Gas Leak Detection Device and Gas Leak Detection Method

Abstract

To provide a gas leak detection device which easily detects a leak of a liquid gas in a detection target space so as to specify a leak place and which is free from maintenance, and a gas leak detection method.SOLUTION: A gas leak detection device includes in a ship: a plurality of thermal image cameras 1a, 1b provided facing detection objects 101, 102 for storing a liquid gas; and a controller 2 for acquiring thermal images from the thermal image cameras 1a, 1b. Each of the thermal image cameras 1a, 1b is individually provided on a plurality of lines making an angle which is a central angle Ac around the center C of a circumscribed sphere S of the detection objects 101, 102 as a predetermined angle.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a gas leak detection device and a gas leak detection method. More specifically, the present invention relates to a gas leak detection device and a gas leak detection method that can easily detect the leakage of liquefied gas in a detection target space, identify the leakage location, and are maintenance-free.

Background Art

[0002] Liquefied gases such as liquefied ammonia and LPG (liquefied petroleum gas) are used as fuels in ships in addition to cargo, and the demand is increasing.

[0003] When liquefied gas leaks due to damage or deterioration of tanks for storing liquefied gas, pipes for feeding liquefied gas, etc. inside a ship, it is necessary to detect the leakage in order to ensure the safety of crew members.

[0004] Conventionally, as methods for detecting leakage of liquefied gas, there are a method using a semiconductor-type solid sensor and a method using a constant potential ionization-type electrochemical sensor.

[0005] Patent Document 1 describes a hydrogen leak detection device that detects the temperature rise of a hydrogen storage part made of a hydrogen storage alloy with a temperature sensor and discriminates the presence or absence of hydrogen leakage.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] Incidentally, for the above-described solid sensor and electrochemical sensor, it is necessary to select a sensor of a type suitable for the composition (type) of the liquefied gas for which leakage is to be detected. Therefore, in a ship that transports or uses liquefied gases of a plurality of compositions (types), sensors of a plurality of types must be used, and the number of necessary sensors increases.

[0008] In addition, these solid sensors and electrochemical sensors require a great deal of labor because they need to be periodically replaced and calibrated. Such labor-intensive maintenance can be promptly addressed in regular ships, but not in tramp ships.

[0009] Also, since the leaked liquefied gas vaporizes and diffuses into the space, depending on the fixed gas detection sensor, if the leakage point and the sensor installation point are far apart, it takes a long time for the vaporized gas to reach the sensor before detection.

[0010] Furthermore, depending on the fixed gas detection sensor or the fixed temperature sensor described in Patent Document 1, since the detectable area is limited, when the detection target space is large or there are many target devices, a large number of sensors must be installed, and the labor and cost of installation become extremely high. In this case, a method of detecting the vaporized gas by aggregating it using a ventilation fan can be considered, but a large number of devices are required for the configuration, and the labor and cost of installation become extremely high.

[0011] Depending on the fixed gas detection sensor or temperature sensor, it is complicated to identify the leakage point because an airtightness test or the like must be performed. Also, for the case of leakage from the liquid supply pipe, a method of installing a drip tray and a temperature sensor in this drip tray can be considered, but the temperature change cannot be grasped until the leaked material is aggregated in the drip tray, and if the leaked material is not aggregated, the leakage of the liquefied gas cannot be detected.

[0012] Note that although it is conceivable to use a thermal imaging camera to detect locations that have been cooled due to leakage of liquefied gas, the shapes of tanks, pipes, etc. on ships are complex, and they may be installed not only in the ship's interior but also in open spaces such as on the deck. Therefore, it has been difficult to arrange the thermal imaging camera so that there are no blind spots, i.e., so that all surfaces of the tanks, pipes, etc. can be imaged.

[0013] Therefore, an object of the present invention is to provide a gas leak detection device and a gas leak detection method that can easily detect leakage of liquefied gas in a detection target space without any undetected locations, can identify the leakage location, and are maintenance-free.

[0014] Other objects of the present invention will become apparent from the following description.

