High-efficiency hydrogen liquefaction system and hydrogen liquefaction process using same

Abstract

The present invention relates to a high-efficiency hydrogen liquefaction system and a hydrogen liquefaction process using same. The high-efficiency hydrogen liquefaction system comprises: a cooling cycle unit including a first pre-cooling cycle configured to circulate a first pre-cooling refrigerant, a second pre-cooling cycle configured to perform cooling at a relatively low temperature compared to the first pre-cooling cycle, and a main cooling cycle configured to circulate a main cooling refrigerant; a cooling line unit through which an object to be cooled by the cooling cycle unit passes; and a heat exchange unit for exchanging heat between the cooling cycle unit and the cooling line. The second pre-cooling cycle may include a 2-1 gas-liquid separator, a 2-1 pre-cooling line, a 2-2 pre-cooling line, a 2-2 gas-liquid separator, a 2-3 pre-cooling line, a 2-4 pre-cooling line, a 2-5 pre-cooling line, a 2-6 pre-cooling line, and a 2-7 pre-cooling line.

Description

High-efficiency hydrogen liquefaction system and hydrogen liquefaction process using the same

[0001] [Cross-citation with related applications]

[0002] This invention claims the benefit of priority from Korean Patent Application No. 10-2024-0095307, filed July 18, 2024, the entire contents of which are incorporated herein by reference.

[0003] [Technical Field]

[0004] The present invention relates to a high-efficiency hydrogen liquefaction system and a hydrogen liquefaction process using the same.

[0005] With the recent expansion of hydrogen fuel use across various fields, the need for large-scale hydrogen liquefaction processes is emerging. Unlike unstable gaseous hydrogen, liquid hydrogen can be stored at atmospheric pressure and has a relatively small volume, offering superior safety and cost-effectiveness relative to its area.

[0006] Figure 1 is a schematic diagram illustrating the flow of an exemplary hydrogen liquefaction process. Figure 2 is a schematic diagram illustrating the temperature range of an exemplary hydrogen liquefaction process. Figure 3 is a pressure-temperature graph illustrating the Joule-Thomson coefficients of each substance.

[0007] The hydrogen liquefaction process, as illustrated, can be broadly divided into pre-cooling and liquefaction stages. The pre-treatment steps can be performed sequentially, and the pre-cooling process for the pre-treated hydrogen can be performed.

[0008] The gaseous hydrogen is cooled to an appropriate temperature through a pre-cooling process. The appropriate temperature here refers to a condition suitable for the subsequent liquefaction process, and can be selected by referring to the pressure-temperature graph based on the Joule-Thomson coefficient in Fig. 3. In Fig. 3, the horizontal axis represents pressure in atmospheric pressure (atm), and the vertical axis represents temperature in Kelvin (K), the absolute temperature.

[0009] Referring to the graph in Fig. 3, there are sections where the Joule-Thomson coefficient is positive and sections where it is negative. The Joule-Thomson coefficient represents the value of the temperature change according to the pressure change at the same enthalpy. In other words, if the Joule-Thomson coefficient is positive, the temperature decreases according to the pressure decrease when the gas expands. Therefore, in order to liquefy hydrogen by reducing the temperature through Joule-Thomson expansion, the gaseous hydrogen must be placed in the section where the Joule-Thomson coefficient is positive as shown in the graph, and this preliminary state before liquefaction is achieved through pressurization and precooling. For example, precooling can be performed to 80 K (-193 °C), which is a temperature in the section where the Joule-Thomson coefficient of hydrogen is positive, by using the heat of vaporization of liquid nitrogen.

[0010] In the main refrigeration, pre-cooled hydrogen can be liquefied by cooling it to 20K (-253℃). Joule-Thomson expansion can be achieved using a Joule-Thomson valve in the main refrigeration. In other words, liquefaction at atmospheric pressure requires cooling to 20K (-253℃).

[0011] Therefore, in order to improve the efficiency of the entire hydrogen liquefaction process, it is necessary to optimize the pre-cooling process and main cooling process with an efficient configuration.

[0012] The object of the present invention is to provide a high-efficiency hydrogen liquefaction system and a hydrogen liquefaction process using the same by efficiently configuring a pre-cooling process and a main cooling process.

[0013] In one example, a high-efficiency hydrogen liquefaction system includes a cooling cycle section including a first pre-cooling cycle configured to circulate a first pre-cooling refrigerant, a second pre-cooling cycle configured to circulate a second pre-cooling refrigerant that performs cooling at a lower temperature than the first pre-cooling refrigerant, and a main cooling cycle configured to circulate a main cooling refrigerant, a cooling line section through which a cooling object to be cooled by the cooling cycle section passes, and a heat exchange section for heat-exchanging the cooling cycle section and the cooling line, wherein the second pre-cooling cycle includes a 2-1 gas-liquid separator configured to separate gas and liquid from an incoming second pre-cooling refrigerant, a 2-1 pre-cooling line through which a gaseous second pre-cooling refrigerant discharged from the 2-1 gas-liquid separator passes, a 2-2 pre-cooling line through which a liquid second pre-cooling refrigerant discharged from the 2-1 gas-liquid separator passes, and a 2-1 pre-cooling line connected to the 2-1 pre-cooling line and configured to separate the 2-2 pre-cooling refrigerant flowing from the 2-1 pre-cooling line. It may include a 2-2 gas-liquid separator configured to separate gas and liquid, a 2-3 pre-cooling line configured to allow a second pre-cooled refrigerant in a gaseous state discharged from the 2-2 gas-liquid separator to pass through, a 2-4 pre-cooling line configured to allow a second pre-cooled refrigerant in a liquid state discharged from the 2-2 gas-liquid separator to pass through, a 2-5 pre-cooling line branched from the 2-1 pre-cooling line, a 2-6 pre-cooling line connected to the 2-3 pre-cooling line and the 2-4 pre-cooling line, and a 2-7 pre-cooling line connected to at least one of the 2-2 pre-cooling line, the 2-5 pre-cooling line, or the 2-6 pre-cooling line, and connected to the 2-1 gas-liquid separator to introduce the second pre-cooled refrigerant into the 2-1 gas-liquid separator.

[0014] In another example, the second pre-cooling cycle further includes a second pre-cooling expander arranged in the second-first pre-cooling line, and a point at which the second-fifth pre-cooling line branches out of the second-first pre-cooling line may be located downstream of the second-first pre-cooling expander.

[0015] In another example, the second pre-cooling cycle may further include a second-second pre-cooling expander disposed in the second-third pre-cooling line.

[0016] In another example, the second pre-cooling cycle may further include a second-1 pre-cooling expansion valve disposed in the second-2 pre-cooling line and a second-1 pre-cooling compressor disposed in the second-2 pre-cooling line, but disposed downstream of the second-1 pre-cooling expansion valve.

[0017] In another example, the second pre-cooling cycle may further include a second-second pre-cooling expansion valve disposed in the second-fourth pre-cooling line.

[0018] In another example, the second pre-cooling cycle may further include a 2-2 pre-cooling compressor arranged in the 2-5 pre-cooling line and a 2-3 pre-cooling compressor arranged in the 2-6 pre-cooling line.

