EP1559955B1 - Burner - Google Patents

Description

Technical application

The invention relates to a burner according to the preamble of claim 1. A preferred application for such burners are the combustion chambers of gas turbines; Such burners continue to be used, for example, in atmospheric boiler furnaces.

State of the art

From the EP 0 321 809 is a multi-shell conical burner, a so-called double-cone burner, according to the preamble of claim 1 known. By means of the conical swirl generator composed of several shells, a swirl flow is generated in the conical interior enclosed by the partial cone shells. Due to a jump in cross section at a combustion chamber end of the burner, the swirl flow becomes unstable, and turns into an annular swirling flow with backflow in the core. This backflow allows the stabilization of a flame front at the burner outlet. The shells of the swirl generator are assembled in such a way that tangential air inlet slots for combustion air are formed along the burner axis. At the inflow edge of the conical shells formed thereby are feeds for a gaseous premix fuel, provided, which have distributed in the direction of the burner axis outlet openings for the premixed gas. The gas is injected through the outlet openings or bores transversely to the air inlet gap. This injection, in conjunction with the swirl generated in the swirl space of the combustion air-fuel gas flow to a good mixing of the fuel or premixed gas with the combustion air. Good mixing in such premix burners is the prerequisite for low NO _x values during the combustion process.

To further improve such a burner is from the EP 0 780 629 a burner for a heat generator known, which has an additional mixing section for further mixing of fuel and combustion air following the swirl generator. This mixing section can be designed, for example, as a downstream tube, into which the flow emerging from the swirl generator is transferred without appreciable flow losses. Through this additional mixing section, the degree of mixing can be further increased and thus the pollutant emissions can be reduced.

The WO 93/17279 shows another known premix burner, in which a cylindrical swirl generator is used with an additional conical inner body. In this burner, the premix gas is also injected via feeders with corresponding outlet openings in the swirl space, along the axially extending air inlet slots are arranged. This burner has in the conical inner body in addition to a central supply of fuel gas, which can be injected near the outlet opening of the burner for piloting into the swirl space. This additional pilot stage is used to start the burner. However, the supply of the pilot gas in the outlet region of the burner leads to increased NO _x emissions, since in this area only an insufficient mixing with the combustion air can take place.

The EP 0918191 A1 shows a generic burner for operating a heat generator, which also has a second feed for another fuel type, which is matched to the other type of fuel in parallel to a first feed for fuel. Both feeds can be controlled independently of each other. With this configuration, the burner can be operated without reshaping with different types of fuel.

In all the illustrated burners, the premixing gas is injected into the air inlet gap by means of feeds with outlet openings arranged essentially in the direction of the burner axis. Thus, the characteristic of the injection with regard to penetration depth and mixing of the gas jets and the fuel distribution along the air inlet slots or the burner axis are predetermined. The arrangement of the outlet openings thus already determines the mixing quality of the gas and the combustion air and the fuel distribution at the burner outlet. These sizes are again crucial for NO _x emissions, extinguishing and flashback limits and burner stability with regard to combustion pulsations.

At different loads, gas qualities or gas preheating temperatures, however, different gas pressures occur at the outlet openings, which in turn lead to different premixing conditions and mixture qualities at the fuel outlet. Different premixing conditions result in different emission levels and stability conditions depending on load, gas quality and gas preheating. The known burners can therefore be optimally operated only for very specific value ranges of these parameters.

The problem with the operation of premix burners, especially in gas turbines, is the partial load range, since here only comparatively small amounts of fuel are added to the combustion air. In the complete mixing of the fuel with the entire air but creates a mixture which is no longer flammable, especially in the lower part load range, or only a very unstable flame is able to form. This can lead to harmful combustion pulsations or complete extinguishment of the flame.

