Steam turbine having a nozzle box arranged at an upstream side of a steam passage that divides a space between a rotor and a casing into spaces that are sealed from each other

A steam turbine has a stationary section, a turbine rotor, nozzle diaphragms, a steam passage section, a nozzle box and a sealing. The stationary section includes a casing. The turbine rotor includes moving blade stages. Each of the moving blade stages has turbine moving blades. Each of the nozzle diaphragms has turbine nozzles. The moving blade portions and the turbine nozzle portions constitute the steam passage. The nozzle box is held by the stationary section and arranged at an upstream side of the steam passage coaxially with the turbine rotor. The sealing divides a space between the turbine rotor and the casing into a first space provided at an inner side and a second space provided at an outer side of the nozzle box.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2007-215768, filed in the Japanese Patent Office on Aug. 22, 2007, the entire content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a steam turbine and, more particularly, it relates to steam turbine designed to achieve a high efficiency by improving the nozzle box arrangement in the steam inlet section.

Generally, a steam turbine comprises a rotatable turbine rotor, moving blade stages, a casing and nozzle diaphragms. The casing and the nozzle diaphragms constitute as a stationary section. The rotor is rotatably provided in the casing. The nozzle diaphragms are arranged substantially coaxially with the turbine rotor, supported on the casing. The moving blade stages are provided on the turbine rotor so as to rotate together with the turbine rotor. Each of the moving blade stages comprises a plurality of moving blades arranged in the circumferential direction of the turbine rotor.

Each of the nozzle diaphragms comprises a plurality of turbine nozzles arranged in the circumferential direction relative to the turbine rotor and arranged at the upstream side of one of the moving blade stage. A pair of a nozzle diaphragm and a moving blade stage provided at the upstream side of the nozzle diaphragm forms a turbine stage. An ordinary steam turbine has a plurality of turbine stages.

More specifically, nozzle diaphragms, a turbine rotor and moving blade stages are substantially coaxially arranged in the casing. The steam led to a nozzle diaphragm passes through a plurality of turbine nozzles of the nozzle diaphragm and change its flowing direction. Then, the steam flowing out from the nozzle diaphragm is led to a moving blade portion of a moving blade stage that forms a pair with the nozzle diaphragm. The steam drives the moving blade stage and the turbine rotor as it passes between the plurality of moving blades of the moving blade stage.

As pointed out above, an ordinary steam turbine has a plurality of turbine stages. The steam that passes through one turbine stage is led to an adjacent turbine stage. More specifically, a plurality of moving blade stages are provided on the turbine rotor, separated from each other in the axial direction. The nozzle diaphragms are arranged in the casing so as to be placed between the moving blade stages in the axial direction of the turbine rotor. The moving blade portions of a plurality of moving blade stages and the turbine nozzle portions of a plurality of nozzle diaphragms form a steam passage.

Especially, for a high pressure turbine, a nozzle box is provided in the casing to lead the steam introduced in the casing to the turbine nozzles of the first stage, which constitute as a part of the steam passage. Known nozzle boxes include one described in Japanese Patent Application Laid-Open Publication No. 03-066484, the entire content of which is incorporated herein by reference.

Like the casing, the nozzle box constitutes as the stationary section. The nozzle box comprises a plurality of turbine nozzles of the first stage, which are arranged in the circumferential direction, provided at the outlet side of the nozzle box. In other words, the nozzle box and the nozzle diaphragm of the first stage (e.g. the first stage nozzle diaphragm) are arranged integrally and the steam introduced into the nozzle box is led to the steam passage, that includes the first moving blade stage that forms a pair with the first stage nozzle diaphragm provided with the nozzle box.

FIGS. 8 and 9are schematic axial cross-sectional views of a known steam turbine having a nozzle box.FIG. 8is a schematic axial cross-sectional view along a vertical direction andFIG. 9is a schematic axial cross-sectional view along an angle inclined relative to the vertical direction by 45°.

The steam turbine1has a casing2, a turbine rotor3rotatably arranged in the casing2, a nozzle diaphragms4a1,4a2,4a3, . . . that are rigidly secured to the casing2. The casing2includes an outer casing2aand an inner casing2b.

