JP2011064381A - Method of estimating metal temperature of boiler heat transfer pipe and method of estimating lifetime - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple method of estimating a metal temperature of a boiler heat transfer pipe having general versatility and capable of estimating the metal temperature of the heat transfer pipe with high accuracy. <P>SOLUTION: A relational expression of the metal temperature of the heat transfer pipe, a boiler operating time, and a thickness of oxidized scale formed on an inner face or an outer face of the heat transfer pipe is determined, the metal temperature of a gas downstream-side heat transfer pipe is estimated on the basis of a measured thickness of the oxidized scale of the gas downstream-side heat transfer pipe and a measured boiler operating time by using the relational expression, and the increase of metal temperature due to the oxidized scale of a gas upstream-side heat transfer pipe is determined on the basis of the estimated metal temperature as an initial metal temperature of the gas upstream-side heat transfer pipe, a measured thickness of the oxidized scale of the upstream-side heat transfer pipe, and the measured boiler operating time by using the operational expression, thus the metal temperature of the gas upstream-side heat transfer pipe is estimated. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a metal temperature estimation method and a life estimation method for a high-temperature section heat transfer tube such as a thermal power generation boiler device and a garbage incineration boiler device.

  FIG. 1 is a schematic configuration diagram of a thermal power generation boiler apparatus. As shown in the figure, a large number of burners 2 are installed on the lower side of the boiler body 1, and a superheater 4 and a reheater 5 are disposed in a flue 3 through which combustion gas generated by combustion of the burner 2 circulates. Various heat exchangers such as are installed. These heat exchangers such as the superheater 4 and the reheater 5 are composed of a combination of heat transfer panels (not shown) in which a large number of heat transfer tubes are arranged in a vertical direction at a predetermined pitch.

FIG. 2 is an enlarged cross-sectional view of the superheater heat transfer tube.
The superheater 4 and the reheater 5 are heat exchangers that generate high-temperature and high-pressure steam, and the superheated steam 9 (see FIG. 3) is circulated inside the heat transfer pipe 6 constituting the heat exchanger. A steam oxidation scale 7 is generated and deposited on the inner surface of the heat tube 6, while a high temperature oxide scale 8 is generated and deposited on the outer surface of the heat transfer tube 6.

  In the steam oxidation scale 7, since the diffusion of oxygen or metal components (Fe, Cr, etc.) in the oxide scale becomes a rule of scale growth, when the temperature is constant, the growth of the steam oxidation scale 7 with respect to time. Follow the parabolic law. For this reason, the corrosion margin of the heat transfer tube material frequently used in the superheater 4 and the reheater 5 is calculated according to the temperature condition and reflected in the initial wall thickness setting.

  However, as is apparent from FIG. 2, even in the same heat transfer tube 6, steam oxidation generated on the inner surface of the heat transfer tube 6 on the upstream side in the combustion gas flow direction is more affected by the heat load than on the downstream side in the combustion gas flow direction. The scale 7 is thick. Thus, when the steam oxidation scale 7 is formed thickly, the metal temperature of the heat transfer tube 6 is increased as compared with the heat transfer tube 6 on the downstream side in the combustion gas flow direction, which may cause accelerated oxidation thinning and creep damage.

  FIG. 3 is a model diagram showing changes in the metal temperature due to the generation of the high-temperature oxidation scale 8 and the steam oxidation scale 7. In the drawing, reference numeral 10 denotes a temperature distribution (dotted line) before scale generation, and reference numeral 11 denotes a temperature distribution (solid line) after scale generation.

  Since the thermal conductivity of the oxide scale is about 1/20 to 1/50 of the thermal conductivity of the tube material, which is a very low value, the metal temperature of the heat transfer tube 6 on the upstream side in the combustion gas flow direction where the heat load is particularly high, As is clear from the temperature difference between the dotted line and the solid line on the scale, it rises due to the heat transfer inhibition by the oxide scale. The repeated increase in metal temperature and acceleration of scale growth increase internal pressure stress, accelerate creep damage, reach the life earlier than the creep life assumed in the design stage, and finally creep blast There are things to do.

