JP2003254009A - Horizontal type steam turbine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a horizontal type steam turbine wherein a temperature difference between the upper and lower halves of an external casing is reduced with little thermal cycle loss. <P>SOLUTION: This horizontal type steam turbine 1 is equipped with nozzles 2, 2 for jetting a part of reheat steam into a middle area 81 at high speed. The nozzles 2, 2 are fitted at a lower position than the rotational center line of a turbine rotor 5 of a wall section surrounding a reheat steam flowing-in part 62 in an internal casing 6 to jet a part of reheat steam into the middle area 81 as a high-speed jet flow 21 and form a circulating flow 22 in the steam within the middle area 81. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a horizontal shaft type steam turbine having a casing configured to have an inner and outer double structure,
The present invention relates to a structure capable of reducing the temperature difference between the upper half and the lower half of the outer casing with a small amount of heat cycle loss.

[0002]

2. Description of the Related Art A steam turbine rotates a turbine rotor by passing a high-speed steam flow obtained by expanding high-temperature and high-pressure steam through a stationary blade to the rotor blade, or moving the steam with the stationary blade. It is a device that generates power according to the principle of rotating the turbine rotor with the reaction force when ejecting high-speed steam flow obtained by successively passing through the blades and reducing the pressure at each, and generating it from the moving blades. It is used as a driving source for In a steam turbine having a large output capacity, a turbine rotor having a rotor blade mounted thereon and a casing formed by forming an inner casing and an outer casing into an inner and outer double layers are used as the casing covering the steam flow. Generally, it is a horizontal axis type in which the central axis line is arranged to be substantially horizontal.

A conventional horizontal axis type steam turbine will be described below with reference to FIG. FIG. 3 is a side sectional view showing the outline of a horizontal axis type steam turbine of a conventional example.
What is indicated by -X is the central axis of rotation of the turbine rotor, and this is the same also in FIG. 1 below. In FIG. 3, reference numeral 9 indicates a conventional example including a casing 8 having an outer casing 7 and an inner casing 6, a turbine rotor 5, a stationary blade 69, a moving blade 59, and a stationary blade holder 4 for holding a part of the stationary blade 69. It is a horizontal axis type steam turbine. The steam turbine 9 is a steam turbine for high and medium pressure stages, and belongs to a reheat turbine according to the classification according to the state of steam at the inlet and outlet. Further, the steam turbine 9 is a steam turbine of an extraction-free cycle, and is used together with a gas turbine in a combined cycle power plant, for example.

In the steam turbine 9, the stationary blades 69 form an annular blade row and are held in multiple stages on the inner surface side of the inner casing 6 and the stationary blade holder 4 as shown in the drawing, and the moving blades 59 of the stationary blades 69 of each stage. The turbine blades 5 are implanted in the turbine rotor 5 so as to form a blade row in combination with the turbine blade row. The high-temperature, high-pressure main steam 99 is supplied to the steam turbine 9 from a main steam valve portion 71 provided in the upper portion of the outer casing 7, flows into the annular main steam inflow portion 61 of the inner casing 6, and is mainly shown in FIG. Flow to the left towards. The main steam 99, which has consumed energy by driving the turbine rotor 5 at this portion and whose temperature and pressure have been lowered, is discharged from the high pressure casing exhaust portion 72 of the outer casing 7 to the outside of the steam turbine 9 as high pressure casing exhaust steam 98. And is heated by a steam reheating device (boiler reheater) not shown.

The high-pressure casing exhaust steam 98 heated by the steam reheating device is reheated steam (not shown) from the reheated steam inlet 73 (shown by a dotted line in FIG. 3) of the outer casing 7 to the steam turbine 9. It is supplied again and flows into the annular reheat steam inflow portion 62 of the inner casing 6. The reheated steam flows from the reheated steam inflow portion 62 to the right side toward the paper surface of FIG. 3, flows through the parts of the inner casing 6 and the vane holder 4, and drives a low-pressure stage steam turbine (not shown). The exhaust gas 97 of the medium-pressure compartment is used for the exhaust from the exhaust section 74 of the medium-pressure compartment of the outer casing 7 to the outside of the steam turbine 9. The reheated steam passes through the gap 82 when flowing into the vane holder 4 from the inner casing 6. Gap 82
Since the reheated steam passing through the part of (1) drives the turbine rotor 5 in the part of the inner casing 6 and consumes energy, the temperature and pressure thereof are lower than the values in the reheated steam inflow part 62. .

The casing 8 is composed of an inner casing 6 and an outer casing 7, both of which are tubular in shape, and has an inner and outer double structure. An annular intermediate space 81 surrounded by the casing 8 and the stationary blade holder 4 has an airtight structure except for the gap 82. Further, the inner casing 6, the outer casing 7, and the stationary blade holder 4 are each divided into upper and lower parts in order to assemble the steam turbine 9. Then, the intermediate air space 81 is filled with the steam whose temperature and pressure have been lowered as described above, which flows from the gap portion 82. Therefore, the internal pressure value in the intermediate air space 81 is intermediate between the pressure value inside the inner casing 6 (for example, the pressure value of the main steam 99) and the atmospheric pressure value outside the outer casing 7.

