BOG recondensation system based on high-pressure cold energy utilization

Abstract

The application provides a BOG recondensation system based on high-pressure cold energy utilization, comprising: a fuel tank; a BOG compression unit connected with the fuel tank and used for compressing BOG volatilized in the fuel tank; a BOG recondensation unit connected with the BOG compression unit and used for condensing the compressed BOG for recycling; a low-pressure fuel supply unit comprising a fuel supply path and a user supply path, the fuel supply path being connected between the fuel tank and the BOG recondensation unit and used for conveying fuel in the fuel tank to the BOG recondensation unit to condense the compressed BOG, and the user supply path being connected with the fuel supply path to supply fuel to a low-pressure user; and a high-pressure fuel supply unit connected with the BOG recondensation unit and used for supplying fuel passing through the BOG recondensation unit to a high-pressure user.

Description

Technical Field

[0001] This invention relates to the field of BOG condensation technology, and in particular to a BOG recondensation system based on the utilization of high-pressure cold energy. Background Technology

[0002] Currently, the shipping industry accounts for 3% of global carbon emissions, and it faces severe pressure to reduce emissions. Against this backdrop, ship propulsion needs to achieve a zero-carbon transition.

[0003] Currently, dual-fuel high-pressure main engines require gas supply pressures as high as 300~380 Barg (LNG: 300~325 Barg, LEG: 380 Barg), while fuel tank pressures are generally 0.7~4.5 Barg. Boil-off gas (BOG) generated in the tank cannot be directly supplied to the main engine. Common BOG handling methods include: 1. Equipping a high-pressure BOG compressor to pressurize the BOG to meet the main engine requirements, but high-pressure BOG compressors are expensive and the range of manufacturers available is limited; 2. Using a low-pressure BOG compressor to pressurize the BOG and supply it to the dual-fuel generator or boiler. However, if the boiler uses GCU mode combustion, there is fuel energy waste in the BOG, and this method is not suitable for many converted vessels that only add a dual-fuel main engine; 3. Equipping a subcooler to cool the fuel tank, thus converting the BOG in the fuel tank into liquid, or adding a BOG re-condensation system to re-condense the BOG and send it back to the fuel tank or supply it directly to the main engine via a pump. However, using this method requires an additional system, resulting in significant investment in both cost and energy consumption.

[0004] Furthermore, taking LNG as an example, 4.5 Barg of LNG corresponds to a saturation temperature of approximately -135°C. After being pressurized to 300 Barg, it needs to reach -70°C to vaporize, resulting in unused subcooling. With the widespread application of high-pressure main engines, recovering the usable cold energy after pump pressurization has become a key path to improve ship energy efficiency.

[0005] CN120351081A discloses a BOG recondensation system for dual-fuel ships, including a BOG pretreatment unit, a BOG recondensation unit, a low-pressure gas supply unit, and a high-pressure gas supply unit. The BOG pretreatment unit includes a BOG preheater, a BOG inlet tank, a compressor, a primary oil-gas separator, a BOG aftercooler, and a secondary oil-gas separator connected in sequence. The recondensation unit includes a secondary oil-gas separator, a BOG precooler, a BOG recondenser, a high-pressure pump, and a high-pressure vaporizer connected in sequence. The low-pressure gas supply unit includes a low-pressure pump located in the fuel tank, a dual gas filter connected in sequence to the outlet of the low-pressure pump, a BOG recondenser, and a high-pressure pump. The high-pressure gas supply unit includes a high-pressure vaporizer connected in sequence to the outlet of the high-pressure pump, a BOG precooler, a high-pressure gas buffer tank, an engine gas supply main valve group, and an engine. This invention enables the recondensation of BOG, and the recondensed liquid can be returned to the fuel tank via a control valve or mixed into the high-pressure pump to prepare fuel. However, it has the following drawbacks: the switching between returning the recondensed liquid to the fuel tank or entering the high-pressure pump relies solely on human experience, and the recondensation system lacks automatic and scientific means of switching operating modes; the fixed compressor is a normal-temperature oil-filled compressor, which limits the system design flexibility by only considering cost factors, and there is a risk of oil and gas freezing and damaging the high-pressure pump; the overpressured fuel gas and non-fuel non-condensable gas in the BOG recondenser are not distinguished, but the gas is directly sent to the compressor for further processing; the use of a container-type BOG recondenser has problems such as complex design, large space occupation, and poor processing efficiency, and the lack of consideration for supercooling means will cause the liquid after pressure reduction to re-vaporize during the return to the fuel tank, which is not conducive to controlling the fuel tank pressure; it only considers the methane and ethane fuel supply systems and ignores the application of the recondensation system in the ammonia fuel supply system. Summary of the Invention

[0006] In view of the shortcomings of the above-mentioned related technologies, the purpose of this invention is to provide a BOG recondensation system based on high-pressure cold energy utilization.

