JP2012067604A - Exhaust chamber of steam turbine and its modification method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust chamber of a steam turbine that achieves a big diffuser effect without the change of accuracies of a current manufacture and assembly, and free from the effect of a clearance flow between a flow guide and a center rib, and as a result, increases the efficiency of a turbine plant.SOLUTION: The exhaust chamber of the steam engine includes: an exhaust chamber inside casing including a turbine rotor; an annular flow guide installed continuously in the outer circumference of the exhaust chamber inside casing, in the downstream of a rotor blade constituting a final paragraph fixed to the turbine rotor; an exhaust chamber outside casing enclosing the exhaust chamber inside casing and the flow guide; and the center rib extending in the direction of a rotor shaft installed in the exhaust chamber outside casing. A clearance flow prevention member installed in a fitting part of the flow guide and the center rib, and caulking a clearance formed in the fitting part, is provided in the exhaust chamber of the turbine, which introduces exhaust after driving a turbine, into a downward condenser.

Description

  The present invention relates to an exhaust chamber structure of a steam turbine.

  A power plant that generates electricity 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 that has passed through the high-pressure turbine and the low-pressure turbine in order and finished the rotary work is finally introduced into the condenser, where it condenses to condensate, and returns to the steam generator again.

  Immediately after the exit of each of the high, medium, and low pressure turbines, there is a steam passage called an exhaust chamber. Generally, it has a shape accompanied by a sudden flow reversal, so the steam flow is disturbed and pressure loss is likely to occur. . In particular, since the pressure loss in the low-pressure exhaust chamber, which is the steam flow path from the outlet of the low-pressure turbine to the condenser, has a great influence on the plant performance, it is important to reduce this pressure loss.

  In fact, many of the low-pressure exhaust chambers in recent years employ a diffuser channel structure in which the steam channel is smoothly expanded toward the downstream side. Converting the kinetic energy of steam into pressure energy by smoothly expanding the steam in the diffuser channel is called a diffuser effect. Using the diffuser effect, active exhaust chamber performance improvements aiming to restore the pressure on the downstream side to a higher state than the upstream side are being made.

  When the diffuser effect is effectively exerted, the outlet pressure of the low-pressure turbine can be lowered. As a result, the difference in steam pressure between the turbine inlet and outlet becomes large, and the turbine can be operated with high output.

  The diffuser flow path is configured as a flow path sandwiched between an annular member called a flow guide attached to the outlet of the final stage of the low-pressure turbine and the wall surface on the rotor or bearing side. The performance is improved by devising. This type of exhaust chamber is reported, for example, in JP-A-2005-233154 (Patent Document 1).

JP 2005-233154 A

  By the way, as one of the internal strength members of the outer casing of the exhaust chamber, a plate-shaped center rib is provided at the central cross-sectional position in the exhaust chamber axial direction.

  When the flow guide is installed at the outer peripheral end portion of the inner casing as in Patent Document 1, it cannot interfere with the center rib as it is and cannot be assembled. Therefore, the flow guide is manufactured with a notch, and the center rib is assembled into the notch.

  However, the steam guide and the center rib cannot be fixed after assembling or manufactured in advance integrally because of the influence of the difference in the axial direction during plant operation. For this reason, it is necessary to design the gap between the steam guide and the center rib. However, the low-pressure exhaust chamber and its internal structure have large individual dimensions and are finally assembled on site. For this reason, it is generally difficult to maintain high production / assembly accuracy.

  As a result, the width of the cut portion of the flow guide becomes slightly larger than the thickness of the center rib, and a gap is formed between the steam guide and the center rib. This gap varies depending on the size of the exhaust chamber. For example, in the case of a plant with an output of several hundred to 1,000 MW, it is on the order of several tens of mm on the left and right in the thickness direction of the center rib. It can be about twice that. When viewed structurally, the size of this gap is smaller than the size of the low-pressure exhaust chamber (number of sides from 10 m to 10 m), and performance evaluation has not been easy. . However, by conducting a detailed three-dimensional fluid analysis, it was found that the main flow was disturbed by the flow ejected from this gap, and the performance of the diffuser flow path was not necessarily maximized.

