Archive for July 25th, 2010

Coal Fired Boiler Explosions

Sunday, July 25th, 2010

     Try this for a tongue-twister:  Coal fired electric utility power plant boiler…  If you’ve been reading along with us for the last couple of weeks, you now have a pretty good idea of what these are and what they do.

     These boilers are contained within furnaces in coal fired power plants.  The furnace’s job is to combine coal and air to create a combustion process.  It is like a big, insulated enclosure that keeps the heat energy from the combustion process from escaping before it can be absorbed by the water and steam in the boiler tubes.  The heat energy is then funneled to the steam turbine to spin an electrical generator, creating the energy which will eventually find its way into our homes and businesses.

     During the operation of the boiler, coal and air must be introduced into the furnace at carefully measured rates to maintain a proper fuel-to-air ratio which will enable the release of heat energy from the coal at a safe, controlled rate.  Fuel-air ratio is the amount of coal entering the furnace divided by the amount of air entering the furnace.  If this ratio isn’t precisely maintained, conditions may be right for an explosion to occur.  Specifically, the ratio has to fall within an “explosive range.”  Once within this range, all that is needed is an ignition source, such as hot ash, or even mere static electricity, and the result may be a furnace explosion.  

     There are certain times at which furnace explosions are more likely to occur than others, such as when the boiler is being started, operated at less than full capacity, or shut down.  When a furnace explodes, a pressure wave moves out from the center of the blast.  This pressure wave will bear up against the sides of the furnace with great force, and if the pressure is high enough the sides of the furnace, which are made of heavy steel components, will actually bend and split open.  Boiler tubes may even rupture, releasing high pressure steam and water into the power plant and furnace.  At the very least, the boiler will be down for expensive repairs and no electricity can be produced by its turbine generator.  This down time can last for many months and results in lost revenue to the energy producer.

     Aside from an explosive fuel-to-air ratio, there are other potential causes of furnace explosions.  For example, poor coal quality can lead to incomplete combustion, or the flame going out completely, encouraging unburned coal particles to settle and accumulate in the furnace.  The accumulation of coal can grow to the point where it forms an explosive mixture when combined with the right amount of air.

     So how can boiler explosions be prevented?  The National Fire Protection Association (NFPA) looked into the problem and developed an industry standard.  This standard is known as NFPA 85, Boiler and Combustion Systems Hazards Code.  Its purpose is to contribute to operating safety and prevent uncontrolled fires, explosions, and implosions of coal fired boilers.  NFPA 85 lays out guidelines to follow when designing, building, and operating boiler fuel handling systems, air handling systems, and combustion control systems.  Following its guidelines will certainly significantly decrease the probability of explosions occurring.

     Another means of explosion prevention includes implementing a boiler operator training program.  These enable attendees to better understand operating procedures and equip them with the knowledge to safely control the combustion process, particularly when a furnace explosion is most likely to occur.  This training can be done with a combination of classroom instruction along with time on a simulator and may be followed up with hands-on training in the plant itself.

     Lastly, boiler explosions can be prevented by implementing an effective inspection and maintenance program to locate and repair or replace boiler components, averting the possibility of a potential disaster occurring.  Things such as check lists can be used to ensure that nothing is missed.  This is a strategy that all pilots must use before starting their planes, and it is now being used in hospitals as well to cut back on the rate of patient infection due to carelessness on the part of hospital staff.

     Hey, we’re all human, and humans are not perfect.  But remember that an ounce of prevention is truly worth a pound of cure, and then some.  A properly placed check on the list could mean lives will be saved.