JPS62108903A - Boiler-stress monitor controller - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a stress monitoring and control device for a boiler, and in particular, stress monitoring of a boiler plant operating under intermediate load, which requires frequent startup/shutdown and load change operation. The present invention relates to a boiler stress monitoring and control device suitable for control.

[Background of the invention]

When operating a boiler plant, especially during startup/stopping and load changes, apply to thick pressure-resistant parts such as secondary superheater outlet headers, especially inner nozzle corners.

Thermal stress occurs due to the difference between the internal fluid temperature and the metal temperature, and this is the main cause of fatigue life consumption.

Furthermore, during rated operation, creep life consumption becomes significant due to the principal stress that is the sum of the thermal stress and the internal pressure stress due to the pressure of the internal fluid.

Therefore, in order to ensure safe operation of a boiler plant, it is necessary to suppress the thermal stress or principal stress that causes the above-mentioned life consumption to prevent excessive life consumption from occurring.

Conventionally, methods for monitoring and controlling thermal stress or principal stress include:
The current value of thermal stress or principal stress is estimated based on the measured values such as metal temperature and temperature, pressure, flow rate of the internal fluid at the evaluation point, and if it exceeds the alarm value.

The operator manually and empirically reduces the temperature increase rate during startup, and during load operation, reduces the load change rate and load change noise to suppress thermal stress.

However, with this method, the amount of fuel and water supply is adjusted after detecting that the thermal stress exceeds the limit value.
There is a delay in operation. In other words, there is a time delay of on the order of one minute until the difference between the average temperature of the metal and the inner surface temperature decreases and the thermal stress decreases, and as a result, the thermal stress may exceed the limit value. There is.

On the other hand, the thermal stress limit value is used as a constant when designing the boiler plant, and is set at the start of plant operation, assuming the start-stop operation pattern and the number of times each pattern will occur over the plant's service life.

However, in reality, the operating pattern of the plant and the number of times each pattern is used differs from the planned value, so that the cumulative life consumption, in other words, the remaining life, deviates from the planned value. As a result, if the originally planned service life is assumed to be 5, there will be situations where the conditions for limiting thermal stress are either too strict or too loose.

In the former case, this means that the start-up or load response of the plant is being unnecessarily restricted, and in the latter case, it means that the plant is operating at a shorter service life than planned. ing.

In addition, multiple different points were set as evaluation points for thermal stress.
All of these need to be monitored, and any of them (
In this case as well, it is most desirable to bring the temperature rise rate and load closer to the target values in order to keep the stress below the limit value, but conventionally, boiler plant operations have not been controlled at all based on this perspective. It wasn't taken into account.

[Object of the Invention] The object of the present invention is to eliminate the above-mentioned conventional drawbacks, suppress the thermal stress at the evaluation point of the boiler plant within a limit commensurate with the remaining life, and moreover, provide a safe and quick boiler start/stop system. An object of the present invention is to provide a boiler thermal stress monitoring and control device that enables load operation.

[Summary of the invention]

In order to achieve the above object, the present invention monitors and controls stress at evaluation points set at desired locations in piping of a boiler plant.

Its configuration features include a means for calculating the current value of the internal fluid flow rate at the evaluation point, a means for calculating the metal temperature distribution at the evaluation point based on the calculated value of the internal fluid flow rate, and a means for calculating the metal temperature distribution. a stress calculation unit comprising means for calculating thermal stress based on the value, means for calculating internal pressure stress from the pressure of internal fluid, and means for calculating principal stress from the thermal stress and internal pressure stress; A means for calculating the remaining life of an evaluation point from the principal stress obtained by the calculation section, a means for calculating a new stress limit value from the calculated remaining life value, and a stress for predicting the principal stress of the evaluation point at a future point in time. a prediction means, a main steam temperature prediction means for predicting the main steam temperature at the same time in the future, a load prediction means for predicting the load at the same time in the future, a deviation of the stress prediction value from the stress limit value, and a main steam temperature prediction means for predicting the main steam temperature at the same time in the future; At least one of the deviation of the temperature predicted value from the target value and the deviation of the load predicted value from the load command is maintained within a tolerance value, and the evaluation value of the remaining deviation (for example, the sum of the squares of the deviations)
The present invention also includes means for setting each operation amount so as to minimize the amount of operation.

[Embodiments of the invention]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before showing embodiments of the present invention, an overview of the main parts of an oil-fired constant pressure once-through boiler plant to which the present invention is applied will be described below with reference to FIGS. 2 and 4.

In FIG. 4, fuel is supplied to a burner 101 with its flow rate controlled by a fuel flow control valve 100. The combustion air is
The forced draft fan 102 controls the flow rate with a damper 103 and sends it to the burner 101 .

On the other hand, the water supply is pressurized by the water supply pump 104, and the water supply flow t
The flow rate is controlled by the f4 mode valve 105 and the water is supplied to the boiler 200.

As can be seen from Figure 2, the boiler plant operates in two stages: start-up bypass operation from ignition of burner 101 to full opening of superheater stop valve 6, and side-flow operation from then on to load operation and stop operation. Divided into modes.

First, startup bypass operation will be explained. As shown in FIG. 4, water supplied from the water supply pump 104 via the control valve 105 is preheated by the economizer 201 of the boiler 200 and heated by the water wall 202.

The heating fluid then leaks through the primary superheater bypass valve 1,
and from the primary superheater 203 to the secondary superheating addition 1 (Ipass valve 2
through the respective flash tanks 206,
Meanwhile, the steam is further vented to the secondary superheater 5204 through the superheater vent valve 5.

The steam superheated in the secondary superheater 204 passes through the turbine bypass valve 7 to the flash tank 206 and the condenser 4.
00 to warm the main steam pipe.

Next, when the pressure in the flash tank 206 rises to a predetermined value, the main blocking valve bypass valve 9 is opened and the turbine 3
10,330, and the turbine speed is increased. The turbines 310 and 330 have a rated rotational speed (3600 r in this example).
pm), synchronously join the tank and take the initial load with flood tank steam.

-Next week, the enthalpy of the outlet fluid of the heater 203 is
The primary superheater outlet temperature is controlled to a specified level by controlling the opening degree of the secondary superheater bypass valve 2 so as to be equal to the enthalpy of the flash tank steam.

When the specified load is reached after the initial load of the turbine is added, the control of the main stop valve bypass valve 9 is switched to the control of the main stop valve 8 by opening the main stop valve 8.

After that, when the target load exceeds the specified value, the superheater pressure reducing valve 3 is opened, and when the population pressure of the secondary superheater 204 becomes higher than the operating pressure of the furanoyu tank, the reverse pressure on the superheater ventilation system is opened. A stop valve (installed downstream of the superheater vent valve 5) switches the steam source to the primary superheater 203.

