JPH03290002A - Nozzle box - Google Patents

Abstract

PURPOSE:To prevent occurrence of unstable vibration of a rotor as a result of closing the space between the high pressure portion and the reheating portion and limiting the axial length as short as possible by providing a faucet and a key in the space between the nozzle box and the outer casing, which forms the dividing portion of the high pressure portion and the middle pressure portion. CONSTITUTION:In a high/low pressure casing of a free expansion type reheating turbine having a nozzle box 16 relatively movable against an outer casing 17 due to thermal expansion difference and the like, a faucet portion 18, which fixes the upper half nozzle box 16 to the outer casing 17, extends to the position of an outer casing welded portion 15. The faucet 18, made with uneven surface, has a gap so as to absorb the thermal difference of the nozzle box 16 and a key 14 is provided on the end of the faucet 18. Also, a key 22 is fixed to the bottom half nozzle box (not shown on the sketch) so as to engage with the upper half nozzle box 16. The steam passages in front and in the rear of the nozzle box are closed by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a reheat turbine high and intermediate pressure casing with a free expansion type casing.

[Conventional technology]

Conventionally, regarding the free expansion method - heavy casing structure, "Steam Turbine - Theory and Structure - J, No. 52
0,521,524,526 describes its structure.

[Problem to be solved by the invention]

In the case of non-reheat type turbines such as industrial turbines, a free expansion type single casing structure is often used. This structure will be explained with reference to FIG. High pressure first stage section 1
The steam 2 that has flowed into the first stage sequentially flows to the second stage and subsequent stages, but the steam 3 that has detoured from the high-pressure first stage section 1 flows into the packing section 5 of FIG. 6 through the gap 4 of FIG. 7.

The feature of this structure is that the nozzle pock 16 is connected to the outer casing 1.
This is why it is called a free expansion structure because it can move relative to 7 due to differences in thermal expansion. However, with regard to relative displacement in the axial direction, only a very small gap is allowed between the nozzle box 16 and the rotor, so it is necessary to restrain the nozzle box 16 and the rotor to such an extent. On the other hand, as shown in the AA cross section of FIG. 4, a method is used in which the nozzle box and the outer casing 17 are restrained by a pilot. In this way, by restricting the axial direction to some extent but allowing thermal expansion freely in the upward, downward, leftward, and rightward directions, it is possible to be aware of the thermal stress that becomes particularly noticeable during starting and stopping.

When this structure is applied to a reheat turbine having a structure in which a high-pressure inlet section and a reheat inlet section are adjacent to each other, the following problems arise.

To explain this with reference to FIG. 3, the steam 7 that has flowed into the high-pressure first stage section 6 passes through the high-pressure stages in sequence, passes through the high-pressure exhaust pipe 8, is reheated by the reheat boiler, becomes medium-pressure reheat steam, and is then reheated. The hot steam enters the intermediate pressure stage 10 through the inlet pipe 9 . On the other hand, leak steam 11 from the high-pressure first stage passes through the gap 12 in FIG. 4 and flows into the intermediate-pressure stage 10 in FIG. 3. Further, a gap is provided in the horizontal surface 18 of the nozzle box 16 to allow thermal expansion.
Steam can also come in and out from this part.

In this way, in the case of this structure, the chamber 6 after the high-pressure first stage and the upper chamber O of the reheat steam inlet remain penetrating.

Therefore, a partition plate 21 shown in FIG. 8 is provided to completely block off the post-high-pressure first stage and the reheat steam inlet.

The partition plate 21 has a very large pressure difference (for example, 100 kg
/a1 or more), a considerable thickness is required, and as shown in FIG. 8, a large space is required in the axial direction. This increase in space directly leads to an increase in the length of the rotor, resulting in a decrease in the critical speed of the rotor and causing unstable vibration of the rotor.

Furthermore, the number of parts and the weight of the casing and rotor increase, resulting in an increase in manufacturing costs.

[Means to solve the problem]

An object of the present invention is to reduce manufacturing costs by reducing the axial length as much as possible to prevent unstable vibrations of the rotor, and at the same time making the turbine compact.

For this purpose, we provide a nozzle box that takes advantage of the original features of the free expansion structure and also functions as a partition plate.

