Coupling energy supply system based on LNG and fuel cell and control method

Abstract

The invention relates to a coupling energy supply system based on LNG and a fuel cell and a control method.The system comprises a gas supply unit, a power generation unit, a liquefaction unit and a refrigeration unit, the gas supply unit comprises an LNG storage tank and an LNG gasifier which are connected through an LNG pipeline, and the LNG gasifier is connected with a downstream gas pipeline through the gas supply pipeline; the power generation unit comprises a cooling heat exchanger and a fuel cell, 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, and electric energy generated by the fuel cell is merged into a user power internal network. The liquefaction unit comprises a first liquefaction compressor, a first liquefaction heat exchanger and a first gas-liquid separator, the refrigeration unit comprises 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, and the system has the advantages of being good in stability and high in safety; the method has the advantages of simple process, safety and reliability.

Description

Technical Field

[0001] The present invention relates to an energy supply system, in particular to a coupled energy supply system based on LNG and a fuel cell, and a control method of the system. Background Art

[0002] For LNG receiving stations, LNG storage tanks are both receiving equipment and LNG storage equipment. During the storage process, external heat will continuously be transferred to the inside of the storage tank through the tank body and the attached pipes. After the heat is absorbed by the LNG, it will cause partial evaporation and generate gas (BOG). If the BOG is not discharged in time, it is easy to cause overpressure in the tank and bring safety risks. At present, the following two methods are mainly used to deal with BOG in this field: one is direct compression, and the other is re-condensation. Both methods have relatively high energy consumption and there is a problem of difficulty in handling operations when the external transmission load fluctuates. Summary of the invention

[0003] The purpose of the present invention is to provide a coupled energy supply system based on LNG and fuel cells and a control method. The system has the advantages of simple structure, convenient operation, good stability and high safety; the method has the advantages of simple process, safety and reliability.

[0004] In order to solve the above problems existing in the prior art, the present invention provides a coupled energy supply system based on LNG and fuel cells, including a gas supply unit, a power generation unit, a liquefaction unit and a refrigeration unit, wherein the gas supply unit includes an LNG storage tank and an LNG vaporizer connected by an LNG pipeline, and the LNG vaporizer is connected to a downstream gas pipeline through a gas supply pipeline, the power generation unit includes a cooling heat exchanger and a fuel cell, and two ports on the secondary side of the cooling heat exchanger are connected to the water inlet and outlet of the fuel cell correspondingly to form a cooling circuit, the primary side inlet of the cooling heat exchanger is connected to the LNG storage tank through a BOG pipeline, and a first throttle valve is provided on the BOG pipeline, the primary side outlet of the cooling heat exchanger is connected to the gas inlet of the fuel cell through a fuel pipeline, the fuel pipeline is connected to the gas supply pipeline through a natural gas 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, the liquefaction unit includes a first liquefaction compressor, a first liquefaction heat exchanger and a first A gas-liquid separator, an inlet of the first liquefaction compressor is connected to the BOG pipeline between the LNG storage tank and the first throttle valve, 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 the 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.

[0005] Furthermore, the present invention provides a coupled energy supply system based on LNG and fuel cells, wherein a third throttle valve is provided on the gas phase pipeline one, 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 one 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 correspondingly connected 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 a 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 two.

[0006] Furthermore, the present invention 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.

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

[0008] Furthermore, the present invention 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 present invention 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 for heat exchange between the natural gas and the 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 present invention 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 LNG and working fluid one flowing therethrough, working fluid one refers to a working medium that circulates in a primary refrigeration circuit and transfers energy, and the second refrigeration heat exchanger is used to perform heat exchange between working fluid one and working fluid two flowing therethrough.

[0011] Furthermore, the present invention provides a coupled energy supply system based on LNG and fuel cells, wherein the LNG gasifier is a seawater open-frame gasifier or an immersed combustion gasifier.

[0012] Furthermore, the present invention provides a coupled energy supply system based on LNG and fuel cells, wherein the fuel cell is a natural gas solid oxide fuel cell.

[0013] Based on the same concept, the present invention also provides a control method for the above-mentioned coupled energy supply system, comprising the following steps:

[0014] S1. Start the high-pressure pump. The LNG in the LNG storage tank enters the LNG vaporizer through the LNG pipeline and the primary side of the first refrigeration heat exchanger, and enters the downstream gas pipeline through the gas supply pipeline after being gasified into natural gas. The BOG generated in the LNG storage tank enters the fuel cell through the BOG pipeline, the primary side of the cooling heat exchanger and the fuel pipeline. The electric energy generated by the fuel cell is incorporated into the user's power grid.

