EP2938927B1

EP2938927B1 - Gas turbine burner assembly equipped with a helmholtz resonator

Info

Publication number: EP2938927B1
Application number: EP13831874.6A
Authority: EP
Inventors: Giuseppe Canepa; Sergio Fasce; Sergio Rizzo; Domenico Zito
Original assignee: Ansaldo Energia SpA
Current assignee: Ansaldo Energia SpA
Priority date: 2012-12-28
Filing date: 2013-12-27
Publication date: 2019-02-06
Anticipated expiration: 2033-12-27
Also published as: WO2014102749A1; CN105121961A; KR20150103032A; ITMI20122265A1; CN105121961B; EP2938927A1

Description

TECHNICAL FIELD

The present invention relates to a turbine burner assembly equipped with a Helmholtz resonator.

BACKGROUND ART

As known, the problem of thermoacoustic oscillations, which may cause flame instability and a significant degradation in the quality of combustion, needs be solved in large-sized gas turbines, in particular those used in plants for the production of electricity. Therefore, machine performance in terms of power and efficiency, and plant flexibility are highly penalized. Emissions may degrade as well.
A solution which is becoming popular includes the use of Helmholtz resonators, which have the effect of damping acoustic oscillations in given frequency bands. A Helmholtz resonator comprises a resonant chamber placed in fluidic communication with the outside, in particular with the combustion chamber, through fluidic openings or channels. The volume of the resonant chamber and the features of the fluidic channels determine the frequency band in which the resonator is effective.
The known resonators are generally installed about the combustion chamber either on the burner inserts or directly on the burners.
In the first case, the resonators are fixed to the outer wall of the combustion chamber and communicate with the inside through the side wall itself. This solution allows to make high-volume resonators but on the other hand has many disadvantages. Firstly, the combustion chamber needs to be specifically modified for the purpose of accommodating the resonators. Furthermore, the presence of the resonators affects the step of cooling and results in a large weight bearing on the structure.
The resonators installed aboard the inserts are simple to be applied, but allow to obtain only modest volumes given the small available space.
The resonators installed aboard the burner are arranged so that the resonant chamber is directly in fluidic continuity with the inside of the burner, in particular with the air and fluid mixing channels. The connection is generally obtained by an opening downstream of the fluid injection nozzles. This solution is critical because it acts directly on the pressure oscillations which propagate from the combustion zone into the mixing channels. The pressure oscillations may not be adequately damped, or could even be amplified, if the resonator is not perfectly tuned to the frequency to be damped.
According to EP 1 342 953 A1 , a turbine burner assembly comprises a main burner and a Helmholtz resonator. The main burner extends about an axis and comprises an inner body and an outer body with a frustoconical wall and a diagonal swirler arranged therebetween. An inlet of the swirler being located at a larger base of the frustoconical wall of the outer body. The Helmholtz resonator has a resonant chamber and passages for fluidic connection of the resonant chamber to the outside.
Other examples of known burner assemblies are disclosed in EP 2 187 125 A1 and in US 5 644 918 A .

DISCLOSURE OF INVENTION

Therefore, it is the object of the present invention to provide a burner for a turbine which allows to overcome the described constraints.
According to the present invention, a turbine burner assembly is provided as defined in claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying drawings, which show some non-limitative embodiments thereof, in which:

figure 1 is a side view, taken along a longitudinal plane, of a portion of a gas turbine system;
figure 2 is a side view, taken along a longitudinal plane, of a burner assembly in accordance with an embodiment of the present invention incorporated in the system in figure 1;
figure 3 is a perspective view, taken along a different longitudinal plane and with parts removed for clarity, of an enlarged detail of the burner assembly in figure 2; and
figure 4 is a different perspective view of the detail in figure 3, with parts removed for clarity.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figure 1, a gas turbine system for the production of electricity is indicated as a whole by reference numeral 1 and comprises a compressor 2, a combustion chamber 3 and a turbine 5.
Compressor 2, combustion chamber 3 and turbine 5 form a turbine assembly which may be fed with fluid fuels of various type, in particular, but not only, natural gas, syngas, diesel.
Compressor 2 and turbine 5 are mounted to the same shaft in order to form a rotor 7, which is accommodated in a casing 8 and extends along an axis A.
More in detail, rotor 7 is provided with a plurality of compressor rotor blades 10 and turbine rotor blades 11, organized in annular arrays, which are arranged in sequence along axis A of the rotor 7 itself.
Arrays of compressor stator blades 12 and turbine stator blades 13 are fixed to casing 8 and spaced apart between the compressor rotor blade 10 and the turbine rotor blades 11, respectively.
In the embodiment described herein, the combustion chamber 3 is of the toroidal type and arranged about rotor 7 between compressor 2 and turbine 5. However, this must not be considered limitative, because the invention may be advantageously used also with combustion chambers of different type, in particular of the silo type.
The combustion chamber 3 comprises a plurality of burner assemblies 15, which are arranged on a circumference and are evenly angularly spaced apart. The burner assemblies 15 are mounted to respective burner seats 16 of the combustion chamber by respective burner inserts 17.
Figure 2 shows in detail one of the burner assemblies 15 used for feeding fuel, in particular a gas, to the combustion chamber 3. The burner assembly 15 extends along an axis B and comprises a main peripheral burner 20, a central pilot burner 21, coaxial to the main burner 20, and a Helmholtz resonator 22.
The main burner 20 is of the premixing type, arranged about the pilot burner 21 and fixed to the respective burner insert 17. More in detail, the main burner 20 extends through a central opening 17a of the burner insert 17, so that the outlet of the main burner 20 is within the combustion chamber 3.
The main burner 20 is provided with a vortex or turbulence- generating device, referred to as diagonal swirler, and indicated by reference numeral 23.
The diagonal swirler 23 extends about axis B and is radially defined between an inner body 25 and an outer body 26 of the main burner 20. The inner body 25 has a cylindrical axial cavity in which the pilot burner 21 is accommodated and is substantially frustoconical in shape towards the outside. The outer body 26 is axially hollow and comprises a frustoconical wall 26a and a cylindrical wall 26b, connected to each other by a joining portion 26c. The frustoconical wall 26a accommodates the inner body 25, so that a substantially annular space forming a passage for feeding the air-fuel mixture is defined between the frustoconical wall 26a of the outer body 26 and the inner body 25.
The diagonal swirler 23 further comprises an array of blades 28 which extend in the space between the inner body 25 and the outer body 26 and define respective mixing channels 30 to convey a mixture of combustion supporting air and fuel towards the combustion chamber 3 with a diagonal pattern with respect to axis B. The blades 28 are fixed to the outer body 16 by specific nuts 29a arranged through respective holes 29b made in the frustoconical wall 26a along a circumference. The seals 29c ensure the fluidic decoupling between the volume of resonator 22 and the premixing channel 30. The inlet 31 of the mixing channels 30 is defined at a larger base of the frustoconical wall 26a of the outer body 26 and allows the introduction of an air flow from compressor 2. Nozzles 32, arranged close to the inlet 31 of the mixing channels 30, are connected to a premix feeding line (not shown) and allow the injection of a controlled fuel flow rate inside the mixing channels 30 themselves. In an embodiment, the nozzles 32 are arranged on the blades 28. The air from compressor 2 and the injected fuel through nozzles 32 admix in the mixing channels 30. The air-fuel mixture flow thus produced develops towards the cylindrical wall 26b, which leads into the combustion chamber 3.
The Helmholtz resonator 22 comprises a resonant chamber 35 and necks 36 for fluidly connecting the resonant chamber 35 to the outside.