  The steam flow discharged from the turbine last stage moving blade is accelerated in the vicinity of the flow guide surface when passing through the diffuser flow path. As a result, the pressure on the surface of the flow guide becomes lower than the surroundings. On the other hand, the area on the back side of the flow guide is generally in a state where the flow is stagnant, so that the pressure is higher than the surroundings. Therefore, the steam on the back side of the flow guide is ejected from the gap with the center rib to the main flow side, disturbing the flow in the diffuser flow path and generating a mixing loss, and the performance as expected cannot be obtained. However, such a problem is not considered at all in Patent Document 1.

  Therefore, the object of the present invention is to reduce the turbulence in the flow of the diffuser flow path due to the gap flow between the flow guide and the center rib without changing the current manufacturing and assembly accuracy, and to exert a high diffuser effect. An object of the present invention is to provide an exhaust chamber of a steam turbine capable of improving turbine plant efficiency.

  In order to achieve the above object, in the present invention, the exhaust chamber inner casing containing the turbine rotor and the rotor blade constituting the final stage fixed to the turbine rotor are continuously connected to the outer peripheral portion of the exhaust chamber inner casing. An annular flow guide installed in the exhaust chamber, an exhaust chamber outer casing surrounding the exhaust chamber inner casing and the flow guide, and a center rib extending in the rotor axial direction provided inside the exhaust chamber outer casing, and a turbine. A gap formed between the flow guide and the center rib in the fitting portion between the flow guide and the center rib in the exhaust chamber of the steam turbine for guiding the exhaust after being driven to the condenser below. A crevice flow prevention member is provided to block the gap.

  According to the present invention, it is possible to reduce the turbulence in the flow of the diffuser flow path due to the gap flow between the flow guide and the center rib of the low-pressure exhaust chamber without changing the current manufacturing and assembly accuracy, and to exhibit a high diffuser effect. This can improve the efficiency of the turbine plant.

It is a sectional side view showing typically the basic structure of the exhaust device of a steam turbine. It is sectional drawing by the II cross section in FIG. FIG. 3 is a side cross-sectional view schematically showing the upper half of the diffuser flow path section in the exhaust chamber and the periphery of the turbine final stage. It is a perspective view which shows typically the main structure of a low pressure turbine outer casing lower half part. It is the figure which looked at the flow guide which is one of the components of a diffuser flow path from the axial direction. It is the figure which looked at the flow guide which is one of the components of a diffuser flow path from the side. FIG. 2 is a perspective view of a turbine upstream portion in a state where the turbine exhaust device in FIG. 1 is cut along a II-II section. It is the enlarged view which looked at the part V enclosed by the dotted line in FIG. 7 from the axial direction. It is the enlarged view which looked at the part IV enclosed with the dotted line in FIG. 6 from the side surface. 1 is a side view showing a first embodiment according to the present invention. It is an axial front view showing a 1st embodiment concerning the present invention. It is III-III sectional drawing in FIG. It is III-III sectional drawing of FIG. 11 in the 2nd Embodiment of this invention.

  Hereinafter, the form for implementing the turbine exhaust apparatus of this invention is demonstrated in detail with reference to drawings suitably.

  Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. In order to facilitate understanding of the present invention, the structure of the conventional turbine exhaust chamber is first described with reference to FIGS. 1 to 9, and then the structure of the turbine exhaust chamber according to the present embodiment is used with reference to FIGS. 10 to 12. I will explain.

  FIG. 1 is a side sectional view schematically showing a basic structure of a low-pressure turbine exhaust chamber, and FIG. 2 is a sectional view taken along a line II in FIG. In FIG. 2, the bearing cone 3 is not shown for explanation.

  The turbine exhaust chamber 101 illustrated in FIGS. 1 and 2 guides exhaust after driving the turbine rotor 1 to a condenser (not shown) below. The turbine exhaust chamber 101 includes an exhaust chamber 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 6 that is continuously installed on the outer periphery of the exhaust chamber inner casing 2 and an exhaust chamber outer casing 5 that is formed so as to surround all of them are provided downstream of the moving blade 10 that constitutes the rotor blade 10. The turbine exhaust chamber 101 is connected to a lower condenser through an exhaust chamber outlet 4 opened below the exhaust chamber outer casing 5. The outer peripheral wall surface of the bearing cone 3, the wall surface of the flow guide 6, and the inner wall surface of the exhaust chamber outer casing 5 are configured to smoothly condense the steam discharged from the final stage rotor blade outlet annulus 11 while recovering the pressure. An annular diffuser channel leading to the vessel is formed.

