JP2001082107A - Steam turbine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit thermal deformation of a turbine internal structure by introducing low pressure steam introduced in the midway stage of the steam turbine into a turbine cylinder, and installing an introducing pipe, one side of which is communicated with a low pressure steam outlet connected to the turbine cylinder, the other side being communicated with the interior of the turbine cylinder. SOLUTION: An internal introducing pipe 10 for introducing low pressure steam 1 is installed with one side thereof connected to an outlet of a low pressure steam introducing pipe 3 and the other side thereof communicated with the interior of a medium pressure exhaust part 11. The internal introducing pipe 10 is extended from the outlet of the low pressure introducing pipe 3 toward a rotor shaft 9 to branch off in two directions along the circumferential direction of the turbine internal cylinder 5. Accordingly, the low pressure steam 1 is introduced from the connecting part between the low pressure steam introducing pipe 3 and the turbine external cylinder 2 to flow in the medium pressure exhaust part 11 through the internal introducing pipe 10. At this time, low pressure steam 1 and the medium pressure exhaust part steam 4 heat-exchange through the internal introducing pipe 10, so that a temperature difference between both steam 1, 4 can be reduced and also thermal deformation of the internal structure can be inhibited.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a steam turbine for a combined cycle power plant.

[0002]

2. Description of the Related Art In a triple pressure combined cycle power plant, high-pressure main steam, reheat steam and low-pressure steam are introduced into a steam turbine. In this case, the low-pressure steam is introduced into the middle stage of the stage pressure steam turbine lower than the pressure, but the low-pressure steam temperature and the stage temperature do not always match. Exposure of the internal structure of the steam turbine to such steam having a temperature difference causes thermal stress and thermal deformation,
This could be a factor in crack initiation.

[0003]

Conventionally, a low-pressure steam pipe has generally been connected to a medium-pressure exhaust portion of a turbine in consideration of a space for introducing low-pressure steam. At this time, since the low-pressure steam is directly introduced into the turbine from the steam pipe, a part of the internal casing of the final stage of the intermediate-pressure turbine is exposed to both the steam passing through the intermediate-pressure turbine stage and the low-pressure steam. Since the stage temperature and the low-pressure steam temperature of the final stage of the intermediate-pressure turbine are usually different from each other, a non-uniform temperature distribution occurs in the inner casing in the circumferential direction with respect to the rotation center of the steam turbine. As a result, the elongation of the inner casing becomes uneven, and the center of the inner casing, which coincides with the rotation center of the steam turbine, is shifted. Further, a temperature difference also occurs in the thickness direction of the inner casing, which causes thermal stress. Furthermore, if cool air is introduced into the high-pressure operating section, a rapid thermal stress is involved, which may cause cracking.

[0004] The present invention has been made in view of the above problems, and an object of the present invention is to provide a steam turbine that suppresses thermal deformation of an internal structure of the steam turbine.

[0005]

In order to achieve the above object, a steam turbine according to the present invention includes a steam turbine having a structure for introducing low-pressure steam into a middle stage of the turbine.
The low-pressure steam is introduced into the turbine casing, one of which is introduced from the outside and communicates with a low-pressure steam outlet connected to the turbine casing, and the other communicates with the inside of the space of the turbine casing. A tube is provided.

Further, the steam turbine of the present invention is a steam turbine having a structure for introducing low-pressure steam into a turbine medium-pressure steam exhaust portion, wherein the low-pressure steam is introduced into a turbine casing. An introduction pipe is provided which communicates with a low-pressure steam outlet which is introduced from the outside and which is connected to the turbine casing, and which communicates with the inside of the turbine casing on the downstream side of the medium-pressure steam exhaust part.

Preferably, the introduction pipe extends from a low-pressure steam outlet connected to the turbine casing toward the rotor shaft, and is formed to have a shape branching from a middle position along the circumferential direction of the rotor shaft. Things.

Preferably, the introduction tube has a fin or an uneven portion.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the drawings.

A typical example of a system for introducing low-pressure steam into a middle stage of a steam turbine is a triple-pressure combined cycle power plant. Hereinafter, a steam turbine used in the triple pressure combined cycle power plant will be described as an example.

