Fire-protection guidelines for handling and storing PRB coal
Most plants that burn PRB coal were not designed to deal with the fuel’s propensity to ignite in bunkers, silos, and hoppers. Recognizing this, the PRB Coal Users’ Group has come up with a set of recommended practices for safely preventing, detecting, and extinguishing coal ﬁres at power plants.
By Edward B.Douberly, Utility FPE Group Inc.
he PRB Coal Users’ Group has developed recommended fire-prevention practices and guidelines for plants that burn PRB coal by itself or in blends. The guidelines are not equipment-specific because the physical layouts of coal-handling facilities vary signiﬁcantly and because all ﬁres are unique. The guidelines also are not comprehensive; their purpose is torecommend general practices that must be adapted for the specific needs of your plant. The guidelines provide information about three areas: ﬁre prevention and detection, firefighting equipment and training, and ﬁreﬁghting.
Fire prevention and detection
Operators familiar with the unique requirements of burning PRB coal will tell you that it’s not a case of “if” you will have a PRB coal ﬁre, it’s“when.” The prevention of fires and explosions is the foremost objective for any plant burning PRB coal. Although prevention is cheaper than repairing fire and explosion damage, its costs always seem difficult to justify. Fire prevention must be addressed in the following areas. Housekeeping. Housekeeping means controlling dust and preventing spills. For example, float dust must be containedwithin transfer points, and spillage from belts must be minimized. The accumulation of PRB coal below a conveyor or on conveyor parts can contribute to spontaneous combustion. Float dust either in the air or settled on beams, pipes, conduits, equipment, and fixtures provides fuel for explosions. A manual, daily washdown with a hose is beneficial but generally is not totally effective in removing PRBcoal debris from under conveyors or from overheads (Figure 1). Fixed washdown systems designed for 100% coverage are commercially avail70
able, greatly reduce labor costs, and significantly improve housekeeping over manual washdown. Plants that have installed these systems report being satisfied with their performance. Preplanning. For planned outages, operators should take every precautionto ensure that all idle bunkers and silos are completely empty and verify that by visual checks. Bunkers and silos should be thoroughly cleaned by washing down their interior walls and any interior structural members—but not their horizontal surfaces. Idle bunkers and silos that contain PRB coal should be monitored frequently for signs of spontaneous combustion by using CO monitors, infraredscanning, or temperature scanning. Don’t rely just on your
senses—by the time you see or smell burning coal, a fire is already under way (Figure 2). Some plants make bunkers or silos of PRB coal inert with carbon dioxide (CO2) when they are expected to sit idle. For this practice to be effective, the enclosure must be completely sealed—especially the bottom cone, because CO2 is about 1.5 timesheavier than air. The amount of CO2 needed to effectively render an enclosure inert is 3.3 lbs per ft3, so a silo measuring 22 feet in diameter and 55 feet high would require 3.2 tons of CO2. A bulk supply of CO 2 and an extensive piping system for bunkers and silos may be necessary to implement this system. Bunker and silo design. An active bunker or silo typically doesn’t experience
1. Debrisdump. An extreme case of PRB coal accumulation at the tail of a conveyor not
designed for PRB coal. Courtesy: Utility FPE Group Inc.
| October 2003
BURNING PRB COAL
of the silo’s design. Although directly attacking a ﬁre using a piercing rod is most effective, using a rod on a fire in a silo taller than 55 ft is extremely difficult. You should consider...