阅读说明：本技术 一种锅炉水冷壁高温腐蚀预测及寿命评估方法 (Method for predicting high-temperature corrosion of boiler water-cooled wall and evaluating service life of boiler water-cooled wall ) 是由 张恩先 丁守一 岳峻峰 帅云峰 陈波 黄亚继 刘鑫雅 耿察民 杨振 陈华桂 王亚 于 2019-10-28 设计创作，主要内容包括：本发明公开了一种锅炉水冷壁高温腐蚀预测及寿命评估方法,包括：建立水冷壁高温腐蚀反应模型,确定腐蚀反应的化学反应以及影响反应速率的影响因素；结合腐蚀反应的反应机理,确定H<Sub>2</Sub>S在反应界面的扩散速率和化学反应速率；通过守恒原理计算腐蚀过程中锅炉水冷壁的金属基体厚度的变化规律,建立腐蚀物理量与时间之间的函数关系；根据电站锅炉水冷壁的安全运行要求,建立腐蚀寿命评估准则,计算出指定情况下水冷壁金属基体的最大寿命。本发明能够基于化学反应机理和数学推导,结合数理统计理论,建立腐蚀物理量随时间变化的数学模型,并进行水冷壁管道寿命评估,综合考虑了温度和H<Sub>2</Sub>S浓度对腐蚀寿命的影响权重,确定了水冷壁管道的高温腐蚀剩余寿命时间。(The invention discloses a method for predicting high-temperature corrosion of a boiler water wall and evaluating service life, which comprises the following steps: establishing a water-cooled wall high-temperature corrosion reaction model, and determining a chemical reaction of a corrosion reaction and influence factors influencing the reaction rate; determination of H in conjunction with the reaction mechanism of the corrosion reaction 2 The diffusion rate and the chemical reaction rate of S at the reaction interface; calculating the change rule of the thickness of the metal matrix of the boiler water-cooling wall in the corrosion process by a conservation principle, and establishing a functional relation between corrosion physical quantity and time; and establishing a corrosion life evaluation criterion according to the safe operation requirement of the water-cooled wall of the power station boiler, and calculating the maximum life of the metal matrix of the water-cooled wall under the specified condition. The method can establish a mathematical model of the change of the corrosion physical quantity along with time based on a chemical reaction mechanism and mathematical derivation combined with a mathematical statistics theory, evaluate the service life of the water-cooled wall pipeline, and comprehensively consider the temperature and H 2 Effect of S concentration on Corrosion LifeAnd determining the high-temperature corrosion residual life time of the water wall pipeline according to the response weight.)

1. A method for predicting high-temperature corrosion of a boiler water wall and evaluating service life is characterized by comprising the following steps:

s1: establishing a water-cooled wall high-temperature corrosion reaction model, and determining a chemical reaction of a corrosion reaction and influence factors influencing the reaction rate;

s2: determining H according to the reaction model established in the step S1 and combining the reaction mechanism of the corrosion reaction₂The diffusion rate and the chemical reaction rate of S at the reaction interface;

s3: calculating the change rule of the thickness of the metal matrix of the boiler water-cooling wall in the corrosion process by a conservation principle, and establishing a functional relation between corrosion physical quantity and time;

s4: and establishing a corrosion life evaluation criterion according to the safe operation requirement of the water-cooled wall of the power station boiler, and calculating the maximum life of the metal matrix of the water-cooled wall under the specified condition.

2. The method for predicting high-temperature corrosion and estimating life of a boiler water wall according to claim 1, wherein in step S1, the process of establishing a water wall high-temperature corrosion reaction model, and determining chemical reactions of corrosion reactions and influencing factors influencing reaction rates comprises the following steps:

based on the chemical reaction of hydrogen sulfide with metallic iron: h₂S+Fe→FeS+H₂Establishing a water-cooled wall high-temperature corrosion reaction model, wherein the generated corrosion product FeS does not fall off and is always attached to the surface of the metal matrix in the whole corrosion period, the corrosion product FeS grows towards the gas direction and the metal matrix direction simultaneously, and L_bInitial thickness of metal matrix for water wall, L_iThickness of metal substrate not corroded at time t, L₀The integral thickness of the boiler water-cooling wall subjected to corrosion at the time t is shown, wherein the boiler water-cooling wall subjected to corrosion comprises a metal matrix which is not corroded and a corrosion product layer which grows;

the influencing factors influencing the reaction rate include: corrosive gas H₂S is the diffusion speed of the solid phase corrosion product layer to the metal matrix direction, and the chemical reaction rate of the hydrogen sulfide and the metal iron at the reaction interface.

