JP2014228258A - Boiler furnace wall tube sulfide corrosion prediction method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To predict a furnace wall tube sulfide corrosion degree using calculation of reaction fluid.SOLUTION: A concentration relational expression between a gas concentration of chemistry element that can be attained through calculation of reaction fluid at a step S4 and a gas concentration of specified chemistry element that cannot be attained through calculation of reaction fluid at the step S4 is obtained using thermodynamics balance calculation at a step S13 (step S14). Then, a gas concentration distribution in an analysis target region of the specified chemistry element that cannot be attained under a calculation of reaction fluid at the step S4 is calculated using the temperature distribution and gas concentration distribution calculated at a step S31 and a concentration relational expression calculated at the step S14 (step S32). Then, a distribution of corrosion amount in a region to be analyzed is calculated using a corrosion rate expression, a furnace wall tube temperature calculated at step S21, and a gas concentration distribution of the specified chemistry element calculated at the step S32 (step S41). Then, a distribution of a furnace wall tube sulfide corrosion in the object region to be analyzed is estimated using the calculated distribution of a corrosion amount (S42).

Description

  The present invention relates to a method for predicting sulfide corrosion of a boiler furnace wall tube, which predicts sulfide corrosion of a boiler furnace wall tube.

  Conventionally, the formation of a strong reducing atmosphere in the furnace of a thermal boiler increases the rate of progress of corrosion / thinning (hereinafter simply referred to as corrosion) of a furnace wall tube constituting the furnace. There's a problem.

  Therefore, Patent Document 1 discloses a method for evaluating the life of a furnace wall tube based on the relationship between the corrosion of a furnace wall tube of a boiler and the concentration of hydrogen sulfide gas.

However, it is not always appropriate to use only hydrogen sulfide (H ₂ S) gas as an evaluation standard because there are circumstances in which thermal boilers are operated under various combustion conditions and the types of coal used as fuel are diversified. However, it cannot be said that accurate evaluation of corrosion cannot be performed.

  Therefore, Patent Document 2 discloses a method for evaluating sulfide corrosion in which the amount of corrosion of a material is evaluated only by the partial pressure of oxygen gas and the partial pressure of sulfur gas.

Japanese Patent Laid-Open No. 2003-4201 JP 2011-39011 A

By the way, in the method disclosed in Patent Document 2, the partial pressure of oxygen gas and sulfur gas are measured by actually measuring the composition (concentration) of H ₂ , H ₂ O, CO, CO ₂ , and H ₂ S gas. Seeking the partial pressure. Therefore, it is conceivable to obtain these gas concentrations not by actual measurement but by reaction fluid calculation. However, due to the computational load, many difficulties are involved in the reaction fluid calculation considering all chemical species generated during the combustion of pulverized coal. Therefore, in many cases, a reaction model in which reaction fluid calculation is simplified by limiting chemical species to be calculated is used. However, many of these reaction models do not incorporate chemical species that will be required later when evaluating sulfide corrosion.

  An object of the present invention is to provide a method for predicting sulfidation corrosion of a boiler wall tube, which can predict the degree of sulfidation corrosion of the furnace wall tube using reaction fluid calculation.

  The method for predicting sulfidation corrosion of a boiler furnace wall pipe according to the present invention predicts the degree of sulfidation corrosion of a boiler furnace wall pipe that predicts the degree of sulfidation corrosion of the furnace wall pipe using the amount of corrosion of the furnace wall pipe of a boiler fueled with pulverized coal. In the method, in the analysis target region provided along the furnace wall of the boiler in the boiler, the chemical species to be calculated are limited from all the chemical species generated during the combustion of the pulverized coal, and the reaction A reaction fluid calculation step for performing a fluid calculation, a gas concentration of a chemical species that can be obtained by the reaction fluid calculation by a thermodynamic equilibrium calculation, and the amount of corrosion necessary to calculate the reaction fluid calculation. The concentration relational expression derivation step for obtaining the concentration relational expression with the gas concentration of the specific chemical species that cannot be obtained by the above, and the high temperature corrosion test of the metal material forming the furnace wall pipe, the temperature of the furnace wall pipe, and the specific Chemical species Based on the result of the reaction fluid calculation based on the corrosion rate equation derivation step for obtaining the corrosion rate equation that is a relational expression between the gas concentration and the elapsed time, the temperature distribution in the analysis target region and the reaction fluid calculation are obtained. Using the temperature / concentration calculation step for calculating the gas concentration distribution in the analysis target region of the chemical species obtained, the temperature distribution and gas concentration distribution calculated in the temperature / concentration calculation step, and the concentration relational expression, A concentration calculating step for calculating a gas concentration distribution of the specific chemical species in the analysis target region, the corrosion rate equation, a temperature of the furnace wall tube, and a gas concentration distribution of the specific chemical species calculated in the concentration calculating step Corrosion amount calculation step for calculating the distribution of the corrosion amount in the analysis target region, and the distribution of the corrosion amount calculated in the corrosion amount calculation step Used, and having a prediction step of predicting the distribution of the sulfidation corrosion degree of the furnace wall tubes in the analysis target area.

