Patent Publication Number: US-11047260-B2

Title: Turbine casing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application (No. 2018-235131), filed on Dec. 17, 2018; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments of the present invention relate to a turbine casing. 
     BACKGROUND 
     A supercritical CO 2  power generation system is a power generation system which uses a working fluid containing carbon dioxide (CO 2 ) in a supercritical state as a main component, and is attracting attention because of concern for the environment. This power generation system can collect supercritical CO 2  generated during power generation as needed, and can dramatically decrease CO 2  which is released into the atmosphere by using CCS (Carbon dioxide Capture and Storage) and CCU (Carbon dioxide Capture and Utilization) in a combined manner. 
     One example of a structure of a supercritical CO 2  turbine  10  configuring a supercritical CO 2  power generation system will be described by using  FIG. 5 .  FIG. 5  illustrates a partial cross section of a vertical plane (xz plane), in which a longitudinal direction indicates a vertical direction z, a lateral direction indicates a first horizontal direction x, and a direction orthogonal to the paper surface indicates a second horizontal direction y. Further, in  FIG. 5 , flows of working media F 1 , F 2 , F 3  are indicated by arrow marks of heavy solid lines, the left side indicates an upstream side Us, and the right side indicates a downstream side Ds. Besides, in  FIG. 5 , flows of cooling media CF 1 , CF 2 , CF 3 , CF 4  are indicated by arrow marks of heavy broken lines. 
     As illustrated in  FIG. 5 , the supercritical CO 2  turbine  10  includes a turbine casing  20  and a turbine rotor  40 , and is configured such that when the working medium F 1  containing carbon dioxide (CO 2 ) in a supercritical state as a main component is supplied thereto, the turbine rotor  40  is rotated inside the turbine casing  20 . Here, the supercritical CO 2  turbine  10  is a multistage axial flow turbine, and plural turbine stages  60  are arranged in an axial direction along a rotation center axis AX of the turbine rotor  40  (the first horizontal direction x). 
     Concrete contents of respective parts configuring the supercritical CO 2  turbine  10  will be described in order. 
     The turbine casing  20  has an inner casing  21  and an outer casing  22 , and has a double structure in which the inner casing  21  is housed inside the outer casing  22 . 
     The turbine casing  20  includes a first inner casing  211 , a second inner casing  212 , and a third inner casing  213  as the inner casing  21 , and the first inner casing  211 , the second inner casing  212 , and the third inner casing  213  are arranged in order from the upstream side Us toward the downstream side Ds. 
     A gland part  23  is provided to an inner peripheral surface of the turbine casing  20 . The gland part  23  includes a first packing head  231  and a second packing head  232 . The first packing head  231  is provided to an inner peripheral surface of the third inner casing  213 . The second packing head  232  is provided to an inner peripheral surface of the outer casing  22 , at an end part on a side where the third inner casing  213  is positioned. An axial seal member  233  is provided between the first packing head  231  and the second packing head  232 . 
     Further, to inner peripheral surfaces of the respective outer casing  22 , first inner casing  211 , first packing head  231 , and second packing head  232 , packing rings  24  are provided. The packing ring  24  has a fin, and is disposed to suppress leakage by narrowing a gap interposed between the packing ring  24  and the turbine rotor  40 . 
     An annular exhaust hood S 213  is interposed between the third inner casing  213  and the first packing head  231 . A diffuser  25  is provided inside the exhaust hood S 213 . The diffuser  25  is fixed to the second inner casing  212 . Further, a radial seal member  251  is provided between the third inner casing  213  and the diffuser  25 . 
     The turbine rotor  40  is a column-shaped bar body, and is housed inside the turbine casing  20  so that the rotation center axis AX extends in the first horizontal direction x. The turbine rotor  40  is coupled to a power generator (whose illustration is omitted), and when the turbine rotor  40  is rotated, the power generator (whose illustration is omitted) is driven to generate power. 
     The turbine stage  60  includes a stationary blade  61  and a rotor blade  62 . 
