A coupling energy supply system based on LNG and fuel cell and a control method thereof

Abstract

The application relates to a coupling energy supply system and a control method based on LNG and fuel cells, the system comprising a gas supply unit, a power generation unit, a liquefaction unit and a refrigeration unit, the gas supply unit comprising an LNG storage tank and an LNG gasifier connected through an LNG pipeline, the LNG gasifier being connected with a downstream gas pipeline through a gas supply pipeline, the power generation unit comprising a cooling heat exchanger and a fuel cell, a primary side inlet of the cooling heat exchanger being connected with the LNG storage tank through a BOG pipeline, a primary side outlet of the cooling heat exchanger being connected with an air inlet of the fuel cell through a fuel pipeline, electric energy generated by the fuel cell being incorporated into a user power inner network, the liquefaction unit comprising a first liquefaction compressor, a first liquefaction heat exchanger and a first gas-liquid separator, and the refrigeration unit comprising 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 good stability and high safety; the method has the advantages of simple flow process and safety and reliability.

Description

Technical Field

[0001] This invention relates to an energy supply system, specifically to a coupled energy supply system based on LNG and a fuel cell, and a control method for the system. Background Technology

[0002] For LNG receiving terminals, LNG storage tanks serve as both receiving and storage equipment for LNG. During storage, external heat is continuously transferred into the tank through the tank body and auxiliary piping. This heat is absorbed by the LNG, causing partial evaporation and generating bound gas (BOG). If BOG is not promptly removed, it can easily lead to overpressure within the tank and pose safety risks. Currently, the main methods for handling BOG in this field are direct compression and recondensation. Both methods have relatively high energy consumption and present operational difficulties when the external load fluctuates. Summary of the Invention

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

[0004] To address the aforementioned problems in the existing technology, this invention provides 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 includes an LNG storage tank and an LNG vaporizer connected via an LNG pipeline. The LNG vaporizer is connected to a downstream gas pipeline via the gas supply pipeline. The power generation unit includes a cooling heat exchanger and a fuel cell. The two ports on the secondary side of the cooling heat exchanger are connected to the inlet and outlet of the fuel cell to form a cooling circuit. The primary side inlet of the cooling heat exchanger is connected to the LNG storage tank via a BOG pipeline, which is equipped with a first throttle valve. The primary side outlet of the cooling heat exchanger is connected to the fuel cell inlet via a fuel pipeline. The fuel pipeline is connected to the gas supply pipeline via a natural gas pipeline, which is equipped with a second throttle valve. The electricity generated by the fuel cell is fed into the user's internal power grid. The liquefaction unit includes a first liquefaction compressor, a first liquefaction heat exchanger, and a first... The gas-liquid separator has its inlet connected to the BOG pipeline between the LNG storage tank and the first throttle valve. The two ports of the primary side of the first liquefaction heat exchanger are connected to the outlet of the first liquefaction 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, 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 a gas phase pipeline. 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 secondary side of the first refrigeration compressor, 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 located on the LNG pipeline. The secondary side of the second refrigeration compressor, 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 first gas phase pipeline, and the liquefaction unit further 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 first gas phase pipeline 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 to the outlet of the second liquefaction compressor and the inlet of the second gas-liquid separator, respectively. The secondary side of the second liquefaction heat exchanger is arranged in 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 a second gas phase pipeline.

[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, and 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 second gas phase pipeline.

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

[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 exchange heat between the cooling water and natural gas flowing through it.

[0009] Furthermore, the present invention provides a coupled energy supply system based on LNG and fuel cells, wherein the first liquefaction heat exchanger and the second liquefaction heat exchanger are used to exchange heat between the natural gas flowing through them and the second working medium, which refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

[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 exchange heat between the LNG flowing through it and working medium one, where working medium one refers to the working medium that circulates and transfers energy in the primary refrigeration circuit, and the second refrigeration heat exchanger is used to exchange heat between working medium one and working medium two flowing through it.

