JP2016217285A - Steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine capable of restricting the corrosion of a moving blade while improving the diffuser performance by restricting the burble of flow in an exhaust hood.SOLUTION: In a steam turbine 10 according to an embodiment, at the last turbine stage, a diaphragm outer ring 26a includes: an expanded portion 80 whose inner diameter expands radially outward as it goes to the downstream side; and an extended portion 81 extending horizontally from a downstream end of the expanded portion 80 opposite the leading end of a moving blade 24a from the radially outer side. A stationary blade 28a includes a guide vane 90 attached between the expanded portion 80 and a diaphragm inner ring 27a and disposed between the adjacent stationary blades so as to be inclined radially outward with respect to the axial direction of a turbine rotor. In a vertical cross section along the axial direction of the turbine rotor, an extension line L2 obtained by extending a cord line L1 of the guide vane 90 passes through a contact point p between the inner peripheral side of the extended portion 81 and a steam guide 40 constituting an annular diffuser 60.SELECTED DRAWING: Figure 2

Description

  Embodiments described herein relate generally to a steam turbine including an exhaust chamber.

Improving the thermal efficiency of steam turbines used in thermal power plants and the like is an important issue that leads to effective use of energy resources and reduction of carbon dioxide (CO ₂ ) emissions. An improvement in the thermal efficiency of a steam turbine can be achieved by effectively converting the given energy into mechanical work. For that purpose, it is necessary to reduce various internal losses.

  The internal loss of a steam turbine is typified by the turbine blade row loss based on the profile loss due to the blade shape, steam secondary flow loss, steam leakage loss, steam wetting loss, etc., steam valves and crossover pipes. There are passage portion loss in passages other than the blade row, turbine exhaust loss due to the turbine exhaust chamber, and the like.

  Among these losses, the turbine exhaust loss is a large loss that accounts for 10 to 20% of the total internal loss. The turbine exhaust loss is a loss that occurs between the outlet of the turbine stage of the final stage and the condenser inlet. Turbine exhaust loss is further classified into leaving loss, hood loss, annular area limit loss, turn-up loss, and the like. Of these, the hood loss is the pressure loss from the exhaust chamber to the condenser. This hood loss depends on the type, shape and size of the exhaust chamber including the diffuser.

  In general, the pressure loss increases in proportion to the square of the steam flow velocity. Therefore, it is effective to reduce the steam flow rate by increasing the size of the exhaust chamber within an allowable range. However, when the size of the exhaust chamber is increased, there are restrictions from the manufacturing cost and the layout space of the building. Such restrictions are also imposed when the size of the exhaust chamber is increased in order to reduce the hood loss.

  The hood loss depends on the axial flow speed that is the speed in the turbine rotor axial direction, in other words, the volume flow rate passing through the exhaust chamber. Also, the hood loss depends on the design of the exhaust chamber including the diffuser. The exhaust chamber of the low-pressure turbine occupies a large capacity in the entire steam turbine. Therefore, enlarging the size of the exhaust chamber in order to reduce the hood loss greatly affects the size and manufacturing cost of the entire steam turbine. Therefore, it is important to have a shape with a small pressure loss with a limited exhaust chamber size.

  For example, in a conventional double flow type (double flow type) low pressure turbine having a lower exhaust type exhaust chamber, in order to reduce the loss (static pressure loss) in the exhaust chamber, it is composed of a steam guide and a bearing cone. It is most important to slow down the flow in the annular diffuser and restore sufficient static pressure. In conventional low-pressure turbines, it has been studied to increase the length of the bearing cone in the turbine axial direction to increase the length of the diffuser in the turbine axial direction to sufficiently recover the static pressure.

  However, in recent years, from the viewpoint of making the steam turbine more compact, it has been studied to sufficiently recover the static pressure while reducing the length of the bearing cone in the turbine axial direction. Specifically, in a compact exhaust chamber, performance is improved by optimizing the shapes of the steam guide and the bearing cone.

  Here, FIGS. 4 and 5 show the turbine blades 310 in the final stage of the double-flow exhaust type (double flow type) low-pressure turbine 300 having a conventional lower exhaust type exhaust chamber and the vertical direction of the rotor blades 310 in the vicinity thereof. It is the figure which showed a part of meridian cross section.

  As shown in FIG. 4, a steam guide 320 and a bearing cone 330 are provided on the downstream side of the moving blade 310 in the final turbine stage. An annular diffuser 340 is formed between the steam guide 320 and the bearing cone 330. The annular diffuser 340 constitutes an enlarged flow path through which the steam that has passed through the moving blade 310 of the turbine stage at the final stage is guided. Further, the annular diffuser 340 constitutes a part of the exhaust chamber. The steam guided to the annular diffuser 340 flows out radially outward.

