EP0619457B1 - Premix burner - Google Patents

Description

Technical field

The invention relates to premix burners according to the double-cone principle with essentially two hollow, conical partial bodies nested one inside the other in the direction of flow, the respective central axes of which are offset from one another, the adjacent walls of the two partial bodies in their longitudinal extension forming tangential gaps for the combustion air, and in the area of the tangential ones Gaps in the walls of the two partial bodies are provided in the longitudinal direction distributed gas inflow openings.

State of the art

Such double-cone burners are known, for example, from EP-B1-0 321 809 and are described later in relation to FIGS. 1 and 2. The fuel, there natural gas, is injected into the combustion air flowing in from the compressor through a series of injector nozzles. As a rule, these are evenly distributed over the entire gap.

In order to achieve a reliable ignition of the mixture in the downstream combustion chamber and a sufficient burnout, an intimate mixture of the fuel with the air is required. Good mixing also helps to avoid so-called "hot spots" in the combustion chamber, which lead, among other things, to the formation of the undesired NO _x .

The above-mentioned injection of the fuel using conventional means, such as, for example, a cross-jet mixer, is difficult since the fuel itself has an insufficient impulse to achieve the required large-scale distribution and the fine-scale mixture.

Devices for intensive mixing of fuel and combustion air are known from EP-B-0 520 163. These are vortex installation surfaces in the form of delta wings, which are set in a channelized flow. If such wings are flown from the tip, a dead water area arises on the one hand downstream of the wing and on the other hand the flow through the employed surface experiences a not inconsiderable drop in pressure. The arrangement of such a delta wing in a channel must be carried out using flow-restricting aids such as struts, ribs or the like. In addition, problems arise with the cooling of such elements in a hot gas flow, for example.

Presentation of the invention

The invention is based on the object of equipping a double-cone burner of the type mentioned at the outset with a device with which longitudinal vortices can be generated without a recirculation area in the inlet gap through which flow passes.

According to the invention this is achieved with the characterizing features of patent claim 1.

With the new static mixer, which is represented by the 3-dimensional vortex generators, it is possible to achieve extraordinarily short mixing distances at the inlet to the burner with a low pressure drop. A coarse mixing of the two streams takes place after just one full vortex revolution, while a fine mixing due to turbulent flow occurs after a distance that corresponds to a few gap heights.

This type of mixture is particularly suitable for mixing the fuel into the combustion air at a relatively low admission pressure and with great dilution. A low admission pressure of the fuel is particularly advantageous when using medium and low calorific fuel gases. The energy required for mixing is largely drawn from the flow energy of the fluid with the higher volume flow, namely the combustion air.

The advantage of such an element can be seen in its particular simplicity in every respect. In terms of production technology, the element consisting of three walls with flow around it is completely problem-free. The roof surface can be joined with the two side surfaces in a variety of ways. The element can also be fixed to flat or curved gap walls in the case of weldable materials by simple weld seams. Of course, the vortex generators can also be cast together with the limiting walls. From a fluidic point of view The element has a very low flow around it Pressure loss and it creates vortices without a dead water area. Finally, due to its generally hollow interior, the element can be cooled in a variety of ways and with various means.

If the combustion air flows evenly into the inlet gaps, it is appropriate to choose the ratio of the height h of the connecting edge of the two side faces to the gap height H so that the generated vortex immediately downstream of the vortex generator is the full gap height or the full height of the vortex generator fills the assigned gap part.

Due to the fact that several vortex generators are arranged side by side without gaps across the width of the inlet gap, the entire gap cross section is fully acted upon by the vortexes shortly behind the vortex generators.

With a varying speed field in the inlet gaps, it makes sense to provide different heights for the vortex generators arranged next to one another in such a way that the absolute pressure loss along the inlet column remains constant.

It makes sense if the two side surfaces including the arrow angle α are arranged symmetrically about an axis of symmetry. This creates swirls of equal swirl.

Further advantages of the invention, in particular in connection with the arrangement of the vortex generators, result from the subclaims.