  According to the above configuration, the concentration relational expression between the gas concentration of the chemical species that can be obtained by the reaction fluid calculation and the gas concentration of the specific chemical species that cannot be obtained by the reaction fluid calculation is obtained by thermodynamic equilibrium calculation. By using the calculated temperature distribution, gas concentration distribution, and concentration relational expression, the gas concentration distribution in the analysis target region of the specific chemical species that cannot be obtained by the reaction fluid calculation can be calculated. As a result, the corrosion rate distribution in the analysis target region can be calculated using the corrosion rate equation, the temperature of the furnace wall tube, and the gas concentration distribution of the specific chemical species. The distribution of the degree of sulfidation corrosion can be predicted. Specifically, it is possible to predict where and how much corrosion will occur in which region of the analysis target region. In this way, by interpolating the gas concentration of a specific chemical species that cannot be obtained by reaction fluid calculation using the concentration relational equation obtained by thermodynamic equilibrium calculation, sulfidation corrosion of the furnace wall tube using reaction fluid calculation The degree can be predicted.

  Moreover, in the sulfide corrosion prediction method for a boiler furnace wall tube according to the present invention, the analysis target region is provided in the vicinity of the furnace wall of the boiler, and is divided into a plurality of blocks. For each block, by calculating the average value of the temperature and the average value of the gas concentration of the chemical species obtained by the reaction fluid calculation, the temperature distribution and gas concentration distribution in the vicinity of the furnace wall of the boiler are calculated, The concentration calculating step calculates the gas concentration distribution of the specific chemical species in the vicinity of the boiler wall of the boiler by calculating the gas concentration of the specific chemical species for each block, and the corrosion amount calculating step includes: By calculating the amount of corrosion for each block, the distribution of the amount of corrosion in the vicinity of the furnace wall of the boiler is calculated. To, to predict the sulfidation corrosion degree of the furnace wall tube, or to predict the distribution of sulfidation corrosion degree of the furnace wall tubes in the furnace wall near the boiler. According to the above configuration, the temperature distribution and the gas concentration distribution in the vicinity of the boiler wall of the boiler are calculated by dividing the analysis target region into a plurality of blocks and calculating an average value of the temperature and the gas concentration for each block. And it can make evaluation easy by calculating | requiring the gas density | concentration and corrosion amount of specific chemical species for every block, and estimating the sulfurization corrosion degree of a furnace wall pipe for every elapsed time and every block.

  Further, in the sulfide corrosion prediction method for a boiler furnace wall tube according to the present invention, the reaction fluid calculation step performs the reaction fluid calculation while changing parameters related to coal combustion until the result of the reaction fluid calculation matches the actual measurement data. You can repeat it. According to the above configuration, by repeating the reaction fluid calculation while changing the parameters related to coal combustion until the result of the reaction fluid calculation matches the actual measurement data, the calculation result along the combustion in the actual boiler can be obtained. Can do. Thereby, the sulfurization corrosion degree of the furnace wall tube can be predicted with high accuracy.

  According to the method for predicting sulfidation corrosion of boiler furnace wall pipes of the present invention, by using the concentration relational expression obtained by thermodynamic equilibrium calculation, by interpolating the gas concentration of a specific chemical species that cannot be obtained by reaction fluid calculation, the reaction Fluid calculation can be used to predict the degree of sulfidation corrosion of furnace wall tubes.

