Plant and method for producing hydrogen at cryogenic temperatures - Patents.com

Abstract

A plant for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures, comprising an electrolyzer (2) having an oxygen outlet and a hydrogen outlet, a hydrogen circuit (3) to be cooled, the hydrogen circuit (3) comprising an upstream end connected to the hydrogen outlet and a downstream end connected to a member (23) for cooling and / or collecting liquefied hydrogen, the plant (1) also comprising a set of heat exchangers (4, 5, 6, 7, 8) in heat exchange with the hydrogen circuit (3) to be cooled, the plant (1) further comprising at least one cooling device (9, 10) in heat exchange with at least a part of the set of heat exchangers (4, 5, 6, 7, 8). 0), wherein the hydrogen circuit (3) to be cooled comprises a system (18) for expanding a hydrogen stream and at least one hydrogen compressor (19) upstream of the hydrogen stream expansion system (18), the hydrogen stream expansion system (18) comprising at least one expansion turbine (18), wherein the at least one expansion turbine (18) and the at least one compressor (19) are coupled to the same rotating shaft (20) for transferring expansion action from the pressurized hydrogen stream to the compressor (19) for compressing the hydrogen stream upstream of the turbine.

Description

[Technical field]

[0001] The present invention relates to a plant and a method for producing hydrogen at cryogenic temperatures.

[0002] The invention more particularly relates to a plant for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures, comprising an electrolyser provided with an oxygen outlet and a hydrogen outlet, a hydrogen circuit to be cooled comprising an upstream end connected to the hydrogen outlet and a downstream end intended to be connected to a member for cooling and / or collecting liquefied hydrogen, the plant comprising a set of heat exchangers in heat exchange with the hydrogen circuit to be cooled, the plant comprising at least one cooling device in heat exchange with at least a part of the set of heat exchangers, the hydrogen circuit to be cooled comprising a hydrogen flow expansion system and at least one hydrogen compressor upstream of the hydrogen flow expansion system, the hydrogen flow expansion system comprising at least one expansion turbine. [Background technology]

[0003] The two main methods for producing hydrogen (molecular hydrogen, H2) are chemical production by electrolysis and steam methane reforming (SMR).

[0004] In the case of electrolysis, water molecules are split, which produces hydrogen on the one hand and oxygen (O2) on the other hand. Regarding electrolysis technologies, there are three main types: "PEM" (Proton Exchange Membrane), "Alkaline" and "Solid Oxide".

[0005] These techniques operate optimally at near atmospheric pressure due to the energy performance and efficiency of the chemical reaction of splitting water molecules.

[0006] PEM technology makes it possible to operate at high pressures without significantly affecting the energy performance of the electrolysis: for example, in the prior art, electrolysers of several megawatts of power can produce hydrogen and oxygen at 30 absolute pressure at room temperature.

[0007] Although described, for example, in documents US Pat. No. 4,530,744 or US Pat. No. 1,035,1962, the use of oxygen produced under high pressure is not generally practiced industrially. Summary of the Invention [Problem to be solved by the invention]

[0008] These known solutions are, however, of little industrial interest in hydrogen liquefaction processes, since they are not energy efficient.

[0009] One object of the present invention is to overcome all or some of the above-mentioned shortcomings of the prior art. [Means for solving the problem]

[0010] For this purpose, the plant according to the invention, further complying with the general definition given in the preamble above, is essentially characterized in that said at least one expansion turbine and said at least one compressor are coupled to the same rotating shaft, in order to transmit to the compressor the function of expanding a hydrogen flow under pressure in order to compress the hydrogen flow upstream of the turbine.

[0011] Such a plant makes it possible to efficiently utilise the pressure of the hydrogen produced by the electrolyser (especially at high pressures) for pre-cooling or cooling a flow of hydrogen to cryogenic temperatures.

[0012] This solution makes it possible to reduce the investment costs for such plants, in particular by eliminating or reducing the cooling of the hydrogen to be liquefied to 80-130 K. This makes it possible, for example, to reduce or eliminate the need for liquid nitrogen pre-cooling systems with nitrogen compression stations as found in the prior art.

[0013] The solution makes it possible to significantly reduce the corresponding operating costs for such plants (e.g. specific energy, e.g. 30% less in kWh / kg liquefied H2).

