Method for recycling water in an electrolyzer unit and electrolyzer system

Abstract

The invention relates to a method for recycling cathode water (7) in an electrolyzer unit (1), in particular a PEM or AEM electrolyzer unit (1), wherein, prior to the cathode water (7) leaving an electrolysis cell stack (10) of the electrolyzer unit (1) being fed back into a medium supply (20) of the electrolyzer unit (1), hydrogen (8) present in the cathode water (7) is separated, wherein, in a hydrogen separation device (50) of the electrolyzer unit (1), in a first separation step, hydrogen (8) is separated from the hydrogen-rich cathode water (7) by an overpressure in a first volume (51) of the hydrogen separation device (50), and in a second separation step following the first separation step, by a residence time of the now hydrogen-poor cathode water (7) in a second volume (52) of the hydrogen separation device different from the first volume (51). (50),further hydrogen (8) is separated.,

Description

[0001] The invention relates to a method for recirculating cathode water in an electrolyzer unit. Furthermore, the invention relates to an electrolyzer system for an electrolyzer plant, comprising at least one electrolyzer unit. State of the art

[0002] During water electrolysis using an electrolyzer unit (stationary or mobile), e.g., an electrolyzer system, an electrolysis plant, an electrochemical conversion or splitting of, in particular, treated and, in particular, demineralized water takes place using electrical energy into hydrogen and oxygen, generating heat. The electrolyzer unit comprises at least one membrane electrode device (membrane with transport layers and electrodes arranged between them), e.g., an AEM (anion exchange membrane) or a PEM (proton exchange membrane). Typically, the electrolyzer unit is configured with a plurality of membrane electrode devices arranged in a stack and bipolar plates arranged between them, the so-called electrolysis cell stack with a plurality of individual electrolysis cells. Task

[0003] Efforts are constantly underway to improve electrolyzer units and their process control. Mixtures of the product gases hydrogen and oxygen from electrolysis cell stacks of electrolyzer units exhibit a wide range of potentially explosive molar ratios. To reliably prevent an explosion, care must be taken to avoid mixing these two product gases. - It is an object of the invention to reliably prevent the formation of potentially explosive gas mixtures at various points in the electrolyzer unit or in the electrolyzer system. Disclosure of the invention

[0004] The object of the invention is achieved by a method for recirculating cathode water in an electrolyzer unit, in particular a PEM or AEM electrolyzer unit; and by means of an electrolyzer system, in particular a PEM or AEM electrolyzer system, for an electrolyzer system having at least one electrolyzer unit. Advantageous developments, additional features, and / or advantages of the invention emerge from the dependent claims and the following description.

[0005] In the method according to the invention, hydrogen present in the cathode water is separated prior to the cathode water leaving an electrolysis cell stack of the electrolyzer unit being fed back into a medium supply of the electrolyzer unit. In a hydrogen separation device of the electrolyzer unit, hydrogen is separated from the hydrogen-rich cathode water in a first separation step by applying excess pressure in a first volume of the hydrogen separation device. In a second separation step following the first separation step, further hydrogen is separated by allowing the cathode water, now with less hydrogen, to remain in a second volume of the hydrogen separation device for a different period than the first volume.

[0006] In this case, the cathode water naturally originates from a cathode of the electrolysis cell stack. The overpressure is specifically the (fluid) pressure that arises in the first volume due to the operating pressure of the electrolysis cell stack. The overpressure can essentially correspond to the operating pressure (losses) or be an intentionally reduced overpressure compared to the operating pressure. The "overpressure" refers to a normal ambient pressure.

[0007] In the recirculation process, a cathode side of the electrolysis cell stack can be operated with an overpressure of approximately 5 bar to approximately 100 bar, preferably approximately 20 bar to approximately 40 bar, and preferably equal to or greater than approximately 5 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar, or 50 bar, each ±2 bar, relative to an anode side of the electrolysis cell stack. Of course, the invention is also applicable from the field of low-pressure electrolysis (overpressures up to 0.5 bar) to the field of high-pressure electrolysis (overpressures up to over 100 bar).

[0008] This (degassing) results in at least a two-stage process for managing the hydrogen concentration in the cathode water. This allows for largely hydrogen-free cathode water to be recycled, and this cathode water can be added to the recycled anode water. Another advantage is that a continuous supply of pressurized hydrogen is possible, since pressure relief can only take place after the first volume and before / in a second or subsequent volume separate from the first volume. Thus, the pressurized hydrogen can be made available, for example, to a hydrogen storage facility.

