LNG storage maintenance method

Abstract

The invention relates to an LNG (Liquefied Natural Gas) storage and maintenance method, which belongs to the technical field of natural gas transportation and storage, and comprises the following steps: flash steam in a film tank is liquefied, a buffer tank is arranged at the top of the film tank, a suction mechanism provides suction pressure for the buffer tank along a third pipeline, and the buffer tank sucks liquefied natural gas at the bottom of the film tank to the buffer tank through a second pipeline; and the suction mechanism and the second pipeline are closed, the first pipeline is opened, the buffer tank sprays liquefied natural gas to the top of the film tank through the first pipeline, flash steam liquefaction is achieved, and the problem of large energy consumption caused by conventional flash steam external liquefaction is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas transportation and storage, and in particular relates to an LNG storage and maintenance method. Background Art

[0002] Liquefied natural gas (LNG), a clean and efficient energy source, is primarily transported in cryogenic, atmospheric, or pressurized storage tanks. During transportation, some LNG can vaporize into flash gas (BOG) due to factors such as ambient temperature fluctuations, tank sway, and heat penetration. BOG not only causes energy loss but also increases internal pressure in membrane tanks, posing a safety hazard.

[0003] Existing technologies for flash steam generated during liquefied natural gas (LNG) transportation primarily involve extracting it from membrane tanks and sending it to gas engines for combustion, or using external equipment to reliquefy and cool the flash steam before returning it to the storage tanks. However, since flash steam can be generated throughout the LNG transportation process, gas engines don't actually require such large amounts of gas, and the flash steam extraction process exacerbates flash steam generation in the membrane tanks. Furthermore, sending the flash steam to an external facility for reliquefaction consumes significant amounts of electricity. Therefore, existing technologies currently lack a reliable method for recovering and utilizing flash steam. Summary of the Invention

[0004] In response to one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides an LNG storage and maintenance method to solve the problem of flash steam waste or high energy consumption in recovery in existing membrane tanks.

[0005] To achieve the above object, the present invention provides an LNG storage and maintenance method, comprising the following steps:

[0006] Flash steam liquefaction in membrane tanks:

[0007] The suction mechanism provides suction pressure to the cache tank along the third pipeline, and the cache tank sucks the liquid natural gas at the bottom of the membrane tank into the cache tank through the second pipeline;

[0008] The suction mechanism and the second pipeline are closed, and the first pipeline is opened. The buffer tank sprays liquid natural gas to the top of the membrane tank through the first pipeline to achieve flash steam liquefaction.

[0009] The following steps are also included before the flash steam is liquefied in the membrane tank:

[0010] S1. Inject nitrogen into the film tank and discharge the air in the film tank;

[0011] S2, injecting methane into the membrane tank and discharging nitrogen from the membrane tank;

[0012] S3, spraying liquid natural gas into the membrane tank to cool the membrane tank;

[0013] S4. Injecting liquefied natural gas into the membrane tank to achieve liquefied natural gas storage.

[0014] As a further improvement of the present invention, step S1 includes:

[0015] A portion of the air flow from the nitrogen storage unit is injected into the bottom of the membrane tank along the fourth pipeline, the first transfer pipe, and the second pipeline;

[0016] Another part of the air flow in the nitrogen storage unit inputs nitrogen along the venturi tube and the incineration component to form negative pressure suction. The venturi tube draws out the air from the top of the membrane tank along the bypass pipe and the fifth pipeline.

[0017] As a further improvement of the present invention, step S2 includes:

[0018] The second methane storage unit injects methane into the top of the membrane tank along the fifth pipeline;

[0019] The first methane storage part inputs methane along the venturi tube and the incineration component to form negative pressure suction; the venturi tube draws nitrogen out from the bottom of the membrane tank along the third pipeline, the first transfer tube and the second pipeline.

[0020] As a further improvement of the present invention, step S3 includes:

[0021] The liquid cargo supply unit injects liquefied natural gas into the buffer tank along the sixth pipeline, and the buffer tank sprays liquefied natural gas onto the top of the membrane tank along the first pipeline to cool the inside of the membrane tank;

[0022] The first methane storage part inputs methane along the venturi tube and the combustion assembly to form negative pressure suction; the venturi tube draws away the methane gas along the bypass pipe and the fifth pipeline along the top of the membrane tank to achieve pressure balance inside the membrane tank.

[0023] Furthermore, the LNG storage and maintenance method is implemented by an LNG storage system, and the LNG storage system includes:

[0024] A storage tank, wherein a membrane tank is provided inside the storage tank, an installation gap is left between the storage tank and the membrane tank, and a buffer tank is provided in the installation gap; the buffer tank is provided on the top of the membrane tank, and the buffer tank is connected to a first pipeline and a second pipeline; the first pipeline is connected to the top of the membrane tank, the second pipeline is connected to the bottom of the membrane tank, and valves are provided on the first pipeline and the second pipeline;

[0025] A suction mechanism connected to the cache tank and configured to provide negative pressure to the cache tank; the suction mechanism includes a venturi tube, the three ports of which are respectively connected to a gas processing mechanism, a third pipeline, and a nitrogen storage unit, the third pipeline being connected to the top of the membrane tank; the circulating airflow formed by the nitrogen storage unit, the venturi tube, and the gas processing mechanism causes negative pressure suction to the third pipeline;

[0026] a first gas cleaning mechanism connected to the membrane tank and configured to replace the air in the membrane tank with an inert gas; the first gas cleaning mechanism comprising a first transfer pipe, the nitrogen storage unit, and a fifth pipeline; the first transfer pipe being disposed between the second pipeline and the suction mechanism, the buffer tank being connected to the second pipeline via a branch pipe; the nitrogen storage unit being connected to the first transfer pipe via a fourth pipeline; one end of the fifth pipeline being connected to the top of the membrane tank and the other end being connected to the venturi tube;

[0027] a second gas cleaning mechanism connected to the membrane tank and configured to replace the inert gas in the membrane tank with methane; the second gas cleaning mechanism comprising a first methane storage portion, wherein the first methane storage portion and the nitrogen storage portion are both connected to the same port of the venturi tube via a branch pipe; and a second methane storage portion, wherein the second methane storage portion is connected to the fifth pipeline;

[0028] The third pipeline is connected to a bypass pipe through a branch pipe, and the bypass pipe is connected to the fifth pipeline.

