MIL-HDBK-1003/7
separate compartments with each compartment provided with a large hatch cover. Hatch
covers are moved to the open position by means of cables attached to the unloader
bucket. These cables are also used to lower a bulldozer into each compartment for final
cleanup of coal.
The unloader boom may be extended on both sides of the tower structure,
which allows the unloader to be used also for coal reclaim from an onshore stockpile.
The boom may also be provided with a movable operating cab which can be positioned to
serve at either end of the boom.
The unloader bucket is supported by cables from a trolley that moves back
and forth along the boom. The unloader mechanism includes a holding hoist to raise,
lower, and hold the bucket, a closing hoist that opens and closes the bucket, a trolley
winch that moves the trolley, and a tower drive (if the tower is of the movable type).
The tower structure supports a machinery house that contains DC motor driven
hoisting and trolley movement equipment, motor generator sets, and electrical control
equipment. Coal is dropped into a receiving hopper from which it is discharged to a
yard belt conveyor.
Coal Crushing. If unsized coal such as run of mine is delivered to the plant,
9.2
a coal crusher must be provided to reduce the coal to uniform lump size suitable for
storage and firing or pulverizing.
In climates where frozen coal may be a problem, a coal cracker for breaking
up frozen lumps, should be provided on the conveyor system feeding plant bunkers or
silos.
For additional information relative to coal crushing equipment, see MIL-
HDBK-1003/6.
Coal Storage. Storage shall be as required in MIL-HDBK-1003/6, under
9.3
paragraph titled "Fuel Handling," except that the outside storage reserve stockpile
shall be designed to store 90 days usage of coal at full plant capacity.
Coal Reclaiming. Coal reclaiming is usually done by means of bull dozing the
9.4
coal from the reserve stockpile into a separate reclaim hopper which shall include a
feeder and a conveyor that transports the reclaimed coal onto an unloading belt or
bucket elevator.
Plant Bunker or Silo Storage. In-plant bunkers and silos are used for storage
9.5
of coal for day-to-day operation of feeding the boiler coal burning system. The amount
of coal for this storage should be equivalent to 96 hours of plant operation at full
load. Separate bunkers or silos should be provided for each boiler. For additional
information see MIL-HDBK-1003/6.
Bunker or Silo Filling Systems. The bunker or silo filling system will
9.6
consist of a bucket elevator or belt conveyor that is used to elevate the coal from
reclaim hopper discharge to top of bunker/silo coal gallery. The coal gallery will
contain a coal distribution system consisting of a belt tripper flight conveyor or
cascading belts. The bunker/silo fill system capacity should be equivalent to twice the
maximum coal burn rate plus 15 percent. For description of system components and
requirements see MIL-HDBK-1003/6.
Coal Scales. Railroad track scales and truck scales are optional for use in
9.7
measuring the amount of coal received; however, if an unloading belt conveyor is used,
the use of belt type scales is more economical than track or truck scales. Conveyor
belt type scales can also be used to measure the amount of coal stockpiled or delivered
to the in-plant bunkers or silos.
Magnetic Separators. Magnetic separators shall be used in coal conveying
9.8
systems to separate tramp iron (including steel) from the coal. Basically, two types
are available. One type incorporates permanent or electromagnets into the head pulley
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