EP1336800B1 - Method for reducing the oscillations induced by the combustion in combustion systems and premix burner for carrying out the method - Google Patents

Description

Technical area

The invention relates to a premix burner for reducing combustion-driven vibrations within a combustion system, in particular one with low acoustic damping, as is frequently encountered in combustion chambers of flow engines.

State of the art

In the operation of turbomachinery, such as gas turbine plants, occur in the combustion chambers often combustion-driven thermoacoustic oscillations, which arise at the burner as fluid mechanical Instabilitätswellen and lead to eddies that greatly affect the entire combustion process and lead to unwanted periodic heat releases within the combustion chamber. This results in pressure fluctuations of high amplitude, which can lead to undesirable effects, such as a high mechanical load of the combustion chamber, increased NO _x emissions by inhomogeneous combustion or even to extinguishment of the flame within the combustion chamber.

Thermoacoustic oscillations are based, at least in part, on flow instabilities of the burner flow, which manifest themselves in coherent flow structures, and which influence the mixing processes between combustion air and fuel.

There is now known a number of techniques to counteract thermoacoustic oscillations, for example. With the aid of a cooling air film which is passed over the combustion chamber walls or by an acoustic coupling of so-called Helmholtz damper in the combustion chamber or in the region of the cooling air.

Furthermore, it is known that the combustion instabilities occurring in the burner can be counteracted by stabilizing the fuel flame by additional injection of fuel. Such injection of additional fuel takes place via the head of the burner, in which a nozzle for the pilot fuel gas supply lying on the burner axis is provided, which leads to an enrichment of the central flame stabilization zone. However, this method of reducing thermoacoustic vibration amplitudes involves the disadvantage that the injection of fuel at the head stage is accompanied by an increase in the emission of NO _x .

Studies on the formation of thermoacoustic vibrations have shown that often flow instabilities lead to these instabilities. Of particular importance here are the shear layers forming between two mixing flows which initiate waves perpendicular to the direction of flow (Kevin Helmholtz waves). These instabilities on shear layers in combination with the ongoing combustion process are mainly responsible for the thermoacoustic oscillations caused by reaction rate fluctuations. These largely coherent waves result in a burner of the aforementioned type under typical operating conditions to vibrations at frequencies in the range of 100 Hz. Since this frequency coincides with typical fundamental eigenmodes of many ring burners in gas turbine plants, the thermoacoustic oscillations pose a problem following publications: Oster & Wygnanski 1982, "The forced mixing layer between parallel streams", Journal of Fluid Mechanics, Vol. 123, 91-130 ; Paschereit et al. 1995, "Experimental investigation of subharmonic resonance in an axisymmetric jet", Journal of Fluid Mechanics, Vol. 283, 365-407 ; Paschereit et al., 1998, "Structure and Control of Thermoacoustic Instabilities in a Gas Turbine Burner, Combustion, Science & Technology, Vol. 138, 213-232 ).

As can be seen from the above publications, it is possible to influence the forming within the shear layers coherent structures by deliberately introducing an acoustic excitation in such a way that the formation of such vortex is largely prevented. This prevents fluctuations in heat release and reduces pressure fluctuations.

Premixed flames require low velocity zones to be stabilized. To stabilize the flame backflow zones, which are generated either by the lag behind sturgeons, so-called flame holders, or by aerodynamic methods (vortex breakdown). The stability of the backflow zone is another criterion for the stability of the combustion and the avoidance of thermoacoustic instabilities.

US 5325660 describes embodiments of burners of the former category. To stabilize the flame, a flow-influencing body is arranged downstream of the premixing zone of the burner such that a backflow zone forms downstream. In burner mode, the flame sits directly behind the flame holder. Such designed burners are not well suited for operation in connection with fluid power engines, such as gas turbines. The flame holders are subject to high wear due to their exposed position and the enormous thermal and chemical stresses. Waste parts would have devastating effects on the downstream turbine. In modern gas turbine plants such burners are therefore no alternative.

EP 321 809 B1 discloses a premix burner with a return flow zone forming downstream of the burner exit which stabilizes the flame without the need for a mechanical flame holder. This burner consists of at least two hollow, nested Teilkegelkörpern whose longitudinal axes are offset from each other such that tangential slots for supplying the combustion air form, which flows like a spiral through an enclosed by the part cone bodies, conically expanding premixing zone to the burner outlet. Centrally arranged in the premixing lance for fuel injection is arranged.

After the in DE 195 45 309 notified teaching are in a burner according to EP 321 809 thereby reducing NO _x emissions and stabilizing the backflow zone by extending the fuel lance to at least the lower third of the premix zone and having a fuel nozzle at its downstream end. This measure of shortening the distance between the fuel nozzle and Rückströmzone not only pulsations are reduced, but also reduces the fuel requirements to stabilize the flame.

