EP0635676B1 - Method and burner for the combustion of liquid and gaseous fuels - Google Patents

Abstract

In a method and a burner for the combustion of liquid or gaseous fuels, a considerable portion of the fuel is fed to an area lying downstream of a baffle plate (17) and adjoining the inner wall of the burner tube. Exhaust gases located in the combustion chamber are fed back by internal exhaust-gas recirculation into vacuum zones built up downstream of the baffle plate (17), and guide devices (25, 27; 29) piercing the burner tube (1) and projecting into the vacuum zones are used for this purpose. <IMAGE>

Description

The invention is concerned with the low-pollutant, in particular low-NO _x combustion of liquid or gaseous fuels in combustion plants with a burner projecting into a combustion chamber of a boiler, the burner tube of which has at least one fuel nozzle arranged therein for the supply of the fuel and a subsequent baffle plate . The invention is based on a method and a device in which exhaust gases or combustion products located in the combustion chamber are returned to the burner tube by internal recirculation.

When burning fossil fuels in combustion plants, nitrogen oxides NO _x are formed in addition to other combustion products. The reaction mechanisms that lead to such nitrogen oxides are largely known and are generally described as thermal and prompt or primary NO _x formation, and as NO _x formation by oxidation of the nitrogen chemically bound in the fuel.

It is also known that the recirculation of part of the exhaust gases from the combustion chamber of the boiler into the combustion process results in a reduction in NO _x emissions, in particular thermal NO _x formation; in any case, if this reduces the flame temperature, the oxygen partial pressure and the radicals in the fuel-combustion air mixture required to split the nitrogen compounds. For this purpose, it is known that the cooler exhaust gases, which only have a small unburned fraction, are led from the combustion chamber into a combustion zone in the burner tube downstream of the baffle plate.

A blower gas burner with internal exhaust gas recirculation is known from EP 0 347 834 B1 (DREIZLER). The blower gas burner described therein comprises a burner head, the burner tube of which receives a device having a burner plate for the supply, distribution and swirling of the fuel and the combustion air. On the upstream end of the burner tube there is a web ring with webs or sheet metal tabs projecting radially inwards. The web ring is followed downstream by a flame tube at such a distance that an annular gap is formed between the burner tube and the flame tube. The webs or tabs of the web ring create a build-up on the upstream side in the heat flow of the flame and downstream vacuum zones, which lead to the suction of the exhaust gases from the combustion chamber into the annular gap and from there into the flame tube and thus cause the exhaust gas recirculation. As a result, the exhaust gas only partially reaches the NO _x -forming flame areas.

Burners with internal exhaust gas recirculation are also known for oil combustion plants.

DE-OS 40 08 692 A1 (KÖRTING) describes an oil blower burner with: a mixing tube as a passage for the combustion air, which tapers conically at its downstream end; a baffle plate arranged in the area of the conical taper; and an attachment tube adjoining the mixing tube and overlapping it to form an annular gap. Here too arise as a result of Flow conditions at the end of the mixing tube Negative pressure zones that lead to internal gas recirculation. Exhaust gases from the combustion chamber are mainly returned to the outer area of the flame. No such gases are injected into the hot zones inside the flame - where most NO _{x is} produced -.

The German utility model G 89 09 288.0 (ELECTRO-OIL) also describes an oil burner with internal exhaust gas recirculation, in which exhaust gases from the combustion chamber are blown into the edge area of the flame. For this purpose, nozzles are arranged on the inside of the burner tube to accelerate the combustion air and to generate a vacuum area. Openings in the burner tube wall lead into this vacuum region, so that exhaust gases are sucked in from the combustion chamber and are fed to the edge region of the flame together with the combustion air via an annular channel running on the inner wall of the burner tube.

Incidentally, burners for reducing nitrogen values are also known, which are designed for the combustion of liquid or gaseous fuels.

DE 40 09 222 A1 (ELCO) describes a burner with internal exhaust gas recirculation with: a burner tube, a fuel nozzle arranged therein, an air supply line surrounding the fuel nozzle, and an adjoining baffle plate. In the area facing the baffle plate, the burner tube is provided with slots through which exhaust gas is drawn into the combustion zone of the burner tube as a result of the flow injector effect. However, these exhaust gases do not always reach the areas of greatest NO _x production.

