Liquefied gas subcooling system using mixed refrigerant

Abstract

The present invention relates to a liquefied gas subcooling system comprising: a compressor; a separator; a first line through which a liquid refrigerant separated by the separator flows via a first pressure-reducing valve; a second line through which a gaseous refrigerant separated by the separator flows after being reintroduced into a first heat exchanger, a second heat exchanger, a second pressure-reducing valve, and the second heat exchanger; a third line through which a mixed refrigerant joined from the first line and the second line flows via the first heat exchanger, the compressor, and the separator; and an anti-freezing unit having a bypass line branched from the second line, and adjusting the temperature of the mixed refrigerant on the second line by adjusting the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided in the bypass line.

Description

Liquefied gas subcooling system using mixed refrigerant

[0001] Cross-citation with related applications

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2024-0127696 filed on September 20, 2024, and all contents disclosed in the document of said Korean Patent Application are incorporated herein as part of this specification.

[0003] Technology field

[0004] The present invention relates to a system for supercooling liquefied gas using a mixed refrigerant.

[0005] Liquefying natural gas reduces its volume, making storage and transportation easier. Natural gas in this state is called liquefied gas. For example, among liquefied gases, LNG has a liquefaction temperature of minus 163 degrees Celsius at atmospheric pressure, so storage tanks with excellent insulation performance are used to maintain cryogenic conditions.

[0006] However, it is impossible to completely block the inflow of heat into the storage tank from the outside; if heat is introduced, the liquefied gas inside the tank vaporizes, generating Boil-Off Gas (BOG). When BOG is generated, the existing liquefied gas turns into gas, expanding in volume and increasing the pressure within the storage tank, creating a risk of explosion. Furthermore, economic losses occur because the transportable volume decreases proportionally to the amount of liquefied gas that vaporizes.

[0007] Various measures are being studied to solve the problems caused by BOG. ​​Representative methods include re-liquefying vaporized natural gas and supercooling the liquefaction.

[0008] Both of the above methods utilize a cooling cycle that cools natural gas through the circulation of a refrigerant, and methods such as increasing efficiency through process changes in the cooling cycle or increasing heat exchange efficiency by using mixed refrigerants are being applied.

[0009] In particular, if the mixed refrigerant contains heavy elements such as pentane, the temperature may drop excessively during the heat exchange process, and freezing may occur. Since freezing can cause equipment failure, it is necessary to control the temperature of the mixed refrigerant.

[0010] The objective 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.

[0011] A liquefied gas subcooling system according to one embodiment of the present invention is a system for subcooling liquefied gas using a mixed refrigerant, comprising: a compressor for compressing the mixed refrigerant; a separator provided at the downstream end of the compressor for separating the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; a first line through which the liquid refrigerant separated in the separator flows via a first heat exchanger, a first pressure reducing valve, and a junction; a second line through which the gaseous refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, re-inflow into the second heat exchanger, and a junction; and a third line through which the mixed refrigerant joined at the junction flows via the first heat exchanger, the compressor, and the separator. The apparatus includes a bypass line and a freezing prevention unit that controls the temperature of the mixed refrigerant on the first line, second line, or third line by controlling the inflow of the mixed refrigerant at a relatively high temperature through a bypass valve provided in the bypass line, wherein in the first heat exchanger, the liquid refrigerant separated from the separator and flowing along the first line, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant joined at the junction and flowing along the third line exchange heat, and in the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second line, and the liquefied gas exchange heat so that the liquefied gas can be supercooled.

[0012] In one example, in the first pressure reducing valve, the liquid refrigerant passing through the first heat exchanger along the first line is reduced in pressure and its temperature is lowered, and in the second pressure reducing valve, the mixed refrigerant passing through the second heat exchanger along the second line is reduced in pressure and its temperature is lowered.

[0013] In one example, the anti-freezing unit can control a first temperature of the mixed refrigerant passing through the first pressure reducing valve along the first line, and a second temperature of the mixed refrigerant before entering the first heat exchanger along the third line.

[0014] In one example, the anti-freezing unit includes a first bypass valve, and the first bypass valve may be provided on a first bypass line that branches off from the first line between the separator and the first heat exchanger and connects to the first line between the first heat exchanger and the first pressure reducing valve.

[0015] In one example, the anti-freezing unit includes a second bypass valve, and the second bypass valve may be provided on a second bypass line that branches off from the second line between the separator and the first heat exchanger and connects to the first line between the first heat exchanger and the first pressure reducing valve.

[0016] In one example, the anti-freezing unit includes a third bypass valve, and the third bypass valve may be provided on a third bypass line that branches off from the third line between the compressor and the separator and connects to the first line between the first heat exchanger and the first pressure reducing valve.

[0017] In one example, the above-mentioned anti-freezing unit can control the third temperature of the mixed refrigerant that has passed through the second pressure reducing valve along the second line.

[0018] In one example, the anti-freezing unit includes a fourth bypass valve, and the fourth bypass valve may be provided on a fourth bypass line that branches off from the second line between the separator and the first heat exchanger and is connected to the second line between the downstream of the second pressure reducing valve and the second heat exchanger.

[0019] In one example, the above-mentioned anti-freezing unit can control the fourth temperature of the mixed refrigerant entering the compressor along the third line.

