Pressure regulation system for refrigerant cycle of marine reliquefaction system

Abstract

A pressure regulation system for a refrigerant cycle of a marine reliquefaction system is disclosed. a refrigerant cycle having a heat exchanger provided in a reliquefaction system of a ship for cooling evaporated gas supplied from a storage tank; a refrigerant circulation line through which a refrigerant for cooling the evaporated gas in the heat exchanger circulates; a refrigerant compressor provided in the refrigerant circulation line for compressing the refrigerant discharged after cooling the evaporated gas in the heat exchanger; and an expander for expanding and cooling the refrigerant compressed by the refrigerant compressor and then cooled in the heat exchanger, and supplying it as refrigerant for the heat exchanger; an inventory tank for storing refrigerant to be filled in the refrigerant cycle; a refrigerant supply line connected from the inventory tank to the upstream of the refrigerant compressor for refilling the refrigerant to the refrigerant cycle; a refrigerant discharge line connected from the downstream of the refrigerant compressor to the inventory tank for discharging the refrigerant from the refrigerant cycle to the inventory tank; and a pressure adjustment line branching off from the refrigerant discharge line, and the refrigerant cycle is depressurized by discharging the refrigerant from the refrigerant cycle into the refrigerant discharge line or the pressure adjustment line.

Description

[Technical field]

[0001] The present invention relates to a pressure regulation system for a refrigerant cycle of a reliquefaction system for a ship, and more particularly to a system for regulating the pressure of a refrigerant cycle of a refrigerant circulating in a reliquefaction system that reliquefies evaporated gas generated on a ship. [Background technology]

[0002] Natural gas is primarily composed of methane and emits almost no environmental pollutants when burned, so it has been drawing attention as an environmentally friendly fuel. Liquefied natural gas (LNG) is obtained by liquefying natural gas by cooling it to about -163°C under standard atmospheric pressure. LNG is very suitable for long-distance transportation by sea, as its volume is reduced to about 1 / 600 of that of natural gas in gaseous state. For this reason, natural gas is mainly stored and transported in the form of liquefied natural gas, which is easy to store and transport.

[0003] Since the liquefaction point of natural gas is an extremely low temperature of approximately -163°C at standard atmospheric pressure, LNG storage tanks are usually insulated to maintain LNG in a liquid state. However, even if LNG storage tanks are insulated, there is a limit to how much they can block external heat, and external heat is continuously transferred to the LNG storage tank. Therefore, during the LNG transportation process, LNG naturally vaporizes continuously inside the LNG storage tank, generating boil-off gas (BOG).

[0004] Evaporative gases that are continuously generated in LNG storage tanks cause the internal pressure of the LNG storage tanks to increase. If the internal pressure of the storage tank exceeds a preset safety pressure, an emergency such as tank rupture may occur, so it is necessary to use a safety valve to release the evaporated gases to the outside of the storage tank. However, since evaporated gases are a type of LNG loss and are a significant issue in terms of LNG transportation efficiency and fuel efficiency, various methods are used to treat the evaporated gases generated in storage tanks.

[0005] In recent years, methods have been developed and applied in which the evaporated gas is used at the fuel demand point, such as in ship engines, or the evaporated gas is reliquefied and collected in a storage tank, or a combination of these two methods is used. Summary of the Invention [Problem to be solved by the invention]

[0006] When applying a reliquefaction cycle to reliquefy evaporated gas on a ship, the liquefaction methods that can be adopted include processes using the SMR cycle and the C3MR cycle. The C3MR cycle (Propane-precooled Mixed Refrigerant Cycle) is a process in which natural gas is cooled using a single refrigerant, propane, and then liquefied and supercooled using a mixed refrigerant. The SMR cycle (Single Mixed Refrigerant Cycle) is a process in which natural gas is liquefied using a mixed refrigerant composed of multiple components.

[0007] Since these SMR and C3MR cycles all use a mixed refrigerant, refrigerant leakage occurs as the liquefaction process progresses, and the liquefaction efficiency decreases due to changes in the composition ratio of the mixed refrigerant. Therefore, it is necessary to continuously measure the composition ratio of the mixed refrigerant and to maintain the refrigerant composition by filling in the missing refrigerant components.

[0008] An alternative reliquefaction cycle for reliquefying evaporated gas is a single cycle liquefaction process using nitrogen refrigerant.

