JPS63280801A - Stationary blade for steam turbine - Google Patents

Abstract

PURPOSE:To prevent a moving blade from being eroded by drain produced on the surface of a stationary blade by forming a drain catching groove extending longitudinally from a position separated from the outer circumferential wall of a flow path toward the inner ring of the stationary blade in at least one face on back side or front side of the stationary blade. CONSTITUTION:A stationary blade 3 of a steam turbine is supported at the outer circumferential end portion by the outer circumferential wall 1 of a flow path and at the inner circumferential end portion by a stationary blade inner ring 2. A drain catching groove 4 is formed in the longitudinal direction of the stationary blade 3 closely to the trailing edges of the back side face and the front side face of the stationary blade 3. The drain catching groove 4 does not open to the outer circumferential wall 1 side of the flow path, where the distance D between the outer circumferential side end of the groove 4 and the outer circumferential wall 1 of the flow path is set longer than about 3mm. The inner circumferential end of the groove 4 is formed closer to the inner ring 2 side than 75% of the height of stator blade with reference to the outer circumferential face of the stator blade inner ring 2. Consequently, drain produced on the surface of the stationary blade 3 can be caught and erosion of the moving blade 7 due to drain can be prevented.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to stationary blades of steam turbines, and particularly to corrosion of the blades caused by condensate in steam colliding with the tips of the rotor blades. The present invention relates to a stator blade for a steam turbine suitable for preventing performance deterioration.

(Prior Art) In most stages of nuclear power turbines and geothermal turbines, or in the low-pressure stage of thermal power turbines, a portion of steam, which is the working fluid, condenses and becomes drain, flowing on the surface of the stationary blade.
These condensates are known to erode downstream rotor blades and reduce turbine efficiency.

The condensate generated on the surface of the stationary blade grows and collects, flows to the trailing edge, and is scattered from there, colliding with the moving blade without being able to follow the speed of the mainstream steam. The collision speed is faster at the tip of the wing, and most condensate occurs near the outer periphery of the wing. Therefore, the tip of the rotor blade is intensively eroded. Furthermore, the collision of the drain against the rotor blades acts as a brake on the rotation of the rotor blades, causing a reduction in turbine efficiency.

In order to improve such problems, conventional methods such as those shown in Figs.
A steam turbine equipped with a moisture separator as shown in the figure has been proposed.

In FIG. 8, approximately 50 to 100 stator blades 3 are radially fixed between the flow path outer circumferential wall 1 and the stator blade inner ring 2 by welding, casting, or the like.

As shown in FIG. 9, a drain capture groove 4 is formed on the downstream side of the ventral surface 3a of the stationary blade 3, and this drain capture groove 4 extends from the flow channel outer peripheral wall 1 side in the longitudinal direction to near the center of the flow channel. has been done. Further, the drain capture groove 4 is communicated with a drain recovery chamber 5 provided in the outer circumferential wall 1 of the flow path via a communication hole 6.

Drain suction slits 8 are provided in the flow path outer peripheral wall 1 on the upstream and downstream sides of the stationary blade 3 and communicate with the drain recovery chamber 5 .

The drain recovery chamber 5 is connected to a low pressure condenser (not shown) or the like. Furthermore, a moving blade 10 embedded in a wheel 9 is disposed downstream of the stationary blade 3.

The mainstream steam flows into the stationary blade 3 from the left in FIG.
Rotate this. In a steam turbine stage through which wet steam with low temperature and pressure flows, a portion of the steam condenses on the stationary blades 3 and the outer circumferential wall 1 of the flow path to generate drain. Drain flowing on the ventral side of the stationary blade 3 is captured by the drain capture groove 4, sucked into the drain collection chamber 5 through the communication hole 6, and discharged out of the flow path. The drain on the outer peripheral wall 1 of the flow path is discharged to the outside of the flow path via the drain suction slit 8.

(Point m to be solved by the invention) There is a drain flow on the dorsal side of the stationary blade 3, similar to the ventral side, and the amount is 20% to 12% of the drain flowing on the ventral side.
It reaches 0%, and there are many drains that adhere and grow near the downstream of the dorsal surface. Looking at the distribution of condensate in the radial direction, most of the condensate is concentrated outward from the center of the channel, and is particularly concentrated outside 75% of the channel height. A large amount of drain flows in the form of a film even on the outer circumferential wall 1 of the flow path.

