Patent Abstract:
The invention relates to a segmented inner ring for holding guide blades. According to the invention, a lateral wall opposing the front side of the inner ring and pertaining to a shaft shoulder formed on the rotor shaft extends radially, and respectively one half of a labyrinth seal is formed on the front side of the inner ring and on the shaft shoulder. The aim of the invention is to apply an arrangement of stacked labyrinth seals, known from airplane turbines, to a stationary gas turbine having a separation plane. To this end, a method is used to mount an inner ring of a gas turbine. The invention also relates to a stationary gas turbine comprising a segmented inner ring.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2004/008052, filed Jul. 19, 2004 and claims the benefit thereof. The International Application claims the benefits of European Patent application No. 03019002.9 EP filed Aug. 21, 2003. All of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a stationary gas turbine having a segmented inner ring for holding guide vanes. It also relates to a method for assembling a segmented inner ring for guide vanes of a stationary gas turbine. 
     BACKGROUND OF THE INVENTION 
     DE 37 12 628 has disclosed an inner ring for holding guide vanes of a stationary gas turbine. The guide vanes which are arranged in a star shape around the rotor to form a guide vane ring are secured to the housing of the gas turbine by means of their radially outer guide vane roots. The radially extending guide vanes, on their side facing the rotor, have the guide vane head, which is connected to the stationary inner ring. This inner ring, which is U-shaped in cross section, engages coaxially around the rotor of the gas turbine and connects the guide vanes of a guide vane ring to one another in order to increase the stability of the guide vane ring and to improve the vibrational properties of the guide vanes. A gap is in this case formed between the web of the U-shaped inner ring, its flanks and the corresponding circumferential and end faces associated with the rotor. Likewise, the web of the U-shaped inner ring, on its surface facing the rotor, has one half of a labyrinth seal, which together with the second half arranged on the rotor forms the labyrinth seal. 
     When the gas turbine is operating, the working fluid which flows within the flow passage is only supposed to flow past the guide vanes of a guide vane ring. However, the working fluid can also flow through the gap formed by stationary and rotating components, as a leakage flow. 
     To reduce the extent of the leakage flow, the gap between the stationary and rotating components is sealed by means of the labyrinth seal. 
     Furthermore, it is known to provide a plurality of labyrinth seals in the gap between the flank of the inner ring and of the shaft shoulder, in order to achieve an improved sealing action. In this case, two labyrinth seals are arranged axially and radially offset with respect to one another, in a terraced arrangement, in the gap between the flank and shaft shoulder. 
     The terraced arrangement of a plurality of labyrinth seals takes up a large amount of space and is only used for stationary gas turbines. Stationary gas turbines have a parting plane located between a lower housing half and an upper housing half and are fitted together radially during assembly. In the process, the finished rotor is inserted into the lower housing half, which has already been preassembled and onto which the upper housing half is then fitted, so that only labyrinth seals which are offset in terraced fashion with respect to one another are possible between the rotor and the housing. 
     U.S. Pat. No. 5,222,742 has disclosed a stacked labyrinth seal between the securing ring for the guide vane of a turbine and a rotor blade mounted on the rotor of the turbine. The turbine is an axially assembled aircraft turbine, i.e. the axially successive rotor blade rings and guide vane rings of the individual compressor stages and/or turbine stages are mounted in succession ring by ring, so that a stacked arrangement is possible. Further labyrinth seals which have been stacked in this way for aircraft turbines are known from DE 199 31 765 and FR 2 241 691. 
     Since stacked labyrinth seals have hitherto only been known for aircraft turbines, a person skilled in the art was not hitherto in a position to transfer stacked labyrinth seals to stationary gas turbines, on account of the axial method of assembly. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the invention is to design a stationary gas turbine with a parting gap in such a way that the leakage flow is reduced by means of the stacked arrangement of labyrinth seals which is known from aircraft turbines. A further object is to provide a method for assembling an inner ring which allows a stacked arrangement of labyrinth seals. 
