JPH0467001B2 - - Google Patents

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 an improvement in a bypass device.

[Technical background of the invention]

In a typical reheat steam turbine plant, as shown in Fig. 6, high-temperature, high-pressure steam generated in a boiler superheater 1 passes through a main steam pipe 2, passes through a main steam stop valve 3 and a steam control valve 4, and then passes through a high-pressure turbine. sent to 6. The steam that has done work in this high-pressure turbine 6 is led to a reheater 10 through a check valve 8 and a low-temperature reheat pipe 9, where it is resuperheated, and then the high-temperature reheat pipe 1
1. Enters the intermediate pressure turbine 14 via the reheat steam stop valve 12 and the intercept valve 13. Further, the steam that has finished its work in the intermediate pressure turbine 14 is supplied to the low pressure turbines 16 and 17 via the crossover pipe 15, and after doing work there, it is sent to the condenser 18 and becomes condensed water.

Furthermore, a bypass system is provided to prevent extreme overheating of the turbine body or dry firing of the reheater 10 during startup or at extremely low load. That is, a part of the steam passing through the main steam pipe 2 is transferred to the high pressure bypass pipe 7, the high pressure bypass valve 19, and the desuperheater 2.
The steam that has passed through the reheater 10 is then passed through the high temperature reheat pipe 11, the low pressure bypass pipe 5, and the low pressure bypass valve 2.
1 and a desuperheater 22, and then collected in a condenser 18.

Generally, the pressure in the main steam pipe 2 is called the main steam pressure or the pressure before the high-pressure bypass valve, and the pressure in the high-temperature reheat pipe 11 is called the high-temperature reheat pressure or the pressure before the low-pressure bypass valve. The pressure in front of the high-pressure bypass valve is controlled by flowing steam downstream, and the low-pressure bypass valve 21 also controls the pressure in front of the low-pressure bypass valve by flowing excess 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-dotted lines in FIG. The main steam pressure is maintained at a constant pressure called the minimum control pressure, and then as the load increases, the main steam pressure is increased so that a pressure slightly higher than the pressure indicated by the dashed line, that is, a constant pressure bias is applied. Similarly, the low pressure bypass valve 21 also maintains the high temperature reheat pressure at the minimum control pressure A until the load increases to a certain extent, as shown by the solid line in FIG. The high-temperature reheat pressure is controlled so that a constant pressure bias is applied to the pressure slightly higher than the pressure indicated by the dashed line, that is, the pressure equivalent to the load.

On the other hand, before starting the turbine, the high pressure bypass valve 19
Since the entire amount of steam passing through is flowed to the condenser through the low pressure bypass valve 21, the high temperature reheat pressure at startup is the lowest control pressure A of the low pressure bypass valve 21.

When the turbine is started, the low-temperature reheat pipe 9 and the reheater 10 already have a predetermined pressure, so the low-temperature reheat pipe 9 and the high-pressure turbine 6 are separated by the check valve 8, and the high-pressure turbine 6 The check valve 8 is operated without being opened until the internal pressure becomes equal to the pressure of the low temperature reheat pipe 9, which is a so-called shut-off operation. Therefore, in addition to the temperature inside the turbine rising, the temperature in the exhaust chamber upstream of the check valve 8 also rises.

In order to suppress the temperature rise due to such shut-off operation, the high-pressure turbine 6 and the intermediate-pressure turbine 14
At the same time, the amount of steam in the high pressure turbine 6 controlled by the steam control valve 4 is made larger than the amount of steam in the intermediate pressure turbine 14 controlled by the intercept valve 13. This increases the cooling effect.

FIG. 8 shows the load at startup of the turbine and the amount of steam flowing into the intermediate pressure turbine 14 versus the high pressure turbine 6.
This shows the relationship between the ratio of the amount of steam flowing into the
Increase the amount of steam on the high-pressure turbine 6 side until the load increases to a certain extent, and when the check valve 8 starts to open, the cooling effect increases, so the amount of steam on the high-pressure turbine 6 side can be small. The amount of steam on the turbine 6 side is gradually reduced to return to a one-to-one relationship similar to the rated load state.

Fig. 9 shows the relationship between the flow rate of the steam control valve 4 and the intercept valve 13 and the load in order to provide such a flow rate ratio. The flow rate is approximately 1/2 times that of the steam control valve 4, and the intercept valve 13 is opened slowly in the first half and quickly in the second half so that the flow rate of both is the same when the load condition is c. It has a certain flow rate ratio. Further, after the load condition reaches c, the intercept valve 13 enters a fully open operation, and is fully opened at the corner point B of the pressure curve shown in FIG. 7b.