Drain capture groove 4 is installed on the surface of static W3 in the longitudinal direction as shown above.
It has been observed that when a drain is provided, the drain is captured here, the speed of the drain in the mainstream direction is lost, and the rest is flowed toward lower pressure due to the static pressure gradient along the groove.

In other words, in the above-mentioned conventional technology, not only is the drain flowing on the dorsal side of the stator vane not captured at all, but also the drain that is captured in the drain capture groove 4 on the ventral side rarely reaches the communication hole 6 due to the resistance of the static pressure gradient. There is a high possibility that it will be limited to a portion and the rest will leak out again. In addition, the communication hole 6 is filled with a large amount of drain flowing through the outer peripheral wall 1, and the drain capture groove 4
There is also a possibility that the drain will flow backwards. Although it is possible to enlarge the communication hole 6 to prevent such a phenomenon, it is possible to
Even the steam that does effective work will be emitted, leading to a decrease in turbine efficiency.

Therefore, the present invention solves the above-mentioned drawbacks of conventional steam turbine stationary blades in terms of drain discharge, prevents corrosion of the rotor blades due to drain generated on the surface of the stationary blades, and improves turbine efficiency. The purpose is to

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the present invention has a stator blade whose outer end is supported on the outer peripheral wall of the flow path and whose inner end is supported on the inner ring of the stator vane. A drain trap S% is provided on at least one of the dorsal surface and the ventral surface of the stator vane and extends in the longitudinal direction from a position spaced apart from the outer circumferential wall of the flow path toward the inner ring side of the stator vane.
? ? It is characterized by forming n.

(Function) According to the present invention, the drain flowing on the surface of the stationary blade is caught in the drain trapping groove, and the drain is trapped by the static pressure gradient in the groove, where the static pressure on the outer circumferential wall side is higher than the static pressure on the inner ring side. The drain flows toward the inner ring and is guided to a position in the radial direction where the circumferential speed of the rotor blade located downstream of the stator blade becomes sufficiently small. Near the point where the groove disappears, the drain flows out onto the surface of the stator blade again and is removed from the trailing edge. scatter. Here, unlike near the tips of the rotor blades, the circumferential speed is low, so the impingement speed of the drain against the rotor blades is low, the rotor blades are not eroded, and the decrease in turbine efficiency due to braking is also small. Furthermore, since drain steam is not discharged to the outside from the flow path, steam loss is also reduced.

(Example) Hereinafter, an example of a stationary blade of a steam turbine according to the present invention will be described with reference to FIGS. 1 to 3. Note that the same parts as in FIG. 8 are denoted by the same reference numerals, and explanations thereof will be omitted.

In FIG. 1, drain capture grooves 4 are formed along the longitudinal direction of the stator blade 3 near the trailing edges of the dorsal and ventral surfaces of the stator blade 3. This groove 4 has a shape that does not open toward the outer periphery ul side of the flow path, and in this embodiment, the outer peripheral end of the groove 4 and the outer peripheral wall 1 of the flow path are separated by a distance of about 3 mm or more. On the other hand, the inner peripheral end of the groove 4 is formed to be closer to the inner ring 2 than 75% of the height of the stator blade based on the outer peripheral surface of the inner ring 2 of the stator blade.

The groove 4 on the back side of the stator blade 3 is formed near the trailing edge so as to be almost parallel to the trailing edge, and the groove 4 on the ventral side of the stator blade 3 is formed so that the outer peripheral end is on the front edge side of the profile and on the inner peripheral side. The end portion is formed closer to the rear edge side of the profile.

Next, the operation of the stationary blade of the steam turbine in the present invention will be explained.

In a steam turbine in which wet steam flows, when the steam flows between the stator blades 3, the moisture in the steam cannot follow the speed change in the flow direction and collides with the surface of the stator blades 3, or the stator blades 3. As it flows along the surface, it condenses and condensation occurs on the static A3 surface.

