METHOD FOR MINIMIZING THE GAP BETWEEN A ROTOR AND A HOUSING

Abstract

A method for minimizing the gap between a rotor, particularly a rotor vane, and a housing, particularly a housing of a turbine, wherein the gap between rotor and housing is adjustable is provided. The method includes displacing rotor and housing with respect to one another, to provide a simple way of minimizing the gap between rotor and housing. An output signal from a structure-borne sound monitoring system assigned to the rotor and/or housing is taken as a metric for the size of the gap and thus for setting a minimum gap.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2013/064901 filed Jul. 15, 2013, and claims the benefit thereof. The International Application claims the benefit of German Application No. DE 102012213016.0 filed Jul. 25, 2012. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a method for minimizing the gap between a rotor, especially a rotor blade, and a housing, especially a housing of a turbine, wherein the gap between rotor and housing can be adjusted, especially by displacement of the rotor and the housing in relation to each other. It also relates to a turbine, especially a gas turbine, comprising a rotor, especially a rotor blade, and a housing, wherein the gap between rotor and housing can be adjusted by means of an adjusting device, especially by displacement of rotor and housing in relation to each other.

BACKGROUND OF INVENTION

A turbine is a turbomachine which converts the internal energy (enthalpy) of a flowing fluid (liquid or gas) into rotational energy and ultimately into the mechanical driving energy. Some of its internal energy is extracted from the fluid flow by the laminar circumflow—which is swirl free as far as possible—around the turbine blades, which portion of internal energy is transferred to the rotor blades of the turbine. Via these rotor blades, the turbine shaft is then made to rotate, the useful power being transmitted to a coupled working machine, such as a generator. Rotor blades and shaft are parts of the movable rotor or rotating component of the turbine which is arranged inside a housing.

As a rule, a plurality of blades are mounted on the shaft. Rotor blades which are mounted in one plane form a blade wheel or rotor wheel in each case. The blades are profiled with a slight curve, similar to an aircraft airfoil. A stator wheel is customarily located in front of each rotor wheel. These stator blades project from the housing into the flowing medium and cause it to swirl. The swirl which is generated in the stator wheel (kinetic energy) is utilized in the following rotor wheel in order to cause rotation of the shaft upon which the rotor wheel blades are mounted.

Stator wheel and rotor wheel together are referred to as a stage. A plurality of such stages are frequently connected in series. Since the stator wheel is stationary, its stator blades can be fastened both on the inside of the housing and on the outside of the housing, and therefore provide a support for the shaft of the rotor wheel.

A gap, which for example serves for compensation of the heat expansion during operation, usually exists between the rotor blade tips of the rotor and the housing. In order to achieve a high level of efficiency, the gap between blade tip and housing is to be minimal, however, since fluid flows through the gap past the rotor blades and therefore does not contribute to energy generation.

Contingent upon the conical shape of the turbine and of the housing enclosing it, it is possible to influence the gap size by a displacement of the rotor in relation to the housing by means of a corresponding adjusting device. Methods for displacement of rotor relative to the housing are known from DE 42 23 495 and WO 00/28190, for example. Methods for gap minimization are known from DE 39 10 319 C2, DE 39 01 167 A1 and EP 1 524 411 B1. It is known especially from the last named to determine the gap size by means of determining electrical resistance coefficients in the case of an electrically conducting contact between rotor and housing.

Further methods for gap minimization, which, however, are based on the detection of vibrations in the event of contact between housing and rotor, are known for example from GB 2396438A, US 2009/0226302 A1 or US 2005/0286995 A1. These methods which are known from the prior art, however, necessitate a high equipment cost or are not very accurate so that in practice only a displacement of the rotor by a fixed, predetermined length is frequently applied. Therefore, a further improvement with regard to the equipment cost is desired.

SUMMARY OF INVENTION

It is therefore an object of the invention to disclose a method by means of which the gap between rotor and housing is minimized in a simple manner at low equipment cost.

The object is achieved according to the invention by an output signal of a structure-borne sound monitoring system, which is associated with the rotor and/or housing, being used as a measure for the size of the gap and therefore for setting a minimum gap, wherein the structure-borne sound monitoring system is a component part of a foreign-body detection system.

