Liquefied gas supercooling system using mixed refrigerants

Abstract

The present invention is a liquefied gas supercooling system, which supercools a liquefied gas using a mixed refrigerant, and includes: a compressor that compresses the mixed refrigerant; a separator provided downstream of the compressor that phase-separates the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant; a fourth line through which the liquid phase refrigerant separated in the separator flows via a first pressure reducing valve; a fifth line through which the gas phase refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-inflow into the second heat exchanger; a sixth line through which the mixed refrigerant combined from the fourth line and the fifth line flows via the first heat exchanger, the compressor, and the separator; and an anti-icing unit that adjusts the temperature of the mixed refrigerant on the fifth line or the sixth line.

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0003084, filed January 9, 2023, Korean Patent Application No. 10-2023-0127311, filed September 22, 2023, and Korean Patent Application No. 10-2024-0003555, filed January 9, 2024, and all contents disclosed in the documents of the relevant Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a system for subcooling a liquefied gas using a mixed refrigerant. [Background technology]

[0003] When natural gas is liquefied, its volume decreases, making it easier to store and transport. Natural gas in this state is called liquefied gas. For example, LNG, a type of liquefied gas, liquefies at -163°C under atmospheric pressure, so storage tanks with excellent insulation are used to maintain the cryogenic temperature.

[0004] However, it is not possible to completely block the inflow of heat from the outside into a storage tank, and if heat flows in, the liquefied gas inside the storage tank will vaporize, generating boil-off gas (BOG). When BOG is generated, the existing liquefied gas turns into gas, increasing its volume, increasing the pressure inside the storage tank and creating the risk of explosion. In addition, as the liquefied gas vaporizes, the amount that can be transported decreases, resulting in economic losses.

[0005] Various methods have been investigated to solve the problems caused by BOG, typically including re-liquefaction of vaporized natural gas and subcooling of the liquefied natural gas.

[0006] Both of the above two methods use a refrigeration cycle that cools natural gas by circulating a refrigerant, but methods are applied that increase efficiency by changing the refrigeration cycle process or by using a mixed refrigerant to increase heat exchange efficiency.

[0007] In particular, if the mixed refrigerant contains a heavy element such as pentane, the temperature may drop excessively during the heat exchange process, causing freezing. If freezing occurs, it may cause equipment failure, so it is necessary to adjust the temperature of the mixed refrigerant. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide a liquefied gas supercooling system that increases the efficiency of the liquefied gas supercooling system and prevents freezing of the mixed refrigerant. [Means for solving the problem]

[0009] A liquefied gas supercooling system according to one embodiment of the present invention is a system for supercooling a liquefied gas using a mixed refrigerant, the system comprising: a compressor for compressing the mixed refrigerant; a first separator, provided downstream of the compressor, for phase-separating the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant; a first line through which the liquid phase refrigerant separated in the first separator flows via a first pressure reducing valve; a second line through which the gas phase refrigerant separated in the first separator flows via a first heat exchanger and a second separator; a second separator, provided downstream of the first heat exchanger, for phase-separating the mixed refrigerant separated in the first separator and passed through the second line into a gas phase refrigerant and a liquid phase refrigerant; and a second-1 line through which the gas phase refrigerant separated in the second separator flows via a second heat exchanger, a second pressure reducing valve, and re-entering the second heat exchanger. the second heat exchanger includes a second-phase refrigerant separated in the second separator and flowing through a third pressure reducing valve; and a third line along which a mixed refrigerant merged from the first line, the second-phase refrigerant separated in the first separator and flowing along the second line, and a mixed refrigerant flowing along the third line, through which the mixed refrigerant is separated in the first separator and flowing along the second line, and a second-phase refrigerant separated in the second separator and flowing through the second pressure reducing valve along the second-phase refrigerant separated in the second separator and flowing through the third line, and a second heat exchanger between the mixed refrigerant separated in the second separator and flowing through the second pressure reducing valve and the liquefied gas, and the liquefied gas can be subcooled by the heat exchange in the second heat exchanger.

[0010] In one example, the first pressure reducing valve reduces the pressure of the liquid phase refrigerant separated in the first separator and flowing along the first line to reduce its temperature, the second pressure reducing valve reduces the pressure of the mixed refrigerant passed through the second heat exchanger along the 2-1 line to reduce its temperature, and the third pressure reducing valve reduces the pressure of the liquid phase refrigerant separated in the second separator and flowing along the 2-2 line to reduce its temperature.

[0011] In one example, the refrigerating system may further include a confluence unit connected to the first line, the 2-1 line, and the 2-2 line at a previous stage and connected to the third line at a subsequent stage, wherein the mixed refrigerant joined at the confluence unit flows along the third line and passes through the first heat exchanger, and the liquid-phase refrigerant that has passed through the first pressure reducing valve, the mixed refrigerant that has passed through the second heat exchanger via the second pressure reducing valve, and the liquid-phase refrigerant that has passed through the third pressure reducing valve may be joined at the confluence unit.

[0012] In one example, the system may further include a junction unit connected to the first line, the 2-1 line, and the 2-2 line at a front end and connected to the third line at a rear end, and may further include an anti-icing unit having a bypass line branching off from at least one of the second line and the 2-1 line, adjusting the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided in the bypass line, and adjusting the temperature of the mixed refrigerant on the 2-1 line or the 2-2 line.

[0013] In one example, the anti-icing unit may control a first temperature of the mixed refrigerant along the 2-1 line before entering the junction.

[0014] A liquefied gas supercooling system according to one embodiment of the present invention is a system for supercooling a liquefied gas using a mixed refrigerant, and includes: a compressor for compressing the mixed refrigerant; a separator provided downstream of the compressor for phase-separating the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant; a fourth line through which the liquid phase refrigerant separated in the separator flows via a first pressure reducing valve; a fifth line through which the gas phase refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-inflow into the second heat exchanger; a sixth line through which the mixed refrigerant combined from the fourth line and the fifth line flows via the first heat exchanger, the compressor, and the separator; and a sixth line through which at least one of the fifth line and the sixth line flows. and an anti-icing unit that adjusts the temperature of the mixed refrigerant on the fifth line or the sixth line by adjusting the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided on the bypass line, and adjusts the temperature of the mixed refrigerant on the fifth line or the sixth line. In the first heat exchanger, heat exchange occurs between the gas-phase refrigerant separated in the separator and flowing along the fifth line and the mixed refrigerant flowing along the sixth line. In the second heat exchanger, heat exchange occurs between the mixed refrigerant that has passed through the first heat exchanger along the fifth line, the mixed refrigerant that has passed through the second pressure reducing valve along the fifth line, and the liquefied gas, and the liquefied gas can be subcooled by the heat exchange in the second heat exchanger.

[0015] In one example, the liquid phase refrigerant separated in the separator and flowing along the fourth line may be depressurized by the first depressurizing valve to lower its temperature, and the mixed refrigerant passing through the second heat exchanger along the fifth line may be depressurized by the second depressurizing valve to lower its temperature.

[0016] In one example, the system further includes a confluence unit connected to the fourth line and the fifth line at an upstream stage and connected to the sixth line at a downstream stage, and the anti-icing unit can control a fifth temperature of the mixed refrigerant along the sixth line before entering the first heat exchanger.

[0017] In one example, the anti-icing unit includes a fifth bypass valve, which may be provided on a fifth bypass line branching off from at least one of the fourth line, the fifth line, and the sixth line and connected to the fourth line upstream of the first pressure reducing valve or downstream of the first pressure reducing valve.

