LNG powered ship fuel gas recovery system and control method thereof, and ship

Abstract

The application belongs to the technical field of ship power, and discloses an LNG-powered ship fuel gas recovery system, a control method thereof and a ship, wherein the output end of an LNG storage tank is connected with the input end of a BOG recovery system, which is used for recovering the evaporation gas generated in the LNG storage tank after heat exchange with the outside world; a high-pressure nitrogen gas purging system is connected with one of the one-way outlets of a natural gas supply system, and is used for purging the residual natural gas in the pipeline of the natural gas supply system by nitrogen gas to form a nitrogen gas and natural gas mixture. The technical scheme of the application fully utilizes the cold energy in the LNG vaporization process, recovers the evaporation gas and the excess natural gas in the fuel supply pipeline, reduces fuel waste, realizes full utilization of energy, and improves the safety and economy of the system.

Description

Technical Field

[0001] This invention belongs to the field of marine power technology, and particularly relates to an LNG-powered ship gas recovery system and its control method, and the ship itself. Background Technology

[0002] In the field of ship design and manufacturing, natural gas engines are among the most important marine propulsion equipment. Due to the significant emissions generated during the operation of marine natural gas engines, countries worldwide and the International Maritime Organization (IMO) have introduced regulations to limit their emissions. To meet increasingly stringent regulations, retrofitting existing natural gas engines by installing new fuel supply systems and using cleaner fuels has become a hot research topic.

[0003] Among various clean fuels, natural gas is widely used as marine fuel due to its abundant reserves, high octane number, high energy density, and clean combustion. In ships, natural gas is typically stored as cryogenically pressurized liquefied natural gas (LNG). For marine natural gas engines powered by LNG, considering the cryogenic insulation properties of LNG storage tanks, heat exchange with the outside environment is inevitable, causing the LNG inside the tank to vaporize and produce boil-off gas (BOG), increasing the pressure inside the tank. When the pressure inside the tank exceeds the safe pressure, a safety valve opens to release natural gas, preventing excessive pressure from causing tank deformation or even explosion. If this boil-off gas is reliquefied and recovered, it can be reused as fuel for the natural gas engine.

[0004] After a natural gas engine stops operating, it is usually necessary to vent the remaining natural gas in the supply pipeline to protect the fuel supply system. Directly releasing the remaining natural gas into the atmosphere not only wastes fuel but also severely pollutes the ship's environment and affects its normal operation.

[0005] Adding a fuel supply system to marine equipment such as natural gas engines allows for the recovery of evaporative gases and excess natural gas from the natural gas supply pipelines. This not only ensures the safety of marine natural gas engine operation but also improves the economic efficiency of ship operation.

[0006] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0007] (1) The following solutions are commonly used for the treatment of evaporation gas: First, direct venting and combustion, which not only pollutes the environment but also leads to huge energy waste; Second, pressure regulation and reuse of evaporation gas, but it cannot provide a stable amount of evaporation gas generation when there are large temperature differences; Third, adding independent reliquefaction equipment to recover evaporation gas and cooling and liquefying it, but this method fails to make full use of the cold energy of LNG and the recovery system has high energy consumption.

[0008] (2) The usual treatment of high-pressure residual gas in the gas supply pipeline of LNG-powered ships is to discharge the residual high-pressure gas into the atmosphere through relevant valve groups. This treatment method will discharge a large amount of natural gas, pollute the environment and waste fuel, and will also affect the safety of ship operation.

[0009] (3) The shortcomings of the existing technology are:

[0010] The first option: Direct emission without considering the recovery of fuel gas and its impact on the environment;

[0011] The second type: unable to continuously and effectively utilize the gas;

[0012] The third type: The reliquefaction process of gas recovery requires a lot of energy, and the recovery system fails to make full use of the cold energy of LNG.

[0013] The difficulty in solving the above problems and defects is as follows:

[0014] LNG has a low liquefaction temperature, making it difficult to liquefy through direct compression. Reliquefying and recovering fuel gas in LNG-powered ships requires significant energy, increasing their operating costs. Utilizing the LNG vaporization process and heat exchange for cooling during fuel gas reliquefaction can reduce additional energy consumption.

