Low-capacity, high-voltage electrolytic device

Abstract

Provided is a small-scale high-pressure electrolyzer for generating hydrogen and oxygen, comprising one or more units each comprising a plurality of high-pressure electrolytic cells, the electrolytic cells of each unit being electrically connected in series; a central electrolyte header operatively connected to each of the electrolytic cells for supplying liquid electrolyte to the cells; a central hydrogen header connected to each of the electrolytic cells for exhausting generated hydrogen from the cells; a central oxygen header connected to each of the electrolytic cells for exhausting generated oxygen from the cells; and a DC power supply for supplying power to each unit of series-connected electrolytic cells, wherein the units of series-connected electrolytic cells are electrically connected in parallel.

Description

[Technical Field]

[0001] The present invention relates to a novel high-pressure electrolysis device for producing hydrogen and oxygen that is particularly suitable for small-scale plants (less than 500 kW). [Background technology]

[0002] The electrolytic production of hydrogen is well known, see for example WO2004 / 076721 and the US patent publications cited therein.

[0003] As described in the introduction to WO 2004 / 076721, electrolysis devices, also known in the art as "electrolyzers," that use a liquid electrolyte to generate hydrogen operate as follows: Two electrodes are placed in a bath of liquid electrolyte, such as an aqueous solution of potassium hydroxide (KOH). A wide range of potassium hydroxide concentrations can be used, but a KOH solution with a concentration of about 25-35% by weight is typically used. The electrodes are separated from each other by a separator membrane that selectively allows liquid to pass through but prevents gas from passing through. When a voltage, typically about 2-3 volts, is applied between the electrodes, a current flows through the electrolyte between the electrodes. Hydrogen gas is produced at the cathode, and oxygen gas is produced at the anode. As the gas bubbles rise through the liquid electrolyte, the separator membrane keeps the hydrogen and oxygen gases separated. Above the liquid electrolyte is a disengagement space comprised of two separate chambers or sections isolated from each other by an airtight barrier, one chamber or section receiving hydrogen gas and the other chamber or section receiving oxygen gas, the two gases being separately removed from each section of the disengagement space for storage or release.

[0004] Currently available electrolysers are primarily low pressure electrolysers of stacked design, where a set of prefabricated components are stacked together to assemble the electrolyser. The nature of the stacked design limits the pressure to around 30 bar.

[0005] High-pressure electrolyzers have attracted considerable interest because they offer advantages over low-pressure electrolyzers, such as being suitable for use in high-pressure applications, transportation, and storage without the need for downstream compressor stages. Various designs of high-pressure electrolyzers have been described in the art, often based on polymer electrolyte membrane (PEM) technology. See, for example, WO 2011 / 012507 A1. However, PEM technology has significant drawbacks: it requires expensive rare-metal catalysts, and the catalyst layer in the electrolysis cell degrades faster than alkaline electrolytes at various load requirements.

[0006] NL2023212 discloses a high-voltage electrolysis unit comprising a large block of conductive metal, constituting either the anode or the cathode, and an arrangement of interconnected vertical and horizontal cylindrical channels, closed except for a channel for a water inlet connection and a channel for a hydrogen and oxygen outlet connection, the inner surface of the channel arrangement being partially coated with an electrical isolation coating, and a counter electrode, constituting the corresponding cathode or anode, located in the vertical channel enclosed by the cylindrical membrane and supported and connected by an electrode support rod located in a horizontal channel at the top of the housing.

[0007] WO 2021 / 029768 A1 discloses a high-pressure alkaline electrolysis unit comprising an assembly of conductive metal tubes and pipes that constitute either the anode or the cathode, wherein the high-pressure alkaline electrolysis unit has vertical and horizontal tube and pipe configurations that are closed except for pipes for a water inlet connection and hydrogen and oxygen outlet connections, the inner surfaces of the channel configurations are covered with an electrically insulating coating, and corresponding counter electrodes that constitute the cathode or anode are disposed in the vertical pipes enclosed by a cylindrical membrane, and are supported and connected by electrode support rods installed in the horizontal pipes at the top of the housing. The high-pressure electrolysis device further comprises one or more pressure-resistant isolated electrical conductors that supply power from the outside to the inside of the electrolysis device.

[0008] WO 2004 / 076721 A2, corresponding to EP 1597414 B1, discloses an electrolyzer cell for the electrolysis of water, comprising a generally tubular cathode within which an anode is disposed, separated from the cathode by a generally tubular separator membrane that divides the electrolysis chamber into an anode subchamber and a cathode subchamber. The electrolyzer apparatus includes an array of individual cells, each of which is energized by a DC generator via electrical leads. Hydrogen gas generated from the electrolyte in the cells is removed via a hydrogen gas outlet line and a hydrogen manifold line. By-product oxygen is removed from the cells via an oxygen outlet line and an oxygen manifold line.

