JPS59224406A - Protective mechanism of nuclear turbine - Google Patents

Abstract

PURPOSE:To control the thermal stress of a low pressure turbine rotor accurately by introducing the main steam or high pressure gas bled out of turbine to the moisture separating, reheater output system of a nuclear steam turbine, and by controlling the amount of this introduced steam. CONSTITUTION:In a nuclear turbine plant, the steam discharged by a high pressure turbine H.P. is reheated by a moisture separating, reheater 29 to be then fed to a low pressure turbine L.P. As the source of reheating steam, the main steam or gas bled out of the high pressure turbine is supplied to this reheater 29. The low pressure turbine is, on the other hand, supplied with the main steam or the steam from said gas bled out of high pressure turbine, through regulator valves 26, 25. Stress in the rotor is determined from signals given by a revolving speed sensor 11 and a centrifugal stress sensor 12 as well as signals given by an input pressure sensor 8, input steam temp. sensor 27 and rotor thermal stress calculator 10, to be compared with the allowable value at a stress judgement device 16 so as to serve control of the degree of opening of valves 26, 25 through a valve adjuster 18. Thus control of the thermal stress in low pressure rotor is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a stress control device for a turbine operated in wet steam and superheated steam, and particularly for a nuclear steam turbine having a moisture separator reheater. The present invention relates to a stress control device suitable for controlling stress generated in a rotor.

[Background of the invention]

Conventionally, nuclear power turbines have been used for base load operations to manage rotor stress due to load changes by starting using a prediction curve without directly measuring stress.

Even when directly measured, the temperature of the steam flowing into the steam turbine was not controlled as a one-sided system.

In recent years, nuclear power turbine plants have also been operated by temporarily lowering the plant's output to the required internal output until the accident is restored in the event of an accident in the external line system.

So-called independent operation within the plant is required.

Due to the rapid load changes during isolated station operation and the process of increasing output after isolated operation at the station, excessive stress is applied to the turbine rotor, which consumes the rotor life. Since the number of stops and starts is increasing, nuclear power turbines may be required to operate under intermediate loads in the future, and stress management of nuclear turbine rotors has become necessary.

As the load on the steam turbine changes, the temperature of the casing or rotor of the steam turbine changes, and a typical example of this is shown in FIG. Now, we will explain the case of cold start, that is, the case where the rotor temperature is approximately equal to room temperature and high temperature steam flows in. First, with the inflow of steam, the rotor surface temperature 2 increases, and the rotor surface stress 5 becomes compressive stress. Here, the thermal stress is highest at a portion where stress is concentrated, such as the root of the disk, and the stress exceeds the minus yield point 7 and generates a tensile residual stress 6 in a steady state. On the other hand, during this process, a change in the rotor center hole temperature 3 causes a rotor center hole stress 4 in the opposite direction to the rotor surface. When the turbine is stopped, the rotor temperature remains high and approaches the steam temperature 1, and at this time the rotor surface stress 5 becomes tensile stress, and conversely, the rotor center hole stress 4 becomes compressive pressure.

In order to deal with the occurrence of such thermal stress, in conventional nuclear power turbines, a method has been adopted in which the rotor stress is visually observed by ensuring the allowable load change period and time using the prediction curve shown in FIG.

In a conventional thermal power turbine, as shown in FIG.
The heat transfer coefficient K of the rotor surface is calculated from the thermal stress calculator 10 of the rotor surface and the center hole.

The rotational speed measured by the rotor rotational speed measuring device 11 is input to the centrifugal stress calculator 1-2, and the combined stress with the thermal stress is calculated by the calculator 1.
In step 3, the system calculates calculations 1 through 1 and further calculates the creep life of the rotor and checks the stress.

In conventional nuclear power turbines, these systems are as shown in Figure 4. Since there is a unique relationship between wet steam pressure and saturation temperature due to the amount of steam, steam pressure is measured instead of temperature, and the stress list of the rotor is measured. There is a system to monitor There is also a thermal stress management system for reheaters and low-pressure turbines based on heating steam control of moisture-separated reheaters.

The shortcomings of the prior art as a stress theory for nuclear turbine rotors with moisture separator reheaters are described below.

Firstly, during the load change according to the predicted curve shown in Figure 1, and during the load fluctuation, there are various operational change modes in actual operation, especially sudden load changes such as load shedding in the event of an accident or isolated operation within the station. Also, it was not possible to manage stress due to changes in rotational speed. In addition, due to the poor accuracy of rotor temperature control, it may take longer than necessary to restart and increase the load after such an accident, or to respond to an increase in load after isolated operation within the plant. Or 1. There was a risk of excessive stress due to the normal load change curve.

