Gas turbine exhaust duct structure

Abstract

To improve the durability of the exhaust duct structure of gas turbines. [Solution] The exhaust duct structure 10 comprises a center cone 11, an exhaust duct 12 surrounding the center cone 11, an exhaust passage 13 defined between the center cone 11 and the exhaust duct 12 through which exhaust from the turbine 5 flows, and a stay 14 connecting the center cone 11 to the exhaust duct 12. The exhaust duct 12 includes an inner cylinder 20 to which the stay 14 is fixed, and an outer cylinder 30 surrounding the inner cylinder 20. The inner cylinder 20 is configured to have lower rigidity compared to the outer cylinder 30.

Description

Technical Field

[0001] The present invention relates to an exhaust duct structure of a gas turbine.

Background Art

[0002] Patent Document 1 discloses an exhaust duct of a gas turbine including an inner casing that covers the rear end of a turbine shaft and an outer casing that surrounds the inner casing. Exhaust gas from the turbine is discharged to the outside air through an exhaust passage defined between the inner casing and the outer casing. The inner casing is supported by the outer casing via struts.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The exhaust gas is at a high temperature of about 600°C. Therefore, the inner casing and the struts tend to expand radially outward due to thermal expansion. On the other hand, since the outer casing is exposed to the relatively low-temperature outside air, it restrains the thermal expansion of the inner casing and the struts. Therefore, cracks are likely to occur in the struts.

[0005] An object of the present invention is to improve the durability of an exhaust duct structure of a gas turbine.

Means for Solving the Problems

[0006] One aspect of the present invention provides an exhaust duct structure for a gas turbine, comprising a center cone, an exhaust duct surrounding the center cone, an exhaust passage defined between the center cone and the exhaust duct through which exhaust from a turbine flows, and a stay connecting the center cone to the exhaust duct, wherein the exhaust duct includes an inner cylinder to which the stay is fixed and an outer cylinder surrounding the inner cylinder, and the inner cylinder is configured to have lower rigidity compared to the outer cylinder.

[0007] According to the above configuration, the exhaust duct is configured as a double-cylinder structure including an inner cylinder and an outer cylinder, and the center cone is connected to the inner cylinder via a stay. The inner cylinder is covered by the outer cylinder and is not directly exposed to the outside air. Furthermore, the inner cylinder is configured to have lower rigidity compared to the outer cylinder. Therefore, even if the center cone and stay undergo thermal expansion due to the effects of exhaust, the restraining force of the exhaust duct against thermal expansion is significantly reduced. Consequently, cracks are less likely to occur in the stay, and the durability of the exhaust duct structure is improved.

[0008] The inner cylinder may have a free end on one side in the axial direction of the inner cylinder that is free from the outer cylinder, and a mounting portion provided on the other side in the axial direction of the inner cylinder that is fixed to the outer cylinder.

[0009] According to the above configuration, the inner cylinder is fixed to the outer cylinder on one axial side, while being free from the outer cylinder on one axial side. This structurally achieves a configuration in which the rigidity of the inner cylinder is reduced relative to that of the outer cylinder.

[0010] The multiple mounting portions may be arranged at intervals in the circumferential direction of the inner cylinder, and each of the multiple stays may be arranged between two adjacent mounting portions in the circumferential direction.

[0011] In this configuration, the area between two adjacent mounting points has structurally lower rigidity compared to the area where the two mounting points are located. With this configuration, since the stay is connected to the inner cylinder in this area, the restraining force on the exhaust duct against the thermal expansion of the stay is further reduced.

[0012] Each of the aforementioned stays may be positioned midway between two adjacent mounting portions in the circumferential direction.

[0013] Here, the intermediate position between two adjacent mounting points has particularly low rigidity in the circumferential direction. The "intermediate position" refers to any position within the central region when the area between the two mounting points is divided into an odd number of equal parts (e.g., three). With the above configuration, each stay is positioned at such an intermediate position, further reducing the restraining force on the exhaust duct against the thermal expansion of the stays.

[0014] The stay may be fixed to one side of the inner cylinder in the axial direction.