  FIG. 3 is a detailed cross-sectional view around the turbine final stage and the diffuser flow path. The exhaust chamber inner casing includes a stationary blade 12 supported by a diaphragm outer ring 14 and an inner ring 13 on the inner peripheral side thereof, and a turbine stage together with a moving blade (only the moving blade 10 is shown) installed on the turbine rotor 1. Forming. In general, a diaphragm outer ring 14 and an inner ring 13 (the whole is not shown), which are attachment parts of a stationary blade, are provided in an annular shape on the inner peripheral side of the exhaust chamber inner casing. The stationary diaphragm inner ring 13 and the rotating turbine rotor 1 arranged in an annular shape face each other with an appropriate gap. A seal 30 is provided between the turbine rotor 1 that rotates about the rotor central axis 20 and the diaphragm inner ring 13 to prevent exhaust leakage. A bearing (not shown) that supports the turbine rotor 1 is installed in the space on the inner peripheral side of the bearing cone 3.

  Hereafter, among the wall surfaces of the flow guide 6, the wall surface on the rotor side where the turbine outlet exhaust comes into contact immediately after flowing into the diffuser passage is referred to as the flow guide surface portion 6a, and the wall surface on the back side is referred to as the flow guide back surface portion 6b. To.

  FIG. 4 is a perspective view schematically showing the main structure of the lower half portion of the exhaust chamber outer casing 5 of the low-pressure turbine. In order to facilitate understanding of the installation position of the center rib 50, the turbine blades, the turbine rotor, the bearings, the casing inside the exhaust chamber, the pipe-like member, and the like are not shown. The exhaust chamber inner casing containing the turbine blades and the turbine rotor is installed so as to be supported by the claw foot support 40, and the flow guide is attached to the exhaust chamber inner casing. Since FIG. 4 is drawn assuming a double-flow type low-pressure turbine exhaust chamber, only one half of the outer casing that is symmetrical in the axial direction is shown. Therefore, the claw foot support 40 is also displayed only in two places, which is half of the actual size.

  A plurality of strength members that reinforce members for supporting the turbine assembly including the exhaust chamber inner casing are provided inside the exhaust chamber outer casing 5. As one of the strength members, a center rib 50 extending parallel to the rotor axial direction is installed at the center of the exhaust chamber outer casing 5.

  FIG. 5 is a view of the flow guide 6 that is one of the components of the diffuser flow path as seen from the axial direction, and FIG. 6 is a view of the flow guide 6 as seen from the side. As shown in FIG. 5, a notch 7 is provided in the lower part of the flow guide 6. The turbine exhaust chamber shown in FIGS. 1 and 2 is assembled by inserting the cut portion 7 into the center rib 50.

  FIG. 7 is a schematic perspective view of a turbine upstream portion in a state where the turbine exhaust device in FIG. 1 is cut along a II-II cross section. However, in order to facilitate understanding of the joining relationship between the center rib 50 and the flow guide 6, the center rib 50 is indicated by a dotted line without being cut.

  FIG. 8 is an enlarged view of the fitting portion V between the center rib 50 and the flow guide 6 surrounded by a dotted line in FIG. 7 as viewed from the axial direction. The cut portion 7 of the flow guide 6 is formed slightly larger than the thickness of the center rib 50 in order to facilitate on-site assembly and in consideration of a difference in thermal elongation. Therefore, when the cutout portion 7 is inserted into the center rib 50 and the exhaust chamber is assembled, a gap exists between the center rib 50 and the flow guide 6 in the state shown in FIG.

  When the present inventor conducted a detailed three-dimensional fluid analysis, there is a problem that the flow of the main flow is disturbed by the flow ejected from the gap, and the performance of the diffuser flow path is not necessarily maximized. found.