3. The method for predicting high-temperature corrosion and evaluating life of boiler water wall according to claim 2, wherein in step S2, the H is determined according to the reaction model established in step S1 and by combining the reaction mechanism of the corrosion reaction₂The process of the diffusion rate and the chemical reaction rate of S at the reaction interface comprises the following steps:

s21: calculating H by combining the following formula₂Diffusion rate of S at the reaction interface:

wherein J is H₂S gas diffusion flux in mg/(m)²S); d is H₂The diffusion coefficient of S gas in the corrosion product FeS layer is m²S; c is H₂S gas concentration in mg/Nm³(ii) a dC/dL is H₂S, the concentration gradient of the gas along the thickness direction of the metal layer;

taking boundary conditions: (a) l ═ L_i，C＝C_i；(b)L＝L₀，C＝C₀Integration of the above equation yields:

s22: calculating H by combining the following formula₂Chemical reaction rate of S on the reaction interface:

wherein m is_H2STo take part in chemical reactions₂Mass of S gas in mg; k is the intrinsic speed of the chemical reaction and has the unit of m/s; s is the surface area of the metal exposed to the corrosive atmosphere in m²；

S23: during the corrosion process, the diffusion flux J is expressed as:

s24: all the formulas are combined, and C is_iElimination is carried out to obtain:

4. the method for predicting high-temperature corrosion and evaluating service life of a boiler water-cooling wall according to claim 3, wherein in the step S3, the process of calculating the change rule of the thickness of the metal matrix of the boiler water-cooling wall in the corrosion process through the conservation principle and establishing the functional relation between the physical corrosion quantity and the time comprises the following steps:

s31: according to the main chemical reaction equation, the H participating in the reaction₂The mole numbers of S and Fe are the same, and the change of the thickness of the metal matrix which is not corroded is calculated by combining the following formula:

wherein M is_H2SIs H₂The molar mass of S is g/mol; rho_FeIs the density of metallic Fe in kg/m³；M_FeIs the molar mass of Fe, in g/mol;

s32: according to the main reaction equation, the molar amount of Fe participating in the reaction is equal to the molar amount of FeS generated, i.e.:

n_Fe＝n_FeS

is equivalent to:

simplifying to obtain:

s33: establishing a functional relationship between the physical corrosion quantity and the time, the following can be obtained:

integration yields:

boundary conditions are adopted: substituting t as 0 and Li as Lb to obtain C as 0;

s34: defining the value of the initial metal thickness of the corroded layer as the average corrosion rate X of the metal:

calculating the function relationship of the average corrosion rate X of the metal and the time t:

wherein, V_FeIs the molar volume of Fe, m³/mol×10³；V_FeSIs the molar volume of FeS, m³/mol×10³。

5. The method for predicting high-temperature corrosion and evaluating life of the boiler water wall according to claim 1 or 4, wherein in the step S4, establishing a corrosion life evaluation criterion according to the safe operation requirement of the utility boiler water wall, and the process of calculating the maximum life of the water wall metal matrix under the specified condition comprises the following steps:

calculating to obtain a corresponding high-temperature corrosion evaluation criterion threshold value phi according to the safe operation requirement of the water-cooled wall of the power station boiler, and when the average corrosion rate X of metal is greater than phi, considering that the service life of the metal of the water-cooled wall of the boiler is prolonged and the risk of tube explosion of the water-cooled wall is encountered;

and (4) calculating to obtain the maximum service life value of the boiler water wall metal used safely under the corresponding safe operation requirement.

6. The method for predicting the high-temperature corrosion of the boiler water wall and evaluating the service life of the boiler water wall according to claim 5, wherein the influence factors of the evaluation criterion threshold value phi of the high-temperature corrosion comprise a pipeline tensile stress or compressive stress parameter, a temperature parameter, and the concentration of other known corrosive gases except FeS in a corrosive medium.

7. The method for predicting high-temperature corrosion and evaluating life of a boiler water wall according to claim 1, further comprising:

and estimating the corrosion degree of the metal matrix of the water-cooled wall by combining the service time of the metal of the water-cooled wall and the local parameter conditions.

Technical Field

The invention relates to the technical field of safe operation of large power station boilers, in particular to a method for predicting high-temperature corrosion of a water wall of a boiler and evaluating the service life of the water wall of the boiler.

Background

In order to reduce the pollutant emission of coal-fired power stations, various large power plants are generally transformed into ultra-low emission. In order to control the discharge amount of NOX, the generation amount of NOX in the furnace is reduced by adopting a concentration deviation combustion and air staged combustion mode, so that a strong reducing atmosphere is easily formed. Some power plants blend high sulfur coal in order to reduce fuel costs. The fuel is heated in a reducing atmosphere to release a large amount of ferrous sulfide, atomic sulfur and hydrogen sulfide, and the atomic sulfur and hydrogen sulfide gas can permeate through a loose iron oxide layer to perform a vulcanization reaction with the internal matrix metal, so that a serious corrosion problem is caused. The problem of tube explosion of the water wall caused by corrosion seriously affects the operation safety of a power plant and also adversely affects the stable operation of a power grid. According to statistics, the unplanned outage hours of thermal power generating units in China caused by water wall tube explosion account for about 37.8% of the total annual unplanned outage time of the units, so that huge economic loss is brought, and the economic benefit of a power plant is seriously influenced.

There are many factors that cause high temperature corrosion, such as: coal quality, burner structure and mode of operation, water wall temperature conditions, and the like. And the corrosion degree of the water-cooled wall is difficult to measure visually and quantificationally while the boiler is running, and the corrosion degree can be evaluated only by measuring the thickness of the water-cooled wall during the overhaul shutdown period. This greatly limits the timeliness of handling corrosion safety issues, bringing great potential safety hazards.

