JP2002349209A - Seal structure for turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve turbine efficiency by forming a low friction layer between a packing ring and a packing ring holder for reducing a friction coefficient itself and uncertainty of friction force. SOLUTION: In this seal structure for a turbine, a gap 14 between a stationary part and a rotation part of the turbine is sealed with turbine packing. The turbine packing is provided with the packing ring holder 9 fixed on the stationary part and the packing ring 10 retained by the packing ring holder 9 and including a fin segment for sealing. A low friction layer 19 is formed on a surface where the packing ring holder 9 and the packing ring 10 get into contact.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a turbine sealing structure in which a gap between a stationary portion and a rotating portion of a turbine is sealed by a turbine packing, and more particularly to a turbine sealing structure in which the gap between the stationary portion and the rotating portion is stabilized. The present invention relates to a turbine seal structure that can be improved.

[0002]

2. Description of the Related Art Generally, a gap between a stationary part and a rotating part of a turbine is sealed by a turbine packing. The turbine packing is fixed to the stationary part, and is held by the packing ring holder. And a packing ring having fin segments.

[0003] In recent years, improvement in turbine performance, especially turbine efficiency, has been emphasized in response to requests for reduction of environmental load. Various measures have been proposed to improve the turbine efficiency, but the most effective measure is the turbine working fluid in the gap between the stationary part and the rotating part, which is inevitably present in each part of the turbine. To reduce leakage.

[0004] Turbine packing, which is means for preventing leakage of the turbine working fluid, is roughly applied to three types of locations. The first turbine packing is called a nozzle packing applied to a gap between a nozzle inner ring as a stationary part fixed to a casing and a turbine axle as a rotating part rotating on the inner peripheral side. The second turbine packing is a turbine packing called a chip fin that seals a gap between a nozzle outer ring that is a stationary part and a turbine rotor blade that is a rotating part. The third turbine packing is called a gland packing that seals a gap between a turbine casing as a stationary part and a turbine axle as a rotating part.

The smaller the gap between the fin tip of the nozzle packing ring and the turbine axle, the tip of the tip fin ring or the fin tip of the gland packing and the turbine axle, the more the working fluid leaks. And the performance can be improved. However, on the other hand, if the gap between the stationary part and the rotating part is excessively reduced, the stationary part and the rotating part come into contact during turbine operation due to thermal expansion or the like, and the rotating part is damaged, the seal fins are damaged, and the shaft vibration is reduced. , And the deformation of the rotating part due to frictional heat is concerned. Such contact between the fixed part and the rotating part is caused by a transitional pressure change or thermal deformation at the time of starting and stopping the turbine, in a situation where the gap between the stationary part and the rotating part changes, and at the time of turbine rated operation. Maintains a relatively stable gap.

Therefore, recently, a large number of gap adjusting devices have been proposed which maintain a large gap between the stationary portion and the rotating portion when the turbine is started and stopped, and reduce a gap between the stationary portion and the rotating portion during the rated operation of the turbine (for example, Japanese Patent Application Laid-Open No. H11-157556). Fairness 4-37310
No., Tokuhei 7-65481, Tokuhei 7-39805
No. JP-A-8-284609).

Most of such a gap adjusting device utilizes a pressure difference of a working fluid. For example, an elastic body for urging a packing ring toward an outer periphery of a turbine and a high-pressure working fluid are introduced into a packing ring holder. And a fluid pressurizing means for pressurizing the packing ring toward the inner peripheral side of the turbine.

When the gasket is stationary, the packing ring is pressed against the outer peripheral side by an elastic body to secure a sufficient gap. On the other hand, as the pressure difference of the working fluid increases with an increase in the load on the turbine, the packing ring is placed behind the packing ring. The introduced working fluid presses the packing ring against the inner peripheral side, thereby narrowing the gap between the stationary part and the rotating part. That is, the gap between the stationary portion and the rotating portion is kept large when the turbine is stopped, and the gap between the stationary portion and the rotating portion is reduced during the rated operation of the turbine.

[0009]

The conditions under which the turbine clearance adjusting device operates depend on the pressing force of the working fluid,
It is determined by the pressing force of the elastic body, the frictional force between the packing ring and the packing ring holder, the balance condition of the weight of the packing ring, and the like. Among them, the estimation of the frictional force between the packing ring and the packing ring holder has many errors, and the friction coefficient of the contact surface may change during the aging operation.

