Abstract: The known method of burning solid fuel by means of a fluidized bed is improved so as to reduce the amount of generated NO.sub.x and to enhance the efficiency of combustion. Primary air, secondary air and tertiary air are respectively fed through a primary air feed port opening at the fluidized bed, through a secondary air feed port opening at a free board downstream of the fluidized bed and through a tertiary air feed port opening downstream of the secondary air feed port. The feed rates of the primary air, secondary air and tertiary air are respectively controlled so that the air ratios with respect to the theoretical amount of air after charging of the primary air, after charging of the secondary air and after charging of the tertiary air may become about 0.6-0.8, about 0.8-1.0 and about 1.0 or higher, respectively. Preferably, unburnt ash sputtered from the fluidized bed is recirculated into the fluidized bed.

Abstract: A pulverized fuel firing apparatus comprises a first pulverized fuel injection compartment so constructed that the combined amount of primary air and secondary air to be consumed is less than the theoretical amount of air required for the combustion of the pulverized fuel to be fed as mixed with the primary air to a furnace, a second pulverized fuel injection compartment so constructed that the combined primary and secondary air amount is substantially equal to the theoretical air for the pulverized fuel to be fed together with the primary air, and a supplementary air compartment for injecting supplementary air into the furnace. The three compartments are arranged close to one another and control the NOx production upon combustion of the pulverized fuel.

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.