An air nozzle arrangement for a fluidized bed boiler, comprising an air feed pipe and an air nozzle which limit an air feed duct configured to supply air to the furnace of the fluidized bed boiler. The air nozzle arrangement comprises a surface configured to guide coarse material along said surface. At least part of said surface is thermally insulated from the air nozzle and/or the air feed pipe. Furthermore, at least part of said surface is configured to protect at least part of said air nozzle and/or air feed pipe. Thus, the temperature of said surface is configured to be high when the fluidized bed boiler is in operation, whereby the solidification of molten material of the fluidized bed in the air nozzle arrangement is reduced.

A furnace including a combustion chamber for burning fuel can have increased fuel burning efficiency, increased heating efficiency, and decreased harmful emissions of combustion byproducts. A combustion air delivery system delivers primary and secondary combustion air to the combustion chamber. Primary and secondary combustion air may be delivered at amounts that increase burning efficiency. An amount of secondary combustion air can be controlled by a valve system. A heat transfer device efficiently transfers heat from products of combustion for heating an enclosed space.

A gas burner, comprising: gas outlet openings arranged in a ring for providing flames directed towards an interior of the ring; and at least one lower secondary air outlet located below the gas outlet openings for providing secondary air along an interior side of the flames.

A gas burner, comprising: gas outlet openings arranged in a ring for providing flames directed towards an interior of the ring; and at least one lower secondary air outlet located below the gas outlet openings for providing secondary air along an interior side of the flames.

A combustion apparatus includes a housing and injection members. The housing has a bottom wall and side walls which enclose a combustion chamber having an opening at the top. The injection members are arranged on two side walls opposite each other and include at least one first injector and at least one second injector. The first injector supplies to the combustion chamber a mixture having a first-part oxidant and a combustible gas, with the volume percentage of the combustible gas in the mixture being greater than an upper combustion limit of the combustible gas. The second injector supplies a second-part oxidant to the combustion chamber. The total amount of the first-part oxidant and the second-part oxidant supplied to the combustion chamber reach stoichiometric balance with the amount of the combustible gas supplied to the combustion chamber. The combustion apparatus can produce short flames with high safety and good stability.

A burner including a first burner element having a first annular oxidant nozzle surrounding a first inner fuel nozzle; a second burner element having a second annular oxidant nozzle surrounding a second inner fuel nozzle, the second burner element being positioned adjacent to and spaced apart from the first burner element; a staging nozzle configured to flow secondary oxidant and being positioned adjacent to and spaced apart from the second burner element and separated from the first burner element by the second burner element; wherein the first inner nozzle and the second inner nozzle each have a major axis defined by a length L and a minor axis defined by a height h.sub.f; wherein 5<=L/h.sub.f<=15; wherein the staging nozzle has a major axis; and wherein the major axes of the first and second inner nozzles and the staging nozzle are substantially parallel with each other.

A burner including a first burner element having a first annular oxidant nozzle surrounding a first inner fuel nozzle; a second burner element having a second annular oxidant nozzle surrounding a second inner fuel nozzle, the second burner element being positioned adjacent to and spaced apart from the first burner element; a staging nozzle configured to flow secondary oxidant and being positioned adjacent to and spaced apart from the second burner element and separated from the first burner element by the second burner element; wherein the first inner nozzle and the second inner nozzle each have a major axis defined by a length L and a minor axis defined by a height h.sub.f; wherein 5<=L/h.sub.f<=15; wherein the staging nozzle has a major axis; and wherein the major axes of the first and second inner nozzles and the staging nozzle are substantially parallel with each other.

A radiant tube burner, wherein an opening cross section of the tube is virtually divided into four areas with two straight lines as boundaries, the two straight lines being obtained by tilting a minor axis of the oval, which is a shape of the opening cross section, by 45 with a center of the oval as a center, and a flow rate of primary combustion air injected from primary combustion air nozzles located in the areas containing the minor axis of the oval of the virtually divided four areas is lower than a flow rate of the primary combustion air injected from the primary combustion air nozzles located in the areas not containing the minor axis of the oval the four areas.

A radiant tube burner, wherein an opening cross section of the tube is virtually divided into four areas with two straight lines as boundaries, the two straight lines being obtained by tilting a minor axis of the oval, which is a shape of the opening cross section, by 45 with a center of the oval as a center, and a flow rate of primary combustion air injected from primary combustion air nozzles located in the areas containing the minor axis of the oval of the virtually divided four areas is lower than a flow rate of the primary combustion air injected from the primary combustion air nozzles located in the areas not containing the minor axis of the oval the four areas.