WO2013027239A1

WO2013027239A1 - Axial flow turbine

Info

Publication number: WO2013027239A1
Application number: PCT/JP2011/004682
Authority: WO
Inventors: 英樹小野; 村田　健一; 茂樹妹尾
Original assignee: 株式会社日立製作所
Priority date: 2011-08-24
Filing date: 2011-08-24
Publication date: 2013-02-28

Abstract

In order to reduce a shock wave loss due to an increase in annulus area and a loss due to separation to thereby improve turbine efficiency in an axial flow turbine, an axial flow turbine is provided with a turbine stage configured from a stationary blade affixed to a stationary body and a moving blade affixed to a turbine rotor, and a working fluid flow path (2) having a plurality of turbine stages in the axial direction of the turbine. The axial flow turbine is provided with a bypass flow path (11) that is provided outside the working fluid flow path (2) and allows part of a working fluid flowing in from the upstream side in the flow direction of the working fluid to bypass the outer peripheral side of at least one of the turbine stages and to be introduced into a turbine stage located on the downstream side in the flow direction of the working fluid from the bypassed turbine stage.

Description

Axial flow turbine

The present invention relates to an axial flow turbine such as a steam turbine or a gas turbine.

In Patent Document 1, a plurality of turbine stages, each including a stationary blade fixed to an outer peripheral diaphragm and an inner peripheral diaphragm, and a moving blade fixed to a turbine rotor rotating around a turbine central axis, are provided in a working fluid flow path. An axial flow turbine having a function of converting kinetic energy generated when a high-pressure working fluid expands toward a low-pressure portion in a flow path into a rotational force by a turbine stage composed of stationary blades and moving blades is disclosed. Yes.

In axial flow turbines, there is a demand to increase the flow rate, which is the mass of the working fluid that flows per unit time, in order to increase the output per stage. By increasing the flow rate and increasing the output per paragraph, it is possible to increase the amount of power generation without changing the number of paragraphs.

Here, in order to increase the flow rate, it is known that it is effective to increase the annular area, which is the area seen from the turbine rotation axis direction of the portion where the working fluid flows. Therefore, in the case of an axial turbine, the ring zone area is the product of the blade length and the average diameter obtained by adding the outer peripheral end diameter and the inner peripheral end diameter of the blade and dividing by two, and multiplying by the circular ratio. Therefore, in order to increase the ring zone area, the blade length and the average diameter are increased.

JP 2003-27901 A

Generally, at the turbine stage inlet, the total specific enthalpy H ₀ , which is the sum of the enthalpy per unit mass of the working fluid (specific enthalpy) and the kinetic energy per unit mass divided by the square of the flow velocity divided by 2, is the rotation The value is substantially constant from the inner peripheral side close to the shaft to the outer peripheral side. On the other hand, the specific enthalpy h ₁ between the stationary blade and the moving blade becomes larger toward the outer peripheral side than the inner peripheral side so as to balance with the swirling flow between the stationary blades. Accordingly, the specific enthalpy difference H ₀ −h ₁ becomes smaller toward the outer peripheral side. The velocity of the flow leaving the stationary blade is proportional to the square root of this specific enthalpy difference H ₀ -h ₁ . That is, the stationary blade outflow speed becomes smaller toward the outer peripheral side.

By the way, as described above, when the annulus area is increased, that is, when the blade length and the average diameter are increased, the specific enthalpy difference H ₀ -h ₁ on the outer peripheral side is further reduced, and the stationary blade outflow speed is also reduced. As described above, when the annular area is increased, the specific enthalpy difference H ₀ -h ₁ on the outer peripheral side and the stationary blade outflow speed are reduced, which may cause the following problems.

