EP2775096B1 - Diffuser assembly for an exhaust housing of a steam turbine, and steam turbine with the same - Google Patents

Description

The present invention relates to a diffuser assembly for an exhaust steam housing of a steam turbine according to the preamble of claim 1, and to a steam turbine equipped with such a diffuser arrangement.

Such a diffuser arrangement, ie comprising a diffuser having an inlet end for receiving exhaust steam in the flow direction behind a provided with a shroud blade ring of a final stage of the steam turbine, and with a diverging viewed in the flow direction annular wall which limits a flowing into the Abdampfgehäuse diffuser flow path is made the general state of the art concerning steam turbine plants.

In particular, the final stage of condensing steam turbines is usually followed by a diffuser to convert kinetic energy of the exhaust steam into potential energy before the exhaust steam is supplied to the condenser of the relevant water-steam cycle. The static pressure of the exhaust steam is thereby advantageously raised (to a "condenser inlet pressure"), which is why one speaks in this context of a pressure recovery.

As a result of the positive pressure gradient in the region of the diffuser, as viewed in the flow direction, the flow in the diffuser in particular tends to detach on the housing side. Such demolition of the boundary layer flow reduces the effectiveness of the diffuser and thus reduces turbine efficiency.

This problem of boundary layer separation in the diffuser arises especially when the relevant blade ring of the final stage is designed with a so-called shroud, ie with a circumferential on the outer circumference of the blade ring trained stabilization structure. In this case, the otherwise existing flow-stabilizing effect of a gap flow existing there (energization of the boundary layer) is eliminated.

By using free-standing blades, so a blade ring without shroud, this problem is indeed avoided. In this case, however, higher Dampfleckagemengen arise over the blade ring, resulting in a corresponding reduction in the efficiency of the power amplifier.

document US2012 / 0163969 discloses a diffuser assembly for an exhaust steam housing of a steam turbine. In this document, steam is tapped from the exhaust steam box.

It is an object of the present invention, in a diffuser arrangement of the type mentioned in the beginning to achieve a low tendency for boundary layer separation with a simultaneously low steam leakage rate over the blade ring.

According to the invention, this object is achieved by a diffuser arrangement according to claim 1 or a steam turbine equipped therewith (claim 5).

• eine mit Dampf, welcher aus dem Abdampfgehäuse und/oder aus einer höheren Druckstufe der Dampfturbine abgezapft wurde, versorgbare Ringnut in der Ringwand, welche in Strömungsrichtung betrachtet an der Stelle des Laufschaufelkranzes angeordnet ist, zur Einleitung des abgezapften Dampfes in einen Ringspalt zwischen der Ringwand und dem Laufschaufelkranz, und
• eine am Einlassende des Diffusors in Umfangsrichtung umlaufend ausgebildete und in Axialrichtung entgegen der Strömungsrichtung in den Ringspalt hineinragende Strömungsführungslippe zur Aufteilung des eingeleiteten Dampfes einerseits in eine Sperrdampfströmung am Außenumfang des Laufschaufelkranzes und andererseits in eine Grenzschichtströmung entlang der Ringwand.

The diffuser assembly according to the invention comprises

• a with steam, which was tapped from the Abdampfgehäuse and / or from a higher pressure stage of the steam turbine, supplyable annular groove in the annular wall, which is arranged in the flow direction at the location of the blade ring, for introducing the tapped steam into an annular gap between the annular wall and the blade ring, and
• a flow guide lip circumferentially formed at the inlet end of the diffuser and projecting in the axial direction counter to the flow direction into the annular gap for dividing the steam introduced on the one hand into a sealing steam flow on the outer circumference of the rotor blade ring and on the other hand into a boundary layer flow along the annular wall.

In other words, it is provided when using the invention to remove steam from the exhaust steam housing or a higher pressure stage (based on the "final stage" or said rotor blade ring, ie in particular, for example, so-called high-pressure stage or medium-pressure stage) and a part of this tapped steam as "sealing steam" (with sealing effect for the annular gap between the diffuser ring wall and turbine blade ring) reintroduce over the Endstufenlaufschaufelkranz, wherein another part of the tapped steam is blown down along the annular wall, so to speak, in the boundary layer downstream of the blade ring. The flow guide lip provided according to the invention in this case brings about in a simple manner the desired distribution of the vapor on the one hand into the sealing vapor flow and on the other hand into the boundary layer flow.

