A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit and a dynamic BOG management method.

Abstract

This invention discloses a gas supply system for roll-on / roll-off (Ro-Ro) vessels with recondensation and a low-pressure circuit, and a dynamic BOG (Boat-Oven) management method. The system includes two IMO Type C storage tanks, a TCS (Total Gas Storage System) room, port and starboard refueling stations, a vacuum double-walled pipe, a gas storage room, a ventilation double-walled pipe, a gas generator, a gas boiler, and a main engine with a shaft-driven generator. The gas storage room includes a compressor skid, a vaporizer skid, a high-pressure pump skid, and a buffer tank main valve skid. The vaporizer skid includes a BOG recondensation system and a high- and low-pressure LNG gas supply system. Specifically, the BOG management method prioritizes using the low-pressure LNG gas supply system to supply gas to the gas generator and gas boiler; it also prioritizes using recondensed BOG to drive the shaft-driven generator of the main engine, as the shaft-driven generator has a higher power generation efficiency than the gas generator, further improving energy utilization efficiency.

Description

Technical Field

[0001] This invention relates to the field of gas supply technology for roll-on / roll-off (Ro-Ro) ships, and more specifically to a gas supply system for Ro-Ro ships with recondensation and low-pressure circuits, and a dynamic management method for BOG (Board of Gas). Background Technology

[0002] With the implementation of new international environmental regulations aimed at reducing nitrogen oxide and sulfur oxide emissions, the use of liquefied natural gas (LNG) as ship fuel is becoming increasingly common. Compared to LNG carriers, roll-on / roll-off (Ro-Ro) ships have much smaller LNG storage tanks, typically around 1700m³. 3 Around (compared to 170,000 m³ of LNG carriers) 3 The cargo tank capacity is much smaller. Therefore, the evaporation rate of BOG (boil of gas) is much lower, eliminating the need for a large BOG reliquefaction system. The traditional method involves liquefying BOG in a reliquefaction unit and then reinjecting it into the main engine or supplying it to the main unit. BOG is then compressed by a BOG compressor and supplied to gas generators and gas boilers.

[0003] Traditional methods face the following problems: 1. Gas generators and gas boilers can only be supplied by BOG compressors. If the load on electricity or the gas boiler increases, the amount of BOG that evaporates naturally may not meet the needs of the gas generator and gas boiler due to the small size of the storage tank. 2. BOG compressors consume a large amount of electricity (compared to low-pressure pumps), and the power generation efficiency of gas generators is low (compared to main engine shaft-driven generators), resulting in unoptimized energy utilization. 3. There is no precise BOG management strategy to ensure that the temperature, pressure, and liquid level inside the storage tank do not exceed safe ranges while ensuring optimal energy utilization. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuits, as well as a dynamic management method for BOG (Bottle-Oil Gas). This addresses the problem that traditional methods, which use BOG compressors to supply BOG to gas generators and gas boilers, cannot meet the demands of electricity and steam loads. Furthermore, it can further reduce the energy consumption of BOG compressors, improve the power generation efficiency of generators, and achieve precise management of BOG temperature, pressure, and LNG level within the storage tank.

[0005] The technical solution adopted by this invention to solve the technical problem is: a gas supply system for roll-on / roll-off ships with recondensation and a low-pressure circuit. The gas supply system includes two IMO Type C storage tanks, a TCS room, port and starboard refueling stations, a vacuum double-walled pipe, a gas compartment, a ventilation double-walled pipe, a gas generator, a gas boiler, and a main engine with a shaft and generator. The vacuum double-walled pipe is located between the refueling station and the TCS room, and between the TCS room and the gas compartment, and connects both TCS rooms. The gas compartment includes a compressor skid, a vaporizer skid, a high-pressure pump skid, and a buffer tank main valve skid. The ventilation double-walled pipe is located between the gas compartment and the gas generator, the gas boiler, and the main engine with a shaft and generator. The vaporizer skid includes a BOG recondensation system and a high- and low-pressure LNG gas supply system.

[0006] Furthermore, the storage tank is located above the ballast tanks of the roll-on / roll-off ship and below the fourth deck, the TCS room is located above the storage tank, and the refueling station includes a port refueling station located above the seventh deck and a starboard refueling station located above the fifth deck.

