Distributed fiber grating temperature measurement method for boiler wall temperature measurement

Abstract

The invention relates to the technical field of optical fiber sensing, and provides a distributed fiber bragg grating temperature measurement method for boiler wall temperature measurement, which comprises the following steps of: firstly, preparing a sensor probe consisting of grating optical fibers, connecting the sensor probe with a demodulator, and starting the demodulator after the sensor probe is mounted; the laser is started, a wide-spectrum light source emitted by the laser enters the optical fiber, when the wall temperature of the boiler changes, the effective refractive index and the grating period of the grating are changed, then the Bragg wavelength moves, the data demodulation module detects the movement amount of the wavelength and converts the movement amount into corresponding temperature data, and the temperature data are transmitted to the optical fiber. Then analyzing, calculating and displaying the data; the temperature of the temperature measuring point of the furnace wall is measured through the sensor probe based on the fiber bragg grating, the demodulator analyzes the temperature data and displays the temperature data through the display screen, and therefore accurate temperature measurement of the furnace wall is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of optical fiber sensing, in particular to a distributed optical fiber grating temperature measurement method for measuring boiler wall temperature. Background Art

[0002] In the relevant technology, the power supply is still mainly coal-fired power generation. The complex working conditions of coal-fired power generation units lead to unstable combustion in the furnace, over-temperature operation, low-cycle fatigue damage and scale problems in the heating surface tubes. Among them, temperature is one of the main factors for damage to metal components in power plants. The heating surface tubes of power plants are heated by high-temperature flue gas in the furnace, and their temperature range is about 450-650 degrees. The single-point temperature measurement method cannot accurately reflect the overall temperature distribution of the heating surface tubes. The stability and reliability of traditional temperature measurement equipment in high temperature and complex electromagnetic environments are poor. The real-time and accuracy of data transmission are also difficult to meet the requirements. In addition, the control method based on traditional temperature measurement equipment is not easy to capture temperature changes sensitively, and during the operation of the boiler, it is impossible to accurately detect the over-temperature operation of the heating surface tubes, which is easy to cause safety hazards such as damage to the heating surface tubes due to high temperature. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature. Silicon dioxide and rare earth powder are used as raw materials, and a Bragg grating optical fiber sensor probe is prepared through multiple complex processes, and the probe is applied to the distributed fiber Bragg grating temperature measurement method to achieve accurate measurement of boiler wall temperature. This high-precision probe preparation process combined with the temperature measurement system can keenly capture temperature changes. During the operation of the boiler, the over-temperature operation condition of the heating surface tube can be detected in time and accurately, and the safety hazards such as damage to the heating surface tube caused by high temperature can be effectively reduced, thereby effectively ensuring the service safety of the high-temperature pressure-bearing metal parts of the unit under complex working conditions, and improving the stability and reliability of the entire coal-fired power generation system.

[0004] A distributed fiber grating temperature measurement method for measuring boiler wall temperature, comprising: Used in a fiber Bragg grating temperature measurement system, the fiber Bragg grating temperature measurement system includes a sensor and a demodulator, the sensor includes an optical fiber, a sensor probe and a laser, the sensor probe is connected to one end of the optical fiber, the laser is located in the optical fiber, a grating is arranged in the sensor probe, the demodulator includes a data demodulation module, a data processing and display module, the other end of the optical fiber is connected to the data demodulation module, the data demodulation module demodulates the reflected light signal emitted by the grating, and transmits it to the data processing and display module, wherein the sensor probe is made of silicon dioxide and rare earth powder as raw materials, and is formed into a basic optical fiber through raw material block preparation, glass tube drawing, microstructure arrangement, and high-temperature resistant optical fiber drawing by a drawing tower, and then a grating is engraved in the basic optical fiber based on the femtosecond grating technology, and the outer surface of the basic optical fiber after the grating is engraved is sprayed with gold, and then it is fused with the optical fiber, and finally the sensor probe is prepared by armoring; The distributed fiber grating temperature measurement method for measuring boiler wall temperature comprises: Step 1. The sensor probe is arranged in the test area of ​​the boiler, and the sensor probe is close to the tube wall of the boiler; Step 2. Start the demodulator; Step 3. Start the laser, the wide-spectrum light source emitted by the laser is incident into the sensor probe, the reflected light signal emitted by the grating is reflected to the data demodulation module, the data demodulation module demodulates the reflected light signal and converts it into corresponding temperature data according to a preset algorithm; Step 4. The data processing and display module analyzes the received temperature data and displays it on the display screen.

