A flash steam liquefaction system and an LNG storage system

Abstract

The present invention discloses a flash steam liquefaction system and an LNG storage system, belonging to the technical field of natural gas transportation and storage. It includes a storage tank and a thin film tank arranged inside the storage tank. A buffer tank is also arranged in the storage tank. The buffer tank is arranged on the top of the thin film tank. The buffer tank is communicated with the top of the thin film tank through a first pipeline, and the buffer tank is communicated with the bottom of the thin film tank through a second pipeline. Valves are arranged on the first pipeline and the second pipeline; a suction mechanism, which is connected to the buffer tank. In the flash steam liquefaction system of the present invention, a buffer tank is arranged on the top of the thin film tank. The buffer tank sprays liquid natural gas to the top of the thin film tank along the first pipeline by its own gravity, and uses the low temperature of the liquid natural gas itself to cool the upper layer of the thin film tank, so as to liquefy the flash steam at the top of the thin film tank; and the second pipeline cooperates with the suction mechanism to suck the liquid natural gas at the bottom of the thin film tank into the buffer tank, realizing self-cooling inside the thin film tank and avoiding the problem of high energy consumption caused by external liquefaction of conventional flash steam.

Description

Technical Field

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

[0002] Liquefied natural gas (LNG), as a clean and efficient energy source, is mainly transported through cryogenic atmospheric pressure or pressure storage tanks. During the actual transportation process, due to factors such as environmental temperature fluctuations, tank body shaking, and heat penetration, part of the LNG will vaporize into flash gas (BOG). The BOG itself will not only cause energy loss but also increase the internal pressure of the membrane tank, posing a safety hazard.

[0003] Regarding the flash gas generated during the transportation of liquefied natural gas, the existing technology mainly pumps the flash gas in the membrane tank away and sends it to a gas engine for combustion treatment, or through an external circulation, uses external equipment to re-liquefy and cool the flash gas and then send it back to the storage tank. However, since flash gas may be generated throughout the entire process of LNG transportation, the actual gas engine does not require so much gas, and the process of pumping away the flash gas will exacerbate the generation of flash gas in the membrane tank; while the method of sending the flash gas to external re-liquefaction requires a large amount of electricity consumption. Therefore, there is currently no good way to recover and utilize flash gas in the existing technology. Summary of the Invention

[0004] In view of one or more of the above-mentioned defects or improvement requirements of the existing technology, the present invention provides a flash gas liquefaction system to solve the problem of waste of flash gas in the existing membrane tank or high energy consumption for recovery.

[0005] To achieve the above object, the present invention provides a flash gas liquefaction system, which includes:

[0006] A storage tank, in which a membrane tank is provided. There is an installation gap between the storage tank and the membrane tank, and a buffer tank is provided in the installation gap; the buffer tank is arranged on the top of the membrane 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 membrane tank, the second pipeline is communicated with the bottom of the membrane tank, and valves are provided on both the first pipeline and the second pipeline;

[0007] And a suction mechanism, which is connected to the buffer tank and is used to provide negative pressure to the buffer tank.

[0008] 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 with a gas input mechanism, a gas treatment mechanism, and a third pipeline, and the third pipeline is connected with the buffer tank.

[0009] As an alternative embodiment of the present invention, the gas input mechanism is a first methane storage unit, and the gas treatment mechanism is a combustion assembly.

[0010] As an alternative embodiment of the present invention, it further includes a first adapter pipe, and the suction mechanism is connected to the first adapter pipe through a third pipeline;

[0011] There are multiple buffer tanks, each buffer tank is connected to the first adapter pipe, and valves are provided on the connecting pipelines between each buffer tank and the first adapter pipe.

[0012] As an alternative embodiment of the present invention, it further includes a pressure detection mechanism, and the detection end of the pressure detection mechanism is communicated with the membrane tank.

[0013] The present invention further includes an LNG storage system, which includes the flash gas liquefaction system, and

[0014] a first gas cleaning mechanism, the first gas cleaning mechanism is connected to the membrane tank, and the first gas cleaning mechanism is used to replace the air in the membrane tank with an inert gas;

[0015] a second gas cleaning mechanism, 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.

[0016] As an alternative embodiment of the present invention, it further includes a liquid cargo supply unit, and the liquid cargo supply unit is connected to the buffer tank through a sixth pipeline.

[0017] As an alternative embodiment of the present invention, the first gas cleaning mechanism includes a first adapter pipe, the first adapter 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;

[0018] a nitrogen storage unit, the nitrogen storage unit is connected to the first adapter pipe through a fourth pipeline;

[0019] a fifth pipeline, one end of the fifth pipeline communicates with the top of the membrane tank, and the other end communicates with the suction mechanism.