[0007] To achieve the above and other related objectives, the present invention provides a BOG recondensation system based on high-pressure cold energy utilization, comprising: a fuel tank; a BOG compression unit connected to the fuel tank for compressing BOG volatilized within the fuel tank; a BOG recondensation unit connected to the BOG compression unit for condensing the compressed BOG for recycling; a low-pressure fuel supply unit including a fuel supply path and a user supply path, the fuel supply path being connected between the fuel tank and the BOG recondensation unit for transporting fuel from the fuel tank to the BOG recondensation unit for condensing the compressed BOG, the user supply path being connected to the fuel supply path for supplying fuel to low-pressure users; and a high-pressure fuel supply unit connected to the BOG recondensation unit for supplying fuel passing through the BOG recondensation unit to high-pressure users.

[0008] Optionally, the BOG compression unit includes a preheater, a gas-liquid separator, and a compressor skid. The preheater, the gas-liquid separator, and the compressor skid are connected in sequence. The preheater inlet is connected to the fuel tank, and the connection between the preheater inlet and the fuel tank is controlled by a compression unit control valve. The compressor skid outlet branches into two branches: one branch is connected to the BOG recondensation unit, and the other branch is connected to the user supply line to supply fuel to low-pressure users.

[0009] Optionally, the fuel supply path includes a low-pressure pump, a dual filter, and a high-pressure fuel supply valve, wherein the low-pressure pump, the dual filter, and the high-pressure fuel supply valve are connected in sequence, the low-pressure pump is connected to the fuel tank, and the high-pressure fuel supply valve is connected to the BOG recondensation unit.

[0010] Optionally, the system further includes a return pipeline connected between the BOG recondensation unit and the fuel tank, for allowing the condensed BOG to flow back to the fuel tank.

[0011] Optionally, the BOG recondensation unit includes a recondenser, the first inlet of which is connected to the BOG compression unit, the fuel supply line is connected to the second inlet of the recondenser, the first outlet of the recondenser is connected to the return-to-tank pipeline, the user supply line is connected to the fuel supply line through the condenser, and the high-pressure fuel supply unit is connected in parallel with the user supply line at the second outlet of the recondenser.

[0012] Optionally, the high-pressure fuel supply unit includes a high-pressure pump and a high-pressure vaporizer. The inlet of the high-pressure pump is connected to the second outlet of the re-condenser, and the outlet of the high-pressure pump is connected to the third inlet of the re-condenser to cool the BOG with the condensed high-pressure fuel. The high-pressure vaporizer is connected to the third outlet of the re-condenser to vaporize the high-pressure fuel and deliver it to the high-pressure user.

[0013] Optionally, the user supply route includes a low-pressure fuel supply valve, a low-pressure vaporizer, and a low-pressure buffer tank. The low-pressure fuel supply valve, the low-pressure vaporizer, and the low-pressure buffer tank are connected in sequence. The low-pressure buffer tank is used to supply fuel to low-pressure users. The low-pressure fuel supply valve and the high-pressure pump inlet are connected in parallel to the second outlet of the recondenser.

[0014] Optionally, the return pipeline includes a two-way valve, a spray valve, and a bottom injection valve. The spray valve and the bottom injection valve are connected in parallel to the outlet of the two-way valve, and the inlet of the two-way valve is connected to the first outlet of the recondenser.

[0015] Optionally, the BOG recondensation unit includes a pre-condenser and a recondenser. The first inlet of the pre-condenser is connected to the BOG compression unit, and the first outlet of the pre-condenser and the fuel supply path are respectively connected to the first inlet and the second inlet of the recondenser. The system also includes a non-condensable gas treatment unit. The outlet of the recondenser is connected to the inlet of the non-condensable gas treatment unit, and the non-condensable gas treatment unit is connected to the high-pressure fuel supply unit.

[0016] Optionally, the high-pressure fuel supply unit includes a recondensation supply valve, a high-pressure pump, and a high-pressure vaporizer. The inlet of the high-pressure pump is connected to the outlet of the non-condensable gas processing unit through the recondensation supply valve. The outlet of the high-pressure pump is connected to the second inlet of the pre-condenser, and the second outlet of the pre-condenser is connected to the high-pressure vaporizer.

[0017] Optionally, the non-condensable gas treatment unit has a non-condensable gas release pipeline with a gas release valve. The outlet of the gas release valve branches into two branches. One branch is used to connect to the venting system and is equipped with a gas venting valve. The other branch is connected to the BOG compression unit and is equipped with a gas circulation valve.

[0018] Optionally, the user supply path includes a low-pressure fuel supply valve, a direct-flow control valve, a low-pressure fuel throttle valve, a non-condensable gas treatment control valve, a low-pressure vaporizer, and a low-pressure buffer tank. The inlet of the low-pressure fuel supply valve is connected to the fuel supply path, and the outlet of the low-pressure fuel supply valve branches into two branches. One branch is sequentially connected to the direct-flow control valve, the low-pressure vaporizer, and the low-pressure buffer tank. The other branch is sequentially connected to the low-pressure fuel throttle valve and the non-condensable gas treatment control valve, and this branch is connected between the direct-flow control valve and the low-pressure vaporizer after passing through the non-condensable gas treatment unit.

