EP4642951A1

EP4642951A1 - Low-capacity high-pressure electrolysis device

Info

Publication number: EP4642951A1
Application number: EP23832850.4A
Authority: EP
Inventors: Arie Meerkerk
Original assignee: Hydro Gen BV
Current assignee: Hydro Gen BV
Priority date: 2022-12-27
Filing date: 2023-12-22
Publication date: 2025-11-05
Also published as: NL2033845B1; WO2024144398A1; KR20250129009A; CN120390829A; JP2025542447A; AU2023417560A1

Abstract

A small scale high-pressure electrolyzer for generating hydrogen and oxygen is provided comprising one or more units each comprising a plurality of high-pressure electrolytic cells, wherein the electrolytic cells of each unit are electrically connected in series, as well as a central electrolyt header, functionally connected to each electrolytic cell for the supply of liquid electrolyt to the cell; a central hydrogen header connected to each electrolytic cell for the discharge of generated hydrogen from the cell; a central oxygen header connected to each electrolytic cell for the discharge of generated oxygen from the cell; a direct current power source for the power supply to each unit of serially connected electrolytic cells; wherein the units of serially connected electrolytic cells are electrically connected in parallel.

Description

Low-capacity high-pressure electrolysis device

Field of the Invention

The present invention relates to a new high-pressure electrolysis device for generating hydrogen and oxygen which is in particular suitable for small scale plants (<500kW).

Background

Electrolytic production of hydrogen is well known. See, for example, WO 2004/076721 and the U.S. patent publications cited therein.

As described in the introduction of WO 2004/076721 , known electrolytic eguipment, also referred to in the art as "electrolyzers", using liguid electrolyte to generate hydrogen, operates in the following way. Two electrodes are placed in a bath of liguid electrolyte, such as an agueous solution of potassium hydroxide (KOH). A broad range of potassium hydroxide concentration may be used, but usually a concentration of about 25 to 30% by weight KOH solution is used. The electrodes are separated from each other by a separation membrane that selectively allows passage of liguid but no gas. When a voltage is impressed across the electrodes, commonly about 2-3 Volts, current flows through the electrolyte between the electrodes. Hydrogen gas is produced at the cathode and oxygen gas is produced at the anode. The separation membrane keeps the hydrogen and oxygen gases separated as the generated gas bubbles rise through the liguid electrolyte. There is a disengagement space above the liguid electrolyte comprised of two separate chambers or two sections isolated from each other by being separated by a gas-tight barrier into two separate sections, one chamber or section to receive the hydrogen gas and the other to receive the oxygen gas. The two gases are separately removed from the respective sections of the disengagement space for storage or venting.

The currently available electrolyzers are mainly low-pressure electrolyzers with a stacked design, with sets of prefabricated parts stacked to assemble the electrolyzer. Due to the nature of stacked designs the pressure is limited to about 30 bar.

High-pressure electrolyzers are becoming of major interest since they have the advantage over low-pressure electrolyzers in that they are suitable to be used in high pressure applications, transport and storage without the need for a downstream compressor stage. A variety of designs of high-pressure electrolyzers has been described in the art which are often based on polymer electrolyte membrane (“PEM”) technology. See, for example, WO 2011/012507 A1. However, an important drawback of the PEM technology is that it reguires an expensive catalyst of rare metallic material and the catalyst layers in the electrolysis cells degrade faster at varying load reguirements than in the alkali electrolysis. NL 2023212 discloses a high-pressure electrolysis unit comprising a massive block of electrically conductive metal, which constitutes either the anode or the cathode, with an arrangement of interconnected vertical and horizontal cylindrical channels, which are closed with the exception of the channels for water inlet connection and hydrogen and oxygen outlet connections, wherein the internal face of the channel arrangement is partially coated with an electrically insulating coating, and wherein the counter electrodes which constitute the cathodes or anodes, respectively, are positioned in the vertical channels enveloped by a cylindrical membrane and supported and connected by electrode support bars installed in horizontal channels in the upper part of the housing.

WO 2021/029768 A1 discloses a high-pressure alkaline electrolysis unit comprising an assembly of tubes and pipes of electrically conductive metal which constitute either the anode or the cathode, with an arrangement of interconnected vertical and horizontal pipes and tubes, which are closed, with the exception of the pipes for water inlet connection and hydrogen and oxygen outlet connections, wherein the internal face of the channel arrangement is coated with an electrically isolated coating, and the counterelectrodes constituting the cathodes or anodes, respectively, are positioned in the vertical pipes being enveloped by a cylindrical membrane and supported and connected by electrode support bars which are installed in horizontal pipes in the upper part of the housing. The high-pressure electrolysis device further comprises one or more pressure-tight isolated electrical conductors to conduct electrical power supply from the outside to the inside of the electrolysis device.

