EP1048822B1 - Heat shield for a gas turbine - Google Patents

Description

TECHNICAL AREA

The present invention relates to the field of gas turbines. It relates to a heat shield for a gas turbine according to the preamble of claim 1

Such a heat shield is e.g. known from the document US-A-4,650,394. Further heat shields are known from the documents US-A-4,177,004, US-A-4,551,064, US-A-5,071,313, US-A-5,584,651 or EP-A1-0 516 322.

STATE OF THE ART

Heat shields for gas turbines, which surround the blades of a turbine stage annular and on the one hand limit the hot gas channel to the outside and On the other hand keep the gap between the outer wall of the hot gas channel and the ends of the blades for reasons of efficiency as small as possible without causing a sliding contact with changing temperatures, have long been known. Such heat shields usually consist of a plurality of circular segment-shaped curved heat shield segments, which are arranged one behind the other in the circumferential direction form a closed ring.

The individual heat shield segments are often releasably attached to a carrier which concentrically surrounds the heat shield. For reasons of different thermal expansion of the various items is taken to ensure that between the heat shield segments and the adjacent elements which define the hot gas channel to the outside, radial gaps or annular gap-shaped cavities.

The heat shield or the individual heat shield segments are exposed to a high thermal load during operation of the gas turbine. On the one hand, this thermal load can have negative effects on the heat shield itself. On the other hand, the heat can be directed by the shield to the outside and cause damage there. It is therefore usually taken precautions to cool the heat shield segments from the back or the outside by compressed cooling air, which usually comes from the compressor part of the gas turbine or the plenum, in a suitable manner. This cooling should be as even and efficient as possible and include all exposed areas of the heat shield. In addition, hot gas should be prevented from entering the adjacent column in the outer wall of the hot gas channel and undesirably heating the parts of the structure behind it.

In US-A-4,177,004 a heat shield for a gas turbine is disclosed (there Fig.1, 2 and 4), in which only on the downstream longitudinal side of the heat shield segments cooling air from the underlying cavity (52) through cooling holes (66) in the adjacent space (48) is sent and from There is passed through cooling grooves (67) in the clamp part (43) in the hot gas channel (Fig. 4, Fig. 5). The upstream longitudinal side of the heat shield segment (FIG. 3), on the other hand, is only surrounded externally by cooling air which flows in other ways into the cavity (62) lying behind it. This arrangement has the disadvantage that the heat shield segment is cooled unevenly overall, because on the upstream-oriented longitudinal side of the heat shield segment, a cooling from the back practically does not take place. A further disadvantage is that the cooling grooves (67) have been introduced into the clamping element (43), which leads to a considerable additional expenditure in terms of production technology.

Also in the solution described in US-A-4,551,064 (oblique) cooling holes (55) are arranged only in the region of the downstream longitudinal edge of the heat shield segment. Both adjacent to the heat shield segments column (64, 68) are flooded by cooling air streams (59 and 65 in Fig. 1), which are brought by separate holes (63, 67) from outside the heat shield.

In US-A-5,584,651 a heat shield is disclosed in which segments in the upstream edge an internal cavity (38) is formed (Figure 2) through which cooling air flows and through outlet ports (44) located directly at the edge exit the hot gas channel. On the other hand, no special cooling is provided in the downstream edge area or in the region of the area there, so that even in this case a very uneven cooling of the heat shield segments is to be expected. Particularly concerned are the downstream inner arms of the heat shield segments with the edges (28b in Fig. 1).

A somewhat further cooling is achieved by the cooling holes (80) extending further downstream in the case of the heat shield from EP-A1-0 516 322. However, here too the downstream longitudinal edge of the heat shields with the inner arms (44) is virtually uncooled.

PRESENTATION OF THE INVENTION

It is therefore an object of the invention to provide a heat shield for a gas turbine, which avoids the disadvantages of known heat shields and at the same time simple structure by efficient and uniform cooling over the entire thermally loaded surface of the heat shield segments and in particular on the longitudinal edges axially projecting inner Poor character.