Means for Solving the Problems

[0015] The above problems are solved by the following inventions. 1. In a ship, a plurality of thermal imaging cameras arranged apart from each other and directed toward a detection target space in which a detection target object storing liquefied gas is arranged, and a control device that acquires an image taken by the thermal imaging camera as a thermal image are provided, wherein each of the thermal imaging cameras is arranged one by one on two straight lines with a central angle around the center of the circumscribed sphere of the detection target object being approximately 30° to approximately 180°, and a total of two cameras are arranged. A gas leak detection device characterized by the above. 2. In a ship, a plurality of thermal imaging cameras arranged apart from each other and directed toward a detection target space in which a detection target object storing liquefied gas is arranged, and a control device that acquires an image taken by the thermal imaging camera as a thermal image are provided, wherein each of the thermal imaging cameras is arranged one by one on three straight lines with a central angle around the center of the circumscribed sphere of the detection target object being approximately 120°, and a total of three cameras are arranged. A gas leak detection device characterized by the above. 3. In a ship, a plurality of thermal imaging cameras that are directed toward a detection target space in which a detection target object for storing liquefied gas is arranged and are arranged apart from each other, and a control device that acquires an image captured by the thermal imaging camera as a thermal image are provided, wherein each of the thermal imaging cameras is arranged one by one on four straight lines in which a central angle around the center of the circumscribed sphere of the detection target object is approximately 90° to approximately 110°, and a total of four cameras are arranged. A gas leakage detection device characterized by this. 4. In a ship, a plurality of thermal imaging cameras that are directed toward a detection target space in which a detection target object for storing liquefied gas is arranged and are arranged apart from each other, and a control device that acquires an image captured by the thermal imaging camera as a thermal image are provided, wherein each of the thermal imaging cameras is arranged one by one on the front side, the rear side, the left side, the right side, and the upper side of the detection target space, and a total of five cameras are arranged. A gas leakage detection device characterized by this. 5. In a ship, a plurality of thermal imaging cameras that are directed toward a detection target space in which a detection target object for storing liquefied gas is arranged and are arranged apart from each other, and a control device that acquires an image captured by the thermal imaging camera as a thermal image are provided, wherein each of the thermal imaging cameras is arranged two by two facing each other on each axis of an xyz orthogonal coordinate system having the center of the circumscribed sphere of the detection target object as the origin, and a total of six cameras are arranged, wherein the xyz orthogonal coordinate system is rotated with respect to the detection target space, and the arrangement of the thermal imaging cameras on the floor surface of the detection target space is avoided. A gas leakage detection device characterized by this. 6. When the ratio (α) of the area (At) of the region having a temperature equal to or lower than the threshold temperature (Tr) in the thermal image to the area (A0) of the thermal image is equal to or higher than the threshold ratio (αr), the control device determines that the liquefied gas is leaking. The gas leak detection device according to any one of the above 1 to 5, characterized in that... 7. The threshold temperature (Tr) is set to an arbitrary temperature between the saturation temperature of the liquefied gas under atmospheric pressure and the air temperature. The gas leak detection device according to the above 6, characterized in that... 8. The area (A0) of the thermal image is the area of the thermal image obtained by one of the thermal image cameras. In the thermal image obtained by at least one of the thermal image cameras, when the ratio (α) is equal to or greater than the threshold ratio (αr), it is determined that the liquefied gas is leaking. The gas leak detection device according to the above 6, characterized in that... 9. The area (A0) of the thermal image is the sum of the areas of the plurality of thermal images obtained by the plurality of thermal image cameras. In the entirety of the plurality of thermal images obtained by the plurality of thermal image cameras, when the ratio (α) is equal to or greater than the threshold ratio (αr), it is determined that the liquefied gas is leaking. The gas leak detection device according to the above 6, characterized in that... 10. In a ship, a plurality of thermal image cameras directed toward a detection target space in which a detection target object storing liquefied gas is disposed and spaced apart from each other, a control device that acquires an image captured by the thermal image camera as a thermal image, and comprising: When the ratio (α) of the area (At) of the region having a temperature equal to or lower than the threshold temperature (Tr) in the thermal image to the area (A0) of the thermal image is equal to or greater than the threshold ratio (αr), the control device determines that the liquefied gas is leaking. The gas leak detection device, characterized in that... 11. The threshold temperature (Tr) is set to an arbitrary temperature between the saturation temperature of the liquefied gas under atmospheric pressure and the air temperature. The gas leak detection device according to the above 10, characterized in that... 12. The area (A0) of the thermal image is the area of the thermal image obtained by one of the thermal image cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the thermal image obtained by at least one of the thermal image cameras, it is determined that the liquefied gas is leaking. The gas leak detection device according to item 10, characterized in that. 13. The area (A0) of the thermal image is the sum of the areas of a plurality of thermal images obtained by the plurality of thermal image cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the entirety of the plurality of thermal images obtained by the plurality of thermal image cameras, it is determined that the liquefied gas is leaking. The gas leak detection device according to item 10, characterized in that. 14. On a ship, a plurality of thermal image cameras directed at a detection target space in which a detection target object storing liquefied gas is arranged are separated from each other, and one is arranged on each of two straight lines around the center of the circumscribed sphere of the detection target object with a central angle of approximately 30° to approximately 180°, for a total of 2 cameras. The thermal image cameras are used to photograph the detection target space. An image photographed by the thermal image cameras is obtained as a thermal image. A gas leak detection method characterized by the above. 