Electrolysis system and method for operating same

Abstract

The invention relates to an electrolysis system comprising an electrolysis stack (1) having multiple electrolytic cells (101) which each comprise a cathode chamber (102) and an anode chamber (103) and are designed to electrolytically split water in the anode chamber (103) into hydrogen and oxygen. The hydrogen generated in the cathode chamber (102) is fed to a first gas-liquid separator (9) through a cathode outlet (2) of the electrolysis stack (1) and via a medium line (7) connected thereto. A second gas-liquid separator (15) can be connected to the cathode outlet (2). Depending on the pressure in the electrolysis stack (1), the cathode outlet is connected to the first gas-liquid separator (9) or to the second gas-liquid separator (15).

Description

[0001] title

[0002] Electrolysis system and method for operating the same

[0003] The invention relates to an electrolysis system as used to electrolytically split water into hydrogen and oxygen, and to a method for operating this electrolysis system.

[0004] State of the art

[0005] Electrical energy can be converted into chemical energy by electrolytically splitting water into hydrogen and oxygen. This can be achieved using an electrolyzer, which comprises an electrolytic cell containing an anode and a cathode compartment. The anode and cathode compartments are separated from each other by a semipermeable membrane. The membrane is provided with an anode electrode on the anode side and a cathode electrode on the cathode side, between which a direct current is applied during operation. The anode compartment and—depending on the type of electrolyzer—the cathode compartment are filled with water or an electrolytic aqueous solution. The water is catalytically split at the anode electrode, and the resulting IT ions diffuse—driven by the electrical voltage—through the membrane into the cathode compartment.There, the IT ions recombine with the electrons from the cathode electrode to form hydrogen gas. Water always enters the cathode chamber with the T ions, as the T ions are surrounded by a hydration shell during diffusion ("water drag"). Electrolyzers using this operating principle are of the so-called PEM type, meaning that the semipermeable membrane is permeable to protons—i.e., T ions—while 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 such an electrolysis system is known from DE 10 2021 214 205 A1. The oxygen produced in the anode compartment is flushed out together with the water and fed to a gas-liquid separator, where the oxygen is separated from the water and usually vented into the ambient air. The water collected in the gas-liquid separator is then pumped back into the circuit, with the used water being continuously replaced. The hydrogen produced in the cathode compartment, together with the penetrating water and possibly water vapor, is also fed to a gas-liquid separator, where the hydrogen is separated from the water. The gaseous hydrogen is stored or diverted for other uses.

[0006] In electrolysis systems, it is necessary to inertize the stacks and at least parts of the lines under certain operating conditions, particularly during scheduled shutdown of the electrolyzer for maintenance, emergency shutdowns, and possibly also during standby operation. This is done to remove 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 through the membrane over time and mix with the oxygen present in the anode compartment. This inerting can be carried out using an inert gas, particularly nitrogen, but this leads to contamination of the product gas and thus reduces the Fh yield. Deionized water (DI water) can also be used for inerting or rinsing.

[0007] The water produced in the gas-liquid separator during the separation of hydrogen and water can be used to flush the cathode chamber(s) of the electrolysis stack. For this purpose, the water should have the same pressure that normally prevails in the cathode chamber during normal operation. However, in some operating conditions, the electrolyzer only has a lower pressure in the cathode chamber, so the pressure in the gas-liquid separator also drops accordingly. This water can no longer be used to flush the stack at high pressures, so it must either be discarded or the water must be further compressed. However, additional water consumption means additional resource requirements, which should be avoided, especially in arid regions. However, additional compression of the water leads to reduced efficiency of the electrolysis system due to the additional energy consumption and thus less hydrogen production.

