TM 5-810-15
bunker designs are the square upside down pyramid
runoff water and leachate. Treatment facilities will
and silo types. Cantenary, straight, or parabolic
be provided if required.
type bunkers will not be used because the flow of
(3) Care must be taken in the method of
coal from all outlets is not uniform which creates
constructing the coal pile. Coal is placed in maxi-
dead pockets and causes a spontaneous combustion
mum 18-inch thick layers and then compacted with
hazard. Cylindrical or silo type bunkers are used to
the use of a front-end loader or rubber tired dozer
reduce danger of spontaneous ignition of coals. To
to eliminate air spaces within the pile.
reduce stagnation and coal segregation, separate
(4) The designer will take into account the
bunkers will be provided for each boiler. At least
"weathering" process or loss of coal heating value,
the bottom of each bunker should be in the building
that takes place with long term storage of coal.
to preclude bottom freezing. Discharge hoppers
(5) Coal handling personnel will be assigned
will be sloped at least 55 degrees. An emergency
to check a long term storage pile on a daily basis,
discharge chute will be provided for each bunker to
to guard against localized hot spots caused by
remove coal from the bunker in emergency
spontaneous combustion.
situations. Silo design type bunkers are more
(6) A liner may be required underneath the
frequently used because they have been found to be
coal pile to prevent coal pile runoff from being
less susceptible to rat holing and hangups than
absorbed by surrounding subsoil. Soil permeability
other shapes.
tests will be taken in the area where the coal pile is
d. Material. The designer will carefully analyze
to be located.
the type of material being used for the bunker, to
b. Environmental regulations. Local and State
insure the material is compatible with the type of
Regulation Agencies may have environmental reg-
coal being stored.
ulations which prohibit open storage of coal, be-
e. Location. Coal bunkers should be located to
cause of fugitive dust emissions and runoff. In this
provide a coal flow which is as vertical as possible.
case the designer should investigate the use of
Current trend is to replace plant storage bunkers
outside coal storage silos or covered barn struc-
with inside silos which require less building volume
tures. Both silos and barns are high capital expense
and structural support steel. On the average, it has
items. Some agencies will allow open storage of
been determined that the silo and related support
coals with wet suppression.
steel structure were less expensive than a bunker of
the same capacity. The cylindrical shape of a silo
5-24.
Fire protection and prevention.
has an inherent strength advantage. A properly
a. General. Fire protection and prevention for a
designed bunker generally can match a silo*s flow
conveying system and its related structures, re-
efficiency, therefore such factors as moisture
quires that the designer ensure careful planning
content, temperature and storage time have the
during the initial design stage to reduce coal dust.
greatest influence on the type of silo or bunker that
Fire protection systems are playing a more impor-
is selected.
tant role in the design of conveying systems. New
code standards developed by the NFPA and indus-
5-23.
Long term coal storage.
try requirements are forcing designers to reexamine
a. General. The long term coal storage pile is
coal handling system design and the suitability of
created for the sole purpose of having an adequate
the fire protection system. A fire protection system
supply of coal on hand to supply coal to the boilers
can make a difference between minor damage and
in the event of an interruption of coal supplies to
total destruction.
the plant.
(1) Western subbituminous type coals are
(1) The reserve or long term coal storage
less dense, more susceptible to spontaneous
pile should be maintained at the boiler plant. Refer
combustion than the eastern coals. The amount of
to TM 5-848-3 for the criteria for determining the
fire protection required for any system largely
quantity of coal to be stored.
depends on the type of coal to be burned at the
(2) The method of storing and reclaiming
facility. Some coals can be stored in bunkers for
coal in an outside storage pile should be determined
years without any spontaneous combustion
to satisfy regulatory environmental restraints.
generated fires, while other coals such as some
types of western subbituminous C type coals
treatment, coal water separation and neutralizing
cannot be left in a bunker for a period over 30
effluent will be included in design. Local, State and
days. An emergency bunker unloading system will
Federal environmental regulations will determine
be included in the design to enable the bunkers to
limits for suspended solids and pH of coal pile
be emptied. Western coals tend to produce a higher
5-15
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