[0015] Here, the rigidity is structurally lower on one side in the axial direction compared to the other side where the mounting portion is provided. With the above configuration, since the stay is connected to the inner cylinder on one side in the axial direction, the restraining force on the exhaust duct against the thermal expansion of the stay is further reduced.

[0016] The exhaust duct may further include a connecting cylinder connected to the end of the outer cylinder, the end of the outer cylinder being provided with an annular outer cylinder flange protruding radially outward, the connecting cylinder being provided with an annular connecting flange axially opposite to the outer cylinder flange, and the mounting portion of the inner cylinder being sandwiched radially inward from the gap between the outer cylinder flange and the connecting flange.

[0017] According to the above configuration, a double-cylinder structure can be realized in which only the other axial side of the inner cylinder is fixed to the outer cylinder. The structure for fixing the inner cylinder to the outer cylinder can be incorporated into the structure for connecting the outer cylinder and the connecting cylinder, thereby avoiding complexity in the exhaust duct structure.

[0018] The exhaust duct structure of the gas turbine may be positioned radially on the outer circumference with respect to the mounting portion, and may further include a sealing member provided in the gap.

[0019] According to the above configuration, while adopting a structure in which the attachment portion of the inner cylinder is sandwiched between the outer cylinder and the connection cylinder, it is possible to prevent exhaust gas from leaking from the exhaust passage to the outside air.

[0020] The exhaust duct may further include an outer peripheral passage defined between the inner cylinder and the outer cylinder and communicating with the exhaust passage.

[0021] According to the above configuration, high-temperature exhaust gas also flows on the outer peripheral side of the inner cylinder. Therefore, the restraining force of the inner cylinder against the thermal expansion of the stay is further reduced.

[0022] The exhaust duct may further include a positioning structure provided on the inner cylinder and the outer cylinder for aligning the central axis of the inner cylinder with the central axis of the outer cylinder.

[0023] According to the above configuration, due to the action of the positioning structure, the gap between the inner cylinder and the outer cylinder becomes uniform in the circumferential direction. The restraining force of the inner cylinder against the thermal expansion of the stay is reduced uniformly in the circumferential direction.

Effect of the Invention

[0024] According to the present invention, the durability of the exhaust duct structure of the gas turbine can be improved.

Brief Description of the Drawings

[0025] [Figure 1] Schematic diagram of a gas turbine to which the exhaust duct structure according to the embodiment is applied. [Figure 2] Cross-sectional view of the exhaust duct structure of FIG. 1. [Figure 3] View taken along the arrow III-III of FIG. 2. [Figure 4] Partial enlarged view of FIG. 2. [Figure 5] Partial enlarged view of FIG. 2.

Mode for Carrying Out the Invention

[0026] Embodiments will be described below with reference to the drawings. The same or corresponding elements are denoted by the same reference numerals throughout the drawings, and redundant detailed descriptions will be omitted.

[0027] As schematically shown in Figure 1, the exhaust duct structure 10 according to this embodiment is applied to the gas turbine 1 and constitutes a part of the gas turbine 1.

[0028] The gas turbine 1 comprises a main shaft 2, a compressor 3, a combustor 4, and a turbine 5. The compressor 3 is located on one side of the main shaft 2 (left side of Figure 1), and the turbine 5 is located on the other side of the main shaft 2 (right side of Figure 1). The compressor 3 takes in air from the outside and compresses it. The compressed air is sent to the combustor 4. The combustor 4 burns a mixture of the compressed air and fuel to produce combustion gas. The turbine 5 is rotationally driven by the combustion gas. This rotates the main shaft 2, which in turn drives the compressor 3 and the load L. The load L is, for example, a generator or a pump, and is connected to one end of the main shaft 2 via a reduction gear 6.

[0029] The exhaust duct structure 10 includes a center cone 11, an exhaust duct 12 surrounding the center cone 11, an exhaust passage 13 defined between the center cone 11 and the exhaust duct 12 through which exhaust from the turbine 5 flows, and a stay 14 connecting the center cone 11 to the exhaust duct 12.

[0030] The main shaft 2, center cone 11, exhaust duct 12, and exhaust passage 13 are coaxial. In the following description, "central axis A" refers to the common center line of the main shaft 2, center cone 11, exhaust duct 12, and exhaust passage 13. The axial, radial, and circumferential directions are based on central axis A.

