JP2015098824A - Steam turbine low-pressure exhaust chamber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steam turbine low-pressure exhaust chamber capable of further exhibiting a pressure loss reduction effect due to expansion of an upper half of a low-pressure turbine outer casing without changing current basic specifications such as a size of a lower half of the low-pressure turbine outer casing.SOLUTION: A low-pressure exhaust chamber includes: a low-pressure turbine outer casing 5 of upper/lower-half split structure surrounding a low-pressure turbine inner casing 2, a bearing cone 3, and a flow guide 4; and an inner strength member 15 provided in the low-pressure turbine outer casing 5. An axial size of an upper half of the low-pressure turbine outer casing 5 is larger than that of a lower half of the low-pressure turbine outer casing 5, an axial size of an upper half of the bearing cone 3 is larger than that of a lower half of the bearing cone 3 in response to axial extension of the upper half of the low-pressure turbine outer casing 5, the upper half is smaller than the lower half in a distance from an outer wall of the bearing cone 3 to a central axis O of a turbine rotor 1 in each in-plane cross-section orthogonal to the central axis O of the turbine rotor 1.

Description

  The present invention relates to a low pressure exhaust chamber of a steam turbine.

  A power plant that generates power by rotating a turbine with steam generated by a steam generator such as a boiler is generally composed of a plurality of turbines corresponding to steam pressure, such as a high-pressure turbine and a low-pressure turbine. The steam generated by the steam generator sequentially passes from the high-pressure turbine to the low-pressure turbine, finishes the rotary work, and is finally introduced into the condenser. There, it condenses into condensate and returns to the steam generator again.

  Immediately after the exit of each of the high, medium, and low pressure turbines, a steam flow path portion called an exhaust chamber is provided, and the turbine efficiency is improved by improving the static pressure recovery performance accompanying the improvement of the flow path portion. . The exhaust chamber generally has a shape with a sudden flow diversion. For this reason, in the exhaust chamber, the flow of steam is disturbed and pressure loss is likely to occur. In particular, the pressure loss in the low-pressure exhaust chamber, which is the steam passage section from the outlet of the low-pressure turbine to the condenser, has a great influence on the plant performance. For this reason, it is important to reduce the pressure loss in the low pressure exhaust chamber.

  In recent years, a low-pressure exhaust chamber generally includes a low-pressure turbine internal casing that encloses a turbine rotor, and a low-pressure turbine external casing having a vertically divided structure that surrounds the low-pressure turbine internal casing. Furthermore, it has an enlarged flow path called a diffuser composed of a flow guide connected to the end of the low-pressure turbine internal casing and a cover provided around or around the outer wall of the bearing cone surrounding the turbine rotor bearing. By devising this channel shape, high static pressure recovery performance is realized.

  The most effective method for reducing the pressure loss in the low-pressure exhaust chamber is to increase the external dimensions of the low-pressure exhaust chamber, that is, the dimensions of the low-pressure turbine outer casing. As a result, it is possible in principle to significantly reduce the pressure loss by significantly reducing the flow velocity of the steam discharged from the low-pressure turbine. However, increasing the external dimensions not only increases the cost of the turbine body and turbine building, but is also not preferable from the viewpoint of rotor shaft vibration. Therefore, in practice, the external dimensions of the low-pressure exhaust chamber are limited to a certain width. However, this restriction is mainly applied to the low-pressure turbine outer casing on the lower half side that supports the load of the turbine rotor, etc., and the low pressure on the upper half side that is separated from direct interference with the turbine rotor and bearings. The turbine outer casing is less restrictive to dimensional changes than the lower half.

  As a method for reducing the pressure loss in the low-pressure exhaust chamber considering the difference in the constraints on the upper and lower half of the low-pressure turbine outer casing, the upper half side plate of the low-pressure turbine outer casing is pivoted with respect to the lower half side plate of the low-pressure turbine outer casing. There is one in which the fluid flowing out from the diffuser is smoothly turned by expanding in the direction and expanding the diffuser flow path in the upper half (see Patent Document 1).

JP-A-8-260904

  The technique described in Patent Document 1 described above discloses only a two-dimensional configuration and does not fully consider the influence of a three-dimensional flow field. For this reason, there is a case where the effect of reducing the pressure loss due to the enlargement of the upper half of the low pressure turbine external casing cannot be fully exhibited. In particular, when the ratio of the axial dimension of the diffuser flow path to the moving blade length in the final stage of the turbine is significantly lower than the appropriate dimension ratio, the influence becomes large.

  For example, the bearing cone and its cover are usually formed so as to be vertically symmetrical, that is, the curvature of the wall surfaces of the upper and lower half portions of the bearing cone and the like are the same. However, when the axial dimensions of the low-pressure turbine outer casing are made different in the upper and lower half parts, the appropriate curvature of the bearing cone and the like also differs in the upper and lower half parts accordingly. Therefore, when the upper half of the low pressure turbine external casing is extended in the axial direction relative to the lower half, even if the upper half of the bearing cone is extended without changing the curvature in the axial direction, It is not an appropriate diffuser flow path for improving the performance of the low-pressure exhaust chamber, and the effect of reducing the pressure loss is not sufficiently exhibited. In particular, when the ratio of the axial dimension of the diffuser flow path to the blade length becomes small, the difference in the appropriate curvature of the upper and lower half portions of the bearing cone and the like becomes more conspicuous, which greatly affects the effect of reducing pressure loss.