Advantageously, the injected boundary layer flow along the annular wall causes a reduction in the risk of boundary layer separation, wherein at the same time advantageously the vapor leakage amount over the blade ring is reduced by the sealing steam flow.

In one embodiment, it is provided that the axial extent of the flow guide lip is greater than 50% of the axial extent of the shroud and / or the axial extent of the flow guide lip is less than 200% of the axial extent of the shroud.

In one embodiment, the flow-guiding lip protrudes into the annular gap over an axial extent of 10% of the shroud and / or projects the flow-guiding lip into the annular gap over an axial extent of less than 60% of the axial extent of the shroud.

In one embodiment, the axial extent of the annular groove is less than 50% of the axial extent of the shroud and / or greater than 5% of the axial extent of the shroud.

Viewed in the axial direction, the annular groove is preferably arranged at least approximately in the middle between the axial ends of the shroud.

In one embodiment, viewed in the axial direction, the flow guide lip protrudes into the annular gap into the region of the annular groove.

As regards the section of the flow guide lip which faces away from the annular gap and projects into the diffuser flow path in the region of the inlet end of the diffuser, this lip section is preferably likewise curved in adaptation to a curved course of the annular wall, for instance to provide a flow direction substantially constant Cross-sectional area between lip and ring wall.

In one embodiment, it is provided that the flow-guiding lip has a radially inwardly directed shoulder, viewed in the axial direction, at the location of the rear end of the outer circumference of the blade ring.

With such a shoulder, an effect of the sealing steam flow improving axial gap (narrowed point) between this shoulder and the outer periphery of the blade ring can be advantageously provided.

The flow guide lip can, for. B. configured and arranged so that the introduced into the annular gap between the annular wall and the blade ring tapped steam is divided into more than 20% in the sealing steam flow and / or more than 20% in the boundary layer flow.

In one embodiment it is provided that a supply of the annular groove with the tapped steam by at least one radially extending through the diffuser passage.

If this passage completely penetrates the diffuser in the radial direction and the radially outer end of the passage opens into the exhaust steam housing, steam can be tapped out of the exhaust steam housing in a simple manner and guided via the passage to the annular groove.

Alternatively or in addition to such a steam branching from the exhaust steam housing, steam can also be branched off from a higher pressure stage (viewed in the turbine flow direction in front of said rotor blade ring of the final stage or upstream of this final stage) and fed to the annular groove. One or more such bleed passages can each lead directly to the annular groove, or, if present, open into the mentioned radial passage in the diffuser. From such radial passages in the diffuser may be provided more, z. B. distributed at equal angular intervals over the circumference of the diffuser.

In one embodiment, it is provided that a provided for supplying the annular groove with the tapped steam passage is provided with a check valve. This passage may in particular z. B. act to the aforementioned radial passage in the diffuser. With the check valve advantageously a backflow can be avoided. The term "check valves" is to be interpreted broadly in the context of the invention and should therefore not only include such a check valve in the strict sense but also other to avoid backflow suitable fittings.

According to a further aspect of the invention, the object stated at the outset is achieved by a steam turbine, which with a diffuser assembly of the type described is equipped.

The steam turbine can hereby z. B. in a conventional manner as Kondensationsdampfturbine in a water-steam cycle (condensing turbine plant) can be used.

Fig. 1

eine schematische Längsschnittansicht einer Dampfturbine von herkömmlicher Bauart, und

Fig. 2

ein Detail aus Fig. 1, jedoch in modifizierter Ausgestaltung, zur Veranschaulichung eines Ausführungsbeispiels der Erfindung.

The invention will be further described by means of embodiments with reference to the accompanying drawings. They show:

Fig. 1

a schematic longitudinal sectional view of a steam turbine of conventional design, and

Fig. 2

a detail from Fig. 1 but in modified form, to illustrate an embodiment of the invention.

Fig. 1 shows a steam turbine 10 which is coupled via a turbine rotor shaft 12 to a rotary driven work machine 14 (eg electrical generator).

The turbine 10 includes a turbine housing 16 having a turbine rotor 18 rotatably mounted therein about an axial axis A. Blades 20 are mounted on the circumference of the turbine rotor 18 in the radial direction thereof which cooperate with stator blades 22 stationarily mounted in the turbine housing 16 in turbine operation to operate in a turbine Steam flow to convert energy from supplied steam to mechanical rotary energy of the turbine rotor shaft 12.

