PROBLEM TO BE SOLVED: To provide a marine boiler structure improving bias of corrosion progression by uniforming a temperature distribution of combustion gas passing through a superheater, and reducing a level of NOx included in the combustion gas.
SOLUTION: The marine boiler structure is composed such that the combustion gas generated by combustion of a burner 3 flows from a furnace 2 by passing through the superheater 5 and an evaporation tube group 6. A bottom air port 20 is provided to supply one part of combustion air from a bottom section 2a of the furnace 2 as bottom air, the bottom air port 20 is positioned in a superheater 5 side more than a burner center line CL, and a blowout direction of the bottom air is set within a range between a vertically upward direction and a slanting direction toward a burner.
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