Electrolysis system

Abstract

Electrolysis system comprising an electrochemical stack (1) having an inlet (8) through which water can be introduced and an outlet (9) through which water or gas can be discharged from the stack (1). The outlet (9) is connected via a line (10) to a gas-water separator (11), in which the gas exiting the stack (1) is separated from the water exiting it. The gas-water separator (11) is connected via a drain line (13) to a water tank (20) for storing the separated water, the water tank (20) being connected to the inlet (8) of the stack (1) via a purge line (22).

Description

[0001] The invention relates to an electrolysis system which can be used for the electrolytic splitting of water into hydrogen and oxygen using electrical energy. State of the art

[0002] Electrical energy can be converted into chemical energy in the form of hydrogen. For this purpose, a so-called electrolyzer can be used. This comprises an electrochemical cell in which an anode and a cathode compartment are formed. The anode and cathode compartments are separated from each other by a semipermeable membrane. The membrane is coated with an anode electrode on the anode side and a cathode electrode on the cathode side, between which a direct electrical voltage can be applied. To carry out the electrolysis, the anode compartment and - depending on the type of electrolyzer - also the cathode compartment are filled with water or an electrolytic aqueous solution. The water is catalytically split at the anode electrode, and the resulting H + -Ions diffuse - driven by the electrical voltage - through the membrane into the cathode compartment. There, the H +-ions with the electrons in the cathode electrode to form hydrogen. With the H + -ions, water always enters the cathode compartment, since the H + -ions are surrounded by a hydration shell during diffusion (so-called water drag). Electrolyzers with this operating principle are of the so-called PEM type, which means that the semi-permeable membrane for protons - i.e. H + -ions - is permeable (proton exchange membrane), while the membrane is largely impermeable to other substances. Other electrolyzers are also known, for example, those in which the membrane is permeable to OH - - or O 2 -ions. An example of an electrolysis system is known from DE 10 2021 214 205 A1.

[0003] In the electrochemical cell, hydrogen is produced in the cathode chamber and oxygen in the anode chamber. These reaction gases are carried away by the water, which is continuously pumped through the anode chamber and, if necessary, the cathode chamber, and each is fed to a gas-water separator (gas-liquid separator = GLS). There, the hydrogen or oxygen is separated from the water and the hydrogen is stored for further use. Even in an electrolyzer with a dry cathode, in which no water flows through the cathode chamber, water collects there over time through diffusion and water drag, and flows out of the cathode chamber with the hydrogen. The water collected in the gas-water separators is then pumped back into the circuit, whereby the water used in the anode chamber is continually replaced.

[0004] In electrolysis systems, it is common practice to inertize the stacks and at least parts of the lines under certain operating conditions, particularly during scheduled shutdowns of the electrolyzer for maintenance, emergency shutdowns, and possibly also during standby operation. This removes the hydrogen and, if necessary, the oxygen from the cathode or anode compartment. Otherwise, there is a risk that the hydrogen, in particular, will diffuse into the anode compartment over time and mix with the oxygen present there. This inerting can be performed using nitrogen as the inert gas, but this leads to contamination of the product gas and thus reduces the H2 yield. Deionized water (DI water) can also be used for inerting or rinsing. Advantages of the invention

[0005] The electrolysis system according to the invention has the advantage that it is possible to purge and thus remove the reaction gases from an electrolysis stack without contaminating the desired product gases - in particular the hydrogen - during the purging process or exposing the stack to severe chemical or mechanical stress. For this purpose, the electrolysis system comprises an electrochemical stack with an inlet through which water can be introduced and an outlet through which water and / or gas can be discharged from the stack. The outlet is connected via a line to a gas-water separator in which the gas escaping from the stack is separated from the escaping water. The gas-water separator is connected via a drain line to a water tank for storing the separated water. The water tank is connected to the stack inlet via a purge line.

