Combined System of Flash Vapor Boosting Gas Supply and Re-Liquefaction Cycle and Liquid Cargo Ship

Abstract

The present application provides a combined system of flash steam pressurization gas supply and re-liquefaction cycle and a liquid cargo ship. The combined system includes a first heat exchanger, a second heat exchanger, a compression device with multiple stages of compression, a re-liquefaction pipeline, and a gas-liquid separation module. Flash steam is input to the first side of the first heat exchanger. The main inlet of the compression device is connected to the first side of the first heat exchanger, and the main outlet is connected to a first user. A liquid return port is provided in the pipeline before the last stage of compression in the compression device. The inlet of the re-liquefaction pipeline is connected to the liquid return port, and the outlet is respectively connected to the second side of the first heat exchanger and the inlet of the first side of the second heat exchanger through a first pipeline and a second pipeline in parallel. The outlets of the second side of the first heat exchanger and the first side of the second heat exchanger are connected to the liquid inlet of the gas-liquid separation module. The liquid outlet is connected to the liquid cargo tank, and at least part of the gas discharged from the gas outlet is sent to the pipeline before the compression of the stage before the liquid return port and the pipeline after the first stage of compression through the second side of the second heat exchanger. The present application realizes high-pressure gas supply and medium-pressure re-liquefaction of flash steam, reduces energy consumption, and improves the re-liquefaction capacity.

Description

Technical Field

[0001] The present application relates to the technical field of flash gas treatment for liquid cargo ships, and more specifically, to a combined system for flash gas boosting and supply and re-liquefaction cycle, and a liquid cargo ship. Background Art

[0002] In a liquefied natural gas (LNG) carrier, during the storage and transportation of LNG, due to the influence of external heat, part of the LNG will evaporate into gas, that is, flash gas (Boil Off Gas, BOG). LNG flash gas is mainly composed of nitrogen and methane. Since the boiling point of nitrogen (-196°C) is much lower than that of methane (-161.5°C), the nitrogen concentration in the flash gas increases significantly. In actual flash gas, the nitrogen content generally accounts for 5% - 15% (up to 20% in extreme cases), the methane content accounts for about 85% - 95%, and there is also a trace amount of ethane. Due to the large volume of the ship's liquid cargo tank, a large amount of flash gas is generated. When the dual-fuel main engine or other gas-consuming equipment on the ship does not consume flash gas or consumes less, a re-liquefaction system needs to be configured for the carrier to meet the requirement of maintaining the pressure of the liquid cargo tank.

[0003] In the prior art, an international patent application with the publication number WO2019027063A1 discloses a re-liquefaction system for evaporation gas, which boosts the volatile flash gas to the outlet of a five-stage compressor and then liquefies all of it. Then, it returns through a reflux pipeline at the outlet of the five-stage compressor, and nitrogen is separated by reducing the pressure through a throttle valve. The separated nitrogen enters the inlet of the first-stage compressor again, and the liquid separated by throttling returns to the liquid cargo tank.

[0004] However, the gas used in this re-liquefaction solution is the high-pressure gas at the outlet of the five-stage compressor, and its pressure is very high, resulting in high energy consumption of the compressor. After all the nitrogen in the flash gas is liquefied, since liquid nitrogen will flash and vaporize significantly again during the pressure reduction process, the energy consumption of liquefied nitrogen is wasted. In addition, the gas (mainly nitrogen separated from gas-liquid) after flashing and vaporizing again during pressure reduction is introduced into the inlet of the first-stage compressor, reducing the suction capacity of the first-stage cylinder of the compressor for the flash gas in the liquid cargo tank, thereby resulting in high energy consumption of the re-liquefaction system and low re-liquefaction capacity. Summary of the Invention

[0005] The purpose of the present application is to provide a combined system for flash gas boosting and supply and re-liquefaction cycle, and a liquid cargo ship. Among them, the combined system for flash gas boosting and supply and re-liquefaction cycle realizes medium-pressure re-liquefaction of flash gas while achieving the purpose of high-pressure gas supply, significantly reduces the system energy consumption, effectively utilizes the cold energy of the separated gas after re-liquefaction, and improves the re-liquefaction capacity.

[0006] In a first aspect, a combined system of flash steam pressurization gas supply and re-liquefaction cycle is provided, which includes a first heat exchanger, a compression device, a re-liquefaction pipeline, a second heat exchanger and a gas-liquid separation module. Both the first heat exchanger and the second heat exchanger include a first side and a second side. The inlet of the first side of the first heat exchanger is used to input flash steam. The compression device includes a main inlet and a main outlet. The main inlet is connected to the outlet of the first side of the first heat exchanger. The compression device is used for multi-stage compression of the input gas, and the main outlet is used to supply a first user.

[0007] A liquid return port is provided in the pipeline before the last-stage compression in the compression device. The gas-liquid separation module includes a liquid inlet, a liquid outlet and a gas outlet. The inlet of the re-liquefaction pipeline is connected to the liquid return port. The outlet side of the re-liquefaction pipeline includes a first pipeline and a second pipeline connected in parallel. The outlet of the first pipeline is connected to the inlet of the second side of the first heat exchanger, and the outlet of the second pipeline is connected to the inlet of the first side of the second heat exchanger.