     The object relating to the gas turbine is achieved by the features herein disclosed. The object relating to the method is also achieved by the features herein disclosed. Advantageous configurations are given in this specification. 
     By carrying out the working steps of the invention, it is now possible for the first time for the arrangement of stacked labyrinth seals which is known from aircraft turbines also to be transferred to stationary gas turbines. It is therefore possible for a plurality of labyrinth seals which are stacked radially on top of one another to be arranged in a stationary gas turbine with a parting plane, and for the improved sealing action which ensues to be utilized for a stationary gas turbine. The leakage flow which reduces the efficiency of the stationary gas turbine is considerably reduced as a result. 
     The space required for the radially stacked labyrinth seals is reduced compared to the terraced arrangement. In particular, the size of the seal and of the entire inner ring in the axial direction have been reduced. 
     A gas turbine of this type is dismantled by carrying out the working steps of the invention in the reverse order. 
     If each labyrinth seal has a first coaxial balcony on the end side of the inner ring and a further coaxial balcony on the shaft shoulder, which balconies each, project in the axial direction, it is possible for the two balconies, in the assembled state of the inner ring, to lie radially opposite one another. This stacked arrangement of the balconies allows the series connection of labyrinth seals and forms a meandering gap for the leakage flow. 
     The labyrinth seal is advantageously formed by a sealing surface and at least one sealing tooth, the first balcony having the coaxial sealing surface, which faces the further balcony, and the further balcony, on its circumferential surface which faces the first balcony, having at least one circumferential sealing tooth which extends toward the sealing surface. 
     For axial securing purposes, the inner ring can be fixed to the rotationally fixed modules and/or to the guide vanes. 
     If the inner ring is arranged between two rotor blade rings, it can be secured against axial displacement by means of a securing ring. In this case, the securing ring is segmented and is mounted on the guide vane. 
     It is expedient for the securing ring to be arranged upstream of the inner ring. 
     It is advantageous for the sealing surfaces and the sealing teeth provided on the balconies to be designed in such a manner that intended axial displacement of the rotor counter to the direction of flow of the working fluid is possible without any change in the sealing action. Consequently, while the gas turbine is operating the rotor can be displaced without any deterioration in the sealing action. This is important in particular if the gap between the rotor blade tip and the radially outer, conical inner wall of the hot gas duct is to be reduced in size by the displacement of the rotor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained with reference to a drawing, in which: 
         FIG. 1  shows a segmented securing ring for guide vanes of a first turbine stage, 
         FIG. 2  shows the segmented inner ring for the guide vanes of a second, third and fourth turbine stage, and 
         FIG. 3  shows a partial longitudinal section through a gas turbine. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows a stationary gas turbine  1  in the form of a partial longitudinal, section. In its interior, it has a rotor  3 , which is mounted such that it can rotate about an axis of rotation  2  and is also referred to as the turbine rotor or rotor shaft. An intake housing  4 , a compressor  5 , a toroidal annular combustion chamber  6  with a plurality of coaxially arranged burners  7 , a turbine  8  and the exhaust-gas housing  9  follow one another along the rotor  3 . The annular combustion chamber  6  in this case forms a combustion space  10  which is in communication with an annular hot-gas duct  11 , where four turbine stages  12  connected in series form the turbine  8 . Each turbine stage  12  is formed from two blade/vane rings. As seen in the direction of flow of a working fluid  14 , a guide vane ring  17  is followed in the hot-gas duct  11  by a ring  15  formed from rotor blades  18 . The guide vanes  16  are secured to the stator  19 , whereas the rotor blades  18  of a ring  15  are secured to the rotor  3  by means of a turbine disk  20 . A generator (not shown) is coupled to the rotor  3 . 
