JPS60228710A - Control device for steam turbine - Google Patents

Abstract

PURPOSE:To effect smooth starting, by selecting a pressure setting value to a first pressure function equal to a load corresponding pressure when a high and/or low pressure bypass valve is opened, while selecting the pressure setting value to a second pressure function obtained by adding pressure bias to the first pressure function when both the bypass valves are fully closed. CONSTITUTION:A pressure setting value for controlling a low pressure bypass valve 21 is selected to either a first pressure function equal to the minimum value of high temperature reheating pressure under load less than a predetermined value and equal to a load corresponding pressure under load not less than the predetermined value or a second pressure function obtained by adding a fixed pressure bias or a load proportional pressure bias to the first pressure function. Then, the pressure setting value as selected is outputted from a pressure setting section. Thus, the low pressure bypass valve 21 is controlled according to the first pressure function when at least one of high and low pressure bypass valves 19 and 21 is opened, while being controlled according to the second pressure function when both the bypass valves 19 and 21 are fully closed. Accordingly, an intercept valve 13 may be securely fully opened at starting to thereby prevent increase in temperature in an exhaust chamber of a high pressure turbine 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for a steam turbine, and particularly to improvements in a bypass device.

[Technical background of the invention]

In a typical reheat steam turbine plant, as shown in the figure, high-temperature, high-pressure steam generated in the boiler superheater passes through the main steam pipe 2, passes through the main steam stop valve 3 and the steam control valve, and then passes through the high-pressure turbine. Sent to Party B. The steam that has done work in this high-pressure turbine t is led to the reheater 10 through the check valve and the low-temperature reheat pipe, and after being reheated here, the high-temperature reheat pipe //, the reheat steam stop valve /J and Intercept valve/
3 and enters the intermediate pressure turbine/4'. In addition, the steam that has finished its work in this intermediate pressure turbine is transferred to a crossover pipe/! i
through the low pressure turbine/6. /7, and after doing work there, it is sent to the condenser /g and becomes condensate.

In addition, a bypass system is provided to prevent extreme overheating of the turbine body or dry firing of the reheater 10 during start-up or extremely low load.

In other words, a part of the steam passing through the main steam pipe λ is transferred to the high pressure steam heater 1.
The steam that passes through 0 is reheated at high temperature and passes through a low-pressure bypass pipe! , a low-pressure bypass valve and a desuperheater, and are recovered in a condenser/g.

Generally, the pressure in the main steam pipe λ is called the main steam pressure in front of the high-pressure bypass valve, and the pressure in the high-temperature reheat pipe is called the high-temperature reheat pressure or the pressure in front of the low-pressure bypass valve. The pressure in front of the high-pressure bypass valve is controlled by flowing surplus steam downstream, and the low-pressure bypass valve 21 also controls the pressure in front of the low-pressure bypass valve by flowing surplus steam downstream.

In this case, the main steam pressure and high temperature reheat pressure with respect to the load conditions are in the relationship shown by the dashed lines in FIG. 7(&) and (b), and the high pressure bypass valve 19 is as shown in the solid line in FIG. The main steam pressure is maintained at a constant pressure called the minimum control pressure until the load increases to a certain extent, and then as the load increases, the pressure shown by the dashed line increases slightly.
That is, the main steam pressure is controlled so that a constant pressure bias is applied, and in the same way, the low pressure bypass valve is also kept at a high temperature until the load increases to a certain extent, as shown by the solid line in Figure 7(b). The reheat pressure is maintained at the minimum control pressure A, and as the load increases, the high temperature reheat is applied so that a pressure slightly higher than the pressure indicated by the dashed line, that is, a constant pressure bias is applied to the pressure equivalent to the load. Control heat pressure.

On the other hand, before starting the turbine, the entire amount of steam passing through the high-pressure bypass valve /q is flowed to the condenser through the low-pressure bypass valve 2/, so the high temperature reheat pressure at the time of startup is equal to the minimum control pressure A of the low-pressure bypass valve 2/. It has become.