In order to achieve the above purpose, the steam passage 12 in FIG.
A structure that eliminates the 18th part will suffice. By expanding the part of the inlet that connects the nozzle box and the external casing at the boundary of the high-medium pressure section upward and downward, and by installing a key at the connection between the end of the part of the inlet and the casing, the gap can be improved. 12 can be occluded. Furthermore, the gap 20 in the horizontal plane of the nozzle box can also be closed by installing the key with some play in the upward and downward directions.

In this way, the purpose can be achieved using simple methods such as spigots and keys while maintaining the ability to slide freely against thermal expansion.

[Effect]

A part of the inlet for fixing the high-pressure first-stage nozzle box to the external casing is expanded upward and downward, and a key is installed at the joint between the end of the inlet part and the casing.
By installing a key on the horizontal surface of the nozzle pock, the high-pressure first-stage rear chamber and the reheat steam inlet chamber are shut off. Since the nozzle box has an extremely rigid structure against the pressure difference between the front and rear, the key and part of the spigot used in the steam cutoff part are weak in terms of strength, and there is also the advantage that a small structure is sufficient. Also,
A reheat steam chamber is required on the reheat side of the nozzle box, so
Since there is a space long enough to install the labyrinth packing on the shaft side of the nozzle box, the labyrinth packing can be installed directly on the nozzle box, and the structure can be extremely compact.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows only the upper half of the casing, but the lower half also has a similar structure. The spigot part 18 that fixes the nozzle box 16 to the outer casing 17 is extended to the location of the outer casing weld 15. The pilot part 18 has an uneven structure as shown in FIG. 2(a), and gaps are provided to absorb thermal expansion of the nozzle box 16. The pilot part 18 has a structure in which a key 14 is installed at its end. Figure 2(b) is B- in Figure 1.
B cross section is shown. It is necessary to install the key 22 also in this part. In this embodiment, the key 22 is fixed to a lower half nozzle box (not shown) and placed so as to engage with the upper half nozzle box 16. The void 23 is a gap for allowing a difference in expansion.

As a result of the above, the steam passages before and after the nozzle box are closed.

Although the above-mentioned structure uses a spigot and a key in combination, it is of course possible to omit the keys 14 and 22 and adopt a spigot structure.

According to the present invention, the labyrinth packing for shaft sealing with the reheating steam chamber after the high-pressure first stage can be installed on the inner diameter side of the nozzle box, and the axial dimension can be significantly reduced.

〔Effect of the invention〕

According to the present invention, a free expansion type heavy casing with a structure that prevents leakage steam from the high pressure section from entering the intermediate pressure section can be supplied, so a free expansion type single casing can be adopted even in a reheat turbine. , it is possible to significantly reduce the axial dimension, avoid unstable vibrations of the rotor, and design a low-cost and compact turbine.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a turbine according to an embodiment of the present invention, Fig. 2 is a detailed view of the "A" part in Fig. 1, Fig. 3 is a sectional view of a reheat turbine, and Fig. 4 is a sectional view of the reheat turbine. BB line sectional view, Figure 5 is the 4th
A-A arrow view in the figure, FIG. 6 is a cross-sectional view of the non-reheat turbine,
FIG. 7 is a sectional view taken along the line CC in FIG. 6, and FIG. 8 is a sectional view of a turbine provided with a partition plate. l...High pressure first stage part, 2...Working steam, 3...Detour steam of high pressure first stage part, 4...Gap between inner and outer casings,
5... Packing part, 6... High pressure first stage part, 7... Working steam, 8... High pressure exhaust pipe, 9... Reheating steam inlet pipe, 10 Medium pressure stage. 4 Fig. 1 Fig. 3 (Adding 21) Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Claims] 1. In the high and intermediate pressure casing of a reheat turbine with a free expansion type single casing structure, there is a space between the nozzle box and the outer casing, which is the boundary between the high pressure section and the intermediate pressure section. A nozzle box characterized in that a spigot and a key are installed to join the nozzle box and the external casing in a relatively slidable manner, thereby closing off the space between the high pressure part and the reheating part. 2. The nozzle box according to claim 1, wherein the joint portion is closed only by a spigot. 3. The nozzle box according to claim 1, wherein a labyrinth packing for a shaft seal is installed on the inner circumference of the nozzle box.