[0007] Furthermore, the vacuum double-walled pipe includes a double-layered pipe and a rigid inner pipe support, with a vacuum drawn between the inner and outer pipes; the ventilation double-walled pipe includes a double-layered pipe and a flexible inner pipe support, with air flowing between the inner and outer pipes to dilute any leaked natural gas fuel and ventilate it outside the hull space.

[0008] Furthermore, the compressor skid receives BOG from the storage tank in the TCS room, pressurizes the BOG and supplies it to the recondensation system located in the vaporizer skid, and also bypasses the buffer tank and the main valve skid; the buffer tank and the main valve skid use the ventilation double-wall pipe to supply gas to the gas generator and the gas boiler.

[0009] Furthermore, the BOG recondensation system includes a BOG preheater, a buffer tank, a BOG aftercooler, a mass flow meter, a BOG precooler, and a BOG recondenser. The BOG recondensation system cools the BOG at 9 barg pressure at the compressor skid outlet in the BOG aftercooler using water-glycol as a medium. After further cooling, the BOG enters the recondenser to recondense with the low-pressure LNG from the TCS room of the storage tank. The recondensed low-pressure LNG is supplied to the high-pressure pump skid. The high-pressure LNG is heated by the BOG precooler and then by the high-pressure vaporizer before being delivered to the buffer tank. After passing through the mass flow meter and GVT, it is supplied to the main engine with the shaft and generator via the gas ventilation double-wall pipe.

[0010] Furthermore, the low-pressure LNG gas supply system receives low-pressure LNG from the TCS room of the storage tank, which is then vaporized in the low-pressure vaporizer using water glycol as a medium and supplied to the main valve skid of the buffer tank via a mass flow meter. After that, it is supplied to the gas generator and gas boiler via the ventilation double-wall pipe.

[0011] Furthermore, the BOG preheater, BOG aftercooler, BOG precooler, low-pressure vaporizer, and high-pressure vaporizer use printed circuit board shell-type heat exchangers with diffusion connection technology; the mass flow meter before the BOG precooler, the mass flow meter in the low-pressure LNG gas supply system, and the mass flow meter before the GVT transmit mass flow signals to the central control console to ensure that 10% of the total fuel for the gas generator and the main engine with the shaft and generator is supplied by the BOG recondensation system.

[0012] Furthermore, the BOG recondenser includes an LNG bottom inlet, an LNG top spray inlet, a BOG bottom inlet, an LNG bottom outlet, an LNG level sensor, a temperature sensor, and BOG and LNG heat exchange structured packing.

[0013] A dynamic management method for BOG (Boiler Gas) in a roll-on / roll-off (Ro-Ro) ship gas supply system with recondensation and a low-pressure circuit is disclosed. Specifically, the BOG management method prioritizes using the low-pressure LNG gas supply system to supply gas to the gas generator and gas boiler (instead of using the BOG compressor). Under the control of this BOG management strategy, the BOG pressure in the storage tank will not exceed the safety valve setting pressure of 4 barg, and the LNG level, pressure, and temperature in the storage tank can be precisely controlled under voyage conditions. The recondensed BOG is preferentially used to drive the shaft-driven generator of the main engine, and the power generation efficiency of the shaft-driven generator is higher than that of the gas generator, further improving energy utilization efficiency.

[0014] Furthermore, the BOG management method includes Strategy 1 and Strategy 2; Strategy 1 is implemented when the main engine is operating at half load, and Strategy 2 is implemented when the main engine is operating at full load; when Strategy 1 is implemented, the main engine shaft generator is shut down, the recondensing system is shut down, and the ship's power is provided by the gas generator; the gas generator's fuel is preferentially provided by the low-pressure LNG gas supply system; the main engine's fuel is provided by the high-pressure gas system; when Strategy 2 is implemented, the main engine shaft generator is turned on, the recondensing system is turned on, the ship's power is mainly provided by the shaft generator, the extra power for the outbound full-load voyage is shared by the gas generator, and the entire power for the return ballast voyage is provided by the shaft generator; the gas generator's fuel is preferentially provided by the low-pressure LNG gas supply system, and the main engine's fuel is jointly provided by the recondensing system and the high-pressure gas system.