[0005] Compared with the prior art, the present invention has the following beneficial effects: The present invention uses silicon dioxide and rare earth powder as raw materials, prepares Bragg grating optical fiber sensor probes through multiple complex processes, and applies the probes to the distributed optical fiber grating temperature measurement method, thereby realizing accurate measurement of boiler wall temperature. This high-precision probe preparation process combined with the temperature measurement system can keenly capture temperature changes. During the operation of the boiler, the over-temperature operation condition of the heating surface tube can be discovered in a timely and accurate manner, effectively reducing safety hazards such as damage to the heating surface tube caused by high temperature, thereby effectively ensuring the service safety of the high-temperature pressure-bearing metal parts of the unit under complex working conditions, and improving the stability and reliability of the entire coal-fired power generation system.

[0006] Preferably, in step 1, the sensor probe is fixed to the pipe wall by a pipe clamp, and when the sensor probe is arranged in the area to be measured, the spacing distance of the grating is determined according to the spatial resolution and accuracy requirements of the measurement. The higher the temperature gradient monitoring requirement for the area, the smaller the spacing distance of the grating and the higher the spatial resolution requirement.

[0007] Preferably, in step 3, the sensor probe is also used to obtain stress and strain data of the pipe wall, and the data processing and display module decodes, filters, calibrates and corrects the stress and strain data, and then stores them in a repository of the data processing and display module.

[0008] Preferably, in step 3, the process of the data demodulation module interpreting the temperature signal is as follows: When the broad spectrum light source is incident on the sensor probe, the grating will reflect the narrow spectrum component with the Bragg wavelength λ as the central wavelength. In the transmission spectrum, this part of the component will disappear. The Bragg wavelength λ changes with the effective refractive index and the grating period, and the changes in the refractive index and the grating period are related to stress and temperature. When the stress or temperature at the temperature measuring point of the tube wall changes, the central wavelength changes. The stress and temperature affect the refractive index through the elastic-optical effect and the thermo-optical effect, and affect the grating period through the length change and the thermal expansion effect, thereby causing the Bragg wavelength λ of the grating to move, and the temperature signal is demodulated from the wavelength movement data.

[0009] Preferably, in step 3, the calculation process of the demodulator preset algorithm in the data demodulation module is as follows: Assume that the temperature change at the temperature measuring point i is The initial value of the Bragg wavelength is , the wavelength variation coefficient caused by temperature change is ; It is determined by the thermo-optical coefficient and thermal expansion coefficient of the optical fiber material and can be obtained through experimental calibration; Wavelength shift:

[0010] The data demodulation module demodulates the reflected light signal and detects the wavelength movement of the temperature measurement point i. , according to the formula:

[0011] Will Add the initial temperature as the actual temperature data for the corresponding temperature measurement point i , i represents the i-th temperature measurement point.

[0012] Preferably, in step 4, the data processing and display module analyzes the received temperature data in the following process: For distributed measurement, there are n temperature measurement points i, and the temperature data of each point constitutes a temperature vector ; Assume the coordinates of the i-th temperature measurement point is , the coordinates of the jth temperature measurement point are , for any point e in the temperature measurement area , its temperature Calculated by two-dimensional linear interpolation formula:

[0013] Through the above calculation, the data of each point in the temperature measurement area is obtained, and the discrete data is converted into continuous temperature field distribution data.

