JP7278903B2 - turbine exhaust chamber - Google Patents

Description

Embodiments of the present invention relate to turbine exhaust chambers.

Improving the thermal efficiency of steam turbines used in thermal power plants and the like has become an important issue leading to effective utilization of energy resources and reduction of carbon dioxide (CO ₂ ) emissions. For that purpose, it is necessary to reduce various internal losses.

Steam turbine internal losses include profile loss due to blade shape, steam secondary flow loss, steam leakage loss, turbine blade cascade loss based on steam wetness loss, steam valves and crossover pipes. There are passage loss in passages other than the cascade of blades, turbine exhaust loss downstream of the final stage of the turbine stage, and so on.

Among these losses, turbine exhaust losses account for 10-20% of total internal losses. Turbine exhaust loss is specifically the loss that occurs between the final stage outlet of the turbine stage and the condenser inlet. Turbine exhaust losses are further classified into reeving losses, hood losses, turnup losses, and the like.

Of these, the hood loss is the pressure loss in the exhaust chamber. Hood loss depends on the type, shape and size of the exhaust chamber.

In general, the pressure loss increases in proportion to the square of the steam flow velocity. Therefore, in order to reduce the hood loss, it is necessary to reduce the flow velocity in the exhaust chamber. For this purpose, it is effective to increase the size of the exhaust chamber. However, from the viewpoint of manufacturing cost and building size, it is desirable that the size of the exhaust chamber is small. Therefore, a method of providing a diffuser structure in the exhaust chamber to reduce the flow velocity of the steam while suppressing the enlargement of the exhaust chamber has been studied.

FIG. 6 is a view showing a vertical meridional section of a conventional double-flow exhaust type (double-flow type) low-pressure turbine 200 provided with a downward exhaust type exhaust chamber.

As shown in FIG. 6 , the steam that has passed through the rotor blades 210 of the final turbine stage is guided to an annular diffuser 222 composed of a steam guide 220 and a bearing cone 221 . The steam led to the annular diffuser 222, which is an enlarged flow path, is decelerated and the static pressure is restored. The steam guided to the annular diffuser is then guided radially outward and discharged into the space 223 surrounded by the outer casing 230 .

Note that the radial direction is a direction perpendicular to the direction of the central axis of the turbine rotor (hereinafter referred to as the axial direction). The radially outer side refers to the side in the radial direction and away from the central axis of the turbine rotor.

The steam released into the space 223 is redirected by the outer casing 230 or the like, and finally guided to a condenser installed below the steam turbine.

In such a low-pressure turbine 200, in order to reduce the pressure loss (static pressure loss) in the exhaust chamber, it is important to decelerate the flow with the annular diffuser 222 and sufficiently recover the static pressure.

In such a conventional low-pressure turbine 200 exhaust chamber, emphasis has been placed on suppressing flow separation at the inlet of the steam guide 220 in order to reduce hood loss. Further, in the conventional exhaust chamber, the hood loss is reduced by making the radially outward expansion of the downstream end of the steam guide 220 uneven in the circumferential direction.

JP 2010-216321 A JP 2018-115581 A

As described above, in the exhaust chamber of the conventional low-pressure turbine 200, reduction of pressure loss within the annular diffuser 222 is mainly considered.

Here, as shown in FIG. 6, the outlet 224 of the annular diffuser 222 defines the width between the outlet end 220a of the steam guide 220 and the inner surface 231a of the side wall 231 in the outer casing 230 in the axial direction from the outlet end 220a. It is composed of passages that are formed along the circumferential direction. Note that the circumferential direction means the circumferential direction around the center axis of the turbine rotor.

Also, in the upper half space 223, the flow of steam that has flowed out of the outlet 224 of the annular diffuser 222 is turned from the radial direction to the axial direction by approximately 90 degrees, as shown in FIG. The diverted steam then passes through passageway 225 .

The passage 225 is formed in the circumferential direction with a width between the outlet end 220a of the steam guide 220 and the inner surface 232a of the upper wall 232 of the outer casing 230 radially outward from the outlet end 220a. be.

