Recycling system for volatile gas of liquefied natural gas (LNG) ship liquid cargo tank

Abstract

The invention relates to the technical field of control and utilization of liquefied gas evaporation, in particular to an LNG ship liquid cargo tank volatile gas recycling system. A liquefied natural gas (LNG) ship liquid cargo tank volatile gas recycling system comprises a gas pipeline connected to the interior of a liquid cargo tank, a fuel cell unit is connected to the gas pipeline, a distribution board used for transporting power generated by the fuel cell unit outwards is connected to the fuel cell unit, and a gas turbine is further connected to an exhaust port of the fuel cell unit. An output shaft of the gas turbine is connected with a power generator, the output end of the power generator is connected to the distribution board, the system further comprises a propulsion motor connected to the distribution board and used for being connected with a propeller, and the fuel cell unit is a solid oxide fuel cell unit. The problem that in the prior art, volatile natural gas in an LNG ship is burnt and consumed through an internal combustion engine, and consequently pollution emission is high is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of controlling and utilizing liquefied gas evaporation, and in particular to a volatile gas recovery and utilization system for a liquid cargo tank of an LNG ship. Background Art

[0002] Faced with increasingly severe ecological and environmental pollution, people are turning to natural gas as a clean, efficient, and high-quality energy and fuel to optimize energy consumption, improve the atmospheric environment, and achieve sustainable economic development. Both industrial and civilian applications are becoming increasingly reliant on natural gas. Liquefied natural gas (LNG), the liquid form of natural gas, offers several advantages over its gaseous form in certain circumstances.

[0003] As a ship transporting LNG, the liquid cargo tank will inevitably evaporate naturally during transportation. Excessive natural gas accumulated in the pipeline will cause pressure to rise, affecting the safety of the LNG ship. Therefore, the naturally evaporated natural gas must be processed. Currently, mainstream ships use dual-fuel internal combustion engines to burn and utilize volatile natural gas. However, dual-fuel internal combustion engines vibrate greatly during use, which makes them noisy. They can only be concentrated in the engine room or auxiliary engine room, occupying a large space. In addition, the combustion of natural gas may result in incomplete combustion. During the combustion process, in a high temperature environment, natural gas may react with nitrogen in the air, causing the emission of nitrogen oxides to exceed the standard. In certain specific areas, the emission requirements for nitrogen oxides are more stringent. In this case, a denitrification device needs to be installed, further increasing the occupied space and cost. Summary of the Invention

[0004] In view of this, the present invention provides a volatile gas recovery and utilization system for a liquid cargo tank of an LNG ship, which is used to solve the problem in the prior art of high pollution emissions caused by the combustion and consumption of volatile natural gas in LNG ships through internal combustion engines.

[0005] A volatile gas recovery and utilization system for the liquid cargo tank of an LNG ship includes a gas pipeline connected to the liquid cargo tank, a fuel cell unit connected to the gas pipeline, a distribution board for transmitting the electricity generated by the fuel cell unit to the outside connected to the fuel cell unit, a gas turbine connected to the exhaust port of the fuel cell unit, a generator connected to the output shaft of the gas turbine, and an output end of the generator connected to the distribution board. The system also includes a propulsion motor connected to the distribution board for connecting to a propeller, and the fuel cell unit is a solid oxide fuel cell unit.

[0006] Furthermore, the system also includes a gas valve train unit connected to the fuel cell unit, and the gas valve train unit is connected to the gas dome of the ship's liquid cargo tank.

[0007] Furthermore, the system also includes a natural gas replenishment unit for gasifying liquid natural gas and transporting it to the fuel cell unit and the gas turbine. The natural gas replenishment unit includes a gasification device for gasifying the natural gas and a compressor for transporting the natural gas to a specific location.

[0008] Furthermore, the distribution board includes a busbar, and the system also includes a power-consuming module connected to the busbar. A converter is provided between the power-consuming module and the busbar to convert the busbar power supply into power suitable for the power-consuming module. The converter includes a DC / DC converter and an inverter.

[0009] Furthermore, a jumper switch is provided on the busbar, and the power modules are arranged symmetrically in pairs about the jumper switch.

[0010] Furthermore, the jumper switch is also connected to an energy storage unit.

[0011] Furthermore, a supercapacitor is provided on the distribution board, and a DC / DC converter is connected between the supercapacitor and the distribution board.

[0012] Furthermore, the propulsion motor is a DC motor powered by DC electricity.

[0013] Furthermore, the fuel cell unit is also provided with a waste heat recovery system.

