A cargo reliquefaction device for a marine liquid cargo system and a liquid cargo ship

Abstract

This invention provides a cargo reliquefaction device and a cargo ship for a ship's liquid cargo system. The reliquefaction device includes a refrigeration cycle loop connected to at least a first cargo tank. The refrigeration cycle loop is configured to use at least a portion of the liquid cargo that has evaporated into gas in the first cargo tank as a refrigerant. This refrigerant is processed through the refrigeration cycle loop to form a cryogenic refrigerant, which is used to cool target objects, including liquid cargo in other cargo tanks and / or, at least one fluid to be cooled in another refrigeration cycle loop. The reliquefaction device provided by this invention uses at least one type of liquid cargo in a cargo tank as the refrigerant in the refrigeration cycle loop and can use this refrigerant to cool liquid cargo in two or more compartments. This reduces the number of reliquefaction devices required, as well as the space occupied by the refrigerant storage structure and delivery pipelines on the cargo ship, thereby reducing the cost and operating expenses of the reliquefaction device.

Description

Technical Field

[0001] This invention relates to the field of evaporative gas reliquefaction technology, and more specifically, to a cargo reliquefaction device and a liquid cargo ship for a marine liquid cargo system. Background Technology

[0002] A liquefied gas carrier is a vessel specifically designed for ocean-going transport of liquid cargo. During ocean transport, the extreme temperature difference between the inside and outside of the cargo tanks causes external heat to inevitably seep into the tanks. Additionally, the rocking motion of the cargo during navigation generates heat, causing the liquid to evaporate and form vaporized gas. This leads to increased pressure within the cargo tanks, compromising the safety of liquefied gas transport. Therefore, to maintain the temperature and pressure of the liquid cargo within the design range, liquefied gas carriers are typically equipped with a reliquefaction system, which condenses the vaporized gas back into liquid and recovers it.

[0003] Chinese patent CN204963420U discloses a BOG reliquefaction device for LNG storage tanks in LNG receiving terminals and peak-shaving stations, and for LNG carriers. The device includes a main heat exchanger, an LNG storage tank, a BOG heat exchanger, a BOG compressor, a cooler A, a booster turbine expander, a cooler B, and a separator. The main heat exchanger has a BOG forward flow channel, a BOG reverse flow channel, and a non-condensable gas channel. The booster turbine expander has a pressurization end and an expansion end. The LNG storage tank, BOG heat exchanger, BOG forward flow channel, separator, and LNG storage tank are sequentially connected in the flow direction. Similarly, the BOG heat exchanger, BOG compressor, cooler A, pressurization end, cooler B, and BOG heat exchanger are sequentially connected. This patent boasts high recycling efficiency, recovers the cold energy of non-condensable gases, and has high energy utilization. However, it can only be used in one specific liquid cargo transportation scenario.

[0004] For liquid cargo ships carrying multiple types of goods, multiple reliquefaction units are typically required. For example, reliquefaction unit 1 performs gas phase treatment on the liquid cargo tank carrying cargo A, while reliquefaction unit 2 performs gas phase treatment on the liquid cargo tank carrying cargo B. These multiple reliquefaction units operate independently, requiring independent piping and corresponding switching valves. The reliquefaction units must be activated when gas phase treatment is needed during voyage or during cargo loading. Ships carrying multiple types of goods typically require 2-3 reliquefaction units. Operating multiple reliquefaction units for gas treatment under these conditions occupies valuable ship space and consumes significant amounts of electricity. Furthermore, using multiple reliquefaction units involves complex start-up and purging procedures, making onboard operation inconvenient. Summary of the Invention

[0005] The purpose of this invention is to provide a cargo reliquefaction device for a ship liquid cargo system, which is applied to a liquid cargo ship carrying two or more liquid cargoes, and uses at least one of the liquid cargoes as a cooling medium for the other cargoes, thereby managing the pressure in the cargo holds of the other cargoes, reducing the number of reliquefaction devices, reducing their space occupation, and lowering the layout cost.

[0006] This invention discloses a cargo reliquefaction device for a ship's liquid cargo system, used in a liquid cargo ship, wherein the liquid cargo ship is provided with two or more liquid cargo tanks, including at least a first liquid cargo tank and a second liquid cargo tank, for storing at least two different types of liquid cargo, and the reliquefaction device includes:

[0007] A refrigeration cycle loop, which is at least connected to the first cargo tank, is configured to:

[0008] At least a portion of the liquid cargo that has evaporated into gas in the first liquid cargo tank is used as a refrigerant. This refrigerant is processed through the refrigeration cycle loop to form a cryogenic refrigerant, which is used to cool a target object, including liquid cargo in other liquid cargo tanks and / or, at least one other fluid to be cooled in a refrigeration cycle loop.

[0009] Furthermore, the refrigeration cycle loop includes a first refrigeration cycle loop, which includes a first compressor inlet buffer tank, a first stage compressor, a first economizer, a first stage compressor, a first aftercooler, a first liquid receiver, a first pressure reducing valve, and a first subcooling heat exchanger; the vapor outlet of the first liquid cargo tank is connected to the inlet of the first compressor inlet buffer tank, the outlet of the first compressor inlet buffer tank is connected to the inlet of the first stage compressor, the outlet of the first stage compressor is connected to the first inlet of the first economizer, the outlet of the first economizer is connected to the inlet of the first stage compressor, and the outlet of the first stage compressor is connected to the first aftercooler. The inlet of the cooler is connected, the outlet of the first aftercooler is connected to the inlet of the first liquid receiver, the outlet of the first liquid receiver is connected to the inlet of the first pressure reducing valve, the outlet of the first pressure reducing valve is connected to the refrigerant inlet of the first subcooling heat exchanger, the refrigerant outlet of the first subcooling heat exchanger is connected to the inlet of the first compressor inlet buffer tank, the target object flows through the first subcooling heat exchanger for heat exchange with the low-temperature refrigerant formed in the first refrigeration cycle loop, a first cargo tank spray valve is provided in the first liquid cargo tank, and the outlet of the first pressure reducing valve is also connected to the first cargo tank spray valve for transporting part of the low-temperature refrigerant back to the first liquid cargo tank.

[0010] Furthermore, the target of the first refrigeration cycle loop is the liquid cargo in the second liquid cargo tank. A second transfer pump and a second cargo tank spray valve are installed in the second liquid cargo tank. The second transfer pump is used to transport the liquid cargo in the second liquid cargo tank to the first subcooling heat exchanger to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second liquid cargo tank through the second cargo tank spray valve.

[0011] Furthermore, the cargo ship also includes a third cargo tank, the liquid cargo stored in which is at least different from the liquid cargo in the first cargo tank. The first refrigeration cycle also includes a second subcooling heat exchanger, the outlet of the first pressure reducing valve is connected to the refrigerant inlet of the second subcooling heat exchanger, the refrigerant outlet of the second subcooling heat exchanger is connected to the inlet of the first compressor inlet buffer tank, and the target material of the second subcooling heat exchanger flows through the second subcooling heat exchanger for heat exchange with the low-temperature refrigerant formed in the first refrigeration cycle, wherein the target material of the first refrigeration cycle is the liquid cargo in the second cargo tank. The cargo hold is equipped with a second transfer pump and a second cargo hold spray valve. The second transfer pump is used to transport the liquid cargo in the second liquid cargo tank to the first subcooling heat exchanger for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second liquid cargo tank through the second cargo hold spray valve. The target of the second subcooling heat exchanger is the liquid cargo in the third liquid cargo tank. The third liquid cargo tank is equipped with a third transfer pump and a third cargo hold spray valve. The third transfer pump is used to transport the liquid cargo in the third liquid cargo tank to the second subcooling heat exchanger for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third liquid cargo tank through the third cargo hold spray valve.