[0015] S2. When the BOG generated by the LNG storage tank is less than the natural gas required for fuel cell power generation, the opening of the first throttle valve is adjusted to the maximum, and the opening of the second throttle valve is adjusted to allow the natural gas in the gas supply pipeline to enter the fuel cell through the natural gas pipeline to supplement the natural gas required for power generation;

[0016] S3. When the BOG generated by the LNG storage tank is more than the natural gas required for the fuel cell to generate electricity, the opening of the first throttle valve is reduced, the second throttle valve is closed, and the first liquefaction compressor, the second liquefaction compressor, the first refrigeration compressor, and the second refrigeration compressor are started;

[0017] S4, the working medium 1 circulates in the primary refrigeration circuit. When the working medium 1 flows through the first refrigeration heat exchanger, it absorbs the cold of LNG and becomes a low-temperature liquid. After flowing through the first expansion valve, it changes from a low-temperature liquid to a low-temperature gas. When the low-temperature gaseous working medium 1 flows through the second refrigeration heat exchanger, it absorbs the heat of the working medium 2. After absorbing heat and heating up, the working medium 1 enters the first refrigeration heat exchanger after being pressurized by the first refrigeration compressor.

[0018] S5, the working medium 2 circulates in the secondary refrigeration circuit. When the working medium 2 flows through the second refrigeration heat exchanger, it absorbs the cold of the working medium 1 and becomes a low-temperature liquid. After flowing through the second expansion valve, 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 and the second liquefied heat exchanger, it absorbs the heat of the natural gas. After absorbing heat and heating up, the working medium 2 enters the second refrigeration heat exchanger after being pressurized by the second refrigeration compressor.

[0019] S6, BOG enters the first liquefaction heat exchanger after being pressurized by the first liquefaction compressor, BOG absorbs the cold of the second working medium at the first liquefaction heat exchanger and is liquefied to become a gas-liquid mixture, the gas-liquid mixture is separated for the first time by the first gas-liquid separator to produce LNG and natural gas, the LNG produced by the first separation is incorporated into the LNG pipeline, part of the natural gas produced by the first separation is incorporated into the BOG pipeline, and part of it enters the second liquefaction heat exchanger after being pressurized by the second liquefaction compressor, the natural gas absorbs the cold of the second working medium at the second liquefaction heat exchanger and is liquefied to become a gas-liquid mixture, the gas-liquid mixture is separated again by the second gas-liquid separator to produce LNG and natural gas, the LNG produced by the second separation is incorporated into the LNG pipeline, and the natural gas produced by the second separation is incorporated into the BOG pipeline;

[0020] The working medium 1 refers to the working medium that circulates and transfers energy in the primary refrigeration circuit, and the working medium 2 refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

[0021] Compared with the prior art, the coupled energy supply system and control method based on LNG and fuel cell of the present invention has the following advantages: the present invention arranges 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 ports on the secondary side 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 arranged on the BOG pipeline, and a second throttle valve is arranged 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 connects the inlet of the first liquefied compressor to the BOG pipeline between the LNG storage tank and the first throttle valve, and connects the two ports on the primary side of the first liquefied heat exchanger to the outlet of the first liquefied compressor and the inlet of the first gas-liquid separator correspondingly, wherein 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 the gas phase pipeline 1, so that the refrigeration unit is provided with the first refrigeration compressor, the first refrigeration heat exchanger, the first expansion valve, the second refrigeration compressor, the second refrigeration heat exchanger and the second expansion valve, and 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, 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 liquefied heat exchanger are connected in sequence to form a secondary refrigeration circuit, and the primary side of the first refrigeration heat exchanger is arranged on the LNG pipeline. Thus, a coupled energy supply system based on LNG and fuel cells is formed, which has a simple structure, convenient 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 supply system of gas supply and power generation coupled operation. Compared with the prior art, by using BOG as the natural gas required for fuel cell power generation, the excess BOG is liquefied and incorporated into the gas supply unit, which not only solves the problem of BOG emission treatment and ensures safety, but also reduces energy consumption by recycling the cold energy of LNG, and improves system stability by setting a two-stage refrigeration circuit and a first throttle valve and a second throttle valve.

[0022] The following is a further detailed description of a coupled energy supply system based on LNG and a fuel cell and a control method of the present invention in conjunction with the specific embodiments shown in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of a coupled energy supply system based on LNG and fuel cells according to the present invention. DETAILED DESCRIPTION

[0024] First of all, it should be explained 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 the scope of protection of the present invention.