[0014] The beneficial effects of the volatile gas recovery and utilization system for the liquid cargo tank of an LNG ship in the present invention are as follows: in the present invention, by connecting the liquid cargo tank and the solid oxide fuel cell unit through a gas pipeline, the volatile natural gas can be transported to the fuel cell unit through the gas pipeline, and the fuel cell unit can convert the natural gas into electrical energy; the provision of a distribution board facilitates the transportation of electricity, facilitating the use of subsequent electrical appliances; by connecting a gas turbine to the exhaust port of the fuel cell unit, and the gas turbine to a generator, the underutilized natural gas in the fuel cell unit is facilitated for secondary utilization, and the content of pollutants in the exhaust gas is further reduced, which is beneficial to environmental protection; at the same time, since the generator also transmits electricity to the distribution board, the unified allocation and use of electricity is facilitated; by connecting a propulsion motor to the distribution board, the ship can be propelled by electricity, and an internal combustion engine is not required; in addition, the use of fuel cells can also improve the energy utilization rate of natural gas, facilitate energy conservation and emission reduction, and thus solve the problem of high pollution emissions caused by the combustion and consumption of volatile natural gas in LNG ships by internal combustion engines in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is a schematic diagram of the structure of the natural gas supply of the volatile gas recovery and utilization system of the LNG ship liquid cargo tank in the present invention;

[0017] Figure 2 This is a structural schematic diagram of the power usage of the volatile gas recovery and utilization system for the LNG ship cargo tank in the present invention.

[0018] The meanings of the numbers in the figure are: 1. busbar; 2. supercapacitor; 3. DC / DC converter; 4. fuel cell unit; 5. gas turbine; 6. AC generator; 7. generator rectifier; 8. switch; 9. jumper switch; 10. domestic power inverter; 11. 1000V / 220V transformer; 12. liquid cargo equipment; 13. engine room equipment; 14. electric propulsion controller; 15. propulsion motor; 16. communication battery pack; 17. communication equipment; 18. AC domestic power distribution board; 19. gas dome; 20. gas valve group unit; 21. distribution board; 22. compressor; 23. gasification device; 24. pneumatic pump; 25. liquid cargo tank; 26. propeller. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clearly apparent, the present invention is described below using specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely illustrative and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0020] The terms used in this disclosure are for the purpose of describing specific embodiments only and are not intended to limit the disclosure. As used in this disclosure and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0021] It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various information, such information should not be limited to these terms and should not be understood to indicate or imply relative importance. These terms are only used to distinguish information of the same type from each other. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information without departing from the scope of this disclosure. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining."

[0022] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0023] In the description of the present invention, unless otherwise specified and limited, it should be noted that the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal communication between two components. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances.

[0024] In the following description, the suffixes such as "module", "component" or "unit" used to represent elements are only used to facilitate the description of the present invention and have no specific meaning. Therefore, "module" and "component" can be used interchangeably.

[0025] In order to better understand the technical solution of the present invention, the present invention is described in detail below with reference to the accompanying drawings.

[0026] In Example 1 of the LNG ship cargo tank volatile gas recovery and utilization system (hereinafter referred to as the recovery and utilization system) of the present invention:

[0027] like Figure 1 and Figure 2As shown, the recycling system in this embodiment includes a cargo tank 25 for holding liquid natural gas, with a gas dome 19 formed on the top of the cargo tank 25. Under natural conditions, some of the liquid natural gas gradually vaporizes, becoming gaseous natural gas that moves upward until it gathers at the gas dome 19 of the cargo tank 25. The recycling system also includes a gas pipeline connected to the gas dome 19 of the cargo tank 25. A gas valve assembly unit 20 is connected to the gas pipeline, and a fuel cell unit 4 is connected downstream of the gas valve assembly unit 20. Through the intelligent distribution and supply of the gas valve assembly unit 20, the gaseous natural gas is transported to the interior of the fuel cell unit 4, where it is converted into electrical energy. The electrical energy generated by the fuel cell unit 4 needs to be transmitted externally, so a distribution board 21 for transmitting electricity is also connected to the output end of the fuel cell. Electrical appliances or motors are connected to the distribution board 21 to facilitate the use of the electrical energy.

[0028] During operation, the fuel cell unit 4 cannot fully utilize natural gas. It may produce carbon monoxide, unreacted hydrogen, and methane. Directly discharging these exhaust gases not only wastes energy but also pollutes the environment. In this embodiment, a gas turbine 5 is connected to the exhaust port of the fuel cell unit 4. This gas turbine 5 performs secondary combustion on the exhaust gas from the fuel cell, facilitating the secondary utilization of any carbon monoxide, hydrogen, and methane it may contain. An AC generator 6 is connected to the output shaft of the gas turbine 5 to further convert the mechanical energy generated by the gas turbine 5 into electrical energy. The electrical energy generated by the fuel cell unit 4 is direct current (DC), while the electricity generated by a generator is generally alternating current (AC). To ensure unified distribution of this energy, a generator rectifier 7 is provided between the generator and the distribution board 21 to convert the AC power into DC power, which is then distributed uniformly on the distribution board 21. Furthermore, during operation, the fuel cell's intense chemical reaction generates a high temperature. In this embodiment, a waste heat recovery system is also provided on the fuel cell unit 4 to facilitate heating or hot water use for the crew.