[0009] EP3498886A1 discloses an electrolysis system for carrying out oxidation-reduction reactions, the electrolysis system comprising one or more electrolysis cells formed by at least one pair of electrodes and an electrolyte between the electrodes, an assembly of said one or more electrolysis cells defining an electrolysis cell, and an energy supply source for supplying electrical signals to the electrolysis cell. The electrical signals received by the one or more electrolysis cells forming the electrolysis cell correspond to DC pulses configured to cause the cells of each electrolysis cell to operate in a charging transient state of each cell during the current pulses and in a charging transient state of each cell during the times between the DC pulses, said charging and discharging transient states being defined by the structure of each electrolysis cell in the form of a cylindrical plate capacitor.

[0010] U.S. Patent No. 3,984,303 discloses an electrolytic cell for the production of halogen gases and alkali metal oxides, having a hollow tubular cathode member and a hollow tubular anode member concentrically disposed within the cathode, each electrode member having a liquid-permeable wall to allow electrolyte circulation. The anode has a conductive membrane covering its exterior, separating the anode and cathode surfaces. This membrane is tubular in shape and attached to the exterior of the anode. The tubular membrane may be made of a material that selectively permeates ions and blocks the hydrodynamic flow of the electrolyte. Such cells may also be connected in series to form larger multi-cell electrolytic cells.

[0011] Unpublished international patent application PCT / NL2022 / 050648, corresponding to NL2029726, discloses a high-voltage electrolysis device comprising multiple high-voltage electrolysis units arranged in series, each unit comprising a conductive metal body made up of an assembly of interconnected horizontal and vertical tubes, which constitute an electrode connectable to a DC power source. The assembly comprises three horizontal tubes and at least two vertical tubes, each housing an elongated central electrode and a tubular membrane, and each vertical tube, together with the central electrode, membrane, and electrolyte, constitutes an electrolysis cell. The electrolysis cells within each unit are connected in parallel, and each unit further comprises at least two vertical tubes that do not house a central electrode, with a first vertical tube connecting a lower horizontal tube to a first upper horizontal tube and a second vertical tube connecting the lower horizontal tube to a second upper horizontal tube.

[0012] The differential voltage between units connected in series is equal to the number of units multiplied by the voltage drop per unit, which is in the range of 2-3 Vdc. The current is equal to the number of parallel cells multiplied by the current through a single cell, which depends on the detailed design of the cells and the voltage applied to the cells.

[0013] The system described in PCT / NL2022 / 050648 is very suitable for large scale applications as it consists of a high voltage electrolysis unit connected in parallel with electrolysis cells and allows large currents to be passed through the unit.

[0014] However, for smaller capacity systems with fewer electrolysis cells, such systems result in extremely low voltages, which is not optimal for the design of the upstream power converter and rectifier system required to operate the electrolyzer system. In particular, for small-scale units, the system described in PCT / NL2022 / 050648 results in low voltages and high currents, making it inefficient and uneconomical. The ideal design of the converter and rectifier system is based on the highest possible voltage and the lowest possible current.

[0015] Small capacity high pressure electrolyser systems have significant advantages over large scale systems as high pressure technology can be more easily applied, there is a lot of development going on for such applications and importantly the use of compressors can be avoided. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] WO2004 / 076721 [Patent Document 2] WO2011 / 012507A1 [Patent Document 3] NL2023212 [Patent Document 4] WO2021 / 029768A1 [Patent Document 5] WO2004 / 076721A2 [Patent Document 6] EP1597414B1 [Patent Document 7] EP3498886A1 [Patent Document 8] U.S. Patent No. 3,984,303 [Patent Document 9] PCT / NL2022 / 050648 [Patent Document 10] NL2029726 Summary of the Invention [Problem to be solved by the invention]

[0017] There is therefore a need for a simple, efficient and cost-effective small-scale high-pressure electrolyzer for hydrogen production and other industrial processes that is compact, flexible, modular, scalable and requires low maintenance. It is an object of the present invention to provide such a small-scale high-pressure electrolysis device having the above-mentioned beneficial properties. [Means for solving the problem]

[0018] In one aspect of the invention, there is provided a small-scale high-pressure electrolyzer for generating hydrogen and oxygen, comprising: - one or more units each comprising a plurality of high-pressure electrolytic cells, the electrolytic cells of each unit being electrically connected in series; - a central electrolyte header operatively connected to each electrolysis cell for supplying liquid electrolyte to the cells; - a central hydrogen header operatively connected to each electrolysis cell for the discharge of hydrogen generated from the cell; - a central oxygen header operatively connected to each electrolysis cell for exhausting oxygen generated from the cell; - a DC power source operatively connected to each unit of the series-connected electrolytic cells for the power supply of each unit of the series-connected cells; Equipped with - The series-connected electrolytic cell units are electrically connected in parallel to provide a small-scale high-pressure electrolyzer.