It is a schematic diagram of a boiler. It is a flowchart which shows the sulfide corrosion prediction method of a boiler furnace wall pipe. It is a permeation | transmission perspective view of a boiler. It is a diagram showing the relationship between the gas concentration and the gas concentration of H _{2 S} in the CO. It is a figure which shows the test result of a high temperature gas corrosion test. It is a diagram showing the relationship between the parameters and the concentration of H _{2 S} to determine the corrosion rate. It is the figure which mapped the corrosion prediction result.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Boiler configuration)
The boiler furnace wall pipe sulfide corrosion prediction method (sulfide corrosion prediction method) according to this embodiment is performed on the boiler 1. As shown in FIG. 1, the boiler 1 is disposed from the upper side to the lower side of the furnace 2 in which the pulverized coal supplied from the pulverizer 5 is burned by the burner 3 or the like to generate heat, and burns inside. And a heat transfer tube group 6 that exchanges heat by flowing gas, and the combustion gas generated in the boiler 1 is discharged from the chimney. The heat transfer tube group 6 includes an upper heat transfer section including a secondary superheater, a tertiary superheater, a final superheater, and a secondary reheater arranged in parallel at a predetermined interval above the furnace 2, And a rear heat transfer section including a primary superheater, a primary reheater, and a economizer disposed at the rear.

  In the present embodiment, a plurality of burners 3 are connected to the lower part of the furnace 2 in three upper and lower stages. A plurality of two-stage combustion air ports 4 that supply the two-stage combustion air into the furnace 2 are connected to the upper part of the furnace 2 and above the burner 3 in two stages. In FIG. 1, only the burner 3 and the two-stage combustion air port 4 connected to the left side wall of the furnace 2 are illustrated, but the front wall of the furnace 2 and the rear side of the figure are illustrated. A plurality of burners 3 and two-stage combustion air ports 4 are also connected to the side wall, the right side wall in the figure. Further, the arrangement of the burner 3 and the two-stage combustion air port 4 is not limited to the illustrated one. In the furnace 2, the pulverized coal injected from the burner 3 and the combustion air are mixed and burned, and further, two-stage combustion is performed by the two-stage combustion air blown out from the two-stage combustion air port 4. . The high-temperature combustion gas generated in this way is guided from the furnace 2 to the heat transfer tube group 6 and is subjected to heat exchange.

  On the inner wall surface of the furnace 2, a large number of furnace wall tubes (not shown) whose longitudinal direction is the vertical direction are arranged along the inner wall surface in the horizontal direction. Steam is circulated in each furnace wall tube, and the steam pressure in each furnace wall tube is increased by heat generated by combustion in the furnace 2.

(Sulfuric corrosion prediction method)
Next, the sulfide corrosion prediction method of this embodiment will be described with reference to the flowchart shown in FIG. The sulfide corrosion prediction method of this embodiment predicts the degree of sulfide corrosion of a furnace wall tube using the amount of corrosion of the furnace wall tube of the boiler 1 using pulverized coal as a fuel, and a reaction fluid incorporating a coal combustion model. A step of calculating, a step of calculating a flue gas composition by thermodynamic equilibrium calculation, a step of obtaining a corrosion rate equation by a high temperature corrosion test, a step of calculating a temperature distribution and a gas concentration distribution, and an evaluation of sulfide corrosion environment And steps.

(Reaction fluid calculation incorporating a coal combustion model)
The step of calculating the reaction fluid incorporating the coal combustion model (hereinafter referred to as the reaction fluid calculation step) is performed by limiting the chemical species to be calculated from all the chemical species generated during the combustion of pulverized coal. This is a step of performing fluid calculation.

  When numerically analyzing pulverized coal combustion, a method is considered in which the solid-gas two-phase flow is divided into a continuous phase (fluid) and a dispersed phase (pulverized coal particles) and these interactions are solved together with the governing equations. There are many cases. The governing equation of the continuous phase is generally composed of a continuous equation, a momentum conservation equation, an energy conservation equation, and a chemical species conservation equation as an incompressible / viscous fluid. Further, the governing equation of the dispersed phase is generally composed of an equation of motion, an energy conservation equation, and a chemical species conservation equation.

  As a coal combustion model, a model is widely used in which volatile components are released and fixed carbon components undergo a surface reaction while being gas-combusted. An Arrhenius type reaction rate equation or its improved equation is often used for the release rate of volatile matter and the reaction rate of solid carbon. An example is shown below.