[0009] In the second separation step, further hydrogen can be separated by at least one pressure release of the now hydrogen-poor cathode water upstream of the second volume or in the second volume of the hydrogen separation device. This (degassing) results in an at least three-stage process for managing the hydrogen concentration in the cathode water.

[0010] In at least one separation step following the second separation step, further hydrogen can be separated from the cathode water by applying a further overpressure that is less than the overpressure in the first volume, by a further residence time, and / or by further pressure relief in at least one additional volume of the hydrogen separation device that is different from the first and second volumes. This (degassing) allows the two- or three-stage process for managing the hydrogen concentration in the cathode water to be expanded to include additional stages.

[0011] Fresh water can be supplied and / or added to the cathode water downstream of the first volume and upstream of a water reservoir of the electrolyzer unit. The cathode water is naturally unmixed cathode water originating from the electrolysis cell stack. The fresh water can be supplied and / or added to the cathode water at a single or multiple points between the first volume and the water reservoir.

[0012] The fresh water can be and / or be supplied to the cathode water upstream of, into, or downstream of the last, in particular second, volume. - The fresh water is, in particular, treated and / or demineralized fresh water, e.g., from a water treatment facility. - This (dilution) results in at least a four-stage process for managing the hydrogen concentration in the cathode water, based on the three-stage process.

[0013] After the separation steps, the cathode water can be fed back into the water reservoir from which it originated. Anode water leaving the electrolysis cell stack can be fed back into the water reservoir from which it originated.

[0014] The first volume can be supplied with, or is supplied with, the hydrogen-rich cathode water from a cathode of the electrolysis cell stack. The second volume can be supplied with, or is supplied with, the less hydrogen-rich cathode water from the first volume. The water reservoir can be supplied with, or is supplied with, the substantially degassed cathode water from the second volume. In embodiments, hydrogen can be continuously provided from the first volume. Furthermore, a permanent overpressure can be established in the first volume in the first separation step. Furthermore, no pressure relief can be carried out in the first volume in the first separation step.

[0015] An overpressure in the first volume and / or a pressure relief in the second volume can be approximately 5 bar to approximately 100 bar, preferably approximately 20 bar to approximately 40 bar, and preferably equal to or greater than approximately: 5 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar, or 50 bar, each ±2 bar. The pressure relief in the second volume can be carried out essentially continuously or essentially suddenly. The pressure relief in the second volume can be carried out to a specific pressure level or to an ambient pressure level.

[0016] The second volume can be filled with the cathode water with a lower hydrogen content due to the pressurized cathode water with a lower hydrogen content. The substantially degassed cathode water can be conveyed or can be conveyed from the second or further volume into the water reservoir by a conveying device of the hydrogen separation device. The recirculation process can be carried out and / or can be carried out by an electrolyzer system according to the invention.

[0017] A feature explained below in the context of an electrolyzer system is naturally applicable to the recirculation process explained above. Furthermore, a feature explained above in the context of the recirculation process is naturally applicable to the electrolyzer system explained below.

[0018] The electrolyzer system according to the invention comprises at least one electrolyzer unit, wherein the electrolyzer unit has a hydrogen separation device downstream of its electrolysis cell stack for separating hydrogen present in a cathode water originating from the electrolysis cell stack. The hydrogen separation device has two spatially separated volumes for separating hydrogen, the first volume being that of a gas / liquid pressure separator and the second volume being that of a separation tank.

[0019] The gas / liquid pressure separator can be designed such that hydrogen can be separated from the hydrogen-rich cathode water by applying an overpressure within its volume. Furthermore, the separation tank and / or a cathode-side disposal path can be designed such that further hydrogen can be separated by a residence time and / or pressure relief of the now hydrogen-poor cathode water.

[0020] The overpressure in the gas / liquid pressure separator can be generated by an overpressure on a cathode side of the electrolysis cell stack relative to an anode side of the electrolysis cell stack. The separation tank and / or the cathode-side disposal path can have a fluid throttle of the hydrogen separation device, by means of which the pressure relief of the lower-hydrogen cathode water can be carried out.

