Method and system for producing hydrogen and / or oxygen

Abstract

The invention relates to a method (100) for producing hydrogen and / or oxygen by means of electrolysis, in which an electrolysis unit (10) is supplied with a direct current (2) which is provided from an alternating current (1) using a rectifier (20), wherein the electrolysis unit (10) is supplied with water using a water circuit (110). The rectifier (20) is cooled using a cooling water which is provided using a sub-flow (5) of water being conducted in the water circuit (110) and / or water supplied to the water circuit. The invention likewise relates to a corresponding system.

Description

[0001] Description

[0002] Process and plant for the production of hydrogen and / or oxygen

[0003] The invention relates to a process and a plant for producing hydrogen and / or oxygen by electrolysis.

[0004] background

[0005] The production of hydrogen and / or oxygen by water electrolysis is known and described, for example, in the article “Hydrogen” in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, June 15, 2000, DOI: 10.1002 / 14356007.a13_297, particularly in Section 4.2, “Electrolysis”.

[0006] In a water electrolysis plant, water is split into hydrogen and oxygen using electrical current. A power supply unit adjusts the voltage level of an alternating current via an AC transformer. The alternating current is converted into direct current using a rectifier, as an electrolysis cell stack requires this type of current.

[0007] Part of the electrical power supplied to the power supply unit is converted into heat and must be continuously dissipated. The invention aims to improve this.

[0008] Disclosure of the invention

[0009] Against this background, a process and a plant for producing hydrogen and / or oxygen by electrolysis are proposed, each with the features of the independent patent claims. Further embodiments are the subject of the dependent patent claims and the following description.

[0010] For water electrolysis, electrolysis cells with

[0011] Proton exchange membranes (PEMs) are used. In corresponding electrolysis cells, a solid polymer electrolyte, the proton exchange membrane, is used. The proton exchange membrane serves to conduct protons, separate the product gases, and electrically insulate the anode and cathode sides. By using electrolysis cells with proton exchange membranes, some of the problems associated with partial load operation and the low potential current densities that occur with conventional alkaline electrolysis can be overcome.

[0012] Due to the comparatively high pressure of the hydrogen produced when using electrolysis cells with proton exchange membranes, consumers can be supplied directly. The high current densities that can be used lead to comparatively low operating costs, especially in cases where dynamic electrical energy sources such as wind and solar are used, where peaks in energy supply cannot otherwise be utilized. The polymer electrolyte enables the use of thin membranes, for example, approximately 100 to 200 pm, at high pressures. This leads to low ohmic losses, which are primarily caused by the conduction of protons through the membrane and the formation of pressurized hydrogen.

[0013] Due to its rigid structure, the polymer electrolyte membrane exhibits a low gas transfer rate, which can lead to very high product gas purity. This can be particularly advantageous for storage safety and for direct use, for example, in a fuel cell.

[0014] The anode reaction in a proton exchange membrane electrolysis cell is commonly referred to as the oxygen evolution reaction (OER). At the anode, the liquid reactant water is fed to the catalyst and oxidized to oxygen, protons, and electrons.

[0015] The cathode reaction is commonly referred to as the hydrogen evolution reaction (HER). In this reaction, the supplied electrons combine with the protons passing through the membrane, producing gaseous hydrogen.

[0016] Although the present invention is described below (at least predominantly) with reference to electrolysis using proton exchange membranes, embodiments of the present invention are also fundamentally suitable for other electrolysis processes in which the problems described here may occur in the same way. These may, for example, include conventional water electrolysis in which an aqueous alkaline solution, typically potassium hydroxide, is used as the electrolyte (AEL, alkaline electrolysis). The electrolysis is carried out using a unipolar or bipolar electrode arrangement at atmospheric pressure or, on an industrial scale, even significantly higher.

[0017] In the process proposed here, a gas mixture known as anode gas is extracted from the anode side of an electrolysis device. This gas mixture is typically saturated with water and consists predominantly of oxygen, but also contains a significant amount of hydrogen.

[0018] Typically, a corresponding electrolysis device in which proton exchange membranes are used utilizes a plurality of electrolysis cells, wherein the electrolysis cells may, in particular, be part of one or more electrolysis cell stacks of known type. In the case of electrolysis using a proton exchange membrane, such an electrolysis cell stack comprises a plurality of arrangements each comprising an anode, a proton exchange membrane, and a cathode, each separated from one another by separating devices and means for water feed or gas removal. In other electrolysis processes, the elements present therein may also be present in plural. Feed or collecting lines may be provided that supply the electrolysis cell stack(s) as a whole.

