EP2687781B1 - Grid burners and method for monitoring the formation of a flame in a grid burner - Google Patents

Description

The invention relates to a surface burner according to the preamble of patent claim 1 and a method for monitoring flame formation in a surface burner according to claim 18.

Surface burners are usually operated with gas, such as natural gas or biogas. However, liquid fuels such as heating oil, ethanol or methanol can also be considered as possible fuels. As a rule, a gaseous fuel-air mixture is generated in a mixing chamber and fed through a perforated metal distributor plate to the burner surface, which can have a fiber knitted fabric, for example made of metal fibers or a ceramic fleece. The distributor plate serves to evenly distribute the fuel-air mixture that is burned on the side of the fiber-knitted fabric facing away from the distributor plate. There is therefore a flame area on the fiber knitted fabric or on the burner surface. The term fiber-knitted fabric is representative of any known type of flat fiber system or thread system and thus includes fiber materials or thread materials produced by knitting, warp knitting, crocheting, weaving, felting, fulling and / or pressing. Due to the statistical distribution of the fibers, threads, meshes and / or pores, their geometry cannot be reproducibly produced with the same precision as in other machining processes (e.g. machining).

Such surface burners are used in particular in heating devices and hot water devices. With the aid of a monitoring electrode, for example an ionization electrode, the Combustion quality and in particular the level of an oxygen content in the combustion mixture. Due to the high temperature of the flame, the combustion mixture is ionized and has a measurable conductivity, which is measured with the aid of the monitoring electrode and made available to a control unit. This regulates the composition of the fuel-air mixture.

An oversupply of combustion air, i.e. too much air in the fuel-air mixture, should be avoided, since this leads to a poor energy yield and thus to a reduced degree of efficiency. A corresponding control is also known as air ratio control or lambda control and is used, for example, in SCOT technology (system control technology). Theoretically, optimal combustion values are always achieved regardless of the fuel quality, with no need to adapt the surface burner to the available fuel quality.

However, with surface burners with a fiber-knitted fabric, it is hardly possible to generate clearly defined and locally reproducible flames (for example in the area of the monitoring electrode). A fiber knitted fabric cannot be produced completely uniformly. Due to the non-reproducible knitted geometry, there are no clearly defined flames in terms of flame geometry (flame shape, length, shape, etc.) or combustion parameters (flame temperature, burnout speed, the flame lifts off or the flame sits on the burner surface, etc.). Therefore, these values scatter relatively strongly over the burner surface. In addition, the knitted fiber fabric changes over its service life and thus also influences the formation of flames. Since the flame ionization fluctuates due to the dependencies set out above, precise regulation of the air ratio or the residual oxygen content on the basis of the ionization current flowing through the flame over a large modulation range is hardly possible.

In DE 10 2005 056 499 A1 It is proposed to reduce a flow rate of the fuel-air mixture in the monitoring area compared to the main area in order to ensure adequate flame monitoring even when the flame is different To ensure gas properties and modes of operation, whereby the monitoring electrode is assigned to the monitoring area.

In EP 0 339 499 A2 on the other hand, it is proposed to generate flames with a greater length in the monitoring area than in the main area, which is achieved, for example, by providing smaller outlet openings in the distributor plate or reducing the air content in the fuel-air mixture. This is to ensure that the monitoring electrode always has a flame that can be used for ionization measurement.

However, this measure does not completely eliminate the spread of the flame formation. In particular over a longer period of time, the flame pattern can change.
The invention is based on the object of eliminating the disadvantages of the prior art and of achieving a defined flame formation in the monitoring area, so that in particular a precise air ratio control is possible.

According to the invention, this object is achieved with the features of patent claim 1 or with the features of patent claim 18. Advantageous further developments can be found in the subclaims.