[0019] In another example, the main cooling cycle may include a main cooling gas-liquid separator configured to separate incoming main cooling refrigerant into gas and liquid, a first main cooling line configured to receive gaseous main cooling refrigerant discharged from the main cooling gas-liquid separator, a second main cooling line configured to receive liquid main cooling refrigerant discharged from the main cooling gas-liquid separator and connected to the first main cooling line, and a third main cooling line branched from the second main cooling line, wherein the second main cooling line may be configured to supply the main cooling refrigerant to the main cooling gas-liquid separator.

[0020] In another example, the main refrigeration cycle may further include a main refrigeration expander disposed in the third main refrigeration line, a main refrigeration expansion valve disposed downstream of a branch point of the third main refrigeration line among the second main refrigeration lines, and a main refrigeration compressor disposed upstream of a branch point of the third main refrigeration line among the second main refrigeration lines.

[0021] In another example, the third main cooling line may be connected to a second main cooling connection point located downstream of a first main cooling connection point where the second main cooling line and the first main cooling line are connected among the second main cooling lines.

[0022] In another example, the first pre-cooling cycle may include a 1-1 gas-liquid separator configured to separate gas-liquid from an incoming first pre-cooled refrigerant, a 1-1 pre-cooling line configured to pass a gaseous first pre-cooled refrigerant discharged from the 1-1 gas-liquid separator, a 1-2 pre-cooling line configured to pass a liquid first pre-cooled refrigerant discharged from the 1-1 gas-liquid separator, a first connection pre-cooling line connected to the 1-1 pre-cooling line and the 1-2 pre-cooling line, a 1-2 gas-liquid separator configured to separate gas-liquid from a refrigerant introduced from the first connection pre-cooling line, a 1-3 pre-cooling line configured to pass a gaseous pre-cooled refrigerant discharged from the 1-2 gas-liquid separator and connected to the 1-1 gas-liquid separator, and a 1-4 pre-cooling line configured to pass a liquid pre-cooled refrigerant discharged from the 1-2 gas-liquid separator and connected to the 1-1 gas-liquid separator. there is.

[0023] In another example, the first pre-cooling cycle may further include a 1-1 pre-cooling expansion valve disposed in the 1-1 pre-cooling line, a 1-1 pre-cooling compressor disposed in the 1-1 pre-cooling line but downstream of the 1-1 pre-cooling expansion valve, a 1-2 pre-cooling expansion valve disposed in the 1-2 pre-cooling line, a 1-2 pre-cooling compressor disposed in the 1-2 pre-cooling line but downstream of the 1-2 pre-cooling expansion valve, a 1-3 pre-cooling compressor disposed in the 1-3 pre-cooling line, and a 1-4 pre-cooling pump disposed in the 1-4 pre-cooling line to pump the pre-cooled refrigerant in the 1-4 pre-cooling line toward the 1-1 gas-liquid separator.

[0024] In another example, the heat exchanger may include a first heat exchanger configured to exchange heat between the first pre-cooling cycle, the second pre-cooling cycle, and the main cooling cycle and the cooling line section, and a second heat exchanger configured to exchange heat between the first pre-cooling cycle, the second pre-cooling cycle, and the main cooling cycle and the cooling line section, but passing downstream of a point where the first heat exchanger passes among the cooling line sections.

[0025] In another example, the first heat exchanger may be arranged so that the 1-1 pre-cooling line and the 1-2 pre-cooling line pass through it, and the second heat exchanger may be arranged so that the 1-1 pre-cooling line passes through it.

[0026] In another example, the heat exchanger may include a third heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, a fourth heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, but passing downstream of a point where the third heat exchanger passes among the cooling line sections, a fifth heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, but passing downstream of a point where the fourth heat exchanger passes among the cooling line sections, and a sixth heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, but passing downstream of a point where the fifth heat exchanger passes among the cooling line sections.

[0027] In another example, the third heat exchanger, the fourth heat exchanger, the fifth heat exchanger, and the sixth heat exchanger may be arranged so that the 2-6 pre-cooling line passes through them, the third heat exchanger and the fourth heat exchanger may be arranged so that the 2-5 pre-cooling line passes through them, and the fifth heat exchanger may be arranged so that the 2-1 pre-cooling line passes through them.

[0028] In another example, the third heat exchanger may be arranged so that the 2-2 pre-cooling line and the 2-7 pre-cooling line pass through it.

[0029] In another example, the heat exchanger may include a seventh heat exchanger, which is arranged to heat-exchange the main cooling cycle and the cooling line section and has a portion thereof located downstream of the second main cooling connection point, an eighth heat exchanger, which is arranged to heat-exchange the second pre-cooling cycle and the main cooling cycle and the cooling line section and has a portion thereof located between the second main cooling connection point and the first main cooling connection point, and a ninth heat exchanger, which is arranged to heat-exchange the second pre-cooling cycle and the main cooling cycle and the cooling line section and has a portion thereof located upstream of the first main cooling connection point.

[0030] In another example, the compression ratio of the 2-3 pre-cooling compressor may be greater than or equal to the compression ratios of the 2-1 pre-cooling compressor and the 2-2 pre-cooling compressor.

[0031] In another example, the compression ratio of the first-first pre-cooling compressor may be greater than the compression ratio of the first-second pre-cooling compressor.

[0032] For example, a hydrogen liquefaction process includes a pre-cooling step of cooling a gaseous object to be cooled and a main cooling step of liquefying the pre-cooled gaseous object to be cooled, wherein the pre-cooling step is performed by a first pre-cooling cycle and a second pre-cooling cycle that performs cooling at a relatively low temperature compared to the first pre-cooling cycle, and the main cooling step is performed by a main cooling cycle, and the second pre-cooling cycle includes a 2-1 gas-liquid separator that is provided to separate gas and liquid from an incoming second pre-cooled refrigerant, a 2-1 pre-cooling line through which a gaseous second pre-cooled refrigerant discharged from the 2-1 gas-liquid separator passes, a 2-2 pre-cooling line through which a liquid second pre-cooled refrigerant discharged from the 2-1 gas-liquid separator passes, a 2-2 gas-liquid separator that is connected to the 2-1 pre-cooling line and is provided to separate gas and liquid from a gaseous second pre-cooled refrigerant discharged from the 2-2 gas-liquid separator. It may include a 2-3 pre-cooling line through which a pre-cooled refrigerant passes, a 2-4 pre-cooling line through which a second pre-cooled refrigerant in a liquid phase discharged from the 2-2 gas-liquid separator passes, a 2-5 pre-cooling line branched from the 2-1 pre-cooling line, a 2-6 pre-cooling line connected to the 2-3 pre-cooling line and the 2-4 pre-cooling line, and a 2-7 pre-cooling line connected to the 2-2 pre-cooling line, the 2-5 pre-cooling line, and the 2-6 pre-cooling line, and connected to the 2-1 gas-liquid separator to introduce the second pre-cooled refrigerant into the 2-1 gas-liquid separator.

[0033] According to the present invention, a highly efficient hydrogen liquefaction system and a hydrogen liquefaction process using the same can be obtained by efficiently configuring a pre-cooling process and a main cooling process.

[0034] Figure 1 is a conceptual diagram showing the flow of an exemplary hydrogen liquefaction process.

[0035] Figure 2 is a conceptual diagram showing the temperature range of an exemplary hydrogen liquefaction process.