That is, the loss increases due to the supersonic speed of the relative inflow Mach number of the moving blades. Increasing the blade length and the average diameter increases the peripheral speed, which is the rotational speed of the moving blade. The peripheral speed of the moving blade is greatest at the outer peripheral end where the radial position is the largest, that is, at the tip of the moving blade. If the peripheral Mach number obtained by dividing the peripheral speed of the moving blade by the sonic speed exceeds 1 and becomes supersonic, and the rotational direction component of the flow from the stationary blade is not sufficient, the relative velocity of the flow flowing into the moving blade is Supersonic speed. When the relative inflow velocity becomes supersonic, a shock wave accompanied by a discontinuous pressure rise occurs on the upstream side of the blade, and in addition to the entropy rise due to the shock wave itself, the shock wave interferes with the boundary layer of the blade surface, and the discontinuous The boundary layer thickness increases with increasing pressure. In addition, entropy increases due to peeling. Due to the entropy increase due to the shock wave, the rotational force corresponding to the increased flow rate, that is, the output may not increase even though the annular zone area of the turbine stage is increased and the flow rate of the working fluid is increased. Therefore, it is important to eliminate or weaken the shock wave generated at the inlet of the moving blade in order to realize an increase in output per paragraph by enlarging the annular zone area beyond the limit peripheral speed. Therefore, it is necessary to reduce the relative inflow speed of the rotor blade.

Therefore, an object of the present invention is to provide an axial flow turbine that can suppress shock wave loss due to an increase in annulus area and improve turbine efficiency.

In order to achieve the above object, an axial turbine including a plurality of turbine stages each having a stationary stage fixed to a stationary body and a moving blade fixed to a turbine rotor in a working fluid flow path is provided outside the working fluid flow path. And a bypass flow path that bypasses at least one stage of the turbine stage and introduces a part of the working fluid from the upstream side in the working fluid flow direction to the turbine stage on the downstream side in the working fluid flow direction of the bypassed turbine stage. .

According to the present invention, in an axial flow turbine, it is possible to suppress a shock wave loss due to an increase in annulus area and improve turbine efficiency.

It is meridional sectional drawing showing the principal part structure of the turbine stage part of a steam turbine. It is meridional sectional drawing showing the principal part structure of the turbine stage part of the steam turbine which concerns on the 1st Embodiment of this invention. It is a graph showing the specific enthalpy distribution of the blade height direction of the conventional steam turbine. It is explanatory drawing which represented typically the relationship of the stationary blade outflow speed of the steam turbine which concerns on the 1st Embodiment of this invention, and a moving blade peripheral speed, and a moving blade relative inflow speed. It is a graph showing the blade height direction distribution of the moving blade relative inflow Mach number when the peripheral speed is high in the conventional steam turbine. It is a graph showing the specific enthalpy distribution of the blade height direction of the steam turbine which concerns on the 1st Embodiment of this invention. It is a graph showing the blade height direction distribution of the moving blade inlet angle measured from the circumferential direction of the steam turbine according to the first embodiment of the present invention. It is a graph showing blade height direction distribution of a moving blade relative inflow Mach number of a steam turbine concerning a 1st embodiment of the present invention. It is meridional sectional drawing showing the principal part structure of the turbine stage part of the steam turbine which concerns on the 1st Embodiment of this invention. It is meridional sectional drawing showing the principal part structure of the turbine stage part of the steam turbine which concerns on the 2nd Embodiment of this invention. It is meridional sectional drawing showing the principal part structure of the turbine stage part of the steam turbine which concerns on the 3rd Embodiment of this invention.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate. In addition, the same code | symbol is attached | subjected to the equivalent component through each drawing.

As a first embodiment of the present invention, an example in which the present invention is applied to the final paragraph of a steam turbine will be described below.

First, the basic configuration and operation of a general steam turbine stage will be described.

FIG. 1 is a meridional cross-sectional view showing a main structure of a turbine stage part of a general steam turbine. In the turbine stage of the steam turbine, the steam high pressure part P ₀ on the upstream side in the flow direction of the steam 1 as the working fluid (hereinafter simply referred to as upstream side) and the downstream side in the steam flow direction (hereinafter simply referred to as downstream side) are described. It is provided in the steam main flow path 2 between the vapor low-pressure portion P ₁ of). The turbine stage includes a stationary blade 6 fixed between the outer peripheral diaphragm 4 and the inner peripheral diaphragm 5 and a moving blade 7 fixed to the turbine rotor 8 so as to face the downstream side of the stationary blade 6. Is done. When the turbine stage is a multi-stage turbine composed of a plurality of stages, a plurality of turbine stages are repeatedly provided from the high pressure part P ₀ toward the low pressure part P ₁ along the turbine central axis 9. . The paragraph closest to the steam inlet of the high-pressure part P ₀ is called the first paragraph, and the paragraph closest to the steam outlet of the low-pressure part P ₁ is called the last paragraph.