  The low-pressure exhaust chamber is an extremely three-dimensional flow field and is divided into a plurality of small chambers (spaces) by a plurality of strength members that reinforce the exhaust chamber. A partial enlargement of the upper half does not necessarily produce the intended flow. In particular, of the flow discharged from the diffuser flow path, the flow in the vicinity of the virtual horizontal plane (side flow) passing through the joint surfaces of the upper and lower halves of the low pressure turbine external casing spreads in the width direction of the low pressure turbine external casing. However, the analysis shows that it is greatly influenced by the plate-like strength member provided in the lower half of the low-pressure turbine outer casing. That is, there is a great difference in the uniformity of the flow distribution depending on which of the plurality of small rooms (spaces) divided by the strength member passes through this side flow. In general, the pressure loss increases with non-uniform flow distribution.

  The present invention has been made to solve the above problems, and its purpose is to change the basic specifications such as the dimensions of the lower half of the current low-pressure turbine outer casing and the support structure of the turbine rotor. In addition, the present invention provides a low-pressure exhaust chamber for a steam turbine that can further exhibit the effect of reducing the pressure loss by expanding the upper half of the low-pressure turbine outer casing.

In order to solve the above problems, for example, the configuration described in the claims is adopted.
The present application includes a plurality of means for solving the above-described problems. For example, the low-pressure exhaust chamber of the steam turbine that guides exhaust after driving the turbine rotor to a condenser below, A low-pressure turbine internal casing containing the turbine rotor, a bearing cone installed so as to surround the turbine rotor bearing or a cover provided around the bearing cone, and a final paragraph fixed to the turbine rotor are configured. An annular flow guide installed continuously on the outer periphery of the low-pressure turbine inner casing downstream of the moving blade, and the upper and lower sides surrounding the low-pressure turbine inner casing, the bearing cone or the cover, and the flow guide A low-pressure turbine external casing having a two-part structure, and an internal strength member provided in the low-pressure turbine external casing. The upper half is formed such that its axial dimension is longer than the lower half of the low pressure turbine outer casing, and the upper half of the bearing cone or the cover has an axial dimension of the low pressure turbine outer vehicle. Each cross section in a plane perpendicular to the central axis of the turbine rotor is formed so as to be longer than the lower half of the bearing cone or the cover according to the axial extension with respect to the lower half of the upper half of the chamber The distance from the outer wall of the bearing cone or the cover to the central axis of the turbine rotor in the upper half is shorter than the lower half.

According to the present invention, the upper half of the bearing cone or cover extends in the axial direction from the lower half, and the distance from the outer wall of the upper half of the bearing cone or cover to the central axis of the turbine rotor is the distance in the lower half. Because it is shorter, the flow in the upper half of the low pressure turbine outer casing can be appropriately expanded, decelerated, and turned, and the basic specifications such as the dimensions of the lower half of the current low pressure turbine outer casing and the support structure of the rotor Without changing, it is possible to further exert the effect of reducing the pressure loss due to the enlargement of the upper half of the low pressure turbine outer casing.
Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

It is a side view shown in the state which saw through the structure of a 1st embodiment of the low-pressure exhaust room of the steam turbine of the present invention. It is a top view shown in the state which saw through the structure of 1st Embodiment of the low pressure exhaust chamber of the steam turbine of this invention shown in FIG. FIG. 2 is a perspective view showing the structure of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention shown in FIG. 1 in a transparent state. It is a longitudinal cross-sectional view which shows typically the basic structure of the conventional general low pressure exhaust chamber. It is the cross-sectional view which looked at the conventional general low pressure exhaust chamber shown in FIG. 4 from the VV arrow. It is a stream diagram which shows the analysis result of the internal flow of the conventional general low pressure exhaust chamber in the state seen from the front. FIG. 7 is a streamline diagram showing the analysis result of the internal flow of the conventional general low-pressure exhaust chamber shown in FIG. 6 as viewed from the side. It is explanatory drawing which shows the effect | action of 1st Embodiment of the low pressure exhaust chamber of the steam turbine of this invention, and is a side view shown in the state which saw through 1st Embodiment of the low pressure exhaust chamber of the steam turbine of this invention is there. It is explanatory drawing which shows the effect | action of 1st Embodiment of the low pressure exhaust chamber of the steam turbine of this invention, and is a top view shown in the state which saw through 1st Embodiment of the low pressure exhaust chamber of the steam turbine of this invention is there. It is a side view shown in the state which saw through the structure of a 2nd embodiment of the low-pressure exhaust room of the steam turbine of the present invention. It is a top view shown in the state which saw through the structure of 2nd Embodiment of the low pressure exhaust chamber of the steam turbine of this invention shown in FIG. It is a perspective view shown in the state which saw through the structure of the 2nd Embodiment of the low pressure exhaust chamber of the steam turbine of this invention shown in FIG. It is a side view shown in the state which saw through the structure of a 3rd embodiment of the low-pressure exhaust room of the steam turbine of the present invention. It is a top view in the state which saw through the structure of 3rd Embodiment of the low pressure exhaust chamber of the steam turbine of this invention shown in FIG. It is a perspective view shown in the state which saw through the structure of 3rd Embodiment of the low pressure exhaust chamber of the steam turbine of this invention shown in FIG.

