EP1158247B1 - Apparatus to reduce acoustic vibrations in a combustion chamber - Google Patents

Description

Technical application

The present invention relates to a device for damping acoustic vibrations in a combustion chamber and a combustion chamber arrangement, in particular a gas or steam turbine, which includes the device.

The main field of application of the present invention is in the field of industrial gas turbines. On industrial gas turbines all over the world, especially in power plant applications, ever higher demands are placed on operational readiness, service life and exhaust gas quality. The increasing awareness of environmental protection and environmental compatibility requires compliance with the lowest possible pollutant emissions.

Low emissions can be achieved economically in industrial gas turbines only by the use of premix burners. However, this type of combustion tends in closed combustion chambers by the formation of coherent structures and resulting fluctuating heat release for generating thermoacoustic oscillations in the combustion chamber. These thermoacoustic vibrations not only negatively affect the quality of the combustion, but can also drastically reduce the life of the highly loaded components.

State of the art

mit:

V =

Volumen des Helmholtz-Resonators 4

R =

Radius des Verbindungskanals 2

l =

Länge des Verbindungskanals 2

S =

Fläche der Öffnung, durch die die Anregung erfolgt

For damping such thermoacoustic oscillations, the use of the principle of the so-called Helmholtz resonator has long been known. This principle will be explained in more detail below with reference to FIG. The figure shows the basic structure of a Helmholtz resonator 4, which consists of a resonant volume 3 and a connecting channel 2 to the chamber 1, in which the thermoacoustic oscillations occur. Such a device can be considered analogous to a mechanical spring-mass system. The volume V of the Helmholtz resonator 4 acts as a spring and the gas in the connecting channel 2 acts as a mass. With the help of the cavity dimensions, the resonance frequency f _{0 of} the system can be calculated. $$f_0=\frac{\mathrm{<figure-callout\; id="2"\; label="c"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c</figure-callout>}}{2\pi }*\sqrt{\frac{S}{V\left[I+\frac{\mathrm{<figure-callout\; id="2R"\; label="\pi "\; filenames="imgf0001.png"\; state="\{\{state\}\}">\pi </figure-callout>}}{2}R\right]}}$$

With:

V =

Volume of the Helmholtz resonator 4

R =

Radius of the connection channel 2

l =

Length of the connection channel 2

S =

Area of the opening through which the excitation takes place

At this resonance frequency f ₀ , a Helmholtz resonator behaves acoustically like an infinitely large opening, ie it prevents the formation of a standing wave at this frequency.

This technique of damping thermoacoustic oscillations with the help of a Helmholtz resonator is also already used for damping the vibrations in combustion chambers of gas or steam turbines. When used in gas or steam turbines, however, the problem arises that the frequency to be damped is determined not by an intermittent combustion, but by the fulfillment of the Rayleigh criterion in the combustion chamber and the acoustic response of the surrounding system of inflow, burner, combustion chamber and acoustic termination condition.

The frequency to be damped can therefore not be determined with the required accuracy in advance in these systems with the currently available computational tools. However, this is the prerequisite in order to take into account the exact dimensioning of the resonance volume in the construction of the gas turbine. Furthermore, the acoustic behavior of the system and thus the frequencies of the vibrations to be damped in a change in the operating point can change significantly, so that under certain circumstances additional resonators that are tuned to other frequencies must be used.

Such an arrangement with several Helmholtz resonators is known for example from DE 33 24 805 A1. The document describes a device for preventing pressure oscillations in combustion chambers, in which a plurality of Helmholtz resonators with different resonance volumes along the gas line path to the burner are arranged. Due to the different resonance volumes, vibrations of different frequencies can be dampened with this system. The optimal However, dimensioning of the individual Helmholtz resonators here again requires knowledge of the frequencies occurring during operation of the system, which can not yet be specified exactly during the construction of the system. Furthermore, the arrangement of several Helmholtz resonators is unfavorable due to the required additional space.

