Seal Structure and Control Method Therefor

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a seal structure provided for a steam turbine and a control method therefor.

2. Description of the Related Art

For power-generating plants in which a turbine (steam turbine) is rotated for electric generation by steam generated by a steam generator such as a boiler or the like, the steam turbine includes a high-pressure turbine, a medium-pressure turbine and a low-pressure turbine installed in that order from the upstream side of steam flow. The steam having rotated the low-pressure turbine is introduced via an exhaust hood into a condenser, in which the steam is condensed as feed-water, which is returned to the steam generator.

In the steam turbine constituting part of the power-generating plant as described above, a stator blade secured to the inside of a casing is disposed between rotor blades rotated integrally with a rotor. In this way, the stator blade and the rotor blade constitute a stage.

The steam introduced into the inside of the casing flows inside the casing of the steam turbine and expands to rotate the rotor while alternately passing through between the stator blades and the corresponding rotor blades secured to the rotor rotatably supported by the casing. The steam passing a rotor blade installed on the most downstream portion of the rotor, i.e., a final-stage rotor blade is discharged to the outside of the casing.

In the steam turbine as described above, steam impinges on the rotor blade to rotate the rotor. Therefore, to utilize the steam efficiently, it is required to improve sealing performance between a fixed portion and a rotating portion, such as e.g. between the stator blades and the rotor, to minimize leakage of steam through a clearance between the fixed portion and the rotating portion.

To deal with such a problem, the following technology of seal structure has heretofore been disclosed. A labyrinth seal device having fins (seal fins) is disposed between the rotating portion such as a rotor and the fixed portion such as a stator blade. In addition, a member (abradable metal) superior in the easiness of the abrasion is used at a position facing the fin. (See e.g. JP-2002-228013-A). According to the technology disclosed in JP-2002-228013-A, even if the fin and the abradable metal come into contact with each other, the fin abrades the abradable metal. Thus, the fin can be prevented from being damaged.

To improve the sealing performance, the fin and the abradable metal are disposed to reduce the clearance between the rotating portion and the fixed portion as much as possible. In such a case, however, the fin and the abradable metal often come into contact with each other to increase resistance (rotational resistance) against the rotation of the rotating portion. Therefore, when steam has relatively low pressure, for example, such as during the initial period of starting up the steam turbine, the rotor becomes hard to be rotated. This poses a problem in that it becomes difficult to smoothly start up the steam turbine.

Further, for example, the fins provided on the rotating portion and the abradable metal provided on the fixed portion come into contact with each other to generate frictional heat. This frictional heat is transmitted to the rotating portion, which has high-temperature. Thus, this heat transmission causes thermal deformation of the rotating portion such as thermal expansion or thermal bending, which affects the rotation of the rotating portion. This poses a problem of lowering the turbine efficiency of the steam turbine.

To eliminate such a problem, the technology of a seal structure having a thermal insulation layer suppressing the thermal transmission to the rotating portion has been disclosed. (See e.g., JP-2007-16704-A).

The technology disclosed in JP-2007-16704-A has a thermal insulation layer between fins provided on the rotating portion and the rotating portion, for example. This prevents frictional heat generated by the contact between the rotating portion and the fixed portion from being transmitted to the rotating portion.

SUMMARY OF THE INVENTION

In the technology disclosed in JP-2007-16704-A, however, if the rotating portion is continuously rotated for a long period of time so that the fins and the abradable metal are in contact with each other for a long period of time, the frictional heat thus generated is accumulated in the thermal insulation layer. This poses a problem in that the heat accumulated in the thermal insulation layer is transmitted to the rotating portion, which has high-temperature.

When the contact between the fins and the abradable metal increases rotational resistance and steam pressure is low, the rotor does not rotate smoothly so that the smooth start-up of the steam turbine cannot be achieved.

If the clearance between the fins and the abradable metal is increased in order to prevent the contact between the fins and the abradable metal, the clearance between the rotating portion and the fixed portion is increased to increase the leakage of steam. Thus, it is not probable that the turbine efficiency of the steam turbine can be improved.

Accordingly, it is an object of the present invention to provide a seal structure and a control method therefor that can improve sealing performance between a rotating portion and a fixed portion, smoothly start up a steam turbine, and suppress the temperature rise of the rotating portion even if the rotating portion is continuously rotated for a long period of time.

According to an aspect of the present invention, there are provided a seal structure and a control method therefor in which a fin provided on a rotating portion and a spacer provided on a fixed portion are opposed to each other, a fin provided on the fixed portion and a spacer provided on the rotating portion are opposed to each other, the spacers are made of breathable metal and the fin and the spacer provided on the fixed portion are shiftable in a direction coming close to or moving away from the rotating portion.

The aspect of the present invention can provide the seal structure and the control method therefor that can improve sealing performance between the rotating portion and the fixed portion, smoothly start up a steam turbine, and suppress the temperature rise of the rotating portion even if the rotating portion is continuously rotated for a long period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic system diagram of a power-generating plant provided with a steam turbine according to an embodiment of the present invention.

FIG. 2 is a partially enlarged view of the steam turbine of FIG. 1.

FIG. 3 is an enlarged view of an A1-portion of FIG. 2.

FIG. 4 is an enlarged view of an A2-portion of FIG. 3.

FIG. 5A is a cross-sectional view taken along the line X1-X1 in FIG. 2.

FIG. 5B is an enlarged view of an A3-portion of FIG. 5A.

FIG. 6 is a schematic view illustrating one configurational example of a high-low labyrinth seal device, in which a seal base-plate is provided with seal fins.

FIG. 7 is a schematic view illustrating one configurational example of a high-low labyrinth seal device, in which a rotor is provided with seal fins.

FIG. 8A is a cross-sectional view taken along the line X2-X2 in FIG. 2.

FIG. 8B is an enlarged view of an A4-portion of FIG. 8A.

FIG. 9 is a schematic view illustrating a distal end of a rotor blade.

FIG. 10 is a schematic view illustrating one configurational example of a labyrinth seal device equipped with compression springs connecting together piston bodies in a circumferential direction.

FIG. 11 is a schematic diagram illustrating one configurational example of a labyrinth seal device in which driving steam is allowed to flow into a pressurizing chamber from a high-pressure steam supply source to thereby move a piston head.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described in detail with reference to the drawings.

Referring to FIG. 1, a power-generating plant 1 is configured to include a boiler 10, a steam turbine 2 (a high-pressure turbine 12, a medium-pressure turbine 14, and a low-pressure turbine 16), a generator 18, and a condenser 20. A rotor 2a of the low-pressure turbine 16 is coupled to a drive shaft 22 of the generator 18. Rotation of the low-pressure turbine 16 drives the generator 18 for electric generation.

The boiler 10 is a steam generator, which is provided with a reheater 24. The boiler 10 is connected to an inlet side of the high-pressure turbine 12 via a pipe 26. An outlet side of the high-pressure turbine 12 is connected to the reheater 24 of the boiler 10 via a pipe 28. The reheater 24 is connected to an inlet side of the medium-pressure turbine 14 via a pipe 30. An outlet side of the medium-pressure turbine 14 is connected to an inlet side of the low-pressure turbine 16 via a pipe 32.

The pipes 26 and 30 are provided with respective adjusting valves B, each of which functions as a control valve to control an amount of steam St flowing into a corresponding one of the high-pressure turbine 12 and the medium-pressure turbine 14. The adjusting valves B are controlled by a controller 54 to control the amount of steam St flowing into the high-pressure turbine 12 and the medium-pressure turbine 14.