Embodiments of a low-pressure exhaust chamber of a steam turbine according to the present invention will be described below with reference to the drawings.
[First Embodiment]
1 to 3 are views showing a first embodiment of a low-pressure exhaust chamber of the steam turbine of the present invention, and FIG. 1 shows a structure of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention. FIG. 2 is a plan view showing the structure of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention shown in FIG. 1, and FIG. 3 is the book shown in FIG. It is a perspective view shown in the state which saw through the structure of a 1st embodiment of the low-pressure exhaust room of the steam turbine of the invention. In FIG. 1, the turbine rotor in the low-pressure exhaust chamber is indicated by a two-dot chain line.

  1 to 3, the low-pressure exhaust chamber of the steam turbine guides exhaust after driving the turbine rotor 1 to a condenser (not shown) below. The low-pressure exhaust chamber includes a low-pressure turbine internal casing 2 containing the turbine rotor 1, a bearing cone 3 installed so as to surround a bearing (not shown) of the turbine rotor 1, and a final paragraph fixed to the turbine rotor 1. An annular flow guide 4 that is installed downstream of the moving blade 10 that constitutes (described later) in the outer periphery of the low-pressure turbine internal casing 2, the low-pressure turbine internal casing 2, the bearing cone 3, and the flow And a low-pressure turbine outer casing 5 surrounding all of the guide 4.

  The low-pressure turbine internal casing 2 includes a stationary blade (not shown) on the inner peripheral side thereof. The stationary blade constitutes a turbine stage together with the moving blade (only the moving blade 10 of the final stage is shown in FIG. 1). An annular opening is formed between the tip diameter and the root diameter of the final stage moving blade 10, and this opening is referred to as the final stage moving blade outlet annulus 11 (see FIG. 5).

  The low-pressure turbine outer casing 5 is divided into upper and lower portions at a height near the horizontal plane including the central axis O of the turbine rotor 1, and the outer casing upper half 6 surrounding the upper portion of the turbine rotor 1, and the outer casing The lower half part 7 of the external casing is connected to the lower side of the upper half part 6. The outer casing upper half 106 and the outer casing lower half 7 are joined at a height near the central axis O of the turbine rotor 1. As shown in FIG. 3, the wall portion of the outer casing upper half 6 has an arcuate ceiling when viewed in a cross section along a plane perpendicular to the central axis O of the turbine rotor 1 (not shown in FIG. 3). Is formed. The outer casing lower half 7 is formed in a frame having a rectangular horizontal cross section and a substantially constant vertical cross sectional area. As shown in FIG. 1, the lower half 7 of the outer casing is provided with a low pressure exhaust chamber outlet 14 opening downward at the lower end thereof, and a lower condenser (not shown) is provided via the low pressure exhaust chamber outlet 14. Z).

  The bearing cone 3 is provided with one end side in the axial direction continuous to the inner peripheral portion of the final stage moving blade outlet annulus 11, and the other end side extending to the end wall surface in the axial direction of the low pressure turbine external casing 5. Further, like the low-pressure turbine outer casing 5, it has an upper and lower split structure, and is composed of an upper half 3a and a lower half 3b. The flow guide 4 is continuously provided on the outer peripheral portion of the final stage rotor blade outlet annulus 11 so as to surround the outer peripheral side of the bearing cone 3.

  The outer wall surface of the bearing cone 3, the inner wall surface of the flow guide 4, and the inner wall surface of the low-pressure turbine outer casing 5 are smoothly disposed below the steam discharged from the final stage rotor blade outlet annulus 11 while recovering the pressure. A diffuser flow path leading to the condenser is formed.

  A plurality of plate-like internal strength members that reinforce the low-pressure turbine external casing 5 are provided inside the low-pressure turbine external casing 5. For example, a first support rib 15 and a second support rib 16 as internal strength members that support the low-pressure turbine inner casing 2 are provided in the lower half 7 of the outer casing. The first support rib 15 is along a plane perpendicular to the central axis O of the turbine rotor 1, and the second support rib 16 is along a vertical plane parallel to the central axis O of the turbine rotor 1, respectively. It spans in the part 7, and the 1st and 2nd support ribs 15 and 16 are mutually orthogonally crossed. The first support ribs 15 are disposed at the axial center of the lower half 7 of the external casing, and the second support ribs 16 are disposed at both ends in the width direction of the low-pressure turbine internal casing 2.

  In addition, an upper flow guide 17 that guides the exhaust discharged from the upper side of the flow guide 4 to the lower condenser is provided on the upper side inside the low-pressure turbine outer casing 5. The upper flow guide 17 is provided along the outer peripheral surface of the low pressure turbine internal casing 2 and extends obliquely downward from the upper end of the low pressure turbine internal casing 2.

  The greatest feature of the low-pressure exhaust chamber configured as described above is that the external casing upper half 6 is extended by the extension of the outer casing upper half 6 toward the axial bearing cone 3 with respect to the outer casing lower half 7. Is to reduce the flow of the flow with low loss by changing the shape of the upper half 3a of the bearing cone 3 associated therewith.