In the turbine stage, the outer peripheral diaphragm 4 is fixed to the casing 3. The casing 3 includes a diaphragm support 16 and an extraction chamber partition plate 17. The diaphragm support 16 has a plate-like structure having a thickness in the vertical direction on the paper surface, and a plurality of diaphragm supports 16 are provided around the rotation axis. The extraction chamber partition plate 17 has an axisymmetric structure around the rotation axis. A bleed chamber 18 is formed inside the casing 3. Part of the working steam that passes through the steam main flow path 2 is introduced into the extraction chamber, and is sent out of the turbine by extraction means (not shown). In FIG. 1, higher specific enthalpy and high-pressure working steam is extracted in the upstream extraction chamber. In this embodiment, the turbine stage has four stages and the

extraction chambers

18a, 18b, and 18c are provided. However, the number of stages and the number of extraction chambers are not particularly limited to this example.

The turbine rotor 8 is mechanically connected to a generator (not shown). In the steam turbine, kinetic energy generated when high-pressure steam expands toward a low-pressure portion is converted into rotational force by a turbine stage composed of stationary blades 6 and moving blades 7, and is electrically generated by a generator via a turbine rotor 8. It converts into energy and generates electricity.

FIG. 3 is a graph showing the specific enthalpy distribution in the blade height direction of the turbine last stage of the steam turbine shown in FIG. The horizontal axis represents the specific enthalpy, and the axial direction is determined so that the specific enthalpy increases toward the left as the working fluid vapor flows from left to right in FIG. The vertical axis represents the blade height direction, and BH represents the blade exit height.

In FIG. 3, H ₀ is the total specific enthalpy which is the sum of the specific enthalpy per unit mass at the paragraph inlet and the kinetic energy per unit mass divided by the square of the working fluid flow velocity divided by 2, and h ₁ is the stationary and moving blade The specific enthalpy between and h ₂ represents the specific enthalpy of the paragraph exit. The total specific enthalpy H ₀ at the paragraph inlet is substantially constant in the blade height direction. The specific enthalpy h ₁ between the stationary blades and the moving blades increases toward the outer peripheral side in the turbine radial direction (hereinafter simply referred to as the outer peripheral side) so as to balance with the centrifugal force mainly due to the swirling speed between the stationary blades. As a result, the specific enthalpy difference Δh applied to the outer stationary vane is reduced, and the stationary blade outflow speed proportional to the square root of the specific enthalpy difference is also reduced. The tendency of the specific enthalpy difference and the stationary blade outflow speed of the stationary blade to decrease is that the blade diameter and the average diameter obtained by adding the outer peripheral end diameter and the inner peripheral end diameter of the blade and dividing by 2 are increased. As the annular area increases, the outer peripheral end position of the wing becomes more prominent as it comes to the outer peripheral side.

FIG. 4 schematically shows the relationship among the stationary blade outflow speed, the moving blade peripheral speed, and the relative inflow speed of the moving blade when the peripheral speed of the moving blade is large. Vapor pressure P _0, by passing through the stationary blade 6, the acceleration, the flow deflection by the speed V (hereinafter referred to as the speed and stator blade outlet velocity V). Looking at this stationary blade outflow velocity V in a relative coordinate system that rotates together with the moving blade 7, the moving blade 7 rotates at a peripheral speed U around the turbine central axis (the direction of rotation is indicated by an arrow 22). By combining the stationary blade outflow velocity vector V and the peripheral velocity vector U, the steam flowing into the moving blade 7 becomes a flow having a relatively speed W (hereinafter referred to as a moving blade relative inflow velocity W). A triangle formed by the stationary blade outflow velocity vector V, the peripheral velocity vector U, and the moving blade relative inflow velocity vector W is referred to as a velocity triangle. As apparent from the speed triangle, when the moving blade circumferential speed U increases, the moving blade relative speed W flowing into the moving blade 7 increases. In order to reduce the moving blade relative inflow velocity W, it is necessary to increase the stationary blade outflow velocity V.