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

[0012] Furthermore, the present invention provides a coupled energy supply system based on LNG and a fuel cell, wherein the fuel cell refers to 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 power supply system, comprising the following steps:

[0014] S1. Start the high-pressure pump. LNG in the LNG storage tank enters the LNG vaporizer through the LNG pipeline and the primary side of the first refrigeration heat exchanger. After being vaporized into natural gas, it enters the downstream gas pipeline through the gas supply pipeline. 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 electricity generated by the fuel cell is connected to the user's power grid.

[0015] S2. When the BOG produced 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 natural gas in the gas supply pipeline is allowed to enter the fuel cell through the natural gas pipeline by adjusting the opening of the second throttle valve to supplement the natural gas required for power generation.

[0016] S3. When the BOG produced by the LNG storage tank exceeds the natural gas required for fuel cell power generation, reduce the opening of the first throttle valve, close the second throttle valve, and start the first liquefaction compressor, the second liquefaction compressor, the first refrigeration compressor, and the second refrigeration compressor.

[0017] S4. The working fluid 1 circulates in the first-stage refrigeration circuit. When the working fluid 1 flows through the first refrigeration heat exchanger, it absorbs the cold energy 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 fluid 1 flows through the second refrigeration heat exchanger, it absorbs the heat of the second working fluid. After absorbing heat and becoming heated, the working fluid 1 is pressurized by the first refrigeration compressor and then enters the first refrigeration heat exchanger.

[0018] S5. The second working fluid circulates in the secondary refrigeration loop. When the second working fluid flows through the second refrigeration heat exchanger, it absorbs the cold energy of the first working fluid 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 fluid flows through the first liquefaction heat exchanger and the second liquefaction heat exchanger, it absorbs the heat of the natural gas. After absorbing heat and becoming hotter, the second working fluid is pressurized by the second refrigeration compressor and then enters the second refrigeration heat exchanger.

[0019] S6. After being pressurized by the first liquefaction compressor, BOG enters the first liquefaction heat exchanger. BOG absorbs the cooling energy of the second working medium at the first liquefaction heat exchanger and liquefies into a gas-liquid mixture. The gas-liquid mixture undergoes initial separation in the first gas-liquid separator to produce LNG and natural gas. The LNG produced in the initial separation is incorporated into the LNG pipeline. Part of the natural gas produced in the initial separation is incorporated into the BOG pipeline, and part of it is pressurized by the second liquefaction compressor and enters the second liquefaction heat exchanger. The natural gas absorbs the cooling energy of the second working medium at the second liquefaction heat exchanger and liquefies into a gas-liquid mixture. The gas-liquid mixture undergoes further separation in the second gas-liquid separator to produce LNG and natural gas. The LNG produced in the second separation is incorporated into the LNG pipeline, and the natural gas produced in the second separation is incorporated into the BOG pipeline.