[0019] The gas mixture referred to here as anode gas refers to the entire gas extracted from the anode side of the cell stack(s) or a portion thereof. When using proton exchange membranes, the anode gas is extracted together with water from the anode side, i.e., a two-phase flow is initially conducted from the anode side. After separation into the gas and liquid phases in a separator, the anode gas is present as the gas phase.

[0020] The terms “feed side”, “anode side” and “cathode side” refer to the positions or devices at or by means of which water as feed, an anode gas as product (optionally with water) and a cathode gas as product are withdrawn from an electrolysis cell stack or a module or another higher-level unit, i.e. an electrolysis unit as used here. As an umbrella term for “anode side” and “cathode side”, the term “product side” is used hereinafter in the case of withdrawal of the anode gas or cathode gas. As mentioned, the anode gas withdrawn on the anode side is withdrawn in a two-phase mixture with water during electrolysis with proton exchange membranes. For ease of reference, the term “anode water” is also used hereinafter.

[0021] In a low-voltage rectifier, the required heat dissipation is usually achieved through air cooling, e.g., by means of one or more fans. However, water cooling would also be attractive, at least for a medium-voltage rectifier. However, due to the compact design and narrow channels, standard cooling water cannot typically be used for rectifier cooling. One known prior art solution, for example, involves providing a cooling circuit that uses a water-glycol mixture as the cooling medium.

[0022] Large-scale electrolysis plants are typically constructed in modules, combining multiple electrolysis cell stacks (as explained above) into a so-called main water circuit (oxygen-hydrogen separation, pump, heat exchanger) required for electrolysis. Several such modules can be used to provide the total required electrolysis capacity.

[0023] Embodiments of the present invention are now based on the finding that the main water circuit in the electrolysis already comprises ultrapure water, or that ultrapure water is supplied to the main water circuit in an inlet, and a water-cooled rectifier can therefore be integrated with particular advantage into the main water circuit of the electrolysis or its inlet.

[0024] In general, when an element, a part, a component or a process step is referred to in the singular (“an” electrolysis cell stack, “an” electrolysis module with “an” electrolysis cell stack, “a” rectifier, “a” power supply unit, etc.), it should not be excluded that corresponding elements, parts, components or process steps may also be present in plural and may each be implemented in the same, identical, essentially identical, comparable or different manner.

[0025] A method for producing hydrogen and / or oxygen by electrolysis is proposed, in which an electrolysis unit is fed with direct current provided from alternating current using a rectifier, the electrolysis unit being operated using a water circuit. The rectifier is cooled using cooling water provided using a partial flow of water circulating in and / or supplied to the water circuit.

[0026] The process proposed here firstly avoids the disadvantage of conventional air cooling, especially indoors, which consists in the extremely high HVAC (heating, ventilation, and air conditioning) requirements to ensure the required cooling. The comparatively high capital expenditures (CAPEX) and operating expenses (OPEX) of rectifiers with an independent (water-glycol) cooling circuit, as well as the maintenance effort, can also be reduced in the designs proposed here.

[0027] The complex piping required, particularly when using multiple rectifiers in a system not according to the invention, if a shared pump and heat exchanger are used, is eliminated. However, if individual circuits are used per electrolysis module, a correspondingly large number of pumps and heat exchangers can be dispensed with.

[0028] In embodiments of the proposed method, water is withdrawn from the electrolysis unit in a two-phase stream with an anode gas, with the two-phase stream being fed to a separator unit. Such embodiments are particularly advantageous in electrolysis with a proton exchange membrane.

[0029] In particular, water can be extracted from a corresponding separator unit and at least partially fed to a cooling unit. The cooling unit can be provided, in particular, as a heat exchanger operated with cooling water, an air cooler, or another heat exchanger or cooler of a known type. Separate coolers for cooling the cooling water can advantageously be dispensed with in corresponding embodiments.

[0030] For this purpose, in embodiments of the present invention, the partial flow used to provide the cooling water is branched off, in particular, from a water flow taken from the cooling unit. In this way, the cooling water flow already has a suitable temperature.

[0031] A residual flow of the water stream taken from the cooling unit, or a portion thereof, remaining after the partial flow is diverted can be used in embodiments to provide the water that feeds the electrolysis unit. In this way, the water circuit is closed. Preferably, as mentioned, no additional components are required to effect cooling. In other words, a main water pump of the water circuit can also be used to pump the cooling water flow through the rectifier, and a main heat exchanger can also be used to cool the rectifier.