     The stationary gas turbine  1  has a housing  60  which with respect to a parting plane  61  running parallel to the horizontal plane can be divided into an upper housing half  62  and a lower housing half  64 . In the subsequent text using the terms “upward” and “downward” or “upper half of the . . . ” and “lower half of the . . . ”, this is in each case to be understood as meaning with respect to the parting plane  61  of the gas turbine  1  for the object in question. 
     While the gas turbine  1  is operating, the compressor  5  sucks in air  21  through the intake housing  4  and compresses it. The air  21  provided at the turbine end of the compressor  5  is fed to the burners  7 , where it is mixed with a fuel. The mixture is then burnt so as to form the working fluid  14  in the combustion space  10 . From there, the working fluid  10  flows past the guide vanes  16  and the rotor blades  18  in the hot-gas duct  11 . The working fluid  14  expands at the rotor blades  18 , transmitting its momentum as it does so, so that the rotor  3  is driven, and with it the generator coupled to it is also driven. 
     On their side facing the housing  13 , the guide vanes  16  have a guide vane root, by means of which they are hooked in an annular guide vane carrier. At their end facing the rotor  3 , i.e. the guide vane head, they are connected to an inner ring  30 . 
       FIG. 1  shows an excerpt from the gas turbine  1  between the guide vane  16  of the first turbine stage  12  and the rotor  3 . The inner wall, located on the radially inner side, of the combustion chamber  6  delimits the hot-gas duct  11  toward the inside. As seen in the direction of flow of the working fluid  14 , the guide vane  16  of the first turbine stage  12  is followed by the rotor blade  18 . 
     On the rotor  3  is the turbine disk  20 , which at its outer circumference holds the rotor blades  18 . To secure the rotor blades  18  against axial displacement, at a side wall  22  of the turbine disk  20  a covering element  23  is hooked to the turbine disk  20  by means of a plurality of radially spaced hooks. The covering element  23 , together with the turbine disk  20 , forms a shaft shoulder  24 . 
     A plurality of balconies  25 ′  25 ″,  25 ′″,  25 ″″, which extend in the axial direction and are coaxially encircling, are arranged on a side wall  51 , facing the combustion chamber  6 , of the covering element  23 . 
     In each case three sealing teeth  26 ′,  26 ″,  26 ′″,  26 ″″ extend coaxially on that circumferential surface of each balcony  25  which faces away from the rotor  3 . 
     Three modules  33 ,  34 ,  35  are mounted rotationally fixedly on the stator  19 , between the inner wall, located on the radially inner side, of the combustion chamber  6  and the rotor  3 . The rotationally fixed inner ring  30  is provided between the modules  33 ,  34 ,  35  and the covering element  23 . 
     On its end side  52  facing the shaft shoulder  24 , the inner ring  30  has a plurality of balconies  29 ′,  29 ″,  29 ′″,  29 ″″ extending in the axial direction and coaxially encircling. Sealing surfaces  27 ′,  27 ″,  27 ′″,  27 ″″ are in each case provided on those circumferential surfaces of the balconies  29  which face the sealing teeth  26 . Each sealing surface  27 , together with its corresponding sealing teeth  26 , forms a labyrinth seal  28 . 
     A meandering gap  38 , in which therefore four labyrinth seals  28 ′,  28 ″,  28 ′″,  28 ″″ are connected sequentially, of which the three labyrinth seals  28 ′,  28 ″,  28 ′″ are stacked radially on top of one another, is formed between the covering element  23  and the inner ring  30 . 
     The labyrinth seal  28 ″″ is not stacked radially with respect to the next labyrinth seal  28 ′″ radially inward, but rather is arranged in terraced fashion, i.e. the labyrinth seal  28 ″″ is axially offset with respect to the labyrinth seal  28 ′″. 
     At its end side  52  facing the combustion chamber  6 , the inner ring  30  has an axially extending arm  46 , on the free end of which a projection  37 , which extends radially inwards, is formed integrally. 
     On its side facing the inner ring  30 , the module  34  comprises a projection  36 , which forms a hooked engagement with the projection  37  of the inner ring  30 . 
