EP2011963B1 - Method for operating a gas turbine with axial thrust balance - Google Patents

Description

Technical area

The invention relates to a method for operating a gas turbine with axial thrust compensation and a gas turbine with apparatus for carrying out the method.

State of the art

The axial thrust of a gas turbine is the resulting force of aerodynamic forces and compressive forces, which exert an axial force on the rotor in the compressor and turbine, as well as all acting in the axial direction of the rotor pressure forces. The resulting thrust is absorbed by a thrust bearing. Typically, gas turbines are designed to have a minimum thrust at idle. The axial thrust increases proportionally to the load. To compensate for the axial thrust, a counterforce to the thrust balance can be applied against the increasing axial load with the load. As a result, the maximum thrust to be absorbed by the thrust bearing can be reduced. Accordingly, the size and the power loss of the thrust bearing can be reduced.

The thrust of turbines and compressors as well as the compressive forces acting on the rotor in the axial direction are determined by operating parameters, in particular the position of compressor guide vanes and compressor discharge pressure as well as the design. He is determined by the selected geometries, in particular by the geometries of the blade channels and the degrees of reaction of the turbine stages. The operating parameters are of the desired Process and operating concept of the gas turbine dependent. The load-dependency of the thrust can not be changed once the design has been selected.

The problem of thrust balance in gas turbines has long been known and a large number of approaches have been proposed in the literature. In particular, various ways to compensate for the axial thrust via pressure compensation cylinder and thus to reduce the load on the thrust bearings are known. To control the thrust balance by means of a counterforce in a gas turbine, various methods have also been developed.

In the US4730977 A method for operating a gas turbine with thrust balance will be described. The method is based on that at idle and deep part load compressed air is introduced via inlet valves in a cavity, so that an axial force is exerted on the turbine rotor. This allows a negative thrust, which arises at idle and deep part load to compensate. At higher load or full load, the inlet valves are closed, so that no compressed air is introduced into the cavity and no additional thrust is exerted.

In the US5735666 a method is described in which, via a magnetically operated thrust load compensation device, the thrust loads, which load on a thrust bearing regulated. In particular, the thrust load compensation device generates a compensation thrust as soon as a sensor detects a rotational speed of the thrust bearing which is below a threshold value.

In the US5760289 is proposed for thrust balance, downstream of the turbine to provide a pressure equalizing piston and to pressurize it with compressed air. To regulate the pressure in the balance piston and thus the compensation force depending on the operating state, a complex algorithm is needed. In addition, a periodic calibration of the algorithm to compensate for aging or possible modifications to the gas turbine is proposed.

Another embodiment of a pressure compensating piston is in the US4653267 shown. Here is the pressure balance piston in the middle part, that is the between compressor and turbine geiegenen part, running a two-shaft system. The axial force of the piston is reduced in normal operation by a second chamber pressurized with leakage air. Air can be discharged from this second chamber via a valve and thus the pressure level in this chamber can be reduced. By changing the pressure level in the second chamber, the resulting axial force of the pressure compensating piston is regulated. The advantage of this arrangement is that the air discharged from the second chamber for control can continue to be used for turbine cooling. In US5760289 and in US4653267 Additional structural parts are needed to generate the pressure compensation piston. In addition, compressed air is lost, without power output, via seals from the pressure equalizing piston or can only be used at a significantly lower pressure level. To accommodate the pressure equalizing piston also expensive space is required
and in particular in embodiments according to US5760289 An extension of the axle is necessary.

