Equipment and method for liquefying gases
The gas liquefaction plant with a dual-purity purification system accelerates startup by directly supplying high-purity gas to the cycle circuit, reducing the need for pre-cooling and stabilization, thereby shortening the startup time.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
- Filing Date
- 2024-05-03
- Publication Date
- 2026-06-26
AI Technical Summary
Conventional gas liquefaction plants require a lengthy startup sequence due to the need for pre-cooling and stabilization at intermediate temperatures to achieve high-purity cycle gases, especially when starting up or after maintenance, which extends the startup time.
A gas liquefaction plant with a purification device that operates in two modes to provide gases with different purities, allowing direct supply of high-purity gas to the cycle circuit, eliminating the need for pre-cooling and stabilization, and including a filling pipe and valve to transfer purified gas to the cycle circuit.
This configuration significantly reduces the startup time of the plant by enabling rapid purification and direct use of high-purity gas, thus eliminating the need for intermediate temperature stabilization steps.
Smart Images
Figure 2026521145000001_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a plant for liquefying a gas and a liquefaction method using such a plant.
Background Art
[0002] In a conventionally known method, a gas liquefaction plant includes a liquefier, and a part of the cooling power of the liquefier is generated through a cooling cycle having a cycle gas.
[0003] When the liquefaction temperature of the gas to be liquefied is low (for example, 20 K or less at atmospheric pressure), the cycle gas needs to be cooled to the same order of temperature. This generally requires a cycle gas mainly containing hydrogen and / or helium. Further, this requires the cycle gas to be a cycle gas of very high purity in order to avoid crystallization of any impurities that may prevent the liquefaction method from proceeding accurately.
[0004] One known solution is to use an adsorption gas separation unit (or adsorption unit) at low temperature by operating the adsorption unit at an intermediate temperature between the ambient temperature and the liquefaction temperature of the gas to be liquefied.
[0005] During the first startup of the plant or during a restart after, for example, maintenance work, it is not possible to quickly reach such a temperature level. Therefore, the startup sequence needs to include a pre-cooling step and a step of stabilizing the adsorption unit at an intermediate temperature in order to purify the gas by adsorption at low temperature to fill the cooling cycle with a cycle gas of very high purity.
[0006] The problem is that this startup sequence significantly extends the startup time of the plant.
Summary of the Invention
Means for Solving the Problems
[0007] The object of the present invention is to effectively solve these drawbacks by proposing a plant for liquefying gases (especially gases mainly containing hydrogen), and the plant is... - A supply circuit for supplying a gas to be liquefied, having an upstream end intended to be connected to a gas source and a downstream end for discharging the liquefied gas, - A liquefier comprising at least one heat exchanger that exchanges heat with a supply circuit, wherein the liquefier comprises a cooler having a cooling cycle for a cycle gas that exchanges heat with the heat exchanger, the cooler comprises a cycle circuit for circulating the cycle gas, and the cycle circuit comprises a cycle gas compression mechanism and a cycle gas expansion mechanism, and The plant includes, - A purification device installed in the supply circuit upstream of a liquefier, wherein the purification device is configured to purify gas from a gas source and supply purified gas, and is configured to operate selectively in a first mode in which the purified gas has a first purity and in a second mode in which the purified gas has a second purity, wherein the second purity is higher than the first purity, and the second purity is, for example, 99.9999 mol% or higher. - A filling pipe configured to transfer a purified gas having a second purity from a supply circuit to a cycle circuit, wherein the filling pipe is equipped with a valve, and It is characterized by including.
[0008] Such a configuration can shorten the startup time of a gas liquefaction plant and is particularly useful during the initial startup of such a plant or during startup after maintenance work. This eliminates the need for a pre-cooling step and / or stabilization step of the plant at an intermediate temperature to fill the cycle circuit with cycle gas and purify the gas by adsorption at low temperatures during startup.
[0009] According to one embodiment, the first purity is such that the purified gas contains at least 10 ppm of impurities.
[0010] According to one embodiment, the first purity is within a first range of values, and the second purity is within a second range of values.
[0011] According to one embodiment, all values in the first range are lower than the values in the second range of values.
[0012] According to one embodiment, the gas to be liquefied and the cyclic gas are gases with the same properties.
[0013] According to one embodiment, the gas to be liquefied mainly contains hydrogen.