Here, when the state quantity of the steam at the paragraph inlet is fixed, in order to increase the stationary blade outflow velocity V, the specific enthalpy h ₁ between the stationary and moving blades is decreased, and the specific enthalpy of the stationary blade is reduced. It is necessary to increase the difference Δh. However, specific enthalpy between the static-blades increases as the outer peripheral side by the swirl velocity field of the stationary blade outlet, as the blade length increases, the influence of the swirling velocity field is strong, it is difficult to reduce the h ₁ Become. That is, as the blade length increases, it becomes more difficult to increase the specific enthalpy difference Δh of the stationary blade, and it is difficult to increase the stationary blade outflow velocity V.

FIG. 5 is a graph showing the blade height direction distribution of the blade relative inflow Mach number when the blade peripheral speed is high. As shown in FIG. 5, it can be seen that on the outer peripheral side of the wing, the Mach number exceeds 1.0 and supersonic inflow occurs. Here, if the specific enthalpy difference H ₀ -h ₂ of the turbine stage itself is increased in order to increase the specific enthalpy difference Δh of the outer stationary blade, the relative inflow Mach number of the moving blade at the inner peripheral end becomes 1.0. In order to achieve supersonic inflow, it is difficult to solve the problem of supersonic inflow by increasing the specific enthalpy difference of the entire paragraph.

Based on the above, the first embodiment of the present invention will be described with reference to the drawings.

The basic configuration and operation of the steam turbine according to the first embodiment of the present invention will be described.

FIG. 2 is a meridional cross-sectional view of the main structure of the turbine stage part of the steam turbine according to the first embodiment of the present invention. As shown in FIG. 2, in the steam turbine according to this embodiment, the steam flow path to the final stage includes a steam main flow path 2 and a bypass flow path 11 provided outside the steam main flow path 2. The bypass flow path 11 is a flow path for introducing a part of the main steam flowing from the upstream side into a turbine stage downstream of the bypassed turbine stage by bypassing at least one stage of the turbine stage.

Further, a stationary blade bypass channel partition cover 12 is provided between the stationary blades 6a adjacent to each other in the circumferential direction at the final stage. A stationary blade bypass passage partition cover 12 divides the passage between the stationary blades into a steam main passage 2 on the inner peripheral side and a stationary blade bypass passage 19 on the outer peripheral side in the radial direction. Steam that flows down the bypass passage 11 flows into the stationary blade bypass passage 19, and the main steam flows into the steam main passage 2 on the inner peripheral side.

Similarly, a blade bypass passage partition cover 13 is provided between the blades 7a adjacent in the circumferential direction of the final stage. The blade bypass passage partition cover 13 divides the passage between the rotor blades into the steam main passage 2 on the inner peripheral side and the blade bypass passage 20 on the outer peripheral side in the radial direction. The steam that flows down through the bypass flow path 11 and the stationary blade bypass flow path 19 mainly flows into the moving blade bypass flow path 20, and the main steam flow flows into the steam main flow path 2 on the inner peripheral side. The moving blade bypass flow path partition cover 13 includes a type in which a plurality of moving blades 7a are collected and fixed by one member, a type that is closely attached by a blade integrated cover having a pitch between blades, etc. Any form may be used as long as it has a function of dividing the flow path so that the steam of the steam main flow path 2 and the bypass flow path 11 are not in direct contact with each other.

The bypass flow path 11 is a cylindrical flow path centered on the turbine central shaft 9 provided in the casing portion, and communicates the upstream extraction chamber 18b and the stationary blade bypass flow path 19 with each other. The extraction chamber 18b is an extraction chamber into which the extracted steam extracted immediately upstream of the turbine stage one upstream of the final stage flows.