The object is solved by the entirety of the features of claim 1. The essence of the invention is to guide on both longitudinal sides of the heat shields, so both upstream and downstream, from the lying behind the segments cavity cooling air through corresponding cooling holes in the adjacent column and so simultaneously and uniformly to cool the two longitudinal edge portions of the heat shield segments and to flood the column against ingress of hot gases. The entire cooling and flooding devices are arranged (in the form of cooling holes or cooling grooves) on the heat shield segment itself, which makes the production much easier and makes an adjustment of the other parts of the hot gas channel superfluous. The outflow of the cooling air on both longitudinal sides of the heat shield segments also has the consequence that the cooling air sweeps more uniformly over the outer sides of the segments delimiting the cavity and thus uniformly cools the entire segment surface. As a result, the thermal load is uniformly reduced over the entire surface and significantly extends the life of the heat shield segments.

This includes that the heat shield segments are fastened by means of brackets on the carrier, which engage with brackets with L-shaped inwardly bent ends from both sides under the support in the intermediate spaces formed between the pairs of arms that the effluent from the cooling holes cooling air in the spaces between the L-shaped inwardly bent ends of the brackets and the inner arms of the heat shield segments to the columns is guided, and that for guiding the emerging from the cooling holes cooling air in the outer sides of the inner arms to the cooling holes aligned cooling grooves are recessed. The cooling grooves in the inner arms increase the heat transfer area on the arms and substantially homogenize and improve the cooling of the arms (farthest from the cool air filled cavity).

A preferred embodiment of the heat shield according to the invention is characterized in that in order to reduce the bending of the heat shield during temperature changes on the outside of the heat shield segments in the region of the cavity axially extending stiffening ribs are arranged or formed, that spaced within the cavity and from the outside of the heat shield segments is arranged in the circumferential direction, provided with openings impingement cooling plate, and that within the stiffening ribs, radially outwardly projecting lugs or pins are arranged, on which the impingement cooling plate rests. The stiffening ribs with the formed tabs stiffen the heat shield segments in the axial direction and thereby reduce the risk of brushing the blades on the heat shield. They also improve the heat transfer between the segment and the cooling air flowing through the cavity. The lugs that serve to support the baffle plate, can be formed together with the stiffening ribs in a simple manner when casting the segments with.

An undesirable outflow of the cooling air from the gaps to the outside is effectively prevented if, according to a further preferred embodiment of the invention above the cooling holes between the brackets and the longitudinal sides of the heat shield segments first axial elastic seals are arranged.

Further embodiments emerge from the dependent claims.

BRIEF EXPLANATION OF THE FIGURES

Fig. 1

in einer teilweise längsgeschnittenen Darstellung in einem Ausschnitt die Anordnung eines Hitzeschildes in einer Gasturbine gemäss einem ersten bevorzugten Ausführungsbeispiel der Erfindung;

Fig. 2

den Querschnitt durch ein Segment des Hitzeschildes nach Fig. 1 (ohne Darstellung der Kühlbohrungen und -nuten);

Fig. 3

den Längsschnitt durch das Hitzeschildsegment nach Fig. 2 in der Schnittebene A - A;

Fig. 4

den Schnitt durch die Längskanten des Segmentes aus Fig. 3 in der Schnittebene B - B;

Fig. 5

den Schnitt durch die Längskanten des Segmentes aus Fig. 3 in der Schnittebene C - C;

Fig. 6

den zu Fig. 2 vergleichbaren Querschnitt durch eine Hitzeschildsegment gemäss einem weiteren bevorzugten Ausführungsbeispiel der Erfindung mit angeformter, rückseitiger, axialer Versteifungsrippe und Auflagepins für eine Prallkühlblech;

Fig. 7

den Schnitt durch das Hitzeschildsegment aus Fig. 6 in der Schnittebene B - B;

Fig. 8

den Schnitt durch das Hitzeschildsegment aus Fig. 6 in der Schnittebene A - A;

Fig. 9

das Hitzeschildsegment aus Fig. 6 mit aufliegendem Prallkühlblech;

Fig. 10

den Schnitt durch das Hitzeschildsegment aus Fig. 9 in der Schnittebene B - B; und

Fig. 11

ein anderes Ausführungsbeispiel eines Hitzeschildes nach der Erfindung mit mehrfachen axialen Dichtungen zur Verhinderung eines Kühlluftverlustes in den Spalten.

