JPS5843602Y2 - Turbine casing thermal stress monitoring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal stress monitoring device for a turbine casing, and particularly to a thermal stress monitoring device for a turbine casing that is suitable for application to a steam turbine that requires rapid load changes.

Conventionally, thermal stress monitoring of a turbine casing has been carried out by providing temperature detectors inside and outside the casing, and determining the thermal stress of the turbine casing using the measured temperature.

This method has a problem in that even if there is a sudden load change, the temperature of the inner and outer walls of the turbine casing changes, so it is not possible to know how much the thermal stress will change.

Therefore, in a steam turbine that is forced to undergo severe load fluctuations, it is forced to operate with a considerable margin from the allowable value, which has the disadvantage that efficient and safe operation cannot be performed.

An object of the present invention is to provide a thermal stress monitoring device for a turbine casing that eliminates the above-mentioned drawbacks and enables safe and efficient turbine operation.

The feature of this invention is that the steam temperature after the first stage of the turbine is estimated from the main steam temperature, pressure, flow rate, and the inner and outer walls of the turbine casing are estimated from the estimated steam temperature and the outside air temperature of the turbine casing. This is the point where we are looking for thermal stress.

The present invention will be explained in detail below.

Without further ado, let's consider the effects of thermal stress on the turbine casing.

FIG. 3 shows the relationship between thermal stress σ and strain ε.

In the figure, point A indicates the elastic limit point, and if the stress changes within the range of OA, when the thermal stress returns to O, the strain ε will also become almost O.

However, when the thermal stress exceeds point A and enters the plastic deformation region,
For example, when the thermal stress changes at point D, even if the thermal stress is returned to O, a residual strain ε occurs through a process similar to DE.

The occurrence of this strain ε not only makes plastic deformation more likely, but also causes breakage, so it can also cause damage during plant operation.
Driving beyond point A must be avoided.

The biggest problem with turbine casings is the effect of this thermal stress.

The structure of the turbine is shown in Figure 5. In this figure, 30
3 is a turbine rotor, 31 is a rotor surface, 32 is a rotor bore, 33 is a first stage rotating blade, 34 is a fixed blade, 35 is a nozzle, 36 is a nozzle box, 37 is a labyrinth packing, and 38 is a steam flow.

In this turbine structure, the temperature change is greatest near the first stage of the turbine, and the thermal stress is greatest.

FIG. 6 shows the steam temperature θ18° near the first stage of the turbine and the temperature θml of the inner and outer walls of the turbine casing when the main steam flow rate fs changes in a ramp-like manner.

0 m2, thermal stress on the inner and outer walls of the turbine casing.

1. It shows the temporal change of σ2.

As can be seen from this figure, the thermal stress σ1 on the inner and outer surfaces of the turbine casing. σ2 changes greatly depending on the change in steam flow rate.

There is no particular problem if the maximum value σmax of thermal stress is within the allowable value, but it is necessary to avoid allowing σmax to exceed the allowable value.

Even in such a case, the target value change rate (
=d! s) Measures for t such as adding a limit to r are required. In order to take such measures, it is necessary to predict the thermal stress after a certain time.

In the present invention, the turbine casing is monitored by predicting this thermal stress.

Next, embodiments of the present invention will be described in detail.

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

As shown in the figure, 1 is the main steam pressure detector, 2 is the main steam temperature detector, 3 is the main steam flow rate detector, 4 is the casing outside air temperature detector, 5 is the casing inner wall temperature detector, and 6 is the casing outer wall. Temperature detector, 7 is a main steam pressure signal, 8 is a main steam temperature signal, 9 is a main steam flow rate signal, 10 is a casing outside air temperature signal, 11 is a casing inner wall temperature signal, 12 is a casing outer wall temperature signal, 13 is a turbine no. 14 is a steam temperature estimation device that estimates the steam temperature after the first stage; 14 is a steam temperature estimate; 15 is a temperature change prediction device that predicts temperature changes on the inner and outer walls of the casing; 16 is a predicted casing inner wall temperature; and 17 is a casing outer wall temperature. Predicted value, 18 is a thermal stress calculation device that calculates casing thermal stress, 19 is a casing thermal stress prediction value, 20 is a heat transfer coefficient calculation device, 21 is the heat transfer coefficient from steam to metal, 22 is the heat transfer coefficient from metal to outside air Indicates heat transfer coefficient.