[0021] The first volume can be brought into substantially direct fluid communication with the electrolysis cell stack or can be in substantially direct fluid communication with the first volume. Furthermore, the second volume can be brought into direct fluid communication with the first volume or can be in substantially direct fluid communication with the first volume. Furthermore, the second or another volume can be brought into fluid communication with a water reservoir of the electrolyzer unit by gravity or by means of a conveying device of the hydrogen separation device, or can be in fluid communication with the water reservoir.

[0022] In the cathode-side disposal path, a (supply) connection for fresh water (treated water for the electrochemical function) can be provided, which is located downstream of the gas / liquid pressure separator and upstream of a water reservoir of the electrolyzer unit. A single or multiple connections for the fresh water can be provided between the gas / liquid pressure separator and the water reservoir.

[0023] A fresh water connection can be installed in a line upstream of the separation tank, on / in the separation tank, or in a line downstream of the separation tank in the cathode-side disposal path. A fresh water connection can be implemented as a distributor (T-piece, Y-piece) in a line of the cathode-side disposal path, as a connector on / in the separation tank, or through a mixer in the cathode-side disposal path.

[0024] A fresh water line, in particular a fresh water line of a water treatment facility, can open into the water reservoir. Furthermore, degassed cathode water from the separation tank can be conveyed into the water reservoir by means of a conveying device of the hydrogen separation facility. Furthermore, anode water leaving the electrolysis cell stack can be fed back into the water reservoir from which it originated.

[0025] The electrolyzer system can comprise a plurality of electrolyzer units. A gas / liquid pressure separator can be assigned to each electrolysis cell stack, or a single gas / liquid pressure separator can be assigned to a plurality of electrolysis cell stacks. Furthermore, a single separation tank can be assigned to a plurality of gas / liquid pressure separators. Furthermore, a fresh water line, in particular a fresh water line of a water treatment device, can open, in particular upstream, within, or downstream of a single separation tank of the electrolyzer system. Furthermore, a conveying device for conveying water, in particular from the single separation tank, can be assigned to each water reservoir of the electrolyzer system. Short description of the characters

[0026] The invention is explained in more detail below using exemplary embodiments with reference to the attached schematic and not-to-scale drawing. In the invention, a feature can be configured positively, i.e., present, or negatively, i.e., absent. In this specification, a negative feature is not explicitly explained as a feature unless it is important for the invention to be absent. This means that the invention actually made, and not one constructed by the prior art, consists in omitting this feature. The absence of a feature (negative feature) in an exemplary embodiment indicates that the feature may be optional (to a person skilled in the art). - In the merely exemplary figures (Fig.) of the drawing: The Fig. 1 shows a simplified block diagram of an embodiment of an electrolyzer unit with an electrochemical electrolysis cell stack for an electrolyzer system, the Fig. 2 a flow diagram of a method according to the invention for recycling cathode water in an electrolyzer unit, in particular a PEM or an AEM electrolyzer unit, and the Fig. 3 and Fig. 4 each show an embodiment of an electrolyzer system, in particular a PEM electrolyzer system, for an electrolyzer plant, with a ( Fig. 3) or a plurality ( Fig. 4) of electrolyzer units. Embodiments of the invention

[0027] The invention is described below using an electrolyzer system 0 (see the Fig. 3 and Fig. 4) with at least one electrolyzer unit 1 (see also the Fig. 1) with at least one electrolysis cell stack 10 for a water electrolysis for converting treated and in particular demineralized water 4 (deionized water) into hydrogen 8 and oxygen 6 and a process (cf. the Fig. 2) for recirculating cathode water 7 in an electrolyzer unit 1 is explained in more detail. The invention is applicable to a plurality of electrolyzer systems 0 with one or a plurality of electrolyzer units 1, wherein an electrolyzer unit 1 can be designed for, for example, PEM electrolysis, AEM electrolysis, etc.

[0028] The drawing shows only those sections of an electrolyzer unit 1 of an electrolyzer system 0, e.g., an electrolyzer plant (not shown), which are necessary for understanding the invention. Although the invention is described and illustrated in detail using preferred embodiments, the invention is not limited to the disclosed embodiments. Other variations can be derived therefrom without departing from the scope of the invention.