DE 196 40 980 A1 describes another known device for damping thermoacoustic oscillations in a combustion chamber. In this device, the lateral wall of the resonance volume of the Helmholtz resonator is designed as a mechanical spring. An additional mechanical mass is attached to the wall of the end face of the resonance volume which oscillates due to the spring action. With this arrangement, the virtual volume of the Helmholtz resonator is influenced and a greater damping performance is achieved. By changing the mechanical mass on the resonator, a fine-tuning of the resonant frequency can be carried out subsequently. However, this also requires a subsequent intervention in the construction of the gas turbine plant.

In the past, Helmholtz resonators for vibration damping were also used in the field of exhaust systems of internal combustion engines. From this area, the use of adjustable resonators for changing the resonance frequency is known. For example, during the First World War, the two-stroke diesel engines for Zeppelin airships from Maybach were adapted to the respective operating point by means of adjustable resonators in the exhaust pipe. For this purpose, cylinders were shifted into one another by mechanical gears, thereby changing the resonance volume. This technique proves to be practicable in the aforementioned exhaust systems due to the good accessibility of these systems and the prevailing there relatively low pressure and temperature ratio. However, such a solution is completely eliminated for use in the printing sector of modern industrial gas turbines. The implementation of a mechanical transmission through the pressure housing of a gas turbine would cause unavoidable leaks and therefore lead to intolerable losses. In addition, the temperature effects prevailing in industrial gas turbines could only be compensated by a very complicated transmission.

US 5 103 931 A describes a device for soundproofing of internal combustion engines, in which in one embodiment, a Helmholtz resonator is also used. The Helmholtz resonator is bounded on one side by an expandable membrane with which the resonator volume can be adjusted and which separates the resonator volume from a fluid chamber.

The present invention has for its object to provide a device for damping thermoacoustic vibrations and a combustion chamber arrangement with this device, which allows continuous adaptation to the frequencies of the vibrations to be damped, even under high pressure conditions, such as those in gas turbines.

Presentation of the invention

The object is achieved with the device or the combustion chamber arrangement according to claims 1 and 7, respectively. Advantageous embodiments of the device and the combustion chamber arrangement are the subject of the dependent claims.

The device is composed of a Helmholtz resonator with a connecting channel which is connected to the combustion chamber, for example the combustion chamber of a gas turbine. In contrast to the known damping devices in the present device is provided by supplying or discharging a fluid via a supply line variable in volume hollow body which is either disposed within the Helmholtz resonator or adjacent to such that the resonant volume of the Helmholtz resonator changed with a change in the volume of the hollow body, wherein the fluid is a gas, the supply or discharge is controlled by a regulator.

With an arrangement of the volume-variable hollow body in the Helmholtz resonator thus reduces the resonant volume when the hollow body is inflated via the feed line with the gas. In the opposite case, the resonant volume of the Helmholtz resonator increases when a certain amount of the gas is discharged from the hollow body. The change in the resonance volume causes a change in the resonance frequency in a known manner.

In this way, the resonant frequency of the Helmholtz resonator can be adjusted at any time by simply inflating or deflating the hollow body to the occurring in the chamber volume thermo-acoustic vibration frequencies. An exact knowledge of the frequencies occurring during operation in the construction of the corresponding system is therefore no longer necessary. The vibrations can be customized over a wide range adjustable frequencies are attenuated. In practical use, by changing the resonance volume, which is possible at any time during the operation of the system, the resonance frequency of the built-in resonators can be adjusted to match the respective operating point.

A particular advantage results from the fact that the resonant volume of the Helmholtz resonator, which is usually arranged within the pressure housing of the gas turbine, can be changed without the need for moving parts have to be passed through the wall of the pressure vessel. The supply line to the hollow body can be designed as a rigid tube and therefore easily be performed with high density through the pressure housing through to the outside.

In a further embodiment of the present device, the Helmholtz resonator has a position-variable wall, to which the hollow body adjoins. The position variable wall is pressed by a spring mechanism against the hollow body. In this way, when the hollow body is inflated, the positionally variable wall is pressed inwards against the spring force and thus reduces the resonant volume of the Helmholtz resonator. In the reverse case of the discharge of gas from the hollow body, the resonance volume increases by displacement of the wall due to the force acting in the direction of the hollow body spring force. The Helmholtz resonator can in this case be designed in the form of a bellows, as is known from the initially mentioned DE 196 40 980 A1. It goes without saying, however, that other possibilities of a corresponding embodiment the Helmholtz resonator are possible, in which the above effect is achieved.

