Patent ID: 12203383

DESCRIPTION OF EMBODIMENTS

Hereinafter, some embodiments of the present disclosure will be described with reference to the accompanying drawings. Dimensions, materials, shapes, relative arrangements, and the like of components described as embodiments or illustrated in the drawings are not intended to limit the scope of the present disclosure, but are merely explanatory examples.

For example, an expression indicating a relative disposition or an absolute disposition, such as “in a direction”, “along a direction”, “parallel”, “orthogonal”, “center”, “concentric”, or “coaxial”, not only strictly represents such a disposition, but also represents a state of being relatively displaced with a tolerance, or an angle or a distance to the extent that the same function can be obtained.

For example, expressions such as “identical”, “equal”, and “homogeneous”, which indicate that things are in the same state, not only represent a state of being strictly equal, but also represent a state in which there is a tolerance, or a difference to the extent that the same function can be obtained.

For example, an expression indicating a shape such as a square shape or a cylindrical shape not only represents a shape such as a square shape or a cylindrical shape in a geometrically strict sense, but also represents a shape that includes concave and convex portions, chamfered portions, or the like to the extent that the same effects can be obtained.

Meanwhile, an expression such as “comprising”, “possessing”, “provided with”, “including”, or “having” one component is not an exclusive expression excluding the presence of other components.

FIG.1is a schematic system diagram of steam turbine equipment that includes a steam turbine according to one embodiment. Steam turbine equipment1includes, as main equipment, a boiler2, a high-pressure turbine4, a medium-pressure turbine8, a low-pressure turbine10, a condenser11, and a generator12. The high-pressure turbine4, the medium-pressure turbine8, and the low-pressure turbine10are connected by a rotor13, and the rotor13is connected to the generator12.

Main steam generated in the boiler2flows down through a main steam pipe3and is led to an inlet of the high-pressure turbine4. Exhaust steam discharged by driving the high-pressure turbine4flows down through a low-temperature reheat pipe5from the high-pressure turbine4, is led to a reheater6of the boiler2, and is reheated. The steam heated in the reheater6flows down through a high-temperature reheat pipe7, is led to the medium-pressure turbine8, drives the medium-pressure turbine8, and then flows down through a main steam pipe9to be led to the low-pressure turbine10. The exhaust steam discharged by driving the low-pressure turbine10is introduced into the condenser11, cooled to be converted into water, and then reintroduced into the boiler2as feed water. As described above, the high-pressure turbine4, the medium-pressure turbine8, and the low-pressure turbine10are connected by the rotor13, rotational power is transmitted to the generator12through the rotor13, and the rotational power is converted into electric power by the generator12.

The main steam pipe3through which the main steam flows from the boiler2to the high-pressure turbine4is provided with a main steam stop valve14and a main steam adjusting valve15from an upstream side toward a downstream side in a steam flow direction. Further, a bypass pipe16is provided to branch from the main steam pipe3between the main steam stop valve14and the main steam adjusting valve15. The bypass pipe16branched from the main steam pipe3is connected to an intermediate stage of the high-pressure turbine4, and a portion of the main steam flowing through the main steam pipe3bypasses a part of an upstream side stage of the high-pressure turbine4and is introduced into the high-pressure turbine4from the intermediate stage. The bypass pipe16is provided with an overload valve17to control an amount of bypass steam flowing through the bypass pipe16.

FIG.2is a sectional view schematically showing a structure of a steam turbine20according to one embodiment of the present disclosure.

The steam turbine20according to one embodiment is a medium-high pressure integrated type steam turbine in which the high-pressure turbine4and the medium-pressure turbine8are integrally configured. InFIG.2, there is mainly shown a structure of the high-pressure turbine4out of the high-pressure turbine4and the medium-pressure turbine8that are integrally configured.

The high-pressure turbine4shown inFIG.2includes an outer casing41, an annular member43, and a front-stage vane ring45.

In the high-pressure turbine4shown inFIG.2, the outer casing41is divided, in a horizontal plane, into an outer casing upper half portion41U and an outer casing lower half portion41L. In the following description, in a case where it is not necessary to distinguish the outer casing upper half portion41U and the outer casing lower half portion41L from each other, the outer casing upper half portion41U and the outer casing lower half portion41L are sometimes simply referred to as the outer casing41.

