EP0619456B1 - Fuel supply system for combustion chamber - Google Patents

Description

Technical field

The invention relates to a fuel supply system for a combustion chamber with premix combustion, in which a gaseous and / or liquid fuel is injected as a secondary flow into a gaseous, channeled main flow, the secondary flow having a substantially smaller mass flow than the main flow, and the flow through which the premix channel has curved walls having,

State of the art

The mixing of fuel into a combustion air flow flowing in a premixing duct generally takes place by means of radial injection of the fuel into the duct by means of cross-jet mixers. However, the momentum of the fuel is so low that an almost complete mixing takes place only after a distance of approximately 100 channel heights. Venturi mixers are also used. The injection of the fuel via grid arrangements is also known. Finally, spraying in front of special swirl bodies is also used.

The devices operating on the basis of transverse jets or stratified flows either have very long mixing distances result or require high injection pulses. With premixing under high pressure and substoichiometric mixing ratios, there is a risk of the flame flashing back or even of self-ignition of the mixture. Flow separations and dead water zones in the premixing tube, thick boundary layers on the walls or possibly extreme speed profiles over the cross-section through which the flow is flowing can be the cause of auto-ignition in the tube or form paths through which the flame can strike back from the downstream combustion zone into the premixing tube. The geometry of the premixing section must therefore be given the greatest attention. Document EP-A-0 520 163 discloses a burner with swirl mounting surfaces.

Presentation of the invention

The invention is therefore based on the object of providing, in a combustion chamber with premix combustion, a measure with which intimate mixing of combustion air and fuel is achieved within a very short distance, with a simultaneous uniform distribution of speed in the mixing zone. The measure should also be suitable for retrofitting existing premix combustion chambers.

• dass die Hauptströmung über Wirbel-Generatoren geführt wird, von denen über dem Umfang des durchströmten Kanals an mindestens einer Kanalwand mehrere nebeneinander angeordnet sind, und dass die Sekundärströmung im unmittelbaren Bereich der Wirbel-Generatoren in den Kanal eingeleitet wird,
• dass ein Wirbel-Generator drei frei umströmte Flächen aufweist, die sich in Strömungsrichtung erstrecken und von denen eine die Dachfläche und die beiden anderen die Seitenflächen bilden,
• dass die Seitenflächen mit einer gleichen Kanalwand bündig sind und miteinander den Pfeilwinkel α einschliessen,
• dass die Dachfläche mit einer quer zum durchströmten Kanal verlaufenden Kante an der gleichen Kanalwand anliegt wie die Seitenwände,
• und dass die längsgerichteten Kanten der Dachfläche, die bündig sind mit den in den Strömungskanal hineinragenden längsgerichteten Kanten der Seitenflächen unter einem Anstellwinkel Θ zur Kanalwand verlaufen.

According to the invention this is achieved in that

• that the main flow is conducted via vortex generators, of which several are arranged next to one another on at least one channel wall over the circumference of the channel, and that the secondary flow is introduced into the channel in the immediate area of the vortex generators,
• that a vortex generator has three free-flowing surfaces which extend in the direction of flow and one of which forms the roof surface and the other two form the side surfaces,
• that the side surfaces are flush with the same duct wall and enclose the arrow angle α with one another,
• that the roof surface rests on the same channel wall as the side walls, with an edge running transversely to the flow channel,
• and that the longitudinal edges of the roof surface, which are flush with the longitudinal edges of the side surfaces projecting into the flow channel, extend at an angle of attack Θ to the channel wall.

With the new static mixer, which is represented by the 3-dimensional vortex generators, it is possible to achieve extraordinarily short mixing distances in the combustion chamber with a low pressure drop. The generation of longitudinal vortices without a recirculation area results in a rough mixing of the two streams after a full vortex revolution, while fine mixing due to turbulent flow and molecular diffusion processes occurs after a distance that corresponds to a few channel heights.

The advantage of vortex generators can be seen in their 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 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 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.