[0031] The exhaust duct structure 10 is located on the opposite side of the turbine 5 from the compressor 3 in the axial direction. The exhaust duct structure 10 directs the exhaust from the turbine 5 from one axial side (left side of Figure 1) to the other axial side (right side of Figure 1), releasing the exhaust into the outside air. The one axial side corresponds to the turbine side or the upstream side in the exhaust flow direction, and the other axial side corresponds to the outside air side or the downstream side in the exhaust flow direction.

[0032] Referring to Figure 2, the center cone 11 is a frustoconical shape with at least one axial end closed and has a circular cross-section. To reduce the velocity of the exhaust gas, the outer diameter of the center cone 11 decreases from one axial side to the other.

[0033] The exhaust duct 12 is generally cylindrical. One end of the exhaust duct 12 is connected to the casing 5a of the turbine 5. The exhaust duct 12 extends axially from the casing 5a to the other side.

[0034] One end of the center cone 11 protrudes axially to one side relative to the exhaust duct 12 and is surrounded by the casing 5a. The exhaust duct 12 surrounds almost the entire remaining portion of the center cone 11. The exhaust duct 12 protrudes axially to the other side relative to the center cone 11.

[0035] The exhaust passage 13 is defined at one axial end by the outer circumferential surface of the center cone 11 and the inner circumferential surface of the casing 5a. For most of the remaining portion, the exhaust passage 13 is defined by the outer circumferential surface of the center cone 11 and the inner circumferential surface of the exhaust duct 12. The exhaust passage 13 has an annular passage cross-section throughout its entire axial direction, and this passage cross-section gradually widens from one side to the other in the axial direction. Exhaust from the turbine 5 flows through the exhaust passage 13 and is discharged to the outside air through the other end opening of the exhaust duct 12.

[0036] The stay 14 extends radially within the exhaust passage 13. The stay 14 is fixed to the outer circumferential surface of the center cone 11 on its radially inner side. The stay 14 is fixed to the inner circumferential surface of the exhaust duct 12 on its radially outer side. Note that there are multiple stays 14 (for example, three), and they are spaced apart from each other in the circumferential direction (see Figure 3).

[0037] Referring to Figure 2, the exhaust duct 12 includes an inner cylinder 20, an outer cylinder 30, and a connecting cylinder 40. The inner cylinder 20, the outer cylinder 30, and the connecting cylinder 40 are generally cylindrical in shape. The outer cylinder 30 surrounds the inner cylinder 20 and is axially connected to the connecting cylinder 40.

[0038] The exhaust duct 12 has a double-cylinder structure consisting of an inner cylinder 20 and an outer cylinder 30 on one axial side, and a single-cylinder structure consisting of a connecting cylinder 40 on the other axial side. The outer circumferential surface of the exhaust duct 12 is formed by the outer circumferential surfaces of the outer cylinder 30 and the connecting cylinder 40 and is exposed to the outside air. The inner circumferential surface of the exhaust duct 12 is formed by the inner circumferential surfaces of the inner cylinder 20 and the connecting cylinder 40 and defines the exhaust passage 13.

[0039] The exhaust duct 12 includes an outer peripheral passage 25 defined between the inner cylinder 20 and the outer cylinder 30. The outer peripheral passage 25 extends axially, is separated from the exhaust passage 13 via the inner cylinder 20, is located on the outer periphery of the exhaust passage 13, and has an annular cross-section. The outer peripheral passage 25 communicates with the exhaust passage 13 via an inlet 26 at one axial end and an outlet 27 at the other axial end. A portion of the exhaust from the turbine 5 flows from the exhaust passage 13 into the outer peripheral passage 25 via the inlet 26, flows through the outer peripheral passage 25 from one axial side to the other, and flows out of the outer peripheral passage 25 into the exhaust passage 13 via the outlet 27. The exhaust flows along both the inner and outer circumferential surfaces of the inner cylinder 20.

