Flash steam liquefaction system and LNG (Liquefied Natural Gas) storage system

Abstract

The invention discloses a flash steam liquefaction system and an LNG storage system, and belongs to the technical field of natural gas transportation and storage, the flash steam liquefaction system comprises a storage tank and a film tank arranged in the storage tank, a buffer tank is further arranged in the storage tank, the buffer tank is arranged at the top of the film tank, and the buffer tank communicates with the top of the film tank through a first pipeline; the buffer tank is communicated with the bottom of the film tank through a second pipeline; valves are arranged on the first pipeline and the second pipeline; and the suction mechanism is connected with the buffer tank. According to the flash steam liquefaction system, the buffer tank is arranged at the top of the thin film tank, the buffer tank sprays the liquefied natural gas to the top of the thin film tank along the first pipeline by utilizing the gravity of the buffer tank, and the upper layer of the thin film tank is cooled by utilizing the low temperature of the liquefied natural gas, so that the flash steam at the top of the thin film tank is liquefied; and the second pipeline is matched with the suction mechanism to suck the liquefied natural gas at the bottom of the film tank into the buffer tank, so that the internal self-cooling of the film tank is realized, and the problem of high energy consumption caused by external liquefaction of conventional flash steam is avoided.

Description

Technical Field

[0001] The present invention belongs to the technical field of natural gas transportation and storage, and in particular relates to a flash steam liquefaction system and an LNG storage system. Background Art

[0002] As a clean and efficient energy source, liquefied natural gas (LNG) is mainly transported through low-temperature atmospheric pressure or pressure storage tanks. During the actual transportation process, due to factors such as ambient temperature fluctuations, tank shaking, and heat penetration, some LNG will vaporize into flash steam (BOG). BOG itself will not only cause energy loss, but also increase the internal pressure of the membrane tank, causing safety hazards.

[0003] In the case of flash steam generated during the transportation of liquefied natural gas, the existing technology mainly extracts the flash steam in the membrane tank and sends it to the gas engine for combustion treatment, or uses external circulation to reliquefy and cool the flash steam using external equipment and then sends it back to the storage tank. However, since flash steam may be generated during the entire LNG transportation process, the actual gas engine does not need so much gas, and the flash steam extraction process will intensify the generation of flash steam in the membrane tank; and the method of sending the flash steam to the outside for reliquefaction consumes a lot of electricity. Therefore, there is currently no better way to recover and utilize flash steam in the existing technology. Summary of the invention

[0004] In view of one or more of the above defects or improvement needs in the prior art, the present invention provides a flash steam liquefaction system 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 a flash steam liquefaction system, which comprises: A storage tank, wherein a film tank is arranged inside the storage tank, an installation gap is left between the storage tank and the film tank, and a buffer tank is arranged inside the installation gap; the buffer tank is arranged on the top of the film tank, and the buffer tank is connected with a first pipeline and a second pipeline; the first pipeline is communicated with the top of the film tank, the second pipeline is communicated with the bottom of the film tank, and valves are arranged on the first pipeline and the second pipeline; and a suction mechanism, wherein the suction mechanism is connected to the cache tank and is used to provide negative pressure to the cache tank.

[0006] As an optional embodiment of the present invention, the suction mechanism includes a venturi tube, and three ports of the venturi tube are respectively connected to a gas input mechanism, a gas processing mechanism and a third pipeline, and the third pipeline is connected to the cache tank.

[0007] As an optional embodiment of the present invention, the gas input mechanism is a first methane storage unit, and the gas processing mechanism is a combustion assembly.

[0008] As an optional embodiment of the present invention, it further includes a first transfer tube, and the suction mechanism is connected to the first transfer tube via a third pipeline; There are multiple cache tanks, each of which is connected to the first transfer tube, and a valve is provided on the connecting pipeline between each cache tank and the first transfer tube.

[0009] As an optional embodiment of the present invention, it further comprises a pressure detection mechanism, and a detection end of the pressure detection mechanism is connected to the film tank.

[0010] The present invention also includes an LNG storage system, which includes the flash steam liquefaction system, and a first gas cleaning mechanism, the first gas cleaning mechanism being connected to the membrane tank, and the first gas cleaning mechanism being used to replace the air in the membrane tank with an inert gas; The second gas cleaning mechanism is connected to the membrane tank, and the second gas cleaning mechanism is used to replace the inert gas in the membrane tank with methane.

[0011] As an optional embodiment of the present invention, it also includes a liquid cargo supply part, and the liquid cargo supply part is connected to the cache tank through a sixth pipeline.

