CROSS REFERENCE TO RELATED APPLICATIONS
This application is the US National Stage of International Application No. PCT/EP2010/053917, filed Mar. 25, 2010 and claims the benefit thereof. The International Application claims the benefits of European application No. 09004469.4 filed Mar. 27, 2009. All of the applications are incorporated by reference herein in their entirety.
FIELD OF INVENTION
The invention refers to a sealing plate for forming a ring consisting of sealing plates for the rotor of a gas turbine, which sealing plate is formed principally from a multiplicity of metal sheets. In addition, the invention refers to a rotor blade system, especially for a gas turbine, having a number of rotor blades which are arranged annularly on a turbine disk, wherein a number of sealing plates are arranged on a side surface of the turbine disk. It furthermore refers to a gas turbine having such a rotor blade system.
BACKGROUND OF INVENTION
Gas turbines are used in many fields for driving generators or driven machines. In this case, the energy content of a fuel is utilized for producing rotational movement of a turbine shaft. To this end, the fuel is combusted in a combustion chamber, wherein compressed air is supplied from an air compressor. The operating medium, under high pressure and at high temperature, which is produced in the combustion chamber as a result of the combustion of the fuel, is directed in this case through a turbine unit—which is connected downstream to the combustion chamber—where it expands, performing work.
For producing the rotational movement of the turbine shaft, in this case a number of rotor blades, which are customarily assembled into blade groups or blade rows, are arranged on this shaft. In this case, a turbine disk, on which the rotor blades are fastened by means of their blade root, are customarily provided for each turbine stage. For flow guiding of the operating medium in the turbine unit, moreover, stator blades which are connected to the turbine casing and assembled to form stator-blade rows, are customarily arranged between adjacent rotor blade rows.
The combustion chamber of the gas turbine can be constructed as a so-called annular combustion chamber in which a large number of burners, which are arranged around the turbine shaft in the circumferential direction, open into a common combustion chamber space which is enclosed by a high temperature-resistant surrounding wall. To this end, the combustion chamber is designed in its entirety as an annular structure. In addition to a single combustion chamber, provision may also be made for a multiplicity of combustion chambers.
Usually connected directly to the combustion chamber is a first stator blade row of a turbine unit, which together with the immediately subsequent rotor blade row, as seen in the flow direction of the operating medium, forms a first turbine stage of the turbine unit, to which further turbine stages are customarily connected downstream.
In the design of such gas turbines, in addition to the achievable power, a particularly high efficiency is customarily a design aim. An increase of the efficiency can be achieved in this case, for thermodynamic reasons, basically by an increase of the exit temperature at which working medium discharges from the combustion chamber and flows into the turbine unit. In this case, temperatures of about 1200° C. to 1500° C. are aimed at and also achieved for such gas turbines.
With such high temperatures of the operating medium, however, the components and parts which are exposed to this are subjected to high thermal loads. In order to protect the turbine disk and the turbine shaft against penetration of hot operating medium, provision is made on the turbine disks for sealing plates—as known from EP 1 944 472 A1, for example—which are attached in a circular encompassing manner on the turbine disk on the surfaces normal to the turbine axis in each case. In this case, provision is customarily made in each case for one sealing plate per turbine blade on each side of the turbine disk. These overlap in a shingle-like manner and customarily have a sealing wing which extends up to the adjacent stator blade in each case in such a way that penetration of hot operating medium in the direction of the turbine shaft is avoided.
The sealing plates, however, fulfill even further functions. On the one hand, they form the axial fixing of the turbine blades by means of corresponding fastening elements, and on the other hand, they seal not only the turbine disk against penetration of hot gas from outside but also avoid escape of cooling air which is guided inside the turbine disk and is customarily passed on for cooling of the turbine blades themselves.
Such sealing plates with integrated sealing wing are customarily produced by vacuum investment casting (for example in the lost-wax investment casting process). In this case, a certain overmeasure is to be provided in order to be able to compensate for process-induced dimensional inaccuracies. Contingent upon geometry—the sealing plates having wide, very thin regions and mass accumulations in other places—warping and a certain porosity, especially in the thin regions, cannot be avoided in the vacuum investment casting. On account of the requirement profile of the sealing plates, these, however, can frequently be produced from alloys which, near net shape, cannot be produced in a process other than in the described vacuum investment casting.
For this reason, such sealing plates, after casting, must frequently be compressed at high temperatures and high pressure by means of hot-isostatic pressing for eliminating porosity and finally brought to the finished contour by means of time-consuming mechanical machining processes. For one thing, the described process with hot-isostatic pressing, mechanical after-machining and material loss associated therewith, is very time-consuming and costly in this case, and for another thing, even after the after-machining uneven mass distribution may continue to exist which may later severely limit the function of the sealing plate during operation and may involve losses with regard to the efficiency of the gas turbine.