[0040] The outer cylinder 30 is fastened to the casing 5a at one axial end and extends from the casing 5a to the other axial end. The connecting cylinder 40 is connected to the other axial end of the outer cylinder 30 at one axial end and extends from the outer cylinder 30 to the other axial end.

[0041] Referring to Figures 2 and 3, the inner cylinder 20 has a plurality (for example, three) of mounting portions 23 provided on the other axial side. The plurality of mounting portions 23 are spaced apart in the circumferential direction. The mounting portions 23 protrude radially outward from the other axial end of the inner cylinder 20 and are sandwiched between the outer cylinder 30 and the connecting cylinder 40. In this way, the plurality of mounting portions 23 are fixed to the outer cylinder 30. The inner cylinder 20 extends cantilevered from the mounting portions 23 to one axial side, forming a free end 20a that is free from the outer cylinder 30 on that axial side.

[0042] The outer cylinder 30 is connected to the casing 5a and the connecting cylinder 40 at both ends in the axial direction, respectively. On the other hand, the inner cylinder 20 is fixed to the outer cylinder 30 only at the other end in the axial direction, and at a limited number of points (for example, 3 points) in the circumferential direction. In this way, the inner cylinder 20 is configured to have lower rigidity compared to the outer cylinder 30.

[0043] In the axial direction, the inner cylinder 20 is structurally more flexible on the side forming the free end 20a compared to the other side where the mounting portion 23 is provided and fixed to the outer cylinder 30. In the circumferential direction, the inner cylinder 20 is structurally more flexible in the region between two adjacent mounting portions 23 compared to the location where the mounting portion 23 is provided. The inner cylinder 20 is particularly structurally flexible at the intermediate position between the two mounting portions 23, and is most structurally flexible at the exact center position between the two mounting portions 23. The intermediate position is any position within the central region when the region between the two mounting portions 23 is divided into an odd number of equal parts (for example, three). The exact center position is an example of an intermediate position and is located within the central region.

[0044] The stay 14 is fixed to the inner circumferential surface of the inner cylinder 20, which is part of the inner circumferential surface of the exhaust duct 12. The stay 14 is fixed to one side of the inner cylinder 20 in the axial direction. Each of the multiple stays 14 is positioned in the circumferential direction between two adjacent mounting parts 23, or more precisely, midway between two adjacent mounting parts 23. If the stay 14 is positioned exactly in the middle of two mounting parts 23, and the number of stays 14 is equal to the number of mounting parts 23, then the multiple stays 14 and multiple mounting parts 23 are arranged alternately one by one in the circumferential direction and at equal intervals.

[0045] The stay 14 is fixed to the inner cylinder 20, which is configured to have lower rigidity compared to the outer cylinder 30. The stay 14 is fixed to a particularly low-rigidity or structurally flexible part of the inner cylinder 20. Furthermore, because the inner cylinder 20 defines the exhaust passage 13 and the outer peripheral passage 25, the temperature difference between the inner and outer peripheral surfaces is smaller compared to the outer cylinder 30 and connecting cylinder 40, which are exposed to the outside air.

[0046] Therefore, even if the center cone 11 and stay 14 undergo thermal expansion due to the exhaust, the restraining force of the exhaust duct 12 against thermal expansion is significantly reduced. This makes it less likely for cracks to occur in the stay 14, improving the durability of the exhaust duct structure 10.

[0047] The exhaust duct structure 10 configured as described above may be manufactured, as an example, using a method comprising the following steps a) to d). The configuration of the exhaust duct structure 10 will be described in more detail below in accordance with these steps. a) Secure the stay 14 to the inner cylinder 20 and the center cone 11. b) Position the inner cylinder 20 relative to the outer cylinder 30. Simultaneously, form the outer peripheral passage 25 and its outlet 27. c) Connect the connecting cylinder 40 to the outer cylinder 30. At the same time, fix the inner cylinder 20 to the outer cylinder 30 and seal the exhaust passage 13 with the sealing member 15. d) Connect the outer cylinder 30 to the casing 5a. Simultaneously, form the inlet 26 of the outer peripheral passage 25.

