Furnace, Two-Stage

the furnace of a type of boiler unit intended for combustion of pulverized fuel. It consists of two consecutively arranged chambers, separated by a bundle of slag-catching tubes. In the first chamber the combustion of fuel occurs at a temperature of 1500°-1600°C. At this temperature the ashes contained in the fuel melt, and the slag is removed from the chamber in liquid state. This liquefaction reduces by some 50–60 percent the quantity of ashes entering the gas flues of the boiler unit, simplifies the removal of ashes from the flue gas, and reduces the abrasive wear of tubes. The second chamber is used for the afterburning of the fuel and for cooling the flue gases to a temperature at which the particles that were not captured in the first chamber solidify and cease to adhere to the tube banks; this eliminates clogging of the tubes by slag. Two-stage furnaces are suitable for combustion of high-energy fuels with nonrefractory ash.