EP 0 378 517 A2 (FÜLLEMANN) discloses a burner with a burner tube, which is followed by a mixing head. The burner contains a fuel nozzle for oil supply, which sprays the fuel against the hot inner wall of the burner tube in order to achieve better atomization and evaporation of the fuel.

Finally, DE 82 21 304 U1 (KLAMKE) describes a burner with internal exhaust gas recirculation via a plurality of supply channels distributed around the circumference of the burner tube.

Also EP 0288031 B1 (Weishaupt) _x NO describes a low-carbon burner for the combustion of fuel oil or fuel gas. In contrast to the systems described so far, this is a burner with a so-called external exhaust gas recirculation, ie with an exhaust pipe running outside the boiler room and a recirculation fan used in this pipe. An external exhaust gas recirculation of this type is associated with a considerably higher expenditure on equipment than the internal exhaust gas recirculation. In addition, malfunctions can easily occur due to the formation of condensate or contamination in the exhaust gas recirculation line.

Based on the prior art described above, the invention aims to provide another method and another burner for the combustion of liquid or gaseous fuels, which in particular reduces pollutant emissions, especially NO _x emissions.

This object is achieved by the subject matter of claims 1 and 4.

Thereafter: - via appropriately arranged and designed fuel nozzles - a considerable part of the fuel is fed to an area downstream of the baffle plate and adjacent to the inner wall of the burner tube, exhaust gases located in the combustion chamber by internal recirculation in vacuum areas built up downstream of the baffle plate (in the burner tube) are recycled and for this purpose guide devices which break through the burner tube and lead into the vacuum areas are used.

According to the invention, a considerable concentration of substances is built up in an area which is displaced downstream from the baffle plate and adjoins the inner wall of the burner tube. A type of fuel jacket is formed downstream of the baffle plate and against the inner wall of the burner tube. As a result, hot zones of the flame and thus areas of greatest NO _x production are also displaced radially outward from the baffle plate downstream and from the center of the burner tube. This results in an overall expansion of the flame or the flame front, so that the exhaust gases returned from the combustion chamber via the guide devices penetrate directly into the hot zones of the flame. As a result, the flame temperature and the oxygen partial pressure are effectively reduced, particularly where the NO _x formation is greatest. In other words, the flame areas with the greatest risk of NOx formation per se are relocated to where they can be conveniently exposed to exhaust gas, in particular such exhaust gas that is already cooler and has only a small unburned portion.

In known oil burners, part of the fuel often gets into the edge region of the burner tube anyway. However, such oil burners do not have the guide devices according to the invention.

The guide devices are preferably used as flow backflow and / or swirl surfaces (claim 2).

If the fuel / combustion air mixture flows against such flow impoundment areas, overpressure zones form upstream of the accumulation areas and underpressure zones downstream thereof from, the latter cause both a flame stabilization due to hot backflow zones, as well as an increased injection by suction of the exhaust gases from the combustion chamber. If the guiding devices are used as mung swirl surfaces, the fuel / combustion air mixture is swirled. This results in an improved mixing of the fuel with the combustion air and thus the most complete possible combustion of the fuel.

The amount of fuel supplied is preferably controlled as a function of the output of the combustion plants and thus in an energy-saving manner (claim 3).

One or more fuel nozzles, in particular fuel gas nozzles, are preferably guided up to the inner wall of the burner tube, in particular in such a way that they blow the fuel axially along the inner wall of the burner tube and / or radially against them (claims 5 to 7). As a result, the fuel, in particular fuel gas, transport according to the invention can be implemented particularly easily in an area located downstream of the baffle plate and adjoining the inner wall of the burner tube.

The guiding devices against which the fuel flows are preferably uniformly distributed over the circumference of the burner tube and designed as baffle and / or swirl surfaces (claim 8). Such an arrangement of the guide devices enables particularly effective exhaust gas injection into the flame, in particular as a result of the negative pressure zones which form behind such storage areas. In addition, such negative pressure zones in the shadow of the guide devices cause hot exhaust gases to be returned directly from the flame to the root of the flame in a turbulent flow. This leads to a stable shift of flame root areas to the control devices and thus overall for a stable expansion of the flame in the direction of the inner wall of the burner tube.

The guide devices are preferably designed as pipe sections (claim 9). Such a design of the control devices is technically particularly easy to implement. In addition, such pipe sections can protrude with their mouth into any vacuum areas located downstream of the baffle plate and use the accumulation effect of such vacuum areas, for example in the flow shadow directly behind the baffle plate, for exhaust gas recirculation. In addition, the cool exhaust gases in the pipe sections heated by the flame are heated, which increases their flow rate.

