Coupling energy supply system based on LNG and fuel cell

Abstract

The utility model relates to a coupling energy supply system based on LNG and a fuel cell, a gas supply unit comprises an LNG storage tank and an LNG vaporizer which are connected through an LNG pipeline, the LNG vaporizer is connected with a downstream gas pipeline through a gas supply pipeline, a power generation unit comprises a cooling heat exchanger and the fuel cell, a cooling loop is arranged between the secondary side of the cooling heat exchanger and the fuel cell, and the fuel cell is connected with the cooling loop. A primary side inlet of the cooling heat exchanger is connected with the LNG storage tank through a BOG pipeline, a primary side outlet of the cooling heat exchanger is connected with a gas inlet of the fuel cell through a fuel pipeline, electric energy generated by the fuel cell is merged into a user electric power internal network, and the system has the advantages of being good in stability and high in safety.

Description

Technical Field

[0001] The utility model relates to an energy supply system, in particular to a coupled energy supply system based on LNG and a fuel cell. Background Art

[0002] At LNG receiving stations, LNG storage tanks serve as both receiving and storage equipment. During storage, external heat is continuously transferred into the tank through the tank body and associated piping. This heat is absorbed by the LNG, causing partial evaporation and the generation of BOG (Burning Gas). If the BOG is not promptly discharged, it can easily lead to overpressure within the tank, posing a safety risk. Currently, two main methods are used to handle BOG: direct compression and recondensation. Both methods are energy-intensive and pose operational challenges when external loads fluctuate. Utility Model Content

[0003] The purpose of the utility model is to provide a coupled energy supply system based on LNG and fuel cells, which has the advantages of simple structure, convenient operation, good stability and high safety.

[0004] LNG and fuel cell coupled energy supply system, including gas supply unit, power generation unit, liquefaction unit and refrigeration unit, gas supply unit including LNG storage tank and LNG gasifier connected by LNG pipeline, LNG gasifier is connected to downstream gas pipeline through gas supply pipeline, power generation unit including cooling heat exchanger and fuel cell, two ports on secondary side of cooling heat exchanger are connected to water inlet and outlet of fuel cell to form cooling circuit, primary inlet of cooling heat exchanger is connected to LNG storage tank through BOG pipeline, BOG pipeline is provided with a first throttle valve, primary outlet of cooling heat exchanger is connected to gas inlet of fuel cell through fuel pipeline, fuel pipeline is connected to gas supply pipeline through natural gas pipeline, natural gas pipeline is provided with a second throttle valve, electric energy generated by fuel cell is incorporated into user's power intranet, liquefaction unit including first liquefaction compressor, first liquefaction heat exchanger and first gas-liquid separator, inlet of first liquefaction compressor is connected to LNG storage tank and first The BOG pipeline between the throttle valves is connected, the two ports on the primary side of the first liquefaction heat exchanger are correspondingly connected to the outlet of the first liquefaction compressor and the inlet of the first gas-liquid separator, the liquid phase outlet of the first gas-liquid separator is connected to the LNG pipeline, and the gas phase outlet of the first gas-liquid separator is connected to the BOG pipeline between the cooling heat exchanger and the first throttle valve through gas phase pipeline 1. The refrigeration unit includes a first refrigeration compressor, a first refrigeration heat exchanger, a first expansion valve, a second refrigeration compressor, a second refrigeration heat exchanger, and a second expansion valve. The first refrigeration compressor, the secondary side of the first refrigeration heat exchanger, the first expansion valve, and the primary side of the second refrigeration heat exchanger are connected in sequence to form a primary refrigeration circuit. The primary side of the first refrigeration heat exchanger is arranged on the LNG pipeline, and the second refrigeration compressor, the secondary side of the second refrigeration heat exchanger, the second expansion valve, and the secondary side of the first liquefaction heat exchanger are connected in sequence to form a secondary refrigeration circuit; the LNG vaporizer is a seawater open-frame vaporizer or an submerged combustion vaporizer, and the fuel cell is a natural gas solid oxide fuel cell.