When the turbine is started, the low-temperature reheat pipe and the reheater 10 already have a predetermined pressure, so the low-temperature reheat pipe and the high-pressure turbine 6 are separated by the check valve r.
The check valve is not opened until the internal pressure of the high-pressure turbine becomes equal to the pressure of the low-temperature reheat pipe.
Deadline operation will occur. Therefore, not only the temperature inside the turbine increases, but also the temperature in the exhaust chamber at the previous stage of each check valve.

In order to keep the temperature rise due to such shut-off operation to a low level,
The intercept valve 13 simultaneously supplies steam to the high-pressure turbine t and the intermediate-pressure turbine slag to start them up, and controls the amount of steam in the high-pressure turbine t controlled by the steam control valve 13.
The cooling effect of the steam is enhanced by increasing the amount of steam from the intermediate pressure turbine/Q- controlled by the

Figure 2 shows the relationship between the load at startup of the turbine and the ratio of the amount of steam flowing into the high-pressure turbine t to the amount of steam flowing into the intermediate-pressure turbine/l. When the check valve g is opened, the cooling effect increases, so the amount of steam on the high pressure turbine 2 side can be reduced. Therefore, by opening the check valve t, the amount of steam on the high pressure turbine 6 side is gradually reduced. The relationship is reduced to 1 vs. / as in the rated load state.

Figure 2 shows the relationship between the flow rate and load of the steam control valve G and intercept valve/3 in order to have such a flow rate ratio. The flow rate of 3 is approximately I times the flow rate of the steam control valve.When the load condition is C, the flow rate ratio described above is adjusted by gradually opening the intercept valve/3 so that the flow rates of both are the same. Also, if the load state is C
After that, intercept valve/3 had to be operated fully open.
It is fully opened at the bending point B of the pressure curve shown in FIG. 7(b).

In this way, intercept valve/3 is fully opened at corner point B, but even if it is not fully opened at corner point B, the high temperature reheat pressure increases with the load at loads of 8 or more, and the necessary flow rate can be secured. Therefore, in reality, the full opening operation of intercept valve/3 is delayed.

This delay in the full opening operation increases the throttling loss in the steam passage section, leading to a corresponding decrease in efficiency on the turbine side.

By the way, in this type of turbine plant,
o As shown in the figure, the high-pressure turbine 20 main body wall and low-temperature reheat pipe or high-temperature reheat pipe l/higher pressure feed water heater,
Although the configuration is such that steam is extracted to Na and 2Jb, the high-pressure feed water heaters and 2ja and nb do not perform their original operations because they are in warm-up operation when the turbine is started. Therefore, this extracted portion flows into the high-temperature reheat pipe // through the reheater /θ, and the high-temperature reheat pressure is increased by this increased flow rate. As a result, as shown in FIG. 1, the opening degree of intercept valve /3, which is 11 in the normal state, is kept at 12 (<11).

This means that even if an attempt is made to maintain the same relationship between the opening degree of the intercept valve /3 and the opening degree of the steam control valve 1, this relationship is broken and the intercept valve 13 side opens more. 1st
The diagram below shows this relationship, and the intercept valve 13
The opening degree of this intercept valve/J is from 1 to 12, and the opening degree for steam control is also from C1 to C.
2, and the load is actually the same moving from Ll to L2.

Although not shown in the figure, when the high temperature reheating pressure decreases, the flow rate decreases even if the opening degree of the intercept valve remains the same, and in this case, the steam control valve ≠ the same flow rate. Therefore, in order to take the same load, the steam control valve must ≠, the opening degree of the intercept valve 13 increases slightly.

On the other hand, the opening degree of the steam control valve is not fully opened to the maximum load, but the intercept valve 13 is located downstream of the steam control valve, and the high pressure bypass valve 9 and the low pressure bypass valve 2 are fully closed. under load, i.e., at corner point B shown in FIG. 7(b).
Fully open operation is performed with a load of . These relationships are shown in FIG. 73.

[Problems with background technology]

Thus, in the conventional turbine control device, the high pressure bypass valve 19 and the low pressure bypass valve 21 are both of the same capacity under the prepressure condition at rated load;
Additionally, since the low-temperature reheat pipe or the bleed line of the high-temperature reheat pipe l/ upstream as seen from the low-pressure bypass valve 21 does not operate normally at startup, the amount of steam flowing through the high-temperature reheat pipe l/ is lower than that during normal operation. The high temperature reheating pressure increases because there are more people than busy.