The steam St generated in the boiler 10 flows into the low-pressure turbine 16 via the high-pressure turbine 12 and the medium-pressure turbine 14 to rotate the rotor 2a provided in the low-pressure turbine 16. The steam St discharged from the low-pressure turbine 16 by the rotation of the rotor 2a passes through an exhaust hood 3 and is condensed and turned into water (feed-water) in the condenser 20. Thereafter, the feed-water is fed to and heated in the feed-water heater 21 and introduced into the boiler 10 or the steam generator via another feed-water heater (not illustrated), a high-pressure feed-water pump (not illustrated) and the like.

Referring to FIG. 2, the steam turbine 2 (e.g. the high-pressure turbine 12 illustrated in FIG. 1) includes a plurality of rotor blades 2b externally-circumferentially secured to the rotor 2a and axially arranged in a plurality of rows.

Further, the steam turbine 2 includes a casing 2d embracing the rotor 2a and the rotor blades 2b, and a plurality of stator blades 2c secured to the casing 2d via corresponding nozzle diaphragm outer-rings 80. The plurality of rotor blades 2b and the plurality of stator blades 2c are alternately arranged in the axial direction of the rotor 2a to form stages.

The externally circumferential direction of the rotor 2a is hereinafter referred to as a circumferential direction. That is to say, the rotor 2a is rotated in the circumferential direction.

Steam St generated in the boiler 10 (see FIG. 1) flows into the inside of the casing 2d of the steam turbine 2. Then, the steam St passes through between the stator blades 2c and the corresponding rotor blades 2b alternately while being reduced in pressure and expanded, thereby rotating the rotor 2a.

The steam St passing a rotor blade 2b installed on the most downstream portion of the rotor 2a, i.e., a final-stage rotor blade 2b is discharged to the outside of the casing 2d.

In the steam turbine 2 configured as above, to efficiently rotate the rotor 2a by the steam St passing through the inside of the casing 2d, it is required to improve sealing performance between the rotor 2a and the rotor blades 2b which are a rotating portion and the casing 2d and the stator blades 2c which are a fixed portion to reduce an amount of steam St (leakage steam) leaking from the clearance between the rotating portion and the fixed portion.

For example, to reduce rotational resistance against the rotation of the rotor 2a, a clearance may be provided between a nozzle diaphragm inner-ring 70 installed on distal ends of the stator blades 2c and the rotor 2a in some cases. This clearance causes leakage of steam St flowing to the stator blades 2c. The steam St becoming the leakage steam does not contribute to the rotation of the rotor 2a. Therefore, the increased amount of leakage steam lowers the turbine efficiency of the steam turbine 2. Thus, it is preferable to reduce the amount of leakage steam in order to improve the turbine efficiency of the steam turbine 2.

For this reason, a configuration is generally employed in which a seal device such as a labyrinth seal device 60 is assembled between the nozzle diaphragm inner-ring 70 and the rotor 2a to reduce the clearance between the rotor 2a and the stator blades 2c. This configuration can improve the sealing performance between the rotor 2a and the stator blades 2c to thereby reduce the amount of leakage steam.

Referring to FIGS. 3 and 4, the nozzle diaphragm inner-ring 70 according to the embodiment is provided on the rotor 2a side with a seal base-plate 61 equipped with a plurality of seal fins 62.

The seal base-plate 61 is provided at given intervals with a plurality of grooves 63 circumferentially formed in line in the axial direction of the rotor 2a. The seal fins 62 are secured to the respective grooves 63 by caulking.

Further, also the rotor 2a is provided at given intervals with a plurality of grooves 2a2 circumferentially formed in line in the axial direction of the rotor 2a. Seal fins 2a1 are secured to the respective grooves 2a2 by caulking.

The seal fins 62 on the seal base-plate 61 side and the corresponding seal fins 2a1 on the rotor 2a side are arranged to alternately overlap each other in the axial direction of the rotor 2a.

As described above, the labyrinth seal device 60 is configured to include the seal base-plate 61 provided with the plurality of seal fins 62.

In the past, the seal fins 62 on the seal base-plate 61 side and the rotor 2a have been configured so as not to be in contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the seal base-plate 61 have been configured so as not to be in contact with each other. With this configuration, a minute clearance is defined between each of the seal fins 62 and the rotor 2a and between each of the seal fins 2a1 and the seal base-plate 61, whereby rotational resistance against the rotation of the rotor 2a is reduced.

However, steam St passing through these clearances becomes leakage steam without contribution to the rotation of the rotor 2a. The leakage steam causes a steam leakage loss, which lowers the turbine efficiency of the steam turbine 2 (see FIG. 1).

For this reason, in the embodiment, a breathable spacer 4 (spacer) made of breathable metal is attached between each of the seal fins 62 on the seal base-plate 61 side and the rotor 2a and between each of the seal fins 2a1 on the rotor 2a side and the seal base-plate 61.

Further, the seal base-plate 61 provided with the seal fins 62 and with the breathable spacers 4 is installed shiftably in a direction coming close to or moving away from the rotor 2a, i.e., in the rotational-radial direction of the rotor 2a.

Hereinafter, the breathable spacer 4 on the seal base-plate 61 side is denoted with reference numeral 4a and the breathable spacer 4 on the rotor 2a side is denoted with reference numeral 4b.

With this configuration, the seal fins 62 and the breathable spacers 4a provided for the stator blade 2c (see FIG. 2) which is the fixed portion are shiftable in the direction coming close to and moving away from the rotor 2a which is the rotating portion.

As illustrated in FIG. 3, the breathable spacers 4b are attached to the rotor 2a at respective positions opposed to the corresponding seal fins 62 on the seal base-plate 61 side.

In addition, the breathable spacers 4a are attached to the seal base-plate 61 at respective positions opposed to the corresponding seal fins 2a1 on the rotor 2a side.

This configuration provides a seal structure in which the breathable spacers 4 made of breathable metal are attached to both the rotor 2a (the rotating portion) and the seal base-plate 61 (the fixed portion).

A method of attaching the breathable spacer 4 to the rotor 2a and the seal base-plate 61 is not restrictive. For example, the breathable spacer 4 may be secured to the rotor 2a and the seal base-plate 61 by e.g. brazing.

The breathable spacers 4b on the rotor 2a side are each circumferentially attached to the outer circumference of the rotor 2a. In addition, the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side are configured to be constantly opposed to each other even during the rotation of the rotor 2a. Further, the seal fins 2a1 on the rotor 2a side are provided in the circumferential direction. The seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side are configured to be opposed to each other even during the rotation of the rotor 2a.

Breathable metal used to form the breathable spacer 4 according to the present embodiment is a metal material structured such that space portions (pores) of porous metal are connected together and gas (steam St) can pass through the inside thereof. The breathable metal is material (abradable metal) superior in the easiness of the abrasion. For example, if the rotor 2a is rotated in the state where the distal ends of the seal fins 62 on the seal base-plate 61 side are in contact with the corresponding breathable spacers 4b on the rotor 2a side (in the contact state), the breathable spacers 4 (4b) are abraded as shown in FIG. 4 but the seal fins 62 are not damaged.

In this way, the configuration in which the distal ends of the seal fins 62 come into contact with the respective breathable spacers 4b on the rotor 2a side can improve the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

Similarly, the configuration in which the distal ends of the seal fins 2a1 on the rotor 2a side come into contact with the respective breathable spacers 4a (see FIG. 3) on the seal base-plate 61 side can improve the sealing performance between the stator blades 2c and the rotor 2a.

