Patent Application
20240344231
The present invention concerns an electrolyser comprising at least two electrolytic cells respectively provided with anodic and cathodic frames; the frames being equipped with a feed/discharge channel design that reduces stray currents and facilitates cell assembly. The electrolyser may be advantageously employed for alkaline water electrolysis (AWE).
Electrochemical industrial applications often require electrolysers comprising a plurality of electrochemical cells, electrically and hydraulically connected with each other, each cell being provided with opposite electrodes facing each other and immersed in a current conductive liquid media, the electrolyte. This basic configuration of mutually connected conductive elements represents a complex electric network that may lead to uncontrolled stray currents. The latter may cause power loss, deterioration of the electrolyser equipment and/or cause hazard to the operating personnel.
In many industrial electrolysers, the individual electrodes are housed within a supporting frame and the electrolyte is fed to the electrode and subsequently discharged via one or more channels, or manifolds, that in some instances may traverse each frame.
In a variety of applications, such as for instance industrialized pressurized AWE electrolysers with internal manifolds, the feed and discharge channels are mostly manufactured by drilling cylindrical channels within the cell frames, or by molding the frames with the use of mobile parts, thereby creating a direct straight hydraulic connection between the manifolds and the active area of the electrode.
For instance, GB 1 145 751 describes a frame for an electrolyser cell which consists of a ring of having at least two apertures 18, 21 extending therethrough and at least one port extending from the inner surface of the ring to one of the apertures. DE 869 941 C describes a cell frame for electrolysers where each cell frame is divided into two half-frames having side surfaces which are profiled by an arrangement of interlocking tongues and grooves. U.S. Pat. No. 4,758,322 A describes an electrolysis apparatus for the electrolysis of solutions. The apparatus comprises bipolar elements formed of a conductive plate peripherally surrounded by an insulating frame provided with feeding and discharging channels extending in a circular fashion along peripheral zones of the frame. EP 3 696 298 A1 describes cell frame for an electrolysis cell comprising an opening for accommodating a membrane, collector duct openings for media supply and media discharge through the cell frame, a distributor duct structure configured for media supply from a respective supplying collector duct opening to an associated half space of the cell, and a sealing structure for sealing the cell frame, wherein the distributor duct structure is composed of a groove duct structure formed only on a first main side of the cell frame and a plurality of through bores extending between the groove duct structure and the associated half space. U.S. Pat. No. 4,107,023 A describes a filter press halate cell where a plurality of electrode units are arranged to form a cell. Each unit comprises a synthetic organic polymeric electrolytic cell frame housing an anode and a cathode in spaced relationship with each other comprising means for introducing feed through an inlet, and withdrawing electrolyte through an outlet.
In the above scenarios, it is extremely hard to manufacture channels with geometries that depart from the straight line. The latter is, in practice, the only viable option for mass production of the frame channels when using the aforementioned techniques. In this case, the overall length of the feed/discharge channels created within the frames will not exceed the distance between the manifolds and the electrode compartment.
The ensuing limited length of the feed and discharge channels has a negative impact on the electrolyser performance.
First, when the cells are in hydraulic parallel configuration, the pressure loss of the manifolds may determine a higher electrolyte flow in the first cells with respect to the last ones. This, in turn, may cause detrimental effects such as overheating or gas accumulation inside the cell.
Second, short channels may favor high stray currents throughout the electrolyte circuit. In fact, the electrical resistance of the electrolyte circuit can be considered, at least in first instance, roughly proportional to its length, so a shorter circuit will have a lower electrical resistance. Since the electrolyte circuit is electrically in parallel with the stack of cells, decreasing its resistance will increase the stray current flowing across the system, while decreasing the current actually flowing through the cells. As a consequence, the stray currents will negatively impact on the overall electrolyser performance.
Another negative side effect of the channels of the prior art is the unpredictable flow regime of the biphasic fluid circulating along the internal manifold, which is consequence of the fact that the short channels are usually drilled along the radial direction of the manifold, often of circular shape, and the flow regime may be affected by the speed of the fluid, its composition, the overall shape and dimensions of the manifold and of any pipes attached thereto, and the operating pressure conditions.
