JP2004353603A - Steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a steam turbine in which a turbine nozzle box can secure high level of strength guarantee by coping with superhigh temperature reheated steam. <P>SOLUTION: In the steam turbine, an intermediate pressure turbine 2 is divided into a first intermediate pressure turbine 2a and a second intermediate pressure turbine 2b. The divided first intermediate pressure turbine 2a is arranged as a top turbine. The second intermediate pressure turbine 2b is assembled in a steam turbine part 1 arranged as a bottom turbine. While steam from a high pressure turbine in the steam turbine part 1 is supplied to a turbine nozzle box 31 mounted in the first intermediate pressure turbine 2a as cooling steam and a wall inside surface of a wall 37 in the turbine nozzle box is covered with a shield plate 41. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a steam turbine, and more particularly, to a steam turbine that copes with a high temperature of steam and maintains a high strength guarantee of a turbine nozzle box.
[0002]
[Prior art]
The higher temperature of the steam skillfully utilizes the characteristics of the Rankine cycle, and it is said that the higher the steam temperature, the higher the thermal efficiency of the plant.
[0003]
For this reason, the steam turbine is almost settled at the single-stage reheating of the steam temperature of 538 ° C./566° C. or 538 ° C./538° C. due to the relatively low temperature and low pressure steam conditions.
[0004]
However, recently, global warming phenomena and environmental destruction due to pollutants such as CO ₂ and NOx have been highlighted on a global scale. Research and development to increase the capacity has been promoted, and one of them is to classify the intermediate pressure turbine into a first intermediate pressure turbine and a second intermediate pressure turbine, and arrange the divided first intermediate pressure turbine as a top turbine, Incorporating the second intermediate-pressure turbine in a conventional steam turbine section arranged as a bottom turbine in the same manner as before, and supplying reheated steam from the reheater of the boiler to the first intermediate-pressure turbine at a temperature of 700 ° C. or higher. Has been proposed (see Patent Document 1).
[0005]
In the case where the reheat steam temperature is 700 ° C. or higher, the first intermediate pressure turbine arranged as the top turbine has many problems to be solved. One of the problems is a turbine connected to the reheat steam supply pipe. There is the strength of the nozzle box.
[0006]
This turbine nozzle box functions as a steam chamber when the reheat steam supplied from the reheater of the boiler is supplied to the turbine stage via the reheat steam supply pipe, but it takes more than a minute. High strength assurance is required just because of direct exposure to high temperature reheated steam. We are currently exploring securing a high strength guarantee.
[0007]
[Patent Document 1]
Japanese Patent Application No. 2003-125672
[Problems to be solved by the invention]
Conventionally, in a thermal power plant, a turbine nozzle box has been installed on a steam inlet side of a high-pressure turbine in a conventional steam turbine section, and has been adapted to cope with main steam having a temperature of 538 ° C to 566 ° C to maintain high strength.
[0009]
However, even if the turbine nozzle box installed on the high-pressure turbine is installed on the first intermediate-pressure turbine as the top turbine as it is, if the temperature of the reheated steam becomes significantly higher than 700 ° C., a high strength is guaranteed. Is becoming more difficult to maintain.
[0010]
For this reason, it is desired for a steam turbine to realize a new technology capable of maintaining a high strength assurance even when the turbine nozzle box is installed in the first intermediate-pressure turbine. Is underway.
[0011]
However, the use of steam cooling is an undeveloped field for steam turbines, and trial and error has been repeated.
[0012]
The present invention has been made based on such background art, and an object of the present invention is to provide a steam turbine capable of coping with superheated reheated steam and maintaining a high strength guarantee in a turbine nozzle box.
[0013]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the steam turbine according to the present invention divides the intermediate-pressure turbine into a first intermediate-pressure turbine and a second intermediate-pressure turbine, and divides the intermediate-pressure turbine into first and second intermediate-pressure turbines. In a steam turbine in which the intermediate-pressure turbine is arranged as a top turbine and the second intermediate-pressure turbine is incorporated in a steam turbine section arranged as a bottom turbine, a turbine nozzle in which steam in the steam turbine section is accommodated in the first intermediate-pressure turbine The cooling nozzle is supplied to the box as cooling steam, and a shield plate is provided on the inner surface of the wall of the turbine nozzle box.