[0015] The significance of solving the above problems and defects is as follows:

[0016] With current restrictions on emissions from natural gas engines, the use of LNG as marine fuel is gradually becoming a trend. However, the natural gas produced after LNG vaporization is a greenhouse gas, necessitating the recovery of excess fuel during the operation of LNG-powered ships. Utilizing the cold energy of LNG to exchange heat with the evaporated gas and residual fuel in the piping system can reduce energy consumption during LNG liquefaction, improve the system's energy efficiency, and enhance the safety of ship operations. Summary of the Invention

[0017] To address the problems existing in the prior art, this invention provides an LNG-powered ship gas recovery system and its control method, as well as the ship itself.

[0018] The present invention is implemented as follows: an LNG-powered ship gas recovery system includes an LNG storage tank and a natural gas supply system. The LNG storage tank is connected to the natural gas supply system. The LNG-powered ship gas recovery system also includes a BOG recovery system. The output end of the LNG storage tank is connected to the input end of the BOG recovery system, which is used to recover the evaporation gas generated inside the LNG storage tank after heat exchange with the outside.

[0019] A high-pressure nitrogen purging system is connected to one of the unidirectional outlets of the natural gas supply system. The system uses nitrogen to purge residual natural gas in the pipeline of the natural gas supply system, forming a mixture of nitrogen and natural gas.

[0020] Preferably, it further includes: a high-pressure natural gas recovery system, which is connected to the output end of the natural gas supply system, and is used to separate nitrogen and LNG and liquefy and recover LNG.

[0021] Preferably, the BOG recovery system includes a first one-way valve, a first compressor, a first heat exchanger, and a reliquefaction device connected in sequence. The inlet of the first one-way valve is connected to the interior of the LNG storage tank, the outlet of the first one-way valve is connected to the inlet of the first compressor, the outlet of the first compressor is connected to the inlet of the reliquefaction device, and the outlet of the reliquefaction device is connected to the interior of the LNG storage tank.

[0022] Preferably, the natural gas supply system includes a fuel supply pump, a second check valve, a second heat exchanger, a third heat exchanger, a mass flow meter, an electric heater, and a pressure reducing valve connected in sequence, with the outlet of the pressure reducing valve connected to the inlet of the high-pressure gas rail.

[0023] Preferably, a temperature sensor is installed on the pipe connecting the electric heater and the pressure reducing valve; and a flow regulating valve is installed on the pipe connecting the third heat exchanger and the cylinder cooling water unit.

[0024] Preferably, the high-pressure nitrogen purging system includes a high-pressure nitrogen device, a filter, and a switching valve connected in sequence, with the outlet end of the switching valve connected to the outlet end of a second one-way valve.

[0025] Preferably, the high-pressure natural gas recovery system includes a high-pressure gas rail, a solenoid valve, a cryogenic device, and a gas-liquid separator connected in sequence, and the outlet end of the solenoid valve is connected to the reliquefaction equipment.

[0026] Preferably, a rail pressure sensor is installed inside the high-pressure gas rail; a natural gas sensor is installed on the pipeline connecting the solenoid valve and the cryogenic device.

[0027] This invention provides a control method applicable to the above-mentioned LNG-powered ship gas recovery system, the control method comprising:

[0028] S1. The evaporated gas is pressurized by the first compressor, cooled by the first heat exchanger, and then liquefied by the reliquefaction equipment. The LNG is recovered and enters the LNG storage tank.

[0029] S2. Obtain the temperature sensor reading to adjust the cooling water flow rate through the flow control valve; obtain the mass flow meter 20 reading and, in conjunction with the temperature sensor reading, calculate the heating power of the electric heater.

[0030] S3. When the natural gas engine stops, the second check valve closes, the switch valve and solenoid valve open, and the high-pressure nitrogen flows through the filter. The filtered high-pressure nitrogen enters the supply pipeline.

[0031] S4. Analyze the status of the natural gas engine and, based on whether the natural gas engine is shut down or running: when the natural gas engine is shut down, separate the gas-liquid mixture and recover the natural gas; when the natural gas engine is running, recover the natural gas according to the pressure limit.

[0032] Preferably, S4 specifically includes:

[0033] S401: Determine the status of the natural gas engine. If the natural gas engine is stopped, proceed to step S402. If the natural gas engine is running normally, proceed to step S403.