Another approach to reducing the axial forces is in the EP0447886 explained. In the gas turbine design shown there, in which the shaft part lying between the turbine and the compressor is a drum which is surrounded by a drum cover and wherein the annular channel formed between drum and drum cover takes over the guidance of the cooling air taken from the compressor to the end face of the turbine rotor , a significant proportion of the axial forces are applied by the pressure on the first turbine disk. In the EP0447886 the axial force is reduced by the fact that the static pressure is reduced in front of the end face of the turbine rotor. This is achieved by the rotor-side cooling air is deflected within the annular channel through a swirl lattice and at the highest possible tangential speed, in the direction of rotation of the rotor, is accelerated. In addition to the advantages of this design, which in the EP0447886 themselves are shown, compared to the use of pressure equalizing piston to notice that no additional structural parts or axial length are needed to create a pressure equalizing piston. In addition, no compressed air is lost via pressure equalizing piston. But there is no way to control the axial thrust in this embodiment. This has the consequence that at full load a significant residual thrust on the thrust bearing is to be included or at low load thrust reversal is to be accepted. Depending on the design and arrangement of the thrust bearings, increased thrusting can lead to increased vibrations and, in the worst case, an overload of the thrust bearing can occur at even lower loads. Moreover, with modifications to the gas turbine that have an impact on thrust, such as upgrading with a new compressor or turbine, this design has no way to compensate for this change in thrust.

Presentation of the invention

The object of the present invention is to provide a controllable thrust balance in gas turbines without the use of additional structural components, which at high load and in particular at the design point has no additional cooling air consumption for acting on pressure equalizing piston or the like result. In addition, the controllable thrust balance in gas turbines to be retrofitted, the one accordingly EP0447886 have executed middle part.

The invention relates to a method according to claim 1.

To achieve the above object, a gas turbine is designed with respect to aerodynamic forces and compressive forces exerting an axial force on the rotor so that it has a negative thrust at idle and deep part load. A negative thrust is a thrust that points from the turbine towards the compressor. Further, it is designed so that it has a positive thrust at high gas turbine load and especially at full load. In order to ensure a positive force on the at least one axial bearing in the entire load range of the gas turbine, an additional thrust in the main thrust direction, that is to say a positive thrust in the direction of the compressor to the turbine, is applied at idle and part load.

The resulting maximum thrust force to be absorbed by the at least one thrust bearing is consequently smaller than in a conventionally designed gas turbine without thrust balance. In addition, a thrust reversal in loading or unloading of the gas turbine is prevented by the additional thrust. The load range in which an additional thrust is applied is, for example, in the range from idle to about 60% full load. In a gas turbine that is optimized for full load operation, the part load range in which an additional boost is applied, for example, to about 90% full load range. For retrofitting, the partial load range in which additional thrust is applied, for example, only up to about 10% full load range.

The additional thrust is generated by a method for regulating the pressure on the end face or on a partial surface of the end face of the turbine rotor.

For this purpose, a substantially annular space between the drum cover and the first turbine disk, which is closed by a rotor seal a turbine blade root seal, divided by a seal in an outer and an inner annulus. For example, the turbine rotor is supplied with high-pressure cooling air from the outer annular space, which is fed into this annular space with the highest possible tangential velocity. In this case, the static pressure in the outer annulus is due to the strong acceleration to the highest possible tangential velocity significantly below the compressor end pressure. To accelerate the cooling air to the highest possible tangential velocity, a swirl nozzle is used, for example. However, it is also possible, for example, to use directional bores for acceleration in the tangential direction.

With the control valve closed, if no additional compressed air is supplied to the inner annulus, the ratio of the pressure drop across the rotor seal and turbine disk seal is inversely proportional to the ratio of the equivalent areas of both seals. Typically, the rotor seal has a significantly smaller equivalent area than the turbine disk seal. The pressure drop across the rotor seal is correspondingly much larger than that over the turbine disk seal. The pressure in the inner annular space is therefore determined when the control valve is closed essentially by the pressure in the outer annular space.

In order to produce an additional thrust in the main direction of thrust, the inner annular space is acted upon by at least one line from Kompressorplenum or other suitable extraction point with compressed air. To control the pressurization at least one control valve is provided. By applying pressure an additional force is applied in the main direction of thrust, so that in the entire operating range of the gas turbine, a positive resulting thrust is ensured on the at least one thrust bearing and thrust reversal is avoided.

