A system for handling excess BOG in an LNG carrier

Abstract

The application provides a system for processing excess BOG of an LNG ship, and belongs to the technical field of ships.The system comprises a BOG supply system, an excess BOG utilization system, a flue gas energy storage system, a flue gas energy release system and an inerting system.Based on the complex sailing conditions of a ship, when the LNG ship sails at low load, sails in a maneuvering mode or is anchored, the excess BOG generated in the LNG liquid cargo tank is sent into a boiler for combustion, and then the energy of the excess BOG is converted into the pressure energy of flue gas and stored through a series of devices, so that the problem of waste of the BOG in the excess state is effectively solved; when the ship sails at high load or is unloaded at a discharge port, the energy of the flue gas is released, so that the energy of the BOG is reused.In addition, the stored flue gas can also be used for inerting of low-temperature pipelines and equipment at normal temperature or at a temperature of 0 DEG C to -60 DEG C, so that the inerting cost of the ship is reduced.

Description

Technical Field

[0001] This invention belongs to the field of marine technology, specifically relating to a system for handling excess BOG on LNG carriers. Background Technology

[0002] In recent years, with the booming development of liquefied natural gas (LNG) in the global energy market, the demand for LNG worldwide has been increasing daily, and the number of LNG carriers has also been growing. Furthermore, LNG, as a marine fuel, can significantly reduce emissions of harmful gases such as sulfur oxides and nitrogen oxides, as well as greenhouse gases, making it a relatively ideal alternative fuel for ships. Therefore, LNG carriers primarily use the LNG they carry as fuel.

[0003] LNG is typically stored in liquid form at -163°C in LNG cargo tanks. During ship navigation, there is a temperature difference of approximately 200°C between LNG and the external environment. Even with good insulation in the LNG cargo tanks, external heat inevitably seeps into the tanks, generating LNG boil-off gas (BOG, primarily composed of methane). Furthermore, the violent rolling motion caused by wind and waves during navigation converts the mechanical energy contained within the LNG into heat, further exacerbating BOG generation.

[0004] The daily cargo evaporation rate of LNG carriers is approximately 0.1% to 0.15%, 1m 3 LNG can vaporize into approximately 625m³ at room temperature. 3 Methane (i.e., BOG), such as in a 174,000 cubic meter LNG carrier, is approximately 250 m³ per day. 3 LNG is vaporized into BOG, and ships produce approximately 150,000 m³ of BOG daily. 3 LNG typically has a density of 430 kg / m³. 3 ~470kg / m 3Therefore, LNG carriers generate approximately 100 tons of BOG (Boiled Air Gathering) daily. Most LNG carriers are not equipped with BOG reliquefaction units. Since ships generate a large amount of BOG daily, and BOG's main component is methane, whose greenhouse effect is about 25 times that of CO2, directly releasing BOG into the atmosphere would not only severely damage the atmospheric environment and contribute to the greenhouse effect, but also waste clean energy. Currently, the main methods for handling BOG on LNG carriers are: using BOG as fuel for the ship's main propulsion system, or burning the BOG in the LNG cargo tanks using a gas combustion unit (GCU). When a ship travels at high speeds, the main engine can generally consume all the BOG generated in the LNG cargo tank. When the BOG cannot meet the ship's fuel requirements, some liquid LNG needs to be vaporized and supplied to the main engine. However, when the ship is sailing at low loads, maneuvering, or anchored, the ship requires less propulsion power, and the main engine cannot consume all the BOG generated in the LNG cargo tank. In this case, the excess BOG generated in the LNG cargo tank usually needs to be sent to the GCU for combustion, which inevitably leads to serious energy waste of BOG.