[0020] As an alternative embodiment of the present invention, it further includes a Venturi tube, and the three ports of the Venturi tube are respectively connected to a gas treatment mechanism, a third pipeline and the nitrogen storage unit, and the third pipeline is connected to the top of the membrane tank;

[0021] The circulating air flow formed by the nitrogen storage unit, the Venturi tube and the gas treatment mechanism sucks the third pipeline in a negative pressure manner.

[0022] As an alternative embodiment of the present invention, the second gas cleaning mechanism includes a first methane storage section, and both the first methane storage section and the nitrogen storage section are connected to the same port of the Venturi tube through branch pipes;

[0023] A second methane storage section, which is connected to the fifth pipeline.

[0024] As an alternative embodiment of the present invention, the third pipeline is connected with a bypass pipe through a branch pipe, and the bypass pipeline communicates with the fifth pipeline.

[0025] As an alternative embodiment of the present invention, the gas treatment mechanism includes a combustion component and an incineration component. Both the combustion component and the incineration component are connected to the same port of the Venturi tube through branch pipes, and valves are provided on the connecting pipelines of the combustion component and the incineration component to the Venturi tube.

[0026] As an alternative embodiment of the present invention, it further includes a gas detection mechanism, and the detection end of the gas detection mechanism is connected to communicate with the top of the membrane tank.

[0027] This application also includes an LNG storage system, which includes:

[0028] A storage tank, in which a membrane tank is provided. There is an installation gap between the storage tank and the membrane tank. A buffer tank is provided in the installation gap. The buffer tank is arranged on the top of the membrane tank. The buffer tank is connected with a first pipeline and a second pipeline. The first pipeline is connected to the top of the membrane tank, and the second pipeline is connected to the bottom of the membrane tank. Valves are provided on both the first pipeline and the second pipeline;

[0029] A suction mechanism, which is connected to the buffer tank through a third pipeline;

[0030] A first adapter, which is connected to the third pipeline and is communicated with the second pipeline;

[0031] A nitrogen storage section, which is connected to the top of the membrane tank through a fourth pipeline, and the fourth pipeline is connected to the first adapter. A valve is provided on the connection path of the fourth pipeline and the first adapter;

[0032] A second methane storage section, which is connected to the top of the membrane tank through a fifth pipeline. The fifth pipeline is connected to the suction mechanism through a bypass pipe;

[0033] A liquid cargo supply section, which is connected to the buffer tank through a sixth pipeline.

[0034] As an alternative embodiment of the present invention, the suction mechanism includes a Venturi tube, and the three ports of the Venturi tube are respectively connected to a gas input mechanism, a gas treatment mechanism, and the third pipeline.

[0035] As an alternative embodiment of the present invention, the gas input mechanism is a first methane storage unit, the gas treatment mechanism includes a combustion component and an incineration component, both the combustion component and the incineration component are connected to the same port of the Venturi tube through a branch pipe, and valves are provided on the connecting pipelines of the combustion component and the incineration component connecting the Venturi tube.

[0036] As an alternative embodiment of the present invention, it further 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 inside the thin film tank.

[0037] As an alternative embodiment of the present invention, it further includes a liquid cargo output unit, the liquid cargo output unit is connected to the bottom of the thin film tank through a pipeline, and a liquid cargo pump is provided at the end of the pipeline connecting the thin film tank.

[0038] As an alternative embodiment of the present invention, it further includes a helium storage unit, the helium storage unit is respectively connected to a first adapter pipe and a second adapter pipe through a seventh pipeline, the second adapter pipe is communicated with the fifth pipeline, and the helium storage unit is communicated with the pipeline of the liquid cargo output unit through a branch pipe.

[0039] This application also includes an LNG storage and maintenance method, which is realized through the LNG storage system, and specifically includes the following steps:

[0040] Liquefaction of the flash gas in the thin film tank:

[0041] The suction mechanism provides a suction pressure to the buffer tank along the third pipeline, and the buffer tank sucks the liquid natural gas at the bottom of the thin film tank into the buffer tank through the second pipeline;

[0042] Close the suction mechanism and the second pipeline, open the first pipeline, and the buffer tank sprays liquid natural gas to the top of the thin film tank through the first pipeline to achieve liquefaction of the flash gas.

[0043] As an alternative embodiment of the present invention, the following steps are further included before the liquefaction of the flash gas in the thin film tank:

[0044] S1. Inject nitrogen into the inside of the thin film tank and discharge the air in the thin film tank;

[0045] S2. Inject methane into the inside of the thin film tank and discharge the nitrogen in the thin film tank;

[0046] S3. Spray liquid natural gas into the inside of the thin film tank to cool the thin film tank;

[0047] S4. Inject liquid natural gas into the inside of the thin-film tank to achieve the storage of liquid natural gas.