It is particularly expedient if the pipe section mouth protrudes into a flow region of the fuel / combustion air mixture lying downstream of the baffle plate and adjoining the inner wall of the burner pipe (claim 10). Exhaust gas (in the manner of a water or steam jet pump) is "carried away" by the fuel-combustion air mixture flowing past the pipe section at high speed, so that exhaust gas is constantly sucked out of the combustion chamber into the combustion zone of the burner tube. This effect is further increased if the pipe sections are arranged so inclined against the burner pipe wall that the pipe section mouth is downstream of the pipe section entrance (claim 11).

As an alternative to this, the guide devices preferably each comprise an opening in the burner tube wall which serves for exhaust gas circulation and a guide plate which projects into the combustion chamber from the upstream boundary edge of the opening (claim 12). On such guide plates, a storage area builds up on the upstream side and a vacuum area on the downstream side, which - as described above - has a favorable effect on the exhaust gas recirculation with a corresponding angle of attack. The guide plates practice with appropriate Inclination against the burner tube axis and / or suitable shaping additionally has a swirl effect on the fuel gas / combustion air mixture. The suction of the exhaust gases from the combustion chamber is further increased by the fact that the guide plates protrude into the flow region of the fuel / combustion air mixture lying downstream of the baffle plate and adjoining the inner wall of the burner tube (claim 13). Here, too, the flow of the fuel-combustion air mixture running along the inner wall of the burner tube increases the exhaust gas injection.

The guide plates preferably have a polygonal and / or curved, in particular delta wing-shaped plan (claim 14). As a result, vortices of various geometries and in particular delta wing effects can be generated in the flow of the fuel / combustion air mixture. In cooperation with the stabilization of the flame on such guide plates, a particularly homogeneous fuel / combustion air mixture is hereby achieved in the area of the flame root, so that complete combustion occurs with a largely homogeneous temperature distribution.

It is also advantageous if the guide plate is a wall section cut free from the burner tube wall and then bent inwards (claim 15). Such a design of the guide plate is particularly simple and inexpensive to manufacture.

Suction deflectors are preferably arranged on the outer wall of the burner tube downstream of the exhaust gas recirculation openings in order to prevent recirculation of exhaust gases with too much unburned content through the exhaust gas recirculation openings (claim 16). The still hot exhaust gases do not lead to effective cooling of the flame, at most they serve to improve flame stability. Therefore, it is advantageous to have a recirculation flow from the Exhaust gases escaping from the burner tube with excessive unburned content are to be prevented by appropriate suction deflectors on the outer wall of the burner tube.

Flow lines are preferably led from the inlet openings of the exhaust gas guide devices into the space located radially outside of the burner tube, in such a way that exhaust gases can be recirculated from predetermined points in the combustion chamber (claim 17). This has the advantage that cooler exhaust gases with a particularly low unburned fraction can be sucked off specifically from certain points in the combustion chamber and returned to the points at risk of NO _x production. In the case of so-called flame reversal boilers, there is in particular the possibility that exhaust gases from the exhaust gas reversal flow located within the combustion chamber are sucked into the burner tube via such flow lines and returned to the flame.

Fig. 1

ein Ausführungsbeispiel des erfindungsgemäßen Brenners im Längsschnitt;

Fig. 2a,b

einen Längs- und einen Querschnitt durch den mit Leiteinrichtungen einer ersten Ausführungsform bestückten Abschnitt des Brennerrohres;

Fig. 3a,b

einen Längs- und einen Querschnitt durch den mit Leiteinrichtungen einer zweiten Ausführungsform bestückten Abschnitt des Brennerrohres; und

Fig. 4a-f

jeweils einen Ausschnitt aus einer Abwicklung des mit den Leiteinrichtungen bestückten Brennerrohrabschnittes, wobei jede Figur ein anderes Ausführungsbeispiel der Leiteinrichtungen veranschaulicht.

Further advantages and refinements of the invention result from the following description of preferred exemplary embodiments. Therein, reference is made to the attached schematic drawing. The drawing shows:

Fig. 1

an embodiment of the burner according to the invention in longitudinal section;

2a, b

a longitudinal and a cross section through the portion equipped with guide devices of a first embodiment of the burner tube;

3a, b

a longitudinal and a cross section through the portion of the burner tube equipped with guide devices of a second embodiment; and

4a-f

in each case a section of a development of the burner tube section equipped with the guide devices, each figure illustrating a different exemplary embodiment of the guide devices.

