Burner for reducing NOX emissions and method for operating the burner

Abstract

The invention relates to a burner (10; 11; 12) for heating a heating space (55; 55'), with reduction of NOx emissions. The burner (10; 11; 12) comprises a mixing and combustion chamber (54; 54'), a mixing and igniting device (51) which is arranged in the mixing and combustion chamber (54; 54'), and a fuel supply (50) which is connected to the mixing and igniting device (51) and is designed to supply fuel to the mixing and igniting device (51). Furthermore, an air supply (30, 30') is provided, which is designed to supply at least one partial air flow (L1) to the mixing and combustion chamber (54; 54'). A combustion chamber opening (53; 53') opens the mixing and combustion chamber (54; 54') toward a heating space (55; 55') to be heated. In addition, control means (60) are designed to control a fuel flow (B) via the fuel supply (50) and to control at least one partial air flow (L1) via the air supply (30; 30'), the burner (10; 11; 12) and the control means (60) being designed for operation of the burner (10; 11; 12) with a stable flame (56; 56') which extends from the mixing and igniting device (51) into the heating space (55; 55') through the combustion chamber opening (53; 53'). The cross-sectional area of the combustion chamber opening (53; 53'), which area is relative to the burner power, lies in the range between 1.5 mm2 / kW and 10 mm2 / kW.

Description

[0001] The invention relates to a burner for heating a boiler room with a reduction in NOx emissions, comprising a mixing and combustion chamber and a combustion chamber opening that opens the mixing and combustion chamber towards the boiler room to be heated. A flame is generated in the mixing and combustion chamber, the heat from which is used to heat the boiler room. The invention further relates to a method for operating such a burner.

[0002] These types of burners are used particularly for heating furnace chambers in industrial thermal processing plants, such as chamber furnaces for heat treatment, bogie hearth furnaces for heating and forging, roller hearth furnaces, or rotary hearth furnaces. However, these examples are merely illustrative, as the applications of such industrial burners are manifold.

[0003] The burners are operated with a gaseous or liquid fuel together with air or oxygen. Increasingly, pulse or high-performance burners are used, in which fuel and air are mixed and ignited in a combustion chamber. The resulting hot combustion gases flow at high speed through a combustion chamber opening into the heating chamber. This heating chamber can be the furnace chamber itself or a radiant tube that extends gas-tight through a furnace wall into the furnace chamber.

[0004] The aim is to achieve the lowest possible NOₓ levels during combustion, which, however, depends on various interacting parameters. For example, operating an industrial burner in two modes has proven advantageous, with the second mode involving flameless oxidation, which enables low NOₓ levels.

[0005] For example, EP 0 685 683 B1, which forms the basis for the two-part design, discloses an industrial burner that can be switched between a start-up mode with a flame inside a mixing and combustion chamber and a heating mode with flameless oxidation outside the mixing and combustion chamber. For this purpose, two different fuel nozzle assemblies are provided, with which fuel can be selectively directed either into the mixing and combustion chamber (start-up mode) or to the vicinity of a combustion chamber outlet opening (heating mode). The switch between start-up and heating modes occurs after a predetermined temperature is reached in the heating chamber, this temperature being above the ignition temperature of the fuel / air mixture so that the mixture can burn for flameless oxidation without additional ignition in the area of ​​the combustion chamber outlet opening.

[0006] This type of industrial furnace, however, requires two separate fuel feeds and a switchover during high-temperature operation. Furthermore, due to flameless oxidation, it cannot achieve its low NOx emissions in areas of a boiler room that do not reach, or have not yet reached, the specified ignition temperature. Additionally, the industrial furnace requires complex monitoring because the flame in the mixing and combustion chamber goes out after switching to heating operation, meaning the furnace can no longer be monitored by detecting the presence of this flame.

[0007] Other burners of this type are described in EP 0 164 576 A2, EP 2 498 002 A1 and EP 2 778 521 A2.

[0008] The object of the invention is therefore to provide a burner and a method for operating the burner with which low NO x values ​​can be achieved while avoiding, in particular, the aforementioned disadvantages.