[0019] Optionally, the outlet of the low-pressure fuel throttle valve branches into two branches: one branch is connected to the non-condensable gas treatment control valve, and the other branch is connected to the third inlet of the pre-condenser. The third outlet of the pre-condenser is connected between the straight-through control valve and the low-pressure vaporizer.

[0020] Optionally, the first outlet of the pre-condenser is connected to the first inlet of the re-condenser via one of the outlets of a three-way control valve, and the system further includes a return pipeline, with the other outlet of the three-way control valve connected to the fuel tank via the return pipeline.

[0021] Optionally, the pre-condenser outlet is provided with a subcooling differential pressure indicator, which is used to send a signal to the three-way control valve, and the three-way control valve controls the flow direction of BOG based on the subcooling differential pressure indicator.

[0022] Optionally, the non-condensable gas processing unit is equipped with a pressure sensor, which is used to send a signal to the gas release valve to control the opening and closing of the gas release valve.

[0023] Optionally, the non-condensable gas processing unit is equipped with a liquid level sensor, which sends a signal to the recondensation supply valve, and the recondensation supply valve opens and closes based on the liquid level sensor to supply fuel to the high-pressure pump.

[0024] As described above, the BOG recondensation system based on high-pressure cold energy utilization of the present invention has the following beneficial effects: The present invention cleverly combines the need for improved ship energy efficiency with the unavoidable handling of BOG, achieving dual optimization of energy utilization and BOG management. Compared to the additional BOG recondensation unit that uses refrigerant, it achieves a win-win situation in terms of energy consumption and cost. Attached Figure Description

[0025] Figure 1 The diagram shown is a schematic diagram of the recondensation system in Embodiment 1 of the present invention.

[0026] Figure 2 The diagram shown is a schematic diagram of the recondensation system in Embodiment 2 of the present invention.

[0027] Figure 3 The diagram shown is a schematic diagram of the recondensation system in Embodiment 3 of the present invention.

[0028] Component designation explanation

[0029] E1, Fuel Tank; E2, Low-Pressure Pump; E3, Dual Filter; E4, Recondenser; E5, Non-Condensing Gas Handling Unit; E6, High-Pressure Pump; E7, Pre-condenser; E8, Low-Pressure Vaporizer; E9, Compressor Skid; E10, High-Pressure Vaporizer; E11, Low-Pressure Buffer Tank; E12, High-Pressure Gas Valve Assembly; E13, Generator Gas Valve Assembly; E14, Boiler Gas Valve Assembly; E15, Dual-Fuel Main Unit; E16, Generator; E17, Boiler; E18, Preheater; E19, Gas-Liquid Separator; V1, High-Pressure Fuel Supply Valve; V2, Low-Pressure Fuel Supply Valve; V3, Non-Condensing Gas Handling Unit; V4, Spray valve; V5, Three-way control valve; V6, Bottom injection valve; V7, Low-pressure fuel throttle valve; V8, Compression unit control valve; V9, Recondensation control valve; V10, Low-pressure supply control valve; V11, Main engine gas main valve; V12, Generator gas main valve; V13, Boiler gas main valve; V14, Gas release valve; V15, Recondensation supply valve; V16, Gas vent valve; V17, Gas circulation valve; V18, Straight-through control valve; V51, Two-way valve; I1, Subcooling differential pressure indicator; I2, Pressure sensor; I3, Liquid level sensor. Detailed Implementation

[0030] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0031] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0032] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for the device in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it can be the only layer between the two layers, or there may be one or more layers in between. The phrase “between” as used herein includes both endpoint values.

[0033] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0034] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0035] Example 1

[0036] like Figure 1 As shown, this embodiment provides a BOG recondensation system based on high-pressure cold energy utilization. The system includes a fuel tank E1, a BOG compression unit, a BOG recondensation unit, a non-condensable gas treatment unit E5, a low-pressure fuel supply unit, and a high-pressure fuel supply unit.

[0037] The BOG compression unit includes a preheater E18, a gas-liquid separator E19, and a compressor skid E9; the BOG recondensation unit includes a precondenser E7 and a recondenser E4; the low-pressure fuel supply unit includes a low-pressure pump E2, a dual filter E3, a high-pressure fuel supply valve V1, a low-pressure vaporizer E8, a low-pressure buffer tank E11, a generator gas valve assembly E13, and a boiler gas valve assembly E14; the low-pressure pump E2, the dual filter E3, and the high-pressure fuel supply valve V1 constitute the fuel supply path, while the low-pressure vaporizer E8, the low-pressure buffer tank E11, the generator gas valve assembly E13, and the boiler gas valve assembly E14 constitute the user supply path; the low-pressure fuel supply unit is used to supply fuel to low-pressure users, including generators E16 and boilers E17; the high-pressure fuel supply unit includes a high-pressure pump E6, a high-pressure vaporizer E10, and a high-pressure gas valve assembly E12, and is used to supply fuel to high-pressure users, including dual-fuel main units E15.