Here, the tangent at the outlet end 220a of the steam guide 220 has an angle α with respect to the axial direction. This tangent line is a tangent line to the inner surface of the steam guide 220 (the surface on the annular diffuser 222 side) at the outlet end 220a, as shown in FIG.

Even if sufficient static pressure is restored at the outlet 224 of the annular diffuser 222, if the passage area of the passage 225 is smaller than the passage area of the outlet 224, the flow will be accelerated. This increases the pressure loss.

Also, when the passage area of the passage 225 is larger than the passage area of the outlet 224, the flow deflected in the axial direction is biased radially outward. A high-speed region is formed on the radially outer side, and a low-speed region is formed on the inner peripheral side of the high-speed region. As a result, as shown in FIG. 6, a flow field is formed in which the flow passes through the passage 225 but reverses to the passage 225 side. This reverse flow 240 makes it difficult for the steam to flow smoothly toward the condenser. Then, the pressure loss increases and the hood loss increases.

Also, when the angle α is small, the radially outward drift of the flow deflected in the axial direction becomes pronounced, and the pressure loss due to the reverse flow 240 increases.

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to provide a turbine exhaust chamber that can reduce flow pressure losses downstream of an annular diffuser.

The turbine exhaust chamber of the embodiment passes the working fluid that has flowed out from the final turbine stage of the axial flow turbine including the turbine rotor. The turbine exhaust chamber includes a casing comprising: a first casing portion having an arcuate wall portion curved outwardly; and a tubular second casing portion connected to the first casing portion; provided on the downstream side of the final-stage turbine stage in the interior, has a cylindrical guide and a cylindrical cone provided inside the guide, and directs the working fluid that has passed through the final-stage turbine stage radially outward. and an annular diffuser that discharges towards.

Two imaginary straight lines connecting the two joint points of the first casing portion and the second casing portion and the central axis of the turbine rotor in a cross section perpendicular to the central axis of the turbine rotor. S1 is the passage area of the outlet of the annular diffuser formed in the circumferential direction and configured to include the outlet end of the guide, and When the passage area of the passage formed in the circumferential direction having a width between the end and the inner surface of the first casing portion in the radial direction is S2, the ratio of S2 to S1 (S2/S1) is 0. .8 or more and 1.6 or less, and the angle of the tangent line at the outlet end of the guide with respect to the central axis direction of the turbine rotor is 45 degrees or more and 120 degrees or less , and the outlet end of the guide and the first casing portion A space in which the working fluid that has passed through the passage can flow to the outside of the guide, which is different from the annular diffuser side of the guide, on the downstream side in the flow direction of the working fluid from the passage formed between the inner surface of the is formed .

1 is a view showing a vertical meridional section of a steam turbine having an exhaust chamber according to an embodiment; FIG. It is a figure which shows the meridian cross section of the vertical direction of the exhaust chamber of embodiment. FIG. 3 is a sectional view showing the AA section of FIG. 2; FIG. 4 is a diagram showing the relationship between the angle of the tangential line at the outlet end of the steam guide with respect to the axial direction and the hood loss. FIG. 4 is a diagram showing the relationship between the passage area ratio (S2/S1) at the outlet of the annular passage and the annular diffuser and the hood loss. 1 is a view showing a vertical meridional section of a conventional double-flow exhaust type low-pressure turbine provided with a downward exhaust type exhaust chamber; FIG.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a view showing a vertical meridional section of a steam turbine 1 having an exhaust chamber 30 according to the embodiment. Here, a steam turbine is exemplified as the axial flow turbine. Also, as the steam turbine, a double-flow exhaust type low-pressure turbine having a downward exhaust type exhaust chamber will be exemplified and explained. Therefore, in the following embodiments, the working fluid is steam.

As shown in FIG. 1 , in the steam turbine 1 , an inner casing 11 is provided inside an outer casing 10 . A turbine rotor 12 extends through the inner casing 11 . The turbine rotor 12 is formed with a rotor disk 13 protruding radially outward along the circumferential direction. The rotor disk 13 is formed in multiple stages in the axial direction (turbine rotor central axis direction).

