Facility for liquefying a gas and liquefaction method

Abstract

The invention relates to a facility (1) for liquefying a gas, the facility comprising: a supply circuit (4) for supplying a gas to be liquefied, the circuit having an upstream end (2) that is intended to be connected to a gas source and a downstream end (3) for delivering a liquefied gas; a liquefier (7) comprising a heat exchanger (6) and a refrigerator (12) having a cycle for refrigerating a cycle gas, the refrigerator (12) comprising a cycle circuit (5) for circulating the cycle 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 deliver a purified gas.

Description

Gas liquefaction plant and liquefaction process

[0001] The present invention relates to a gas liquefaction installation and a liquefaction method using such an installation.

[0002] As is known per se, a gas liquefaction installation comprises a liquefier, part of the cold power of which is produced 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 less than 20K at atmospheric pressure, the cycle gas must drop to temperatures of the same order. This generally requires a cycle gas comprising mainly hydrogen and / or helium. This also requires that the cycle gas be of very high purity in order to avoid the crystallization of any impurities that could hinder the smooth running of the liquefaction process.

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

[0005] When the plant is first started up or when it is restarted, for example following a maintenance operation, such temperature levels cannot be reached quickly. The start-up sequence must therefore include a pre-cooling step and a step to stabilize the adsorption unit at an intermediate temperature in order to purify the gas by adsorption at cryogenic temperature to fill the refrigeration cycle with cycle gas of very high purity.

[0006] The problem is that this boot sequence significantly increases the installation boot time.

[0007] The present invention aims to effectively overcome these drawbacks by proposing an installation for liquefying a gas, the gas comprising in particular mainly hydrogen, the installation comprising: a supply circuit for 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 heat exchange with the supply circuit, the liquefier comprising a refrigerator with a cycle for refrigerating a cycle gas, in heat exchange with the heat exchanger, the refrigerator comprising a cycle circuit for circulating the cycle gas, the cycle circuit comprising a cycle gas compression mechanism and a cycle gas expansion mechanism;characterized in that the installation comprises:a purification device mounted in the supply circuit upstream of the liquefier, the purification device being configured to purify the gas from the gas source and provide a purified gas, the purification device being configured to operate selectively in a first mode in which the purified gas has a first degree of purity and in a second mode in which the purified gas has a second degree of purity, the second degree of purity being greater than the first degree of purity, the second degree of purity being for example greater than or equal to 99.9999 mol%;a filling line configured to allow the purified gas with the second degree of purity to be transferred into the cycle circuit from the supply circuit, the filling line being provided with a valve.;

[0008] Such a configuration makes it possible to reduce the start-up time of a gas liquefaction plant, which is particularly useful during the first start-up of such a plant or during start-up after a maintenance operation. This makes it possible to avoid, at the time of start-up, having to resort to a pre-cooling step and / or a step of stabilizing the plant at an intermediate temperature for the purification of the gas by adsorption at a cryogenic temperature for filling the cycle circuit with the cycle gas.

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

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

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

[0012] According to one embodiment, the gas to be liquefied and the cycle gas are of the same nature.

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

[0014] According to one embodiment, the cycle gas mainly comprises hydrogen, in particular having an impurity level of less than 1 ppm.

[0015] Alternatively, the gas to be liquefied comprises mainly helium and the cycle gas comprises mainly helium.

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

[0017] According to one embodiment, the purification device is configured to operate selectively: in the first mode in which it reaches the first degree of purity with a first efficiency; and in the second mode in which it reaches the second degree of purity with a second efficiency, the second efficiency being lower than the first efficiency.

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

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

[0020] According to one embodiment, the purification device operating in the first mode, the regulator is configured to maintain the degree of purity substantially constant regardless of the gas flow rate at the inlet of the purification device.

[0021] According to one embodiment, the purification device operating in the second mode, the regulator is configured to maintain the degree of purity substantially constant regardless of the gas flow rate at the inlet of the purification device.