[0036] Figure 3 is a pressure-temperature graph showing the Joule-Thomson coefficient of each material.

[0037] Figure 4 is a conceptual diagram showing a hydrogen liquefaction system according to one embodiment of the present invention.

[0038] Figures 5 to 7 are drawings illustrating a high-efficiency liquefaction system according to another embodiment.

[0039] Hereinafter, some embodiments of the present invention will be described in detail with reference to exemplary drawings. When designating components in each drawing, identical components are given the same reference numerals, wherever possible, even if they appear in different drawings. Furthermore, when describing embodiments of the present invention, detailed descriptions of known related structures or functions will be omitted if they are deemed to hinder understanding of the embodiments of the present invention.

[0040] Additionally, terms such as first, second, A, B, (a), (b), etc. may be used to describe components of embodiments of the present invention. These terms are only intended to distinguish the components from other components, and the nature, order, or sequence of the components are not limited by the terms. When it is described that a component is "connected," "coupled," or "connected" to another component, it should be understood that the component may be directly connected or connected to the other component, but another component may also be "connected," "coupled," or "connected" between each component.

[0041] Meanwhile, the terms "upstream" and "downstream" in this specification may refer to the direction of fluid flow. For example, if the fluid flows from left to right, the left side may be considered upstream, and the right side may be considered downstream.

[0042] Basic structure of a hydrogen liquefaction system

[0043] Figure 4 is a conceptual diagram illustrating a hydrogen liquefaction system according to one embodiment of the present invention. The hydrogen liquefaction system according to one embodiment of the present invention may include a cooling cycle unit (10), a cooling line unit (20), and a heat exchange unit (30). The cooling cycle unit (10) may include a first pre-cooling cycle (100), a second pre-cooling cycle (200), and a main cooling cycle (300). In the specification of the present invention, a cycle may mean a closed circuit that undergoes compression, condensation, expansion, and evaporation processes. The evaporation and condensation processes may occur by a heat exchange unit (30) described later.

[0044] The first pre-cooling cycle (100) may be configured to circulate a first pre-cooling refrigerant. For example, the first pre-cooling refrigerant may be a mixed refrigerant containing at least one of nitrogen, C1 (methane), C2 (ethane), C3 (propane), or C4 (butane), or a combination thereof.

[0045] The second pre-cooling cycle (200) may be configured to circulate a second pre-cooling refrigerant. For example, the second pre-cooling refrigerant may be a mixed refrigerant containing at least one of nitrogen, hydrogen, helium, or a combination thereof.

[0046] The main cooling cycle (300) may be configured to circulate a main cooling refrigerant. For example, the main cooling refrigerant may be hydrogen.

[0047] A hydrogen liquefaction system according to one embodiment of the present invention includes a first pre-cooling cycle (100) and a second pre-cooling cycle (200), so that the second pre-cooling cycle (200) can distribute the cooling load of the main cooling cycle (300), thereby forming an efficient cooling cycle.

[0048] The cooling line section (20) may be a section through which a cooling target to be cooled by the cooling cycle section (10) passes. The cooling target may be hydrogen. The specification of the present invention describes that gaseous hydrogen flows into the cooling line section (20) and is liquefied and discharged. However, if it is a gaseous substance, a substance other than hydrogen may be applied and liquefied, and the cooling target is not limited to hydrogen.

[0049] The cooling line section (20) may include a cooling line (21). The cooling line (21) may be a line through which gaseous hydrogen may flow. In the present invention, the term "line" may refer to a structure that allows fluid to flow through its interior. For example, the line may have a pipe shape. However, even if it is not a pipe, it may be used as a line as long as fluid can flow through its interior.

[0050] The cooling line section (20) may include a cooling expansion valve (22). For example, the cooling expansion valve (22) may be a Joule-Thomson expansion valve for ultimately liquefying hydrogen cooled by the heat exchange section (30) by Joule-Thomson expansion. To increase expansion efficiency, the cooling expansion valve (22) may further include an expander for isentropically expanding hydrogen in the cooling line, and may be formed by a combination of the expansion valve and the expander. The expander may lower the temperature of the hydrogen and, incidentally, generate power from the expansion of the hydrogen.

[0051] The cooling line section (20) may include a cooling gas-liquid separator (23). The cooling gas-liquid separator (23) may be configured to separate hydrogen passing through the expansion valve into gas and liquid to ultimately obtain liquefied hydrogen.

[0052] The heat exchange unit (30) can exchange heat between the cooling cycle unit (10) and the cooling line unit (20). The heat exchange unit (30) can perform a heat exchange process in the cycle. For example, the heat exchange unit (30) can perform a heating or evaporation process during the cycle. In addition, the heat exchange unit (30) can perform a cooling or condensation process during the cycle. The heat exchange unit (30) can liquefy hydrogen passing through the cooling line unit (20). The liquefied hydrogen can be discharged through the cooling line (21).

[0053] The heat exchange unit (30) may include a plurality of heat exchangers and a plurality of conversion modules (30'). The conversion module (30') may be placed in some of the plurality of heat exchangers. In the conversion module (30'), ortho-para conversion, which converts ortho-hydrogen into para-hydrogen by cooling and a catalyst, may occur. In the conversion module (30'), cooling or condensation of hydrogen passing through a cooling line may occur.

[0054] Main cooling cycle (300)

[0055] The main cooling cycle (300) may include a main cooling gas-liquid separator (310), a first main cooling line (320), a second main cooling line (330), and a third main cooling line (340).

[0056] The main cold gas-liquid separator (310) can be provided to separate the incoming main cold refrigerant into gas and liquid.

[0057] The first main cooling line (320) can be provided to allow the main cooling refrigerant in the gaseous state discharged from the main cooling gas-liquid separator (310) to flow in.

[0058] The second main cooling line (330) may be provided to allow the liquid main cooling refrigerant discharged from the main cooling gas-liquid separator (310) to flow in. The first main cooling line (320) may be connected to the second main cooling line (330). The second main cooling line (330) may be provided to supply the main cooling refrigerant back to the main cooling gas-liquid separator (310).

[0059] The third main cooling line (340) may be branched from the second main cooling line (330). The third main cooling line (340) may be connected to the second main cooling line (330). The third main cooling line (340) may be connected to the second main cooling connection point (332) located downstream of the first main cooling connection point (331) where the second main cooling line (330) and the first main cooling line (320) are connected among the second main cooling lines (330).

[0060] The main cooling cycle (300) may further include a main cooling expander (341), a main cooling expansion valve (333), and a main cooling compressor (334). The main cooling expander (341) may be arranged in the third main cooling line (340). The main cooling expander (341) may be arranged to expand the main cooling refrigerant flowing into the third main cooling line (340).

[0061] The low-temperature main-cooling refrigerant expanded in the third main-cooling line (340) can be introduced into the second main-cooling line (330). By introducing the second main-cooling line (330) and the main-cooling expander (341), more efficient cooling can be performed in the main-cooling cycle (300).

[0062] The main cold expansion valve (333) may be arranged downstream of the branch point of the third main cold line (340) among the second main cold lines (330). The main cold expansion valve (333) may be arranged to expand the main cold refrigerant before it flows into the main cold gas-liquid separator (310). In order to increase the expansion efficiency, the main cold expansion valve (333) may further include an expander that isentropically expands hydrogen in the cooling line, and may be formed as a combination of the expansion valve and the expander. The expander may lower the temperature of the hydrogen and, incidentally, produce power from the expansion of the hydrogen.

