EP1217295B1 - Burner for generating a hot gas - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of burner technology. It relates to a burner for the production of hot gases according to the preamble of claim 1.

STATE OF THE ART

The fluid mechanical stability of a gas turbine burner is of crucial importance for the occurrence of thermoacoustic vibrations. Fluid-mechanical instability waves, which arise at the burner, lead to the formation of vortices (coherent structures), which influence the combustion and can lead to periodic heat release with the associated pressure fluctuations (thermoacoustic oscillations). The thermoacoustic Vibrations pose a threat to any type of combustion application. They result in high amplitude pressure oscillations, a limitation of the operating range, and can increase pollutant emissions. This is especially true for low acoustic attenuation combustion systems. In order to allow high power conversion over a wide operating range with respect to pulsations and emissions, active control of the combustion vibrations may be necessary.

In the past, a large number of proposals have already been made and possibilities shown how to damp or completely suppress the undesired thermoacoustic oscillations in such burners, in particular also the so-called double-cone burners, as described, for example, in EP-A2-0 881 432 can.

In EP-A1-0 918 152 it is proposed to control the thermoacoustic oscillations in a combustion system by arranging means for the acoustic excitation of the working gas in the region of the burner. However, this is associated with additional equipment and control effort. A similar acoustic concept (EP-A1-1 050 713) works with an active suppression by a feedback control loop with corresponding phase rotation.

In EP-A1-0 987 495 it is proposed to additionally mix an inert gas such as N ₂ , CO ₂ or the like for minimizing thermoacoustic oscillations in gas turbine combustors to the fuel stream. However, this means an additional supply and piping system for the mixed inert gas.

Other solutions modify the geometry of the burner, in particular at the burner outlet: In EP-A1-1 002 992 it is proposed to arrange a plurality of nozzles for controlling flow instabilities in the burner on the inside of the burner outlet along the circumference, which are injected by injection of air introduce axial vorticity into the flow at an angle to the flow direction.

EP-A1-0 985 877 further proposes to accelerate the flow in the axial direction by minimizing thermoacoustic oscillations in gas turbine combustion chambers by nozzle-like design of the burner outlet, or nozzle-like shaped attachments are attached to the burner.

Finally, EP-A1-1 048 898 discloses a burner (double-cone burner) in which a plurality of internals projecting into the flow are provided in the burner cone for introducing axial vortical strength.

In contrast, the present invention is based on the following consideration: Coherent structures play a crucial role in mixing processes between air and fuel. The dynamics of these structures consequently influence the combustion and thus the heat release. Controlling the combustion instabilities is possible by influencing the shear layer between the fresh gas mixture and the recirculated exhaust gas (see, for example, Paschereit et al., "Structure and Control of Thermoacoustic Instabilities in a Gas-turbine Burner, Combustion, Slicing & Technology, Vol. 138, pp. 213-232 (1998)). In particular, it makes sense to influence the formation of coherent structures by influencing the outflow boundary layer at the burner outlet.

PRESENTATION OF THE INVENTION

It is an object of the invention to provide a burner in which limited by very simple structural means thermoacoustic oscillations or can be completely suppressed.

The object is solved by the entirety of the features of claim 1.

The basic idea of the invention is to influence the formation of coherent structures so that the generation of high-frequency combustion-driven vibrations is prevented. Coherent structures are to be understood as flow vortices that arise due to flow instabilities in the shear layers forming at the burner exit. The influence of coherent structures on combustion instabilities is most pronounced when the flow instability has overlapped its highest growth rate and the vortices have reached their maximum size. The axial position of the highest growth rate can be influenced inter alia by changing the thickness of the outflow boundary layer. By preventing the formation of vortex structures in the region of the flame, a periodic heat release is prevented. However, a periodic heat release would be the basis for the occurrence of thermoacoustic vibrations, which is thus prevented.

A preferred embodiment of the invention is characterized in that the means for changing the thickness of the Abströmgrenzschicht comprise a shear layer fence, which extends along the exit edge of the burner outlet and protrudes with its height substantially parallel to the flow direction into the combustion chamber. Due to the shear layer fence, which preferably has a height of a few millimeters, the thickness of the outflow boundary layer is increased in a particularly simple manner and thus the vortex formation in the axial direction is displaced out of the area of the flame, so that the periodic heat release associated with the vortex formation is avoided.

The burner is preferably designed as a double-cone burner and comprises at least two hollow, conical, nested in the flow direction part body whose center axes are offset from each other, such that adjacent walls of the body part tangential air inlet channels for the inflow of combustion air in the bounded by the partial body interior, wherein the combustion chamber side edges of the partial body form the outlet edges of the burner outlet.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

in der Draufsicht von vorn (entgegen der Strömungsrichtung) die Struktur eines an sich bekannten Doppelkegelbrenners, wie er zur Verwirklichung der Erfindung besonders geeignet ist;

Fig. 2

im Längsschnitt entlang der Ebene II-II aus Fig. 1 den Doppelkegelbrenner aus Fig. 1 in der herkömmlichen Ausgestaltung;

Fig. 3

in einer zu Fig. 2 analogen Darstellung einen Doppelkegelbrenner gemäss einem bevorzugten Ausführungsbeispiel der Erfindung mit einem Scherschichtzaun an der Austrittskante des Brenneraustritts; und

Fig. 4

ein Diagramm von gemessenen Druckamplituden in Abhängigkeit von der thermischen Leistung eines beispielhaften Brenners mit und ohne Scherschichtzaun.