The invention is based in this case on the consideration that a particularly simple monitoring of the gap size would be possible by means of sensors which are as non-invasive as possible and are to be attached in the outer regions. A simple signal, which is generated in the event of contact of rotor and housing, is the sound which is propagated, moreover, by solid bodies, such as a turbine housing. As a result, an acoustic detection of vibrations, which are generated by blade tips colliding with the housing, is enabled in the outer regions of the housing. Therefore, a structure-borne sound monitoring system allows a particularly simple and technically inexpensive checking of a possible contact of blade tips and housing during a displacement of housing and rotor in relation to each other. This enables an accurate setting of a minimum gap.

According to the invention, the structure-borne sound monitoring system is a component part of a foreign-body detection system, especially of the turbine. Foreign-body detection systems are frequently used in turbines in order to detect in good time possibly penetrating foreign bodies or breaking-away parts of the turbine itself and to initiate a shutdown of the turbine.

Foreign-body detection systems are based on acoustic detection. Therefore, it is advantageous to also use the structure-borne sound monitoring system of the foreign-body detection system in the manner of a dual-use system for setting a minimum gap. It may be the case that no constructional interventions at all in the turbine are even necessary for this purpose, but only a corresponding adjustment of sensors and control electrics.

In an advantageous embodiment, the rotor can be displaced in an axial direction in relation to the housing for adjusting the size of the gap. Owing to the typically conical shape of the turbine, a uniform reduction of the gap over the entire circumference and in each turbine stage is achieved as a result.

The rotor is advantageously displaced just until there is no longer a contact which generates output signals. That is to say, the rotor is displaced until the turbine rotor blading comes into contact with the housing. This contact is monitored by means of a structure-borne sound monitoring system and as a result of this limits the range of travel. As soon as a first contact indication is registered, the rotor—after a possibly short reverse displacement—is fixed directly at the limit for contact.

In a turbine, especially a gas turbine, comprising a rotor, especially a rotor blade, and a housing, the gap between rotor and housing is advantageously minimized by means of the described method.

It is also an object of the invention to disclose a turbine in which the gap between rotor and housing is minimal. This is to be carried out at low equipment cost.

The object is achieved by a structure-borne sound monitoring system being associated with the rotor and/or housing in a turbine and on the output side being connected to the adjusting device.

Also with regard to the turbine, the structure-borne sound monitoring system is advantageously a component part of a foreign-body detection system and/or the rotor can be advantageously displaced in an axial direction in relation to the housing for adjusting the size of the gap.

In an advantageous embodiment, the rotor, particularly at the tips of the rotor blades, can be at least partially abradable. That is to say that corresponding abrasion points are provided and are designed for a slight contact of the housing during the adjustment process. At the abrasion points, material is then possibly worn away, but these points are designed so that no structural damage to the rotor, especially to the rotor blades, occurs as a result. Therefore, the rotor can displaced without risk up to the point of the slight signal-generating contact, which enables an optimum gap setting.

A power plant advantageously comprises a described turbine.

The advantages which are achieved using the invention are especially that by the contact detection between rotor and housing by means of a foreign-body detection system, minimization of the radial gaps is made possible with technically particularly simple means. The efficiency of the turbine is consequently maximized and the power output increased. This also offers advantages with regard to environmental friendliness since by means of a control system modification a significant saving in fuel and emissions is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to a drawing.

In this respect, the FIGURE shows a gas turbine.

DETAILED DESCRIPTION OF INVENTION

The FIGURE shows a turbine 100, in this case a gas turbine, in a longitudinal partial section. Inside, the gas turbine 100 has rotor 103 which is rotatably mounted around a rotational axis 102 (axial direction) and which is also referred to as a turbine rotor.

Arranged in series along the rotor 103 are an intake housing 104, a compressor 105, a toroidal combustion chamber 110—especially an annular combustion chamber 106—with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust gas housing 109.

The annular combustion chamber 106 communicates with an annular hot gas passage 111. Four series-connected turbine stages 112, for example, form the turbine 108 there. Each turbine stage 112 is formed from two blade rings. In the hot gas passage 111, a row 125 formed from rotor blades 120 follows a stator blade row 115, as seen in the flow direction of a working medium 113.

The stator blades 130 are fastened on the stator 143 in this case, whereas the rotor blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133. The rotor blades 120 therefore form component parts of the rotor or rotating component 103. A generator or a working machine (not shown) is coupled to the rotor 103.

