Electrolyser and method for operating electrolyser

Abstract

The invention relates to an electrolyser (1) for producing hydrogen (H2) and oxygen (O2) as product gases, comprising an electrolysis module (3) and a gas separator (5) which is designed to phase-separate the product gases from water, the electrolysis module (3) being connected to the gas separator (5) via a product flow line (7) for the product gases, and wherein a return line (9) for the separated water is provided, which return line connects the gas separator (5) to the electrolysis module (3). The gas separator (5) is designed and arranged at a height difference ([delta] h) above the electrolysis module (3) in such a way that the electrolysis module (3) can be automatically filled with water only driven by the height difference ([delta] h) in a shut-down state. The invention also relates to a method for operating an electrolyzer (1) having an electrolysis module (3), in which the electrolysis current is stopped and a safe shut-off is started during operation in a shut-down state.

Description

Technical Field

[0001] The invention relates to an electrolyser and a method for operating an electrolyser. Background Art

[0002] An electrolyser is an industrial facility that uses an electric current to cause a chemical transformation, the so-called electrolysis. There are a variety of electrolysers for different electrolysis processes, for example electrolysers for water electrolysis, i.e. the decomposition of water as a reactant into the product gases oxygen and hydrogen.

[0003] For some time, it has been increasingly considered to use excess energy from renewable energy sources, i.e., above-average solar or wind power generation, to produce valuable substances during times of high sun and high wind. The valuable substance may be hydrogen, which is produced using a water electrolyzer. For example, so-called EE gas can be produced using hydrogen.

[0004] The electrolyzer usually has a plurality of electrolysis cells, which are arranged and stacked adjacent to each other. In the electrolysis cells, water is decomposed into hydrogen and oxygen by means of water electrolysis. In a PEM electrolyzer, distilled water is typically supplied as a reactant on the anode side and split into hydrogen and oxygen at a proton-permeable membrane (English: "Proton-Exchange-Membrane", PEM). In this case, water is oxidized to oxygen at the anode. Protons pass through the proton-permeable membrane. Hydrogen is produced on the cathode side. Water is usually supplied to the anode chamber and / or cathode chamber from the bottom.

[0005] In an electrolyser, the individual electrolysis cells are typically stacked into modules comprising a plurality of single cells in the axial direction and assembled into said modules or electrolysis modules. An electrolyser here generally has a plurality of modules, which as a whole form a so-called electrolysis stack or simply a "stack". For example, 50 electrolysis cells can be stacked axially into a module, and for example 5 modules can be stacked in turn into a stack in the axial direction, so that such an electrolysis stack can therefore comprise, for example, 250 cells in an axially integrated composite structure.

[0006] In a PEM electrolyser, once the electrolysis module or electrolysis cell or electrolysis stack has been filled with water for the first time, for example after production, it must be ensured that the water (reactant water) or the water-gas mixture always remains in the module during operation of the electrolyser. Dry operation or drying out must be prevented in every operating phase, since this would cause irreversible damage to the electrolyser. Firstly, the membrane must always remain in a moist environment, but other functional components and assemblies, such as catalysts or electrodes, must not also dry out.

[0007] In operating phases of the electrolyzer from a normal operating state, for example during planned and upcoming maintenance or repairs for service purposes, the shutdown management of the electrolyzer can generally be planned well and predictively, and corresponding preventive measures and shutdown procedures can be initiated routinely and reliably, so that in particular the water remains in the module even after shutdown and, if necessary, is additionally circulated.

[0008] On the other hand, an unexpected and especially safety-related rapid shutdown within a short time frame or even an instantaneous emergency shutdown in the event of a fault can cause significant problems. This can only be controlled with considerable difficulty and technically with great effort, especially with regard to preventing dry operation of the module during shutdown operation. This is especially true when there are different types of electrolyzers, each of which has a different structure and different operating parameters, with which special operating risks and reasons for safety or emergency shutdowns are to be taken into account. Thus, for example, atmospheric pressure electrolyzers are known, which operate at atmospheric or only low operating pressures, or pressure electrolyzers, which operate at high operating pressures of 35 bar or more. Summary of the invention

[0009] The object of the present invention is therefore to provide an electrolyser in which shutdown operation can be realized in a technically simple and reliable manner so that dry running is prevented. Another object is to provide a method for operating an electrolyser in shutdown operation with low susceptibility to failure and high flexibility.

