Steam turbine

Abstract

The steam turbine includes: a rotor shaft that rotates about an axis; multiple rows of moving blade cascades that are fixed to the radially outer side of the rotor shaft and are arranged at intervals in the axial direction along the axis; a casing that is arranged to cover the rotor shaft and the multiple moving blade cascades; and a stationary blade cascade that is fixed to the radially inner side of the casing and is arranged at intervals in the axial direction, and is arranged on the first side in the axial direction with respect to each row of the multiple rows of moving blade cascades. The stationary blade cascade includes: stationary blades that are arranged at intervals in the circumferential direction and each extend radially; an outer ring that is annular and is arranged on the radially outer side of the multiple stationary blades; an inner ring that is annular and is arranged on the radially inner side of the multiple stationary blades; a recess that is formed in the inner circumferential surface of the ring facing radially inward in the outer ring and recesses radially outward between the stationary blades adjacent in the circumferential direction; and a discharge portion that opens into the recess and discharges the droplets remaining in the recess to the outside.

Description

Technical Field

[0001] The present invention relates to a steam turbine. Background Art

[0002] A steam turbine has multiple compression stages within a casing. The steam flowing from the upstream side to the downstream side through the multiple compression stages within the casing expands as it approaches the downstream side, resulting in a decrease in pressure and temperature. In particular, near the final compression stage, the humidity of the steam increases, and sometimes the moisture in the steam forms droplets. The increase in the humidity of the steam leads to a decrease in the efficiency of the steam turbine. Also, if the moisture in the steam forms droplets, it sometimes causes so-called erosion where the moving blades of the final stage are corroded by the droplets scattered from the stationary blades.

[0003] In contrast, for example, Patent Document 1 discloses a structure having a suction portion on the inner peripheral surface of a diaphragm outer ring provided on a casing for recovering droplets (water droplets or water films) from the inner peripheral surface of the diaphragm outer ring. In this structure, the suction portion communicates with a hollow portion formed on the diaphragm outer ring from the back side of the stationary blade toward the ventral side of the adjacent stationary blade. According to this structure, by sucking the droplets adhering to the blade surface of the stationary blade of the final-stage stator blade row or the inner wall surface of the diaphragm outer ring by the suction portion, the droplets are prevented from reaching the leading edge of the wake-side moving blade, thereby reducing erosion.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2019-35384 Summary of the Invention

[0007] Technical Problem to be Solved by the Invention

[0008] However, there has always been a desire to more effectively suppress the occurrence of erosion.

[0009] The present invention has been completed to solve the above problems, and an object thereof is to provide a steam turbine capable of more effectively suppressing the occurrence of erosion.

[0010] Means for Solving the Technical Problem

[0011] To solve the above problems, the steam turbine according to the present invention includes: a rotor shaft that rotates about an axis; multiple rows of moving blade cascades that are fixed to the radially outer side of the rotor shaft and are arranged at intervals in the axial direction along the axis; a casing that is arranged to cover the rotor shaft and the multiple moving blade cascades; and a stationary blade cascade that is fixed to the radially inner side of the casing and is arranged at intervals in the axial direction, and is arranged on the first side in the axial direction with respect to each row of the multiple moving blade cascades. The stationary blade cascade includes: stationary blades that are arranged at intervals in the circumferential direction and extend radially respectively; an outer ring that is annular and arranged on the radially outer side of the multiple stationary blades; an inner ring that is annular and arranged on the radially inner side of the multiple stationary blades; a concave portion that is formed on the inner circumferential surface of the ring facing the radially inner side in the outer ring and is recessed radially outward between the stationary blades adjacent in the circumferential direction; and a discharge portion that opens in the concave portion and discharges the droplets remaining in the concave portion to the outside.

[0012] Advantages of the Invention

[0013] According to the steam turbine of the present invention, the occurrence of erosion can be more effectively suppressed. Description of the Drawings

[0014] Figure 1 It is a schematic diagram showing the schematic structure of the steam turbine in the embodiment of the present invention.

[0015] Figure 2 It is a cross-sectional view showing the stationary blade cascade and the moving blade cascade of the final row in the steam turbine of the first embodiment of the present invention.

[0016] Figure 3 It is a perspective view showing a part of the stationary blade cascade of the final row in the first embodiment of the present invention.

[0017] Figure 4 It is a diagram showing the cross-sectional shape of the stationary blade constituting the stationary blade cascade of the final row in the first embodiment of the present invention.

[0018] Figure 5 It is a cross-sectional view of the stationary blade cascade of the final row in the first embodiment of the present invention observed from the axial direction, and is Figure 2 a cross-sectional view taken along the line A-A.

[0019] Figure 6 It is a view of the outer ring of the stationary blade cascade of the final row in the first embodiment of the present invention observed from the radially inner side, and is Figure 2 a view taken along the line B-B.

[0020] Figure 7 It is a view of the outer ring of the stationary blade cascade of the final row in the second embodiment of the present invention observed from the radially inner side.

[0021] Figure 8 It is a cross-sectional view of the stator blade row of the final stage in the second embodiment of the present invention observed axially.

[0022] Figure 9 It is a cross-sectional view of the stator blade row of the final stage in a modified example of the second embodiment of the present invention observed axially.

[0023] Figure 10 It is a view of the outer ring of the stator blade row of the final stage in the third embodiment of the present invention observed from the radially inner side. Detailed Embodiments

[0024] <First Embodiment>

[0025] (Structure of Steam Turbine)

[0026] As Figure 1 shown, the steam turbine 1A of the present embodiment has a rotor 20 that rotates about an axis O and a casing 10.

[0027] In addition, for the convenience of the following description, the direction in which the axis O extends is defined as the axial direction Da, the radial direction in the shaft core part 22 described later with respect to the axis O is defined only as the radial direction Dr, and the circumferential direction of the shaft core part 22 about the axis O is defined only as the circumferential direction Dc.