The surface burner according to the invention thus has a distributor plate with a monitoring area and a main area, the fuel-air mixture flowing through the first fiber knitted fabric in the main area and being unaffected by the first fiber knitted fabric in the monitoring area. The condition and the shape of the first fiber knitted fabric have no effect whatsoever on the flame formation in the monitored area. Rather, a flame is formed in the monitored area independently of the first knitted fiber fabric. In the main area, the distribution plate is furthermore protected from excessively high temperatures by the first knitted fiber fabric, so that the desired service life of the surface burner can be achieved. Since the flame formation in the monitoring area is not influenced or disturbed by the first fiber knitted fabric, it is possible to generate a geometrically precisely defined flame. This creates defined flame conditions without any scatter between different surface burners and without change over the service life. The defined relationships enable precise control over a large modulation range.

In particular, in the monitoring area on the monitoring electrode, a mixture outflow geometry that is reproducible from burner to burner and thus reproducible flame parameters are created, which allow ionization measurement that is reproducible from burner to burner and that is not age-dependent.

It is particularly preferred that the monitoring area is made much smaller than the main area, the monitoring area having a size of approximately 5 cm ² to 15 cm ² , in particular approximately 10 cm ² . The monitored area is, for example, 50 mm x 20 mm and accordingly very small compared to the main area. Heat conduction in the distribution plate from the monitoring area into the main area, which is protected by the first fiber knitted fabric and accordingly has a lower temperature, is therefore possible without any problems, so that excessive overheating of the distribution plate in the monitoring area is not to be feared. A higher flow rate of the fuel-air mixture is often required in the monitoring area in order to generate a strong flame, which also means that the flame does not lie directly on the surface of the distributor plate, but also without the additional first fiber knitted fabric from the distribution plate is spaced. This ensures that a sufficiently strong flame is still generated in the monitoring area, even at low loads, in order to receive a usable ionization signal. Overheating of the distributor plate is therefore not to be feared even with low power.

In order not to interrupt heat conduction paths from the monitored area into the main area of the distributor plate, slot-shaped outlet openings can be provided in the distributor plate at least in the monitored area, which run perpendicular to the respectively closest edge of the monitored area. This ensures reliable heat dissipation from the monitored area into the main area.

In the monitoring area, the distributor plate can be designed to be more permeable to the fuel-air mixture than in the main area. This can be achieved, for example, in that the sum of the open cross-sections per area is higher in the monitored area than in the main area. In particular, when the required power is low, a relatively strong flame is ensured in the monitoring area, which flame can be used to generate a sufficient ionization signal.

Additionally or alternatively, the distributor plate can have a greater thickness in the monitored area than in the main area. For example, the distributor plate is made from a metal or stainless steel sheet with a thickness of approximately 0.6 mm. In the monitored area, the thickness of the distribution plate is then increased to, for example, 1 mm or 1.5 mm. For this purpose, an additional sheet metal, for example, made of stainless steel or a high temperature-resistant alloy such as a nickel-based alloy, which is welded to the distributor plate in the monitoring area. This further improves the dissipation of heat in the monitored area. This ensures that the first knitted fiber fabric is positioned securely on the distributor plate, ensuring that the first knitted fiber fabric does not protrude into the monitored area and thus influence the formation of flames in the monitored area. In the case of a metal fiber knitted fabric, welding is a particularly simple option for fixing the first fiber knitted fabric to the distributor plate. The welding takes place, for example, via individual welding points.

In a preferred embodiment, the monitoring area is free from the first fiber knitted fabric. The flame image generated in the monitored area is then essentially determined by the openings in the distributor plate. The burner surface in the monitoring area can be completely free, i.e. the distributor plate can be exposed so that the flames are generated in the monitoring area without the interposition of a burner medium.

In a preferred embodiment, the distribution plate is covered downstream in the monitoring area by a second fiber knitted fabric, which has a lower flow resistance than the first fiber knitted fabric and forms part of the burner surface. The second fiber knitted fabric then protects the Distribution plate in the monitoring area, but has a significantly lower impact on the flow of the fuel-air mixture than the first fiber-knitted fabric. The first fiber knitted fabric can be produced from a proven, relatively thick metal fiber fabric that is sold, for example, under the name NIT 100 SE by Bekaert Combustion Technology. In contrast, the second fiber knitted fabric is very thin, the ratio of covered areas to holes being very low, so that the fuel-air mixture can flow through the second fiber knitted fabric almost undisturbed. Influencing the flame pattern is then essentially determined by the shape of the openings in the distributor plate and is hardly influenced by the second fiber fabric. A metal-fiber knitted fabric offered by the Bekaert company under the name NIT 100 A can be used as the second fiber knitted fabric. In particular with a stronger flow through the distributor plate in the monitoring area than in the main area, overheating of the second fiber knitted fabric is not to be feared, since a slightly lifted flame and increased cooling is obtained in the monitoring area.