[0010] The purpose of the electrolyzer is achieved according to the present invention by an electrolyzer for producing hydrogen and oxygen as product gases, the electrolyzer having an electrolysis module and a gas separator, the gas separator being designed to separate the product gas from water, wherein the electrolysis module is connected to the gas separator via a product flow pipeline for the product gas, and wherein a return pipeline for the separated water having a delivery pump is provided, the return pipeline connecting the gas separator to the electrolysis module, wherein the gas separator is designed and arranged at a height difference above the electrolysis module so that in a shutdown state the electrolysis module can be automatically filled with water driven solely by the height difference, wherein the delivery pump has a low pressure loss coefficient in the shutdown state, so that rapid filling in a current-free state is ensured in conjunction with the gas separator that can be emptied via the return pipeline.

[0011] The invention is based here on the problem finding from the observation and assessment of risks for different reasons, that, for example, in an electrolysis module at least partially filled with gas, with hydrogen on the cathode side and oxygen on the anode side, a very rapid diffusion of gas occurs through a thin proton-permeable membrane. In particular, small molecules of hydrogen then diffuse back to the oxygen side. This effect is stronger at higher operating pressures of the electrolyzer, since local pressure differences are the driving force for the diffusion. Diffusion can lead to dangerous gas concentrations in the minute range, i.e. for increasing the hydrogen concentration on the oxygen side up to above the lower explosion limit of 4 vol%. Since ignition sources, such as dried catalysts, cannot be excluded, an explosion is possible in the worst case.

[0012] In the described case, dry running of the electrolysis module must be prevented at all costs.

[0013] In normal operation, a mixed phase is produced in the module, i.e. a phase mixture of water and product gas. As soon as the flow supply of the electrolysis is stopped and no further measures are taken, the mixture will quickly separate and form a gas phase at least in the upper region of the electrolysis module. Therefore, in all conceivable faults, rapid water supply and gas discharge are also mandatory in order to prevent drying out. Therefore, safety measures must be taken immediately.

[0014] Furthermore, one development goal of PEM electrolysis is to use thinner and thinner membranes, whereby the resistance becomes lower and the efficiency of the electrolyser becomes higher. However, thinner membranes disadvantageously lead to even higher diffusion and thus to an increase in the possible risk of explosion.

[0015] It is therefore increasingly important to ensure that the electrolysis modules are filled with water particularly quickly in the electrolyzer during shutdown operation. Current solutions are either insufficient or very complex and not very flexible with respect to the operating pressure of the electrolyzer.

[0016] For this purpose, the present invention proposes a filling scheme for an electrolysis module for an electrolyzer, which is completely self-sufficient and very reliable in nature. The filling scheme is independent of additional and expensive external supply devices and redundant systems or backup solutions for conveying or filling by means of pumps. The facility scheme for the electrolyzer can be used advantageously independently of the working pressure of the electrolyzer, that is, it can be flexibly applied not only to atmospheric electrolyzers, but also to pressure electrolyzers. In particular, critical operating states caused by explosion hazards, for example, can be avoided, while dry operation is prevented, because the corresponding pressure difference caused by the water column is automatically caused and driven by the horizontal compensation caused by the height difference. Rapid exhaust of the gas separator. In particular, there is no need for an external or specially maintained pump unit and an expensive emergency power supply system for electricity to cause safe and very fast filling of the electrolysis module. Therefore, the electrolysis cell and especially the membrane are protected because the components are filled and kept moist by the water flowing back through the return line. By designing and arranging the gas separator at a height above the electrolysis module, the liquid level or level of the water in the gas separator is maintained during operation, and a hydrostatic delivery pressure is already achieved in the system, providing a shutdown operation for emergency shutdowns, in particular for safety purposes. Of course, this filling concept can also be advantageously used for conventional and planned shutdowns, for example for maintenance purposes.

