Combustion chamber, in particular for a gas turbine, with at least two resonator devices

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

The present invention concerns a gas turbine with at least a combustion chamber and at least two resonator devices for damping acoustic oscillations in the combustion chamber.

DESCRIPTION OF THE RELATED ART

A gas turbine plant includes for example a compressor and a combustion chamber, as well as a turbine. The compressor pro- vides for compressing intake air with which a fuel is then mixed. Combustion of the mixture takes place in the combus¬ tion chamber, with the combustion exhaust gases being passed to the turbine. There, heat energy is taken from the combus¬ tion exhaust gases and converted into mechanical energy.

Fluctuations in the quality of the fuel and other thermal or acoustic disturbances however result in fluctuations in the amount of heat liberated and thus the thermodynamic effi¬ ciency of the plant. In that situation, there is an interac- tion of acoustic and thermal disturbances which can push themselves up. Thermoacoustic oscillations of that nature in the combustion chambers of gas turbines - or also combustion machines in general - represent a problem in terms of design¬ ing and operating new combustion chambers, combustion chamber parts and burners for gas turbines or combustion machines .

The exhaust gases produced in the combustion process are at a high temperature. They are therefore diluted with cooling air in order to reduce the temperature to a level which is ten¬ able for the combustion chamber wall and the turbine compo- nents . The cooling air passes into the combustion chamber through cooling air openings in the combustion chamber wall. In addition so-called seal air passes into the combustion chamber, that is to say, air which serves to prevent the en¬ try of hot gas from the combustion chamber into gaps between adjacent elements of a heat-protective lining of the combus¬ tion chamber. In that case the seal air is blown through the gaps between adjacent elements of the heat-protective lining into the combustion chamber.

Diluting the combustion gases with cooling and seal air how¬ ever results in a higher level of pollutant emissions. In or¬ der to reduce the pollutant emissions of gas turbines, the cooling and seal air flows are therefore kept low in modern plants. As a result however that also reduces the acoustic damping effect so that thermoacoustic oscillations can in¬ crease. That can involve a mutually increasing interaction between thermal and acoustic disturbances which can cause high levels of stress and loading for the combustion chamber and increasing emissions.

Therefore, in the state of the art, for the purposes of re¬ ducing thermoacoustic oscillations, for example Helmholtz resonators are used for damping thermoacoustic oscillations in combustion chambers of gas turbines, which damp the ampli- tude of the oscillations.

In order to be able to damp the thermoacoustic oscillations in a greater frequency range, DE 33 24 805 Al proposed using a plurality of Helmholtz resonators involving different reso- nance frequencies, which are arranged laterally at the air passage to the combustion chamber. In that case each Helm¬ holtz resonator damps different frequencies of the acoustic

oscillations. It will be noted that cooling air has to be ad¬ ditionally used. That either increases the cooling air con¬ sumption, or it means that less cooling air is available for cooling the combustion exhaust gases, whereby there is an in- crease in the proportion of pollutants in the combustion ex¬ haust gases .

Therefore there is a need for a combustion chamber and a gas turbine in which the arrangement of different damping devices is such that the additional cooling air requirement can re¬ main relatively low.

SUMMARY OF THE INVENTION

A combustion chamber according to the invention, in particu¬ lar for a gas turbine, includes at least one combustion cham¬ ber wall through which flows cooling fluid, in particular cooling air, and at least one resonator device. In this re¬ spect the term resonator device is used to denote a damping device for damping acoustic oscillations which includes at least one Helmholtz resonator. The combustion chamber accord¬ ing to the invention is distinguished in that the resonator device is integrated into the combustion chamber wall in such a way that it has the cooling fluid flow flowing there- through.

In the combustion chamber according to the invention, the fact that the resonator device is integrated into the chamber wall of the combustion chamber and has the flow of cooling fluid flowing therethrough provides that the cooling fluid flow which is used for cooling the resonator device is also still available for cooling the chamber wall and/or for seal¬ ing gaps and/or for diluting the combustion exhaust gases . In that way the pollutant content in the combustion exhaust gases can be kept at a low level and at the same time the ef¬ fects of thermoacoustic oscillations can be effectively re¬ duced by means of the resonator device.

Preferably the combustion chamber has at least two resonator devices with different resonance frequencies. At least one resonator device can be in the form of a high frequency damp- ing device and at least one resonator device can be in the form of a medium frequency damping device.