[0014] Furthermore, embodiments of the invention may include one or more of the following features: - the assembly including the expansion turbine and the compressor coupled to the same rotating shaft is a passive mechanical system, i.e. does not include a power unit for driving the rotating shaft other than the hydrogen flow, or is an active mechanical system, i.e. includes a power unit for driving the rotating shaft; the hydrogen circuit comprises several hydrogen compressors arranged in series and / or in parallel upstream of a hydrogen flow expansion system, which comprises a plurality of expansion turbines arranged in series and / or in parallel, each of the compressors being coupled to a rotating shaft to which at least one turbine is likewise coupled, the hydrogen circuit to be cooled comprises several compressors arranged in series upstream of a hydrogen flow expansion system, which comprises a number of expansion turbines arranged in series, the compressors and turbines being coupled in pairs to the respective rotating shafts, the turbines are arranged in series in a hydrogen circuit to be cooled, the hydrogen circuit comprising a separate respective portion for heat exchange between at least a part of the set of heat exchangers and the hydrogen flow at the outlet of each turbine, the set of heat exchangers comprises several heat exchangers arranged in series and exchanging heat with the hydrogen circuit to be cooled between an upstream end and a downstream end of the hydrogen circuit to be cooled, - the plant comprises a first cooling device and a second cooling device in heat exchange with the hydrogen circuit to be cooled, the first cooling device in heat exchange with a first group of heat exchangers of a set of heat exchangers and the second cooling device in heat exchange with a second group of heat exchangers, the first group of heat exchangers being located upstream of the second group of heat exchangers in the hydrogen circuit to be cooled, the first cooling device comprising a hydrogen flow expansion system to ensure pre-cooling of the hydrogen circuit before the additional cooling performed by the second cooling device, - the second cooling device includes a cycle gas refrigeration cycle refrigeration apparatus, the refrigeration apparatus of the second cooling device including, arranged in series in a cycle circuit, a mechanism for compressing the second cycle gas, a member for cooling the second cycle gas, a mechanism for expanding the second cycle gas, and a member for heating the expanded second cycle gas; - the hydrogen flow expansion system is located in the part of the hydrogen circuit to be cooled that exchanges heat with the first group of heat exchangers; - a hydrogen flow expansion system is located in the part of the hydrogen circuit to be cooled that exchanges heat with the second group of heat exchangers; - the plant comprises a hydrogen cooling system at the outlet of at least some of the compressors, the plant includes an oxygen circuit including an upstream end connected to an oxygen outlet and a downstream end connected to a recovery system; - the oxygen circuit comprises an oxygen flow expansion system and at least one heat exchange between the expanded oxygen flow and a hydrogen circuit to be cooled, the oxygen circuit comprises at least one oxygen compressor arranged upstream of the oxygen flow expansion system, the oxygen flow expansion system comprises an expansion turbine, said expansion turbine and said compressor being coupled to the same rotating shaft in order to transmit to the compressor the function of expanding the oxygen flow under pressure in order to compress the oxygen flow upstream of the turbine, - the assembly with the expansion turbine and the compressor coupled to the same rotating shaft is a passive mechanical system, i.e. does not include a power unit for driving the rotating shaft apart from the oxygen flow, or is an active mechanical system, i.e. includes a power unit for driving the rotating shaft; the oxygen circuit comprises several oxygen compressors arranged in series and / or in parallel upstream of an oxygen flow expansion system, the oxygen flow expansion system comprising a plurality of expansion turbines, each of the compressors being coupled to a rotating shaft to which at least one turbine is also coupled, the oxygen circuit comprises several compressors arranged in series and upstream of an oxygen flow expansion system, the oxygen flow expansion system comprising a plurality of expansion turbines, the compressors and turbines being coupled in pairs to respective rotating shafts, - the turbines are arranged in series in an oxygen circuit, the oxygen circuit comprising a separate respective section for heat exchange between a set of heat exchangers and the oxygen flow at the outlet of each turbine, the plant comprises an oxygen cooling system at the outlet of at least some of the compressors, the plant includes a third cooling device in heat exchange with at least a portion of the first group of heat exchangers.

[0015] The invention also relates to a method for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures using a plant according to any one of the preceding features, the method comprising the steps of supplying a hydrogen flow, e.g. at a pressure of 15 to 150 bar, by an electrolyser to an upstream end of a hydrogen circuit, supplying an oxygen flow, e.g. at a pressure of 15 to 150 bar, by an electrolyser to an upstream end of an oxygen circuit, the method comprising the steps of compressing and then expanding the hydrogen flow, the expansion being carried out by at least one turbine coupled to a shaft which in turn is coupled to at least one compressor ensuring compression of the hydrogen flow before its expansion.

[0016] The invention may also relate to any alternative device or method comprising any combination of the above or below features falling within the scope of the claims.

[0017] Other particular features and advantages will become apparent from a reading of the following description, taken in conjunction with the drawings, in which: [Brief description of the drawings]

[0018] [Figure 1] 1 shows a schematic partial view illustrating a first embodiment of the structure and operation of a plant according to the invention; [Diagram 2] 3 shows a schematic partial view illustrating a second embodiment of the construction and operation of a plant according to the invention; [Diagram 3] 3 shows a schematic partial view illustrating a third embodiment of the construction and operation of a plant according to the invention; [Figure 4] 4 shows a schematic partial view illustrating a fourth embodiment of the construction and operation of a plant according to the invention; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The illustrated hydrogen production plant 1 is a device for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures.

[0020] This plant 1 preferably comprises an electrolyser 2 of the "PEM" (Proton Exchange Membrane) type operating at high pressure, ie between 15 and 150 bar, for example equal to 30 bar, for producing gaseous hydrogen and oxygen.

[0021] The electrolytic cell 2 has an oxygen outlet and a hydrogen outlet.

[0022] The plant 1 comprises a hydrogen circuit 3 (or pipe) to be cooled, having an upstream end connected to the hydrogen outlet of the electrolyser 2 and a downstream end intended to be connected to a member 23 for cooling and / or collecting the liquefied hydrogen (e.g. for storage and / or user use).

[0023] The plant 1 comprises a set of heat exchangers 4, 5, 6, 7, 8 exchanging heat with a hydrogen circuit 3 to be cooled in order to reach a temperature favourable for the liquefaction of hydrogen.