It is also known from GB 947,553 to secure the rotor blades of a gas turbine against an axial displacement by means of solid cover rings. In this case, obliquely set baffle plates with openings are fastened on the cover rings, which openings are to capture the cooling air which is provided in the space next to the disk and to direct the cooling air to the rotor blades by means of openings which are arranged in the cover rings. In the case of this design, however, cast cover rings are again necessary.
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The invention is therefore based on the object of disclosing a sealing plate and a rotor blade system which, with a highest possible efficiency of a gas turbine, allows in each case a simplified construction at the same time.
This object is achieved according to the invention using a sealing plate according to the features of the independent claims.
The invention is based in this case on the consideration that a particularly simple producibility of the sealing plate would be achievable if the previously customary investment casting process with subsequent mechanical after-machining could be either simplified or completely replaced by another production process. In this case, casting processes other than the described vacuum investment casting are not a possibility on account of the selected materials for the sealing plates. Therefore, the sealing plate should not be produced in an archetypal process, such as casting, but in a forming process. In order to be able to realize the complex shape of the sealing plates during this, the sealing plates should be produced from a multiplicity of basic parts by means of forming. This can be achieved in a particularly simple manner by forming of prefabricated metal sheets, that is to say the sealing plate should be produced from a multiplicity of metal sheets. The sealing plate in this case comprises two metal sheets which are arranged a distance apart and parallel to the plane of the sealing plate. These form the respective end faces of the sealing plate and via the distance between the two metal sheets the thickness of the sealing plate can be accurately selected. In this case, a gap remains between the metal sheets and can be utilized for conducting cooling air and therefore for internal cooling of the sealing plate. On the one hand, a particularly simple construction of the sealing plate is therefore possible, and on the other hand, as a result of active component cooling, the sealing plate can stand up to the most adverse circumstances during operation so that particularly high temperatures during operation of the gas turbine become possible and therefore particularly high efficiency is achieved.
In an advantageous development, an intermediate metal sheet with a number of cutouts is arranged between the metal sheets in this case. Such an intermediate metal sheet stabilizes the connection between the metal sheets of the sealing plate which function as end faces and enables a precise, specific choice of the distance. As a result of the cutouts in the intermediate metal sheet, in this case a conducting of cooling air through the interior of the sealing plate still remains possible with the described advantages.
The respective metal sheet, on the side facing the middle of the turbine disk, advantageously has a bend in this case. Such a bend, which can be simply produced by forming, enables the sealing plate to be fixed in a groove provided for it on the side facing the middle of the turbine disk and so to ensure a secure retention of the sealing plate and of the rotor blades on the turbine disk. This offers the advantage that despite the altered construction of the sealing plate the previously used fastening devices on the turbine disk do not have to be modified and therefore a particularly simple construction of the rotor blade system with sealing plate and turbine disk is possible. In order to ensure a particularly simple feed and supply of the sealing plate with cooling air, the respective metal sheet advantageously has a number of cooling air holes. On the inlet side, the cooling air holes should be facing the turbine disk in this case so that a cooling air feed through the turbine disk into the sealing plate is possible, and on the outlet side provision should be made for cooling air holes which point towards adjacent components or attached metal sheets of the sealing plate, for example, so that active cooling of these components is also possible.
In order to safeguard the function of sealing wings for sealing the regions lying between two turbine disks against penetration of hot gas from the hot gas passage of the gas turbine, the sealing plate advantageously comprises a metal sheet which points from the plane of the sealing plate. This should reach up to the adjacent rotor blade row and so prevent penetration of hot gas in the direction of the turbine shaft in order to protect the components which are provided there.
In an advantageous development, the various metal sheets are welded and/or soldered to each other. As a result, a particularly simple construction of the sealing plate consisting of a multiplicity of metal sheets is possible.
The construction of the sealing plate which is achieved in this way, especially with a triple-layer design with two metal sheets forming the end faces and an intermediate metal sheet with cutouts for cooling air, is in a position to provide a tongue-in-groove connection for sealing a plurality of sealing plates, lying next to each other, in the circumferential direction. To this end, a groove and/or a tongue is advantageously arranged in the region of an edge of the respective sealing plate. Such a groove, in the case of a triple-layer design of the sealing plate in the style described above is simply possible by shortening the intermediate metal sheet on the edge or a tongue is possible by lengthening the intermediate metal sheet on the edge. As a result, a particularly good and simple to realize seal in the circumferential direction between a plurality of sealing plates is possible.