[0008] Advantages of the invention

[0009] The electrolysis system according to the invention has the advantage that virtually all of the water produced in the gas-liquid separators can be used to render the electrolysis stack inert without compromising the efficiency of the overall system. For this purpose, the electrolysis system comprises an electrolysis stack comprising a plurality of electrolytic cells, each with a cathode chamber and an anode chamber, which are designed to electrolytically split water into hydrogen and oxygen. The hydrogen generated in the cathode chamber is fed to a first gas-liquid separator via a cathode outlet of the electrolysis stack and a media line connected thereto. A second gas-liquid separator can be connected to the cathode outlet.

[0010] When the electrolysis stack is in normal operation, the pressure in the cathode chamber is increased, for example, 10 to 100 bar. The hydrogen produced in this state is fed to the first gas-liquid separator, where this increased pressure also prevails. In some operating conditions, however, the pressure in the cathode chamber is significantly reduced, which would inevitably also lead to a reduction in the pressure in the gas-liquid separator and thus reduce the usability of the water produced there for inerting the electrolysis stack. To avoid this, in operating conditions with a lower pressure, the hydrogen or the hydrogen-liquid mixture from the cathode chambers can be fed to a second gas-liquid separator, where the water is also separated from the hydrogen and is available for further use at a lower pressure than in the first gas-liquid separator.This water can also be used to inertize the electrolysis stack when it is in such a low-pressure state. This also avoids the additional water consumption that would be incurred if this low-pressure water were discarded. Advantageously, during normal operation, the pressure in the first gas-liquid separator is the same as in the cathode compartment of the electrolytic cells. This means that this water can be used directly to flush the electrolysis stack to remove the hydrogen present there. For this purpose, the first gas-liquid separator can be connected to a cathode inlet of the electrolysis stack via a flushing line, allowing the water from the first gas-liquid separator to be directed into the cathode compartments of the electrolysis stack.Since the water fed into the cathode chamber from the gas-liquid separator is fed back into the gas-liquid separator after passing through the electrolysis stack, the water can be pumped through the electrolysis stack until the hydrogen has been removed from the electrolysis stack.

[0011] In a further advantageous embodiment, the first gas-liquid separator can be connected to a pressure tank in which water can be stored at a pressure corresponding to the pressure in the first gas-liquid separator during normal operation. During operation, water accumulates in the first gas-liquid separator, which must be discarded, returned to the electrolysis stack, or stored in a tank. The use of a pressure tank allows the water to be stored at the existing pressure for later use to flush the electrolysis stack. A diaphragm pressure accumulator, for example, can be used as the pressure tank. The pressure tank can advantageously be connected to the cathode inlet of the electrolysis stack.

[0012] In a further advantageous embodiment, the first gas-liquid separator can be connected to the second gas-liquid separator via a drain line through which water from the first gas-liquid separator can be directed into the second gas-liquid separator. This allows water to be directed from the first gas-liquid separator to the second gas-liquid separator if the fill level there is insufficient for proper operation.

[0013] In a further advantageous embodiment, the electrolysis stack has an anode inlet through which water can be fed into the anode compartments of the electrolytic cells, and an anode outlet from which the water exits again. The anode outlet is connected via a connecting line to a third gas-liquid separator, in which oxygen and hydrogen are separated. Advantageously, the second gas-liquid separator can be connected to the third gas-liquid separator via a drain line, so that water from the second gas-liquid separator can be fed into the third gas-liquid separator. The water separated from the oxygen in the third gas-liquid separator is returned to the anode compartments of the electrolysis stack.

[0014] In a further advantageous embodiment, the electrolysis system comprises a pure water supply through which purified water can be supplied to the first gas-liquid separator, the second gas-liquid separator, and / or the third gas-liquid separator. This can be used to replace the water split by electrolysis in the anode chambers and to compensate for a water level in the gas-liquid separators that is too low for rinsing.

[0015] In a further advantageous embodiment of the invention, the electrolysis system comprises several electrolysis stacks whose cathode outlets are connected to a common first gas-liquid separator. In this case, even at different operating points of the electrolysis stacks, the pressure in the first gas-liquid separator can be maintained, ensuring the supply of hydrogen and liquid under pressure.