[0038] BOG compression unit connection method:

[0039] The inlet of preheater E18 is connected to the outlet of the vapor phase pipe of fuel tank E1. A compression unit control valve V8 is installed on the connecting pipeline between preheater E18 and fuel tank E1. The outlet of preheater E18 is connected to the inlet of gas-liquid separator E19. The outlet of gas-liquid separator E19 is connected to the inlet of compressor skid E9. The outlet of compressor skid E9 is divided into two paths: one path connects to low-pressure buffer tank E11, and a low-pressure supply control valve V10 is installed between low-pressure buffer tank E11 and compressor skid E9; the other path connects to pre-condenser E7, and a re-condensation control valve V9 is installed between pre-condenser E7 and compressor skid E9.

[0040] The design of the BOG recondensation system is highly dependent on the selection of the core compressor within compressor skid E9. If the core compressor in compressor skid E9 is a normal temperature compressor, the BOG compression unit must include a preheater E18. If the core compressor in compressor skid E9 is a low temperature compressor, the BOG compression unit does not include a preheater E18. In addition to the core compressor, compressor skid E9 should also include auxiliary units to ensure the smooth operation of the BOG compression unit. If the core compressor in compressor skid E9 is an oil-lubricated compressor, the auxiliary units include an oil circulation unit and a BOG aftercooler. If the core compressor in compressor skid E9 is an oil-free compressor, the auxiliary units only include a BOG aftercooler. The specific compressor selection and system design can be flexibly tailored to the actual engineering application needs and cost considerations.

[0041] The lubricating oil circulation unit includes a lubricating oil pump, a lubricating oil cooler, an oil separator, and a lubricating oil filter. Before starting the oil-filled compressor, it is necessary to ensure that the lubricating oil system is operating normally. The flow rate, temperature, and cleanliness of the lubricating oil must meet the requirements through appropriate equipment. In addition, the oil content of the BOG at the compressor outlet must be limited in conjunction with the E6 requirements of the high-pressure pump to prevent the oil and gas from freezing and damaging the high-pressure pump in the direct liquid supply mode.

[0042] When BOG (Boiled Gas) is generated in fuel tank E1 due to heat intrusion, the compression unit control valve V8 opens. The low-temperature BOG is preheated by preheater E18 to meet the inlet temperature requirements of compressor skid E9, and then enters gas-liquid separator E19 for gas-liquid separation. It then enters compressor skid E9 for compression and pressurization. The main function of gas-liquid separator E19 is to ensure that the compressor inlet pressure in compressor skid E9 is stable and free of liquid. The BOG after compressor skid E9 can be divided into two paths: one path enters low-pressure buffer tank E11 through low-pressure supply control valve V10, ultimately supplying low-pressure users; the other path enters pre-condenser E7 through re-condensation control valve V9 for BOG re-condensation.

[0043] The BOG recondensation unit is connected as follows:

[0044] The first inlet of the pre-condenser E7 is connected to the outlet of the compressor skid E9. The first outlet of the pre-condenser E7 is connected to a three-way control valve V5. The outlet of the three-way control valve V5 is connected to the first inlet of the re-condenser E4 and the fuel tank E1, respectively. A return pipeline is connected between the pre-condenser E7 and the fuel tank E1. This return pipeline is divided into a bottom injection pipeline and a spray pipeline. A spray valve V4 is installed on the spray pipeline, and a bottom injection valve V6 is installed on the bottom injection pipeline. The outlet of the re-condenser E4 is connected to the inlet of the non-condensable gas treatment unit E5.

[0045] The BOG (Boiled Gas) processed by the compressor can be re-condensed by the BOG re-condensation unit. The BOG re-condensation unit has two operating modes: condensate return and direct liquid supply. The two operating modes are switched via a three-way control valve V5. When operating in return mode, the BOG is only condensed by the pre-condenser E7 and then returned to the compartment via the spray valve V4 or the bottom injection valve V6 after passing through the three-way control valve V5. When operating in direct liquid supply mode, the BOG is pre-cooled by the pre-condenser E7 and then condensed by the re-condenser E4, and then passes through the non-condensable gas treatment unit E5 before being supplied with liquid.

[0046] The connection configuration of the non-condensable gas handling unit is as follows:

[0047] The outlet of the non-condensable gas processing unit E5 is connected to the inlet of the high-pressure pump E6, and a recondensation supply valve V15 is installed between the non-condensable gas processing unit E5 and the high-pressure pump E6. A gas release valve V14 is installed on the non-condensable gas release pipeline of the non-condensable gas processing unit E5. The outlet of the gas release valve V14 branches into two lines: one line connects to the venting system and is equipped with a gas venting valve V16; the other line connects to the inlet of the preheater E18 and is equipped with a gas circulation valve V17. To liquefy the gas within the non-condensable gas processing unit E5, a branch pipeline from the low-pressure fuel supply unit is included within the unit. This branch pipeline is in the form of a cooling coil and is equipped with a low-pressure fuel throttle valve V7 and a non-condensable gas processing control valve V3. This configuration allows the liquefaction of the non-condensable gas using the cold energy of the fuel.