In the high-pressure turbine4shown inFIG.2, a plurality of turbine stages are provided in an axial direction on an inner periphery side of the outer casing41, and a main steam flow path21through which the main steam flows is formed. The turbine stage includes a plurality of rotor blades18fixed in a circumferential direction of the rotor13, and a stator vane19fixed to the annular member43or to the front-stage vane ring45, which will be described in detail later, so as to face the upstream side of each of the rotor blades18.

In the medium-pressure turbine8shown inFIG.2, a plurality of turbine stages are provided in the axial direction on the inner periphery side of the outer casing41, and a main steam flow path81through which the main steam flows is formed. The turbine stage includes a plurality of rotor blades83fixed in the circumferential direction of the rotor13, and a stator vane85fixed to a vane ring87so as to face the upstream side of each of the rotor blades83.

The steam turbine20according to one embodiment is provided with a plurality of pipe stands. The plurality of pipe stands include, for example, a first inlet pipe stand91for supplying main steam Sin from the main steam pipe3to the high-pressure turbine4, a second inlet pipe stand92for supplying bypass steam Sby from the bypass pipe16to the high-pressure turbine4, an air bleeding pipe stand93for discharging steam Sbl that is bled from the high-pressure turbine4, an outlet pipe stand94for discharging exhaust steam Sout, which drives the high-pressure turbine4and is then discharged, to the low-temperature reheat pipe5, a third inlet pipe stand95for supplying reheated steam Sr from the high-temperature reheat pipe7to the medium-pressure turbine8, and the like.

(Annular Member43)

In the high-pressure turbine4shown inFIG.2, the annular member43is a single member provided on the radial inner side of the outer casing41, and is formed with a seal region431, a rear-stage stator vane holding region433, and an inner casing region435.

In the high-pressure turbine4shown inFIG.2, the seal region431is provided between the high-pressure turbine4and the medium-pressure turbine8which are integrally provided. In the high-pressure turbine4shown inFIG.2, the seal region431is a region in which a sealing device51for sealing a gap between an outer peripheral surface13aof the rotor13and the annular member43is disposed. The sealing device51is, for example, a labyrinth seal having seal fins.

In the high-pressure turbine4shown inFIG.2, the rear-stage stator vane holding region433is a region that holds the rear-stage stator vanes19.

In the high-pressure turbine4shown inFIG.2, the inner casing region435is a region that connects the seal region431and the rear-stage stator vane holding region433.

In the high-pressure turbine4shown inFIG.2, the annular member43corresponds to a single member in which a dummy ring, a vane ring, and an inner casing are formed in a steam turbine of the related art.

A recessed portion437is provided in an inner peripheral portion431of the annular member43between the seal region431and the rear-stage stator vane holding region433. The front-stage vane ring45, which will be described in detail below, is disposed in the recessed portion437. The recessed portion437is separated by the front-stage vane ring45into a region on an axial upstream side and a region on an axial downstream side.

The region on the axial upstream side separated by the front-stage vane ring45, of the recessed portion437, forms a first cavity71, which will be described later. The region on the axial downstream side separated by the front-stage vane ring45, of the recessed portion437, forms a second cavity72, which will be described later.

Further, in the annular member43, a third cavity73for air bleeding is formed on the axial downstream side with respect to the second cavity72.

The first cavity71is connected to the first inlet pipe stand91. The second cavity72is connected to the second inlet pipe stand92. The third cavity73is connected to the air bleeding pipe stand93.

In the high-pressure turbine4shown inFIG.2, the annular member43is formed with a first contact portion438that restricts movement of the front-stage vane ring45toward the axial downstream side. The first contact portion438is formed on a surface on a radial outer side of an inner peripheral surface of the recessed portion437.

In the high-pressure turbine4shown inFIG.2, the annular member43is divided, in a horizontal plane, into an annular member upper half portion43U and an annular member lower half portion43L. The annular member upper half portion43U and the annular member lower half portion43L are joined together by a plurality of joining bolts that include a first joining bolt76and a second joining bolt77(refer toFIG.3to be described later).