[0018] In one example, the system may further include a junction unit connected to the fourth line and the fifth line at a front end and connected to the sixth line at a rear end, wherein the anti-icing unit may control a sixth temperature of the mixed refrigerant that has passed through the second pressure reducing valve along the fifth line.

[0019] In one example, the anti-icing unit includes a seventh bypass valve, which may be provided on a seventh bypass line branching off from the fifth line between the separator and the first heat exchanger and connected to the fifth line upstream of the second pressure reducing valve or downstream of the second pressure reducing valve.

[0020] In one example, the compressor further includes a confluence unit connected to the fourth line and the fifth line at a front end and connected to the sixth line at a rear end, and the anti-icing unit can control a seventh temperature of the mixed refrigerant entering the compressor along the sixth line.

[0021] In one example, the anti-icing unit may include an eighth bypass valve, which may be provided on an eighth bypass line branching from the sixth line between the compressor and the separator and connecting to the sixth line between the first heat exchanger and the compressor.

[0022] In one example, the fourth line passes through the first heat exchanger upstream of the first pressure reducing valve, and in the first heat exchanger, heat exchange can be performed between the liquid-phase refrigerant separated in the separator and flowing along the fourth line, the gas-phase refrigerant separated in the separator and flowing along the fifth line, and the mixed refrigerant flowing along the sixth line.

[0023] In one example, the anti-icing unit includes a fifth bypass valve, which may be provided on a fifth bypass line branching off from at least one of the fourth line, the fifth line, and the sixth line and connected to the fourth line upstream of the first pressure reducing valve or downstream of the first pressure reducing valve. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram showing a liquefied gas supercooling system according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a diagram showing a liquefied gas supercooling system according to a second embodiment of the present invention. [Figure 3] FIG. 10 is a diagram showing a liquefied gas supercooling system according to a third embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing a liquefied gas supercooling system according to a fourth embodiment of the present invention. [Figure 5] FIG. 10 is a diagram showing a liquefied gas supercooling system according to a fifth embodiment of the present invention. [Figure 6] FIG. 10 is a diagram showing a liquefied gas supercooling system according to a sixth embodiment of the present invention. [Figure 7] FIG. 10 is a diagram showing a liquefied gas supercooling system according to a seventh embodiment of the present invention. [Figure 8] FIG. 10 is a diagram showing a liquefied gas supercooling system according to an eighth embodiment of the present invention. [Figure 9] FIG. 13 is a diagram showing a liquefied gas supercooling system according to a ninth embodiment of the present invention. [Figure 10] FIG. 19 is a diagram showing a liquefied gas supercooling system according to a tenth embodiment of the present invention. [Figure 11] FIG. 14 is a diagram showing a liquefied gas supercooling system according to an eleventh embodiment of the present invention. [Figure 12] FIG. 22 is a diagram showing a liquefied gas supercooling system according to a twelfth embodiment of the present invention. [Figure 13] FIG. 22 is a diagram showing a liquefied gas supercooling system according to a thirteenth embodiment of the present invention. [Figure 14]FIG. 22 is a diagram showing a liquefied gas supercooling system according to a fourteenth embodiment of the present invention. [Figure 15] FIG. 20 is a diagram showing a liquefied gas supercooling system according to a fifteenth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0025] Some embodiments of the present invention will be described in detail below with reference to exemplary drawings. When assigning reference numerals to components in each drawing, it should be noted that the same reference numerals are used to refer to the same components even when they are displayed in different drawings. Furthermore, when describing the embodiments of the present invention, if it is determined that a detailed description of related known structures or functions would hinder understanding of the embodiments of the present invention, such a detailed description will be omitted.

[0026] Furthermore, when describing components of an embodiment of the present invention, terms such as first, second, A, B, (a), (b), etc. may be used. These terms are used to distinguish the component from other components, and do not limit the nature, order, or sequence of the components. When a component is described as being "coupled," "coupled," or "connected" to another component, it should be understood that the component may be directly coupled or connected to the other component, but that there may also be other components "coupled," "coupled," or "connected" between the components.

[0027] In this specification, the terms "front-rear," "left-right," and "up-down" are used for the sake of convenience and may be mutually orthogonal. However, these directions are determined relatively, and the "up-down" direction does not necessarily mean the vertical direction.

[0028] A liquefied gas supercooling system for use in a ship that transports liquefied gas will be briefly described with reference to first to third embodiments.

[0029] First to Third Embodiments FIG. 1 is a diagram showing a liquefied gas supercooling system according to a first embodiment of the present invention.

[0030] FIG. 2 is a diagram showing a liquefied gas supercooling system according to a second embodiment of the present invention.

[0031] FIG. 3 is a diagram showing a liquefied gas supercooling system according to a third embodiment of the present invention.

[0032] In the case of a ship that transports liquefied gas, the liquefied gas and BOG, which is the evaporated liquefied gas, are stored in a tank 500. When the ship is in operation, the BOG is extracted from the tank, pressurized to a predetermined pressure by a BOG compressor 520, and then supplied to a main engine 560 or a power generation engine 570 for use as fuel. If the liquefied gas evaporates in excess of the amount required for fuel, problems such as an increase in pressure inside the tank occur, and to solve this problem, a system for supercooling the liquefied gas is required.

[0033] By subcooling the liquid LNG, the BOG compressor 520 may be eliminated.

[0034] Referring to FIG. 1, a liquefied gas supercooling system 1 according to a first embodiment of the present invention includes a mixed refrigerant heat exchanger 540, a liquefied gas heat exchanger 550, a compressor 530, and a pressure reducing valve 580. The low-temperature mixed refrigerant cooled while circulating through the subcooling system exchanges heat with liquefied gas extracted from the liquefied gas heat exchanger 550 via a pump 510 to the outside of the tank 500, thereby supercooling the liquefied gas. Although the temperature of the mixed refrigerant increases after heat exchange with the liquefied gas, it remains relatively low compared to the mixed refrigerant that subsequently passes through the compressor. Therefore, by exchanging heat between two mixed refrigerants in the mixed refrigerant heat exchanger 540, the temperature of the mixed refrigerant can be lowered without additional external energy input, thereby improving the efficiency of the refrigeration cycle. The mixed refrigerant cooled in the mixed refrigerant heat exchanger 540 is cooled to a cryogenic temperature via the pressure reducing valve 580 and then undergoes heat exchange with the liquefied gas again.

[0035] Referring to FIG. 2, a liquefied gas supercooling system 1 according to the second embodiment of the present invention includes a compressor 530, two mixed refrigerant heat exchangers 540 and 541, one liquefied gas heat exchanger 550, a separator 590, and two pressure-reducing valves 581 and 582. This differs from the first embodiment in that the separator 590 is added to separate the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant. This prevents oil or heavy elements such as C4 and C5 contained in the liquid phase refrigerant from freezing in the low-temperature section through the cycle. Because there is a risk of cooling when exchanging heat with the liquefied gas, the liquid phase refrigerant does not flow into the liquefied gas heat exchanger 550. Instead, it is cooled by the pressure-reducing valve 581 and re-flows into the mixed refrigerant heat exchanger 541. For specific details about the flow of the mixed refrigerant, see the fourth to fifteenth embodiments below.

[0036] 3, the liquefied gas supercooling system 1 according to the third embodiment of the present invention includes a compressor 530, three mixed refrigerant heat exchangers 540, 541, and 542, one liquefied gas heat exchanger 550, two separators 590 and 591, and three pressure reducing valves 581, 582, and 583. Compared to the second embodiment, because there are two separators 590 and 591, oil and heavy elements that are not separated in the first separator 590 can be separated in the second separator 591, further reducing the risk of freezing.