  Specifically, the outer casing upper half 6 is formed such that its axial dimension is longer than that of the outer casing lower half 7, and has the same axial dimension as the outer casing lower half 7. It is comprised from the chamber main-body part 8 and the vehicle interior expansion | extension part 9 extended | stretched to the axial direction outer side from the compartment main-body part 8. As shown in FIG. That is, the end wall surface 6a on the bearing cone 3 side of the upper half portion 6 of the outer casing is positioned on the outer side in the axial direction with respect to the end wall surface 7a on the bearing cone 3 side of the lower half portion 7 of the outer casing.

  Further, the upper half 3a of the bearing cone 3 has an axial dimension that is longer than that of the lower half 3b in accordance with the axial extension of the outer casing upper half 6 with respect to the outer casing lower half 7. Is formed. The distance Ca from the outer wall of the upper half 3a of the bearing cone 3 to the center axis O of the turbine rotor 1 in each cross section in a plane orthogonal to the center axis O of the turbine rotor 1 is from the outer wall of the lower half 3b. The distance is set to be shorter than the distance Cb to the center axis O of the turbine rotor 1. That is, when the bearing cone 3 has a curved surface, the upper half 3a of the bearing cone 3 has a curvature of each cross section in the plane including the central axis O of the turbine rotor 1 that is the curvature of the lower half 3b. It is formed to be smaller. When the bearing cone 3 is formed in the shape of a truncated cone, the upper half 3 a of the bearing cone 3 has a central axis O of the turbine rotor 1 in each cross section in a plane including the central axis O of the turbine rotor 1. The inclination angle with respect to is smaller than the inclination angle of the lower half 3b. Each of the upper half 3a and the lower half 3b of the bearing cone 3 has a semicircular cross section on a plane orthogonal to the central axis O of the turbine rotor 1.

Next, the operation of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention will be described with reference to FIGS.
First, in order to facilitate understanding of the operation of the first embodiment of the low pressure exhaust chamber of the steam turbine of the present invention, the basic structure of a conventional general low pressure exhaust chamber as a comparative example and the flow field thereof are described. This will be described with reference to FIGS.
4 is a longitudinal sectional view schematically showing a basic structure of a conventional general low-pressure exhaust chamber, and FIG. 5 is a transverse sectional view of the conventional general low-pressure exhaust chamber shown in FIG. 6 is a streamline diagram showing the analysis result of the internal flow of the conventional general low-pressure exhaust chamber as seen from the front, and FIG. 7 is the analysis of the internal flow of the conventional general low-pressure exhaust chamber shown in FIG. It is a streamline figure which shows a result in the state seen from the side. In FIG. 4, the bearing cone is omitted. In FIGS. 6 and 7, the streamlines are displayed on only half surfaces, and the shading of the streamlines indicates the difference in the start points of the streamlines. 4 to 7, the same reference numerals as those shown in FIGS. 1 to 3 are the same parts, and detailed description thereof is omitted.

The difference between the structure of the first embodiment of the low pressure exhaust chamber of the steam turbine of the present invention and the structure of a conventional general low pressure exhaust chamber is mainly the following two points.
First, in the present embodiment, the outer casing upper half 6 is formed such that its axial dimension is longer than the outer casing lower half 7. On the other hand, in the conventional general low pressure exhaust chamber, as shown in FIGS. 4 and 5, the outer casing upper half 106 is formed so that the axial dimension thereof is the same as the outer casing lower half 7. ing.

  Secondly, in the present embodiment, the upper half 3a of the bearing cone 3 is formed to extend in the axial direction from the lower half 3b. The distance Ca from the outer wall of the upper half 3a of the bearing cone 3 to the center axis O of the turbine rotor 1 in each cross section in a plane orthogonal to the center axis O of the turbine rotor 1 is from the outer wall of the lower half 3b. The distance is set to be shorter than the distance Cb to the center axis O of the turbine rotor 1. On the other hand, in the conventional general low pressure exhaust chamber, as shown in FIGS. 4 and 5, the bearing cone 103 is formed so as to be vertically symmetrical. That is, the distance Ca from the outer wall of the upper half 3a of the bearing cone 3 to the center axis O of the turbine rotor 1 in each cross section in a plane orthogonal to the center axis O of the turbine rotor 1 is from the outer wall of the lower half 3b. It is set to be the same as the distance Cb to the center axis O of the turbine rotor 1.

Next, FIGS. 6 and 7 show the flow field inside the conventional low-pressure exhaust chamber and the influence of the internal strength member provided in the low-pressure exhaust chamber on the flow field and pressure loss in the low-pressure exhaust chamber. Conceptually explained by using.
In the structure of a conventional general low pressure exhaust chamber, as shown in FIGS. 6 and 7, the steam S passing through the diffuser flow path flows in a generally radial manner, and then gradually merges with the downstream condenser (see FIG. 6). (Not shown). Specifically, of the steam S that flows radially, the steam (downward flow) S1 that flows to the lower half side of the low-pressure exhaust chamber goes to the condenser below without changing the traveling direction so much. The steam (upward flow) S2 flowing in the upper half part side of the low pressure exhaust chamber suddenly turns in the traveling direction toward the low pressure turbine inner casing 2 side, and then turns downward along the upper half part 106 of the outer casing. Gradually join the downward flow and head to the condenser. Further, the steam (side flow) S3 flowing in the vicinity of the joint surface between the outer casing upper half 106 and the outer casing lower half 7 of the low-pressure turbine outer casing 105 spreads in the width direction of the low-pressure exhaust chamber and extends downward. After that, it gradually merges with the downward flow and heads toward the condenser.