[0006] If the stack is switched off, practically no new hydrogen is produced, but hydrogen gas is still present in the stack and can mix with the oxygen that is also present through diffusion processes. To prevent this, the stack must be flushed or inerted with water after shutdown (so-called purging) to prevent the hydrogen and oxygen from mixing. The water that is separated in the gas-water separator (gas liquid separator: GLS) is largely free of gases, especially hydrogen gas, and can be used as ultrapure water directly to flush the stack. Since a larger quantity of water can be kept in the water tank, it is immediately available for purging the stack. The water is produced directly at the stack orGLS and does not need to be supplied separately, so that the stack can be flushed and thus safely shut down at any time, regardless of an external supply or the availability of water.

[0007] In an advantageous development of the invention, a conveying device, in particular a pump, can be provided in the flushing line. This pump supplies the water from the water tank to the stack at a predeterminable pressure, so that, in particular, the cathode chamber of the stack can be flushed at a pressure corresponding to the operating pressure in the cathode chamber. Flushing at operating pressure reduces the mechanical stress on the stack and thus increases its service life.

[0008] In a further advantageous embodiment, the water tank is designed as a pressurized water tank in which the water is stored at the same pressure as in the GLS. This means that it is available at operating pressure and can be used to purge the stack without the need for a separate pump and therefore without an external power supply. In particular, if the cathode chamber is to be purged, where a pressure of 10 to 30 bar (1 to 3 MPa) or more prevails during operation, this reduces the mechanical stress on the stack because pressure changes during purging are avoided. If necessary, several water tanks can be filled from the GLS. Purging several stacks with water from the water tank(s) is also easily possible if the water quantity is sufficient.

[0009] Advantageously, the volume of the water tank connected to the reaction chamber is greater than or equal to the volume in the stack connected to the inlet. If multiple stacks are to be flushed, the volume of the water tank corresponds at least to the sum of all stack volumes. This ensures that the corresponding space in the stack can be completely filled with water and thus flushed at least once.

[0010] Another advantageous feature of the gas-water separator is a water connection for supplying purified water. Especially at the beginning of operation, only a small amount of water is present in the gas-water separator (GWS), as this water is gradually formed, particularly in the cathode chamber. Therefore, the electrolyzer must be operated for some time to ensure sufficient water is available for purging. However, to ensure sufficient water is available at all times, the GWS can be filled with a sufficient amount of water via the water connection before operation begins. The water level in the GWS is preferably monitored using a level sensor.

[0011] The stack has an anode compartment and a cathode compartment separated by a semipermeable membrane. Both reaction compartments can be connected to a GLS, and the water can be used to purge the anode compartment or the cathode compartment. The water from the cathode compartment can be advantageously used to flush the cathode compartment, as it is already under sufficient pressure. However, the water from the anode compartment can also be used for this purpose, although it may need to be compressed using a pump. drawing

[0012] The drawing shows schematically various embodiments of the electrolysis system according to the invention. Fig. 1 a schematic representation of the electrolysis system, showing only the essential components, Fig. 2 a schematic representation of an electrochemical cell as part of a stack and Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7 and Fig. 8 further embodiments of the electrolysis system according to the invention in the same representation as Fig. 1. Description of the embodiments

[0013] Fig. Figure 1 shows a first embodiment of an electrolysis system according to the invention in a schematic representation, with only the essential components shown. The electrolysis system comprises an electrochemical stack 1, which comprises at least one, but usually a plurality of, electrochemical cells 2. Fig. Figure 2 shows a schematic representation of an electrochemical cell 2. The electrochemical cell 2 comprises two reaction chambers, an anode chamber 3 and a cathode chamber 4, which are separated from each other by a semipermeable membrane 5. An anode electrode 6 is arranged on the side of the semipermeable membrane 5 facing the anode chamber 3, and a cathode electrode 7 is arranged on the side facing the cathode chamber 4, wherein the electrodes 6, 7 can be designed, for example, as a coating of the membrane 5. During operation of the electrochemical stack 1, the anode chamber 3 is flushed with water (not shown in the drawing), and a direct current is applied between the anode electrode 6 and the cathode electrode 7. Through catalytic splitting of the water in the anode chamber 3, the hydrogen (protons) diffuses through the semipermeable membrane 5 into the cathode chamber 4, where H +-Ions recombine with the electrons of the cathode electrode 7 to form hydrogen and flow out as H2 molecules via a drain line 10.

