CN107219019B - LNG storage tank perlite settlement monitoring system and method based on distributed optical fibers - Google Patents
LNG storage tank perlite settlement monitoring system and method based on distributed optical fibers Download PDFInfo
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- CN107219019B CN107219019B CN201710546024.0A CN201710546024A CN107219019B CN 107219019 B CN107219019 B CN 107219019B CN 201710546024 A CN201710546024 A CN 201710546024A CN 107219019 B CN107219019 B CN 107219019B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
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- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P90/00—Enabling technologies with a potential contribution to greenhouse gas [GHG] emissions mitigation
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Abstract
The invention relates to an LNG storage tank perlite settlement monitoring system and method based on distributed optical fibers, which are characterized in that: the device comprises a plurality of distributed temperature measuring optical fibers, an optical fiber junction box, a distributed optical fiber temperature measuring host machine at least provided with two channels and a display screen upper computer; each distributed temperature measuring optical fiber is respectively laid on the inner wall of one or more LNG storage tank outer tanks, the starting end and the tail end of each distributed temperature measuring optical fiber are respectively connected with an optical fiber junction box, and the optical fiber junction box is connected with each channel of a distributed optical fiber temperature measuring host through the distributed optical fiber; the distributed optical fiber temperature measuring host machine carries out two-channel bidirectional emission and demodulation on the initial end and the tail end of each distributed temperature measuring optical fiber to obtain a final temperature measured value, and sends the final temperature measured value to the display screen upper computer for display through the TCP/IP communication interface, and sends the final temperature measured value to the centralized control system for further processing through the standard communication interface. The invention can be widely applied to monitoring the perlite settlement of the LNG storage tank.
Description
Technical Field
The invention relates to the technical field of LNG (liquefied natural gas) and LNG storage tanks, in particular to a distributed optical fiber-based LNG storage tank perlite settlement monitoring system and a distributed optical fiber-based LNG storage tank perlite settlement monitoring method.
Background
As an economic and efficient clean energy source, the LNG industry is facing the Huang Jinfa expansion period, and various links of the LNG industry chain involve a certain number of LNG storage tanks of different scales, such as a natural gas liquefaction plant, an LNG carrier, an LNG receiving station, a small satellite station, an LNG filling station, and the like. Under the encouragement of energy policies in China, the construction force on LNG Chu Yunji places is continuously increased in China, a plurality of large LNG Chu Yunji places are being planned, and the number of single LNG storage tanks of Chu Yunji places can exceed 20.
As a large-scale storage device for low-temperature liquid, the temperature of the LNG stored in the storage tank is as low as-165 ℃, the LNG storage tank can leak under abnormal conditions such as overfilling, earthquake and the like, once leakage occurs, overflowed LNG can be quickly evaporated into flammable and explosive gas if remedial measures are not timely taken, serious safety accidents can be caused, and immeasurable losses are caused to personnel, buildings, equipment and the like around the LNG storage tank. In addition, cool keeping is carried out through filling perlite in the LNG storage tank annular space, along with the increase of LNG storage tank operation year, the perlite in the LNG storage tank annular space will descend gradually, if not in time fill up, the LNG cold energy in the inner tank will be transmitted to outer jar inner wall fast, directly influences outer jar lining board, outer jar reinforced concrete's structural feature to bring irreversible great influence to LNG storage tank structure's security. Meanwhile, the cold energy output can reduce the cold insulation performance of the LNG storage tank, and the excessive evaporation amount can negatively affect the production safety and economic benefits.
The existing LNG storage tank perlite settlement monitoring system generally adopts a point type temperature sensor (RTD) to measure, and has the defects of limited laying points, difficulty in integrated installation of a large number of cables, shorter service life and the like, so that a safer and more reliable LNG storage tank perlite settlement monitoring system is required to be provided.
Disclosure of Invention
Aiming at the problems, the invention aims to provide the LNG storage tank perlite settlement monitoring system and method based on the distributed optical fiber, which can comprehensively and effectively monitor the running state and abnormal settlement of the LNG storage tank perlite settlement system on line.
