JP2018040282A - Axial flow turbine and diaphragm outer ring thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an axial flow turbine and its diaphragm outer ring capable of improving the reduction effect of the mixture loss.SOLUTION: An axial flow turbine comprises: a moving blade shroud 6 attached on the outer peripheral side of a moving blade 5; multiple steps of seal fins 14A to 14E that are provided on an inner peripheral surface of a diaphragm outer ring 1 opposite the outer peripheral surface of the moving blade shroud 6 and that protrude in a turbine radial direction; an inlet opening 16 and an outlet opening 17 formed in a pair on one side of the diaphragm outer ring 1 opposite the downstream side end surface of the moving blade shroud 6; and a bypass flow passage 18 formed in the interior of the diaphragm outer ring 1 so as to communicate the inlet opening 16 with the outlet opening 17 for flowing out the fluid flowing from the inlet opening 16 in a turbine axial direction from the outlet opening 17. The inlet opening 16 opens on the downstream side of the outer peripheral surface of the moving blade shroud 6 in the turbine axial direction; and the outlet opening 17 is located radially inward from the turbine from the inlet opening 16.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an axial turbine used for a steam turbine, a gas turbine, or the like of a power plant, and a diaphragm outer ring thereof.

  From the viewpoint of resource saving and environmental load reduction, improvement in power generation efficiency of power plants is required. Axial turbines are suitable for medium- and large-capacity power plants, and are widely used in steam turbines and gas turbines. Therefore, improvement in turbine performance can greatly contribute to improvement in power generation efficiency.

  Factors that govern turbine performance include paragraph loss, exhaust loss, and mechanical loss. Since the turbine has a plurality of paragraphs in which the stationary blade row and the moving blade row are combined, it is considered that the reduction of the paragraph loss is most effective for improving the performance. The breakdown of the paragraph loss is as follows: (1) Airfoil loss due to the blade shape itself, (2) Secondary flow loss due to the flow crossing between the blades, and (3) Working fluid (steam, gas, etc.) is the main flow path There is leakage loss caused by leaking outside.

  Leakage loss is (a) bypass loss caused when part of the working fluid (leakage fluid) flows out from the main flow path to the leak flow path, and the energy of the leaking fluid is not effectively used. (B) This is composed of mixing loss that occurs when reflowing from the leakage flow path into the main flow path, (c) interference loss that occurs when leakage fluid reflowing into the main flow path interferes with the downstream blade row, and the like. In order to reduce this leakage loss, it is important to reduce the flow rate of the leakage fluid and the mixing loss.

  In the prior art described in Patent Document 1, a plurality of stages of seal fins protruding in the turbine radial direction are provided on the inner peripheral surface of the groove portion of the diaphragm outer ring facing the outer peripheral surface of the rotor blade shroud. In addition, a protrusion projecting in the turbine axial direction is provided on the downstream side surface of the groove portion of the diaphragm outer ring facing the downstream end surface of the blade shroud. As a result, the flow rate of the leakage fluid is reduced in the leakage flow path formed between the rotor blade shroud and the groove portion of the diaphragm outer ring.

  In addition, a circulation flow generation chamber is formed on the outer peripheral side of the above-described protrusion, and a plurality of shielding plates extending in the turbine axial direction and the turbine radial direction are provided in the circulation flow generation chamber. Although the leakage fluid that has flowed into the leakage flow path from the main flow path (downstream side of the stationary blade row) has a large circumferential velocity component, a part of it flows into the circulation flow generation chamber and collides with the shielding plate, Generates a circulating flow with reduced circumferential velocity component. Then, due to the interference of the circulating flow, the circumferential velocity component is effectively reduced with respect to the flow of the leaked fluid flowing out from the leak channel to the main channel (downstream side of the rotor blade row). Accordingly, the mixing loss is reduced by matching the flow direction of the leakage fluid with the flow direction of the working fluid in the main flow path.

JP 2011-106474 A

  However, in the conventional technique described in Patent Document 1, when the interval in the turbine axial direction from the blade shroud to the circulating flow generation chamber is large, the ratio of the leaked fluid flowing into the circulating flow generation chamber is small. The effect of reducing the circumferential velocity component of the fluid is reduced. Further, since the circulation flow generated in the circulation flow generation chamber is weakened, the circumferential velocity component cannot be sufficiently reduced with respect to the leaked fluid that has not flowed into the circulation flow generation chamber.

  An object of the present invention is to provide an axial turbine and a diaphragm outer ring that can enhance the effect of reducing mixing loss.

