Boil-off gas reliquefaction system and method
By using a combination of low-temperature coils and exhaust pipes in the reliquefaction system of the liquefied gas transporter, the system performance deterioration and complexity increase when the low-boiling goods are separated from the non-condensing gas are solved, and the effective separation of low-boiling goods and the improvement of system economy is achieved.
Patent Information
- Application Number
- CN202510393990.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-31
- Publication Date
- 2025-07-11
AI Technical Summary
When the existing liquefied gas transport reliquefaction system is separated from the non-condensable gas, the system performance will deteriorate or the complexity will increase, resulting in the problem of increased costs.
A combined system of cargo tank, first compression device, condenser, liquid collector, exhaust pipe line and low-temperature coil is adopted to reduce the temperature in the liquid collector through the low-temperature coil, separate low-boiling goods, and timely discharge evaporated gas using the exhaust pipe line to control the system's condensation pressure.
Without reducing system performance and complexity, reduce waste of low-boiling point goods, reduce the content of low-boiling point goods during exhaust, and improve the economics and working performance of the system.
Smart Images
Figure CN120288188A_ABST
Abstract
Description
Technical Field
[0001] The present application relates to the technical field of ship design, and in particular, to a boil-off gas re-liquefaction system and method. Background Art
[0002] A liquefied gas carrier is a ship specially designed to transport liquefied gases or liquid fuels, such as liquefied petroleum gas, liquefied natural gas, liquid ammonia, etc. The liquefied goods transported by the liquefied gas carrier are usually gaseous at normal temperature, and the intrusion of heat during transportation will cause some of the liquefied goods to evaporate, generating boil-off gas (BOG). During long-distance transportation, a large amount of BOG will be generated from the transported liquefied goods, and a re-liquefaction system needs to be configured on the liquefied gas carrier to condense and liquefy the generated boil-off gas and then return it to the liquid cargo tank. Due to the limited space on the ship, the re-liquefaction system of a large liquefied gas carrier generally adopts an open re-liquefaction system with the transported liquefied goods as the circulating working medium, and the circulating condenser uses seawater as the circulating medium. The condensation pressure of the re-liquefaction temperature of different goods is determined by the seawater temperature.
[0003] The liquefied goods transported by the liquefied gas carrier contain non-condensable gases. For example, liquefied petroleum gas contains non-condensable gases with low boiling points such as methane. During the loading and unloading of the liquefied goods, the liquid cargo tank needs to be inerted and replaced, so the liquefied goods will also contain non-condensable gases such as nitrogen. In addition, during the loading and unloading of the liquefied goods, impurity gases and other non-condensable gases may also be mixed in. The non-condensable gases have a low boiling point and are difficult to condense into a liquid state in the condenser, so they cannot be returned to the liquid cargo tank. When the re-liquefaction system operates, the non-condensable gases will accumulate in the liquid collector, resulting in an increase in the condensation pressure. The increase in the condensation pressure will cause an increase in the power consumption of the compressor, and further lead to a deterioration in the performance of the re-liquefaction system.
[0004] To maintain the re-liquefaction system in an operating state under the optimal condensation pressure, it is necessary to regularly discharge non-condensable gases. However, some gaseous goods will inevitably be discharged during the discharge process, resulting in a waste of the transported liquefied gas and an exacerbation of the greenhouse effect. To solve the problem of the discharge of gaseous goods, it is necessary to separate the low-boiling-point goods from the non-condensable gases. In the prior art, generally, the separation of low-boiling-point goods from non-condensable gases is carried out by increasing the condensation pressure or by leading the non-condensable gases to a separate pressure vessel for secondary cooling. However, increasing the condensation pressure will cause an increase in the power consumption of the compressor and a deterioration in the system performance. Although the secondary cooling method can achieve the separation effect of low-boiling-point goods and non-condensable gases, it will increase the system complexity and production cost. Summary of the Invention
[0005] The purpose of the present application is to provide a boil-off gas re-liquefaction system and method, which are used to solve the problems that in the prior art, the system performance deteriorates when separating low-boiling point goods from non-condensable gases in the re-liquefaction system, or the system complexity increases, resulting in increased costs.