[0028] (Structure of Rotor)

[0029] The rotor 20 has a rotor shaft 21 and a moving blade row 31.

[0030] The rotor shaft 21 is configured to be rotatable about the axis O. The rotor shaft 21 has a shaft core part 22 and a plurality of disk parts 23. The shaft core part 22 is cylindrical about the axis O and extends in the axial direction Da. The plurality of disk parts 23 are arranged at intervals in the axial direction Da. Each disk part 23 is arranged to extend outward from the shaft core part 22 in the radial direction Dr to the outer side Dro.

[0031] (Structure of Moving Blade Row)

[0032] The moving blade row 31 is fixed to the outer side Dro in the radial direction Dr of the rotor shaft 21. The moving blade row 31 is installed on the outer peripheral part of the rotor shaft 21, that is, the outer periphery of the disk part 23. The moving blade row 31 is arranged in multiple rows at intervals along the axial direction Da of the rotor shaft 21. In the case of the present embodiment, for example, four rows of moving blade rows 31 are arranged. Therefore, in the case of the present embodiment, as the moving blade row 31, the moving blade rows 31 from the first stage to the fourth stage are arranged.

[0033] As Figure 2As shown, the moving blade rows 31 of each column have a plurality of moving blades 32 arranged circumferentially along Dc, shrouds 34, and platforms 35. Each moving blade 32 extends radially along Dr. The shroud 34 is disposed on the outer side Dro in the radial direction Dr of the moving blade 32. The platform 35 is disposed on the inner side Dri in the radial direction Dr of the moving blade 32. Steam S flows through the annular space between the shroud 34 and the platform 35 in the moving blade 32.

[0034] (Structure of the housing)

[0035] As Figure 1 shown, the housing 10 is formed to cover the rotor 20. A stator blade row 41 is fixed to the inner side Dri in the radial direction Dr of the housing 10. A plurality of stator blade rows 41 are arranged at intervals along the axial direction Da. In the present embodiment, four columns of stator blade rows 41 are arranged, which is the same as the number of columns of the moving blade rows 31. Each stator blade row 41 is adjacently arranged on the first side Dau in the axial direction Da with respect to each column of the plurality of moving blade rows 31. The first side Dau in the axial direction Da is the upstream side in the flow direction of the steam S in the housing 10. That is, the steam S flows from the first side Dau to the second side Dad in the housing 10.

[0036] (Structure of the stator blade row)

[0037] As Figure 2 , Figure 3 shown, the stator blade row 41 mainly includes stator blades 42, an outer ring 43, and an inner ring 44. A plurality of stator blades 42 are arranged at intervals along the circumferential direction Dc. The outer ring 43 is annular and disposed on the outer side Dro in the radial direction Dr of the plurality of stator blades 42. The inner ring 44 is annular and disposed on the inner side Dri in the radial direction Dr of the plurality of stator blades 42. Steam S flows through the annular space between the outer ring 43 and the inner ring 44.

[0038] (Structure of the stator blade)

[0039] The inner ends 42s on the inner side Dri in the radial direction Dr of each stator blade 42 are fixed to the inner ring 44. The outer ends 42t on the outer side Dro in the radial direction Dr of each stator blade 42 are fixed to the outer ring 43.

[0040] As Figure 4 shown, the stator blade 42 extends from the first side edge portion 48 on the first side Dau in the axial direction Da to the second side edge portion 49 on the second side Dad in the axial direction Da, and from the radial direction Dr (and Figure 4It has a blade cross-sectional shape in a cross-section orthogonal to the plane of the paper (direction). The stationary blade 42 has a ventral surface 42a facing one side Dc1 in the circumferential direction Dc and a dorsal surface 42b facing the other side Dc2 in the circumferential direction Dc. The stationary blade 42 is formed by a ventral member 45 and a dorsal member 46. The ventral member 45 forms the ventral surface 42a of the stationary blade 42. The ventral member 45 is bent in a concave shape so as to be recessed toward the other side Dc2 in the circumferential direction Dc. The dorsal member 46 forms the dorsal surface 42b of the stationary blade 42. The dorsal member 46 is bent in a convex shape so as to protrude toward the other side Dc2 in the circumferential direction Dc. The ventral member 45 and the dorsal member 46 are members that bend a metal plate-like member into a predetermined shape respectively. The stationary blade 42 is formed by combining and welding the ventral member 45 and the dorsal member 46 to each other. Thus, a hollow portion 47 is formed inside the stationary blade 42, that is, between the ventral member 45 and the dorsal member 46.

[0041] As Figure 2 shown, for example, the second side edge portion 49 of the stationary blade 42 may have a second side convex portion 49a, a second side concave portion 49b, and a blade tip extension portion 49c.

[0042] The second side convex portion 49a is formed on the inner side Dri in the radial direction Dr with respect to the intermediate position 42m between the outer end 42t and the inner end 42s of the stationary blade 42. The second side convex portion 49a is bent in a convex shape so as to protrude toward the second side Dad in the axial direction Da. More specifically, the second side convex portion 49a is bent so as to protrude more toward the second side Dad in the axial direction Da than the inner end 42s and the intermediate position 42m.

[0043] For example, the intermediate position 42m may be the center of the two ends of the stationary blade 42 in the radial direction Dr in the second side edge portion 49.

[0044] The second side concave portion 49b is continuously formed on the outer side Dro in the radial direction Dr with respect to the intermediate position 42m. The second side concave portion 49b is formed to be bent and recessed on the first side Dau in the axial direction Da. The second side concave portion 49b is bent in a concave shape so as to be recessed more toward the first side Dau in the axial direction Da than the intermediate position 42m and the outer end 42t.