By the bypass flow path 11, a part of the steam extracted from the steam main flow path immediately upstream of the turbine stage one upstream of the final stage bypasses the turbine stage one upstream of the final stage, and the stationary blades of the final stage and It flows into the blade bypass passage. Therefore, steam having a high specific enthalpy is introduced from the upstream extraction chamber 18 b into the moving blade bypass passage 20 through the stationary blade bypass passage 19 by the bypass passage 11.

In addition, in order to introduce the working steam immediately upstream of the final stage into the extraction chamber 18a, the bypass channel 11 is provided with a plurality of extraction tubes 14 in the circumferential direction.

FIG. 6 is a graph showing the specific enthalpy distribution in the blade height direction of the final stage of the steam turbine according to the present embodiment and one upstream stage thereof. The steam main flow path 2 is below the span position BH _c , and the bypass flow path 11 is above. H ₀ is the total specific enthalpy upstream of the stationary blade 6b shown in FIG. Similarly, h ₁ , H ₂ , h ₃ , and h ₄ are specific enthalpy h and total specific enthalpy, respectively, upstream of the moving blade 7b, upstream of the stationary blade 6a, upstream of the moving blade 7a, and downstream of the moving blade 7a of the steam main flow path 2. H. h ₃ ′ is a specific enthalpy h upstream of the moving blade 7 a of the bypass flow path 11. The specific enthalpy drop on the outer peripheral side of the final stage is conventionally Δh, but in the bypass flow path, the specific enthalpy drop Δh ′ on the outer periphery of the moving blade is increased because the specific enthalpy of the inlet is increased. Therefore, on the outer peripheral side, the steam outflow speed of the stationary blade increases and the steam inflow speed of the moving blade inlet decreases.

FIG. 7 shows the blade height direction distribution of the moving blade inlet angle measured from the circumferential direction of the final stage of the steam turbine according to the present embodiment. In this embodiment, in the span height BH _c, it is designed such that the relative inflow angle of the main steam flow path and bypass flow of the rotor blade 7a is continuous.

FIG. 8 is a graph showing the blade height direction distribution of the moving blade relative inflow Mach number in the final stage of the steam turbine according to the present embodiment shown in FIG. 2. M _r3 ′ shown by a solid line is the moving blade relative inflow Mach number of the final stage of the steam turbine according to the present embodiment, and M _r3 shown by a broken line is the relative inlet of the moving blade of the general last stage of the steam turbine shown in FIG. Mach number. In the final-stage bypass passage, the specific enthalpy difference of the stationary blade is increased from Δh to Δh ′, so that the stationary blade outflow speed on the outer peripheral side of the stationary blade is increased, and as described with reference to FIG. Sonic inflow is avoided.

According to the steam turbine according to the present embodiment, the specific enthalpy difference Δh on the outer peripheral side of the stationary blade is increased by increasing the total specific enthalpy H ₀ on the outer peripheral side of the final stage inlet. Thereby, the stationary blade outflow speed can be increased. Therefore, the speed component in the turning direction of the stationary blade outflow speed component V can be increased, and the relative inflow speed of the moving blade flowing into the moving blade in the final stage can be reduced even though the circumferential speed U is the same. . Therefore, the supersonic inflow to the moving blade can be avoided, the generation of the shock wave at the moving blade inlet can be suppressed, and the loss accompanying the generation of the shock wave can be suppressed.

By the way, when the annular zone area of the turbine stage is increased, the expansion rate of the meridian plane flow path, that is, the increase rate of the flow path height of the paragraph outlet with respect to the flow path height of the turbine stage inlet increases. On the other hand, even if the annular zone area of the turbine stage is increased, the axial length of the stage cannot generally be increased because of the restriction of the overall length of the turbine. The increase is generally realized by increasing the spread angle of the meridional flow path shape at the outer peripheral end or inner peripheral end of the stationary blade portion. It is known that if the spread angle of the meridional flow path is increased, peeling occurs and a loss occurs, which is particularly remarkable on the outer peripheral side. In the present embodiment, the working steam on the outer peripheral side passes through the bypass flow path substantially parallel to the axis, and therefore no separation occurs.