[0020] In one example, the anti-freezing unit includes a fifth bypass valve, and the fifth bypass valve may be provided on a fifth bypass line that branches off from the third line between the compressor and the separator and connects to the third line between the first heat exchanger and the compressor.

[0021] In one example, a third heat exchanger is further included, said third heat exchanger may be arranged so that the mixed refrigerant passing through the first heat exchanger along the third line and the mixed refrigerant passing through the compressor along the third line exchange heat.

[0022] A liquefied gas subcooling system according to one embodiment of the present invention is a system for subcooling liquefied gas using a mixed refrigerant, comprising: a compressor for compressing the mixed refrigerant; a separator provided at the downstream end of the compressor for separating the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; a first line through which the liquid refrigerant separated in the separator flows via a first pressure reducing valve and a junction; a second line through which the gaseous refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, re-inflow into the second heat exchanger, and a junction; and a third line through which the mixed refrigerant joined at the junction flows via the first heat exchanger, the compressor, and the separator. The apparatus includes a bypass line and a freezing prevention unit that controls the temperature of the mixed refrigerant on the first line, second line, or third line by controlling the inflow of the mixed refrigerant at a relatively high temperature through a bypass valve provided in the bypass line, wherein in the first heat exchanger, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant joined at the junction and flowing along the third line exchange heat, and in the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second line, and the liquefied gas exchange heat so that the liquefied gas can be supercooled.

[0023] In one example, at the first pressure reducing valve, the liquid refrigerant separated from the separator and flowing along the first line is reduced in pressure and its temperature is lowered, and at the second pressure reducing valve, the mixed refrigerant that has passed through the second heat exchanger along the second line is reduced in pressure and its temperature is lowered.

[0024] In one example, the anti-freezing unit can control the second temperature of the mixed refrigerant before it enters the first heat exchanger along the third line.

[0025] In one example, the anti-freezing unit includes a second bypass valve, and the second bypass valve may be provided on a second bypass line that branches off from the second line between the separator and the first heat exchanger and connects to the first line between the separator and the first pressure reducing valve.

[0026] In one example, the anti-freezing unit includes a third bypass valve, and the third bypass valve may be provided on a third bypass line that branches off from the third line between the compressor and the separator and connects to the first line between the separator and the first heat exchanger.

[0027] A liquefied gas subcooling system according to one embodiment of the present invention is a system for subcooling liquefied gas using a mixed refrigerant, comprising: a compressor for compressing the mixed refrigerant; a circulation line through which the mixed refrigerant that has passed through the compressor flows back to the compressor after passing through a heat exchanger, a pressure reducing valve, and a re-entry into the heat exchanger; and a bypass line, and includes an anti-freezing unit that controls the temperature of the mixed refrigerant on the circulation line by controlling the inflow of the mixed refrigerant at a relatively high temperature through a bypass valve provided in the bypass line, wherein in the heat exchanger, the mixed refrigerant flowing out of the compressor, the mixed refrigerant that has passed through the pressure reducing valve, and the liquefied gas exchange heat so that the liquefied gas can be subcooled.

[0028] In one example, at the pressure reducing valve, the mixed refrigerant that has passed through the heat exchanger can be depressurized and its temperature lowered before being re-entered into the heat exchanger.

[0029] In one example, the above-mentioned anti-freezing unit can control the fifth temperature of the mixed refrigerant that has passed through the above-mentioned pressure reducing valve.

[0030] In one example, the above-mentioned anti-freezing unit includes a sixth bypass valve, and the sixth bypass valve may be provided on a sixth bypass line that branches off from the circulation line between the compressor and the heat exchanger and connects to the circulation line between the heat exchanger and the pressure reducing valve.

[0031] A liquefied gas subcooling system according to one embodiment of the present invention is a system for subcooling liquefied gas using a mixed refrigerant, comprising: a compressor for compressing the mixed refrigerant; a separator provided at the downstream end of the compressor for separating the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; a first line through which the liquid refrigerant separated in the separator flows via a first pressure reducing valve; a second line through which the gaseous refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-entry into the second heat exchanger; and a third line through which the mixed refrigerant joined from the first line and the second line flows via the first heat exchanger, the compressor, and the separator. The apparatus includes a bypass line branched from the second line, and a freezing prevention unit that controls the temperature of the mixed refrigerant on the second line by controlling the inflow of a mixed refrigerant at a relatively high temperature through a bypass valve provided in the bypass line, wherein in the first heat exchanger, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant flowing along the third line exchange heat, and in the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second line, and the liquefied gas exchange heat, and the liquefied gas may be supercooled by the heat exchange in the second heat exchanger.

[0032] In one example, the liquid refrigerant separated from the separator and flowing along the first line is depressurized at the first pressure reducing valve and its temperature is lowered, and the mixed refrigerant passing through the second heat exchanger along the second line is depressurized at the second pressure reducing valve and its temperature is lowered.

[0033] In one example, the system further includes a junction connected to the first line and the second line at the front end and connected to the third line at the rear end, and the anti-freezing unit can control the first temperature of the mixed refrigerant passing through the second pressure reducing valve along the second line.

[0034] In one example, the bypass line may be branched from the second line between the first heat exchanger and the second heat exchanger and connected to the second line upstream of the second pressure reducing valve or downstream of the second pressure reducing valve.

