A device for reducing BOG emissions from LNG storage tanks

Abstract

This invention provides a device for reducing BOG emissions from LNG storage tanks, comprising an LNG storage tank unit, a liquid nitrogen unit, a pressure remote detection unit, a liquid nitrogen supply regulating valve, and a liquid nitrogen outlet shut-off valve. The liquid nitrogen unit includes a first liquid nitrogen storage tank, a second liquid nitrogen storage tank, a first pipeline, and a second pipeline. The first end of the first pipeline extends into the first liquid nitrogen storage tank, and the second end extends into the gas phase space of the LNG storage tank unit. The first end of the second pipeline extends into the second liquid nitrogen storage tank, and the second end extends into the gas phase space of the LNG storage tank unit and connects to the second end of the first pipeline. The portions of the first and second pipelines located in the gas phase space are heat exchange coils. The pressure remote detection unit is connected to the LNG storage tank unit. The liquid nitrogen supply regulating valve is located in the first pipeline, and the liquid nitrogen outlet shut-off valve is located in the second pipeline. The liquid nitrogen supply regulating valve is interlocked with the pressure remote detection unit. One technical advantage of this invention is that it can effectively reduce BOG emissions from LNG storage tanks.

Description

Technical Field

[0001] This utility model belongs to the field of emission technology for LNG storage tank BOG, and specifically relates to a device for reducing LNG storage tank BOG emissions. Background Technology

[0002] LNG (liquefied natural gas) is a high-quality, efficient, and economical clean energy source that plays an increasingly important role in social production and daily life, especially in the transportation sector.

[0003] LNG in LNG storage tanks can absorb heat and heat up due to various factors, producing BOG (Boil-Off Gas). Direct release of BOG into the atmosphere not only wastes energy and causes economic losses but also poses safety and environmental risks. Currently, BOG recovery processes at LNG terminals mainly include liquefaction recovery and regasification followed by injection into gas pipelines for natural gas supply. However, liquefaction recovery requires deep cooling of the BOG, which is complex and necessitates the construction of deep cooling equipment, resulting in high investment and operating costs and increased maintenance workload. Regasification followed by injection into gas pipelines for natural gas supply is constrained by the availability of existing gas pipelines nearby and requires the construction of new pressurization and heat exchange equipment, leading to high investment costs. Furthermore, selling LNG as natural gas after regasification results in lower prices and poor economic viability.

[0004] In summary, there is an urgent need for a device to reduce BOG emissions from LNG storage tanks using a low-cost process, which is of great significance for improving the economic efficiency and safety management of LNG terminals. Utility Model Content

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art and provide a new technical solution for a device to reduce BOG emissions from LNG storage tanks.

[0006] According to one aspect of this application, an apparatus for reducing BOG emissions from LNG storage tanks is provided, comprising:

[0007] An LNG storage tank unit and a liquid nitrogen unit; the LNG storage tank unit has a gas phase space and a liquid phase space, and the gas phase space is located above the liquid phase space;

[0008] The liquid nitrogen unit includes a first liquid nitrogen storage tank, a second liquid nitrogen storage tank, a first pipeline, and a second pipeline. A first end of the first pipeline extends into the first liquid nitrogen storage tank, and a second end extends into the gas phase space of the LNG storage tank unit. A first end of the second pipeline extends into the second liquid nitrogen storage tank, and a second end extends into the gas phase space of the LNG storage tank unit and connects to the second end of the first pipeline. The first liquid nitrogen storage tank stores liquid nitrogen as a cooling medium, and the second liquid nitrogen storage tank stores liquid nitrogen after heat exchange. The portions of the first and second pipelines located in the gas phase space of the LNG storage tank unit are heat exchange coils.

[0009] The system includes a pressure remote detection unit, a liquid nitrogen supply regulating valve, and a liquid nitrogen outlet shut-off valve. The pressure remote detection unit is connected to the LNG storage tank unit and is used to detect the pressure of the LNG storage tank unit. The liquid nitrogen supply regulating valve is located in the first pipeline, and the liquid nitrogen outlet shut-off valve is located in the second pipeline. The liquid nitrogen supply regulating valve is interlocked with the pressure remote detection unit, and the liquid nitrogen outlet shut-off valve is normally open.

[0010] In this embodiment, when the pressure remote detection unit detects an increase in the pressure of the LNG storage tank unit, it interlocks and opens the liquid nitrogen supply regulating valve. Liquid nitrogen passes sequentially through the first liquid nitrogen storage tank, the first pipeline, the LNG storage tank unit, the second pipeline, and the second liquid nitrogen storage tank to cool the gas phase space of the LNG storage tank unit and cool the BOG into LNG. When the pressure remote detection unit detects that the pressure of the LNG storage tank unit has dropped to a preset range, it interlocks and closes the liquid nitrogen supply regulating valve.

[0011] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a vacuum insulation layer, a vacuum valve, and a vacuum sight valve;

[0012] Both the LNG storage tank unit and the liquid nitrogen unit are housed within the vacuum insulation layer, which has a closed chamber.

