dumper. The CR dumper delivers low
power advantages and fast cycle times
and, when combined with multiple
positioners or indexers, achieves
maximum productivity.
Railcar dumper vs. bottom
dump
The railcar dumper and bottom
discharge railcars are the accepted
methods for unloading railcars. Selecting
between the two systems means that a
number of factors must be considered,
namely capital costs, maintenance,
climate, versatility and economics.
Capital costs
Unlike operating costs, which are the
daily or monthly expenses related to the
routine operation of a power plant, a
capital cost is the one-time expenditure
incurred in the purchase of new
equipment, which increases production
and often lasts for years. Capital costs
are fixed and are therefore independent
of the level of output. Both systems
represent such an expense. Both
methods involve a receiving pit to be
dug in the ground with a system of
conveyers to carry newly-dumped
material to its destination, but the rotary
dumper requires a single large piece of
equipment, while the corresponding cost
for a bottom dump system includes a
substantially deeper pit structure with a
shaker mechanism. Either system could
also incorporate auxiliary equipment,
such as a train positioning system, to
carry out the unloading procedure.
Maintenance
In addition to fixing equipment should it
become out of order or broken,
preventative maintenance involves
performing routine actions to keep the
device in working order and prevent
trouble from arising. Railcar dumpers
only have one centralised system to
maintain, rather than entire train lines.
With a rotary dump system, there are
also no door seals to replace, no railcar
gate failures, no railcar linkages and no
hot shoe maintenance. Bottom dump
railcars feature sloped chutes covered by
door hatches for unloading and use the
force of gravity to allow the material to
fall out of the car. Any imperfection in
the seals of the doors can allowmaterial
to spill onto the track, while every door
will be slightly different.
Climate
As temperature drops, it becomes more
of a factor in the transfer of bulk materials
than some may realise. Materials such
as coal, coke, lignite, iron ore and wood
chips all tend to clump together as the
water moisture they contain turns to ice.
In fact, there is a greater opportunity for a
load of coal to freeze if the haul is more
than one day away from the receiving
station. Clumped or frozen materials are
easily discharged with a railcar
dumper through the large single opening
in the top of a coal car, but not so easily
through a bottom dump car’s smaller
chutes. Bottom dump systems employ a
mechanical shaker to pound the side of a
railcar and break up the material it
contains, but the pieces may still be
unable to pass through the chutes and
there is a risk that the car itself may
become damaged in the process. Bottom
dump cars often must be kept in thaw
sheds overnight to allow the unloading
process to be more free‑flowing. The
railcars can also face demurrage
charges while they are detained, payable
either to the shipper for holding the car
The travelling hammermill is Heyl & Patterson's solution to breaking up clumped or
frozen coal that falls onto the grizzly from railcars as they are dumped.
Heyl & Patterson's hybrid machine can dump coal like a rotary dumper and also
receive bottom dump railcars.
58
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World Coal
|
June 2015
