Patent Publication Number: US-7594795-B2

Title: Steam turbine

Description:
RELATED APPLICATION 
   The present application claims priority under 35 USC § 119 to Swedish Patent Application No. 01012/05. filed Jun. 14, 2005, the contents of which are hereby incorporated by reference in their entirety. 
   TECHNICAL FIELD 
   The invention relates to a steam turbine, in particular for a power plant. 
   PRIOR ART 
   The steam turbine conventionally has an outer casing and an inner casing arranged therein. A plurality of guide blade rows are arranged axially one behind the other in the inner casing and consist in each case of a plurality of guide blades arranged next to one another in a circumferential direction. 
   For a high efficiency of the steam turbine, it is of critical importance to avoid leakage flows which bypass the guide blades of the blade tips. Effective sealing off of the regions of the blade tips is often made difficult due to the fact that the inner casing experiences asymmetric deformation when the steam turbine is in operation. Deformations of the inner casing are attributable to the high pressures and to the high thermal loads. Asymmetric deformations of the inner casing arise particularly when the inner casing consists of two inner casing halves which are fastened to one another along a midplane via external lateral flanges. The inner casing necessarily possesses a different flexion behavior in the region of the flanges from that between the flanges. The original circular cross section of the inner casing may be deformed due to the compressive load occurring during operation, for example elliptically or ovally or due to a contraction in the region of the flanges, which may lead locally to an enlargement of the radial clearance of the blade tips. Undesirable leakages may occur correspondingly there. Two-part inner casings are used in order to simplify the mounting and demounting of the steam turbine. 
   In order to reduce the asymmetric deformation of the inner casing, it is basically possible to fasten the two inner casing halves to one another not via laterally projecting flanges, but via tension rings which are drawn from outside onto the inner casing halves lying one on the other. However, the outlay required for this purpose is relatively high. In particular, the subsequent removal of the tension rings is sometimes difficult. 
   PRESENTATION OF THE INVENTION 
   The invention is intended to remedy this. The invention, as characterized in the claims, is concerned with the problem of specifying for a steam turbine of the type initially mentioned an improved embodiment which is distinguished particularly by reduced leakage. 
   This problem is solved, according to the invention, by means of the subject matter of the independent claim. Advantageous embodiments are the subject matter of the dependent claims. 
   The invention is based on the general idea of arranging at least some of the guide blade rows in a blade ring which is itself arranged in the inner casing. A blade ring of this type can be sealed off efficiently with respect to the inner casing in a relatively simple way. 
   Furthermore, the blade ring is not exposed to the overall compressive load of the steam turbine when it does not have all the guide blade rows, but only some of these. The forces arising at the blade ring are correspondingly comparatively low. The lower these forces arising are, the more simply a symmetrical deformation of the blade ring can be achieved. However, a symmetric deformation leads to no or to only slight leakage flows. In the steam turbine according to the invention, the inner casing is decoupled from those deformation forces which arise in the region of the guide blade rows arranged in the blade ring. A deformation of the inner casing is to that extent already reduced. In the region of the blade ring, the inner casing serves mainly for the axial support of the axial forces acting on the guide blade rows of the blade ring. The moments acting on the blade ring in the circumferential direction can also be absorbed by the inner casing. 
   Preferably, the blade ring is fixed axially to the inner casing in an axial fixing and is otherwise freely movable axially in relation to the inner casing. The blade ring is thereby decoupled kinematically from the inner casing, but can absorb the axial forces acting on the blade ring via the guide blades arranged therein. 
   A development is particularly advantageous in which the axial fixing is configured, moreover, as a seal which prevents or at least impedes a flow around the blade ring. For this purpose, fixing between the blade ring and inner casing has a contact zone which runs completely around annularly and which, in particular, allows radial movement between the blade ring and inner casing. A particularly effective seal between the inner casing and the blade ring can thereby be implemented in a structurally simple and therefore cost-effective way. 
   Further important features and advantages of the steam turbine according to the invention may be gathered from the subclaims, from the drawings and from the accompanying figure description with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, identical reference symbols referring to identical or similar or functional identical components. In the drawings, in each case diagrammatically, 
       FIG. 1  shows a perspective part view of the steam turbine according to the invention, 
       FIG. 2  shows a top view of the steam turbine from  FIG. 1 , 
       FIG. 3  shows an enlarged detail III from  FIG. 2 , 
       FIG. 4  shows a cross section corresponding to the sectional lines IV in  FIG. 2  and  FIG. 3 , 
       FIG. 5  shows an enlarged detail V from  FIG. 4 , 
       FIG. 6  shows a longitudinal section corresponding to the sectional lines VI in  FIG. 2 , 
       FIG. 7  shows an enlarged detail VII from  FIG. 6 , 
       FIG. 8  shows a cross section corresponding to the sectional lines VIII in  FIG. 7 . 