WO 2004/076721 A2 which corresponds to EP 1597414 B1 discloses an electrolyzer cell for the electrolysis of water which comprises a cathode of generally tubular configuration within which is disposed an anode separated from the cathode by a separation membrane of generally tubular configuration which divides the electrolyte chamber into an anode subchamber and a cathode sub-chamber. An electrolyzer apparatus includes an array of individual cells across each of which an electric potential is imposed by a DC generator via electric leads. Hydrogen gas generated within cells from electrolyte is removed via hydrogen gas take-off lines and hydrogen manifold line. By-product oxygen is removed from cells by oxygen gas take-off lines and oxygen manifold line.

EP 3 498 886 A1 discloses an electrolysis system to conduct oxidation and reduction reactions comprising one or more electrolytic cells, the electrolytic cells being formed by at least a pair of electrodes and an electrolyte between the electrodes, wherein the assembly of said one or more electrolytic cells defines an electrolyzer; and an energy source that supplies an electrical signal to the electrolyzer. The electrical signal received by the electrolytic cells or cell that form the electrolyzer correspond to a direct current pulse which is configured for each electrolyzer’s cells to operate: in a charge transient regime of each cell during the current pulse; and in a discharge transient regime of each cell during the time between the direct current pulses; wherein said charge and discharge transient regimes are defined by the construction of each electrolytic cell in the form of a cylindrical plates capacitor.

US 3,984,303 discloses an electrolytic cell for the production of halogen gas and alkali metal hydroxide, having a hollow tubular cathode member with a hollow tubular anode member disposed concentrically within the cathode, each electrode member having liquid permeable walls to allow the circulation of electrolyte. The anode is covered on its outer surface with an electrically conductive membrane, thereby separating the anode and cathode surfaces. This membrane is tubular in shape, and is fitted over the outer surface of the anode. The tubular membrane may be of a material selectively permeable to the passage of ions and impervious to hydrodynamic flow of the electrolyte. Such cells may also be connected in series to form a larger multi-cell electrolyzer.

In the non-prepublished International Patent Application PCT/NL2022/050648, which corresponds to NL2029726, a high-pressure electrolysis device is disclosed comprising a plurality of high-pressure electrolysis units which are arranged in series, wherein each unit comprises a body of electrically conductive metal made up of an assembly of interconnected horizontal and vertical tubes, which constitutes an electrode connectable to a source of DC electricity. The assembly comprises three horizontal tubes and at least two vertical tubes, the vertical tubes each accommodating an elongated central electrode and a tubular membrane, wherein each vertical tube together with the central electrode, the membrane and an electrolyte constitute an electrolytic cell. The electrolytic cells within each unit are connected in parallel, wherein each unit further comprises at least two vertical tubes not accommodating central electrodes, the first vertical tube connecting the lower horizontal tube to the first upper horizontal tube and the second vertical tube connecting the lower horizontal tube with the second upper horizontal tube.

The differential voltage over the serially connected units is equal to the number of units multiplied by the voltage drop over a single unit, which is in the range of 2-3 Vdc. The electrical current is equal to the number of parallel cells multiplied by the current through a single cell, which is dependent on the detailed design of the cell and the voltage applied over the cell.

The system described in PCT/NL2022/050648 is very suitable for large scale applications because the high-pressure electrolysis units consist of parallel connected electrolysis cells, which can accept large currents through the units. However, for small capacity systems having a lower number of electrolysis cells, such a system would result in a very low voltage, which is not optimal for the design of the upstream power transformation and rectifier system, which is necessary to operate the electrolyzer system. In particular, for small scale units, the system described in PCT/NL2022/050648 would result in low voltages and high electrical currents, which is inefficient and uneconomic. The ideal design of a transformation and rectifier system is based upon the highest possible voltage and the lowest possible electrical current.

Small capacity high-pressure electrolyzer systems have a major advantage over large scale systems, since high pressure technology can be easier applied, there are numerous developments for such applications, and, importantly, the use of compressors can be avoided.

Therefore, there is a need for simple, efficient, and cost-effective small scale high- pressure electrolyzers for the production of hydrogen and other industrial processes, which are compact, flexible, modular, scalable and require low maintenance. It is an object of the present invention to provide such a small-scale high-pressure electrolysis device with such beneficial properties.

Summary of the Invention

In one aspect of the present invention a small scale high-pressure electrolyzer for generating hydrogen and oxygen is provided, comprising:

- one or more units, each comprising a plurality of high-pressure electrolytic cells, wherein the electrolytic cells of each unit are electrically connected in series,

- a central electrolyt header which is functionally connected to each electrolytic cell for the supply of liquid electrolyt to the cell;

- a central hydrogen header which is functionally connected to each electrolytic cell for the discharge of generated hydrogen from the cell;

- a central oxygen header which is functionally connected to each electrolytic cell for the discharge of generated oxygen from the cell;

- a direct current power source which is functionally connected to each unit of serially connected electrolytic cells, for the power supply of each unit of serially connected cells;

- wherein the units of serially connected electrolytic cells are electrically connected in parallel.