     The stationary blades  61  are disposed at each of an inner peripheral surface of the first inner casing  211  and an inner peripheral surface of the second inner casing  212  in the inner casing  21 . The stationary blades  61  are arranged in plural numbers in a rotational direction R (circumferential direction) of the turbine rotor  40 , and the plural stationary blades  61  configure a stationary blade cascade. The stationary blade cascades are provided in plural stages, and the plural stages of stationary blade cascades are arranged along the axial direction (x) along the rotation center axis AX of the turbine rotor  40 . 
     The rotor blades  62  are arranged in plural numbers in the rotational direction R of the turbine rotor  40 , and the plural rotor blades  62  configure a rotor blade cascade. Similarly to the stationary blade cascades, the rotor blade cascades are provided in plural stages, and the plural stages of rotor blade cascades are arranged along the axial direction (x) along the rotation center axis AX of the turbine rotor  40 . Specifically, the stationary blade cascade and the rotor blade cascade are alternately arranged along the axial direction (x). 
     In the supercritical CO 2  turbine  10 , a combustor casing  80  configuring a combustor (whose illustration is omitted) is joined to an inlet part of the outer casing  22  by using bolts  81 . 
     Further, the supercritical CO 2  turbine  10  is provided with an inlet guide pipe  801 . The inlet guide pipe  801  has one end coupled to the combustor (whose illustration is omitted) and the other end coupled to the turbine stage  60  of an initial stage. The inlet guide pipe  801  is disposed so as to penetrate the inside of the combustor casing  80  and penetrate the inside of a through hole formed on the inlet part of the outer casing  22  and the inside of a through hole formed on the first inner casing  211 . Here, an inlet sleeve  802  is provided to the through hole formed on the inlet part of the outer casing  22  and the through hole formed on the first inner casing  211 , and the inlet guide pipe  801  penetrates the inside of the inlet sleeve  802 . 
     In the supercritical CO 2  turbine  10 , an exhaust pipe  90  is joined, via a welded portion  91 , to a pipe barrel part  22   a  provided to an outlet part of the outer casing  22 . One end of the exhaust pipe  90  is joined to the outer casing  22 , and the other end thereof positioned on the opposite side of the one end is joined to an on-site pipe  93  via a welded portion  92 . 
     Further, the supercritical CO 2  turbine  10  is provided with an outlet sleeve  901 . The outlet sleeve  901  penetrates the pipe barrel part  22   a  of the outer casing  22 , one end thereof is coupled to a pipe barrel part  213   a  of the third inner casing  213 , and the other end thereof is coupled to the exhaust pipe  90 . 
     Hereinafter, operations in which the working media F 1 , F 2 , F 3  flow, and operations in which the cooling media CF 1 , CF 2 , CF 3 , CF 4  flow in the above-described supercritical CO 2  turbine  10  will be described in order. 
     In the supercritical CO 2  turbine  10 , the working medium F 1  is a medium containing carbon dioxide (CO 2 ) in a supercritical state as a main component, and is introduced into the turbine stages  60  from the combustor (whose illustration is omitted) via the inlet guide pipe  801 . Subsequently, the working medium F 1  flows in the axial direction along the rotation center axis AX, to thereby perform work in each of the plural turbine stages  60 . Further, the working medium F 2  flowed through the final stage of the turbine stages  60  is discharged to the exhaust hood S 213 . After that, the working medium F 3  is discharged from the exhaust hood S 213  to the on-site pipe  93  via the outlet sleeve  901  and the exhaust pipe  90 . 
     In the supercritical CO 2  turbine  10 , the cooling medium CF 1  is, for example, carbon dioxide, and is a medium whose temperature is lower than that of the working medium F 1 . The cooling medium CF 1  is introduced into a flow path provided between an inner peripheral surface of the combustor casing  80  and an outer peripheral surface of the inlet guide pipe  801 . Subsequently, the cooling medium CF 1  flows through a flow path provided between an inner peripheral surface of the inlet sleeve  802  and the outer peripheral surface of the inlet guide pipe  801 . Further, although the illustration is omitted, the cooling medium CF 1  is introduced into holes provided to each of the stationary blades  61  and the rotor blades  62 , and after cooling the stationary blades  61 , the rotor blades  62 , and the turbine rotor  40 , for example, it is discharged to the outside of the supercritical CO 2  turbine  10  via a discharge port (whose illustration is omitted) or mixed to the flow of the working medium F 1  or the cooling medium CF 2 . 