[0019] In a preferred embodiment, the functional connections between the central electrolyte header and the electrolysis cells, between the central hydrogen header and the electrolysis cells, and between the central oxygen header and the electrolysis cells are achieved via non-conductive hydraulic hoses.

[0020] In another preferred embodiment, the central hydrogen header and the central oxygen header are each operatively connected to the central electrolyte header, preferably via non-conductive hydraulic hoses.

[0021] In yet another preferred embodiment, the central electrolyte header also comprises a supply connection for the supply of demineralized water to the electrolyte 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.

[0022] In a further embodiment of the invention, each electrolysis cell comprises a pressure-resistant, vertically disposed conductive metal tube constituting the anode, an elongated cathode housed in the center of the vertical tube, and a separator membrane surrounding the cathode that divides the electrolysis cell into an anode subchamber and a cathode subchamber.

[0023] In another embodiment of the present invention, the vertical tube of each electrolysis cell has a lower end and an upper end, the lower end being closed and the upper end being sealed with an electrically insulating, gas-tight, pressure-resistant seal.

[0024] In yet another embodiment of the present invention, an elongated central cathode extends from the bottom of the vertical tube and projects beyond the top end of the vertical tube through an electrically insulating seal.

[0025] In a further embodiment, the vertical tube has at least three openings in the side wall of the tube at different heights: a lower opening at the lower end of the tube for the supply of demineralized water or electrolyte, an upper opening for the discharge of evolved hydrogen, and a central opening for the discharge of evolved oxygen gas.

[0026] In yet another embodiment, an airtight seal is provided between the separation membrane and the inner wall of the vertical tube at a height between the top opening and the central opening, the seal also supporting the separation membrane.

[0027] In another embodiment, the separator has a lower end and an upper end, the lower end extending downwardly beyond the lower end of the central cathode and the upper end connected to the gas-tight seal, the separator sealing against the passage of gas but allowing the passage of liquid and ions of the electrolyte contained therein.

[0028] These and other aspects of the present invention are more fully outlined in the detailed description below with reference to a specific embodiment thereof, namely, the production of hydrogen and oxygen by high-pressure electrolysis of water, although those skilled in the art will recognize that the present invention may be utilized in other embodiments.

[0029] Conventional known devices such as pressure and flow sensing devices, control devices for operating valves and pumps, etc. have been largely omitted from the description as such devices and their uses are well known in the art. [Brief explanation of the drawings]

[0030] [Figure 1] 1 is a schematic diagram of an embodiment of a high-pressure electrolyzer according to the present invention; [Figure 2] Figure 1. Electrolyzer flow sheet. [Figure 3] FIG. 1 is a perspective view of a schematic prototype of an electrolytic cell according to the present invention. [Figure 4] 1 is a perspective view of an embodiment of an electrolysis cell forming part of a high pressure electrolyzer according to the present invention; FIG. [Figure 5] FIG. 5 is a detailed view of the top of two electrolysis cells shown in FIG. 4 connected in series via a connector according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] The following detailed description should be read with reference to the drawings, in which like elements in different drawings are numbered the same. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention.

[0032] According to the present invention, there is provided a small-scale high-pressure electrolyzer for generating hydrogen and oxygen, comprising one or more units, each comprising a plurality of electrolytic cells connected in series, e.g., 3 to 20, up to 100 or more electrolytic cells. A preferred range for a series of series-connected electrolytic cells is 20 to 100 cells, more preferably 50 to 100 cells. As a result, the current flowing through the system is equal to the current of one cell, which is determined by the detailed design of the cells and the voltage applied to the cells. Furthermore, the differential voltage between the series-connected cells is equal to the number of cells multiplied by the voltage drop per cell, and is in the range of 2 to 3 Vdc. A preferred range for the number of series-connected electrolytic cell units is currently 1 to 10 units, more preferably 1 to 5 units.

[0033] The advantages of the present invention are a higher voltage between the series-connected cells and a lower current through the cells, which is beneficial to the power conversion system. There is a smaller step-down from the supplied AC voltage to the required voltage, which allows for a smaller converter. The lower current also reduces the overall material required to rectify and transport the current, thereby reducing the overall system cost.