[0048] When the BOG recondenser unit operates in direct liquid supply mode, the fuel liquid from the recondenser E4 undergoes gas-liquid separation in the non-condensable gas treatment unit E5 to ensure that the inlet of the high-pressure pump E6 is free of gas, thereby guaranteeing the safe operation of the pump. The non-condensable gas in the gas phase space of the non-condensable gas treatment unit E5 can be liquefied by cooling with low-pressure fuel that has been vaporized after being depressurized by the low-pressure fuel throttle valve V7. If the pressure continues to rise during the liquefaction process of the non-condensable gas, it can be assumed that it contains non-condensable nitrogen, and the gas release valve V14 and gas release valve can be opened. Vent valve V16 discharges it into the venting system; when the low-pressure user is not activated or the low-pressure fuel supply unit is not used for cold energy treatment of non-condensable gases, the non-condensable gas treatment control valve V3 is closed. If too much fuel gas accumulates in the gas phase space of the non-condensable gas treatment unit E5, causing the pressure to rise to a certain value, the gas release valve V14 and the gas circulation valve V17 can be opened to send the non-condensable fuel gas back to the BOG compression unit for recompression or directly back to the fuel tank, avoiding direct emission that would waste fuel gas and cause environmental harm.

[0049] The low-pressure fuel supply unit is connected as follows:

[0050] Low-pressure pump E2 is located inside fuel tank E1. The outlet of low-pressure pump E2 is connected to the inlet of dual filter E3. The outlet of dual filter E3 is connected to the inlet of low-pressure vaporizer E8. A low-pressure fuel supply valve V2 is installed between dual filter E3 and low-pressure vaporizer E8. The outlet of low-pressure fuel supply valve V2 branches into two branches. One branch is connected to the inlet of low-pressure fuel throttle valve V7, and the other branch is connected to low-pressure vaporizer E8 through a straight-through control valve V18. The outlet of low-pressure vaporizer E8 is connected to the inlet of low-pressure buffer tank E11. The outlet of low-pressure buffer tank E11 branches into two branches. One branch is connected to the inlet of generator gas valve group E13, and a generator gas main valve V12 is installed on this pipeline. The other branch is connected to the inlet of boiler gas valve group E14, and a boiler gas main valve V13 is installed on this pipeline. The outlets of generator gas valve group E13 and boiler gas valve group E14 are respectively connected to generator E16 and boiler E17.

[0051] The liquid fuel in fuel tank E1 is pressurized by low-pressure pump E2 and then filtered through dual filter E3. The filtered liquid fuel then passes through low-pressure fuel supply valve V2 and is heated by low-pressure vaporizer E8 to obtain gaseous fuel that meets the user's temperature requirements. This gas then enters low-pressure buffer tank E11 for pressure stabilization. The gas in the buffer tank is then supplied to the user after pressure regulation by the gas valve assembly. When low-pressure fuel throttle valve V7 is open, the direct-flow control valve V18 must be closed (if the direct-flow control valve V18 is opened simultaneously, the flow distribution will be affected by resistance, resulting in insufficient flow through the low-pressure fuel throttle valve V7 branch, which is insufficient for cooling). The low-pressure fuel through this branch can provide cooling for the BOG recondensation unit and the non-condensable gas handling unit.

[0052] The high-pressure fuel supply unit is connected as follows:

[0053] The second inlet of the recondenser E4 is connected to the outlet of the dual filter E3 of the low-pressure gas supply unit, and a high-pressure fuel supply valve V1 is installed between the recondenser E4 and the dual filter E3; the outlet of the recondenser E4 is connected to the non-condensable gas processing unit E5; the outlet of the non-condensable gas processing unit E5 is connected to the inlet of the high-pressure pump E6; the outlet of the high-pressure pump E6 is connected to the second inlet of the precondenser E7; the second outlet of the precondenser E7 is connected to the inlet of the high-pressure vaporizer E10; the outlet of the high-pressure vaporizer E10 is connected to the inlet of the high-pressure gas valve group E12, and a main gas valve V11 is installed between the high-pressure vaporizer E10 and the high-pressure gas valve group E12; the outlet of the high-pressure gas valve group E12 is connected to the inlet of the dual-fuel main engine E15.

[0054] Open the high-pressure fuel supply valve V1. The fuel liquid, after initial pressurization and filtration by the low-pressure fuel supply unit, is first mixed with the BOG pre-cooled from the pre-condenser E7 in the re-condenser E4 and the BOG is condensed. The mixed liquid fuel is then separated into gas and liquid by the non-condensable gas treatment unit E5 and enters the high-pressure pump E6 to be pressurized to meet the pressure requirements of the dual-fuel main unit E15. After passing through the high-pressure pump E6, the high-pressure fuel liquid first passes through the pre-condenser E7 as a cold source for pre-cooling the BOG, and then is heated and vaporized by the high-pressure vaporizer E10 into gaseous fuel that meets the temperature requirements of the dual-fuel main unit E15. Open the main unit gas main valve V11, and the gaseous fuel is supplied to the dual-fuel main unit E15 after the pressure is regulated by the high-pressure gas valve group E12.