[0012] Furthermore, the cargo ship also includes a third cargo tank, the liquid cargo stored in which is at least different from the liquid cargo in the first cargo tank. The first subcooling heat exchanger is a multi-flow subcooling heat exchanger, which includes three or more sets of inlets and outlets, one of which is connected to the outlet of the first pressure reducing valve and the inlet of the first compressor inlet buffer tank, respectively. A second transfer pump and a second cargo tank spray valve are installed in the second cargo tank. The second transfer pump and the second cargo tank spray valve are connected to another set of inlets and outlets in the multi-flow subcooling heat exchanger. The second transfer pump is used to transfer the liquid cargo in the second cargo tank... The liquid cargo is transported to the multi-stream flow cooling heat exchanger to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second cargo tank via the second cargo tank spray valve. A third transfer pump and a third cargo tank spray valve are installed in the third cargo tank. The third transfer pump and the third cargo tank spray valve are connected to another set of inlet and outlet in the multi-stream flow cooling heat exchanger. The third transfer pump is used to transport the liquid cargo in the third cargo tank to the multi-stream flow cooling heat exchanger to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank via the third cargo tank spray valve.

[0013] Furthermore, the cargo ship also includes a third cargo tank, the liquid cargo stored in the third cargo tank being at least different from the liquid cargo in the first cargo tank. The refrigeration cycle also includes a second refrigeration cycle, the second refrigeration cycle comprising a second compressor inlet buffer tank, a second primary compressor, a second economizer, a second secondary compressor, a second aftercooler, a second liquid receiver, a second pressure reducing valve, and a second subcooling heat exchanger. The vapor phase outlet of the first cargo tank, or the vapor phase outlet of the second cargo tank, is connected to the inlet of the second compressor inlet buffer tank, the outlet of the second compressor inlet buffer tank is connected to the inlet of the second primary compressor, and the outlet of the second primary compressor is connected to the... The first inlet of the second economizer is connected, the outlet of the second economizer is connected to the inlet of the second secondary compressor, the outlet of the second secondary compressor is connected to the inlet of the second aftercooler, the outlet of the second aftercooler is connected to the inlet of the second liquid receiver, the outlet of the second liquid receiver is connected to the inlet of the second pressure reducing valve, the outlet of the second pressure reducing valve is connected to the refrigerant inlet of the second subcooling heat exchanger, the refrigerant outlet of the second subcooling heat exchanger is connected to the inlet of the second compressor inlet buffer tank, and the target material of the second subcooling heat exchanger flows through the second subcooling heat exchanger for heat exchange with the low-temperature refrigerant formed in the second refrigeration cycle loop.

[0014] Furthermore, when the inlet of the second compressor inlet buffer tank is connected to the vapor phase outlet of the first liquid cargo tank, the second aftercooler exchanges heat with the external cooling medium and condenses; when the inlet of the second compressor inlet buffer tank is connected to the vapor phase outlet of the second liquid cargo tank, the second aftercooler exchanges heat with the first subcooling heat exchanger and condenses through the cooling medium.

[0015] Furthermore, when the inlet of the second compressor inlet buffer tank is connected to the gas phase outlet of the first liquid cargo tank: the target of the first refrigeration cycle loop is the liquid cargo in the second liquid cargo tank. A second transfer pump and a second cargo tank spray valve are provided in the second liquid cargo tank. The second transfer pump is used to transport the liquid cargo in the second liquid cargo tank to the first subcooling heat exchanger for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second liquid cargo tank through the second cargo tank spray valve. The target of the second subcooling heat exchanger is the liquid cargo in the third liquid cargo tank. A third transfer pump and a third cargo tank spray valve are provided in the third liquid cargo tank. The third transfer pump is used to transport the liquid cargo in the third liquid cargo tank to the second subcooling heat exchanger for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third liquid cargo tank through the third cargo tank spray valve.

[0016] When the inlet of the second compressor inlet buffer tank is connected to the gas phase outlet of the second liquid cargo tank:

[0017] The target of the first refrigeration cycle is the fluid to be cooled in the second refrigeration cycle. The fluid to be cooled is the cooling medium between the second aftercooler and the first subcooling heat exchanger, which is used to condense the second aftercooler. A second cargo tank spray valve is provided in the second liquid cargo tank. The outlet of the second pressure reducing valve is also connected to the second cargo tank spray valve, which is used to transport part of the low-temperature refrigerant generated by the second refrigeration cycle back to the second liquid cargo tank.

[0018] The target of the second subcooling heat exchanger is the liquid cargo in the third cargo tank. The third cargo tank is equipped with a third transfer pump and a third cargo tank spray valve. The third transfer pump is used to transport the liquid cargo in the third cargo tank to the second subcooling heat exchanger for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank through the third cargo tank spray valve.

[0019] Furthermore, the first aftercooler exchanges heat and condenses with the external cooling medium.

[0020] The present invention also discloses a liquid cargo ship, including the cargo reliquefaction device of the ship liquid cargo system as described above.

[0021] Compared with existing technologies, the cargo reliquefaction device for ship liquid cargo systems described in this invention has the following advantages:

[0022] The reliquefaction device provided by this invention can simultaneously perform tank pressure treatment on liquid cargo tanks containing two types of cargo using a single device. For liquid cargo ships carrying multiple types of cargo, it can reduce the number of reliquefaction devices, reduce system power consumption, and reduce the number of condensate pipelines in the reliquefaction devices, thereby reducing the difficulty and cost of layout on the liquid cargo ship. This invention uses at least one type of liquid cargo in the liquid cargo tank as a refrigerant in the refrigeration cycle and can use this refrigerant to cool liquid cargo in two or more compartments, reducing the space occupied by the refrigerant storage structure and transportation pipelines on the liquid cargo ship, and lowering the reliquefaction cost. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the cargo reliquefaction device of the ship liquid cargo system described in Embodiment 1 of the present invention;

[0024] Figure 2 This is a schematic diagram of the cargo reliquefaction device of the ship liquid cargo system described in Embodiment 2 of the present invention;

[0025] Figure 3 This is a schematic diagram of the cargo reliquefaction device of the ship liquid cargo system described in Embodiment 3 of the present invention;

[0026] Figure 4 This is a schematic diagram of the cargo reliquefaction device of the ship liquid cargo system described in Embodiment 4 of the present invention;

[0027] Figure 5 This is a schematic diagram of the cargo reliquefaction device of the ship liquid cargo system described in Embodiment 5 of the present invention.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1. First cargo tank; 11. First cargo tank spray valve; 12. First steam valve; 2. Second cargo tank; 21. Second transfer pump; 22. Second outlet valve; 23. Second cargo tank spray valve; 24. Second steam valve; 3. Third cargo tank; 31. Third transfer pump; 32. Third outlet valve; 33. Third cargo tank spray valve; 41. First compressor inlet buffer tank; 42. First stage compressor; 43. First and second stage compressors; 44. First aftercooler; 45. First liquid receiver; 46. First spray valve; 47. First economizer; 48. First pressure reducing valve; 49. First subcooling heat exchanger; 51. Second compressor inlet buffer tank; 52. Second stage compressor; 53. Second and second stage compressor; 54. Second aftercooler; 55. Second liquid receiver; 56. Second spray valve; 57. Second economizer; 58. Second pressure reducing valve; 59. Second subcooling heat exchanger. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the described embodiments are only some, not all, of the embodiments of this invention. The specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0031] The following describes in detail, with reference to the accompanying drawings, an embodiment of the present invention: a cargo reliquefaction device for a marine liquid cargo system and a liquid cargo ship.

[0032] Example 1

[0033] This embodiment provides a cargo reliquefaction device for a ship liquid cargo system, such as... Figure 1 As shown, this is for a liquid cargo ship, which has two or more liquid cargo tanks, including at least a first liquid cargo tank 1 and a second liquid cargo tank 2, for storing at least two different types of liquid cargo. The reliquefaction device includes:

[0034] A refrigeration cycle loop, wherein the refrigeration cycle loop is at least connected to the first cargo tank 1, and the refrigeration cycle loop is configured as follows:

[0035] At least a portion of the liquid cargo that has evaporated into gas in the first liquid cargo tank 1 is used as a refrigerant. This refrigerant is processed by the refrigeration cycle loop to form a cryogenic refrigerant, which is used to cool a target object, including liquid cargo in other liquid cargo tanks and / or, at least one other fluid to be cooled in a refrigeration cycle loop.