[0017] In addition to the maintained height difference, a delivery pump is connected in the return line, which has a low or very low pressure loss coefficient in the idle state, so that the combination of the pressure difference maintained due to the set height difference and the design of the delivery pump results in particularly rapid filling in the return line.

[0018] The pressure loss factor, pressure loss coefficient or also resistance coefficient (commonly known by the formula symbol ζ-Zeta) is a dimensionless measure for the pressure loss in a component through which a flow passes, such as a pipeline or a fitting. In other words, the pressure loss coefficient indicates what pressure difference must exist between the inflow and outflow in order to maintain a certain flow through the component. The pressure loss coefficient always applies to a certain geometry and is usually dependent on the Reynolds number and, if necessary, on the surface roughness of the flow-conducting component.

[0019] In normal operation of the electrolyzer, it is very advantageous to actively feed the water separated in the gas separator back into the electrolysis process, so a delivery pump is provided in the return line, which pumps the water back. However, the delivery pump is a fluid element with resistance, which, for example, resists the rapid return flow of water during filling in the shutdown operation. Therefore, it is advantageous to set the delivery pump with the smallest possible pressure loss coefficient in the shutdown state, so that even in the non-current state, rapid filling and flow through the return line by the delivery pump is achieved.

[0020] Therefore, the facility concept for the electrolyzer achieves safe and rapid filling of the electrolysis module with water by the elevated position of the gas separator. The safety concept of the invention is superior to known solutions for electrolyzers because it does not require redundancy and can achieve supply independently of the working pressure of the electrolyzer.

[0021] Therefore, for example, a pressure electrolyzer is operated at a pressure of, for example, 35 bar. Under the high operating pressure, the volume gas portion in the electrolysis module is small, that is, only a small amount of gas can be separated in terms of volume after shutting down. Usually, the pipeline pipeline of the electrolysis module is led to the gas separator in an ascending manner, so that after shutting down, water can also be partially separated in the pipeline pipeline and can flow back into the electrolysis module. However, this cannot be carried out quickly enough during emergency shutdown, for example in the case of explosion danger, and active components are required in addition to actively and quickly transport water to the electrolysis module. For the described situation, the corresponding liquid level in the gas separator must also be maintained accordingly. By operating under pressure, the diffusion of hydrogen from the cathode side of the electrolysis cell through the membrane to the anode side is increased, which is a safety-related problem, which becomes more and more serious as the membrane is designed to be thinner and thinner.

[0022] Compared with pressure electrolyzers, when the electrolyzer is operated at normal pressure, a large volume of gas is present in the electrolysis module under operating conditions. The electrolysis module is directly connected to the gas separator located above not only via the inlet but also via the outlet. Due to the natural circulation process, it is usually not necessary to install a pump. As long as there is enough and sufficiently dispersed gas in the electrolysis module, the natural circulation will not stop due to the density difference caused thereby. After the natural circulation stops, the water level in the electrolysis module is significantly lower than the water level of the gas separator, and there is no serious installation component with pressure loss in between, so that water can flow freely from the gas separator into the module, and the water level in the module can be ensured.

[0023] The conventional possibility for ensuring fault protection in the case of forced circulation by means of pumps is to use redundant pumps. In the case of a pump failure, the remaining pump capacity can be used to quickly fill the module with water. In order to also be able to overcome power failures, an uninterrupted power supply is necessary. In addition, the pumps should be controlled completely separately in order to also be able to overcome control system failures. This makes this solution very complex and expensive.