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

[0021] Compared with existing technologies, the present invention provides a coupled energy supply system and control method based on LNG and fuel cells, which has the following advantages: The present invention sets up a gas supply unit, a power generation unit, a liquefaction unit, and a refrigeration unit. The gas supply unit is equipped with an LNG storage tank and an LNG vaporizer connected via an LNG pipeline. The LNG vaporizer is connected to a downstream gas pipeline via the gas supply pipeline. The power generation unit is equipped with a cooling heat exchanger and a fuel cell. The two ports of the secondary side of the cooling heat exchanger are connected to the inlet and outlet of the fuel cell to form a cooling circuit. The primary side inlet of the cooling heat exchanger is connected to the LNG storage tank via a BOG pipeline. The primary side outlet of the cooling heat exchanger is connected to the inlet of the fuel cell via a fuel pipeline. The fuel pipeline is connected to the gas supply pipeline via a natural gas pipeline. A first throttle valve is installed on the BOG pipeline, and a second throttle valve is installed on the natural gas pipeline. The electricity generated by the fuel cell is integrated into the user's power grid. The liquefaction unit is equipped with a first liquefaction compressor, a first liquefaction heat exchanger, and... The first gas-liquid separator connects the inlet of the first liquefaction compressor to the BOG pipeline between the LNG storage tank and the first throttle valve. The two ports of the primary side of the first liquefaction heat exchanger are connected to the outlet of the first liquefaction 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, 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 via a gas phase pipeline. The refrigeration unit consists of 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 secondary side of the first refrigeration compressor, 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 secondary side of the second refrigeration compressor, the second refrigeration heat exchanger, the second expansion valve, and the secondary side of the first liquefaction heat exchanger are sequentially connected to form a secondary refrigeration circuit. The primary side of the first refrigeration heat exchanger is connected to the LNG pipeline. This results in a simple, easy-to-operate, stable, and safe LNG and fuel cell-based coupled energy supply system. During operation, the gas supply unit provides the user with the required natural gas, and the power generation unit provides the user with the required electricity, forming a combined gas supply and power generation system. Compared with 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, the emission treatment problem of BOG is solved, ensuring safety. Furthermore, the energy consumption is reduced through the recovery and utilization of LNG's cold energy. In addition, the system stability is improved by setting up a two-stage refrigeration circuit and a first and second throttling valve.

[0022] The following detailed description, in conjunction with the accompanying drawings, illustrates a coupled energy supply system and control method based on LNG and fuel cells according to the present invention. Attached Figure Description

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

[0024] First, it should be noted that the directional terms such as up, down, left, right, front, and back used in this invention are merely descriptions based on the accompanying drawings for ease of understanding, and are not intended to limit the technical solution or the scope of protection claimed in this invention.

[0025] like Figure 1 The present invention illustrates 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 equipped with 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 is equipped with a cooling heat exchanger 3 and a fuel cell 4. The two ports on the secondary side of the cooling heat exchanger 3 are connected to the 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, and the primary side outlet of the cooling heat exchanger 3 is connected to the 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 installed on the BOG pipeline, and a second throttle valve 6 is installed on the natural gas pipeline. The electrical energy generated by the fuel cell 4 is integrated into the user's internal power grid. The liquefaction unit is equipped 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. 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 a gas phase pipeline. The refrigeration unit is configured 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 secondary side of the first refrigeration compressor 10, the first refrigeration heat exchanger 11, the first expansion valve 12, and the second refrigeration heat exchanger 14 are sequentially connected to form a first-stage refrigeration circuit. The secondary side of the second refrigeration compressor 13, 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 second-stage refrigeration circuit. The primary side of the first refrigeration heat exchanger 11 is located on the LNG pipeline.