  By the way, as shown in FIG. 7, the flow of steam is different between the left and right sides of the first support rib 15 as an internal strength member provided in the lower half 7 of the outer casing, and the first support rib 15 flows. It turns out that it has a big influence on the field.

  In the conventional structure, the internal strength member is not necessarily arranged with priority on the performance of the low-pressure exhaust chamber, but is mainly arranged with priority on strength. Therefore, it is generally considered that the flow path performance of the low-pressure exhaust chamber is deteriorated from an ideal state. In particular, the plate-like member for supporting the low pressure turbine internal casing 2 such as the first support rib 15 forcibly divides the internal flow path in the lower half of the low pressure exhaust chamber into a plurality of flow paths. The steam discharged from the diffuser flow path is not equally distributed to each flow path divided by the first support ribs 15, and tends to have a flow distribution that is biased to some flow paths. In fact, when the flow field is analyzed in detail by fluid analysis, it is found that in many cases, the flow distribution of steam to each flow path is biased, resulting in a region where the flow velocity is fast and a region where the flow velocity is slow.

  Specifically, as shown in FIG. 7, the flow distribution is biased toward the flow path on the bearing cone 103 side (right side in FIG. 7) from the first support rib 15, and the interior of the low-pressure turbine is shifted from the first support rib 15. The flow rate of the flow path on the passenger compartment 2 side (left side in FIG. 7) is smaller than that on the right side. In particular, most of the side flow S <b> 3 flows in the flow path on the right side of the first support rib 15, and only the remaining part flows in the flow path on the left side of the first support rib 15. For this reason, the region on the right side of the first support rib 15 is a region having a faster flow velocity than the region on the left side.

  There are two main causes of the pressure loss that occurs in the low-pressure exhaust chamber: those caused by mixing of steam and those caused by friction on the wall surface. Since both the pressure losses increase in proportion to the square of the flow velocity, if there is a region where the flow velocity is locally high, the pressure loss is larger than that in the case of the flow averaged as a whole.

Next, among the effects of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention, the flow is uniformized by the axial extension of the upper half of the outer casing (appropriate flow distribution to each channel) ) Will be conceptually described with reference to FIGS. 8 and 9 in comparison with a conventional low-pressure exhaust chamber.
FIGS. 8 and 9 are explanatory views showing the operation of the first embodiment of the low pressure exhaust chamber of the steam turbine of the present invention, and FIG. 8 shows the first embodiment of the low pressure exhaust chamber of the steam turbine of the present invention. FIG. 9 is a plan view showing the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention in a see-through state. In FIG. 8 and FIG. 9, a broken-line area indicated by reference numeral A indicates area A, a broken-line area indicated by reference numeral B indicates area B, and a broken-line area indicated by reference numeral C indicates area C. The arrows indicate streamlines, and the two-dot chain line indicates the position of the end wall surface 106a of the upper half 106 of the external casing of the conventional low-pressure exhaust chamber. In FIG. 8 and FIG. 9, the same reference numerals as those shown in FIG. 1 to FIG.

  When attention is paid to a specific region of the flow field, generally, the direction of the subsequent flow is determined by the balance between the inertial force of the portion and the surrounding pressure gradient. Usually, the more along the direction of the original flow, or the greater the negative pressure gradient, the easier it is to flow in that direction.

  Specifically, in FIG. 8 and FIG. 9, the steam discharged from the turbine to the region A finally flows toward the condenser located below, but part of the steam passes through the region C, and the rest is the region. Pass through B. Here, the region A is a region near the outlet of the flow guide 4 in the upper half 6 of the outer casing, and the region B is a region near the upper flow guide 17 on both sides in the width direction above the low-pressure turbine inner casing 2. C shows a region on the right side of the first support rib 15 on both sides in the width direction in the lower half 7 of the outer casing.

  In region A, which is the start of the diffuser flow path, the flow is accelerated, so the pressure is low. Thereafter, the flow decelerates as the flow path area increases, and the pressure increases. If there is no compartment extension 9 and the axial dimension of the upper half 6 of the external compartment is the same as that of the lower half 7 of the external compartment as in the conventional low pressure exhaust chamber, as shown in FIG. Since the flow Sb from the region A to the region B needs to be turned at a very short distance, a rapid pressure increase accompanied by a loss is likely to occur before the region B. As a result, the pressure in the region B is higher than that in the region A. On the other hand, as shown in FIG. 8 and FIG. 9, the region C has a larger space than the region A, so the flow Sc from the region A is easy to smoothly expand and decelerate without causing loss. For this reason, the pressure in the region C is higher than that in the region B.