Further, if the estimation of the frictional force is erroneous, the gap cannot be completely tightened at the time of rated operation, which may cause a decrease in performance, or the turbine may stop without sufficiently opening the gap, and the stationary part and the rotating part may come into contact with each other. There is a concern that For this reason,
It is required to reduce the operation instability of the packing ring due to the uncertainty of the frictional force.

However, the conventional sealing structure cannot always sufficiently meet these requirements, leaving room for improvement in the stability of the turbine gap adjusting device, and also does not improve the degree of freedom in setting the operation of the turbine gap adjusting device. There are enough aspects.

The present invention has been made in view of such circumstances, and in particular, by reducing the frictional force between the packing ring and the packing ring holder and greatly reducing the error in estimating the frictional force, It is an object of the present invention to provide a turbine seal structure that can improve the efficiency of a turbine, thereby improving the stability of the turbine gap adjusting device, and further increase the degree of freedom in setting the operation of the turbine gap adjusting device.

[0013]

According to an aspect of the present invention, there is provided a turbine sealing structure for sealing a gap between a stationary portion and a rotating portion of a turbine with turbine packing. Turbine packing is
In a device provided with a packing ring holder fixed to the stationary portion and a packing ring held by the packing ring holder and having a sealing fin segment, a surface where the packing ring holder and the packing ring are in contact with each other has a low height. Provided is a turbine seal structure having a friction layer formed thereon.

According to the second aspect of the present invention, the low friction layer is provided on one or both of the surfaces of the packing ring holder and the packing ring which are in contact with each other on the downstream side in the working fluid leakage direction, or on the packing. 2. The ring holder and the packing ring are formed on one or both of the surfaces parallel to the working fluid leakage direction, or on a plurality of surfaces obtained by combining these, in each of the surfaces contacting each other. A turbine seal structure.

According to the third aspect of the present invention, the low friction layer includes a turbine packing for sealing a gap between the turbine nozzle inner ring and the turbine axle, a turbine packing for sealing a gap between the turbine nozzle outer ring and the turbine rotor blade outer periphery, and a turbine casing. The seal structure for a turbine according to claim 1 or 2, wherein the seal is applied to at least one portion of a turbine packing that seals a gap between the turbine and a turbine axle.

According to a fourth aspect of the present invention, the low friction layer is formed by any one or more means selected from adhesion of a fluororesin sheet, coating of a fluororesin, and coating of a high hardness alloy. A turbine seal structure according to any one of claims 1 to 3, characterized by:

In the invention according to claim 5, the low friction layer includes an elastic body for urging the packing ring toward the outer peripheral side of the turbine and a high-pressure working fluid introduced into the packing ring holder so that the packing ring is connected to the inner peripheral side of the turbine. A seal structure for a turbine is provided which is applied to a turbine packing provided with a gap adjusting device having a fluid pressurizing means for pressurizing the turbine.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 8 show a turbine seal structure according to an embodiment of the present invention.

FIG. 1 is a configuration diagram showing a main part of a seal structure of a turbine according to the present embodiment, and FIG. 2 is an overall configuration diagram for explaining types, arrangement, and the like of the seal structure shown in FIG.

First, the overall configuration will be described with reference to FIG.
FIG. 2 shows two types of turbine packings provided in the paragraph section of the steam turbine. The first turbine packing A is a nozzle packing that seals a gap between a nozzle inner ring 1 as a stationary portion fixed to the casing 1a and a turbine axle 2 as a rotating portion that rotates further inside the nozzle inner ring 1. It is called. The turbine packing A has a configuration in which a nozzle packing ring 4 having a large number of fins 4a is held in a nozzle packing ring holder 3 provided on a nozzle inner ring 1. Further, the second turbine packing B is a turbine packing called a chip fin that seals a gap between the nozzle outer ring 8 that is a stationary portion and the turbine rotor blade 5 that is a rotating portion. The second turbine packing has a configuration in which a tip fin ring 7 having a large number of fins 7a is held in a tip fin ring holder 6 provided on a nozzle outer ring 8. In addition, in addition to the turbine packings A and B, a turbine packing (not shown) called a gland packing, which seals a gap between the turbine casing 1a and the turbine axle 2, is provided for preventing steam leakage.