  In order to achieve the above object, an axial turbine according to the present invention includes a plurality of stator blades attached in the circumferential direction to the inner peripheral side of the diaphragm outer ring, and a plurality of stator blades attached in the circumferential direction to the outer peripheral side of the rotor. A moving blade disposed on the downstream side, a moving blade shroud attached to the outer peripheral side of the moving blade, and an inner peripheral surface of the diaphragm outer ring facing the outer peripheral surface of the moving blade shroud, A plurality of protruding seal fins, an inlet opening and an outlet opening formed in pairs on one surface of the diaphragm outer ring facing the downstream end face of the blade shroud, and the inlet opening and the outlet inside the diaphragm outer ring A bypass passage that is formed so as to communicate with the opening and flows out of the fluid flowing in from the inlet opening in the turbine axial direction from the outlet opening. Open to the outer peripheral surface turbine axial direction downstream side of the downstream end of the Udo, the outlet opening is from the inlet opening to the inside of the turbine radial direction.

  In the present invention, the leakage fluid that has passed through the gap between the tip of the final-stage seal fin and the outer peripheral surface of the blade shroud has a large circumferential velocity component, but a part of the leakage fluid flows into the bypass channel and flows out. Thus, a turbine axial flow is generated. In other words, the circumferential velocity component of the leaked fluid that has flowed into the bypass channel is reduced. At this time, even if the interval in the turbine axial direction from the blade shroud to the bypass passage is large, the ratio of the leaking fluid flowing into the bypass passage is large, so the effect of reducing the circumferential velocity component of the leaking fluid is large. Become. Further, since the turbine axial flow generated in the bypass flow path is strengthened, the circumferential velocity component is sufficiently reduced with respect to the leaked fluid that has not flowed into the bypass flow path due to the interference of the turbine axial flow. be able to. Therefore, the effect of reducing the mixing loss can be enhanced by matching the flow direction of the leakage fluid with the flow direction of the working fluid in the main flow path.

It is sectional drawing of the turbine axial direction which represents typically the partial structure of the steam turbine in one Embodiment of this invention. FIG. 2 is a partial enlarged cross-sectional view of a portion II in FIG. 1 and shows a structure of a leakage channel and a bypass channel. FIG. 3 is an arrow view taken along section III-III in FIG. 2 and represents a structure of a bypass channel. It is a partial expanded sectional view showing the structure of the leak flow path and the bypass flow path in the 1st modification of this invention. It is a partial expanded sectional view showing the structure of the leak flow path and the bypass flow path in the 2nd modification of this invention.

  Hereinafter, an embodiment when the present invention is applied to a steam turbine will be described with reference to the drawings.

  FIG. 1 is a cross-sectional view in the turbine axial direction schematically showing a partial structure of a steam turbine in the present embodiment. FIG. 2 is a partial enlarged cross-sectional view taken along the line II in FIG. 1 and shows the structure of the leakage flow path and the bypass flow path. 3 is an arrow view taken along section III-III in FIG. 2 and represents the structure of the bypass channel.

  As shown in FIGS. 1 to 3, the steam turbine has a plurality of diaphragm outer rings 1 (stationary bodies) attached to the inner peripheral side of a casing (not shown) and an inner peripheral side of the plurality of diaphragm outer rings 1, respectively. A plurality of rows of stationary blades 2 attached to each other and a plurality of diaphragm inner rings 3 attached to the inner peripheral side of the plurality of rows of stationary blades 2 are provided. Each row of the stationary blades 2 includes a plurality of stationary blades 2 arranged at a predetermined interval in the circumferential direction between the diaphragm outer ring 1 and the diaphragm inner ring 3.

  In addition, the steam turbine includes a rotor 4 (rotary body) that rotates about the rotation axis O, a plurality of rows of moving blades 5 attached to the outer periphery of the rotor 4, and an outer periphery of the plurality of rows of moving blades 5 ( In other words, it includes a plurality of blade shrouds 6 attached to the tip side). The moving blades 5 in each row are composed of a plurality of moving blades 5 arranged at predetermined intervals in the circumferential direction between the rotor 4 and the moving blade shroud 6.

  The main flow path 7 for steam (working fluid) is a flow path formed between the inner peripheral surface 8 of the diaphragm outer ring 1 and the outer peripheral surface 9 of the diaphragm inner ring 3, or the inner peripheral surface 10 of the rotor blade shroud 6 and the rotor 4. It is comprised by the flow path etc. which were formed between the outer peripheral surfaces 11 of this. A plurality of rows of stationary blades 2 are disposed in the main flow path 7, and a plurality of rows of moving blades 5 are disposed on the downstream side of the plurality of rows of stationary blades 2. That is, the combination of one row of stationary blades 2 and one row of moving blades 5 constitutes one paragraph and has a plurality of paragraphs. In FIG. 1, only two paragraphs are shown for convenience, but two or more paragraphs are provided.

