Liquid cargo storage system

Abstract

The utility model discloses a liquid cargo storage system, which belongs to the technical field of natural gas transportation and storage, and comprises a film tank and a tank body, a plurality of primary monitoring subsystems are arranged between the film tank and the tank body, and the primary 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 a plurality of branch pipes, openings are formed in the tail ends of the branch pipes, and air pressure detection devices are arranged on the branch pipes and can measure the air pressure at the branch pipes. The primary monitoring subsystems are arranged on all the faces of the thin film tank, the branch pipes and the air pressure detection devices of the primary monitoring subsystems are used for monitoring the pressure of all the areas of the thin film tank, 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 utility model belongs to the technical field of natural gas transportation and storage, and particularly relates to a liquid cargo storage system. 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 are mainly equipped with pressure monitors, gas monitors, etc. in the shielding layer to monitor whether there is natural gas leakage in the tank. However, in the actual LNG transportation process, the LNG tank has a large size, and the conventional monitoring method can only monitor whether there is 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 hazard cannot be effectively solved. Summary of the Utility Model

[0004] In view of one or more of the above-mentioned defects or improvement requirements of the prior art, the utility model provides a liquid cargo storage system to solve the problem that when the existing liquid cargo transportation is damaged and leaks, it is impossible to effectively monitor and alleviate the natural gas leakage.

[0005] To achieve the above object, the utility model provides a liquid cargo storage system, which includes:

[0006] A thin-film tank for storing liquid natural gas;

[0007] A tank body disposed on the outer periphery of the thin-film tank, and a shielding layer is formed between the thin-film tank and the tank body;

[0008] A plurality of primary monitoring subsystems are provided in the shielding layer, the outer periphery of the thin-film tank is divided into a plurality of protection areas, and each primary monitoring subsystem is correspondingly arranged with a protection area; each primary monitoring subsystem is interconnected through pipelines, and two-way valves are provided on the pipelines between each primary monitoring subsystem;

[0009] A protective gas input end, one end of which passes through the tank body and is connected to an external protective gas source, and the other end is connected to each primary monitoring subsystem through a pipeline;

[0010] A gas output end, one end of which passes through the tank body, and the other end of which is connected to each of the first-level monitoring subsystems through a pipeline;

[0011] Each of the first-level monitoring subsystems includes multiple branch pipes. The branch pipes of the same first-level monitoring subsystem are distributed at different positions of the same protection area of ​​the film tank. The tail end of the branch pipe has an opening, and an air pressure detection device is provided on the branch pipe. The air pressure detection device can measure the air pressure at the branch pipe.

[0012] As a further improvement of the present invention, the primary monitoring subsystem includes a plurality of secondary monitoring subsystems, and the plurality of secondary monitoring subsystems belonging to the same primary monitoring subsystem are distributed in the same protection area around the film tank;

[0013] Each of the secondary monitoring subsystems comprises two spaced apart gas sensing parts, each of the gas sensing parts has an opening, the opening of any of the gas sensing parts is connected to the protective gas input end and the gas output end, 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;

[0014] The gas sensing unit includes a connecting pipeline, and a plurality of tail pipes are connected to the connecting pipeline. The plurality of tail pipes are open at one end away from the connecting pipeline.

[0015] 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;

[0016] The circulation pipeline comprises a first circulation pipeline and a second circulation pipeline;

[0017] 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.

[0018] 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;

[0019] 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.

[0020] As a further improvement of the present utility model, a third differential pressure detection mechanism is provided between any adjacent secondary monitoring subsystems, and the third differential pressure detection mechanism can measure the differential pressure between two adjacent secondary monitoring subsystems.

[0021] As a further improvement of the present utility model, two gas sensing parts of the same secondary monitoring subsystem are connected through a branch pipe, and valves are provided on the branch pipes connected to the two gas sensing parts.

[0022] As a further improvement of the present utility model, a vacuum pump is also provided on the pipeline of the gas output end.

[0023] As a further improvement of the present utility model, a gas monitoring mechanism is also connected to the gas output end, and the gas monitoring mechanism is used to identify the type of gas output from the gas output end.

[0024] As a further improvement of the present utility model, the flexible tank is also connected with a liquid cargo supply device, and the liquid cargo supply device is connected to the top of the flexible tank through a pipeline.

