JPH10299410A - Moisture discharging structure of steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent erosion of a dynamic blade from occurring, by installing a moisture induction groove, which promotes the drain discharging downstream from the back edge end of a stator blade, on an inner wall of an external ring which holds the stator blade of a stream turbine, and by structuring the moisture induction groove such that its width is widened in the flowing direction of fluid or its depth is slanted. SOLUTION: In a stream turbine, plural stator blades 3 are radially arranged in the enlarged passage, these stator blades 3 are held by an external and an internal ring forming the enlarged passage, and a dynamic blade is installed downstream of these static blades 3. On the outer surface of the inflow end downstream of the outer ring, a annual circumferencial slit 7 is formed, and in this case, a moisture induction groove 9 which expands from a back edge end 8 of the stator blade 3 to the circumferencial slit 7 is installed along the flow direction of the fluid from the back edge end 8 of each stator blade 3 to the end of the outer ring. Therefore, drain gathered on a inner wall 10 of the outer ring is flown down by the moisture induction groove 9, and all drain are lead to the circumferencial slit 7, and are discharged from the slit 7 in an annular groove on outside of the turbine passage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a structure for discharging moisture from a steam turbine.

[0002]

2. Description of the Related Art In a large-capacity steam turbine, moisture, such as water droplets and a water film, is discharged from a turbine passage in order to prevent erosion caused by droplets in wet steam in a turbine passage colliding with a rotor blade. Is provided.

FIG. 8 shows a conventional example of a drain discharge structure provided in a low-pressure final stage of a steam turbine. In FIG.
And an outer circumferential ring 7 which holds a stationary blade 3 disposed in front of the outer ring 2 and an annular circumferential slit 7 is formed in the outer peripheral portion of the inflow end at the tip of the moving blade 5 downstream of the outer ring 2.

The drain 11 accumulated on the inner wall 10 of the outer ring 2 flows downstream by the steam flow, is discharged from the circumferential slit 7 into an annular groove 12 outside the turbine passage, and is further condensed through a hole 13 (not shown). It is discharged to the low pressure side of the vessel.

[0005]

In the above-described structure, on the inner wall 10 of the outer race 2, as shown in detail in FIG. 9, the drain 11 condensed in the low pressure portion has a higher inertia than the steam, so that the stationary blade 3 is pressed against the abdominal surface 15 and flows. Further, a part of the drain 11 concentrated on the abdominal surface 15 reaches the blade back surface 16 by the secondary flow in the cascade.

As a result, the drain 11 is formed on the abdominal surface 15 of the stationary blade 3.
Then, it concentrates on the back surface 16 and reaches the trailing edge 8 of the vane 3. The wing trailing edge 8 has a wing thickness, and a part of the water film flow of the drain 11 is torn to become a water droplet 17. Although a part of the water droplet 17 adheres again to the inner wall 10 of the outer ring 2 due to the centrifugal force, the water droplet 17 flows out from the trailing edge 8 of the vane 3 at an initial velocity of zero, so that the centrifugal force is small, and most of the water droplet flows down with the steam flow. However, it is difficult to discharge from the circumferential slit 7.

As a result, a part of the drain 11 flowing along the inner wall 10 of the outer ring 2 separates from the inner wall 10 of the outer ring 2 before reaching the circumferential slit 7, and the rotor blades arranged rearward Since the water droplets 17 are concentrated and flow down to the tip of the blade 5, the occurrence of partial erosion at the tip of the bucket 5 has been a problem.

Further, since the circumferential slit 7 has a narrow gap so as to prevent steam from leaking as much as possible, the drain 11 flowing into the circumferential slit 7 becomes a water film and closes the circumferential slit 7, so that the amount of inflow is reduced. And the balance of emissions cannot be maintained. As a result, the drain 11 not discharged by the circumferential slit 7 flows down to the rotor blade 5 together with the steam flow, which causes erosion.

An object of the present invention is to provide a drain discharge structure for a steam turbine which can reliably discharge drain flowing along the inner wall of an outer ring to the outside of a passage, thereby effectively preventing erosion of a moving blade. It is in.

[0010]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention promotes drain discharge on the inner wall of an outer ring holding a stationary blade of a steam turbine, downstream of the trailing edge of the stationary blade. A moisture guiding groove is provided, and the shape of the moisture guiding groove extending from the trailing edge of the stationary blade to the circumferential slit is gradually widened or inclined in the flow direction of the fluid.

Further, the length of the slit is reduced or a plurality of narrow grooves for preventing water film are formed along the circumferential slit so that moisture guided to the circumferential slit does not block the circumferential slit as a water film. It is provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated practical examples. FIG. 1 is a longitudinal sectional view showing a partial section of a paragraph section employed in a steam turbine.
In this paragraph, an enlarged flow path is formed by the outer ring 2 held by the turbine inner casing 1 and the inner ring 4 holding the stationary blades 3. Are located. The stationary blade 3 is held by the outer ring 2 and the inner ring 4 forming an enlarged flow path. A moving blade 5 is planted on a disk 6 downstream of the stationary blade 3. An outer ring 2 that holds a stationary blade 3 disposed in front of a moving blade 5, and an annular circumferential slit 7 in an outer peripheral portion of an inflow end of the moving blade 5 downstream of the outer ring 2.
Are formed. A moisture guiding groove extending from the trailing edge 8 of the stationary blade 3 to the circumferential slit extends from the trailing edge 8 of each stationary blade 3 to the end of the outer ring 2 as shown in FIGS. It is provided along the flow direction of the fluid.