In the following description, in a case where it is not necessary to distinguish the annular member upper half portion43U and the annular member lower half portion43L from each other, the annular member upper half portion43U and the annular member lower half portion43L are sometimes simply referred to as the annular member43.

(Front-Stage Vane Ring45)

FIG.4is a sectional view schematically showing part A inFIG.2.

In the high-pressure turbine4shown inFIG.2, as shown inFIG.4, the front-stage vane ring45is a member different from the annular member43, and is a vane ring that is mounted on the annular member43and that holds the front-stage stator vanes19. The front-stage vane ring45includes an inner region451that extends in the axial direction and that holds the stator vanes19, and an outer region452that protrudes radially outward from the inner region451.

The inner region451holds a plurality of stages of stator vanes19including a first stator vane19A which is the stator vane19in a most upstream stage.

A back surface451bon the radial outer side of the inner region451is radially separated from an inner peripheral surface437iof the recessed portion437of the annular member43.

The outer region452is a portion between an inclined surface453that faces the axial upstream side toward the radial inner side and an end surface454on the axial downstream side of the front-stage vane ring45.

In the high-pressure turbine4shown inFIG.2, the inclined surface453linearly extends to face the axial upstream side toward the radial inner side, in a cross section along a radial direction and the axial direction.

In the high-pressure turbine4shown inFIG.2, an axial wall thickness t (refer toFIG.4) of the front-stage vane ring45increases toward the radial inner side between the inclined surface453and the end surface454on the axial downstream side in the outer region452.

The front-stage vane ring45is formed with a second contact portion455that is a protrusion portion protruding radially outward from the outer region452. A surface455aon the axial downstream side of the second contact portion455comes into contact with a surface438aon the axial upstream side of the first contact portion438of the annular member43.

In the high-pressure turbine4shown inFIG.2, the end surface454of the front-stage vane ring45extends in a direction orthogonal to the axial direction. The end surface454of the front-stage vane ring45may extend in a direction inclined with respect to the radial direction, or may have a curved shape in the cross section along the radial direction and the axial direction.

In the high-pressure turbine4shown inFIG.2, the front-stage vane ring45is divided, in a horizontal plane, into a front-stage vane ring upper half portion45U and a front-stage vane ring lower half portion45L. In the following description, in a case where it is not necessary to distinguish the front-stage vane ring upper half portion45U and the front-stage vane ring lower half portion45L from each other, the front-stage vane ring upper half portion45U and the front-stage vane ring lower half portion45L are sometimes simply referred to as the front-stage vane ring45.

(First Cavity71)

In the high-pressure turbine4shown inFIG.2, the first cavity71is a cavity to which the main steam Sin from the main steam pipe3is supplied.

The first cavity71is formed by a region on the axial upstream side separated from the front-stage vane ring45, of the recessed portion437, and the front-stage vane ring45. Specifically, the first cavity71is defined by the inner peripheral surface of the region on the axial upstream side separated from the front-stage vane ring45, of the recessed portion437, the inclined surface453of the front-stage vane ring45, and the back surface451bof the inner region451.

The main steam Sin supplied to the first cavity71flows from the first cavity71toward the first stator vane19A, which is the stator vane19in the most upstream stage, and flows into the main steam flow path21.

(Second Cavity72)

In the high-pressure turbine4shown inFIG.2, the second cavity72is a cavity to which the bypass steam Sby from the bypass pipe16is supplied.

The second cavity72is formed by a region on the axial downstream side separated from the front-stage vane ring45, of the recessed portion437, and the front-stage vane ring45. Specifically, the second cavity72is defined by the inner peripheral surface of the region on the axial downstream side separated from the front-stage vane ring45, of the recessed portion437, and the end surface454on the axial downstream side of the front-stage vane ring45.

The bypass steam Sby supplied to the second cavity72flows from the second cavity72toward the stator vane19in the most upstream stage, among the stator vanes19mounted on the rear-stage stator vane holding region433, and flows into the main steam flow path21.

