EP0620403B1 - Mixing and flame stabilizing device in a combustion chamber with premixing combustion - Google Patents

Description

Technical field

The invention relates to a mixing and flame stabilization device in a combustion chamber with premix combustion, in which a gaseous and / or liquid fuel is injected into the combustion air.

State of the art

With regard to low emissions, premix combustion requires extremely good mixing of the combustion air and fuel.

In the combustion chamber there can be cold streaks in the main flow, for example caused by the introduction of cooling air into the combustion air. Such strands can lead to insufficient burnout in the combustion zone. Measures must therefore be taken to mix combustion air, cooling air and fuel intimately. The mixing of a secondary flow with a main flow present in a channel usually takes place by radial injection of the secondary flow into the channel. The momentum of the secondary flow is so small, however, that an almost complete mixing only takes place after a distance of approx. 100 channel heights.

Presentation of the invention

The invention is therefore based on the object of providing a measure in a combustion chamber with premix combustion with which intimate mixing of combustion air and fuel is achieved within the shortest distance and with which the flame can be stabilized aerodynamically at the same time.

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

It is already known from US Pat. No. 3,974,646 to pass part of the combustion air in a combustion chamber via vortex generators and then to mix it in a swirling state in an enrichment zone within the combustion zone with the fuel flowing in from another channel. These vortex generators, however, are half deltas with which no opposing vortexes are produced.

With the new static mixer, which the vortex generators represent, it is possible to achieve extremely short mixing distances with low pressure loss. A coarse mixing of the two streams takes place after just one full vortex revolution, while a fine mixing due to turbulent flow and molecular diffusion processes occurs after a distance that corresponds to a few channel heights.

The advantage of the vortex generators according to the invention can be seen in the particular simplicity of the element 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 channel walls in the case of weldable materials by simple weld seams. From a fluidic point of view, the element has a very low pressure drop when flowing around 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.

It is expedient for the present applications if the angle of attack Θ of the roof surface and / or the arrow angle α of the side surfaces are selected such that the vortex generated by the flow bursts in the region of the vortex generator. With the possible variation of the two angles, one has a simple aerodynamic stabilizing means in hand, regardless of the cross-sectional shape of the flowed channel, which can be both wide and low as well as narrow and high, and can be provided with flat or curved channel walls.

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.

If the two side surfaces enclosing the arrow angle α form an at least approximately sharp connecting edge with one another, the flow cross-section is hardly impaired by blocking.

If the sharp connecting edge is the exit-side edge of the vortex generator and it runs perpendicular to the channel wall with which the side surfaces are flush, then the non-formation of a wake area is advantageous. A vertical connecting edge also leads to side surfaces that are also perpendicular to the channel wall, which gives the vortex generator the simplest possible form and the most favorable form in terms of production technology.

It is appropriate to choose the ratio of the height h of the connecting edge of the two side surfaces to the channel height H so that the vortex generated fills the full channel height or the full height of the channel part assigned to the vortex generator immediately downstream of the vortex generator. The large-scale vortices generated ensure that the same speed distribution is present on every level behind the vortex generator.

Preferably, without gaps, a plurality of vortex generators are arranged side by side across the width of the channel through which the flow passes. With this measure, shortly after the vortex generators, the entire channel cross section is fully loaded by the vortexes.

If the axis of symmetry runs parallel to the channel axis, and the connecting edge of the two side surfaces forms the downstream edge of the vortex generator, while the edge of the roof surface which runs transversely to the flow through the channel is the edge which is first acted upon by the channel flow, so two identical opposing vortices are generated on a vortex generator. There is a swirl-neutral flow pattern in which the direction of rotation of the two vortices is ascending in the region of the connecting edge, so that the vortices impinge on the opposite wall which is not equipped with vortex generators and which can be cooled in this way, for example.