[0055] A subcooling differential pressure indicator I1 is installed on the outlet pipe of precondenser E7. The subcooling differential pressure indicator I1 can send a signal to the three-way control valve V5. The subcooling differential pressure indicator I1 can determine the subcooling of BOG at this temperature by comparing the pressure difference between the saturation pressure and the actual pressure at this temperature. The three-way control valve V5 can manually or automatically adjust the flow rate of BOG returning to the chamber or directly supplying it based on this detection signal. Specifically, it can be programmed. When there is a certain degree of cooling that meets the return chamber requirements, the three-way control valve V5 will prioritize opening the return chamber mode. When the BOG at the precondenser outlet is in a gaseous state or a gas-liquid mixture, the three-way control valve V5 will automatically open the direct liquid supply mode to send the BOG into the recondenser E4 for recondensation.

[0056] The non-condensable gas processing unit E5 is equipped with a pressure sensor I2, whose signal is transmitted to the gas release valve V14. The unit also has a liquid level sensor I3, whose signal is transmitted to the recondensation supply valve V15. When the pressure sensor I2 detects a high pressure within the non-condensable gas processing unit E5, it is assumed that the unit contains a large amount of non-condensable gas. In this case, the low-pressure fuel throttle valve V7 and the non-condensable gas processing control valve V3 can be opened to process the non-condensable gas using low-pressure fuel. If the pressure continues to rise, and exceeds a set value, the gas release valve V14 will automatically open to release the non-condensable gas from the container. If the gas is determined to be nitrogen, the gas vent valve V16 can be opened to directly discharge it into the venting system. If the gas is determined to be primarily fuel gas, the gas recirculation valve V17 can be opened to send the gas into the compressor for further compression or directly back into the fuel tank. Through the liquid level sensor I3, when the liquid level in the container meets the requirements, the recondensation supply valve V15 can be opened to supply liquid fuel to the high-pressure pump E6.

[0057] The outlet of the low-pressure fuel throttle valve V7 branches into two lines: one line enters the non-condensable gas processing unit E5, and the other line connects to the third inlet of the pre-condenser E7. The outlets of both branch lines are connected to the inlet of the low-pressure vaporizer E8. The cold energy of the vaporized low-pressure fuel after throttling can be used to further cool the non-condensable gas and subcool the BOG condensed by the pre-condenser E7. The two lines correspond to the two operating modes of condensate return to the BOG re-condensation unit and direct liquid supply, respectively. The low-pressure fuel after heat exchange is supplied to low-pressure users after passing through the low-pressure vaporizer E8.

[0058] The BOG recondensation system requires a water glycol circulation system as an auxiliary heat exchange medium. The users of the water glycol system include the high-pressure vaporizer E10, the low-pressure vaporizer E8, the preheater E18, and the compressor skid E9. Water glycol acts as a heat source in the high-pressure vaporizer E10, the low-pressure vaporizer E8, and the preheater E18 to heat the fuel. In the compressor skid E9, water glycol mainly acts as a cold source to cool the lubricating oil and the compressed BOG gas. With proper design, the water glycol system can achieve efficient energy utilization by utilizing thermal balance.

[0059] The pre-condenser E7 uses a three-stream printed circuit board heat exchanger; the re-condenser E4 uses a re-condenser gas-liquid mixer; the preheater E18 and the low-pressure vaporizer E8 use plate-and-shell heat exchangers; and the high-pressure vaporizer E10 uses either a shell-and-tube heat exchanger or a printed circuit board heat exchanger. When selecting a heat exchanger, it is necessary to ensure that it matches the key parameters such as heat exchange type, heat exchange medium, design pressure, and heat exchange capacity.

[0060] Example 2

[0061] like Figure 2As shown, the difference from Embodiment 1 is that this recondensation system does not include the return chamber spray pipe and bottom injection pipe, nor does it include the subcooling differential pressure indicator I1. The outlet of the precondenser E7 is only connected to the inlet of the recondenser E4, and a two-way valve V51 is installed on the pipeline. The BOG flowing out of the precondenser E7 flows directly into the recondenser E4 through the two-way valve V51. In this case, the precondenser E7 is replaced with a two-stream printed circuit board heat exchanger, which can effectively save costs.

[0062] The signal from the pressure sensor I2 located in the non-condensable gas processing unit E5 is transmitted to the two-way valve V51. The pressure signal from the non-condensable gas processing unit E5 determines the BOG condensation capacity of the BOG recondensation system and adjusts the BOG flow rate accordingly.

[0063] Example 3

[0064] like Figure 3 As shown, the difference from Embodiment 1 is that the recondensation system does not include the non-condensable gas processing unit E5, the pre-condenser E7, the low-pressure fuel throttle valve V7, the gas release valve V14, the recondensation supply valve V15, the gas vent valve V16, the gas circulation valve V17, the straight-through control valve V18 and the corresponding pipelines, and does not include the pressure sensor I2 and the liquid level sensor I3. The three-way control valve V5 is changed to a two-way valve V51.

[0065] The first inlet of the recondenser E4 is connected to the outlet of the compressor skid E9; the first outlet of the recondenser E4 is connected to the fuel tank E1 via a return pipeline, and a two-way valve V51 is installed on the return pipeline; the pipeline connecting the recondenser E4 and the fuel tank E1 is divided into a bottom injection pipeline and a spray pipeline, with a spray valve V4 installed on the spray pipeline and a bottom injection valve V6 installed on the bottom injection pipeline; the BOG recondensation unit only operates in a condensate return mode, and the BOG return flow rate is regulated by the two-way valve V51.