Aim of the present invention is to reduce the stray currents in the electrolyte circuit and to ensure an improved electrolyte flow across the electrolyser and inside its internal manifolds, if present, thereby overcoming the shortcomings of the electrolysers known in the art.
Under one aspect, the present invention relates to an electrolyser comprising at least two electrolytic cells, each electrolytic cell comprising an anodic half-cell equipped with an anode, a cathodic half-cell equipped with a cathode, and a separator arranged between the anode and the cathode. The cathodic and the anodic half-cells are respectively provided with a cathodic frame and an anodic frame, which accommodate a cathode and an anode.
Each frame is provided with an inner and outer surface. The frames are mutually arranged with respect to each other so that the inner surface of the anodic frame faces the inner surface of the cathodic frame.
The anodic frame and the cathodic frame each comprise a feed inlet and a feed outlet connected via a feed channel for feeding the electrolyte from an anodic and a cathodic manifold respectively into the anodic and cathodic compartments (i.e. the enclosures that are formed around the electrodes by the separator and the frame and that are filled with the electrolyte).
The anodic frame and the cathodic frame each comprise a discharge inlet and a discharge outlet for discharging the electrolyte respectively from the anodic compartment and from the cathodic compartment into the manifold, and the discharge inlet and the discharge outlet are connected via a discharge channel.
According to the present invention the anodic and cathodic feed and discharge channels are all created over the inner surface of the anodic frame. Furthermore, the anodic feed outlet and the anodic discharge inlet abut on the external surface of the anodic frame; and the cathodic feed outlet and the cathodic discharge inlet abut on the external surface of the cathodic frame, i.e. the respective feed outlets and discharge inlets open into the respective external surfaces.
With the term channel it is meant any receded or raised profile, either closed or open along its length. In case the channel is open along the direction of electrolyte flow, it becomes suitable for flowing liquids once it is set or pressed against a surface or any other element closing its open side.
The inlet and outlet of each feed and discharge channel shall be understood to coincide with the peripherical sections of the channel that are respectively placed in correspondence of the entrance and of the exit of the channel, where the terms “entrance” and “exit” refer to electrolyte flow when the electrolyser is operating.
Without prejudice to the scope of the claimed invention, the frame may comprise a plurality of feed inlets and feed outlets connected by corresponding feed channels, and/or a plurality of discharge inlets and discharge outlets connected by corresponding discharge channels.
The anodic and cathodic frames may be made of any suitable insulating material to be chosen by the skilled person in accordance with the characteristics of the electrolyte and the operating conditions of the electrolyser. Materials such as engineering plastics, and specifically PTFE, PSU, PPS, PEEK and PPA, have been found by the inventors to work particularly well in AWE and Anion Exchange Membrane Water Electrolysis (AEM-WE) applications.
In alternative, the anodic and cathodic frames may be made of a composite material. The material may comprise a conductive core, to ensure a greater mechanical strength, covered with an insulating material.
The anodic and cathodic frames may be obtained by any suitable technique, such as by milling or machining sheets, or by molding, 3D printing, or a combination thereof. The anodic and cathodic feed and discharge channels may be obtained by any technique suitable to form a receded or raised channel profile with respect to the surface of the corresponding frame and apt to depart from a straight line. Advantageous techniques, because of their availability and flexibility, may include engraving, milling, molding, 3D printing, machining or combinations thereof.
The sealing of each channel may be achieved by appropriately placing a gasket along the channel contour. The gasket may be positioned either on the same surface of the channel, along its profile, or on the opposite frame facing said channel, mirroring its profile. In alternative to the channel manufacturing techniques above, the channel profiles may be created by applying, molding, or printing suitably shaped ridges over the surface of the frame. In some instances, these ridges may also take the function of a gasket to ensure appropriate sealing of the channel besides conveying the electrolyte flow.