[0029] As a further improvement of the present invention, the LNG storage system further includes a liquid cargo supply unit, which is connected to the cache tank via a sixth pipeline.

[0030] As a further improvement of the present invention, the gas processing mechanism includes a combustion component and an incineration component, and the combustion component and the incineration component are both connected to the same port of the venturi tube through a branch pipe, and valves are provided on the connecting pipes between the combustion component and the incineration component and the venturi tube.

[0031] As a further improvement of the present invention, the LNG storage system further includes a gas detection mechanism, and a detection end of the gas detection mechanism is connected to the top of the membrane tank.

[0032] As a further improvement of the present invention, the LNG storage system further includes:

[0033] a first gas cleaning mechanism connected to the membrane tank, the first gas cleaning mechanism being used to replace the air in the membrane tank with an inert gas;

[0034] A second gas cleaning mechanism is connected to the membrane tank and is used to replace the inert gas in the membrane tank with methane.

[0035] As a further improvement of the present invention, it further includes a liquid cargo supply part, which is connected to the cache tank through a sixth pipeline.

[0036] As a further improvement of the present invention, the first gas cleaning mechanism includes a first transfer pipe, the first transfer pipe is arranged between the second pipeline and the suction mechanism, and the buffer tank is connected to the second pipeline through a branch pipe;

[0037] a nitrogen storage unit connected to the first transfer pipe via a fourth pipeline;

[0038] A fifth pipeline, one end of which is connected to the top of the film tank, and the other end of which is connected to the suction mechanism.

[0039] As a further improvement of the present invention, it further comprises a venturi tube, wherein the three ports of the venturi tube are respectively connected to the gas processing mechanism, the third pipeline and the nitrogen storage unit, and the third pipeline is connected to the top of the membrane tank;

[0040] The circulating airflow formed by the nitrogen storage portion, the venturi tube and the gas processing mechanism causes negative pressure suction on the third pipeline.

[0041] As a further improvement of the present invention, the second gas cleaning mechanism includes a first methane storage portion, and the first methane storage portion and the nitrogen storage portion are both connected to the same port of the venturi tube through a branch pipe;

[0042] A second methane storage unit is connected to the fifth pipeline.

[0043] As a further improvement of the present invention, the third pipeline is connected to a bypass pipe through a branch pipe, and the bypass pipe is connected to the fifth pipeline.

[0044] As a further improvement of the present invention, the gas processing mechanism includes a combustion component and an incineration component, and the combustion component and the incineration component are both connected to the same port of the venturi tube through a branch pipe, and valves are provided on the connecting pipes between the combustion component and the incineration component and the venturi tube.

[0045] As a further improvement of the present invention, it further comprises a gas detection mechanism, wherein the detection end of the gas detection mechanism is connected to the top of the film tank.

[0046] As a further improvement of the present invention, the LNG storage system further includes:

[0047] A storage tank, wherein a film tank is provided in the storage tank, an installation gap is left between the storage tank and the film tank, a buffer tank is provided in the installation gap, the buffer tank is provided on the top of the film tank, the buffer tank is connected to a first pipeline and a second pipeline, the first pipeline is connected to the top of the film tank, the second pipeline is connected to the bottom of the film tank, and valves are provided on the first pipeline and the second pipeline;

[0048] a suction mechanism connected to the cache tank via a third pipeline;

[0049] a first transfer tube, the first transfer tube being connected to the third pipeline and the first transfer tube being in communication with the second pipeline;

[0050] a nitrogen storage unit, the nitrogen storage unit being connected to the top of the membrane tank via a fourth pipeline, the fourth pipeline being connected to the first transfer pipe, and a valve being provided on the connection path between the fourth pipeline and the first transfer pipe;

[0051] a second methane storage portion, the second methane storage portion being connected to the top of the membrane tank via a fifth pipeline, and the fifth pipeline being connected to the suction mechanism via a bypass pipe;

[0052] A liquid cargo supply unit is connected to the cache tank via a sixth pipeline.

[0053] As a further improvement of the present invention, the suction mechanism includes a venturi tube, and the three ports of the venturi tube are respectively connected to the gas input mechanism, the gas processing mechanism and the third pipeline.

[0054] As a further improvement of the present invention, the gas input mechanism is a first methane storage unit, and the gas processing mechanism includes a combustion component and an incineration component. The combustion component and the incineration component are both connected to the same port of the venturi tube through a branch pipe, and valves are provided on the connecting pipes connecting the combustion component and the incineration component to the venturi tube.

[0055] As a further improvement of the present invention, it further comprises a pressure detection mechanism and a gas detection mechanism, wherein the detection ends of the pressure detection mechanism and the gas detection mechanism are both arranged in the film tank.

[0056] As a further improvement of the present invention, it further comprises a liquid cargo output portion, which is connected to the bottom of the film tank through a pipeline, and a liquid cargo pump is provided at the end of the pipeline connected to the film tank.

[0057] As a further improvement of the present invention, the device further includes a helium storage unit, which is connected to the first transfer pipe and the second transfer pipe respectively through a seventh pipeline, the second transfer pipe is connected to the fifth pipeline, and the helium storage unit is connected to the pipeline of the liquid cargo output unit through a branch pipe.