Brief description of the drawing

Fig. 1

einen Teillängsschnitt einer Brennkammer;

Fig. 2A

einen Querschnitt durch einen Vormischbrenner im Bereich des Brenneraustritts;

Fig. 2B

einen Querschnitt durch einen Vormischbrenner im Bereich der Kegelspitze;

Fig. 3

eine perspektivische Darstellung eines Wirbel-Generators;

Fig. 4

eine Ausführungsvariante des Wirbel-Generators;

Fig. 5

eine Anordnungsvariante des Wirbel-Generators nach Fig. 3;

Fig. 6a-c

die gruppenweise Anordnung von Wirbel-Generatoren in einem Eintrittsspalt im Längsschnitt, in einer Draufsicht und in einer Hinteransicht;

Fig. 7a-c

eine Ausführungsvariante einer gruppenweisen Anordnung von Wirbel-Generatoren in gleicher Darstellung wie Fig. 3 mit einer Variante der Brennstofführung;

Fig. 8

eine Vorderansicht eines Eintrittsspaltes mit eingebauten Wirbel-Generatoren;

Fig. 9

eine Anordnungvariante der Wirbel-Generatoren im Eintrittsspalt.

Several exemplary embodiments of the invention are shown schematically in the drawing. Show it:

Fig. 1

a partial longitudinal section of a combustion chamber;

Figure 2A

a cross section through a premix burner in the region of the burner outlet;

Figure 2B

a cross section through a premix burner in the region of the cone tip;

Fig. 3

a perspective view of a vortex generator;

Fig. 4

a variant of the vortex generator;

Fig. 5

a variant of the arrangement of the vortex generator of FIG. 3;

6a-c

the grouped arrangement of vortex generators in an inlet gap in longitudinal section, in a plan view and in a rear view;

7a-c

an embodiment of a group arrangement of vortex generators in the same representation as Figure 3 with a variant of the fuel management.

Fig. 8

a front view of an entrance slit with built-in vortex generators;

Fig. 9

an arrangement variant of the vortex generators in the inlet gap.

Only the elements essential for understanding the invention are shown. The direction of flow of the work equipment is indicated by arrows. In the various figures, the same elements are provided with the same reference symbols. Elements not essential to the invention such as Housing, fastenings, line bushings, the fuel supply, the control devices and the like are omitted.

Way of carrying out the invention

In FIG. 1, several premix burners 101 are arranged in the dome-shaped end of a combustion chamber in the combustion chamber wall 100. Gas is preferably used as fuel. The combustion air passes from an annular air inlet 102 into the housing interior 103, from where it flows into the burner 101 in the direction of the arrow.

The schematically illustrated premix burner 101 according to FIGS. 1 and 2 is a so-called double-cone burner, as is known for example from EP-B1-0 321 809. It essentially consists of two hollow, conical partial bodies 111, 112 which are nested one inside the other in the direction of flow. The respective central axes 113, 114 of the two partial bodies are offset from one another. The adjacent walls of the two partial bodies in their longitudinal extent form tangential slots 20 for the combustion air, which in this way reaches the interior of the burner. A first fuel nozzle 116 for liquid fuel is arranged there. The fuel is injected into the hollow cone at an acute angle. The resulting conical fuel profile is enclosed by the combustion air flowing in tangentially. The concentration of the fuel is continuously reduced in the axial direction due to the mixing with the combustion air. In the example, the burner is also operated with gaseous fuel. For this purpose, gas inflow openings 117 distributed in the longitudinal direction are provided in the region of the tangential slots 20 in the walls of the two partial bodies. In gas operation, the mixture formation begins with the combustion air thus already in the zone of the inlet slots 20. It goes without saying that mixed operation with both types of fuel is also possible in this way.

At the burner outlet 118, a fuel concentration that is as homogeneous as possible is established over the loaded cross-section in the form of a ring. A defined dome-shaped return flow zone is created at the burner outlet, at the tip of which the ignition takes place.

So far, double-cone burners are known from EP-B1-0 321 809 mentioned at the beginning. Before the installation of the new mixing device in the burner is discussed, the vortex generator essential for the mode of operation of the invention is first described.

