Mixing device and burner head for a burner with reduced nox emissions

1. A mixing device ( 10 ) for a burner ( 16 ) having reduced NOx production, comprising:

a first mixing unit ( 18 ) arranged centrally for producing a first fuel-air mixture for a primary flame zone ( 120 ), wherein the first mixing unit ( 18 ) has at least one first fuel nozzle ( 38 ) and a baffle plate ( 40 );

a second mixing unit ( 20 ) for producing a second fuel-air mixture for a secondary flame zone ( 122 ), which encloses the primary flame zone ( 120 ), wherein the second mixing unit ( 20 ) has multiple second fuel nozzles ( 70 ), and wherein the second mixing unit ( 20 ) is designed to deliver the second fuel-air mixture into the secondary flame zone ( 122 );

a third mixing unit ( 22 ) for premixing and swirling a third fuel-air mixture and for delivering the premixed and swirled third fuel-air mixture into a swirled flame zone ( 124 ), which is arranged between the primary flame zone ( 120 ) and the secondary flame zone ( 122 ); and

a sealing air producing unit ( 24 ) arranged downstream of the baffle plate ( 40 ) for producing a sealing air flow in a sealing air zone ( 126 ), which encloses the primary flame zone ( 120 ) of the first mixing unit ( 18 ) and is enclosed by the swirled flame zone ( 124 ) of the third mixing unit ( 22 ).

2. The mixing device according to claim 1 , characterized in that the third mixing unit is arranged, in particular radially, between the sealing air producing unit ( 24 ) and the second mixing unit ( 20 ) and has a swirl generator ( 76 ) and at least one third fuel nozzle ( 74 ), which is arranged upstream of the swirl generator ( 76 ) in a premixing zone ( 78 ), through which an air flow flows to the swirl generator ( 76 ), to premix fuel from the third fuel nozzle ( 74 ) with the air flow before the swirl generation.

3. The mixing device according to claim 2 , characterized in that a baffle plate construction ( 132 ) is provided which has, viewed from a centre of the mixing device ( 10 ) outward, in this sequence:

the baffle plate ( 40 ) having at least one opening ( 50 ) for the first fuel nozzle ( 38 );

a sealing air duct for producing the sealing air flow, provided with at least one first partition wall ( 54 ) for partitioning the sealing air flow in relation to the primary flame zone and/or a second partition wall ( 56 ) for partitioning the sealing air flow in relation to the outlet of the swirl generator;

the swirl generator ( 76 ); and

a guiding unit ( 88 ) for delimiting an outer air gap ( 119 ) for the second mixing unit ( 20 ).

4. The mixing device according to claim 1 , characterized in that the baffle plate ( 40 ) is designed to produce a swirl in the primary flame zone ( 120 ).

5. The mixing device ( 10 ) according to claim 1 , characterized in that a positioning unit ( 100 ) is provided for increasing or reducing in size an air gap ( 119 ), wherein the positioning unit ( 100 ) is designed to change the size of the air gap ( 119 ) in dependence on a load operating state.

6. The mixing device according to claim 5 , characterized in that the positioning unit is designed to change the size of the air gap by changing the axial location of at least a part of the first mixing unit ( 18 ) and/or the sealing air producing unit ( 24 ) and/or the swirl generator ( 76 ) and/or an air guiding unit ( 88 ).

7. The mixing device ( 10 ) according to claim 1 , characterized by a fuel supply unit ( 26 ) for supplying the first, second, and third mixing units ( 18 , 20 , 22 ) with fuel, wherein the fuel supply unit ( 26 ) is designed in such a way that the ratio of the fuel quantities flowing to the second and third mixing units ( 20 , 22 ) is changeable.

8. The mixing device ( 10 ) according to claim 7 , characterized by at least one, multiple, or all of the following features:

a fuel supply controller is provided for controlling the fuel supply unit ( 26 ), wherein the fuel supply controller is designed in such a way that a fuel supply ( 28 ) to the third mixing unit ( 22 ) is throttled or closed in a part-load mode and is open in a full-load mode;

the fuel supply unit ( 26 ) has a control valve ( 104 ) for changing a flow cross section of a fuel supply line ( 36 ) of the at least one third fuel nozzle ( 74 ); and/or

a positioning element ( 106 ) of the control valve ( 104 ) is coupled to the positioning unit ( 100 ) for joint movement.

9. The mixing device ( 10 ) according to claim 1 , characterized in that the sealing air producing unit ( 24 ) has a ring body ( 52 ) having a ring duct ( 58 ) for the sealing air.

10. The mixing device ( 10 ) according to claim 9 , characterized by at least one, multiple, or all of the following features:

the ring duct ( 58 ) is formed on a baffle plate ring body ( 64 ), which forms the baffle plate ( 40 ) and the ring body ( 52 );

the swirl generator ( 76 ) has a ring-shaped arrangement ( 82 ) of swirl generating blades ( 80 ) arranged around the ring duct ( 58 ); and/or

the arrangement ( 82 ) of swirl generating blades ( 80 ) is formed on the ring body ( 52 ).

11. A burner head ( 14 ) for a burner ( 16 ) having reduced NOx production, comprising a burner tube ( 12 ) and the mixing device ( 10 ) of claim 1 arranged in the burner tube ( 12 ).

12. The burner head ( 14 ) according to claim 11 , having the mixing device of claim 3 , wherein the outer air gap ( 119 ) for delivering the second fuel-air mixture of the second mixing unit ( 20 ) is delimited on the outside by a region of the burner tube ( 12 ).

13. A burner ( 16 ) having the mixing device ( 10 ) of claim 1 .

14. A method for combusting a fuel having reduced NOx production, comprising:

providing a first fuel-air mixture for producing a central primary flame in a central primary flame zone ( 120 ) by means of a first fuel nozzle ( 38 ) and a baffle plate ( 40 ) associated with the first fuel nozzle ( 38 );

providing a second fuel-air mixture for producing a secondary flame in an outer secondary flame zone ( 122 ), which encloses the primary flame zone ( 120 ), by means of a second fuel nozzle ( 70 );

producing a sealing air flow, which encloses the primary flame zone ( 120 ), between the primary flame zone ( 120 ) and the secondary flame zone ( 122 ); and

providing a third fuel-air mixture by premixing fuel and air in a premixing zone ( 78 ), swirling the premixed fuel-air mixture, and delivering the swirled premixed fuel-air mixture into a swirled air zone, which is arranged between the sealing air flow enclosing the primary flame zone ( 120 ) and the secondary flame zone ( 122 ), wherein the swirled premixed fuel-air mixture is provided by a swirl generator ( 76 ) and at least one third fuel nozzle ( 74 ) disposed upstream of the swirl generator ( 76 ).

15. The method according to claim 14 , carried out using the mixing device ( 10 ) claim 1 .

16. The method according to claim 14 , carried out using the burner head ( 14 ) of claim 11 .

17. The method according to claim 14 , carried out using the burner ( 16 ) of claim 13 .

18. The burner head ( 14 ) according to claim 11 , having the mixing device of claim 5 , wherein the outer air gap ( 119 ) for delivering the second fuel-air mixture of the second mixing unit ( 20 ) is delimited on the outside by a region of the burner tube ( 12 ).

19. A burner ( 16 ) having the burner head ( 14 ) of claim 11 .

20. The burner of claim 19 , further having the mixing device ( 10 ) of claim 1 .