[0058] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0059] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0060] (1) The flash steam liquefaction system of the present invention is characterized in that a buffer tank is arranged on the top of the membrane tank. The buffer tank sprays liquid natural gas to the top of the membrane tank along the first pipeline under the action of its own gravity, and uses the low temperature of the liquid natural gas itself to cool the upper layer of the membrane tank to achieve liquefaction of the flash steam on the top of the membrane tank; at the same time, the second pipeline cooperates with the suction mechanism to suck the liquid natural gas at the bottom of the membrane tank into the buffer tank, thereby achieving self-cooling inside the membrane tank and avoiding the problem of high liquefaction energy consumption caused by conventional external liquefaction of flash steam. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of the overall structure of the flash steam liquefaction system in an embodiment of the present invention;

[0062] Figure 2 Schematic diagram of gas flow of evacuated air from an LNG storage system according to an embodiment of the present invention;

[0063] Figure 3 2. FIG. 1 is a gas flow diagram of evacuating nitrogen from an LNG storage system according to an embodiment of the present invention;

[0064] Figure 4 Schematic diagram of gas and liquid flow in a cooling membrane tank of an LNG storage system according to an embodiment of the present invention;

[0065] Figure 5 Schematic diagram of the gas-liquid flow of liquefied flash steam in the LNG storage system according to an embodiment of the present invention.

[0066] In all the drawings, the same reference numerals represent the same technical features, specifically:

[0067] 101. Storage tank; 102. Membrane tank; 103. Buffer tank; 104. First pipeline; 105. Second pipeline; 106. First transfer tube; 107. Third pipeline; 108. Pressure detection mechanism; 109. Combustion component; 110. Incineration component; 111. Nitrogen storage unit; 112. Fourth pipeline; 113. Fifth pipeline; 114. Venturi tube; 115. Bypass pipe; 116. Gas detection mechanism; 117. First methane storage unit; 118. Second methane storage unit; 119. Liquid cargo supply unit; 120. Sixth pipeline; 121. Liquid cargo pump; 122. Helium storage unit; 123. Seventh pipeline; 124. Liquid cargo output unit; 125. Second transfer tube. DETAILED DESCRIPTION

[0068] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate 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 may be combined with each other as long as they do not conflict with each other.

[0069] In the description of the present invention, it should be understood that, unless otherwise specified, the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships 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 operate in a specific orientation, and therefore should not be understood as limiting the present invention.

[0070] Furthermore, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specified.

[0071] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0072] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0073] Example:

[0074] See also Figures 1 to 5 The boundaries of the membrane tank 102 in the drawings of this application specification are for illustration only. The external pipelines of the tank body are connected to the membrane tank 102 or the buffer tank 103, rather than to the installation gap. At the same time, the arrows in the drawings of the specification point to the flow direction of gas or liquid natural gas.

[0075] The flash steam liquefaction system in a preferred embodiment of the present invention includes a storage tank 101, a membrane tank 102 is provided within the storage tank 101, and an installation gap is left between the storage tank 101 and the membrane tank 102, and a buffer tank 103 is provided within the installation gap. The buffer tank 103 is arranged on the top of the membrane tank 102, and the buffer tank 103 is connected to a first pipeline 104 and a second pipeline 105, wherein the first pipeline 104 is connected to the top of the membrane tank 102, and the second pipeline 105 is connected to the bottom of the membrane tank 102, and valves are provided on the first pipeline 104 and the second pipeline 105; the LNG storage system in this application is also provided with a suction mechanism, which is connected to the buffer tank 103.

[0076] The flash steam liquefaction system in the present application is configured by setting a buffer tank 103 on the top of the membrane tank 102. The buffer tank 103 can use its own gravity and internal pressure to spray liquid natural gas to the top of the membrane tank 102, and use the low temperature of the liquid natural gas itself to cool the membrane tank 102 to achieve liquefaction of the flash steam on the top of the membrane tank 102; at the same time, the present application can use the second pipeline 105 and the suction mechanism to suck the liquid natural gas at the bottom of the membrane tank 102 at a lower temperature into the buffer tank 103 to cool the flash steam, thereby achieving self-cooling inside the LNG storage system, that is, the top of the membrane tank 102 is cooled by the liquid natural gas inside the membrane tank 102, thereby avoiding the waste of natural gas and the high consumption of liquefaction energy caused by conventional flash steam treatment methods. Optionally, a pressure difference detection device is provided between the cache tank 103 and the membrane tank 102, and a connecting pipeline is provided between the cache tank 103 and the membrane tank 102, which can be freely opened and closed by a valve; the pressure balance between the cache tank 103 and the membrane tank 102 can be achieved through the connecting pipeline to avoid the problem that the internal pressure of the membrane tank 102 is too high when the flash steam increases, resulting in the liquid natural gas in the cache tank 103 cannot be ejected from the first pipeline 104; when it is necessary to use a suction mechanism to suck the liquid natural gas at the bottom of the membrane tank 102 into the cache tank 103, the connecting pipeline between the cache tank 103 and the membrane tank 102 needs to be closed to avoid the failure of negative pressure suction in the cache tank 103.

[0077] It's worth noting that storage tank 101 protects the exterior of membrane tank 102, and an insulating layer is provided between storage tank 101 and membrane tank 102. Although flash steam may form inside membrane tank 102 due to external temperature or transport kinetic energy, the temperature inside membrane tank 102 remains relatively low. That is, the flash steam itself is relatively low, while the temperature of the liquefied natural gas at the bottom of membrane tank 102 is relatively low. This allows the flash steam to self-liquefy using the liquefied natural gas without the need for further external factors. However, when the flash steam is transported to the outside, the ambient temperature is relatively high, causing the flash steam to quickly equilibrate with the ambient temperature, increasing the difficulty and energy consumption of reliquefaction.