   

   WAYS OF IMPLEMENTING THE INVENTION 
   According to  FIG. 1 , a steam turbine  1  according to the invention, which is employed preferably in a power plant, preferably as the medium-pressure turbine or high-pressure turbine, comprises an outer casing  2  in which an inner casing  3  is arranged. A steam turbine  1  of this type comprises, furthermore, a multiplicity of guide blade rows, which, however, are not illustrated here. 
   What are shown, however, are guide blade receptacles  4 , into which guide blades or guide blade carriers can be inserted individually or in groups. The guide blade rows, not shown, are thus represented here by the guide blade receptacles and are also designated below by  4 . The individual guide blade rows  4  are arranged one behind the other in the axial direction of the steam turbine  1 . The individual guide blades are arranged next to one another in the circumferential direction in the respective guide blade row  4 . 
   Moreover, the steam turbine  1  conventionally has a rotor, not shown here, which carries a corresponding number of moving blade rows. 
   The steam turbine  1  according to the invention is distinguished in that it is equipped with at least one blade ring  5  which carries some of the guide blade rows  4 . The blade ring  5  is in this case arranged in the inner casing  3 , and the guide blade rows  4  assigned to the blade ring  5  are arranged in the blade ring  5 . 
   According to  FIGS. 1 and 2 , said blade ring  5  is fixed axially to the inner casing  3  with the aid of exactly one axial fixing  6 . Otherwise, that is to say outside the fixing  6 , the blade ring  5  is axially loose or freely movable in relation to the inner casing  3 . The fixing  6  is in this case arranged near an inflow-side end of the blade ring  5 . In the preferred embodiment shown here, the fixing  6  is formed by a collar  7  which projects radially outward from the blade ring  5  and runs around annularly on the latter. Furthermore, the collar  7  is supported axially on the supporting surface  8  which is formed on the inner casing  3 . This supporting surface  8  is formed here by an annular groove  9  which is made in the inner casing  3  and into which the collar  7  engages radially. The collar  7  and supporting surface  8  are expediently designed such that the fixing  6  additionally acts as a seal. The supporting surface  8  is then a sealing surface which is also designated below by  8 . This is achieved, for example, by means of a contact zone between the collar  7  and the supporting or sealing surface  8 , said contact zone running around, closed, in the circumferential direction and, moreover, expediently extending in a plane which is perpendicular to the longitudinal axis of the steam turbine  1 . The axial seal formed by the fixing  6  or in the fixing  6  prevents or impedes a flow around the blade ring  5 . 
   In the exemplary embodiment shown here, the steam turbine  1  is designed as a double-flow steam turbine  1 , each flow  10  constituting a turbine, and these being coupled to one another via the common rotor. The two turbines or flows  10  are designed asymmetrically here. In particular, only one of the two turbines or flows  10  is equipped with the blade ring  5 . In principle, in another embodiment, each flow or turbine  10  could have such a blade ring  5 . In another embodiment, the steam turbine  1  may also be designed as a single-flow steam turbine  1 . 
   In the embodiment shown here, within the respective flow or turbine  10 , some, in particular the plurality, of the guide blade rows  4  are arranged on the blade ring  5 , while all the other guide blade rows  4  are arranged on the inner casing  3 . It is notable in this case that the first guide blade row  4  is arranged on the blade ring  5  within this flow  10 , while the last guide blade row  4  is arranged on the inner casing  3 . In this case, the first guide blade row  4  is adjacent to an inflow space  11  which is arranged centrally between the two flows  10 , while the last guide blade row is arranged adjacently to an outflow space  12  which is located essentially between the inner casing  3  and the outer casing  2 . The inflow space  11  in this case forms a steam inlet into the turbine of the respective flow  10 , while the outflow space  12  forms a steam outlet from this turbine. 
   Steam turbine  1  or the turbine of the respective flow  10  has an extraction pressure space  13  between the associated steam inlet or inflow space  11  and the associated steam outlet or outflow space  12 . This extraction pressure space  13  is connected to at least one extraction line  14 , with the aid of which extraction steam can be extracted from the steam turbine  1  or the turbine of the respective flow  10 . Depending on the turbine stage to which the extraction pressure space  13  is connected, the extraction steam has a corresponding pressure level and/or a corresponding temperature level. In the left flow  10  shown in  FIGS. 1 ,  2  and  6 , the extraction pressure space  13  is arranged approximately in the last third of the turbine stages, that is to say the extraction pressure space  13  communicates with a turbine stage arranged in the last third. In contrast to this, in the flow  10  shown in each case on the right, the extraction pressure space  13  is arranged approximately in the middle of the turbine stages, that is to say the extraction pressure space  13  is connected to a turbine stage which is located approximately in the middle of the turbine stages. In this case, the respective extraction pressure space  13  communicates with the respectively assigned turbine stage via an extraction gap  15  which is arranged between two guide blade rows  4 . 