In this way, the intercept valve 13 is fully opened at the corner point B, but even if it is not fully opened at the corner point B, the high temperature reheat pressure increases with the load at a load higher than the point B, and the necessary flow rate can be secured. In reality, the full opening operation of the intercept valve 13 will be delayed.

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

By the way, in this type of turbine plant, as shown in FIG.
The structure is such that steam is extracted to the higher pressure feed water heaters 23a and 23b, but since the turbine is in warm-up operation when the turbine is started, the high pressure feed water heaters 23a and 23
b does not perform the original operation. Therefore, this extracted portion passes through the reheater 10 and is added to the high temperature reheat pipe 11.
The high temperature reheat pressure is increased by the increased flow rate. As a result, as shown in FIG. 11, the opening degree of the intercept valve 13, which is i ₁ in the normal state, is kept at i ₂ (<i ₁ ).

This means that the opening degree of the intercept valve 13 and
If the opening degree of the steam control valve 4 is maintained in the same relationship, the flow rate on the intercept valve 13 side will increase, and the above-mentioned relationship in flow rate ratio will collapse. Therefore, the opening degree of the intercept valve 13 is decreased by the increase in the high temperature reheating pressure, and the opening degree of the steam control valve 4 is also decreased accordingly. FIG. 12 shows this relationship, where the opening degree of the intercept valve 13 changes from i ₁ to i ₂ with respect to the increase in the flow rate of the intercept valve 13.
The opening degree of the steam control 4 also decreases from C ₁ to C ₂ , and actually moves from L ₁ to L ₂ with the same load.

Although not shown, when the high temperature reheating pressure decreases, the flow rate is small even if the opening degree of the intercept valve is the same, and at this time, the steam control valve 4 has the same flow rate.
Therefore, in order to take the same load, the steam control valve 4
The opening degree of the intercept valve 13 increases slightly.

On the other hand, the opening degree of the steam control valve 4 does not fully open to the maximum load, but the intercept valve 13 is located downstream of the steam control valve 4, and at a load where the high pressure bypass valve 19 and the low pressure bypass valve 21 are fully closed, That is, a full-open operation is performed with the load at the turning point B shown in FIG. 7b. These relationships are shown in FIG.

[Problems with background technology]

Thus, in the conventional turbine control device, the high pressure bypass valve 19 and the low pressure bypass valve 2
1 is that the same capacity is used under the pre-pressure condition at rated load, and that the bleed line of the low-temperature reheat pipe 9 or the high-temperature reheat pipe 11 upstream from the low-pressure bypass valve 21 is in normal operation at startup. By not performing this, the amount of steam flowing through the high-temperature reheat pipe 11 is larger than that during normal operation, and the high-temperature reheat pressure increases.

As a result, if the opening degree of the intercept valve 13 is not changed, the steam flow rate will increase and the flow rate ratio with the steam control valve 4 will deviate, so the intercept valve 13 is set to a low opening degree.

In other words, during normal operation, the bending point B in Fig. 7b
The intercept valve 21 can be fully opened at startup, but since the high temperature and reheat pressure is high at startup, a large amount of steam flows even at a low opening, making it impossible to fully open the intercept valve 21. The drawback was that it caused an increase in room temperature.

[Purpose of the invention]

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

[Summary of the invention]

To achieve this objective, the present invention controls the opening degree of the low pressure bypass valve so that the deviation between the high temperature reheat pressure detection signal and the setting signal becomes zero during turbine bypass operation of the steam turbine by the turbine bypass system. a first 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 the predetermined load; a pressure setting section capable of outputting signals each according to a second pressure function to which a constant pressure bias or a pressure bias that changes in proportion to the load is added; and when at least one of the high pressure bypass valve and the low pressure bypass valve is open. The output state of the pressure setting unit is on the side where the signal according to the first pressure function is output, and on the side where the 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. and a set pressure switching section for switching the pressure, and a signal output from the pressure setting section is used as a setting signal for the high temperature reheat pressure.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below 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, which is equipped with a pressure control system shown in FIG. That is, when the load signal S24 is applied, as shown in Figure 15a, while the load is lower than point b, it is equal to the lowest pressure of the high temperature reheat pressure,
The function generator 25 outputs the high temperature reheat pressure setting signal S25 with a constant pressure bias added to the load equivalent pressure shown by the dashed line while the high temperature reheat pressure setting signal S25 and the high temperature reheat pressure are exceeded. An adder 26 that compares the thermal pressure detection signal S27 to find the deviation between the two, and outputs an opening command signal S29 for the low pressure bypass valve 21 shown in FIG. 15b in accordance with the deviation obtained by the adder 26. A signal converter 28, also called a pressure gain, is used.