A rotor disk 13 of the turbine rotor 12 has a plurality of rotor blades 14 implanted in the circumferential direction to form a rotor blade cascade. This moving blade cascade is provided in a plurality of stages in the axial direction. The turbine rotor 12 is rotatably supported by rotor bearings 15 .

A diaphragm outer ring 16 and a diaphragm inner ring 17 are provided inside the inner casing 11 . Between the diaphragm outer ring 16 and the diaphragm inner ring 17, a plurality of stator vanes 18 are arranged in the circumferential direction to form a stator vane cascade.

The stator blade cascades are arranged so as to alternate with the rotor blade cascades in the axial direction. A single turbine stage is composed of a stator blade cascade and a rotor blade cascade immediately downstream of the stator blade cascade. Here, the rotor blade provided in the final stage turbine stage (hereinafter referred to as the final turbine stage) is shown as the final stage rotor blade 14a. The final turbine stage is the final turbine stage through which it passes before entering the exhaust chamber 30 .

The center of the steam turbine 1 is provided with an intake chamber 20 into which steam from the crossover pipe 19 is introduced. Steam is distributed and introduced from the intake chamber 20 to the left and right turbine stages.

Next, the exhaust chamber 30 into which the steam that has passed through the final turbine stage flows will be described. This exhaust chamber 30 functions as a turbine exhaust chamber.

FIG. 2 is a view showing a vertical meridional section of the exhaust chamber 30 of the embodiment. FIG. 3 is a cross-sectional view showing the AA cross section of FIG. 3 is a cross-sectional view of the exhaust chamber 30 perpendicular to the turbine rotor central axis O (hereinafter referred to as the central axis O) viewed from the downstream side of the steam guide 60. FIG. In addition, in FIG. 3, for convenience, a part of the configuration is omitted.

The exhaust chamber 30 includes a casing 40 forming an outer shell of the exhaust chamber 30, as shown in FIG. Here, the casing 40 also functions as the outer casing 10 of the steam turbine 1 shown in FIG. Therefore, hereinafter, the casing 40 will be described as the outer casing 10 .

The outer casing 10, which forms the outer shell of the exhaust chamber 30, has an arc-shaped casing portion 41 having an arc-shaped wall portion that is convexly curved outward in the cross section shown in FIG. A cylindrical casing portion 42 is provided. The arcuate casing portion 41 functions as a first casing portion, and the cylindrical casing portion 42 functions as a second casing portion.

Here, the arcuate casing portion 41 has an arcuate wall portion that curves upward. Further, the tubular casing portion 42 is connected to the lower portion of the arcuate casing portion 41 .

In addition, in the cross section shown in FIG. 3 , the shape of the arcuate casing portion 41 is not limited to an arc around the central axis O. A portion of the arcuate casing portion 41 may be linear as shown in FIG.

Here, connecting portions between the arc-shaped casing portion 41 and the cylindrical casing portion 42 are defined as connecting points 43 and 44 in the cross section shown in FIG. Note that the connection points 43 and 44 function as junction points.

The cross-sectional shape of the arcuate casing portion 41 is an arcuate curved outwardly. The arcuate casing portion 41 has a cross-sectional shape that extends in the direction along the central axis O (the direction perpendicular to the paper surface).

The tubular casing portion 42 is a tubular body with an open radial end. In the cross section shown in FIG. 3, the two side walls 42a, 42b of the cylindrical casing portion 42 extend linearly in the vertical direction, for example. The tubular casing portion 42 has a shape in which the cross-sectional shape shown in FIG. 3 extends in the direction along the central axis O (the direction perpendicular to the paper surface). The cylinder constituting the cylindrical casing portion 42 is a box such as a rectangular parallelepiped or a cube having an open surface on the side of the arcuate casing portion 41 and a surface facing the surface on the side of the arcuate casing portion 41 .

Both axial ends of the arcuate casing portion 41 and the cylindrical casing portion 42 are closed by walls.

Here, in the cross section shown in FIG. 3, a virtual straight line connecting the connection point 43 and the central axis O is called a virtual straight line L1, and a virtual straight line connecting the connection point 44 and the central axis O is called a virtual straight line L2.