[0045] The blade tip extension portion 49c is continuously formed on the outer side Dro in the radial direction Dr with respect to the second side concave portion 49b. The blade tip extension portion 49c protrudes and extends from the second side concave portion 49b toward the second side Dad in the axial direction Da and is connected to the outer ring 43.

[0046] Thus, the second side edge portion 49 has an S shape when viewed from the circumferential direction Dc.

[0047] For example, the first side edge portion 48 of the stationary blade 42 may have a first side concave portion 48a and a first side convex portion 48b and be formed in an S shape.

[0048] For example, the second side edge portion 49 may have an S shape extending from the outer end 42t to the inner end 42s of the stationary blade 42.

[0049] The first side recess 48a is formed on the inner side Dri in the radial direction Dr of the stationary blade 42. The first side recess 48a is formed to be recessed in a concave shape toward the second side Dad in the axial direction Da.

[0050] The first side protrusion 48b is continuously formed on the outer side Dro in the radial direction Dr with respect to the first side recess 48a. The first side protrusion 48b is formed to protrude in a convex shape toward the first side Dau in the axial direction Da.

[0051] For example, the stationary blade 42 may have a communication hole 50.

[0052] The communication hole 50 is formed on the outer side Dro in the radial direction Dr rather than at the intermediate position 42m in the radial direction Dr.

[0053] The communication hole 50 is formed to communicate the outer surface of the ventral member 45 of the stationary blade 42 with the hollow portion 47.

[0054] For example, the communication hole 50 may be a slit continuously extending in the radial direction Dr.

[0055] For example, the communication hole 50 may be one or more holes communicating the outer surface of the ventral member 45 of the stationary blade 42 with the hollow portion 47 instead of the slit.

[0056] For example, the communication hole 50 may be formed only at a position on the outer side Dro in the radial direction Dr rather than at the intermediate position 42m in the outer surface of the ventral member 45 of the stationary blade 42 in the radial direction Dr.

[0057] For example, the communication hole 50 may also be formed at a position closer to the second side edge portion 49 than the first side edge portion 48 in the outer surface of the ventral member 45 of the stationary blade 42.

[0058] (Structure of the outer ring)

[0059] As Figure 5 、 Figure 6 shown, a recess 61, a protrusion 62, and a discharge portion 71 are formed on the outer ring 43.

[0060] The recess 61 is formed on the inner peripheral surface 43f of the ring of the outer ring 43 facing the inner side Dri in the radial direction Dr. The recess 61 is formed between the stationary blades 42 adjacent in the circumferential direction Dc. The recess 61 is formed on the side closer to the back surface 42b of the stationary blade 42 disposed on one side Dc1 in the circumferential direction Dc among the two stationary blades 42 adjacent in the circumferential direction Dc. The recess 61 is formed in a concave shape so as to be recessed toward the outer side Dro in the radial direction Dr.

[0061] For example, the recess 61 may extend along the axial direction Da.

[0062] For example, the recess 61 may extend in the direction along the inner circumferential surface 43f of the ring and in the direction along the back surface 42b of the stationary blade 42.

[0063] The convex portion 62 is formed on the stationary blade 42 disposed on the other side Dc2 in the circumferential direction Dc among the two stationary blades 42 adjacent in the circumferential direction Dc with respect to the recess 61, on the side closer to the front surface 42a. The convex portion 62 is formed in a convex shape so as to bulge toward the inner side Dri in the radial direction Dr.

[0064] For example, the convex portion 62 may extend along the axial direction Da.

[0065] For example, the convex portion 62 may extend in the direction along the inner circumferential surface 43f of the ring and in the direction along the front surface 42a of the stationary blade 42.

[0066] The convex portion 62 can be easily formed on the inner circumferential surface 43f of the outer ring 43 by surfacing, for example.

[0067] The discharge portion 71 is formed in the recess 61. The discharge portion 71 is a slit or one or more holes that open in the recess 61. The slit or hole forming the discharge portion 71 is connected to a condenser or the like disposed outside the steam turbine 1A. The discharge portion 71 discharges the droplets or the liquid film formed by the droplets (these droplets or liquid films are sometimes also referred to as drain pipes) that flow into the recess 61 to the external condenser or the like.

[0068] (Function and effect)

[0069] According to the steam turbine 1A as described above, between the stationary blades 42 adjacent to each other in the circumferential direction Dc, a recess 61 that is recessed toward the outer side Dro in the radial direction Dr is formed on the inner circumferential surface 43f of the outer ring 43. Thus, the droplets contained in the steam S that flow into the housing 10 from the first side Dau in the axial direction Da and adhere to the inner circumferential surface 43f of the outer ring 43 are trapped in the recess 61. The trapped droplets are discharged to the outside from the discharge portion 71. As a result, the amount of droplets reaching the moving blade row 31 on the second side Dad in the axial direction Da can be suppressed. As a result, a reduction in erosion can be achieved.