[0005] Based on this, if a system for handling excess BOG on LNG ships is designed, the excess BOG can be fed into a boiler for combustion. The steam turbine can convert the thermal energy of the boiler steam into mechanical energy, which can then drive a compressor to compress and store the flue gas generated during the ship's voyage. When the ship is at a higher speed or unloading cargo at port, the energy can be released for the ship's power plant or other purposes. This would effectively solve the problem of waste when BOG is in excess. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by proposing a system for handling excess BOG on LNG carriers. This system includes a BOG supply system, an excess BOG utilization system, a flue gas energy storage system, a flue gas energy release system, and an inerting system.

[0007] The BOG supply system includes: an LNG cargo tank, a BOG exhaust valve, a compressor, a BOG three-way valve, a refrigerant heat exchanger, a cylinder liner water heater, a circulating pump, a diesel engine intake valve, a diesel engine, a generator, a propulsion motor, and a propeller.

[0008] The excess BOG utilization system includes: boiler, steam turbine, and compressor.

[0009] The flue gas energy storage system includes a flue gas energy storage tank, a flue gas four-way valve, a seawater cooling unit, a filtration and separation unit, and a check valve.

[0010] The flue gas energy release system includes: a three-flow heat exchanger, an expander, and an expander generator.

[0011] The inerting system includes an inerting unit.

[0012] In the BOG supply system, the LNG cargo tank is filled with LNG. Above the LNG cargo tank, there is an exhaust pipe that is sequentially connected to the BOG exhaust valve, compressor, BOG three-way valve, and refrigerant heat exchanger. The refrigerant heat exchanger is sequentially connected to the diesel engine intake valve and diesel engine via pipes. The diesel engine and generator are connected via a drive shaft to form a diesel generator set. Multiple diesel generator sets are installed on the ship. The generator is connected to the ship's electrical grid via wiring. The ship's main engine is connected to the propulsion motor via wiring. The propulsion motor is connected to the propeller via a drive shaft.

[0013] The refrigerant heat exchanger, cylinder liner water heater, and circulating pump are connected in sequence through pipelines to form a circulation pipeline.

[0014] In the excess BOG utilization system, a pipe is provided below the boiler and connected to one outlet of a BOG three-way valve, and a pipe is provided above the boiler and connected to a steam turbine, and the steam turbine is connected to a compressor via a drive shaft.

[0015] In the flue gas energy storage system, the diesel engine is connected to the flue gas four-way valve through a pipeline. The three outlets of the flue gas four-way valve are respectively connected to the seawater cooling unit, the three-stream heat exchanger, and the atmosphere. The exhaust port above the boiler is connected to the check valve through a pipeline. The check valve is connected to the pipeline between the flue gas four-way valve and the seawater cooling unit through a pipeline. The seawater cooling unit is connected to the filtration and separation unit, the compressor, and the flue gas energy storage tank in sequence through pipelines.

[0016] In the flue gas energy release system, the flue gas energy storage tank is connected in sequence to a three-stream heat exchanger and an expander via pipelines. The expander is connected to an expansion generator via a drive shaft, and the expansion generator is connected to the ship's electrical grid via a signal. The two inlets of the three-stream heat exchanger are respectively connected to a four-way flue gas valve and steam generated by the boiler.

[0017] In the inerting unit, the inerting unit is connected to the flue gas storage tank through a pipeline. The inerting unit is a low-temperature piping system and equipment on the ship that requires inerting at ambient temperature or at a temperature between 0°C and -60°C.

[0018] When the ship is sailing at normal speed, the BOG (Boiled Gas) in the LNG cargo tank reaches the compressor through the BOG vent valve. Under the action of the compressor, the BOG is pressurized. At this time, the outlet of the BOG three-way valve connected to the boiler closes, while the outlet connected to the refrigerant heat exchanger opens. The pressurized BOG enters the refrigerant heat exchanger. Simultaneously, cylinder liner heating water enters the cylinder liner water heater to exchange heat with the refrigerant. The refrigerant circulates under the action of the circulation pump, absorbing heat from the cylinder liner water to heat the BOG entering the refrigerant heat exchanger. Then, the diesel engine intake valve opens, and the heated BOG is sent to the diesel engine for combustion. The diesel engine then drives the generator to generate electricity, which is sent to the ship's electrical grid. The ship's electrical grid powers the propulsion motor, which in turn drives the propeller to rotate, providing power to the ship.