[0034] Each high-pressure electrolytic cell comprises a pair of electrodes, a separator membrane, and a liquid electrolyte between the cells. The cell is composed of a pressure-resistant, vertically arranged conductive metal tube constituting a first electrode, which may be either an anode or a cathode; a central, elongated second or counter electrode, which may be either a cathode or an anode, electrically insulated from the vertical tube and located in the center of the vertical tube; and a separator membrane surrounding the counter electrode. The first electrode of the electrolytic cell can be connected to a DC power source or the central, elongated counter electrode of the preceding electrolytic cell. The second or counter electrode of the same electrolytic cell can be connected to the first electrode (the vertically arranged tube of that cell) of the succeeding electrolytic cell or to a DC power source. Preferably, the vertical tube, separator membrane, and central electrode of each electrolytic cell are arranged coaxially with each other.

[0035] In a preferred embodiment of the invention, the vertical tube constitutes the anode (+) and an elongated central electrode in the middle of the tube constitutes the cathode (-) of the electrolysis cell.

[0036] The terms "tube" and "pipe" are often used interchangeably in the art, although there are differences between tubes and pipes. See, for example, http: / / www.wermac.org / pipes / pipe_vs_tube.html. As used herein, unless otherwise stated, "tube" and "pipe" are collectively referred to as "tube." Those skilled in the art will have no problem understanding which materials are required when applying designs in accordance with the present invention.

[0037] The vertical tube has a lower end and an upper end, the lower end being closed and the upper end being sealed with an electrically insulating, gas-tight, pressure-resistant seal. In a preferred embodiment, the upper end of the vertical tube is threaded to facilitate maintenance of the electrolysis cell. The vertical tube may be closed with a readily available pressure fitting known in the art, such as a threaded pressure fitting.

[0038] An elongated central electrode extends from the bottom of the vertical tube, penetrates an electrically insulating seal, and protrudes beyond the top of the vertical tube. The central electrode is connectable to a DC power source 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.

[0039] The vertical pipe has at least three openings in the side wall of the pipe at different heights: a lower opening at the lower end of the pipe for supplying demineralized water or electrolyte, an upper opening for venting the generated hydrogen gas, and a central opening for venting the generated oxygen gas. In one embodiment, the openings are connected to corresponding headers via non-conductive connections for further transport of the gas to a pressurized vessel for further processing and storage, and for supply from a demineralized water storage tank, respectively. In another embodiment, the openings may be provided with suitable non-conductive fittings for connecting hydraulic hoses, pipes, etc. to the respective headers. The high-pressure electrolyzer and electrolytic cell according to the present invention are further connected by a common supply conduit for liquid electrolyte and demineralized water, and gas withdrawal conduits for hydrogen gas and oxygen gas.

[0040] To overcome short circuits between the series-connected cells, the supply of electrolyte and the collection of evolved gases are realized by connecting the electrolysis cells to a central header, also called a manifold, by means of non-conductive connections, the central header and the connections forming part of the electrolysis cell according to the invention.

[0041] Demineralized water or liquid electrolyte is supplied to a pressurized electrolyte header which is connected to each electrolysis cell via a non-conductive connection for distribution of the liquid to the cells.

[0042] The generated hydrogen and oxygen gases are mixed with a portion of the electrolyte, discharged from the electrolysis cell, and sent via non-conductive connections to a central hydrogen header and a central oxygen header, respectively, for collection, separation from the electrolyte, and further transport.

[0043] In each electrolysis cell, a sleeve or disk-shaped airtight seal is provided between the separation membrane in the upper half of the vertical tube and the inner wall of the vertical tube, at a position between the top opening and the central opening of the tube, and the seal also supports the membrane.

[0044] A separation membrane, preferably of tubular configuration, is provided within each vertical tube and surrounds the central electrode, dividing the vertical tube into an anode subchamber and a cathode subchamber. The separation membrane prevents the passage of gases but allows the passage of liquids and liquid ions. The separation membrane is supported at its top by a sleeve or disk-shaped seal and extends beyond the lower outer edge of the central electrode to said seal. Preferably, the separation membrane is open on its bottom side. In another preferred embodiment, the membrane is a ZIRFON® separation membrane.

[0045] The upper part of the elongated central electrode, i.e., the part above the sleeve or disk-shaped gas-tight seal in the vertical tube, is preferably electrically insulated from the seal around its upper circumference to prevent gas generation in the upper part of the cathode subchamber, thereby enabling the production of high-quality gas.

[0046] The electrolytic cell is filled with a liquid electrolyte, usually a potassium hydroxide (KOH) solution in demineralized water. A wide range of potassium hydroxide concentrations can be applied, but typically a KOH solution with a concentration of about 25-30% by weight is used. The electrodes, i.e., the vertical tubes that make up the anode and the elongated central cathode, are exposed to the liquid electrolyte during operation and generate gas in contact with it.

