Method and system for producing hydrogen with decreased electricity consumption

Abstract

The invention relates to a method for producing hydrogen via steam electrolysis, the method comprising the following steps: - producing steam (112) by heating liquid water (204); and - electrolysing, in an electrolysis unit (102), at least a portion of the steam (112) to provide a first output stream (116) rich in hydrogen and a second output stream (118) rich in oxygen; characterised in that the steam is produced by at least one heat pump circuit reusing a portion of the heat from at least one of the output streams (116, 118) in order to vaporise the liquid water. The invention also relates to a system (400) implementing such a method.

Description

DESCRIPTION Title: Process and system for producing hydrogen with reduced electricity consumption

[0001] The present invention relates to a process for producing hydrogen by high-temperature electrolysis of steam with reduced electrical consumption. It also relates to a hydrogen production system by high-temperature electrolysis of steam implementing such a process.

[0002] The field of the invention is generally the field of hydrogen production by high-temperature electrolysis of water vapor, and in particular in a solid oxide electrolyzer operating at high temperature. State of the art

[0003] Several hydrogen production techniques currently exist. One such technique is the electrolysis of steam in a solid oxide electrolyzer (SOEL). In short, water is heated to produce steam at a temperature above 150°C. This steam is then introduced into an electrolysis unit maintained at a temperature between 700°C and 850°C and powered by an electric current. The electrolysis unit decomposes the water vapor (H₂O) into hydrogen (H₂) and oxygen (O₂) molecules, resulting in a hydrogen-rich (H₂) stream and an oxygen-rich (O₂) stream exiting the unit.

[0004] This solution requires an external energy input, particularly for producing steam at the desired temperature. This reduces the overall efficiency of hydrogen production, especially with regard to its electricity consumption.

[0005] One object of the present invention is to remedy at least one of the drawbacks of the prior art.

[0006] Another objective of the invention is to offer a solution for the production of hydrogen by electrolysis of water vapor with improved overall efficiency, and in particular with reduced electrical consumption. Description of the invention

[0007] The invention proposes to achieve at least one of the aforementioned goals by a process for producing hydrogen by electrolysis of steam, comprising the following steps: - production of steam by heating liquid water, and - electrolysis, in an electrolysis unit, of at least a portion of said water vapor, to provide a first hydrogen-rich output stream and a second oxygen-rich output stream; wherein the production of water vapor is carried out by at least one heat pump circuit reusing a portion of the heat from at least one of said output streams to vaporize the liquid water.

[0008] Thus, in a conventional manner, the process according to the invention proposes to produce hydrogen from steam introduced into an electrolysis unit powered by an electric current. Such an electrolysis operation is conventionally known to those skilled in the art and will not be described in further detail here.

[0009] In an innovative approach, the invention proposes to utilize at least some of the heat from at least one of the output streams generated by the electrolysis unit to produce steam from liquid water using at least one heat pump circuit. In other words, the invention enables the production of hydrogen by utilizing at least some of the heat from one or more output streams of the electrolysis unit, using a heat pump circuit. Indeed, each output stream from the electrolysis unit contains thermal energy which, in current processes, is rejected. The invention proposes to use some of this thermal energy to produce steam from liquid water, that is, to vaporize the liquid water.

[0010] Therefore, the invention makes it possible to produce hydrogen with a higher overall efficiency than current solutions, since it reduces the electricity consumption required to produce the water vapor given as input to the electrolysis unit.

[0011] As mentioned above, in the present invention, water vapor is produced by at least one heat pump circuit using at least a portion of the heat from at least one of the outlet streams. In particular, the at least one heat pump may use: - at least some of the heat from the first hydrogen-rich outlet stream, and / or - at least some of the heat from the second oxygen-rich output stream, or one consisting solely of oxygen. Thus, depending on the embodiments, the heat from each output stream can be used to produce the water vapor introduced into the electrolysis unit.

[0012] As will be described later, the heat recovered from at least one outlet stream can be used immediately to produce water vapor by vaporizing liquid water. In this case, at least one heat pump circuit is used to transfer some of the heat from said at least one outlet stream to the liquid water, or a stream of liquid water, for vaporization.