[0014] According to one embodiment, the cycle gas mainly contains hydrogen, particularly having an impurity content of less than 1 ppm.
[0015] As an example of variation, the gas to be liquefied mainly contains helium, while the cycle gas mainly contains helium.
[0016] According to one embodiment, the purification device includes an adsorption device.
[0017] According to one embodiment, the purification device is - In a first mode in which a first purity is reached in a first yield, and - A second mode in which a second purity is reached with a second yield, wherein the second yield is lower than the first yield. It is configured to operate selectively.
[0018] According to one embodiment, the purification device is configured to operate in a first mode having a first phase time and in a second mode having a second phase time, wherein the second phase time is less than the first phase time, and the phase time takes into account, in particular, a constant gas flow at the inlet of the purification device.
[0019] According to one embodiment, the purification device includes a regulator configured to change the phase time depending on whether the purification device is operating in a first mode or a second mode.
[0020] According to one embodiment, when the purification device is operating in the first mode, the regulator is configured to maintain substantially constant purity regardless of the gas flow rate at the inlet of the purification device.
[0021] According to one embodiment, when the purification device is operating in the second mode, the regulator is configured to maintain substantially constant purity regardless of the gas flow rate at the inlet of the purification device.
[0022] According to one embodiment, the regulator is configured to adjust the phase time according to the gas flow rate at the inlet of the purification device.
[0023] According to one embodiment, the adsorption device includes at least two adsorbers configured to operate alternately, and includes a pressure swing adsorption unit including at least one bed of an adsorbent including alumina or carbon or molecular sieve.
[0024] According to one embodiment, the purified gas enters the cycle circuit at ambient temperature (for example, 5°C to 55°C, particularly 10°C to 50°C, preferably 15°C to 45°C).
[0025] According to one embodiment, the purification device includes at least a first adsorption device configured to achieve a first purity and a second adsorption device configured to achieve a second purity.
[0026] According to one embodiment, the filling pipe is in fluid communication with the supply circuit and the cycle circuit, the filling pipe is configured to transfer the purified gas to the cycle circuit, the purified gas is drawn from the supply circuit, and the purified gas is drawn upstream of the heat exchanger, in particular, at ambient temperature (for example, 5°C to 55°C, particularly 10°C to 50°C, preferably 15°C to 45°C).
[0027] According to one embodiment, the valve is configured to allow or prevent the purified gas from entering the cycle circuit.
[0028] According to one embodiment, the plant is configured such that when the purification device is operating in a second mode, the purified gas can enter the cycle circuit.
[0029] According to one embodiment, the plant is configured to prevent purified gas from entering the cycle circuit when the purification device is operating in a first mode.
[0030] According to one embodiment, the plant is - When the purification device is operating in the second mode, the purified gas enters the cycle circuit, and / or - When the purification device is operating in mode 1, the purified gas enters the liquefaction. It includes a control unit configured to control valves and purification devices so that they can be controlled.
[0031] According to one embodiment, the control unit is configured to control a valve and the purification device to prevent purified gas from entering the cycle circuit when the purification device is operating in a first mode.
[0032] Furthermore, the present invention relates to a liquefaction method using the above-described plant, - A step of supplying a purified gas to a cyclic circuit, wherein the purification device operates in a second mode, and the purified gas is introduced into the cyclic circuit at a pressure of 15 bar (absolute pressure) to 40 bar (absolute pressure) considered upstream of the valve and / or at a pressure of 5 bar (absolute pressure) to 15 bar (absolute pressure) considered downstream of the valve. - A step of liquefying the gas to be purified by a purification device operating in a first mode, and This relates to a liquefaction method that includes [specific details].
[0033] According to one embodiment, the step of supplying purified gas to a cycle circuit while the purified gas passes through a heat exchanger is performed without substantially modifying the temperature of the purified gas between the upstream and downstream of the heat exchanger.
[0034] According to one embodiment, in the step of supplying to the cycle circuit, the purified gas enters the cycle circuit at ambient temperature (for example, 0°C to 55°C, particularly 5°C to 50°C, preferably 15°C to 45°C).
[0035] According to one embodiment, the step of supplying to the cycle circuit is a series of the following steps: - A step of introducing purified gas into a cyclic circuit, wherein the valve is configured in particular to fluidly communicate the cyclic circuit with the supply circuit, - In particular, the step of expanding the cycle gas in a cycle circuit by an expansion member, wherein the valve is configured to fluidly separate the cycle circuit from the supply circuit, and the step of expanding the cycle gas Includes.
