Facility and liquefaction method for liquefied gas

Abstract

The invention relates to a device (1) for liquefying a gas, comprising:-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 delivering the liquefied gas; -a liquefier (7) comprising a heat exchanger (6) and a chiller (12) having a refrigeration cycle for a recycle gas, the chiller (12) comprising a circulation circuit (5) for circulating the recycle gas; -a purification device (13) mounted in the supply circuit (4) upstream of the liquefier (7), the purification device (13) being configured to purify the gas from the gas source and to provide a purified gas.

Description

[0001] The present invention relates to a device for liquefying a gas and to a liquefaction method using such a device.

[0002] In a manner known per se, a gas liquefaction device comprises a liquefier, a part of the cooling capacity of which is generated via a refrigeration cycle of a cycle gas.

[0003] When the liquefaction temperature of the gas to be liquefied is low, for example equal to or lower than 20 K at atmospheric pressure, the cycle gas must be brought down to a temperature of the same order of magnitude. This generally requires the cycle gas to mainly comprise hydrogen and / or helium. Furthermore, it also requires the cycle gas to have a very high purity, in order to avoid the crystallization of any impurities, which could prevent the liquefaction process from proceeding normally.

[0004] A known solution is to use, at low temperature, an adsorption gas separation unit (or adsorption unit) by operating it at an intermediate temperature between the ambient temperature and the liquefaction temperature of the gas to be liquefied.

[0005] During the first start-up of the device or during a re-start after a maintenance operation for example, it is not possible to quickly reach such a temperature level. The start-up procedure must therefore include a pre-cooling step and a step of stabilizing the adsorption unit at the intermediate temperature, in order to purify the gas by low-temperature adsorption, in order to fill the refrigeration cycle with a cycle gas of very high purity.

[0006] The problem is that this start-up procedure significantly lengthens the start-up time of the device.

[0007] The present invention aims to efficiently solve these drawbacks by proposing a device for liquefying a gas, in particular mainly comprising hydrogen, comprising: - 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 delivering a liquefied gas; - a liquefier comprising at least one heat exchanger in thermal exchange with the supply circuit, the liquefier comprising a refrigerator having a refrigeration cycle of a cycle gas, the cycle gas being in thermal exchange with the heat exchanger, the refrigerator comprising a circulation circuit for circulating the cycle gas, the circulation circuit comprising a cycle gas compression mechanism and a cycle gas expansion mechanism; characterized in that it comprises: - a purification device installed in the supply circuit upstream of the liquefier, the purification device being configured to purify the gas from the gas source and to provide a purified gas, the purification device being configured to selectively operate in a first mode and in a second mode, in the first mode the purified gas having a first purity level and in the second mode the purified gas having a second purity level, the second purity level being greater than the first purity level, the second purity level being for example greater than or equal to 99.9999 mol%. - a filling duct configured to allow the purified gas having the second purity level to be transferred from the supply circuit into the circulation circuit, the filling duct being equipped with a valve.

[0008] This configuration makes it possible to reduce the start-up time of the gas liquefaction installation, which is particularly useful during the first start-up of such an installation or during a start-up after a maintenance operation. This makes it possible to avoid, at start-up, the need for a pre-cooling step and / or a stabilisation step of the installation at an intermediate temperature (these steps being used to purify the gas by cryo-adsorption, in order to fill the circulation circuit with circulation gas).

[0009] According to one embodiment, the first purity level is such that the purified gas contains at least 10 ppm of impurities.

[0010] According to one embodiment, the first purity level is in a first range of values and the second purity level is in a second range of values.

[0011] According to one embodiment, the values of the first range are all lower than the values of the second range of values.

[0012] According to one embodiment, the gas to be liquefied and the circulation gas have the same nature.

[0013] According to one embodiment, the gas to be liquefied mainly comprises hydrogen.

[0014] According to one embodiment, the circulation gas mainly comprises hydrogen, in particular with an impurity content of less than 1 ppm.

[0015] As a variant, the gas to be liquefied mainly comprises helium and the circulation gas mainly comprises helium.

[0016] According to one embodiment, the purification device comprises an adsorption device.

