Boil-off gas reliquefaction system of low-temperature container

Abstract

The utility model relates to a boil-off gas reliquefaction system of a low-temperature container. The boil-off gas reliquefaction system comprises a storage tank, a low-temperature liquid supply unit, a heat exchange unit and an overpressure prevention unit. The low-temperature liquid supply unit comprises a low-temperature liquid storage tank. The heat exchange unit is arranged in the storage tank and located in the gas phase space of the storage tank, and a liquid inlet of the heat exchange unit communicates with the liquid phase space of the low-temperature liquid storage tank. The overpressure prevention unit is used for detecting the pressure in the storage tank and adjusting the amount of low-temperature liquid supplied to the heat exchange unit by the low-temperature liquid supply unit according to the pressure change in the storage tank. Due to the fact that the heat exchange unit is installed in the storage tank, the liquid which is liquefied again after heat exchange can flow back to the liquid phase space of the storage tank under the action of the gravity of the liquid. Therefore, a boil-off gas leading-out pipeline and a liquid backflow pipeline do not need to be designed, the system structure is simplified, and cost is greatly saved. The heat exchange capacity of the heat exchange unit can be adjusted through the overpressure prevention unit so as to adjust the pressure in the storage tank, overpressure of the storage tank is prevented, and the system stability is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of cryogenic liquid storage, and in particular to a boil-off gas reliquefaction system of a cryogenic container. Background Art

[0002] With the adjustment of global energy structure and the improvement of environmental protection requirements, liquefied natural gas (LNG), as a clean and efficient energy source, is increasingly widely used in the field of energy supply. However, during the storage of LNG, a certain amount of boil-off gas (BOG) will be generated due to the temperature difference inside the storage tank and the infiltration of external heat. The generation of BOG not only causes energy waste, but also may pose a threat to the safe operation of the storage tank. Therefore, how to achieve efficient liquefaction and recovery of BOG and safe operation of storage tanks has become an urgent problem to be solved in the field of LNG storage and processing.

[0003] The traditional BOG liquefaction method is mainly to directly pressurize the BOG produced in the storage tank through a cryogenic compressor and then enter the recondenser for cooling and liquefaction. However, this method requires large imported cryogenic compressors and recondensing equipment, which has problems such as high energy consumption, complex equipment, large floor space, and high investment costs. In addition, for large storage tanks, due to their large storage capacity and high BOG production, the traditional liquefaction method is difficult to meet actual needs. Utility Model Content

[0004] One purpose of the utility model is to solve the deficiencies in the prior art and provide a boil-off gas reliquefaction system for a cryogenic container with a simple structure, low cost and reliable operation. To solve the above technical problems, the utility model adopts the following technical solutions:

[0005] A boil-off gas reliquefaction system for a cryogenic container, comprising:

[0006] Storage tanks are used to store cryogenic liquids. When the cryogenic liquids are heated, they generate evaporation gas, forming a gas phase space in the storage tanks.

[0007] A cryogenic liquid supply unit is arranged outside the storage tank, and the cryogenic liquid supply unit comprises a cryogenic liquid storage tank, and the cryogenic liquid storage tank is used to store the cryogenic liquid;

[0008] A heat exchange unit is disposed inside the storage tank and located in the gas phase space of the storage tank, the liquid inlet of the heat exchange unit is connected to the liquid phase space of the cryogenic liquid storage tank, and the heat exchange unit is used to utilize the cryogenic liquid to exchange heat with the boil-off gas to liquefy the boil-off gas; and

[0009] The overpressure prevention unit is arranged outside the storage tank. The overpressure prevention unit is used to detect the pressure in the storage tank and adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit to the heat exchange unit according to the pressure change in the storage tank.

[0010] In one of the embodiments, the reliquefaction system further includes a control unit, which is control-connected to the overpressure prevention unit and the cryogenic liquid supply unit, and the control unit is used to receive a signal detected by the overpressure prevention unit and control the amount of cryogenic liquid supplied by the cryogenic liquid supply unit to the heat exchange unit according to the signal.