[0014]
According to a second aspect of the present invention, there is provided a steam turbine, wherein the turbine nozzle box includes a cooling steam passage inside the wall, and the cooling passage passes from the cooling passage to the inner surface of the wall. And a jet port for jetting the cooling steam toward the shielding plate provided in the above.
[0015]
Further, in the steam turbine according to the present invention, in order to achieve the above-described object, as described in claim 3, a shielding plate covering the inner surface of the wall of the turbine nozzle box is provided on the inner surface of the wall of the turbine nozzle box. The whole area is intermittently covered.
[0016]
Further, in the steam turbine according to the present invention, in order to achieve the above-described object, as described in claim 4, a shielding plate covering the inner surface of the wall of the turbine nozzle box is provided on the inner surface of the wall of the turbine nozzle box. The entire area is sealed and covered.
[0017]
Further, in the steam turbine according to the present invention, in order to achieve the above object, as described in claim 5, the shielding plate covering the inner surface of the wall of the turbine nozzle box is a flat heat-resistant plate. It is a feature.
[0018]
In order to achieve the above object, the steam turbine according to the present invention is characterized in that, as described in claim 6, the shielding plate that covers the inner surface of the wall of the turbine nozzle box is a corrugated plate. Things.
[0019]
Further, in order to achieve the above object, the steam turbine according to the present invention is configured such that the shielding plate for covering the inner surface of the wall of the turbine nozzle box is supported by the support portion, as described in claim 7. It is.
[0020]
Further, in the steam turbine according to the present invention, in order to achieve the above-described object, as described in claim 8, a shielding plate that covers the inner surface of the wall of the turbine nozzle box is provided on the inner surface of the wall of the turbine nozzle box. Are arranged in layers, and a passage is formed between the shielding plates arranged in layers.
[0021]
In the steam turbine according to the present invention, in order to achieve the above-described object, as described in claim 9, the shielding plate for sealingly covering the entire inner surface of the wall of the turbine nozzle box supplies cooling steam. And a cooling steam recovery port for recovering the cooling steam.
[0022]
Further, in order to achieve the above object, in the steam turbine according to the present invention, as described in claim 10, the shielding plate that seals and covers the entire inner surface of the wall of the turbine nozzle box is divided into a plurality. The cooling steam inlet and the cooling steam recovery port are provided for each of the plurality of divided shielding plates.
[0023]
Further, in order to achieve the above object, in the steam turbine according to the present invention, as described in claim 11, the shielding plate for sealingly covering the entire inner surface of the wall of the turbine nozzle box includes the turbine nozzle box. With respect to the inner surface of the wall, a passage is formed between the shielding plates arranged in layers and arranged in layers, and a cooling steam recovery port for collecting cooling steam to be injected into each passage from the cooling steam inlet is provided. is there.
[0024]
Further, in order to achieve the above-mentioned object, in the steam turbine according to the present invention, as described in claim 12, the shielding plate that seals and covers the entire inner surface of the wall of the turbine nozzle box is formed of the turbine nozzle box. A partition is provided on the inner surface of the wall, and a cooling steam passage is provided in each partition.
[0025]
Further, in the steam turbine according to the present invention, in order to achieve the above-described object, as described in claim 13, the cooling steam passage provided in the partition is arranged to meander alternately with respect to the partition. It is configured.
[0026]
In order to achieve the above object, the steam turbine according to the present invention is characterized in that, as described in claim 14, the cooling steam is high-pressure turbine extraction of a high-pressure turbine in a steam turbine section. It is.
[0027]
Further, in the steam turbine according to the present invention, in order to achieve the above object, as described in claim 15, the cooling steam is medium-pressure turbine bleed of the first intermediate-pressure turbine arranged as a top turbine. It is characterized by the following.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a steam turbine according to the present invention will be described with reference to the drawings and reference numerals attached to the drawings.
