JPH0754089B2 - Steam valve for steam turbine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a steam valve used to control steam for driving a steam turbine.

[Prior Art] When warming up this type of valve (preheating so as to match the steam temperature), in the prior art, the opening / closing time of the warm-up valve is adjusted.

This warm-up valve is operated in the turbine start-up mode (cold,
There is a fixed interval regardless of whether it is a worm or hot. For this reason, when the metal temperature of the steam control valve is relatively low, the temperature difference between the steam guide wall and the outer wall tends to become the limit value or more at the start of warm-up, and when the limit value is reached, the warm-up is interrupted. Therefore, the time required to complete the warm-up was long.

Regarding an example of the method for warming up the steam control valve according to the related art,
This will be described with reference to FIG. Warm-up valve 5 of steam control valve 3
Is set to a constant opening degree and the seat drain valve 6 installed in the steam control valve 3 is fully opened → fully closed and fully closed → fully opened at a certain fixed cycle. As described above, in the conventional warm-up method, it takes time to raise the metal temperature of the steam control valve 3 to the target temperature in order to switch the warm-up valve at a certain cycle regardless of the turbine start mode.

In order to quickly raise the metal temperature of the steam control valve 3 in the cooled state, the steam control valve warming valve 5 may be fully opened and warmed up. In this method, the inner wall and the outer wall of the steam control valve 3 are heated. Since the difference in metal temperature between and is abruptly generated, excessive thermal stress occurs.

FIG. 3 (a) is a chart showing changes in the steam control valve inner wall temperature Ti and changes in the steam control valve outer wall temperature T _S when the warming control valve is fully opened at the start of warming. . The maximum value ΔT _max of the temperature difference ΔT between the two temperatures is large.

In order to reduce the above-mentioned temperature difference, it is possible to open and close the warm-up control valve as shown in FIG. 3 (b). According to such a method, many opening / closing operations of the warm-up valve 5 are required, and a stagnation time between opening / closing operations is required. Therefore, it takes a long time to raise the metal temperature to a target value. .

[Problems to be solved by the invention]

In the warm-up method according to the above-mentioned conventional technique, the steam control valve is opened / closed at a constant interval, so the steam control is performed after the turbine has been stopped for a long time (that is, when the metal temperature of the control valve 3 is low). When high temperature steam for valve warm-up flows,
Excessive thermal stress was generated in the steam chamber of the regulator valve 3.

In order to prevent the occurrence of excessive thermal stress, the inner wall temperature 7 and the outer wall temperature 8 of the steam control valve shown in FIG. 4 are detected, and if the temperature difference exceeds the limit value, an alarm is issued. The warm-up operation is stopped, and the warm-up valve 5 is closed until the temperature difference becomes small (less than or equal to the limit value), so the warm-up operation is stopped. Therefore, there is a disadvantage that the plant startup time becomes long.

In addition, because the main steam condition (boiler outlet temperature) rises during such a long warm-up time, mismatching during turbine ventilation (mismatch between turbine metal temperature and steam temperature)
And the thermal stress generated in the turbine rotor after ventilation increases, which is a secondary disadvantage.

The conventional steam control valve is decreased to the shape as shown in FIG. 4, the difference between the just inner wall temperature 7 and the outer wall temperature 8 for flowing the warming-up steam to the inside of the control valve the steam chamber 9 occurs. Furthermore, since the control valve steam chamber 9 has a long cylinder length and has an uneven wall thickness, stress concentration is likely to occur and it is disadvantageous in view of the thermal stress generated during warm-up. Absent.

The present invention has been made in view of the above circumstances, and an object thereof is to prevent generation of excessive thermal stress,
It is intended to provide a steam valve capable of promptly warming up.

[Means for solving problems]

In order to achieve the above object, a steam valve of the present invention is a steam valve for controlling driving steam supplied to a steam turbine, wherein a steam chamber is formed in a substantially spherical shape, and at least double inside and outside, and A space is provided between them, and means for circulating the steam for warming up is provided in the space.

[Action]

According to the above configuration, by making the steam chamber substantially spherical, the thickness of the steam chamber can be made thin, and the warm-up time of the steam valve can be shortened. It is possible to shorten the warm-up time by circulating the steam for the machine and heating the steam chamber from both the inside and the outside to rapidly raise the temperature without causing a large temperature difference. In addition, since the thickness of the steam chamber can be made uniform, the location where heat stress concentrates can be reduced, the strength of the steam chamber can be improved, and there is no fear of generating excessive heat stress, and the warming can be performed quickly. The machine can be completed.