The following technology is a heretofore known one as described earlier. The clearance between the seal fins 62 and the rotor 2a and between the seal fins 2a1 and the seal base-plate 61 is eliminated or made small to improve the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a as shown in FIG. 3. For this purpose, the spacers made of a raw material superior in the easiness of the abrasion, such as e.g. abradable metal are provided on the rotor 2a at respective positions opposed to the corresponding seal fins 62, and on the seal base-plate 61 at respective positions opposed to the corresponding seal fins 2a1.

However, in this technology, frictional heat resulting from friction between the spacers rotating integrally with the rotor 2a and the seal fins 62, for example, is transmitted to the rotor 2a, which has high-temperature. Thus, the rotor 2a is thermally deformed such as thermally bent due to e.g. nonuniform temperature distributions so that there is a possibility of a problem of causing shaft vibration.

Also, the following technology is thought. A heat-insulating layer made of a heat-insulating member not illustrated is provided between the spacers on the rotor 2a side and the rotor 2a. Even with this technology, the rotor 2a may continuously be rotated for a long period of time so that the spacers rotated integrally with the rotor 2a are in contact with the seal fins 62 for a long period of time. In such a case, the frictional heat between the seal fins 62 and the spacers is gradually accumulated so that the heat-insulating layer has high-temperature. In this way, the heat of the heat-insulating layer is transmitted to the rotor 2a, which has high-temperature. Thus, the rotor 2a causes thermal deformation such as thermal bending due to nonuniform temperature distributions.

As illustrated in FIG. 4, for example, if the spacer attached to the rotor 2a uses the breathable spacer 4 (4b) made of breathable metal, a slight amount of steam St passes through the inside of the breathable spacer 4 (4b).

The steam St passing through the inside of the breathable spacer 4 uniformly keeps the breathable spacer 4 at a temperature equal to that of the steam St. In other words, the breathable spacer 4 will not have temperature higher than the steam St.

A steam-breathable amount of the breathable spacer 4 has only to be such an amount as not to affect sealing performance and to be an amount that uniformly keeps the breathable spacer 4 at a temperature equal to that of the steam St. The steam-breathable amount of breathable metal used to form the breathable spacer 4 is slight and is a characteristic value of the breathable metal depending on the arrangement density and size of pores. Therefore, it is only necessary to form the breathable spacer 4 by using breathable metal that does not affect sealing performance and can ensure a steam-breathable amount in which an effect is expected of uniformly keeping the breathable spacer 4 at a temperature equal to that of the steam St.

As described above, the temperature of the breathable spacer 4 is uniformly kept equally to that of the steam St. The rotor 2a may be rotated for a long period of time so that, for example, the seal fins 62 and the breathable spacers 4b rotated integrally with the rotor 2a are in contact with each other for a long period of time. Even in such a case, the temperature of the breathable spacers 4b will not become higher than that of the steam St. Thus, an effect is produced in which the temperature of the rotor 2a can be prevented from becoming higher than that of steam St. The rotor 2a is designed to have heat resistance against the temperature of steam St. If the temperature of the rotor 2a is kept at the temperature of the steam St, since e.g. excessive thermal stress and thermal deformation such as thermal bending do not occur, the operation of the steam turbine 2 (see FIG. 1) is not affected.

Incidentally, the labyrinth seal device 60 illustrated in FIG. 3 may be configured such that the breathable spacers 4 are provided on only one of the rotor 2a side and the seal base-plate 61 side.

The amount of steam St passing through the breathable spacer 4 as illustrated in FIG. 4 is slighter than that leaking from the clearance between the seal fin 62 and the rotor 2a. Therefore, the amount of steam St passing through the breathable spacer 4 does not have an influence on the turbine efficiency of the steam turbine 2 (see FIG. 1).

Further, the seal base-plate 61 according to the present embodiment is installed shiftably in a direction coming close to or moving away from the rotor 2a.

Referring to FIG. 5A, the nozzle diaphragm inner-ring 70 is provided on the distal ends of the stator blades 2c on the inner circumferential side thereof so as to extend in the circumferential direction. In addition, e.g. six seal base-plates 61 equally divided in the circumferential direction are provided on the end of the nozzle diaphragm inner-ring 70 on the inner circumferential side thereof so as to surround the rotor 2a.

Referring to FIG. 5B, the seal fins 62 are secured to one seal base-plate 61 on the rotor 2a side by caulking or the like so as to extend upright therefrom along the circumferential direction of the rotor 2a. The breathable spacers 4b made of breathable metal are attached to the outer circumference of the rotor 2a at respective positions opposed to the corresponding seal fins 62.

As illustrated in FIG. 3, the breathable spacers 4a made of breathable metal are attached to one seal base-plate 61 at respective positions opposed to the corresponding seal fins 2a1 on the rotor 2a side so as to be shaped along the circumferential direction.

In the present embodiment, all the seal base-plates 61 are installed on the nozzle diaphragm inner-ring 70 shiftably in a direction coming close to or moving away from the rotor 2a, i.e., in the rotational-radial direction of the rotor 2a.

As illustrated in FIG. 3, the nozzle diaphragm inner-ring 70 is formed with a hollow pressurizing chamber 71. The hollow pressurizing chamber 71 is internally provided with a piston head 64 reciprocating in a direction coming close to or moving away from the rotor 2a. The piston head 64 is elastically supported by a plurality of return springs 66 (biasing means) circumferentially arranged, e.g., in two lines. The piston head 64 is biased at an appropriated biasing force by the return springs 66 in a direction moving away from the rotor 2a.

Incidentally, the number of the return springs 66 may be determined appropriately.

The pressurizing chamber 71 is configured to communicate with the outside of the nozzle diaphragm inner-ring 70 through a steam passage 72. In addition, steam St flowing through the outside of the nozzle diaphragm inner-ring 70 flows into the pressurizing chamber 71. When the pressure of the steam St is applied to the piston head 64, the piston head 64 is shifted in a direction coming close to the rotor 2a.

The piston head 64 is provided with a piston body 65. The piston body 65 extends from the pressurizing chamber 71 toward the rotor 2a and has an end portion terminating at the outside of the nozzle diaphragm inner-ring 70. The seal base-plate 61 is attached to the end portion.

The piston body 65 may be formed integrally with the piston head 64, for example. A method of attaching the seal base-plate 61 to the piston body 65 is not restrictive. For example, the seal base-plate 61 may be secured to the piston body 65 by means of screws not illustrated.

Thus, a movable portion is configured to include the piston head 64, the piston body 65, and the seal base-plate 61.

When the piston head 64 is supported by the biasing force of the return springs 66 at a position away from the rotor 2a, the seal base-plate 61 is in a state shifted to a position away from the rotor 2a. In this state, the seal fins 62 on the seal base-plate 61 side are not in contact with the corresponding breathable spacers 4b, opposed thereto, on the rotor 2a side (the non-contact state). Thus, a clearance is defined between the seal fins 62 and the corresponding breathable spacers 4b.

Similarly, the seal fins 2a1 on the rotor 2a side are not in contact with the corresponding breathable spacers 4a, opposed thereto, on the seal base-plate 61 side. In this state, a clearance is defined between the seal fins 2a1 and the corresponding breathable spacers 4a.

The labyrinth seal device 60 in the present embodiment is configured to include the pressurizing chamber 71, the steam passage 72, the piston head 64, the piston body 65, and the return springs 66 in addition to the seal base-plate 61.

The seal structure including the labyrinth seal device 60 and the seal fins 2a1 and breathable spacers 4b on the rotor 2a side is assembled into the steam turbine 2 (see FIG. 1).

After the steam St generated in the boiler 10 (see FIG. 1) flows into the steam turbine 2, when the steam St passes through between the stator blades 2c and the rotor blades 2b, a portion of the steam St passes through the steam passage 72 and flows into the pressurizing chamber 71.