  Here, in order to improve the performance in a compact exhaust chamber, for example, the flow 350 spreads at an optimal spread angle at the inlet of the annular diffuser 340, that is, the outlet of the moving blade 310 of the turbine stage in the final stage, and the steam guide It is important to be able to flow along the inner surface 320a of 320 and exhibit the diffuser effect. In addition, it is important that the flow 350 flowing into the annular diffuser 340 does not peel on the inner surface 320 a of the steam guide 320. For this purpose, it is a condition that the spread angle of the flow 350 outward in the radial direction with respect to the turbine rotor axial direction is a spread angle α in a predetermined range.

  In the conventional low-pressure turbine 300 shown in FIG. 4, the shroud portion 311 that is the tip of the moving blade 310 is configured horizontally. The inner surface 360a of the diaphragm outer ring 360 surrounding the rotor blade 310 from the outer periphery is also configured horizontally. A predetermined gap 365 is formed between the shroud portion 311 and the inner surface 360a. For example, the inner surface 360 a of the diaphragm outer ring 360 is provided with, for example, seal fins 370 to seal the gap 365.

  The steam guide 320 is inclined outwardly in the radial direction from the downstream end of the diaphragm outer ring 360 toward the downstream side in the turbine rotor axial direction with a predetermined enlarged inclination angle with respect to the turbine rotor axial direction.

  However, the flow of steam is rectified by passing through the moving blade 310. Therefore, on the inner surface 320a side of the steam guide 320 at the inlet of the annular diffuser 340, the spread angle of the steam flow is less than the spread angle α. As a result, the steam flow may be separated on the inner surface 320 a of the steam guide 320.

  On the other hand, in the conventional low-pressure turbine 300 shown in FIG. 5, the diaphragm outer ring 360 in the final stage turbine stage includes a step portion 361 whose inner diameter increases radially outward between the stationary blade 380 and the moving blade 310. Yes. By providing the stepped portion 361, a wall surface 361a perpendicular to the turbine rotor axial direction is formed on the upstream side of the tip end side of the rotor blade 310.

  In this case, the leaked steam 351 flowing in the gap 365 is guided radially outward on the upstream side of the moving blade 310 and flows into the gap 365. Therefore, the flow rate of the leakage steam 351 flowing through the gap 365 is reduced as compared with the conventional low-pressure turbine 300 shown in FIG.

  On the other hand, in the vicinity of the turbine stage of the final stage, the steam becomes wet steam and contains water droplets. The water droplets adhere to the inner surface 360b of the diaphragm outer ring 360 provided with the stationary blades 380 by centrifugal force to form a liquid film. The liquid film flows along the inner surface 360b, blows off at the boundary with the wall surface 361a forming the stepped portion 361, and collides with the moving blade 310.

JP 2010-216321 A

  As described above, in the conventional steam turbine, the steam flow may be separated on the outer peripheral side in the annular diffuser 340, and sufficient static pressure recovery may not be obtained. Moreover, the moving blade 310 may be eroded by the collision of the droplets, and the life of the moving blade 310 may be shortened.

  The problem to be solved by the present invention is to provide a steam turbine capable of improving the diffuser performance by suppressing the separation of the flow in the exhaust chamber and suppressing the erosion of the moving blade by the droplets.

  The steam turbine according to the embodiment includes a casing, a moving blade cascade that is provided in the casing and in which a plurality of moving blades are implanted in a circumferential direction of the turbine rotor, and a diaphragm outer ring that is provided inside the casing. And a diaphragm inner ring provided inside the diaphragm outer ring, and a plurality of stationary blades attached in a circumferential direction between the diaphragm outer ring and the diaphragm inner ring, and alternately arranged in the rotor blade cascade and the turbine rotor axial direction. A plurality of turbine stages including a stationary blade cascade arranged in the turbine, the stationary blade cascade and the moving blade cascade immediately downstream of the stationary blade cascade, and steam that has passed through the turbine stage in the final stage is discharged. With an annular diffuser.

  And, in the turbine stage of the final stage in the steam turbine, the diaphragm outer ring has a widened portion in which the inner diameter increases radially outward as it goes downstream, and a horizontal direction from the downstream end of the widened portion. An extension portion that is opposed to the tip of the moving blade from the outside in the radial direction, and the stationary blade is attached between the expansion portion of the outer ring of the diaphragm and the inner ring of the diaphragm and is adjacent thereto A guide blade provided between the stationary blades and inclined radially outward with respect to the turbine rotor axial direction is provided, and an extension line extending the chord line of the guide blade in a vertical section along the turbine rotor axial direction is provided. , Passing through a contact point on the inner peripheral side between the extended portion and the outer wall constituting the annular diffuser.