[0005] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein a third throttle valve is provided on the gas phase pipeline 1, and the liquefaction unit also includes a second liquefaction compressor, a second liquefaction heat exchanger and a second gas-liquid separator, the inlet of the second liquefaction compressor is connected to the gas phase pipeline 1 between the third throttle valve and the first gas-liquid separator, the two ports on the primary side of the second liquefaction heat exchanger are connected correspondingly to the outlet of the second liquefaction compressor and the inlet of the second gas-liquid separator, the secondary side of the second liquefaction heat exchanger is arranged on the secondary refrigeration circuit between the second refrigeration compressor and the second expansion valve, the liquid phase outlet of the second gas-liquid separator is connected to the LNG pipeline, and the gas phase outlet of the second gas-liquid separator is connected to the BOG pipeline between the cooling heat exchanger and the first throttle valve through the gas phase pipeline 2.

[0006] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein a high-pressure pump is provided on the LNG pipeline between the LNG storage tank and the first refrigeration heat exchanger, the connection points between the liquid phase outlets of the first gas-liquid separator and the second gas-liquid separator and the LNG pipeline are both located between the high-pressure pump and the LNG storage tank, and a fourth throttle valve is provided on the gas phase pipeline 2.

[0007] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein the user's power intranet is connected to the first liquefaction compressor, the first refrigeration compressor, the second refrigeration compressor, the second liquefaction compressor and the high-pressure pump through cables and provides power to them.

[0008] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein the cooling heat exchanger is used to perform heat exchange between cooling water and natural gas flowing therethrough.

[0009] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein the first liquefied heat exchanger and the second liquefied heat exchanger are respectively used to perform heat exchange on the natural gas and working medium 2 flowing therethrough, and the working medium 2 refers to the working medium that circulates in the secondary refrigeration circuit and transfers energy.

[0010] Furthermore, the utility model provides a coupled energy supply system based on LNG and fuel cells, wherein the first refrigeration heat exchanger is used to perform heat exchange between the LNG and working fluid 1 flowing therethrough, working fluid 1 refers to the working medium that circulates in the primary refrigeration circuit and transfers energy, and the second refrigeration heat exchanger is used to perform heat exchange between working fluid 1 and working fluid 2 flowing therethrough.

[0011] The utility model discloses a coupled energy supply system based on LNG and fuel cell, which has the following advantages compared with the prior art: the utility model provides a gas supply unit, a power generation unit, a liquefaction unit and a refrigeration unit, so that the gas supply unit is provided with an LNG storage tank and an LNG vaporizer connected by an LNG pipeline, and the LNG vaporizer is connected to the downstream gas pipeline through the gas supply pipeline, and the power generation unit is provided with a cooling heat exchanger and a fuel cell, and the two secondary side ports of the cooling heat exchanger are connected to the water inlet and outlet of the fuel cell to form a cooling circuit, and the primary side inlet of the cooling heat exchanger is connected to the LNG storage tank through the BOG pipeline, and the primary side outlet of the cooling heat exchanger is connected to the gas inlet of the fuel cell through the fuel pipeline, and the fuel pipeline is connected to the gas supply pipeline through the natural gas pipeline, and a first throttle valve is provided on the BOG pipeline, and a second throttle valve is provided on the natural gas pipeline, and the electric energy generated by the fuel cell is incorporated into the user's power intranet, and the liquefaction unit is provided with a first liquefaction compressor, a first liquefaction heat exchanger and The first gas-liquid separator is connected to the inlet of the first liquefied compressor and the BOG pipeline between the LNG storage tank and the first throttle valve. The two ports on the primary side of the first liquefied heat exchanger are connected to the outlet of the first liquefied compressor and the inlet of the first gas-liquid separator respectively. The liquid phase outlet of the first gas-liquid separator is connected to the LNG pipeline. The gas phase outlet of the first gas-liquid separator is connected to the BOG pipeline between the cooling heat exchanger and the first throttle valve via gas phase pipeline 1. The refrigeration unit is provided with a first refrigeration compressor, a first refrigeration heat exchanger, a first expansion valve, a second refrigeration compressor, a second refrigeration heat exchanger, and a second expansion valve. The first refrigeration compressor, the secondary side of the first refrigeration heat exchanger, the first expansion valve, and the primary side of the second refrigeration heat exchanger are sequentially connected to form a primary refrigeration circuit. The second refrigeration compressor, the secondary side of the second refrigeration heat exchanger, the second expansion valve, and the secondary side of the first liquefied heat exchanger are sequentially connected to form a secondary refrigeration circuit. The primary side of the first refrigeration heat exchanger is provided on the LNG pipeline. The LNG vaporizer is a seawater open-frame vaporizer or an submerged combustion vaporizer, and the fuel cell is a natural gas solid oxide fuel cell. The result is a coupled energy supply system based on LNG and fuel cells that features a simple structure, easy operation, good stability, and high safety. During operation, the gas supply unit provides users with the required natural gas, and the power generation unit provides users with the required electricity, forming a combined gas supply and power generation system. Compared to existing technologies, by using BOG as the natural gas required for fuel cell power generation and liquefying excess BOG and incorporating it into the gas supply unit, this not only solves the BOG discharge and treatment problem and ensures safety, but also reduces energy consumption by recovering the cold energy of LNG. Furthermore, the provision of a two-stage refrigeration circuit and a first throttle valve and a second throttle valve improves system stability.