Force (pressing force) adapted to shift the piston head 64 in a direction coming close to the rotor 2a results from the pressure of the steam St flowing into the pressurizing chamber 71. If this force is smaller than the biasing force of the plurality of return springs 66, the return springs 66 support the piston head 64 at a position away from the rotor 2a.

For example, if a load connected to the steam turbine 2 (see FIG. 1) is increased so that the pressure of the steam St flowing through the steam turbine 2 is increased, also the pressure of the steam St flowing into the pressurizing chamber 71 is increased. The pressing force, resulting from the pressure of the steam St, adapted to shift the piston head 64 in the direction coming close to the rotor 2a becomes equal to or greater than the biasing force of the return springs 66. At this time, the piston head 64 is shifted by the pressure of the steam St in the direction coming close to the rotor 2a. In addition, the seal base-plate 61 connected to the piston head 64 via the piston body 65 is shifted in the direction coming close to the rotor 2a.

When the piston head 64, in the pressurizing chamber 71, is shifted to a stop position on the side close to the rotor 2a, the seal fins 62 on the seal base-plate 61 side come into contact with the corresponding breathable spacers 4b on the rotor 2a side. With this configuration, if the pressure of the steam St flowing into the pressurizing chamber 71 is increased, the seal fins 62 and the corresponding breathable spacers 4b opposed thereto come into contact with each other. Thus, the clearance between the seal fins 62 and the corresponding breathable spacers 4b can be eliminated, thereby improving the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

Similarly, when the piston head 64, in the pressurizing chamber 71, is shifted to the stop position on the side close to the rotor 2a, the breathable spacers 4a on the seal base-plate 61 side come into contact with the corresponding seal fins 2a1 on the rotor 2a side. With this configuration, if the pressure of the steam St flowing into the pressurizing chamber 71 is increased, the breathable spacers 4a come into contact with the corresponding seal fins 2a1 opposed thereto, thereby improving the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

As described above, the seal fins 62 on the seal base-plate 61 side are in contact with the corresponding breathable spacers 4b on the rotor 2a side and the seal fins 2a1 on the rotor 2a side are in contact with the corresponding breathable spacers 4a on the seal base-plate 61 side. In this case, rotational resistance against the rotation of the rotor 2a is increased; however, if the pressure of the steam St is high, the rotor 2a can be rotated against the rotational resistance increased by the contact between the seal fins 62 and the corresponding breathable spacers 4b and between the seal fins 2a1 and the corresponding breathable spacers 4a. That is to say, the rotor 2a can be rotated without the influence of the rotational resistance increased by the contact between the seal fins 62 and the corresponding breathable spacers 4 and between the seal fins 2a1 and the corresponding breathable spacers 4.

In other words, it is only necessary for the biasing force of the plurality of return springs 66 to be set so that the piston head 64 can be shifted in the direction coming close to the rotor 2a by the pressure of the steam St that can rotate the rotor 2a without undergoing an influence of the rotational resistance increased by the contact between the seal fins 62 and the corresponding breathable spacers 4b and between the seal fins 2a1 and the corresponding breathable spacers 4a.

Incidentally, the steam St flowing through the inside of the steam turbine 2 (see FIG. 1) expands and reduces in pressure from the upstream toward the downstream. Therefore, the return springs 66 installed in the labyrinth seal device 60 of the stator blade 2c may be configured to have respective biasing forces that are gradually decreased as the flow of the steam St goes toward the downstream side.

The labyrinth seal device 60 may be such that the number of the seal base-plates 61 is not limited to six but seven or more seal base-plates 61 are provided along the circumferential direction. Alternatively, the labyrinth seal device 60 may be provided with five or less seal base-plates 61 along the circumferential direction.

In the steam turbine 2 (see FIG. 1) into which the seal structure configured as described above is assembled, during the initial period of start-up low in the pressure of steam St, the seal fins 62 on the seal base-plate 61 side are not in contact with the corresponding breathable spacers 4b on the rotor 2a side. In addition, the seal fins 2a1 on the rotor 2a side are not in contact with the corresponding breathable spacers 4a on the seal base-plate 61 side.

In this way, the rotational resistance against the rotation of the rotor 2a is reduced so that the rotor 2a is efficiently rotated by the steam St at low pressure.

If the load of the steam turbine 2 (see FIG. 1) is increased to increase the pressure of the steam St, the seal fins 62 are in contact with the corresponding breathable spacers 4b and the seal fins 2a1 are in contact with the corresponding breathable spacers 4a. In this way, the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a is improved. Thus, the turbine efficiency of the steam turbine 2 is improved.

The steam St with high pressure can efficiently rotate the rotor 2a without undergoing an influence of the rotational resistance increased by the contact between the seal fins 62 and the corresponding breathable spacers 4b and between the seal fins 2a1 and the corresponding breathable spacers 4a.

That is to say, during the initial period of start-up or the like in the steam turbine 2 (see FIG. 1), when the pressure of the steam St is relatively low, the seal fins 62 on the seal base-plate 61 side are not in contact with the corresponding breathable spacers 4b on the rotor 2a side and the seal fins 2a1 on the rotor 2a side are not in contact with the corresponding breathable spacers 4a on the seal base-plate 61 side. In this way, the rotational resistance against the rotation of the rotor 2a is reduced. Thus, the rotor 2a is efficiently rotated by the steam St with low pressure, thereby smoothly starting up the steam turbine 2.

When the steam turbine 2 (see FIG. 1) is increased in load to increase the pressure of steam St, the seal fins 62 on the seal base-plate 61 side come into contact with the corresponding breathable spacers 4b on the rotor 2a side and the seal fins 2a1 on the rotor 2a side come into contact with the corresponding breathable spacers 4a on the seal base-plate 61 side. In this way, the amount of leakage steam between the stator blades 2c (see FIG. 2) and the rotor 2a is reduced, thereby improving the turbine efficiency.

The description has thus so far been given of the following configurational examples. In one of them, the plurality of breathable spacers 4 are attached to the rotor 2a and the labyrinth seal device 60. In the other one, the seal base-plate 61 constituting part of the labyrinth seal device 60 is provided on the nozzle diaphragm inner-ring 70 so as to be shiftable in the direction coming close to or moving away from the rotor 2a. However, the configuration of the invention is not limited to these.

Examples of the labyrinth seal device 60 include a high-low labyrinth seal device in addition to the device shaped as illustrated in FIG. 3. The present invention can be applied to also the high-low labyrinth seal device.

Referring to FIG. 6, a high-low labyrinth seal device 60a is provided with a seal base-plate 61 on a nozzle diaphragm inner-ring 70. The seal base-plate 61 is provided with seal fins 62 projecting upright along the circumferential direction and shiftably in a direction coming close to or moving away from a rotor 2a. The rotor 2a is formed with projecting portions 2a3 along the circumferential direction on the outer circumference thereof. The seal fins 62 on the seal base-plate 61 side are each arranged to face a corresponding one of the projecting portions 2a3 and recessed portions 2a4 of the rotor 2a, each of the recessed portions 2a4 being formed between the projecting portions 2a3.

Further, the labyrinth seal device 60a is configured to include a pressurizing chamber 71, a steam passage 72, a piston head 64, a piston body 65, and a plurality of return springs 66 circumferentially arranged in two lines.

As illustrated in FIG. 6, breathable spacers 4b are attached to the corresponding projecting portions 2a3 and recessed portions 2a4 formed on the rotor 2a so as to face the corresponding seal fins 62 on the seal base-plate 61 side.