WO 01/96785 discloses a generic same premix burner, which is characterized by a stable operation in the partial load range and thermoacoustic instabilities, which can lead to a complete extinction of the flame, especially in the part-load range, reduced. This is accomplished by a locally variable fuel injection into the premix zone via at least a first group and at least a second group of fuel supply means. In this case, the burner lance should preferably be equipped with more than one group of fuel supply and extend relatively far into the premixing zone.

Subject of the US 5487274 is a gas turbine combustion chamber with low-emission combustion. A number of premix zones for supplying a fuel-air mixture are coupled to the combustion chamber. The premix zones each consist of a cylindrical jacket tube with an inner cylindrical central body, so they have an annular cross-section. The central body ends shortly before the outlet of the premixing zone in the combustion chamber. At the entrance of the premixing zone are vortex elements for the combustion air and from the central body radially outgoing, projecting into the combustion air flow lances for injecting fuel into the flowing combustion air. Starting from the jacket pipe or the central body protrude at the combustion chamber side outlet the premixing zone includes a plurality of, approximately two to six, flow elements radially into the annular premixing zone which interfere with the formed flow patterns and thus inhibit the formation of coherent structures.

Presentation of the invention

The invention has for its object to provide a premix burner for reducing combustion-driven thermoacoustic oscillations within a combustion system, in particular one with a low acoustic damping, which further reduces the formation of coherent flow instabilities at the burner outlet and which is to create with little equipment.

According to the invention, the object is achieved by a premix burner of the type mentioned in the independent claim.

The concept of the invention advantageously further features are the subject of the dependent claims and the following description.

Starting from a combustion system comprising a premix burner according to EP 0 321 809 B1 protected design, the basic idea of the invention is to further stabilize the central backflow zone forming downstream of the burner outlet, within which the fuel / air mixture ignites. Due to the stabilization of the backflow zone and the reduction of the formation of coherent vortex structures at the burner outlet, the periodic heat releases within the combustion chamber which cause the occurrence of thermoacoustic oscillations are largely prevented.

The fluidic stabilization of the Rückströmzone according to the invention is carried out by providing the central fuel nozzle in the form of a burner lance, as is commonly used for pilot gas supply, wherein the burner lance has a length downstream of the burner head in a length of 60 to 80% in the burner protrudes, is arranged centrally to the burner axis and in her The fuel discharge takes place by at least one fuel nozzle opening attached to the end of the lance in such a way that the fuel discharged into the interior of the burner mixes finely distributed with incoming air and is at the same time swirled. In particular, the wake at the end of the lance provides further stabilization of the aerodynamically generated return flow zone. In particular, the fuel input according to the invention in a downstream displaced position within the burner interior prevents a periodic outflow and re-entry of the flame forming within the return flow zone into the burner. Due to the spatial proximity of the fuel discharge to form within the combustion chamber Rückströmzone just that vortex breakdown can be supported by the propagating in the flow direction, turbulent fuel / air mixture, whereby the Rückströmzone and associated flame are significantly stabilized.

It has been recognized that different forms of lances can influence the formation of coherent structures. In the following, a number of preferred lance configurations will be presented. These configurations have in common, by a diversification of the vortex movement, the formation of coherent structures in addition to inhibit.

In a further embodiment, the lance is equipped in a manner known per se with means which allow an independent supply of two fluid media. Such a design makes it possible to introduce additional fuel air into the burner interior in addition to a fuel injection. By a known modulated supply of this additional air combustion chamber vibrations thus can be additionally counteracted.

In particular, in an operating mode of the premix burner with fuel supply into the combustion air entering tangentially into the burner interior via nozzles arranged along the jacket, the measure according to the invention carries a partial fuel injection via the central fuel lance pushed into the interior space and having an expanding cross section in the end region to stabilize the flame forming within the backflow zone.

Ways to carry out the invention

The invention will now be described by way of example without limitation of the general inventive idea by means of embodiments with reference to the drawings.

Fig. 1

schematisierten Längsschnitt durch einen kegelförmig ausgebildeten Brenner mit verlängerter Brennerlanze,

Fig. 2

Diagrammdarstellung zur Abhängigkeit der Länge der Brennerlanze auf das akustische Dämpfungsverhalten,

Fig. 3

Diagrammdarstellung zur Abhängigkeit der Länge der Brennerlanze auf das akustische Dämpfungsverhalten im Hinblick auf unterschiedliche Lanzenkonfigurationen,

Fig. 4

Diagrammdarstellung der Abhängigkeit der Länge der Brennerlanze auf die NO_x-Emissionen im Hinblick auf unterschiedliche Lanzenkonfigurationen,

Fig. 5-8

unterschiedliche Brennerlanzenkonfigurationen.