[0012] The following is a further detailed description of the coupled energy supply system based on LNG and fuel cells of the present invention in conjunction with the specific embodiments shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a structural schematic diagram of a coupled energy supply system based on LNG and fuel cells in the present utility model. DETAILED DESCRIPTION

[0014] First of all, it should be noted that the directional words such as up, down, left, right, front and back described in the present invention are only described according to the drawings for the convenience of understanding, and are not intended to limit the technical solution and scope of protection of the present invention.

[0015] like Figure 1 The utility model shows a specific embodiment of a coupled energy supply system based on LNG and a fuel cell, comprising a gas supply unit, a power generation unit, a liquefaction unit, and a refrigeration unit. The gas supply unit is provided with an LNG storage tank 1 and an LNG vaporizer 2 connected via an LNG pipeline, and the LNG vaporizer 2 is connected to a downstream gas pipeline via a gas supply pipeline. The power generation unit is provided with a cooling heat exchanger 3 and a fuel cell 4, and the two secondary ports of the cooling heat exchanger 3 are connected to the water inlet and outlet of the fuel cell 4 to form a cooling circuit. The primary inlet of the cooling heat exchanger 3 is connected to the LNG storage tank 1 via a BOG pipeline, and the primary outlet of the cooling heat exchanger 3 is connected to the air inlet of the fuel cell 4 via a fuel pipeline. The fuel pipeline is connected to the gas supply pipeline via a natural gas pipeline. A first throttle valve 5 is provided on the BOG pipeline, and a second throttle valve 6 is provided on the natural gas pipeline. The electricity generated by the fuel cell 4 is then integrated into the user's power grid. The liquefaction unit is provided with a first liquefaction compressor 7, a first liquefaction heat exchanger 8 and a first gas-liquid separator 9, the inlet of the first liquefaction compressor 7 is connected to the BOG pipeline between the LNG storage tank 1 and the first throttle valve 5, the two ports on the primary side of the first liquefaction heat exchanger 8 are connected to the outlet of the first liquefaction compressor 7 and the inlet of the first gas-liquid separator 9 respectively, and the liquid phase outlet of the first gas-liquid separator 9 is connected to the LNG pipeline, and the gas phase outlet of the first gas-liquid separator 9 is connected to the BOG pipeline between the cooling heat exchanger 3 and the first throttle valve 5 through the gas phase pipeline 1. The refrigeration unit is provided with a first refrigeration compressor 10, a first refrigeration heat exchanger 11, a first expansion valve 12, a second refrigeration compressor 13, a second refrigeration heat exchanger 14, and a second expansion valve 15. The first refrigeration compressor 10, the secondary side of the first refrigeration heat exchanger 11, the first expansion valve 12, and the primary side of the second refrigeration heat exchanger 14 are sequentially connected to form a primary refrigeration circuit. The second refrigeration compressor 13, the secondary side of the second refrigeration heat exchanger 14, the second expansion valve 15, and the secondary side of the first liquefaction heat exchanger 8 are sequentially connected to form a secondary refrigeration circuit. The primary side of the first refrigeration heat exchanger 11 is provided on the LNG pipeline. The LNG vaporizer 2 is a seawater open-frame vaporizer or a submerged combustion vaporizer, and the fuel cell 4 is a natural gas solid oxide fuel cell.