The attachment of the breathable spacers 4b as described above can improve the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

A seal structure including the labyrinth seal device 60a and the breathable spacers 4b on the rotor 2a side are assembled into the steam turbine 2 (see FIG. 1).

Incidentally, the high-low labyrinth seal device 60a illustrated in FIG. 6 may be configured such that the breathable spacers 4b are attached to either one of the projecting portions 2a3 and recessed portions 2a4 of the rotor 2a.

Also in the high-low labyrinth seal device 60a, the seal base-plate 61 can be installed on the nozzle diaphragm inner-ring 70 shiftably in a direction coming close to or moving away from the rotor 2a.

With this configuration, the seal fins 62 provided on the stator blade 2c (see FIG. 2) which is a fixed portion can be shiftable in a direction coming close to or moving away from the rotor 2a which is a rotating portion.

Similarly to the configuration illustrated in FIG. 3, steam St passes through the steam passage 72 and flows into the pressurizing chamber 71. The pressure of the steam St may be high and a pressing force adapted to shift the piston head 64 in a direction coming close to the rotor 2a may be equal to or greater than the biasing force of the plurality of return springs 66. In such a case, the piston head 64 is shifted in the direction coming close to the rotor 2a so that the seal base-plate 61 operating integrally with the piston head 64 via the piston body 65 is shifted in the direction coming close to the rotor 2a.

When the piston head 64, in the pressurizing chamber 71, is shifted to a stop position on the side close to the rotor 2a, the seal fins 62 on the seal base-plate 61 side come into contact with the corresponding breathable spacers 4b attached to the corresponding projecting portions 2a3 and recessed portions 2a4 of the rotor 2a. With this configuration, when the pressure of the steam St flowing into the pressurizing chamber 71 is high, the seal fins 62 on the seal base-plate 61 side come into contact with the corresponding breathable spacers 4b attached to the projecting portions 2a3 and recessed portions 2a4 of the rotor 2a. In this contact state, a clearance between the seal fins 62 and the corresponding breathable spacers 4b is eliminated, thereby improving the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

As illustrated in FIG. 7, a high-low labyrinth seal device 60b may be acceptable in which a plurality of seal fins 2a5 are provided on the outer circumference of a rotor 2a.

In this case, a seal base-plate 61a is formed with a plurality of projecting portions 61a₁and a plurality of recessed portions 61a₂which are circumferentially formed to be lined in the axial direction of the rotor 2a. In addition, breathable spacers 4a shaped along the circumferential direction are attached to the plurality of corresponding projecting portions 61a₁and recessed portions 61a₂.

The labyrinth seal device 60b is configured to include the seal base-plate 61a attached with the breathable spacers 4a, a pressurizing chamber 71, a steam passage 72, a piston head 64, a piston body 65, and a plurality of return springs 66 arranged e.g. in the circumferential direction in two lines.

Further, the rotor 2a is provided on the outer circumference with the seal fins 2a5 which are provided upright along the circumferential direction at respective positions opposed to the corresponding projecting portions 61a₁and recessed portions 61a₂of the seal base-plate 61a.

A seal structure including the labyrinth seal device 60b and the seal fins 2a5 on the rotor 2a side are assembled into the steam turbine 2 (see FIG. 1).

Also in the high-low labyrinth seal device 60b, the seal base-plate 61a can be installed on the nozzle diaphragm inner-ring 70 shiftably in a direction coming close to or moving away from the rotor 2a.

With this configuration, the breathable spacers 4a provided on the stator blade 2c (see FIG. 2) which is a fixed portion can be shiftable in a direction coming close to or moving away from the rotor 2a which is a rotating portion.

Similarly to the labyrinth seal device 60 illustrated in FIG. 3, steam St passes through the steam passage 72 and flows into the pressurizing chamber 71. The pressure of the steam St may be high and a pressing force adapted to shift the piston head 64 in a direction coming close to the rotor 2a may be equal to or greater than the biasing force of the plurality of return springs 66. In such a case, the piston head 64 is shifted in the direction coming close to the rotor 2a so that the seal base-plate 61a operating integrally with the piston head 64 via the piston body 65 is shifted in the direction coming close to the rotor 2a.

When the piston head 64, in the pressurizing chamber 71, is shifted to a stop position on the side close to the rotor 2a, the breathable spacers 4a on the seal base-plate 61a side come into contact with the corresponding seal fins 2a5 on the rotor 2a side. With this configuration, when the pressure of the steam St flowing into the pressurizing chamber 71 is high, the breathable spacers 4a on the seal base-plate 61a side come into contact with the corresponding seal fins 2a5 on the rotor 2a side. In this contact state, a clearance between the breathable spacers 4a and the corresponding seal fins 2a5 is eliminated, thereby improving the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a.

As described above, the labyrinth seal device 60b can be configured such that the high-low seal base-plate 61a is provided on the nozzle diaphragm inner-ring 70 shiftably in the direction coming close to or moving away from the rotor 2a. Thus, the labyrinth seal device 60b can produce the same effect as that of the labyrinth seal device 60 illustrated in FIG. 3.

The present embodiment can be applied to a labyrinth seal device installed between the nozzle diaphragm outer-ring 80 (see FIG. 2) and the rotor blades 2b (see FIG. 2).

Referring to FIG. 8A, a cover 2g is provided at the distal ends of the rotor blades 2b to reduce the clearance between the rotor blades 2b and the nozzle diaphragm outer-ring 80 (see FIG. 2). As illustrated in FIG. 8B, the cover 2g is provided with a plurality of seal fins 2g1.

As illustrated in FIG. 8A, the cover 2g is provided at the distal ends of the rotor blades 2b so as to extend circumferentially annularly. In addition, the seal fins 2g1 (see FIG. 8B) are provided on the cover 2g so as to extend upright along the circumferential direction.

Seal base-plates 91 are installed on the nozzle diaphragm outer-ring 80 so as to face the cover 2g provided on the rotor blades 2b.

The nozzle diaphragm outer-ring 80 on the rotor blade 2b side is formed to extend in the circumferential direction. In addition, e.g. six seal base-plates 91 equally divided in the circumferential direction are installed between the nozzle diaphragm outer-ring 80 and the rotor blades 2b so as to surround the rotor blades 2b.

As illustrated in FIG. 8B, breathable spacers 4a are circumferentially attached to one seal base-plate 91 on the rotor blade 2b side. In addition, the seal fins 2g1 are provided on the cover 2g at respective positions opposed to the corresponding breathable spacers 4a.

In the present embodiment, all the seal base-plates 91 are installed on the nozzle diaphragm outer-ring 80 shiftable in a direction coming close to or moving away from the rotor blades 2b, i.e., in the rotational-radial direction of the rotor blades 2b.

Referring to FIG. 9, the seal base-plate 91 is of e.g. a high-low-type. Specifically, the seal base-plate 91 is formed with a plurality of projecting portions 91a and a plurality of recessed portions 91b. The projecting portions 91a and the recessed portions 91b are shaped to extend along the rotational direction of the rotor blade 2b, i.e., in the circumferential direction and are formed in line in the axial direction of the rotor 2a (see FIG. 2). The breathable spacers 4a are attached to the corresponding projecting portions 91a and recessed portions 91b so as to be shaped in the circumferential direction.

With this configuration, the breathable spacers 4a provided for the casing 2d (see FIG. 2) which is a fixed portion can be shifted in a direction coming close to or moving away from the rotor blade 2b which is a rotating portion.

The Seal fins 2g1 are circumferentially installed on the cover 2g of the rotor blade 2b to extend upright at respective positions opposed to the corresponding projecting portions 91a and recessed portions 91b of the seal base-plate 91.

