JPS5916484Y2 - Thermal stress strength fracture prevention device for turbine metal parts - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal stress strength fracture prevention device, and particularly to a thermal stress strength fracture prevention device for turbine metal parts suitable for turbines that require large load changes.

Conventional technology for preventing thermal stress strength fractures of this kind of turbine metal parts has been limited to simply calculating thermal stress from the current temperature of the turbine metal parts and using the calculated results to limit changes in turbine load. It belonged to

Therefore, with this type of technology, it is difficult to know how thermal stress will change in the future, and in order to keep the maximum value of thermal stress within the permissible limit, the turbine must have a considerable margin from the permissible value. I had no choice but to drive with caution.

On the other hand, thermal power plants are expected to be used for daily load adjustment as the number of nuclear power plants increases.

In this case, the turbine of a thermal power plant is affected by sudden load changes,
As they will be stopped and started frequently, the issue of thermal stress will become even more important.

This invention was made to solve the above problem, and it predicts changes in thermal stress due to changes in load and controls the strength of turbine metal parts due to thermal stress by controlling the change so that it does not exceed an allowable value. An object of the present invention is to provide a device for preventing strength destruction of a turbine metal part.

The feature of this invention is that when the load changes, the current load, main steam temperature, and turbine casing inner wall temperature are detected, the load change rate is determined from these and the load change request, and the turbine is operated based on the load change rate. That's what I did.

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In this example, a turbine rotor will be explained, but the present invention can be implemented similarly for other types of casings, for example.

In the figure, 10 is a load actual value signal, 11 is a main steam temperature actual value signal, 12 is a main steam pressure actual value signal, 14 is a turbine casing inner wall temperature signal, 15 is a steam temperature predicted value signal after the first stage of the turbine, Reference numeral 16 indicates a temperature distribution signal of the turbine rotor, 17 indicates a thermal stress maximum value reset signal, 18 indicates a maximum value signal of a predicted thermal stress value, and 1 indicates a load change rate setting signal.

Further, 30 predicts the steam temperature after the first stage of the turbine in time series from the load actual value signal 10, the main steam temperature actual value signal 11, the main steam pressure actual value signal 12, and the load change rate setting signal 19. This is a steam temperature prediction device.

31 estimates the initial temperature distribution of the turbine rotor from the turbine casing inner wall temperature signal 14 and outputs the load request signal 13.
This is a temperature distribution estimating device that emits a signal that sets the maximum value of thermal stress when it is emitted.

32 is the steam temperature predicted value signal 15 after the first stage of the turbine.
This is a thermal stress maximum value prediction device that predicts the maximum value of thermal stress caused by a load change from the temperature distribution signal 16 of the turbine rotor and the turbine rotor.

23 is a load change rate determination device that compares the thermal stress maximum value signal 18 and the allowable maximum thermal stress and determines the set value of the load change rate based on the degree of the difference.

The operation in such a configuration will be explained next.

First, prediction of the steam temperature θ15 after the first stage of the turbine will be explained.

FIG. 2 is a block diagram showing an example of predicting θist.

In FIG. 2, in block 34, a load change amount prediction calculation device predicts a load change amount 20 from the actual load value signal 10, the target load, and the load change rate by calculating the following equation.

Here, L8 (i): Actual load value La(i+n
); Predicted load value Δt after n samples from the current time; Sampling period LR; Target load dLR; Load change rate t In block 35, the main steam temperature actual measurement value signal 11 and the main steam pressure actual measurement value signal 12 are used to calculate the Find the main steam enthalpy.

In block 36, the steam temperature θ+st, (i+n) after the first stage of the turbine after n samples is determined from this enthalpy and the predicted load change value obtained in block 34.

The relationship between enthalpy, load, and steam temperature is determined in advance by simulation or analysis of past data and stored.

Next, the operation of the temperature distribution estimating device 31 that estimates the initial value of the temperature distribution of the turbine rotor will be explained.

This temperature distribution estimating device 31 estimates the temperature distribution inside the rotor using the following equation.

That is, the temperature distribution inside the rotor was solved by equation (3), which expresses the heat conduction equation in cylindrical coordinates, assuming that the initial temperature of the rotor is O'C and the surface steam temperature θ1st is held constant (
4) Obtained by Eq.

Here, λ; thermal conductivity of rotor material (kcal/mh'C);
Specific heat of rotor material (kcal/Kg' C) r; Specific weight of rotor material (kg/m3) K; λ/cr Temperature transfer coefficient (m2/h) h; /m2h 'C)to
; Time after θISt becomes constant (h) A: h
r (Biot number) α.

;A/ri3. :13nJ, (A)-AJo
(A) = positive root of o JOr first kind zero order Be5se
l function J1: Be5sel function of first order of type 1 Next, a method for determining the maximum value of the predicted thermal stress value will be described.