For adaptation of the known burners to certain emission values or to a specific stability window with different loads, environmental conditions, gas qualities and preheating temperatures, there is currently the possibility of being used of multi-burner arrangements to rate the premix gas supply to individual burner groups. However, this is only possible with multi-row burner arrangements. For single-row annulare combustion chambers, this technique has the disadvantage that sets a non-uniform temperature profile in the combustion chamber outlet in the circumferential direction.

Another possibility is to equip Brenner with a so-called pilot fuel supply, as briefly mentioned above. The burners are then operated at very high air ratios as a diffusion burner. On the one hand, this results in superior flame stability, but on the other hand in high emission values and other operational disadvantages.

From the EP 433 790 a double-cone burner or a method for operating a double-cone burner has become known, in which over nozzles disposed along the tangential air inlet openings a first fuel, for example natural gas, is injected into the combustion air stream, while upstream of the entry of the air into the burner in the region of the inlet slots channels are formed with injectors, via which a second, different from the first fuel fuel, for example, a mittelkalorisches gas which usually contains easily flammable hydrogen is injected.

The object of the present invention is to provide a burner which can be operated stably even in the case of changes in the load, the gas quality or the gas preheating temperature with approximately constant NO _x emission values, preferably in the premixing mode.

Presentation of the invention

The object is achieved with the burner according to claim 1. Advantageous embodiments and further developments of the burner are the subject of the dependent claims.

The proposed burner consists of a swirl generator for a combustion air flow, a swirl space and means for introducing fuel into the combustion air flow, the swirl generator having combustion air inlet openings for the combustion air flow entering tangentially into the swirl space, the means for introducing fuel into the combustion air flow one or a plurality of first fuel feeds having a first group of fuel burner outlets arranged substantially in the direction of the burner axis for a first premix fuel quantity; and the burner comprising one or more second fuel feeders having a second group of fuel burner outlets arranged substantially in the direction of the burner axis for a second quantity of fuel , preferably a premix fuel quantity, which second fuel feeds are independent of the first or the first fuel feeds can be acted upon with fuel. The proposed burner is characterized in that in the swirl space, an inner body is arranged, wherein the fuel outlet openings of at least one second fuel supply are arranged distributed substantially in the direction of the burner axis on the inner body. In one embodiment, the inner body is a fuel lance which is arranged in the swirl space on the burner axis.

Preferably, one or more of the first groups of fuel outlet openings are arranged in the region of at least one of the combustion air inlet openings.

In the present application, an arrangement essentially in the direction of the burner axis is to be understood to mean an arrangement on axes which run parallel or at an angle of <45 ° to the burner axis.

In one possible embodiment of the present burner, some of the second fuel feeds are also arranged directly next to the first fuel feeds, preferably parallel to them. In this case, at least a second fuel supply should be provided next to each first fuel supply.

There may be conical swirl generators, as they are known from the cited prior art documents, for example, with two, four or more air inlet slots used. Other geometries, such as cylindrical swirl generators or cylindrical swirl generators with conical or cylindrical inner bodies can be used.

In one embodiment of the burner, some of the second fuel feeds are arranged on the outer shell of the swirl body and, in particular, on the air inlet slots along the latter. It is essential in the case of the present burner that the second fuel feeds have a plurality of fuel discharge openings distributed essentially in the direction of the burner axis, in order to be able to achieve a sufficient premix. The outlet openings are usually parallel to or below a predetermined by a conical shape of the swirl generator or inner body angle to the burner axis axes.

Depending on the desired influence possibilities on the premix, the second fuel outlet openings of the second fuel supply lines may have different mutual distances or flow-through cross sections compared to the first fuel outlet openings. Especially in the case of an arrangement in which at least one second fuel feed is provided immediately adjacent to a first fuel feed, the respective fuel discharge openings may also have the same mutual distances, but may be arranged offset from one another. This leads to a more uniform injection of Vormischbrennstoffes in the swirl chamber. Furthermore, for example, the first fuel outlet openings over the entire axial extent of the combustion air inlet openings, the second fuel outlet openings However, be arranged only in a specific axial portion. In the same way it is also possible to provide the first fuel outlet openings only in a first axial portion and the second fuel outlet openings only in a subsequent to the first portion second axial portion - or vice versa. Different possibilities of influence on the operation of the burner due to these different design options, the combination of which no practical limits are set, can be found in the exemplary embodiments.