In parallel with this, the secondary superheater bypass valve 2 is automatically closed, while the superheater vent valve 5 is closed when the population pressure of the superheater stop valve 6 exceeds a specified value.

In the next step, the superheater pressure reducing valve 3 is opened in response to the load request signal, and the % load is increased from the haiku load to about 20% load. When the load reaches 20%, the superheater stop valve 6 is gradually opened in stages until the superheater pressure reducing valve 3 is fully opened, and after the valve 3 is fully opened, it is opened continuously.

- 10,000, the primary superheater bypass valve 1 is closed in response to the above operation, and is fully closed when the load is about 25%.

As shown above, until the superheater stop valve 6 is fully opened,
As shown in Fig. 2, the startup bypass operation and the mass flow operation (normal operation) are the operation phase after the superheater stop valve 6 is fully opened, and the load is , is regulated by the turbine control valve 10 until plant shutdown. The turbines 310, 330.

It rotates due to the adiabatic expansion of superheated steam and generates electricity in the first power generating unit SOO.
In particular, the internal nozzle corner NC is a part where significant stress is applied throughout the entire operating range of the plant, including startup, loading, and stopping, because the metal is thick and the structure is complex. This is a typical part of stress evaluation points under severe conditions.

In addition to this, there is also a reheater outlet header header section 208.

Although it is thinner than the above, its interior is exposed to higher-temperature steam, and significant leap stress acts on the inner nozzle corner, making it an important part as a stress evaluation point.

In addition, in variable voltage operation boiler plants, there are also brackish water separators and brackish water 11+! The inner nozzle corner of the W tank is an important evaluation point.

In order to operate such a thermal power plant smoothly in accordance with load request commands, it is necessary to appropriately control each control valve, damper, etc. FIG. 3 shows a schematic diagram of a single thermal power plant automatic control system that has been used conventionally.

An outline of its functional operation will be explained below with reference to FIG.

First, the load (output of the generator 500) request signal 60G to the thermal power plant is sent to the load change rate limiter 601 by the setting device 6.
02, the load change rate is limited to within a preset load change rate, and is added to the main steam pressure correction bias adder 603.

The output signal of the load change rate limiter 601 also serves as a demand signal to the governor control 604.

MW 605 (starter output) is set to the specified value.

Controlling the turbine control valve 10 - A main steam pressure correction bias is created by the subtractor 60B and the main steam pressure control 609 so that the main steam pressure 606 becomes equal to the set value 607, and the adder 603 Add this to the signal.

Create a boiler manual command 〇The boiler input command is converted into a command signal by the water supply program 610 to supply water ff, 1i commensurate with the boiler input, and is guided to the water supply control 612 as a set value of the water supply flow rate 611,
It is used for controlling the water supply flow TA14 node valve 105.

The boiler input command is also converted by a fuel program 613 into a fuel quantity command signal commensurate with the load.

Deviation between main steam temperature 614 and its setting @615 (reduction 1i
ii615A), the main steam temperature correction bias signal created by the main steam temperature control 616 and the fuel amount command signal are added by the VT device 617.

It is given to the fuel side control 619 as a set value (fuel amount command) for the fuel flow 1i 618. Then, the fuel flow control valve lOO is controlled by the control output.

The above fuel quantity directive also applies. As a control signal commensurate with the deviation of excess exhaust gas 0.620 from the set value 621 (obtained by the subtracter 622), the 02 correction bias signal created by the 02 correction control 623 is added by the adder 624, and the air flow rate command signal is becomes.

In the air setting @625, the forced draft rock damper 103 is controlled so that the air flow t626 becomes equal to the air flow command signal.

The above is an overview of the automatic control system for thermal power plants.

FIG. 1 is a block diagram showing the overall configuration of an embodiment in which the present invention is applied to the boiler plant control system shown in FIG. In Fig. 2, the same or equivalent parts as in Fig. 3 are indicated by the same symbols.In this example, the case where the stress evaluation point is the nozzle corner NC on the inner surface of the header conduit at the beginning of the secondary overheating will be explained. .

What differs from the conventional system in FIG. 1 is that the following functional blocks have been added.

(1) Stress calculation function Bronc 1000 (2) Remaining life calculation block 1100 (3) Stress limit (direct calculation function block 1200) (4) Main steam temperature prediction function block 2000 (5) Stress prediction function block 210
0 (6) Load prediction function block 3000 (7) Control evaluation function block 4000 (8) Optimal operation amount search function block 500° (9) Optimal operation amount output function block 60000 @ Priority hook selection mechanization block 7000 Stress correction The functional block 1000 is a part that calculates the current value of the principal stress in consideration of both the thermal stress and the internal pressure stress at the stress evaluation point.

The remaining life calculation function block 1100 is a part that calculates the cumulative life consumption rate based on the current principal stress value calculated above, and calculates the remaining life from this.

The stress limit value calculation function block 1200 is a part that recalculates the stress limit value based on the above-mentioned remaining life calculation value.

The main steam temperature prediction function block 2000 is a part that predicts the main steam temperature after a specified time.

The stress prediction function block 2100 is based on the main steam temperature prediction I.
l! This is a part that predicts the stress after the specified time based on this.

The load prediction function block 3000 is a part that predicts the load level after a specified time.

The control evaluation function block 4000 calculates the deviation (deviation 1) between the predicted steam OA degree and the set 1st shift, the load predicted value, and This is a part for determining and evaluating whether either one or both of the deviation (deviation 2) from the target signal (deviation 2) is at least 1.

If the determination result is not good, the optimal operation lid search function block 5ooo+c searches for an optimal operation lid that reduces the above-mentioned deviation.

Based on this, the main steam temperature prediction function block 200
0, the stress prediction function block 2100, and the load prediction function block 3000 recalculate each predicted value.

The above search is repeated until the determination condition is satisfied in the controller side functional block 4000.

If the determination condition is satisfied, the manipulated variable at that time is output as the optimal value via the optimal manipulated variable output function block 6000.

Each functional block will be explained in detail below.

FIG. 5 shows a detailed functional diagram of the % stress calculation function block 1000. This gIM example calculates the metal temperature distribution at the stress evaluation point between the steady temperature distribution calculation model and the irregular temperature distribution calculation model according to the flow rate and pressure of the internal fluid as shown in Figure 2. This is done with high precision by switching.

2. In this case, the flow rate calculation of the internal fluid is also divided into synchronous combined flow (flow rate li calculation 1) and combined flow rate calculation 1 (flow rate calculation 2), and is calculated using a method such as that described in 1985-53856, for example.

Hereinafter, a specific example of the stress calculation function block 1000 will be described in detail using FIGS. 2, 4, and 5.