[0013] Alternatively, or in addition, at least some of the heat from at least one outlet stream can be transferred to a thermal storage medium. In this case, at least one heat pump circuit is used to transfer heat from said thermal storage medium to liquid water for vaporization. In other words, in this case, the thermal storage medium is located between: - at least one heat pump circuit used to vaporize the water, and - at least one output stream.

[0014] According to embodiments, the production of water vapor can be achieved by a set of at least two heat pump circuits, connected in series, reusing part of the heat from at least one of said output flows to vaporize liquid water and produce water vapor.

[0015] Using multiple heat pump circuits optimizes heat recovery from at least one outlet stream, thus reducing the system's overall electricity consumption. Indeed, it is possible to increase the heat recovered from at least one outlet stream by using heat pumps in series.

[0016] Depending on the embodiment, the aforementioned at least two heat pump circuits can reuse the heat from the same outlet flow. In this case, steam production involves: - a first heat pump circuit reusing, and in particular recovering, at least part of the heat from said outlet flow, and - a second heat pump circuit reusing, and in particular recovering, at least part of the heat from said same output flow; said heat pump circuits being connected in series so that the first heat pump circuit heats the heat transfer fluid of the second heat pump circuit.

[0017] Thus, it is possible to increase the amount of heat reused and recovered from the output stream. Furthermore, it is possible, for example, to use heat pump circuits whose operation is optimized for the output stream temperatures at each reuse or recovery stage, thereby reducing electricity consumption while increasing the heat reused from the same output stream.

[0018] Depending on the embodiment, the production of steam can be achieved by: - a first heat pump circuit reusing, and in particular recovering, at least part of the first outlet flow, and - a second heat pump circuit reusing, and in particular recovering, at least some of the heat from the second output flow; said heat pump circuits being connected in series so that one of the heat pump circuits heats the heat transfer fluid of the other of the heat pump circuits.

[0019] In this embodiment, one of the heat pump circuits increases the temperature of the heat transfer fluid in the other heat pump circuit. This allows for the optimization of the sizing and configuration of the heat pump circuits to improve and maximize heat recovery from the outlet flows.

[0020] Furthermore, the heat from each of the output streams produced by the electrolysis unit can be optimally reused, thus reducing the overall electricity consumption of the hydrogen production process. For example, heat pump circuits can be used whose operation is optimized for the output stream temperatures at each heat reuse stage, thereby reducing electricity consumption while increasing the heat recovered from the output streams.

[0021] According to embodiments, the process according to the invention may include recovering at least part of the heat from at least one outlet stream by at least one heat pump circuit producing water vapor.

[0022] In this case, the heat recovered from at least one outlet stream is transferred directly from said at least one outlet stream to the liquid water for vaporization, by said at least one heat pump circuit.

[0023] In other words, at least one heat pump circuit is located between the water flow and at least one outlet flow. For example, at least one heat pump circuit: - receives said at least one output stream at the level of an evaporator of said at least one heat pump circuit, to recover heat from said at least one output stream, and - receives the water flow at the level of at least one condenser of said at least one heat pump circuit, to transfer heat to said liquid water flow and vaporize said liquid water.

[0024] Depending on embodiments, at least a portion of the heat from at least one outlet stream can be recovered by at least one device heat recovery and stored in a thermal storage means, at least one heat pump circuit producing water vapor from heat stored in said thermal storage means.

[0025] In this case, at least one heat pump circuit does not recover heat from at least one outlet stream. This heat is recovered by one or more heat recovery devices located between the thermal storage unit and at least one outlet stream.

[0026] The heat recovery device can be any type of device to recover heat from at least one outlet stream.

[0027] Depending on the embodiment, the heat recovery system may include, or may be, at least one heat pump.

[0028] Alternatively, or in addition, the heat recovery system may include other means such as, for example, at least one heat exchanger, etc.

[0029] The thermal storage method can be of any type.

[0030] For example, the thermal storage medium, also called a thermal reservoir, can be an insulated tank containing a heat transfer fluid heated by at least one heat recovery device. Such a heat transfer fluid can be, for example, oil, water, or any other fluid.

[0031] According to embodiments, the process according to the invention may further include the production of heat from a renewable energy source.

