Process for recycling cathode medium and electrolyzer unit

Abstract

The invention relates to a method for recycling cathode medium (7) in an electrolyzer unit (1), in particular a PEM or AEM electrolyzer unit (1), wherein, before the cathode medium (7) leaving an electrolysis cell stack (10) of the electrolyzer unit (1) is fed back into a medium reservoir (23) of a medium supply (20) of the electrolyzer unit (1), hydrogen (8) present in the cathode medium (7) is separated, and further, before the cathode medium (7) is fed back into the medium reservoir (23), fresh supply medium (3) is fed to the cathode medium (7) in a dilution step (V) of the recycling process, thus reducing a concentration of hydrogen (8) in the cathode medium (7).

Description

The invention relates to a method for recycling cathode medium in an electrolyser assembly. The invention further relates to an electrolyser system, in particular a PEM or AEM electrolyser system, for an electrolyser installation.Prior ArtIn electrolysis (AEM-EL, PEM-EL, AEL, etc.; see below) by an electrolyser unit, for example of an electrolysis system (stationary or mobile), optionally an electrolysis plant (stationary), electrochemical splitting of water molecules takes place with the aid of electrical energy into hydrogen and oxygen with the formation of heat. In this case, the electrolyser assembly comprises at least one membrane electrode device (membrane with transport layers and electrodes respectively arranged therebetween) having, for example, an AEM (anion exchange membrane), a PEM (proton exchange membrane) or a diaphragm (AEL: alkaline electrolysis). As a rule, the electrolyser assembly is formed with a multiplicity of membrane electrode devices arranged in a stack and bipolar plates arranged therebetween, the so-called electrolysis cell stack (stack) having a multiplicity of individual electrolysis cells (individual cells).Object Setting Up To AchieveEfforts are constantly being made to improve electrolyser assemblies and a process for electrolyser assemblies. Mixtures of the product gases hydrogen and oxygen from electrolysis cell stacks of the electrolyser assemblies have a broad range of explosive molar ratios (oxyhydrogen gases). In other words, in order to be able to reliably avoid an explosion, care must be taken to reliably avoid an explosive molar ratio of these two product gases.Disclosure of the InventionThe object of the invention is achieved by a method for recirculating cathode medium in an electrolyser assembly, in particular a PEM or AEM electrolyser assembly; and by means of an electrolyser system, in particular a PEM or AEM electrolyser system, for an electrolyser installation.In the method according to the invention, fresh supply medium is supplied to the cathode medium in a thinning step of the recirculation method, and in this way a concentration of hydrogen in the cathode medium is reduced, temporally before refeeding the cathode medium leaving an electrolysis cell stack of the electrolyser aggregate into a medium reservoir of a medium supply of the electrolyser aggregate, a hydrogen present in the cathode medium being separated off, wherein, preferably, furthermore, fresh supply medium is supplied to the cathode medium temporally before refeeding the cathode medium into the medium reservoir, in a thinning step of the recirculation method.The fresh supply medium is in particular processed fresh supply medium, e.g. from a processing device for water or an alkali solution. Furthermore, the cathode water naturally originates from a cathode of the electrolysis cell stack. In the recirculation method, a cathode side of the electrolysis cell stack can be operated with an excess fluid pressure of equal to or greater than about: 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar or 50 bar, in each case ±2 bar, in relation to an anode side of the electrolysis cell stack. Of course, the invention is also applicable from the field of low-pressure electrolysis (fluid overpressures up to 0.5 bar) to the field of pressure electrolysis (fluid overpressures up to over 100 bar).Furthermore, in a first separation step of the recycling method, hydrogen can be separated from the hydrogen-rich cathode medium by means of an excess fluid pressure in a first volume. Furthermore, in a second separation step of the recirculation method, which second separation step follows the first separation step in time, further hydrogen can be separated by a dwell time of the now lower-hydrogen cathode medium in a second volume different from the first volume. - The fluid overpressure refers to a normal pressure in the environment of the electrolyser assembly, wherein the fluid overpressure is preferably that fluid pressure which is established on the basis of an operating pressure downstream of the electrolysis cell stack.This (degassing and dilution) results in an at least 3-stage method for managing a concentration of hydrogen in the cathode medium. As a result, substantially hydrogen-free cathode water can be recirculated, wherein this cathode medium can be added to recirculated anode medium. It is furthermore advantageous that a continuous provision of printed hydrogen is possible, since a pressure relief can take place only after the first volume and before / in a second or further volume separated from the first volume and in this way the printed hydrogen can be made available to a hydrogen storage unit, for example.In the second separation step, further hydrogen can be separated off by at least one depressurization of the now hydrogen-poor cathode medium upstream of the second volume or in the second volume. This (additional degassing) results in an at least 4-stage method for the management of the concentration of hydrogen in the cathode medium. In at least one separation step following the second separation step in time, further hydrogen can be separated from the cathode medium by a further fluid overpressure, a further dwell time and / or a further depressurization in at least one further volume different from the first and second volumes. As a result (additional degassing), the 3- or 4-stage process for the management of the concentration of hydrogen