[0006] To achieve the above and other related purposes, the present application provides a boil-off gas re-liquefaction system, including a liquid cargo tank, a first compression device, a condenser, a liquid collector, an exhaust pipe and a cryogenic coil;
[0007] The liquid cargo tank is connected to the first compression device, the condenser and the liquid collector in sequence through pipelines. The liquid collector has a first inlet, a first outlet and a second outlet. The exhaust pipe is connected to the first outlet, and the second outlet is connected to the liquid cargo tank through a pipeline. The cryogenic coil is located in the liquid collector and is used to lower the temperature in the liquid collector;
[0008] The liquid cargo tank is used to store liquefied goods. Evaporation gas is generated by the liquefied goods in the liquid cargo tank. After being compressed by the first compression device, the evaporation gas enters the condenser for cooling to form condensate. The condensate and the remaining evaporation gas flow into the liquid collector through the first inlet. The exhaust pipe can discharge the evaporation gas in the liquid collector, and the condensate in the liquid collector flows back into the liquid cargo tank through the second outlet.
[0009] Optionally, the cryogenic coil is located at the bottom of the liquid collector. The outlet of the cryogenic coil is connected to the pipeline between the liquid cargo tank and the first compression device through a pipeline, and the inlet of the cryogenic coil is connected to the second outlet through a pipeline.
[0010] Optionally, the boil-off gas re-liquefaction system further includes an intercooler. The outlet of the cryogenic coil is connected to the inlet of the intercooler through a pipeline, and the outlet of the intercooler is connected to the pipeline between the liquid cargo tank and the first compression device.
[0011] Optionally, the boil-off gas re-liquefaction system further includes:
[0012] A first flow regulating valve, located between the cryogenic coil and the intercooler, for controlling the flow between the cryogenic coil and the intercooler;
[0013] A second flow regulating valve, for controlling the flow at the outlet of the intercooler.
[0014] Optionally, the boil-off gas re-liquefaction system further includes a second compression device. The second compression device is located between the first compression device and the liquid cargo tank. The outlet of the cryogenic coil is connected to the pipeline between the first compression device and the second compression device through a pipeline.
[0015] Optionally, there is a diversion node between the second outlet and the inlet of the low-temperature coil. At the diversion node, part of the condensate flowing out from the second outlet flows to the low-temperature coil, and the other part flows to the liquid cargo tank;
[0016] The boil-off gas re-liquefaction system further includes a first throttle valve, which is located between the diversion node and the inlet of the low-temperature coil.
[0017] Optionally, the boil-off gas re-liquefaction system further includes a second throttle valve, which is located between the second outlet and the liquid cargo tank. At least part of the condensate flowing out from the second outlet flows back into the liquid cargo tank through the second throttle valve.
[0018] Optionally, the boil-off gas re-liquefaction system further includes a subcooling heat exchanger, which is located between the second outlet and the second throttle valve. At least part of the condensate flowing out from the second outlet is subcooled by the subcooling heat exchanger and then flows back into the liquid cargo tank through the second throttle valve.
[0019] Optionally, the boil-off gas re-liquefaction system further includes an exhaust valve, which is connected to the exhaust pipe for controlling the flow rate of the exhaust pipe.
[0020] This application also provides a method for re-liquefying boil-off gas, which uses any of the boil-off gas re-liquefaction systems in the foregoing embodiments to re-liquefy the boil-off gas generated by liquefied goods, and includes the following steps:
[0021] Start the boil-off gas re-liquefaction system;
[0022] Obtain the pressure in the liquid collection device;
[0023] When the pressure in the liquid collection device increases to the first pressure threshold, make the low-temperature coil work normally;
[0024] When it is detected that the pressure in the liquid collection device is greater than the second pressure threshold, and when it is detected again that the pressure in the liquid collection device is greater than the second pressure threshold after the first time interval, discharge the boil-off gas in the liquid collection device through the exhaust pipe until the pressure in the liquid collection device is less than the third pressure threshold.