[0032] The heat thus produced can be used immediately, for example to preheat liquid water, or to heat the heat transfer fluid of at least one heat pump circuit.

[0033] Alternatively, or in addition, the heat thus produced can be stored in the thermal reservoir for later reuse.

[0034] For example, the process according to the invention may include the production of heat from solar radiation, for example by solar panels, or any other known technique.

[0035] For example, the process according to the invention may include heat production by geothermal energy.

[0036] Depending on embodiments, the process according to the invention may comprise at least one heat exchange between at least one outlet flow and: - liquid water and / or - the water vapor produced from said liquid water.

[0037] In particular, the process according to the invention may include at least one first heat exchange, within a heat exchanger, between at least one outlet stream to heat, or preheat, the liquid water, particularly before its vaporization. In this case, the heat exchange may heat the liquid water without causing its vaporization. Of course, a small portion of the liquid water may be vaporized during said heat exchange even if the objective is not to vaporize the liquid water. The objective of said at least first heat exchange may be to heat the liquid water to a temperature less than or equal to 100°C, and in particular to 105°C, without vaporizing it.

[0038] Alternatively, or in addition, the process according to the invention may include at least one second heat exchange, within a heat exchanger, between at least one outlet stream and the steam produced to superheat the steam. In this case, the heat exchange occurs after the liquid water has vaporized and is used to raise the temperature of the steam. Of course, a small portion of the liquid water may remain in vapor form; this portion is then vaporized during said heat exchange, even if the objective is not to vaporize the liquid water but to superheat the steam. The objective of said at least second heat exchange may be to heat the steam to a temperature greater than or equal to 140°C, and in particular to 150°C.

[0039] Optionally, when the recovered heat is not sufficient for the production of steam, it can be supplemented by heat produced from an active heater powered by electricity produced from an external source, for example the electrical grid.

[0040] According to another aspect of the present invention, a system for producing hydrogen by steam electrolysis is proposed, said system comprising: - a steam production unit using liquid water heating, and - at least one electrolysis unit of at least a portion of said water vapor to provide a first output stream rich in hydrogen and a second output stream rich in oxygen; said water vapor production unit comprising at least one heat pump circuit reusing a portion of the heat from at least one of said output streams to vaporize liquid water.

[0041] The system according to the invention has the same advantages as those described above with reference to the process according to the invention, which will not be repeated here for the sake of brevity.

[0042] Furthermore, the system according to the invention may include, in terms of technical means, at least one, or any combination of at least two, of the optional features described above with reference to the method according to the invention, and which are not all repeated in detail below, for the sake of brevity.

[0043] In particular, the steam production unit may include at least two heat pump circuits, connected in series, reusing some of the heat from at least one of said output streams to vaporize liquid water and produce steam.

[0044] Heat pump circuits can be configured to recover heat from the same output stream or from different output streams, as described above, with reference to the process according to the invention.

[0045] Depending on the embodiment, at least one heat pump circuit can be arranged between at least one outlet flow and the liquid water, such that: - recover at least some of the heat from said at least one outlet stream, and - to transfer said heat to the liquid water in order to vaporize it.

[0046] In this case, the heat used by the steam production unit to vaporize the liquid water is recovered directly by at least one heat pump circuit from at least one outlet stream.

[0047] Depending on the embodiment, the steam production unit may further include: - at least one heat recovery device from at least one of the outlet streams, and - a thermal storage tank, also called a thermal reservoir, to store at least some of the heat recovered by said heat recovery device.

[0048] In this case, at least one heat pump circuit used to vaporize the water recovers heat to vaporize the liquid water from said thermal reservoir.

[0049] The heat recovery means is disposed between the thermal storage means and at least one output flow.

[0050] Depending on the embodiment, the heat recovery device may include, or may be, at least one heat pump. In this case, heat recovery from at least one outlet stream is carried out by said at least one heat pump circuit disposed between said at least one outlet stream and the thermal storage means.

[0051] Alternatively, or in addition, the heat recovery device may include, or may be, at least one heat exchanger, etc.

[0052] The thermal storage medium, or thermal reservoir, can be of any type, such as for example an insulated heat transfer fluid reservoir.

[0053] The heat transfer fluid can, for example, be oil, water, or any other fluid.