[0063] The main cold compressor (334) may be placed upstream of the branch point of the third main cold line (340) among the second main cold lines (330). The main cold compressor (334) may be provided to compress the main cold refrigerant that has returned after passing through the heat exchange unit (30) described later.

[0064] 1st pre-cooling cycle (100)

[0065] The first pre-cooling cycle (100) may include a first-first gas-liquid separator (110), a first-first pre-cooling line (120), a first-second pre-cooling line (130), and a first connection pre-cooling line (140). The first-first gas-liquid separator (110) may be provided to separate the introduced first pre-cooling refrigerant into gas and liquid. The first-first pre-cooling line (120) may be provided to allow the first pre-cooling refrigerant in a gaseous state discharged from the first-first gas-liquid separator (110) to pass therethrough. The first-second pre-cooling line (130) may be provided to allow the first pre-cooling refrigerant in a liquid state discharged from the first-first gas-liquid separator (110) to pass therethrough. The first connection pre-cooling line (140) may be connected to the first-first pre-cooling line (120) and the first-second pre-cooling line (130).

[0066] For example, a first pre-cooling mixer (141) may be arranged in the first connection pre-cooling line (140). The first pre-cooling mixer (141) may mix the first pre-cooling refrigerants flowing in from the 1-1 pre-cooling line (120) and the 1-2 pre-cooling line (130). This first pre-cooling mixer (141) may be a conventional mixer. As another example, the first pre-cooling mixer (141) may not be a separate mixer, but may be a connecting structure between the 1-1 pre-cooling line (120) and the 1-2 pre-cooling line (130), that is, a structure that is interconnected to induce mixing of the first pre-cooling refrigerants of each line.

[0067] The first pre-cooling cycle (100) may further include a first-second gas-liquid separator (150), a first-third pre-cooling line (160), and a first-fourth pre-cooling line (170). The first-second gas-liquid separator (150) may be provided to separate the gas and liquid of the refrigerant introduced from the first connection pre-cooling line (140). The first-third pre-cooling line (160) may be provided to allow the first pre-cooled refrigerant in a gaseous state discharged from the first-second gas-liquid separator (150) to pass therethrough, and may be connected to the first-first gas-liquid separator (110). The first-fourth pre-cooling line (170) may be provided to allow the first pre-cooled refrigerant in a liquid state discharged from the first-second gas-liquid separator (150) to pass therethrough, and may be connected to the first-first gas-liquid separator (110).

[0068] The first pre-cooling cycle (100) may include a first-first pre-cooling expansion valve (121), a first-first pre-cooling compressor (122), a first-second pre-cooling expansion valve (131), and a first-second pre-cooling compressor (132).

[0069] The first-first pre-cooling expansion valve (121) may be arranged in the first-first pre-cooling line (120) to expand the first pre-cooling refrigerant in the gas phase discharged from the first-first gas-liquid separator (110). The first-first pre-cooling compressor (122) may be arranged to compress the first pre-cooling refrigerant of the first-first pre-cooling line (120) that has undergone cooling through the heat exchange unit (30).

[0070] The 1-2 pre-cooling expansion valve (131) may be arranged in the 1-2 pre-cooling line (130) to expand the first pre-cooling refrigerant in liquid form discharged from the 1-1 gas-liquid separator (110). The 1-2 pre-cooling compressor (132) may be arranged to compress the first pre-cooling refrigerant of the 1-2 pre-cooling line (130) that has undergone cooling through the heat exchange unit (30).

[0071] The first precooling cycle (100) may further include a first-third precooling compressor (161) and a first precooling pump (171). The first-third precooling compressor (161) may be arranged in the first-third precooling line (160). The first-third precooling compressor (161) may be arranged to compress the first precooling refrigerant in a gaseous state discharged from the first-second gas-liquid separator (150). An aftercooler (162) may be arranged downstream of the first-third precooling compressor (161). However, it should be understood that the aftercooler (162) may also be arranged downstream of all other compressors described above and below.

[0072] The first pre-cooling pump (171) may be arranged in the 1-4 pre-cooling line (170) to pump the first pre-cooling refrigerant in liquid form within the 1-4 pre-cooling line (170) toward the 1-1 gas-liquid separator (110).

[0073] Second pre-cooling cycle (200)

[0074] The second pre-cooling cycle (200) may include a second-first gas-liquid separator (210), a second-first pre-cooling line (220), and a second-second pre-cooling line (230). The second-first gas-liquid separator (210) may be provided to separate the introduced second pre-cooling refrigerant into gas and liquid.

[0075] The 2-1 pre-cooling line (220) may be provided to allow the second pre-cooling refrigerant in a gaseous state discharged from the 2-1 gas-liquid separator (210) to pass therethrough. The 2-2 pre-cooling line (230) may be provided to allow the second pre-cooling refrigerant in a liquid state discharged from the 2-1 gas-liquid separator (210) to pass therethrough.

[0076] The second pre-cooling cycle (200) may further include a second-second gas-liquid separator (240), a second-third pre-cooling line (250), a second-fourth pre-cooling line (260), a second-fifth pre-cooling line (270), a second-sixth pre-cooling line (280), and a second-seventh pre-cooling line (290).

[0077] The 2-2 gas-liquid separator (240) may be connected to the 2-1 pre-cooling line (220) and may be provided to separate the 2-2 pre-cooled refrigerant flowing in from the 2-1 pre-cooling line (220) into gas and liquid. The 2-3 pre-cooling line (250) may be provided to allow the gaseous second pre-cooled refrigerant discharged from the 2-2 gas-liquid separator (240) to pass through it. The 2-4 pre-cooling line (260) may be provided to allow the liquid second pre-cooled refrigerant discharged from the 2-2 gas-liquid separator (240) to pass through it.

[0078] The 2-5 pre-cooling line (270) can be branched from the 2-1 pre-cooling line (220). The 2-6 pre-cooling line (280) can be connected to the 2-3 pre-cooling line (250) and the 2-4 pre-cooling line (260).

[0079] For example, a 2-1 pre-cooling mixer (281) may be arranged in the 2-6 pre-cooling line (280). The 2-1 pre-cooling mixer (281) may mix the second pre-cooling refrigerant flowing in from at least one of the 2-3 pre-cooling line (250) and the 2-4 pre-cooling line (260). This 2-1 pre-cooling mixer (281) may be a conventional mixer. As another example, the 2-1 pre-cooling mixer (281) may not mean a separate mixer, but rather a connecting structure between the 2-3 pre-cooling line (250) and the 2-4 pre-cooling line (260), that is, a structure that is interconnected to induce mixing of the second pre-cooling refrigerants of each line.

[0080] The 2-7 pre-cooling line (290) may be connected to at least one of the 2-2 pre-cooling line (230), the 2-5 pre-cooling line (270), and the 2-6 pre-cooling line (280). The 2-7 pre-cooling line (290) may be connected to the 2-1 gas-liquid separator (210) to introduce the second pre-cooling refrigerant into the 2-1 gas-liquid separator (210).

