Pulverized-Fuel Furnace

a chamber furnace for burning pulverized solid fuel. Pulverized-fuel furnaces are used in boiler units with ratings of 50–2,500 tons per hour. Virtually all types of solid fuel, including the lowest-grade types (brown coals, peat, bituminous shales), can be used with high efficiency in pulverized-fuel furnaces.

The fuel, which is crushed and dried in a pulverizer, is mixed with primary air, which carries it into the furnace through burners. The primary air is 12–50 percent of the total air supplied. The secondary air is fed into the furnace through separate ducts in the burner or through special nozzles. The total quantity of air is usually 15–25 percent greater than that theoretically required for complete combustion. The furnaces attain temperatures of 1800°-2000°K and have heating capacities of 2 giga-watts or more. Mazut and natural gas are usually used for preheating (firing) a cold furnace; in some cases these fuels are also used to sustain combustion of the prime fuel (auxiliary firing), for example, during thorough unloading of the furnace.

Pulverized-fuel furnaces may be of the one-chamber, two-chamber, or three-chamber type. The two-chamber furnace is divided into a combustion zone and an afterburning and cooling zone; three-chamber furnaces have separate after burning and cooling zones. To increase the temperature in the combustion zone, the furnace waterwalls are covered with a refractory lining. Pulverized fuel furnaces are divided into vortex and air-jet furnaces, depending on the nature of the movement and interaction of the gas flows.