The actual inlet gap, through which a main flow symbolized by a large arrow flows, is not shown in FIGS. 3-5. According to these figures, a vortex generator 9 essentially consists of three freely flowing triangular surfaces. These are a roof surface 10 and two side surfaces 11 and 13. In their longitudinal extent, these surfaces run at certain angles in the direction of flow.

In all the examples shown, the two side surfaces 11 and 13 are perpendicular to the gap wall 21, it being noted that this is not mandatory. The side walls, which consist of right-angled triangles, are fixed with their long sides on this gap wall 21, preferably gas-tight. They are oriented so that they form a joint on their narrow sides, including an arrow angle α. The joint is designed as a sharp connecting edge 16 and is also perpendicular to the gap wall 21 with which the side surfaces are flush. The two side surfaces 11 enclosing the arrow angle α, 13 are symmetrical in shape, size and orientation and are arranged on both sides of an axis of symmetry 17 (Fig. 6b, 7b). This axis of symmetry 17 is rectified like the gap axis.

The roof surface 10 abuts the same gap wall 21 as the side walls 11, 13 with a very pointed edge 15 running transversely to the inlet gap and its longitudinal edges 12, 14 are flush with the longitudinal edges of the side surfaces protruding into the flow gap. The roof surface extends at an angle of inclination Θ to the gap wall 21. Its longitudinal edges 12, 14 form a tip 18 together with the connecting edge 16.

Of course, the vortex generator can also be provided with a bottom surface with which it is fastened in a suitable manner to the gap wall 21. However, such a floor area is not related to the mode of operation of the element.

In Fig. 3, the connecting edge 16 of the two side surfaces 11, 13 forms the downstream edge of the vortex generator. The edge 15 of the roof surface 10 which runs transversely to the inlet gap through which it flows is thus the edge which is first acted upon by the gap flow.

The vortex generator 9 works as follows: When flowing around the edges 12 and 14, the main flow is converted into a pair of opposing vortices. Their vortex axes lie in the axis of the main flow. There is a swirl-neutral flow pattern in which the direction of rotation of the two vortices is ascending in the area of the connecting edge. The number of twists and the location of the vortex breakdown (vortex break down), if the latter is desired at all, are determined by a corresponding choice of the angle of attack Θ and the arrow angle α. With increasing angles, the vortex strength or the number of swirls is increased and the location of the vortex bursting moves upstream into the area of the vortex generator itself. Depending on the application, these two angles Θ and α are predetermined by the structural conditions and by the process itself. All that then has to be adjusted is the height h of the connecting edge 16 (FIG. 6a).

6a and 6b, in which the inlet slit through which flow is indicated by 20, it can be seen that the vortex generator can have different heights compared to the slit height H. As a rule, the height h of the connecting edge 16 will be coordinated with the gap height H in such a way that the vortex generated immediately downstream of the vortex generator already has such a size that the full gap height H is filled. Another criterion that can influence the ratio h / H to be selected is the pressure drop that occurs when the vortex generator flows around. It goes without saying that the pressure loss coefficient also increases with a larger ratio h / H.

4 shows a so-called half "vortex generator" 9a based on a vortex generator 9 according to FIG. 3, in which only the one of the two side surfaces is provided with the arrow angle α / 2. The other side surface is straight and oriented in the direction of flow. In contrast to the symmetrical vortex generator 9, only one vortex is generated on the arrowed side. Accordingly, there is no vortex-neutral field downstream of the vortex generator 9a, but a swirl is imposed on the flow if the vortex generator 9a is alone.

In contrast to FIG. 3, in FIG. 5 the sharp connecting edge 16 of the vortex generator 9 is the point which is first acted upon by the gap flow. The element is rotated by 180 °. As can be seen from the illustration, the two opposite vortices have changed their sense of rotation.

FIG. 6 shows how a plurality of vortex generators 9, here 3 vortex generators 9, are arranged side by side without gaps across the width of the inlet gap 20. In this case, the entry gap 20 has a rectangular shape, but this is not essential to the invention.

