DE102012108281A1 - Boundary layer blowing using vapor barrier leakage - Google Patents

Abstract

A steam turbine includes a turbine output stage (306), an axial or radial flow diffuser (300) receiving a main flow from the turbine end stage, a divergent wall (302) in the axial or radial flow diffuser that is from a diffuser inlet (304) to a diffuser outlet (30). 308) and a central body (310) in the axial or radial flow diffuser. An opening is provided in the diverging wall and an opening is provided in the center body to fluidly move the main stream. The apertures are located downstream of the diffuser inlet and upstream from a point where boundary layer separation would occur in a diffuser with no openings along the walls. A plurality of openings are provided in the diverging wall, and an end packing seal (16, 18, 20) is disposed adjacent an end portion of the turbine output stage. An annular manifold (22) collects fluid from the leakage flow from the end packing seal and distributes the leakage flow to the ports.

Description

GENERAL PRIOR ART

The invention relates to steam turbine performance and, more particularly, to a fluidic flow scheme source for improved diffuser performance in a steam turbine.

In condensing steam turbines used for power generation, steam exiting the last row of turbine blades generally flows through an annular, outwardly expanding channel, the so-called diffuser, located between the turbine shell and the exhaust vent. The diffuser is limited by an outwardly expanding flow guide, which adjoins the turbine housing. The steam passes from the diffuser into the body of a collector or a "steam hood" and is finally discharged from the exhaust hood into a condenser.

The purpose of the diffuser is to slow down or spread the exhaust stream flowing through it. This deceleration causes a reduction in the kinetic energy of the vapor and a pressure increase, the net effect of which is that the entrance to the diffuser has the lowest pressure on the way from the turbine to the condenser, so that the steam is released from the last turbine blade into a zone in which a minimum pressure prevails, whereby the velocity of the steam flowing through the blades increases, and the energy available to the turbine for its work increases.

Each rotating airfoil generates a wake stream, i. In the typical large turbine, there are one hundred or more wake streams. In steam turbines, these wake streams are particularly thick when the turbine is operating at condenser pressures which are higher than the condenser pressure for which it is designed, because under such conditions the boundary layer flow passing over and from the surfaces of the last turbine airfoils is either immediately ahead the detachment of the airfoil surfaces is or already partially detached.

The U.S. Patent No. 6,896,475 ('475 patent) describes a turbine diffuser which is assisted with a fluidic mechanism of action. The '475 patent recognizes that the performance of a steam turbine exhaust system is limited by geometric constraints and stall problems. For example, the downstream axial length of the hood can not be increased without changing the bearing pitch of the machine rotor, and the maximum area ratio allowed on the steam guide flow path before stalling results in a low value of 0.3 for the pressure recovery coefficient for the entire exhaust hood. For an axial flow diffuser type used in steam turbines, the maximum internal angle that can be tolerated before any appreciable demolition (and losses) occurs is on the order of 10-15 degrees. This problem, in addition to the constraints on the length of the diffuser, limits the boil-off pressure recovery coefficient to a value of 0.25-0.3.

Previous options found for improving diffuser performance over conventional designs include the use of shovel blades, eddy current generators, and wall fins. Shard blades have the disadvantage of increasing surface friction (and hence losses) and appear to work well only with uniform inlet flows. For example, intake vortices can significantly reduce performance. Vortex generators and other passive devices require a pulse-rich core flow to rejuvenate the interface and retard delamination. Basically, it is expected that they will not be able to cause a significant increase in diffuser performance if, as is the case downstream of the last turbine stage at the diffuser inlet, the airfoil at the diffuser inlet is very distorted and through large regions of fluid is marked with low momentum near the break-off point. There is no firm evidence of improvement in diffuser performance due to the use of ribs on the diverging diffuser walls.

The patent '475 overcomes the disadvantages and deficiencies of prior art designs with a diffuser assisted with fluidic action mechanism. The present invention relates to a fluidic source.

