COMBUSTION CHAMBER FOR A GAS TURBINE AND BURNER ARRANGEMENT

Abstract

A combustion chamber (10, 20) for a gas turbine (1) with at least two combustion zones (23, 24) and at least one burner arrangement (11, 28) for the combustion of a fuel/air mixture in the combustion zones (23, 24). The burner arrangement (11, 28) has at least one premixing passage (29) that opens into the combustion zones (23, 24) to provide a fuel/air mixture, and an air supply (32) and at least one fuel supply (33) encompassed in the burner arrangement (11, 28) and open into the premixing passage (29). The combustion chamber permits a particularly effective damping of combustion chamber pressure fluctuations. To this end, the air supply (32) is designed in a stepped manner such that the outlet openings (34, 34a, 34b, 34c) of the stepped air supply that open into the premixing passage can be assigned different delay times (τ1, τ2, τ3), which damps the fluctuations.

Description

The invention relates to a combustion chamber for a gas turbine having at least one combustion zone and at least one burner arrangement for the combustion of a fuel/air mixture, wherein the burner arrangement comprises at least one premixing passage which opens into the combustion zone and which serves for the provision of a fuel/air mixture, and an air supply encompassed by the burner arrangement and at least one fuel supply open into the premixing passage.

The invention also relates to a gas turbine having a combustion chamber of said type and to a burner arrangement.

Known gas turbines comprise a compressor and a turbine in addition to a combustion chamber as mentioned in the introduction. The compressor compresses the air supplied to the gas turbine, wherein a part of said air serves for the combustion of fuel in the combustion chamber and a part is used for cooling the gas turbine and/or the combustion gases. The hot gases provided in the combustion chamber as a result of the combustion process are introduced from the combustion chamber into the turbine, wherein said gases expand and cool therein and, performing work, set turbine blades in rotation in the process. By means of said rotational energy, the gas turbine drives a work machine. The work machine may for example be a generator.

The fuel/air mixture provided by the at least one burner arrangement is premixed in the at least one premixing passage for then being ignited after flowing into the combustion zone. The premixing of the fuel with the air reduces the pollutant emissions generated during the combustion in relation to the hitherto conventional direct injection of the fuel into the combustion zone. A disadvantage of the premixing of the fuel is however that said arrangement is significantly more susceptible to the occurrence of combustion chamber pressure fluctuations. If pressure fluctuations occur in the combustion zone, concentration fluctuations in the fuel/air mixture in the premixing passage also arise, which lead to heat release fluctuations during the combustion. These thermoacoustic instabilities in turn intensify the combustion chamber pressure fluctuations, wherein, in the arrangement, there are predominant frequencies for these escalating combustion chamber pressure fluctuations. The concentration fluctuations in the fuel/air mixture, that is to say variations in the fuel/air mixture ratio over time, may also be referred to as air number fluctuations. The air number fluctuations result from varying acoustic resistances of the air supply and fuel supply. For damping the combustion chamber pressure fluctuations, known gas turbines have resonators arranged in the housing. Since the resonators directly adjoin the combustion zone and furthermore interrupt a heat shield arrangement in the housing and must therefore be cooled, such a design of the combustion chamber is cumbersome. An alternative design of a known combustion chamber provides, for the suppression of such combustion chamber pressure fluctuations, that the fuel nozzles that open into the premixing passage are arranged so as to be distributed in the axial direction along the premixing passage, such that mixing zones with different delay times are formed in the premixing passage. Said stepped design of the fuel supply makes it possible for the concentration fluctuations, caused by the combustion chamber pressure fluctuation, in the fuel injected through the fuel supply to be smoothed. The fuel nozzles may also be referred to as outlet openings of the fuel supply.

It is an object of the invention to specify a combustion chamber of the type mentioned in the introduction, a gas turbine having a combustion chamber of said type, and also a burner arrangement encompassed by a combustion chamber of said type, which permits particularly effective damping of combustion chamber pressure fluctuations.