[0019] When the ship is sailing at low load, maneuvering, or anchored, the BOG (Boiled Gas) in the LNG cargo tank reaches the compressor through the BOG exhaust valve. Under the action of the compressor, the BOG is pressurized. At this time, the ship requires less propulsion power, so both outlets of the BOG three-way valve are open. A portion of the BOG is sent to the diesel engine for combustion via the refrigerant heat exchanger and diesel engine intake valve. The diesel engine then drives the generator to generate electricity, which is fed into the ship's electrical grid. The ship's electrical grid powers the propulsion motor, which in turn drives the propeller to rotate, providing power to the ship. The remaining BOG is sent to the boiler for combustion. The flue gas generated by the boiler enters the seawater cooling unit through the check valve. Simultaneously, the outlet of the flue gas four-way valve connected to the seawater cooling unit opens, while the other two outlets close. The flue gas generated by the diesel engine merges with the flue gas from the boiler through the flue gas four-way valve and enters the seawater cooling unit together for cooling and removal of most of the water vapor. The flue gas then enters the filtration and separation unit, where impurities are filtered out, and any remaining small amounts of water vapor and dust are separated. After undergoing cooling, filtration, and separation, the flue gas enters the compressor and is compressed to a high-pressure state. It then passes through a seawater cooling unit for further cooling and water vapor removal before being stored in a flue gas storage tank. During the compression process, the compressor is driven by a steam turbine. Steam generated by the boiler enters the turbine, which converts the thermal energy of the steam into rotational mechanical energy, directly driving the compressor to compress the flue gas.

[0020] In the flue gas energy release system, the high-pressure flue gas in the flue gas storage tank enters the three-flow heat exchanger for heating. Then, the high-temperature gas in gaseous state expands and does work in the expander. The expander drives the expander generator through the drive shaft to generate electricity. The generated electricity is fed into the ship's power grid. The electricity output from the ship's power grid can then be used for the ship's electric propulsion when the ship is sailing under high load or for the operation of the unloading pump when the ship arrives at the unloading port to unload cargo.

[0021] When inerting is required for cryogenic piping systems and equipment on ships at ambient or temperatures between 0°C and -60°C, an inerting system is used. The flue gas in the flue gas storage tank is sent to the inerting unit to participate in the inerting of various ambient or cryogenic piping systems and equipment.

[0022] Beneficial effects of this invention:

[0023] 1. This invention utilizes devices such as boilers, compressors, and flue gas storage tanks to convert the energy of excess BOG (Boat-Oxide Gas) into the pressure energy of flue gas when a ship is sailing under low load, anchored, or maneuvering, thus avoiding the serious waste of excess BOG under low load conditions.

[0024] 2. This invention releases the stored flue gas energy when the ship is sailing under high load or arriving at the unloading port to unload cargo, and then uses it for the operation of the ship's electric propulsion system or unloading pump, realizing the energy reuse of BOG. ​​At the same time, after the flue gas energy is released, the flue gas energy storage tank can be recycled when the ship stores flue gas energy again, thereby saving the space of the ship to install the flue gas energy storage tank.

[0025] 3. The flue gas in the flue gas storage tank of the present invention can also be used for inerting of normal temperature or low temperature piping systems and equipment, which greatly reduces the inerting cost of ships. Attached Figure Description

[0026] Figure 1 This is a system diagram of the present invention;

[0027] In the attached diagram: 1. LNG cargo tank; 2. BOG exhaust valve; 3. Compressor; 4. BOG three-way valve; 5. Refrigerant heat exchanger; 6. Cylinder liner water heater; 7. Circulating pump; 8. Diesel engine intake valve; 9. Diesel engine; 10. Generator; 11. Propulsion motor; 12. Propeller; 13. Boiler; 14. Steam turbine; 15. Compressor; 16. Flue gas storage tank; 17. Flue gas four-way valve; 18. Seawater cooling unit; 19. Filtration and separation unit; 20. Three-stream heat exchanger; 21. Expander; 22. Expander generator; 23. Check valve; 24. Inerting unit. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] like Figure 1 As shown, a system for handling excess BOG on an LNG carrier includes a BOG supply system, an excess BOG utilization system, a flue gas energy storage system, a flue gas energy release system, and an inerting system.

