Stress analysis method and stress on-line monitoring system for water-cooled wall lower header

Abstract

The invention relates to a stress analysis method of a water-cooled wall lower header. The stress analysis method comprises the following steps: establishing a stress mathematical model of the water-cooled wall lower header; performing finite element analysis on the stress mathematical model of the water-cooled wall lower header; carrying out fault diagnosis by utilizing stress feature extraction; a stress on-line monitoring system of a water-cooled wall lower header comprises a sensor module, a data acquisition and transmission module and a monitoring center software platform. Through combination of the two methods, comprehensive management from theoretical analysis to actual monitoring and from fault prediction to timely treatment of the water-cooled wall lower header can be realized, safe and stable operation of equipment is guaranteed to the greatest extent, the production efficiency is improved, and the operation cost and risk are reduced.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of detection of a water wall lower header of a boiler, and particularly relates to a stress analysis method and a stress online monitoring system for a water wall lower header of a boiler. BACKGROUND

[0002] In the process of thermal power generation, the water wall lower header of a boiler, as a key component, bears the circulation flow of a high-temperature and high-pressure mixture of steam and water, and at the same time, bears the thermal expansion and contraction constraint from the water wall pipe, the internal medium pressure, and the complex thermal stress and mechanical stress caused by the start and stop of the boiler and the load change. The traditional stress detection means is mostly offline detection after periodic shutdown, such as the use of strain gauges for patch measurement. This way not only consumes a large amount of manpower, material resources and downtime, but also cannot capture the real-time stress changes in the actual operation process of the boiler, and it is difficult to make timely early warning of sudden stress abnormal conditions. With the continuous improvement of the reliability requirements of the power industry on equipment and the rapid development of sensor technology, data transmission technology and computer analysis technology, it is extremely urgent to develop a method and system that can accurately analyze the stress of the water wall lower header of a boiler online. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies of the prior art and provide a stress analysis method and a stress online monitoring system for a water wall lower header of a boiler.

[0004] The purpose of the present application is achieved by a stress analysis method for a water wall lower header of a boiler, comprising the following steps:

[0005] S1: establishing a stress mathematical model of the water wall lower header of the boiler;

[0006] S2: performing finite element analysis on the stress mathematical model of the water wall lower header of the boiler;

[0007] S3: performing fault diagnosis by using stress feature extraction.

[0008] In the step S1, the drawings of the lower header and the water wall pipe and the basic information of the related components are sorted out to establish a basic information database; the database contains the basic parameters of the unit and the related equipment, the corresponding drawings, the product manual, the installation record, the inspection record, the subsequent maintenance plan and the internal self-checking record.

[0009] The stress mathematical model of the water wall lower header of the boiler comprises a header stress model and a water wall pipe stress model.

[0010] The lower header stress model comprises that there is a temperature difference ΔT between the inner wall and the outer wall of the lower header, the inner wall of the lower header will generate axial stress and tangential stress, and the outer wall of the lower header is subjected to tensile stress; the calculation formulae of the axial and tangential stresses of the outer wall of the lower header are:

[0011]

[0012] The calculation formulas for the axial and tangential stresses on the inner wall of the lower header are:

[0013]

[0014] Where: are the axial tensile stress, tangential tensile stress, axial compressive stress, and tangential compressive stress of the outer wall of the lower header respectively; E is the elastic modulus of the material; ΔT is the maximum temperature difference between the inner and outer walls; μ is the Poisson's ratio; β is the ratio of the inner and outer diameters, β=r a / r w .

[0015] The water-cooled wall tube stress model includes: the circumferential stress σ along the tangent direction θ , axial stress σ along the axis r , and radial stress σ along the radial direction γ :

[0016]

[0017] Where: d1, d2 are the inner radius and outer radius of the water-cooled wall tube; P is the internal pressure of the water-cooled wall tube,

[0018] When the water-cooled wall tube is a thin-walled tube, it can be considered that the stress is evenly distributed along the wall thickness. Due to the stress balance, the circumferential stress σ can be obtained. θ and axial stress σ r :

[0019]

[0020] The radial stress decreases linearly from the inner wall to the outer wall along the tube wall thickness. The radial stress at the inner wall is σ γ1 =-P, the outer wall is σ γ2 =0.

