Gas detection method

Abstract

This technology provides a way to effectively detect gas leaks using laser light. [Solution] A virtual leak point (200) and a virtual gas cloud region (210) based on it are set in the gas pipe (110). The virtual gas cloud region (210) is scanned by irradiating it with laser light (LB). The laser light (LB) that has passed through the virtual gas cloud region (210) is received and the change in its intensity is detected to detect the gas leaking from the gas pipe (110).

Description

Technical Field

[0001] The present invention relates to a method for detecting gas.

Background Art

[0002] Conventionally, gas detectors using lasers have been known (see, for example, Patent Documents 1 and 2). In a laser gas detector, in principle, sensitivity is obtained by the collision of laser light with gas molecules, such as methane molecules.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a laser gas detector, when the gas concentration is high or when it is widely filled in a space, the indicated value becomes high. Generally, since a high-concentration gas exists near the gas leakage point, conventionally, laser light is irradiated on the place where leakage is suspected to inspect the presence or absence of gas leakage.

[0005] However, if no gas is actually leaking from the place where leakage is suspected, the gas is not detected. Therefore, when gas is leaking from an unexpected location, it may be difficult to detect the gas. Also, even when gas is detected outside the place where leakage is suspected, it is difficult to specify the gas leakage point from the detection result. Thus, in the above conventional technology, there remains room for improvement from the viewpoint of effectively detecting gas leakage by laser light.

[0006] One aspect of the present invention aims to provide a technique for effectively detecting gas leaks using laser light. [Means for solving the problem]

[0007] To solve the above problems, a gas detection method according to one aspect of the present invention is a method for detecting gas leaking from equipment by irradiating the area around the equipment with laser light having a wavelength absorbed by the gas to be measured, and includes the steps of: setting a virtual leak point in the equipment assuming that the gas is leaking from the equipment; setting a virtual gas cloud region based on the expected distribution of the gas leaking from the virtual leak point; scanning the virtual gas cloud region by irradiating it with the laser light; and receiving the laser light that has passed through the virtual gas cloud region and detecting a change in its intensity. [Effects of the Invention]

[0008] According to one aspect of the present invention, a technique for effectively detecting gas leaks using laser light can be provided. [Brief explanation of the drawing]

[0009] [Figure 1] This figure schematically shows an example of a gas facility to which the gas detection method according to one embodiment of the present invention is applied. [Figure 2] This diagram illustrates the process of setting a virtual leak point in one embodiment of the present invention. [Figure 3] This diagram illustrates the process of setting up a virtual gas cloud region in one embodiment of the present invention. [Figure 4] This figure schematically shows a first example of the direction of laser light irradiation onto a virtual gas cloud region in one embodiment of the present invention. [Figure 5] This figure schematically shows a second example of the direction of laser light irradiation onto a virtual gas cloud region in one embodiment of the present invention. [Figure 6] This figure schematically shows a third example of the direction of laser light irradiation onto a virtual gas cloud region in one embodiment of the present invention. [Figure 7] This figure schematically shows a first example of the scanning trajectory of a laser beam in a virtual gas cloud region in one embodiment of the present invention. [Figure 8] This figure schematically shows a second example of the scanning trajectory of a laser beam in a virtual gas cloud region in one embodiment of the present invention. [Figure 9] This figure schematically shows a third example of the scanning trajectory of a laser beam in a virtual gas cloud region in one embodiment of the present invention. [Figure 10] This diagram illustrates the process of resetting a virtual leak point in one embodiment of the present invention. [Figure 11] This diagram illustrates the process of setting up a virtual gas cloud region in one embodiment of the present invention. [Figure 12] This diagram illustrates the process of verifying the actual leak point in one embodiment of the present invention. [Modes for carrying out the invention]

[0010] One embodiment of the present invention will be described in detail below. This embodiment is a method for detecting gas leaking from equipment by irradiating the area around the equipment containing the gas with laser light of a wavelength absorbed by the gas to be measured.

[0011] In this embodiment, the gas equipment is equipment that handles the gas to be measured and is the equipment that is subject to inspection for gas leaks. Examples of the gas equipment include petrochemical complexes that produce the gas, businesses that use the gas as fuel, and gas pipelines for transporting the gas.

[0012] In the present embodiment, for gas detection, a laser gas detector that detects gas by irradiating laser light and detecting the irradiated laser light can be used. Further, since it is to detect the leaked gas in the gas facility, a portable gas detector is preferably used for gas detection. For such a laser gas detector, it is possible to use a portable known detector such as the "Laser Methane (registered trademark)" series of devices manufactured by Tokyo Gas Engineering Solutions Co., Ltd.