A plurality of moving blade stages3a1,3a2,3a3, . . . , are arranged on the turbine rotor3, which is a rotating section of the steam turbine1, in the axial direction from the upstream side to the downstream side. Each of the moving blade stages3a1,3a2,3a3has a plurality of moving blades, the plurality of moving blades of the moving blade stages being denoted respectively by3b1,3b2,3b3, . . . , and rotating force is generated as steam flows, passing through the moving blades3b1,3b2,3b3, . . . .

Nozzle diaphragms4a1,4a2,4a3, . . . that are supported by the inner casing2bare arranged between the moving blade stages3a1,3a2,3a3, . . . such that they are substantially coaxial and separated from each other in the axial direction. A pair of the nozzle diaphragms4a1,4a2,4a3, . . . and the moving blade stages3a1,3a2,3a3, . . . , respectively, constitutes a turbine stage. A plurality of turbine nozzles4b1,4b2,4b3, . . . are provided in the circumferential direction, respectively, with the nozzle diaphragms4a1,4a2,4a3, . . . .

The nozzle diaphragms4a1,4a2,4a3, . . . are supported by the casing2so as to constitute a stationary section of the steam turbine1. The steam flow flowing through between the plurality of nozzle blades4b1,4b2,4b3, . . . arranged in the circumferential direction is changed its flowing direction so as to be led to the moving blades3b1,3b2,3b3, . . . of the moving blade stages3a1,3a2,3a3, . . . of the pairs. The flow path of the steam including the portions of the turbine nozzles4b1,4b2,4b3, . . . of the nozzle diaphragms4a1,4a2,4a3, . . . and the portions of the moving blades3b1,3b2,3b3, . . . of the moving blade stages3a1,3a2,3a3constitute as steam passage8. The steam led to the steam turbine1flows through the steam passage8from an upstream side to a downstream side.

The steam turbine1is provided with a steam inlet pipe7and a nozzle box5that constitutes as members for introducing steam into the steam passage8. The nozzle box5is a pressure vessel that deals with high temperature and high pressure steam. An inlet section of the nozzle box5is connected to the steam inlet pipe7. A steam outlet section, namely, outlet section, of the nozzle box5is integrally provided with the first stage nozzle diaphragm4a1and the plurality of turbine nozzles4b1that are arranged in the circumferential direction.

The nozzle box5is rigidly secured to the casing2by a support member6arranged on the inner casing2b. The plurality of first stage turbine nozzles4b1, integrally arranged in the circumferential direction at the outlet section, serves as the first stage nozzle diaphragm4a1. The nozzle box5is arranged substantially coaxial with the turbine rotor3.

Thus, the steam flowed into the nozzle box5from the steam inlet pipe7is then led to the first stage nozzle diaphragm4a1that constitute as a part of steam passage8. The steam led to the steam passage8expands as it passes through between the turbine nozzles4b1,4b2,4b3, . . . and the moving blades3b1,3b2,3b3, . . . and the thermal energy is converted into kinetic energy to drive the moving blade stages3a1,3a2,3a3, . . . and the turbine rotor3.

Note that the support member6is a member for supporting the nozzle box5in the inner casing2b. The support member6is not arranged entirely along the nozzle box5in the circumferential direction as seen inFIG. 9.

The nozzle box5is arranged in a space formed between the inner casing2band the turbine rotor3. The pressure of the space around the nozzle box5is substantially equal to the pressure of the steam passage8near the outlet of the first moving blade stage3a1.

More particularly, in the steam turbine1as shown inFIG. 9, a part of the steam flowing out from the first stage nozzle diaphragm4a1of the nozzle box5does not flow along the steam passage8into the first moving blade stage3a1, which outputs rotation energy converted from thermal energy. The steam, which does not flow along the steam passage8at the downstream side of the first stage nozzle diaphragm4a1of the nozzle box5, leaks to the space around the nozzle box5and bypasses to the downstream side of the first moving blade stage3a1via an outer circumferential side of the nozzle box5(e.g. a space between the nozzle box5and the inner casing2b), as indicated by dotted arrows inFIG. 9. This problem becomes particularly significant in a turbine having a large degree of reaction where the pressure difference between the outlet of the first stage turbine nozzles4b1and the outlet of the first moving blade stage3a1is large.

Additionally, in the known steam turbine1, the pressure of the space around the nozzle box5is substantially equal to the pressure at the outlet of first moving blade stage3a1, which has a large pressure difference with that of the steam flowing into the nozzle box5. Therefore, when the steam conditions such as the temperature and the pressure of the steam flowing into the steam turbine1are raised in order to improve the efficiency of the steam turbine1, further studies are necessary including the wall thickness of the nozzle box5and the materials suitable for the nozzle box5such as heat-resistant steel. The net result will be a raised cost of such a steam turbine1.