[0029] The Fig. 1 shows an electrolyzer unit 1 according to a general embodiment, comprising at least one, in particular a plurality of, individual electrochemical cells 11 (individual electrolysis cell 11) bundled into an electrolysis cell stack 10, which are accommodated, in particular with end plates of the electrolysis cell stack 10, in a preferably fluid-tight stack housing 16. Each individual cell 11 comprises an electrode chamber 12 configured as an anode chamber 12 and an electrode chamber 13 configured as a cathode chamber 13, which are spatially and electrically separated from one another by a membrane or a membrane-electrode device 15.

[0030] A membrane electrode assembly 15 comprises a membrane, two electrodes, and preferably two transport layers, with at least one electrode being provided on the membrane and / or at least one electrode being provided directly opposite the membrane on a transport layer. Of course, both electrodes can also be provided on the membrane (membrane electrode assembly) or on the transport layers. The membrane or the membrane electrode assembly, including the transport layers provided thereon, can be sealingly brought into contact with a bipolar plate 14.

[0031] The membrane electrode device 15 can comprise an AEM (Anion Exchange Membrane) or a PEM (Proton Exchange Membrane), e.g., in the form of a CCM (Catalyst Coated AEM / PEM as membrane electrode assembly). A transport layer on a large-area side of the membrane electrode device 15 can comprise a transport structure, a transport layer, a PTL (Porous Transport Layer), a GDL (Gas Diffusion Layer), a sintered metal element, a fiber element, a flow structure, and / or a flow field, etc. The transport layers not explicitly shown in the drawing are arranged in the anode compartments 12 and the cathode compartments 13 of the electrolysis cell stack 10.

[0032] Between two directly adjacent membrane electrode devices 15, 15, including a respective anode compartment 12 and a respective cathode compartment 13, a bipolar plate 14 is arranged, which serves, among other things, to supply / discharge media 4 / 5, (6); 7, (8) to / from an anode compartment 12 of a first individual cell 11 and to / from a cathode compartment 13 of a directly adjacent second individual cell 11, and furthermore establishes an electrically conductive connection between these individual cells 11, 11. - The cathode compartments 13 and, if applicable, their common inflow area or their actual electrodes form a cathode 39 (-); and the anode compartments 12 and, if applicable, their common inflow area or their actual electrodes form an anode 29 (+) of the electrolysis cell stack 10.

[0033] In addition to the electrolyzer unit 1, the electrolyzer system comprises peripheral system components, such as a water treatment device 60, a control unit, which can be one of the electrolyzer system itself, the hydrogen storage unit 40, etc. - To supply the electrolysis cell stack 10 with water 4 / (3, (5), (7)) as a supply medium 4, the electrolyzer unit 1 has a medium supply 20 designed as a water supply 20. And to remove the media 5, 6; 7, 8 from the electrolysis cell stack 10, the electrolyzer unit 1 has a media removal 30.

[0034] The water supply 20 comprises, in particular, a water reservoir 23 for the water 4 (flowing in), a supply path 21 (medium path 21), and a conveying device 26 on / in the supply path 21 for the water 4. The media withdrawal 30 has at least one disposal path 31 (medium path 31, water return line 31) for an anode water 5 back into the water reservoir 23. For this purpose, the water reservoir 23 can have an oxygen separator or be designed as an oxygen separator 23. Alternatively or additionally, the disposal path 31 of the media withdrawal 30 can lead in a different direction (shown in dashed lines), e.g., into the environment 2. This can be realized in particular if the electrolysis cell stack 10 is cooled independently of the water 4.

[0035] Furthermore, an actual product medium 8 of the electrolyzer unit 1, i.e., the produced hydrogen 8, can be transported away through a product medium path 32 (medium path 32) of the medium removal 30. A gas / liquid separator 34 / 51 with a valve 33 can be installed in the product medium path 32 to separate cathode water 7 in the product medium path 32. The cathode water 7 separated in the gas / liquid separator 34 / 51 can be conveyed back into the water reservoir 23 (see below) or in another direction, e.g., into the environment 2, possibly by gravity. The produced hydrogen 8 can be stored, for example, in a hydrogen storage unit 40, wherein the product medium path 32 can flow directly into the hydrogen storage unit 40. Another method of transporting the hydrogen 8 is, of course, also applicable.

[0036] Depending on the embodiment of the electrolyzer unit 1, a media guide within the electrolysis cell stack 10 can be designed differently. In this case, it is possible to provide a temperature control that differs from an electrochemical function of the electrolysis cell stack 10, in particular water cooling, and / or to implement the temperature control together with the electrochemical function of the electrolysis cell stack 10 (cf. Fig. 3 and Fig. 4).