in the cathode medium can be extended by further stages.In embodiments, the cathode media of a plurality of electrolyser assemblies can be brought together and diluted with the fresh supply medium, wherein the bringing together and diluting of the cathode media can take place substantially simultaneously in time in a dilution stage or successively in time in two devices. - The fresh supply medium can be feedable to and / or be supplied to the cathode medium downstream of the first volume and upstream of the medium reservoir. Furthermore, the fresh supply medium can be supplied and / or supplied to the cathode medium upstream of the volume which is last, in particular second, downstream. Furthermore, the fresh supply medium can be supplied and / or supplied to the cathode medium upstream of a conveying device of the medium supply.The cathode medium is of course unmixed cathode medium originating from the electrolysis cell stack. In this case, the fresh supply medium can be feedable to and / or supplied to the cathode medium at a single or a plurality of points between the first volume and the water reservoir. Temporally after the thinning step and optionally the separation steps, the cathode medium can be fed into the medium reservoir from which it originates and the (additional) fresh supply medium. Furthermore, an anode medium leaving the electrolysis cell stack can be fed back into the medium reservoir from which it originates.The first volume can be supplied from a cathode of the electrolysis cell stack with the hydrogen-rich cathode medium or is supplied therewith. The downstream second volume can be supplied from the first volume with the cathode medium with a low hydrogen content or is supplied therewith. The water reservoir can be supplied or is supplied with the substantially degassed and diluted cathode medium from the second or last volume downstream. Furthermore, in the first separation step, a permanent overpressure can be set up in the first volume. Furthermore, in the first separation step, no pressure relief can be carried out in the first volume.An excess fluid pressure in the first volume and / or a pressure relief in the second volume can be about: 5 bar, 10 bar, 15 bar, 20 bar, 25 bar, 30 bar, 35 bar, 40 bar, 45 bar or 50 bar, in each case ±2 bar. The pressure relief in the second volume may be performed substantially continuously or substantially suddenly. The pressure relief in the second volume can be carried out to a specific pressure level or to an ambient pressure level.Filling of the second volume with the low-hydrogen cathode medium can be carried out on account of the printed low-hydrogen cathode medium. The substantially degassed and diluted cathode medium can be conveyable or be conveyed from the second or the further volume into the water reservoir by a conveying device of the hydrogen separation device. The recirculation method can be performable and / or carried out by an electrolyser system according to the invention.A feature explained below in the context of an electrolyser system is of course applicable to the recirculation method explained above. Further, a feature explained above in the recycling method is of course applicable to the electrolyser system explained below.The electrolyser assembly according to the invention comprises, downstream of its electrolysis cell stack, a hydrogen separation device for separating off hydrogen which is present in a cathode medium originating from the electrolysis cell stack, wherein the hydrogen separation device preferably has, upstream of a medium reservoir of a medium supply of the electrolyser assembly, a dilution stage by means of which fresh supply medium can be fed to the cathode medium and a concentration of hydrogen in the cathode medium can be reduced in this way.The hydrogen separation device can have at least two spatially separated volumes for separating hydrogen, wherein the first volume is that of a gas / liquid pressure separator and the second volume is that of a separation tank. The gas / liquid pressure separator can be designed in such a way that, by means of an excess fluid pressure, hydrogen can be separated in its volume from the cathode medium rich in hydrogen there. The separation tank and / or a cathode-side disposal path can be designed such that further hydrogen can be separated off by a dwell time and / or a depressurization of the already hydrogen-depleted cathode medium.The fluid overpressure in the gas / liquid pressure separator can be generated by a fluid overpressure of a cathode side of the electrolysis cell stack opposite an anode side of the electrolysis cell stack. The separation tank and / or the cathode-side disposal path can have a fluid restrictor of the hydrogen separation device, by means of which the pressure relief of the cathode medium with low hydrogen content can be carried out.The first volume may be substantially in direct fluid communication with the electrolysis cell stack or substantially in 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 substantially in direct fluid communication with the first volume. In addition, the second or a further volume can be brought by gravity or by means of a conveying device of the hydrogen separation device into fluid communication with the water reservoir of the electrolyser assembly or can be in fluid communication with the water reservoir.The dilution stage can be arranged in the cathode-side disposal path downstream of the gas / liquid pressure separator and upstream of the medium reservoir. Furthermore, the dilution stage can have at least one dilution device, by means of which the fresh supply medium can be fed to the cathode medium. The dilution device can be configured in a line upstream of the separation tank, at / in the separation tank, and / or in a line downstream of the separation tank or upstream of the medium reservoir. The dilution device can be formed, for example, as a connection, a T-piece, a Y-piece, a mixer, etc. Furthermore, an anode medium leaving the electrolysis cell stack can be re-fed into the water reservoir from which it originates.The dilution stage may comprise the separation tank and the dilution