EP0733861A2 - Combustor for staged combustion - Google Patents

Abstract

The combustion chamber has primary burners (110) of the premix type, in which fuel injected by jets (117) is intensively mixed with the combustion air within a premix cavity (115). The primary burners are flame-stabilising, without the need to use a mechanical flame holder. The primary burners have tangential inflow of the combustion air into the premix cavity. Downstream of the precombustion chamber (61), there are secondary burners (150). These are in the form of premix burners which are not self-operating. The primary burners may operate on the double cone principle.

Description

Technical field

The invention relates to a combustion chamber with two-stage combustion, with at least one primary burner of the premix type, in which the fuel injected via nozzles is intensively mixed with the combustion air prior to ignition within a premixing chamber, and with at least one secondary burner which is arranged downstream of a pre-combustion chamber.

State of the art

Combustion with the largest possible excess of air, given that the flame is still burning at all and furthermore that not too much CO is produced, not only reduces the amount of NO _x pollutants, but also lowers other pollutants, namely CO and unburned hydrocarbons. This allows a larger excess air number to be selected, in which case larger amounts of CO are initially generated, but these can react further to CO ₂ , so that ultimately the CO emissions remain low. On the other hand, due to the large excess of air, little additional NO is formed. Since a larger number of burners are usually arranged in a combustion chamber for, for example, gas turbines, only so many elements are operated with fuel in the load control that are suitable for the respective operating phase (start, partial load, full load) gives the optimal excess air figure.

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. A good mixing also helps to avoid so-called "hot spots" in the combustion chamber, which among other things lead to the formation of the undesired NO _x . For this reason, two-stage combustion chambers with premix burners of the type mentioned at the outset are increasingly being used in the primary stage.

The single-stage combustion chambers with premix burners have the inadequacy that, at least in the operating states in which only some of the burners are operated with fuel, or in which the individual burners are supplied with a reduced amount of fuel, the flame stability is pushed close to the limit . In fact, due to the very lean mixture and the resulting low flame temperature under typical gas turbine conditions, the extinguishing limit is already reached with an excess air ratio of approximately 2.0.

This fact leads to a relatively complicated operation of the combustion chamber with a correspondingly complex regulation. Another way of expanding the operating range of premix burners is to support the burner with a small diffusion flame. This pilot flame receives its fuel pure, or at least poorly premixed, which on the one hand leads to a stable flame but on the other hand results in the high NO _x emissions typical of diffusion combustion.

In premix burners, it can be used both in oil operation at very high pressure and in gas operation with gases that contain a lot of hydrogen occur that the ignition delay times become so short that flame-retardant burners can no longer be used as so-called low-nox burners.

The mixing of fuel into a combustion air flow flowing in a premixing duct is usually done by 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 result in very long mixing distances 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.

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.

Presentation of the invention

The invention tries to avoid all these disadvantages. It is particularly based on the task of creating low-emission secondary combustion.

According to the invention, this is achieved in that the primary burner is a flame-stabilizing premix burner without a mechanical flame holder, with at least approximately tangential inflow of the combustion air into the premixing chamber, and in that the secondary burner is a non-self-sufficient premix burner.

Such flame-holding premix burners can be, for example, the burners of the so-called double-cone type, as are known from EP-B1-0 321 809 and are described later in relation to FIGS. 1 to 3B. The fuel, there gas, is injected in the tangential inlet gaps into the combustion air flowing in from the compressor via a series of injector nozzles. As a rule, these are evenly distributed over the entire column.

The advantage of the invention can be seen in such a lean / lean operating mode of the combustion chamber in a particular NO _X-neutral secondary combustion.

Because the burners remain operational when the mixture is very lean, the control can also be simplified insofar as the combustion chamber is loaded and unloaded, it is possible to cross air ratio ranges which, as a rule, could not be traversed with the previous premix combustion without using separate means extinguishing the flame must be avoided.

In order to achieve the necessary intimate mixing, a gaseous and / or liquid fuel is injected into the combustion air in the channel of the secondary burner, the combustion air being conducted via vortex generators, several of which are arranged next to one another over the circumference of the channel through which the flow passes.

These vortex generators are characterized by a roof surface and two side surfaces, the side surfaces being flush with the same channel wall and including an arrow angle α and the longitudinal edges of the roof surface being flush with the longitudinal edges of the side surfaces projecting into the flow channel and below an angle of attack Θ to the duct wall.