[0011] In one embodiment, the overpressure prevention unit comprises:

[0012] A pressure detection device, which is arranged on the storage tank and is used to detect the pressure in the storage tank;

[0013] A flow regulating valve is provided on a pipeline connecting the cryogenic liquid storage tank and the heat exchange unit;

[0014] The pressure detection device and the flow control valve are both connected to the control unit. The control unit can receive the signal detected by the pressure detection device and control the opening of the flow control valve according to the signal.

[0015] In one embodiment, the cryogenic liquid supply unit further includes a self-boosting device disposed outside the cryogenic liquid storage tank, wherein the liquid inlet of the self-boosting device is connected to the liquid phase space of the cryogenic liquid storage tank, and the gas outlet of the self-boosting device is connected to the gas phase space of the cryogenic liquid storage tank.

[0016] In one embodiment, the self-pressurizer is connected to the control unit so as to be controlled by the control unit to pressurize the cryogenic liquid storage tank.

[0017] In one embodiment, the heat exchange unit is a tube-fin heat exchanger.

[0018] In one embodiment, the cryogenic liquid is liquid nitrogen;

[0019] The reliquefaction system also includes a nitrogen recovery unit, which is arranged outside the storage tank and is connected to the gas outlet of the heat exchange unit. The nitrogen recovery unit is used to receive and process the nitrogen generated after heat exchange in the heat exchange unit.

[0020] In one embodiment, the nitrogen recovery and utilization unit includes a nitrogen buffer tank, the gas outlet of the heat exchange unit is connected to the gas inlet of the nitrogen buffer tank, and the gas outlet of the nitrogen buffer tank can be connected to the nitrogen user end.

[0021] In one embodiment, the nitrogen recovery unit further includes a nitrogen heater, an air inlet of the nitrogen heater is connected to an air outlet of the heat exchange unit, and an air outlet of the nitrogen heater is connected to an air inlet of the nitrogen buffer tank.

[0022] In one embodiment, the storage tank is a double-layer storage tank, which includes an inner tank for storing liquefied gas and an outer tank wrapped around the outer side of the inner tank;

[0023] A heat-insulating space is formed between the inner tank and the outer tank, and the gas outlet of the nitrogen buffer tank is connected to the heat-insulating space.

[0024] It can be seen from the above technical solution that the utility model has at least the following advantages and positive effects:

[0025] In the utility model, the low-temperature liquid supply unit, the heat exchange unit inside the storage tank and the overpressure prevention unit work in coordination, so that the boil-off gas is efficiently reliquefied, and the safe operation of the storage tank is ensured.

[0026] Since the heat exchange unit is installed inside the storage tank, the reliquefied liquid after heat exchange can flow back to the liquid phase space of the storage tank under its own gravity. Therefore, there is no need to design boil-off gas outlet pipelines and liquid return pipelines, and the use of BOG compressors can be avoided, thereby simplifying the system structure and greatly saving costs.

[0027] The overpressure prevention unit can detect the pressure change in the storage tank in real time, and automatically adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit to the heat exchange unit to adjust the heat exchange capacity of the heat exchange unit. In this way, the pressure in the storage tank can be quickly adjusted to prevent the occurrence of overpressure and improve the stability of the system.

[0028] The reliquefaction system has a simple structure and is easy to operate. It is suitable for BOG liquefaction and overpressure prevention in large storage tanks and has a high market promotion value. When the reliquefaction system is used for LNG storage and transportation, it can directly reliquefy the gasified BOG in the LNG storage tank into LNG in the tank, effectively ensuring the safe operation of the LNG storage tank and reducing the loss of LNG. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of a boil-off gas reliquefaction system of a cryogenic container according to one embodiment of the present invention.

[0030] The following are the descriptions of the reference numerals:

[0031] 100-storage tank; 110-inner tank; 120-outer tank; 130-insulated space;

[0032] 200-cryogenic liquid supply unit;

[0033] 210-cryogenic liquid storage tank; 220-self-boosting device;

[0034] 300-heat exchange unit;

[0035] 400-overpressure prevention unit; 410-pressure detection device; 420-flow control valve;

[0036] 500 - Control unit.

