A leakage monitoring system and monitoring method for a liquid cargo membrane tank

Abstract

The present invention discloses a leakage monitoring system and method for a liquid cargo membrane tank, belonging to the technical field of natural gas transportation and storage. It includes a plurality of first-level monitoring subsystems, which are arranged circumferentially around the membrane tank, and each first-level monitoring subsystem is connected through a pipeline; a protective gas input end and a gas output end, both of which are connected to each first-level monitoring subsystem through a pipeline; each first-level monitoring subsystem includes two gas sensing parts, the gas sensing parts are attached to the outer wall of the membrane tank, and a first differential pressure detection mechanism is arranged between the two gas sensing parts. In this application, by arranging first-level monitoring subsystems on each surface of the membrane tank and monitoring the pressure of each area of the membrane tank through each second-level monitoring subsystem, precise monitoring of the natural gas leakage point is realized; and by inputting and extracting gas from the fixed-point area of the membrane tank through the protective gas input end and the gas output end, the suppression of natural gas leakage at the leakage point is realized, effectively alleviating the problem of natural gas leakage.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas transportation and storage, and particularly relates to a leakage monitoring system and method for a liquid cargo membrane tank. Background Art

[0002] As a clean and efficient energy source, liquefied natural gas (LNG) is mainly transported through cryogenic atmospheric or pressure storage tanks. Due to its own low temperature and highly compressed state, the transportation of LNG has high requirements for sealing and stability. Based on the transportation regulations of LNG, it is usually required that the natural gas storage tank has a cargo containment system with a complete or partially complete secondary shielding space, and the secondary shielding space needs to be filled with dry protective gas to ensure the safety of the transportation vehicle in case of cargo leakage.

[0003] Existing LNG storage tanks mainly set pressure monitors, gas monitors, etc. in the shielding layer to monitor whether there is a natural gas leakage problem in the storage tank. However, in the actual LNG transportation process, the size of the LNG tank is large, and the conventional monitoring method can only monitor whether there is a leakage in the tank, and cannot accurately know the specific leakage location; at the same time, when the tank actually leaks, it is also impossible to control the diffusion and leakage of natural gas in the shielding layer of the tank, and the potential safety hazards cannot be effectively solved. Summary of the Invention

[0004] In view of one or more of the above-mentioned defects or improvement requirements of the prior art, the present invention provides a leakage monitoring system for a liquid cargo membrane tank to solve the problem that the existing LNG transportation storage tank cannot effectively monitor and relieve the natural gas leakage problem during breakage and leakage.

[0005] To achieve the above object, the present invention provides a leakage monitoring system for a liquid cargo membrane tank, which is arranged in the shielding layer between the membrane tank and the tank body, and includes:

[0006] A plurality of first-level monitoring subsystems, which are respectively arranged circumferentially around the membrane tank, and the plurality of first-level monitoring subsystems are interconnected through pipelines, and two-way valves are arranged on the pipelines between the first-level monitoring subsystems;

[0007] A protective gas input end, which is connected to each of the first-level monitoring subsystems through a pipeline;

[0008] A gas output end, which is connected to each of the first-level monitoring subsystems through a pipeline;

[0009] Wherein, each of the first-level monitoring subsystems includes a plurality of second-level monitoring subsystems, and the plurality of second-level monitoring subsystems belonging to the same first-level monitoring subsystem are distributed in different areas on one side of the membrane tank;

[0010] Each of the secondary monitoring subsystems includes two spaced-apart gas sensing parts, which are attached to the outer wall of the film tank. A first pressure difference detection mechanism is provided between the two gas sensing parts, and the first pressure difference detection mechanism can measure the gas pressure difference between the two gas sensing parts.

[0011] As a further improvement of the present invention, the protective gas input end and the gas output end are both connected to each of the primary monitoring subsystems through a circulation pipeline;

[0012] The circulation pipeline comprises a first circulation pipeline and a second circulation pipeline;

[0013] The first circulation pipeline and the second circulation pipeline are both arranged around the circumference of the membrane tank, and each of the primary monitoring subsystems is connected to the first circulation pipeline and the second circulation pipeline.

[0014] As a further improvement of the present invention, a plurality of second differential pressure detection mechanisms are further provided in the circumferential direction of the second circulation pipeline, the second circulation pipeline is provided in multiple sections corresponding to each of the first-level monitoring subsystems, and each section of the second circulation pipeline is provided with the second differential pressure detection mechanism in parallel;

[0015] The second differential pressure detection mechanisms are connected to form a loop through pipelines, and valves are provided at both ends of the second differential pressure detection mechanisms.

[0016] As a further improvement of the present invention, a third pressure difference detection mechanism is provided between any adjacent secondary monitoring subsystems, and the third pressure difference detection mechanism can measure the gas pressure difference between two adjacent secondary monitoring subsystems.

