JPS6011002A - Controller for boiler load - 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 The present invention relates to a boiler load control device, and more particularly to a boiler load control device that optimizes load followability while monitoring stress generated in each part of a boiler.

Thermal power plants are often operated at intermediate loads due to demand for electricity, and as a result of this intermediate load operation, startup, shutdown, or rapid load changes are required within a short period of time.

When intermediate load operation is performed to meet this demand, stress generated in thick-walled pipes of pressure-resistant parts such as turbine rotors in turbine plants and pressure-resistant parts such as superheaters in boiler plants and the resulting loss of service life become a problem.

BACKGROUND ART Conventionally, in turbine plants, turbine control systems have been developed that predict thermal stress in the rotor section in order to ensure earlier startup, shutdown, and rapid negative change while guaranteeing the life of the turbine.

The life consumption of the turbine rotor is estimated from the expected operating pattern at the time of planning, and stress limit values for each operating mode are determined based on this. In actual operation, the generated stress is calculated by predicting the steam state at an arbitrary time point, depending on whether the turbine is in load control mode or speed control mode, and this is combined with a pre-planned stress limit 1f! Compare Ee and search for the maximum load change rate and maximum acceleration rate within a range that does not exceed the lifting and stress limit values. The load change rate obtained in this way is called A L R (Automatic 'Load
Regul, ator) setting value, acceleration rate i'A S
R (Automatic Speed Regulat
or) a control system with a set value was used.

As described above, the control systems used in conventional turbine plants have the following drawbacks.

The stress limit value of a turbine plant is determined by the lifetime consumption calculated from the total number of FiJJ operations and the expected operation pattern, so if the actual operation pattern differs from the planned one, the stress limit value may become stricter. , or it may be gradual.

Furthermore, in actual operation, since the total life consumption up to the present time is not integrated, the operation results up to that point cannot be reflected in subsequent operations.

To predict the stress generated in the turbine rotor, since the rotor is a rotating body, the metal temperature cannot be measured directly, so the temperature distribution is calculated by estimating the heat transfer coefficient from the steam to the metal based on the steam state. The generated stress was predicted by Therefore, there is a natural limit to the improvement in accuracy of generated stress.

However, in boiler plants, boiler thick-walled tubes such as superheaters are high-temperature, high-pressure internal pressure devices, so the temperature of the inner and outer surfaces of the metal can be directly measured, making it possible to calculate the generated stress. Therefore, the accuracy of estimating the generated stress can be further improved.

Furthermore, in the life consumption of the rotor of a turbine, fatigue damage due to repeated thermal stress occurring in the rotor is dominant, so monitoring and control of thermal stress has become a subject, but in boiler plants, Because it is a high-temperature, high-pressure internal pressure device, in addition to fatigue due to repeated thermal stress, a large proportion of its life is consumed by creep. For this reason, it is necessary to accumulate creep damage data on various boiler materials and to establish online creep damage evaluation technology or to complete an online boiler life management system.

In addition, in order to optimize the lifetime consumption of the entire thermal power plant, it is necessary to manage the stress generated and lifetime consumption in both the boiler and turbine plants, and at the same time, coordinate control between them. There was no coordinated control.

In other words, in the turbine thermal stress management system,
If the thermal stress becomes excessive during operation, the load change rate of the turbine is reduced, but even if the load change rate is reduced to zero (load maintenance), the thermal stress of the turbine is not sufficiently reduced, especially at the time of plant startup. In such a case, it is necessary to reduce the temperature increase rate (fuel change rate) of the boiler, and cooperative control of the boiler and turbine is required.

The present invention attempts to eliminate the drawbacks of the conventional technology.
The purpose is to obtain a boiler load control device that can perform load control based on stress limit settings.

In order to achieve the above-mentioned object, the present invention includes a current stress value calculator that predicts all current stress values based on measured values from a boiler pressure-resistant part, a stress limit value setter that calculates a stress limit setting value planned in advance, A comparator is provided to compare the current stress value and the stress limit set value, and the current stress value and the stress limit set value are compared to control the load change rate within a range that does not exceed the stress limit set value. It is something.