[0017] According to one embodiment, the purification device is configured to be selectively operated in: - the first mode, in which the purification device reaches the first purity level with a first yield; and - the second mode, in which the purification device reaches the second purity level with a second yield, the second yield being lower than the first yield.

[0018] According to one embodiment, the purification device is configured to be operated in the first mode with a first phase time and in the second mode with a second phase time, the second phase time being less than the first phase time, these phase times being in particular considered for a constant gas flow rate at the inlet of the purification device.

[0019] According to one embodiment, the purification device comprises a regulator configured to vary the stage time depending on whether the purification device is running in a first mode or in a second mode.

[0020] According to one embodiment, when the purification device is running in the first mode, the regulator is configured to maintain the purity grade substantially constant whatever the gas flow at the inlet of the purification device.

[0021] According to one embodiment, when the purification device is running in the second mode, the regulator is configured to maintain the purity grade substantially constant whatever the gas flow at the inlet of the purification device.

[0022] According to one embodiment, the regulator is configured to adjust the stage time depending on the gas flow at the inlet of the purification device.

[0023] According to one embodiment, the adsorption device comprises a pressure swing adsorption unit comprising at least two adsorbers configured to run alternately, and each adsorber comprises at least one adsorbent bed containing alumina or carbon or molecular sieves.

[0024] According to one embodiment, the purified gas enters the circulation loop at ambient temperature, for example between 5°C and 55°C, in particular between 10°C and 50°C, preferably between 15°C and 45°C.

[0025] According to one embodiment, the purification device comprises at least a first adsorption device configured to achieve a first purity grade and a second adsorption device configured to achieve a second purity grade.

[0026] According to one embodiment, the filling duct is in fluid communication with the supply circuit and the circulation loop, the filling duct being configured to allow the transfer of the purified gas into the circulation loop, the purified gas being extracted from the supply circuit, in particular when the purified gas is extracted upstream of the heat exchanger, the purified gas being at ambient temperature, for example between 5°C and 55°C, in particular between 10°C and 50°C, preferably between 15°C and 45°C.

[0027] According to one embodiment, the valve is configured to allow or prevent the entry of the purified gas into the circulation loop.

[0028] According to one embodiment, the device is configured to allow the entry of the purified gas into the circulation loop when the purification device is running in the second mode.

[0029] According to one embodiment, the device is configured to prevent the entry of the purified gas into the circulation loop when the purification device is running in the first mode.

[0030] According to one embodiment, the device comprises a control unit configured to control the valve and the purification device so as to: - cause the purified gas to enter the circulation loop when the purification device is running in the second mode; and / or - cause the purified gas to enter the liquefier when the purification device is running in the first mode.

[0031] According to one embodiment, the control unit is configured to control the valve and the purification device so as to prevent the purified gas from entering the circulation loop when the purification device is running in the first mode.

[0032] The application further relates to a liquefaction method using a device as described above, the method comprising the following successive steps: - supplying the purified gas to the circulation loop, the purification device being running in the second mode, in particular the purified gas being introduced into the circulation loop at a pressure of between 15 and 40 bar absolute, this pressure being considered as the pressure upstream of the valve, and / or at a pressure of between 5 and 15 bar absolute, this pressure being considered as the pressure downstream of the valve; - liquefying the gas purified by the purification device running in the first mode.

[0033] According to one embodiment, the step of supplying the purified gas to the circulation loop is performed while the purified gas passes through the heat exchanger, without the temperature of the purified gas substantially changing between upstream and downstream of the heat exchanger.

[0034] According to one embodiment, in the step of supplying to the circulation loop, the purified gas enters the circulation loop at ambient temperature, for example between 0°C and 55°C, in particular between 5°C and 50°C, preferably between 15°C and 45°C.

[0035] According to one embodiment, the step of supplying to the circulation loop comprises the following successive steps: - introducing the purified gas into the circulation loop, the valve being in particular configured to place the circulation loop in fluid communication with the supply circuit; - expanding the circulation gas inside the circulation loop, in particular by means of the expansion member, the valve being configured to fluidly isolate the circulation loop from the supply circuit.

[0036] According to one embodiment, the method comprises a plurality of series of steps of introducing the purified gas and expanding the circulation gas alternately.