  Therefore, it is necessary to select the material of the heat transfer tube with high heat load and to estimate the corrosion allowance based on the life diagnosis considering the metal temperature rise due to the generation of oxide scale. For that purpose, the heat transfer tube of the actually installed heat transfer tube is required. It is necessary to estimate the metal temperature with high accuracy.

JP 2004-116810 A JP 2006-300601 A JP 2003-344261 A

In order to solve the above problems, the following proposals have been made as a method for estimating the heat transfer tube metal temperature during operation.
Patent Document 1 (Japanese Patent Application Laid-Open No. 2004-116810) proposes a method for detecting different metal temperatures of a heat transfer tube panel simply and at low cost, but a specific device called a suspended heat transfer tube of an exhaust heat recovery boiler device. , For the part, and therefore not versatile.

  Further, Patent Document 2 (Japanese Patent Laid-Open No. 2006-300601) proposes a method for estimating a use temperature by utilizing a change in the content of a precipitated substance deposited on a used steel material. However, in order to measure the content of the precipitated substance, it is necessary to identify and quantify only the precipitated substance by ICP emission analysis and X-ray diffraction analysis, which makes the operation complicated.

  Further, Patent Document 3 (Japanese Patent Application Laid-Open No. 2003-344261) proposes a temperature estimation method using a change in hardness due to aging of ferritic heat resistant steel. However, this method can be applied only to ferritic heat-resistant steel whose hardness decreases monotonically with temperature and time. Therefore, the material of the heat transfer tube is limited and is not versatile.

  As described above, there is no effective means for simply estimating the metal temperature and life diagnosis of a boiler heat transfer tube having a high heat load.

  The object of the present invention is to eliminate such drawbacks of the prior art, and is a simple and versatile boiler heat transfer tube that can accurately estimate the metal temperature of the actually installed heat transfer tube. An object of the present invention is to provide a metal temperature estimation method and a life estimation method based thereon.

In order to achieve the above object, the first means of the present invention is a method for estimating the metal temperatures of the upstream and downstream heat transfer tubes in the combustion gas flow direction,
Obtain a relational expression in advance between the metal temperature of the heat transfer tube, the boiler operation time, and the thickness of the oxide scale formed on the inner surface or outer surface of the heat transfer tube,
From the measured thickness of the oxide scale of the gas downstream heat transfer tube and the measured boiler operation time, the metal temperature of the gas downstream heat transfer tube is estimated using the relational expression,
The estimated metal temperature is used as the initial metal temperature of the gas upstream heat transfer tube, from the initial metal temperature, the measured thickness of the oxide scale of the gas upstream heat transfer tube, and the measured boiler operation time, using the relational expression, The metal temperature rise by the oxidation scale of the gas upstream heat transfer tube is obtained, and the metal temperature of the gas upstream heat transfer tube is estimated.

  According to a second means of the present invention, in the first means, the oxide scale is a steam oxide scale generated on the inner surface of the heat transfer tube.

According to a third means of the present invention, in the method for estimating the life of the upstream and downstream heat transfer tubes in the combustion gas flow direction,
Obtain a relational expression in advance between the metal temperature of the heat transfer tube, the boiler operation time, and the thickness of the oxide scale formed on the inner surface or outer surface of the heat transfer tube,
From the measured thickness of the oxide scale of the gas downstream heat transfer tube and the measured boiler operation time, the metal temperature of the gas downstream heat transfer tube is estimated using the relational expression,
The estimated metal temperature is used as the initial metal temperature of the gas upstream heat transfer tube, from the initial metal temperature, the measured thickness of the oxide scale of the gas upstream heat transfer tube, and the measured boiler operation time, using the relational expression, Obtain the metal temperature rise due to the oxide scale of the gas upstream heat transfer tube, estimate the metal temperature of the gas upstream heat transfer tube,
Using the relationship between the metal temperature, creep rupture time and stress of the heat transfer tube obtained in advance, the gas upstream heat transfer tube is calculated from the estimated metal temperature and stress of the gas upstream heat transfer tube and the measured boiler operation time. It is characterized by estimating the creep life of the material.

