Liquid cargo film tank leakage monitoring system and monitoring method

Abstract

The invention discloses a liquid cargo film tank leakage monitoring system and monitoring method, and belongs to the technical field of natural gas transportation and storage, the liquid cargo film tank leakage monitoring system comprises a plurality of first-level monitoring subsystems, the first-level monitoring subsystems are arranged in the circumferential direction of a film tank in a surrounding mode, and the first-level monitoring subsystems are communicated through pipelines; the protective gas input end and the gas output end are connected with each primary monitoring subsystem through pipelines; each primary monitoring subsystem comprises two gas sensing parts, the gas sensing parts are attached to the outer wall of the thin film tank, and a first pressure difference detection mechanism is arranged between the two gas sensing parts. According to the system, the primary monitoring subsystems are arranged on all the faces of the thin film tank, the pressure of all the areas of the thin film tank is monitored through the secondary monitoring subsystems, and accurate monitoring of natural gas leakage point positions is achieved; and gas input and extraction are performed on the fixed-point area of the thin film tank through the protective gas input end and the gas output end, natural gas leakage suppression at the leakage point is achieved, and the natural gas leakage problem is effectively relieved.

Description

Technical Field

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

[0002] As a clean and efficient energy source, liquefied natural gas is mainly transported through low-temperature atmospheric pressure or pressure tanks. Due to its low temperature and high compression characteristics, the transportation of liquefied natural gas has higher sealing and stability requirements. Based on the transportation regulations of liquefied natural gas, natural gas storage tanks are usually required to have a complete or partially complete secondary shielding space cargo containment system, and the secondary shielding space needs to be filled with dry protective gas to ensure the safety of the transportation vehicle in the event of cargo leakage.

[0003] Existing liquefied natural gas storage tanks are mainly equipped with pressure monitors and gas monitors in the shielding layer to monitor whether there is a natural gas leak in the tank. However, in the actual LNG transportation process, the size of the LNG tank is relatively large, and the conventional monitoring method can only monitor whether there is a leak in the tank, but cannot accurately know the specific leak location; at the same time, when the tank actually leaks, it is impossible to control the diffusion and leakage of natural gas in the shielding layer of the tank, and it is impossible to effectively solve the safety hazards. Summary of the invention

[0004] In response to one or more of the above defects or improvement needs of the prior art, the present invention provides a liquid cargo membrane tank leakage monitoring system to solve the problem that the existing LNG transport storage tanks cannot effectively monitor and alleviate natural gas leakage when they are damaged and leaking.

[0005] To achieve the above object, the present invention provides a liquid cargo film tank leakage monitoring system, which is arranged in the shielding layer between the film tank and the tank body, and comprises: 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 one side of the film tank; 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.

[0006] 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; 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.

[0007] 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; 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.

[0008] 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.

[0009] 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.

[0010] 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.

[0011] 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: 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 the first pressure difference detection mechanism, which is the leakage point of the membrane tank.

[0012] As a further improvement of the present invention, the protective gas input to the protective gas input end is nitrogen, 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 from the adjacent second level monitoring subsystem of the second level monitoring subsystem through a pipeline; S103, the protective gas input end injects protective gas into the shielding layer through the previous secondary monitoring subsystem that extracts gas, and the gas output end extracts gas from the next adjacent secondary monitoring subsystem through a pipeline; S104, repeat step S103 until each secondary monitoring subsystem completes the input of protective gas.

[0013] As a further improvement of the present invention, step S2 includes: the protective gas input end uses a first-level monitoring subsystem at the side wall of the membrane tank to inject protective gas into the shielding layer, and the gas output end uses a first-level monitoring subsystem away from the side of the protective gas input end to extract the gas in the shielding layer.

[0014] As a further improvement of the present invention, the present invention further comprises step S4: Spraying liquid natural gas on the top layer of the membrane tank to cool the membrane tank; Adjust the shielding gas input and output to increase the shielding layer pressure.

[0015] As a further improvement of the present invention, the present invention further comprises step S5: 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 from the secondary monitoring subsystem circumferentially through the secondary monitoring subsystem.

[0016] As a further improvement of the present invention, 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.