     Other than the above, in the supercritical CO 2  turbine  10 , the cooling medium CF 2  flows through a space interposed between the third inner casing  213  and the outer casing  22 . This cooling medium CF 2  is, for example, carbon dioxide, and is a medium whose temperature is lower than that of the working medium F 2 . Further, the cooling medium CF 2  is introduced from a conduit (whose illustration is omitted) communicated with a space interposed between the third inner casing  213  and the outer casing  22 . This makes it possible to prevent a temperature of the outer casing  22  from increasing due to heat caused by convection or radiation. 
     After that, the cooling medium CF 3  flows through a flow path positioned between an inner peripheral surface of the pipe barrel part  22   a  provided to the outlet part of the outer casing  22  and an outer peripheral surface of the outlet sleeve  901 . This makes it possible to prevent a temperature of the outer casing  22  from increasing due to heat caused by convection or radiation. Further, after the cooling medium CF 4  flows through a flow path positioned between an inner peripheral surface of the exhaust pipe  90  and the outer peripheral surface of the outlet sleeve  901 , for example, the cooling medium CF 4  is discharged to the outside of the supercritical CO 2  turbine  10  via a discharge port (whose illustration is omitted) formed on the exhaust pipe  90 . 
     Note that it is also possible that a cooling medium (whose illustration is omitted) is introduced from the outside into the flow path positioned between the inner peripheral surface of the pipe barrel part  22   a  provided to the outlet part of the outer casing  22  and the outer peripheral surface of the outlet sleeve  901 . 
     Hereinafter, materials and so on used in the above-described supercritical CO 2  turbine  10  will be described. 
     In the turbine casing  20 , the outer casing  22  is required to be thick in order to obtain large strength, by considering an inside pressure. Further, the outer casing  22  has a large size. For this reason, the outer casing  22  is generally manufactured by casting. 
     In the supercritical CO 2  turbine  10 , the working medium F 1  introduced into an inlet at which it is supplied from the combustor, has a temperature of 800° C. or more and a pressure of 20 MPa or more. Further, the working medium F 3  discharged from the outlet of the outer casing  22  has a temperature of 650° C. or more and a pressure of 2 MPa or more. In order to obtain high strength and excellent oxidation resistance at a temperature of 650° C. or more, it can be considered to form respective parts by using, not ferritic heat resistant steel, but austenitic heat resistant steel such as a Ni-based alloy. 
     However, when manufacturing a large-sized casting by using the austenitic heat resistant steel such as the Ni-based alloy, it is highly possible that a casting defect occurs, and besides, problems regarding segregation and anisotropy of a metal structure arise in some cases. In this case, since it becomes difficult to perform an internal defect inspection due to enlargement of crystal grains, it is not easy to secure a product quality. Depending on materials, it is sometimes technically impossible to perform manufacture. Besides, a unit price of the material is expensive. When these points are taken into consideration, it is not realistic to form the entire outer casing  22  by using the austenitic heat resistant steel such as the Ni-based alloy. 
     Based on the circumstances as described above, in the above-described supercritical CO 2  turbine  10 , the outer casing  22  is manufactured through casting by using the ferritic heat resistant steel. Further, parts which are directly brought into contact with exhaust air of high temperature (the third inner casing  213 , the first packing head  231 , the outlet sleeve  901 , the exhaust pipe  90 , the diffuser  25 ) are manufactured through casting by using the austenitic heat resistant steel such as the Ni-based alloy. Further, as described above, in order to prevent the temperature of the outer casing  22  from being a temperature exceeding a heatproof temperature, cooling is performed by using the cooling media CF 1 , CF 2 , CF 3 , CF 4 . 