[0048] As an alternative embodiment of the present invention, step S1 specifically includes:

[0049] A part of the gas flow in the nitrogen storage part injects nitrogen into the bottom of the thin-film tank along the fourth pipeline, the first adapter pipe, and the second pipeline;

[0050] Another part of the gas flow in the nitrogen storage part inputs nitrogen along the Venturi tube and the incineration component to form a negative pressure suction. The Venturi tube extracts the air at the top of the thin-film tank along the bypass pipe and the fifth pipeline.

[0051] As an alternative embodiment of the present invention, step S2 specifically includes:

[0052] The second methane storage part injects methane into the top of the thin-film tank along the fifth pipeline;

[0053] The first methane storage part inputs methane along the Venturi tube and the incineration component to form a negative pressure suction; the Venturi tube extracts nitrogen from the bottom of the thin-film tank along the third pipeline, the first adapter pipe, and the second pipeline.

[0054] As an alternative embodiment of the present invention, step S3 specifically includes:

[0055] The liquid cargo supply part injects liquid natural gas into the buffer tank along the sixth pipeline, and the buffer tank sprays liquid natural gas onto the top of the thin-film tank along the first pipeline to cool the inside of the thin-film tank;

[0056] The first methane storage part inputs methane along the Venturi tube and the combustion component to form a negative pressure suction; the Venturi tube extracts methane gas from the top of the thin-film tank along the bypass pipe and the fifth pipeline to achieve pressure balance inside the thin-film tank.

[0057] As long as the above-mentioned improved technical features do not conflict with each other, they can be combined with each other.

[0058] Generally speaking, compared with the prior art, the beneficial effects of the above technical solutions conceived by the present invention include:

[0059] (1) In the flash steam liquefaction system of the present invention, by arranging a buffer tank at the top of the thin-film tank, the buffer tank sprays liquid natural gas onto the top of the thin-film tank along the first pipeline under its own gravity, and uses the low temperature of the liquid natural gas itself to cool the upper layer of the thin-film tank to achieve the liquefaction of the flash steam at the top of the thin-film tank; at the same time, the second pipeline cooperates with the suction mechanism to suck the liquid natural gas at the bottom of the thin-film tank into the buffer tank, realizing self-cooling inside the thin-film tank and avoiding the problem of large liquefaction energy consumption caused by the external liquefaction of conventional flash steam. Description of the Drawings

[0060] Figure 1It is a schematic diagram of the overall structure of the flash steam liquefaction system in an embodiment of the present invention;

[0061] Figure 2 It is a schematic diagram of the gas flow direction for exhausting air in the LNG storage system in an embodiment of the present invention;

[0062] Figure 3 It is a schematic diagram of the gas flow direction for exhausting nitrogen in the LNG storage system in an embodiment of the present invention;

[0063] Figure 4 It is a schematic diagram of the gas-liquid flow direction for cooling the thin-film tank in the LNG storage system in an embodiment of the present invention;

[0064] Figure 5 It is a schematic diagram of the gas-liquid flow direction for liquefying flash steam in the LNG storage system in an embodiment of the present invention.

[0065] In all the drawings, the same reference numerals represent the same technical features, specifically:

[0066] 101, storage tank; 102, thin-film tank; 103, buffer tank; 104, first pipeline; 105, second pipeline; 106, first adapter; 107, third pipeline; 108, pressure detection mechanism; 109, combustion assembly; 110, incineration assembly; 111, nitrogen storage part; 112, fourth pipeline; 113, fifth pipeline; 114, Venturi tube; 115, bypass pipe; 116, gas detection mechanism; 117, first methane storage part; 118, second methane storage part; 119, liquid cargo supply part; 120, sixth pipeline; 121, liquid cargo pump; 122, helium storage part; 123, seventh pipeline; 124, liquid cargo output part; 125, second adapter. Detailed implementation manners

[0067] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0068] In the description of the present invention, it should be understood that, unless otherwise specified, the orientation or positional relationship indicated by terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present invention.

[0069] In addition, unless otherwise specified, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0070] In the present invention, unless otherwise clearly defined and limited, the terms such as "mounted", "connected", "connected to", "fixed" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0071] In the present invention, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "under" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0072] Embodiment 1

[0073] Please refer to Figures 1 to 5 , in the attached drawings of the specification of this application, the boundary of the thin film tank 102 is only for illustration. The pipelines outside the tank body are all connected to the thin film tank 102 or the buffer tank 103, rather than connected to the installation gap. At the same time, the arrow directions in the attached drawings of the specification represent the flow directions of gas or liquefied natural gas.