It is a figure which shows the meridional section of the perpendicular direction of the steam turbine of 1st Embodiment. It is the figure which expanded the meridional section of the perpendicular direction of the turbine stage of the last stage in the steam turbine of a 1st embodiment, and a part of annular diffuser. It is the figure which expanded the meridional section of the vertical direction of the turbine stage of the last stage in a steam turbine of a 2nd embodiment, and a part of annular diffuser. It is the figure which showed a part of vertical meridian cross section of the moving blade of the turbine stage of the last stage of the double stage exhaust type low pressure turbine provided with the conventional lower exhaust type exhaust chamber, and its vicinity. It is the figure which showed a part of vertical meridian cross section of the moving blade of the turbine stage of the last stage of the double stage exhaust type low pressure turbine provided with the conventional lower exhaust type exhaust chamber, and its vicinity.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a diagram showing a meridional section in the vertical direction of the steam turbine 10 of the first embodiment. Here, the steam turbine 10 will be described by exemplifying a double-flow exhaust type low-pressure turbine having a lower exhaust type exhaust chamber.

  As shown in FIG. 1, in the steam turbine 10, an inner casing 21 is provided in the outer casing 20. A turbine rotor 22 is provided in the inner casing 21. The turbine rotor 22 is formed with a rotor disk 23 that protrudes radially outward in the circumferential direction. The rotor disk 23 is formed in a plurality of stages in the turbine rotor axial direction.

  A plurality of rotor blades 24 are implanted in the circumferential direction on the rotor disk 23 of the turbine rotor 22 to constitute a rotor blade cascade 170. The rotor blade cascade 170 is provided in a plurality of stages in the turbine rotor axial direction. The turbine rotor 22 is rotatably supported by a rotor bearing 25.

  A diaphragm outer ring 26 and a diaphragm inner ring 27 are provided inside the inner casing 21. Between the diaphragm outer ring 26 and the diaphragm inner ring 27, a plurality of stationary blades 28 are disposed in the circumferential direction to form a stationary blade cascade 180. The stationary blade cascade 180 is arranged so as to alternate with the moving blade cascade 170 in the turbine rotor axial direction. The stationary blade cascade 180 and the moving blade cascade 170 immediately downstream of the stationary blade cascade 180 constitute one turbine stage. Further, the diaphragm outer ring 26 extends downstream and surrounds the moving blade 24 immediately downstream of the stationary blade 28.

  In the center of the steam turbine 10, an intake chamber 30 into which steam from the crossover pipe 29 is introduced is provided. Steam is distributed and introduced from the intake chamber 30 to the left and right turbine stages.

  An annular diffuser 60 is formed on the downstream side of the final stage turbine stage by an outer peripheral steam guide 40 and an inner peripheral bearing cone 50. The annular diffuser 60 discharges steam, for example, radially outward. For example, a rotor bearing 25 is provided inside the bearing cone 50.

  For example, a condenser (not shown) is provided below the lower exhaust type exhaust chamber provided with the annular diffuser 60.

  Note that the outer casing 20, the inner casing 21, the steam guide 40, the bearing cone 50, and the like described above have a vertically split structure. For example, a cylindrical steam guide 40 is constituted by the steam guides 40 on the upper half side and the lower half side. Similarly, a cylindrical bearing cone 50 is constituted by the bearing cones 50 on the upper half side and the lower half side. And the annular diffuser 60 is comprised by the cylindrical steam guide 40 and the cylindrical bearing cone 50 provided in the inner side. The configurations of the upper half side and the lower half side of the steam guide 40 and the bearing cone 50 are the same.

  Next, the configuration of the last turbine stage will be described in detail.

  FIG. 2 is an enlarged view of a vertical meridional section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 10 of the first embodiment. In FIG. 2, for convenience of explanation, “a” is added to the constituent parts of the turbine stage at the final stage in addition to the reference numerals of the constituent parts shown in FIG. 1. The configuration shown in FIG. 2 is not limited to the vertical cross section along the turbine rotor axial direction, but is the same in the vertical cross section along the turbine rotor axial direction.

  As shown in FIG. 2, the diaphragm outer ring 26 a in the last turbine stage includes an expanded portion 80 and an extending portion 81.

  The expanding portion 80 has an inner diameter that expands radially outward as it goes downstream in the turbine rotor axial direction. The inner surface 82 of the expanding portion 80 expands, for example, linearly outward in the radial direction as it goes downstream in the turbine rotor axial direction. The inner surface 82 is inclined at an enlarged inclination angle β (degrees) with respect to the turbine rotor axial direction.