[0025] like Figure 1 The specific implementation of the coupled energy supply system based on LNG and fuel cells of the present invention is shown, including 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 by an LNG pipeline, and the LNG vaporizer 2 is connected to the downstream gas pipeline through the gas supply pipeline. The power generation unit is provided with a cooling heat exchanger 3 and a fuel cell 4, and the 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, and the primary side inlet of the cooling heat exchanger 3 is connected to the LNG storage tank 1 through the BOG pipeline, and the primary side outlet of the cooling heat exchanger 3 is connected to the air inlet of the fuel cell 4 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 5 is provided on the BOG pipeline, and a second throttle valve 6 is provided on the natural gas pipeline, and the electric energy generated by the fuel cell 4 is incorporated into the user's power intranet. 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 correspondingly, 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 connected in sequence 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 connected in sequence to form a secondary refrigeration circuit, and the primary side of the first refrigeration heat exchanger 11 is set on the LNG pipeline.

[0026] The above arrangement constitutes a coupled energy supply system based on LNG and fuel cells with simple structure, convenient 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 supply system with coupled operation of gas supply and power generation. Compared with the prior art, 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, which not only solves the problem of BOG discharge treatment and ensures safety, but also reduces energy consumption by recycling the cold energy of LNG, and improves system stability by setting a two-stage refrigeration circuit and the first throttle valve 5 and the second throttle valve 6. 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 enters the downstream gas pipeline through the gas supply pipeline after being gasified into natural gas. 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 electric energy 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 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; 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 fluid 1 circulates in the primary refrigeration circuit, and when the working fluid 1 flows through the first refrigeration heat exchanger 11 The cooling energy of LNG is absorbed and turned into a low-temperature liquid. After flowing through the first expansion valve 12, the low-temperature liquid turns into a 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 rises in temperature, 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 a low-temperature liquid. After flowing through the second expansion valve 15, it turns into a low-temperature gas. The low-temperature gaseous working medium 2 flows through The first liquefied heat exchanger 8 absorbs the heat of BOG, and the working medium 2 after absorbing heat and heating is pressurized by the second refrigeration compressor 13 and enters the second refrigeration heat exchanger 14; the BOG enters the first liquefied heat exchanger 8 after being pressurized by the first liquefied compressor 7, and BOG absorbs the cold of the working medium 2 at the first liquefied heat exchanger 8 and is liquefied to become 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 treatment is integrated into the LNG pipeline, and the natural gas produced by the separation treatment is integrated into the BOG pipeline.It should be noted that the LNG vaporizer 2 and the fuel cell 4 are both existing equipment in the field, and their structures, principles and connection methods are well known to technicians. Among them, the LNG vaporizer 2 can adopt a seawater open-frame vaporizer or an immersed combustion vaporizer, and the fuel cell 4 refers to a natural gas solid oxide fuel cell. It should also be pointed out that the natural gas in this article specifically refers to gaseous natural gas, and BOG specifically refers to the gas formed by LNG evaporating in the storage tank due to endothermic absorption. BOG and natural gas should be understood as the same gaseous substance.

[0027] As an optimization scheme, 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, 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 a first liquefaction pipeline composed of a first liquefaction compressor 7, a first liquefaction heat exchanger 8 and a first gas-liquid separator 9, which not only improves the liquefaction effect, but also enhances the system stability. In practical applications, the present invention 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 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 present invention 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.

[0028] As a specific implementation method, in order to facilitate the understanding of technical personnel, the functions of each heat exchanger in the coupled energy supply system are briefly explained as follows: the cooling heat exchanger 3 is used for heat exchange between cooling water and natural gas flowing therethrough, the first liquefied heat exchanger 8 and the second liquefied heat exchanger 18 are respectively used for heat exchange between natural gas and working medium 2 flowing therethrough, the first refrigeration heat exchanger 11 is used for heat exchange between LNG and working medium 1 flowing therethrough, and the second refrigeration heat exchanger 14 is used for heat exchange between working medium 1 and working medium 2 flowing therethrough, 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.

[0029] Based on the same concept, the present invention also provides a control method for the above-mentioned coupled energy supply system, comprising the following steps:

[0030] 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, and enters the downstream gas pipeline through the gas supply pipeline after being gasified into natural gas. 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 electric energy generated by the fuel cell 4 is incorporated into the user's power grid.

[0031] 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.

[0032] S3. When the BOG produced by the LNG storage tank 1 is more than the natural gas required for the fuel cell 4 to generate electricity, 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.

[0033] S4, working medium 1 circulates in the primary refrigeration circuit. When working medium 1 flows through the first refrigeration heat exchanger 11, it absorbs the cold 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 the low-temperature gaseous working medium 1 flows through the second refrigeration heat exchanger 14, it absorbs the heat of working medium 2. After absorbing heat and heating up, the working medium 1 enters the first refrigeration heat exchanger 11 after being pressurized by the first refrigeration compressor 10.

