KR100641408B1 - Temperature measurement system used fiber bragg grating sensor - Google Patents

Abstract

A temperature measurement system of an LNG(Liquefied Natural Gas) carrier by using an FBG(Fiber Bragg Grating) sensor is provided to prevent accidents such as explosion of a tank by monitoring the temperature change of a storage tank in real time. In a temperature measurement system of an LNG carrier by using an FBG sensor(111), a storage tank(101) stores an LNG. A temperature detecting part(110) is composed of the FBG sensor reflecting a wavelength of a specific spectrum band among input light and a casing(113) detachably coupled with a sensor installing part(123) of a bracket(120). An optical cable(130) transmits an optical signal detected from the temperature detecting part. A signal converting part converts the optical signal transmitted through the optical cable into an electric signal. And a central controlling unit judges whether the temperature of the storage tank is normal or not in comparison with a preset temperature value and outputs a result through an output part.

Description

TEMPERATURE MEASUREMENT SYSTEM USED FIBER BRAGG GRATING SENSOR}

1 is a conceptual view showing a storage tank temperature measuring system of a typical LNG carrier.

2 is a conceptual diagram of a typical FBG sensor.

3 is a graph illustrating an example of reflection and transmission by wavelength when the FBG sensor of FIG. 2 is processed to reflect light of 1575 nm.

4 is a conceptual diagram showing a temperature measurement system for an LNG carrier using an FBG sensor according to the present invention.

5 is a configuration diagram of a temperature measurement system for an LNG carrier using an FBG sensor according to the present invention.

FIG. 6 is a schematic diagram illustrating a modification system of the signal converter and the temperature detector of FIG. 5. FIG.

Figure 7 is an exploded perspective view showing a temperature detector and the installation structure according to the present invention.

8 is a flowchart illustrating a temperature measurement method for an LNG carrier using an FBG sensor according to the present invention.

<Description of the symbols for the main parts of the drawings>

101: storage tank 110: temperature detector

111: FBG sensor 113: casing

113a: metal tube 113b: outer diameter tab

113c: cap member 120: mounting bracket

121: junction portion 121a: through hole

121b: bolt 123: sensor mounting portion

123a: guide hole 123b: inner diameter tab

130: optical cable 140: optical signal splitter

150: signal conversion unit 151: channel

153: spare channel 160: central control unit

The present invention relates to a temperature measurement system for LNG carriers, and particularly, to fabricate a temperature detector using an FBG sensor, and to monitor the temperature change outside the thermal insulation bulkhead of the LNG storage tank by using the temperature detector in real time to make a minute crack and destruction in the storage tank. The present invention relates to a temperature measurement system for LNG carriers using an FBG sensor that can prevent large accidents caused by an explosion of a storage tank by judging the signs in advance.

At present, demand for liquefied natural gas (Liquefied Natural Gas or LNG) is increasing worldwide due to a sharp rise in crude oil prices and a sharp increase in demand for clean energy.

The LNG is to use a variety of transport means, largely using a pipeline and a method using an LNG carrier.

The LNG carrier is designed to store and transport LNG in a high pressure vessel, and the high pressure vessel has a risk of explosion even in a small crack, and as a result, it is possible to secure a thorough safety device due to its characteristics, which can lead to a large economic loss. It is required.

At this time, the LNG is to be stored and stored in an ultra-low temperature state, it is very important for the real-time analysis of the maintenance and temperature distribution of LNG for this purpose.

Therefore, the LNG carriers and LNG storage tanks are installed and operated with a temperature analysis system capable of precise temperature measurement, the installation, operation, maintenance is a significant cost.

Four LNG storage tanks are provided in a general LNG carrier, and about 30 temperature sensors are installed in each LNG storage tank. As a result, approximately 120 temperature sensors are used on a single LNG carrier, and the temperature measured by these temperature sensors is transmitted to an independent temperature sensing system or central control unit.