The connection point 43 and the connection point 44 are end points on the inner surface side (the inner surface side of the outer casing 10) of the joint portion between the arc-shaped casing portion 41 and the cylindrical casing portion 42. As shown in FIG.

As shown in FIG. 3, connection points 43 and 44 between the arcuate casing portion 41 and the cylindrical casing portion 42 are located on the arcuate casing portion 41 side of the horizontal straight line passing through the central axis O, for example. Here, the connection points 43 and 44 are located above the horizontal straight line passing through the central axis O. As shown in FIG.

Therefore, in the cross section shown in FIG. 3, the virtual straight line L1 and the virtual straight line L2 extend obliquely from the central axis O toward the arcuate casing portion 41 side. That is, the imaginary straight line L1 is a straight line obtained by rotating a horizontal straight line extending from the central axis O toward the connection point 43 (left side in FIG. 3) around the central axis O by a predetermined angle. The imaginary straight line L2 is a straight line obtained by rotating a horizontal straight line extending from the central axis O toward the connection point 44 (right side in FIG. 3) counterclockwise about the central axis O by a predetermined angle.

Here, for the sake of convenience, the area on the side of the arcuate casing portion 41 that includes the virtual straight lines L1 and L2 will be referred to as the area on the side of the arcuate casing portion.

As shown in FIG. 2, the exhaust chamber 30 includes an annular diffuser 50 into which the steam that has passed through the final turbine stage flows, and an exhaust passage 80 that guides the steam discharged from the annular diffuser 50 to the outlet 31 of the exhaust chamber 30. . Note that the outlet 31 of the exhaust chamber 30 may be, for example, an opening or may be configured by a flat plate member having a plurality of openings.

A condenser (not shown), for example, is provided downstream of the outlet 31 of the exhaust chamber 30 . In the embodiment shown here, below the outlet 31 of the exhaust chamber 30, for example, a condenser (not shown) is provided.

The annular diffuser 50 discharges steam that has passed through the final turbine stage radially outward. The annular diffuser 50 is an annular passage formed by a tubular steam guide 60 and a tubular bearing cone 70 provided inside the steam guide 60 . That is, the annular diffuser 50 is an annular channel formed between the steam guide 60 and the bearing cone 70 . The steam guide 60 functions as a guide, and the bearing cone 70 functions as a cone.

An upstream end 70a of the bearing cone 70 is positioned slightly downstream of the rotor disk 13 in which the final stage rotor blade 14a is implanted. The bearing cone 70 curves radially outward as it goes downstream. That is, the bearing cone 70 is formed in an enlarged tubular shape that expands like a trumpet toward the downstream side. A downstream end 70 b of the bearing cone 70 abuts the downstream wall 45 of the outer casing 10 . For example, the rotor bearing 15 is arranged inside the bearing cone 70 .

Here, the steam guide 60 and the bearing cone 70 are configured in a vertically split structure. The steam guide 60 and the bearing cone 70 are divided into upper and lower halves on a horizontal plane including the central axis O, for example.

For example, a cylindrical steam guide 60 is composed of an upper half steam guide and a lower half steam guide. Similarly, a cylindrical bearing cone 70 is composed of the upper half bearing cone and the lower half bearing cone.

The upper half steam guide and the lower half steam guide are, for example, configured with the same shape. The upper half side bearing cone and the lower half side bearing cone are configured with the same shape, for example.

An upstream end 60a of the steam guide 60 is connected to a downstream end 16a of the diaphragm outer ring 16 surrounding the last stage rotor blade 14a. The steam guide 60 curves radially outward as it goes downstream.

That is, the steam guide 60 is configured in an enlarged tubular shape that expands toward the downstream side like a trumpet. In other words, the steam guide 60 expands in a trumpet shape while expanding radially outward as it goes in the turbine exhaust direction and in the axial direction.