[0047] In operation, hydrogen gas is produced at the cathode of each electrolysis cell and oxygen gas is produced at the anode, with a separator membrane keeping the hydrogen and oxygen gases separated as the gas bubbles rise through the liquid electrolyte.

[0048] The series-connected electrolytic cells of the electrolytic cell according to the present invention are preferably arranged in an electrically isolated, adjacent array. As shown in the examples of Figures 1 and 5, the electrolytic cells are electrically connected so that the anode (+) of the body of a first unit is connected to a DC power source, the cathode (-) of the central cathode of the first unit is connected to the body of a second adjacent electrolytic cell, the central cathode of the second electrolytic cell is connected to the body of the next adjacent electrolytic cell, and so on, with the final central cathode (-) being connected to a DC power source. The differential voltage between the series-connected cells is equal to the number of cells multiplied by the voltage drop per cell, and is in the range of 2 to 3 Vdc. The current flowing through one unit of series-connected cells is equal to the current flowing through a single cell and depends on the detailed design of the cells and the voltage applied to the cells.

[0049] The wall thickness of the vertical tube depends on the desired generated pressure, material properties such as yield strength, and the electrical conductivity of the metal from which the tube is made. Generally, the wall thickness can vary from about 0.65 to 1.60 cm. Typically, the length of the vertical tube of a high-pressure cell ranges from 500 to 2000 mm and can be further extended up to 4000 mm. Typically, the diameter of the central cathode ranges from 10 to 30 mm and can be further extended up to 100 mm. These values ​​are merely suggestive and should not be construed as limiting the invention in any respect.

[0050] In a preferred embodiment of the present invention, a cooling and drying device is provided that forms part of a high-pressure electrolyzer. The device includes one or more cooling and drying units connected to the outlet conduits for the produced hydrogen gas and oxygen gas from the central hydrogen header and central oxygen header. The gases are transported to the cooling and drying device and cooled by a cooling medium, for example, cooling water. After cooling, the oxygen gas is reduced to atmospheric pressure, which causes another temperature drop due to the thermodynamic behavior of oxygen. The oxygen at ambient conditions is then used to further cool the hydrogen gas, which is still under high pressure. The gas cooling unit is designed so that condensed water is returned to the electrolysis unit. This avoids condensation of water vapor in downstream systems. Therefore, by cooling the hydrogen gas to a temperature below ambient temperature, the hydrogen gas is dried to a saturation temperature below atmospheric conditions, thereby preventing water condensation in downstream systems.

[0051] In another aspect of the invention, there is provided one or more pressure vessels forming part of the electrolysis device according to the invention, the pressure vessels preferably being removably connected to a cooling and drying unit for storage of the dried and purified gas.

[0052] The electrolyzer according to the invention has several advantages over prior art electrolyzers of similar type, which relate inter alia to a) a high pressure environment, b) gas-liquid separation, c) natural circulation and removal of product gases from the electrolysis cell by gravity effect, d) isolation of the central cathode, e) simplified maintenance of the device, and f) cooling of product gases.

[0053] For high-pressure environments, pressure containment is also performed at one of the electrodes. The coaxial anode / cathode configuration allows for very high-pressure hydrogen generation using practical wall thicknesses of conventional materials in the containment achieved by the anode. The conventional stacked concept has large plates, allowing high currents to flow through the system. The perimeter of the plates is also the perimeter that must remain pressure-resistant. The electrolyzer is designed so that the circumference of the anode / cathode configuration and the opening at the top of the cell is significantly smaller than the perimeter of the plates in the stacked concept, thereby reducing the potential area for flammable gas leakage.

[0054] High pressure in the electrolysis unit results in a smaller gas volume in the electrode area and therefore a larger electrolyte volume, which results in lower electrical resistance and therefore higher efficiency.

[0055] The ability of the apparatus and method of the present invention to produce hydrogen (and oxygen) at pressures up to 1000 bar or higher exceeds the maximum pressure of known prior art electrolysers. The apparatus and method of the present invention can produce such high-pressure hydrogen without the need for a separate compressor to pressurise the product hydrogen gas. High-pressure electrolyser systems have a significant advantage in small-scale systems in that they allow the use of small-capacity, low-efficiency downstream compressors to be avoided. Small-scale compressors are relatively expensive compared to large-scale compressors.

[0056] The device according to the present invention allows for high pressure hydrogen production to be performed in a unique manner that reduces component costs and system complexity so that the equipment is inexpensively available and the device is scalable to any given production capacity.