[0029]
Prior to the description of the embodiment of the steam turbine according to the present invention, first, an embodiment of a steam turbine plant that uses ultrahigh-temperature reheated steam having a temperature of 700 ° C. or higher will be described with reference to FIG.
[0030]
In the steam turbine plant according to the present embodiment, of the conventional steam turbine section 1, the intermediate pressure turbine 2 is divided into a first intermediate pressure turbine 2a and a second intermediate pressure turbine 2b, and the divided first intermediate pressure turbine 2a is divided. Is arranged as a top turbine, a renewable steam having a temperature of 700 ° C. or more is expanded, and an ultrahigh-temperature reheat steam is supplied to the first intermediate-pressure turbine 2a so that the bottom turbine can be sufficiently assured in strength. Of the conventional steam turbine unit 1 arranged as the above, uses the high-pressure turbine bleed air from the middle stage of the high-pressure turbine 3 as cooling steam, and supplies the cooling steam to the first intermediate-pressure turbine 2 a via the high-pressure turbine bleed system 5. While the steam cooling system 4 is provided, the intermediate-pressure turbine exhaust that has completed the expansion work in the first intermediate-pressure turbine 2 a is passed through the intermediate-pressure turbine exhaust system 12. It is provided superheater 6 for heating a feed water feed water system 14.
[0031]
A conventional steam turbine unit 1 arranged as a bottom turbine is provided with a high-pressure turbine 3, a second intermediate-pressure turbine 2b, a double-flow type low-pressure turbine 7, and a generator 8 by axially coupling each other. Is supplied to the high-pressure turbine 3, where the expansion work is performed, and the high-pressure turbine exhaust that has completed the expansion work is supplied to the reheater 11 of the boiler 9 via the low-temperature reheating system 10, where the temperature of 700 ° C. or higher is obtained. The reheat steam generated in the reheat steam is supplied to the first intermediate pressure turbine 2a as a top turbine.
[0032]
The first intermediate-pressure turbine 2a causes the reheat steam to perform expansion work, supplies the intermediate-pressure turbine exhaust that has completed the expansion work to the superheater 6 via the intermediate-pressure turbine exhaust system 12, and the remainder to the steam turbine unit 1 To the second intermediate-pressure turbine 2b, to perform expansion work again, and to supply the low-pressure turbine 7 with the intermediate-pressure turbine exhaust that has completed the expansion work. 8 is driving.
[0033]
Further, the steam turbine plant according to the present embodiment includes a condensing system 13 and a water supply system 14.
[0034]
The condensing system 13 includes a condenser 15, a condensing pump 16, a first low-pressure feed water heater 17, a second low-pressure feed water heater 18, a third low-pressure feed water heater 19, and a fourth A low-pressure feedwater heater 20 is provided, and low-pressure turbine exhaust from the low-pressure turbine is condensed by a condenser 15 to be condensed, and this condensate is pumped by a condensate pump 16, and first to fourth low-pressure feedwater heaters 17 are provided. , 18, 19, and 20, the low-pressure extracted steam from the low-pressure turbine 7 is sequentially preheated (regenerated) as a heat source.
[0035]
On the other hand, the water supply system 14 includes a deaerator 21, a water supply pump 22, a first high-pressure water heater 23, a second high-pressure water heater 24, a third high-pressure water heater 25, and a fourth A high-pressure feed water heater 26 and a superheater 27 are provided. The deaerator 21 converts the condensate supplied from the fourth low-pressure feed water heater 20 of the condensing system 13 to a medium pressure from the second intermediate-pressure turbine 3 b of the steam turbine unit 1. The extracted steam is heated and degassed as a heat source to supply water, the pressure of the supplied water is increased by a water supply pump 22, and the first to fourth high-pressure water heaters 23, 24, 25, and 26 use the second medium-pressure turbine of the steam turbine unit 1. The medium pressure turbine extraction from 3b, the high pressure turbine extraction from the high pressure turbine 3, the high pressure turbine exhaust from the high pressure turbine 3, the superheated steam from the superheater 6, etc. are sequentially preheated as heat sources, and then returned to the boiler 9.