[0025] The boil-off gas re-liquefaction system and method provided by this application have at least the following beneficial effects:
[0026] In the boil-off gas re-liquefaction system of the present application, when the condensation pressure of the system is too high, the boil-off gas in the accumulator is discharged in time through the exhaust pipeline to reduce the condensation pressure of the system and improve the working performance of the system. A low-temperature coil is arranged in the accumulator, which can reduce the temperature in the accumulator, thereby condensing and separating the low-boiling-point goods in the boil-off gas, reducing the pressure in the accumulator, slowing down the vaporization of the low-boiling-point goods in the condensate into boil-off gas, and further reducing the content of low-boiling-point goods in the boil-off gas discharged from the exhaust pipeline, reducing the waste of liquefied goods.
[0027] Therefore, the boil-off gas re-liquefaction system of the present application can effectively reduce the content of low-boiling-point goods in the discharged non-condensable gas without reducing the working performance of the system and without increasing the complexity of the system, reduce the waste of goods during the exhaust process, and save the system cost. Moreover, the reduction of the accumulator temperature separates the low-boiling-point goods in the boil-off gas, which can reduce the number of valve openings for system exhaust, indirectly reduce the exhaust pressure of the compressor, and improve the economy of the system. The boil-off gas re-liquefaction method of the present application uses the above-mentioned boil-off gas re-liquefaction system for re-liquefying boil-off gas, so it also has the above-mentioned beneficial effects. BRIEF DESCRIPTION OF THE DRAWINGS
[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the embodiments. It should be understood that the following drawings only show some embodiments of the present application, so they should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other related drawings can also be obtained based on these drawings.
[0029] Figure 1 It shows a schematic diagram of the principle of a boil-off gas re-liquefaction system provided by Embodiment 1 of the present application.
[0030] Figure 2 It shows a schematic diagram of the principle of another boil-off gas re-liquefaction system provided by Embodiment 1 of the present application.
[0031] Figure 3 It shows a schematic flowchart of a boil-off gas re-liquefaction method provided by Embodiment 2 of the present application.
[0032] Schematic illustration of reference numerals:
[0033] 11. Liquid cargo tank; 121. First compression device; 122. Second compression device; 13. Condenser; 14. Liquid collector; 141. First inlet; 142. First outlet; 143. Second outlet; 144. First opening; 145. Second opening; 15. Low-temperature coil; 151. First throttle valve; 16. Exhaust pipeline; 161. Exhaust valve; 17. Intercooler; 171. First flow regulating valve; 172. Second flow regulating valve; 18. Subcooling heat exchanger; 181. Second throttle valve. Detailed implementation manners
[0034] To make the technical objectives, technical solutions and technical effects of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of this application, rather than all of the embodiments. Usually, the components of the embodiments of this application described and shown in the drawings here can be arranged and designed in various different configurations.
[0035] Therefore, the following detailed description of the embodiments of this application is not intended to limit the scope of this application that is claimed, but merely represents the selected embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without making creative efforts fall within the scope of protection of this application. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.
[0036] In the description of this application, it should be noted that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to this application.
[0037] In the description of this application, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection or a detachable connection. In addition, the description with reference to terms such as "one embodiment", "some embodiments", "schematic embodiments", "examples", "specific examples" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiments or examples are included in at least one embodiment or example of this application. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples.
[0038] Example 1
[0039] This embodiment provides a boil-off gas re-liquefaction system, which is used to solve the problems in the prior art that when the re-liquefaction system of a ship separates low-boiling point goods from non-condensable gases, the performance of the re-liquefaction system deteriorates, or the system complexity increases, resulting in increased costs. The boil-off gas re-liquefaction system of this embodiment includes a liquid cargo tank 11, a first compression device 121, a condenser 13, a liquid collector 14, an exhaust pipe 16, and a cryogenic coil 15.