[0037] The mixed refrigerant cycles shown in Figures 1 to 3 are merely examples for explaining a liquefied gas supercooling system operating on a ship, and are not limited thereto. For example, the specific configurations of the mixed refrigerant cycles shown in Figures 1 to 3 can be replaced with the configurations of the fourth to fifteenth embodiments described below.

[0038] For a specific flow of the mixed refrigerant, refer to the following fourth to fifteenth embodiments.

[0039] Hereinafter, a liquefied gas supercooling system including a plurality of separators that separate the phases of the mixed refrigerant and an anti-freezing unit that prevents freezing will be described in detail with reference to fourth to sixth embodiments.

[0040] <Fourth embodiment> FIG. 4 is a diagram showing a liquefied gas supercooling system according to a fourth embodiment of the present invention.

[0041] Referring to Figure 4, the liquefied gas supercooling system 1 according to the fourth embodiment of the present invention includes a compressor 210, a first separator 220, a second separator 230, a first heat exchanger 240, a second heat exchanger 250, a confluence section 260, a first pressure reducing valve 270, a second pressure reducing valve 280, a third pressure reducing valve 290, a first line L101, a second line L102, and a third line L103.

[0042] Below, each component, its role, and the process flow will be explained.

[0043] For convenience, the first line L101, the second line L102, and the third line L103 will be defined first.

[0044] The first line L101 is a path through which the liquid phase refrigerant separated in the first separator 220 passes through the first pressure reducing valve 270.

[0045] The second line L102 is a path through which the gas phase refrigerant separated in the first separator 220 passes through the first heat exchanger 240 and the second separator 230.

[0046] The 2-1 line L102-1 indicates a path through which the gas phase refrigerant separated in the second separator 230 passes through the second heat exchanger 250, the second pressure reducing valve 280, and re-flows into the second heat exchanger 250.

[0047] The 2-2 line L102-2 is a path through which the liquid phase refrigerant separated in the second separator 230 passes through the third pressure reducing valve 290.

[0048] The mixed refrigerant along the first line L101, the mixed refrigerant along the 2-1 line L102-1, and the mixed refrigerant along the 2-2 line L102-2 join together and flow along the third line L103.

[0049] The third line L103 refers to a path through which the mixed refrigerant merged from the first line L101, the 2-1 line L102-1, and the 2-2 line L102-2 passes through the first heat exchanger 240, the compressor 210, and the first separator 220. The third line L103 may further include a junction unit 260 connected to the first line L101, the 2-1 line L102-1, and the 2-2 line L102-2 at an upstream stage (inlet) and connected to the third line L103 at a downstream stage (discharge). The following description will be given including the junction unit 260, but is not limited thereto.

[0050] The compressor 210 compresses the mixed refrigerant at high pressure. Because the temperature of the mixed refrigerant rises during the compression process, a cooler (not shown) can be installed downstream of the compressor 210 to lower this temperature. The cooler can lower the temperature of the mixed refrigerant to a temperature close to that of seawater by heat exchange with seawater. For example, this temperature can be 40°C with seawater, but this temperature can vary depending on the temperature of the seawater and the performance of the cooler.

[0051] The installation of a cooler after the compressor is a common feature in the use of compressors and is not separately shown in the drawings.

[0052] The mixed refrigerant passing through the compressor 210 enters the first separator 220 along the third line L103 and is separated into a gas phase refrigerant and a liquid phase refrigerant. For example, among the components constituting the mixed refrigerant, light components such as C1 and C2 can be separated into a gas phase refrigerant, and heavy components such as C5 can be separated into a liquid phase refrigerant. In addition, as the mixed refrigerant passes through the compressor 210, oil contained in the mixed refrigerant can also be separated into a liquid phase refrigerant in the first separator 220. The reason for separating the mixed refrigerant into a gas phase and a liquid phase is that if a liquid phase refrigerant is subjected to heat exchange with a cryogenic liquefied gas, freezing may occur, and therefore only the gas phase refrigerant is subjected to heat exchange with the liquefied gas.

[0053] The mixed refrigerant, i.e., the liquid phase refrigerant and the gas phase refrigerant separated in the first separator 220, can flow along the first line L101 and the second line L102, respectively, as will be described in detail below.

[0054] The liquid phase refrigerant separated in the first separator 220 passes through the first pressure reducing valve 270 along the first line L101 and enters the junction 260, where it merges with the mixed refrigerant entering the junction 260 along the 2-1 line L102-1 described below and the mixed refrigerant entering the junction 260 along the 2-2 line L102-2.

[0055] The gas refrigerant separated in the first separator 220 enters the first heat exchanger 240 along the second line L102 and can be cooled by heat exchange with the mixed refrigerant entering the first heat exchanger 240 along the third line L103. In the first heat exchanger 240, heat exchange occurs between two types of refrigerant, namely, the gas refrigerant along the second line L102 and the mixed refrigerant along the third line L103. The gas refrigerant that has passed through the first heat exchanger 240 then enters the second separator 230 and is separated again into gas refrigerant and liquid refrigerant. Even if phase separation has already occurred once in the first separator 220, the separated gas refrigerant is cooled through the first heat exchanger 240, so that the second separator 230 can contain not only the gas refrigerant but also the mixed refrigerant that has become liquid.

[0056] The gas phase refrigerant separated in the second separator 230 enters the second heat exchanger 250 along the 2-1 line L102-1. The mixed refrigerant passing through the second heat exchanger 250 is decompressed and cooled through the second pressure-reducing valve 280. The mixed refrigerant then re-enters the second heat exchanger 250 along the 2-1 line L102-1 and reaches the junction 260. During the cooling process in the second pressure-reducing valve 280, the mixed refrigerant is cooled to a temperature of -170°C or below. This is because the temperature of liquefied gas is normally around -160°C, and subcooling it reduces the temperature to -170°C. Furthermore, the temperature of the mixed refrigerant passing through the second pressure-reducing valve 280 may suddenly drop, causing freezing. To address this issue, an anti-icing unit is provided, which will be described in the fifth embodiment of the present invention.

[0057] The mixed refrigerant passing through the second pressure reducing valve 280 re-enters the second heat exchanger 250 and exchanges heat with the liquefied gas to subcool the liquefied gas. After completing the heat exchange, the mixed refrigerant reaches the junction 260 and merges with two streams of mixed refrigerant that enter the junction 260 along the first line L101 and the second-second line L102-2. If the heat exchange between the mixed refrigerant passing through the second heat exchanger 250 along the second-first line L102-1 and the liquefied gas is not performed properly, the temperature of the mixed refrigerant may not rise sufficiently. For example, the mixed refrigerant passing through the second heat exchanger 250 along the second-first line L102-1 should be discharged at approximately 0°C, but if heat exchange is not performed sufficiently, it may be discharged from the second heat exchanger 250 at a lower temperature (below zero). This can cause freezing of the mixed refrigerant and oil contained in the mixed refrigerant flowing along the first line L101 and the 2-2 line L102-2 that join at the junction 260. To solve this problem, an anti-icing unit is introduced, which will be described in the fifth embodiment of the present invention. In the second heat exchanger 250, heat exchange occurs between three types of refrigerant: the mixed refrigerant entering the second heat exchanger 250 along the 2-1 line L102-1, the mixed refrigerant re-entering the second heat exchanger 250 via the second pressure reducing valve 280 along the 2-1 line L102-1, and the liquefied gas.