Second, compared to conventional nuclear power turbines, in nuclear power turbines with a moisture separation reheater, the inlet steam of the low-pressure turbine is at a high temperature in the dry region in normal lotus rotation, and the moisture separation rate is low at startup. Because the thermal steam temperature is also low, the low-pressure turbine inlet steam may become wet steam, and the required equipment temperatures for the thermal stress management of the moisture separation reheater and the low-pressure turbine thermal stress management are different. There is a drawback that stress management systems for turbines or nuclear power turbines cannot be applied in exactly the same way.

Thirdly, at extremely low loads or during isolated operation within the plant, the turbine stage flow rate becomes low, which causes the temperature of the low pressure turbine to rise, and in the final stage of the low pressure turbine, the low pressure exhaust chamber spray is activated and one spray of water is generated. There was a problem in which erosion occurred near the final stage rotor blade of the low-pressure turbine due to being caught in the final stage rotor blade of the low-pressure turbine. The present invention provides a new rotor stress management mechanism that accurately determines the thermal stress of a nuclear turbine rotor and manages both centrifugal stress and creep life.

[Summary of the invention]

The key points of the present invention are to introduce main steam or steam from a high-pressure turbine into the output system of the moisture separator reheater of a nuclear power turbine, and to control the amount of this steam.・Steam temperature entering the low-pressure turbine The purpose is to control the thermal stress of the steam turbine rotor, calculate the thermal stress of the steam turbine rotor, and manage the stress of the rotor.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

Figure 5 shows a nuclear power turbine equipped with a moisture separator reheater.
-S diagram is shown.

The reactor generated steam is located at 28 points, and at rated load the high pressure turbine inlet is at point B, and the high pressure turbine outlet is at point 0 due to work being done. The moisture separator reheater is located between the high-pressure turbine and the low-pressure turbine, and is composed of a moisture separator and a reheater using main steam and high-pressure turbine bleed air, so that the high-pressure turbine outlet steam is At point 0, the enthalpy on the vertical axis in FIG. Also.

At the outlet of the low-pressure turbine, the point is E on the exhaust pressure line.

At partial load, the pressure at each stage decreases due to the decrease in the amount of steam at the steam turbine inlet. Points B, C, D, and E are Bl and CI, respectively.
, DI, moves to E1 point.

The minimum load for normal/nuclear turbines is rated at 25°.
・Furthermore, during in-station isolated operation where the steam turbine stage pressure drops rapidly, the in-station load is small at about 3%, but the reactor side requires about 40% of the feed water flow rate, so the high-pressure turbine extraction amount is large, and therefore, When the station is operating independently, the high-pressure turbine inlet flow rate is relatively large compared to the station load, and the area after the first stage of the high-pressure turbine is in a humid region.

On the other hand, when the inlet steam of the low-pressure turbine is acting on the moisture separator reheater as main steam or reheated steam using high-pressure turbine extraction air as the heating source, Since the low-pressure turbine inlet steam becomes dry steam, special stress control is required. In other words, in conventional nuclear power turbines, the low-pressure turbine inlet is a humid region, whereas the nuclear low-pressure turbine inlet steam with a moisture-separating reheater makes effective use of reheated steam during normal operation. It becomes dry steam, but if reheated steam is not used effectively such as when starting a cold machine,
Furthermore, if the moisture separator efficiency is low due to a low flow rate, the low pressure turbine inlet steam becomes humid steam.

In this way, the low-pressure turbine inlet steam has a large temperature change, so when the rotor temperature is low such as during cold startup, the moisture separator reheater outlet is In addition, when the rotor temperature is relatively high, such as when transitioning from constant load to in-house isolated operation, the amount of heating steam to the outlet of the moisture separator reheater is ensured. By controlling the temperature to a certain extent, it is possible to reduce the occurrence of thermal stress caused by the difference between the rotor temperature and the steam temperature.

Therefore, the turbine steam temperature detection locations for rotor thermal stress management are: the moisture separator reheater outlet where steam temperature changes are large, the low pressure turbine inlet/before the first stage of the low pressure turbine, and the low pressure turbine first stage. Dango etc. can be considered.

Based on this basic idea, one embodiment of the present invention will be explained with reference to FIG.

The target of this stress management system is the example of a nuclear power turbine with a moisture separator reheater targeted at the low pressure turbine inlet.

In FIG. 6, a rotation speed measuring device 11 is a device that measures the rotor rotation speed during each operation. In the rotor centrifugal stress calculation device 2, data regarding the rotation speed and center hole centrifugal stress σP are inflicted in advance, and the rotation speed measurement device 11
Each rotor centrifugal stress σP for the rotation speed detected by
Calculate.