[0013] The light to be detected may be the irradiated laser light itself or the reflected light of the irradiated laser light. The reflected light may be total reflection light or scattered light. In the detection of the irradiated laser light, depending on the type of light to be detected, attenuation other than absorption by the gas in the laser light (such as attenuation in the atmosphere or attenuation due to reflection by reflectors such as walls) can be appropriately corrected. The correction of the attenuation can be realized based on known techniques in the laser detector.

[0014] The gas only needs to be detectable by the aforementioned laser gas detector. Examples of the type of gas include liquefied natural gas, liquefied petroleum gas, ammonia gas, carbon monoxide gas, particulate matter, and butane gas. Liquefied natural gas and liquefied petroleum gas are widely used as fuels, and examples thereof include methane gas, ethane gas, propane gas, and butane gas. From the perspective of the usefulness of gas leak detection, the gas can be a gas containing methane.

[0015] The gas detection method of the present embodiment includes a leakage point setting step of setting a virtual leakage point, a gas cloud region setting step of setting a virtual gas cloud region, a scanning step of irradiating and scanning the virtual gas cloud region with the laser light, and a detection step of receiving the laser light and detecting the change in its intensity.

[0016] 〔Leakage point setting step〕 The leakage point setting process is a process of setting a virtual leakage point in the equipment assuming that gas is leaking from the gas equipment. Gas is usually transported through pipes. Therefore, locations where gas leakage is suspected include flange parts, threaded parts, and parts where rust has occurred in the pipes, and such locations can be set as virtual leakage points.

[0017] 〔Gas cloud region setting process〕 The gas cloud region setting process is a process of setting a virtual gas cloud region based on the predicted distribution of the gas leaking from the above-mentioned virtual leakage point.

[0018] Regarding the diffusion of the leaked gas, it is known that even with a slight wind, it diffuses in a state of gathering in a relatively narrow range. For example, although methane gas is lighter than air, it does not easily diffuse and tends to be distributed in a thin region where both the horizontal expansion angle and the vertical expansion angle at the apex are 10° or less. Methane gas tends to be distributed in the above-mentioned thin region even with a small wind speed, and heavier gases such as propane gas tend to be distributed in the above-mentioned thin region as the wind speed increases (for example, when the wind speed becomes 1 m / s or more).

[0019] In the gas cloud region setting process, based on the above-mentioned known findings, the distribution of the leaking gas is predicted and a virtual gas cloud region is set. The gas cloud region means a region where the gas exists at a certain concentration. The virtual gas cloud region may be a region where the gas concentration is above the threshold value, or may be a region predicted to be likely to distribute the gas based on the above-mentioned findings.

[0020] Furthermore, leaking gas, regardless of its type, tends to flow downwards, and if airflow is present, it tends to flow or diffuse under the influence of the airflow. In the case of virtually no wind at the hypothetical leak point, a region extending downwards from the hypothetical leak point and horizontally relative to the shielding object, due to the diffusion tendency described above, can be defined as the hypothetical gas cloud region. If airflow is present at the hypothetical leak point, a region extending downwind, due to the diffusion tendency described above, can be defined as the hypothetical gas cloud region. Thus, the hypothetical gas cloud region is usually defined three-dimensionally rather than in a two-dimensional plane.

[0021] Based on the above findings, setting a virtual gas cloud region as an area where gas is expected to be easily distributed is preferable from the viewpoint of more easily setting a gas cloud region at the site of gas concentration testing, and also from the viewpoint of more appropriately setting a virtual gas cloud region because it sets a region that is more in line with the general behavior of gas leaked into the atmosphere. From the above viewpoint, in the gas cloud region setting process, it is preferable to set a roughly conical region extending downwind with a virtual leakage point as the apex as the virtual gas cloud region, and it is preferable to set the spread angle (unfolding angle) of the virtual gas cloud region from the above apex (virtual leakage point) to 10° or less.

[0022] When the wind speed at the virtual leakage point increases, the expansion angle of the gas cloud region decreases, making it difficult to predict an appropriate gas cloud region. Therefore, when setting a virtual gas cloud region in the above-mentioned approximately conical region, the wind speed is preferably 5 m / s or less, more preferably 3 m / s or less, and even more preferably 2 m / s or less, from the viewpoint of setting it in a region with a higher gas concentration. Furthermore, the expansion angle of the virtual gas cloud region may be 10° or less based on the behavior of gas expansion, but it may be set to be narrower within the range in which the effects of the present invention can be obtained.