In the Fig. 1 drawn arrows illustrate this steam flow, starting from a live steam inlet 24 to a Abdampfauslass 26th

The rotary bearing of the turbine rotor shaft 12 is in the illustrated embodiment by means of a first bearing device 28 and a second storage device 30 accomplished.

The section of the turbine housing 16, which is traversed by the steam in the last turbine operation and opens into the exhaust steam outlet 26, is referred to as Abdampfgehäuse 32.

In the illustrated embodiment, the turbine 10 according to the pressure level of the steam flowing through the turbine 10, a high-pressure stage 40, a medium-pressure stage 42 and a low pressure stage or power amplifier 44, which are sequentially flowed through by the steam as shown, and in each case from structurally combined running and Leitschaufelkränzen are formed. The attachment of the vanes 22 in the individual turbine stages 40, 42 and 44 is realized with respective vane carriers 46, 48 and 50, respectively.

The basic construction of the steam turbine 10 described so far is known from the prior art (cf. WO 2012/175328 A1 ).

In the usual use of a steam turbine of Fig. 1 Furthermore, it is known from the general state of the art that the final stage, in this case the low-pressure stage 44, is arranged downstream of a so-called diffuser or the output of the relevant turbine stage with such a steam generator Design diffuser functionality. With the diffuser kinetic energy of the exhaust steam is converted into potential energy and thus advantageously raises the static pressure of the exhaust steam to the usually higher condenser pressure.

In the example shown according to Fig. 1 For this purpose, a so-called diffuser arrangement in the exhaust steam housing 32 is provided downstream in the axial region of the detail or area shown at II.

Fig. 2 illustrates the example of a modification of in Fig. 1 shown at II details at the output of the output stage 44 of the turbine 10, a diffuser assembly according to the invention 60. By a corresponding modification of the steam turbine 10 of Fig. 1 In this area, a steam turbine according to the invention is thus provided.

With Fig. 2 illustrated diffuser assembly 60 is hereinafter for use in the steam turbine 10 of Fig. 1 explained.

The diffuser assembly 60 ( Fig. 2 ) is in this case in the exhaust steam housing 32 ( Fig. 1 ) and comprises a diffuser (diffuser housing 62) with an inlet end 64 for receiving Abdampf in the flow direction behind the provided according to this modification with a shroud 66 last blade ring 68 of the output stage 44, and with a diverging viewed in the flow direction annular wall 70, a into the exhaust steam housing 32 opening diffuser flow path (see, arrow in Fig. 2 ) limited.

Fig. 2 shows only the in Fig. 1 upper part (detail II in Fig. 1 ) of the overall ring-like around the axial axis A around extending diffuser assembly 60th

The blade ring 68 is formed by a plurality of blades 20 protruding radially from the turbine runner 18 in the illustrated area, the distal ends (radially outer ends) of which are connected by the circumferential circumferential stabilizing shroud 66.

As a result of the divergent design of the diffuser 62 or its annular wall 70, the desired pressure increase (pressure recovery) takes place in the exhaust steam flow along the diffuser flow path (see arrow) to a pressure p3, which in the example shown is, for. B. the input pressure of a connected to the output of Abdampfauslasses 26 of the steam turbine 10 (not shown) capacitor corresponding to the steam turbine plant concerned. When the exhaust steam enters the diffuser 62, ie at the inlet end 64 of the diffuser 62, there is a pressure p2 (p2 <p3). The pressure immediately before the illustrated blade ring 68 is denoted by p1 and, depending on the configuration of the blade ring 68, is usually greater than p2, so that the following applies: p1 <p2 <p3.

Due to the relatively large orifice cross-sectional area from the exit of the diffuser 62 (in FIG Fig. 2 right) into the exhaust steam housing 32, a pressure pA in the exhaust steam housing substantially corresponds to the diffuser outlet pressure p3.