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

Fig. 1 is a schematic system diagram of the boiler load control device of the present invention, Fig. 2 is a characteristic diagram showing time on the horizontal axis and load change rate on the vertical axis, and Fig. 3 is a characteristic diagram showing time on the horizontal axis and stress prediction on the vertical axis. FIG. 3 is a characteristic diagram showing the values, and shows changes in the predicted stress value due to changes in the load change rate shown in FIG. 2. Figure 4 is a vertical cross-sectional view of the boiler thick-walled tube, which is the stress monitoring point, Figure 5 is an enlarged view of the cylindrical model for calculating the temperature distribution in the X-X cross section of the fourth line, and Figure 6 is the metal tube. Temperature distribution curve in the plate thickness direction. Figure 7 is a design fatigue diagram with the horizontal axis showing the allowable number of repetitions and the vertical axis showing stress fragment amplitude. Figure 8 is the horizontal axis showing time and the vertical axis showing principal stress. Fig. 9 is a schematic diagram of the generation of principal stress difference showing the difference. Fig. 9 is a schematic diagram of the stress generated during boiler operation, with time on the horizontal axis and stress on the vertical axis. Fig. 10
The figure shows a stress relaxation line section with time on the horizontal axis and relaxed stress values on the vertical axis, Figure 11 is a creep rupture line diagram with rupture time on the horizontal axis and relaxed stress values on the vertical axis, and Figure 12 is a horizontal Stress limit value on axis,
It is a characteristic diagram showing life consumption on the vertical axis.

Hereinafter, the outline of the boiler load control device will be explained using the eleventh example.

The nozzle corner 2 of the high-temperature, high-pressure steam header (header) 1 of the superheater will be explained as a typical example of a thermal stress monitoring point in a boiler, but multiple such thermal stress monitoring points may be provided in the entire boiler. .

In order to reduce the thermal stress at the monitoring points of the boiler, first measure the metal temperature values 3.4 on the inner and outer surfaces of the header 1 using the metal inner surface temperature detector 5 to measure the metal inner surface temperature 6, and then measure the metal outer surface using the metal outer surface temperature sensor 7. Detect the temperature 8 respectively, add these two signals 6.8 to the temperature distribution calculator 9, and add these two signals 6.
．． 8, a metal thickness direction temperature distribution calculation value 1o is calculated.

On the other hand, the pressure measurement value 11 is sent from inside the header 1 to the pressure detector 12.
The steam pressure signal 13 obtained by detecting this pressure gauge side value 11 from the pressure detector 12 is applied to the current stress value calculator 14.

This current stress value calculator 14 calculates the current stress by adding the thermal stress based on the metal thickness direction temperature distribution calculation value 10 and the internal pressure based on the steam pressure signal 13 detected by the pressure detector 12. Calculate the value 15.

The life consumption calculator 16 calculates the life consumption calculation value 17 due to fatigue and creep based on the current stress value 15, and the stress limit value setting device 18 calculates the actual life consumption value 17 from the life distribution determined at the time of planning for each monitoring point and each operation mode. Calculate the remaining life by subtracting the life consumption calculation value 17 in operation, and further determine the allowable life consumption per future operation mode from the remaining life and the remaining number of operations, and it is planned that this life consumption will be achieved. The generated stress is set as the stress limit setting value 19 of the spatula 1.

The stress limit set value 19 in this stress limit value setter 18 can be updated every arbitrary number of times of starting and stopping.

Next, the current stress value 15 and the stress limit setting value 19 are compared using a comparator, and this fruiting current stress value 15 is the stress limit setting value 19.
When the load hold signal 22 is exceeded, the load hold signal 22 is generated by the load hold signal generator 21 and sent to the boiler load controller section.

On the other hand, if the current stress value 15 is less than or equal to the stress limit set value 19, one of multiple load change rates set in advance to determine the optimum load change rate (fuel change rate, pressure change rate) for the boiler. From there, the maximum value is set as the load change rate set value 5 using the load change rate setting device.