As previously mentioned, in FIG.
Stress is generated in the inner nozzle corner NC of the Node Lohenda pipe header 205 (hereinafter referred to as evaluation point -J-ru) even after the blunt is stopped, so stress is generated not only from plant startup to shutdown, but also continues even after shutdown. stress should be monitored.

In that case, the metal temperature distribution at evaluation point 205 follows unsteady temperature distribution characteristics when internal fluid is flowing in the main steam pipe ZOG and water pipe 22, but follows steady temperature distribution characteristics when internal fluid is not flowing. Follow.

Therefore, in order to accurately calculate the metal temperature distribution, it is necessary to appropriately switch the calculation model depending on the state of the internal fluid.

However, the fluid flow rate inside the evaluation point 205 is
It cannot be measured directly. Accordingly, in the present invention, the turbine bypass valve 7 is
It is calculated from the opening degree of , the differential pressure between the outlet fluid pressure of the secondary superheating 1vF 204 and the internal pressure of the flash tank 206, and after synchronous addition, it is calculated from the turbine load.

As explained above, the secondary superheater outlet header, that is, the evaluation point 205, is in the condition after the boiler is turned on until the superheater vent valve 5 and the turbine bypass valve 7 are opened.

No internal fluid flows. Therefore, the metal temperature distribution at the evaluation point 205 is calculated according to the steady metal temperature distribution calculation model.

On the other hand, when both valves 5 and 7 are open, the superheater stop valve 6
Until the is closed, the evaluation score is 205.

Since the internal fluid flows, the metal temperature distribution is calculated according to an unsteady metal temperature distribution IT calculation model.

In addition, in the unsteady metal temperature distribution calculation, in order to calculate the amount of heat transfer from the internal fluid to the metal, it is necessary to calculate the flow rate of the internal fluid.

As shown in Fig. 2, until synchronous joining, the opening degree of the turbine bypass valve 7, the opening/closing of the upper seat drain valve 12 in front of the main blocking valve, the opening degree of the main steam pipe drain valve 11, and the initial load are controlled. The low pressure and medium φ high pressure Tahin 310, 330 are used as a human power signal for the Tahin rotation speed R during the speed up process until the
Calculate the flow rate of the internal fluid (flow rate calculation 1 in Figure 2).

On the other hand, after joining, the turbine load MW (or generation 4 (4s
The flow rate is calculated using the output of OO) as a manual signal (flow rate calculation 2 in FIG. 2).

Next, the operation of each part in FIG. 5 will be explained.

First, when the device starts operating, the metal temperature distribution initial value calculation unit 1001 calculates the internal fluid temperature measurement value Tf and the external metal temperature measurement value Tyu at the evaluation point 205. is used to calculate the initial value of the metal temperature distribution at the evaluation point 205 based on a steady metal temperature distribution calculation model (described in detail later).

Next, when the burner is ignited and the plant is started, the burner ignition signal is detected, and the model switching condition determination unit 1002
is operated to continuously monitor the internal fluid pressure measurement value p and flow rate calculation value G at the evaluation point ◇And the superheater ventilation ff5
The internal fluid pressure measurement value P,
The determination is made based on whether both the flow rate calculation value G and the flow rate calculation value G are equal to or greater than a specified value.

That is, if at least one of the calculated flow rate G and the measured value Pf is less than the specified value, it is determined that the internal fluid is not flowing, and the steady metal temperature distribution calculation model 1003 is operated. Then, the selector switch (A) l 004 is switched to a@, that is, the steady metal temperature distribution calculation model side, and the calculation result is stored in the metal temperature distribution storage unit 1006.

When both of the elbow measurement values are equal to or greater than the specified value, the unsteady metal temperature distribution calculation model 1005 is operated. Then, the selector switch (A) 1004 is switched to the b side, that is, the unsteady metal temperature distribution calculation model Ioos side, and the metal temperature distribution storage section 1006 stores the calculation results.

In unsteady metal @ degree distribution calculation, first (this).

As mentioned above, due to the different calculation methods before and after the same haiku,
Internal fluid flow rate calculation unit 1007 based on various process amounts Da
The thermal stress calculation unit 1008 calculates the heat transfer coefficient from the internal fluid to the metal using the calculated internal fluid flow rate G and the measured values Tf and Ff of the temperature and pressure of the internal fluid.

Next, based on the boundary condition of the inner surface metal obtained by substituting the above heat transfer coefficient into equation (4) described later, the changeover switch (B) 1009 is switched to bIltll to obtain the metal temperature distribution storage section 1006. Using the contents (calculation results by steady metal temperature distribution calculation model 1003) as the initial temperature distribution, unsteady metal temperature distribution calculation model 1
005 to calculate the metal temperature distribution.

Further, the above calculation result is corrected using the outer surface metal temperature measurement value TMO, and the correction result is transferred to the metal temperature distribution storage unit 10 via human power of the switch (person) 1004 b 111+1.
Store in 06.

When the plant is stopped, the superheater stop valve 6 in FIG. 4 is closed and the internal fluid at the evaluation point 205 is reduced.

When the model switching condition determination unit 1002 detects that at least one of the flow rate and pressure of the internal fluid has become less than the specified value, contrary to the above, the metal temperature distribution calculation model is changed to unsteady metal temperature distribution calculation. The model 1005 is switched to the steady metal temperature distribution calculation model 1003.

As the initial value of the metal temperature distribution at this time, the contents of the metal temperature distribution storage section 1006 are set to the changeover switch (B) 10.
Switch 09 to a tjllll and use it for one history. Furthermore, the changeover switch (A) 1004 is also a I! ! I
The calculation result of the steady metal temperature distribution calculation model 1003 is stored in the metal temperature distribution storage unit 1006.

The thermal stress is calculated by the thermal stress calculation unit 1010 based on the contents of the metal temperature distribution storage unit 1006 calculated and stored as described above. On the other hand, the internal pressure stress is determined by the internal pressure stress calculation unit 10 based on the pressure measurement 1 of the internal fluid.
Calculate with 11.

The principal stress calculation unit 1012 calculates the principal stress from the calculated values of the thermal stress and internal pressure stress obtained as described above.

Next, practical examples of metal temperature distribution calculation and stress calculation will be described in more detail.

First, the metal temperature distribution initial value needle 3, which uses the same calculation formula, is part 1001 and the steady metal temperature calculation model 1003.
Explaining the secondary superheater outlet header, that is, the evaluation point 205,
It is assumed that it is an infinite cylinder with the dimensions of each part as shown in Figure 21, and that no temperature distribution occurs in the axial direction.In other words, it is assumed that the temperature distribution in the radial direction is the same at any position in the axial direction. do.

As shown in FIG. 22, the metal temperature T at the i-th division point among the eight radial division points at the FF value point 205
1 (i is O-N) using the steady temperature distribution calculation formula of the following equation (1) ■T;ktnr・+B
--- (1) However.