[0023] The length of the virtual gas cloud region is expressed as the distance from the virtual leak point to the furthest horizontal edge of the virtual gas cloud region. The length of the virtual gas cloud region can be appropriately determined according to the shape of the gas cloud region, since the gas concentration in the gas cloud region needs to be high enough to be sufficiently detectable. For example, in the case of the aforementioned approximately conical region, the length of the virtual gas cloud region is the length from the virtual leak point to the edge of the virtual gas cloud region (the base of the cone) on the downwind side. From the viewpoint of making the gas concentration in the virtual gas cloud region detectable, from the viewpoint of making it easier to set up the virtual gas cloud region, and from the viewpoint of making it easier to scan the laser beam in the subsequent scanning process, the length of the approximately conical virtual gas cloud region is preferably 10m or less, more preferably 5m or less, and even more preferably 3m or less.

[0024] Furthermore, in the gas cloud region setting process, a region extending along one or both of the ground surface and the surface of a shielding object downwind may be set as a virtual gas cloud region. If a shielding object exists downwind, the gas distribution will extend along the surface of the shielding object. Examples of shielding objects include the ground surface, walls, and the outer surface of gas pipes. If a shielding object exists, the virtual gas cloud region may be set to extend from a virtual leakage point along the surface of the shielding object. Setting a virtual gas cloud region that takes shielding objects into consideration in this way is preferable from the viewpoint of setting the virtual gas cloud region more appropriately, as it further considers the trend of gas distribution depending on the conditions of the measurement site.

[0025] [Scanning process] The scanning process involves scanning the aforementioned virtual gas cloud region by irradiating it with the aforementioned laser light.

[0026] In the scanning process, the scanning speed may be appropriately determined according to the detection interval of the laser beam. The scanning speed may be constant or varied within the set virtual gas cloud region. For example, if gas accumulation is suspected in a particular part of the virtual gas cloud region, the scanning speed in that part may be made slower.

[0027] In the scanning process, the laser beam is scanned to cover the entire virtual gas cloud region. The scanning direction may be parallel to the central axis of the virtual gas cloud region passing through the virtual leak point, or it may be along a group of radial lines centered on the virtual leak point, or it may be in a direction transverse to the central axis. If the virtual gas cloud region includes or is set along such an obstruction, scanning along the obstruction is preferable from the viewpoint of improving the accuracy of gas detection. For example, if the obstruction is a pipe, it is preferable to scan around the pipe in a circular motion.

[0028] Furthermore, a scanning direction that moves from the outer edge of the virtual gas cloud region toward the virtual leak point, or in the case of wind flow, toward the virtual leak point, is preferable from the viewpoint of improving the accuracy of gas detection, as the gas detection signal tends to gradually strengthen during a single scan.

[0029] Furthermore, during the scanning process, it is preferable to scan in the direction of the airflow if the device is outdoors. Scanning in the direction of the airflow allows the laser light to travel through the area for a longer period, increasing the chances of collision between the laser light and the molecules of the gas being detected, and thus increasing the probability of detecting the gas (leak).

[0030] When there is wind flow, the virtual gas cloud region is set to be longer in the direction of the wind flow. Therefore, in this case, it is preferable to irradiate the virtual gas cloud region with laser light along its longitudinal direction during the scanning process, as this increases the intensity of gas detection as described above.

[0031] In the scanning process, it is preferable to irradiate the virtual gas cloud region with laser light from the downwind side. In this case, the laser light is irradiated from the downwind side toward the virtual leakage point, that is, from the area with a lower probability of gas presence toward the area with a higher probability of gas presence. Therefore, the possibility of detection increases when gas is present in the virtual gas cloud region. Thus, this is preferable from the viewpoint of further improving the intensity and accuracy of gas detection.

[0032] [Detection process] The detection step involves receiving laser light that has passed through the aforementioned virtual gas cloud region and detecting changes in its intensity. The received light may be the laser light itself, as described above, or it may be scattered light from the laser light. Laser light detection can be performed using a detector capable of detecting the laser light, and examples of such detectors include photodiodes (PDs). In laser light detection, an optical system including a focusing lens or the like to focus the scattered light from the laser light onto the detector may also be used.