[0016] In a method according to the invention for operating the electrolysis system, the cathode outlet is connected to the first gas-liquid separator and the second gas-liquid separator in such a way that, when the pressure in the cathode chamber is above a predetermined threshold pressure, the hydrogen or the hydrogen-water mixture is fed to the first gas-liquid separator, and when the pressure falls below the predetermined threshold pressure, it is fed to the second gas-liquid separator. Thus, the water from the cathode chambers is collected in the first or second gas-liquid separator, depending on the prevailing pressure, and can then be reused.

[0017] In an advantageous development of the process, when a maximum fill level is exceeded, water is drained from the first gas-liquid separator into the second gas-liquid separator. This allows the water level necessary for optimal operation of the gas-liquid separator to be maintained. Drawing

[0018] The drawing shows an electrolysis system according to the invention. It shows

[0019] Fig. 1 shows a schematic representation of an electrolysis system according to the invention, with only the essential components being shown, and

[0020] Fig. 2 is a schematic representation of a single electrolytic cell.

[0021] Description of the embodiment

[0022] Fig. 1 shows a schematic representation of an electrolysis system according to the invention, wherein, for the sake of clarity, only the components essential for explaining the invention are shown. The electrolysis system comprises an electrolysis stack 1, which comprises a plurality of electrolytic cells 101, which, when stacked one above the other, form the electrolysis stack 1. Fig. 2 shows a schematic representation of a single electrolytic cell 101. This cell has a cathode compartment 102 and an anode compartment 103, which are separated from one another by a semipermeable membrane 104. On the side facing the cathode compartment 102, a cathode electrode 105 is applied to the membrane 104, and on the opposite side, an anode electrode 106. A direct electrical voltage can be applied between the anode electrode 106 and the cathode electrode 105. During operation, the anode compartment is filled with pure water or an electrolyte solution.The electrical voltage causes the water present in the anode compartment 103 to be catalytically split at the anode electrode 106, and the resulting IT ions migrate—in the case of PEM electrolysis—through the membrane 104 into the cathode compartment 102, where they recombine with electrons at the cathode electrode 105 to form hydrogen gas. The resulting hydrogen gas is removed from the cathode compartment 102. Since the IT ions are surrounded by a hydration shell as they pass through the membrane 104, some water (so-called drag water) always enters the cathode compartment 102 along this path. A mixture of hydrogen gas and both liquid and gaseous water thus collects in the cathode compartment 102. The electrolysis stack 1 has a housing with a cathode outlet 2, a cathode inlet 3, an anode outlet 4 and an anode inlet 5 for the supply and removal of water or electrolytic solutions and the gases hydrogen and oxygen produced during electrolysis.The hydrogen gas produced in the cathode chambers 102, together with water and possibly water vapor, is passed through the cathode outlet 2 of the electrolysis stack 1 and a media line 7 into a first gas-liquid separator 9, where the water 11 is separated from the hydrogen gas 10. The resulting hydrogen gas 10 is discharged via a hydrogen outlet 12 and either stored or diverted for other uses. The water 11 produced in the first gas-liquid separator 9 can be used in various ways:

[0023] The first gas-liquid separator 9 is connectable to a pressure tank 24 via a drain line 25, with a shut-off valve 26 located in the drain line 25. Since a high pressure of 10 to 100 bar, preferably 30 to 40 bar, prevails in the first gas-liquid separator 9 during operation, as well as in the cathode chambers 102 of the electrolytic cells 101, this pressure continues in the first gas-liquid separator 9. The pressurized water 11 is fed into the pressure tank 24, where it can be stored at this pressure and used to rinse the cathode chambers 102 of the electrolysis stack 1. For this purpose, the pressure accumulator 24 is designed, for example, as a diaphragm pressure accumulator and is connected via a connecting line 27 to a flushing line 20 which is connected to the cathode inlet 3 of the electrolysis stack 1, wherein a pump 28 or another conveying device can be provided in the flushing line 20.Bypassing the pressure reservoir 24, the water can also be directed from the first gas-liquid separator 9 directly into the purge line 20, with the flow being regulated by a shut-off valve 21. The water can thus be directed directly from the gas-water separator 9 through the electrolysis stack 1 and then through the electrolysis stack 1 and back into the first gas-liquid separator 9 until the hydrogen gas is removed from the electrolysis stack 1.