[0058] The liquid phase refrigerant separated in the second separator 230 passes through the third pressure reducing valve 290 along the 2-2 line L102-2 and enters the junction 260, where it merges with the mixed refrigerant entering the junction 260 along the 2-1 line L102-1 and the mixed refrigerant entering the junction 260 along the first line L101. Here too, the temperature of the mixed refrigerant passing through the third pressure reducing valve 290 drops sharply, which can cause freezing. To solve this problem, an anti-icing unit is provided, which will be described in the sixth embodiment of the present invention.

[0059] The mixed refrigerant joined at the joining point 260 flows along the third line L103 into the first heat exchanger 240. As described above, the mixed refrigerant that has entered the first heat exchanger 240 along the third line L103 exchanges heat with the gas phase refrigerant separated in the first separator 220. After completing the heat exchange, the mixed refrigerant flows back into the compressor 210 along the third line L103.

[0060] Fifth Embodiment FIG. 5 is a diagram showing a liquefied gas supercooling system according to a fifth embodiment of the present invention.

[0061] The anti-icing unit is configured to sense the temperature at a specific point in order to prevent the mixed refrigerant from freezing, and to control the temperature so that it does not drop below a predetermined value.

[0062] 5, a liquefied gas supercooling system 1 according to a fifth embodiment of the present invention includes a first bypass valve 301 as a component for adjusting a first temperature T1 310 to prevent freezing, and a 2-1 bypass valve 302-1 and a 2-2 bypass valve 302-2 as a component for adjusting a second temperature T2 320 to prevent freezing. However, in FIG. 5, at least one of the 2-1 bypass valve 302-1 and the 2-2 bypass valve 302-2 may be omitted. Other configurations are the same as those in the fourth embodiment, and therefore description thereof will be omitted.

[0063] The first bypass valve 301 is configured to control the temperature (hereinafter referred to as "first temperature T1 310") of the mixed refrigerant before it enters the junction 260 along the 2-1 line L102-1. The first bypass line L111 refers to a path that branches off from the 2-1 line L102-1 between the second separator 230 and the second heat exchanger 250 and is connected to the 2-1 line L102-1 between the second heat exchanger 250 and the junction 260. The first bypass valve 301 is provided on the first bypass line L111.

[0064] When the first temperature 310 is sensed and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the second separator 230 and flowing along the 2-1 line L102-1 is caused to flow into the front stage of the junction 260 via the first bypass line L111 by adjusting the first bypass valve 301, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0065] The 2-1 bypass valve 302-1 and the 2-2 bypass valve 302-2 are configured to control the temperature (hereinafter referred to as "second temperature T2 320") of the mixed refrigerant after it passes through the second pressure reducing valve 280 along the 2-1 line L102-1. The 2-1 bypass line L112-1 refers to a path that branches off from the 2-1 line L102-1 between the second separator 230 and the second heat exchanger 250 and is connected to the 2-1 line L102-1 between the downstream side of the second heat exchanger 250 and the second pressure reducing valve 280. The 2-2 bypass line L112-2 refers to a path that branches off from the 2-1 line L102-1 between the second separator 230 and the second heat exchanger 250 and is connected to the 2-1 line L102-1 between the downstream side of the second pressure reducing valve 280 and the second heat exchanger 250. The 2-1 bypass valve 302-1 is provided on the 2-1 bypass line L112-1, and the 2-2 bypass valve 302-2 is provided on the 2-2 bypass line L112-2.

[0066] When the second temperature 320 is sensed and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the second separator 230 and flowing along the 2-1 line L102-1 is allowed to flow into the upstream of the second pressure reducing valve 280 via the 2-1 bypass line L112-1 by adjusting the 2-1 bypass valve 302-1, or the high-temperature mixed refrigerant is allowed to flow into the downstream of the second pressure reducing valve 280 via the 2-2 bypass line L112-2 by adjusting the 2-2 bypass valve 302-2, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0067] By controlling the temperature, it is possible to prevent the mixed refrigerant from freezing, which in turn makes it possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0068] Sixth Embodiment FIG. 6 is a diagram showing a liquefied gas supercooling system according to a sixth embodiment of the present invention.

[0069] 6, the liquefied gas supercooling system 1 according to the sixth embodiment of the present invention includes a 3-1 bypass valve L303-1 and a 3-2 bypass valve L303-2 as components for preventing freezing by adjusting the third temperature T3 330. The other components are the same as those in the fourth embodiment, and therefore, a description thereof will be omitted.

[0070] The 3-1 bypass valve 303-1 and the 3-2 bypass valve 303-2 are configured to control the temperature (hereinafter referred to as "third temperature T3 330") of the mixed refrigerant after it has passed through the third pressure reducing valve 290 along the 2-2 line L102-2. The 3-1 bypass line L113-1 refers to a path that branches off from the second line L102 between the first separator 220 and the first heat exchanger 240 and is connected to the 2-2 line L102-2 between the second separator 230 and the third pressure reducing valve 290. The 3-1 bypass valve 303-1 is provided on the 3-1 bypass line L113-1. The 3-2 bypass line L113-2 refers to a path branching from the second line L102 between the first separator 220 and the first heat exchanger 240 and connecting to the 2-2 line L102-2 between the third pressure reducing valve 290 and the junction 260. The 3-2 bypass valve 303-2 is provided on the 3-2 bypass line L113-2.

[0071] When the third temperature 330 is sensed and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the first separator 220 and flowing along the second line L102 is allowed to flow into the upstream of the third pressure reducing valve 290 via the 3-1 bypass line L113-1 by adjusting the 3-1 bypass valve 303-1, or the high-temperature mixed refrigerant is allowed to flow into the downstream of the third pressure reducing valve 290 via the 3-2 bypass line L113-2 by adjusting the 3-2 bypass valve 303-2, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0072] By preventing the mixed refrigerant from freezing, it is possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0073] Below, a liquefied gas supercooling system that does not include a separator that separates the phases of the mixed refrigerant or that includes a single separator and that includes an anti-freezing unit that prevents freezing will be described in detail in accordance with seventh to fifteenth embodiments.

[0074] Seventh Embodiment FIG. 7 is a diagram showing a liquefied gas supercooling system according to a seventh embodiment of the present invention.

[0075] Referring to Figure 7, a liquefied gas supercooling system 1 according to a seventh embodiment of the present invention includes a compressor 10, a separator 20, a first heat exchanger 30, a second heat exchanger 40, a confluence section 70, a first pressure reducing valve 80, a second pressure reducing valve 90, a fourth bypass valve 101, a fourth line L1, a fifth line L2, and a sixth line L3.

[0076] Below, each component, its role, and the process flow will be explained.

[0077] For convenience, the fourth line L1, the fifth line L2, and the sixth line L3 will be defined first.

[0078] The fourth line L1 indicates a path through which the liquid phase refrigerant separated in the separator 20 passes through the first heat exchanger 30 and the first pressure reducing valve 80.

[0079] The fifth line L2 represents the path along which the vapor-phase refrigerant separated in the separator 20 passes through the first heat exchanger 30, the second heat exchanger 40, the second pressure reducing valve 90, and re-flows into the second heat exchanger 40. The refrigerant along the fourth line L1 and the refrigerant along the fifth line L2 join together and flow along the sixth line L3.

[0080] The sixth line L3 refers to a path through which the mixed refrigerant that has joined the fourth line L1 and the fifth line L2 passes through the first heat exchanger 30, the compressor 10, and the separator 20.