In order to achieve the above purpose, the present invention adopts the following technical scheme: LNG storage tank pearlite subsides monitoring system based on distributed optical fiber, its characterized in that: the device comprises a plurality of distributed temperature measuring optical fibers, an optical fiber junction box, a distributed optical fiber temperature measuring host machine at least provided with two channels and a display screen upper computer; each distributed temperature measuring optical fiber is respectively laid on the inner wall of the outer tank of more than one LNG storage tank, the starting end and the tail end of each distributed temperature measuring optical fiber are respectively connected with the optical fiber junction box, and the optical fiber junction box is connected with each channel of the distributed optical fiber temperature measuring host through the distributed optical fiber; and the distributed optical fiber temperature measuring host machine carries out two-channel bidirectional emission and demodulation on the initial end and the tail end of each distributed temperature measuring optical fiber to obtain a final temperature measured value, and sends the final temperature measured value to the display screen upper computer for display through a TCP/IP communication interface, and sends the final temperature measured value to the centralized control system through a standard communication interface.
The arrangement method of each distributed temperature measuring optical fiber on the inner wall of the outer tank of the LNG storage tank comprises the following steps: the start end of the distributed temperature measuring optical fiber is connected with an interface of the optical fiber junction box arranged on the LNG storage tank top, the tail end of the distributed temperature measuring optical fiber enters from the LNG storage tank top nozzle, and is vertically downwards laid along the outer tank inner wall of the LNG storage tank for a certain distance and then is wound around the outer tank inner wall for a circle, and then is continuously vertically downwards laid for a certain distance and then is wound around the outer tank inner wall for a circle, and the operation is repeated until the distributed temperature measuring optical fiber covers the preset lowest position where perlite in the LNG storage tank annular space is likely to subside, and is vertically upwards laid along the outer tank inner wall and is led out from the LNG storage tank top nozzle and then is connected with the other interface of the optical fiber junction box.
The interval distance of every two circles of distributed optical fibers on the inner wall of the outer tank of the LNG storage tank is determined by measurement accuracy.
The distributed temperature measuring optical fiber adopts redundant configuration, namely two distributed temperature measuring optical fiber loops with the same specification are laid on the inner wall of the outer tank of the LNG storage tank in the same way, and the distributed temperature measuring optical fiber loops are used for one time.
The distributed optical fiber temperature measurement host comprises an optical signal generation unit, an optical signal transmitting and receiving unit, an optical signal modulation and demodulation unit, a photoelectric signal conversion unit, a data acquisition and processing unit, a self-calibration unit and a computer processing unit; the optical signal generating unit is used for generating optical pulse signals and transmitting the optical pulse signals to the beginning and the end of each distributed temperature measuring optical fiber through the optical signal transmitting and receiving unit; the optical signal transmitting and receiving unit transmits the received back scattering signals generated by the distributed temperature measuring optical fibers to the optical signal modulation and demodulation unit; the optical signal modulation and demodulation unit is used for demodulating the received back scattering signal and sending the demodulated optical signal to the photoelectric signal conversion unit; the photoelectric signal conversion unit is used for converting the demodulated optical signal into an electric signal and sending the electric signal to the data acquisition and processing unit; the data acquisition and processing unit is used for analyzing the received electric signals to obtain initial temperature measured values of all measuring points and sending the initial temperature measured values to the self-calibration unit; the self-calibration unit is used for calibrating the initial temperature measured value of each measuring point to obtain the final temperature measured value of each measuring point and transmitting the final temperature measured value to the computer processing unit; and the computer processing unit is used for generating an alarm signal according to the received final temperature measured value and sending the final temperature measured value and the alarm signal to the display screen upper computer for display.
The computer processing unit is provided with an absolute low temperature alarm module, a temperature drop rate alarm module and a space and time alarm verification module; the absolute low temperature alarm module is preset with a low temperature alarm threshold, and when the final temperature measured value of each measuring point is lower than the low temperature alarm threshold, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm checking module; a temperature drop rate threshold value is preset in the temperature drop rate alarm module, and when the temperature drop rate of each measuring point is greater than the temperature drop rate threshold value, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm check module; the space and time alarm checking module is used for checking the space and time of the received alarm signals, and sending the alarm signals to the upper computer of the display screen for display when the space area around the alarm point meets the preset alarm point space range threshold value requirement and the alarm time meets the preset alarm time threshold value.
And a visual monitoring module is arranged in the display screen upper computer and used for displaying the LNG storage tank temperature distribution map and the alarm signal in real time according to the received temperature measurement data and the alarm signal.