[0074] In the flash steam liquefaction system of the preferred embodiment of the present invention, there is a storage tank 101. Inside the storage tank 101, there is a thin film tank 102, and an installation gap is left between the storage tank 101 and the thin film tank 102. Inside the installation gap, there is a buffer tank 103. The buffer tank 103 is arranged on the top of the thin film tank 102, and the buffer tank 103 is connected with a first pipeline 104 and a second pipeline 105. Among them, the first pipeline 104 is communicated with the top of the thin film tank 102, the second pipeline 105 is communicated with the bottom of the thin film tank 102, and valves are arranged on both the first pipeline 104 and the second pipeline 105; the LNG storage system in this application is also provided with a suction mechanism, and this suction mechanism is connected with the buffer tank 103.

[0075] In the flash steam liquefaction system of this application, by arranging a buffer tank 103 on the top of the thin film tank 102, the buffer tank 103 can spray liquid natural gas to the top of the thin film tank 102 by its own gravity and internal pressure, and use the low temperature of the liquid natural gas itself to cool the thin film tank 102, so as to realize the liquefaction of the flash steam at the top of the thin film tank 102; at the same time, through the second pipeline 105 and the suction mechanism in this application, the liquid natural gas with a lower temperature at the bottom of the thin film tank 102 can be sucked into the buffer tank 103 to cool the flash steam, realizing the self-cooling inside the LNG storage system, that is, cooling the top of the thin film tank 102 through the liquid natural gas inside the thin film tank 102, avoiding the problems of natural gas waste and large liquefaction energy consumption caused by the conventional flash steam treatment method. Optionally, a differential pressure detection device is also arranged between the buffer tank 103 and the thin film tank 102, and a communication pipeline is arranged between the buffer tank 103 and the thin film tank 102, and this communication pipeline can be freely opened and closed through a valve; through this communication pipeline, the pressure balance between the buffer tank 103 and the thin film tank 102 can be realized, so as to avoid the problem that the internal pressure of the thin film tank 102 is too large when the flash steam increases, resulting in the liquid natural gas in the buffer tank 103 not being able to spray out from the first pipeline 104; when it is necessary to use the suction mechanism to suck the liquid natural gas at the bottom of the thin film tank 102 into the buffer tank 103, the communication pipeline between the buffer tank 103 and the thin film tank 102 needs to be closed to avoid the inability to form negative pressure suction inside the buffer tank 103.

[0076] It should be noted that the storage tank 101 is used to form a protection outside the thin film tank 102, and an insulating layer is arranged between the storage tank 101 and the thin film tank 102. Although flash steam will be generated inside the thin film tank 102 due to the influence of external temperature or transportation kinetic energy, the internal temperature of the thin film tank 102 is still in a relatively low state, that is, the temperature of the flash steam itself is relatively low, and the temperature of the liquid natural gas at the bottom of the thin film tank 102 is relatively low. The self-liquefaction of the flash steam can be realized by using the liquid natural gas without the intervention of more external factors. When the flash steam is transported to the outside, the external environmental temperature is relatively high, which makes the flash steam quickly balance with the external environmental temperature, increasing the difficulty and energy consumption of flash steam re-liquefaction.

[0077] The usage method of the flash steam liquefaction system in this application is as follows: When it is detected that the pressure at the top of the thin-film tank 102 increases to the set threshold value, it means that the flash steam inside the thin-film tank 102 is approaching the critical value; close the first pipeline 104, open the second pipeline 105, and turn on the suction mechanism. By means of the suction mechanism, the buffer tank 103 is sucked. A negative pressure is generated inside the buffer tank 103 to suck the liquefied natural gas at the bottom of the thin-film 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 liquefied natural gas in the buffer tank 103 is sprayed onto the top of the thin-film tank 102 under the action of gravity and the pressure inside the tank. The liquefied natural gas cools the flash steam, and the flash steam is liquefied into liquefied natural gas.

[0078] Furthermore, as an optional embodiment of the present invention, the flash steam liquefaction system in this application further includes a first adapter pipe 106, and the suction mechanism is connected to the first adapter pipe 106 through a third pipeline 107; at the same time, there are multiple buffer tanks 103 in this application, and multiple buffer tanks 103 are all connected to the first adapter pipe 106, and valves are provided on the connection pipelines between each buffer tank 103 and the first adapter pipe 106. During the liquefaction process of the flash steam, due to the relatively large overall size of the thin-film tank 102, it is difficult to cool and liquefy the flash steam at all positions with a single-position spraying structure. Therefore, multiple groups of cooling mechanisms need to be arranged at the top of the thin-film tank 102. According to the liquefaction requirements of the flash steam at different positions of the thin-film tank 102, the corresponding cooling mechanisms are opened for cooling. At the same time, through the valve between the buffer tank 103 and the first adapter pipe 106, the suction mechanism can suck a single or part of the buffer tanks 103 to realize the independent use of each cooling mechanism.

