Electrolysis system

Abstract

The invention relates to an electrolysis system for electrolytically splitting water into hydrogen and oxygen, comprising an electrolytic cell (1) having an anode chamber (2) and a cathode chamber (3) that are separated from one another by a semipermeable barrier, and comprising an anode water circuit (4) which supplies the anode chamber (2) with water via an anode inlet (5) and which receives water from the anode chamber (2) via an anode outlet (6), wherein a gas-water separator (8) and a pump device (9) are disposed in the anode water circuit (4). The water from the cathode chamber (3) is received in a cathode water pathway (14) and fed into the anode water circuit (4), with a second gas-water separator (17) being disposed in the cathode water pathway (14) and an ion exchanger (10) for removing metal ions being disposed in the anode water circuit (4). A free-radical scavenger (20) is disposed in the cathode water pathway (14).

Description

[0001] R. 413412

[0002] - 1 -

[0003] title

[0004] Electrolysis system

[0005] The invention relates to an electrolysis system, such as is used to produce hydrogen and oxygen by electrolytic splitting of water.

[0006] State of the art

[0007] Electrolysis systems are used to split water electrolytically into hydrogen and oxygen. For example, a so-called PEM electrolyzer (PEM: proton exchange membrane) is used for this purpose. It comprises an anode compartment and a cathode compartment separated by a semipermeable barrier. This barrier is formed, for example, by a membrane that is selective for hydrogen. +The electrolyzer is permeable to hydrogen ions. An anode electrode with a catalytic coating is located in the anode compartment, and a cathode electrode serves as the opposite pole in the cathode compartment. During operation, a direct current voltage is applied between the electrodes, with the anode compartment filled with water. The water in the anode compartment is thus catalytically split, and the resulting hydrogen ions are released. + Ions migrate – driven by the electrical voltage – through the membrane and enter the cathode compartment, where they recombine with electrons at the cathode electrode to form water. Since the H + Since ions are surrounded by a hydration shell as they move through the membrane, water also enters the cathode space, so-called drag water.

[0008] The anode chamber is continuously permeated with water, which carries along the oxygen produced there and flows into a gas-water separator, where the water is separated from the oxygen gas. The water is then returned to the anode chamber, replacing the water consumed by electrolysis. The returned water is then treated before the R. 413412

[0009] - 2 - The water is re-injected into the anode compartment and, if necessary, treated by temperature control and removal of suspended solids. The water on the cathode side, containing dissolved hydrogen gas, is fed to a further gas-water separator where the hydrogen gas is separated from the water. The water from the cathode compartment can then either be discarded or also fed into the anode water circuit.

[0010] Electrolysis requires highly purified water, particularly to maintain the chemical properties of the membrane and catalyst. However, impurities are generated during operation, such as metal ions that dissolve into the water through corrosion, especially on the anode side. These substances can impair electrolysis and must be continuously removed. Therefore, it is known to incorporate an ion exchanger in the anode water circuit to remove the metal ions. Other ions can also be generated, particularly through the dissolution of hydrogen fluorides from the membrane.

[0011] From KR 10-2610119 B1, it is known to provide a radical scavenger in addition to the ion exchanger in the anode water circuit. The reason for this is the formation of radicals during the electrolysis process, in particular hydroxyl radicals (HO-) through a so-called Fenton reaction.

[0012] Advantages of the invention

[0013] In the electrolysis system according to the invention, water quality is effectively maintained, thus achieving a long service life of the electrolysis system. For this purpose, the electrolysis system comprises an electrolytic cell with an anode compartment and a cathode compartment, which are separated from each other by a semipermeable barrier, and an anode water circuit that supplies the anode compartment with water via an anode inlet and receives water from the anode compartment via an anode outlet. A gas-water separator and a pump device are arranged in the anode water circuit. The water from the cathode compartment is received by a cathode water path that feeds the water into the anode water circuit. A second gas-water separator R. 413412 is located in the cathode water path.

[0014] - 3 - is arranged. In the anode water circuit, an ion exchanger is arranged for the removal of metal ions, and in the cathode path, a radical scavenger is arranged.

[0015] In so-called PEM (proton exchange membrane) electrolyzers, the anode compartment of the electrolytic cell must be supplied with highly purified water. During the electrolytic process, water is catalytically split, and the resulting ionic ions migrate to the cathode compartment, where they recombine to form hydrogen gas. The oxygen remaining in the anode compartment is removed as oxygen gas along with the water, which is continuously pumped through the anode compartment, and separated from the water by a gas-water separator. Over time, corrosion causes metal ions to dissolve in the water, which can disrupt the electrolysis process. Further impurities arise from the degradation of the membrane that separates the anode compartment from the cathode compartment. These ions are removed by the ion exchanger in the anode-water circuit. In addition, radicals, primarily the hydroxyl radical (HO-), are generated, especially on the cathode side.Because the radical scavenger is located in the cathode water path, these radicals are removed very effectively near their point of origin, thus significantly reducing the damage caused by these highly reactive chemical compounds. Since considerably less water flows out of the cathode compartment than from the anode compartment, the radical scavenger can be designed for low water flow rates and is therefore correspondingly cost-effective.