■-■-■ and IV-IV cross sections of stationary blade 3 (see Figure 1)
The static pressure distribution on the profile surface has the relationship shown in Figure 3, with the ■-■ cross section blade on the outer circumference side being IV-IV on the inner circumference side.
The pressure is higher than the cross section. Therefore, when the drain capture groove 4 is formed, a pressure difference occurs along the groove 4 on both the dorsal and ventral sides, such that it is higher on the outer peripheral side and lower on the inner peripheral side. In FIG. 3, this pressure difference is indicated by ΔP and ΔP2 on the ventral and dorsal sides, respectively. However, on the dorsal side, a sufficient pressure difference is generated just by making the groove 4 parallel to the trailing edge, but on the ventral side, as is clear from Figure 3, this is not enough, so the outer edge of the groove 4 is The pressure difference is increased by forming the profile closer to the front edge and the inner peripheral end closer to the profile rear edge.

Drain on the surface of the stator blade 3 is captured by the drain capture groove 4 as it flows on the surface of the blade, is flown to the inner circumference side by the static pressure gradient in the groove 4, and flows out again near the part where the groove 4 disappears. It is swept up to the trailing edge of the stationary blade 3.

The drain path during this period is indicated by the symbol Fd in FIG. The drain that reaches the trailing edge is scattered from there and collides with the rotor blade 7, but since the drain capture groove 4 is sufficiently long and the radius of the point where the drain collides is sufficiently small, the collision speed of the drain is Small enough.

On the other hand, experiments have shown that there is a large amount of condensate flowing in the form of a film on the outer circumferential wall 1 of the flow path.
There is a gap of 3 mm or more between the drain capture groove 4 and the flow path outer circumferential wall 1, so that the drain on the outer circumferential wall 1 does not flow into the groove 4, and the drain on the outer circumferential wall 1 is downstream of the stationary blade 3. The drain is efficiently sucked into the drain suction slit 8.

Normally, for final stage rotor blades up to about 26 inches, 7 inches from the tip.
The range up to 5% height is due to the collision speed with the drain and is severely eroded. In this embodiment, at least this area is protected by forming the drain capture groove 4.

As described above, by directing the drain generated on the surface of the stator blade 3 to the inner circumferential portion where the collision speed when colliding with the rotor blade is sufficiently small, corrosion of the rotor blade can be significantly reduced, resulting in reliability. This improves performance and reduces turbine repair costs. Furthermore, since the collision loss to the rotor blades is reduced, the stage efficiency of the turbine is improved. In this embodiment, since drain and steam do not flow out of the flow path, there is no loss of steam.

Furthermore, in the final stage stator blade, the velocity of the steam flowing out of the stator blade increases as it approaches the inner circumference, so guiding the condensate toward the inner circumference and then letting it flow out makes the condensate particles scattered from the trailing edge of the stator blade more fine. This has the effect of further reducing rotor blade erosion.

According to the present invention, the structure is as simple as providing grooves on the surface of the stationary blade 3, so not only can the cost of a turbine using wet steam as a working fluid be reduced, but it can also be easily applied to existing equipment and operated. It is possible to prevent erosion of blades and improve performance at a low cost.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 and 5. Note that FIG. 5 is a cross-sectional view taken along the line ■-■ of the stationary blade 3 shown in FIG.

In FIG. 4, a plurality of drain capture grooves 4 are formed on both the dorsal and ventral sides of the stationary blade 3. The outer peripheral side ends of all the grooves 4 are separated by a distance from the flow path outer peripheral wall 1 in the same manner as shown in FIG. - All the grooves 4, including the ventral side, are formed so that the inner circumferential end portions are located at different positions in the radial direction.

With this configuration, it is possible to reliably capture condensate that could not be captured by one groove 4 alone or newly generated condensate downstream of the first groove 4, and to determine the radial position from which the condensate flows. It is possible to prevent the condensate from colliding with the rotor blades by dispersing it and concentrating it even at low speeds.

Further, other embodiments will be described with reference to FIGS. 6 and 7. In addition, Fig. 7 shows the vt-vt of the stationary blade in Fig. 6.
FIG.

The stationary vane 3 has a hollow structure, and the inside thereof is a cavity 11. Near the dorsal front edge and the ventral rear edge, where the surface pressure is almost equal, there is a drain suction slit 10 that communicates the outside with the cavity 11. is formed. The slit 10 is formed along the longitudinal direction of the stator blade 3 and perpendicular to the flow, and is divided into three parts so as not to reduce the strength of the stator blade 3 (see FIG. 6). A drain recovery chamber 5 communicating with the cavity 11 is provided inside the outer circumferential wall 1 of the flow path, and this recovery chamber 5 is connected to a portion having a lower pressure, such as a condenser. Furthermore, a drain capture groove 4 is formed on the back side near the rear edge of the stationary blade 3 in parallel with the rear edge.