[0017] As a further improvement of the present invention, the two gas sensing parts of the same secondary monitoring subsystem are connected through a branch pipe, and valves are provided on the branch pipes connecting the two gas sensing parts.

[0018] As a further improvement of the present invention, the gas sensing unit includes a connecting pipeline, the connecting pipeline is connected to a plurality of tail pipes, and the plurality of tail pipes are open at one end away from the connecting pipeline.

[0019] The present application also includes a liquid cargo film tank leakage monitoring method, which is monitored by the liquid cargo film tank leakage monitoring system, and includes the following steps:

[0020] S1. Replace the air in the shielding layer with protective gas to form protection outside the film tank;

[0021] S2, the shielding gas input end continuously fills the shielding layer with shielding gas, and the gas output end continuously extracts the gas in the shielding layer to form a shielding gas flow around the membrane tank;

[0022] S3. Obtain the differential pressure detection data at each first differential pressure detection mechanism, establish a differential pressure - time change graph for each first differential pressure detection mechanism, and obtain the initial differential pressure change point of the first differential pressure detection mechanism. This initial differential pressure change point of the first differential pressure detection mechanism is the leakage point of the thin - film tank.

[0023] As a further improvement of the present invention, the protective gas input at the protective gas input end is nitrogen. The step S1 includes:

[0024] S101. The protective gas input end inputs the protective gas from the bottom of the thin - film tank through a pipeline, and the gas output end extracts the protective gas from the top of the thin - film tank through a pipeline.

[0025] S102. The protective gas input end injects the protective gas into the shielding layer through the gas sensing part of one of the secondary monitoring subsystems through a pipeline, and the gas output end extracts the gas from the adjacent secondary monitoring subsystem of this secondary monitoring subsystem through a pipeline.

[0026] S103. The protective gas input end injects the protective gas into the shielding layer through the secondary monitoring subsystem that extracted the gas last time, and the gas output end extracts the gas from the next adjacent secondary monitoring subsystem through a pipeline.

[0027] S104. Repeat step S103 until the protective gas input for each secondary monitoring subsystem is completed.

[0028] As a further improvement of the present invention, the step S2 includes: The protective gas input end injects the protective gas into the shielding layer through the primary monitoring subsystem at the side wall of the thin - film tank, and the gas output end extracts the gas in the shielding layer through the primary monitoring subsystem on the side opposite to the protective gas input end.

[0029] As a further improvement of the present invention, it further includes step S4:

[0030] Spray liquefied natural gas onto the top layer inside the thin - film tank to cool the thin - film tank.

[0031] Adjust the input amount and output amount of the protective gas to increase the pressure in the shielding layer.

[0032] As a further improvement of the present invention, it further includes step S5:

[0033] The protective gas input end increases the injection amount of the protective gas into the secondary monitoring subsystem at the leakage point of the thin - film tank; the gas output end takes the secondary monitoring subsystem at the leakage point of the thin - film tank as the center and extracts the gas through the circumferential secondary monitoring subsystems of this secondary monitoring subsystem.

[0034] As a further improvement of the present invention, the amount of protective gas injected at the protective gas input end in step S5 is less than the amount of gas extracted at the gas output end, so that the shielding layer at the leakage point of the thin-film tank is in a negative pressure state.

[0035] As long as the above-mentioned improved technical features do not conflict with each other, they can be combined with each other.

[0036] Generally speaking, compared with the prior art, the beneficial effects of the above technical solutions conceived by the present invention include:

[0037] (1) For the liquid cargo thin-film tank leakage monitoring system of the present invention, its periphery is completely covered by the primary monitoring subsystem to achieve comprehensive monitoring of the outer periphery of the thin-film tank; and multiple secondary monitoring subsystems are formed on each surface of the thin-film tank by each primary monitoring subsystem to achieve monitoring of the outer peripheral area of the thin-film tank, so as to improve the precise monitoring of the leakage position of the thin-film tank. Secondly, in this application, two gas sensing parts are extended from the secondary monitoring subsystem to the outer peripheral wall surface of the thin-film tank. When there is a leakage on the surface of the thin-film tank, the gas sensing part near the leakage point will be impacted by the leaked natural gas, causing air pressure fluctuations at this point. The pressure difference between the leakage point and the non-leakage point is identified by the first pressure difference detection mechanism, and then the accurate position of the natural gas leakage can be obtained according to the area where the secondary monitoring subsystem is located. Moreover, in this application, through the two-way valve between the protective gas input end and the primary monitoring subsystem, protective gas can be directionally output to the natural gas leakage area, suppressing the natural gas leakage at the leakage point by increasing the protective gas output volume, and pumping air from the primary monitoring subsystem beside the leakage point through the gas output end, timely removing the gas around the leakage point, preventing the natural gas from spreading to the entire shielding layer, and ensuring the pressure balance in the shielding layer.