  For example, on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the expansion inclination angle β is a predetermined expansion angle α (degrees) when the steam flow 185 extends radially outward with respect to the turbine rotor axial direction. Is set to be Here, the predetermined spread angle is, for example, an angle in a range where flow separation does not occur on the inner surface 41 of the steam guide 40.

  As shown in FIG. 2, the stationary blade 28a of the turbine stage at the final stage is attached between the expanded portion 80 of the diaphragm outer ring 26a and the diaphragm inner ring 27a.

  The extending portion 81 extends in the horizontal direction (the turbine rotor axial direction) from the downstream end of the expanding portion 80, and faces the tip of the rotor blade 24a from the outside in the radial direction. That is, the extending portion 81 surrounds the rotor blade 24a from the outer periphery.

  A predetermined gap is formed between the horizontal inner surface 83 of the extending portion 81 extending in the horizontal direction and the shroud 130 at the tip of the rotor blade 24a. A seal portion 110 is formed in this gap. For example, as shown in FIG. 2, the seal portion 110 is formed by providing a plurality of seal fins 111 on the inner surface 83.

  The steam guide 40 is adjacent to the downstream end surface 84 of the extending portion 81. The steam guide 40 constitutes an outer wall of the annular diffuser 60. For example, as shown in FIG. 2, the upstream end surface 42 of the steam guide 40 is in contact with the radially inner portion of the downstream end surface 84 of the extending portion 81. Specifically, in the cross section shown in FIG. 2, for example, the radially inner end of the upstream end surface 42 of the steam guide 40 and the radially inner end of the downstream end surface 84 of the extending portion 81 are in contact with each other. Yes.

  Note that a point where the radially inner ends are in contact is referred to as a contact point P. This contact point P is the innermost radial contact among the contact portions between the radially inner end of the upstream end surface 42 of the steam guide 40 and the radially inner end of the downstream end surface 84 of the extending portion 81. Part.

  The steam guide 40 is configured in an enlarged cylindrical shape that expands radially outward as it goes downstream in the turbine rotor axial direction. For example, as shown in FIG. 2, the upstream portion of the steam guide 40 linearly expands outward in the radial direction as it goes downstream in the turbine rotor axial direction. For example, as shown in FIG. 1, the downstream portion of the steam guide 40 expands while curving radially outward as it goes downstream in the turbine rotor axial direction.

  The shape of the steam guide 40 is not limited to this. For example, the steam guide 40 may be configured in a trumpet shape that expands while curving outward in the radial direction from the upstream end to the downstream end as it goes downstream in the turbine rotor axial direction.

  As shown in FIG. 2, the inner surface 41 at the inlet of the steam guide 40 is inclined radially outward with an enlarged inclination angle θ <b> 2 with respect to the turbine rotor axial direction as it goes downstream in the turbine rotor axial direction. . When the steam guide 40 expands from the upstream end to the downstream end while curving outward in the radial direction as it goes downstream in the turbine rotor axial direction, the expansion inclination angle θ2 (degrees) is shown in FIG. In the cross section shown, it is defined by the angle formed between the tangent line at the upstream end of the inner surface 41 of the steam guide 40 and the turbine rotor axial direction.

  Here, the enlarged inclination angle θ <b> 2 is set to such an angle that the steam that has passed through the last turbine stage does not peel on the inner surface 41 of the steam guide 40. The expansion inclination angle θ2 is set to an angle within a range of ± 20 degrees of the expansion inclination angle β, for example.

  The bearing cone 50 is configured in an enlarged cylindrical shape that expands radially outward while curving as it goes downstream in the axial direction of the turbine rotor. As shown in FIG. 2, the upstream end of the bearing cone 50 is adjacent to the radially outer portion of the downstream end surface of the rotor disk 23a to the extent that it does not contact the rotating rotor disk 23a. As shown in FIG. 1, the downstream end of the bearing cone 50 is in contact with the inner wall surface 141 of the side wall 140 on the downstream side in the turbine rotor axial direction of the outer casing 20.

  Here, as shown in FIG. 2, a guide vane 90 is provided between the adjacent stationary vanes 28a. For example, the guide blade 90 is inclined at an inclination angle θ1 (degrees) radially outward with respect to the turbine rotor axial direction. Specifically, the chord line L1 which is a straight line connecting the leading edge 91 and the trailing edge 92 in the guide blade 90 is inclined radially outward with respect to the turbine rotor axial direction so that the inclination angle θ1 (degrees) is inclined. Guide vanes 90 are arranged.

  For example, the inclination angle θ1 is preferably equal to or larger than the expansion inclination angle θ2. By setting the inclination angle θ1 within this range, the flow of steam can be spread on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 to have an angle α. Further, the expansion inclination angle θ2 is preferably equal to or less than the expansion angle α so that the flow does not peel from the inner surface 41 of the steam guide 40.