Next, the stress predicted value calculator section calculates the predicted stress value 27 that will occur after 211 minutes when the engine is operated at the load change rate set value 5 shown in FIG. Note that the Δτ axis is given as the target child side time 29 of the target prediction time setter array.

The predicted generated stress value 27 and the stress limit value 19 are compared with the comparator 3o, and if the predicted generated stress value n is less than or equal to the stress limit value 19, the set load change rate set value 5 is the final load change rate 31 based on the generated stress. is determined as. However, at the stage of calculating the predicted stress value 27, if the predicted stress value 27 exceeds the stress limit value 19, the load change rate setting value 5, which is one level lower than the load change rate setting value, is selected and the stress occurs again. A predicted stress value of 27 ft is calculated, and the steps of adding the load change rate setting device, load change rate setting value 5, stress predicted value calculator, generated stress predicted value 27, and comparator are repeated in the same manner as described above.

The final load change rate 31 determined in this way and the turbine load change rate limit setting value 33 of the turbine thermal stress monitoring device 32
A comparator compares the two values, sets the smaller value of both as the final load change rate 35 in the optimum load change rate setter 36, and sends the optimum load change rate set value 37 to the boiler load controller O. .

In this way, the desired period Δτ, (〈Δτ,
), the optimum load change rate can be determined while constantly monitoring the generated stress.

Next, an example of determining the boiler load change rate will be explained using FIGS. 2 and 3.

In Fig. 2, assuming that the boiler has been operated at the load change rate A up to the present time T0, and has been operated at the same load change rate B until time T after Δτ1, the stress forecast a++ is the + value of the third worst factor. The curve becomes curved, and at time T, the stress limit value 19 is exceeded.

In this case, as described above (select the load change rate set value 25, which is one step lower with the load change rate setter U in Fig. 1, and set the comparator 3
The stress prediction curve determines the boiler load change rate C as shown by curve E in FIG. 3, for example.

On the other hand, recently, thermal stress monitoring and control equipment 32 has been installed in turbine plants, and this turbine thermal stress monitoring equipment 32 originally controls the turbine so that the thermal stress in each part of the turbine is within the allowable value. It controls the load change rate (steam amount change rate), especially when starting the boiler (
During the temperature increase process), the turbine load increase rate is reduced to zero (load maintenance).
Even so, it may not be possible to reduce the turbine thermal stress to a permissible value or less unless the rate of steam temperature rise is reduced. In such a case, as shown in FIG. 1, the turbine thermal stress monitoring device 32 also sends the turbine load change rate limit setting value 33.

If this turbine load change rate limit set value 33 is equal to or less than the load change rate C described above, the turbine load change rate set value is determined as the optimum boiler load change rate, and coordinated load control of the boiler and turbine is possible. Become.

Figure 4 shows an enlarged cross section of the header 1 of the boiler.
Focusing on the nozzle corner part 2, which is the stress concentration part, the generated stress and life consumption are monitored.

The stress generated in the nozzle corner portion 2 can be determined by multiplying the stress generated in the cylindrical portion of the header 1 by a stress concentration factor.

The thermal stress of the cylindrical part is determined from the temperature distribution in the thickness direction of the cylindrical part, and the temperature distribution is determined by the heat conduction method of the cylindrical part (1) Formula α: Metal temperature conductivity T: Metal temperature 12 hours r:
Divide the distance from the center of the cylinder into N equal parts into the concentric cylinders shown in FIG. 5, set contact points at equal intervals, and solve by difference. The difference formula is represented by (2) formula % formula % i: node parameter j: time parameter, and (N-1) unknowns Tx, j+1 (N=
L 2+ """ r "1), (N-1)
equations are obtained and the boundary value T. , j+1. Tn, J+
1 is the current measured value 3.4 of the metal inner and outer surface temperatures, given by the respective metal inner surface temperature signal 6 and metal outer surface temperature signal 8.

Therefore, the calculated value of the temperature distribution in the thickness direction inside the metal is 1°, that is, T) + + 1 + x (N = 1 to n -1) as (
2) It can be determined by the formula.

An example of the calculated temperature distribution value 10 is shown in FIG.