[0030] The BOG supply system includes: LNG cargo tank 1, BOG exhaust valve 2, compressor 3, BOG three-way valve 4, refrigerant heat exchanger 5, cylinder liner water heater 6, circulating pump 7, diesel engine intake valve 8, diesel engine 9, generator 10, propulsion motor 11, and propeller 12.

[0031] The excess BOG utilization system includes: boiler 13, steam turbine 14, and compressor 15.

[0032] The flue gas energy storage system includes a flue gas energy storage tank 16, a flue gas four-way valve 17, a seawater cooling unit 18, a filtration and separation unit 19, and a check valve 23.

[0033] The flue gas energy release system includes: a three-flow heat exchanger 20, an expander 21, and an expander generator 22.

[0034] The inerting system includes an inerting unit 24.

[0035] In the BOG supply system, the LNG cargo tank 1 is filled with LNG. An exhaust pipe is provided above the LNG cargo tank 1 and is connected in sequence to the BOG exhaust valve 2, compressor 3, BOG three-way valve 4, and refrigerant heat exchanger 5. The refrigerant heat exchanger 5 is connected in sequence to the diesel engine intake valve 8 and diesel engine 9 through pipes. The diesel engine 9 and generator 10 are connected through a drive shaft to form a diesel generator set. Multiple diesel generator sets are provided on the ship. The generator 10 is connected to the ship's power grid through a line. The ship's main engine is connected to the propulsion motor 11 through a line. The propulsion motor 11 is connected to the propeller 12 through a drive shaft.

[0036] The refrigerant heat exchanger 5, cylinder liner water heater 6, and circulating pump 7 are connected in sequence through pipelines to form a circulation pipeline.

[0037] In the excess BOG utilization system, a pipe is provided below the boiler 13 to connect to one outlet of the BOG three-way valve 4, and a pipe is provided above the boiler 13 to connect to the steam turbine 14. The steam turbine 14 is connected to the compressor 15 through a drive shaft.

[0038] In the flue gas energy storage system, the diesel engine 9 is connected to the flue gas four-way valve 17 via a pipeline. The three outlets of the flue gas four-way valve 17 are respectively connected to the seawater cooling unit 18, the three-stream heat exchanger 20, and the atmosphere. The exhaust port above the boiler 13 is connected to the check valve 23 via a pipeline. The check valve 23 is connected to the pipeline between the flue gas four-way valve 17 and the seawater cooling unit 18 via a pipeline. The function of the seawater cooling unit 18 is to use seawater to cool the high-temperature flue gas and remove most of the water vapor contained in the flue gas. The seawater cooling unit 18 is connected to the filtration and separation unit 19, the compressor 15, and the flue gas energy storage tank 16 in sequence via pipelines. The function of the filtration and separation unit 19 is to filter out impurities in the flue gas and separate the small amount of water vapor and dust still contained in the flue gas. The flue gas energy storage tank 16 is a high-pressure resistant storage tank.

[0039] In the flue gas energy release system, the flue gas energy storage tank 16 is connected in sequence to the three-stream heat exchanger 20 and the expander 21 via pipelines. The expander 21 is connected to the expander generator 22 via a drive shaft, and the expander generator 22 is connected to the ship's electrical grid via a signal. The two inlets of the three-stream heat exchanger 20 are respectively connected to the flue gas four-way valve 17 and the steam generated by the boiler 13. The function of the three-stream heat exchanger 20 is to heat the flue gas, thereby increasing the temperature of the flue gas at the inlet of the expander 21 and thus increasing the output power of the expander 21. The heating source of the three-stream heat exchanger 20 comes from the flue gas from the diesel engine 9 of the flue gas four-way valve 17 or the steam generated by the boiler 13. Under normal circumstances, the two heating sources are not used simultaneously.