The LNG storage tank perlite settlement monitoring method based on the distributed optical fiber based system is characterized by comprising the following steps of: 1) The LNG storage tank perlite settlement monitoring system based on the distributed optical fiber comprises the distributed optical fiber, an optical fiber junction box, a distributed optical fiber temperature measuring host and a display screen upper computer, wherein the distributed optical fiber temperature measuring host comprises an optical signal generating unit, an optical signal transmitting and receiving unit, an optical signal modulation and demodulation unit, an photoelectric signal conversion unit, a data acquisition and processing unit, a self-calibration unit and a computer processing unit; 2) An optical signal generating unit in the distributed optical fiber temperature measuring host machine simultaneously transmits optical pulse incident signals to the starting end and the tail end of each distributed temperature measuring optical fiber through an optical signal transmitting and receiving unit; 3) The optical signal transmitting and receiving unit in the distributed optical fiber temperature measuring host transmits the received back scattering signal generated by the distributed temperature measuring optical fiber to the optical signal modulation and demodulation unit for demodulation; 4) The optical signal modulation and demodulation unit demodulates the received back scattering signal and sends the demodulated optical signal to the optical signal conversion unit; 5) The photoelectric signal conversion unit converts the demodulated optical signal into an electric signal and sends the electric signal to the data acquisition and processing unit; 6) The data acquisition and processing unit analyzes the received electric signals to obtain initial temperature measured values and sends the initial temperature measured values to the self-calibration unit; 7) The self-calibration unit calibrates the initial temperature measured value to obtain a final temperature measured value and sends the final temperature measured value to the computer processing unit; 8) And the computer processing unit generates an alarm signal according to the received final temperature measured value, and sends the final temperature measured value and the alarm signal to the display screen upper computer for display.
In the step 7), the computer processing unit generates an alarm signal according to the received final temperature measurement value, and mainly comprises the following steps: (1) the absolute low-temperature alarm module compares the received final temperature measured value of each measuring point with a preset low-temperature alarm threshold value, and if the final temperature measured value of the measuring point is lower than the low-temperature alarm threshold value, an alarm signal is generated according to the position of the measuring point and is sent to the space and time verification module; (2) the temperature drop rate alarm module calculates the temperature drop rate of each temperature measuring point according to the received final temperature measurement value of each measuring point, compares the temperature drop rate of each temperature measuring point with a preset temperature drop rate threshold, and generates an alarm signal according to the position of each measuring point and sends the alarm signal to the space and time verification module when the temperature drop rate of each measuring point is greater than the preset temperature drop rate threshold; (3) the space and time checking module is used for checking according to the received alarm signals, and sending the alarm signals to the upper computer of the display screen for display when the alarm signals pass the checking.
Due to the adoption of the technical scheme, the invention has the following advantages: 1. according to the invention, as the distributed temperature measuring optical fiber is adopted to carry out temperature multipoint measurement on the LNG storage tank, the single-point information monitoring cost and the total cost of a plurality of storage tanks in application can be effectively reduced, and the single-point temperature monitoring cost is reduced by at least 70%. 2. The distributed temperature measuring optical fiber has long service life, and the redundant configuration is adopted, so that the distributed temperature measuring optical fiber is maintenance-free for a long time, and the service life is prolonged by at least 10 years. 3. According to the invention, all measurement points can be covered by one distributed temperature measuring optical fiber, so that the engineering installation is convenient, and the integrated laying of a large number of cables is avoided. 4. The distributed temperature measuring optical fiber system (DTS) has more setting points, and the distributed temperature measuring optical fiber is in direct and close contact with the annular space of the perlite filler, so that the temperature result can reflect the real cold insulation effect, and the abnormal position where settlement occurs can be positioned conveniently, so that the monitoring result is more accurate. 5. The distributed optical fiber is adopted for information transmission, so that the invention is free from electromagnetic interference, intrinsically safe and improves the monitoring safety. 6. According to the invention, the distributed optical fiber temperature measuring host adopts a two-channel bidirectional transmitting and demodulating method, so that the reliability of data analysis is ensured, and the measured temperature value data are sent to the upper computer of the display screen for display, so that the LNG storage tank is more intuitively monitored, and related operators can conveniently operate and process according to the display data. 7. The invention has stable DTS measurement result, average temperature deviation smaller than the abnormal change of the annular space temperature, and can eliminate false alarm of DTS by the alarm management module in the computer processing unit, thereby further improving the monitoring reliability. Therefore, the invention can be widely applied to monitoring the perlite settlement of the LNG storage tank.
