EP0903468B1 - Gap sealing device - Google Patents

Description

Technical field

The invention relates to a device for sealing the gap between the Blades and the conical contoured housing one Turbo machine, the blades being provided with circumferential cover plates are, which form radial gaps against the one provided with sealing strips Seal housing.

State of the art

Such devices are known. They make a smooth or stepped Half-labyrinth with pure radial gaps. Such a seal is later on in the descriptive Fig. 2 shown.

• Die dabei gebildete grosse Kavität im Eintrittsbereich der Dichtung bewirkt einen ungünstigen Queraustausch von Strömungsmaterial mit der Hauptströmung im Schaufelkanal. Dieser Queraustausch ist begünstigt durch die in der Ebene der Schaufelvorderkante ausserordentlich grosse Schwankung der Druckdifferenz zwischen zwei benachbarten Schaufeln. Ausserdem wird in diesem Bereich durch die Hauptströmung und die Seitenwand des Deckbandes ein starker Wirbel angetrieben. Zur Verminderung der nachteiligen Wirkungen einer grossen Eingangskavität wird gemäss der in US 4662820 beschriebenen Lösung dieser Raum durch Anordnung eines Festkörpers, beispielsweise in Form eines eingesetzten Rings oder als Bestandteil des Stators, ausgefüllt. Allerdings unterliegt die Auslegung engen, durch die Differenzdehnungen zwischen Rotor und Stator gesetzten Grenzen. Um ein Anstreifen sicher auszuschliessen, muss der verbleibende Spalt stets ausreichend gross belassen werden. Insbesondere in den Niederdruckteilen von Kondensationsdampfturbinen, die durch erhebliche radiale und axiale Differenzdehnungen gekennzeichnet sind, verbleiben daher zwangsläufig relativ grosse Kavitäten.
• Wenig wirksam ist das Halb-Labyrinth mit den Dichtstreifen, mit denen das Gehäuse versehen ist und die gegen das umlaufende Deckband dichten, wie beispielsweise in der vorgenannten US-Druckschrift wiedergegeben. Dies, weil bei den vorliegenden Verhältnissen das Betriebsspiel eine Grösse von ca. 1/3 der freien Kammerhöhe aufweisen muss. Auch mehrere Dichtstreifen sind deshalb nicht wesentlich effektiver als ein einziger.
• Schliesslich erlaubt auch die grosse Kavität im Austrittsbereich der Dichtung einen unerwünschten Queraustausch mit der Hauptströmung im Schaufelkanal, da auch hier die Druckdifferenz zwischen zwei benachbarten Schaufelspitzen grossen Schwankungen unterliegt. Zudem geht in diesem Bereich die Führung der Hauptströmung vollständig verloren.
• Von Nachteil ist ausserdem bei diesen Dichtungen der hinter den aussen liegenden Dichtstreifen gebildete grosse Wirbelraum, welcher eine grosse Dissipation der austrittsseitigen Spaltströmung bewirkt.

As a result of better efficiency and greater reliability, this type of gap seal is now also used in the blades of the penultimate stage of condensation steam turbines. The mechanical requirements are quite high with circumferential speeds of 450 m / sec, while the thermal conditions are modest at around 90 ° C. The geometric requirements are problematic. On the one hand because of the strong taper, which leads to deep cavities of the known sealing device in the housing wall; on the other hand because of the large differential expansion between the rotor and the housing, which leads to wide cavities with the above-mentioned half-labyrinths.

• The large cavity formed in the inlet area of the seal causes an unfavorable cross exchange of flow material with the main flow in the blade channel. This cross exchange is favored by the extraordinarily large fluctuation in the pressure difference between two adjacent blades in the plane of the blade leading edge. In addition, a strong vortex is driven in this area by the main flow and the side wall of the shroud. To reduce the disadvantageous effects of a large entrance cavity, according to the solution described in US Pat. No. 4,662,820, this space is filled by arranging a solid, for example in the form of an inserted ring or as part of the stator. However, the design is subject to narrow limits set by the differential expansion between the rotor and stator. The remaining gap must always be left sufficiently large in order to ensure that it cannot be touched. Particularly in the low-pressure parts of condensation steam turbines, which are characterized by considerable radial and axial differential expansions, relatively large cavities inevitably remain.
• The semi-labyrinth with the sealing strips with which the housing is provided and which seal against the circumferential shroud, as shown for example in the aforementioned US publication, is not very effective. This is because, given the prevailing conditions, the operating clearance must be around 1/3 of the free chamber height. This means that several sealing strips are not much more effective than one.
• Finally, the large cavity in the outlet area of the seal also permits undesired cross-exchange with the main flow in the blade channel, since here too the pressure difference between two adjacent blade tips is subject to large fluctuations. In addition, the guidance of the main flow is completely lost in this area.
• Another disadvantage of these seals is the large swirl space formed behind the outer sealing strips, which causes a large dissipation of the gap-side flow on the outlet side.