[0015] The beneficial effects of this invention are as follows: Compared with the prior art, the gas supply system and BOG dynamic management method for roll-on / roll-off ships with recondensation and low-pressure circuit provided by this invention considers adding a shaft-driven generator to the main engine. It utilizes the LNG cooling capacity from the high-pressure pump outlet and the LNG cooling capacity from the low-pressure pump outlet of the recondensation system to condense the BOG, simultaneously supplying the condensed BOG and LNG to the main engine (the proportion of condensed BOG is 10% of the total fuel for the main engine and gas generator). The load of the shaft-driven generator driven by the main engine is provided by 10% of the recondensed BOG, and the low-pressure circuit of the low-pressure pump is preferentially used to supply gas to the gas generator and gas boiler to meet additional power and steam loads. This has the following advantages: 1. Under a precise BOG management strategy, even if the low-pressure pump is preferentially used to supply gas to the gas generator and gas boiler (instead of using the BOG compressor), the BOG pressure in the storage tank will not exceed the safety pressure set by the safety valve at 4 barg. 2. By preferentially using the low-pressure pump instead of the BOG compressor to supply gas to the generator and gas boiler, the low-pressure pump has lower technical power consumption for the same gas supply volume, achieving energy savings for the BOG compressor. 3. Re-condensed BOG is used to drive the shaft generator of the main engine to generate electricity. The efficiency of the shaft generator is higher than that of the gas generator, thus improving the generator's power generation efficiency. 4. If the electricity and steam loads exceed the load generated by the BOG (Ro-Ro ship storage tanks are small, and the amount of BOG is limited), low-pressure LNG is regasified to supply gas to the gas generator and boiler, solving the problem of insufficient BOG in small storage tanks. Attached Figure Description

[0016] Appendix Figure 1 This is a process flow diagram of the marine gas supply system of the present invention;

[0017] Appendix Figure 2 This is a process flow diagram of the vaporizer skid in the gas supply system of the present invention;

[0018] Appendix Figure 3 Finite element analysis of heat leakage in the storage tank of this invention;

[0019] Appendix Figure 4 The voyage conditions for the roll-on / roll-off vessel of this invention;

[0020] Appendix Figure 5 This refers to the BOG recondenser in the recondensation system of the present invention;

[0021] Appendix Figure 6 This invention relates to the management of outgoing temperature and pressure in storage tanks.

[0022] Appendix Figure 7 This invention relates to the management of return temperature and pressure in storage tanks.

[0023] Appendix Figure 8 This invention relates to the management of outgoing liquid level in storage tanks.

[0024] Appendix Figure 9 This invention relates to the management of return liquid level in storage tanks.

[0025] Explanation of reference numerals in the attached drawings: 1a. IMO Type C port side tank; 1b. IMO Type C starboard side tank; 11a. Port side tank submersible pump; 11b. Starboard side tank submersible pump; 2a. Port side TCS room; 2b. Starboard side TCS room; 3a. Port side refueling station; 3b. Starboard side refueling station; 4. Vacuum double-walled pipe; 5. Gas compartment; 51. Compressor skid; 52. Vaporizer skid; 521. Recondensation system; 522. BOG preheater; 523a, 523b, 523c. Buffer tank; 524. BOG aftercooler; 525. Mass flow meter; 526. BOG precooler; 527. 527a. BOG recondenser; 527b. LNG bottom inlet; 527c. BOG bottom inlet; 527d. Structured packing; 527e. Recondenser outlet; 528. High-pressure vaporizer; 529. Low-pressure vaporizer; 53. High-pressure pump skid; 54. Buffer tank main valve skid; 541. Low-pressure loop mass flow meter; 6. Ventilation double-wall pipe; 7. Gas generator; 8. Gas boiler; 9. Main engine with shaft and generator; 91. Main engine mass flow meter; 92. GVT. Detailed Implementation

[0026] The present invention will be further illustrated below with specific embodiments. However, these examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0027] Example

[0028] like Figure 1 and 2 As shown, this invention provides a gas supply system for roll-on / roll-off ships with recondensation and a low-pressure circuit, and a dynamic BOG management method. It features an improved low-pressure vaporizer circuit to supply low-pressure gas to the buffer tank and main valve skid, ultimately providing sufficient gas to the gas generator and gas boiler, even under low BOG evaporation rates (due to…). Figure 3 Finite element analysis of heat leakage in the storage tanks shows that the BOG evaporation rate in the ro-ro ship storage tanks is relatively low. Meanwhile, the use of a high-efficiency recondenser with structured packing and a printed circuit board shell-type heat exchanger with diffusion bonding technology as the heat exchangers for the BOG preheater 522, BOG aftercooler 524, BOG precooler 526, low-pressure vaporizer 529, and high-pressure vaporizer 528 can significantly reduce the volume, weight, and space required for the heat exchangers, thereby reducing the overall cost of the vaporizer skid.