[0078] The flash steam liquefaction system in the present application is used as follows: when it is detected that the pressure at the top of the membrane tank 102 increases to a set threshold value, it means that the flash steam inside the membrane tank 102 is close to the critical value; close the first pipeline 104, open the second pipeline 105, and open the suction mechanism. The suction mechanism sucks the buffer tank 103, and a negative pressure is generated inside the buffer tank 103 to suck the liquid natural gas at the bottom of the membrane tank 102 into the buffer tank 103. Close the transmission pipeline between the suction mechanism and the buffer tank 103, close the valve between the buffer tank 103 and the second pipeline 105, open the first pipeline 104, and the liquid natural gas in the buffer tank 103 is sprayed to the top of the membrane tank 102 under the action of gravity and the pressure inside the tank. The liquid natural gas cools the flash steam, and the flash steam is liquefied into liquid natural gas.

[0079] Furthermore, as an optional embodiment of the present invention, the flash steam liquefaction system in the present application also includes a first transfer pipe 106, and the suction mechanism is connected to the first transfer pipe 106 through a third pipe 107; at the same time, there are multiple cache tanks 103 in the present application, and the multiple cache tanks 103 are all connected to the first transfer pipe 106, and valves are provided on the connecting pipes between each cache tank 103 and the first transfer pipe 106. During the liquefaction process of the flash steam, due to the large overall size of the membrane tank 102, it is difficult to cool and liquefy the flash steam at all positions using a single-position spray structure. Therefore, it is necessary to set multiple groups of cooling mechanisms on the top of the membrane tank 102, and open the cooling mechanisms at the corresponding positions for cooling according to the liquefaction requirements of the flash steam at different positions of the membrane tank 102. At the same time, through the valve between the cache tank 103 and the first transfer pipe 106, the suction mechanism can suck a single or part of the cache tanks 103 to realize the independent use of each cooling mechanism.

[0080] Optionally, the end of the first pipeline 104 connected to the membrane tank 102 in this application is provided with multiple branches, each of which can spray the top surface of the membrane tank 102 to increase the efficiency of flash steam liquefaction. Alternatively, the end of the first pipeline 104 connected to the membrane tank 102 is provided with multiple groups of branches vertically. Branches at different heights can cool the flash steam at different heights to increase the efficiency of flash steam liquefaction. Correspondingly, the bottom end of the second pipeline 105 connected to the membrane tank 102 is also provided with multiple branches, thereby increasing the efficiency of delivering liquefied natural gas to the buffer tank 103.

[0081] Furthermore, as an optional embodiment of the present invention, the flash steam liquefaction system of the present application further includes a pressure detection mechanism 108, and the detection end of the pressure detection mechanism 108 is connected to the membrane tank 102. The pressure detection mechanism 108 is used to detect the internal pressure of the membrane tank 102. When flash steam is generated inside the membrane tank 102, the internal pressure of the membrane tank 102 will increase accordingly. By monitoring the internal pressure of the membrane tank 102, quantitative monitoring of the flash steam in the membrane tank 102 is achieved. Optionally, there are multiple pressure detection mechanisms 108. Since the membrane tank 102 is relatively large overall, there are partial pressure differences in different areas of the membrane tank 102. Therefore, multiple pressure detection mechanisms 108 can be provided to monitor the pressure in different areas of the membrane tank 102.

[0082] Furthermore, as an optional embodiment of the present invention, one end of the suction mechanism in this application is connected to the buffer tank 103, and the other end is connected to the combustion assembly 109. The gas extracted from the buffer tank 103 by the suction mechanism in this application is natural gas, which is not suitable for direct discharge. Instead, it can be used as fuel for the combustion assembly 109 to generate heat or electricity.

[0083] Furthermore, as an optional embodiment of the present invention, the suction mechanism in this application includes a venturi tube 114. The three ports of the venturi tube 114 are respectively connected to the gas input mechanism, the gas processing mechanism, and the third pipeline 107. The third pipeline 107 is connected to the buffer tank 103. Through the linkage of the gas input mechanism, the venturi tube 114, and the gas processing mechanism, the present application can achieve negative pressure suction of the third pipeline 107, thereby sucking the liquefied natural gas in the membrane tank 102 into the buffer tank 103.

[0084] Optionally, the suction component in the present application may be any type of pump body with suction kinetic energy.

[0085] Furthermore, the gas input mechanism in this application is the first methane storage unit 117, and the gas processing mechanism is the combustion assembly 109. Natural gas itself is primarily composed of methane, and the methane output by the gas input mechanism is a homogeneous gas. After mixing, the two can still be used as fuel to provide energy. It is worth noting that in this application, the internal pressure of the first methane storage unit 117 is relatively high, and the methane flows rapidly when it is output from the first methane storage unit 117, which, in conjunction with the venturi tube 114, can create a significant negative pressure.

[0086] As another optional embodiment of the present invention, the present application also includes an LNG storage system, which includes the above-mentioned flash steam liquefaction system, and a first gas cleaning mechanism, the first gas cleaning mechanism is used to replace the air in the membrane tank 102 with an inert gas, the first gas cleaning mechanism is connected to the bottom of the membrane tank 102, and the suction mechanism is connected to the top of the membrane tank 102 through a pipeline. In addition to realizing the self-liquefaction of flash steam during transportation, the LNG storage system in the present application can also realize the air exhaust before the liquid cargo is tanked. The present application uses an inert gas to inject into the bottom of the membrane tank 102, and uses a suction mechanism to extract air along the top of the membrane tank 102 to realize the replacement of inert gas and air, so as to protect the membrane tank 102 and facilitate the subsequent injection of methane and liquid natural gas. Optionally, the purge gas of the first gas cleaning mechanism can be nitrogen or argon.