[0025] As a further improvement of the present utility model, a buffer tank is also provided in the flexible tank, the buffer tank is arranged at the top of the flexible tank, the buffer tank is connected to the liquid cargo supply device through a pipeline, and the buffer tank is communicated with the top of the flexible tank through multiple branch pipes;

[0026] Valves are provided on the multiple branch pipes, and the open ends of the multiple branch pipes are distributed in different areas of the top of the flexible tank.

[0027] As long as the above-mentioned improved technical features do not conflict with each other, they can be combined with each other.

[0028] Generally speaking, compared with the prior art, the beneficial effects of the above technical solutions conceived by the present utility model include:

[0029] (1) The liquid cargo storage system of the present utility model covers the external area of the membrane tank through the primary monitoring subsystem, monitors different areas of the membrane tank by using the branch pipes of the primary monitoring subsystem, and detects the air pressure at different areas through the air pressure detection devices on the branch pipes to realize the monitoring of the pressures in different areas of the membrane tank. When the membrane tank leaks, the pressure detected by the air pressure detection device at the corresponding area fluctuates to obtain the accurate position of the membrane tank leak. At the same time, in this application, the protective gas input end and the gas output end are connected to each primary monitoring subsystem through pipelines. When the primary monitoring subsystem leaks, the protective gas input end can be controlled by a valve to perform fixed-point delivery of the protective gas to this area, so as to increase the gas pressure outside the membrane tank at the leak point, reduce the pressure difference between the inside and outside of the membrane tank wall surface, and slow down the leakage of natural gas. At the same time, the gas in the non-leaking area of the membrane tank is pumped away through the gas output end to stabilize the pressure of the shielding layer and pump away the generated natural gas to prevent the natural gas from spreading to the entire area of the shielding layer.

[0030] (2) The liquid cargo storage system of the present utility model has the secondary monitoring subsystems distributed in different areas on the outer periphery of the membrane tank. When the membrane tank leaks, the accurate identification of the leak point can be realized through the secondary monitoring subsystem. At the same time, when the leak point of the membrane tank is identified, the protective gas can be transported along the pipeline to the area where the corresponding secondary monitoring subsystem is located through the protective gas input end, and by increasing the pressure at the leak point, the pressure difference between the inside and outside of the membrane tank wall surface can be reduced to slow down the leakage of natural gas. Moreover, the secondary monitoring subsystems adjacent to the secondary monitoring subsystem at the leak point can be connected to the gas output end through the differential pressure detection mechanism loop and the circulation pipeline to pump out the natural gas generated at the leak point, prevent the leaked natural gas from spreading to other areas, and ensure the safety inside the tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the overall structural schematic diagram of the liquid cargo storage system in the embodiment of the present utility model;

[0032] Figure 2 is the structural schematic diagram of the primary monitoring subsystem in the embodiment of the present utility model;

[0033] Figure 3 is the structural schematic diagram of the secondary monitoring subsystem in the embodiment of the present utility model;

[0034] Figure 4 is the air flow schematic diagram of the protective gas replacing air in the monitoring method of the liquid cargo storage system in the embodiment of the present utility model;

[0035] Figure 5 is the air flow schematic diagram of the partial gas replacement on the outer wall of the membrane tank in the monitoring method of the liquid cargo storage system in the embodiment of the present utility model;

[0036] Figure 6It is a schematic diagram of the protective air flow formed on the outer periphery of the thin-film tank in the monitoring method of the liquid cargo storage system according to the embodiment of the present utility model.

[0037] In all the drawings, the same reference numerals represent the same technical features, specifically:

[0038] 1. Primary monitoring subsystem; 2. Secondary monitoring subsystem; 3. Protective gas input end; 4. Gas output end; 5. Gas sensing part; 6. First pressure difference detection mechanism; 7. First circulation pipeline; 8. Second circulation pipeline; 9. Second pressure difference detection mechanism; 10. Third pressure difference detection mechanism; 11. Tail pipe; 12. Thin-film tank; 13. Tank body. Specific embodiments

[0039] In order to make the objectives, technical solutions and advantages of the present utility model clearer, the present utility model will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present utility model and are not used to limit the present utility model. In addition, the technical features involved in the various embodiments of the present utility model described below can be combined with each other as long as they do not conflict with each other.

