Burner, combustion device, boiler, and burner control method

A burner, comprising:

• an inner gas nozzle which extends along an axis while surrounding the axis, and which is capable of supplying a furnace with an inner combustion oxygen containing gas;
• a fuel supply nozzle surrounding the inner gas nozzle as seen in a direction along the axis, the fuel supply nozzle being capable of supplying the furnace with a fluid mixture of a solid powder fuel and a carrier gas;
• an outer gas nozzle surrounding the fuel supply nozzle as seen in the direction along the axis, the outer gas nozzle being capable of supplying the furnace with an outer combustion oxygen containing gas;
• an inner flame holder disposed on an outlet section of the inner gas nozzle and configured to contract a flow of the inner combustion oxygen containing gas;
• an outer flame holder disposed on an outlet section of the outer gas nozzle and configured to deviate a flow of the outer combustion oxygen containing gas from the axis;
• a flow-velocity-ratio adjustment apparatus capable of adjusting a relative flow velocity ratio of a discharge flow velocity of the inner combustion oxygen containing gas to a discharge flow velocity of the outer combustion oxygen containing gas;
• and
• a plurality of middle flame holders extending between an outlet section of the inner gas nozzle and an outlet section of the outer gas nozzle so as to intersect an outlet section of the fuel supply nozzle.

A method of controlling a burner which comprises:

• an inner gas nozzle which extends along an axis while surrounding the axis, and which is capable of supplying a furnace with an inner combustion oxygen containing gas;
• a fuel supply nozzle surrounding the inner gas nozzle as seen in a direction along the axis, the fuel supply nozzle being capable of supplying the furnace with a fluid mixture of a solid powder fuel and a carrier gas;
• an outer gas nozzle surrounding the fuel supply nozzle as seen in the direction along the axis, the outer gas nozzle being capable of supplying the furnace with an outer combustion oxygen containing gas;
• a flow-velocity-ratio adjustment apparatus capable of adjusting a relative flow velocity ratio of a discharge flow velocity of the inner combustion oxygen containing gas to a discharge flow velocity of the outer combustion oxygen containing gas;
• and
• a plurality of middle flame holders extending between an outlet section of the inner gas nozzle and an outlet section of the outer gas nozzle so as to intersect an outlet section of the fuel supply nozzle,
• wherein, at downstream of an outlet of the fuel supply nozzle, flame holding regions are formed on a side of a discharge flow of the inner combustion oxygen containing gas and a side of a discharge flow of the outer combustion oxygen containing gas, respectively, of a discharge flow of the fluid mixture,
• wherein the inner gas nozzle includes two or more inner gas flow passages each of which surrounds the axis as seen in the direction along the axis, and
• wherein the burner further comprises a flow-rate regulator capable of regulating the flow rate of the inner combustion oxygen containing gas flowing through an innermost combustion gas supply flow passage disposed innermost as seen in the direction along the axis from among the two or more inner gas flow passages,
• the method comprising:
• setting an opening of the flow-rate regulator to be smaller when a fuel ratio of the solid powder fuel is higher than a threshold, than when the fuel ratio of the solid powder fuel is not higher than the threshold.