[0009] According to the invention, this problem is solved by a burner according to independent claim 1. Advantageous embodiments of the burner are described in dependent claims 2-9.

[0010] The invention is further solved by a method for operating such a burner according to claim 10 and an advantageous embodiment of the method according to claim 11. It should be noted that the features listed individually in the claims can be combined with one another in any technically sensible manner and demonstrate further embodiments of the invention within the scope of the claims. The description further characterizes and specifies the invention, particularly in conjunction with the figures.

[0011] The burner according to the invention can be used to heat a heating chamber, which may be, for example, a furnace chamber or a radiant tube projecting into a furnace chamber to be heated. The burner can therefore be operated with an open combustion system or a radiant tube. Various types of radiant tubes can be used. For example, a SER-type (Single Ended Radiant Tube) radiant tube can be used. However, P-type or DP-type radiant tubes can also be used. Preferably, a furnace chamber is equipped with several burners. This is an industrial burner, which is used in particular for the direct heating of furnace chambers in industrial thermal processing plants. The design and operation of the burner according to the invention reduce NOx emissions, and the burner also offers further advantages.

[0012] The burner according to the invention comprises a mixing and combustion chamber within which a mixing and ignition device is arranged. A fuel supply is connected to the mixing and ignition device and is designed to supply fuel to the mixing and ignition device. Furthermore, an air supply is provided, which is designed to supply a first partial air flow to the mixing and combustion chamber. The burner is operated with air and a fuel that is liquid or, preferably, gaseous. For example, natural gas is used. The mixing and combustion chamber opens to the heating chamber via a combustion chamber opening.

[0013] Furthermore, the burner includes control means designed to control a fuel flow B via the fuel supply and to control at least a partial air flow via the air supply. The burner and these control means are designed to operate the burner with a stable flame that extends from the mixing and ignition device through the combustion chamber opening into the boiler room. Such an elongated flame exhibits flame zones with different characteristics. At a minimum, there is a first flame zone within the mixing and combustion chamber, which can be detected, for example, by an ionization electrode. Outside the combustion chamber opening, a second flame zone is formed, characterized by the high velocity of the exiting streams.

[0014] According to the invention, the cross-sectional area of ​​the combustion chamber opening, related to the burner output, lies in the range between 1.5 mm² / kW and 10 mm² / kW. In one embodiment of the invention, the cross-sectional area of ​​the combustion chamber opening, related to the burner output, lies in the range between 1.5 mm² / kW and 8 mm² / kW, preferably between 1.5 mm² / kW and 6 mm² / kW, and particularly preferably between 1.5 mm² / kW and 5 mm² / kW.

[0015] These values ​​allow for very high exhaust velocities in the combustion chamber opening area, which in turn draws exhaust gases from the boiler room into the flame in this area to a greater extent. The cross-section of the combustion chamber opening is chosen to be significantly smaller than in known burners. For example, in known air / fuel burners, cross-sectional areas of the combustion chamber opening, relative to the burner output, often exceed 10 mm² / kW. A significant reduction of this value is avoided because experience has shown that the flame can then no longer be operated stably and reliably. However, the invention is based on the understanding that, with suitable burner design and operation, values ​​significantly below 10 mm² / kW can also be achieved. This is particularly true when combined with the generation of a stable flame in the area of ​​the ignition and mixing device.The control means and the mixing and ignition device are therefore designed to generate a stable flame in the mixing and combustion chamber.

[0016] The invention results in higher exhaust velocities at the combustion chamber opening, which in turn enhances the intake of exhaust gases from the boiler room, thereby reducing NOx emissions. NOx values ​​in the range of 5 to 100 mg / Nm³ or, with a SER jet tube, 50 to 150 mg / Nm³ based on 3% O₂ in the dry exhaust gas can be achieved. Furthermore, the increased exhaust velocities, particularly with a long SER jet tube, improve the temperature profile in the boiler room.