[0070] In the steam turbine 1A as described above, the steam S flow in the stationary blade row 41 contacts the ventral surface 42a of the stationary blade 42 located on the other side Dc2 in the circumferential direction Dc. Therefore, between two adjacent stationary blades 42 in the circumferential direction Dc, the pressure on the side of the stationary blade 42 located on the other side Dc2 in the circumferential direction Dc near the ventral surface 42a becomes higher, and the pressure on the side of the stationary blade 42 located on one side Dc1 in the circumferential direction Dc near the dorsal surface 42b becomes lower. In contrast, by forming a recess 61 on the side of the stationary blade 42 located on one side Dc1 in the circumferential direction Dc near the dorsal surface 42b, the flow path of the steam S between the inner ring 44 and the outer ring 43 becomes larger in the radial direction Dr at the portion where the recess 61 is formed. That is, the cross-sectional area of the flow path of the steam S between the inner ring 44 and the outer ring 43 increases at the portion where the recess 61 is formed. Then, at the portion where the recess 61 is formed, the flow velocity of the steam S decreases and the pressure of the steam S rises. As a result, the pressure on the side of the stationary blade 42 located on one side Dc1 in the circumferential direction Dc near the dorsal surface 42b rises between two adjacent stationary blades 42 in the circumferential direction Dc. Therefore, the pressure difference in the circumferential direction Dc between the stationary blade 42 on one side Dc1 and the stationary blade 42 on the other side Dc2 adjacent in the circumferential direction Dc becomes smaller. As a result, it is possible to suppress the cross-flow Fb (refer to Figure 6 ) of the steam S flowing toward the circumferential direction Dc caused by the pressure difference between adjacent stationary blades 42 in the circumferential direction Dc. Thus, it is possible to improve the entrainment of droplets caused by the cross-flow Fb and suppress the amount of droplets reaching the rotor blade row 31 on the second side Dad in the axial direction Da. As a result, it is possible to achieve a reduction in erosion.

[0071] The steam turbine 1A as described above is provided with a convex portion 62 formed on the side of the stationary blade 42 located on the other side Dc2 in the circumferential direction Dc near the ventral surface 42a. At the portion where the convex portion 62 is formed, the flow path of the steam S between the inner ring 44 and the outer ring 43 becomes smaller in the radial direction Dr. That is, the cross-sectional area of the flow path of the steam S between the inner ring 44 and the outer ring 43 decreases at the portion where the convex portion 62 is formed. Then, at the portion where the convex portion 62 is formed, the flow velocity of the steam S rises and the pressure of the steam S decreases. As a result, the pressure on the side of the stationary blade 42 located on the other side Dc2 in the circumferential direction Dc near the ventral surface 42a decreases between two adjacent stationary blades 42 in the circumferential direction Dc. Therefore, the pressure difference in the circumferential direction Dc between the stationary blade 42 on one side Dc1 and the stationary blade 42 on the other side Dc2 adjacent in the circumferential direction Dc becomes further smaller (equalized). As a result, it is possible to further suppress the cross-flow Fb of the steam S flowing toward the circumferential direction Dc caused by the pressure difference between adjacent stationary blades 42 in the circumferential direction Dc. Thus, it is possible to improve the entrainment of droplets caused by the cross-flow Fb and suppress the amount of droplets reaching the rotor blade row 31 on the second side Dad in the axial direction Da. As a result, it is possible to achieve a reduction in erosion.

[0072] In the steam turbine 1A as described above, the second side concave portion 49b of the second side edge portion 49 of the stationary blade 42 is recessed toward the first side Dau of the axial direction Da. Accordingly, the gap S1 in the axial direction Da between the second side concave portion 49b and the moving blade 32 of the final stage moving blade row 31F becomes larger. Thus, due to the effect of the centrifugal force generated by the rotating flow flowing out from the stationary blade 42, the droplets move along with Figure 2 the steam flow represented by the imaginary line L1 in the figure from the stationary blade 42 toward the second side of the axial direction Da and at the same time toward the outer side Dro in the radial direction Dr. Accordingly, the amount of droplets reaching the end portion 32a on the first side Dau in the axial direction Da of the moving blade 32 can be suppressed. As a result, reduction of erosion can be achieved.

[0073] Moreover, in the second side edge portion 49 of the stationary blade 42, the second side convex portion 49a projects toward the second side Dad in the axial direction Da. Accordingly, the gap S2 between the second side convex portion 49a and the final stage moving blade row 31F can be made smaller than the gap S1 of the portion of the second side concave portion 49b. Thus, reduction of the turbine performance can be suppressed. Also, by reducing the gap S2 between the second side convex portion 49a and the moving blade 32 of the final stage moving blade row 31F, increase in the bearing span can be suppressed, and reduction of the shaft vibration reliability can be suppressed. Further, since the second side convex portion 49a is formed on the inner side Dri in the radial direction Dr, the circumferential velocity of the steam S flow is also smaller than that on the outer side Dro in the radial direction Dr, and erosion is less likely to occur. As a result, generation of erosion can be suppressed more effectively.

[0074] The steam turbine 1A as described above further includes a blade tip extension portion 49c that is continuously formed on the outer side Dro in the radial direction Dr with respect to the second side concave portion 49b and extends along the second side Dad in the axial direction Da.

[0075] Thus, due to the effect of the centrifugal force generated by the rotating flow flowing out from the stationary blade 42, the droplets flowing toward the outer side Dro in the radial direction Dr can be prevented from staying in the second side concave portion 49b. Accordingly, the droplets are smoothly guided from the blade tip extension portion 49c to the outer shroud 43. In this way, by guiding the droplets to the outer shroud 43, the amount of droplets reaching the end portion 32a of the moving blade 32 on the first side Dau in the axial direction Da can be suppressed more effectively.

[0076] According to the steam turbine 1A as described above, the first side edge portion 48 has a first side concave portion 48a and a first side convex portion 48b and has an S shape.

[0077] Thus, compared with the case where the first side edge portion 48 of the stationary blade 42 is formed as a straight line extending along the radial direction Dr, it is possible to suppress the local increase in the blade surface length of the stationary blade 42 when connecting the first side edge portion 48 and the second side edge portion 49 along the axial direction Da. Specifically, it is possible to suppress a large difference in the flow path length from the first side concave portion 48a to the second side convex portion 49a and the flow path length from the first side convex portion 48b to the second side concave portion 49b along the axial direction Da. Thereby, it is possible to suppress a large local difference in the frictional loss generated between the surface of the droplet and the stationary blade 42 in the radial direction Dr.