15. On a ship, a plurality of thermal image cameras directed at a detection target space in which a detection target object storing liquefied gas is arranged are separated from each other, and one is arranged on each of three straight lines around the center of the circumscribed sphere of the detection target object with a central angle of approximately 120°, for a total of 3 cameras. The thermal image cameras are used to photograph the detection target space. An image photographed by the thermal image cameras is obtained as a thermal image. A gas leak detection method characterized by the above. 16. On a ship, a plurality of thermal image cameras directed at a detection target space in which a detection target object storing liquefied gas is arranged are separated from each other, and one is arranged on each of four straight lines around the center of the circumscribed sphere of the detection target object with a central angle of approximately 90° to approximately 110°, for a total of 4 cameras. The thermal image cameras are used to photograph the detection target space. Obtaining the image captured by the thermal imaging camera as a thermal image A gas leakage detection method characterized by the above. 17. On a ship, a plurality of thermal imaging cameras directed at a detection target space where a detection target object storing liquefied gas is arranged are spaced apart from each other, and one camera is arranged on each of the front side, rear side, left side, right side, and upper side of the detection target space, for a total of five cameras. Using the thermal imaging camera to capture the detection target space Obtaining the image captured by the thermal imaging camera as a thermal image A gas leakage detection method characterized by the above. 18. On a ship, a plurality of thermal imaging cameras directed at a detection target space where a detection target object storing liquefied gas is arranged are spaced apart from each other, and two cameras are arranged opposite to each other on each axis of the xyz orthogonal coordinates with the center of the circumscribed sphere of the detection target object as the origin, for a total of six cameras. Using the thermal imaging camera to capture the detection target space Obtaining the image captured by the thermal imaging camera as a thermal image A gas leakage detection method characterized by the above. 19. When the ratio (α) of the area (At) of the region with a temperature below the threshold temperature (Tr) in the thermal image to the area (A0) of the thermal image is equal to or greater than the threshold ratio (αr), it is determined that the liquefied gas is leaking The gas leakage detection method according to any one of the above 14 to 18, characterized by the above. 20. The threshold temperature (Tr) is set to an arbitrary temperature between the saturation temperature of the liquefied gas under atmospheric pressure and the air temperature The gas leakage detection method according to the above 19, characterized by the above. 21. The area (A0) of the thermal image is the area of the thermal image obtained by one of the thermal imaging cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the thermal image obtained by at least one of the thermal imaging cameras, it is determined that the liquefied gas is leaking The gas leakage detection method according to item 19, characterized in that... 22. The area (A0) of the thermal image is the sum of the areas of a plurality of thermal images obtained by the plurality of thermal image cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the entirety of the plurality of thermal images obtained by the plurality of thermal image cameras, it is determined that the liquefied gas is leaking. The gas leakage detection method according to item 19, characterized in that... 23. In a ship, a plurality of thermal image cameras directed toward a detection target space in which a detection target object storing liquefied gas is disposed are arranged apart from each other. The detection target space is photographed by the thermal image cameras. An image photographed by the thermal image cameras is obtained as a thermal image. When the ratio (α) of the area (At) of a region having a temperature equal to or lower than the threshold temperature (Tr) in the thermal image to the area (A0) of the thermal image is equal to or greater than the threshold ratio (αr), it is determined that the liquefied gas is leaking. A gas leakage detection method, characterized in that... 24. The threshold temperature (Tr) is set to an arbitrary temperature between the saturation temperature of the liquefied gas under atmospheric pressure and the air temperature. The gas leakage detection method according to item 23, characterized in that... 25. The area (A0) of the thermal image is the area of a thermal image obtained by one of the thermal image cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the thermal image obtained by at least any one of the thermal image cameras, it is determined that the liquefied gas is leaking. The gas leakage detection method according to item 23, characterized in that... 26. The area (A0) of the thermal image is the sum of the areas of a plurality of thermal images obtained by the plurality of thermal image cameras. When the ratio (α) is equal to or greater than the threshold ratio (αr) in the entirety of the plurality of thermal images obtained by the plurality of thermal image cameras, it is determined that the liquefied gas is leaking. The gas leakage detection method according to item 23, characterized in that...