[0008] The outlet of the second side of the first heat exchanger and the outlet of the first side of the second heat exchanger are connected to the liquid inlet of the gas-liquid separation module. The liquid outlet of the gas-liquid separation module is used to be connected to a liquid cargo tank; at least part of the gas discharged from the gas outlet of the gas-liquid separation module is transported to the pipeline before the compression before the liquid return port and after the first-stage compression through the second side of the second heat exchanger.

[0009] In an implementable solution, a first liquefaction control valve is provided on the first pipeline, and a second liquefaction control valve is provided on the second pipeline.

[0010] In an implementable solution, the gas-liquid separation module includes a first gas-liquid separator, which includes an A1 liquid inlet, an A2 liquid outlet and an A3 gas outlet; the gas-liquid mixture discharged from the outlet of the second side of the first heat exchanger and the outlet of the first side of the second heat exchanger is transported to the A1 liquid inlet of the first gas-liquid separator. The A2 liquid outlet is used to be connected to the liquid cargo tank, and the A3 gas outlet is connected to the inlet of the second side of the second heat exchanger.

[0011] In an implementable solution, the gas-liquid separation module further includes a second gas-liquid separator, which includes a B1 liquid inlet, a B2 liquid outlet and a B3 gas outlet; the outlet of the second side of the first heat exchanger and the outlet of the first side of the second heat exchanger are both connected to the B1 liquid inlet. The B2 liquid outlet is connected to the A1 liquid inlet of the first gas-liquid separator, and the B3 gas outlet is connected to the pipeline before the compression before the liquid return port and after the first-stage compression through a first exhaust pipeline.

[0012] In an implementable solution, the connection position of the B3 gas outlet to the pipeline before the previous stage of compression and after the first-stage compression of the liquid return port through the first exhaust pipeline is node M; the connection position of the second-side outlet of the second heat exchanger to the pipeline before the previous stage of compression and after the first-stage compression of the liquid return port is node N; node N is located upstream of node M, and the pipeline between node N and node M includes at least one compression process.

[0013] In an implementable solution, a first throttle valve is provided on the inlet side of the A1 liquid, a second throttle valve is provided on the pipeline between the A2 liquid outlet and the liquid cargo tank; a pressure control valve is provided on the pipeline between the A3 gas outlet and the second-side inlet of the second heat exchanger.

[0014] In an implementable solution, the combined system of flash gas boosting gas supply and re-liquefaction cycle further includes a buffer tank, whose inlet is connected to a predetermined pipeline position after the first-stage compression and before the last-stage compression of the compression device, and whose outlet is used to supply a second user.

[0015] In an implementable solution, the combined system of flash gas boosting gas supply and re-liquefaction cycle further includes a buffer tank, whose inlet is connected to a predetermined pipeline position from after the first-stage compression to before the last-stage compression of the compression device, and whose outlet is used to supply a second user; the B3 gas outlet of the second gas-liquid separator is connected to the buffer tank through a second exhaust pipeline, and the second exhaust pipeline is in parallel with the first exhaust pipeline.

[0016] In an implementable solution, a first exhaust control valve is provided on the first exhaust pipeline, and a second exhaust control valve is provided on the second exhaust pipeline.

[0017] In an implementable solution, the liquid return port includes a first liquid return port and a second liquid return port, both the first liquid return port and the second liquid return port are connected to the inlet of the re-liquefaction pipeline; a first liquid return switch valve is provided at the first liquid return port, and a second liquid return switch valve is provided at the second liquid return port; wherein, there is at least one compression process between the first liquid return port and the second liquid return port.

[0018] In an implementable solution, the compression device includes a first-stage compressor, a second-stage compressor, a third-stage compressor, a fourth-stage compressor and a fifth-stage compressor connected in series in sequence.

[0019] In an implementable solution, a first cooler is connected in series to the outlet of the first-stage compressor, a second cooler is connected in series to the outlet of the second-stage compressor, a third cooler is connected in series to the outlet of the third-stage compressor, a fourth cooler is connected in series to the outlet of the fourth-stage compressor, and a fifth cooler is connected in series to the outlet of the fifth-stage compressor.

[0020] In an implementable solution, the liquid return port is arranged between the fourth-stage compressor and the fifth-stage compressor, and / or between the fourth-stage compressor and the third-stage compressor.

[0021] In an implementable solution, the gas outlet of the gas-liquid separation module is connected to one or more of the locations between the fourth-stage compressor and the third-stage compressor, between the third-stage compressor and the second-stage compressor, and between the second-stage compressor and the first-stage compressor.

[0022] In an implementable solution, the pipeline between the second-stage compressor and the third-stage compressor is connected to a buffer tank, and the outlet of the buffer tank is used for conveying to a second user.

[0023] In a second aspect, a liquid cargo ship is further provided, which includes a liquid cargo tank and further includes the aforementioned combined system of flash gas boosting and supply and re-liquefaction cycle. The flash gas outlet of the liquid cargo tank is connected to the first-side inlet of the first heat exchanger of the combined system of flash gas boosting and supply and re-liquefaction cycle, and the liquid outlet of the gas-liquid separation module of the combined system of flash gas boosting and supply and re-liquefaction cycle is connected to the liquid cargo tank.

