Integrated method and system for producing and purifying hydrogen with improved performance

Abstract

The invention relates to a method for producing hydrogen that comprises the following steps: - high-temperature electrolysis of steam in an electrolysis unit (102) taking as input a first flow (F1) comprising steam and a second flow (F2) comprising air, the electrolysis providing a third flow (F3) comprising hydrogen and nitrogen; and - separating the hydrogen and the nitrogen in the third flow (F3), in a purification unit (110), provided to receive the third flow (F3) and provide a fourth flow (F4) essentially comprising hydrogen, and a fifth flow (F5) comprising hydrogen and nitrogen; characterised in that the method further comprises recovering the hydrogen contained in the fifth flow (F5) for the electrolysis. The invention also relates to a system (300) implementing such a method.

Description

DESCRIPTION Title: Integrated process and system for the production and purification of hydrogen with improved performance

[0001] The present invention relates to an integrated process for producing and purifying hydrogen by high-temperature electrolysis of water vapor, with improved performance. It also relates to a system implementing such a process.

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

[0003] There are currently several techniques for producing hydrogen. One of these techniques is the electrolysis of water vapor in a solid oxide electrolyzer (SOEL). In short, water is heated to obtain water vapor. The water vapor is introduced into an electrolysis unit maintained at a temperature between 650°C and 850°C and supplied with electricity to decompose the water vapor molecule H2O into molecules of H2 and O2.

[0004] In some current architectures, the electrolysis unit takes as input on the one hand a first flow comprising water vapor to be electrolyzed, and on the other hand a second flow, generally comprising air and therefore nitrogen, among other things to balance the pressure within the electrolyzer and evacuate the oxygen which forms during electrolysis. At the output, the electrolyzer provides a third flow comprising hydrogen and an air flow enriched with oxygen.

[0005] Very often, the nitrogen in the second stream passes through the electrolysis cells and mixes with the hydrogen in the third stream. Thus, current systems include, in addition to the electrolysis unit, a purification unit for separating hydrogen from the other components of said third stream, and in particular from nitrogen and residual water vapor. The purification unit takes the third stream as input and provides as output a fourth stream comprising essentially hydrogen and a fifth stream containing most of the nitrogen. However, nitrogen and hydrogen are compounds that are very difficult to separate, so that the fifth stream includes a significant amount of residual hydrogen, for example of the order of 10% of the hydrogen produced, which degrades the overall performance of the system. Indeed, the residual hydrogen in the fifth stream is lost, released into the air or burned.

[0006] An aim of the present invention is to remedy the aforementioned drawback.

[0007] Another aim of the invention is to propose a solution for producing hydrogen by high-temperature electrolysis of water vapor, with improved performance compared to current solutions. Statement of the invention

[0008] The invention proposes to achieve at least one of the aforementioned aims by a process for producing hydrogen comprising the following steps: - high temperature electrolysis of water vapor in an electrolysis unit taking as input a first stream comprising water vapor and a second stream comprising air, said electrolysis providing a third stream comprising hydrogen and nitrogen; and - separation of hydrogen and nitrogen in said third stream, in a purification unit, designed to receive said third stream and provide a fourth stream comprising essentially hydrogen, and a fifth stream comprising hydrogen and nitrogen; characterized in that said method further comprises a recovery of at least part or all of said fifth stream for said electrolysis.

[0009] Currently, the fifth gas stream provided by the purification unit, and comprising a significant amount of hydrogen, is rejected, so that the hydrogen in this stream is lost. This rejection degrades the overall performance of the hydrogen production system, not to mention the pollution and danger that this can present. Unlike current solutions, the invention proposes to recover some or all of the hydrogen in the fifth stream, for the electrolysis reaction, which makes it possible to improve the overall performance of the process according to the invention. Such recovery can be carried out in different ways, as described in the embodiments set out below.

[0010] Furthermore, the solution proposed by the invention does not aim to separate all the residual hydrogen found in the fifth gaseous flow, which is a difficult operation to carry out, but to use part or all of the fifth gaseous flow during the recovery, without having to separate the hydrogen from the other components, and in particular from the nitrogen, found in said fifth gaseous flow, which is simpler to implement compared to a solution which would require isolating the hydrogen found in said fifth gaseous flow.