[0029] The present invention includes two IMO Type C storage tanks (1a and 1b), TCS rooms (2a and 2b), port and starboard refueling stations (3a and 3b), vacuum double-wall pipe 4, gas chamber 5, ventilation double-wall pipe 6, gas generator 7, gas boiler 8, main engine with shaft and generator 9, and corresponding dynamic management method for storage tank BOG.

[0030] The storage tank is located above the ballast tanks of the roll-on / roll-off ship and below the fourth deck. The TCS room is located above the storage tank. The refueling stations include a port refueling station located above the seventh deck and a starboard refueling station located above the fifth deck.

[0031] The vacuum double-walled pipe is located between the refueling station and the TCS room, and between the TCS room and the gas room, connecting both TCS rooms. The vacuum double-walled pipe includes a double-layered pipe and a rigid inner pipe support, with a vacuum drawn between the inner and outer pipes.

[0032] The gas storage room 5 includes a compressor skid 51, a vaporizer skid 52, a high-pressure pump skid 53, a buffer tank skid 54, and a main valve skid 54. The compressor skid 51 receives BOG (Battery-Oxide Gas) from the storage tank in the TCS (Total Gas Storage System) room, pressurizes the BOG, and supplies it to the recondensing system located in the vaporizer skid 52, while also bypassing the buffer tank and the main valve skid. The buffer tank and the main valve skid use the ventilation double-walled pipe to supply gas to the gas generator and gas boiler.

[0033] The ventilation double-walled pipe 6 is located between the gas chamber 5 and the gas generator 7, gas boiler 8, and main engine 9 with shaft and generator. The ventilation double-walled pipe 6 includes a double-layered pipe and a flexible inner pipe support, with air flowing between the inner and outer pipes to dilute any leaked natural gas and vent it outside the hull space.

[0034] The vaporizer skid 52 includes a BOG re-condensation system and a high- and low-pressure LNG gas supply system. The BOG re-condensation system includes a BOG preheater 522, a buffer tank 523a, a BOG aftercooler 524, a mass flow meter 525, a BOG precooler 526, and a BOG recondenser 527. The BOG re-condensation system cools the BOG at 9 barg pressure at the compressor skid outlet in the BOG aftercooler using water-glycol as a medium. Then, it passes through the BOG precooler and exchanges heat with the low-temperature LNG from the high-pressure pump outlet for further cooling before entering the recondenser to re-condense with the low-pressure LNG from the TCS room of the storage tank. The re-condensed low-pressure LNG is supplied to the high-pressure pump skid. The high-pressure LNG, after being heated by the BOG aftercooler and then heated by the high-pressure vaporizer, is delivered to the buffer tank. After passing through the mass flow meter and GVT, it is supplied to the main engine with the shaft and generator via the gas ventilation double-wall pipe.

[0035] The low-pressure LNG gas supply system (low-pressure circuit) receives low-pressure LNG from the TCS room of the storage tank. After being vaporized in the low-pressure vaporizer using water glycol as a medium, it is supplied to the main valve skid of the buffer tank via a mass flow meter, and then supplied to the gas generator and gas boiler via the ventilation double-wall pipe.

[0036] The BOG preheater 522, BOG aftercooler 524, BOG precooler 526, low-pressure vaporizer 529, and high-pressure vaporizer 528 utilize printed circuit board shell-type heat exchangers with diffusion bonding technology. Simultaneously, the recondenser is a high-efficiency condenser with structured packing. These two heat exchanger structures significantly reduce the volume, weight, and space required for the heat exchangers, thereby reducing the overall cost of the vaporizer skid. The recondenser includes an LNG bottom inlet 527a, an LNG top spray inlet 527b, a BOG bottom inlet 527c, an LNG bottom outlet, an LNG level sensor, a temperature sensor, and structured heat exchange packing.