[0066] The outlet of the dual filter E3 is connected to the second inlet of the recondenser E4; the second outlet of the recondenser E4 is connected to the inlet of the low-pressure vaporizer E8 through the low-pressure fuel supply valve V2; compared with embodiment 1, this embodiment directly provides the low-pressure fuel cooling capacity to the recondenser E4.

[0067] The second outlet of the recondenser E4 is simultaneously connected to the inlet of the high-pressure pump E6; the outlet of the high-pressure pump E6 is then connected to the third inlet of the recondenser E4, and then flows out from the third outlet of the recondenser E4 and into the high-pressure vaporizer E10; the high-pressure fuel supply valve V1 is opened, and the fuel liquid, after being initially pressurized and filtered by the low-pressure fuel supply unit, first uses low-pressure cold energy in the recondenser E4 to provide cooling for the BOG recondensation, and then enters the high-pressure pump E6 to be pressurized to meet the pressure requirements of the dual-fuel main unit E15. The high-pressure fuel liquid after exiting the high-pressure pump E6 enters the recondenser E4 again to provide cooling for the BOG recondensation, and then is heated and vaporized by the high-pressure vaporizer E10 into gaseous fuel that meets the temperature requirements of the dual-fuel main unit E15. The main unit gas main valve V11 is opened, and the gaseous fuel is supplied to the dual-fuel main unit E15 after the pressure is regulated by the high-pressure gas valve group E12.

[0068] A subcooling differential pressure indicator I1 is installed on the inlet pipe of the high-pressure pump E6. The subcooling differential pressure indicator I1 transmits the signal to the two-way valve V51. The two-way valve V51 can adjust the BOG recondensation amount according to the subcooling of the inlet of the high-pressure pump E6 to ensure that there is no gas at the inlet of the high-pressure pump E6 and to ensure the safe operation of the high-pressure pump E6.

[0069] Compared to Example 1, the precooling and recondensation of BOG in Example 1 are achieved only through the recondenser E4; the recondenser E4 adopts a three-stream printed circuit board heat exchanger, and the reduction of equipment can effectively simplify the system and save costs.

[0070] This invention cleverly combines the need for improved ship energy efficiency with the unavoidable handling of BOG (Boiled Air Gathering), achieving a dual optimization of energy utilization and BOG management. Compared to the additional BOG recondensation unit that uses refrigerant, it achieves a win-win situation in terms of energy consumption and cost.

[0071] This invention includes two technical routes: re-condensation of BOG and / or direct supply. This design takes into account the dynamic balance between different BOG production rates and main engine load, eliminates energy loss caused by direct BOG combustion, and achieves comprehensive, stable, and efficient management of BOG. ​​In practical applications, one of these methods can be flexibly selected according to requirements, and the system can be simplified accordingly.

[0072] This invention features a three-way control valve V5, which receives a signal from the subcooling differential pressure indicator I1 at the outlet of the recondenser E4. The flow rate can be adjusted automatically or manually, adjusting the BOG throughput based on the subcooling and selecting either return to the chamber or direct supply to the high-pressure pump. This effectively achieves precise system control and improves system performance.

[0073] The design of the recondensation system is highly dependent on the selection of the compressor. This system can use either a normal temperature or a low temperature compressor, and the choice of whether to configure a preheater depends on the selection. If only the return to the cabin is considered, an oil-filled compressor can be used first, as the system is simpler. If the high-pressure pump E6 supplies power directly, an oil-free compressor should be preferred. In this case, if an oil-filled compressor is to be used, the oil content of the BOG at the compressor outlet must be specified to prevent oil vapor from freezing and damaging the high-pressure pump E6.

[0074] This invention includes a non-condensable gas processing unit E5 for separating liquid fuels and non-condensable gases. For example, if the fuel is LNG, the non-condensable gas is nitrogen; if the fuel is ethane, the non-condensable gas is methane. This unit is equipped with a cooling coil, utilizing the cooling energy of a low-pressure pump to further cool the non-condensable gases. Depending on the actual situation, non-condensable fuel gases can be selectively sent back to the compressor for reprocessing, while non-condensable nitrogen is directly discharged into the venting system. This ensures that the inlet of the high-pressure pump E6 is gas-free, guaranteeing the safety of the high-pressure pump E6, while preventing fuel gas waste and environmental hazards that would result from direct discharge after gas-liquid separation alone.

[0075] In addition to handling non-condensable gases, the fuel liquid from the low-pressure fuel supply unit can also be throttled and vaporized to subcool the BOG after it has been condensed in the pre-condenser E7, so that it meets the requirements for return to the tank. This system not only recovers the usable cold energy after the high-pressure pump E6, but also utilizes the cold energy after the low-pressure pump E2, making its energy utilization more comprehensive.