[0040] In the description of the present utility model, 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. It is only for the convenience of describing the present utility model 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 cannot be understood as a limitation to the present utility model.

[0041] In addition, unless otherwise specified, the terms "first" and "second" are only used for descriptive purposes and cannot be understood 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 utility model, "a plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0042] In the present utility model, unless otherwise clearly defined and limited, terms such as "installation", "connection", "attachment", "fixation" and the like shall be construed in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral body; it may be a mechanical connection or an electrical connection; it may be a direct connection or an indirect connection through an intermediate medium, and it may be the internal communication of two components or the interaction relationship between two components, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model may be understood according to specific circumstances.

[0043] In the present utility model, 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 in indirect 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.

[0044] Embodiment

[0045] The liquid cargo storage 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.

[0046] Please refer to Figures 1 - 6, in the preferred embodiment of the present utility model, the liquid cargo storage system includes a membrane tank 12 for storing liquefied natural gas; a tank body 13 disposed on the outer periphery of the membrane tank 12 for forming an external protection for the membrane tank 12; and a shielding layer is formed between the membrane tank 12 and the tank body 13 for forming a gas protection on the outer periphery of the membrane tank 12 to prevent natural gas from directly escaping to the outside when the membrane tank 12 is damaged. A plurality of first-level monitoring subsystems 1 are provided in the shielding layer; the outer periphery of the membrane tank 12 is correspondingly divided into a plurality of protection areas, and each first-level monitoring subsystem 1 is arranged in one-to-one correspondence with the protection area, and the first-level monitoring subsystems 1 are interconnected through pipelines, and two-way valves are provided on the pipelines between the first-level monitoring subsystems 1. The liquid cargo storage system further includes a protective gas input end 3 and a gas output end 4, wherein one end of the protective gas input end 3 passes through the tank body 13 and is connected to an external protective gas source, and the other end is connected to each first-level monitoring subsystem 1 through a pipeline; one end of the gas output end 4 also passes through the tank body 13 for discharging the gas generated in the shielding layer to the outside, and the other end is connected to each first-level monitoring subsystem 1. At the same time, each first-level monitoring subsystem 1 includes a plurality of branch pipes. The branch pipes of the same first-level monitoring subsystem 1 are distributed at different positions in the same protection area of the membrane tank 12, and the tail ends of the branch pipes have openings, and a pressure detection device is provided on the branch pipes, and the pressure detection device can measure the pressure at the branch pipes.

[0047] The liquid cargo storage system of the present utility model covers the external area of the membrane tank 12 through the first-level monitoring subsystem 1, monitors different areas of the membrane tank 12 by using the branch pipes of the first-level monitoring subsystem 1, and detects the pressure at different areas through the pressure detection device on the branch pipes to realize the monitoring of the pressure in different areas of the membrane tank 12. When the membrane tank 12 leaks, the pressure detected by the pressure detection device at the corresponding area fluctuates to obtain the accurate position of the leak of the membrane tank 12; at the same time, in this application, the protective gas input end 3 and the gas output end 4 are connected to each first-level monitoring subsystem 1 through pipelines. When the first-level monitoring subsystem 1 leaks, the protective gas input end 3 can be controlled by a valve to perform fixed-point delivery of the protective gas to this area to increase the gas pressure outside the membrane tank 12 at the leak point, reduce the pressure difference between the inside and outside of the wall of the membrane tank 12, and slow down the leakage of natural gas; at the same time, the gas in the non-leaking area of the membrane tank 12 is pumped away through the gas output end 4 to stabilize the pressure of the shielding layer and pump away the generated natural gas to prevent the natural gas from spreading to the entire area of the shielding layer.