[0078] Moreover, in this steam turbine 1A, at least a part of the droplets can be recovered in the hollow portion 47 inside the stationary blade 42 through the communication hole 50. Thereby, it is possible to more effectively suppress the amount of droplets reaching the end portion 32a of the moving blade 32 on the first side Dau in the axial direction Da. Thus, while suppressing a decrease in turbine performance and a decrease in the reliability of shaft vibration, it is possible to more significantly exhibit the effect of effectively suppressing erosion.

[0079] Moreover, in this steam turbine 1A, since the communication hole 50 is formed at a position closer to the outer side Dro in the radial direction Dr than the intermediate position 42m, it is possible to reduce the machining area of the communication hole 50.

[0080] Moreover, in this steam turbine 1A, since the communication hole 50 is formed at a position closer to the outer side Dro in the radial direction Dr than the intermediate position 42m, it is possible to reduce the hollow portion 47 of the stationary blade 42 in association with the position of the communication hole 50. Thus, the droplets inside the hollow portion 47 are easily discharged.

[0081] Moreover, in this steam turbine 1A, the communication hole 50 is formed only at a position closer to the second side edge portion 49 than the first side edge portion 48 on the outer surface of the ventral member 45 of the stationary blade 42. Thus, the second side edge portion 49 of the stationary blade 42 can be made into a heat insulation structure.

[0082] (Second Embodiment)

[0083] Next, a second embodiment of the steam turbine according to the present invention will be described. The difference between the steam turbine shown in this second embodiment and the steam turbine of the first embodiment is that a first groove 63 is provided in the recess 61. Thus, in the description of the second embodiment, the same reference numerals are given to the same parts as those in the first embodiment, and repeated descriptions are omitted. That is, the description of the structures of the respective parts of the steam turbine that are common to the structures already described in the first embodiment is omitted.

[0084] As Figure 7 、 Figure 8As shown, the outer ring 43B of the steam turbine 1B of the present embodiment includes a concave portion 61, a convex portion 62, a first groove 63, and a discharge portion 71.

[0085] The first groove 63 is formed within the concave portion 61. The first groove 63 is formed to be recessed from the concave portion 61 toward the outer side Dro in the radial direction Dr. The first groove 63 extends along the axial direction Da. The first groove 63 extends intersecting with the direction connecting the ventral surface 42a of the stationary blade 42 on the other side Dc2 in the circumferential direction Dc and the dorsal surface 42b of the stationary blade 42 on one side Dc1 in the circumferential direction Dc.

[0086] For example, the first groove 63 may extend along the direction of the inner circumferential surface 43f of the ring and along the ventral surface 42a of the stationary blade 42.

[0087] For example, the first groove 63 may extend in the direction in which the concave portion 61 extends.

[0088] The discharge portion 71 is formed within the first groove 63. The discharge portion 71 is a slit or a hole that opens within the first groove 63. The discharge portion 71 is connected to a condenser or the like disposed outside the steam turbine 1B. The discharge portion 71 discharges droplets or a liquid film formed by the droplets that flow into the first groove 63 from within the concave portion 61 to the external condenser or the like.

[0089] (Function and effect)

[0090] According to the steam turbine 1B as described above, similar to the first embodiment, the occurrence of erosion can be more effectively suppressed.

[0091] Moreover, in this steam turbine 1B, the droplets that flow into the concave portion 61 can be effectively recovered through the first groove 63 and discharged to the outside through the discharge portion 71.

[0092] Furthermore, according to the steam turbine 1B as described above, the first groove 63 extends along the axial direction Da. Thus, through the cross-flow Fb generated by the pressure difference between the stationary blades 42 adjacent to each other in the circumferential direction Dc, the droplets moving along the inner circumferential surface 43f of the ring toward the circumferential direction Dc can be effectively trapped in the first groove 63.

[0093] (Modification of the second embodiment)

[0094] As Figure 9 shown, the stator vane row 41 of the steam turbine 1B as described above may be composed of a plurality of stator vane row segments 41S divided along the circumferential direction Dc. Each stator vane row segment 41S integrally has a ring segment 43S that divides the outer ring 43 into a plurality of parts along the circumferential direction Dc, an inner ring segment 44S that divides the inner ring 44 into a plurality of parts along the circumferential direction Dc, and a stationary blade 42. The stator vane row segments 41S are butt-jointed and joined to each other in the circumferential direction Dc.

[0095] In this structure, the above-mentioned discharge portion 71 or the first groove 63 is formed at the joint between the annular segment bodies 43S adjacent to each other in the circumferential direction Dc. In this case, notches 43k are respectively formed on one annular segment body 43S located on one side Dc1 of the circumferential direction Dc and another annular segment body 43S located on the other side Dc2 of the circumferential direction Dc. The discharge portion 71 or the first groove 63 is formed by docking the notches 43k of the annular segment bodies 43S adjacent to each other in the circumferential direction Dc with each other.

[0096] Thus, by forming the discharge portion 71 or the first groove 63 at the joint between the annular segment bodies 43S, when the annular segment bodies 43S are connected to each other during the assembly of the stator vane row 41, the discharge portion 71 or the first groove 63 can be easily formed.

[0097] (Third Embodiment)

[0098] Next, a third embodiment of the steam turbine according to the present invention will be described. The difference between the steam turbine of this third embodiment and the steam turbine shown in the second embodiment is only that it is provided with a second groove 65 and a second discharge portion 73. Therefore, in the description of the third embodiment, the same reference numerals are given to the same parts, and the repeated description is omitted. That is, the description will be centered on the differences from the second embodiment, and the description of the structure common to the first embodiment and the second embodiment will be omitted.

[0099] As Figure 10 shown, the outer ring 43C of the steam turbine 1C of the present embodiment includes a concave portion 61, a convex portion 62, a first groove 63, a discharge portion 71, a second groove 65, and a second discharge portion 73.