In a preferred embodiment, the functional connection between the central electrolyt header and the electrolytic cells, between the central hydrogen header and the electrolytic cells and between the central oxygen header and the electrolytic cells is realized through non-conductive hydraulic hoses. In another preferred embodiment, the central hydrogen header and the central oxygen header are each functionally connected to the central electrolyt header, preferably also through non-conductive hydraulic hoses.

In still another preferred embodiment, the central electrolyt header also comprises a supply connection for the supply of demin water to the electrolyt header, the central hydrogen header also comprises a discharge connection for the discharge of hydrogen from the hydrogen header, and the central oxygen header also comprises a discharge connection for the discharge of oxygen from the oxygen header.

In a further embodiment of the present invention, each electrolytic cell is composed of a pressure-resistant, vertically arranged tube of electrically conductive metal constituting the anode, an elongated cathode housed in the center of the vertical tube, and a separation membrane surrounding the cathode which divides the electrolysis cell into an anode subchamber and a cathode sub-chamber.

In another embodiment of the invention, the vertical tube of each electrolytic cell has a lower end and a top end, the lower end being closed, and the top end being sealed with an electrically insulating gas-tight and pressure-resistant seal.

In still another embodiment of the invention, the elongated central cathode extends from the lower portion of the vertical tube and protrudes through the electrically insulating seal to beyond the top end of the vertical tube.

In a further embodiment, the vertical tube has at least three openings in the side wall of the tube at different heights, the lower opening at the lower end of the tube for the supply of demin water or electrolyte, the upper opening for the discharge of generated hydrogen and the middle opening for the discharge of generated oxygen gas.

In still a further embodiment, a gas-tight seal is provided between the separation membrane and the inner wall of the vertical tube at a height between the upper opening and the middle opening, where the seal also supports the separation membrane.

In another embodiment, the separation membrane has a lower end and an upper end, the lower end extending downward beyond the lower end of the central cathode and the upper end being connected to said gas-tight seal, the separation membrane sealing against the passage of gases, but allowing the passage of the liquid and the ions of the electrolyte contained therein.

These and other aspects of the present invention will be more fully outlined in the detailed description which follows with reference to a particular embodiment thereof, i.e. the production of hydrogen and oxygen by high-pressure electrolysis of water. However, those skilled in the art will recognize that the invention may also be utilized in other embodiments. Conventional known devices such as pressure-sensing and flow-rate sensing devices, and controls to operate valves and pumps, have been largely omitted from the description, as such devices and their use are well known in the art.

Brief Description of the Drawings

Figure 1 is a schematic view of an embodiment of a high-pressure electrolyzer according to the invention;

Figure 2 is a flow sheet of the electrolyzer of Figure 1 ;

Figure 3 is a perspective view of a schematic prototype of an electrolyzer according to the invention;

Figure 4 is a perspective view of an embodiment of an electrolysis cell which forms part of the high-pressure electrolyzer according to the invention;

Figure 5 is a detailed view of the upper part of two electrolysis cells as shown in Figure 4, which are connected in series through a connector according to the invention.

The following detailed description should be read with reference to the drawings in which like elements in different drawings are numbered identically. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention.

Detailed Description of the Invention

In accordance with the present invention a small scale high-pressure electrolyzer for generating hydrogen and oxygen is provided comprising one or more units, each comprising a plurality of electrolytic cells, e.g. from three to twenty up to 100 or more electrolytic cells, which are connected in series. A preferred range of a row of serially connected electrolytic cells is between 20 and 100 cells, more preferably between 50 and 100 cells. As a result, the current through the system equals the current of one cell which is dependent on the detailed design of the cell and the voltage applied over the cell. Further, the differential voltage over the serially connected cells is equal to the number of cells multiplied by the voltage drop over a single cell, which is in the range of 2-3 Vdc. A preferred range of units of serially connected electrolytic cells currently is 1 to 10 units, more preferably 1 to 5 units.

The advantage of the present invention is a higher voltage over the serially connected cells and a lower current through the cells. This is beneficial for the electric power transformation system. The step down of the supplied AC voltage to the required voltage will be smaller, resulting in a smaller transformer. And the lower current will reduce the overall material needed to rectify and transport the electric current which results in lower costs for the complete system. Each high-pressure electrolytic cell comprises a pair of electrodes, a separation membrane and a liquid electrolyte between the cells, wherein the cell is composed of a pressure-resistant, vertically arranged tube of electrically conductive metal which constitutes the first electrode, the anode or cathode, an elongated central second or counter electrode, the cathode or anode, respectively, in the middle of the vertical tube which is electrically insulated from the vertical tube, and the separation membrane surrounding the counter electrode. The first electrode of the electrolytic cell is connectable to a source of DC electricity or to the elongated central counter electrode of a preceding electrolytic cell. The second or counter electrode of the (same) electrolytic cell is connectable to the first electrode of the subsequent electrolytic cell, being the vertically arranged tube of that cell, or to a source of DC electricity. Preferably, the vertical tube, the separation membrane and the central electrode of each electrolytic cell are arranged coaxially relative to each other.