[0033] [Identifying the leak point] In this embodiment, it is possible to identify the gas leak point by performing further steps. Examples of further steps include an information acquisition step to obtain information on the amount of gas detected, and a leak location identification step to identify the actual location of the gas leak.

[0034] [Information acquisition process] The information acquisition process is a process of acquiring information on the amount of gas corresponding to the change in the intensity of the laser light detected in the aforementioned detection process.

[0035] In the information acquisition process, for example, in the laser-type gas detector mentioned above, the gas is determined by column density, which is in units of concentration × length (ppm·m). In other words, the amount of gas molecules along the optical path of the laser light is detected. This column density provides information about the amount of gas in a virtual gas cloud region. Detecting gas quantity by column density offers higher detection accuracy compared to detecting gas concentration, and even gases with low concentrations in the virtual gas cloud region can be easily detected. If a change in the gas quantity value is observed during the information acquisition process, it is preferable to repeat the scanning process to confirm the reproducibility of the change, from the viewpoint of further improving the accuracy of gas detection.

[0036] [Leak location identification process] The leak location identification process is a process that identifies the actual location of a gas leak in the gas equipment by referring to the gas quantity information obtained in the information acquisition process.

[0037] In this embodiment, the closer the laser beam irradiation position is to the actual gas leak point, the greater the amount of gas detected. For example, gas tends to be present in high concentrations within a few centimeters of the actual leak point. In the aforementioned laser gas detector, high values ​​are shown even when the optical path length of the irradiated laser beam is short. When gas is detected at such a high concentration, the actual gas leak location in the gas equipment is identified by referring to the gas quantity information acquired in the information acquisition process.

[0038] Such a leak location identification process can be carried out, for example, by repeatedly performing the steps of: identifying the irradiation position of the laser beam when a high concentration of gas is detected; and scanning the laser beam around that irradiation position to identify the irradiation position where a larger amount of gas is detected.

[0039] In this embodiment, further including the above-described information acquisition step and leak location identification step is preferable from the viewpoint of more efficiently identifying the actual gas leak location, and it is possible to more easily identify the actual gas leak location compared to, for example, conventional suction-type gas detection technology.

[0040] [Leakage point confirmation process] In this embodiment, a leak point confirmation step may be further performed in which a laser is irradiated onto the identified leak location to confirm that it is an actual gas leak point. Since gas leaks from an actual gas leak point, a sufficiently large amount of gas will be detected regardless of the length of the laser beam's optical path. The leak point confirmation step may be performed using the laser gas detector described above, or it may be performed using another type of gas detector. Furthermore, when performing the leak point confirmation step using the laser gas detector described above, the energy of the irradiated laser beam may be the same as that of the previous steps, or it may be different (for example, lower).

[0041] [Leak point resetting process] Even after performing the detection steps described above, there may be cases where no gas is substantially detected. In such cases, a leak point resetting step may be performed to set a virtual leak point other than the previously set virtual leak point. The reset virtual leak point can be set appropriately according to the inspection of the virtual gas cloud area performed beforehand. For example, the reset virtual leak point may be a location suspected of gas leakage upwind of the previously set virtual gas cloud area. When inspecting gas facilities continuously, the reset virtual leak point does not have to be a location suspected of gas leakage as described above; for example, it may be a location in the gas facility that is separated from the previous virtual leak point by the length of the previously set virtual gas cloud area.

[0042] After the leak point resetting process, a virtual gas cloud area is set as described above, and the process of scanning and detecting with a laser beam is repeated the required number of times. In this way, by repeatedly performing the leak point setting process, gas cloud area setting process, scanning process, and detection process described above, the presence or absence of gas leaks in the gas equipment can be inspected.

[0043] [Explanation using a specific example] A gas detection method according to an embodiment of the present invention will be further described with reference to the figures. Hereinafter, embodiments of the present invention will be described more specifically, with an example of a gas pipe being the target of gas leak inspection. In the following embodiment, the gas is, for example, methane gas, and the wavelength of the laser light LB is, for example, 1.6 μm. Figure 1 is a schematic diagram showing an example of a gas facility to which the gas detection method of this embodiment is applied.

[0044] As shown in Figure 1, a gas pipe 110 is positioned along the ground surface 100, directly above it. The gas pipe 110 is connected by flanges 120 and has a rusted section 130 on the side facing the ground surface 100. Wind is blowing around the gas pipe 110 in the direction indicated by the arrows (from left to right relative to the plane of the figure) at a wind speed of approximately 1 to 3 m / s. In reality, there is a gas leak point 140 at the joint of flange 120.