[0048] Further, as an optional embodiment of the utility model, the primary monitoring subsystem 1 in the present application includes multiple secondary monitoring subsystems 2, and the multiple secondary monitoring subsystems 2 belonging to the same primary monitoring subsystem 1 are distributed in the same protection area around the membrane tank 12; each secondary monitoring subsystem 2 includes two gas sensing parts 5 arranged at intervals, the gas sensing part 5 has an opening, and the opening of any gas sensing part 5 is connected to the protective gas input end 3 and the gas output end 4 through a pipeline; 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 at the two gas sensing parts 5 can be measured by the first pressure difference detection mechanism 6. Specifically, the gas sensing part 5 includes a connecting pipeline, and multiple tail pipes 11 are provided on the connecting pipeline, and the multiple tail pipes 11 are opened at one end away from the connecting pipeline. In order to facilitate the overall layout of the protection system, the multiple branch pipes of the primary monitoring subsystem 1 of the present application are divided into each secondary monitoring subsystem 2, and the present application completes the identification of the leakage point through two gas sensing parts 5 with openings and the first pressure difference detection mechanism 6. When natural gas leaks from the membrane tank 12 , the gas sensing unit 5 close to the leakage point is impacted by the natural gas, while the other gas sensing unit 5 far from the leakage point is impacted less, thereby forming a pressure difference that is recognized by the first pressure difference detection mechanism 6 .

[0049] 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 perform zone monitoring on the membrane tank 12, so as to facilitate the first pressure difference detection mechanism 6 to detect and identify the leakage point.

[0050] Further, as an optional embodiment of the present utility model, 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.

[0051] Optionally, a protective gas input source is connected to the protective gas input end 3 in this application. The protective gas can be one of nitrogen, argon, or helium. It should be noted that when different protective gases are selected, the mass ratios of the protective gas to air and natural gas need to be considered to facilitate the control of the gas flow direction within the shielding layer. When the protective gas is argon or helium, when evacuating the air within the shielding layer, the protective gas needs to be injected from the top of the thin film tank 12, and the gas is extracted from the bottom of the thin film tank 12. Optionally, a pump body is provided at the gas output end 4 in this application to extract the gas within the shielding layer.

[0052] Furthermore, as an optional embodiment of the present utility model, a plurality of second differential pressure detection mechanisms 9 are also provided circumferentially on the second circulation pipeline 8 in this application. The second circulation pipeline 8 is correspondingly set in multiple segments for each first-level monitoring subsystem 1, and a second differential pressure detection mechanism 9 is arranged in parallel for each segment of the second circulation pipeline 8; each second differential pressure detection mechanism 9 is connected into a loop through pipelines, and valves are provided 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 large when the air pressure around 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, it is necessary to inject the protective gas at the corresponding point and extract the gas from the side. Through this second differential pressure detection mechanism 9, the differential pressure situation of the shielding layer at the leakage point can be monitored. When the pressure at this first monitoring subsystem is too large or too small, the pressure in other areas needs to be adjusted correspondingly to keep the overall pressure of the shielding layer within a safe range.

[0053] Furthermore, as an optional embodiment of the present utility model, a third differential pressure detection mechanism 10 is also provided between any two adjacent second-level monitoring subsystems 2 in this 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 this 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.

[0054] Furthermore, as an alternative embodiment of the present utility model, the two gas sensing parts 5 of the same secondary monitoring subsystem 2 in this application are both connected through branch pipes, and valves are provided on the branch pipes where the two gas sensing parts 5 are connected. In this application, the secondary monitoring subsystem 2 mainly determines whether there is natural gas leakage at the monitoring point based on the magnitude of the airflow received by the gas sensing part 5. When the first differential pressure detection mechanism 6 identifies the leakage point, in order to improve the suppression 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 gas to the leakage point, so as to reduce the loss of the protective gas.

[0055] It should be noted that the differential pressure detection mechanism in this application has directivity. When the airflow at both ends of the differential pressure detection mechanism is 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.

[0056] Optionally, a vacuum pump is provided on the pipeline of the gas output end 4 in this application. The vacuum pump is used to increase the suction force of the gas output end 4, so as to improve the replacement efficiency of the gas in the shielding layer.

[0057] Optionally, a gas monitoring mechanism is also connected to the gas output end 4. The gas monitoring mechanism is mainly used to identify the type of gas output from the gas output end 4, so as to accurately identify different states such as air evacuation, nitrogen circulation, and natural gas leakage in the shielding layer.

