Wide-range optical fiber temperature sensor for monitoring steam temperature of power station boiler

Abstract

A wide-range optical fiber temperature sensor for monitoring the steam temperature of a power plant boiler comprises a broadband light source EDFA with the central wavelength being 1550 nm, after the broadband light source passes through a circulator, one path of the broadband light source is connected with an optical fiber SD sensing structure, and the other path of the broadband light source is connected with a spectrograph; the tail end of the optical fiber SD sensing structure is provided with a reflection end face, the broadband light source outputs an optical signal, the optical signal enters from a port 1 of the circulator, passes through the optical fiber SD sensing structure at a port 2 of the circulator, is reflected by the reflection end face, passes through the optical fiber SD sensing structure again and returns to a port 3 of the circulator, and wavelength demodulation is carried out by the spectrograph module of the port 3. The optical fiber SD sensing structure is simple to manufacture, low in cost and small in sensing area, does not need to be additionally coated with a temperature-sensitive material, and does not need special packaging; the temperature and the wavelength measured by the optical fiber SD sensing structure have an excellent linear relationship, and the sensitivity is as high as 106 pm / DEG C and is improved by nearly 10 times compared with a common optical fiber grating temperature sensor.

Description

Technical Field

[0001] The invention relates to the technical field of power plant boiler steam temperature monitoring, and in particular to a wide-range optical fiber temperature sensor used for power plant boiler steam temperature monitoring. Background Art

[0002] China's power plant boiler industry is a broad economic field, involving multiple industries such as thermal power generation, thermal power generation, and nuclear power. With the steady development of China's power plant boiler industry, its market size continues to expand. At present, power plant boilers are widely used and used frequently. Steam temperature is one of the key factors affecting the efficiency of generator sets. Maintaining a suitable steam temperature can enable the unit to operate in the best state and achieve a higher power generation efficiency. If the steam temperature is too low, the unit's work capacity will decrease and the power generation efficiency will decrease; while if the temperature is too high, it may exceed the equipment's tolerance and cause failures, which will also affect the power generation efficiency. In addition, too high a temperature is also prone to safety accidents and threaten the lives of workers. Therefore, monitoring the steam temperature is an indispensable link. According to research, the design value of the main steam temperature of a general ultra-supercritical unit is usually around 600°C. In actual operation, a reasonable temperature range and alarm value will be set according to the specific conditions of the equipment and safety considerations. When the steam temperature approaches or exceeds the set upper limit, the monitoring system will sound an alarm to remind the operating personnel to take measures to make adjustments or shut down for maintenance to avoid equipment damage and safety accidents. The specific temperature limit needs to be determined based on the specific equipment and operating procedures of the power plant.

[0003] At present, the sensors used for temperature measurement in the power industry include distributed fiber temperature sensors (DTS), fiber Bragg grating temperature sensors, and fiber fluorescence temperature sensors. Among them, distributed fiber temperature sensors (DTS): In practical applications, the common measurement range is about -40℃ to 300℃, and its system cost is relatively high, especially for long-distance measurement applications. Fiber Bragg grating temperature sensor: The temperature measurement range is generally between -270℃ and 1000℃, and the grating manufacturing process is complex and the cost is relatively high; fiber Bragg gratings are also sensitive to factors other than temperature, such as stress and strain, and temperature compensation is required in practical applications to improve the accuracy of the measurement. Fiber fluorescence temperature sensor: Temperature measurement range: usually around -40℃ to 250℃, the performance of the fluorescent material will gradually decay over time, which may affect the long-term stability of the sensor, and the measurement results are greatly affected by the characteristics of the fluorescent material and environmental factors. Summary of the invention

[0004] In view of the problems in the prior art, the present invention provides a wide-range optical fiber temperature sensor for monitoring the steam temperature of a power plant boiler, aiming to reduce production costs and meet the requirements of sensitivity and temperature measurement range.

[0005] A wide-range optical fiber temperature sensor for monitoring boiler steam temperature in a power plant comprises a broadband light source with a central wavelength of 1550nm, the broadband light source comprises a 980nm pump laser, the 980nm pump laser is connected to an erbium-doped optical fiber after passing through a wavelength division multiplexer, the output end of the erbium-doped optical fiber is the output end of the broadband light source and is used for connecting to a circulator, the broadband light source is connected to an optical fiber SD sensing structure through one path after passing through the circulator, and is connected to a spectrometer through another path, and the spectrometer is used for recording changes in interference spectrum; a reflective end face is arranged at the tail end of the optical fiber SD sensing structure, the broadband light source outputs an optical signal, enters from port 1 of the circulator, passes through the optical fiber SD sensing structure at port 2 of the circulator, is reflected by the reflective end face and returns to port 3 of the circulator through the optical fiber SD sensing structure again, and wavelength demodulation is performed by a spectrometer module at port 3.