BRIEF DESCRIPTION OF THE INVENTION

In one embodiment, a steam turbine includes a turbine output stage, an axial or radial flow diffuser that receives a main flow from the turbine output stage, a divergent wall in the axial or radial flow diffuser that extends from a diffuser inlet to a diffuser exit, and a centerbody in the axial flow. or radial flow diffuser. An opening is provided in the diverging wall, and an opening is provided in the centerbody for fluidly influencing the main flow. The openings are located downstream of the diffuser inlet and upstream of a point where a diffuser would come to a stall without the openings along the walls. A plurality of openings are provided in the diverging wall, and an end packing seal is disposed adjacent an end portion of the turbine output stage. An annular manifold collects fluid from a leakage flow from the end pack seal and distributes the leakage flow to the ports.

In one embodiment, a steam turbine includes a turbine output stage, an axial or radial flow diffuser receiving a main flow from the turbine output stage, a divergent wall in the axial or radial flow diffuser extending from a diffuser inlet to a diffuser exit, and a centerbody in the axial flow. or radial flow diffuser. An opening is provided in the diverging wall, and an opening is provided in the centerbody to fluidly influence the main flow. A vapor seal collector collects fluid from a leakage current from at least the turbine output stage. The openings in the diverging wall and centerbody are downstream of the diffuser inlet and upstream of a point where boundary layer separation along the walls would occur in a diffuser without openings. Steam is withdrawn from the vapor seal collector and directed into the openings in the diverging wall to charge the boundary layer with energy.

In another embodiment, a method of improving diffuser performance includes the steps of passing a main stream through the diffuser; the provision of an opening in a diffuser wall; the use of a vapor seal collector as a fluid source; introducing fluid from the vapor seal collector into the opening to prevent separation of the main flow from the diffuser wall; and directing the fluid at an angle with respect to the main flow and with respect to the diffuser wall, wherein the steering of the fluid at an angle precedes the passage of the fluid through a curved channel having a curvature that is convex relative to the main flow prior to insertion of the fluid in the opening.

BRIEF DESCRIPTION OF THE DRAWING

1 is a schematic representation of a steam turbine;

2 shows a Axialstromdiffusor a steam turbine, which is supported by a fluid power actuation;

3 shows a downstream exhaust hood of a steam turbine, which is supported with fluid technology Wirkschema; and

4 is a schematic representation of a steam turbine that uses Endpackungs leakage as fluidic source.

DETAILED DESCRIPTION OF THE INVENTION

In 1 is a steam turbine 10 shown a high-pressure (HP) section 12 , a medium pressure (IP) section 13 and a low pressure (LP) section 14 having. The steam turbine 10 also has associated high pressure seals 16 , Medium pressure seals 18 and low pressure seals 20 which are generally in the form of end packs provided at the end of each of the HP, IP and LP sections (referred to as N1, N2, N3 and N4) to seal the stator / rotor gaps).

Hot steam or hot fluid from an inlet line is directed to flow to a plurality of blades of a first blade stage. When the fluid acts on the plurality of blades of the first blade stage, the fluid orbits the multiple blades, a wheel member, and a rotor. The fluid then passes the number of blades of the first stage in the downstream direction towards a second stage. The fluid passes through the several downstream stages in a similar manner, causing the rotor to rotate even more at each stage. By turning the rotor, the fluid makes work in the steam turbine. Fluid that does no work by flowing through the plurality of blades and rotating the rotor is considered to be a leaking fluid.

End-pack leakage currents (N2, N3 and N4) are measured in a vapor seal collector (SSH) 22 collected. Part of the flow (about 1 lbm / s) is used to prevent the leakage of the LP end pack via a line 24 to seal, and the remaining stream (about 1 lbm / s) is via a line 26 derived in the exhaust hood. It can be diverted either in the steam guide (the outer wall of the diffuser) or in the inner surface of the diffuser (in the bearing cone), depending on where the current dissipation occurs. As will be described in more detail below, the preferred embodiments utilize the effluent in the inner and outer wall surfaces of the diffuser (at certain radial and tangential flow angles) to energize the boundary layer, thereby providing separation even at higher area ratios or at sharper wall angles in the case of shorter diffuser is avoided. A higher area ratio leads to a higher ideal CP (a static Pressure recovery), resulting in greater expansion in the final stage and higher power output.