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, which together with the longitudinal edges of the roof surface forms a tip, 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.

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, whereas the edge of the roof surface which runs transversely to the channel through which the flow is flowing is the edge first acted upon by the channel flow, then a vortex generator generated two identical opposite vortices. 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.

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

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

Fig. 1

eine perspektivische Darstellung eines Wirbel-Generators;

Fig. 2

eine Ausführungssvariante des Wirbel-Generators;

Fig. 3

die Ringbrennkammer einer Gasturbine mit eingebauten Wirbel-Generatoren nach Fig. 1;

Fig. 4

einen teilweisen Längsschnitt durch eine Brennkammer nach Linie 4-4 in Fig. 3

Fig. 5

mehrere Varianten der Sekundärströmungsführung;

Fig. 6 a,b

eine zweite Anordnungsvariante der Wirbel-Generatoren in einer Ringbrennkammer;

Fig. 7 a,b

eine dritte Anordnungsvariante der Wirbel-Generatoren in einer Ringbrennkammer;

Fig. 8 a,b

eine vierte Anordnungsvariante der Wirbel-Generatoren nach Fig. 2 in einer Ringbrennkammer;

Fig. 9 a,b

eine zylindrische Brennkammer mit einer ersten Anordnungsvariante der Wirbel-Generatoren;

Fig. 10 a,b

eine zylindrische Brennkammer mit einer zweiten Anordnungsvariante der Wirbel-Generatoren;

Fig. 11 a,b

eine zylindrische Brennkammer mit einer Anordnungsvariante der Wirbel-Generatoren nach Fig. 2;

Fig. 12 a,b

eine Anordnungsvariante wie in Fig. 9 mit einer zentralen Brennnstoff-Einführung;

Fig. 13 a,b

eine mit Wirbel-Generatoren bestückte Brennstofflanze.

Show it:

Fig. 1

a perspective view of a vortex generator;

Fig. 2

an embodiment of the vortex generator;

Fig. 3

the annular combustion chamber of a gas turbine with built-in vortex generators according to Fig. 1;

Fig. 4

3 shows a partial longitudinal section through a combustion chamber according to line 4-4 in FIG. 3

Fig. 5

several variants of secondary flow control;

Fig. 6 a, b

a second variant of the arrangement of the vortex generators in an annular combustion chamber;

Fig. 7 a, b

a third arrangement variant of the vortex generators in an annular combustion chamber;

8 a, b

a fourth arrangement variant of the vortex generators according to Figure 2 in an annular combustion chamber.

9 a, b

a cylindrical combustion chamber with a first arrangement variant of the vortex generators;

10 a, b

a cylindrical combustion chamber with a second arrangement variant of the vortex generators;

11 a, b

a cylindrical combustion chamber with a variant arrangement of the vortex generators according to FIG. 2;

Fig. 12 a, b

an arrangement variant as in Figure 9 with a central fuel introduction.

Fig. 13 a, b

a fuel lance equipped with vortex generators.

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 housings, fastenings, cable bushings and the like, have been omitted.

Way of carrying out the invention

Before going into the actual combustion chamber, the vortex generator essential for the mode of operation of the invention is first described.

In Figures 1, 2 and 5, the actual channel, which is flowed through by a main flow symbolized by a large arrow, is not shown. 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.

The side walls of the vortex generator, which consist of right-angled triangles, are fixed with their long sides on a channel 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 vertical to that channel wall 21 with which the side surfaces are flush. The two side surfaces 11, 13 enclosing the arrow angle α are symmetrical in shape, size and orientation in FIG. 1 and are arranged on both sides of an axis of symmetry 17. This axis of symmetry 17 is rectified like the channel axis.

The roof surface 10 lies with a very narrow edge 15 running transversely to the flow through the channel on the same channel wall 21 as the side walls 11, 13. Its longitudinal edges 12, 14 are flush with the longitudinal edges of the side surfaces projecting into the flow channel. The roof surface extends at an angle of inclination Θ to the channel 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 channel wall 21. However, such a floor area is not related to the mode of operation of the element.