[0035] In one example, the system further includes a junction connected to the first line and the second line at the front end and connected to the third line at the rear end, and the anti-freezing unit can control the sixth temperature of the mixed refrigerant before it passes through the first heat exchanger along the second line and enters the second heat exchanger.

[0036] In one example, the bypass line may be branched from the second line between the separator and the first heat exchanger and connected to the second line between the first heat exchanger and the second heat exchanger.

[0037] A liquefied gas subcooling system according to one embodiment of the present invention is a system for subcooling liquefied gas using a mixed refrigerant, comprising: a compressor for compressing the mixed refrigerant; a separator provided at the downstream end of the compressor for separating the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; a first line through which the liquid refrigerant separated in the separator flows via a first pressure reducing valve; a second line through which the gaseous refrigerant separated in the separator flows via a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-entry into the second heat exchanger; and a third line through which the mixed refrigerant joined from the first line and the second line flows via the first heat exchanger, the compressor, and the separator. The apparatus includes a bypass line branched from the third line, and an anti-freezing unit that controls the temperature of the mixed refrigerant on the third line by controlling the inflow of the mixed refrigerant at a relatively high temperature through a bypass valve provided in the bypass line, wherein in the first heat exchanger, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant flowing along the third line exchange heat, and in the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second line, and the liquefied gas exchange heat, and the liquefied gas may be supercooled by the heat exchange in the second heat exchanger.

[0038] In one example, the liquid refrigerant separated from the separator and flowing along the first line is depressurized at the first pressure reducing valve and its temperature is lowered, and the mixed refrigerant passing through the second heat exchanger along the second line is depressurized at the second pressure reducing valve and its temperature is lowered.

[0039] In one example, the system further includes a junction connected to the first line and the second line at the front end and connected to the third line at the rear end, and the anti-freezing unit can control the second temperature of the mixed refrigerant before it enters the first heat exchanger along the third line.

[0040] In one example, the bypass line may be branched from the third line between the compressor and the separator and connected to the third line at the rear end of the junction.

[0041] According to the present invention, cooling efficiency through a pressure reducing valve is increased, and freezing of the mixed refrigerant can be prevented.

[0042] FIG. 1 is a drawing showing a liquefied gas supercooling system according to a first embodiment of the present invention.

[0043] FIG. 2 is a diagram showing a liquefied gas supercooling system according to a second embodiment of the present invention.

[0044] FIG. 3 is a diagram showing a liquefied gas supercooling system according to a third embodiment of the present invention.

[0045] FIG. 4 is a diagram showing a liquefied gas supercooling system according to a fourth embodiment of the present invention.

[0046] FIG. 5 is a diagram showing a liquefied gas supercooling system according to the fifth embodiment of the present invention.

[0047] FIG. 6 is a diagram showing a liquefied gas supercooling system according to the 6th embodiment of the present invention.

[0048] FIG. 7 is a diagram showing a liquefied gas supercooling system according to the seventh embodiment of the present invention.

[0049] FIG. 8 is a diagram showing a liquefied gas supercooling system according to the eighth embodiment of the present invention.

[0050] FIG. 9 is a diagram showing a liquefied gas supercooling system according to the ninth embodiment of the present invention.

[0051] Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. It should be noted that in assigning reference numerals to the components of each drawing, the same components are given the same reference numeral whenever possible, even if they are shown in different drawings. Furthermore, in describing the embodiments of the present invention, if it is determined that a detailed description of related known components or functions would hinder understanding of the embodiments of the present invention, such detailed description is omitted.

[0052] In addition, terms such as first, second, A, B, (a), (b), etc., may be used when describing the components of the embodiments of the present invention. These terms are intended merely to distinguish the components from other components, and the essence, order, or sequence of the components is not limited by these terms. Where it is stated that a component is "connected," "combined," or "joined" to another component, it should be understood that the component may be directly connected or joined to the other component, but that another component may also be "connected," "combined," or "joined" between each component.

[0053] In this specification, the front-back, left-right, and up-down directions are referred to for convenience of explanation and may be directions orthogonal to one another. However, these directions are determined relatively, and the term "up-down direction" does not necessarily mean a vertical direction.

[0054]

[0055] <1st Example>

[0056] FIG. 1 is a drawing showing a liquefied gas supercooling system according to a first embodiment of the present invention.

[0057] Referring to FIG. 1, a liquefied gas supercooling system (1) according to a first embodiment of the present invention includes a compressor (10), a separator (20), a first heat exchanger (30), a second heat exchanger (40), a junction (70), a first pressure reducing valve (80), a second pressure reducing valve (90), a first bypass valve (101), a first line (L1), a second line (L2), and a third line (L3).

[0058] Below, each component, its role, and the flow of the process are described.

[0059] For convenience, the first line (L1), second line (L2), and third line (L3) are defined first.

[0060] The first line (L1) refers to the path through which the liquid refrigerant separated from the separator (20) passes through the first heat exchanger (30), the first pressure reducing valve (80), and the junction (70).

[0061] The second line (L2) refers to the path through which the gaseous refrigerant separated from the separator (20) passes through the first heat exchanger (30), the second heat exchanger (40), the second pressure reducing valve (90), the re-entry into the second heat exchanger (40), and the merging section (70). The refrigerant following the first line (L1) and the refrigerant following the second line (L2) merge at the merging section (70) and follow the third line (L3).