Show it:

Fig. 1

schematized longitudinal section through a conical burner with extended burner lance,

Fig. 2

Diagram showing the dependence of the length of the burner lance on the acoustic damping behavior,

Fig. 3

Diagram showing the dependence of the length of the burner lance on the acoustic damping behavior with regard to different lance configurations,

Fig. 4

Diagram depicting the dependence of the length of the burner lance on the NO _x emissions with regard to different lance configurations,

Fig. 5-8

different burner lance configurations.

In FIG. 1 is shown in longitudinal section a premix burner 1, as in its basic structure, for example, from the EP 0 321 809 evident. The premix burner 1 consists of two half-shell-shaped, conically widening partial bodies 1 a and 1 b, which are arranged axially parallel and offset from one another such that they form tangential gaps in two overlapping areas lying opposite each other in mirror image. The resulting from the displacement of the longitudinal axes of the body part 1 a and 1 b column serve as inlet channels through which the combustion air 7 flows tangentially into the burner interior 2 in the burner operation. Along these inlet channels are injection openings, through which a preferably gaseous Fuel 8 is injected into the passing combustion air 7. In addition to this fuel injection 8 on the burner jacket, this abovementioned type of burner has in a central arrangement in the starting region of the burner interior 2 a nozzle for introducing further, preferably liquid fuel. With the formation of a swirl flow 6, combustion air 7 and fuel 8 pass through the burner interior 2 with intensive mixing. At the burner outlet, the swirl flow 6 breaks down to form a backflow zone 5 with an effect stabilizing the flame front acting there. Further details of the structure and operation of this burner 1 are shown in the aforementioned EP document and other sources of information known to those skilled in the art.

According to the invention, a burner lance 3 protrudes parallel to the burner axis into the burner interior 2 as an extension of the mentioned central fuel nozzle. The lance 3, which has a length I which is preferably in the region of approximately 2/3 of the axial extent of the burner 1, has a centrally arranged lance Fuel channel 31, which ends downstream of the end of the lance in a fuel nozzle 32.

After the in Fig.1 In addition, radially oriented nozzles 33, from which air is introduced into the burner interior 2 for additional damping in the combustion system forming thermoacoustic oscillations, open out in the region of the end of the lance. This air, as well as the fuel, can be fed modulated. The in a swirl flow 6 through the burner interior 2 in the combustion chamber 4 propagating fuel / air mixture is able to stabilize within the combustion chamber 4 forming Rückströmzone 5, especially since the vortex of the fuel / air mixture before and during ignition the vortex decay within the combustion chamber. 4 favors, whereby the Rückströmzone 5 is stabilized. This can prevent the Rückströmzone 5 changes its position periodically, which is ultimately the cause of propagating within the combustion system thermoacoustic oscillations.

In FIG. 2 is a diagram representation illustrating the effect of inventively designed burner lance 3 on the suppression of instabilities in the form of pressure oscillations in the 120 Hz range. The pulsations measured in pressure values (Pa) along the ordinate in FIG. 2 are plotted as a function of the position of the lance end in the burner 1. Along the abscissa, the ratio I / L is plotted, ie the ratio of the length of the burner lance 3 to the total axial extent L of the burner. The position I / L = 0 corresponds to the original position of the central fuel nozzle, as mentioned above.

• Die durchgehend, horizontal eingetragene Linie entspricht der Basislinie, gemäß der an sich bekannte Brennersysteme ohne die Vorkehrung der erfindungsgemäß ausgebildeten Lanze bei vorgegebenen Betriebsbedingungen schwingen. Der mit Quadraten durchsetzte Funktionsverlauf gibt das Schwingungsverhalten eines Brenners im Premixbetrieb wieder, bei dem lediglich die zentrale Brennerlanze vorgesehen ist, durch die jedoch kein Brennstoffeintrag in den Brenner erfolgt. Die mit den ausgefüllten Rauten durchsetzte Linie gibt den Betrieb unter Verwendung einer erfindungsgemäß ausgebildeten Brennerlanze 3 wieder, bei der 2 kg Brennstoffaustrag pro Std. als Brennstoffzugabe durch die Brennerlanze 3 gewählt wurde. Schließlich zeigt die mit Dreiecken durchsetzte punktierte Linie einen Fall unter Verwendung der erfindungsgemäß ausgebildeten Brennerlanze 3, gleichsam jenem mit der Rauten durchsetzten Linie, jedoch mit einer Brennstoffzugabe von 5 kg pro Std.

The different functional curves shown in the diagram correspond to the following measuring conditions, as they are known from the legend of the FIG. 2 can be removed:

• The continuous, horizontal registered line corresponds to the baseline, according to the known burner systems oscillate without the provision of inventively designed lance at predetermined operating conditions. The interspersed with squares function curve shows the vibration behavior of a burner in the premix mode again, in which only the central burner lance is provided by which, however, no fuel enters the burner. The interspersed with the solid diamonds line shows the operation using a burner lance formed according to the invention 3 again, in which 2 kg fuel discharge per hour was selected as fuel addition by the burner lance 3. Finally, the dotted line interspersed with triangles shows a case using the burner lance 3 constructed according to the invention, as it were the line interspersed with the diamonds, but with a fuel addition of 5 kg per hour.