(Third Cavity73)

In the high-pressure turbine4shown inFIG.2, the third cavity73is a cavity provided for air bleeding on the axial downstream side with respect to the second cavity72.

The steam that has flowed into the third cavity73from the main steam flow path21is discharged to the outside of the high-pressure turbine4through the air bleeding pipe stand93.

FIG.5is a sectional view schematically showing a structure of a part of a steam turbine4X of the related art, in which a dummy ring431X, a vane ring433X, and an inner casing435X are separate members.

In the steam turbine4X of the related art, due to the pressure of the main steam supplied to the steam turbine4X, a relatively large thrust force to move the dummy ring431X to the axial upstream side acts on the dummy ring431X. Therefore, in order to ensure the strength of a fitting portion431Xa that fits into the inner casing435X in the dummy ring431X, the size of the dummy ring431X is made relatively large. As a result, the physical size of the turbine including the inner casing435X and an outer casing41X increases.

In the high-pressure turbine4shown inFIG.2, as described above, the seal region431, the rear-stage stator vane holding region433, and the inner casing region435are formed in the annular member43, which is a single member. Therefore, there is no fitting portion431Xa of the dummy ring431X in the steam turbine4X of the related art, so that compared to the steam turbine4X of the related art, the annular member43can be made smaller than the inner casing435X in the steam turbine4X of the related art. In this way, the high-pressure turbine4and the steam turbine20shown inFIG.2can be downsized. In other words, in the high-pressure turbine4shown inFIG.2, it is possible to supply higher-pressure steam while maintaining the same physical size as the physical size of the outer casing of the steam turbine of the related art.

Further, in the high-pressure turbine4shown inFIG.2, the number of the stator vanes19which are mounted on the rear-stage stator vane holding region433of the annular member43can be reduced by the number of the stator vanes19which are mounted on the front-stage vane ring45. Therefore, vane planting work of mounting the stator vanes19on the front-stage vane ring45and vane planting work of mounting the stator vanes19on the rear-stage stator vane holding region433of the annular member43can be performed in parallel. In this way, compared to a case where all the stator vanes19are mounted on the annular member43, a time required for the vane planting work can be shortened.

Further, in the high-pressure turbine4shown inFIG.2, the front-stage vane ring45which is mounted on the annular member43and holds the front-stage stator vanes19is provided, so that the first cavity71or the second cavity72can be formed between the annular member43and the front-stage vane ring45.

For example, in a case where the annular member43is formed by casting, there is considered a case where the front-stage vane ring45is integrally cast as the same member without being made a separate member from the annular member43. In this case, the first cavity71or the second cavity72becomes a relatively enclosed space such as a closed space, so that castability becomes poor, and, for example, a probability of casting defects occurring increases, so that it becomes difficult to ensure the reliability of a material.

According to the high-pressure turbine4shown inFIG.2, since the portion of the annular member43where the front-stage vane ring45is disposed is open to be relatively large, castability is improved, and in addition, after casting, trimming such as finishing the surfaces defining the first cavity71or the second cavity72becomes easier.

In the high-pressure turbine4shown inFIG.2, in order to secure the volume of the first cavity71to which the main steam from the main steam pipe3is supplied, the diameter of a radial outer wall surface forming the first cavity71, that is, the surface facing radially inward in the recessed portion437, has to be secured to a certain extent or more. Therefore, in the high-pressure turbine4shown inFIG.2, even if the portion corresponding to the front-stage vane ring45is formed in the annular member43which is a single member, the outer diameter of the annular member43does not become small. Therefore, from the viewpoint of downsizing the annular member43, there is almost no advantage in forming the portion corresponding to the front-stage vane ring45in the annular member43which is a single member.

On the contrary, in the high-pressure turbine4shown inFIG.2, the front-stage vane ring45is made to be a separate member from the annular member43, so that a time required for the vane planting work can be shortened as described above.