[0014] The cathode chamber 4 has an inlet 8 and an outlet 9. During normal operation, the hydrogen produced in the cathode chamber 4 and the water diffused in are discharged via the outlet 9 as well as via the inlet 8 and a connecting line 14, whereby a valve 40 in the connecting line 14 is opened. Depending on the design of the stack, the connecting line 14 can also be omitted. However, water can also be introduced into the cathode chamber 4 via the inlet 8 and flow out via the outlet 9, whereby the valve 40 is then closed. In the same way, the anode chamber 3 can also have an inlet and an outlet to supply the anode chamber 3 with water and to discharge gas and / or water from the anode chamber 3. A line analogous to the connecting line 14 is not provided for the anode chamber 3, since it is constantly flushed with water even during normal operation.

[0015] In the electrolysis system, the cathode compartment 4 can be rinsed with pure water, as described below. This can also be applied to the anode compartment 3, which can be rinsed with water, especially when shutting down the electrochemical stack. As described in Fig. As shown in Figure 1, the cathode chamber 4 is connected to a gas-water separator 11 via the drain line 10. Hydrogen gas is generated in the cathode chamber 4 during operation of the electrolyzer – i.e., the electrochemical stack 1. Furthermore, hydrogen gas penetrates the cathode chamber due to the H +-Diffusion during operation always causes so-called drag water to flow through the membrane 5 from the anode chamber 3 into the cathode chamber 4, so that a mixture of hydrogen gas and water escapes via the drain line 10. The gas-water separator 11 serves to separate the hydrogen gas from the water, with the hydrogen gas being discharged via a gas outlet 15 and collected for further use, for example in a pressure vessel (not shown here). The water collected in the gas-water separator 11 is drained via a drain line 13 into a water tank 20, with a drain valve 32 being arranged in the drain line 13. There can also be several stacks 1, illustrated here as an example by another stack 1a.The further stack 1a is also connected via a line 10a to the same gas-water separator 11, where the separation of gas and water of both stacks 1, 1a takes place, and the inlet can also be connected to the outlet via a connecting line 14a with a valve 40a.

[0016] If the electrochemical stack 1 has been operated for a while, more and more water collects in the gas-water separator 11. As soon as a maximum water level is reached in the gas-water separator 11, the remaining water is drained via a drain line 13 by opening a drain valve 32 into a water tank 20, where it is stored. During operation of the electrochemical stack 1, a relatively high pressure of, for example, 40 bar (4 MPa) prevails in the cathode chamber 4 and, accordingly, this pressure also prevails in the gas-water separator 11 and the water tank 20. The water tank 20 is then designed as a pressurized water tank in which the water can be stored for extended periods of time under a flushing pressure that at least essentially corresponds to the pressure in the gas-water separator 11. A diaphragm pressure accumulator, in which the water is always under pressure even when the fill level changes, is useful in this case.

[0017] The water tank 20 is connected to the inlet 8 of the electrochemical stack 1 via a flushing line 22. A flushing valve 33 is arranged in the flushing line and is opened as needed. The other stack 1a can also be flushed via the flushing line 22. If necessary, additional valves can be provided to selectively flush only one of the stacks 1, 1a or all stacks 1, 1a simultaneously.

[0018] In order to flush the electrochemical stack 1 with water, a minimum volume must be present in the water tank 20 or in the gas-water separator 1. If this is not the case, additional deionized water can be supplied from a water treatment system, for example, an EDI (electrodeionization) device, which can produce ultrapure water. The EDI 25 is connected to the gas-water separator 11 via a line 27, in which a pump 26 is arranged, so that deionized water can be supplied to the gas-water separator 11. An additional line 29 with another pressure pump 28 and a shut-off valve 30 also allows the supply of deionized water to the water tank 20, so that the required amount of water can be supplied to the water tank 20 and the gas-water separator 11 as needed.The fill level 35 in the gas-water separator 11 is monitored by a fill level sensor 36 to ensure that the water level does not exceed or fall below a certain level. If excess water occurs in the gas-water separator 11, for example, because the water tank 20 is already completely full, it is drained via a drain line 16 with a drain valve 17. A drain line can also be provided additionally or alternatively in the water tank 20 to drain excess water.