FIG. 1 is a cross-sectional view along the axial direction of the steam turbine, showing a structure for introducing low-pressure steam into the turbine medium-pressure exhaust portion. Low-pressure steam 1 from a boiler (not shown) flows into the turbine from below through a low-pressure steam introduction pipe 3 connected to a turbine exterior casing 2. To allow the low pressure steam 1 to flow into the turbine, its pressure P _LP
It is slightly set higher than the pressure P _IP of pressure exhaust portion steam 4 in which is discharged to the pressure exhaust portion 11 medium through the not-shown turbine stage.

At this time, the temperature T _{IP of} the intermediate-pressure exhaust steam 4 and the temperature T _LP of the low-pressure steam 1 do not usually coincide with each other, and the temperature difference ΔT between T _IP and T _LP becomes about several tens of degrees Celsius. It is also possible to introduce steam with a large temperature difference. On the upper side, the medium-pressure exhaust section 11 of the turbine interior casing 5 is exposed only to the medium-pressure exhaust section steam 4, and on the lower side, in addition to the medium-pressure exhaust section steam 4, a low-pressure steam introduction pipe 3 is further provided. Exposed to the low-pressure steam 1 supplied by the fuel cell. For this reason, a temperature difference occurs between the upper part and the lower part of the turbine inner casing 5.

FIG. 2 is a diagram showing a deformed state when a temperature difference occurs in the turbine interior casing. As previously mentioned,
The upper casing 51 is exposed only to the medium-pressure exhaust steam 4 and the lower casing 52 is exposed to the low-pressure steam 1.
In contrast to 1, the temperature of the lower casing 52 becomes lower, and due to the difference in the amount of thermal expansion, the inner casing central axis 6 is deformed so as to project upward with respect to the turbine central axis 7. Deformation due to such non-uniform elongation difference causes, in addition to thermal stress, inconsistency between the inner casing center axis 6 and the turbine center axis 7, resulting in a rotating body composed of the rotor blade 8 and the rotor shaft 9. There is a possibility that it may cause sliding with a stationary body such as a turbine interior compartment.

Therefore, in the present embodiment, the structure described below is used to reduce the thermal stress and the temperature difference of steam, which is a cause of uneven thermal deformation.

FIG. 3 is a longitudinal sectional view of the steam turbine shown in FIG. 1 as viewed from the exhaust side. In the present embodiment, in addition to the configuration shown in FIG. 1, one is connected to the outlet of the low-pressure steam introduction pipe 3, and the other is an internal introduction pipe 10 that communicates with the inside of the medium-pressure exhaust unit 11 and introduces low-pressure steam. Has been installed. The internal introduction pipe 10 first extends from the outlet of the low-pressure steam introduction pipe 3 toward the rotor shaft 9, and is branched and arranged in two directions along the circumferential direction of the rotor shaft 9 or the turbine interior casing 5. It is formed as follows.

By installing the internal introduction pipe 10 as described above, the low-pressure steam 1 introduced from the connection between the low-pressure steam introduction pipe 3 and the turbine exterior casing 2 is installed in the medium-pressure exhaust section 11. After passing through the internal introduction pipe 10, it flows into the medium pressure exhaust unit 11. When the low-pressure steam 1 passes through the inside of the internal introduction pipe 10, heat exchange is performed between the low-pressure steam 1 and the medium-pressure exhaust steam 4 through the internal introduction pipe 10. Therefore, the steam temperature _PLT of the low-pressure steam 1 flowing into the turbine and the steam 4
The temperature difference ΔT of the steam temperature T _IP, and if there is no internal inlet tube 10, the turbine inner low pressure steam 1 that is directly made it possible to reduce in comparison with the case that flows.

In the present embodiment shown in FIG.
Is branched in two directions on the way from the connection between the low-pressure steam introduction pipe 3 and the turbine exterior casing 2 to perform heat exchange with two pipes. The pipe shapes are low-pressure steam 1 and medium-pressure exhaust steam. 4
The number, diameter,
Set the length to a more suitable one.

In general, the number or diameter of the pipes is designed so that the flow velocity of the steam flowing inside the pipes is suppressed low and the pressure loss does not increase. Also, when the steam in a certain state flows at a constant flow rate, if the number or diameter of the piping is increased,
It is generally known that the steam flow rate decreases in inverse proportion, and the number or diameter of the pipes used is selected so as to obtain a flow rate within the limit value.