[0036] According to one embodiment, the method includes a series of steps, which are performed alternately multiple times, in which a purified gas is introduced and a cycle gas is expanded.
[0037] This allows for the precise content of the cycle gas at any point in the cycle circuit due to the dilution phenomenon.
[0038] According to one embodiment, the expansion member includes, for example, a discharge pipe that includes a valve configured to release a portion of the cycle gas through the discharge pipe.
[0039] According to one embodiment, the step of liquefying the purified gas includes the step of cooling the purified gas with a heat exchanger.
[0040] According to one embodiment, the method includes, for example, the step of inactivating the cycle circuit before supplying it, by discharging an inert gas (e.g., nitrogen) into the cycle circuit.
[0041] The present invention will be better understood by reading the following description and examining the accompanying drawings. These drawings are given as examples only and are not intended to limit the present invention in any way. [Brief explanation of the drawing]
[0042] [Figure 1] Figure 1 is a schematic diagram of a plant according to the present invention. [Figure 2] Figure 2 is a schematic diagram of the steps of the method according to the present invention. [Modes for carrying out the invention]
[0043] Identical, similar, or identical elements shall retain the same reference numeral in each drawing.
[0044] Figure 1 shows plant 1, which liquefies gases.
[0045] Plant 1 includes a supply circuit 4 for supplying a gas to be liquefied, the supply circuit 4 having an upstream end 2 intended to be connected to a gas source, and a downstream end 3 for discharging the liquefied gas.
[0046] In the example from Figure 1, the gas to be liquefied mainly contains hydrogen.
[0047] The gas source may include, for example, an electrolytic cell or a gas network.
[0048] Plant 1 in Figure 1 can operate with other gases (e.g., helium).
[0049] Furthermore, the plant 1 includes a liquefier 7 which includes at least one heat exchanger 6 that exchanges heat with the supply circuit 4, preferably a heat exchanger 6 located in at least one cold box. The liquefier 7 includes a cooler 12 which has a cooling cycle for the cyclic gas and exchanges heat with the heat exchanger 6.
[0050] A cycle gas is a gas with the same properties as the gas to be liquefied. A possible example is hydrogen, with a purity of 99.9999 mol% or higher. In other words, the cycle gas contains impurities of 1 ppm or less.
[0051] The cooler 12 includes a cycle circuit 5 for circulating the cycle gas.
[0052] The cycle circuit 5 includes a cycle gas compression mechanism 8, a cycle gas cooling system, a cycle gas expansion mechanism 9, and a system for reheating the cycle gas before restarting the cycle. During operation, the cycle circuit subjects the cycle gas to a thermodynamic cycle that brings the cycle gas to a low temperature at at least one low-temperature end (or more low-temperature ends).
[0053] This cooling force is transferred to the gas in the supply circuit, where it is cooled / liquefied by heat exchange in one or more heat exchangers (in particular, one or more counterflow heat exchangers that cool and reheat the cyclic gas at two points in the cycle).
[0054] The compression mechanism 8 includes at least one compressor. The expansion mechanism 9 includes at least one valve and / or one turbine.
[0055] Furthermore, Plant 1 includes a purification device 13 installed in the supply circuit 4 upstream of the liquefier 7.
[0056] The purification device 13 is configured to purify gas from a gas source and supply the purified gas. In other words, the purification device 13 receives gas from an upstream gas source and sends the purified gas downstream.
[0057] Furthermore, the purification device 13, - In a first mode in which the purified gas has a first purity, and - In a second mode in which the purified gas has a second purity, It is configured to operate selectively.
[0058] The fact that the purification device 13 is configured to operate selectively in a first mode and a second mode means, in particular, that the purification device 13 is configured to be controlled to selectively switch from one mode to another (and vice versa) depending on the desired purity requirements.
[0059] The second purity level is higher than the first purity level.
[0060] The second purity level is 99.9999 mol% or higher.
[0061] The first purity level is such that, for example, the purified gas contains at least 10 ppm of impurities.
[0062] Furthermore, Plant 1 includes a filling pipe 11 configured to transfer purified gas having a second purity from the supply circuit 4 to the cycle circuit 5, and the filling pipe 11 is equipped with a valve 10.