[0081] For example, a 2-2 pre-cooling mixer (291) may be arranged in the 2-7 pre-cooling line (290). The 2-2 pre-cooling mixer (291) may mix the second pre-cooling refrigerants flowing from the 2-2 pre-cooling line (230), the 2-5 pre-cooling line (270), and the 2-6 pre-cooling line (280). This 2-2 pre-cooling mixer (291) may be a conventional mixer. As another example, the 2-2 pre-cooling mixer (291) may not mean a separate mixer, but rather a connecting structure between the 2-2 pre-cooling line (230), the 2-5 pre-cooling line (270), and the 2-6 pre-cooling line (280), that is, a structure that is interconnected to induce mixing of the second pre-cooling refrigerants of each line.

[0082] The second pre-cooling cycle (200) may further include a second-first pre-cooling expander (221). The second-first pre-cooling expander (221) may be arranged in the second-first pre-cooling line (220). The second-first pre-cooling expander (221) may be configured to expand the second pre-cooling refrigerant in a gaseous state discharged from the second-first gas-liquid separator (210). The second pre-cooling refrigerant in a gaseous state separated from the second-first gas-liquid separator (210) may be introduced into the second-first pre-cooling expander (221) and expanded to a second intermediate pressure (MP2).

[0083] The point at which the 2-5 pre-cooling line (270) branches out from the 2-1 pre-cooling line (220) may be located downstream compared to the 2-1 pre-cooling expander (221).

[0084] The second pre-cooling cycle (200) may further include a second-second pre-cooling expander (251). The second-second pre-cooling expander (251) may be arranged in the second-third pre-cooling line (250). The second-second pre-cooling expander (251) may be arranged to expand the second pre-cooling refrigerant in a gaseous state discharged from the second-second gas-liquid separator (240).

[0085] The second pre-cooling cycle (200) may further include a second-first pre-cooling expansion valve (231). The second-first pre-cooling expansion valve (231) may be arranged in the second-second pre-cooling line (230). The second-first pre-cooling expansion valve (231) may be configured to expand the second pre-cooling refrigerant in a liquid phase discharged from the second-first gas-liquid separator (210). The second pre-cooling refrigerant in a liquid phase separated in the second-first gas-liquid separator (210) may be introduced into the second-first pre-cooling expansion valve (231) and expanded to a first intermediate pressure (MP1).

[0086] The second pre-cooling cycle (200) may further include a second-second pre-cooling expansion valve (261). The second-second pre-cooling expansion valve (261) may be arranged in the second-fourth pre-cooling line (260). The second-second pre-cooling expansion valve (261) may be arranged to expand the second pre-cooling refrigerant in a liquid phase discharged from the second-second gas-liquid separator (240).

[0087] The second precooling cycle (200) may further include a second-first precooling compressor (232). The second-first precooling compressor (232) may be disposed in the second-second precooling line (230), and may be disposed downstream of the second-first precooling expansion valve (231). The second-first precooling compressor (232) may compress the second precooling refrigerant that has passed through the third heat exchanger (33), the second heat exchanger (32), and the first heat exchanger (31), which will be described later. The second-first precooling compressor (232) may be configured to compress a refrigerant (Heavy MR) having a relatively heavy component, such as nitrogen, among the second precooling refrigerants. This structure has the effect of being able to utilize nitrogen, which is relatively inexpensive among low-boiling-point mixtures that can be utilized as refrigerants in the corresponding cooling section, as the main component.

[0088] The second precooling cycle (200) may further include a second-second precooling compressor (271). The second-second precooling compressor (271) may be arranged in the second-fifth precooling line (270). The second-second precooling compressor (271) may compress the second precooling refrigerant that has passed through the fourth heat exchanger (34), the third heat exchanger (33), the second heat exchanger (32), and the first heat exchanger (31), which will be described later. The second-second precooling compressor (271) may be configured to compress a refrigerant having a relatively middle weight component (Middle MR) among the second precooling refrigerants.

[0089] The second precooling cycle (200) may further include a second-third precooling compressor (282). The second-third precooling compressor (282) may be arranged in the second-sixth precooling line (280). The second-second precooling compressor (271) may compress the second precooling refrigerant that has passed through the sixth heat exchanger (36), the fifth heat exchanger (35), the fourth heat exchanger (34), the third heat exchanger (33), the second heat exchanger (32), and the first heat exchanger (31), which will be described later. The second-third precooling compressor (282) may be configured to compress a refrigerant having a relatively light component (Light MR) or a refrigerant having a low pressure among the second precooling refrigerants.

[0090] The compression ratio of the 2-3 pre-cooling compressor (282) may be greater than or equal to the compression ratios of the 2-1 pre-cooling compressor (232) and the 2-2 pre-cooling compressor (271).

[0091] In the case of the hydrogen liquefaction system according to the present invention, since the second pre-cooling cycle (200) has a parallel structure and a separate compression structure, the load on the compressor can be reduced by independently configuring the expansion and compression sections and flow rates according to the target temperature of cooling, and the refrigerant flow rate and expander recovery pressure can be adjusted according to the target temperature of cooling, which has the advantage of increasing the degree of freedom in process design. In other words, by efficiently configuring the pre-cooling process, high hydrogen liquefaction efficiency can be obtained.

[0092] Heat exchanger (30)

[0093] The heat exchange unit (30) may include a first heat exchanger (31) and a second heat exchanger (32). The first heat exchanger (31) and the second heat exchanger (32) may be arranged to exchange heat between the first pre-cooling cycle (100), the second pre-cooling cycle (200), and the main cooling cycle (300) and the cooling line unit (20). The second heat exchanger (32) may be arranged to pass downstream of the point where the first heat exchanger (31) passes among the cooling line units (20). For example, a cryogenic adsorber may be arranged to pass through the second heat exchanger (32).

[0094] The hydrogen in the cooling line section (20) that has passed through the second heat exchanger (32) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the first heat exchanger (31). The first heat exchanger (31) may be arranged so that the 1-1 pre-cooling line (120) and the 1-2 pre-cooling line (130) pass through it. In addition, the first heat exchanger (31) may be arranged so that the 2-2 pre-cooling line (230), the 2-5 pre-cooling line (270), the 2-6 pre-cooling line (280) and the 2-7 pre-cooling line (290) pass through it. In addition, the first heat exchanger (31) may be arranged so that the 2nd main cooling line (330) passes through it.

[0095] The second heat exchanger (32) may be arranged so that the 1-1 pre-cooling line (120) passes through it. This may mean that, unlike the first heat exchanger (31), the 1-2 pre-cooling line (130) does not pass through the second heat exchanger (32).

[0096] In addition, the second heat exchanger (32) may be arranged so that the 2-2 pre-cooling line (230), the 2-5 pre-cooling line (270), the 2-6 pre-cooling line (280), and the 2-7 pre-cooling line (290) pass through it. In addition, the second heat exchanger (32) may be arranged so that the 2nd main cooling line (330) passes through it.

[0097] The heat exchange unit (30) may further include a third heat exchanger (33), a fourth heat exchanger (34), a fifth heat exchanger (35), and a sixth heat exchanger (36). The third heat exchanger (33), the fourth heat exchanger (34), the fifth heat exchanger (35), and the sixth heat exchanger (36) may be provided to exchange heat between the second pre-cooling cycle (200) and the main cooling cycle (300) and the cooling line unit (20).