[0038] (2) For the liquid cargo thin-film tank leakage monitoring system of the present invention, in addition to monitoring the leakage situation in each area of the thin-film tank through the secondary monitoring subsystem, the leakage situation in the areas of different secondary monitoring subsystems can also be monitored through the third pressure difference detection mechanism. During the leakage process of the thin-film tank, when the coverage area of the secondary monitoring subsystem is small, both gas sensing parts of a single secondary monitoring subsystem are covered by the leaked natural gas, resulting in the first pressure difference detection mechanism being unable to accurately identify. At this time, the air pressure of the entire secondary monitoring subsystem in the gas leakage area is affected by the leaked natural gas and will be greater than the pressure of the adjacent secondary monitoring subsystem that is not affected. At this time, the leakage point can be identified through the third pressure difference detection mechanism to make up for the problem that the first pressure difference detection mechanism cannot identify in time. Description of the Drawings

[0039] Figure 1 is the overall structural schematic diagram of the liquid cargo thin-film tank leakage monitoring system in the embodiment of the present invention;

[0040] Figure 2 It is a schematic structural diagram of the primary monitoring subsystem in the embodiment of the present invention;

[0041] Figure 3 It is a schematic structural diagram of the secondary monitoring subsystem in the embodiment of the present invention;

[0042] Figure 4 It is a schematic airflow diagram of replacing air with protective gas in the method for monitoring leakage of a liquid cargo membrane tank in the embodiment of the present invention;

[0043] Figure 5 It is a schematic airflow diagram of local gas replacement on the outer wall of the membrane tank in the method for monitoring leakage of a liquid cargo membrane tank in the embodiment of the present invention;

[0044] Figure 6 It is a schematic airflow diagram of forming a protective airflow around the membrane tank in the method for monitoring leakage of a liquid cargo membrane tank in the embodiment of the present invention;

[0045] Figure 7 It is a schematic flowchart of the method for monitoring leakage of a liquid cargo membrane tank in the embodiment of the present invention;

[0046] Figure 8 It is a schematic flowchart of forming a protection outside the membrane tank in the embodiment of the present invention.

[0047] In all the drawings, the same reference numerals represent the same technical features, specifically:

[0048] 1. Primary monitoring subsystem; 2. Secondary monitoring subsystem; 3. Protective gas input end; 4. Gas output end; 5. Gas sensing part; 6. First differential pressure detection mechanism; 7. First circulation pipeline; 8. Second circulation pipeline; 9. Second differential pressure detection mechanism; 10. Third differential pressure detection mechanism; 11. Tail pipe; 12. Membrane tank. Detailed implementation manners

[0049] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0050] In the description of the present invention, it should be understood that unless otherwise specified, the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation on the present invention.

[0051] In addition, unless otherwise specified, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0052] In the present invention, unless otherwise clearly defined and limited, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0053] In the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0054] Embodiment

[0055] The liquid cargo thin film tank leakage monitoring system in this application is applicable to the monitoring and protection of liquid cargo such as LNG, methanol, ethanol, ethane, etc. during storage and transportation, and is particularly applicable to the monitoring of ship LNG transportation. In the embodiments of this application, the leakage of liquefied natural gas is mainly taken as an example for description.

[0056] Please refer to Figures 1 to 8 , in the leakage monitoring system of the liquid cargo membrane tank in the preferred embodiment of the present invention, it is arranged in the shielding layer between the membrane tank 12 and the tank body, and is used for gas monitoring and protection of the outer periphery of the membrane tank 12 to prevent the direct leakage of natural gas in the membrane tank 12 to the outside. Specifically, the leakage monitoring system of the liquid cargo membrane tank includes a plurality of first-level monitoring subsystems 1, and the plurality of first-level monitoring subsystems 1 are respectively arranged around the circumference of the membrane tank 12, and the plurality of first-level monitoring subsystems 1 are interconnected through pipelines, and two-way valves are provided on the pipelines between each of the first-level monitoring subsystems 1; at the same time, the leakage monitoring system of the liquid cargo membrane tank also includes a protective gas input end 3 and a gas output end 4, wherein the protective gas input end 3 is connected to each of the first-level monitoring subsystems 1 through a pipeline, and the gas output end 4 is also connected to each of the first-level monitoring subsystems 1 through a pipeline. And each of the first-level monitoring subsystems 1 includes a plurality of second-level monitoring subsystems 2, and the plurality of second-level monitoring subsystems 2 belonging to the same first-level monitoring subsystem 1 are distributed in different areas on one side of the membrane tank 12. Each of the second-level monitoring subsystems 2 includes two gas sensing parts 5 arranged at intervals. The gas sensing part 5 has an opening, and the opening of any one of the gas sensing parts 5 is communicated with the protective gas input end and the gas output end; the gas sensing part 5 is attached to the outer wall of the membrane tank 12, and a first pressure difference detection mechanism 6 is provided between the two gas sensing parts 5, and the gas pressure difference between the two gas sensing parts 5 can be measured through the first pressure difference detection mechanism 6.