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it

Fig. 1

in the plan view from the front (opposite to the flow direction), the structure of a conventional double-cone burner, as it is particularly suitable for implementing the invention;

Fig. 2

in a longitudinal section along the plane II-II of Figure 1 the double-cone burner of Figure 1 in the conventional embodiment.

Fig. 3

in a representation analogous to Fig. 2 a double-cone burner according to a preferred embodiment of the invention with a shear layer fence at the exit edge of the burner outlet; and

Fig. 4

a diagram of measured pressure amplitudes as a function of the thermal performance of an exemplary burner with and without shear layer fence.

WAYS FOR CARRYING OUT THE INVENTION

In Fig. 1, the structure of a double-cone burner is shown in the plan view from the front (contrary to the flow direction), as known for example from EP-A1-1 048 898 and is particularly suitable for the realization of the invention. The burner 10 comprises two conical partial bodies 11 and 12, which are offset from one another in a central plane, such that adjacent walls of the partial bodies 11, 12 form tangential air inlet ducts for the inflow of combustion air into the interior 25 delimited by the partial bodies 11, 12. Of the Interior 25 opens with a burner outlet 22 to a subsequent combustion chamber 23 (Fig. 2). The combustion chamber side edges of the body parts 11, 12 form the outlet edges 16, 17 of the burner outlet 22. Around the burner outlet 22 around a transverse to the flow direction extending front plate 14 is attached, which is provided with a plurality of distributed holes 15 is provided.

In the interior 25 of the burner 10 fuel is injected through a central fuel nozzle 13 and swirled with the tangential incoming air to a fuel-air mixture. Parallel to the emerging from the burner outlet 22 fuel-air mixture flows through the holes 15 air. The fuel-air mixture burns in the combustion chamber 23 with a flame 20. At the outlet edges 16, 17 of the burner outlet 22 form between the outflowing fuel-air mixture and the surrounding air, a Abströmgrenzschicht 18. In the Abströmgrenzschicht 18 shear layers are formed Flow instabilities that lead to the formation of coherent structures in the form of flow vortices. The influence of these coherent structures on the combustion instabilities in the combustion chamber 23 is most pronounced when the flow instability has overlapped its highest growth rate and the vortices 19 have reached their maximum size (FIG. 2).

If the position of the maximum size swirls 19 in the region of the flame 20, as shown in Fig. 2, comes to periodic heat releases that lead to the unwanted thermoacoustic oscillations. However, the axial position of the highest growth rate of the coherent structures can be influenced inter alia by changing the thickness of the outflow boundary layer 18. According to a preferred embodiment of the invention, this is achieved in that, according to FIG. 3, a shear layer fence 21, for example in the form of a sheet metal strip, is provided, which extends along the exit edge 16, 17 of the burner outlet 22 and with its height substantially parallel to the flow direction in FIG the combustion chamber 23 protrudes. By preferably a few millimeters, for example 5 mm high shear layer fence 21, the formation of vortex structures in the area the flame 20 and thus prevent a periodic heat release (the vortex maximum size 19 move into an area outside the flame 20). However, a periodic heat release would be the basis for the occurrence of thermoacoustic vibrations, which is thus prevented.

FIG. 3 shows the effect of the invention on the suppression of a pressure oscillation in the 1000 Hz range. FIG. 3 shows the pressure amplitudes (Amp) measured with two transducers as a function of the thermal output (power) of a burner with shear layer fence 21 (solid circles and rectangles) and without shear layer fence (empty circles and rectangles). It is clearly evident from FIG. 3 that the occurrence of vibrations above a certain power point can be largely prevented with the aid of the shear layer fence.

LIST OF REFERENCE NUMBERS

10

Burner (double cone burner)

11.12

conical part body

13

fuel nozzle

14

front panel

15

Bore (front panel)

16.17

Exit edge (burner exit)

18.18 '

outflow boundary

19

Whirl of maximum size

20

flame

21

Shear layer fence

22

burner outlet

23

combustion chamber

24

midplane

25

inner space

Claims (4)

1. Burner (10) for generating a hot gas, which burner (10) opens out, by way of a burner outlet (22) delimited by an outlet edge (16, 17), into a combustion chamber (23), in which a fuel/air mixture which flows out of the burner outlet (22), forming an outflow boundary layer (18, 18'), after ignition of the burner (10), forms a flame (20), characterized in that to prevent the periodic release of heat and associated thermo-acoustic oscillations in the combustion chamber (23), means (21) for altering the thickness of the outflow boundary layer (18, 18') are arranged at the burner outlet (22).
2. Burner according to Claim 1, characterized in that the means for altering the thickness of the outflow boundary layer (18, 18') comprise a shearing layer fence (21) which runs along the outlet edge (16, 17) of the burner outlet (22) and the height of which projects into the combustion chamber (23) substantially parallel to the direction of flow.
3. Burner according to Claim 2, characterized in that the height of the shearing layer fence (21) is a few millimetres, preferably about 5 mm.
4. Burner according to one of Claims 1 to 3, characterized in that the burner (10) is designed as a double-cone burner and comprises at least two hollow, conical part-bodies (11, 12) which are offset with respect to one another in a centre plane (24) in such a manner that adjacent walls of the part-bodies (11, 12) form tangential air inlet passages for combustion air to flow into the interior (25) delimited by the part-bodies (11, 12), the combustion chamber edges of the part-bodies (11, 12) forming the outlet edges (16, 17) of the burner outlet (22).

Images