[0045] First, as step S1, a virtual leak point 200 is set as shown in Figure 2. The suspected gas leak could be either the rusted section 130 or the flange 120. First, the wind direction is identified, and the rusted section 130, which is located further downwind, is set as the virtual leak point 200.

[0046] Next, in step S2, a virtual gas cloud region 210 is set up as shown in Figure 3. The virtual gas cloud region 210 includes the downwind portion of the virtual leak point 200 and is set up near the ground surface 100. The virtual gas cloud region 210 includes the virtual leak point 200, but does not necessarily have to. As mentioned above, gas first flows downwards. Therefore, if gas is leaking from the virtual leak point 200, the gas is blocked by the ground surface 100. After that, the gas flows along the ground surface 100 in the direction of the wind. In this way, leaked gas, regardless of the type of gas, usually tends to flow in a band along the ground surface or wall surface if there is even a slight wind. In the illustrated case, the ground surface 100 shields the gas flow and restricts the direction in which the gas flows. The surface of such a shielding object that restricts the gas flow (ground surface 100) is also called the "reference plane".

[0047] In step S2, a hypothetical gas cloud region 210 is defined as a square pyramidal region having its apex below the hypothetical leak point 200, touching the reference plane, and extending in the wind direction at an angle of approximately 10° from there. The distance from the hypothetical leak point 200 to the downwind end of the hypothetical gas cloud region 210 is preferably about 5m from the viewpoint of turbulent diffusion of gas due to wind. The magnitudes of the apex angles in the horizontal and vertical directions of the hypothetical gas cloud region 210 may be the same or different. In this embodiment, from the above viewpoint, both are set to approximately 10° or less. If gas is actually leaking, the gas can be sufficiently detected even at a shallower angle.

[0048] Next, in step S3, a laser beam LB is irradiated from a laser-type gas detector 220 onto the virtual gas cloud region 210 and scanned, passing through the virtual gas cloud region 210. Examples of the irradiation direction of the laser beam are shown in Figures 4 to 6, and examples of scanning with the laser beam are shown in Figures 7 to 9. The irradiation distance of the laser beam LB from the gas detector 220 to the virtual gas cloud region 210 is set to approximately 2 to 5 m, for example, from the viewpoint of detection accuracy and mitigating the effects of gas on inspection personnel. Furthermore, the scanning speed of the laser beam LB in the virtual gas cloud region 210 is set to a slow speed, such as one detection every 0.1 seconds, in relation to the detection speed, so that at least 2 to 3 points are detected when scanning the virtual gas cloud region 210 in one direction.

[0049] In step 3, as shown in Figure 4, a laser beam LB can be irradiated from the gas detector 220 onto the virtual gas cloud region 210 in a direction intersecting the axis of the virtual gas cloud region 210 in the vertical direction. Irradiating the virtual gas cloud region 210 with the laser beam LB in this direction and scanning the virtual gas cloud region 210 is preferable from the viewpoint of identifying the horizontal leakage points in the actual gas cloud region when gas is present in the virtual gas cloud region 210.

[0050] Alternatively, in step 3, as shown in Figure 5, a laser beam LB can be irradiated onto the virtual gas cloud region 210 from the upwind gas detector 220 along the longitudinal direction of the virtual gas cloud region 210. Irradiating the virtual gas cloud region 210 with the laser beam LB in this direction and scanning the virtual gas cloud region 210 is preferable from the viewpoint of detecting the extent of the actual gas cloud region's spread downwind when gas is present in the virtual gas cloud region 210. Furthermore, since the laser beam LB is irradiated from the upwind side, the possibility of inspection personnel being exposed to leaked gas is reduced, which is preferable from the viewpoint of reducing the impact of leaked gas on inspection personnel, for example, in the detection of toxic gases.

[0051] Alternatively, in step 3, as shown in Figure 6, a laser beam LB can be irradiated onto the virtual gas cloud region 210 from the downwind gas detector 220 along the axis of the virtual gas cloud region 210. In this way, the laser beam LB is irradiated along a line from the pyramidal bottom surface of the virtual gas cloud region 210 toward the virtual leak point 200. At this time, the optical path of the laser beam LB does not have to strictly pass through the virtual leak point 200, but it is sufficient if it is roughly parallel to the line and passes through the virtual gas cloud region 210. Irradiating the laser beam LB in this direction and scanning the virtual gas cloud region 210 is preferable from the viewpoint that gas leakage can be detected more clearly when gas is present in the virtual gas cloud region 210.