[0087] Preferably, the first gas cleaning mechanism in the present application includes a first transfer tube 106, which is arranged between the second pipeline 105 and the suction mechanism, and the above-mentioned buffer tank 103 is connected to the second pipeline 105 through a branch pipe to avoid conflict between the buffer tank 103 and the first transfer tube 106; and a nitrogen storage unit 111, which is connected to the first transfer tube 106 through a fourth pipeline 112; and a fifth pipeline 113, one end of which is connected to the top of the membrane tank 102, and the other end of which is connected to the suction mechanism. Specifically, the nitrogen storage unit 111 in the present application injects nitrogen into the bottom of the membrane tank 102 along the fourth pipeline 112, the first transfer tube 106 and the second pipeline 105, and at the same time, the suction mechanism extracts the air at the top of the membrane tank 102 through the fifth pipeline 113 to achieve nitrogen replacement of air. Optionally, during the air discharge stage, the nitrogen is cold nitrogen, which has a density greater than that of air, so that the nitrogen sinks to the bottom of the film tank 102 to squeeze the air toward the upper layer of the film tank 102 to facilitate the discharge of the air.

[0088] Furthermore, as another optional embodiment of the present invention, the LNG storage system in the present application also includes a venturi tube 114. The three ports of the venturi tube 114 are respectively connected to the gas processing mechanism, the third pipeline 107, and the nitrogen storage unit 111. The third pipeline 107 is connected to the top of the membrane tank 102. The circulating airflow formed by the nitrogen storage unit 111, the venturi tube 114, and the gas processing mechanism can negatively pump the third pipeline 107 to extract the air from the membrane tank 102. Here, in addition to supplying nitrogen to the bottom of the membrane tank 102, the nitrogen storage unit 111 can also branch out and connect to the venturi tube 114 to generate negative pressure to extract the air from the membrane tank 102.

[0089] Furthermore, as an optional embodiment of the present invention, the LNG storage system of the present application can not only replace the air within membrane tank 102 with nitrogen, but also replace the nitrogen within membrane tank 102 with methane gas, facilitating the subsequent injection of liquid cargo into membrane tank 102. Specifically, the LNG storage system also includes a second gas purge mechanism, which is used to replace the inert gas within membrane tank 102 with methane gas. The second gas purge mechanism is connected to the top of membrane tank 102; at the same time, a suction mechanism is connected to the bottom of membrane tank 102 via a pipeline. Methane is lighter than nitrogen, so methane needs to be injected from the top of membrane tank 102 and nitrogen needs to be extracted from the bottom of membrane tank 102. Therefore, the second gas purge mechanism needs to be connected to the top of membrane tank 102 to inject methane, and the suction mechanism needs to be connected to the bottom of membrane tank 102 via a pipeline to extract nitrogen from the bottom, achieving the replacement of protective gas with methane and facilitating the subsequent injection of liquid cargo into membrane tank 102.

[0090] Optionally, the second gas cleaning mechanism in the present application includes a first methane storage unit 117, wherein the first methane storage unit 117 and the nitrogen storage unit 111 are both connected to the same port of the venturi tube 114 via a branch pipe; and a second methane storage unit 118, wherein the second methane storage unit 118 is connected to the fifth pipeline 113. When it is necessary to replace the nitrogen in the membrane tank 102 with methane gas, since the density of methane is lower than that of nitrogen, the methane in the second methane storage unit 118 can be injected into the top of the membrane tank 102 through the second methane storage unit 118 and the fifth pipeline 113 connected to the top of the membrane tank 102. At the same time, the venturi tube 114 extracts the nitrogen inside the membrane tank 102 from the bottom along the third pipeline 107, the first transfer pipe 106, and the second pipeline 105, thereby achieving the replacement of nitrogen with methane.

[0091] Furthermore, as an optional embodiment of the present invention, the gas processing mechanism in the present application includes a combustion component 109 and an incineration component 110, and the combustion component 109 and the incineration component 110 are both connected to the same port of the venturi tube 114 through a branch pipe, and valves are provided on the connecting pipes between the combustion component 109 and the incineration component 110 and the venturi tube 114. When methane is used to replace nitrogen, methane is a combustible gas, and directly discharging it will cause a large amount of energy waste. In the initial process of nitrogen discharge, the proportion of nitrogen is relatively large, and the nitrogen and methane mixed gas cannot be burned, which is likely to cause problems such as methane waste and air pollution. Therefore, the first methane storage unit 117 is used to provide suction force so that the proportion of methane in the mixed gas discharged from the gas processing mechanism meets the combustion requirements, so that the methane can be burned and utilized. It is worth noting that in the later stage of nitrogen exhaust, the mixed gas flowing through the gas processing mechanism basically meets the engine power combustion requirements. Therefore, the gas processing mechanism is provided with a combustion component 109 and an incineration component 110. The incineration component 110 is used to process the mixed gas with a higher nitrogen ratio to avoid methane waste; the combustion component 109 is used to process the mixed gas with a higher methane ratio to achieve kinetic energy supply.

[0092] Furthermore, as an optional embodiment of the present invention, the third pipeline 107 in the present application is connected to a bypass pipe 115 via a branch pipe, and the bypass pipe 115 is connected to the fifth pipeline 113. The fifth pipeline 113, the bypass pipe 115, and the venturi tube 114 can form a suction system for sucking gas from the top of the membrane tank 102, thereby achieving suction of the gas from the top of the membrane tank 102.