[0024] Among them, when the combined system of flash gas boosting and supply and re-liquefaction cycle of the present application operates, the flash gas in the liquid cargo tank enters the first side of the first heat exchanger through a pipeline, and then enters the compression device through the main inlet of the compression device for multi-stage compression and multi-stage cooling. The compression device supplies the working medium after multi-stage compression to a high-pressure user (i.e., the first user) through the main outlet. When the demand of the high-pressure user decreases or there is no demand, the working medium (referred to as medium-pressure working medium) in the pipeline before the last-stage compression of the compression device enters the re-liquefaction pipeline, and a part of it is conveyed to the second side of the first heat exchanger, and the other part is conveyed to the first side of the second heat exchanger. The medium-pressure working medium on the second side of the first heat exchanger exchanges heat with the flash gas passing through the first side of the first heat exchanger. The working medium passing through the first side of the first heat exchanger absorbs heat and increases in temperature, and the working medium passing through the second side of the first heat exchanger decreases in temperature. The working medium passing through the second side of the first heat exchanger and the first side of the second heat exchanger is conveyed to the gas-liquid separation module, and the condensed liquid and part of the non-condensable gas in the working medium are separated in the gas-liquid separation module. The separated condensed liquid returns to the liquid cargo tank again to complete partial liquefaction. Among the non-condensable gases separated in the gas-liquid separation module, at least part of them passes through the second side of the second heat exchanger and exchanges heat with the medium-pressure working medium passing through the first side of the second heat exchanger. The working medium passing through the second side of the second heat exchanger absorbs heat and increases in temperature, and the working medium passing through the first side of the second heat exchanger decreases in temperature. The gas passing through the second side of the second heat exchanger and other parts of the gas discharged from the gas-liquid separation module return to the pipelines before the previous stage of compression before the liquid return port of the compression device and after the first-stage compression according to their pressure magnitudes, and participate in the cycle again with the new compressed gas.

[0025] As can be seen from the working process of the combined system of flash steam pressurization gas supply and re-liquefaction cycle of this application, compared with the prior art, the beneficial effects of this application at least include: In the combined system of flash steam pressurization gas supply and re-liquefaction cycle of this application, the compressed gas entering the re-liquefaction pipeline does not need to complete all multi-stage compression processes, especially at least does not need to perform the last-stage compression process, which can significantly reduce the compression energy consumption. In particular, for LNG, nitrogen belongs to impurities. Since nitrogen will also cause significant flashing gasification after the re-liquefaction process, part of the working medium (including methane and nitrogen) in the pipeline before the last-stage compression of the compression device is transported to the re-liquefaction pipeline, which enables a considerable part of nitrogen not to complete all multi-stage compression processes, thus significantly reducing the nitrogen compression energy consumption and further reducing the overall energy consumption during the compression process.

[0026] At the same time, the rear end of the re-liquefaction pipeline passes through the second side of the first heat exchanger, and the out-of-cabin flash steam passes through the first side of the first heat exchanger. It can not only use the out-of-cabin flash steam to cool the re-liquefied working medium to improve the re-liquefaction efficiency, but also heat up the out-of-cabin flash steam, which helps to reduce the compression energy consumption to a certain extent.

[0027] Among them, the rear end of the re-liquefaction pipeline also passes through the first side of the second heat exchanger. Since the temperature of the gas separated by the gas-liquid separation module is still relatively low, a part of it is introduced into the second side of the second heat exchanger. Then, when the re-liquefied working medium passing through the second pipeline passes through the first side of the second heat exchanger, it absorbs the cold energy of the re-flash gas on the second side of the second heat exchanger for cooling and condensation. Thus, the effective utilization of the cold energy of the re-flash gas of the gas-liquid separation module is realized. At the same time, the first pipeline and the second pipeline perform a parallel condensation process, which helps to share the condensation pressure and also helps to improve the re-liquefaction capacity.

[0028] Moreover, the gas (mainly nitrogen) separated by the subsequent gas-liquid separation module, including the part passing through the second side of the second heat exchanger, is at least transported to the pipeline before the previous stage of compression before the liquid return port of the compression device and after the first stage of compression. This is equivalent to discharging the difficult-to-condense nitrogen from the re-liquefaction process, thereby being able to reduce the actual condensation pressure during the re-liquefaction process. And because the gas separated by the gas-liquid is not directly connected to the main inlet of the compression device, it will not affect the suction capacity of the flash steam in the liquid cargo tank during the first-stage compression process, thus will not additionally increase the system power consumption, and can ensure that a sufficient amount of flash steam in the liquid cargo tank is pumped into the compression device, thereby being able to improve the re-liquefaction capacity of the system. Description of the Drawings

[0029] To more clearly illustrate the technical solutions of the embodiments of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as a limitation of the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a schematic diagram of the first combined system of flash steam pressurization gas supply and re-liquefaction cycle shown in the embodiments of the present application.

[0031] Figure 2 It is a schematic diagram of the second combined system of flash steam pressurization gas supply and re-liquefaction cycle shown in the embodiments of the present application.

[0032] Figure 3 It is a schematic diagram of the first combined system of flash steam pressurization gas supply and re-liquefaction cycle with low-pressure gas supply shown in the embodiments of the present application.

[0033] Figure 4 It is a schematic diagram of the second combined system of flash steam pressurization gas supply and re-liquefaction cycle with low-pressure gas supply shown in the embodiments of the present application.

[0034] Figure 5 It is a schematic diagram of the third combined system of flash steam pressurization gas supply and re-liquefaction cycle with low-pressure gas supply shown in the embodiments of the present application.

[0035] Figure 6 It is a schematic diagram of a combined system of flash steam pressurization gas supply and re-liquefaction cycle with multiple liquid return ports shown in the embodiments of the present application.