[0017] The invention further has the advantage that the stable flame in the area of ​​the mixing and ignition device can be continuously detected and thus monitored. In one embodiment of the invention, flame monitoring devices are therefore provided in the mixing and combustion chamber, designed to detect a flame in the area of ​​the mixing and ignition device. These flame monitoring devices are, for example, an ionization bar that projects into the area of ​​the flame. The flame monitoring devices are used to monitor the presence of the flame in the mixing and combustion chamber, which is comparatively simple and reliable compared to solutions with high-temperature switching.

[0018] The burner's function can thus be easily monitored by detecting the presence of a flame in the combustion chamber. The invention therefore offers the possibility of achieving low NOx values ​​in the range of 5 to 100 mg / Nm³ or 50 to 150 mg / Nm³ based on 3% O₂ in dry exhaust gas, particularly without having to use flameless oxidation, the monitoring of which is complex and comparatively unreliable, since there is no monitorable flame.

[0019] Furthermore, with the burner according to the invention, NOx reduction is possible even at a heating chamber temperature of approximately 300 to 500 °C, whereas with flameless oxidation this is only possible at temperatures of approximately 800 °C. Thus, the burner according to the invention can be advantageously used in areas of a thermal processing plant where high performance is required, but the temperature in the area to be heated does not yet exceed 800 °C. For example, the burner according to the invention is fully effective in the high-performance first zones of a continuous furnace.

[0020] Preferably, a recuperator is also provided, which at least partially surrounds the burner's air supply. However, the invention can also be used with burner designs without a recuperator. Such recuperators can be designed in a variety of ways and essentially comprise means for receiving hot exhaust gases from a combustion chamber into the recuperator. Furthermore, they comprise means for supplying combustion air to the recuperator and for heating this combustion air by means of the hot exhaust gases passed through the recuperator. The recuperator is designed to achieve suitable heat transfer between the hot exhaust gases and the supplied combustion air. A second airflow L2 can thus be supplied via the recuperator to the mixing and combustion chamber or to the combustion chamber outside the mixing and combustion chamber.Whether this second airflow L2 is supplied from the recuperator of the mixing and combustion chamber or directly to the boiler room to be heated depends on the burner design. The first airflow L1 can optionally also be preheated by the recuperator.

[0021] The achievable cross-sectional areas of the combustion chamber opening also depend significantly on the design of the burner with recuperator, since the combustion air preheated by the recuperator can be supplied via various combustion methods. In one embodiment of the invention, the air supply is formed, for example, by an air supply pipe within which the mixing and ignition device is arranged such that the mixing and combustion chamber is formed. The air supply pipe thus forms the combustion chamber opening. With such a design, very small diameters for the combustion chamber opening can be achieved, with the cross-sectional area of ​​the combustion chamber opening, relative to the burner output, being, for example, in the range between 1.5 mm² / kW and 5 mm² / kW, and particularly preferably between 2.5 mm² / kW and 3.5 mm² / kW.

[0022] In a design with a recuperator, the second air flow L2 is directed from the recuperator into the boiler room. Instead of a second, preheated air flow L2 being fed directly into the mixing and combustion chamber, this second air flow L2 is directed to the flame area outside the mixing and combustion chamber.

[0023] In another design of the burner with recuperator, the air supply is also formed by an air supply pipe, within which the mixing and ignition device is arranged such that the mixing and combustion chamber is formed. In this embodiment, however, the recuperator forms the combustion chamber opening, while the second, preheated air partial flow L2 is preferably also directed from the recuperator into the mixing and combustion chamber. The total air flow into the mixing and combustion chamber is thus higher than in the previously described embodiment, but very small diameters for the combustion chamber opening can still be achieved, with the cross-section of the combustion chamber opening, relative to the burner output, being in the range between 3 mm² / kW and 10 mm² / kW, particularly preferably between 3 mm² / kW and 6 mm² / kW.

[0024] According to the invention, the control means are further configured to increase the ratio of fuel flow B to air flow after reaching a predetermined parameter value. In designs with a recuperator and thus multiple air partial flows, the ratio of fuel flow B to the sum of the first and second, preheated air flows is varied, in particular increased. According to the invention, the control means are configured to increase the fuel flow B after reaching a predetermined parameter value while maintaining an approximately constant air flow (in particular, the sum of the first and second, preheated air flows).