[0093] Furthermore, as an optional embodiment of the present invention, the LNG storage system of the present application can also cool the membrane tank 102 to facilitate the injection of liquid cargo and the delivery of liquid cargo to the membrane tank 102. Specifically, the LNG storage system of the present application also includes a liquid cargo supply unit 119, which is connected to the buffer tank 103 via a sixth pipeline 120. At the point where liquid natural gas is injected, there is no liquid natural gas remaining in the buffer tank 103, so the liquid cargo supply unit 119 is required to supply liquid natural gas to the buffer tank 103, and then the buffer tank 103 sprays liquid natural gas through the first pipeline 104 to cool the membrane tank 102. When the temperature in the membrane tank 102 drops to an appropriate range, the flow rate can be increased and the buffer tank 103 can be used to inject liquid natural gas into the membrane tank 102 to achieve the injection of liquid cargo; at the same time, during the cooling and liquid cargo injection stages of the membrane tank 102, the suction mechanism extracts the methane gas in the membrane tank 102 through the bypass pipe 115 and the fifth pipeline 113 to achieve pressure balance in the membrane tank 102.

[0094] Optionally, the sixth pipeline 120 in this application is connected to the first transfer pipe 106, which is connected to multiple cooling mechanisms. The combination of multiple buffer tanks 103 and the first pipeline 104 can achieve rapid cooling of the entire film tank 102 and rapid injection of liquid cargo.

[0095] Optionally, the LNG storage system of the present application further includes a gas detection mechanism 116, the detection end of which is connected to the top of the membrane tank 102. The gas detection mechanism 116 is mainly used to detect the gas composition in the membrane tank 102, thereby monitoring the air content and nitrogen content in the membrane tank 102.

[0096] Optionally, the LNG storage system in the present application also includes a liquid level detection component, which is mainly used to determine the storage volume of liquid natural gas during liquid cargo input and transportation. The liquid level detection during input is mainly used to control the liquid cargo transportation volume; the liquid level detection during transportation is mainly used to adapt to monitoring the flash steam pressure to avoid excessive overall pressure in the membrane tank 102.

[0097] As an optional embodiment of the present invention, the LNG storage system in the present application also includes a liquid cargo output part 124, which is connected to the bottom of the membrane tank 102 through a pipeline, and a liquid cargo pump 121 is provided at the end of the pipeline connected to the membrane tank 102, so as to extract the liquid cargo in the membrane tank 102 for liquid cargo transshipment.

[0098] As an optional embodiment of the present invention, the LNG storage system herein further includes a helium storage unit 122, which is connected to the first transfer tube 106 and the second transfer tube 125 via a seventh pipeline 123. Helium storage unit 122 is connected to the first transfer tube 106 and the second transfer tube 125 via the seventh pipeline 123, and is then connected to various pipelines of the LNG storage system via the first transfer tube 106 and the second transfer tube 125. Helium can be used to detect minor leaks in the LNG storage system pipelines, valves, and membrane tank 102, thereby ensuring the overall sealing of the storage system.

[0099] It is worth noting that the nitrogen storage unit 111, the first methane storage unit 117, the second methane storage unit 118, the helium storage unit 122 and the liquid cargo supply unit 119 in the present application are all used to provide corresponding gas or liquid cargo. Each storage unit can be a separate storage tank 101 structure, or it can represent a pipeline output node connected to other gas or liquid cargo.

[0100] As another embodiment of the present invention, the present application also includes an LNG storage system, which includes a storage tank 101, a membrane tank 102 is provided inside the storage tank 101, and an installation gap is left between the storage tank 101 and the membrane tank 102, a cache tank 103 is provided in the installation gap, the cache tank 103 is located on the top of the membrane tank 102, and the cache tank 103 is connected to a first pipeline 104 and a second pipeline 105, wherein the first pipeline 104 is connected to the top of the membrane tank 102, the second pipeline 105 is connected to the bottom of the membrane tank 102, and valves are provided on the first pipeline 104 and the second pipeline 105; and a suction mechanism, the suction mechanism is connected to the cache tank 103 through a third pipeline 107; the first transfer pipe 106, the first transfer pipe 106 is connected to the third pipeline 107, and the first transfer pipe 106 is connected to the second pipeline 105; the nitrogen storage part 111, the nitrogen storage part 111 is connected to the top of the membrane tank 102 through the fourth pipeline 112, and the fourth pipeline 112 is connected to the first transfer pipe 106, and a valve is provided on the connection path between the fourth pipeline 112 and the first transfer pipe 106; the second methane storage part 118, the second methane storage part 118 is connected to the top of the membrane tank 102 through the fifth pipeline 113, and the fifth pipeline 113 is connected to the suction mechanism through the bypass pipe 115; the liquid cargo supply part 119, the liquid cargo supply part 119 is connected to the buffer tank 103 through the sixth pipeline 120.

[0101] The present application also provides a system that can realize air evacuation, nitrogen replacement, cooling of the membrane tank 102 and liquid cargo injection before liquid cargo storage in the membrane tank 102. Specifically, the nitrogen storage unit 111 in the present application injects nitrogen into the bottom of the membrane tank 102 along the fourth pipeline 112, the first transfer pipe 106 and the second pipeline 105, and the suction mechanism is connected to the top of the membrane tank 102 along the fifth pipeline 113, and extracts the air inside the membrane tank 102; after the air inside the membrane tank 102 is emptied, the nitrogen storage unit 111 no longer injects nitrogen into the membrane tank 102, and the second methane storage unit 118 injects methane gas into the top of the membrane tank 102 through the fifth pipeline 113. At the same time, the suction mechanism extracts the nitrogen gas in the membrane tank 102 from the bottom along the third pipeline 107, the first transfer pipe 106 and the second pipeline 105 until the membrane tank 102 is filled with methane. The gas in the membrane tank 102 is completely replaced with methane; after the nitrogen inside the membrane tank 102 is completely replaced, the liquid cargo supply unit 119 inputs the liquid natural gas into the buffer tank 103 along the sixth pipeline 120, and the buffer tank 103 then sprays the liquid natural gas to the top of the membrane tank 102 through the first pipeline 104 to cool the membrane tank 102. At the same time, the suction mechanism extracts the methane gas in the membrane tank 102 along the bypass pipe 115 and the fifth pipeline 113 to achieve pressure balance inside the membrane tank 102; as the temperature of the membrane tank 102 gradually decreases, the input amount of liquid natural gas can be appropriately increased until the liquid natural gas is finally completely stored in the membrane tank 102 to achieve liquid cargo input. In this application, the cooling and liquefaction of the flash steam in the membrane tank 102 by the buffer tank 103, the first pipeline 104, the second pipeline 105 and the suction mechanism have been mentioned in the previous part and will not be repeated here.

