EP0881432A2 - Burner for operating a hot gas generating unit - Google Patents

Abstract

The burner comprises two hollow conical body parts (1,2) with offset centre axes. A burner front plate (18/27) is mounted on the outlet side of the burner with its outer end (27) inclined inwards at an acute angle. The outer end of the front plate comprises a ring-shaped truncated cone set on the flank-side circumference of a vertical front plate (18). The fuel nozzle (11) is mounted on the top side on the burner axis. The through-flow cross-section of the inner space formed by the body parts increases uniformly in the flow direction.

Description

Technical field

The present invention relates to a burner for operating an assembly for Generation of a hot gas according to the preamble of claim 1.

State of the art

The flame stabilization of many modern low NOx burners, so from EP-B1-0 321 809, is based on the creation of a backflow zone or backflow bubble (= Vortex breakdown). These burners are often referred to as premix burners, based on the fact that the premix of the used coming fuel made within a distance belonging to the burner becomes. With an unfavorable design of the swirl generator resp. the swirl formation of such a premix burner goes because of a too high swirl number desired short backflow zone due to the swirling of the vortex into a long one almost cylindrical backflow zone over. When operating such a premix burner without a subsequent combustion chamber, or if the combustion chamber is too large, resp. in a combustion chamber, the combustion chamber walls of which are relatively cold, what is typically the case with boilers becomes the backflow Flue gases removed the heat. This leads to a, especially at the start insufficient flame stabilization, and when operating the premix burner with a liquid fuel to an insufficient pre-evaporation of the Fuel drop. This behavior can also be seen with burners for boiler systems with a passive flue gas recirculation in the combustion chamber. This Problems can lead to flame extinction or vibrations an undesired special starting procedure is necessary. For heating systems a very long start-up phase must also be provided during which increased pollutant emissions occur. This essentially depends together with the fact that the entire boiler with its relatively large thermal Inertia must be warmed up until the back-flowing exhaust gases have a sufficient temperature.

a) Erhöhung der Gefahr eines Flammenrückschlages ins Innere des Vormischbrenners;

b) aus a) ergibt sich dann die Konsequenz, dass der Betriebsbereich mit einer optimalen Flammenposition beschränkt bleibt;

c) die Verbrennung ist Pulsationen unterworfen, die mannigfaltig zu einer Destabilisierung der Flammenposition und/oder zu einer Erhöhung der Schadstoff-Emissionen, insbesondere der NOx-Emissionen führen;

d) es entstehen grosse Abweichungen hinsichtlich der optimalen Strömungsbedingungen, wodurch das Potential des Vormischbrenners nicht vollständig ausgenutzt werden kann;

e) das Startprozedere ist aus obengenannten Unzulänglichkeiten problematisch zu handhaben.

For the premix burner itself, with such a constellation and with certain operating modes of the burner, the following imperfections or Shortcomings:

a) increasing the risk of a flashback inside the premix burner;

b) from a) there follows the consequence that the operating range remains limited with an optimal flame position;

c) the combustion is subject to pulsations which in many ways lead to the destabilization of the flame position and / or to an increase in pollutant emissions, in particular NOx emissions;

d) large deviations arise with regard to the optimal flow conditions, as a result of which the potential of the premix burner cannot be fully utilized;

e) the starting procedure is difficult to handle due to the above-mentioned shortcomings.

Presentation of the invention

The invention seeks to remedy this. The invention as set out in the claims is characterized, the task is based on a burner at the beginning to submit proposals that address the above imperfections and to remedy shortcomings.

The main advantage of the invention is that the main body of the burner, as far as the formation of the critical swirl number is concerned remains unchanged. Only to remedy the disadvantages mentioned above as well to maximize flame stabilization and strengthen the output of the The burner's backflow zone will be in the area of the burner outlet Precautions to strengthen the outer stabilization area intended. Basically, this external stabilization thereby achieve that the flow of hot gases at the burner outlet in a radial Direction is influenced by the front panel so that a direct and close recirculation of hot gases in the area of the flame front under immediate Shielding of the exhaust gases from the combustion chamber, which in itself already have experienced a cooling, can take place.

Advantageous and expedient developments of the task solution according to the invention are characterized in the further dependent claims.

Exemplary embodiments of the invention are described below with reference to the drawings explained in more detail. None for the immediate understanding of the invention necessary elements have been omitted. The same elements are in the different figures with the same reference numerals. The flow direction the media is indicated by arrows.

Brief description of the drawings

Fig. 1

einen Vormischbrenner in perspektivischer Darstellung, mit einem abschirmenden Ring im Bereich der Frontplatte und

Fig. 2

eine weitere perspektivische Darstellung des Vormischbrenners gemäss Fig. 1, aus anderer Ansicht, in vereinfachter Form.

It shows:

Fig. 1

a premix burner in perspective, with a shielding ring in the area of the front panel and

Fig. 2

another perspective view of the premix burner according to FIG. 1, from a different view, in a simplified form.