The invention will be explained in more detail with reference to embodiments in conjunction with the drawings. Show it

Fig. 1

in a partially cutaway view in a detail of the arrangement of a heat shield in a gas turbine according to a first preferred embodiment of the invention;

Fig. 2

the cross section through a segment of the heat shield of Figure 1 (without representation of the cooling holes and -nuten).

Fig. 3

the longitudinal section through the heat shield segment of Figure 2 in the sectional plane A - A.

Fig. 4

the section through the longitudinal edges of the segment of Figure 3 in the sectional plane B - B.

Fig. 5

the section through the longitudinal edges of the segment of Figure 3 in the sectional plane C - C;

Fig. 6

comparable to Figure 2 cross-section through a heat shield segment according to a further preferred embodiment of the invention with integrally formed, rear, axial stiffening rib and support pins for an impingement cooling plate.

Fig. 7

the section through the heat shield segment of Figure 6 in the sectional plane B - B.

Fig. 8

the section through the heat shield segment of Figure 6 in the sectional plane A - A.

Fig. 9

the heat shield segment of Figure 6 with resting impingement cooling plate.

Fig. 10

the section through the heat shield segment of Figure 9 in the sectional plane B - B. and

Fig. 11

another embodiment of a heat shield according to the invention with multiple axial seals for preventing a cooling air loss in the columns.

WAYS FOR CARRYING OUT THE INVENTION

In Fig. 1, the partially longitudinally-sectioned arrangement of a heat shield in a gas turbine 10 according to a first preferred embodiment of the invention is shown in a section. The figure shows a section of the (rotationally symmetrical) hot gas channel 11 of the gas turbine, which of the hot combustion gases from the (not shown) combustion chamber of the gas turbine flows through in the direction of the drawn four parallel arrows. In the hot gas duct 11 guide vanes 13 are arranged, which extend in the radial direction and merge at its outer end in an outer ring 14 which limits the hot gas channel 11 in the region of the guide vanes 13 outwardly. On the vanes 13 follow downstream blades 12 which are mounted on a (not shown) rotor of the gas turbine and rotate together with this around the turbine axis, when they are charged with the hot gas flowing in the hot gas channel 11 hot gas. Behind the ring of blades 12 can follow downstream more Leitschaufel- and blade rings, which need not be further referred to here. In any case, the hot gas channel 11 is bounded behind the blades 12 to the outside by an intermediate ring 15 or by a downstream vane.

The ring of the rotor blades 12 is surrounded concentrically by a heat shield, which is composed of a plurality of circular segment-shaped individual heat shield segments 17 arranged one behind the other in the circumferential direction. Such a heat shield segment 17 is shown in Fig. 1 within the overall arrangement and in Fig. 2 per se taken in cross section. The heat shield as a whole delimits the hot gas channel 11 in the region of the rotor blades 12 and at the same time determines the gap between the channel wall and the outer end of the rotor blades 12.

The individual heat shield segments 17 are curved plates, which have on their longitudinal sides, that is, the transversely oriented to the flow direction or the turbine axis sides, circumferentially extending, possibly provided with incisions, rails, each having a pair in the axial direction protruding, parallel and spaced apart arms 21, 22 and 23, 24 respectively (see also the comparable Fig. 3 of US-A-5,071,313). The heat shield segments 17 are fixed to form a cavity 20 on the inside of a concentrically encircling annular support 16. The attachment takes place in each case via two brackets 18 and 19, with the L-shaped inwardly bent ends from both sides under the support 16 in between engage the arm pairs 21, 22 and 23, 24 formed intermediate spaces 25 and 26 respectively. In order to have sufficient clearance for different thermal expansion, radial gaps 29 and 30 are left between the brackets 18 and 19 and the respective adjacent wall elements 15 and 14.