  The guide blade 90 has a streamlined blade shape. As the guide wing 90, for example, a wing having a shape symmetrical to the chord line L1 can be used. In addition, the shape of the guide blade 90 is not restricted to this.

  For example, the guide blade 90 is disposed such that an extension line L2 obtained by extending the chord line L1 passes through the contact point P described above. That is, the blade height position of the stationary blade 28a where the guide blade 90 is disposed is set to a position where the extension line L2 passes through the contact point P, for example.

  In this way, by arranging the guide vanes 90 so that the extension line L2 passes through the contact point P, the steam flow may spread on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 and have an angle α. it can.

  The position of the leading edge 91 of the guide blade 90 in the turbine rotor axial direction may be the same as the position of the leading edge 100 of the stationary blade 28a in the turbine rotor axial direction, for example, as shown in FIG. On the other hand, the trailing edge 92 of the guide vane 90 may protrude downstream from the trailing edge 101 of the stationary vane 28a.

  The position of the leading edge 91 of the guide vane 90 and the chord length of the guide vane 90 (the length of the chord line L1) can be arbitrarily set. For example, the chord length is adjusted so that the leading edge 91 of the guide blade 90 protrudes to the upstream side of the leading edge 100 of the stationary blade 28a, and the trailing edge 92 of the guiding blade 90 is more than the trailing edge 101 of the stationary blade 28a. You may make it protrude downstream. Further, by adjusting the chord length, the leading edge 91 of the guide blade 90 is positioned downstream of the leading edge 100 of the stationary blade 28a, and the trailing edge 92 of the guiding blade 90 is positioned more than the trailing edge 101 of the stationary blade 28a. It may be located upstream.

  In addition, when making the front edge 91 and the rear edge 92 of the guide blade 90 protrude, it makes it protrude so that a protrusion part may not contact the moving blades 24 and 24a.

  For example, the guide vane 90 may be constituted by a single blade between adjacent vanes 28a. Further, the guide vanes 90 may be divided into, for example, two parts between the adjacent stationary vanes 28a. In this case, a single blade is formed between the adjacent stationary blades 28a when the divided surfaces come into contact with each other. The guide blade 90 is joined to the stationary blade 28a by, for example, welding.

  By providing the guide vanes 90 described above, it is possible to guide the flow of steam in the inclination direction of the guide vanes 90. Thereby, even if it receives the rectifying action in the moving blade 24a, the flow of the steam can spread on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 and have an angle α.

  Further, as shown in FIG. 2, a guide vane 95 may be provided on the inner peripheral side of the guide vane 90 between the adjacent stationary vanes 28a. For example, the guide blade 95 is inclined at an inclination angle θ5 (degrees) radially outward with respect to the turbine rotor axial direction. Specifically, the guide vane 95 is such that a chord line L3, which is a straight line connecting the leading edge 96 and the trailing edge 97, of the guide vane 95 is inclined radially outward with respect to the turbine rotor axial direction by an inclination angle θ5. Is arranged.

  The inclination angle θ5 may be set to be the same as or different from the inclination angle θ1 of the guide blade 90, for example. In order to correspond to the flow direction of steam induced by the guide vanes 90, the inclination angle θ5 is preferably set in the range of the inclination angle θ1 ± 10 degrees, for example.

  The shape of the guide vanes 95 is the same as the shape of the guide vanes 90 described above. The guide wing 95 functions as a second guide wing. Here, an example in which one guide vane 95 is provided is shown, but the present invention is not limited to this configuration. For example, a plurality of guide vanes 95 may be provided on the inner peripheral side of the guide vanes 90 between the adjacent stationary vanes 28a. Note that the interval between the guide vanes 90 and the guide vanes 95 and the interval between the guide vanes 95 can be arbitrarily set.

  By providing the guide vanes 95, the effect of the above-described guide vanes 90 can be further improved. That is, the flow of steam can be guided in the inclined direction by the guide blades 95 together with the guide blades 90. Further, by providing the guide vanes 95, the steam passing through the stationary vanes 28a can be entirely guided in the tilt direction.

  Here, in the cross section shown in FIG. 2, when a part of the shroud 130 provided at the tip of the moving blade 24a is located downstream of the extension line L2, as shown in FIG. It is preferable that the end portion is composed of an inclined surface 131 that protrudes downstream as it goes to the tip.

  The inclination angle θ3 of the inclined surface 131 with respect to the turbine rotor axial direction is preferably an inclination angle θ1 ± 10 degrees in order to correspond to the flow direction of steam induced by the guide vanes 90.

  If a part of the shroud 130 is not located downstream of the extension line L2, the flow of steam guided by the guide vanes 90 is not hindered by the shroud 130, and therefore the inclined surface 131 may not be provided. . For the same reason as this, the upstream end portion of the shroud 130 located on the upstream side of the extension line L2 may not include an inclined surface.