The channel design of the electrolyser according to the present invention has been found to promote an easier and more streamlined electrolyser assembly. Indeed, since for a given channel the channel inlet is always on the opposite surface of the channel outlet, the gaskets sealing those channels don't cross over the other gaskets sealing the other elements of the cell, such as the separator, the current collector and/or the bipolar plates, where present. Additionally, with the presently described techniques and channel design, much longer and/or thinner channels can be obtained, and with more complex shapes, taking full advantage of the free surface of the frame and overcoming the drawbacks of the straight and short channels known in the art.
The electrolytic cells may be electrically connected in series, and/or hydraulically connected in parallel through an internal manifold circulating the electrolyte.
It is understood that the conductive liquid media composition circulating within the anodic compartment, i.e. the anolyte, may differ from that circulating within the cathodic compartment, i.e. the catholyte. In the present application these compositions are generically referred to, either collectively or individually, as the electrolyte.
In general, the anodic and cathodic feed inlets and the discharge outlets are hydraulically connected to the respective internal or external manifolds.
Internal manifolds can be successfully employed, for example, in electrolysers for pressurized AWE, i.e. electrolysers operating at a pressure above or equal to 5 bar, as opposed to the external manifold design of atmospheric electrolysers, and they are typically associated with very short feed and discharge channels for each cell.
Under one embodiment, the anodic/cathodic feed and discharge channels of the electrolyser according to the invention perform at least one (1) change in direction along the inner surface of the anodic and cathodic frames respectively. Preferably, the number of changes in direction is equal to or above two (2), and even more preferably is in the range of 2-50.
The changes in direction signify departing from a straight-line geometry, which allows longer channel designs and to take advantage of the free surface of the frame, thus reducing stray currents and their negative impact on the electrolyser performance, as well as improving electrolyte flow across the electrolyser.
Preferably, the electrolyser according to the invention is characterized by anodic and cathodic feed and discharge channels that have an overall length of at least twice the distance LM-C between the manifold and the anodic/cathodic compartment. Preferably the cathodic feed and discharge channels have an overall length of 2-50 LM-C. The term “distance between the manifold and the anodic/cathodic compartment” denotes the shortest distance connecting the inner surface of a manifold with the inner surface of the anodic/cathodic compartment via a straight line.
It is known that the circuit resistance is also affected by the cross section of the channels. The claimed invention allows the skilled person to appropriately reduce the cross section of the channel, by taking into account relevant parameters, such as channel length, number of cells, electrolyte resistance and current load.
Under a further embodiment, the separator in the electrolyser according to the invention is a diaphragm or a membrane, and/or each of said electrolytic cells is optionally arranged in a zero-gap configuration.
Under a further embodiment, the anode and/or the cathode of the electrolyser according to the present invention are a foraminous structure or a continuous sheet of conductive material, preferably made of titanium, nickel, iron or alloys thereof, and optionally coated with one or more catalytic and/or protective layers.
By foraminous structure it is meant any rigid or flexible conductive element provided with through or blind holes, such as, without limitation, expanded meshes, woven meshes, punched sheets, perforated sheets, louvers and any other spongy, porous, pierced conductive structure suitable to operate as an electrode.
Under one embodiment, in the electrolyser according to the present invention, the feed outlets and the discharge inlets of the anodic and cathodic compartments are connected to an array of distribution channels, optionally in hydraulic parallel configuration with each other, created over the external surface of the anodic and cathodic frame respectively.
The advantageous techniques (such as engraving, milling, molding, 3D printing, machining or combinations thereof) used to manufacture the anodic and cathodic frames hereinbefore described, and those described for the manufacturing of the feed and discharge channels, further allow to implement a slanted design for these channels with respect to an internal manifold aperture at their connection point (inlet or outlet). This design proves particularly advantageous in case of two-phase fluids, i.e. including liquid and gaseous components, or one-phase fluids made of two different liquids or two gasses with a very different density, circulating to/from the channel from/to the manifold, as shall be clarified hereinafter.
It is noted, as an example, that the fluid discharged after the electrochemical reaction is often a two-phase fluid, comprising the liquid electrolyte and the gas evolved at the electrode.