[0100] The second groove 65 is formed on the first side Dau in the axial direction Da with respect to the plurality of stator vanes 42 constituting the stator vane row 41 on the inner circumferential surface 43f of the ring. The second groove 65 continuously extends along the circumferential direction Dc. The second groove 65 is formed to be recessed toward the outer side Dro in the radial direction Dr.

[0101] The second discharge portion 73 opens in the second groove 65. The second discharge portion 73 is a slit or a hole that opens in the second groove 65. The second discharge portion 73 is connected to a condenser or the like disposed outside the steam turbine 1C. The second discharge portion 73 discharges the droplets or the liquid film formed by the droplets flowing into the second groove 65 to the external condenser or the like.

[0102] (Function and Effect)

[0103] According to the steam turbine 1C as described above, similar to the first embodiment and the second embodiment, the occurrence of erosion can be more effectively suppressed.

[0104] In addition, in this steam turbine 1C, by means of the second groove 65 formed on the first side Dau in the axial direction Da with respect to the stationary blades 42 of the stationary blade row 41, droplets contained in the steam S can be trapped and discharged to the outside from the second discharge portion 73. Thereby, the amount of droplets reaching the second side Dad closer to the axial direction Da than the second groove 65 can be reduced.

[0105] (Other embodiments)

[0106] Furthermore, the present invention is not limited to the above-described embodiments, and the design can be changed without departing from the gist of the present invention.

[0107] For example, in the above-described embodiment, the second side convex portion 49a and the second side concave portion 49b of the second side edge portion 49 are respectively formed in a curved shape, but their specific shapes are not limited in any way. For example, the second side convex portion 49a and the second side concave portion 49b may be curved with a constant curvature, and the second side convex portion 49a and the second side concave portion 49b may have locally different curvatures.

[0108] Moreover, although the first side edge portion 48 and the second side edge portion 49 are provided in an S shape, it is not limited thereto. The first side edge portion 48 and the second side edge portion 49 may be linear, for example.

[0109] And, for example, as the number of stages of the moving blade row 31 and the stationary blade row 41, etc., the structure of each part of the steam turbines 1A, 1B, and 1C can be appropriately changed.

[0110] <Supplementary Note>

[0111] The steam turbines 1A, 1B, and 1C described in each embodiment can be understood as follows, for example.

[0112] (1) The steam turbines 1A, 1B, and 1C according to the first mode include: a rotor shaft 21 that rotates about an axis O; multiple rows of moving blade cascades 31 that are fixed to the outer side Dro in the radial direction Dr of the rotor shaft 21 and are arranged at intervals in the axial direction Da along the axis O; a casing 10 that is arranged to cover the rotor shaft 21 and the multiple moving blade cascades 31; and a stationary blade cascade 41 that is fixed to the inner side Dri in the radial direction Dr of the casing 10 and is arranged at intervals in the axial direction Da, and is arranged on the first side Dau in the axial direction Da with respect to each row of the multiple rows of moving blade cascades 31. The stationary blade cascade 41 includes: stationary blades 42 that are arranged at intervals in the circumferential direction Dc and each extend along the radial direction Dr; outer rings 43, 43B, 43C that are annular and are arranged on the outer side Dro in the radial direction Dr of the multiple stationary blades 42; an inner ring 44 that is annular and is arranged on the inner side Dri in the radial direction Dr of the multiple stationary blades 42; a recess 61 that is formed on the inner circumferential surface 43f of the ring facing the inner side Dri in the radial direction Dr in the outer rings 43, 43B, 43C and is recessed toward the outer side Dro in the radial direction Dr between the stationary blades 42 adjacent to each other in the circumferential direction Dc; and a discharge portion 71 that opens into the recess 61 and discharges the droplets remaining in the recess 61 to the outside.

[0113] As an example of the discharge portion 71, a slit or a hole can be cited.

[0114] In the steam turbines 1A, 1B, and 1C, between the stationary blades 42 adjacent to each other in the circumferential direction Dc, a recess 61 that is recessed toward the outer side Dro in the radial direction Dr is formed on the inner circumferential surface 43f of the outer rings 43, 43B, 43C. Thus, the droplets contained in the steam S that flow into the casing 10 from the first side Dau in the axial direction Da and adhere to the inner circumferential surface 43f of the outer rings 43, 43B, 43C are trapped in the recess 61. The trapped droplets are discharged to the outside from the discharge portion 71. As a result, the amount of droplets reaching the moving blade cascade 31 on the second side Dad in the axial direction Da can be suppressed. As a result, a reduction in erosion can be achieved.

[0115] (2) In the steam turbines 1A, 1B, and 1C according to the second mode, in the steam turbines 1A, 1B, and 1C in (1), the stationary blade 42 has: a pressure surface 42a that is formed toward one side Dc1 in the circumferential direction Dc and is curved in a concave shape; and a suction surface 42b that is formed toward the other side Dc2 in the circumferential direction Dc and is curved in a convex shape. The recess 61 is formed on the side closer to the suction surface 42b of the stationary blade 42 arranged on one side Dc1 in the circumferential direction Dc among the two stationary blades 42 adjacent to each other in the circumferential direction Dc.