[0013] The vacuum insulation layer is equipped with a vacuum valve and a vacuum sight valve that communicate with the sealed chamber.

[0014] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a main shut-off valve;

[0015] The first pipeline is equipped with the main shut-off valve near the first liquid nitrogen storage tank, and the main shut-off valve is normally open.

[0016] Optionally, the heat exchange coil is equipped with fins, and the coil configuration is determined according to the shape of the LNG storage tank. Guide baffles are provided on the wall of the heat exchange coil, and drain holes are evenly distributed at the lowest point of the guide baffles. This effectively facilitates the drainage of the heat exchange coil.

[0017] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a third pipeline and a first shut-off valve;

[0018] The first end of the third pipe is connected to the first pipe, the second end of the third pipe is connected to the second pipe, and the first shut-off valve is provided on the third pipe.

[0019] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a fourth pipeline and a first regulating valve;

[0020] One end of the fourth pipeline is connected to the second liquid nitrogen storage tank, and the first regulating valve is installed on the fourth pipeline;

[0021] Nitrogen gas is supplied to the second liquid nitrogen storage tank through the fourth pipeline.

[0022] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a fifth pipeline and a second regulating valve;

[0023] One end of the fifth pipeline is connected to the first liquid nitrogen storage tank, and the second regulating valve is installed on the fifth pipeline;

[0024] Nitrogen gas is supplied to the first liquid nitrogen storage tank through the fifth pipeline.

[0025] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a venting pipe and a venting valve;

[0026] One end of the venting pipe is connected to the first pipe, and the connection point between the venting pipe and the first pipe is located between the liquid nitrogen supply regulating valve and the main shut-off valve; the venting pipe is equipped with the venting valve.

[0027] Optionally, the device for reducing BOG emissions from LNG storage tanks further includes a first pressure regulating pipeline, a first pressure regulating valve, a second pressure regulating pipeline, and a second pressure regulating valve;

[0028] One end of the first pressure regulating pipeline is connected to the first liquid nitrogen storage tank, and the other end is connected to the plant venting system; the first pressure regulating valve is installed in the first pressure regulating pipeline;

[0029] One end of the second pressure regulating pipeline is connected to the second liquid nitrogen storage tank, and the other end is connected to the plant venting system; the second pressure regulating valve is installed on the second pressure regulating pipeline.

[0030] Optionally, the device for reducing BOG emissions from LNG storage tanks further includes a first safety valve, a first rupture disc, a second safety valve, and a second rupture disc;

[0031] Both the first safety valve and the first rupture disc are installed in the first pressure regulating pipeline, and the first safety valve and the first rupture disc are respectively connected in parallel with the first pressure regulating valve;

[0032] The second safety valve and the second rupture disc are both installed in the second pressure regulating pipeline, and the second safety valve and the second rupture disc are respectively connected in parallel with the second pressure regulating valve.

[0033] One technical advantage of this application is:

[0034] In this embodiment, when the pressure remote detection unit detects an increase in the pressure of the LNG storage tank unit, it interlocks and opens the liquid nitrogen supply regulating valve. Liquid nitrogen passes sequentially through the first liquid nitrogen storage tank, the first pipeline, the LNG storage tank unit, the second pipeline, and the second liquid nitrogen storage tank to cool the gas phase space of the LNG storage tank unit and cool the BOG into LNG. When the pressure remote detection unit detects that the pressure of the LNG storage tank unit has dropped to a preset range, it interlocks and closes the liquid nitrogen supply regulating valve.

[0035] Therefore, this device for reducing BOG emissions from LNG storage tanks can effectively reduce BOG emissions from LNG storage tanks. It involves intermittently injecting liquid nitrogen into the LNG storage tank unit (allowing for extended operation after each injection). The liquid nitrogen sequentially passes through a first liquid nitrogen tank, a first pipeline, the LNG storage tank unit, a second pipeline, and a second liquid nitrogen tank to cool the gas phase space of the LNG storage tank unit and convert the BOG into LNG, thereby significantly reducing BOG emissions and increasing economic benefits. Furthermore, it requires minimal modification to existing facilities, has a short construction period, and low modification costs. It also effectively addresses the investment, land occupation, heat loss, operation and maintenance, safety, and management issues associated with constructing various new equipment, pipelines, and valves for BOG recovery in existing technologies. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a device for reducing BOG emissions from LNG storage tanks according to an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the structure of a heat exchange coil of a device for reducing BOG emissions from LNG storage tanks according to an embodiment of the present invention.

[0038] Figure 3 for Figure 2 Cross-sectional view along the AA direction;

[0039] Figure 4 for Figure 2 Cross-sectional view along the BB direction;

[0040] Figure 5 for Figure 2 Cross-sectional view along the CC direction.