[0037] This makes it possible to ensure the correct content of the circulation gas at any location in the circulation loop by means of the dilution phenomenon.

[0038] According to one embodiment, the expansion means comprise a discharge duct comprising, for example, a valve configured to enable a portion of the cycle gas to be discharged via the discharge duct.

[0039] According to one embodiment, the step of liquefying the purified gas comprises a step of cooling the purified gas by means of a heat exchanger.

[0040] According to one embodiment, the method comprises a step of inerting the cycle loop before the step of supplying to the cycle loop, for example by flushing the cycle loop with an inert gas such as nitrogen.

[0041] The application will be better understood by reading the following description, and by studying the attached drawings. These drawings are given purely as an illustration and do not limit the application in any way.

[0042] [ Figure 1 ] is a schematic illustration of a device according to the application; and

[0043] [ Figure 2 ] is a schematic illustration of the steps of a method according to the application.

[0044] The same, similar or analogous elements are kept with the same reference numerals between the various figures.

[0045] Figure 1 denotes a device 1 for liquefying a gas.

[0046] The device 1 comprises a supply circuit 4 for supplying a gas to be liquefied, this supply circuit having an upstream end 2 intended to be connected to a source of gas and a downstream end 3 for delivering the liquefied gas.

[0047] In the example from Figure 1 , the gas to be liquefied mainly comprises hydrogen.

[0048] For example, the source can comprise an electrolyser or a gas network.

[0049] Figure 1 The device in may be operated with other gases, such as helium.

[0050] The device 1 further comprises a liquefier 7 comprising at least one heat exchanger 6 placed, preferably, in at least one cold box, in heat exchange with the supply circuit 4. The liquefier 7 comprises a refrigerator 12 having a refrigeration cycle for a cycle gas, this cycle gas being in heat exchange with the heat exchanger 6.

[0051] The cycle gas has the same properties as the gas to be liquefied. In the example considered, the cycle gas is hydrogen and its purity is greater than or equal to 99.9999 mol%. In other words, the cycle gas has 1 ppm or less of impurities.

[0052] The refrigerator 12 comprises a cycle loop 5 for circulating a cycle gas.

[0053] The cycle loop 5 comprises 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. In operation, the cycle loop subjects the cycle gas to a thermodynamic cycle that brings the cycle gas to a low temperature at at least one cold end (one or more cold ends).

[0054] This cooling capacity is transferred to the feed circuit gas to be cooled / liquefied by heat exchange in one or more heat exchangers, in particular one or more counterflow heat exchangers providing both cooling and reheating of the cycle gas at two locations in the cycle.

[0055] The compression mechanism 8 comprises at least one compressor. The expansion mechanism 9 comprises at least one valve and / or one turbine.

[0056] The apparatus 1 further comprises a purification device 13 installed in the feed circuit 4 upstream of the liquefier 7.

[0057] The purification device 13 is configured to purify a gas from a gas source and to provide a purified gas. In other words, the purification device 13 receives a gas from an upstream gas source and delivers a purified gas downstream.

[0058] In addition, the purification device 13 is configured to selectively operate in: - a first mode in which the purified gas has a first purity grade, and - a second mode in which the purified gas has a second purity grade.

[0059] The fact that the purification device 13 is configured to selectively operate in the first mode and in the second mode particularly means that it is configured to be controlled to selectively switch from one mode to the other mode, and vice versa, depending on the purity requirements desired.

[0060] The second purity grade is greater than the first purity grade.

[0061] The second purity grade is greater than or equal to 99.9999 mol%.

[0062] For example, the first purity grade is such that the purified gas contains at least 10 ppm of impurities.

[0063] The apparatus 1 further comprises a filling duct 11 configured to allow the purified gas having the second purity grade to be transferred from the feed circuit 4 into the cycle loop 5, the filling duct 11 being equipped with a valve 10.

[0064] Preferably, the filling conduit 11 is configured to draw the purified gas having the second purity level in the supply circuit 4 upstream of the liquefier 7.

[0065] As a variant, the filling conduit 11 is configured to draw the purified gas having the second purity level in the liquefier 7, for example upstream of the refrigerator 12.