[0081] The system may further include a junction 70 connected to the fourth line L1 and the fifth line L2 at the front end (inlet) and connected to the sixth line L3 at the rear end (outlet). The following description will be given including the junction 70, but is not limited thereto.

[0082] Compressor 10 compresses the mixed refrigerant at high pressure. The mixed refrigerant that passes through compressor 10 enters separator 20 along sixth line L3 and undergoes phase separation into gas and liquid refrigerants. For example, among the components that make up the mixed refrigerant, light components such as C1 and C2 can be separated into gas refrigerant, and heavy components such as C5 can be separated into liquid refrigerant. The reason for separating the mixed refrigerant into gas and liquid phases is that if a liquid refrigerant exchanges heat with a cryogenic liquefied gas, freezing may occur, and only the gas refrigerant exchanges heat with the liquefied gas.

[0083] The mixed refrigerant separated in the separator 20, i.e., the liquid phase refrigerant and the vapor phase refrigerant, can flow along the fourth line L1 and the fifth line L2, respectively, as will be described in detail below.

[0084] The liquid-phase refrigerant separated in the separator 20 enters the first heat exchanger 30 along the fourth line L1 and can be cooled by heat exchange with the mixed refrigerant entering the first heat exchanger 30 along the sixth line L3. In the first heat exchanger 30, heat exchange occurs between three types of refrigerant: the liquid-phase refrigerant along the fourth line L1, the gas-phase refrigerant along the fifth line L2, and the mixed refrigerant along the sixth line L3. Thereafter, the liquid-phase refrigerant that has passed through the first heat exchanger 30 is decompressed and cooled by the first pressure reducing valve 80.

[0085] In a typical process, the liquid refrigerant enters the pressure reducing valve directly without passing through a heat exchanger. However, in the present invention, the liquid refrigerant is primarily cooled in the first heat exchanger 30 before passing through the first pressure reducing valve 80, allowing a relatively lower temperature liquid refrigerant to enter the first pressure reducing valve 80. By primarily cooling the liquid refrigerant in the first heat exchanger 30 before passing through the first pressure reducing valve 80, the cooling efficiency of the first pressure reducing valve 80 is increased. However, because a cooling process is added before the pressure reducing valve, the temperature of the liquid refrigerant passing through the pressure reducing valve drops rapidly, which can cause freezing. To solve this problem, an anti-icing unit is installed, which will be described later.

[0086] The liquid-phase refrigerant that has passed through the first pressure reducing valve 80 reaches the junction 70 and merges with the refrigerant that enters the junction 70 along the fifth line L2. The refrigerant that enters the junction 70 along the fifth line L2 in the separator 20 is a gas-phase refrigerant, or may contain a mixed refrigerant that has been partially converted to a liquid phase after passing through the second heat exchanger 40 or the second pressure reducing valve 90 in addition to the gas-phase refrigerant.

[0087] The vapor refrigerant separated in the separator 20 flows along the fifth line L2 into the first heat exchanger 30 and is cooled by heat exchange with the mixed refrigerant flowing into the first heat exchanger 30 along the sixth line L3. Because the vapor refrigerant may change phase as it passes through the first heat exchanger 30, the second heat exchanger 40, the second pressure-reducing valve 90, etc., the term "mixed refrigerant" will be used hereafter to avoid confusion. The mixed refrigerant then flows along the fifth line L2 into the second heat exchanger 40. The mixed refrigerant passing through the second heat exchanger 40 is decompressed and cooled by the second pressure-reducing valve 90. The mixed refrigerant then flows back into the second heat exchanger 40 along the fifth line L2 and reaches the junction 70. During the cooling process in the second pressure-reducing valve 90, the mixed refrigerant is cooled to a temperature of -170°C or below. This is because the temperature of liquefied gas is usually around -160°C, and when it is supercooled, the temperature drops to -170°C. In addition, the temperature of the mixed refrigerant that passes through the second pressure reducing valve 90 drops rapidly, which can cause freezing. To solve this problem, an anti-freeze unit is installed, which will be described later.

[0088] The mixed refrigerant that has passed through the second pressure reducing valve 90 re-enters the second heat exchanger 40 and exchanges heat with the liquefied gas to subcool the liquefied gas. After completing the heat exchange, the mixed refrigerant reaches the junction 70 and merges with the mixed refrigerant that enters the junction 70 along the fourth line L1. In the second heat exchanger 40, heat exchange occurs between three types of refrigerant: the mixed refrigerant that has passed through the first heat exchanger 30 along the fifth line L2, the mixed refrigerant that re-enters through the second pressure reducing valve 90 along the fifth line L2, and the liquefied gas.

[0089] The mixed refrigerant that joins at the joining section 70 enters the first heat exchanger 30 along the sixth line L3. Here, the mixed refrigerant that enters along the fourth line L1 comes into contact with the low-temperature mixed refrigerant that enters along the fifth line L2, which can cause freezing. To solve this problem, an anti-icing unit is provided, which will be described later. The anti-icing unit prevents freezing of the refrigerant and the oil.

[0090] The mixed refrigerant that has entered the first heat exchanger 30 along the sixth line L3 exchanges heat with the mixed refrigerant that has entered the first heat exchanger 30 along the fourth line L1 and the mixed refrigerant that has entered the first heat exchanger 30 along the fifth line L2, as described above. After completing the heat exchange, the mixed refrigerant returns to the compressor 10 along the sixth line L3.

[0091] The anti-icing section will now be described.

[0092] The anti-icing unit is configured to detect the temperature at a specific point and control the temperature so that it does not drop below a predetermined value in order to prevent freezing of the mixed refrigerant and oil.

[0093] Referring to FIG. 7, the first embodiment of the present invention includes a fourth bypass valve 101 as an anti-icing unit.

[0094] The fourth bypass valve 101 is configured to control the temperature downstream of the first pressure reducing valve 80 (hereinafter referred to as the "fourth temperature T4 110") and the temperature between the junction 70 and the first heat exchanger 30 (hereinafter referred to as the "fifth temperature T5 120"). The fourth bypass valve 101 is provided on a fourth bypass line L11 that branches off from the fourth line L1 between the separator 20 and the first heat exchanger 30 and is connected to the fourth line L1 between the first heat exchanger 30 and the first pressure reducing valve 80.

[0095] The fourth temperature 110 and the fifth temperature 120 are sensed, and if the lower of the sensed temperatures is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the separator 20 and flowing along the fourth line L1 is regulated by the fourth bypass valve 101 to flow into the upstream of the first pressure reducing valve 31 via the fourth bypass line L11, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0096] Although the description has been given taking as an example a case where the high-temperature mixed refrigerant flows into a stage upstream of the first pressure reducing valve 80 via the fourth bypass line L11, the present invention is not limited thereto. For example, the high-temperature mixed refrigerant may flow into a stage downstream of the first pressure reducing valve 80 via the fourth bypass line L11.

[0097] By preventing the mixed refrigerant from freezing, it is possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0098] <Eighth and Ninth Embodiments> FIG. 8 is a diagram showing a liquefied gas supercooling system 1 according to an eighth embodiment of the present invention.

[0099] FIG. 9 is a diagram showing a liquefied gas supercooling system 1 according to a ninth embodiment of the present invention.

[0100] The seventh embodiment includes a fourth bypass line L11 as a configuration for controlling the fourth temperature 110 and the fifth temperature 120, while the eighth and ninth embodiments include a fifth bypass line L12 and a sixth bypass line L13 as a configuration for controlling the fourth temperature 110 and the fifth temperature 120.