[0041] In the diagram: 1. LNG storage tank unit; 2. Liquid nitrogen unit; 21. First liquid nitrogen storage tank; 22. Second liquid nitrogen storage tank; 23. First pipeline; 24. Second pipeline; 3. Pressure remote detection unit; 4. Liquid nitrogen supply regulating valve; 5. Liquid nitrogen outlet shut-off valve; 61. First injection pipeline; 62. First switching valve; 71. Second injection pipeline; 72. Second switching valve; 8. Main shut-off valve; 9. Third pipeline; 10. First shut-off valve; 11. Fourth pipeline; 121. First regulating valve; 122. First pressure transmitter; 13. Fifth pipeline; 141. Second regulating valve; 142. Second pressure transmitter 15. Nitrogen source pipeline in the plant area; 16. Vent pipeline; 17. Vent valve; 181. First pressure regulating pipeline; 182. First pressure regulating valve; 183. Second pressure regulating pipeline; 184. Second pressure regulating valve; 185. First safety valve; 186. First rupture disc; 187. Second safety valve; 188. Second rupture disc; 191. Vacuum insulation layer; 192. Vacuum valve; 193. Vacuum sight valve; 20. Heat exchange coil; 201. Guide baffle; 31. First branch; 311. Third regulating valve; 312. Third pressure transmitter; 32. First level gauge; 33. Second level gauge. Detailed Implementation

[0042] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0043] The embodiments of this application will now be described in detail. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0044] The terms "first" and "second" in the specification and claims of this application may explicitly or implicitly include one or more of the features. In the description of this application, unless otherwise stated, "multiple" means two or more. Furthermore, "and / or" in the specification and claims indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0045] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0046] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0047] According to a first aspect of the invention, see Figures 1 to 5 This invention provides a device for reducing BOG emissions from LNG storage tanks. It can be applied to various LNG terminals to reduce BOG emissions, particularly LNG refueling stations and LNG receiving terminals that lack natural gas liquefaction capabilities but have LNG storage tanks. Furthermore, it utilizes liquid nitrogen to cool the gas phase space of the LNG storage tank, thereby reducing BOG emissions. This device offers advantages such as low investment, efficient space utilization, reduced operating costs, safety and environmental friendliness, and wide applicability.

[0048] Specifically, the device for reducing BOG emissions from LNG storage tanks includes:

[0049] LNG storage tank unit 1 and liquid nitrogen unit 2; the LNG storage tank unit 1 has a gas phase space and a liquid phase space, and the gas phase space is located above the liquid phase space;

[0050] The liquid nitrogen unit 2 includes a first liquid nitrogen storage tank 21, a second liquid nitrogen storage tank 22, a first pipe 23, and a second pipe 24. The first end of the first pipe 23 extends into the first liquid nitrogen storage tank 21, and the second end extends into the gas phase space of the LNG storage tank unit 1. The first end of the second pipe 24 extends into the second liquid nitrogen storage tank 22, and the second end extends into the gas phase space of the LNG storage tank unit 1 and connects to the second end of the first pipe 23. The first liquid nitrogen storage tank 21 stores liquid nitrogen as a cooling medium, and the second liquid nitrogen storage tank 22 stores liquid nitrogen after heat exchange. The portions of the first pipe 23 and the second pipe 24 located in the gas phase space of the LNG storage tank unit 1 form heat exchange coils 20. That is, liquid nitrogen sequentially passes through the first liquid nitrogen storage tank 21, the first pipe 23, the LNG storage tank unit 1, the second pipe 24, and the second liquid nitrogen storage tank 22 to cool the gas phase space of the LNG storage tank unit 1 and cool BOG into LNG, thereby significantly reducing BOG emissions and increasing economic benefits.

[0051] The system includes a pressure remote detection unit 3, a liquid nitrogen supply regulating valve 4, and a liquid nitrogen outlet shut-off valve 5. The pressure remote detection unit 3 is connected to the LNG storage tank unit 1 and is used to detect the pressure of the LNG storage tank unit 1. The liquid nitrogen supply regulating valve 4 is located in the first pipeline 23, and the liquid nitrogen outlet shut-off valve 5 is located in the second pipeline 24. The liquid nitrogen supply regulating valve 4 is interlocked with the pressure remote detection unit 3, and the liquid nitrogen outlet shut-off valve 5 is normally open.

[0052] In this embodiment, when the pressure remote detection unit detects an increase in the pressure of the LNG storage tank unit, it interlocks and opens the liquid nitrogen supply regulating valve. Liquid nitrogen passes sequentially through the first liquid nitrogen storage tank, the first pipeline, the LNG storage tank unit, the second pipeline, and the second liquid nitrogen storage tank to cool the gas phase space of the LNG storage tank unit and cool the BOG into LNG. When the pressure remote detection unit detects that the pressure of the LNG storage tank unit has dropped to a preset range, it interlocks and closes the liquid nitrogen supply regulating valve.