[0016] The above arrangement forms a coupled energy supply system based on LNG and fuel cells with a simple structure, easy operation, good stability, and high safety. During operation, the gas supply unit can provide users with the required natural gas, and the power generation unit can provide users with the required electricity, forming a combined power supply system with coupled gas supply and power generation. Compared with the existing technology, by using BOG as the natural gas required for power generation by the fuel cell 4, the excess BOG is liquefied and incorporated into the gas supply unit. This not only solves the BOG discharge and treatment problem and ensures safety, but also reduces energy consumption by recovering the cold energy of LNG. In addition, the provision of a two-stage refrigeration circuit and the first throttle valve 5 and the second throttle valve 6 improves system stability. The specific process of system operation is as follows: after the system is started, the LNG in the LNG storage tank 1 enters the LNG vaporizer 2 through the LNG pipeline and the primary side of the first refrigeration heat exchanger 11, and after being gasified into natural gas, enters the downstream gas pipeline through the gas supply pipeline. The BOG generated by the LNG storage tank 1 enters the fuel cell 4 through the BOG pipeline, the primary side of the cooling heat exchanger 3 and the fuel pipeline, and the electricity generated by the fuel cell 4 is incorporated into the user's power grid; when the BOG generated by the LNG storage tank 1 is less than the natural gas required for power generation by the fuel cell 4, the opening of the first throttle valve 5 is adjusted to the maximum, and the opening of the second throttle valve 6 is adjusted to allow the natural gas in the gas supply pipeline to enter the fuel cell 4 through the natural gas pipeline to supplement the natural gas required for power generation; when the BOG generated by the LNG storage tank 1 is more than the natural gas required for power generation by the fuel cell 4, the opening of the first throttle valve 5 is reduced, the second throttle valve 6 is closed, and the first liquefaction compressor 7, the first refrigeration compressor 11 and the second refrigeration compressor 13 are started; the working medium 1 circulates in the primary refrigeration circuit, and when the working medium 1 flows through the first refrigeration heat exchanger 11 The cooling energy of LNG is absorbed and turned into low-temperature liquid. After flowing through the first expansion valve 12, the low-temperature liquid changes into low-temperature gas. When the low-temperature gaseous working medium 1 flows through the second refrigeration heat exchanger 14, it absorbs the heat of the working medium 2. After the working medium 1 absorbs heat and heats up, it enters the first refrigeration heat exchanger 11 after being pressurized by the first refrigeration compressor 10. The working medium 2 circulates in the secondary refrigeration circuit. When the working medium 2 flows through the second refrigeration heat exchanger 14, it absorbs the cooling energy of the working medium 1 and turns into low-temperature liquid. After flowing through the second expansion valve 15, it changes into low-temperature gas. The low-temperature gaseous working medium 2 flows through The first liquefaction heat exchanger 8 absorbs the heat of the BOG. ​​After absorbing the heat and heating the working medium 2, it is pressurized by the second refrigeration compressor 13 and then enters the second refrigeration heat exchanger 14. The BOG is pressurized by the first liquefaction compressor 7 and enters the first liquefaction heat exchanger 8. After absorbing the cold energy of the working medium 2 in the first liquefaction heat exchanger 8, the BOG is liquefied into a gas-liquid mixture. The gas-liquid mixture is separated by the first gas-liquid separator 9 to produce LNG and natural gas. The LNG produced by the separation process is added to the LNG pipeline, and the natural gas produced by the separation process is added to the BOG pipeline.It should be noted that the natural gas in this article refers specifically to gaseous natural gas, and BOG refers specifically to the gas formed by LNG evaporating in the storage tank due to heat absorption. BOG and natural gas should be understood as the same gaseous substance.