  The steam flow discharged from the turbine last stage moving blade is accelerated near the surface of the flow guide 6 when passing through the diffuser flow path. As a result, the pressure on the surface of the flow guide 6 becomes lower than the surroundings. On the other hand, the area on the back side of the flow guide is generally in a state where the flow is stagnant, so that the pressure is higher than the surroundings. Therefore, the steam on the back side of the flow guide is ejected from the gap with the center rib to the main flow side, disturbing the flow in the diffuser flow path and generating a mixing loss, and the performance as expected cannot be obtained.

  The present invention solves the above-described problems.

  FIG. 9 is an enlarged view of a portion IV surrounded by a dotted line in FIG. 6 as viewed from the side, and shows the structure of the lower end portion of the conventional flow guide 6.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 10 is an explanatory view of the flow guide 6 showing the first embodiment according to the present invention, and FIG. 11 is an axial front view thereof. 12 is a cross-sectional view taken along the line III-III shown in FIG.

  In the present embodiment, the flow guide 6 is a low-pressure exhaust chamber of a steam turbine, and is extended to the outer peripheral portion of the casing inside the exhaust chamber. A gap flow prevention plate 60 for closing the gap of the fitting portion between the flow guide 6 and the center rib 50 is provided. In FIG. 10, the flow guide 6 itself is seen through from the flow guide surface portion side, and the gap flow preventing plate 60 is installed on the flow guide rear surface side as shown in FIG. The gap flow prevention plate 60 is configured to be attachable after the flow guide 6 is installed.

  Specifically, as shown in FIG. 11, a gap flow prevention plate 60 manufactured in advance continuously or piecewise in the long axis direction is formed in a fitting portion between the flow guide 6 and the center rib 50. It is attached to the back side of either the center rib 50 or the flow guide 6 along the gap so as to fill the gap, and is fixed by rivets, bolting or welding.

  However, since the center rib 50 is basically a strength member, it is desirable in terms of reliability that the center rib 50 is attached to the center rib 50 side.

  The gap flow preventing plate 60 is a member that blocks the gap formed in the fitting portion between the center rib and the flow guide and prevents the gap flow. As shown in FIG. It is the board manufactured by bending so that the shape of this may be followed. The cross-sectional shape is not particularly limited to this example, and may be any shape that closes the gap formed in the fitting portion.

  According to the turbine exhaust chamber structure of the present embodiment, after the flow guide 6 is installed, it is only necessary to attach the gap flow prevention plate 60 while confirming the size of the gap. Is simple.

  In addition, since the gap formed in the fitting portion is closed, it is possible to prevent the steam on the back side of the flow guide from being ejected to the main stream side through the gap with the center rib, so that the flow in the diffuser flow path is disturbed. Without any mixing loss. Therefore, since a high diffuser effect can be exhibited, the turbine plant efficiency can be improved as a result.

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

  Therefore, according to the turbine exhaust chamber structure of the present embodiment, the turbulence of the diffuser flow path due to the gap flow between the flow guide and the center rib of the low pressure exhaust chamber is reduced without changing the current manufacturing and assembly accuracy. The turbine plant efficiency can be improved by exhibiting a high diffuser effect.

  Next, a second embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 13, the present embodiment is characterized in that the cross-sectional shape of the gap flow preventing plate 60 described in the first embodiment is formed into a shape that is bent into a generally “<” shape.

  The gap flow preventing plate of this embodiment is composed of two flat plate portions 60a and 60b with a bent portion interposed therebetween, and one flat plate portion 60b of the two flat plate portions is fixed to the center rib, and the other flat plate portion. The part 60a is not fixed to the flow guide back surface part 6b but is installed so as to contact.

  The flat plate portion 60a may be fixed to the flow guide back surface portion 6b, and the flat plate portion 60b may be contacted without being fixed to the center rib 50.

  According to the turbine exhaust chamber structure of the present embodiment, after the flow guide 6 is installed in the same manner as in the first embodiment, it is only necessary to attach the gap flow prevention plate 60 while confirming the size of the gap. Therefore, high assembly accuracy is required. The installation work on the site is easy.