In a preferred embodiment of the invention, the vertical tube constitutes the anode (+) and the elongated central electrode in the middle of the tube constitutes the cathode (-) of the electrolytic cell.

The words “tubes” and “pipes” are frequently used interchangeably in the art, although there are differences between tubes and pipes. Reference may be made to, e.g., used herein, “tubes” and “pipes” are collectively referred to as “tubes”, unless stated otherwise. A skilled person in the art will have no problem in understanding which materials are needed when applying a design according to the invention.

The vertical tube has a lower end and a top end, the lower end being closed, and the top end being sealed with an electrically insulating gas-tight and pressure-resistant seal. In a preferred embodiment, the top end of the vertical tube is threaded to facilitate maintenance of the electrolytic cell. The vertical tube may be closed with a readily available pressure fitting which is known in the art, such as a threaded pressure fitting.

The elongated central electrode extends from the lower portion of the vertical tube and protrudes through the electrically insulating seal to beyond the top end of the vertical tube. The central electrode is connectable to a source of DC electricity or to the first electrode of a subsequent electrolysis cell. In a preferred embodiment, the elongated central electrode is a solid, cylindrical bar or rod type electrode.

The vertical tube has at least three openings in the side wall of the tube at different heights, the lower opening at the lower end of the tube for the supply of demin water or electrolyte, the upper opening for the discharge of the generated hydrogen gas and the middle opening for the discharge of the generated oxygen gas. In one embodiment, the openings are connected to the corresponding headers through non-conductive connections for further transport to pressurized containers for further processing and storage of the gases and supply from demin water storage tanks, respectively. In another embodiment, the openings are provided with suitable non-conductive fittings for connecting hydraulic hoses, pipes, or the like, to the respective headers. The high-pressure electrolyzer and the electrolytic cells according to the invention are further bound by common feeding conduits of liquid electrolyte and demin water, as well as gas take-off conduits of the hydrogen and oxygen gases.

To overcome short circuitry between the serial connected cells, the electrolyte supply and collection of the generated gases is realized by connecting the electrolytic cells to central headers, also referred to as manifolds, by non-conductive connections. The central headers and the connections form part of the electrolyzer according to the invention.

Demin water or liquid electrolyt is supplied to a pressurized electrolyt header which is connected through non-conductive connections to the respective electrolytic cells for distribution of the liquid to the cells.

The generated hydrogen and oxygen gases together with and in mixture with part of the electrolyte, are discharged from the electrolytic cells and transferred to the respective central hydrogen and oxygen headers through non-conductive connections for collection, separation from electrolyt and further transport.

A sleeve or disc-shaped gas-tight seal is provided in each electrolytic cell between the separation membrane and the inner wall of the vertical tube at the upper half of the vertical tube at a position between the upper opening and the middle opening of the tube, wherein the seal also supports the membrane.

The separation membrane, preferably of tubular configuration, is provided within each vertical tube, surrounds the central electrode, thus dividing the vertical tube into an anode sub-chamber and a cathode sub-chamber. The separation membrane prevents the passage therethrough of gases but permits the passage of liquid and liquid borne ions. The separation membrane is top supported by the sleeve or disc-shaped seal and extends from beyond the lower outer end of the central electrode up to said seal. Preferably, the separation membrane is open at the lower side. In another preferred embodiment, the membrane is a ZIRFON® separation membrane¹.

The upper part of the elongated central electrodes, i.e. the part above the sleeve or disc-shaped gas-tight seal in the vertical tube, is preferably electrically insulated around their circumference upwards from the seal to prevent generation of gases in the upper part of the cathode sub-chamber, enabling high quality of the gas produced.

¹ ZIRFON® is a registered trademark The electrolytic cells are filled with a liquid electrolyte, usually a solution of potassium hydroxide (KOH) in demineralized water. A broad range of potassium hydroxide concentrations may be applied, but generally a concentration of about 25 to 30 wt.% KOH solution is used. The electrodes, i.e. the vertical tubes constituting the anodes and the elongated central cathodes are exposed to, and in contact with, the liquid electrolyte to generate gases when in operation.

When in operation, hydrogen gas is produced at the cathode and oxygen gas is produced at the anode of each electrolytic cell. The separation membrane keeps the hydrogen and oxygen gases separated as the generated gas bubbles rise through the liquid electrolyte.