BRIEF SUMMARY OF THE INVENTION

An object of the present invention is to provide a high performance steam turbine that can improve the efficiency of known steam turbine including the steam turbine having the nozzle box of above-mentioned structure.

According to the present invention, there is provided a steam turbine comprising: a stationary section that includes a casing; turbine rotor that includes a plurality of moving blade stages arranged in an axial direction, each of the moving blade stages being provided with a plurality of turbine moving blades arranged in a circumferential direction, and rotatably provided in the casing; a plurality of nozzle diaphragms, wherein each of the nozzle diaphragms having a plurality of turbine nozzles arranged in the circumferential direction, arranged substantially coaxially with the turbine rotor by being supported on the stationary section; a steam passage formed with moving blade portions of the plurality of moving blade stages and turbine nozzle portions of the plurality of nozzle diaphragms; a nozzle box supported on the stationary section, wherein the nozzle box is arranged at an upstream side of the steam passage substantially coaxially with the turbine rotor; and a sealing that divides a space between the turbine rotor and the casing into a first space provided at an inner side of the nozzle box and a second space provided at an outer side of the nozzle box.

DETAILED DESCRIPTION OF THE INVENTION

Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate preferred embodiments of the invention.

FIG. 1is a schematic axial cross-sectional view of the first embodiment of steam turbine according to the present invention, taken along a plane inclined by 45° from the vertical direction. InFIG. 1, the components same as those of the known steam turbine shown inFIGS. 8 and 9are denoted respectively by the same reference symbols and will not be described any further unless necessary.

The steam turbine1of this embodiment has a casing2, a turbine rotor3rotatably arranged in the casing2and nozzle diaphragms4a1,4a2,4a3, . . . rigidly secured to the casing2. The casing2includes an outer casing2aand an inner casing2b.

A plurality of moving blade stages3a1,3a2,3a3, . . . are arranged on the turbine rotor3, which is a rotating section of the steam turbine1, in the axial direction from the upstream side to the downstream side. Each of the moving blade stages3a1,3a2,3a3has a plurality of moving blades, the plurality of moving blades of the moving blade stages being denoted respectively by3b1,3b2,3b3, . . . , and rotating force is generated as steam flows, passing between the moving blades3b1,3b2,3b3, . . . .

Nozzle diaphragms4a1,4a2,4a3, . . . that are supported by the inner casing2bare arranged between the moving blade stages3a1,3a2,3a3, . . . such that they are substantially coaxial with the turbine rotor3and separated from each other in the axial direction. A pair of the nozzle diaphragms4a1,4a2,4a3, . . . and the moving blade stages3a1,3a2,3a3, . . . , respectively, constitutes a turbine stage. A plurality of turbine nozzles4b1,4b2,4b3, . . . are provided in the circumferential direction, respectively with the nozzle diaphragms4a1,4a2,4a3, . . . .

The nozzle diaphragms4a1,4a2,4a3, . . . are supported by the inner casing2so as to constitute a stationary section of the steam turbine1. The steam flow flowing through between the plurality of turbine nozzles4b1,4b2,4b3, . . . arranged in the circumferential direction is changed its direction so as to be led to the moving blades3b1,3b2,3b3, . . . of the moving blade stages3a1,3a2,3a3, . . . of the pairs. The flow path of the steam including the portions of the turbine nozzles4b1,4b2,4b3, . . . of the nozzle diaphragms4a1,4a2,4a3, . . . and the portions of the moving blades3b1,3b2,3b3, . . . of the moving blade stages3a1,3a2,3a3constitute as a steam passage8. The steam led to the steam turbine1flows through the steam passage8from an upstream side to a downstream side.

A shaft sealing device12is provided between the turbine rotor3and the inner casing2bso as to prevent steam in the vicinity of the turbine rotor3from leaking to the space outside the inner casing2b. The shaft sealing device12comprises a main body and a plurality of packing heads that circumferentially engage with the main body.