  A fourth means of the present invention is characterized in that, in the third means, the oxide scale is a steam oxide scale formed on the inner surface of the heat transfer tube.

  The present invention has the above-described configuration, is simple, versatile, and can accurately estimate the metal temperature of a heat transfer tube that is actually installed, with high accuracy. In addition, a life estimation method based thereon can be provided.

It is a schematic block diagram of the boiler apparatus for thermal power generation. It is an expansion cross-sectional view of a superheater heat exchanger tube. It is a model figure which shows the change of the heat exchanger tube metal temperature by the production | generation of a high temperature oxidation scale and a steam oxidation scale. In the Example of this invention, it is a characteristic view for estimating a metal temperature from the thickness of an internal surface oxidation scale, and a boiler operation time. In the Example of this invention, it is a figure for demonstrating the idea of calculating an equivalent time from inner surface oxidation scale thickness and metal temperature, and estimating a scale growth. In the Example of this invention, it is the figure which repeated the calculation which estimates the growth of a scale from the said equivalent time for every time step, and put together the calculation result. In the Example of this invention, it is a characteristic view for estimating the metal temperature of a heat exchanger tube from boiler operation time. In the Example of this invention, it is a characteristic view which shows the relationship between the boiler operating time calculated | required from the estimated metal temperature, steam oxidation scale thickness, the size of a heat exchanger tube, and the internal pressure of a heat exchanger tube, and the creep damage rate of a heat exchanger tube. In the Example of this invention, it is a schematic block diagram for demonstrating the metal temperature and lifetime estimation system of a heat exchanger tube using the UT scale thickness measuring apparatus.

Next, embodiments of the present invention will be described in detail with reference to formulas and drawings.
In the embodiment of the present invention, ferritic low alloy steel (Cr-Mo steel) of STBA24 is used as the material for the superheater or reheater heat transfer tube, the boiler operation time is 50,000 hours, and the gas upstream heat transfer tube A case where the measured thickness of the steam oxide scale is 0.8 mm and the measured thickness of the steam oxide scale of the gas downstream side heat transfer tube is 0.5 mm will be described as an example.

First, the metal temperature of the gas downstream side heat transfer tube with a low heat load is estimated.
When the heat load is low, the metal temperature can be regarded as constant because there is almost no influence of the temperature rise due to the generation of the steam oxidation scale. In this case, the growth of the steam oxidation scale is because the diffusion of oxygen or metal components (Fe, Cr, etc.) in the oxide scale becomes the law of the steam oxidation scale growth. Follow the parabolic law over time as shown in the equation.

Y = √ (Kp × t) (1)
Here, Y is the oxide scale thickness (μm), Kp is a parabolic law rate constant, and t is time (hours). The logarithm of the parabolic law rate constant Kp is expressed by the following equation (2).

log (Kp) = a / T + b (2)
Here, T is a temperature (K), and a and b are constants. The constants a and b are calculated based on experimental data for each steel type and are stored in a database.

Here, when the a value of the STBA24 (Cr—Mo steel) is 21 and the b value is −1.7 × 10 ⁴ , the thickness of the steam oxidation scale formed on the inner surface of the heat transfer tube as shown in FIG. Is determined by the metal temperature and boiler operation time. Curve A in the figure is a characteristic curve when the metal temperature is 580 ° C., curve B is the metal temperature is 560 ° C., curve C is the metal temperature is 540 ° C., and curve D is the characteristic curve when the metal temperature is 520 ° C. In the case of the present embodiment as indicated by Δ in the figure, the boiler operation time is 50,000 hours, so that the metal temperature at which the scale thickness is 0.5 mm is estimated to be 560 ° C. as described above.