As a result, the intercept valve /3 is set to a low opening degree because the steam flow rate increases and the flow rate ratio with the steam control valve deviates even if the opening degree does not change.

That is, during normal operation, the intercept valve 21 can be fully opened at the bending point B in Fig. 7(b), but at startup, the high temperature and reheat pressure are high, so even at a low opening degree, a lot of steam flows and it is difficult to fully open the intercept valve 21. However, there was a drawback that the reduction in the amount of steam in the high-pressure turbine B caused the temperature in the exhaust chamber to rise.

[Purpose of the invention]

The present invention has been made to eliminate the above-mentioned drawbacks.
An object of the present invention is to provide a control device for a steam turbine that can reliably fully open an intercept valve at startup, thereby preventing a rise in temperature in the exhaust chamber of a high-pressure turbine.

[Summary of the invention]

To achieve this objective, the present invention provides a turbine bypass system in which the high temperature reheat pressure during turbine bypass operation is determined by a low pressure bypass valve and an intercept valve. a first pressure function equal to the minimum pressure and equal to the load equivalent pressure above a predetermined load; and a first pressure function to which a constant pressure bias or a pressure via that varies proportionally to the load is added. a pressure setting section capable of switching and outputting pressure setting signals according to the first pressure function, and outputting a pressure setting signal according to the first pressure function when at least one of the high pressure bypass valve and the low pressure bypass valve is open; a set pressure switching section for switching the pressure setting section to the side where a pressure setting signal according to the second pressure function is output when both the high pressure bypass valve and the low pressure bypass valve are fully closed; The low pressure bypass valve is controlled by a pressure setting signal output from a pressure setting section.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings, together with the configuration and characteristics of a pressure control system of a low-pressure bypass valve.

First, the high temperature reheat pressure is controlled by a low pressure bypass valve, and the 14th! It is equipped with the pressure control system shown in the figure.

That is, when the load signal sy is applied, as shown in Fig. 15 (a), while the load is smaller than point b, it is equal to the minimum pressure of the high temperature reheating pressure, and while the load exceeds point b, it is indicated by a dashed line. A function generator J outputs a high temperature reheat pressure setting signal sg with a constant pressure bias added to the load equivalent pressure, and this high temperature reheat pressure setting signal sg and high temperature reheat pressure detection signal S27 are compared. An adder that calculates the deviation between the two,
Figure 1j (b) according to the deviation obtained by this adder J.
The signal converter U, also called a pressure gain, outputs an opening command signal sxq for the low pressure bypass valve 2/ shown in FIG.

Note that the load-equivalent pressure referred to herein refers to the pressure generated by the flow rate of the busy high-temperature reheating pipe during turbine load operation, and changes in proportion to the load as shown by the dashed line.

If the pressure is set as shown by the solid line in Figure IS<&), the intercept valve 21 can be fully opened during normal operation, but at startup, the high temperature reheat pressure is high, so the intercept valve 2/ is throttled and not fully opened. cormorant.

Here, the output characteristics of the function generator 3 are shown in FIG. 16 (a
), by using a device that outputs a high temperature reheat pressure setting signal that is equal to the minimum force of the high temperature reheat pressure until the load reaches the bl point and corresponds to the load equivalent pressure at the b1 point or higher, the 76th If the opening command signal shown in Fig. (bJ) is output, the load to fully open the intercept valve /3 will be higher by the load difference (bl-b), and as a result, the lift characteristics of the intercept valve can be made looser. It can be said that the swing of the valve lift can be reduced in response to load fluctuations during full-open operation, and stable control can be performed.

However, in this case, the high pressure feed water heater 2 at startup
There is no problem during warm-up operation using 3a and 3bK, but when the load drops during normal operation, the load equivalent pressure line also breaks at point Bi and passes through the lowest pressure line to point A. reach

In such a situation, even if the pressure increases due to small pressure fluctuations,
High temperature reheat pressure detection signal 827 is high temperature reheat pressure setting signal S
This causes the output of the adder to turn positive and open the low pressure bypass valve 2/, causing steam to be dumped into the condenser and reducing the efficiency of the plant.