[0054] Optionally, the steam production unit may also include at least one means of producing heat from a renewable energy source.

[0055] For example, the steam production unit may include at least one means of heat production using solar energy.

[0056] For example, the steam production unit may include at least one means of heat production using geothermal energy.

[0057] The heat produced by said at least one means of heat production can be used immediately for the production of steam or stored in the thermal reservoir.

[0058] According to embodiments, the system according to the invention may include at least one first heat exchanger to carry out a heat exchange between at least one outlet flow to heat the liquid water, in particular before its vaporization.

[0059] Alternatively, or in addition, the system according to the invention may include at least one second heat exchanger to achieve heat exchange between at least one outlet stream and the steam produced to superheat the steam.

[0060] Depending on embodiments, the electrolysis unit may include at least one high-temperature steam electrolyzer, for example an electrolyzer operating, i.e. carrying out steam electrolysis, at a temperature between 700°C and 850°C.

[0061] Depending on the embodiment, the electrolysis unit may include at least one solid oxide electrolyzer.

[0062] In particular, the electrolysis unit may include several solid oxide electrolyzers arranged in series, or in parallel.

[0063] At least one electrolyzer may include one or more stacks, or aggregations, of solid oxide electrolysis cells. Description of the figures and methods of implementation

[0064] Other advantages and features will become apparent upon examination of the detailed description of non-limiting embodiments and the accompanying drawings, in which: - FIGURE 1 is a schematic representation of an example of a hydrogen production system according to the state of the art; - Figures 2-4 are schematic representations of non-limiting examples of embodiments of a system according to the invention; and - FIGURES 5-8 are schematic representations of non-limiting examples of embodiments of a steam production unit that can be implemented in the present invention.

[0065] It is understood that the embodiments described below are by no means exhaustive. In particular, variants of the invention may be conceived comprising only a selection of the features described below, isolated from the other features described, if this selection of features is sufficient to confer a technical advantage or to differentiate the invention from the prior art. This selection includes at least one preferably functional feature without structural details, or with only a portion of the structural details if this portion alone is sufficient to confer a technical advantage or to differentiate the invention from the prior art.

[0066] In particular, all the variants and embodiments described can be combined with each other if there are no technical obstacles to this combination.

[0067] In the figures and in the rest of the description, elements common to several figures retain the same reference.

[0068] FIGURE 1 is a schematic representation of an example of a hydrogen production system according to the state of the art.

[0069] The system 100 in FIGURE 1 can be used to produce hydrogen by electrolysis of water vapor, especially at high temperature, for example at a temperature between 700°C and 850°C.

[0070] System 100 includes an electrolysis unit 102 for performing steam electrolysis. The electrolysis unit 102 may include one or more stacks 104, also called stacks, of electrolysis cells. The stacks 104 may be arranged in parallel or in series. In the example shown in Figure 1, without loss of generality, only one stack is represented.

[0071] To carry out the electrolysis of water vapor, the electrolysis unit 102, and in particular each stack 104, is supplied by an electric current denoted I in FIGURE 1.

[0072] Stack 104 is placed in a closed chamber 106, also called a hotbox, in which the temperature is between 700°C and 850°C.

[0073] System 100 may include one or more IO81-IO82 heat exchangers to perform heat exchange between the outgoing and incoming flows of stack 104. In the example shown, the IO81-IO82 exchangers are located in the hotbox 106. Alternatively, at least one of these heat exchangers may be located outside the hotbox 106.

[0074] System 100 also includes a hydrogen processing unit 110.

[0075] During operation, the electrolysis unit 102 receives an input stream 112, entirely or mainly composed of water vapor FbOv. In the case of high-temperature electrolysis of water vapor in a solid oxide electrolysis unit, the first input stream 112 is supplied to the stack 104 at a temperature between 700°C and 850°C.

[0076] Optionally, the electrolysis unit 102, and more specifically the stack 104, can also receive a second inlet flow 114. This second inlet flow regulates the pressures within the electrolysis unit 102, and more precisely within the stack 104. This second inlet flow 114 is designed to circulate within the stack without mixing with the first inlet flow 112. The second inlet flow 114 can be a flow of air, a neutral gas, etc. In the case of high-temperature electrolysis of steam in a solid oxide electrolysis unit, the second input stream 114 is supplied to stack 104 at a temperature between 700°C and 850°C.