Next, the operation of the thermal stress monitoring device having such a configuration will be explained.

1. The steam temperature estimation device 13 that estimates the steam temperature θ1s after the first stage of the turbine uses the output signal 7 of the main steam pressure detector 1, the output signal 8 of the main steam temperature detector 2, and the main steam flow rate detector. 3 is taken in to estimate the steam temperature θ1s after the first stage of the turbine.

1s, θ 1s=f(PS, θs1 fs)...
...(1) However, Ps is the main steam pressure signal and corresponds to signal 7 in the figure.

θS: Main steam temperature signal; Corresponds to No. 8.

fs; Main steam flow rate signal; Corresponds to No. 9.

Even if the function f in equation (1) is calculated in advance by simulation etc., <.

A detailed block diagram of this steam temperature estimating device 13 is shown in FIG. 4.

In FIG. 4, 23 is the flow rate target rate of change, 24 is the predicted value of the main steam flow rate after time At, 25 is the estimated main steam enthalpy value, and 26 is the target flow rate change rate 23 and the main steam flow rate signal 9. 27 is an enthalpy meter N device that takes in the main steam pressure signal 7 and the main steam temperature signal 8 and calculates the enthalpy of the main steam; 28 is the main steam flow rate after At time; Taking the predicted value 24 of the steam flow rate and the enthalpy 25 of the main steam, the steam temperature θxs (t+At
) is shown.

The prediction in the flow rate prediction device 26 is also performed by the following equation.

f s (t + A t ) - f 5 (t) + history plow r
At -(2)t On the other hand, the enthalpy calculation device 27 takes in the main steam pressure signal 7 and the main steam temperature signal 8, and calculates the main steam enthalpy H5 using a steam value representing a function of the main steam temperature and enthalpy.
(t) (25) is calculated.

The main steam enthalpy Hs(t) calculated here is taken into the estimation device 28 together with the main steam flow rate fs(24).

The estimating device 28 estimates the steam temperature θ1s (t+At) after the first stage of the turbine, which is set after 4 hours, using the input Hs(t)i= and fs.

This estimation is uniquely performed by using the relationship between enthalpy and the steam temperature after the first stage of the turbine.

The steam temperature signal 14 obtained here is the temperature prediction device 1
5 and serves as an input to the heat transfer coefficient calculation device 20.

The temperature prediction device 15 takes in the output signal 14 of the steam temperature estimation device 13, the output signal 10 of the casing outside air temperature detector 4, and the output signals 21 and 22 of the heat transfer coefficient calculation device 20, and calculates the casing inner wall temperature θm1 and the casing outer wall temperature. Predictively calculate the temperature θmn.

An example of a specific method for this calculation will be shown using drawings and mathematical formulas.

FIG. 2 is a diagram showing heat transfer characteristics in the first stage of the turbine.

Using this diagram, the casing is divided into n equal parts in the thickness direction from the inner wall, and the dynamic characteristics of the casing temperature are determined.

If the temperature characteristics of the divided block 1 are considered as a lumped constant system, the following relationship holds true.

2・θml+θ4 i+1) ...(5) however, θ 1 1 i; flock i 1 to i amount of heat transfer A; heat transfer area λ ; thermal conductivity d; Thickness of casing θmi; metal temperature of block i M; Casing weight C: Specific heat of casing In addition, the heat transfer coefficient from steam to the casing is αSm.

When the heat transfer coefficient from the casing to the outside air is αma, the amount of heat transferred from the steam to the casing Qsm and the amount of heat transferred from the casing to the outside air Qma are calculated as shown in the following equation.

QSm-A・αSm・(θIS-θml)...
・(6) Qma=A-ctma-(θmn-θa)
-(7) However, θ1s is the output of the steam temperature estimating device 13, and is the estimated value of the steam temperature after the first stage of the turbine casing.

θm1; Turbine casing inner wall temperature θmn; Turbine casing outer wall temperature θa; Turbine casing outside air temperature Note that both α5ITI and αma described above are calculated by the heat transfer coefficient calculation device 20 and output as a signal 2L22.

Using equations (6) and (7), the turbine casing inner wall temperature θm I J=? The dynamic characteristics of the turbine casing outer wall temperature θmn and the turbine casing outer wall temperature θmn are expressed by the following equation.