• eine mit Dampf, welcher aus dem Abdampfgehäuse 32 und/oder aus einer höheren Druckstufe, z. B. einem weiter stromaufwärts gelegenen Teil der Endstufe 44, oder der Mitteldruckstufe 42, oder der Hochdruckstufe 40, abgezapft wurde, versorgbare Ringnut 72 in der Ringwand 70, welche in Strömungsrichtung (vgl. Pfeil) betrachtet an der Stelle des Laufschaufelkranzes 68 angeordnet ist, zur Einleitung des abgezapften Dampfes in einen Ringspalt 74 zwischen der Ringwand 70 und dem (an seinem Außenumfang mit dem Deckband 66 versehenen) Laufschaufelkranz 68, und
• eine am Einlassende 64 des Diffusors 62 in Umfangsrichtung umlaufend ausgebildete und in Axialrichtung (vgl. Achse A) entgegen der Strömungsrichtung (vgl. Pfeil) in den Ringspalt 74 hineinragende Strömungsführungslippe 76 zur Aufteilung des eingeleiteten Dampfes (vgl. kleine Pfeile in Fig. 2) einerseits in eine Sperrdampfströmung am Außenumfang des Laufschaufelkranzes 68 bzw. Deckbandes 66 und andererseits in eine Grenzschichtströmung entlang der Ringwand 70.

A special feature of the diffuser arrangement 60 (or the steam turbine equipped therewith) is that the diffuser arrangement 60 further comprises:

• one with steam, which from the Abdampfgehäuse 32 and / or from a higher pressure level, z. B. a further upstream part of the output stage 44, or the intermediate-pressure stage 42, or the high-pressure stage 40 was tapped, supplyable annular groove 72 in the annular wall 70, which in the flow direction (see arrow) is viewed at the location of the blade ring 68, for introducing the tapped steam into an annular gap 74 between the annular wall 70 and the (provided on its outer periphery with the shroud 66) blade ring 68, and
• a flow-guiding lip 76 extending circumferentially around the inlet end 64 of the diffuser 62 and projecting in the axial direction (see axis A) against the flow direction (see arrow) into the annular gap 74 for dividing the introduced steam (compare small arrows in FIG Fig. 2 On the one hand into a sealing steam flow on the outer circumference of the blade ring 68 or shroud 66 and on the other hand in a boundary layer flow along the annular wall 70th

The flow guide lip 76 is thus used to guide and split the tapped and the ring groove 72 again recycled steam flow and is z. B. executed as a separate (eg., Annular rotationally symmetric) component and can in this case z. B. be secured by means of suitable spacers on the diffuser 62.

Advantageously, with this design, on the one hand by the sealing steam flow, the leakage rate of exhaust steam flowing over the blade ring 68 (in the annular gap 74) is advantageously reduced and, on the other hand, the boundary layer flow advantageously reduces the risk of boundary layer separation which reduces the diffuser efficiency.

For operation of the diffuser assembly 60, the annular groove 74 must be supplied with steam of a sufficiently high pressure (here: greater than p2), so that this steam can be divided into the two mentioned partial flows.

In the example shown, this steam supply is realized in a simple manner by disposing, distributed over the circumference of the diffuser 62, a number of radial passages (eg boreholes), of which Fig. 2 one can be seen and designated 78.

Through this radial passage (s) 78, a vapor transfer takes place from the exhaust steam housing 32 to the annular gap 74.

The radial passage 78 passes through the diffuser 62 in the radial direction for this purpose.

To avoid a backflow such supply passages with suitable control valves such. B. the in Fig. 2 to be provided at 80 symbolized check valve.

The advantage of the illustrated diffuser arrangement 60 is the avoidance or reduction of the flow losses which often occur in this area in known steam turbines.

On the one hand can be reduced by the Sperrbedampfung the leakage amount above the corresponding tread. On the other hand, by introducing a portion of the branched vapor into the diffuser, the boundary layer (at the annular wall 70) is stabilized. Both effects lead to an advantageous increase in turbine efficiency.

In the example shown, the flow guide lip 76 in the axial direction at the location of the rear end of the outer periphery of the blade ring 68 has a radially inwardly directed shoulder 82, so that the sealing steam flow in this area forcibly also a little way in the radial direction in an annular gap between the shroud 66 and this shoulder 82 must flow, which further improves the leakage reduction. Such a shoulder extends in the radial direction preferably as shown to the inner periphery of the respective shroud.