[0009] Although cycles using nitrogen refrigerant are less efficient than those using mixed refrigerants, they have the advantage of being safer because the refrigerant is inert, and since there is no phase change of the refrigerant, they are easier to apply to ships.

[0010] In the case of a reliquefaction system using nitrogen refrigerant, the load of the reliquefaction system is adjusted by supplying refrigerant charged in the inventory tank to the refrigerant cycle of the reliquefaction system and charging or discharging refrigerant from the refrigerant cycle depending on the load.

[0011] The present invention proposes a system that allows smooth replenishment or drainage of refrigerant into or from the refrigerant cycle, thereby regulating the load on the reliquefaction system and reducing the use of equipment for replenishing nitrogen refrigerant. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention provides a refrigerant cycle provided in a reliquefaction system of a ship, the refrigerant cycle having a heat exchanger for cooling evaporated gas supplied from a storage tank, a refrigerant circulation line through which a refrigerant for cooling the evaporated gas in the heat exchanger circulates, a refrigerant compressor provided in the refrigerant circulation line for compressing the refrigerant discharged from the heat exchanger after cooling the evaporated gas in the heat exchanger, and an expander for expanding and cooling the refrigerant compressed by the refrigerant compressor and then cooled in the heat exchanger, and supplying the refrigerant to the heat exchanger, the refrigerant cycle comprising: an inventory tank for storing refrigerant to be filled in the refrigerant cycle; a refrigerant supply line connected from the inventory tank to the upstream of the refrigerant compressor for refilling the refrigerant to the refrigerant cycle; a refrigerant discharge line connected from the downstream of the refrigerant compressor to the inventory tank for discharging the refrigerant of the refrigerant cycle to the inventory tank; and a pressure adjustment line branching off from the refrigerant discharge line, the refrigerant cycle is depressurized by discharging the refrigerant of the refrigerant cycle into the refrigerant discharge line or the pressure adjustment line. When the refrigerant cycle is depressurized, the refrigerant is preferentially discharged to the inventory tank through the refrigerant discharge line, and after the pressure in the inventory tank and the refrigerant cycle is reversed, the refrigerant is discharged to the pressure adjustment line, whereby the refrigerant cycle is depressurized and the refrigerant discharged through the pressure adjustment line is not discharged outside the ship, but is reused as at least one of the refrigerant to be replenished to the refrigerant cycle, the utility gas to be supplied on board, and the blanket gas to be supplied on board.The present invention provides a pressure regulation system for a refrigerant cycle of a marine reliquefaction system, comprising:

[0013] In the present invention, the cooling system further includes a first valve provided upstream of a branch point of the refrigerant discharge line with the pressure regulation line, a second valve provided in the pressure regulation line, and a third valve provided downstream of a branch point of the refrigerant discharge line with the pressure regulation line. El .

[0014] In addition, the present invention further includes a buffer tank provided on the ship for storing utility N2 to be supplied to the ship, a drying and filtering section for drying and filtering the utility N2 supplied from the buffer tank to lower the dew point, and a boost compressor for compressing the nitrogen refrigerant that has passed through the drying and filtering section before supplying it to the inventory tank.

[0015] In addition, in the present invention, the pressure regulating line is connected to the buffer tank, and the buffer tank is operated at a lower pressure than the inventory tank.

[0016] Also, in the present invention, the pressure regulating line is connected upstream of the boost compressor.

[0017] In addition, in the present invention, the reliquefaction system includes a gas-liquid separator to which the evaporated gas cooled in the heat exchanger is supplied and which undergoes phase separation, the pressure regulating line is connected to the gas-liquid separator, and the refrigerant discharged from the refrigerant cycle is supplied to an upper portion of the gas-liquid separator as an inert gas for maintaining the pressure within the gas-liquid separator.

[0018] In addition, in the present invention, the inventory tank is supplied with the nitrogen refrigerant compressed by the boost compressor and includes a high-pressure tank that supplies the supplied nitrogen refrigerant upstream of the refrigerant compressor, and a low-pressure tank that operates at a lower pressure than the high-pressure tank, and the pressure adjustment line is connected to the low-pressure tank.