  The steam (mainstream steam) in the main flow path 7 is flowing as indicated by white arrows in FIG. Then, the internal energy (in other words, pressure energy) of the steam is converted into kinetic energy (in other words, velocity energy) by the stationary blades 2 in each row, and the kinetic energy of the steam is converted into the rotor by the moving blades 5 in each row. Is converted into a rotational energy of 4. In addition, a generator (not shown) is connected to the end of the rotor 4, and the rotational energy of the rotor 4 is converted into electric energy by this generator.

  The flow of steam (main flow) in the main flow path 7 will be described in detail. The steam flowing between the vanes of the stationary vane 2 has almost no circumferential velocity component. Then, when passing between the blades of the stationary blade 2, the velocity is increased and turned to become a flow having a large circumferential velocity component. Most of the steam flowing out between the blades of the stationary blade 2 collides with the moving blade 5 to rotate the rotor 4. At this time, the steam is decelerated and turned into a turbine axial flow having almost no circumferential velocity component.

  By the way, a groove (notch) 12 is formed in each diaphragm outer ring 1, and a leakage flow path 13 is formed between the groove 12 and the blade shroud 6. Then, a part of the steam (leakage steam) flows into the leakage passage 13 from the downstream side of the stationary blade 2 of the main passage 7 (in other words, the upstream side of the moving blade 5), and the leakage steam passes through the leakage passage 13. Then, it flows out downstream of the rotor blade 5 in the main flow path 7 (leakage flow). Therefore, the internal energy of the leaked steam is not effectively used, and a bypass loss occurs. In order to reduce this bypass loss, that is, in order to reduce the flow rate of the leaked steam from the main flow path 7 to the leak flow path 13, the leak flow path 13 is provided with a labyrinth seal.

  In the labyrinth seal of this embodiment, a plurality of stages of seal fins 14A to 14E projecting in the turbine radial direction are provided on the inner peripheral surface of the groove portion 12 of each diaphragm outer ring 1 facing the outer peripheral surface of each blade shroud 6. Yes. The tip portions of the seal fins 14A to 14E have a wedge shape with a sharp cross section. Step portions (protrusions) 15A and 15B are formed on the outer peripheral surface of the moving blade shroud 6 so as to face the second-stage seal fin 14B and the fourth-stage seal fin 14D, respectively. The gap dimension between the tip of each seal fin and the outer peripheral surface of the moving blade shroud 6 facing the seal fin is set so that the flow rate of the leaked steam is minimized while preventing contact between the stationary body side and the rotating body side.

  The mainstream steam on the downstream side of the stationary blade 2 of the main flow path 7 has a large circumferential speed component as described above, and the leaked steam flowing into the leak flow path 13 also has a large circumferential speed component. It has become a flow. The leaked steam that has flowed into the leakage flow path 13 is a gap (throttle) between the tip of the first-stage seal fin 14A and the outer peripheral surface of the blade shroud 6, and the tip of the second-stage seal fin 14B and the blade shroud. 6, the gap (throttle) between the outer peripheral surface of the sixth stage, the gap (throttle) between the tip of the third stage seal fin 14 </ b> C and the outer peripheral surface of the blade shroud 6, the tip of the fourth stage seal fin 14 </ b> D and the blade shroud 6. The gap (throttle) between the outer peripheral surface and the gap (throttle) between the tip of the fifth-stage seal fin 14E and the outer peripheral surface of the rotor blade shroud 6 are sequentially passed. At this time, the total pressure of the leaked steam is reduced due to the throttle loss. Further, although the axial velocity of the leaking steam increases, the circumferential velocity does not vary substantially. That is, the leaked steam that has passed through the gap between the tip of the final-stage seal fin 14E and the outer peripheral surface of the blade shroud 6 still has a flow having a large circumferential velocity component.

  On the other hand, the mainstream steam that has passed through the moving blade 5 in the main flow path 7 is a flow that has almost no circumferential velocity component as described above. Therefore, temporarily, the leaked steam that has passed through the gap between the tip of the final-stage seal fin 14E and the outer peripheral surface of the moving blade shroud 6 remains downstream of the moving blade 5 in the main flow path 7 while maintaining a flow having a large circumferential velocity component. When it flows out to the side, the mixing loss increases.