[0021] A stress online monitoring system for a water-cooled wall lower header comprises a sensor module, a data acquisition and transmission module and a monitoring center software platform.

[0022] The sensor modules are arranged on the surface of the lower header of the water-cooled wall and key internal parts. According to the stress distribution law and the identification results of the vulnerable area, the strain gauge sensors, temperature sensors and pressure sensors are reasonably arranged.

[0023] The data acquisition and transmission module constructs a dedicated data acquisition system to quickly collect and summarize the data transmitted by the sensors.

[0024] The monitoring center software platform receives real-time data from the data acquisition system, first carries out data cleaning, inputs the processed data into a pre-established stress analysis model, and carries out real-time stress calculation and fault diagnosis.

[0025] The present application has the following beneficial effects: by establishing a stress mathematical model and performing finite element analysis, the stress distribution of the lower header of the water wall under different working conditions can be simulated more accurately, the stress state is comprehensively understood, reliable basis is provided for accurately evaluating the safety of the structure, potential structural safety problems are found in advance, and equipment damage or even safety accidents caused by excessive stress are avoided. The stress online monitoring system can continuously and stably operate and long-term monitor the lower header of the water wall. By finding and processing small problems in time, equipment performance degradation caused by problem accumulation is prevented, the reliability and stability of the entire system are improved, and the equipment is kept in good working condition during long-term operation. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 Fig. 1 is a cross-sectional view of a lower header opening pipe model of the present application.

[0027] Figure 2 Fig. 2 is an analysis model diagram of the lower header of the present application.

[0028] Figure 3 Fig. 3 is a mesh division diagram of the analysis model of the lower header of the present application.

[0029] Figure 4 Fig. 4 is a temperature field distribution contour diagram of the lower header of the present application. Figure 4 Fig. 5 is an equivalent stress field distribution contour diagram of the lower header of the present application.

[0030] Figure 5 Fig. 6 is a stress analysis method of a lower header of a water wall. DETAILED DESCRIPTION

[0031] The present application will be further described below with reference to the accompanying drawings.

[0032] Example 1

[0033] As shown in Fig. 6, a stress analysis method of a lower header of a water wall includes the following steps: Figures 1-5

[0034] S1: establishing a stress mathematical model of the lower header of the water wall;

[0035] S2: performing finite element analysis on the stress mathematical model of the lower header of the water wall;

[0036] S3: performing fault diagnosis by using stress feature extraction.

[0037] ​In step S1, drawings of the lower header, water-cooled wall tubes, and basic information of related components are sorted out to establish a basic information database; the database includes basic parameters of the unit and related equipment, corresponding drawings, product manuals, installation records, previous maintenance, inspection records, subsequent maintenance plans, and internal self-inspection records.

[0038] The stress mathematical model of the water-cooled wall lower header includes a box stress model and a water-cooled wall tube stress model.

[0039] The stress model of the lower header includes: there is a temperature difference ΔT between the inner and outer walls of the lower header, the inner wall of the lower header will generate axial stress and tangential stress, and the outer wall of the lower header is subjected to tensile stress. The calculation formula of the axial and tangential stress of the outer wall of the lower header is:

[0040]

[0041] The calculation formulas for the axial and tangential stresses on the inner wall of the lower header are:

[0042]

[0043] Where: are the axial tensile stress, tangential tensile stress, axial compressive stress, and tangential compressive stress of the outer wall of the lower header respectively; E is the elastic modulus of the material; ΔT is the maximum temperature difference between the inner and outer walls; μ is the Poisson's ratio; β is the ratio of the inner and outer diameters, β=r a / r w .