The burner shown in Fig. 1 is designed for the low-pollutant combustion of fuel gas. However, this is not to be understood as restrictive, since burners according to the invention are also suitable for the combustion of liquid fuels.

The burner essentially has a burner tube 1 which projects into a combustion chamber 3 of a boiler 5 indicated by its wall. The combustion air is fed to the burner tube 1 in the direction of arrow I, preferably with the aid of a corresponding blower or a suction device. The fuel is supplied via a burner lance 13, which is arranged in the burner tube 1 and which leads into fuel nozzles 15, not shown.

In the burner tube 1, a baffle plate 17 is arranged downstream of the burner fuel nozzles 15 and extends perpendicular to the longitudinal axis of the burner tube and, in the usual way, has a central opening 19 for the passage of part of the fuel / combustion air mixture. Radially extending slots for the supply and swirling of combustion air can be provided between the central opening 19 and the outer boundary edge of the baffle plate 17. Another portion of the fuel-combustion air mixture flows through the space between the outer edge of the baffle plate 17 and the inner wall of the burner tube.

A combustion zone 23 adjoins the baffle plate downstream, in which the fuel-air mixture introduced is ignited. The flame then emerges from the downstream End of the burner tube 1 in the combustion chamber 3 of the boiler 5.

According to the invention, a considerable part of the fuel is supplied to an area downstream of the baffle plate 17 and adjoining the inner wall of the burner tube. Accordingly, there is a high fuel concentration, the highest in the example shown. For this purpose, several burner lances 13 are arranged near the inner wall of the burner tube coaxially to the axis of the burner tube and distributed uniformly over the circumference of the burner tube. Their fuel nozzles 15 are guided upstream of the baffle plate 17 up to the inner wall of the burner tube.

1 illustrates different orientations of the fuel nozzles 15. The fuel nozzles 15 are preferably oriented such that they blow the fuel in the axial direction along the inner wall of the burner tube (solid line). Alternatively, blow the fuel radially against the inner wall of the burner tube (dashed line) or with an axial and a radial component. As a result, the fuel is transported to the desired area together with the combustion air flowing in from behind. A type of flow jacket of the fuel / combustion air mixture is obtained, the layer thickness of which is approximately 30 mm downstream of the baffle plate. Most of the fuel is enriched within an approx. 10 mm thick jacket layer adjacent to the inner wall of the burner tube.

In the exemplary embodiment shown, a further, centrally arranged burner lance 13 'runs along the burner tube axis and blows a comparatively small amount of fuel through the central opening 19 of the baffle plate 17 into the combustion zone 23 of the burner tube 1 with its fuel nozzle 15'.

According to the invention, therefore, hot zones of the flame and thus the flame areas with the greatest NOx production per se are displaced from the baffle plate 17 downstream and radially outward in the direction of the inner wall of the burner tube. There, they can be supplied with cool exhaust gas comparatively easily by internal exhaust gas recirculation.

For this purpose, exhaust gas recirculation openings 25 are introduced downstream of the baffle plate 17 (at a distance of approximately 40 mm) in the burner tube wall - evenly distributed over the circumference of the burner tube 1. A guide plate 27 projects into the combustion zone 23 of the burner tube 1 from the upstream boundary edge of these openings 25. The guide plates 27 can have the shape of a delta wing (cf. FIG. 2a, b) or some other suitable flow form, for example one of the ones shown in FIG. 4a, c, d, e and / or f forms shown. They consist of a burner tube wall section cut out of the burner tube wall and then bent inwards.

Each baffle plate 27 causes a jam in front of it, ie upstream, and a vacuum zone behind it, ie downstream, in the fuel / combustion air flow jacket adjacent to the inner wall of the burner tube. These vacuum zones suck in the exhaust gases from the combustion chamber 3 and thus lead to exhaust gas recirculation. The shape according to the invention in the manner of a delta wing leads to "standing vortices" on the guide plates 27, which contribute to flame stabilization. In this way, an expansion of the flame in the direction of the inner wall of the burner tube and displacement of flame root areas toward the guide plates 27 is achieved. As a result, the recirculated exhaust gases are injected into the hot zones of the flame and thus into the areas of greatest NO _x production.