FIG.3is a diagram schematically showing a part of a cross section taken along line II-II inFIG.2and viewed in a direction of an arrow. InFIG.3, illustration of the rotor13is omitted. As shown inFIG.3, the high-pressure turbine4according to one embodiment includes the first joining bolt76which is a joining bolt that joins the annular member upper half portion43U and the annular member lower half portion43L, and which is disposed within a range in which the seal region431is formed along the axial direction. The high-pressure turbine4according to one embodiment includes the second joining bolt77which is disposed on the radial outer side with respect to the first joining bolt76, and whose position in the axial direction overlaps with the first joining bolt76. In the example shown inFIG.3, the first joining bolt76and the second joining bolt77are disposed at the same axial position.

In the high-pressure turbine4according to one embodiment, as described above, compared to the steam turbine4X of the related art, the annular member43can be made smaller than the inner casing435X in the steam turbine4X of the related art. In this way, the first joining bolt76and the second joining bolt77can be disposed side by side in the radial direction without increasing the size of the outer casing41. Therefore, it is possible to increase the pressure of the supplied steam without increasing the size of the outer casing41.

In the high-pressure turbine4according to one embodiment, as described above, the seal region431and the front-stage vane ring45form the first cavity71to which the main steam Sin is supplied, between the seal region431and the front-stage vane ring45.

In this way, since it is not necessary to separately provide a chamber for steam supply, an increase in the physical size of the high-pressure turbine4(the steam turbine20) can be suppressed.

In the high-pressure turbine4according to one embodiment, as described above, the front-stage vane ring45and the rear-stage stator vane holding region433form the second cavity72to which the bypass steam Sby from the bypass pipe16is supplied, between the front-stage vane ring45and the rear-stage stator vane holding region433.

In this way, the bypass steam Sby that is supplied in order to obtain an output exceeding the rated output in the high-pressure turbine4can be supplied to the second cavity72. In this way, an output exceeding the rated output can be obtained in the high-pressure turbine4.

In the high-pressure turbine4according to one embodiment, as shown inFIG.4, the front-stage vane ring45has a protrusion portion458that protrudes toward the axial downstream side at an end portion457that is located on the radial inner side with respect to the second cavity72and faces the rear-stage stator vane holding region433.

The protrusion portion458is, for example, a protrusion extending along the circumferential direction.

In this way, the flow of the bypass steam Sby flowing from the second cavity72through the gap between the front-stage vane ring45and the rear-stage stator vane holding region433is restricted by the protrusion portion458, so that it is possible to prevent a flow rate of the bypass steam Sby flowing toward the stator vanes19held by the rear-stage stator vane holding region433from becoming non-uniform in the circumferential direction.

As shown inFIGS.2and4, in the high-pressure turbine4according to one embodiment, a central axis C1 of the first inlet pipe stand91for supplying the main steam Sin to the first stator vane19A located on a most upstream side in the axial direction is located on the axial downstream side with respect to the first stator vane19A.

In this way, for example, in a case where two steam turbines (the high-pressure turbine4and the medium-pressure turbine8) are accommodated in one outer casing41, as in the steam turbine20according to one embodiment, an axial distance between the pipe stand (the third inlet pipe stand95) for supplying steam to the adjacent steam turbine (the medium-pressure turbine8) and the first inlet pipe stand91for supplying the main steam Sin can be secured. In this way, an axial length of the steam turbine20can be suppressed.

As shown inFIGS.2and4, in the high-pressure turbine4according to one embodiment, the inclined surface453of the front-stage vane ring45faces the first cavity71to which the main steam Sin is supplied. The inclined surface453is inclined with respect to the radial direction and the axial direction so as to face the axial upstream side toward the radial inner side.

In this way, the main steam Sin flowing into the first cavity71from the first inlet pipe stand91is guided by the inclined surface453and the back surface451bconnected to the inclined surface453, and is guided toward the axial upstream side. In this way, a pressure loss within the first cavity71can be suppressed.

The main steam Sin guided toward the axial upstream side is guided by the wall surface of the recessed portion437of the annular member43, flows toward the first stator vane19A, and flows into the main steam flow path21.

As shown inFIGS.2and4, in the high-pressure turbine4according to one embodiment, the front-stage vane ring45may have the inclined surface453that faces the axial upstream side toward the radial inner side.