     When the gas turbine  1  is operating, a working fluid  14  flows within the hot-gas duct  11 . To prevent the working fluid  14  from penetrating as a leakage flow into a gap  38  formed by stationary and rotating components, the gap  38  has a plurality of labyrinth seals  28  which are stacked radially on top of one another and act jointly, in terms of flow, as a seal  31 . 
     The three labyrinth seals  28 ′,  28 ″,  28 ′″, which are stacked without any axial offset with respect to one another, allow a more compact design combined, at the same time, with an improvement in the sealing action as a result of the increase in the number of labyrinth seals  28 . 
       FIG. 2  shows an excerpt of a gas turbine  1  located between the hot-gas duct  11  and the axis of rotation  2  of the rotor  3 . The turbine disk  20 ″ bears the rotor blade  18 ″ of the second turbine stage and the turbine disk  20 ′″ bears the rotor blade  18 ′″ of the third turbine stage. On the side wall  22 ″ of the turbine disk  20 ″, the covering element  23 ″ secures the rotor blade  18 ″ against axial displacement. The covering element  23 ″ is hooked to the turbine disk  20 ″ by means of two hooked engagements that are radially spaced apart from one another. In the same way, the covering element  23 ′″ secures the rotor blade  18 ′″ against axial displacement. In this case, the covering element  23 ′″ and the turbine disk  20 ′″ are hooked together on the side wall  22 ′″. 
     The inner ring  30  with a securing ring  40  is provided in the groove-shaped recess  42  formed between the two turbine disks  20 ″,  20 ′″. The securing ring  40  is connected to the inner ring  30  on its side facing the rotor  3  by means of a hooked engagement  41  and is connected to the guide vane  16 ′″ on its side facing away from the rotor  3 . For this purpose, the inner ring  30  is bolted to the guide vane  16 ′″ by means of a bolt  45 , whereas the securing ring  40  is clamped to the guide vane  16 ′″. The securing ring  40  has a groove  43  into which extends a projection  44  arranged on the guide vane  16 ′″. 
     The side wall  51  facing away from the turbine disk  20 ′″, the covering element  23 ′″ has three balconies  25 ′,  25 ″,  25 ′″ which extend in the axial direction and are coaxially encircling. In each case three coaxially encircling sealing teeth  26 ′,  26 ″,  26 ′″ are provided on the outer circumference of the individual balconies  25 ′,  25 ″,  25 ′″. On its end side  52  assigned to the turbine disk  20 ′″, the inner ring  30  likewise has three balconies  29 ′,  29 ″,  29 ′″, which extend in the direction of the shaft shoulder  24  and are coaxially encircling transversely with respect thereto. Each balcony  29 , on its inner circumferential surface, has a sealing surface  27  facing the balconies  25  of the covering element  23 ′″ located further inward in the radial direction. In this case, the sealing surface  27 ′ together with the sealing tooth  26 ′ forms a labyrinth seal  28 ′, the sealing surface  27 ″ together with the sealing tooth  26 ″ forms a further labyrinth seal  28 ″, and the sealing surface  27 ′″ together with the sealing tooth  26 ′″ forms the third labyrinth seal  28 ′″. 
     The seal  31  shown in  FIG. 2  can be put together by the sequence of the following assembly steps: 
     At the start of assembly of the stationary gas turbine  1  having the parting plane  61 , first of all the lower housing half  64  is put in place. In each case the lower halves of the guide vane rings  17  have already been completed in the lower housing half  64  by means of preassembled guide vanes  16 . 
     Only the covering element  23 ″ has been mounted on the rotor  3 , which has not yet been fitted; the side wall  22 ′″ does not yet have a covering element  23 ′″. 
     For each inner ring  30  according to the invention, the lower half of the securing ring  40 , which is formed by a single-part or multi-part segment of a total size of 180°, is placed into the lower housing half  64 , so that the projection  44  engages in the groove  43 . Then, the lower half of the inner ring  30  is mounted in the lower housing half  64  which in each case hooks to the inner ring  30  and is partly bolted to the guide vanes  16  in order to secure them against relative movements. The lower half of the securing ring  30  is likewise formed from one or more segments totaling a size of 180°. 