[0058] Optionally, the thin-film tank 12 in this application is also connected with a liquid cargo supply device. The liquid cargo supply device is connected to the top of the thin-film tank 12 through a pipeline and is used to inject liquid cargo into the thin-film tank 12. When natural gas leaks, the flash steam in the thin-film tank 12 increases, the pressure increases, and there is a tendency to expand outward, which is likely to cause damage to the thin-film tank 12. Therefore, it is necessary for the liquid cargo supply device to inject liquid natural gas into the top layer of the thin-film tank 12 to cool the flash steam inside it and reduce the internal pressure of the thin-film tank 12, so as to slow down the expansion of the thin-film tank 12.

[0059] Furthermore, a buffer tank is also provided inside the thin-film tank 12 in the present application. The buffer tank is located at the top of the thin-film tank 12 and is connected to the liquid cargo supply device through a pipeline. At the same time, the buffer tank is connected to the top of the thin-film tank 12 through multiple branch pipes. Valves are provided on the multiple branch pipes, and the open ends of the multiple branch pipes are distributed in different areas of the top of the thin-film tank 12. In addition to the method of injecting liquid cargo through an external liquid cargo supply device, a buffer tank can also be provided inside the thin-film tank 12 in the present application. The buffer tank is located inside the thin-film tank 12, and its temperature is relatively low, which can avoid the liquefaction of liquefied natural gas and improve the liquefaction efficiency of flash steam. At the same time, the buffer tank is independent of the external liquid cargo, can store part of the liquefied natural gas, and can independently cool the thin-film tank 12 to avoid the problem that the thin-film tank 12 cannot be cooled when it is not connected to the external liquid cargo supply device. Correspondingly, when using the buffer tank for cooling, a pressurizing device needs to be provided on the buffer tank or a pressure balance structure needs to be set up with the thin-film tank 12 to avoid the problem that the internal pressure of the thin-film tank 12 is too high, resulting in the inability of the liquefied natural gas in the buffer tank to be ejected.

[0060] Furthermore, the present application also correspondingly includes a monitoring method for a liquid cargo storage system, which includes the following steps:

[0061] S1. Replace the air inside the shielding layer with a protective gas to form a protection outside the thin-film tank 12.

[0062] 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 inside the shielding layer to form a protective air flow around the thin-film tank 12.

[0063] S3. Obtain the differential pressure detection data at each first differential pressure detection mechanism 6, establish a differential pressure-time change diagram for each first differential pressure detection mechanism 6, and obtain the initial differential pressure change points in each first differential pressure detection mechanism 6. The initial differential pressure change points of the first differential pressure detection mechanism 6 are the leakage points of the thin-film tank 12.

[0064] Specifically, for the monitoring method of the liquid cargo storage system 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 gas flow is formed outside the film layer by using the pipelines of the primary monitoring subsystem 1 and the secondary monitoring subsystem 2 to achieve the protection of the film tank 12. When a break occurs outside the film tank 12 resulting in natural gas leakage, 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 until the area stabilizes. It can be seen that when the film 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 film tank 12 can be determined. At the same time, when the amount of natural gas leaked from the film 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 with the pressure difference data of the first pressure difference detection mechanism 6 around and the first pressure difference detection mechanism 6 at the leakage point to ensure the accuracy of the leakage monitoring of the film tank 12.

[0065] Further, 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 film tank 12 are as follows:

[0066] S101. The protective gas input end 3 inputs the protective gas from the bottom of the film tank 12 through a pipeline, and the gas output end 4 extracts the protective gas from the top of the film tank 12 through a pipeline;

[0067] S102. The protective gas input end 3 injects the protective gas into the shielding layer through the pipeline from the gas sensing part 5 of one of the secondary monitoring subsystems 2, and the gas output end 4 extracts the gas from the adjacent secondary monitoring subsystem 2 of the secondary monitoring subsystem 2 through a pipeline;

[0068] 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;

[0069] S104. Repeat step S103 until the protective gas input of each secondary monitoring subsystem 2 is completed.

[0070] Specifically, when performing gas replacement on the periphery of the membrane tank 12, considering that the quality of nitrogen and air is close, 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 by nitrogen. 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 further air evacuation is required. Based on this, the present application achieves the discharge of air 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 a single area through the secondary monitoring subsystem 2, and then extracting gas from the adjacent secondary monitoring subsystem 2; then repeating the above operations, evacuating the outside of the film tank 12 step by step in turn, and completing the replacement of air in all areas of the shielding layer.