Here, the thermal stress in the three axial directions, that is, the radial thermal stress σr
t, circumferential thermal stress σθt, and axial thermal stress σzt can be determined by the following equations.

・・・・・・・・・(3) ・・・・・・・・・(4) Here, σrt: Radial thermal stress E: Young's modulus σθt
: Circumferential thermal stress α′ Bilateral expansion coefficient σzt : Axial thermal stress C : Boann ratio Next, the three-direction stress due to internal pressure is (
6) (7) Obtained from equations (8).

σrp”f) ・・・・・・・・・・・・・・・(6)
Here, σrp: radial internal pressure stress, P: internal pressure σ6. Internal pressure stress in the two-layer direction Di = Internal pressure stress in the axial direction of the mini inner diameter cell t: Greater than or equal to the plate thickness Equations (3) to (8) are the stresses generated in the cylinder-crotch area, and the stress generated in stress concentration areas such as the nozzle is Multiply the stress occurring in the general area by the stress concentration factor. I wanted to,
The three-directional stress of the current stress value 15 generated in the nozzle corner portion 2 is obtained from (9) to (11).

σr=Krt−σrt+Krp”arp””’°−−
−−−−−−−°−(9) σθ = to θ [@σθ to θ
p@σθp song/song...song...αO)σz:Kzt,
σzt 10 Kzp σzp ゛°°４′″゛--Ql)
Here, Krt: radial thermal stress concentration coefficient θt:
Circumferential thermal stress concentration coefficient Kzt: Axial thermal stress concentration coefficient Krp: Radial internal pressure stress concentration coefficient θp: Circumferential internal pressure stress concentration coefficient Kzp: Axial internal pressure stress concentration coefficient σr= Radial total stress σθ: Circumferential total Stress σ2: Axial total stress Next, the life consumption calculator 16 calculates fatigue life consumption and creep life consumption based on the current stress value 15.

First, the fatigue life consumption is calculated from the principal stress difference e (12) to (14) based on the formulas (9) to (11).

Sl-σθ-σ2...Song...α2)S
! = σ2− σr ・・・・・・・・・・・・・・・
α3) S, = σr−σθ ・・・・・・・・・・・・
Q4) Next, calculate the stress amplitude for the three principal stress differences and calculate the fatigue life consumption from the design fatigue diagram shown in FIG. FIG. 8 shows the fluctuation of the principal stress difference S, and the stress amplitudes Z11Z12 can be seen. Similarly for S, , 83, "I r ""2... zl: , z-
I get criticized.

That is, S+ K ツ95 Z'+ , Z't (Z'+ >
"'t)S, K Tsuki Z-, Z", -(Z", )Z'
,) ・)83 K two az, , 'l”l ・
・'(""t>"t>"'), and the stress piece amplitude H,, H,,... is (15) (16
) Formula % Formula %) ) From the stress piece amplitude H,, H, ...... and the seventh design fatigue diagram, the allowable number of repetitions N1. N2... is obtained, and the fatigue life consumption φf can be calculated using the formula 07).

On the other hand, creep life consumption can be reduced by following the steps below. 9th
The figure shows a schematic diagram of the generated stress. The generated stress changes to the compressive stress side due to fluctuations in thermal stress during cold start and hot start, and then as steady operation begins, the thermal stress decreases and becomes mainly tensile stress due to internal pressure stress. The stress that reaches the initial stress σi will relax over time and become σ
It fluctuates as shown in (1). Therefore, the time is divided into Δt, and the relaxation stress value σ(1) in each section is calculated from the stress relaxation diagram shown in FIG. Next, from the creep rupture diagram shown in Fig. 11, the rupture time t corresponding to the relaxation stress value σ(1)
Find r(σ(t)).

The creep life consumption during time Δt is obtained by Δt/lr, and the creep life consumption φC between one start and stop is (18
) is determined by the formula.

Then, the life consumption calculation value 5 is calculated by equation (19) using the generally used linear equation.

φ−φf×φC・・・・・・・・・・・・α9)
Here, the life consumption calculation is performed by treating the start/stop period as one cycle and calculating the product n.