[0044] The water-cooled wall tube stress model includes: the circumferential stress σ along the tangent direction θ , axial stress σ along the axis r , and radial stress σ along the radial direction γ :

[0045]

[0046] Where: d1, d2 are the inner radius and outer radius of the water-cooled wall tube; P is the internal pressure of the water-cooled wall tube,

[0047] When the water-cooled wall tube is a thin-walled tube, it can be considered that the stress is evenly distributed along the wall thickness. Due to the stress balance, the circumferential stress σ can be obtained. θ and axial stress σ r :

[0048]

[0049] The radial stress decreases linearly from the inner wall to the outer wall along the tube wall thickness. The radial stress at the inner wall is σ γ1 =-P, the outer wall is σ γ2 =0.

[0050] The present invention utilizes stress analysis methods to gain an in-depth understanding of the stress concentration areas of the water-cooled wall lower header, providing direction for equipment design optimization, such as adjusting structural dimensions, changing material selection, etc. At the same time, during equipment operation, a reasonable maintenance plan is formulated based on the stress analysis results, and high-stress areas are inspected and maintained in a targeted manner to improve the service life and operational reliability of the equipment. Fault diagnosis using stress feature extraction can promptly detect abnormal stress changes in the water-cooled wall lower header during operation. These changes may be early signs of equipment failure. Through early warning, timely measures can be taken to repair or replace components, reducing downtime, reducing maintenance costs, and ensuring the continuity of the production process.

[0051] Example 2

[0052] like Figures 1-5 As shown, a stress analysis method for a water-cooled wall lower header includes the following steps:

[0053] S1: Establish the stress mathematical model of the lower header of the water-cooled wall;

[0054] In step S1, drawings of the lower header, water-cooled wall tubes, and basic information of related components are sorted out to establish a basic information database; the database includes basic parameters of the unit and related equipment, corresponding drawings, product manuals, installation records, previous maintenance, inspection records, subsequent maintenance plans, and internal self-inspection records.

[0055] The stress mathematical model of the water-cooled wall lower header includes a box body stress model and a water-cooled wall tube stress model.

[0056] The stress model of the lower header includes: there is a temperature difference ΔT between the inner and outer walls of the lower header, the inner wall of the lower header will generate axial stress and tangential stress, and the outer wall of the lower header is subjected to tensile stress. The calculation formula of the axial and tangential stress of the outer wall of the lower header is:

[0057]

[0058] The calculation formulas for the axial and tangential stresses on the inner wall of the lower header are:

[0059]

[0060] Where: are the axial tensile stress, tangential tensile stress, axial compressive stress, and tangential compressive stress of the outer wall of the lower header respectively; E is the elastic modulus of the material; ΔT is the maximum temperature difference between the inner and outer walls; μ is the Poisson's ratio; β is the ratio of the inner and outer diameters, β=r a / r w .

[0061] Further, the elastomer is isotropic, and the thermal stress is generated when the temperature changes and is constrained, the strain caused by the temperature change is set as the initial strain, that is

[0062]

[0063] In the formula, γ is the angular strain.

[0064] The strain in each direction can be expressed as:

[0065]

[0066] The stress model of the water wall tube includes: the circumferential stress σ θ in the tangential direction, the axial stress σ r in the axial direction, and the radial stress σ γ in the radial direction:

[0067]

[0068] In the formula, d1 and d2 are the inner radius and the outer radius of the water wall tube; P is the internal pressure borne by the water wall tube,

[0069] When the water wall tube is a thin-walled tube, it can be considered that the stress is uniformly distributed along the wall thickness load, and due to stress balance, the circumferential stress σ θ and the axial stress σ r can be obtained:

[0070]

[0071] The radial stress decreases linearly along the wall thickness from the inner wall to the outer wall, and the radial stress at the inner wall is σ γ1 =-P, and the radial stress at the outer wall is σ γ2 =0.