  Here, the configuration in the present embodiment is, for example, a steam turbine that reduces the length of the bearing cone 50 in the turbine axial direction to achieve a compact size and sufficiently recovers the static pressure in the annular diffuser 60. It is suitable for.

  Specifically, the steam turbine in which the ratio (L / D) of the length L in the turbine rotor axial direction of the bearing cone 50 to the outer diameter D of the rotor blade 24a in the last turbine stage is 2/5 or less, for example. In addition, the configuration in this embodiment is preferable (see FIG. 1).

  Here, as shown in FIG. 1, the length L is the distance from the end of the bearing cone 50 on the moving blade 24 a side to the inner wall 141 of the side wall 140 where the downstream end of the bearing cone 50 contacts. The outer diameter D is equal to the diameter of a circle drawn by the tip of the rotor blade 24a when the rotor blade 24a rotates. In addition, in the moving blade 24a provided with the shroud 130, the outer diameter includes the shroud 130.

  In a steam turbine having an L / D of 2/5 or less, the exhaust chamber is sufficiently miniaturized, and costs for manufacturing and installation are reduced. Note that L / D can be set to about 1/5 in consideration of bending loss in the annular diffuser 60 and the like.

  Next, the operation of the steam turbine 10 will be described with reference to FIGS. 1 and 2.

  As shown in FIG. 1, the steam that flows into the intake chamber 30 in the steam turbine 10 through the crossover pipe 29 branches and flows to the left and right turbine stages. Then, the steam passes through the steam flow path including the stationary blade 28 and the moving blade 24 of each turbine stage, and rotates the turbine rotor 22.

  As shown in FIG. 2, in the final stage turbine stage, the steam passing through the stationary blade 28a is guided by the guide blade 90 having the inclination angle θ1, and flows into the moving blade 24a while spreading outward in the radial direction. When the guide vanes 95 are provided, the steam passing through the stationary vanes 28a is also guided by the guide vanes 95 and flows into the moving blades 24a while spreading outward in the radial direction.

  The steam that has flowed into the rotor blade 24a undergoes a rectifying action in the rotor blade 24a, but the steam flow spreads and has an angle α on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60a.

  Here, for example, as shown in FIG. 2, when the inclined surface 131 is provided at the downstream end of the shroud 130, the steam flowing on the inner peripheral side of the shroud 130 is guided to the inclined surface 131 and is radially outward. It flows while spreading.

  On the other hand, in the last turbine stage, the steam condenses into water droplets and adheres to the inner surfaces 82 and 83 of the diaphragm outer ring 26a by centrifugal force. The attached water droplet becomes a liquid film and flows downstream along the inner surfaces 82 and 83. Then, the liquid film passes through the final turbine stage and is guided to the annular diffuser 60. The liquid film passes over the seal fins 111 and is guided downstream along the inner surface 83.

  Thus, the liquid film is guided to the annular diffuser 60 along the inner surfaces 82 and 83 of the diaphragm outer ring 26a. Therefore, as in the conventional steam turbine described above (see FIG. 5), the liquid film can be prevented from being blown off into droplets and colliding with the moving blade 24a. Thereby, the erosion of the moving blade 24a by the droplet can be prevented.

  Note that leakage steam flowing between the diaphragm outer ring 26 a and the shroud 130 is suppressed by the seal portion 110.

  And the vapor | steam which flowed in in the annular diffuser 60 flows along the inner surface 41 of the steam guide 40, without peeling. Then, the flow is decelerated by the annular diffuser 60. In the annular diffuser 60, the static pressure is sufficiently recovered.

  At the outlet of the annular diffuser 60, the steam flows radially outward as shown in FIG. The steam that has flowed radially outward is diverted downward. Then, the redirected steam is guided to, for example, a condenser (not shown) installed below the turbine rotor 22.

  As described above, according to the steam turbine 10 of the first embodiment, the flow of the steam can be induced in the inclination direction of the guide blade 90 by providing the guide blade 90. Thereby, even if it receives the rectifying action in the moving blade 24a, the flow of the steam can spread on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 and have an angle α. Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the diffuser performance can be improved.

  Further, the liquid film formed by condensing the vapor flows downstream along the inner surfaces 82 and 83 of the diaphragm outer ring 26 a and is guided to the annular diffuser 60. Therefore, it is possible to prevent erosion of the rotor blades 24a caused by the liquid film blown off.