[0024] As shown, at least one separate heat exchanger 25 may be provided at the outlet of the electrolyser 2 for cooling the hydrogen flow (e.g. by heat exchange with a heat transfer fluid such as water or air) to bring it to a temperature close to ambient temperature. The electrochemical reaction for the production of hydrogen by electrolysis typically results in a temperature increase of several tens of degrees.

[0025] The plant 1 further comprises at least one cooling device 9,10 in heat exchange with at least a part of the set of heat exchangers 4,5,6,7,8.

[0026] Furthermore, the plant 1 may include an oxygen circuit 190 (at least one pipe) comprising an upstream end connected to the oxygen outlet of the electrolyzer 2 and a downstream end. The downstream end may for example be connected to a device 27 for collecting and / or using the oxygen. This collection device may for example include an oxygen liquefaction system, an oxygen (pre)cooling system, a system for compressing and packaging oxygen in cylinders or for pressurized storage, a combustion system, a ventilation system, etc.

[0027] As shown, the hydrogen circuit 3 to be cooled comprises a hydrogen flow expansion system 18 and at least one hydrogen compressor 19 upstream of the hydrogen flow expansion system 18. Preferably, all (the entire) of the hydrogen flow to be cooled / liquefied is expanded in the turbine expansion system 18. In other words, all of the flow to be cooled / liquefied is expanded in one or more turbines 18, and this expanded flow is cooled by a cooling device, for example in a set of exchangers, in order to be cooled. The hydrogen flow expansion system 18 comprises at least one hydrogen flow expansion turbine 18, said expansion turbine 18 and said compressor 19 coupled to the same rotating shaft 20 in order to transmit to the compressor 19 the action of expanding the hydrogen flow under pressure in order to compress the hydrogen flow upstream of the turbine 18. The assembly with the expansion turbine 18 and the compressor 19 coupled to the same rotating shaft 20 is preferably a passive mechanical system, i.e. it does not comprise a power unit for driving the rotating shaft 20 other than the hydrogen flow.

[0028] As shown, the hydrogen circuit 3 preferably includes several hydrogen compressors 19 arranged in series upstream of a hydrogen flow expansion system 18 .

[0029] The hydrogen flow expansion system preferably includes an equal number of serially arranged expansion turbines 18, with each of the compressors 19 coupled to a rotating shaft 20 to which at least one turbine 18 is also coupled. For example, the compressors 19 and turbines are associated in pairs with separate respective rotating shafts 20 (e.g., a first upstream compressor 19 coupled to a first upstream turbine 20, etc.).

[0030] As shown, at the outlet of each turbine 18, the expanded hydrogen flow may optionally pass through a separate heat exchanger from upstream to downstream of a first group of heat exchangers 4, 5, 6, 7, respectively, to ensure pre-cooling of the hydrogen.

[0031] It becomes possible to utilize the pressure of these expansion stage 18 hydrogen flows (with or without intermediate cooling), which can replace or complement the pre-cooling mentioned above.

[0032] This cold provided without energy consumption makes it possible to reduce the work that would be input to cool the hydrogen to its target temperature (e.g., via the second cooling device 10, as described in more detail below).

[0033] Of course, this method of expanding and utilizing the pressure of the hydrogen flow is not limited to this example: the expansion of hydrogen from ambient temperature to a given pre-cooling temperature can thus be performed in several stages of radial expansion or in a single stage of expansion, for example via a volumetric expansion valve, in particular to reduce costs.

[0034] This pre-cooling of the hydrogen may be completed downstream of the circuit 3 by a second cooling device 10 in heat exchange with the hydrogen circuit 3 to be cooled.

[0035] As shown, for example, the first cooling device 9 mentioned above (expansion of hydrogen with pre-compression) is made to exchange heat with the first upstream group of heat exchangers 4 , 5 , 6 , 7 of the set of heat exchangers 4 , 5 , 6 , 7 , 8 .

[0036] The second cooling device 10 may itself be brought into heat exchange with a second downstream group of heat exchangers 8 (here represented by a single heat exchanger but several heat exchangers in series and / or parallel are also envisaged).

[0037] After this pre-cooling of the hydrogen circuit 3, for example to a temperature of 80-100 K, the second cooling device 10 provides additional cooling of the hydrogen, for example to approximately 20 K, in order to liquefy the hydrogen.

[0038] As shown diagrammatically, the second cooling device 10 may include a cycle gas refrigeration cycle refrigeration device (e.g. containing hydrogen or helium, or neon, or an optimal combination of the three) to improve the efficiency of the device 10 for final cooling of hydrogen. Conventionally, this refrigeration device of the second cooling device 10 may include, arranged in series in a cycle circuit, a mechanism 15 (one or more compressors) for compressing the second cycle gas, a member 24 (e.g. a heat exchanger) for cooling the second cycle gas, a mechanism 16 (a turbine and / or an expansion valve) for expanding the second cycle gas, and a member 8 for heating the expanded second cycle gas (a heat exchanger and in particular a heat exchanger for exchanging heat with the hydrogen flow to be cooled).