The cooling of the heat shield segments 17 takes place from the outside via the cavity 20. In this cavity compressed air from the plenum of the gas turbine is admitted to a (not shown) point, which then arranged by both sides of the heat shield segment 17 cooling holes 27, 28 in the interstices 25 and 26 between the arm pairs 21, 22 and 23, 24 flows out (see the curved arrows in the cavity 20 of FIG. 1). The cooling holes 27, 28 are arranged so that the cooling air between the inner sides (lower sides) of the L-shaped bent ends of the brackets 18, 19 and the outer sides (tops) of the inner arms 21, 23 outwardly into the gaps 29 and 30th flows and exits from there into the hot gas duct 11. Thus, the cooling air flow can take place largely unhindered, cooling grooves 31, 32 are recessed on the outer sides of the inner arms 21, 23 to the cooling holes 27, 28. Fig. 3 shows these cooling grooves 31, 32 in the plan view, Figs. 4 and 5 show the cooling grooves and cooling holes in cross section.

Due to the described type of cooling air guide several requirements are safely and easily met: Since the cooling air exits uniformly on both sides of the cavity 20, the bottom of the cavity 20 and the outside of the heat shield segment is uniformly and over the entire surface with cooling air applied, so that local overheating can be safely avoided. At the same time it is prevented that too much heat passes through heat conduction into the outer arms 22, 24 and from there into the carrier. Furthermore, the brackets 18, 19 are effectively cooled at their angled end, so that they also conduct only little heat to the outside. In addition, the inner arms 21, 23 are effectively protected against overheating. Finally, the leaking cooling air, the column 29, 30 flooded with cooling air, whereby an undesirable penetration of hot gas is reliably avoided in the column. In In this context, it is particularly favorable in terms of flow when the cooling bores 27, 28 and the cooling grooves 31, 32 aligned therewith - as can be seen in the illustration in FIG. 3 - in the plane of the heat shield segment 17 from the axial direction to the direction of rotation 42 of the blade 12 and gas turbine are arranged tilted out.

As already mentioned above, the position of the heat shield segments 17 decisively determines the gap between the heat shield and the outer end of the rotor blades 12. On the one hand, this gap should be as small as possible to minimize efficiency losses. On the other hand, the gap must be sufficiently large to avoid abrasive contact between the blades and heat shield at different temperatures and the associated different expansions of the elements as far as possible. In order to be able to keep the tolerances tight, it is advantageous to reduce the temperature-induced bending of the heat shield segments by arranging, as shown in FIGS. 6 to 10 on the outside of the heat shield segments 17 ', an axial stiffening rib 33 extending to the other longitudinal side. These stiffening ribs 33 can be advantageously formed when casting the heat shield segments 17 '.

It is particularly advantageous if projections and / or pins 34, 35 projecting radially outwards are also integrally formed with and within the stiffening ribs 33 at the same time, on which then an impingement cooling plate 36 circulating around the heat shield within the cavities 20 (FIG , 10) can support. The impingement cooling plate 36 can thus be placed close to the outside of the heat shield segments 17 'without special shaping, as a result of which the cooling effect of the cooling air flowing through the openings 37 in the impingement cooling plate 36 is markedly increased. At the same time increase the lugs or pins 34, the heat transfer surface and provide additional turbulence of the cooling air.

A further improvement of the cooling can be achieved or prevent a local overheating by an undesirable cooling air leakage, if undesirable Cooling air losses are effectively limited or completely avoided. For this purpose, as shown in FIG. 11 between the L-shaped bent ends of the brackets 18, 19 and the opposite longitudinal sides of the heat shield segments 17 axial elastic seals 39, 41 are provided which drain the flowing out of the cooling holes 27, 28 cooling air into the gaps between prevents the brackets 18, 19 and the carrier 16. Since the cooling air flows past the seals 39 directly, the seals are effectively cooled at the same time. Additional axial resilient seals 38, 40 disposed between the brackets 18, 19 and the carrier 16 further enhance the seal. On the one hand, the advantage of this sealed arrangement is that it prevents hot gas from breaking in and leading to local overheating. On the other hand, the cooling air leakage is minimized and the cooling air is used at the cooling points where it is actually required. The reduced leakage and the targeted use of cooling air lead to an improvement in the efficiency of the turbine stage or the machine as a whole.