[0024] The media line 7 can also be connected to a second gas-liquid separator 15 via a 3 / 2-way valve 8. The 3 / 2-way valve 8 is controlled such that the hydrogen from the electrolysis stack 1 is fed into the second gas-liquid separator at a lower pressure, which can occur under certain operating conditions. There, just as in the first gas-liquid separator 9, the hydrogen gas is separated from the water. This water 17 can also be introduced into the purge line 20 via a connecting line 30 and a shut-off valve 31, and the electrolysis stack 1 can be purged with this water 17 at lower pressure. The resulting hydrogen gas 19 is also discharged via a hydrogen outlet 16 for further use.In order to supplement any missing water in the second gas-liquid separator 15, to reduce the pressure in the first gas-liquid separator 9 or to drain excess water from it, a drain line 33 with a shut-off valve 34 is provided between the first gas-liquid separator 9 and the second gas-liquid separator 15, which is opened when necessary.

[0025] Water containing dissolved oxygen produced during electrolysis flows from the anode outlet 4 of the electrolysis stack 1. This water is fed via a connecting line 22 to a third gas-liquid separator 38, where the water 40 is separated from the oxygen 39. The oxygen 39 can be released into the environment via an oxygen outlet 41 or used for other purposes, while the water 40 is fed back to the anode inlet 5 via an anode purge line 42 and, if necessary, a pump 43, where it again enters the anode compartments 103 of the electrolytic cells 101. Since water is split during electrolysis, it must be continuously replaced. This is done via a pure water supply 50, which provides ultrapure water, which can be fed into the third gas-liquid separator 38 via a third supply line 55 and, if necessary, a pump 56.In order to replace or refill any water levels that may be too low in the first gas-liquid separator 9 and in the second gas-liquid separator 15, the first gas-liquid separator 9 can be filled from the pure water supply 50 via a first supply line 51 with a pump 52 and the second gas-liquid separator 15 can be filled via a second supply line 53 with a pump 54.

[0026] The electrolysis system works as follows: During normal operation of the electrolysis stack 1, hydrogen is produced in the cathode compartments and oxygen in the anode compartments. The hydrogen is fed through the cathode outlet 2, together with the water collecting there, into the first gas-liquid separator 9 when the pressure in the cathode compartments 102 is above a threshold pressure ps. As a result, this pressure also prevails in the first gas-liquid separator 9 and in the pressure tank 24, into which the water 11 from the first gas-liquid separator 9 is passed. This water can be fed via the purge line 20 into the cathode inlet 3 of the electrolysis stack 1 if necessary to remove the hydrogen gas from the cathode compartments 102.If the pressure in the electrolysis stack 1—i.e., in the cathode chambers 102 there—is lower, which occurs under certain operating conditions, the 3 / 2-way valve 8 is switched so that the hydrogen-water mixture is fed to the second gas-liquid separator 15, where the water is separated from the hydrogen under lower pressure. The water from the second gas-liquid separator 15 can also be discharged into another pressure tank (not shown in the drawing) and stored there, or the water is used directly from the second gas-liquid separator 15 to rinse the electrolysis stack 1. If too much water accumulates in the second gas-liquid separator 15, it can also be discharged via a drain line 44 with a shut-off valve 45 into the third gas-liquid separator 38 and thus ultimately into the anode inlet 5.

[0027] The use of pump 28 in the purge line 20 may be unnecessary if sufficient water is present at the appropriate pressure in the pressure tank 24 or in the first gas-liquid separator 9. This increases the efficiency of the electrolysis system, since no additional energy is required to purge the cathode chambers 102.

