Electrolysis system and method for rinsing an electrolysis device

Abstract

Electrolysis system with an electrolysis device (1) having an inlet (2) through which a liquid can be introduced and an outlet (3) through which a liquid and / or a gas can be conducted, wherein the outlet (3) is connected via an outlet line (4) to a gas-liquid separator (5) in which gas escaping from the electrolysis device (1) is separated from the escaping liquid. The inlet (2) can be connected to a pressure tank (10) in which the liquid is maintained at a flushing pressure.

Description

Technical Field

[0001] This invention relates to an electrolysis system, such as one that can be used to electrolyze water into hydrogen and oxygen using electrical energy, and to a method for rinsing an electrolysis apparatus. Background Technology

[0002] Electrical energy can be converted into chemical energy in the form of hydrogen gas. This is done using a so-called electrolysis device, which comprises an electrochemical cell containing an anode chamber and a cathode chamber. The anode and cathode chambers are separated from each other by a semi-permeable membrane, wherein an anode electrode is coated on the anode side and a cathode electrode is coated on the cathode side. A direct current voltage can be applied between the anode and cathode electrodes. To perform electrolysis, the anode chamber and—depending on the type of electrolysis device—also the cathode chamber is filled with water, or an electrolytic aqueous solution. By applying a voltage between the anode and cathode electrodes, water is catalytically decomposed on the anode side, and H₂O is produced. + Ions diffuse through the membrane into the cathode chamber. There, H... + Ions recombine with electrons at the cathode electrode to form hydrogen gas. Electrolytic devices operating on this principle are so-called PEM-type devices, meaning that a semi-permeable membrane allows for the exchange of protons—that is, H+—with electrons. + The membrane is permeable to ions (proton exchange membrane), but largely impermeable to other substances. Other electrolytic devices are also known, for example, in which the membrane is permeable to OH-. - ions or O 2- Ions are permeable. An example of an electrolysis system is known from DE 10 2021 214 205 A1.

[0003] In an electrochemical cell, hydrogen is produced in the cathode chamber and oxygen in the anode chamber. These reactant gases are discharged by continuously pumping water or an aqueous solution through the anode and cathode chambers and supplied to a gas-liquid separator (GLS). There, either hydrogen or oxygen is separated from the water, and the hydrogen is supplied to a storage container for further use. In electrolysis units with dry cathodes, the cathode chamber is not traversed by water; even in such units, water flowing out of the cathode chamber along with hydrogen accumulates over time through drag and diffusion. The water accumulated in the gas-liquid separator is then pumped back into the circulation loop, where the water consumed in the anode chamber is continuously replenished.

[0004] In electrolysis systems, it is common practice to inert the fuel cell stack and at least a portion of the piping under specific operating conditions, particularly during planned shutdowns for maintenance, emergency shutdowns, and possibly standby operation. Here, hydrogen, and if necessary, oxygen, is removed from the cathode or anode chamber because otherwise there is a risk that hydrogen would diffuse into the anode chamber over time and mix with the oxygen present there. This inertization can be carried out using nitrogen as the inert gas, but this would contaminate the product gases and thus reduce H2 production. Alternatively, deionized water (DI water) can be used for inertization or rinsing. Summary of the Invention

[0005] The electrolysis system according to the invention has the advantage of enabling rapid and reliable inerting or flushing of the electrolysis unit, wherein the mechanical load on the electrolysis unit is minimized. To this end, the electrolysis system has an electrolysis unit with an inlet and an outlet, through which liquid can be introduced and through which liquid and / or gas can be discharged, wherein the outlet is connected via a pipeline to a gas-liquid separator, in which gas escaping from the electrolysis unit is separated from escaping liquid. The inlet can be connected to a pressure tank in which the liquid is maintained at a flushing pressure.

[0006] During operation of the electrolysis unit, hydrogen is formed in the cathode chamber and oxygen in the anode chamber. These gases are continuously vented along with a liquid, which may be water or an aqueous solution. The hydrogen produced in the cathode chamber is subjected to an elevated pressure, for example, 40 bar, to reduce the hydrogen compression work required for subsequent storage at hundreds of bar or for use in other subsequent processes. If the electrolysis unit is shut down, hydrogen formation ceases, but the cathode chamber remains filled with hydrogen, which, especially during longer shutdowns, may diffuse into the anode chamber and mix with oxygen there. To prevent this, the cathode chamber must be flushed with water after shutdown. This is done by maintaining water in a pressure tank, and when necessary, the water is forced into the cathode chamber via connecting lines, where it displaces the hydrogen. After flushing the cathode chamber, the electrolysis unit can remain in the off state for an extended period. The electrolysis unit can also be flushed in this way to remove other contaminants.