[0036] By utilizing the gas generated by the evaporation of the liquid cargo itself within the cargo tank as the working fluid in the refrigeration cycle, the refrigerant source is no longer entirely dependent on external supply, significantly reducing operating and maintenance costs. Furthermore, depending on actual needs, the reliquefaction device provided in this example can use the cryogenic refrigerant generated in the refrigeration cycle to cool different types of liquid cargo in other cargo tanks, or it can be used to subcool the cooling medium in another refrigeration cycle. Compared to existing cargo ships where each type of cargo requires an independent reliquefaction device, this reduces the number of reliquefaction devices, saves internal space on the cargo ship, and lowers the cost of reliquefaction. Specifically, the cryogenic refrigerant enters the subcooling heat exchanger after passing through a pressure reducing valve, cooling the target object flowing through the subcooling heat exchanger.

[0037] As an example of the present invention, the refrigeration cycle circuit includes a first refrigeration cycle circuit, which includes a first compressor inlet buffer tank 41, a first stage compressor 42, a first economizer 47, a first stage compressor 43, a first aftercooler 44, a first liquid receiver 45, a first pressure reducing valve 48, and a first subcooling heat exchanger 49; the gas phase outlet of the first liquid cargo tank 1 is connected to the inlet of the first compressor inlet buffer tank 41, the outlet of the first compressor inlet buffer tank 41 is connected to the inlet of the first stage compressor 42, and the outlet of the first stage compressor 42 is connected to the first inlet of the first economizer 47. The outlet of the first liquid cargo tank 43 is connected to the inlet of the first secondary compressor 43. The outlet of the first secondary compressor 43 is connected to the inlet of the first aftercooler 44. The outlet of the first aftercooler 44 is connected to the inlet of the first liquid receiver 45. The outlet of the first liquid receiver 45 is connected to the inlet of the first pressure reducing valve 48. The outlet of the first pressure reducing valve 48 is connected to the refrigerant inlet of the first subcooling heat exchanger 49. The refrigerant outlet of the first subcooling heat exchanger 49 is connected to the inlet of the first compressor inlet buffer tank 41. The target object flows through the first subcooling heat exchanger 49 to exchange heat with the low-temperature refrigerant formed in the first refrigeration cycle. The first aftercooler 44 receives external cooling medium through an external cooling medium inlet ② and an external cooling medium outlet ① to cool the high-temperature liquid cargo delivered by the first secondary compressor 43. The external cooling medium can be seawater or other cooling media in the refrigeration cycle, which will not be elaborated here. A first vapor valve 12 is provided between the vapor outlet of the first liquid cargo tank 1 and the inlet of the first compressor inlet buffer tank 41. With the above configuration, the gas generated by the natural evaporation of the low-boiling-point liquid cargo in the first cargo tank 1 is directly introduced into the first refrigeration cycle loop as a refrigerant. After compression, cooling, and depressurization, it forms a cryogenic fluid. This cryogenic fluid exchanges heat with the target object in the first subcooling heat exchanger 49 and then returns to the first compressor inlet buffer tank 41 to participate in the next cycle. In this case, the refrigerant in the first refrigeration cycle loop is entirely taken from the liquid cargo itself, eliminating the need for additional refrigerant storage and replenishment devices, significantly reducing operating costs. Furthermore, the configuration of the first compressor inlet buffer tank 41 ensures that the evaporated gas from the first cargo tank 1 is buffered and stabilized before entering the first stage compressor 42, preventing compressor surge due to gas volume fluctuations and ensuring the stability of the refrigeration cycle.Optionally, the first aftercooler 44 uses seawater, which is readily available in the ship's navigation environment, as a cooling medium to condense the high-temperature and high-pressure refrigerant discharged from the first and second stage compressors 43. This eliminates the need for a separate cooling water source for the reliquefaction unit, making full use of the ship's existing resources and reducing equipment investment and operating energy consumption. The first steam valve 12 allows the evaporated gas in the first cargo tank 1 to be supplied to the refrigeration cycle circuit as needed. When the pressure in the cargo tank does not reach the set value, the valve remains closed to avoid unnecessary refrigeration cycle startup, which helps save energy.

[0038] Furthermore, the first refrigeration cycle circuit also includes a first spray valve 46. The outlet of the first liquid receiver 45 is connected to the second inlet of the first economizer 47 through the first spray valve 46, for depressurizing a portion of the liquid in the first liquid receiver 45 and spraying it into the first economizer 47. Through the above configuration, the first spray valve 46 throttles and cools the high-pressure liquid refrigerant in the first liquid receiver 45 before spraying it into the first economizer 47. This low-temperature liquid is used to intermediately cool the high-temperature vapor discharged from the first stage compressor 42, significantly reducing the temperature of the refrigerant entering the first stage compressor 43, thereby reducing the power consumption of the second stage compressor and improving the energy efficiency ratio of the entire refrigeration cycle.

[0039] Preferably, a first cargo tank spray valve 11 is provided in the first liquid cargo tank 1, and the outlet of the first pressure reducing valve 48 is also connected to the first cargo tank spray valve 11 for transferring a portion of the cryogenic refrigerant back to the first liquid cargo tank 1. With this configuration, a portion of the cryogenic liquid refrigerant, after being throttled and cooled by the first pressure reducing valve 48, is directly sprayed back to the first liquid cargo tank 1 through the first cargo tank spray valve 11. The cryogenic liquid absorbs a large amount of heat from the tank, rapidly reducing the temperature and pressure within the first liquid cargo tank 1, thus achieving pressure management of the first liquid cargo tank 1 itself.

[0040] As an example of the present invention, the target of the first refrigeration cycle loop is the liquid cargo in the second cargo tank 2. A second transfer pump 21 and a second cargo tank spray valve 23 are provided in the second cargo tank 2. The second transfer pump 21 is used to transport the liquid cargo in the second cargo tank 2 to the first subcooling heat exchanger 49 for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second cargo tank 2 via the second cargo tank spray valve 23. Specifically, a second outlet valve 22 is provided between the second transfer pump 21 and the first subcooling heat exchanger 49. With the above setup, the high-temperature liquid cargo in the second cargo tank 2 is sent to the first subcooling heat exchanger 49 by the second transfer pump 21. After exchanging heat with the low-temperature refrigerant and cooling it, it is sprayed back into the tank through the second cargo tank spray valve 23. The low-temperature liquid cargo absorbs a large amount of heat from the second cargo tank 2, effectively suppressing the evaporation rate of the liquid cargo in the second cargo tank 2 and controlling the tank pressure within a safe range. This achieves synchronous pressure management of two different cargo tanks by a single refrigeration cycle loop. The second outlet valve 22 allows the liquid cargo in the second cargo tank 2 to enter the first subcooling heat exchanger 49 for cooling as needed. When the pressure of the second cargo tank 2 is within the normal range, the valve remains closed to avoid unnecessary liquid cargo circulation and waste of cooling capacity, which helps to reduce the energy consumption of the second transfer pump 21.

[0041] As a preferred example, the piping between the first liquid receiver 45 and the first pressure reducing valve 48 passes at least partially through the interior of the first economizer 47. With this arrangement, the piping between the first liquid receiver 45 and the first pressure reducing valve 48 is routed through the interior of the first economizer 47 (preferably, the piping is coiled inside the first economizer 47). This allows the high-pressure liquid refrigerant flowing from the first liquid receiver 45 to exchange heat with the low-temperature liquid in the first economizer 47 before entering the first pressure reducing valve 48, thus achieving further cooling. The subcooled liquid refrigerant, after being throttled by the first pressure reducing valve 48, can obtain an even lower temperature, further improving the cooling effect of the first subcooling heat exchanger 49.