(Second Embodiment)
FIG. 3 is an enlarged view of a vertical meridional section of a turbine stage and a part of the annular diffuser 60 in the final stage in the steam turbine 11 of the second embodiment. In FIG. 3, as in FIG. 2, for convenience of explanation, “a” is added to the constituent parts of the turbine stage in the final stage in addition to the reference numerals of the constituent parts shown in FIG. 1. Moreover, in FIG. 3, the same code | symbol is attached | subjected to the component same as the steam turbine 10 of 1st Embodiment, and the overlapping description is abbreviate | omitted or simplified.

  In the second embodiment, the shape of the tip of the moving blade and the shape of the shroud in the turbine stage at the final stage are different from those in the first embodiment. Here, this different configuration will be mainly described.

  As shown in FIG. 3, the tip of the moving blade 24a in the turbine stage of the final stage and the shroud 135 provided at the tip are inclined radially outward with respect to the turbine rotor axial direction at an inclination angle θ4. The inclination angle θ4 is preferably equal to or less than the inclination angle θ1 so that the flow from the guide vanes 90 does not separate at the shroud 135. In order to suppress the separation of the flow on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the inclination angle θ4 is preferably greater than or equal to the enlarged inclination angle θ2.

  The inner surface 136 of the upstream end portion of the shroud 135 is preferably located on the inner peripheral side of the extension line L2 obtained by extending the chord line L1 of the guide vane 90. Thereby, for example, the steam that has passed through the inner peripheral side of the guide blade 90 can be guided to the blade effective portion of the moving blade 24 a on the inner peripheral side of the shroud 135.

  Further, since the shroud 135 is inclined radially outward with respect to the turbine rotor axial direction, it is not necessary to provide the inclined surface 131 as in the first embodiment at the downstream end of the shroud 130. .

  For example, as shown in FIG. 3, the seal portion 110 is formed by providing a plurality of seal fins 111 on the inner surface 83 of the extending portion 81 and the outer peripheral surface of the shroud 135 in the diaphragm outer ring 26 a.

  In the steam turbine 11 having the above-described configuration, as shown in FIG. 3, the steam passing through the stationary blade 28a of the final turbine stage is guided by the guide blade 90 having the inclination angle θ1, and moves while spreading outward in the radial direction. It flows into the wing 24a. When the guide vanes 95 are provided, the steam passing through the stationary vanes 28a is also guided by the guide vanes 95 and flows into the moving blades 24a while spreading outward in the radial direction.

  Since the shroud 135 of the moving blade 24a is inclined radially outward with respect to the turbine rotor axial direction, the steam flowing into the moving blade 24a also passes through the moving blade 24a while spreading outward in the radial direction. Further, the steam flowing into the moving blade 24a is subjected to a rectifying action in the moving blade 24a, but the flow of the steam spreads on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 and has an angle α.

  On the other hand, in the last turbine stage, the steam condenses into water droplets and adheres to the inner surfaces 82 and 83 of the diaphragm outer ring 26a by centrifugal force. The attached water droplet becomes a liquid film and flows downstream along the inner surfaces 82 and 83. Then, the liquid film passes through the final turbine stage and is guided to the annular diffuser 60. The liquid film passes over the seal fins 111 provided on the inner surface 83 and is guided downstream along the inner surface 83.

  Thus, the liquid film is guided to the annular diffuser 60 along the inner surfaces 82 and 83 of the diaphragm outer ring 26a. Therefore, as in the conventional steam turbine described above (see FIG. 5), the liquid film can be prevented from being blown off into droplets and colliding with the moving blade 24a. Thereby, the erosion of the moving blade 24a by the droplet can be prevented.

  Note that leakage steam flowing between the diaphragm outer ring 26 a and the shroud 130 is suppressed by the seal portion 110.

  And the vapor | steam which flowed in in the annular diffuser 60 flows along the inner surface 41 of the steam guide 40, without peeling. Then, the flow is decelerated by the annular diffuser 60. In the annular diffuser 60, the static pressure is sufficiently recovered.

  At the outlet of the annular diffuser 60, the steam flows radially outward as shown in FIG. The steam that has flowed radially outward is diverted downward. Then, the redirected steam is guided to, for example, a condenser (not shown) installed below the turbine rotor 22.

  As described above, according to the steam turbine 11 of the second embodiment, the flow of steam can be induced in the inclination direction of the guide blade 90 by providing the guide blade 90. Further, by inclining the shroud 135 of the moving blade 24a radially outward with respect to the turbine rotor axial direction, the steam flowing on the tip side of the moving blade 24a can be guided in the inclining direction of the shroud 135.

  By providing the guide blade 90 and the shroud 135 as described above, the flow of steam spreads and has an angle α on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60 even if it receives the rectifying action in the moving blade 24a. Can do. Therefore, separation of the steam flow along the inner surface 41 of the steam guide 40 is suppressed, and the diffuser performance can be improved.