The object is achieved according to the invention, in the case of a combustion chamber of the type mentioned in the introduction, in that the air supply is of stepped form such that outlet openings, which open into the premixing passage, of the stepped air supply can be assigned different delay times.

By means of the known fuel supply with fuel nozzles arranged so as to be distributed in the axial direction along the premixing passage, it is indeed possible to compensate for fluctuations, caused by combustion chamber pressure fluctuations, in the fuel flow rate admixed to the air stream along the premixing passage. However, owing to the different acoustic resistances of the air and of the fuel, said known stepped configuration is not suitable for injecting the fuel into the air stream in such a way that a constant ratio of fuel and air and a constant fuel flow rate per unit of time exits the premixing passage and enters the combustion zone. Therefore, according to the invention, for the suppression of combustion chamber pressure fluctuations and thus also of heat release fluctuations, it is proposed that the air supply that opens into the premixing passage be of stepped form, and thus the density fluctuations, caused by combustion chamber pressure fluctuations, in the air stream passing through the premixing passage be smoothed. Owing to the high compressibility of air in relation to, for example, a liquid fuel, and the relatively low pressure in the air supply line in relation to the pressure in the fuel supply line, this is particularly effective for the suppression of combustion chamber pressure fluctuations.

According to the invention, the stepped air supply comprises outlet openings that open into the premixing passage, which outlet openings can be assigned different delay times. The stepped air supply may furthermore comprise further outlet openings which may be assigned redundant delay times. The delay time may also be referred to as a convective time delay. Said time delay is defined as the time required for a fluid element entering the premixing passage to pass to the combustion zone. The outlet openings may also be referred to as exit openings.

The burner arrangement may for example comprise a pilot burner with a premixing passage with pilot burner lance arranged centrally therein, wherein the pilot burner lance is connected to a fuel supply and comprises fuel nozzles. An air supply opens into the premixing passage of the pilot burner. Around the pilot burner there may be arranged a multiplicity of main mixers encompassed by the burner arrangement. Each of the main mixers may have a premixing passage encompassed by a cylindrical housing, into which premixing passage an air supply opens, and axially in which premixing passage there is arranged a lance which is connected to a fuel supply and which has fuel nozzles. The lance may for example be supported on the housing via swirl vanes. According to the invention, in the case of the burner arrangement specified by way of example, at least one of the premixing passages comprises a stepped air supply. It is for example possible for the air supply of each of the main mixers to be of stepped form by virtue of the swirl vanes forming air outlet openings which open into the premixing passage and which can be assigned different delay times. Said delay times may preferably be selected such that, at least in the frequency range of a predominant combustion chamber pressure fluctuation, density fluctuations caused by the latter in the supplied air cancel one another out, or attenuate one another, owing to the different delay times of the air outlet openings.

One advantageous refinement of the invention may provide that, in addition to the air supply of stepped form, a fuel supply which opens into the premixing passage and which can be charged with gaseous fuel is likewise of stepped form.

Since the gaseous fuel likewise exhibits high compressibility in relation to air, the additional stepped configuration of the fuel supply that can be charged with gaseous fuel makes it possible for fluctuations, caused by combustion chamber pressure fluctuations, in concentration and density of the fuel/air mixture flowing out of the premixing passage into the combustion zone to be dampened with even greater effectiveness. If the premixing passage comprises more than one fuel supply that can be charged with gaseous fuel, it is possible for one or more of said fuel supplies that can be charged with gaseous fuel to be of stepped form.

It may advantageously also be provided that the outlet openings of the stepped supply can be assigned delay times, wherein, for a minimum delay time τ_min and a maximum delay time τ_max with regard to a combustion chamber pressure fluctuation, of frequency f, which is to be suppressed, the following applies: τ_max−τ_min>1/f.

By means of said condition, it is ensured that, at least in the frequency range of the combustion chamber pressure fluctuation to be suppressed, density fluctuations, caused by the latter, in the fluid supplied through the stepped supply are attenuated in an effective manner. The stepped supply is the stepped air supply. If yet further supplies that open into the premixing passage are of stepped form, the condition may also apply to said supplies. The minimum and maximum delay times specified in the condition relate respectively to the shortest and the longest of the delay times assigned to the outlet openings of a supply.