With the new static mixer, which is represented by the 3-dimensional vortex generators, it is possible to achieve extremely short mixing distances in the secondary burners 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 already exists after a distance that corresponds to a few channel 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 vortex generators can be seen in their particular simplicity. 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 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.

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 two identical but opposite vortices are generated. 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 fuel, result from the subclaims.

Brief description of the drawing

In the drawing, an embodiment of the invention is shown schematically using an annular combustion chamber for a gas turbine.

Fig. 1

einen Teillängsschnitt einer Brennkammer;

Fig. 2A

einen Teilquerschnitt durch die Brennkammer nach Linie 2-2 in Fig. 1;

Fig. 2B

einen Teilquerschnitt durch eine Anordnungsvariante der Wirbel-Generatoren in den Sekundärbrennern;

Fig. 3A

einen Querschnitt durch einen Vormischbrenner der Doppelkegel-Bauart im Bereich seines Austritts;

Fig. 3B

einen Querschnitt durch denselben Vormischbrenner im Bereich der Kegelspitze;

Fig. 4

eine perspektivische Darstellung eines Wirbel-Generators;

Fig. 5

eine Ausführungsvariante des Wirbel-Generators;

Fig. 6

eine Anordnungsvariante des Wirbel-Generators nach Fig. 4;

Fig. 7

einen Wirbel-Generator in einem Kanal;

Fig. 8 bis 14

Varianten der Brennstoffzuführung;

Fig. 15

eine perspektivische Teilansicht vom Austritt der Sekundärbrenner;

Fig. 16

eine perspektivische Teilansicht vom Eintritt der Sekundärbrenner mit Brennstoffzufuhr;

Fig. 16A

die Wirbelbildung am Eintritt der Sekundärbrenner;

Fig. 17

eine Anordnungsvariante von nebeneinanderangeordneten Wirbel-Generatoren;

Fig. 18

eine weitere Ausführungsvariante des Wirbel-Generators;

Fig. 19

eine Anordnungsvariante von nebeneinanderangeordneten Wirbel-Generatoren nach Fig. 17;

Fig. 20

ein Schaubild Temperatur längs der Brennkammer-Erstreckung;

Fig. 21

eine Ausführungsvariante des Primärbrenners.

Show it:

Fig. 1

a partial longitudinal section of a combustion chamber;

Figure 2A

a partial cross section through the combustion chamber along line 2-2 in Fig. 1;

Figure 2B

a partial cross section through an arrangement of the vortex generators in the secondary burners;

Figure 3A

a cross section through a premix burner of the double cone type in the region of its outlet;

Figure 3B

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

Fig. 4

a perspective view of a vortex generator;

Fig. 5

a variant of the vortex generator;

Fig. 6

a variant of the arrangement of the vortex generator according to FIG. 4;

Fig. 7

a vortex generator in a channel;

8 to 14

Variants of fuel supply;

Fig. 15

a partial perspective view of the outlet of the secondary burner;

Fig. 16

a partial perspective view of the entry of the secondary burner with fuel supply;

Figure 16A

the vortex formation at the entry of the secondary burner;

Fig. 17

an arrangement variant of side-by-side vortex generators;

Fig. 18

a further embodiment of the vortex generator;

Fig. 19

a variant of arrangement of side-by-side vortex generators according to Fig. 17;

Fig. 20

a graph of temperature along the combustion chamber extension;

Fig. 21

a variant of the primary burner.

Only the elements essential for understanding the invention are shown. For example, the complete combustion chamber and its assignment to a system are not 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 which are not essential to the invention, such as housings, fastenings, line bushings, the provision of fuel, the control devices and the like have been omitted.

Way of carrying out the invention About the combustion chamber structure:

In Fig. 1, 50 is a jacketed plenum, which generally receives the combustion air delivered by a compressor, not shown, and supplies it to an annular combustion chamber 1. This combustion chamber is constructed in two stages and essentially consists of a pre-combustion chamber 61 and a downstream post-combustion chamber 172, both of which are encased with a combustion chamber wall 63, 63 '.