For the independent application of the premix fuel to the first and second fuel feeds, these are equipped with different connections. Preferably, in addition, means are provided for the independent regulation or control of the premix fuel supply to the first and the second fuel feeds. The different supply can be controlled for example by a suitable control valve.

By means of an embodiment in which several of the second fuel feeds can also be acted upon by premix fuel independently of one another-and acted upon, an even finer graduated adaptation of the mixture distribution and the mixing quality to different boundary conditions can be carried out.

Furthermore, the invention also includes such embodiments, in which in addition to first and second Also third, fourth, etc. fuel supplies available and can be acted upon independently with fuel.

For operation of the burner, the supply of the fuel via the first fuel feeds is controlled or regulated separately from the supply of the fuel via the second fuel feeds, the same fuel being supplied to the first and second fuel feeds. By controlling the mass flow ratio of air supplied via the first fuel feeds first quantity of fuel to a supplied through the second fuel supply conduits second quantity of fuel during operation of the burner, the burner _x -Emissionswerten can be stable even when changes in the load, the gas quality or Gasvorwärmtemperatur with approximately constant NO operate.

In the preferred embodiment, the fuel is used as a premix fuel and divided in a variable mass flow ratio to the first and second feeders. The feed of premix fuel differs from the feed of pilot fuel, ie fuel for the realization of a pilot stage, in that premix fuel having a higher momentum, preferably transverse to the flow of combustion air, is introduced into the swirl space. By contrast, when introducing fuel as a pilot fuel, the burner is operated in a diffusion mode.

Preferably, the fuel is distributed depending on the load on the first and second fuel feeds introduced into the burner.

In a further preferred mode of operation of the burner, in a first operating state substantially the entire amount of fuel is supplied via the first or the first fuel feeds and introduced via the first group of fuel outlet openings in the combustion air flow, and in a further operating state, at least part of the total amount of fuel introduced into the combustion air stream via at least one of the second fuel feeds with the second group of fuel outlet openings.

If the burner is operated in a heat generator, then in a partial load state of the heat generator all the fuel can be supplied via the first fuel feeds, and in full load operation of the heat generator, the fuel can be split between the first fuel feeds and one or more second fuel feeds.

In addition to the above-mentioned load-dependent distribution of the fuel to the first and second fuel feeds, the distribution can also be controlled according to other operating variables. Thus, for example, the fuel can also be used as a function of measured combustor pulsations of a gas turbine, of pollutant emissions, of measured material temperatures, of the flame position detected by a flame position sensor or of other measuring or Operating parameters are distributed to the first and second fuel supply lines.

By the one or more second fuel feeds, through which the amount of premix fuel, which is injected via the second group of fuel discharge openings in the swirl space, - and thus the fuel pre-pressure - can be set independently of the amount of premix fuel, over the flows first fuel feeds, can be a simple adaptation of the mixing distribution and the mixing quality to achieve different boundary conditions. Furthermore, a compensation of different Wobbe numbers can be achieved by this embodiment, for example, by carrying the first fuel supply a certain power or a certain volume flow and the rest of the power or the volume flow is driven over the second fuel supply. By suitable arrangement of the second fuel supply lines with the corresponding second groups of fuel outlet openings relative to the first fuel supply lines with the first groups of fuel outlet openings, the axial and radial fuel distribution in the burner can be favorably influenced. Thus, it is possible to achieve a selective enrichment of the mixture with fuel in partial load operation in certain areas of the burner outlet in order to improve the flame stability. At high burner load, the fuel can then be evenly distributed, resulting in low emissions.