The first knitted fiber fabric is advantageously connected to the second knitted fiber fabric, in particular welded. This ensures that the distribution plate is covered by a knitted fiber fabric at the transition from the monitored area to the main area so that local overheating cannot occur. A welding of metal-fiber-knitted fabrics, even of different mesh sizes and material thicknesses, is possible without any problems and represents a particularly simple and durable connection.

In an alternative embodiment, the distributor plate is covered in the downstream monitoring area with a perforated, temperature-resistant metal sheet that forms a part with the burner surface. The sheet metal is made, for example, of a high-temperature-resistant stainless steel alloy and is perforated and / or perforated. Edges of the metal sheet adjoin the first fiber knitted fabric or are covered by the first fiber knitted fabric so that no thermally overloaded areas arise. The metal sheet protects the distribution sheet in the monitored area. The distribution plate is for example at a distance of 1 mm to 3 mm from the distribution plate in the monitored area arranged. The geometry of the perforation of the metal sheet can be produced with a very high repetition accuracy, so that a precisely defined flame is obtained.

The sheet metal on the surface burner can be held freely stretchable in a longitudinal direction. This is possible, for example, by combining a fixed bearing with a floating bearing, with the sheet metal being fixed on only one narrow side and being displaceably mounted on an opposite narrow side and / or on the adjacent long sides. This avoids the occurrence of temperature stresses due to the different expansion behavior of the sheet metal in relation to the distributor plate.

The distribution plate is preferably interrupted in the monitored area. The size of this interruption corresponds to the size of the monitoring area. The flow of the fuel-air mixture in the monitoring area is then not influenced at all by the distributor plate, but only by the sheet metal. Overall, this results in a very low flow resistance, so that the formation of a strong flame in the monitored area is ensured even at low power levels.

In an alternative preferred embodiment, the first knitted fiber fabric is penetrated by nozzles in the monitoring area. As a result, the entire distribution plate can be covered by the first knitted fiber fabric and thus protected from overheating, while at the same time ensuring that the first knitted fiber fabric in the monitoring area cannot influence the flow of the fuel-air mixture. Rather, the fuel-air mixture in the monitoring area is guided through the layer of the first fiber-knitted fabric and past this fiber-knitted fabric with the help of the nozzles and can thus be used to generate a defined flame.

At the same time, the nozzles can be used to hold the first knitted fiber fabric in place, for example to avoid sagging of the knitted fiber fabric, which can lead to stretching of the knitted fabric over its service life. For this purpose, the first fiber-knitted fabric can, for example, be force-fit at the nozzles and / or be held in a form-fitting manner. For this purpose, the nozzles pierce the fiber knitted fabric, so to speak, whereby the stitches of the fiber knitted fabric are stretched. Individual fibers of the fiber-knitted fabric are therefore not damaged. The nozzles can easily have a diameter of about 5 mm. Additionally or alternatively, the nozzles can also be welded or otherwise connected to the first fiber knitted fabric.

For a uniform distribution of the fuel-air mixture, the nozzles can each have a plurality of outlet channels. It is particularly preferred that the outlet channels run at least partially at an angle greater than or equal to 0 ° and less than 90 ° to a longitudinal axis of the nozzle. As a result, the fuel-air mixture escapes to the side, so that the flame lifts less from the burner surface. This is advantageous for an accurate ionization measurement in the flame and thus for setting and regulating an air ratio (residual oxygen content).