The lower the static pressure in the annular space with the control valve closed, the greater the control range of the additional thrust force when using compressor discharge air. The above-mentioned reduction of the static pressure by feeding the cooling air through a swirl nozzle thus leads to an increase in the control range.

To pressurize, for example, externally supplied compressed air or steam can be used or an externally supplied medium can be used in combination with compressor air.

In addition to the use of existing structural parts, the advantage of this method is that in the high load range no additional pressurization is required and thus no compressed air is consumed under performance and Wirkungsgradeinbusse. Even if the pressurization is active at partial load, the air escaping via the seal between the inner and outer annular space is usefully added to the rotor cooling air.

Various methods are conceivable for regulating the pressurization. For example, the at least one control valve may be open at low load and closed when a discrete limit is exceeded. Conversely, the at least one control valve is opened again when it falls below the discrete limit value. In order to avoid constant switching of the at least one control valve at loads close to the limit value, a hysteresis can be provided.

Another control option is, for example, a closure of the control valve proportional to the load.

In a further regulation, the position of the control valve is not specified as a function of the load, but the pressure ratio between the inner annular space and compressor discharge pressure is predetermined and this ratio is regulated via the control valve. The target value is not necessarily constant, but is, for example, a function of the load. The function can, for example, be determined in such a way that a constant axial thrust is achieved over the widest possible operating range.

The position of the control valve or the target value of the pressure conditions in the inner annular space can for example also be provided as a function of the Verdichtereintrittsleitschaufelwinkel or the relative load. Regulations depending on combinations of parameters or other relevant parameters are also possible.

In addition to the application of the process for the design and development of new plants, a special case is the application in connection with the upgrade of a gas turbine. When upgrading a gas turbine, a change in one of the main components turbine or compressor can lead to a reduction of the axial thrust. This will be the case, for example, when the compressor thrust increases due to an upgrade compressor with virtually unchanged intake mass flow and thus virtually unchanged compressor discharge pressure and turbine thrust. The increase in compressor thrust can cause a thrust reverser after the upgrade. To avoid this, the method according to the invention can be used and a controlled additional thrust can be applied.

In addition to the method, a gas turbine with reduced maximum axial thrust, with at least one pressurizable partial surface of the turbine rotor is described.

One embodiment is a gas turbine with a seal that divides the substantially annular space between the drum cover and the first turbine disk into an outer and an inner annular space. It has at least one line from the compressor plenum to the drum cover, at least one control valve in this line and at least one inlet into the inner annulus. There are various ways known to those skilled to perform a seal between the end face of the turbine rotor and drum cover. A labyrinth seal is an example of a suitable seal.

In a gas turbine with more than one turbine annular spaces for pressurization at the end face of at least one turbine or in combination divided at several or all turbines and running with at least one adjustable compressed air supply.

For the introduction of compressed air into the inner annulus various possibilities are also known. This can be, for example, a hole through the drum cover. In another exemplary embodiment, the introduction into the inner annulus of the drum cover is a generally annular plenum connected to the inner annulus through a plurality of orifices.

In a further embodiment, at least one pressure gauge is also provided in the inner annulus and in the compressor plenum.

In a further embodiment, the at least one supply line for pressurizing the inner plenum is not connected to the Kompressplplenum, but another suitable extraction point for compressor air via at least one control valve.

Brief description of the drawings

The invention is based on embodiments in the Fig. 1 to 4 shown schematically.

• Fig. 1 Schnitt durch die Mittelpartie einer Gasturbine mit innerem und äusserem Ringraum sowie einer Zuführung für Druckbeaufschlagung des inneren Ringraumes.
• Fig. 2 Detailsauschnitt des Schnittes der Mittelpartie für eine Ausführung der Turbinenscheibendichtung als Labyrinthdichtung.
• Fig. 3 Schubverlauf über Last bei Regelung über einen Grenzwert mit Hysterese.
• Fig. 4 Idealisierter Schubverlauf über Last bei Regelung auf das lastabhängige Druckverhältnis zwischen Druck im inneren Ringraum und Kompressorenddruck.