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a gas leak detection device and a gas leak detection method that can easily detect the leakage of liquefied gas in a detection target space without any undetected locations, can identify the leakage location, and are maintenance-free.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Modes for Carrying Out the Invention

[0018] 〔First Embodiment〕 Hereinafter, preferred embodiments of the present invention will be described. FIG. 1 is a block diagram showing the configuration of the gas leak detection device according to the first embodiment.

[0019] As shown in FIG. 1, the gas leak detection device of this embodiment is configured to include a plurality of thermal imaging cameras 1a and 1b. The plurality of thermal imaging cameras 1a and 1b are arranged on a ship facing a detection target space 103 where detection targets 101 and 102 for storing liquefied gas are arranged. Each of the thermal imaging cameras 1a and 1b is arranged separately from each other.

[0020] The detection targets 101 and 102 for storing liquefied gas are, for example, a tank 101 for storing liquefied gas and / or a pipe 102 for feeding liquefied gas, etc., but are not limited to only the tank 101 and the pipe 102, and various articles for storing liquefied gas may be included in the detection targets. The "tank for storing liquefied gas" includes various tanks such as a "fuel tank" and a "buffer tank", and includes those that are not pressurized, those that are pressurized, those that are not cryogenic, those that are cryogenic, etc. The liquefied gas stored in the detection targets 101 and 102 is not particularly limited, and is, for example, liquefied ammonia, liquefied petroleum gas (LPG), etc. Note that in the tank 101 and the pipe 102 for storing liquefied gas, there may be a gas phase part and a liquid phase part. That is, the liquefied gas stored as a liquid is vaporized into a gas in the space above the liquid level in the tank 101 and the pipe 102. Further, "gas leak" includes any of the release of gas from the gas phase part to the atmosphere, the release of liquefied gas from the liquid phase part to the atmosphere, and the release of a gas-liquid mixed fluid, part of which is vaporized gas, from the gas phase part and the liquid phase part to the atmosphere.

[0021] The detection target space 103 is, for example, a fuel adjustment room, but is not limited thereto, and it does not matter whether it is in a ship's cabin or on the deck. Further, the detection target space 103 is not limited to a space closed by a ceiling, a wall surface, and a floor surface, and may be an open space regarded as a certain area.

[0022] The thermal imaging cameras 1a and 1b are, for example, infrared thermal imaging cameras, and for example, "Chino Thermal Imaging Camera CPA-T1000 / CPA-T800 / CPA-T500" manufactured by Chino Corporation can be used. The infrared thermal imaging camera can capture thermal images that are color-coded according to the surface temperature of the detection target (solid) such as the tank 101 and the pipe 102.

[0023] This gas leak detection device includes a control device 2. The control device 2 receives image signals captured by the thermal imaging cameras 1a and 1b and acquires the images captured by the thermal imaging cameras 1a and 1b as thermal images. The control device 2 displays the acquired thermal images on a display device (not shown).

[0024] When liquefied gas leaks into the atmosphere due to defects such as corrosion of the detection objects 101, 102 or loose joints, the surfaces of the detection objects 101, 102 that come into contact with the low-temperature leaked liquefied gas absorb heat and are cooled to below the air temperature, and when the leaked liquefied gas vaporizes, the surfaces of the detection objects 101, 102 absorb the heat of vaporization and are cooled to below the air temperature. The areas that have been cooled by the leakage of liquefied gas can be identified early and easily in the thermal images captured by the thermal imaging cameras 1a, 1b.

[0025] Figure 2 is a schematic diagram showing examples of thermal images captured by a thermal imaging camera. (a) is an image of a normal state with no leakage, (b) is an image of a state with leakage from a welded joint of the tank, and (c) is an image of a state with leakage from a flange surface.

[0026] The locations cooled by the leakage of liquefied gas are detected by the thermal imaging cameras 1a and 1b as shown in FIG. 2. In FIG. 2, the tank 101 and the pipe 102 are shown as the objects to be detected. FIG. 2(a) is an image of the normal tank 101 and pipe 102 without leakage. This tank 101 is placed on the drip tray 107, and the pipe 102 is connected at the welding point 104. Also, the pipe 102 is connected to another pipe 102 by a flange 105. The periphery of the flange 105 is covered by a heat insulating material 106.

[0027] As shown in FIG. 2(b), when the liquefied gas in the tank 101 leaks from the welding point 104, the leaked liquefied gas 108 becomes low temperature by being exposed to the atmospheric pressure, and the periphery of the leaked liquefied gas 109 dripping on the periphery of the leakage point and on the drip tray 107 becomes low temperature, and is detected in the thermal image captured by the thermal imaging cameras 1a and 1b.

[0028] Also, as shown in FIG. 2(c), when the liquefied gas in the tank 101 leaks from the mating surface of the flange 105, the leaked liquefied gas 109 drips onto the drip tray 107 from the gap of the heat insulating material 106, and the periphery thereof becomes low temperature, and is detected in the thermal image captured by the thermal imaging cameras 1a and 1b.

[0029] In addition, in either case of FIGS. 2(b) and 2(c), depending on the type of the liquefied gas in the tank 101, if a dedicated lens is used, the vaporized gas can also be detected, and the detection area can be made wider.

[0030] Also, by providing a zoom function for magnifying the leakage point, the accuracy of calculating the area of the leakage point can be improved. Furthermore, by recording the thermal image together with the imaging time information, even at a time after the leakage time, the leakage point and the leakage time can be specified.

[0031] The thermal imaging cameras 1a and 1b do not require maintenance such as replacement or replenishment of sensors and chemicals as long as there are no problems such as failures, and are so-called maintenance-free.

[0032] The detection of the leakage location (cooling location) of the liquefied gas by the thermal imaging cameras 1a and 1b is performed by setting an arbitrary temperature between the saturation temperature of the target liquefied gas under atmospheric pressure and the air temperature as the threshold temperature (leakage detection temperature) Tr, and identifying the location where the measured temperature Te is equal to or lower than the threshold temperature (leakage detection temperature) Tr as the cooling location. Note that the cooling of the surfaces of the detection objects 101 and 102 due to the leakage of the liquefied gas may be lower than the saturation temperature of the target liquefied gas under atmospheric pressure.