[0022] According to one embodiment, the regulator is configured to regulate the phase time as a function of the gas flow rate at the inlet of the purification device.

[0023] According to one embodiment, the adsorption device comprises a pressure modulation adsorption unit comprising at least two adsorbers configured to operate alternately and each comprising at least one adsorbent bed comprising alumina or carbon or molecular sieve.

[0024] According to one embodiment, the purified gas enters the cycle circuit at an 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 the first degree of purity and a second adsorption device configured to achieve the second degree of purity.

[0026] According to one embodiment, the filling pipe is in fluid communication with the supply circuit and with the cycle circuit, the filling pipe being configured to allow the transfer of the purified gas into the cycle circuit, the purified gas being taken from the supply circuit, the purified gas being at an 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, in particular being taken upstream of the heat exchanger.

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

[0028] According to one embodiment, the installation is configured to allow the entry of the purified gas into the cycle circuit, when the purification device operates in the second mode.

[0029] According to one embodiment, the installation is configured to prevent the entry of purified gas into the cycle circuit, when the purification device operates in the first mode.

[0030] According to one embodiment, the installation comprises a control unit configured to control the valve and the purification device to allow: the purified gas to enter the cycle circuit, when the purification device operates in the second mode; and / or the purified gas to enter the liquefier, when the purification device operates in the first mode.

[0031] In one embodiment, the control unit is configured to control the valve and the purification device to prevent purified gas from entering the cycle circuit when the purification device is operating in the first mode.

[0032] The invention further relates to a liquefaction method using an installation as described above, the method comprising the following successive steps: supplying the cycle circuit with the purified gas, the purification device operating in the second mode, the purified gas being introduced in particular into the cycle circuit with a pressure of between 15 bara and 40 bara, the pressure being considered upstream of the valve and / or with a pressure of between 5 bara and 15 bara, the pressure being considered downstream of the valve; liquefaction of the purified gas by the purification device operating in the first mode.

[0033] According to one embodiment, the step of supplying the cycle circuit with the purified gas is implemented while the purified gas passes through the heat exchanger without its temperature being significantly modified between upstream and downstream of the heat exchanger.

[0034] According to one embodiment, at the step of supplying the cycle circuit, the purified gas enters the cycle circuit at an 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 the cycle circuit comprises the following successive steps: introduction of purified gas into the cycle circuit, the valve being configured in particular to put the cycle circuit into fluid communication with the supply circuit; expansion of the cycle gas inside the cycle circuit, in particular by means of an expansion member, the valve being configured to fluidically isolate the cycle circuit from the supply circuit.

[0036] According to one embodiment, the method comprises alternating a plurality of times the succession of steps of introduction of purified gas and expansion of the cycle gas.

[0037] This ensures the correct content of the cycle gas at all points in the cycle circuit thanks to a dilution phenomenon.

[0038] According to one embodiment, the expansion member comprises an evacuation pipe comprising for example a valve configured to allow the evacuation of a portion of the cycle gas via the evacuation pipe.

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

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

[0041] The invention will be better understood by reading the following description and examining the accompanying figures. These figures are given only for illustrative purposes but in no way limit the invention.

[0042] is a schematic representation of an installation according to the invention; and

[0043] is a schematic representation of the steps of a method according to the invention.

[0044] Identical, similar, or analogous elements retain the same reference from one figure to another.

[0045] It represents a gas liquefaction installation 1.

[0046] The installation 1 comprises a supply circuit 4 for 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 a liquefied gas.

[0047] In the example of the, the gas to be liquefied mainly contains hydrogen.

[0048] The source may include an electrolyser or a gas network for example.

[0049] The installation can operate with other gases, such as helium.

[0050] The installation 1 further comprises a liquefier 7 comprising, preferably arranged in at least one cold box, at least one heat exchanger 6 in heat exchange with the supply circuit 4. The liquefier 7 comprises a refrigerator 12 with a cycle for refrigerating a cycle gas, in heat exchange with the heat exchanger 6.