[0066] According to one embodiment, the filling conduit 11 is configured to draw the purified gas having the second purity level downstream of a cryogenic purification device of the liquefier 7, the purified gas being drawn at ambient temperature. In this embodiment, the cryogenic purification device of the liquefier 7 is located downstream of the refrigerator 12, the cryogenic purification device comprising for example a temperature swing adsorption unit.

[0067] Thus, in this embodiment, the purified gas enters the cryogenic purification device while being purified at the second purity level.

[0068] In the example from Figure 1 , the purification device 13 comprises an adsorption device 13, in particular a gas phase adsorption device 13.

[0069] The purification device 13 is configured to selectively operate in: - a first mode in which the purification device reaches the first purity level with a first productivity; and - a second mode in which the purification device reaches the second purity level with a second productivity, the second productivity being lower than the first productivity.

[0070] The purification device 13 is configured to operate with a first phase time in the first mode and with a second phase time in the second mode, the second phase time being less than the first phase time.

[0071] The first phase time and the second phase time are considered for a constant gas flow at the inlet of the purification device 13, that is to say for a constant supply flow, in particular for a constant feed gas flow.

[0072] The purification device 13 comprises a pressure swing adsorption unit comprising at least two adsorbers configured to operate alternately, and each comprising at least one adsorbent bed containing alumina or carbon or molecular sieves.

[0073] Adsorption units, for example pressure swing adsorption units (also called PSA units), are generally used for the separation and / or purification of a feed gas (in particular in the field of production of hydrogen, helium or carbon dioxide, drying, separation of air constituents, etc.).

[0074] Generally, a PSA unit is composed of a plurality of adsorbers which execute in turn a run cycle (for convenience, hereinafter called "PSA cycle") with a time lag, this cycle being evenly distributed into as many phase times as the number of adsorbers in operation, and this cycle being formed of elementary steps, namely: - adsorption at a substantially high pressure of the cycle; - generally downflow pressure reduction from the high pressure of the cycle; - generally upflow pressure reduction to the low pressure of the cycle; - elution at a substantially low pressure of the cycle; and - repressurization from the low pressure of the cycle to the high pressure of the cycle.

[0075] Downflow pressure reduction generally comprises one or more equalization steps and at least one feed-sweep step providing an elution gas.

[0076] Repressurization generally comprises a corresponding equalization step and a final repressurization with a production gas or an elution gas.

[0077] These steps define the characteristic pressures of the PSA.

[0078] The main operating constraints of a PSA unit in steady state consist of the purity level of the product. Under such operating conditions, the treatment performance of the PSA unit is then generally optimized to maximize the efficiency (i.e. the extraction efficiency, which equals the amount of gas produced divided by the amount of this gas present in the feed gas), or to minimize the energy consumed.

[0079] What is obtained in this way is a nominal run cycle of the PSA unit, which is directly determined according to nominal operating conditions (flow rate of the feed gas, flow rate of the treated gas, composition of the feed gas, operating temperature of the unit, pressure, etc.). In the first operating mode, the adsorption device is thus in nominal operating conditions.

[0080] When the operating conditions deviate from the nominal conditions, for example when the adsorption device is in the second mode, one solution is to adjust the operation of the PSA unit by adjusting one or more parameters of the nominal cycle. Two provisions belonging to this approach are: - the "capacity" adjustment, which consists in varying the duration of the phase times in the cycle according to the variation of the flow rate of the feed gas; and - the "purity control" adjustment, which consists in varying the phase times according to the purity of the treated gas.

[0081] It is proposed here to define the meaning of cycle time and phase time (or more simply phase).

[0082] As already described above, the adsorbers thus carry out a cycle of adsorption starting at high pressure until they are loaded with the component or components to be captured, and are then regenerated by depressurization and extraction of the adsorbed compounds, after which they are restored in order to start again a new adsorption cycle. The adsorbers have thus completed a "pressure cycle", and the specific principle of the PSA process is to link these cycles together successively; thus, it is a cyclic process. The time taken for the adsorbers to return to their initial state is called the cycle time. In principle, each adsorber follows the same cycle with a time lag, called the phase time or more simply the phase. The following relationship thus exists:

[0083] Phase time = cycle time / number of adsorbers, and it is seen that the number of phases is equal to the number of adsorbers.