[0033] If the minimum temperature in winter is, for example, -20°C, when the target liquefied gas is liquefied ammonia, the saturation temperature under atmospheric pressure is -33°C, so the threshold temperature Tr can be set to -33°C to -21°C. When the target liquefied gas is liquefied petroleum gas, the saturation temperature under atmospheric pressure is -42°C, so the threshold temperature Tr can be set to -42°C to -21°C.

[0034] When there are two thermal imaging cameras 1a and 1b arranged separately from each other as in this embodiment, these thermal imaging cameras 1a and 1b are arranged one by one on two straight lines where the central angle Ac around the center C of the circumscribed sphere S of the detection objects 101 and 102 is from approximately 30° to approximately 180°. If the central angle Ac is 30° or more, it can be said that the thermal imaging cameras 1a and 1b are separated from each other.

[0035] Regarding the positional relationship between the thermal imaging cameras, it is preferable to use the circumscribed sphere of the detection object as a reference. Since all the detection objects are inside the circumscribed sphere and there are no detection objects outside the circumscribed sphere, it is necessary to photograph inside the circumscribed sphere and there is no need to photograph outside the circumscribed sphere.

[0036] By using the circumscribed sphere determined by the object to be detected as a reference, in a detection target space such as a fuel adjustment chamber, when detection targets such as tanks and pipes are unevenly installed, that is, even when there are detection targets only in one corner of the fuel adjustment chamber, each thermal imaging camera can be arranged at an appropriate position according to the shape and position of the detection target to be photographed, regardless of the shape of the fuel adjustment chamber or the position of the wall surface. However, each thermal imaging camera does not necessarily have to be arranged outside the circumscribed sphere. For the surface of the detection target, if there is no location where imaging cannot be performed, that is, if there is no dead angle, it may be arranged on the spherical surface of the circumscribed sphere or inside the circumscribed sphere.

[0037] Also, when the detection target space where the detection target is installed is an open space such as on the deck rather than in the ship's cabin, by using the circumscribed sphere determined by the detection target as a reference, each thermal imaging camera can be arranged at an appropriate position according to the shape and position of the detection target to be photographed.

[0038] Note that the plane including the center C of the circumscribed sphere S and the two straight lines on which the thermal imaging cameras 1a and 1b are arranged is not limited to the horizontal plane, and may be an inclined plane or a vertical plane. Also, the distances between the center C of the circumscribed sphere S and each thermal imaging camera do not have to be equal to each other, and may be different distances for each thermal imaging camera. These are the same in other embodiments described later in which three or more thermal imaging cameras are used.

[0039] The thermal imaging cameras 1a and 1b are arranged so that there is no location where imaging cannot be performed on the surfaces of the detection targets 101 and 102, that is, so that no dead angle occurs. To ensure that no dead angle occurs, it is preferable to arrange one thermal imaging camera on each of two straight lines with a central angle of approximately 180° around the center of the circumscribed sphere S of the detection target. Depending on the shape and arrangement of the detection targets 101 and 102, if a dead angle occurs with the two thermal imaging cameras 1a and 1b, it may be possible to arrange three or more thermal imaging cameras as in other embodiments described later.

[0040] FIG. 3 is a flowchart showing the procedure of the gas leak detection method according to the embodiment.

[0041] The control device 2 also has a function of analyzing the thermal images captured by the thermal imaging cameras 1a and 1b. That is, as shown in FIG. 3, the control device 2 executes the gas leak detection method of the embodiment. This gas leak detection method is also executed in the gas leak detection devices of other embodiments described later.

[0042] The control device 2, which also functions as an image analysis device, sets a threshold temperature Tr (°C), a threshold ratio αr, and a detection interval t (sec) in step st1, and proceeds to step st2.

[0043] In step st2, the control device 2 measures the temperature Te (°C) in the thermal images (detection range) captured by the thermal imaging cameras 1a and 1b, calculates the area At of the region where the temperature Te (°C) is equal to or lower than the threshold temperature Tr (°C), and proceeds to step st3.

[0044] In step st3, the control device 2 determines whether the ratio α (= At / A0) of the area At to the area A0 of the thermal image is equal to or greater than the threshold ratio αr. If the ratio α is less than the threshold ratio αr, it proceeds to step st4, and if the ratio α is equal to or greater than the threshold ratio αr, it proceeds to step st5. Note that the threshold ratio αr is preferably set as low as possible, for example, preferably about 1%.