[0036]
On the other hand, in contrast to the conventional steam turbine section 1 arranged as a bottom turbine, the first intermediate pressure turbine 2a arranged as a top turbine has a high pressure used as cooling steam extracted from an intermediate stage of the high pressure turbine 3 of the steam turbine section 1. Turbine bleed air is supplied via a low-temperature reheating system 10 and a steam cooling system 4.
[0037]
Further, as shown in FIG. 2, the first intermediate pressure turbine 2 a has a double casing structure of an outer casing 32 and an inner casing 33, and also uses the super-high temperature reheat steam supplied from the reheat steam pipe 27. A turbine nozzle box that collects the reheated steam and jets the collected reheated steam to a turbine stage 28 composed of turbine nozzles 29 and turbine blades 30 provided in multiple stages along the axial direction of a turbine rotor 34 accommodated in an inner casing 33. 31 are provided.
[0038]
As shown in FIGS. 3 and 4, this turbine nozzle box 31 has one side connected to a reheat steam pipe 27 and the other side facing the turbine stage 28 has a steam chamber provided with a nozzle port (throttle port) 35. A cooling steam passage 38 provided inside the wall 37 forming the steam chamber 36 and an outlet 39 for jetting cooling steam from the cooling steam passage 38 toward the inner surface of the wall 37; It is supported by the support part 40, intermittently covers the entire inner surface of the wall surface 37, and includes a shielding plate 41 provided with a cooling steam outlet 45.
[0039]
As the shielding plate 41, for example, a flat heat-resistant plate, specifically, an austenitic alloy SUS310 excellent in oxidation resistance is used.
[0040]
In the first intermediate-pressure turbine 2a having such a configuration, as shown in FIG. 1, a high-pressure turbine bleed air extracted from an intermediate stage of the high-pressure turbine 3 of the steam turbine unit 1 is provided in a turbine nozzle box 31. 5, is supplied as cooling steam through the steam cooling system 4. Although the high-pressure turbine bleed air is used as the cooling steam, the present invention is not limited thereto, and the medium-pressure turbine bleed air of the first intermediate-pressure turbine 2a may be used, or the steam being heated by the boiler may be used.
[0041]
The cooling steam supplied to the turbine nozzle box 31 cools the wall 37 while flowing through the cooling steam passage 38 formed inside the wall 37 as shown in FIGS. The gas is ejected toward the plate 41, and further ejects from the cooling medium outlet 45 toward the steam chamber 36.
[0042]
FIG. 14 is a temperature distribution diagram applied to the wall 37 when the shield plate 41 is provided when the superheated reheat steam is supplied to the turbine nozzle box 31. The horizontal axis indicates the wall 37 of the turbine nozzle box 31, Each position of the shielding plate 41 on the inner surface side of the wall 37 is schematically shown, and the vertical axis indicates the temperature.
[0043]
From this figure, it was found that the presence of the shield plate 41 reduced the amount of heat given to the wall 37 of the turbine nozzle box 31 from the ultra-high temperature reheated steam.
[0044]
As described above, in the present embodiment, the cooling steam passage 38 for flowing the cooling steam is formed inside the wall 37 of the turbine nozzle box 31, and the temperature difference between the ultra-high temperature reheat steam and the wall 37 of the turbine nozzle box 31 is reduced. In addition to reducing the heat, the inner surface of the wall of the turbine nozzle box 31 is intermittently covered with a shielding plate 41 so as to shield the heat given to the wall 37 of the turbine nozzle box 31 from the ultra-high temperature reheat steam. Thermal stress or the like generated on the wall 37 of the nozzle box 31 can be reduced, and a high strength can be maintained, so that the steam turbine can be operated stably.