[0039] As shown in FIG. 1, the plant 1 may include a third cooling device 17 in heat exchange with at least some of the heat exchangers 4, 5, 6, 7. This third cooling device 17 (optional) may include a cooling fluid loop (e.g. countercurrently circulating liquid nitrogen, liquefied natural gas, oxygen, etc.) that provides cold to the heat exchangers 4, 5, 6, 7 to also ensure some of the hydrogen pre-cooling.

[0040] Pre-cooling, carried out via hydrogen expansion as described above, makes it possible in particular to reduce (and in particular to halve) the consumption of such cooling fluids (eg involving liquid nitrogen or gas mixing cycles, etc.).

[0041] As shown in FIG. 2, the oxygen circuit 190 may optionally include an oxygen flow expansion system 13 and at least one heat exchange between the expanded oxygen flow (which is therefore cooled by expansion) and the hydrogen circuit 3 to be cooled. This heat exchange may be used in particular to pre-cool the hydrogen in its refrigeration and / or liquefaction process.

[0042] As mentioned above, the oxygen circuit 190 may include at least one oxygen compressor 12 disposed upstream of an oxygen flow expansion system 13. The oxygen flow expansion system 13 includes at least one expansion turbine 13. The oxygen expansion turbine 13 and the upstream oxygen compressor 12 are coupled to the same rotating shaft 14 for transmitting the action of expansion of the oxygen flow under pressure to the compressor 12 for compressing the oxygen flow upstream of the expansion turbine 13.

[0043] The assembly comprising the expansion turbine 13 and the compressor 12 coupled to the same rotating shaft 14 is preferably a passive mechanical system, i.e. it does not include a power device for driving the rotating shaft 14 other than the oxygen flow. The expansion turbine 13 is therefore mechanically braked by the compressor 12 which is also coupled to the same shaft 14. Naturally, this is not limiting and therefore it may be envisaged to provide a system with a power device (where appropriate to improve the efficiency of the plant) whose shaft is coupled to the turbine and the compressor.

[0044] As in the case of hydrogen, the transfer of this work for the oxygen flow results in a "turboboosting" which therefore consists of integrating one or more cryogenic expansion turbines 13 whose working fluid is the oxygen previously produced by the electrolyzer 2. The system for braking these turbines is one or more compressors 12 coupled to the same shaft 14. This makes it possible to inject an work that expands this gas flow as an upstream flow booster at ambient temperature.

[0045] As shown, in order to transfer this generated cold energy to the hydrogen flow, it is possible to integrate a specific passage independent of the main hydrogen flow in one or more exchangers 4, 5, 6, 7 to allow the cooled oxygen to exchange cold / heat energy with the hydrogen to be cooled.

[0046] The integration of the expanded oxygen flow in the sequence of heat exchangers 4, 5, 6, 7 of the hydrogen refrigeration / liquefaction system makes it possible, among other things, to reduce its volume. The costs are also reduced by sharing the heat exchange lines in the same equipment. Furthermore, it makes it possible to use an intermediate heat transfer fluid, typically inert, helium, nitrogen, argon, etc., so as not to run the risk of contacting hydrogen and oxygen in the same equipment.

[0047] For example, the hydrogen is cooled to a target temperature, for example of about 20 K. To this end, the hydrogen flow may be precooled from the temperature at the outlet of the electrolyser to a temperature between 220 and 90 K, and for example of about 100 K.

[0048] Before expansion (downstream of compressor 12), the oxygen may be brought to a pressure of 15-150° C. and to a temperature close to ambient temperature, thanks to exchangers for cooling between (and then at) the compression stages with a cold source, such as industrial water. All or part of this pre-cooling may be performed via the expanded oxygen as described above.

[0049] The inventors have determined that this use of overpressure oxygen and / or hydrogen pressure, in particular for a plant producing 25 tons of hydrogen daily to be cooled from 300K to 85K, makes it possible to save approximately 45% in liquid nitrogen consumption (savings in electrical energy consumed to produce liquid nitrogen).

[0050] Of course, this advantage remains valid in the case of the use of a separate pre-cooling device (eg, a nitrogen cycle cooler).

[0051] If the pressure of the oxygen flow at the outlet of the electrolyser 2 is approximately 70 bar, then for the function of pre-cooling the hydrogen flow, operating cost savings of approximately 50-70% can be achieved.

[0052] As shown, the oxygen circuit 190 may include several oxygen compressors 12 arranged in series upstream of an oxygen flow expansion system 13. The oxygen flow expansion system includes a number of expansion turbines 13, each of the compressors 12 coupled to a rotating shaft 14 to which at least one turbine 13 is also coupled.

[0053] For example, all or some of these elements may be integrated into a (eg, single) turbomachine having n turbines and n compressors mounted on either side of the same shaft.

[0054] In the illustrated non-limiting example, the oxygen circuit 190 includes an equal number of upstream serially arranged compressors 12 with downstream serially arranged expansion turbines 13, the compressors and turbines 13 being coupled in pairs to respective rotating shafts 14. For example, a first turbine (upstream) is coupled to a first compressor (upstream), a second turbine is coupled to a second compressor, etc.

[0055] Of course, the invention is not limited to this configuration including only a turbo booster, but it is possible to provide this type of turbo booster and, additionally, one or more conventional turbines (the same applies to the hydrogen flow compression / expansion system described above).