[0048] With respect to step a), referring to Figures 3 and 4, the stay 14 is fixed to the center cone 11 and the inner cylinder 20 by welding. For the convenience of welding, the center cone 11, the stay 14, and the inner cylinder 20 are made of the same type of metal material, such as steel or other ferrous material.

[0049] The inner cylinder 20 has a cylindrical inner cylinder body 21 and a flange 22 provided at the other end of the inner cylinder body 21.

[0050] The flange 22 is rim-shaped. Multiple (for example, three) mounting portions 23 are integrally provided on the flange 22 and are arranged at equal intervals in the circumferential direction. Hereinafter, when simply referred to as "flange 22," it may refer to the portion of the flange 22 that does not have mounting portions 23. The mounting portions 23 are tabs that extend radially and circumferentially, and protrude more significantly from the flange 22 on the radially outer side.

[0051] The flange 22 is fitted onto the other end of the inner cylinder body 21 and welded around its entire circumference from both sides in the axial direction. This joins multiple mounting portions 23 to the inner cylinder body 21. Compared to the case where multiple mounting portions 23 are joined to the inner cylinder body 21 individually, the positional accuracy and joining strength of the multiple mounting portions 23 to the inner cylinder body 21 are improved.

[0052] The stay 14 is a rectangular plate. The stay 14 is positioned between the center cone 11 and the inner cylinder 20 with a pair of surfaces extending in the axial and radial directions.

[0053] The stay 14 has a first joint portion 14a formed by bending the outer peripheral edge in the radial direction, and a second joint portion 14b formed by bending the inner peripheral edge in the radial direction. The first joint portion 14a and the second joint portion 14b are bent to opposite sides and both extend in the axial direction. The first joint portion 14a is shorter than the second joint portion 14b.

[0054] The first joint portion 14a is welded to the inner cylinder body 21 in a state of surface contact with the inner circumferential surface of the inner cylinder body 21. Each of the multiple first joint portions 14a is positioned midway between two adjacent mounting portions 23 in the circumferential direction. The axial center position C14a of the first joint portion 14a is located on one side in the axial direction relative to the axial center position C20 of the inner cylinder 20. As a result, the stay 14 is fixed to the inner cylinder 20 with the stay positioned towards one side in the axial direction of the inner cylinder 20.

[0055] One end of the inner cylinder body 21 is enlarged in diameter in the axial direction. The first joint 14a is welded to the inner cylinder body 21 such that one end of the first joint 14a in the axial direction aligns with the starting position of the diameter enlargement. This aligns the axial positions of the multiple first joints 14a with respect to the inner cylinder 20.

[0056] The center cone 11 is tapered in diameter from one side to the other in the axial direction. Accordingly, the second joint portion 14b is also inclined so as to move from one side to the other in the axial direction toward the radial center. After fixing the multiple stays 14 to the inner cylinder 20, when the center cone 11 is inserted into the inside of the stays 14 from one side in the axial direction, the outer surface of the center cone 11 makes surface contact with the multiple second joint portions 14b, and the insertion stops. In this state, the second joint portions 14b are welded to the center cone 11.

[0057] As a result, multiple stays 14 are fixed to the inner cylinder 20 at the same position in the axial direction, and also fixed to the center cone 11 at the same position in the axial direction. The center cone 11 is supported by the inner cylinder 20 via the stays 14 in a coaxial state with the inner cylinder 20.

[0058] Next, with respect to step b), referring to Figures 4 and 5, the outer cylinder 30 has a cylindrical outer cylinder body 31, a base flange 32 provided at one end of the outer cylinder body 31, and an outer cylinder flange 33 provided at the other end of the outer cylinder body 31.

[0059] The outer cylinder flange 33 is annular in shape. The inner periphery of the outer cylinder flange 33 is welded to the outer circumferential surface of the peripheral portion of the other end opening of the outer cylinder body 31. The outer cylinder flange 33 protrudes radially outward from the other end of the outer cylinder body 31.

[0060] The inner diameter of the outer cylinder body 31 is larger than the outer diameter of the inner cylinder body 21, while it is smaller than the outer diameter of the mounting portion 23. In other words, the projection length of the mounting portion 23 from the inner cylinder body 21 is greater than the difference between the inner diameter of the inner cylinder body 21 and the outer diameter of the outer cylinder body 31.