On the pre-combustion chamber 61, which is located at the head end of the combustion chamber 1 and its combustion chamber through a front plate 54 is limited, an annular dome 55 is placed. A burner 110 is arranged in this dome in such a way that the burner outlet is at least approximately flush with the front plate 54. The longitudinal axis 51 of the primary burner 110 runs in the longitudinal axis 52 of the pre-combustion chamber 61. A plurality, here 30, of such are distributed over the circumference Burners 110 arranged side by side on the annular front plate 54 (Fig. 2A, B). The combustion air flows from the plenum 50 into the interior of the dome and acts on the burners via the dome wall perforated at its outer end. The fuel is supplied to the burner via a fuel lance 120 which penetrates the plenum and dome walls.

In the plane in which the pre-combustion chamber 61 merges into the after-combustion chamber 172, a number of secondary burners 150 open into the after-combustion chamber. These are also premix burners. Their longitudinal axis 153 extends at an angle of, for example, approximately 30 ° to the longitudinal axis of the pre-combustion chamber 61. In the present example, the cross-sections through which the primary burners 110 and secondary burners 150 flow are dimensioned for approximately half of the total volume flow to be processed.

A gaseous and / or liquid fuel is injected into the combustion air in the channel 154 of the secondary burner 150. The latter also reaches channel 154 via plenum 50, which is not shown. It is guided via vortex generators 9, 9a, of which several are arranged side by side in two channel levels over the circumference.

In the annular arrangement of the primary burner 110 and secondary burner 150 shown, the secondary burners 150 are arranged radially on the outside. This radial staggering creates a compact combustion chamber.

At the outlet of the pre-combustion chamber 61 in the region of the confluence of the secondary burners 150, swirl-generating troughs 161 are provided on the combustion chamber wall 63 'of the pre-combustion chamber. The transition from the pre-combustion chamber 61 to the post-combustion chamber 172 is provided with a constriction 171 on the combustion chamber wall 63 opposite the confluence of the secondary burners 150.

The confluence of the secondary burners in the post-combustion chamber 172 is selected such that the mixture has not yet completely burned out in the pre-combustion chamber 61.

As can be seen from FIGS. 2A and 2B to be described later, an equal number, here 30 pieces, of primary burners 110 and secondary burners 150 is arranged over the circumference. In Fig. 2A, their axes are offset by half a division in the circumferential direction. In FIG. 2B, the axes of the primary burner 110 and secondary burner 150 lie on the same radial. It is understood that the number and arrangements shown are not mandatory.

The mixture was completely burned out in the afterburning chamber 172. The hot flue gases then reach the turbine inlet 173 via a transition zone ZT, in which they are accelerated and generally mixed with cooling air.

To the primary distillers:

1, 3A and 3B schematically shown premix burners 110 are in each case a so-called double-cone burner, as was already mentioned above and is known for example from EP-B1-0 321 809. It essentially consists of two hollow, conical partial bodies 111, 112, which are nested in the flow direction and thereby enclose the premixing chamber 115. The respective central axes 113, 114 of the two partial bodies are offset from one another. The adjacent walls of the two partial bodies form in their longitudinal extension tangential slots 119 for the combustion air, which in this way reaches the interior of the burner, ie the premixing chamber 115. A first central 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 119 in the walls of the two partial bodies. In gas operation, the mixture formation with the combustion air thus already begins in the zone of the inlet slots 119. It goes without saying that mixed operation with both types of fuel is also possible in this way.

At the burner outlet 118 of the burner 110, a fuel concentration that is as homogeneous as possible is established over the applied annular cross section. At the burner outlet, a defined dome-shaped recirculation zone 123 is formed, at the tip of which the ignition takes place. The flame itself is stabilized by the recirculation zone in front of the burner without the need for a mechanical flame holder.

To the secondary burners:

According to the invention, the secondary burner 150 should now be a non-self-operating premix burner. This is understood to mean that permanent ignition must be present for the mixture combustion of the secondary burner. In the present case, this permanent ignition takes place via the flame at the outlet of the pre-combustion chamber 61. When driving with low partial loads, only the primary burners are operated with fuel. The main flow of the secondary burners is then used as dilution air.

About the vortex generators:

Before the installation of the mixing device in the secondary burners 150 is discussed, the vortex generator that is essential for the mixing process is described first.

The actual channel, through which a main flow symbolized by a large arrow flows, is not shown in FIGS. 4, 5 and 6. 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 extension, 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 perpendicular to that channel wall 21 with which the side surfaces are flush. The two enclosing the arrow angle α 4, side surfaces 11, 13 are symmetrical in shape, size and orientation 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. 4, the connecting edge 16 of the two side surfaces 11, 13 forms the downstream edge of the vortex generator 9. 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 number of swirls is increased and the location of the vortex bursting moves upstream into the area of the vortex generator themselves. Depending on the application, these two angles Θ and α are determined by the design 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. 7).