[0025] According to the invention, the predetermined parameter value is a temperature value, wherein it is a reference temperature in a room to be heated or in a specific zone within the room to be heated (zone temperature). The reference temperature is selected or experimentally determined such that, for example, when using natural gas as fuel, the ratio of fuel flow B to air flow can be changed from 1:20 to 1:10 according to the invention from this temperature onwards. This temperature is, for example, between 200°C and 500°C. Other suitable mixing ratios may result with other gaseous fuels, so that the specified change in the mixing ratio for natural gas serves only as an example to illustrate the invention.

[0026] With this type of control mechanism, it is possible to start the burner in its cold state with a fuel flow ratio (B) to air flow (specifically, the sum of the first and second, preheated air flows) of 1:20. This allows for the formation of a stable flame that extends through the combustion chamber opening into the heating chamber. As the burner and furnace heat up during operation, the ratio can be increased to 1:10 without destabilizing the flame. The burner is preferably initially operated at half power with full air volume and can then be operated at full power once certain temperature conditions are reached, which also ensure sufficient flame stabilization. In this way, a stable flame can be generated at the various heating stages of the burner, despite the high exit velocity in the combustion chamber opening.

[0027] Optionally, the burner includes means to switch to flameless oxidation operation. For this purpose, means for redirecting the fuel flow and / or the initial air flow are provided. When activated by the control system, these redirections destabilize and extinguish the flame. The burner is further designed so that flameless oxidation of fuel and air then occurs outside the combustion chamber opening, with the mixture exiting the chamber at high velocity. This requires that the temperature in this area has reached a value above the ignition temperature of the mixture, i.e., approximately 800°C. Appropriate temperature monitoring devices, connected to the control system, are provided for this purpose.Even in this flameless oxidation process, the increased exit velocities of fuel and air at the combustion chamber opening result in a beneficial intake of exhaust gases to an increased degree, which in turn reduces NOx levels.

[0028] Such a flow deflection for switching to flameless oxidation can be achieved, for example, by an extended fuel lance that projects into the area of ​​the combustion chamber opening, as proposed in EP 0 685 683 B1. It is also possible to control a modified fuel outlet from the ignition and mixing device.

[0029] The invention also includes a method for operating a burner according to an embodiment of the invention, in which the control means control a fuel flow and at least a partial air flow in such a way that a stable flame is formed, which extends from the mixing and ignition device through the combustion chamber opening into the heating chamber.

[0030] During the heating phase, the procedure includes the measure that, once a predetermined parameter value is reached, the control system increases the ratio of fuel flow to air flow. This is achieved by increasing the fuel flow while maintaining a nearly constant air flow, as previously described. The control system changes the fuel flow to air flow ratio from 1:20 to 1:10. In designs with a recuperator, the aforementioned air flow consists of a first and second air flow. Consequently, the procedure also assumes that the predetermined parameter value is a temperature in the room to be heated, and that this temperature lies between 200°C and 500°C. This procedure offers the advantages mentioned above.

[0031] For an optional switch to flameless oxidation operation, one embodiment of the method provides that a temperature TH of the combustion chamber is determined and, upon reaching a predetermined temperature TH above the ignition temperature of the fuel / air mixture, the flow of the fuel stream and / or the first air stream is redirected in such a way that the flame is destabilized and extinguished, and then flameless oxidation of the fuel and air exiting the combustion chamber opening takes place outside the combustion chamber opening. This method has the aforementioned advantages.

[0032] Further advantages, special features and expedient further developments of the invention will become apparent from the dependent claims and the following presentation of preferred embodiments with reference to the illustrations.

[0033] The illustrations show: Fig. 1 shows a schematic section through a first embodiment of a burner according to the invention; Fig. 2 shows a flow diagram of an embodiment of control means for controlling a burner; Fig. 3 shows a schematic section through a second embodiment of a burner according to the invention; and Fig. 4 shows a schematic section through a third embodiment of a burner according to the invention.