Aggressive steam turbine exhaust systems with high potential pressure recovery (high area ratio, short axial length) can be designed to implement a flow control (blowing) to prevent boundary layer wall separation. 2 shows an axial flow diffuser, and 3 shows a downstream exhaust hood. For both exhaust steam systems, the implementation of the wall blowing technique may allow a design that allows high pressure returns (low energy losses) within the geometric constraints of the exhaust steam configuration. As a result, increased removal of work from the machine can be achieved.

An example of a reinforced steam turbine axial flow diffuser 300 is in 2 shown. The entry points in 2 and 3 are shown closer to the blade of the last stage; however, this location may also change depending on the diffuser, the last stage blade, the amount of blade tip leakage, and so on. The invention is not necessarily limited to the illustrated construction. The annular diffuser 300 has a central body 310 and a diverging diffuser wall 302 on, that of a diffuser input section 304 , the last turbine stage 306 adjacent to the diffuser exit plane 308 runs. The main stream 312 , which is indicated by the current direction arrow, flows from the last turbine stage 306 through the diffuser 300 and over the diffuser exit plane 308 , Brands 314 and 311 indicate the approximate locations of the boundary layer injection ports. Note that injection ports 311 . 314 along the outer diverging diffuser wall 302 and the straight centerbody 310 available. The injection ports should be located immediately upstream of the point where boundary layer separation occurs. Likewise is an injection opening 311 at the centerbody 310 is provided, downstream of the injection port 314 arranged at the diffuser wall 302 is provided.

In the downstream exhaust hood housing, which in 3 Given the current geometry, there is very little pressure recovery: for typical engine operating conditions, Cp is about 0.3, indicating significant energy losses through the duct. However, the geometric constraints and the flow separation prevent a performance increase. Flow control (blowing) allows the design and implementation of a more aggressive larger area ratio exhaust hood geometry with potentially higher pressure recovery while preventing boundary layer separation and associated losses. Because most of the diffusion in a downstream exhaust hood 330 through the outer surface of the diffuser (steam duct) 332 takes place ( 3 , a high aspect ratio steam channel has the potential to provide higher pressure recovery as long as flow separation is prevented). Bubbles will be in one place 334 around the perimeter of the steam pipe 332 around to energize or remove the weakened boundary layer, and a flow separation of the main flow 342 to prevent.

The current can be injected into the inner wall or storage cone, depending on the diffuser design, bucket design, operating conditions, etc.

In the Axialstromdiffusor, as in 2 As shown, annular slots or discrete holes may be used for the geometry of the injection ports.

One or more circular slots extending over a portion of the perimeter of the outer wall 302 and the centerbody 310 extend are near the diffuser entrance 304 arranged.

Discrete holes give secondary rays with strong momentum from the outer wall 302 and the centerbody 310 into the wall boundary layers of the main stream 312 at the diffuser entrance 304 from. In order to achieve maximum efficiency for a particular purpose, provisions have been made to control the angle between the axis of the second jet and the main flow direction and the angle between the axis of the secondary jet and the local diffuser wall slope. Note that this embodiment takes the case of discrete holes emitting secondary rays which tangentially contact the divergent diffuser walls in the direction of the axis of the diffuser, and includes the case of secondary rays parallel to the main flow direction.

For the downstream exhaust hood, as in 3 can be used, annular slots or discrete openings can be used. Ring-shaped slots at the steam guide or the storage cone 336 are arranged and around a part of the scope of the steam guide 332 run around can be used.

Discrete holes, the secondary jet with strong impulse from the steam guide 332 into the wall boundary layers of the main stream 342 near the hood entrance 336 can also be used. To get maximum effectiveness for a given application Provision is made to control the angle between the axis of the secondary jet and the flow direction and the angle between the axis of the secondary jet and that of the local steam guide slope. Note that this embodiment includes the case of discrete holes that emit secondary rays that tangentially contact the vapor guide walls in the direction of the axis of the hood and the case of secondary rays that are parallel to the mainstream direction.

In the case of injection tangential to the exhaust diffuser / hood walls, the Coanda effect can be used to hold the secondary jets / film layers in firm contact with the walls.

In comparison with the slots, the discrete holes have the advantage of easier implementation in a steam turbine exhaust system. From the blowing source, the blowing fluid can be collected in an annular collecting tube which is mounted around the circumference of the outer Abdampfgehäuses. Small circular tubes connected to the collection tube may be used to inject secondary rays into the main flow. The cross-section of the manifold should be at least 15 to 20 times larger than the diameter of the holes to avoid an injection with variation in the circumferential direction. Alternatively, small tubes may be used to direct the secondary flow directly from the blower source to the injection site into the mainstream.