[0042] In this example, preferably, the liquid cargo stored in the first cargo tank 1 is A, and the liquid cargo stored in the second cargo tank 2 is B, where the boiling point of A is lower than that of B. In this example, liquid cargo A with a lower boiling point is selected as the refrigerant to cool liquid cargo B with a higher boiling point. This utilizes the characteristic of the low evaporation temperature of the low-boiling-point liquid cargo, enabling it to achieve a lower temperature level than the object being cooled in the refrigeration cycle. This ensures a sufficient heat transfer temperature difference during the heat exchange process and improves heat exchange efficiency.

[0043] Example 2

[0044] This embodiment provides a cargo reliquefaction device for a ship liquid cargo system. The reliquefaction device is similar to that of Embodiment 1, and includes the same first refrigeration cycle loop as in Embodiment 1. The difference is that:

[0045] like Figure 2 As shown, the cargo ship also includes a third cargo tank 3, the liquid cargo stored in the third cargo tank 3 being at least different from the liquid cargo in the first cargo tank 1. The refrigeration cycle circuit also includes a second refrigeration cycle circuit, the second refrigeration cycle circuit including a second compressor inlet buffer tank 51, a second primary compressor 52, a second economizer 57, a second secondary compressor 53, a second aftercooler 54, a second liquid receiver 55, a second pressure reducing valve 58, and a second subcooling heat exchanger 59; the vapor phase outlet of the first cargo tank 1 is also connected to the inlet of the second compressor inlet buffer tank 51, the outlet of the second compressor inlet buffer tank 51 is connected to the inlet of the second primary compressor 52, and the outlet of the second primary compressor 52 is connected to the second economizer 57. The first inlet connection is established. The outlet of the second economizer 57 is connected to the inlet of the second secondary compressor 53. The outlet of the second secondary compressor 53 is connected to the inlet of the second aftercooler 54. The outlet of the second aftercooler 54 is connected to the inlet of the second liquid receiver 55. The outlet of the second liquid receiver 55 is connected to the inlet of the second pressure reducing valve 58. The outlet of the second pressure reducing valve 58 is connected to the refrigerant inlet of the second subcooling heat exchanger 59. The refrigerant outlet of the second subcooling heat exchanger 59 is connected to the inlet of the second compressor inlet buffer tank 51. The target material of the second subcooling heat exchanger 59 flows through the second subcooling heat exchanger 59 for heat exchange with the low-temperature refrigerant formed in the second refrigeration cycle loop. The second aftercooler 54 receives external cooling medium through an external cooling medium inlet ② and an external cooling medium outlet ① to cool the high-temperature liquid goods delivered by the second secondary compressor 53. A first steam valve 12 is provided between the gas phase outlet of the first liquid cargo tank 1 and the inlet of the first compressor inlet buffer tank 41, and between the gas phase outlet of the first liquid cargo tank 1 and the inlet of the second compressor inlet buffer tank 51.

[0046] With the above configuration, when the liquid cargo ship has a third liquid cargo tank 3, the reliquefaction device achieves cooling of the liquid cargo in the third liquid cargo tank 3 by adding a second refrigeration cycle loop. In this example, the two refrigeration cycle loops share the evaporated gas in the first liquid cargo tank 1, achieving separate cooling of the liquid cargo in the second liquid cargo tank 2 and the third liquid cargo tank 3 under single refrigerant supply conditions. The two refrigeration cycle loops operate relatively independently and can be started and stopped separately according to the pressure conditions of their respective liquid cargo tanks without interfering with each other. The system is highly flexible and avoids the additional space required for configuring a separate reliquefaction device for the third type of cargo. In addition to cost input, the second aftercooler 54 uses an external cooling medium to condense the high-temperature and high-pressure refrigerant discharged from the second and second stage compressors 53, ensuring that the refrigerant entering the second liquid receiver 55 is in a liquid state, providing the necessary conditions for subsequent throttling and cooling, and ensuring that the second refrigeration cycle loop can independently and stably output cooling capacity; by setting a first vapor valve 12 between the gas phase outlet of the first liquid cargo tank 1 and the two sets of refrigeration cycle loops, unified control of the refrigerant supply of the two sets of loops is realized, simplifying the pipeline valve configuration. When the liquid cargo tank does not require cooling treatment, the valve can be closed to cut off all refrigerant supply, making operation simple and convenient.

[0047] Furthermore, the second refrigeration cycle also includes a second spray valve 56. The outlet of the second liquid receiver 55 is connected to the second inlet of the second economizer 57 via the second spray valve 56, for depressurizing a portion of the liquid in the second liquid receiver 55 and spraying it into the second economizer 57. Through this arrangement, the second spray valve 56, in conjunction with the second economizer 57, provides intermediate cooling to the refrigerant vapor before it enters the second stage compressor 53 in the second refrigeration cycle, reducing the suction temperature and compression ratio of the second stage compressor 53, decreasing compression power consumption, and ensuring the economical operation of the second refrigeration cycle.

[0048] Preferably, the outlet of the second pressure reducing valve 58 is also connected to the first cargo hold spray valve 11 to transport a portion of the cryogenic refrigerant back to the first liquid cargo tank 1. Through this configuration, a portion of the cryogenic refrigerant in the second refrigeration cycle, after being throttled and cooled by the second pressure reducing valve 58, is returned to the first liquid cargo tank 1 via the first cargo hold spray valve 11. Under the condition that the evaporating gas in the first liquid cargo tank 1 simultaneously supplies two refrigeration cycle circuits, more cryogenic return liquid is replenished, ensuring that the pressure of the first liquid cargo tank 1 itself can also be effectively controlled, avoiding the continuous supply of refrigerant caused by excessively low pressure in the first liquid cargo tank 1 due to large-scale gas extraction.

[0049] As an example of the present invention, the target of the second subcooling heat exchanger 59 is the liquid cargo in the third cargo tank 3. A third transfer pump 31 and a third cargo tank spray valve 33 are provided in the third cargo tank 3. The third transfer pump 31 is used to transport the liquid cargo in the third cargo tank 3 to the second subcooling heat exchanger 59 for heat exchange with the cryogenic refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank 3 via the third cargo tank spray valve 33. Specifically, a third outlet valve 32 is provided between the third transfer pump 31 and the second subcooling heat exchanger 59. With the above configuration, the third cargo tank 3, in conjunction with the third transfer pump 31 and the third cargo tank spray valve 33, achieves cyclic cooling of the liquid cargo with the second subcooling heat exchanger 59. Its cooling circuit is independent of the cooling circuit of the second cargo tank 2. The two cooling circuits can be started and stopped independently according to the pressure changes of their respective cargo tanks, without interfering with each other, and the operation is flexible. In addition, the third outlet valve 32 is used to connect or disconnect the channel for the liquid cargo in the third cargo tank 3 to enter the second subcooling heat exchanger 59 as needed. When the third cargo tank 3 does not need cooling, closing the valve can stop the liquid cargo circulation, avoiding unnecessary energy consumption and cooling waste of the third transfer pump 31.

[0050] As a preferred example, the piping between the second liquid receiver 55 and the second pressure reducing valve 58 passes at least partially through the interior of the second economizer 57. This arrangement, where the liquid receiver to pressure reducing valve piping passes through the economizer in the second refrigeration cycle, subcools the liquid refrigerant before it enters the second pressure reducing valve 58, increasing the temperature drop after throttling and thus enhancing the cooling capacity of the second subcooling heat exchanger 59.

[0051] In this example, preferably, the liquid cargo stored in the first cargo tank 1 is A, the liquid cargo stored in the second cargo tank 2 is B, and the liquid cargo stored in the third cargo tank 3 is C. The boiling point of A is lower than that of B, and the boiling point of B is lower than that of C. Liquid cargo A serves as the refrigerant for the other two liquid cargoes. Liquid cargo B, as the target of the first refrigeration cycle, is cooled to a low temperature in the first subcooling heat exchanger 49. Liquid cargo C, as the target of the second refrigeration cycle, is cooled to a low temperature in the second subcooling heat exchanger 59.