[0116] In this structure, the steam S flow in the stator vane row 41 contacts the ventral surface 42a of the stator vane 42 located on the other side Dc2 of the circumferential direction Dc. Therefore, between two adjacent stator vanes 42 in the circumferential direction Dc, the pressure on the side of the stator vane 42 located on the other side Dc2 of the circumferential direction Dc and close to the ventral surface 42a becomes higher, and the pressure on the side of the stator vane 42 located on one side Dc1 of the circumferential direction Dc and close to the dorsal surface 42b becomes lower. In contrast, by forming a recess 61 on the side of the stator vane 42 located on one side Dc1 of the circumferential direction Dc and close to the dorsal surface 42b, in the portion where the recess 61 is formed, the flow path of the steam S between the inner ring 44 and the outer rings 43, 43B, 43C becomes larger in the radial direction Dr. That is, the cross-sectional area of the flow path of the steam S between the inner ring 44 and the outer rings 43, 43B, 43C increases in the portion where the recess 61 is formed. Then, in the portion where the recess 61 is formed, the flow velocity of the steam S decreases and the pressure of the steam S rises. As a result, between two adjacent stator vanes 42 in the circumferential direction Dc, the pressure on the side of the stator vane 42 located on one side Dc1 of the circumferential direction Dc and close to the dorsal surface 42b rises, and thus the pressure difference in the circumferential direction Dc between the stator vane 42 on one side Dc1 and the stator vane 42 on the other side Dc2 adjacent in the circumferential direction Dc becomes smaller. As a result, it is possible to suppress the cross-flow Fb of the steam S flowing in the circumferential direction Dc caused by the pressure difference between the adjacent stator vanes 42 in the circumferential direction Dc. Thereby, it is possible to improve the entrainment of droplets caused by the cross-flow Fb and suppress the amount of droplets reaching the rotor vane row 31 on the second side Dad in the axial direction Da. As a result, it is possible to achieve a reduction in erosion.

[0117] (3) The steam turbines 1A, 1B, 1C according to the third embodiment further include a convex portion 62 in the steam turbines 1A, 1B, 1C according to (1) or (2). The convex portion 62 is formed on the side of the stator vane 42 located on the other side Dc2 of the circumferential direction Dc and close to the ventral surface 42a with respect to the recess 61 among two adjacent stator vanes 42 in the circumferential direction Dc, and bulges toward the inner side Dri in the radial direction Dr.

[0118] According to this structure, if a convex portion 62 is formed on the side of the stationary blade 42 closer to the ventral surface 42a and disposed on the other side Dc2 of the circumferential direction Dc, then in the portion where the convex portion 62 is formed, the flow path of the steam S between the inner ring 44 and the outer rings 43, 43B, 43C becomes smaller in the radial direction Dr. That is, in the portion where the convex portion 62 is formed, the cross-sectional area of the flow path of the steam S between the inner ring 44 and the outer rings 43, 43B, 43C decreases. As a result, in the portion where the convex portion 62 is formed, the flow velocity of the steam S increases and the pressure of the steam S decreases. Thus, between two adjacent stationary blades 42 in the circumferential direction Dc, the pressure on the side of the stationary blade 42 closer to the ventral surface 42a and disposed on the other side Dc2 of the circumferential direction Dc decreases. Therefore, the pressure difference in the circumferential direction Dc between the stationary blade 42 on one side Dc1 and the stationary blade 42 on the other side Dc2 adjacent in the circumferential direction Dc becomes smaller. As a result, it is possible to further suppress the cross-flow Fb of the steam S flowing toward the circumferential direction Dc caused by the pressure difference between the adjacent stationary blades 42 in the circumferential direction Dc. Thus, it is possible to improve the entrainment of droplets caused by the cross-flow Fb and suppress the amount of droplets reaching the moving blade row 31 on the second side Dad in the axial direction Da. As a result, it is possible to achieve a reduction in erosion.

[0119] (4) In the steam turbines 1B, 1C according to the fourth aspect, in the steam turbines 1B, 1C according to any one of (1) to (3), a first groove 63 recessed toward the outer side Dro in the radial direction Dr is formed in the concave portion 61, and the discharge portion 71 opens in the first groove 63.

[0120] Thus, the droplets flowing into the concave portion 61 can be effectively recovered through the first groove 63 and discharged to the outside through the discharge portion 71.

[0121] (5) In the steam turbines 1B, 1C according to the fifth aspect, in the steam turbines 1B, 1C in (4), the first groove 63 extends along the axial direction Da.

[0122] Thus, through the cross-flow Fb generated by the pressure difference between the adjacent stationary blades 42 in the circumferential direction Dc, the droplets moving toward the circumferential direction Dc along the inner peripheral surface 43f of the ring can be effectively trapped in the first groove 63.

[0123] (6) In the steam turbine 1B according to the sixth aspect, in the steam turbine 1B in (4) or (5), the outer ring 43C is composed of a plurality of ring segments 43S divided along the circumferential direction Dc, and the first groove 63 is formed at the joint between the adjacent ring segments 43S in the circumferential direction Dc.

[0124] In this way, by forming the first groove 63 at the joint between the ring segments 43S, the first groove 63 can be easily formed when the ring segments 43S are connected to each other during the assembly of the stationary blade row 41.

[0125] (7) The steam turbine 1C according to the seventh aspect, in the steam turbine 1C according to any one of (1) to (6), further includes: a second groove 65 formed on the inner peripheral surface 43f of the ring on the first side Dau in the axial direction Da with respect to the stationary blade 42 and recessed outward in the radial direction Dr; and a second discharge portion 73 opening in the second groove 65 and discharging droplets that have entered the second groove 65 to the outside.

[0126] Accordingly, the second groove 65 formed on the first side Dau in the axial direction Da with respect to the stationary blade 42 of the stationary blade row 41 can capture droplets contained in the steam S and discharge them to the outside through the second discharge portion 73. As a result, the amount of droplets reaching the second side Dad in the axial direction Da closer to the second side Dad than the second groove 65 can be reduced.

[0127] (8) The steam turbines 1A, 1B, and 1C according to the eighth aspect, in the steam turbines 1A, 1B, and 1C according to any one of (1) to (7), in the final stationary blade row 41F disposed closest to the second side Dad in the axial direction Da among the plurality of stationary blade rows 41, the second side edge portion 49 of the stationary blade 42 has an S shape, and the S shape has: a second side convex portion 49a formed on the inner side Dri in the radial direction Dr with respect to the intermediate position 42m between the outer end 42t on the outer side Dro in the radial direction Dr and the inner end 42s on the inner side Dri in the radial direction Dr of the stationary blade 42 and bent and protruding toward the second side Dad in the axial direction Da; and a second side concave portion 49b formed on the outer side Dro in the radial direction Dr with respect to the intermediate position 42m and bent and recessed toward the first side Dau in the axial direction Da.

