JPS63176602A - Steam turbine - Google Patents

Abstract

PURPOSE:To aim at abatement in erosion of a moving blade, by installing a drain extract port in a steam pass space at the inside of a nozzle outer ring, and also installing an annular fine at the downstream side of the drain extract port. CONSTITUTION:A drain extract port 8 is installed in a stem pass space at the inside of a nozzle outer ring. A drain groove 6 connecting this drain extract port 8 is connected to a drain discharge port 7. An annular fin 11, being projected to a steam pass space, is installed at the downstream side of the drain extract port 8. With this constitution, a liquid film on a nozzle outer ring inner surface and a nozzle blade surface is effectively eliminated, thus erosion in a moving blade is abatable.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention removes droplets generated in wet steam flowing in a steam turbine, and reduces the amount of erosion of rotor blades caused by the droplets. The present invention also relates to a steam turbine capable of reducing moisture loss.

(Prior Art) Since the price of crude oil has skyrocketed in recent years, the dependence on nuclear turbines has gradually increased. In addition, thermal power turbines are required to improve their efficiency in order to compete with nuclear power turbines.

In general, the vicinity of the low-pressure final stage of thermal power turbines and most of the stages of nuclear power turbines operate in humid steam containing many droplets, and these droplets can cause problems such as erosion of rotor blades and increased moisture loss. It is occurring.

Due to the increase in the number of nuclear power turbines with high humidity and the increase in the length of the final stage rotor blades due to the increase in the capacity of thermal power and nuclear power turbines, effective countermeasures to the above problems are increasingly required.

As a droplet removing device in a stage of a steam turbine, a droplet removing device such as that described in Japanese Utility Model Publication No. 55-18485 is known.

FIG. 5 shows a vertical cross-sectional view of a conventional droplet removal device.
An outer ring contact plate 2 is welded to the inner surface of the nozzle outer ring 1.1' (numerals with a dash indicate the same parts in the next paragraph, but their indication will be omitted in the following explanation). Nozzle blades 3 are welded to the outer ring contact plate 2. The nozzle blades 3 are also welded to an inner ring abutment plate 4, and the inner ring abutment plate 4 is welded to the nozzle inner ring 5 so as to form a nozzle.

Nozzle grooves 6 are provided in the inner surface of the nozzle outer ring 1 in the circumferential direction, and these nozzle grooves 6 and the steam passage portion communicate through drain extraction holes 8 provided in the outer ring backing plate 2.

Further, a drain discharge hole 7 communicating with a drain groove 6 is provided to pass through the nozzle outer ring 1 on the lower half side, and is connected to a condenser.

In the nozzle, rotor blades 9 are arranged so as to be embedded in a rotor disk 10, and together with the nozzle, a turbine stage is formed.

(Problems to be Solved by the Invention) By the way, the conventional droplet removal device shown in FIG. 5 cannot sufficiently remove droplets, and is not very effective in reducing rotor blade erosion and moisture loss. It wasn't.

I will now explain the reason in a little more detail.

Figure 6 shows the expansion line of a steam turbine in a general commercial thermal power plant, where point A shows the steam state at the nozzle inlet of the stage before the final stage (hereinafter referred to as L-1),
Similarly, point B indicates the steam state at the L-1 nozzle outlet, and point C
indicates the steam state at the L-1 rotor blade inlet, the dot indicates the steam state at the nozzle outlet of the final stage (hereinafter referred to as L-0), and E indicates the steam state at the L-0 nozzle outlet.
This shows the steam condition at the rotor blade outlet.

As can be seen from FIG. 6, the steam changes from dry steam to wet steam in the nozzle L-1, and the humidity reaches nearly 10% at the exit of the rotor blade L-0.

However, even if the vapor reaches the theoretical wet region due to expansion, it does not immediately start condensing, and only after expanding in a non-equilibrium state until the wetness reaches about 3 to 5%, droplets are generated. That is, droplets are generally generated within the rotor blade L-1.

In this case, the diameter of the generated droplets is about 0.1 to 1 μm, and the droplets grow little by little as the vapor expands. At this time, some of the droplets collide with and adhere to the surfaces of the nozzle and rotor blades, but because the particle size is small, there is almost no erosion of the blades at this stage. However, the droplets within the rotor blades are subjected to centrifugal force, Coriolis, and steam force, and the movement toward the outer circumference becomes dominant, resulting in a considerable number of droplets adhering to the inner surface of the outer ring of the L-0 nozzle. Become.