[0072] Further, when the inner wall metal reaches the elastic-plastic limit state, if the internal pressure is further increased, an annular plastic zone will be formed near the inner wall of the cylinder, and with the increase of the internal pressure P, the plastic zone will continuously expand and increase outward. At this time, the tube wall is divided into two parts: the inner layer plastic zone and the outer layer elastic zone. Set the boundary radius of the elastic-plastic zone as r P , and the corresponding internal pressure as P P , when r P is equal to the outer radius r2 of the water wall tube, the entire wall thickness of the water wall tube enters the plastic state, at this time, it is called the plastic limit state, and the internal pressure load corresponding to this state becomes the limit load (limit pressure) P CBefore reaching the limit state, the plastic deformation of the water wall tube inside is not possible to be very large due to the constraint of the outer elastic zone, and can only be in the same order of magnitude as the elastic deformation. But from the limit state, the above constraint is removed, and the circular tube begins to produce large plastic deformation, which is an unconstrained plastic deformation. Before the limit state, the tube can be considered to be able to work normally, and after the limit state, it is considered to be no longer a normal working stage, because a slight increase in internal pressure can lead to excessive plastic deformation of the water wall tube and be damaged.

[0073] The components of several material combinations with different expansion coefficients, when the temperature distribution is uneven, if a part of the object is considered, the expansion and contraction parts will also be constrained due to the influence of adjacent parts with different temperatures, which will also generate internal stress. The above several internal stresses caused by uneven temperature distribution or constrained expansion and contraction are all thermal stresses.

[0074] Thermal stress is easy to cause during the start and stop of the boiler and the change of load. This temperature difference mainly causes axial thermal stress, which can be calculated by the following formula:

[0075] σ' = α1EΔtβ

[0076] In the formula: Δt is the maximum temperature difference; E is the Young's modulus; β is the correction coefficient; α1 is the linear expansion coefficient.

[0077] The stress caused by the expansion of the length direction is blocked: when the smooth tube is uniformly heated and the expansion direction is blocked, compression occurs in the tube, which causes stress in the tube, as follows:

[0078] σ' = -α1EΔt

[0079] The thermal elastic stress distribution caused by the radial temperature difference is: the water wall tube not only plays the role of a pressure boundary, but also more importantly, it transfers heat, transferring the heat in the flue gas outside the tube to the water or steam inside the tube. There must be a temperature difference between the inside and outside of the tube. When the tube is only subjected to the radial temperature difference Δt, the maximum thermal elastic stress occurs in the circumferential stress on the inner surface of the tube, and its value is calculated by the following formula:

[0080]

[0081] In the formula: μ is the Poisson's ratio of the material. When the heated surface tube is in normal operation, the heat flow always flows from the outer wall to the inner wall. At this time, the temperature of the outer wall is always higher than that of the inner wall, and the thermal elastic stress of the outer wall is compressive stress, and that of the inner wall is tensile stress.

[0082] S2: finite element analysis of the stress mathematical model of the water wall lower header;

[0083] Firstly, the model of the lower header of the water wall is established. The material of the lower header is 12Cr1MoV, and the specification is Φ305mm x 45mm. The material of the connecting pipe is 12CrlMoV, and the specification is Φ270mm x 38mm. The working parameters of the lower header are 10.1MPa and 580℃. The model is established by taking 1000mm of the length of the lower header and 200mm of the pipe extension. The full section view of the model is shown in FIG. 1. Figure 1

[0084] In the formula, A is the connecting pipe section of the lower header; B is the lower header; C is the inner connecting surface of the lower header and the connecting pipe; and D is the outer connecting surface of the lower header and the connecting pipe.

[0085] Since the model of the lower header is an axisymmetric model, the 1 / 4 three-dimensional model of the lower header is taken as the research object. The performance parameters of 12Cr1MoVg are shown in Table 1.

[0086]

[0087] Table 1: Performance parameters of 12Cr1MoVg

[0088] Since the calculation model takes 1 / 4 of the actual model, the boundary conditions need to be constrained, that is, the Z-axis direction displacement on the longitudinal section of the header is constrained, the X-axis direction displacement on the transverse section is constrained, and the Y-axis displacement at the key nodes is constrained.