[0077] In stack 104, the electrolysis of water vapor produces hydrogen and oxygen according to the following relationship:

[0078] Thus, the electrolysis unit 102 provides, at its outlet, a first output stream 116 consisting essentially of hydrogen, H2, and possibly including undecomposed water vapor. In the case of high-temperature electrolysis of water vapor in a solid oxide electrolysis unit, the first output stream 116 exits the stack 104 at a temperature between 700°C and 850°C.

[0079] The electrolysis unit 102 provides, at the output, a second output stream 118 essentially composed of oxygen, O2, and other components, particularly when using the second input stream 114. In the case of high-temperature electrolysis of water vapor in a solid oxide electrolysis unit, the second output stream 118 exits the stack 104 at a temperature between 700°C and 850°C.

[0080] In some cases, some of the heat from the first hydrogen-rich outlet stream 116 can be transferred to the first water vapor inlet stream 112, using the optional heat exchanger IO81. In FIGURE 1, the first inlet stream 112 is labeled: - 112i upstream of the IO81 heat exchanger, and - 1122 downstream of the IO81 heat exchanger. Furthermore, in FIGURE 1, the first output stream 116 is noted: - II61 upstream of the heat exchanger IO81, and - II62 downstream of the heat exchanger IO81.

[0081] In some cases, some of the heat from the oxygen-rich second outlet stream 118 can be transferred to the optional second inlet stream 114 using the optional heat exchanger IO82. In FIGURE 1, the second inlet stream 114 is labeled: - 114i upstream of the IO82 heat exchanger, and - 1142 downstream of the IO82 heat exchanger. Furthermore, in FIGURE 1, the second output stream 118 is noted: - 118i upstream of the IO82 heat exchanger, and - II82 downstream of the heat exchanger IO82.

[0082] The second outlet stream 116, possibly after heat exchange with the first inlet stream 112 in the heat exchanger IO81, is then treated in the hydrogen treatment unit 110 to separate the hydrogen from any residual water vapor. For example, the first outlet stream 116, or II62, is cooled to a temperature below 100°C to condense the water vapor in said stream. Thus, the treatment unit 110 provides a second stream 116 of pure hydrogen and a stream 120 of liquid water. In FIGURE 1, the first outlet stream 116 is labeled: - II62 upstream of treatment unit 110, and - II63 downstream of treatment unit 110.

[0083] It is understood that system 100 requires steam for electrolysis. However, steam production is generally achieved by vaporizing liquid water in an active heater (not shown in FIGURE 1), which is electrically powered and consumes a significant amount of electricity. Such steam production from liquid water substantially increases the electrical consumption of system 100.

[0084] The invention proposes to address this problem and reduce the overall electrical consumption of system 100.

[0085] FIGURE 2 is a schematic representation of a non-limiting example embodiment of a hydrogen production system according to the invention.

[0086] The 200 system in FIGURE 2 can be used to produce hydrogen by electrolysis of water vapor, particularly at high temperatures, for example at a temperature between 700°C and 850°C.

[0087] The 200 system in FIGURE 2 includes all the elements of the 100 system in FIGURE 1.

[0088] The system 200 further includes a unit 202 for producing steam 112 from liquid water 204. Non-limiting examples of steam production units 202 will be described later.

[0089] The steam production unit 202 uses part of the heat from at least one of the outlet streams 116 and 118. In the example shown in FIGURE 2, the steam production unit 202 uses part of the heat from the first outlet stream 116, i.e. part of the heat from the hydrogen-rich stream.

[0090] More specifically, the first flow II62 exiting the heat exchanger IO81 is directed to the steam production unit 202, which recovers and uses some of the heat from said first outlet flow II62 to produce steam from liquid water. Of course, if the system 200 does not include the heat exchanger IO81, then the first outlet flow 116 can be directed directly to the steam production unit 202 without prior heat exchange.

[0091] Optionally, the first output stream II63 downstream of the hydrogen processing unit 100 can also be redirected to the steam production unit 202, which recovers and uses some of the heat from said stream II63.