As a result, the main steam 9 is contained in the casing 8.
When the withstanding pressure corresponding to the pressure value of 9 is provided, the inner casing 6 and the outer casing 7 are thinned by utilizing the inner pressure value having the above value of the intermediate air space 81, and the structure of the casing 8 is rationalized. . In FIG. 3, reference numeral 89 denotes a drain port for the intermediate air space 81, which is installed at the lowest position of the outer casing 7 in contact with the intermediate air space 81. By the way, in the steam turbine, since the moving blades have to rotate in the circumferential direction, there is always a gap between the moving blades and the casings that surround the outer circumference of the moving blades and form the flow paths of the main steam and the reheated steam. In addition, the stationary blade always has a gap with the rotating turbine rotor. In order to cope with a decrease in efficiency due to leakage of main steam or the like generated in these gaps, a steam turbine is generally provided with a steam seal portion at this portion.

Also in the case of the steam turbine 9, a portion of the stationary blade 69 facing the outer surface of the turbine rotor 5 and the moving blade 59.
Each of the portions facing the inner casing 6 and the inner surface of the stationary blade holder 4 is provided with a labyrinth seal portion using a seal fin (not shown) for sealing the main steam 99 and the like. In order to obtain a seal portion having a required sealing performance, the gap length between these seal fins and the facing portion is set to an extremely narrow value of 1 mm or less.

[0009]

Since the horizontal shaft type steam turbine 9 according to the prior art is constructed as described above, it is possible to rationalize the casing by using the double casing 8. In recent years, the following problems have come to the fore as problems, and their solutions are desired. That is, since the steam turbine 9 is a steam turbine of a non-bleed cycle, the steam in the intermediate air space 81 is in a substantially stationary stagnant state during steady operation of the steam turbine 9. Due to the common properties of fluids in a stationary state,
According to the difference in specific gravity, the vapor in the intermediate air space 81 in the stagnant state is distributed such that the vapor having a higher specific gravity is on the lower layer side, and the temperature is higher in the upper part and lower in the lower part.

As a result, the upper half portion of the outer casing 7 becomes hotter than the lower half portion of the outer casing 7, and due to the difference in thermal expansion due to this temperature difference, the outer casing 7 is thermally deformed and the outer casing 7 The lower half part of the lower part of the turbine rotor 5 is deformed in a direction in which a part immediately below the turbine rotor 5 is lifted upward. This deformation pushes the inner casing 6 upwards,
In the worst case, there is a concern that the seal fins provided on the stationary blade 69 and the moving blade 59 may be rubbed.

In the steam turbine 9, in order to keep the temperature difference between the upper half portion and the lower half portion of the outer casing 7 below a predetermined value, when this temperature difference increases, the intermediate air space 81
It has been attempted to extract the relatively low-temperature steam in the lower layer portion of the intermediate air space 81 from the drain port 89 and let the alternative steam flow into the intermediate air space 81 from the gap 82. This makes it possible to prevent the occurrence of rubbing at the seal fins. However, it is not easy to equalize the steam temperature in the intermediate air space 81 with this method, and the amount of steam extracted from the drain port 89 is 0. 5 to 1.0%
It has been pointed out as a new problem that the heat cycle loss becomes large because the amount becomes large.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object thereof is to reduce the temperature difference between the upper half portion and the lower half portion of the outer casing with a small amount of heat cycle loss. An object is to provide a shaft type steam turbine.

[0013]

SUMMARY OF THE INVENTION In the present invention, the above-mentioned objects are as follows: 1) A casing having an inner casing and an outer casing which are dual in inner and outer sides, and a turbine rotor covered with the casing and driven by steam. In a horizontal-axis steam turbine including: an inner casing having an ejection portion for ejecting a part of the steam at a high speed into an intermediate air space partitioned by the inner casing and the outer casing, and ejecting the steam into the intermediate air space. As the steam, steam having a pressure value higher than the pressure in the intermediate air space is used, or 2) in the means described in the above item 1, the ejection portion is provided at a position lower than the rotation center axis of the turbine rotor. It is achieved by being.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. In the following description, FIG.
The same parts as those of the conventional horizontal axis type steam turbine shown in FIG. Further, in the drawings used for the following description, the reference numerals given in FIG. 1 is a side sectional view showing an outline of a horizontal shaft type steam turbine according to an example of an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA in FIG. In FIGS. 1 and 2, reference numeral 1 denotes a nozzle 2 as an ejection portion for ejecting a part of the reheated steam into the intermediate air space 81 at a high speed with respect to the horizontal axis steam turbine 9 according to the conventional example shown in FIG. 2 is a horizontal axis type steam turbine.