[0052] The boiling points of the three liquids are distributed in a stepped pattern of A < B < C. Liquid A, which has the lowest boiling point, is selected as the refrigerant. Its evaporation temperature is lower than that of liquids B and C, which can provide sufficient heat exchange temperature difference for the two liquids with higher boiling points. This ensures that both the first subcooling heat exchanger 49 and the second subcooling heat exchanger 59 have high heat exchange efficiency.

[0053] Example 3

[0054] This embodiment provides a cargo reliquefaction device for a ship liquid cargo system. The reliquefaction device is similar to that of Embodiment 1, and includes a structure similar to the first refrigeration cycle loop in Embodiment 1, the difference being:

[0055] like Figure 3 As shown, the cargo ship also includes a third cargo tank 3, in which the cargo stored is at least different from the cargo in the first cargo tank 1. The first refrigeration cycle also includes a second subcooling heat exchanger 59. The outlet of the first pressure reducing valve 48 is also connected to the refrigerant inlet of the second subcooling heat exchanger 59. The refrigerant outlet of the second subcooling heat exchanger 59 is connected to the inlet of the first compressor inlet buffer tank 41. The target of the second subcooling heat exchanger 59 flows through the second subcooling heat exchanger 59 for heat exchange with the low-temperature refrigerant formed in the first refrigeration cycle.

[0056] Compared to Example 2, this example only uses one refrigeration cycle loop. In this loop, the first subcooling heat exchanger 49 and the second subcooling heat exchanger 59 are connected in parallel downstream of the first pressure reducing valve 48. The low-temperature refrigerant, after being throttled and cooled by the first pressure reducing valve 48, flows through the first subcooling heat exchanger 49 and the second subcooling heat exchanger 59 respectively, cooling two different types of cargo. Compared to Example 2, which requires two complete sets of compression, cooling, and throttling equipment, this example only requires one compressor unit and one aftercooler to meet the cooling needs of two of the three types of cargo, significantly reducing equipment investment costs and the space occupied by the liquid cargo ship.

[0057] As an example of the present invention, the target of the second subcooling heat exchanger 59 is the liquid cargo in the third cargo tank 3. A third transfer pump 31 and a third cargo tank spray valve 33 are provided in the third cargo tank 3. The third transfer pump 31 is used to transport the liquid cargo in the third cargo tank 3 to the second subcooling heat exchanger 59 for heat exchange with the cryogenic refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank 3 via the third cargo tank spray valve 33. Specifically, a third outlet valve 32 is provided between the third transfer pump 31 and the second subcooling heat exchanger 59. Through the above configuration, the third cargo tank 3 achieves cyclic cooling of the liquid cargo through the third transfer pump 31 and the third cargo tank spray valve 33. In this embodiment, the liquid cargo in the third cargo tank 3 and the liquid cargo in the second cargo tank 2 share the same cryogenic refrigerant. The flow rate of the liquid cargo in each tank can be adjusted according to the heat load difference to match different cooling requirements, which has good flexibility and adaptability. In addition, the configuration of the third outlet valve 32 allows the liquid cargo cooling circuit of the third cargo tank 3 to be activated or deactivated as needed. When the pressure of the third cargo tank 3 is normal, closing the third outlet valve 32 can stop the liquid cargo circulation of this circuit, avoiding unnecessary energy consumption and cooling waste.

[0058] Example 4

[0059] This embodiment provides a cargo reliquefaction device for a ship liquid cargo system. The reliquefaction device is similar to that of Embodiment 1, and includes a structure similar to the first refrigeration cycle loop of Embodiment 1, except that:

[0060] like Figure 4 As shown, the liquid cargo ship also includes a third liquid cargo tank 3, in which the liquid cargo stored is at least different from that in the first liquid cargo tank 1. The first subcooling heat exchanger 49 is a multi-flow subcooling heat exchanger, which includes three or more sets of inlets and outlets. One set of inlets and outlets is connected to the outlet of the first pressure reducing valve 48 and the inlet of the first compressor inlet buffer tank 41, respectively. At least another set of inlets and outlets is connected to the second barge pump 21 and the second cargo hold spray valve 23, respectively. At least another set of inlets and outlets is connected to the third barge pump 31 and the third cargo hold spray valve 33, respectively.

[0061] Compared to Embodiment 3, in this embodiment, two relatively independent subcooling heat exchangers arranged in parallel are integrated into a single multi-flow subcooling heat exchanger. The low-temperature refrigerant (gas naturally evaporated in the first liquid cargo tank 1), the liquid cargo in the second liquid cargo tank 2, and the liquid cargo in the third liquid cargo tank 3 in the refrigeration cycle flow through different channels inside the heat exchanger, completing heat exchange within the same shell. Compared to Embodiment 3, where the two relatively independent heat exchangers need to be connected to the first pressure reducing valve 48 and the first compressor inlet buffer tank 41 respectively, the multi-flow subcooling heat exchanger eliminates intermediate connecting pipes and corresponding valves and instruments, reducing potential leakage points. The equipment structure is more compact, and installation and maintenance are more convenient. At the same time, the heat exchange area inside the multi-flow heat exchanger can be flexibly allocated according to the difference in the heat exchange required by each fluid, thereby optimizing the overall efficiency of the first subcooling heat exchanger 49.

[0062] In embodiments 3 and 4, preferably, the liquid cargo stored in the first cargo tank 1 is A, and the liquid cargo stored in the second cargo tank 2 and the third cargo tank 3 is B or C, wherein the boiling point of A is lower than that of B, and the boiling point of B is lower than that of C. With the above configuration, liquid cargo A is used as the refrigerant for the other two liquid cargoes. In embodiment 3, the liquid cargo in the second cargo tank 2 is cooled to a low temperature in the first subcooling heat exchanger 49, and the liquid cargo in the third cargo tank 3 is cooled to a low temperature in the second subcooling heat exchanger 59. In embodiment 4, the liquid cargo in the second cargo tank 2 and the third cargo tank 3 are cooled to a low temperature in the first subcooling heat exchanger 49 (multi-stream subcooling heat exchanger).

[0063] Example 5

[0064] This embodiment provides a cargo reliquefaction device for a ship liquid cargo system. The reliquefaction device is similar to that of Embodiment 2, and includes a first refrigeration cycle loop and a second cycle loop similar to those in Embodiment 2. The difference is that:

[0065] like Figure 5 As shown, the vapor outlet of the first cargo tank 1 is connected only to the inlet of the first compressor inlet buffer tank 41, the inlet of the second compressor inlet buffer tank 51 is connected to the vapor outlet of the second cargo tank 2, and the second aftercooler 54 exchanges heat with the first subcooling heat exchanger 49. The target of the second subcooling heat exchanger 59 is the liquid cargo in the third cargo tank 3. A third transfer pump 31 and a third cargo tank spray valve 33 are provided in the third cargo tank 3. The third transfer pump 31 is used to transport the liquid cargo in the third cargo tank 3 to the second subcooling heat exchanger 59 for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank 3 through the third cargo tank spray valve 33. Specifically, a third outlet valve 32 is provided between the third transfer pump 31 and the second subcooling heat exchanger 59. It should be noted that, in this embodiment, the second cargo tank 2 is no longer equipped with the second transfer pump 21, which has a gas phase outlet, and a second steam valve 24 is provided between the gas phase outlet and the inlet of the second compressor inlet buffer tank 51.