In the present embodiment, the rotational force extracted by the paragraph composed of the stationary blade 6b and the moving blade 7b is reduced, but the decrease is extracted as rotational force in the paragraph composed of the stationary blade 6a and the moving blade 7a. Therefore, the rotational power of the turbine as a whole is not reduced. Rather, it is possible to increase the rotational force as the loss is reduced.

In the present embodiment, the shroud cover 10 is provided on the outer peripheral side of the final stage rotor blade, but the shroud cover 10 is not necessarily required in the configuration of the present invention, and a configuration without the shroud cover 10 may be employed (FIG. 9).

In this embodiment, an example in which the turbine stage is bypassed by one stage has been described, but the present invention is not limited to this, and one or more stages may be bypassed.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 10 is a meridional cross-sectional view showing the main structure of the turbine stage part of the steam turbine according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the component equivalent to 1st Embodiment, and description is abbreviate | omitted. In the present embodiment, the steam pressure is designed to be substantially equal at a portion where the bypass flow passage 11 and the steam main flow passage 2 join the upstream portion of the final stage moving blade 7a downstream of the final stage stationary blade 6a. Since the steam merged from the bypass flow path 11 and the steam main flow path 2 does not drift in the radial direction, the blade bypass flow path partition cover 13 is unnecessary.

Here, the steam from the bypass flow path 11 and the steam main flow path 2 are not necessarily the same in speed and flow direction. Therefore, a shear layer is formed at the junction of the bypass flow path 11 and the steam main flow path 2, and energy loss occurs. However, the loss due to the shear layer is negligible for the shaft power generated in the final paragraph. Rather, since the centrifugal stress design value of the moving blade 7a can be afforded by eliminating the moving blade bypass flow path partition cover 13, it is possible to further increase the length of the blade and increase the annular zone area. The output can be increased without increasing.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 11 is a meridional cross-sectional view illustrating a main structure of a turbine stage portion of a steam turbine according to a third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the component equivalent to 1st Embodiment, and description is abbreviate | omitted. In the final stage of the steam turbine, the pressure and specific enthalpy level are low, and the working steam becomes wet steam. A liquid film is formed on the surface of the stationary blade 6a, and coarse droplets are discharged from the trailing edge of the stationary blade 6a to the moving blade 7a. Coarse droplets are refined by working steam between the stationary blades, but a part of them collides with the tip of the blade and erodes the blade 7a. The progress of erosion has a problem that it is accompanied by a decrease in shaft power and blade strength.

For the above problems, in the embodiment of the present invention, the moisture removal slit 15 is provided in the outer wing portion located in the stationary blade bypass passage 19 of the stationary blade 6a. The stationary blade bypass channel partition cover 12, the outer wing portion of the stationary blade 6a, and the outer diaphragm 4a are formed hollow, and the steam upstream of the stationary blade 6a is the outer wing portion of the stationary blade bypass channel partition cover 12 and the stationary blade 6a. From the inside of the outer peripheral side diaphragm 4a, it is led out to the extraction chamber 18a. The moisture removal slit 15 communicates with the inside and outside of the stationary blade, and the pressure outside the stationary blade is higher than the inside of the stationary blade. Therefore, the liquid film formed on the stationary blade passes through the moisture removal slit 15 and is removed to the extraction chamber 18a. Since there are no coarse droplets discharged to the wake of the stationary blade 6a, no erosion of the moving blade occurs.

As described above, the example in which the present invention is applied to the final paragraph of the steam turbine has been described. However, the present invention is not limited to the final paragraph, and can be applied to the upstream paragraph. Further, the present invention is applicable not only to a steam turbine but also to a gas turbine.

In addition, when the present invention is applied to the final paragraph of the steam turbine, there are the following two advantages in addition to the advantages described in the embodiments.