In this embodiment, the volume-changeable hollow body must be fixed at one point relative to the Helmholtz resonator within the pressure housing in order to be able to exert the corresponding counterforce on the position-variable wall of the Helmholtz resonator.

The volume-variable hollow body is preferably designed as an inflatable temperature-resistant balloon or as an inflatable metallic bellows. The supply line to the hollow body can be made flexible or rigid.

The gas supply to the hollow body or the gas discharge from the hollow body is automatically carried out by a controller which is provided outside the pressure housing on the supply line. This controller alters the resonance volume of the Helmholtz resonator as a function of the frequency of the highest-amplitude thermoacoustic oscillations occurring in the combustion chamber in which it blows or discharges the gas into the hollow body. The respective vibration amplitudes and vibration frequencies are in this case measured with a corresponding sensor, as is known to the person skilled in the art. Preferably, the controller controls the resonance volume or the volume of the hollow body by supplying or discharging compressor air, which he receives from the compressor outlet of the gas turbine. In this way, an optimal vibration damping can be achieved at any time during operation of the gas turbine, since the controller can adjust the resonance volume at any time exactly to the respective frequencies occurring.

Fig. 1

den prinzipiellen Aufbau eines Helmholtz-Resonators;

Fig. 2

ein erstes Ausführungsbeispiel für den Aufbau der vorliegenden Vorrichtung; und

Fig. 3

ein zweites Ausführungsbeispiel für den Aufbau der vorliegenden Vorrichtung.

The present device or combustion chamber arrangement will be briefly explained again by means of exemplary embodiments in conjunction with the figures. Hereby show:

Fig. 1

the basic structure of a Helmholtz resonator;

Fig. 2

a first embodiment of the structure of the present device; and

Fig. 3

A second embodiment of the structure of the present device.

Ways to carry out the invention

Figure 1 shows the basic structure of a Helmholtz resonator 4 with the resonance volume 3 and a connection channel 2, as it is known from the prior art. Details of this have already been set out in the introduction to the description.

A first exemplary embodiment of a device according to the invention on a combustion chamber 1 of a gas turbine is shown in FIG. In this figure, the tunable Helmholtz resonator 4 can be seen, which is connected via a connecting channel 2 with the combustion chamber 1. Within the Helmholtz resonator 4, a hollow body 6 is arranged, whose volume is variable by supplying or discharging gas via a supply line 5. The hollow body 6 consists in this example of a metallic bellows, which is inflated by air 10 from the compressor outlet of the gas turbine or by venting this air is relaxed. As a result, the interior of the Helmholtz resonator 4 filled with combustion gases, the so-called resonance volume 3, is enlarged or reduced starting from a central position, as indicated by the arrow in the figure. The control of the inflation or deflation of the bellows 6 via a corresponding controller 7, which adjusts the volume as a function of each to be damped thermoacoustic vibration frequencies. The design of the hollow body 6 as a metallic bellows is particularly suitable for use under high temperatures.

The supply line 5 to the bellows 6 takes place through the pressure housing 8 of the gas turbine. This passage through the pressure housing 8 can be sealed well, since it contains no moving components. With the present device, it is therefore possible to change the resonance volume 3 of the Helmholtz resonator 4, which is mounted within the pressure housing 8, from outside the pressure housing, without increasing the risk of leakage of the pressure housing 8.

Decisive influence on the resonant frequency of the tunable Helmholtz resonator 4 not only have the size of the resonant volume 3 and the length of the connecting channel 2 to the combustion chamber 1, but also the length of the supply line 5 to the controller 7 and the temperature of the control air, ie that for the inflation the hollow body 6 used gas. The connections are, however, relatively complex. As a guideline, it can be stated that the frequency range which can be controlled by the device increases with increasing temperature difference in the Helmholtz resonator 4 adjacent gases - combustion air in the resonance volume 3 and control air in the hollow body 6 - is increased. By suitable choice or adaptation of the temperature of the control air used to inflate the hollow body 6, this frequency range can thus be increased.

