JPH0471122B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a boiler stress monitoring method. In particular, the present invention relates to a boiler stress monitoring method suitable for stress monitoring and life management of boiler plants operating under intermediate loads, which require frequent startup/shutdown and load change operations. [Background of the Invention] When operating a boiler, during start-up, stop, and load changes, pressure is applied to thick-wall pressure-resistant parts such as the secondary superheater outlet header, especially the nozzle corner, based on the difference between the internal fluid temperature and metal temperature. Thermal stresses are generated, which consumes fatigue life. Also, during rated operation,
The problem is the cleave rupture life due to internal pressure stress due to internal fluid pressure. Therefore, in order to appropriately manage the life of a boiler, in the short term it is necessary to periodically grasp the thermal stress during operation, and in the long term, the cumulative life consumption through past operations can be measured at any time. It is essential to be able to understand the This requirement is particularly acute for medium-load boiler plants, which are subject to rapid and frequent plant startup and shutdown and operations with large and rapid load changes. Conventionally, there has been no method to understand and monitor thermal stress in short periods during boiler operation, and for life management, as shown in Figure 1, a typical operation pattern has been developed using internal fluid temperature change rate and change width as parameters. A method is used in which a static lifetime consumption diagram is created in advance and the lifetime consumption is cumulatively managed based on this diagram. However, according to the conventional method, if the operating conditions (e.g., fluid flow rate, pressure, etc.) at which the main line diagram was created differ from the conditions at the time of application, errors may occur due to differences in heat transfer to the metal temperature, etc. .
In order to eliminate this problem, there is an idea to provide various types of diagrams with various flow rates and pressures as parameters, but this is not realistically possible because a variety of operating conditions can be considered. Therefore, even if the life consumption per start-up is defined based on the life consumption diagram and the fluid temperature change rate is determined accordingly, if the operating conditions differ from the conditions in the life consumption diagram, the life consumption will change. From above, it can be extremely safe, and it can also be extremely dangerous. As mentioned above, according to the conventional method, it is difficult to realize a rapid start-up that makes effective use of the life consumption allowed for a single start-up or a large and rapid load operation that faithfully adheres to the allowable stress. Ta. [Object of the Invention] The object of the present invention is to provide a highly reliable boiler that quickly and accurately estimates thermal stress during operation, calculates lifetime consumption based on this, and enables optimal operation of the boiler plant. The present invention provides a stress monitoring method. [Summary of the Invention] In order to prevent a decrease in reliability due to system down due to detector failure, it is desirable to be able to calculate thermal stress using as few detection signals as possible. In addition, highly accurate thermal stress calculations are desired in accordance with the state of plant equipment and the characteristics of process quantities at stress monitoring points. In view of these points, in one aspect of the present invention, (1) the temperature distribution inside the thick-walled pressure-resistant part metal is determined by the temperature sensor signal attached to the outer surface of the thick-walled pressure-resistant part metal and the boundary between the internal fluid and the metal; The method is mainly calculated based on the surface heat transfer coefficient and the heat balance based on this, but (2) under operating conditions before or immediately after plant load ramping, internal fluid flows through thick pressure-resistant parts. Since we have just started and the state of the internal fluid is still unstable, we calculate the temperature distribution based on the signal from the temperature sensor attached near the inner surface of the thick pressure-resistant metal and the temperature sensor attached to the outer surface. It is characterized by (3) In areas where the main steam flow rate is high after the plant load ramping permission conditions are met and ramping has started, the final temperature distribution calculated using the method (2) above is used as the initial value, and the method described in (1) above is used. (4) Diagnose the detector signal required for each of the above two calculation methods, and if the detector signal is abnormal, calculate the one with a normal detector. The feature is that the metal temperature distribution calculation is continued by switching to the method. [Examples of the Invention] The present invention will be described in more detail below based on specific examples. FIG. 2 is an embodiment of the present invention, and shows the relationship between a boiler stress monitoring device 100 using a digital computer and related input signals from a boiler plant. In this FIG. 2, the boiler stress monitoring device 10
0 is a digital computer 101, an alarm display 10
2, CRT display device 103, typewriter 104,
and a hard copy device 105.
