EP0863296A2 - Guide vane for steam turbines - Google Patents

Abstract

The guide blade has a cavity (18) under low pressure, e.g. connected directly to the condenser, inside it, and has an aperture (3) for fluid suction in the region of its rear edge. This aperture has a porous cover (7) with capillaries which are filled with the fluid being sucked during operation. The porous cover is anchored in the blade by a mechanical fixing element (20) in the form of a spring-loaded quick lock. It consists of a bush (21) which locates the cover in the blade aperture. The cylindrical part (24) projects into the blade cavity. A movable mandrel (25) in the bush is loaded by a spring (26) and has a cap (28) on the inner wall of the blade.

Description

TECHNICAL AREA

The invention relates to a guide vane for steam turbines with a by a vacuum in the interior of the blade, with at least a cover provided with a porous capillary Opening for a fluid suction from the blade surface, preferably in the Area of the blade trailing edge, the opening opening into the cavity and the cover is dimensioned so that all capillaries during of the company are filled with the fluid to be extracted.

STATE OF THE ART

Guide vanes in the low-pressure section of steam turbines are generally known are equipped with water suction. Show guide vanes of this type for example, in the area of their rear edge openings that are parallel as slots to the blade edge or as bores, and which in one Guide the cavity inside the guide vane. The cavities of all guide vanes are connected to an annular channel that connects itself to the capacitor the steam turbine plant is connected. The cavity becomes from the capacitor inside the guide vane with a comparatively low vacuum acted upon. With the help of this vacuum, the surface of the Guide vane condensed water is sucked into the openings and gets from there further into the capacitor. Without this suction would be on the Vane form water droplets that extend from the downstream Remove the blade edge and onto the rotating blades rotating at high speed the steam turbine would hit. This impact of the drops of water can cause significant erosion on the blades. By the water suction can eliminate this source of erosion.

Through these openings, which have a comparatively large cross section, usually steam is also sucked off together with the water, which entails a reduction in the efficiency of the steam turbine. Further the edges of these openings disrupt the flow of steam along the Guide vanes.

DE-A1-2 038 047 also discloses these openings for water extraction covered with porous, liquid-permeable material. With With the help of a comparatively large pressure drop, the porous material becomes permanent partially vacuumed to create enough open pores in which then the water wetting the blade surface with the help of the capillary action is drawn in. With the help of the pressure gradient, the water is then aspirated from the pores into the blade cavity. With this type of exploitation of the comparatively large pressure drop despite the porous Covering a certain portion of the steam flowing around the blade also suctioned off, which results in a reduction in the performance of the turbine. To maintain the comparatively large pressure drop for the Water extraction uses a comparatively large amount of energy.

A guide vane of the type mentioned is known from DE-A1-195 04 631. This vane is characterized by the porous cover and the liquid-filled Capillaries to withstand negative pressure Wall formed. This wall is only where it is wetted with the fluid for the fluid permeable. The porous cover has a pore size that the fluid to be extracted and the vacuum are adjusted. The openings for the fluid suction have a comparatively small effective cross section on. Between the vacuum cavity and the steam-exposed turbine interior is always a sealed wall during operation present that is made up of the porous material of the cover and that in all Capillaries this cover builds up fluid contained. This dense wall holds continuously the pressure drop between the turbine interior called the barrier pressure and the inner cavity pressurized. The water wetting the surface of the guide vane passes through this wall through, but steam can not be carried away, because for him the Wall is solid and impenetrable. The efficiency of the steam turbine will not significantly reduced by the water suction on the guide vanes, However, their availability is significantly increased because of water drops conditional erosion no longer occur.

The openings for the covers are in the blade in the area of the rear edge as a single or multi-part groove running parallel to the blade edge educated. The porous cover is flat with the guide vane or partial soldering, by welding, by gluing and / or connected by mechanical caulking. All of these known Fastening methods make it difficult to replace the cover in the If necessary.

PRESENTATION OF THE INVENTION

The invention is based on the object, a guide vane at the beginning to provide the type mentioned with detachable means for fluid suction.

According to the invention this is achieved in that the porous cover a mechanical fastener is anchored in the guide vane.

It is useful if the fastener is a spring-loaded Quick release is essentially made up of one in the blade cavity protruding sleeve and an axially displaceable inside the sleeve Thorn that penetrates the bottom of the can and at its end with a cap resting on the inner wall of the blade is provided. With this An extremely flat element can be designed to measure as close as possible to the trailing edge of the blade to be drained can.