[0092] Optionally, the heat generated at the hydrogen processing unit 110, and in particular the heat generated by condensation of the water vapor in the first outlet stream 116, or II62, can also be recovered and used by the water vapor production unit 202.

[0093] Thus, heat is recovered from the first output stream at different stages of operation of the hydrogen production system.

[0094] FIGURE 3 is a schematic representation of another non-limiting embodiment of a hydrogen production system according to the invention.

[0095] The 300 system in FIGURE 3 can be used to produce hydrogen by electrolysis of water vapor, particularly at high temperatures, for example at a temperature between 700°C and 850°C.

[0096] The 300 system in FIGURE 3 includes all the elements of the 100 system in FIGURE 1.

[0097] System 300 further includes unit 202 for producing steam 112 from liquid water 204.

[0098] The steam production unit 202 uses some of the heat from at least one of the outlet streams 116 and 118. In the example shown in FIGURE 3, the steam production unit 202 uses some of the heat from the second outlet stream 118, i.e. some of the heat from the oxygen-rich stream.

[0099] More specifically, the second flow II82 exiting the heat exchanger IO82 is directed to the steam production unit 202, which recovers and uses some of the heat from said flow II82 to produce steam from liquid water. Of course, if the system 200 does not include the heat exchanger IO82, then the second outlet flow 118, exiting the stack 114, can be directed directly to the steam production unit 202 without prior heat exchange.

[0100] FIGURE 4 is a schematic representation of another non-limiting embodiment of a hydrogen production system according to the invention.

[0101] The 400 system in FIGURE 4 can be used to produce hydrogen by electrolysis of water vapor, particularly at high temperatures, for example at a temperature between 700°C and 850°C.

[0102] System 400 in FIGURE 4 is a combination of systems 200 and 300 in FIGURES 2 and 3. In system 400, the steam production unit 202 recovers and uses: - a portion of the heat from the first outlet flow 116, as described with reference to system 200; and - part of the heat from the second outlet flow 118, as described with reference to system 300.

[0103] FIGURE 5 is a schematic representation of a non-limiting example embodiment of a steam production unit that can be implemented in the present invention.

[0104] The steam production unit 500, shown in FIGURE 5, can be unit 202 in FIGURES 2-4.

[0105] The water vapor production unit 500 includes a heat pump circuit 502 comprising a compressor 504, a condenser 506, an expansion valve 508 and an evaporator 510. The heat pump circuit 502 recovers, at the evaporator 510, a portion of the heat from the first outlet flow 116, or II62, to transfer it to the liquid water 204 at the condenser 506 so as to vaporize the liquid water 204 to produce water vapor.

[0106] The use of the heat pump circuit 502 allows a good part of the heat from the first outlet flow 116 to be transferred so as to provide the latent heat necessary for the vaporization of the liquid water 204. The electrical consumption of the heat pump circuit 502 remains lower than the electrical energy that an electric heater would have consumed to vaporize liquid water.

[0107] Optionally, downstream of the heat pump circuit 502, the first outlet flow 116, or II62, can be used to preheat the liquid water 204, in a heat exchanger 514, before its vaporization by the heat pump circuit 502.

[0108] Optionally, upstream of the heat pump circuit 502, the first outlet flow 116, or II62, can be used to superheat the water vapor produced by the heat pump circuit 502, in a heat exchanger 514.

[0109] According to an embodiment not shown, the first output stream 116, or II62, can be replaced by the second output stream 118, or II82 in the example in FIGURE 5

[0110] FIGURE 6 is a schematic representation of another non-limiting embodiment of a steam production unit that can be implemented in the present invention. [YES] The steam production unit 600 in FIGURE 6 can be the steam production unit 202 in FIGURES 2-4.

[0112] The 600 steam production unit includes all the elements described above with reference to the 500 steam production unit.

[0113] The steam production unit 600 further includes a second heat pump circuit, referenced 602. The second heat pump circuit 602 includes a compressor 604, a condenser 606, an expansion valve 608 and an evaporator 610. The second heat pump circuit 602 recovers, at the evaporator 610, some of the heat from the second outlet stream 118, or II82, to transfer it to the heat transfer fluid used in the first heat pump circuit 502 at the condenser 606.