Signals from a pressure detector 8 that detects the pressure at the inlet of the low-pressure turbine, a temperature converter 20 that converts the pressure to a saturation temperature, and a temperature detector 26 that detects the temperature at the inlet of the low-pressure turbine enter the steam temperature selector 22. The structure is as follows. The steam temperature selected by the steam temperature selector 22 is determined by the temperature change Δ
The heat transfer coefficient of the rotor surface is determined from the calculation unit 9 that calculates T and the low-pressure turbine inlet pressure measured by the pressure detector 8, and the rotor thermal stress is calculated by the thermal stress calculation unit 1o.

The rotor thermal stress calculator 1o calculates stress on the rotor surface and center hole.

The composite stress calculator 13 is a calculator that combines centrifugal stress σF and centrifugal stress 0, and furthermore, the operating time measuring device 14
Based on the operating time stored in , creep wear is calculated by a creep wear calculator 15 and connected to a rotor stress determiner 16.

If the stress tolerance σT^ is exceeded, the valve controller 18 is instructed to adjust the valve. Further, if it is within the allowable value, a signal indicating that continued operation 17 is possible is issued.

The valve opener 19 is a device that opens and closes the first steam valve 25 and the second heating steam valve 26 at the outlet of the moisture separation reheater in response to a signal from the valve regulator 18.

Next, the operation of the rotor stress management system shown in FIG. 6 will be explained.

Pressure detector 8° installed at the low pressure turbine inlet The pressure at the low pressure turbine inlet that can be detected by the temperature sensor 26
The temperature TI is determined and selected by a steam temperature selector. In other words, if the saturation temperature T8 converted from the steam amount with respect to the pressure Pi is determined to be equal to the detected temperature T1 within a certain error range, the converted saturation temperature T8 will be the same as the detected temperature T1 because it is wet steam.
is the temperature at the inlet of the low-pressure turbine, and when TS<TI, it is dry steam, so the temperature T detected by the temperature detector is
Let I be the temperature at the inlet of the low pressure turbine, and the temperature selector 22
Select by.

Moreover, a wet steering (not shown) may be installed to determine whether the low-pressure turbine inlet steam is wet steam or dry steam.

The low pressure turbine inlet temperature TS selected in this way
, or from T1 and low pressure turbine inlet pressure P1.
The heat transfer coefficient of the rotor surface is calculated, and the thermal stress σ is calculated using the calculator 10.
Calculate T. Also, the rotor centrifugal stress calculator 12 calculates the centrifugal stress σr from the rotational speed determined by the rotational speed measuring device 11, and calculates the composite stress σF+σ! with the thermal stress 0 previously calculated. The rotor stress determiner 16 compares and determines the operating time memorized by the operating time measuring device 14 and the pre-scheduled stress per cycle considering creep wear calculated by the slip-leap wear calculator 15 as an allowable value. If the combined stress is below the allowable value,
A continuation operation instruction 17 is issued, and if the 1 resultant stress is greater than the allowable value, the valve controller 18 causes the valve switch 19 to switch off the first stream of the heating steam line from the high-pressure turbine bleed air to the moisture separator reheater outlet. By adjusting the reheat steam regulating valve 25 and the second reheat steam regulating valve 26 from the main steam, the centrifugal stress and the thermal stress are adjusted.・The operating time measured by the operating time measuring device 14 , the amount of rotor life wear and tear is integrated and stored.

The control of the first heating and second heating steam regulating valves is constant regardless of load changes when the opening of the first heating steam regulating valve is constant, because the first heating steam uses the main steam at a constant pressure as the steam source. A large amount of high-temperature steam flows into the reheater, but since the second reheating steam uses high-pressure turbine extraction air as the steam source, even when the opening degree of the second heating steam regulating valve is constant, the reheater will change due to load changes. The steam flow rate to the outlet decreases and the steam temperature also decreases.

Therefore, since a change in the amount of first heating steam has a greater influence on the low-pressure turbine inlet temperature than a change in the second heating steam temperature, if you want to increase the temperature change in the low-pressure turbine inlet, the first heating It is controlled by the steam regulating valve 25, and when the temperature change width is small, the second heating steam regulating valve 26 is controlled by the determining device 2.
Adjust by 8.

In addition, when the rotor temperature is low, such as when starting a cold machine, the regulating valve 26 is opened and closed to close the heated steam regulating valve to lower the steam temperature to the low-pressure rotor, and to lower the rotor temperature during isolated operation at a station from constant load. When the temperature is high, the steam temperature of the low pressure rotor is increased by opening the heating steam regulating valve to reach the steam temperature of the low pressure rotor, thereby controlling the thermal stress of the rotor.

On the other hand, during isolated operation within the station, the low-pressure exhaust chamber spray operation detector 30 detects the operation of the spray water, and the rotor stress determiner 1 detects the operation of the spray water.
By closing the reheat steam regulating valves 25 and 26 within the allowable range of 6, the low-pressure exhaust stage steam can be turned into wet steam, so the spray water does not operate and erosion near the low-pressure final stage is reduced. It can be prevented.