[0037] 600-nitrogen recovery and utilization unit; 610-nitrogen buffer tank; 620-nitrogen heater. DETAILED DESCRIPTION

[0038] Typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention can have various changes in different embodiments without departing from the scope of the present invention, and the descriptions and illustrations therein are essentially for illustrative purposes rather than for limiting the present invention.

[0039] In the description of the present application, it should be understood that in the embodiments shown in the drawings, the indications of directions or positional relationships (such as up, down, left, right, front and back, etc.) are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation. These descriptions are appropriate when these elements are in the positions shown in the drawings. If the descriptions of the positions of these elements change, the indications of these directions also change accordingly.

[0040] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0041] Refrigeration and liquefaction of gas refers to the process of converting gas into liquid by lowering the temperature. The liquid formed by refrigeration and liquefaction of gas is usually called cryogenic liquid. Cryogenic containers are containers used to store and transport cryogenic liquids. However, due to the low boiling point of cryogenic liquids, such as liquid helium, liquid hydrogen, liquid nitrogen, liquid oxygen, liquid carbon dioxide, liquefied natural gas (LNG), etc., it is very easy to form a vapor state. Therefore, in the storage and transportation of various cryogenic liquids, it is very easy to cause the loss of cryogenic liquids, and even cause safety problems.

[0042] Among them, LNG is a liquid that natural gas becomes after being compressed and cooled to its freezing point (-161.5°C). Usually LNG is stored in low-temperature storage tanks at -161.5°C and about 0.1MPa. Its main component is methane, which is transported by special ships or tank trucks and re-gasified when used. However, as recorded in the background technology, during the storage process of LNG, a certain amount of boil-off gas (BOG) will be generated due to the temperature difference inside the storage tank and the infiltration of external heat. The generation of BOG will not only cause a waste of energy, but may also pose a threat to the safe operation of the storage tank.

[0043] Based on this, the utility model provides a boil-off gas reliquefaction system for a cryogenic container, which can realize the reliquefaction of boil-off gas (BOG) of various types of cryogenic liquids, and ensure the stable storage and transportation of various cryogenic liquids. Therefore, when the reliquefaction system is applied to the storage and transportation of LNG, the gasified BOG in the LNG storage tank can be reliquefied into LNG, ensuring the safe operation of the LNG storage tank and reducing the loss of LNG.

[0044] In the following specific implementation manner of the present invention, the scheme of the present invention is described in detail mainly by taking the BOG reliquefaction process in the LNG storage tank as an example.

[0045] like Figure 1 As shown, the boil-off gas reliquefaction system of the cryogenic container according to the embodiment of the utility model comprises a storage tank 100 , a cryogenic liquid supply unit 200 , a heat exchange unit 300 , an overpressure prevention unit 400 , a control unit 500 and a nitrogen recovery and utilization unit 600 .

[0046] Among them, the storage tank 100 can be an LNG storage tank, which is used to store LNG. The storage tank 100 can be a double-vault single-capacity tank. Specifically, the storage tank 100 includes an inner tank 110 and an outer tank 120, and the inner tank 110 is used to store LNG. The outer tank 120 is wrapped and arranged outside the inner tank 110. An insulating space 130 is formed between the inner tank 110 and the outer tank 120, and the insulating space 130 is used to fill with insulating materials such as perlite.

[0047] Due to the temperature difference and the infiltration of external heat inside the inner tank 110, LNG partially evaporates into BOG, so that a liquid phase space and a gas phase space are naturally formed inside the inner tank 110. That is, the storage tank 100 has a liquid phase space and a gas phase space inside.

[0048] like Figure 1 As shown, the heat exchange unit 300 is disposed inside the storage tank 100 and is located in the gas phase space of the storage tank 100. The heat exchange unit 300 can use a low-temperature heat exchange medium to perform heat exchange on the BOG in the storage tank 100, so that the BOG is reliquefied into LNG. Since the heat exchange unit 300 is installed in the gas phase space of the storage tank 100, the LNG reliquefied after heat exchange can flow back to the liquid phase space of the storage tank 100 under its own gravity. Therefore, there is no need to design a BOG outlet pipeline and an LNG return pipeline, and the use of a BOG compressor can be avoided, thereby simplifying the system structure and greatly saving costs.