     As described above, in the supercritical CO 2  turbine  10 , the exhaust pipe  90  is joined, via the welded portion  91 , to the pipe barrel part  22   a  (exhaust pipe connecting part) provided to the outlet part of the outer casing  22 . The pipe barrel part  22   a  (exhaust pipe connecting part) of the outer casing  22  is formed of the ferritic heat resistant steel. On the contrary, the exhaust pipe  90  is formed of the austenitic heat resistant steel such as the Ni-based alloy. For this reason, the following problems may arise. 
     Concretely, chemical components are greatly different between the ferritic heat resistant steel and the austenitic heat resistant steel, so that when the both steels are joined by welding, there is a case where a structural stability at a boundary surface is not maintained over a long period of time. 
     Since a linear expansion coefficient of the ferritic heat resistant steel and a linear expansion coefficient of the austenitic heat resistant steel are different, when the both steels are joined by welding, a large residual stress is generated in some cases. As a result of this, there is a case where a crack occurs in the welded portion  91  at which different materials are welded, or in the vicinity of the welded portion  91 . 
     The ferritic heat resistant steel and the austenitic heat resistant steel have different material strengths, and have different temperature ranges in which a structure has a stable state. For this reason, it is not easy to precisely set temperature conditions in heat treatment to be performed after welding (PWHT: Post Weld Heat Treatment). Consequently, there is a case where removal of the residual stress becomes insufficient. Further, the structure changes in some cases in the vicinity of the welded portion  91  at which the different materials are welded. 
     It is not easy to perform an internal defect inspection with respect to the welded portion  91  at which the different materials are welded. Further, there is a need to carry out a welding procedure test and a material evaluation test before performing manufacture by welding of different materials. As a result of this, an increase in manufacturing cost, an increase in length of time taken for the manufacture, and so on occur. 
     In particular, when the temperature and the pressure of the working medium are increased to realize high efficiency of the power generation system, it becomes necessary to use the Ni-based alloy as the austenitic heat resistant steel. Consequently, it becomes further difficult to perform welding of different materials. 
     Based on such circumstances, in the above-described supercritical CO 2  turbine  10 , it is not easy to sufficiently improve reliability regarding the connection between the pipe barrel part  22   a  (exhaust pipe connecting part) provided to the outlet part of the outer casing  22  and the exhaust pipe  90 . 
     Also in each of turbines other than the supercritical CO 2  turbine  10  (a steam turbine, a gas turbine, a medium turbine, and so on), reliability regarding a connection with an exhaust pipe becomes insufficient in some cases, similarly to the above. 
     Therefore, the problem to be solved by the present invention is to provide a turbine casing capable of easily realizing improvement of reliability regarding a connection with an exhaust pipe. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view illustrating a substantial part of a turbine according to a first embodiment. 
         FIG. 2  is a view illustrating a substantial part of a turbine according to a second embodiment. 
         FIG. 3  is a view illustrating a substantial part of a turbine according to a third embodiment. 
         FIG. 4  is a view illustrating a substantial part of a turbine according to a modified embodiment. 
         FIG. 5  is a view illustrating a substantial part of a turbine according to a related art. 
     
    
    
     DETAILED DESCRIPTION 
     A turbine casing according to an embodiment includes an exhaust pipe connecting part formed of ferritic heat resistant steel, to which an exhaust pipe formed of austenitic heat resistant steel is connected. Here, the exhaust pipe connecting part and the exhaust pipe are fastened by using screws. 
     First Embodiment 
     A supercritical CO 2  turbine  10  according to a first embodiment will be described by using  FIG. 1 .  FIG. 1  illustrates a cross section of a vertical plane (xz plane), similarly to  FIG. 5 , and illustrates a part of the cross section in an enlarged manner. 