[0037] In most electrolyzer units 1, the water 4 is supplied in excess to the electrolysis cell stack 10, whereby the water 4 additionally takes over the function of cooling the electrolysis cell stack 10. In particular, this creates, cf. Fig. 1, Fig. 3 and Fig. 4, each starting from the supply path 21 via the electrolysis cell stack 10 and via the disposal paths 31, 33, a 'circular' circuit for using the water 4 / 3, 5, 7 with: feeding (21, 26; 4), if necessary cooling (21, 27; 4), if necessary cleaning (21, 28; 4), splitting (10; 4 → 5, 6 ; 7, 8), anode-side recirculation (31; 5, 6 → 23; 5), and in parallel cathode-side separation of the hydrogen 8 (50) and cathode-side recirculation (33; 7 → 23; 7); and then feeding again (21, 26; 4 / (3, 5, 7)) etc.

[0038] Particularly in PEM electrolysis, but also in AEM electrolysis, in addition to an anode-side water circuit (returnable anode water 5), a portion of the water 4 is transported across the membranes of the membrane electrode devices 15 and must be separated again in a cathode-side gas / liquid separator 34 / 51. From a plant engineering perspective, it is often advisable to return this cathode water 7 back to the original water circuit, for example, to reduce energy consumption for the initial water treatment device 60, cf. Fig. 3 and Fig. 4.

[0039] Since product gas mixtures of hydrogen 8 and oxygen 6 exhibit a wide range of explosive molar ratios, care must be taken to largely avoid mixing these two product gases. When cathode water 7 is returned to one anode side, for example, residues of dissolved hydrogen 8 in the cathode water 7 can be introduced into the anode circuit along with the anode water 5. This must be avoided as much as possible.

[0040] Possible ways to safely reduce the proportion of hydrogen 8 in the cathode water 7 include, for example, a long residence time of the two-phase mixture 7 of water and hydrogen 8 in the gas / liquid separator 34, the use of pressure control (by releasing the pressure, the dissolved hydrogen 8 escapes more quickly from the cathode water 7), the use of temperature control (at higher temperatures, the dissolved hydrogen 8 escapes more quickly from the cathode water 7), etc.

[0041] The Fig. 2 shows, by way of example, two hydrogen separation steps I, II, hereinafter referred to simply as separation step(s) I, II, of a method for recycling cathode water 7 in an electrolyzer unit 1. Here, the cathode water 7 flows in a medium path 32, 33 of the electrolyzer unit 1 from the electrolysis cell stack 10 back to the water reservoir 23 (refeed), which may be designed with or as an oxygen separator (cf. also the Fig. 1, Fig. 3 and Fig. 4).

[0042] Initially, a two-phase mixture 7 of water with hydrogen 8 (cathode water 7) is present downstream of a cathode 39 of the electrolysis cell stack 10. For the sake of simplicity, this two-phase mixture 7 is referred to as cathode water 7. This cathode water 7 is then successively freed of hydrogen 8, which takes place in or by a hydrogen separation device 50 of the electrolyzer unit 1.

[0043] In a first separation step I, hydrogen 8 is separated from the hydrogen-rich cathode water 7 in a first volume 51 of the hydrogen separation device 50 by means of an overpressure. The separated hydrogen 8 can flow into a hydrogen storage device 40 or otherwise. The first volume 51 can be configured as a gas / liquid pressure separator 51.

[0044] In a second separation step II, which preferably follows at a later time, further hydrogen 8 is separated in a second volume 52 of the hydrogen separation device 50 by a residence time of the now less hydrogen-containing cathode water 7. Preferably, the second volume 52 is different from the first volume 51, whereby both volumes 51, 52 can be formed in a single device or separately from one another. The second volume 52 is preferably formed as a separation tank 52 (buffer tank 52).

[0045] Furthermore, in the second separation step II, further hydrogen 8 can be separated by at least one pressure relief of the cathode water 7 with a lower hydrogen content upstream and / or downstream of the second volume 52 and / or also in the second volume 52 of the hydrogen separation device 50. In this case, the cathode water 7 can expand in the disposal path 33 into the second or in the second volume 52 to a desired pressure level or the ambient pressure level. Alternatively and / or additionally, the cathode water 7 can expand in the disposal path 33 itself to a desired pressure level or the ambient pressure level. The pressure relief is preferably carried out by a fluid throttle 54 (only in the Fig. 3).