The vacuum areas immediately downstream of the baffle plate 17, which are due to the stall at the Forming boundary edges of the baffle plate 17 contribute to increasing the suction of the exhaust gases from the combustion chamber 3.

Furthermore, an annular diaphragm 28 is arranged around the outer wall of the burner tube 1 downstream of the exhaust gas return openings 25 as a return deflector in order to prevent recirculation of exhaust gases with an excessively high unburned content directly from the combustion zone 23.

In the embodiment shown in FIGS. 2a and 2b, several - here eighteen - radially inwardly projecting guide plates 27 are evenly distributed over the circumference of the burner tube 1 and each have approximately the shape of a delta wing or an equilateral or only isosceles triangle.

3a and 3b show a further preferred exemplary embodiment of the exhaust gas guide devices according to the invention. There, the guide devices according to the invention are designed as pipe sections 29 which break through the burner pipe wall downstream of the baffle plate 17 and are inclined in such a way that the pipe section mouth lies downstream of the pipe section entrance. The pipe section mouth protrudes here into the flow jacket of the fuel / combustion air mixture lying downstream of the baffle plate 17 and adjoining the inner wall of the burner pipe. The gas-air mixture flowing past the pipe piece mouths entrains cool exhaust gases from the combustion chamber 3 of the boiler 5 (Bernoulli principle), which leads to internal exhaust gas recirculation.

3a shows the uniform distribution of the - here eighteen - pipe sections 29 over the circumference of the burner pipe wall.

Figures 4a, b, c, d, e and f illustrate different configurations of the guide devices 27 and 29, respectively. Each figure schematically represents a section from a settlement of the section of the burner tube 1 equipped with the guide devices 27, 29.

4a and c-f, the guide devices 27 are each designed as a wall section cut free from the burner tube wall and then bent inwards. The bending edge 31 thereof runs in FIGS. 4c-e at right angles to the longitudinal axis of the burner tube 1; however, in FIGS. 4a and 4f, at an angle to the longitudinal axis of the burner. The flow angle of the guide plates 27 can be changed by bending the guide plates 27 to different degrees around their bending edge 31. If the guide plates 27 - as seen in the direction of flow - are symmetrical and they have a bending edge 31 running at right angles to the longitudinal axis of the burner tube, then they have practically no swirl effect on the fuel / combustion air mixture. Corresponding configurations are shown in FIGS. 4c, d and e. If, on the other hand, the bending edges 31 run obliquely to the longitudinal axis of the burner tube and / or the guide plates 27 - as seen in the flow direction - are designed asymmetrically, then the guide plates 27 also exert a swirl effect on the fuel / combustion air mixture. Corresponding configurations are shown in FIGS. 4a and 4f. In addition, a swirl effect on the flow mixture can also be exerted by the fact that the guide plates — as seen in the flow direction — are asymmetrical. Again, reference is made to FIGS. 4a and 4f. Finally, a swirl effect can also be exerted on the flow mixture by the fact that the guide plates twist in themselves and / or have a different curvature transversely to the longitudinal axis of the burner tube.

4a, the guide plates 27 are essentially in the form of right-angled lobes, but with a bending edge 31 that runs obliquely to the longitudinal axis of the burner tube. The guide plates 27 according to FIG. 4d essentially correspond to FIG. 4a, but have a right angle to the longitudinal axis of the burner tube running bending edge 31. In FIG. 4b tubular guide devices 29 are shown which taper towards the inside of the burner tube. 4c illustrates guide plates 27 in the form of isosceles triangles with an upstream base or bending edge 31 and a downstream tip.

4e illustrates guide plates 27 in the form of a symmetrical trapezoid, the narrow side of which is the upstream bending edge 31. This guide plate 27 is also in the manner of a delta wing against the flow. 4f, the guide plates 27 have the shape of a right-angled triangle, the edges of which lie at right angles to one another lie transversely to and in the direction of the longitudinal axis of the burner tube and the base of which extends obliquely to the axis of the burner tube.

In summary, a burner is taught which, due to the fuel supply according to the invention and the design and arrangement of the exhaust gas guiding devices according to the invention, achieves a particularly effective reduction in NOx emissions in the combustion zone of the burner tube. In addition, the burner according to the invention is characterized by an almost complete combustion of the fuel-combustion air mixture, so that in addition to the NO _x values, the other pollutant emission values are reduced to a considerable extent. The effort required for the design of the burner according to the invention is low, since in particular the fuel supply according to the invention and the control devices can be implemented inexpensively.