[0011] Furthermore, according to the invention, the hydrogen in the fifth gas stream is used for the electrolysis of water vapor in the process according to the invention. This makes it possible to release the performance requirement for the purification unit so that less efficient, but also less expensive and less complex to implement, purification units can be used. Certainly, a less efficient purification unit would provide a fifth stream whose hydrogen concentration would be higher. But since the fifth stream, and therefore the hydrogen in said fifth stream, is used for electrolysis, this would have little or no impact on the overall performance of the process according to the invention, while reducing its complexity, its cost, and increasing its simplicity of implementation.

[0012] According to embodiments, the recovery may comprise combustion of at least a portion of the fifth stream in a fuel cell. fuel for producing electricity, at least part of which is supplied to the electrolysis unit.

[0013] The fuel cell can be of any type.

[0014] The fuel cell may be a solid oxide fuel cell, SOFC (for "Solid Oxide Fuel Cell" in English), carrying out combustion of part or all of the fifth stream comprising hydrogen.

[0015] The electricity generated by the fuel cell can be used, in part or in whole, to power the electrolysis unit to carry out high-temperature electrolysis of water vapor. In particular, the electricity generated by the fuel cell and supplied to the electrolysis unit can be used for high-temperature electrolysis of water vapor.

[0016] According to embodiments, the recovery may comprise combustion, in a burner, of at least a portion of the fifth stream to generate a sixth hot stream, and use of the heat of said sixth stream for electrolysis.

[0017] Combustion can be achieved with air.

[0018] Combustion can be carried out with a flow of pure oxygen or oxygen-enriched air.

[0019] The combustion of at least part of the fifth stream makes it possible to obtain a sixth hot thermal stream, part or all of the heat of which can be reused for the electrolysis of water vapor in the electrolysis unit.

[0020] Of course, the burner can be of any type. For example, the burner can be a flame burner. In one embodiment, the burner can be a catalytic burner.

[0021] According to embodiments, the recovery may comprise a use of at least a portion of the heat of the sixth flow to heat: - the electrolysis unit; and / or - the first flow given at the input of said electrolysis unit; and / or - the second flow given at the input of said electrolysis unit.

[0022] To do this, at least a portion of the sixth flow can be supplied to at least one heat exchanger carrying out the exchange between said at least a portion of the sixth heat flow and: - the electrolysis unit, and in particular a stack of electrolysis cells of the electrolysis unit. In this case, the heat exchanger may be arranged in an enclosure in which said stack of electrolysis cells is located; and / or - the first stream, and / or - the second stream.

[0023] The heat exchanger can be of any type, such as those generally used in the technical field.

[0024] According to embodiments, the recovery may comprise using at least a portion of the heat of the sixth stream to produce a portion of the water vapor contained in the first stream.

[0025] For example, at least some of the heat from the sixth stream may be used to heat a water stream and produce water vapor from said water stream.

[0026] According to embodiments, the recovery may comprise: - on the one hand, a use of part of the heat of the sixth flow to produce part of the water vapor contained in the first flow, and - on the other hand, use of at least part of the heat of the sixth flow to heat: ■ the electrolysis unit; and / or ■ the first flow given at the input of said electrolysis unit; and / or ■ the second flow given at the input of said electrolysis unit. These two uses can be done in parallel, or in series.

[0027] According to embodiments, the valorization may comprise a use of at least a portion of the sixth stream to produce, in a generator, electricity of which at least part is supplied to the electrolysis unit.

[0028] The generator can be a steam turbine driven by the sixth stream.

[0029] According to another aspect of the present invention, there is provided a hydrogen production system comprising: - a high-temperature water vapor electrolysis unit, taking as input a first stream comprising water vapor and a second stream comprising air, said electrolysis providing a third stream comprising hydrogen and nitrogen; - a purification unit for separating the hydrogen contained in said third stream, designed to receive said third stream and provide a fourth stream comprising essentially hydrogen, and a fifth stream comprising hydrogen and nitrogen; characterized in that said system further comprises a unit for recovering at least a portion of said fifth stream for said electrolysis.