device. Furthermore, the dilution device can be arranged downstream of the separation tank in the disposal path or at / in the separation tank. Furthermore, the dilution device can be set up on / in the separation tank. Here, the three functions (expansion, dwell and thinning) can be realized in a single component.The electrolyser system may comprise a plurality of electrolyser assemblies, each electrolysis cell stack being associated with a gas / liquid pressure separator, or a plurality of electrolysis cell stacks being associated with a single gas / liquid pressure separator. Furthermore, a single separation tank can be assigned to a plurality of gas / liquid pressure separators. Upstream, within or downstream of the single separation tank of the electrolyser system, a medium line of a treatment device can open out. Furthermore, each medium reservoir of the electrolyser system can be assigned a conveying device for conveying diluted supply medium from, in particular, the single deposition tank.Such an electrolyser system can have a single dilution stage for a plurality of electrolyser assemblies, in particular all electrolyser assemblies. Furthermore, in the dilution stage, the cathode media of a plurality of electrolyser assemblies can be combined and diluted therein with the fresh supply medium. Furthermore, the dilution stage can be designed structurally as a single, buildable device or structurally as two devices which can be built separately from one another in the electrolyser system.Furthermore, in such an electrolyser system, each medium reservoir of the electrolyser system can be assigned a conveying device for conveying diluted cathode medium from, in particular, the single deposition tank. Furthermore, the diluted cathode medium can be conveyable by a preferably single conveying device of the processing device. In addition, the dilution stage can comprise a central mixer which can be operated by a conveying device of the treatment device. - A method according to the invention for recycling cathode medium can be carried out or can be carried out by means of the electrolyser system.Brief Description of the FiguresThe invention is explained in more detail below on the basis of exemplary embodiments with reference to the attached schematic drawing. In the invention, a feature may be positive, i.e. present, or negative, i.e. absent. In this specification, a negative feature is not explicitly explained as a feature unless the invention claims the absence thereof. That is, the invention actually made, rather than one constructed by the prior art, is to omit this feature. The absence of a feature (negative feature) in an exemplary embodiment shows that the feature is optional (as appropriate by a person skilled in the art).FIG. 1 shows a simplified block diagram of embodiments of an electrolyser assembly for the AEM-EL, PEM-EL, AEL, etc., having an electrochemical electrolysis cell stack for an electrolysis system,FIG. 2 shows a flow diagram of a method according to the invention for recycling cathode medium in an electrolyser unit, in particular for the AEM-EL, the PEM-EL or the AEL,FIGS. 3 and 4 each show, in the form of a hydraulic circuit diagram, an embodiment of an electrolysis system for an electrolysis plant, having one (FIG. 3 ) or a plurality (FIG. 4 ) of electrolyser assemblies (FIG. 1 ),FIGS. 5 to 8 each in the form of a hydraulic circuit diagram show an embodiment of a dilution stage for a cathode medium of the electrolysis cell stack in a medium outlet of the electrolysis cell stack, andFIGS. 9 and 10 show embodiments of a dilution stage in the form of a separation tank with a dilution device for the cathode medium provided thereon / therein.Embodiments of the InventionThe invention is explained in more detail below with reference to an electrolysis system (cf. FIGS. 3 and 4 ) having at least one electrolyser assembly 1 (cf. furthermore FIG. 1 ) having at least one electrolysis cell stack 10 for electrolysis (EL) of a supply medium 4 in hydrogen 8 and oxygen 6, and a method (cf. FIG. 2 ) for recycling cathode medium 7 in an electrolyser assembly 1. - The invention is additionally applicable to a multiplicity of electrolysis systems having one or a plurality of electrolyser assemblies 1, wherein an electrolyser assembly 1 can be designed, for example, for an AEM electrolysis (AEM-EL), a PEM electrolysis (PEM-EL), an alkaline electrolysis (AEL), etc.Only those sections of an electrolyser assembly 1 of an electrolysis system, for example of an electrolysis plant (not shown), which are necessary for an understanding of the invention are shown in the drawing. - Although the invention is described and illustrated in more detail by preferred exemplary embodiments, the invention is not restricted by the disclosed exemplary embodiments. Other variations may be derived therefrom without departing from the scope of the invention.FIG. 1 shows an electrolyser assembly 1 according to a general embodiment, having at least one, in particular a plurality of electrochemical individual cells 11 (individual electrolysis cell 11) which are bundled to form an electrolysis cell stack 10 and are accommodated in a preferably fluid-tight stack housing 16. Each individual cell 11 comprises an electrode space 12 designed as an anode space 12 and an electrode space 13 designed as a cathode space 13, which are spatially and electrically separated from one another by a membrane of a membrane electrode device 15.A membrane electrode device 15 has a membrane, two electrodes and preferably two transport layers, wherein at least one electrode is provided on the membrane and / or at least one electrode is provided on a transport layer directly opposite the membrane. Of course, both electrodes can also be provided on the membrane (membrane-electrode unit) or on the transport layers. The membrane or the membrane electrode unit, including the transport layers provided thereon, can be brought into sealing contact with a bipolar plate 14.The membrane electrode device 15 can have an AEM or a PEM, for example in the form of a CCM (Catalyst Coated AEM / PEM as membrane electrode unit), or a diaphragm. A transport layer on a large-area side of