Short description of the drawing

Figur 1

ein erstes Beispiel für einen vorgeschlagenen Brenner;

Figur 2

ein zweites Beispiel für einen vorgeschlagenen Brenner;

Figur 3

ein drittes Beispiel für einen vorgeschlagenen Brenner;

Figur 4

ein Beispiel für die Betriebsweise eines vorgeschlagenen Brenners; und

Figur 5

ein viertes Beispiel für einen vorgeschlagenen Brenner;

Figuren 6 bis 11

Beispiele für die Ausgestaltung des Konturverlaufs des Drallerzeugers eines vorgeschlagenen Brenners;

Figuren 12 und 13

Beispiele für Ausgestaltungen der Drallerzeuger im Querschnitt ;

Figuren 14 und 15

schematisch zwei Beispiele für die Ausgestaltung der Brennstoffzuführungen zum Betrieb eines vorgeschlagenen Brenners.

The proposed burner and also the Betiebsverfahren also described will be explained in more detail using exemplary embodiments in conjunction with the drawings. Hereby show:

FIG. 1

a first example of a proposed burner;

FIG. 2

a second example of a proposed burner;

FIG. 3

a third example of a proposed burner;

FIG. 4

an example of the operation of a proposed burner; and

FIG. 5

a fourth example of a proposed burner;

FIGS. 6 to 11

Examples of the configuration of the contour of the swirl generator of a proposed burner;

FIGS. 12 and 13

Examples of embodiments of the swirl generator in cross section;

FIGS. 14 and 15

schematically two examples of the design of the fuel supply to operate a proposed burner.

Ways to carry out the invention

In the following figures, the burners are shown in a highly schematized design, so that only the essential features for the respective explanation are highlighted in each case at one position. The further design of the burners shown is familiar to the person skilled in the art, inter alia, from the documents cited as state of the art, which form an integral part of the present description. Furthermore, in the embodiments, reference is made in part to the injection of gaseous fuel. It goes without saying, however, that liquid fuel can also be introduced into the combustion air flow via the fuel outlet openings. The fuel continues to be referred to as premix fuel; It goes without saying that a portion of the total amount of fuel in certain load ranges can also be introduced as a pilot fuel to further increase the flame stability. Feeders for pilot fuel are not shown in any of the figures, since they are not essential to the invention; however, knowing the state of the art, the person skilled in the art will readily be able to implement these in the burners illustrated by way of example, if he considers this necessary.

First exemplary embodiments of a burner described in the claims are in the FIGS. 1 to 3 to shown. The illustrated Burners comprise the conical swirl body 1, in the outer form of which at the inflow edges of the air inlet slots a first group of outlet openings 6 for premixing gas are arranged. The burners are further provided with a central fuel lance 12, which may have at its combustion chamber end, ie at its tip, a nozzle - as in the present example - which can be used for a liquid fuel 13 or for a pilot fuel. Around this nozzle around outlet openings for umbrella air 14 may be provided in a known manner. In addition to the fuel feeds to the first group of outlet openings 6 and a fuel supply for injection liquid fuel 13 at the top of the fuel lance 12, the burner shown a further fuel supply to a second group of outlet openings 8 in the fuel lance 12. The outlet openings 8 of the second group are arranged substantially in the direction of the burner axis in the lateral surface of the fuel lance 12, as shown in Figures 19 to 21 can be seen, and preferably distributed radially symmetrically about the axis of the fuel lance 12. They allow the radially from the fuel lance 12 outwardly directed injection of fuel into the swirl space. The number and size of these outlet openings 8 and their distribution on the fuel lance 12 - in the axial direction and circumferential direction - is selected as a function of the respective requirements of the burner such as extinction limits, pulsations and kickback limits.

The fuel lance 12 may extend relatively far into the swirl space, so-called "Long Lance EV Brenner ", as in the Figures 1 and 2 represented, or protrude only a short distance in the swirl chamber as in the FIG. 3 shown. In both cases, the second group of outlet openings 8 is preferably arranged in the rear, ie farthest from the combustion chamber, the region of the swirl space on the fuel lance 12, as indicated in the figures.