[0056] Preferably, an oxygen cooling system 21 is provided at the outlet of at least some of the compressors 12. For example, a cooler (a cooling exchanger with a fluid, e.g. air or water) may be inserted at the outlet of each compressor to improve the isothermal efficiency of each compression stage.

[0057] As in the embodiment of [Figure 1], the set of heat exchangers 4, 5, 6, 7, 8 therefore preferably comprises several heat exchangers arranged in series and exchanging heat with the hydrogen circuit 3 to be cooled between the upstream and downstream ends of the hydrogen circuit 3 to be cooled.

[0058] Moreover, preferably, after leaving the series turbine 13, the oxygen flow passes through heat exchangers 4, 5, 6, 7 in series, from upstream to downstream, respectively, which pass through the exchangers thus resulting in cooling or heating of the oxygen flow after each expansion stage (cooling or heating depending on the pressure conditions of the oxygen flow and the temperatures of the associated exchangers 4, 5, 6, 7). In particular, when the pressure drop of the oxygen flow at the end of the turbine is relatively large, the heat exchange with the heat exchangers 4, 5, 6, 7 located at the outlet tends to heat the flow (with the aim of thermodynamic optimization of the hydrogen flow refrigeration cycle), whereas when the pressure drop is relatively low, the pass through the heat exchangers 4, 5, 6, 7 located at the outlet tends to cool the flow (as shown in FIG. 2).

[0059] [Figure 2] thus shows another possible embodiment, which differs from that of [Figure 1] essentially in that it additionally includes a system for utilizing the pressure of the oxygen flow, and for the sake of brevity, the same elements are not described again and are indicated with the same reference numbers (as in the subsequent embodiments).

[0060] In the embodiments of [Figures 1] and [Figure 2], the hydrogen flow compressor 19 is located upstream of the first group of exchangers 4, 5, 6, 7 for pre-cooling (for example to ambient temperature) and the turbine 18 in the pre-cooling section (heat exchange at the outlet of the turbine 18 with these pre-cooling heat exchangers 4, 5, 6, 7). This arrangement is not limiting.

[0061] Thus, the embodiment of [Fig. 3] differs essentially from that of [Fig. 2] in that the hydrogen flow compressor 19 is located downstream of the first group of pre-cooling exchangers 4, 5, 6 and upstream of the second group of cooling exchangers 8 (in the part of the circuit 3 where the hydrogen is already pre-cooled). In other words, the compression of the hydrogen flow is carried out after pre-cooling and before the final cooling. This makes it possible to obtain higher compression ratios with the very light H2 molecule (molar mass of about 2 g / mol). Moreover, the expansion turbine 18 is inserted in the cooling section (heat exchange at the outlet of the turbine 18 with these heat exchangers 8 of the second group).

[0062] It should also be noted that the embodiment of [Figure 3] illustrates the optional possibility (which may also be applied to the other embodiments) of providing cooling 26 of the oxygen flow leaving the electrolyzer 2 upstream of the first compressor 12.

[0063] In the embodiment of [Figure 2], the hydrogen flow compressor 19 is located upstream of the first group of pre-cooling exchangers 4, 5, 6, 7 and the turbine in the pre-cooling section (heat exchange at the outlet of the turbine 18 with these pre-cooling heat exchangers 4, 5, 6, 7).

[0064] Thus, in the embodiment of [Figure 3], the compression of the hydrogen flow is carried out after pre-cooling and before cooling, and furthermore, an expansion turbine 18 is inserted in the cooling section (heat exchange at the outlet of the turbine 18 with these heat exchangers 8 of the second group).

[0065] The embodiment of [Figure 4] differs from that of [Figure 3] essentially in that a hydrogen flow compressor 19 is located upstream of the first group of pre-cooling exchangers 4, 5, 6. In other words, compression of the hydrogen flow is performed before pre-cooling (e.g. to room temperature), while expansion is performed in the cold cooling section (after pre-cooling).

[0066] As shown diagrammatically in [Figure 4] (which may also apply to other embodiments), the second refrigeration device 10 may include one or more turbines 16 in series and / or parallel. Furthermore, the upstream and downstream flows of the one or more compressors 15 may exchange heat countercurrently in the same heat exchanger 150. One or more flows at the outlet of the one or more turbines may optionally be exchanged in a second group of one or more heat exchangers 8 (shown in dotted lines).

[0067] Of course, although shown in Figures 3 and 4, the oxygen flow compression and expansion system may be omitted.

[0068] The turbines are preferably of the radial flow and radial technology type, which allows the pooling of expansion technologies throughout the liquefaction plant.

[0069] The compressor is preferably of the centrifugal type.

[0070] In a variant not shown in detail, the oxygen circuit 190 produces liquefied oxygen downstream, which is recovered. For this purpose, all or part of the oxygen flow can pass through a heat exchanger separate from the exchangers 4, 5, 6, 7, 8 exchanging with the hydrogen flow.