[0066] This embodiment differs from embodiments 1-4. In this embodiment, the gas evaporated from the liquid cargo in the first cargo tank 1 is used as the cooling medium for another refrigeration cycle. Cooling coupling between the two refrigeration cycles is achieved in the first subcooling heat exchanger 49. Specifically, the first refrigeration cycle uses the liquid cargo in the first cargo tank 1 as the refrigerant. The resulting low-temperature cooling energy is not directly used to cool the liquid cargo in the cargo tank, but rather subcools the cooling medium (fluid to be cooled) in the aftercooler 54 of the second refrigeration cycle through the first subcooling heat exchanger 49. Through this arrangement, the cooling energy of the first refrigeration cycle is transferred to the second refrigeration cycle. This arrangement allows the second refrigeration cycle to receive additional cooling energy beyond its own compression and cooling, further enhancing its cooling effect and achieving a lower cooling temperature. The cooling energy of the two refrigeration cycles forms a tiered utilization relationship, resulting in higher energy utilization efficiency. Furthermore, the third outlet valve 32 is used to control the flow of liquid from the third cargo tank 3 into the second subcooling heat exchanger 59. When the third cargo tank 3 does not require cooling, closing the valve will stop the circulation and avoid wasting cooling capacity. In this embodiment, the liquid in the second cargo tank 2 is no longer the object to be cooled, but rather serves as the refrigerant in the second refrigeration cycle. The liquid in the second cargo tank 2 has the lowest boiling point, and the vaporized gas of the low-boiling-point liquid is directly introduced into the second refrigeration cycle as a refrigerant. This setting fully utilizes the low-boiling-point characteristics of the liquid in the second cargo tank 2, allowing its vaporized gas to participate in the complete thermodynamic cycle of compression, cooling, throttling, and evaporation in the second refrigeration cycle as a working fluid, significantly improving the cooling effect. The second steam valve 24 allows the vaporized gas in the second cargo tank 2 to be supplied to the second refrigeration cycle as needed.

[0067] In this embodiment, preferably, the liquid cargo stored in the first cargo tank 1 is C, the liquid cargo stored in the second cargo tank 2 is A, and the liquid cargo stored in the third cargo tank 3 is B. The boiling point of A is lower than that of B, and the boiling point of B is lower than that of C. The distribution of the boiling points of the three liquid cargoes A, B, and C as A < B < C is such that A, with the lowest boiling point, serves as the refrigerant in the second refrigeration cycle, B, with a medium boiling point, is the object being cooled, and C, with the highest boiling point, serves as the refrigerant in the first refrigeration cycle. In the first refrigeration cycle, although C, with its higher boiling point, has a relatively higher evaporation temperature, the cooling capacity it generates is sufficient to subcool the external cooling medium of the second refrigeration cycle to a lower temperature. This assists the second refrigeration cycle in obtaining a lower cooling temperature to cool B, which has a medium boiling point. This arrangement fully utilizes the temperature differences between the three liquid cargoes, achieving a stepped matching and efficient utilization of cooling capacity at different temperature levels.

[0068] Specifically, the operation process of the reliquefaction device provided in this embodiment is as follows: When the pressure in the first liquid cargo tank 1 reaches a preset value, the first steam valve 12 and the first cargo tank spray valve 11 are opened, and the first refrigeration cycle circuit is then opened. The steam in the first liquid cargo tank 1 enters the first stage compressor 42 after passing through the first compressor inlet buffer tank 41. After being compressed by the first stage compressor 42, it enters the first economizer 47. After being cooled by the first economizer 47, it enters the first stage compressor 43. After being pressurized by the first stage compressor 43, it enters the first aftercooler 44, where it exchanges heat with the external medium and is cooled down. Then it enters the first liquid receiver 45. Part of the high-pressure liquid in the first liquid receiver 45 passes through the first... After being depressurized by spray valve 46, the liquid enters the first economizer 47. Another portion of the high-pressure liquid is cooled by exchanging heat with the liquid in the first economizer 47 through the pipeline and then depressurized by the first pressure reducing valve 48. The portion of the liquid after being depressurized by the first pressure reducing valve 48 enters the first subcooling heat exchanger 49 to exchange heat with the external medium in the second aftercooler 54 in the second refrigeration cycle, thereby cooling the high-temperature liquid cargo flowing through the second aftercooler 54. The liquid that has been heated by the first subcooling heat exchanger 49 becomes gas and returns to the first compressor inlet buffer tank 41 to participate in the subsequent refrigeration cycle. Another portion of the liquid after being depressurized by the first pressure reducing valve 48 returns to the first liquid cargo tank 1 through the first cargo tank spray valve 11 to reduce the pressure in the first liquid cargo tank 1. During the above operation, while the liquid cargo in the first refrigeration cycle loop manages its own liquid cargo tank pressure, the output cooling capacity is used to pre-cool or subcool the external cooling medium in the second refrigeration cycle loop. This is equivalent to providing an additional stage of cooling capacity for the second refrigeration cycle upstream of the second aftercooler 54. This allows the refrigerant in the second refrigeration cycle loop to obtain a lower condensation temperature when entering the second aftercooler 54 than when simply using seawater cooling, thereby improving the overall efficiency of the second refrigeration cycle loop.

[0069] When the pressure in the second cargo tank 2 reaches a preset value, the second steam valve 24 and the second cargo tank spray valve 23 are opened, and then the second refrigeration cycle loop is activated. The steam in the second cargo tank 2 enters the second-stage compressor 52 after passing through the second compressor inlet buffer tank 51. After being compressed by the second-stage compressor 52, it enters the second economizer 57. After being cooled by the second economizer 57, it enters the second-stage compressor 53. After being pressurized by the second-stage compressor 53, it enters the second aftercooler 54, where it exchanges heat with the low-temperature external medium after exchanging heat with the first subcooling heat exchanger 49, and then enters the second liquid receiver 55. Part of the high pressure in the second liquid receiver 55... After being depressurized by the second spray valve 56, the liquid enters the second economizer 57. Another portion of the high-pressure liquid is cooled by exchanging heat with the liquid in the second economizer 57 through the pipeline and then depressurized by the second pressure reducing valve 58. The portion of the liquid after being depressurized by the second pressure reducing valve 58 enters the second subcooling heat exchanger 59 to exchange heat with the target medium (the cargo in the third liquid cargo tank 3). The liquid that has been heated by the second subcooling heat exchanger 59 becomes gas and returns to the second compressor inlet buffer tank 51 to participate in the subsequent refrigeration cycle. Another portion of the liquid after being depressurized by the second pressure reducing valve 58 returns to the second liquid cargo tank 2 through the second cargo tank spray valve 23 to reduce the pressure in the second liquid cargo tank 2. After the second refrigeration cycle is started, the compressed high-temperature and high-pressure refrigerant exchanges heat with the external medium pre-cooled by the first subcooling heat exchanger 49 in the second aftercooler 54. The condensation temperature is significantly lower than that of direct cooling with room temperature seawater, resulting in more complete condensation. The condensed liquid refrigerant can achieve a lower evaporation temperature after throttling, thus achieving more complete cooling of the liquid cargo B in the third cargo tank 3 in the second subcooling heat exchanger 59. In addition, some of the cryogenic liquid after being depressurized by the second pressure reducing valve 58 returns to the second cargo tank 2 through the second cargo tank spray valve 23, which also plays a role in regulating the pressure of the second cargo tank 2 itself.

[0070] When the pressure in the third cargo tank 3 reaches a preset value, the third outlet valve 32 and the third cargo tank spray valve 33 are opened, and the third transfer pump 31 is started. The high-temperature cargo in the third cargo tank 3 is cooled by heat exchange in the second subcooling heat exchanger 59 and then returned to the third cargo tank 3, thereby reducing the pressure in the third cargo tank 3. Through the above settings, the liquid cargo B in the third cargo tank 3 is cooled by the low-temperature refrigerant provided by the second refrigeration cycle loop in the second subcooling heat exchanger 59 and then sprayed back into the tank. The low-temperature liquid cargo B continuously absorbs heat from the third cargo tank 3, reducing further evaporation of liquid cargo B and maintaining the tank pressure within a safe range.