[0026] The above configuration constitutes a simple, easy-to-operate, stable, and safe LNG and fuel cell-based coupled energy supply system. During operation, the gas supply unit provides the user with the required natural gas, and the power generation unit provides the user with the required electricity, forming a combined gas supply and power generation system. Compared with existing technologies, by using BOG as the natural gas required for power generation in fuel cell 4, and liquefying excess BOG and incorporating it into the gas supply unit, the emission treatment problem of BOG is solved, ensuring safety. Furthermore, the energy consumption is reduced through the cold energy recovery and utilization of LNG. In addition, the system stability is improved by setting up a two-stage refrigeration circuit and the first throttle valve 5 and the second throttle valve 6. The specific operation process of the system is as follows: After the system starts, the LNG in LNG storage tank 1 enters LNG vaporizer 2 through the LNG pipeline and the primary side of the first refrigeration heat exchanger 11, and after vaporization into natural gas, it enters the downstream gas pipeline through the gas supply pipeline. The BOG generated by LNG storage tank 1 enters fuel cell 4 through the BOG pipeline, the primary side of the cooling heat exchanger 3, and the fuel pipeline. The electricity generated by fuel cell 4 is connected to the user's power grid. When the BOG generated by LNG storage tank 1 is less than the natural gas required for 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 fuel cell 4 through the natural gas pipeline to supplement the natural gas required for power generation. When the BOG generated by LNG storage tank 1 is more than the natural gas required for 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 first refrigeration compressor 10, and the second refrigeration compressor 13 are started. The working fluid 1 circulates in the first-stage refrigeration loop. When the working fluid 1 flows through the first refrigeration heat exchanger 11... The working fluid absorbs the cold energy of LNG and becomes a cryogenic liquid. After flowing through the first expansion valve 12, it changes from a cryogenic liquid to a cryogenic gas. When the cryogenic gaseous working fluid 1 flows through the second refrigeration heat exchanger 14, it absorbs heat from the second working fluid. After absorbing heat and becoming warmer, the working fluid 1 is pressurized by the first refrigeration compressor 10 and then enters the first refrigeration heat exchanger 11. The second working fluid 2 circulates in the secondary refrigeration loop. When the second working fluid 2 flows through the second refrigeration heat exchanger 14, it absorbs the cold energy of the first working fluid and becomes a cryogenic liquid. After flowing through the second expansion valve 15, it changes from a cryogenic liquid to a cryogenic gas. The cryogenic gaseous working fluid 2 then flows through... The first liquefaction heat exchanger 8 absorbs heat from the BOG. ​​After absorbing heat and heating up, the working fluid 2 is pressurized by the second refrigeration compressor 13 and 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. The BOG absorbs the cold energy of the working fluid 2 at the first liquefaction heat exchanger 8 and liquefies 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 incorporated into the LNG pipeline, and the natural gas produced by the separation process is incorporated into the BOG pipeline.It should be noted that both the LNG vaporizer 2 and the fuel cell 4 are existing devices in the field, and their structures, principles, and connection methods are well known to those skilled in the art. The LNG vaporizer 2 can be an open-rack seawater vaporizer or a submerged combustion vaporizer, and the fuel cell 4 refers to a natural gas solid oxide fuel cell. Furthermore, it should be pointed out that in this article, "natural gas" specifically refers to gaseous natural gas, and "BOG" specifically refers to the gas formed by the endothermic evaporation of LNG in the storage tank. BOG and natural gas should be understood as the same gaseous substance.

[0027] As an optimization, this specific embodiment adds a third throttle valve 16 to the first gas phase pipeline for easier 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. The inlet of the second liquefaction compressor 17 is connected to the first gas phase pipeline 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 set 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 second gas phase pipeline. This structure, by adding a two-stage liquefaction pipeline consisting of a second liquefaction compressor 17, a second liquefaction heat exchanger 18, and a second gas-liquid separator 19, combined with a first-stage liquefaction pipeline consisting of a first liquefaction compressor 7, a first liquefaction heat exchanger 8, and a first gas-liquid separator 9, forms a two-stage liquefaction pipeline. This not only improves the liquefaction effect but also enhances system stability. In practical applications, this invention installs a high-pressure pump 20 on the LNG pipeline between the LNG storage tank 1 and the first refrigeration heat exchanger 11 to control LNG delivery. The connection points of the liquid phase outlets of the first and second gas-liquid separators 9 and 19 to the LNG pipeline are both located between the high-pressure pump 20 and the LNG storage tank 1 to prevent LNG backflow into the first and second gas-liquid separators 9 and 19. A fourth throttle valve 21 is installed on the second gas phase pipeline to improve control convenience. Meanwhile, the present invention allows the user's internal power grid to be connected to the first liquefied compressor 7, the first refrigeration compressor 10, the second refrigeration compressor 13, the second liquefied compressor 17 and the high-pressure pump 20 respectively via cables, so as to provide the power required for operation of each device through the user's internal power grid.