FIG. 5 shows a so-called "half" vortex generator 9a based on a vortex generator according to FIG. 4. Here, only one of the two side surfaces, namely surface 11, is provided with the arrow angle α / 2. The other side surface 13 is straight and aligned 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 this vortex generator 9a, but a swirl is forced on the flow.

In contrast to FIG. 4, in FIG. 6 the sharp connecting edge 16 of the vortex generator 9b is the point which is first acted upon by the channel flow. The element is rotated by 180 °. As can be seen from the illustration, the two opposite vortices have changed their sense of rotation.

7, the vortex generators 9 are installed in a channel 154. 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. This leads to a uniform speed distribution in the cross-section applied. 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.

For vortex generator arrangement

In the example according to FIG. 2A and its detail D2A, four half vortex generators 9a are provided in each of the 30 secondary burners in the outlet area. Their non-arrowed walls 13 (FIG. 5) adjoin the radial burner boundary walls 155. The resulting flow field within the circular ring segment is indicated by arrows. It can be seen that the total flow is directed radially inwards, specifically along the boundary walls 155.

In the example according to FIG. 2B and its detail D2B, two vortex generators 9 and 9b are provided in each of the 30 secondary burners in the outlet area. They are distributed over the circumference of the corresponding circular ring segment without a gap. Of course, the vortex generators could also be strung together on their respective wall segments in the circumferential direction in such a way that gaps between the boundary wall and the side walls are left free. Ultimately, the vortex to be generated is decisive here.

It can be seen from the detail D2B and FIG. 1 that the radially outer vortex generators 9 according to FIG. 4 are arranged, so that their leading edges 15 are first acted upon by the flow. The radially inner vortex generators 9b, on the other hand, are oriented according to FIG. 6, ie the connecting edges 16 are acted upon first by the flow here. The resulting flow field within the circular ring segment is again identified by arrows. It can be seen that the total flow is likewise directed radially inward, but not along the boundary walls 155 on the outside, but in the middle of the segment.

With these different arrangements of the vortex generators and the possibility of displacing the primary burners in the circumferential direction, one has a means in hand to create optimal mixing conditions when the two streams meet.

The vortex generators are therefore mainly used to mix two flows. The main flow in the form of combustion air attacks the transverse inlet edges 15 and the connecting edges 16 in the direction of the arrow. The secondary flow in the form of a gaseous and / or liquid fuel generally has a substantially smaller mass flow than the main flow, provided that it is not a low-calorie fuel such as for example top gas. In the present case, it is introduced into the main flow upstream of the vortex generators 9 and 9a on the outlet side.

At this point in time, the main flow is already eddy, since according to FIG. 1, a vortex generator arrangement is already provided upstream of the central fuel lance 151. "Half" vortex generators 9a are staggered in the same plane here radially outwards and radially inwards so that the vortices are now directed in the middle of the segment with the same direction of rotation, contrary to those of the outlet-side arrangement.

• die Strömung radial einwärts lenken;
• die Strömung wie ein Venturi beschleunigen, um ein Rückschlagen der Flamme zu vermeiden. Dieses Ergebnis wird durch eine gewisse Sperrung des durchströmten Querschnittes durch die Wirbel-Generatoren erreicht;
• Stromabwärts der Sekundärbrenner ist ein Wirbelaufplatzen zur aerodynamischen Stabilisierung der Flamme vorteilhaft.

It goes without saying that the number of axially staggered vortex generators and thus the length of the secondary burners depends on the degree of the desired mixing quality. At least the vortex generators on the outlet side should perform the following functions in addition to the mixing task:

• direct the flow radially inward;
• accelerate the flow like a venturi to prevent the flame from kicking back. This result is achieved by a certain blocking of the cross section through which the vortex generators flow;
• Downstream of the secondary burners, vortexing is advantageous for aerodynamically stabilizing the flame.

For fuel supply to the secondary burners:

1, the fuel is injected into the secondary burners 150 via a central fuel lance 151. A cross-jet injection of the fuel is shown, the fuel pulse having to be approximately twice that of the main flow. A longitudinal injection in the direction of flow could just as well be provided. In this case, the injection pulse corresponds approximately to that of the main flow pulse.