[0028] The pressure in the cathode circuit, i.e., in the cathode chambers of the electrolysis stack 1 and in the first gas-liquid separator 9, can be controlled via an additional control valve in the hydrogen outlet 12 and the shut-off valves 21, 26, and 34. This pressure control is particularly important when several electrolysis stacks are present in the electrolysis system, which are connected to a common first gas-liquid separator 9.

Claims

Claims 1. An electrolysis system comprising an electrolysis stack (1) comprising a plurality of electrolytic cells (101), each having a cathode chamber (102) and an anode chamber (103) and configured to electrolytically split water in the anode chamber (103) into hydrogen and oxygen, wherein the hydrogen generated in the cathode chamber (102) is fed to a first gas-liquid separator (9) via a cathode outlet (2) of the electrolysis stack (1) and a media line (7) connected thereto, characterized in that a second gas-liquid separator (15) is connectable to the cathode outlet (2).

2. Electrolysis system according to claim 1, characterized in that during operation the same pressure prevails in the first gas-liquid separator (9) as in the cathode chamber (102) of the electrolytic cells (101).

3. Electrolysis system according to one of claims 1 or 2, characterized in that the first gas-liquid separator (9) can be connected to a cathode inlet (3) of the electrolysis stack (1) via a flushing line (20), so that the water from the first gas-liquid separator (9) can be conducted into the cathode spaces (102) of the electrolysis stack (1).

4. Electrolysis system according to claim 1 or 2, characterized in that the first gas-liquid separator (9) is connectable to a pressure tank (24) in which water can be stored under a pressure corresponding to the pressure in the first gas-liquid separator (9) during normal operation.

5. Electrolysis system according to claim (4), characterized in that the pressure tank (24) can be connected to a cathode inlet (3) of the electrolysis stack (1), so that the water from the pressure tank (24) can be led into the cathode chambers (102) of the electrolysis stack (1).

6. Electrolysis system according to one of claims 1 to 5, characterized in that the first gas-liquid separator (9) can be connected to the second gas-liquid separator (15) via a drain line (33) through which water can be passed from the first gas-liquid separator (9) into the second gas-liquid separator (15).

7. Electrolysis system according to one of claims 1 to 6, characterized in that the electrolysis stack (1) has an anode inlet (5) through which water can be fed into the anode chambers (103) of the electrolytic cells (101), and an anode outlet (4) from which the water exits again, wherein the anode outlet (4) is connected via a connecting line (22) to a third gas-liquid separator (38) in which the oxygen and water are separated.

8. Electrolysis system according to claim 7, characterized in that the second gas-liquid separator (15) can be connected to the third gas-liquid separator (38) via a drain line (44) so ​​that water can be passed from the second gas-liquid separator (15) into the third gas-liquid separator (38).

9. Electrolysis system according to claim 7 or 8, characterized in that the third gas-liquid separator (38) can be connected to the anode inlet (5) of the electrolysis stack (1), so that the water from the third gas-liquid separator (38) can be returned to the anode spaces (103) of the electrolysis stack (1).

10. Electrolysis system according to one of claims 1 to 9, characterized in that purified water from a pure water supply (50) can be supplied to the first gas-liquid separator (9), the second gas-liquid separator (15) and / or the third gas-liquid separator (38).

11. Electrolysis system according to one of claims 1 to 10, characterized in that the cathode outlets (4) of several electrolysis stacks (1) are connected to the first gas-liquid separator (9).

12. A method for operating an electrolysis system according to one of claims 1 to 11, characterized in that the cathode outlet (2) of the electrolysis stack (1) is fed to the first gas-liquid separator (9) during normal operation at a pressure which is greater than a predetermined threshold pressure (ps) and to the second Gas-liquid separator (15).

13. The method according to claim 12, characterized in that when a maximum filling quantity is exceeded, water is drained from the first gas-liquid separator (9) into the second gas-liquid separator (15).

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