The angle θ of the tangent line M at the outlet end 60b of the steam guide 60 with respect to the axial direction is set to 45 degrees or more. Here, the angle θ will be specifically described. An end portion on the inner peripheral side (passage side as the annular diffuser 50) of the outlet end 60b is defined as an inner peripheral end portion 60c.

Further, let N be a horizontal line extending from the inner peripheral end 60c toward the downstream wall 45 side, and let M be a tangent to the inner peripheral end 60c. In other words, the horizontal line N is a line extending in the axial direction. In this case, the angle θ is the counterclockwise angle from the horizontal line N to the tangent line M.

The outlet end 60b of the steam guide 60 is formed, for example, with an angle θ in the circumferential direction.

Here, as shown in FIG. 3, in the arcuate casing portion side region, there is a width W1 between the outlet end 60b of the steam guide 60 and the inner surface 46 of the outer casing 10 in the radial direction from the outlet end 60b. A passage 90 is formed in the circumferential direction. In addition, in FIG. 3, the passage 90 is indicated by a dashed-dotted line.

As shown in FIG. 3, the passageway 90 is a portion of a substantially annular passageway circumferentially formed between the outlet end 60b of the steam guide 60 and the inner surface 46 of the outer casing 10. As shown in FIG.

In addition, in the arc-shaped casing portion side region, as shown in FIG. 3, when a part of the arc-shaped casing portion 41 is linear, the width W1 may vary depending on the position in the circumferential direction.

Here, by setting the angle θ to 45 degrees or more, the flow is smoothly diverted to the passage 90 side after passing through the annular diffuser 50 in the arc-shaped casing portion side region. Thereby, the pressure loss (hood loss) in the exhaust passage 80 can be reduced.

Further, by setting the angle θ to 45 degrees or more in the circumferential direction, the direction of the flow toward the passage 90 after passing through the annular diffuser 50 is done smoothly. The area other than the arc-shaped casing side area is an area below the virtual straight lines L1 and L2.

Here, setting the angle .theta. As a result, it is possible to smoothly turn the flow toward the passage 90 after passing through the annular diffuser 50 . From this point of view, it is more preferable to set the angle θ to 70 degrees or more.

When the angle θ exceeds 90 degrees, the outlet end 60b side of the steam guide 60 warps to the side opposite to the downstream wall 45 side of the outer casing 10 . At a portion where the angle θ exceeds 90 degrees in the steam guide 60, it is difficult to make the flow flow along the steam guide 60 completely. However, the shape of the outlet end 60 b of the steam guide 60 follows the flow from the outlet 51 of the annular diffuser 50 to the passage 90 . Therefore, an angle θ exceeding 90 degrees does not cause an increase in pressure loss.

However, from the viewpoint of manufacturing, it is preferable to set the upper limit of the angle θ to about 120 degrees. Even if the angle θ is set in a range exceeding 120 degrees, the effect of further reducing the pressure loss cannot be obtained.

Therefore, it is preferable that the angle θ is set to 45 degrees or more and 120 degrees or less. Further, it is more preferable that the angle θ is set to be 60 degrees or more and 100 degrees or less. Furthermore, it is more preferable that the angle θ is set to 70 degrees or more and 90 degrees or less.

Here, in the arc-shaped casing portion side region, the passage area of the outlet 51 of the annular diffuser 50 formed in the circumferential direction is set to S1, and the passage area of the passage 90 is set to S2.

The outlet 51 of the annular diffuser 50 is, for example, as shown in FIG. It is composed of a passage formed along the circumferential direction with a width W2 between itself and the inner surface 45a. That is, the shape of the passage at the outlet 51 is the shape of a cylindrical side surface.

Here, FIG. 2 shows an example in which the outlet 51 of the annular diffuser 50 is formed between the inner peripheral end 60c of the steam guide 60 and the inner surface 45a of the downstream wall 45. As shown in FIG. For example, when the downstream end 70b of the bearing cone 70 extends up to the same horizontal plane as the inner peripheral end 60c of the steam guide 60, the outlet 51 of the annular diffuser 50 includes the inner peripheral end 60c and the bearing cone. It is formed between the inner surface of the downstream end 70b of 70 (passage side as the annular diffuser 50).