Drawings
FIG. 1 is a schematic diagram of the arrangement of a distributed temperature measurement optical fiber on an LNG storage tank;
FIG. 2 is a schematic diagram of the overall framework of the monitoring system of the present invention;
FIG. 3 is a schematic diagram of a distributed optical fiber temperature measuring host according to the present invention;
FIG. 4 is a schematic diagram of a computer processing unit in a distributed optical fiber temperature measuring host according to the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and examples.
As shown in fig. 1 and 2, the distributed optical fiber-based monitoring system for the perlite settlement of the LNG storage tank comprises a plurality of distributed temperature measuring optical fibers 1, an optical fiber junction box 2, a distributed optical fiber temperature measuring host 3 at least provided with two channels and a display screen upper computer 4. Each distributed temperature measuring optical fiber 1 is respectively laid on the inner wall of the outer tank of more than one LNG storage tank 5, the starting end and the tail end of each distributed temperature measuring optical fiber 1 are respectively connected with an optical fiber junction box 2, and the optical fiber junction box 2 is connected with each channel of a distributed optical fiber temperature measuring host 3 through a distributed optical fiber 6. The distributed optical fiber temperature measuring host 3 carries out two-channel bidirectional emission and demodulation on the initial end and the tail end of each distributed temperature measuring optical fiber 1 to obtain a final temperature measured value, and sends the final temperature measured value to the display screen upper computer 4 for display through the TCP/IP communication interface 7, and sends the final temperature measured value to the centralized control system 9 for further processing through the standard communication interface 8 such as a serial RS232 or RS485 communication interface, and sends the final temperature measured value to the existing USB equipment through the USB interface 10.
The arrangement method of each distributed temperature measuring optical fiber 1 on the inner wall of the outer tank of the LNG storage tank 5 comprises the following steps: the start end of the distributed temperature measuring optical fiber 1 is connected with an interface of the optical fiber junction box 2 arranged on the tank top of the LNG storage tank 5, the tail end of the distributed temperature measuring optical fiber 1 enters from the tank top nozzle of the LNG storage tank 5, is vertically downwards laid for a certain distance along the inner wall of the outer tank and then surrounds the inner wall of the outer tank for a circle, then is continuously downwards laid for the same distance and then surrounds the inner wall of the outer tank for a circle, and the process is repeated until the distributed temperature measuring optical fiber 1 covers the lowest position where perlite in the preset annular space of the LNG storage tank 5 is likely to be settled, is vertically upwards laid along the inner wall of the outer tank, and is connected with another interface of the optical fiber junction box 2 after being led out from the tank top nozzle of the LNG storage tank 5. Wherein the lowest position in the annular space of the LNG storage tank where the perlite may have settled is determined based on empirical values. The distance between every two circles of distributed optical fibers on the inner wall of the outer tank of the LNG storage tank is determined by measurement accuracy.
As shown in fig. 3, the distributed optical fiber temperature measuring host 3 includes an optical signal generating unit 31, an optical signal transmitting and receiving unit 32, an optical signal modulating and demodulating unit 33, an optical-electrical signal converting unit 34, a data collecting and processing unit 35, a self-calibration unit 36, and a computer processing unit 37. The optical signal generating unit 31 is used for generating an optical pulse signal and transmitting the optical pulse signal to the beginning and the end of each distributed temperature measuring optical fiber 1 through the optical signal transmitting and receiving unit 32; the optical signal transmitting and receiving unit 32 receives the back scattering signals generated by the distributed temperature measuring optical fibers 1 and transmits the back scattering signals to the optical signal modulation and demodulation unit 33; the optical signal modulation/demodulation unit 33 is configured to demodulate the received back-scattered signal, and send the demodulated optical signal to the optical-electrical signal conversion unit 34; the photoelectric signal conversion unit 34 is configured to convert the demodulated optical signal into an electrical signal and send the electrical signal to the data acquisition and processing unit 35; the data acquisition and processing unit 35 is configured to analyze the received electrical signals, obtain initial temperature measurement values of each measurement point, and send the initial temperature measurement values to the self-calibration unit 36; the self-calibration unit 36 is configured to calibrate the initial temperature measurement value of each measurement point, obtain a final temperature measurement value of each measurement point, and send the final temperature measurement value to the computer processing unit 37; the computer processing unit 37 is used for generating an alarm signal according to the received final temperature measurement value, and sending the final temperature measurement value and the alarm signal to the display screen upper computer 4 for display.