[0040] Refer to Figure 1 , the liquid cargo tank 11 is sequentially connected to the first compression device 121, the condenser 13, and the liquid collector 14 through pipelines. The liquid collector 14 has a first inlet 141, a first outlet 142, and a second outlet 143. The exhaust pipe 16 is connected to the first outlet 142, and the second outlet 143 is connected to the liquid cargo tank 11 through a pipeline. The cryogenic coil 15 is located in the liquid collector 14 and is used to reduce the temperature in the liquid collector 14. The liquid cargo tank 11 is used to store liquefied goods. Evaporation gas is generated in the liquid cargo tank 11 for the liquefied goods. The evaporation gas is compressed by the first compressor and then enters the condenser 13 to be cooled to form condensate. The condensate and the remaining uncondensed evaporation gas in the condenser 13 flow into the liquid collector 14 through the first inlet 141. The exhaust pipe 16 is used to discharge the evaporation gas in the liquid collector 14. The condensate in the liquid collector 14 flows back into the liquid cargo tank 11 through the second outlet 143.
[0041] In this embodiment, the evaporation gas is a mixed gas other than the liquefied goods stored in the liquid cargo tank 11. During the transportation of the liquefied goods, the liquefied goods in the liquid cargo tank 11 will also be vaporized to generate evaporation gas due to the influence of the storage environment. The evaporation gas is transported to the first compression device 121 through a pipeline. After being compressed by the first compression device 121, it forms high-temperature and high-pressure evaporation gas. The high-temperature and high-pressure evaporation gas is cooled by the condenser 13 to form condensate. Optionally, the circulating medium of the condenser 13 can be seawater, for example. The condensate generated by the condenser 13 and the remaining uncondensed evaporation gas flowing out of the condenser 13 enter the liquid collector 14 through the first inlet 141. The liquid collector 14 stores condensate and uncondensed evaporation gas. The condensate in the liquid collector 14 may also be vaporized to generate evaporation gas due to the influence of the environment. The evaporation gas in the liquid collector 14 is discharged from the boil-off gas re-liquefaction system through the exhaust pipe 16, and the condensate flows back into the liquid cargo tank 11 through the second outlet 143.
[0042] In the evaporative gas re-liquefaction system provided in this embodiment, when the condensation pressure in the system is too high, the evaporative gas in the accumulator 14 can be discharged in time through the exhaust pipeline 16 to reduce the condensation pressure of the system and improve the working performance of the system; the accumulator 14 is used to collect the condensate formed after the evaporative gas is condensed by the condenser 13 and the remaining uncondensed evaporative gas in the pipeline, and provide a place for the separation of non-condensable gases and low-boiling-point goods in the evaporative gas; a low-temperature coil 15 is arranged in the accumulator 14, and the low-temperature coil 15 can reduce the temperature in the accumulator 14. Through cooling and condensation, the low-boiling-point goods in the evaporative gas can be separated, and the process of the low-boiling-point goods in the condensate gasifying into evaporative gas can be slowed down. Furthermore, the content of low-boiling-point goods in the evaporative gas discharged from the exhaust pipeline 16 can be reduced, and the waste of liquefied goods can be reduced.
[0043] Therefore, the evaporative gas re-liquefaction system of this embodiment can effectively reduce the content of low-boiling-point goods in the discharged non-condensable gases without reducing the working performance of the system and without increasing the complexity of the system, reduce the waste of goods during the exhaust process, reduce the enterprise cost. Moreover, when the temperature of the accumulator 14 decreases, the low-boiling-point goods in the evaporative gas can be separated, the number of valve openings for system exhaust is reduced, the exhaust pressure of the compressor is indirectly reduced, and the economy of the system is improved.
[0044] In this embodiment, the evaporative gas re-liquefaction system may further include an intercooler 17. The inlet of the low-temperature coil 15 is connected to the second outlet 143 of the accumulator 14 through a pipeline, the outlet of the low-temperature coil 15 is connected to the inlet of the intercooler 17 through a pipeline, and the outlet of the intercooler 17 is connected to the pipeline between the liquid cargo tank 11 and the first compression device 121. Optionally, the accumulator 14 further has a first opening 144 and a second opening 145. The inlet of the low-temperature coil 15 is connected to the second outlet 143 through the first opening 144 by a pipeline, and the outlet of the low-temperature coil 15 is connected to the inlet of the intercooler 17 through the second opening 145 by a pipeline.