[0084] There can be any number N of adsorbers, but generally N is between 2 and 32, more typically between 4 and 16.

[0085] In practice, there are a large number of options for performing a (capacity and / or purity) adjustment, the result of which is to make the PSA run under predetermined purity and efficiency conditions.

[0086] The action of the adjuster should be adjusted to ensure that the purity will be maintained with respect to the desired target value.

[0087] The filling duct 11 is in fluid communication with the supply circuit 4 and the circulation circuit 5. The filling duct 11 is configured to allow the transfer of purified gas into the circulation circuit 5, the purified gas being extracted from the supply circuit 4, in particular when the purified gas is extracted upstream of the heat exchanger 6, the purified gas being at ambient temperature, for example between 5°C and 55°C, in particular between 10°C and 50°C, preferably between 15°C and 45°C.

[0088] The filling duct 11 is configured to allow the purified gas leaving the purification device 13 to enter the circulation circuit 5 without having to undergo heat exchange in the heat exchanger 6 or without having to undergo additional purification, for example by cryogenic purification means of the liquefier 7.

[0089] That is to say, the purified gas can be extracted from the supply circuit 4 at ambient temperature, for example between 5°C and 55°C, in particular between 10°C and 50°C, preferably between 15°C and 45°C.

[0090] The valve 10 is configured to allow or prevent the entry of purified gas into the circulation circuit 5.

[0091] The device 1 is configured to allow the entry of purified gas into the circulation circuit 5 when the purification device 13 is running in the second mode.

[0092] Furthermore, the device 1 is also configured to prevent the purified gas from entering the circulation loop 5 when the purification means 13 are operating in the first mode.

[0093] The device 1 comprises a control unit configured to control the valve 10 and the purification means 13 so as to: - cause the purified gas to enter the circulation loop 5 when the purification means 13 are operating in the second mode; and / or - cause the purified gas to enter the liquefier 7 when the purification means 13 are operating in the first mode.

[0094] The control unit is configured to control the valve 10 and the purification means 13 so as to prevent the purified gas from entering the circulation loop 5 when the purification means 13 are operating in the first mode.

[0095] Figure 2 The liquefaction process using the device 1 as described above is represented.

[0096] The method comprises the following successive steps: - supplying E2, E3 the circulation loop 5 with a purified gas, the purification means 13 being operated in the second mode, in particular the purified gas being introduced into the circulation loop 5 at a pressure of between 15 and 40 bar absolute (this pressure being considered as the pressure upstream of the valve 10) and / or at a pressure of between 5 and 15 bar absolute (this pressure being considered as the pressure downstream of the valve 10); - liquefying E4 the gas purified by the purification means 13 operating in the first mode.

[0097] In an exemplary embodiment of the method, during the supply steps E2, E3, the liquefier 7 is closed, i.e. the liquefier is for example at a temperature higher than its operating temperature. The supply steps E2, E3 can be carried out while the circulation loop is at least partially emptied of its circulation gas.

[0098] The method preferably comprises a step E1 of inerting the circulation loop 5 before the steps E2, E3 of supplying the circulation loop 5.

[0099] The step E1 of inerting the circulation loop 5 comprises a step of injecting an inert gas, such as nitrogen, into the circulation loop 5.

[0100] The step of supplying E2, E3 the circulation loop 5 comprises the following successive steps: - introducing E2 the purified gas into the circulation loop 5, the valve 10 being in particular configured to place the circulation loop 5 in fluid communication with the supply circuit 4; - expanding E3 the circulation gas inside the circulation loop 5, in particular by means of an expansion member, the valve 10 being configured to fluidically isolate the circulation loop 5 from the supply circuit 4.

[0101] The step E4 of liquefying the purified gas comprises a step E4 of cooling the purified gas by means of a heat exchanger 6.

[0102] As variants or combinations, the method comprises a step E2, E3 of supplying to the circuit 5 hydrogen gas having a purity grade of at least 99.9999 mol%, for example originating from a dedicated source (such as a grid) or from a pressurized liquefied hydrogen tank vaporized.