The nozzles are preferably connected to the distributor plate, in particular welded or riveted. The position of the nozzles in relation to the distributor plate and the monitoring electrode is then clearly defined so that the nozzles can be used to position the fiber-knitted fabric. It is also possible to design the nozzles in one piece with the distributor plate, in which case these are in particular deep-drawn. This ensures a smooth transition from the distributor plate to the nozzles without the need for additional work steps.

The invention is also achieved by a method for monitoring flame formation in a surface burner in that flame formation is monitored in a monitoring area, a fuel-air mixture in the monitoring area being guided past a first fiber fabric that covers a main area. It is provided that the monitored area is kept free from the fiber knitted fabric so that the fuel-air mixture in the monitored area can emerge unhindered from the first fiber knitted fabric from the distributor plate and can be used for geometrically defined flame formation. Instead of the first fiber knitted fabric, other burner media such as a second fiber knitted fabric or a metal sheet can then be used in the monitoring area be arranged to support the distributor plate in the monitoring area and to ensure a defined flame formation. The features and advantages explained in connection with the surface burner thus also result in connection with the method.

Fig. 1

einen Flächenbrenner in räumlicher Darstellung;

Fig. 2

einen Flächenbrenner in Draufsicht;

Fig. 3

einen Flächenbrenner einer ersten Ausführungsform im Schnitt;

Fig. 4

einen Flächenbrenner einer zweiten Ausführungsform im Schnitt;

Fig. 5

einen Flächenbrenner einer weiteren Ausführungsform im Schnitt;

Fig. 6a

einen Flächenbrenner einer weiteren Ausführungsform im Schnitt;

Fig. 6b

den Flächenbrenner nach Fig. 6a im Betriebszustand;

Fig. 7

eine weitere Ausführungsform des Flächenbrenners im Schnitt;

Fig. 8

ein Detail des Flächenbrenners im Schnitt und

Fig. 9

eine Düse des Flächenbrenners in Schnittansicht.

Exemplary embodiments of the invention are shown in the drawing. Show here:

Fig. 1

a surface burner in a spatial representation;

Fig. 2

a surface burner in plan view;

Fig. 3

a surface burner of a first embodiment in section;

Fig. 4

a surface burner of a second embodiment in section;

Fig. 5

a surface burner of a further embodiment in section;

Figure 6a

a surface burner of a further embodiment in section;

Figure 6b

the surface burner Figure 6a in operating condition;

Fig. 7

a further embodiment of the surface burner in section;

Fig. 8

a detail of the surface burner in section and

Fig. 9

a nozzle of the surface burner in sectional view.

In Figure 1 a surface burner 1 is shown in three-dimensional representation, which has a box-shaped burner frame 2 in which a mixing chamber is formed. The surface burner 1 has a first fiber knitted fabric 3, which is arranged between the sides of the burner frame 2. The first fiber knitted fabric 3 forms a burner surface.

A monitoring area 4 is free of the first fiber knitted fabric 3, so that a distribution plate 5 can be seen. The distribution plate 5 extends over the entire upper side of the surface burner 1 and is covered outside of the monitored area 4 in a main area 6 by the first fiber knitted fabric 3. Slit-shaped outlet openings 7 are formed in the distributor plate 5, each of which runs perpendicular to the nearest edge 8 of the monitoring area 4. This creates heat conduction paths, the heat from the monitored area 4 into the main area 6 transport, not interrupted by the outlet openings 7, so that a uniform and rapid heat dissipation can take place.

A fuel-air mixture located in the mixing chamber inside the burner frame 2 can flow through the distributor plate 5 to the burner surface above the first fiber knitted fabric 3 in the main area 6 and above the distributor plate 5 in the monitoring area 4. The fuel-air mixture thus reaches the top of the first fiber knitted fabric 3 facing away from the distributor plate 5. The fuel-air mixture is ignited there and directly above the distributor plate 5 in the monitoring area 4 and the flames can then form.

In order to achieve a greater mixture volume throughput in the monitoring area 4 and thus generate a stronger flame formation, several and / or larger outlet openings 7 can be provided in the area of the monitoring area 4 of the distributor plate 5 than in the main area 6. This ensures that the in the monitoring area 4 lift the flames generated from the distributor plate 5 so that it is not thermally overloaded. At the same time, the larger volume flow provides additional cooling.