In this case, the outlet 51 of the annular diffuser 50 extends circumferentially with a width W2 between the inner peripheral edge 60c and the inner surface of the downstream end 70b of the bearing cone 70 axially from the inner peripheral edge 60c. It consists of a passageway formed through it.

The above-described passage area S1 is the passage area of the outlet 51 located in the arc-shaped casing portion side region among the outlets 51 formed in the circumferential direction. In the cross section shown in FIG. 3, when the point where the imaginary straight line L1 and the outlet end 60b of the steam guide 60 intersect is P, and the point where the imaginary straight line L2 and the outlet end 60b of the steam guide 60 intersect is Q, a circular arc PQ (the arc on the side of the arcuate casing portion 41) is the outlet 51 in the area on the side of the arcuate casing portion.

In the arc-shaped casing portion side region, the passage 90 and the outlet 51 of the annular diffuser 50 are set so that the ratio (S2/S1) of the passage area S2 to the passage area S1 is 0.8 or more and 1.6 or less. .

Here, in the arc-shaped casing portion side region, the steam flowing out from the outlet 51 and turned toward the passage 90 flows biased radially outward. That is, the main stream of the flow toward the passage 90 side is biased toward the inner surface 46 side of the arcuate casing portion 41 . This drift increases the flow rate of steam on the radially outer side.

Therefore, even if S2/S1 is less than 1.0, if S2/S1 is greater than or equal to 0.8, the throttling action will not work and the diverted flow will not be significantly accelerated in passage 90. FIG. As a result, even if S2/S1 is less than 1, when it is 0.8 or more, the pressure loss caused by acceleration can be suppressed.

On the other hand, when S2/S1 is less than 0.8, the reduction in passage area from outlet 51 to passage 90 is large and the diverted flow is accelerated. Therefore, the pressure loss increases and the hood loss increases.

For this reason, the lower limit of S2/S1 is set to 0.8 or more.

When S2/S1 is greater than or equal to 1.0, there is no decrease in passage area from outlet 51 to passage 90. However, when S2/S1 exceeds 1.6, a low-speed region is formed on the inner peripheral side (radially inward) in the flow field of the steam that flows biased radially outward and is diverted to the passage 90 side.

As a result, a flow field is formed in which the flow that has passed through the passage 90 flows backward to the passage 90 side, similar to the flow field that forms the reverse flow 240 shown in FIG. This reverse flow makes it difficult for the steam to flow smoothly toward the condenser. As a result, the pressure loss increases and the hood loss increases.

For this reason, the upper limit of S2/S1 is set to 1.6 or less.

Therefore, S2/S1 is set to 0.8 or more and 1.6 or less. From the viewpoint of further reducing hood loss, S2/S1 is more preferably set to 1.0 or more and 1.2 or less even within this range.

Here, the flow of steam in the steam turbine 1 and the exhaust chamber 30 will be described with reference to FIGS. 1 to 3. FIG.

As shown in FIG. 1 , the steam that has flowed into the intake chamber 20 in the steam turbine 1 via the crossover pipe 19 branches and flows into left and right turbine stages. Then, the steam passes through the steam flow path provided with the stationary blades 18 and moving blades 14 of each turbine stage while performing expansion work, and rotates the turbine rotor 12 . After passing through the final turbine stage, the steam flows into annular diffuser 50 .

As shown in FIGS. 2 and 3, the steam that has flowed into the annular diffuser 50 flows toward the outlet 51 while its flow direction is turned radially outward. At this time, the steam flow is decelerated and static pressure is restored. Then, the steam flows radially outward from the outlet 51 into the exhaust passage 80 .

Here, the angle θ of the tangent line M at the outlet end 60b of the steam guide 60 with respect to the axial direction is set within the range described above. Therefore, the working fluid flowing out of the outlet 51 is smoothly diverted to the passage 90 side. As a result, the pressure loss when turning to the passage 90 side is reduced.

For example, in the arc-shaped casing portion side region, the flow direction of the working fluid that has flowed out from the outlet 51 is turned to the passage 90 side and is turned downward. Then, the working fluid whose flow direction is turned downward flows toward the outlet 31 of the exhaust chamber 30 .