[0098] The fourth heat exchanger (34) may be arranged downstream of the point where the third heat exchanger (33) passes through the cooling line section (20). The fifth heat exchanger (35) may be arranged downstream of the point where the fourth heat exchanger (34) passes through the cooling line section (20). The sixth heat exchanger (36) may be arranged downstream of the point where the fifth heat exchanger (35) passes through the cooling line section (20).

[0099] The hydrogen in the cooling line section (20) that has passed through the third heat exchanger (33) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the second heat exchanger (32). The hydrogen in the cooling line section (20) that has passed through the fourth heat exchanger (34) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the third heat exchanger (33). The hydrogen in the cooling line section (20) that has passed through the fifth heat exchanger (35) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the fourth heat exchanger (34). The hydrogen in the cooling line section (20) that has passed through the sixth heat exchanger (36) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the fifth heat exchanger (35).

[0100] The third heat exchanger (33) may be arranged so that the 2-5 pre-cooling line (270) passes through it. In addition, the third heat exchanger (33) may be arranged so that the 2-2 pre-cooling line (230), the 2-6 pre-cooling line (280), and the 2-7 pre-cooling line (290) pass through it. In addition, the third heat exchanger (33) may be arranged so that the 2nd main cooling line (330) passes through it.

[0101] The fourth heat exchanger (34) may be arranged so that the 2-5 pre-cooling line (270) passes through it. In addition, the fourth heat exchanger (34) may be arranged so that the 2-6 pre-cooling line (280) passes through it. This may mean that, unlike the third heat exchanger (33), the fourth heat exchanger (34) does not pass through the 2-2 pre-cooling line (230) and the 2-7 pre-cooling line (290). In addition, the fourth heat exchanger (34) may be arranged so that the 2nd main cooling line (330) passes through it.

[0102] The fifth heat exchanger (35) may be arranged so that the 2-1 pre-cooling line (220) passes through it. In addition, the fifth heat exchanger (35) may be arranged so that the 2-6 pre-cooling line (280) passes through it. In addition, the fifth heat exchanger (35) may be arranged so that the 2nd main cooling line (330) passes through it.

[0103] The sixth heat exchanger (36) may be arranged so that the second-sixth pre-cooling line (280) passes through it. This may mean that, unlike the fifth heat exchanger (35), the sixth heat exchanger (36) does not pass through the second-first pre-cooling line (220). In addition, the sixth heat exchanger (36) may be arranged so that the second main cooling line (330) passes through it.

[0104] The heat exchanger (30) may include a seventh heat exchanger (37), an eighth heat exchanger (38), and a ninth heat exchanger (39). The seventh heat exchanger (37), the eighth heat exchanger (38), and the ninth heat exchanger (39) may be arranged to exchange heat between the main cooling cycle (300) and the cooling line section (20). The eighth heat exchanger (38) may be arranged to pass downstream of a point where the seventh heat exchanger (37) passes in the cooling line section (20). The ninth heat exchanger (39) may be arranged to pass downstream of a point where the eighth heat exchanger (38) passes in the cooling line section (20).

[0105] The hydrogen in the cooling line section (20) that has passed through the seventh heat exchanger (37) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the eighth heat exchanger (38). The hydrogen in the cooling line section (20) that has passed through the eighth heat exchanger (38) may be at a lower temperature than the hydrogen in the cooling line section (20) that has passed through the ninth heat exchanger (39).

[0106] The seventh heat exchanger (37) may be positioned so that a portion located downstream of the second main cooling connection point (332) passes therethrough. The eighth heat exchanger (38) may be positioned so that a portion located between the second main cooling connection point (332) and the first main cooling connection point (331) passes therethrough. The ninth heat exchanger (39) may be positioned so that a portion located upstream of the first main cooling connection point (331) passes therethrough.

[0107] The main cold refrigerant circulated through the second main cold line (330) sequentially passes through the 8th heat exchanger (38), the 7th heat exchanger (37), the 6th heat exchanger (36), the 5th heat exchanger (35), the 4th heat exchanger (34), the 3rd heat exchanger (33), the 2nd heat exchanger (32), and the 1st heat exchanger (31) from the 9th heat exchanger (39), and can cool the hydrogen in the cooling line section (20). In this process, the temperature of the hydrogen in the cooling line section (20) that passes through each heat exchanger can decrease as it goes from the 1st heat exchanger (31) to the 9th heat exchanger (39).

[0108] A conversion module may be placed in the second heat exchanger (32), the third heat exchanger (33), the fourth heat exchanger (34), the fifth heat exchanger (35), the sixth heat exchanger (36), the seventh heat exchanger (37), the eighth heat exchanger (38), and the ninth heat exchanger (39).

[0109] For example, the main cold refrigerant flowing into the 9th heat exchanger (39) may have a temperature of about 20K.

[0110] Figures 5 to 7 are drawings illustrating a high-efficiency liquefaction system according to another embodiment. Figures 5 to 7 differ in some respects from the high-efficiency liquefaction system according to Figure 4 in the form of a second pre-cooling cycle.

[0111] Hereinafter, for convenience of explanation, a 2-1 pre-cooling junction point and a 2-2 pre-cooling junction point are defined. The 2-1 pre-cooling junction point may be a point of the 2-7 pre-cooling line (290) where the 2-2 pre-cooling line (230) junctions. The 2-2 pre-cooling junction point may be a point of the 2-2 pre-cooling line (230) or the 2-7 pre-cooling line (290) where the 2-5 pre-cooling line (270) junctions.

[0112] As another example, as illustrated in FIG. 5, the 2-1 pre-cooling junction point may be a point of the 2-7 pre-cooling line (290), and the 2-2 pre-cooling junction point may be a point of the 2-2 pre-cooling line (230). In this case, the 2-2 pre-cooling junction point may be located downstream of the 2-1 pre-cooling compressor (232).

[0113] As another example, as illustrated in FIG. 6, the 2-1 pre-cooling junction point may be a point of the 2-7 pre-cooling line (290), and the 2-2 pre-cooling junction point may be a point of the 2-2 pre-cooling line (230). At this time, the 2-2 pre-cooling junction point may be located upstream of the 2-1 pre-cooling compressor (232). At this time, the second pre-cooling refrigerant that has passed through the 2-2 pre-cooling compressor (271) may be introduced again into the 2-1 pre-cooling compressor (232). At this time, the compression ratio of the 2-2 pre-cooling compressor (271) may be the same as that of the 2-1 pre-cooling compressor (232).

[0114] As another example, as illustrated in FIG. 7, the 2-1 pre-cooling confluence point may be a point of the 2-7 pre-cooling line (290), and the 2-2 pre-cooling confluence point may be another point of the 2-7 pre-cooling line (290). In this case, the 2-2 pre-cooling confluence point may be located upstream of the 2-1 pre-cooling confluence point.

[0115] At this time, the 2-1 pre-cooling compressor (232') and the 2-2 pre-cooling compressor (271') may be arranged in the 2-7 pre-cooling line (290). The 2-1 pre-cooling compressor (232') may be arranged downstream of the 2-3 pre-cooling compressor (282). The 2-2 pre-cooling compressor (271') may be arranged downstream of the 2-3 pre-cooling compressor (282) and upstream of the 2-1 pre-cooling compressor (232').