On the other hand, in the internal introduction pipe 10 used in this embodiment, not only the flow rate of the steam but also the low-pressure steam 1
This takes into account efficient heat exchange between the steam and the intermediate-pressure exhaust section steam 4. If you keep the steam flow rate low,
Since the heat transfer with the inner surface of the pipe becomes small, it is preferable to make the inside diameter of the pipe small as long as the pressure loss can be tolerated.
In addition, since the heat transfer area for heat exchange increases as the length of the pipe becomes longer, the heat exchange amount per unit length is calculated for pipes of a predetermined number and diameter, and the low pressure steam is calculated. It is preferable to use one that takes into account the amount of heat exchange required to reduce the temperature difference ΔT between the steam temperature T _{LP of the first} and the steam temperature T _IP of the intermediate-pressure exhaust section steam 4.

Further, fins may be provided on the inner surface or the outer surface of the internal introduction pipe 10 for more efficient heat transfer, or irregularities may be formed. As described above, by adding a means for improving heat transfer such as providing fins, it is possible to select a pipe diameter capable of further reducing pressure loss and to shorten the length of the pipe. It is very effective in improving the performance of the system and further reducing the cost of the plant.

As described above, in this embodiment, the low-pressure steam 1 and the turbine intermediate-pressure exhaust steam 4 are connected to the low-pressure steam introduction pipe 3.
The low-pressure steam 1 is introduced into the turbine intermediate-pressure exhaust unit 11 in a state where the temperature difference is reduced. For this reason, since the formation of an uneven temperature distribution in the turbine interior casing 5 is suppressed, it is possible to suppress the occurrence of thermal deformation or cracks due to differences in thermal stress or uneven elongation. became. Further, in the related art, the center axis 6 of the inner casing and the center axis 7 of the bin are displaced due to deformation due to a difference in the amount of elongation, and the rotating body including the rotor blades 8 and the rotor shaft 9 and the turbine Although there was a possibility of causing sliding with a stationary body such as a chamber, in the present embodiment, since the temperature difference of the low-pressure steam 1 is reduced as described above, such a problem can be solved. became.

In the above description, the structure of the low-pressure steam inlet portion of the steam turbine used in the triple pressure combined cycle power plant has been described. However, the present invention suppresses the occurrence of thermal stress or deformation of the internal structure of the steam turbine. The same effect can be obtained by applying the present invention to another steam turbine such as a double pressure combined cycle power plant.

[0023]

As described above, according to the present invention, it is possible to provide a steam turbine that suppresses thermal deformation of the internal structure of the steam turbine.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view along an axial direction of a steam turbine.

FIG. 2 is a deformation state diagram when a temperature difference occurs in a turbine interior casing.

FIG. 3 is a longitudinal sectional view of a steam turbine showing one embodiment of the present invention.

[Description of Signs] 1 ... Low-pressure steam, 2 ... Tube outer casing, 3 ... Low-pressure steam introducing pipe, 4 ... Medium-pressure exhaust steam, 5 ... Turbine inner casing, 6
... Center axis of inner casing, 7 ... Center axis of turbine, 8 ... Rotating blade, 9
... rotor shaft, 10 ... internal introduction pipe, 11 ... medium pressure exhaust part, 51 ... upper casing, 52 ... lower casing.

Claims (4)

[Claims] 1. A steam turbine having a structure for introducing low-pressure steam in a middle stage of a turbine, wherein the low-pressure steam is introduced into a turbine case, and one of the low-pressure steam is introduced from the outside to the turbine case. A steam turbine, further comprising an introduction pipe communicating with a low-pressure steam outlet to be connected and the other communicating with the inside of the space of the turbine casing. 2. A steam turbine having a structure for introducing low-pressure steam to a turbine medium-pressure steam exhaust portion, wherein the low-pressure steam is introduced into a turbine casing, and one of the low-pressure steam is introduced from the outside and the turbine A steam turbine, further comprising an inlet pipe communicating with a low-pressure steam outlet connected to the chamber and the other communicating with the inside of the turbine casing on the downstream side of the medium-pressure steam exhaust unit. 3. The introduction pipe extends from a low-pressure steam outlet connected to a turbine casing toward a rotor shaft.
The steam turbine according to claim 1, wherein the steam turbine is formed in a shape branched from a middle position along a circumferential direction of the rotor shaft. 4. The steam turbine according to claim 1, wherein the introduction pipe has a fin or an uneven portion.