It makes sense if the cap has four on its cylindrical outer circumference Flattened is provided. There are two opposing flats chosen so that the cap against insertion when inserted into the blade cavity Spring force penetrates the opening. Then the cap is turned over by means of the mandrel Rotated 90 ° and with two further flats opposite each other from the spring force to the inner walls of the opening that delimit the opening Shovel pressed. The cover can be installed and removed with it in the simplest way.

If the spring means are formed from a package of disc springs, with the corresponding spring selection the contact or prestressing forces on the existing conditions are adjusted.

BRIEF DESCRIPTION OF THE DRAWING

Fig. 1

eine mit drei gestaffelten Abdeckungen versehene Leitschaufel;

Fig. 2

einen Teilschnitt durch die Leitschaufel nach Linie II-II in Fig. 1;

Fig. 3

das Detail III aus Fig. 2;

Fig. 4

einen Schnitt durch eine Kapillare einer mit einem Fluid getränkten porösen Abdeckung;

Fig. 4a und 4b

das Durchtreten des Fluids durch die poröse Abdeckung;

Fig. 5

den durch die fluidgetränkte poröse Abdeckung gehaltenen Sperrdruck in Abhängigkeit von der Korngrösse des für die Herstellung der porösen Abdeckung verwendeten Materials;

Fig. 6

die Menge des durch die poröse Abdeckung durchtretenden Fluids in Abhängigkeit von der Korngrösse des für die Herstellung der porösen Abdeckung verwendeten Materials und vom auf die Abdeckung einwirkenden Druck;

Fig. 7

ein vorgefertigtes, einbaufertiges Befestigungselement.

In the drawing, an embodiment of the invention is shown schematically.
Show it:

Fig. 1

a vane provided with three staggered covers;

Fig. 2

a partial section through the guide vane along line II-II in Fig. 1;

Fig. 3

the detail III from Fig. 2;

Fig. 4

a section through a capillary of a porous cover soaked with a fluid;

4a and 4b

the passage of the fluid through the porous cover;

Fig. 5

the barrier pressure held by the fluid-soaked porous cover depending on the grain size of the material used to manufacture the porous cover;

Fig. 6

the amount of fluid passing through the porous cover depending on the grain size of the material used to manufacture the porous cover and the pressure acting on the cover;

Fig. 7

a prefabricated, ready-to-install fastener.

WAY OF CARRYING OUT THE INVENTION

Fig. 1 shows a schematic diagram of a guide vane 1 of a steam turbine, the Blade 2 is welded together from two preformed sheets and which is connected to the foot 5 by means of a welded connection. In the The surface of the airfoil 2 is a plurality of mutually overlapping openings 3 milled in the form of longitudinal grooves. These extend parallel to downstream blade edge 4. These grooves 3 do not have to run over the entire length of the guide vane 1, but are only there provided where liquid is to be aspirated. Usually you will Load the suction device on the radially outer third of the bucket.

In the foot 5 of the guide vane 1, a cavity 6 is provided, which is in the inner cavity 18 of the airfoil 2 extends. In this cavity 18th the grooves 3 open. The cavities 6 and 18 are with the, not shown, pressurized condenser of the steam turbine system connected and are therefore under negative pressure. With 8 is the outflow direction of the water to be withdrawn from the cavity 6 into the condenser.

For water extraction, each groove 3 is provided with a porous cover 7, which closes against the surface of the airfoil 2. The porous Cover 7 in the form of a strip of a highly porous sintered material Chromium-nickel base lies on a shoulder 9 of the groove flank (Fig. 3). The differential pressure the porous cover 7 is usually in the range of 10 up to 50 mbar, preferably at about 20 mbar.

In an experimental set-up, evidence was provided that the suction of water flowing in thin strands over the airfoil 2 into the targeted quantities is possible. Above all, it was clearly evident that the Water was immediately drawn into the capillaries of the porous cover 7. The differential pressure of 20 mbar is sufficient here to pass the water through the porous Convey cover 7 into the groove 3.

4, 4a and 4b are considered in more detail to explain the mode of operation. A section through a single, simplified representation is shown schematically Capillary 11 of a porous cover 7 completely saturated with a fluid. The capillary 11 is, like all other capillaries 11, of the porous cover 7 filled with a fluid. The capillaries 11 are in the porous cover 7 with one another cross-linked, so that when a fluid hits a point the porous cover 7 immediately all of the capillaries 11 with this fluid fills. In steam turbines, the fluid is usually distilled water. Because of the Surface tension of the water and due to the capillary action forms in the capillary 11 from a water column 12. On both, the respective surface the porous cover 7 facing sides of the water column 12 forms each have a meniscus 13a, 13b. The shape of the menisci 13a, 13b is determined by determines the surface tension of the water. The meniscus 13a is the assigned to the steam-applied side of the porous cover 7. The surface 14 of the porous cover 7 is also the side exposed to steam assigned while the surface 15 of this cover the capacitor side, is assigned to the side of the cover 7 which is subjected to negative pressure.