[0116] The second pre-cooled refrigerant that has passed through the 2-2 pre-cooling compressor (271') can be introduced again into the 2-1 pre-cooling compressor (232'). In addition, the second pre-cooled refrigerant that has passed through the 2-3 pre-cooling compressor (282) can be introduced again into the 2-1 pre-cooling compressor (232') through the 2-2 pre-cooling compressor (271').

[0117] At this time, the compression ratio of the 2-2 pre-cooling compressor (71') may be the same as that of the 2-1 pre-cooling compressor (232').

[0118] The above description is merely an illustrative illustration of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are intended to illustrate, rather than limit, the technical idea of ​​the present invention, and the scope of the technical idea of ​​the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included in the scope of the rights of the present invention.

[0119]

[0120] [Explanation of symbols]

[0121] 10: Cooling cycle section

[0122] 20: Cooling line section

[0123] 21: Cooling line

[0124] 22: Cooling expansion valve

[0125] 23: Cooling gas-liquid separator

[0126] 30: Heat exchanger

[0127] 30': Conversion module

[0128] 31: First heat exchanger

[0129] 32: Second heat exchanger

[0130] 33: Third heat exchanger

[0131] 34: 4th heat exchanger

[0132] 35: Fifth heat exchanger

[0133] 36: 6th heat exchanger

[0134] 37: Heat exchanger 7

[0135] 38: Heat exchanger 8

[0136] 39: 9th heat exchanger

[0137] 100: First pre-cooling cycle

[0138] 110: 1-1 Gas-liquid separator

[0139] 120: 1-1 Pre-cooling Line

[0140] 121: No. 1-1 pre-cooling expansion valve

[0141] 122: No. 1-1 pre-cooling compressor

[0142] 130: 1st-2nd pre-cooling line

[0143] 131: 1-2 pre-cooling expansion valve

[0144] 132: 1-2 pre-cooling compressor

[0145] 140: First connection pre-cooling line

[0146] 141: First pre-cooling mixer

[0147] 150: 1-2 Gas-Liquid Separator

[0148] 160: 1-3 pre-cooling lines

[0149] 161: 1-3 Pre-cooling Compressor

[0150] 162: Aftercooler

[0151] 170: 1-4 pre-cooling lines

[0152] 171: First precooling pump

[0153] 200: Second pre-cooling cycle

[0154] 210: 2-1 Gas-Liquid Separator

[0155] 220: 2-1 Pre-cooling Line

[0156] 221: 2-1 Pre-cooling expander

[0157] 230: 2-2nd pre-cooling line

[0158] 231: 2-1 Pre-cooling expansion valve

[0159] 232, 232': 2-1 pre-cooling compressor

[0160] 240: 2-2 Gas-Liquid Separator

[0161] 250: 2nd-3rd pre-cooling line

[0162] 251: 2-2 Pre-cooling expander

[0163] 260: 2nd-4th pre-cooling line

[0164] 261: 2-2 Pre-cooling expansion valve

[0165] 270: 2-5 Pre-cooling Line

[0166] 271, 271': 2-2 pre-cooling compressor

[0167] 280: 2-6 Pre-cooling Line

[0168] 281: 2-1 Pre-cooling mixer

[0169] 282: 2-3 Pre-cooling Compressor

[0170] 290: 2-7th pre-cooling line

[0171] 291: 2-2 Pre-cooling mixer

[0172] 300: Main cooling cycle

[0173] 310: Main cold gas-liquid separator

[0174] 320: First main cooling line

[0175] 330: Second main cooling line

[0176] 331: First main cold connection point

[0177] 332: Second main cold connection point

[0178] 333: Main cooling expansion valve

[0179] 334: Main refrigeration compressor

[0180] 340: Third Bon-Neng Line

[0181] 341: Main cold expander

Claims

1. A cooling cycle unit including a first pre-cooling cycle configured to circulate a first pre-cooling refrigerant, a second pre-cooling cycle configured to circulate a second pre-cooling refrigerant that performs cooling at a lower temperature than the first pre-cooling refrigerant, and a main cooling cycle configured to circulate a main cooling refrigerant; A cooling line section through which a cooling target object to be cooled by the cooling cycle section passes; and It includes a heat exchanger that exchanges heat between the cooling cycle section and the cooling line, The above second pre-cooling cycle is, A second-1 gas-liquid separator provided to separate the incoming second pre-cooled refrigerant into gas and liquid; A 2-1 pre-cooling line through which the second pre-cooling refrigerant in the gaseous state discharged from the 2-1 gas-liquid separator passes; A 2-2 pre-cooling line through which the second pre-cooling refrigerant in liquid form discharged from the 2-1 gas-liquid separator passes; A 2-2 gas-liquid separator connected to the 2-1 pre-cooling line and configured to separate the 2-2 pre-cooling refrigerant flowing from the 2-1 pre-cooling line into gas and liquid; A 2-3 pre-cooling line through which the second pre-cooling refrigerant in the gaseous state discharged from the 2-2 gas-liquid separator passes; A 2-4 pre-cooling line through which the second pre-cooling refrigerant in liquid form discharged from the 2-2 gas-liquid separator passes; A 2-5 pre-cooling line branching from the 2-1 pre-cooling line; A 2-6 pre-cooling line connected to the 2-3 pre-cooling line and the 2-4 pre-cooling line; and A hydrogen liquefaction system comprising a 2-7 pre-cooling line connected to at least one of the 2-2 pre-cooling line, the 2-5 pre-cooling line, or the 2-6 pre-cooling line, and connected to the 2-1 gas-liquid separator to introduce the second pre-cooling refrigerant into the 2-1 gas-liquid separator.

2. In claim 1, The above second pre-cooling cycle is, Further comprising a 2-1 pre-cooling expander arranged in the 2-1 pre-cooling line; A hydrogen liquefaction system, wherein the point at which the 2-5 pre-cooling line branches out from the 2-1 pre-cooling line is located downstream from the 2-1 pre-cooling expander.

3. In claim 2, The above second pre-cooling cycle is, A hydrogen liquefaction system further comprising a 2-2 pre-cooling expander arranged in the 2-3 pre-cooling line.

4. In claim 1, The above second pre-cooling cycle is, A 2-1 pre-cooling expansion valve arranged in the 2-2 pre-cooling line; and A hydrogen liquefaction system further comprising a 2-1 pre-cooling compressor disposed in the 2-2 pre-cooling line and disposed downstream of the 2-1 pre-cooling expansion valve.

5. In claim 4, The above second pre-cooling cycle is, A hydrogen liquefaction system further comprising a 2-2 pre-cooling expansion valve arranged in the 2-4 pre-cooling line.

6. In claim 4, The above second pre-cooling cycle is, A 2-2 pre-cooling compressor arranged in the 2-5 pre-cooling line; and A hydrogen liquefaction system further comprising a 2-3 pre-cooling compressor arranged in the 2-6 pre-cooling line.