[0079] Optionally, a plurality of branch pipes are arranged at the end of the first pipeline 104 connected to the thin-film tank 102, and the plurality of branch pipes can spray the top surface of the thin-film tank 102 to increase the liquefaction efficiency of the flash steam. Optionally, a plurality of groups of branch pipes are arranged vertically at the end of the first pipeline 104 connected to the thin-film tank 102, and the branch pipes at different heights can cool the flash steam at different heights to increase the liquefaction efficiency of the flash steam. Correspondingly, a plurality of branch pipes are also arranged at the bottom end of the second pipeline 105 connected to the thin-film tank 102, so as to increase the conveying efficiency of the liquefied natural gas to the buffer tank 103.

[0080] Further, as an alternative 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 thin film tank 102. The pressure detection mechanism 108 is used to detect the internal pressure of the thin film tank 102. When flash steam is generated inside the thin film tank 102, the internal pressure of the thin film tank 102 will increase accordingly. By monitoring the pressure inside the thin film tank 102, quantitative monitoring of the flash steam inside the thin film tank 102 is achieved. Optionally, there are multiple pressure detection mechanisms 108. The overall size of the thin film tank 102 is relatively large, and there are partial pressure differences in the pressure of the thin film tank 102 in different regions. Therefore, multiple pressure detection mechanisms 108 can be set to monitor the pressure in different regions of the thin film tank 102.

[0081] Further, as an alternative 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 is connected to a combustion assembly 109. The gas extracted by the suction mechanism in the present application from the buffer tank 103 is natural gas, which is not suitable for directly discharging the natural gas. It can be used as the fuel of the combustion assembly 109 for heating or power generation.

[0082] Further, as an alternative embodiment of the present invention, the suction mechanism in the present application includes a Venturi tube 114. The three ports of the Venturi tube 114 are respectively connected to a gas input mechanism, a gas treatment mechanism, and a third pipeline 107, and the third pipeline 107 is connected to the buffer tank 103. The present application can achieve negative pressure suction of the third pipeline 107 through the linkage of the gas input mechanism, the Venturi tube 114, and the gas treatment mechanism, so as to suck the liquefied natural gas in the thin film tank 102 into the buffer tank 103.

[0083] Optionally, the suction component in the present application can be various pump bodies with suction kinetic energy.

[0084] Further, the gas input mechanism in the present application is a first methane storage part 117, and the gas treatment mechanism is a combustion assembly 109. The main component of natural gas itself is 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 should be noted that the internal pressure of the first methane storage part 117 in the present application is relatively large, and the flow rate of methane when it is output from the first methane storage part 117 is relatively large, which can cooperate with the Venturi tube 114 to form a relatively large negative pressure.

[0085] 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.

[0086] 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 membrane 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 membrane tank 102 along the fourth pipeline 112, the first transfer tube 106 and the second pipeline 105, and the suction mechanism extracts the air from the top of the membrane 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.

[0087] 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.

[0088] Further, as an alternative 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 gas inside the membrane tank 102 with methane gas to facilitate subsequent injection of liquid cargo into the membrane tank 102. Specifically, the LNG storage system further includes a second gas cleaning mechanism for replacing the inert gas in the membrane tank 102 with methane gas. The second gas cleaning mechanism is connected to the top of the membrane tank 102; meanwhile, the suction mechanism is connected to the bottom of the membrane tank 102 through a pipeline. Methane is lighter than nitrogen, so 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 realize the replacement of the protective gas with methane and facilitate the subsequent injection of liquid cargo into the membrane tank 102.

[0089] Optionally, the second gas cleaning mechanism in the present application includes a first methane storage part 117. The first methane storage part 117 and the nitrogen storage part 111 are both connected to the same port of the Venturi tube 114 through branch pipes; and a second methane storage part 118, which is connected to the fifth pipeline 113. When it is necessary to replace the nitrogen gas 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 part 118 can be injected into the top of the membrane tank 102 through the connection between the second methane storage part 118, the fifth pipeline 113 and the top of the membrane tank 102. At the same time, the Venturi tube 114 extracts the nitrogen gas inside the membrane tank 102 from the bottom along the third pipeline 107, the first adapter 106 and the second pipeline 105, so as to realize the replacement of nitrogen with methane.