LIST OF REFERENCE NUMBERS

10

gas turbine

11

Hot-gas duct

12

blade

13

vane

14

outer ring

15

intermediate ring

16

carrier

17.17 '

Heat shield segment

18.19

clip

20

Cavity (for cooling air)

21.22

poor

23.24

poor

25.26

gap

27.28

cooling hole

29.30

gap

31.32

cooling groove

33

Stiffening rib (axial)

34.35

Nose (pin)

36

Impingement plate

37

Opening

38-41

axial seal (elastic)

42

Direction of rotation (blade 12)

Claims (6)

1. Heat shield for a gas turbine (10), which heat shield encloses in an annular manner the moving blades (12), rotating in the hot-gas duct (11) of the gas turbine (10), of a stage of the gas turbine (10) and consists of a plurality of heat-shield segments (17, 17') which are arranged one behind the other in the circumferential direction, are curved in the shape of a segment of a circle and are cooled from outside, and the longitudinal sides of which are designed as correspondingly curved rails running in the circumferential direction and having in each case a pair of arms (21, 22 and 23, 24 resp.) which project in the axial direction, run in parallel and are at a distance from one another, the heat-shield segments (17, 17'), while forming a cavity (20) to which cooling air can be admitted, are fastened to the inside of an annular carrier (16), which concentrically surrounds the heat shield in such a way that in each case a radial gap (29, 30) is formed between the longitudinal sides of the heat-shield segments (17, 17') and the adjacent elements (14, 15) which define the hot-gas duct (11) on the outside, cooling holes (27, 28) being provided in both longitudinal sides of the heat-shield segments, through which cooling holes (27, 28) cooling air flows from the cavity (20) into the intermediate spaces (25, 26) formed between the arm pairs (21, 22 and 23, 24 resp.) and flows from there into the gaps (29, 30) and can counteract the ingress of hot gases from the hot-gas duct (11) into the gaps (29, 30), the heat-shield segments (17, 17') being fastened to the carrier (16) by means of clamps (18, 19), which, with ends bent inward in an L-shape, engage from both sides under the carrier (16) in the intermediate spaces (25, 26) formed between the arm pairs (21, 22 and 23, 24 resp.), and the cooling air flowing out of the cooling holes (27, 28) being directed in the intermediate spaces (25, 26) between the ends, bent inward in an L-shape, of the clamps (18, 19) and the inner arms (21, 23) of the heat-shield segments (17, 17') to the gaps (29, 30), characterized in that cooling slots (31, 32) in alignment with the cooling holes (27, 28) are made in the outsides of the inner arms (21, 23) in order to direct the cooling air discharging from the cooling holes (27, 28).
2. Heat shield according to Claim 1, characterized in that the cooling holes (27, 28) and cooling slots (31, 32) are arranged in the plane of the heat-shield segment (17, 17') in such a way as to slant away from the axial direction in the direction of rotation of the gas turbine (10).
3. Heat shield according to Claim 1 or 2, characterized in that, to reduce the deflection of the heat shield during temperature changes, axially running stiffening ribs (33) are arranged or integrally formed on the outside of the heat-shield segments (17, 17') in the region of the cavity (20).
4. Heat shield according to Claim 3, characterized in that an impingement-cooling plate (36) running in the circumferential direction and provided with openings (37) is arranged inside the cavity (20) and at a distance from the outside of the heat-shield segments (17, 17'), and in that individual lugs or pins (34, 35), which project radially outward and on which the impingement-cooling plate (36) is supported, are arranged inside the stiffening ribs (33).
5. Heat shield according to Claim 1, characterized in that, to prevent the cooling air from flowing off to the outside, first axial elastic seals (39, 41) are arranged above the cooling holes (27, 28) between the clamps (18, 19) and the longitudinal sides of the heat-shield segments (17, 17').
6. Heat shield according to Claim 5, characterized in that second axial, elastic seals (38, 40) are additionally arranged between the clamps (18, 19) and the carrier (16).

Images