[0007] In an advantageous configuration of the invention, the volume of the pressure tank is greater than or equal to the volume of the electrolysis unit into which the inlet is introduced. Therefore, there is always sufficient water or flushing fluid available to flush the volume of the electrolysis unit and thus safely remove hydrogen or other contaminants.

[0008] In another advantageous configuration, the pressure tank is constructed as a diaphragm pressure reservoir. In this diaphragm pressure reservoir, a high pressure on the liquid can be maintained, ensuring that the flushing water or flushing fluid is always present at the required flushing pressure.

[0009] In another advantageous configuration, the pressure tank has a movable piston that limits the volume filled with liquid and is pressurized. Therefore, the pressure is maintained within the liquid-filled volume, allowing the electrolysis unit to be flushed at a constant pressure.

[0010] In another advantageous configuration, the pressure tank has two sub-volumes, both limited by movable pistons connected together. Thus, the first sub-volume can be emptied, while the second sub-volume can be refilled with water from the gas-liquid separator. This design allows for longer flushing times by repeatedly guiding the initially maintained volume through the electrolysis unit until the hydrogen concentration in the flushing liquid is sufficiently low, which can also be regulated via sensor signals. Depending on the design and desired operation, the reservoir can be directly attached to the gas-liquid separator, or an additional pressure reservoir can be connected intermediately for better decoupling from level regulation and flushing operations within the gas-liquid separator.

[0011] In another advantageous configuration, the gas-liquid separator has a discharge port through which liquid can be introduced into a pressure tank via a filling line. The pressure tank can then be supplied with water produced in the gas-liquid separator. If necessary, in another configuration of the invention, a pump can be arranged in the flushing line to compress the liquid and establish a corresponding pressure in the pressure tank. If the gas-liquid separator is connected to the cathode side of the electrolysis unit, where a high pressure already exists from the cathode chamber, the pressure tank can also be filled with this high pressure. In this case, the pump can usually be omitted.

[0012] In another advantageous configuration, the liquid is water or an aqueous solution, especially an electrolyte solution. Typically, the rinsing is performed with pure water, but an electrolyte solution may be required when necessary, particularly when the anode chamber of a so-called AEM electrolysis device (anion exchange membrane) should be rinsed.

[0013] The method for flushing an electrolysis unit according to the invention can be applied to such an electrolysis unit configured to electrolyze water into hydrogen and oxygen by means of an electric current. For this purpose, the electrolysis unit has an inlet and an outlet through which liquid can be introduced and through which liquid or gas can be discharged. A pressure tank is connected to the inlet via a flushing line, wherein the liquid in the pressure tank is maintained at a raised pressure and the flushing line has a shut-off valve. To perform the method, the current in the electrolysis unit is first turned off. Then the shut-off valve is opened, allowing liquid to flow from the pressure tank into the inlet and out through the outlet. This flushing is continued for such a long period that the gas concentration in the electrolysis unit drops below a predetermined limit. This can be done by measuring the concentration or by flushing within a previously determined time period. Subsequently, the shut-off valve is closed again. By this method, the chemical gases present in the electrolysis unit are safely removed, allowing the electrolysis unit to be shut down for extended periods without undesirable chemical reactions and mixing of gases present therein, and the electrolysis unit can be safely restarted.