[0019] The electrolysis system works as follows: During operation of the electrochemical stack 1, hydrogen gas is produced in the cathode compartment 4. In addition, water from the anode compartment 3 passes through the membrane 5 into the cathode compartment 4, so that a mixture of water and hydrogen gas from the cathode compartment 4 passes through the outlet 9 and the line 10 into the gas-water separator 11. At the same time, oxygen gas is produced in the anode compartment 3, which is dissolved in water and discharged from the anode compartment 3 and fed to another Fig. 1, where the oxygen is separated from the hydrogen. The oxygen can simply be vented into the atmosphere or used for other purposes, while the water, which is essentially at ambient pressure, can be pumped back into the anode chamber 3. The water separated in the gas-water separator 11 is then passed via the drain line 13 into the water tank 20 by opening the drain valve 32 as soon as the gas-water separator 11 is sufficiently filled. The water is stored there for flushing the stack 1.

[0020] If the electrochemical stack 1 is to be shut down, the hydrogen gas must be removed from the cathode compartment 4 of all electrochemical cells to prevent a mixing of hydrogen and oxygen in the stack 1 or in the lines and valves over time. Hydrogen is highly diffusive and, if left idle for a long time, can pass through the semipermeable membrane 5 into the anode compartment 3. The pressure in the water tank 20 is practically the same as in the gas-water separator 11 or in the cathode compartment 4, so that after the purge valve 33 is opened, the water is forced via the purge line 22 into the inlet 8 of the stack 1, where it flows through the cathode compartment 4 of the electrochemical cell 2 or all electrochemical cells 2 in the electrochemical stack 1. The water—possibly mixed with residual hydrogen gas—flows back into the gas-water separator 11 via the outlet 9.This purging process continues until the hydrogen is removed from the cathode chamber 4.

[0021] For this purpose, the cathode chamber 4 can, for example, be flushed with a volume of water that corresponds to twice the volume of the cathode chamber 4. If the water flushing the cathode chamber 4 returns directly to the pressurized water tank 20 via the gas-water separator 11, the flushing process can be restarted immediately. Otherwise, after the flushing valve 33 is closed, the water tank 20 is refilled with water from the gas-water separator 11 during normal operation of the electrolyzer.

[0022] In Fig. 3 shows a further embodiment of the electrolysis system according to the invention, the essential difference compared to the embodiment according to Fig. 1 in a flushing pump 21 in the flushing line 22 and in a bypass line 18, with which the water tank 20 can be bypassed. A connecting line 14 analogous to the embodiment according to Fig. 1 is not shown here. If the high pressure of the gas-water separator 11 does not prevail in the water tank 20, but the water is stored there under a lower pressure, in particular ambient pressure, the water must be compressed with the help of a flushing pump 21 in order to flush the stack 1. The embodiment shown here also allows a flushing process bypassing the water tank 20, for example because it is already full and only a small amount of water is required for flushing, which can be taken directly from the gas-water separator 11. For this purpose, a 3 / 2-way drain valve 32' is arranged in the drain line 13 so that the water from the gas-water separator 11 can be fed either into the water tank 20 or via the bypass line 18 directly to the pump 21. The bypass line 18 enables the stack 1 to be flushed several times if the volume of the water tank 20 is smaller than the amount of water to be used for flushing.In this case, the water is passed through the stack 1 into the gas-water separator 11 and from there flows via the bypass line 18 again into the stack 1.