[0045]
In this embodiment, a flat heat-resistant plate is used for the shielding plate 41 that covers the outside of the turbine nozzle box 31. However, the present invention is not limited to this example. For example, as shown in FIG. May be used. It is effective in effectively absorbing heat transfer.
[0046]
Further, in the present embodiment, the shielding plate 41 that intermittently covers the inner side surface of the wall of the turbine nozzle box 31 is supported at the support portion 40 at the same height from the inner surface of the wall 37, but is not limited to this example. For example, as shown in FIG. 6, the support portion 41 is made higher than the other support portions 40b and 40c, and the space portion 43 between the inner side surface of the wall 37 of the turbine nozzle box 31 and the shielding plate 41 is more widely secured. To recover the pressure of the cooling steam spouted from the spout 39. Further, for example, as shown in FIG. 7, the support portions 40a, 40b, 40c,. Are sequentially raised from the inner surface of the wall of the turbine nozzle box 31 toward the steam chamber 36, and the passages 44a, 44b,... Are formed by the shielding plates 41a, 41b, 41c,. 41b, 1c, ... inner diameter side of, may be cooled by flowing cooling steam to both sides of the outer diameter side.
[0047]
8 and 9 are sectional views showing a second embodiment of the turbine nozzle box 31 applied to the steam turbine according to the present invention.
[0048]
In the steam turbine according to the present embodiment, the entire inner surface of the wall of the wall 37 of the turbine nozzle box 31 is hermetically sealed and covered with the shielding plate 41, and the sealed shielding plate 41 is supported by the support portion 40. A jet port 4b for jetting the cooling steam from the cooling steam passage 38 into a space 47 formed between the cooling steam passage 38 provided inside the wall 37 and the shielding plate 41, and cooling the jetted cooling steam again. As described above, this embodiment is provided with the recovery port 48 for recovering the steam in the steam passage 38. In this embodiment, the shield plate 41 is provided so as to cover the entire inner surface of the wall 37 of the turbine nozzle box 31 in a closed manner. A nozzle 46 for ejecting and recovering the cooling steam between the space portion 47 and the cooling steam passage 38, and a recovery port 48, respectively. Since the first wall 37 is configured to shield the heat given from the reheated steam having a very high temperature, the thermal stress generated in the turbine nozzle box 31 can be suppressed low, and the steam turbine can be operated stably. .
[0049]
In the steam turbine according to the present embodiment, the shielding plate 41 that covers the entire inner surface of the wall 37 of the turbine nozzle box 31 is sealed, and the cooling steam is supplied between the sealed space 47 and the cooling steam passage 38. An outlet 46 for performing ejection and recovery, respectively, and a recovery port 47 are provided. However, the present invention is not limited to this example. For example, as shown in FIG. Are covered with a shielding plate 41, and the shielding plate 41 to be hermetically sealed is divided into a plurality of first shielding plates 41a, second shielding plates 41b,... And formed on each of the divided shielding plates 41a, 41b,. , And the cooling steam passage 38, an ejection port 46 and a recovery port 48 may be provided. Further, as shown in FIG. 11, for example, shielding plates 41a, 41b, 41c, Support… The support portions 40a, 40b, 40c,... Are sequentially raised from the inner surface of the wall 37 of the turbine nozzle box 31 toward the steam chamber 36, and the passages 44a, 44b are formed by the shielding plates 41a, 41b, 41c,. May be formed, and cooling steam may be flown to both the inner and outer diameter sides of the shielding plates 41a, 41b, 41c,.
[0050]
FIG. 12 is a partially cutaway conceptual view showing a third embodiment of a turbine nozzle box 31 applied to the steam turbine according to the present invention.
[0051]
In the steam turbine according to the present embodiment, the entire inner surface of the wall 37 of the turbine nozzle box 31 is hermetically sealed and covered with a shield plate 41, and the sealed shield plate 41 is, for example, a high-pressure turbine 3 shown in FIG. Cooling steam supply port 49 for supplying high-pressure turbine bleed air as cooling steam, and cooling steam recovery for cooling the cooling steam after cooling wall 37 of turbine nozzle box 31 to, for example, an intermediate stage of first intermediate pressure turbine 2a. A mouth 50 is provided. Note that the shielding plate 41 is supported by the support portion 40.