• Die axiale Ausdehnung der Lippe (76) beträgt mehr als 50% der axialen Ausdehnung des Deckbandes (66) und/oder weniger als 200% der axialen Ausdehnung des Deckbandes (66).
• Die Lippe (76) ragt um mehr als 10% der axialen Ausdehnung des Deckbandes (66) und/oder um weniger als 60% der axialen Ausdehnung des Deckbandes (66) in den Ringspalt (74) hinein.
• Die Lippe (76) endet im Ringspalt (74) an einer axialen Stelle, an welcher auch die Ringnut (72) vorgesehen ist. Im dargestellten Beispiel endet die Lippe 76 z. B. am axial betrachtet stromabwärtigen Ende der Ringnut 72.
• Die Lippe (76) besitzt einen an den gekrümmten (divergierenden) Verlauf der Ringwand (70) angepasst ebenfalls gekrümmten Verlauf. Im dargestellten Beispiel ist eine derartige Krümmung der Lippe 76 sowohl auf ihrer radial äußeren als auch auf ihrer radial inneren Seite vorgesehen. Die Krümmung an der radial äußeren Seite ist bevorzugt zur Schaffung eines ringförmigen Grenzströmungspfades mit im Pfadverlauf einheitlichem Strömungsquerschnitt vorgesehen.
• Die Lippe (76) besitzt eine Wandungsstärke, die sich in Richtung des Diffusorströmungspfades kontinuierlich verjüngt.

With regard to the highest possible effectiveness of the flow guide lip 76, its configuration or arrangement in the diffuser or diffuser inlet region 64 can be optimized for the respective application. In this aspect, in general z. B. the following design details, individually or in combination, be beneficial:

• The axial extent of the lip (76) is more than 50% of the axial extent of the shroud (66) and / or less than 200% of the axial extent of the shroud (66).
• The lip (76) projects into the annular gap (74) by more than 10% of the axial extent of the shroud (66) and / or by less than 60% of the axial extent of the shroud (66).
• The lip (76) ends in the annular gap (74) at an axial point at which the annular groove (72) is provided. In the example shown, the lip 76 ends z. B. at the axially downstream end of the annular groove 72nd
• The lip (76) has a curve which is also adapted to the curved (divergent) course of the annular wall (70). In the illustrated example, such a curvature of the lip 76 is provided both on its radially outer and on its radially inner side. The curvature on the radially outer side is preferably provided for providing an annular boundary flow path with a flow cross-section uniform in the path.
• The lip (76) has a wall thickness that tapers continuously in the direction of the diffuser flow path.

Claims (5)

1. Diffuser assembly (60) for an exhaust steam casing (32) of a steam turbine (10), comprising a diffuser (62) with an inlet end (64) for receiving exhaust steam downstream, as seen in the flow direction, of a rotor blade ring (68), provided with a shroud (60), of a final stage (44) of the steam turbine (10), and with an annular wall (70) which is diverging as seen in the flow direction and bounds a diffuser flow path that opens into the exhaust steam casing (32),
   wherein the diffuser assembly (60) comprises:

   - an annular slot (72) in the annular wall (70), which annular slot can be supplied with steam bled from the exhaust steam casing (32) and/or from a higher pressure stage (44, 42, 40) of the steam turbine (10), and which is arranged at the location of the rotor blade ring (68) as seen in the flow direction, for the purpose of introducing the bled steam into an annular gap (74) between the annular wall (70) and the rotor blade ring (68);

   the diffuser assembly is characterized in that it further comprises:

   - a circumferentially continuous flow guiding lip (76) formed at the inlet end (64) of the diffuser (52) and projecting, in the axial direction counter to the flow direction, into the annular gap (74) for the purpose of splitting the introduced steam on one hand into a barrier steam flow at the outer circumference of the rotor blade ring (68) and on the other hand into a boundary layer flow along the annular wall (70).
2. Diffuser assembly (60) according to Claim 1, wherein the flow guiding lip (76) has, as seen in the axial direction, at the location of the rear end of the outer circumference of the rotor blade ring (68), a radially inwardly oriented shoulder (82).
3. Diffuser assembly (60) according to either of the preceding claims, wherein the annular slot (72) is supplied with the bled steam by at least one passage (78) extending through the diffuser (62) in the radial direction.
4. Diffuser assembly (60) according to one of the preceding claims, wherein a passage (78) provided for supplying the annular slot with the bled steam is provided with a check valve (80).
5. Steam turbine (10), equipped with a diffuser assembly (60) according to one of the preceding claims.

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