The serial connected electrolysis cells of the electrolyzer according to the invention are preferably arranged in an electrically insulated adjacent array. As illustrated in the embodiment of Fig. 1 and Fig. 5, the electrolysis cells are electrically connected such that the anode (+) of the body of the first unit is connected a source of DC electricity, the cathode (-) of the central cathode of the first unit is connected to the body of the second adjacent electrolysis cell, the central cathode of the second electrolysis cell to the body of the next adjacent electrolysis cell, and so on, and the last central cathode (-) is connected to the source of DC electricity. The differential voltage over the serially connected cells is equal to the number of cells multiplied by the voltage drop over a single cell, which is in the range of 2-3 Vdc. The current through one unit of serially connected cells, which is equal to the current through a single cell and is dependent on the detailed design of the cell and the voltage applied over the cell.

The wall thickness of the vertical tubes is dictated by the desired generation pressure, by material properties such as yield strength and electrical conductivity of the metal from which the tubes are is made. Generally, the wall thickness may vary from about 0.65 to 1.60 cm. Typically, the length of the vertical pipes of the high-pressure cells is in the range of 500 to 2000 mm and may be further developed up to 4000 mm. Typically, the diameter of the central cathode is ranging from 10 to 30 mm and may be further developed up to 100 mm. These values are merely indicative and not to be construed as limiting the invention in any respect.

In a preferred embodiment of the invention a cooling and drying device is provided which forms part of the high-pressure electrolyzer. The device comprises one or more cooling and drying units which are connected with take-off conduits of the produced hydrogen and oxygen gases from the central hydrogen header and central oxygen header. The gases are conveyed to the cooling and drying device to be cooled down by a cooling medium, e.g. cooling water. After cooling, the oxygen gas is reduced to atmospheric pressure which results in another temperature reduction due to the thermodynamic behavior of oxygen. The oxygen at ambient conditions is then used to further cool down the hydrogen gas which still is under high pressure. The gas cooling unit is designed such that condensed water runs back into the electrolysis units. Condensation of water vapor in the downstream systems is avoided. Thus, by cooling the hydrogen gas below ambient temperature it will be dried to a saturation temperature below atmospheric conditions, thereby preventing water condensation in downstream systems.

In another aspect of the invention, one or more pressure containers are provided which form part of the electrolysis device according to the present invention. The pressure containers are preferably releasably connected to the cooling and drying units for storage of the dried and purified gases.

The electrolyzer according to the invention has several advantages as compared to prior art electrolyzers of a similar type. These advantages inter alia relate to: a) the high- pressure environment, b) gas-liquid separation, c) natural circulation and removal of produced gases from the electrolytic cells by gravity effects, d) isolation of the central cathode, e) simplified maintenance of the apparatus, f) cooling of the produced gases.

Regarding the high-pressure environment, the pressure containment is also one of the electrodes. The coaxial anode/cathode configuration allows very high-pressure hydrogen generation with practical wall thicknesses of conventional materials in the containment body provided by the anode. Conventional stacked concepts have large plates, which enable that high currents flow through the system. The perimeter of the plates is also the perimeter which must be kept pressure-tight. The present electrolyzer is designed such that the anode/cathode configuration and the circumference of the openings at the top of the cell are significantly smaller than the perimeter of the plates in stacked concepts, which results in a reduced area for potential leakages of combustible gases.

The high pressure in the electrolysis units results in smaller gas volumes in the electrode area and subsequently large electrolyt volume, which in turn results in lower electrical resistance and thus a better efficiency.

The ability of the apparatus and method of the present invention to enable hydrogen (and oxygen) production at pressures of up to or even exceeding 1000 bar exceeds the highest pressure of the known prior art electrolyzers. The apparatus and method of the present invention can produce such high-pressure hydrogen without need for a separate compressor to pressurize the product hydrogen gas. High-pressure electrolyzer systems have a major advantage in small scale systems in that the use of small capacity and low efficient downstream compressors can be avoided. Small scale compressors are relatively expensive compared to large scale compressors. The device according to the present invention allows high-pressure hydrogen production to be performed in a unique way that reduces the component cost and system complexity so that the equipment is easily affordable. The device is scalable to any given production capacity.

The produced gases are removed from the electrode surfaces by natural draft which improves the capacity of the system. No active circulation system is needed. Collecting headers are included in the electrolyzer according to the invention to enable or improve the natural circulation and gas separation in the high-pressure electrolysis units.

Regarding maintenance of the apparatus, the outer upper parts of the vertical tubes which accommodate the central electrode are preferably threaded and provided with releasably threaded pressure fittings. Furthermore, the central electrode and surrounding separation membranes are preferably top supported only, enabling easy removal of the central electrode and membranes for maintenance or replacement. Therefore, the maintenance of the apparatus is simplified, more efficient and cheaper.

Regarding the cooling of the produced gases, the gas cooling unit according to the invention provides that by cooling the hydrogen gas it will be dried to a saturation temperature below atmospheric conditions, thereby preventing water condensation in the downstream systems. The prior art is silent about this feature.