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 will by adjusting the ignition delay time of the fuel and the mixing time of the vortices, which ensures a minimization of emissions.

If a gaseous fuel is to be burned, the fuel can also be supplied to the channel 154 in another way. 1, it is possible to introduce the fuel directly into the area of the vortex generators via gas supply channels 152.

FIGS. 8 to 14 show such possible forms of introducing the fuel into the combustion air with regard to the secondary burners. These variants can be combined with each other and with a central fuel injection in a variety of ways.

8, in addition to wall bores 22a downstream of the vortex generators, the fuel is injected via wall bores 22c which are located directly next to the side walls 11, 13 and in their longitudinal extent in the same wall 21 on which the vortex generators are arranged are. Introducing the fuel through the wall bores 22c gives the generated vortices an additional impulse, which extends its life.

9 and 10, the fuel is injected on the one hand via a slot 22e or via wall bores 22f, which are located directly in front of the edge 15 of the roof surface 10 running transversely to the flow channel and in its longitudinal extent in the same wall 21 on which the eddies are located Generators are arranged. The geometry of the wall bores 22f or of the slot 22e is selected such that the fuel is injected into the main flow at a specific injection angle and the subsequent vortex generator flows around as a protective film against the hot main flow.

In the examples described below, the secondary flow is first introduced through the channel wall 21 into the hollow interior of the vortex generator by means not shown. This creates an internal cooling facility for the vortex generators.

11, the fuel is injected via wall bores 22g, which are located within the roof area 10 directly behind the edge 15 running transversely to the flowed channel and in its longitudinal extent. The vortex generator is cooled more externally than internally. The secondary flow emerging forms a protective layer shielding the hot main flow when it flows around the roof surface 10.

According to FIG. 12, the fuel is injected via wall bores 22h, which are staggered within the roof surface 10 along the line of symmetry 17. With this variant, the channel walls are particularly well protected from the hot main flow, since the fuel is first introduced on the outer circumference of the vortex.

13, the fuel is injected via wall bores 22j, which are located in the longitudinal edges 12, 14 of the roof surface 10. This solution ensures good cooling of the vortex generators, since the fuel escapes from its extremities and thus completely flushes the inner walls of the element. The secondary flow is fed directly into the resulting vortex, which leads to defined flow conditions.

14, the injection takes place via wall bores 22d, which are located in the side surfaces 11 and 13 on the one hand in the area the longitudinal edges 12 and 14 and on the other hand in the area of the connecting edge 16. This variant is similar in effect to that from the bores 22a in FIG. 8 and from the bores 22j in FIG. 13.

Fig. 15 shows a partial perspective view of the meeting of the secondary burners and the pre-combustion chamber. The vortex generators provided here in the outlet area of the secondary burners correspond to those according to FIG. 2A. The radially inner "half" vortex generators 9a shown are flowed to first with the connecting edge 16, which is here in the same radial as the segment boundary wall 155; the radially outer "half" vortex generators 9a are first flowed over with the edge 15 running in the circumferential direction.

As already mentioned above, vortex-generating troughs 161 are provided at the outlet of the pre-combustion chamber 61 in the region of the confluence of the secondary burners 150 on the combustion chamber wall 63 'of the pre-combustion chamber and are constructed similarly to the vortex generators described so far. In contrast to these, the two side surfaces and the roof surface do not form a specific tip. As shown in FIG. 1, the radially outer flow of the pre-combustion chamber is swirled radially outward by these stepped troughs and impinges on the mixture of secondary burners flowing inwards.

To compensate for this radially deflected partial flow, the transition from the pre-combustion chamber 61 to the afterburning chamber 62 is provided with a constriction 171 on the combustion chamber wall 63 opposite the troughs 161, so as not to disturb the surface conditions.

Fig. 16 shows a partial perspective view of the entrance of the secondary burner, again in this first level half vortex generators 9a are arranged according to FIG. 5, but in a different arrangement than that at the secondary burner outlet. A central fuel lance 151 for oil and gas feed pipe 156 to the vortex generators are provided for the individual burners. 16A, which shows a detailed view of FIG. 16, shows the eddy formation on both sides of the radially running segment boundary wall 155; the fact that the half vortex generators arranged next to one another in the circumferential direction alternately act upon the edge 15 and the edge 16 by the air first, creates a total vortex in the same direction in the counterclockwise direction.