The resonant chamber 35 is substantially annular in shape and arranged about the frustoconical wall 26a of the-outer body 26, between the inlet 31 of the diagonal swirler 23 and the burner insert 17. According to the invention, the resonant chamber 35 is placed in one edge of the outer body 26 adjacent to the inlet 31 of the diagonal swirler 23. More in detail, the resonant chamber 35 is delimited internally by the frustoconical wall 26a of the outer body 26 and externally by, an annular closing wall 38. In axial direction, the annular closing wall 38 extends on the side of compressor 2 to one edge of the outer body 26 corresponding to the inlet 31 of the mixing channel 30. Towards the burner insert 17, instead, the annular closing wall 38 is delimited by a connection ring 39 of the outer body 26, by which the burner assembly 15 is coupled to the burner insert 17 itself. In one embodiment, the annular closing wall 38 is reversibly coupled to the frustoconical wall 26a of the outer body 26, e.g. by screw fastening means (not shown). Alternatively, the annular closing wall 38 may be welded to or made integrally in one piece with the frustoconical wall 26a. The annular closing wall 38 has a plurality of connection holes 37, which are arranged along a circumference and define passages to allow the introduction of an air flow from compressor 2 into the resonant chamber 35.
The connection ring 39 (figure 3) has a T-shaped crosswise section, and a first portion 39a and a second portion 39b. The first portion 39a, which is planar and defines a leg of the T-shaped section, substantially extends on a plane perpendicular to axis B of the burner assembly 15 and delimits the resonant chamber 35 in axial direction on the side towards the burner insert 17 and the combustion chamber 3. The second portion 39b of the connection ring 39 is substantially cylindrical and extends perpendicular to the first portion 39a on opposite sides thereof. On the compressor side, the second portion 39a of the connection ring 39 is in contact with the annular closing wall 38, while an outer side surface is coupled to the burner insert 17.
The second portion 39b has cooling passages 40, defined by grooves made on an outer face along a circumference and extending in axial direction. The cooling passages 40 put the delivery air of compressor 2 into communication with the combustion chamber 3, thus cooling the burner insert 17. In particular, the inlet of the cooling passages 40 is on the side towards compressor 2 with respect to the first portion 39a of the connection ring 39. The cooling passages 40 ensure a continuous cooling of the burner insert 17 independently of the assembly uncertainties and of the effects of thermal expansion.
The necks 36 of the Helmholtz resonator 22 run on the outer surface of the frustoconical wall 26 and extend through the connection ring 39 and the burner insert 17. The resonant chamber 35 and the openings of necks 36 are on opposite sides with respect to the burner insert 17. The necks 36 are thus arranged to put the resonant chamber 35 into fluidic communication with the outside through the connection ring 39 and the burner insert 17.
The resonant chamber 35 is free from direct fluidic connections with the mixing channels 30 of the diagonal swirler 23. The separation of the two environments is ensured by the frustoconical wall 26a and by the seals 29c between the frustoconical wall 26a and the nuts 29a, which prevent leakages through the holes 29b.
The resonant chamber 35 is fluidly coupled only to the combustion chamber 3 through the necks 36.
The connection holes 37 in the annular closing wall 38 have a three-fold effect: they allow to maintain an air flow from compressor 2 to combustion chamber 3 through the resonant chamber 35, thus avoiding backflows of hot fumes towards the resonant chamber 35 itself; they allow to maintain the thermodynamic properties inside the resonant chamber 35 approximately constant; and they expand the resonance band of the dynamic pressure fluctuations in combustion chamber 3.
In system 1, the Helmholtz resonators 22 may be fitted either on all the burner assemblies 15 or only on some, as needed. Furthermore, the Helmholtz resonators 22 may be mutually different. The band features of each Helmholtz resonator 22 are indeed determined by the geometry of resonant chamber 35, necks 36 and connection holes 37. In order to optimize the thermoacoustic oscillation damping effect on the most critical frequency bands, the Helmholtz resonators 22 may be tuned to respective frequencies by selecting, for each one, the volume and shape of the resonant chamber 35, the number, length and cross section (area and profile) of the necks 36 and the number, position and diameter of the connection holes 37. In one embodiment, for example, each Helmholtz resonator 22 has a respective damping band, and the damping bands of Helmholtz resonators of different burner assemblies do not coincide, although they may be partially overlapping.
The burner assemblies of the described type have various advantages. Firstly, large volume resonant chambers may be obtained without major modifications to the combustion chamber (also for retrofitting interventions) and without significantly bearing on the structure. Indeed, on one hand, the available space about the main burner up to the inlet of the swirler is wide, and thus Helmholtz resonators of relatively large, volume can be manufactured. On the other hand, the resonant chamber is partially delimited by structural elements which belong to the main burner. The addition of the annular closing wall only allows to complete the resonant chamber without noticeable changes to the burner assembly and without a significant increase of weight. Minor adaptations are thus sufficient to accommodate the necks of the Helmholtz resonator. Furthermore, the described solution allows to select the most appropriate geometries for the Helmholtz resonator, with a wide margin of flexibility.
A further advantage is that the burner assemblies, in particular the inlet region of the diagonal swirlers, are easily accessible. The maintenance or retrofitting interventions may thus be carried out easily.