[0032] Additional water can be withdrawn from the separator unit, at least a portion of which, in particular an adjustable portion, can be used to provide the water that feeds the electrolysis unit, bypassing the cooling unit. This makes it possible to adjust the temperature of this water to a suitable value. By diverting the cooling water flow upstream of a bypass recirculation, it can advantageously be provided at a lower temperature.

[0033] The cooling water, or a portion thereof, is typically fed to a purification unit after use. However, it may also be provided that a portion of it is returned to the separator unit after use to cool the rectifier.

[0034] In embodiments of the method proposed here, the water withdrawn from the separator unit can have a temperature in a temperature range of 50 to 80°C, in particular 55 to 75°C or 55 to 60°C, and / or the water stream withdrawn from the cooling unit can have a temperature in a temperature range of less than 50°C, in particular less than 45°C or less than 43°C, and / or the water supplied to the electrolysis unit can have a temperature in a temperature range of 50 to 80°C, in particular 50 to 75°C. These temperatures can be adapted as appropriate.

[0035] In embodiments of the method proposed here, the water circuit may include a purification circuit, wherein the partial flow used to provide the cooling water is a partial flow of the water conducted in the purification circuit. If this is not the case, the cooling water flow reduces the water conducted in a corresponding purification circuit and the heat requirement.

[0036] The proposed plant for producing hydrogen and / or oxygen is equipped with an electrolysis unit and a rectifier. The rectifier is configured to supply the electrolysis unit with direct current and to provide the direct current from alternating current. The plant is configured to supply the electrolysis unit with water using a water circuit. The proposed plant is configured to cool the rectifier using cooling water and to provide the cooling water using a partial flow of water circulated in and / or supplied to the water circuit.

[0037] For further features and advantages of a corresponding system and embodiments thereof, reference is expressly made to the above explanations concerning the method proposed according to the invention and its embodiments, since these apply equally to this.

[0038] In summary, the advantages of the invention are that no separate cooling circuit is required for rectifier cooling, no separate pump or heat exchanger needs to be provided for this purpose, and short piping is sufficient, since a separator unit, a main water pump, a heat exchanger, the rectifier, and the electrolysis unit can be arranged in close proximity in an electrolysis module. Since the water temperature to a purification unit is reduced, an additional heat exchanger upstream of it can be reduced in size or eliminated. These advantages result in reduced CAPEX and OPEX, as well as lower maintenance requirements.

[0039] The same applies to a system which, according to an embodiment of the invention, is designed to carry out a method according to any embodiment of the present invention.

[0040] Short description of the drawing

[0041] Embodiments of the invention are described below purely by way of example with reference to the accompanying drawings, in which

[0042] Figure 1 illustrates a method according to an embodiment of the invention.

[0043] Embodiments of the invention

[0044] The embodiments described below are described solely for the purpose of assisting the reader in understanding the claimed and previously discussed features. They are merely representative examples and are not intended to be exhaustive and / or limiting with regard to the features of the invention. It is to be understood that the advantages, embodiments, examples, functions, features, structures, and / or other aspects described above and below are not to be considered as limitations on the scope of the invention as defined in the claims or as limitations on equivalents to the claims, and that other embodiments may be utilized and changes may be made without departing from the scope of the claimed invention.

[0045] Different embodiments of the invention may include, have, consist of, or consist essentially of other useful combinations of the described elements, components, features, parts, steps, means, etc., even if such combinations are not specifically described here. Furthermore, the disclosure may cover other inventions that are not currently claimed but that may be claimed in the future, particularly if they are encompassed by the scope of the independent claims. Explanations relating to devices, apparatus, arrangements, systems, etc. according to embodiments of the present invention may also apply to methods, processes, methods, etc. according to embodiments of the present invention, and vice versa. Identical, similarly acting, functionally corresponding, structurally identical, or comparably constructed elements, method steps, etc.may be indicated with identical reference symbols.

[0046] The present invention and embodiments thereof are explained below with reference to electrolysis using a proton exchange membrane. However, as mentioned several times, the invention is not limited to this.

[0047] Figure 1 illustrates a method according to an embodiment of the invention and is designated overall by 100.

[0048] The process 100 serves to produce hydrogen and / or oxygen by electrolysis, although the hydrogen production is not separately illustrated. An electrolysis unit 10 is supplied with direct current 2, which is generated from alternating current 1 using a rectifier 20. The current flows are each illustrated by dashed arrows.