[0057] Specifically, for the leakage monitoring system of the liquid cargo membrane tank in the present application, it completely covers the periphery of the membrane tank 12 through the first-level monitoring subsystem 1 to achieve comprehensive monitoring of the outer periphery of the membrane tank 12; and uses each first-level monitoring subsystem 1 to form a plurality of second-level monitoring subsystems 2 on each surface of the membrane tank 12 to achieve monitoring of the outer peripheral area of the membrane tank 12, so as to improve the precise monitoring of the leakage position of the membrane tank 12; secondly, the present application extends two gas sensing parts 5 from the second-level monitoring subsystem 2 to the outer wall surface of the membrane tank 12. When there is a leakage on the surface of the membrane tank 12, the gas sensing part 5 near the leakage point will be impacted by the leaked natural gas, causing the air pressure at this point to fluctuate. The pressure difference between the leakage point and the non-leakage point is recognized by the first pressure difference detection mechanism 6, and then the accurate position of the natural gas leakage can be known according to the area where the second-level monitoring subsystem 2 is located. And, through the two-way valve between the protective gas input end 3 and the first-level monitoring subsystem 1 in the present application, protective gas can be directionally output to the natural gas leakage area, suppress the natural gas leakage at the leakage point by increasing the protective gas output volume, and pump air to the first-level monitoring subsystem 1 beside the leakage point through the gas output end 4, and timely remove the gas around the leakage point to ensure the pressure balance in the shielding layer.

[0058] Specifically, the present application can divide the thin-film tank 12 into multiple regions, and arrange a primary monitoring subsystem 1 for each region of the thin-film tank 12. Each secondary monitoring subsystem 2 corresponding to a primary monitoring subsystem 1 is located in the same partition to monitor different regions of the thin-film tank 12 respectively. When there is a leak in the thin-film tank 12, the leakage point can be quickly located according to the position of the first differential pressure detection mechanism 6, which is convenient for subsequent maintenance and repair of the thin-film tank 12. At the same time, the primary monitoring subsystem 1 and the secondary monitoring subsystem 2 in the present application are pipeline structures, which are mainly used to arrange the gas sensing part 5 on the outer periphery of the thin-film tank 12 to perform zonal monitoring on the thin-film tank 12, so as to facilitate the first differential pressure detection mechanism 6 to detect and identify the leakage point.

[0059] Further, as an optional embodiment of the present invention, both the protective gas input end 3 and the gas output end 4 in the present application are connected to each primary monitoring subsystem 1 through a circulation pipeline. The circulation pipeline includes a first circulation pipeline 7 and a second circulation pipeline 8. The first circulation pipeline 7 and the second circulation pipeline 8 are both arranged circumferentially around the thin-film tank 12, and each primary monitoring subsystem 1 is connected to the first circulation pipeline 7 and the second circulation pipeline 8. Specifically, the first circulation pipeline 7 and the second circulation pipeline 8 are formed on the outer periphery of the primary monitoring subsystem 1 in the present application, and the protective gas input end 3 and the gas output end 4 are both connected to the first circulation pipeline 7 and the second circulation pipeline 8. This enables the protective gas emitted from the protective gas input end 3 and the gas extracted by the gas output end 4 to adjust the gas transmission direction according to requirements and not conflict with each other, realizing the input of the protective gas and the extraction of the gas at the fixed-point area on the outer wall of the thin-film tank 12.

[0060] Optionally, the protective gas input end 3 in the present application is connected to a protective gas input source. The protective gas can be one of nitrogen, argon or helium. It should be noted that when different protective gases are selected, the mass ratio of the protective gas to air and natural gas needs to be considered to facilitate the control of the gas flow direction in the shielding layer. When the protective gas is argon or helium, when evacuating the air in the shielding layer, the protective gas needs to be injected from the top of the thin-film tank 12 and the gas needs to be extracted from the bottom of the thin-film tank 12. Optionally, a pump body is provided at the gas output end 4 in the present application to extract the gas in the shielding layer.

[0061] Further, as an alternative embodiment of the present invention, a plurality of second differential pressure detection mechanisms 9 are further provided circumferentially on the second circulation pipeline 8 in the present application. The second circulation pipeline 8 corresponding to each first-level monitoring subsystem 1 is arranged in multiple sections, and a second differential pressure detection mechanism 9 is arranged in parallel for each section of the second circulation pipeline 8; each second differential pressure detection mechanism 9 is connected by a pipeline to form a loop, and valves are arranged at both ends of each second differential pressure detection mechanism 9. The pressure of each first-level monitoring subsystem 1 can be monitored through the second differential pressure detection mechanism 9 to ensure that the pressure in some areas will not be too high when the air pressure outside the periphery of the thin-film tank 12 is monitored as a whole. When a leakage occurs in a fixed-point area of the thin-film tank 12, protective gas needs to be injected at the corresponding point and gas needs to be extracted from the side. The differential pressure situation of the shielding layer at the leakage point can be monitored through the second differential pressure detection mechanism 9. When the pressure at the first monitoring subsystem is too high or too low, the pressure in other areas needs to be adjusted correspondingly so that the overall pressure of the shielding layer is within a safe range.