At the edge 8, which represents a transition between the main area 6 and the monitoring area 4, the first knitted fiber fabric 3, which is designed as a metal fiber knitted fabric, is welded to the distributor plate 5, which can be designed as a perforated stainless steel sheet, for example. On the one hand, this results in a stabilization of the first fiber knitted fabric 3, and on the other hand it is ensured that the fuel-air mixture cannot be influenced by the first fiber knitted fabric 3 in the monitoring area 4. Regardless of the aging of the first fiber knitted fabric 3, a defined flame can thus be generated in the monitoring area 4 and used for air ratio regulation, that is to say for monitoring residual oxygen.

In Figure 1 there is no knitted fiber fabric or other burner medium above the monitoring area 4. However, it is also possible to cover the distribution plate 5 in the monitoring area 4 with a second fiber-knitted fabric 21 that is lighter and / or thinner than the first fiber-knitted fabric 3 in order to cover the distribution plate 5 to protect against thermal stress also in the monitoring area. The second fiber knitted fabric should then have a lower flow resistance than the first fiber knitted fabric 3. This configuration is shown in FIG Fig. 3 shown.

In Figure 2 the surface burner 1 is shown in plan view. In this embodiment, the distributor plate 5 is covered in the monitoring area 4 by a metal sheet 9 which has defined openings 10. The sheet metal 9 is designed as a perforated stainless steel sheet.

The first fiber knitted fabric 3 is welded to the metal sheet 9 at the edge 8. In addition, the first fiber knitted fabric 3 is welded to the burner frame 2 and thus clearly positioned. In the monitoring area 4, the first fiber knitted fabric 3 can therefore not have any influence on the flame formation. Rather, the fuel-air mixture is passed through the metal sheet 9 or its openings 10, so that a defined flame can be generated.

Fig. 3 shows the surface burner Fig. 1 in cross section. A second, much lighter and more permeable fiber knitted fabric 21 made of metal fibers is arranged in the monitoring area 4 than in the main area 6, so that the fuel-air mixture in the monitoring area is not or hardly influenced. This creates a defined flame in the monitored area.

Fig. 4 shows an opposite of the representation in Fig. 3 only a slightly modified embodiment in which the second fiber knitted fabric 21 is not formed as a metal fiber knitted fabric but from a different material. Otherwise, the in Fig. 4 surface burners shown in Fig. 3 embodiment shown.

Figure 5 shows the embodiment according to Figure 2 in cross section. The mixing chamber 11, which is surrounded by the burner frame 2, is covered on its upper side by the distributor plate 5. In the main area 6, the first fiber-knitted fabric 3 is located on the distributor plate 5. In the monitoring area 4, the metal sheet 9 is located at a distance of about 1mm to 3mm above the distributor plate 5. The metal sheet 9 is on its narrow side 12 facing the burner frame 2 held freely movable on the burner frame 2 (floating bearing). At its opposite On the narrow side 13, the sheet metal 9 is firmly connected to the distributor plate 5, so that a fixed bearing is formed. The metal sheet 9 can therefore expand freely in the longitudinal direction, so that no thermal stresses occur.

A fuel-air mixture passes from the mixing chamber 11 through the outlet openings 7 of the distributor plate 5 and flows through the first fiber knitted fabric 3 in the main area 6, so that flames can be formed on a side of the first fiber knitted fabric 3 facing away from the distributor plate 5. In the monitoring area 4, the fuel-air mixture flows through the openings 10 of the metal sheet 9, so that a defined flame is formed on a side of the metal sheet 9 facing away from the distributor plate 5. The distribution plate 5 is therefore protected in the main area 6 by the first fiber knitted fabric 3 and in the monitoring area 4 by the metal sheet 9 from thermal stress from the flames. Accordingly, the distributor plate 5 can be made relatively thin and, for example, have a thickness of 0.6 mm.