  Like the characteristic curves A, B, C, D... In this figure, the relationship between the metal temperature of the heat transfer tube, the boiler operation time, and the thickness of the steam oxidation scale formed on the inner surface of the heat transfer tube is obtained in advance. Formulated or tabulated.

Next, the metal temperature of the gas upstream heat transfer tube having a high heat load is estimated.
The metal temperature in the upstream portion of the gas at the initial stage of boiler operation in which no steam oxidation scale is generated does not increase in temperature due to the heat load, so the metal temperature of the heat transfer tube on the downstream side of the gas (as described above, 560 in this embodiment). ° C). First, using this initial metal temperature, the metal temperature rise caused by the heat load and the steam oxidation scale is estimated by the following method.

  The metal temperature at the initial stage of boiler operation is set to 560 ° C., the metal temperature determined from the scale thickness and the temperature rise is obtained for each time step, and the scale growth at that temperature is calculated. Scale growth is predicted using a scale growth curve (characteristic curve) at each temperature obtained by the above equations (1) and (2). When the metal temperature changes every moment, the scale thickness and the metal are It is necessary to predict the scale growth by calculating the equivalent time from the temperature.

  The concept will be described with reference to FIG. In the figure, the horizontal axis represents time, and the vertical axis represents the thickness of the internal oxide scale. In the figure, when the metal temperature changes from temperature T1 to temperature T2, an equivalent time (t2) equal to the scale thickness at time t1 is calculated, and scale growth is predicted from that time. This calculation is repeated at predetermined time steps (4000 hours in this embodiment), and the calculation results are summarized in FIG.

  In the figure, a curve E is a characteristic curve of a temperature increase of 60 ° C./mm, a curve F is a temperature increase of 40 ° C./mm, a curve G is a temperature increase of 20 ° C./mm, and a curve H is a characteristic curve of a temperature increase of 0 ° C./mm. Based on this characteristic diagram, the temperature rise at which the scale thickness becomes 0.8 mm after 50,000 hours of operation is estimated to be 40 ° C./mm of curve F. If the temperature rise is known in this way, the metal temperature of the gas upstream heat transfer tube can be estimated from the following equation (3) from the change in scale thickness as shown in FIG.

Tm = Tf + Ys × ΔT (3)
Here, Tm is the metal temperature (° C) of the gas upstream side heat transfer tube, Tf is the metal temperature (° C) at the initial stage of boiler operation, Ys is the thickness of the scale (mm), and ΔT is the temperature rise (° C / mm).

  Next, the creep life is estimated from the estimated metal temperature of the gas upstream heat transfer tube and the thickness of the scale. The rupture time (tr) due to creep damage can be arranged by the LMP (Larson Miller parameter) shown in the following equation (4) which is a temperature / time parameter, and LMP is a function of the stress (MPa) shown in the following (5) equation. Is approximated by

LMP = T × [log (tr) + C] (4)
Here, T is a metal absolute temperature (K), tr is a creep rupture time (hour), and C is a constant.

LMP = A ₀ + A ₁ × logσ + A ₂ × (logσ) ² + A ₃ × (logσ) ³ ... (5)
Here, σ is stress (MPa), and A ₀ , A ₁ , A ₂ , and A ₃ are constants.

  The stress σ is calculated by using the average diameter equation shown in the following equation (6) based on the outer diameter, thickness, and internal pressure of the heat transfer tube.

σ = [P × (D−d)] / (2 × d) (6)
Here, σ is stress (MPa), P is the internal pressure (MPa) of the heat transfer tube, D is the outer diameter (mm) of the heat transfer tube, and d is the wall thickness (mm) of the heat transfer tube. The wall thickness d of the heat transfer tube decreases as the scale is generated. Generally, since half of the scale thickness is the thickness reduction amount, the thickness d can be expressed by the following equation (7).

d = df−Ys / 2 (7)
Here, df is the initial thickness (mm) before scale generation, and Ys is the scale thickness (mm).