[0071] In the reliquefaction device, the opening degree of the first spray valve 46 and / or the second spray valve 56 is controlled by the liquid level in their corresponding first economizer 47 and / or second economizer 57. When the liquid level in the first economizer 47 and / or second economizer 57 is greater than a set value, the opening degree of the first spray valve 46 and / or second spray valve 56 decreases; when the liquid level in the first economizer 47 and / or second economizer 57 is less than the set value, the opening degree of the first spray valve 46 and / or second spray valve 56 increases. Specifically, the opening degree of the first spray valve 46 and / or second spray valve 56 is constrained by the motor power limit of their corresponding first secondary compressor 43 and / or second secondary compressor 53 during the adjustment process. When the motor power of the first secondary compressor 43 and / or second secondary compressor 53 reaches a preset value, the opening degree of the first spray valve 46 and / or second spray valve 56 will not increase even if the liquid level in the first economizer 47 and / or second economizer 57 is less than the set value. This is because if the opening of the first spray valve 46 and / or the second spray valve 56 is increased at this time, the flow rate into the first and / or second stage compressors 43 and / or 53 will increase, which may easily cause a motor alarm. The above settings can effectively avoid motor alarms and ensure the normal operation of the first and / or second stage compressors 43 and / or 53.

[0072] As an example of this application, the first pressure-reducing valve 48 and / or the second pressure-reducing valve 58 are controlled by the liquid level in their respective first liquid receiver 45 and / or second liquid receiver 55. When the liquid level in the first liquid receiver 45 and / or the second liquid receiver 55 is greater than a set value, the opening of the first pressure-reducing valve 48 and / or the second pressure-reducing valve 58 increases; when the liquid level in the first liquid receiver 45 and / or the second liquid receiver 55 is less than the set value, the opening of the first pressure-reducing valve 48 and / or the second pressure-reducing valve 58 decreases. Through this setting, when the liquid level in the liquid receiver is high, the opening of the pressure-reducing valve is increased, allowing excess liquid refrigerant to expand and absorb heat in the subcooling heat exchanger, thus maintaining the stability of the liquid level in the liquid receiver and enhancing the heat exchange effect of the subcooling heat exchanger. When the liquid level in the liquid receiver is low, the opening of the pressure-reducing valve is decreased, ensuring sufficient liquid refrigerant is supplied to the economizer for cooling. This setting allows the refrigeration cycle loop to maintain a stable operating state under different heat load conditions, avoiding system oscillations or a decrease in cooling effect caused by liquid level fluctuations.

[0073] It should be noted that in embodiments 1-5, the first aftercooler 44 receives external cooling medium through the external cooling medium inlet ② and the external cooling medium outlet ① to cool the high-temperature liquid goods delivered by the first secondary compressor 43. The external cooling medium can be seawater, fresh water, or other cooling media in a refrigeration cycle, which will not be elaborated further here.

[0074] It should be noted that when the number of liquid cargo tanks is three or more, the reliquefaction device in this application can be improved according to the processing principles of any one of Embodiments 2-5, and all of them are within the protection scope of this application, and will not be described in detail here.

[0075] Example 6

[0076] This embodiment provides a cargo reliquefaction device for a ship's liquid cargo system, specifically based on an example from Embodiment 5. Cargo A is ethylene, cargo B is ethane, and cargo C is propylene. During operation, the pressure of the compressor inlet buffer tank corresponding to cargo A is 0.2 barg, and the temperature is -95°C; the pressure of the first-stage compressor outlet is 4 barg, and the temperature is 50°C; the temperature in the economizer is -64°C; the pressure of the second-stage compressor outlet is 15 barg, and the temperature is 25°C; and the temperature after heat exchange in the aftercooler is -35°C.

[0077] For product C, the compressor inlet buffer tank pressure is 0.2 barg and the temperature is -40℃; the first-stage compressor outlet pressure is 4 barg and the temperature is 50℃; the economizer temperature is 3℃; the second-stage compressor outlet pressure is 15 barg and the temperature is 65℃; and the temperature after heat exchange in the aftercooler is 40℃.

[0078] The outlet pressure of the transport pump corresponding to cargo B is 4 barg, the temperature is -86℃, and the temperature after heat exchange is -91℃.

[0079] It should be noted that the cargo tanks on the liquefied cargo ship can carry more than ten types of goods. When different goods are loaded into the cargo tanks, the reliquefaction unit ensures stable operation by adjusting the first spray valve 46 / second spray valve 56 and the first pressure reducing valve 48 / second pressure reducing valve 58. When the reliquefaction unit is running smoothly, the temperature, pressure, and other parameters of each device in the reliquefaction unit change with the different goods and the different temperatures of the cooling medium.

[0080] It should be understood that the specific types of goods listed in this embodiment and their corresponding operating parameters are only used to illustrate the actual operating state of the reliquefaction device provided in this application, and are not used to limit the specific types of liquid goods or the operating parameters.

[0081] Example 7

[0082] This embodiment provides a liquid cargo ship, including a cargo reliquefaction device for a ship liquid cargo system as described in any of Embodiments 1 to 6.

[0083] The advantages of the liquid cargo ship provided in this embodiment compared to the prior art are the same as those of the cargo reliquefaction device of the ship liquid cargo system provided in any of Embodiments 1 to 6, and will not be repeated here.

[0084] It should be understood that the liquid cargo ship also includes conventional components such as the power system that a conventional liquid cargo ship should have, and specific details can be found in existing technologies, which will not be limited here.

[0085] It should be noted that all directional and positional terms used in this invention, such as "up," "down," "left," "right," "front," "back," "vertical," "horizontal," "inner," "outer," "top," "lower," "tail end," "head end," and "center," are only used to explain the relative positional relationships and connection situations between components in a specific state. They are merely for the convenience of describing the invention and do not require the invention to be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on the invention. Furthermore, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0086] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A cargo reliquefaction device for a ship liquid cargo system, characterized in that, For use in a liquid cargo ship, the liquid cargo ship having two or more liquid cargo tanks, including at least a first liquid cargo tank (1) and a second liquid cargo tank (2), for storing at least two different liquid cargoes, the reliquefaction device comprising: A refrigeration cycle loop, which is at least connected to the first cargo tank (1), is configured as follows: At least a portion of the liquid cargo that has evaporated into gas in the first liquid cargo tank (1) is used as a refrigerant, which is processed by the refrigeration cycle loop to form a cryogenic refrigerant, which is used to cool a target object, the target object including liquid cargo in other liquid cargo tanks, and / or, at least one other fluid to be cooled in another refrigeration cycle loop.

2. The cargo reliquefaction device for a ship liquid cargo system as described in claim 1, characterized in that, The refrigeration cycle includes a first refrigeration cycle, which includes a first compressor inlet buffer tank (41), a first stage compressor (42), a first economizer (47), a first stage compressor (43), a first aftercooler (44), a first liquid receiver (45), a first pressure reducing valve (48), and a first subcooling heat exchanger (49). The gas phase outlet of the first liquid cargo tank (1) is connected to the inlet of the first compressor inlet buffer tank (41), the outlet of the first compressor inlet buffer tank (41) is connected to the inlet of the first stage compressor (42), the outlet of the first stage compressor (42) is connected to the first inlet of the first economizer (47), the outlet of the first economizer (47) is connected to the inlet of the first stage compressor (43), and the outlet of the first stage compressor (43) is connected to the first aftercooler (44). The inlet of the first aftercooler (44) is connected, the outlet of the first aftercooler (44) is connected to the inlet of the first liquid receiver (45), the outlet of the first liquid receiver (45) is connected to the inlet of the first pressure reducing valve (48), the outlet of the first pressure reducing valve (48) is connected to the refrigerant inlet of the first subcooling heat exchanger (49), the refrigerant outlet of the first subcooling heat exchanger (49) is connected to the inlet of the first compressor inlet buffer tank (41), the target object flows through the first subcooling heat exchanger (49) for heat exchange with the low-temperature refrigerant formed by the first refrigeration cycle loop, a first cargo tank spray valve (11) is provided in the first liquid cargo tank (1), the outlet of the first pressure reducing valve (48) is also connected to the first cargo tank spray valve (11) for transporting part of the low-temperature refrigerant back to the first liquid cargo tank (1).

3. The cargo reliquefaction device for a ship liquid cargo system as described in claim 2, characterized in that, The target of the first refrigeration cycle loop is the liquid cargo in the second liquid cargo tank (2). The second liquid cargo tank (2) is equipped with a second transfer pump (21) and a second cargo tank spray valve (23). The second transfer pump (21) is used to transport the liquid cargo in the second liquid cargo tank (2) to the first subcooling heat exchanger (49) to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second liquid cargo tank (2) through the second cargo tank spray valve (23).