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

Brief description of the drawing

Fig. 1a-d

eine Darstellung eines Wirbel-Generators in der Perspektive, in einer Hinteransicht, einer Draufsicht und einer Seitenansicht mit Brennstoffeindüsung;

Fig. 2a-d

eine Ausführungsvariante des WirbelGenerators in gleicher Darstellung ohne Brennstoffeindüsung;

Fig. 3

einen "halben" Wirbel-Generator in einer Perspektive;

Fig. 4-5

mehrere Varianten der Brennstoffeindüsung;

Fig. 6-9

die gruppenweise Anordnung von Wirbel-Generatoren in einer rechteckigen, einer kreisförmigen und in einer kreisringförmigen Brennkammer;

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

1a-d

an illustration of a vortex generator in perspective, in a rear view, a plan view and a side view with fuel injection;

2a-d

a variant of the vortex generator in the same representation without fuel injection;

Fig. 3

a "half" vortex generator in one perspective;

Fig. 4-5

several variants of fuel injection;

Fig. 6-9

the grouped arrangement of vortex generators in a rectangular, a circular and an annular combustion chamber;

Way of carrying out the invention

The actual channel, through which a main flow symbolized by a large arrow flows, is not shown in FIGS. 1 to 5. According to these figures, a vortex generator essentially consists of three free-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 of the examples shown, the two side surfaces 11, 11v, 11h and 13, 13v, 13h are perpendicular to the channel wall 21, it being noted that this is not mandatory. The side walls, which in the projection consist of essentially right-angled triangles, are fixed with their long sides on this channel wall 21, preferably gas-tight. They are oriented in such a way that they form a joint on their narrow sides, including an arrow angle α, αv, αh. The joint is designed as a sharp connecting edge 16 and is also perpendicular to the channel wall 21 with which the side surfaces are flush. The two side surfaces 11, 11v, 11h and 13, 13v, 13h enclosing the arrow angle α, αh, αv are symmetrical in shape, size and orientation and are arranged on both sides of an axis of symmetry 17 which lies in the channel axis.

The roof surface 10, 10v lies with a very narrow edge 15 running transversely to the channel through which it flows, on the same channel wall 21 as the side walls 11, 11v, and 13, 13v ,. Its longitudinal edges 12, 14 are flush with the longitudinal edges of the side surfaces protruding into the flow channel. The roof surface runs at an angle of attack Θ, Θv to the duct wall 21. Your 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 channel wall 21. However, such a floor area is not related to the mode of operation of the element.

The vortex generators 9 are designed so that their angle of attack of the roof surface and their arrow angle of the side surfaces increase in the direction of flow.

According to FIG. 1, this is done on the one hand by dividing the roof area into two sub-areas 10v, 10h with different positions (Θv, Θh). On the other hand, the increase in the arrow angle of the side surfaces is carried out by dividing them into two with different swept (αv, αh) partial surfaces 11v, 11h, 13v, 13h.

2, the increase in the angle of attack Θ of the roof surface 10 and the arrow angle α of the side surfaces 11, 13 runs continuously from the edge 15 running transversely to the flow channel to the tip 18.

In all of the figures, the connecting edge 16 of the two side surfaces 11, 11h and 13, 13h forms the downstream edge of the vortex generator. The edge 15 of the roof surface 10, 10v running transversely to the flow through the channel is thus the edge first acted upon by the channel flow.

The vortex generator works as follows: When flowing around the edges 12 and 14, the main flow coming from the edge 15 is converted into a pair of opposing vortices. Their vortex axes lie in the axis of the main flow. The swirl number and the location of the vortex burst (vortex breakdown) are determined by appropriate selection 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. Then only the length L of the element and the height h of the connecting edge 16 need to be adjusted (FIG. 9).

In FIG. 1, the front inflow parts of the vortex generator designated by v are set at a flat angle Θv and have a relatively sharp arrow αv. In this way, the large-scale vortices required for mixing purposes are generated. At the downstream side, the vortex generator has a large pitch Anh and a wide arrow angle αh. This provokes the vortex runways, which are favorable for flame stabilization. As an example, it can be stated that the downstream angles Θh and αh are approximately twice as large as the angles Θv and αv on the downstream side.