[0062] The third line (L3) refers to the path through which the mixed refrigerant combined at the junction (70) passes through the first heat exchanger (30), the compressor (10), and the separator (20).

[0063] The compressor (10) compresses the mixed refrigerant to a high pressure. Since the temperature of the mixed refrigerant rises during the compression process, a cooler (not shown in the drawing) may be installed at the downstream end of the compressor (10) to lower this temperature. The cooler can lower the temperature of the mixed refrigerant to near the temperature of the seawater through heat exchange with the seawater. For example, this temperature may be 40°C, but it may vary depending on the temperature of the seawater or the performance of the cooler.

[0064] Installing a cooler downstream of the compressor is a standard practice in compressor operation, so it is not separately illustrated in the drawing.

[0065] The mixed refrigerant that has passed through the compressor (10) enters the separator (20) along the third line (L3) and can be separated into a gaseous refrigerant and a liquid refrigerant. For example, among the components of the mixed refrigerant, light components such as C1 and C2 can be separated into a gaseous refrigerant, and heavy components such as C5 can be separated into a liquid refrigerant. The reason for separating the mixed refrigerant into gaseous and liquid phases is that, in the case of the liquid refrigerant, there is a risk of freezing if it exchanges heat with the cryogenic liquefied gas, so only the gaseous refrigerant undergoes heat exchange with the liquefied gas.

[0066] The mixed refrigerant separated in the separator (20), namely the liquid refrigerant and the gaseous refrigerant, can flow along the first line (L1) and the second line (L2), respectively. This will be explained in detail below.

[0067] The liquid refrigerant separated in the separator (20) enters the first heat exchanger (30) along the first line (L1) and can be cooled by heat exchange with the mixed refrigerant entering the first heat exchanger (30) along the third line (L3). In the first heat exchanger (30), heat exchange is performed between the three flows of three types of refrigerants: the liquid refrigerant following the first line (L1), the gaseous refrigerant following the second line (L2), and the mixed refrigerant following the third line (L3). Afterward, the liquid refrigerant that has passed through the first heat exchanger (30) is cooled by pressure reduction at the first pressure reducing valve (80).

[0068] In a normal process, the liquid refrigerant enters the pressure reducing valve directly without passing through a heat exchanger, but 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), thereby allowing the liquid refrigerant at a relatively lower temperature to enter the first pressure reducing valve (80). Since the liquid refrigerant is primarily cooled in the first heat exchanger (30) before passing through the first pressure reducing valve (80), it has the effect of increasing the cooling efficiency of the first pressure reducing valve (80). However, as the cooling process is added before the pressure reducing valve, the temperature of the liquid refrigerant passing through the pressure reducing valve drops rapidly, which may cause freezing. An anti-freezing unit has been introduced to solve this problem, which will be explained again later.

[0069] The liquid refrigerant passing through the first pressure reducing valve (80) reaches the junction (70) and is combined with the refrigerant entering the junction (70) along the second line (L2). The refrigerant entering the junction (70) along the second line (L2) from the separator (20) may be a gaseous refrigerant, or may include a mixed refrigerant in which a portion becomes liquid while passing through the second heat exchanger (40) or the second pressure reducing valve (90) in addition to the gaseous refrigerant.

[0070] The gaseous refrigerant separated from the separator (20) enters the first heat exchanger (30) along the second line (L2) and is cooled by heat exchange with the mixed refrigerant entering the first heat exchanger (30) along the third line (L3). Since the phase of the gaseous refrigerant may change as it passes through the first heat exchanger (30), the second heat exchanger (40), the second pressure reducing valve (90), etc., to avoid confusion, the gaseous refrigerant and the liquid refrigerant are not distinguished below, and the term "mixed refrigerant" is used consistently. Subsequently, the mixed refrigerant enters the second heat exchanger (40) along the second line (L2), and the mixed refrigerant that has passed through the second heat exchanger (40) is cooled by pressure reduction at the second pressure reducing valve (90). Subsequently, it is re-introduced into the second heat exchanger (40) along the second line (L2) and reaches the junction section (70). During the cooling process in the second pressure reducing valve (90), the mixed refrigerant is cooled to a temperature of minus 170 degrees or lower. This is because the temperature of the liquefied gas is usually around minus 160 degrees, and when it is supercooled, the temperature is lowered to minus 170 degrees. In addition, the temperature of the mixed refrigerant passing through the second pressure reducing valve (90) drops rapidly here as well, which may cause freezing. An anti-freezing unit has been introduced to solve this problem, which will be explained again later.

[0071] The mixed refrigerant passing through the second pressure reducing valve (90) is recirculated into the second heat exchanger (40) to exchange heat with the liquefied gas and subcool the liquefied gas. Afterward, the mixed refrigerant, having completed the heat exchange, reaches the junction (70) and merges with the mixed refrigerant entering the junction (70) along the first line (L1). In the second heat exchanger (40), heat exchange is performed between three flows of refrigerants: the mixed refrigerant passing through the first heat exchanger (30) along the second line (L2), the mixed refrigerant recirculated through the second pressure reducing valve (90) along the second line (L2), and the liquefied gas.

[0072] The mixed refrigerant combined at the junction (70) enters the first heat exchanger (30) along the third line (L3). At this time, since the mixed refrigerant entering along the first line (L1) may freeze upon contact with the low-temperature mixed refrigerant entering along the second line (L2), an anti-freezing unit is introduced to resolve this, which will be explained later.