[0034] S402: The solenoid valve opens, and high-pressure nitrogen purges the pipeline. The residual natural gas in the pipeline is cooled by the cryogenic device to form a gas-liquid mixture of nitrogen and LNG. The gas-liquid separator separates the LNG. After the natural gas sensor reading falls below the set threshold again, the high-pressure natural gas recovery system is shut down.

[0035] S403: The rail pressure sensor monitors the pressure of the high-pressure gas rail. When the pressure of the high-pressure gas rail exceeds the safe pressure, it controls the opening of the solenoid valve. Excess natural gas in the high-pressure gas rail is recovered after being processed by the cryogenic device and the gas-liquid separator.

[0036] The present invention provides an LNG-powered vessel, including a vessel body, wherein a natural gas engine is provided within the vessel body, and the natural gas engine is connected to the aforementioned LNG-powered vessel gas recovery system.

[0037] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows: Compared with existing natural gas engines that use diesel fuel, natural gas engines using natural gas can reduce emissions of nitrogen oxides and soot. The above-mentioned fuel recovery system and its control method can recover evaporated gas and residual natural gas in the pipeline, and can utilize the cold energy during the phase change of liquefied natural gas (LNG), thereby improving fuel utilization and system economy. Specifically, this is manifested in:

[0038] First, LNG needs to absorb a lot of heat during the vaporization process. The natural gas recovery system uses the cold energy of LNG to cool the evaporated gas, reducing the energy consumption of the recovery system.

[0039] Secondly, LNG exchanges heat with the cylinder liner cooling water system, and liquefied natural gas (LNG) absorbs heat and vaporizes into gaseous fuel, saving the electrical energy required to heat LNG.

[0040] Third, the natural gas recovery system recovers the evaporated gas from the LNG storage tank and the residual high-pressure natural gas in the supply pipeline, reducing fuel waste and protecting the environment. Attached Figure Description

[0041] Figure 1 This is a connection diagram of an LNG-powered ship gas recovery system provided in an embodiment of the present invention;

[0042] 1. LNG storage tank; 2. Fuel supply pump; 3. First check valve; 4. Second check valve; 5. Switch valve; 6. High-pressure nitrogen unit; 7. Filter; 8. Reliquefaction equipment; 9. First compressor; 10. First heat exchanger; 11. Expansion valve; 12. Second compressor; 13. Second heat exchanger; 14. Gas-liquid separator; 15. Cryogenic unit; 16. Natural gas sensor; 17. Third heat exchanger; 18. Flow control valve; 19. Cylinder cooling water unit; 20. Mass flow meter; 21. Electric heater; 22. Temperature sensor; 23. Pressure reducing valve; 24. Rail pressure sensor; 25. High-pressure gas rail; 26. Solenoid valve. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0044] Traditional LNG-powered ships, due to the cryogenic insulation properties of their storage tanks, inevitably exchange heat with the outside environment, causing LNG to vaporize and produce boil-off gas (BOG), increasing the pressure inside the tank. Directly releasing this BOG without considering its recovery and environmental impact is problematic; it prevents the continuous and efficient use of the BOG; and the reliquefaction process for BOG recovery consumes a large amount of energy, failing to fully utilize the cold energy of LNG. Based on these shortcomings, liquefied natural gas (LNG), with its low liquefaction temperature, is difficult to liquefy through direct compression. The reliquefaction and recovery of LNG-powered ships requires significant energy, increasing operating costs. Therefore, recovering boil-off gas and excess natural gas from the fuel supply pipeline not only ensures the safety of the natural gas engine operation and improves the economics of ship operation, but also fully utilizes the cold energy of LNG phase change, improving energy efficiency and saving fuel consumption.