The digital computer 101 calculates primary superheating based on the main steam pressure P, the main steam flow rate G, the main steam temperature T _f , and the inner metal temperature T _Mi and outer metal temperature T _Me of the secondary superheater outlet header header 205. Steam temperature at outlet
Thermal stress and life of the nozzle corner Nc of the secondary superheater outlet header header 205 using the signal states of T _S , primary superheater bypass valve opening BV ₁ , and secondary superheater bypass valve opening BV ₂ as calculation conditions. The amount of consumption is calculated at a predetermined cycle, and regarding thermal stress, the fact is displayed on the alarm display 102 at the time of alarm, and the CRT display 103
typewriter 104 while displaying relevant information on the typewriter 104.
print it on. In addition, the CRT display device 103
Displays trend graphs and numerical values of calculated thermal stress values, life consumption data per start/stop, and cumulative life consumption data.
4, data other than the above-mentioned trend display is displayed and printed according to the operator's request.
Information such as a trend graph display displayed on the CRT display device 103 can be recorded by a hard copy device 105 upon request. Next, the boiler plant section in FIG. 2 will be explained. The figure shows the relevant parts of a UP type once-through boiler, and the operation modes after ignition of the burner 207 until the rated load is reached are divided into two: start-up bypass operation and once-through operation. The relationship between the two operation modes is shown in Figure 3. The operation will be explained below using FIGS. 2 and 3. First, the start-up bypass operation refers to the operation after the light oil burner ignition and before the turbine steam control valve starts to open, as shown in FIG. In FIG. 2, feed water is preheated by an economizer 201 of a boiler 200 and heated by a water wall 202. The heating fluid then passes from the primary superheater bypass valve 1 and through the primary superheater 203 to 2
The steam is led from the secondary superheater bypass valves 2 to the flash tank 206, respectively, and is vented to the secondary superheater 204 through the flash tank generated steam vent valve 5. For control, as shown in Figure 3,
Next, the inlet fluid temperature of the superheater is adjusted by adjusting the fuel.
The temperature is increased at a predetermined rate of change to reach a predetermined temperature (in the figure).
320℃). In this operation mode, since the turbine steam control valve is closed, no steam flows into the secondary superheater outlet header header 205, but the temperature continues to rise. Next, in the once-through operation, the superheater pressure reducing valve front valve 3 and the superheater pressure reducing valve 4 are opened, steam is allowed to flow into the secondary superheater 204, pressure is increased, and the turbine is heated by adjusting the opening of the turbine steam control valve 301. Increase speed. When the turbine reaches its rated speed, a generator is added,
Transition from primary superheater inlet fluid temperature control to main steam temperature control. Then, while maintaining the initial load,
Switch the heavy oil burner and adjust the fuel so that the conditions for load ramping are met. When the load ramping conditions are met, the primary superheater bypass valve 1, secondary superheater bypass valve 2, and flash tank steam vent valve 5 are closed, and load ramping is performed by the turbine steam control valve 301 and main steam temperature control. Increase pressure P and temperature T _f to rated values. As explained above, the internal fluid of the secondary superheater outlet header header 205 starts flowing from the time when the turbine speed starts to increase, and becomes stable only when the load ramping start condition is satisfied, and is unstable before that. Therefore, it is difficult to estimate the metal temperature distribution of the outlet header header 205 of the secondary superheater 204 from the state of the internal fluid during the process from light oil burner ignition to turbine speed up and until the start of ramping. be.
This problem disappears after the load ramping start conditions are met. FIG. 4 shows the processing of the boiler stress monitoring device 100 in blocks. Using this diagram,
Let's explain its operation. First, the first metal temperature calculation unit 10 sets the metal inner surface temperature detector signal T _Mi and the metal outer surface temperature detector signal T _Mp as boundary conditions, and when performing calculation for the first time, sets the initial temperature distribution to be equal to the metal outer surface temperature T _Mp . If the temperature distribution calculation result is already stored in the storage unit 20, the output of the initialization unit 21 is used as an input parameter to calculate the metal temperature distribution, and the metal temperature calculation result is sent via the switching unit 13. is stored in the storage unit 20. Next, the thermal stress calculation section 15 calculates thermal stress based on this metal temperature distribution. In the life calculation section 16,
The life is calculated based on the internal pressure stress calculated by the internal pressure stress calculation section 22 based on this thermal stress and internal fluid pressure. Next, the second metal temperature calculation unit 11 calculates the metal outer surface temperature detector signal T _Mp and the internal fluid temperature.