[0024] By contrast, with the solution of the invention, both pressure electrolyzers and atmospheric electrolyzers can be protected very effectively against dry running, and particularly rapid and self-sufficient filling is possible without redundancy requirements. This solution has proven to be particularly advantageous in atmospheric electrolyzers, but, as described, is not limited thereto.

[0025] In a particularly preferred embodiment of the electrolyser, the gas separator is designed as a horizontal container, so that a large surface is available as phase interface between the liquid phase and the gas phase.

[0026] The described design of the electrolyzer allows a relatively small overall structural height of the gas separator, which is very advantageous in the case of a height difference arranged above the electrolysis module. Therefore, the gas separator designed as a container has a container bottom with a length dimension and a width dimension, which are respectively significantly larger than the container height. As a result, despite the required height difference, structural space is still saved. In addition, the horizontal construction method realizes a correspondingly large phase interface between the water at the bottom of the container and the product gas in the gas phase above the phase interface, oxygen or hydrogen, in the gaseous phase, which is conducive to a more effective phase separation between water in the phase mixture and the product gas in normal operation.

[0027] In a preferred embodiment, the return line opens into the lower region of the electrolysis module.

[0028] Due to the height difference between the gas separator and the electrolysis module in the electrolyzer, the highest possible hydrostatic pressure difference is provided by the connection method of the return line. In the case of a safety shutdown, the higher pressure difference ensures a faster return of water and a complete filling of the electrolysis module. Here, the pressure difference is simply generated by the hydrostatic pressure of the water column, which is generated in the case of a height difference between the normal liquid level in the gas separator and the level of the connection of the return line to the electrolysis module. The driving force for filling is the higher water level in the gas separator relative to the electrolysis module, so that an automatic level compensation can be caused.

[0029] In this case, the height difference is preferably set in such a way that at least 0.05 bar to 0.5 bar, in particular 0.1 bar, is available as a driving pressure difference for filling.

[0030] It has been proven in terms of design technology that, given the pressure differences described in typical electrolyzers, sufficient drive pressure is usually available for level compensation in order to initiate a filling as quickly as possible if necessary. A sufficient pressure difference level and thus a higher positioning of the gas separator relative to the electrolysis module can advantageously be adapted to the respective situation, wherein line cross sections, components and parts that influence the flow resistance in the return line and in the entire electrolysis module to be filled can also be taken into account. This can result in a varying pressure difference and, if necessary, a higher required pressure difference.

[0031] It has been found that the pressure loss coefficient ζ of the delivery pump is preferably less than ζ=5, in particular less than ζ=3. This provides a sufficient volume flow of water through the delivery pump or backflow even in the stationary state. However, the pressure difference caused by the height difference between the gas separator and the electrolysis module remains the driving force. However, a correspondingly matched and designed delivery pump is now advantageously integrated into the electrolysis facility, which delivery pump passively supports the filling due to the low pressure loss coefficient.

[0032] In a preferred embodiment, a plurality of electrolysis modules are provided, which are connected to the gas separator via a common product stream line.

[0033] Thus, the power of an electrolyser or electrolysis facility can be expanded simply and flexibly by providing additional electrolysis modules. The electrolysis modules can be operated in parallel or in series as a so-called module train or a combination thereof. Conceptually, the parallel connection can involve a purely electronic connection in terms of the electrolysis current or electrolysis voltage and / or in terms of the material flow, for example, the process water is guided and conducted through the electrolysis modules as a reactant flow.

[0034] In a particularly preferred embodiment, in the case of a plurality of electrolysis modules, the electrolysis modules are connected to the return line via corresponding connecting lines, wherein a regulating valve is arranged in at least one of the connecting lines. A preferred embodiment is hereby provided in which a corresponding regulating valve is arranged in each of the connecting lines, since this allows a particularly large operating flexibility, so that, for example, only one or only a single electrolysis module can be primed as required for maintenance purposes or in the event of a safety shutdown.