In that case, in accordance with this application, the term high frequency is preferably used to denote the range from about 250 Hertz, in particular from about 500 Hertz. The term medium frequency or medium frequency range is preferably used to denote the range between about 30 and 750 Hertz, in par¬ ticular between 50 and 500 Hertz. However, deviations by up to 50% of the specified values and ranges are also possible.

Division into two frequency bands, wherein oscillations in the various frequency bands are damped by the different reso¬ nator devices, permits an effective reduction in the oscilla¬ tions which occur. The frequency bands can overlap, in par- ticular at the edges, but do not have to do so. In addition it is also possible to use three or more different frequency bands, that is to say three or more resonator devices, which respectively differ from each other in respect of their reso¬ nance frequencies .

The resonator devices are preferably integrated into the com¬ bustion chamber wall in such a way that they each have par¬ tial flows of the cooling fluid flow passing therethrough. In that case, the resonator devices can be integrated into the combustion chamber wall in such a way that either they form parallel flow paths for the partial flows of the cooling fluid flow, they form flow paths which are connected in suc¬ cession for the partial flows of the cooling fluid flow, or they form both parallel flow paths and also flow paths which are connected in succession, for the partial flows of the cooling fluid flow. It is in that way that the flow condi¬ tions in the individual resonator devices - and thus the con-

ditions prevailing in the resonator devices - can be specifi¬ cally and targetedly adjusted.

The cooling fluid flow can have in particular regions involv- ing different pressures. In the resonator devices which each have at least one entry as a flow inlet and at least one exit as a flow outlet, the entries and/or the exits of resonator devices with a first resonance frequency can then be con¬ nected to a different pressure level than the entries or ex- its of resonator devices with a second resonance frequency which is different from the first one. By selecting suitable pressures for the respective entries and exits of the resona¬ tor devices, it is possible to specifically and targetedly adjust the flow conditions in the individual resonator de- vices - and thus the general conditions prevailing in the resonator devices .

Preferably the flow through the resonator devices is con¬ nected in parallel relationship with the flow through an inlet valve for inlet of the fluid into the combustion cham¬ ber.

A gas turbine according to the invention includes at least one combustion chamber according to the invention.

Although the invention is described herein generally in rela¬ tion to gas turbines, the use thereof is not limited to gas turbines. It is also possible for the invention to be used in relation to other turbines and combustion machines .

Further features, properties and advantages of the present invention will become apparent from the description hereinaf¬ ter of the embodiment by way of example with reference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a diagrammatic view of an embodiment of a combus¬ tion chamber according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 diagrammatically shows a portion from the head plate 24 of a combustion chamber 1 of a gas turbine 2, as an em- bodiment by way of example of a combustion chamber according to the invention. The gas turbine 2 includes an outer casing 18 which surrounds the combustion chamber 1. Provided at the combustion chamber 1 is a burner 20 of which only a portion is illustrated in the Figure and at the sides of which are arranged air inlet valves 25 for the feed of air for the com¬ bustion process (only one of the air inlet valves 25 can be seen in Figure 1) . The air is passed through the chamber wall 3 to the air inlet valves 25. The chamber wall 3 includes a rear chamber wall 26 and a lining 4 which forms a front cham- ber wall. The intermediate space 23 between the rear chamber wall 26 and the lining 4 in that arrangement forms at least one flow passage for the feed of air to the air inlet valves 25. The air flowing through the flow passage is not intended exclusively for the combustion process but also serves as cooling air for cooling the lining 4 and/or optionally as seal air for blocking gaps between adjacent elements of the lining 4.

Associated with the combustion chamber 1 are resonator de- vices 5, 6 for damping thermoacoustic oscillations, which are integrated in the region of the head plate 24 into the cham¬ ber wall 3 of the combustion chamber 1, in particular into the lining 4. In that respect a resonator device 5 serves for damping thermoacoustic oscillations in the medium frequency range and includes a Helmholtz resonator 9, referred to here¬ inafter as the IF-resonator. The other resonator device 6 serves for damping thermoacoustic oscillations in the high

frequency range and includes two Helmholtz resonators 7, 8, referred to hereinafter as the HF-resonator. Although only- two resonator devices 5, 6 are illustrated in Figure 1, the combustion chamber 1 may also include further resonator de- vices. In addition the Helmholtz resonators do not necessar¬ ily need to be arranged in the head plate of a combustion chamber. For example, in an annular combustion chamber, a plurality of resonator devices 5, 6 can be distributed over the periphery of the chamber wall 3. They can also differ in respect of their resonance frequencies from the resonator de¬ vices 5, 6 shown in Figure 1.