In the steam turbine stator vane constructed in this way, the condensate flowing on the surface of the vane is sucked into the cavity 11 through the condensate suction slit 10, passes through the condensate recovery chamber 5, and is discharged to the low-pressure section in Section 2. .

By the way, since the stator vane drain suction slit 10 on the back side is formed near the leading edge, even if all the drain is sucked in here, the drain will be generated downstream due to condensation. This drain is captured by the drain capture groove 4 near the rear edge of the back side and guided to a position where the position in the radial direction is sufficiently small. In this example, since drain suction and drain movement through the grooves 4 are used together, it is particularly effective for turbine stages with high humidity and a large amount of drain, which could not be prevented with conventional hollow stator vanes with only suction slits. Erosion caused by drain occurring downstream on the dorsal side can be effectively prevented.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, drain from the surface of the stator blade is transferred to the rotor blade through the drain capture groove formed on at least one of the dorsal surface and the ventral surface of the stator blade. Since the rotor is guided to a position in the radial direction that does not cause corrosion, corrosion of the rotor blades can be prevented and the efficiency of the turbine stage can be improved.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of the final stage of a steam turbine showing an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along the line ■-■ in FIG. 1, and FIG. 3 is a cross-sectional view taken along ■-■ in FIG. FIG. 4 is a longitudinal sectional view of a steam turbine final stage stator blade showing another embodiment, and FIG.
■Cross-sectional view, Figure 6 is a vertical cross-section of the final stage of a steam turbine showing another embodiment, Figure 7 is a cross-sectional view taken along ■--■ of Figure 6, and Figure 8 is a vertical cross-section of the final stage of a conventional steam turbine. Figure 9 is the 8th
It is a sectional view taken along line IX-IX in the figure. DESCRIPTION OF SYMBOLS 1...Flow path outer peripheral wall, 2...Stator blade inner ring, 3...Stator blade, 4...Drain capture groove, 5...Drain collection cavity, 6
... Communication hole, 7... Moving blade, 8... Drain suction slit, ]0... Stationary blade drain suction slit, 11...
Stationary blade cavity, Fd...Drain flow. Applicant's agent Sato -Yuman 1 Figure 4 Figure 5 Figure 6 Figure 8 Figure 8 You 9 Figure

Claims (1)

[Scope of Claims] 1. A stator blade having an outer peripheral end supported on the outer peripheral wall of the flow path and an inner peripheral end supported on the inner ring of the stator vane, and at least one of the dorsal surface or the ventral surface of the stator vane. A stator blade for a steam turbine, characterized in that a drain capture groove is formed on a surface thereof from a position spaced apart from the outer circumferential wall of the flow path and extends in the longitudinal direction toward the inner ring side of the stator blade. 2. The groove is such that the outer circumferential end of the groove is separated from the outer circumferential wall of the flow path by at least 3 mm or more, and the inner circumferential edge of the groove is 75 mm above the height of the stator vane based on the outer circumferential surface of the inner ring of the stator vane. % or less. 3. The stationary blade for a steam turbine according to claim 1, wherein the groove is formed near the trailing edge of the back side and substantially parallel to the trailing edge. 4. For the above groove, the outer circumferential end of the groove is closer to the front edge of the profile,
Further, the groove is formed such that the inner circumferential end thereof is located near the rear edge of the profile, and the static pressure within the groove decreases from the outer circumferential end toward the inner circumferential end. A stator blade for a steam turbine according to claim 1. 5. Two or more grooves are formed in parallel in the same plane on the dorsal or ventral side of the stationary blade, and the length of the grooves is formed so that the grooves closer to the trailing edge become shorter. A stator blade for a steam turbine according to claim 1. 6. The stationary blade is formed into a hollow structure, and a slit is provided along the longitudinal direction of the stationary blade and perpendicular to the steam flow on the leading edge side of the profile on the back side and the trailing edge side of the profile on the ventral side where the steam pressure is the same. In addition to forming a shaped drain suction port,
2. The stationary blade for a steam turbine according to claim 1, wherein the groove is formed near the trailing edge of the back surface so as to be substantially parallel to the trailing edge.