A low-temperature hose leakage monitoring system and method based on distributed optical fiber

Abstract

The present invention belongs to the technical field of natural gas transmission, and relates to a cryogenic hose leakage monitoring system and method based on distributed optical fiber, comprising: a plurality of distributed optical fibers, an optical fiber temperature measurement host, and an emergency disconnection unit; each distributed optical fiber is spirally laid on the cold insulation layer of the cryogenic hose, the starting end and the ending end of each distributed optical fiber are both connected to the optical fiber temperature measurement host, and the optical fiber temperature measurement host is connected to the emergency disconnection unit. When a leakage of the cryogenic hose is detected, the emergency disconnection unit is started to cut off the liquefied natural gas transmission of the cryogenic hose. It can comprehensively and effectively monitor the leakage of liquefied natural gas in the cryogenic hose for transporting natural gas online, improve the accuracy and timeliness of the liquefied natural gas leakage monitoring of the cryogenic hose, and at the same time effectively reduce the false alarm rate, making the monitoring results more reliable.

Description

Technical Field

[0001] The invention relates to a distributed optical fiber-based cryogenic hose leakage monitoring system and method, belonging to the technical field of natural gas transmission, and in particular to the field of cryogenic hose leakage monitoring for natural gas transmission. Background Art

[0002] A floating liquefied natural gas (LNG) production storage and offloading unit (FLNG) is a floating production unit used for the development of offshore natural gas fields. It is positioned at sea through a mooring system and has the functions of extracting, processing, liquefying, storing and loading and unloading natural gas. It can also be used in conjunction with a liquefied natural gas (LNG) ship to achieve the extraction of offshore natural gas fields and transportation of natural gas.

[0003] In view of the harsh sea conditions in the South my country Sea, the existing mooring technology is difficult to effectively solve the problem of differentiated movement between the FLNG floating platform and the carrier of the transport ship. A specially designed cryogenic unloading system is needed to meet the stringent requirements of low temperature and swaying conditions. The cryogenic hose delivery system has obvious comprehensive advantages in weight, flexibility, corrosion resistance, and thermal insulation. When FLNG is transported out, an effective way is to use tandem mooring, connect it to the LNG transport ship through the mooring cable, and use a cryogenic hose to connect the FLNG and the LNG transport ship for unloading, and transfer the LNG stored in the FLNG to the transport ship. Therefore, the cryogenic hose is required to be able to withstand ultra-low temperature conditions while also overcoming the influence of relative movement between the FLNG and the LNG transport ship.

[0004] Since the cryogenic hose is exposed to harsh shaking conditions at the seaside and needs to be coiled on the bow or dock after use, and ultra-low temperature fluid flows in the cryogenic hose, the cryogenic hose is likely to leak. Once the cryogenic hose leaks, it will pose a threat to the safety of the surrounding sea areas, and the leakage of LNG will also cause economic losses. Summary of the invention

[0005] In view of the above problems, the purpose of the present invention is to provide a cryogenic hose leakage monitoring system and method based on distributed optical fiber, which can perform comprehensive and effective online monitoring of natural gas leakage in cryogenic hoses for transporting natural gas.

[0006] To achieve the above object, the present invention proposes the following technical solution: A cryogenic hose leakage monitoring system based on distributed optical fiber, comprising: a plurality of distributed optical fibers, an optical fiber temperature measurement host, and an emergency disconnection unit; each distributed optical fiber is spirally laid on the cold insulation layer of the cryogenic hose, the start end and the end of each distributed optical fiber are connected to the optical fiber temperature measurement host, and the optical fiber temperature measurement host is connected to the emergency disconnection unit. When a leakage of the cryogenic hose is detected, the emergency disconnection unit is activated to cut off the natural gas transmission of the cryogenic hose.

[0007] Further, the winding angle of the distributed optical fiber laid in a spiral shape is 45°, and the phases of the wave peaks and wave valleys of two adjacent optical fibers differ by 180°.

[0008] Further, the structure of the distributed optical fiber includes: a stainless steel hose disposed at the innermost part, a stainless steel braided mesh laid outside the stainless steel hose, and a polytetrafluoroethylene laid outside the stainless steel braided mesh.

[0009] Further, the diameter of the distributed optical fiber is less than 5 mm.