To keep the gap losses as low as possible and the games very low to design, labyrinth seals are also known, in which the The cover band of the blades seals against a honeycomb arrangement. there Prongs of the cover tape form either a smooth or a stepped labyrinth with pure radial gaps or, as discussed in EP 0536575, with radial and Diagonatspalten. A brush against certain transient operating phases is relatively unproblematic in this type of gap seals, since the Honeycomb inserts are made of an abradable material. in case of a When rubbed, there is a local abrasion of the wear layer, the then, however, in the case of flow channels of pronounced conicity among the important stationary nominal operating conditions again large column and so that big company games can result.

Presentation of the invention

The invention seeks to remedy this. It is based on the task To provide blades of the type mentioned a labyrinth seal that the operational play further reduced and large cavities in the entrance area of the Seal avoids.

This is according to the invention with the characterizing features of the patent claim 1 reached.

The advantage of the invention can be seen, inter alia, in the fact that the new Seal only small amounts of gap occur. In addition, a good introduction of the Crevice flow reached in the main flow.

Brief description of the drawing

In the drawing, an embodiment of the invention is based on the penultimate Stage of an axially flow-through condensation steam turbine is shown.

Fig. 1 ;

einen Teillängsschnitt einer Niederdruck-Dampfturbine mit Deckplattendichtung;

Fig. 2

einen Teillängsschnitt der Laufschaufelspitze der vorletzten Stufe mit Deckplattendichtung gemäss Stand der Technik;

Fig. 3

einen Teillängsschnitt der Laufschaufelspitze der vorletzten Stufe mit Deckplattendichtung gemäss Erfindung;

Fig. 4 und 5

einen Teillängsschnitt der Laufschaufelspitze der vorletzten Stufe mit einer Deckplatten-Ausführungsvariante;

Fig. 6

einen Teillängsschnitt der Laufschaufelspitze einer Stufe mit schwacher Konizität mit einer Deckplatten-Ausführungsvariante;

Fig. 7

einen Teillängsschnitt der Laufschaufelspitze einer Stufe mit starker Konizität mit einer Deckplatten-Ausführungsvariante.

Show it:

Fig. 1;

a partial longitudinal section of a low-pressure steam turbine with cover plate seal;

Fig. 2

a partial longitudinal section of the blade tip of the penultimate stage with cover plate seal according to the prior art;

Fig. 3

a partial longitudinal section of the blade tip of the penultimate stage with cover plate seal according to the invention;

4 and 5

a partial longitudinal section of the blade tip of the penultimate stage with a cover plate embodiment;

Fig. 6

a partial longitudinal section of the blade tip of a step with weak taper with a cover plate embodiment;

Fig. 7

a partial longitudinal section of the blade tip of a step with strong taper with a cover plate design variant.

They are only the elements essential for understanding the invention shown. The direction of flow of the working fluid is indicated by arrows.

Way of carrying out the invention

According to the figure. 1 are the middle three, each from a leading row Le and a running row The existing stages of low-pressure blading are shown. The Level Le3 / La3 corresponds to the penultimate level. The one with her feet 21 in Rotations of the rotor 9 used blades La are at their Blade ends provided with cover plates 16. The radially outer contours of the Depending on the row, cover plates are geometrically differently graded. Under Formation of labyrinths 15 seal with their steps against sealing strips, which are arranged in a suitable manner in the stator 8. The with their feet 13 in Turnings of the stator 8 inserted guide blades Le are on their Provide blade ends with cover plates 20. Forming labyrinths 19 they also seal against sealing strips which are arranged in the rotor 9 in a suitable manner are.

The flow through channel 50 has the conically extending as the starting position outer contour 51 on the stator and the cylindrical inner contour 11 on the rotor. However, neither is mandatory. Regardless of the actual course in any case, the walls become the outer flow-restricting one Contour 10 in the area of the airfoil through the channel facing Cover plate 16 of the blades La formed. Immediately upstream of the Cover plates 16, 20 are axial gaps 18, which are the labyrinth entrances 40 represent. Immediately downstream of these cover plates 16, 20 are Radial gaps 26, which represent the labyrinth outlets 42. Usually on the other hand, the mentioned gaps are limited by stator parts, which the Take over flow guidance in the non-bladed levels.

In Fig. 2 is the cover plate seal of the row La3, as the beginning corresponds to the prior art mentioned. It essentially exists from the cover plate 16A, which extends over the entire blade width and with their outer diameter and the four sealing strips caulked in the stator 8A 17A forms a half-labyrinth with pure radial gaps. The are recognizable spacious labyrinth entry 40A and the unfavorably designed labyrinth exit 42A. With 54 the channel wall is designated when it is in a tap empties.