An embodiment variant with two full (9) and two half (9a) vortex generators adjoining it on both sides is shown in FIG. 7. With the same gap height H and the same angle of attack Θ of the roof surface 10 as in FIG. 6, the elements differ in particular by their greater height h. If the angle of attack remains the same, this inevitably leads to a greater length L of the element and consequently - because of the same division - to a smaller arrow angle α. In comparison with FIG. 6, the vortices produced will have a lower swirl strength, but will completely fill the gap cross section within a shorter interval. If in both cases a vortex burst is intended, for example to stabilize the flow, this will be done later with the vortex generator according to FIG. 7 than with that according to FIG. 6.

The ducts shown in FIGS. 6 and 7 represent rectangular low-pressure air ducts. It is pointed out once again that the shape of the inlet gap through which the air flows is not essential for the mode of operation of the invention. With the help of the vortex generators 9, 9a, two flows are mixed together. The main flow in the form of combustion air attacks the transverse inlet edges 15 in the direction of the arrow. The secondary flow in the form of fuel has a substantially smaller mass flow than the main flow. and will in the immediate Area of the vortex generators introduced into the main flow.

6, this injection takes place via individual bores 22a which are made in the wall 21a. The wall 21a is the wall on which the vortex generators are arranged. The bores 22a are located on the line of symmetry 17 downstream behind the connecting edge 16 of each vortex generator. With this configuration, the fuel is fed into the already existing large-scale vortices.

FIG. 7 shows an embodiment variant of an inlet gap in which the fuel is also injected via wall bores 22b. These are located downstream of the vortex generators in that wall 21b on which the vortex generators are not arranged, that is to say on the wall opposite the wall 21a. The wall bores 22b are each made centrally between the connecting edges 16 of two adjacent vortex generators, as can be seen in FIG. 4. In this way, the fuel reaches the vortex in the same way as in the embodiment according to FIG. 6, but with the difference that it is no longer mixed into the vortex of a pair of vertebrae generated by the same vortex generator, but in one each Vortex of two neighboring vortex generators. Since the adjacent vortex generators are arranged without a gap and generate vortex pairs with the same direction of rotation, the injections according to FIGS. 6 and 7 have the same effect.

8 it is assumed that there is a speed field which varies in magnitude. At the tip of the cone in the burner head, the speed is about 1.5 to 2 times as high as at the end of the gap near the burner outlet. The dynamic pressure in the gap thus varies approximately by a factor of 3. In order not to disturb the flow inside the burner, the absolute pressure loss along the inlet gap should be constant. This is achieved by the different heights of the vortex generators shown in FIG. 8. Of course, the different heights also result in a different pressure drop. The result now is that the pressure loss of the burner is increased only by the pressure loss of the vortex generators. Overall, this is less than 10% of the burner pressure drop.

It goes without saying that it is not necessary to disclose absolute values at this point, since these are not meaningful anyway due to their dependence on too many parameters. As an example, it should only be stated that tests on a certain design of vortex generators have shown that - with a given speed distribution along the rectangular gap - a height of the vortex generators of approximately 1/4 gap height in the head of the burner is approximately the same Pressure loss, like vortex generators at the end of the burner, fills 3/4 of the gap height. In the area of the cone tip, the vortex generators therefore have a height that does not correspond to the recommended minimum height of 50% of the gap height. However, the optimum mixture not achieved there is further balanced downstream on the relatively long mixing section up to the burner mouth. Overall, perfect premixing can be expected with the burner flow field unchanged.

In FIG. 8, the vortex generators all have the same sweep and the same angle of attack, which according to FIGS. 2A and 2B leads to different lengths of the vortex generators for a given height. If one wants to carry out the fuel supply according to the rules given in FIG. 6 in the plane of the connecting edges, this naturally leads also to an uneven distance and consequently the diameter of the individual holes.

9 it is assumed that there is a speed field which varies in magnitude and in the direction. In addition to adjusting the pressure drop, it is important to ensure that the angle of the incoming combustion air is not changed. Accordingly, the axis of symmetry of the vortex generators runs in the direction of flow, i.e. at a certain angle to the longitudinal axis of the gap. In this example, the vortex generators have the same arrow angles but different angles of attack. The length of all elements is the same. The holes for the fuel injection are equidistant.