[0101] 8, a liquefied gas supercooling system 1 according to an eighth embodiment of the present invention includes a fifth bypass line L12 as a configuration for preventing freezing by adjusting the fourth temperature 110 and the fifth temperature 120. The other configurations are the same as those of the first embodiment, and therefore a description thereof will be omitted.

[0102] The fifth bypass valve 102 is provided on a fifth bypass line L12 that branches off from the fifth line L2 between the separator 20 and the first heat exchanger 30 and is connected to the fourth line L1 between the first heat exchanger 30 and the first pressure reducing valve 80.

[0103] As another example, the fifth bypass valve 102 is provided on a fifth bypass line L12 that branches off from a part of the fourth line L1 between the separator 20 and the first heat exchanger 30 and is connected to another part of the fourth line L1 between the first heat exchanger 30 and the first pressure reducing valve 80.

[0104] The fourth temperature 110 and the fifth temperature 120 are sensed, and if the lower of the four temperatures is low enough to cause freezing of the mixed refrigerant, the mixed refrigerant is separated in the separator 20 and the high-temperature mixed refrigerant flowing along the fifth line L2 is regulated by the fifth bypass valve 102 so that the mixed refrigerant flows into the upstream of the first pressure reducing valve 80 via the fifth bypass line L12, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0105] Although the description has been given taking as an example a case where the high-temperature mixed refrigerant flows into the upstream side of the first pressure reducing valve 80 via the fifth bypass line L12, the present invention is not limited thereto. For example, the high-temperature mixed refrigerant may flow into the downstream side of the first pressure reducing valve 80 via the fifth bypass line L12.

[0106] 9, the liquefied gas supercooling system 1 according to the ninth embodiment of the present invention includes a sixth bypass valve 103 as a component for preventing freezing by adjusting the fourth temperature 110 and the fifth temperature 120. The other components are the same as those in FIG. 7, and therefore, description thereof will be omitted.

[0107] The sixth bypass valve 103 is provided on a sixth bypass line L13 that branches off from the sixth line L3 between the compressor 10 and the separator 20 and is connected to the fourth line L1 between the first heat exchanger 30 and the first pressure reducing valve 80. For example, the sixth bypass line L13 may be connected to a part of the fourth line L1 that passes through the first heat exchanger 30 in the upstream stage of the first pressure reducing valve 80.

[0108] The fourth temperature 110 and the fifth temperature 120 are sensed, and if the lower of these temperatures is low enough to cause freezing of the mixed refrigerant, the sixth bypass valve 103 is adjusted so that the high-temperature mixed refrigerant discharged from the compressor 10 flows into the upstream of the first pressure reducing valve 80 via the sixth bypass line L13, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0109] Although the example has been described in which the high-temperature mixed refrigerant flows into the upstream side of the first pressure reducing valve 80 via the sixth bypass line L13, the present invention is not limited thereto. For example, the high-temperature mixed refrigerant may flow into the downstream side of the first pressure reducing valve 80 via the sixth bypass line L13.

[0110] By controlling the temperature, it is possible to prevent the mixed refrigerant from freezing, which in turn makes it possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0111] Tenth Embodiment FIG. 10 is a diagram showing a liquefied gas supercooling system 1 according to a tenth embodiment of the present invention.

[0112] 10, the liquefied gas supercooling system 1 according to the tenth embodiment of the present invention includes a seventh bypass valve 104 as a component for preventing freezing by adjusting the sixth temperature 130. The other components are the same as those in the first embodiment, and therefore, a description thereof will be omitted.

[0113] The seventh bypass valve 104 is configured to control the temperature (hereinafter referred to as "sixth temperature 130") before re-flowing into the second heat exchanger 40 downstream of the second pressure reducing valve 90 along the fifth line L2. The seventh bypass valve 104 is provided on a seventh bypass line L14 that branches off from the fifth line L2 between the separator 20 and the first heat exchanger 30 and is connected to the fifth line L2 between the second pressure reducing valve 90 and the second heat exchanger 40.

[0114] When the sixth temperature 130 is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the separator 20 and flowing along the fifth line L2 is regulated by the seventh bypass valve 104 to flow into the rear of the second pressure reducing valve 90 via the seventh bypass line L14, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0115] The seventh bypass line L14 may branch off from the fifth line L2 and be connected to a portion of the fifth line L2 that has first passed through the second heat exchanger 40. The seventh bypass line L14 may branch off from the fifth line L2 and be connected to a portion of the fifth line L2 that is after the second pressure reducing valve 90 after first passing through the second heat exchanger 40.

[0116] Although the description has been given taking as an example a case where the high-temperature mixed refrigerant flows into the rear stage of the second pressure reducing valve 90 via the seventh bypass line L14, the present invention is not limited thereto. For example, the high-temperature mixed refrigerant may flow into the front stage of the second pressure reducing valve 90 via the seventh bypass line L14.

[0117] By controlling the temperature, it is possible to prevent the mixed refrigerant from freezing, which in turn makes it possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0118] Eleventh Embodiment FIG. 11 is a diagram showing a liquefied gas supercooling system 1 according to an eleventh embodiment of the present invention.

[0119] 11, the liquefied gas supercooling system 1 according to the eleventh embodiment of the present invention includes an eighth bypass valve 105 as a component for preventing freezing by adjusting the seventh temperature 140. The other components are the same as those in the first embodiment, and therefore, a description thereof will be omitted.

[0120] The eighth bypass valve 105 is configured to control the temperature (hereinafter referred to as "seventh temperature 140") upstream of the compressor 10 along the sixth line L3. The eighth bypass valve 105 is provided on an eighth bypass line L15 that branches off from the sixth line L3 between the compressor 10 and the separator 20 and is connected to the sixth line L3 between the first heat exchanger 30 and the compressor 10.

[0121] The eighth bypass line L15 may branch off from the rear stage of the compressor 10 on the sixth line L3 and be connected to the front stage of the compressor 10.

[0122] When the seventh temperature 140 is detected and the temperature is low enough to cause droplets to form at the inlet of the compressor 10, the eighth bypass valve 105 is adjusted to allow the high-temperature mixed refrigerant compressed by the compressor 10 to flow into the upstream stage of the compressor 10 via the eighth bypass line L15, thereby increasing the temperature of the mixed refrigerant and preventing the formation of droplets.

[0123] By preventing the generation of droplets, it is possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0124] <Twelfth and Thirteenth Embodiments> FIG. 12 is a diagram showing a liquefied gas supercooling system 1 according to a twelfth embodiment of the present invention.

[0125] FIG. 13 is a diagram showing a liquefied gas supercooling system 1 according to a thirteenth embodiment of the present invention.

[0126] 12 and 13, the liquefied gas supercooling systems 1 according to the twelfth and thirteenth embodiments of the present invention are different from the liquefied gas supercooling systems 1 according to the seventh to eleventh embodiments of the present invention in that the liquid phase refrigerant separated in the separator 20 is directly depressurized and cooled in the first pressure reducing valve 80 without passing through the first heat exchanger 30. That is, the fourth line L1' according to the twelfth and thirteenth embodiments refers to the path through which the liquid phase refrigerant separated in the separator 20 passes through the first pressure reducing valve 80 and the junction 70. The fifth line L2 and the sixth line L3 are the same as those in the first to eleventh embodiments described above.

[0127] In addition, in FIG. 12, at least one of the seventh bypass valve 104 and the eighth bypass valve 105 may be omitted.