4. The cargo reliquefaction device for a ship liquid cargo system as described in claim 2, characterized in that, The cargo ship also includes a third cargo tank (3), the cargo stored in the third cargo tank (3) being at least different from the cargo in the first cargo tank (1), the first refrigeration cycle also includes a second subcooling heat exchanger (59), the outlet of the first pressure reducing valve (48) is also connected to the refrigerant inlet of the second subcooling heat exchanger (59), the refrigerant outlet of the second subcooling heat exchanger (59) is connected to the inlet of the first compressor inlet buffer tank (41), the target of the second subcooling heat exchanger (59) flows through the second subcooling heat exchanger (59) for heat exchange with the low-temperature refrigerant formed by the first refrigeration cycle, wherein the target of the first refrigeration cycle is the cargo in the second cargo tank (2), and a second transfer pump is provided in the second cargo tank (2). 21) and the second cargo hold spray valve (23), the second transfer pump (21) is used to transport the liquid cargo in the second liquid cargo tank (2) to the first subcooling heat exchanger (49) to exchange heat with the low temperature refrigerant therein, and the liquid cargo after heat exchange is transported back to the second liquid cargo tank (2) through the second cargo hold spray valve (23); the target object of the second subcooling heat exchanger (59) is the liquid cargo in the third liquid cargo tank (3), and the third transfer pump (31) and the third cargo hold spray valve (33) are provided in the third liquid cargo tank (3), the third transfer pump (31) is used to transport the liquid cargo in the third liquid cargo tank (3) to the second subcooling heat exchanger (59) to exchange heat with the low temperature refrigerant therein, and the liquid cargo after heat exchange is transported back to the third liquid cargo tank (3) through the third cargo hold spray valve (33).

5. The cargo reliquefaction device for a ship liquid cargo system as described in claim 2, characterized in that, The cargo ship also includes a third cargo tank (3), in which the liquid cargo stored is at least different from that in the first cargo tank (1). The first subcooling heat exchanger (49) is a multi-flow subcooling heat exchanger, which includes three or more sets of inlets and outlets, one of which is connected to the outlet of the first pressure reducing valve (48) and the inlet of the first compressor inlet buffer tank (41), respectively. A second transfer pump (21) and a second cargo tank spray valve (23) are provided in the second cargo tank (2). The second transfer pump (21) and the second cargo tank spray valve (23) are connected to another set of inlets and outlets in the multi-flow subcooling heat exchanger. The second transfer pump (21) is used to transfer the liquid cargo in the second cargo tank (2) to the first cargo tank (2). The liquid cargo is transported to the multi-flow cooling heat exchanger to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the second cargo tank (2) through the second cargo tank spray valve (23). A third transfer pump (31) and a third cargo tank spray valve (33) are provided in the third cargo tank (3). The third transfer pump (31) and the third cargo tank spray valve (33) are connected to another set of inlet and outlet in the multi-flow cooling heat exchanger. The third transfer pump (31) is used to transport the liquid cargo in the third cargo tank (3) to the multi-flow cooling heat exchanger to exchange heat with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third cargo tank (3) through the third cargo tank spray valve (33).

6. The cargo reliquefaction device for a ship liquid cargo system as described in claim 2, characterized in that, The cargo ship also includes a third cargo tank (3), the cargo stored in the third cargo tank (3) being at least different from the cargo in the first cargo tank (1). The refrigeration cycle also includes a second refrigeration cycle, the second refrigeration cycle including a second compressor inlet buffer tank (51), a second first-stage compressor (52), a second economizer (57), a second second-stage compressor (53), a second aftercooler (54), a second liquid receiver (55), a second pressure reducing valve (58), and a second subcooling heat exchanger (59). The vapor phase outlet of the first cargo tank (1) is connected to the inlet of the second compressor inlet buffer tank (51), or the vapor phase outlet of the second cargo tank (2) is connected to the inlet of the second compressor inlet buffer tank (51), and the outlet of the second compressor inlet buffer tank (51) is connected to the inlet of the second first-stage compressor (52). The outlet of the machine (52) is connected to the first inlet of the second economizer (57), the outlet of the second economizer (57) is connected to the inlet of the second secondary compressor (53), the outlet of the second secondary compressor (53) is connected to the inlet of the second aftercooler (54), the outlet of the second aftercooler (54) is connected to the inlet of the second liquid receiver (55), the outlet of the second liquid receiver (55) is connected to the inlet of the second pressure reducing valve (58), the outlet of the second pressure reducing valve (58) is connected to the refrigerant inlet of the second subcooling heat exchanger (59), the refrigerant outlet of the second subcooling heat exchanger (59) is connected to the inlet of the second compressor inlet buffer tank (51), and the target object of the second subcooling heat exchanger (59) flows through the second subcooling heat exchanger (59) for heat exchange with the low-temperature refrigerant formed in the second refrigeration cycle loop.

7. The cargo reliquefaction device for a ship liquid cargo system as described in claim 6, characterized in that, When the inlet of the second compressor inlet buffer tank (51) is connected to the gas phase outlet of the first liquid cargo tank (1), the second aftercooler (54) exchanges heat with the external cooling medium and condenses; when the inlet of the second compressor inlet buffer tank (51) is connected to the gas phase outlet of the second liquid cargo tank (2), the second aftercooler (54) exchanges heat with the first subcooling heat exchanger (49) through the cooling medium and condenses.

8. The cargo reliquefaction device for a ship liquid cargo system as described in claim 7, characterized in that, When the inlet of the second compressor inlet buffer tank (51) is connected to the gas phase outlet of the first liquid cargo tank (1): the target of the first refrigeration cycle is the liquid cargo in the second liquid cargo tank (2). A second transfer pump (21) and a second cargo tank spray valve (23) are provided in the second liquid cargo tank (2). The second transfer pump (21) is used to transport the liquid cargo in the second liquid cargo tank (2) to the first subcooling heat exchanger (49) for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo passes through the second cargo tank spray valve. The spray valve (23) is sent back to the second cargo tank (2); the target of the second subcooling heat exchanger (59) is the liquid cargo in the third cargo tank (3). The third cargo tank (3) is equipped with a third transfer pump (31) and a third cargo tank spray valve (33). The third transfer pump (31) is used to transport the liquid cargo in the third cargo tank (3) to the second subcooling heat exchanger (59) for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is sent back to the third cargo tank (3) through the third cargo tank spray valve (33). When the inlet of the second compressor inlet buffer tank (51) is connected to the gas phase outlet of the second liquid cargo tank (2): The target of the first refrigeration cycle is the fluid to be cooled in the second refrigeration cycle. The fluid to be cooled is the cooling medium between the second aftercooler (54) and the first subcooling heat exchanger (49), which is used to condense the second aftercooler (54). A second cargo tank spray valve (23) is provided in the second liquid cargo tank (2). The outlet of the second pressure reducing valve (58) is also connected to the second cargo tank spray valve (23), which is used to transport part of the low-temperature refrigerant generated by the second refrigeration cycle back to the second liquid cargo tank (2). The target of the second subcooling heat exchanger (59) is the liquid cargo in the third liquid cargo tank (3). The third liquid cargo tank (3) is equipped with a third transfer pump (31) and a third cargo tank spray valve (33). The third transfer pump (31) is used to transport the liquid cargo in the third liquid cargo tank (3) to the second subcooling heat exchanger (59) for heat exchange with the low-temperature refrigerant therein. After heat exchange, the liquid cargo is transported back to the third liquid cargo tank (3) through the third cargo tank spray valve (33).

9. The cargo reliquefaction device for a ship liquid cargo system as described in any one of claims 2-8, characterized in that, The first aftercooler (44) exchanges heat with the external cooling medium and condenses.

10. A liquid cargo ship, characterized in that, Includes a cargo reliquefaction device for a ship liquid cargo system as described in any one of claims 1-9.

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