(A) Release rate of volatile matter

Here, V: volatile loss, _{k V:} reaction rate constant, _{A V:} frequency factor, _{T p:} particle temperature, R: gas constant, _{E V:} activation energy, ^{V *:} rapid volatile content, Q: rapid temperature Volatilization coefficient when warm, V _IA : volatile content in industrial analysis.

(B) Reaction rate of fixed carbon content

Here, C ₁ : diffusion rate, c ₁ : diffusion rate coefficient, T _p : particle temperature, T _∞ : fluid temperature, d _p : particle diameter, C ₂ : surface reaction rate, c ₂ : frequency factor, E _c : Activation energy, R: gas constant, C: fixed carbon content, A _p : particle surface area, p _o2 : oxygen partial pressure.

  However, due to the computational load, many difficulties are involved in the reaction fluid calculation considering all chemical species generated during the combustion of pulverized coal. Therefore, a reaction model in which chemical species to be calculated are limited and reaction fluid calculation is simplified is often used. The reaction model used in the present embodiment is shown below.

_{C a H b O c S d} N e + nO 2 → αCO + βH 2 O + δSO 2 + εN 2 ··· (7)
C + 1 / 2O ₂ → CO (8)
CO + 1 / 2O ₂ → CO ₂ (9)

  Here, the first term on the left side of the formula (7) is a chemical species that simulates a volatile component determined from elemental analysis and rapid volatile content.

The specific procedure of this calculation is shown here. First, the following four pieces of information are necessary for this calculation.
(A) Boiler geometric information (the shape of the boiler 1, the position of the burner 3, the position of the air port 4 for two-stage combustion, etc.),
(B) Combustion air conditions (total air ratio, combustion air flow rate / temperature / composition at each two-stage combustion air port 4),
(C) Coal properties (industrial analysis [water, ash, volatile matter / fixed carbon content], elemental analysis [C, H, N, O, S]),
(D) Coal supply amount (coal supply amount from each burner 3).

  First, as shown in FIG. 3, which is a transparent perspective view of the boiler 1, an analysis target region 11 is provided along the furnace wall of the boiler 1 based on the boiler geometric information (step S <b> 1, hereinafter, It is simply called S1. Here, rather than providing the analysis target region 11 on the furnace wall surface of the boiler 1, the accuracy of the calculation result is improved when the analysis target region 11 is provided near the furnace wall of the boiler 1. Therefore, in the present embodiment, the analysis target region 11 is provided in the vicinity of the furnace wall of the boiler 1. The furnace wall of the boiler 1 is provided with a burner connection portion 3a to which the burner 3 is connected and a two-stage combustion air port connection portion 4a to which the two-stage combustion air port 4 is connected.

  Then, the combustion conditions (coal supply amount, combustion air flow rate / temperature / composition) and other boundary conditions are set for each burner 3 and two-stage combustion air port 4 (S2). Next, parameters related to coal combustion (reaction rate constant of fixed carbon, rapid volatile content, etc.) are set (S3).

Thereafter, in the analysis target region 11, reaction fluid calculation is performed using the set combustion conditions, boundary conditions, and parameters relating to coal combustion (S4). _{Thus, O 2, CO, H 2} O, SO 2, N 2, gas concentration and temperature of CO ₂ is calculated. This calculation result is compared with the actual measurement data of the boiler 1 (such as the unburned rate at the furnace outlet and the actual measurement result of gas and temperature in the furnace) (S5). And it is determined whether a calculation result corresponds with the measurement data of the boiler 1 (S6).

  If it is determined that the calculation result does not match the actual measurement data of the boiler 1 (S6, NO), the process returns to step S3 to reset the parameters relating to coal combustion. That is, the reaction fluid calculation is repeated while changing the parameters related to coal combustion until the result of the reaction fluid calculation matches the actually measured data. Thereby, the calculation result along combustion in the actual boiler 1 can be obtained. On the other hand, when it is determined that the calculation result matches the actual measurement data of the boiler 1 (S6, YES), the process proceeds to step S31.

(Combustion exhaust gas composition calculation by thermodynamic equilibrium calculation)
The step of calculating the flue gas composition by the thermodynamic equilibrium calculation (hereinafter referred to as the flue gas composition calculation step) includes the gas concentration of the chemical species that can be obtained in the reaction fluid calculation step by the thermodynamic equilibrium calculation, It is a step (concentration relation derivation step) for obtaining a concentration relational expression with a gas concentration of a specific chemical species that is necessary in the sulfide corrosion environment evaluation step described later and cannot be obtained in the reaction fluid calculation step described above. Performed in parallel with the calculation step.