Claims (17)

1. Process for low-pollutant, in particular low-NO_x combustion of liquid or gaseous fuels in furnaces having a burner projecting into a combustion chamber (3) of a boiler (5), the burner pipe (1) of which burner having at least one fuel nozzle (15; 15') arranged therein for supplying the fuel and a baffle plate (17) connecting thereto, in which:

   a) a considerable part of the fuel is supplied to a region lying downstream of the baffle plate (17) and adjoining the internal wall of the burner pipe,

   b) waste gases situated in the combustion chamber are returned by internal recirculation in negative pressure regions in the burner pipe (1) formed downstream of the baffle plate (17), wherein one or more conduit devices (27, 25; 29) breaching the burner pipe (1) and projecting into the negative pressure regions are used for this.
2. Process according to claim 1, characterised in that the conduit devices (27, 25; 29) are used as baffle and/or swirl surfaces for the flow.
3. Process according to one of the preceding claims, characterised in that the supplied quantity of fuel is controlled as a function of the capacity of the burner.
4. Burner, in particular for carrying out the process according to one of the preceding claims, having a burner pipe (1) projecting into a combustion chamber (3) of a boiler (5), at least one fuel nozzle (15; 15') arranged therein for supplying the fuel and a baffle plate (17) connecting thereto, wherein:

   a) the fuel nozzles (15; 15') are arranged in the burner pipe (1) such that a considerable part of the fuel is supplied to a region situated downstream of the baffle plate (17) and adjoining the internal wall of the burner pipe, and

   b) one or more waste gas conduit devices (25, 27; 29) breaching the burner pipe (1) lead to negative pressure regions in the burner pipe (1) formed downstream of the baffle plate (17) such that they return waste gases situated in the combustion chamber (3) by internal recirculation to the negative pressure regions.
5. Burner according to claim 4, characterised in that at least one fuel nozzle (15), in particular fuel gas nozzle, is introduced as far as the internal wall of the burner pipe.
6. Burner according to claim 5, characterised in that the fuel nozzle (15) blows the fuel in the axial direction along the internal wall of the burner pipe.
7. Burner according to claim 5 or 6, characterised in that the fuel nozzle (15) blows the fuel radially against the internal wall of the burner pipe.
8. Burner according to one of claims 4 to 7,
   characterised in that the conduit devices (25, 27; 29) with flowing fuel are arranged to be distributed evenly over the periphery of the burner pipe (1) and are designed as baffle and/or swirl surfaces.
9. Burner according to one of claims 4 to 8,
   characterised in that the conduit devices (25, 27; 29) are designed as pipe pieces (29).
10. Burner according to claim 9, characterised in that the pipe piece mouth projects into a flow region of the fuel-combustion air mixture lying downstream of the baffle plate (17) and adjoining the internal wall of the burner pipe.
11. Burner according to claim 10, characterised in that the pipe pieces (29) are arranged against the burner pipe wall at an angle such that the pipe piece mouth lies downstream of the pipe piece entrance.
12. Burner according to one of claims 4 to 8,
    characterised in that the conduit devices (25, 27; 29) comprise in each case an opening (25) in the burner pipe wall serving for waste gas circulation and a deflecting plate (27) projecting into the burner pipe (1) from the upstream limiting edge (31) of the opening.
13. Burner according to claim 12, characterised in that the deflecting plates (27) project into the flow region of the fuel-combustion air mixture lying downstream of the baffle plate (17) and adjoining the internal wall of the burner pipe.
14. Burner according to claim 12 or 13, characterised in that the deflecting plates (27) have a polygonal and/or curved, in particular delta-wing-shaped outline.
15. Burner according to one of claims 12 to 14,
    characterised in that one or more deflecting plates (27) are designed in each case as a wall section cut free from the burner pipe wall and then bent inwards.
16. Burner according to one of claims 4 to 15,
    characterised in that back-suction deflectors (28) are arranged on the outer wall of the burner pipe (1) downstream of the waste gas return openings (25), in order to prevent recirculation of waste gases with too high a non-combusted portion through the waste gas return openings (25) .
17. Burner according to one of claims 4 to 16,
    characterised in that flow pipes are introduced into the chamber situated radially outside the burner pipe (1) from the entrance openings (25) of the waste gas-conduit devices (25, 27; 29), such that waste gases can be recirculated from preset points in the combustion chamber (3).

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