A thrust force to move the front-stage vane ring45toward the axial downstream side with respect to the annular member43acts on the front-stage vane ring45due to the pressure of the main steam Sin. Therefore, as described above, the annular member43is formed with the first contact portion438that restricts the movement of the front-stage vane ring45toward the axial downstream side. Further, the front-stage vane ring45is formed with the second contact portion455that comes into contact with the first contact portion438.

Since during operation of the high-pressure turbine4, the thrust force acts on the front-stage vane ring45due to the pressure of the main steam Sin that is supplied, the second contact portion455comes into contact with the first contact portion438and receives a reaction force. The reaction force generates stress in the front-stage vane ring45.

In the high-pressure turbine4according to one embodiment, the high-pressure turbine4includes the inclined surface453, so that an axial dimension of the front-stage vane ring45can be increased toward the radial inner side. In this way, the stress that is generated in the front-stage vane ring45can be reduced.

In the high-pressure turbine4according to one embodiment, the inclined surface453may linearly extend to face the axial upstream side toward the radial inner side, in the cross section along the radial direction and the axial direction shown inFIGS.2and4.

In this way, compared to a case where the inclined surface453is a concave surface, the wall thickness of the front-stage vane ring45can be increased by the amount corresponding to the thickness when the inclined surface453is not a concave surface. In this way, the stress that is generated in the front-stage vane ring45can be reduced.

As shown inFIGS.2and4, in the high-pressure turbine4according to one embodiment, the axial wall thickness t (refer toFIG.4) of the front-stage vane ring45may increase toward the radial inner side between the end surface454on the axial downstream side of the front-stage vane ring45and the inclined surface453.

In this way, the stress that is generated in the front-stage vane ring45can be reduced.

As shown inFIGS.2and4, in the high-pressure turbine4according to one embodiment, the number of the stator vanes19that are held by the front-stage vane ring45may be smaller than the number of the stator vanes19that are held by the rear-stage stator vane holding region433.

By suppressing the number of stages in the front-stage vane ring45, it is possible to suppress a thrust force acting on the front-stage vane ring45due to the difference in steam pressure between the upstream side and the downstream side of the front-stage vane ring45. In this way, the first contact portion438and the second contact portion455, which are portions provided to restrict the movement of the front-stage vane ring45toward the axial downstream side, can be prevented from becoming large. Therefore, this contributes to downsizing of the high-pressure turbine4(the steam turbine20).

As shown inFIG.2, the steam turbine20according to one embodiment may be a medium-high pressure integrated type steam turbine20which includes a high-pressure section (the high-pressure turbine4) and a medium-pressure section (the medium-pressure turbine8). The high-pressure section (the high-pressure turbine4) may include the annular member43and the front-stage vane ring45described above.

In this way, the medium-high pressure integrated type steam turbine20can be downsized. Further, according to the steam turbine20according to one embodiment, a time required for vane planting work can be shortened.

In the steam turbine20according to one embodiment, the main steam Sin that is supplied to the first cavity71may be supercritical pressure steam. That is, the high-pressure turbine4according to one embodiment may be a supercritical pressure steam turbine.

According to the steam turbine20according to one embodiment, since the outer casing41, the annular member43, and the front-stage vane ring45described above are provided, the supercritical pressure steam turbine can be downsized. Further, according to the steam turbine20according to one embodiment, a time required for vane planting work in the supercritical pressure steam turbine can be shortened.

The present disclosure is not limited to the embodiments described above, and includes modified forms of the embodiments described above or forms in which these forms are combined as appropriate.

The contents described in each of the embodiments described above are understood as follows, for example.

(1) The steam turbine20(the high-pressure turbine4) according to at least one embodiment of the present disclosure includes the outer casing41. The steam turbine20(the high-pressure turbine4) according to at least one embodiment of the present disclosure includes the annular member43which is a single member provided on a radial inner side of the outer casing41, and which is formed with the seal region431in which the sealing device51for sealing the gap between the member and the outer peripheral surface13aof the rotor13is disposed, the rear-stage stator vane holding region433that holds the rear-stage stator vane19, and the inner casing region435that connects the seal region431and the rear-stage stator vane holding region433. The steam turbine20(the high-pressure turbine4) according to at least one embodiment of the present disclosure includes the front-stage vane ring45that is mounted on the annular member43and that holds the front-stage stator vane19.

