Burner, combustion device, boiler, and burner control method

A burner equipped with: an inside gas nozzle extending along an axis line while surrounding that axis line and capable of supplying to a furnace an oxygen-containing gas for inside combustion; a fuel supply nozzle that, when viewed in the direction along the axis line, surrounds the inside gas nozzle, and is capable of supplying to the furnace a fluid mixture of a solid powder fuel and a carrier gas; an outside gas nozzle that, when viewed in the direction along the axis line, surrounds the fuel supply nozzle, and is capable of supplying to the furnace an oxygen-containing gas for outside combustion; and a flow speed ratio adjustment mechanism capable of adjusting the relative flow speed ratio of the spray flow speed of the oxygen-containing gas for inside combustion and the spray flow speed of the oxygen-containing gas for outside combustion. Downstream from the outlet of the fuel supply nozzle, flame-holding regions are formed in the sprayed flow of the fluid mixture, these regions being formed respectively on the side of the sprayed flow of the oxygen-containing gas for inside combustion and on the side of the sprayed flow of the oxygen-containing gas for outside combustion.