FIG. 3 shows a so-called half "vortex generator" based on a vortex generator according to FIG. 1, in which only one of the two side surfaces of the vortex generator 9 has an arrow angle αv / 2 and αh / which varies in the direction of flow. 2 is provided. The other side surface is straight and oriented in the direction of flow. In contrast to the symmetrical vortex generator, only one vortex is generated on the arrowed side. Accordingly, there is no vortex-neutral field downstream of the vortex generator, but a dall is imposed on the flow.

The vortex generators are used on the one hand as a mixer for two flows. 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 a gaseous and / or liquid fuel has a substantially smaller mass flow than the main flow. It is introduced into the main flow in the immediate area of the vortex generators.

The introduction into the flow channel of the gaseous and / or liquid fuel to be mixed into the combustion air can be designed in many ways according to FIGS. 4 to 6b.

4, the outflow into the combustion air takes place via wall bores 22a, which are staggered in the longitudinal edges 12 and 14 (or at least in their immediate area). The fuel thus goes directly into the resulting vortex, which rises in the injection area. There are defined flow conditions here.
5, the fuel flows out of individual bores 22b which are provided in the region of the tip 18 of the vortex generator. Here the agent is injected directly into the fully developed vertebra and also in its ascending branch.

In the variant shown in FIGS. 1a, 1b and 1b, the gas is injected from wall bores 22c, which are located in the channel wall 21 along the edge 15 of the vortex generator. The injection angle is selected (FIG. 1b) so that the gas flows around the roof surface of the vortex generator as a film before it is mixed in. This "cold" film forms a protective layer for the roof surface in the case of a hot main flow. 1 is particularly suitable for dual operation, in which both gaseous and liquid fuel is mixed into the main flow and later burned. The liquid fuel, here oil, is injected via a single bore 22f opening directly at the edge 15, preferably at the same injection angle as the gas. This oil is also distributed as a film over the roof surface before being atomized in the vortex.

Instead of the wall bores 22c, a slot 22d (not shown here) could also be used, as can be seen in FIG. 6b to be described later.

6 to 9 show different arrangement variants for the vortex generators described

According to FIG. 6, the combustion chamber channel 20 through which flow is rectangular. It is pointed out that the shape of the flow channel is not essential to the operation of the invention. Instead of the rectangle shown, the channel could also be a ring segment, i.e. the walls and would be curved. In this case, the narrow boundary walls of the cross-section flowed through would be radial ribs which segment the circular ring. In such a case, the above statement that the side surfaces are perpendicular to the channel wall must of course be relativized. It is important that the connecting edge 16 lying on the line of symmetry 17 is perpendicular to the corresponding wall. In the case of annular walls, the connecting edge 16 would thus be aligned radially, as is shown in FIG. 8.

In Fig. 6 a vortex generator 9 are arranged on the two narrow walls of the rectangle or possibly on the radial ribs, which extend over the entire narrow side. In the case of rectangular channels, this arrangement has that Bumping the floor surface at a corner, the advantage that the fuel supply and a coolant for the vortex generators could come from the longitudinal walls and would not have to be done via otherwise necessary hollow ribs. In addition, a vortex generator is arranged on each of the two longitudinal walls. This configuration is the best possible of the vortex formation. It can be seen from FIG. 6b that measures have been taken here that contribute to different vortex formation. First, vortex generators of different geometries are used. Furthermore, the vortex generators of the long side are not arranged in the same plane with their connecting edge. This is advantageous, for example, if space for a central fuel lance would have to be provided in the middle of the tips.

Although the vortex generators in the network have different heights, their height relative to the height of the channel part assigned to the corresponding vortex generator is at least approximately the same. As a rule, the height h of the connecting edge 16 will be coordinated with the channel height H in such a way that the vortex generated immediately downstream of the vortex generator already reaches such a size that the full channel height H is filled, which results in a uniform V distribution in the applied Cross section leads. 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 larger the ratio h / H, the higher the pressure loss coefficient.