To the mixing zone:

The vortex generators in the secondary burners can be designed so that recirculation zones downstream are largely avoided. As a result, the residence time of the fuel particles in the hot zones is very short, which has a favorable effect on the minimal formation of NOx. However, as in the present case, the vortex generators can also be designed and staggered in the depth of the channel 154 in such a way that a defined backflow zone 170 arises at the outlet of the secondary burners, which stabilizes the flame in an aerodynamic manner, i.e. without mechanical flame holder.

The mixture leaves the secondary burner 150 with a vortex and enters the flame from the pre-combustion chamber 61. As a result of the collision of the two eddy currents, there is intimate mixing over the shortest distance and a renewed vortex burst, which leads to the backflow zone 170 already mentioned.

The intensive mixing results in a good temperature profile over the cross-section through which the air flows and also reduces the possibility of thermoacoustic instability. Due to their presence alone, the vortex generators act as a damping measure against thermoacoustic vibrations.

With the burners described, the partial load operation of combustion chambers can be easily implemented by means of a graduated fuel supply to the individual modules. If only the primary burners are operated with a premix flame, the main flow of the secondary burners is used as dilution air. This strongly swirled main flow mixes very quickly with the hot gases emerging from the primary stage at the outlet of the secondary burners. A uniform temperature profile is thus generated downstream. When the burner is loaded, fuel is gradually injected into the secondary burner and mixed intensively into the combustion air before ignition. So these secondary burners always work in premix mode; they are ignited and stabilized from the primary burners.

The burner aerodynamics consist of two radially graded vortex images. The radially outer vortices depend on the number and geometry of the vortex generators 9. The radially inner vortex structure emanating from the double-cone burner can be influenced by adapting certain geometric parameters on the double-cone burner. The quantity distribution between the primary burner and the secondary burner can be carried out as required by appropriately coordinating the areas through which the flow flows, taking into account the pressure losses. Because the vortex generators have a relatively low pressure drop, the secondary burners can flow through at a higher speed than the primary burner. A higher speed at the outlet of the secondary burner has a favorable effect on the flame's kickback.

An annular combustion chamber is proposed in FIG. 17 , in which the radially stepped vortex images described above are precisely defined. The radially inner large-scale vortex and the radially outer vortex have the opposite direction of rotation. In order to achieve this, a number of vortex generators 9a according to FIG. 5 are grouped around the double-cone burner 101. These are so-called half vortex generators, 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 aligned in the burner axis. 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. After the vortex generators evenly distributed in the circumferential direction all have the same orientation, the originally swirl-free main flow downstream of the vortex generators creates a swirl which is rectified over the circumference, as indicated in FIG. 17.

FIGS. 18 and 19 show a top view of an embodiment variant of a vortex generator 9c and a front view of its arrangement in an annular channel. The two side surfaces 11 and 13 enclosing the arrow angle α have a different length. This means that the roof surface 10 rests with an edge 15a running obliquely to the flow through the channel on the same channel wall as the side walls. The vortex generator then naturally has a different angle of attack stell across its width. Such a variant has the effect that vertebrae with different Strength are generated. For example, this can act on a swirl adhering to the main flow. Or, due to the different vortices, a swirl is forced on the originally swirl-free main flow downstream of the vortex generators.

Such configurations are well suited as an independent, compact burner unit. When using several such units, for example in an annular combustion chamber, the swirl imposed on the main flow can be exploited to improve the cross-ignition behavior of the burner configuration, e.g. at partial load.

How it works:

20 shows in a self-explanatory diagram how the temperatures develop along the extent of the combustion chamber. 173 (as in FIG. 1) denotes the first turbine guide vane row.

115

Vormischbereich im Primärbrenner 110

61

Vorbrennkammer

SMF

erster Vormischbereich und Brennstoffeindüsung im Sekundärbrenner 150

S2M

zweiter Vormischbereich im Sekundärbrenner 150

M

Mischzone

BO

Ausbrandzone in der Nachbrennkammer 62

ZT

Übergangszone zum Turbineneintritt 173

The following zones, plotted above the diagram and also designated in FIG. 1, mean:

115

Premixing area in primary burner 110

61

Pre-combustion chamber

SMF

first premixing area and fuel injection in secondary burner 150

S2M

second premixing area in secondary burner 150

M

Mixing zone

BO

Burnout zone in the afterburning chamber 62

ZT

Transition zone to turbine inlet 173

EI

Ort der Fremdzündung beim Primärbrenner

SI

Ort der Selbstzündung in der Mischzone M

Further mean:

EGG

Point of ignition at the primary burner

SI

Place of auto-ignition in the mixed zone M

T_F

Flammen-Temperatur

T_T

Turbineneintritts-Temperatur

T_SI

Selbstzünd-Temperatur

T_IN

Temperatur des Brennstoff/Luftgemisches

The following temperatures are plotted on the abscissa:

T _F

Flame temperature

T _T

Turbine inlet temperature

T _SI

Auto-ignition temperature

T _IN

Temperature of the fuel / air mixture

δT_1C

Temperaturerhöhung infolge Verbrennung

δT_1m

Temperatursenkung infolge Vermischung

δT_2m

Temperaturerhöhung infolge Vermischung

δT_2C

Temperaturerhöhung infolge Verbrennung

Further mean:

δT _1C

Increase in temperature due to combustion

δT _1m

Temperature decrease due to mixing

δT _2m

Temperature increase due to mixing

δT _2C

Increase in temperature due to combustion

The effect of the new measure is as follows: On the occasion of the pre-combustion, as a result of the split in half between the primary burner and secondary burner, only half of the total volume flow as a result of the temperature increase δT _1C produces nitrogen. This half volume flow has only a short dwell time in the pre-combustion chamber 61 until it is mixed with the mixture from the secondary burners, which has a favorable effect on the NO _x production.

When the hot flue gases from the pre-combustion chamber 61 are mixed with the fuel / air mixture from the secondary burners, the mixing temperature must not drop below the compression ignition temperature T _SI .

After auto-ignition, the temperature increase δT _{2C of} the entire volume flow is too low and the period until the complete burnout in zone BO is too short to produce significant NO _x .

It can be seen from all of this that with this lean / lean concept, the averaged volume flow is only exposed to the high flame temperature for a reduced period of time in comparison to a classic single-stage premix combustion.

Equivalent solutions:

In principle, the invention is not limited to the use of primary burners of the double-cone type shown. Rather, it can be used in all combustion chamber zones in which flame stabilization is generated by a prevailing air velocity field. As another example of this, reference is made to the burner shown in FIG. 21. In this FIG. 21, all functionally identical elements are provided with the same reference numerals as in the burner according to FIGS. 1-3B. This is despite a different structure, which applies in particular to the tangential inflow gaps 119 which run here cylindrically. The area of the premixing chamber 115 which flows through in the direction of the burner outlet is formed in this burner by a centrally arranged insert 130 in the form of a straight circular cone, the cone tip being in the region of the front plate plane. It goes without saying that the lateral surface of this cone can also be curved. Incidentally, this also applies to the course of the partial surfaces 111, 112 in the burners shown in FIGS. 1-3B.

Of course, in deviation from the 2-stage combustion shown and described, more than 2 stages can also be used. The number of combustion stages and the type of fuel and air distribution over the several stages ultimately depends on the desired performance of the combustion chamber.

Reference list

1

Combustion chamber

9.9a, 9b, 9c

Vortex generator

10th

Roof area

11

Side surface

12th

Long edge

13

Side surface

14

Long edge

15, 15a

transverse edge of 10

16

Connecting edge

17th

Line of symmetry

18th

top

21

Canal wall

22, a-j

Wall hole

Θ

Angle of attack

α, α / 2

Arrow angle

H

Height of 16

H

Channel height

L

Length of the vortex generator

50

plenum

51

Longitudinal axis of the primary burner

52

Longitudinal axis of the pre-combustion chamber

54

Front plate of the pre-combustion chamber

55

Cathedral

61

Pre-combustion chamber

63.63 '

Combustion chamber wall

110

Primary burner

111

Partial body

112

Partial body

113

Central axis

114

Central axis

115

Premixing room

116

Fuel nozzle

117

Gas inflow opening

118,

Burner outlet

119,

tangential gap

120

Fuel lance

123

Reverse flow dome (vortex breakdown)

130

conical insert (Fig. 22)

150

Secondary burner

151

Fuel lance

152

Secondary burner gas supply duct

153

Longitudinal axis of the secondary burner

154

channel

155

radial boundary wall

156

Secondary burner gas supply nozzle

161

Tubs

170

Reverse flow zone (vortex breakdown)