[0019] In addition, in the present invention, the operating pressure of the low-pressure tank is operated at the suction pressure of the boost compressor, and the pressure of the low-pressure tank is maintained by pressurizing the low-pressure tank with the refrigerant discharged to the pressure adjustment line and discharging the refrigerant from the low-pressure tank upstream of the boost compressor. Effect of the Invention

[0020] The refrigerant cycle pressure regulation system of the present invention allows smooth replenishment or drainage of refrigerant from the refrigerant cycle to regulate the load of the reliquefaction system.

[0021] In particular, in the present invention, when the refrigerant cycle is depressurized to reduce the load of the reliquefaction system, the refrigerant is discharged and sent to the inventory tank, and the refrigerant that cannot be sent to the inventory tank due to pressure reversal is supplied to a buffer tank, a low pressure tank, or upstream of the boost compressor to be reused in the refrigerant cycle or used as blanketing N2 in the gas-liquid separator of the reliquefaction system, thereby reducing the use of equipment for supplying nitrogen on board. As a result, power consumption is reduced, and operating expenses (OPEX) can be reduced. [Brief description of the drawings]

[0022] [Figure 1] 1 shows a schematic of a pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to a basic embodiment of the present invention. [Diagram 2] 1 is a schematic diagram showing a pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to a first embodiment of the present invention; [Diagram 3] 5 shows a schematic diagram of a pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to a second embodiment of the present invention. [Figure 4] 13 is a schematic diagram showing a pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to a third embodiment of the present invention; [Diagram 5]13 is a schematic diagram showing a pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to a fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The operating advantages and objects attained by the practice of the invention will now be described, by way of example only, with reference to the accompanying drawings and the contents thereof, in which: FIG.

[0024] Hereinafter, the configuration and operation of the embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the drawings, the same components of the embodiment of the present invention will be denoted by the same reference numerals whenever possible.

[0025] The ships according to the embodiments of the present invention described below include all types of ships that are provided with storage tanks for storing liquefied gas. For example, the ships according to the embodiments of the present invention include ships that have self-propelling capabilities, such as LNG carriers, liquid hydrogen carriers, and LNG RVs (regasification vessels), as well as floating offshore structures that do not have propulsion capabilities, such as LNG FPSOs (floating production storage offloading) and LNG FSRUs (floating storage regasification units).

[0026] In addition, the present invention can liquefy gas to a low temperature for transportation, and can be applied to the reliquefaction cycle of all kinds of liquefied gases that generate evaporated gas in the storage state. Such liquefied gases include liquefied petroleum gases such as LNG (Liquefied Natural Gas), LEG (Liquefied Ethane Gas), LPG (Liquefied Petroleum Gas), liquefied ethylene gas, and liquefied propylene gas. However, in the embodiment described below, the application of LNG, which is one of the representative liquefied gases, will be described as an example.

[0027] Fig. 1 shows a schematic diagram of a pressure regulation system for a refrigerant cycle of a reliquefaction system for a marine vessel according to a basic embodiment of the present invention. Fig. 2 to Fig. 5 show schematic diagrams of pressure regulation systems for a refrigerant cycle of a reliquefaction system for a marine vessel according to first to fourth embodiments of the present invention.

[0028] In the refrigerant cycle pressure adjustment system of this embodiment, the pressure of the refrigerant cycle is adjusted by replenishing or discharging refrigerant from the refrigerant supply unit 300, which supplies refrigerant to the refrigerant cycle of the ship's reliquefaction system, to adjust the load of the reliquefaction system.

[0029] In the reliquefaction system, evaporated gas generated from liquefied gas stored in the storage tank of the ship is compressed and cooled to be reliquefied and returned to the storage tank. The reliquefaction system includes, for example, a compressor for compressing the evaporated gas, a heat exchanger for cooling the compressed evaporated gas, a pressure reducing device for reducing the pressure of the evaporated gas cooled by the heat exchanger, and a gas-liquid separator for separating the evaporated gas reduced in pressure by the pressure reducing device into gas and liquid.

[0030] 1 to 5, the refrigerant cycle is configured such that a refrigerant for cooling an evaporated gas circulates in a heat exchanger 100. The heat exchanger 100 of this embodiment cools a compressed evaporated gas line RL using a refrigerant circulation line CL that circulates in the refrigerant cycle and an uncompressed evaporated gas line GL that is supplied from a storage tank to a compressor as cold heat sources.