  That is, when the estimated metal temperature, inner surface oxide scale thickness, heat transfer tube dimensions (outer diameter, wall thickness) and internal pressure of the heat transfer tube and the internal pressure of the heat transfer tube are known as the equations (4) to (7), the heat transfer tube creep rupture time (tr) Can be obtained.

  Therefore, the creep rupture time (tr) is calculated from the estimated metal temperature and steam oxidation scale thickness for each time step, and the creep life consumption rate due to the temperature increase ΔT due to the scale adhesion for the step time is expressed by the following equation (8): Calculate with

Creep life consumption rate = ΔT / tr (8)
The equation (8) is calculated for each time step, and the creep life consumption rate at each step is summed as the creep damage rate.

Estimated metal temperature and steam oxidation scale thickness and heat transfer tube dimensions (outer diameter: 50 mm, wall thickness: 5 mm) and the internal pressure of the heat transfer tube are 6 MPa, and the constants of the LMP are C = 19, A ₀ = 1.9 × The calculation results with 10 ⁴ , A ₁ = 4.5 × 10, A ₂ = −2.3 × 10 ³ , and A ₃ = 0 are shown in the characteristic curve I of FIG. In the figure, the horizontal axis indicates the boiler operation time, and the vertical axis indicates the creep damage rate of the heat transfer tube.

  In addition, the characteristic curve J in the figure shows the relationship between the boiler operating time and the heat transfer tube creep damage rate obtained by the conventional method when the metal temperature not considering the temperature rise is estimated to be 580 ° C. Similarly, the characteristic curve K is a characteristic curve showing the relationship between the boiler operating time and the creep damage rate of the heat transfer tube obtained by the conventional method when the metal temperature not considering the temperature rise is estimated to be 560 ° C.

  As is apparent from the characteristic curve I, the creep damage rate considering the temperature rise becomes 0.1 at a boiler operation time of 50,000 hours, and the boiler operation time to reach the creep life (creep damage rate = 1.0) is It can be estimated as 96,000 hours. On the other hand, in the conventional method (characteristic curves J and K), the boiler operation time reaching the creep life cannot be estimated as 96,000 hours, which may be erroneously estimated.

  As described above, the feature of the present invention is to estimate the metal temperature of the gas upstream side heat transfer tube having a high heat load only by measuring the thickness of the steam oxidation scale inside the tube of the gas upstream side and the gas downstream side heat transfer tube. It is a simple and versatile metal temperature estimation method. In addition, by applying this metal temperature estimation method, it is possible to accurately perform a creep life evaluation considering the metal temperature change.

  The above-described thickness measurement of the pipe inner surface steam oxidation scale necessary for the estimation of the metal temperature can be performed while the boiler apparatus is stopped, such as periodic inspection, without using the apparatus to conduct an extubation investigation. Therefore, by simultaneously measuring the scale thickness of the gas upstream and downstream gas heat transfer tubes and inputting the heat transfer tube material and boiler operating time, the metal temperatures of the gas upstream and gas downstream heat transfer tubes can be estimated instantaneously. By utilizing a UT scale thickness measurement device with a metal temperature evaluation and life estimation function, a large amount of data can be acquired, which can contribute to improving the reliability of the boiler device.

FIG. 9 is a schematic configuration diagram for explaining a metal temperature and life estimation system for a heat transfer tube using a UT scale thickness measuring apparatus.
In the figure, reference numeral 12 denotes a thermal load, 13 denotes an oxide scale removing unit, 14 denotes a probe unit, 15 denotes a UT scale thickness measuring device, and 16 denotes a metal temperature / creep life calculating device. The magnitude of the arrow of the heat load 12 indicates the level of the heat load.

  As shown in the figure, the high-temperature oxide scale 8 formed on the outer surface of the gas upstream and downstream heat transfer tubes 6 is partially removed to form an oxide scale removal unit 13. The thickness of the high-temperature oxidation scale 8 is calculated by applying the probe unit 14 of the UT scale thickness measuring device 15.

