Gas turbine with a stator blade

A gas turbine with a stator blade is disclosed. The stator blade is fastened on a blade carrier and includes a blade airfoil which extends inwards in the radial direction from an outer platform into a hot gas passage. A cooling medium can flow through an interior of the blade airfoil, such as cooling air, which flows through an access in the blade carrier into a first plenum which is arranged above the outer platform, and from there, via an inlet which is provided in the outer platform, flows into the interior of the blade airfoil.

RELATED APPLICATIONS

This application claims priority as a continuation application under 35 U.S.C. §120 to PCT/EP2009/055768, which was filed as an International Application on May 13, 2009, designating the U.S., and which claims priority to Swiss Application 00790/08 filed in Europe on May 26, 2008. The entire contents of these applications are hereby incorporated by reference in their entireties.

FIELD

The disclosure relates to the field of gas turbine technology, in particular, a gas turbine with a stator blade.

BACKGROUND INFORMATION

Gas turbines with sequential combustion are known and have been useful in industrial operation.

A gas turbine, known as GT24/26, is disclosed, for example, in an article by Joos, F. et al., “Field Experience of the Sequential Combustion System for the ABB GT24/GT26 Gas Turbine Family”, IGTI/ASME 98-GT-220, 1998 Stockholm. FIG. 1 of this publication is reproduced in the present application asFIG. 1. Furthermore, such a gas turbine is disclosed in EP-B1-0 620 362.

FIG. 1shows a gas turbine10with sequential combustion, in which a compressor11, a first combustion chamber14, a high-pressure turbine (HPT)15, a second combustion chamber17and a low-pressure turbine (LPT)18are arranged along an axis19. The compressor11and the two turbines15,18are part of a rotor which rotates around the axis19. The compressor11draws in air and compresses it. The compressed air flows into a plenum and from there into premix burners where this air is mixed with at least one fuel which is introduced via the fuel supply12. Such premix burners are disclosed, for example, in EP-A1-0 321 809 and EP-A2-0 704 657.

The compressed air flows into the premix burners, where the mixing with at least one fuel takes place. This fuel/air mixture then flows into the first combustion chamber14, in which this mixture can be combusted, forming a stable flame front. The hot gas which is thus made available is partially expanded in the adjoining high-pressure turbine15, performing work, and then flows into the second combustion chamber17where a further supply16of fuel can take place. As a result of the high temperatures which the hot gas, which is partially expanded in the high-pressure turbine15, still has, a combustion, which is based on self-ignition, takes place in the second combustion chamber17. The hot gas which is reheated in the second combustion chamber17is then expanded in a multistage low-pressure turbine18.

The low-pressure turbine18includes a plurality of rows, arranged in series in the flow direction, of rotor blades and stator blades, which can be arranged in alternating sequence. For example, the stator blades of the third stator blade row in the flow direction are provided with the designation20′ inFIG. 1.

With the high hot-gas temperatures of gas turbines of the latest generation, it is desirable to cool the stator blades and rotor blades of the turbine. For this, a gaseous cooling medium (for example compressed air from the compressor of the gas turbine or steam if the gas turbine is part of a combined cycle power generating plant) can be delivered through cooling passages (frequently extending in a serpentine manner) which can be arranged in the blade, and/or discharged outwards at different points of the blade through corresponding openings (holes, grooves), for example, to form a cooling film on the outer side of the blade (film cooling). An example of such a cooled blade is disclosed in U.S. Pat. No. 5,813,835.

Cooling of the platforms, in particular the outer platform of a gas-turbine stator blade, in which special cooling holes and impingement cooling techniques are used, is known, for example, from printed publication DE-A1-10 2005 013 795. Such cooling devices and cooling techniques, however, require a comparatively high production and installation outlay.

SUMMARY

A gas turbine is disclosed including a stator blade fastened on a blade carrier. The stator blade includes a blade airfoil which extends inwards in a radial direction from an outer platform into a hot gas passage. An access in the blade carrier into a first plenum is arranged above the outer platform for a cooling medium to flow, via an inlet provided in the outer platform, into an interior of the stator blade. A first means controls the cooling-medium pressure in the first plenum. A second means cools the outer platform by directing the cooling medium from the first plenum.

DETAILED DESCRIPTION

The disclosure relates to the case of the gas-turbine stator blade, to provide simplified and efficient cooling of the outer platform.

In an exemplary embodiment of the disclosure first means for controlling controls a cooling-medium pressure in a first plenum above an outer platform of a stator blade and second means effects cooling of the outer platform by a cooling medium which escapes in a directed manner from the first plenum. As a result of this, leakage cooling medium which escapes in a directed manner can be used for cooling the outer platform before it flows out into the hot gas passage.

According to the disclosure, the first means can be arranged in the region of the first plenum. The first means includes a throttling element which throttles the flow of cooling medium through the inlet in the outer platform. The throttling element can be formed as a plate which covers the inlet except for one or more, for example circular, throttling openings which are provided in the plate.

In an exemplary embodiment of the disclosure, access to the first plenum can be formed as a throttling opening. As a result of the throttling devices, the pressure in the first plenum and leakage of the cooling medium from the plenum can be adjusted.