   In the turbine or flow  10  equipped with the blade ring  5 , the guide blade row  4  which is connected upstream to the extraction gap  15  is formed by the last guide blade row  4  of the blade ring  5 . In contrast to this, the guide blade row  4  connecting downstream to the extraction gap  15  is already arranged on the inner casing  3 . This is, in particular, the first guide blade row  4  of the inner casing  3 . 
   This design is in this case particularly important since, in this way, the blade ring  5  does not incur the entire pressure difference, but only a large part of the pressure difference arising between the inflow space  11  and outflow space  12  of this turbine or flow  10 . The pressure forces to be absorbed by the blade ring  5  are therefore lower than the overall pressure forces occurring, so the blade ring  5  may have a correspondingly small dimensioning. Consequently, in particular, design for the blade ring  5  may be selected which exhibits an approximately symmetrical deformation behavior. 
   As may be gathered particularly from  FIG. 1 , a two-part construction is preferred for the blade ring  5 , so that the blade ring  5  is assembled from two blade ring halves  16 ,  17 . The blade ring halves  16 ,  17  are in this case fastened to one another along an axial midplane. This midplane corresponds in  FIG. 2  to the drawing plane. So that the two blade ring halves  16 ,  17  can be fastened to one another, external lateral flanges  18 ,  19 , which are screwed to one another with the aid of screws  20 , are formed on the blade ring halves  16 ,  17  on each side. Since the expected compressive loads on the blade ring  5  are comparatively low, the flanges  18 ,  19  can have a relatively compact build, so that they project only slightly beyond the blade ring halves  16 ,  17  in the radial direction. In particular, the flanges  18 ,  19  can thereby be configured such that a circumferentially essentially symmetrical deformation behavior is established for the blade ring  5 . A symmetrical deformation is advantageous in terms of small gaps of the blade tips. 
   Preferably, the inner casing  3  is also assembled from two inner casing halves  21  which are fastened to one another on an axial midplane. Preferably, for this purpose, corresponding external lateral flanges, not designated in any more detail here, are provided, which make it possible to screw the two inner casing halves  21  together. The outer casing  2  expediently also consists of two outer casing halves  22  which are screwed to one another correspondingly via external lateral flanges, the outer casing halves  22  also bearing against one another in an axial midplane. The midplane of the inner casing halves  21  or of the outer casing halves  22  lies in the drawing plane of  FIG. 2  and thus coincides with the midplane of the blade ring halves  16 ,  17 . Such a two-part construction with casing halves  21 ,  22  and blade ring halves  16 ,  17  simplifies the mounting and demounting of the steam turbine  1 . 
   As can be seen particularly clearly, for example, from the enlarged views of  FIGS. 3 ,  5  and  7 , the blade ring  5  is expediently arranged in the inner casing  3  with a radial clearance  23 . This achieves a decoupling between the blade ring  5  and inner casing  3  in terms of a transmission of radial forces. In particular, therefore, a deformation of the blade ring  5  does not automatically lead to a deformation of the inner casing  3 . 
   According to  FIG. 2 to 5 , the blade ring  5  is supported on the inner casing  3 , in the vicinity of the fixing  6 , via at least one axial vertical support  24 . Preferably, two vertical supports  24  of this type are provided, which are arranged mirror-symmetrically on sides facing away from one another. The two vertical supports  24  are in this case configured such that they allow axial relative movements between the blade ring  5  and inner casing  3 . For this purpose, the vertical supports  24  lie in a sliding bearing plane extending parallel to that midplane which at the same time forms the parting plane of the blade ring  5  and, in particular, of the two casings  2 ,  3 . As may be gathered from  FIGS. 2 and 4  and particularly clearly from  FIGS. 3 and 5 , each vertical support  24  comprises a carrier  25  which projects radially from the blade ring  5 . In this case, the respective carrier  25  cooperates directly or indirectly with a carrying step  26  which is formed on the inner casing  3 . The carrier  25  in this case expediently lies via a sliding plate  27  on the associated carrying step  26 . In the mounted state, support takes place in the direction of gravity. The respective carrier  25  is expediently formed on the blade ring half  17  which is the lower in the mounted state, specifically preferably on the flange  19  of the latter. The carrying step  26  is also provided correspondingly on the inner casing half  21  which is the lower in the mounted state. To form the carrying step  26 , the inner casing  3  has worked out in it a recess which is delimited downwardly by the carrying step  26  and upwardly by a guide step  28 . The guide step  28  thus extends parallel to the carrying step  26 . The carrier  25  is also supported on the guide step  28 , specifically preferably again via a sliding plate  29 . In this case, the guide step  28  is formed on the inner casing half  21  which is the upper in the mounted state. The contact zones between the individual components of the vertical support  24  expediently extend rectilinearly in the axial direction and preferably in axial planes which run parallel to the separating plane or midplane of the blade ring halves  16 ,  17  or of the inner casing halves  21 . 
