EP0597138B1 - Combustion chamber for gas turbine - Google Patents

Description

Technical field

The invention relates to a gas turbine combustion chamber according to the preamble of patent claim 1.

State of the art

The so-called "lean premix combustion" has recently become established for the low-pollutant combustion of a gaseous or liquid fuel. The fuel and combustion air are premixed as evenly as possible and only then fed to the flame. If this is done with a high excess of air, as is customary in gas turbine plants, relatively low flame temperatures arise, which in turn leads to the desired, low formation of nitrogen oxides.

Combustion chambers of the type mentioned at the outset are known from EP-A1-387 532. The front plate is formed by a single wall on which premixing burners of the double-cone type are arranged.

Modern, highly loaded gas turbines require increasingly complex and effective cooling methods. In order to achieve low NO _x emissions, an attempt is made to pass an increasing proportion of the air through the burners themselves. This compulsion to reduce the cooling air flows also arises for reasons related to the increasing hot gas temperature when a modern gas turbine enters. Because the cooling of the other parts of the system, such as blading, machine shaft etc., must also meet increasingly stringent requirements, and because the hot gas temperatures, which are constantly increasing in the interest of high thermal efficiency, also directly lead to a greatly increased thermal load on the combustion chamber walls, must also be included the combustion chamber cooling air can be used very sparingly. These requirements generally lead to multi-stage cooling techniques, whereby the pressure loss coefficient, ie the total pressure drop caused by the cooling divided by a dynamic pressure when the cooling air enters the combustion chamber, can be quite high.

Gas turbine combustion chambers with air-cooled flame tubes are also known, for example from US 4,077,205 or US 3,978,662. The flame tube is essentially constructed from wall parts which overlap in the turbine axial direction. On their side facing away from the combustion chamber, the wall parts each have a plurality of inlet openings distributed over the circumference, via which air is introduced into a distribution chamber arranged in the flame tube and communicating with the combustion chamber. In the cooling system there, the respective flame tube has a lip which extends over the slot through which the cooling air film emerges. This cooling air film should adhere to the wall of the flame tube in order to form a cooling barrier layer for it.

The known gas turbine combustion chambers mentioned above now have the disadvantage that the air consumption for cooling purposes is much too high and that as a result of the infeed of the Cooling air into the flame tube interior downstream of the flame, this air is not available to the actual combustion process. As a result, the combustion chamber cannot be operated with the required high excess air ratio.

In conventional combustion chambers, cooling generally plays an extremely important role in the soundproofing of the combustion chamber. The above-mentioned reduction of the cooling air mass flow paired with a greatly increased pressure loss coefficient of the entire combustion chamber wall cooling now leads to an almost complete suppression of the sound insulation. The consequence of this development is an increasing vibration level in modern LOW-NO _x combustion chambers.

A combustion chamber for a rocket engine, in which the combustion chamber inlet is equipped with a plurality of burners which are attached to a front plate, is known from FR-A-2570129. For vibration damping, damping chambers which are open on both sides and which communicate with the combustion chamber via passage pipes are arranged in each case in the area of the fuel injection.

Presentation of the invention

The invention has for its object to significantly increase the soundproofing of a combustion chamber in a gas turbine combustion chamber of the type mentioned with minimal cooling air consumption by damping the thermo-acoustically fanned vibrations.

According to the invention, this object is achieved with the features of the claims.

The advantage of the invention can be seen, inter alia, in the fact that the proximity of the Helmholtz damper to the combustion zones dampens the thermoacoustic vibrations occurring in the flame fronts particularly intensively.

Because the damping tubes in the Helmholtz dampers are designed to be interchangeable, and because the walls of the combustion chamber are provided with a manhole, the dampers can be matched to the vibration to be dampened in the combustion chamber without having to cover the machine.

Brief description of the drawing

Fig. 1

einen Teillängsschnitt der Gasturbine;

Fig. 2

ein vergrösserter Ausschnitt der Primärzone der Brennkammer;

Fig. 3

einen Teilquerschnitt durch die Primärzone der Brennkammer nach Linie 3-3 in Fig. 2;

Fig. 4

einen Längsschnitt eines Helmholtzresonators.

In the drawing, an embodiment of the invention is shown using a single-shaft gas turbine with axial flow.
Show it:

Fig. 1

a partial longitudinal section of the gas turbine;

Fig. 2

an enlarged section of the primary zone of the combustion chamber;

Fig. 3

a partial cross section through the primary zone of the combustion chamber according to line 3-3 in Fig. 2;

Fig. 4

a longitudinal section of a Helmholtz resonator.

Only the elements essential for understanding the invention are shown. The system does not show, for example, the complete exhaust housing with exhaust pipe and chimney, as well as the inlet parts of the compressor part. The direction of flow of the work equipment is indicated by arrows.