Show it:

• Fig. 1 Section through the middle part of a gas turbine with inner and outer annular space and a supply for pressurizing the inner annulus.
• Fig. 2 Detail section of the section of the central part for an execution of the turbine disk seal as a labyrinth seal.
• Fig. 3 Thrust curve over load at control over a limit value with hysteresis.
• Fig. 4 Idealized shear progression via load during regulation to the load-dependent pressure ratio between pressure in the inner annulus and compressor discharge pressure.

Embodiment of the invention

A gas turbine with a device for carrying out the method according to the invention essentially has at least one compressor, at least one combustion chamber and at least one turbine, which drives the compressor and a generator via at least one shaft.

Fig. 1 shows a section through the middle part of a gas turbine, that is, the area between the compressor and turbine and the final stage of the compressor and the first stage of the turbine.

The compressor 1 compresses the air. Most of the air is introduced via the Kompressplplenum 2 in a combustion chamber 3 and mixed with fuel, which burns there. From there, the hot fuel gases flow under labor output through a turbine 4. Turbine 4 and compressor 1 are arranged on a common shaft 18, wherein the part of the shaft located between compressor 1 and turbine 4 is designed as a drum 6.

The high-pressure part of the rotor cooling air is swirled after the last compressor blade discharged through an annular channel 7 between the rotor drum 6 and drum cover 5 and introduced via the rotor cooling air supply 12 and a swirl grille 13 in an annular space between the drum cover and a first turbine disk. This annulus is divided by a seal 9 in an inner annulus 10 and an outer annulus 11.

The outer annular space is bounded, for example, by the rear side of a drum cover 5, an inner platform of a first turbine guide vane facing the rotor 18, a first turbine disk and the seal 9.

The inner annular space is bounded, for example, by the rear side of a drum cover 5, a seal 9, a first turbine disk of a rotor seal 8 and the walls of a part of an annular channel 7 lying downstream of a rotor seal 8.

The seal 9 can be performed, for example, as a labyrinth seal 21. For receiving the labyrinth seal 21, for example, as in Fig. 2 shown, offset from each other, referred to as balconies projections on a drum cover 19 and a first turbine disk 20 are provided.

The rotor cooling air supply 12 may be connected, for example via a swirl grille 13 with an outer annular space 11 that accelerates the rotor cooling air tangentially and thus lowers the static pressure in an outer annular space 11. From the one outer annular space 11, the rotor cooling air enters a first turbine disk. An annular space is divided by a seal 9 into an inner 10 and outer annular space 11 in front of a first turbine disk, ie the substantially annular space between the drum cover 5 and the first turbine disk, which is closed by a rotor seal 8, a turbine blade root seal 24. This division makes it possible to pressurize the inner annulus 10 via a pressure line 14 and a control valve 15 with compressed air from the Kompressplplenum 2. The introduction 16 of the compressed air into the inner annular space 10 can take place via holes through the drum cover or, as in Fig. 1 represented, via a plenum 17. In this case, the compressed air is fed via the at least one pressure line 14 into the plenum 17. From there it passes via the introduction 16, which is designed, for example, as a plurality of holes in the inner annular space 10th

The inner annular space 10 is applied at partial load to increase the thrust by opening the control valve 15 via the pressure line 14 and the introduction 16 with pressure. About the turbine disk seal 9, this air passes together with the leakage air of the rotor seal 8 in the outer annular space 11. For the regulation of the pressurization several possibilities are given.