  Further, since the gap formed in the fitting portion is closed, it is possible to prevent the steam on the back side of the flow guide from being ejected to the mainstream side through the gap with the center rib, and the flow in the diffuser flow path is disturbed. In addition, the occurrence of mixing loss can be suppressed. Therefore, since a high diffuser effect can be exhibited, the turbine plant efficiency can be improved as a result.

  In addition, according to the turbine exhaust chamber structure of the present embodiment, the following effects can be obtained.

  Since the structure is fixed to only one of the center rib 50 or the flow guide 6, no problem occurs even if a difference in axial thermal expansion occurs between the inner casing and the outer casing.

  Further, when a shape bent in a “<” shape is adopted, one surface 60a of the flat plate portions 60a and 60b having two sides is fixed to the back surface portion of the flow guide 6, and the other surface 60b is fixed to the center rib. If it is installed so as to contact 50, it is better for the following reason. That is, the gap flow prevention plate 60 is pressed against the contact surface of the center rib 50 by installing the gap flow prevention plate 60 on the back side of the flow guide 6 having a relatively higher pressure than the diffuser flow path side. There is no risk of vibrations caused by the steam that is about to be ejected from the gap.

  As described above, the present invention has been devised based on the knowledge obtained from the CFD analysis results, and the effect can be expected more reliably than the conventional technology.

  Therefore, according to the turbine exhaust chamber structure of the present embodiment, the turbulence of the diffuser flow path due to the gap flow between the flow guide and the center rib of the low pressure exhaust chamber is reduced without changing the current manufacturing and assembly accuracy. The turbine plant efficiency can be improved by exhibiting a high diffuser effect.

DESCRIPTION OF SYMBOLS 1 Turbine rotor 2 Exhaust chamber inner casing 3 Bearing cone 4 Exhaust chamber outlet 5 Exhaust chamber outer casing 6 Flow guide 10 Rotor blade 11 Final stage rotor blade outlet ring 12 Stator vane 13 Diaphragm inner ring 14 Diaphragm outer ring 20 Rotor center shaft 30 Seal 40 Clawfoot support 50 Center rib
60 Clearance flow prevention plate 101 Turbine exhaust chamber

Claims (5)

An exhaust chamber inner casing containing the turbine rotor, an annular flow guide continuously installed on the outer peripheral portion of the exhaust chamber inner casing downstream of the moving blade constituting the final stage fixed to the turbine rotor, and the exhaust An exhaust chamber outer casing that surrounds the indoor casing and the flow guide, and a center rib that extends in the axial direction of the rotor provided inside the exhaust chamber outer casing, and exhausts the exhaust gas after driving the turbine to the lower condensate In the exhaust chamber of the steam turbine leading to the
An exhaust chamber of a steam turbine, comprising: a gap flow preventing member that is installed at a fitting portion between the flow guide and the center rib and closes a gap formed between the flow guide and the center rib.   2. The exhaust chamber of a steam turbine according to claim 1, wherein the gap flow preventing member is fixed only to either the center rib or the back surface of the flow guide.   The gap flow preventing member is a plate-like member whose cross-sectional shape is bent in a dogleg shape, and has two flat plate portions sandwiching the bent portion, and either one of the two flat plate portions is connected to the flow. The exhaust chamber of the steam turbine according to claim 2, wherein the exhaust chamber of the steam turbine is fixed to the back surface of the guide, and the other flat plate is in contact with the center rib.   4. The gap flow preventing member is configured to be able to be joined to the flow guide or the center rib after the flow guide is installed in an exhaust chamber of the steam turbine. The exhaust chamber of the steam turbine according to claim 1. An exhaust chamber inner casing containing the turbine rotor, an annular flow guide continuously installed on the outer peripheral portion of the exhaust chamber inner casing downstream of the moving blade constituting the final stage fixed to the turbine rotor, and the exhaust chamber An exhaust chamber outer casing that surrounds the inner casing and the flow guide, and a center rib that extends in the axial direction of the rotor provided inside the exhaust chamber outer casing, and exhausts after driving the turbine to the lower condenser A method of remodeling the exhaust chamber of a leading steam turbine,
An exhaust chamber of a steam turbine, wherein a member that closes the gap is formed in a gap between the flow guide and the center rib, which is formed when the center rib is inserted into the cut portion of the flow guide. Remodeling method.

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