[0073] The mixed refrigerant that enters the first heat exchanger (30) along the third line (L3) exchanges heat with the mixed refrigerant that enters the first heat exchanger (30) along the first line (L1) and the mixed refrigerant that enters the first heat exchanger (30) along the second line (L2), as previously explained. The mixed refrigerant that has completed heat exchange then enters the compressor (10) again along the third line (L3).

[0074] The anti-freezing section is explained below.

[0075] The anti-freezing unit is a component that detects the temperature at a specific point to prevent the mixed refrigerant from freezing and controls it so that the temperature does not drop below a certain level.

[0076] Referring to FIG. 1, Embodiment 1 of the present invention includes a first bypass valve (101) as an anti-freezing unit.

[0077] The first bypass valve (101) is configured to control the temperature downstream of the first pressure reducing valve (80) (hereinafter referred to as the 'first temperature (T1)') and the temperature between the junction (70) and the first heat exchanger (hereinafter referred to as the 'second temperature (T2)'). The first bypass valve (101) is provided on a first bypass line (L11) that branches off from the first line (L1) between the separator (20) and the first heat exchanger (30) and connects to the first line (L1) between the first heat exchanger (30) and the first pressure reducing valve (80).

[0078] A first temperature (T1) and a second temperature (T2) are detected, and if the lower of the two temperatures is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated from the separator (20) and flowing along the first line (L1) is controlled by adjusting the first bypass valve (101) to flow into the upstream side of the first pressure reducing valve (31) through the first bypass line (L11) to control the temperature.

[0079] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0080]

[0081] <2nd and 3rd Examples>

[0082] FIG. 2 is a drawing showing a liquefied gas supercooling system (1) according to a second embodiment of the present invention. FIG. 3 is a drawing showing a liquefied gas supercooling system (1) according to a third embodiment of the present invention.

[0083] The first embodiment includes a first bypass line (L11) as a configuration for controlling a first temperature (T1) and a second temperature (T2), but the second and third embodiments include a second bypass line (L12) and a third bypass line (L13) as a configuration for controlling the first temperature (T1) and the second temperature (T2).

[0084] Referring to FIG. 2, the liquefied gas supercooling system (1) according to the second embodiment of the present invention is configured to prevent freezing by controlling a first temperature (T1) and a second temperature (T2), and includes a second bypass line (L12). Other configurations are the same as those in Embodiment 1, so a description is omitted.

[0085] The second bypass valve (102) is provided on a second bypass line (L12) that branches off from the second line (L2) between the separator (20) and the first heat exchanger (30) and connects to the first line (L1) between the first heat exchanger (30) and the first pressure reducing valve (80).

[0086] A first temperature (T1) and a second temperature (T2) are detected, and if the lower of the two temperatures is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated from the separator (20) and flowing along the second line (L2) is controlled by adjusting the second bypass valve (102) to flow into the upstream side of the first pressure reducing valve (80) through the second bypass line (L12) to control the temperature.

[0087] Referring to FIG. 3, the liquefied gas supercooling system (1) according to the third embodiment of the present invention includes a third bypass valve (103) as a configuration for preventing freezing by controlling a first temperature (T1) and a second temperature (T2). Other configurations are the same as those in FIG. 1, so a description is omitted.

[0088] A third bypass valve (103) is provided on a third bypass line (L13) that branches off from a third line (L3) between a compressor (10) and a separator (20) and connects to a first line (L1) between a first heat exchanger (30) and a first pressure reducing valve (80). For example, the third bypass line (L13) may be connected to a portion of the first line (L1) that passes the first heat exchanger (30) upstream of the first pressure reducing valve (80).

[0089] A first temperature (T1) and a second temperature (T2) are detected, and if the lower of the two temperatures is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant from the compressor (10) is controlled by adjusting the third bypass valve (103) to flow into the upstream side of the first pressure reducing valve (80) through the third bypass line (L13) to control the temperature.

[0090] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0091]

[0092] <Fourth Example>

[0093] FIG. 4 is a drawing showing a liquefied gas supercooling system (1) according to the fourth embodiment of the present invention.

[0094] Referring to FIG. 4, the liquefied gas supercooling system (1) according to the fourth embodiment of the present invention includes a fourth bypass valve (104) as a configuration for preventing freezing by controlling a third temperature (T3). Other configurations are the same as those in Embodiment 1, so a description is omitted.

[0095] The fourth bypass valve (104) is configured to control the temperature (hereinafter referred to as the 'third temperature (T3)') before recirculation to the second heat exchanger (40) downstream of the second pressure reducing valve (90) along the second line (L2). The fourth bypass valve (104) is provided on a fourth bypass line (L14) that branches off from the second line (L2) between the separator (20) and the first heat exchanger (30) and connects to the second line (L2) between the second pressure reducing valve (90) and the second heat exchanger (40).

[0096] When the third temperature (T3) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant separated from the separator (20) and flowing along the second line (L2) is controlled by adjusting the fourth bypass valve (104) to flow into the downstream end of the second pressure reducing valve (90) through the fourth bypass line (L14) to control the temperature.