The apparatus and method of the present invention may be utilized to generate high- pressure hydrogen on site at locations such as factories, office buildings or residential areas for on-site energy storage and/or use as fuel for fuel cell, internal combustion engines or heating applications.

Turning to the drawings, with particular reference to Figure 1 and also to the flow sheet of Figure 2, there is shown an embodiment of a high-pressure electrolyzer 100, comprising a unit of four electrolytic cells 50 which are electrically connected in series. Each electrolytic cell is composed of a pressure-resistant, vertically arranged tube 1 of electrically conductive metal constituting the anode, an elongated central cathode 2 housed in the center of the vertical tube, and a separation membrane 3 surrounding the cathode which divides the electrolysis cell into an anode sub-chamber 8 and a cathode sub-chamber 9. The vertical tube 1 is closed at the bottom end 10, whereas the top end is sealed with an insulating pressure-resistant seal 5. The elongated cathode 2 protrudes through the seal.

The electrolytic cells are electrically connected by electrical serial connectors 6 such that the anode (+) of the body of the first unit is connected a source of DC electricity, the cathode (-) of the central cathode of the first unit is connected to the body of the second adjacent electrolysis cell, the central cathode of the second electrolysis cell to the body of the next adjacent electrolysis cell, and so on, and the last central cathode (-) is connected to the source of DC electricity.

Each electrolysis cell is interconnected with the three headers 15, 16 and 17 by the non-conductive hydraulic hoses 1g, 1 h and 1 i, which run from the openings 21 , 22 and 23 of the cell to respective the electrolyte headers 15, the oxygen header 16 and the hydrogen header 17.

The oxygen header and hydrogen header are connected by hydraulic hoses 1e and 1f, respectively, to enable separated electrolyt to return to the electrolyte header. By gravity differences between the electrolytic cells 50 and the assembled parts 15, 16, 17, 1e and 1f a natural circulation flow of electrolyt will be established.

Hydrogen outlet 12 will release the excessive hydrogen to downstream systems, such as storage tanks or pipeline.

Oxygen outlet 13 will release the excessive hydrogen to downstream systems, such as storage tanks or pipeline.

To compensate the electrochemical reacted water, demin water is supplied via demin water inlet 10.

Demin water will be intermittently dosed by valve 24 from demin water tank(s) 18. The demin water tank 18 will be filled under atmospheric conditions by means of a simple pumping device, which is not part of the current invention.

When the tank 18 is filled with demin water, oxygen from the electrolytic cells 50 is fed into the tanks to pressurize the tank 18 via valve 20. During this filling, the pressure in the electrolytic cells 50 is increased temporarily to realize a higher pressure in the tanks 18 than during normal operation in the electrolytic cells 50. As soon as the pressure in the tank 18 is reduced (as the water volume reduces) to a value close to the electrolyzer operational pressure, the electrolytic cells 50 will start operating at a higher pressure again to fill the tank 18 with pressurized oxygen again via valve 20. This sequence is repeated until the tank 18 is empty. As soon as the tank 18 is empty, it is depressurized via valve 19 so it can be filled with demin water again.

Figure 3 shows a schematic prototype of a compact small-scale electrolyzer according to the invention, with five pressurized demin water tanks 18 for the supply of demin water to the central electrolyt header 15. Two units of serially connected electrolysis cells 50 are shown, together with the central oxygen header 16 and central hydrogen header 17. Connectors and connecting pipes or hoses are not represented in this figure.

Figure 4 shows a modular electrolysis cell for small scale high-pressure applications. Each electrolysis cell is interconnected with the three headers 15, 16 and 17 by the non- conductive hydraulic hoses 1g, 1 h and 1 i, which run from the openings 21 , 22 and 23 of the cell to the respective headers. The serial connection is realized by connector 6, which in this embodiment is of a special design, enabling to connect the vertical anode tube 1 of one cell to the concentric positioned central cathode 2 of an adjacent cell, thus forming a compact array of serial connected cells. This is further illustrated in the detailed view of Figure 5, showing the top of two electrolytic cells which are connected through connector 6. This connector 6 is fitted to the anode tube 1 by a threaded connection and to the threaded upper end of the left-hand cathode 2 with fixing nut 25.

Operation (see Figures 1 and 2)

The empty electrolytic cells of a unit are filled with electrolyte via the central electrolyte header 15 (first filling, the electrolyte being a solution of 25-30% potassium hydroxide in demineralized water) with all venting devices in open position, until a level in the central hydrogen header 17 and central oxygen header 16 is secured.