[0051] The cycle gas is of the same nature 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 contains 1 ppm of impurities or less.

[0052] The refrigerator 12 includes a cycle circuit 5 for the circulation of the cycle gas.

[0053] The cycle circuit 5 comprises a cycle gas compression mechanism 8, a cycle gas cooling system, a cycle gas expansion mechanism 9 and a cycle gas reheating system before restarting the cycle. In operation, the cycle circuit subjects the cycle gas to a thermodynamic cycle which brings it to a cryogenic temperature at at least one cold end (cold end(s)).

[0054] This cold power is transferred to the gas in the feed circuit to be cooled / liquefied by heat exchange in one or more heat exchangers, in particular one or more counter-current heat exchangers ensuring 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 installation 1 further comprises a purification device 13 mounted in the supply circuit 4 upstream of the liquefier 7.

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

[0058] The purification device 13 is further configured to operate selectively: in a first mode in which the purified gas has a first degree of purity, and in a second mode in which the purified gas has a second degree of purity.

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

[0060] The second degree of purity is higher than the first degree of purity.

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

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

[0063] The installation 1 further comprises a filling line 11 configured to allow the purified gas with the second degree of purity to be transferred into the cycle circuit 5 from the supply circuit 4, the filling line 11 being provided with a valve 10.

[0064] Preferably, the filling line 11 is configured to take the purified gas with the second degree of purity, in the supply circuit 4, upstream of the liquefier 7.

[0065] Alternatively, the filling line 11 is configured to take the purified gas with the second degree of purity, from the liquefier 7, for example upstream of the refrigerator 12.

[0066] According to one embodiment, the filling line 11 is configured to take the purified gas with the second degree of purity, downstream of a cryogenic purification device of the liquefier 7, the purified gas being taken at ambient temperature. In this embodiment, the cryogenic purification device of the liquefier 7 is arranged downstream of the refrigerator 12, the cryogenic purification device comprising for example a temperature modulation adsorption unit.

[0067] Thus, in this embodiment, the purified gas enters the cryogenic purification device being purified with the second degree of purity.

[0068] In the example of the, 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 operate selectively: in the first mode in which it achieves the first degree of purity with a first efficiency; and in the second mode in which it achieves the second degree of purity with a second efficiency, the second efficiency being lower than the first efficiency.

[0070] The purification device 13 is configured to operate in the first mode with a first phase time and to operate in the second mode with a second phase time, 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 rate at the inlet of the purification device 13, that is to say for a constant feed flow rate, in particular for a constant feed gas flow rate.

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

[0073] Adsorption units, for example pressure swing adsorption units (also called PSA units for "Pressure Swing Adsorption"), are commonly used for the separation and / or purification of feed gases, particularly in the fields of hydrogen, helium, carbon dioxide production, drying, separation of air constituents, etc.

[0074] Generally speaking, a PSA unit consists of several adsorbers which follow, with a time shift, an operating cycle, subsequently called for convenience the "PSA cycle", which is distributed uniformly into as many phase times as there are adsorbers in operation, and which is formed of basic stages, namely the stages: adsorption at substantially high cycle pressure; co-current depressurization, generally from the high cycle pressure; counter-current depressurization, generally down to the low cycle pressure; elution at substantially the low cycle pressure; and repressurization, from the low cycle pressure to the high cycle pressure.

[0075] Cocurrent depressurization typically includes one or more equilibration stages and at least one feed-purge stage that provides elution gas.

[0076] Repressurization typically includes the corresponding equilibration steps and a final repressurization with production gas or elution gas.

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

[0078] The main operating constraint of a PSA unit in steady state is the product purity level. Under this operating condition, the processing performance of a PSA unit is then generally optimized either to maximize the yield (i.e. the extraction efficiency which is equal to the quantity of gas produced divided by the quantity of this gas present in the feed gas), or to minimize the energy consumed.