As shown in fig. 4, an absolute low temperature alarm module 371, a temperature drop rate alarm module 372, and a space and time alarm check module 373 are provided in the computer processing unit 37. The absolute low temperature alarm module 371 is preset with a low temperature alarm threshold, and when abnormal settlement in the LNG storage tank is detected, namely, the final temperature measured value of each measuring point is lower than the low temperature alarm threshold, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm checking module 373. The temperature drop rate alarm module 372 is preset with a temperature drop rate threshold, and when the temperature drop rate of each measuring point on the inner wall of the outer tank is monitored to be larger than the temperature drop rate threshold, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm verification module 373. The space and time alarm checking module 373 is used for checking the space and time of the received alarm signal, when the space area around the alarm point meets the requirement of the space range threshold of the preset alarm point, the alarm time passes the checking when meeting the threshold of the preset alarm time, and the alarm signal is sent to the upper computer 4 of the display screen for display.
Preferably, the distributed temperature measuring optical fiber 1 adopts redundant configuration, and two distributed temperature measuring optical fiber loops with the same specification are laid in the tank area in the same way, and are used for one time.
Preferably, the number of LNG storage tanks laid by the distributed temperature measuring optical fibers is determined by the length of the distributed temperature measuring optical fibers which can be measured by the distributed optical fiber temperature measuring host. When the distributed temperature measuring optical fibers 1 need to be laid on the inner walls of the outer tanks of the LNG storage tanks 5, the initial ends of the distributed temperature measuring optical fibers 1 are connected with one interface of the optical fiber junction box 2, the tail ends of the distributed temperature measuring optical fibers enter from the tank top nozzles of the first LNG storage tank 5 and are led out, the distributed temperature measuring optical fibers continue to enter from the tank top nozzles of the second LNG storage tank 5, the distributed temperature measuring optical fibers are laid on the inner walls of the outer tanks of the LNG storage tanks 5 in sequence in the same arrangement mode, and finally the distributed temperature measuring optical fibers are led out from the tank top nozzles of the last LNG storage tank 5 and are connected with the other interface of the optical fiber junction box 2.
Preferably, a visual monitoring module is arranged in the display screen upper computer 4 and is used for displaying the LNG storage tank temperature distribution diagram and the alarm signal in real time according to the received temperature measurement data and the alarm signal.
Based on the LNG storage tank perlite settlement monitoring system based on the distributed optical fiber, the invention also provides an LNG storage tank perlite settlement monitoring method based on the distributed optical fiber, which comprises the following steps:
1) The optical signal generating unit 31 in the distributed optical fiber temperature measuring host 3 sends optical pulse incident signals to the starting end and the tail end of each distributed temperature measuring optical fiber 1 through the optical signal sending and receiving unit 32;
2) The optical signal transmitting and receiving unit 32 in the distributed optical fiber temperature measuring host 3 transmits the received back scattering signal generated by the distributed temperature measuring optical fiber 1 to the optical signal modulation and demodulation unit 33 for demodulation;
3) The optical signal modulation and demodulation unit 33 demodulates the received back-scattered signal and transmits the demodulated optical signal to the photoelectric signal conversion unit 34;
4) The photoelectric signal conversion unit 34 converts the demodulated optical signal into an electrical signal and sends the electrical signal to the data acquisition and processing unit 35;
5) The data acquisition and processing unit 35 analyzes the received electrical signals to obtain an initial temperature measurement value and sends the initial temperature measurement value to the self-calibration unit 36;
6) The self-calibration unit 36 calibrates the initial temperature measurement value to obtain a final temperature measurement value and sends the final temperature measurement value to the computer processing unit 37;
7) The computer processing unit 37 generates an alarm signal according to the received final temperature measurement value, and sends the final temperature measurement value and the alarm signal to the display screen upper computer 4 for display.
The computer processing unit 37 generates an alarm signal based on the received final temperature measurement, mainly comprising the steps of:
(1) the absolute low temperature alarm module 371 compares the received final temperature measurement value of each measurement point with a preset low temperature alarm threshold, and if the final temperature measurement value of the measurement point is lower than the low temperature alarm threshold, generates an alarm signal according to the position of the measurement point and sends the alarm signal to the space and time verification module 373.