[0049] The electrolysis unit 10 is further supplied with water using a water circuit, designated overall by 110. The rectifier 20 is cooled using cooling water, which is provided using a partial stream 5 of water conducted in the water circuit 110 and / or supplied to the water circuit. The latter, the supply using a partial stream of water supplied to the water circuit 110, ie, makeup water, is not separately illustrated.

[0050] Water 4 is withdrawn from the electrolysis unit 10 in a two-phase stream 4, 6 with an anode gas 6, wherein the two-phase stream 4, 6 is fed to a separator unit 30. In the separator unit 30, the water 4 separates from the anode gas 6, i.e. predominantly oxygen, the latter being able to be fed, for example, for suitable processing or use or released into the atmosphere. Water, now designated 7, is withdrawn from the separator unit 30 and at least partially fed to a cooling unit 50. In the example illustrated here, the partial stream 5 used to provide the cooling water is branched off from a water stream 8 taken from the cooling unit 50. It therefore has the temperature reached in the cooling unit 50.A residual stream 9 of the water stream 8 taken from the cooling unit 50, or a part thereof, remaining after the branching off of the partial stream 5 is used to provide the water 3 with which the electrolysis unit 10 is fed.

[0051] To adjust the temperature of the water 3, in the example illustrated here, additional water 7 is taken from the separator unit 30, at least a portion of which is used to provide the water 3, which is fed to the electrolysis unit 10, bypassing the cooling unit 50. For this purpose, a corresponding bypass is provided via a valve 60.

[0052] After being used to cool the rectifier 20, the cooling water 5, or a portion 5b thereof, is fed to a purification unit 80 integrated into the water circuit 110. A further portion 5a of the cooling water 5 can be returned to the separator unit 30. The return of cooling water to the separator unit 30 is optional; that is, the entire cooling water 5 can also be passed through the purification unit 80, as illustrated by portion 5b.

Claims

Patent claims 1 . A method (100) for producing hydrogen and / or oxygen by electrolysis, in which an electrolysis unit (10) is fed with direct current (2) which is provided from alternating current (1) using a rectifier (20), the electrolysis unit (10) being fed with water using a water circuit (110), characterized in that the rectifier (20) is cooled using cooling water which is provided using a partial flow (5) of water conducted in the water circuit (110) and / or supplied to the water circuit (110).

2. Method (100) according to claim 1, wherein water (4) is withdrawn from the electrolysis unit (10) in a two-phase stream (4, 6) with an anode gas (6), wherein the two-phase stream (4, 6) is fed to a separator unit (30).

3. Method (100) according to claim 2, wherein water (7) is removed from the separator unit (30) and at least partially fed to a cooling unit (50).

4. Method (100) according to claim 3, wherein the partial flow (5) used to provide the cooling water is branched off from a water flow (8) taken from the cooling unit (50).

5. Method (100) according to claim 4, wherein a residual stream (9) of the water stream (8) withdrawn from the cooling unit (50) remaining after the branching off of the partial stream (5) or a part thereof is used to provide the water (3) with which the electrolysis unit (10) is fed.

6. The method (100) according to claim 5, wherein at least a portion of the water (7) withdrawn from the separator unit (30) is used to provide the water (3) with which the electrolysis unit (10) is fed, bypassing the cooling unit (50).

7. Method (100) according to one of claims 2 to 6, wherein the cooling water or a part thereof is fed to a cleaning unit (80) integrated into the water circuit (110) after use for cooling the rectifier (10).

8. Method (100) according to one of the preceding claims, in which the water (7) taken from the separator unit (30) has a temperature in a temperature range of 50 to 80 °C and / or in which the water stream (8) taken from the cooling unit (50) has a temperature in a temperature range of less than 50 °C and / or in which the water (3) with which the electrolysis unit (10) is fed has a temperature in a temperature range of 50 to 80 °C.

9. Method (100) according to one of the preceding claims, wherein the water circuit (110) comprises a cleaning circuit, wherein the partial flow (5) used to provide the cooling water is a partial flow of the water conducted in the cleaning circuit.

10. Plant for producing hydrogen and / or oxygen, comprising an electrolysis unit (10) and a rectifier (20), wherein the rectifier (20) is designed to feed the electrolysis unit (10) with direct current (2) and to provide the direct current from alternating current (1), wherein the plant is designed to feed the electrolysis unit (10) with water using a water circuit (110), characterized in that the plant is designed to cool the rectifier (20) using cooling water and to provide the cooling water using a partial flow (5) of water conducted in the water circuit (110) and / or supplied to the water circuit. 11 . Plant according to claim 10, which is arranged to carry out a method according to one of claims 1 to 9.

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