[0062] Further, as an alternative embodiment of the present invention, a third differential pressure detection mechanism 10 is further provided between any two adjacent second-level monitoring subsystems 2 in the present application. The third differential pressure detection mechanism 10 can measure the gas differential pressure between two adjacent second-level monitoring subsystems 2. In addition to monitoring the leakage situation of each area of the thin-film tank 12 through the second-level monitoring subsystem 2 in the present application, the leakage situation of different second-level monitoring subsystem 2 areas can also be monitored through the third differential pressure detection mechanism 10. During the leakage process of the thin-film tank 12, when the coverage area of the second-level monitoring subsystem 2 is small, both gas sensing parts 5 of a single second-level monitoring subsystem 2 are covered by the leaked natural gas, resulting in the first differential pressure detection mechanism 6 being unable to accurately identify. At this time, the air pressure of the entire second-level monitoring subsystem 2 in the gas leakage area is affected by the leaked natural gas and will be greater than the pressure of the second-level monitoring subsystem 2 on the side that is not affected. At this time, the leakage point can be identified through the third differential pressure detection mechanism 10 to make up for the problem that the first differential pressure detection mechanism 6 cannot identify in time.

[0063] It should be noted that the first differential pressure detection mechanism 6, the second differential pressure detection mechanism 9, and the third differential pressure detection mechanism 10 in the present application are all connected to other components of the liquid cargo thin-film tank leakage monitoring system through pipelines. And based on the detection mechanism of the differential pressure detection mechanism, each detection mechanism is connected to the overall pipeline of the system, so that the connecting pipelines of each differential pressure detection mechanism can form a circulation loop in the liquid cargo thin-film tank leakage monitoring system.

[0064] Further, as an alternative embodiment of the present invention, in the present application, two gas sensing parts 5 of the same secondary monitoring subsystem 2 are both connected through branch pipes, and valves are provided on the branch pipes where the two gas sensing parts 5 are connected. In the present application, the secondary monitoring subsystem 2 mainly determines whether there is natural gas leakage at the monitoring point by the magnitude of the air flow received by the gas sensing part 5. When the first differential pressure detection mechanism 6 identifies the leakage point, in order to improve the inhibitory effect of the protective gas on the leakage point, the valve on the branch pipe can be used to control the protective gas input end 3 to only supply the protective gas to this leakage point, so as to reduce the loss of the protective gas.

[0065] It should be noted that the differential pressure detection mechanism in the present application has directivity. When the air flows at both ends of the differential pressure detection mechanism are unbalanced, the magnitude of the differential pressure on both sides can be identified through the differential pressure detection mechanism, so as to determine the specific leakage point of natural gas.

[0066] Further, as an alternative embodiment of the present invention, the gas sensing part 5 in the present application includes a connecting pipeline, and a plurality of tail pipes 11 are connected to the connecting pipeline, and one end of the plurality of tail pipes 11 facing away from the connecting pipeline is open. The gas sensing part 5 in the present application is mainly connected to the side wall of the thin film tank 12 through the tail pipes 11. When there is natural gas leakage at the corresponding point, natural gas is input into the tail pipes 11, so that the pressures at both ends of the two gas sensing parts 5 are unbalanced, and the first differential pressure detection mechanism 6 can correspondingly detect the pressure fluctuation to identify the natural gas leakage point.

[0067] Further, for the liquid cargo thin film tank leakage monitoring system in the present application, the present application also includes a liquid cargo thin film tank leakage monitoring method, which includes the following steps:

[0068] S1. Replace the air in the shielding layer with a protective gas to form a protection outside the thin film tank 12;

[0069] S2. The protective gas input end 3 continuously fills the shielding layer with the protective gas, and the gas output end 4 continuously extracts the gas in the shielding layer to form a protective air flow outside the thin film tank 12;

[0070] S3. Obtain the differential pressure detection data at each first differential pressure detection mechanism 6, establish a differential pressure-time change graph of each first differential pressure detection mechanism 6, and obtain the initial differential pressure change point in each first differential pressure detection mechanism 6. The initial differential pressure change point of this first differential pressure detection mechanism 6 is the leakage point of the thin film tank 12.