Of course, even in these embodiments, the fuel supply to the first group of outlet openings 6 regardless of the fuel supply to the second group of outlet openings 8 can control or regulate with fuel.

The embodiment of the Fig. 1 allows a very advantageous stepped operation of the burner, in which both the fuel feeds to the first group of outlet openings 6 and the fuel feeds to the second group of outlet openings 8 are fed with premixed gas. The independent control possibility of the fuel supply to the first and second group of outlet openings 6, 8 allows an optimally adapted to the respective operating conditions of the burner or the burner using the system operation. The second group of outlet openings 8 on the fuel lance 12 are in this example outlet openings of the first group of outlet openings 6 on the swirler 1, so that the first and second group of outlet openings 6, 8 in certain operating conditions, for example, exclusively, ie without the other Group, can be fueled.

In principle, the burner shown in the figure can also be operated in the diffusion mode with appropriate supply of the fuel and corresponding configuration of the second group of outlet openings via these outlet openings 8. By the spatial separation of the outlet openings 8 of the injection liquid fuel 13 at the top of the fuel lance 12 can be avoided in this case, in contrast to known burners, the penetration of fuel droplets or fuel vapor into the fuel supply system for the second group of outlet openings 8.

FIG. 2 shows an embodiment of a burner, which can also be operated in the very advantageous stepped mode. At the second group of outlet openings 8 opposite regions of the swirl body 1, the outlet openings 6 are closed or there are no outlet openings 6 are provided because their function is taken over by the outlet openings 8 on the fuel lance 12. FIG. 21 shows the same burner with shortened fuel lance 12, which is designed for the same mode of operation.

During operation of these burners, both groups of outlet openings 6, 8 are supplied with premix gas. Ignition and starting of the burner are carried out in an operating mode in which the premix gas is introduced into the swirl chamber mainly via the outlet openings 8 on the fuel lance 12, hereinafter also referred to as stage 1. As the load increases, the supply of premix gas becomes Stage 1 is reduced and the supply of premixed gas via the first group of outlet openings 6, hereinafter referred to as stage 2, increased. Such a distribution of the premix fuel to the stages 1 and 2, depending on the operating condition of the burner can exemplify the FIG. 4 be removed. In this way, for example, a gas turbine with such a burner from ignition to base load can be operated without a pilot stage.

Another embodiment of a burner, in this example using a cylindrical swirl generator 1 with a conical inner body 9, for carrying out the present method is exemplified in US Pat FIG. 5 shown. FIG. 5 again shows the first 5 and the second feed channel 7 with the corresponding outlet openings 6, 8. In the embodiment of the FIG. 5 the first feed channel is arranged in the outer formwork of the swirl body 1 and the second feed channel 7 is arranged on the cylindrical inner body 9. The second supply channel 7 is hereby preferably arranged within the outer wall of the inner body 9, wherein in this case too, as in the preceding examples, a symmetrical distribution of a plurality of feed channels 7 around the burner axis 3 can be selected. In this example, however, it is also possible to let the second supply line 7 run centrally in the inner body 9, in which case the outlet openings 8 must be formed via corresponding radially extending channels to the swirl space 2. In the front tapered region of the inner body 9 can also have one or more additional outlet openings be provided with a correspondingly separate feed for fuel (as a pilot stage) or air.

The FIGS. 6 to 9 show schematically examples of swirler geometries, with which the burner described can be realized. In the figures, a burner with conical swirl body 1 and conical inner body 9, a burner formed with an inverted cone swirl body 1 and conical inner body 9, a burner with tulpenförmigem and a burner with funnel-shaped swirl body 1 are shown from top to bottom. In all of these burner geometries, as in the preceding examples, the second feeds can be arranged both in the swirl body 1 and in the inner body 9. All of the geometries shown here have in common that the axial flow cross-section of the swirl space in the area of the swirl body increases towards the burner outlet. Although this is not absolutely necessary for a generic premix burner, but is an advantageous embodiment of the swirl generator.