[0045] Note that the area A0 of the thermal image may be the area of the thermal image by one thermal imaging camera, or may be the sum of the areas of a plurality of thermal images by a plurality of thermal imaging cameras. When the area A0 of the thermal image is the area of the thermal image by one thermal imaging camera, when the ratio α is equal to or greater than the threshold ratio αr in the thermal image by at least any one of the thermal imaging cameras, it proceeds to step st5.

[0046] When the area A0 of the thermal image is the whole of a plurality of thermal images obtained by a plurality of thermal imaging cameras, in the whole of the plurality of thermal images, when the ratio α is equal to or higher than the threshold ratio αr, the process proceeds to step st5. In this case, the threshold ratio is determined as αr / n (∵ n: number of thermal imaging cameras). In this case, even if one region that is at or below the threshold temperature Tr (°C) is imaged in parts in a plurality of thermal images and the area of the part is small in one thermal image, the areas of these parts are summed up and correctly discriminated.

[0047] In step st4, the control device 2 determines that there is no leakage of the liquefied gas and returns to step st2.

[0048] In step st5, the control device 2 determines that there is a leakage of the liquefied gas, issues a leakage signal, records the thermal image, and proceeds to step st6.

[0049] In step st6, the control device 2 notifies the ship's interior that there is a leakage of the liquefied gas based on the leakage signal. This notification is made by sounding a warning sound using a siren or the like, playing a pre-recorded warning message, emitting warning light using a red lamp or the like.

[0050] After measures are taken against the leakage of the liquefied gas, the control device 2 starts again from step st1. Alternatively, when it is not necessary to re-set the threshold temperature Tr (°C), the threshold ratio αr, and the detection interval t (sec), it may start from step st2.

[0051] In the gas leakage detection method of the present invention, by determining the presence or absence of gas leakage based on the ratio α (= At / A0) of the area At (the area of the region where the temperature Te (°C) is equal to or lower than the threshold temperature Tr (°C)) of the thermal image to the area A0 of the thermal image, the following effects are obtained. That is, instead of discriminating only based on the temperature of a fixed single point, stable discrimination can be performed by quantifying the region (area) where the temperature is equal to or lower than the threshold temperature Tr (°C). Also, if all the image data is recorded, the accumulated data volume will become extremely large. However, in the gas leak detection device of the present invention, only the numerical value of the ratio α needs to be recorded, so the accumulated data volume can be reduced. Furthermore, if the threshold ratio αr is set, the discrimination can be fully automated.

[0052] As a method that does not use the ratio α, a method of comparing the pixels of a certain acquired image with the pixels of the next acquired image (after the detection interval t (sec)) can be considered. However, it is difficult to detect a temperature that changes continuously and gradually according to a gas leak. In the gas leak detection method of the present invention, even when the temperature changes continuously and gradually, since the area ratio α changes, the gas leak can be surely detected. Also, depending on the external environment, there may be an air flow with a stronger wind force than the leaked gas. In this case, since the flow of the leaked gas changes, it is difficult to detect by comparing pixels. In the gas leak detection method of the present invention, even when the flow of the leaked gas changes, since the area ratio α changes, the gas leak can be surely detected.

[0053] 〔Second Embodiment〕 FIG. 4 is a block diagram showing the configuration of a gas leak detection device according to the second embodiment.

[0054] In this embodiment, as shown in FIG. 4, a plurality of thermal imaging cameras 1a, 1b, 1c are arranged one by one on three straight lines with a central angle Ac of approximately 120° around the center C of the circumscribed sphere S of the detection objects 101, 102, for a total of three cameras.

[0055] By using three thermal imaging cameras 1a, 1b, 1c, it is possible to prevent dead angles from occurring on the surfaces of the detection objects 101, 102 compared to the case of using two cameras.

[0056] Note that the central angle Ac around the center C of the circumscribed sphere S can be appropriately set according to the shapes and arrangements of the detection objects 101 and 102. Also, the heights of the arrangement positions of the thermal imaging cameras 1a, 1b, and 1c can be appropriately set according to the shapes and arrangements of the detection objects 101 and 102.

[0057] Also in this embodiment, the plane including the center C of the circumscribed sphere S and the two straight lines on which any two of the thermal imaging cameras 1a, 1b (1a, 1c) (1b, 1c) are arranged is not limited to the horizontal plane, and may be an inclined plane or a vertical plane. Further, the thermal imaging cameras 1a, 1b, and 1c do not necessarily have to be arranged on one plane including the center C of the circumscribed sphere S, and two of them may be arranged on each of the three planes including the center C of the circumscribed sphere S.

[0058] Also in this embodiment, the gas leakage detection method described in the first embodiment is executed by the control device 2.

[0059] 〔Third Embodiment〕 FIG. 5 is a block diagram showing the configuration of the gas leakage detection device according to the third embodiment.

[0060] In this embodiment, as shown in FIG. 5, a plurality of thermal imaging cameras 1a, 1b, 1c, and 1d are arranged one by one on four straight lines around the center C of the circumscribed sphere S of the detection objects 101 and 102, with the central angle Ac being approximately 90° to approximately 110°. A total of four cameras are arranged.