(2) The temperature drop rate alarm module 372 calculates the temperature drop rate of each temperature measurement point according to the received final temperature measurement value of each measurement point, compares the temperature drop rate of each temperature measurement point with a preset temperature drop rate threshold, and generates an alarm signal according to the position of each measurement point and sends the alarm signal to the space and time verification module 373 when the temperature drop rate of each measurement point is greater than the preset temperature drop rate threshold.
(3) The space and time checking module 373 is used for checking according to the alarm signal received, send the alarm signal to the upper computer 4 of the display screen to display while checking.
When the space and time verification module performs space verification on the received alarm signals, firstly, a distance is respectively unfolded around the alarm point as a center, all the alarm points on the optical fiber in the range are monitored, and when the alarm points have continuity and meet the minimum threshold value of the sedimentation area, the alarm points pass the space verification; and then time verification is carried out, and as sedimentation alarm is not required to have real-time performance, after an alarm point is monitored, an alarm value verification process for a period of time is set, and the alarm value needs to be continuously and stably output for a period of time and then can pass time verification.
The foregoing embodiments are only for illustrating the present invention, wherein the structures, connection modes, manufacturing processes, etc. of the components may be changed, and all equivalent changes and modifications performed on the basis of the technical solutions of the present invention should not be excluded from the protection scope of the present invention.
Claims (6)
1. LNG storage tank pearlite subsides monitoring system based on distributed optical fiber, its characterized in that: the device comprises a plurality of distributed temperature measuring optical fibers, an optical fiber junction box, a distributed optical fiber temperature measuring host machine at least provided with two channels and a display screen upper computer;
each distributed temperature measuring optical fiber is respectively laid on the inner wall of the outer tank of more than one LNG storage tank, the starting end and the tail end of each distributed temperature measuring optical fiber are respectively connected with the optical fiber junction box, and the optical fiber junction box is connected with each channel of the distributed optical fiber temperature measuring host through the distributed optical fiber; the distributed optical fiber temperature measuring host machine carries out two-channel bidirectional emission and demodulation on the initial end and the tail end of each distributed temperature measuring optical fiber to obtain a final temperature measured value, and sends the final temperature measured value to the display screen upper computer for display through a TCP/IP communication interface, and sends the final temperature measured value to the centralized control system through a standard communication interface;
the arrangement method of each distributed temperature measuring optical fiber on the inner wall of the outer tank of the LNG storage tank comprises the following steps: the start end of the distributed temperature measuring optical fiber is connected with an interface of the optical fiber junction box arranged on the LNG storage tank top, the tail end of the distributed temperature measuring optical fiber enters from the LNG storage tank top nozzle, is vertically downwards laid for a certain distance along the outer tank inner wall of the LNG storage tank and then is wound around the outer tank inner wall, is continuously vertically downwards laid for a certain distance and then is wound around the outer tank inner wall, and the process is repeated until the distributed temperature measuring optical fiber covers the preset lowest position where perlite in the LNG storage tank annular space is likely to be settled, is vertically upwards laid along the outer tank inner wall, is led out from the LNG storage tank top nozzle and is connected with the other interface of the optical fiber junction box;
the distributed optical fiber temperature measurement host comprises an optical signal generation unit, an optical signal transmitting and receiving unit, an optical signal modulation and demodulation unit, a photoelectric signal conversion unit, a data acquisition and processing unit, a self-calibration unit and a computer processing unit; the optical signal generating unit is used for generating optical pulse signals and transmitting the optical pulse signals to the beginning and the end of each distributed temperature measuring optical fiber through the optical signal transmitting and receiving unit; the optical signal transmitting and receiving unit transmits the received back scattering signals generated by the distributed temperature measuring optical fibers to the optical signal modulation and demodulation unit; the optical signal modulation and demodulation unit is used for demodulating the received back scattering signal and sending the demodulated optical signal to the photoelectric signal conversion unit; the photoelectric signal conversion unit is used for converting the demodulated optical signal into an electric signal and sending the electric signal to the data acquisition and processing unit; the data acquisition and processing unit is used for analyzing the received electric signals to obtain initial temperature measured values of all measuring points and sending the initial temperature measured values to the self-calibration unit; the self-calibration unit is used for calibrating the initial temperature measured value of each measuring point to obtain the final temperature measured value of each measuring point and transmitting the final temperature measured value to the computer processing unit; the computer processing unit is used for generating an alarm signal according to the received final temperature measured value, and sending the final temperature measured value and the alarm signal to the display screen upper computer for display;
the computer processing unit is provided with an absolute low temperature alarm module, a temperature drop rate alarm module and a space and time alarm verification module; the absolute low temperature alarm module is preset with a low temperature alarm threshold, and when the final temperature measured value of each measuring point is lower than the low temperature alarm threshold, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm checking module; a temperature drop rate threshold value is preset in the temperature drop rate alarm module, and when the temperature drop rate of each measuring point is greater than the temperature drop rate threshold value, an alarm signal is generated according to the position of the measuring point and sent to the space and time alarm check module; the space and time alarm checking module is used for checking the space and time of the received alarm signals, and sending the alarm signals to the upper computer of the display screen for display when the space area around the alarm point meets the preset alarm point space range threshold value requirement and the alarm time meets the preset alarm time threshold value.