Therefore, depending on the change in θ1s1 θa, (5), (8
) and (9), it is possible to predict 0m1 and θmn.

Next, details of the heat transfer coefficient calculation device 20 that calculates the heat transfer coefficient used for the above prediction will be explained.

This device operates under relatively low steam conditions.

In a steady state, the left sides of equations (5), (8), and (9) all become O.

Therefore, the casing conductivity is hardly affected by changes in steam conditions, and if this change is ignored, the respective thermal conductivities αsm and αma become as follows.

FIG. 7 shows a specific example of the processing of the heat transfer coefficient calculation device 20.

In this figure, 201 to 203 are adders, 204 and 205 are dividers, and 206 and 207 are coefficient units.

The heat transfer coefficients αsm and αms are θISsθm1.0mn1
It is obtained from θa as shown in the figure.

Here, θ1a is the output signal 14 of the steam temperature estimation device 13
, θml is the output signal 11 of the casing inner wall temperature detector 5, θmn is the output signal 12 of the casing outer wall temperature detector 6, and θa is the output signal 10 of the casing outside air temperature detector 4.

This heat transfer coefficient may be set externally.

The turbine casing inner and outer wall temperature prediction values 17 and 16 predicted by the temperature prediction device 15 are taken into the casing thermal stress calculation device 18, where the thermal stresses σ1. σ2 is calculated.

This calculation is as shown in the following equation. However, tension □ 20m i / n 1=1 (14) E; Young's modulus β; coefficient of linear expansion of the turbine casing; Poisson's ratio In this way, the thermal stress of the turbine casing after a certain time is determined, Operating conditions are limited by checking whether the thermal stress exceeds a predetermined value.

As explained in detail above, the present invention can predict how much thermal stress will change depending on the temperature, pressure, and flow rate of the main steam, and the temperature of the inner and outer walls of the turbine casing, thereby ensuring efficient and safe operation. It is possible to do this.

[Brief Description of the Drawings] Figure 1 is a block diagram showing one embodiment of the present invention, Figure 2 is a diagram showing heat transfer characteristics in the first stage of the turbine, and Figure 3 is the relationship between thermal stress and strain. Figure 4 is a more detailed block diagram of the steam temperature estimating device that estimates the steam temperature after the first stage of the turbine, Figure 5 is a sectional view of the turbine showing the structure of the turbine, and Figure 6 is the turbine FIG. 7, which is a diagram showing temporal changes in casing thermal stress, shows a detailed block diagram of a heat transfer coefficient calculation device. 1... Main steam pressure detector, 2... Main steam temperature detector, 3... Main steam flow rate detector, 4... Casing outside air temperature detector, 5... Casing inner wall temperature detector, 6.
...Casing outer wall temperature detector, 13... Steam temperature estimation device, 15... Temperature change prediction device, 18... Thermal stress calculation device, 20... Heat transfer coefficient calculation device, 26...
Flow rate prediction device, 27...Enthalpy calculation device, 28
... Estimation device, 201-203 ... Adder, 204
~205...Divider, 206~207...Coefficient unit.

Claims (1)

[Scope of utility model registration request] A main steam temperature detector for detecting the main steam temperature of the turbine, a main steam pressure detector for detecting the main steam pressure, and a main steam flow rate detector for detecting the main steam flow rate to monitor thermal stress in the casing of the turbine. The apparatus includes an outside air temperature detector that detects the outside air temperature of the turbine casing, and receives output signals from the main steam temperature detector, the main steam pressure detector, and the main steam flow rate detector, and detects the output signals after the first stage of the turbine. a steam temperature estimating device for estimating the steam temperature of the casing; a heat transfer coefficient calculation device that calculates a heat transfer coefficient from the metal to the outside air and a heat transfer coefficient from the metal to the outside air; a set of heat transfer coefficient signals calculated by the heat transfer coefficient calculation device and the outside air temperature of the casing; a casing inner and outer wall temperature change prediction device that predicts the inner and outer wall temperatures of the casing after a predetermined time using a detection signal as an input signal; 1. A thermal stress monitoring device for a turbine casing, comprising: a thermal stress calculation device for calculating thermal stress; and monitoring whether the calculated thermal stress of the casing exceeds a predetermined value.