According to the configuration of the above (1), the seal region431, the rear-stage stator vane holding region433, and the inner casing region435are formed in the annular member43which is a single member. Therefore, compared to the steam turbine4X of the related art, the annular member43can be made smaller than the inner casing435X in the steam turbine4X of the related art. In this way, the steam turbine20(the high-pressure turbine4) according to one embodiment can be downsized. In other words, according to the configuration of the above (1), it is possible to supply higher-pressure steam while maintaining the same physical size as the physical size of the outer casing41X of the steam turbine4X of the related art.

Further, according to the configuration of the above (1), the number of the stator vanes19which are mounted on the rear-stage stator vane holding region433of the annular member43can be reduced by the number of the stator vanes19which are mounted on the front-stage vane ring45. Therefore, vane planting work of mounting the stator vanes19on the front-stage vane ring45and vane planting work of mounting the stator vanes19on the rear-stage stator vane holding region433of the annular member43can be performed in parallel. In this way, compared to a case where all the stator vanes19are mounted on the annular member43, a time required for the vane planting work can be shortened.

(2) In some embodiments, in the configuration of the above (1), the annular member43may include an upper half portion (the annular member upper half portion43U) and a lower half portion (the annular member lower half portion43L) joined together in a horizontal plane. In some embodiments, a plurality of joining bolts (for example, the first joining bolt76and the overlapping second joining bolt77) that join the upper half portion (the annular member upper half portion43U) and the lower half portion (the annular member lower half portion43L) may be provided. The plurality of joining bolts may include the first joining bolt76disposed within a range in which the seal region431is formed along the axial direction, and the second joining bolt77that is disposed on the radial outer side with respect to the first joining bolt76and whose position in the axial direction overlaps with the first joining bolt76.

According to the configuration of the above (2), compared to the steam turbine4X of the related art, the annular member43can be made smaller than the inner casing435X in the steam turbine4X of the related art. In this way, the first joining bolt76and the second joining bolt77can be disposed side by side in the radial direction without increasing the size of the outer casing41. Therefore, it is possible to increase the pressure of the supplied steam without increasing the size of the outer casing41.

(3) In some embodiments, in the configuration of the above (1) or (2), the seal region431and the front-stage vane ring45may form the first cavity71to which first steam (the main steam Sin) is supplied, between the seal region431and the front-stage vane ring45.

According to the configuration of the above (3), since it is not necessary to separately provide a chamber for steam supply, an increase in the physical size of the steam turbine20(the high-pressure turbine4) can be suppressed.

(4) In some embodiments, in the configuration of the above (3), the front-stage vane ring45and the rear-stage stator vane holding region433may form the second cavity72to which second steam (the bypass steam Sby) is supplied, between the front-stage vane ring45and the rear-stage stator vane holding region433.

According to the configuration of the above (4), as the second steam, for example, external steam (the bypass steam Sby) that is supplied to obtain an output exceeding the rated output in a steam turbine can be supplied to the second cavity72. In this way, an output exceeding the rated output is obtained in the steam turbine20(the high-pressure turbine4).

(5) In some embodiments, in the configuration of the above (4), the front-stage vane ring45may have the protrusion portion458that protrudes toward the axial downstream side at the end portion457that is located on the radial inner side with respect to the second cavity72and faces the rear-stage stator vane holding region433.

According to the configuration of the above (5), the flow of steam (the bypass steam Sby) flowing from the second cavity72through the gap between the front-stage vane ring45and the rear-stage stator vane holding region433is restricted by the protrusion portion458, so that the flow rate of the steam (the bypass steam Sby) flowing toward the stator vanes19held by the rear-stage stator vane holding region433can be prevented from becoming non-uniform in the circumferential direction.