The relationship between the heat balance between the metal and the fluid using the heat transfer coefficient calculated by the heat transfer coefficient calculation unit 12 based on T _f , the pressure P, and the flow rate G and the initialization unit 21 or the storage unit 20 as described above. The metal temperature distribution is calculated based on the temperature distribution and is stored in the storage unit 20 via the switching unit 13.
The calculation results are stored in . The following calculations are as described above. The first metal temperature calculation unit 10 is used from the ignition of the light oil burner to the start of load ramping.
The load ramping permission condition determination unit 14 checks each of the secondary superheater outlet temperature T _S , the total fuel flow rate FF, the primary superheater bypass valve opening degree BV ₁ , and the secondary superheater bypass valve opening degree BV ₂ . If the conditions are met here, the process is switched to the second metal temperature calculation section 11. At this time, the value in the storage section 20 is set as the initial temperature distribution. In addition, as a special case, the diagnostic circuit 24,
Alternatively, when an abnormality in one of the detectors is detected in step 25, a switching command is issued to the switching unit 13 to switch the calculation to the other metal temperature calculation unit. Note that the alarm processing section 17 compares the set value of the alarm setting section 22 with the calculated value, and displays an alarm on the alarm display 102. The CRT display processing unit 18 displays the thermal stress calculation results, related data, and life calculation results on the CRT display device 103. typewriter 1
9 prints data at the time of alarm generation and thermal stress and life consumption data when requested by the operator. Next, a method of calculating metal temperature distribution in the first metal temperature calculating section 10 will be explained. Assuming that the secondary superheater outlet header 205 is an infinite cylinder as shown in FIG. 5, and that no temperature distribution occurs in the axial direction, the temperature distribution in the metal is expressed by the following equation. 1/α ∂T/∂t=∂ ² T/∂r ² +1/r ∂T/
∂r... T (a, t) = T _Mi (t) ... T (b, t) = T _Mp (t) ... However, α: thermal diffusivity T: metal at radius r from center, time t Temperature T _Mi : Metal temperature measurement value at time t on the metal inner surface (r=a) T _Mp : Metal temperature measurement value at time t on the metal outer surface (r=b) In order to calculate the formula ~ with a digital computer,
As shown in Figure 6, the metal is divided into N parts in the radial direction, and the metal temperature T _i (j) at each division point is determined.
It is converted into a differential format with the division unit length as Δr and the temperature distribution calculation period as Δt. The state of this conversion is shown in FIG. In FIG. 7, 70 is a table storing data from temperature T _Mi (j) near the inner surface of the metal to temperature T _Mp (j) of the outer surface of the metal. Note that (j) indicates data at time j. 71 is a conversion unit that inputs this data and converts it into a differential format. 72
is a table that stores the conversion results of the conversion unit 71. 70, T _Mi (j), T ₁ (j), T ₂ (j), ...T _k-2 (j),
Data of T _k-1 (j), T _k (j), T _k+1 (j), ...T _N-1 (j), T _Np (j) are stored. Here, T _Mi (j) is the temperature near the inner surface of the metal at time j, T _Mp (j) is the temperature of the outer surface of the metal at time j, and T _i (j) is the dividing point i of the metal (i = 1, 2,
...k-2, k-1, k, K+1, ...N-1) at time j. These 70 data are
The conversion unit 71 converts it into a differential format. That is, T ₀ (j+1)=T _Mi (j) BT ₀ (j+1)−AT ₁ (j+1)+T ₂ (j+1) =−BT ₀ (j)+CT ₁ (j)−T ₂ (j) 〓 BT _{k -1} (j+1)−AT _k (j+1)+T _k+1 (j+1) =−BT _k-1 (j)+CT _k (j)−T _k+1 (j) 〓 −B/AT _N-2 (j -1)+T _N-1 (j+1)-1/AT _N (
j+1)=B/AT _N-2 (j)-C/AT _N-1 (j)+1/AT _N (j
) becomes. However, A={1/(Δr) ² +1/αΔt}/1/2Δr(1/
Δr+1/2r) B=1/2Δr+(1/Δr−1/2r)/1/2Δr(1
/Δr+1/2r) C={1/(Δr) ² −1/αΔt}/1/2Δr(1/
Δr+1/2r) T _Mi (j): Temperature at time j near the inner surface of the metal T _Mp (j): Temperature at time j of the outer surface of the metal T _i (j): Temperature at time j at dividing point i of the metal Δt: Sampling Period α: Thermal diffusivity Δr: Radial division unit length of metal r: Distance from the center of the cylinder The results of this conversion are stored as a table 72. Next, the method of metal temperature distribution calculation in the second metal temperature calculation section 11 will be explained together with the heat transfer coefficient calculation section 12. In this part, the temperature distribution inside the metal is expressed by the following equation. 1/α ∂T/∂r=∂ ² T/∂r ² +1/r ∂T/∂r...