[0035] If, for example, a plurality of electrolysis modules or rows of modules connected in parallel are supplied via pumps or pumping stations, corresponding regulating valves are therefore preferably provided in order to achieve an individually controllable inflow to each electrolysis module or each row of modules.

[0036] When using a plurality of pumps connected in parallel, for example to provide redundancy, it is preferred that the flow through the pumps, i.e. the pressure loss coefficient, is also sufficiently determined. This advantageously allows, for example, the so-called push-off and replacement of the pumps and continued operation with at least one pump that can flow freely. A shut-off slide - also a gas slide or a water slide - is a fitting that is usually used to completely open or close the entire flow cross section of a pipe or pipeline. In contrast to a valve, a shut-off slide is not primarily used to regulate the flow and is not used at very high pressures. A shut-off slide is usually used for pre-cut-off, i.e. in order to enable maintenance work at a subsequent fitting, which in normal operation takes on the shut-off or regulation.

[0037] In the embodiment of the invention for an electrolysis plant, if additional components are used in the flow path, such as heat exchangers, valves, filters, the permissible pressure loss coefficient at the component level is usually reduced. This can be compensated advantageously and at least within certain limits by adapting the height difference, that is to say by using a higher pressure difference than corresponds to the driving force for the filling.

[0038] Preferably, the regulating valve is mechanically designed for a minimum flow rate, which cannot be lowered during regulation. The minimum opening can be achieved by a corresponding mechanical locking device. A corresponding design of the regulating valve is preferably also provided in a plurality of regulating valves, which are respectively connected to the connecting line.

[0039] This minimum opening of the valve position for regulating the minimum flow of the valve is advantageous together with the pressure loss coefficient of the delivery pump and / or the pressure loss coefficient of a pump station comprising a plurality of pumps, which are set and designed in the electrolyzer so that a sufficiently rapid automatic return of water from the gas separator to the electrolysis module to be filled is ensured solely due to pressure differences or height differences.

[0040] The object of the method is achieved according to the invention by a method for operating an electrolyser, wherein in normal operation an electrolysis current is supplied to an electrolysis module so that water produces hydrogen and oxygen as product gases in the electrolysis module, wherein the product gases are supplied as a phase mixture of water and product gases to a gas separator, wherein the water is separated from the product gases in the gas separator, and wherein in shutdown operation the electrolysis current is stopped and a safety shutdown is initiated. In this case, in shutdown operation water is automatically driven from the gas separator through a return line into the electrolysis module solely due to the height difference, wherein water flows through a feed pump arranged without current and the electrolysis module is filled, wherein rapid filling is ensured in the currentless state.

[0041] Preferably, the electrolysis module is automatically filled with water until the fill levels of the water in the gas separator and in the electrolysis module are equalized.

[0042] In the event of a sudden stop of operation, for example due to a safety shutdown or emergency shutdown of the electrolyzer, product gas and water are separated in the electrolysis module. A certain water level or liquid level appears in the electrolysis module. By setting the gas separator higher, water is immediately and quickly driven into the electrolysis module by means of the set pressure difference, and the fluid elements present in the pipeline can also flow through quickly enough. As a result, level compensation is very quickly and automatically brought about and a rapid filling of the electrolysis module is achieved. The electrolysis cells and especially the sensitive membranes in the electrolysis module are completely soaked with water and do not dry out. Dry operation is reliably prevented.

[0043] The further advantages of the method result correspondingly from the above-mentioned advantages of the electrolyser. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The present invention will be described in detail below based on the accompanying drawings. It should be noted that the embodiments shown in the accompanying drawings are mainly used to illustrate the present invention. However, the embodiments should not limit the present invention.

[0045] This is shown schematically and greatly simplified:

[0046] Figure 1 An electrolyser having one electrolysis module is shown;

[0047] Figure 2 An electrolyser having a plurality of electrolysis modules is shown;

[0048] Figure 3 The diagram shows the time profile of the filling level during a safety shutdown.

