aggregate. The hoppers should be clad with 410 stainless steel on the cone
section of the bunker. Parabolic suspension bunkers are not recommended
because the flow of coal from all outlets is not uniform; this creates dead
pockets and causes a spontaneous combustion hazard. Cylindrical bunkers are
used to reduce danger of spontaneous ignition of coals containing over 1
percent sulfur. With this design, stagnation and coal segregation are
minimized. At least the bottom of each bunker should be in the building to
preclude bottom freezing. Discharge hoppers should be sloped at least 60
degrees. An emergency discharge chute or screw conveyor should be provided
for each bunker to remove coal from the bunker in emergency situations.
Bunker Fires. Carbon dioxide protection should be
considered for bunkers as required in para. 10.13. Provide detectors to sense
gas mixtures caused by heating of the bunker. Mechanical coal handling
equipment shall be provided to remove hot coal to the building exterior when
it cannot be burned in the boiler within a reasonably short period.
Silos. Cylindrical silos can be used when coal sulfur
content is less than one percent. These silos combine active and reserve
storage in one structure. Their live storage capacity is less than that of a
bunker and requires bucket elevators to utilize the entire storage volume.
Common practice is to put live storage in the upper portion of the structure
and reserves in the lower. When the live storage is full, coal spills over to
reserve, which discharges to the pickup point of an elevator or conveyor. The
silo bottom hoppers or cones should be sloped at least 60 degrees and lined
with type 410 stainless steel (The slope of the cones depends on the coal
available; the slope for western bituminous coal is 70 degrees). The outlet
gates should be heated sufficiently to prevent freezing. Recirculating
conveyor systems should be installed to recycle coal from bottom to top to
deter spontaneous combustion should coal be retained in the silo for an
extended period of time. Capacity should be 96 hours of coal storage for
consumption at total plant capacity. Live bottom silos (without storage
shelves) should be used where coal sulfur content is more than one percent.
Receiving and Storage
a) Storage and receiving of fuel oil is covered in NAVFAC DM-22,
Petroleum Fuel Facilities, and NAVFAC MO-230, Maintenance Manual Petroleum
Fuel Facilities. Minimum oil storage at plant must be equivalent to 120 hours
operation at total plant capacity. Total activity storage must not be less
than 30 days supply based on coldest 30 day requirement for primary or backup
fuel. The preferred storage, is 30 days supply at plant capacity.
b) The complete oil unloading and storage facilities shall satisfy
the pollution abatement requirements specified in EPA 38 CFR 237 Environmental
Protection Agency, Oil Pollution Prevention, Non-Transportation Related
Onshore and Offshore Facilities.