The steam turbine1is provided with a nozzle box5that introduces steam into the steam passage8. The nozzle box5is a pressure vessel that deals with high temperature and high pressure steam. Like the known steam turbine shown inFIG. 8, a steam inlet pipe (not shown) is connected to the steam inlet section of the nozzle box5. At the outlet section of the nozzle box5, namely a steam outlet section of the nozzle box5, constitutes as part of the steam passage8, a plurality of first stage turbine nozzles4b1are arranged in the circumferential direction. In other words, the first stage nozzle diaphragm4a1is structurally integrally provided at the outlet section of the nozzle box5.

The nozzle box5is supported on the inner casing2bsubstantially coaxial with the turbine rotor3. A bulkhead9, as a sealing, secures nozzle box5to the inner casing2b. The bulkhead9is arranged between the nozzle box5and the inner casing2b, which is a stationary section, along the entire circumferential direction of the nozzle box5so that a space between the turbine rotor3and the inner casing2bis divided into two spaces including an inner space10athat is located inside relative to the steam passage8and an outer space10bthat is located outside relative to the steam passage8. The inner space10ameans a space including an inner peripheral side (inner side) of the nozzle box5, and the outer space10bmeans a space including at least an outer peripheral side (outer side) of the nozzle box. The outer peripheral side of the nozzle box5includes outer peripheral side of the steam passage8. Steam is prevented from flowing from the inner space10ato the outer space10band vice versa by the bulkhead9provided as the sealing between the nozzle box5and a stationary section other than the nozzle box5.

Thus, the steam flowed into the nozzle box5is then led to the steam passage8from the outlet section of the nozzle box5. The steam led to the steam passage8expands as it passes through between the turbine nozzles4b1,4b2,4b3, . . . and the moving blades3b1,3b2,3b3, . . . and converts its thermal energy into kinetic energy so as to drive the moving blade stages3a1,3a2,3a3, . . . and the turbine rotor3.

Having this bulkhead9as a sealing, the steam that flows out from the outlet section of the nozzle box5(e.g. the first stage nozzle diaphragm4a1) does not bypass to the outlet side of the first moving blade stage3a1via the outer space10b. Therefore, most of the steam flowing out from the first stage nozzle diaphragm4a1can be led to the first moving blade stage3a1along the steam passage8. As a result, the thermal energy of the steam flowing out from the first stage nozzle diaphragm4a1can be efficiently converted into kinetic energy to improve the efficiency of the steam turbine1.

Additionally, in this embodiment, an anti-leakage steam seal11is arranged between the first moving blade stage3a1and the nozzle box5. With this arrangement, the flow of steam leaking out from the steam passage8between the outlet section of the nozzle box5and the adjacently located moving blade stage3a1can be reduced by the anti-leakage steam seal11to improve the performance of the steam turbine1.

The bulkhead9, which is a sealing, is integrally formed with the nozzle box5in this embodiment. However, it may alternatively be arranged integrally with the inner casing2bor separately relative to the nozzle box5and the inner casing2bas long as it is arranged between the nozzle box5and some other stationary section of the steam turbine1and can prevent the flow of steam between the inner space10aand the outer space10b.

FIGS. 2 and 3illustrate modified embodiments of this embodiment.FIGS. 2 and 3are schematic axial cross-sectional views of the modified embodiments taken along a plane inclined by 45° from the vertical direction of the steam turbine. InFIGS. 2 and 3, the components same as those of the steam turbine ofFIG. 1are denoted respectively by the same reference symbols and will not be described in detail any further.

In these modified embodiments of steam turbine1, the space formed around the nozzle box5between the turbine rotor3and the inner casing2bis divided into two spaces including an inner space10athat is located inside relative to the steam passage section8and an outer space10bthat is located outside relative to the steam passage section8by a sealing other than a bulkhead as shown inFIG. 1. Otherwise, the configuration of each of these modified embodiments is the same as that of the first embodiment shown inFIG. 1.

In the embodiment described inFIG. 1, the bulkhead9is provided as a sealing dividing the inner space10aand the outer space10b. In this modified embodiment, in contrast, a nozzle box sealing device13is provided as a sealing instead of the bulkhead9as shown in each ofFIGS. 2 and 3. In other words, in each of the modified embodiments, the space formed around the nozzle box5between the turbine rotor3and the inner casing2bis divided into two spaces including an inner space10athat is located inside relative to the steam passage8and an outer space10bthat is located outside relative to the steam passage8by the nozzle box sealing device13. The inner space10ameans a space including an inner peripheral side (inner side) of the nozzle box5, and the outer space10bmeans a space including at least an outer peripheral side (outer side) of the nozzle box. The outer peripheral side of the nozzle box5includes outer peripheral side of the steam passage8.