[0017] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0018] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects: (1) The liquid cargo membrane tank leakage monitoring system of the present invention completely covers the periphery of the membrane tank through the primary monitoring subsystem to achieve comprehensive monitoring of the periphery of the membrane tank; and uses each primary monitoring subsystem to form multiple secondary monitoring subsystems on each surface of the membrane tank to achieve peripheral area monitoring of the membrane tank, so as to improve the accurate monitoring of the leakage position of the membrane tank; secondly, the present application extends two gas sensing parts to the peripheral wall surface of the membrane tank through the secondary monitoring subsystem. When there is a leak on the surface of the membrane tank, the gas sensing part near the leakage point will be impacted by the leaking natural gas, causing the air pressure at the point to fluctuate. The pressure difference between the leakage point and the non-leakage point is identified by the first pressure difference detection mechanism, and then the exact location of the natural gas leak can be known according to the area where the secondary monitoring subsystem is located. In addition, the present application can output protective gas to the natural gas leakage area in a direction through the two-way valve between the protective gas input end and the first-level monitoring subsystem, suppress the natural gas leakage at the leakage point by increasing the output of the protective gas, and pump gas to the first-level monitoring subsystem next to the leakage point through the gas output end, so as to promptly remove the gas around the leakage point, prevent the natural gas from spreading to the entire shielding layer, and ensure that the pressure in the shielding layer is maintained balanced.

[0019] (2) The liquid cargo membrane tank leakage monitoring system of the present invention, in addition to monitoring the leakage situation in each area of ​​the membrane tank through the secondary monitoring subsystem, can also monitor the leakage situation in different secondary monitoring subsystem areas through the third pressure difference detection mechanism. During the membrane tank leakage process, when the secondary monitoring subsystem covers a small area, the two gas sensing parts of a single secondary monitoring subsystem are covered by the leaking natural gas, resulting in the inability of the first pressure difference detection mechanism to accurately identify. At this time, the air pressure of the entire secondary monitoring subsystem in the gas leakage area is affected by the leaking natural gas, which will be greater than the pressure of the unaffected secondary monitoring subsystem next to it. At this time, the leakage point can be identified by the third pressure difference detection mechanism to make up for the problem that the first pressure difference detection mechanism cannot identify it in time. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the overall structure of the liquid cargo membrane tank leakage monitoring system in an embodiment of the present invention; Figure 2 is a schematic diagram of the structure of a primary monitoring subsystem in an embodiment of the present invention; Figure 3 is a schematic diagram of the structure of a secondary monitoring subsystem in an embodiment of the present invention; Figure 4 Schematic diagram of airflow of protective gas replacing air in the method for monitoring leakage of liquid cargo membrane tanks according to an embodiment of the present invention; Figure 5Schematic diagram of the air flow of local gas replacement on the outer wall of a membrane tank in the method for monitoring leakage of a liquid cargo membrane tank according to an embodiment of the present invention; Figure 6 Schematic diagram of airflow forming a protective airflow around the membrane tank in the liquid cargo membrane tank leakage monitoring method according to an embodiment of the present invention; Figure 7 It is a schematic flow chart of a method for monitoring leakage of a liquid cargo membrane tank according to an embodiment of the present invention; Figure 8 It is a schematic diagram of the process of forming protection on the outside of the film tank in an embodiment of the present invention.

[0021] In all the drawings, the same reference numerals represent the same technical features, specifically: 1. Primary monitoring subsystem; 2. Secondary monitoring subsystem; 3. Protective gas input terminal; 4. Gas output terminal; 5. Gas sensing unit; 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 DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with 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 intended 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.

[0023] In the description of the present invention, it should be understood that, unless otherwise specified, terms such as “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0024] In addition, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0025] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0026] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0027] Example

[0028] The liquid cargo membrane tank leakage monitoring system in the present application is suitable for the monitoring and protection of liquid cargoes such as LNG, methanol, ethanol, and ethane during storage and transportation, and is particularly suitable for ship LNG transportation monitoring. The embodiments of the present application are mainly described using liquid natural gas leakage as an example.