[0014] Here, the rinsing is advantageously carried out with water or an aqueous solution, especially an electrolytic solution. Preferably, the cathode chamber of the electrolysis device is rinsed, in which hydrogen gas is generated during operation. Attached Figure Description

[0015] Different embodiments of the electrolysis system according to the present invention are shown in the accompanying drawings. For example: Figure 1 : A schematic diagram of the first embodiment, Figure 2 Schematic diagram of the electrolysis apparatus. Figure 3 Another embodiment, illustrated in the figure. Figure 1 , Figure 4 The first embodiment of the pressure tank, Figure 5 The second embodiment of the pressure vessel, and Figure 6 The third embodiment of the pressure vessel. Detailed Implementation

[0016] exist Figure 1 The diagram schematically illustrates an electrolysis system according to the present invention, wherein only the main components are shown. The electrolysis system includes an electrolysis device 1 configured to obtain hydrogen and oxygen from water by means of an electric current through electrolytic decomposition. Here, the electrolysis device 1 typically includes a plurality of electrolytic cells 101, one of which is... Figure 2 The diagram is schematically shown. Here, hundreds of such cells 101 can be installed in the electrolysis unit 1, these electrolytic cells arranged stacked on top of each other as a stack and connected in series. Figure 2 As shown, the electrolytic cell 101 includes an anode chamber 25 and a cathode chamber 26 separated from each other by a semi-permeable membrane 27. An anode electrode 28 is disposed on the side of the membrane 27 facing the anode chamber 25, and a cathode electrode 29 is disposed on the side facing the cathode chamber 26. During operation, a DC voltage is applied between the anode electrode 28 and the cathode electrode 29. To operate the electrolytic device 1, the anode chamber 25 is filled with water or an electrolyte solution, or is traversed by water or an electrolyte solution. Water is catalytically decomposed into H+ by a catalytic coating on the membrane 27 in the region of the anode electrode 28. + Ions and O 2- Ions. The generated H+ + Ions (protons) diffuse across membrane 27 due to voltage and recombine into hydrogen gas at cathode electrode 29, which accumulates in cathode chamber 26. This type of electrolysis device is called a PEM electrolysis device (proton exchange membrane). Because H... + As the ions pass through the membrane, they are surrounded by a hydrate shell, so water always reaches the cathode chamber 26 along with the hydrogen ions (so-called drag water).

[0017] Cathode chamber 26 has inlet 2 and outlet 3. In the electrolysis system shown here, hydrogen and water produced in cathode chamber 26 are discharged via outlet 3 and reach gas-liquid separator 5 via outlet pipe 4. There, water and hydrogen are separated. In gas-liquid separator 5, water 7 accumulates downward due to gravity and can be discharged via discharge port 9 when the liquid level reaches a limited height. Hydrogen gas 6 is discharged via gas outlet 8 for storage or further use. During operation of electrolysis unit 1, the pressure in cathode chamber 26 is significantly increased and is typically between 10 bar and 70 bar (1 to 7 MPa), while only a slightly increased pressure relative to the ambient pressure exists in anode chamber 25. Pressure regulation in cathode chamber 26 is performed, for example, via pressure regulation at gas outlet 8 of gas-liquid separator 5, thereby placing gas-liquid separator 5 and cathode chamber 26 at the same pressure. In other configurations of pressure regulation, the pressure in gas-liquid separator 5 may be reduced relative to the pressure in cathode chamber 26.

[0018] Pressure tank 10 can be filled with deionized water at a desired flushing pressure via an external water supply device. However, the water can also be removed from the gas-liquid separator 5, which is already under pressure, as in... Figure 3As shown in another embodiment. The water 7 separated in the gas-liquid separator 5 is discharged via the outlet 9 of the gas-liquid separator 5 and valve 17, wherein the water is compressed by means of pump 16 and ultimately supplied to pressure tank 10 when needed. Because there is an increased pressure, for example 40 bar, in the cathode chamber 26 during operation, it is advantageous that the cathode chamber 26 is also flushed at this pressure, as this reduces the mechanical load on the electrolysis unit 1 and, in particular, the membrane 27. If there is excess water, the excess water can be discharged via drain 18 by opening drain valve 19.

[0019] If the electrolysis unit 1 is to be shut off, hydrogen gas remains in the cathode chamber 26. This hydrogen gas is diffusive and, due to the pressure difference between the cathode chamber 26 and the anode chamber 25, diffuses over time through the membrane 27 into the anode chamber 25, where it mixes with oxygen, forming a reactive gas mixture (explosive gas). To avoid this, in the electrolysis system according to the invention, the cathode chamber 26 is flushed with water. For this purpose, the inlet 2 of the cathode chamber 26 is connected to a pressure tank 10, in which water is maintained at a flushing pressure, which is substantially equivalent to the pressure present in the cathode chamber 26 during normal operation of the electrolysis unit 1, so as to minimize the mechanical load on the electrolysis unit 1.