The injected fuel is dragged along by the vortices and mixed with the air. It follows the helical course of the vertebrae and is evenly finely distributed in the interior of the Benner downstream of the vertebrae. This reduces the risk of impact jets on the opposite wall and the formation of so-called “hot spots” —with the previously customary radial injection of fuel into a swirling flow.

Since the main mixing process takes place in the vortices and is largely insensitive to the injection pulse of the fuel, the fuel injection can be kept flexible and adapted to other boundary conditions. In this way, the same injection pulse can be maintained throughout the load range. Since the mixing is determined by the geometry of the vortex generators and not by the machine load, in this case the gas turbine output, the burner configured in this way works optimally even under partial load conditions.

Of course, the invention is not limited to the examples described and shown. With regard to the arrangement of the vortex generators in the network, many combinations are possible without leaving the scope of the invention. The introduction of the secondary flow into the main flow can also be carried out in a variety of ways.

Reference list

100

Combustion chamber wall

101

Premix burner

102

Air intake

103

Interior of the housing

111

Partial body

112

Partial body

113

Central axis

114

Central axis

116

Fuel nozzle

117

Gas inflow opening

118

Burner outlet = combustion chamber

20th

tangential gap = entry gap

9, 9a

Vortex generator

10th

Roof area

11

Side surface

12th

Long edge

13

Side surface

14

Long edge

15

transverse edge of 10

16

Connecting edge

17th

Line of symmetry

18th

top

20, a

Entrance gap

21, a, b

Gap wall

22, a, b

Wall hole

24th

Gas supply

Θ

Angle of attack

α, α / 2

Arrow angle

H

Height of 16

H

Gap height

L

Length of the vortex generator

Claims (6)

1. Premixing burner on the double-cone principle with, essentially, two hollow conical partial bodies (111, 112) which are interleaved in the flow direction and whose respective centre lines (113, 114) are offset relative to one another, the adjacent walls of the two partial bodies forming tangential gaps (20) in their longitudinal extent for the combustion air, and gas inlet openings (117) distributed in the longitudinal direction being provided in the region of the tangential gaps in the walls of the two partial bodies, characterized in that the air is guided into the tangential gaps (20) via vortex generators (9), of which a plurality are arranged adjacent to one another and preferably without intermediate spaces over the width or the periphery of the gap through which flow occurs, the height (h) of the vortex generators being at least 50% of the height (H) of the gap through which flow occurs, and in that the fuel is introduced into the gaps (20) in the immediate region of the vortex generators (9),

   - a vortex generator (9) having three surfaces around which flow can take place freely, which surfaces extend in the flow direction, one of them forming the top surface (10) and the two others forming the side surfaces (11, 13),

   - the side surfaces (11, 13) abutting the same gap wall (21) and enclosing the V-angle (a, ah) between them, d

   - and in that the top surface (10) edge (15) extending transversely to the inlet gap (20) through which flow occurs being in contact with the same gap wall (21) as the side walls,

   - and the longitudinally directed edges (12, 14) of the top surface, which abut the longitudinally directed edges of the side surfaces protruding into the flow gap, extending at an angle of incidence (θ) to the gap wall (21).
2. Premixing burner according to Claim 1, characterized in that the ratio of the height (h) of the vortex generator (9, 9a) to the gap height (H) is selected in such a way that the vortex generated fills the complete gap height immediately downstream of the vortex generator.
3. Premixing burner according to Claim 1, characterized in that the two vortex generator (9) side surfaces (11, 13) enclosing the V-angle (a) are arranged symmetrically about an axis of symmetry (17).
4. Premixing burner according to Claim 1, characterized in that the two side surfaces (11, 13) enclosing the V-angle (a) include between them a connecting edge (16) which, together with the longitudinally directed edges (12, 14) of the top surface (10), form [sic] a point (18), and in that the connecting edge advantageously extends at right angles to the gap wall (21) which the side surfaces abut.
5. Premixing burner according to Claim 4, characterized in that the connecting edge (16) and/or the longitudinally directed edges (12, 14) of the top surface are configured so as to be at least approximately sharp.
6. Premixing burner according to Claim 1, characterized in that the vortex generators (9) arranged adjacent to one another in the gap (20) have different heights (h).

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