〔Example〕

FIG. 1 is an explanatory diagram in which a steam system is added to a cross-sectional view of a steam valve according to the present invention. Main steam a supplied from the boiler
Is guided to the turbine by opening and closing the regulator valve 12 above the valve seat 11 of the internal steam chamber 10. A cover 14 for guiding the valve rod 13 is provided above the internal steam chamber 10. An outer steam chamber 16 is provided on the outer periphery of the inner steam chamber 10 with spaces 15a and 15b separated from each other. Further, a hole 18 is provided for guiding the leaked steam, which has passed through the fitting gear tap 17 of the valve rod 13 and the cover 14, to the spaces 15a and 15b. External steam room 16
A hole 21 into which warmed-up steam from the main steam a via the warm-up valve 19 enters is provided above.

In addition to the above, the hot wall temperature 7 and the outer wall temperature 8 of the internal steam chamber are detected, and the output signals thereof are guided to the temperature setting device 23 and are communicated to the discriminator 24 for comparing and discriminating the temperatures of these two. Discriminator
The warm-up valve 19 is opened and closed by the signal of 24. Steam opening regulator 25
A signal is also sent to the drain valve opening regulator 27 that opens and closes the drain valve 26 installed at the lower part of the external steam chamber 16
Open and close 26.

In this apparatus, the starting method when the steam chamber of the steam control valve is at room temperature will be described. In the warm-up operation in this case, the steam temperature flowing into the steam control valve chamber has a low steam condition (because of initial startup), and naturally the temperature is also low. Further, in order to warm up the outer wall of the inner steam chamber 10, the main steam a is guided to the hole 21 of the outer steam chamber 16 via the warm-up valve 19, and the outer periphery of the inner steam chamber 10 and the inner surface of the outer steam chamber 16 are separated from each other. The gaps 15a and 15b are made to flow as shown by the arrows to fill the gaps. In this case, the drain valve 26 is fully closed. Therefore, the spaces 15a and 15b become a sealed room, and the steam temperature gradually decreases. Therefore, there is a temperature difference Δ between the inner wall temperature 7 and the outer wall temperature 8 of the inner steam chamber 10.
T occurs. If the temperature difference ΔT is within the permissible range, it is left as it is, and if it is outside the permissible range, the drain valve 26 is opened by the signal from the discriminator 24 via the drain valve opening adjuster 27, so that the space 15a, Discharge warm-up steam in 15b. That is, the warm steam of the main steam a can be introduced to raise the outer wall temperature 8 of the inner steam chamber 10, and the temperature difference ΔT can be kept within the allowable temperature. In the conventional technique, the temperature of the inner wall is raised by the steam in the steam chamber 10 and the temperature of the outer wall is raised by the metal heat transfer, so that the temperature difference between the inner and outer walls occurs and the outer wall temperature 8 becomes within the allowable temperature difference. It takes a long time to raise the temperature, and there is a fear that excessive thermal stress may be generated.

However, in this embodiment, the inner wall and the outer wall of the steam chamber are simultaneously heated by warm-up steam, and the outer wall temperature 8 is always compared and discriminated by the discriminator 24 based on the inner wall temperature 7 and the drain valve 26 is fully closed within the allowable temperature difference. If the temperature difference is out of the allowable temperature difference, the drain valve 26 can be opened to automatically control to raise the temperature to the target metal temperature within the allowable temperature difference in a short time.

When carrying out the present invention, it is possible to warm up by using the auxiliary steam source 20 instead of the main steam a.

After the warm-up operation has proceeded as described above, the signal of the discriminator 24 that finally raises the temperature of the steam chamber to the target metal temperature is sent to the warm-up valve opening adjuster 25, and the warm-up valve is adjusted. Fully close 19. After that, the steam for warming up, which is sent to the outer space 15a, 15b of the internal steam chamber 10, is covered by the leaked steam from the gear cup 17 between the valve rod 14 and the cover 14. With this configuration,
Since warm-up steam always flows into the outer wall of the inner steam chamber 10 even during operation, there is no difference in temperature between the inner and outer walls.

FIG. 5 shows the steam control valve inner wall temperature T _i in the embodiment of the present invention.
And the outer wall temperature T _S are charts showing changes between the metal temperature T _O and the target temperature T. Maximum value of the difference between both temperatures Δ
T _max is significantly smaller than that of the conventional example (FIG. 3).

In addition, in the starting operation (hot start) in the state where the metal temperature of the steam chamber is close to the target temperature T, the warm-up valve 19
It is sufficient to warm up the valve stem leakage steam without opening the valve.