Furthermore, all burner geometries can be provided with a premix tube 10, as shown by way of example in FIG FIG. 10 for a cone burner and in FIG. 11 is illustrated for a cylindrical burner with conical inner body 9.

It will be apparent to those skilled in the art that the present invention can be practiced with a variety of burner types and combinations of swirlers, inner bodies, premix tubes, and other known features of burners.

The FIGS. 12 and 13 Finally, schematically show two examples of the structure of a swirl body in cross-section, as it can be used in the burner according to the invention. In FIG. 12 a swirler is shown, which is composed of four mutually offset shells 1a, 1b, 1c, 1d, which form four tangential air inlet slots 4 in the illustrated arrangement. The shells may be formed differently in the cross section shown, for example circular segment, elliptical or oval. In the dargestllten configuration, the body part 1a, 1b, 1c, 1d are arranged so that their respective central axes 3a, 3b, 3c, 3d are arranged offset to the actual burner axis. The design of a burner, with or without Vormischrohr, with such a geometry can in detail of the EP 321 809 or the EP 0780629 be removed. In FIG. 13 a monolithic swirl body 1 with tangential air inlet openings 4 introduced therein is shown. The air inlet openings 4 may be formed, for example, as milled air inlet slots or as rows of air inlet holes.

The FIGS. 14 and 15 show examples of the supply of a fuel amount P0 to the burner. In both examples, the fuel line branches to divide the total fuel amount P0 to a fuel amount P1 for the first group of exhaust ports 6 and to a fuel amount P2 for the second group of exhaust ports 8.

In FIG. 14 the setting of the division or mass flow ratio via a respective valve 15 and 16 in each of the branches. FIG. 15 shows an embodiment in which a valve 16 is arranged in front of the branch for adjusting the total fuel amount P0 and another valve 15 in the branch to the first group of outlet openings 6. By controlling the valve 15, the mass flow ratio between P1 and P2 can also be changed here. Of course, in this example, the valve 15 may also be arranged in the branch to the second group of outlet openings 8.

Furthermore, such an arrangement can also supply a plurality of burners with fuel simultaneously in the set mass flow ratio, as indicated by the dashed lines in the figures.

In both exemplary embodiments, the mass flow ratio P1 / P2 is changed by controlling the valves in dependence on the operating state of the burner. The change in the mass flow ratio may be controlled or regulated depending on various measurement and operating characteristics, as already stated in a previous part of the present description. The illustrated embodiments are independent of the burner geometry and can be used in all burners of the preceding embodiments.

LIST OF REFERENCE NUMBERS

1

swirl generator

1a

Swirl generator partial body

1b

Swirl generator partial body

1c

Swirl generator partial body

1d

Swirl generator partial body

2

swirl space

3

Brenner

3a

Axle of a swirl generator part body

3b

Axle of a swirl generator part body

3c

Axle of a swirl generator part body

3d

Axle of a swirl generator part body

4

Inlet openings / air slots

5

first fuel feeds

6

first fuel outlet openings

7

second fuel feeds

8th

second fuel outlet openings

9

inner body

10

premix

11

combustion air

12

fuel lance

13

liquid fuel

14

Abschirmluft

15

control valve

16

control valve

P0

Total amount of fuel

P1

first premix fuel

P2

second premix fuel

Claims (20)