In this case, the nozzles 2 and 2 are mounted on the wall portion of the inner casing 6 surrounding the reheated steam inflow portion 62 at a position lower than the central axis of rotation of the turbine rotor 5. As described in the “Prior Art” section, in the steam turbine 1 in operation, the reheat steam inflow section 62 is
The pressure value of the reheated steam flowing through is always higher than the pressure value of the steam in the intermediate air space 81. By utilizing this pressure difference, the nozzle 2 ejects a part of the reheated steam into the steam-filled intermediate space 81 as a high-speed jet stream 21 having an initial velocity of about 600 m / s. The jet flow 21 ejected from the nozzle 2 flows through the inside of the intermediate air space 81 so as to be parallel to the inner wall surface of the outer casing 7 in contact with the intermediate air space 81, as schematically shown by the thick broken line in FIG. While gradually reducing the speed, the reheated steam joins the main stream in the gap 82.

When the jet flow 21 flows through the intermediate air space 81, the velocity energy of the jet flow 21 is transferred to the steam in the peripheral portion of the jet flow 21, so that the steam in the intermediate air space 81 becomes the jet flow 21. Movement along the direction occurs. Then, this movement causes a circulating flow 22 to be generated in the steam in the intermediate air space 81, as schematically shown by connecting short lines with arrows in FIG. The circulating flow 22 circulates largely in the intermediate air space 81 from the lower half to the upper half as shown in the figure, but at that time, since it transfers thermal energy, the temperature of the steam in the intermediate air space 81 is uniform over a wide range. Turn into. That is, the nozzle 2 forms a circulation flow 22 that largely circulates in the intermediate air space 81 by the high-speed jet flow 21 obtained by bypassing a part of the reheated steam, and the circulation flow 22 acts to cause the circulation flow 22 in the intermediate air space 81. Reduce the temperature difference between the top and bottom of the steam.

As a result, in the steam turbine 1, the amount of thermal deformation of the outer casing 7 is reduced, and the stationary blades 69 and the moving blades 5 are formed.
The rubbing of the seal fin provided in 9 is eliminated. Then, in the steam turbine 1, the circulation flow 22 obtained by the jet flow 21 is used in place of the operation of extracting the steam from the drain port 89, which is performed in the steam turbine 9 of the conventional example, and thus the case of the conventional example is used. It is possible to suppress the temperature difference between the upper half portion and the lower half portion of the outer casing 7 to a predetermined value with a small amount of steam of about half or less, and to significantly reduce the heat cycle loss amount. Further, since the amount of thermal deformation of the outer casing 7 is reduced, it is also possible to narrow the gap length between the portion facing the seal fin, and the amount of main steam leaking from this portion can be reduced, so that the steam turbine 1 The efficiency can be improved. Furthermore, since the temperature difference between the upper half portion and the lower half portion of the outer casing 7 can be reduced, the operational reliability of the steam turbine 1 is improved.

It should be noted that a part of the reheated steam is ejected at high speed 21
Another advantage of the method used for the steam turbine 1 ejecting into the intermediate air space 81 is that the circulation flow 22 can be generated in the steam in the intermediate air space 81 without installing a pump device or the like. As a result, in the steam turbine 1, without increasing its outer shape or installation area,
The objective has been achieved without any appreciable increase in manufacturing costs. Further, the mounting position of the nozzle 2 on the wall portion surrounding the reheated steam inflow portion 62 is not limited to a position lower than the rotation center axis line of the turbine rotor 5, but the rotation center of the turbine rotor 5 is not limited. By installing the nozzle 2 at a position lower than the axis, the thermal energy of the reheated steam can be directly applied to the steam in the lower layer in the intermediate air space 81, which has a relatively low temperature. That is, it is necessary to install the nozzle 2 at a position lower than the rotation center axis of the turbine rotor 5 by using the reheated steam for making the temperature difference between the upper half portion and the lower half portion of the outer casing 7 less than a predetermined value. It is effective in minimizing the amount.

[0019]

In the horizontal shaft type steam turbine according to the present invention, by adopting the structure described in the section of the means for solving the above problems, the high-speed jet flow 21 jetted from the nozzle 2 as the jet portion is used. Circulating flow of steam 22 in the intermediate air space 81
Therefore, the amount of reheated steam used to suppress the temperature difference between the upper half and the lower half of the outer casing 7 to a predetermined value should be reduced to about half or less of that in the conventional example. It is possible to obtain the effect that the heat cycle loss amount can be reduced correspondingly.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an outline of a horizontal shaft type steam turbine according to an example of an embodiment of the present invention.

FIG. 2 is a sectional view taken along line AA in FIG.

FIG. 3 is a side sectional view showing an outline of a conventional horizontal axis steam turbine.

[Explanation of symbols]

1 Horizontal axis steam turbine 2 Spouting part (nozzle) 21 jet flow 22 Circulating flow 5 turbine rotor 6 Inner casing 62 Reheated steam inlet 81 Middle airspace

Claims (2)

[Claims] 1. A horizontal-axis steam turbine comprising: a casing having an inner casing and an outer casing, which are double-sided inside and outside; and a turbine rotor covered with the casing and driven by steam. The inner casing has a spouting part for spurting a part of the steam at high speed in the intermediate air space partitioned by the outer casing, and the steam spouting into the intermediate air space has a pressure value higher than the pressure in the intermediate air space. A horizontal axis type steam turbine characterized by using steam. 2. The horizontal axis steam turbine according to claim 1, wherein the jet portion is provided at a position lower than a rotation center axis of the turbine rotor.