[0046] Furthermore, in at least one separation step following the first separation step I or the second separation step II, further hydrogen 8 can be separated from the cathode water 7. This can take place in a further volume of the hydrogen separation device 50 that is different from the first and second volumes 51, 52, wherein a further overpressure, a further residence time, and / or a further pressure relief can be applied.

[0047] Furthermore, fresh water 3, in particular from a water treatment device 60, can be added to the cathode water 7 on its way back to the water reservoir 23, which takes place in particular downstream of the first volume 51. In particular, the fresh water can be added to the second volume 52. This dilutes the cathode water 7, whereby any hydrogen 8 still present in the cathode water 7 is further diluted. This can be further supported by a (very) low oxygen content in the fresh water 3, i.e., away from potentially explosive molar ratios of hydrogen 8 in the cathode water 7 and oxygen in the fresh water 3.

[0048] Subsequently, the cathode water 7 or the mixture of cathode water 7 and fresh water 3 is fed into the water reservoir 23, in particular conveyed or pumped by means of the conveying device 53. Alternatively or additionally, the fresh water 3 can be fed into the water reservoir 23. Furthermore, anode water 5 leaving the electrolysis cell stack 10 can preferably also be fed into the water reservoir 23. In this case, both the cathode water 7 and the anode water 5 originate from this water reservoir 23.

[0049] For the recirculation process, the cathode water 7 in the product medium path 32, i.e., immediately downstream of the electrolysis cell stack 10, is initially present as a two-phase mixture 7 of water and hydrogen 8, with the hydrogen 8 content in the two-phase mixture 7 or the cathode water 7 in the disposal path 33 decreasing progressively over time. The medium path 32, 33 is formed by the upstream product medium path 32 and the downstream disposal path 33, with the first volume 51 or the gas / liquid pressure separator 51 preferably being arranged between these two medium paths 32, 33.

[0050] The Fig. 3 and Fig. 4 show PEM electrolysis systems 0 for carrying out an embodiment of the recirculation process, wherein the electrolysis systems 0 shown are of course exemplary. Fig. 3 an electrolysis system 0 with a single PEM electrolyzer unit 1 and the Fig. 4 shows an electrolysis system 0 with at least two PEM electrolyzer units 1, wherein each electrolyzer unit 1 has exactly one electrolysis cell stack 10. It is of course possible for an electrolyzer unit 1 to comprise at least two electrolysis cell stacks 10. - The invention is also analogously applicable to AEM electrolysis systems 0 or other electrolysis systems 0.

[0051] Starting from the water reservoir 23, each medium supply 20 preferably has, in its supply path 21, a conveying device 26 or a pump 26, preferably downstream thereof a heat exchanger 27 for temperature control, in particular a cooler 27, and preferably downstream thereof a water purifier 28. A different sequence of conveying device 26, heat exchanger 27, and water purifier 28 is of course applicable. The water purifier 28 can be designed as a mixed-bed exchanger for deionizing (demineralizing or demineralizing) the supply medium 4 to a deionized water, essentially immediately upstream of the electrolysis cell stack 10.

[0052] Starting from the electrolysis cell stack 10, each media withdrawal point 30 has, on the anode side, a disposal path 31 leading into the water reservoir 23, which can be configured with or as an oxygen separator 23. On the cathode side, the respective media withdrawal point 30 has, in addition to the product medium path 32 through which the produced hydrogen 8 can be transported away, in particular the hydrogen separation device 50. The hydrogen separation device 50 here comprises a first volume 51 on / in its disposal path 33 and a second volume 52 on / in its disposal path 33. Furthermore, a further volume (not shown) can be arranged on / in the disposal path 33. It is of course possible to consider the disposal path 33 separately from the hydrogen separation device 50.

[0053] Here, the first volume 51 is designed as a gas / liquid pressure separator 51 (preferred) or a separation tank. Furthermore, the second volume 52 is designed as a separation tank 52 (preferred) or buffer tank 52 or a gas / liquid pressure separator. The respective separation tank (52) is preferably provided with at least one, only in the Fig. 3. The fluid throttle 54 can be provided on / in the separation tank 52 or upstream or downstream thereof in the disposal path 33. A plurality of fluid throttles 54 can, of course, be used. The fluid throttle 54 can have a fixed or a variable cross-section, wherein in the latter case, the variable cross-section can be controlled and / or regulated.