[0089] Figures 2 to 5 The analysis model, the meshing of the model, the temperature field distribution, and the stress field distribution are shown in FIGS. 2, 3, 4, and 5, respectively.

[0090] Figure 4 The temperature field distribution contour map of the lower header is shown in FIG. 4. Figure 4 It can be seen that the maximum temperature of the lower header in the running state is 520℃, and the minimum temperature is 498℃. The inner wall of the lower header and the inner side of the connecting part of the lower header and the connecting pipe have the highest temperature.

[0091] Figure 5 The equivalent stress field distribution contour map of the lower header is shown in FIG. 5. Figure 5 It can be seen that the maximum stress of the connecting part of the lower header and the connecting pipe in the running state is 127MPa. Since the inner side of the connecting part of the lower header and the connecting pipe is the most dangerous in the running process, attention should be paid to the supervision and detection in the normal running process.

[0092] From the above analysis, it can be seen that the connecting part of the lower header and the connecting pipe has the maximum stress, and is the most easily damaged place. The generation of the cracks of the header is likely to be mainly caused by the failure of the connecting part of the header and the connecting pipe.

[0093] S3: Fault diagnosis is performed by using stress feature extraction.

[0094] ​A stress online monitoring system of a water wall lower header, comprising a sensor module, a data acquisition and transmission module and a monitoring center software platform.

[0095] The sensor module is arranged on the surface and key internal parts of the water wall lower header, and strain gauge sensors, temperature sensors and pressure sensors are arranged according to the stress distribution law and the identification results of the vulnerable areas.

[0096] High-precision strain gauge sensors are selected to measure the linear strain of the surface of the lower header, and the measurement accuracy can reach ±1με; at the same time, temperature sensors are equipped to monitor the temperature change of the lower header, and the accuracy is controlled within ±0.5℃ to consider the influence of thermal stress; in addition, in order to real-time master the pressure situation inside the lower header, pressure sensors are installed, and the measurement accuracy is 0.1MPa; the sensor module is connected with the acquisition terminal through reliable data transmission lines to ensure real-time and stable data transmission.

[0097] The data acquisition and transmission module constructs a special data acquisition system to quickly acquire and aggregate the data transmitted by the sensors.

[0098] A high-speed A / D converter is used to convert the analog signal into a digital signal, and the sampling frequency is set to more than 10Hz to meet the real-time monitoring requirements. Wireless transmission technology (such as Wi-Fi, Bluetooth or 4G / 5G module, selected according to the power plant site environment) or wired transmission mode (such as industrial Ethernet) is used to timely transmit the collected data to the server of the monitoring center, to ensure the timeliness and reliability of data transmission.

[0099] The monitoring center software platform receives real-time data from the data acquisition system, first performs data cleaning, inputs the processed data into a pre-established stress analysis model, and performs real-time stress calculation and fault diagnosis.

[0100] The monitoring center software platform receives real-time data from the data acquisition system, first performs data cleaning, removes abnormal values and noise interference, and uses sliding window average method and other algorithms to smooth the data. Then, the processed data is input into a pre-established stress analysis model for real-time stress calculation and fault diagnosis. Finally, through intuitive graphical interfaces such as two-dimensional stress cloud map, three-dimensional model dynamic display and real-time curve, the current stress state, historical change trend and potential fault risk of the water wall lower header are displayed to the operation and maintenance personnel, so that the operation and maintenance personnel can make timely decisions.

[0101] The application can deeply understand the stress concentration area of the water-cooled wall lower header by using the stress analysis method, and provide a direction for the design optimization of the equipment, such as adjusting the structure size, changing the material selection, etc. Meanwhile, during the operation of the equipment, a reasonable maintenance plan can be made according to the stress analysis result, and the high stress area can be checked and maintained in a targeted manner, so as to improve the service life and operation reliability of the equipment. The stress feature extraction is used for fault diagnosis, and the abnormal stress change of the water-cooled wall lower header in the operation process can be found in time. These changes can be early signs of equipment failure. Through early warning, measures can be taken in time for maintenance or replacement of parts, so as to reduce the downtime of the equipment, reduce the maintenance cost, and ensure the continuity of the production process.