  If the relative pressures of the three regions are expressed qualitatively, for example, in a conventional low-pressure exhaust chamber that does not have the passenger compartment extension 9, it can be expressed as low in region A, medium to high in region B, and high in region C. In this case, the steam flows from the low pressure region A to the relatively high pressure region B due to the inertial force, but the pressure in the region B is medium to high, so the reverse pressure gradient from the region A to the region B is Since it becomes a large resistance, it tends to flow even in the region C where the pressure is high.

  On the other hand, in the present embodiment, the space in the region A is expanded from the conventional low-pressure exhaust chamber by the vehicle compartment extension 9 of the upper half 6 of the external vehicle compartment, so that the flow in the region A is further decelerated. The pressure increases accordingly. In this case, for example, the pressure in the three regions is medium in region A, medium in region B, and high in region C, and the reverse pressure gradient from region A to region B is relaxed. Further, since the flow turns after the deceleration, the flow easily flows into the region B more smoothly (low loss). As a result, the flow rate in the region on the low pressure turbine internal casing 2 side (left side in FIGS. 8 and 9) from the first support rib 15 increases, and the flow rate distribution to the right and left regions of the first support rib 15 is increased. Is optimized and pressure loss is reduced.

  Next, among the effects of the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention, FIG. 1 shows the flow uniformity by the appropriate diffuser flow path (adequate flow distribution to each flow path). This will be described with reference to FIGS. 6, 7 and 9.

  In the present embodiment, in order to improve the static pressure recovery performance and make the flow uniform, the outer casing upper half 6 is extended in the axial direction, so that the space of the outer casing upper half 6 is expanded. Accordingly, the shape of the upper and lower half portions of the bearing cone for configuring an appropriate diffuser flow path is not necessarily symmetric. In particular, when the ratio of the axial dimension of the diffuser flow path to the turbine final stage moving blade length is small, the axial dimension is different between the upper half 6 of the outer casing and the lower half 7 of the outer casing. The difference in the proper shape of the upper and lower half portions of the bearing cone becomes more prominent.

  If an appropriate diffuser flow path is not formed even if the outer casing upper half 6 extends in the axial direction, as shown in FIGS. 6 and 7, the outer casing upper half 6 and the outer casing lower The flow (side flow) S3 passing through the vicinity of the joint surface with the half portion 7 does not flow from the first support rib 15 to the low-pressure turbine inner casing 2 side (left side in FIG. 7), but the first support rib. 15 easily flows to the bearing cone 103 side (the right side in FIG. 7). As a result, the flow is only partially uniformized.

  Therefore, in the present embodiment, the distance from the outer wall of the bearing cone 3 to the central axis O of the turbine rotor 1 is set as shown in FIG. 1, and the upper half 3a of the bearing cone 3 is more than the lower half 3b. Since it is set to be shorter, an appropriate diffuser flow path is configured for the axial extension of the outer casing upper half 6 to the outer casing lower half 7, and the flow of the diffuser flow can be further reduced. , Pressure can be restored. In addition, since the flow turns after deceleration, it is possible to turn with a lower loss. In particular, as shown in FIG. 9, the side flow S3 is turned by the bearing cone 3 and along the side wall surface 6b of the lower outer casing upper half 6 from the first support rib 15 to the low pressure turbine inner casing 2. It becomes easy to flow to the region on the side (left side in FIG. 9). For this reason, the flow rate in the left region of the first support rib 15 is increased, the flow distribution to the right and left regions of the first support rib 15 is further optimized, and the pressure loss is further reduced.

  Therefore, even when the ratio of the axial dimension of the diffuser flow path to the blade length is small, the flow in the upper half of the low pressure exhaust chamber can be appropriately expanded, decelerated, and turned. A pressure loss reducing effect higher than that of the chamber can be obtained.

  The structure of the low-pressure exhaust chamber of the present embodiment described above is devised based on the knowledge obtained from the result of CFD analysis, and the effect can be expected more reliably than the conventional technology.

  Further, an external casing upper half 106 having the same axial dimension as the outer casing lower half 7 is extended from the existing lower pressure exhaust chamber in the axial direction with respect to the outer casing lower half 7. The upper half portion 103a of the bearing cone 103, which is replaced with the upper half portion 6 of the casing, is symmetrical in the vertical direction, and the axial dimension is longer than the lower half portion 3b by the axial extension of the upper half portion 6 of the outer casing. Is replaced with the upper half 3a whose distance from the outer wall of the turbine rotor 1 to the central axis O of the turbine rotor 1 is shorter than the lower half 3b, thereby supporting the dimensions of the lower half of the existing low-pressure turbine outer casing 5 and the support of the turbine rotor 1 Without changing the basic specifications such as the structure, the low pressure turbine can be easily modified to a low pressure exhaust chamber that can further exhibit the effect of reducing the pressure loss by expanding the upper half of the low pressure turbine outer casing 5.

  As described above, according to the first embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention, the upper half 3a of the bearing cone 3 (or cover) is extended in the axial direction from the lower half 3b, and the bearing Since the distance from the outer wall of the upper half 3a of the cone 3 (or cover) to the central axis O of the turbine rotor 1 is shorter than the lower half 3b, the flow in the upper half of the low pressure turbine external casing 5 is appropriately expanded. -Deceleration and turning are possible, and expansion of the upper half of the low-pressure turbine external casing 5 is possible without changing the basic specifications of the lower half of the current low-pressure turbine external casing 5 and the support structure of the turbine rotor 1, etc. The effect of reducing the pressure loss due to can be further exhibited.