1 is a conceptual view showing a storage tank temperature measurement system of a general LNG carrier, the prior art as shown in the figure is a temperature detector 10 installed in the LNG storage tank (1), and the temperature detector 10 The temperature transmitter 20 for transmitting the signal by converting the signal into an electrical signal, the electrical cable 30 for transmitting the transmission signal, and the safety device for preventing excessive current from flowing in the electrical cable 30. It comprises a barrier 40 (Intrinsically Safe Barrier), and the central control unit 50 to receive and analyze the electrical signal that is stably supplied through the IS barrier (40).

In this case, the temperature detector 10 uses a thermocouple capable of low temperature measurement, and the electric signal fed back from each of the thermocouples is measured by a temperature transmitter 20. It is converted into an electrical signal corresponding to the temperature and then transmitted to the central controller 50. In this process, the IS barrier 40 is used as a safety device for preventing excessive current from flowing.

However, the LNG carrier temperature measurement system according to the prior art having the configuration as described above has a problem that the inconvenience and complexity that is provided with a safety device of several stages, such as the IS barrier 40 is provided to block the over-current In addition, there was a problem that the reliability of the safety of the temperature measurement system was deteriorated due to malfunctions in the safety devices for each step.

In addition, in the prior art, each of the temperature sensors, that is, the temperature detectors 10 and the central controller 50 are connected by separate electric cables 30, thereby having a very complicated wiring structure.

In order to fundamentally solve the safety problem of the conventional temperature measurement system, a method of using a fiber bragg grating (FBG) sensor may be considered. Hereinafter, the FBG sensor will be described with reference to FIGS. Explain.

FIG. 2 is a conceptual diagram of a general FBG sensor, and the FBG sensor as shown in the drawing induces a change in refractive index at regular intervals by irradiating ultraviolet light to an optical fiber core forming a specific pattern (lattice) on a surface thereof. By selectively reflecting only light of a specific wavelength (Bragg wavelength), the wavelength of light reflected by the lattice spacing changes.

Using this characteristic, when the lattice spacing changes due to external stress, the change in the lattice spacing, that is, the strain may be measured by observing a change in the wavelength of reflected light.

3 is a graph illustrating an example of reflection and transmission for each wavelength when the FBG sensor of FIG. 2 is processed to reflect light of 1575 nm. Referring to the case of the FBG sensor processed to reflect light of 1575 nm as shown in the graph, FIG. Most of the light of the corresponding wavelength is reflected, and the light of the remaining wavelength is passed as it is, and the reflected wavelength is changed according to the temperature around the FBG sensor and the stress applied to the FBG.

Since the FBG sensor is integrally formed inside the optical fiber, the FBG sensor does not require an additional structure unlike other optical fiber sensors, and the manufacturing method is simple, the accuracy and signal stability are excellent, and the physical characteristics are not affected by electromagnetic waves. This has an excellent advantage.

However, as described above, the FBG sensor itself has a very high tensile force per unit area, whereas the diameter is very small as 125 μm, and is basically made of glass (silica), so that it is easily damaged by external impact.

For this reason, the FBG sensor has a problem that it is difficult to install and handle widely because of its excellent measuring ability.

The present invention is to solve the problems of the prior art, by installing a predetermined number or more of the temperature detector using a fiber optic element on the surface of the storage tank for LNG carriers to store liquefied natural gas to monitor the temperature change of the storage tank in real time The purpose is to provide a temperature measurement system for LNG carriers so that dangerous situations can be detected.

The present invention has another object to provide a temperature measurement system for LNG carriers by forming a temperature detector of a simple structure including a metal casing and the FBG sensor, thereby reducing the management cost according to the maintenance and repair.

In addition, the present invention is another object of the present invention to provide a temperature measurement system for LNG carriers with a low risk of damage to the temperature detector, easy installation and simple wiring structure of the signal transmission cable.

Furthermore, the present invention connects the two channels in one loop so that the operation of the remaining temperature detector connected to the loop is maintained even if the optical cable is cut at any point or a specific temperature detector fails. Another object is to provide a temperature measurement system for LNG carriers.