Claims

A turbine burner assembly comprising:
a main burner (20) extending about an axis (B); and

a Helmholtz resonator (22) having a resonant chamber (35) and passages (36, 37) for fluidic connection of the resonant chamber (35) to the outside;

wherein the main burner (20) comprises:
an inner body (25) and an outer body (26), which extend about the axis (B), wherein the outer body (26) has a frustoconical wall (26a); and

a diagonal swirler (23) arranged between the inner body (25) and the outer body (26) and defining mixing channels (30), an inlet (31) of the swirler (23) being located at a larger base of the frustoconical wall (26a) of the outer body (26);

characterized in that the resonant chamber (35) extends about one edge of the outer body (26) adjacent to the inlet (31) of the swirler (23); and in that the outer body (26) delimits a portion of the resonant chamber (35) and is shaped so as to prevent direct fluidic connections between the Helmholtz resonator (22) and the mixing channels (30).
A burner assembly as claimed in Claim 1, wherein the resonant chamber (35) is substantially annular.
A burner assembly as claimed in any one of the foregoing Claims, comprising an annular closing wall (38) which externally delimits the resonant chamber (35).
A burner assembly as claimed in Claim 3, wherein the passages (36, 37) comprise connection holes (37) in the annular closing wall (38).
A burner assembly as claimed in any one of the foregoing Claims, comprising a burner insert (17) for connection to a burner seat (17a) of a gas turbine combustion chamber (3); and wherein the resonant chamber (35) extends about the outer body (26), between the inlet (31) of the swirler (23) and the burner insert (17).
A burner assembly as claimed in Claim 5, wherein the passages (36) comprise necks (36) arranged to fluidly couple the resonant chamber (35) to the outside through the burner insert (17).
A burner assembly as claimed in Claim 6, wherein the necks (36) extend through the burner insert (17).
A burner assembly as claimed in Claim 3 and any one of Claims 6 to 8, wherein the outer body (26) comprises a connecting ring (39) by which the outer body (26) is connected to the burner insert (17); and wherein the annular closing wall (38) extends about the outer body (26), between the inlet (31) of the swirler (23) and the connecting ring (39).
A burner assembly as claimed in one of the foregoing Claims, wherein the frustoconical wall (26a) has fastening holes (29b) for the blades (28) of the swirler (23); and the frustoconical wall (26a) and seals (29c) in the fastening holes (29b) fluidly separate the resonant chamber (35) from the mixing channels (30).
A burner assembly as claimed in any one of the foregoing Claims, wherein the resonant chamber (35) is fluidly coupled to the outside exclusively through the passages (36, 37).
A burner assembly as claimed in any one of the foregoing Claims, wherein the resonant chamber (35) has no fluidic connections to the swirler (23) through the outer body (26).
A burner assembly as claimed in any one of the foregoing Claims, comprising a pilot burner (21) coaxial with the main burner (20).
A turbine assembly comprising a combustion chamber (3); and a plurality of burner assemblies (15) as claimed in any one of the foregoing Claims, fitted to respective burner seats (16) of the combustion chamber (3).
A turbine assembly as claimed in Claim 13, wherein each Helmholtz resonator has a respective damping band, and the damping bands of Helmholtz resonators of separate burner assemblies (15) are not coincident.