  Further, the liquid film formed by condensing the vapor flows downstream along the inner surfaces 82 and 83 of the diaphragm outer ring 26 a and is guided to the annular diffuser 60. Therefore, it is possible to prevent erosion of the rotor blades 24a caused by the liquid film blown off.

  According to the embodiment described above, it is possible to improve the diffuser performance by suppressing the separation of the flow in the exhaust chamber, and to suppress the erosion of the moving blade by the droplets.

  In the above-described embodiment, the diaphragm outer ring 26a in the turbine stage at the final stage has a configuration including the expanding portion 80 and the extending portion 81. However, the configuration of the diaphragm outer ring 26 in the other turbine stages is as follows. The configuration is not limited to this. In the above-described embodiment, an example in which the configuration of the guide blade 90 or the like is provided in the turbine stage of the final stage is shown, but the configuration of the guide blade 90 or the like may be provided in another turbine stage.

  In the above embodiment, the double flow exhaust type low-pressure turbine provided with the lower exhaust type exhaust chamber has been described as an example. However, the configuration of the present embodiment includes, for example, an axial flow exhaust provided with an annular exhaust chamber. It can also be applied to low pressure turbines of the type.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10,11 ... Steam turbine, 20 ... Outer casing, 21 ... Inner casing, 22 ... Turbine rotor, 23, 23a ... Rotor disk, 24, 24a ... Rotor blade, 25 ... Rotor bearing, 26, 26a ... Diaphragm outer ring, 27, 27a ... Diaphragm inner ring, 28, 28a ... Stator blade, 29 ... Crossover tube, 30 ... Intake chamber, 40 ... Steam guide, 41, 82, 83, 136 ... Inner surface, 42 ... Upstream end surface, 50 ... Bearing cone, 60 ... Annular diffuser, 80 ... expanded part, 81 ... extended part, 84 ... downstream end face, 90,95 ... guide vane, 91,96,100 ... front edge, 92,97,101 ... rear edge, 110 ... seal part, DESCRIPTION OF SYMBOLS 111 ... Seal fin, 130, 135 ... Shroud, 131 ... Inclined surface, 140 ... Side wall, 141 ... Inner wall surface, 170 ... Rotor blade cascade, 180 ... Stator blade cascade

Claims (5)

A casing,
A blade cascade provided in the casing and configured by implanting a plurality of blades in the circumferential direction of the turbine rotor;
A diaphragm outer ring provided inside the casing;
A diaphragm inner ring provided inside the diaphragm outer ring;
A plurality of stationary blades are attached in a circumferential direction between the diaphragm outer ring and the diaphragm inner ring, and the stationary blade cascade arranged alternately in the rotor blade cascade and the turbine rotor axial direction;
A plurality of turbine stages constituted by the stationary blade cascade and the moving blade cascade immediately downstream of the stationary blade cascade;
An annular diffuser for discharging steam that has passed through the turbine stage in the final stage,
In the turbine stage of the final stage,
The diaphragm outer ring is
An expanded portion whose inner diameter expands radially outward as it goes downstream;
An extending portion that extends in a horizontal direction from a downstream end portion of the expanding portion, and that extends from a radially outer side to a tip of the moving blade,
The stationary blade is
Attached between the expanded portion of the diaphragm outer ring and the diaphragm inner ring,
A guide blade provided between the adjacent stationary blades and inclined radially outward with respect to the axial direction of the turbine rotor,
In a vertical section along the axial direction of the turbine rotor, an extension line obtained by extending a chord line of the guide blade passes through a contact point on an inner peripheral side between the extension portion and an outer wall constituting the annular diffuser. Steam turbine.   2. The steam turbine according to claim 1, wherein an angle θ <b> 1 of the guide blade with respect to the turbine rotor axial direction is equal to or larger than an angle θ <b> 2 with respect to the turbine rotor axial direction of the outer wall at the inlet of the annular diffuser. In a vertical section along the turbine rotor axial direction, when a part of the shroud provided at the tip of the moving blade in the turbine stage at the final stage is located downstream of the extension line,
The downstream end of the shroud has an inclined surface that protrudes downstream as it goes to the tip,
The steam turbine according to claim 1 or 2, wherein an angle θ3 of the inclined surface with respect to a turbine rotor axial direction is the angle θ1 ± 10 degrees. The tip of the moving blade and the shroud provided at the tip in the turbine stage at the final stage are inclined at an angle θ4 radially outward with respect to the turbine rotor axial direction,
The steam turbine according to claim 1 or 2, wherein the angle θ4 is equal to or less than the angle θ1.   2. A second guide vane provided on the inner peripheral side of the guide vanes between the adjacent stationary vanes and inclined radially outward with respect to the turbine rotor axial direction. The steam turbine of any one of thru | or 4.

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