[0052] Furthermore, in step S3, as shown in Figure 7, the laser beam LB may be scanned in a meandering manner across the longitudinal direction of the virtual gas cloud region 210, from the leeward end of the virtual gas cloud region 210 toward the virtual leakage point 200. Such a scanning method is preferred for the irradiation configuration of the laser beam LB shown in Figure 4 or Figure 5 described above.

[0053] Alternatively, in step S3, the laser beam LB may be scanned in a meandering manner across the longitudinal direction of the virtual gas cloud region 210, as shown in Figure 8. Such a scanning method is preferred for the irradiation configuration of the laser beam LB shown in Figure 4 or Figure 5 described above.

[0054] Alternatively, in step S3, as shown in Figure 9, the laser beam LB may be scanned in a meandering manner across the virtual gas cloud region 210 in a longitudinal cross-section of the virtual gas cloud region 210. In this case, for example, the laser beam LB is scanned in a meandering manner across the largest cross-section (the face at the leeward end (the base of the square pyramid)), then the laser beam LB is scanned in a meandering manner across a smaller cross-section 211 (for example, a cross-section of the central part in the longitudinal direction of the virtual gas cloud region 210), and then the laser beam LB is scanned in a meandering manner across an even smaller cross-section 212 (for example, a cross-section of the virtual gas cloud region 210 closer to the virtual leak point 200 than the central part in the longitudinal direction). Such a scanning method is suitable for the irradiation configuration of the laser beam LB shown in Figure 6 above. Thus, when the laser beam LB is scanned in a meandering manner in the longitudinal cross-section of the virtual gas cloud region 210 so as to converge toward the virtual leak point 200, the detected gas level tends to increase when gas is actually leaking from the virtual leak point 200.

[0055] Next, in step S4, the laser light LB that has passed through the virtual gas cloud region 210 is received by a detector such as a photodiode, and the change in its intensity is detected. If gas is actually present in the virtual gas cloud region 210, the laser light LB that has passed through the virtual gas cloud region 210 is partially absorbed by the gas in the optical path, and is scattered by shielding objects such as the ground surface or walls in the direction of irradiation, and the scattered light is detected by the detector. Therefore, in the above case, the gas component is correctly detected.

[0056] Next, in step S5, information on the amount of gas (column density) corresponding to the change in intensity of the detected laser light LB is acquired. This acquisition of gas amount information can be performed, for example, by the control device of the gas detector 220. At this time, the attenuation of the laser light LB in the atmosphere and the attenuation due to reflection by shielding materials when the laser light LB is detected as scattered light are appropriately corrected.

[0057] Next, in step S6, the actual gas leak location in the gas pipe 110 is identified by referring to the acquired gas column density information. If a change in the column density value is observed, the laser beam LB is scanned back and forth at the scanning position of the laser beam LB where the change is observed and in its vicinity to confirm the reproducibility of the change. In step S6, if a change in column density is observed and gas leakage is suspected, the system approaches the suspected gas leakage area (e.g., a virtual leak point 200) and irradiates the area around the virtual leak point 200 with the laser beam LB to search for the location where the column density is highest. Gas is usually present at a higher concentration a few centimeters from the leak point. In this case, a high column density is shown even if the optical path length of the laser beam LB is short.

[0058] If no change in the intensity of the laser beam LB detected in step S4 is detected, or if the actual leak location cannot be identified in step S6, then in step S7, the virtual leak point is reset. For example, as shown in Figure 10, if gas leakage from the rusted area 130 cannot be confirmed, the boundary of the flange 120, which is a suspected gas leak location further upwind, is set as the virtual leak point 300.

[0059] Next, in step S8, the virtual gas cloud region 310 is reset based on the virtual leak point 300 in the same manner as in step S2 described above. Then, as in steps S3 to S6 described above, the scanning of the laser beam LB and identification of the actual leak location are performed. That is, when an increase in the gas column density is confirmed at the virtual leak point 300, the vicinity of the virtual leak point 300 is scanned in more detail with the laser beam LB, as shown in Figure 12, in the same manner as in step S6. In this way, the actual gas leak point 140 is identified.

[0060] In this manner, if no actual gas leak point is detected within the set virtual leak point and virtual gas cloud region, further virtual leak points and virtual gas cloud regions are set, the laser beam LB is scanned, and these operations are repeated to check for gas leaks in the gas pipe 110.