The nozzle diaphragm outer-ring 80 is provided with a hollow pressurizing chamber 81. The hollow pressurizing chamber 81 is internally provided with a piston head 92 reciprocating in a direction coming close to or moving away from the rotor blade 2b. The piston head 92 is elastically supported by a plurality of return springs 94 (biasing means) circumferentially arranged, e.g., in two lines. In this way, the piston head 92 is biased by the return springs 94 in a direction moving away from the rotor blade 2b.

Incidentally, the number of the return springs 94 may be set appropriately.

The pressurizing chamber 81 is configured to communicate with the outside of the nozzle diaphragm outer-ring 80 through a steam passage 82. Steam St flowing through the outside of the nozzle diaphragm outer-ring 80 flows into the pressurizing chamber 81. When the pressure of the steam St is applied to the piston head 92, the piston head 92 is shifted in a direction coming close to the rotor blade 2b.

The piston head 92 is provided with a piston body 93. The piston body 93 extends from the pressurizing chamber 81 toward the rotor blade 2b and has an end portion terminating at the outside of the nozzle diaphragm outer-ring 80. The seal base-plate 91 is attached to the end portion.

The piston body 93 may be formed integrally with the piston head 92, for example. A method of attaching the seal base-plate 91 to the piston body 93 is not restrictive. For example, the seal base-plate 91 may be secured to the piston body 93 by means of screws not illustrated.

Thus, a movable portion is configured to include the piston head 92, the piston body 93, and the seal base-plate 91.

The labyrinth seal device 90 in the present embodiment is configured to include the seal base-plate 91, the piston head 92, the piston body 93, the plurality of return springs 94, the pressurizing chamber 81, and the steam passage 82.

A seal structure including the labyrinth seal device 90 and the seal fins 2g1 on the rotor blade 2b side is assembled into the steam turbine 2 (see FIG. 1).

When the piston head 92 of the labyrinth seal device 90 is supported by the biasing force of the return springs 94 at a position away from the rotor blade 2b, the seal base-plate 91 is shifted to a position away from the rotor blade 2b. In this state, the breathable spacers 4a on the seal base-plate 91 side are not in contact with the corresponding seal fins 2g1, opposed thereto, on the cover 2g side of the rotor blades 2b. Thus, a clearance is defined between the breathable spacers 4a and the corresponding seal fins 2g1.

After the steam St generated in the boiler 10 (see FIG. 1) flows into the steam turbine 2 (see FIG. 1), when the steam St passes through the outside of the nozzle diaphragm outer-ring 80, a portion of the steam St passes through the steam passage 82 and flows into the pressurizing chamber 81.

The pressure of the steam St flowing into the pressurizing chamber 81 causes a pressing force adapted to shift the piston head 92 in a direction coming close to the rotor blade 2b. If this pressing force is smaller than the biasing force of the plurality of return springs 94, the return springs 94 support the piston head 92 at a position away from the rotor blade 2b.

When the piston head 92 is supported at a position away from the rotor blade 2b by the biasing force of the return springs 94, the seal base-plate 91 is shifted to a position away from the rotor blade 2b. In this state, the breathable spacers 4a on the seal base-plate 91 side are not in contact with the corresponding seal fins 2g1, opposed thereto, on the cover 2g side of the rotor blade 2b. Thus, a clearance is defined between the breathable spacers 4a and the corresponding seal fins 2g1.

If the pressure of the steam St flowing into the steam turbine 2 (see FIG. 1) is increased, also the pressure of the steam St flowing into the pressurizing chamber 81 is increased. The pressure of the steam St causes a pressing force adapted to shift the piston head 92 in the direction coming close to the rotor blade 2b. If this pressing force becomes equal to or greater than the biasing force of the return springs 94, the piston head 92 is shifted in the direction coming close to the rotor blade 2b by the pressure of the steam St. In addition, the seal base-plate 91 connected to the piston head 92 via the piston body 93 is shifted in the direction coming close to the rotor blade 2b.

When the piston head 92, in the pressurizing chamber 81, is shifted to a stop position on the side close to the rotor blade 2b, the breathable spacers 4a on the seal base-plate 91 side come into contact with the corresponding seal fins 2g1 on the cover 2g side of the rotor blades 2b. With this configuration, if the pressure of the steam St flowing into the pressurizing chamber 81 is increased, the breathable spacers 4a on the seal base-plate 91 side come into contact with the corresponding seal fins 2g1 on the cover 2g side of the rotor blades 2b. Consequently, the clearance between the seal fins 2g1 and the corresponding breathable spacers 4a can be eliminated. Thus, the sealing performance between the nozzle diaphragm outer-ring 80 and the rotor blades 2b is improved.

Similarly to the labyrinth seal device 60 illustrated in FIG. 3, it is only necessary for the biasing force of the plurality of return springs 94 to be set so that the piston head 92 can be shifted in the direction coming close to the rotor blade 2b by the pressure of the steam St that can rotate the rotor 2a without undergoing an influence of the rotational resistance increased by the contact between the seal fins 2g1 and the breathable spacers 4a.

The steam St flowing through the inside of the steam turbine 2 (see FIG. 1) expands and reduces in pressure from the upstream toward the downstream. Therefore, similarly to the labyrinth seal device 60 illustrated in FIG. 3, the return springs 94 may be configured to have respective biasing forces that are gradually decreased as the flow of the steam St goes toward the downstream side.

The number of the seal base plates 91 is not limited to six. The labyrinth seal device 90 circumferentially provided with seven or more seal base-plates 91 may be acceptable. Alternatively, the labyrinth seal device 90 circumferentially provided with five or less seal base-plates 91 may be acceptable.

In the steam turbine 2 (see FIG. 1) including the labyrinth seal device 90 and the seal fins 2g1 on the cover 2g side of the rotor blades 2b illustrated in FIG. 9, during the initial period of start-up relatively low in the pressure of steam St, the breathable spacers 4a on the seal base-plate 91 side are not in contact with the corresponding seal fins 2g1 on the cover 2g side of the rotor blade 2b. A clearance is defined between the breathable spacers 4a and the corresponding seal fins 2g1 so that the rotational resistance against the rotation of the rotor blade 2b (the rotating portion) is reduced. The rotor 2a is efficiently rotated by the steam St with low pressure to smoothly start up the steam turbine 2.

When the steam turbine 2 (see FIG. 1) is increased in load to increase the pressure of steam St, the breathable spacers 4a on the seal base-plate 91 side come into contact with the seal fins 2g1 on the cover 2g side of the rotor blades 2b to eliminate the clearance between the breathable spacers 4a and the corresponding seal fins 2g1. In this way, the sealing performance between the nozzle diaphragm outer-ring 80 and the rotor blades 2b is improved. Thus, an amount of leakage steam occurring between the nozzle diaphragm outer-ring 80 and the rotor blades 2b is reduced to thereby improve the turbine efficiency of the steam turbine 2.

Incidentally, the labyrinth seal device 90 illustrated in FIG. 9 is configured such that the plurality of breathable spacers 4a are attached to the seal base-plate 91 and the plurality of seal fins 2g1 are provided on the cover 2g. However, the labyrinth seal device 90 may be configured such that the seal fins are provided on the seal base-plate 91 and the breathable spacers are attached to the cover 2g.

Alternatively, the labyrinth seal device 90 may be configured such that the plurality of seal fins are provided on both the seal base-plate 91 and the cover 2g. In this case, the breathable spacers are configured to be attached to the cover 2g at respective positions opposed to the corresponding seal fins on the seal base-plate 91 side and to the seal base-plate 91 at respective positions opposed to the corresponding seal fins on the cover 2g side.