[0014] Preferably, after the discrete data is converted into continuous temperature field distribution data, a two-dimensional temperature field distribution model is constructed for the furnace wall based on the data. The specific process is as follows: Fitting via a bivariate polynomial function:

[0015] Where m is the degree of the polynomial, is the fitting coefficient to be determined, p represents the power of x, q represents the power of y, this function can describe the distribution change of temperature on the plane, f represents the predicted data mark in the fitting function, and the temperature field distribution curves of different shapes can be fitted by adjusting the coefficients; Use the least squares method to determine the fitting function Parameters in ,The goal of the least square method is to minimize the sum of square errors between the predicted values ​​of the fitting function and the actual measured values ​​at each temperature measurement point; The error sum of squares S is defined as:

[0016] Through Find the fitting parameters The partial derivative of , and set it equal to zero, get a set of linear equations, solve this linear equations, that is, get the value of the fitting parameter, substitute it into the fitting function , thus obtaining the fitting model about temperature and position, and then substituting the coordinates of different coordinate points on the plane into the fitting function expression, the temperature values ​​of different coordinate points on the plane can be calculated.

[0017] Preferably, in step 4, the data processing and display module draws contour lines on the plane of the pipe wall at preset temperature intervals based on the calculated temperature values ​​of different coordinate points on the plane of the pipe wall, or assigns different colors according to the size of the temperature values, and displays them on the display screen.

[0018] Preferably, in step 4, the data processing and display module has a storage repository for storing the temperature data so that historical data can be viewed and analyzed at any time.

[0019] Preferably, in step 4, the data processing and display module also provides real-time monitoring and alarm functions, allows remote access and control, and regularly generates reports for performance evaluation and fault diagnosis.

[0020] Compared with the prior art, the present invention also has the following beneficial effects: The present invention realizes effective analysis and intuitive display of boiler wall temperature data through real-time monitoring and data processing, including the construction of a two-dimensional temperature field distribution model. It realizes a comprehensive grasp of the operation of the boiler under complex working conditions, and the staff can quickly detect abnormal temperature changes and prevent low-cycle fatigue damage and oxide scale caused by temperature fluctuations in advance. When operating at high parameters and deep peak load, it can better cope with the challenges brought by power supply fluctuations and ensure the safety and service life of boiler metal parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a flow chart of the steps of the method of the present invention; Figure 2 It is a schematic diagram of the temperature calculation process during temperature measurement of the present invention; Figure 3 It is a specific flow chart of step 4 of the present invention. DETAILED DESCRIPTION

[0022] The following embodiments of the present invention are described in further detail in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0023] Among the relevant technologies, electricity supply is still dominated by coal-fired power generation. However, coal-fired power generation technology needs to become efficient and clean, and improving operating parameters has become inevitable, which puts higher requirements on the service safety of the high-temperature pressure-bearing metal components of the unit.

[0024] At the same time, the large-scale application of renewable energy power generation has led to fluctuations in power supply, and coal-fired power generation units are deeply involved in peak load regulation. Variable load operation damages the safety and service life of metal components of the units. High parameters and deep peak load regulation operation have brought new challenges to the technical supervision of metal components of power station boilers. Complex working conditions have led to unstable combustion in the furnace, over-temperature operation, low-cycle fatigue damage and oxide scale problems in the heating surface tubes, which are major safety hazards. Among them, temperature is one of the main factors for damage to metal components in power stations. The heating surface tubes of power stations are heated by high-temperature flue gas in the furnace, and their temperature range is about 450-650 degrees.

[0025] However, the traditional single-point temperature measurement method cannot accurately reflect the overall temperature distribution of the heating surface pipe. When facing a large area of ​​heating surface pipes, there is a monitoring blind spot, which is easy to miss the local over-temperature point. In addition, the stability and reliability of traditional temperature measurement equipment in high temperature and complex electromagnetic environments are poor, and the real-time and accuracy of data transmission are difficult to meet the strict requirements of power plant boiler safety monitoring.