[0063] Preferably, the filling pipe 11 is configured to draw the purified gas having a second purity into the supply circuit 4 upstream of the liquefaction unit 7.
[0064] As an example of a variation, the filling pipe 11 is configured to draw a purified gas having a second purity into the liquefaction unit 7 (for example, upstream of the cooler 12).
[0065] In one embodiment, the filling pipe 11 is configured to draw in a purified gas having a second purity downstream of the low-temperature purification device of the liquefier 7, drawing in the purified gas at ambient temperature. In this embodiment, the low-temperature purification device of the liquefier 7 is positioned downstream of the cooler 12, and the low-temperature purification device includes, for example, a temperature swing adsorption unit.
[0066] Therefore, in this embodiment, the purified gas enters the low-temperature purification device while being purified to a second purity.
[0067] In the example shown in Figure 1, the purification device 13 includes an adsorption device 13, in particular a gas-phase adsorption device 13.
[0068] The purification device 13 is - In a first mode in which a first purity is reached in a first yield, and - A second mode in which a second purity is reached with a second yield, wherein the second yield is lower than the first yield. It is configured to operate selectively.
[0069] The purification device 13 is configured to operate in a first mode having a first phase time and in a second mode having a second phase time, wherein the second phase time is less than the first phase time.
[0070] The first and second phase times take into account a constant gas flow at the inlet of the purification device 13, i.e., a constant supply flow, in particular a constant supply gas flow.
[0071] The purification device 13 includes a pressure swing adsorption unit which includes at least two adsorbents configured to operate alternately, each containing at least one bed of adsorbent including alumina, carbon, or molecular sieves.
[0072] Adsorption units, such as pressure swing adsorption units (also known as PSA units), are commonly used for supply gas separation and / or purification, particularly in fields that generate hydrogen, helium, or carbon dioxide, in drying fields, and in fields that separate components of air.
[0073] Generally, a PSA unit consists of several adsorbents, described below, which have operating cycles, hereafter referred to as "PSA cycles," that are evenly distributed over the same phase time as the adsorbents in operation, and the PSA cycle is formed from the following basic steps: - Adsorption at substantially high pressures during the cycle - Generally, simultaneous depressurization from high pressure in the cycle. - Generally, countercurrent depressurization towards lower pressure in the cycle. - Elution at substantially low pressures during the cycle - Re-pressurizing the cycle from low pressure to high pressure.
[0074] Simultaneous depressurization generally includes one or more equalization steps and at least one supply purification step of supplying eluted gas.
[0075] Repressurization generally involves a corresponding equalization step and a final repressurization using the generated gas or eluted gas.
[0076] These steps define the characteristic pressure of the PSA.
[0077] The primary operating constraint of a PSA unit in a steady state is the purity of the product. Under these operating conditions, the processing performance of the PSA unit is then generally optimized to maximize efficiency (i.e., extraction efficiency equal to the amount of product gas divided by the amount of this gas present in the feed gas) or to minimize energy consumption.
[0078] In this way, the nominal operating cycle of the PSA unit is obtained, and the nominal operating cycle is directly determined by the nominal operating conditions (supply gas flow rate, processed gas flow rate, supply gas composition, unit operating temperature, pressure, etc.). Therefore, in the first operating mode, the adsorption device is under the nominal operating conditions.
[0079] If the operating conditions deviate from the nominal conditions, for example, if the adsorption device is in a second mode, one solution is to adjust the operation of the PSA unit by adjusting one or more parameters of the nominal cycle. The two adjustments that fall under this method are as follows: - "Capacity" adjustment, which involves correcting the duration of the cycle's phase time in response to fluctuations in the supply gas flow rate. - "Purity control" adjustment, which involves correcting this phase time according to the purity of the processed gas.
[0080] Here, it is desirable to define what is understood by cycle time and phase time (or simply phase).
[0081] As described above, the adsorbent begins an adsorption period under high pressure until the adsorbent is clogged with one or more components to be taken in. The adsorbent is then regenerated by reduced pressure and extraction of the adsorbed compounds before being repaired to begin a new adsorption period. The adsorbent has now completed a “pressure cycle,” and the principle of the PSA method is to link these cycles together, thus making it a periodic method. The time it takes for the adsorbent to return to its initial state is called the cycle time. In principle, each adsorbent follows the same cycle with a time delay known as the phase time, or more simply, the phase. Thus, the following relationship exists: (phase time = cycle time / number of adsorbents), and it can be seen that the number of phases is equal to the number of adsorbents.