[0114] Thus, the second heat pump circuit 602 allows at least part of the heat from the second output flow to be recovered and used for the production of steam from liquid water.

[0115] According to an embodiment not shown, the first and second output streams can be interchanged in the example of FIGURE 6.

[0116] FIGURE 7 is a schematic representation of another non-limiting embodiment of a steam production unit that can be implemented in the present invention.

[0117] The steam production unit 700 in FIGURE 7 can be the steam production unit 202 in FIGURES 2-4.

[0118] The steam production unit 700 includes a thermal storage device, also called a thermal reservoir, 702, for storing thermal energy. The thermal reservoir 702 can be of any type, such as a heat transfer fluid reservoir. The heat transfer fluid can be, for example, oil, water, or any other fluid.

[0119] The water vapor production unit 700 further includes the heat pump 502 which vaporizes the liquid water 204 into water vapor 112. However, unlike the water vapor production units 500 and 600, the heat pump circuit 502 vaporizes the water using heat supplied by, or consumed from, the thermal reservoir 702.

[0120] Optionally, the steam production unit 700 can include the heat exchanger 514 allowing the steam 112 to be superheated by heat exchange with the first outlet stream 116, or 1102.

[0121] The thermal reservoir 702 can be supplied by one, or any combination of at least two, of the heat recovery devices described below.

[0122] According to a first option, a heat exchanger 704 can be used to transfer some of the heat from the first outlet stream 116, in particular from the first outlet stream II62, to the thermal reservoir 702.

[0123] According to a second option, some of the heat generated at the hydrogen processing unit 110 can be recovered to supply the thermal storage tank 702, for example, using a heat exchanger (not shown). Indeed, the compression of the first outlet flow II62 at the hydrogen processing unit 110 causes the water vapor in said first flow II62 to condense: this condensation produces a significant amount of thermal energy corresponding to the latent heat of condensation of the water vapor. At least some of this latent heat can be transferred to the heat transfer fluid of the thermal storage tank 702, and more generally to the thermal storage tank itself.

[0124] According to a third option, it is possible to use a heat pump circuit 706 to recover heat from the first output stream 106, for example from the first output stream IO63 downstream of the hydrogen processing unit 110, and transfer it into the thermal reservoir 702.

[0125] According to a fourth option, the thermal reservoir 702 can be supplied with heat by a means 708 of heat production from solar radiation: - directly, for example by circulating the heat transfer fluid through a surface heated by solar radiation, or - via a heat exchanger (not shown), or - by an active driver powered by electric current generated by solar radiation.

[0126] According to a fifth option, the thermal reservoir 702 can be supplied with heat by a means 710 of geothermal heat production: - directly, for example by circulating the heat transfer fluid in a geothermal circuit, or - via a heat exchanger (not shown).

[0127] Of course, in each of the examples described, the steam production unit may include other components than those described here.

[0128] According to embodiments not shown, each of the options described above can be combined with the embodiments of FIGURES 5 and 6, if there is no technical obstacle to this combination.

[0129] FIGURE 8 is a schematic representation of another non-limiting embodiment of a steam production unit that can be implemented in the present invention.

[0130] The steam production unit 800 in FIGURE 8 can be the steam production unit 202 in FIGURES 2-4.

[0131] The steam production unit 800 in FIGURE 8 includes all the elements of the steam production unit 700 in FIGURE 7, except for the differences indicated below.

[0132] In the steam production unit 800, it is the second outlet flow 118, or II82, which is used instead of the first outlet flow 116, or II62.

[0133] Furthermore, the steam production unit 800 cannot include the second option described above with reference to FIGURE 7 to supply the thermal tank 702.

[0134] According to an embodiment not shown, it is possible to combine the embodiments of FIGURES 7 and 8 within the same steam production unit.

[0135] In all the examples given, the 102 unit of water vapor electrolysis can be of any type.

[0136] In particular, and without loss of generality, the electrolysis unit 102 may include at least one solid oxide electrolyzer, SOEL, in particular a high-temperature SOEL, for example at a temperature between 700°C and 850°C. Preferably, the electrolysis unit comprises several solid oxide electrolyzers arranged in series or in parallel.