In Fig. 1, 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 flow through the channel is thus the edge which is first acted upon by the channel flow.

The vortex generator works as follows: When flowing around 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. The number of swirls and the location of the vortex breakdown (if the latter is desired at all) are determined by appropriate selection of the angle of attack Θ and the arrow angle α. With increasing angles, the vortex strength or the swirl number becomes increased and the location of the vortex burst moves upstream into the area of the vortex generator itself. Depending on the application, these two angles e and a 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. 4).

FIG. 2 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 9a 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, only one vortex is generated on the arrowed side. Accordingly, there is no vortex-neutral field downstream of the vortex generator, but a swirl is forced on the flow.

The vortex generators are mainly used on the one hand as a mixer of 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 FIG. 5.

Thus, the outflow of the fuel into the combustion air can take place via wall bores 22c, which are staggered in the longitudinal edges 12 and 14 (or at least in their immediate area) are. The fuel is first introduced here through means, not shown, through the channel wall 21 into the hollow interior of the vortex generator. From the wall bores 22c, it thus arrives directly into the vortex which arises and which rises in the injection region. There are defined flow conditions here.

The fuel can also be injected from wall bores 22a, which are located in the channel wall 21 along the edge 15 of the vortex generator. The injection angle is then selected so that the fuel flows around the roof surface of the vortex generator as a film before it is mixed in. This "cold" film forms a protective layer against a hot main current for the roof surface. This solution according to is particularly well suited for dual operation, in which both gaseous and liquid fuel are mixed into the main flow and later burned. The liquid fuel, here oil, is then injected via a single bore (not shown) which opens directly at the edge 15, preferably at the same injection angle as the gas. This oil also spreads over the surface of the roof as a protective film before it is atomized. Instead of the wall bores 22b, a slot (not shown here) could also be used.

Wall bores 22b can also be provided downstream of the vortex generators, through which the fuel is blown into the ascending vortex.

In a departure from the options shown, the fuel can also be injected from a single hole which is made in the area of the tip 18 of the vortex generator. In this case, the agent is injected directly into the fully developed vertebra and also in its ascending branch.

Finally, it goes without saying that the methods mentioned can also be combined with each other or individually

Various different installation options for the vortex generators in the premixing chamber of the combustion chamber are described below.

3 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. 1 are lined up in the circumferential direction without any free spaces so that the connecting edges 16 are separated by two opposite vortexes. Generators lie in the same radial. If the same heights h are assumed for opposite vortex generators, FIG. 3 shows that the vortex generators on the inner channel ring 21b have a smaller arrow α. In the longitudinal section in FIG. 4 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. 3, two vortex pairs, each with small vertebrae, are generated, which leads to a shorter mixing length.

4, the liquid fuel is injected here via a central fuel lance 24, the mouth of which is located downstream of the vortex generators 9 in the area of the tip 18 thereof. In this example, the gaseous fuel is injected twice according to the methods described in FIG. 5. On the one hand, as indicated by arrows, via wall bores in the vortex generators themselves and on the other hand via wall bores 22b in the channel wall 21b behind the vortex generators, these wall boreholes being able to be supplied via a ring line.

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.

In the solutions shown in FIGS. 6 to 8, the gaseous fuel can be injected through wall bores which are fed from ring lines provided in the interior of the channel. Of course, in contrast to the radially inserted lance shown in FIG. 4, central lances for liquid fuel can also be provided be, a plurality of which is distributed over the circumference of the ring channel.

Fig. 6 shows a configuration like Fig. 3, but with smaller radii of the ring walls and large channel height. The height of the opposing vortex generators is very different.

As a rule, the height h of the connecting edge 16 will be coordinated with the channel height H or the height of the channel part, which is assigned to the vortex generator, 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 leads to a uniform speed distribution in the applied cross section. 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.