[0061] Therefore, when assembling the inner cylinder 20 to the outer cylinder 30, the inner cylinder 20 is inserted into the outer cylinder 30 from the other axial side. The mounting portion 23 cannot pass through the other end opening of the outer cylinder body 31 and abuts against the end face of the outer cylinder flange 33. Insertion of the inner cylinder 20 stops, and the inner cylinder 20 is positioned axially relative to the outer cylinder 30.

[0062] Referring to Figures 3 and 5, the exhaust duct structure 10 is provided in an inner cylinder 20 and an outer cylinder 30, and includes a positioning structure 50 that aligns the central axis of the inner cylinder 20 with the central axis of the outer cylinder 30. In this embodiment, the positioning structure 50 is provided in the mounting portion 23 and the outer cylinder flange 33.

[0063] The positioning structure 50 consists of a positioning projection 51 that protrudes from the outer cylinder flange 33 to the other axial side, and a positioning hole 52 provided in the mounting portion 23 that engages with the positioning projection 51. The positioning projection 51 can be realized by a pin that is welded to the outer cylinder flange 33.

[0064] When the mounting portion 23 abuts against the outer cylinder flange 33, the positioning projection 51 is fitted into the positioning hole 52. As a result, the inner cylinder 20 is positioned radially and circumferentially relative to the outer cylinder 30, and the inner cylinder 20 becomes coaxial with the outer cylinder 30.

[0065] The outer circumferential passage 25 is defined by the inner circumferential surface of the outer circumferential surface of the outer circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the outer circumferential surface of the outer circumferential surface of the positioning structure 50, so that the width of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the outer circumferential surface of the inner inner circumferential surface of the inner circumferential surface of the inner circumferential surface of the inner circumferential

[0066] Since the outer diameter of the mounting portion 23 is larger than the inner diameter of the outer cylinder body 31, the mounting portion 23 locally closes the other end opening of the outer cylinder body 31, i.e., the other axial end of the outer peripheral passage 25. On the other hand, the outer diameter of the flange 22 is smaller than the inner diameter of the outer cylinder body 31. Therefore, the other end opening of the outer cylinder body 31 is open in an arc shape in the region between the two adjacent mounting portions 23 in the circumferential direction, and in the region on the outer circumference side of the flange 22 in the radial direction. This open region serves as the outlet 27 of the outer peripheral passage 25.

[0067] Next, with respect to step c), referring to Figures 4 and 5, the connecting cylinder 40 has a cylindrical connecting cylinder body 41 and a connecting flange 42 provided at one end of the connecting cylinder body 41. The connecting flange 42 is annular. The inner periphery of the connecting flange 42 is welded to the outer circumferential surface of the periphery of the opening at one end of the connecting cylinder body 41. The connecting flange 42 protrudes radially outward from the other end of the connecting cylinder body 41. The connecting flange 42 faces the outer cylinder flange 33 in the axial direction.

[0068] The connecting cylinder 40 is assembled to the outer cylinder 30 with the inner cylinder 20. A mounting portion 23 is attached to the end face of the outer cylinder flange 33. The connecting flange 42 is abutted against the mounting portion 23 and spaced apart from the outer cylinder flange 33, and is fastened to the outer cylinder flange 33 with multiple sets of bolts 61, 63 and nuts 62, 64. The mounting portion 23 is inserted into the gap 35 between the outer cylinder flange 33 and the connecting flange 42 from the radial inner circumference side, and is sandwiched axially between the outer cylinder flange 33 and the connecting flange 42.

[0069] Multiple sets of bolts 61, 63 and nuts 62, 64 are spaced apart from each other in the circumferential direction and are provided radially on the outer circumference of the mounting portion 23. Some of the bolts 61 are inserted from one axial side of the outer cylinder flange 33 and screwed into nuts 64 located on the other axial side of the connecting flange 42. The remaining bolts 63 are inserted from the other axial side of the connecting flange 42 and screwed into nuts 64 located on one axial side of the outer cylinder flange 33.