In the stress limit value setting device 18, the number of operations for each operation mode at the time of planning is N: (number of cold starts), N: (number of warm starts), N: (number of hot starts), and the corresponding life allocation money φ:, φ;.

φ: Then, the allowable life consumption for each mode at the time of planning is given as each, and the operation port a for each mode up to now is N
'c, N-, N;, the total life consumption for each mode is φ)
. ,φ)1. Assuming φI, the allowable life consumption per activation/stop of each mode in the future is (21).

It can be obtained from equations (22) and (23).

Next, from the stress limit value-life consumption diagram shown in FIG. 12, the stress corresponding to the allowable life consumption is set as stress limit value 19.

In addition, in the embodiment shown in Fig. 1, a method for estimating the current stress value of 15 is shown based on the measured value of the metal temperature on the inner and outer surfaces of the tube, which is 3.4, but as an applied example, a strain gauge may be installed directly at the stress monitoring point. The same effect can be obtained by directly measuring the generated stress.

As described above, according to the boiler load control device of the present invention, life consumption associated with plant operation can be carried out in a planned manner, and the planned life can be used effectively. In other words, it becomes possible to operate with high reliability and safety during the scheduled period, which also leads to improved economic efficiency. Furthermore, since load control is performed based on stress values, there is no need to perform gentle load control that takes into account excessive merge yfe to limit stress, and load followability is also improved.

When newly performing boiler load control as in the present invention, even if the boiler is already installed, it is economical to install a metal thermocouple or the like at the stress monitoring location.

The present invention includes a current stress value calculator that predicts a current stress value based on a side value from a boiler pressure section, a stress limit value setter that calculates a stress limit setting value planned in advance, and a current stress value and stress limit setting. A comparator is provided to compare the current stress value and the stress limit set value, and control is performed to obtain a load change rate within a range that does not exceed the stress limit set value. Load control can be performed and load followability can be improved.

[Brief explanation of drawings]

Figure 1 is a schematic system diagram of the boiler load control device of the present invention, Figure 2 is a characteristic diagram with time on the horizontal axis and load change rate on the vertical axis, and Figure 3 is a characteristic diagram with time on the horizontal axis and stress prediction on the vertical axis. Characteristic diagram showing values,
Figure 4 is a vertical cross-sectional view of the boiler thick-walled tube (header), which is the stress monitoring point, and Figure 5 is an enlarged view of the cylindrical model used to calculate the temperature distribution in the X-X cross section of Figure 4. The 6th problem is the temperature distribution calculation in the metal plate thickness direction, the 7th L! ! ,
1 is a design fatigue diagram in which the horizontal axis shows the allowable number of repetitions and the vertical axis shows the stress strip amplitude. Figure 8 is a schematic diagram of principal stress difference generation with time on the horizontal axis and principal stress difference on the vertical axis. , Figure 9 is a schematic diagram of stress generated during boiler operation, with time on the horizontal axis and stress on the vertical axis, Figure 10 is a stress relaxation diagram with time on the horizontal axis, and relaxation stress values on the vertical axis, 1111 is a creep rupture diagram in which the horizontal axis shows the rupture time and the vertical axis shows the relaxation stress value, and FIG. 12 is a characteristic diagram in which the horizontal axis shows the stress limit value and the vertical axis shows the life consumption. l... Header, 2... Curved nozzle corner section, 3,
4...Thermometer side value, 11... Surface pressure gauge 611j
Value, 14...Current stress value calculator, 15...
...Current stress value, 18... Stress limit value setter,
19... Stress limit value, addition four... Comparator, 35...
...Optimum load change rate. Fig. 1 2 Fig. 2 Fig. 3 Fig. 4 Fig. 7 Fig. 8 Fig. 12

Claims (1)

[Claims] A current stress value calculator that predicts the current stress value based on the measurement value from the boiler pressure-resistant part, a stress limit value setter that calculates the stress limit setting value planned in advance, and a comparison that compares the current stress value and the stress limit setting value. 1. A boiler load control device comprising: a current stress value and a stress limit setting value, and the control is performed so as to obtain a load change rate within a range that does not exceed the stress limit setting value.