[0082] There can be any number N of adsorbents, but generally, N is between 2 and 32, and more typically between 4 and 16.
[0083] In practice, there are numerous options for performing adjustments (of volume and / or purity), and the result of these adjustments is to operate the PSA under specified purity and efficiency conditions.
[0084] The regulator's operation should be adjusted to ensure that the purity is maintained at the desired target value.
[0085] The filling pipe 11 is in fluid communication with the supply circuit 4 and the cycle circuit 5. The filling pipe 11 is configured to transfer the purified gas to the cycle circuit 5, which is drawn in from the supply circuit 4 and is at ambient temperature (e.g., 5°C to 55°C, particularly 10°C to 50°C, preferably 15°C to 45°C) as it is drawn in, in particular, upstream of the heat exchanger 6.
[0086] The filling pipe 11 is configured so that the purified gas can exit the purification device 13 and enter the cycle circuit 5 without undergoing heat exchange in the heat exchanger 6 or additional purification by, for example, the low-temperature purification device of the liquefaction unit 7.
[0087] In other words, the purified gas can be drawn in from the supply circuit 4 at ambient temperature (for example, 5°C to 55°C, particularly 10°C to 50°C, preferably 15°C to 45°C).
[0088] The valve 10 is configured to allow or prevent the purified gas from entering the cycle circuit 5.
[0089] Plant 1 is configured so that when the purification device 13 is operating in the second mode, the purified gas can enter the cycle circuit 5.
[0090] Furthermore, Plant 1 is configured to prevent the purified gas from entering the cycle circuit 5 when the purification device 13 is operating in the first mode.
[0091] Plant 1 is - When the purification device 13 is operating in the second mode, the purified gas enters the cycle circuit 5, and / or - When the purification device 13 is operating in the first mode, the purified gas enters the liquefaction unit 7. The system includes a control unit configured to control the valve 10 and the purification device 13 in order to enable this function.
[0092] The control unit is configured to control the valve 10 and the purification device 13 to prevent the purified gas from entering the cycle circuit 5 when the purification device 13 is operating in the first mode.
[0093] Figure 2 illustrates the liquefaction method using Plant 1 as described above.
[0094] The method is, - Steps E2 and E3 of supplying purified gas to the cycle circuit 5, wherein the purification device 13 operates in a second mode, and the purified gas is introduced into the cycle circuit 5 at a pressure of 15 bar (absolute pressure) to 40 bar (absolute pressure) considered upstream of the valve 10 and / or at a pressure of 5 bar (absolute pressure) to 15 bar (absolute pressure) considered downstream of the valve 10, - Step E4, which liquefies the gas to be purified by the purification device 13 operating in the first mode, Includes.
[0095] In an exemplary embodiment of the method, during the supply steps E2 and E3, the liquefier 7 is stopped, i.e., the liquefier is at a temperature exceeding its operating temperature, for example. The supply steps E2 and E3 can be performed while at least partially emptying the cycle gas of the cycle circuit.
[0096] Preferably, the method includes step E1 of deactivating the cycle circuit 5 before steps E2 and E3 of supplying the cycle circuit 5.
[0097] Step E1 for inactivating the cycle circuit 5 includes injecting an inert gas (e.g., nitrogen) into the cycle circuit 5.
[0098] Steps E2 and E3, which supply the cycle circuit 5, are the following consecutive steps: - Step E2 of introducing purified gas into the cycle circuit, wherein the valve 10 is configured to fluidly communicate the cycle circuit 5 with the supply circuit 4, - In particular, step E3 involves expanding the cycle gas within the cycle circuit 5 by an expansion member, and the valve 10 is configured to fluidly separate the cycle circuit 5 from the supply circuit 4, and step E3 involves expanding the cycle gas. Includes.
[0099] Step E4, which liquefies the purified gas, includes step E4, which cools the purified gas by the heat exchanger 6.
[0100] As a variation, or in combination, the method includes steps E2, E3 of supplying hydrogen gas having a purity of at least 99.9999 mol% to the cycle circuit 5, wherein the hydrogen gas is generated, for example, from a dedicated source (e.g., a mesh) or from a tank of evaporatively pressurized liquid hydrogen.