[0045] In an alternative embodiment, the first opening 144 and the second opening 145 are located in the area of the side wall of the accumulator 14 close to its bottom, the first inlet 141 is located in the area of the side wall of the accumulator 14 close to its top, the first outlet 142 is located at the top of the accumulator 14, and the second outlet 143 is located at the bottom of the accumulator 14.
[0046] Part of the condensed liquid flowing out of the second outlet 143 of the liquid collector 14 enters the low-temperature coil 15 to provide a working medium for the low-temperature coil 15. Thus, the low-temperature coil 15 can operate normally without the intervention of an external working medium, effectively reducing the system complexity and saving system costs. The intermediate cooler 17 is used to store the condensed liquid flowing out of the outlet of the low-temperature coil 15 to prevent the liquid from flowing into the first compression device 121. The condensed liquid stored in the intermediate cooler 17 will vaporize to generate a low-temperature evaporation gas. The low-temperature evaporation gas flows through a pipeline from the outlet of the intermediate cooler 17 into the pipeline between the liquid cargo tank 11 and the first compression device 121 and mixes with the evaporation gas flowing out of the liquid cargo tank 11, which can reduce the temperature of the evaporation gas flowing into the first compression device 121 and improve the system performance.
[0047] In an alternative embodiment, the inlet of the intermediate cooler 17 is located in a region of the side wall of the intermediate cooler 17 near its top, and the outlet of the intermediate cooler 17 is located at the top of the intermediate cooler 17.
[0048] In an alternative embodiment, the evaporation gas re-liquefaction system further includes a first flow regulating valve 171 and a second flow regulating valve 172. The first flow regulating valve 171 is located between the low-temperature coil 15 and the intermediate cooler 17 and is used to control the flow rate between the low-temperature coil 15 and the intermediate cooler 17. The condensed liquid flowing out of the outlet of the low-temperature coil 15 flows into the intermediate cooler 17 through the first flow regulating valve 171. The second flow regulating valve 172 is used to control the flow rate at the outlet of the intermediate cooler 17 and is located between the outlet of the intermediate cooler 17 and the pipeline node where the evaporation gas converges into the pipeline between the liquid cargo tank 11 and the first compression device 121. The evaporation gas flowing out of the outlet of the intermediate cooler 17 converges into the pipeline between the liquid cargo tank 11 and the first compression device 121 through the second flow regulating valve 172.
[0049] In this embodiment, referring to Figure 2 , the evaporation gas re-liquefaction system may further include a second compression device 122. The second compression device 122 is located between the first compression device 121 and the liquid cargo tank 11. The evaporation gas flowing out of the liquid cargo tank 11 is compressed by the second compression device 122 and then flows into the first compression device 121 through a pipeline for a second compression. Optionally, the first compression device 121 is a high-pressure compressor, and the second compression device 122 is a low-pressure compressor. By compressing the evaporation gas twice, the working efficiency of the system can be improved.
[0050] In an alternative embodiment, the outlet of the low-temperature coil 15 is connected via a pipeline between the first compression device 121 and the second compression device 122. The evaporated gas is compressed by the second compression device 122 to form an evaporated gas with a higher temperature and a higher pressure. The low-temperature evaporated gas flowing out of the outlet of the intermediate cooler 17 converges and mixes with the higher-temperature evaporated gas in the pipeline, which can significantly reduce the temperature of the evaporated gas entering the first compression device 121, thereby improving the working performance of the evaporated gas re-liquefaction system.
[0051] In an alternative embodiment, the evaporated gas re-liquefaction system may further include a first throttle valve 151. There is a flow splitting node between the second outlet 143 of the liquid collector 14 and the inlet of the low-temperature coil 15. Part of the condensate flowing out of the second outlet 143 flows into the low-temperature coil 15 at the flow splitting node, and the other part flows back into the liquid cargo tank 11. A tee pipe can be arranged at the position where the flow splitting node is located or other suitable means can be adopted to form the flow splitting node. The first throttle valve 151 is located between the flow splitting node and the inlet of the low-temperature coil 15. Part of the condensate in the liquid collector 14 flows into the low-temperature coil 15 through the second outlet 143, the flow splitting node and the first throttle valve 151 in sequence. The first throttle valve 151 is used to throttle the condensate flowing to the low-temperature coil 15 to form low-temperature condensate. Through the low-temperature condensate, the temperature in the liquid collector 14 can be reduced, so that the low-boiling-point goods in the evaporated gas at the top of the liquid collector 14 are condensed into a liquid state, and the vaporization of the condensate in the liquid collector 14 is reduced, and the content of low-boiling-point goods in the top evaporated gas is reduced.