[0031] The refrigerant cycle includes a refrigerant circulation line CL through which a refrigerant circulates, a refrigerant compressor 210 that is provided in the refrigerant circulation line CL and compresses the refrigerant discharged from the heat exchanger 100 after cooling the evaporated gas in the heat exchanger 100, and an expander 200 that expands and cools the refrigerant compressed in the refrigerant compressor 210 and then cooled in the heat exchanger 100, and supplies the refrigerant to the heat exchanger 100. The refrigerant compressor 210 and the expander 200 are axially connected and provided as a compander that utilizes the expansion energy of the refrigerant to compress the refrigerant.

[0032] The refrigerant that is circulated through the refrigerant circulation line CL and supplied to the heat exchanger 100 may be, for example, nitrogen (N2).

[0033] The refrigerant supply unit 300 is a part that supplies a refrigerant to the refrigerant cycle. The refrigerant supply unit 300 includes a drying and filtering unit 330 that dries the utility N2 supplied from a buffer tank NT that stores the utility N2 supplied to the ship to lower the dew point, a boost compressor 320 that compresses the nitrogen supplied from the drying and filtering unit 330 and fills it into an inventory tank 310, and an inventory tank 310 that stores the nitrogen supplied from the boost compressor 320 and supplies the stored nitrogen to the refrigerant cycle as a refrigerant.

[0034] The amount of cold energy required in the reliquefaction system changes with the change in the amount of evaporated gas generated from the storage tank and reliquefied. In this case, without adjusting the variable geometry nozzle (VGN) of the expander 200, the compression ratio / expansion ratio of the refrigerant compressor 210 and the expander 200 is kept fixed, and the amount of cold energy in the refrigerant circulation line CL is adjusted by changing the mass flow rate of the refrigerant by partially replenishing the refrigerant from the refrigerant supply unit 300 to the refrigerant cycle or discharging a portion of the refrigerant from the refrigerant circulation line CL. This adjusts the load of the reliquefaction system.

[0035] Therefore, a refrigerant supply line SL is provided that is connected from the inventory tank 310 to the upstream of the refrigerant compressor 210 and replenishes refrigerant to the refrigerant cycle, and a refrigerant discharge line DL is provided that is connected from the downstream of the refrigerant compressor 210 to the inventory tank 310 and discharges the refrigerant from the refrigerant cycle into the inventory tank 310.

[0036] More specifically, when the refrigeration requirement of the reliquefaction system increases, the compander compression ratio / expansion ratio is fixed at a constant value without adjusting the VGN, and some refrigerant is replenished from the inventory tank 310 via the refrigerant supply line SL upstream of the refrigerant compressor 210 to increase the mass flow rate of the refrigerant cycle.

[0037] Conversely, when the amount of cold required by the reliquefaction system decreases, a portion of the refrigerant in the refrigerant cycle is discharged from the downstream of the refrigerant compressor 210 to the inventory tank 310 via the refrigerant discharge line DL to reduce the mass flow rate of the refrigerant cycle. At this time, if the operating pressure of the inventory tank 310 and the pressure of the refrigerant discharged from the refrigerant circulation line CL through the refrigerant discharge line DL are reversed and it is no longer possible to discharge the refrigerant into the inventory tank 310, the refrigerant is discharged to the outside of the refrigerant supply unit 300 via the vent line VL, thereby reducing the pressure of the refrigerant cycle by the required amount.

[0038] In this way, the load of the reliquefaction system is adjusted by adjusting the mass flow rate of the refrigerant cycle. However, since refrigerant loss occurs every time capacity control is performed by discharging refrigerant to the outside through the vent line VL, it is necessary to charge refrigerant into the inventory tank 310 each time. In addition, in order to replenish refrigerant to the refrigerant cycle, it is necessary to supply utility N2 from the buffer tank NT on board to operate devices such as the dry filter unit 330 and the boost compressor 320, which increases nitrogen consumption on board and increases power consumption to operate the devices.

[0039] The first to fourth embodiments described below are designed to solve these problems and reduce the amount of nitrogen consumed on board by reusing or recycling the nitrogen refrigerant discharged to adjust the amount of cold energy in the refrigerant cycle or by reducing the amount of electricity consumed.

[0040] 2 to 5, pressure adjustment lines PLa, PLb, PLc, and PLd are branched from the refrigerant discharge line DL, and first valves V1a, V1b, V1c, and V1d are provided upstream of the branch point of the refrigerant discharge line DL with each of the pressure adjustment lines PLa, PLb, PLc, and PLd. Second valves V2a, V2b, V2c, and V2d are provided in each of the pressure adjustment lines PLa, PLb, PLc, and PLd. Third valves V3a, V3b, V3c, and V3d are provided downstream of the branch point of the refrigerant discharge line DL with each of the pressure adjustment lines PLa, PLb, PLc, and PLd.