Way of carrying out the invention

The system, of which only the half lying above the machine axis 10 is shown in FIG. 1, essentially consists on the gas turbine side (1) of the rotor 11 bladed with rotor blades and the blade carrier 12 equipped with guide blades. The blade carrier 12 is over projections hooked into corresponding receptacles in the turbine housing 13. The exhaust housing 14 is flanged to the turbine housing 13.

In the illustrated case, the turbine housing 13 also includes the collecting space 15 for the compressed combustion air. From this collecting space, part of the combustion air passes through a perforated cover 30 in the direction of the arrow directly into the annular combustion chamber 3, which in turn enters the turbine inlet, i.e. flows upstream of the first guide row. The compressed air arrives in the collecting space from the diffuser 22 of the compressor 2. Only the last four stages of the latter are shown. The blading of the compressor and the turbine sit on the common shaft 11, the central axis of which represents the longitudinal axis 10 of the gas turbine unit.

The combustion chamber 3 is equipped at its head end with premix burners 20, as are known, for example, from EP-A1-387 532. Such a premix burner, shown only schematically in FIG. 2, is a so-called double-cone burner. It essentially consists of two hollow, conical partial bodies 26, 27 which are nested one inside the other in the direction of flow. The respective central axes of the two partial bodies are offset from one another. The adjacent walls of the two partial bodies in their longitudinal extent form tangential slots 28 for the combustion air, which in this way reaches the interior of the burner. A fuel nozzle 29 for liquid fuel is arranged there. The fuel is injected into the hollow cone at an acute angle. The resulting conical liquid fuel profile is enclosed by the combustion air flowing in tangentially. The concentration of the fuel is continuously reduced in the axial direction due to the mixing with the combustion air. The burner can also be operated with gaseous fuel. For this purpose, in the area of the tangential slots in the walls of the two partial bodies provided in the longitudinal direction of the gas inflow openings. In gas operation, the mixture formation with the combustion air thus begins in the zone of the inlet slots 28. It goes without saying that mixed operation with both types of fuel is also possible in this way. At the burner outlet, a fuel concentration that is as homogeneous as possible is established over the loaded cross-section. A defined dome-shaped return flow zone is created at the burner outlet, at the tip of which the ignition takes place.

On the occasion of the combustion, the combustion gases reach very high temperatures, which places special demands on the combustion chamber walls to be cooled. This applies all the more when so-called low NO _x burners, for example the premix burners used here, are used, which require large flame tube surfaces with relatively modest amounts of cooling air. The annular combustion chamber extends downstream of the burner orifices up to the turbine inlet. It is limited both inside and outside by walls to be cooled, which are usually designed as self-supporting structures.

The present combustion chamber is equipped with 72 of the said burners 20. 3, which shows a quarter-circle section, shows the arrangement thereof. Two burners are arranged radially one above the other on a front segment 31. 36 of these adjacent front segments form a closed circular ring, which in this way forms a heat shield. The two burners from adjacent front segments are each radially offset. This means that the radially outer burner of every second front segment directly adjoins the outer ring wall of the combustion chamber, as can also be seen in FIG. 3. The radially inner burners of the other front segments are therefore arranged in the immediate vicinity of the inner ring wall. This results in an uneven thermal load on the corresponding ring walls over the circumference.

At the free end of each front segment 31, which is not occupied by a burner, a rinsed Helmholtz resonator 21 is now housed for soundproofing the combustion chamber. 4, such a Helmholtz damper essentially consists of the actual resonance volume 50, an air inlet opening to the Helmholz volume, which is designed here as a feed pipe 51, and a damping pipe 52 opening into the combustion chamber interior. The purge air is drawn from the head space 49 by the damper.

For the functionality of the Helmholtz resonator, the feed tubes 51 are dimensioned such that they cause a relatively high pressure drop for the air flow. The damping tubes 52, on the other hand, allow the air to enter the interior of the combustion chamber with a low residual pressure drop. The limitation of the pressure drop in the damping tubes results from the requirement that even with an uneven pressure distribution on the inside of the combustion chamber wall, an adequate air flow into the combustion chamber always remains guaranteed. Of course, hot gas must not enter the Helmholtz resonator in the opposite direction at any point.

The choice of the size of the Helmholtz volume 50 results from the requirement that the phase angle between the fluctuations in the damping air mass flows through the supply and damping tubes should be greater than or equal to π / 2. For a harmonic vibration with a predetermined frequency on the inside of the combustion chamber wall, this requirement means that the volume should be at least so large that the Helmholtz frequency of the resonator, which is formed by the volume 50 and the openings 51 and 52, is at least the frequency of the combustion chamber vibration to be damped. It also follows that the volume of the Helmholtz resonator used is preferably at the lowest natural frequency of the combustion chamber is designed. It is also possible to choose an even larger volume. It is thereby achieved that a pressure fluctuation on the inside of the combustion chamber leads to a strongly opposite-phase fluctuation in the air mass flow, because the fluctuations in the damping air mass flows through the supply pipes and the damping pipes are no longer in phase.