Particularly, in modified embodiment shown inFIG. 2, the nozzle box sealing device13comprises a casing side sealing device13a, which seals a gap between the nozzle box5and the inner casing2b, and a rotor side sealing device13b, which seals a gap between the nozzle box5and the shaft sealing device12, in order to prevent steam flow flowing from the inner space10ato the outer space10band vice versa. This arrangement provides advantages similar to those of the first embodiment ofFIG. 1.

With another modified embodiment shown inFIG. 3, the nozzle box sealing device13comprises a packing head13c, which seals a gap between the nozzle box5and the turbine rotor3, and a groove section13dcircumferentially provided on an outer surface of the nozzle box5facing to the turbine rotor3. The packing head13ccomprises a plurality of segments arranged in the circumferential direction inserted into the groove section13dof the nozzle box5for engagement, so that as a whole the gap between the nozzle box5and the turbine rotor3is sealed along the entire periphery of the turbine rotor3.

With this arrangement, the maintainability of the packing head13cis improved, so that the packing head13ccan be readily replaced by new ones when steam leaks due to degradation of the packing head13coccurs. The modified embodiment ofFIG. 3has two nozzle box sealing devices13, each having a packing head13cand a groove section13d, that are arranged in series in the axial direction. However, the number of nozzle box sealing devices13may be one or more than two appropriately depending on the required pressure difference between the inner space10aand the outer space10b.

Now, the steam turbine of the second embodiment will be described below by referring toFIG. 4.

FIG. 4is a schematic axial cross-sectional view of the second embodiment of steam turbine according to the present invention taken along a plane inclined by 45° from the vertical direction. InFIG. 4, the components same as those of the steam turbine ofFIG. 1are denoted respectively by the same reference symbols and will not be described in detail any further.

The nozzle box5is integrally provided with the first stage nozzle diaphragm4a1and the nozzle box5holds the first stage turbine nozzles4b1in the steam turbine of the first embodiment. In this second embodiment, the nozzle box5holds not only the first stage turbine nozzles4b1but also at least another stage of turbine nozzles, the second stage turbine nozzles4b2for instance.

More specifically, in this embodiment as shown inFIG. 4, the outer peripheral side member of the nozzle box5extends to the downstream side in the axial direction. A hook section is provided at the extended portion (e.g. the outer peripheral side member of the nozzle box5extended to the downstream side in the axial direction). The second stage nozzle diaphragm4a2engages with the hook section. A plurality of second stage turbine nozzles4b2are arranged in the circumferential direction on the second stage nozzle diaphragm4a2. Thus, the second stage turbine nozzles4b2are secured to the nozzle box5having the second stage nozzle diaphragm4a2therebetween. Otherwise, this embodiment is same as the first embodiment. Note that the bulkhead9separating the inner space10aand the outer space10bis integrally formed with the inner casing2b.

The second stage nozzle diaphragm4a2that supports the second stage turbine nozzles4b2is arranged separately with the nozzle box5inFIG. 4. Alternatively, the second stage nozzle diaphragm4a2may be arranged integrally with the nozzle box5like the first stage nozzle diaphragm4a1.

With this arrangement, the pressure of the outer space10bof the space around the nozzle box5is substantially equal to the pressure of the steam passage8at the outlet of the second moving blade stage3a2. As a result, the pressure of the outer space10bcan be further reduced so that the wall thickness of the inner casing2bcan be reduced.

Additionally, since the space around the nozzle box5is divided into the outer space10band the inner space10aby the bulkhead9, the steam flowing out from the turbine nozzles4b1of the first stage nozzle diaphragm4a1would not bypass through the space around the nozzle box5and flow out along the steam passage8so that the steam turbine of this embodiment can achieve a high efficiency.

This embodiment can be modified in various different ways like the first embodiment. Modified embodiments of the second embodiment will be described below by referring toFIGS. 5 through 7.

FIGS. 5 through 7are schematic axial cross-sectional views of the modified embodiments of the second embodiment taken along a plane inclined by 45° from the vertical direction. In FIGS.5through7, the components same as those of the steam turbines ofFIGS. 1 through 4are denoted respectively by the same reference symbols and will not be described in detail any further.