the membrane electrode device 15 may include 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 spaces 12 and the cathode spaces 13 of the electrolysis cell stack 10.A bipolar plate 14 is arranged between two membrane electrode devices 15, 15 directly adjacent to one another, including a relevant anode space 12 and a respective cathode space 13, which bipolar plate serves, inter alia, for the supply / discharge of media 4 / 5 (anode medium), 6 (oxygen); 7 (cathode medium), 8 (hydrogen) into / from an anode space 12 of a first individual cell 11 and into / from a cathode space 13 of a second individual cell 11 directly adjacent thereto and additionally implements an electrically conductive connection between these individual cells 11, 11. - The cathode spaces 13 and optionally their common inflow region, or their actual electrodes, form a cathode 39(-); and the anode spaces 12 and, if appropriate, their common inflow region, or their actual electrodes, form an anode 29 (+) of the electrolysis cell stack 10.The electrolysis system and of course also the electrolysis plant (cf. above) comprises, in addition to the electrolyser unit 1, peripheral system components, such as, for example: a control unit, a treatment device 60 for producing fresh supply medium 3, a hydrogen storage 40, optionally an oxygen storage 50, etc.For supplying the electrolysis cell stack 10 with the supply medium 4 / 3, 5, ( 7), the electrolyser assembly 1 has a medium supply 20. In the case of the AEM EL (mild alkaline supply water 4) and the PEM EL (neutral supply water 4), a (process) medium 4; 3, 5, 7 is naturally (process) water 4; 3, 5, 7, and in the case of the AEL a (process) medium 4; 3, 5, 7 is naturally a (process) liquor 4; 3, 5, 7, in particular (process) potassium liquor 4; 3, 5, 7. - For removing the media 5, 6; 7, 8 of the electrolysis cell stack 10, the electrolyser assembly 1 has a media removal 30. - The medium supply 20 comprises in particular a medium reservoir 23 for the supply medium 4 (flowing in), a supply path 21 (medium path 21) and a conveying device 26 on / in the supply path 21 for the supply medium 4.The media removal 30 has at least one disposal path 31 (media path 31) for an anode medium 5 back into the medium reservoir 23. For this purpose, the medium reservoir 23 can have an oxygen separator or can be designed as an oxygen separator 23. The oxygen 6 separated in the oxygen separator ( 23) can be conveyed into an oxygen storage tank 50 (collecting tank 50, storage tank 50, etc.). Alternatively or additionally, the disposal path 31 of the media removal 30 can lead in another direction (shown in dashed lines), for example into the environment 2. This can be realized in particular when cooling of the electrolysis cell stack 10 takes place independently of the supply medium 4.Furthermore, an actual product medium 8 of the electrolyser assembly 1, i.e. the hydrogen 8 produced, can be transported away through a product medium path 32 (medium path 32) of the medium outlet 30. In this case, a gas / liquid separator 34 with a valve 33 can be configured in the product medium path 32 in order to separate cathode medium 7 in the product medium path 32. The cathode medium 7 deposited in the gas / liquid separator 34 can be conveyed back into the medium reservoir 23 (cf. below) or in another direction, for example into the environment 2, optionally gravitationally. The hydrogen 8 produced can be stored, for example, in a hydrogen storage tank 40 (collecting tank 40, storage tank 40 etc.), wherein the product medium path 32 can open directly into the hydrogen storage tank 40. Another removal of the hydrogen 8 is of course applicable.Depending on an embodiment of the electrolyser assembly 1, a medium guide within the electrolysis cell stack 10 can be of different design. In this case, it is possible to provide a temperature control, in particular cooling, which is different from an electrochemical function of the electrolysis cell stack 10 and / or to realize the temperature control or cooling together with the electrochemical function of the electrolysis cell stack 10 via the supply medium 4 for the electrolysis.In the case of membrane electrode devices 15 with AEMs, it is possible to arrange, in addition to an anode- and cathode-side, an optionally exclusively anode-side (dotted arrow at the anode 29) supply of the supply medium 4, optionally also as a cooling medium. Furthermore, in the case of membrane electrode devices 15 with PEMs, it is possible, in addition to an exclusively anode-side, an optionally exclusively cathode-side 39 supply of supply medium 4, optionally also to configure it as cooling medium (dotted arrow in the case of the cathode 39). In the AEL, in addition to an anode- and cathode-side, an optionally exclusively anode-side (dotted arrow at the anode 29) supply of the supply medium 4 can optionally also be configured as a cooling medium.In most electrolyser assemblies 1, the supply medium 4 is supplied to the electrolysis cell stack 10 in an excess, the supply medium 4 additionally assuming the function of cooling the electrolysis cell stack 10. As a result, in each case starting from the supply path 21 via the electrolysis cell stack 10 and via the disposal paths 31, 33, a "circular" interconnection for use of the supply medium 4 / 3, 5, (7) is produced, with: feeding (21, 26:4), optionally cooling (21:4), optionally cleaning (21:4), splitting (10:4=> 5, 6; 7, 8), anode-side recirculation (31:5, 6=> 23:5 (=> 23:4)), and, in parallel therewith, cathode-side separation of the hydrogen 8 (34:8=> 40:8) and, optionally, cathode-side recirculation (33:7=> 23:7 (=> 23:4)); and subsequently refeeding (21, 26:4 / 3, 5, (7)), etc.In electrolysis, in particular PEM electrolysis and AEM electrolysis, but also alkaline electrolysis (AEL), in addition to an anode-side medium circuit (anode medium 5 to be fed back), a portion of the medium 4 is transported via the membranes or diaphragms of the membrane electrode devices 15 and has to be separated off again in the cathode-side gas / liquid separator 34. It is often expedient from the plant standpoint to recycle this cathode medium 7 back into the original medium