[0041] In this embodiment, when the refrigerant cycle is depressurized, the first valves V1a, V1b, V1c, V1d and the third valves V3a, V3b, V3c, V3d are opened to preferentially discharge the refrigerant to the inventory tank 310 through the refrigerant discharge line DL, and after the pressure between the inventory tank 310 and the refrigerant cycle is reversed, the third valves V3a, V3b, V3c, V3d are closed and the second valves V2a, V2b, V2c, V2d are opened to discharge the refrigerant to the pressure regulation lines PLa, PLb, PLc, PLd, thereby depressurizing the refrigerant cycle and reducing the mass flow rate of the refrigerant. Each embodiment uses the refrigerant discharged through the pressure regulation lines PLa, PLb, PLc, PLd in different ways.

[0042] First, in the system of the first embodiment shown in Fig. 2, the pressure adjustment line PLa is connected to the buffer tank NT. Since the buffer tank NT operates at a lower pressure than the inventory tank 310, the refrigerant is discharged to the inventory tank 310 via the refrigerant discharge line DL. After the pressures of the inventory tank 310 and the refrigerant cycle are reversed, the second valve V2a is opened to discharge the refrigerant in the refrigerant circulation line CL to the buffer tank NT, thereby adjusting the pressure of the refrigerant cycle.

[0043] By sending nitrogen to the buffer tank NT and reusing it instead of discharging it overboard, the use of nitrogen generators and supply devices to generate and supply the ship's utility N2 is reduced, and electricity consumption is also reduced.

[0044] 3, the pressure adjustment line PLb is connected upstream of the boost compressor 320 of the refrigerant supply unit 300. The refrigerant that cannot be sent to the inventory tank 310 is not discharged overboard, but is instead supplied upstream of the boost compressor 320, compressed, stored, and reused, thereby reducing nitrogen consumption on board and reducing power consumption due to the use of equipment for supplying nitrogen.

[0045] In the system of the third embodiment shown in FIG. 4, a pressure regulating line PLc is connected to the upper part of a gas-liquid separator 400 of the reliquefaction system. For example, when the separated liquefied gas is discharged from the gas-liquid separator 400, an inert gas is supplied to the gas-liquid separator 400 to prevent a vacuum state from occurring and to maintain the pressure inside the gas-liquid separator 400. In this embodiment, the pressure regulating line PLc is connected to the upper part of the gas-liquid separator 400, and supplies the nitrogen refrigerant discharged from the refrigerant cycle to the gas-liquid separator 400. Since the nitrogen discharged from the refrigerant cycle can be used as blanketing N2 in this way, the amount of nitrogen consumed on board the ship is reduced, and the amount of power consumed by the use of a device for supplying nitrogen is also reduced.

[0046] 5 includes a high-pressure tank 310a that receives nitrogen refrigerant compressed by a boost compressor 320 and supplies the nitrogen refrigerant to the upstream of the refrigerant compressor 210, and a low-pressure tank 310b that operates at a lower pressure than the high-pressure tank 310a. An inventory tank is formed of two types of tanks 310a and 310b having different operating pressures, and a pressure adjustment line PLd is provided to be connected to the low-pressure tank 310b.

[0047] The operating pressure of the low pressure tank 310b is driven by the suction pressure of the boost compressor 320.

[0048] When the refrigerant cycle is depressurized, the first and third valves V1d and V3d are opened to preferentially discharge the refrigerant to the high-pressure tank 310a in the inventory tank through the refrigerant discharge line DL. After the pressure between the high-pressure tank 310a and the refrigerant cycle is reversed, the third valve V3d is closed and the second valve V2d is opened to discharge the refrigerant to the low-pressure tank 310b through the pressure adjustment line PLd, thereby reducing the refrigerant mass flow rate in the refrigerant circulation line CL.

[0049] By pressurizing the low-pressure tank 310b with the refrigerant discharged to the pressure adjustment line PLd, the refrigerant is discharged from the low-pressure tank 310b upstream of the boost compressor 320. This maintains the pressure in the low-pressure tank 310b, and the refrigerant discharged from the low-pressure tank 310b is compressed by the boost compressor 320 and then supplied to the high-pressure tank 310a, thereby replenishing the refrigerant cycle.