[0128] Since the liquid phase refrigerant is cooled without passing through the first heat exchanger 30, there is no risk of freezing occurring downstream of the first pressure reducing valve 80, so there is no need to control the fourth temperature 110, and only the fifth temperature 120 needs to be controlled.

[0129] Due to the above differences, the configuration of the anti-icing unit that adjusts the fifth temperature 120 also changes slightly. However, the configurations of the anti-icing units that adjust the sixth temperature 130 and the seventh temperature 140 are the same.

[0130] 12, a fifth bypass valve 102′ is included as a component for adjusting the fifth temperature 120 to prevent freezing. The fifth bypass valve 102′ is provided on a fifth bypass line L12′ that branches off from the fifth line L2 between the separator 20 and the first heat exchanger 30 and is connected to the fourth line L1 between the separator 20 and the first heat exchanger 30.

[0131] As another example, the fifth bypass valve 102' is provided on a fifth bypass line L12' that branches off from a part of the fourth line L1' upstream of the first pressure reducing valve 80 and is connected to another part of the fourth line L1' downstream of the first pressure reducing valve 80.

[0132] When the fifth temperature 120 is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated in the separator 20 is diverted to the upstream of the first pressure reducing valve 80 via the fifth bypass line L12' by adjusting the fifth bypass valve 102', thereby increasing the temperature of the mixed refrigerant and preventing freezing of the mixed refrigerant and oil.

[0133] Although the high-temperature mixed refrigerant has been described as flowing into the upstream side of the first pressure reducing valve 80 via the fifth bypass line L12', the present invention is not limited thereto. For example, the high-temperature mixed refrigerant may flow into the downstream side of the first pressure reducing valve 80 via the fifth bypass line L12'.

[0134] Although the fifth bypass line L12′ is connected to the fourth line L1′ and is described as preventing the mixed refrigerant from freezing, the present invention is not limited to this. For example, the fifth bypass line L12′ may be omitted.

[0135] The seventh bypass line L14 and the seventh bypass valve 104 refer to the tenth embodiment, and the eighth bypass line L15 and the eighth bypass valve 105 refer to the eleventh embodiment. As another example, the liquefied gas supercooling system 1 in Fig. 12 may omit the seventh bypass line L14 and the seventh bypass valve 104, or the eighth bypass line L15 and the eighth bypass valve 105.

[0136] Although not shown in FIG. 12, the twelfth embodiment may further include a sixth bypass line L13' and a sixth bypass valve 103' of the thirteenth embodiment.

[0137] 13, a sixth bypass valve 103′ is included as a component for preventing freezing by adjusting the fifth temperature 120. The sixth bypass valve 103′ is provided on a sixth bypass line L13′ that branches off from the sixth line L3 between the compressor 10 and the separator 20 and is connected to the fourth line L1 between the separator 20 and the first heat exchanger 30.

[0138] When the fifth temperature 120 is detected and the detected temperature is low enough to cause freezing of the mixed refrigerant, the sixth bypass valve 103' is adjusted to allow the high-temperature mixed refrigerant discharged from the compressor 10 to flow through the sixth bypass line L13' to the upstream of the first pressure reducing valve 80, thereby increasing the temperature of the mixed refrigerant and preventing freezing. By preventing freezing of the mixed refrigerant, it is possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0139] <Fourteenth embodiment> FIG. 14 is a diagram showing a liquefied gas supercooling system 1 according to a fourteenth embodiment of the present invention.

[0140] 14, the liquefied gas supercooling system 1 according to the fourteenth embodiment of the present invention further includes a third heat exchanger 50 compared to the liquefied gas supercooling system 1 according to the seventh embodiment. However, the present invention is not limited to this, and the third heat exchanger 50 may be added not only to the seventh embodiment but also to the eighth to thirteenth embodiments in the same manner.

[0141] The sixth line L3' according to the fourteenth embodiment refers to a path through which the mixed refrigerant joined at the joining section 70 passes through the first heat exchanger 30, the third heat exchanger 50, the compressor 10, re-enters the third heat exchanger 50, and passes through the separator 20. The fourth line L1 and the fifth line L2 are the same as those in the seventh to eleventh embodiments described above.

[0142] The third heat exchanger 50 is disposed so as to exchange heat between the mixed refrigerant that has passed through the first heat exchanger 30 along the sixth line L3′ and the mixed refrigerant that has passed through the compressor 10 along the sixth line L3′. The mixed refrigerant that has completed the heat exchange in the third heat exchanger 50 enters the separator 20 and undergoes phase separation.

[0143] Specifically, the high-temperature mixed refrigerant that has passed through the third heat exchanger 50 and compressor 10 is cooled by heat exchange with the relatively low-temperature mixed refrigerant that has passed through the first heat exchanger 30 along the sixth line L3' before entering the separator 20 and undergoing phase separation. Cooling the mixed refrigerant once before separation has the effect of improving phase separation. For example, the mixed refrigerant that has been cooled in the third heat exchanger 50 before flowing into the separator 20 can undergo phase separation more effectively in the separator 20 than a mixed refrigerant that has not passed through the third heat exchanger 50.

[0144] <Fifteenth embodiment> FIG. 15 is a diagram showing a liquefied gas supercooling system 1 according to a fifteenth embodiment of the present invention.

[0145] Referring to FIG. 15, a liquefied gas supercooling system 1 according to a fifteenth embodiment of the present invention includes a compressor 10, a heat exchanger 60, a pressure reducing valve 100, a ninth bypass valve 106, and a circulation line L4.

[0146] The circulation line L4 refers to a path through which the mixed refrigerant compressed by the compressor 10 returns to the compressor 10 via the heat exchanger 60, the pressure reducing valve 100, and the heat exchanger 60 again.

[0147] The mixed refrigerant compressed by the compressor 10 flows along the circulation line L4 into the heat exchanger 60 and is cooled by heat exchange with the mixed refrigerant that passes through the pressure reducing valve 100 and re-enters the heat exchanger 60. The primarily cooled mixed refrigerant is decompressed and cooled by the pressure reducing valve 100, and then re-enters the heat exchanger 60. The re-entered mixed refrigerant exchanges heat with the liquefied gas to subcool the liquefied gas, and returns to the compressor 10 along the circulation line L4.

[0148] Since no phase separation occurs, the mixed refrigerant containing heavy components such as C5 reaches an extremely low temperature during the cooling process, but this can cause the C5 to freeze. Therefore, an anti-freeze unit is required to adjust the temperature before re-entering the heat exchanger 60 downstream of the pressure reducing valve 100 (hereinafter referred to as the "eighth temperature 150").

[0149] The ninth bypass valve 106 is configured to control the eighth temperature 150. The ninth bypass valve 106 is provided on a ninth bypass line L16 that branches off from the circulation line L4 between the compressor 10 and the heat exchanger 60 and is connected to the circulation line L4 between the pressure reducing valve 100 and the heat exchanger 60.

[0150] When the eighth temperature 150 is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant discharged from the compressor 10 is diverted to the upstream of the pressure reducing valve 100 via the ninth bypass line L16 by adjusting the ninth bypass valve 106, thereby increasing the temperature of the mixed refrigerant and preventing freezing.

[0151] By preventing the mixed refrigerant from freezing, it is possible to prevent breakdowns in the liquefied gas supercooling system 1.

[0152] The liquefied gas supercooling systems 1 according to the first to fifteenth embodiments of the present invention can contain pentane as a component thereof.