In the vortex generators shown in FIG. 7, the connecting edges of two opposite vortex generators are offset by half a division. As a result, the vortex structure downstream of the vortex generators is changed such that the vortices generated on the same side have the same direction of rotation and may merge into one large vortex that fills the entire channel cross section in the corresponding angular sector. On the one hand, this allows the mixing quality to be improved and, on the other hand, a longer lifespan of the vortex can be achieved. This solution offers the possibility, not shown, of raising the height of the inner vortex generators so that their tips can engage between the side walls of the two opposite vortex generators.

In Fig. 8 so-called "half" vortex generators 9a are strung together in the circumferential direction on both ring walls. As can be seen from the arrows, the individual vertebrae, which all have the same direction of rotation, combine to form a large rotating vertebra that acts on the entire channel.

The three arrangements described below are particularly suitable for initial installation or as a "retrofit" measure in premixing chambers with a circular cross section of the channel 20 through which flow passes. The previous nozzle grids or mixing tubes for the gaseous fuel are simply replaced by a ring line 25 arranged in the interior of the premixing chamber, from which the slots or bores 22e are fed in front of the vortex generators. A central fuel lance could also be arranged in this network.

According to FIG. 9, four vortex generators 9 are strung together on the wall 21a in the circumferential direction in such a way that no gaps are left on the channel wall. The mode of operation of the elements in such a network corresponds to that of the outer vortex generators in FIG. 3.

10 runs with the same basic arrangement of the vortex generators 9 whose axis of symmetry 17 obliquely to the channel axis. The two side surfaces thus have a different sweep compared to the main flow. This creates vortices with different swirl numbers on both sides of the vortex generator. As a result, there is a twist in the flow downstream of the elements.

With the solution according to FIG. 11, the entire cross-section through which flow passes is whirled. The arrangement consists of 4 groups of 3 vortex generators 9a each according to FIG. 2. In one group the three vortex generators are equipped with increasing height. All vortices generated are the same rotation.

12, in turn, 4 vortex generators are arranged over the circumference. In a departure from the position shown in FIG. 9, however, the respective connecting edge 16 is the point which is first acted upon by the channel flow. The elements are rotated by 180 ° in comparison with FIG. 9. As can be seen from the illustration, the two opposite vortices have changed their sense of rotation. They rotate above the roof surface of the vortex generator and strive towards the wall on which the vortex generator is mounted. This solution offers itself for the installation of a central lance 24 with which the fuel is injected into the radials in which the axes of symmetry of the vortex generators run. The fuel goes directly into the vortices rotating against the wall.

Finally, FIG. 13 shows a variant with vortex generators 9 which is particularly suitable as an exchange unit in cylindrical premixing chambers. It is also designed for dual operation, which means that both liquid and gaseous fuel can be mixed into the combustion air. The kit which can be inserted axially into the premixing tube (not shown) consists of a central lance 24 which is provided with vortex generators 9 at its end. The liquid fuel passes through an oil line 26 arranged in the central lance 24 to the injection head, from which it is injected into the channel via nozzles. The nozzles are directed in the direction of the arrow in the symmetry line of the vortex generators. The fuel is captured by the rising vortices. The gaseous fuel, which is also supplied via the gas line 29 in the central lance, passes via hollow ribs 27 into a gas ring 28 with which the system is centered and fixed in the tube. The fuel is added to the main flow from this gas ring 28.

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. Of course, the variant according to FIG. 9 is also suitable, for example, in combustion chambers of the "can" principle.