[0090] Further, as an alternative embodiment of the present invention, the gas treatment mechanism in the present application includes a combustion assembly 109 and an incineration assembly 110. Both the combustion assembly 109 and the incineration assembly 110 are connected to the same port of the Venturi tube 114 through branch pipes, and valves are provided on the connecting pipelines of the combustion assembly 109 and the incineration assembly 110 to the Venturi tube 114. When replacing nitrogen with methane, methane is a combustible gas, and directly discharging it will cause a large amount of energy waste. During the initial process of discharging nitrogen, the proportion of nitrogen is relatively large, and the nitrogen-methane mixed gas cannot burn, easily causing 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 treatment mechanism reaches the combustion requirement to burn and utilize methane. It should be noted that in the later stage of nitrogen evacuation, the mixed gas flowing through the gas treatment mechanism basically meets the engine power combustion requirement. Therefore, the gas treatment mechanism is provided with a combustion assembly 109 and an incineration assembly 110. The incineration assembly 110 is used to process the mixed gas with a relatively high nitrogen proportion to avoid methane waste; the combustion assembly 109 is used to process the mixed gas with a relatively high methane proportion to achieve kinetic energy supply.

[0091] Further, as an alternative embodiment of the present invention, a bypass pipe 115 is connected to the third pipeline 107 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 for sucking the gas at the top of the thin film tank 102 by a suction mechanism to achieve the suction of the gas at the top of the thin film tank 102.

[0092] Further, as an alternative embodiment of the present invention, the LNG storage system in the present application can also cool the thin film tank 102 to facilitate the injection of liquid cargo and transport the liquid cargo to the thin film tank 102. Specifically, the LNG storage system in the present application further includes a liquid cargo supply unit 119, and the liquid cargo supply unit 119 is connected to the buffer tank 103 through a sixth pipeline 120. At the initial stage of injecting liquefied natural gas, there is no liquefied natural gas retained in the buffer tank 103. Therefore, the liquid cargo supply unit 119 needs to supply liquefied natural gas to the buffer tank 103, and then the buffer tank 103 sprays liquefied natural gas through the first pipeline 104 to cool the thin film tank 102. When the temperature in the thin film tank 102 drops to an appropriate range, the flow rate can be increased, and the buffer tank 103 is used to inject liquefied natural gas into the thin film tank 102 to achieve the injection of liquid cargo; at the same time, during the cooling and liquid cargo injection stages of the thin film tank 102, the suction mechanism extracts the methane gas in the thin film tank 102 through the bypass pipe 115 and the fifth pipeline 113 to achieve pressure balance in the thin film tank 102.

[0093] Optionally, the sixth pipeline 120 in the present application is communicated with the first adapter 106, and a plurality of cooling mechanisms are connected to the first adapter 106. Through the combination of a plurality of buffer tanks 103 and the first pipeline 104, rapid cooling of the overall thin-film tank 102 and rapid injection of the liquid cargo can be achieved.

[0094] Optionally, the LNG storage system in the present application further includes a gas detection mechanism 116, and the detection end of the gas detection mechanism 116 is communicated with the top of the thin-film tank 102. The gas detection mechanism 116 is mainly used to detect the gas components in the thin-film tank 102, so as to monitor the air content and nitrogen content in the thin-film tank 102.

[0095] Optionally, the LNG storage system in the present application further 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. During input, the liquid level detection is mainly used to control the liquid cargo transportation volume; during transportation, the liquid level detection is mainly used to adapt to monitor the flash steam pressure to avoid excessive overall pressure of the thin-film tank 102.

[0096] As an optional embodiment of the present invention, the LNG storage system in the present application further includes a liquid cargo output part 124. The liquid cargo output part 124 is connected to the bottom of the thin-film tank 102 through a pipeline, and a liquid cargo pump 121 is arranged at the end of the pipeline connected to the thin-film tank 102 to pump out the liquid cargo in the thin-film tank 102 for liquid cargo transfer.

[0097] As an optional embodiment of the present invention, the LNG storage system in the present application further includes a helium storage part 122. The helium storage part 122 is respectively connected to the first adapter 106 and the second adapter 125 through the seventh pipeline 123. The helium storage part 122 is connected to the first adapter 106 and the second adapter 125 through the seventh pipeline 123, and then can be communicated with each pipeline of the LNG storage system through the first adapter 106 and the second adapter 125. Helium can be used to detect minute leaks in the pipelines, valves and thin-film tank 102 of the LNG storage system to ensure the overall tightness of the storage system.

[0098] It should be noted that the nitrogen storage part 111, the first methane storage part 117, the second methane storage part 118, the helium storage part 122 and the liquid cargo supply part 119 in the present application are all used to provide corresponding gases or liquid cargo. Each storage part can be a separate storage tank 101 structure, or can also represent a pipeline output node communicated with other gases or liquid cargo.