circuit in order, for example, to reduce an energy consumption for the initial treatment device 60, cf. FIGS. 3 and 4.Since product gas mixtures of hydrogen 8 and oxygen 6 have a wide range of explosive substance quantity ratios, care must be taken to avoid mixing of these two product gases to a large extent. In the case of a return of cathode medium 7 to an anode side, residues of dissolved hydrogen 8 in the cathode medium 7 can be introduced into the anode circuit together with the anode medium 5. This must be substantially avoided.Possible ways of reliably reducing the proportion of hydrogen 8 in the cathode medium 7 consist, for example, in a long residence time of the two-phase mixture 7 of medium and hydrogen 8 in a gas / liquid separator, utilization of pressure control / regulation (the dissolved hydrogen 8 escapes more quickly from the cathode medium 7) by means of pressure expansion, utilization of temperature control / regulation (at a higher temperature, the dissolved hydrogen 8 escapes more quickly from the cathode medium 7), dilution (a concentration of hydrogen 8 is reduced by an additional introduction of a supply medium 3, 4 without relevant dissolved proportions of hydrogen 8), etc.FIG. 2 shows, by way of example, two hydrogen separation steps A I, A II referred to below merely as separation step(s) A I, A II and three options of thinning steps V of a method for recycling cathode medium 7 in an electrolyser assembly 1. In this case, the cathode medium 7 flows through a medium path 32 (product medium path), 33 (disposal path) of the electrolyser assembly 1 from the electrolysis cell stack 10 back to the medium reservoir 23 (refeeding), which is optionally configured with one or as an oxygen separator (cf. also FIGS. 1, 3 and 4 ).First, downstream of the cathode 39 of the electrolysis cell stack 10, there is a two-phase mixture 7 of a disposal medium including. Hydrogen 8 before (cathode medium 7). For the sake of simplicity, the two-phase mixture 7 is already referred to as cathode medium 7. This cathode medium 7 is now freed of hydrogen 8 and diluted, which takes place in or through a hydrogen separation device 100 of the electrolyser assembly 1. As a result, the cathode medium 7 freed of hydrogen 8 and diluted with respect to hydrogen 8 can be (again) fed into the medium reservoir 23.The recycling method (FIG. 2 ) has at least one separation step A and at least one thinning step V for this purpose. In a separation step A, hydrogen 8 is separated from the cathode medium 7, while in a thinning step V the hydrogen 8 in the cathode medium 7 is diluted by fresh supply medium 3 (cf. FIGS. 3 to 8 ) - Here, a thinning step V can take place temporally after a first separation step A I, temporally before a second separation step A II, temporally during the second separation step A II and / or temporally after a second separation step A II. The thinning step V takes place temporally before the (re) current application of the cathode medium 7 into the medium reservoir 23.In the (first) separation step A I( cf. in particular FIGS. 2 to 4 ), hydrogen 8 is separated from the hydrogen-rich cathode medium 7 in a first volume 101 of the hydrogen separation device 100 by means of an excess fluid pressure. The separated hydrogen 8 can flow off into a hydrogen storage 40 or in some other way. The first volume 101 can be designed as a gas / liquid pressure separator 101. The fluid overpressure is preferably that pressure which is established in the gas / liquid pressure separator 101 on the basis of the operating pressure of the electrolysis cell stack 10 (i.e. operating pressure≈fluent overpressure>urmotenso pressure).In the preferably temporally subsequent second separation step A II( cf. in particular FIGS. 2 to 4 ), further hydrogen 8 is separated in a second volume 102 of the hydrogen separation device 100 by a residence time of the now hydrogen-poor cathode medium 7. Preferably, the second volume 102 is different from the first volume 101, wherein both volumes 101, 102 can be formed in a single device or else separately from one another. The second volume 102 is preferably designed as a separation tank 102 (buffer tank 102, buffer tank 102).Furthermore, in the second separation step A, II further hydrogen 8 can be separated off by at least one depressurization of the low-hydrogen cathode medium 7 upstream and / or downstream of the second volume 102 and / or also in the second volume 102 of the hydrogen separation device 100. In this case, the cathode medium 7 in the disposal path 33 can expand into the second or in the second volume 102 to a desired pressure level or the ambient pressure level. Alternatively and / or additionally, the cathode medium 7 can self-expand in the disposal path 33 to a desired pressure level or the ambient pressure level. The pressure relief is preferably effected by a fluid throttle 105 (only shown in FIG. 3 ).In addition, in at least one separation step following the first separation step A I or the second separation step A II in time, further hydrogen 8 can be separated from the cathode medium 7. This can take place in a further volume of the hydrogen separation device 100 different from the first and second volumes 101, 102, wherein a further fluid overpressure, a further dwell time and / or a further pressure relief can be applied.Furthermore, in the thinning step V, fresh supply medium 3 is added to the cathode medium 7 on its way back into the medium reservoir 23, in particular from a processing device 60. This takes place in particular at an ambient pressure level of the cathode medium 7 and thus preferably in and / or downstream of the second volume 102. As a result, the cathode medium 7 dilutes, as a result of which any hydrogen 8 still present in the cathode medium 7 dilutes further. - This can optionally be further supported by a (very) low oxygen content in the fresh supply medium 3, that is to say away from possible explosive molar ratios of hydrogen 8 in the cathode medium 7 and oxygen in the fresh supply medium 3.In a temporal connection, the mixture of cathode medium 7 and fresh supply medium 3 is fed into the medium reservoir 23, in particular is conveyed or