JPS585412A - Controller for steam turbine plant with reheater - Google Patents

Abstract

PURPOSE:To protect the rotor of a low pressure turbine and a reheater in a nuclear power plant, by calculating the thermal stress in the rotor and the reheater to control the quantity of heating steam for the reheater to prevent excessive cooling and heating. CONSTITUTION:Various kinds of detected values are applied from temperature detectors or the like to a control valve regulator 19 through a relaying unit 20 so that the regulator calculates the thermal stress in the rotor of a low pressure turbine 9 and a reheater 8 and determines the degree of opening of a heating steam control valve 14 to optimize the thermal stress. The relaying unit 20 selects the higher or lower one of plural detected values applied from an identical detection point or excludes a detected value having shown an excessive change during the measurement, to heighten the reliability. The detection signals from the identical detection point are applied to a stop valve controller 17 through a protective relaying unit 37 so that a stop valve 13 is completely closed through a valve position determination unit 16 when more than a half of the plural detected values from the identical detection point have become higher or lower than a set value. Since a control system and a protection system are independent of each other, sure protection is enabled even if the control system is defective.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a steam turbine plant having a reheater in a nuclear power plant.

The steam produced in nuclear power plants is generally lower in temperature than the steam produced in fossil fuel-based steam generators, near the saturation temperature. The steam lines generated in a nuclear reactor plant are led to a high-pressure turbine and the energy is converted into power, which is then used to generate power in a low-pressure turbine; in this case, the high-pressure The steam discharged from the turbine has low temperature and pressure, and high humidity, so in addition to separating the moisture, a reheater that uses reactor generated steam as a heating source is sometimes used. In this reheater, the exhaust steam from the high-pressure turbine is heated and guided to the low-pressure turbine to obtain power, thereby increasing the driving power of the low-pressure turbine. The thermal efficiency of nuclear power plants can be improved. A prior art example of a control system for this reheater consists of an air-operated heating steam control valve and a motor-operated cam that transmits an air signal to the heating steam control valve. The driver operates these devices to control the heating steam control valve.

Also, Special Publication No. 53-47842, Special Publication No. 55-2124
Example 3 shows a method for continuously and automatically controlling steam reheating work. The two examples above each include a turbine temperature detector, a control system for controlling the amount of heating steam, a temperature reference signal source, a comparator, an integrator circuit, a relation generator, and a control system for 2'4I numbers. One of the modes controls the reheat system. The important control parameter in these examples is the turbine inlet temperature, which includes controlling the rate of temperature change, controlling the maximum temperature at the end and inlet of the low-pressure turbine, and preventing excessive cooling of the low-pressure turbine. is being carried out. However, the conventional method has a drawback in that it is not possible to monitor the thermal stress inside the reheater and the rotor of the low-pressure turbine, which actually requires monitoring. That is, the areas that require the most thermal stress monitoring are the inside of the reheater and the rotor of the low-pressure turbine. A tube is generally disposed inside the reheater, and heating steam passes through the inner surface of the tube to heat steam drawn from the high-pressure turbine exhaust flowing outside the tube. If a sudden temperature change is applied to the tube, it may deform and generate excessive thermal stress between the tube and the support, or thermal stress may be generated in the tube itself. Compared to the stationary side of the turbine, the tubes and tube supports that are the internal structure of the reheater have better heat transfer with the steam, so thermal stress monitoring is more necessary inside the reheater. It's a thing. Similarly, since the turbine rotor has higher heat transfer than the turbine stationary body side, the temperature of the turbine rotor changes more easily due to the inflowing steam, and the thermal stress becomes higher.

The purpose of the present invention is to control the amount of heating steam supplied to the reheater so that the thermal stress inside the reheater and the low pressure turbine rotor is within an allowable range, and to An object of the present invention is to provide a control device for a steam turbine plant having a reheater that can protect both by avoiding cooling and overheating.

Next, a control device for a steam turbine plant having a reheater, which is an embodiment of the present invention, will be described.