[0012] As an optional embodiment of the present invention, the first gas cleaning mechanism includes a first transfer tube, the first transfer tube is arranged between the second pipeline and the suction mechanism, and the buffer tank is connected to the second pipeline through a branch pipe; A nitrogen storage unit, wherein the nitrogen storage unit is connected to the first transfer tube via a fourth pipeline; 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.

[0013] As an optional embodiment of the present invention, it further comprises a venturi tube, wherein three ports of the venturi tube are respectively connected to a gas processing mechanism, a third pipeline and the nitrogen storage unit, and the third pipeline is 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 suctions the third pipeline under negative pressure.

[0014] As an optional embodiment of the present invention, the second gas cleaning mechanism includes a first methane storage part, and the first methane storage part and the nitrogen storage part are both connected to the same port of the venturi tube through a branch pipe; A second methane storage unit is connected to the fifth pipeline.

[0015] As an optional embodiment 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.

[0016] As an optional embodiment 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 pipelines between the combustion component and the incineration component and the venturi tube.

[0017] As an optional embodiment of the present invention, it further comprises a gas detection mechanism, wherein a detection end of the gas detection mechanism is connected to the top of the film tank.

[0018] The present application also includes an LNG storage system, comprising: A storage tank, wherein a film tank is arranged inside the storage tank, an installation gap is left between the storage tank and the film tank, a buffer tank is arranged inside the installation gap, the buffer tank is arranged on the top of the film tank, the buffer tank is connected with a first pipeline and a second pipeline, the first pipeline is connected with the top of the film tank, the second pipeline is connected with the bottom of the film tank, and valves are arranged on the first pipeline and the second pipeline; A suction mechanism, the suction mechanism is connected to the cache tank through a third pipeline; A first transfer tube, wherein the first transfer tube is connected to the third pipeline, and the first transfer tube is communicated with the second pipeline; A nitrogen storage unit, wherein the nitrogen storage unit is connected to the top of the membrane tank through a fourth pipeline, and the fourth pipeline is connected to the first transfer tube, and a valve is provided on the connection path between the fourth pipeline and the first transfer tube; a second methane storage part, the second methane storage part is connected to the top of the membrane tank through a fifth pipeline, and the fifth pipeline is connected to the suction mechanism through a bypass pipe; A liquid cargo supply unit is connected to the cache tank via a sixth pipeline.

[0019] As an optional embodiment of the present invention, the suction mechanism includes a venturi tube, and three ports of the venturi tube are respectively connected to the gas input mechanism, the gas processing mechanism and the third pipeline.

[0020] As an optional embodiment 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, 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 pipelines connecting the combustion component and the incineration component to the venturi tube.

[0021] As an optional embodiment of the present invention, it also includes a pressure detection mechanism and a gas detection mechanism, and the detection ends of the pressure detection mechanism and the gas detection mechanism are both arranged in the film tank.

[0022] As an optional embodiment of the present invention, it further comprises a liquid cargo output part, 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.

[0023] As an optional embodiment of the present invention, it also includes a helium storage unit, which is connected to the first transfer tube and the second transfer tube respectively through a seventh pipeline, the second transfer tube 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.

[0024] The present application also includes an LNG storage maintenance method, which is implemented by the LNG storage system and specifically includes the following steps: 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 liquid natural gas to the top of the membrane tank through the first pipeline to achieve flash steam liquefaction.

[0025] As an optional embodiment of the present invention, 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.

[0026] As an optional embodiment of the present invention, step S1 specifically includes: A part of the gas flow of 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 airflow in the nitrogen storage unit is input into nitrogen along the venturi tube and the incineration component to form negative pressure suction. The venturi tube draws out the air on the top of the membrane tank along the bypass pipe and the fifth pipeline.

[0027] As an optional embodiment of the present invention, step S2 specifically includes: 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.

[0028] As an optional embodiment of the present invention, step S3 specifically includes: 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.

[0029] The above-mentioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0030] In general, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects: (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 uses its own gravity to spray liquid natural gas toward the top of the membrane tank along the first pipeline, and uses the low temperature of the liquefied natural gas itself to cool the upper layer of the membrane tank, so as to realize the 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 liquefied natural gas at the bottom of the membrane tank into the buffer tank, so as to realize self-cooling of the membrane tank and avoid the problem of high liquefaction energy consumption caused by the external liquefaction of conventional flash steam. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a schematic diagram of the overall structure of a flash steam liquefaction system in an embodiment of the present invention; Figure 2 is a schematic diagram of gas flow direction of exhaust air of an LNG storage system according to an embodiment of the present invention; Figure 3 Schematic diagram of gas flow direction of exhausting nitrogen from an LNG storage system according to an embodiment of the present invention; Figure 4 Schematic diagram of gas and liquid flow direction of a cooling film tank of an LNG storage system according to an embodiment of the present invention; 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.