[0006] Further, the optical fiber SD sensing structure is a cascade structure formed by fusion splicing a section of single-mode optical fiber and a section of dispersion-compensating optical fiber through an optical fiber fusion splicer. The single-mode optical fiber is connected to a circulator, and the free end of the dispersion-compensating optical fiber is cut to form a reflective end face.

[0007] Further, the coating layer of one end of the single-mode optical fiber used for connection with the dispersion-compensating optical fiber is stripped, and all the coating layers of the dispersion-compensating optical fiber are stripped, and the exposed portion of the single-mode optical fiber and the dispersion-compensating optical fiber with the coating stripped are placed in a fiber fusion splicer for fusion splicing, and the length of the exposed portion of the single-mode optical fiber is 5 mm; the dispersion-compensating optical fiber with the coating stripped is cut so that the length of the dispersion-compensating optical fiber is greater than 7 mm and less than 9 mm.

[0008] Furthermore, the length of the dispersion compensating optical fiber is 7 mm or 8 mm.

[0009] Further: The spectrometer module is a GouMax full-band miniaturized spectrometer module with a detection wavelength of 1523nm~1572nm The beneficial effects of the present invention are as follows: the optical fiber SD sensing structure is simple to manufacture, low in cost, has a small sensing area, does not require additional coating of temperature-sensitive materials, and does not require special packaging; there is an excellent linear relationship between the temperature and wavelength measured by the optical fiber SD sensing structure, and the sensitivity is as high as 106pm / ℃, which is nearly 10 times higher than that of ordinary optical fiber grating temperature sensors; and the temperature measurement range is wide, with excellent linearity of 500-800℃. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a structural block diagram of the present invention; Figure 2 The interference spectrum change diagram of the optical fiber SD sensing structure when the length of the dispersion compensation optical fiber is 7 mm and the temperature rises from room temperature to 200°C; Figure 3 This is the interference spectrum change diagram of the optical fiber SD sensing structure when the length of the dispersion compensation optical fiber is 8 mm and the temperature rises from room temperature to 200°C; Figure 4 This is the interference spectrum change diagram of the optical fiber SD sensing structure when the length of the dispersion compensation optical fiber is 9 mm and the temperature rises from room temperature to 200°C; Figure 5 This is the interference spectrum change diagram of the optical fiber SD sensing structure when the length of the dispersion compensation optical fiber is 10 mm and the temperature rises from room temperature to 200°C; Figure 6 This is the interference spectrum change diagram of the optical fiber SD sensing structure when the length of the dispersion compensation optical fiber is 11 mm and the temperature rises from room temperature to 200°C; Figure 7 This is the interference spectrum of the optical fiber SD sensing structure in the temperature range of 600℃~700℃; Figure 8 This is the wavelength fitting diagram of the optical fiber SD sensing structure in the temperature range of 600℃~700℃. DETAILED DESCRIPTION

[0011] The present invention is described in detail below in conjunction with the accompanying drawings. The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention. The directional terms such as left, middle, right, top, and bottom in the embodiments of the present invention are only relative concepts or are based on the normal use state of the product, and should not be considered as restrictive.

[0012] A wide-range optical fiber temperature sensor for monitoring steam temperature of a power plant boiler comprises a broadband light source 100 with a central wavelength of 1550 nm, the broadband light source 100 comprises a 980 nm pump laser 1, the 980 nm pump laser 1 is connected to an erbium-doped optical fiber 3 through a wavelength division multiplexer 2, thereby forming the broadband light source 100, the output end of the erbium-doped optical fiber 3 is the output end of the broadband light source 100 and is used for connecting to a circulator 4, the broadband light source 100 is connected to an optical fiber SD sensing structure 200 through the circulator 4 in one way and to a spectrometer 5 in another way, and the spectrometer 5 is used for recording changes in interference spectrum; the tail end of the optical fiber SD sensing structure 200 is provided with a reflective end face 8, the broadband light source 10 0 outputs an optical signal, enters from port 1 of the circulator 4, passes through the optical fiber SD sensing structure 200 at port 2 of the circulator 4, is reflected by the reflective end face 8 and returns to port 3 of the circulator 4 through the optical fiber SD sensing structure 200 again, and is wavelength demodulated by the spectrometer 5 at port 3. The spectrometer module 5 is a GouMax full-band miniaturized spectrometer module with a detection wavelength of 1523nm~1572nm. Among them, the optical fiber SD sensing structure 200 is a cascade structure formed by fusion splicing a section of single-mode optical fiber 6 and a section of dispersion-compensating optical fiber 7 by an optical fiber fusion splicer. The single-mode optical fiber 6 is connected to the circulator 4, and the free end of the dispersion-compensating optical fiber 7 is cut to form a reflective end face 8. Specifically, the coating layer of one end of the single-mode optical fiber 6 for connection with the dispersion-compensating optical fiber 7 is stripped, and all the coating layers of the dispersion-compensating optical fiber 7 are stripped, and the exposed portion of the single-mode optical fiber 6 and the dispersion-compensating optical fiber 7 with the coating stripped are placed in an optical fiber fusion splicer for fusion splicing, and the length of the exposed portion of the single-mode optical fiber 6 is 5 mm; the dispersion-compensating optical fiber 7 with the coating stripped is cut so that the length of the dispersion-compensating optical fiber 7 is greater than 7 mm and less than 9 mm. It can be known from the Michelson interference principle that in fact, the change in the length of the dispersion-compensating optical fiber 7 causes the change in the optical path difference in the interference, so different lengths of the dispersion-compensating optical fiber 7 correspond to different interference fringes; when it is less than 7 mm, the fusion splicing of the single-mode optical fiber 6 and the dispersion-compensating optical fiber 7 will be affected by the cutting and disconnected; when it is greater than 9 mm, such as Figure 5 and Figure 6 As mentioned above, there are obvious burrs in the interference spectrum, such as Figure 4 As shown in Figure 2, there are many interference peaks, but they are not easy to distinguish. Figure 2 and Figure 3 As shown, the length of the dispersion compensating optical fiber 7 is preferably 7 mm or 8 mm, and the 7 mm dispersion compensating optical fiber 7 is suitable for use in scenarios with a larger temperature range as a wide-range temperature sensor; the 8 mm dispersion compensating optical fiber 7 is suitable for use in scenarios with higher requirements for accuracy and sensitivity as a high-sensitivity temperature sensor; the temperature of the power plant boiler steam is a wide range, and the temperature range that needs to be monitored is mainly 500-800°C, so the dispersion compensating optical fiber 7 is selected as a 7 mm sensing structure.