[0034] S5, working medium 2 circulates in the secondary refrigeration circuit. When working medium 2 flows through the second refrigeration heat exchanger 14, it absorbs the cold of 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 natural gas. After absorbing heat and heating, the working medium 2 is pressurized by the second refrigeration compressor 13 and enters the second refrigeration heat exchanger 14.

[0035] S6. BOG is pressurized by the first liquefaction compressor 7 and enters the first liquefaction heat exchanger 8. After BOG absorbs the cold of the second working medium at the first liquefaction heat exchanger 8, it is liquefied to become a gas-liquid mixture. The gas-liquid mixture is first separated by the first gas-liquid separator 9 to produce LNG and natural gas. The LNG produced by the first separation is incorporated into the LNG pipeline. Part of the natural gas produced by the first separation is incorporated into the BOG pipeline, and part of it is pressurized by the second liquefaction compressor 17 and enters the second liquefaction heat exchanger 18. The natural gas absorbs the cold of the second working medium at the second liquefaction heat exchanger 18 and is liquefied to become a gas-liquid mixture. The gas-liquid mixture is separated again by the second gas-liquid separator 19 to produce LNG and natural gas. The LNG produced by the second separation is incorporated into the LNG pipeline, and the natural gas produced by the second separation is incorporated into the BOG pipeline.

[0036] The control method of the coupled energy supply system provided by the present invention has the advantages of simple process, safety and reliability.

[0037] The above embodiments are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the protection scope of 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 protection scope 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 a gas supply unit, a power generation unit, a liquefaction unit and a refrigeration unit. The gas 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 the gas 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 OG 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, 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 comprises 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 LNG storage tank (1) and the first throttle valve (5) The first liquefaction heat exchanger (8) is connected to the BOG pipeline, 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, 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 includes a first refrigeration compressor (10), a first refrigeration heat exchanger (11), a first expansion valve (12), and 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 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.

2. According to claim 1, a coupled energy supply system based on LNG and fuel cells is characterized in that: A third throttle valve (16) is provided on the gas phase pipeline one, and the liquefaction unit further comprises 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 one 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) correspondingly. 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.

3. The coupled energy supply system based on LNG and fuel cells according to claim 2 is 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 is characterized in that: The user's 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 to them.

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 to perform 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 is characterized in that: The first liquefied heat exchanger (8) and the second liquefied 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 is characterized in that: The first refrigeration heat exchanger (11) is used to perform heat exchange between LNG and working medium 1 flowing therethrough, working medium 1 referring 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.

8. The coupled energy supply system based on LNG and fuel cells according to claim 4 is characterized in that: The LNG gasifier (2) is a seawater open-frame gasifier or a submerged combustion gasifier.

9. The coupled energy supply system based on LNG and fuel cells according to claim 4, characterized in that: The fuel cell (4) is a natural gas solid oxide fuel cell.

10. A control method for the coupled energy supply system according to claim 4, characterized in that: The following steps are involved: S1, starting 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), and after being gasified into natural gas, 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, and the electric energy generated by the fuel cell (4) is incorporated into the user's power grid; S2. When the BOG generated 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, so as to supplement the natural gas required for power generation; S3. When the BOG generated by the LNG storage tank (1) is greater than the natural gas required for the fuel cell (4) to generate electricity, 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; S4, the working medium 1 circulates in the primary refrigeration circuit. When the working medium 1 flows through the first refrigeration heat exchanger (11), it absorbs the cold of the 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 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 absorbing heat and raising the temperature, the working medium 1 enters the first refrigeration heat exchanger (11) after being pressurized by the first refrigeration compressor (10); S5, 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 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 enters the second refrigeration heat exchanger (14). S6, BOG is pressurized by the first liquefaction compressor (7) and enters the first liquefaction heat exchanger (8). The BOG absorbs the cold energy of the second working medium at the first liquefaction heat exchanger (8) and is liquefied to become a gas-liquid mixture. The gas-liquid mixture is separated for the first time by the first gas-liquid separator (9) to produce LNG and natural gas. The LNG produced by the first separation is introduced into the LNG pipeline. A part of the natural gas produced by the first separation is introduced into the BOG pipeline, and a 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 at the second liquefaction heat exchanger (18) and is liquefied to become a gas-liquid mixture. The gas-liquid mixture is separated again by the second gas-liquid separator (19) to produce LNG and natural gas. The LNG produced by the second separation is introduced into the LNG pipeline, and the natural gas produced by the second separation is introduced into the BOG pipeline. The working medium 1 refers to the working medium that circulates and transfers energy in the primary refrigeration circuit, and the working medium 2 refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

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