[0052] Further, the low-temperature coil 15 is located at the bottom of the liquid collector 14, so that during the transportation of the liquefied goods, the low-temperature coil 15 is at least partially immersed in the condensate in the liquid collector 14, improving the cooling efficiency of the overall space in the liquid collector 14. When the temperature in the liquid collector 14 is relatively high, the temperature of the evaporated gas at the top and the condensate at the bottom in the liquid collector 14 can be reduced in time, ensuring that the non-condensable gas and the low-boiling-point goods in the evaporated gas can be separated in time, and further reducing the vaporization of the condensate in the liquid collector 14.
[0053] In an alternative embodiment, the evaporated gas re-liquefaction system may further include a second throttle valve 181. The second throttle valve 181 is located between the second outlet 143 of the liquid collector 14 and the liquid cargo tank 11. At least part of the condensate in the liquid collector 14 flows back into the liquid cargo tank 11 through the second outlet 143 and the second throttle valve 181 in sequence. The second throttle valve 181 can throttle the condensate flowing back to the liquid cargo tank 11, reducing the temperature of the condensate flowing back to the liquid cargo tank 11, and obtaining condensate with a pressure close to that of the liquefied goods in the liquid cargo tank 11 and a lower temperature, thereby improving the temperature in the liquid cargo tank 11 and reducing the vaporization of the liquefied goods. Further, the second throttle valve 181 is located between the flow splitting node and the liquid cargo tank 11.
[0054] In this embodiment, the boil-off gas re-liquefaction system may further include a subcooling heat exchanger 18. The subcooling heat exchanger 18 is located between the second outlet 143 of the accumulator 14 and the cargo tank 11. At least part of the condensate flowing out from the second outlet 143 is subcooled by the subcooling heat exchanger 18 and then flows back into the cargo tank 11. Optionally, the subcooling heat exchanger 18 is located between the second outlet 143 of the accumulator 14 and the second throttle valve 181; further, the subcooling heat exchanger 18 is located between the diversion node and the second throttle valve 181. At least part of the condensate flowing out from the second outlet 143 flows into the cargo tank 11 through the second outlet 143, the diversion node, the subcooling heat exchanger 18 and the second throttle valve 181 in sequence. By providing the subcooling heat exchanger 18, the temperature of the condensate flowing out from the second outlet 143 can be further reduced, so that the condensate flowing out from the second throttle valve 181 has a lower temperature, and then the condensate flowing back into the cargo tank 11 can have a temperature lower than that of the liquefied goods in the cargo tank 11.
[0055] In an alternative embodiment, the boil-off gas re-liquefaction system may further include an exhaust valve 161. The exhaust valve 161 is connected to the exhaust pipe 16 and is used to control the flow rate and the opening and closing of the exhaust pipe 16, so that the pressure in the accumulator 14 is within the expected range that meets the design requirements, ensuring that the boil-off gas re-liquefaction system has the optimal working performance.
[0056] Embodiment Two
[0057] This embodiment provides a boil-off gas re-liquefaction method, which applies any one of the boil-off gas re-liquefaction systems in Embodiment One to re-liquefy the boil-off gas generated by the liquefied goods.
[0058] The boil-off gas re-liquefaction method provided in this embodiment includes steps S1 to S4, specifically including:
[0059] S1: Turn on the boil-off gas re-liquefaction system;
[0060] S2: Obtain the pressure in the accumulator 14;
[0061] S3: When the pressure in the accumulator 14 increases to the first pressure threshold, make the low-temperature coil 15 work normally;
[0062] S4: When it is detected that the pressure in the accumulator 14 is greater than the second pressure threshold and it is detected again that the pressure in the accumulator 14 is greater than the second pressure threshold after the first time interval, use the exhaust pipe 16 to discharge the boil-off gas in the accumulator 14 until the pressure in the accumulator 14 is less than the third pressure threshold.