The feed pipe 51 determines the pressure drop. The speed at the end of the feed pipe is adjusted so that the dynamic pressure of the jet together with the losses corresponds to the pressure drop across the combustion chamber. The average flow velocity in the damping tube in the present case of a gas turbine combustion chamber can typically be 2 to 4 m / s with an ideal design. So it is very small compared to the vibration amplitude, which means that the air particles move back and forth pulsating in the damping tube. Nevertheless, only enough air is allowed to flow through that a significant heating of the resonator is avoided. Heating by radiation from the area of the combustion chamber would result in the frequency not remaining stable. The flushing should therefore only dissipate the radiated heat.

The location of the damping is decisive for the stabilization of a thermoacoustic oscillation. The greatest increase occurs when the reaction rate and the pressure disturbance oscillate in phase. The strongest reaction rate usually occurs near the center of the combustion zone. Therefore, the highest fluctuation in the reaction rate will also be there, if one takes place. The arrangement of the dampers at the radially outer or inner end of the front segments has a favorable effect, since in this way the respective damper is located in the middle of three burners.

The housing of the Helmholtz damper is screwed into the respective front segment 31 from the head space 49 by means of a hollow threaded pin 55. The damping tube 52 protruding into the volume 50 is designed to be exchangeable. For this purpose, it penetrates the hollow threaded pin from the combustion chamber and is latched in the front segment by means of a bayonet lock 53. Spring means 54 ensure that the bayonet catch on the front segment is positively locked.

When the combustion chamber is commissioned, the frequency spectrum is measured with Helmholtz dampers sealed with blind flanges. Using the vibration to be damped, the required length and inner diameter of the damping tubes can be calculated for a given damping volume. The pipes determined in this way are then installed with the combustion chamber turned off. It goes without saying that several critical vibrations of different frequencies can also be damped in this way by installing different damper tubes.

In order to get to the Helmholtz dampers from the outside, the generally cooled walls of the combustion chamber must be provided with a manhole. In the present case, these walls are of a special kind in order not to impair the cooling.

The thermally highly loaded interior of the combustion chamber is divided into two zones, the walls of which are cooled in different ways.

A secondary zone 32 lying downstream and opening into the turbine inlet is delimited by a double-walled flame tube. It consists both on its inner ring 33 and on its outer ring 34 from a flangeless, welded sheet metal construction, which is held together by spacers, not shown. Both rings 33 and 34 are open at their turbine end and form the entrance there for the cooling air. The annular space 35 between the double wall of the outer ring 34 draws the air directly from the collecting space 15, as can be seen in FIG. 1. With efficient convection cooling, the air flows in counterflow to the combustion chamber flow in the direction of the primary zone 36. The annular space 37 between the double wall of the inner ring 33 is supplied with air from a hub diffuser 38. This hub diffuser, which connects to the compressor diffuser 22, is delimited on the one hand by a drum cover 24 and on the other hand by an annular shell 39. The latter is connected to the drum cover 24 via ribs (not shown). In this annular space 37, too, the air flows in the counterflow to the combustion chamber flow in the direction of the primary zone 36.

The cooling of the highly stressed primary zone walls is now carried out by means of individually cooled cooling segments 40. These cooling segments lined up in the circumferential direction and in the axial direction form their flow-limiting wall over the entire axial extent of the primary zone 36. Single cooling has the advantage of a low pressure drop.

The thermally highly stressed cooling segments 40 consist of a high-temperature, precision cast alloy. They are suspended in the circumferential direction with two feet 42 each provided with supporting teeth in corresponding grooves in a supporting structure, in a manner similar to how guide vane feet are fastened in blade carriers. Similarly to blade carriers, this support structure, hereinafter referred to as segment carrier 43, consists of two cast half-shells with a horizontal parting plane and not shown claws with which it is supported in the turbine housing.

In this way, three such cooling segments are arranged side by side in the axial direction (FIG. 2). In the circumferential direction, the number of cooling segments 40 arranged next to one another corresponds to the number of front segments 31, so that each front segment and a cooling segment is assigned to the burner 20 closest to the wall (FIG. 3).

A cooling segment is supplied with cooling air via a radially directed opening 46 which penetrates the segment carrier 43 and connects the collecting space 15 to one end of the cooling chamber 44 lying in the circumferential direction. At the opposite end of this same cooling chamber is the outlet opening 47 in the segment carrier. Both the opening 46 and the outlet opening 47 can either be individual bores or elongated holes that extend in the axial direction over a large part of the segment width.