[0079] This gives a nominal operating cycle for the PSA unit, determined directly as a function of the nominal operating conditions (feed gas flow rate, treated gas flow rate, feed gas composition, unit operating temperature, pressures, etc.). In the first operating mode, the adsorption device is thus in nominal operating conditions.

[0080] When operating conditions deviate from the nominal conditions, for example when the adsorption device is in the second mode, one solution is to regulate the operation of the PSA unit by adjusting one or more parameters of the nominal cycle. Two regulations that fall under this approach are: "capacity" regulation, which consists of modifying the duration of the cycle phase time according to the variation of the feed gas flow rate; and "purity control" regulation, which consists of modifying this phase time according to the purity of the gas treated.

[0081] Here it is appropriate to define what is meant by cycle time and phase time (or more simply phase).

[0082] As described above, an adsorber will therefore begin an adsorption period until it is loaded with the constituent(s) to be stopped at high pressure and will then be regenerated by depressurization and extraction of the adsorbed compounds before being restored to begin a new adsorption period. The adsorber has then completed a "pressure cycle" and the very principle of the PSA process is to chain these cycles one after the other; it is therefore a cyclic process. The time it takes for an adsorber to return to its 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. We therefore have the relationship:

[0083] Phase time = cycle time / Number of adsorbers and we see that the number of phases is equal to the number of adsorbers.

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

[0085] In practice, there are a large number of possibilities for achieving regulation (capacity and / or purity) which result in the PSA operating under predetermined purity and efficiency conditions.

[0086] Regulator actions need to be adjusted to ensure that purity will be maintained relative to a desired target value.

[0087] The filling line 11 is in fluid communication with the supply circuit 4 and with the cycle circuit 5. The filling line 11 is configured to allow the transfer of the purified gas into the cycle circuit 5, the purified gas being taken from the supply circuit 4, the purified gas being at an 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, in particular being taken upstream of the heat exchanger 6.

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

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

[0090] Valve 10 is configured to allow or prevent the entry of purified gas into cycle circuit 5.

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

[0092] The installation 1 is further configured to prevent the entry of purified gas into the cycle circuit 5, when the purification device 13 operates in the first mode.

[0093] The installation 1 comprises a control unit configured to control the valve 10 and the purification device 13 to allow: the purified gas to enter the cycle circuit 5, when the purification device 13 operates in the second mode; and / or the purified gas to enter the liquefier 7, when the purification device 13 operates in the first mode.

[0094] 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.

[0095] It represents a liquefaction process using a plant 1 as described above.

[0096] The method comprises the following successive steps: supply E2, E3 of the cycle circuit 5 with the purified gas, the purification device 13 operating in the second mode, the purified gas being introduced in particular into the cycle circuit 5 with a pressure of between 15 bara and 40 bara, the pressure being considered upstream of the valve 10 and / or with a pressure of between 5 bara and 15 bara, the pressure being considered downstream of the valve 10; liquefaction E4 of the purified gas by the purification device 13 operating in the first mode.

[0097] In an exemplary implementation of the method, during the feed step E2, E3, the liquefier 7 is stopped, that is to say that the liquefier is for example at a temperature higher than its operating temperature. The feed step E2, E3 can be implemented while the cycle circuit is at least partially emptied of its cycle gas.

[0098] The method preferably comprises a step E1 of inerting the cycle circuit 5 prior to the step E2, E3 of supplying the cycle circuit 5.

[0099] The inerting step E1 of the cycle circuit 5 comprises a step of injecting an inerting gas such as nitrogen into the cycle circuit 5.

[0100] The supply step E2, E3 of the cycle circuit 5 comprises the following successive steps: introduction E2 of purified gas into the cycle circuit 5, the valve 10 being configured in particular to put the cycle circuit 5 into fluid communication with the supply circuit 4; expansion E3 of the cycle gas inside the cycle circuit 5, in particular by means of an expansion member, the valve 10 being configured to fluidly isolate the cycle circuit 5 from the supply circuit 4.