Here, r: Distance from the center of the cylinder a: Cylinder inner radius b = Cylinder outer radius TM□: External metal temperature measurement value Tf: Internal fluid temperature measurement value Next, temperature distribution 1 based on the unsteady metal temperature calculation model The formula will be explained.

Similarly to the above, assuming that the evaluation point 205 is an infinite cylinder and that no temperature distribution occurs in the axial direction, the unsteady metal temperature distribution in the radial direction is as follows (3) to (5).
O is calculated by the formula where:

λ: Thermal conductivity of the metal h: Heat transfer coefficient from the internal fluid to the metal T: Calculated temperature of the internal metal It is equal to the product of the temperature gradient on the inner thorny surface of the metal and the thermal conductivity of the metal, and the above equation (5) shows that the outer surface of the metal is in a thermal equilibrium state. It is.

The above equations (3) to (5) are calculated using a digital computer (not shown).
In order to calculate this, the evaluation point metal is divided into N parts in the radial direction, as in the case of steady temperature distribution calculation.

In order to obtain the metal temperature T, (i) at each division point, it is necessary to convert into the differential format shown in FIG. 23, where the division unit length is Δr and the temperature distribution calculation cycle is Δt.

In FIG. 23, 60 is a table that stores data before conversion, and 61 is a conversion unit that converts data into a differential format. Further, 62 is a table that stores the data after conversion.

The data stored in 60 is converted by the conversion unit 61 as shown in equation (6) below. i.e. here.

A.

J However, Tf(i) : Temperature T(j) of internal fluid at time j - Temperature a of metal dividing point i at time j, : Heat dissipation rate (time j
) λ: Thermal conductivity (value at time j) h: Heat transfer coefficient (value at time j) Δr: Unit length of cylindrical division of metal Next, the heat transfer coefficient is the heat transfer coefficient calculation unit 1008 is calculated based on the following equations (7) to (lO).

(See page 89 of "Heat Transfer Engineering", co-authored by Naoji Tomoe, Morikita Publishing Co., Ltd.).

w = G・v/9
・・・・・・・・・(7) “ 2 s= −3・・・・・・・・・(8) Here.

W: Steam flow rate G: Internal fluid flow rate V: Internal fluid specific volume (function of temperature T and pressure P) S: Channel cross-sectional area FL: Raynozzle number ν: Kinematic viscosity coefficient (function of temperature T and pressure P) )K: Thermal conductivity (function of temperature Tf and pressure P) P Nibrandtl number (function of temperature T1 and pressure P) The internal fluid flow rate G in the above equation (7) is determined by the internal fluid flow rate calculation unit 1007 as follows: It is calculated using the following equation (11).

Here, G1: Flow rate of the turbine bypass valve 7 G2: Flow rate of the upper seat drain square 12 in front of the main blocking valve G8 = Flow rate of the main steam pipe drain valve 11 012 Steam flow rate of the 1st stage reheater 207 Above G,, G2. G can be determined from a general flow rate calculation formula 1 based on the differential pressure characteristics of each valve.

In other words, the flow jtG+ is 2? :Using the pressure of Ka heat release steam pressure and furanone 1-tack finger pressure.

Also, the flow rate G2. The peaks can each be calculated based on valve characteristics such as the cross-sectional area of each valve passage using the differential pressure between the secondary superheated crystal outlet steam pressure and the condenser pressure.

On the other hand, G1□ can be calculated by multiplying the maximum fluidity before the haiku by the ratio to the rated rotational speed of the turbine.

In addition, the coefficient 1/4 in the above formula is a coefficient for proportionally dividing (!A'II-) the flow rate of each header/rudder from the total steam amount for a plant where two live steam snows 20 are installed. be.

Next, the circular fluid flow rate G after joining is determined by storing the main steam flow rate for the turbine load in advance as a table.
Based on this data, calculations can be made using supplementary calculations.

According to the above procedure, the results calculated using the unsteady metal temperature distribution calculation formula are as follows: (a) The metal inner surface heat transfer coefficient matches Equation 5 (10) using the outer metal temperature measurement constant TMO.

moreover, b) Make the external metal temperature match the measured value number.

Corrected. In other words, according to the size of the difference between the calculated inner metal temperature value T and the calculated outer metal temperature value 1v7LTH, (111To-TMl≧0.5℃ (the temperature difference is large), using the idea of proportional distribution, here.

To-TN h・Δr However, T: Calculated value of metal temperature at dividing point 1 before correction T, ′: Calculated value of metal temperature at dividing point i after correction.

(When 211To-TNI<0.5℃ (temperature difference is small), use the idea of parallel movement as shown in Figure 24,
r,' = T, -(TN-T,.)
. . . - (The metal temperature distribution is corrected and calculated using the formula 15i.

Next, the thermal stress calculation section 1010 will be explained. Here, using the result (metal temperature distribution) calculated and corrected by the above method and stored in the metal temperature distribution storage unit 1006, the evaluation point 2 is calculated using the linear equations (16) and (17).
Calculate the thermal stress of the general part (parts other than the nozzle corner part NC) of 05.

here.

σθ, Internal thermal stress in two local directions σzt ” Axial internal thermal stress T: Metal volume average temperature ve'E: Young's modulus α: Coefficient of linear expansion ν: Poisson's ratio T1m Memorized value of metal temperature at bisection point i Tom: Internal surface Memorized value of metal temperature T: Memorized value of external metal temperature 8m Since Young's modulus E and Iwa expansion coefficient α in the above equation depend on the metal volume average temperature, they are determined by interpolation calculation from a constant table using this as a parameter. is desirable.

Next, the internal pressure stress calculation section will be explained. Here, based on the pressure measurement value of the internal fluid, the internal pressure stress is calculated as follows (18
) (19).

a--p, ・・・・・・
...U delivery 'p Here, σ1.Internal pressure stress in two radial directions σ, :Internal pressure core strength town :Internal pressure Di=Pipe inner diameter t :Based on thermal stress and internal pressure stress calculated above plate thickness .

The principal stress calculation unit 1012 considers the stress concentration on the inner nozzle corner part NC with respect to the general part of the evaluation point 205,
The principal stress at the inner nozzle corner is calculated using the following equations (20), (21), and (22).

a ″ゞ °0 ・・・・・・・・・
(To) r rp rp σα = θ1 − σθ, + θp・σp ・・・・・・
...Shυσ2= Kzt@σit+KZp・σp
・・・・・・・・・C21 Here, K: 2. for the circumferential thermal stress concentration coefficient. : 44I11 direction thermal stress concentration coefficient K : radial direction internal pressure stress concentration coefficient p Kθ, : circumferential direction internal pressure stress concentration coefficient 2. : ++a+ direction internal pressure stress concentration coefficient σr Bilateral radial direction principal stress σθ : Circumferential direction principal stress σ : Axial direction principal stress Note that in the above example, the calculated value of the internal fluid flow wrinkles and the actual measured value of the internal fluid pressure and the respective Although the metal temperature distribution calculation model was switched between steady state and unsteady state based on the comparison result with the reference value, the above switching may be performed depending on the open/closed state of the superheater stop valve 6.