[0017] As an optimization solution, this specific embodiment provides a third throttle valve 16 on the gas phase pipeline one to facilitate control, and adds a second liquefaction compressor 17, a second liquefaction heat exchanger 18 and a second gas-liquid separator 19 to the liquefaction unit, wherein the inlet of the second liquefaction compressor 17 is connected to the gas phase pipeline one between the third throttle valve 16 and the first gas-liquid separator 9, and the two ports on the primary side of the second liquefaction heat exchanger 18 are correspondingly connected to the outlet of the second liquefaction compressor 17 and the inlet of the second gas-liquid separator 19. The secondary side of the second liquefaction heat exchanger 18 is arranged on the secondary refrigeration circuit between the second refrigeration compressor 13 and the second expansion valve 15. The liquid phase outlet of the second gas-liquid separator 19 is connected to the LNG pipeline, and the gas phase outlet of the second gas-liquid separator 19 is connected to the BOG pipeline between the cooling heat exchanger 3 and the first throttle valve 5 through the gas phase pipeline two. This structure forms a two-stage liquefaction pipeline by adding a second liquefaction compressor 17, a second liquefaction heat exchanger 18, and a second gas-liquid separator 19, and cooperating with a first-stage liquefaction pipeline composed of a first liquefaction compressor 7, a first liquefaction heat exchanger 8, and a first gas-liquid separator 9. This not only improves the liquefaction effect but also enhances the stability of the system. In actual application, the utility model sets a high-pressure pump 20 on the LNG pipeline between the LNG storage tank 1 and the first refrigeration heat exchanger 11 to control the delivery of LNG, and the connection points of the liquid phase outlets of the first gas-liquid separator 9 and the second gas-liquid separator 19 with the LNG pipeline are both located between the high-pressure pump 20 and the LNG storage tank 1 to prevent LNG from flowing back into the first gas-liquid separator 9 and the second gas-liquid separator 19; and a fourth throttle valve 21 is set on the gas phase pipeline 2 to improve the convenience of control. At the same time, the utility model allows the user's power intranet to be connected to the first liquefaction compressor 7, the first refrigeration compressor 10, the second refrigeration compressor 13, the second liquefaction compressor 17 and the high-pressure pump 20 through cables, so as to provide the power required for the operation of each device through the user's power intranet.

[0018] As a specific implementation method, to facilitate technical personnel's understanding, the functions of each heat exchanger in the coupled energy supply system are briefly described below: the cooling heat exchanger 3 is used to perform heat exchange on the cooling water and natural gas flowing through it, the first liquefaction heat exchanger 8 and the second liquefaction heat exchanger 18 are respectively used to perform heat exchange on the natural gas and working medium 2 flowing through it, the first refrigeration heat exchanger 11 is used to perform heat exchange on the LNG and working medium 1 flowing through it, and the second refrigeration heat exchanger 14 is used to perform heat exchange on the working medium 1 and working medium 2 flowing through it, wherein working medium 1 refers to the working medium that circulates and transfers energy in the primary refrigeration circuit, and working medium 2 refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

[0019] To facilitate understanding by technicians, the following briefly describes the operation process of the coupled energy supply system, which includes the following steps:

[0020] S1. Start the high-pressure pump 20. The LNG in the LNG storage tank 1 enters the LNG vaporizer 2 through the LNG pipeline and the primary side of the first refrigeration heat exchanger 11. After being vaporized into natural gas, it enters the downstream gas pipeline through the gas supply pipeline. The BOG generated in the LNG storage tank 1 enters the fuel cell 4 through the BOG pipeline, the primary side of the cooling heat exchanger 3, and the fuel pipeline. The electricity generated by the fuel cell 4 is incorporated into the user's power grid.

[0021] S2. When the BOG produced by the LNG storage tank 1 is less than the natural gas required for the fuel cell 4 to generate electricity, the opening of the first throttle valve 5 is adjusted to the maximum, and the opening of the second throttle valve 6 is adjusted to allow the natural gas in the gas supply pipeline to enter the fuel cell 4 through the natural gas pipeline to supplement the natural gas required for power generation.

[0022] S3. When the BOG generated by the LNG storage tank 1 is more than the natural gas required for power generation by the fuel cell 4, the opening of the first throttle valve 5 is reduced, the second throttle valve 6 is closed, and the first liquefaction compressor 7, the second liquefaction compressor 17, the first refrigeration compressor 10 and the second refrigeration compressor 13 are started.