pumped by means of the conveying device 104. - Furthermore, an anode medium 5 leaving the electrolysis cell stack 10 is preferably likewise fed into the medium reservoir 23. In this case, both the cathode medium 7 (away from the fresh supply medium 3) and the anode medium 5 derive from this medium reservoir 23.For the recirculation method, the cathode medium 7 is located in the product medium path 32, i.e. directly downstream of the electrolysis cell stack 10, first of all as a two-phase mixture 7 of the disposal medium. The concentration of hydrogen 8 in the two-phase mixture 7 or the cathode medium 7 in the disposal path 33 is decreasing more and more in the chronological sequence. The medium path 32, 33 is formed by the upstream product medium path 32 and the downstream disposal path 33, wherein the first volume 101 or the gas / liquid pressure separator 101 is preferably set up between these two medium paths 32, 33.FIGS. 3 and 4 show PEM electrolysis systems for carrying out an embodiment of the recirculation process, the electrolysis systems shown being of course exemplary. In this case, FIG. 3 shows an electrolysis system with a single PEM electrolyser assembly 1 and FIG. 4 shows an electrolysis system with at least two PEM electrolyser assemblies 1, wherein a respective electrolyser assembly 1 has exactly one electrolysis cell stack 10. It is of course possible for an electrolyser assembly 1 to comprise at least two electrolysis cell stacks 10. AEM electrolysis systems can be constructed analogously to FIGS. 3 and 4.A respective medium supply 20 preferably has, starting from a medium reservoir 23 in its supply path 21, firstly a delivery 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 cleaner 28. A different sequence of conveying device 26, heat exchanger 27 and medium cleaner 28 is of course applicable. The medium purifier 28 can be configured for supply water 4 as a supply medium 4 as a mixed bed exchanger for deionization (demineralized or demineralized) of the supply water 4 to form a deionate substantially directly upstream of the electrolysis cell stack 10.A respective medium removal 30 has, on the anode side, a disposal path 31 starting from the electrolysis cell stack 10, which leads into the medium reservoir 23, which can be formed with or as an oxygen separator 23. - On the cathode side, the respective medium removal 30 has, in particular the hydrogen separation device 100, next to the product medium path 32, through which the produced hydrogen 8 can be transported away. The hydrogen separation device 100 comprises a first volume 101 at / in its disposal path 33 and a second volume 102 at / in its disposal path 33. Furthermore, a further volume (not shown) can be set up at / in the disposal path 33.Furthermore, the hydrogen separation device 100 comprises a dilution stage 110, which is explained in more detail in particular with reference to FIGS. 5 to 10 further below. The dilution stage 110 reduces a concentration of hydrogen 8 in the cathode medium 7 by adding fresh supply medium 3. The addition of fresh supply medium 3 is only shown in FIGS. 3 and 4 by arrows on the disposal path 33.The first volume 101 is formed as a gas / liquid pressure separator 101 (preferred) or a separation tank. Furthermore, the second volume 102 is formed as a separation tank 102 (preferred) or buffer tank 102 or buffer tank 102 or a gas / liquid pressure separator. In this case, at least one fluid throttle 105 is preferably assigned to the relevant separation tank ( 102), which throttle is only shown in FIG. 3. Here, the fluid restrictor 105 may be provided at / in the separation tank 102 or upstream or downstream thereof in the disposal path 33. A plurality of fluid restrictors 105 are of course applicable. The fluid throttle 105 can have a fixed or a variable cross section, wherein in the second case the variable cross section can be controllable and / or regulable.In the gas / liquid pressure separator 101, hydrogen 8 can be separated from the cathode medium 7 by a fluid overpressure (lossy operating pressure of the electrolysis cell stack 10) of the cathode medium 7 (cathode water 7, cathode liquor 7). In the deposition tank 102, hydrogen 8 can be separated from the cathode medium 7 by a dwell time and / or a pressure relief (fluid throttle 105 at the deposition tank 102) of the cathode medium 7. Alternatively or additionally, hydrogen 8 can be separated from the cathode medium 7 by a fluid restrictor 105 in the disposal path 33.Preferably downstream of the separation tank 102 or preferably upstream of the medium reservoir 23, there is a conveying device 104 of the hydrogen separation device 100. By means of this conveying device 104, the cathode medium 7, (3) present in the separation tank 102 and optionally diluted (cf. below) can be conveyed into the medium reservoir 23. The anode medium 5 (anode water 5, anode liquor 5) can also be introduced into this medium reservoir 23, it being possible for oxygen 6 to have already been separated out of this medium reservoir before it is introduced into the actual medium reservoir 23, that is to say the supply medium 4 / 3, 5, 7 present there.In the electrolyser system having a plurality of electrolyser assemblies 1, as illustrated for example in FIG. 4, the entire electrolyser system for at least two or else all electrolyser assemblies 1 can have only a single deposition tank 102, which supplies the relevant electrolyser assemblies 1 or their medium reservoirs 23 with optionally diluted (cf. below) cathode medium 7, (3). Furthermore, only a single conveying device 104 can optionally be provided for at least two or also all of the electrolyser assemblies 1 (not shown in FIG. 4 ).The dilution stage 110 for the dilution step V of the recycling process is explained in more detail below. In addition to the separation of hydrogen 8, e.g. also characterizable as separation stage(s), a further stage for the separation of hydrogen 8 used is a dilution of the cathode medium 7, in particular by utilizing the prepared fresh supply medium 3 to be newly supplied for the chemical reaction in the electrolysis cell stack 10. In this case, it is possible to reduce a number of the