[0061] Furthermore, if the next virtual leak point is set close to the previous virtual leak point, the next virtual gas cloud region may overlap with the previous virtual gas cloud region. However, in this embodiment, such overlapping of virtual gas cloud regions is acceptable.

[0062] As is clear from the above description, according to the above embodiment, it is possible to effectively measure gas leaks in gas equipment using a laser-type gas detector.

[0063] Furthermore, according to the above embodiment, by setting a virtual leak point and gas cloud region and scanning them with laser light, it is possible to detect the presence or absence of gas leakage and the location of the leakage. Therefore, it is possible to efficiently inspect for gas leaks in places that are not easily accessible, such as the ceiling of a factory building.

[0064] Furthermore, laser-type gas detectors have high detection sensitivity for methane gas and high detection selectivity. In other words, a laser-type gas detector for methane gas will not detect gases other than methane gas. Therefore, the gas detection method of this embodiment is suitable when conducting leak inspections of the target gas in an environment where the target gas and other gases coexist, for example, when conducting leak inspections of city gas in a place where gases other than city gas, which mainly consists of methane gas, are present.

[0065] [Variation] In the above embodiment, the laser light may be irradiated as scattered light. When the laser light irradiated onto the virtual gas cloud region is reflected by a mirror surface, the total reflected light of the scattered light is detected, and the same result as when the scattered light is detected is obtained.

[0066] In setting up a gas cloud region, it is possible to pre-acquire data on gas cloud regions under various conditions corresponding to the type of gas, wind speed, and obstructions, and then set up a virtual gas cloud region by selecting the optimal data from the pre-acquired predicted data of gas cloud regions according to the situation at the virtual leakage point. Predicted data for gas cloud regions may be acquired, for example, by training an AI (Artificial Intelligence) using measured data of gas cloud regions as training data.

[0067] Furthermore, if there is a wall around the gas pipe, for example, if the gas pipe is positioned along both the ground surface and the wall of a building, the gas leaking from the gas pipe will flow along both the ground surface and the wall surface. In this case, for example, with the irradiation direction configuration shown in Figures 5 and 6, the laser beam LB is irradiated along both the ground surface and the wall surface, and approximately parallel to the direction of wind flow. Also, when conducting a leak inspection along a gas pipe (when the shielding object is a gas pipe), the laser beam LB is scanned in a circular motion around the gas pipe along the outer wall surface of the gas pipe.

[0068] Furthermore, in step S6 described above, an alarm may be sounded in response to changes in the gas column density. For example, a threshold of 100 ppm·m may be used, and an alarm may be sounded when the gas column density exceeds 100 ppm·m. The longer the distance between the gas detector 220 and the virtual gas cloud region 210, the larger the threshold may be. Such alarm sounding is preferable from the viewpoint of more reliably detecting changes in column density.

[0069] Furthermore, this embodiment may further include the step of placing a reflective material at the edge of the virtual gas cloud region. The detection of the laser light described above in the inspection of outdoor gas equipment may be affected by weather conditions (such as snow or rain), and may also be affected by the physical properties of the materials of the gas equipment and surrounding structures (such as mirrors, shiny metals, or certain resin materials (PE)). The reflective material may be, for example, a component that diffusely reflects the laser light and produces scattered light. Including the step of placing the reflective material is preferable from the viewpoint of further improving the accuracy of the laser light detection result.

[0070] 〔summary〕 A first aspect of the present invention is a method for detecting gas leaking from a gas facility (gas pipe 110) by irradiating the area around the facility with laser light (LB) having a wavelength absorbed by the gas to be measured (methane gas), and the method includes the steps of: setting a virtual leak point (200) in the facility assuming that gas is leaking from the facility; setting a virtual gas cloud region (210) based on the expected distribution of gas leaking from the virtual leak point; irradiating and scanning the virtual gas cloud region with laser light; and receiving the laser light that has passed through the virtual gas cloud region and detecting the change in its intensity. According to the first aspect, it is possible to irradiate and scan with laser light a region in which gas is more likely to be present when a gas leak occurs. Therefore, gas leaks can be effectively detected by laser light.

