Patent ID: 8714096

Claim:
A pulverized coal boiler comprising burners installed on a furnace wall for feeding pulverized coal into the furnace together with combustion air and burning the pulverized coal at lower than a theoretical air ratio and lower and upper after-air nozzles installed respectively on the furnace wall on a downstream side of the burners for feeding combustion air of a deficiency of the burners into the furnace which are arranged at two stages on the downstream side and an upstream side, wherein: among the lower and upper after-air nozzles interconnected to an inside of the furnace, a downstream side of at least one lower after-air nozzle of the lower after-air nozzles positioned on the upstream side is formed in a rectangular flow path with a rectangular shape, a cylindrical section for defining a minimum flow path area of combustion air flowing through a flow path of the at least one lower after-air nozzle is installed inside of the rectangular flow path coaxially with the rectangular flow path, a leak hole through which a part of the combustion air flowing inside the cylindrical section flows to an outer wall side of the cylindrical section is formed on a wall surface of the cylindrical section, a swirl blade for giving a swirl force to the combustion air flowing through the flow path of the at least one lower after-air nozzle is installed inside of the cylindrical section, and the flow path of the at least one lower after-air nozzle is formed so that a flow path area of the flow path of the at least one lower after-air nozzle through which the combustion air flows from a position where the cylindrical section is installed toward an opening of the at least one lower after-air nozzle is expanded.