[0032] In all the drawings, the same reference numerals represent the same technical features, specifically: 101. Storage tank; 102. Film 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

[0033] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0034] In the description of the present invention, it should be understood that, unless otherwise specified, terms such as “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0035] In addition, unless otherwise specified, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0036] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0037] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0038] Example 1

[0039] See also Figures 1 to 5 The boundaries of the membrane tank 102 in the drawings of the present 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 the gas or liquefied natural gas.

[0040] The flash steam liquefaction system in the preferred embodiment of the present invention includes a storage tank 101, a membrane tank 102 is arranged in 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 arranged in the installation gap. The buffer tank 103 is arranged on the top of the membrane tank 102, and the buffer tank 103 is connected with 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 arranged on the first pipeline 104 and the second pipeline 105; the LNG storage system in the present application is also provided with a suction mechanism, which is connected to the buffer tank 103.

[0041] The flash steam liquefaction system in the present application is provided with a buffer tank 103 on the top of the membrane tank 102. The buffer tank 103 can spray liquid natural gas to the top of the membrane tank 102 by using its own gravity and internal pressure, and cool the membrane tank 102 by using the low temperature of the liquid natural gas itself, so as to realize the liquefaction of the flash steam on the top of the membrane tank 102; at the same time, the present application can suck the liquid natural gas with a lower temperature at the bottom of the membrane tank 102 to the buffer tank 103 through the second pipeline 105 and the suction mechanism, so as to cool the flash steam, and realize the internal self-cooling of 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 further provided between the buffer tank 103 and the membrane tank 102, and a connecting pipeline is provided between the buffer tank 103 and the membrane tank 102, and the connecting pipeline can be freely opened and closed by a valve; the pressure balance between the buffer tank 103 and the membrane tank 102 can be achieved through the connecting pipeline, so as 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 buffer tank 103 cannot be sprayed out 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 buffer tank 103, the connecting pipeline between the buffer tank 103 and the membrane tank 102 needs to be closed, so as to avoid the failure of negative pressure suction in the buffer tank 103.

[0042] It is worth noting that the storage tank 101 is used to form protection outside the membrane tank 102, and an insulation layer is provided between the storage tank 101 and the membrane tank 102. Although flash steam is generated inside the membrane tank 102 due to the external temperature or transportation kinetic energy, the temperature inside the membrane tank 102 is still relatively low, that is, the temperature of the flash steam itself is low, and the temperature of the liquid natural gas at the bottom of the membrane tank 102 is relatively low. The self-liquefaction of the flash steam can be achieved by using the liquid natural gas without the intervention of more external factors. When the flash steam is transported to the outside, the external environment temperature is high, which makes the flash steam quickly balance with the external environment temperature, increasing the difficulty and energy consumption of flash steam reliquefaction.

[0043] 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 buffer tank 103 is sucked by the suction mechanism, 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 sprays liquid natural gas 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.

[0044] Further, as an optional embodiment of the present invention, the flash steam liquefaction system in the present application also includes a first transfer tube 106, and the suction mechanism is connected to the first transfer tube 106 through a third pipeline 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 tube 106, and valves are provided on the connecting pipelines between each cache tank 103 and the first transfer tube 106. In 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 according to the liquefaction requirements of the flash steam at different positions of the membrane tank 102, open the cooling mechanisms at the corresponding positions for cooling. At the same time, through the valve between the cache tank 103 and the first transfer tube 106, the suction mechanism can suck a single or part of the cache tanks 103 to achieve the independent use of each cooling mechanism.

[0045] Optionally, the end of the first pipeline 104 in the present application connected to the membrane tank 102 is provided with multiple branches, and the multiple branches can spray the top surface of the membrane tank 102 to increase the liquefaction efficiency of the flash steam. Optionally, the end of the first pipeline 104 connected to the membrane tank 102 is vertically provided with multiple groups of branches, and the branches at different heights can cool the flash steam at different heights to increase the liquefaction efficiency of the flash steam. Correspondingly, the bottom end of the second pipeline 105 connected to the membrane tank 102 is also arranged with multiple branches, so as to increase the delivery efficiency of the liquefied natural gas to the buffer tank 103.