Claims
1. A plant (1) for liquefying gases (especially gases mainly containing hydrogen), - A supply circuit (4) for supplying a gas to be liquefied, having an upstream end (2) intended to be connected to a gas source and a downstream end (3) for discharging the liquefied gas, - A liquefier (7) comprising at least one heat exchanger (6) that exchanges heat with the supply circuit (4), wherein the liquefier (7) comprises a cooler (12) having a cooling cycle for a cycle gas that exchanges heat with the heat exchanger (6), the cooler (12) comprises a cycle circuit (5) that circulates the cycle gas, and the cycle circuit (5) comprises a cycle gas compression mechanism (8) and a cycle gas expansion mechanism (9), and In a plant (1) including, - A purification device (13) installed in the supply circuit (4) upstream of the liquefier (7), wherein the purification device (13) is configured to purify the gas from the gas source and supply the purified gas, and the purification device (13) is configured to selectively operate in a first mode in which the purified gas has a first purity and in a second mode in which the purified gas has a second purity, wherein the second purity is higher than the first purity, and the second purity is, for example, 99.9999 mol% or more, - A filling pipe (11) configured to transfer the purified gas having the second purity from the supply circuit (4) to the cycle circuit (5), wherein the filling pipe (11) is equipped with a valve (10), - A control unit, - When the purification device (13) is operating in the second mode, the purified gas enters the cycle circuit (5), and / or - When the purification device (13) is operating in the first mode, the purified gas enters the liquefaction device (7). The valve (10) and the purification device (13) are configured to control them so that they can do so. The control unit is configured to control the valve (10) and the purification device (13) to prevent the purified gas from entering the cycle circuit (5) when the purification device (13) is operating in the first mode. A plant (1) characterized by including
2. The aforementioned purification device (13) - In the first mode in which the first purity is achieved in the first yield, and - A second mode in which the second purity is achieved in a second yield, wherein the second yield is lower than the first yield. The plant (1) according to claim 1, configured to operate selectively.
3. The plant (1) according to claim 1 or 2, wherein the purification device (13) is configured to operate in a first mode having a first phase time and in a second mode having a second phase time, the second phase time being less than the first phase time, and the phase time takes into account a constant gas flow at the inlet of the purification device (13).
4. The plant (1) according to any one of claims 1 to 3, wherein the filling pipe (11) is in fluid communication with the supply circuit (4) and the cycle circuit (5), the filling pipe (11) is configured to transfer the purified gas to the cycle circuit (5), the purified gas is drawn in from the supply circuit (4), and the purified gas is drawn in particularly upstream of the heat exchanger (6) at an ambient temperature, for example, 5°C to 55°C, particularly 10°C to 50°C, preferably 15°C to 45°C.
5. The plant (1) according to any one of claims 1 to 4, wherein the purification device (13) is configured to allow the purified gas to enter the cycle circuit (5) when it is operating in the second mode.
6. The plant (1) according to any one of claims 1 to 5, wherein the purification device (13) is configured to prevent the purified gas from entering the cycle circuit (5) when it is operating in the first mode.
7. A liquefaction method using the plant (1) described in any one of claims 1 to 6, - Steps (E2, E3) of supplying purified gas to the cycle circuit (5), wherein the purification device (13) operates in a second mode, and the purified gas is introduced into the cycle circuit (5) at a pressure of 15 bar (absolute pressure) to 40 bar (absolute pressure) considered upstream of the valve (10) and / or at a pressure of 5 bar (absolute pressure) to 15 bar (absolute pressure) considered downstream of the valve (10), - Step (E4) of liquefying the gas that is purified by the purification device (13) operating in the first mode and A liquefaction method including the following.
8. The steps (E2, E3) supplied to the cycle circuit (5) are the following consecutive steps: - Step (E2) of introducing purified gas into the cycle circuit (5), wherein the valve (10) is configured to fluidly communicate the cycle circuit (5) with the supply circuit (4), - In particular, step (E3) of expanding the cycle gas in the cycle circuit (5) by an expansion member, wherein the valve (10) is configured to fluidly separate the cycle circuit (5) from the supply circuit (4), and The liquefaction method according to claim 7, including the method described in claim 7.