DE19721936A1 - Burner for operating a unit for generating a hot gas - Google Patents

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, as in EP B1-0 321 809, is based on the creation of a backflow zone or backflow bubble (= vortex breakdown). These burners are often used as premix burners records, based on the fact that the premix of the used coming fuel within a distance belonging to the burner is taken. With an unfavorable design of the swirl generator resp. the swirl bil of such a premix burner is due to the high swirl number wanted a short backflow zone due to the vortex bursting into a long one almost cylindrical backflow zone over. When operating such a premix burner ners without a subsequent combustion chamber, or if the combustion is too large space, 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 in the core extracted the heat. This leads, especially at the start, insufficient flame stabilization, and when operating the premix  burner with a liquid fuel to an insufficient pre-evaporator drop of fuel. This behavior can also be used for burners Detect boiler systems with passive flue gas recirculation in the combustion chamber len. These problems can lead to flame extinction or vibrations, and make an undesired special starting procedure necessary. With Hei Firing systems must also provide a very long start-up phase the one that leads to increased pollutant emissions. This essentially depends together with the fact that the entire boiler with its relatively large thermi Inertia must be warmed up until the back-flowing exhaust gases have a sufficient temperature.

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 front mixed burners;
• b) from a) it follows that the operating range with ei optimal flame position remains limited;
• c) the combustion is subject to pulsations that manifold to one Destabilization of the flame position and / or an increase in the Pollutant emissions, especially those of NOx emissions;
• d) there are large deviations with regard to the optimal flow conditions whereby the potential of the premix burner is incomplete dig can be exploited;
• e) the starting procedure is problema from the above-mentioned shortcomings table to handle.

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 are incomplete able to remedy inconveniences and shortcomings.

The main advantage of the invention is that the main body of the burner remains essentially unchanged. Just to fix the disadvantages mentioned above as well as to strengthen themselves at the exit of the burner Backflow zone forming have the inner walls of those forming the burner Shells built-in guide bodies, which take over the task, in advance the combustion air flowing purely tangentially into the interior of the burner, wel che preferably consists of an air / exhaust gas mixture, in the axial direction redirect. The inflow angle of this guide body takes, which are preferably designed as guide vanes, seen from the burner tip in the direction of flow. In the area of the burner outlet, these guide bodies have up to a vertical position with respect to the burner axis. So that these Guides can work properly, their number will be within the length of the Brenners chosen so that the ratio between the distance of the guide body to each other other and the width of the tangential inflow channel into the interior of the Brenners is approximately 1.

Advantageous and expedient developments of the task according to the invention Solutions 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 currents The direction of the media is indicated by arrows.

Brief description of the drawings

It shows:

Fig. 1 a premix burner in a perspective view;

Fig. 2 shows a further perspective view of the premix burner according to

Fig. 1, from a different view, in simplified form,

Figure 3 gates. A radial section through the premix burner with view of the Injek,

Fig. 4 is an axial section through the premix burner according to FIG. 3, with pa rallelem course of hole plates compared to the Einströmungsebenen, with representation of guide vanes in the interior of the premix burner,

Fig. 5 shows a further radial section through the premix burner with a view of the injectors and

Fig. 6 is an axial section through the premix burner of FIG. 5 with egg ner another configuration of the injectors in the flow direction.

WAYS OF CARRYING OUT THE INVENTION, INDUSTRIAL APPLICABILITY

Fig. 1 shows a premix burner in perspective. For a better understanding of the subject matter, it is advantageous if, at the same time, at least FIG. 2, possibly FIG. 3 are used in the detection of FIG. 1. The first-mentioned figures have the main purpose of marking out the type and function of such a burner.

The premix burner according to Fig. 1 consists of two hollow conical partial bodies 1, 2, are offset interleaved with each other. This burner is operated with a gaseous and / or liquid fuel. The term "cone-shaped" here is not only understood to mean the cone shape shown, which is characterized by a fixed opening angle, but also includes other configurations of the partial bodies, such as a diffuser or diffuser-like shape and a confuser or confuser-like shape. These forms are not specifically shown here, since they are readily familiar to the person skilled in the art. The offset of the respective central axis or longitudinal axis of symmetry of the partial bodies 1 , 2 to one another (see FIG. 2, items 3 , 4 ) creates a tangential air inlet duct 5 , 6 on both sides, in a mirror-image arrangement, through which the combustion air 7 in Interior of the premix burner, ie flows into the cone cavity 8 . The two tapered part body 1 , 2 each have a cylindrical starting part 9 , 10 , which also, analogously to the aforementioned Teilkör pern 1 , 2 , offset to each other, so that the tangential air inlet channels 5 , 6 are present over the entire length of the premix burner. In the loading area of the cylindrical initial part, a nozzle 11 is housed for the preferred atomization of a liquid fuel 12 , such that its nozzle approximately coincides with the narrowest cross section of the cone cavity 8 formed by the partial bodies 1 , 2 . The injection capacity and the operating mode of this nozzle 11 depend on the specified parameters of the respective premix burner. The fuel 12 injected through the nozzle 11 can, if necessary, be enriched with 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 designed in a purely conical manner, that is to say without cylindrical starting parts 9 , 10 . The sub-bodies 1 , 2 also each have egg ne fuel line 13 , 14 which are arranged along the tangential inlet channels 5 , 6 and are provided with injection openings 15 through which a gaseous fuel 16 is preferably injected into the combustion air 7 flowing past there , as is symbolized by arrows 16 , this injection also forming the fuel injection plane (cf. FIG. 2, item 22 ) of the system. These fuel lines 13 , 14 are preferably placed at the latest at the end of the tangential inflow, before entering the cone cavity 8 , in order to ensure an optimal air / fuel mixture.