[0020] To flush the cathode chamber 26, the current supply between the anode electrode 28 and the cathode electrode 29 is interrupted. The cathode chamber 26 is filled with hydrogen gas and a certain amount of water. Since the electrolysis device 1, or each electrolytic cell, is a capacitor, electrolysis does not end instantaneously but continues to produce a small amount of hydrogen gas for a certain period of time. This hydrogen gas also accumulates in the cathode chamber 26 until the capacitor formed by the cathode and anode electrodes discharges. To remove the hydrogen gas from the cathode chamber 26, the shut-off valve 11 is opened, and water flows from the pressure tank 10 into the cathode chamber 26 and further from there into the gas-liquid separator 5 via the outlet 3. This flushing process is maintained for such a long time that the hydrogen gas is removed from the cathode chamber 26. Subsequently, the shut-off valve 11 is closed again. If there is excess water, the excess water can be discharged through the drain outlet 18 by opening the drain valve 19.

[0021] The flushing process can be time-controlled, meaning that the cathode chamber 26 is flushed within a pre-determined timeframe. Flow control is also possible, in which a pre-determined volume of liquid, such as the entire liquid volume of the pressure tank 10, is directed through the cathode chamber 26. Regulation via a sensor that measures the concentration of hydrogen in the liquid during the flushing process can also be easily achieved.

[0022] After the flushing process, pressure tank 10 is refilled with water at the flushing pressure, either by the gas-liquid separator 5 or via an external water source, to prepare the pressure tank for the next flushing process. If only water from the gas-liquid separator 5 is used, a closed system is formed, eliminating the need for additional external input of flushing water. The volume of pressure tank 10 and the available water volume must be configured such that cathode chamber 26 can be completely flushed at least once. The volumes of flushing line 12 and outlet line 4 must also be considered, as hydrogen gas may accumulate there. Advantageously, the water volume of pressure tank 10 is two to three times larger than the combined volume of cathode chamber 26 and flushing line 12 and outlet line 4. Because the water in pressure tank 10 is at operating pressure, the flushing process can be initiated simply by opening shut-off valve 11, without the need for pumps or other electrically driven units. Depending on the pressure in electrolysis unit 1, a check valve must be installed in addition to valve 11 to prevent backflow into pressure tank 10.

[0023] In order to maintain the increased pressure of the water in pressure tank 10 throughout the flushing process, pressure tank 10 must be constructed to maintain the pressure even during evacuation. Such a pressure tank 10... Figure 4 As schematically shown. Pressure tank 10 has a water volume V1, which is either filled via a gas-liquid separator 5 - such as Figure 3 As shown, the water is either filled via an external water supply device that provides high-purity water. The water volume V1 is limited by a movable piston 20, which is forcefully loaded toward the water volume V1 via a rod 21. This force results in a largely constant pressure within the water volume V1, causing the cathode chamber to be flushed by a constant flow of water under such pressure, which is largely equivalent to the pressure predominant in the cathode chamber 26 during normal operation. Because the piston 20 follows as the volume V1 is emptied, the pressure is maintained.

[0024] exist Figure 5 Another embodiment of the pressure tank 10 is shown. The pressure tank 10 is configured here as a diaphragm pressure reservoir, in which the water volume V1 and the pressurized gas volume V1 are... D Separation is achieved through a flexible membrane 22. The pressure gas volume V... D The water is placed under pressure and thus compressed to a volume V1. If the water volume V1 is emptied, the pressure gas volume V... D Although the pressure in the middle has decreased slightly, it can still maintain sufficient flushing pressure.

[0025] exist Figure 6Another embodiment of the pressure tank 10 is shown. The pressure tank 10 here has two water volumes V1 and V2, which are respectively limited by pistons 20a or 20b. These two pistons 20a and 20b are connected by a rod 21. If the two pistons 20a and 20b move, for example, toward the water volume V1, volume V1 is emptied, while volume V2 can be refilled with water simultaneously. This application has the advantage that water can be continuously replenished to the gas-liquid separator while simultaneously flushing the electrolysis unit 1. Depending on the design and desired operation, the reservoir can be directly attached to the gas-liquid separator 5 via the two volumes V1 and V2, or an additional pressure reservoir can be connected intermediately to better decouple the liquid level regulation in the gas-liquid separator 5 from the flushing operation on the other hand.