[0023] S3. Working medium 1 circulates in the primary refrigeration circuit. When flowing through the first refrigeration heat exchanger 11, working medium 1 absorbs the cold energy of LNG and becomes a low-temperature liquid. After flowing through the first expansion valve 12, it changes from a low-temperature liquid to a low-temperature gas. When flowing through the second refrigeration heat exchanger 14, the low-temperature gaseous working medium 1 absorbs the heat of working medium 2. After absorbing heat and heating up, the working medium 1 is pressurized by the first refrigeration compressor 10 and then enters the first refrigeration heat exchanger 11.

[0024] S4. The working medium 2 circulates in the secondary refrigeration circuit. When the working medium 2 flows through the second refrigeration heat exchanger 14, it absorbs the cold energy of the working medium 1 and becomes a low-temperature liquid. After flowing through the second expansion valve 15, it changes from a low-temperature liquid to a low-temperature gas. When the low-temperature gaseous working medium 2 flows through the first liquefied heat exchanger 8 and the second liquefied heat exchanger 18, it absorbs the heat of the natural gas. After absorbing heat and heating up, the working medium 2 is pressurized by the second refrigeration compressor 13 and then enters the second refrigeration heat exchanger 14.

[0025] S5. After being pressurized by the first liquefaction compressor 7, the BOG enters the first liquefaction heat exchanger 8. The BOG absorbs the cold energy of the second working medium in the first liquefaction heat exchanger 8 and liquefies to form a gas-liquid mixture. The gas-liquid mixture undergoes a primary separation in the first gas-liquid separator 9 to produce LNG and natural gas. The LNG produced by the primary separation is fed into the LNG pipeline. Part of the natural gas produced by the primary separation is fed into the BOG pipeline, and part of the natural gas is pressurized by the second liquefaction compressor 17 and enters the second liquefaction heat exchanger 18. The natural gas absorbs the cold energy of the second working medium in the second liquefaction heat exchanger 18 and liquefies to form a gas-liquid mixture. The gas-liquid mixture undergoes a secondary separation in the second gas-liquid separator 19 to produce LNG and natural gas. The LNG produced by the secondary separation is fed into the LNG pipeline, and the natural gas produced by the secondary separation is fed into the BOG pipeline.

[0026] The above embodiments are merely descriptions of preferred implementations of the present invention and do not limit the scope of protection requested for the present invention. Without departing from the design concept of the present invention, various modifications made by those skilled in the art based on the technical solution of the present invention should fall within the scope of protection determined by the claims of the present invention.

Claims

1. A coupled energy supply system based on LNG and fuel cells, characterized in that: The invention comprises an air supply unit, a power generation unit, a liquefaction unit and a refrigeration unit. The air supply unit comprises an LNG storage tank (1) and an LNG vaporizer (2) connected via an LNG pipeline. The LNG vaporizer (2) is connected to a downstream gas pipeline via an air supply pipeline. The power generation unit comprises a cooling heat exchanger (3) and a fuel cell (4). Two ports on the secondary side of the cooling heat exchanger (3) are connected to the water inlet and outlet of the fuel cell (4) to form a cooling circuit. The primary side inlet of the cooling heat exchanger (3) is connected to the LNG storage tank (1) via a BOG pipeline. A first throttle valve (5) is provided on the BOG pipeline. The primary side outlet of the cooling heat exchanger (3) is connected to the air inlet of the fuel cell (4) through a fuel pipeline, and the fuel pipeline is connected to the gas supply pipeline through a natural gas pipeline. A second throttle valve (6) is provided on the natural gas pipeline. The electric energy generated by the fuel cell (4) is incorporated into the user's power grid. The liquefaction unit includes a first liquefaction compressor (7), a first liquefaction heat exchanger (8) and a first gas-liquid separator (9). The inlet of the first liquefaction compressor (7) is connected to the BOG pipeline between the LNG storage tank (1) and the first throttle valve (5). The two ports on the primary side of the first liquefaction heat exchanger (8) correspond to the first gas-liquid separator (9). The outlet of a liquefaction compressor (7) is connected to the inlet of a first gas-liquid separator (9), the liquid phase outlet of the first gas-liquid separator (9) is connected to an LNG pipeline, the gas phase outlet of the first gas-liquid separator (9) is connected to a BOG pipeline between a cooling heat exchanger (3) and a first throttle valve (5) through a gas phase pipeline, and the refrigeration unit includes a first refrigeration compressor (10), a first refrigeration heat exchanger (11), a first expansion valve (12), a second refrigeration compressor (13), a second refrigeration heat exchanger (14) and a second expansion valve (15), the first refrigeration compressor (10), the first refrigeration The secondary side of the heat exchanger (11), the first expansion valve (12) and the primary side of the second refrigeration heat exchanger (14) are connected in sequence to form a primary refrigeration circuit, the primary side of the first refrigeration heat exchanger (11) is arranged on the LNG pipeline, the second refrigeration compressor (13), the secondary side of the second refrigeration heat exchanger (14), the second expansion valve (15) and the secondary side of the first liquefaction heat exchanger (8) are connected in sequence to form a secondary refrigeration circuit; the LNG vaporizer (2) is a seawater open-frame vaporizer or an immersed combustion vaporizer, and the fuel cell (4) is a natural gas solid oxide fuel cell.