[0046] Further, as an optional embodiment of the present invention, the flash steam liquefaction system in 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 pressure inside 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, the overall size of the membrane tank 102 is relatively large, and there is a partial pressure difference in the pressure of the membrane tank 102 at different regions. Therefore, multiple pressure detection mechanisms 108 can be set to monitor the pressure at different regions of the membrane tank 102.

[0047] Further, as an optional embodiment of the present invention, one end of the suction mechanism in the present application is connected to the buffer tank 103, and the other end thereof is connected to the combustion assembly 109. The gas extracted from the buffer tank 103 by the suction mechanism in the present application is natural gas, which is not suitable for direct discharge and can be used as fuel for the combustion assembly 109 to generate heat or electricity.

[0048] Further, as an optional embodiment of the present invention, the suction mechanism in the present application includes a venturi tube 114, and 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, and the third pipeline 107 is connected to the buffer tank 103. The present application can realize negative pressure suction of the third pipeline 107 through the linkage of the gas input mechanism, the venturi tube 114 and the gas processing mechanism, so as to suck the liquid natural gas in the membrane tank 102 to the buffer tank 103.

[0049] Optionally, the suction assembly in the present application may be any type of pump body having suction kinetic energy.

[0050] Furthermore, the gas input mechanism in the present application is the first methane storage unit 117, and the gas processing mechanism is the combustion assembly 109. The natural gas itself is mainly composed of methane, and the methane output by the gas input mechanism is a homogeneous gas. After the two are mixed, they can still be used as fuel to achieve energy supply. It is worth noting that the internal pressure of the first methane storage unit 117 in the present application is relatively large, and the flow rate of methane when it is output from the first methane storage unit 117 is relatively large, which can cooperate with the venturi tube 114 to form a relatively large negative pressure.

[0051] 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 achieve the replacement of the inert gas and the 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.

[0052] 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 the 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 film tank 102, and the other end is connected to the suction mechanism. Specifically, the nitrogen storage unit 111 in the present application injects nitrogen into the bottom of the film 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 from the top of the film tank 102 through the fifth pipeline 113 to achieve the replacement of air by nitrogen. 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.

[0053] Further, 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 which 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, and 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 inside the membrane tank 102. Here, in addition to delivering 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 inside the membrane tank 102.

[0054] Further, as an optional embodiment of the present invention, in addition to replacing the air in the membrane tank 102 with nitrogen, the LNG storage system in the present application can also replace the nitrogen in the membrane tank 102 with methane gas, so as to facilitate the subsequent injection of liquid cargo into the membrane tank 102. Specifically, the LNG storage system also includes a second gas cleaning mechanism, which is used to replace the inert gas in the membrane tank 102 with methane gas, and the second gas cleaning mechanism is connected to the top of the membrane tank 102; at the same time, the suction mechanism is connected to the bottom of the membrane tank 102 through a pipeline. Methane is lighter than nitrogen, and methane needs to be injected from the top of the membrane tank 102 and nitrogen needs to be extracted from the bottom of the membrane tank 102. Therefore, the second gas cleaning mechanism needs to be connected to the top of the membrane tank 102 to inject methane, and the suction mechanism needs to be connected to the bottom of the membrane tank 102 through a pipeline to extract nitrogen from the bottom, so as to achieve the replacement of the protective gas and methane, and facilitate the subsequent injection of liquid cargo into the membrane tank 102.

[0055] Optionally, the second gas cleaning mechanism in the present application includes a first methane storage unit 117, the first methane storage unit 117 and the nitrogen storage unit 111 are both connected to the same port of the venturi tube 114 through a branch pipe; and a second methane storage unit 118, which 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, and 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 tube 106 and the second pipeline 105, thereby realizing the replacement of nitrogen with methane.

[0056] Further, 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 connected to the same port of the venturi tube 114 through a branch pipe, and valves are provided on the connecting pipes of 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 large, and the nitrogen and methane mixed gas cannot be burned, which is easy to cause 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 demand, so as to burn and utilize the methane. 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.

[0057] Further, as an optional embodiment of the present invention, the third pipeline 107 in the present application is connected to a bypass pipe 115 through 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 system in which a suction mechanism sucks toward the top of the membrane tank 102, so as to realize the suction of the gas at the top of the membrane tank 102.