[0049] The same reference numerals have the same meaning in the figures. DETAILED DESCRIPTION

[0050] exist Figure 1 1 shows an electrolysis facility 1 for electrolyzing water. The electrolyzer 1 has a circuit on the hydrogen side, which is simplified in the figure. A corresponding circuit is also possible on the oxygen side with a similar view. This is a simple embodiment for the electrolyzer 1 in order to implement the invention and to illustrate the principle. The electrolyzer 1 has an electrolysis module 3 and a gas separator 5. The gas separator 5 is connected to the electrolysis module 3 via a product stream line 7. The electrolysis module 3 typically comprises Figure 1 An electrolysis cell stack not shown in detail in the figure, which has a plurality of electrolysis cells stacked in the axial direction. Here, the anode half-cell and the cathode half-cell of the electrolysis cell are separated by a proton-permeable membrane. It is also feasible that a plurality of electrolysis modules 3 are connected together to form a module group. The electrolyzer 1 is designed to produce hydrogen H2 and oxygen O2 as product gases in a PEM electrolysis process, for example under atmospheric pressure conditions. The electrolysis module 3 is connected to the gas separator 5 via a product flow pipeline 7 for the product gas. The gas separator 3 is designed here to separate the product gas from water, and currently the gaseous hydrogen H2 is separated from the phase mixture with water in the gas separator 3. The return pipeline 9 for the separated water connects the gas separator 3 to the electrolysis module 3 in terms of flow technology. Here, the return pipeline 9 is introduced into the electrolysis module 3 at the deepest possible connection point, so that the water column in the gas separator 5 is relatively close to the liquid level L S A correspondingly high hydrostatic pressure is achieved. A feed pump 13 is connected to the return line 9 and, in normal operation of the electrolyser, actively feeds or circulates the water separated from the phase mixture from the gas separator 3 into the electrolysis module 3. The feed pump 13 is supplied with electric current.

[0051] In normal operation of the electrolysis module 3, Figure 1 The simple circuit described above supplies water for the electrolysis reaction, wherein the water is also used to cool the battery cells. As a product gas of the electrolysis, the hydrogen produced is introduced into the gas separator 3 for hydrogen together with excess water as a phase mixture. Phase separation occurs in the gas separator 3, and the gaseous hydrogen is separated from the liquid water, extracted from the circuit via the gas line 19 for hydrogen H2 and supplied to other applications. In order to maintain the water circulation in the circuit, a delivery pump 4 is provided in the circuit. In addition, the consumed water is compensated by adding softened water, so-called "VE water", to the gas separator 3 in a controlled manner via a delivery line 21 with a regulating fitting 23.

[0052] The gas separator 5 is designed and arranged at a height difference Δh above the electrolysis module 3 so that in the shutdown state, the electrolysis module 3 can be automatically filled with water only by the height difference Δh. Here, the height difference Δh is set so that the liquid level L in the electrolysis module 3 is provided. M and the liquid level L in the gas separator 3 S The pressure difference between the available and driven pressure is at least 0.05 bar to 0.5 bar, in particular 0.1 bar, see correspondingly Figure 3 , which explains the principle of horizontal compensation.

[0053] The filling concept for the electrolysis module 3 is completely self-sufficient and inherently very reliable. It does not rely on additional and expensive external supply devices and redundant systems or backup solutions for conveying or filling with the aid of pumps. By designing and arranging the gas separator 5 at a sufficient height above the electrolysis module 3, a water level L is usually maintained in the gas separator 5 during operation. S or horizontal L S , and the hydrostatic delivery pressure is already provided inherently in the system for possible shut-off operations, especially in emergency shut-offs on safety technology. Of course, this filling scheme can also be advantageously used for conventional and planned shut-offs, for example for maintenance purposes.