Here, in the arc-shaped casing portion side region, the passage area ratio (S2/S1) between the passage 90 and the outlet 51 of the annular diffuser 50 is set within the range described above. Therefore, the flow smoothly flows without being accelerated. Thereby, the pressure loss that occurs when the working fluid flows through the exhaust passage 80 can be suppressed. Furthermore, the flow that has passed through the passage 90 does not flow back to the passage 90 side.

On the other hand, the flow direction of the working fluid flowing out from the outlet 51 on the lower half side is turned downward. Then, the working fluid whose flow direction is turned downward flows toward the outlet 31 of the exhaust chamber 30 .

The working fluid discharged from the outlet 31 of the exhaust chamber 30 flows into, for example, a condenser (not shown).

(Evaluation of hood loss)
FIG. 4 is a diagram showing the relationship between the angle θ of the tangential line M at the outlet end 60b of the steam guide 60 with respect to the axial direction and the hood loss. In FIG. 4, the horizontal axis represents the angle θ, and the vertical axis represents the hood loss. The results shown in FIG. 4 were obtained by numerical analysis with the passage area ratio (S2/S1) of the passage 90 and the outlet 51 of the annular diffuser 50 set to 1.0.

Here, in the arc-shaped casing portion side region, the threshold value is the point at which the hood loss that occurs downstream of the outlet 51 of the annular diffuser 50 becomes the maximum allowable value from the viewpoint of performance.

As shown in FIG. 4, the hood loss decreases as the angle θ increases. The hood loss becomes equal to or less than the threshold when the angle θ is 45 degrees or more. The hood loss becomes substantially constant when the angle θ is 70 degrees or more. The hood loss is maintained at a constant value even when the angle θ is 120 degrees.

From the results shown in FIG. 4, it can be seen that the hood loss is suppressed to a small value below the threshold when the angle θ is 45 degrees or more. Also, it can be seen that the small value is maintained even when the angle θ is 120 degrees.

Next, FIG. 5 is a diagram showing the relationship between the passage area ratio (S2/S1) in the passage 90 and the outlet 51 of the annular diffuser 50 and the hood loss. In FIG. 5, the horizontal axis represents S2/S1, and the vertical axis represents hood loss. The results shown in FIG. 5 were obtained by numerical analysis when the angle θ of the tangential line M at the outlet end 60b of the steam guide 60 with respect to the axial direction was 70 degrees. Note that the definition of the threshold is the same as the definition of the threshold in FIG.

As shown in FIG. 5, the hood loss decreases to 1.1 as S2/S1 increases, and gradually increases when S2/S1 exceeds 1.1. The hood loss is equal to or less than the threshold when S2/S1 is 0.8 or more and 1.6 or less. The hood loss shows a small value when S2/S1 is 1.0 or more and 1.2 or less.

From the results shown in FIG. 4, it can be seen that the hood loss is suppressed to a small value below the threshold when S2/S1 is in the range of 0.8 to 1.6.

(Other embodiments)
In the embodiment described above, as shown in the cross section of FIG. 3, an example in which the virtual straight line L1 and the virtual straight line L2 extend obliquely from the central axis O toward the arcuate casing portion 41 side has been shown. That is, in the embodiment described above, an example in which the connection points 43 and 44 are positioned above the horizontal straight line passing through the central axis O is shown. In the above-described embodiment, an example is shown in which the connection points 43 and 44 between the arcuate casing portion 41 and the cylindrical casing portion 42 are positioned closer to the arcuate casing portion 41 than the horizontal straight line passing through the central axis O. .

However, the positions of the connection points 43 and 44 between the arcuate casing portion 41 and the cylindrical casing portion 42 are not limited to this configuration.

For example, connection points 43 and 44 between the arcuate casing portion 41 and the cylindrical casing portion 42 may be on a horizontal straight line passing through the central axis O. In this case, in the cross section shown in FIG. 3, an imaginary straight line L1 connecting the connecting point 43 and the central axis O and an imaginary straight line L2 connecting the connecting point 44 and the central axis O are on the same straight line passing through the central axis O. .

