Patent ID: 7681508

Claim:
An after-air nozzle for a two-stage combustion boiler, comprising: a windbox outer casing for surrounding an outside of an after-air nozzle, an opening of the windbox provided on the windbox outer casing to flow air for combustion into the after-air nozzle; a vena contracta adapted such that an outside diameter of a flow passage diminishes towards an air-jetting port which supplies air to the boiler; and a changing apparatus of a flow passage cross-sectional area of the vena contracta, wherein air for combustion flows into the after-air nozzle from the opening of the window, streams through the changing apparatus of the flow passage cross-sectional area and jets into the boiler from the air-jetting port, the changing apparatus of the flow passage cross-section area is provided with a member which defines a minimum flow passage area of the vena contracta in the after-air nozzle, the after-air nozzle further comprising a first slide member for moving the changing apparatus of the flow passage cross-sectional area in a direction of a flow passage so that the flow passage area of the vena contracta can be changed, and a second slide member provided on the windbox outer casing for changing an area of the opening of the windbox for air flowing into the after-air nozzle.