The embodiments of the present invention have been described thus far. However, the invention is not limited to the embodiments described above and can appropriately be modified in design in a range not departing from the gist of the invention.

In the labyrinth seal device 60 illustrated in FIG. 3, the seal base-plate 61 is biased by the return springs 66 elastically supporting the piston head 64 in the pressurizing chamber 71 in the direction moving away from the rotor 2a. However, for example, respective piston bodies 65 of adjacent seal base-plates 61 may circumferentially be connected to each other via compression springs 66a (biasing means) as illustrated in FIG. 10.

The compression springs 66a are installed between the adjacent piston bodies 65 in a compressed state so as to bias the piston body 65 in a direction moving the adjacent piston bodies 65 away from each other.

One piston body 65 is elastically supported by the compression springs 66a in a state shifted to a position away from the rotor 2a. The seal base-plate 61 is attached to the piston body 65 so that the seal base-plate 61 is supported at a position away from the rotor 2a.

When steam St (see FIG. 3) flows into the pressurizing chamber 71, the pressure of the steam St causes a pressing force adapted to shift the piston head 64 in a direction coming close to the rotor 2a. If this pressing force exceeds the biasing force of the compression springs 66a, the piston head 64 is shifted in a direction coming close to the rotor 2a. As the piston head 64 is shifted, the seal base-plate 61 is shifted in a direction coming close to the rotor 2a.

Thus, the same effect as that of the labyrinth seal device 60 illustrated in FIG. 3 is produced.

The labyrinth seal device 60 illustrated in FIG. 3 is configured such that the piston head 64 is driven by the pressure of the steam St flowing through the steam turbine 2 (see FIG. 1). For example, the following configuration illustrated in FIG. 11 may be acceptable. The piston head 64 is shifted in a direction coming close to the rotor 2a by the high pressure of steam (driving steam) for driving the piston head 64, the steam flowing into the pressurizing chamber 71 from a high-pressure steam supply source 102.

A labyrinth seal device 60c illustrated in FIG. 11 is configured to include a valve control device 100, an operating condition detecting device 101, the high-pressure steam supply source 102, and an electromagnetic valve 103 in addition to the labyrinth seal device 60 illustrated in FIG. 3.

A seal structure including the labyrinth seal device 60c and the plurality of seal fins 2a1 and plurality of breathable spacers 4b on the rotor 2a1 side is assembled into the steam turbine 2 (see FIG. 1).

The high-pressure steam supply source 102 is connected to the pressurizing chamber 71 via the electromagnetic valve 103. Further, the valve control device 100 for controlling the opening/closing of the electromagnetic valve 103 is provided.

Preferably, the valve control device 100 is configured to control the opening/closing of the electromagnetic valve 103 on the basis of the operating condition of the steam turbine 2 (see FIG. 1). The valve control device 100 is provided with the operating condition detecting device 101 for detecting the operating condition of the steam turbine 2.

With this configuration, the valve control device 100 can shift a movable portion including the piston head 64, the piston body 65, and the seal base-plate 61 in a direction coming close to the rotor 2a on the basis of the operating condition of the steam turbine 2.

A drive device is configured to include the pressurizing chamber 71, the valve control device 100, the high-pressure steam supply source 102, and the electromagnetic valve 103.

Preferably, the operating condition of the steam turbine 2 (see FIG. 2) is detected based on e.g. the rotation speed of the rotor 2a. The operating condition detecting device 101 is a rotation speed detecting device for detecting the rotation speed of the rotor 2a.

The operating condition detecting device which is the rotation speed detecting device detects the rotation speed of the rotor 2a and converts it to a detection signal, which is sent to the valve control device 100.

The valve control device 100 calculates the rotation speed of the rotor 2a on the basis of the detection signal supplied from the operating condition detecting device 101 (the rotation speed detecting device).

If the calculated rotation speed of the rotor 2a is smaller than a predetermined rotation speed, the valve control device 100 sends a control signal to the electromagnetic valve 103 for closing.

The predetermined rotation speed in this case may appropriately set based on the performance or the like of the steam turbine 2 (see FIG. 1).

The electromagnetic valve 103 is closed based on a control signal sent from the valve control device 100 to cut off the inflow of driving steam to the pressurizing chamber 71 from the high-pressure steam supply source 102.

When the driving steam does not flow into the pressurizing chamber 71, the piston head 64 is shifted by the biasing force of the return springs 66 in a direction moving away from the rotor 2a.

When the piston head 64 is shifted in the direction moving away from the rotor 2a, the seal base-plate 61 is shifted in the direction moving away from the rotor 2a. In this way, the seal fins 62 on the seal base-plate 61 side are not in contact with the corresponding breathable spacers 4b on the rotor 2a side. In addition, the breathable spacers 4a on the seal base-plate 61 side are not in contact with the corresponding seal fins 2a1 on the rotor 2a side. Thus, rotational resistance against the rotation of the rotor 2a is reduced.

If the calculated rotation speed of the rotor 2a is equal to or higher than the predetermined rotation speed, the valve control device 100 sends a control signal to the electromagnetic valve 103 for opening.

The electromagnetic valve 103 is opened based on the control signal sent from the valve control device 100, so that the driving steam flows into the pressurizing chamber 71 from the high-pressure steam supply source 102.

The piston head 64 is shifted in a direction coming close to the rotor 2a by the pressure of the driving steam flowing into the pressurizing chamber 71 from the high-pressure steam supply source 102.

When the piston head 64 is shifted in the direction coming close to the rotor 2a, the seal base-plate 61 is shifted in the direction coming close to the rotor 2a. In this way, the seal fins 62 on the seal base-plate 61 side come into contact with the corresponding breathable spacers 4b on the rotor 2a side. In addition, the seal fins 2a1 on the rotor 2a side come into contact with the corresponding breathable spacers 4a on the seal base-plate 61 side.

Thus, the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a is improved.

If the rotation speed of the rotor 2a is low e.g. during the initial period of starting up the steam turbine 2 (see FIG. 1), the valve control device 100 closes the electromagnetic valve 103 to bring the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side into non-contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side are brought into non-contact with each other. In this way, the rotational resistance against the rotation of the rotor 2a is reduced. Thus, the rotor 2a is efficiently rotated by the steam St and the steam turbine 2 is smoothly started up.

When the steam turbine 2 (see FIG. 1) is started up and the rotation speed of the rotor 2a is increased, the valve control device 100 opens the electromagnetic valve 103 to bring the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side into contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side are brought into contact with each other.

Thus, the steam turbine 2 is improved in the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a, thereby improving turbine efficiency.

Preferably, the pressure of the driving steam is pressure that can shift the piston head 64 in a direction coming close to the rotor 2a against the biasing force of the return springs 66.

A configuration may be acceptable in which the operating condition of the steam turbine 2 is detected by use of e.g. the pressure of the steam St. In this case, the operating condition detecting device 101 is a pressure detecting device for detecting the pressure of the steam St.

The operating condition detecting device 101 which is the pressure detecting device detects the pressure of steam St flowing through the steam turbine 2 (see FIG. 1) and sends a detection signal to the valve control device 100. The valve control device 100 calculates the pressure of the steam St.

If the pressure of the steam St is lower than a predetermined pressure value, the valve control device 100 sends a control signal to the electromagnetic valve 103 for closing.

The electromagnetic valve 103 is closed based on the control signal sent from the valve control device 100 to cut off the inflow of the driving steam to the pressurizing chamber 71 from the high-pressure steam supply source 102.

It is only necessary for the predetermined pressure value to be appropriately set based on the performance or the like of the steam turbine 2 (see FIG. 1).