[0049] In the present application, the heat exchange unit 300 is cleverly arranged in the gas phase space inside the storage tank 100. The structural design of the heat exchange unit 300 fully considers the temperature distribution and fluid flow characteristics inside the storage tank 100 to ensure the maximization of the heat exchange efficiency and ensure that the liquefied LNG can automatically flow back to the liquid phase space of the storage tank 100 under the action of its own gravity.

[0050] In one embodiment, the heat exchange unit 300 is a tube-fin heat exchanger. The tube-fin heat exchanger has closely arranged heat exchange tubes, and a fin structure is wound around the heat exchange tubes. In this embodiment, the heat exchange unit 300 adopts a tube-fin heat exchanger, which increases the heat exchange area of ​​the heat exchange unit 300, thereby improving the heat exchange efficiency. The special fin-wound structure of the tube-fin heat exchanger increases the contact area between the fluid and the tube wall, allowing heat to be transferred more quickly. By optimizing the parameters such as the length, diameter, and arrangement of the heat exchange tubes in the tube-fin heat exchanger, efficient liquefaction of BOG can be achieved.

[0051] See also Figure 1 The cryogenic liquid supply unit 200 is disposed outside the storage tank 100. The cryogenic liquid supply unit 200 includes a cryogenic liquid storage tank 210 for storing cryogenic liquid. The cryogenic liquid supply unit 200 is used to provide cryogenic liquid as a heat exchange medium to the heat exchange unit 300.

[0052] It can be understood that when the cryogenic liquid stored in the storage tank 100 is LNG, the cryogenic liquid used for heat exchange can be liquid nitrogen, liquid helium, etc., which have a lower boiling point than LNG. When the cryogenic liquid stored in the storage tank 100 is liquid oxygen, the cryogenic liquid used for heat exchange can be liquid nitrogen, liquid helium, etc., which have a lower boiling point than liquid oxygen. When the cryogenic liquid stored in the storage tank 100 is liquid carbon dioxide, the cryogenic liquid used for heat exchange can be liquid nitrogen, liquid oxygen, etc., which have a lower boiling point than liquid carbon dioxide.

[0053] In other words, in the reliquefaction system of the present invention, the cryogenic liquid is a medium for heat exchange cooling of the BOG of the cryogenic liquid. For different types of cryogenic liquids stored in the storage tank 100, the cryogenic liquids stored in the cryogenic liquid storage tank 210 are also different. That is, the boiling point of the cryogenic liquid of the present invention is lower than the boiling point of the cryogenic liquid. Optionally, the cryogenic liquid can be a liquid having a boiling point about 20°C lower than the boiling point of the cryogenic liquid, so that the cryogenic liquid can better heat exchange and cool the BOG of the cryogenic liquid.

[0054] In one embodiment of the present application, the cryogenic liquid may be liquid nitrogen. Liquid nitrogen is an excellent cooling medium with an extremely low boiling point and excellent thermal conductivity. In this embodiment, liquid nitrogen is used as a heat exchange medium, and the liquid nitrogen is stably transported to the heat exchange unit 300 in the storage tank 100 through the cryogenic liquid supply unit 200 to achieve rapid cooling and liquefaction of BOG.

[0055] In this embodiment, since the boiling point of liquid nitrogen is -196° C., it can be used to cool BOG of cryogenic liquids such as LNG having a boiling point higher than -196° C., thereby achieving efficient liquefaction of BOG.

[0056] It can be understood that the cryogenic liquid itself is also a cryogenic liquid, and its boiling point is low, and it is very easy to form a vapor state. Therefore, a liquid phase space and a gas phase space can be naturally formed inside the cryogenic liquid storage tank 210. The liquid phase space of the cryogenic liquid storage tank 210 is connected to the liquid inlet of the heat exchange unit 300, so the cryogenic liquid storage tank 210 can supply cryogenic liquid to the heat exchange unit 300 to achieve heat exchange.

[0057] See also Figure 1 In one embodiment, the cryogenic liquid supply unit 200 further includes a self-boosting device 220 disposed outside the cryogenic liquid storage tank 210, a liquid inlet of the self-boosting device 220 being connected to the liquid phase space of the cryogenic liquid storage tank 210, and a gas outlet of the self-boosting device 220 being connected to the gas phase space of the cryogenic liquid storage tank 210.