[0099] As another embodiment of the present invention, the present application further includes an LNG storage system, which includes a storage tank 101. Inside the storage tank 101, there is a membrane tank 102, and there is an installation gap between the storage tank 101 and the membrane tank 102. A buffer tank 103 is provided in this installation gap. The buffer tank 103 is located at the top of the membrane tank 102, and the buffer tank 103 is connected with a first pipeline 104 and a second pipeline 105. 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 both the first pipeline 104 and the second pipeline 105; and a suction mechanism, the suction mechanism is connected with the buffer tank 103 through a third pipeline 107; a first adapter 106, the first adapter 106 is connected with the third pipeline 107, and the first adapter 106 is communicated with the second pipeline 105; a nitrogen storage part 111, the nitrogen storage part 111 is connected with the top of the membrane tank 102 through a fourth pipeline 112, and the fourth pipeline 112 is connected with the first adapter 106, and a valve is provided on the connection path of the fourth pipeline 112 and the first adapter 106; a second methane storage part 118, the second methane storage part 118 is connected with the top of the membrane tank 102 through a fifth pipeline 113, and the fifth pipeline 113 is connected with the suction mechanism through a bypass pipe 115; a liquid cargo supply part 119, the liquid cargo supply part 119 is connected with the buffer tank 103 through a sixth pipeline 120.

[0100] The present application also provides a system that can achieve air evacuation, nitrogen replacement, cooling of the thin-film tank 102, and liquid cargo injection before liquid cargo storage in the thin-film tank 102. Specifically, in the present application, the nitrogen storage unit 111 injects nitrogen into the bottom of the thin-film tank 102 along the fourth pipeline 112, the first adapter 106, and the second pipeline 105. The suction mechanism communicates with the top of the thin-film tank 102 along the fifth pipeline 113 and evacuates the air inside the thin-film tank 102. After the air inside the thin-film tank 102 is evacuated, the nitrogen storage unit 111 stops injecting nitrogen into the thin-film tank 102, and the second methane storage unit 118 injects methane gas into the top of the thin-film tank 102 through the fifth pipeline 113. At the same time, the suction mechanism evacuates the nitrogen gas in the thin-film tank 102 from the bottom along the third pipeline 107, the first adapter 106, and the second pipeline 105 until all the gas in the thin-film tank 102 is replaced with methane. After all the nitrogen inside the thin-film tank 102 is replaced, the liquid cargo supply unit 119 inputs 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 thin-film tank 102 through the first pipeline 104 to cool the thin-film tank 102. At the same time, the suction mechanism evacuates the methane gas in the thin-film tank 102 along the bypass pipe 115 and the fifth pipeline 113 to achieve pressure balance inside the thin-film tank 102. As the temperature of the thin-film tank 102 gradually decreases, the input amount of liquefied natural gas can be appropriately increased until the liquefied natural gas is finally completely stored in the thin-film tank 102 to achieve liquid cargo input. The cooling and liquefaction of the flash steam in the thin-film tank 102 through the buffer tank 103, the first pipeline 104, the second pipeline 105, and the suction mechanism have been mentioned in the foregoing part and will not be elaborated herein.

[0101] As an alternative 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 a gas input mechanism, a gas treatment mechanism, and the third pipeline 107. The present application mainly realizes the negative pressure of the third pipeline 107 through the air flow drive of the gas input mechanism, the Venturi tube 114, and the gas treatment mechanism, and then extracts the gas inside the thin-film tank 102 through the first adapter 106 and provides negative pressure for the buffer tank 103.

[0102] As an alternative embodiment of the present invention, the gas input mechanism in the present application is the first methane storage unit 117, and the gas treatment mechanism includes a combustion component 109 and an incineration component 110. Both 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 pipelines of the combustion component 109 and the incineration component 110 to the Venturi tube 114.

[0103] As an alternative embodiment of the present invention, the LNG storage system in the present application further 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 inside the membrane tank 102 to detect the gas pressure and gas type inside the membrane tank 102.

[0104] As an alternative embodiment of the present invention, the LNG storage system in the present application further includes a liquid cargo output section 124. The liquid cargo output section 124 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 connecting the membrane tank 102 to pump out the liquid cargo in the membrane tank 102 to achieve liquid cargo transfer.

[0105] As an alternative embodiment of the present invention, the LNG storage section in the present application further includes a helium storage section 122. The helium storage section 122 is respectively connected to the first adapter 106 and the second adapter 125 through the seventh pipeline 123. The second adapter 125 is communicated with the fifth pipeline 113. The helium storage section 122 connects all the pipelines of the LNG storage system through the first adapter 106 and the second adapter 125 to detect minute leaks in each pipeline, valve and membrane tank 102 of the LNG storage system.

[0106] Furthermore, as an alternative embodiment of the present invention, the present application further includes an LNG storage maintenance method, which is realized through the above LNG storage system, and specifically includes the following steps:

[0107] Liquefaction of the flash gas in the membrane tank 102:

[0108] The suction mechanism provides a suction pressure to the buffer tank 103 along the third pipeline 107, and the buffer tank 103 sucks the liquid natural gas at the bottom of the membrane tank 102 into the buffer tank 103 through the second pipeline 105.