If the driving steam does not flow into the pressurizing chamber 71, the piston head 64 is shifted in a direction moving away from the rotor 2a by the biasing force of the return springs 66.

When the piston head 64 is shifted in the direction moving away from the rotor 2a, the seal base-plate 61 is shifted in the direction moving away from the rotor 2a. In this way, the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side are not in contact with each other. In addition, the breathable spacers 4a on the seal base-plate 61 side, and the corresponding seal fins 2a1 on the rotor 2a side are not in contact with each other. Thus, the rotational resistance against the rotation of the rotor 2a is reduced.

If the pressure of the steam St is equal to or greater than the predetermined pressure value, the valve control device 100 sends a control signal to the electromagnetic valve 103 for opening.

When the piston head 64 is shifted in the direction coming close to the rotor 2a, the seal base-plate 61 is shifted in the direction coming close to the rotor 2a. In this way, the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side come into contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side come into contact with each other.

Thus, the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a is improved.

When the pressure of the steam St is lower than the predetermined pressure value, e.g., during the initial period of starting up the steam turbine 2 (see FIG. 1), the valve control device 100 closes the electromagnetic valve 103. In this way, the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side are brought into non-contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side are brought into non-contact with each other. This reduces the rotational resistance against the rotation of the rotor 2a. Thus, the rotor 2a is efficiently rotated by the steam St with low-pressure and the steam turbine 2 is smoothly started up.

The steam turbine 2 (see FIG. 2) is started up and the pressure of the steam St becomes equal to or greater than the predetermined pressure value. Then, the valve control device 100 opens the electromagnetic valve 103 to bring the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side into contact with each other. In addition, this brings the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side into contact with each other.

The steam turbine 2 is improved in the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a, thereby improving turbine efficiency.

That is to say, when the pressure of the steam St is lower than the predetermined pressure value, such as during the initial period of start-up or the like, the steam turbine 2 (see FIG. 2) is such that the clearance is defined between the stator blades 2c (see FIG. 2) and the rotor 2a. This reduces rotational resistance against the rotation of the rotor 2a, so that the rotor 2a is efficiently rotated by the steam St for smooth start-up. When the pressure of the steam St becomes equal to or greater than the predetermined pressure value, the steam turbine 2 is improved in the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a, thereby improving turbine efficiency.

Incidentally, the labyrinth seal device 60c illustrated in FIG. 11 is configured such that the driving steam is allowed to flow into the pressurizing chamber 71 from the high-pressure steam supply source 102 to shift the piston head 64 in a direction coming close to the rotor 2a. However, a configuration may be acceptable in which the piston head 64 is shifted in a direction coming close to the rotor 2a by a driving means such as an actuator or the like not illustrated.

The seal structure (see FIG. 9) assembled between the nozzle diaphragm outer-ring 80 and the rotor blades 2b may be made to have the same configuration as that of the seal structure illustrated in FIG. 11.

As described above, the steam turbine 2 (see FIG. 1) according to the present embodiment has the seal structure assembled between the stator blades 2c (see FIG. 2) which are the fixed portion and the rotor 2a which is the rotating portion, the seal structure including the labyrinth seal device 60, the seal fins 2a1 on the rotor 2a side, and the breathable spacers 4b on the rotor 2a side, as illustrated in FIG. 3.

In addition, the seal fins 62 on the seal base-plate 61 side of the labyrinth seal device 60 come into contact with the corresponding breathable spacers 4b on the rotor 2a side and the seal fins 2a1 on the rotor 2a side come into contact with the corresponding breathable spacers 4a on the seal base-plate 61 side. This configuration improves the sealing performance between the stator blades 2c and the rotor 2a, thereby producing an excellent effect of suppressing the lowering of turbine efficiency due to leakage steam.

Further, the breathable spacer 4 (4a, 4b) is formed of breathable metal which is abradable material superior in the easiness of the abrasion. With this configuration, even if the seal fin 62 and the seal fin 2a1 each come into contact with the breathable spacer 4, the breathable spacer 4 is abraded. Therefore, an excellent effect is produced in which the seal fin 62 and the seal fin 2a1 are prevented from being damaged.

The breathable spacer 4 made of breathable metal can aerate a slight amount of steam St. Therefore, frictional heat resulting from the contact between each of the seal fins 62 and 2a1 and the breathable spacer 4 can be cooled by the steam St passing through the breathable spacer 4. Thus, the breathable spacer 4 can be prevented from having temperature higher than that of the steam St.

For example, also even if the rotor 2a is rotated for a long period of time and the seal fins 62 and 2a1 and the breathable spacer 4 cause frictional heat for a long period of time, the breathable spacer 4 will not have temperature higher than that of the steam St. The rotor 2a and the seal base-plate 61 each of which is attached with the breathable spacer 4 do not have temperature higher than that of the steam St. Thus, an excellent effect can be produced in which the rotor 2a and the seal base-plate 61 are prevented from causing thermal deformation.

For example, the spacer made of porous metal is abradable material superior in the easiness of the abrasion. If the seal fins 62 and 2a1 each come into contact with the spacer made of porous metal, since the spacer made of porous metal is abraded, the seal fins 62 and 2a1 can be prevented from being damaged.

However, pores of the porous metal may sometimes not communicate with each other. In such a case, the spacer made of porous metal cannot aerate steam St. Thus, the frictional heat caused by the contact between each of the seal fins 62 and 2a1 and the spacer made of porous metal cannot be cooled by the steam St.

In the present embodiment, because of the provision of the breathable spacer 4 made of breathable metal, the frictional heat caused by the contact between each of the seal fins 62 and 2a1 and the breathable spacer 4 can be cooled by the steam St passing through the breathable spacer 4.

The seal base-plate 61 provided with the seal fins 62 and the breathable spacers 4a is installed on the nozzle diaphragm inner-ring 70 shiftably in a direction coming close to or moving away from the rotor 2a. When the steam St has low pressure, the seal fins 62 on the seal base-plate 61 side and the corresponding breathable spacers 4b on the rotor 2a side are not in contact with each other. In addition, the seal fins 2a1 on the rotor 2a side and the corresponding breathable spacers 4a on the seal base-plate 61 side are not in contact with each other.

With this configuration, when the steam St has low pressure, such as e.g. during the initial period of starting up the steam turbine 2 (see FIG. 1), the seal fins 62 and 2a1 are not in contact with the corresponding breathable spacers 4. This can reduce the rotational resistance against the rotation of the rotor 2a. Thus, even if the pressure of the steam St is low, the rotor 2a can efficiently be rotated, thereby producing an excellent effect of smoothly starting up the steam turbine 2.

When the load of the steam turbine 2 is increased to increase the pressure of the steam St, the seal fins 62 and 2a1 are brought into contact with the corresponding breathable spacers 4. This can improve the sealing performance between the stator blades 2c (see FIG. 2) and the rotor 2a. Thus, an excellent effect of preventing the lowering of the turbine efficiency of the steam turbine 2 can be produced.

Incidentally, the seal structure including the labyrinth seal device 60, the plurality of seal fins 2a1, and the plurality of breathable spacers 4b illustrated in e.g. FIG. 3 can be assembled not only between the nozzle diaphragm inner-ring 70 and the rotor 2a but also between another fixed portion and another rotating portion such as between the casing 2d (see FIG. 2) and the rotor 2a.

Even a labyrinth seal device 60 in which the seal fins 62 and breathable spacers 4a on the fixed portion side are installed so as not to be shifted in a direction coming close to or moving away from the rotating portion can produce a cooling effect resulting from the breathable spacers 4 aerating the steam St.

Seal Structure and Control Method Therefor

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