The water column 12 remains in the normal case, it is by the pending pressure difference, the so-called barrier pressure, not from the capillary 11, or removed from the entirety of all capillaries 11. The porous cover 7 forms one with the water columns 12 present in all capillaries 11 pressure-tight wall that always withstands the existing barrier pressure, so that none Steam can be sucked through this wall into the condenser so that in this embodiment of the porous cover 7 no loss of efficiency Steam turbine occurs due to steam loss.

According to FIG. 4a, a strand 16 flows from the surface 14 Guide vane 1 condensed water. As soon as this strand 16 has a capillary 11 reached, the upper meniscus 13a of the water column 12 is destroyed. The capillary action and the surface tension of the lower meniscus 13b is now sufficient no longer out to keep the water column 12 stationary, the water from the Strand 16 penetrates capillary 11 and lower meniscus 13b merges in a bulge 17. The bulge 17 takes because of the Capillary 11 after flowing water to a drop shape, as in Fig. 4b shown. The drop of water thus created then drips off and is removed by the Vacuum conveyed into the condenser. This draining continues until all the water of the strand 16 in this and the neighboring capillaries 11 has flowed out. After the last water residue has drained and drained the capillaries 11 filled with the water column 12 remain and seal the porous cover 7 again against the barrier pressure and thus avoid one undesired passage of steam. It proves to be particularly advantageous that the entire associated with the side of the cover 7 which is subjected to negative pressure Surface 15 is available for draining because of the water distributed through the interconnected capillaries so that it is on the entire Surface 15 emerges. This arrangement is comparatively for the passage of suitable for large amounts of water.

In Fig. 5 is held by the fluid-soaked porous cover 7 Barrier pressure depending on the grain size for the manufacture of the porous cover 7 material used, and thus indirectly from the size of capillaries 11. On the ordinate of this diagram is the Barrier pressure in bar and on the abscissa is the average grain size for the Production of the porous cover 7 material used in microns. With a coarser grain of the material particles used in the Sintering necessarily larger diameters of the capillaries 11. The menisci 13a, 13b thus also have a larger one due to the barrier pressure acted area. If the capillary 11 is not due to the barrier pressure may be emptied, the barrier pressure must be reduced accordingly.

6 shows the amount of water passing through the porous cover 7 as a function of the grain size of the material used to produce the porous cover. The barrier pressure acting on the cover 7 is indicated in the diagram as a further parameter. On the ordinate of this diagram, the amount of water passing through an hourly porous cover 7 with an effective area of 10 cm ² is plotted and on the abscissa the mean grain size of the material used for producing the porous cover 7 is plotted in μm. This diagram clearly shows that with a coarser grain of the material particles used during sintering, larger diameters of the capillaries 11 and, in connection therewith, also larger amounts of the water passing through result. In the underlying model test, the water strikes the porous cover 7 in the form of a single strand 16 and wets an area of approximately 50 mm ² lying on the surface 14. The water is distributed in the capillary system of the porous cover 7 and emerges on the entire surface 15 of the cover 7 which is subjected to negative pressure, in this case this is approximately 1000 mm ² , which are available for dripping off the water which has passed through. Only in this way is it at all possible to discharge such comparatively large amounts of water through the porous cover 7. It is clearly shown that the porous covers 7 designed in this way allow the amounts of condensed water which occur in today's steam turbines on the guide vanes 1 to be discharged properly.

The cover laid on paragraph 9 must be suitably matched with the Guide blade to be fixed. According to the invention, this connection is now releasably executed. 2 is a partial section of the local position of a fastener 20 shown in the area of the blade trailing edge 4. In the 3 and 7 is a preferred embodiment of the fastener shown enlarged.

As can be seen from FIG. 3, the cover 7 provided with the capillaries lies on a shoulder 9 of the groove 3 arranged in the blade wall 2. On your it is flush with the outside of the channel through which the air flows Outside wall of the shovel. In the area of the fastener 20, it is with a preferably cylindrical through bore 32, which in turn has a recess 22.