Next, a specific example of the remaining life #n functional block 1100 will be described. FIG. 6 shows the remaining life calculation flow. The calculation method will be explained below along this flow.

First, the procedure for calculating fatigue life will be explained.

First, in step 1101, the above equations (20) to (2
2), the inner principal stress difference (9, ~S,) is calculated using the following formula (
23) to (25).

9, = Lee σz ”'”'
”' Trouble 9, = σ − σ
......Q S, =σ, -σθ
(251) Next, in step 1102, the stress type width is determined for each principal stress difference S, ~S, calculated by the above equations (23) to (25), and this Calculate the life consumption from the design fatigue diagram based on .

For example, if the principal stress difference S shows a temporal variation as shown in FIG. 7, then the total stress amplitude 2. ．． 2
2 is required. Similarly, if you lie on C2, S3■■Rinho, z, l z2 + "" + Zl
+ z2+ ”' can be found respectively.

In other words, from among the many minimum values and maximum values that appear on each principal stress difference change curve, first pick up the pair of minimum and maximum values that have the largest amplitude, and then do the same for the remaining minimum and maximum values. and so on.

8I
・)nu in S, (If you get stuck, Zl + Z2 +-・(Zl
> Z2-) II ml S, for Zl, Z2, ・-(Zl
>Z2 >-).

+1 Next, to the total amplitude of these stresses ~Z, (i=1+...
n), as shown in the following equation (26), the maximum value is sequentially selected to obtain the stress oscillation @H8,1(2, . . . ).

In step 1103, the allowable number of repetitions Nl + N, I, etc. is determined from the design fatigue diagram as shown in FIG. From the reciprocal of the number of repetitions N, I N2!..., step 1104 J, the following formula (27) is obtained.
Calculate the fatigue life consumption amount φf per cycle shown in

Next, we will explain the calculation procedure for creep damage life consumption.〇The temporal f:dynamics of the principal stress difference at the time of starting the boiler is expressed in the θ direction (
Fig. 9 schematically shows the secondary heating (circumferential direction) for the 1-stage header section, regardless of whether it is a cold start or a hot start. In other words, it changes to the compression side once after startup.

Then, as the pressure increases, it changes to the tensile side, and the initial stress σ,
After slowing down, it gradually eases.

The creep damage life is determined by storing the relaxation curve for each initial stress σ in a computer and calculating it according to the value of the initial stress σ□, as shown in Figure ioJ. Select the sum curve a, and calculate the stress σ(T) and time width Δ at the elapsed time T from the relaxation start point S of the stress relaxation curve shown in Figure 11(,).
Find T.

Then, using this σ(T), the rupture time tr(σ(T)
) is determined, and the creep damage during the above ΔT is determined as Δt/lr.

In step 1106 of FIG. 6, s'fJtJ notation (2
The stress σθ in the inner circumferential direction obtained in 1) is in the compression direction (i.e.

(negative side in FIG. 9), the process moves to step 1107, and it is checked whether the equivalent stress σ calculated in step 1105 and shown in the following equation (28) is the maximum value so far.

If it is the maximum, this and the metal average temperature at this time are stored in the memory.

If the stress σθ in the inner circumferential direction changes to the tensile direction (i.e., upward in FIG. 9), the metal average temperature enters the creep region (for example, 510° C. for the secondary superheater outlet header) in step 1108. Determine whether or not.

When the creep region is entered, a creep holding time counter is started for counting the elapsed relaxation time T after the initial stress of the stress relaxation curve. Then, in step 1109, the initial stress σ is determined.

Calculate.

FIG. 12 shows a detailed flowchart of the initial stress calculation in step l l O'9 of FIG.

The procedure for calculating the initial stress will be explained below using this flowchart and FIGS. 13 to 417.

In the example of the stress strain diagram shown in Fig. 13, when the initial point is 0 point, the maximum equivalent stress S on the compressive side occurs, the value exceeds the yield stress Y1 on the compressive side at the temperature at that time, and then the stress It shows the path where σ turned to the tensile direction and reached the maximum value σ,
σ is the initial stress, and its straight line is expressed by the following equation (29).

Further, when the vJ period stress exceeds the yield stress Y at the rated temperature, it becomes as shown in the figure σ,' and is expressed by the following equation (3o).

P.

Here, E: Young's modulus at rated temperature, P S
Strong high temperature tensile properties at rated temperature.

It is.

First, in step 1109A, the yield stress Y on the compression side is determined using the stress strain diagram shown in FIG.

High temperature tensile properties at the maximum stress generation temperature on the compression side.

The Young's modulus E at the temperature at which the maximum equivalent stress on the compression side occurs is calculated.

In the next step 1109B, as shown in FIG.
The compression side maximum stress SB is determined from the S stress σ,2 and the compression side maximum equivalent stress σ2 using the following equation (31).

9B = 90-σP2+σ, scream...
・-C3υThis maximum stress on the compression side 9B and the yield stress -Y1 are compared in step 1109C, and 5IB(-Y,
If so, proceed to step 1109D, otherwise proceed to step 1109H.

In step 1109D, the tensile side equivalent stress of three people is calculated by the following formula (3
Find as in 2).

9A=('3B+Yl)(--1)+SO・-・kawa・-
Compare C3 Riko's tensile side equivalent stress with the yield stress Y at the rated temperature in step 1109E, and 9A>Y.

If so, the process moves to step 1109F; otherwise, the process moves to step 1109G.

When proceeding to step 11091;', that is, when yield occurs on both the compression side and the tension side, the initial stress σA2 is calculated using the following equation (33) as shown in FIG.

The transition to S-7-cup 1109 () occurs when the boiler is stopped and restarted as shown in Fig. 14, when the stress is relaxed and has decreased to SO, and yields on the compression side. Find the initial stress σ when

In step 1109H, the tensile side equivalent stress s.

and the yield stress Y3 at the rated temperature, and if 90≦Y3, proceed to step 1I09I, and! 90>Y
.

In this case, the process moves to step 1109J.

When proceeding to step 1109I, that is, when there is no yield on either the compression side or the tension side as shown in FIG.
The initial stress is the same as SO, so the initial stress and □' are 90
Set it as equal to . Alternatively, calculate the initial stress σA1'.

When proceeding to step 1109J, that is, when yielding does not occur on the compression side but yields on the tension side as shown in FIG. 16, the initial stress σA2' is determined by the following equation (34).