[0061] By using the four thermal imaging cameras 1a, 1b, 1c, and 1d, it is possible to prevent dead angles from occurring on the surfaces of the detection objects 101 and 102 compared to the case of using three cameras.

[0062] Note that the central angle Ac around the center C of the circumscribed sphere S can be appropriately set according to the shapes and arrangements of the detection objects 101 and 102. Also, the heights of the arrangement positions of the thermal imaging cameras 1a, 1b, 1c, and 1d can be appropriately set according to the shapes and arrangements of the detection objects 101 and 102.

[0063] Also in this embodiment, the plane including the center C of the circumscribed sphere S and the two straight lines on which any two thermal imaging cameras are arranged is not limited to the horizontal plane, and may be an inclined plane or a vertical plane. Further, the thermal imaging cameras 1a, 1b, 1c, and 1d do not have to be arranged on one plane including the center C of the circumscribed sphere S, and two of them may be arranged on each of the four planes including the center C of the circumscribed sphere S.

[0064] FIG. 6 is a block diagram showing another example of the configuration of the gas leak detection device according to the third embodiment. When the central angle Ac between any two thermal imaging cameras is all set to approximately 110° and two of them are arranged on each of the four planes including the center C of the circumscribed sphere S, as shown in FIG. 6, the four thermal imaging cameras 1a, 1b, 1c, and 1d are arranged at the positions of the vertices of a regular tetrahedron centered on the center C of the circumscribed sphere S. The central angle Ac in this case is 2tan -1 √2 ≈ 109.47°.

[0065] Also in this embodiment, the gas leak detection method described in the first embodiment is executed by the control device 2.

[0066] 〔Fourth Embodiment〕 FIG. 7 is a block diagram showing the configuration of the gas leak detection device according to the fourth embodiment.

[0067] In this embodiment, as shown in FIG. 7, a total of five thermal imaging cameras 1a, 1b, 1c, 1d, and 1e are arranged, one each on the front side, rear side, left side, right side, and upper side of the detection target space 103.

[0068] By using the five thermal imaging cameras 1a, 1b, 1c, 1d, and 1e, it is possible to prevent dead angles from occurring on the surfaces of the detection objects 101 and 102 more effectively than in the case of using four cameras.

[0069] In this embodiment, the thermal imaging camera 1e arranged on the upper side (ceiling) can image the entire horizontal plane direction of the detection target space 103. Also, by not arranging a thermal imaging camera on the lower side (floor surface), it does not interfere with the arrangement of the detection targets 101 and 102 in the detection target space 103 and walking.

[0070] Note that the arrangement positions (direction and height) of the thermal imaging cameras 1a, 1b, 1c, 1d, and 1e can be appropriately set individually for each of the thermal imaging cameras 1a, 1b, 1c, 1d, and 1e according to the shape and arrangement of the detection targets in the detection target space 103.

[0071] Also in this embodiment, the gas leakage detection method described in the first embodiment is executed by the control device 2.

[0072] 〔Fifth Embodiment〕 FIG. 8 is a block diagram showing the configuration of the gas leakage detection device according to the fifth embodiment.

[0073] In this embodiment, as shown in FIG. 8, two thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f are arranged opposite to each other on each axis of the xyz orthogonal coordinates with the center C of the detection target in the detection target space 103 as the origin, for a total of six cameras. The xyz orthogonal coordinates are rotated with respect to the detection target space 103, and the arrangement of the thermal imaging cameras on the floor surface of the detection target space 103 is avoided.

[0074] By using the six thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f, it is possible to prevent dead angles from occurring on the surfaces of the detection targets 101 and 102 compared to the case of using five cameras.

[0075] In this embodiment, since the thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f can be arranged at point-symmetrical positions with respect to all directions around the center C of the circumscribed sphere S of the object to be detected, it is possible to correspond to various shapes and various arrangements of the objects to be detected in the detection target space 103. Further, by not arranging the thermal imaging camera on the lower side (floor surface), it does not interfere with the arrangement and walking of the objects 101 and 102 to be detected in the detection target space 103.

[0076] In this embodiment, the central angle Ac between any two thermal imaging cameras is all 90°, and the six thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f are arranged at the positions of the vertices of a regular octahedron centered on the center C of the circumscribed sphere S.

[0077] Note that the arrangement positions (directions and heights) of the thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f can be appropriately set individually for each of the thermal imaging cameras 1a, 1b, 1c, 1d, 1e, and 1f according to the shape and arrangement of the object to be detected in the detection target space 103.

[0078] Also in this embodiment, the gas leak detection method described in the first embodiment is executed by the control device 2.