[0026] Based on the above problems, the present invention proposes a method for preparing a sensor probe. The sensor probe is made of silicon dioxide and rare earth powder as raw materials, and is formed into a basic optical fiber through raw material block preparation, glass tube drawing, microstructure arrangement, and high-temperature resistant optical fiber drawing by a drawing tower. A grating is then engraved in the basic optical fiber based on femtosecond grating engraving technology, and gold is sprayed on the outer surface of the basic optical fiber after the grating is engraved. The sensor probe is then fused with the optical fiber, and finally the sensor probe is prepared through armoring.

[0027] The fiber grating sensor probe is prepared based on silicon dioxide and rare earth powder. The melting point of silicon dioxide is about 1713°C, that is, silicon dioxide has a high melting point and good thermal stability. The rare earth powder can be at least one of scandium, yttrium and lanthanide elements. Doping the silicon dioxide with rare earth powder can use a lower energy light source to write the grating, and can also improve the stability and reflection efficiency of the grating.

[0028] Gold is sprayed on the outer surface of the base optical fiber. Spraying gold can form a uniform metal film on the surface of the base optical fiber. The metal film has a high melting point and good conductivity, which improves the stability and reliability of the signal transmitted by the sensor probe.

[0029] In addition, the control method based on traditional temperature measurement equipment is not easy to capture temperature changes sensitively, and during the operation of the boiler, it is also impossible to accurately detect the over-temperature operation of the heating surface tube, which is easy to cause safety hazards such as damage to the heating surface tube due to high temperature. Distributed temperature measurement has limited in-depth analysis and processing capabilities for temperature data, and cannot build an effective temperature field model to intuitively display the temperature change trend, which is not conducive to the staff to predict potential safety risks in advance. Therefore, it is necessary to design an advanced distributed fiber Bragg grating temperature measurement key equipment and method to overcome the limitations of existing temperature measurement technology, and realize high-resolution, real-time, and accurate monitoring and in-depth analysis of the temperature of key components such as heating surface tubes, thereby providing a strong guarantee for the safe and stable operation of power plant boilers.

[0030] Therefore, the present application provides a distributed fiber grating temperature measurement method for boiler wall temperature measurement, which is used for a fiber grating temperature measurement system. The fiber grating temperature measurement system includes a sensor and a demodulator. The sensor includes a sensor probe. The sensor probe is prepared by the above-mentioned sensor probe preparation method. The sensor probe prepared based on the above-mentioned method has high stability and reliability in transmitting signals.

[0031] The sensor includes an optical fiber, a sensor probe and a laser. The sensor probe is connected to one end of the optical fiber. The laser is located in the optical fiber. A grating is arranged in the sensor probe. The demodulator includes a data demodulation module, a data processing and display module. The other end of the optical fiber is connected to the data demodulation module. The data demodulation module demodulates the reflected light signal emitted by the grating and transmits it to the data processing and display module.

[0032] For example, in areas near burners that are prone to overheating risks, two optical fibers are installed on each connecting pipe, and three distributed optical fiber temperature sensors are evenly arranged on each optical fiber as temperature measurement points. The sensors are tightly fixed with pipe clamps to make them close to the pipe wall. Ensure that the pipe clamps are tightly fixed and the sensors are close to the pipe wall to ensure good heat conduction.

[0033] The distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement includes: Step 1. The sensor probe is arranged in the test area of ​​the boiler, and the sensor probe is close to the tube wall of the boiler; specifically, the sensor probe is arranged in the test area of ​​the heating surface tube in the boiler furnace.

[0034] Step 2. Start the demodulator; Step 3. Start the laser, the wide-spectrum light source emitted by the laser is incident into the sensor probe, and the reflected light signal emitted by the grating is reflected to the data demodulation module, which demodulates the reflected light signal and converts it into corresponding temperature data according to a preset algorithm.

[0035] When the boiler wall temperature changes, the effective refractive index and grating period of the grating change through the thermo-optical effect and thermal expansion effect, which causes the Bragg wavelength to move. The data demodulation module demodulates the reflected light signal through a demodulator, detects the amount of wavelength movement, and converts it into corresponding temperature data according to the internal preset algorithm, and transmits it to the data processing and display module.