[0029] The evaporation rate of natural gas in the cargo tank 25 is generally relatively stable, while electricity consumption fluctuates significantly depending on user usage and navigation speed. This can result in power generation being less than power consumption, thus impacting the normal operation or use of the vessel. In this embodiment, the recycling system also includes a natural gas replenishment unit that is directly connected to the liquefied natural gas in the cargo tank 25 and converts the liquefied natural gas into a gaseous state. The natural gas replenishment unit includes a pneumatic pump 24 connected to the liquefied natural gas and a vaporizer 23 for vaporizing the liquefied natural gas. The natural gas is then transported to the gas valve train unit 20 for centralized distribution via a compressor 22. Specifically, when power generation is less than power consumption, the natural gas replenishment unit intervenes. The pneumatic pump 24 transports the liquefied natural gas to the vaporizer 23, where it is converted into a gaseous state. The compressor 22 then transports this excess natural gas to the gas valve train unit 20, where it is distributed to the fuel cell unit 4, thereby increasing power generation.

[0030] The distribution board 21 includes a busbar 1 and components such as circuit breakers and ammeters for current control. Busbar 1 is a 1000V DC busbar, and the fuel cell unit 4 and the generator rectifier 7 connected to the AC generator 6 are both connected to busbar 1. Other electrical appliances and components are connected to busbar 1 according to specific needs. Specifically, since fluctuations in power consumption at the user end can cause grid fluctuations, to reduce grid fluctuations, a supercapacitor 2 is connected to busbar 1 via a DC / DC converter 3. When busbar 1 power usage is low, supercapacitor 2 enters a charging state to store energy, allowing power supply equipment to operate in an optimal operating state without having to operate in a low-power state, such as when a ship is sailing at a constant speed at sea or anchored at anchor. When busbar 1 power usage suddenly increases, such as when a ship's speed increases significantly or cargo is being loaded or unloaded at a dock, supercapacitor 2 enters a discharging state to release energy, allowing the power supply equipment to load more smoothly.

[0031] Since busbar 1 uses a 1000V DC busbar, the rated power of most electrical equipment is less than 1000V, especially household electricity, which usually uses 220V. Therefore, a household power inverter 10 and a 1000V / 220V transformer 11 electrically connected to the household power inverter 10 are also connected to the busbar 1 to convert 1000V DC into 220V AC. It is then connected to an AC household power distribution board 18 to facilitate the crew's use of conventional electrical equipment.

[0032] At the same time, in order to realize the basic functions of the LNG ship, liquid cargo equipment 12 and engine room equipment 13 electrically connected to the busbar 1 are also provided. At the same time, in order to advance the ship, a propulsion motor 15 electrically connected to the busbar 1 is also provided. The propulsion motor 15 is a DC motor. An electric propulsion controller 14 is also provided between the propulsion motor 15 and the busbar 1 to adjust and control the propulsion motor 15. A propeller 26 is also fixedly provided on the output shaft of the propulsion motor 15. In this embodiment, the propulsion motor 15 adopts a dual-machine dual-propeller system, which has higher maneuverability and reliability. Since the propulsion motor 15 is a DC motor, an inverter or the like is no longer needed for current conversion, which is beneficial to reducing energy loss during the conversion process. It is worth noting that in this embodiment, a switch 8 is provided between the corresponding electrical equipment and the busbar 1, which facilitates the on-off of the circuit through the switch 8.

[0033] In addition, if Figure 1 As shown, in this embodiment, the electrical appliances are arranged symmetrically in pairs. Specifically, electrical devices with the same function are located in different zones, connected by a jumper switch 9. When the jumper switch 9 is open, each zone can only independently power the electrical devices in its corresponding zone. When the jumper switch 9 is closed, each zone can power not only the electrical devices in its corresponding zone, but also the electrical devices in other zones. Furthermore, a conductive battery pack 16 is provided at the jumper switch. Only one conductive battery pack 16 is provided, and it is directly connected to the jumper switch 9. Furthermore, a conductive device 17 and an AC household power distribution board 18 are provided above the conductive battery pack.