During operation of the gas turbine 100, air 135 is inducted by the compressor 105 through the intake housing 104 and compressed. The compressed air which is made available at the turbine-side end of the compressor 105 is directed to the burners 107 and mixed with a combustible medium there. The mixture is then combusted in the combustion chamber 110, forming a working medium 113. From there, the working medium 113 flows along the hot gas passage 111 past the stator blades 130 and the rotor blades 120. On the rotor blades 120 the working medium 113 is expanded, transmitting an impulse, so that the rotor blades 120 drive the rotor 103 and this drives the working machine which is coupled to it.

The components which are exposed to the hot working medium 113 are subjected to thermal loads during operation of the gas turbine 100. The stator blades 130 and rotor blades 120 of the first turbine stage 112, as seen in the flow direction of the working medium 113, are thermally loaded most of all next to the heat shield tiles which line the combustion chamber 106. In order to withstand the temperatures prevailing there, these are cooled by means of a cooling medium. By the same token, the blades 120, 130 may have coatings which are resistant to corrosion (MCrAlX; M=Fe, Co, Ni, rare earths) and to heat (thermal barrier layer, for example ZrO₂, Y₂O₄—ZrO₂).

The stator blade 130 has a stator blade root (not shown here) which faces the inner housing 138 of the turbine 108 and a stator blade tip which lies opposite the stator blade root. The stator blade tip faces the rotor 103 and is fastened on a fastening ring 140 of the stator 143.

On the control system side, the gas turbine 100 has a foreign-body detection system which is not shown in more detail according to the FIGURE. This serves for detecting foreign bodies penetrating the gas turbine 100 along with the air 135 or for detecting foreign bodies which have broken away due to damage in the turbine 100 and, if necessary, for initiating a rapid shutdown of the turbine 100. To this end, the foreign-body detection system comprises a structure-borne sound monitoring system which is connected to a multiplicity of sensors on the rotor 103 and housing 138 which emit output signals with regard to the acoustic vibrations which occur in the turbine 100.

Furthermore, the rotor 103 can be axially displaced along the axis 102. On account of the conicity of the tips of the rotor 103 and of the housing 138 in relation to each other, the gap d between rotor 103—especially the rotor blade tips—and the housing 138 is decreased or increased by an axial displacement of the rotor 103 or of the housing 138. The axial displacement is carried out hydraulically.

By an axial displacement of the rotor 103 in relation to the housing 138, the existing gap d is made narrower and until finally a first contact is made, leading to vibrations and therefore to the creation of sound. This sound is transmitted by the housing 138 and is detected by the structure-borne sound monitoring system and converted into corresponding output signals.

Depending on the axial displacement of the rotor blades 120 in relation to the housing 138, a contact of lesser or greater force is made between the turbine blades 120 and the housing 138, as a result of which the strength of the generated structure-borne sound, and therefore of the output signals, are also changed. In this way, different output signals are produced as a function of the value of the axial displacement.

If a first contact has been made, the stator blades 120 are fixed or—in the case of a contact of excessive force—shifted back again just until there is no longer a contact indicated by a corresponding output signal. A minimum gap d is then set. This setting of the minimum gap can be carried out during operation of the turbine 100, typically after it has warmed up.

The turbine blade 120 has an outer wear layer. The outer wear layer is porous and/or ceramic, for example, so that even a slight contact does not cause any permanent damage.

Claims

1.-10. (canceled)

11. A method for minimizing the gap between a rotor and a housing,

wherein the gap between rotor and housing is adjusted, by displacement of the rotor and the housing in relation to each other,

wherein an output signal of a structure-borne sound monitoring system, which is associated with the rotor and/or the housing, is used as a measure for the size of the gap and consequently for the setting of a minimum gap, and

wherein the structure-borne sound monitoring system is a component part of a foreign-body detection system of a turbine.

12. The method as claimed in claim 11,

in which the rotor is displaced in an axial direction in relation to the housing for adjusting the size of the gap.

13. The method as claimed in claim 11,

wherein the rotor is displaced just until there is no longer a contact between rotor and housing which generates output signals.

14. A turbine comprising a rotor and a housing, comprising

an adjusting device wherein the gap between rotor and housing can be adjusted by means of the adjusting device, by displacement of rotor and housing in relation to each other,

a structure-borne sound monitoring system associated with the rotor and/or the housing and on the output side connected to the adjusting device,

wherein the structure-borne sound monitoring system is a component part of a foreign-body detection system of a turbine.

15. The turbine as claimed in claim 14,

in which the rotor can be displaced in an axial direction in relation to the housing for adjusting the size of the gap.

16. The turbine as claimed in claim 14,

in which the rotor is at least partially abradable.

17. A power plant with a turbine as claimed in claim 14.