Temperature measuring system for LNG carrier using the FBG sensor according to the present invention for achieving the above object, a storage tank for storing liquefied natural gas; Detachable state is installed on the outer wall of the storage tank using a mounting bracket to detect the temperature change value of the storage tank in the form of an optical wavelength, but by forming a specific pattern on the surface of the optical fiber to reflect only the wavelength of a specific spectrum band of the input light rays A temperature detector comprising a FBG sensor and a casing coupled to the FBG sensor in a lengthwise direction to be protected from an external environment, and to be detachably attached to the sensor mounting portion of the mounting bracket; An optical cable for transmitting the optical signal detected by the temperature detector; A signal converter which receives an optical signal transmitted through the optical cable and converts the optical signal into an electrical signal; And a central controller configured to receive data from the signal converting unit and compare the data with a preset temperature to determine whether the temperature of the storage tank is normal, and to output the determination result through the output unit. do.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a conceptual diagram showing a temperature measurement system for an LNG carrier using an FBG sensor according to the present invention.

As shown in the figure, the present invention provides a storage tank 101 for storing liquefied natural gas (LPG) and a temperature change value of the storage tank 101 installed on an outer wall of the storage tank 101 to form an optical wavelength. A temperature detector 110 for detecting a signal, an optical cable 130 for transmitting an optical signal detected by the temperature detector 110, and a signal for converting an optical signal transmitted through the optical cable 130 into an electrical signal Receives data from the conversion unit 150 and the signal conversion unit 150 and compares it with a predetermined temperature value to determine whether the temperature of the storage tank 101 is normal, so that the determination result is output through the output unit It includes a central control unit 160.

At this time, the storage tank 101 is made of a double insulating partition wall made of steel, the surface temperature of the liquefied natural gas is filled in the interior temperature reaches -163 ℃.

On the outer surface of the storage tank 101, a temperature detector 110 according to an embodiment of the present invention is installed to perform real-time temperature detection and feedback.

FIG. 5 is an exploded perspective view illustrating a storage tank 101 installation structure according to an embodiment of the temperature detector 110, and a separate unit for attaching the temperature detector 110 to the outer wall of the steel tank of the storage tank 101 in a detachable state. The structure of the mounting bracket 120 is shown together.

As shown in the drawing, the mounting bracket 120 has a surface contact portion 121 which is in surface contact with the surface of the storage tank 101 to achieve thermal conductivity, and protrudes to one side of the surface junction portion 121 to detect a temperature ( 110 is composed of a sensor installation unit 123 having a guide hole (123a) for insertion guide.

In this case, a welding and bolting method may be used as a method for surface joining the surface joining portion 121 to the storage tank 101. In FIG. 5, a predetermined number of through holes 121a are formed on the surface joint part 121 to fasten the bolt 121b. In addition, a columnar sensor installation unit 123 is integrally formed at one side of the surface joint part 121, and a circular column guide hole 123a is formed at the center of the sensor installation unit 123, and the guide hole is formed. The temperature detector 110 is coupled to the detachable state 123a. Here, the inner diameter tab 123b for helical coupling may be formed at the entrance of the guide hole 123a.

The temperature detector 110 forms a specific pattern on the surface of the optical fiber so that only a wavelength of a specific spectrum band of the input light beam is reflected, and the FBG sensor 111 extends in the longitudinal direction and is inserted into the external environment. It is composed of a casing 113 that is protected from and coupled to the sensor mounting portion 123 of the mounting bracket 120 in a detachable state.

Here, the casing 113 is coupled to the cap member 113c at the rear end of the circular metal tube 113a for the guided insertion of the FBG sensor 111 to prevent the departure of the FBG sensor 111 at the same time the movement. It is made of a fixed structure. At this time, the outer diameter tab 113b for helical coupling may be formed at the tip of the cap member 113c.

In addition, the optical signal splitter 140 is used as an apparatus for simultaneously supplying one optical signal supplied through the signal converter 150 to two or more devices, that is, the plurality of temperature detectors 110 at the same time. The optical signal splitter 140 as described above allows the plurality of temperature detectors 110 to be simultaneously connected to the optical cable 130 of one line connected to the signal converter 150, thereby simplifying the wiring structure of the signal transmission cable. You can configure it.

Here, the signal converter 150 converts an optical signal corresponding to the temperature value detected by the temperature detector 110 into an electrical signal, and serves to input data to the central controller 160.