Therefore, in the present invention, as shown in FIG. 1, the pressure bias setter 30 outputs a constant pressure bias signal of 5K, the relay 37 is excited by the interlock circuit 3.2, and the output of the function generator Δa. relay,? An adder 33 is newly added to add the pressure bias signal of the pressure bias setting device 3° obtained through the contact point .

In this case, as shown in FIG. 76(a)K, the function generator ga is equal to the minimum pressure of the high temperature reheating pressure when it is smaller than the predetermined load b1, and is equal to the load equivalent pressure when it is larger than the predetermined load bl. A type with no pressure bias is used. In addition, as shown in FIG. 2, the interlock circuit 32 includes three normally open contacts a of a relay (not shown) that operates when the high-pressure bypass valve 19 is fully closed, and a low-pressure bypass valve:
1. It is a series circuit of the normally open contact 32b of V- (not shown) which operates when l is fully closed.
It is configured to excite.

The operation of this embodiment configured as described above will be explained below with reference to FIG. 3 and FIG.

First, during turbine bypass operation, the high pressure bypass valve/9
and low pressure bypass valve U is opened. By the way, V-,
? / does not operate and the low pressure bypass is activated based on the deviation between the pressure setting signal S3 of the function generator Ba and the high temperature reheat pressure detection signal 827.
The opening degree of the system valve is controlled.

As shown in Fig. 3, the opening degrees (or flow rates) of the high-pressure bypass valve 19 and the low-pressure bypass valve ν were as high as the spray water. As the load increases, the high-pressure bypass valve/9 is fully closed at load L3, and the low-pressure bypass valve 21 is fully closed at load Lm.

This means that since there is no surplus steam left, the high pressure bypass valve 19 is fully closed to prevent steam from flowing to the low temperature reheat pipe, and the low pressure bypass valve U is fully closed to prevent steam from escaping to the condenser IT. That's exactly what I did.

Thus, when the load becomes L4, the interlock circuit 32
V-J/ is excited by the action of , and the pressure bias signal from the pressure bias setter 30 is added to the adder together with the pressure setting signal S3 from the function generator 3a. As a result,
This means that the pressure function shown in FIG. 3 (1) has been switched to the pressure function shown in the fsJ diagram (b) to which a constant pressure bias has been added.

That is, when the load is less than Lx, the high temperature reheat pressure is set according to the pressure function shown in FIG. The high temperature reheat pressure is set according to the pressure function shown in Fig. μ (b) until the load starts to open.

Note that the pressure line A'-B'X in Figure μ(b) is higher than the lowest pressure A by the pressure bias amount d,
When either the high pressure bypass valve/I or the low pressure bypass valve U opens, the pressure bias setting device 30 is excluded by the action of the interlock circuit 32, and the pressure immediately returns to the lowest pressure A. Therefore, the minimum pressure A is always set during turbine bypass operation.

On the other hand, when the check valve t starts to open again after it is fully closed due to load cutoff, etc., the pressure in the low-temperature reheat pipe is controlled to the minimum pressure A by the low-pressure bypass valve, so the exhaust chamber of the high-pressure turbine B The pressure increases only to the minimum pressure A, and it is possible to prevent the exhaust chamber temperature from overheating due to high exhaust chamber pressure.

In the above embodiment, the pressure bias setter 30 provides a constant pressure bias, but for example, as shown in FIG.
By using a pressure bias setting device that is proportional to the load between 100 and 100% load and has an appropriate size at 100% load, the pressure function shown in Figure 3 (b) is obtained, and the high pressure bypass valve /9 and the low pressure bypass Depending on whether both valves ν are fully closed or not, the pressure function shown in Fig. μ (,) and Fig. 5 (
By switching between the pressure functions shown in b), appropriate pressure control can be achieved at low loads without applying excessive pressure bias.