[0034] Fig. 1 Figure 1 schematically shows a first embodiment of a burner 10 according to the invention, which is used to illustrate the essential features of the invention. However, the design of the burner is not to be understood as limiting. Fig. 1 It only provides a schematic representation of the components and component dimensions. The same applies to the Figuren 3 and 4 , which show further embodiments. Designs without a recuperator are also included.

[0035] The burner 10 is installed in a furnace wall 20 and generates a flame 56, which is used to heat a heating chamber 55. In this embodiment, it is an open flame that directly heats the heating chamber 55. However, other embodiments with indirect heating are also possible, in which a radiant tube is used. One such embodiment is shown. Fig. 4 .

[0036] The burner 10 has a mixing and combustion chamber 54, which is formed by an air supply 30 in the form of an air supply pipe. Combustion air is introduced into this air supply 30 (not shown) and flows as the first partial air flow L1 into the mixing and combustion chamber 54. An ignition and mixing device 51 is located inside this air supply pipe 30 and is connected to a fuel supply 50, through which fuel is supplied to the ignition and mixing device 51. The fuel is, for example, natural gas.

[0037] The ignition and mixing device 51 is suitably designed such that the fuel exits it in such a way that a stable flame 56 can be produced by igniting the mixture of fuel stream B and first partial air stream L1. In the schematic representation of the Fig. 1 For this purpose, several fuel streams exit the ignition and mixing device 51 laterally at an angle, but this is not to be understood as a limitation. Any other suitable ignition and mixing device 51 can also be used.

[0038] In this embodiment, the burner further comprises a recuperator 40, which surrounds the air supply pipe 30. Hot exhaust gases A1 are drawn from the combustion chamber 55 into the recuperator 40, and a second air stream L2 is heated in counterflow. Optionally, the first air stream L1 can also be preheated in the recuperator 40. The second, preheated air stream L2 is supplied to the combustion chamber 55. This occurs within the area of ​​an elongated flame 56, which has different flame zones. A first flame zone 56a is located within the mixing and combustion chamber 54, with the air supply pipe 30 forming a combustion chamber opening 53 through which the flame 56 extends from the ignition and mixing device 51. A second flame zone 56b forms in the combustion chamber 55 in front of the combustion chamber opening 53. The second, preheated air partial flow L2 from the recuperator 40 is supplied to this flame area 56b.At the same time, hot exhaust gases A2 from the boiler room 55 are drawn into the flame area 56b.

[0039] In this burner design, the cross-sectional area of ​​the combustion chamber opening 53, relative to the burner output, is in the range of 1.5 mm² / kW to 5 mm² / kW, particularly preferably between 2.5 mm² / kW and 3.5 mm² / kW. This results in high exhaust velocities at the combustion chamber opening 53, which in turn lead to low NOx values ​​in the flame region 56b. Combined with the NOx formation of the flame 56 within the mixing and combustion chamber, overall low NOx values ​​in the range of 5 to 100 mg / Nm³ (based on 3% O₂) in the dry exhaust gas can be achieved with open combustion. Furthermore, the flame 56 can be easily monitored, for which purpose an ionization rod 52 is provided in the mixing and combustion chamber 54, which can be used to detect the presence of the flame 56.

[0040] To put the burner into operating mode Fig. 1 To achieve this, a preheating phase is carried out with specific control of fuel flow B and the air partial flows L1, L2, in order to generate a stable flame 56 even with a cold burner 10. Control means 60 are provided for this purpose, the design of which is exemplified by the following. Fig. 2 As can be seen from the diagram. A burner 10 is equipped with control devices 60 that enable the supply of fuel and air to the burner 10. The fuel is referred to as gas in the following for simplicity. For the gas flow, a control valve 61, a gas valve 63, a compensator 64, and a ball valve 65 for connection to a gas supply are provided in series from the burner 10 (not shown). For the air flow, a control valve 66, an air valve 67, a compensator 68, and a slide valve 69 for connection to an air supply are provided in series from the burner 10 (not shown). A constant pressure regulator 62 with a gas valve and another gas valve 62a in bypass are connected in parallel between the control valve 61 and the gas valve 63. A pulse line 70 branches off between the control valve 66 and the air valve 67 to the constant pressure regulator 62 with the gas valve.