Out FIG. 2 It becomes clear that the resulting instabilities in the premix operation at the FIG. 1 The best way is to suppress the burner shown with a lance position of I / L = 0.6 - 0.8. The preferred lance position is I / L = 0.7.

The suppression of instabilities in the burner operation, which essentially by improved flame stability and by the destruction of coherent structures can be ensured can be improved by the lance end is configured as a bluff body 10, 11, 13, to introduce vorticity in the flow direction. From the Figures 6-8 Go to different Störkörpergeometrien show, according to which the end of the lance is to be formed. Depending on the geometry of the faulty bodies shown in these figures, the in FIG. 3 shown characteristics are shown for illustrating the operation of the suppression of instabilities.

In the FIG. 3 Diagram representation shown is with the in FIG. 2 comparable. The affiliation of the individual function curves to the differently shaped disturbance body geometries can also be taken directly from the legend of the figure. Again, the fact is that suppression of instabilities with a burner lance length of I / L = 0.6 - 0.8 is most pronounced.

Of all investigated Störgeometrien proves the conical burner lance ( Figure 7 ) is particularly suitable for suppressing instabilities (see the dashed line in. with inverted triangles in Fig. 3 ).

In FIG. 4 the evaluation of the individual interfering geometries with regard to the nitrogen oxide emission is shown. In this case, the burner lance interspersed with a multiplicity of fuel outlets proves to be particularly advantageous FIG. 5 is shown. In the FIG. 5 The illustrated interference geometry as well as the geometries shown in the following figures can be formed, for example, as threaded screw tops, which are screwed into the burner head and in particular can be easily exchanged for test purposes.

In the FIG. 5 illustrated burner lance 3 is equipped with a plurality of the shell laterally penetrating fuel outlet openings 9. By an axial fanning of the fuel injection, a homogeneous mixing of fuel and combustion air is ensured. The injection takes place preferably in the region of the second lance half, as viewed in the direction of flow.

FIG. 6 shows a star-shaped Lanzenendgeometrie, FIG. 7 a conically shaped Lanzenendgeometrie, wherein the fuel discharge from the lance 3 by axially aligned outlet openings 12, 32 takes place, as it were the lance geometry in FIG. 8 showing a burner lance to which a plate 13 is attached.

The Störgeometrien assets, as above based on Fig. 3 described to decisively influence the premix flow.

LIST OF REFERENCE NUMBERS

1

burner

1a; 1b

shells

2

Burner interior

3

burnerlance

31

fuel line

32

axial fuel outlet opening on the lance. 3

33

radial air injection

4

combustion chamber

5

backflow

6

swirl flow

7

combustion air

8th

fuel

9

Fuel outlet on the lance 3

10

star-shaped Lanzenendgeometrie

11

conical lance end geometry

12

Fuel outlet on the lance 3

13

Plate at the end of the lance

I

Length of the burner lance

Claims (6)

1. Premixing burner for the reduction of combustion-driven oscillations within a combustion system, in particular a combustion chamber (4) of a turbomachine, essentially comprising a swirl generator consisting of two semimonocoque conically widening part bodies (1a) and (1b) which are arranged axially parallel, and offset to one another, in such a way that they form tangential gaps in two overlap regions located mirror-symmetrically opposite one another, said gaps serving as inlet ducts for the combustion air (7) into the burner interior (2), furthermore comprising at least one central fuel nozzle within the interior (2) enclosed by the part bodies (1a) and (1b), wherein the central fuel nozzle is designed in the form of a coaxially oriented burner lance (3) which projects into the burner interior (2) and terminates in a range of between 60% and 80% of the axial length of the burner interior (2), and the burner lance (3) is equipped, at least in its downstream end region, with means for the discharge of at least one fluid into the burner interior (2), characterized in that the lance (3) has a widening cross section at least in its downstream end region.
2. Premixing burner according to Claim 1, characterized in that the lance (3) has an end region widening conically in the flow direction.
3. Premixing burner according to Claim 1, characterized in that the lance (3) has an end region widening in a star-shaped manner in the flow direction.
4. Premixing burner according to Claim 1, characterized in that the lance (3) has in its end region a plate (13) oriented perpendicularly to the flow direction.
5. Premixing burner according to Claim 1, characterized in that the end region of the burner lance (3) is equipped with outlet orifices (32) and (33) for fuel and combustion air.
6. Premixing burner according to Claim 1, characterized in that the casing of the burner lance (3) is equipped with outlet orifices (9) for fuel.

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