[0071] Specifically, for the method of monitoring the leakage of the liquid cargo membrane tank in this application, the air inside the shielding layer can be replaced with a protective gas through the protective gas input end 3 and the gas output end 4, and a protective air flow is formed outside the membrane layer by using the pipelines of the primary monitoring subsystem 1 and the secondary monitoring subsystem 2 to achieve the protection of the membrane tank 12. When a break occurs outside the membrane tank 12 and natural gas leaks, the air pressure at the leakage point will increase accordingly. At the same time, the leaked natural gas will spread around with the leakage point as the center. The pressure difference between the two gas sensing parts 5 of the secondary monitoring subsystem 2 at the leakage point tends to balance, and the pressure value detected by the first pressure difference detection mechanism 6 at this point drops from the peak to zero; at the same time, the leaked natural gas spreads around, and the pressure value of the secondary monitoring subsystem 2 adjacent to the leakage point also correspondingly rises to zero; this spreads to the next adjacent area, and finally the area stabilizes. It can be seen that when the membrane tank 12 leaks, the first pressure difference detection mechanism 6 at the leakage point first shows pressure difference data and then returns to zero; at the next time node, the first pressure difference detection mechanism 6 adjacent to the leakage point shows pressure difference data and then returns to zero, and so on and spreads outwards. By the first occurrence node of the pressure difference data and the location of the corresponding secondary monitoring subsystem 2, the leakage point of the membrane tank 12 can be judged. At the same time, when the amount of natural gas leaked from the membrane tank 12 is small, the data fluctuation of a single first pressure difference detection mechanism 6 may be ignored. Therefore, it is necessary to confirm the pressure difference data between the surrounding first pressure difference detection mechanisms 6 and the first pressure difference detection mechanism 6 at the leakage point to ensure the accuracy of the leakage monitoring of the membrane tank 12.

[0072] Furthermore, as an optional embodiment of the present invention, the protective gas input by the protective gas input end 3 in this application is nitrogen. The specific steps for forming the external protection of the membrane tank 12 are as follows:

[0073] S101. The protective gas input end 3 inputs the protective gas from the bottom of the membrane tank 12 through a pipeline, and the gas output end 4 extracts the protective gas from the top of the membrane tank 12 through a pipeline;

[0074] S102. The protective gas input end 3 injects the protective gas into the shielding layer through the pipeline to the gas sensing part 5 of one of the secondary monitoring subsystems 2, and the gas output end 4 extracts the gas from the secondary monitoring subsystem 2 adjacent to the secondary monitoring subsystem 2 through a pipeline;

[0075] S103. The protective gas input end 3 injects the protective gas into the shielding layer through the secondary monitoring subsystem 2 that extracted the gas last time, and the gas output end 4 extracts the gas from the next adjacent secondary monitoring subsystem 2 through a pipeline;

[0076] S104. Repeat step S103 until the protective gas input of each secondary monitoring subsystem 2 is completed.

[0077] Specifically, when performing gas replacement on the periphery of the membrane tank 12, considering that the quality of nitrogen is close to that of air, the present application uses cold nitrogen, so that the protective gas is more easily deposited at the bottom of the shielding layer. When achieving the initial evacuation of air, the primary monitoring subsystem 1 located at the bottom of the membrane tank 12 is connected through the protective gas input terminal 3, and finally the protective gas is injected from the bottom into the shielding layer through the gas sensing unit 5 of the secondary monitoring subsystem 2, and at the same time, the air is extracted from the top of the membrane tank 12 through the gas output terminal 4, so as to achieve the replacement of air with nitrogen, such as Figure 4 As shown. After the initial replacement is completed, the similar quality of air and nitrogen makes it easy for the two to mix, resulting in some air remaining in the shielding layer. When natural gas leaks in the membrane tank 12, flash explosion is likely to occur, so the air needs to be further evacuated. Based on this, the present application achieves air discharge by replacing the gas at fixed points in each area of ​​the membrane tank 12. Specifically, the present application achieves air evacuation in a single area by injecting protective gas into the secondary monitoring subsystem 2, and then extracting gas from the secondary monitoring subsystem 2 next to it; then repeat the above operation, and evacuate the outside of the membrane tank 12 step by step in turn to complete the replacement of air in all areas of the shielding layer, as shown. Figure 5 shown.

[0078] It is worth noting that in step S102 of the present application, a single primary monitoring subsystem 1 is connected to the gas input end and the gas output end 4 through a one-way pipeline, and it is difficult for the pipeline of a single primary monitoring subsystem 1 to simultaneously realize the shielding gas input and gas extraction of two adjacent secondary monitoring subsystems 2. Therefore, when the secondary monitoring subsystem of a certain primary monitoring subsystem 1 inputs shielding gas, it is necessary to extract gas through the primary monitoring subsystem 1 next to it, and each secondary monitoring subsystem 2 is connected through the second pressure difference detection mechanism 9 to realize the gas extraction of the secondary monitoring subsystem 2 next to the leakage point.