[0070] The mounting portion 23 is secured by tightening bolts 61, 63 or nuts 62, 64, thereby realizing a double-cylinder structure in which only the other axial side of the inner cylinder 20 is fixed to the outer cylinder 30. The structure for fixing the inner cylinder 20 to the outer cylinder 30 can be incorporated into the structure for connecting the outer cylinder 30 and the connecting cylinder 40, simplifying the configuration and manufacturing process of the exhaust duct structure 10.

[0071] The inner diameter of one axial end of the connecting cylinder body 41 is approximately the same as the inner diameter of the outer cylinder body 31 and is larger than the outer diameter of the flange 22. Therefore, the outlet 27 of the outer peripheral passage 25 is not narrowed by the connecting cylinder 40. The exhaust gas that has passed through the outer peripheral passage 25 can smoothly merge into the exhaust passage 13 via the outlet 27.

[0072] The exhaust duct structure 10 is positioned radially on the outer circumference of the mounting portion 23 and includes a sealing member 15 provided in the gap 35. The sealing member 15 is made of a metal material and is an annular plate. The thickness of the sealing member 15 is approximately the same as the thickness of the mounting portion 23.

[0073] When assembling the connecting cylinder 40 to the outer cylinder 30, the sealing member 15 is interposed between the outer cylinder flange 33 and the connecting flange 42. Bolts 61 and 63 are inserted through the sealing member 15, and the sealing member 15 is tightly fitted to both the outer cylinder flange 33 and the connecting flange 42 by the tightening torque. As a result, in a structure in which the mounting portions 23 are discretely arranged in the circumferential direction within the gap 35 between the outer cylinder 30 and the connecting cylinder 40, the gap 35 is sealed. This prevents exhaust gas from leaking to the outside air from the exhaust passage 13 or the outer peripheral passage 25.

[0074] Next, with respect to step d), referring to Figures 4 and 5, the base flange 32 of the outer cylinder 30 is annular. The inner periphery of the base flange 32 is welded to the outer circumferential surface of the periphery of the opening at one end of the outer cylinder body 31. The base flange 32 protrudes radially outward from one end of the outer cylinder body 31.

[0075] The base flange 32 is brought into contact with the casing 5a from the other axial side and fastened to the casing 5a with a number of bolts 65. In this way, the exhaust duct structure 10 is assembled to the casing 5a and forms part of the gas turbine 1. One end of the center cone 11 is received by the casing 5a.

[0076] In step b), when the inner cylinder 20 is positioned axially relative to the outer cylinder 30, one axial end of the inner cylinder body 21 is positioned slightly to the other axial side relative to the base flange 32. When the base flange 32 is connected to the casing 5a, one end of the inner cylinder body 21 faces the casing 5a with an axial gap between them. This gap serves as the inlet 26 for the outer peripheral passage 25. A portion of the exhaust from the turbine 5 can flow radially outward and enter the outer peripheral passage 25 through the inlet 26.

[0077] Although embodiments have been described so far, the above configuration is merely an example and can be modified as appropriate within the scope of the present invention.

[0078] In the above embodiment, one axial side is defined as the turbine side or the upstream side in the exhaust flow direction, and the other axial side is defined as the outside air side or the downstream side in the exhaust flow direction. The inner cylinder 20 is fixed to the outer cylinder 30 on the other axial side, and a free end 20a is formed on one axial side. This directional definition may be reversed. One axial side may be defined as the outside air side, and the other axial side may be defined as the turbine side. In this case, the inner cylinder 20 is fixed to the outer cylinder 30 on the upstream side in the exhaust flow direction (the other side when the definition is reversed), and a free end 20a is formed on the downstream side in the exhaust flow direction (the one side when the definition is reversed). The connecting cylinder 40 is positioned on the downstream side in the exhaust flow direction when viewed from the outer cylinder 30. When the definition is reversed, the "other end" in the axial direction of the connecting cylinder 40 is connected to the "one end" in the axial direction of the outer cylinder 30.

[0079] The number of mounting parts 23 and the number of stays 14 do not necessarily have to be the same. The positioning projection 51 is not limited to a welded pin, but may be another axial member, such as a bolt screwed into the outer cylinder flange 33. The positioning hole 52 may be provided in the outer cylinder 30 (outer cylinder flange 33), and the positioning projection 51 may be provided in the inner cylinder 20 (mounting part 23).