6 for dual operation, the fuel is supplied from the oil and gas lines 25 which run in the wall. The injection into the channel 20 takes place as in the solution described in FIG. 1, with instead of individual wall bores here a slot 22f is provided along the edge 15 for the gas.

The injected fuel is dragged along by the vortices and mixed with the main flow. It follows the helical course of the vertebrae and is evenly finely distributed in the chamber downstream of the vertebrae. This reduces the risk of impinging jets on the opposite wall and the formation of so-called "hot spots" - in the case of the radial injection of fuel into an undisturbed flow mentioned at the beginning.

Since the main mixing process takes place in the vortices and is largely insensitive to the injection pulse of the secondary flow, 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. The combustion process is optimized by adjusting the ignition delay time of the fuel and mixing time of the vortices, which ensures a minimization of emissions.

Furthermore, the effective mixing results in a good temperature profile over the cross section through which the flow is flowing and also reduces the possibility of the occurrence of thermoacoustic instability. Due to their presence alone, the vortex generators act as a damping measure against thermoacoustic vibrations.

To further stabilize the flame, the vortex generators are located downstream in the plane where the not shown Ignition takes place, a diffuser 26, here a shock diffuser, is arranged.

In Fig. 7, two "half" vortex generators are arranged symmetrically in a circular combustion chamber. Its straight long side lies against the wall of the cylindrical channel, while the swept side surface protrudes into the flow. Depending on the design of the vortex generators, it is possible that the vortex generated downstream form a single vortex that fills the circular cross section, which imposes a swirl on the flow. As in the solution according to FIG. 6, the fuel is injected via a wall slot 22d (gas) and a single bore 22f (oil) arranged in the middle of the edge 15. The path of the fuel until it is mixed is shown using the self-explanatory arrows.

FIG. 8 shows a combustion chamber with a channel 20 through which flow flows in a simplified manner. On both channel walls 21a and 21b, an equal number of vortex generators according to FIG. 2 are lined up in the circumferential direction without free spaces so that the connecting edges 16 are separated by two opposite vortex Generators lie in the same radial. If the same heights h are assumed for opposite vortex generators, FIG. 8 shows that the vortex generators on the inner channel ring 21b have a smaller arrow α. In the longitudinal section in FIG. 9 it can be seen that this could be compensated for by a larger angle of attack Θ if swirl-like vortices in the inner and outer ring cross-section are desired. In this solution, as indicated in FIG. 8, two vortex pairs are generated, each with smaller vertebrae, which leads to a shorter mixing length.

According to FIG. 9, the liquid fuel is injected here via a central fuel lance 24, the mouth of which is located are located downstream of the vortex generators 9 in the area of their tip 18. In this example, the gaseous fuel is injected twice. On the one hand, as indicated by arrows, via wall bores in the vortex generators themselves according to the methods according to FIG. 4 and on the other hand via wall bores 22e in the channel wall 21b behind the vortex generators, these wall bores being able to be supplied via a ring line .

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. In a departure from the vortex generators shown in FIG. 8, the connecting edges of which lie on the same radial, the connecting edges of two opposite vortex generators could also be offset by half a division. This would change the vortex structure downstream of the vortex generators such that the vortices generated on the same side then have the same direction of rotation and possibly merge into a large vortex that fills the entire channel cross section.

Reference list

9

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

20th

channel

21, a, b

Canal wall

22, a, b, c, e

Wall hole for gas

22, d

Wall slot

22, f

Wall hole for oil

24th

Fuel lance

25th

management

26

Diffuser

Θ, v, h

Angle of attack

α, v, h

Arrow angle

H

Height of 16

H

Channel height

L

Length of the vortex generator

Claims (14)

1. Mixing and flame stabilization appliance in a combustion chamber with premixed combustion in which a gaseous and/or liquid fuel is introduced into the combustion air,

   - the combustion air being guided by means of vortex generators (9) of which a plurality are arranged adjacent to one another over the width or the periphery of the combustion chamber duct (20) through which flow takes place and the fuel being introduced into the duct (20) in the immediate region of the vortex generators (9),

   - in that a vortex generator (9) has 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),