FIG. 3 is a block diagram showing an example of how to obtain this.

In the figure, numeral 37 is a temperature distribution calculation device that predicts the rotor temperature distribution using the initial value estimation signal 16 of the temperature distribution of the turbine rotor and the steam temperature prediction value signal 15 after the first stage of the turbine.

This prediction of the rotor temperature distribution is obtained by dividing the rotor into m parts in the radial direction and calculating a dynamic characteristic model equation when the temperature characteristics of the divided tubular shapes are treated as a lumped constant system.

That is, here, Qsr+ + heat transfer amount from steam to rotor Qr+, rj+I + heat transfer amount from rotor tubular block rj to rt+1 Qrl, r2: rotor tubular block r, to r
2 Qrj-1+r4: Amount of heat transferred to the tubular block rj of the rotor The temperature distribution of the rotor determined in this manner is stored in the temperature distribution storage device 38 and output to three average temperature calculation devices. be done.

These three average temperature calculating devices calculate the volume average temperature Qr of the rotor using the following formula.

The rotor volume average temperature 25 calculated in this manner is output to the thermal stress calculation device 40, and the thermal stress calculation device 40 calculates the thermal stress (f, , 6b) based on this input.

This calculation follows the following well-known formula. E: Young's modulus β: coefficient of thermal expansion of the rotor C: Poisson's ratio (10) The thermal stress obtained by equation (n) is taken in as a signal 26 to the thermal stress comparator 41, where it compares the values up to the previous sampling. The maximum value and the current thermal stress are compared.

If the current value is larger than the previous maximum value, the current value is stored as the maximum value and a recalculation request signal 22 is output to the temperature distribution calculation device 37.

The temperature distribution calculation device 37 calculates the temperature distribution based on the signal, the average temperature calculation device 39 calculates the average temperature, and the thermal stress is calculated from the average temperature.

Then, the thermal stress comparator 41 again compares the maximum value up to the previous time.

If the current value is equal to or less than the maximum value up to the previous time, the maximum value up to the previous time is output as the maximum thermal stress value.

In addition, when the thermal stress maximum value reset signal 17 is issued, the calculated value up to the previous time is ignored, and the calculation is performed again using the current calculated value as the maximum value.

The maximum thermal stress value ("Sma") obtained using the method shown in Figure 3
X, (5'bmax) is the load change rate setting device 23
(l incorporated, maximum allowable thermal stress (crsL, Q'bl
−) is compared with

Then, the load change rate "↓l" is set accordingly.

d-yf, l of the formula for calculating 1 is the following t As shown in Eq.

Using the new load change rate setting value found in this way, θ1st (1+n) is found again, and m1n(Q”
SL Q'smax, Q"bL"bmax
)≧0, it is possible to always keep the thermal stress within the allowable value.

As explained in detail above, the present invention determines in advance how much the thermal stress will change and limits the amount of load change so that the thermal stress does not exceed the allowable value. This can prevent the steel from becoming too large and causing strength failure.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are block diagrams showing the contents of the blocks shown in FIG. 1 in more detail. 30... Steam temperature prediction device, 31... Temperature distribution estimation device, 32... Thermal stress maximum value prediction device, 33... Load change rate determination device, 37... Temperature distribution calculation device, 38
... Temperature distribution storage device, 39 ... Average temperature calculation device, 40 ... Thermal stress calculation device, 41 ... Thermal stress comparison device.

Claims (1)

[Scope of utility model registration request] A load detector that detects the load on the turbine, a main steam temperature detector that detects the main steam temperature, a main steam pressure detector that detects the pressure of the main steam, and a casing inner wall temperature detector that detects the inner wall temperature of the turbine casing. and a setting device for setting a load change request signal, and the device controls the operation within a range in which the thermal stress of the turbine does not exceed a predetermined allowable value when the load changes. , a load change amount prediction calculation device that calculates a load change amount predicted value using the output signal of the load detector and the output signal of the setter of the set load change request signal as input signals; means for determining main steam enthalpy from the output signal and the output signal of the main steam pressure detector using a steam table; and input signals for the output signal of the load change amount prediction calculation device and the output signal of the means for determining enthalpy. a prediction calculation means for predicting the steam temperature after the first stage of the turbine after a predetermined time; an output signal of a casing inner wall temperature detector of the turbine; and a load request signal given at the current moment of the turbine; means for estimating and calculating the initial temperature distribution of the turbine based on the predicted calculation of the steam temperature signal after the first stage of the turbine, the calculated temperature distribution signal, and the given load request signal according to a load change; The method includes means for predicting the maximum value of thermal stress that will occur, and means for correcting the current load change rate using a signal of the difference between the predicted maximum value of thermal stress and a preset allowable maximum thermal stress. and controlling the load of the turbine at the modified load change rate.