2. The coupled energy supply system based on LNG and fuel cells according to claim 1, characterized in that: A third throttle valve (16) is provided on the gas phase pipeline 1, and the liquefaction unit further includes a second liquefaction compressor (17), a second liquefaction heat exchanger (18) and a second gas-liquid separator (19). The inlet of the second liquefaction compressor (17) is connected to the gas phase pipeline 1 between the third throttle valve (16) and the first gas-liquid separator (9). The two ports on the primary side of the second liquefaction heat exchanger (18) are connected to the outlet of the second liquefaction compressor (17) and the inlet of the second gas-liquid separator (19) respectively. The secondary side of the second liquefaction heat exchanger (18) is arranged on the secondary refrigeration circuit between the second refrigeration compressor (13) and the second expansion valve (15). The liquid phase outlet of the second gas-liquid separator (19) is connected to the LNG pipeline, and the gas phase outlet of the second gas-liquid separator (19) is connected to the BOG pipeline between the cooling heat exchanger (3) and the first throttle valve (5) through the gas phase pipeline 2.

3. The coupled energy supply system based on LNG and fuel cells according to claim 2, characterized in that: A high-pressure pump (20) is provided on the LNG pipeline between the LNG storage tank (1) and the first refrigeration heat exchanger (11); the connection points between the liquid phase outlets of the first gas-liquid separator (9) and the second gas-liquid separator (19) and the LNG pipeline are both located between the high-pressure pump (20) and the LNG storage tank (1); and a fourth throttle valve (21) is provided on the gas phase pipeline II.

4. The coupled energy supply system based on LNG and fuel cells according to claim 3, characterized in that: The user power intranet is connected to the first liquefaction compressor (7), the first refrigeration compressor (10), the second refrigeration compressor (13), the second liquefaction compressor (17) and the high-pressure pump (20) through cables and provides power thereto.

5. The coupled energy supply system based on LNG and fuel cells according to claim 4 is characterized in that: The cooling heat exchanger (3) is used for performing heat exchange between cooling water and natural gas flowing through it.

6. The coupled energy supply system based on LNG and fuel cells according to claim 4, characterized in that: The first liquefaction heat exchanger (8) and the second liquefaction heat exchanger (18) are respectively used to perform heat exchange between the natural gas and the second working medium flowing therethrough, wherein the second working medium refers to the working medium that circulates in the secondary refrigeration circuit and transfers energy.

7. The coupled energy supply system based on LNG and fuel cells according to claim 4, characterized in that: The first refrigeration heat exchanger (11) is used to perform heat exchange between LNG and working medium 1 flowing therethrough, where working medium 1 refers to a working medium that circulates in a primary refrigeration circuit and transfers energy, and the second refrigeration heat exchanger (14) is used to perform heat exchange between working medium 1 and working medium 2 flowing therethrough.

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