[0054] In this case, the gas separator 5 is designed as a horizontal container, which has a surface 11 as large as possible as a phase interface, so that despite the elevated arrangement of the gas separator 5 relative to the electrolysis module 3 at the height difference Δh, a particularly effective phase separation and a reduced installation space, especially in terms of the installation height, are possible. The delivery pump 13 in the return line 9 is designed so that it has a low pressure loss coefficient in the idle state, so that rapid filling is ensured in cooperation with the gas separator 3 emptied via the return line 9. Typically, a pressure loss coefficient ζ of less than ζ=5, in particular less than ζ=3, is set in the delivery pump.

[0055] During normal operation or regulation operation of the electrolyzer 1, an electrolysis current is supplied to the electrolysis module 3, so that water generates hydrogen H2 and oxygen as product gases in the electrolysis module 3. The hydrogen H2 is supplied as a product gas in a mixture with water to the gas separator 3, wherein water is separated from the hydrogen H2 in the gas separator 3. During shutdown operation, the electrolysis current is stopped and the safety shut-off device is activated. Here, due to the height difference Δh, water is automatically driven from the gas separator 3 into the electrolysis module 3, so that the electrolysis module 3 is completely filled with water. Here, the electrolysis module is automatically filled with water until the liquid level L of the water in the gas separator 3 reaches Δh. S and the liquid level L in the electrolysis module M A stationary and safe state is thereby achieved, and the electrolysis module 5 with its critical components such as membranes and electrodes is immersed in water. Dry operation is essentially prevented, in particular, and in particular no active electrical supply system or redundant backup solutions have to be used.

[0056] Taking into account the design and arrangement of safety technology, the filling scheme of the present invention can be flexibly applied to more complex electrolyzers 1. Figure 2, an electrolyser 1 with a plurality of electrolysis modules 3a, 3b, 3c is described by way of example. Here, three electrolysis modules 3a, 3b, 3c are provided, which are connected to the gas separator 3 via a common product flow line 7. For this purpose, on the output side of the electrolysis modules 3a, 3b, 3c, the corresponding lines lead into the common product flow line 7. In addition, the electrolysis modules 3a, 3b, 3c are connected to the return line 9 via corresponding connecting lines 15a, 15b, 15c. In each of the connecting lines 15a, 15b, 15c, a regulating valve 17a, 17b, 17c is provided so that individual control is achieved. The regulating valves 15a, 15b, 15c are mechanically designed for a minimum flow rate, which cannot be lowered during regulation, so that a rapid and largely unimpeded return flow through the return line 9 can be achieved for filling one or more of the electrolysis modules 3a, 3b, 3c. In said electrolyser 1 as well, in an emergency situation, water is then automatically driven from the gas separator 3 into the electrolysis module 3 due to the height difference Δh, so that the electrolysis module 3 is completely filled with water.

[0057] exist Figure 3 1 shows a simplified diagram of the time profile of the liquid level L during safety shutdown in order to explain the principle. The time t is plotted on the abscissa and the level L of the liquid level of the corresponding component is plotted on the ordinate. Starting from the time t0, starting from normal operation, the shutdown state operation of the electrolyzer 1 is started. At this time, the level L is present in the gas separator 5. S And in the electrolysis module L M There is level L M . L applies here S >L M , so that initially a correspondingly high pressure difference is provided in the electrolysis facility 1 due to the predetermined height difference Δh as a driving force for causing rapid filling by level compensation.

[0058] In the shutdown mode, at time t0, the electrolysis current is stopped and the safety shut-off device is activated. In this case, due to the height difference Δh, water is automatically driven from the gas separator 3 into the electrolysis module 3, and the electrolysis module 3 is quickly filled with water. Filling is automatically carried out with water until the liquid level L in the gas separator 5 reaches S and the liquid level or level L in the electrolysis module 3 M Balance. The liquid level or level L of the water in the gas separator 5 S As time t decreases, the liquid level or level L in the electrolysis module 3 M Increase accordingly until the two liquid levels L M and L S Therefore, a level compensation is caused in a short time, so that the time t AAccording to the design of the electrolyzer 1, the time interval t for level compensation is A Only about 60-120 seconds to several minutes. This is fast enough to reliably prevent dry running.