[0030] The system may comprise, in terms of technical means, each of the characteristics, and the alternatives relating thereto, described above with reference to the method according to the invention and which will not be repeated here in detail for the sake of conciseness.

[0031] According to embodiments, the recovery unit may comprise a fuel cell, and in particular a solid oxide fuel cell, for generating, from at least a portion of the fifth stream, electricity, at least a portion of which is supplied to the electrolysis unit.

[0032] Combustion can be carried out with a flow of pure oxygen or with a flow of air.

[0033] According to embodiments, the recovery unit may comprise a burner for the combustion of at least a portion of the fifth stream to generate a sixth hot stream, and a use of the heat of said sixth stream for electrolysis.

[0034] In this case, the recovery unit may include an exchanger to recover at least part of the heat from the sixth stream to heat: - the electrolysis unit; and / or - the first flow given at the input of the electrolysis unit, and / or - the second flow given at the input of the electrolysis unit.

[0035] According to embodiments, the recovery unit may comprise a heat exchanger for producing a portion of the water vapor contained in the first stream by using at least a portion of the heat from the sixth stream.

[0036] For example, at least part of the heat of the sixth stream can be used to heat a water stream and produce water vapor from said water stream, in an exchanger.

[0037] Preferably, the electrolysis unit may comprise at least one solid oxide electrolyzer.

[0038] According to exemplary embodiments, the electrolysis unit may comprise a stack of several solid oxide electrolysis cells, arranged in an enclosure and maintained at high temperature, for example at a temperature between 650°C and 850°C.

[0039] According to embodiments, the electrolysis unit can carry out electrolysis of water vapor at a temperature between 650°C and 850°C. Description of figures and embodiments

[0040] Other advantages and characteristics will appear on examining the detailed description of non-limiting embodiments, and the attached drawings in which: - FIGURE 1 is a schematic representation of a hydrogen production system according to the state of the art; and - FIGURES 2-5 are schematic representations of non-limiting exemplary embodiments of a system according to the invention.

[0041] It is understood that the embodiments which will be described below are in no way limiting. In particular, it is possible to imagine variants of the invention comprising only a selection of characteristics described below isolated from the other characteristics described, if this selection of characteristics is sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art. This selection includes at least one preferably functional characteristic without structural details, or with only part of the structural details if it is this part which is only sufficient to confer a technical advantage or to differentiate the invention compared to the state of the prior art.

[0042] In particular, all the variants and embodiments described can be combined with each other if there is no technical obstacle to this combination.

[0043] In the figures and in the rest of the description, the elements common to several figures retain the same reference.

[0044] FIGURE 1 is a schematic representation of a state-of-the-art hydrogen production system.

[0045] System 100 of FIGURE 1 performs hydrogen production by high temperature electrolysis of water vapor.

[0046] The system 100 comprises an electrolysis unit 102 performing high-temperature electrolysis of water vapor, for example electrolysis of steam at a temperature between 650°C and 850°C. In particular, the electrolysis unit 102 comprises a stack 104 of electrolysis cells, arranged in an enclosure 106, also called a hotbox. The stack 104 is maintained at a temperature between 650°C and 850°C.

[0047] The electrolysis unit 102 receives as input a first flow F1 comprising water vapor, and a second flow F2, which is generally air, and which therefore comprises nitrogen.

[0048] The electrolysis unit 102 provides a third stream F3 comprising hydrogen, and in particular dihydrogen H2, and nitrogen, and in particular dinitrogen N2, and an oxygen-enriched stream (not shown).

[0049] The electrolysis unit 102, and in particular the stack of cells 104, is powered by an electric current, denoted I in FIGURE 1, to carry out the electrolysis reaction of the water vapor.

[0050] The system 100 further comprises a purification unit 110 receiving the third stream F3 as an input. This purification unit 110 has the function of separating the hydrogen from the nitrogen present in the third stream F3.

[0051] According to non-limiting exemplary embodiments, the purification unit 110 may be, or comprise, a pressure swing adsorption purification unit, also called pressure swing adsorption or PSA, or VPSA ink (for “Vacuum Pressure Swing Adsorption” in English). According to another exemplary embodiment, the purification unit 110 may be a membrane.

