JP2016135998A - Steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine capable of improving a diffuser performance and restricting peeling-off of flow at an exhaust hood.SOLUTION: A steam turbine 10 in accordance with the preferred embodiment comprises a plurality of turbine stages constituted by a row of stator blades 180 and a row of rotor blades 170 at just downstream side of the row of stator blades 180 and an annular diffuser 60 for discharging steam passed through the final turbine stage. Then, at the final turbine stage, a diaphragm outer ring 26a comprises a stage 80 of which inner diameter is expanded in a radial outward side between a stator blade 28a and a rotor blade 24a, an extended part 100 extending from an outer peripheral end of the stage 80 in a horizontal direction and opposing from the radial outside to the extremity end of the rotor blade 24a, and a protrusion 90 formed at an inner peripheral part of an end surface 81 of the stage 80 opposing from the upstream side at the extremity end of the rotor blade 24a in a peripheral direction and protruded at the downstream side.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. It is also important that the flow 350 from the inlet of the annular diffuser 340 does not delaminate on the inner surface 320a of the steam guide 320. For that purpose, it is a condition that the spread angle α of the flow 350 to the radially outer side with respect to the turbine rotor axial direction is an angle within 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, in such a conventional low-pressure turbine 300, the flow rate of the leaked steam 351 flowing through the gap 365 is large. Further, the leaked steam 351 flowing into the gap 365 flows out in the horizontal direction. Therefore, the flow of steam cannot maintain the spread angle α at the inlet of the annular diffuser 340. Further, 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.

  However, with this reduced amount, the steam flow at the inlet of the annular diffuser 340 is affected by the leaked steam 351 flowing into the gap 365 as in the conventional low-pressure turbine 300 shown in FIG. This prevents the steam flow from spreading at the inlet of the annular diffuser 340 and maintaining the angle α. Further, the steam flow may be separated on the inner surface 320 a of the steam guide 320.

  In the conventional low-pressure turbine 300 shown in FIG. 5, a slant type whose tip portion is inclined radially outward with a predetermined angle with respect to the turbine rotor axial direction as it goes downstream in the turbine rotor axial direction. Can also be used. However, when this slant type moving blade is used, the sealing performance in the gap 365 is lowered. Then, the flow along the tip of the moving blade is disturbed by the flow of the leaked steam 351 flowing out from the gap 365. Further, the steam flow may be separated on the inner surface 320 a of the steam guide 320.

JP 2010-216321 A

  As described above, in the conventional steam turbine, the flow of the leaked steam that has passed through the gap between the rotor blade and the diaphragm outer ring hinders the spread of the flow in the diffuser, or the flow of the steam on the outer peripheral side in the annular diffuser. May occur. Therefore, there is a need for a technique that can reliably reduce the pressure loss in the exhaust chamber in a steam turbine.

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

  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 plurality of stationary blades attached in the circumferential direction between the inner ring and the diaphragm inner ring, the stationary blade cascade arranged alternately in the moving blade cascade and the turbine rotor axial direction, the stationary blade cascade and the stationary blade cascade A plurality of turbine stages constituted by the moving blade cascade immediately downstream, and an annular diffuser for discharging steam that has passed through the turbine stage at the final stage.

  In the turbine stage of the final stage, the diaphragm outer ring extends in a horizontal direction from a step part having an inner diameter extending radially outward between the stationary blade and the moving blade, and an outer peripheral end of the step part. An extending portion that faces the tip of the moving blade from the outside in the radial direction, and an inner peripheral portion of the end surface of the step portion that faces the tip of the moving blade from the upstream side in the circumferential direction. And a projecting ridge portion protruding from the surface.

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 meridional section of the moving blade of the turbine stage of the last stage of the low pressure turbine of the double flow exhaust type (double flow 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 meridional section of the moving blade of the turbine stage of the last stage of the low pressure turbine of the double flow exhaust type (double flow 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.