[0097] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0098] <5th Example>

[0099] FIG. 5 is a drawing showing a liquefied gas supercooling system (1) according to the fifth embodiment of the present invention.

[0100] Referring to FIG. 5, the liquefied gas supercooling system (1) according to the fifth embodiment of the present invention includes a fifth bypass valve (105) as a configuration for preventing freezing by controlling the fourth temperature (140). Other configurations are the same as those in Embodiment 1, so they are omitted from the description.

[0101] The fifth bypass valve (105) is configured to control the temperature upstream of the compressor (10) along the third line (L3) (hereinafter referred to as the 'fourth temperature (T4)'). The fifth bypass valve (105) is provided on a fifth bypass line (L15) that branches off from the third line (L3) between the compressor (10) and the separator (20) and connects to the third line (L3) between the first heat exchanger (30) and the compressor (10).

[0102] When the fourth temperature (140) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant compressed in the compressor (10) is controlled by adjusting the fifth bypass valve (105) to flow into the front of the compressor (10) through the fifth bypass line (L15) to control the temperature.

[0103] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0104]

[0105] <Examples 6 and 7>

[0106] FIG. 6 is a drawing showing a liquefied gas supercooling system (1) according to the 6th embodiment of the present invention.

[0107] FIG. 7 is a drawing showing a liquefied gas supercooling system (1) according to the 7th embodiment of the present invention.

[0108] Referring to FIGS. 6 and 7, the liquefied gas subcooling system (1) according to the 6th and 7th embodiments of the present invention differs from the liquefied gas subcooling system (1) according to the 1st to 5th embodiments of the present invention in that the liquid refrigerant separated from the separator (20) is cooled by being depressurized directly at the first pressure reducing valve (80) without passing through the first heat exchanger (30). That is, the first line (L1') according to the 6th and 7th embodiments refers to the path through which the liquid refrigerant separated from the separator (20) passes through the first pressure reducing valve (80) and the junction (70).

[0109] The second line (L2) and the third line (L3) are identical to the first to fifth embodiments described above. Additionally, as anti-freezing parts, the fourth bypass line (L14), the fifth bypass line (L15), the fourth bypass valve (104), and the fifth bypass valve (105) can also be applied in the same way as the fourth and fifth embodiments described above.

[0110] In the liquefied gas supercooling system (1) according to the 6th and 7th embodiments of the present invention, since the liquid refrigerant is cooled without passing through the first heat exchanger (30), there is no risk of freezing occurring at the downstream end of the first pressure reducing valve (80), so there is no need to control the first temperature (T1), and only the second temperature (T2) needs to be controlled.

[0111] According to the above differences, the configuration of the anti-freezing unit for controlling the second temperature (T2) is also partially different. Referring to FIG. 6, the configuration for controlling the second temperature (T2) to prevent freezing includes a second bypass valve (102'). The second bypass valve (102') is provided on a second bypass line (L12') that branches off from the second line (L2) between the separator (20) and the first heat exchanger (30) and connects to the first line (L1) between the separator (20) and the first heat exchanger (30).

[0112] When the second temperature (T2) is detected and the temperature is low enough to cause the mixed refrigerant to freeze, the high-temperature mixed refrigerant separated from the separator (20) is controlled by adjusting the second bypass valve (102') to flow into the upstream side of the first pressure reducing valve (80) through the second bypass line (L12') to control the temperature.

[0113] Referring to FIG. 7, a third bypass valve (103') is included as a configuration for controlling the second temperature (T2) to prevent freezing. The third bypass valve (103') is provided on a third bypass line (L13') which branches off from the third line (L3) between the compressor (10) and the separator (20) and connects to the first line (L1) between the separator (20) and the first heat exchanger (30).

[0114] When the second temperature (T2) is detected and the temperature is low enough to cause the mixed refrigerant to freeze, the high-temperature mixed refrigerant from the compressor (10) is controlled by adjusting the third bypass valve (103') to flow into the upstream side of the first pressure reducing valve (80) through the third bypass line (L13') to control the temperature. By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0115] Referring again to FIG. 6, the liquefied gas supercooling system (1) according to the sixth embodiment of the present invention may include a seventh bypass valve (107) as a configuration for preventing freezing by controlling a third temperature (T3).

[0116] The seventh bypass valve (107) is configured to control the third temperature (130). The seventh bypass valve (107) is provided on a seventh bypass line (L17) that branches off from the second line (L2) between the first heat exchanger (30) and the second heat exchanger (40) and connects to the second line (L2) upstream of the second pressure reducing valve (90) or downstream of the second pressure reducing valve (90).

[0117] In FIG. 6, the seventh bypass line (L17) is connected to the rear end of the second pressure reducing valve (90) as an example, but is not limited thereto.

[0118] When the third temperature (T3) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant flowing through the first heat exchanger (30) along the second line (L2) is controlled by adjusting the seventh bypass valve (107) to flow into the downstream end of the second pressure reducing valve (90) through the seventh bypass line (L17) to control the temperature.

[0119] Referring further to FIG. 6, the liquefied gas supercooling system (1) according to the sixth embodiment of the present invention may include an eighth bypass valve (108) as a configuration for preventing freezing by controlling the sixth temperature (160), which is the temperature of the mixed refrigerant before it passes through the first heat exchanger (30) along the second line (L2) and enters the second heat exchanger (40).