By slanted design it is meant that the channel meets said manifold aperture at an angle α with respect to the perpendicular to the tangent in that point, where a is not zero and is comprised between −90° and +90°.
In general, two-phase fluids in pipes/manifolds have different flow regimes depending on the operating conditions (pressure, temperature, mass flow), on the shape and dimensions of the pipe/manifold and on the fluid itself (its phases and physical properties).
The resulting flow regime can range from a stratified flow, where the gas and the liquid are almost completely separated one from the other subject to gravity, to a bubbly flow, where small gas bubbles are included in the liquid flow, to a plug-flow, with relatively large bubbles interspersed within the fluid.
Each flow regime offers different challenges from both a mechanical and/or a process point of view, a few examples:
It is possible to work around these issues in the pipe/manifold design, but this requires knowing in advance what flow regime will be present and it can limit the design options available and/or increase the manufacturing and maintenance costs.
The purpose of the present solution is to ensure that at the manifold there is a pre-defined flow regime, even at different operating conditions, with well-identified behaviour that works well in case of bends and changes of directions of the manifold itself and of any further tubes/pipes attached to it, if present.
In the designs of the prior art, where the channels are typically drilled, they are connected to the manifold aperture at a direction perpendicular to the tangent at the contact point (likely due to the fact that this technique forces a short and straight channel geometry). This design does not allow to control or predict any flow regime so it is not possible to ensure that the fluid transport efficiency is not adversely affected.
On the other hand, the design of the present invention imparts to the fluid entering into the manifold a velocity component tangential to the manifold surface where the channel and manifold meet.
In case of a two-phase fulid (or one-phase fluids made of two different liquids or two gasses with very different density), this tangential component affects the fluid dynamics in the manifold. Fluid dynamic simulations show that it imparts a tangential component to the velocity of the fluid, which proceeds with an helicoidal flow. The tangential velocity pattern appears higher in a region close to the surface of the manifold, and lower in the inner core of the manifold. This velocity pattern roughly separates the two phases (or the two different one-phase components) according to their density and affects the dynamics of their individual flow. The lighter element tends to concentrate and flow along the inner core of the manifold, whereas the denser element tends to concentrate towards the surface. Both proceed with an helicoidal flow.
This predictable and controlled dynamics is advantageous in case the path of the fluid bends, especially from the horizontal to the vertical direction, and allows to control the mechanical stress exerted on the manifold and on any pipe attached thereto, and the accuracy of any instruments probing the fluid, thus addressing the issues that characterize the above-mentioned type of multiphase flows.
The slanted design may be implemented in the electrolyser hereinbefore described. However, it may also be more generally used in any electrolytic cell where biphasic fluids are generated as result of the electrochemical reaction and/or are fed into the system.
Therefore, under a further aspect, the present invention relates to an electrode frame for an electrolytic cell comprising a channel, said channel being connected to a manifold aperture at a connection point, wherein the direction of said channel at the connection point forms an angle α with respect to the perpendicular to the tangent of the manifold aperture at said connection point, and a is not zero and is comprised between-90° and +90°.
Typically, the above channel will mutually connect an inlet and an outlet, thereby allowing the fluid flowing within the electrolytic cell to feed or discharge into a manifold aperture. The contact point between the channel and the manifold aperture shall be the inlet or the outlet, depending on the frame design and cell assembly.
Preferably, α is comprised between −80° and −20°, and +20° and +80°, even more preferably α is comprised between −70° and −30°, and +30° and +70°. This latter embodiment has been found to work particularly well with a bi-phasic fluid comprising a liquid phase of an aqueous solution of potassium hydroxide at 25%-35% in weight percentage and a gaseous phase comprising hydrogen or oxygen.
While it is particularly advantageous to use the slanted design for the discharge channels of anodic or cathodic frames, since these channels carry biphasic fluids, e.g. a mixture of liquid electrolyte and gases that are discharged into the manifold at a certain speed, it is not excluded that it may be beneficially implemented also at the feed channels, for instance in case the feed manifold contains a certain (albeit small) percentage of gases within the liquid electrolyte.