A gas turbine advantageously comprises such a rotor blade system and also a gas and steam turbine plant comprises a gas turbine with such a rotor blade system.
The advantages which are achieved using the invention are especially that as a result of the construction of the sealing plate by means of a multiplicity of metal sheets a particularly simple design and construction of the sealing plate become possible. The production costs and material costs are low in this case in comparison to other methods. As a result of the flexible material pairing, the material use and costs arising therefrom can be reduced. After-machining of the large plane surfaces—as is necessary in the case of the casting process—is not necessary when using preformed metal sheets, wherein a particularly good sealing effect of the sealing plate during operation is still achieved. As a result of this, and as a result of the active component cooling by means of conducting cooling air in the sealing plate, lower restrictions for the hot gas temperature in a gas turbine ensue and a higher efficiency can be achieved overall.
BRIEF DESCRIPTION OF THE DRAWINGS
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An exemplary embodiment of the invention is explained in more detail with reference to a drawing. In the drawing:
FIG. 1 shows a half-section through a rotor blade system,
FIG. 2 shows a section through a sealing plate after the casting process,
FIG. 3 shows a cross section through a sealing plate after mechanical after-machining,
FIG. 4 shows a cross section through a sealing plate which is produced from a plurality of metal sheets,
FIG. 5 shows a top view of an intermediate metal sheet for a sealing plate,
FIG. 6 shows a top view of a sealing plate which is produced from a multiplicity of metal sheets, and
FIG. 7 shows a half-section through a gas turbine.
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Like parts are provided with the same designations in all the figures.
FIG. 1 shows a rotor blade system 1 as a section through the outer circumference of a turbine disk 6, attached on a turbine shaft, of a rotor blade stage of a gas turbine according to the prior art.
A rotor blade 12 is arranged in a rotor blade retaining slot 30 by its blade root 32 in this case. The blade root 32 of the rotor blade 12 is of a firtree shape in cross section and corresponds to the firtree shape of the rotor blade retaining slot 30. The schematic representation of the contour of the rotor blade root 32 and that of the rotor blade retaining slot 30 is reproduced in a manner rotated by 90° compared with the rest of the view of FIG. 2. Therefore, the depicted rotor blade retaining slot 30 extends between the side surfaces 34 of the turbine disk 6.
Adjacently provided in each case are stator blades 36, not shown in more detail, which are arranged upstream and downstream of the rotor blade 12—as seen in the flow direction of the operating medium of the gas turbine. The stator blades 36 are arranged radially in rings in this case.
On both sides of the turbine disk 6, sealing plates 40 are inserted in each case on the sidewalls 34 in an encompassing shingle-like manner. These are retained by their upper side in a groove 42 which is introduced into the rotor blade 12 and by their lower side are fixed by means of a locking bolt, which is not shown in more detail.
The sealing plates 40 fulfill a plurality of tasks in this case. On the one hand, by means of added-on sealing wings 46, which extend essentially in the axial and azimuthal directions, they seal the gap between turbine disk 36 and adjacent stator blades 36 against penetration of hot operating medium M from the turbine. On the other hand, the sealing plates 40 also ensure axial fixing of the blade root 32 in the rotor blade retaining slot 30 and so secure these against axial displacement. The axial and azimuthal securing is already achieved as a result of the firtree shape of the rotor blade retaining slot 30. Furthermore, the sealing plates 40 prevent escape of cooling air which is introduced through cooling air passages 48, via the turbine disk 36, into the blade root 32 and into the rotor blade 12.
FIGS. 2 and 3 schematically show a cross section perpendicular to the plane 49 of a sealing plate 40 according to the prior art in two different stages of the production process.
The sealing plate 40 in this case, as shown in FIG. 2, is first cast with a specific dimension. In this case, a vacuum investment casting process is customarily used and then the sealing plates 40, after casting, are compressed by means of hot-isostatic pressing for eliminating porosity. A mechanical after-machining is then carried out in order to bring the sealing plate 40 to the finished contour shown in FIG. 3.
Such a production process is relatively time-consuming and cost-intensive. In order to simplify the production process for the sealing plate 40, the sealing plate 40 should therefore be produced from a multiplicity of metal sheets 50, as shown in FIG. 4.