  As shown in FIG. 2, the stationary blade 28a of the turbine stage of the final stage is attached between the diaphragm outer ring 26a and the diaphragm inner ring 27a. The inner surface 70 of the diaphragm outer ring 26a to which the outer periphery of the stationary blade 28a is attached expands radially outward, for example, linearly as it goes downstream in the turbine rotor axial direction. The inner surface 70 is inclined radially outward with an enlarged inclination angle θ1 with respect to the turbine rotor axial direction as it goes downstream in the turbine rotor axial direction (rightward in FIG. 2).

  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 θ1 is set so that the expansion angle α of the steam flow 185 radially outward with respect to the turbine rotor axial direction is a predetermined angle. Is set. Here, the predetermined angle is, for example, an angle in a range where no flow separation occurs on the inner surface 41 of the steam guide 40.

  The diaphragm outer ring 26a includes a stepped portion 80 having an inner diameter extending radially outwardly between the stationary blade 28a and the moving blade 24a. In other words, the stepped portion 80 is formed by the inner diameter of the diaphragm outer ring 26a extending radially outward on the downstream side of the stationary blade 28a and the upstream side of the moving blade 24a. Here, the radial direction is a direction perpendicular to the turbine rotor axial direction. As shown in FIG. 2, the stepped portion 80 faces the tip of the moving blade 24 a.

  Here, as shown in FIG. 2, for example, a shroud 130 is provided at the tip of the moving blade 24a. In such a moving blade 24a, when the blade length of the blade effective portion including the shroud 130 is 1, the tip portion of the moving blade 24a is about 0.01 to 0.1 from the blade tip including the shroud 130. Say. By setting it as this range, while making a vapor | steam pass appropriately to a blade effective part and obtaining work, the sealing performance between the moving blade 24a and the diaphragm outer ring | wheel 26a mentioned later can be maintained.

  An end surface 81 on the downstream side of the stepped portion 80 facing the tip of the moving blade 24a is, for example, perpendicular to the turbine rotor axial direction. On the inner peripheral portion of the end surface 81, a ridge 90 is formed that protrudes downstream in the circumferential direction. The protruding length of the protruding portion 90 toward the downstream side is set within a range not contacting the moving blade 24a when the diaphragm outer ring 26a, the turbine rotor 22 and the like are thermally expanded, for example.

  For example, as shown in FIG. 2, the shape of the protrusion 90 is a triangle in a vertical section along the axial direction of the turbine rotor, specifically, a meridional section in the vertical direction. The radially inner side surface 91 of the ridge 90 is indicated by a straight line that is continuous with the straight line along the inner surface 70. That is, the inner surface 91 exists on a straight extension line along the inner surface 70. The radially outer side surface 92 of the ridge 90 is inclined, for example, toward the downstream side at a predetermined angle θ2 (degrees) radially inward with respect to the turbine rotor axial direction.

  In addition, the shape of the protrusion part 90 is not restricted to this. The shape of the protrusion 90 may be, for example, a substantially trapezoid whose width in the radial direction becomes narrower toward the downstream in a vertical cross section along the turbine rotor axial direction. In other words, in the triangular protrusion 90 shown in FIG. 2, the downstream apex may be cut off to form a side.

  Thus, the shape of the protrusion 90 is not limited to the shape shown in FIG. 2, and may be any shape that protrudes downstream.

  The diaphragm outer ring 26a includes an extending portion 100 that extends in the horizontal direction at the outer peripheral end of the stepped portion 80 and faces the tip of the moving blade 24a from the outside in the radial direction. A predetermined gap is formed between the horizontal inner surface 101 of the extending portion 100 extending in the horizontal direction and the tip of the moving 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 horizontal inner surface 101.

  Here, the recess 120 is formed in the space surrounded by the horizontal inner surface 101, the end surface 81, and the outer surface 92 described above. By providing the recess 120, when a part of the steam flowing along the inner surface 70 of the diaphragm outer ring 26a flows as the leaked steam 190, the flow direction is largely changed. Therefore, the flow rate of the leaked steam 190 flowing into the recess 120 can be reduced.