Next, the main structure of the turbine packing will be described with reference to FIG. In the following description, the above-described nozzle packing ring holder 3, the tip fin ring holder 6, the packing ring holder for the gland packing, and the like provided on the stationary portion side are collectively described as a "packing ring holder 9". The packing ring 4, the tip fin ring 7, the packing ring of the gland packing, and the like will be similarly described as a "packing ring 10." In addition, the turbine axle 2, the turbine rotor blade 5, and the like will be described as a "rotating unit 11."

As shown in FIG. 1, the packing ring holder 9 is in the form of a hollow ring having a substantially rectangular cross section, and its inner peripheral wall 13 faces the rotating portion 11 and the inner peripheral wall 1
3 has an opening 15 for holding a packing ring. The packing ring 10 is a ring having a substantially I-shaped cross section. A wide outer diameter ring portion 16 is inserted and held in the space 12 in the packing ring holder 9, and a narrower neck portion 17 is formed in the opening of the packing ring holder 9. The fin block 18 is slidably inserted into the fin 15 and holds a fin 18 b on the inner diameter side of the neck portion 17. The packing ring holder 9 is divided into two parts in consideration of the assemblability, and the packing ring 10 is divided into four parts or more. These packing ring holder 9 and packing ring 10
In such a configuration made of a steel material or the like, a low friction layer 19 made of a material having a small friction coefficient is formed on a surface of the packing ring 10 on a predetermined surface in contact with the packing ring holder 9. . That is, in the present embodiment, the low friction layer 19 is formed of the packing ring holder 9 of the outer diameter ring portion 16 of the packing ring 10.
And a side surface (hereinafter, referred to as the “side surface”) of the packing ring holder 9 at the downstream side of the neck portion 17 along the leak direction a of the working fluid such as steam.
The outer surface of the fin block 18 which is in contact with the inner peripheral wall 13 of the packing ring holder 9 (the surface is parallel to the leak direction a of the working fluid).
8a are formed respectively.

These low friction layers 19 are formed by, for example, adhesion of a fluororesin sheet, coating of a fluororesin, or coating of a high hardness alloy. Bonding of the fluororesin sheet is suitable for use in a low temperature region up to a working fluid temperature of about 200 ° C. In a medium temperature range exceeding the operating temperature range of the adhesive and up to about 350 ° C., it is desirable to directly coat the packing ring 9 with a fluororesin. Further, in a higher temperature range, it is desirable to form a low friction layer 19 by coating a high-hardness alloy such as a WC-based high-hardness alloy or a Co-based high-hardness alloy. When the low friction layer 19 is coated, there is no problem even if the low friction layer 19 is formed on the non-contact surface of the packing ring 10 with the packing ring holder 9 in manufacturing.

FIG. 3 shows an example of the configuration of a clearance adjusting device applied to such a turbine packing. This figure 3
The gap adjusting device shown in (1) utilizes a pressure difference of a working fluid. That is, the elastic body 20 that urges the packing ring 10 toward the turbine outer peripheral side is provided in the space 12 of the packing ring holder 9. Further, a high-pressure side working fluid introduction passage 21 is provided in the space portion 12 of the packing ring holder 9, and the packing ring 10 is added toward the turbine inner peripheral side by introducing the high-pressure working fluid into the space portion 12. Pressure.

In the stationary state, the packing ring 10 is pressed against the outer peripheral side by the elastic body 20.
A sufficient gap can be secured between the packing ring 10 and the rotating part 11. On the other hand, as the pressure of the working fluid increases with an increase in the load on the turbine, the working fluid introduced to the back side of the packing ring 10 presses the packing ring 10 toward the inner circumference, and the gap between the stationary portion and the rotating portion is increased. 14
Is narrowed. As a result, the gap 14 between the stationary part and the rotating part is kept large when the turbine starts and stops, and the gap 14 between the stationary part and the rotating part is kept during the rated operation of the turbine.
Is provided.

Next, the operation will be described with reference to FIGS. The following operation can be similarly obtained in any of the nozzle packing ring 4, the tip fin ring 6, and the gland packing. First, the operation principle of the above-described gap adjusting device will be described in detail with reference to FIG.