[0052]
As described above, in the present embodiment, the cooling steam is directly supplied to the inner surface of the wall 37 of the turbine nozzle box 31 that is sealed by the shielding plate 41 to cool the turbine nozzle box 31. Wall 37 can be cooled well.
[0053]
In the present embodiment, a cooling steam supply port 49 and a cooling steam recovery port 50 are provided on a shielding plate 41 that covers the entire inner surface of the wall 37 of the turbine nozzle box 31 in a closed manner, and the wall 37 of the turbine nozzle box 31 is provided. The cooling steam was directly supplied to the turbine nozzle box 31. However, the present invention is not limited to this example. For example, as shown in FIG. , A plurality of partitions 51, 51,... Are provided, and cooling steam passages 52, 52,... Are provided at alternately meandering positions of the partitions 51, 51,. Wall 37 may be cooled.
[0054]
【The invention's effect】
As described above, the steam turbine according to the present invention covers the entire inner surface of the wall of the turbine nozzle box with the shielding plate, and supplies the cooling steam to the space formed by covering the turbine nozzle box wall with the shielding plate. Since the heat is supplied directly from the superheated reheated steam to the wall of the turbine nozzle box, there is no excessive thermal stress due to the heat of the superheated reheated steam. The box can maintain a high strength guarantee.
[Brief description of the drawings]
FIG. 1 divides an intermediate-pressure turbine into a first intermediate-pressure turbine and a second intermediate-pressure turbine, and arranges the divided first intermediate-pressure turbine as a top turbine; Schematic diagram of a steam turbine plant for supplying steam.
FIG. 2 is a schematic longitudinal sectional view of the first intermediate pressure turbine shown in FIG.
FIG. 3 is a schematic sectional view showing a first embodiment of a turbine nozzle box applied to the steam turbine according to the present invention.
FIG. 4 is a partially enlarged sectional view of a part X in FIG. 3;
FIG. 5 is a partial sectional view showing a first modified example of the turbine nozzle box in FIG. 3;
FIG. 6 is a partial sectional view showing a second modification of the turbine nozzle box in FIG. 3;
FIG. 7 is a partial sectional view showing a third modification of the turbine nozzle box in FIG. 3;
FIG. 8 is a schematic sectional view showing a second embodiment of the turbine nozzle box applied to the steam turbine according to the present invention.
FIG. 9 is a partially enlarged sectional view of a Y part in FIG. 8;
FIG. 10 is a conceptual diagram showing a first modification of the turbine nozzle box in FIG. 9;
FIG. 11 is a conceptual diagram showing a second modification of the turbine nozzle box in FIG.
FIG. 12 is a conceptual diagram showing a third modification of the turbine nozzle box in FIG.