     As illustrated in  FIG. 1 , in the present embodiment, an exhaust pipe  90  formed of austenitic heat resistant steel is connected to a pipe barrel part  22   a  (exhaust pipe connecting part) of an outer casing  22  formed of ferritic heat resistant steel in a turbine casing  20  (refer to  FIG. 5 ). Further, an outlet sleeve  901  formed of the austenitic heat resistant steel is disposed so as to penetrate the pipe barrel part  22   a  of the outer casing  22 . One end (upper end in  FIG. 1 ) of the outlet sleeve  901  is coupled to a pipe barrel part  213   a  of a third inner casing  213  formed of the austenitic heat resistant steel. Further, the other end (lower end in  FIG. 1 ) of the outlet sleeve  901  is coupled to the exhaust pipe  90 . Other than the above, in the present embodiment, a cooling medium CF 3  flows through a space interposed between the outer casing  22  and the third inner casing  213 , and a cooling medium CF 4  flows through a space interposed between the exhaust pipe  90  and the outlet sleeve  901 . 
     However, in the present embodiment, the state where the exhaust pipe  90  is connected to the pipe barrel part  22   a  of the outer casing  22  is different from that of the above-described related art (refer to  FIG. 5 ). Except this point and a point related to this, the present embodiment is similar to the case of the above-described related art. For this reason, explanation of overlapped matters will be appropriately omitted. 
     In the present embodiment, the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  are fastened by using bolts  31  (male screw components) being screws. 
     Concretely, in the present embodiment, a flange F 90  is formed on the exhaust pipe  90 . In the flange F 90  of the exhaust pipe  90 , insertion holes H 90  into which the bolts  31  are to be inserted are formed. Further, in the pipe barrel part  22   a  of the outer casing  22 , holes H 22   a  formed with female screw portions are formed. 
     Each of the bolts  31  includes a head portion  311  and a shaft portion  312  formed with a male screw portion, the shaft portion  312  is inserted into the insertion hole H 90  formed in the flange F 90  of the exhaust pipe  90 , and is attached to the hole H 22   a  formed with the female screw portion in the pipe barrel part  22   a  of the outer casing  22 . Consequently, the exhaust pipe  90  is fixed to the outer casing  22 . The bolt  31  is formed of the austenitic heat resistant steel such as the Ni-based alloy, for example. Other than the above, it is also possible to use the bolt  31  formed of a high Cr-based material in accordance with a temperature. 
     As described above, in the present embodiment, the exhaust pipe  90  formed of the austenitic heat resistant steel and the pipe barrel part  22   a  (exhaust pipe connecting part) of the outer casing  22  formed of the ferritic heat resistant steel are fastened by using the bolts  31  being the screws. For this reason, in the present embodiment, it is possible to connect the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  more easily when compared to the case of connecting them by welding. 
     Further, in the present embodiment, it becomes unnecessary to perform the internal defect inspection and the like regarding the welded portion  91  at which different materials are welded (refer to  FIG. 1 ), so that it is possible to greatly reduce a period of time for the manufacture. Further, in the present embodiment, the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  are in a state of being physically separated, so that the reduction in structural stability does not occur, unlike the case of joining them by welding. As a result of this, in the present embodiment, it is possible to improve the reliability over a long period of time. 
     Note that although the above-described embodiment describes the case where the shaft portion  312  of the bolt  31  is attached to the hole H 22   a  formed with the female screw portion in the pipe barrel part  22   a  of the outer casing  22 , the embodiment is not limited to this. Although the illustration is omitted, it is also possible that, for example, a tap-end stud having no head portion and including a shaft portion having male screw portions formed on one end side and the other end side thereof, is inserted from the one end side into the insertion hole H 90  and the hole H 22   a  to be attached, and then a nut is attached to the other end side, to thereby perform fastening. 
     Second Embodiment 
     A supercritical CO 2  turbine  10  according to a second embodiment will be described by using  FIG. 2 .  FIG. 2  illustrates a partial cross section of a vertical plane (xz plane), similarly to  FIG. 1 . 
     As illustrated in  FIG. 2 , in the present embodiment, the configuration of the exhaust pipe  90  and the outlet sleeve  901  (refer to  FIG. 1 ) is different from that of the above-described first embodiment (refer to  FIG. 1 ). Except this point and a point related to this, the present embodiment is similar to the case of the first embodiment. For this reason, explanation of overlapped matters will be appropriately omitted. 