−λ・∂T/∂r | _rna = h (T _f −T ₀ ) ... T (b, t) = T _Mp (t) ... However, λ: Metal thermal conductivity h: Heat transfer coefficient T _f : Internal fluid temperature=T _f (t) T ₀ : Calculated value of inner metal temperature When formulas ~ are converted into differential form in the same manner as in the first metal temperature calculation section 10, the result is as shown in FIG. In FIG. 8, 80 is a table that stores data before conversion, and 81 is a conversion unit that converts into a differential format. 82 is a table that stores the converted data. The data stored in 80 is converted by converter 81 as follows. That is, −B・D/A+B・DTf(j+1)+T ₀ (j+
1) -1+B/A+B・DT ₁ (j+1) =B・D/A+B・DT _f (j)−C+B・D/A
+B・DT ₀ (j)+1+B/A+B・DT ₁ (j) B・T ₀ (j+1)−A・T ₁ (j+1)+T ₂ (j+1) =−BT ₀ (j)+C・T ₁ (j) −T ₂ (j) 〓 B・T _k-1 (j+1)−AT _k (j+1)+T _k+1 (j+
1) =−BT _k-1 (j)+C・T _k (j)−T _k+1 (j) B・T _k (j+1)−A・T _k+1 (j+1)+T _k+2 (j+
1) =−B・T _k (j)+C・T _k+1 (j)−T _k+2 (j) 〓 −B/AT _N-2 (j+1)+T _N-1 (j+1)−1/AT _Mp
(j+1)=B/AT _N-2 (j)-C/AT _N-1 (j)+1/AT _M
p (j) Here, A={1/(Δr) ² +1/α′Δt}/1/Δr(1/
Δr+1/2r) B=1/2Δr+(1/Δr−1/2r)/1/2Δr(1
/Δr+1/2r) C={1/(Δr) ² −1/α′Δt}/1/2Δr(1
/Δr+1/2r) D=2hδr/λ T _f (j): Temperature of internal fluid at time j T _i (j): Temperature of dividing point i of metal at time j T _M (j): Time j of outer surface of metal Temperature α': Thermal diffusivity λ: Thermal conductivity h: Heat transfer coefficient Δr: Length of the metal cylinder divided unit length r: Distance from the center of the cylinder Next, the heat transfer coefficient h is calculated based on the following formula. . w=G・v/S … S=π/4a ² … R _p =w・2a/ν … h=0.023・R _p ^0.8・P _r ^0.4・K/2a … where w: Steam flow rate G: Internal fluid flow rate v: Specific volume (function of temperature T _f and pressure P) S: Channel cross-sectional area R _p : Reynozzle number ν: Kinematic viscosity coefficient (function of temperature T _f and pressure P) K: Thermal conductivity (Function of temperature T _f and pressure P) P _r : Prandtl number (function of temperature T _f and pressure P) a : Inner radius Next, the thermal stress calculation method in the thermal stress calculation section 15 will be explained. The thermal stress at time t at a point with radius r from the center of the cylinder is expressed in polar coordinates using the following equation: radial thermal stress σ _r (r, t), circumferential thermal stress σ 〓 (r, t) axial thermal stress σ When _z (r, t), these are calculated using the following formula. σ _r (r, t)=Eα′/1−ν{1/b ² a ² (1−a ² /r ²
)∫ ^b _a T(r,t)rdr−1/r ² ∫ ^r _a T(r,t)rdr}
... σ〓(r,t)=Eα′/1−ν{1/b ² a ² (1+a ² /r
² )∫ ^b _a T(r,t)rdr−1/r ² ∫ ^r _a T(r,t)rdr
−T(r, t)}... σ _z (r, t)=Eα′/1−ν{2/b ² a ² ∫ ^b _a T(r,
t)rdr−T(r,t)}... However, E: Young's modulus α': Linear expansion coefficient ν: Poisson's ratio (=constant) Young's modulus E and linear expansion coefficient α' are based on the metal temperature distribution calculation values. Based on this, the metal volume average temperature is determined, and this is selected as a parameter from a constant table stored in advance. The thermal stress is most severe at the inner surface of the metal, that is, at the point r=a (corresponding to division point 0 in FIG. 6), and is calculated from the following equation where r=a in the above equation. σ _r (a, t)=0 ... σ〓(a, t)=Eα'/1−ν={2/b ² a ² ∫ ^b _a T(
r, t) rdr−T(a, t)}... σ _z (a, t)=Eα′/1−ν{2/b ² a ² ∫ ^b _a T(r,
t)rdr−T(a,t)}... Here, σ _r (a, r)=0, σ〓(a, t)=σ _z (a
,
Since the relationship t) holds true, the thermal stress in the general part inside the metal cylinder is evaluated using σ〓(a, t) as a representative value. The following table shows examples of permission conditions for starting load ramping.