[0079] Further, as an optional embodiment of the present invention, step S2 of the present application includes: the protective gas input end 3 injects the protective gas into the shielding layer with the primary monitoring subsystem 1 at the side wall of the film tank 12, and the gas output end 4 extracts the gas in the shielding layer with the primary monitoring subsystem 1 away from the side of the protective gas input end 3, such as Figure 6 As shown. In the present application, the protective gas in the shielding layer is not in a static state, but in a dynamic equilibrium state, that is, the protective gas input end 3 continuously injects protective gas into the shielding layer, and the gas output end 4 continuously extracts excess gas in the shielding layer. Based on this, the present application injects protective gas on one side of the film tank 12 and extracts protective gas from the other side, so that the protective gas forms a circulation around the periphery of the film tank 12, so as to provide gas protection to the periphery of the film tank 12.

[0080] Further, as an alternative embodiment of the present invention, the present application further includes step S4: spraying liquefied natural gas on the top layer inside the thin-film tank 12 to cool the thin-film tank 12; adjusting the input and output amounts of the protective gas to increase the pressure of the shielding layer. When natural gas leaks from the thin-film tank 12, more gaseous natural gas will be generated inside the thin-film tank 12, the internal pressure of the thin-film tank 12 will increase, and the overall thin-film tank 12 has a tendency to expand outward, which will also correspondingly squeeze the space of the shielding layer. To avoid excessive expansion of the thin-film tank 12, on the one hand, the present application needs to spray liquefied natural gas on the top layer inside the thin-film tank 12 to reduce the content of flash steam inside the thin-film tank 12, reduce the internal pressure of the thin-film tank 12, and slow down the expansion of the thin-film tank 12 from the inside; on the other hand, by increasing the protective gas input at the protective gas input end 3 and reducing the gas output at the gas output end 4, the pressure of the shielding layer is increased to limit the expansion of the thin-film tank 12 from the outside.

[0081] Further, as an alternative embodiment of the present invention, the present application further includes step S5:

[0082] The protective gas input end 3 increases the injection amount of the protective gas into the secondary monitoring subsystem 2 at the leakage point of the thin-film tank 12; the gas output end 4 takes the secondary monitoring subsystem 2 at the leakage point of the thin-film tank 12 as the center and extracts gas circumferentially through the secondary monitoring subsystem 2. When natural gas leaks from the outer wall of the thin-film tank 12, it is necessary to increase the output of the protective gas through the secondary monitoring subsystem 2 at the leakage point, increase the pressure at the leakage point, so as to reduce the pressure difference inside and outside the leakage point of the thin-film tank 12 and inhibit the leakage of natural gas; at the same time, the leaked gas is extracted through the secondary monitoring subsystem 2 around the leakage point to maintain the internal pressure of the shielding layer within a safe range and prevent natural gas from spreading to the entire shielding layer space.

[0083] Further, as an alternative embodiment of the present invention, in step S5 of the present application, the injection amount of the protective gas injected by the protective gas input end 3 is less than the amount of gas extracted by the gas output end 4, so that the shielding layer at the leakage point of the thin-film tank 12 is in a negative pressure state. By adjusting the gas output amount and the gas input amount, the leakage point is in a negative pressure state, and the negative pressure will correspondingly extract the natural gas at the leakage point, resulting in an increase in the natural gas content in the gas output by the gas output end 4, which is convenient for the gas monitoring mechanism at the end of the gas output end 4 to identify the natural gas leakage to prompt the staff to carry out subsequent maintenance work. It should be noted that at this time, the leakage point is adjusted to a negative pressure state only for a short time to ensure the accurate identification of the leakage point. After the leakage point is identified, it is still necessary to increase the injection amount of the protective gas at the protective gas input end 3 to increase the pressure at the leakage point to inhibit the leakage of natural gas.

[0084] Those skilled in the art can easily understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A liquid cargo membrane tank leakage monitoring system, which is arranged in the shielding layer between the membrane tank and the tank body, characterized in that: include: A plurality of primary monitoring subsystems, wherein the plurality of primary monitoring subsystems are respectively arranged around the circumference of the membrane tank, and the plurality of primary monitoring subsystems are interconnected through pipelines, and two-way valves are provided on the pipelines between the primary monitoring subsystems; A shielding gas input terminal, wherein the shielding gas input terminal is connected to each of the first-level monitoring subsystems through a pipeline; A gas output end, the gas output end is connected to each of the first-level monitoring subsystems through a pipeline; Wherein, each of the first-level monitoring subsystems includes a plurality of second-level monitoring subsystems, and the plurality of second-level monitoring subsystems belonging to the same first-level monitoring subsystem are distributed in different areas on the same side of the film tank; Each of the secondary monitoring subsystems comprises two spaced apart gas sensing parts, each of which has an opening, and the opening of any of the gas sensing parts is connected to the protective gas input end and the gas output end; the gas sensing part is attached to the outer wall of the film tank, and a first pressure difference detection mechanism is provided between the two gas sensing parts, and the first pressure difference detection mechanism can measure the pressure difference between the two gas sensing parts; A third pressure difference detection mechanism is provided between any adjacent secondary monitoring subsystems, and the third pressure difference detection mechanism can measure the pressure difference between two adjacent secondary monitoring subsystems.