[0041] These control methods initially activate the burner in its cold state with a

[0042] The fuel-to-air ratio is initially set to approximately 1:20, which enables the formation of a stable flame 56. The full air volume is already supplied, while the fuel flow via valve 62a is initially reduced. Depending on the burner 10 design and the ambient conditions in the furnace, the fuel flow will be increased from a predetermined temperature, as the flame 56 now stabilizes even with a higher fuel content. At this temperature, the fuel flow is switched from valve 62a to valve 62, thus increasing the fuel flow and establishing a fuel-to-air ratio of approximately 1:10.

[0043] Fig. 3 Figure 1 shows an alternative embodiment of the burner 11 according to the invention, in which, however, the recuperator 40 forms the combustion chamber opening 53'. Thus, the second air partial flow L2', preheated in the recuperator 40', flows together with the first air partial flow L1 into the mixing and combustion chamber 54'. The flame 56 with the two flame regions 56a and 56b is formed analogously, and the other components also correspond to the embodiment of the Fig. 1 . Only the cross-section of the combustion chamber opening 53', which is related to the burner output, lies here in the range between 3 mm 2< / kW and 10 mm 2< / kW, particularly preferably between 3 mm 2< / kW and 6 mm 2< / kW.

[0044] Fig. 4 shows a burner 12 according to the embodiment of the Fig. 3, in which a heating chamber 55' is arranged within a flame tube 42. The flame tube 42 is surrounded by a radiant tube 41, which projects from the furnace wall 20 into the furnace interior for indirect heating. The flame tube 42 within the radiant tube 41 allows the flow of hot exhaust gases A3 back to the burner 12, whereby they are either fed to the recuperator as exhaust gases A1 or drawn in by the flame area 56b as exhaust gases A2. When using, for example, a SER radiant tube, NOx values ​​in the range of 50 to 150 mg / Nm³ based on 3% O₂ in the dry exhaust gas can be achieved with the invention. Reference symbol list:

[0045] 10, 11, 12 Burner 20 Furnace wall 30, 30' Air supply, air supply pipe 40, 40' Recuperator 41 Radiant tube 42 Flame tube 50 Fuel supply 51 Mixing and ignition device 52 Flame monitoring device, ionization rod 53 Burner chamber opening 54, 54' Mixing and combustion chamber 55, 55' Boiler room 56 Flame 56a, 56b Flame area 60 Control device 61 Gas adjusting valve 62 Constant pressure regulator with gas valve V2 62a Gas valve bypass 63 Gas valve V1 64 Compensator 65 Ball valve 66 Air adjusting valve 67 Air valve 68 Compensator 69 Slide valve 70 Impulse line L1 Air partial flow L2 Air partial flow, preheated B Fuel flow A1 Exhaust gas flow in recuperator A2 Exhaust gas flow in flame A3 Exhaust gas flow recirculation

Claims

1. Burner (10; 11; 12) for heating a heating chamber (55; 55') with reduction of NOx emissions, comprising: a mixing and combustion chamber (54;54'); a mixing and ignition device (51) which is arranged in the mixing and combustion chamber (54; 54'); a fuel supply (50) which is connected to the mixing and ignition device (51) and is designed to supply fuel to the mixing and ignition device (51); an air supply (30; 30') which is designed to supply at least one air partial flow (L1) to the mixing and combustion chamber (54; 54'); a combustion chamber opening (53; 53') which opens the mixing and combustion chamber (54; 54') towards a heating chamber (55; 55') to be heated; control means (60) which are designed to control a fuel flow (B) via the fuel supply (50) and to control at least one air partial flow (L1) via the air supply (30; 30'), wherein the burner (10; 11; 12) and the control means (60) are designed to operate the burner (10; 11; 12) with a stable flame (56; 56') which extends from the mixing and ignition device (51) through the combustion chamber opening (53; 53') into the heating chamber (55; 55'); wherein the cross section of the combustion chamber opening (53; 53') related to the burner power lies between 1.5 mm2 / kW and 10 mm2 / kW, characterized in that the control means (60) are designed to set a ratio of fuel flow to air flow of 1:20 when starting up the burner (10; 11; 12) in the cold state and, after reaching a predetermined temperature in the heating chamber (55; 55'), to increase the fuel flow (B) at approximately the same air flow, in order that a fuel flow to air flow ratio of 1:10 is set.

