Firing Bituminous Coal
Bituminous coal is a broad category encompassing many different burning characteristics and properties. Generally speaking, bituminous coals ignite and burn easily with a relatively long flame. They are also characterized by excess smoke and soot when improperly fired.
The side bank method is commonly recommended for firing bituminous coal. It consists of moving the live coals to one side or the other of the grate and placing a fresh fuel charge on the opposite side. Variations of this firing method call for placing the live coals at the back of the grate or covering the fresh fuel charge with a layer of fine coal. The side bank method results in a slower and more uni- form release of volatile gases.
Other recommendations that should be followed when firing bituminous coal include the following:
• Fire bituminous coal in small quantities at short intervals. This results in a better combustion because the fuel supply is maintained more nearly proportional to the air supply.
• Never fire bituminous coal over the entire fuel bed at one time. A portion of the glowing fuel should always be left exposed to ignite the gases leaving the fresh fuel charge.
• Use a stoking bar to break up a fresh charge of coking coal approximately 20 minutes to 1 hour after firing.
• Do not bring the stoking bar up to the surface of the fuel.
Doing so will bring ash into the high-temperature zone at the top of the fire, where it will melt and form clinkers.
A stoking bar should always be kept as near the grate as possible and should be raised only enough to break up the fuel. The ash will usually be dislodged when stoking, making it unnecessary to shake the grates.
Alternate or checker firing is a bituminous coal firing method in which the fuel is fired alternately on separate sides of the grate. This method tends to decrease the amount of smoke and maintain a higher furnace or boiler temperature.
A similar effect is produced by the coking method of firing bituminous coal. The coal is first fired close to the firing door, and the coke is moved back into the furnace just before firing again.