2. The liquid cargo membrane tank leakage monitoring system according to claim 1 is characterized in that: The protective gas input end and the gas output end are both connected to each of the primary monitoring subsystems through a circulation pipeline; The circulation pipeline comprises a first circulation pipeline and a second circulation pipeline; The first circulation pipeline and the second circulation pipeline are both arranged around the circumference of the membrane tank, and each of the primary monitoring subsystems is connected to the first circulation pipeline and the second circulation pipeline.

3. The liquid cargo film tank leakage monitoring system according to claim 2 is characterized in that: A plurality of second differential pressure detection mechanisms are further provided in the circumferential direction of the second circulation pipeline, the second circulation pipeline is configured into multiple sections corresponding to each of the first-level monitoring subsystems, and each section of the second circulation pipeline is provided with the second differential pressure detection mechanism in parallel; The second differential pressure detection mechanisms are connected to form a loop through pipelines, and valves are provided at both ends of the second differential pressure detection mechanisms.

4. The liquid cargo membrane tank leakage monitoring system according to claim 1 is characterized in that: The two gas sensing parts of the same secondary monitoring subsystem are connected through a branch pipe, and valves are provided on the branch pipes connecting the two gas sensing parts.

5. The liquid cargo membrane tank leakage monitoring system according to claim 1 is characterized in that: The gas sensing unit comprises a connecting pipeline, a plurality of tail pipes are connected to the connecting pipeline, and the plurality of tail pipes are open at one end away from the connecting pipeline.

6. A method for monitoring leakage of a liquid cargo film tank, which is performed by monitoring leakage of a liquid cargo film tank as claimed in any one of claims 1 to 5, characterized in that: The steps include: S1. Replace the air in the shielding layer with protective gas to form protection outside the film tank; S2, the shielding gas input end continuously fills the shielding layer with shielding gas, and the gas output end continuously extracts the gas in the shielding layer to form a shielding gas flow around the membrane tank; S3. Obtain the pressure difference detection data at each first pressure difference detection mechanism, establish the pressure difference-time change diagram of each first pressure difference detection mechanism, and obtain the initial pressure difference change point of each first pressure difference detection mechanism, which is the leakage point of the membrane tank.

7. The method for monitoring leakage of a liquid cargo film tank according to claim 6, characterized in that: The protective gas input end inputs nitrogen as the protective gas, and the step S1 comprises: S101, the protective gas input end inputs the protective gas from the bottom of the membrane tank through the pipeline, and the gas output end extracts the protective gas from the top of the membrane tank through the pipeline; S102, the protective gas input end injects protective gas into the shielding layer through a pipeline to the gas sensing part of one of the first and second level monitoring subsystems, and the gas output end extracts gas through a pipeline to the adjacent second level monitoring subsystem of the second level monitoring subsystem; S103, the protective gas input end injects protective gas into the shielding layer through the upper secondary monitoring subsystem that extracts gas, and the gas output end extracts gas through a pipeline to the next adjacent secondary monitoring subsystem; S104, repeat step S103 until each secondary monitoring subsystem completes the input of protective gas.

8. The method for monitoring leakage of a liquid cargo film tank according to claim 6, characterized in that: The step S2 includes: the protective gas input end injects the protective gas into the shielding layer through the primary monitoring subsystem at the side wall of the membrane tank, and the gas output end extracts the gas in the shielding layer through the primary monitoring subsystem away from the protective gas input end.

9. The method for monitoring leakage of a liquid cargo film tank according to claim 6, characterized in that: The step S4 is also included: Liquid natural gas is sprayed onto the top layer inside the membrane tank to cool the membrane tank; the input and output of the protective gas are adjusted to increase the pressure of the shielding layer.

10. The method for monitoring leakage of a liquid cargo film tank according to claim 6, characterized in that: The step S5 is also included: The protective gas input end increases the amount of protective gas injected into the secondary monitoring subsystem at the leakage point of the membrane tank; the gas output end takes the secondary monitoring subsystem at the leakage point of the membrane tank as the center and extracts gas through the secondary monitoring subsystems around the secondary monitoring subsystem.

11. The method for monitoring leakage of a liquid cargo film tank according to claim 10, characterized in that: In step S5, the amount of protective gas injected into the protective gas input end is less than the amount of gas extracted from the gas output end, so that the shielding layer at the leakage point of the membrane tank is in a negative pressure state.

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