FIG. 1 shows a steam turbine plant for nuclear power generation, which is the object of the present invention. In the figure, the ≠ air generated in the steam generator 1 is transferred to the main steam stop valve 2 and the steam control valve 3.
and is led to the high pressure turbine 6. Main steam stop valve 2
The steam control valve 3 is opened and closed by the control and drive device 5 so as to reach the target speed based on the speed signal from the speed detector 4 of the steam turbine rotor. The steam that does work in the high-pressure turbine 6 and drives the high-pressure turbine has a lower pressure and temperature, and an increased moisture content in the steam, so after the moisture is separated in the moisture separator 7, It is guided to a reheater 8. The heat source of the reheater 8 uses steam generated by the steam generator 1, and branches from the upstream side of the main steam stop valve. The steam whose temperature has increased by exchanging heat with the heated steam in the reheater 8 is called reheated steam.
It is guided to a low pressure turbine 9. The high pressure turbine 6 and the low pressure turbine 9 are coupled to a generator 10 to drive the generator. The steam that performs work in the low-pressure turbine and generates driving power is
The water is guided to the condenser 11, condenses and becomes water, and is sent to the feed water heater 1.
Leads to 2. The heated steam heat-exchanged in the reheater is also introduced to this feedwater heater, and the water from the condenser is heated. The heated water is supplied to the steam generator 1.

A heating steam stop valve 13 and a heating steam control valve 14 are installed in the heating steam piping, and are opened and opened by a control and driving device 15.

FIG. 2 shows a control device for a steam turbine plant, which is an embodiment of the present invention. The heating steam stop valve 13 is opened and closed by the stop valve drive and valve position determiner 16, and is either fully open or fully closed. Opening/closing is done by the stop valve control device 17
Directed by. The reheat steam control valve 14 is opened and closed by the control valve drive and valve position determiner 18, and the reheat steam control valve 14 is opened and closed by the control valve drive and valve position determiner 18.
The opening degree is instructed by the control valve control device 19, not only in the case of fully closing but also in the case of intermediate opening degree. The control valve control device 19 calculates the thermal stress inside the low-pressure turbine rotor and reheater based on the detected values from various detectors, sets the opening degree of each heating steam control valve 1 to be optimal, and adjusts the opening degree. instruct. The detected values of the various detectors are sent to the control valve controller #19 via the detected value repeater 20.

The detector repeater 20 performs signal transmission.

Furthermore, when multiple detectors are placed at the same detection point, the detector repeater 20 can select a high value, select a low value, or exclude a detected value that shows an excessive change in detected value during measurement. This increases the reliability of detected values.

Additionally, protection detectors are provided, which send detected values to the stop valve controller 17 via a protection detector repeater 37 .

The protective detector repeater 37 performs signal transmission. The signal is sent to the stop valve controller 17, and when the value exceeds or falls below a predetermined value for equipment protection, a signal is sent to the stop valve drive and valve position determiner 16 to fully close the stop valve. send. At this time, a plurality of detectors may be placed at the same detection point, and a stop valve fully closed signal may be output when a majority of the plurality of detection values exceeds or falls below a set value. Furthermore, a stop valve fully closed signal may be output when two detected values among the plurality of detected values exceed or fall below a set value.

As described above, by making the control system from the detector to the control valve and the protection system from the detector to the stop valve independent of each other, equipment can be safely protected even when the control system malfunctions.

In addition, when the detected value by the detector exceeds or falls below a preset reset value, the fully closed signal is canceled, and when a reset signal from the central controller 38 enters the stop valve controller 17, the stop valve is closed. The valve is fully opened to prepare for startup.

The manual controller 34 sends valve opening/closing signals to the stop valve controller 17 and the control valve controller 19 by manual operation at the driver's discretion. As a result, in an emergency, the valve can be opened and closed at the driver's discretion, and the stop valve and control valve can be tested for opening and closing.

Next, optimal control by the reheat steam control valve 14 will be described. The low-pressure turbine thermal stress and the reheater internal thermal stress are calculated and controlled so that they fall within allowable values.