[0058] In this embodiment, taking the cryogenic liquid as liquid nitrogen as an example, the liquid nitrogen in the cryogenic liquid storage tank 210 can be gasified by the self-boosting device 220, and the generated nitrogen enters the gas phase space of the cryogenic liquid storage tank 210, increasing the pressure inside the cryogenic liquid storage tank 210, so that the cryogenic liquid storage tank 210 has the ability to transport liquid nitrogen outward. Therefore, by setting the self-boosting device 220, the cryogenic liquid storage tank 210 can automatically supply cryogenic liquid to the heat exchange unit 300. Therefore, the system does not need to set up power equipment such as pumps, which effectively reduces the equipment investment cost and system operation cost. It can be understood that when the cryogenic liquid is other deep-cold liquids, the self-boosting device 220 can also be used to realize the automatic outward transportation of the cryogenic liquid.

[0059] See also Figure 1 As shown, in one embodiment of the present application, the overpressure prevention unit 400 is disposed outside the storage tank 100. The overpressure prevention unit 400 is used to detect the pressure in the storage tank 100 and adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit 200 to the heat exchange unit 300 according to the pressure change in the storage tank 100.

[0060] In this embodiment, the overpressure prevention unit 400 can detect the pressure change in the storage tank 100 in real time, and automatically adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit 200 to the heat exchange unit 300 to adjust the heat exchange capacity of the heat exchange unit 300. Thus, the pressure in the storage tank 100 can be quickly adjusted to prevent the occurrence of overpressure, thereby improving the stability of the system.

[0061] like Figure 1As shown, in one embodiment, the reliquefaction system of the storage tank further includes a control unit 500, which is control-connected to the overpressure prevention unit 400 and the cryogenic liquid supply unit 200, and the control unit 500 is used to receive a signal detected by the overpressure prevention unit 400, and control the amount of cryogenic liquid supplied by the cryogenic liquid supply unit 200 to the heat exchange unit 300 according to the signal. The control unit 500 may be a DCS (Distributed Control System).

[0062] See also Figure 1 In one embodiment, the overpressure prevention unit 400 includes a pressure detection device 410. The pressure detection device 410 is disposed on the storage tank 100 and is used to detect the pressure in the storage tank 100. The pressure detection device 410 may be a pressure transmitter.

[0063] See also Figure 1 In one embodiment, the overpressure prevention unit 400 further includes a flow regulating valve 420, which is disposed on a pipeline connecting the cryogenic liquid storage tank 210 and the heat exchange unit 300. The flow regulating valve 420 may be a pneumatic diaphragm regulating valve.

[0064] like Figure 1 As shown, the pressure detection device 410 and the flow control valve 420 are both connected to the control unit 500. The control unit 500 can receive the signal detected by the pressure detection device 410 and control the opening of the flow control valve 420 according to the signal.

[0065] It should be noted that the normal working pressure of the LNG atmospheric pressure storage tank is generally 5-20KPa. When the control unit 500 receives the signal detected by the pressure detection device 410 and obtains through analysis that the internal pressure of the storage tank 100 exceeds the preset safety threshold, such as 18KPa, the control unit 500 can control the flow regulating valve 420 to increase the flow, thereby increasing the amount of cryogenic liquid supplied from the cryogenic liquid storage tank 210 to the heat exchange unit 300. This enhances the BOG liquefaction capacity of the heat exchange unit 300 in the storage tank 100, quickly reduces the pressure in the storage tank 100, and prevents the occurrence of overpressure.

[0066] When the control unit 500 receives the signal detected by the pressure detection device 410 and obtains through analysis that the internal pressure of the storage tank 100 is reduced to a safe range, the control unit 500 can control the flow control valve 420 to close.

[0067] Therefore, through the coordinated work of the anti-overpressure unit 400 and the control unit 500, the system can automatically adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit 200 to the heat exchange unit 300 according to the pressure changes in the storage tank 100, ensuring that the internal pressure of the storage tank 100 is always maintained within a safe range, thereby improving system stability.