[0045] To address the problems existing in the prior art, the present invention provides the following detailed description of the invention, implemented as described below with reference to the accompanying drawings:

[0046] Combination Figure 1 Example 1 discloses a natural gas supply system and its control method, including: LNG storage tank 1, BOG recovery system, natural gas supply system, high-pressure nitrogen purging system and high-pressure natural gas recovery system, wherein LNG storage tank 1 is used to store liquefied natural gas, and the natural gas pressure in LNG storage tank 1 is 1MPa as an example to illustrate this example in detail;

[0047] The BOG recovery system is used to recover the evaporation gas generated inside LNG storage tank 1 after heat exchange with the outside environment;

[0048] A natural gas supply system is used to deliver natural gas to natural gas engines;

[0049] The high-pressure nitrogen purging system uses nitrogen to purge residual natural gas in the pipelines of the natural gas supply system, forming a mixture of nitrogen and natural gas.

[0050] High-pressure natural gas recovery system is used to separate nitrogen and LNG and to liquefy and recover LNG.

[0051] Combined with appendix Figure 1As shown, the LNG storage tank 1 is directly connected to the outlet end of the reliquefaction equipment 8, and the LNG storage tank 1 is connected to the inlet end of the reliquefaction equipment 8 through the first compressor 9. It should be further noted that a first check valve 3 is installed on the pipeline connecting the first compressor 9 and the LNG storage tank 1, and a first heat exchanger 10 is installed on the pipeline between the inlet end of the liquefaction equipment 8 and the first compressor 9.

[0052] The function of the first one-way valve 3 is to prevent the evaporated gas from flowing back into the LNG storage tank 1, thereby reducing the loss of the evaporated gas recovery and improving the recovery efficiency of the evaporated gas.

[0053] The function of the first heat exchanger 10 is to exchange heat with the evaporating gas and reduce the temperature of the evaporating gas.

[0054] Furthermore, in order to recycle the heat exchange medium that exchanges heat with the evaporating gas, it is necessary to further cool the heat exchange medium to restore its pressure and temperature to the state before it exchanged heat with the evaporating gas.

[0055] Specifically, the first heat exchanger 10, the second compressor 12, the second heat exchanger 13, and the expansion valve 11 are connected to form a heat exchange cycle subsystem. In this example, the heat exchange medium in the heat exchange cycle subsystem is propane. Liquid propane exchanges heat with the evaporated gas through the first heat exchanger 10, absorbing heat and vaporizing. The vaporized propane is then pressurized and liquefied by the second compressor 12, and the compressed propane enters the second heat exchanger 13, releasing the heat absorbed from the evaporated gas. The cooled propane enters the expansion valve 11 to depressurize, restoring the pressure and temperature to their state before heat exchange with the evaporated gas, thus enabling the subsystem to achieve a good heat exchange cycle.

[0056] The working process of evaporative gas recovery:

[0057] When the vaporized gas in LNG storage tank 1 reaches the safe pressure, the BOG recovery system is activated, the first one-way valve 3 opens, and the vaporized gas passes sequentially along the pipeline through the first one-way valve 3, the first compressor 9, the first heat exchanger 10, and the reliquefaction equipment 8. The vaporized gas is pressurized by the first compressor 9, and the high-pressure vaporized gas exchanges heat with the heat exchange medium propane in the first heat exchanger 10. The high-pressure vaporized gas is then cooled and liquefied into LNG by the reliquefaction equipment 8, thus recovering the vaporized gas.

[0058] The overall vaporization process of liquefied LNG in a natural gas supply system:

[0059] Fuel supply pump 2 pumps liquefied natural gas (LNG) from LNG storage tank 1. The LNG passes through the second heat exchanger 13 and the third heat exchanger 17, where it exchanges heat with the two heat exchangers and is completely vaporized into high-pressure natural gas.

[0060] In the overall vaporization process of liquid LNG, in order to further improve the vaporization rate of LNG, a cylinder cooling water unit 19 is equipped at the location of the third heat exchanger 17. When the natural gas engine is working normally, the cylinder cooling water unit 19 provides cylinder liner water, which heats the LNG in the third heat exchanger 17, and the LNG is completely vaporized.

[0061] In order to further maintain the pressure of the vaporized LNG within a specific range, the flow control valve 18 is used to control the flow rate of the cylinder liner cooling water flowing through the third heat exchanger 11, thereby controlling the temperature of the natural gas in the supply pipeline. The pressure reducing valve 23 reduces the pressure of the high-pressure natural gas, so that the pressure of the high-pressure gas rail 25 is maintained between 0.5-0.7 MPa.