Under a further aspect, the present invention relates to the use of the electrolyser hereinbefore described for AWE applications, and even more advantageously for high pressure AWE applications, i.e. applications where the electrolyser operates at a pressure above or equal to 5 bar.
Under a further aspect, the present invention relates to the use of the electrolyser hereinbefore described for AEM-WE applications.
A number of embodiments of the invention are described by way of example below with reference to the appended drawings, the purpose of which is solely to illustrate the mutual arrangement of the various elements relating to certain embodiments of the invention. The drawings are schematic representations and are not drawn to scale. However, same numbers correspond to essentially the same functional elements.
The anodic frame (100) also comprises a discharge channel (120) for discharging the electrolyte from the anodic compartment into the manifold aperture (351) through a discharge inlet and a discharge outlet, respectively placed at the electrolyte flow entrance and exit of the discharge channel.
The cathodic feed and discharge channels (not shown) are on the inner surface (201) of the cathodic frame and are respectively connected to the manifold apertures (305) and (355).
In the illustrated embodiment, the anodic feed and discharge channels (110, 120) and the cathodic feed and discharge channels (210, 220) are grooves, i.e. receded openings, traced on the inner surface of the respective frames (100, 200), and are therefore open along their greater length.
The anodic feed and discharge channels (110, 120) are respectively contoured with gaskets (181, 182), which are placed along their profile to ensure proper sealing.
In the presently illustrated embodiment, the gaskets (185, 186) of the cathodic feed and discharge channels are placed on the inner surface (101) of the anodic frame, in order to advantageously speed up the cell assembly. The gaskets (185, 186) also contour the manifold apertures (302, 352) of the anodic frame (100) and they are shaped so as to mirror the profile of the cathodic feed and discharge channels traced on the opposite inner surface (201) of the cathodic frame (200). When the two frames (100) and (200) are pressed together, the gaskets (181, 182, 185, 186) adhere to both inner surfaces (101) and (201), thereby closing all the anodic/cathodic feed/discharge channels and ensuring leak-tight sealing of the same.
The frames (100, 200) are provided with through holes (301, 302, 305, 306, 351, 351, 355, 356). These apertures, equipped with appropriate gaskets, compose the internal manifolds once all the frames of the adjacent cells of the electrolyser are pressed against each other. The manifolds ensure circulation of the electrolyte, with the gaskets preventing any spills and providing leak tight sealing even under pressure.
The anodic feed and discharge channels (110, 120) are visible on the internal surface (101) of the anodic frame (100), and the cathodic feed and discharge channels (210, 220) are visible on the internal surface (201) of the cathodic frame (200).
The anodic feed channel (110) contributes to deliver the electrolyte from the manifold aperture (301) to the anodic compartment. The electrolyte exits the feed channel through the anodic feed outlet (112), which abuts on the external surface (102) of the anodic frame. From there, the electrolyte reaches the anodic compartment, in correspondence of the space (190), either directly or through an appropriately designed path or a plurality thereof. For instance, a collector (500) placed in hydraulic communication with an array of channels (not visible) reaching the space (190) may be used, in analogy with the design further detailed in
The cathodic feed channel (210) contributes to deliver the electrolyte from the manifold (305) to the cathodic compartment. The electrolyte exits the feed channel through the cathodic feed outlet (212), which abuts on the external surface (202) of the cathodic frame. From there the electrolyte reaches the cathodic compartment in correspondence of space (290) either directly or through an appropriately designed path or a plurality thereof. For instance, a collector (550) placed in hydraulic communication with an array of channels (not visible) reaching the cathodic compartment may be used, in analogy with the design detailed in
The anodic/cathodic discharge channel (120)/(220) contributes to deliver the electrolyte from the anodic/cathodic compartment to the manifold aperture (351)/(355). The electrolyte enters the anodic/cathodic discharge channel (120)/(220), which is placed on the anodic/cathodic internal surface (101)/(201), from the external surface (102)/(202) of the anodic/cathodic frame through the anodic/cathodic discharge inlet (121)/(221). From the enclosure (190)/(290), the electrolyte may be collected towards the discharge inlet (121)/(221) either directly or through an appropriately designed path or a plurality thereof. For instance it is possible to use a collector (501)/(551) connected to the compartment situated in correspondence of the space (190)/(290) through an array of channels abutting thereon, in analogy with the design detailed in
The cathodic feed inlet (211) and the cathodic discharge outlet (222) are on the internal surface of the cathodic frame, in that the entrance section of the channel is contained within the inner surface (201). The cathodic feed and discharge channels (210, 220) are grooves traced on the inner surface (201): they are not closed along their length and are receded with respect to the cathodic inner surface (201). The cathodic feed outlet (212) and the cathodic discharge inlet (221) abut on the external surface of the cathodic frame (not shown).