[0036] Step 4. The data processing and display module analyzes the received temperature data and displays it on the display screen.

[0037] The staff monitors the temperature data on the display screen in real time and pays attention to any abnormal conditions. If remote monitoring is required, ensure that the 5G network connection is normal, upload the data to the cloud monitoring platform and then transmit it to the remote port for staff to monitor.

[0038] By using silicon dioxide and rare earth powder as raw materials and going through multiple complex processes to prepare Bragg grating fiber sensor probes, which are applied to distributed fiber grating temperature measurement methods, accurate measurement of boiler wall temperature is achieved. This high-precision probe preparation process combined with the temperature measurement system can keenly capture temperature changes.

[0039] Start temperature measurement: During the operation of the equipment, after starting the laser, the broad spectrum light source is incident on the optical fiber; When the boiler load changes and causes the wall temperature to fluctuate, the effective refractive index and grating period of the grating change rapidly due to the thermo-optical effect and thermal expansion effect, causing the Bragg wavelength to move. The demodulator in the data demodulation module demodulates the reflected light signal in a timely manner, accurately detects the wavelength movement, and converts it into corresponding temperature data according to the preset algorithm.

[0040] This high-precision probe preparation process combined with the temperature measurement system can keenly capture temperature changes. During boiler operation, it can promptly and accurately detect over-temperature operation conditions of the heating surface tubes, effectively reducing safety hazards such as damage to the heating surface tubes caused by high temperature, thereby effectively ensuring the service safety of the unit's high-temperature pressure-bearing metal components under complex working conditions and improving the stability and reliability of the entire coal-fired power generation system.

[0041] The present invention uses silicon dioxide and rare earth powder as raw materials, prepares Bragg grating optical fiber sensor probes through multiple complex processes, and applies the probes to the distributed optical fiber grating temperature measurement method, thereby realizing accurate measurement of boiler wall temperature. This high-precision probe preparation process combined with the temperature measurement system can keenly capture temperature changes. During the operation of the boiler, the over-temperature operation condition of the heating surface tube can be discovered in a timely and accurate manner, effectively reducing safety hazards such as damage to the heating surface tube caused by high temperature, thereby effectively ensuring the service safety of the high-temperature pressure-bearing metal parts of the unit under complex working conditions, and improving the stability and reliability of the entire coal-fired power generation system.

[0042] The present invention also provides a raw material processing sensor probe and applies the sensor probe to detect the boiler wall temperature, including: Step 1. Prepare the sensor probe composed of grating optical fiber: first, take silicon dioxide and rare earth powder as raw materials, prepare raw material blocks, draw glass tubes, arrange microstructures, and draw high-temperature resistant optical fibers in a drawing tower to form a basic optical fiber structure. Then, based on femtosecond grating technology and gold spraying and welding the basic optical fiber structure, finally, armoring and jumper are used to complete the preparation of the Bragg grating optical fiber sensor probe. Step 2. Prepare the core components of the fiber Bragg grating temperature measurement system: including distributed fiber optic temperature measurement sensors based on grating fiber sensor probes, lasers, data demodulation modules based on demodulators, data processing and display modules, and ensure that the performance indicators of each component meet the requirements; Step 3. Assemble and install the equipment: Assemble the equipment prepared in step 2 into a fiber Bragg grating temperature measurement system, arrange the sensing probe of the distributed fiber Bragg grating sensor in the boiler to be measured area, ensure proper distribution and connection, use a pipe clamp to fix the sensor on the pipe wall, ensure that the pipe clamp is tightly fixed and the sensor is close to the pipe wall; Step 4. Connect the transmission module and start: ensure that the sensor probe is connected to the data demodulation module through the optical fiber so that the sensor data can be transmitted to the demodulator, and start the demodulator and the data processing and display module; Step 5. Distributed temperature measurement and data processing: Start the laser, and the wide-spectrum light source emitted by the laser is incident on the optical fiber. When the boiler wall temperature changes, the effective refractive index and grating period of the grating change through the thermo-optical effect and thermal expansion effect, which causes the Bragg wavelength to move. The data demodulation module demodulates the reflected light signal through the demodulator, detects the wavelength movement, and converts it into corresponding temperature data according to the internal preset algorithm, and transmits it to the data processing and display module; Step 6. Data analysis, calculation and display, and staff monitoring: The data processing and display module analyzes the received temperature data and displays it on the display screen. The staff monitors the temperature data on the display screen in real time and pays attention to any abnormal conditions. If remote monitoring is required, ensure that the 5G network connection is normal. The data is uploaded to the cloud monitoring platform and then transmitted to the remote port for staff monitoring. At the same time, the data processing and display module has its own storage function, which can record data so that historical data can be viewed and analyzed at any time to understand the system operation status and changing trends.