[0062] When the natural gas engine starts:

[0063] Because the heat generated by the cylinder liner cooling water is affected by the frequency of heat exchange and the external environment, the water temperature is not stable. Before and immediately after starting the natural gas engine, it cannot function as a continuous heat exchange medium. Therefore, the natural gas supply system also includes a mass flow meter 20, an electric heater 21, and a temperature sensor 22. When the natural gas engine is first started, the cylinder liner cooling water temperature is too low to meet the heating requirements, so the flow regulating valve 18 is opened to its maximum. The temperature sensor 22 measures the outlet temperature of the electric heater 21, and the mass flow meter 20 measures the mass flow rate of the natural gas flowing through the supply pipeline. The heating power of the electric heater 21 is determined by the readings of the temperature sensor 22, the target natural gas temperature, and the mass flow meter 16. The electric heater 21 heats the natural gas in the natural gas supply system, and the temperature sensor 22 provides a feedback signal for control.

[0064] When the natural gas engine is started and running normally:

[0065] As the cylinder liner cooling water temperature gradually increases, the heat provided by the third heat exchanger 17 increases, and the power of the electric heater 21 is reduced simultaneously to ensure that the outlet natural gas temperature of the natural gas supply system meets the requirements. When the cylinder liner cooling water continues to heat up and the heat provided by the third heat exchanger 17 meets the heating requirements of LNG, the electric heater 21 is turned off and the opening of the flow control valve 18 is adjusted to dynamically maintain the natural gas temperature provided by the natural gas supply system.

[0066] When the natural gas engine stops:

[0067] In this example, the high-pressure nitrogen purging system includes a high-pressure nitrogen device 7, a filter 6, and a switching valve 5. When the natural gas engine stops, the second check valve 4 is closed, and the switching valve 5 and the solenoid valve 26 are opened. The high-pressure nitrogen device 7 provides high-pressure nitrogen (1MPa). After impurities and moisture are removed by the filter 6, the high-pressure nitrogen enters the supply pipeline for purging.

[0068] The high-pressure natural gas recovery system includes a rail pressure sensor 24, a high-pressure gas rail 25, a solenoid valve 26, a natural gas sensor 16, a cryogenic device 15, and a gas-liquid separator 14. When the natural gas engine stops, the high-pressure nitrogen purging system starts. Residual natural gas in the pipeline is purged by high-pressure nitrogen to form a mixture. After being cooled by the cryogenic device 15, a gas-liquid mixture of nitrogen and LNG is formed. The mixture enters the gas-liquid separator 14 for separation. The separated LNG enters the reliquefaction unit 8, and the separated gas is discharged through the ship's exhaust duct. When the natural gas engine is running normally, the rail pressure sensor 24 monitors the natural gas pressure in the high-pressure gas rail 25 in real time. When the pressure value measured by the rail pressure sensor 24 is greater than the set safety value, the solenoid valve 26 is opened, and the excess natural gas is pressurized and liquefied through the recovery system and processed by gas-liquid separation. The LNG separated by the gas-liquid separator 14 enters the reliquefaction unit 8, which cools and depressurizes the LNG. The LNG is then recovered into the LNG storage tank 1. The natural gas sensor 16 monitors the natural gas concentration in the recovery pipeline. When the concentration falls below the set threshold again, the high-pressure natural gas recovery system is shut down.

[0069] Example 2:

[0070] An LNG-powered vessel includes a vessel body, wherein a natural gas engine is provided within the vessel body, and the natural gas engine is connected to the LNG-powered vessel gas recovery system of Embodiment 1.

[0071] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

[0072] It should be understood that this disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure should be limited by the appended claims.