[0029] See also Figure 1 to Figure 8The liquid cargo membrane tank leakage monitoring system in the preferred embodiment of the present invention is arranged in the shielding layer between the membrane tank 12 and the tank body, and is used to monitor and protect the gas on the periphery of the membrane tank 12 to prevent the natural gas in the membrane tank 12 from directly leaking to the outside. Specifically, the liquid cargo membrane tank leakage monitoring system 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 first-level monitoring subsystem 1; at the same time, the liquid cargo membrane tank leakage monitoring system also includes a protective gas input terminal 3 and a gas output terminal 4, wherein the protective gas input terminal 3 is connected to each first-level monitoring subsystem 1 through a pipeline, and the gas output terminal 4 is also connected to each first-level monitoring subsystem 1 through a pipeline. Furthermore, each first-level monitoring subsystem 1 includes multiple second-level monitoring subsystems 2, and the multiple second-level monitoring subsystems 2 belonging to the same first-level monitoring subsystem 1 are distributed in different areas of one side of the film tank 12, and each second-level monitoring subsystem 2 includes two spaced-apart gas sensing parts 5, the gas sensing parts 5 have openings, and the opening of any gas sensing part 5 is connected to the protective gas input end and the gas output end; the gas sensing part 5 is attached to the outer wall of the film tank 12, and a first pressure difference detection mechanism 6 is provided between the two gas sensing parts 5, and the gas pressure difference at the two gas sensing parts 5 can be measured by the first pressure difference detection mechanism 6.

[0030] Specifically, the liquid cargo membrane tank leakage monitoring system in the present application completely covers the periphery of the membrane tank 12 through the first-level monitoring subsystem 1, thereby realizing comprehensive monitoring of the periphery of the membrane tank 12; and each first-level monitoring subsystem 1 is used to form multiple second-level monitoring subsystems 2 on each surface of the membrane tank 12, so as to realize monitoring of the peripheral area of ​​the membrane tank 12, so as to improve the accurate monitoring of the leakage position of the membrane tank 12; secondly, the present application extends two gas sensing parts 5 to the peripheral wall surface of the membrane tank 12 through the second-level monitoring subsystem 2. When there is a leak on the surface of the membrane tank 12, the gas sensing part 5 near the leakage point will be impacted by the leaking natural gas, causing the air pressure at the point to fluctuate, and the pressure difference between the leakage point and the non-leakage point is identified by the first pressure difference detection mechanism 6, and then the exact location of the natural gas leak can be known according to the area where the second-level monitoring subsystem 2 is located. Furthermore, the present application can output protective gas to the natural gas leakage area in a directional manner through a two-way valve between the protective gas input terminal 3 and the primary monitoring subsystem 1, suppress the natural gas leakage at the leakage point by increasing the output of the protective gas, and pump gas to the primary monitoring subsystem 1 next to the leakage point through the gas output terminal 4, so as to promptly remove the gas around the leakage point and ensure that the pressure in the shielding layer remains balanced.

[0031] Specifically, the present application can divide the membrane tank 12 into multiple areas, and arrange a primary monitoring subsystem 1 for each area of ​​the membrane tank 12. Each secondary monitoring subsystem 2 corresponding to a primary monitoring subsystem 1 is located in the same partition to monitor different areas of the membrane tank 12 respectively; when there is a leak in the membrane tank 12, the leak point can be quickly located according to the location of the first differential pressure detection mechanism 6, which is convenient for subsequent maintenance and repair of the membrane 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 periphery of the membrane tank 12 to monitor the membrane tank 12 in a partitioned manner, so as to facilitate the first differential pressure detection mechanism 6 to detect and identify the leak point.

[0032] Further, as an optional embodiment of the present invention, the protective gas input terminal 3 and the gas output terminal 4 in the present application are both connected to each primary monitoring subsystem 1 through a circulation pipeline; wherein the circulation pipeline includes a first circulation pipeline 7 and a second circulation pipeline 8, and the first circulation pipeline 7 and the second circulation pipeline 8 are both arranged around the circumference of the membrane tank 12, and each primary monitoring subsystem 1 is connected to the first circulation pipeline 7 and the second circulation pipeline 8. Specifically, the present application forms a first circulation pipeline 7 and a second circulation pipeline 8 on the periphery of the primary monitoring subsystem 1, and the protective gas input terminal 3 and the gas output terminal 4 are both connected to the first circulation pipeline 7 and the second circulation pipeline 8, which enables the protective gas emitted by the protective gas input terminal 3 and the gas extracted by the gas output terminal 4 to adjust the gas transmission direction according to demand without conflicting with each other, thereby realizing the protective gas input and gas extraction in the fixed point area of ​​the outer wall of the membrane tank 12.