[0052] At the outlet, the purification unit 110 provides a fourth stream F4 essentially comprising hydrogen. In particular, depending on the nature of the purification unit 110, the fourth stream F4 comprises a concentration of Fb greater than or equal to 99%.

[0053] The purification unit 110 further provides a fifth stream F5 comprising mainly nitrogen N2 but also hydrogen H2. In particular, depending on the nature of the purification unit 110, the fifth stream F5 comprises a concentration of Fb of the order of 90%. It is generally very difficult to obtain a concentration of Fb of less than 10% in the fifth stream F5.

[0054] The fifth stream F5 is sent to a vent. Thus, the energy linked to the hydrogen present in the fifth stream is lost and released into the atmosphere.

[0055] FIGURE 2 is a schematic representation of a non-limiting exemplary embodiment of a hydrogen production system according to the invention.

[0056] System 200 of FIGURE 2 performs hydrogen production by high temperature electrolysis of water vapor.

[0057] The system 200 of FIGURE 2 includes all of the elements of the system 100 of FIGURE 1. In addition, the system 200 includes a fuel cell, PAC, 202, and in particular a solid oxide fuel cell, or SOFC.

[0058] The PAC 202 receives as input part or all of the fifth flow F5 and carries out combustion of the hydrogen molecules present in said fifth flow F5, for example with an air flow or an oxygen flow (not shown). The PAC 202 provides an electric current, denoted II, which is used to power the electrolysis unit 102.

[0059] In the example shown, current II is not sufficient to supply the electrolysis unit 102 and is supplemented by a current 12 supplied by an external source (not shown).

[0060] FIGURE 3 is a schematic representation of a non-limiting exemplary embodiment of a hydrogen production system according to the invention.

[0061] System 300 of FIGURE 3 performs hydrogen production by high temperature electrolysis of water vapor.

[0062] The system 300 of FIGURE 3 includes all of the elements of the system 100 of FIGURE 1.

[0063] In addition, the system 300 comprises a burner 302 for carrying out combustion of at least a portion of the fifth stream F5. The burner 302 may be of any type.

[0064] The burner 302 receives as input part or all of the fifth flow F5 and carries out combustion of the hydrogen molecules located in said fifth flow F5, for example with an air flow or an oxygen flow. (not shown). Burner 302 provides a sixth stream F6 comprising water vapor, HzOv.

[0065] In addition, the system 300 comprises a heat exchanger 304 for carrying out a heat exchange between the sixth flow F6 and the first flow F1. This heat exchange makes it possible to transfer at least part of the calories from the sixth flow F6 to the first flow F1 and to heat the first flow F1. Thus, the heat generated by the combustion of the fifth flow F5 is used to heat the first flow F1.

[0066] According to embodiments not shown, the sixth flow F6 can, alternatively or in addition, be used to heat: - the second flow F2, and / or - the stack of cells 104 located in the enclosure 106.

[0067] FIGURE 4 is a schematic representation of a non-limiting exemplary embodiment of a hydrogen production system according to the invention.

[0068] System 400 of FIGURE 4 performs hydrogen production by high temperature electrolysis of water vapor.

[0069] The system 400 of FIGURE 4 includes all of the elements of the system 300 of FIGURE 3, except the heat exchanger 304.

[0070] Unlike system 300, system 400 includes a heat exchanger 402 used to vaporize a water stream and produce some or all of the first stream F1. More particularly, the heat of the sixth stream F6 is transferred to a water stream in the heat exchanger 402. The heated water with the calories transferred to it transforms into water vapor. This water vapor is used to form the first stream, alone or by mixing with other gaseous components.

[0071] FIGURE 5 is a schematic representation of a non-limiting exemplary embodiment of a hydrogen production system according to the invention.

[0072] System 500 of FIGURE 5 performs hydrogen production by high temperature electrolysis of water vapor.

[0073] The system 500 of FIGURE 5 includes all of the elements of the system 300 of FIGURE 3, except the heat exchanger 304.