     In the present embodiment, the exhaust pipe  90  and the outlet sleeve  901  are integrally formed, unlike the case of the first embodiment (refer to  FIG. 1 ). For example, the exhaust pipe  90  and the outlet sleeve  901  are in a state of being joined to each other by welding, and in a state where they cannot be separated from each other. Other than the above, it is also possible that the exhaust pipe  90  and the outlet sleeve  901  are formed by monoblock casting. 
     As described above, in the present embodiment, by the integration of the exhaust pipe  90  and the outlet sleeve  901  (refer to  FIG. 1 ), the number of components is reduced, and the structure is simplified. Along with this, in the present embodiment, it is possible to prevent the cooling medium CF 3  which flows through the space interposed between the exhaust pipe  90  and the outlet sleeve  901  (refer to  FIG. 1 ) from being leaked to the inside from a gap between the exhaust pipe  90  and the outlet sleeve  901  (refer to  FIG. 1 ). Further, it is possible to prevent the working medium F 3  which flows through the inside of the outlet sleeve  901  (refer to  FIG. 1 ) from being passed through the space interposed between the exhaust pipe  90  and the outlet sleeve  901  (refer to  FIG. 1 ) to be mixed to the flow of the cooling medium CF 4 . As a result of this, in the present embodiment, it is possible to effectively cool the pipe barrel part  22   a  of the outer casing  22 , so that the reliability can be further improved. 
     Third Embodiment 
     A supercritical CO 2  turbine  10  according to a third embodiment will be described by using  FIG. 3 .  FIG. 3  illustrates a partial cross section of a vertical plane (xz plane), similarly to  FIG. 1 . 
     As illustrated in  FIG. 3 , in the present embodiment, the state where the exhaust pipe  90  is connected to the pipe barrel part  22   a  of the outer casing  22  is different from that of the above-described first embodiment (refer to  FIG. 1 ). Except this point and a point related to this, the present embodiment is similar to the case of the first embodiment. For this reason, explanation of overlapped matters will be appropriately omitted. 
     In the present embodiment, the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  are fastened by using bolts  31  (male screw components) and nuts  32  (female screw components). 
     Concretely, in the present embodiment, the flange F 90  is formed on the exhaust pipe  90 . In the flange F 90  of the exhaust pipe  90 , the insertion holes H 90  into which the bolts  31  are to be inserted are formed. 
     In the present embodiment, a flange F 22  is formed also on the pipe barrel part  22   a  of the outer casing  22 . In the flange F 22  formed on the pipe barrel part  22   a  of the outer casing  22 , insertion holes H 22  into which the bolts  31  are to be inserted are formed. 
     Each of the bolts  31  includes a head portion  311  and a shaft portion  312  formed with a male screw, and the shaft portion  312  of the bolt  31  is sequentially inserted into the insertion hole H 90  formed in the flange F 90  of the exhaust pipe  90  and the insertion hole H 22  formed in the flange F 22  of the pipe barrel part  22   a.  Subsequently, the nut  32  formed with a female screw portion is attached to the shaft portion  312  formed with the male screw of the bolt  31 . Consequently, the exhaust pipe  90  is fixed to the outer casing  22 . 
     The bolt  31  and the nut  32  are formed of the austenitic heat resistant steel such as the Ni-based alloy or the high Cr-based heat resistant steel, for example. The pipe barrel part  22   a  of the outer casing  22  is formed of the ferritic heat resistant steel. When there is a difference in linear expansion coefficient or a temperature difference between the bolt  31  and the pipe barrel part  22   a  of the outer casing  22 , an expansion difference is generated. As in the case of the first embodiment, when the female screw portion is formed on the pipe barrel part  22   a,  there is a risk that the fastening is performed excessively to damage the female screw portion formed on the pipe barrel part  22   a  of the outer casing  22 , due to this expansion difference. 
     However, in the present embodiment, the female screw portion is not formed on the pipe barrel part  22   a  of the outer casing  22 . As a result of this, if the female screw portion formed on the pipe barrel part  22   a  of the outer casing  22  is damaged in the case of the first embodiment, it is not easy to perform maintenance, but, in the present embodiment, since the female screw portion is not formed on the pipe barrel part  22   a  of the outer casing  22 , it is possible to easily carry out maintenance only by exchanging the bolt  31  and the nut  32 . 