[0040] In the inerting unit 24, the inerting unit 24 is connected to the flue gas storage tank 16 through a pipeline. The inerting unit 24 is a low temperature piping system and equipment on the ship that requires inerting at room temperature or at a temperature between 0℃ and -60℃.

[0041] When the ship is sailing at normal speed, the BOG (Boiled Gas) in the LNG cargo tank 1 reaches the compressor 3 through the BOG exhaust valve 2. The BOG is pressurized by the compressor 3. At this time, the outlet of the BOG three-way valve 4 connected to the boiler 13 is closed, while the outlet connected to the refrigerant heat exchanger 5 is opened. The pressurized BOG enters the refrigerant heat exchanger 5. Simultaneously, cylinder liner heating water enters the cylinder liner water heater 6 to exchange heat with the refrigerant. The refrigerant circulates under the action of the circulating pump 7, absorbing heat from the cylinder liner water to heat the BOG entering the refrigerant heat exchanger 5. At this time, the diesel engine intake valve 8 opens, and the heated BOG is sent to the diesel engine 9 for combustion. The diesel engine 9 then drives the generator 10 to generate electricity, which is sent to the ship's electrical grid. The ship's electrical grid supplies power to the propulsion motor 11, which in turn drives the propeller 12 to rotate, providing power to the ship.

[0042] When the ship is sailing under low load, maneuvering, or anchored, the BOG in the LNG cargo tank 1 reaches the compressor 3 through the BOG exhaust valve 2. The BOG is pressurized by the compressor 3. At this time, the ship requires less propulsion power, so both outlets of the BOG three-way valve 4 are open. Part of the BOG is sent to the diesel engine 9 for combustion through the refrigerant heat exchanger 5 and the diesel engine intake valve 8. Then, the diesel engine 9 drives the generator 10 to generate electricity, which is sent to the ship's electrical grid. The ship's electrical grid supplies power to the propulsion motor 11, which in turn drives the propeller 12 to rotate, providing power to the ship. The remaining BOG is sent to the boiler 13 for combustion. The flue gas generated by the boiler 13 enters the seawater cooling unit 18 through the check valve 23. At the same time, the outlet of the flue gas four-way valve 17 connected to the seawater cooling unit 18 is opened, and the other two outlets are closed. The flue gas generated by the diesel engine 9 merges with the flue gas from the boiler 13 through the flue gas four-way valve 17 and enters the seawater cooling unit 18 together for cooling and to remove most of the water vapor contained in the flue gas. The flue gas then enters the filtration and separation unit 19, where impurities are filtered out, and small amounts of water vapor and dust remaining are separated. After cooling, filtration, and separation, the main component of the flue gas is CO2. The flue gas then enters the compressor 15, where it is compressed to a high-pressure state. The compressor 15 is driven by the steam turbine 14, which converts the steam generated by the boiler 13 into rotational mechanical energy, directly driving the compressor 15 to compress the flue gas. After compression in the compressor 15, the flue gas generates heat, causing a temperature increase, and also produces some water vapor. Therefore, the seawater cooling unit 18 is used to further cool and remove water vapor from the compressed flue gas. Finally, the flue gas is stored in the flue gas storage tank 16. This invention utilizes a boiler 13, a compressor 15, a flue gas storage tank 16, and other devices to convert the energy of excess BOG into the pressure energy of flue gas, thus avoiding the serious energy waste caused by simply treating excess BOG in low-load conditions of ships through GCU combustion or direct emission.