Furthermore, in the above embodiment, the pressure function is equal to the lowest pressure of the high temperature reheating pressure until it rises to a predetermined load, and does not apply a pressure bias to the load equivalent pressure above the predetermined load;
A predetermined pressure bias is applied to this pressure function to create another pressure function, and these side pressure functions are switched.
There is a pressure setting section that can switch between λ function generators that each output a similar pressure setting signal, and a function switching section that can switch the function of the pressure setting section depending on whether both the high pressure bypass valve and the low pressure bypass valve are fully closed. If a set pressure switching section is provided to perform the setting pressure switching section, the same operation as described above can be performed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, there is provided a seventh pressure function that is equal to the lowest pressure of the high temperature reheat pressure below a predetermined load and equal to the load equivalent pressure above a predetermined load; a pressure setting unit capable of switching and outputting pressure setting signals according to a second pressure function in which a constant pressure bias or a pressure bias that varies in proportion to load is added to the seventh pressure function; When at least one of the bypass valve and the low pressure bypass valve is open, the seventh
The pressure setting section is placed on the side where the pressure setting signal according to the pressure function of 1 is output, and the pressure setting section is placed on the side where the pressure setting signal according to the pressure function of 1 is output when both the high pressure bypass valve and the low pressure bypass valve are fully closed. Since it is equipped with a set pressure switching section, the intercept valve can be reliably fully opened even if the high temperature reheat pressure increases at startup, and
Excessive rise in temperature in the exhaust chamber of the turbine can be prevented.

[Brief explanation of the drawing]

FIG. 7 is a block diagram showing the configuration of an embodiment of the present invention, FIG. 2 is a circuit diagram showing the detailed configuration of the main elements of the embodiment, and FIGS. 3 and μ show the operation of the embodiment. FIG. 3 is a characteristic diagram for explaining the operation of another embodiment, FIG. 6 and FIG. IO are system diagrams of a reheat steam turbine plant to which the present invention is applied, Fig. 7 to Fig. 1 and Fig. 11 to Fig. 1 (Fig. 1 is a characteristic diagram for explaining the operation of this reheat steam turbine plant;
FIG. 1 is a block diagram showing the configuration of the main parts of a conventional control device, and FIG. IS and FIG. 1A are characteristic diagrams for explaining the operation of this control device. 6...High pressure turbine, lt...Intermediate pressure turbine, /A
, /7...Low pressure turbine, 13...Intercept valve, 19...High pressure bypass valve, 2)...Low pressure bypass valve, Ja...Function generator, 30...Pressure bias setting device, 32...Interlock circuit, 3/...
relay. Applicant's agent Kiyoshi Inomata Engraving of the drawings (no changes to the contents) Figure 1 Akira 2 Figure Child 3 Figure Child 6 Figure 1 Figure 7 (α) (b) Child Figure 8 Bird 9 Figure Oni Figure 10 Figure 12 Bird Figure 13% Figure 14 Procedural Amendment Document May 5, 1980 Director General of the Patent Office Mr. Kazuo Wakasugi 1 Indication of Case 1989 Patent Application No. 85341 2 Name of Invention Steam Turbine Control Device 3 Case of Person Making Amendment Relationship with Patent applicant (307) Toshiba Corporation 4 Agent

Claims (1)

[Claims] In a steam turbine that has a turbine bypass system and in which the high temperature reheat pressure during turbine bypass operation is determined by a low pressure bypass valve and an intercept valve, it is equal to the lowest pressure of the high temperature reheat pressure when the load is less than a predetermined load, and the load is equal to the minimum pressure of the high temperature reheat pressure when the load is above a predetermined load. A pressure setting signal according to a first pressure function equal to the equivalent pressure, and a λth pressure function obtained by adding a constant pressure bias or a pressure via that changes in proportion to the load to the first pressure function, respectively. a pressure setting section that can be switched and output; a side K to which a pressure setting signal according to the first pressure function is output when at least one of the high pressure bypass valve and the low pressure bypass valve is listening; a high pressure bypass valve and a low pressure bypass valve; and a setting pressure switching section for switching the pressure setting section on the side from which a pressure setting signal according to the second pressure function is output when both are fully closed, and the pressure setting output from the pressure setting section. A control device for a steam turbine, characterized in that the low pressure bypass valve is controlled by a signal.