[0057] The produced gases are removed from the electrode surfaces by natural draft, improving the capacity of the system. No active circulation system is required. A collection header is included in the electrolyzer according to the invention to enable or improve natural circulation and gas separation in the high pressure electrolysis unit.

[0058] Regarding maintenance of the device, the outer upper part of the vertical tube housing the central electrode is preferably screwed and provided with a removable threaded pressure joint. Furthermore, the central electrode and the surrounding separation membrane are preferably only top-supported, allowing for easy removal of the central electrode and membrane for maintenance or replacement. This simplifies maintenance of the device, making it more efficient and inexpensive.

[0059] With regard to cooling of the produced gas, the gas cooling unit according to the present invention allows the hydrogen gas to be dried to a saturation temperature below atmospheric conditions by cooling it, preventing water condensation in downstream systems, a feature not mentioned in the prior art.

[0060] The apparatus and methods of the present invention may be utilized for on-site generation of high-pressure hydrogen at locations such as factories, office buildings, or residential areas for on-site energy storage and / or use as a fuel for fuel cells, internal combustion engines, or heating applications.

[0061] Turning now 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 four electrolysis cell 50 units electrically connected in series. Each electrolysis cell comprises a pressure-resistant, vertically arranged conductive metal tube 1 constituting the anode, an elongated central cathode 2 housed in the center of the vertical tube, and a separator membrane 3 surrounding the cathode, dividing the electrolysis cell into an anode subchamber 8 and a cathode subchamber 9. The vertical tube 1 is closed at its bottom end 10 and sealed at its top end using an insulating, pressure-resistant seal 5. The elongated cathode 2 protrudes through the seal.

[0062] The electrolytic cells are electrically connected by serial electrical connectors 6 such that the anode (+) of the body of the first unit is connected to a DC power source, the cathode (-) of the central cathode of the first unit is connected to the body of the second adjacent electrolytic cell, the central cathode of the second electrolytic cell is connected to the body of the next adjacent electrolytic cell, and so on, with the final central cathode (-) being connected to the DC power source.

[0063] Each electrolysis cell is interconnected with three headers 15, 16, and 17 by non-conductive hydraulic hoses 1g, 1h, and 1i, which extend from openings 21, 22, and 23 of the cell to the electrolyte header 15, oxygen header 16, and hydrogen header 17, respectively.

[0064] The oxygen and hydrogen headers are connected to hydraulic hoses 1e and 1f, respectively, allowing the separated electrolyte to return to the electrolyte headers. The gravity differential between the electrolysis cell 50 and assemblies 15, 16, 17, 1e, and 1f establishes a natural circulation flow of the electrolyte.

[0065] A hydrogen outlet 12 releases excess hydrogen to a downstream system such as a storage tank or pipeline.

[0066] The oxygen outlet 13 releases excess hydrogen to a downstream system such as a storage tank or pipeline.

[0067] Demineralized water is supplied via demineralized water inlet 10 to supplement the electrochemical reaction water.

[0068] Demineralized water is intermittently admitted from a demineralized water tank 18 by a valve 24. The demineralized water tank 18 may be filled under atmospheric conditions by a simple pumping device (not part of this invention).

[0069] As the tank 18 is filled with demineralized water, oxygen from the electrolytic cell 50 is supplied to the tank and pressurizes the tank 18 via valve 20. During this filling, the pressure in the electrolytic cell 50 temporarily rises, achieving a higher pressure in the tank 18 than would occur during normal operation of the electrolytic cell 50. As soon as the pressure in the tank 18 is reduced (the water volume is reduced) to a value close to the operating pressure of the electrolyzer, the electrolytic cell 50 begins operating again at the higher pressure and refills the tank 18 with pressurized oxygen via valve 20. This procedure is repeated until the tank 18 is empty, at which point it can be depressurized via valve 19 and refilled with demineralized water.

[0070] Figure 3 shows a schematic prototype of a compact small-scale electrolyser according to the invention, with five pressurized demineralized water tanks 18 for the supply of demineralized water to a central electrolyte header 15. Two units of electrolysis cells 50 connected in series are shown, along with a central oxygen header 16 and a central hydrogen header 17. Connectors and connecting pipes or hoses are not shown in this view.

[0071] Figure 4 shows a modular electrolysis cell for small-scale, high-pressure applications. Each electrolysis cell is interconnected using three headers 15, 16, and 17, each with non-conductive hydraulic hoses 1g, 1h, and 1i, which extend from cell openings 21, 22, and 23 to the respective headers. The series connection is achieved by a connector 6 (of special design in this example) that allows the vertical anode tube 1 of one cell to be connected to the concentrically arranged central cathode 2 of an adjacent cell, thereby forming a compact array of series-connected cells. This is further illustrated in the detailed view of Figure 5, which shows the tops of two electrolysis cells connected via connector 6. This connector 6 is attached to the anode tube 1 by a threaded connection and to the threaded top end of the left-hand cathode 2 by a fixing nut 25.