[0071] 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.

[0072] Further, as an optional embodiment of the present utility model, step S2 of the present application includes: the protective gas input end 3 injects 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 on the side away from the protective gas input end 3. 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 to provide gas protection to the periphery of the film tank 12.

[0073] Further, as an alternative embodiment of the present utility model, 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 from the protective gas input end 3 and reducing the gas output from 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.

[0074] Further, as an alternative embodiment of the present utility model, the present application further includes step S5:

[0075] 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.

[0076] Further, as an alternative embodiment of the present utility model, in step S5 of the present application, the amount of the protective gas injected by the protective gas input end 3 is less than the amount of the 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 from 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 identifying the leakage point, it is still necessary to increase the injection amount of the protective gas from the protective gas input end 3 to increase the pressure at the leakage point to inhibit the leakage of natural gas.

[0077] Those skilled in the art can easily understand that the above is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the present utility model shall be included within the protection scope of the present utility model.

Claims

1. A liquid cargo storage system, characterized in that: include: A membrane tank, wherein the membrane tank is used to store liquid natural gas; A tank body, wherein the tank body is arranged at the periphery of the film tank, and a shielding layer is formed between the film tank and the tank body; A plurality of primary monitoring subsystems are arranged in the shielding layer, the outer periphery of the membrane tank is divided into a plurality of protection areas, and each of the primary monitoring subsystems is arranged in one-to-one correspondence with the protection area; each of the primary monitoring subsystems is interconnected through a pipeline, and a two-way valve is arranged on the pipeline between each of the primary monitoring subsystems; A shielding gas input end, one end of which passes through the tank body and is connected to an external shielding gas source, and the other end of which is connected to each of the primary monitoring subsystems through a pipeline; A gas output end, one end of which passes through the tank body, and the other end of which is connected to each of the first-level monitoring subsystems through a pipeline; Each of the first-level monitoring subsystems includes multiple branch pipes. The branch pipes of the same first-level monitoring subsystem are distributed at different positions of the same protection area of ​​the film tank. The tail end of the branch pipe has an opening, and an air pressure detection device is provided on the branch pipe. The air pressure detection device can measure the air pressure at the branch pipe.

2. The liquid cargo storage system according to claim 1, characterized in that: The primary monitoring subsystem includes a plurality of secondary monitoring subsystems, and the plurality of secondary monitoring subsystems belonging to the same primary monitoring subsystem are distributed in the same protection area around the membrane tank; Each of the secondary monitoring subsystems comprises two spaced apart gas sensing parts, each of the gas sensing parts has an opening, the opening of any of the gas sensing parts is connected to the protective gas input end and the gas output end, and a first pressure difference detection mechanism is connected between the two gas sensing parts, and the first pressure difference detection mechanism can measure the pressure difference between the two gas sensing parts; The gas sensing unit includes a connecting pipeline, and a plurality of tail pipes are connected to the connecting pipeline. The plurality of tail pipes are open at one end away from the connecting pipeline.

3. The liquid cargo storage system according to claim 1, 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.

4. The liquid cargo storage system according to claim 3, 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.

5. The liquid cargo storage system according to claim 2, 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.

6. The liquid cargo storage system according to claim 2, 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.

7. The liquid cargo storage system according to claim 1, characterized in that: A vacuum pump is also provided on the pipeline at the gas output end.

8. The liquid cargo storage system according to claim 1, characterized in that: The gas output end is also connected to a gas monitoring mechanism, and the gas monitoring mechanism is used to identify the type of gas output by the gas output end.

9. The liquid cargo storage system according to claim 1, characterized in that: The film tank is also connected to a liquid cargo supply device, and the liquid cargo supply device is connected to the top of the film tank through a pipeline.

10. The liquid cargo storage system according to claim 9, characterized in that: A buffer tank is also provided in the film tank, and the buffer tank is provided on the top of the film tank. The buffer tank is connected to the liquid cargo supply device through a pipeline, and the buffer tank is connected to the top of the film tank through a plurality of branch pipes; Valves are arranged on the plurality of branch pipes, and the opening ends of the plurality of branch pipes are distributed in different areas on the top of the film tank.

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