TM 5-810-15
d. Railcar thawing. If the plant is located in a
occur.
(1) Sizing. A double hopper arrangement,
geographical area where the coal would be subject
to extreme freezing conditions either from stockpil-
approximately 28 feet long by 14 feet wide will
ing the coal, travel time of coal in railcars, or
allow a 100 ton capacity railcar to be placed over
railcars parked on rail sidings for extended periods
the unloading hopper without respotting the car.
(2) Design considerations. The structure
of time, the designer should make an economic cost
comparison to justify whether a railcar thawing
will be designed to support the fully loaded railcar
system is viable. The car thaw system is used to
and a fully loaded hopper. Bar grating will be
melt frozen coal from the walls and the bottom of
provided to protect against personnel and vehicles
railcars. The thaw system is not intended to
falling into the hopper. Grating will support the
completely thaw the entire amount of coal inside
weight of a truck or front end loader. Grate spacing
the railcar, but rather loosen the bond between the
should be a maximum of 6 inches square. The slope
railcar sides and the contents.
angle of all sides of the hoppers will not be less
(1) Methods. There are two very distinct
than 65 degrees from horizontal. The angle of the
methods used for railcar thawing. The more
hopper where two sides meet or valley angle will
expensive method is to spray a chemical freeze
not be less than 60 degrees from horizontal.
conditioning agent onto the coal as it is being
Provide capped poke holes at the hopper outlets
loaded into the railcar at the mine site. The other
for use if the hopper becomes plugged.
(3) Materials. A number of track hopper
method that is employed is electric or gas infrared
radiant energy generation. A combination chemical
construction options exist and these should be
treatment and thawing system is often used, but this
evaluated by the designer for each particular
is usually very expensive. Direct flame against the
application and the type of coal used. The more
side of the rail cars or the use of explosive charges
common construction materials include three types.
to dislodge coal inside the railcar, will definitely be
The first is A588 also known as weathering steel
avoided. A steam thawing system may be required
with minimum 3/8-inch plate thickness. This type
at an AAP due to the explosive atmosphere, where
material should not be used for high sulfur coal.
The second type is A-36 mild steel minimum -
be prohibited. Steam thawing is not very efficient
inch plate thickness, with minimum -inch thick
and can only be effectively used when large
type 304 stainless steel bolted or plug welded liners
amounts of steam are readily available. This type of
or studs. This type should not be used for high
system should be avoided where possible.
sulfur coal. The third type is solid stainless steel,
(2) Design considerations. The car thaw
minimum %-inch plate thickness. The type of
system should be provided with an enclosure or
material used for hopper construction will be
shed around the thawing area. The shed should be
determined by the type of coal being handled. Solid
at least long enough to accommodate one heating
stainless steel hoppers are not usually installed due
and one soak zone, when using stationary bottom
to the extremely high cost of the material.
dump railcars. The shed length should be increased
to handle in motion or unit trains. The car thaw
5-8. Belt conveyors.
heaters are located between the rails and along the
a. Conveyor design. Belt conveyors are used
walls of the shed. Reflecting side panels may also
most extensively in coal handling systems. They
be utilized to deflect radiant heat into the railcar.
have high handling capacities and offer unlimited
e. Unloading hoppers. The coal hopper must be
possible combinations of length, speed, and capac-
sized to accommodate the unloading capacity of
ity. Operating costs and power requirements are
the delivery system regardless if the coal is deliv-
low and they are reliable and quiet. Belt conveyors
ered by rail or truck. The hopper should have
can be designed for practically any desired path of
enough capacity to hold at least 100 tons of coal
travel limited only by the strength of the belt,
from a stationary positioned railcar, without the
conveyor incline or decline, or the space available
coal spilling over the tracks. The actual unloading
for installation. Troughed belt conveyors normally
schedule of the railcars or trucks is very important
require more space than other types of conveying
and should be timed to prevent overloading a
equipment. The designer must make sure that all
limited capacity hopper. If railcars are to be
conveyor components are suitable for use in a coal
unloaded quickly or on the move, the sequencing of
dust atmosphere as described by the NFPA and
the railcars, the track hopper size, and the size of
NEMA.
the track hopper conveyor must all be coordinated
b. Angle of conveyor incline and belt width.
together so that a choking condition does not
5-4
Previous Page