  Here, the shroud 130 at the tip of the moving blade 24a may have, for example, an inclined surface 131 that protrudes upstream as the end on the upstream side goes to the tip. FIG. 2 shows an example in which an inclined surface is also provided at the downstream end of the shroud 130. In this case, the angle of the downstream inclined surface with respect to the turbine rotor axial direction is configured to be equal to the angle of the upstream inclined surface 131 with respect to the turbine rotor axial direction, for example.

  The inclined surface 131 on the upstream side of the shroud 130 faces the outer surface 92 of the ridge 90. As shown in FIG. 2, when the angle of the inclined surface 131 with respect to the turbine rotor axial direction is θ3 (degrees), the angle θ3 and the angle θ2 of the outer surface 92 with respect to the turbine rotor axial direction described above are, for example, It is preferable that the relationship of the following formula (1) is satisfied.

                    Angle θ2 = Angle θ3 ± 10 degrees Formula (1)

  By setting the angle θ2 in this range, it is possible to reduce the loss as much as possible and guide the leaked steam 190 to the recess. It is more preferable to make the angle θ2 equal to the angle θ3.

  Although an example in which the inclined surface 131 is provided in the shroud 130 at the tip of the rotor blade 24a is shown here, a configuration without the inclined surface 131 may be used. That is, the upstream and downstream ends of the shroud 130 may have a certain length in the distal direction. In this case, the relationship of the above formula (1) is not established.

  The steam guide 40 is adjacent to the downstream end of the diaphragm outer ring 26 a, that is, the downstream end surface 102 of the extending portion 100. As shown in FIG. 2, the upstream end of the steam guide 40 is in contact with the radially inner portion of the downstream end surface 102 of the extending portion 100. 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> 4 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 radially outward as it goes downstream in the turbine rotor axial direction, the expansion inclination angle θ4 (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 θ4 is set to such an angle that the steam that has passed through the turbine stage at the final stage does not peel on the inner surface 41 of the steam guide 40. The enlarged inclination angle θ4 is set to an angle within a range of ± 20 degrees of the enlarged inclination angle θ1, 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, in the vertical cross section along the axial direction of the turbine rotor shown in FIG. 2, the inner surface of the steam guide 40 that forms the inlet of the annular diffuser 60 on a line that extends downstream along the inner surface 70 of the diaphragm outer ring 26 a. 41 may be located. In this case, the enlarged inclination angle θ4 of the inner surface 41 at the entrance of the steam guide 40 is equal to the enlarged inclination angle θ1 of the inner surface 70 of the diaphragm outer ring 26a. In this way, the inner surface 41 of the steam guide 40 is positioned on a line that extends the line along the inner surface 70 to the downstream side, so that the steam flow is smoothly guided to the steam guide 40 and the flow from the inner surface 41 is separated. Can be suppressed.

  The enlarged inclination angle θ1 is, for example, on the inner surface 41 of the steam guide 40 when the flow of steam that has passed through the moving blade 24a, that is, the flow of steam at the inlet of the annular diffuser 60 is not affected by the leakage flow. The angle is set so as not to peel off.

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

  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.

  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 flowing along the inner surface 70 of the diaphragm outer ring 26 a flows with an enlarged inclination angle θ <b> 1 of the inner surface 70. Further, on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the spread angle α of the steam flow 185 outward in the radial direction with respect to the turbine rotor axial direction is maintained at a predetermined angle. Further, the projecting ridge 90 extending downstream helps the flow spreading angle α to be maintained at a predetermined angle at the inlet of the annular diffuser 60.

  Here, for example, as shown in FIG. 2, when the downstream end of the shroud 130 is also provided with an inclined surface, the inclined surface has a flow spreading angle α at a predetermined angle at the inlet of the annular diffuser 60. Further help to be maintained.