[Second Embodiment]
Next, a second embodiment of the low pressure exhaust chamber of the steam turbine of the present invention will be described with reference to FIGS.
10 to 12 are views showing a second embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention, and FIG. 10 shows the structure of the second embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention. FIG. 11 is a plan view showing the second embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention shown in FIG. 10, and FIG. 12 is the book shown in FIG. It is a perspective view shown in the state which saw through the structure of a 2nd embodiment of the low-pressure exhaust chamber of the steam turbine of the invention. In FIG. 10 to FIG. 12, the same reference numerals as those shown in FIG. 1 to FIG.
In the second embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention, the guide portion 30 is provided on the discontinuous surface 3c of the bearing cone 3 of the first embodiment shown in FIGS.

  When the bearing cone 3 is manufactured such that the distance from the outer wall of the bearing cone 3 to the central axis O of the turbine rotor 1 is different between the upper half 3a and the lower half 3b as in the first embodiment, FIG. 2 and FIG. 3, a discontinuous surface 3c occurs. The discontinuous surface 3c may cause a disturbance to the flow field having a vertical velocity component in the vicinity thereof, and may eventually cause a pressure loss.

  Therefore, in the present embodiment, as shown in FIGS. 10 to 12, a guide portion 30 is provided on the discontinuous surface 3c of the bearing cone 3 (see FIGS. 2 and 3). The guide portion 30 is such that the distance from the outer wall to the central axis O of the turbine rotor 1 in each cross section in the plane including the central axis O of the turbine rotor 1 is between the outer casing upper half 6 and the outer casing lower half 7. It gradually decreases from the joint surface 12 to above the upper half 6 of the outer casing. Further, the distance Ca from the outer wall in the cross section in the joint surface 12 between the upper half 6 of the outer casing and the lower half 7 of the outer casing to the central axis O of the turbine rotor 1 is the bearing in the cross section in the joint surface 12. The distance Cb is the same as the distance Cb from the outer wall of the lower half 3 b of the cone 23 to the center axis O of the turbine rotor 1. That is, the guide portion 30 of the bearing cone 23 smoothly connects the upper half portion 23a to the lower half portion 3b. Thereby, the discontinuous surface 3c shown in FIG. 2 is eliminated, and the pressure loss can be reduced.

  As described above, according to the second embodiment of the low pressure exhaust chamber of the steam turbine of the present invention, the upper half portion 23a of the bearing cone 23 is smoothly connected to the lower half portion 3b by the guide portion 30. The effect of reducing pressure loss by expanding the upper half of the low pressure turbine external casing 5 without changing the basic specifications such as the dimensions of the lower half of the current low pressure turbine external casing 5 and the support structure of the turbine rotor 1. It can be further demonstrated.

[Third Embodiment]
Next, a third embodiment of the low pressure exhaust chamber of the steam turbine of the present invention will be described with reference to FIGS.
FIGS. 13 to 15 are views showing a third embodiment of the low pressure exhaust chamber of the steam turbine of the present invention, and FIG. 13 shows the structure of the third embodiment of the low pressure exhaust chamber of the steam turbine of the present invention. FIG. 14 is a side view showing in a transparent state, FIG. 14 is a plan view showing the structure of the third embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention shown in FIG. 13, and FIG. 15 is a book shown in FIG. It is a perspective view shown in the state seen through of the structure of a 3rd embodiment of the low-pressure exhaust room of the steam turbine of the invention. In FIG. 14, arrows indicate streamlines. In FIG. 13 to FIG. 15, the same reference numerals as those shown in FIG. 1 to FIG.

  The third embodiment of the low-pressure exhaust chamber of the steam turbine of the present invention shown in FIGS. 13 to 15 is the end wall surface 6a on the bearing cone 23 side of the upper half 6 of the external casing constituting the second embodiment. The guide plate 40 is disposed at a corner portion formed by the side wall surface 6b of the outer casing upper half 6 in the width direction.

  As described in the first embodiment, the flow (side flow) S3 passing near the joint surface 12 between the outer casing upper half 6 and the outer casing lower half 7 is the first flow. It does not flow from the support rib 15 to the low-pressure turbine internal casing 2 side (left side in FIG. 7), but tends to flow from the first support rib 15 to the bearing cone 103 side (right side in FIG. 7) (see FIG. 7). For this reason, even in the case of the first and second embodiments, a part of the steam discharged from the upper half of the diffuser flow path is closer to the low pressure turbine internal casing 2 side than the first support rib 15. However, the flow does not flow into the flow path directly, but flows directly below the diffuser flow path, so that the flow is not uniformized to the maximum extent.

  Therefore, in the present embodiment, as shown in FIGS. 13 to 15, the end wall surface 6 a on the bearing cone 23 side of the outer casing upper half 6 and the side wall surface 6 b in the width direction of the outer casing upper half 6. The guide plate 40 is arranged at the corner formed by the tie so as to connect the end wall surface 6a and the side wall surface 6b. As shown in FIG. 14, the guide plate 40 is formed so as to curve toward a corner formed by the end wall surface 6a and the side wall surface 6b. The guide plate 40 guides the side flow S3 smoothly along the side wall surface 6b of the upper half 6 of the external compartment. As a result, the lateral flow S3 passes over the first support rib 15 and flows into the region on the low-pressure turbine internal casing 2 side (left side in FIG. 14) from the first support rib 15, thereby further homogenizing the flow. Is called.