1. Burner, consisting essentially of a swirl generator (1) for a combustion airflow (11), a swirl space (2) and means for introducing fuel into the combustion airflow, the swirl generator (1) having combustion air inlet openings (4) for the combustion airflow entering tangentially into the swirl space (2), which means include means for introducing fuel into the combustion airflow of at least one first fuel supply conduit (5) with a first group of fuel outlet openings (6), essentially arranged in the direction of a burner centre line (3), for a first premix fuel quantity (P1), and the burner has one or a plurality of second fuel supply conduits (7) with a second group of fuel outlet openings (8), essentially arranged in the direction of the burner centre line (3), for a second fuel quantity (P2), it being possible to admit fuel to these second fuel supply conduits (7) independently of the first fuel supply conduits (5), characterized in that an inner body (9, 10) is arranged in the swirl space (2), the fuel outlet openings (8) of at least one second fuel supply conduit (7) being arranged on the inner body (9) in such a way that they are essentially distributed in the direction of the burner centre line (3).
2. Burner according to Claim 1, characterized in that the inner body (9) is a fuel lance (12) which has, at its combustion-space end, at least one outlet nozzle for liquid fuel (13) and/or pilot fuel.
3. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (8), which are arranged in such a way that they are distributed on the inner body (9) in the direction of the burner centre line (3), are arranged in a partial axial region of the inner body (9) remote from the combustion-space end.
4. Burner according to one of the preceding claims, characterized in that the second group of fuel outlet openings (8) is designed for the supply of premix fuel.
5. Burner according to one of the preceding claims, characterized in that at least one of the groups of fuel outlet openings is arranged in the region of at least one of the fuel inlet openings (4).
6. Burner according to one of the preceding claims, characterized in that a plurality of first fuel supply conduits (5) and a plurality of second fuel supply conduits (7) are provided, at least one second fuel supply conduit (7) being associated with each of the first fuel supply conduits (5).
7. Burner according to one of the preceding claims, characterized in that second fuel supply conduits (7) are arranged immediately adjacent to first fuel supply conduits (5).
8. Burner according to one of the preceding claims, characterized in that the fuel inlet openings (4) are tangential inlet slots extending essentially in the direction of the burner centre line (3).
9. Burner according to Claim 8, characterized in that a first fuel supply conduit (5) with a first group of fuel outlet openings (6) is arranged along each inlet slot.
10. Burner according to one of Claims 8 or 9, characterized in that at least one second fuel supply conduit (7) with a second group of fuel outlet openings (8) is arranged along each inlet slot.
11. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (8) of one or a plurality of second fuel supply conduits (7) are arranged at axial positions between the fuel outlet openings (6) of one or a plurality of first fuel supply conduits (5).
12. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (6, 8) of all groups are distributed over the whole of the axial extent of the combustion-air inlet openings (4).
13. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (6, 8) of at least one of the groups are distributed over the whole of the axial extent of the combustion-air inlet openings (4) and the fuel outlet openings (6, 8) of at least of one further group are distributed over a partial axial region of the combustion-air inlet openings (4).
14. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (6, 8) of at least one of the groups are distributed over a first partial axial region of the combustion-air inlet openings (4) and the fuel outlet openings (6, 8) of other groups are distributed over further partial axial regions of the combustion-air inlet openings (4).
15. Burner according to Claim 14, characterized in that the partial axial regions do not overlap.
16. Burner according to Claim 14, characterized in that at least two of the partial axial regions overlap at least partially.
17. Burner according to one of the preceding claims, characterized in that the fuel outlet openings (6, 8) of two or more groups have different flow cross sections.
18. Burner according to one of the preceding claims, characterized in that means are provided for the independent control of the premix fuel supply to the first fuel supply conduit or conduits (5) and to the second fuel supply conduit or conduits (7).
19. Burner according to Claim 18, characterized in that means for the independent control of the premix fuel supply have a common fuel line, which branches into a first supply line to the first fuel supply conduit or conduits (5) and into a second supply line to the second fuel supply conduit or conduits (7), a valve (15, 16) for setting the fuel flow quantity being arranged at least in one of the supply lines.
20. Burner according to one of the preceding claims, characterized in that fuel can be admitted to a plurality of the second fuel supply conduits (7) independently of one another.

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