[0026] The electrolysis system for rinsing the cathode chamber 26, as illustrated here using the cathode chamber 26 as an example, can also be used similarly for rinsing the anode chamber 25. For this purpose, either a separate pressure tank 10 can be provided, or the same pressure tank 10 can be connected not only to the anode chamber 25 but also to the cathode chamber 26. Rinsing of the anode chamber 25 is preferably carried out at a low pressure, only slightly higher than the ambient pressure, which corresponds to the operating pressure in the anode chamber 25. Depending on the type of electrolysis apparatus, instead of rinsing with pure water, an aqueous solution, such as an electrolyte solution, can also be maintained in the pressure tank 10 for rinsing the anode chamber 25 or also the cathode chamber 26.

Claims

1. An electrolysis system having an electrolysis device (1), said electrolysis device having an inlet (2) and an outlet (3), through which liquid can be introduced and through which liquid and / or gas can be discharged, wherein, The outlet (3) is connected to a gas-liquid separator (5) via an outlet pipe (4), in which the gas escaping from the electrolysis device (1) is separated from the escaping liquid. Its features are, The inlet (2) can be connected to a pressure tank (10) in which the liquid is maintained at a flushing pressure.

2. The electrolysis system according to claim 1, characterized in that, The volume of the pressure tank (10) is greater than or equal to the volume of the electrolysis device (1) fed into the inlet (2).

3. The electrolysis system according to claim 1 or 2, characterized in that, The pressure tank (10) is constructed as a diaphragm pressure storage device.

4. The electrolysis system according to claim 1 or 2, characterized in that, The pressure vessel (10) has a movable piston (20) that limits the volume (V1) filled with liquid and is pressurized.

5. The electrolysis system according to claim 1, characterized in that, The pressure vessel (10) has two sub-volumes (V1; V2), both of which are bounded by movable pistons (20a; 20b), wherein the two pistons (20a; 20b) are connected and move synchronously.

6. The electrolysis system according to any one of claims 1 to 5, characterized in that, The gas-liquid separator (5) has a discharge port (9) through which liquid can be introduced into the pressure tank (10) via a filling pipe (15).

7. The electrolysis system according to claim 6, characterized in that, A pump (16) is arranged in the filling line (15), which compresses the liquid to create an increased pressure in the pressure tank (10).

8. The electrolysis system according to any one of claims 1 to 7, characterized in that, The liquid is water or an aqueous solution, especially an electrolytic solution.

9. The electrolysis system according to any one of claims 1 to 8, characterized in that, The inlet (2) and the outlet (3) lead into the anode chamber (25) or cathode chamber (26) of the electrolysis device (1).

10. A method for flushing an electrolysis device (1), the electrolysis device having an inlet (2) and an outlet (3), through which liquid can be introduced and through which liquid and / or gas can be discharged, and the electrolysis device (1) being configured to electrolyze water into hydrogen and oxygen by means of an electric current, and the electrolysis device having a pressure tank (10), the pressure tank being connected to the inlet (2) via a flushing line (12) and in which liquid is maintained at a flushing pressure, wherein, A shut-off valve (11) is arranged in the flushing pipeline (12). Its features are, - Turn off the current in the electrolysis device (1), - Open the shut-off valve (11) to allow the liquid to flow from the pressure tank (10) into the inlet (2) of the electrolysis device (1) and out through the outlet (3). - Rinse the electrolysis device (1) until the gas concentration in the rinsed area of ​​the electrolysis device (1) drops below a predetermined limit value. - Close the shut-off valve (11).

11. The method according to claim 10, characterized in that, The rinsing time of the electrolysis device (1) is controlled, the amount is controlled, or it is based on the measured gas concentration in the liquid.

12. The method according to claim 10 or 11, characterized in that, The liquid is water or an aqueous solution, especially an electrolytic solution.

13. The method according to claim 10, 11 or 12, characterized in that, The inlet (2) leads into the cathode chamber (25) of the electrolysis device (1), where hydrogen gas is formed during the operation of the electrolysis device (1).

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