Based on the initial stress σ□ obtained in step 1109, in step 1110 of FIG.
As shown in Figure 8, the stress relaxation curve (dashed line) to be applied is determined by interpolation. Note that the solid line in FIG. 18 is a stress relaxation curve stored in advance.

Then, the creep damage life is calculated as follows in correspondence with the value T of the creep retention time force wanta.

The procedure for calculating creep damage life is shown in Figures 19(a) to (c).
) will be explained according to the specific example shown. Figure 19 (
In a) to (c) the applied stress relaxation curves are shown.

The stress relaxation curve is determined by the creep retention time of the compensation axis (in Figure 9,
Time elapsed since the principal stress difference reached its peak value) 0,1
, 0,2 , 0,4 , 0,7 , and 1.0 hours, respectively σ(0,1) lσ(0,2)
.

The values σ(0,4), σ(0,7), and σ(1,0) are given (that is, stored).

FIGS. 19(a) to (C) show cases where the creep retention time T is on the left side of two adjacent intermediate time points of the above time (0.4 and 0.7 in FIG. 19a). T is located to the left of the midpoint 0.55).

If it matches the above time point, if it is to the right of the intermediate time point (in Figure 19C, T is located to the right of the midpoint 0.3 between 0.2 and 0.4) It represents.

In this example, it is assumed that the stress for evaluating creep damage matches the stress at the above-mentioned time point, and by setting the duration ΔT using this stress as a representative curve, the life consumption of creep damage can be reduced. This is intended to simplify calculations.

According to the example of glQ diagram (a), the stress and its duration ΔT
The relationship is that the stress of σ(0,1) is ΔT, =(0,15−0,1
) time, the stress of σ(0,2) is ΔT2-(0,3-0
-15) time, and the stress of σ(0,4) is ΔT3=(
T-0, 3) Time.

Assume that each is retained.

In the example of Fig. 19(b), the stress of σ(0,1,) is ΔT,'=(0,15-0,
1) Time and stress of σ(0,2) are ΔT,'= (
0,4-0,15) hours, respectively, and further.

In the example of Fig. 19(e), the stress of σ(0,1) is ΔT,''= (0,15-0,
1) Time and stress of σ(0,2) are ΔT,”= (
T −0, 15) time, respectively.

Here, the above σ(Oll) +σ(0,2) rσ(
0,4).

The rupture time corresponding to . . . is 'It
It is given as t2+ t3+... From these, creep damage life consumption φ. are respectively shown in Figure 19 (
, ) to (c), the following equations (35) to
(37).

Creep damage life consumption φ determined in this way
. and the fatigue life consumption φ.

In steps 1111 and 1112 of FIG.

The total life consumption φ1 and the cumulative total life φ7 are calculated as follows.

First, in step 1111, the total life consumption φ is calculated for each cycle, that is, for each cycle i, using the following equation (38).

φi−φfi+φ□ ・・・・・・
...(To) Next, in step 1112, the cumulative total life φ7 up to the current Nth cycle is calculated using the following formula (39).
In step 1113, the allowable life per cycle is calculated as described above.

Therefore, the reference data is 1, for example, for each startup mode, that is, for each cold start mode, warm start mode, and hot start mode, the allowable number of startups is Noc, N0VI, and N0H, respectively, and the total life consumption is φ, respectively. , φ'rw+φ,H, and are initially allocated in advance.

Therefore, the allowable life consumption φpc + φpw + φP of the initial cycle corresponding to each mode is determined by the following equation (40).

According to this, the number of operations in each mode up to the first cycle is Ni, , Ni. , Ni□, and the total life consumption is φ'To +φ'TV Iψ'TH, the allowable life of the next cycle (i+1) is determined by the following equation (41) for each mode.

Here, the numerator of equation (41) is the remaining allowable life, that is, the remaining life, and the denominator is the remaining allowable number of operations.

Next, the stress limit calculation function block 1200 U (Fig. 1)
I will explain about it.

In this block, the remaining life calculator 9th block 1100
Then, the total life consumption φ calculated using equation (38) is
The maximum equivalent stress on the compression side σ in that cycle, [Equation (28)
By accumulating and learning the following information, a set diagram as shown in FIG. 20 is created and updated for each cold, warm, and hot operation mode.

In FIG. 20, the horizontal axis is σ. is the initial stress limit value, σ1
+1 is the stress limit value for the (i+1)th cycle, φ on the II axis is the initial allowable life consumption * (+ per cycle), φ is the stress limit value per cycle, and L
pi+1 each represents the allowable life allowed for the (i + 1)th cycle.

Based on this diagram, block 1200 of FIG.
The stress that makes it impossible to meet the allowable life newly calculated using equation (41),
That is, in the example shown in FIG. 20, the stress corresponding to the intersection point P r1 is determined as the new stress limit value.

The main steam temperature prediction unit 2000 in FIG.
Mei 1 of No. 8-29429! [+As disclosed to Kutsu.

It is formed from the functional blocks shown in FIG.

According to the Cal7 filter theory, the main steam temperature T after time Δt (where n is an integer and Δt is the sampling period)
rp+n,i).

As shown in FIG. 25, among the process detection values at time 1, the main steam temperature Tf is equal to the calculated variable X+(+)
The signal is taken in as a signal and input to the adder 131j together with the observation noise W (i).

7II] calculation output of the adder 131 is manually input to the calculation block 133 via the calculation 5132. Computation block 1
The output of 33 is passed through an adder 134 to a delay element 135
Secondary superheater MJ characteristic model 13 installed in stages 8 and 0
6-1 ~ Human power is applied to the first stage of the mouth.

The secondary superheater inlet steam temperature 1fTs is the calculation variable U+(i)
As such, it is manually input to the calculation block 136a of the secondary superheater dynamic characteristic model 136-0. In addition, this dynamic characteristic model 1
The output of the delay element 135 is input to the pond calculation block 136b of 36-0.

The outputs of these arithmetic blocks 136a and 136b are added by an addition of $5136cf, and the outputs of the adder 13
2 is inputted as a subtraction signal, and on the other hand, it is inputted to the Calo calculator 134 as an addition signal.

Although the internal description of the secondary superheater dynamic characteristic models 136-1 to 136-n is omitted, they have the same configuration as the secondary superheater dynamic characteristic models 136-0. Further, as will be described later, process detection values necessary for calculation are input manually into the secondary superheater dynamic characteristic model 136-0.

Next, the operation of the steam temperature prediction section 2000 will be explained. Now, the main steam temperature Tf at time t is xIs
Secondary superheater metal temperature T, x2% secondary superheater steam temperature TS, UI, secondary superheater gas temperature T. Let be U2,
Considering minute fluctuations in these variables near the steady state, and assuming that heat transfer in the secondary superheater is a constant pressure process, the dynamic characteristic model of the secondary superheater can be calculated using the following equations (42) to (49). .