Claims

1. An apparatus (1) for liquefying a gas, particularly comprising primarily hydrogen, the apparatus (1) comprising: - A supply circuit (4) for supplying the gas to be liquefied, having an upstream end (2) intended to be connected to a gas source and a downstream end (3) for delivering the liquefied gas. - A liquefier (7) comprising at least one heat exchanger (6) that exchanges heat with the supply circuit (4), the liquefier (7) comprising a refrigerator (12) having a refrigeration cycle for a circulating gas that exchanges heat with the heat exchanger (6), the refrigerator (12) comprising a circulation loop (5) for circulating the circulating gas, the circulation loop (5) comprising a circulating gas compression mechanism (8) and a circulating gas expansion mechanism (9); characterized in that the device (1) comprises: - A purification device (13), installed in the supply circuit (4) upstream of the liquefier (7), is configured to purify the gas from the gas source and provide purified gas. The purification device (13) is configured to selectively operate in a first mode and a second mode, wherein the purified gas has a first purity level in the first mode and a second purity level in the second mode, the second purity level being greater than the first purity level, for example greater than or equal to 99.9999 mol%; - A filling pipe (11) configured to allow purified gas of the second purity grade to be transferred from the supply loop (4) to the circulation loop (5), the filling pipe (11) being equipped with a valve (10). - A control unit configured to control the valve (10) and the purification device (13) so as to: - When the purification device (13) is operating in the second mode, the purified gas enters the circulation loop (5); and / or -When the purification device (13) is operating in the first mode, the purified gas enters the liquefier (7). The control unit is configured to control the valve (10) and the purification device (13) when the purification device (13) is operating in the first mode to prevent purified gas from entering the circulation loop (5).

2. The apparatus (1) as described in the preceding claim, wherein the purification device (13) is configured to operate selectively in the following conditions: - The first mode, wherein the purification apparatus achieves the first purity level with a first yield; and - The second mode, wherein the purification device achieves the second purity level with a second yield, which is lower than the first yield.

3. The device (1) according to any one of the preceding claims, wherein the purification device (13) is configured to operate in the first mode for a first stage time and in the second mode for a second stage time, the second stage time being shorter than the first stage time, the stage times being particularly taken into account for a constant gas flow rate at the inlet of the purification device (13).

4. The apparatus (1) according to any one of the preceding claims, wherein the filling conduit (11) is in fluid communication with the supply circuit (4) and the circulation circuit (5), the filling conduit (11) being configured to allow the purified gas to be transferred into the circulation circuit (5), the purified gas being drawn from the supply circuit (4), particularly when the purified gas is drawn upstream of the heat exchanger (6), the purified gas being at an ambient temperature, for example between 5°C and 55°C, particularly between 10°C and 50°C, preferably between 15°C and 45°C.

5. The device (1) according to any one of the preceding claims is configured to allow the purified gas to enter the circulation loop (5) when the purification device (13) is operating in the second mode.

6. The device (1) according to any one of the preceding claims is configured to prevent the purified gas from entering the circulation loop (5) when the purification device (13) is operating in the first mode.

7. A liquefaction method using the apparatus (1) as described in any one of the preceding claims, comprising the following successive steps: - The purified gas (E2, E3) is supplied to the circulation loop (5), and the purification device (13) operates in the second mode, specifically the purified gas is introduced into the circulation loop (5) at a pressure between 15 bar and 40 bar - which is considered the pressure upstream of the valve (10) - and / or at a pressure between 5 bar and 15 bar - which is considered the pressure downstream of the valve (10); -Liquefaction (E4) is the gas purified by the purification device (13) operating in this first mode.

8. The method of claim 1, wherein the step of supplying (E2, E3) to the loop (5) comprises the following successive steps: - The purified gas is introduced into the circulation loop (5) (E2), and the valve (10) is specially configured to make the circulation loop (5) fluidly connected to the supply loop (4); - The circulating gas expands (E3) inside the circulating circuit (5), and the valve (10) is configured to fluidly isolate the circulating circuit (5) from the supply circuit (4) by means of an expansion member.

Images