Pulverized coal burner, pulverized coal boiler and method of burning pulverized coal

A powder heating apparatus comprising:

• a combustion chamber for burning pulverized coal in air to produce combustion gases, said combustion chamber including at least one burner each of which comprising:
• a coal duct for pulverized coal and primary air entraining said coal in a flow along said coal duct, said coal duct having an axis and an outlet nozzle at one axial end thereof,
• at least one secondary air duct for secondary air for combustion of said coal having an outlet nozzle adjacent said outlet nozzle of said coal duct, such that said coal and primary air and said secondary air mix outside said nozzles in a mixing zone at which combustion occurs,
• coal distribution means in said coal duct for providing in said flow, along said coal duct adjacent said outlet nozzle thereof, at least one outer zone spaced from said axis having a higher concentration of said coal in said primary air and at least one inner zone nearer said axis than said outer zone having a lower concentration of said coal in said primary air, and
• slowing means for slowing said coal flowing at said higher concentration in said outer zone relative to the flow at said inner zone, prior to said mixing zone;
• a chamber for heating powder;
• and
• means communicating said powder heating chamber with said combustion chamber in that said combustion gases pass to said powder heating chamber.

A boiler for heating water by combustion of pulverized coal comprising a combustion chamber for burning pulverized coal in air and means for heating said water as a result of the combustion of the pulverized coal, said combustion chamber including at least one burner each of which comprising:

• an annular coal duct for a low of pulverized coal and primary air containing said coal, said coal duct having an axis, an outlet nozzle at an axial end thereof, and an outer bounding wall and an inner bounding wall defining an annular flow passage for said flow;
• and
• an annular secondary air duct surrounding said coal duct and having an outlet nozzle around said outlet nozzle of said coal duct,
• wherein a portion of said inner bounding wall close to said outlet nozzle of said coal duct has a frusto-conical shape of diameter reducing in the flow direction along said coal duct, and
• wherein at least one baffle extends inwardly from said outer bounding wall at said outlet nozzle of said coal duct over a radial distance which is not more than 20% of the diameter of said outer bounding wall at the outlet nozzle.

A burner for pulverized coal comprising:

• an annular coal duct for a flow of pulverized coal and primary air containing said coal, said coal duct having an axis, an outlet nozzle at an axial end thereof, and an outer bounding wall and an inner bounding wall defining an annular flow passage for said flow;
• and
• an annular secondary air duct surrounding said coal duct and having an outlet nozzle around said outlet nozzle of said coal duct,
• wherein a portion of said inner bounding wall close to said outlet nozzle of said coal duct has a frusto-conical shape of diameter reducing in the flow direction along said coal duct, and
• wherein at least one baffle extends inwardly from said outer bounding wall at said outlet nozzle of said coal duct over a radial distance which is not more than 20% of the diameter of said outer bounding wall at the outlet nozzle.

A boiler for heating water by combustion of pulverized coal comprising a combustion chamber for burning pulverized coal in air and means for heating said water as a result of the combustion of the pulverized coal, said combustion chamber including at least one burner each of which comprising:

• a coal duct for pulverized coal and primary air entraining said coal in a flow along said coal duct, said coal duct having an axis and an outlet nozzle at an axial end thereof;
• and
• at least one secondary air duct for secondary air for combustion of said coal having an outer nozzle adjacent said outlet nozzle of said coal duct, such that said coal and primary air and said secondary air mix outside said nozzles in a mixing zone at which combustion occurs;
• coal distribution means in said coal duct for providing in said flow, along said coal duct adjacent said outlet nozzle thereof, at least one outer zone spaced from said axis having a higher concentration of said coal in said primary air and at least one inner zone nearer said axis than said outer zone having a lower concentration of said coal in said primary air;
• and
• slowing means for slowing said coal flowing at said higher concentration in said outer zone relative to the flow at said inner zone, prior to said mixing zone.

A burner for pulverized coal comprising:

• an coal duct for pulverized coal and primary air entraining said coal in a flow along said coal duct, said coal duct having an axis and an outlet nozzle at an axial end thereof;
• and
• at least one secondary air duct for secondary air for combustion of said coal having an outer nozzle adjacent said outlet nozzle of said coal duct, such that said col and primary air and said secondary air mix outside said nozzles in a mixing zone at which combustion occurs,
• wherein said coal duct includes over at least part of its length a core portion which provides at least one wall surface bounding said flow in said coal duct, said core portion having, close to said outlet nozzle of said coal duct, a region of gradually reducing cross-section in the direction of said flow such that the flow cross-section in said duct increases gradually in the direction of said flow, and
• wherein said outlet nozzle includes baffle means arranged to interrupt said flow in said coal duct at at least one outer zone thereof spaced from said axis and leave free said flow in said coal duct at at least one inner zone close to said axis than said outer zone, said baffle means having baffle surfaces facing said flow in said coal duct at an angle in the range 90.degree. to 120.degree. with respect to the axial direction of said flow.

A boiler for heating water by combustion of pulverized coal comprising a combustion chamber for burning pulverized coal in air and means for heating said water as a result of the combustion of the pulverized coal, said combustion chamber including at least one burner each of which comprising:

• an coal duct for pulverized coal and primary air entraining said coal in a flow along said coal duct, said coal duct having an axis and an outlet nozzle at an axial end thereof;
• and
• at least one secondary air duct for secondary air for combustion of said coal having an outer nozzle adjacent said outlet nozzle of said coal duct, such that said coal and primary air and said secondary air mix outside said nozzles in a mixing zone at which combustion occurs,
• wherein said coal duct includes over at least part of its length a core portion which provides at least one wall surface bounding said flow in said coal duct, said core portion having, close to said outlet nozzle of said coal duct, a region of gradually reducing cross-section in the direction of said flow such that the flow cross-section in said duct increases gradually in the direction of said flow, and
• wherein said outlet nozzle includes baffle means arranged to interrupt said flow in said coal duct at at least one outer zone thereof spaced from said axis and leave free said flow in said coal duct at at least one inner zone closer to said axis than said outer zone, said baffle means having baffle surfaces facing said flow in said coal duct at an angle in the range 90.degree. to 120.degree. with respect to the axial direction of said flow.