〔Effect of the invention〕

According to the present invention, thermal stress,
It becomes possible to estimate internal pressure stress and lifetime consumption based on these quickly and with high accuracy during operation. It is possible to significantly and rapidly operate the load while ensuring the safety of the boiler plant.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the conventional life management method;
The figures are examples of the present invention, Figure 3 is an explanatory diagram of operation mode switching conditions, Figure 4 is an explanatory diagram of the processing method of the present invention, Figures 5, 6, 7, and 8. The figure shows an explanatory diagram of the metal temperature distribution calculation method. 100...Boiler stress monitoring device, 101...Digital computer, 102...Alarm indicator, 103
...LRT display device, 104 ...typewriter,
105...hard copy, 200...boiler, 2
01...Cost saving device, 202...Water wall, 203...1
Secondary superheater, 204... Secondary superheater, 205...2
Next superheater outlet header header, 206... Flash tank, 207... Burner, 300... Turbine, 301... Turbine steam control valve, 400...
Condenser, 1... Primary superheater bypass valve, 2...2
Next superheater bypass valve, 3...superheater pressure reducing valve front valve,
4... Superheater pressure reducing valve, 5... Flash tank generated steam vent valve, 6... Superheater stop valve, 7... Flash tank steam dump valve, P... Main steam pressure,
FF... Total fuel amount, G... Main steam flow rate, T _f ... Main steam temperature, T _S ... Primary superheater outlet steam temperature, T _Mi
...Secondary superheater outlet header pipe inner surface metal temperature,
T _Mp ... Secondary superheater outlet header pipe outer surface metal temperature, BV ₁ ... Primary superheater bypass valve opening degree, BV ₂ ...
...Secondary superheater bypass valve opening degree, Nc...Nozzle corner section.

Claims (1)

[Scope of Claims] 1. In a boiler stress monitoring method that calculates thermal stress in a thick-walled pressure-resistant part of a boiler plant during operation of the boiler plant, the metal temperature distribution of the pressure-resistant part necessary for thermal stress calculation is calculated from the start of plant startup. A boiler stress monitoring method characterized in that before or immediately after a load ramping condition with a low main steam flow rate is established, estimated calculations are performed based on signals from temperature detectors attached to the inner and outer surfaces of the metal of the pressure-resistant part. 2. In a boiler stress monitoring method that calculates the thermal stress of a thick-walled pressure-resistant part of a boiler plant during operation of the boiler plant, the metal temperature distribution of the pressure-resistant part necessary for thermal stress calculation is calculated from the start of plant startup to load ramping with a low main steam flow rate. Before or immediately after the conditions are established, the temperature sensor installed on the inner and outer surfaces of the metal of the pressure-resistant section is estimated and calculated based on the signal, and after the start of load ramping, in areas where the main steam flow rate is high, the temperature sensor installed on the outer surface of the metal of the pressure-resistant section is A method for monitoring stress in a boiler, characterized in that an estimated calculation is performed based on a temperature detector signal, a heat transfer coefficient at an interface between a fluid inside the pressure-resistant part and an inner surface of a metal, and a heat balance based on the heat transfer coefficient. 3. In the boiler stress monitoring method according to claim 2, the detector signal necessary for metal temperature distribution calculation is diagnosed, and if the detection signal is abnormal, the metal temperature distribution of the one whose detector is normal is diagnosed. A boiler stress monitoring method characterized by switching to a calculation model and continuing metal temperature distribution calculation.