Explanation of Signs

[0079] 1a Thermal imaging camera 1b Thermal imaging camera 1c Thermal imaging camera 1d Thermal imaging camera 1e Thermal imaging camera 1f Thermal imaging camera 2 Control device 101 Tank (object to be detected) 102 Pipe (object to be detected) 103 Detection target space 104 Weld point 105 Flange 106 Heat insulating material 107 Drip tray 108 Leaked liquefied gas 109 Leaked liquefied gas Circumscribed sphere of the object to be detected S Center C of the circumscribed sphere Central angle Ac

Claims

1. In a ship, a plurality of thermal imaging cameras arranged apart from each other and directed toward a detection target space in which a detection target object for storing liquefied gas is disposed, and a control device configured to obtain an image captured by the thermal imaging camera as a thermal image. The control device determines that the liquefied gas is leaking when a ratio (α) of a total area (At) of regions having a temperature equal to or lower than a threshold temperature (Tr) in a plurality of thermal images obtained by the plurality of thermal imaging cameras to a total area (A0) of the plurality of thermal images obtained by the plurality of thermal imaging cameras is equal to or higher than a threshold ratio (αr). A gas leak detection device, characterized in that.

2. The threshold temperature (Tr) is set to an arbitrary temperature between a saturation temperature of the liquefied gas under atmospheric pressure and an air temperature. The gas leak detection device according to claim 1, characterized in that.

3. The control device records only a numerical value of the ratio (α). The gas leak detection device according to claim 2, characterized in that.

4. Each of the thermal imaging cameras is disposed one by one on two straight lines having a central angle of 30° to 180° around the center of the circumscribed sphere of the detection target object, and a total of two cameras are disposed. The gas leak detection device according to any one of claims 1 to 3, characterized in that.

5. Each of the thermal imaging cameras is disposed one by one on three straight lines having a central angle of 120° around the center of the circumscribed sphere of the detection target object, and a total of three cameras are disposed. The gas leak detection device according to any one of claims 1 to 3, characterized in that.

6. Each of the thermal imaging cameras is disposed one by one on four straight lines having a central angle of 90° to 110° around the center of the circumscribed sphere of the detection target object, and a total of four cameras are disposed. The gas leak detection device according to any one of claims 1 to 3, characterized in that.

7. Each of the thermal imaging cameras is arranged one by one on the front side, rear side, left side, right side and upper side of the detection target space, and a total of five cameras are arranged. The gas leak detection device according to any one of claims 1 to 3, characterized in that.

8. Each of the thermal imaging cameras is arranged two by two facing each other on each axis of the xyz orthogonal coordinates with the center of the circumscribed sphere of the detection target as the origin, and a total of six cameras are arranged. The xyz orthogonal coordinates are rotated with respect to the detection target space, and the arrangement of the thermal imaging cameras on the floor surface of the detection target space is avoided. The gas leak detection device according to any one of claims 1 to 3, characterized in that.

9. In a ship, a plurality of thermal imaging cameras directed at a detection target space in which a detection target for storing liquefied gas is arranged are arranged apart from each other. The detection target space is photographed by the thermal imaging camera. An image captured by the thermal imaging camera is acquired as a thermal image. When the ratio (α) of the total area (At) of the regions having a temperature equal to or lower than the threshold temperature (Tr) in the plurality of thermal images by the plurality of thermal imaging cameras to the total area (A0) of the plurality of thermal images by the plurality of thermal imaging cameras is equal to or higher than the threshold ratio (αr), it is determined that the liquefied gas is leaking. A gas leak detection method characterized by that.

10. The threshold temperature (Tr) is set to an arbitrary temperature between the saturation temperature of the liquefied gas under atmospheric pressure and the air temperature. The gas leak detection method according to claim 9, characterized in that.

11. Only the numerical value of the ratio (α) is recorded. The gas leak detection method according to claim 9, characterized in that.

12. The plurality of thermal imaging cameras are arranged one by one on two straight lines with a central angle around the center of the circumscribed sphere of the detection target being 30° to 180°, and a total of two cameras are arranged. The gas leakage detection method according to any one of claims 9 to 11, characterized in that...

13. The plurality of thermal imaging cameras are arranged one by one on three straight lines with a central angle of 120° around the center of the circumscribed sphere of the object to be detected, for a total of three cameras. The gas leakage detection method according to any one of claims 9 to 11, characterized in that...

14. The plurality of thermal imaging cameras are arranged one by one on four straight lines with a central angle of 90° to 110° around the center of the circumscribed sphere of the object to be detected, for a total of four cameras. The gas leakage detection method according to any one of claims 9 to 11, characterized in that...

15. The plurality of thermal imaging cameras are arranged one by one on the front side, rear side, left side, right side and upper side of the detection target space, for a total of five cameras. The gas leakage detection method according to any one of claims 9 to 11, characterized in that...

16. The plurality of thermal imaging cameras are arranged in pairs, two on each axis of the xyz orthogonal coordinates with the center of the circumscribed sphere of the object to be detected as the origin, for a total of six cameras. The gas leakage detection method according to any one of claims 9 to 11, characterized in that...

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