That is, as shown in FIG. 7, in L-0 paragraph J,
The shaded area F indicates a liquid film, the broken line G indicates a vapor streamline, and the solid line H indicates a droplet streamline. As you can see from this figure, the droplet is L-
It occurs within the rotor blade of the first stage ■, and as shown by the droplet streamline H, it adheres to the inner and outer surfaces of the sizzle outer ring and the nozzle blade surface of the L-0 stage, forming a liquid film F, which does not develop. to the trailing edge of the nozzle at L-0. The liquid film F that has reached the trailing edge of the L-0 nozzle is blown away from the trailing edge by the steam force and mixed into the steam, and is sprayed in the form of rough water droplets, but the diameter of the droplets formed at this time is The droplets reach 100 to 500 μm, which is much larger than naturally occurring droplets.

Therefore, the giant droplet collides with the rotor blade of L-0 without being sufficiently accelerated by the steam force, causing erosion of the rotor blade.

Figure 8 shows the humidity inside the nozzle of L-0, and it is clear from this that the humidity is rapidly increasing at the outer periphery of the nozzle, and that the droplets are unevenly distributed around the outer periphery. .

As described above, most of the wet vapor droplets in the nozzle are unevenly distributed around the outer periphery of the nozzle, but the same can be said of the liquid film. That is, a liquid film is formed in which droplets with a diameter of about 0.5 to 1 μm adhere to the nozzle blade surface or the inner surface of the nozzle outer ring, collect and develop as they flow downstream along the surface by the steam force. Therefore, the liquid film is formed only on the outer circumference of the nozzle blade surface and the inner surface of the nozzle outer ring. Also,
The liquid film rapidly develops and becomes thicker as it approaches the trailing edge of the nozzle.

This situation will be explained using FIG. 9. This figure is an enlarged view of the outer periphery of the conventional nozzle, and the liquid film F is formed on the inner surface of the outer ring contact plate 2 and the surface of the nozzle blade 3. On the other hand, since the inside of the drain groove 6 communicates with the rotor blade outlet through the drain discharge hole 7, the pressure in the drain groove 6 is lower than the pressure in the nozzle steam passage. As a result, a part of the liquid film F is exposed to the outer ring contact plate 2.
It passes through the drain extraction hole 8 provided in the drain hole 8 and is sucked into the drain groove 6 as shown by the flow K of the liquid film.

However, since the liquid film F is subjected to considerable steam force within the nozzle flow path, it is swept downstream before being sufficiently sucked through the drain extraction hole 8.

In order to increase the suction amount of the liquid film, it is possible to make the drain extraction holes 8 larger or increase the number, but this would also suck in a large amount of main steam and the turbine performance would be extremely poor.
With conventional methods, it is not possible to actively remove the liquid film inside the nozzle.
Drain removal was not very effective.

[Structure of the Invention] (Means for Solving the Problems) The steam turbine of the present invention includes a nozzle outer ring, a nozzle blade,
In a steam turbine equipped with a turbine nozzle consisting of an inner nozzle ring, a plurality of drain extraction holes are opened in the steam passage inside the nozzle outer ring, a drain groove connecting these drain extraction holes is provided in the nozzle outer ring, and the drain This device is characterized in that an annular fin is provided on the downstream side of the extraction hole in the steam flow direction, protruding into the steam passage.

(Function) In the steam turbine of the present invention configured as described above, the liquid film flowing on the inner surface of the nozzle outer ring is blocked by the fins, so that it is not easily flowed downstream by the steam force received within the nozzle flow path. . As a result, most of the liquid film flowing from the drain extraction hole to the inner surface of the nozzle outer ring is removed into the drain groove 6, which greatly reduces rotor blade erosion, reduces moisture loss, and improves turbine efficiency and reliability. do.

(Embodiments) Hereinafter, embodiments of the present invention and their effects will be described with reference to FIGS. 1 to 4.

FIG. 1 is a longitudinal cross-sectional view of a nozzle in a steam turbine of the present invention, and the same parts as in FIG. 5 are given the same reference numerals, and their explanation will be omitted.

The difference between this embodiment and the conventional example is that a plurality of fins 11 are provided on the outer periphery of the nozzle steam passage. That is, a plurality of fins 11 are provided in an annular shape on the inner surface side of the outer ring abutment plate so as to protrude into the steam passage section. Furthermore, these fins 11 are provided slightly downstream of the drain extraction hole 8 provided in the nozzle contact plate 2 in the steam flow direction.

The nozzle of a steam turbine may be integrally formed by casting, or may be formed by welding as shown in FIG.

In the former case of casting, the fins 11 can be easily formed by providing grooves for the fins 11 in the mold. In addition, in the case of the latter welding assembly type, as shown in FIG. 2(A), a groove 12 into which the fin 11 is fitted is provided in an annular shape on the downstream side of the drain extraction hole 8 in the outer ring contact plate 2, and the fin After fitting the base portion of the groove 11, the end portion of the groove 12 is crushed as shown in FIG. .