[0053] Therefore, this device for reducing BOG emissions from LNG storage tanks can effectively reduce BOG emissions from LNG storage tanks. Specifically, it intermittently injects liquid nitrogen into LNG storage tank unit 1 (allowing for extended operation after each injection). The liquid nitrogen sequentially passes through the first liquid nitrogen storage tank 21, the first pipeline 23, LNG storage tank unit 1, the second pipeline 24, and the second liquid nitrogen storage tank 22 to cool the gas phase space of LNG storage tank unit 1 and convert the BOG into LNG, thereby significantly reducing BOG emissions and increasing economic benefits. Furthermore, this device requires only a small additional floor space and a limited amount of equipment. The modification work for existing stations is minimal, with a short construction period and low cost. It also effectively addresses the investment, land occupation, heat loss, operation and maintenance, safety, and management issues associated with the construction of various new equipment, pipelines, and valves required for BOG recovery in existing technologies.

[0054] Optionally, the device for reducing BOG emissions from LNG storage tanks further includes a first injection pipe 61, a first switching valve 62, a second injection pipe 71, and a second switching valve 72. The first injection pipe 61 is connected to the first liquid nitrogen storage tank 21, and the first injection pipe 61 is equipped with the first switching valve 62. The second injection pipe 71 is connected to the second liquid nitrogen storage tank 22, and the second injection pipe 71 is equipped with the second switching valve 72. Liquid nitrogen can be injected into the first liquid nitrogen storage tank 21 through the first injection pipe 61, and liquid nitrogen can be injected into the second liquid nitrogen storage tank 22 through the second injection pipe 71.

[0055] Optionally, the heat exchange coil 20 is provided with fins, and the coil configuration is determined according to the shape of the LNG storage tank. The tube wall of the heat exchange coil 20 is provided with guide baffles 201, and drain holes are evenly distributed at the low point of the guide baffles 201. This can effectively achieve draining of the heat exchange coil 20.

[0056] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a main shut-off valve 8;

[0057] The first pipeline 23 is equipped with the main shut-off valve 8 near the first liquid nitrogen storage tank 21, and the main shut-off valve 8 is normally open.

[0058] In the above embodiment, the main shut-off valve 8 helps to quickly close the first pipeline 23.

[0059] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a third pipeline 9 and a first shut-off valve 10;

[0060] The first end of the third pipe 9 is connected to the first pipe 23, the second end of the third pipe 9 is connected to the second pipe 24, and the first shut-off valve 10 is provided on the third pipe 9.

[0061] In the above embodiment, the connection between the first liquid nitrogen storage tank 21 and the second liquid nitrogen storage tank 22 can be realized through the third pipe 9, which helps to replenish liquid nitrogen to the first liquid nitrogen storage tank 21 through the second liquid nitrogen storage tank 22, and also realizes the recycling of liquid nitrogen.

[0062] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a fourth pipeline 11, a first regulating valve 121, a fifth pipeline 13, and a second regulating valve 141;

[0063] One end of the fourth pipe 11 is connected to the second liquid nitrogen storage tank 22, and the first regulating valve 121 is installed on the fourth pipe 11; the other end of the fourth pipe 11 is connected to the nitrogen source pipe 15 in the plant area; nitrogen is supplied to the second liquid nitrogen storage tank 22 through the fourth pipe 11.

[0064] One end of the fifth pipe 13 is connected to the first liquid nitrogen storage tank 21, and the second regulating valve 141 is installed on the fifth pipe 13; the other end of the fifth pipe 13 is connected to the nitrogen source pipe 15 in the plant area; nitrogen is replenished into the first liquid nitrogen storage tank 21 through the fifth pipe 13.

[0065] In the above embodiment, the pressure of the second liquid nitrogen storage tank 22 is regulated by the fourth pipe 11, and the pressure of the first liquid nitrogen storage tank 21 is regulated by the fifth pipe 13.

[0066] For example, a first pressure transmitter 122 is provided on the fourth pipe 11; and a second pressure transmitter 142 is provided on the fifth pipe 13.

[0067] In one specific embodiment, the device for reducing BOG emissions from LNG storage tanks further includes a first branch line 31, a third regulating valve 311, and a third pressure transmitter 312; one end of the first branch line 31 is connected to the nitrogen source pipeline 15 in the plant area, and the other end is connected to the venting pipeline 16.

[0068] For example, the device for reducing BOG emissions from LNG storage tanks also includes a first level gauge 32 and a second level gauge 33. The first level gauge 32 is connected to the first liquid nitrogen storage tank 21 and is used to measure the liquid level of the first liquid nitrogen storage tank 21. The second level gauge 33 is connected to the second liquid nitrogen storage tank 22 and is used to measure the liquid level of the second liquid nitrogen storage tank 22.

[0069] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a vent pipe 16 and a vent valve 17;

[0070] One end of the vent pipe 16 is connected to the first pipe 23, and the connection point between the vent pipe 16 and the first pipe 23 is located between the liquid nitrogen supply regulating valve 4 and the main shut-off valve 8; the vent pipe 16 is provided with the vent valve 17. For example, the connection point between the vent pipe 16 and the first pipe 23 is located between the liquid nitrogen supply regulating valve 4 and the connection point between the third pipe 9 and the first pipe 23.