  Therefore, as a feature of the present embodiment, a pair of inlet openings 16 and outlet openings 17 are formed on the upstream end face of each diaphragm outer ring 1 facing the downstream end face of each blade shroud 6. Further, a bypass channel 18 that communicates the inlet opening 16 and the outlet opening 17 is formed inside each diaphragm outer ring 1. In particular, in the present embodiment, a plurality of combinations of the inlet opening 16, the outlet opening 17, and the bypass flow path 18 are formed for each diaphragm outer ring 1, and a predetermined interval in the circumferential direction (specifically, for example, the moving blade 5 Are arranged at substantially the same interval in the circumferential direction (angle conversion).

  The inlet opening 16 has the same position in the turbine radial direction as the outer peripheral surface of the moving blade shroud 6 (in other words, the outer peripheral surface of the downstream end portion of the moving blade shroud 6) facing the final-stage seal fin 14E. This makes it easy for leaked steam that has passed through the gap between the tip of the last-stage seal fin 14 </ b> E and the outer peripheral surface of the rotor blade shroud 6 to flow into the inlet opening 16. 2 shows an example in which the center of the inlet opening 16 is located at the same position in the turbine radial direction as the outer peripheral surface of the downstream end of the rotor blade shroud 6, but the present invention is not limited to this. A portion other than the center of the opening 16 may have the same position in the turbine radial direction as the outer peripheral surface of the downstream end portion of the blade shroud 6. That is, the inlet opening 16 only needs to open to the downstream side in the turbine axial direction of the downstream end portion of the outer peripheral surface of the rotor blade shroud 6, and in the turbine radial direction of the downstream end portion of the outer peripheral surface of the rotor blade shroud 6. The position should just be an outer peripheral side from the inner peripheral side wall surface of the inlet opening 16, and an inner peripheral side from the outer peripheral side wall surface.

  The outlet opening 17 is located on the inner side in the turbine radial direction than the inlet opening 16. In addition, the edge part of the inlet opening 16 and the outlet opening 17 is chamfered, for example in circular arc shape.

  The bypass flow path 18 includes, for example, a first flow path portion extending from the inlet opening 16 in the turbine axial direction and a second flow path portion bent from the first flow path portion and extending in the turbine radial direction. And a third flow path portion that is bent from the second flow path portion and extends in the turbine axial direction to reach the outlet opening, and the cross-sectional areas of all the flow path portions are substantially the same. . And the leaked steam which flowed in from the inlet opening 16 is made to flow out in the turbine axial direction from the outlet opening 17 (refer arrow A in FIG. 2).

  In the present embodiment configured as described above, the leaked steam that has passed through the gap between the tip of the last-stage seal fin 14E and the outer peripheral surface of the rotor blade shroud 6 has a large circumferential velocity component, but part of it. Flows into and out of the bypass flow path 18 to generate a turbine axial flow. In other words, the circumferential velocity component of the leaked fluid that has flowed into the bypass channel 18 is reduced. At this time, even if the turbine axial distance d from the blade shroud 6 to the bypass flow path 18 is large, the ratio of the leaked steam flowing into the bypass flow path 18 is large, so the circumferential speed component of the leaked steam is reduced. The effect to make becomes large. Further, since the flow in the turbine axial direction generated in the bypass flow path 18 is strengthened, the circumferential speed component is sufficiently increased with respect to the leaked steam that has not flowed into the bypass flow path 18 due to interference of the flow in the turbine axial direction. Can be reduced. Therefore, the flow direction of the leaked steam indicated by the arrow B in FIG. 2 can be matched with the flow direction of the mainstream steam, and the effect of reducing the mixing loss can be enhanced.

  In the first embodiment, the bypass channel 18 has been described by taking the case where the cross-sectional areas of all the channel portions are substantially the same as an example. However, the present invention is not limited to this, and the gist and technical idea of the present invention are not limited thereto. Modifications can be made without departing from the scope. Specifically, for example, as in the first modification shown in FIG. 4, the cross-sectional area of the second flow path portion described above is enlarged from the cross-sectional area of the first and third flow path portions described above. Also good. That is, the bypass channel 18A may include the buffer unit 19 having an enlarged channel cross section. Thereby, for example, when the flow rate of the leakage steam flowing from the main flow path 7 into the leakage flow path 13 is relatively large (in other words, when the flow rate of the leakage vapor flowing into the bypass flow path 18A is relatively large), the bypass flow The effect of reducing the circumferential velocity component of the leaked steam by stagnating the leaked steam flowing into the path 18A may be enhanced.