Also, the connection points 43 and 44 may be positioned below the horizontal straight line passing through the central axis O. In this case, in the cross section shown in FIG. 3, the connection points 43 and 44 between the arcuate casing portion 41 and the cylindrical casing portion 42 are positioned closer to the cylindrical casing portion 42 than the horizontal straight line passing through the central axis O. .

In this case, in the cross section shown in FIG. 3, the virtual straight line L1 and the virtual straight line L2 extend obliquely from the central axis O toward the tubular casing portion 42 side. That is, the imaginary straight line L1 is a straight line obtained by rotating a horizontal straight line extending from the central axis O to the connection point 43 side (left side in FIG. 3) counterclockwise about the central axis O by a predetermined angle. The imaginary straight line L2 is a straight line obtained by rotating a horizontal straight line extending from the central axis O to the connection point 44 side (right side in FIG. 3) clockwise around the central axis O by a predetermined angle.

Also in the other embodiment described above, the arc-shaped casing side region is configured to satisfy the ratio (S2/S1) of the passage area S2 to the passage area S1. Furthermore, the exit end 60b of the steam guide 60 is configured to satisfy the angle θ described above.

In the above-described embodiment, the steam turbine 1 is described by exemplifying a double-flow exhaust type low-pressure turbine having a downward exhaust type exhaust chamber. It can also be applied to turbines. Further, the exhaust chamber 30 of the embodiment can be applied not only to the exhaust chamber of a low-pressure steam turbine, but also to the exhaust chamber of a high-pressure or intermediate-pressure steam turbine.

According to the embodiments described above, it is possible to reduce the pressure loss of the flow downstream of the annular diffuser.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and equivalents thereof.

DESCRIPTION OF SYMBOLS 10... Outer casing, 11... Inner casing, 12... Turbine rotor, 13... Rotor disk, 14... Moving blade, 14a... Last-stage moving blade, 15... Rotor bearing, 16... Diaphragm outer ring, 16a... Downstream end, 17... Diaphragm Inner ring 18 Stator vane 19 Crossover pipe 20 Intake chamber 30 Exhaust chamber 31, 51 Outlet 40 Casing 41 Circular casing 42 Cylindrical casing 42a, 42b Side wall 43, 44 Connection point 45 Downstream wall 45a, 46 Inner surface 50 Annular diffuser 60 Steam guide 60a, 70a Upstream end 60b Outlet end 60c Inner peripheral end 70... Bearing cone, 70b... Downstream end, 80... Exhaust passage, 90... Annular passage.

Claims (1)

A turbine exhaust chamber through which a working fluid flowing out from a final stage turbine stage of an axial flow turbine having a turbine rotor passes,
a casing comprising a first casing portion having an arc-shaped wall portion curved outwardly and a cylindrical second casing portion connected to the first casing portion;
provided in the casing on the downstream side of the final-stage turbine stage, and having a cylindrical guide and a cylindrical cone provided inside the guide; with an outwardly emitting annular diffuser and
Two imaginary straight lines connecting the two joint points of the first casing portion and the second casing portion and the central axis of the turbine rotor in a cross section perpendicular to the central axis of the turbine rotor. In the area on the side of the first casing part including
Let S1 be the passage area of the exit of the annular diffuser formed in the circumferential direction and configured to include the exit end of the guide ,
When the passage area of the passage formed in the circumferential direction having the width between the outlet end of the guide and the inner surface of the first casing portion in the radial direction from the outlet end is S2,
The ratio of S2 to S1 (S2/S1) is 0.8 or more and 1.6 or less, and the angle of the tangent line at the outlet end of the guide with respect to the central axis direction of the turbine rotor is 45 degrees or more and 120 degrees or less ,
on the outer side of the guide different from the annular diffuser side of the guide on the downstream side in the flow direction of the working fluid from the passage formed between the outlet end of the guide and the inner surface of the first casing portion. A turbine exhaust chamber , wherein a space is formed in which the working fluid that has passed through the passage can flow .

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