[0036] In the figure: 1, the first heat exchanger; 201, the main inlet; 202, the main outlet; 203, the liquid return port; 2031, the first liquid return port; 2032, the second liquid return port; 2033, the first liquid return switch valve; 2034, the second liquid return switch valve; 21, the first-stage compressor; 211, the first cooler; 22, the second-stage compressor; 221, the second cooler; 23, the third-stage compressor; 231, the third cooler; 24, the fourth-stage compressor; 241, the fourth cooler; 25, the fifth-stage compressor; 251, the fifth cooler; 3, the re-liquefaction pipeline; 31, the first pipeline; 301, the first liquefaction control valve; 32, the second pipeline; 302, the second liquefaction control valve; 4, the second heat exchanger; 5, the first gas-liquid separator; 6, the second gas-liquid separator; 61, the first exhaust pipeline; 62, the second exhaust pipeline; 7, the first throttle valve; 8, the second throttle valve; 9, the pressure control valve; 10, the first exhaust control valve; 11, the second exhaust control valve; 12, the buffer tank; 100, the gas-liquid separation module. Detailed implementation manners

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. Components of the embodiments of this application usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of this application claimed, but merely represents selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of this application without creative efforts fall within the scope of protection of this application.

[0039] As Figure 1 shown, this application first provides an embodiment of a combined system of flash gas boosting and supply and re-liquefaction cycle. The combined system of flash gas boosting and supply and re-liquefaction cycle includes a first heat exchanger 1, a compression device, a re-liquefaction pipeline 3, and a gas-liquid separation module 100.

[0040] Among them, the first heat exchanger 1 includes a first side and a second side, and its first side inlet is used to input flash gas (BOG). The compression device includes a main inlet 201 and a main outlet 202. The main inlet 201 is connected to the first side outlet of the first heat exchanger 1. The compression device is used for multi-stage compression of the input gas, and the main outlet 202 is used to supply a first user. It should be noted that the compression device generally also performs multi-stage cooling on the input gas.

[0041] A liquid return port 203 is provided in the pipeline before the last-stage compression in the compression device. The gas-liquid separation module 100 includes a liquid inlet, a liquid outlet, and a gas outlet.

[0042] The inlet of the re-liquefaction pipeline 3 is connected to the liquid return port 203. The outlet side of it includes a first pipeline 31. The outlet of the first pipeline 31 is connected to the second side inlet of the first heat exchanger 1. The second side outlet of the first heat exchanger 1 is connected to the liquid inlet of the gas-liquid separation module 100. The liquid outlet of the gas-liquid separation module 100 is used to be connected to the liquid cargo tank. The gas outlet of the gas-liquid separation module 100 is connected to the pipeline before the previous stage of compression before the liquid return port 203 and after the first stage of compression.

[0043] When the combined system of flash vapor boosting gas supply and re-liquefaction cycle in this embodiment is working, the flash vapor in the liquid cargo tank enters the first side of the first heat exchanger 1 through a pipeline, and then enters the compression device through the main inlet 201 of the compression device for multi-stage compression and multi-stage cooling. The compression device supplies the working medium after multi-stage compression to a high-pressure user (i.e., the first user) through the main outlet 202. When the demand of the high-pressure user decreases or there is no demand, the working medium (referred to as the medium-pressure working medium) in the pipeline before the last-stage compression of the compression device enters the re-liquefaction pipeline 3 and is transported to the second side of the first heat exchanger 1 to exchange heat with the flash vapor passing through the first side of the first heat exchanger 1. The working medium passing through the first side of the first heat exchanger 1 absorbs heat and increases in temperature, and the working medium passing through the second side of the first heat exchanger 1 decreases in temperature. The working medium passing through the second side of the first heat exchanger 1 is transported to the gas-liquid separation module 100, and the condensed liquid and part of the non-condensable gas in the working medium are separated in the gas-liquid separation module 100. The condensed liquid returns to the liquid cargo tank again to complete partial liquefaction, and the non-condensable gas returns to the pipeline before the previous stage of the liquid return port 203 of the compression device and after the first-stage compression according to its pressure, and participates in the cycle again with the new compressed gas.

[0044] When the high-pressure gas supply demand decreases or even there is no demand, the demand for re-liquefaction increases. From the working process, it can be seen that in the combined system of flash vapor boosting gas supply and re-liquefaction cycle in this embodiment, the compressed gas entering the re-liquefaction pipeline 3 does not need to complete all the multi-stage compression processes, especially at least does not need to perform the last-stage compression process, which can significantly reduce the compression energy consumption. In particular, for LNG, nitrogen belongs to impurities. Since nitrogen will also generate a large amount of flashing gasification after the re-liquefaction process, part of the working medium (including methane and nitrogen) in the pipeline before the last-stage compression of the compression device is transported to the re-liquefaction pipeline 3, which enables a considerable part of nitrogen not to complete all the multi-stage compression processes, thus significantly reducing the nitrogen compression energy consumption and further reducing the overall energy consumption of the compression process.

[0045] At the same time, the rear end of the re-liquefaction pipeline 3 passes through the second side of the first heat exchanger 1, and the out-of-cabin flash vapor passes through the first side of the first heat exchanger 1. Therefore, it can not only use the out-of-cabin flash vapor to cool the re-liquefied working medium to improve the re-liquefaction efficiency, but also heat up the out-of-cabin flash vapor, which helps to reduce the compression energy consumption to a certain extent.