[0037] The mass flow meter 525 before the BOG precooler, the low-pressure circuit mass flow meter 541, and the main engine mass flow meter 91 before the GVT transmit mass flow signals to the central control console to ensure that 10% of the total fuel for the gas generator 7 and the main engine 9 with shaft generator is supplied by the BOG recooling system.

[0038] The described BOG management method prioritizes using the low-pressure circuit of the low-pressure pump to supply gas to the gas generator and gas boiler (instead of using the BOG compressor). This ensures that the BOG pressure in the storage tank will not exceed the safety valve's set pressure, and allows for precise control of the tank's level, pressure, and temperature under various voyage conditions (including full-load and ballast voyages). This invention prioritizes using the low-pressure circuit of the low-pressure pump instead of the BOG compressor to supply gas to the generator and gas boiler. With the same gas supply volume, the low-pressure pump requires less power, achieving optimized energy utilization and solving the problem of insufficient BOG in small storage tanks. Furthermore, prioritizing the use of recondensed BOG to drive the shaft-driven generator of the main engine further improves energy efficiency, as the shaft-driven generator is more efficient than the gas generator.

[0039] The specific BOG management and control strategy is as follows: Figure 4 The diagram shows typical voyage conditions for a roll-on / roll-off (Ro-Ro) ship, including the outbound journey (fully loaded) and the return journey (ballasted). The BOG (Board of Loads) management strategy is divided into two types based on whether the main engine is at full load.

[0040] Strategy 1 (Main Engine Under Full Load): Whether on the outbound or return journey, during departure, maneuvering, transit through the Suez Canal, anchorage, port entry, or unloading / loading, the ship's speed is not at full capacity. During these times, the main engine 9 with its shaft and generator is not operating at full load. The main engine shaft and generator are shut down, the re-condensation system 521 is shut down, and the BOG compressor in the compressor skid 51 is shut down. LNG fuel, after being pressurized by the port and starboard submersible pumps 11a and 11b, merges with the LNG in the vacuum double-walled pipe 4 and enters the gas chamber 5. The LNG fuel is then split into two streams. One stream goes through a low-pressure circuit to the low-pressure vaporizer 529, then into the buffer tank main valve skid 54, and finally into the gas generator 7 via the ventilation double-wall pipe 6. The gas generator 7 provides all the ship's electricity (when shore power is not used). The other stream goes through the BOG recondenser 527 (at which time the recondenser is unloaded), then into the BOG precooler 526, high-pressure vaporizer 528, buffer tank 523c, main engine mass flow meter 91, and GVT 92, and then into the main engine 9 with shaft generator via the ventilation double-wall pipe 6. At this time, the shaft generator is shut down and does not participate in the power supply.

[0041] Strategy Two (Main Engine Full Load): Whether on the outbound or return voyage, during ocean voyages, the ship reaches a speed of 16 knots. At this point, the main engine 9 with its shaft generator operates at full load, the main engine shaft generator is activated, the re-condensation system 521 is activated, and the BOG compressor in compressor skid 51 is activated. The ship's power is primarily supplied by the main engine 9 with its shaft generator (for the outbound voyage at full load, power is provided by the gas generator 7; for the return voyage, all power is provided by the main engine 9 with its shaft generator). At this time, the BOG in storage tank 1 converges through vacuum double-wall pipe 4 and enters the vaporizer skid 52 in the gas chamber 5. After passing through the BOG preheater 522 and buffer tank 523a, it splits into two parallel paths and enters the compressor skid 51. After being pressurized by the compressor, it enters the re-condensation system 521 in the vaporizer skid 522. In the re-condensation system, it sequentially passes through buffer tank 523b, BOG aftercooler 524, mass flow meter 525, and BOG precooler 526, finally condensing in the BOG re-condenser 527. Meanwhile, the LNG in storage tank 1, after being pressurized by submersible pump 11, merges in vacuum double-walled pipe 4 and enters gas chamber 5. The LNG fuel is then split into two streams: one stream goes through a low-pressure circuit to low-pressure vaporizer 529, then into buffer tank main valve skid 54, and finally supplies gas to gas generator 7 through ventilation double-walled pipe 6, satisfying part of the electrical load beyond the shaft generator load during the full-load outbound voyage; the other stream goes to BOG recondenser 527 to condense the aforementioned BOG entering the recondenser. Figure 5As shown, the condensation method employed is as follows: BOG enters from the bottom inlet 527c of the recondenser, while LNG enters simultaneously from the top spray port 527b and the bottom inlet 527a. The intermediate layer is filled with structured packing 527d. As BOG rises and LNG falls, the BOG condenses after mass and heat transfer within the structured packing 527d. The LNG and BOG mix and then flow out through the bottom recondenser outlet 527e. After being pressurized by the high-pressure pump skid 53, the BOG enters the BOG precooler 526 in the vaporizer skid 52, where it reheats with the aforementioned BOG (using the heat from the BOG to heat the high-pressure LNG to save energy, while simultaneously using the cold energy of the high-pressure LNG to condense the BOG). After passing through the high-pressure vaporizer 528, buffer tank 523c, main engine mass flow meter 91, and GVT 92, the BOG is supplied to the main engine 9 with a shaft-driven generator via a ventilation double-wall pipe 6 (at this time, the shaft-driven generator is open).