It may also be considered advantageous for the outlet openings, which open into the premixing passage, of the stepped supply to be arranged such that density fluctuations, caused by at least one predominant combustion chamber pressure fluctuation of frequency f′, in the fluid supplied through the outlet openings are superposed on one another in the premixing passage owing to the different delay times assigned to the outlet openings, in such a way that said density fluctuations substantially cancel one another out.

In one advantageous refinement of the invention, it may be provided that the burner arrangement is arranged in the region of a second axial stage, with at least one premixing passage that opens into the combustion zone, wherein the combustion zone follows downstream of a first combustion zone with a first burner arrangement.

By means of a second axial stage, the heat release can be distributed further over the entire available combustion chamber, such that the susceptibility of the combustion system to thermoacoustic instabilities is further reduced. Furthermore, a stepped air supply to at least one premixing passage of the burner arrangement of the second axial stage can be realized particularly easily in terms of apparatus.

A preferred refinement of the invention may provide that the burner arrangement comprises a fuel distributor ring arranged around the outside of a combustion chamber housing and comprises multiple premixing passages, wherein the premixing passages open at one end thereof into the combustion zone in the combustion chamber housing and correspond to at least one fuel supply that branches off from the fuel distributor ring, wherein outlet openings of a stepped air supply are arranged so as to be distributed at least along one of the premixing passages.

Said stepped air supply to at least one premixing passage of the burner arrangement of the second axial stage can be realized particularly easily in terms of apparatus. The premixing passages may for example be of hose-like form, wherein, for the present invention, it is very generally the case that the position of the air outlet openings along the premixing passages, or the delay times corresponding thereto, may be adaptable to the frequency of the combustion chamber pressure fluctuations to be suppressed. For example, the hose-like premixing passage may be composed of elastic material, wherein the length of said premixing passage—and thus also the delay times corresponding to the outlet openings—can be adapted to a frequency to be suppressed.

It is a further object of the invention to specify a gas turbine having at least one combustion chamber as mentioned in the introduction, which permits particularly effective damping of combustion chamber pressure fluctuations.

For this purpose, the gas turbine has at least one combustion chamber which is designed as claimed in one of claims 1 to 4.

It is a further object of the invention to specify a burner arrangement which is encompassed by the combustion chamber mentioned in the introduction and which permits particularly effective damping of combustion chamber pressure fluctuations.

For this purpose, the burner arrangement is a constituent part of the combustion chamber as claimed in one of claims 1 to 4.

Further expedient refinements and advantages of the invention are described in the description of exemplary embodiments of the invention with reference to the figure of the drawing, wherein the same reference signs are used for equivalent components.

In the drawing:

FIG. 1 shows a schematic sectional view of a gas turbine according to the prior art,

FIG. 2 shows, in a schematic sectional view, a detail of a combustion chamber with a second axial stage according to an exemplary embodiment of the invention, and

FIG. 3 shows, in a schematic sectional view, a detail view of the exemplary embodiment illustrated in FIG. 2 in the region of the stepped air supply.

FIG. 1 shows a schematic sectional view of a gas turbine 1 according to the prior art. The gas turbine 1 has, in the interior, a rotor 3 which is mounted so as to be rotatable about an axis of rotation 2 and which has a shaft 4 also referred to as turbine rotor. Arranged in succession along the rotor 3 are an intake housing 6, a compressor 8, a combustion system 9, a turbine 14 and an exhaust-gas housing 15, the combustion system having a number of combustion chambers 10 which each comprise a burner arrangement 11 and a combustion chamber housing 12.