required delivery devices, in particular pumps, in the electrolysis system or the electrolysis plant.The supply of fresh supply medium 3 takes place downstream of the first volume 101 or the gas / liquid pressure separator 101 and upstream of, into or downstream of the second volume 102 or the separation tank 102 (cf. FIGS. 3 and 4 ) and brings about a dilution of the concentration of hydrogen 8 in the cathode medium 7. furthermore, a supply of fresh supply medium 3 takes place upstream of the medium reservoir 23. subsequently, the diluted cathode medium 7, 3 can be fed from the second volume 102 into the medium reservoir 23, for example via a conveying device 104.Supplying fresh supply medium 3 to the cathode medium 7 can generally be formed by a dilution device 111 of the dilution stage 110, which can be formed, for example, as a connection 111, a T-piece 111, a Y-piece 111, a mixer 111 etc. When using a T-piece 111, the Venturi effect can be used, among other things, so that cathode medium 7 can be supplied in a targeted manner by means of suction of the fresh supply medium 3 or fresh supply medium 3 can be supplied in a targeted manner by means of suction of the cathode medium 7.FIG. 5 shows a combination of a two-stage separation (first and second volume 101 (pressure release), 102 (dwell time, optionally pressure release)) and a subsequent dilution of hydrogen 8 in the cathode medium 7 by supplying fresh supply medium 3 via a T-piece 111 downstream of the second volume 102. The second volume 102 and the dilution device 111 embodied in the present case as a T-piece 111 can be realized in a single structural unit. The embodiment shown in FIG. 5 is based on electrolyser assemblies 1 according to FIG. 3, but can of course also be transferred to embodiments according to FIG. 4.FIG. 6 shows on the left a combination of separation and dilution of hydrogen 8 in a single component, referred to as mixer 111 (dilution device 111), in which the separation tank 102 with its second volume 102 is integrated. The mixer 111 comprises a plurality of medium feeds (in particular when used in an electrolysis system or an electrolysis plant having n medium circuits and / or m electrolyser assemblies), including a feed for the fresh supply medium 3 and a discharge line for separated hydrogen 8 (also FIG. 5 ).Here, the three functions (expansion, dwell and thinning) can be realized in a single component, the mixer 111. The second volume 102 of the mixer 111 preferably has internal 3D struts and / or 3D surfaces which promote mixing of the fresh supply medium 3 with the cathode medium 7 and separation of the hydrogen 8, and thus achieve rapid, uniform mixing.In addition, by supplying the fresh supply medium 3 into the disposal path 33, in particular downstream of the first volume 102 or the gas / liquid pressure separator 102, into the second volume 102 or the mixer 111, and / or downstream of the second volume 102 or the mixer 111, it is possible to dispense with at least one conveying device in the electrolysis system or the electrolysis plant or to reduce the number of conveying devices.FIG. 7 shows, in application to FIG. 4, a central mixer 111 (dilution device 111) which is driven by a conveying device 62, in particular a pump 62, of the processing device 60. That is, a mass flow of the fresh supply medium 3 is conveyed and supplied by the conveying device 62 into the n medium reservoirs 23 of the anode sides of the electrolyser assemblies 1. A division to the n medium reservoirs 23 can be effected, for example, via control valves.In this case, all the cathode medium 7 of the electrolyser assemblies 1 is combined and diluted in the central mixer 111. In this case, the conveying device 62 is used for supplying the fresh supply medium 3 in order to drive the distribution or return of all the cathode medium 7 into the n medium reservoirs 23, resulting in a saving of conveying devices per strand. In this case, it is possible, instead of one medium reservoir 23 for one electrolyser assembly 1, to provide a single medium reservoir 23 for a plurality of electrolyser assemblies 1 in the electrolysis system or the electrolysis plant.FIG. 8 shows, when applied to FIG. 4, a supply of the fresh supply medium 3 and thus a dilution of the hydrogen 8 in the returning cathode medium 7. The dilution is effected as a subsequent step for the total gas-liquid separation per strand. In this case too, the implementation with a central conveying device 62 is possible by means of the processing device 60. An alternative embodiment consists, for example, of a plurality of small conveying devices, in particular one conveying device per strand (cf. FIG. 4 ).FIG. 9 shows an exemplary embodiment of the dilution stage 110 from FIG. 6, which is designed as a mixer 111, wherein the mixer 111 is a combination of a separation tank 102 (second volume 102) with the dilution device 111. Depending on the number of electrolyser assemblies 1 in the electrolysis system or electrolysis plant, mixer 111 has inlets for cathode medium 7 corresponding to this number. The inlets are preferably located on an upper edge of deposition tank 102, in particular combined with a pressure relief via fluid chokes 105, for example in the form of throttling valves 105.A dilution of the cathode medium 7 with fresh supply medium 3 can take place at different points of the separation tank 102 of the mixer 111. Thus, the fresh supply medium 3 can likewise be supplied to the separation tank 102 at the upper edge and / or in a lower region. Furthermore, it is possible to feed the fresh supply medium 3 at an outlet of the mixer 111, which can be effected by the conveying device 62 of the processing device 60.FIG. 10 shows a possible internal configuration of the mixer 111. Depending on a number of feed lines for the cathode medium 7, guide plates 112 are arranged in the interior, which guide plates set a dwell time of the cathode medium 7. A surface of the baffle plates 112 may be enlarged by, for example, crimping, a hole structure, etc., whereby the separation of the hydrogen 8 can be further improved. It is also possible for the guide plates 112 to be meandering or spirally twisted.