[0071] A second aspect of the present invention is, in the first aspect, a step in setting a virtual gas cloud region, in which a substantially conical region extending downwind from a virtual leakage point is set as the virtual gas cloud region. Furthermore, a third aspect of the present invention is, in the second aspect, the spread angle of the virtual gas cloud region from the apex is 10° or less. Both the second and third aspects set a virtual gas cloud region that is more in line with the general behavior of gas leaked into the atmosphere. Therefore, they are more effective from the viewpoint of appropriately setting a virtual gas cloud region.

[0072] A fourth aspect of the present invention is that, in the step of setting a virtual gas cloud region in any of the first to third aspects, a region extending along one or both of the ground surface and the surface of a shield on the downwind side is set as the virtual gas cloud region. In the fourth aspect, a virtual gas cloud region is set that further takes into account the trend of gas distribution due to the conditions of the measurement site. Therefore, it is even more effective from the viewpoint of appropriately setting a virtual gas cloud region.

[0073] A fifth aspect of the present invention is that, in any of the first to fourth aspects, during the scanning process, the virtual gas cloud region is irradiated with laser light along the longitudinal direction of the virtual gas cloud region. The fifth aspect makes it possible to detect the gas more clearly. Therefore, it is even more effective from the viewpoint of increasing the intensity of gas detection.

[0074] A sixth aspect of the present invention is the fifth aspect, wherein in the scanning process, a virtual gas cloud region is irradiated with laser light from the downwind side. The sixth aspect enables gas detection that further takes into account the trend of gas distribution due to the conditions of the measurement site. Therefore, it is even more effective in terms of improving the intensity and accuracy of gas detection.

[0075] A seventh aspect of the present invention further includes, in any of the first to sixth aspects, a step of acquiring information on the amount of gas corresponding to the change in the intensity of the laser light detected in the change detection step, and a step of identifying the actual gas leak location in the equipment by referring to the acquired information on the amount of gas. The seventh aspect makes it possible to identify the actual gas leak location more easily than conventional suction-type gas detection technology. Therefore, it is even more effective from the viewpoint of efficiently identifying the actual gas leak location.

[0076] The eighth aspect of the present invention is a gas containing methane, in any of the first to seventh aspects. The eighth aspect makes it possible to detect leaked gas in accordance with the general behavior of leaked gas, even if methane has a lower specific gravity than air. Therefore, it is even more effective from the viewpoint of effectively detecting leaks of methane-containing gas.

[0077] This invention makes it possible to perform gas leak inspections in gas facilities using laser-type gas detectors more accurately and easily. With these advantages, this invention is expected to contribute to achieving goals such as Goal 9 of the United Nations' Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0078] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Explanation of symbols]

[0079] 100 Ground surface 110 gas pipe 120 flange 130 Rust section 140 Leakage points 200, 300 virtual leak points 210, 310 Virtual gas cloud region 211, 212 Cross-sections 220 Gas Detectors LB laser light

Claims

1. A method for detecting gas leaking from equipment by irradiating the area around the equipment with laser light of a wavelength absorbed by the gas to be measured, A step of setting a hypothetical leak point in the equipment, assuming that the gas is leaking from the equipment, A step of setting a virtual gas cloud region based on the expected distribution of the gas leaking from the virtual leak point, The process involves scanning the virtual gas cloud region by irradiating it with the laser light, A step of receiving the laser light that has passed through the virtual gas cloud region and detecting the change in its intensity, A method for detecting gases, including the detection of gases.

2. The gas detection method according to claim 1, wherein in the step of setting up the virtual gas cloud region, a substantially conical region extending downwind with the virtual leakage point as its apex is set up as the virtual gas cloud region.

3. The gas detection method according to claim 2, wherein the spread angle of the virtual gas cloud region from the vertex is 10° or less.

4. The gas detection method according to claim 1, wherein in the step of setting the virtual gas cloud region, the region extending along one or both of the ground surface and the surface of a shielding object on the leeward side is set as the virtual gas cloud region.

5. The gas detection method according to claim 1, wherein in the scanning step, the virtual gas cloud region is irradiated with the laser light along the longitudinal direction of the virtual gas cloud region.

6. The gas detection method according to claim 5, wherein in the scanning step, the virtual gas cloud region is irradiated with the laser light from the downwind side.

7. The process of detecting the change includes a step of acquiring information on the amount of gas corresponding to the change in the intensity of the laser light detected in the aforementioned change detection step, A step of identifying the actual location of the gas leak in the equipment by referring to the acquired information on the amount of gas, The method for detecting a gas according to claim 1, further comprising:

8. The method for detecting a gas according to claim 1, wherein the gas is a gas containing methane.

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