[0033] Optionally, the shielding gas input end 3 in the present application is connected to a shielding gas input source, and the shielding gas can be one of nitrogen, argon or helium. It is worth noting that when different shielding gases are selected, the mass ratio of the shielding gas to air and natural gas needs to be considered to control the flow direction of the gas in the shielding layer. When the shielding gas is argon or helium, when the air in the shielding layer is evacuated, the shielding gas needs to be injected from the top of the film tank 12 and the gas needs to be extracted from the bottom of the film tank 12. Optionally, the gas output end 4 in the present application is provided with a pump body for extracting the gas in the shielding layer.

[0034] Further, as an optional embodiment of the present invention, the second circulation pipeline 8 in the present application is also provided with a plurality of second differential pressure detection mechanisms 9 in the circumferential direction, and the second circulation pipeline 8 is provided with multiple sections corresponding to each primary monitoring subsystem 1, and each section of the second circulation pipeline 8 is provided with a second differential pressure detection mechanism 9 in parallel; each second differential pressure detection mechanism 9 is connected to form a loop through a pipeline, and valves are provided at both ends of each second differential pressure detection mechanism 9. The pressure of each primary monitoring subsystem 1 can be monitored by the second differential pressure detection mechanism 9 to ensure that the pressure in some areas is not too high when the air pressure around the membrane tank 12 is monitored as a whole. When a leak occurs in a fixed point area of ​​the membrane tank 12, it is necessary to inject protective gas at the corresponding point and extract gas from the side. The pressure difference of the shielding layer at the leaking point can be monitored by the second differential pressure detection mechanism 9. When the pressure at the first monitoring subsystem is too high or too low, the pressure at other areas needs to be adjusted accordingly so that the overall pressure of the shielding layer is within a safe range.

[0035] Further, as an optional embodiment of the present invention, a third pressure difference detection mechanism 10 is also provided between any two adjacent secondary monitoring subsystems 2 in the present application, and the third pressure difference detection mechanism 10 can measure the gas pressure difference between the two adjacent secondary monitoring subsystems 2. In addition to monitoring the leakage situation in each area of ​​the film tank 12 through the secondary monitoring subsystem 2, the present application can also monitor the leakage situation in different areas of the secondary monitoring subsystem 2 through the third pressure difference detection mechanism 10. During the leakage of the film tank 12, when the secondary monitoring subsystem 2 covers a small area, the two gas sensing parts 5 of the single secondary monitoring subsystem 2 are covered by the leaking natural gas, resulting in the inability of the first pressure difference detection mechanism 6 to accurately identify. At this time, the air pressure of the entire secondary monitoring subsystem 2 in the gas leakage area is affected by the leaking natural gas, which will be greater than the pressure of the unaffected secondary monitoring subsystem 2 on the side. At this time, the leakage point can be identified by the third pressure difference detection mechanism 10 to make up for the problem that the first pressure difference detection mechanism 6 cannot identify it in time.

[0036] It is worth noting that the first pressure differential detection mechanism 6, the second pressure differential detection mechanism 9 and the third pressure differential detection mechanism 10 in the present application are all connected to other components of the liquid cargo membrane tank leakage monitoring system through pipelines, and based on the detection mechanism of the pressure differential detection mechanism, each detection mechanism is connected to the overall pipeline of the system, so that the connecting pipelines of each pressure differential detection mechanism can form a circulation loop in the liquid cargo membrane tank leakage monitoring system.