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

[0102] Alternatively or in combination, the method comprises a step E2, E3 of supplying the cycle circuit 5 with gaseous hydrogen having a degree of purity at least equal to 99.9999 mol%, said gaseous hydrogen coming for example from a dedicated source such as a network, or from a tank of vaporized pressurized liquid hydrogen.

Claims

Installation (1) for liquefying a gas, the gas comprising in particular mainly hydrogen, the installation (1) comprising: a supply circuit (4) for 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 a liquefied gas; a liquefier (7) comprising at least one heat exchanger (6) in heat exchange with the supply circuit (4), the liquefier (7) comprising a refrigerator (12) with a refrigeration cycle of a cycle gas, in heat exchange with the heat exchanger (6), the refrigerator (12) comprising a cycle circuit (5) for circulating the cycle gas, the cycle circuit (5) comprising a compression mechanism (8) for the cycle gas and an expansion mechanism (9) for the cycle gas;characterized in that the installation (1) comprises: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 provide a purified gas, the purification device (13) being configured to operate selectively in a first mode in which the purified gas has a first degree of purity and in a second mode in which the purified gas has a second degree of purity, the second degree of purity being greater than the first degree of purity, the second degree of purity being for example greater than or equal to 99.9999 mol%;a filling line (11) configured to allow the purified gas with the second degree of purity to be transferred into the cycle circuit (5) from the supply circuit (4), the filling line (11) being provided with a valve (10);a control unit configured to control the valve (10) and the purification device (13) to allow:the purified gas to enter the cycle circuit (5), when the purification device (13) operates in the second mode; and / orthe purified gas to enter the liquefier (7), when the purification device (13) operates in the first mode;the control unit being 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) operates in the first mode.; Installation (1) according to the preceding claim, the purification device (13) being configured to operate selectively: in the first mode in which it reaches the first degree of purity with a first yield; and in the second mode in which it reaches the second degree of purity with a second yield, the second yield being lower than the first yield. Installation (1) according to one of the preceding claims, the purification device (13) being configured to operate in the first mode with a first phase time and to operate in the second mode with a second phase time, the second phase time being less than the first phase time, the phase times being considered in particular for a constant flow rate of gas at the inlet of the purification device (13). Installation (1) according to one of the preceding claims, the filling pipe (11) being in fluid communication with the supply circuit (4) and with the cycle circuit (5), the filling pipe (11) being configured to allow the transfer of the purified gas into the cycle circuit (5), the purified gas being taken from the supply circuit (4), the purified gas being at an 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, in particular being taken upstream of the heat exchanger (6). Installation (1) according to one of the preceding claims, configured to allow the entry of the purified gas into the cycle circuit (5), when the purification device (13) operates in the second mode. Installation (1) according to one of the preceding claims, configured to prevent the entry of the purified gas into the cycle circuit (5), when the purification device (13) operates in the first mode. Liquefaction method using an installation (1) according to one of the preceding claims, comprising the following successive steps: supplying (E2, E3) the cycle circuit (5) with the purified gas, the purification device (13) operating in the second mode, the purified gas being introduced in particular into the cycle circuit (5) with a pressure of between 15 bara and 40 bara, the pressure being considered upstream of the valve (10) and / or with a pressure of between 5 bara and 15 bara, the pressure being considered downstream of the valve (10); liquefaction (E4) of the purified gas by the purification device (13) operating in the first mode. Method according to the preceding claim, the step of supplying (E2, E3) the cycle circuit (5) comprising the following successive steps: introduction (E2) of purified gas into the cycle circuit (5), the valve (10) being in particular configured to put the cycle circuit (5) into fluid communication with the supply circuit (4); expansion (E3) of the cycle gas inside the cycle circuit (5), in particular by means of an expansion member, the valve (10) being configured to fluidically isolate the cycle circuit (5) from the supply circuit (4).

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