[0102] The sensor module is reasonably arranged on the surface and the key internal parts of the water-cooled wall lower header, and can obtain the stress, temperature, pressure and other data of the equipment in real time. The data acquisition and transmission module collects and summarizes the data quickly, the monitoring center software platform receives and processes the data in real time, and the real-time monitoring of the state of the water-cooled wall lower header is realized. Once an abnormal situation occurs, the system can quickly issue an alarm, so that the operation and maintenance personnel can take measures in time to avoid the expansion of the fault.

Claims

1. A stress analysis method for a water-cooled wall lower header, characterized by: The following steps are involved: S1: Establish the stress mathematical model of the lower header of the water-cooled wall; S2: Conduct finite element analysis on the stress mathematical model of the water-cooled wall lower header; S3: Fault diagnosis using stress feature extraction.

2. The stress analysis method for a water-cooled wall lower header according to claim 1, characterized in that: In step S1, drawings of the lower header and water-cooled wall tubes and basic information of related components are sorted out to establish a basic information database.

3. The stress analysis method for a water-cooled wall lower header according to claim 2, characterized in that: The stress mathematical model of the water-cooled wall lower header includes a box stress model and a water-cooled wall tube stress model.

4. The stress analysis method for a water-cooled wall lower header according to claim 3, characterized in that: The stress model of the lower header includes: there is a temperature difference ΔT between the inner and outer walls of the lower header, the inner wall of the lower header will generate axial stress and tangential stress, and the outer wall of the lower header is subjected to tensile stress. The calculation formula of the axial and tangential stress of the outer wall of the lower header is: The calculation formulas for the axial and tangential stresses on the inner wall of the lower header are: Where: are the axial tensile stress, tangential tensile stress, axial compressive stress, and tangential compressive stress of the outer wall of the lower header respectively; E is the elastic modulus of the material; ΔT is the maximum temperature difference between the inner and outer walls; μ is the Poisson's ratio; β is the ratio of the inner and outer diameters, β=r a / r w .

5. The stress analysis method for a water-cooled wall lower header according to claim 4, characterized in that: The water-cooled wall tube stress model includes: the circumferential stress σ along the tangent direction θ , axial stress σ along the axis r , and radial stress σ along the radial direction γ : Where: d1, d2 are the inner radius and outer radius of the water-cooled wall tube; P is the internal pressure of the water-cooled wall tube, When the water-cooled wall tube is a thin-walled tube, it can be considered that the stress is evenly distributed along the wall thickness. Due to the stress balance, the circumferential stress σ can be obtained. θ and axial stress σ r : The radial stress decreases linearly from the inner wall to the outer wall along the tube wall thickness. The radial stress at the inner wall is σ γ1 =-P, the outer wall is σ γ2 =0.

6. An online stress monitoring system for a water-wall lower header, characterized by: It includes sensor module, data acquisition and transmission module and monitoring center software platform.

7. The online stress monitoring system for the water-cooled wall lower header according to claim 6, characterized in that: The sensor modules are arranged on the surface of the lower header of the water-cooled wall and key internal parts, and are reasonably arranged according to the stress distribution law and the identification results of the vulnerable area. The sensor modules include strain gauge sensors, temperature sensors, and pressure sensors.

8. The online stress monitoring system for the water-cooled wall lower header according to claim 7, characterized in that: The data acquisition and transmission module constructs a dedicated data acquisition system to quickly collect and summarize the data transmitted by the sensors.

9. The online stress monitoring system for the water-cooled wall lower header according to claim 8, characterized in that: The monitoring center software platform receives real-time data from the data acquisition system, first performs data cleaning, and inputs the processed data into a pre-established stress analysis model to perform real-time stress calculation and fault diagnosis.

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