In Fig. 3 the resulting axial thrust for control is shown as a function of the gas turbine load in regulation with a limit value and hysteresis. In this case, the control valve 15 is initially open at low load of the gas turbine. After exceeding a limit value α, the control valve is closed and remains closed in the upper load range (solid line). When reducing the load, the control valve 15 when falling below the load β is opened again (dashed line). In addition, dashed lines show the thrust profile with thrust reversal, which would result without additional thrust in the lower load range.

Fig. 4 shows the idealized thrust curve (solid line) over gas turbine load when controlling the load-dependent pressure ratio between pressure in the inner annulus and compressor end pressure. Again, the control valve 15 is initially open at low load of the gas turbine. From reaching a target thrust, for example, at the load γ, the thrust is kept constant by changing the pressure in the inner annulus. Only when the control valve 15 is completely closed, which is the case, for example, at the load δ, the thrust continues to increase to reach its maximum value at full load. The dependence of the pressure ratio of load can be determined by model calculations or from experiments and programmed in the gas turbine controller. In addition, dashed lines show the thrust curve with thrust reversal, which would result without additional thrust.

Of course, the invention is not limited to the embodiments shown and described here. For example, the seals (8 and / or 9) can be designed as a brush seal.

LIST OF REFERENCE NUMBERS

1

Compressor (only the last two stages shown)

2

compressor plenary

3

combustion chamber

4

Turbine (only the first stage shown)

5

drum cover

6

Rotor drum

7

annular channel

8th

rotor seal

9

Turbine disc seal

10

Inner annulus

11

Outer annulus

12

Rotor cooling air supply

13

swirl cascade

14

pressure line

15

control valve

16

introduction

17

plenum

18

wave

19

Projection of the shaft cover

20

Projection of the first turbine disk

21

labyrinth seal

22

blade root

23

blade

24

Turbine blade root seal

Claims (8)

1. Method for operating a gas turbine with axial thrust balance, wherein the gas turbine is configured, with respect to aerodynamic forces and compressive forces which exert axial forces on the rotor, such that these forces result in a negative thrust during no-load operation and at low partial load and in a positive thrust at high load and at full load, and such that a positive auxiliary thrust is applied with which the resulting axial bearing force is kept positive in the entire load range, and that at the high load range, no compressed air is consumed for pressurisation, characterised in that the auxiliary thrust is produced by controlling the pressure at the front face or at a partial front face of the turbine rotor, wherein a substantially annular chamber between the drum cover and a first turbine disc is divided by a seal into an outer annular chamber (11) and an inner annular chamber (10), and one of these two chambers is pressurised for thrust control.
2. The method according to claim 1, characterised in that the outer annular chamber (11) is used to supply cooling air to the turbine rotor, and the inner annular chamber (10) is used for thrust control.
3. Method according to one of claims 1 or 2, characterised in that

   - compressed air from a compressor plenum (2), and/or

   - compressed air from a compressor take-off before the compressor end, and/or

   - compressed air from an external source, and/or

   - steam from an external source

   is used for thrust control.
4. Method according to any of claims 1 to 3, characterised in that the thrust force is controlled via at least one control valve (15) for pressurisation, which valve is opened at low load and closed when the pressure exceeds a discrete limit value, and the control valve (15) is opened again when the pressure falls below the discrete limit value.
5. Method according to claim 4, characterised in that the limit value for opening of the at least one control valve (15) is higher than the limit value for closure.
6. Method according to any of claims 1 to 3, characterised in that the at least one control valve (15) for setting the additional thrust is closed in proportion to the load.
7. Method according to any of claims 1 to 3, characterised in that to control the additional thrust, the pressure ratio between the inner annular chamber (10) and the compressor end pressure (2) is predefined and that this ratio is controlled via the at least one control valve (15).
8. Method according to claim 7, characterised in that the pressure ratio between the inner annular chamber and the compressor end pressure is

   - a function of the load, or

   - a function of another relevant operating parameter or a combination of operating parameters of the gas turbine.

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