The tuning of the resonance volume 3 via the automatic controller 7, which, as already stated, depending on the frequency position of the highest vibration amplitude in the combustion chamber, the bellows 6 increases or decreases. Since the position of this amplitude changes on the frequency axis during operation of the burner only within a relatively narrow band, no particularly fast control is required in order to achieve optimum adaptation.

Finally, FIG. 3 shows a further example of a possible embodiment of the device according to the invention. In this example, the hollow body 6 is not arranged inside the Helmholtz resonator 4, but adjoins a position-variable wall 11 of this resonator 4. The operating principle is the same as already explained in connection with FIG. In this embodiment, the Helmholtz resonator 4 as well as the hollow body 6 - at least partially - designed as a bellows, wherein an end face of the Helmholtz resonator 4 adjacent to an end face of the hollow body 6. The opposite end face of the hollow body 6 is fixed to a corresponding anchoring 9 in the pressure housing 8.

If, in this embodiment, the hollow body 6 is inflated via the feed line 5 and the controller 7, the positionally variable wall 11 of the Helmholtz resonator 4 shifts to the left in the figure, so that the resonance volume 3 is reduced. In the opposite case, there is a shift to the right, wherein the resonance volume 3 is increased. For this displacement, however, it is necessary for a spring mechanism to press the position-variable wall 11 of the Helmholtz resonator 4 against the hollow body 6. This spring mechanism can be achieved for example by an elastic configuration of the wall material of the bellows. Alternatively, a spring may be provided within the Helmholtz resonator 4 for this purpose.

LIST OF REFERENCE NUMBERS

1

combustion chamber

2

connecting channel

3

resonance volume

4

Helmholtz resonator

5

supply

6

Hollow body; Bellows.

7

regulator

8th

pressure housing

9

anchoring

10

Air from the compressor outlet

11

position adjustable wall

Claims (8)

1. Apparatus for damping acoustic vibrations in a combustion chamber (1), comprising a Helmholtz resonator (4) having a variable resonant volume (3) and a connecting duct (2), by means of which the combustion chamber (1) can be connected to the resonant volume (3),
   characterized
   in that a hollow body (6) whose volume can be varied by supplying or discharging a fluid via a supply line (5) is contained within the Helmholtz resonator (4) or is adjoined by the latter in such a way that the resonant volume (3) of the Helmholtz resonator (4) varies with a change in volume of the hollow body (6), the fluid being a gas which is supplied or discharged in a manner controlled by a closed-loop controller.
2. Apparatus according to Claim 1,
   characterized
   in that the variable-volume hollow body (6) is an inflatable, heat-resistant balloon.
3. Apparatus according to Claim 1,
   characterized
   in that the variable-volume hollow body (6) is an inflatable metallic bellows.
4. Apparatus according to one of Claims 1 to 3,
   characterized
   in that, when the hollow body (6) is arranged in the Helmholtz resonator (4), the supply line (5) runs through an aperture in a wall of the Helmholtz resonator (4).
5. Apparatus according to one of Claims 1 to 3,
   characterized
   in that the Helmholtz resonator (4) has at least one moveable wall (11), which is adjoined by the hollow body (6), and also a spring mechanism which presses the wall (11) against the hollow body (6).
6. Apparatus according to one of Claims 1 to 5,
   characterized
   in that the closed-loop controller (7) controls the supply or discharge of the fluid via the supply line (5) as a function of the frequency of the highest instantaneous vibration amplitude in the combustion chamber (1).
7. Combustion chamber arrangement having an apparatus according to one of the preceding claims, in which the combustion chamber (1) and the Helmholtz resonator (4) are arranged within a pressure casing (8) of a gas or steam turbine,
   characterized
   in that the supply line (5) to the hollow body (6) is passed out through the pressure casing (8).
8. Combustion chamber arrangement according to Claim 7,
   characterized
   in that the supply line (5) is arranged in such a way that compressor air from the gas or steam turbine can be supplied to it.

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