As described above, in the reaction fluid calculation step, a reaction model in which reaction calculation is simplified by limiting chemical species to be calculated is frequently used. However, many of these reaction models do not incorporate a specific chemical species required in the sulfide corrosion environment evaluation step described later. In such a case, it is necessary to interpolate the gas concentration of the specific chemical species with respect to the reaction fluid calculation result obtained in step S4. In the present embodiment, it is necessary to interpolate the gas concentration of H ₂ S required in the sulfide corrosion environment evaluation step.

Therefore, by calculating the combustion exhaust gas composition by thermodynamic equilibrium calculation, it is necessary in the gas concentration of chemical species that can be obtained by the reaction fluid calculation of this embodiment and the sulfide corrosion environment evaluation step. A concentration relational expression with a gas concentration of a specific chemical species that cannot be obtained by the reaction fluid calculation is derived. Specifically, a concentration relational expression between the CO gas concentration that can be obtained by the reaction fluid calculation of the present embodiment and the H ₂ S gas concentration that cannot be obtained by the reaction fluid calculation of the present embodiment is derived. . Here, the thermodynamic equilibrium calculation is a method of calculating an equilibrium composition that minimizes the Gibbs free energy based on the coal properties and the combustion conditions of the coal using an optimization method.

  First, the theoretical air amount is calculated from the coal properties (elemental analysis) (S11). Then, the combustion condition is set using the air ratio (the ratio of the actual air amount to the theoretical air amount) as a parameter (S12). Next, thermodynamic equilibrium calculation is performed under the set combustion conditions, and the gas composition at each temperature is extracted (S13).

Next, the above calculation is executed by increasing the number of parameters, and the gas concentration of the chemical species (CO) that can be obtained by the reaction fluid calculation of this embodiment and the specific chemistry required in the sulfide corrosion environment evaluation step. A concentration relational expression with the gas concentration of the seed (H ₂ S) is obtained (S14). FIG. 4 shows a concentration relational expression between the CO gas concentration and the H ₂ S gas concentration for each temperature.

(Calculation of corrosion rate equation by high temperature corrosion test)
The step of obtaining the corrosion rate equation by the high-temperature corrosion test (hereinafter referred to as the corrosion rate equation calculating step) includes the temperature of the furnace wall tube and the specific chemical species (H ₂₎ by the high temperature corrosion test of the metal material forming the furnace wall tube. S) is a step for obtaining a corrosion rate equation (corrosion rate equation deriving step) which is a relational expression between the gas concentration and the elapsed time, and is performed in parallel with the reaction fluid calculation step and the combustion exhaust gas composition calculation step.

In the corrosion rate equation calculating step, a corrosion rate equation is calculated (S21). Here, the corrosion rate is a corrosion amount per unit time (corrosion loss), and is a mass reduction amount (for example, mg / (m ² · year)) or a thickness reduction amount (for example, mm / year) per unit area. Expressed. The numerical value of the corrosion rate is estimated by directly measuring the corrosion weight loss or measuring the corrosion current density by an electrochemical method. Generally, the corrosion rate is used as an index when general corrosion or uniform corrosion occurs, and is usually a corrosion-resistant material if the corrosion rate is 0.1 mm / year or less, but local corrosion often occurs. Need attention.

In obtaining the corrosion rate equation, first, a high temperature gas corrosion test established in JIS Z2291 was performed, and the weight change and corrosion thickness due to corrosion of the metal material forming the furnace wall tube were measured. At this time, the surface temperature of the furnace wall tube, the gas concentration of H ₂ S, and the presence or absence of ash were used as parameters. The test results are shown in FIG.

  Here, the growth rate equation of the coating film due to the corrosion product is generally expressed by equation (10), although it varies depending on the film thickness.

δ = k _δ t ⁿ (10)

Here, δ is a thickness reduction [μm] due to corrosion, k _δ is a coefficient determined by an Arrhenius type reaction rate equation, t is an elapsed time [hr], and n is a corrosion index (corrosion rate). Index).

  Also, the amount of change in weight due to corrosion is expressed by equation (11), as in the case of film thickness.