[0023] Fig. Figure 4 shows a further embodiment in which each stack 1, 1a is connected to the water tank 20 via a separate flushing line 22, 22a. A separate flushing pump 21a is present in each flushing line 22, 22a—if necessary—so that the water from the water tank 20 can be used to flush multiple stacks 1, 1a, with only two electrochemical stacks 1, 1a being shown here as an example. This is particularly advantageous if the stacks are operated at different operating points and flushing is to be performed, for example, only for individual stacks.

[0024] Fig. Figure 5 shows another embodiment of the electrolysis system. The gas-water separator 11 is connected via several drain lines 13, 13a to a water tank 20, 20a (here, two water tanks are shown as an example), each of which can be filled with water. Likewise, both water tanks 20, 20a can be filled with deionized water from the EDI. The water from the two water tanks 20, 20a is fed to a respective electrochemical stack 1, 1a when a rinsing process is intended.

[0025] Alternatively, several water tanks 20, 20a may be connected together with a common flushing line 22, as shown in Fig. 6. This flushing line 22 connects both water tanks 20, 20a with the electrochemical stacks 1, 1a, so that a more compact design can be achieved. It is also possible, as in Fig. 7 shows that the electrochemical stacks 1, 1a are not flushed with water in parallel, but are connected in series, so that the water first flows through the cathode compartment of the first electrochemical stack 1 and then the cathode compartment of the second electrochemical stack 1a. Here, too, the use of several water tanks 20, 20a is possible, as in Fig. 8 shown. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2021 214 205 A1

[0002]

Claims

[1] Electrolysis system with an electrochemical stack (1) having an inlet (8) through which water can be introduced, and with an outlet (9) through which water or gas can be discharged from the stack (1), wherein the outlet (9) is connected via a line (10) to a gas-water separator (11) in which the gas emerging from the stack (1) is separated from the escaping water, characterized by that the gas-water separator (11) is connected via a drain line (13) to a water tank (20) for storing the separated water, wherein the water tank (20) is connected to the inlet (8) of the stack (1) via a flushing line (22). [2] Electrolysis system according to claim 1, characterized by that a conveying device (21), in particular a pump (21), is arranged in the flushing line (22), which pumps the water under increased pressure into the inlet (8) of the reaction chamber (3; 4). [3] Electrolysis system according to claim 1 or 2, characterized by that the water tank (20) is designed as a pressurized water tank in which the water can be stored under a flushing pressure. [4] Electrolysis system according to claim 3, characterized by that the flushing pressure is greater than 1 bar (0.1 MPa), preferably 10 to 50 bar (1 to 5 MPa). [5] Electrolysis system according to claim 3 or 4, characterized by that the drain line (13) is connected to several water tanks (20; 20a). [6] Electrolysis system according to one of claims 1 to 5, characterized by that several electrochemical stacks (1; 1a) are present, each of which is connected to a water tank (20; 20a) via a flushing line (22; 22a). [7] Electrolysis system according to one of claims 1 to 6, characterized by that the volume of the water tank (20) connected to the stack (1) is greater than or equal to the volume within the stack (1) connected to the inlet (8). [8] Electrolysis system according to one of claims 1 to 7, characterized by that the gas-water separator (11) and / or the water tank (20) has a water connection (23) for supplying water. [9] Electrolysis system according to one of claims 1 to 8, characterized by that the gas-water separator (11) has a level sensor (36) for monitoring the water level (35). [10] Electrolysis system according to one of claims 1 to 9, characterized by that the stack (1) has an anode chamber (3) and a cathode chamber (4) which are separated from one another by a semipermeable membrane (5), wherein an anode electrode (6) is arranged on the side of the semipermeable membrane (5) facing the anode chamber (3) and a cathode electrode (7) is arranged on the side facing the cathode chamber (4), and an electrical direct voltage can be applied between the anode electrode (6) and the cathode electrode (7). [11] Electrolysis system according to claim 10, characterized by that the inlet (8) and the outlet (9) open into the cathode chamber (4). [12] Electrolysis system according to claim 11, characterized by that during operation of the stack (1) gas and / or water exits the cathode chamber (4) via the outlet (9) and the gas, in particular hydrogen, is separated from the water in the gas-water separator (11).

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