The mechanical fastening element 20 is a spring-loaded quick-release fastener educated. Stainless steel is preferably used as the material. It consists on the one hand of a sleeve 21, which has a in the recess 22 inserted ring flange 23 the cover in the blade opening 3 fixed. With its cylindrical part 24, the sleeve protrudes into the blade cavity 18 in. On the other hand, there is an axially displaceable mandrel 25 in the interior of the sleeve provided which is equipped with spring means 26. This is a package of stacked disc springs between the mandrel base 33 and the bottom 27 of the sleeve are guided. The thorn penetrates this floor 27 of the can and is at its end with one on the inner wall of the shovel overlying cap 28 provided. The cap is preferably with the mandrel welded. When assembled, it is with the inner walls of your Hollow part guided on the cylindrical outer wall of the sleeve and can slide along.

The cap 28 is on its cylindrical outer circumference with four flats Mistake. Two flats 29 lying opposite one another (FIG. 7) extend over the entire height of the cap and are chosen in their dimensions so that the cap penetrates the groove 3 when it is inserted into the blade cavity. To completely insert the cap, the mandrel is removed using a tool raised against the spring force. For this purpose, the mandrel base has a slot 31 For example, to accommodate a screwdriver.

By rotating the mandrel through 90 °, the cap is now placed on the support brought the inner walls of the blade delimiting the opening 3. For these overlays are the two other flats lying opposite each other 30 provided, which are only attached to the lower part of the cap. she are dimensioned in such a way that when the mandrel is relieved, the cap follows the spring force is lowered to the edges of the groove and there with little lateral Game sits.

Of course, the invention is not limited to that shown and described Embodiment limited.

For example, at certain points on the guide vane 1 large amounts of condensed water can be used there instead of the one shown narrow strips also large-area porous covers 7 are provided and the grooves 3 can by according to the further requirements shaped openings are replaced in whole or in part. Depending on Length of the covers can also be more than the two shown in FIG. 1 Fasteners are provided per cover.

In deviation from the hollow vane shown, the guide vane can of course be used just as well be solid and made of GGG40, for example be poured. A groove-shaped can then be formed in the surface of the airfoil Be poured or milled opening 3. The required paragraph 9 is milled or eroded using a copy milling machine. During the milling process care is taken at the same time that casting residues that have the groove cross section unacceptably reduce. The base of the guide vane will in turn have a cavity 6 in which the porous Cover 7 provided groove opens.

As a detachable mechanical fastening element, a simple, Screw connection conceivable, whereby countersunk head screws screwed into the blade wall or hexagon bolts can be used. Here, the Hexagon screws either over a washer or over a Hold the cover down over the length of the filter. In the case of countersunk screws, these can be part of your circumference act directly on the filter with the appropriate bevel. The disadvantage of these solutions is that threads in the blade walls are to be attached.

LIST OF DESIGNATIONS

1

vane

2nd

Airfoil

3rd

Opening, groove

4th

Bucket edge

5

Foot

6

Cavity in 5

7

porous cover

8th

arrow

9

paragraph

10th

deepening

11

capillary

12th

Water column

13a, b

meniscus

14.15

surface

16

Streak

17th

Bulge

18th

Cavity in 2nd

20th

Fastener

21

rifle

22

Recess

23

Ring flange from 21

24th

cylindrical part of 21

25th

mandrel

26

Spring means

27

Floor of 21

28

cap

29

Flattening

30th

Flattening

31

Slot in 25th

32

cylindrical bore in 7

33

Dornboden

Claims (4)

Guide blade (1) for steam turbines with a cavity (18) in the blade interior which is acted upon by a vacuum, with at least one opening (3) provided with a porous capillary (11) having a capillary (11) for fluid suction from the blade surface, preferably in the region the trailing edge of the blade (4), the opening opening into the cavity and the cover being dimensioned such that all the capillaries are filled with the fluid to be extracted during operation,
characterized,
that the porous cover (7) is anchored in the guide vane with a mechanical fastening element (20). Guide vane according to claim 1, characterized in that the mechanical fastening element (20) is a spring-loaded quick-release fastener, consisting essentially of a bushing (21) which fixes the cover in the blade opening (3) via an annular flange (23) lying in a recess (22) in the cover (7) and projects with its cylindrical part (24) into the blade cavity (18), and an axially displaceable mandrel (25) inside the sleeve, which is equipped with spring means (26), penetrates the bottom (27) of the sleeve and is provided at its end with a cap (28) resting on the inner wall of the blade. Guide vane according to claim 2, characterized in that the cap (28) provided with four flats on its cylindrical outer circumference , of which two opposing flats (29) are selected so that the cap when inserted into the blade cavity penetrates the opening, then is turned by 90 ° using the mandrel and with two further flats (30) lying opposite one another from the spring force to the inner walls delimiting the opening the shovel is pressed. Guide vane according to claim 2, characterized in that the spring means (26) are formed from a package of disc springs.

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