As shown in FIG. 4, a force (hereinafter referred to as "elastic body reaction force") F applied to the packing ring 10 by, for example, the above-described elastic body 20 toward the outer peripheral side of the turbine.
(F1) is given. The elastic body reaction force F1
Instead of the lifting method, a method of pushing up toward the outer diameter side of the turbine or a method of pushing up in the circumferential direction can be applied. The resultant force such as the pressing force of the elastic body 20 acts outward in the radial direction, and the packing ring 1
0 is pressed against the outer peripheral side, and the reaction force F (F
2) and balance the force (F1 = F2). Actually, in addition to the reaction force F (F2) from the outer peripheral side, the packing ring 10
, The friction of the contact surface, the circumferential restraining force of the elastic body 20, the reaction force of the packing ring end face, and the like, and these resultant forces can be regarded as the reaction force F from the outer peripheral side during assembly.

When the rotation speed of the turbine increases and the output starts increasing, the working fluid force starts to act on the packing ring 10. That is, by introducing a high-pressure working fluid to the outer peripheral side of the packing ring 10, a pressure is generated in a direction of pushing the packing ring 10 toward the inner peripheral side, and a pressure difference is generated with the inner peripheral side of the packing ring 10 (fin installation surface). As a result, the fluid force P
Acts as 1. When the fluid force further increases, as shown in FIG. 5, the packing ring 10 is further pressed to the inner peripheral side, and moves in a direction to close the gap 14 between the stationary part and the rotating part. FIG. 6 shows the balance of the radial force in FIGS. 4 and 5 viewed from the working fluid leakage direction.

When the output of the turbine further rises, the packing ring 10 exerts a fluid force P2 on the packing ring 10 in addition to the radially inner force P1 and also the flow direction of the leaked fluid accompanying the leak of the working fluid.
Works. When the frictional force of the holder sliding surface 17a is considered, the operating condition of the packing ring 10 is expressed by the following equation (1).

[0030]

F + μP2 <P1 (1) where F is the reaction force from the outer peripheral side during assembly, μ is the maximum friction coefficient of the holder sliding surface, and P2 is the high-pressure fluid pressure pI.
Pressure difference Δ due to the fluid force resulting from the difference between
It is proportional to p = pI-pO. On the other hand, the fluid force P2 is as shown in FIG.
As shown in (1), it is expressed as a resultant force of the fluid pressure distribution on the inner surface side of the packing ring. Fluid force P2 and fluid force difference ΔP (= P1
-P2) is not strictly proportional, but, for example, in the case of the packing ring shape shown in FIG. 7, the average pressure difference between the upper and lower surfaces is substantially proportional to Δp as shown in FIG. Therefore,
P1 = A1Δp, P2 = Equivalent area A1, A with A2Δp
2 can be considered, and using this symbol, the operation start condition of the packing ring 10 is substantially

F <(A1-μA2) Δp (2) Here, A1 and A2 are the packing rings 10
, The fin shape and the fin configuration.

In the case of the packing ring 10 having the shape shown in FIG. 7, A1 / A2 has a value of about 0.75. On the other hand, the coefficient of friction μ of steel is generally about 0.15 to 0.3.

Under such conditions, when the error of the pressure difference Δp1 at the start of the operation of the packing ring is calculated, from the equation (2),

Since F <((A1 / A2) -μ) Δp (3), A1 / A2 = 0.75 in the packing ring shape shown in FIG. 7 and the maximum value of the friction coefficient μ of steel are shown. (=
0.3) and the minimum value (= 0.15), and calculating the ratio, (0.75)
Since (−0.15) / (0.75−0.3) = 1.33, an estimation error of about 33% occurs. Also,
The contact surface deteriorates due to aging, and μ = 0.5-1.
It has been reported that the pressure becomes zero, in which case the pressure at which the packing ring 10 starts operating further increases. In this example, under the condition of μ> 0.75, the packing ring does not start operating even if the pressure increases.

When the packing normally starts moving in the direction to close the gap due to the increase in turbine output, the balance of the forces acting on the packing ring 10 is as follows.