(6) In some embodiments, in the configuration of any one of the above (1) to (5), the central axis C1 of the pipe stand (the first inlet pipe stand91) for supplying the first steam (the main steam Sin) to the first stator vane19A that is located on the most upstream side in the axial direction may be located on the axial downstream side with respect to the first stator vane19A.

According to the configuration of the above (6), for example, in a case where two steam turbines (the high-pressure turbine4and the medium-pressure turbine8) are accommodated in one outer casing41, as in the steam turbine20according to one embodiment, the axial distance between the pipe stand (the third inlet pipe stand95) for supplying steam to the adjacent steam turbine (the medium-pressure turbine8) and the first inlet pipe stand91for supplying the main steam Sin can be secured. In this way, an axial length of the steam turbine20can be suppressed.

(7) In some embodiments, in the configuration of any one of the above (1) to (6), the front-stage vane ring45may have the inclined surface453that faces the axial upstream side toward the radial inner side.

According to the configuration of the above (7), the inclined surface453is provided, so that the axial dimension of the front-stage vane ring45can be increased toward the radial inner side. In this way, the above-described stress that is generated in the front-stage vane ring45can be reduced.

(8) In some embodiments, in the configuration of the above (7), the inclined surface453may linearly extend to face the axial upstream side toward the radial inner side, in the cross section along the radial direction and the axial direction.

According to the configuration of the above (8), compared to a case where the inclined surface453is a concave surface, the wall thickness of the front-stage vane ring45can be increased by the amount corresponding to the thickness when the inclined surface453is not a concave surface. In this way, the above-described stress that is generated in the front-stage vane ring45can be reduced.

(9) In some embodiments, in the configuration of the above (7) or (8), the axial wall thickness t of the front-stage vane ring45may increase toward the radial inner side between the end surface454on the axial downstream side of the front-stage vane ring45and the inclined surface453.

According to the configuration of the above (9), the above-described stress that is generated in the front-stage vane ring45can be reduced.

(10) In some embodiments, in the configuration of any one of the above (1) to (9), the number of the stator vanes19that are held by the front-stage vane ring45may be smaller than the number of the stator vanes19that are held by the rear-stage stator vane holding region433.

According to the configuration of the above (10), by suppressing the number of stages in the front-stage vane ring45, it is possible to suppress a thrust force acting on the front-stage vane ring45due to the difference in steam pressure between the upstream side and the downstream side of the front-stage vane ring45. In this way, the portions (the first contact portion438and the second contact portion455) which are provided to restrict the movement of the front-stage vane ring45toward the axial downstream side can be prevented from becoming large in both the front-stage vane ring45and the annular member43. Therefore, this contributes to downsizing of the steam turbine20(the high-pressure turbine4)

(11) In some embodiments, in the configuration of any one of the above (1) to (10), the steam turbine20may be a medium-high pressure integrated type steam turbine20which includes a high-pressure section (the high-pressure turbine4) and a medium-pressure section (the medium-pressure turbine8). The high-pressure section (the high-pressure turbine4) may include the annular member43and the front-stage vane ring45.

According to the configuration of the above (11), the medium-high pressure integrated type steam turbine20can be downsized. Further, according to the configuration of the above (11), a time required for vane planting work in the medium-high pressure integrated type steam turbine20can be shortened.

(12) In some embodiments, in the configuration of any one of the above (1) to (11), the seal region431and the front-stage vane ring45may form the first cavity71to which first steam (the main steam Sin) is supplied, between the seal region431and the front-stage vane ring45. The first steam (main steam Sin) may be supercritical pressure steam.

According to the configuration of the above (12), the supercritical pressure steam turbine can be downsized. Further, according to the configuration of the above (12), a time required for vane planting work in the supercritical pressure steam turbine can be shortened.

REFERENCE SIGNS LIST

4: high-pressure turbine19: stator vane19A: first stator vane20: steam turbine41: outer casing43: annular member45: front-stage vane ring51: sealing device71: first cavity72: second cavity76: first joining bolt77: second joining bolt91: first inlet pipe stand92: second inlet pipe stand431: seal region433: rear-stage stator vane holding region435: inner casing region437: recessed portion453: inclined surface454: end surface457: end portion458: protrusion portion