ΔW = k _W t ⁿ (11)

Here, [Delta] W is the weight change due to corrosion _{^{[mg / cm 2], k}} W is a constant. Regardless of which equation (10) or equation (11) is used, the corrosion index n is obtained by plotting the test result on a log-log graph with elapsed time on the horizontal axis and weight change ΔW on the vertical axis. be able to.

  In addition, as an equation for predicting the chemical reaction rate at a certain temperature, the Arrhenius type reaction rate equation represented by the equation (12) is used.

Here, A is a frequency factor, E _a is activation energy, and R is a gas constant. The numerical value of each index can be obtained by placing the test result on an Arrhenius plot.

  In this case, the thickness reduction length δ [mm] due to corrosion was calculated from the equation (13).

δ [mm] = ΔW [mg / cm ² ] ÷ Density [g / cm ³ ] × 10 ² (13)

Here, the density refers to the density of the coating formed by corrosion. In the present embodiment, as a result of separate investigation, the thickness reduction length δ due to corrosion was calculated with a density of 0.4 [g / cm ³ ].

In the case of sulfidation corrosion, an important corrosion amount is a thickness reduction amount, and it is important to obtain a relational expression between the thickness reduction amount, time, temperature, and H ₂ S concentration. That is, the relational expression between the thickness reduction amount δ, the time t, the temperature T, and the H ₂ S concentration x is Expression (14).

  δ = f (t, T, x) (14)

  Since the thickness reduction amount δ can be expressed by equation (10), when equation (12) is substituted into equation (10), equation (15) is obtained.

Here, corrosion index n, frequency factor A, and the activation energy E _a, and rearranging respective relationships between the concentration of H 2 _S x, as shown in FIG. 6, corrosion index n, frequency factor A, and the activation energy E _a, relationship between the concentration of H 2 _S x is derived, respectively. Therefore, assuming that the corrosion index n, the frequency factor A, and the activation energy E _a are related to the H ₂ S concentration x, Equation (15) becomes Equation (16).

The equation (16) thus obtained is a corrosion rate equation that is a relational expression between the temperature T of the furnace wall tube, the gas concentration x of the specific chemical species (H ₂ S), and the elapsed time t.

(Calculation of temperature distribution and gas concentration distribution)
The step of calculating the temperature distribution and the gas concentration distribution (hereinafter referred to as the calculation step) is based on the result of the reaction fluid calculation step and the chemical species obtained by the temperature distribution in the analysis target region 11 and the reaction fluid calculation. Using the step (temperature / concentration calculation step) of calculating the gas concentration distribution in the analysis target region 11 of the gas, the calculated temperature distribution and gas concentration distribution, and the concentration relational expression obtained in the combustion exhaust gas composition calculating step. And a step of calculating a gas concentration distribution of the specific chemical species in the region 11 (concentration calculating step).

  Here, when the sulfide corrosion environment evaluation step described later is taken into consideration, it becomes easier to evaluate by dividing the analysis target region 11 into blocks of a certain size and calculating an average value for each block. Therefore, in the present embodiment, as shown in FIG. 3, the analysis target region 11 is divided into approximately 1 m square blocks 11a, and the average value is calculated for each block 11a, whereby the temperature distribution and gas in the analysis target region 11 are calculated. The concentration distribution is calculated.

  In step S6 of FIG. 2, when it is determined that the result of the reaction fluid calculation matches the actual measurement data of the boiler 1 (S6, YES), the temperature distribution in the analysis target region 11 based on the result of the reaction fluid calculation, and The gas concentration distribution in the analysis target region 11 of the chemical species obtained by the reaction fluid calculation is calculated (S31). Specifically, the temperature distribution and gas concentration in the vicinity of the furnace wall of the boiler 1 are calculated for each block 11a by calculating the average value of the temperature and the average value of the gas concentration of the chemical species obtained by the reaction fluid calculation. Calculate the distribution.