[0074] Additionally, and unlike system 300 of FIGURE 3, the system 500 comprises a steam turbine 502. The sixth stream F6, exiting the burner 302, is supplied to the steam turbine 502 to produce an electric current 13. Part or all of the current 13 is supplied to the electrolysis unit 102 to power it.

[0075] In the example shown, the current 13 is not sufficient to supply the electrolysis unit 102 and is supplemented by a current 14 supplied, for example, by an external source (not shown).

[0076] Of course, the invention is not limited to the examples which have just been described.

Claims

CLAIMS 1. A process for producing hydrogen comprising the following steps: - high temperature electrolysis of water vapor in an electrolysis unit (102) taking as input a first flow (F1) comprising water vapor and a second flow (F2) comprising air, said electrolysis providing a third flow (F3) comprising hydrogen and nitrogen; and - separation of hydrogen and nitrogen in said third stream (F3), in a purification unit (110), provided to receive said third stream (F3) and provide a fourth stream (F4) comprising essentially hydrogen, and a fifth stream (F5) comprising hydrogen and nitrogen; characterized in that said method further comprises a recovery of at least part or all of said fifth stream (F5) for said electrolysis.

2. Method according to the preceding claim, characterized in that the recovery comprises an oxidation of at least a part of the fifth flow (F5) in a fuel cell (202) to produce electricity (II) of which at least a part is supplied to the electrolysis unit (102).

3. Method according to any one of the preceding claims, characterized in that the recovery comprises combustion, in a burner (302), of at least a part of the fifth flow (F5) to generate a sixth hot flow (F6), and use of the heat of said sixth flow (F6) for electrolysis.

4. Method according to the preceding claim, characterized in that the recovery comprises a use of at least part of the heat of the sixth flow (F6) to heat: - the electrolysis unit (102); and / or - the first flow (Fl) given at the input of the electrolysis unit (102), and / or - the second flow (F2) given at the input of the electrolysis unit (102).

5. Method according to any one of claims 3 or 4, characterized in that the recovery comprises a use of at least part of the heat of the sixth flow (F6) to produce part of the water vapor contained in the first flow (F1).

6. Method according to any one of claims 3 to 5, characterized in that the recovery comprises a use of at least a part of the sixth flow (F6) to produce, in a generator (602), electricity (13) of which at least a part is supplied to the electrolysis unit (102).

7. Hydrogen production system (200;300;400;500) comprising: - a unit (102) for high-temperature electrolysis of water vapor, taking as input a first flow (F1) comprising water vapor and a second flow (F2) comprising air, said electrolysis providing a third flow (F3) comprising hydrogen and nitrogen; - a purification unit (110) for separating the hydrogen contained in said third stream (F3), designed to receive said third stream (F3) and provide a fourth stream (F4) essentially comprising hydrogen, and a fifth stream (F5) comprising hydrogen and nitrogen; characterized in that said system further comprises a unit for recovering at least a portion of said fifth stream (F5) for said electrolysis.

8. System (200) according to the preceding claim, characterized in that the recovery unit comprises a fuel cell (202) for generating, from at least part of the fifth flow (F5), electricity (II) of which at least part is supplied to the electrolysis unit (102).

9. System (300;400;500) according to any one of claims 7 or 8, characterized in that the recovery unit comprises a burner (302) for the combustion of at least part of the fifth flow (F5) to generate a sixth hot stream (F6), and a use of the heat of said sixth stream (F6) for electrolysis.

10. System (300) according to the preceding claim, characterized in that the recovery unit comprises a heat exchanger (304) for recovering at least part of the heat from the sixth flow (F6) for heating: - the electrolysis unit (102); and / or - the first flow (Fl) given at the input of the electrolysis unit (102), and / or - the second flow (F2) given at the input of the electrolysis unit (102).

11. System (400) according to any one of claims 9 or 10, characterized in that the recovery unit comprises a heat exchanger (402) for producing part of the water vapor contained in the first flow by using at least part of the heat of the sixth flow.

12. System (200; 300; 400; 500) according to any one of claims 7 to 11, characterized in that the electrolysis unit (102) comprises at least one solid oxide electrolyser.

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