[0043] In step 1, the sensor probe is fixed to the pipe wall with a pipe clamp, and when the sensor probe is arranged in the area to be measured, the spacing distance of the grating is determined according to the spatial resolution and accuracy requirements of the measurement. The higher the temperature gradient monitoring requirements for the area, the smaller the spacing distance of the grating and the higher the spatial resolution requirement.

[0044] In step 3, the sensor probe is also used to obtain stress and strain data of the pipe wall. The data processing and display module decodes, filters, calibrates and corrects the stress and strain data, and then stores them in the storage library of the data processing and display module.

[0045] The process of the data demodulation module to interpret the temperature signal is as follows: When a wide-spectrum light source is incident on the sensor probe, the grating will reflect the narrow spectrum component with the Bragg wavelength λ as the central wavelength. In the transmission spectrum, this part of the component will disappear. The Bragg wavelength λ changes with the effective refractive index and the grating period, and the changes in the refractive index and the grating period are related to stress and temperature. When the stress or temperature at the temperature measuring point of the tube wall changes, the central wavelength changes. The stress and temperature affect the refractive index through the elastic-optical effect and the thermo-optical effect respectively, and affect the grating period through the length change and the thermal expansion effect, thereby causing the Bragg wavelength λ of the grating to move, and the temperature signal is demodulated from the wavelength shift data.

[0046] Assume that the temperature change at the temperature measuring point i is The initial value of the Bragg wavelength is , the wavelength variation coefficient caused by temperature change is ; Determined by the thermo-optical coefficient and thermal expansion coefficient of the optical fiber material, it can be obtained through experimental calibration; wavelength shift:

[0047] The data demodulation module demodulates the reflected light signal and detects the wavelength movement of the temperature measurement point i. , according to the formula:

[0048] Will Add the initial temperature as the actual temperature data for the corresponding temperature measurement point i , i represents the i-th temperature measurement point; The data is transmitted to the data processing and display module. The data processing and display module conducts in-depth analysis of a large amount of temperature data, constructs a two-dimensional temperature field distribution model, uses binary polynomial function fitting and least squares method to determine the fitting parameters, and accurately calculates the temperature values ​​of different coordinate points on the furnace wall plane.

[0049] For distributed measurement, there are n temperature measurement points i, and the temperature data of each point constitutes a temperature vector ; Assume the coordinates of the i-th temperature measurement point is , the coordinates of the jth temperature measurement point are , for any point e in the temperature measurement area , its temperature Calculated by two-dimensional linear interpolation formula:

[0050] The data of each point in the temperature measurement area is calculated by the above formula, and the discrete data is converted into continuous temperature field distribution data.

[0051] This calculation method can provide a more reasonable temperature estimate near the known temperature measurement point. However, it is essentially a local estimation method based on linear assumptions. When the temperature field distribution is complex, such as a sharp change in temperature gradient, complex distribution of heat flow, etc., linear interpolation may not be able to describe the change law of the entire temperature field well.