[0068] See also Figure 1 As shown, in one embodiment, the self-booster 220 is connected to the control unit 500, so as to be controlled by the control unit 500 to pressurize the cryogenic liquid storage tank 210. When the control unit 500 receives the signal detected by the pressure detection device 410, and after analysis, it is found that the internal pressure of the storage tank 100 exceeds the preset safety threshold, the control unit 500 can control the self-booster 220 to start working, so as to increase the pressure in the cryogenic liquid storage tank 210, speed up the output of the cryogenic liquid, and then increase the amount of cryogenic liquid supplied from the cryogenic liquid storage tank 210 to the heat exchange unit 300. Thereby, the BOG liquefaction capacity of the heat exchange unit 300 in the storage tank 100 can be enhanced, the pressure in the storage tank 100 can be quickly reduced, and the occurrence of overpressure can be prevented.

[0069] In the embodiment of the present application, the control unit 500 receives and processes the signal sent by the pressure detection device 410, and automatically controls the working state of the cryogenic liquid supply unit 200 and the flow control valve 420 according to the processing result. Intelligent management and precise control of the BOG liquefaction process and the overpressure prevention performance of the storage tank 100 are effectively realized.

[0070] See also Figure 1 As shown, in one embodiment, the nitrogen recovery and utilization unit 600 is disposed outside the storage tank 100. The nitrogen recovery and utilization unit 600 is used to communicate with the gas outlet of the heat exchange unit 300 to receive and process the nitrogen generated after heat exchange in the heat exchange unit 300. By providing the nitrogen recovery and utilization unit 600, the nitrogen generated in the BOG liquefaction process of the system can be recovered and utilized, the system derivatives can be effectively utilized, and the application scope of the system can be broadened.

[0071] It can be understood that after the liquid nitrogen enters the heat exchange unit 300 in the storage tank 100, it exchanges heat with the BOG, absorbs the heat of the BOG and liquefies it. At the same time, the liquid nitrogen itself is gasified, and the nitrogen generated after gasification enters the nitrogen recovery unit 600 for recovery and utilization. For example, the nitrogen recovery unit 600 can use nitrogen for other process, such as equipment instrument gas, or as protective gas, purge gas, etc., to achieve comprehensive utilization of nitrogen and reduce operating costs.

[0072] Specifically, the nitrogen recovery unit 600 includes a nitrogen buffer tank 610, and the gas outlet of the heat exchange unit 300 is connected to the gas inlet of the nitrogen buffer tank 610. The gas outlet of the nitrogen buffer tank 610 can be connected to the nitrogen user end.

[0073] It should be noted that the temperature of the nitrogen after gasification by the heat exchange unit 300 is generally between -165 and -170°C. Since the low-temperature nitrogen cannot be directly recycled, the nitrogen recycling unit 600 also includes a heating device for reheating the nitrogen. Figure 1As shown, in one embodiment, the nitrogen recovery unit 600 further includes a nitrogen heater 620, the air inlet of the nitrogen heater 620 is connected to the air outlet of the heat exchange unit 300, and the air outlet of the nitrogen heater 620 is connected to the air inlet of the nitrogen buffer tank 610. By providing the nitrogen heater 620, the nitrogen can be reheated, so that the nitrogen can be used in conventional use scenarios such as equipment and instruments.

[0074] like Figure 1 As shown, in one embodiment, the gas outlet of the nitrogen buffer tank 610 is connected to the insulation space 130. In this embodiment, the gas outlet of the nitrogen buffer tank 610 is connected to the insulation space 130 of the storage tank 100, so that the nitrogen can be used to dry the insulation materials such as perlite in the insulation space 130. Thereby, the insulation effect of the insulation space 130 is ensured, and the safety of the use of the storage tank 100 is improved. At the same time, the derivatives (nitrogen) generated by the BOG liquefaction system are used to maintain the system equipment, so that the storage tank 100 does not need to be connected to additional nitrogen supply equipment, effectively reducing the system operation cost.

[0075] In other embodiments, the gas outlet of the nitrogen buffer tank 610 can also be connected to various equipment and instruments in the factory through pipelines, thereby achieving full utilization of nitrogen resources, effectively reducing operating costs, and broadening the application scope of the system.