2. Burner according to Claim 1, wherein the cross section of the combustion chamber opening (53; 53') related to the burner power lies in the range between 1.5 mm2 / kW and 8 mm2 / kW, preferably between 1.5 mm2 / kW and 6 mm2 / kW, particularly preferably between 1.5 mm2 / kW and 5 mm2 / kW.

3. Burner according to Claim 1 or 2, wherein the air supply is formed by an air supply pipe (30), within which the mixing and ignition device (51) is arranged in such a way that the mixing and combustion chamber (54) is formed, and that the air supply pipe (30) forms the combustion chamber opening (53).

4. Burner according to Claim 3, wherein the cross section of the combustion chamber opening (53) related to the burner power lies in the range between 1.5 mm2 / kW and 5 mm2 / kW, particularly preferably between 2.5 mm2 / kW and 3.5 mm2 / kW.

5. Burner according to one of Claims 1 to 4, wherein it has a recuperator (40; 40') which at least partially surrounds the air supply (30; 30') and via which a second air partial flow (L2) can be supplied to the mixing and combustion chamber (54; 54') or the heating chamber (55; 55') outside the mixing and combustion chamber (54).

6. Burner according to Claim 5, wherein the air supply is formed by an air supply pipe (30'), within which the mixing and ignition device (51) is arranged in such a way that the mixing and combustion chamber (54') is formed, and that the recuperator (40') forms the combustion chamber opening (53'), while the second air partial flow (L2) is directed from the recuperator (40) into the mixing and combustion chamber (54').

7. Burner according to Claim 6, wherein the cross section of the combustion chamber opening (53') related to the burner power lies in the range between 3 mm2 / kW and 10 mm2 / kW, particularly preferably between 3 mm2 / kW and 6 mm2 / kW.

8. Burner according to one of Claims 1 to 7, wherein provided in the mixing and combustion chamber (54; 54') are flame monitoring means (52) which are designed for the detection of a flame (56; 56') in the region of the mixing and ignition device (51).

9. Burner according to one of Claims 1 to 8, wherein means are provided for the flow deflection of the fuel flow (B) and / or the first air partial flow (L1), upon the activation of which by the control means (60) the flame (56; 56') is destabilized and extinguished, and the burner (10; 11; 12) is designed in such a way that a flameless oxidation of fuel and air, which emerge from the combustion chamber opening (53; 53'), then takes place outside the combustion chamber opening (53; 53').

10. Method for operating a burner according to one or more of Claims 1 to 9, in which method the control means (60) actuate a fuel flow (B) and at least one air partial flow (L1) in such a way that a stable flame (56; 56') is formed, which extends from the mixing and ignition device (51) through the combustion chamber opening (53; 53') into the heating chamber (55; 55'), wherein the control means (60) set a ratio of fuel flow to air flow of 1:20 when starting up the burner (10; 11; 12) in the cold state and, after reaching a predetermined temperature in the heating chamber (55; 55'), increase the fuel flow (B) with approximately the same air flow to set a ratio of fuel flow to air flow of 1:10.

11. Method according to Claim 10, wherein the temperature TH of the heating chamber (55; 55') is determined and, when a predetermined temperature TH above the ignition temperature of the fuel / air mixture is reached, the flow of the fuel flow (B) and / or the first air partial flow (L1) is deflected in such a way that the flame (56; 56') is destabilized and extinguished, and a flameless oxidation of fuel and air, which emerges from the combustion chamber opening (53;53'), then takes place outside the combustion chamber opening (53; 53').

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