     When the lower half of each securing ring  40  and inner ring  30  has been mounted in the lower housing half  64 , the rotor  3  is placed into the lower housing half  64 . At least the lower halves of the side wall  22 ′″ of the turbine disks  20 , which subsequently face the end side  52 , must not have a covering element  23 ′″, since otherwise the rotor  3  cannot be placed into the lower housing half  64 . 
     A segment of the covering element  23 ′″ is mounted on the upper half of the side wall  22 ′″ of the rotor  3  which has already been placed into the lower housing half  64 . 
     Then, the rotor  3  is rotated, so that during this rotation the segment of the covering element  23 ′″ which is mounted on the upper half is rotated into the lower housing half  64 . In the process, the axially extending balconies  25  of the covering element  23 ′″ move accurately between the corresponding balconies  29  of the inner ring  30  which is already located in the lower half. 
     Segments of covering elements  23  continue to be mounted on the upper half of the side walls  22  and rotated into the lower housing half  64  until the lower half of the seal  31  has been completely formed. 
     After the upper half of the covering element  23  has then been mounted on the upper half of the rotor  3  on the side wall  22 ′″, the upper half of the inner ring  30  can then be moved radially inward into the recess  42  formed between the turbine disks  20 ″,  20 ′″ in order to complete the inner ring  30 , in order for the balconies  29  thereof then to be moved over the balconies  25  of the covering elements  23 ′″ by displacement in the axial direction. The upper half of the inner ring  30  is positioned on the flanges of the lower half of the inner ring  30  or securing ring  40 . 
     Thereafter, the upper half of the securing ring  40  is moved into the recess  42  and hooked to the inner ring  30  in order to complete the circular, segmented securing ring  40 . 
     Then, in a manner which is already known, the guide vanes  16  of the upper half of the guide vane ring  17  can be mounted. 
     The assembly instructions are carried out in a similar manner for securing the guide vanes  16  of the first turbine stage  12  shown in  FIG. 1 . 
     In the lower housing half  64 , the guide vanes  16  and the modules  35 ,  36 ,  37  have already been preassembled before the rotor  3  without covering element  23  is placed into it. 
     Then, if not already present, one or more segments of the covering element  23  are mounted on the upper half of the side wall  22  of the first turbine disk  20 . Next, the rotor  3  is rotated, so that the segment(s) slide into the lower housing half  64  so as to form the lower half of the seal  31 . 
     After the upper half of the covering element  23  has been mounted on the upper half of the rotor  3  at the side wall  22 , the upper half of the inner ring  30  can then be moved radially inward into the clear space between turbine disk  20  and annular combustion chamber  6 , in order for the balconies  29  thereof then to be pushed in the axial direction over the balconies  25  of the covering elements  23 . The upper half of the inner ring  30  is located on the end sides of the lower half of the inner ring  30 . Then, the modules  33 ,  34  and  36  are successively installed. 
     In an alternative configuration, each segment can be formed from a plurality of pieces. 
     During operation, it is possible for the rotor  3  to be displaced counter to the direction of flow of the working fluid  14  without a balcony  25 ,  29  touching or striking the end side lying opposite it. 
     The inner ring  30 , which is rotationally fixed while the gas turbine  1  is operating, together with the rotating covering elements  23 , forms a gap  38  which is sealed by means of the seal  31 . The working fluid  14  is effectively prevented from leaving the hot-gas duct  11 , so that it flows past the rotor blades  18  as intended. The leakage flow is effectively reduced, which leads to an increase in the efficiency of the stationary gas turbine. 
     Furthermore, the seals  47 ,  48 ,  49 ,  50  reduce the leakage flow between rotating and stationary components.

Technology Classification (CPC): 5