[0102] As an optional embodiment of the present invention, the suction mechanism in this application includes a venturi tube 114, the three ports of which are respectively connected to the gas input mechanism, the gas processing mechanism, and the third pipeline 107. This application mainly uses the airflow driven by the gas input mechanism, the venturi tube 114, and the gas processing mechanism to achieve negative pressure in the third pipeline 107, and then extracts the gas in the membrane tank 102 through the first transfer tube 106 and provides negative pressure for the buffer tank 103.

[0103] As an optional embodiment of the present invention, the gas input mechanism in this application is a first methane storage unit 117, and the gas processing mechanism includes a combustion component 109 and an incineration component 110. The combustion component 109 and the incineration component 110 are both connected to the same port of the venturi tube 114 through a branch pipe, and valves are provided on the connecting pipelines between the combustion component 109 and the incineration component 110 and the venturi tube 114.

[0104] As an optional embodiment of the present invention, the LNG storage system in this application also includes a pressure detection mechanism 108 and a gas detection mechanism 116. The detection ends of the pressure detection mechanism 108 and the gas detection mechanism 116 are both arranged in the film tank 102 to detect the gas pressure and gas type in the film tank 102.

[0105] As an optional embodiment of the present invention, the LNG storage system in the present application also includes a liquid cargo output part 124, which is connected to the bottom of the membrane tank 102 through a pipeline, and a liquid cargo pump 121 is provided at the end of the pipeline connected to the membrane tank 102, so as to extract the liquid cargo in the membrane tank 102 and realize liquid cargo transfer.

[0106] As an optional embodiment of the present invention, the LNG storage unit in this application also includes a helium storage unit 122, which is connected to the first transfer tube 106 and the second transfer tube 125 respectively through the seventh pipeline 123, and the second transfer tube 125 is connected to the fifth pipeline 113. The helium storage unit 122 connects all the pipelines of the LNG storage system through the first transfer tube 106 and the second transfer tube 125 to detect minor leaks in the pipelines, valves and membrane tanks 102 of the LNG storage system.

[0107] Furthermore, as an optional embodiment of the present invention, the present application also includes an LNG storage and maintenance method, which is implemented by the above-mentioned LNG storage system and specifically includes the following steps:

[0108] Flash steam liquefaction in membrane tank 102:

[0109] The suction mechanism provides suction pressure to the cache tank 103 along the third pipeline 107 , and the cache tank 103 sucks the liquefied natural gas at the bottom of the membrane tank 102 into the cache tank 103 through the second pipeline 105 ;

[0110] The suction mechanism and the second pipeline 105 are closed, and the first pipeline 104 is opened. The buffer tank 103 sprays liquefied natural gas to the top of the membrane tank 102 through the first pipeline 104 to achieve flash steam liquefaction.

[0111] As an optional embodiment of the present invention, the following steps are further included before the flash steam is liquefied in the membrane tank 102:

[0112] S1, injecting nitrogen into the film tank 102 and exhausting the air in the film tank 102;

[0113] S2, injecting methane into the membrane tank 102 and discharging nitrogen from the membrane tank 102;

[0114] S3, spraying liquid natural gas into the membrane tank 102 to cool the membrane tank 102;

[0115] S4. Injecting liquefied natural gas into the membrane tank 102 to achieve liquefied natural gas storage.

[0116] As an optional embodiment of the present invention, step S1 specifically includes:

[0117] A portion of the gas flow from the nitrogen storage unit 111 is injected into the bottom of the membrane tank 102 along the fourth pipeline 112, the first transfer pipe 106, and the second pipeline 105;

[0118] Another part of the airflow from the nitrogen storage unit 111 is fed into the nitrogen along the venturi tube 114 and the incineration assembly 110 , forming negative pressure suction. The venturi tube 114 draws out the air from the top of the membrane tank 102 along the bypass pipe 115 and the fifth pipeline 113 .

[0119] When the gas detection mechanism 116 detects that the interior of the membrane tank 102 is substantially nitrogen, the air evacuation is completed. When the air evacuation is completed, the nitrogen content in the membrane tank 102 is determined according to general industry standards, which will not be elaborated here.

[0120] As an optional embodiment of the present invention, step S2 specifically includes:

[0121] The second methane storage unit 118 injects methane into the top of the membrane tank 102 along the fifth pipeline 113;

[0122] The first methane storage unit 117 inputs methane along the venturi tube 114 and the incineration assembly 110 to form negative pressure suction; the venturi tube 114 extracts nitrogen from the bottom of the membrane tank 102 along the third pipeline 107, the first transfer tube 106, and the second pipeline 105.

[0123] When the gas detection mechanism 116 detects that the interior of the membrane tank 102 is substantially filled with methane, the nitrogen replacement is completed.

[0124] As an optional embodiment of the present invention, step S3 specifically includes:

[0125] The liquid cargo supply unit 119 injects liquefied natural gas into the buffer tank 103 along the sixth pipeline 120 , and the buffer tank 103 sprays the liquefied natural gas onto the top of the membrane tank 102 along the first pipeline 104 to cool the interior of the membrane tank 102 ;

[0126] The first methane storage unit 117 inputs methane along the venturi tube 114 and the combustion assembly 109 to form negative pressure suction; the venturi tube 114 draws away the methane gas along the bypass pipe 115 and the fifth pipeline 113 along the top of the membrane tank 102 to achieve pressure balance inside the membrane tank 102.