[0137] Of course, the invention is not limited to the examples that have just been described.

Claims

DEMANDS 1. Process for producing hydrogen by steam electrolysis, comprising the following steps: - production of water vapor (112) by heating liquid water (204), and - electrolysis, in an electrolysis unit (102), of at least a portion of said water vapor (112), to provide a first output stream (116) rich in hydrogen and a second output stream (118) rich in oxygen; wherein the production of water vapor is carried out by at least one heat pump circuit reusing a portion of the heat from at least one of said output streams (116,118) to vaporize the liquid water.

2. A method according to the preceding claim, characterized in that the production of water vapor is carried out by a set of at least two heat pump circuits (502,602), connected in series, reusing part of the heat from at least one of said outlet flows (116,118) to vaporize the liquid water and produce water vapor.

3. A method according to the preceding claim, characterized in that the production of steam is carried out by: - a first heat pump circuit (502) reusing at least part of the heat from the first outlet flow (116), and - a second heat pump circuit (502) reusing at least part of the heat from the second output flow (118); said heat pump circuits (502,602) being connected in series so that one (602) of the heat pump circuits (502,602) heats the heat transfer fluid of the other (502) of the heat pump circuits (502,602).

4. A method according to any one of the preceding claims, characterized in that it comprises recovering at least a portion of the heat from at least one outlet stream by at least one heat pump circuit producing steam.

5. A method according to any one of the preceding claims, characterized in that at least a portion of the heat from at least one outlet stream is recovered by at least one heat recovery device and stored in a thermal storage means, at least one heat pump circuit producing water vapor from heat stored in said thermal storage means.

6. Method according to the preceding claim, characterized in that heat recovery from at least one outlet stream is carried out by at least one heat pump circuit.

7. A method according to any one of the preceding claims, characterized in that it further comprises the production of heat from a renewable energy source.

8. A method according to any one of the preceding claims, characterized in that it comprises: - at least one first heat exchange, within a heat exchanger, between at least one outlet flow (116) to heat the liquid water (204), in particular before its vaporization; - at least one second heat exchange, within a heat exchanger, between at least one outlet flow (116) and the water vapor produced to superheat the water vapor (112).

9. System (200;300;400) for the production of hydrogen by steam electrolysis, said system (200;300;400) comprising: - a unit (500;600;700;800) for producing steam (112) by heating liquid water (204), and - at least one electrolysis unit (102) for at least a portion of said steam (112), to provide a first output stream (116) rich in hydrogen and a second output stream (118) rich in oxygen; said steam production unit (500;600;700;800) comprising at least one heat pump circuit (502;602;706) reusing a portion of the heat from at least one of said outlet flows (116,118) to vaporize the liquid water.

10. System (200;300;400) according to the preceding claim, characterized in that the steam production unit comprises at least two heat pump circuits (502,602), connected in series, reusing part of the heat from at least one of said outlet streams (116,118) to vaporize liquid water and produce steam.

11. System according to any one of claims 9 or 10, characterized in that at least one heat pump circuit (502, 602) is arranged between at least one outlet flow (116, 118) and the liquid water (204), such that: - recover at least some of the heat from said at least one outlet stream (116,118), and - transfer said heat to liquid water (204) to vaporize it.

12. System (200;300;400) according to any one of claims 9 to 11, characterized in that the steam production unit (700;800) further comprises: - at least one heat recovery device (704, 706) from at least one of the outlet streams (116; 118), and - a thermal storage tank (102) for storing at least part of the heat recovered by said at least heat recovery device (704,706).

13. System (200;300;400) according to any one of claims 9 to 12, characterized in that the steam production unit further comprises a means (708,710) for producing heat from a renewable energy source.

14. A system according to any one of claims 9 to 13, characterized in that it comprises: - at least one first heat exchanger (512) to carry out a heat exchange between at least one outlet flow (116) to heat the liquid water (204), in particular before its vaporization; - at least one second heat exchanger (514) to carry out heat exchange between at least one outlet stream (116) and the water vapor (112) produced to superheat said water vapor (112).

15. System (200;300;400) according to any one of claims 9 to 14, characterized in that the electrolysis unit (102) comprises at least one solid oxide electrolyzer.

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