Two outwardly projecting, for example, hook-like fastening elements, for fastening the stator blade on the blade carrier, can be formed on the upper side of the outer platform at a distance from each other. The first plenum can be formed between the two fastening elements.

The second means can include a second plenum which can be arranged on the side of the one fastening element facing away from the first plenum. The second plenum can be supplied from the first plenum with cooling medium which escapes from there, and the second plenum can be in communication with the hot gas passage via throttling means.

Furthermore, the gaps which exist between adjacent stator blades of a stator-blade row can be sealed against the hot gas passage by sealing strips which can be inserted in corresponding sealing grooves in the lateral surfaces of the outer platforms of the stator blades. The sealing strips can be formed as throttling means in the region of the second plenum and in the region of the second plenum can be formed shorter and/or considerably thinner than the associated sealing grooves for achieving a throttling effect.

In an exemplary embodiment of the disclosure the second plenum can be partially delimited by a heat shield segment which is adjacent to the outer platform of the stator blade in the flow direction of the hot gas flow. A stepped gap, via which the second plenum is in communication with the hot gas passage, can be arranged between the heat shield segment and the outer platform towards the hot gas passage.

FIG. 2shows in a perspective side view, an exemplary embodiment of a stator blade which, for example, can be used in the low-pressure turbine of a gas turbine with sequential combustion according to the disclosure.

The disclosure, however, is not limited to a said gas turbine type nor to a special stator blade or rotor blade.

The stator blade20can include a blade airfoil22which can be sharply curved in space and in the longitudinal direction (in the radial direction of the gas turbine) extends between blade tip23and an outer platform21and in the direction of the hot gas flow30reaches from a leading edge27to a trailing edge28. Between the two edges27and28, the blade airfoil22can be delimited on the outside by a suction side29and an (oppositely disposed) pressure side (not to be seen inFIG. 2).

The stator blade20, by a hook-like fastening elements24and25which are formed on the upper side of the outer platform21, can be fastened on the blade carrier (38inFIG. 5), while by the blade tip23it butts against the rotor with sealing effect. The space between the fastening elements24and25, in the installed state of the stator blade (FIG. 5), forms a first plenum (41) for the cooling air, while on the other side of the fastening element25, in the installed state of the stator blade (FIG. 5), a pronounced hollow31can be made a second plenum (42). Sealing grooves, which accommodate sealing strips for sealing the gaps between adjacent stator blades of a blade ring, can be arranged in the lateral surfaces of the upper platform21. A core exit32, which results in the outer platform21from the casting process, is closed off in a flush and therefore flow-favorable manner by a sealing plug, which is not shown in more detail.

Provision is made in the interior of the blade airfoil22for cooling devices (cooling passages, cooling ribs, impingement cooling elements, etc.) (not shown in the figures) which according toFIG. 4can be used with an inlet36in the upper platform21with a cooling medium (cooling air). The cooling medium which flows into the blade can originate from the first plenum41above the outer platform (FIG. 6), into which plenum it finds its way through a throttling opening43in the blade carrier38.

As is evident fromFIGS. 3 and 4, the comparatively large cross section of the inlet36can be closed off by a plate-like throttling element34which is inserted in a flush manner and frees one (seeFIG. 4, item35) or more throttling openings of smaller diameter (seeFIG. 5, item35a). By matching the two free cross sections of the throttling openings35or35aand43to one another, the pressure of the cooling medium51in the first plenum can be efficiently controlled and adjusted. At the same time, the adjusted pressure brings about a directed (controlled) leakage of the cooling medium51cfrom the first plenum41into the adjacent second plenum42and to the part of the outer platform21which forms the wall of the hot gas passage44. As a result of this, the outer platform21, without further constructional measures, can be cooled in a simple, reliable and easily adjustable manner by leakage cooling medium51a-51dfrom the cooling of the blade airfoil (curved arrows inFIG. 6).

The use of the cooling medium which has flown into the second plenum42for cooling the outer platform21can be influenced by two measures which can be seen more clearly inFIGS. 7 and 8: A sealing strip46can be inserted in the sealing groove26beneath the second plenum42and can be formed shorter and/or considerably thinner than the associated sealing groove26(FIG. 8) for achieving a throttling effect. As a result of this, cooling medium can escape in a directed manner from the second plenum42through the gap, which can be sealed with a throttling effect, between adjacent outer platforms21into the hot gas passage and can cool the outer platforms. If the sealing strip is thin, provision can be made for corrugations49,50distributed in the base section48of the strip which is provided with an additional angled section47, in order to fix the position of the sealing strip46in the sealing groove26(FIG. 8).

A stepped gap45, via which the second plenum42is in communication in a directed manner with the hot gas passage44, can be arranged towards the hot gas passage44between a heat shield segment39—which is adjacent to the outer platform21of the stator blade20, lies opposite a rotor blade40, and partially delimits the second plenum42—and the outer platform21. The geometry of the stepped gap45in this case can be such that by two gap widths s1and s2and a distance x (FIG. 7), wherein s1can lie within the range of between 0.1 and 2 mm, s2lies between s1and 0.1 to 1 mm, and x lies within the range of between 0.2 mm and 7 mm.

LIST OF DESIGNATIONS