[0016] In an advantageous embodiment of the invention, the radical scavenger is arranged in the cathode water path downstream of the second gas-water separator. This effectively removes the radicals before the water is fed into the anode water circuit. Furthermore, a portion of the water from the radical scavenger can also be directed back into the cathode compartment to better flush out any HF compounds (fluorine-hydrogen) formed there by membrane degradation and then filter them out in the radical scavenger.

[0017] In a further advantageous embodiment, a water tank is arranged in the anode water circuit, into which the water from the gas-water separator flows. The water tank also serves as a buffer for the water. Consumed R. 413412

[0018] - 4 -

[0019] Water can be easily replaced by refilling this water tank from an external source.

[0020] In a further advantageous embodiment, the ion exchanger is arranged between the gas-water separator and the water tank. The ion exchanger can also be directly connected to the water tank, so that the water in the water tank can be freed of metal ions independently of the water circulation in the anode water circuit.

[0021] In a further advantageous embodiment, a heat exchanger is arranged in the anode water circuit. For proper function, the ion exchanger must not get too hot, while electrolysis occurs at higher temperatures of approximately...

[0022] It operates effectively at 70 °C. The heat exchanger allows for optimal temperature control.

[0023] The electrolysis system has at least one electrolytic cell. However, it typically contains multiple electrolytic cells arranged in a stack, all sharing a common water inlet and outlet. Power is also supplied via a single connection for all cells.

[0024] drawing

[0025] The drawing shows various embodiments of the electrolysis system according to the invention. The following are shown:

[0026] Figures 1 to 5 show a schematic representation of an electrolysis system, with only the essential components shown.

[0027] Description of the exemplary implementations

[0028] Figure 1 schematically illustrates an electrolysis system according to the invention. The system comprises an electrolytic cell 1, which includes an anode compartment 2 and a cathode compartment 3, separated by a semipermeable barrier R. 413412, not shown in detail here but known from the prior art.

[0029] - 5 - are separated from each other, for example, in the form of a semipermeable polymer membrane. Instead of a single electrolytic cell 1, an electrolytic stack can also be present, comprising a plurality of electrolytic cells that are electrically connected in series. For the sake of clarity, only one electrochemical cell 1 is shown here. The semipermeable membrane is permeable to IT ions, while all other chemical substances are largely blocked. In the cathode compartment 3 and in the anode compartment 2, an electrode (not shown here) is present in each case, which is applied, for example, to the sides of the membrane facing the respective reaction compartments 2, 3. Electrolyzers of this type are called PEM electrolyzers (PEM = proton exchange membrane). Unless otherwise stated, the following explanation of the invention assumes such an electrolyzer.However, the invention is also applicable to other types of electrolyzers.

[0030] To operate a PEM electrolyzer, the anode compartment 2 is filled with water and continuously supplied with water during operation. By applying a DC voltage between the cathode and anode electrodes, the water in the anode compartment 2 is split into hydrogen and oxygen ions. The resulting hydrogen ions (H₂) + -ions) diffuse through the membrane and recombine in cathode compartment 3 to form hydrogen gas (IT), while the oxygen ions (O 2 ) remain in the anode compartment 2 and react there to form chlorine molecules. Since the IT ions are surrounded by a hydration shell as they move through the membrane and therefore carry some water with them (so-called drag water), water also continuously enters the cathode compartment 3.

[0031] The anode chamber 2 is continuously supplied with highly purified water as part of an anode-water circuit 4. The water is introduced into the anode chamber 2 via an anode inlet 6 by a pump 9, an ion exchanger 10, and a water filter 11. The water that is not consumed during electrolysis flows together with the generated oxygen gas via an anode outlet 6 to a gas-water separator 8, where the oxygen gas is separated from the water and discharged via an oxygen outlet 12. The now largely gas-free water flows from the gas-water separator 8 back to the pump 9, thus completing the circuit R. 413412.

[0032] - 6 - is closed. The individual components are connected via suitable lines. Since water is consumed during electrolysis, it must be continuously replaced via a water supply, for example via a water connection of the pump device 9 (not shown here).

[0033] During operation of the electrolytic cell, hydrogen gas is produced in the cathode compartment 3, and water accumulates—as explained above—diffused through the membrane from the anode compartment 2. This water flows together with the hydrogen gas via a cathode outlet 16 into a cathode-water path 14, which includes a second gas-water separator 17 where the hydrogen gas is separated from the water. The hydrogen gas is discharged via a hydrogen outlet 18 and sent for further use or storage. The now hydrogen-free water flows via a line 19 into a radical scavenger 20. There, the chemical radicals, especially the hydroxyl radical (HO-), are removed from the water. The treated water is then fed into the anode-water circuit via a water outlet 22, for example, at the first gas-water separator 8.Since the radicals are mainly generated in the cathode compartment 3, they are effectively removed from the cathode water path 14 by the radical scavenger 20, and the water fed into the anode water circuit 4 is accordingly free of chemical radicals. The individual components in the cathode water path 14 are also connected by suitable conduits.