[0046] Moreover, the gas (mainly nitrogen) separated by the subsequent gas-liquid separation module 100 is transported to the pipelines before the pre-stage compression and after the first-stage compression of the liquid return port 203 of the compression device. This is equivalent to discharging the hardly condensable nitrogen from the re-liquefaction process, thereby reducing the actual condensation pressure during the re-liquefaction process. Also, since the gas separated from the gas-liquid is not directly connected to the main inlet of the compression device, it does not affect the suction capacity of the first-stage compression process for the flash gas in the liquid cargo tank, thus not additionally increasing the system power consumption, and ensuring that a sufficient amount of flash gas in the liquid cargo tank is pumped into the compression device, thereby enhancing the re-liquefaction capacity of the system.

[0047] In summary, the flash gas pressurization gas supply and re-liquefaction cycle combined system of the present application realizes the medium-pressure re-liquefaction of the flash gas while achieving the purpose of high-pressure gas supply, significantly reducing the system energy consumption and enhancing the re-liquefaction capacity.

[0048] In some embodiments, as Figure 2 shown, the flash gas pressurization gas supply and re-liquefaction cycle combined system may further include a second heat exchanger 4, and the second heat exchanger 4 includes a first side and a second side. The outlet side of the re-liquefaction pipeline 3 further includes a second pipeline 32. The outlet of the second pipeline 32 is connected to the inlet of the first side of the second heat exchanger 4, and the second pipeline 32 is in parallel with the first pipeline 31. The outlet of the first side of the second heat exchanger 4 is connected to the liquid inlet of the gas-liquid separation module 100, and at least part of the gas discharged from the gas inlet of the gas-liquid separation module 100 is transported to the pipelines before the pre-stage compression and after the first-stage compression of the liquid return port 203 through the second side of the second heat exchanger 4.

[0049] Since the temperature of the gas separated by the gas-liquid separation module 100 is still relatively low, part of it is introduced into the second side of the second heat exchanger 4. Then, the re-liquefied working medium passing through the second pipeline 32 absorbs the cold energy of the re-flashed gas on the second side of the second heat exchanger 4 when passing through the first side of the second heat exchanger 4 for cooling and condensation. Thus, the effective utilization of the cold energy of the re-flashed gas of the gas-liquid separation module 100 is realized. At the same time, the parallel condensation process of the first pipeline 31 and the second pipeline 32 helps to share the condensation pressure and also helps to enhance the re-liquefaction capacity.

[0050] In some embodiments, as Figure 2 shown, a first liquefaction control valve 301 may be provided on the first pipeline 31, and a second liquefaction control valve 302 may be provided on the second pipeline 32. By controlling the on-off of the first liquefaction control valve 301 and the second liquefaction control valve 302, the re-liquefaction of the first pipeline 31 and / or the second pipeline 32 can be selectively used.

[0051] Preferably, in this embodiment, the first liquefaction control valve 301 and the second liquefaction control valve 302 can also be configured to adjust the flow rate ratio of the refrigerant entering the first pipeline 31 and the second pipeline 32. Moreover, temperature measurement, flow measurement, pressure measurement and other devices can be arranged on the outlet pipeline of the liquid cargo tank and the inlet pipeline on the second side of the second heat exchanger 4. According to the temperature difference, flow difference, etc. of the flashed vapor out of the tank and the gas after re-flashing, the opening degrees of the first liquefaction control valve 301 and the second liquefaction control valve 302 are adjusted, so as to control the flow rate ratio of the refrigerant entering the first pipeline 31 and the second pipeline 32, that is, to control the refrigerant ratio passing through the second side of the first heat exchanger 1 and the first side of the second heat exchanger 4, thereby making full use of the cold energy of the flashed vapor out of the tank and the gas after re-flashing and realizing a more efficient condensation and liquefaction process.

[0052] It should be noted that when the system is just started, since the gas-liquid separation module 100 is still at room temperature, there is no cold source on the second side of the second heat exchanger 4 at this time. At this time, the second liquefaction control valve 302 on the second pipeline 32 can be controlled to remain closed, so that all the compressed refrigerant flowing back through the liquid return port 203 only passes through the second side of the first heat exchanger 1. After the gas-liquid separation process in the gas-liquid separation module 100 has officially started and its internal temperature has also decreased, the second liquefaction control valve 302 can be opened again.

[0053] In some embodiments, such as Figure 1 and Figure 2 As shown, the gas-liquid separation module 100 may include a first gas-liquid separator 5, which includes an A1 liquid inlet, an A2 liquid outlet, and an A3 gas outlet. The gas-liquid mixture discharged from the outlet on the second side of the first heat exchanger 1 and the outlet on the first side of the second heat exchanger 4 is transported to the A1 liquid inlet of the first gas-liquid separator 5. The A2 liquid outlet is used to connect to the liquid cargo tank, the A3 gas outlet is connected to the inlet on the second side of the second heat exchanger 4, and the outlet on the second side of the second heat exchanger 4 is connected to the pipeline before the pre-stage compression and after the first-stage compression of the liquid return port 203.