7. In claim 1, The above main cooling cycle is, A main cold gas-liquid separator provided to separate the incoming main cold refrigerant into gas and liquid; A first main cooling line into which the main cooling refrigerant in the gaseous state discharged from the above main cooling gas-liquid separator is introduced; A second main cooling line, which is provided to allow the liquid main cooling refrigerant discharged from the main cooling gas-liquid separator to flow in and is connected to the first main cooling line; and Including a third main cooling line branching from the second main cooling line, The second main cooling line is a hydrogen liquefaction system that supplies the main cooling refrigerant to the main cooling gas-liquid separator.

8. In claim 7, The above main cooling cycle is, A main cooling expander arranged in the third main cooling line; A main cooling expansion valve disposed downstream of the branch point of the third main cooling line among the second main cooling lines; and A hydrogen liquefaction system further comprising a main refrigeration compressor disposed upstream of a branch point of the third main refrigeration line among the second main refrigeration lines.

9. In claim 7, A hydrogen liquefaction system in which the third main cooling line is connected to a second main cooling connection point located downstream of a first main cooling connection point where the second main cooling line and the first main cooling line are connected among the second main cooling lines.

10. In claim 7, The above first pre-cooling cycle is, A 1-1 gas-liquid separator provided to separate the incoming first pre-cooled refrigerant into gas and liquid; A 1-1 pre-cooling line through which the first pre-cooling refrigerant in the gas phase discharged from the 1-1 gas-liquid separator passes; A 1-2 pre-cooling line through which the first pre-cooling refrigerant in liquid form discharged from the 1-1 gas-liquid separator passes; A connecting pre-cooling line connected to the above 1-1 pre-cooling line and the above 1-2 pre-cooling line; A first-second gas-liquid separator provided to separate the refrigerant flowing in from the above-mentioned connecting pre-cooling line into gas and liquid; A 1-3 pre-cooling line through which the pre-cooled refrigerant in the gas phase discharged from the 1-2 gas-liquid separator passes and is connected to the 1-1 gas-liquid separator; and A hydrogen liquefaction system including a 1-4 pre-cooling line through which a liquid pre-cooling refrigerant discharged from the 1-2 gas-liquid separator passes and which is connected to the 1-1 gas-liquid separator.

11. In claim 10, The above first pre-cooling cycle is, A 1-1 pre-cooling expansion valve arranged in the above 1-1 pre-cooling line; A 1-1 pre-cooling compressor arranged in the 1-1 pre-cooling line and disposed downstream of the 1-1 pre-cooling expansion valve; A first-second pre-cooling expansion valve arranged in the first-second pre-cooling line; A 1-2 pre-cooling compressor arranged in the 1-2 pre-cooling line and downstream of the 1-2 pre-cooling expansion valve; A 1-3 pre-cooling compressor arranged in the 1-3 pre-cooling line; and A hydrogen liquefaction system further comprising a first pre-cooling pump arranged in the first-fourth pre-cooling line and configured to pump the pre-cooled refrigerant in the first-fourth pre-cooling line toward the first-first gas-liquid separator.

12. In claim 10, The above heat exchanger, A first heat exchanger configured to exchange heat between the first pre-cooling cycle, the second pre-cooling cycle, and the main cooling cycle and the cooling line section; and A hydrogen liquefaction system, which is arranged to exchange heat between the first pre-cooling cycle, the second pre-cooling cycle, and the main cooling cycle and the cooling line section, and includes a second heat exchanger passing downstream of the point where the first heat exchanger passes among the cooling line sections.

13. In claim 12, The above first heat exchanger, The above 1-1 pre-cooling line and the above 1-2 pre-cooling line are arranged to pass through, The above second heat exchanger is a hydrogen liquefaction system in which the above 1-1 pre-cooling line passes through.

14. In claim 1, The above heat exchanger, A third heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section; A fourth heat exchanger is provided to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, and is located downstream of the point where the third heat exchanger passes among the cooling line sections; A fifth heat exchanger is provided to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, and is located downstream of the point where the fourth heat exchanger passes among the cooling line sections; and A hydrogen liquefaction system, which is provided to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, and includes a sixth heat exchanger passing downstream of the point where the fifth heat exchanger passes among the cooling line sections.

15. In claim 14, The third heat exchanger, the fourth heat exchanger, the fifth heat exchanger and the sixth heat exchanger, The above 2-6 pre-cooling line is arranged to pass through, The third heat exchanger and the fourth heat exchanger are, The above 2-5 pre-cooling line is arranged to pass through, The above fifth heat exchanger is, A hydrogen liquefaction system arranged so that the above-mentioned 2-1 pre-cooling line passes through it.

16. In claim 15, The third heat exchanger is, A hydrogen liquefaction system, in which the above-mentioned 2-2 pre-cooling line and the above-mentioned 2-7 pre-cooling line are arranged to pass through.

17. In claim 9, The above heat exchanger, A seventh heat exchanger configured to exchange heat between the above main cooling cycle and the above cooling line section, and having a portion located downstream of the second main cooling connection point passing therethrough; An eighth heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, and having a portion passing between the second main cooling connection point and the first main cooling connection point; and A hydrogen liquefaction system comprising a ninth heat exchanger configured to exchange heat between the second pre-cooling cycle and the main cooling cycle and the cooling line section, and a portion located upstream of the first main cooling connection point.

18. In claim 6, A hydrogen liquefaction system in which the compression ratio of the above-mentioned 2-3 pre-cooling compressor is greater than or equal to the compression ratios of the above-mentioned 2-1 pre-cooling compressor and the above-mentioned 2-2 pre-cooling compressor.

19. In claim 11, A hydrogen liquefaction system in which the compression ratio of the above-mentioned 1-1 pre-cooling compressor is greater than the compression ratio of the above-mentioned 1-2 pre-cooling compressor.

20. Pre-cooling step for cooling the object to be cooled in the atmosphere; and It includes a main cooling step of liquefying the cooling target object of the above-mentioned pre-cooled gas, The above pre-cooling step is performed by a first pre-cooling cycle and a second pre-cooling cycle that performs cooling at a relatively low temperature compared to the first pre-cooling cycle, The above cooling step is performed by a cooling cycle, The above second pre-cooling cycle is, A second-1 gas-liquid separator provided to separate the incoming second pre-cooled refrigerant into gas and liquid; A 2-1 pre-cooling line through which the second pre-cooling refrigerant in the gaseous state discharged from the 2-1 gas-liquid separator passes; A 2-2 pre-cooling line through which the second pre-cooling refrigerant in liquid form discharged from the 2-1 gas-liquid separator passes; A 2-2 gas-liquid separator connected to the 2-1 pre-cooling line and configured to separate the 2-2 pre-cooling refrigerant flowing from the 2-1 pre-cooling line into gas and liquid; A 2-3 pre-cooling line through which the second pre-cooling refrigerant in the gaseous state discharged from the 2-2 gas-liquid separator passes; A 2-4 pre-cooling line through which the second pre-cooling refrigerant in liquid form discharged from the 2-2 gas-liquid separator passes; A 2-5 pre-cooling line branching from the 2-1 pre-cooling line; A 2-6 pre-cooling line connected to the 2-3 pre-cooling line and the 2-4 pre-cooling line; and A hydrogen liquefaction process, comprising a 2-7 pre-cooling line connected to the 2-2 pre-cooling line, the 2-5 pre-cooling line, and the 2-6 pre-cooling line, and connected to the 2-1 gas-liquid separator to introduce the second pre-cooling refrigerant into the 2-1 gas-liquid separator.

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