   - in that the side surfaces (11, 13) enclose between them the V-angle (α) and abut the same duct wall (21), and in that they include between them a connecting edge (16) which, together with the longitudinally directed edges (12, 14) of the top surface (10), forms a point (18),

   - said top surface (10) being in contact, by means of an edge (15) extending transversely to the duct (20) through which flow takes place, with the same duct wall (21) as the side walls,

   - the longitudinally directed top surface edges (12, 14), which abut the longitudinally directed side surface edges protruding into the flow duct, extending at an angle of incidence (θ) to the duct wall (21),

   - and the angle of incidence (θ) as well as the V-angle (α) varying in the flow direction.
2. Mixing and flame stabilization appliance according to Claim 1, characterized in that, in the downstream part of the vortex generator (9), the angle of incidence (θ, θh) of the top surface (10, 10h) and/or the V-angle (α, αh) of the side surfaces (11, 11h and 13, 13h) are selected in such a way that the vortex generated by the flow has already broken down in the region of the vortex generator.
3. Mixing and flame stabilization appliance according to Claim 1, characterized in that the angle of incidence (θ) of the top surface (10) and/or the V-angle (α) of the side surfaces (11, 13) of the vortex generator (9) increase in the flow direction.
4. Mixing and flame stabilization appliance according to Claim 3, characterized in that the increase in the angle of incidence of the top surface is undertaken by its subdivision into two partial surfaces (10v, 10h) with different incidences (θv, θh), and in that the increase in the V-angle of the side surfaces is undertaken by their subdivision into two partial surfaces (11v, 11h, 13v, 13h) with different V-angles (αv, αh).
5. Mixing and flame stabilization appliance according to Claim 3, characterized in that the increase in the angle of incidence of the top surface (10) and/or of the V-angle (α) of the side surfaces (11, 13) is undertaken continuously to the point (18) from the edge (15) extending transversely to the duct (20) through which flow takes place.
6. Mixing and flame stabilization appliance according to Claim 1, characterized in that the vortex generator (9) connecting edge (16) extending from the duct wall (21) to the point (18) is configured so that it is at least approximately sharp.
7. Mixing and flame stabilization appliance according to Claim 1, characterized in that the ratio between the height (h) of the connecting edge (16) of the vortex generator (9) and the duct height (H) is selected in such a way that the vortex generated fills the complete duct height, or the complete height of the duct part associated with the vortex generator, directly downstream of the vortex generator.
8. Mixing and flame stabilization appliance according to Claim 3, characterized in that only one of the two side surfaces of the vortex generator (9) is provided with a V-angle (αv, αh) which varies in the flow direction, whereas the other side surface is straight and is directed in the flow direction.
9. Mixing and flame stabilization appliance according to Claim 1, characterized in that the two vortex generator (9) side surfaces (11, 13) enclosing the V-angle (α) are arranged symmetrically about an axis of symmetry (17) which extends parallel to the duct axis.
10. Mixing and flame stabilization appliance according to Claim 1, characterized in that the connecting edge (16) of the two side surfaces (11, 13) forms the downstream edge of the vortex generator (9) and the top surface (10) edge (15) extending transversely to the duct (20) through which flow takes place is the edge which the duct flow meets first.
11. Mixing and flame stabilization appliance according to Claim 1, characterized in that the fuel is introduced via wall holes (22a) which are located in the side walls (11, 13) of the vortex generator (9) in the region of the longitudinally directed edges (12, 14) of the top surface (10, 10v, 10h).
12. Mixing and flame stabilization appliance according to Claim 1, characterized in that the fuel is introduced via wall holes (22b) which are located in the region of the point (18) of the vortex generator (9).
13. Mixing and flame stabilization appliance according to Claim 1, characterized in that the fuel is introduced via fuel lances (24) whose openings are located downstream of the vortex generator (9) in the region of its point (18).
14. Mixing and flame stabilization appliance according to Claim 1, characterized in that a diffuser (26) is arranged downstream of the vortex generators (9) for additional flame stabilization.

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