[0043] The flue gas stored in the flue gas storage tank 16 of this invention can be used for various operating conditions, such as: powering the ship's power unit when the ship is sailing under high load, powering the unloading system when the ship arrives at the unloading port to unload cargo, and serving as inert gas for the ship's inerting system.

[0044] The first scenario: When the ship is sailing under high load, after the BOG in the LNG cargo tank 1 is consumed, the flue gas energy release system is activated to continue providing power to the ship. The specific workflow is as follows: the high-pressure flue gas in the flue gas storage tank 16 enters the three-stream heat exchanger 20 for heating. At this time, the heat source of the three-stream heat exchanger 20 is the flue gas from the diesel engine 9. The outlet of the flue gas four-way valve 17 connected to the three-stream heat exchanger 20 is opened, while the other two outlets are closed. The high-temperature flue gas from the diesel engine 9 enters the three-stream heat exchanger 20 to heat the high-pressure flue gas from the flue gas storage tank 16. Subsequently, the high-temperature flue gas expands and does work in the expander 21. The expander 21 drives the expander generator 22 to generate electricity through the drive shaft. The generated electricity is fed into the ship's power grid, which then supplies power to the propulsion motor 11. The propulsion motor 11 drives the propeller 12 to rotate, providing power to the ship.

[0045] LNG carriers typically operate at high speeds during normal navigation, meaning they spend most of their time under high load. Under these conditions, the bulk gas (BOG) in the LNG cargo tank 1 can usually be completely consumed by the diesel engine 9. However, ships frequently navigate under various conditions, such as encountering sudden storms, heavy fog, or other extreme weather, navigating narrow channels or shallow waters, entering and leaving ports, and loading / unloading cargo. Therefore, ships cannot maintain a continuous high-load navigation state. Under these conditions, ships must navigate under low load, maneuver, or anchor. This invention compresses and stores the flue gas emitted by the diesel engine 9 and boiler 13 during low-load navigation, anchoring, or maneuvering, achieving energy storage in the flue gas. When the ship is under high load and the BOG cannot meet its fuel requirements, the high-pressure flue gas stored in the flue gas storage tank 16 is released first to generate electricity, thus releasing the energy from the flue gas and supplementing the ship's electric propulsion power needs. In addition, due to the complex navigation conditions of ships, the ship's speed may change frequently. The flue gas energy storage tank 16 plays a regulatory role in complex navigation conditions. The present invention collects the energy of the flue gas when the ship is sailing at low speed and releases the energy when sailing at high speed. In this process, the flue gas energy storage tank 16 can be recycled. Therefore, the number and volume of the flue gas energy storage tank 16 do not need to be too large, thereby saving space on the ship for installing the flue gas energy storage tank 16. Therefore, the present invention has very good engineering value.

[0046] The second scenario: When the ship arrives at the unloading port to unload cargo, the flue gas energy release system is activated. The high-pressure flue gas in the flue gas storage tank 16 enters the three-stream heat exchanger 20 for heating. At this time, the heat source of the three-stream heat exchanger 20 is the steam from the boiler 13. Subsequently, the flue gas expands and does work in the expander 21. The expander 21 drives the expander generator 22 to do work and generate electricity through the drive shaft. The generated electricity is connected to the ship's power grid, thereby providing power to the unloading pump.

[0047] This system stores energy in flue gas when the ship is sailing under low load, anchored, or maneuvering. It uses devices such as boiler 13, compressor 15, and flue gas energy storage tank 16 to convert the excess BOG energy into the pressure energy of the flue gas. When the ship arrives at the unloading port to unload cargo or sails under high load, the energy of the flue gas is released, which actually realizes the energy reuse of BOG.