  As described above, according to the third embodiment of the low pressure exhaust chamber of the steam turbine of the present invention, the corner portion formed by the end wall surface 6a and the side wall surface 6b of the upper half portion 6 of the outer casing is formed at the end. Since the guide plate 40 is disposed so as to be connected to the wall surface 6a and the side wall surface 6b, the flow distribution to each flow path divided by the first support rib 15 can be made even more uniform. For this reason, the pressure loss due to the expansion of the upper half of the low pressure turbine external casing 5 can be reduced without changing the basic specifications such as the size of the lower half of the low pressure turbine external casing 5 and the support structure of the turbine rotor 1. The reduction effect can be further exhibited.

  In addition, according to the present embodiment, the guide plate 40 is formed so as to bend toward the corner formed by the end wall surface 6a and the side wall surface 6b, so the side flow S3 is the first support rib. 15 can flow more effectively to the region on the low pressure turbine internal casing 2 side (left side in FIG. 14).

[Other embodiments]
In the above-described embodiment, the example in which the diffuser flow path is configured by the outer wall surface of the bearing cone 3, the inner wall surface of the flow guide 4, and the inner wall surface of the low-pressure turbine outer casing 5 is shown. It is also possible to form a diffuser flow path by the outer wall surface of the cover provided around, the inner wall surface of the flow guide 4, and the inner wall surface of the low-pressure turbine outer casing 5. In this case, the distance from the outer wall of the cover to the central axis O of the turbine rotor 1 in each cross section in a plane orthogonal to the central axis O of the turbine rotor 1 is shorter in the upper half of the cover than in the lower half of the cover. Set as follows. As a result, the same effects as those of the above-described embodiment can be obtained.

  Further, the present invention is not limited to the above-described embodiment, and includes various modifications. The above-described embodiment has been described in detail for easy understanding of the present invention, and is not necessarily limited to the one having all the configurations described. For example, part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Moreover, it is also possible to add, delete, or replace another configuration for a part of the configuration of each embodiment.

DESCRIPTION OF SYMBOLS 1 Turbine rotor 2 Low pressure turbine internal compartment 3, 23 Bearing cone 3a Upper half 3b Lower half 4 Flow guide 5 Low pressure turbine external compartment 6 External compartment upper half (Upper half of low pressure turbine external compartment)
6a End wall surface 6b Side wall surface 7 Lower half of external casing (lower half of low pressure turbine outer casing)
10 moving blade 12 joint surface 15 first support rib (internal strength member)
30 Guide part 40 Guide plate O Center axis

Claims (4)

A low-pressure exhaust chamber of a steam turbine that guides exhaust after driving the turbine rotor to a lower condenser,
A low-pressure turbine internal casing containing the turbine rotor;
A bearing cone installed around the bearing of the turbine rotor or a cover provided around the bearing cone;
An annular flow guide installed continuously on the outer periphery of the low-pressure turbine internal casing downstream of the moving blades constituting the final stage fixed to the turbine rotor;
A low-pressure turbine outer casing having a vertically divided structure surrounding the low-pressure turbine inner casing, the bearing cone or the cover, and the flow guide;
An internal strength member provided in the vehicle interior of the low-pressure turbine outside,
The upper half of the low-pressure turbine outer casing is formed such that its axial dimension is longer than the lower half of the low-pressure turbine outer casing,
The upper half of the bearing cone or the cover has an axial dimension corresponding to an axial extension of the lower half of the upper half of the low-pressure turbine outer casing, and the lower half of the bearing cone or the cover. Formed to be longer,
The distance from the bearing cone or the outer wall of the cover to the central axis of the turbine rotor in each cross section in a plane orthogonal to the central axis of the turbine rotor is shorter in the upper half than in the lower half. The low pressure exhaust chamber of the steam turbine. In the low pressure exhaust chamber of the steam turbine according to claim 1,
The bearing cone or the upper half of the cover is
The distance from the outer wall in each cross section in the plane including the central axis of the turbine rotor to the central axis of the turbine rotor is determined from the joint surface between the upper half portion and the lower half portion of the low pressure turbine external casing. The distance in the cross section in the joint surface is a distance from the outer wall of the lower half of the bearing cone or the cover to the central axis of the turbine rotor in the cross section in the joint surface. A low-pressure exhaust chamber of a steam turbine, characterized by having a guide portion that is the same. In the low pressure exhaust chamber of the steam turbine according to claim 1 or 2,
In the corner formed by the end wall surface on the bearing cone side or the cover side of the upper half of the low pressure turbine external casing and the side wall surface in the width direction of the upper half of the low pressure turbine external casing, the end A low pressure exhaust chamber of a steam turbine, further comprising a guide plate arranged to connect the wall surface and the side wall surface. In the low pressure exhaust chamber of the steam turbine according to claim 3,
The low pressure exhaust chamber of a steam turbine, wherein the guide plate is curved toward a corner formed by the end wall surface and the side wall surface.

Images