In the monitored area 4, the outlet openings 7 are arranged at a smaller distance from one another than in the main area 6. As a result, the volume flow per unit area in the monitored area 4 is greater than in the main area 6.

A monitoring electrode 14, with which the conductivity of the burning ionized fuel-air mixture is detected, is arranged outside the surface burner 1 and above the monitoring area 4. From this, the air ratio or the residual oxygen content can be determined and thus an air ratio control can be achieved. The monitoring electrode 14 is therefore also referred to as an ionization electrode.

In Figure 6a a further embodiment of the surface burner 1 is shown in cross section, which largely according to the embodiments Figure 3 and Figure 5 corresponds. However, the distribution plate 5 has an interruption (recess) 15 in the monitoring area 4. The fuel-air mixture thus reaches the metal sheet 9 directly from the mixing chamber 11 through the interruption 15 and can exit through the openings 10. Accordingly, a flow resistance in the monitoring area 4 is very small and, in particular, significantly smaller than in the main area 6. This results in, for example, twice as much flow and thus a rising flame in the monitored area 4, whereby a thermal load on the metal sheet 9 is kept small. At the same time, a strong flame is also ensured when only a low power is required from the surface burner 1 and accordingly relatively little fuel-air mixture is supplied.

In Figure 6b the surface burner 1 is shown in the operating state in which the flames 22 on the burner surface are ignited by a fuel-air mixture flowing out. A much more controlled, defined flame is formed in the monitoring area 4 than in the main area 6.

Otherwise, the surface burner corresponds to 1 in Figures 6a and 6b according to the embodiment Figure 5 .

In Figure 7 Another embodiment of the surface burner 1 is shown in cross section, the entire burner surface, that is to say both the main area 6 and the monitoring area 4, being covered by the first fiber knitted fabric 3. So that the fuel-air mixture is not influenced in the monitored area 4, nozzles 16 are provided in the monitored area 4, which penetrate the first fiber knitted fabric 3. For this purpose, stitches of the first fiber knitted fabric 3 are widened by the nozzles 16, as a result of which the first fiber knitted fabric 3 is held on the nozzles 16 in a force-locking and / or form-locking manner. The nozzles 16 are riveted into the distributor plate 5 and establish a fluid-conducting connection to the mixing chamber 11.

Figure 8 shows an embodiment of the surface burner 1 in which the nozzles 16 are not as in the embodiment according to FIG Figure 7 are riveted, but have been formed in one piece from the distributor plate 5 by deep drawing. This results in very favorable flow conditions. In order to obtain a secure fixation of the first fiber knitted fabric 3, in particular in the area of the monitored area 4, so that the first fiber knitted fabric 3 cannot cover any nozzle openings, the first fiber knitted fabric 3 is welded to the distributor plate 5 in the monitored area 4, with individual spot welds are sufficient.

Figure 9 shows a sectional view of a preferred embodiment of the nozzles 16. The nozzle 16 has an outlet channel 18 lying on the longitudinal axis 17 and two lateral outlet channels 19, 20. This results in a very even distribution of the fuel-air mixture above the monitoring area 4 and thus a strong flame with a light ionization measurement that is reproducible from burner to burner.

The inventive design of the surface burner 1 avoids the fundamental problem of flame scattering in the monitoring area 4, to which a monitoring electrode 14 is assigned, in that the flow of the fuel-air mixture is prevented from being influenced by the first fiber fabric 3 by the first knitted fiber fabric 3 is cut out in this area. Instead, either no burner medium at all is arranged in the monitoring area 4, so that the flames are formed directly above the distributor plate, or burner media are used that offer a lower flow resistance and / or more defined flow conditions than the first fiber knitted fabric 3 either a lighter second fiber knitted fabric is arranged, which has a lower flow resistance, or a metal sheet with openings that is not subject to aging like the fiber knitted fabric and can be manufactured and assembled with high repeatability. In order to achieve a stronger flow through the monitored area compared to the main area, the distributor plate 5 is provided with a larger number of outlet openings in the area of the monitored area. It is also conceivable to interrupt the distribution plate in the area of the monitored area, for example to cut it out.