[0080] In the above embodiment, the inner cylinder 20 is configured to have lower rigidity compared to the outer cylinder 30. To achieve this, the inner cylinder 20 is fixed to the outer cylinder 30 only on the other axial side, while a free end 20a is formed on one axial side of the inner cylinder 20, which is free from the outer cylinder 30. However, this is just one example. The inner cylinder 20 may be fixed to the outer cylinder 30 at both axial ends. In this case, the inner cylinder 20 may be molded from a material that has higher elasticity compared to the outer cylinder 30. This allows the inner cylinder 20 to have lower rigidity compared to the outer cylinder 30, even if the inner cylinder 20 is not structurally flexible relative to the outer cylinder 30. Therefore, similar to the above embodiment, the restraining force on the exhaust duct 12 against thermal expansion can be reduced. [Explanation of Symbols]

[0081] 1 Gas Turbine 2 main shaft 3. Compressor 4 Combustor 5 Turbines 5a Casing 6 Reducer 10 Exhaust duct structure 11 Center cone 12 Exhaust duct 13 Exhaust passage 14 Stay 15 sealing member 20 Inner cylinder 20a free end 21 Inner cylinder body 22 Flange 23 Mounting part 25 Perimeter walkway 26 Inlet 27 Outlet 30 Outer cylinder 31 Outer cylinder body 32 Base flange 33 Outer cylinder flange 35 Gap 40 connecting tubes 41 Connecting cylinder body 42 Connection flange 50 Positioning structure 51 Positioning protrusion 52 Positioning holes 61, 63, 65 bolts 62,64 nuts A center axis C14a,C20 center position L load

Claims

1. Center cone and An exhaust duct surrounding the aforementioned center cone, An exhaust passage is defined between the center cone and the exhaust duct, through which exhaust gas from the turbine flows, The center cone is connected to the exhaust duct by a bracket, Equipped with, The aforementioned exhaust duct, The inner cylinder to which the aforementioned stay is fixed, The outer cylinder surrounds the inner cylinder, Includes, The inner cylinder is configured to have lower rigidity compared to the outer cylinder. Gas turbine exhaust duct structure.

2. The inner cylinder has a free end on one side in the axial direction of the inner cylinder that is free from the outer cylinder, and a mounting portion provided on the other side in the axial direction of the inner cylinder that is fixed to the outer cylinder. The exhaust duct structure for a gas turbine according to claim 1.

3. Multiple mounting portions are arranged at intervals in the circumferential direction of the inner cylinder. Each of the multiple stays is positioned between two adjacent mounting portions in the circumferential direction. The exhaust duct structure for a gas turbine according to claim 2.

4. Each of the aforementioned stays is positioned midway between two adjacent mounting portions in the circumferential direction. The exhaust duct structure for a gas turbine according to claim 3.

5. The stay is fixed to one side of the inner cylinder in the axial direction. The exhaust duct structure for a gas turbine according to claim 2.

6. The exhaust duct further includes a connecting cylinder connected to the end of the outer cylinder, The outer cylinder is provided with an annular outer cylinder flange that protrudes radially outward from its end, and the connecting cylinder is provided with an annular connecting flange that faces the outer cylinder flange in the axial direction. The mounting portion of the inner cylinder is sandwiched in the gap between the outer cylinder flange and the connecting flange from the radial inner circumference side. The exhaust duct structure for a gas turbine according to claim 2.

7. The mounting portion is further provided with a sealing member positioned radially on the outer circumference and in the gap. The exhaust duct structure for a gas turbine according to claim 6.

8. The exhaust duct further includes an outer peripheral passage defined between the inner cylinder and the outer cylinder and communicating with the exhaust passage. The exhaust duct structure for a gas turbine according to any one of claims 1 to 7.

9. The exhaust duct is provided in the inner cylinder and the outer cylinder, and further includes a positioning structure that aligns the central axis of the inner cylinder with the central axis of the outer cylinder. The exhaust duct structure for a gas turbine according to any one of claims 1 to 7.

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