[0071] In the above embodiment, the venting pipe 16 facilitates the venting of the first liquid nitrogen storage tank 21 or the second liquid nitrogen storage tank 22, making the operation very convenient.

[0072] Optionally, the device for reducing BOG emissions from LNG storage tanks further includes a first pressure regulating pipe 181, a first pressure regulating valve 182, a second pressure regulating pipe 183, and a second pressure regulating valve 184.

[0073] One end of the first pressure regulating pipeline 181 is connected to the first liquid nitrogen storage tank 21, and the other end is connected to the plant venting system; the first pressure regulating valve 182 is installed on the first pressure regulating pipeline 181;

[0074] One end of the second pressure regulating pipeline 183 is connected to the second liquid nitrogen storage tank 22, and the other end is connected to the plant venting system; the second pressure regulating valve 184 is installed on the second pressure regulating pipeline 183.

[0075] In the above embodiment, the pressure of the first liquid nitrogen storage tank 21 is regulated by the first pressure regulating pipe 181, and the pressure of the second liquid nitrogen storage tank 22 is regulated by the second pressure regulating pipe 183, which is simple to operate.

[0076] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a first safety valve 185, a first rupture disc 186, a second safety valve 187, and a second rupture disc 188.

[0077] The first safety valve 185 and the first rupture disc 186 are both disposed in the first pressure regulating pipeline 181, and the first safety valve 185 and the first rupture disc 186 are respectively disposed in parallel with the first pressure regulating valve 182;

[0078] The second safety valve 187 and the second rupture disc 188 are both located in the second pressure regulating pipeline 183, and the second safety valve 187 and the second rupture disc 188 are respectively connected in parallel with the second pressure regulating valve 184.

[0079] In the above embodiments, it helps to ensure the safety of the first pressure regulating pipe 181 and the second pressure regulating pipe 183.

[0080] Optionally, the device for reducing BOG emissions from LNG storage tanks also includes a vacuum insulation layer 191, a vacuum valve 192, and a vacuum sight valve 193;

[0081] Both the LNG storage tank unit 1 and the liquid nitrogen unit 2 are disposed within the vacuum insulation layer 191, which has a closed chamber.

[0082] The vacuum insulation layer 191 is provided with a vacuum valve 192 and a vacuum sight valve 193 that communicate with the sealed chamber.

[0083] In the above embodiment, the vacuum insulation layer 191 helps reduce the loss of cooling capacity, resulting in good energy-saving performance. The vacuum valve 192 helps maintain the vacuum level within the vacuum insulation layer 191. The vacuum sight valve 193 helps to monitor the vacuum level within the vacuum insulation layer 191 in real time.

[0084] According to a second aspect of the present invention, a method for reducing BOG emissions from LNG storage tanks is provided, applicable to the apparatus for reducing BOG emissions from LNG storage tanks as described in the first aspect, wherein the normal process includes the following steps:

[0085] When the pressure remote detection unit 3 detects an increase in the pressure of LNG storage tank unit 1, it interlocks and opens the liquid nitrogen supply regulating valve 4. Liquid nitrogen passes sequentially through the first liquid nitrogen storage tank 21, the first pipeline 23, LNG storage tank unit 1, the second pipeline 24, and the second liquid nitrogen storage tank 22 to cool the gas phase space of LNG storage tank unit 1 and cool BOG into LNG. The pressure of the first liquid nitrogen storage tank 21 is greater than the pressure of the second liquid nitrogen storage tank 22. If the pressure of the first liquid nitrogen storage tank 21 is not greater than the pressure of the second liquid nitrogen storage tank 22, pressure replenishment operation of the first liquid nitrogen storage tank 21 or pressure relief operation of the second liquid nitrogen storage tank 22 can be carried out according to the specific operating conditions. See the pressure replenishment process and pressure relief process for details.

[0086] When the pressure remote detection unit 3 detects that the pressure of the LNG storage tank unit 1 has dropped to the preset range, it interlocks and closes the liquid nitrogen supply regulating valve 4.

[0087] In this embodiment, the method for reducing BOG emissions from LNG storage tanks effectively reduces BOG emissions by intermittently injecting liquid nitrogen into the LNG storage tank unit 1 (allowing for extended operation after each injection). The liquid nitrogen sequentially passes through the first liquid nitrogen tank 21, the first pipeline 23, the LNG storage tank unit 1, the second pipeline 24, and the second liquid nitrogen tank 22 to cool the gas phase space of the LNG storage tank unit 1 and convert the BOG into LNG, thereby significantly reducing BOG emissions and increasing economic benefits. Furthermore, it requires less modification work to existing facilities, has a shorter construction period, and lower modification costs. It also effectively addresses the investment, land occupation, heat loss, operation and maintenance, safety, and management issues associated with constructing various new equipment, pipelines, and valves for BOG recovery in existing technologies.