WAYS OF CARRYING OUT THE INVENTION, INDUSTRIAL APPLICABILITY

Fig. 1 shows a premix burner in perspective. For the better Understanding the subject matter is beneficial if at the same time when capturing of Fig. 1 and Fig. 2 is used for what purpose, type and Functioning of such a burner emerge. In addition, EP-B1-0 321 809 pointed out, this document an integral part represents the present description.

The premix burner according to FIG. 1 consists of two hollow conical partial bodies 1, 2, which are nested offset from one another, this one Premix burner operated with a gaseous and / or liquid fuel becomes. The term "cone-shaped" does not only mean the one shown here understood fixed opening angle characterized cone shape, but he also includes other configurations of the partial bodies, such as a diffuser or diffuser-like shape as well as a confuser or confuser-like shape. These forms are not specifically shown here because they are known to the person skilled in the art are well known. The offset of the respective central axis or Longitudinal axis of symmetry of the partial bodies 1, 2 to one another (cf. creates a tangential on both sides in a mirror-image arrangement Air inlet duct 5, 6 free, through which the combustion air 7 in one of the interior of the premix burner formed by the partial bodies, i.e. in the cone cavity 8 streams. The two conical partial bodies 1, 2 each have a cylindrical one Initial part 9, 10, which also, analogously to the aforementioned partial bodies 1, 2, run offset from one another, so that the tangential air inlet ducts 5, 6 are present over the entire length of the premix burner. In the area of the cylindrical The initial part is a nozzle 11 for preferably atomizing a liquid fuel 12 housed, such that their injection in about with the narrowest cross-section of the cone cavity formed by the partial bodies 1, 2 8 coincides. The injection capacity and the operating mode of this nozzle 11 depends on the specified parameters of the respective premix burner. The fuel 12 injected through the nozzle 1 can, if necessary be returned to a recirculated exhaust gas; then it is also possible to accomplish the complementary injection of a quantity of water through the nozzle 11.

Of course, the premix burner can be purely conical, i.e. without a cylindrical one Initial parts 9, 10 may be formed. The sub-bodies 1, 2 also each have one Fuel line 13, 14, which runs along the tangential inlet channels 5, 6 are arranged and provided with injection openings 15, through which preferably a gaseous fuel 16 in the combustion air flowing there 7 is injected, as is symbolized by arrows 16, wherein this injection also the fuel injection level (see FIG. 2, item 22) of the Systems forms. These fuel lines 13, 14 are preferably at the latest placed at the end of the tangential inflow, before entering the cone cavity 8, this to ensure an optimal air / fuel mixture.

On the combustion chamber side, the premix burner has an anchorage for the partial bodies 1, 2 serving front panel 18 with a number of holes 19 through which if necessary, preferably a hot medium 20 the front part of the combustion chamber 17 or its wall is supplied.

If, as already described, the premix burner is used solely by means of a liquid Operated fuel 12, this is done via the central nozzle 11, wherein this fuel 12 then enters the cone cavity 8 at an acute angle or is injected into the combustion chamber 17. The nozzle 11 thus forms a tapered fuel profile 23 rotating from the tangentially flowing Combustion air 7 is enclosed. In the axial direction, the concentration of the injected fuel 12 continuously through the incoming combustion air 7 broken down into an optimal mixture.

If you want to operate the premix burner with a gaseous fuel 16, so this can in principle also be done via the central fuel nozzle 11, however, such an operating mode should preferably be via the injection openings 15 be made, the formation of this fuel / air mixture directly at the end of the air inlet ducts 5, 6.

When the liquid fuel 12 is injected via the nozzle 11, the end the premix burner the optimal, homogeneous fuel concentration over the Cross section reached. Is the combustion air 7 additionally preheated or with a recycled exhaust gas enriched, this supports the evaporation of the liquid fuel 12 sustainably within the length of the premix burner induced premix section. regarding the admixture of a recirculated flue gas is referred to Fig. 3-6.

The same considerations also apply if the fuel lines 13, 14 instead of gaseous liquid fuels should now be supplied.

In the design of the conical part body 1, 2 with respect to the increase the flow cross-section and the width of the tangential air inlet ducts 5, 6 are strict limits to be observed so that the desired flow field the combustion air 7 at the outlet of the premix burner can. The critical swirl number is set at the outlet of the premix burner: A backflow zone 24 (vortex breakdown) also forms there with one opposite the flame front 25 acting there stabilizing effect, in which Meaning that the backflow zone 24 functions as a disembodied flame holder takes over.

The optimal fuel concentration across the cross section is only in the area the vortex runout, that is, in the area of the backflow zone 24. First a stable flame front 25 is then created at this point Effect results from the swirl number in in the cone cavity 8 Flow direction along the cone axis. A backlash of the flame into that This prevents the interior of the premix burner.