[0071] Of course, some compressors or turbines may not be coupled to a shaft to which another wheel of the turbine (or compressor, respectively) is also coupled. In other words, not all turbines (or compressors) may necessarily be coupled to the same shaft as the compressor, and vice versa. Similarly, more than two wheels (compressors and / or turbines) may be coupled to the same shaft. The following is a summary of the claims as originally filed: [1] A plant for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures, comprising an electrolyser (2) provided with an oxygen outlet and a hydrogen outlet, a hydrogen circuit (3) to be cooled, the hydrogen circuit (3) having an upstream end connected to the hydrogen outlet and a downstream end intended to be connected to a member (23) for cooling and / or collecting liquefied hydrogen, the plant (1) comprising a set of heat exchangers (4, 5, 6, 7, 8) in heat exchange with the hydrogen circuit (3) to be cooled, the plant (1) comprising at least one cooling device in heat exchange with at least a part of the set of heat exchangers (4, 5, 6, 7, 8). 1. A plant comprising a hydrogen circuit (3) to be cooled comprising a hydrogen flow expansion system (18) and at least one hydrogen compressor (19) upstream of the hydrogen flow expansion system (18), the hydrogen flow expansion system (18) comprising at least one expansion turbine (18), characterized in that the at least one expansion turbine (18) and the at least one compressor (19) are coupled to the same rotating shaft (20) in order to transmit to the compressor (19) the function of expanding the hydrogen flow under pressure in order to compress the hydrogen flow upstream of the turbine (18). [2] The plant according to [1], characterized in that the assembly comprising the expansion turbine (18) and the compressor (19) coupled to the same rotating shaft (20) is a passive mechanical system, i.e. does not include a power plant for driving the rotating shaft (20) other than the hydrogen flow, or is an active mechanical system, comprising a power plant for driving the rotating shaft (20). [3] The plant according to [1] or [2], characterized in that the hydrogen circuit (3) comprises several hydrogen compressors (19) arranged in series and / or in parallel upstream of the hydrogen flow expansion system (18), the hydrogen flow expansion system comprising a plurality of expansion turbines (18) arranged in series and / or in parallel, each of the compressors (19) being coupled to a rotating shaft (20) to which at least one turbine (18) is likewise coupled. [4] The plant according to any one of [1] to [3], characterized in that the hydrogen circuit (3) to be cooled comprises several compressors (19) arranged in series upstream of the hydrogen flow expansion system (18), the hydrogen flow expansion system comprising a plurality of expansion turbines (18) arranged in series, and the compressors and turbines (18) are coupled in pairs to respective rotating shafts (20). [5] The plant according to [3] or [4], characterized in that the turbines (18) are arranged in series in the hydrogen circuit (3) to be cooled, the hydrogen circuit (3) to be cooled comprising separate respective sections for heat exchange between at least a part of the set of heat exchangers (4, 5, 6, 7) and the hydrogen flow at the outlet of each turbine (18). [6] The plant according to any one of [1] to [5], characterized in that the set of heat exchangers (4, 5, 6, 7, 8) comprises several heat exchangers arranged in series and exchanging heat with the hydrogen circuit (3) to be cooled between the upstream end and the downstream end of the hydrogen circuit (3) to be cooled. [7] The plant according to any one of [1] to [6], characterized in that the plant comprises a first cooling device (9) and a second cooling device (10) in heat exchange with the hydrogen circuit (3) to be cooled, the first cooling device (9) in heat exchange with a first group of heat exchangers (4, 5, 6, 7) of the set of heat exchangers (4, 5, 6, 7, 8) and the second cooling device (10) in heat exchange with a second group of heat exchangers (8), the first group of heat exchangers (4, 5, 6, 7) being located upstream of the second group of heat exchangers (8) in the hydrogen circuit (3) to be cooled, and the first cooling device (9) comprises the hydrogen flow expansion system to ensure pre-cooling of the hydrogen circuit (3) before the additional cooling performed by the second cooling device (10). [8] The plant according to [7], characterized in that the second cooling device (10) includes a cycle gas refrigeration cycle refrigeration apparatus, the refrigeration apparatus of the second cooling device (10) including, arranged in series in a cycle circuit, a mechanism (15) for compressing the second cycle gas, a member (8) for cooling the second cycle gas, a mechanism (16) for expanding the second cycle gas, and a member (8) for heating the expanded second cycle gas. [9] The plant according to [7] or [8], characterized in that the hydrogen flow expansion system (18) is located in the part of the hydrogen circuit (3) to be cooled, which exchanges heat with the first group of heat exchangers (4, 5, 6, 7).

[10] The plant according to any one of [7] to [9], characterized in that the hydrogen flow expansion system (18) is located in a portion of the hydrogen circuit (3) to be cooled that exchanges heat with the second group of heat exchangers (8).

[11] The plant according to any one of [1] to

[10] , further comprising a hydrogen cooling system (22) at an outlet of at least a portion of the compressor (21).

[12] The plant according to any one of [1] to

[11] , comprising an oxygen circuit (190) including an upstream end connected to the oxygen outlet and a downstream end (11) connected to a recovery system.

[13] The plant according to

[12] , characterized in that the oxygen circuit (190) comprises an oxygen flow expansion system (13) and at least one heat exchange between the expanded oxygen flow and the hydrogen circuit (3) to be cooled, the oxygen circuit (190) comprising at least one oxygen compressor (12) arranged upstream of the oxygen flow expansion system (13), the oxygen flow expansion system (13) comprising an expansion turbine (13), and the expansion turbine (13) and the compressor (12) being coupled to the same rotating shaft (14) for transmitting to the compressor (12) the function of expanding the oxygen flow under pressure in order to compress the oxygen flow upstream of the turbine (13).