[0088] Optionally, the liquid pressure process is as follows: when the liquid level of the first liquid nitrogen storage tank 21 is lower than the low alarm level or the liquid level of the second liquid nitrogen storage tank 22 is higher than the high alarm level, the first shut-off valve 10 is opened to replenish liquid nitrogen to the first liquid nitrogen storage tank 21 through the second liquid nitrogen storage tank 22; or, the first pressure regulating valve 182 is opened first to depressurize the first liquid nitrogen storage tank 21 through the first pressure regulating pipe 181, and then the first shut-off valve 10 is opened to replenish liquid nitrogen to the first liquid nitrogen storage tank 21 through the second liquid nitrogen storage tank 22.

[0089] In the above embodiments, the operation of the hydraulic pressurization process is very simple and can effectively reduce the emissions of BOG from LNG storage tanks.

[0090] Optionally, the liquid nitrogen venting process is as follows: when it is necessary to vent the first liquid nitrogen storage tank 21, the venting valve 17 is opened, and the liquid nitrogen in the first liquid nitrogen storage tank 21 is discharged into the plant venting system through the first pipeline 23 and the venting pipeline 16.

[0091] When it is necessary to vent the second liquid nitrogen storage tank 22, close the main shut-off valve 8, open the first shut-off valve 10 and the vent valve 17, and discharge the liquid nitrogen in the second liquid nitrogen storage tank 22 into the plant venting system through the second pipeline 24, the third pipeline 9 and the vent pipeline 16.

[0092] In the above embodiments, it is helpful to drain and empty the first liquid nitrogen storage tank 21 or the second liquid nitrogen storage tank 22, and the operation is simple.

[0093] Optionally, when the liquid level in the first liquid nitrogen storage tank 21 is lower than the low alarm level, a liquid pressure operation can be performed. If the liquid level in the first liquid nitrogen storage tank 21 is still lower than the low alarm level after the liquid pressure operation, liquid nitrogen needs to be added.

[0094] The procedure for replenishing liquid nitrogen is as follows:

[0095] Nitrogen injection process for the first liquid nitrogen storage tank 21: Open the first switch valve 62 to inject liquid nitrogen into the first liquid nitrogen storage tank 21.

[0096] Nitrogen injection process for the second liquid nitrogen storage tank 22: Open the second switch valve 72 to inject liquid nitrogen into the second liquid nitrogen storage tank 22.

[0097] Optionally, the pressure replenishment process is as follows:

[0098] During the normal cooling process, the liquid nitrogen in the first liquid nitrogen storage tank 21 gradually decreases, causing its pressure to drop, which in turn prevents liquid nitrogen from flowing from the first liquid nitrogen storage tank 21 into the heat exchange coil 20. To meet normal operation requirements, nitrogen can be added to the gas phase space of the first liquid nitrogen storage tank 21.

[0099] When the liquid pressure process is started, the initial pressure of the second liquid nitrogen storage tank 22 may be lower than that of the first liquid nitrogen storage tank 21, and nitrogen can be added to the gas phase space of the second liquid nitrogen storage tank 22.

[0100] Specifically, the pressurization process of the first liquid nitrogen storage tank 21 is as follows: nitrogen can be supplied from the plant’s nitrogen source. The second regulating valve 141 is opened to inject nitrogen into the first liquid nitrogen storage tank 21. The pressure inside the first liquid nitrogen storage tank 21 can be monitored by the second pressure transmitter 142.

[0101] The pressurization process for the second liquid nitrogen storage tank 22 is as follows: nitrogen can be supplied from the plant’s nitrogen source. The first regulating valve 121 is opened to inject nitrogen into the second liquid nitrogen storage tank 22. The pressure inside the second liquid nitrogen storage tank 22 can be monitored by the first pressure transmitter 122.

[0102] In one specific implementation, the pressure relief process is as follows:

[0103] During the normal cooling process, the liquid nitrogen in the first liquid nitrogen storage tank 21 gradually decreases, causing its pressure to drop, which in turn prevents liquid nitrogen from flowing from the first liquid nitrogen storage tank 21 into the heat exchange coil 20. To meet normal operation requirements, the pressure in the second liquid nitrogen storage tank 22 can be released.

[0104] When the liquid pressure process is started, the pressure in the second liquid nitrogen storage tank 22 may be lower than that in the first liquid nitrogen storage tank 21. In order to realize the liquid pressure process, the pressure in the first liquid nitrogen storage tank 21 can be depressurized.

[0105] Specifically, the depressurization process of the first liquid nitrogen storage tank 21 is as follows: Open the first pressure regulating valve 182, and the first liquid nitrogen storage tank 21 can be depressurized through the plant venting system.

[0106] The depressurization process for the second liquid nitrogen storage tank 22 is as follows: Open the second pressure regulating valve 184, and the pressure of the second liquid nitrogen storage tank 22 can be depressurized through the plant venting system.