  Further, for example, the area of the outlet opening 17 may be smaller than the area of the inlet opening 16 as in the second modification shown in FIG. Then, the cross-sectional area of the third flow path portion described above may be gradually reduced toward the outlet opening 17. That is, the bypass flow path 18B may have the nozzle portion 20 whose flow path cross-section gradually decreases toward the outlet opening 17. Thereby, for example, when the flow rate of the leaked steam flowing from the main flow path 7 into the leak flow path 13 is relatively small (in other words, when the flow rate of the leaking steam flowing into the bypass flow path 18B is relatively small), the bypass flow The effect of reducing the circumferential speed component of the leaked steam that has not flowed into the bypass flow path 18B may be increased by increasing the axial speed component of the leaked steam flowing out of the path 18B.

  Moreover, in the said one Embodiment and modification, when the circumferential direction space | interval (angle conversion) of a bypass flow path is substantially the same as the circumferential direction space | interval (angle conversion) of the moving blade 5 (in other words, the number of bypass flow paths) Is the same as the number of moving blades 5), but is not limited to this, and modifications can be made without departing from the spirit and technical idea of the present invention. That is, depending on the circumferential speed of the leaked steam flowing from the main flow path 7 into the leak flow path 13, the same effect can be achieved even if the number of bypass flow paths is reduced from the number of the moving blades 5. In such a case, the number of bypass flow paths may be reduced from the number of moving blades 5.

  In the above-described embodiment and modification, the labyrinth seal having the five-stage seal fins 14A to 14E and the two step portions 15A and 15B has been described as an example. Modifications can be made without departing from the concept. That is, the number of stages of the seal fins is not limited to five, and may be two, three, four, or six or more. Moreover, it does not need to have a level | step-difference part, and may have 1 or 3 or more level | step-difference parts. In these cases, the same effect as described above can be obtained.

  In the above description, the steam turbine, which is one of the axial flow turbines, has been described as an application target of the present invention. However, the present invention is not limited to this, and may be applied to a gas turbine or the like. In this case, the same effect as described above can be obtained.

DESCRIPTION OF SYMBOLS 1 Diaphragm outer ring 2 Stator blade 4 Rotor 5 Rotor blade 6 Rotor blade shroud 14A-14E Seal fin 16 Inlet opening 17 Outlet opening 18, 18A, 18B Bypass flow path 19 Buffer part 20 Nozzle part

Claims (4)

A plurality of stator vanes attached in the circumferential direction on the inner peripheral side of the diaphragm outer ring;
A plurality of circumferentially attached rotor blades disposed on the outer circumferential side of the rotor, and disposed on the downstream side of the stationary blade;
A blade shroud attached to the outer peripheral side of the blade;
A plurality of seal fins provided on the inner peripheral surface of the diaphragm outer ring facing the outer peripheral surface of the blade shroud, and projecting in the turbine radial direction;
An inlet opening and an outlet opening formed in pairs on one surface of the diaphragm outer ring facing the downstream end surface of the blade shroud;
The diaphragm outer ring is formed so as to communicate the inlet opening and the outlet opening, and has a bypass flow path for allowing the fluid flowing in from the inlet opening to flow out from the outlet opening in the turbine axial direction,
The inlet opening opens to the downstream side in the turbine axial direction of the downstream end of the outer peripheral surface of the blade shroud, and the outlet opening is located on the inner side in the turbine radial direction from the inlet opening. Turbine. The axial turbine according to claim 1,
The bypass turbine has an axial flow turbine having a buffer section having an enlarged passage section. The axial turbine according to claim 1,
The outlet opening has a smaller area than the inlet opening,
The bypass flow path has an axial flow turbine having a nozzle portion in which the flow path cross-section gradually decreases toward the outlet opening. A diaphragm outer ring of an axial turbine that is attached to the outer peripheral side of a row of stationary blades,
An inner peripheral surface facing the outer peripheral surface of the blade shroud;
A plurality of seal fins provided on the inner peripheral surface and projecting in the turbine radial direction;
An upstream end face facing the downstream end face of the blade shroud;
An inlet opening and an outlet opening formed in pairs on the upstream end face;
The diaphragm outer ring is formed so as to communicate the inlet opening and the outlet opening, and has a bypass flow path for flowing the fluid flowing in from the inlet opening in the turbine axial direction from the outlet opening,
The inlet opening is configured to open to the downstream side in the turbine axial direction of the downstream end portion of the outer peripheral surface of the blade shroud, and the outlet opening is configured to be inside in the turbine radial direction from the inlet opening. Diaphragm outer ring of axial flow turbine featuring.

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