[0042] Under the aforementioned BOG management strategy, both voyages last 31 days. Refueling is done before departure for each voyage, and the tank reaches a steady-state pressure of 1 barg after refueling. The shaft-driven generator operates for 26 days during each voyage. When the gas phase pressure inside the tank reaches 1 barg and the shaft-driven generator is running, the BOG compressor is started, initiating the recondensation process. The gas generator operates for 24.5 days on the outbound full-load voyage and 4.5 days on the return ballast voyage. Until the end of a complete voyage, the tank pressure on the outbound full-load voyage increases from the initial 1 barg to 2.77 barg, the temperature increases from the initial -153.18℃ to -141.6℃, and the liquid phase volume percentage decreases from the initial 89.6% to 31.5%; the tank pressure on the return ballast voyage increases from the initial 1 barg to 2.56 barg, the temperature increases from the initial -153.18℃ to -142.6℃, and the liquid phase volume percentage decreases from the initial 89.6% to 44.5% (e.g., ...). Figure 6-9 (As shown).

[0043] The above-mentioned BOG management strategy has several advantages: 1. Under a precise BOG management strategy, even if the low-pressure circuit of the low-pressure pump is prioritized to supply gas to the gas generator (instead of using the BOG compressor), the BOG pressure in the storage tank will not exceed the safety valve setting pressure of 4 barg, and the temperature and liquid level will remain at normal levels. 2. Prioritizing the use of the low-pressure circuit of the low-pressure pump instead of the BOG compressor to supply gas to the generator results in lower technical power consumption for the same gas supply, achieving optimized energy utilization. 3. Re-condensed BOG is used to drive the shaft generator of the main engine to generate electricity. The efficiency of the shaft generator is higher than that of the gas generator, achieving optimized energy utilization. 4. If the electricity and steam loads exceed the load generated by the BOG (Ro-Ro ship storage tanks are small, and the BOG volume is small), low-pressure LNG can be regasified to supply gas to the gas generator and boiler, solving the problem of insufficient BOG in small storage tanks.

[0044] The above embodiments are only used to illustrate the present invention and are not intended to limit the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims.

Claims

1. A gas supply system for roll-on / roll-off ships with recondensation and a low-pressure circuit, characterized in that: The gas supply system includes two IMO Type C storage tanks, a TCS room, port and starboard refueling stations, a vacuum double-walled pipe, a gas compartment, a ventilated double-walled pipe, a gas generator, a gas boiler, and a main engine with a shaft and generator. The vacuum double-walled pipe is located between the port and starboard refueling stations and the TCS room, and between the TCS room and the gas compartment, connecting both TCS rooms. The gas compartment includes a compressor skid, a vaporizer skid, a high-pressure pump skid, and a buffer tank main valve skid. The ventilated double-walled pipe is located between the gas compartment and the gas generator, gas boiler, and the main engine with a shaft and generator. The vaporizer skid includes a BOG recondensation system and a low-pressure LNG gas supply system. The BOG recondensation system includes a BOG preheater, a buffer tank, a BOG aftercooler, a mass flow meter, a BOG precooler, and a BOG recondenser. The BOG recondensation system cools the BOG at 9 barg pressure at the compressor skid outlet in the BOG aftercooler using water-glycol as a medium. Then, it further cools the BOG by exchanging heat with the cryogenic LNG from the high-pressure pump outlet in the BOG precooler before entering the BOG recondenser to recondense with the low-pressure LNG from the TCS room of the storage tank. The recondensed low-pressure LNG is supplied to the high-pressure pump skid. The high-pressure LNG, after being heated by the BOG precooler and then by the high-pressure vaporizer, is delivered to the buffer tank, and then, after passing through the mass flow meter and GVT, is supplied to the main engine with the shaft and generator via the gas ventilation double-wall pipe.

2. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The storage tank is located above the ballast tanks of the roll-on / roll-off ship and below the fourth deck. The TCS room is located above the storage tank. The refueling station includes a port refueling station located above the seventh deck and a starboard refueling station located above the fifth deck.

3. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The vacuum double-walled pipe includes a double-layered pipe and a rigid inner pipe support, with a vacuum drawn between the inner and outer pipes; the ventilation double-walled pipe includes a double-layered pipe and a flexible inner pipe support, with air flowing between the inner and outer pipes to dilute any leaked natural gas and ventilate it outside the hull space.

4. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The compressor skid receives BOG evaporated from the storage tank in the TCS room, pressurizes the BOG and supplies it to the BOG recondensation system located in the vaporizer skid, and also bypasses the buffer tank and the main valve skid; the buffer tank and the main valve skid use the ventilation double-wall pipe to supply gas to the gas generator and the gas boiler.

5. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The low-pressure LNG gas supply system receives low-pressure LNG from the TCS room of the storage tank. After being vaporized in the low-pressure vaporizer with water glycol as the medium, it is supplied to the main valve skid of the buffer tank via a mass flow meter, and then supplied to the gas generator and gas boiler via the ventilation double-wall pipe.

6. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The BOG preheater, BOG aftercooler, BOG precooler, low-pressure vaporizer, and high-pressure vaporizer use printed circuit board shell-type heat exchangers with diffusion connection technology. The mass flow meter before the BOG precooler, the mass flow meter in the low-pressure LNG gas supply system, and the mass flow meter before the GVT transmit mass flow signals to the central control console to ensure that 10% of the total fuel for the gas generator and the main engine with the shaft and generator is supplied by the BOG recondensation system.

7. A gas supply system for roll-on / roll-off ships with recondensation and low-pressure circuit as described in claim 1, characterized in that: The BOG recondenser includes an LNG bottom inlet, an LNG top spray inlet, a BOG bottom inlet, an LNG bottom outlet, an LNG level sensor, a temperature sensor, and BOG and LNG heat exchange structured packing.

8. The BOG dynamic management method for a roll-on / roll-off marine gas supply system with recondensation and low-pressure circuit as described in claim 1, characterized in that: Specifically, the BOG management method prioritizes the use of the low-pressure LNG gas supply system to supply gas to the gas generator and gas boiler. Under the control of the BOG management method, the BOG pressure in the storage tank will not exceed the safety valve setting pressure of 4 barg, and the liquid level, pressure, and temperature of LNG in the storage tank can be precisely controlled under voyage conditions. Recondensed BOG is preferentially used to drive the shaft generator of the main engine to generate electricity. The power generation efficiency of the shaft generator is higher than that of the gas generator, further improving energy utilization efficiency.

9. A method for dynamic BOG management of a roll-on / roll-off marine gas supply system with recondensation and low-pressure circuit as described in claim 8, characterized in that: The BOG management method includes Strategy 1 and Strategy 2. Strategy 1 is implemented when the main engine is not operating at full load, and Strategy 2 is implemented when the main engine is operating at full load. When Strategy 1 is implemented, the main engine shaft generator is shut down, the BOG re-condensation system is shut down, and the ship's power is provided by the gas generator. The gas generator is primarily fueled by the low-pressure LNG gas supply system, and the main engine is fueled by the high-pressure gas system. When Strategy 2 is implemented, the main engine shaft generator is turned on, the BOG re-condensation system is turned on, and the ship's power is mainly provided by the main engine shaft generator. The extra power for the outbound full-load voyage is shared by the gas generator, and the entire power for the return ballast voyage is provided by the main engine shaft generator. The gas generator is primarily fueled by the low-pressure LNG gas supply system, and the main engine is fueled by both the BOG re-condensation system and the high-pressure gas system.

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