JPH086562B2 - Structure to prevent vertical temperature difference of steam turbine casing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vertical temperature difference prevention structure for a steam turbine casing that prevents thermal deformation of the casing caused by the vertical temperature difference of the turbine casing.

[Conventional technology]

2. Description of the Related Art A steam turbine driven by high-pressure and high-temperature steam is known to have an inner casing having a stator blade that surrounds a rotor blade portion of a turbine axle and forms a stage with the rotor blade, and an outer casing that surrounds the stator casing. . In this case, the space between the inner casing and the outer casing is provided with a fishing pressure hole in the middle of the paragraph of the inner casing so that the steam pressure of the space becomes the fishing pressure with the fishing pressure hole portion in the inner casing. .
By the way, since the space between the inner casing and the outer casing is hermetically closed, natural convection occurs due to heating of high-temperature steam during turbine operation, which causes a temperature difference between the upper and lower portions of the casing, which causes thermal deformation of the casing. The related art will be described below with reference to the drawings.

FIG. 4 is a sectional view of a steam turbine having an inner casing and an outer casing. In the figure, reference numeral 1 denotes a turbine axle provided with a moving blade 2, a balancing piston 1a is provided, 3 has a stationary blade 4 on an inner wall, and combined with the moving blade 2 forms a paragraph to enclose the turbine axle 2 and extract air. An inner casing 5 having a chamber 3a is a pot-shaped outer casing that houses the inner casing 3. The inner casing 3 is fixed to the outer casing 5 by a screw ring 6, and a gland packing lid 9 for closing the opening is attached to the outer casing 5. A closed annular space (fishing pressure chamber) 7 is formed between the inner casing 3 and the outer casing 5,
A fishing pressure hole 8 that connects the fishing pressure chamber 7 and the inside of the inner casing is provided to penetrate the inner casing 3 from a step 10 in the middle of the paragraph. The pressure holes 8 are used to adjust the pressure difference between the inside and outside of the inner casing 3 by adjusting the steam pressure between the pressure chamber 7 and the step 10 of the inner casing 3 to adjust the pressure difference between the inner and outer casings. I have to.

A labyrinth packing 11 is provided in a portion where the turbine axle 1 equipped with the balancing piston 1a penetrates the inner casing 3 in order to reduce the amount of steam leaking from the gap between the turbine axle 1 and the inner casing 3. There is. Reference numeral 12 denotes a drain hole that penetrates the outer casing 5.
A drain pipe 13 is connected to the drain pipe 13 that guides the drain formed by steam condensation when the turbine is started and stopped to the condenser. In addition,
The drain pipe 13 is provided with valves 14 and 14a.

With such a structure, the high-pressure and high-temperature steam is controlled to have a predetermined flow rate, flows into the inner casing 3 through the outer casing 5, flows from the blade inlet chamber 15 into a paragraph, and expands to give a rotational force to the turbine axle 1. The low pressure and low temperature vapor is discharged from the exhaust chamber 16 to the outside. At this time, the inner casing 3, the outer casing 5, the fishing pressure chamber 7 and the like are heated by the steam and rise in temperature. At this time, natural convection occurs in the annular fishing pressure chamber 7 between the inner casing 3 and the outer casing 5 as a circulating flow 16 around the inner casing 3 as shown in FIG. The natural convection becomes an inclined circulation flow as shown in the figure because the axial temperature distribution is high on the steam inlet side and the steam outlet side like the temperature distribution of the outer casing 5 shown in FIG. Because it is low.

FIG. 7 shows the steam temperatures of the inner casing 3, the outer casing 5 and the natural convection due to natural convection as described above.
It is a temperature distribution chart which shows the result measured at the measurement point of the upper part shown in the figure, the measurement point of the middle part, and the measurement point of the lower part.
In the figure, 20 is an inner casing, 21 is an outer casing,
22 is the temperature distribution of the steam that naturally convection. From the figure, it is understood that the temperatures of the inner casing 3 and the outer casing 5 are high in the upper part and low in the lower part. As a result, the inner casing,
The outer casing undergoes a cat-warp thermal deformation due to the temperature difference between the upper and lower sides. Due to this thermal deformation, during operation of the turbine, inconveniences occur, such as contact of the moving blades and the stationary blades with the opposing casing and turbine axle, which hinders operation.

In order to eliminate such a hindrance in operation, the valves 14 and 14a of the drain pipe 13 are opened to release a considerable amount of steam from the drain hole 12 from the fishing pressure chamber 7 to the condenser to prevent natural convection. However, there is no temperature difference between the upper and lower casings.

[Problems to be Solved by the Invention]

As described above, the method of letting a considerable amount of steam escape from the drain hole to the condenser so that natural convection does not occur in the fishing pressure chamber, the steam is discarded to the condenser, which causes a significant decrease in turbine performance. There is.

An object of the present invention is to reduce the deterioration of turbine performance, prevent the occurrence of natural convection in the fishing pressure chamber between the inner casing and the outer casing, and prevent the temperature difference between the upper and lower sides of the steam turbine casing. It is to provide a temperature difference prevention structure.