[0072] Operation (see Figures 1 and 2) The empty electrolysis cells of the unit are filled with electrolyte via the central electrolyte header 15 with all vent devices in the open position until the desired liquid levels are reached in the central hydrogen header 17 and central oxygen header 16 (for the initial fill, the electrolyte is a 25-30% solution of potassium hydroxide in demineralized water).

[0073] The electrolysis process is then initiated by connecting the electrolyzer to a DC power source, creating a voltage drop of 2-3V per single electrolysis cell. Hydrogen gas is produced on the surface of the central electrode (cathode), and oxygen is produced on the inner surface of the vertical tube (anode) surrounding the cathode. The produced gases rise and collect in the hydrogen and oxygen headers. Once all downstream volumes have been purged with the produced gas and there is no air remaining in the downstream system, the vent devices to the headers are closed. Because the volume of produced gas is much greater than the volume of water converted, pressure builds up in the system.

[0074] Natural circulation through the hydrogen and oxygen headers and the connected electrolyte header supports the removal of product gases from the electrolysis cell area and collection of the gases in the headers.

[0075] Once operating pressure is reached, the gas pressure control system blows off excess gas to downstream systems, such as a storage system and / or a pipeline system. The converted water volume is supplemented by demineralized water when the water level is low or reaches a controllable height. The demineralized water is introduced by a pressurized tank or series of pressurized tanks 18, and the demineralized water is stored in the electrolyte header 15.

[0076] The stored demineralized water is pressurized in batches with the generated oxygen. 1) First, the tank 18 is filled with demineralized water at atmospheric conditions. 2) After filling, oxygen from the electrolytic cell 50 is supplied to the tank and pressurizes the tank 18 via the valve 20. During this filling, the pressure in the electrolytic cell 50 temporarily increases, achieving a pressure in the tank 18 higher than that during normal operation of the electrolytic cell 50. 3) After pressurizing the tank 18, demineralized water flows into the electrolytic cell and is controlled by the control valve 24. 4) As soon as the pressure in the tank 18 is reduced to a value close to the operating pressure of the electrolyzer (water volume decreases), the electrolytic cell 50 starts operating again at a higher pressure and refills the tank 18 with pressurized oxygen via the valve 20. 5) This procedure is repeated until the tank 18 is empty. 6) As soon as the tank 18 is empty, it is depressurized via the valve 19 and refilled with demineralized water.

[0077] The produced hydrogen and oxygen gases are separated from the liquid electrolyte in central headers 17 and 16, respectively, and then transported to a cooling device (not shown). In this regard, reference is made to the applicant's unpublished patent application PCT / NL2022 / 050648, in which an identical cooling and drying device is shown and described (see Figures 8-11). This PCT application is incorporated herein by reference. The gases are cooled by a cooling medium, e.g., cooling water. After cooling, the pressure of the oxygen gas is reduced to atmospheric pressure, which results in another temperature drop due to the thermodynamic behavior of oxygen. The cold oxygen at ambient pressure is then used to further cool the still-pressurized hydrogen. The cooling device is designed so that condensed water vapor is returned to the electrolysis cell.

[0078] Cooling the hydrogen gas as described dries the hydrogen gas to a saturation temperature below atmospheric conditions, thereby preventing condensation of water vapor in downstream systems.

[0079] From the foregoing description, those skilled in the art can easily ascertain the essential characteristics of the present invention, and can make various changes and modifications to adapt it to various uses and conditions without departing from the spirit and scope of the present invention. Therefore, these modifications and adaptations are deemed to fall within the scope of protection of the present invention as claimed in the accompanying claims. [Explanation of symbols]

[0080] 1. A vertical tube of conductive metal that constitutes the first electrode of the electrolytic cell 1e. Connection between electrolyte header 15 and oxygen header 16 1f Connection between electrolyte header 15 and hydrogen header 17 1g Connection between the electrolyte header 15 and the opening 21 of the vertical tube 1 1h Connection between oxygen header 16 and opening 22 of vertical pipe 1 1i Connection between hydrogen header 17 and opening 23 of vertical tube 1 2. The elongated second electrode of the electrolytic cell 3. Separation membrane of electrolysis cell 4 Airtight sleeve or disc seal 5 Electrical insulation seal at the top of vertical pipe 1 6 Series Electrical Connectors 7 Electrical insulating ring or nut 8. Anode Subchamber 9. Cathode Subchamber 10 Bottom end of vertical tube 1 11 Desalinated water inlet 12 Hydrogen outlet 13 Oxygen outlet 15 Electrolyte Header 16 Oxygen Header 17 Hydrogen Header 18 Pressurized demineralized water tank 19 Demineralized water tank pressure relief valve 20 Desalinated water pressure valve 21 Opening of vertical pipe for supplying demineralized water 22 Opening of vertical pipe for oxygen discharge 23 Opening of vertical pipe for hydrogen discharge 25 Fixing screws or nuts 50 electrolysis cells 100 Electrolytic cell according to the present invention