On the combustion chamber side, the premix burner has a front plate 18 serving as an anchor for the partial bodies 1 , 2 with a number of bores 19 through which, if necessary, a mixed or cooling air 20 is supplied to the front part of the combustion chamber 17 or its wall.

If, as already described, the premix burner is operated solely by means of a liquid fuel 12 , this is done via the central nozzle 11 , this fuel 12 then being injected into the cone cavity 8 or into the combustion chamber 17 at an acute angle. From the nozzle 11 , a conical fuel profile 23 is formed , which is enclosed by the tangentially flowing rotating combustion air 7 . In the axial direction, the concentration of the injected fuel 12 is continuously reduced by the inflowing combustion air 7 to an optimal mixture.

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

When the liquid fuel 12 is injected via the nozzle 11 , the optimal, homogeneous fuel concentration is achieved over the cross section at the end of the premix burner. If the combustion air 7 is additionally preheated or enriched with a recirculated exhaust gas, this supports the evaporation of the liquid fuel 12 sustainably within the premixing section induced by the length of the pre-mixing burner. As far as the admixture of a recirculated flue gas is concerned, reference is made to FIGS . 3-6.

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

In the design of the conical partial body 1 , 2 with regard to the increase in the flow cross section and the width of the tangential air inlet channels 5 , 6 , strict limits are to be adhered to so that the desired flow field of the combustion air 7 can be set at the outlet of the premix burner. The critical swirl number occurs at the outlet of the premix burner: there also forms a backflow zone 24 (vortex breakdown) with a stabilizing effect compared to the flame front 25 acting there, in the sense that the backflow zone 24 takes over the function of a disembodied flame holder .

The optimum fuel concentration across the cross section is only achieved in the area of the vortex burst, that is to say in the area of the backflow zone 24 . It is only at this point that a stable flame front 25 is created .

In general, it can be said that minimizing the flow opening of the tangential air inlet ducts 6 , 7 is predestined to form the return flow zone 24 from the end of the premixing section. The design of the premix burner is also excellent for changing the flow opening of the tangential air inlet ducts 5 , 6 as required, so that a relatively large operating range can be detected without changing the overall length of the pre-mixing burner. Of course, the sub-bodies 1 , 2 can also be moved to one another in another plane, as a result of which there is even an overlap of the latter in relation to the air inlet plane into the cone cavity 8 (see FIG. 2, item 21 ) 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 to interleave the sub-bodies 1 , 2 in a spiral manner by counter-rotating movement.

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

As far as the number of air inlet ducts is concerned, the premix burner is not limited to the number shown. A larger number is shown, for example, where it is a matter of making the premixing wider or of influencing the swirl number and thus the formation of the backflow zone 24 as a result thereof by a larger number of air inlet channels.

Premix burners of the type described here are also those for which Achieving a swirl flow from a cylindrical or quasi-cylindrical It is assumed that the combustion air flows into the interior of the pipe Pipe via tangentially arranged air inlet ducts, and inside the tube a conical body with in the direction of flow taking cross-section is arranged, which also with this configuration critical swirl number can be achieved at the outlet of the burner.

Fig. 2 shows the same premix burner according to FIG. 1, but from a different perspective and in a simplified representation. This Fig. 2 is essentially intended to properly detect the configuration of this premix burner. In particular, in this Fig. 2, the displacement of the two sub-bodies 1 , 2 to each other, based on the main central axis 26 (= burner axis) of the premix burner, which corresponds to the main axis of the central fuel nozzle 11 , is quite clearly visible. This displacement is a measure of the size of the flow width, respectively. the flow cross section of the tangential air inlet ducts 5 , 6 . The respective central axes 3 , 4 run parallel to one another here.