  On the other hand, a part of the steam flowing along the inner surface 70 of the diaphragm outer ring 26a changes the flow direction from the space between the outer surface 92 of the protrusion 90 and the inclined surface 131 on the upstream side of the shroud 130 to the concave portion 120. Flow into. Then, the leaked steam 190 that has flowed into the recess 120 passes through the seal portion 110 and is jetted to the inlet of the annular diffuser 60 from between the horizontal inner surface 101 and the tip of the moving blade 24a.

  Here, when the leaking steam flows into the recess 120, the flow direction of the leaking steam 190 is greatly changed, and a large pressure loss occurs. Therefore, the flow rate of the leaking steam 190 flowing into the recess 120 is small, and the flow rate and the jetting speed of the leaking steam 190 ejected from the seal portion 110 to the inlet of the annular diffuser 60 are small. As a result, at the inlet of the annular diffuser 60, the flow of the steam spreads at a predetermined spread angle without hindering the spread. Further, it is possible to suppress the steam flow along the inner surface 41 of the steam guide 40 from being disturbed by the ejection of the leaked steam 190 from the seal portion 110.

  As a result, an appropriate flow along the inner surface of the annular diffuser 60 is formed at the inlet of the annular diffuser 60, and separation of the vapor flow along the inner surface 41 of the steam guide 40 is suppressed.

  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 rate of the leaked steam 190 flowing into the seal portion 110 can be reduced by providing the ridge portion 90 on the diaphragm outer ring 26a. Further, the flow rate and the ejection speed of the leaked steam 190 ejected from the seal portion 110 to the inlet of the annular diffuser 60 can be reduced. Therefore, at the inlet of the annular diffuser 60, the flow can be widened to a predetermined spread angle, and the separation of the vapor flow along the inner surface 41 of the steam guide 40 is suppressed. Thus, the diffuser performance can be improved and the flow separation in the exhaust chamber can be suppressed.

(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.

  The second embodiment is different from the first embodiment in that the shape of the protrusion and the flow path for collecting the drain are provided. Here, this different configuration will be mainly described.

  As shown in FIG. 3, in the steam turbine 11, the diaphragm outer ring 26 a includes a stepped portion 80 having an inner diameter extending radially outward between the stationary blade 28 a and the moving blade 24 a. As shown in FIG. 3, the stepped portion 80 faces the tip of the moving blade 24 a.

  On the inner peripheral portion of the end surface 81 on the downstream side of the stepped portion 80 that faces the tip portion of the moving blade 24a, a ridge portion 150 that protrudes downstream is formed in the circumferential direction. The protruding length of the ridge 150 to the downstream side is set, for example, in a range that does not contact the moving blade 24a when the diaphragm outer ring 26a, the turbine rotor 22 and the like are thermally expanded.

  As shown in FIG. 3, the shape of the protrusion 150 is, for example, substantially fan-shaped in a vertical cross section along the turbine rotor axial direction, specifically, a meridional cross section in the vertical direction. The radially inner side surface 151 of the ridge 150 is indicated by a straight line continuous with the straight line along the inner surface 70 of the diaphragm outer ring 26a and a curve continuous with the continuous straight line. The curved portion forms a curved surface that is convex inward in the radial direction.

  Further, the radially outer side surface 152 of the ridge 150 is, for example, horizontal (parallel to the turbine rotor axial direction). In addition, the shape of the protrusion part 150 is not restricted to this. For example, the outer surface 152 of the ridge 150 may be inclined radially inward toward the downstream side.

  Similar to the first embodiment, a recess 121 is formed in a space surrounded by the horizontal inner surface 101, the end surface 81 and the outer surface 152. The diaphragm outer ring 26 a is formed with a flow path 160 that communicates with the recess 121 through the opening 161.