Next, the gas concentration distribution of the specific chemical species in the analysis target region 11 is calculated using the temperature distribution and gas concentration distribution calculated in step S31 and the concentration relational expression obtained in step S14 (S32). Specifically, the gas concentration distribution of the specific chemical species in the vicinity of the furnace wall of the boiler 1 is calculated for each block 11a by calculating the gas concentration of the specific chemical species. More specifically, using the relational expression between the CO gas concentration and the H ₂ S gas concentration shown in FIG. 4 and the temperature distribution and CO gas concentration distribution calculated in step S31, the furnace wall of the boiler 1 is used. A gas concentration distribution of H ₂ S in the vicinity is calculated. In this way, the gas concentration distribution in the analysis target region 11 of the specific chemical species (H ₂ S) that cannot be obtained by the reaction fluid calculation is interpolated. Thereafter, the process proceeds to step S41.

(Sulfurized corrosion environment evaluation)
The step of evaluating the sulfide corrosion environment (hereinafter referred to as the sulfide corrosion environment evaluation step) includes the corrosion rate equation calculated in the corrosion rate equation calculation step, the temperature of the furnace wall tube, and the gas of the specific chemical species calculated in the calculation step. Using the concentration distribution, the step of calculating the corrosion amount distribution in the analysis target region 11 (corrosion amount calculating step) and the degree of sulfurization corrosion of the furnace wall tube in the analysis target region 11 using the calculated distribution of corrosion amount A step of predicting the distribution of (prediction step).

First, the corrosion amount distribution in the analysis target region 11 is calculated using the corrosion rate equation calculated in step S21 of FIG. 2, the temperature of the furnace wall tube, and the gas concentration distribution of the specific chemical species calculated in step S32. (S41). Specifically, the amount of corrosion is calculated for each block 11a by substituting the elapsed time t, the temperature T of the furnace wall tube, and the gas concentration x of the specific chemical species (H ₂ S) into the corrosion rate equation. Thus, the distribution of the corrosion amount in the vicinity of the furnace wall of the boiler 1 is calculated.

  Then, using the calculated distribution of corrosion amount, the distribution of the degree of sulfide corrosion of the furnace wall tube in the analysis target region 11 is predicted (S42). Specifically, the distribution of the degree of sulfidation corrosion of the furnace wall tube in the vicinity of the furnace wall of the boiler 1 is predicted by predicting the degree of sulfidation corrosion of the furnace wall pipe for each elapsed time and for each block 11a. Thereafter, the corrosion prediction result is mapped (S43). FIG. 7 shows the results when the elapsed time t is 1 year, 5 years, and 7 years, respectively. In addition, corrosion prediction is not performed in the block 11a including the burner connection part 3a or the two-stage combustion air port connection part 4a (see FIG. 3). The corrosion prediction result after the elapsed time t of 7 years was in good agreement with the measurement result of the corrosion amount of the boiler wall tube of the boiler after 7 years from the start of operation.

  By mapping the corrosion prediction result, it is possible to predict in which area of the analysis target region 11 when and how much corrosion will occur in block 11a units. Based on this result, the occurrence of sulfide corrosion can be suppressed by performing thermal spraying on a region where sulfide corrosion is expected to occur.

(effect)
As described above, according to the sulfide corrosion prediction method according to this embodiment, the gas concentration of the chemical species that can be obtained by the reaction fluid calculation and the specification that cannot be obtained by the reaction fluid calculation by the thermodynamic equilibrium calculation. By obtaining the concentration relational expression with the gas concentration of the chemical species, the gas in the analysis target region 11 of the specific chemical species that cannot be obtained by the reaction fluid calculation using the calculated temperature distribution and the gas concentration distribution and the concentration relational expression. The concentration distribution can be calculated. Accordingly, the corrosion amount distribution in the analysis target region 11 can be calculated using the corrosion rate equation, the temperature of the furnace wall tube, and the gas concentration distribution of the specific chemical species, and the furnace in the analysis target region 11 can be calculated. The distribution of sulfidation corrosion degree of the wall pipe can be predicted. Specifically, it is possible to predict where and how much corrosion will occur in which region of the analysis target region 11. In this way, by interpolating the gas concentration of a specific chemical species that cannot be obtained by reaction fluid calculation using the concentration relational equation obtained by thermodynamic equilibrium calculation, sulfidation corrosion of the furnace wall tube using reaction fluid calculation The degree can be predicted.

  Moreover, the temperature distribution and gas concentration distribution in the vicinity of the furnace wall of the boiler 1 are calculated by dividing the analysis target region 11 into a plurality of blocks 11a and calculating average values of temperature and gas concentration for each block 11a. Then, by obtaining the gas concentration and corrosion amount of the specific chemical species for each block 11a, and predicting the degree of sulfidation corrosion of the furnace wall tube for each elapsed time and for each block 11a, the evaluation can be facilitated. .