[0063] In step S1, after the boil-off gas re-liquefaction system is started, the first compression device 121, the condenser 13, and the liquid receiver 14 start to work normally. The boil-off gas generated by the liquefied goods in the liquid cargo tank 11 enters the first compression device 121 through a pipeline and is compressed into high-temperature and high-pressure boil-off gas. The high-temperature and high-pressure boil-off gas is cooled into condensate by the condenser 13. The condensate and the uncondensed boil-off gas in the condenser 13 enter the liquid receiver 14. The condensate in the liquid receiver 14 flows back into the liquid cargo tank 11 from the second outlet 143 of the liquid receiver 14. Optionally, the boil-off gas re-liquefaction system further includes a second throttle valve 181. The step of starting the boil-off gas re-liquefaction system includes: opening the second throttle valve 181.
[0064] In step S2, the pressure in the liquid receiver 14 is obtained in real time to control the working state of the boil-off gas re-liquefaction system.
[0065] In step S3, when the boil-off gas re-liquefaction system starts to work, the pressure in the liquid receiver 14 gradually increases. When it is detected that the pressure in the liquid receiver 14 increases to be greater than the first pressure threshold, the low-temperature coil 15 is controlled to work normally to reduce the temperature in the liquid receiver 14, promote the condensation of the low-boiling-point goods in the boil-off gas in the liquid receiver 14, separate it from the non-condensable gas, and thereby reduce the pressure in the liquid receiver 14.
[0066] In an alternative embodiment, the boil-off gas re-liquefaction system further includes a first throttle valve 151, an intercooler 17, a first flow regulating valve 171, and a second flow regulating valve 172. The inlet of the low-temperature coil 15 is connected to the second outlet 143 of the liquid receiver 14 through a pipeline via the first throttle valve 151. The outlet of the low-temperature coil 15 is connected to the inlet of the intercooler 17 through a pipeline. The outlet of the intercooler 17 is connected to the pipeline between the first compression device 121 and the liquid cargo tank 11. When it is detected that the pressure in the liquid receiver 14 increases to be greater than the first pressure threshold, the first throttle valve 151, the first flow regulating valve 171, and the second flow regulating valve 172 are opened to make the low-temperature coil 15 work normally.
[0067] In step S4, the second pressure threshold may be equal to the first pressure threshold, or the second pressure threshold may be greater than the first pressure threshold. When the low-temperature coil 15 starts to work normally, it takes a certain amount of time to reduce the temperature in the accumulator 14. The pressure in the accumulator 14 may first increase and then decrease, and then continue to increase, or it may also increase slowly all the time. Therefore, when it is first detected that the pressure in the accumulator 14 increases to the second pressure threshold, the closed state of the exhaust pipe 16 is maintained first. When it is detected again that the pressure in the accumulator 14 is greater than the second pressure threshold after a first time interval from the first detection of the pressure being greater than the second pressure threshold, the exhaust pipe 16 is controlled to open to discharge the evaporated gas in the accumulator 14 and reduce the pressure in the accumulator 14 until the pressure in the accumulator 14 is less than the third pressure threshold. Optionally, an exhaust valve 161 is provided in the exhaust pipe 16, and the exhaust valve 161 is controlled to open so that the exhaust pipe 16 discharges the evaporated gas in the accumulator 14.
[0068] In this embodiment, the third pressure threshold may be less than the second pressure threshold, or may be between the first pressure threshold and the second pressure threshold, or may be less than the first pressure threshold. The specific values of the first time interval, the first pressure threshold, the second pressure threshold, and the third pressure threshold can be set according to the actual working state of the evaporated gas re-liquefaction system.
[0069] This embodiment provides an evaporated gas re-liquefaction method, which applies any of the evaporated gas re-liquefaction systems in Embodiment 1 to re-liquefy the evaporated gas generated by liquefying the goods, so it also has the beneficial effects of Embodiment 1.