In addition, the signal conversion unit 150 may use an optical analyzer called an interrogator, which is configured to measure various kinds of physical quantities using an FBG sensor, which may be a wavelength of a predetermined spectral band. It is characterized in that it has a function of sending a light ray having a FBG sensor and a simultaneous function of analyzing the wavelength of the light reflected from each FBG sensor position.

Next, the central controller 160 receiving the detected temperature data from the signal converter 150 determines whether the comparison value is a dangerous state by comparing the temperature data with preset temperature data, and determines that the dangerous state is a dangerous state. By alerting the surroundings, the surroundings are ventilated, and the temperature data and the comparison data values input through the central controller 160 may be monitored in real time.

6 is a schematic diagram of a temperature measurement system for an LNG carrier using an FBG sensor according to the present invention, which schematically shows an example of an optimum temperature measuring system in an LNG carrier provided with four storage tanks 101.

First, as shown in the drawing, four channels 151 (shown as channels A to T in FIG. 6) are connected to one storage tank 101, and 15 to each channel A to channel P, respectively. Is connected to the temperature detector 110. In FIG. 6, the temperature detectors 110 connected to the channel A are denoted as A1 to A15, and the temperature detectors 110 connected to the channel B are denoted as B1 to B15, and the temperature detectors 110 connected to the remaining channels are the same. It is written in the same way.

In this case, all of the channels 151 are installed in one signal converter 150, and have at least four spare channels 153 (channels Q to T) that are not connected to the temperature detector 110. It is preferable.

FIG. 7 is a schematic diagram illustrating a modified system of the signal converter and the temperature detector of FIG. 6, which shows a temperature measuring system in which two channels 151 form one loop. Here, a total of 30 temperature detectors 110 are connected by one loop.

As such, when the two channels 151 are connected in a loop shape, even if the optical cable 130 is cut at a certain point or a specific temperature detector 110 fails, the operation of the remaining temperature detector 110 connected to the loop is performed. This has the advantage of being kept on, allowing stable operation of the temperature measurement system.

Hereinafter, a method for measuring a temperature of an LNG carrier using the LNG carrier temperature measuring system of the present invention having the above configuration will be described with reference to FIG. 8.

8 is a flowchart illustrating a temperature measuring method for an LNG carrier using an FBG sensor according to the present invention. Referring to the drawings, the temperature measuring method of the present invention first includes an optical signal input to the temperature detector 110. Step S1 is performed.

In this case, the input optical signal refers to a light ray having a wavelength of a specific spectrum band transmitted from the signal converter 150.

Next, reflecting the wavelength of a specific band included in the optical signal input in the first step (S1) to perform a second step (S2) of detecting the temperature change value of the storage tank 101 in the form of an optical wavelength. do.

At this time, the optical wavelength of a specific band reflected around the temperature detector 110 is changed in response to temperature or stress, and the changed optical wavelength value is detected through the temperature detector 110.

Thereafter, a third step S3 of transmitting the optical signal detected in the second step S2 to the signal converter 150 through the optical cable 130 is performed.

Then, a fourth step S4 of converting the optical signal transmitted in the third step S3 into an electrical signal through the signal converter 150 is performed.

Subsequently, a fifth step S5 of transmitting the electrical signal (temperature data) converted in the fourth step S4 is performed to the central controller 160, and the detection transmitted in the fifth step S5 is performed. The sixth step S6 is performed to determine whether the comparison value is within the normal range by comparing the temperature value (detection temperature data) with the preset temperature data of the central controller 160.

Then, when the determination result in the sixth step (S6), if the comparison value is determined to be out of the normal range, the airtight state of the storage tank 101 is released, that is, the gas leakage state or the storage tank 101 Considering the state that the excess pressure is applied to the) to alert the surroundings to perform the seventh step (S7) to ventilate the surroundings.

Here, the sixth step S6 may further include a step of outputting a detection temperature and a comparison value between the detection temperature and the preset temperature to the monitor.

As described above, the technical contents of the present invention can be variously modified and changed by those skilled in the art without departing from the technical spirit of the present invention. Therefore, the true technical scope of the present invention should not be limited to the contents described in the detailed description of the specification, but should be defined by the claims.