2. The distributed fiber based LNG tank perlite settlement monitoring system of claim 1, wherein: the interval distance of every two circles of distributed optical fibers on the inner wall of the outer tank of the LNG storage tank is determined by measurement accuracy.
3. The distributed fiber based LNG tank perlite settlement monitoring system of claim 1, wherein: the distributed temperature measuring optical fiber adopts redundant configuration, namely two distributed temperature measuring optical fiber loops with the same specification are laid on the inner wall of the outer tank of the LNG storage tank in the same way, and the distributed temperature measuring optical fiber loops are used for one time.
4. The distributed fiber based LNG tank perlite settlement monitoring system of claim 1, wherein: and a visual monitoring module is arranged in the display screen upper computer and used for displaying the LNG storage tank temperature distribution map and the alarm signal in real time according to the received temperature measurement data and the alarm signal.
5. A distributed optical fiber based LNG storage tank perlite settlement monitoring method based on the system of any of claims 1-4, comprising the steps of:
1) The LNG storage tank perlite settlement monitoring system based on the distributed optical fiber comprises the distributed optical fiber, an optical fiber junction box, a distributed optical fiber temperature measuring host and a display screen upper computer, wherein the distributed optical fiber temperature measuring host comprises an optical signal generating unit, an optical signal transmitting and receiving unit, an optical signal modulation and demodulation unit, an photoelectric signal conversion unit, a data acquisition and processing unit, a self-calibration unit and a computer processing unit;
2) An optical signal generating unit in the distributed optical fiber temperature measuring host machine simultaneously transmits optical pulse incident signals to the starting end and the tail end of each distributed temperature measuring optical fiber through an optical signal transmitting and receiving unit;
3) The optical signal transmitting and receiving unit in the distributed optical fiber temperature measuring host transmits the received back scattering signal generated by the distributed temperature measuring optical fiber to the optical signal modulation and demodulation unit for demodulation;
4) The optical signal modulation and demodulation unit demodulates the received back scattering signal and sends the demodulated optical signal to the optical signal conversion unit;
5) The photoelectric signal conversion unit converts the demodulated optical signal into an electric signal and sends the electric signal to the data acquisition and processing unit;
6) The data acquisition and processing unit analyzes the received electric signals to obtain initial temperature measured values and sends the initial temperature measured values to the self-calibration unit;
7) The self-calibration unit calibrates the initial temperature measured value to obtain a final temperature measured value and sends the final temperature measured value to the computer processing unit;
8) And the computer processing unit generates an alarm signal according to the received final temperature measured value, and sends the final temperature measured value and the alarm signal to the display screen upper computer for display.
6. The distributed optical fiber based LNG storage tank perlite settlement monitoring method of claim 5, wherein: in the step 7), the computer processing unit generates an alarm signal according to the received final temperature measurement value, and mainly comprises the following steps:
(1) the absolute low-temperature alarm module compares the received final temperature measured value of each measuring point with a preset low-temperature alarm threshold value, and if the final temperature measured value of the measuring point is lower than the low-temperature alarm threshold value, an alarm signal is generated according to the position of the measuring point and is sent to the space and time verification module;
(2) the temperature drop rate alarm module calculates the temperature drop rate of each temperature measuring point according to the received final temperature measurement value of each measuring point, compares the temperature drop rate of each temperature measuring point with a preset temperature drop rate threshold, and generates an alarm signal according to the position of each measuring point and sends the alarm signal to the space and time verification module when the temperature drop rate of each measuring point is greater than the preset temperature drop rate threshold;
(3) the space and time checking module is used for checking according to the received alarm signals, and sending the alarm signals to the upper computer of the display screen for display when the alarm signals pass the checking.
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