[0070] The above embodiments only illustrate the principles and effects of the present application by way of example, and are not intended to limit the present application. Any person familiar with this technology can modify, change or combine the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present application should still be covered by the claims of the present application.
Claims
1. An evaporation gas re-liquefaction system, characterized in that, It includes a liquid cargo tank, a first compression device, a condenser, a liquid receiver, an exhaust pipeline and a cryogenic coil; The liquid cargo tank is sequentially connected to the first compression device, the condenser and the liquid receiver through pipelines. The liquid receiver has a first inlet, a first outlet and a second outlet. The exhaust pipeline is connected to the first outlet. The second outlet is connected to the liquid cargo tank through a pipeline. The cryogenic coil is located in the liquid receiver and is used to reduce the temperature in the liquid receiver; The liquid cargo tank is used to store liquefied goods. Vapor is generated in the liquid cargo tank. The vapor is compressed by the first compression device and then enters the condenser to be cooled to form condensate. The condensate and the remaining vapor flow into the liquid receiver through the first inlet. The exhaust pipeline can discharge the vapor in the liquid receiver. The condensate in the liquid receiver flows back to the liquid cargo tank through the second outlet.
2. The evaporative gas re-liquefaction system according to claim 1, wherein, The cryogenic coil is located at the bottom of the liquid receiver. The outlet of the cryogenic coil is connected to the pipeline between the liquid cargo tank and the first compression device through a pipeline. The inlet of the cryogenic coil is connected to the second outlet through a pipeline.
3. The evaporative gas re-liquefaction system according to claim 2, wherein, It further includes an intercooler. The outlet of the cryogenic coil is connected to the inlet of the intercooler through a pipeline. The outlet of the intercooler is connected to the pipeline between the liquid cargo tank and the first compression device.
4. The re-liquefaction system for boil-off gas according to claim 3, wherein It further includes: A first flow regulating valve, located between the cryogenic coil and the intercooler, for controlling the flow rate between the cryogenic coil and the intercooler; A second flow regulating valve, for controlling the flow rate at the outlet of the intercooler.
5. The re-liquefaction system for boil-off gas according to claim 1, wherein It further includes a second compression device. The second compression device is located between the first compression device and the liquid cargo tank. The outlet of the cryogenic coil is connected to the pipeline between the first compression device and the second compression device through a pipeline.
6. The evaporative gas re-liquefaction system according to claim 1, wherein There is a flow splitting node between the second outlet and the inlet of the cryogenic coil. At the flow splitting node, part of the condensate flowing out from the second outlet flows to the cryogenic coil and the other part flows to the liquid cargo tank; The vapor re-liquefaction system further includes a first throttling valve. The first throttling valve is located between the flow splitting node and the inlet of the cryogenic coil.
7. The re-liquefaction system for boil-off gas according to claim 1, wherein It further includes a second throttling valve, located between the second outlet and the liquid cargo tank. At least part of the condensate flowing out from the second outlet flows back to the liquid cargo tank through the second throttling valve.
8. The re-liquefaction system for evaporation gas according to claim 7, characterized in that, It further includes a subcooling heat exchanger, located between the second outlet and the second throttling valve. At least part of the condensate flowing out from the second outlet is subcooled by the subcooling heat exchanger and then flows back to the liquid cargo tank through the second throttling valve.
9. The re-liquefaction system for boil-off gas according to claim 1, wherein, It further includes an exhaust valve, connected to the exhaust pipeline, for controlling the flow rate of the exhaust pipeline.
10. A method for re-liquefying boil-off gas, which uses the boil-off gas re-liquefaction system according to any one of claims 1 to 9 to re-liquefy the boil-off gas generated by liquefied goods, characterized in that, It includes the following steps: Start the vapor re-liquefaction system; Obtain the pressure in the liquid receiver; When the pressure in the liquid receiver increases to the first pressure threshold, make the cryogenic coil work normally; When it is detected that the pressure in the liquid collector is greater than the second pressure threshold, and when it is detected again that the pressure in the liquid collector is greater than the second pressure threshold after the first time interval, the evaporation gas in the liquid collector is discharged using the exhaust pipeline until the pressure in the liquid collector is less than the third pressure threshold.