As shown in Fig. 3, according to the invention, both the geometry of the shroud and its embedding in the stator improved.

To the cross exchange of flow material and the vortex intensity too reduce, the radial cavity at the labyrinth entrance in its radial Extension into two partial cavities 40a and 40c, which are offset axially with respect to one another divided, that is in the example with approximately horizontal, am Free end curved sealing strip 52 equipped. For this, the contour runs in the stator 8 initially radially outwards and against the flow direction, then downstream in the axial direction, forming a protruding into the cavity Jagged 41. The cover plate 16 is configured accordingly. You will be with provided with an understitch 43 which is adapted to the shape of the prongs. The axial The running part of the backstitch is dimensioned in such a way that during the assembly and during the operating transient cover plate and Do not touch the stator. With approximately horizontal in its first section running and then curved sealing strips 52 are the individual Partial cavities 40a and 40c sealed. These sealing strips 52 are preferred with its horizontally running section in the axially running housing parts caulked. A comparison with Fig. 2 shows that in the operating position a much smaller passage gap 18 between the stator and Cover plate adjusts. The flow forms within the partial cavity 40c damping vortex chamber 22.

Furthermore, the known half-labyrinth is through after this embodiment replaced a full maze. For this purpose, the outer diameter of the cover plate 16 stepped and provided with only two throttling points. Two caulked into the stator 8 limit radial sealing strips 17, each acting on one step a well functioning vortex chamber 22. Due to the radial displacement of the Throttling points do not influence each other. With this full labyrinth a further reduction in the gap mass flow is achieved.

A third measure serves to improve the re-inflow of the Maze mass flow in the main channel. For this purpose, the stator housing on Labyrinth outlet 42 reduced to a permissible minimum dimension in the radial direction Crevice flow is immediately compared to the general one Tapered outward stator wall taken over. With that you can significantly reduce the harmful cross exchange of flow material and the unnecessary dissipation of the high-energy gap flow largely avoid. In addition, the total pressure profile is through the kinked stator wall the main flow favorably influenced.

For this purpose, the flow-limiting wall of the cover plate 16 is directly on Provide outlet blades La3 with an articulation angle A. This kink angle is dimensioned so that the outflow from the blades with respect to Total pressure and outflow angle is homogenized. In the example, this means that the angle A shown is defined as positive. The broken part of the wall runs radially outwards, i.e. it is from the machine axis, not shown directed away. With this training, the division-dependent pressure field induced cross exchange of flow material reduced. This can namely the cause of detachment on the particularly sensitive suction side the shovels.

The choice of the articulation angle is based on the following considerations: At the outlet the blades have a divergent flow, with swirl at the cylinder. At least the flow in the radially outer zone has an essential higher energy than in the radially inner rotor zone, which is in the form of manifested significantly higher total pressures in the radially outer zone. With the idea behind the articulation angle is that the total pressure and outflow angle inhomogeneity be as low as possible to achieve above the bucket height. The equation for that radial balance teaches that this is primarily about the meridian curvature the streamlines can be reached. This has to be influenced primarily by adjusting the articulation angle. A homogeneous total pressure distribution the outer boundary wall can only be achieved if the corresponding one Kink angle A with respect to the conical contour of the channel in each Fall opens to the outside. Here, the desired total pressure reduction in achieved in this area.

A complete implementation of this articulation angle idea requires a clean guide ahead of the flow over a certain range. This is based on the knowledge that only at a distance - which is half the distance between Blade outlet and guide blade inlet divided by the blade pitch corresponds - slowly the flow inhomogeneities resulting from the blade circulation to lose.

In the exemplary embodiments explained below, the functions are the same Provide elements with the same reference numerals as in FIG. 3.

4 shows a solution in which the shroud has the same taper of approx. Has 25 ° as that in Fig. 2 and 3. The cavity at the labyrinth entrance is in its radial extension in three axially offset partial cavities 40a, 40b and 40c divided. At the labyrinth exit, three are caulked into the stator radial sealing strips 17 arranged.

To improve the re-inflow of the labyrinth mass flow into the Here too, main channel 50 is the cavity at the labyrinth outlet 42 immediately behind the last radial sealing strip 17 in the radial direction to an allowable Minimum dimensions reduced. As a rule, this minimum dimension is also used in the front cavities provided. For this purpose, the cover plate 16 is step-shaped educated. With approximately horizontal in its first section and then curved sealing strips 52 become the individual partial cavities 40a, 40b, 40c sealed. These sealing strips 52 are preferably with their horizontally extending section in the axially extending housing parts caulked. It is understood that other fastening methods and Geometries are possible. The partial cavities separated by the sealing strips 52 40b and 40c form vortex chambers 22.