In the conventional example, the liquid film inside the nozzle could not be effectively removed, but in the embodiment of the present invention, by providing the fins 11, the liquid film inside the nozzle can be effectively removed.

This point will be explained in more detail using FIG. 3.

The droplets adhering to the surface of the nozzle blade 3 and the inner surface of the outer ring contact plate 2 are swept downstream by the steam flowing in the nozzle flow path, forming a liquid film F, which develops and is deposited on the trailing edge of the nozzle. reach

However, due to the presence of the fins 11, the liquid film F flowing on the inner surface of the outer ring contact plate 2 and the surface of the nozzle 3 is temporarily stopped. A drain extraction hole 8 is provided in an annular shape upstream of the fin 11 in the steam flow direction, and the liquid film F is sucked into the drain groove 6 much more effectively than in the conventional example.

Since a plurality of drain extraction holes 8 and fins 11 are provided, the liquid film formed on the downstream side of the most upstream fin is also effectively removed one after another, and eventually a considerable liquid film is removed.

The graph shown in Figure 4 clarifies the above point and shows the results of a comparison of condensate removal between the conventional example and the embodiment of the present invention in the final stage nozzle of a thermal power turbine for general business use. . The horizontal axis shows the relative suction amount, and the vertical axis shows the relative drain capture amount and relative stage performance. The solid line in the graph is for the conventional example, and the broken line is for the example of the present invention.

Looking at the relative amount of condensate captured in the same figure, it is about 3 to 4 times larger in the example of the present invention than in the conventional example, and the amount of liquid film and steam sucked from the drain extraction hole is not large. too,
It can be seen that a considerable amount of drain is captured.

Since the amount of condensate captured is large with a small suction amount, when the amount of main steam suction is the same as in the conventional example, the amount of condensate captured is several times larger, and the humidity level is significantly reduced. Furthermore, if the amount of condensate captured is the same, the amount of main steam sucked in will be considerably smaller, and the reduction in stage performance will be significantly improved. Therefore, the erosion of the rotor blades by droplets is significantly improved, as well as the reduction in turbine efficiency.

[Effects of the Invention] As is clear from the above description, the present invention provides an annular fin on the downstream side of the drain extraction hole on the inner surface of the nozzle outer ring, thereby reducing the liquid film on the inner surface of the nozzle outer ring and the nozzle blade surface. The removal is carried out effectively, and as a result, the amount of erosion of the rotor blades by droplets is significantly reduced, as well as the moisture loss, which improves the turbine efficiency and reliability. can.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view of a nozzle part showing an embodiment of a steam turbine according to the present invention, FIGS. 2(A) and (B) are explanatory views illustrating the fin forming method in FIG. 1, and FIG. FIG. 4 is a flow state diagram of the liquid film in the turbine nozzle according to the present invention; FIG.
The figure is a vertical cross-sectional view showing a conventional turbine stage, Figure 6 is a graph showing an example of the expansion line of a general commercial thermal power turbine, and Figure 7 is a graph of droplets near the final stage groove of a general commercial thermal turbine. An explanatory diagram showing the flow situation, Fig. 8 is a graph showing the relationship between the humidity in the final stage nozzle of a general commercial thermal power turbine and the nozzle height, and Fig. 9 shows the liquid in the turbine nozzle in a conventional example. It is a flow state diagram of a membrane. 1... Nozzle outer ring 2... Outer ring contact plate 3... Nozzle blade 4... Inner ring contact plate 5... Nozzle inner ring 6... ... Drain groove 7 ... Drain discharge hole 8 ... Drain extraction hole 9 ... Moving blade 10 ... Rotor disk 11 ...・Fin 12...Groove 13...Crushing part agent Patent attorney Nori Chika Ken Shu Hirofumi Mitsumata Figure 4 Figure 5 Figure 7 Humidity Figure 8

Claims (2)

[Claims] (1) In a steam turbine equipped with a turbine nozzle consisting of a nozzle outer ring, a nozzle blade, and a nozzle inner ring, a plurality of drain extraction holes are opened in the steam passage inside the nozzle outer ring, and these drain extraction holes are connected. A steam turbine characterized in that a drain groove is provided in a nozzle outer ring, and an annular fin is provided on the downstream side of the drain extraction hole in the steam flow direction so as to protrude into a steam passage section. (2) In a welded assembly type steam turbine, the steam turbine according to claim 1, characterized in that a circumferential groove is provided in the nozzle contact plate, and a root portion of the fin is fitted and fixed in the groove. turbine.