[0120] The eighth bypass valve (108) is configured to control the sixth temperature (160). The eighth bypass valve (108) is provided on an eighth bypass line (L18) that branches off from the second line (L2) between the separator (20) and the first heat exchanger (30) and connects to the second line (L2) between the first heat exchanger (30) and the second heat exchanger (40).

[0121] When the 6th temperature (T6) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant, which is separated from the separator (20) and flows into the first heat exchanger (30) along the second line (L2), is controlled by adjusting the 8th bypass valve (108) to flow into the second line (L2) between the first heat exchanger (30) and the second heat exchanger (40) through the 8th bypass line (L18) to control the temperature.

[0122] Referring further to FIG. 6, the liquefied gas supercooling system (1) according to the sixth embodiment of the present invention may include a ninth bypass valve (109) as a configuration for controlling a second temperature (120) to prevent freezing. The ninth bypass valve (109) is a configuration for controlling the second temperature (120). The ninth bypass valve (109) is provided on a ninth bypass line (L19) that branches off from a third line (L3) between the compressor (10) and the separator (20) and connects to a third line (L3) at the rear end of the junction (70).

[0123] When the second temperature (T2) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant that has passed through the compressor (10) along the third line (L3) is controlled by adjusting the ninth bypass valve (109) to flow into the third line (L3) at the rear of the junction (70) through the ninth bypass line (L19) to control the temperature.

[0124] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0125] The 7th bypass valve (107) and 7th bypass line (L17), 8th bypass valve (108) and 8th bypass line (L18), 9th bypass valve (109) and 9th bypass line (L19) can be applied in the same way even when three flows exchange heat within the aforementioned 1st heat exchanger (30) (1st to 5th embodiments).

[0126] In addition, at least one of the second bypass valve (102), the fourth bypass valve (104), the fifth bypass valve (105), the seventh bypass valve (107), the eighth bypass valve (108), and the ninth bypass valve (109) in FIG. 6 may be omitted (the bypass line in which each bypass valve is provided may also be omitted).

[0127]

[0128] <8th Example>

[0129] FIG. 8 is a drawing showing a liquefied gas supercooling system (1) according to the eighth embodiment of the present invention.

[0130] Referring to FIG. 8, the liquefied gas supercooling system (1) according to the ninth embodiment of the present invention additionally has a third heat exchanger (50) compared to the liquefied gas supercooling system (1) according to the first embodiment. However, not limited thereto, the third heat exchanger (50) can be added in the same way to the second to seventh embodiments as well as to the first embodiment.

[0131] The third line (L3') according to the eighth 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), the third heat exchanger (50), and the separator (20). The first line (L1) and the second line (L2) are identical to the first to fifth embodiments described above.

[0132] The third heat exchanger (50) is arranged so that the mixed refrigerant that has passed through the first heat exchanger (30) along the third line (L3') and the mixed refrigerant that has passed through the compressor (10) along the third line (L3') can exchange heat. The mixed refrigerant that has finished heat exchange in the third heat exchanger (50) can enter the separator (20) and be separated into phases.

[0133] Specifically, the high-temperature mixed refrigerant that has passed through the compressor (10) in the third heat exchanger (50) enters the separator (20) and is cooled by heat exchange with the relatively low-temperature mixed refrigerant that has passed through the first heat exchanger (30) along the third line (L3') before phase separation. By cooling the mixed refrigerant once before separation, the phase separation occurs more effectively. For example, the mixed refrigerant cooled in the third heat exchanger (50) before entering the separator (20) can be phase-separated more effectively in the separator (20) than the mixed refrigerant that has not passed through the third heat exchanger (50).

[0134]

[0135] <9th Example>

[0136] FIG. 9 is a drawing showing a liquefied gas supercooling system (1) according to the ninth embodiment of the present invention.

[0137] Referring to FIG. 9, a liquefied gas supercooling system (1) according to the ninth embodiment of the present invention includes a compressor (10), a heat exchanger (60), a pressure reducing valve (100), a sixth bypass valve (106), and a circulation line (L4).

[0138] The circulation line (L4) refers to the path through which the mixed refrigerant compressed in the compressor (10) returns to the compressor (10) via the heat exchanger (60), the pressure reducing valve (100), and the re-entry into the heat exchanger (60).

[0139] The mixed refrigerant compressed in the compressor (10) enters the heat exchanger (60) along the circulation line (L4) and is cooled by exchanging heat with the mixed refrigerant that is recirculated to the heat exchanger (60) through the pressure reducing valve (100). The mixed refrigerant that is cooled in the first stage is depressurized and cooled at the pressure reducing valve (100), and then recirculated to the heat exchanger (60). The recirculated mixed refrigerant subcools the liquefied gas through heat exchange with the liquefied gas and returns to the compressor (10) along the circulation line (L4).

[0140] Since the phase is not separated, the mixed refrigerant reaches cryogenic temperatures during the cooling process while containing heavy components such as C5, which can cause the C5 to freeze. Therefore, an anti-freezing unit is required to control the temperature (hereinafter referred to as the 'fifth temperature (T5)') before it is recirculated to the heat exchanger (60) downstream of the pressure reducing valve (100).