The first advantage is that wetting loss is reduced. In the general steam turbine shown in FIG. 1, the water film adhering to the blade surface of the moving blade 7 constituting the upstream stage of the final stage is collected on the outer peripheral side by centrifugal force, and toward the stationary blade 6a of the final stage. Released. Therefore, the degree of wetness increases on the outer peripheral side of the final paragraph inlet, which causes an increase in wet loss and an increase in erosion in the final stage where the moving blade peripheral speed is high. On the other hand, when the present invention is applied to the final stage of the steam turbine, the wetness, which is the mass fraction of the liquid phase, is small because the total inlet enthalpy on the outer periphery side of the final stage is large. As a result of the reduced wetness, the present invention reduces wet loss and can suppress the occurrence of erosion. Therefore, turbine efficiency can be improved and the reliability of the steam turbine can be improved.

The second advantage is that the reliability of the wing can be improved. The Wilson line that transitions from superheated steam of a steam turbine to wet steam that is in a two-phase flow state is often located in the turbine stage one upstream of the last stage. The Wilson line moves in the flow direction depending on the turbine load and steam conditions. Therefore, in the turbine stage where the Wilson line exists, the state of dry steam and wet steam is repeated, and corrosion pits are likely to occur. However, when the present invention is applied to the final paragraph, the turbine stage upstream of the final stage where the Wilson line is generated has a small blade length, so that the stress applied to the blade can be reduced, and the reliability of the blade is reduced due to corrosion pits. Can be suppressed.

DESCRIPTION OF SYMBOLS 1 Steam 2 Steam main flow path 3

Casing

4a, 4b, 4c, 4d Outer

peripheral side diaphragm

5a, 5b, 5c, 5d Inner

peripheral side diaphragm

6a, 6b, 6c,

6d Stator blade

7a, 7b, 7c, 7d Rotor blade 8 Turbine rotor 9 Turbine center shaft 10 Shroud cover 11 Bypass passage 12 Stator blade bypass passage partition cover 13 Moving blade bypass passage partition cover 14 Extraction pipe 15 Moisture removal slit 16 Diaphragm support 17 Extraction chamber partition plate 18 Extraction chamber 19 Stabilization blade Bypass passage 20 Rotor bypass passage

Claims

An axial turbine comprising a turbine stage comprising a stationary blade fixed to a stationary body and a moving blade fixed to a turbine rotor, and a working fluid flow path having a plurality of turbine stages in the turbine axial direction,
A part of the working fluid that is provided outside the working fluid flow path and flows in from the upstream side in the working fluid flow direction bypasses at least one stage of the turbine stage, and is downstream of the bypassed working stage in the working fluid flow direction. An axial-flow turbine comprising a bypass flow passage introduced into the turbine stage.
An axial turbine according to claim 1,
The flow path between the stationary blades of the turbine stage into which the bypass flow that has flowed down the bypass flow path is introduced are the outer peripheral side into which the bypass flow flows and the inner peripheral side into which the main working fluid flow that flows down the working fluid flow path. And an axial turbine characterized by being partitioned in a radial direction.
An axial turbine according to claim 2,
The axial flow turbine, wherein the bypass flow is extracted steam extracted at least one stage upstream of a turbine stage into which the bypass flow is introduced.
An axial turbine according to claim 3,
The passage between the blades of the turbine stage into which the bypass flow is introduced is radially divided into an outer peripheral side into which the bypass flow flows and an inner peripheral side into which the working fluid main flow flows down the working fluid flow channel. An axial-flow turbine characterized in that
An axial turbine according to claim 3,
An axial flow turbine characterized in that static pressures of both flows are equal in an upstream portion of a moving blade of a turbine stage into which the bypass flow is introduced and a portion where the bypass flow and the main working fluid flow merge.
An axial turbine according to claim 3,
An axial turbine having a structure for extracting steam immediately upstream of a turbine stage into which the bypass flow is introduced.
An axial turbine according to claim 4,
The stationary blade of the turbine stage into which the bypass flow flowing down the bypass flow path is introduced, the outer wing portion through which the bypass flow passes has a hollow structure and has a slit that communicates the inside and the outside,
An axial turbine having a structure in which a bleed air flow from a working fluid flow path having a static pressure lower than that of the bypass flow passes through the inside of the outer peripheral wing portion.