[0107] For example, the purging process for heat exchanger coil 20 is as follows:

[0108] Purging of heat exchanger coil 20: Connect the nitrogen source in the station, close the main shut-off valve 8, open the third regulating valve 311 and the second pressure regulating valve 184. After purging is completed, close the first shut-off valve 10, the third regulating valve 311 and the second pressure regulating valve 184 in sequence. The purging pressure change can be monitored by the third pressure transmitter 312.

[0109] For example, the emergency venting procedure is as follows:

[0110] The first liquid nitrogen storage tank 21 is equipped with a first safety valve 185 for emergency venting under overpressure conditions. If the safety valve branch is frozen and blocked, it can be vented through the first rupture disc 186. The second liquid nitrogen storage tank 22 is equipped with a second safety valve 187 for emergency venting under overpressure conditions. If the safety valve branch is frozen and blocked, it can be vented through the second rupture disc 188.

[0111] It should be noted that, firstly, to ensure the normal flow of liquid nitrogen in the cooling process, the pressure of the first liquid nitrogen storage tank 21 must be maintained higher than that of the second liquid nitrogen storage tank 22. This can be achieved by using a nitrogen source within the plant area to replenish the pressure, opening the second regulating valve 141 to inject nitrogen into the first liquid nitrogen storage tank 21, and monitoring the pressure inside the first liquid nitrogen storage tank 21 using the second pressure transmitter 142.

[0112] Secondly, the liquid nitrogen outlet shut-off valve 5 is a normally open valve, and the main shut-off valve 8 is also a normally open valve. The pressure remote detection unit 3 of the gas phase space of LNG storage tank unit 1 and the liquid nitrogen supply regulating valve 4 are interlocked. When the pressure of the gas phase space of LNG storage tank unit 1 rises, the interlock opens the liquid nitrogen supply regulating valve 4 to inject liquid nitrogen into the heat exchange coil 20 in LNG storage tank unit 1 to cool the gas phase space in LNG storage tank unit 1. After the pressure of the gas phase space of LNG storage tank unit 1 drops to a reasonable range, the interlock closes the liquid nitrogen supply regulating valve 4.

[0113] Thirdly, as liquid nitrogen continuously flows from the first liquid nitrogen storage tank 21 to the second liquid nitrogen storage tank 22, the pressure in the first liquid nitrogen storage tank 21 continuously decreases, while the pressure in the second liquid nitrogen storage tank 22 continuously increases. Pressure can be replenished using the plant's nitrogen source by opening the second regulating valve 141 to inject nitrogen into the first liquid nitrogen storage tank 21, and the pressure inside the first liquid nitrogen storage tank 21 can be monitored via the second pressure transmitter 142. Alternatively, pressure can be released from the second liquid nitrogen storage tank 22 by opening the second pressure regulating valve 184, which allows for pressure release through the plant's venting system.

[0114] Fourthly, as liquid nitrogen continuously flows from the first liquid nitrogen storage tank 21 to the second liquid nitrogen storage tank 22, the liquid level in the first liquid nitrogen storage tank 21 continuously decreases. When it drops to the low alarm level, the second liquid nitrogen storage tank 22 needs to be pushed back into the first liquid nitrogen storage tank 21. At this time, the pressure in the second liquid nitrogen storage tank 22 is lower than that in the first liquid nitrogen storage tank 21. Pressure can be replenished to the second liquid nitrogen storage tank 22 by using the plant's nitrogen source, opening the first regulating valve 121 to inject nitrogen into the second liquid nitrogen storage tank 22, and monitoring the pressure inside the second liquid nitrogen storage tank 22 using the first pressure transmitter 122. Alternatively, pressure can be released from the first liquid nitrogen storage tank 21 by opening the first pressure regulating valve 182, which allows for pressure release through the plant's venting system.

[0115] Fifthly, liquid nitrogen will be continuously consumed during the production process. When the liquid level in the first liquid nitrogen storage tank 21 is lower than the low alarm level, and the liquid level remains lower than the low alarm level after a liquid pressure operation, liquid nitrogen needs to be replenished. Opening the first switch valve 62 allows liquid nitrogen to be injected into the first liquid nitrogen storage tank 21.

[0116] In this embodiment, firstly, a heat exchange coil 20 is added to the LNG storage tank unit 1, integrating BOG recovery and LNG storage functions, reducing investment and land occupation, and improving economic efficiency. Since the cooling medium, liquid nitrogen, can be circulated between LNG storage tank unit 1 and liquid nitrogen unit 2, liquid nitrogen consumption is low. Therefore, only the first liquid nitrogen storage tank 21 and the second liquid nitrogen storage tank 22 need to be injected before production begins. During normal production, liquid nitrogen can be replenished to the first liquid nitrogen storage tank 21 and the second liquid nitrogen storage tank 22 as needed to maintain stable production, effectively reducing utility consumption. Secondly, this method for reducing BOG emissions from LNG storage tanks has a high degree of automation; the liquid nitrogen circulation volume can be automatically adjusted according to the pressure of LNG storage tank unit 1. Simultaneously, fewer new facilities are required, and the maintenance workload is small, avoiding safety and management problems caused by constructing a large number of new equipment. Thirdly, this device and method for reducing BOG emissions from LNG storage tanks requires low investment, occupies little land, and has a short construction period. Therefore, it is not only suitable for newly built stations but also very friendly to the renovation of existing stations.