In each of the modified embodiments shown inFIGS. 5 and 6, the bulkhead9for dividing the space around the nozzle box5into an inner space10aand an outer space10bas shown inFIG. 4is replaced by a nozzle box sealing device13. Otherwise, the modified embodiments are the same as the second embodiment shown inFIG. 4.

In the modified embodiment shown inFIG. 5, the nozzle box sealing device13comprises a casing side sealing device13a, which seals a gap between the nozzle box5and the inner casing2b, and a rotor side sealing device13b, which seals a gap between the nozzle box5and the main body of the shaft sealing device12like the modified embodiment of the first embodiment shown inFIG. 2.

In the modified embodiment shown inFIG. 6, the nozzle box sealing device13comprises a packing head13c, which seals a gap between the nozzle box5and the turbine rotor3, and a groove section13dcircumferentially provided on an outer surface of the nozzle box5facing to the turbine rotor3. In the modified embodiment shown inFIG. 6, like in the modified embodiment of the first embodiment shown inFIG. 3, the packing head13ccomprises a plurality of segments arranged in the circumferential direction inserted into the groove section13dof the nozzle box5for engagement, so that as a whole the gap between the nozzle box5and the turbine rotor3is sealed along the entire periphery of the turbine rotor3. The modified embodiment ofFIG. 6also has two nozzle box sealing devices13, each having a packing head13cand a groove section13d, that are arranged in series in the axial direction. However, the number of nozzle box sealing devices may be selected appropriately depending on the design conditions and other factors.

The modified embodiment shown inFIG. 7is a further modification of the modified embodiment shown inFIG. 6. In the second embodiment and its modified embodiments shown inFIGS. 4 through 6, the nozzle box5holds the first stage turbine nozzles4b1and the second stage turbine nozzles4b2. On the other hand, in the modified embodiment shown inFIG. 7, the nozzle box5further holds the third stage turbine nozzles4b3.

More specifically, as shown inFIG. 7, the outer peripheral side member of the nozzle box5extends to the downstream side in the axial direction. Two hook sections are provided at the extended portion and the second stage nozzle diaphragm4a2and the third stage nozzle diaphragm4a3are engaged respectively with the two hook sections. A plurality of second stage turbine nozzles4b2and a plurality of third stage turbine nozzles4b3are circumferentially provided respectively with the second stage nozzle diaphragm4a2and the third stage nozzle diaphragm4a3. Thus, in this modified embodiment, the second stage turbine nozzles4b2and the third stage turbine nozzles4b3are secured to the nozzle box5respectively, having the second stage nozzle diaphragm4a2and the third stage nozzle diaphragm4a3therebetween. Otherwise, the configuration of this modified embodiment is the same as that of the modified embodiment of the second embodiment shown inFIG. 6.

With this arrangement, the pressure of the outer space10bof the space around the nozzle box5is substantially equal to the pressure of the steam passage section8at the outlet of the third moving blade stage3a3. As a result, the pressure of the outer space10bcan be further reduced so that the wall thickness of the inner casing2bcan be reduced accordingly.

In this modified embodiment shown inFIG. 7, the second and third stage nozzle diaphragms4a2,4a3are arranged separately with the nozzle box5and the second stage and third stage turbine nozzles4b2,4b3are held by the nozzle box5respectively by having the nozzle diaphragms4a2,4a3therebetween. The arrangement is not limited thereto and the second stage and third stage nozzle diaphragms4a2,4a3may be integrally formed with the outer peripheral member of the nozzle box5extended to the downstream side in the axial direction.

The first through third stage turbine nozzles4b1,4b2,4b3are held by the nozzle box5in the modified embodiment shown inFIG. 7. The fourth and the subsequent turbine nozzles4b4, . . . may also be held by the nozzle box5.

The nozzle box sealing device13including the packing head13cand the groove section13dis provided as a sealing for dividing the space around the nozzle box5into the inner space10aand the outer space10bin the modified embodiment ofFIG. 7. However, the nozzle box sealing device13may be two members including a casing side sealing device13a, which seals a gap between the nozzle box5and the inner casing2band a rotor side sealing device13b, which seals a gap between the nozzle box5and the main body of the shaft sealing device12as shown inFIG. 2orFIG. 5. Alternatively, the nozzle box sealing device13may be replaced by a bulkhead9as shown inFIG. 1orFIG. 4.