[0052] Therefore, after converting the discrete data into continuous temperature field distribution data, a two-dimensional temperature field distribution model is constructed for the furnace wall based on the data. The specific process is as follows: Fitting via a bivariate polynomial function:

[0053] Where m is the degree of the polynomial, is the fitting coefficient to be determined, p represents the power of x, q represents the power of y, this function can describe the distribution change of temperature on the plane, f represents the predicted data mark in the fitting function, and the temperature field distribution curves of different shapes can be fitted by adjusting the coefficients; Use the least squares method to determine the fitting function Parameters in ,The goal of the least square method is to minimize the sum of square errors between the predicted values ​​of the fitting function and the actual measured values ​​at each temperature measurement point; The error sum of squares S is defined as:

[0054] Through Find the fitting parameters The partial derivative of , and set it equal to zero, get a set of linear equations, solve this linear equations, that is, get the value of the fitting parameter, substitute it into the fitting function , thus obtaining the fitting model about temperature and position, and then substituting the coordinates of different coordinate points on the plane into the fitting function expression, the temperature values ​​of different coordinate points on the plane can be calculated.

[0055] The fitting model is achieved by finding a suitable polynomial function to describe the distribution of the entire temperature field as accurately as possible. The model obtained through fitting can more accurately calculate the value of the temperature measurement area and the relationship between position and temperature, solve the estimated values ​​that may appear in the previous calculations, and achieve a comprehensive grasp of the boiler operation conditions under complex working conditions.

[0056] Then, contour lines are drawn on the two-dimensional plane of the furnace wall according to the preset temperature intervals, and different colors are assigned according to the size of the temperature values, which are clearly and intuitively displayed on the display screen.

[0057] The staff in the monitoring room monitors the temperature trend of a certain area in real time through the display screen, and quickly determines possible problems. Based on the problems, the operators adjust the relevant parameters in a timely manner.

[0058] The embodiments of the present invention are provided for the purpose of illustration and description. Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations of the present invention. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement, characterized in that: Used in a fiber Bragg grating temperature measurement system, the fiber Bragg grating temperature measurement system includes a sensor and a demodulator, the sensor includes an optical fiber, a sensor probe and a laser, the sensor probe is connected to one end of the optical fiber, the laser is located in the optical fiber, a grating is arranged in the sensor probe, the demodulator includes a data demodulation module, a data processing and display module, the other end of the optical fiber is connected to the data demodulation module, the data demodulation module demodulates the reflected light signal emitted by the grating, and transmits it to the data processing and display module, wherein the sensor probe is made of silicon dioxide and rare earth powder as raw materials, and is formed into a basic optical fiber through raw material block preparation, glass tube drawing, microstructure arrangement, and high-temperature resistant optical fiber drawing by a drawing tower, and then a grating is engraved in the basic optical fiber based on the femtosecond grating technology, and the outer surface of the basic optical fiber after the grating is engraved is sprayed with gold, and then it is fused with the optical fiber, and finally the sensor probe is prepared by armoring; The distributed fiber grating temperature measurement method for measuring boiler wall temperature comprises: Step 1. The sensor probe is arranged in the test area of ​​the boiler, and the sensor probe is close to the tube wall of the boiler; Step 2. Start the demodulator; Step 3. Start the laser, the wide-spectrum light source emitted by the laser is incident into the sensor probe, the reflected light signal emitted by the grating is reflected to the data demodulation module, the data demodulation module demodulates the reflected light signal and converts it into corresponding temperature data according to a preset algorithm; Step 4. The data processing and display module analyzes the received temperature data and displays it on the display screen.

2. A distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature as claimed in claim 1, characterized in that: In step 1, the sensor probe is fixed to the pipe wall by a pipe clamp, and when the sensor probe is arranged in the area to be measured, the spacing distance of the grating is determined according to the spatial resolution and accuracy requirements of the measurement. The higher the temperature gradient monitoring requirements for the area, the smaller the spacing distance of the grating and the higher the spatial resolution requirement.

3. A distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement as claimed in claim 1, characterized in that: In step 3, the sensor probe is also used to obtain stress and strain data of the pipe wall, and the data processing and display module decodes, filters, calibrates and corrects the stress and strain data, and then stores them in a storage library of the data processing and display module.