``' A21 '' A1 士 A22' Enter 2↑btt
@Ut """"'1.43-↑ Here...I4'71 In addition, in the above formula.

Cp i: Secondary superheater inlet constant pressure specific heat CO: Secondary superheater outlet constant pressure specific heat WF: Secondary superheater internal fluid flow WFR: Secondary superheater internal fluid specific weight Lid γ6: Secondary superheater internal fluid specific weight ■ = Secondary superheater internal volume FG: Boiler gas dispersion FGR: Boiler gas rated flow rate Mm: Secondary superheater metal overlay Cm = Secondary superheater metal specific heat 8 days: Secondary superheater heat transfer area 6g m lR: From waste Heat transfer coefficient to metal in rated state α1118 + R: 4 coefficient of heat transfer from metal to steam in rated state Both equations (42) and (43) have UI + U2 of 1-0.
Based on these equations (SO) and (Sl), the calculation period Δt (Δt=1-1o) time light x+(Δt) and X2 (
, Δt), the following equation (52) is obtained.

In the above formula (52)......53...641...(5%)...Q...・・・・・・6υ ・・・・・・Rut X+(Δt)rX2 obtained by the above equation (52)
By replacing (Δt) with x+(o) and X2(0), respectively, and repeating the calculation of equation (52) 0 times, D・Δ can be expressed as the main steam temperature Tr (n-2℃),
The secondary superheater metal temperature T2° (n·Δt) can be predicted.

The dynamic characteristic model of the secondary superheater expressed by equation (52) is:
This corresponds to the block 136 surrounded by a dotted line in FIG. In addition, in the figure, in order to simplify the diagram, an arbitrary time 1 is used to simulate the following equation (63).

Intersection (1) = φ (1-1) - x (1-t) + H (1-1
)・U(1-1)...Mourning Also, when the observation process of the process detected value is expressed by the following equation (64), the maximum likelihood estimate X(1) of the signal 1(1) can be calculated using the Kalman filter theory. Applying the following equation (65)%, where: 仝(i): m-dimensional observation vector C(i):
mXnXn sharpness matrix i): m dimension 11M 1111 noise vector 1 (
1)=i(i)+p(1)・O'(1)・w (Y(
i)-c (t)turn(1n+sha(January...)
・・・・・・・・・(6!ll here.

+M(i-x)・unit(1-1)・・・・・・・・・
・Kan (i) Q (*-'(1)+c-"(1)・sha-1
・0(1) l-'...Inertia M(1)=-mirror 1-1)・re1-t) i'(t-t
)+M(1-t)・unit(1-1)・M'(1-t)・
...((to) k in the above equation is one point in time of the n-dimensional state variable vector. jy (1) in the above equation is the transition matrix with r-dimensional/stem noise, and 1l(1) is the nxr drive matrix Ru.

As mentioned above, the calculated value x(1) of the main steam temperature τ T obtained by equation (63) is passed through a Kalman filter.
This allows highly accurate predicted values to be obtained.

Note that the secondary superheater gas temperature U2 is obtained by calculating using the following equation (69). U, = (
Hz 10FS + Ha II FA10Hrg 11RG
-161 where, Hr: $ gas calorific value, Hrg: recirculation gas enthalpy.

FS: fuel flow rate, HG: recirculation gas flow rate, Ha: Air enthalpy.

Opg: gas specific heat, FA: Air flow rate.

K: constant 0 In the stress prediction function block 2100 of FIG. Steam temperature T2. Using the following equation (70), 1. Estimated and predicted with N 0 where T: Current main steam temperature Next, using the above main steam temperature T and p, calculate n・Δ after time using the same calculation method as in the stress calculation function block 1000. Calculate the predicted stress value σ1 at time j.

However, in this example, regarding the various process quantities Da and internal fluid pressure P for calculating the internal fluid flow rate, it is assumed that n and Δ do not change after time, and that the external metal temperature "MO"
Correction calculations for metal temperature distribution calculated values are not performed.

On the other hand, when the load change rate is used as the operating level, the load prediction function block aoo'o (Fig. 1) selects eight load change rates R1>R4>R3..., >RN in order from the largest one, Based on the current load MW, the load after n·Δ time (n sampling period light) is estimated by the following equation (71).

MVP −MW + Rjen−Δt
・・・=−−−crυJ (j=1+2+・・N) Then, the stress on the pod is calculated using the main steam temperature prediction and stress prediction method described above from the main steam snow drift, fuel flow rate, and air flow rate commensurate with this predicted load. Predict.

In the bacteriostatic evaluation function block 4000 of FIG.

The various quantities calculated above are defined as follows.

σ, : Stress limit value': Stress prediction at time j Tfj: Predicted main steam temperature value T8j at time j: Main steam temperature set value MVP at time jI, : Predicted load value MW at time J, j: Load command value ε at time -, 2 Tolerance deviation between the above stress limit value and predicted stress value 62: Tolerance deviation ε between the above main steam temperature predicted value and set value, 2 Allowable deviation between the above predicted load value and load command value Depending on whether the selection from the difference priority P selection function block 7000 is stress limit value priority, main steam temperature priority, or load priority, each operates as follows.

(1) When stress limit 1 is given priority Optimum operation amount search function block 5ooo
The main steam temperature change rate R,3 and the load change rate RL3 are searched for. Among the values that satisfy the above equation, the linear equation (73)
A worker who is troubled by this.

Ilj yo (♀, do T.) 2+ (MW5- MW, b
)2 The value that minimizes σJ is output via the optimal manipulated variable output function block 6000.

(2) When main steam temperature is given priority Search for RIllj, RL until the following formula (74) % formula % (41) is satisfied, and among the I's that satisfy the above formula, The work that will be done.

"2j = (j-σL)2"("3- MWs 3
)2=...=.One shift that minimizes CIe is output from the optimal manipulated variable output function block.

(3) In the case of load priority, search R8j and RLj until the following formula (76) % formula % (761) is satisfied, and find the work 3 expressed by linear formula (77) within one shift that satisfies the above formula. The value that minimizes ° is outputted via the optimum manipulated variable output function block 6000. In addition, Equation (72).

Any combination of (74) and (76) is also an oT rudder.

In addition, if there is no priority designation, formulas (72) and (74
).

Search for R8j+RLj that simultaneously satisfies (76).

If a satisfactory solution cannot be obtained, the stress is large during startup bypass operation and stop operation as shown in Fig. Now, switch to mode (2) to give priority to rapid temperature changes, and switch to mode (3) to give priority to load changes after full load operation.
automatically switch to each mode. ' According to the present invention, even if the above equation (72) is not satisfied, in the next cycle, the stress limit value is reset in consideration of the current life consumption, so the life of the boiler will not be shortened. However, the stress limit value per subsequent cycle becomes smaller.