[0037] Further, as an optional embodiment of the present invention, the two gas sensing parts 5 of the same secondary monitoring subsystem 2 in the present application are connected through a branch pipe, and valves are provided on the branch pipes connecting the two gas sensing parts 5. The secondary monitoring subsystem 2 in the present application mainly determines whether there is a natural gas leak at the monitoring point by the size of the airflow received by the gas sensing part 5. When the first pressure difference 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 flow to the leakage point to reduce the loss of protective gas.

[0038] It is worth noting that the pressure difference detection mechanism in the present application is directional. When the airflow at both ends of the pressure difference detection mechanism is unbalanced, the pressure difference on both sides can be identified through the pressure difference detection mechanism to determine the specific point of natural gas leakage.

[0039] Further, as an optional embodiment of the present invention, the gas sensing unit 5 in the present application includes a connecting pipeline, and a plurality of tail pipes 11 are connected to the connecting pipeline, and the plurality of tail pipes 11 are open at one end away from the connecting pipeline. The gas sensing unit 5 in the present application is mainly connected to the side wall of the membrane tank 12 through the tail pipe 11. When there is a natural gas leak at the corresponding point, the natural gas is input into the tail pipe 11, so that the pressure at both ends of the two gas sensing units 5 is unbalanced, and the first pressure difference detection mechanism 6 can detect the pressure fluctuation accordingly to identify the natural gas leakage point.

[0040] Furthermore, with respect to the liquid cargo membrane tank leakage monitoring system in the present application, the present application also includes a liquid cargo membrane tank leakage monitoring method, which includes the following steps: S1, replacing the air in the shielding layer with protective gas to form protection outside the film tank 12; S2, the protective gas input end 3 continuously fills the shielding layer with protective gas, and the gas output end 4 continuously extracts the gas in the shielding layer to form a protective gas flow around the membrane tank 12; S3. Obtain the pressure difference detection data at each first pressure difference detection mechanism 6, establish the pressure difference-time change diagram of each first pressure difference detection mechanism 6, and obtain the initial pressure difference change point in each first pressure difference detection mechanism 6. The initial pressure difference change point of the first pressure difference detection mechanism 6 is the leakage point of the membrane tank 12.

[0041] Specifically, the liquid cargo membrane tank leakage monitoring method in the present application can replace the air inside the shielding layer with protective gas through the protective gas input terminal 3 and the gas output terminal 4, and use the pipelines of the primary monitoring subsystem 1 and the secondary monitoring subsystem 2 to form a protective airflow outside the membrane layer to achieve protection of the membrane tank 12. When the outer part of the membrane tank 12 is damaged and causes natural gas leakage, the air pressure at the leakage point will increase accordingly, and the leaked natural gas will spread around with the leakage point as the center, and the pressure difference at 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 goes from the peak value to zero; at the same time, the leaked natural gas spreads to the surroundings, and the secondary monitoring subsystem 2 adjacent to the leakage point also corresponds to the state where the pressure value rises to zero; thus, it spreads to the next adjacent area, and the area is finally stable. It can be seen that when the membrane tank 12 leaks, the first differential pressure detection mechanism 6 at the leakage point first displays differential pressure data, and then returns to zero; at the next time node, the first differential pressure detection mechanism 6 adjacent to the leakage point displays differential pressure data, and then returns to zero, and so on. The leakage point of the membrane tank 12 can be determined by the first node where the differential pressure data appears and the location of the corresponding secondary monitoring subsystem 2. At the same time, when the membrane tank 12 leaks less natural gas, the data fluctuation of a single first differential pressure detection mechanism 6 may be ignored. Therefore, the differential pressure data of the surrounding first differential pressure detection mechanisms 6 and the first differential pressure detection mechanism 6 at the leakage point need to be verified to ensure the accuracy of the membrane tank 12 leakage monitoring.