[0010] Further, the optical fiber temperature measurement host includes a laser source, an optical pulse modulator, an optical path coupler, a beam splitter, an optical filter, APD photoelectric conversion and amplifier, a data acquisition and processing module, a computer processing unit, and a synchronization controller; the laser emitted by the laser source is modulated by the optical pulse modulator and then irradiated onto the optical path coupler. The optical path coupler is connected to the distributed optical fiber. After the laser passes through the distributed optical fiber, it is received by the beam splitter. The beam splitter is used for splitting the laser. The split optical signal filters out the background signal through the optical filter, and then is converted into an electrical signal by APD photoelectric conversion and amplifier and amplified. The computer processing unit acquires and processes the electrical signal to generate a processing result, and the synchronization controller generates a control instruction according to the processing result.

[0011] Further, the optical fiber temperature measurement host includes a TCP / IP communication interface, an RS485 communication interface, and a USB interface. The TCP / IP communication interface is connected to the upper computer of the display screen, and the RS485 communication interface is connected to the total control system.

[0012] Furthermore, an absolute low-temperature alarm module, a temperature drop rate alarm module, an anti-false alarm module, and a space and time alarm module are provided in the computer processing unit; a low-temperature alarm threshold is preset in the absolute low-temperature alarm module. When the final temperature measurement value of each monitoring point is lower than the low-temperature alarm threshold, an alarm signal is generated according to the position of the measurement point and sent to the space and time alarm verification module. A temperature rate threshold is preset in the temperature drop rate alarm module. When the temperature rate of each monitoring point is greater than the temperature drop rate threshold, an alarm signal is generated according to the position of the monitoring point and sent to the space and time alarm verification module; the space and time alarm module is used to perform space and time verification on the received alarm signals; the anti-false alarm module is used to detect whether the alarm time meets the preset alarm time threshold. If it meets the preset alarm time threshold, the alarm signal is sent to the upper computer of the display screen for display.

[0013] The present invention also discloses a method for monitoring the leakage of a cryogenic hose based on distributed optical fiber, including: setting up the cryogenic hose leakage monitoring system based on distributed optical fiber as described in any one of the above; the optical fiber temperature measurement host sends a laser signal to the distributed optical fiber, receives the backscattered signal generated by the distributed optical fiber, and demodulates the backscattered signal; extracts the measured temperature values of each measurement point on the distributed optical fiber according to the backscattered signal; determines whether the temperature value is lower than the preset temperature threshold or whether the temperature drop rate is greater than the preset temperature drop rate threshold. If so, an initial alarm signal is generated; determines whether the initial alarm signal is continuous in space and time. If so, an alarm signal is generated; uploads the alarm signal to the upper computer of the display screen for display.

[0014] Furthermore, the method for determining whether the initial alarm signal is continuous in space and time is as follows: taking the alarm point corresponding to the initial alarm signal as the center and a preset distance as the radius, obtaining a monitoring range, monitoring all monitoring points within the monitoring range. When the temperature values measured by all monitoring points are continuous and exceed the minimum threshold of each monitoring point within the monitoring area, the initial alarm signal is continuous in space; within the preset time range of the alarm point corresponding to the initial alarm signal, its temperature value is lower than the preset temperature threshold or the temperature drop rate is greater than the preset temperature drop rate threshold, then the initial alarm signal is continuous in time.

[0015] Due to the adoption of the above technical solutions, the present invention has the following advantages:

[0016] 1. In the present invention, the distributed optical fiber is laid in the cold insulation layer of the cryogenic hose. Since the cold insulation layer is not the outermost layer of the cryogenic hose, when the optical fiber detects a leakage of the cryogenic hose, the natural gas does not actually leak outside the pipe, improving the safety of the liquefied natural gas transportation process.

[0017] 2. The present invention uses distributed optical fibers to measure multiple temperature points simultaneously, which can effectively reduce the control cost of single-point information. Moreover, the selection of distributed optical fibers takes into account the requirement of resisting seawater corrosion, which can improve the service life of the optical fibers and reduce the maintenance cost.

[0018] 3. In the present invention, through the anti-false alarm module, the position of the alarm point can be correctly determined, ensuring the correctness of the alarm signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic structural diagram of a low-temperature hose in an embodiment of the present invention;

[0020] Figure 2 is a schematic structural diagram of a low-temperature hose leakage monitoring system in an embodiment of the present invention;

[0021] Figure 3 is a schematic structural diagram of an optical fiber temperature measurement host in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] In order to enable those skilled in the art to better understand the technical direction of the present invention, the present invention is described in detail through specific embodiments. However, it should be understood that the provision of the specific embodiments is only for better understanding of the present invention, and they should not be construed as limitations on the present invention. In the description of the present invention, it should be understood that the terms used are only for the purpose of description and cannot be construed as indicating or implying relative importance.