[0054] Furthermore, a supply line for fresh water 3 from a water treatment device 60 can open into the separation tank 52. It is of course alternatively or additionally possible in the hydrogen separation device 50 to provide the supply line for fresh water 3 upstream or downstream of the separation tank 52 into the disposal path 33. If the fresh water 3 is added away from the separation tank 52, a distributor, a mixer, etc., can be used on / in the disposal path 33 for this purpose.

[0055] In the gas / liquid pressure separator 51, hydrogen 8 can be separated from the cathode water 7 by applying an overpressure to the cathode water 7. In the separation tank 52, hydrogen 8 can be separated from the cathode water 7 by a residence time and / or pressure relief (fluid throttle 54 on the separation tank 52) of the cathode water 7. Alternatively or additionally, hydrogen 8 can be separated from the cathode water 7 by a fluid throttle 54 in the disposal path 33. By adding fresh water 3 upstream of the water reservoir 23, any hydrogen 8 still present in the cathode water 7 can be diluted. By maintaining a (very) low oxygen content in the fresh water 3, the hydrogen concentration in the cathode water 7 upstream of the water reservoir 23 can be further reduced if necessary (see above).

[0056] A conveying device 53 of the hydrogen separation device 50 is preferably located downstream of the separation tank 52 or preferably upstream of the water reservoir 53. By means of this conveying device 53, the water 3, 7 present in the separation tank 52 can be conveyed into the water reservoir 23. The anode water 5 is also introduced into this water reservoir 23, wherein oxygen 6 has preferably already been separated from it before it is introduced into the actual water reservoir 23, i.e. the water 4 / 3, 5, 7 present there.

[0057] In the electrolyzer system 0 with a plurality of electrolyzer units 1, such as in the Fig. 4, the entire electrolyzer system 0 for at least two or even all electrolyzer units 1 can have only a single separation tank 52, which supplies the respective electrolyzer units 1 or their water reservoirs 23 with water 3, 7. Furthermore, for at least two or even all electrolyzer units 1, only a single conveying device 53 can be provided (in the Fig. 4 not shown).