The low-pressure turbine thermal stress can be determined by the rotor stress, which can be calculated as follows.

Eα σs=　　　　　(T-wg　T11)1-ν ・・・=J Tomoe (T-g, '1'・) 1-ν However, σS: rotor surface stress σB two rotor center hole response Force: Rotor material elastic modulus α: Rotor material linear expansion coefficient C: Boisson ratio T1: Rotor surface temperature TB: Rotor center hole temperature T, □Volume average temperature of two rotors However, T: temperature at rotor radius r r1: rotor surface radius r,: rotor pore radius The temperature T of the rotor is determined by the following formula.

t: Time a: The temperature conductivity of the rotor material The boundary condition is Ts: Steam temperature on the rotor surface λ: Thermal conductivity of the rotor material: Heat transfer coefficient between the rotor surface and the steam The steam leaving the reheater Since it is led to the low pressure turbine, the reheater outlet temperature is equal to the steam temperature at the low pressure turbine inlet rotor surface. Therefore, the initial temperature of the turbine rotor before steam flows into the low-pressure turbine is the temperature detected by the low-pressure turbine internal metal temperature detector 32, and then from the reheater exit temperature from the heater, the above calculation formula is calculated. Calculate the rotor surface stress and center hole stress moment by moment. At the same time, the amount of change ΔT'ao in the steam temperature at the outlet of the reheater that can be allowed at a future appropriate time Δtvkt is determined from the calculated stress value and the allowable stress value. The reheater outlet steam temperature can be controlled by adjusting the heated steam temperature and the amount of heated steam entering the reheater. Further, when the reheater inlet steam temperature or the reheater inlet steam amount is changing, the rate of change is considered and the heating steam amount is corrected. Since the reheater inlet steam amount is proportional to the pressure after the first stage of the high pressure turbine, it is calculated from the measured value of the pressure after the first stage of the high pressure turbine. In this way, the range in which the amount of heating steam can be increased or decreased up to Δtvk is determined.

Similarly, regarding the thermal stress inside the reheater, the momentary thermal stress is calculated, and the range in which the amount of heating steam can be increased or decreased is determined until Δt, 1, in order for the thermal stress to fall within the allowable value.

Compare the range in which the amount of heating steam can be increased or decreased, determined from the thermal stress of the low-pressure turbine rotor, and the range in which the amount of heating steam can be increased or decreased, determined from the internal thermal stress of the reheater, and determine the amount to increase or decrease the amount of heating steam within the overlapping area. .

After the heating steam increase/decrease is determined, the opening degree increase/decrease of the heating steam control valve is determined based on the heating steam conditions, and the heating steam control valve is opened/closed.

FIG. 3 shows arithmetic blocks for the above-mentioned control. This calculation function is possessed by the control valve controller.

The reheater inlet steam pressure (detector 27) and the reheater inlet steam temperature (detector 28) are proportional to the turbine load as long as the main steam condition is constant. Since the turbine load is proportional to the pressure after the first stage of the turbine (detector 33), it is sufficient to implement the present invention even if the other two are calculated from the pressure after the first stage of the turbine.

Since the heating steam is taken from the main steam line, its steam conditions are the same as the main steam conditions. Even when the main steam conditions change, the main steam temperature is almost the saturation temperature and often changes because the main steam pressure changes. That is, this is a case where the main steam temperature is approximately saturated and the reactor thermal output is increased to gradually increase the main steam pressure. In such a case, even if the pressure of the heated steam (detector 21) is used and the temperature of the heated steam (detector 22) is controlled using a calculated value without measuring it, the present invention cannot be implemented. It is enough.

There are cases where the turbine is controlled by making a certain relationship between the main steam condition and the turbine load turbine rotation speed. That is, this is a case where the turbine rotational speed is increased while increasing the main steam pressure, and after reaching the rated pressure, the turbine load is started. In this case, the turbine rotation speed (detector 4)
A similar effect can be obtained by determining the main steam conditions from the turbine load and the turbine load. Therefore, detectors 21 and 22 may be omitted.

