Patent ID: 7878130

Claim:
An overfiring air port for supplying an incomplete combustion region with air making up for combustion-shortage, in a furnace in which said incomplete combustion region less than stoichiometric ratio is formed by a burner, wherein said air port comprises a nozzle mechanism for injecting air including an axial velocity component of an air flow and a radial velocity component directed to a center line of said air port, and a control mechanism for controlling a ratio of these velocity components, wherein said nozzle mechanism comprises a first nozzle for injecting air straightly in an axial direction of said airport, a second nozzle for injecting air with a swirling flow in an axial direction of said air port, and a third nozzle for injecting air directed from outside said first nozzle toward a center line of said air port, wherein said third nozzle has a conical front wall and a conical rear wall oppositely arranged against said conical front wall to form a conical air flow passage of said third nozzle between said conical front wall and said conical rear wall, wherein an outlet of said third nozzle is connected to an extremity end of said second nozzle so that an end of said conical rear wall is positioned behind an end of said conical front wall at the outlet of said third nozzle when viewed from an inside of said furnace and thereby the outlet of said third nozzle borders an air flow passage of said second nozzle and said velocity component-ratio control mechanism is configured by a mechanism for controlling a flow rate ratio of airs injected by said respective nozzles, wherein said first nozzle, second nozzle and third nozzle are arranged coaxially and an outlet of said third nozzle borders on an extremity of said second nozzle so that a jet of air issuing from the third nozzle merges with a jet of air issuing from said second nozzle, and wherein said third nozzle has a conical front wall and a conical rear wall oppositely arranged against said front wall, an air flow passage of said third nozzle is formed between said conical front wall and said conical rear wall, said rear wall is axially movable and a flow passage sectional area of said third nozzle can be varied through the movement of said rear wall.