[0034] In this embodiment, the use of fuel cell units can reduce the content of nitrogen oxides in emissions. Furthermore, the use of propulsion motors allows the vehicle to meet Tier III and regional emission control requirements of the 1973 / 78 Pollution Convention, even without a denitrification unit. Furthermore, the solid oxide fuel cell itself operates through a chemical reaction, generating very low noise and vibration levels. The accompanying fans and motors are also low-power devices, generating little noise and vibration. This significantly reduces noise and vibration compared to traditional internal combustion engine generators. Furthermore, the solid oxide fuel cell's power generation process has a high reaction temperature and is simple. Furthermore, it is not limited by the Carnot cycle efficiency, resulting in a power generation efficiency of 50-65%. By utilizing the exhaust gas waste heat and combining it with a gas turbine, the energy conversion efficiency can reach as high as 80-95%. Under the same electrical load, the solid oxide fuel cell significantly outperforms traditional internal combustion engine generators in power generation efficiency.

[0035] Secondly, compared to traditional internal combustion engines, which have fixed dimensions and can only be centrally located in the engine room or auxiliary engine room, solid oxide fuel cells offer the advantages of modularity, modularity, and complete enclosure, making them highly adaptable to various environments. This modularity and modularity allow for flexible deployment, allowing for decentralized or centralized deployment of solid oxide fuel cells, making better use of onboard space. Their complete enclosure prevents evaporation, corrosion, and electrolyte loss, and offers high resistance to moisture, high salinity, high oil mist, and high temperatures, resulting in enhanced safety. Solid oxide fuel cells eliminate the need for fuel tanks, exhaust silencers, and exhaust gas denitrification systems required for traditional internal combustion engines. Due to their higher operating temperatures, solid oxide fuel cells, when utilizing waste heat recovery systems, eliminate the need for boiler systems. This significantly saves space and payload.

[0036] Finally, since a DC busbar is used for power supply in this embodiment, compared with AC three-phase power supply, under the conditions of the same insulation level of the power supply network, the same transmission power, the same line investment cost and basically the same width of the transmission channel, the transmission power of DC is about 1.5 times that of an AC single line, so the DC power supply system has a larger power supply capacity than the AC power supply system; in addition, the DC power supply system does not need to be equipped with reactive compensation equipment and filtering equipment, which reduces the investment in fixed equipment, saves space, and reduces the cost of transmission lines; DC power supply is more compatible with supercapacitors than AC power supply. For communication and navigation equipment, because they are all low-voltage weak-current equipment, DC power supply has higher compatibility.

[0037] It should be understood that the embodiments described are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

Claims

1. A system for recovering and utilizing volatile gases from LNG ship cargo tanks, characterized by: The system comprises a gas pipeline connected to the liquid cargo tank, the gas pipeline is connected to a fuel cell unit, the fuel cell unit is connected to a distribution board for transporting the electricity generated by the fuel cell unit to the outside, the exhaust port of the fuel cell unit is also connected to a gas turbine, the output shaft of the gas turbine is connected to a generator, the output end of the generator is connected to the distribution board, the system also comprises a propulsion motor connected to the distribution board for connecting to a propeller, and the fuel cell unit is a solid oxide fuel cell unit.

2. The LNG ship cargo tank volatile gas recovery and utilization system according to claim 1 is characterized by: The system also includes a gas train unit connected to the fuel cell unit, the gas train unit being connected to a gas dome of the vessel's cargo tank.

3. The LNG ship cargo tank volatile gas recovery and utilization system according to claim 2 is characterized by: The system further includes a natural gas replenishment unit for gasifying liquid natural gas and transporting the gas to the fuel cell unit and the gas turbine. The natural gas replenishment unit includes a gasification device for gasifying the natural gas and a compressor for transporting the natural gas to a specific location.

4. The LNG ship cargo tank volatile gas recovery and utilization system according to any one of claims 1 to 3, characterized in that: The distribution board includes a busbar, and the system also includes a power module connected to the busbar. A converter is provided between the power module and the busbar to convert the busbar power into power suitable for the power module. The converter includes a DC / DC converter and an inverter.

5. The LNG ship cargo tank volatile gas recovery and utilization system according to claim 4 is characterized in that: A jumper switch is provided on the busbar, and each power module is arranged symmetrically with respect to the jumper switch.

6. The LNG ship cargo tank volatile gas recovery and utilization system according to claim 5 is characterized by: The jumper switch is also connected to an energy storage unit.

7. The LNG ship cargo tank volatile gas recovery and utilization system according to any one of claims 1 to 3, characterized in that: The distribution board is also provided with a supercapacitor, and a DC / DC converter is connected between the supercapacitor and the distribution board.

8. The LNG ship cargo tank volatile gas recovery and utilization system according to any one of claims 1 to 3, characterized in that: The propulsion motor is a DC motor powered by DC electricity.

9. The LNG ship cargo tank volatile gas recovery and utilization system according to any one of claims 1 to 3, characterized in that: The fuel cell unit is also provided with a waste heat recovery system.

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