FIG. 13 is a conceptual diagram showing a fourth modification of the turbine nozzle box in FIG. 9;
FIG. 14 is a temperature distribution diagram of reheat steam applied to the turbine nozzle box wall when the inner side surface of the turbine nozzle box is covered with a shielding plate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Steam turbine part 2 Medium pressure turbine 2a 1st medium pressure turbine 2b 2nd medium pressure turbine 3 High pressure turbine 4 Steam cooling system 5 High pressure turbine extraction system 6 Superheater 7 Low pressure turbine 8 Generator 9 Boiler 10 Low temperature reheating system 11 Re Heater 12 Medium-pressure turbine exhaust system 13 Condenser system 14 Water supply system 15 Condenser 16 Feedwater pump 17 First low-pressure feedwater heater 18 Second low-pressure feedwater heater 19 Third low-pressure feedwater heater 20 Fourth low-pressure feedwater heater 21 Deaerator 22 Feedwater pump 23 First high-pressure feedwater heater 24 Second high-pressure feedwater heater 25 Third high-pressure feedwater heater 26 Fourth high-pressure feedwater heater 27 Reheat steam pipe 28 Turbine stage 29 Turbine nozzle 30 Turbine blade 31 Turbine nozzle box 32 Outer casing 33 Inner casing 34 Turbine rotor 35 Nozzle port 36 Steam chamber 37 Wall 38 Cooling steam passage 39 Injection Ports 40, 40a, 40b Supports 41, 41a, 40b Shielding plate 42 Shielding plate 43 Spaces 44a, 44b Passage 45 Cooling steam outlet 46 Spout 47 Space 48 Recovery port 49 Cooling steam supply port 50 Cooling steam Recovery port 51 Partition 52 Cooling steam passage

Claims (15)

The intermediate pressure turbine is divided into a first intermediate pressure turbine and a second intermediate pressure turbine, the divided first intermediate pressure turbine is disposed as a top turbine, and the second intermediate pressure turbine is disposed in a steam turbine section disposed as a bottom turbine. In the incorporated steam turbine, the steam of the steam turbine section is supplied as cooling steam to a turbine nozzle box accommodated in the first intermediate pressure turbine, and a shield plate is provided on an inner surface of a wall of the turbine nozzle box. And steam turbine. 2. The turbine nozzle box according to claim 1, wherein the turbine nozzle box has a cooling steam passage inside the wall, and further has an ejection port for ejecting the cooling steam from the cooling passage toward a shielding plate provided on the inner surface of the wall. Steam turbine. 2. The steam turbine according to claim 1, wherein the shield plate covering the inner surface of the wall of the turbine nozzle box is configured to intermittently cover the entire inner surface of the wall of the turbine nozzle box. 3. The steam turbine according to claim 1, wherein the shield plate that covers the inner surface of the wall of the turbine nozzle box hermetically covers the entire inner surface of the wall of the turbine nozzle box. The steam turbine according to claim 1, wherein the shield plate that covers the inner surface of the wall of the turbine nozzle box is a flat heat-resistant plate. The steam turbine according to claim 1, wherein the shielding plate that covers the inner surface of the wall of the turbine nozzle box is a corrugated plate. The steam turbine according to claim 1, wherein the shield plate that covers the inner surface of the wall of the turbine nozzle box is configured to be supported by a support portion. The shield plate that covers the inner surface of the wall of the turbine nozzle box is arranged in layers with respect to the inner surface of the wall of the turbine nozzle box, and a passage is formed between the shield plates arranged in layers. Item 2. The steam turbine according to Item 1. 5. The cooling plate for sealingly covering the entire inner surface of the wall of the turbine nozzle box with a cooling steam inlet for supplying cooling steam and a cooling steam recovery port for collecting cooling steam. Steam turbine. The shielding plate for sealingly covering the entire inner surface of the wall of the turbine nozzle box is divided into a plurality of sections, and a cooling steam inlet and a cooling steam recovery port are provided for each of the plurality of sectioning shields. The steam turbine according to claim 4, characterized in that: The shielding plate that seals and covers the entire inner surface of the wall of the turbine nozzle box is disposed in a layered manner with respect to the inner surface of the wall of the turbine nozzle box, and a passage is formed between the shielding plates arranged in a layered manner, and cooling steam is formed. 5. The steam turbine according to claim 4, further comprising a cooling steam recovery port for recovering cooling steam to be injected into each passage from the input port. The shielding plate for hermetically covering the entire inner surface of the wall of the turbine nozzle box is provided with partitions on the inner surface of the wall of the turbine nozzle box, and each partition is provided with a cooling steam passage. 4. The steam turbine according to 4. 13. The steam turbine according to claim 12, wherein the cooling steam passages provided in the partition are arranged so as to meander alternately with respect to the partition. The steam turbine according to claim 1, wherein the cooling steam is high-pressure turbine bleed air of a high-pressure turbine in a steam turbine section. The steam turbine according to claim 1, 2 or 9, wherein the cooling steam is medium-pressure turbine bleed air of a first intermediate-pressure turbine arranged as a top turbine.

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