When the steam chamber is formed in a spherical shape as in this embodiment, the required thickness of the steam chamber is half that in the case of the body length. The fact that the wall thickness is thin means that the warm-up time at the time of starting the turbine is short, and good results can be obtained in terms of thermal stress. Moreover, in the case of a spherical shape, it is possible to make the wall thickness relatively uniform, which is convenient from the viewpoint of strength regarding stress concentration.

The theoretical basis of the advantages of the spherical steam chamber described above will be described in detail below.

The thickness of the steam chamber is generally represented by the following formula.

(I) In case of body length Where t ₁ = required wall thickness in case of cylinder length t ₂ = required wall thickness in case of spherical shape P = internal pressure acting on steam chamber r = radius of inner surfaces of cylinder and ball It can be seen that, in case of a spherical shape, it is half as much as in case of a body length. When the wall thickness is thin, the time required for warming up the metal in the steam chamber is half that required when the body length is long. At the same time, the wall thickness of the steam chamber can be formed to be substantially uniform throughout, the location where thermal stress is concentrated can be reduced, and the strength of the steam chamber can be improved.

〔The invention's effect〕

As described above, according to the present invention, the warm-up time of the steam control valve and the thermal stress can be shortened, and the turbine start-up required time can be shortened.

The significance of the effect of reducing the above warm-up time in practical use will be added.

Recent thermal power plants often use DSS, WSS, etc., and the start-up time is extremely shortened. The reduction of the warm-up time of the steam control valve can greatly contribute to the reduction of the time from the ignition of the baler to the ventilation of the turbine.

Further, the application of the present invention has a great effect on the main valve of the ultra high temperature and high pressure turbine which has been studied recently. The steam conditions of the ultra-high temperature and high pressure turbine are 169 atg / 566 ℃ and 246 atg / 5 until now.
The temperature rises from 38 ° C to 315atg-350atg / 593 ° C-649 ° C, and the turbine efficiency in this case is improved by 6-8%. In order to withstand this steam condition, the quality of the valve chamber of the main valve must use austenitic stainless steel. The austenitic stainless steel material has much lower yield strength and higher thermal expansion coefficient than the material properties of the low alloy steel currently used for the steam chamber of the main valve. The thermal stress in the steam chamber is generally expressed by the following equation.

σ _t = α × E × ΔT <σ _ys where σ _t : thermal stress α: thermal expansion coefficient ΔT: temperature difference σ _ys : yield strength of austenitic stainless steel To reduce the thermal stress as can be seen from the above equation Must reduce ΔT. As described above, in the austenitic material, σ _ys has a very low value, and α is large, it is necessary to further suppress ΔT. The effect of reducing the temperature difference (ΔT) according to the present invention sufficiently meets the above-mentioned requirements, and in this sense, the present invention greatly contributes to the development and spread of the ultra-high temperature and high pressure tabine.

[Brief description of drawings]

FIG. 1 is an explanatory diagram in which a steam system and a control system are added to a cross-sectional view of one embodiment of the present invention. Fig. 2 is a warm-up system diagram of the conventional steam control valve, Fig. 3 is a chart showing the relationship between the warm-up valve opening operation and the steam control valve inner / outer wall temperature difference in the conventional warm-up method, and Fig. 4 is FIG. 5 is a cross-sectional view of a conventional steam control valve, and FIG. 5 is a table showing the opening / closing control of the warm-up valve and the drain valve and the steam control valve inner / outer wall temperature difference in one embodiment of the present invention. 1 ... Boiler, 2 ... Main steam stop valve, 3 ... Warm-up valve, 4
...... Turbine, 5 ... Warm-up valve, 6 ... Drain valve, 7 ...
Steam control valve inner wall temperature, 8 ... Steam control valve outer wall temperature, 10 ...
… Steam control valve Internal steam chamber, 11 …… Valve seat, 12 …… Control valve,
13 …… Valve rod, 14 …… Cover, 15a, 15b …… Gap, 16 ……
Steam control valve External steam chamber, 17 ... Gear cup, 18 ... Hole, 19
...... Warm-up valve, 20 …… Auxiliary steam source, 21 …… Hole, 23 …… Temperature setter, 24 …… Discriminator, 25 …… Warm-up valve opening regulator, 26 ……
… Drain valve, 27 …… Drain valve opening regulator, a …… Main steam.

Claims (2)

[Claims] 1. A steam valve for controlling driving steam supplied to a steam turbine, wherein a steam chamber is substantially spherical, and at least double inside and outside are formed, and a space is provided between the steam chamber and the space. A steam valve for a steam turbine, which is provided with means for circulating steam for warm-up. 2. The means for circulating the warm-up steam is provided with valve means that is controlled to open and close based on a temperature difference between the inner and outer walls of the steam chamber. A steam valve for a steam turbine according to item 1.