[0127] The liquid cargo injection in step S4 is similar to the cooling of the membrane tank 102. After the temperature of the membrane tank 102 reaches the set condition, the liquid natural gas input of the liquid cargo supply part 119 can be increased to achieve liquid cargo storage.

[0128] It is worth noting that in the present application, when each pipeline is performing air evacuation, nitrogen replacement, membrane tank 102 cooling, liquid cargo injection and flash steam cooling, valves are provided on each pipeline. Different airflow directions can be achieved by opening and closing different valves. The fact that valves are not mentioned in each pipeline is not a limitation of the present invention.

[0129] It will be easily understood by those skilled in the art that the above description is merely 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 scope of protection of the present invention.

Claims

1. A method for LNG storage and maintenance, characterized in that: The steps include: Flash steam liquefaction in membrane tanks: The suction mechanism provides suction pressure to the cache tank along the third pipeline, and the cache tank sucks the liquid natural gas at the bottom of the membrane tank into the cache tank through the second pipeline; The suction mechanism and the second pipeline are closed, and the first pipeline is opened. The buffer tank sprays liquefied natural gas to the top of the membrane tank through the first pipeline to achieve flash steam liquefaction; The LNG storage and maintenance method is implemented by an LNG storage system, and the LNG storage system includes: A storage tank, wherein a membrane tank is provided inside the storage tank, an installation gap is left between the storage tank and the membrane tank, and a buffer tank is provided in the installation gap; the buffer tank is provided on the top of the membrane tank, and the buffer tank is connected to a first pipeline and a second pipeline; the first pipeline is connected to the top of the membrane tank, the second pipeline is connected to the bottom of the membrane tank, and valves are provided on the first pipeline and the second pipeline; A suction mechanism connected to the cache tank and configured to provide negative pressure to the cache tank; the suction mechanism includes a venturi tube, the three ports of which are respectively connected to a gas processing mechanism, a third pipeline, and a nitrogen storage unit, the third pipeline being connected to the top of the membrane tank; the circulating airflow formed by the nitrogen storage unit, the venturi tube, and the gas processing mechanism causes negative pressure suction to the third pipeline; a first gas cleaning mechanism connected to the membrane tank and configured to replace the air in the membrane tank with an inert gas; the first gas cleaning mechanism comprising a first transfer pipe, the nitrogen storage unit, and a fifth pipeline; the first transfer pipe being disposed between the second pipeline and the suction mechanism, the buffer tank being connected to the second pipeline via a branch pipe; the nitrogen storage unit being connected to the first transfer pipe via a fourth pipeline; one end of the fifth pipeline being connected to the top of the membrane tank and the other end being connected to the venturi tube; a second gas cleaning mechanism connected to the membrane tank and configured to replace the inert gas in the membrane tank with methane; the second gas cleaning mechanism comprising a first methane storage portion, wherein the first methane storage portion and the nitrogen storage portion are both connected to the same port of the venturi tube via a branch pipe; and a second methane storage portion, wherein the second methane storage portion is connected to the fifth pipeline; The third pipeline is connected to a bypass pipe through a branch pipe, and the bypass pipe is connected to the fifth pipeline.

2. The LNG storage and maintenance method according to claim 1, characterized in that: The following steps are also included before the flash steam is liquefied in the membrane tank: S1. Inject nitrogen into the film tank and discharge the air in the film tank; S2, injecting methane into the membrane tank and discharging nitrogen from the membrane tank; S3, spraying liquid natural gas into the membrane tank to cool the membrane tank; S4. Injecting liquefied natural gas into the membrane tank to achieve liquefied natural gas storage.

3. The LNG storage and maintenance method according to claim 2, characterized in that: The step S1 comprises: A portion of the air flow from the nitrogen storage unit is injected into the bottom of the membrane tank along the fourth pipeline, the first transfer pipe, and the second pipeline; Another part of the air flow in the nitrogen storage unit inputs nitrogen along the venturi tube and the incineration component to form negative pressure suction. The venturi tube draws out the air from the top of the membrane tank along the bypass pipe and the fifth pipeline.

4. The LNG storage and maintenance method according to claim 2, characterized in that: The step S2 comprises: The second methane storage unit injects methane into the top of the membrane tank along the fifth pipeline; The first methane storage part inputs methane along the venturi tube and the incineration component to form negative pressure suction; the venturi tube draws nitrogen out from the bottom of the membrane tank along the third pipeline, the first transfer tube and the second pipeline.

5. The LNG storage and maintenance method according to claim 2, characterized in that: The step S3 comprises: The liquid cargo supply unit injects liquefied natural gas into the buffer tank along the sixth pipeline, and the buffer tank sprays liquefied natural gas onto the top of the membrane tank along the first pipeline to cool the inside of the membrane tank; The first methane storage part inputs methane along the venturi tube and the combustion assembly to form negative pressure suction; the venturi tube draws away the methane gas along the bypass pipe and the fifth pipeline along the top of the membrane tank to achieve pressure balance inside the membrane tank.

6. The LNG storage and maintenance method according to claim 1, characterized in that: The LNG storage system further includes a liquid cargo supply unit, which is connected to the cache tank via a sixth pipeline.

7. The LNG storage and maintenance method according to claim 1, characterized in that: The gas processing mechanism includes a combustion component and an incineration component. The combustion component and the incineration component are both connected to the same port of the venturi tube through a branch pipe, and valves are provided on the connecting pipes between the combustion component and the incineration component and the venturi tube.

8. The LNG storage and maintenance method according to claim 1, characterized in that: The LNG storage system further includes a gas detection mechanism, wherein a detection end of the gas detection mechanism is connected to the top of the membrane tank.

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