Reference list

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,

channel

21, a, b

Canal wall

22, a, b, c

Wall hole

22e

Wall hole or wall slot

24th

Fuel lance

25th

Loop

26

Oil pipe

27

rib

28

Gas ring

29

Gas pipe

Θ

Angle of attack

a

Arrow angle

H

Height of 16

H

Channel height

L

Length of the vortex generator

Claims (16)

1. Fuel supply system with premixing combustion in which a gaseous and/or liquid fuel is introduced as a secondary flow into a gaseous, ducted main flow, the secondary flow having a substantially smaller mass flow than the main flow and the premixing duct through which flow takes place having curved walls, characterized in that

   - the main flow is guided via vortex generators (9) of which a plurality are arranged adjacent to one another over the periphery of the duct (20) through which flow takes place on at least one duct wall, and in that the secondary flow is fed into the duct (20) in the immediate region of the vortex generators (9),

   - in that the vortex generators (9) have 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),

   - characterized in that the side surfaces (11, 13) abut the same duct wall (21) and enclose a V-angle (α) between them,

   - characterized in that a top surface (10) edge (15) extending transverse to the duct (20) through which flow takes place is in contact with the same duct wall (21) as the side walls,

   - and characterized in that the longitudinally directed edges (12, 14) of the top surface, which abut the longitudinally directed edges of the side surfaces (11, 13) protruding into the flow duct, extend at an angle of incidence (θ) to the duct wall (21).
2. Fuel supply system according to Claim 1, characterized in that the fuel is introduced via wall holes or slots (22e) which are arranged upstream of the vortex generators and which are fed from an annular duct (25) fitted within the duct wall.
3. Fuel supply system according to Claim 1, characterized in that the fuel is introduced via wall holes (22a, 22b) in the duct wall (21).
4. Fuel supply system according to Claim 1, characterized in that the fuel is introduced via wall holes (22c) which are located in one or a plurality of surfaces (10, 11, 13) of the vortex generator (9).
5. Fuel supply system according to Claim 1, characterized in that the fuel is introduced via a central fuel lance (24) whose openings are located in the plane of the downstream edge of the vortex generator (9).
6. Fuel supply system according to Claim 1, characterized in that the fuel distribution means and the vortex generators are conceived as an exchange unit.
7. Fuel supply system 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).
8. Fuel supply system according to Claim 1, characterized in that only one of the two side surfaces of the vortex generator (9) is provided with a V-angle (α, αh) whereas the other side surface is straight and is directed in the flow direction.
9. Fuel supply system according to Claim 1, characterized in that the two side surfaces (11, 13) enclosing the V-angle (α, αh) 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 extends in the radial of the curved walls.
10. Fuel supply system according to Claim 9, characterized in that the connecting edge (16) and/or the longitudinally directed edges (12, 14) of the top surface (10) are configured to be at least approximately sharp.
11. Fuel supply system according to Claim 9, characterized in that the axis of symmetry (17) of the vortex generator (9) extends parallel to the duct axis, the connecting edge (16) of the two side surfaces (11, 13) forming the downstream edge of the vortex generator (9) and the top surface (10) edge (15) extending transverse to the duct (20) through which flow takes place being the edge which the main flow meets first.
12. Fuel supply system according to Claim 1, characterized in that the ratio of the height (h) of the vortex generator to the duct height (H) is selected in such a way that the vortex generated fills the full duct height, or the full height of the duct part associated with the vortex generator, immediately downstream of the vortex generator (9).
13. Fuel supply system according to Claim 7 or 8, characterized in that the duct (20) is annular and in that an equal number of vortex generators (9) are arranged in a row in the peripheral direction both on the outer annular wall (21a) and on the inner annular wall (21b), the connecting edges (16) of each two opposite vortex generators (9) being located on the same radial.
14. Fuel supply system according to Claim 7 or 8, characterized in that the duct (20) is annular and in that an equal number of vortex generators (9) are arranged in a row in the peripheral direction both on the outer annular wall (21a) and on the inner annular wall (21b), the connecting edges (16) of each two opposite vortex generators (9) being offset by half a pitch relative to one another.
15. Fuel supply system according to Claim 7 or 8 and 9, characterized in that the duct (20) is circular and in that a plurality of vortex generators (9, 9a) are arranged in a row in the peripheral direction on the wall (21a), preferably without intermediate spaces.
16. Fuel supply system according to Claim 14, characterized in that the axis of symmetry (17) of the vortex generators extends oblique to the duct axis. (Fig. 10)

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