This configuration ensures that the flame image can be generated in a very defined manner in the monitoring area. An uncooled area of the distributor plate in the monitored area is kept very small, so that good heat dissipation can take place. In this way, an exact definition of the outflow of the fuel-air mixture is obtained and a defined flame is generated that does not change over a longer period of time.

Claims (18)

1. Surface burner (1) having a distribution plate (5) and a burner surface, which has at least a first fibre knit (3), and having a mixing chamber (11) from which a fuel-air mixture is guided through the distribution plate to the burner surface, wherein the distribution plate has a monitoring region (4) and a main region (6), wherein the fuel-air mixture flows through the first fibre knit (3) in the main region (6), characterized in that the fuel-air mixture is uninfluenced by the first fibre knit (3) in the monitoring region (4), wherein the monitoring region (4) is free from the first fibre knit (3) such that the distribution plate (5) can be seen.
2. Surface burner (1) according to Claim 1, characterized in that the monitoring region (4) is designed to be very much smaller than the main region (6), wherein the monitoring agent (4) has a size of in particular 5 cm² to 15 cm², in particular of approximately 10 cm².
3. Surface burner (1) according to either of Claims 1 and 2, characterized in that the distribution plate (5) has, at least in the monitoring region (4), slot-shaped outlet openings (7) which run perpendicularly to the respectively closest edge (8) of the monitoring region (4).
4. Surface burner (1) according to one of Claims 1 to 3, characterized in that the distribution plate (5) is more permeable to the fuel-air mixture in the monitoring region (4) than in the main region (6) .
5. Surface burner (1) according to one of Claims 1 to 4, characterized in that the distribution plate (5) has a greater thickness in the monitoring region (4) than in the main region (6).
6. Surface burner (1) according to one of Claims 1 to 5, characterized in that the first fibre knit (3) is fixed, in particular welded, to the distribution plate (5) at a transition between the main region (6) and monitoring region (4).
7. Surface burner (1) according to one of Claims 1 to 6, characterized in that the monitoring region (4) is free from the first fibre knit (3).
8. Surface burner (1) according to one of Claims 1 to 7, characterized in that the distribution plate (5) is covered in the monitoring region (4) by a second fibre knit (21) which has a lower flow resistance than the first fibre knit (3) and forms part of the burner surface.
9. Surface burner (1) according to Claim 8, characterized in that the first fibre knit (3) is connected, in particular welded, to the second fibre knit (21) .
10. Surface burner (1) according to one of Claims 1 to 7, characterized in that the distribution plate (5) is covered in the monitoring region (4) by a perforated, temperature-resistant metal sheet (9) which forms part of the burner surface.
11. Surface burner (1) according to Claim 10, characterized in that the metal sheet (9) is held so as to be freely expandable in a longitudinal direction.
12. Surface burner (1) according to Claim 10 or 11, characterized in that the distribution plate (5) is interrupted in the monitoring region (4).
13. Surface burner (1) according to one of Claims 1 to 6, characterized in that the first fibre knit (3) is penetrated in the monitoring region (4) by nozzles (16).
14. Surface burner (1) according to Claim 13, characterized in that the first fibre knit (3) is held on the nozzles (16) in a force-fitting and/or form-fitting manner.
15. Surface burner (1) according to Claim 13 or 14, characterized in that the nozzles (16) have outlet ducts (18, 19, 20) which run at an angle of greater than or equal to 0° and less than 90° to a nozzle longitudinal axis.
16. Surface burner (1) according to one of Claims 13 to 15, characterized in that the nozzles (16) are connected to the distribution plate (5), in particular by welding or riveting.
17. Surface burner (1) according to one of Claims 13 to 15, characterized in that the nozzles (16) are formed in one piece with the distribution plate (5), in particular are deep-drawn.
18. Method for monitoring the formation of a flame in a surface burner (1) according to one of the preceding claims, characterized in that a flame formation is monitored in a monitoring region (4) in particular by a monitoring electrode (14), wherein a fuel-air mixture is guided in the monitoring region (4) past a first fibre knit (3) which covers a main region (6).

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