[0028] As a specific implementation method, to facilitate understanding by technical personnel, the functions of each heat exchanger in the coupled energy supply system are briefly explained below: Cooling heat exchanger 3 is used to exchange heat between the cooling water and natural gas flowing through it; the first liquefaction heat exchanger 8 and the second liquefaction heat exchanger 18 are used to exchange heat between the natural gas and working medium 2 flowing through it, respectively; the first refrigeration heat exchanger 11 is used to exchange heat between the LNG and working medium 1 flowing through it; and the second refrigeration heat exchanger 14 is used to exchange heat between working medium 1 and working medium 2 flowing through it. Here, working medium 1 refers to the working medium that circulates and transfers energy in the primary refrigeration loop, and working medium 2 refers to the working medium that circulates and transfers energy in the secondary refrigeration loop.

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

[0030] S1. Start the high-pressure pump 20. LNG in LNG storage tank 1 enters LNG vaporizer 2 through 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. BOG generated in LNG storage tank 1 enters fuel cell 4 through BOG pipeline, the primary side of cooling heat exchanger 3 and fuel pipeline. The electrical energy generated by fuel cell 4 is connected to the user's power grid.

[0031] S2. When the BOG produced by LNG storage tank 1 is less than the natural gas required for 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 LNG storage tank 1 is more than the natural gas required for power generation by fuel cell 4, reduce the opening of the first throttle valve 5, close the second throttle valve 6, and start the first liquefaction compressor 7, the second liquefaction compressor 17, the first refrigeration compressor 10, and the second refrigeration compressor 13.

[0033] S4. The working fluid 1 circulates in the first-stage refrigeration circuit. When the working fluid 1 flows through the first refrigeration heat exchanger 11, it 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 the low-temperature gaseous working fluid 1 flows through the second refrigeration heat exchanger 14, it absorbs the heat of the second working fluid. After absorbing heat and becoming heated, the working fluid 1 is pressurized by the first refrigeration compressor 10 and then enters the first refrigeration heat exchanger 11.

[0034] S5. The second working fluid circulates in the secondary refrigeration circuit. When the second working fluid flows through the second refrigeration heat exchanger 14, it absorbs the cold energy of the first working fluid 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 fluid flows through the first liquefaction heat exchanger 8 and the second liquefaction heat exchanger 18, it absorbs the heat of the natural gas. After absorbing heat and becoming hotter, the second working fluid is pressurized by the second refrigeration compressor 13 and then enters the second refrigeration heat exchanger 14.

[0035] S6. After being pressurized by the first liquefaction compressor 7, BOG enters the first liquefaction heat exchanger 8. After absorbing the cooling energy of the second working medium at the first liquefaction heat exchanger 8, BOG liquefies into a gas-liquid mixture. After the gas-liquid mixture undergoes initial separation at the first gas-liquid separator 9, LNG and natural gas are produced. The LNG produced from the initial separation is incorporated into the LNG pipeline. Part of the natural gas produced from the initial 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. After absorbing the cooling energy of the second working medium at the second liquefaction heat exchanger 18, the natural gas liquefies into a gas-liquid mixture. After the gas-liquid mixture undergoes further separation at the second gas-liquid separator 19, LNG and natural gas are produced. The LNG produced from the second separation is incorporated into the LNG pipeline, and the natural gas produced from the second separation is incorporated into the BOG pipeline.

[0036] The control method for the coupled power supply system provided by this invention has the advantages of simple process and safety and reliability.