[0076] This invention is applicable not only to LNG fuel supply systems, but also to the treatment of ammonia tail gas in ethane fuel supply systems and ammonia fuel supply systems. This invention is applicable to all types of ships, especially dual-fuel powered ships.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A BOG recondensation system based on high-pressure cold energy utilization, characterized in that, include: Fuel tank; A BOG compression unit, connected to the fuel tank, is used to compress the BOG that evaporates in the fuel tank; The BOG re-condensation unit is connected to the BOG compression unit and is used to condense and compress the BOG for recycling. The low-pressure fuel supply unit includes a fuel supply line and a user supply line. The fuel supply line is connected between the fuel tank and the BOG re-condensation unit and is used to transport the fuel in the fuel tank to the BOG re-condensation unit to condense the compressed BOG. ​​The user supply line is connected to the fuel supply line to supply fuel to low-pressure users. A high-pressure fuel supply unit is connected to the BOG recondensation unit and is used to supply fuel that has passed through the BOG recondensation unit to high-pressure users. The BOG recondensation unit includes a pre-condenser and a recondenser. The first inlet of the pre-condenser is connected to the BOG compression unit. The first outlet of the pre-condenser and the fuel supply line are respectively connected to the first inlet and the second inlet of the recondenser. The system also includes a non-condensable gas treatment unit. The outlet of the recondenser is connected to the inlet of the non-condensable gas treatment unit. The non-condensable gas treatment unit is connected to the high-pressure fuel supply unit. The high-pressure fuel supply unit includes a recondensation supply valve, a high-pressure pump, and a high-pressure vaporizer. The inlet of the high-pressure pump is connected to the outlet of the non-condensable gas processing unit through the recondensation supply valve. The outlet of the high-pressure pump is connected to the second inlet of the pre-condenser, and the second outlet of the pre-condenser is connected to the high-pressure vaporizer.

2. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The BOG compression unit includes a preheater, a gas-liquid separator, and a compressor skid. The preheater, the gas-liquid separator, and the compressor skid are connected in sequence. The preheater inlet is connected to the fuel tank, and the connection between the preheater inlet and the fuel tank is controlled by a compression unit control valve. The compressor skid outlet branches into two branches: one branch is connected to the BOG recondensation unit, and the other branch is connected to the user supply line to supply fuel to low-pressure users.

3. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The fuel supply circuit includes a low-pressure pump, a dual filter, and a high-pressure fuel supply valve. The low-pressure pump, the dual filter, and the high-pressure fuel supply valve are connected in sequence. The low-pressure pump is connected to the fuel tank, and the high-pressure fuel supply valve is connected to the BOG recondensation unit.

4. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The system also includes a return pipeline connected between the BOG recondensation unit and the fuel tank, for allowing the condensed BOG to flow back to the fuel tank.

5. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The non-condensable gas processing unit has a non-condensable gas release pipeline with a gas release valve. The outlet of the gas release valve branches into two branches. One branch is connected to the venting system and is equipped with a gas venting valve. The other branch is connected to the BOG compression unit and is equipped with a gas circulation valve.

6. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The user supply path includes a low-pressure fuel supply valve, a direct-flow control valve, a low-pressure fuel throttle valve, a non-condensable gas treatment control valve, a low-pressure vaporizer, and a low-pressure buffer tank. The inlet of the low-pressure fuel supply valve is connected to the fuel supply path, and the outlet of the low-pressure fuel supply valve branches into two branches. One branch is sequentially connected to the direct-flow control valve, the low-pressure vaporizer, and the low-pressure buffer tank. The other branch is sequentially connected to the low-pressure fuel throttle valve and the non-condensable gas treatment control valve, and after passing through the non-condensable gas treatment unit, it is connected between the direct-flow control valve and the low-pressure vaporizer.

7. The BOG recondensation system based on high-pressure cold energy utilization according to claim 6, characterized in that: The outlet of the low-pressure fuel throttle valve branches into two branches. One branch is connected to the non-condensable gas treatment control valve, and the other branch is connected to the third inlet of the pre-condenser. The third outlet of the pre-condenser is connected between the straight-through control valve and the low-pressure vaporizer.

8. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The first outlet of the pre-condenser is connected to the first inlet of the re-condenser via one outlet of a three-way control valve. The system also includes a return pipeline, and the other outlet of the three-way control valve is connected to the fuel tank via the return pipeline.

9. The BOG recondensation system based on high-pressure cold energy utilization according to claim 8, characterized in that: The pre-condenser outlet is equipped with a subcooling differential pressure indicator, which is used to send a signal to the three-way control valve. The three-way control valve controls the flow direction of BOG based on the subcooling differential pressure indicator.

10. The BOG recondensation system based on high-pressure cold energy utilization according to claim 5, characterized in that: The non-condensable gas processing unit is equipped with a pressure sensor, which is used to send a signal to the gas release valve to control the opening and closing of the gas release valve.

11. The BOG recondensation system based on high-pressure cold energy utilization according to claim 1, characterized in that: The non-condensable gas processing unit is equipped with a liquid level sensor, which sends a signal to the recondensation supply valve. The recondensation supply valve opens and closes based on the liquid level sensor to supply fuel to the high-pressure pump.

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