Due to the lack of reliable real-time measurement means, the occurrence degree of high-temperature corrosion of the water-cooled wall of the existing boiler generally adopts a predictive and empirical method for prediction and evaluation. The following patents are related to the prediction of high temperature corrosion of boiler water wall:

(1) the invention patent 'diagnosis and prevention system for high-temperature corrosion state of boiler water wall' with patent number CN201020253522.X simply combines several influence factors of high-temperature corrosion of water wall, and carries out corrosion state judgment through dimensionless numbers obtained by empirical formula, and the data reliability is not high, and the research on mechanicalness is lacked.

(2) The invention patent CN02139804.6 discloses a method for judging the high-temperature corrosion degree of a water wall of a large-scale power station boiler, which judges the grade of the high-temperature corrosion tendency by a gray clustering method. The influence factors of the high-temperature corrosion of the water cooled wall are simply subjected to weight grading completely through a mathematical method, the actual action of the influence factors is not considered, and the safe service life of the water cooled wall cannot be predicted.

Disclosure of Invention

The invention aims to provide a method for predicting high-temperature corrosion of a boiler water wall and evaluating service life of the boiler water wall, which is based on a chemical reaction mechanism and mathematical derivation and combined with a mathematical statistics theory to establish a mathematical model of the change of corrosion physical quantity along with time and evaluate the service life of a water wall pipelineComprehensively takes into account the temperature and H₂The influence weight of the S concentration on the corrosion life determines the high-temperature corrosion residual life time of the water-cooled wall pipeline, and the method is an effective and feasible corrosion evaluation method.

To achieve the above objective, with reference to fig. 1, the present invention provides a method for predicting high temperature corrosion and evaluating life of a water wall of a boiler, comprising the following steps:

s1: establishing a water-cooled wall high-temperature corrosion reaction model, and determining a chemical reaction of a corrosion reaction and influence factors influencing the reaction rate;

s2: determining H according to the reaction model established in the step S1 and combining the reaction mechanism of the corrosion reaction₂The diffusion rate and the chemical reaction rate of S at the reaction interface;

s3: calculating the change rule of the thickness of the metal matrix of the boiler water-cooling wall in the corrosion process by a conservation principle, and establishing a functional relation between corrosion physical quantity and time;

s4: and establishing a corrosion life evaluation criterion according to the safe operation requirement of the water-cooled wall of the power station boiler, and calculating the maximum life of the metal matrix of the water-cooled wall under the specified condition.

The method mainly aims at the problem of high-temperature corrosion of the water-cooled wall, establishes a one-dimensional mathematical model of the high-temperature corrosion of the water-cooled wall based on a corrosion mechanism and by combining chemical reaction kinetics and mathematical derivation, and evaluates the service life of the water-cooled wall pipeline according to actual parameters.

Compared with the prior art, the technical scheme of the invention has the following remarkable beneficial effects:

(1) based on the chemical reaction mechanism and the mathematical derivation, and in combination with the mathematical statistics theory, a mathematical model of the change of the corrosion physical quantity along with the time is established, the service life of the water-cooled wall pipeline is evaluated, the evaluation result is more accurate, managers can conveniently master the use state of the water-cooled wall pipeline, and the safety coefficient of the water-cooled wall pipeline is improved.

(2) Comprehensively takes into account the temperature and the H₂The weight of the influence of the S concentration on the corrosion life is determinedThe high-temperature corrosion residual life time of the water-cooled wall pipeline simplifies the analysis problem and accelerates the operation speed on the premise of ensuring the accuracy of the evaluation result.

(3) When the evaluation criterion threshold phi of the high-temperature corrosion is calculated, the influence factors such as the tensile stress or compressive stress parameter of the pipeline, the temperature parameter, the concentration of other known corrosive gases except FeS in the corrosion medium and the like are comprehensively considered in combination with the actual situation, and the established evaluation criterion threshold is more consistent with the actual application scene.

(4) And estimating the corrosion degree of the water wall metal through the service time of the water wall metal and the local parameter conditions so as to achieve the aim of monitoring the safety of the water wall in real time.

It should be understood that all combinations of the foregoing concepts and additional concepts described in greater detail below can be considered as part of the inventive subject matter of this disclosure unless such concepts are mutually inconsistent. In addition, all combinations of claimed subject matter are considered a part of the presently disclosed subject matter.

The foregoing and other aspects, embodiments and features of the present teachings can be more fully understood from the following description taken in conjunction with the accompanying drawings. Additional aspects of the present invention, such as features and/or advantages of exemplary embodiments, will be apparent from the description which follows, or may be learned by practice of specific embodiments in accordance with the teachings of the present invention.

Drawings

The drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures may be represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. Embodiments of various aspects of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a flow chart of the method for predicting high-temperature corrosion and evaluating life of a boiler water wall according to the present invention.

FIG. 2 is a schematic structural diagram of a water wall high-temperature corrosion reaction model of the present invention.

Detailed Description

In order to better understand the technical content of the present invention, specific embodiments are described below with reference to the accompanying drawings.