171

Constriction

172

Afterburner

173

1st row of turbine guide vanes

SMF

Premix section and fuel injection (premix section and fuel injection)

S2M

2nd premixing section (2nd premix section)

M

Mixing section

BO

Burn out zone

ZT

Transition zone to the turbine inlet

EGG

Location of external ignition

SI

Place of self-ignition

T _F

Flame temperature

T _T

Turbine inlet temperature

T _SI

Auto-ignition temperature

T _IN

Temperature of the fuel / air mixture

δT _1C

Increase in temperature due to combustion

δT _1m

Temperature decrease due to mixing

δT _2m

Temperature increase due to mixing

δT _2C

Increase in temperature due to combustion

Claims (12)

Combustion chamber with two-stage combustion, with at least one primary burner (110) of the premix type, in which the fuel injected via nozzles (117) is mixed intensively with the combustion air prior to ignition within a premixing chamber (115), and with at least one secondary burner (150), which is arranged downstream of a pre-combustion chamber (61),
characterized, - that the primary burner (110) is a flame-stabilizing premix burner without a mechanical flame holder, with at least approximately tangential inflow of the combustion air into the premixing chamber (115), - And that the secondary burner (150) is a non-self-sufficient premix burner. Combustion chamber according to Claim 1, characterized in that the primary burner (110) works according to the double-cone principle with essentially two hollow, conical, part-bodies (111, 112) nested one inside the other in the direction of flow, the respective central axes (113, 114) of which are offset from one another, the In the longitudinal extension, adjacent walls of the two partial bodies form tangential gaps (119) for the combustion air, and gas inflow openings (117) distributed in the longitudinal direction are provided in the region of the tangential gaps in the walls of the two partial bodies. Combustion chamber according to claim 1, characterized in that a gaseous and / or liquid fuel is injected as a secondary flow into a gaseous main flow into the channel (154) of the secondary burner (150), and that the main flow via vortex generators (9, 9a, 9b, 9c ) is guided, of which several are arranged side by side over the circumference of the channel (154) through which the flow flows. Combustion chamber according to claim 3, characterized in - that a vortex generator (9, 9a, 9b, 9c) has three free-flowing surfaces that extend in the direction of flow and one of which forms the roof surface (10) and the other two the side surfaces (11, 13), - that the side surfaces (11, 13) are flush with the same wall segment (21) of the channel and enclose the arrow angle (α, αh) with one another, - That the roof surface (10) lies with an edge (15) running transversely to the channel (154) through which it flows, on the same wall segment (21) as the side surfaces (11, 13) - And that the longitudinal edges (12, 14) 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 wall segment (21). Combustion chamber according to claim 4, characterized in that the two side surfaces (11, 13) of the vortex generator (9,, 9c) including the arrow angle (α) are arranged symmetrically about an axis of symmetry (17). Combustion chamber according to claim 4, characterized in that the ratio height (h) of the vortex generator to the channel height (H) is chosen so that the generated vortex immediately downstream of the vortex generator (9) the full channel height or the full height of the Fills the channel part assigned to the vortex generator. Combustion chamber according to claim 3, characterized in that the secondary flow is introduced via a fuel lance (151) centrally arranged in the channel (154) by means of longitudinal injection or transverse jet injection. Combustion chamber according to Claim 3, characterized in that in the channel (154) of the secondary burner (150) there are vortex generators (9, 9a, 9b, 9c) arranged next to one another in two planes in the longitudinal direction thereof. Combustion chamber according to claim 1, characterized in that the longitudinal axis (153) of the secondary burner (150) extends at an acute angle to the longitudinal axis (52) of the pre-combustion chamber (61). Combustion chamber according to claim 1, characterized in that in the case of an annular arrangement of a plurality of primary burners (110) and secondary burners (150), the secondary burners (150) are located radially on the outside, preferably at least approximately in the same plane as the primary burners (110). Combustion chamber according to claim 10, characterized in that vortex-generating troughs (161) are provided at the outlet of the pre-combustion chamber (61) in the region of the junction of the secondary burners (150) on the combustion chamber wall (63 ') of the pre-combustion chamber. Combustion chamber according to Claim 11, characterized in that the transition from the pre-combustion chamber (61) to the post-combustion chamber (62) is provided with a constriction (171) on the combustion chamber wall (63) opposite the confluence of the secondary burners (150).

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