As mentioned above, the turbine load is determined by the pressure after the first stage of the high pressure turbine (
Although the turbine load is determined from the pressure after the first stage of the high-pressure turbine because it is proportional to the pressure of the detector 33), it is sufficient to implement the present invention even if the turbine load is determined by detecting the generator output.

It is sufficient to carry out the present invention even if it is considered that the steam after the heating steam control valve undergoes isenthalpic expansion after being throttled by the control valve. Therefore, the temperature after the heating steam control valve may be calculated and determined from the heating steam conditions and the pressure after the heating steam control valve (detector 23).

The steam in the steam turbine plant of a nuclear power plant contains moisture, and by removing the moisture with a dehumidifier inside the turbine or an external dehumidifier,
Steam conditions are maintained near saturation to increase turbine efficiency. If a dehumidifier is not installed inside the turbine, or if it is expected that the humidity will be high even if a dehumidifier is installed,
Alternatively, in order to improve the accuracy of control when the humidity of the main steam is high, the humidity is measured at each steam temperature measurement point. By measuring the humidity and determining the enthalpy, the temperature after the heating steam control valve described above can be calculated with high accuracy, and the heat transfer coefficient between the steam and the turbine rotor can be calculated with high accuracy.

Excluding both or one of the reheater internal metal temperature detector 31 and low-pressure turbine internal metal temperature detector 32 used for control, and calculate the initial detection value of each in a state where there is steam flow immediately before stopping. It is also possible to carry out the present invention by calculating and calculating from the metal temperature obtained by taking into consideration cooling during the turbine stop time.

According to the present invention, a control device for a steam turbine plant having a reheater is capable of controlling the amount of heated steam supplied to the reheater so that the thermal stress inside the reheater and the low-pressure turbine rotor is within an allowable range. This has the effect that it can be realized.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing a steam turbine plant of a nuclear power plant, which is the subject of the present invention, and Fig. 2 is an overall system diagram showing a control device for a steam turbine plant having a reheater, which is an embodiment of the present invention. , FIG. 3 is a control flow diagram showing detailed contents of the control device of the present invention. l...Steam generator, 2...Main steam stop valve, 3...
Steam control valve, 4... Speed detector, 5... Control and drive device, 6... High pressure turbine, 7... Moisture separator,
8... Reheater, 9... Low pressure turbine, 10... Generator, 11... Condenser, 12... Feed water heater, 13
...Heating steam stop valve, 14...Heating steam control valve, 1
5... Control and drive device, 16... Stop valve drive and valve position determiner, 17... Stop valve controller, 18... Control valve drive and valve position determiner, 19... Control valve controller,
20...Detector repeater, 21...Heating steam pressure detector, 22...Heating steam temperature detector, 23...Heating steam control valve rear pressure detector, 24...Heating steam control valve Diameter steam temperature detector, 25...Heating steam reheater outlet pressure detector, 26...Heating steam reheater outlet temperature detector, 27.
... Reheater inlet steam pressure detector, 28... Reheater inlet steam temperature detector, 29... Reheater outlet steam pressure detector, 30... Reheater outlet steam temperature detector, 31...Reheater internal metal temperature detector, 32...Low pressure turbine internal metal temperature detector, 33...High pressure turbine first stage rear pressure detector, 34...Manual controller, 35...Return Heater internal metal temperature detector (for protection), 3G... Low pressure turbine internal metal temperature detector, (for protection), 37... Protective detector repeater, 38... Central control unit.

Claims (1)

[Claims] 1. In a steam turbine plant with a reheater installed in a nuclear power plant, a control valve is installed in the heating steam piping that supplies heating steam to the reheater, and the low pressure turbine section and reheater of the steam turbine plant are installed with a control valve. A calculation device is installed to calculate the thermal stress of the low-pressure turbine rotor and the stress inside the reheater from these temperature detectors. 1. A control device for a steam turbine plant having a reheater, characterized in that the control device comprises a valve control device that operates the control valve so that the control valve is within a permissible value.