[0109] Close the suction mechanism and the second pipeline 105, and open the first pipeline 104. The buffer tank 103 sprays liquid natural gas to the top of the membrane tank 102 through the first pipeline 104 to achieve liquefaction of the flash gas.

[0110] As an alternative embodiment of the present invention, before the liquefaction of the flash gas in the membrane tank 102, the following steps are further included:

[0111] S1. Inject nitrogen into the interior of the membrane tank 102 and discharge the air in the membrane tank 102;

[0112] S2. Inject methane into the interior of the membrane tank 102 and discharge the nitrogen in the membrane tank 102;

[0113] S3. Spray liquid natural gas into the interior of the membrane tank 102 to cool the membrane tank 102;

[0114] S4. Inject liquefied natural gas into the interior of the thin-film tank 102 to achieve the storage of liquefied natural gas.

[0115] As an alternative embodiment of the present invention, step S1 specifically includes:

[0116] A part of the gas flow in the nitrogen storage section 111 injects nitrogen into the bottom of the thin-film tank 102 along the fourth pipeline 112, the first adapter 106, and the second pipeline 105;

[0117] Another part of the gas flow in the nitrogen storage section 111 inputs nitrogen along the Venturi tube 114 and the incineration assembly 110 to form a negative pressure suction, and the Venturi tube 114 extracts the air at the top of the thin-film tank 102 along the bypass pipe 115 and the fifth pipeline 113.

[0118] When the gas detection mechanism 116 detects that the interior of the thin-film tank 102 is basically nitrogen, the air evacuation is completed. When the air evacuation is completed, the nitrogen content inside the thin-film tank 102 is judged according to the general industry standard and will not be elaborated here.

[0119] As an alternative embodiment of the present invention, step S2 specifically includes:

[0120] The second methane storage section 118 injects methane into the top of the thin-film tank 102 along the fifth pipeline 113;

[0121] The first methane storage section 117 inputs methane along the Venturi tube 114 and the incineration assembly 110 to form a negative pressure suction; the Venturi tube 114 extracts nitrogen from the bottom of the thin-film tank 102 along the third pipeline 107, the first adapter 106, and the second pipeline 105.

[0122] When the gas detection mechanism 116 detects that the interior of the thin-film tank 102 is basically methane, the nitrogen replacement is completed.

[0123] As an alternative embodiment of the present invention, step S3 specifically includes:

[0124] The liquid cargo supply section 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 thin-film tank 102 along the first pipeline 104 to cool the interior of the thin-film tank 102;

[0125] The first methane storage section 117 inputs methane along the Venturi tube 114 and the combustion assembly 109 to form a negative pressure suction; the Venturi tube 114 extracts the methane gas from the top of the thin-film tank 102 along the bypass pipe 115 and the fifth pipeline 113 to achieve pressure balance inside the thin-film tank 102.

[0126] The liquid cargo injection in step S4 is similar to the cooling of the thin-film tank 102. After the temperature of the thin-film tank 102 reaches the set condition, the input amount of liquefied natural gas from the liquid cargo supply section 119 can be increased to achieve the storage of liquid cargo.

[0127] It should be noted that when each pipeline in this application performs air evacuation, nitrogen replacement, cooling of the thin-film tank 102, liquid cargo injection, and flash steam cooling, valves are provided on each pipeline. Different air flow directions can be achieved by opening and closing different valves. The pipelines not mentioned with valves are not considered as limitations of the present invention.

[0128] Those skilled in the art can easily understand that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An LNG storage system for storing liquid natural gas in a membrane tank, 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; A suction mechanism, the suction mechanism is connected to the cache tank, and the suction mechanism is used to provide negative pressure to the cache tank; the suction mechanism includes a venturi tube, and the three ports of the venturi tube are respectively connected to a gas processing mechanism, a third pipeline and a 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 sucks the negative pressure of the third pipeline; a first gas cleaning mechanism, the first gas cleaning mechanism is connected to the membrane tank, and the first gas cleaning mechanism is used to replace the air in the membrane tank with an inert gas; the first gas cleaning mechanism includes a first transfer tube, the nitrogen storage unit and a fifth pipeline; 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; the nitrogen storage unit is connected to the first transfer tube through a fourth pipeline; one end of the fifth pipeline is connected to the top of the membrane tank, and the other end thereof is connected to the venturi tube; a second gas cleaning mechanism, 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; the second gas cleaning mechanism includes a first methane storage part, 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 part, the second methane storage part 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 system according to claim 1, characterized in that: It also includes a liquid cargo supply unit, which is connected to the cache tank through a sixth pipeline.

3. The LNG storage system according to claim 1, 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.

4. The LNG storage system according to claim 1, 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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