  The flow path 160 is a flow path for collecting the drain that has flowed into the recess 121. For example, the flow path 160 communicates with a condenser (not shown) that is in a lower pressure state than the pressure in the recess 121 via, for example, a pipe (not shown). As described above, the flow path 160 for sucking the drain from the recess 121 and the passage made of the piping (not shown) are provided.

  By providing the recess 121, when a part of the steam flowing along the inner surface 70 of the diaphragm outer ring 26a flows as the leaked steam 190, the flow direction is largely changed. Therefore, the flow rate of the leaked steam 190 flowing into the recess 121 can be reduced. Further, by forming a part of the ridge 150 with a curved surface, a liquid film flowing along the inner surface 151 of the ridge 150 or a water droplet in the vapor is guided along the curved surface by centrifugal force to the recess 121. Can do. Note that the liquid film and water droplets are vapors condensed due to a decrease in temperature.

  Next, the operation of the steam turbine 11 will be described with reference to FIG.

  As described above, the steam flows through each turbine stage to the final turbine stage. In the turbine stage of the final stage, the steam that flows along the inner surface 70 of the diaphragm outer ring 26 a flows with the enlarged inclination angle θ <b> 1 of the inner surface 70. Further, on the inner surface 41 side of the steam guide 40 at the inlet of the annular diffuser 60, the spread angle α of the steam flow 185 outward in the radial direction with respect to the turbine rotor axial direction is maintained at a predetermined angle. In addition, a part of the ridge 150 extending on the downstream side helps to maintain the flow spread angle α at a predetermined angle at the inlet of the annular diffuser 60.

  On the other hand, a part of the steam flowing along the inner surface 70 of the diaphragm outer ring 26a changes the flow direction from between the outer surface 152 of the protrusion 150 and the inclined surface 131 on the upstream side of the shroud 130 to the concave portion 121. Flow into. Then, the leaked steam 190 that has flowed into the recess 121 passes through the seal portion 110 and is jetted to the inlet of the annular diffuser 60 from between the horizontal inner surface 101 and the tip of the rotor blade 24a.

  Here, when the leaking steam 190 flows into the recess 121, the flow direction of the leaking steam 190 is greatly changed, and a large pressure loss is generated. Therefore, the flow rate of the leaking steam 190 flowing into the recess 121 is small, and the flow rate and the jetting speed of the leaking steam 190 jetted from the seal portion 110 to the inlet of the annular diffuser 60 are small. As a result, at the inlet of the annular diffuser 60, the flow of the steam spreads at a predetermined spread angle without hindering the spread. Further, it is possible to suppress the steam flow along the inner surface 41 of the steam guide 40 from being disturbed by the ejection of the leaked steam 190 from the seal portion 110.

  As a result, an appropriate flow along the inner surface of the annular diffuser 60 is formed at the inlet of the annular diffuser 60, and separation of the vapor flow along the inner surface 41 of the steam guide 40 is suppressed.

  In addition, a liquid film flowing along the inner surface 151 of the ridge 150 or a water droplet in the vapor is guided to the recess 121 along the curved surface of the ridge 150 by centrifugal force. Then, the drain accumulated in the radial direction inside the concave portion 121 due to the centrifugal force is sucked from the opening 161, passes through the flow path 160 and the piping (not shown), and is guided to, for example, a condenser (not shown). Note that when the drain is sucked, a part of the leaked steam 190 is also sucked, but a very small amount.

  The steam that has flowed into the annular diffuser 60 flows along the inner surface 41 of the steam guide 40 without being separated. Then, the flow is decelerated by the annular diffuser 60. In the annular diffuser 60, the static pressure is sufficiently recovered.

  Note that the flow of the steam after passing through the annular diffuser 60 is as described in the first embodiment.

  As described above, according to the steam turbine 11 of the second embodiment, the flow rate of the leaked steam 190 flowing into the seal portion 110 can be reduced by providing the ridge portion 150 on the diaphragm outer ring 26a. Further, the flow rate and the ejection speed of the leaked steam 190 ejected from the seal portion 110 to the inlet of the annular diffuser 60 can be reduced. Therefore, at the inlet of the annular diffuser 60, the flow can be widened to a predetermined spread angle, and the separation of the vapor flow along the inner surface 41 of the steam guide 40 is suppressed. Thus, the diffuser performance can be improved and the flow separation in the exhaust chamber can be suppressed.