Fig. 4 shows the cover plate in the normal operating position. The front sealing strips 52 act on the front edges of the horizontally oriented cover plate gradations. The rear radial sealing strips 17 act horizontally on the last one directional cover plate gradation.

5, the cover plate 16 is in its extreme positions on a somewhat reduced scale shown, namely in the case of transients such as those when starting and leaving of the machine. It can be seen that in the dash-dotted position the sealing strips 52 in the intersection between axially and radially directed Intervene in the step part. One of the ways to make this easier is the radial one Step part formed obliquely against the direction of flow. In addition, the Curvature of the sealing strips a problem-free evasion in the event that the Cover plate would take an even more extreme position. In this position continues to seal the foremost of the radial sealing strips 17 against the horizontal facing rear cover plate part. The sealing strips are in the dashed position 52 no longer engaged. Only the last of the radial seals here Sealing strip 17 and thus prevents uncontrolled working fluid through the Flow through gap 42.

Fig. 6 shows the new solution for a cover plate with a taper of only approx. 10 ° as used in the front stages of low pressure parts Steam turbines. The cavity is divided into two partial cavities 40a and 40c. These partial cavities 40a and 40c are separated by one in its first Section approximately horizontal and then curved sealing strips 52. This strip acts on a simply stepped cover plate 16. Die remaining sealing strips 17 are arranged so that at least in extreme positions one of the strips 52 or 17 is effective.

7 finally shows the new solution for a cover plate 16 with a Taper of approx. 45 °, as used in the rear low pressure stages of steam turbines. It can be seen here that even with such extreme Channel openings the solution of FIG. 4 is easily transferable. moreover this solution offers the advantage that the radially inward and in itself aerodynamically damaging kink angles at the inlet can be avoided can. This means that the cover band contour corresponds to the globally specified one Channel contour.

All the solutions shown and described so far point towards that State of the art has the advantage that due to the gradation and in particular of the inclined radial parts to a significantly increased sealing length Available. In addition, at least the cover plates 16 according to the 4, 6 and 7 also lower cover plate masses.

LIST OF REFERENCE NUMBERS

8th

stator

9

rotor

10

flow limiting wall on the stator side

11

flow-limiting wall on the rotor side

13

Base plate of the guide blades Le

15

Blade Maze

16

Cover plate of the blade La

17

sealing strips

18

axial gap

19

Vane Maze

20

Cover plate of the guide vane Le

21

Base plate of the blade La

22

swirl chamber

26

radial gap

40

Cavity at the labyrinth entrance

40a, 40b, 40c

partial cavities

41

Pink

42

Labyrinth outlet

43

undercut

50

flowed channel

51

outer channel contour

52

horizontal sealing strips

54

Channel contour when tapping

La, La3 ...

blades

Be, Be3 ...

vanes

A

Buckling angle outside behind the impeller

B

Kink angle outside in front of the impeller

P

Intersection with a straight outer channel contour

Claims (5)

1. Arrangement for sealing the gap between moving blades (La), revolving in a conically widening flow duct (50) of a turbomachine, and the outer duct contour (51) of the stator (8), the moving blades (La) being provided at the blade end with revolving shroud plates (16) which project into a cavity in the stator (8), and a labyrinth seal sealing radial gaps between stator (8) and revolving shroud plates (16) by means of sealing strips fixed to the stator, part of the sealing strips being arranged radially, the cavity (40) at the labyrinth inlet being subdivided in its radial extent into at least two sectional cavities axially offset from one another, and the shroud plate (16) being of stepped design with at least two choke points relative to the stator (8), and sealing strips, with a vortex chamber (22) being enclosed, acting on one step each, characterized in that a sealing strip (52) running approximately horizontally in its first section and curved at its free end acts on at least one step of the shroud plate (16) of stepped design.
2. Arrangement according to Claim 1, characterized in that the radially outwardly directed surfaces of the shroud-plate steps are designed to be inclined against the direction of flow.
3. Arrangement according to Claim 1, characterized in that, at the labyrinth inlet, the contour of the cavity (40) in the stator (8) first of all runs radially outwards and against the direction of flow and is then directed downstream in the axial direction while forming a prong (41) projecting into the cavity (40), and in that the shroud plate (16) is provided with an undercut (43) which is adapted to the shape of, the prong (41).
4. Arrangement according to Claim 1, characterized in that the stator casing at the labyrinth outlet (42) is drawn in radially for the purpose of forming a narrow gap of minimum size.
5. Arrangement according to Claim 1, characterized in that the inner flow-defining wall of the shroud plate (16), directly at the trailing edge of the blade body, is provided with a bend angle (A) directed radially outwards.

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