[0042] Further, as an optional embodiment of the present invention, the protective gas inputted by the protective gas input terminal 3 in the present application is nitrogen, and the external protection of the membrane tank 12 is formed by specifically including the following steps: S101, the protective gas input end 3 inputs the protective gas from the bottom of the membrane tank 12 through the pipeline, and the gas output end 4 draws the protective gas from the top of the membrane tank 12 through the pipeline; S102, the protective gas input end 3 injects 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 gas from the adjacent secondary monitoring subsystem 2 of the secondary monitoring subsystem 2 through the pipeline; S103, the protective gas input end 3 injects protective gas into the shielding layer through the secondary monitoring subsystem 2 that extracts gas last, and the gas output end 4 extracts gas from the next adjacent secondary monitoring subsystem 2 through a pipeline; S104, repeat step S103 until each secondary monitoring subsystem 2 completes the input of protective gas.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] Furthermore, as an optional embodiment of the present invention, the present application also includes step S4: spraying liquid natural gas on the top layer inside the membrane tank 12 to cool the membrane tank 12; adjusting the input and output of the protective gas so that the pressure of the shielding layer increases. When a natural gas leak occurs in the membrane tank 12, more gaseous natural gas will be generated in the membrane tank 12, the internal pressure of the membrane tank 12 will increase, and the membrane tank 12 as a whole will tend to expand outward, which will also squeeze the shielding layer space accordingly. In order to avoid excessive expansion of the membrane tank 12, the present application needs to spray liquid natural gas on the top layer inside the membrane tank 12 on the one hand to reduce the flash steam content inside the membrane tank 12, reduce the internal pressure of the membrane tank 12, and slow down the expansion of the membrane 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 shielding layer pressure is increased to limit the expansion of the membrane tank 12 from the outside.

[0047] Furthermore, as an optional embodiment of the present invention, the present application further includes step S5: The protective gas input end 3 increases the amount of protective gas injected into the secondary monitoring subsystem 2 at the leakage point of the membrane tank 12; the gas output end 4 takes the secondary monitoring subsystem 2 at the leakage point of the membrane tank 12 as the center, and extracts gas from the secondary monitoring subsystem 2 around the secondary monitoring subsystem 2. When natural gas leaks from the outer wall of the membrane tank 12, it is necessary to increase the output of protective gas through the secondary monitoring subsystem 2 at the leakage point, and by increasing the pressure at the leakage point, the pressure difference between the inside and outside of the leakage point of the membrane tank 12 is reduced to suppress 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 the spread of natural gas to the entire shielding layer space.

[0048] Further, as an optional embodiment of the present invention, in step S5 of the present application, the amount of protective gas injected into the protective gas input terminal 3 is less than the amount of gas extracted from the gas output terminal 4, so that the shielding layer at the leakage point of the membrane tank 12 is in a negative pressure state. By adjusting the gas output and gas input, the leakage point is in a negative pressure state, and the negative pressure will correspond to the extraction of natural gas at the leakage point, causing the natural gas content in the output gas of the gas output terminal 4 to increase, so that the gas monitoring mechanism at the tail end of the gas output terminal 4 can identify the natural gas leak, so as to prompt the staff to perform subsequent inspection and maintenance work. It is worth noting that at this time, the adjustment of the leakage point to a negative pressure state is only carried out 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 amount of protective gas injected into the protective gas input terminal 3 and increase the pressure at the leakage point to suppress the leakage of natural gas.

[0049] It will be easily understood by those skilled in the art 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 substitutions and improvements made within the spirit and principles of the present invention should be included in 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 includes two gas sensing parts arranged at intervals, each of which has an opening, and the opening of any one 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.

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 membrane 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: 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.

5. 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.

6. 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.

7. A method for monitoring leakage of a liquid cargo film tank, which is performed by monitoring leakage of a liquid cargo film tank as described in any one of claims 1 to 6, 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.

8. The method for monitoring leakage of a liquid cargo film tank according to claim 7, 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 from the adjacent second level monitoring subsystem of the second level monitoring subsystem through a pipeline; S103, the protective gas input end injects protective gas into the shielding layer through the previous secondary monitoring subsystem that extracts gas, and the gas output end extracts gas from the next adjacent secondary monitoring subsystem through a pipeline; S104, repeat step S103 until each secondary monitoring subsystem completes the input of protective gas.

9. The method for monitoring leakage of a liquid cargo film tank according to claim 7, 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.

10. The method for monitoring leakage of a liquid cargo film tank according to claim 7, 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.

11. The method for monitoring leakage of a liquid cargo film tank according to claim 7, 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.

12. The method for monitoring leakage of a liquid cargo film tank according to claim 11, 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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