[0013] When the external temperature rises, the relative optical path difference changes, which causes the wavelength to shift. The optical fiber SD sensing structure 200 is used as the sensing unit of the system. The temperature change experiment is carried out in the Mabo furnace. The spectrometer module 5 is used to observe the interference spectrum change with temperature on the computer terminal. The optical fiber SD sensing structure 200 changes from room temperature to 800℃. Figure 7 It can be observed (the interference spectrum in the range of 600℃~700℃ was selected) that as the temperature gradually increases, the interference wavelength uniformly shifts to the right. Figure 8 It can be seen in (the interference spectrum in the range of 600°C to 700°C was selected) that there is a good linear relationship between temperature and wavelength; therefore, it is believed that the present invention can accurately reflect the temperature change by demodulating the wavelength.

[0014] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A wide-range optical fiber temperature sensor for monitoring steam temperature in power plant boilers, characterized in that: The invention comprises a broadband light source EDFA with a central wavelength of 1550nm, the broadband light source comprises a 980nm pump laser, the 980nm pump laser is connected to the erbium-doped optical fiber after passing through a wavelength division multiplexer, the output end of the erbium-doped optical fiber is the output end of the broadband light source and is used for connecting to a circulator, the broadband light source is connected to an optical fiber SD sensing structure in one way after passing through the circulator, and is connected to a spectrometer module in another way, and the spectrometer module is used for recording changes in interference spectrum; a reflective end face is arranged at the tail end of the optical fiber SD sensing structure, the broadband light source outputs an optical signal, enters from port 1 of the circulator, passes through the optical fiber SD sensing structure at port 2 of the circulator, is reflected by the reflective end face and returns to port 3 of the circulator through the optical fiber SD sensing structure again, and the wavelength is demodulated by the spectrometer module at port 3.

2. The wide-range optical fiber temperature sensor for monitoring steam temperature of power plant boilers according to claim 1 is characterized in that: The optical fiber SD sensing structure is a cascade structure formed by fusion splicing a section of single-mode optical fiber and a section of dispersion-compensating optical fiber through an optical fiber fusion splicer. The single-mode optical fiber is connected to a circulator, and the free end of the dispersion-compensating optical fiber is cut to form a reflective end face.

3. The wide-range optical fiber temperature sensor for monitoring steam temperature of power plant boilers according to claim 2 is characterized in that: The coating layer at one end of the single-mode optical fiber used for connection with the dispersion-compensating optical fiber is stripped, and all the coating layers of the dispersion-compensating optical fiber are stripped. The exposed portion of the single-mode optical fiber and the dispersion-compensating optical fiber with the coating stripped are placed in a fiber fusion splicer for fusion splicing, and the length of the exposed portion of the single-mode optical fiber is 5 mm; the dispersion-compensating optical fiber with the coating stripped is cut so that the length of the dispersion-compensating optical fiber is greater than 7 mm and less than 9 mm.

4. The wide-range optical fiber temperature sensor for monitoring steam temperature in power plant boilers according to claim 2 is characterized in that: The length of the dispersion compensating fiber is 7 mm or 8 mm.

5. The wide-range optical fiber temperature sensor for monitoring steam temperature of power plant boilers according to claim 1 is characterized in that: The spectrometer module is a GouMax full-band miniaturized spectrometer module with a detection wavelength of 1523nm~1572nm.

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