  The data calculated by the UT scale thickness measurement device 15 is transmitted to the metal temperature / creep life calculation device 16 as thickness measurement data. The metal temperature / creep life calculator 16 stores in advance external data necessary for calculating the metal temperature and creep life, such as the boiler operating time, the pipe internal pressure, the pipe outer diameter, and the pipe wall thickness. Yes. The metal temperature and creep life of the heat transfer tube 6 are calculated based on the thickness measurement data of the high-temperature oxide scale and the external data necessary for calculating the metal temperature and creep life. The system is displayed on a display unit (not shown) of the temperature / creep life calculator 16.

  In the above embodiment, the thickness of the steam oxidation scale generated and deposited on the inner surface of the heat transfer tube was measured to estimate the metal temperature of the heat transfer tube, but the high temperature oxidation scale generated and deposited on the outer surface of the heat transfer tube. It is also possible to estimate the metal temperature of the heat transfer tube by measuring the thickness.

1 ... Boiler body,
2 ... Burner,
3 ... Flue,
4 ... Superheater,
5 ... Reheater,
6 ... Heat transfer tube,
7 ... Steam oxidation scale,
8 ... High temperature oxidation scale,
9 ... superheated steam,
10 ... Temperature distribution before scale generation,
11 ... Temperature distribution after scale generation,
12 ... heat load,
13 ... Oxide scale removing part,
14 ... Probe part,
15 ... UT scale thickness measuring device,
16: Metal temperature / creep life calculator.

Claims (4)

In the method of estimating the metal temperature of the upstream and downstream heat transfer tubes in the combustion gas flow direction,
Obtain a relational expression in advance between the metal temperature of the heat transfer tube, the boiler operation time, and the thickness of the oxide scale formed on the inner surface or outer surface of the heat transfer tube,
From the measured thickness of the oxide scale of the gas downstream heat transfer tube and the measured boiler operation time, the metal temperature of the gas downstream heat transfer tube is estimated using the relational expression,
The estimated metal temperature is used as the initial metal temperature of the gas upstream heat transfer tube, from the initial metal temperature, the measured thickness of the oxide scale of the gas upstream heat transfer tube, and the measured boiler operation time, using the relational expression, A method for estimating a metal temperature of a heat transfer tube, wherein a metal temperature increase due to an oxide scale of a gas upstream heat transfer tube is obtained and a metal temperature of the gas upstream heat transfer tube is estimated.   2. The metal temperature estimation method for a heat transfer tube according to claim 1, wherein the oxidation scale is a steam oxidation scale generated on an inner surface of the heat transfer tube. In the method of estimating the life of the upstream and downstream heat transfer tubes in the combustion gas flow direction,
Obtain a relational expression in advance between the metal temperature of the heat transfer tube, the boiler operation time, and the thickness of the oxide scale formed on the inner surface or outer surface of the heat transfer tube,
From the measured thickness of the oxide scale of the gas downstream heat transfer tube and the measured boiler operation time, the metal temperature of the gas downstream heat transfer tube is estimated using the relational expression,
The estimated metal temperature is used as the initial metal temperature of the gas upstream heat transfer tube, from the initial metal temperature, the measured thickness of the oxide scale of the gas upstream heat transfer tube, and the measured boiler operation time, using the relational expression, Obtain the metal temperature rise due to the oxide scale of the gas upstream heat transfer tube, estimate the metal temperature of the gas upstream heat transfer tube,
Using the relationship between the metal temperature, creep rupture time and stress of the heat transfer tube obtained in advance, the gas upstream heat transfer tube is calculated from the estimated metal temperature and stress of the gas upstream heat transfer tube and the measured boiler operation time. Estimating the creep life of a heat transfer tube,   4. The heat transfer tube life estimation method according to claim 3, wherein the oxidation scale is a steam oxidation scale generated on an inner surface of the heat transfer tube.

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