Claims

[1] Method for recycling cathode water (7) in an electrolyzer unit (1), in particular a PEM or AEM electrolyzer unit (1), wherein prior to re-feeding the cathode water (7) leaving an electrolysis cell stack (10) of the electrolyzer unit (1) into a medium supply (20) of the electrolyzer unit (1), hydrogen (8) present in the cathode water (7) is separated, characterized by , that in a hydrogen separation device (50) of the electrolyzer unit (1), in a first separation step (I) by an overpressure in a first volume (51) of the hydrogen separation device (50), hydrogen (8) is separated from the hydrogen-rich cathode water (7), and in a second separation step (II) following the first separation step (I), further hydrogen (8) is separated by a residence time of the cathode water (7), which now has a lower hydrogen content, in a second volume (52) of the hydrogen separation device (50) which is different from the first volume (51). [2] Recycling method according to claim 1, characterized bythat in the second separation step (II) further hydrogen (8) is separated by at least one pressure relief of the now hydrogen-poor cathode water (7) upstream of the second volume (52) or in the second volume (52) of the hydrogen separation device (50), and / or in at least one separation step following the second separation step (II) by a further overpressure, a further residence time and / or a further pressure relief in at least one further volume of the hydrogen separation device (50) different from the first and second volumes (51, 52), further hydrogen (8) is separated from the cathode water (7). [3] Recycling method according to one of the preceding claims, characterized by , that: • fresh water (3) can be and / or is supplied to the cathode water (7) downstream of the first volume (51) and upstream of a water reservoir (23) of the electrolyzer unit (1), • the fresh water (3) can be and / or is supplied to the cathode water (7) upstream of, into or downstream of the last, in particular second, volume (52 / ...), • after the separation steps (I, II, ...) the cathode water (7) is fed back into the water reservoir (23) from which it originates, and / or • anode water (5) leaving the electrolysis cell stack (10) is fed back into the water reservoir (23) from which it originates. [4] Recycling method according to one of the preceding claims, characterized by , that: • an overpressure in the first volume (51) and / or a pressure relief in the second volume (52) is approximately: 5 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar or 50 bar, each ±2 bar, • the pressure relief in the second volume (52) is carried out essentially continuously or essentially suddenly, and / or • the pressure relief in the second volume (52) is carried out to a specific pressure level or to an ambient pressure level. [5] Recycling method according to one of the preceding claims, characterized by , that: • filling the second volume (52) with the cathode water (7) with a lower hydrogen content is carried out due to the pressurised cathode water (7) with a lower hydrogen content, • the substantially degassed cathode water (7) from the second or the further volume (52 / ...) into the water reservoir (23) can be or is conveyed by a conveying device (53) of the hydrogen separation device (50), and / or • the recirculation process is and / or can be carried out by an electrolyzer system according to one of the following claims. [6] Electrolyzer system (0), in particular PEM or AEM electrolyzer system (0), for an electrolyzer plant, with at least one electrolyzer unit (1), wherein the electrolyzer unit (1) has, downstream of its electrolysis cell stack (10), a hydrogen separation device (50) for separating hydrogen (8) which is present in a cathode water (7) originating from the electrolysis cell stack (10), characterized by , that the hydrogen separation device (50) has two spatially separated volumes (51, 52) for separating hydrogen (8), wherein the first volume (51) is that of a gas / liquid pressure separator (51) and the second volume (52) is that of a separation tank (52). [7] Electrolyzer system (0) according to claim 6, characterized bythat the gas / liquid pressure separator (51) is designed such that hydrogen (8) can be separated from the hydrogen-rich cathode water (7) there by an overpressure in its volume (51), and / or the separation tank (52) and / or a cathode-side disposal path (33) is designed such that further hydrogen (8) can be separated by a residence time and / or a pressure relief of the now hydrogen-poor cathode water (7). [8] Electrolyzer system (0) according to one of claims 6 or 7, characterized bythat the overpressure in the gas / liquid pressure separator (51) can be generated by an overpressure of a cathode side of the electrolysis cell stack (10) compared to an anode side of the electrolysis cell stack (10), and / or the separation tank (52) and / or the cathode-side disposal path (33) has a fluid throttle (54) of the hydrogen separation device (50), by means of which the pressure relief of the cathode water (7) with a lower hydrogen content can be carried out. [9] Electrolyzer system (0) according to one of claims 6 to 8, characterized by , that: • a connection for fresh water (3) is provided in the cathode-side disposal path (33), which is arranged downstream of the gas / liquid pressure separator (51) and upstream of a water reservoir (23) of the electrolyzer unit (1), • a connection for the fresh water (3) is provided in a line upstream of the separation tank (52), on / in the separation tank (52) or in a line downstream of the separation tank (52) in the cathode-side disposal path (33), and / or • a connection for the fresh water (3) is realized as a distributor piece in a line of the cathode-side disposal path (33), as a connection piece on / in the separation tank (52) or by a mixer in the cathode-side disposal path (33). [10] Electrolyzer system (0) according to one of claims 6 to 9, characterized by , that: • a fresh water pipe, in particular a fresh water pipe of a water treatment device (60), opens into the water reservoir (23), • degassed cathode water (7) can be conveyed from the separation tank (52) into the water reservoir (23) by means of a conveying device (53) of the hydrogen separation device (50), and / or • anode water (5) leaving the electrolysis cell stack (10) can be fed back into the water reservoir (23) from which it originates. [11] Electrolyzer system (0) according to one of claims 6 to 10, characterized by that the electrolyzer system (0) comprises a plurality of electrolyzer units (1), wherein: • a gas / liquid pressure separator (51) is assigned to each electrolysis cell stack (10), or a single gas / liquid pressure separator (51) is assigned to a plurality of electrolysis cell stacks (10), • a single separation tank (52) is assigned to a plurality of gas / liquid pressure separators (51), • in particular upstream, within or downstream of a single separation tank (52) of the electrolyzer system (0), a fresh water line, in particular a fresh water line of a water treatment device (60), opens, and / or • each water reservoir (23) of the electrolyzer system (0) is assigned a conveying device (53) for conveying water (3, 7) from, in particular, the single separation tank (52). [12] Electrolyzer system (0) according to one of claims 6 to 11, characterized by that a method for recycling cathode water (7) according to one of the preceding claims can be carried out or is carried out by the electrolyzer system (0).

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