  Further, by repeating the reaction fluid calculation while changing the parameters relating to coal combustion until the result of the reaction fluid calculation matches the actual measurement data, the calculation result along the combustion in the actual boiler 1 can be obtained. Thereby, the sulfurization corrosion degree of the furnace wall tube can be predicted with high accuracy.

(Modification of this embodiment)
The embodiment of the present invention has been described above, but only specific examples are illustrated, and the present invention is not particularly limited, and the specific configuration and the like can be appropriately changed in design. Further, the actions and effects described in the embodiments of the invention only list the most preferable actions and effects resulting from the present invention, and the actions and effects according to the present invention are described in the embodiments of the present invention. It is not limited to what was done.

DESCRIPTION OF SYMBOLS 1 Boiler 2 Furnace 3 Burner 4 Two-stage combustion air port 5 Crusher 6 Heat transfer tube group 11 Analysis object area 11a Block

Claims (3)

In the method for predicting sulfidation corrosion of a boiler furnace wall tube that predicts the degree of sulfidation corrosion of the furnace wall pipe using the amount of corrosion of the furnace wall pipe of a boiler fueled with pulverized coal,
In the analysis target region provided along the furnace wall of the boiler in the boiler, the reaction fluid calculation is performed by limiting the chemical species to be calculated from all the chemical species generated during the combustion of the pulverized coal. A reaction fluid calculation step to be performed;
Gas of a specific chemical species that is necessary for calculating the gas concentration of the chemical species that can be obtained by the reaction fluid calculation and the amount of corrosion by thermodynamic equilibrium calculation, and that cannot be obtained by the reaction fluid calculation. A concentration relationship deriving step for obtaining a concentration relationship with the concentration;
Corrosion rate equation derivation step for obtaining a corrosion rate equation which is a relational expression of the temperature of the furnace wall tube, the gas concentration of the specific chemical species, and the elapsed time by a high temperature corrosion test of the metal material forming the furnace wall tube. When,
Based on the result of the reaction fluid calculation, a temperature / concentration calculation step for calculating a temperature distribution in the analysis target region and a gas concentration distribution in the analysis target region of the chemical species obtained by the reaction fluid calculation;
Using the temperature distribution and gas concentration distribution calculated in the temperature / concentration calculating step, and the concentration relational expression, a concentration calculating step for calculating the gas concentration distribution of the specific chemical species in the analysis target region;
Using the corrosion rate equation, the temperature of the furnace wall tube, and the gas concentration distribution of the specific chemical species calculated in the concentration calculating step, a corrosion amount calculation that calculates the distribution of the corrosion amount in the analysis target region Steps,
Using the corrosion amount distribution calculated in the corrosion amount calculation step, a prediction step of predicting a distribution of the degree of sulfide corrosion of the furnace wall tube in the analysis target region;
A method for predicting sulfidation corrosion of a boiler furnace wall tube. The analysis target area is provided near the furnace wall of the boiler, and is divided into a plurality of blocks,
The temperature / concentration calculation step calculates the average value of the temperature and the average value of the gas concentration of the chemical species obtained by the reaction fluid calculation for each block, so that the temperature in the vicinity of the furnace wall of the boiler is calculated. Distribution and gas concentration distribution,
The concentration calculation step calculates the gas concentration distribution of the specific chemical species in the vicinity of the furnace wall of the boiler by calculating the gas concentration of the specific chemical species for each of the blocks,
The corrosion amount calculating step calculates the corrosion amount distribution in the vicinity of the furnace wall of the boiler by calculating the corrosion amount for each block.
The predicting step predicts a distribution of the degree of sulfidation corrosion of the furnace wall pipe in the vicinity of the furnace wall of the boiler by predicting the degree of sulfidation corrosion of the furnace wall pipe for each elapsed time and for each block. The method for predicting sulfidation corrosion of a boiler furnace wall pipe according to claim 1, wherein   3. The boiler furnace according to claim 1, wherein in the reaction fluid calculation step, the reaction fluid calculation is repeated while changing parameters relating to coal combustion until a result of the reaction fluid calculation matches actual measurement data. Method for predicting sulfidation corrosion of wall pipes.

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