     Therefore, in the present embodiment, the fastening between the exhaust pipe  90  and the outer casing  22  can be performed sufficiently, so that it is possible to further improve the reliability over a long period of time. 
     Note that although the above-described embodiment describes the case where the bolt  31  includes the head portion  311  and the shaft portion  312  formed with the male screw, the embodiment is not limited to this. The bolt  31  may also be a double-ended bolt (stud bolt) having no head portion and having male screws formed on respective both ends of a shaft portion thereof. In this case, fastening is performed by attaching nuts to the respective both ends of the double-ended bolt. 
     Further, although the above-described embodiment describes the case where the bolt  31  is provided on the exhaust pipe  90  side, and the nut  32  is provided on the outer casing  22  side, the embodiment is not limited to this. It is also possible to design such that the bolt  31  is provided on the outer casing  22  side, and the nut  32  is provided on the exhaust pipe  90  side. 
     &lt;Others&gt; 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     A modified embodiment will be exemplified by using  FIG. 4 .  FIG. 4  illustrates a partial cross section of a vertical plane (xz plane), similarly to  FIG. 1 . 
     As illustrated in  FIG. 4 , in the present modified embodiment, the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  are fastened by using nuts  32  being screws. Concretely, an outer peripheral surface between the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22  includes parts where male screw portions are formed. Further, the nuts  32  formed with female screw portions are attached to the parts where the male screw portions are formed at the outer peripheral surface between the exhaust pipe  90  and the pipe barrel part  22   a  of the outer casing  22 . Consequently, the exhaust pipe  90  is fixed to the outer casing  22 . Also in the present modified embodiment, it is possible to exhibit an effect such as improvement of reliability over a long period of time, similarly to the case of the above-described embodiments. 
     Further, although each of the above-described embodiments describes the supercritical CO 2  turbine  10  configuring the supercritical CO 2  power generation system, the embodiment is not limited to this. It is also possible that, also in each of turbines other than the supercritical CO 2  turbine  10  (a steam turbine, a gas turbine, a medium turbine, and so on), a part which functions as an exhaust pipe connecting part (a part corresponding to the pipe barrel part  22   a  of the outer casing  22  in the above description) in a turbine casing and an exhaust pipe are fastened by using screws, similarly to the above. This makes it possible to exhibit operations and effects similar to those of the above-described embodiments. The above-described temperature conditions and pressure conditions of the working media indicate values when the working media contain carbon dioxide (CO 2 ) in a supercritical state as a main component, and can be arbitrarily set in accordance with the working media. 
     REFERENCE SIGNS LIST 
       10  . . . supercritical CO 2  turbine,  20  . . . turbine casing,  21  . . . inner casing,  22  . . . outer casing,  22   a  . . . pipe barrel part,  23  . . . gland part,  24  . . . packing ring,  25  . . . diffuser,  31  . . . bolt,  32  . . . nut,  40  . . . turbine rotor,  60  . . . turbine stage,  61  . . . stationary blade,  62  . . . rotor blade,  80  . . . combustor casing,  81  . . . bolt,  90  . . . exhaust pipe,  91  . . . welded portion,  92  . . . welded portion,  93  . . . on-site pipe,  211  . . . first inner casing,  212  . . . second inner casing,  213  . . . third inner casing,  213   a  . . . pipe barrel part,  231  . . . first packing head,  232  . . . second packing head,  233  . . . axial seal member,  251  . . . radial seal member,  311  . . . head portion,  312  . . . shaft portion,  801  . . . inlet guide pipe,  802  . . . inlet sleeve,  901  . . . outlet sleeve, AX . . . rotation center axis, CF 1 , CF 2 , CF 3 , CF 4  . . . cooling medium, Ds . . . downstream side, F 1 , F 2 , F 3  . . . working medium, F 22  . . . flange, F 90  . . . flange, H 22  . . . insertion hole, H 22   a  . . . hole, H 90  . . . insertion hole, R . . . rotational direction, S 213  . . . exhaust hood, Us . . . upstream side