[0058] Further, as an optional embodiment of the present invention, the LNG storage system in the present application can also cool down the membrane tank 102 to facilitate the injection of liquid cargo, and to transport the liquid cargo to the membrane tank 102. Specifically, the LNG storage system in the present application also includes a liquid cargo supply unit 119, which is connected to the buffer tank 103 through a sixth pipeline 120. At the point where the liquid natural gas is injected, there is no liquid natural gas left 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, so as to cool down the membrane tank 102. When the temperature in the membrane tank 102 drops to a suitable range, the flow rate can be increased and liquid natural gas can be injected into the membrane tank 102 using the buffer tank 103 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.

[0059] Optionally, the sixth pipeline 120 in the present application is connected to the first transfer pipe 106, and the first transfer pipe 106 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.

[0060] Optionally, the LNG storage system in the present application further includes a gas detection mechanism 116, and a detection end of the gas detection mechanism 116 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, so as to monitor the air content and nitrogen content in the membrane tank 102.

[0061] 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 liquefied 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 the monitoring of flash steam pressure to avoid excessive overall pressure in the membrane tank 102.

[0062] 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 arranged 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 transportation.

[0063] As an optional embodiment of the present invention, the LNG storage system in the present application further includes a helium storage unit 122, which is connected to the first transfer tube 106 and the second transfer tube 125 through the seventh pipeline 123. The helium storage unit 122 is connected to the first transfer tube 106 and the second transfer tube 125 through the seventh pipeline 123, and then can be connected to each pipeline of the LNG storage system through the first transfer tube 106 and the second transfer tube 125. Helium can be used to detect small leaks in the pipelines, valves and membrane tanks 102 of the LNG storage system to ensure the overall sealing of the storage system.

[0064] 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.

[0065] 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 at 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 tube 106 is connected to the third pipeline 107, and the first transfer tube 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 tube 106, and a valve is provided on the connection path between the fourth pipeline 112 and the first transfer tube 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 cache tank 103 through the sixth pipeline 120.

[0066] 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 storing liquid cargo 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 evacuated, 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 the internal pressure balance of the membrane tank 102; as the temperature of the membrane tank 102 gradually decreases, the input amount of the liquid natural gas can be appropriately increased until the liquid natural gas is finally completely stored in the membrane tank 102 to achieve the input of liquid cargo. 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.

[0067] As an optional embodiment of the present invention, the suction mechanism in the present application includes a venturi tube 114, and 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 present application mainly realizes the negative pressure of the third pipeline 107 through the airflow driven by the gas input mechanism, the venturi tube 114 and the gas processing mechanism, and then extracts the gas in the membrane tank 102 through the first transfer tube 106 and provides the buffer tank 103 with negative pressure.

[0068] As an optional embodiment of the present invention, the gas input mechanism in the present application is a first methane storage unit 117, and the gas processing mechanism 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 pipelines between the combustion component 109 and the incineration component 110 and the venturi tube 114.

[0069] As an optional embodiment of the present invention, the LNG storage system in the present 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 membrane tank 102 to detect the gas pressure and gas type in the membrane tank 102.

[0070] 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.

[0071] As an optional embodiment of the present invention, the LNG storage unit in the present 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 tiny leaks in the pipelines, valves and membrane tanks 102 of the LNG storage system.

[0072] Furthermore, as an optional embodiment of the present invention, the present application also includes an LNG storage maintenance method, which is implemented by the above-mentioned LNG storage system and specifically includes the following steps: Flash steam liquefaction in membrane tank 102: The suction mechanism provides suction pressure to the cache tank 103 along the third pipeline 107, and the cache tank 103 sucks the liquid natural gas at the bottom of the membrane tank 102 to the cache tank 103 through the second pipeline 105; The suction mechanism and the second pipeline 105 are closed, and the first pipeline 104 is opened. The buffer tank 103 sprays liquid natural gas to the top of the membrane tank 102 through the first pipeline 104 to achieve flash steam liquefaction.

[0073] 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: S1, injecting nitrogen into the film tank 102 and exhausting the air in the film tank 102; S2, injecting methane into the membrane tank 102, and discharging nitrogen in the membrane tank 102; S3, spraying liquid natural gas into the membrane tank 102 to cool the membrane tank 102; S4. Injecting liquefied natural gas into the membrane tank 102 to achieve liquefied natural gas storage.

[0074] As an optional embodiment of the present invention, step S1 specifically includes: 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; Another part of the airflow in the nitrogen storage unit 111 is input into nitrogen along the venturi tube 114 and the incineration assembly 110 to form 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.