Fig. 3 is a section approximately in the middle of the premix burner. The mirror-image tangentially arranged feed channels 27 , 28 each fulfill the function of a mixing section, in which the combustion air 7 , which is formed from fresh air 29 and recirculated flue gas 30 , is perfected. The combustion air 7 is processed in an injector system 200 . Upstream of each supply channel 27 , 28 , which serves as a tangential inflow into the interior 8 of the premix burner, the fresh air 29 is distributed uniformly over the entire length of this premix burner via perforated plates 31 , 32 . In the direction of flow to the tangentia len inlet channels 5 , 6 , these perforated plates 31 , 32 are perforated. The perforations fulfill the function of individual injector nozzles 31 a, 32 a, which exert a suction effect on the surrounding flue gas 30 , in such a way that each of these injector nozzles 31 a, 32 a each only sucks a certain proportion of flue gas 30 , whereupon over the entire axial Length of the perforated plates 31 , 32 , which corresponds to the length of the burner, a uniform flue gas admixture takes place. This configuration ensures that intimate mixing takes place at the point of contact of the two media, i.e. the fresh air 29 and the flue gas 30 , so that the flow lengths of the supply channels 27 , 28 reaching the tangential air inlet channels 5 , 6 are minimized for the mixture formation can. In addition, the local injector configuration 200 is distinguished by the fact that the geometry of the premix burner, in particular as regards the shape and the size of the tangential air inlet ducts 5 , 6 , remains dimensionally stable, ie through the uniformly metered distribution of the hot gases 30 along the The entire axial length of the premix burner does not result in any heat-related faults. The same injector configuration as that just described here can also be provided in the area of the head-side fuel nozzle 11 for an axial supply of combustion air. The feed channels 27 , 28 also have guide plates 50 , which will be discussed in more detail in the description of FIG. 4.

Fig. 4 is a schematic representation of the premix burner in direction of flow, in particular the course of the perforated plates belonging to the injector system 31 , 32 with respect to the inflow planes 33 of the feed channels 27 , 28 is expressed. This course is parallel, the Einströmungseben NEN 33 itself also running parallel to the burner axis 26 of the premix burner over the entire burner length. This figure also shows how the injector nozzles 31 a, 32 a are mounted. There are two ways of identifying the guidance of the injector nozzles 31 a, 32 a. On the one hand, the upper illustration shows a completely vertical course of the injector nozzles 32 a. On the other hand, the lower illustration shows a different course of the injector nozzles 31 a: Here they have an inflow angle which changes continuously in the direction of flow relative to the burner axis 26 . From an initially acute angle in the area of the head stage of the premix burner, this gradually increases until the injector nozzles 31 a in the area of the burner end are then approximately perpendicular to the burner axis 26 . Which design variant is used depends on the specific operating parameters and other auxiliary measures. Mixed forms of vertical and oblique injection are also possible. In order to maximize the mixing quality of the air / flue gas mixture 7 and to strengthen the positional stability of the return flow zone (see FIG. 1), the partial bodies 1 , 2 (see FIGS. 1-3) are equipped with guide vanes 50 . These deflect the tangentially and largely vertically inflowing air / flue gas mixture 7 in an axial or quasi-axial direction. The inflow angle α, ie the angle of the corresponding guide vane with respect to the burner axis 26 , increases from the burner head to the burner outlet, the angularity of these guide vanes 50 , of course, depending on the respective inflow plane of the injector nozzles 31 a, 32 a. In the area of the combustion outlet, the last-acting guide vane is essentially almost perpendicular to the burner axis 26 . Expressed in numbers, the angle α increases in the case of vertically acting injector nozzles 31 a from initially approximately 40 ° to an angle α _n of approximately 80 °. So that these guide blades 50 can work properly, their number is selected within the length of the premix burner so that the ratio between the distance S of the guide blades to one another and the width H of the tangential air inlet ducts into the interior of the premix burner is approximately 1. This eliminates the disadvantages discussed above in the "State of the art" chapter.

Fig. 5 and 6 show substantially the same configuration as shown in FIG. 3 and 4, wherein the perforated plates 34, which extend 35 with the associated injector nozzles 34 a 35 a likewise parallel throughout the burner length to the Einströmungsebenen 36 of the feed channels 27 28. However, these inflow planes 36 run conically with respect to the burner axis 26 of the premix burner. The variable inflow angle of the injector nozzles 34 a, 35 a in the direction of flow also largely corresponds to the configuration according to FIGS. 3 and 4, where the gradual erection of these injector nozzles 34 a, 35 a results in a vertical inflow in the region of the outlet of the premix burner primarily directed towards the inflow plane 36 of the respective feed channel. The arrangement and angular position of the guide vanes to be sent here, but not shown in detail, are adapted accordingly to the burner axis 26 due to the predetermined inflow levels of the air / exhaust gas mixture.