Note that the load-equivalent pressure referred to herein refers to the pressure generated by the flow rate of the high-temperature reheat 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 FIG. 15a, the intercept valve 21 can be fully opened during normal operation, but since the high temperature reheat pressure is high at startup, the intercept valve 21 is not fully opened but is throttled.

Here, the output characteristic of the function generator 25 is, for example, as shown in _{FIG .} If the opening command signal shown in FIG. 16b is output by using a device that outputs the high temperature reheat pressure setting signal, the load to fully open the intercept valve 13 will be the load difference (b ₁ - b).
As a result, it can be said that the lift characteristics of the intercept valve can be made gentler, and that fluctuations in the valve lift can be reduced against load fluctuations during full-open operation, and stable control can be performed.

However, in this case, there is no problem during the warm-up operation by the high-pressure feed water heaters 23a and 23b at startup, but when the load drops during normal operation, it falls below the load equivalent pressure line, breaks _at point B, and reaches the lowest point. It passes through the pressure line and reaches point A.

In such a situation, even if the pressure increases due to small pressure fluctuations, the high temperature reheat pressure detection signal S27 becomes larger than the high temperature reheat pressure setting signal S25, and thereby,
The output of the adder 26 turns positive and the low pressure bypass valve 2
1, steam will be dumped into the condenser 18, reducing the efficiency of the plant.

Therefore, in the present invention, as shown in FIG. 1, a pressure bias setting device 30 that outputs a constant pressure bias signal, a relay 31 excited by an interlock circuit 32, and an output of a function generator 25a, An adder 33 that adds the pressure bias signal of the pressure bias setting device 30 obtained through the contacts of the relay 31 is newly added.

In this case, _the function _generator 25a, as shown in FIG. A device with non-bias characteristics is used. In addition, as shown in FIG. 2, the interlock circuit 32 includes a normally open contact 32a of a relay (not shown) that operates when the high pressure bypass valve 19 is fully closed, and a normally open contact 32a of a relay (not shown) that operates when the low pressure bypass valve 21 is fully closed. Normally open contact 3
2b in series, and is configured to energize the relay 31 when the high pressure bypass valve 19 and the low pressure bypass valve 21 are fully closed at the same time.

The operation of this embodiment configured as described above will be explained below with reference to FIGS. 3 and 4.

First, during turbine bypass operation, the high pressure bypass valve 19 and the low pressure bypass valve 21 are opened.
Therefore, the relay 31 does not operate and the function generator 25a
Pressure setting signal S25 and high temperature reheat pressure detection signal S27
The opening degree of the low pressure bypass valve 21 is controlled based on the deviation from the above.

Note that the valve opening degrees (or flow rates) of the high pressure bypass valve 19 and the low pressure bypass valve 21 are as shown in FIG.
While keeping the opening degree higher than that of the spray water,
They are gradually closed as the load increases, and the high pressure bypass valve 19 is fully closed at load _L3 , and the low pressure bypass valve 21 is fully closed at load _L4 .

This means that the high-pressure bypass valve 19 is fully closed and the steam is transferred to the low-temperature reheat pipe 9 because there is no surplus steam left.
This is nothing more than to completely close the low-pressure bypass valve 21 to prevent steam from escaping to the condenser 18.

Thus, when the load reaches _L4 , the relay 31 is energized by the action of the interlock circuit 32,
The pressure bias signal from the pressure bias setter 30 is applied to the adder 26 together with the pressure setting signal S25 from the function generator 25a. As a result, the pressure function shown in FIG. 4a is switched to the pressure function shown in FIG. 4b to which a constant pressure bias is added.

In other words, when the load is less than L ₄ , the high temperature reheat pressure is set according to the pressure function in Figure 4a, and the load is
When L ₄ or more and when the load decreases, the high temperature reheat pressure is set according to the pressure function of FIG. 4b until the load starts to open at least one of the high pressure bypass valve 19 and the low pressure bypass valve 21.