Then the electrolysis process is started by connecting the electrolyzer to an electrical DC source and creating a voltage drop over every single electrolysis cell of 2 - 3V. Hydrogen gas will be produced at the surface of the center electrode (cathode) and oxygen will be produced at the inner surface of the surrounding vertical tube (anode). The gases produced will rise to and collected into the hydrogen and oxygen headers. When all downstream volume has been purged by the produced gases and no air is remaining in the downstream system, the venting devices onto the headers will be closed. Pressure will build up in the system as the volumes of the produced gases are far more larger than the converted water volume.

Natural circulation via the hydrogen and oxygen headers and the connected electrolyt header will support the removal of the produced gases from the electrolytic cell area and the collection of the gases in the headers.

When the operational pressure has been reached, the gas pressure control system will blow off the excess gases to the downstream systems, e.g. storage and/or pipe line system. The converted amount of water will be made up by demineralized water when the water level reaches low or controllable level. Demin water is dosed from a pressurized tank or series of pressurized tank 18 where demin water is stored to the electrolyt header 15.

The stored demin water will be pressurized batchwise by the produced oxygen: 1) first the tank 18 is filled with demin water at atmospheric conditions; 2) after filling, oxygen from the electrolytic cells 50 is fed into the tanks to pressurize the tank 18 via valve 20. During this filling the pressure in the electrolytic cells 50 is increased temporarily to realize a higher pressure in the tank 18 than during normal operation in the electrolytic cells 50; 3) after pressurizing the tank 18, demin water will flow into the electrolytic cells, controlled by a control valve 24; 4) as soon as the pressure in the tank 18 is reduced (as the water volume reduces) to a value close to the electrolyzer operational pressure, the electrolytic cells 50 will start operating at a higher pressure again to fill the tank 18 with pressurized oxygen again via valve 20; 5) this sequence is repeated until the tank 18 are empty; 6) when the tank 18 are empty, it is depressurized via valve 19 and filled with demin water again.

The produced hydrogen and oxygen gases are separated from the liquid electrolyt in the central headers 17 and 16, respectively, and then conveyed to a cooling device. The cooling device is not shown. Reference is made in this connection to the non-prepublished patent application PCT/NL2022/050648 of the same applicant, where an identical cooling and drying device is shown and explained (cf. Figures 8-11). This PCT application is herewith incorporated by reference. The gases are cooled down by a cooling medium, e.g. cooling water. After cooling, the oxygen gas pressure will be reduced to atmospheric pressure, resulting in another temperature reduction due to the thermodynamic behavior of oxygen. The cold oxygen at ambient pressure is then used to cool down the still pressurized hydrogen even further. The cooling devices are designed such that condensed water vapor will run back into the electrolytic cells.

Upon cooling the hydrogen gas as described it will be dried to a saturation temperature below atmospheric conditions, thereby preventing condensation of water vapor in the downstream systems.

From the foregoing description, a person skilled in the art can easily ascertain the essential characteristics of the present invention, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt it to various usages and conditions. These modifications and adaptations are therefore deemed to fall within the scope of protection of this invention as claimed in the appended claims.

List of reference numerals relating to the drawings

1 . vertical tube of conductive metal, constituting the first electrode of the electrolytic cell le. connection between electrolyt header 15 and oxygen header 16 lf. connection between electrolyt header 15 and hydrogen header 17 lg. connection between electrolyt header 15 and opening 21 of vertical tube 1 l h. connection between oxygen header 16 and opening 22 of vertical tube 1 l i. connection between hydrogen header 17 and opening 23 of vertical tube 1

2. elongated second electrode of the electrolytic cell

3. separation membrane of the electroytic cell

4. gas-tight sleeve or disc-shaped seal 5. electrically insulated seal of the top of the vertical tube 1.

6. electrical serial connector

7. electrically insulated ring or nut

8. anode sub-chamber

9. cathode sub-chamber

10. bottom end of the vertical tube 1.

11. demin water inlet

12. hydrogen outlet

13. oxygen outlet

15. electrolyt header

16. oxygen header

17. hydrogen header

18. pressurized demin water tanks

19. demin water tank pressure release valve

20. demin water pressurization valve

21. opening in the vertical tube for demin water supply

22. opening in the vertical tube for the discharge of oxygen

23. opening in the vertical tube for the discharge of hydrogen

25. fixing screw or nut

50. electrolysis cell

100. electrolyzer according to the invention

Claims

1. High-pressure electrolyzer (100) for the generation of hydrogen and oxygen in particular in small scale plants, comprising:

- one or more units, each comprising a plurality of high-pressure electrolysis cells (50), wherein the electrolysis cells of each unit are electrically connected to each other in series;

- a central electrolyte distribution holder (15), functionally connected to each electrolytic cell (50) of the electrolyzer, for supplying liquid electrolyte to the electrolytic cells;

- a central storage and separation container (17), functionally connected to each electrolysis cell (50) of the electrolyzer, for collecting and processing the hydrogen generated from the electrolysis cells;

- a central storage and separation container (16), functionally connected to each electrolysis cell (50) of the electrolyzer, for collecting and processing the oxygen generated from the electrolysis cells; and

- a direct current source, electrically connected to each unit of the series-connected electrolytic cells, for the power supply of each unit of the series-connected electrolytic cells;

- wherein the units of series-connected electrolysis cells are electrically connected in parallel.