[0023] The structure of the low-temperature hose in the present invention is as Figure 1 described. The innermost layer of the low-temperature hose is a corrugated pipe 1. An outer seat bed layer 2 is provided on the outer layer of the corrugated pipe 1. An axial reinforcement layer 3 is provided on the outer layer of the seat bed layer 2. A cold insulation layer 4 is provided on the outer layer of the axial reinforcement layer 3. An intermediate waterproof layer 5 is provided on the outer layer of the cold insulation layer 4. A second cold insulation layer 4 is provided on the outer layer of the intermediate waterproof layer 5. An outer waterproof layer 6 (a total of five cold insulation layers) is provided on the outer layer of the second cold insulation layer 4. The distributed optical fiber 7 for detecting temperature is spirally wound around the third cold insulation layer 4.

[0024] The present invention provides a cryogenic hose leakage monitoring system and method based on distributed optical fiber 7. By laying the distributed optical fiber 7 on the cold insulation layer 4 of the natural gas cryogenic hose, multi-point monitoring of the temperature of the cold insulation layer 4 of the cryogenic hose is realized. Since the distributed optical fiber 7 is in full direct contact with the cold insulation layer 4, when the cryogenic hose does not leak, its temperature can objectively reflect the real-time cold insulation effect of the cryogenic hose. Once liquefied natural gas leaks, the temperature of the cold insulation layer 4 will decrease significantly, and whether the cryogenic hose leaks is judged by monitoring the temperature. If the cryogenic hose leaks, the liquefied natural gas transmission of the cryogenic hose is shut off through the emergency disconnection unit, thereby avoiding the occurrence of accident risks and economic losses. The following describes the technical solutions of the present invention in detail through two embodiments, in combination with the attached Figure 2 , 3 drawings.

[0025] Embodiment 1

[0026] This embodiment discloses a cryogenic hose leakage monitoring system based on distributed optical fiber 7. As Figure 2 shown, it includes: a plurality of distributed optical fibers 7, an optical fiber temperature measurement host, and an emergency disconnection unit;

[0027] Each distributed optical fiber 7 is spirally laid on the third cold insulation layer 4 of the cryogenic hose. Preferably, there are two optical fibers. When spirally laid, the winding angle is 45°, and the phases of the wave peaks and wave valleys of adjacent two optical fibers differ by 180°. The starting ends of the two distributed optical fibers 7 are respectively connected to two channels of the optical fiber temperature measurement host. The optical fiber temperature measurement host provides an input light source for the distributed optical fiber 7, demodulates the backward scattering signal output by the distributed optical fiber 7, extracts the temperature values of each monitoring point on the distributed optical fiber 7, and the optical fiber temperature measurement host is connected to the emergency disconnection unit. When it detects that the cryogenic hose leaks, it starts the emergency disconnection unit to shut off the natural gas transmission of the cryogenic hose. The optical fiber temperature measurement host includes a TCP / IP communication interface, an RS485 communication interface, and a USB interface. The TCP / IP communication interface is connected to the upper computer of the display screen, and the RS485 communication interface is connected to the total control system.

[0028] The structure of the distributed optical fiber 7 includes: a stainless steel hose arranged at the innermost part, a stainless steel braided mesh laid outside the stainless steel hose, and a polytetrafluoroethylene laid outside the stainless steel braided mesh. The diameter of the distributed optical fiber 7 is less than 5 mm. The distributed optical fiber 7 should be able to withstand a low temperature working condition of -160°C.

[0029] As Figure 3As shown in the figure, the optical fiber temperature measurement host includes a laser source, an optical pulse modulator, an optical path coupler, a splitter, an optical filter, APD photoelectric conversion and amplifier, a data acquisition and processing module, a computer processing unit, and a synchronization controller; the laser emitted by the laser source is modulated by the optical pulse modulator and then irradiated onto the optical path coupler. The optical path coupler is connected to the distributed optical fiber 7. After the laser passes through the distributed optical fiber 7, it is received by the splitter. The splitter is used to split the laser. The split optical signal filters out the background signal through the optical filter, and then is converted into an electrical signal by APD photoelectric conversion and amplifier and amplified. The computer processing unit collects and processes the electrical signal to generate a processing result, and the synchronization controller generates a control instruction according to the processing result.