Claims

1. A high-pressure electrolyzer (100) for the generation of hydrogen and oxygen, especially in small-scale plants, comprising: one or more units each comprising a plurality of high-pressure electrolytic cells (50), the electrolytic cells of each unit being electrically connected in series with one another; a central electrolyte distribution holder (15) operatively connected to each electrolysis cell (50) of said electrolysis cell in order to supply said electrolysis cells with liquid electrolyte; a central storage and separation vessel (17) operatively connected to each electrolysis cell (50) of said electrolyzer for collecting and processing the hydrogen generated from said electrolysis cells; a central storage and separation vessel (16) operatively connected to each electrolysis cell (50) of said electrolysis cell for collecting and treating the oxygen generated by said electrolysis cells; a DC power supply electrically connected to each unit of said series-connected electrolytic cells for the power supply of each unit of said series-connected electrolytic cells; Equipped with a high-pressure electrolyser (100) in which said units of series-connected electrolysis cells are electrically connected in parallel.

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

3. 3. The high-pressure electrolyzer according to claim 1, wherein the central hydrogen storage and separation vessel (17) and the central oxygen storage and separation vessel (16) are each operatively connected to the central electrolyte distribution vessel (15).

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

5. 5. A high-pressure electrolyzer according to any one of claims 1 to 4, wherein each electrolysis cell (50) is constructed of a pressure-resistant, substantially vertically arranged conductive metal tube (1) constituting a first electrode, which may be either an anode (+) or a cathode (-), an elongated central second electrode (2) housed in the centre of the substantially vertical tube and constituting a counter electrode, which may be either a cathode (-) or an anode (+), and a separator membrane (3) around the central second electrode dividing the electrolysis cell into an anode subchamber (8) and a cathode subchamber (9).

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

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

8. 8. A 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 projects above the upper end of the vertical tube through the electrically insulating seal (5).

9. 9. The high-pressure electrolyzer according to claim 1, wherein the vertical tube (1) has at least three openings (21, 22, 23) in the side wall at different heights: a lower opening (21) at the bottom of the tube for the supply of electrolyte, an upper opening (22) for the discharge of evolved hydrogen gas, and a central opening (23) for the discharge of evolved oxygen gas.

10. 10. The high-pressure electrolyzer according to claim 1, wherein a gas-tight seal (4) is provided between the separation membrane (3) and the inner wall of the vertical tube at a height between the upper opening (22) and the central opening (23) of the tube.

11. 11. The high-pressure electrolyzer according to any one of claims 1 to 10, wherein the separation membrane (3) has a lower end and an upper end, the lower end extending downwardly beyond the lower end of the central second electrode (2) and the upper end being connected to an airtight seal (4), the separation membrane (3) sealing against the passage of gas but allowing the passage of liquid and ions of the electrolyte contained therein.

12. 12. A 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 to a DC power supply or to a central second electrode (2) of a preceding electrolytic cell, and said central second electrode (2) is connected to the vertical tubular first electrode (1) of a subsequent electrolytic cell or to a DC power supply.

13. 13. The high-pressure electrolyzer according to any one of claims 1 to 12, wherein the electrolysis cells are electrically conductively connected to one another by connectors (6).

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

15. 15. The high-pressure electrolyzer according to any one of claims 1 to 14, wherein the substantially vertical tube (1) forming the first electrode, the central second electrode (2) and the separation membrane (3) are arranged coaxially with one another.

16. 16. The high-pressure electrolyzer according to any one of claims 1 to 15, wherein the upper end of the second electrode (2) in the center of the electrolysis cell (50) is electrically insulated at its outer periphery above the seal (4).

17. 17. The high pressure electrolyzer according to any one of claims 1 to 16, further comprising a cooling and drying unit for the generated hydrogen, operatively connected to the central storage and separation vessel (17) for hydrogen.

18. 18. The high pressure electrolyzer according to any one of claims 1 to 17, further comprising one or more containers (18) for storing and charging demineralized water, operatively connected to the central electrolyte distribution container (15).

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