2. High-pressure electrolyzer according to claim 1 , wherein the functional connection between the central electrolyte distribution container (15) and the electrolytic cells, and between the central hydrogen storage and separation container for hydrogen (17), or oxygen (16), respectively, and the electrolysis cells is realized via non-conductive connections, for example non-conductive hydraulic pressure hoses..

3. High-pressure electrolyzer according to claim 1 or 2, wherein the central storage and separation container for hydrogen (17) and the central storage and separation container for oxygen (16) are each functionally connected to the central distribution container for electrolyte (15).

4. High-pressure electrolyzer according to any one of claims 1 to 3, wherein the central distribution container for electrolyte (15) also comprises a supply line (10) for the supply of demineralized water, the central storage and separation container (17) also comprises a discharge line (12) for the discharge of hydrogen, and the central storage and separation container (16) also comprises a discharge line (13) for the discharge of oxygen.

5. High-pressure electrolyzer according to any one of claims 1 to 4, wherein each electrolytic cell (50) is constructed from a pressure-resistant, substantially vertically arranged tube of electrically conductive metal (1), which constitutes the first electrode, anode (+) or cathode (-), an elongated central second electrode (2), which is housed in the center of the substantially vertical tube and which constitutes the counter electrode, cathode (-) or anode (+), and a separation membrane (3) around the central second electrode that divides the electrolytic cell into an anode sub-chamber (8) and a cathode sub-chamber (9).

6. High-pressure electrolyzer according to claim 5, wherein the substantially vertical tube (1), which constitutes the first electrode, is the anode (+), and the central second electrode (2) which constitutes the counter-electrode, is the cathode (-).

7. High-pressure electrolyzer according to claim 6, wherein the substantially vertical tube (1) has a lower end (10) and an upper end, wherein the lower end is closed and the upper end is sealed with an electrically insulating, gas-tight and pressure-resistant seal (5).

8. High-pressure electrolyzer according to claim 6 or 7, wherein the elongated central second electrode (2) extends from the lower part of the vertical tube (1) and protrudes through the electrically insulating seal (5) above the upper end of the vertical tube.

9. High-pressure electrolyzer according to any one of claims 1 to 8, wherein the vertical tube (1) in the side wall has at least three openings (21, 22, 23) at different heights, the lower opening (21) in the lower part of the tube for the supply of electrolyte, the upper opening (22) for the discharge of generated hydrogen gas and the middle opening (23) for the discharge of generated oxygen gas.

10. High-pressure electrolyzer according to any one of claims 1 to 9, wherein a gastight seal (4) is provided between the separating membrane (3) and the inner wall of the vertical tube at a height between the upper opening (22) and the middle opening (23) of the tube.

11. A high-pressure electrolyzer according to any one of claims 1 to 10, wherein the separating membrane (3) has a lower end and an upper end, the lower end extending downward beyond the lower end of the central second electrode (2) and the upper end being connected to the gas-tight seal (4), where the separating membrane seals against the passage of gases, but allows the passage of the liquid and the ions of the electrolyte contained therein.

12. High-pressure electrolyzer according to any one of claims 1 to 11 , wherein the substantially vertical tubular first electrode (1) of an electrolytic cell is conductively connected electrically to a direct current source or to the central second electrode (2) of a preceding electrolytic cell, and the central second electrode (2) is connected to the vertical tubular first electrode (1) of a subsequent electrolytic cell or to a direct current source.

13. High-pressure electrolyzer according to any one of claims 1 to 12, wherein the electrolysis cells are conductively electrically connected to each other by means of connectors (6).

14. A high-pressure electrolyzer according to any one of claims 1 to 13, wherein the elongated central second electrode (2) is rod-shaped or cylindrical.

15. High-pressure electrolyzer according to any one of claims 1 to 14, wherein the substsantially vertical tube (1) forming the first electrode, the central second electrode (2) and the separating membrane (3) are arranged coaxially with each other.

16. High-pressure electrolyzer according to any one of claims 1 to 15, wherein the upper end of the central second electrode (2) of an electrolytic cell (50) is electrically insulated around its periphery above seal (4).

17. High-pressure electrolyzer according to any one of claims 1 to 16, wherein the electrolyzer also comprises a cooling and drying unit for the generated hydrogen, which is functionally connected to the central storage and separation container for hydrogen (17).

18. High-pressure electrolyzer according to any one of claims 1 to 17, wherein the electrolyzer also comprises one or more containers for the storage and dosing of demineralized water (18), which are functionally connected to the central electrolyte distribution container (15).