   The sliding plates  27 ,  29  are configured such that particularly low coefficients of friction arise. The blade ring  5  is mounted via the sliding plates  27 ,  29  on the carrying step  26  and on the guide step  28  movably in the axial direction and transversely thereto, that is to say perpendicularly to the direction of gravity. Furthermore, the vertical supports  24  absorb a large part of the weight of the blade ring  5 . Moreover, the vertical supports  24  can, by means of the circumferential fixing of the blade ring  5 , transmit to the inner casing  3  moments which are introduced into the blade ring  5  via the guide blades when the steam turbine  1  is in operation. 
   According to  FIG. 6 to 8 , the blade ring  5  is supported on the inner casing  3 , specifically in the circumferential direction, by means of at least one axial guide  30  in the region of an axial portion which is remote from the fixing  6  and is spaced apart from the vertical supports  24 . This axial guide  30  is in this case configured such that it fixes the blade ring  5  to the inner casing  3  in the circumferential direction, while at the same time it allows relative movements between the blade ring  5  and the inner casing  3  in the axial direction and preferably also in the radial direction. This is achieved, here, with the aid of a guide body  31  which, on the one hand, is arranged fixedly on the inner casing  3  and, on the other hand, engages radially into an axial groove  32  formed on the blade ring  5 . The axial groove  32  has two opposite and axially extending walls on which the guide body  31  is supported in the circumferential direction. The blade ring  5  is fixed to the inner casing  3  fixedly in terms of rotation via this axial groove  32  and the guide body  31 , but is otherwise freely movable in the axial direction and radially in relation to the inner casing  3 . In particular, the blade ring  5  is not supported axially or radially on the inner casing  3  at any point in the region of the axial guide  30 . 
   The guide body  31  is a separate component with respect to the inner casing  3 . The guide body  31  is inserted into a guide body holder  33  which is formed on the inner casing  3 . The guide body  31  may, in principle, be anchored firmly in the guide body holder  33 ; a rotatable mounting is likewise possible. The inner casing  3  is provided in the region of the axial guide  30  with an extension  34  which projects toward the blade ring  5  from adjacent regions of the inner casing  3 . The guide body  31  shown here is arranged on that inner casing half  21  which lies at the bottom in the mounted state. The axial groove  32  is also formed correspondingly on the blade ring half  17  which is the lower in the mounted state. The axial guide  30  explained here in more detail is in this case located centrally between the flanges  18 ,  19  or centrally between the vertical supports  24 . Although only a single axial guide  30  is shown here, a plurality of such axial guides  30  may, in principle, be arranged so as to be distributed in the circumferential direction. 
   The blade ring  5  is thus arranged in the inner casing  3  in that the two vertical supports  24  absorb the entire weight forces and moments and at the same time allow relative movements in a horizontal plane, and/or in that the fixing  6  absorbs the entire axial forces, and/or in that the axial guide  30  absorbs moments and at the same time allows relative movements in an axial vertical plane, and/or in that the blade ring  5 , with the exception of the fixing  6 , of the vertical supports  24  and of the axial guide  30 , is arranged contactlessly in the inner casing  3 . 
   LIST OF REFERENCE SYMBOLS 
   
       
         1  Steam turbine 
         2  Outer casing 
         3  Inner casing 
         4  Guide blade receptacle/guide blade row 
         5  Blade ring 
         6  Axial fixing 
         7  Collar 
         8  Supporting surface/sealing surface 
         9  Annular groove 
         10  Flow/turbine 
         11  Inflow space 
         12  Outflow space 
         13  Extraction pressure space 
         14  Extraction line 
         15  Extraction gap 
         16  Blade ring half 
         17  Blade ring half 
         18  Flange 
         19  Flange 
         20  Screw 
         21  Inner casing half 
         22  Outer casing half 
         23  Radial clearance 
         24  Vertical support 
         25  Carrier 
         26  Carrying step 
         27  Sliding plate 
         28  Guide step 
         29  Sliding plate 
         30  Axial guide 
         31  Guide body 
         32  Axial groove 
         33  Guide body holder 
         34  Extension