The combustion system 9 communicates with a hot-gas duct, which is for example of annular form. There, multiple turbine stages positioned in series form the turbine 14. Each turbine stage is formed from vane rings. In the hot duct, as viewed in the flow direction of a working medium, a row formed from guide vanes 17 is followed by a row formed from rotor vanes 18. The guide vanes 17 are in this case fastened to an inner housing of a stator 19, whereas the rotor vanes 18 of a row are for example attached by means of a turbine disk to the rotor 3. A generator (not illustrated), for example, is coupled to the rotor 3.

During the operation of the gas turbine, air is drawn in through the intake housing 6, and compressed, by the compressor 8. The compressed air provided at the turbine-side end of the compressor 8 is conducted to the combustion system 9 and mixed there with a fuel in the region of the burner arrangement 11.

The mixture is then burned with the aid of the burner arrangement 11, such that a working gas stream is formed in the combustion system 9. From there, the working gas stream flows along the hot-gas duct past the guide vanes 17 and the rotor vanes 18. At the rotor vanes 18, the working gas stream expands with a transmission of impetus, such that the rotor vanes 18 drive the rotor 3, and the latter drives the generator (not illustrated) coupled thereto.

FIG. 2 shows a detail of a combustion chamber 20 of a gas turbine according to an exemplary embodiment of the invention. The combustion chamber 20 has a combustion chamber housing 21 which is formed rotationally symmetrically about an axis 22. In the combustion chamber housing 21 there is situated a first combustion zone 23 and a second combustion zone 24, wherein the second combustion zone 24 follows downstream of the first combustion zone 23 in relation to a main flow direction 26. The combustion chamber 20 comprises a first burner arrangement (not illustrated) and a second burner arrangement 28 for the combustion of a fuel/air mixture in the second combustion zone 24. The second burner arrangement 28 comprises a premixing passage 29 which opens into the second combustion zone 24 and which serves for the provision of a fuel/air mixture, wherein an air supply 32, which is encompassed by the second burner arrangement 28, and a fuel supply 33 open into the premixing passage 29, wherein the air supply 32 is of stepped form such that the outlet openings 34, which open into the premixing passage 29, of the stepped air supply 32 can be assigned different delay times.

The second burner arrangement 28 is thus arranged in the region of a second axial stage. The second burner arrangement 28 comprises a fuel distributor ring 36 arranged around the outside of the combustion chamber housing 21 and comprises multiple premixing passages 29, wherein the premixing passages 29 open at one end 37 thereof into the second combustion zone 24 in the combustion chamber housing 21 and correspond in each case to a fuel supply 33 that branches off from the fuel distributor ring 36, wherein outlet openings 34 of a stepped air supply 32 are arranged so as to be distributed along at least one of the premixing passages 29.

In one advantageous refinement of the illustrated exemplary embodiment of the invention, each of the premixing passages 29 of the second burner arrangement 28 may have a stepped air supply 32.

The fuel injected through the fuel supply 33 into the premixing passage 29 mixes with the air entering the premixing passage 29 through the outlet openings 34, such that a fuel/air mixture flows along the premixing passage in the flow direction 39. An air volume exiting an outlet opening 34 will mix with the fuel and, here, proceeding from the position of the outlet opening 34, will require a time period in order to pass into the combustion zone 24. Said time period is referred to as delay time and is defined as the time required for a fluid element entering the premixing passage to pass to the combustion zone. The outlet openings 34 arranged along the premixing passage 29 correspond, owing to their differing arrangement in the premixing passage 29, to different delay times. Each of the outlet openings 34 in the premixing passage 29 can thus be assigned different delay times.