[0054] In some embodiments, such as Figure 1 and Figure 2 As shown, the gas-liquid separation module 100 may further include a second gas-liquid separator 6, which includes a B1 liquid inlet, a B2 liquid outlet, and a B3 gas outlet. The outlet on the second side of the first heat exchanger 1 and the outlet on the first side of the second heat exchanger 4 are both connected to the B1 liquid inlet. The B2 liquid outlet is connected to the A1 liquid inlet of the first gas-liquid separator 5, and the B3 gas outlet is connected to the pipeline before the pre-stage compression and after the first-stage compression of the liquid return port 203 through the first exhaust pipeline 61.

[0055] In some embodiments, such as Figure 1 and Figure 2As shown, a first throttle valve 7 may be provided on the A1 liquid inlet side, and a second throttle valve 8 is generally provided on the pipeline between the A2 liquid outlet and the liquid cargo tank. The B2 liquid outlet of the second gas-liquid separator 6 enters the first gas-liquid separator 5 after being adjusted by the first throttle valve 7. The A2 liquid outlet of the first gas-liquid separator 5 returns to the liquid cargo tank after being adjusted by the second throttle valve 8.

[0056] In some embodiments, as Figure 1 and Figure 2 shown, a pressure control valve 9 may be provided on the pipeline between the A3 gas outlet and the second-side inlet of the second heat exchanger 4 for regulating the pressure inside the first gas-liquid separator 5. Among them, as Figure 1 shown, the low-temperature flashing gas discharged from the A3 gas outlet of the first gas-liquid separator 5 can be directly introduced into the pipeline of the compression device for cooling the exhaust gas after the compressor. Or, as Figure 2 shown, after being discharged through the pressure control valve 9, it is introduced into the pipeline of the compression device after absorbing heat and increasing the temperature on the second side of the second heat exchanger 4.

[0057] It should be noted that the second gas-liquid separator 6 and the first gas-liquid separator 5 are used in series to separate the gas-liquid mixture twice. The second gas-liquid separator 6 preliminarily separates the condensed gas-liquid mixture, separating most of the liquid from nitrogen; the first gas-liquid separator 5 further separates the liquid discharged from the second gas-liquid separator 6 to further remove the flashing gas (mainly nitrogen) after the pressure reduction by the first throttle valve 7, thereby effectively improving the separation efficiency and quality of the entire system.

[0058] In addition, the series arrangement of the two gas-liquid separators helps to better control the pressure and liquid level of the system. The second gas-liquid separator 6 can maintain a relatively stable pressure environment, and the first gas-liquid separator 5 can further adjust and stabilize the pressure inside the system to prevent excessive pressure fluctuations from causing adverse effects on the equipment. At the same time, by separately monitoring and controlling the liquid levels of the two separators, the reflux and storage of the liquid can be managed more precisely.

[0059] In some embodiments, as Figure 1 and Figure 2 shown, the B3 gas outlet is connected to the pipeline at the position before the pre-stage compression and after the first-stage compression of the return liquid port 203 through the first exhaust pipeline 61 at node M, and the second-side outlet of the second heat exchanger 4 is connected to the pipeline at the position before the pre-stage compression and after the first-stage compression of the return liquid port 203 at node N. Among them, node N is located upstream of node M, and the pipeline between node N and node M includes at least one compression process.

[0060] The gas pressures and temperatures discharged from the second gas-liquid separator 6 and the first gas-liquid separator 5 are different. Therefore, by setting different connection positions to the compression device, the flashed gas can be matched to the gas pressure after compression at the corresponding level. When the flashed gas returns to the pipeline of the compression device, the disturbance to the compression process can be reduced, making the working process of the compression device more stable and efficient.

[0061] In some embodiments, as Figure 3 shown, the flashed gas pressurization and supply and re-liquefaction cycle combined system may further include a buffer tank 12, whose inlet is connected to a predetermined pipeline position after the first-stage compression and before the last-stage compression of the compression device, and whose outlet is used to supply a second user. The compressed gas equivalent to the flashed gas is supplied to a low-pressure user, thereby realizing the combined operation of high-pressure and low-pressure gas supply and medium-pressure re-liquefaction cycle.

[0062] In some embodiments, as Figure 2 and Figure 3 shown, the gas discharged from the B3 gas outlet of the second gas-liquid separator 6 can be directly transported to the pipeline before the liquid return port 203 only through the first exhaust pipeline 61. And a first exhaust control valve 10 can be provided on the first exhaust pipeline 61. When the liquid level in the second gas-liquid separator 6 is low and the gas volume is large, the first exhaust control valve 10 can be opened to discharge the gas at the top of the second gas-liquid separator 6 to the predetermined pipeline before the liquid return port 203.

[0063] In some embodiments, as Figure 4 shown, the gas discharged from the B3 gas outlet of the second gas-liquid separator 6 can be directly transported to the buffer tank 12 only through the second exhaust pipeline 62. And a second exhaust control valve 11 can be provided on the second exhaust pipeline 62. When the liquid level in the second gas-liquid separator 6 is low and the gas volume is large, the first exhaust control valve 10 can be opened to discharge the gas at the top of the second gas-liquid separator 6 into the buffer tank 12, further reducing the condensation pressure, and thus realizing the stable operation of the system.

[0064] In some preferred embodiments, as Figure 5 shown, the rear end of the B3 gas outlet of the second gas-liquid separator 6 includes both the first exhaust pipeline 61 and the second exhaust pipeline 62 at the same time. It is transported to the pipeline before the liquid return port 203 through the first exhaust pipeline 61 and to the buffer tank 12 through the second exhaust pipeline 62. The second exhaust pipeline 62 is in parallel with the first exhaust pipeline 61, thereby realizing two circulation paths for the flashed gas, further reducing energy consumption to a certain extent, and realizing the stable operation of the system. And a first exhaust control valve 10 is provided on the first exhaust pipeline 61, and a second exhaust control valve 11 is provided on the second exhaust pipeline 62, whereby the on-off of the second exhaust pipeline 62 and the first exhaust pipeline 61 can be selectively controlled.