The resonators 7, 8, 9 are arranged in the cooling air flow and/or in the seal air flow. The Helmholtz resonators 7, 8, 9 each have a respective resonator volume as well as at least one entry 12, 21, 22 as a flow inlet and at least one exit 15, 16, 17, 21, 22 as a flow outlet, the flow diameters of the inlet and the outlet being smaller than the flow diameter of the resonator volume. Due to the portions, through which the air flow passes, of differing flow cross-section, imposed on the flow is a resonance oscillation which provides for damping of the thermoacoustic oscillations. The resonance frequency and therewith the frequency in respect of which damping of the thermoacoustic oscillations is at the most ef- fective depends on the magnitude of the resonator volume.

The entries 21, 22 of the HF-resonators 7, 8 are at the same time exits of the IF-resonator 9. A further exit 15 of the IF-resonator 9 and the exits 16, 17 of the HF-resonators 7, 8 lead to the combustion chamber 1 of the gas turbine 2 where they serve as cooling and/or seal air outlets .

The air flow occurs from the compressor plenum 13 in which a pressure P3 is present into the intermediate space 23 between the lining 4 and the rear wall 26 and there along the flow path 19. On that occasion the lining 4 of the combustion chamber wall 3 is cooled by the flowing air. The air which is

passed on then enters the burner plenum 14, the pressure be¬ ing reduced to the pressure P2.

From the burner plenum 14 the main part of the air flow goes along the flow path 11 through the air inlet valve 25 into the combustion chamber 1. In parallel therewith a part of the air flow goes along the flow path 10 through the entries 12 into the IF-resonator 9 where there is a pressure PIF which is lower than the pressure P2 in the burner plenum 14. A part of that air flow then flows out of the IF-resonator 9 through the exit 15 directly into the combustion chamber 1 in which a pressure PCC obtains, while another part flows through the exits 21, 22 into the HF-resonators 7, 8 in which there ob¬ tains a pressure PHF which is lower than the pressure PIF in the IF-resonator 9 and higher than the pressure PCC in the combustion chamber 1. The exits 21, 22 of the IF-resonator serve at the same time as entries of the HF-resonators . The partial air flow which is introduced into the HF-resonators 7, 8 through the exits and entries 21, 22 finally also flows through the exits 16, 17 into the combustion chamber 1 where a lower pressure PCC than in the burner plenum 14 obtains. An air flow which passes into the resonator 9 is therefore di¬ vided into three different partial air flows. Two partial air flows are passed to the HF-resonators 7, 8 whereas the third partial air flow is passed from the IF-resonator directly into the combustion chamber 1.

That manner of linking the resonators affords considerable advantages . The IF-resonators 9 for the medium frequency range require a considerably larger volume than the HF- resonators 7, 8 for the high frequency range. Overall the re¬ quired structural volume can be optimised by suitable paral¬ lel and series connection of IF- and HF-resonators . In that respect preferably at least one resonator of the high fre- quency range and at least one resonator of the medium fre¬ quency range are integrated into the combustion chamber wall 3.

The pressure PCC prevailing in the combustion chamber 1 is about 3-6% lower than the pressure P3, that is to say the pressure reduction ΔP/P3 related to P3 is about 3-6%. That pressure reduction is divided into a pressure reduction of about 1-2,5% in the wall cooling passages (from P3 to P2) and a pressure reduction of about 2-3,5% in the air passages through the resonators (from P2 to PCC) .

In an alternative configuration of the combustion chamber ac¬ cording to the invention the linking of the resonators for the high frequency range (HF-range) and the resonators for the medium frequency range (intermediate frequency) (IF- range) is such that it involves connection of the HF- resonator to the compressor plenum 13 at the pressure P3 and connection of the IF-resonator to the burner plenum 14 at the pressure P2. The ratio in respect of area and also volume be¬ tween the HF-range and the IF-range can be freely selected in that case.