[14] The plant according to

[13] , characterized in that the assembly with the expansion turbine (13) and the compressor (12) coupled to the same rotating shaft (14) is a passive mechanical system, i.e. does not include a power plant for driving the rotating shaft (14) apart from the oxygen flow, or is an active mechanical system, i.e. includes a power plant for driving the rotating shaft (14).

[15] The plant according to

[13] or

[14] , characterized in that the oxygen circuit (9) comprises several oxygen compressors (12) arranged in series and / or in parallel upstream of the oxygen flow expansion system (13), the oxygen flow expansion system comprising a plurality of expansion turbines (13), each of the compressors (12) being coupled to a rotating shaft (14) to which at least one turbine (13) is likewise coupled.

[16] The plant according to

[14] or

[15] , characterized in that the oxygen circuit (9) comprises several compressors (12) arranged in series upstream of the oxygen flow expansion system (13), the oxygen flow expansion system (13) comprising a plurality of expansion turbines (13), and the compressors and turbines (13) are coupled in pairs to respective rotating shafts (14).

[17] The plant according to

[15] or

[16] , characterized in that the turbines (14) are arranged in series in the oxygen circuit (9), the oxygen circuit (9) comprising separate respective sections for heat exchange between the set of heat exchangers (4, 5, 6, 7, 8) and the oxygen flow at the outlet of each turbine (13).

[18] The plant according to any one of

[15] to

[17] , further comprising an oxygen cooling system (21) at the outlet of at least a part of the compressor (12).

[19] The plant described in any one of [7] to

[10] , characterized in that it includes a third cooling device (17) that exchanges heat with at least a portion of the first group of heat exchangers (4, 5, 6, 7).

[20] A method for producing hydrogen, in particular liquefied hydrogen, at cryogenic temperatures using a plant (1) according to any one of [1] to

[19] , the method comprising the steps of: supplying a hydrogen flow by an electrolyser (2), for example at a pressure of 15 to 150 bar, to an upstream end of a hydrogen circuit (3), supplying an oxygen flow by the electrolyser (2), for example at a pressure of 15 to 150 bar, to the upstream end of an oxygen circuit (190), the method comprising the steps of compressing and then expanding the hydrogen flow, the expansion being carried out by at least one turbine (18) coupled to a shaft (20), the shaft (20) in turn being coupled to at least one compressor (19) ensuring the compression of the hydrogen flow before its expansion.

Claims

1. A plant (1) for producing hydrogen at low temperatures, comprising an electrolyser (2) provided with an oxygen outlet and a hydrogen outlet, and a hydrogen circuit (3) to be cooled, the hydrogen circuit (3) to be cooled comprising an upstream end connected to said hydrogen outlet and a downstream end intended to be connected to an element (23) for cooling and / or collecting liquefied hydrogen, said plant (1) comprising a set of heat exchangers (4, 5, 6, 7, 8) in heat exchange with said hydrogen circuit (3) to be cooled, said plant (1) comprising at least one cooling device (9, 10) in heat exchange with at least a part of said set of heat exchangers (4, 5, 6, 7, 8), said hydrogen circuit (3) to be cooled comprising a hydrogen flow expansion system (18) and at least one hydrogen compressor (19) upstream of said hydrogen flow expansion system (18), said hydrogen flow expansion system (18) comprising at least one expansion turbine (18), at least one of the expansion turbines (18) and at least one of the hydrogen compressors (19) are coupled to the same rotating shaft (20) for transmitting to the hydrogen compressor (19) the function of expanding the hydrogen flow under pressure to compress the hydrogen flow upstream of the expansion turbine (18); the plant (1) comprises an oxygen circuit (190) including an upstream end connected to the oxygen outlet and a downstream end (11) connected to a recovery system, 1. A plant comprising: an oxygen circuit (190) comprising an oxygen flow expansion system (13) and at least one heat exchange between the expanded oxygen flow and the hydrogen circuit (3) to be cooled.

2. 2. A plant according to claim 1, characterized in that the assembly comprising the expansion turbine (18) and the hydrogen compressor (19) coupled to the same rotating shaft (20) is either a passive mechanical system, i.e. it does not comprise a power plant for driving the rotating shaft (20) apart from the hydrogen flow, or it is an active mechanical system, i.e. it comprises a power plant for driving the rotating shaft (20).

3. 3. A plant according to claim 1 or 2, characterized in that the hydrogen circuit (3) comprises several hydrogen compressors (19) arranged in series and / or in parallel upstream of the hydrogen flow expansion system (18), the hydrogen flow expansion system comprising a plurality of expansion turbines (18) arranged in series and / or in parallel, and each of the hydrogen compressors (19) is coupled to a rotating shaft (20) to which at least one expansion turbine (18) is likewise coupled.

4. 4. A plant according to claim 1, characterized in that the hydrogen circuit (3) to be cooled comprises several hydrogen compressors (19) arranged in series upstream of the hydrogen flow expansion system (18), the hydrogen flow expansion system comprising a plurality of expansion turbines (18) arranged in series, the hydrogen compressors and the expansion turbines (18) being coupled in pairs to respective rotating shafts (20).