  Furthermore, by providing the flow path 160 for collecting the drain that has flowed into the recess 121, the drain can be collected between the stationary blade 28a and the moving blade 24a at the final stage. As a result, it is possible to prevent the rotor blades 24a from being eroded by water drops or blown liquid films. In addition, by forming a part of the ridge 150 with a curved surface, a liquid film flowing along the inner surface 151 of the ridge 150 or water droplets in the vapor can be easily guided to the recess 121.

  In addition, the structure of the channel | path which collect | recovers drains in 2nd Embodiment is applicable also to 2nd Embodiment. Even in this case, it is possible to suppress the rotor blades 24a from being eroded by water droplets or blown liquid films.

  According to the embodiment described above, it is possible to improve the diffuser performance and suppress the separation of the flow in the exhaust chamber.

  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, 70 ... Inner surface, 50 ... Bearing cone, 60 ... Annular diffuser, 80 ... Stepped part, 81 ... end face, 90 ... ridge, 91, 151 ... inner face, 92, 152 ... outer face, 100 ... extension part, 101 ... horizontal inner face, 102 ... downstream end face, 110 ... seal part, 111 ... seal fin, 120 , 121 ... recess, 130 ... shroud, 131 ... inclined surface, 140 ... side wall, 141 ... inner wall surface, 150 ... ridge, 160 ... flow path, 16 ... opening, 170 ... moving blade cascade, 180 ... stationary blade rows, 190 ... steam leakage.

Claims (6)

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 plurality of stationary blades are attached in a circumferential direction between a diaphragm outer ring and a diaphragm inner ring provided inside the casing, and the stationary blade cascade arranged alternately in the moving 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
A step portion having an inner diameter extending radially outward between the stationary blade and the moving blade;
An extending portion that extends in the horizontal direction from the outer peripheral end of the stepped portion, and that faces the tip of the moving blade from the outside in the radial direction;
A steam turbine, comprising: a protrusion formed on the inner peripheral portion of the end surface of the step portion facing the tip portion of the moving blade from the upstream side in a circumferential direction and protruding downstream. A shroud provided at a tip of the rotor blade in the turbine stage of the final stage, and an upstream end portion having an inclined surface protruding upstream as it goes to the tip;
The inclined surface and the outer surface on the radially outer side of the protruding portion are opposed to each other,
The steam turbine according to claim 1, wherein an angle formed by the outer surface with respect to the turbine rotor axial direction is set within a range of ± 10 degrees of an angle formed by the inclined surface with respect to the turbine rotor axial direction. In the vertical section along the turbine rotor axial direction,
3. The steam turbine according to claim 1, wherein an inner side surface on an inner side in the radial direction of the protruding portion is on a straight extension line along an inner surface of the diaphragm outer ring in a portion supporting the stationary blade. 4. In the vertical section along the turbine rotor axial direction,
A radially inner inner surface of the projecting portion is indicated by a straight line continuous with a straight line along an inner surface of the diaphragm outer ring of a portion supporting the stationary blade, and a curve continuous with the continuous straight line. The steam turbine according to claim 1 or 2. In the vertical section along the turbine rotor axial direction,
The inner surface of the outer wall that forms the inlet of the annular diffuser is on a line extending downstream from the inner surface of the diaphragm outer ring of the portion of the turbine stage that supports the stationary blade of the final stage. The steam turbine according to any one of claims 1 to 4.   6. The apparatus according to claim 1, further comprising a passage that communicates with the recessed portion surrounded by the extended portion, the end surface of the stepped portion, and the inner surface of the protruding portion, and that collects drainage from the recessed portion. The steam turbine according to item.

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