[0048] The third scenario: When inerting is required for cryogenic piping systems and equipment on board at ambient temperature or within the temperature range of 0℃ to -60℃, the flue gas in the flue gas storage tank 16 is sent to the inerting unit 24 for inerting. Before fuel is introduced into the LNG supply pipeline, or when maintenance is performed on equipment connected to the LNG supply pipeline, inerting with inert gas is typically required. However, the cost of producing inert gas using the ship's inert gas generator is high. Before being supplied to the diesel engine 9, LNG needs to be heated and vaporized to approximately 20℃ to 45℃. After vaporization, the pipeline through which the LNG flows becomes an ambient temperature pipeline. In this invention, the main component of the flue gas in the flue gas storage tank 16 is CO2, which can be used as an inert gas for the inerting of the aforementioned ambient temperature pipeline. Furthermore, this invention can also be applied to the inerting of cryogenic piping systems and equipment with temperatures between 0℃ and -60℃, but it cannot be applied to the inerting of cryogenic piping systems and equipment with temperatures below -60℃ to avoid the formation of dry ice from CO2 at excessively low temperatures, which could clog the pipelines. By adopting this invention, the cost of producing inert gas on board can be significantly reduced.

[0049] The above description is merely a preferred embodiment of the present invention. The specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A system for handling excess BOG on LNG carriers, characterized in that: The system includes an LNG cargo tank (1), a BOG exhaust valve (2), a compressor (3), a BOG three-way valve (4), a refrigerant heat exchanger (5), a cylinder liner water heater (6), a circulating pump (7), a diesel engine intake valve (8), a diesel engine (9), a generator (10), a propulsion motor (11), a propeller (12), a boiler (13), a steam turbine (14), a compressor (15), a flue gas storage tank (16), a flue gas four-way valve (17), a seawater cooling unit (18), a filtration and separation unit (19), a three-stream heat exchanger (20), an expander (21), an expander generator (22), a check valve (23), and an inerting unit (24). The LNG cargo tank (1), BOG exhaust valve (2), compressor (3), and BOG three-way valve (4) are connected in sequence by pipelines. A pipeline is provided below the boiler (13) and connected to one outlet of the BOG three-way valve (4). A pipeline is provided above the boiler (13) and connected to the steam turbine (14). The steam turbine (14) is connected to the compressor (15) through a drive shaft. The diesel engine (9), flue gas four-way valve (17), and seawater cooling unit (18) are connected in sequence via pipelines. The boiler (13), check valve (23), and seawater cooling unit (18) are connected in sequence via pipelines. The seawater cooling unit (18) is connected in sequence via pipelines to the filtration and separation unit (19), compressor (15), and flue gas storage tank (16). The flue gas storage tank (16) is connected in sequence to the three-stream heat exchanger (20) and the expander (21) via pipelines. The expander (21) is connected to the expander generator (22) via a drive shaft. The expander generator (22) is connected to the ship's electrical grid via a signal. The flue gas storage tank (16) is connected to the inerting unit (24) via a pipeline.

2. A system for handling excess BOG on an LNG carrier according to claim 1, characterized in that: When the ship is sailing under low load, maneuvering, or anchored, the energy of the BOG is converted into the pressure energy of the flue gas and stored using a boiler (13), a steam turbine (14), a compressor (15), a flue gas storage tank (16), a flue gas four-way valve (17), a seawater cooling unit (18), a filtration and separation unit (19), and a check valve (23). When a ship is sailing under heavy load or unloading cargo at a port, the pressure energy of the flue gas in the flue gas storage tank (16) is released and converted into electrical energy to be sent into the ship's power grid.

3. A system for handling excess BOG on an LNG carrier according to claim 1, characterized in that: The inerting unit (24) is a low-temperature piping system and equipment on the ship that requires inerting at room temperature or between 0°C and -60°C.

4. A system for handling excess BOG on an LNG carrier according to claim 1, characterized in that: The two inlets of the three-flow heat exchanger (20) are connected to the flue gas four-way valve (17) and the steam generated by the boiler (13), respectively.

5. A system for handling excess BOG on an LNG carrier according to claim 1, characterized in that: The flue gas storage tank (16) is a high-pressure resistant storage tank.

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