[Means for solving the problem]

In order to solve the above problems, according to the present invention, a turbine casing is provided with a labyrinth packing in a portion that penetrates, and an inner casing that includes a stationary blade that surrounds a moving blade portion of this axle to form a paragraph with this moving blade, and In a steam turbine that includes an outer casing that surrounds the casing, and that guides steam in the inner casing through a fishing pressure hole that penetrates the inner casing by opening to the paragraph in a space between the inner casing and the outer casing, A bypass hole that communicates the space between the casing and the outer casing with the labyrinth packing portion is provided through the inner casing.

[Action]

By providing a bypass hole that communicates the space between the inner casing and the outer casing with the labyrinth packing portion through the inner casing, part of the steam flowing into the inner casing during turbine operation passes through the fishing pressure hole. The steam in the space flows into the labyrinth packing through the bypass hole. Due to this flow, natural convection around the inner casing in the space is prevented, so that a temperature difference between the upper and lower inner casings is prevented. Also, since the steam flowing from the bypass hole to the labyrinth packing will seal the labyrinth packing,
Since less steam leaks to the labyrinth packing from the inlet of the paragraph composed of the stationary blades and the moving blades, the turbine performance is less deteriorated.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a cross-sectional view of a steam turbine having a structure for preventing a temperature difference between upper and lower sides of a steam turbine casing according to an embodiment of the present invention, and FIG. 2 is a detailed view of a labyrinth packing portion of FIG.
FIG. 3 is an enlarged view of portion P in FIG. 1 to 3, the same parts as those in the conventional example of FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted. 1 to 3 are different from the conventional example in that a bypass hole 23 penetrating the inner casing 3 and communicating between the divided rings 11a of the labyrinth packing 11 provided in the balancing piston 1a portion of the turbine axle 1 is provided. Is provided on the circumference of the inner casing 3.

With such a structure, a part of the steam that flows through the paragraph in the inner casing 3 and gives a rotational force to the turbine axle 1 during the turbine operation flows from the fishing pressure hole 8 to the fishing pressure chamber 7 between the inner casing 3 and the outer casing 5. Then, the steam in the fishing pressure chamber 7 flows into the labyrinth packing 11 of the balancing piston 1a through the bypass hole 23, leaks through the labyrinth packing 11 and flows as steam. For this reason, natural convection is prevented in the fishing pressure chamber 7 by this flow, so that the difference in temperature between the upper and lower casings is prevented.

Further, the steam flowing to the labyrinth packing through the fishing pressure hole 8, the fishing pressure chamber 7 and the bypass hole 23 seals the labyrinth packing 11 as described above, and therefore leaks from the blade inlet chamber 15 to the labyrinth packing 11. Less steam
The amount of steam flowing in the paragraph composed of the stationary blades 4 and the moving blades 2 is increased by this amount, so that the deterioration of turbine performance is reduced. This turbine performance reduction rate is 2.5% of the turbine performance reduction rate when the conventional drain hole 12 escapes to the condenser, and the turbine performance reduction rate according to the present invention is extremely small.

〔The invention's effect〕

As is apparent from the above description, according to the present invention, the space between the inner casing and the outer casing and the labyrinth packing part are communicated with each other by the bypass hole penetrating the inner casing, so that the inside of the inner casing during turbine operation is Part of the flowing steam flows into the space through the fishing pressure hole, and the steam that has flowed into the space flows through the bypass hole to the labyrinth packing part, so that the steam flows into the space, and therefore natural convection flows into the space. This prevents the temperature difference between the upper and lower casings from occurring in the inner casing and the outer casing. Therefore, thermal deformation does not occur in the casing, and safe operation can be performed. Further, there is an effect that the deterioration of turbine performance due to the steam flowing through the bypass hole to the labyrinth packing portion is significantly smaller than that of the conventional one.

[Brief description of drawings]

FIG. 1 is a sectional view of a steam turbine having a structure for preventing the temperature difference between the upper and lower sides of a steam turbine casing according to an embodiment of the present invention, and FIG. 2 is a detailed view of the labyrinth packing portion of FIG.
FIG. 3 is an enlarged cross-sectional view of the P part of FIG. 2, FIG. 4 is a cross-sectional view of a conventional steam turbine, FIG. 5 is a view showing a state of natural convection occurring in the steam turbine of FIG. 4, and FIG. FIG. 5 shows the temperature distribution of the outer casing in the axial direction and the temperature measurement points of the inner and outer casings and convection steam due to natural convection. FIG. 7 shows the temperature distribution of the inner and outer casings and convection steam due to natural convection. It is a figure. 1: turbine axle, 2: moving blade, 3: inner casing, 4: stationary blade,
5: outer casing, 7: fishing pressure chamber, 8: fishing pressure hole, 11: labyrinth packing, 23: bypass hole.

Claims (1)

[Claims] 1. An inner casing having a stator vane which is provided with a labyrinth packing in a portion through which a turbine axle penetrates and surrounds a moving blade portion of the axle in a paragraph with the moving blade, and an outer casing which surrounds the casing. In a steam turbine provided with a space between an inner casing and an outer casing, the steam in the inner casing passing through fishing pressure holes penetrating the inner casing and opening in the paragraph, and between the inner casing and the outer casing. A vertical temperature difference prevention structure for a steam turbine casing, characterized in that a bypass hole that connects the space and the labyrinth packing portion is provided through the inner casing.