In the above example, the case where there is one stress evaluation point was explained, but even when there are multiple stress evaluation points at different points, it is easy to set the stress limit value for each evaluation point. It goes without saying that the present invention can be applied to.

〔Effect of the invention〕

According to the present invention, the stress in the boiler thick-wall pressure-resistant part is appropriately limited in accordance with the operating history of the plant! While keeping it within the range,
Safe and quick start, load, and stop operations are possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, Fig. 2 is a time chart explaining the relationship between the present invention and boiler plant operation, and Fig. 3 is a block diagram of a conventional boiler plant control device. , FIG. 4 is a schematic configuration diagram of a boiler plant to which the present invention is applied, FIG. 5 is a detailed block diagram showing an example of the stress calculation block of FIG. 1, and FIG. 6 is a diagram of the remaining life calculation of FIG. 1. Flowchart showing an example of functional block operation; FIGS. 7 and 9 are graphs showing an example of change in principal stress difference; FIG. 8 is a graph showing an example of change in stress width;
0 and 11 are graphs showing examples of changes in stress;
The figure is a detailed flowchart of the initial stress calculation procedure in Figure 6,
Figures 13 to 17 are graphs showing stress-strain relationships used for calculating remaining life, Figure 18 is a graph explaining how to obtain a desired stress relaxation curve, and Figure 19 is a graph for calculating creep damage life. A graph showing the stress-time relationship to explain the procedure, Fig. 20 is a graph to explain the operation of the stress limit value calculation function block in Fig. 1, and Figs. 21 to 24 show the secondary superheater outlet header pipe. FIG. 25, which is a diagram for explaining the temperature distribution calculation means in the near portion, is a detailed block diagram of the main steam temperature prediction section of FIG. 1. 1000...Stress calculation function block, 1100...
Remaining life calculation function block, 1200... Stress limit 1 direct calculation function block, 2000... Main steam temperature prediction function block, 2100... Stress prediction function block, 30
00...Load prediction function block, 4000...Control evaluation function block, 5ooo...Optimum operation amount search function block, 6000...Optimum operation amount output function block, 7000...Priority control selection function block substitute Patent Attorney Michi Hiraki 6th
Fig. 7 Fig. 8 Fig. N, N2 Fig. 9 (゛)) Fig. 13 Fig. 10 Fig. tJ, l 1 1.
Ll Time (Hr) Fig. 11 (a) M Breaking time Fig. 12 Fig. 14 Fig. 15 Fig. 16 Fig. 18 Fig. 20 Fig. ai + I 'Q 'M No. 19
Figure 24

Claims (12)

[Claims] (1) In a boiler stress monitoring and control device that monitors and controls stress at an evaluation point set at a desired location in piping of a boiler plant, means for calculating the current value of internal fluid flow rate at the evaluation point, and internal fluid flow rate calculation. means for calculating the metal temperature distribution at the evaluation point based on the value, means for calculating the thermal stress based on the calculated metal temperature distribution value, means for calculating the internal pressure stress from the pressure of the internal fluid, and the thermal stress and the internal pressure. a stress calculation unit comprising a means for calculating principal stress from the stress, a means for calculating the remaining life of the evaluation point from the principal stress obtained by the stress calculation unit, and a stress limit value from the calculated remaining life value. A stress prediction means for predicting the principal stress at the evaluation point at a future point in time; A main steam temperature prediction means for predicting the main steam temperature at the same point in the future; and a means for predicting the load at the same point in the future. load predicting means; maintaining at least one of the deviation of the stress prediction value from the stress limit value, the deviation of the main steam temperature prediction value from the target value, and the deviation of the load prediction value from the load command within an allowable value; 1. A boiler stress monitoring and control device, comprising means for setting each manipulated variable so as to minimize an evaluation value of deviation. (2) The boiler stress monitoring and control device according to claim 1, wherein the prediction of the main steam temperature at a future point in time is performed based on the main steam temperature change rate and the current main steam temperature. (3) A boiler stress monitoring and control device according to claim 1, characterized in that load prediction at a future point in time is performed based on a load change rate and a current load. (4) In claim 1, the principal stress prediction at the evaluation point is based on the thermal stress obtained based on the metal temperature distribution and the internal pressure stress obtained based on the internal fluid pressure and the dimensions of the piping metal. A boiler stress monitoring and control device characterized in that calculations are made from both. (5) The boiler stress monitoring and control device according to claim 1, wherein the evaluation value of the remaining deviation is the sum of the squares of each remaining deviation. (6) In claim 1, the thermal stress at a future point in time is predicted using the main steam temperature change rate as a parameter, and each manipulated variable is adjusted such that the deviation of the predicted thermal stress value from the limit value is within an allowable range. and predicting the deviation between the main steam temperature target value at a future point in time based on the main steam temperature change rate and the main steam temperature predicted value at the same point in the future,
A boiler stress monitoring and control device characterized in that it is configured to add a fuel bias corresponding to the deviation to a fuel quantity command value. (7) In claim 1, the thermal stress at a future point in time is predicted using the load change rate as a parameter, and each manipulated variable is set so that the deviation of the predicted thermal stress value from the limit value is within an allowable range. At the same time, it determines a rate of change that minimizes the deviation between the target load value at a future point in time based on the load change rate and the predicted load value at the same future point in time, and operates the water supply and fuel in accordance with the deviation. Boiler stress monitoring and control equipment. (8) In claim 1, stress is predicted for each of a plurality of different evaluation points, and the manipulated variable is set so that the deviation of all predicted values from the stress limit value is within an allowable range. A boiler stress monitoring and control device characterized in that it is configured to. (9) Boiler stress monitoring according to claim 1, characterized in that the part that calculates the metal temperature is configured with a theoretical calculation model, and the calculation model is switched depending on the state of the internal fluid at the stress evaluation point. Control device. (10) In claim 1, the theoretical calculation model is composed of a steady metal temperature distribution calculation model and an unsteady metal temperature distribution model, and the pressure of the internal fluid at the stress evaluation point,
A boiler stress monitoring and control device characterized in that metal temperature distribution is calculated using the former model when at least one of the flow rates is less than a specified value, and using the latter model when both flow rates are above the specified value. (11) In claim 10, the unsteady metal temperature distribution calculation model is defined as the temperature of the fluid inside the stress evaluation point,
A boiler stress monitoring control comprising a part that calculates a metal temperature distribution based on measured values of pressure and flow rate, and a part that corrects the metal temperature distribution using the measured value of the outer surface metal temperature at the evaluation point. Device. (12) In claim 11, the amount of correction of the metal temperature distribution is determined when the heat transfer coefficient on the inner surface of the metal at the evaluation point is the same in both the metal temperature distribution before and after the correction, and A boiler stress monitoring and control device characterized in that the temperature on the outer surface of the metal is determined to match the measured value of the outer metal temperature.