[0034] Figure 2 shows a second embodiment of an electrolysis system according to the invention. In the following, and also in the description of the further embodiments in Figures 3 to 5, only the differences from the first embodiment according to Figure 1 and the preceding embodiments will be discussed, with identical components bearing the same reference numerals. Additionally, a water tank 25 is arranged in the anode water circuit 4, in which water is stored. The water tank 25 serves as a buffer, and the consumed water can be replenished from a water supply 26. In this embodiment, the water outlet 22 also opens into the water tank 25. Depending on its size, the water tank 25 also serves as a thermal buffer, which dampens a rapid rise in water temperature when flowing through the cell 1. R. 413412

[0035] - 7 -

[0036] Fig. 3 shows another embodiment in which the ion exchanger 10 is arranged between the gas-water separator 8 and the water tank 25. Since the ion exchanger 10 functions best at moderate temperatures and the water has cooled somewhat after passing through the gas-water separator 8, the operating temperatures of the ion exchanger 10 are favorable. The heat generated in the pumping device 9 can then be used to reach the higher temperature required for operating the electrolyzer more quickly.

[0037] In the embodiment shown in Fig. 4, two heat exchangers 27 and 28 are arranged in the anode water circuit 4. The first heat exchanger 27 serves to temper the water before it is supplied to the anode chamber 2 in order to achieve the optimal operating temperature of the electrolyzer. A second heat exchanger 28 is arranged downstream of the gas-water separator 8. This is directly connected to the ion exchanger 10, which is therefore no longer directly exposed to the water flow. The second heat exchanger 28 serves to reduce the water to a temperature optimal for the ion exchanger.

[0038] In a further embodiment according to Fig. 5, the water from the radical scavenger 20 is not completely discharged into the anode water circuit 4, but at least a portion is returned to the cathode chamber 3. This allows a larger volume of water to flow through the cathode chamber 3, thereby flushing out radicals—including the HF radicals (hydrogen fluoride) generated by membrane degradation—and filtering them out in the radical scavenger. The amount of water returned to the cathode chamber 3 can be adjusted, for example, by means of a control valve.

Claims

R. 413412 - 8 - Claims 1. Electrolysis system for the electrolytic splitting of water into hydrogen and oxygen, comprising an electrolytic cell (1) having an anode compartment (2) and a cathode compartment (3) separated from each other by a semipermeable barrier, and an anode water circuit (4) which supplies the anode compartment (2) with water via an anode inlet (5) and which receives water from the anode compartment (2) via an anode outlet (6), wherein a gas-water separator (8) and a pump device (9) are arranged in the anode water circuit (4), and a cathode water path (14) which receives water from the cathode compartment (3) and feeds it into the anode water circuit (4), wherein a second gas-water separator (17) is arranged in the cathode water path (14) and an ion exchanger (10) for removing metal ions is arranged in the anode water circuit (4), characterized in that that a radical scavenger (20) is arranged in the cathode water path (14).

2. Electrolysis system according to claim 1, characterized in that the radical scavenger (20) is arranged in the cathode water path (14) after the second gas water separator (17).

3. Electrolysis system according to claim 2, characterized in that the water from the radical scavenger (10) is fed into the anode water circuit (4).

4. Electrolysis system according to claim 2, characterized in that at least a part of the water from the radical scavenger (10) is returned to the cathode compartment (3). R. 413412 - 9 - 5. Electrolysis system according to one of claims 1 to 4, characterized in that a water tank (25) is arranged in the anode water circuit (4), into which the water from the gas-water separator (8) flows.

6. Electrolysis system according to claim 5, characterized in that water from an external source is supplied to the water tank (25) to replace the water consumed during electrolysis.

7. Electrolysis system according to one of claims 1 to 6, characterized in that a water filter (11) is arranged in the anode water circuit (4).

8. Electrolysis system according to one of claims 5 to 7, characterized in that the ion exchanger (10) is arranged in the anode water circuit (4) between the gas-water separator (8) and the water tank (25).

9. Electrolysis system according to one of claims 1 to 8, characterized in that a heat exchanger (27; 28) is arranged in the anode water circuit (4).

10. Electrolysis system according to claim 9, characterized in that the heat exchanger (28) is directly connected to the ion exchanger (10).

11. Electrolysis system according to one of claims 1 to 10, characterized in that a plurality of electrolytic cells (1) are present, wherein the electrolytic cells (1) form a stack and the anode spaces (2) of all cells are supplied with water via the anode water circuit (4).

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