[0037] The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Various modifications made by those skilled in the art based on the technical solutions of the present invention without departing from the design concept of the present invention should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A coupled energy supply system based on LNG and fuel cells, characterized in that, It includes a gas supply unit, a power generation unit, a liquefaction unit, and a refrigeration unit. The gas supply unit includes 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 includes a cooling heat exchanger (3) and a fuel cell (4). The two ports on the secondary side of the cooling heat exchanger (3) are connected to the inlet and outlet ports 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. The OG pipeline is equipped with a first throttle valve (5). The primary side outlet of the cooling heat exchanger (3) is connected to the 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. The natural gas pipeline is equipped with a second throttle valve (6). The electrical energy generated by the fuel cell (4) is fed 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 LNG storage tank (1) and the first throttle valve (5). The BOG pipeline is connected, and 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. 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), the second refrigeration heat exchanger (14) and the 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 first-stage refrigeration circuit. The primary side of the first refrigeration heat exchanger (11) is set 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 second-stage refrigeration circuit. The first gas phase pipeline is equipped with a third throttle valve (16). The liquefaction unit also 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 first gas phase pipeline between the third throttle valve (16) and the first gas-liquid separator (9). The two ports of 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). The secondary side of the second liquefaction heat exchanger (18) is set 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. 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 second gas phase pipeline.

2. The coupled energy supply system based on LNG and fuel cells according to claim 1, characterized in that, A high-pressure pump (20) is installed on the LNG pipeline between the LNG storage tank (1) and the first refrigeration heat exchanger (11). 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). A fourth throttle valve (21) is installed on the second gas phase pipeline.

3. The coupled energy supply system based on LNG and fuel cells according to claim 2, characterized in that, The user's internal power grid is connected to the first liquefied compressor (7), the first refrigeration compressor (10), the second refrigeration compressor (13), the second liquefied compressor (17), and the high-pressure pump (20) via cables and provides them with power.

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

5. The coupled energy supply system based on LNG and fuel cells according to claim 3, characterized in that, The first liquefaction heat exchanger (8) and the second liquefaction heat exchanger (18) are used to exchange heat between the natural gas flowing through them and the second working medium, which refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

6. The coupled energy supply system based on LNG and fuel cells according to claim 3, characterized in that, The first refrigeration heat exchanger (11) is used to exchange heat between the LNG flowing through it and the first working medium. The first working medium refers to the working medium that circulates and transfers energy in the first-stage refrigeration circuit. The second refrigeration heat exchanger (14) is used to exchange heat between the first working medium and the second working medium flowing through it.

7. A control method for the coupled power supply system according to claim 3, characterized in that, Includes the following steps: S1. Start the high-pressure pump (20). 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. 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 electrical energy generated by the fuel cell (4) is connected to 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 natural gas in the gas supply pipeline is allowed to enter the fuel cell (4) through the natural gas pipeline by adjusting the opening of the second throttle valve (6) to supplement the natural gas required for power generation. 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, reduce the opening of the first throttle valve (5), close the second throttle valve (6), and start the first liquefaction compressor (7), the second liquefaction compressor (17), the first refrigeration compressor (10), and the second refrigeration compressor (13). S4. The working fluid 1 circulates in the first-stage refrigeration circuit. When the working fluid 1 flows through the first refrigeration heat exchanger (11), it 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 the low-temperature gaseous working fluid 1 flows through the second refrigeration heat exchanger (14), it absorbs the heat of the second working fluid. After absorbing heat and heating up, the working fluid 1 is pressurized by the first refrigeration compressor (10) and then enters the first refrigeration heat exchanger (11). 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 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 liquefaction heat exchanger (8) and the second liquefaction 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). S6. After being pressurized by the first liquefaction compressor (7), BOG enters the first liquefaction heat exchanger (8). After absorbing the cold energy of the working medium II at the first liquefaction heat exchanger (8), BOG is liquefied into a gas-liquid mixture. After the gas-liquid mixture is first separated by the first gas-liquid separator (9), LNG and natural gas are produced. 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). After absorbing the cold energy of the working medium II at the second liquefaction heat exchanger (18), natural gas is liquefied into a gas-liquid mixture. After the gas-liquid mixture is separated again by the second gas-liquid separator (19), LNG and natural gas are produced. 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. The first working medium refers to the working medium that circulates and transfers energy in the primary refrigeration circuit, and the second working medium refers to the working medium that circulates and transfers energy in the secondary refrigeration circuit.

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