[0153] The above description merely exemplifies the technical concept of the present invention, and various modifications and variations are possible within the scope of the essential characteristics of the present invention, as long as they are not deviated from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are for illustrative purposes only, and are not intended to limit the technical concept of the present invention. The scope of protection of the present invention should be interpreted by the following claims, and all technical concepts within the scope equivalent thereto should be interpreted as being within the scope of the present invention.

Claims

1. A system for subcooling a liquefied gas using a mixed refrigerant, comprising: a compressor that compresses the mixed refrigerant; a first separator provided downstream of the compressor and configured to phase-separate the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant; a first line through which the liquid phase refrigerant separated in the first separator flows via a first pressure reducing valve; a second line through which the vapor-phase refrigerant separated in the first separator flows through the first heat exchanger and the second separator; a second separator provided downstream of the first heat exchanger and configured to phase-separate the mixed refrigerant separated in the first separator and passed through the second line into a gas phase refrigerant and a liquid phase refrigerant; A second-1 line through which the gas phase refrigerant separated in the second separator flows via a second heat exchanger, a second pressure reducing valve, and re-flows into the second heat exchanger; a second-2 line through which the liquid phase refrigerant separated in the second separator flows via a third pressure reducing valve; a third line through which the mixed refrigerant combined from the first line, the 2-1 line, and the 2-2 line flows via the first heat exchanger, the compressor, and the first separator; In the first heat exchanger, the gas phase refrigerant separated in the first separator and flowing along the second line and the mixed refrigerant flowing along the third line exchange heat, In the second heat exchanger, heat is exchanged between the gas phase refrigerant separated in the second separator along the 2-1 line, the mixed refrigerant that has passed through the second pressure reducing valve along the 2-1 line, and the liquefied gas, A liquefied gas supercooling system, in which the liquefied gas is supercooled by heat exchange in the second heat exchanger.

2. In the first pressure reducing valve, the liquid phase refrigerant separated in the first separator and flowing along the first line is decompressed and its temperature is lowered, The mixed refrigerant passing through the second heat exchanger along the second-1 line is decompressed by the second pressure reducing valve to lower its temperature, The liquefied gas supercooling system according to claim 1, wherein the liquid phase refrigerant separated in the second separator and flowing along the second-2 line is decompressed by the third pressure reducing valve to lower its temperature.

3. further including a junction portion connected to the first line, the second-1 line, and the second-2 line at a front end thereof and connected to the third line at a rear end thereof; the mixed refrigerant joined at the joining portion flows along the third line and passes through the first heat exchanger, 2. The liquefied gas supercooling system according to claim 1, wherein the liquid phase refrigerant that has passed through the first pressure reducing valve, the mixed refrigerant that has passed through the second heat exchanger via the second pressure reducing valve, and the liquid phase refrigerant that has passed through the third pressure reducing valve are joined at the confluence section.

4. further including a junction portion connected to the first line, the second-1 line, and the second-2 line at a front end thereof and connected to the third line at a rear end thereof; a detour line branching off from at least one of the second line and the second-1 line; 2. The liquefied gas supercooling system of claim 1, further comprising an anti-icing unit that adjusts the temperature of the mixed refrigerant on the 2-1 line or the 2-2 line by adjusting the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided in the bypass line.

5. The liquefied gas supercooling system according to claim 4, wherein the anti-icing unit controls a first temperature of the mixed refrigerant along the 2-1 line before entering the junction.

6. A system for subcooling a liquefied gas using a mixed refrigerant, comprising: a compressor that compresses the mixed refrigerant; a separator provided downstream of the compressor and configured to phase-separate the mixed refrigerant into a gas phase refrigerant and a liquid phase refrigerant; a fourth line through which the liquid phase refrigerant separated in the separator flows via a first pressure reducing valve; a fifth line through which the vapor-phase refrigerant separated in the separator flows through the first heat exchanger, the second heat exchanger, the second pressure reducing valve, and re-enters the second heat exchanger; a sixth line through which the mixed refrigerant combined from the fourth line and the fifth line flows via the first heat exchanger, the compressor, and the separator; a detouring unit including a detouring line branching off from at least one of the fifth line and the sixth line, and adjusting the inflow of a relatively high-temperature mixed refrigerant through a detouring valve provided in the detouring line to adjust the temperature of the mixed refrigerant in the fifth line or the sixth line; In the first heat exchanger, the gas phase refrigerant separated in the separator and flowing along the fifth line and the mixed refrigerant flowing along the sixth line exchange heat with each other, In the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the fifth line, the mixed refrigerant that has passed through the second pressure reducing valve along the fifth line, and the liquefied gas exchange heat, A liquefied gas supercooling system, in which the liquefied gas is supercooled by heat exchange in the second heat exchanger.

7. The liquid-phase refrigerant separated in the separator and flowing along the fourth line is decompressed by the first decompression valve to lower its temperature, The liquefied gas supercooling system according to claim 6, wherein the mixed refrigerant that has passed through the second heat exchanger along the fifth line is decompressed by the second pressure reducing valve to lower its temperature.

8. further including a junction portion connected to the fourth line and the fifth line at a front end and connected to the sixth line at a rear end, The liquefied gas subcooling system of claim 6 , wherein the anti-icing unit controls a fifth temperature of the mixed refrigerant before it enters the first heat exchanger along the sixth line.

9. the ice prevention unit includes a fifth bypass valve; 9. The liquefied gas supercooling system according to claim 8, wherein the fifth bypass valve is provided on a fifth bypass line that branches off from at least one of the fourth line, the fifth line, and the sixth line and is connected to the fourth line upstream of the first pressure reducing valve or downstream of the first pressure reducing valve.

10. a junction portion connected to the fourth line and the fifth line at a front end and connected to the sixth line at a rear end, The liquefied gas supercooling system according to claim 6 , wherein the anti-freezing unit controls a sixth temperature of the mixed refrigerant that has passed through the second pressure reducing valve along the fifth line.

11. the ice prevention unit includes a seventh bypass valve; 11. The liquefied gas supercooling system according to claim 10, wherein the seventh bypass valve is provided on a seventh bypass line that branches off from the fifth line between the separator and the first heat exchanger and is connected to the fifth line upstream of the second pressure reducing valve or downstream of the second pressure reducing valve.

12. a junction portion connected to the fourth line and the fifth line at a front end and connected to the sixth line at a rear end, The liquefied gas subcooling system of claim 6 , wherein the anti-icing unit controls a seventh temperature of the mixed refrigerant entering the compressor along the sixth line.

13. the ice prevention unit includes an eighth bypass valve; 13. The liquefied gas subcooling system according to claim 12, wherein the eighth bypass valve is provided on an eighth bypass line that branches off from the sixth line between the compressor and the separator and is connected to the sixth line between the first heat exchanger and the compressor.

14. the fourth line passes through the first heat exchanger upstream of the first pressure reducing valve; 7. The liquefied gas supercooling system according to claim 6, wherein in the first heat exchanger, heat is exchanged between the liquid-phase refrigerant separated in the separator and flowing along the fourth line, the gas-phase refrigerant separated in the separator and flowing along the fifth line, and the mixed refrigerant flowing along the sixth line.

15. the ice prevention unit includes a fifth bypass valve; 15. The liquefied gas supercooling system according to claim 14, wherein the fifth bypass valve is provided on a fifth bypass line that branches off from at least one of the fourth line, the fifth line, and the sixth line and is connected to the fourth line upstream of the first pressure reducing valve or downstream of the first pressure reducing valve.

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