The present invention as described above by installing a predetermined number or more of the temperature detection unit using the optical fiber element on the surface of the storage tank for LNG carriers to store the liquefied natural gas by real-time monitoring the temperature change of the storage tank to detect a dangerous situation, It is effective in preventing large accidents such as tank explosions.

In addition, the present invention by forming a simple temperature detector including a metal casing and FBG sensor, it is easy to manage according to maintenance and repair, the manufacturing cost of the temperature detector is reduced, and there is an effect to minimize the management cost.

In addition, due to the structure that the FBG sensor is protected by a metal casing, the risk of damage due to external impact is less possible to install by a non-expert, thereby improving workability.

In addition, the present invention has the effect of simplifying the wiring structure of the signal transmission cable by connecting a plurality of temperature detectors to the optical cable of one line by the optical signal distributor.

In addition, the present invention by connecting the two channels in a loop (loop), the effect that the operation of the remaining temperature detector connected to the loop is maintained even if the optical cable is cut at any point, or if the specific temperature detector is broken There is.

Claims (9)

delete delete delete A storage tank 101 for storing liquefied natural gas; It is installed on the outer wall of the storage tank 101 in a detachable state by using the mounting bracket 120 to detect a temperature change value of the storage tank 101 in the form of an optical wavelength, and to form a specific pattern on the surface of the optical fiber to identify a specific input beam. The FBG sensor 111 and the FBG sensor 111 are inserted and extended in the longitudinal direction to reflect only the wavelength of the spectrum band, and are detachable from the sensor mounting part 123 of the mounting bracket 120 while being protected from the external environment. A temperature detector 110 composed of a casing 113 coupled to the body; An optical cable 130 for transmitting the optical signal detected by the temperature detector 110; A signal converter 150 which receives an optical signal transmitted through the optical cable 130 and converts the optical signal into an electrical signal; And The central controller 160 which receives the data from the signal converter 150 and compares it with a preset temperature to determine whether the temperature of the storage tank 101 is normal, and outputs the determination result through the output unit. ); LNG carrier temperature measurement system using the FBG sensor comprising a. The method of claim 4, wherein The signal converter 150, A plurality of channels including at least two are provided, each of which is connected to a predetermined number of temperature detectors 110 and the optical cable 130 installed in the storage tank 101 using an FBG sensor Temperature measurement system for LNG carriers. The method of claim 5, The signal converter 150, Four channels are connected to one storage tank 101, and each channel 151 is connected to fifteen temperature detectors 110 and at least four spare channels that are not connected to the temperature detectors 110. Temperature measurement system for an LNG carrier using an FBG sensor, characterized in that it is provided. The method of claim 5 or 6, Each channel 151 constituting the signal conversion unit 150 is connected to one loop per two channels 151 to form a closed circulation signal transmission structure for an LNG carrier using an FBG sensor Temperature measurement system. A first step of inputting an optical signal to the temperature detector 110; A second step of detecting a temperature change value of the storage tank 101 in the form of an optical wavelength by reflecting a wavelength of a specific band included in the optical signal input in the first step; A third step of transmitting the optical signal detected in the second step to the signal converter 150 through the optical cable 130; A fourth step of converting the optical signal transmitted in the third step into an electrical signal through the signal converter 150; A fifth step of transmitting the electrical signal converted in the fourth step to the central controller 160; A sixth step of comparing the detected temperature value transmitted in the fifth step with a preset temperature value of the central controller 160 to determine whether the comparison value is within a normal range; And As a result of the determination in the sixth step, when it is determined that the comparison value is out of the normal range, the airtight state of the storage tank 101 is released, that is, the gas leaks or the excess pressure acts on the storage tank 101. A seventh step of venting the surroundings by alerting the surroundings to be in a state of being; Temperature measurement method for LNG carrier using the FBG sensor comprising a. The method of claim 8, The sixth step further comprises the step of outputting a detection temperature and a comparison value between the detection temperature and the preset temperature to the monitor, characterized in that the LNG carrier ship temperature measurement method using the FBG sensor.

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