Another advantage of discrete holes versus slots in the circumferential direction is the fact that localized circular beams are expected to promote the development of three-dimensional turbulence in the boundary layer along the diffuser walls. This would increase mixing and, in principle, could reduce the required secondary mass flow rate, thereby increasing the effectiveness of the blowing scheme.

It has already been proposed to inject a continuous secondary stream to prevent separation in a high area ratio exhaust steam geometry. An alternative embodiment that could significantly reduce the amount of secondary current needed is the injection of pulsatile film layers / jets. It is expected that because of the artificial generation and development of n coherent structures in the wall boundary layers, which enhances the mixing of the low-impulse boundary layer current with the impulse rich core, uneven injection is more effective to prevent detachment than a steady injection. Parameters that play a role in the effectiveness of pulsating film layers / jets include pulsatile frequency, duty cycle and pulsation amplitude.

In order to transfer the fluid power control scheme to a steam turbine engine, the selection of a blowing source to provide flow control at the exhaust steam inlet should be addressed. As will be described in more detail below, it is proposed to use an end-pack leakage current as the fluidic source.

4 Figure 11 is a schematic diagram of a steam turbine utilizing end-pack leakage as a source of boundary layer blowing. Leakage currents in the vapor seal collector 22 become a plenum 28 passed the electricity into a pipe 30 dispersed, which is arranged outside the steam guide. Openings in the pipe 30 introduce the leakage current into the main stream to thereby energize the weak boundary layer that has developed in the diffuser.

Blowing the vapor seal leakage current through steam guide slots serves to energize the weak boundary layer and thereby improve pressure recovery. With this construction, the diffuser pressure recovery coefficient, depending on other design parameters, e.g. of the last stage vane, the diffuser and entry design parameters, are increased from 0.1 to 0.5. A CP of 0.1 corresponds to an LP section efficiency of about 0.2-0.3%. Alternatively, or in addition to the construction of the embodiments described above, the axial span of a double-LP turbine can be shortened by increasing the diffuser wall angles by up to 2 to 3 feet.

While the invention has been described in conjunction with what is presently considered to be the best to be practiced and preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments but, on the contrary, covers various modifications and equivalent arrangements disclosed in U.S. Patent Nos. 4,912,355 Thought and scope of the appended claims are included.

A steam turbine has a turbine output stage 306 , an axial or radial flow diffuser 300 , which receives a main flow from the turbine output stage, a diverging wall 302 in the axial or radial flow diffuser coming from a diffuser inlet 304 to a diffuser exit 308 runs, and a middle body 310 in the axial or radial flow diffuser. An opening is provided in the diverging wall and an opening is provided in the centerbody to fluidly affect the main flow. The openings are downstream of the diffuser inlet and upstream of a point where boundary layer separation would occur in a diffuser without openings along the walls. A plurality of openings are provided in the diverging wall, and an end packing seal 16 . 18 . 20 is disposed adjacent to an end portion of the turbine output stage. An annular manifold 22 collects fluid from the leakage flow from the end packing seal and distributes the leakage flow to the ports.

LIST OF REFERENCE NUMBERS

 10

steam turbine

12

High-pressure (HP) section

13

 Intermediate pressure (IP) section

 14

 Low-pressure (LP) section

 16

High pressure seals

 18

 Intermediate pressure seals

 20

Low pressure seals

22

Steam Sealing Collector (SSH)

 24

management

26

Conduction in exhaust steam hood

 28

 gap

 30

pipe

300

Steam turbine Axialstromdiffusor

 302

Diverging diffuser wall

 304

 Diffusoreinlasabschnitt

 306

 Last turbine stage

 308

 Diffuser output level

 310

 midbody

 312

main power

 311, 314

Positions for injection holes

 330

Downstream exhaust hood

 332

Steam conduit

 334

Blasort

 336

 bearing cone

 342

main power

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6896475 [0005, 0007]

Claims (14)