[0141] The sixth bypass valve (106) is configured to control the fifth temperature (T5). The sixth bypass valve (106) is provided on a sixth bypass line (L16) that branches off from the circulation line (L4) between the compressor (10) and the heat exchanger (60) and connects to the circulation line (L4) between the pressure reducing valve (100) and the heat exchanger (60).

[0142] When the fifth temperature (T5) is detected and the temperature is low enough to cause freezing of the mixed refrigerant, the high-temperature mixed refrigerant from the compressor (10) is controlled by adjusting the sixth bypass valve (106) to flow into the upstream side of the pressure reducing valve (100) through the sixth bypass line (L16) to control the temperature.

[0143] By controlling the temperature, freezing of the mixed refrigerant can be prevented. By preventing freezing of the mixed refrigerant, failure of the liquefied gas supercooling system (1) can be prevented.

[0144]

[0145] The liquefied gas supercooling system (1) according to the first to ninth embodiments of the present invention may include pentane as a component.

[0146]

[0147] The foregoing description is merely an illustrative explanation of the technical concept of the present invention, and those skilled in the art to which the present invention pertains will be able to make various modifications and variations within the scope of the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are intended to explain, not limit, the technical concept of the present invention, and the scope of the technical concept of the present invention is not limited by these embodiments. The scope of protection of the present invention shall be interpreted by the claims below, and all technical concepts within an equivalent scope shall be interpreted as being included within the scope of rights of the present invention.

Claims

1. In a system for supercooling liquefied gas using a mixed refrigerant, A compressor for compressing the above-mentioned mixed refrigerant; A separator provided at the downstream end of the above compressor for phase separation of the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; A first line through which the liquid refrigerant separated in the above separator flows via a first pressure reducing valve; A second line through which the gaseous refrigerant separated in the above separator flows, passing through a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-inflow into the second heat exchanger; A third line through which the mixed refrigerant joined from the first and second lines flows, passing through the first heat exchanger, the compressor, and the separator; and It includes an anti-freezing unit that controls the temperature of the mixed refrigerant on the second line by controlling the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided in the bypass line, and has a bypass line branching off from the second line. In the first heat exchanger, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant flowing along the third line exchange heat. In the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second 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.

2. In Claim 1, The liquid refrigerant separated from the separator and flowing along the first line is depressurized at the first pressure reducing valve, and its temperature is lowered. A liquefied gas supercooling system in which a mixed refrigerant passing through the second heat exchanger along the second line is depressurized at the second pressure reducing valve and its temperature is lowered.

3. In Claim 1, It further includes a junction connected to the first line and the second line at the front end, and connected to the third line at the rear end. The above-mentioned anti-freezing unit is a liquefied gas supercooling system that controls a third temperature of the mixed refrigerant passing through the second pressure reducing valve along the second line.

4. In Claim 3, A liquefied gas supercooling system, wherein the bypass line is branched from the second line between the first heat exchanger and the second heat exchanger and connected to the second line upstream of the second pressure reducing valve or downstream of the second pressure reducing valve.

5. In Claim 1, It further includes a junction connected to the first line and the second line at the front end, and connected to the third line at the rear end. The above-mentioned anti-freezing unit controls the sixth temperature of the mixed refrigerant before it passes through the first heat exchanger along the second line and enters the second heat exchanger, in a liquefied gas supercooling system.

6. In Claim 5, A liquefied gas supercooling system, wherein the bypass line is branched from the second line between the separator and the first heat exchanger and connected to the second line between the first heat exchanger and the second heat exchanger.

7. In a system for supercooling liquefied gas using a mixed refrigerant, A compressor for compressing the above-mentioned mixed refrigerant; A separator provided at the downstream end of the above compressor for phase separation of the mixed refrigerant into a gaseous refrigerant and a liquid refrigerant; A first line through which the liquid refrigerant separated in the above separator flows via a first pressure reducing valve; A second line through which the gaseous refrigerant separated in the above separator flows, passing through a first heat exchanger, a second heat exchanger, a second pressure reducing valve, and re-inflow into the second heat exchanger; A third line through which the mixed refrigerant joined from the first and second lines flows, passing through the first heat exchanger, the compressor, and the separator; and It includes an anti-freezing unit that controls the temperature of the mixed refrigerant on the third line by controlling the inflow of a relatively high-temperature mixed refrigerant through a bypass valve provided in the bypass line, and has a bypass line branching off from the third line. In the first heat exchanger, the gaseous refrigerant separated from the separator and flowing along the second line, and the mixed refrigerant flowing along the third line exchange heat. In the second heat exchanger, the mixed refrigerant that has passed through the first heat exchanger along the second line, the mixed refrigerant that has passed through the second pressure reducing valve along the second 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.

8. In Claim 7, The liquid refrigerant separated from the separator and flowing along the first line is depressurized at the first pressure reducing valve, and its temperature is lowered. A liquefied gas supercooling system in which a mixed refrigerant passing through the second heat exchanger along the second line is depressurized at the second pressure reducing valve and its temperature is lowered.

9. In Claim 7, It further includes a junction connected to the first line and the second line at the front end, and connected to the third line at the rear end. The above-mentioned anti-freezing unit is a liquefied gas supercooling system that controls a second temperature of the mixed refrigerant before it enters the first heat exchanger along the third line.

10. In Claim 9, A liquefied gas supercooling system, wherein the above bypass line branches off from the third line between the compressor and the separator and is connected to the third line at the rear end of the junction.

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