[0050] In this way, the refrigerant is not discharged outside the ship but is sent to the low pressure tank 310b and then reused by supplying it upstream of the boost compressor 320, thereby reducing nitrogen consumption on board and enabling stable operation by maintaining constant the pressure of the high pressure tank 310a that replenishes the refrigerant in the refrigerant cycle. In addition, the amount of power consumed by the use of the device for supplying nitrogen is also reduced.

[0051] The present invention is not limited to the above-described embodiments, and it is obvious to a person having ordinary skill in the art to which the present invention pertains that the present invention can be modified or changed in various forms without departing from the technical gist of the present invention.

Claims

1. a heat exchanger in the ship's reliquefaction system for cooling the evaporated gas supplied from the storage tank; and a refrigerant cycle including a refrigerant circulation line through which a refrigerant for cooling the evaporative gas in the heat exchanger circulates, a refrigerant compressor provided in the refrigerant circulation line for compressing the refrigerant discharged from the heat exchanger after cooling the evaporative gas in the heat exchanger, and an expander for expanding and cooling the refrigerant compressed by the refrigerant compressor and then cooled in the heat exchanger, and supplying the refrigerant as a refrigerant for the heat exchanger; an inventory tank for storing a refrigerant to be charged in the refrigeration cycle; and a refrigerant supply line connected from the inventory tank upstream of the refrigerant compressor for replenishing refrigerant to the refrigeration cycle; and a refrigerant discharge line connected downstream of the refrigerant compressor to the inventory tank for discharging the refrigerant of the refrigeration cycle into the inventory tank; and a pressure regulation line branching off from the refrigerant discharge line; The refrigerant cycle is depressurized by discharging the refrigerant from the refrigerant cycle into the refrigerant discharge line or the pressure regulating line; When the refrigerant cycle is depressurized, the refrigerant is preferentially discharged to the inventory tank through the refrigerant discharge line, and after the pressure between the inventory tank and the refrigerant cycle is reversed, the refrigerant cycle is depressurized by discharging the refrigerant to the pressure adjustment line; The refrigerant discharged through the pressure regulating line is not discharged outside the ship, but is reused as at least one of a refrigerant replenished to a refrigeration cycle, a utility gas supplied on board, and a blanket gas supplied on board. Pressure regulation system for the refrigerant cycle of a marine reliquefaction system.

2. a first valve provided upstream of a branch point of the refrigerant discharge line and the pressure regulating line; and a second valve provided in the pressure regulation line; and and a third valve provided downstream of a branch point of the refrigerant discharge line and the pressure adjustment line. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 1.

3. A utility N provided on the ship and supplied to the ship ２ a buffer tank for storing the Utility N supplied from the buffer tank ２ A drying and filtering section for drying and filtering the above-mentioned mixture to lower the dew point; a boost compressor that compresses the nitrogen refrigerant that has passed through the drying and filtering section before supplying it to the inventory tank; 3. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 2.

4. the pressure regulation line is connected to the buffer tank, and the buffer tank is operated at a lower pressure than the inventory tank. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 3.

5. The pressure regulation line is connected upstream of the boost compressor. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 3.

6. The reliquefaction system includes a gas-liquid separator to which the evaporated gas cooled by the heat exchanger is supplied and which performs phase separation; The pressure regulating line is connected to the gas-liquid separator, and the refrigerant discharged from the refrigerant cycle is supplied to an upper portion of the gas-liquid separator as an inert gas for maintaining the pressure in the gas-liquid separator. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 3.

7. The inventory tank includes a high-pressure tank to which the nitrogen refrigerant compressed by the boost compressor is supplied and which supplies the supplied nitrogen refrigerant to an upstream of the refrigerant compressor, and a low-pressure tank operated at a lower pressure than the high-pressure tank, The pressure regulation line is connected to the low pressure tank. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 3.

8. The operating pressure of the low pressure tank is operated at the suction pressure of the boost compressor, The pressure in the low-pressure tank is maintained by pressurizing the low-pressure tank with the refrigerant discharged to the pressure adjustment line and discharging the refrigerant from the low-pressure tank to the upstream of the boost compressor. A pressure regulation system for a refrigerant cycle of a marine reliquefaction system according to claim 7.

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