[0117] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of this utility model, and the utility model is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of this utility model, and these modifications and improvements are also considered to be within the protection scope of this utility model.

Claims

1. An apparatus for reducing BOG emissions from an LNG storage tank, the apparatus comprising: include: An LNG storage tank unit and a liquid nitrogen unit; the LNG storage tank unit has a gas phase space and a liquid phase space, and the gas phase space is located above the liquid phase space; The liquid nitrogen unit includes a first liquid nitrogen storage tank, a second liquid nitrogen storage tank, a first pipeline, and a second pipeline. A first end of the first pipeline extends into the first liquid nitrogen storage tank, and a second end extends into the gas phase space of the LNG storage tank unit. A first end of the second pipeline extends into the second liquid nitrogen storage tank, and a second end extends into the gas phase space of the LNG storage tank unit and connects to the second end of the first pipeline. The first liquid nitrogen storage tank stores liquid nitrogen as a cooling medium, and the second liquid nitrogen storage tank stores liquid nitrogen after heat exchange. The portions of the first and second pipelines located in the gas phase space of the LNG storage tank unit are heat exchange coils. The system includes a pressure remote sensing unit, a liquid nitrogen supply regulating valve, and a liquid nitrogen outlet shut-off valve. The pressure remote sensing unit is connected to the LNG storage tank unit and is used to detect the pressure of the LNG storage tank unit. The liquid nitrogen supply regulating valve is located in the first pipeline, and the liquid nitrogen outlet shut-off valve is located in the second pipeline. The liquid nitrogen supply regulating valve is interlocked with the pressure remote sensing unit, and the liquid nitrogen outlet shut-off valve is normally open.

2. The apparatus of claim 1, wherein, It also includes a vacuum insulation layer, a vacuum valve, and a vacuum sight valve; Both the LNG storage tank unit and the liquid nitrogen unit are housed within the vacuum insulation layer, which has a closed chamber. The vacuum insulation layer is equipped with a vacuum valve and a vacuum sight valve that communicate with the sealed chamber.

3. The apparatus of claim 2, wherein, The heat exchange coil is equipped with fins, and the coil type is determined according to the shape of the storage tank. The heat exchange coil wall is equipped with guide baffles, and drain holes are evenly distributed at the low point of the guide baffles.

4. The apparatus for reducing BOG emissions from an LNG storage tank of claim 3, wherein, It also includes the main shut-off valve; The first pipeline is equipped with the main shut-off valve near the first liquid nitrogen storage tank, and the main shut-off valve is normally open.

5. The apparatus of claim 4, wherein, It also includes a third pipeline and a first shut-off valve; The first end of the third pipe is connected to the first pipe, the second end of the third pipe is connected to the second pipe, and the first shut-off valve is provided on the third pipe.

6. The apparatus of claim 5, wherein, It also includes a fourth pipeline and a first regulating valve; One end of the fourth pipeline is connected to the second liquid nitrogen storage tank, and the first regulating valve is installed on the fourth pipeline; Nitrogen gas is supplied to the second liquid nitrogen storage tank through the fourth pipeline.

7. The apparatus of claim 6, wherein, It also includes a fifth pipe and a second regulating valve; One end of the fifth pipeline is connected to the first liquid nitrogen storage tank, and the second regulating valve is installed on the fifth pipeline; Nitrogen gas is supplied to the first liquid nitrogen storage tank through the fifth pipeline.

8. The apparatus of claim 7, wherein, It also includes vent pipes and vent valves; One end of the venting pipe is connected to the first pipe, and the connection point between the venting pipe and the first pipe is located between the liquid nitrogen supply regulating valve and the main shut-off valve; the venting pipe is equipped with the venting valve.

9. The apparatus of claim 8, wherein, It also includes a first pressure regulating pipe, a first pressure regulating valve, a second pressure regulating pipe, and a second pressure regulating valve; One end of the first pressure regulating pipeline is connected to the first liquid nitrogen storage tank, and the other end is connected to the plant venting system; the first pressure regulating valve is installed in the first pressure regulating pipeline; One end of the second pressure regulating pipeline is connected to the second liquid nitrogen storage tank, and the other end is connected to the plant venting system; the second pressure regulating valve is installed on the second pressure regulating pipeline.

10. The apparatus of claim 9, wherein, It also includes a first safety valve, a first rupture disc, a second safety valve, and a second rupture disc; Both the first safety valve and the first rupture disc are installed in the first pressure regulating pipeline, and the first safety valve and the first rupture disc are respectively connected in parallel with the first pressure regulating valve; The second safety valve and the second rupture disc are both installed in the second pressure regulating pipeline, and the second safety valve and the second rupture disc are respectively connected in parallel with the second pressure regulating valve.

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