of the self-closing glass-covered type for side walls, including a
minimum of four for observing the underside of the grate.
d.
Stoker Grate: Grates shall be made of the best quality, heavy
duty, heat resisting, cast iron or cast alloy carefully cast to
minimize initial strain. Specially design the grates for spreader
stoker firing. Grates shall be of high resistance, air metering
type with closely and uniformly spaced self-cleaning air openings.
The grates shall have close fitting, overlapping edges to
prevent air leakage at the joints. Provide undergrate air seals
at both the front and rear ends fabricated of cast iron and
counterweighted so that they will always be in close contact with
the under sides of the grates. Construct the rear seal to
proportion the air flow through the rear end of the grate to
expedite coking and ignition of the coal, thereby properly
conditioning it for efficient combustion when the fuel bed reaches
the active air admitting area.
Side seals between edge of stoker
grate and boiler shall be approved bellows type.
e.
Grate Thermocouples: Provide two grate temperature sensing
thermocouple arrangements on each grate to indicate and record
grate temperatures on the operator's [interface console] [control
panel].
f.
Tension Adjustment: Provide a conveniently located adjustment
accessible from outside of the boiler or through access plates in
the stoker front cover for regulating the tension of the grate.
Provide adequate adjustment for the chain length.
g.
Stoker Support: Stoker and drive shall be complete with
supporting structural steel framework. Locate and protect
structural supports so that they will not be overheated or damaged
by heat from either the furnace or ash pit.
2.4.2.3
Grate Ash Discharge Enclosure
Enclose front end of grate, where ash is discharged into the hopper below
the floor line, with a dust tight enclosure made of heavy steel plates
properly protected with fire brick where exposed to the furnace. Fit
vertical fronts of this enclosure with cast iron, refractory lined
inspection and access doors, one for each feeder. Seal off roof of this
enclosure with refractory, protecting the metal parts from the furnace
temperature with refractory. Exposed metal parts in the enclosure are not
acceptable. Enclosure shall be compatible with the ash storage hopper as
specified under "Ash Handling System" this section.
2.4.2.4
Feeder Drives
At the option of the Contractor, the drives shall be either individually
driven and controlled feeders or feeders driven by a line shaft with
individual clutch arrangements.
a.
Controlled Feeders: The individually driven and controlled
feeders shall have a variable speed drive on each distributor and
a silicon controlled rectifier (SCR) D.C. motor drive for each
drum or feed box. A master controller shall receive a fuel demand
signal from the combustion control system and control the
individual slave controllers of the individual SCR units to
satisfy the particular fuel demand. Control arrangement shall
SECTION 15502N
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