[0034]

F + kx = (A1−μA2) Δp (4) where x is the moving distance of the packing ring, and k is the spring constant of the elastic body pressing the packing ring. Since the packing ring 10 is pressed against the inner wall and continues to move according to the equation (2) until the operation of the gap adjusting device is completed,
The operation completion condition is

F + kδ = (A1−μA2) Δp2 (5) where δ: gap adjustment amount, Δp2: operation completion pressure difference. Thereafter, when the fluid pressure further increases, the reaction force from the inner wall supports the increase in the fluid force due to the increase in the pressure. If the operation completion pressure difference Δp2 is estimated under the same conditions as in the case of starting the operation, an estimation error of about 33% will also occur due to the uncertainty of the friction coefficient.

Next, in the process from the operation of the turbine to the stop where the turbine output decreases, the frictional force acts inward on the radial line after the reaction force from the inner wall decreases and disappears. For this reason, the pressure difference Δp3 at which the packing ring starts moving in the direction to open the gap and starts the reverse operation
Is as follows:

[0036]

F + kδ = (A1 + μA2) Δp3 (6)

As described above, A1 / A2 = 0.75 and μ =
In the case of 0.15 to 0.3, the reverse operation start pressure difference Δp3
About (0.75 + 0.3) / (0.75 + 0.1
5) From 1.17, an estimation error of about 17% occurs.

Here, for example, the pressure difference between the high pressure side and the low pressure side during the rated operation is defined as Δpope, and Δp <0.3Δpop
In the operation range of e, when the gap 14 between the stationary part and the rotating part needs to be open both when starting and when stopping, Δp
1, p3> 0.3Δpope. From equations (5) and (6), Δp3 / Δp2 = 0.43-0.
67, so that Δp3 / Δpope> 0.45-0.
70. Therefore, as long as the contact surface between the packing ring holder 9 and the packing ring 10 is a steel surface, for example, at the time of partial load operation, that is, at Δp = 0.5Δpope, the gap adjusting device is operated without completing the operation, that is,
There is a case where the operation is performed with the gap 14 not sufficiently closed, and the performance at the time of partial output is sacrificed.

On the other hand, according to the present embodiment, for example, since the friction coefficient of the fluororesin polytetrafluoroethylene is about 0.04 to 0.06, the estimated error of Δp1 and Δp2 is about 2.9%. , The estimation error of Δp3 is 2.5%
The operation instability due to the estimation error of friction is greatly reduced.

Δp3 / Δp2 = 0.85 to 0.9
Therefore, when Δp = 0.3Δpope, Δp2
= 0.33Δpope, the turbine gap adjusting device completes its operation, and a great degree of freedom is set in setting the operating conditions of the gap adjusting device.

When a high-hardness alloy layer is used as the low-friction layer, the effect is not as great as that of the fluororesin. However, when a high-hardness alloy having a friction coefficient of about 0.08 to 0.12 is used, Δ
p1 and Δp2 can be estimated with an estimation error of about 6%, Δp3 can be estimated with an estimation error of about 5%, and Δp3 / Δp2 can be estimated by 0.7.
It is about 2 to 0.81, which can achieve a reduction in operation instability and an increase in the degree of freedom in setting operation conditions. When a high-hardness alloy is used, the change in the friction coefficient due to aging is considered to be small. From this aspect, the uncertainty of the frictional force is reduced, and the operation stability of the packing ring 10 is improved.

Since the frictional force between the packing ring 10 and the packing ring holder 9 that contributes to the start of the operation of the turbine gap adjusting device mainly acts on the holder sliding surface 17a, according to the present embodiment, in particular, according to the present embodiment, the holder slide is used. Due to the low friction layer 19 formed on the moving surface 17a, the uncertainty of the frictional force can be reduced, and the turbine gap adjusting device can be reliably operated.

Therefore, according to this embodiment, by forming the low friction layer 19 on the contact surface between the packing ring 10 and the packing ring holder 9, the friction coefficient itself is reduced, and the uncertainty of the frictional force is reduced. Can be reduced,
Thereby, the efficiency of the turbine can be improved, the stability of the turbine gap adjusting device can be improved, and the degree of freedom in setting the operation of the turbine gap adjusting device can be improved.

In the above-described embodiment, the low friction layer 19 is provided on the inner peripheral surface 16a of the outer diameter ring portion 16 of the packing ring 10 and on the downstream side of the neck portion 17 in the working fluid leakage direction (holder sliding surface). ) 17a and fin block 18
However, the present invention is not limited to this.

