Abstract: A structure of a boiler, of the type in which pulverized fuel is burnt within a square barrel-shaped furnace having a vertical axis, is improved so that ignitability is improved and the amount of NO.sub.x produced is decreased. Burners for injecting pulverized fuel-air mixtures are disposed at the central portions of respective edges in a horizontal cross-section of a furnace wall and are inclined downwardly with respect to a horizontal plane. Also, under air nozzles for feeding air are disposed under the respective burners.

Abstract: A boiler furnace combustion system typically includes main burners disposed on side walls of or at corners of a square-barrel-shaped boiler furnace having a vertical axis, the burner axes being directed tangentially to an imaginary cylindrical surface coaxial to the furnace. Air nozzles are disposed in the boiler furnace at a level above the main burners, so that unburnt fuel left in a reducing atmosphere or a lower oxygen concentration atmosphere of a main burner combustion region can be perfectly burnt by additional air blown through the air nozzles. The present invention provides two groups of air nozzles disposed at higher and lower levels, respectively. The air nozzles at the lower level are provided at the corners of the boiler furnace with their axes directed tangentially to a second imaginary coaxial cylindrical surface having a larger diameter than the first imaginary coaxial cylindrical surface.

Abstract: A fuel combustion apparatus for burning a premix of an air stream and a fuel jet, comprising an air nozzle for issuing air to form a conically spread film of the air stream, and an atomizer for injecting fuel circumferentially unevenly into the conical film of air stream so that a premix uniformly mixed with air but having a circumferentially varied air-fuel ratio which is locally selectively greater than 1 or less than 1.