The sealing plate 40 according to FIG. 4 in this case initially comprises two metal sheets 50, which are arranged a distance apart parallel to the plane 49 of the sealing plate, between which an intermediate metal sheet 52 is introduced. Therefore, a triple-layer construction of the sealing plate 40 is created as a whole. On the side facing the middle of the rotor disk, the metal sheets 50 comprise bends 54 in this case, which simulate the previously cast shape of the sealing plate 40. The intermediate metal sheet 52 is not solidly constructed but comprises a number of cutouts 56 which are also shown in top view in FIG. 5. As a result, a feed of cooling air K through cooling air holes 58 is possible, enabling active cooling of the sealing plate 40.
Furthermore, the sealing plate 40 comprises a metal sheet 50 which points from the plane 49 of the sealing plate, faulting a sealing wing 46. For stabilizing the sealing wing, a further supporting metal sheet 60 is provided in this case. The cooling air holes 58 are oriented on the discharge side so that cooling air K which discharges from the sealing plate 40 flows onto, and so also cools, the sealing wing 46 and additional adjacent components.
The individual metal sheets 50 are welded to each other, which enables a particularly simple construction of the sealing plate 40. Alternatively, the metal sheets 50 can also be high-temperature soldered.
The sealing plate 40 is shown once more in top view in FIG. 6. In this case, the intermediate metal sheet 52 is displaced in the circumferential direction in relation to the two metal sheets 50 which are oriented in parallel so that on one edge 62 of the sealing plate 40 a groove 64 is formed and on the opposite edge 66 a tongue 68 is formed. As a result, adjacent sealing plates 40 can be sealed in the circumferential direction by means of a tongue-in-groove connection.
A gas turbine 101, as shown in FIG. 7, has a compressor 102 for combustion air, a combustion chamber 104 and also a turbine unit 106 for driving the compressor 102 and for driving a generator or a driven machine, which is not shown. To this end, the turbine unit 106 and the compressor 102 are arranged on a common turbine shaft 108 which is also referred to as a turbine rotor to which the generator or the driven machine is also connected, and which is rotatably mounted around its center axis 109. The combustion chamber 104 which is constructed in the style of an annular combustion chamber is equipped with a number of burners 110 for combusting a liquid fuel or gaseous fuel.
The turbine unit 106 has a rotor blade system 1 having a number of rotatable rotor blades 12 which are connected to the turbine shaft 108. The rotor blades 12 are arranged on the turbine shaft 108 in a ring-like manner and therefore form a number of rotor blade rows. Furthermore, the turbine unit 106 comprises a number of fixed stator blades 36 which are also fastened in a ring-like manner on a stator blade carrier 110 of the turbine unit 106, forming stator blade rows. The rotor blades 12 in this case serve for driving the turbine shaft 108 as a result of impulse transfer from the operating medium M which flows through the turbine unit 106. The stator blades 36 on the other hand serve for flow guiding of the operating medium M between two consecutive rotor blade rows or rotor blade rings in each case, as seen in the flow direction of the operating medium M. A consecutive pair, consisting of a ring of stator blades 36 or a stator blade row and a ring of rotor blades 12 or a rotor blade row, in this case is also referred to as a turbine stage.
Like the rotor blades 12, each stator blade 36 has a blade root 118 which, as a wall element, is arranged for the fixing of the respective stator blade 36 on the stator blade carrier 110 of the turbine unit 106. The blade root 118 in this case is a thermally comparatively heavily loaded component which forms the outer limit of a hot gas passage for the operating medium M which flows through the turbine unit 106.
Between the platforms 118—which are arranged at a distance from each other—of the stator blades 36 of two adjacent stator blade rows, a ring segment 121 is arranged in each case on a stator blade carrier 110 of the turbine unit 106. The outer surface of each ring segment 121 is also exposed in this case to the hot operating medium M which flows through the turbine unit 106 and by means of a gap is at a distance in the radial direction from the outer end of the rotor blades 12 which lie opposite it. The ring segments 121 which are arranged between adjacent stator blade rows serve in this case especially as cover elements which protect the inner casing in the stator blade carrier 110, or other installed components in the casing, against theimal overstress as a result of the hot operating medium M which flows through the turbine 106.
The combustion chamber 104 is designed as a so-called annular combustion chamber in the exemplary embodiment, in which a multiplicity of burners 110, which are arranged circumferentially around the turbine shaft 108, open into a common combustion chamber space. For this, the combustion chamber 104 is designed in its entirety as an annular structure which is positioned around the turbine shaft 108.
A sealing plate 40 for a rotor blade system 1, which is produced from various metal sheets 50, offers on the one hand a particularly simple and inexpensive production, and on the other hand a particularly high efficiency of a gas turbine 101 can be achieved as a result of the active component cooling.