[0030] In the computer processing unit, there are set an absolute low temperature alarm module, a temperature drop rate alarm module, and a space and time alarm module; in the absolute low temperature alarm module, a low temperature alarm threshold is preset. When the final temperature measurement value of each monitoring point is lower than the low temperature alarm threshold, an alarm signal is generated according to the position of the measurement point and sent to the space and time alarm verification module. In the temperature drop rate alarm module, a temperature rate threshold is preset. When the temperature rate of each monitoring point is greater than the temperature drop rate threshold, an alarm signal is generated according to the position of the monitoring point and sent to the space and time alarm verification module; the space and time alarm module is used to perform space and time verification on the received alarm signal, detect whether the alarm time meets the preset alarm time threshold, and if it meets the preset alarm time threshold, send the alarm signal to the display upper computer for display.

[0031] Embodiment 2

[0032] Based on the same inventive concept, this embodiment discloses a method for monitoring the leakage of a low-temperature hose based on the distributed optical fiber 7, including:

[0033] S1 Set up the low-temperature hose leakage monitoring system based on the distributed optical fiber 7 in Embodiment 1;

[0034] S2 The optical fiber temperature measurement host sends a laser signal to the distributed optical fiber 7, receives the backscattered signal generated by the distributed optical fiber 7, and demodulates the backscattered signal;

[0035] S3 Extract the measured temperature values of each measurement point on the distributed optical fiber 7 according to the backscattered signal;

[0036] S4 Determine whether the temperature value is lower than the preset temperature threshold, or whether the temperature drop rate is greater than the preset temperature drop rate threshold. If so, generate an initial alarm signal;

[0037] S5 Determine whether the initial alarm signal is continuous in space and time. If so, generate an alarm signal;

[0038] Taking the alarm point corresponding to the initial alarm signal as the center and a preset distance as the radius, a monitoring range is obtained, and all monitoring points within the monitoring range are monitored. When the temperature values measured at all monitoring points are continuous and exceed the minimum threshold of each monitoring point within the monitoring area, the initial alarm signal is continuous in space; within a preset time range, if the temperature value of the alarm point corresponding to the initial alarm signal is lower than the preset temperature threshold or the temperature drop rate is greater than the preset temperature drop rate threshold, the initial alarm signal is continuous in time.

[0039] S6 Uploads the alarm signal to the upper computer of the display screen for display.

[0040] The method in this embodiment can improve the accuracy and timeliness of monitoring the leakage of liquefied natural gas in low-temperature hoses, effectively reduce the false alarm rate at the same time, and make the monitoring results more reliable.

[0041] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the specific implementation manners of the present invention can still be modified or equivalently replaced. Any modification or equivalent replacement without departing from the spirit and scope of the present invention shall be covered by the protection scope of the claims of the present invention. The above content is only the specific implementation manner of this application, but the protection scope of this application is not limited thereto. Any person skilled in the art within the technical scope disclosed in this application can easily think of changes or replacements, which should all be covered by the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

1. A low-temperature hose leakage monitoring system based on distributed optical fiber, characterized in that Including: A plurality of distributed optical fibers, an optical fiber temperature measurement host, and an emergency disconnection unit; Each of the distributed optical fibers is spirally laid on the cold insulation layer of the low-temperature hose. The start end and the end of each distributed optical fiber are connected to the optical fiber temperature measurement host, and the optical fiber temperature measurement host is connected to the emergency disconnection unit. When a leak of the low-temperature hose is detected, the emergency disconnection unit is activated to shut off the natural gas transmission of the low-temperature hose; The optical fiber temperature measurement host includes a computer processing unit, and an absolute low-temperature temperature alarm module, a temperature drop rate alarm module, an anti-false alarm module, and a space and time alarm module are set in the computer processing unit; A low-temperature temperature alarm threshold is preset in the absolute low-temperature temperature alarm module. When the final temperature measurement value of each monitoring point is lower than the low-temperature temperature alarm threshold, an alarm signal is generated according to the position of the monitoring point and sent to the space and time alarm verification module. A temperature rate threshold is preset in the temperature drop rate alarm module. When the temperature rate of each monitoring point is greater than the temperature drop rate threshold, an alarm signal is generated according to the position of the monitoring point and sent to the space and time alarm verification module; the space and time alarm module is used to perform space and time verification on the received alarm signals; the anti-false alarm module is used to detect whether the alarm time meets a preset alarm time threshold. If it meets the preset alarm time threshold, the alarm signal is sent to the upper computer of the display screen for display; The space and time alarm module takes the alarm point corresponding to the initial alarm signal as the center and a preset distance as the radius to obtain a monitoring range, monitors all monitoring points within the monitoring range. When the temperature values measured by all monitoring points are continuous and exceed the minimum threshold of each monitoring point within the monitoring range, the initial alarm signal is continuous in space; Within a preset time range, if the temperature value of the alarm point corresponding to the initial alarm signal is lower than the preset temperature threshold or the temperature drop rate is greater than the preset temperature drop rate threshold, the initial alarm signal is continuous in time.