[0073] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control method for a gas recovery system suitable for LNG-powered ships, comprising an LNG storage tank (1) and a natural gas supply system, wherein the LNG storage tank (1) is connected to the natural gas supply system, characterized in that, The LNG-powered ship gas recovery system also includes: The BOG recovery system connects the output end of the LNG storage tank (1) to the input end of the BOG recovery system, and is used to recover the evaporation gas generated inside the LNG storage tank (1) after heat exchange with the outside. A high-pressure nitrogen purging system is connected to one of the one-way outlets of a natural gas supply system. The system uses nitrogen to purge residual natural gas in the pipeline of the natural gas supply system, forming a mixture of nitrogen and natural gas. A high-pressure natural gas recovery system is connected to the output end of a natural gas supply system. The high-pressure natural gas recovery system is used to separate nitrogen and LNG and to liquefy and recover LNG. The BOG recovery system includes a first check valve (3), a first compressor (9), a first heat exchanger (10), and a reliquefaction device (8) connected in sequence. The inlet of the first check valve (3) is connected to the interior of the LNG storage tank (1), the outlet of the first check valve (3) is connected to the inlet of the first compressor (9), the outlet of the first compressor (9) is connected to the inlet of the reliquefaction device (8), and the outlet of the reliquefaction device (8) is connected to the interior of the LNG storage tank (1). The natural gas supply system includes a fuel supply pump (2), a second check valve (4), a second heat exchanger (13), a third heat exchanger (17), a mass flow meter (20), an electric heater (21), and a pressure reducing valve (23) connected in sequence. The outlet of the pressure reducing valve (23) is connected to the inlet of the high-pressure gas rail (25). A temperature sensor (22) is installed on the pipe connecting the electric heater (21) and the pressure reducing valve (23); a flow regulating valve (18) is installed on the pipe connecting the third heat exchanger (17) and the cylinder cooling water unit (19). The high-pressure nitrogen purging system includes a high-pressure nitrogen device (7), a filter (6) and a switching valve (5) connected in sequence. The outlet end of the switching valve (5) is connected to the outlet end of the second check valve (4). The high-pressure natural gas recovery system includes a high-pressure gas rail (25), a solenoid valve (26), a cryogenic device (15) and a gas-liquid separator (14) connected in sequence. The outlet end of the solenoid valve (26) is connected to the reliquefaction equipment (8). The control method includes: S1. The evaporated gas is pressurized by the first compressor (9), cooled by the first heat exchanger (10), and liquefied by the reliquefaction equipment (8). The LNG is then recovered and enters the LNG storage tank (1). S2. Obtain the reading of the temperature sensor (22) to adjust the flow rate of cooling water flowing through the flow regulating valve (18); obtain the reading of the mass flow meter (20), and calculate the heating power of the electric heater (21) in combination with the reading of the temperature sensor (22); S3. When the natural gas engine stops, the second check valve (4) closes, the switch valve (5) and the solenoid valve (26) open, and the high-pressure nitrogen flows through the filter (6). The filtered high-pressure nitrogen enters the supply pipeline. S4. Analyze the status of the natural gas engine. When the natural gas engine is shut down, separate the gas-liquid mixture and recover the natural gas. When the natural gas engine is running, recover the natural gas according to the pressure limit.

2. The control method for the LNG-powered ship gas recovery system according to claim 1, characterized in that, A rail pressure sensor (24) is installed inside the high-pressure gas rail (25); a natural gas sensor (16) is installed on the pipeline connecting the solenoid valve (26) and the cryogenic device (15).

3. The control method for the LNG-powered ship gas recovery system according to claim 2, characterized in that, Specifically, S4 is: S401: Determine the status of the natural gas engine. If the natural gas engine is stopped, proceed to step S402. If the natural gas engine is running normally, proceed to step S403. S402: The solenoid valve (26) is opened, and the pipeline is purged with high-pressure nitrogen. The residual natural gas in the pipeline is cooled by the cryogenic device (15) to form a gas-liquid mixture of nitrogen and LNG. The gas-liquid separator (14) separates out LNG. After the reading of the natural gas sensor (16) is lower than the set threshold again, the high-pressure natural gas recovery system is shut down. S403: The rail pressure sensor (24) monitors the pressure of the high-pressure gas rail (25). When the pressure of the high-pressure gas rail (25) is greater than the safe pressure, the solenoid valve (26) is opened. The excess natural gas in the high-pressure gas rail (25) is recovered after being processed by the cryogenic device (15) and the gas-liquid separator (14).

4. An LNG-powered vessel, comprising a vessel body, wherein a natural gas engine is disposed within the vessel body, characterized in that, The natural gas engine is connected to the LNG-powered ship gas recovery system as described in any one of claims 1-3.

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