[0075] When the gas detection mechanism 116 detects that the inside of the membrane tank 102 is substantially nitrogen, the air is exhausted. When the air is exhausted, the nitrogen content inside the membrane tank 102 is determined according to general industry standards, which will not be elaborated here.

[0076] As an optional embodiment of the present invention, step S2 specifically includes: The second methane storage unit 118 injects methane into the top of the membrane tank 102 along the fifth pipeline 113; 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 .

[0077] 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.

[0078] As an optional embodiment of the present invention, step S3 specifically includes: 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 liquefied natural gas onto the top of the membrane tank 102 along the first pipeline 104 to cool down the inside of the membrane tank 102; 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.

[0079] 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 input amount of the liquefied natural gas of the liquid cargo supply part 119 can be increased to realize liquid cargo storage.

[0080] It is worth noting that in the present application, when each pipeline is performing air exhaust, nitrogen replacement, membrane tank 102 cooling, liquid cargo injection and flash steam cooling, valves are provided on each pipeline, and 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.

[0081] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A flash steam liquefaction system, characterized in that: include: A storage tank, wherein a film tank is arranged inside the storage tank, an installation gap is left between the storage tank and the film tank, and a buffer tank is arranged inside the installation gap; the buffer tank is arranged on the top of the film tank, and the buffer tank is connected with a first pipeline and a second pipeline; the first pipeline is communicated with the top of the film tank, the second pipeline is communicated with the bottom of the film tank, and valves are arranged on the first pipeline and the second pipeline; and a suction mechanism, wherein the suction mechanism is connected to the cache tank and is used to provide negative pressure to the cache tank.

2. The flash steam liquefaction system according to claim 1, characterized in that: The suction mechanism includes a venturi tube, and three ports of the venturi tube are respectively connected to a gas input mechanism, a gas processing mechanism and a third pipeline, and the third pipeline is connected to the cache tank.

3. The flash steam liquefaction system according to claim 2, characterized in that: The gas input mechanism is a first methane storage unit, and the gas processing mechanism is a combustion component.

4. The flash steam liquefaction system according to claim 1, characterized in that: It also includes a first transfer tube, and the suction mechanism is connected to the first transfer tube through a third pipeline; There are multiple cache tanks, each of which is connected to the first transfer tube, and a valve is provided on the connecting pipeline between each cache tank and the first transfer tube.

5. The flash steam liquefaction system according to claim 1, characterized in that: It also includes a pressure detection mechanism, and a detection end of the pressure detection mechanism is connected to the film tank.

6. An LNG storage system for storing liquid natural gas in a membrane tank, characterized in that: comprising the flash steam liquefaction system as claimed in claim 1, and a first gas cleaning mechanism, the first gas cleaning mechanism being connected to the membrane tank, and the first gas cleaning mechanism being used to replace the air in the membrane tank with an inert gas; The second gas cleaning mechanism is connected to the membrane tank, and the second gas cleaning mechanism is used to replace the inert gas in the membrane tank with methane.

7. The LNG storage system according to claim 6, characterized in that: It also includes a liquid cargo supply unit, which is connected to the cache tank through a sixth pipeline.

8. The LNG storage system according to claim 6, characterized in that: The first gas cleaning mechanism comprises: A first transfer pipe, wherein 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; A nitrogen storage unit, wherein the nitrogen storage unit is connected to the first transfer tube via a fourth pipeline; 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.

9. The LNG storage system according to claim 8, characterized in that: Also includes: A venturi tube, wherein three ports of the venturi tube are respectively connected to a gas processing mechanism, a third pipeline and the nitrogen storage unit, and the third pipeline is 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 suctions the third pipeline under negative pressure.

10. The LNG storage system according to claim 9, characterized in that: The second gas cleaning mechanism comprises: A first methane storage part, wherein the first methane storage part and the nitrogen storage part are both connected to the same port of the venturi tube through a branch pipe; A second methane storage unit is connected to the fifth pipeline.

11. The LNG storage system according to claim 10, characterized in that: The third pipeline is connected to a bypass pipe through a branch pipe, and the bypass pipe is connected to the fifth pipeline.

12. The LNG storage system according to claim 9, characterized in that: The gas processing mechanism comprises a combustion component and an incineration component, both of which are connected to the same port of the venturi tube through a branch pipe, and valves are arranged on the connecting pipelines between the combustion component and the incineration component and the venturi tube.

13. The LNG storage system according to claim 6, characterized in that: It also includes a gas detection mechanism, and a detection end of the gas detection mechanism is connected to the top of the film tank.

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