The grey arrows indicate the 5 changes in direction of the cathodic feed channel (210) and the 2 changes in direction of the cathodic discharge channel (210).
An electrolyser for AWE applications was designed for operating at a pressure of 30 bar. The electrolyser comprises 100 electrolytic cells electrically connected in series. The cells are hydraulically connected in parallel through four internal manifolds for the circulation of an electrolytic solution. The latter consists of an aqueous solution of KOH 30% having an electrical conductivity of roughly 140 S/m at 80° C.
The electrolyser was designed to run at a current density of 10 kA/m2.
Each electrolytic cell comprises an anodic half-cell equipped with an anode consisting of an activated nickel expanded mesh and a cathodic half-cell equipped with an activated nickel woven mesh as the cathode.
Each electrode is housed within a frame of circular shape with an overall diameter of 1,5 m and a thickness of 10 mm that exposes a cell active area of 1 m2.
A diaphragm is arranged between the opposite electrodes in a zero-gap configuration.
Leakages are prevented through an appropriate disposal of gaskets between and on these elements.
Each electrode is electrically connected to the respective bipolar plate through a current collector.
They frames are made of PPS and manufactured by milling plastic sheets.
The anodic/cathodic feed channels are also manufactured with a milling technique and form a receded path of 500 mm in length, 10 mm in width and 4 mm in depth over the anodic/cathodic inner surface. These channels exhibit 5 changes in direction in analogy with the design depicted in
The anodic/cathodic discharge channels are also manufactured with a milling technique and form a receded path of 500 mm in length, 20 mm in width and 4 mm in depth over the anodic/cathodic inner surface. These channels exhibit 2 changes in direction as depicted in
The gaskets preventing leakage from the anodic/cathodic feed/discharge channels are placed as depicted in
Table 1 shows the stray currents calculated for this electrolyser design at different current densities (CD), expressed as percentage of the overall available current load.
The stray currents calculated for this electrolyser design at the design current density amount to 0.5% of the overall available current load.
An electrolyser is designed according to EXAMPLE 1 except the following differences.
The anodic/cathodic frames, made of PPS, are manufactured by milling plastic sheets.
The anodic/cathodic feed/discharge channels are made by drilling a straight through hole within the frame connecting the manifold to the anodic/cathodic compartments.
The anodic/cathodic feed channels are 50 mm long.
The present electrolyser is operated under the same conditions of EXAMPLE 1.
Table 2 shows the stray currents calculated for this electrolyser design at different current densities, expressed as percentage of the overall available current load.
The stray currents calculated for this electrolyser design at the design current density amount to 1.4% of the overall available current load.
The preceding description, including its examples, is not intended to limit the invention, which may be used according to various embodiments without however departing from its general principles, and whose scope is uniquely defined by the appended claims.
In the description and in the claims of the present application, the terms “comprising”, “including” and “containing” are not intended to exclude the presence of other additional elements, components, or process steps.
The discussion of documents, items, materials, devices, articles and the like is included in this description solely with the aim of providing a context for the present invention. It is not suggested or represented that any or all of these topics formed part of the prior art or formed a common general knowledge in the field relevant to the present invention before the priority date for each claim of this application.
| Number | Date | Country | Kind |
|---|---|---|---|
| 21189863.0 | Aug 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/071986 | 8/4/2022 | WO |