5. 5. A plant according to claim 3 or 4, characterized in that the expansion turbines (18) are arranged in series in the hydrogen circuit (3) to be cooled, the hydrogen circuit (3) to be cooled comprising a separate respective section for heat exchange between at least a part of the set of heat exchangers (4, 5, 6, 7) and the hydrogen flow at the outlet of each expansion turbine (18).

6. A plant as described in any one of claims 1 to 5, characterized in that the set of heat exchangers (4, 5, 6, 7, 8) comprises several heat exchangers arranged in series and exchanging heat with the hydrogen circuit (3) to be cooled between the upstream end and the downstream end of the hydrogen circuit (3) to be cooled.

7. 7. The plant according to claim 1, characterized in that it comprises a first cooling device (9) and a second cooling device (10) in heat exchange with the hydrogen circuit (3) to be cooled, the first cooling device (9) in heat exchange with a first group (4,5,6,7) of the set of heat exchangers (4,5,6,7,8) and the second cooling device (10) in heat exchange with a second group (8) of heat exchangers, the first group of heat exchangers (4,5,6,7) being located upstream of the second group (8) of heat exchangers in the hydrogen circuit (3) to be cooled, and the first cooling device (9) is equipped with the hydrogen flow expansion system to ensure pre-cooling of the hydrogen circuit (3) before the additional cooling performed by the second cooling device (10).

8. 8. The plant according to claim 7, characterized in that the second cooling device (10) comprises a cycle gas refrigeration cycle refrigeration apparatus, the cycle gas refrigeration cycle refrigeration apparatus of the second cooling device (10) comprising, arranged in series in a cycle circuit, a mechanism (15) for compressing a second cycle gas, a member (8) for cooling the second cycle gas, a mechanism (16) for expanding the second cycle gas, and a member (8) for heating the expanded second cycle gas.

9. 9. A plant according to claim 7 or 8, characterized in that the hydrogen flow expansion system (18) is located in the part of the hydrogen circuit (3) to be cooled, in heat exchange with the first group of heat exchangers (4, 5, 6, 7).

10. 10. A plant according to any one of claims 7 to 9, characterized in that the hydrogen flow expansion system (18) is located in the part of the hydrogen circuit (3) to be cooled, in heat exchange with the first group of heat exchangers.

11. A plant as described in any one of claims 1 to 10, characterized in that it is provided with a hydrogen cooling system (21) at at least a portion of the outlet of the oxygen compressor (12).

12. A plant as described in any one of claims 1 to 11, characterized in that the oxygen circuit (190) comprises at least one oxygen compressor (12) arranged upstream of the oxygen flow expansion system (13), the oxygen flow expansion system (13) comprising an expansion turbine (13), and the expansion turbine (13) and the oxygen compressor (12) are coupled to the same rotating shaft (14) to transmit to the oxygen compressor (12) the function of expanding the oxygen flow under pressure to compress the oxygen flow upstream of the expansion turbine (13).

13. 13. A plant according to claim 12, characterized in that the assembly comprising the expansion turbine (13) and the oxygen compressor (12) coupled to the same rotating shaft (14) of the oxygen circuit (190) is either a passive mechanical system, i.e. it does not comprise a power plant for driving the rotating shaft (14) apart from the oxygen flow, or it is an active mechanical system, i.e. it comprises a power plant for driving the rotating shaft (14).

14. 14. A plant according to claim 12 or 13, characterized in that the oxygen circuit (9) comprises several oxygen compressors (12) arranged in series and / or in parallel upstream of the oxygen flow expansion system (13), the oxygen flow expansion system comprising a plurality of expansion turbines (13), each of the oxygen compressors (12) being coupled to a rotating shaft (14) to which at least one expansion turbine (13) is likewise coupled.

15. 15. A plant according to claim 13 or 14, characterized in that the oxygen circuit (9) comprises several oxygen compressors (12) arranged in series upstream of the oxygen flow expansion system (13), the oxygen flow expansion system (13) comprising a plurality of expansion turbines (13), and in that the oxygen compressors and expansion turbines (13) are coupled in pairs to respective rotating shafts (14).

16. 16. A plant according to claim 14 or 15, characterized in that the expansion turbines (13) are arranged in series in the oxygen circuit (9), the oxygen circuit (9) comprising separate respective sections for heat exchange between the set of heat exchangers (4, 5, 6, 7, 8) and the oxygen flow at the outlet of each expansion turbine (13).

17. A plant according to any one of claims 14 to 16, characterized in that it comprises an oxygen cooling system (21) at the outlet of at least a part of the oxygen compressor (12).

18. A plant as described in any one of claims 7 to 10, characterized in that it comprises a third cooling device (17) for exchanging heat with at least a part of the first group of heat exchangers (4, 5, 6, 7).

19. A method for producing hydrogen at cryogenic temperatures using a plant (1) according to any one of the preceding claims, said method comprising the steps of: supplying a hydrogen flow by the electrolyser (2) to an upstream end of the hydrogen circuit (3) at a pressure between 15 and 150 bar; and supplying an oxygen flow by the electrolyser (2) to an upstream end of an oxygen circuit (190) at a pressure between 15 and 150 bar, The method comprises the step of compressing and then expanding the hydrogen flow, the expansion being performed by at least one said expansion turbine (18) coupled to a shaft (20), said shaft (20) in turn being coupled to at least one said hydrogen compressor (19) to ensure compression of the hydrogen flow before its expansion.

Images