2. The low-temperature hose leakage monitoring system based on distributed optical fiber according to claim 1, characterized in that, The winding angle of the distributed optical fiber laid in a spiral shape is 45°, and the phases of the wave peaks and wave valleys of two adjacent optical fibers differ by 180°.

3. The cryogenic hose leakage monitoring system based on distributed optical fiber according to claim 1, characterized in that, The structure of the distributed optical fiber includes: a stainless steel hose arranged at the innermost, a stainless steel braided mesh laid outside the stainless steel hose, and a polytetrafluoroethylene laid outside the stainless steel braided mesh.

4. The cryogenic hose leakage monitoring system based on distributed optical fiber according to claim 3, characterized in that The diameter of the distributed optical fiber is less than 5 mm.

5. The low-temperature hose leakage monitoring system based on distributed optical fiber according to claim 1, characterized in that, The optical fiber temperature measurement host further includes a laser source, an optical pulse modulator, an optical path coupler, a splitter, an optical filter, an APD photoelectric conversion and amplifier, a data acquisition and processing module, and a synchronization controller; The laser emitted by the laser source, after being modulated by the optical pulse modulator, irradiates onto the optical path coupler. The optical path coupler is connected to the distributed optical fiber. After passing through the distributed optical fiber, the laser is received by the optical splitter. The optical splitter is used for splitting the laser. The optical signal after splitting filters out the background signal through an optical filter, and then is converted into an electrical signal through the APD photoelectric conversion and amplifier and amplified. The computer processing unit collects and processes the electrical signal to generate a processing result. The synchronization controller generates a control instruction according to the processing result.

6. The cryogenic hose leakage monitoring system based on distributed optical fiber according to claim 5, characterized in that The optical fiber temperature measurement host includes a TCP / IP communication interface, an RS485 communication interface, and a USB interface. The TCP / IP communication interface is connected to the display upper computer, and the RS485 communication interface is connected to the total control system.

7. A method for monitoring leakage of a cryogenic hose based on distributed optical fiber, characterized in that, Including: Setting up the low-temperature hose leakage monitoring system based on distributed optical fiber as described in any one of claims 1-6; The optical fiber temperature measurement host sends a laser signal to the distributed optical fiber, receives the backscattered signal generated by the distributed optical fiber, and demodulates the backscattered signal; Extracting the measured temperature values of each monitoring point on the distributed optical fiber according to the backscattered signal; Judging whether the temperature value is lower than the preset temperature threshold, or whether the temperature drop rate is greater than the preset temperature drop rate threshold. If so, generating an initial alarm signal; Judging whether the initial alarm signal is continuous in space and time. If so, generating an alarm signal; Uploading the alarm signal to the display upper computer for display.

8. The method for monitoring leakage of a cryogenic hose based on distributed optical fiber according to claim 7, wherein The method for judging whether the initial alarm signal is continuous in space and time is: Taking the alarm point corresponding to the initial alarm signal as the center and the preset distance as the radius, obtaining the monitoring range, monitoring all monitoring points within the monitoring range. When the measured temperature values of all monitoring points are continuous and exceed the minimum threshold of each monitoring point within the monitoring range, the initial alarm signal is continuous in space; If the temperature value of the alarm point corresponding to the initial alarm signal is lower than the preset temperature threshold or the temperature drop rate is greater than the preset temperature drop rate threshold within the preset time range, the initial alarm signal is continuous in time.

Images