voltage start] type with [general-purpose] [dust-tight]
[explosion-proof] enclosure.] Stoker controls shall be for
connection to the combustion control system to accurately regulate
the coal feed rate. Manual setting of the coal feed rate shall be
possible without disconnecting linkage, with variation of stoker
feed as required to maintain any desired capacity between 25 and
110 percent of boiler capacity in 10 or more equal increments.
Regulation of the coal feed rate shall be by varying the time
increments between strokes of the ram. A throw-out release shall
protect the coal feeding mechanism from injury in case foreign
materials obstruct normal operation.
c.
Hoppers shall be constructed of steel plates not less than 6.4 mm
1/4 inch thick and shall have a capacity of not less than [_____]
kg pounds. Hoppers shall be provided with clean-out doors.
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 [auxiliary firing doors and] clean-out 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. Water spray pipes and nozzles
shall be provided for quenching the ashes in the ash pit.
2.3.2.2
Single Retort Screw Type Stokers
Single retort, heavy-duty, screw feed stokers shall be equipped with
rectangular firepot, side dump grates, forced-draft fan, electric-motor
drive, and all necessary auxiliary equipment. Coal shall be fed from the
hopper into the retort with a spiral worm conveyor designed to feed a
constant amount of coal and to prevent coal from packing in the worm.
[Dampers shall be provided between ash pits and main air chamber under
stoker to permit control of air distribution to the grate surface. Dampers
shall be arranged to be operated manually from the front plate of the
boiler.] The stoker shall be provided with an integral, forced-draft fan
driven by the stoker motor. Air quantity shall vary in direct proportion
with the coal feed rate and shall be controlled automatically. Retorts and
grates shall be constructed of heavy-duty, heat-resisting cast-iron, shall
be cored for proper air distribution, and shall be designed for easy
replacement of individual sections. Retorts shall be of proper size and
shape to distribute coal uniformly over the entire grate surface.
Stationary grates shall be provided on all sides of the retort as required
to suit the firebox. [Ash dump grates shall be provided on each side of
the retort complete with necessary levers and linkages for hand operation
from the front of the boiler.] Electric motor shall be belt-connected to
an efficient gear reduction unit which shall drive the feed screw and
forced-draft fan. Gear reduction unit shall be immersed in oil in a
dustproof housing. Stoker controls shall be suitable for connection to the
combustion control system to accurately regulate the coal feed rate. Feed
rate control shall allow manual setting for not less than three speeds and
neutral, in equal increments, with speed changes possible while stoker is
running. A suitable release shall protect the coal feeding mechanism from
injury in case foreign materials obstruct normal operation. Motors 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
SECTION 15559A
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