The outlet opening 47 opens into a channel 48 which penetrates the segment carrier 43 in its entire axial extent and is open on both sides. On the turbine side, it opens against the annular space 35 between the double wall of the outer ring 34. As indicated schematically in FIG. 2, this outer ring is flanged to the segment carrier, the contour of the inner wall being matched to the contour of the cooling segments. On the burner side, the channel 48 opens against a head space 49, which is delimited by the cover 30 and the front segments 31. The cover 30 is also flanged to the segment carrier 43.

These axial channels 43, one of which is assigned to a segment in the circumferential direction, thus serve to jointly guide the segment cooling air and the cooling air acting on the secondary zone.

The same measures are taken for cooling the inner wall of the primary zone as is indicated in FIG. 3 with the aid of the cooling segments 140.

2 and 3 it is now shown how access to the interior of the combustion chamber and in particular to the damping tubes of the Helmholz resonators is made possible. A about yourself part 143 of the upper half of the segment carrier 43, which extends several cooling segments and forms the above-mentioned manhole, is designed to be removable together with the cooling segments 40 suspended therein. This detachable part 143 of the segment carrier comprises two cooling segments 40 in the circumferential direction and in the axial direction (shown hatched in FIGS. 2 and 3). The part 143 closing the manhole is screwed to the segment carrier 43 by means of a bracket 45 projecting on all sides. It goes without saying that a part of the turbine housing 13 which corresponds to the size of the manhole must also be opened and is therefore designed as an end cover 113.

Reference list

1

Gas turbine

2nd

compressor

3rd

Combustion chamber

10th

Machine axis

11

rotor

12th

Shovel carrier

13

Turbine casing

113

End cover from 13

14

Exhaust housing

15

Gathering room

20th

burner

21

Helmholtz damper

22 23

Diffuser of 2

24 25

Drum cover

26

Partial body of 20

27

Partial body of 20

28

tangential slot

29

Fuel nozzle

30th

cover

31

Front segment

32

Secondary zone

33

Inner ring of 32

34

Outer ring of 32

35

Annulus of 34

36

Primary zone

37

Annulus of 33

38

Hub diffuser

39

Ring bowl

40, 140

Cooling segment

42

Foot

43

Segment carrier

143

detachable part of 43

44

Cooling chamber

45

hanger

46

opening

47

Outlet opening

48

channel

49

Headroom

50

Resonance volume

51

Feed pipe

52

Damping tube

53

Bayonet lock

54

Spring means

55

hollow threaded pin

Claims (4)

1. Gas turbine combustion chamber having an annular combustion space (32, 36) whose walls extend from the combustion chamber inlet to the inlet to the gas turbine (1), and in which the combustion chamber inlet is equipped with a plurality of burners (20) evenly distributed in the peripheral direction, which burners are fastened to a front plate, characterized in that scavenged Helmholtz dampers (21), consisting of supply tube (51), resonance volume (50) and damping tube (52), are arranged in the region of the burners (20), the damping tubes (52) opening into the interior of the combustion chamber and being designed so as to be exchangeable from there, for which purpose the walls of the combustion space are provided with a manhole.
2. Gas turbine combustion chamber according to Claim 1, characterized in that the front plate consists of a plurality of front segments (31) arranged in series in the peripheral direction to form a circular ring, in that two burners (20) are fastened radially one above the other on each front segment (31) and in that the burners of respectively adjacent front segments are radially offset relative to one another, the Helmholtz dampers (21) being arranged radially above the burners on one half of the front segments and being arranged radially below the burners on the other half of the front segments.
3. Gas turbine combustion chamber according to Claim 1

   - characterized in that a plurality of individually cooled cooling segments (40) form the wall bounding the flow in a primary zone (36) of the combustion space, the cooling segments being suspended in a segment carrier (43) consisting of two half-shells with a horizontal split plane, which segment carrier forms the outer boundary of the primary zone relative to a collecting space (15) guiding the compressed combustion air,

   - in that a secondary zone (32) located downstream is bounded by a double-walled flame tube (33, 34) whose turbine end is open and forms the inlet for the cooling air of the secondary zone,

   - and in that the cooling air from the primary zone (36) and from the secondary zone (32) are supplied in common to the burner inlet, for which purpose axial passages (48) communicating with the burner inlet are arranged in the segment carrier (43),

   - and in that a part (143) of the upper half of the segment carrier (43), extending over a plurality of cooling segments and forming the manhole, together with the cooling segments (40) suspended in it, is designed so that it can be released.
4. Gas turbine combustion chamber according to Claim 3

   - characterized in that the number of cooling segments (40) in series in the peripheral direction corresponds to the number of front segments (31) and in that at least three cooling segments are arranged adjacent to one another in the axial direction

   - and in that the releasable part (143) of the segment carrier (43) encompasses two cooling segments in the peripheral direction and two in the axial direction.

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