In general it can be said that minimizing the flow opening of the tangential Air inlet channels 6, 7 is predestined, the position of the backflow zone 24 To influence the end of the premixing section. The construction of the premix burner the flow opening of the tangential is also particularly suitable To change air inlet channels 5, 6 as required, which means without changing the Length of the premix burner covers a relatively large operating range can be. Of course, the partial bodies 1, 2 are also in another Plane can be shifted towards each other, which even overlaps the air inlet plane into the cone cavity 8 (see FIG. 2, item 21) of the same in the region of the tangential air inlet ducts 5, 6, as can be seen from FIG. 2, can be accomplished. It is then also possible for the partial body 1, 2 to be spirally nested into one another by a counter-rotating movement.

Through a more homogeneous mixture formation achievable in this premix burner achieved between the injected fuels 11, 12 and the combustion air 7 lower flame temperatures and thus lower pollutant emissions, in particular lower NOx values. Then reduce these lower temperatures the thermal load on the material on the burner front and make for example special treatment of the surface is not mandatory.

As far as the number of air inlet ducts is concerned, the premix burner is not open the number shown is limited. A larger number is displayed there, for example, when it comes to making the premixing wider, or the Swirl number and thus the dependent formation of the backflow zone 24 by to influence a larger number of air inlet ducts accordingly.

Premix burners of the type described here are also those which are to be achieved a swirl flow from a cylindrical or quasi-cylindrical tube go out, the inflow of combustion air into the interior of the pipe tangential air inlet channels is also accomplished, and inside of the tube a conical body with decreasing in the flow direction Cross section is arranged, which is also critical with this configuration Swirl number at the output of the burner can be achieved. The front panel 18 has on it flank-side circumference on an attached ring 27, which is bent is directed in such a way that the flame front 25 through this Ring 27 is encased. The axial extent as well as the degree of the angle of the Biasing depends on the respective operating needs. In the foreground with this design is that the effect of the front panel 18 on the radial Flow is specifically increased so that a direct and close recirculation the hot gases in the area of the flame front 25 under direct shielding of the exhaust gases originating from the combustion chamber 17 and have already cooled down can. This ensures that the operation described in chapter "State of the art" can solve the disadvantages.

FIG. 2 shows the same premix burner according to FIG. 1, but from a different one Perspective and in a simplified representation. This Fig. 2 is essentially serve the configuration of this premix burner as well as the design and placement of the baffles better resp. to capture properly. Especially 2, the displacement of the two partial bodies 1, 2 relative to one another is related on the main central axis 26 (= burner axis) of the premix burner, which is the The main axis of the central fuel nozzle 11 corresponds, quite clearly visible. This Dislocation in itself induces the size of the flow openings of the tangential Air inlet ducts 5, 6. The respective central axes 3, 4 run parallel here to each other. On the design of the stabilization ring 27 in the area of Front plate 18 has already been discussed in more detail in FIG. 1.

Reference list

1

Partial conical body

2nd

Partial conical body

3rd

Central axis to 1

4th

Central axis to 2

5

Tangential air inlet duct

6

Tangential air inlet duct

7

Combustion air

8th

Cone cavity, interior of the burner

9

Cylindrical starting part of the burner

10th

Cylindrical starting part of the burner

11

Fuel nozzle

12th

Fuel, liquid fuel

13

Fuel line

14

Fuel line

15

Injection openings of the fuel line 13, 14

16

Fuel, gaseous fuel

17th

Combustion chamber

18th

Front panel

19th

Holes in the front panel

20th

Hot medium, hot gases

21

Air inlet level

22

Fuel injection level

23

Fuel profile

24th

Backflow zone, backflow bubble

25th

Flame front

26

Main central axis, burner axis

27

Stabilization ring

18/27

Burner faceplate

Claims (7)

Burner for operating a unit for generating a hot gas, the burner consisting essentially of at least two hollow, conical, partial bodies nested in the flow direction (1, 2) exists, the central axes (3, 4) of which are offset from one another, that adjacent walls of these partial bodies (1, 2) are tangential Air inlet channels (5, 6) for the inflow of combustion air (7) in form an interior space (8) predetermined by the partial bodies (1, 2), and the burner being operable with at least one fuel nozzle (11, 15) is characterized in that a burner front plate on the burner outlet side (18/27) is arranged, the outer end (27) under a pointed Angle is inclined inwards. Burner according to claim 1, characterized in that the outer end (27) the burner front plate (18/27) from an annular truncated cone exists, and that this truncated cone on the flank-side circumference of a vertical or quasi-vertical front plate (18) placed is. Burner according to claim 1, characterized in that the fuel nozzle (11) is arranged on the head side and on the burner axis (26). Burner according to claim 1, characterized in that in the area of tangential air inlet channels (5, 6) in the longitudinal extension of the burner Number of spaced apart fuel nozzles (15) are. Burner according to claim 1, characterized in that the flow cross section of the interior (8) formed by the partial bodies (1, 2) in Flow direction increases uniformly. Burner according to claim 1, characterized in that the flow cross section of the interior (8) formed by the partial bodies (1, 2) Diffuser, a diffuser-like course, a confuser, a confuser-like Course forms. Burner according to claim 1, characterized in that the partial body (1, 2) are nested in a spiral.

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