FIG. 3 shows a detail view of the combustion chamber according to the invention illustrated in FIG. 2, according to an exemplary embodiment, in the region of the second burner arrangement of a second axial stage. The illustration shows a section of the combustion chamber housing 21 which surrounds a first combustion zone 23 (partially illustrated) and a second combustion zone 24 (partially illustrated) that adjoins said first combustion zone downstream, wherein a premixing passage 29 which is encompassed by the second burner arrangement and which serves for the provision of a fuel/air mixture opens into the second combustion zone 24. Into the premixing passage 29 which is of hose-like form there opens a fuel supply 33, which serves for the injection of fuel 35 into the premixing passage 29, and an air supply 32 which is of stepped form. The air supply 32 which is of stepped form comprises outlet openings 34a, 34b, 34c which open into the premixing passage 29 and which serve for the supply of air 40, wherein the outlet openings 34a, 34b, 34c can be assigned different delay times τ₁, τ₂, τ₃. For example, an air volume exiting the outlet opening 34a will mix with the fuel 35 which has been injected through the fuel supply 33 and which is flowing past, and here, proceeding from the position of the outlet opening 34a, will require a time period τ₁ to pass into the second combustion zone 24. For the damping or suppression of a combustion chamber pressure fluctuation of frequency f, the position of the outlet openings 34a, 34b and 34c may advantageously be selected such that τ₁−τ₃>1/f. The density fluctuations of the air caused by the combustion chamber pressure fluctuation of frequency f in the outlet openings can, owing to the different delay times τ₁, τ₂, τ₃, be superposed during the ignition of the fuel/air mixture in the second combustion zone 24 such that said density fluctuations substantially cancel one another out. The arrangement of the outlet openings 34a, 34b, 34c along the premixing passage 29 may be selected correspondingly for this purpose. The combustion chamber pressure fluctuation of frequency f may be a combustion chamber pressure fluctuation that can be predominantly excited owing to the configuration of the combustion chamber. This may also be referred to as predominant combustion chamber pressure fluctuation. One refinement of the illustrated exemplary embodiment may also provide that the fuel supply 33 is likewise of stepped form (not illustrated here).

Claims

1. A combustion chamber for a gas turbine comprising:

at least one combustion zone and

at least one burner arrangement configured for combustion of a fuel/air mixture in the combustion zone,

the burner arrangement comprising at least one premixing passage which opens into the combustion zone and which provides a fuel/air mixture, at least one fuel supply which opens into the premixing passage, and

an air supply which is of stepped form such that it comprises a plurality of outlet openings, each outlet opening opens into the premixing passage and is configured to provide air flowing through the premixing passage to the combustion zone with a respective different delay time than air provided by the other outlet openings of the stepped air supply, wherein the delay time is defined as the time required for a fluid element entering the premixing passage to pass to the combustion zone, wherein, for a minimum delay time τmin and a maximum delay time τmax of the stepped air supply with regard to a combustion chamber pressure fluctuation having a frequency f, which fluctuation is to be suppressed, the following applies: τmax−τmin>1/f, and the outlet openings of the stepped air supply, which open into the premixing passage are arranged such that the density fluctuations, caused by at least one predominant combustion chamber pressure fluctuation of frequency f′, in the fluid supplied through the outlet openings are superposed on one another in the premixing passage owing to the different delay times assigned to the outlet openings, in such a way that the density fluctuations substantially cancel one another out.

2. The combustion chamber as claimed in claim 1, further comprising, the fuel supply which opens into the premixing passage which is configured to be charged with gaseous fuel also is of stepped form.

3. The combustion chamber as claimed in claim 1, further comprising:

the at least one combustion zone comprises a first combustion zone followed downstream by a second combustion zone;

the burner arrangement is arranged in the region of a second axial stage of the combustion zone and includes at least one premixing passage that opens into the second combustion zone (24), and a second burner arrangement in the first combustion zone.

4. The combustion chamber as claimed in claim 3, further comprising:

the burner arrangement comprises a fuel distributor ring arranged around an outside of a combustion chamber housing around the combustion zone and the burner arrangement comprises multiple premixing passages, each being open at one end thereof into the second combustion zone in the combustion chamber housing and each corresponding to at least one fuel supply that branches off from the fuel distributor ring into the premixing passage, wherein a plurality of the outlet openings of a stepped air supply are distributed along at least one of the premixing passages.

5. A gas turbine comprising at least one of the combustion chambers, as claimed in claim 1.

6. (canceled)

7. The combustion chamber as claimed in claim 1, further comprising the outlet openings being located distributed along the premixing passage, thereby to cause the minimum and maximum delay times by the location of the openings.