[0076] The working process of the boil-off gas reliquefaction system of the cryogenic container of the present application is roughly as follows:

[0077] When the pressure detection device 410 detects that the pressure of the storage tank 100 exceeds the preset safety threshold, the signal is transmitted to the DCS system. The DCS system controls the opening degree of the flow control valve 420 and the operation of the self-booster 220 according to the received pressure signal to adjust the amount of liquid nitrogen supplied from the cryogenic liquid storage tank 210 to the heat exchange unit 300.

[0078] The liquid nitrogen enters the heat exchange unit 300 in the storage tank 100 and exchanges heat with the BOG in the gas phase space in the storage tank 100, so that the BOG is cooled and liquefied. After the BOG is liquefied, it can automatically return to the liquid phase space of the storage tank 100 due to its own gravity.

[0079] At the same time, the liquid nitrogen in the heat exchange unit 300 is vaporized, and the vaporized nitrogen enters the nitrogen heater 620 for reheating, and the reheated nitrogen enters the nitrogen buffer tank 610.

[0080] The nitrogen in the nitrogen buffer tank 610 can be connected to the insulation space 130 of the storage tank 100 to dry the perlite and the like in the insulation space 130; alternatively, the nitrogen can also be provided to the plant instrument gas and the like.

[0081] It can be seen from the above technical solutions that the boil-off gas reliquefaction system of the cryogenic container of the present application has at least the following beneficial effects:

[0082] In the present application, the low-temperature liquid supply unit 200, the heat exchange unit 300 inside the storage tank 100 and the overpressure prevention unit 400 work in coordination to achieve efficient reliquefaction of BOG and ensure safe operation of the storage tank 100.

[0083] Since the heat exchange unit 300 is installed inside the storage tank 100, the LNG reliquefied after heat exchange can flow back to the liquid phase space of the storage tank 100 under its own gravity. Therefore, there is no need to design a BOG outlet pipeline and an LNG return pipeline, and the use of a BOG compressor can be avoided, thereby simplifying the system structure and greatly saving costs.

[0084] The overpressure prevention unit 400 can detect the pressure change in the storage tank 100 in real time, and automatically adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit 200 to the heat exchange unit 300 to adjust the heat exchange capacity of the heat exchange unit 300. Thus, the pressure in the storage tank 100 can be quickly adjusted to prevent the occurrence of overpressure, thereby improving the stability of the system.

[0085] The nitrogen recovery and utilization unit 600 can be used to recover and fully utilize the nitrogen generated during the BOG liquefaction process, effectively reducing the system operating costs and broadening the application scope of the system. Specifically, the recovered nitrogen can be used to dry the insulating materials such as perlite in the insulating space 130 of the storage tank 100. This ensures the insulation effect of the insulating space 130 and improves the safety of the storage tank 100. At the same time, the storage tank 100 does not need to be connected to additional nitrogen supply equipment, which greatly reduces the system operating costs. Alternatively, nitrogen can also be provided to the plant area for instrumentation and the like.

[0086] Through the boil-off gas reliquefaction system of the cryogenic container of the utility model, the boil-off gas in the storage tank 100 can be effectively reliquefied to prevent the storage tank 10 from being over-pressurized. In addition, the system can make full use of nitrogen resources and reduce operating costs. At the same time, the efficient heat transfer performance of the tube-fin heat exchanger improves the heat exchange efficiency of the system, which is conducive to enhancing the reliability of the system.

[0087] The boil-off gas reliquefaction system of the cryogenic container of the present application has a simple structure, convenient operation, low energy consumption, and small footprint, and is suitable for BOG treatment and overpressure prevention requirements of large LNG storage tanks or other cryogenic liquid storage tanks.

[0088] The above embodiments are merely exemplary descriptions of the structures. The structures in the embodiments are not fixed combination structures. In the absence of structural conflicts, the structures in multiple embodiments can be used in any combination.

[0089] Although the utility model has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the utility model can be implemented in a variety of forms without departing from the spirit or essence of the utility model, it should be understood that the above-mentioned embodiments are not limited to any of the aforementioned details, but should be widely interpreted within the spirit and scope defined by the attached claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the attached claims.