Steam turbine, comprising: a turbine output stage ( 306 ); an axial or radial flow diffuser ( 300 ), which receives a main flow from the turbine output stage; a diverging wall ( 302 ) in the axial or radial flow diffuser, the diverging wall being defined by a diffuser entrance (FIG. 304 ) to a diffuser exit ( 308 ) runs; a central body ( 310 ) in the axial or radial flow diffuser; an aperture in the divergent wall and an aperture in the central body for fluidly flowing the main stream, the apertures being located downstream of the diffuser inlet and upstream of a point where boundary layer separation would occur along the walls in a diffuser without the apertures; a plurality of openings in the divergent wall; a final packing seal ( 16 . 18 . 20 ) disposed adjacent to an end portion of the turbine output stage; and an annular collecting tube ( 22 ); collecting fluid from a leakage flow from the end packing seal and distributing the leakage flow to the ports. Steam turbine according to claim 1, wherein the annular collecting pipe is a vapor sealing collector ( 22 ) having. Steam turbine according to claim 2, a plurality of turbine stages ( 12 . 13 . 14 ) and a corresponding plurality of end packing seals ( 16 . 18 . 20 ), wherein the vapor seal collector collects fluid from the leakage flow from the plurality of end packer seals. Steam turbine according to claim 3, further comprising a steam guide ( 332 ) with the vapor seal collector ( 22 ) in fluid communication with the steam guide directing the leakage flow from the vapor seal collector to the axial or radial flow diffuser ( 300 ) to energize a boundary layer in the axial or radial flow diffuser. Steam turbine according to claim 1, further tubes ( 30 ), which the annular collecting line ( 22 ) connect with the openings. Steam turbine according to claim 5, wherein the tubes ( 30 ) are convexly curved with respect to the main flow. Steam turbine, comprising: a turbine output stage ( 306 ); an axial or radial flow diffuser ( 300 ), which receives a main flow from the turbine output stage; a diverging wall ( 302 ) in the axial or radial flow diffuser, the diverging wall being defined by a diffuser entrance (FIG. 304 ) to a diffuser exit ( 308 ) runs; a central body ( 310 ) in the axial or radial flow diffuser; an opening in the diverging wall and an opening in the center body for fluidly influencing the main flow; and a vapor seal collector ( 22 ) collecting fluid from the leakage current of at least the turbine output stage, wherein the openings in the divergent wall and in the centerbody are located downstream of the diffuser inlet and upstream from a point where boundary layer separation would occur in a diffuser with no openings along the walls, wherein vapor is withdrawn from the vapor seal collector and directed into the openings in the diverging wall to energize the boundary layer. Steam turbine according to claim 7, further comprising a plurality of turbine stages ( 12 . 13 . 14 ) and a corresponding plurality of end packing seals ( 16 . 18 . 20 ) disposed adjacent end portions of the respective turbine stages, the vapor seal collector collecting fluid from a leakage current from the plurality of end packer seals. Steam turbine according to claim 8, further comprising a steam guide ( 332 ) in fluid communication with the vapor seal collector ( 22 wherein the steam guide directs the leakage flow from the vapor seal collector to the axial or radial flow diffuser ( 300 ) to energize an interface in the axial or radial flow diffuser. Steam turbine according to claim 7, further tubes ( 30 ) comprising the vapor seal collector ( 22 ) connects to the openings. Steam turbine according to claim 10, wherein the tubes ( 30 ) are convexly curved relative to the main flow. A method of improving diffuser performance, comprising: flowing a main stream through the diffuser ( 300 ); Providing an opening in a diffuser wall ( 302 ); Benefits of a vapor seal collector ( 22 ) as a fluid source; Introducing fluid from the vapor seal collector into the opening to prevent separation of the main flow from the diffuser wall; and Directing the fluid at an angle relative to the main flow and relative to the diffuser wall, wherein the steering of the fluid at an angle, the passage of the fluid through a curved channel ( 30 ) having a curvature that is convex relative to the main flow prior to introduction of the fluid into the opening. The method of claim 12, further comprising positioning a centerbody ( 310 ) within the diffuser ( 300 ) and providing an opening in a wall of the centerbody. The method of claim 13, further comprising introducing fluid from the vapor seal collector (10). 22 ) through the opening of the middle body ( 22 ) and in the diffuser ( 300 ).

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