For example, as shown in FIG. 9, a low friction layer may be formed only on the holder sliding surface 17a of the packing ring 10, and as shown in FIG.
May be formed on both the holder sliding surface 17a and the holder sliding surface 9a of the packing ring holder 9. In short, one or both of the surfaces that contact the packing ring holder 9 and the packing ring 10 on the downstream side in the working fluid leakage direction, or one or both of the surfaces parallel to the working fluid leakage direction, or a combination of these surfaces Can be formed arbitrarily.

[0046]

As described above, according to the present invention, by forming a low friction layer on the contact surface between the packing ring and the packing ring holder, the friction coefficient itself is reduced, and the uncertainty of the frictional force is reduced. Can be reduced, thereby improving the efficiency of the turbine.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a main part showing an embodiment of the present invention.

FIG. 2 is a sectional view showing the configuration of the entire apparatus according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram of a turbine gap adjusting device applied to one embodiment of the present invention.

FIG. 4 is an operation explanatory view according to the embodiment of the present invention, and is a view showing a balance of the force of the packing ring when the gap adjusting device is assembled.

FIG. 5 is an operation explanatory view according to the embodiment of the present invention, and is a balance diagram of the force of the packing ring when the operation of the gap adjusting device is completed.

FIG. 6 is an operation explanatory view according to the embodiment of the present invention, and is a view showing a balance of the force of the packing ring viewed from the working fluid leakage direction.

FIG. 7 is an operation explanatory diagram according to the embodiment of the present invention, and is a diagram of a working fluid pressure distribution acting in the radial direction of the packing ring.

FIG. 8 is an operation explanatory diagram according to one embodiment of the present invention, showing a relationship between a working fluid pressure difference between a high pressure side and a low pressure side and an average pressure difference between upper and lower surfaces of a packing ring.

FIG. 9 is an explanatory view of a main part showing another embodiment of the present invention.

FIG. 10 is an explanatory view of a main part showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Nozzle inner ring 1a Casing 2 Turbine axle 3 Nozzle packing ring holder 4 Nozzle packing ring 4a fin 5 Turbine rotor blade 6 Chip fin ring holder 7 Chip fin ring 7a Fin 8 Nozzle outer ring 9 Packing ring holder 10 Packing ring 11 Rotating part 12 Space part 13 inner peripheral wall 14 gap 15 opening 16 outer diameter ring 17 neck 17a holder sliding surface 18 fin block 18a fin 19 low friction layer 20 elastic body 21 high-pressure side working fluid introduction path

Claims (5)

[Claims] 1. A turbine sealing structure for sealing a gap between a stationary portion and a rotating portion of a turbine by turbine packing, wherein the turbine packing is a packing ring holder fixed to the stationary portion, and the packing ring holder. And a packing ring having a sealing fin segment, wherein a low friction layer is formed on a surface where the packing ring holder and the packing ring are in contact with each other. 2. The low-friction layer is provided on one or both of the surfaces of the packing ring holder and the packing ring that are in contact with each other on the downstream side in the working fluid leakage direction, or between the packing ring holder and the packing ring. 2. The turbine seal structure according to claim 1, wherein, of the surfaces that are in contact with each other, the seal structure is formed on one or both of surfaces parallel to the working fluid leakage direction, or on a plurality of surfaces obtained by combining them. 3. The low friction layer includes a turbine packing for sealing a gap between a turbine nozzle inner ring and a turbine axle, a turbine packing for sealing a gap between a turbine nozzle outer ring and a turbine rotor blade outer periphery, and a gap between a turbine casing and a turbine axle. The turbine seal structure according to claim 1 or 2, wherein the seal is applied to at least one portion of a turbine packing for sealing. 4. The low friction layer is used for bonding a fluororesin sheet,
The turbine seal structure according to any one of claims 1 to 3, wherein the seal structure is formed by one or more means selected from a fluororesin coating and a high-hardness alloy coating. 5. The low friction layer includes: an elastic body that urges the packing ring toward the outer periphery of the turbine; and a fluid that introduces a high-pressure working fluid into the packing ring holder and pressurizes the packing ring toward the inner periphery of the turbine. A seal structure for a turbine, wherein the seal structure is applied to a turbine packing provided with a gap adjusting device having a pressurizing unit.