[0128] Accordingly, the second side concave portion 49b of the second side edge portion 49 of the stationary blade 42 is recessed toward the first side Dau in the axial direction Da. Therefore, the gap S1 in the axial direction Da between the second side concave portion 49b and the moving blade 32 of the final moving blade row 31F becomes larger. As a result, due to the effect of the centrifugal force generated by the rotating flow flowing out from the stationary blade 42, the droplets flow from the stationary blade 42 toward the second side in the axial direction Da while flowing outward in the radial direction Dr. Therefore, the amount of droplets reaching the end portion 32a on the first side Dau in the axial direction Da of the moving blade 32 can be suppressed. As a result, erosion reduction can be achieved.

[0129] Also, in the second side edge portion 49 of the stationary blade 42, the second side convex portion 49a protrudes toward the second side Dad of the axial direction Da. Therefore, the interval S2 between the second side convex portion 49a and the moving blade 32 of the final stage can be made smaller than the interval S1 of the portion of the second side concave portion 49b. Thereby, a decrease in turbine performance can be suppressed. Also, an increase in bearing span can be suppressed, and a decrease in shaft vibration reliability can be suppressed.

[0130] Industrial applicability

[0131] According to the steam turbine described above, the occurrence of erosion can be suppressed more effectively.

[0132] Symbol description

[0133] 1A, 1B, 1C - steam turbines, 10 - housing, 20 - rotor, 21 - rotor shaft, 22 - core portion, 23 - disk portion, 31 - moving blade row, 31F - moving blade row of the final stage, 32 - moving blade, 32a - end portion, 34 - shroud, 35 - platform, 41 - stationary blade row, 41F - stationary blade row of the final stage, 41S - stationary blade row segment, 42 - stationary blade, 42a - ventral surface, 42b - dorsal surface, 42m - intermediate position, 42s - inner end, 42t - outer end, 43, 43B, 43C - outer rings, 43S - ring segment, 43f - inner peripheral surface of the ring, 43k - notch, 44 - inner ring, 44S - inner ring segment, 45 - ventral member, 46 - dorsal member, 47 - hollow portion, 48 - first side edge portion, 48a - first side concave portion, 48b - first side convex portion, 49 - second side edge portion, 49a - second side convex portion, 49b - second side concave portion, 49c - blade tip extension portion, 50 - communication hole, 61 - concave portion, 62 - convex portion, 63 - first groove, 65 - second groove, 71 - discharge portion, 73 - second discharge portion, Da - axial direction, Dad - second side, Dau - first side, Dc - circumferential direction, Dc1 - one side, Dc2 - the other side, Dr - radial direction, Dri - inner side, Dro - outer side, Fb - cross-flow, L1 - imaginary line, O - axis, S - steam.

Claims

1. A steam turbine, comprising: A rotor shaft that rotates about an axis; Multiple rows of moving blade cascades, fixed to the radially outer side of the rotor shaft, and arranged at intervals along the axial direction of the axis; A casing configured to cover the rotor shaft and the multiple moving blade cascades; and A stationary blade cascade, fixed to the radially inner side of the casing, arranged at intervals along the axial direction, and arranged on the first side in the axial direction with respect to each row of the multiple rows of moving blade cascades, The stationary blade cascade includes: Stationary blades, with multiple arranged at intervals in the circumferential direction, each extending radially; An outer ring, annular and arranged on the radially outer side of the multiple stationary blades; An inner ring, annular and arranged on the radially inner side of the multiple stationary blades; A concave portion, formed on the inner circumferential surface of the ring facing the radially inner side in the outer ring, and recessed radially outward between the circumferentially adjacent stationary blades; and A discharge portion, opening into the concave portion and discharging the droplets retained in the concave portion to the outside, The stationary blade has: A ventral surface, formed on one side of the circumferential direction and curved into a concave shape; and A dorsal surface, formed on the other side of the circumferential direction and curved into a convex shape, The concave portion is formed on the side close to the dorsal surface of the stationary blade arranged on the first side in the circumferential direction among the two circumferentially adjacent stationary blades. The steam turbine further includes a convex portion, which is formed on the side close to the ventral surface of the stationary blade arranged on the other side in the circumferential direction among the two circumferentially adjacent stationary blades with respect to the concave portion, and bulges radially inward.

2. The steam turbine according to claim 1, wherein A first groove recessed radially outward is formed in the concave portion, The discharge portion opens into the first groove.

3. The steam turbine according to claim 2, wherein The first groove extends along the axial direction.

4. The steam turbine according to claim 2, wherein The outer ring is composed of multiple ring segments divided in the circumferential direction, The first groove is formed at the joint between the circumferentially adjacent ring segments.

5. The steam turbine according to any one of claims 1 to 4, further comprising: A second groove, formed on the inner circumferential surface of the ring on the first side in the axial direction with respect to the stationary blade and recessed radially outward; and A second discharge portion, opening into the second groove and discharging the droplets that enter the second groove to the outside.

6. The steam turbine according to any one of claims 1 to 4, wherein In the final row of stationary blade cascades arranged closest to the second side in the axial direction among the multiple rows of stationary blade cascades, the second side edge portion on the second side in the axial direction of the stationary blade is in an S shape, and the S shape has: A second side convex portion, formed on the radially inner side with respect to the middle position between the outer end and the inner end in the radial direction of the stationary blade and bending and protruding toward the second side in the axial direction; and A second side concave portion, formed on the radially outer side with respect to the middle position and bending and recessing toward the first side in the axial direction.

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