Claims

1. A boil-off gas reliquefaction system for a cryogenic container, characterized in that: include: A storage tank for storing cryogenic liquid, wherein the cryogenic liquid generates evaporation gas when heated, so that a gas phase space is formed in the storage tank; A cryogenic liquid supply unit, which is arranged outside the storage tank, and the cryogenic liquid supply unit includes a cryogenic liquid storage tank, and the cryogenic liquid storage tank is used to store cryogenic liquid; a heat exchange unit, which is arranged inside the storage tank and located in the gas phase space of the storage tank, wherein the liquid inlet of the heat exchange unit is in communication with the liquid phase space of the cryogenic liquid storage tank, and the heat exchange unit is used to perform heat exchange between the cryogenic liquid and the boil-off gas to liquefy the boil-off gas; as well as An anti-overpressure unit is arranged outside the storage tank, and is used to detect the pressure in the storage tank and adjust the amount of cryogenic liquid supplied by the cryogenic liquid supply unit to the heat exchange unit according to the pressure change in the storage tank.

2. The boil-off gas reliquefaction system for a cryogenic container according to claim 1, characterized in that: It also includes a control unit, which is control-connected to the anti-overpressure unit and the cryogenic liquid supply unit. The control unit is used to receive a signal detected by the anti-overpressure unit and control the amount of cryogenic liquid supplied by the cryogenic liquid supply unit to the heat exchange unit according to the signal.

3. The boil-off gas reliquefaction system of a cryogenic container according to claim 2, characterized in that: The overpressure prevention unit comprises: A pressure detection device, which is provided on the cryogenic container, and is used to detect the pressure in the storage tank; A flow regulating valve, which is arranged on a pipeline connecting the cryogenic liquid storage tank and the heat exchange unit; The pressure detection device and the flow control valve are both connected to the control unit. The control unit can receive a signal detected by the pressure detection device and control the opening of the flow control valve according to the signal.

4. The boil-off gas reliquefaction system for a cryogenic container according to claim 2, characterized in that: The cryogenic liquid supply unit further comprises a self-boosting device arranged outside the cryogenic liquid storage tank, wherein the liquid inlet of the self-boosting device is connected to the liquid phase space of the cryogenic liquid storage tank, and the gas outlet of the self-boosting device is connected to the gas phase space of the cryogenic liquid storage tank.

5. The boil-off gas reliquefaction system for a cryogenic container according to claim 4, characterized in that: The self-boosting device is connected to the control unit to be controlled by the control unit to pressurize the cryogenic liquid storage tank.

6. The boil-off gas reliquefaction system for a cryogenic container according to claim 1, characterized in that: The heat exchange unit is a tube-fin heat exchanger.

7. The boil-off gas reliquefaction system for a cryogenic container according to any one of claims 1 to 6, characterized in that: The cryogenic liquid is liquid nitrogen; The reliquefaction system also includes a nitrogen recovery unit, which is arranged outside the storage tank and is connected to the gas outlet of the heat exchange unit. The nitrogen recovery unit is used to receive and process the nitrogen generated after heat exchange in the heat exchange unit.

8. The boil-off gas reliquefaction system for a cryogenic container according to claim 7, characterized in that: The nitrogen recovery and utilization unit comprises a nitrogen buffer tank, the gas outlet of the heat exchange unit is communicated with the gas inlet of the nitrogen buffer tank, and the gas outlet of the nitrogen buffer tank can be connected to a nitrogen user end.

9. The boil-off gas reliquefaction system for a cryogenic container according to claim 8, characterized in that: The nitrogen recovery and utilization unit further includes a nitrogen heater, an air inlet of the nitrogen heater is communicated with an air outlet of the heat exchange unit, and an air outlet of the nitrogen heater is communicated with an air inlet of the nitrogen buffer tank.

10. The boil-off gas reliquefaction system for a cryogenic container according to claim 8, characterized in that: The storage tank is a double-layer storage tank, which includes an inner tank for storing the cryogenic liquid and an outer tank wrapped around the outer side of the inner tank; A heat-insulating space is formed between the inner tank and the outer tank, and the gas outlet of the nitrogen buffer tank is connected to the heat-insulating space.

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