[0065] In some embodiments, as Figure 6 shown, the liquid return port 203 may include a first liquid return port 2031 and a second liquid return port 2032, and both the first liquid return port 2031 and the second liquid return port 2032 are connected to the inlet of the re-liquefaction pipeline 3. A first liquid return switch valve 2033 is provided at the first liquid return port 2031, and a second liquid return switch valve 2034 is provided at the second liquid return port 2032. Among them, there is at least one compression process between the first liquid return port 2031 and the second liquid return port 2032. This setting can enable more choices for the pressure range of the medium-pressure working fluid entering the re-liquefaction pipeline 3, thereby further reducing energy consumption and enhancing the re-liquefaction capacity.

[0066] Furthermore, in some embodiments, as Figures 1 to 6 shown, the compression device may include a first-stage compressor 21, a second-stage compressor 22, a third-stage compressor 23, a fourth-stage compressor 24, and a fifth-stage compressor 25 connected in series in sequence. The flash vapor after five-stage compression can meet the needs of high-pressure users on the ship.

[0067] In some embodiments, as Figures 1 to 6 shown, a first cooler 211 is connected in series at the outlet of the first-stage compressor 21, a second cooler 221 is connected in series at the outlet of the second-stage compressor 22, a third cooler 231 is connected in series at the outlet of the third-stage compressor 23, a fourth cooler 241 is connected in series at the outlet of the fourth-stage compressor 24, and a fifth cooler 251 is connected in series at the outlet of the fifth-stage compressor 25. Each cooler is used to cool the gas discharged after the compression and temperature rise of each stage of the compressor. The cooling medium of each cooler can be seawater or fresh water on the ship. Among them, two groups in parallel can be provided for the first-stage compressor 21, which can be used alone or simultaneously to increase the suction capacity.

[0068] In some embodiments, as Figure 6 shown, the liquid return port 203 may be provided between the fourth-stage compressor 24 and the fifth-stage compressor 25, and / or between the fourth-stage compressor 24 and the third-stage compressor 23.

[0069] In some embodiments, as Figure 6 shown, the gas outlet of the gas-liquid separation module 100 (i.e., the gas discharge ports of the first gas-liquid separator 5 and the second gas-liquid separator 6) is connected to one or more of the positions between the fourth-stage compressor 24 and the third-stage compressor 23, between the third-stage compressor 23 and the second-stage compressor 22, and between the second-stage compressor 22 and the first-stage compressor 21 (such as points M and N in the figure).

[0070] In some embodiments, as Figure 6 shown, the pipeline between the second-stage compressor 22 and the third-stage compressor 23 is connected to a buffer tank 12, and the outlet of the buffer tank 12 is used for transportation to the second user (i.e., the low-pressure user).

[0071] An embodiment of the present application further provides a liquid cargo ship, which includes a liquid cargo tank (not shown in the figure), and further includes the above-mentioned combined system of flash gas boosting and supply and re-liquefaction cycle. The flash gas outlet of the liquid cargo tank is connected to the first-side inlet of the first heat exchanger 1 of the combined system of flash gas boosting and supply and re-liquefaction cycle, and the liquid outlet of the gas-liquid separation module 100 of the combined system of flash gas boosting and supply and re-liquefaction cycle is connected to the liquid cargo tank.

[0072] The above are only some preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A combined system of flash steam pressurization gas supply and re-liquefaction cycle, characterized in that, It includes a first heat exchanger (1), a compression device, a reliquefaction pipeline (3), a second heat exchanger (4) and a gas-liquid separation module (100); Both the first heat exchanger (1) and the second heat exchanger (4) include a first side and a second side. The inlet of the first side of the first heat exchanger (1) is used to input flash gas; The compression device includes a main inlet (201) and a main outlet (202). The main inlet (201) is connected to the outlet of the first side of the first heat exchanger (1). The compression device is used to perform multi-stage compression on the input gas, and the main outlet (202) is used to supply a first user; A liquid return port (203) is provided in the pipeline before the last-stage compression in the compression device; The gas-liquid separation module (100) includes a liquid inlet, a liquid outlet and a gas outlet; The inlet of the reliquefaction pipeline (3) is connected to the liquid return port (203). The outlet side of it includes a first pipeline (31) and a second pipeline (32) connected in parallel. The outlet of the first pipeline (31) is connected to the inlet of the second side of the first heat exchanger (1), and the outlet of the second pipeline (32) is connected to the inlet of the first side of the second heat exchanger (4); The outlet of the second side of the first heat exchanger (1) and the outlet of the first side of the second heat exchanger (4) are connected to the liquid inlet of the gas-liquid separation module (100). The liquid outlet of the gas-liquid separation module (100) is used to be connected to a liquid cargo tank; At least part of the gas discharged from the gas outlet of the gas-liquid separation module (100) is transported to the pipeline before the previous stage of compression and after the first stage of compression of the liquid return port (203) through the second side of the second heat exchanger (4).

2. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 1, characterized in that, A first liquefaction control valve (301) is provided on the first pipeline (31), and a second liquefaction control valve (302) is provided on the second pipeline (32).

3. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 1, wherein The gas-liquid separation module (100) includes a first gas-liquid separator (5), which includes an A1 liquid inlet, an A2 liquid outlet and an A3 gas outlet; The gas-liquid mixture discharged from the outlet of the second side of the first heat exchanger (1) and the outlet of the first side of the second heat exchanger (4) is transported to the A1 liquid inlet of the first gas-liquid separator (5). The A2 liquid outlet is used to be connected to a liquid cargo tank, and the A3 gas outlet is connected to the inlet of the second side of the second heat exchanger (4).

4. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 3, characterized in that The gas-liquid separation module (100) further includes a second gas-liquid separator (6), which includes a B1 liquid inlet, a B2 liquid outlet and a B3 gas outlet; Both the outlet of the second side of the first heat exchanger (1) and the outlet of the first side of the second heat exchanger (4) are connected to the B1 liquid inlet. The B2 liquid outlet is connected to the A1 liquid inlet of the first gas-liquid separator (5), and the B3 gas outlet is connected to the pipeline before the previous stage of compression and after the first stage of compression of the liquid return port (203) through a first exhaust pipeline (61).

5. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 4, wherein The connection position of the B3 gas outlet and the pipeline before the previous stage of compression and after the first stage of compression of the liquid return port (203) through the first exhaust pipeline (61) is node M; The connection position between the second-side outlet of the second heat exchanger (4) and the pipeline before the previous-stage compression and after the first-stage compression of the liquid return port (203) is node N; The node N is located upstream of the node M, and at least one compression process is included in the pipeline between the node N and the node M.

6. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 5, wherein A first throttle valve (7) is provided on the A1 liquid inlet side, and a second throttle valve (8) is provided on the pipeline between the A2 liquid outlet and the liquid cargo tank; A pressure control valve (9) is provided on the pipeline between the A3 gas outlet and the second-side inlet of the second heat exchanger (4).

7. The combined system of flash steam pressurized gas supply and re-liquefaction cycle according to claim 1, characterized in that, It further includes a buffer tank (12), whose inlet is connected to a predetermined pipeline position after the first-stage compression and before the last-stage compression of the compression device, and whose outlet is used to supply a second user.

8. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 6, wherein It further includes a buffer tank (12), whose inlet is connected to a predetermined pipeline position from after the first-stage compression to before the last-stage compression of the compression device, and whose outlet is used to supply a second user; The B3 gas outlet of the second gas-liquid separator (6) is connected to the buffer tank (12) through a second exhaust pipeline (62), and the second exhaust pipeline (62) is in parallel with the first exhaust pipeline (61).

9. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 8, characterized in that, A first exhaust control valve (10) is provided on the first exhaust pipeline (61), and a second exhaust control valve (11) is provided on the second exhaust pipeline (62).

10. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to any one of claims 1 to 9, characterized in that, The liquid return port (203) includes a first liquid return port (2031) and a second liquid return port (2032), and both the first liquid return port (2031) and the second liquid return port (2032) are connected to the inlet of the re-liquefaction pipeline (3); A first liquid return switch valve (2033) is provided at the first liquid return port (2031), and a second liquid return switch valve (2034) is provided at the second liquid return port (2032); Wherein, at least one compression process is included between the first liquid return port (2031) and the second liquid return port (2032).

11. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 1, wherein, The compression device includes a first-stage compressor (21), a second-stage compressor (22), a third-stage compressor (23), a fourth-stage compressor (24), and a fifth-stage compressor (25) connected in series in sequence.

12. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 11, characterized in that, The outlet of the first-stage compressor (21) is connected in series with a first cooler (211), the outlet of the second-stage compressor (22) is connected in series with a second cooler (221), the outlet of the third-stage compressor (23) is connected in series with a third cooler (231), the outlet of the fourth-stage compressor (24) is connected in series with a fourth cooler (241), and the outlet of the fifth-stage compressor (25) is connected in series with a fifth cooler (251).

13. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 11, wherein The liquid return port (203) is provided between the fourth-stage compressor (24) and the fifth-stage compressor (25), and / or between the fourth-stage compressor (24) and the third-stage compressor (23).

14. The combined system of flash steam pressurization gas supply and re-liquefaction cycle according to claim 13, wherein, The gas outlet of the gas-liquid separation module (100) is connected to one or more of the positions between the fourth-stage compressor (24) and the third-stage compressor (23), between the third-stage compressor (23) and the second-stage compressor (22), and between the second-stage compressor (22) and the first-stage compressor (21).

15. The combined system of flash steam pressurized gas supply and re-liquefaction cycle according to claim 11, wherein, The pipeline between the secondary compressor (22) and the tertiary compressor (23) is connected to a buffer tank (12), and the outlet of the buffer tank (12) is used for conveying to a second user.

16. A liquid cargo ship, including a liquid cargo tank, characterized in that, It further includes the flash gas pressurization gas supply and re-liquefaction cycle combined system according to any one of claims 1 to 15. The flash gas outlet of the liquid cargo tank is connected to the first-side inlet of the first heat exchanger (1) of the flash gas pressurization gas supply and re-liquefaction cycle combined system, and the liquid outlet of the gas-liquid separation module (100) of the flash gas pressurization gas supply and re-liquefaction cycle combined system is connected to the liquid cargo tank.

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