Reference list

1

,

2nd

Partial conical body

3rd

,

4th

Central axis too

1

resp.

2nd

5

,

6

Tangential air intake ducts

7

Combustion air

8th

Cone cavity, interior of the burner

9

,

10th

Cylindrical starting parts of the burner

11

Fuel nozzle

12th

Fuel, liquid fuel

13

,

14

Fuel lines

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

Air, mixed air, cooling air

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

,

28

Feed channels

29

Fresh air

30th

Recirculated flue gas

31

,

32

Perforated plates

31

a,

32

a Injector nozzles

33

Inflow plane of the feed channels

27

,

28

34

,

35

Perforated plates

34

a,

35

a Injector nozzles

36

Inflow plane of the feed channels

27

,

28

50

Guide body, guide vanes

200

Injector system
α inflow angle
α _n

Inflow angle
S Guide blade spacing
H Tangential air inlet duct

Claims (13)

1. burner for operating a unit for generating a hot gas, the burner consisting essentially of at least two hollow, cone-shaped partial bodies ( 1 , 2 ) nested one inside the other in the flow direction, the central axes ( 3 , 4 ) of which are offset with respect to one another, derge stalt, that adjacent walls of these partial bodies ( 1 , 2 ) form tangential air inlet channels ( 5 , 6 ) for the inflow of combustion air ( 7 ) into an interior space ( 8 ) formed by the partial bodies ( 1 , 2 ), and where the burner has at least one Fuel nozzle ( 11 , 15 ) can be operated, characterized in that the partial bodies ( 1 , 2 ) on their inner walls are spaced apart and in operative connection with the combustion air ( 7 ) flowing into the interior ( 8 ) and have guide bodies ( 50 ). 2. Burner according to claim 1, characterized in that the guide body ( 50 ) in the longitudinal direction of the burner have a variable Anströmungswin angle (α, α _n ) with respect to the burner axis ( 26 ). 3. Burner according to claim 2, characterized in that the inflow angle of the guide body ( 50 ) increases between 40 ° at the burner head and 80 ° at the burner outlet. 4. Burner according to claim 1, characterized in that the ratio between the distance (S) of the individual guide bodies ( 50 ) to one another and the width (H) of the tangential air inlet channels ( 5 , 6 ) is approximately 1. 5. Burner according to claim 1, characterized in that the guide body ( 50 ) have the shape of guide vanes. 6. Burner according to claim 1, characterized in that the fuel nozzle ( 11 ) is arranged on the head side and on the burner axis ( 26 ). 7. Burner according to claim 1, characterized in that in the region of the tangential air inlet channels ( 5 , 6 ) in the longitudinal extension of the burner egg ne number of mutually spaced fuel nozzles ( 15 ) are arranged. 8. Burner according to claim 1, characterized in that the flow cross-section of the interior of the partial bodies ( 1 , 2 ) formed ( 8 ) increases uniformly in the flow direction. 9. Burner according to claim 1, characterized in that the flow cross-section of the interior of the partial bodies ( 1 , 2 ) formed ( 8 ) egg NEN diffuser, a diffuser-like course, a confuser, a confu sor-like course. 10. Burner according to claim 1, characterized in that the partial bodies ( 1 , 2 ) are nested spirally one inside the other. 11. Burner according to claim 1, characterized in that extend in the radial or quasi-radial direction relative to the air inlet channels ( 5 , 6 ) to guide channels ( 27 , 28 ), each having at least one injector system ( 200 ) for providing one Fresh air ( 29 ) and flue gas ( 30 ) existing combustion air ( 7 ). 12. Burner according to claim 11, characterized in that the injector system ( 200 ) associated perforated plates ( 31 , 32 ; 34 , 35 ) parallel to the respective inflow plane ( 33 , 36 ) of the combustion air ( 7 ) into the supply channels ( 27 , 28 ) run that the perforated plates in the area of the inflow levels with injector nozzles ( 31 a, 32 a; 34 a, 35 a) are provided, and that the inflow angle of the injector nozzles in the axial direction of the burner relative to the burner axis ( 26 ) is vertical and / or stands quasi-vertically, and / or is continuously changeable. 13. Burner according to claim 12, characterized in that the flow plane through the injector nozzles ( 31 a, 32 a; 34 a, 35 a) in the area of the burner head has an acute angle, and that this angle in the axial direction of the perforated plates ( 31 , 32 ; 34 , 35 ) gradually increases until it is approximately perpendicular to the inflow levels ( 33 , 36 ) of the feed channels ( 25 , 26 ) and / or to the burner axis ( 26 ) of the burner in the area of the burner outlet.