4. A distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement as claimed in claim 3, characterized in that: In step 3, the process of the data demodulation module interpreting the temperature signal is as follows: When the broad spectrum light source is incident on the sensor probe, the grating will reflect the narrow spectrum component with the Bragg wavelength λ as the central wavelength. In the transmission spectrum, this part of the component will disappear. The Bragg wavelength λ changes with the effective refractive index and the grating period, and the changes in the refractive index and the grating period are related to stress and temperature. When the stress or temperature at the temperature measuring point of the tube wall changes, the central wavelength changes. The stress and temperature affect the refractive index through the elastic-optical effect and the thermo-optical effect, and affect the grating period through the length change and the thermal expansion effect, thereby causing the Bragg wavelength λ of the grating to move, and the temperature signal is demodulated from the wavelength movement data.

5. A distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement as claimed in claim 1, characterized in that: In step 3, the calculation process of the preset algorithm in the data demodulation module is as follows: Assume that the temperature change at the temperature measuring point i is The initial value of the Bragg wavelength is , the wavelength variation coefficient caused by temperature change is ; It is determined by the thermo-optical coefficient and thermal expansion coefficient of the optical fiber material and can be obtained through experimental calibration; Wavelength shift: The data demodulation module demodulates the reflected light signal and detects the wavelength movement of the temperature measurement point i. , according to the formula: Will Add the initial temperature as the actual temperature data for the corresponding temperature measurement point i , i represents the i-th temperature measurement point.

6. A distributed fiber Bragg grating temperature measurement method for boiler wall temperature measurement as claimed in claim 1, characterized in that: In step 4, the data processing and display module analyzes the received temperature data as follows: For distributed measurement, there are n temperature measurement points i, and the temperature data of each point constitutes a temperature vector ; Assume the coordinates of the i-th temperature measurement point is , the coordinates of the jth temperature measurement point are , for any point e in the temperature measurement area , its temperature Calculated by two-dimensional linear interpolation formula: The data of each point in the temperature measurement area is calculated by the above formula, and the discrete data is converted into continuous temperature field distribution data.

7. A distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature as claimed in claim 6, characterized in that: After the discrete data is converted into continuous temperature field distribution data, a two-dimensional temperature field distribution model is constructed for the furnace wall based on the data. The specific process is as follows: Fit via a bivariate polynomial function: Where m is the degree of the polynomial, is the fitting coefficient to be determined, p represents the power of x, q represents the power of y, this function can describe the distribution change of temperature on the plane, f represents the predicted data mark in the fitting function, and the temperature field distribution curves of different shapes can be fitted by adjusting the coefficients; Use the least squares method to determine the fitting function Parameters in ,The goal of the least square method is to minimize the sum of square errors between the predicted values ​​of the fitting function and the actual measured values ​​at each temperature measurement point; The error sum of squares S is defined as: Through Find the fitting parameters The partial derivative of , and set it equal to zero, get a set of linear equations, solve this linear equations, that is, get the value of the fitting parameter, substitute it into the fitting function , thus obtaining the fitting model about temperature and position, and then substituting the coordinates of different coordinate points on the plane into the fitting function expression, the temperature values ​​of different coordinate points on the plane can be calculated.

8. A distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature as claimed in claim 7, characterized in that: In step 4, the data processing and display module draws contour lines on the plane of the pipe wall at preset temperature intervals based on the calculated temperature values ​​of different coordinate points on the plane of the pipe wall, or assigns different colors according to the size of the temperature value, and displays them on the display screen.

9. A distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature as claimed in claim 1, characterized in that: In step 4, the data processing and display module has a storage library for storing the temperature data so that historical data can be viewed and analyzed at any time.

10. A distributed fiber Bragg grating temperature measurement method for measuring boiler wall temperature as claimed in claim 1, characterized in that: In step 4, the data processing and display module also has real-time monitoring and alarm functions, allows remote access and control, and regularly generates reports for performance evaluation and fault diagnosis.

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