Claims

Method for recycling cathode medium (7) in an electrolyser assembly (1), in particular a PEM or AEM electrolyser assembly (1), wherein fresh supply medium (3) is fed to the cathode medium (7) in a medium reservoir (23) of a medium supply (20) of the electrolyser assembly (1) temporally before the cathode medium (7) is fed back into a medium reservoir (23) of a medium supply (20) of the electrolyser assembly (1), characterized in that, furthermore, a concentration of hydrogen (8) present in the cathode medium (7) is reduced in this way in a thinning step (V) of the recycling method, further temporally before the cathode medium (7) is fed back into the medium reservoir (23).The recirculation method according to the preceding claim, characterized in that, in a first separation step (A I) of the recirculation method, hydrogen (8) is separated from the hydrogen-rich cathode medium (7) by an excess fluid pressure in a first volume (101), and, in a second separation step (A II) of the recirculation method, which separation step follows the first separation step (A I) in time, further hydrogen (8) is separated by a residence time of the now lower-hydrogen cathode medium (7) in a second volume (102) different from the first volume (101).The recycling method according to any one of the preceding claims, characterized in that in the second separation step (A II) further hydrogen (8) is separated off by at least one depressurization of the now lower-hydrogen cathode medium (7) upstream of the second volume (102) or in the second volume (102), and / or in at least one separation step temporally following the second separation step (A II) further hydrogen (8) is separated off from the cathode medium (7) by a further fluid overpressure, a further dwell time and / or a further depressurization in at least one further volume different from the first and second volumes (101, 102).The recirculation method according to any one of the preceding claims, characterized in that the cathode media (7) of a plurality of electrolyser assemblies (1) are brought together and diluted with the fresh supply medium (3), wherein the bringing together and diluting of the cathode media (7) takes place substantially simultaneously in time in a dilution stage (110) or successively in time in two devices.The recirculation method according to any one of the preceding claims, characterized in that the fresh supply medium (3) can be supplied and / or is supplied to the cathode medium (7): • downstream of the first volume (101) and upstream of the medium reservoir (23), • upstream of the volume (102 / ...) which is last, in particular second, supplied and / or is supplied, • upstream of a conveying device (104), can be supplied and / or is supplied to the medium supply (20), and / or • the recirculation method can be performed and / or is performed by an electrolyser system according to any one of the following claims.Electrolyser system, in particular a PEM or AEM electrolyser system, for an electrolyser plant, having at least one electrolyser assembly (1), wherein the electrolyser assembly (1) has, downstream of its electrolysis cell stack (10), a hydrogen separation device (100) for separating hydrogen (8), which is present in a cathode medium (7) originating from the electrolysis cell stack (10), characterized in that the hydrogen separation device (100) has, upstream of a medium reservoir (23) of a medium supply (20) of the electrolyser assembly (1), a dilution stage (110), by means of which fresh supply medium (3) can be fed to the cathode medium (7) and a concentration of hydrogen (8) in the cathode medium (7) can thus be reduced.Electrolyser system according to Claim 6, characterized in that: • the hydrogen separation device (100) has at least two volumes (101, 102), which are spatially separated from one another, for separating hydrogen (8), wherein the first volume (101) is that of a gas / liquid pressure separator (101) and the second volume (102) is that of a separation tank (102), • the gas / liquid pressure separator (101) is designed such that hydrogen (8) can be separated from the cathode medium (7) which is rich in hydrogen there by an excess fluid pressure in its volume (101), and / or • the separation tank (102) 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 depressurization of the cathode medium (7) which is already lower in hydrogen.Electrolyser system according to either of Claims 6 and 7, characterized in that the fluid overpressure in the gas / liquid pressure separator (101) can be generated by a fluid overpressure of a cathode side of the electrolysis cell stack (10) with respect to an anode side of the electrolysis cell stack (10), and / or the separation tank (102) and / or the cathode-side disposal path (33) has a fluid throttle (105) of the hydrogen separation device (100), by means of which the pressure relief of the cathode medium (7) with low hydrogen can be carried out.Electrolyser system according to one of Claims 6 to 8, characterized in that: • the dilution stage (110) is set up in the cathode-side disposal path (33) downstream of the gas / liquid pressure separator (101) and upstream of the medium reservoir (23), • the dilution stage (110) has at least one dilution device (111), by means of which the fresh supply medium (3) can be fed to the cathode medium (7), and / or • the dilution device (111) is set up in a line upstream of the separation tank (102), at / in the separation tank (102), and / or in a line downstream of the separation tank (102) or upstream of the medium reservoir (23).Electrolyser system according to one of Claims 6 to 9, characterized in that: • the dilution stage (110) comprises the separation tank (102) and the dilution device (111), • the dilution device (111) is set up downstream of the separation tank (102) in the disposal path (33) or on / in the separation tank (102), and / or • the dilution device (111) is set up on / in the separation tank (102).Electrolyser system according to one of Claims 6 to 10, characterized in that the electrolyser system comprises a plurality of electrolyser assemblies (1), wherein: • a gas / liquid pressure separator (101) is associated with each electrolysis cell stack (10), or a single gas / liquid pressure separator (101) is associated with a plurality of electrolysis cell stacks (10), • a single separation tank (102) is associated with a plurality of gas / liquid pressure separators (101), and / or • a medium line of a treatment device (60) opens upstream, within or downstream of the single separation tank (102) of the electrolyser system.Electrolyser system according to one of Claims 6 to 11, characterized in that the electrolyser system comprises a plurality of electrolyser assemblies (1), wherein: • the electrolyser system has a single dilution stage (110) for a plurality of electrolyser assemblies (1), in particular all electrolyser assemblies (1), • the cathode media (7) of a plurality of electrolyser assemblies (1) can be combined in the dilution stage (110) and can be diluted therein with the fresh supply medium (3), and / or • the dilution stage (110) is configured structurally as a single, buildable device or structurally as two devices which can be built separately from one another in the electrolyser system.Electrolyser system according to one of Claims 6 to 12, characterized in that the electrolyser system comprises a plurality of electrolyser assemblies (1), wherein: • each medium reservoir (23) of the electrolyser system is assigned a conveying device (104) for conveying diluted cathode medium (7, 3) from, in particular, the single deposition tank (102), • the diluted cathode medium (7, 3) can be conveyed by a preferably single conveying device (62) of the treatment device (60), and / or • the dilution stage (110) comprises a central mixer (111) which can be operated by a conveying device (62) of the treatment device (60).Electrolyser system according to one of Claims 6 to 13, characterized in that the electrolyser system can be used or is used to carry out a method for recycling cathode medium (7) according to one of the preceding claims.

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