In the figure, 23 is an alarm, 24 is a recorder, 27 is a temperature detector, 29 is a moisture separation reheater, 31 is a judge, and 32 is a control valve.

FIG. 7 shows a different embodiment of FIG. 6 in which the signal from the determiner 28 is sent to the valve switches of regulating valves 33 and 34 provided in the bleed pipe to the reheater 29.

〔Effect of the invention〕

According to the present invention, rotor stress management of a nuclear turbine is
Moreover, the stress management of the nuclear turbine rotor, which has a large temperature change range at the low-pressure turbine inlet of the nuclear turbine having a moisture separation reheater, is carried out within each specified stress.

[Brief explanation of drawings]

Figure 1 is a stress management operating curve diagram for a conventional nuclear power turbine, and Figure 2 is a diagram of the operating curve for stress management during steam temperature fluctuations. Figure 3 is a stress management system diagram for a conventional thermal power turbine; Figure 4 is a diagram showing the pressure and saturation temperature of wet steam; Figure 5 is an I-S diagram of a nuclear turbine; 6 is a block diagram of a control system according to an embodiment of the present invention,
FIG. 7 is a block diagram of another embodiment of the present invention. 8... Low pressure turbine inlet pressure detector, 10... Rotor thermal stress calculator, 11... Rotation speed measuring device, 12...
・Rotor centrifugal stress calculator, 13... resultant stress calculator,
Figure 1 - load t and amount (ru) Figure 2 Takumi Figure 3 Figure 4-Figure 9 and quantity (Figure 4) Figure 5 OK) Figure 6

Claims (1)

[Claims] 1. In a nuclear turbine equipped with a moisture-separating reheater, main steam or steam from a high-pressure turbine is introduced into the outlet system of the moisture-separating reheater to increase the amount of steam. means for adjusting the amount of reheated steam by adjusting the steam temperature at the outlet of the moisture separator reheater, and stress management of the high pressure turbine rotor from changes in rotor temperature or casing temperature of the high pressure turbine. A protection mechanism for a nuclear turbine, characterized in that it comprises means for performing the following steps. 2. According to claim 1, wherein the temperature of the high-pressure turbine rotor or the temperature change of the casing is detected and the thermal stress of the high-pressure turbine rotor is calculated to manage the stress of the rotor. protection mechanism for nuclear power turbines. 3. Calculate the thermal stress of the high-pressure turbine rotor, and calculate the centrifugal stress of the high-pressure turbine rotor from the high-pressure turbine rotation speed, and manage the stress of the high-pressure turbine rotor with the combined stress of the thermal stress and the centrifugal stress. A protection mechanism for a nuclear power turbine according to claim 1 or 2, characterized in that: 4. Stress management of the high-pressure turbine rotor is performed by calculating the thermal stress of the high-pressure turbine rotor and calculating the rotor creep life based on the continuous operation time. A protection mechanism for a nuclear turbine according to paragraph 3. 5. Stress management of the high-pressure turbine rotor is performed by controlling the operation of the turbine so as not to exceed an allowable stress calculated from life management of the high-pressure turbine rotor. 4. Nuclear turbine protection mechanism according to paragraph 3, paragraph 4. 6. When determining wet steam or dry steam, if the difference between the temperature detected by the pressure detector converted to the saturated temperature and the temperature detected by the temperature detector is within the specified error, the steam is determined to be wet steam. It is determined that the converted saturation temperature is the steam temperature, and if it is outside the specified error, it is determined that it is dry steam and the temperature detected by the temperature detector is used as the steam temperature to manage the stress of the high pressure turbine rotor. Claim 1:
Section. The nuclear turbine protection mechanism according to item 2, 3, 4, or 5. 7. The humidity detector indicates that the steam is in a humid area, and
If there is a deviation of more than a certain value between the temperature detected by the pressure detector and the temperature detected by the temperature detector, and if the rotor stress is more than the control value, an alarm will be issued. According to claim 1, 2, 3, 4, 5, or 6, the stress of the high-pressure turbine rotor is managed by issuing or recording the protection mechanism for nuclear power turbines. 8. When detecting steam humidity, if the operating output is larger than the preset turbine output value, the steam is determined to be dry steam, and if the operating output is smaller than the preset turbine output value, the steam is determined to be dry steam. Claims 1, 2, 3, 4, and 5 are characterized in that the steam is determined to be wet steam and stress management of the rotor is performed.
A protection mechanism for a nuclear turbine according to item 6 or 7. 9. In the outlet steam temperature control of the moisture separation reheater, the second heated steam from the main steam is heated more than the first heated steam from the high pressure turbine.
Claims 1, 2, and 3 are characterized in that priority is given to heating steam control. The nuclear turbine protection mechanism according to item 4, 5, 6, 7, or 8.