Note that the pressure line A'-B' ₁ in FIG. 4b is higher than the lowest pressure A by a pressure bias amount d,
1 begins to open, 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, during turbine bypass operation, the minimum pressure A is always
is set to

On the other hand, after the check valve 8 is fully closed due to load interruption, etc.
When this starts to open again, the pressure in the low-temperature reheat pipe 9 is controlled to the minimum pressure A by the low-pressure bypass valve 21, so the exhaust chamber pressure of the high-pressure turbine 6 increases only to the minimum pressure A, and the exhaust chamber temperature decreases. It is also possible to prevent overheating due to high pressure in the exhaust chamber.

In addition, in the above embodiment, the pressure bias setting device 3
0 gives a constant pressure bias, but for example, as shown in FIG. 5a,
Pressure bias is proportional to load between 0 and 100% load,
In addition, by using a pressure bias setting device that has an appropriate size at 100% load, obtain the pressure function shown in FIG. 5b, and check whether both the high pressure bypass valve 19 and the low pressure bypass valve 21 are fully closed. By switching between the pressure function shown in FIG. 4a and the pressure function shown in FIG. 5b, appropriate pressure control can be achieved at low loads without applying excessive pressure bias.

Furthermore, in the above embodiment, there is a pressure function that is equal to the lowest pressure of high-temperature reheat pressure until the load rises to a predetermined load and does not apply a pressure bias to the load equivalent pressure above the predetermined load, and a predetermined pressure function for this pressure function. A pressure bias is applied to create another pressure function, and these two pressure functions are switched.A pressure setting section that can switch between two function generators each outputting a pressure setting signal similar to this, and a high pressure bypass valve are used. The same effect as described above can be achieved by providing a set pressure switching section that switches the function of the pressure setting section depending on whether both the low pressure bypass valve and the low pressure bypass valve are fully closed.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a first pressure function that is equal to the lowest pressure of high temperature reheat pressure below a predetermined load and equal to the load equivalent pressure above a predetermined load; a pressure setting section capable of switching and outputting a pressure setting signal according to a second pressure function loaded with a constant pressure bias or a pressure bias that changes in proportion to the load with respect to the first pressure function; and a high pressure bypass valve. and a pressure setting signal according to the first pressure function is output when at least one of the low pressure bypass valves is open, and according to the second pressure function when both the high pressure bypass valve and the low pressure bypass valve are fully closed. Since a set pressure switching section for switching the pressure setting section is provided on the side where the pressure setting signal is output, the intercept valve can be reliably fully opened even if the high temperature reheat pressure increases at the time of startup, and Excessive rise in temperature in the exhaust chamber of the turbine can be prevented.

[Brief explanation of drawings]

FIG. 1 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 4 show the operation of the embodiment. FIG. 5 is a characteristic diagram for explaining the operation of another embodiment, FIGS. 6 and 10 are system diagrams of a reheat steam turbine plant to which the present invention is applied, 7 to 9 and 11 to 13 are characteristic diagrams for explaining the operation of this reheat steam turbine plant, and FIG. 14 is a block diagram showing the configuration of the main parts of a conventional control device. 15 and 16 are characteristic diagrams for explaining the operation of this control device. 6...High pressure turbine, 14...Intermediate pressure turbine,
16, 17...Low pressure turbine, 13...Intercept valve, 19...High pressure bypass valve, 21...Low pressure bypass valve, 25a...Function generator, 30...
Pressure bias setting device, 32...interlock circuit, 31...relay.

Claims (1)

[Claims] 1. In a steam turbine control device that controls the opening degree of a low pressure bypass valve so that the deviation between the high temperature reheat pressure detection signal and the setting signal becomes zero during turbine bypass operation of the steam turbine by the turbine bypass system, a predetermined a first pressure function equal to the lowest pressure of the hot reheat pressure below the load and equal to the load equivalent pressure above a predetermined load;
a pressure setting section capable of switching and outputting signals according to a second pressure function in which a constant pressure bias or a pressure bias that changes in proportion to load is added to the pressure function; a high pressure bypass valve and a low pressure bypass valve; a side on which a 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 fully closed, and a side on which a 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. and a set pressure switching section that switches an output state of the pressure setting section, and a signal output from the pressure setting section is used as a setting signal for the high temperature reheat pressure.