According to the configuration of this embodiment, the moisture guide groove 9 extending from the trailing edge 8 of the stator vane 3 to the circumferential slit 7 is provided on the inner wall 10 of the outer ring 2. 2
The drain 11 gathered on the inner wall 10 of the outer ring 2 flows down by the moisture guiding groove 9, and all the drain gathered on the inner wall 10 of the outer ring 2 can be guided to the circumferential slit 7 for drain discharge. Then, the gas is discharged from the circumferential slit 7 into the annular groove 12 outside the turbine passage, and further discharged through the hole 13 to a low pressure side such as a condenser (not shown).

Therefore, unlike the conventional structure, the outer ring 2
Part of the drain 11 accumulated on the inner wall 10 of the moving blade 5 is effectively prevented from reaching the tip of the moving blade 5 disposed behind, and erosion is intensively generated at the tip of the moving blade 5. Can be prevented.

Next, another embodiment of the present invention will be described with reference to FIG. The moisture guiding groove 9 extending from the trailing edge 8 of the stator vane 3 to the circumferential slit 7 has a structure in which the groove width is increased toward the circumferential slit 7 and the groove width is increased. Even when the amount of the drain 11 flowing into the guide groove 9 increases, when the moisture guide groove 9 reaches the circumferential slit 7, the groove width of the moisture guide groove 9 is increased, so that the circumferential slit 7 is increased.
The drain does not concentrate on the local area, and the closure of the circumferential slit 7 by the liquid film can be prevented. Therefore, since the drain does not overflow from the circumferential slit 7, there is no scattering of water droplets, and it is possible to prevent erosion from being generated at the tip of the bucket 5.

Further, as shown in FIG. 5, the above-mentioned effect can also be obtained by adopting a structure in which the depth of the moisture guiding groove 9 is increased toward the circumferential slit 7 and the groove depth is increased. It is possible to discharge the drain to the circumferential slit 7 more reliably.

Next, another embodiment of the present invention will be described with reference to FIG. By providing a plurality of water film preventing slits 14 directed toward the exit direction of the slit on a side wall such as an exit portion of the moisture guiding groove 9 on an end portion of the outer ring 2 forming the circumferential slit 7, the moisture guiding groove 9 is formed. When the drained water flows into the circumferential slit 7, it does not become a water film, so that it is possible to prevent the circumferential slit 7 from being closed. Further, since the slit area can be increased only at the outlet of the moisture guiding groove 9 and the slit width of the other portions can be reduced or reduced as in the related art, the amount of steam discharged together with the drain can be reduced, and Performance can be improved.

Next, another embodiment of the present invention will be described with reference to FIG. By reducing the circumferential length of the circumferential slit 7, the area where the drain flowing into the circumferential slit 7 becomes a liquid film is reduced, so that the circumferential slit 7 is not blocked and the drain can be more reliably discharged. It becomes possible to discharge.

By performing the above, drain can be efficiently discharged from the circumferential slit 7.
The drain does not overflow from the circumferential slit 7 and water droplets do not scatter. Therefore, it is possible to prevent erosion from occurring at the tip of the bucket 5.

[0020]

According to the present invention, in the steam turbine, the drain flowing along the inner wall of the outer ring can be reliably discharged to the outside of the passage, whereby the erosion of the rotor blade can be effectively prevented. .

[Brief description of the drawings]

FIG. 1 is a partial longitudinal sectional view showing a stage of a steam turbine of the present invention.

FIG. 2 is an explanatory view showing a moisture guiding groove of the present invention.

FIG. 3 is a longitudinal sectional view showing a moisture guiding groove of the present invention.

FIG. 4 is an explanatory view of a moisture guiding groove showing another embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of a moisture guiding groove showing another embodiment of the present invention.

FIG. 6 is an explanatory view of a water film prevention slit showing another embodiment of the present invention.

FIG. 7 is a longitudinal sectional view of a circumferential slit showing another embodiment of the present invention.

FIG. 8 is a longitudinal sectional view showing a conventional moisture discharge structure of a steam turbine.

FIG. 9 is an explanatory diagram of moisture in FIG. 8;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Casing, 2 ... Outer ring, 3 ... Static wing, 4 ... Inner ring, 5 ...
Rotor blade, 6 disk, 7 peripheral slit, 8 blade edge, 9 moisture guiding groove, 10 inner wall, 11 drain, 12
... annular groove, 13 ... hole, 14 ... water film prevention slit, 15 ...
Abdominal surface, 16 ... rear surface, 17 ... water droplets.

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yasuaki Sawamura 7-2-1, Omika-cho, Hitachi City, Ibaraki Pref. Hitachi, Ltd. Power & Electricity Development Division

Claims (5)

[Claims] 1. A moisture discharging mechanism provided with a circumferential slit for discharging moisture to a low pressure portion such as a condenser downstream of an outer ring to which a plurality of stationary blades of a steam turbine are fixed. A moisture discharge structure for a steam turbine, wherein a moisture guide groove is provided on an inner wall of an outer ring holding a stationary blade from a trailing edge of the stationary blade to an end of the outer ring. 2. The moisture discharge structure for a steam turbine according to claim 1, wherein the moisture guide groove extends from a trailing edge of the stationary blade to an end of the outer ring, and the groove width gradually changes. 3. A moisture discharge structure for a steam turbine according to claim 1, wherein said moisture guide groove extends from the trailing edge of the stationary blade to the end of the outer ring, and the groove depth is gradually changed. 4. The moisture discharging structure of a steam turbine according to claim 1, wherein a plurality of water film preventing slits are provided on a side wall forming the circumferential slit, which is an end of the moisture guiding groove. 5. The moisture discharge structure for a steam turbine according to claim 1, wherein a water film stagnation region is reduced by shortening a circumferential length of the circumferential slit for discharging the moisture.