[0059] When the current supply is suddenly stopped and thus the electrolysis process is stopped, the gas and water are separated in the electrolysis module 3. A certain water level appears in the electrolysis module 3. By arranging the gas separator 3 clearly above the electrolysis module 3 at a corresponding height difference Δh in the electrolysis facility, and by designing the delivery pump 13 and other fluid components to have a small pressure loss coefficient ζ, the pipeline path through the return line 9 can be traversed sufficiently quickly, and very rapid level compensation occurs automatically. The height difference Δh corresponds to the effective pressure loss coefficient ζ of the entire fluid path of the return line 9, including any fluid elements such as pumps or valves. eff can be adapted and can be selected accordingly larger or smaller when designing the electrolyzer 1 .

[0060] The invention provides a self-regulating filling concept for an electrolyser 1 with very high reliability, since no active components are used, and therefore failure of active components is impossible. The facility safety of the electrolyser 1 and the effective protection of the electrolysis module 3 against dry running are also maintained here, even in the case of possible faults, such as power failure, failure of the pump control device, failure of the control valve control device, incorrect operation or pump damage. In addition, a very simple and cost-effective solution is provided by this, since no expensive additional equipment is required, and only the existing equipment and the design of the electrolyser 1 are used in a targeted and intelligent manner. The application of the concept is particularly feasible and advantageous for every electrolyser with a pump device in the circuit - under atmosphere or under pressure.

Claims

1. An electrolyser (1) for producing hydrogen (H2) and oxygen (O2) as product gases, the electrolyser comprising an electrolysis module (3) and a gas separator (5), the gas separator being designed to separate the product gas from water, wherein the electrolysis module (3) is connected to the gas separator (5) via a product flow line (7) for the product gas, and wherein a return line (9) for the separated water is provided with a feed pump (13), the return line connecting the gas separator (5) to the electrolysis module (3), It is characterized in that The gas separator (5) is designed and arranged on a height difference (Δh) above the electrolysis module (3) so that in a shutdown state, the electrolysis module (3) can be automatically filled with water driven only by the height difference (Δh), wherein the delivery pump (13) has a small pressure loss coefficient ζ in the shutdown state, so that rapid filling in a current-free state is ensured in conjunction with the gas separator (3) that can be emptied via the return line (9).

2. The electrolyzer (1) according to claim 1, wherein the gas separator (3) is designed as a horizontal container so that a large surface (11) is provided as a phase interface between the liquid phase and the gas phase.

3. The electrolyser (1) according to claim 1 or 2, wherein the return line (9) opens into the lower region of the electrolysis module (3).

4. The electrolyser (1) according to claim 1, wherein the height difference (Δh) is set in such a way that at least 0.05 bar to 0.5 bar, in particular 0.1 bar, is provided as a driving pressure difference for the filling.

5. The electrolyser (1) according to any one of the preceding claims, wherein the pressure loss coefficient ζ of the delivery pump (13) is less than ζ=5, in particular less than ζ=3.

6. The electrolyser (1) according to any one of the preceding claims, wherein a plurality of electrolysis modules (3a, 3b, 3c) are provided, which are connected to the gas separator (3) via a common product flow line (7).

7. The electrolyzer (1) according to claim 6, wherein the electrolysis modules (3a, 3b, 3c) are connected to the return line (9) via corresponding connecting lines (15a, 15b, 15c), and regulating valves (17a, 17b, 17c) are arranged in the connecting lines.

8. The electrolyser (1) according to claim 7, wherein the regulating valve (15a, 15b, 15c) is mechanically designed for a minimum flow rate, which cannot be dropped below the minimum flow rate during regulation.

9. A method for operating an electrolyser (1), wherein an electrolyser (1) according to any of the preceding claims is provided, and wherein in normal operation an electrolysis current is supplied to an electrolysis module (3), so that water in the electrolysis module (3) produces hydrogen (H2) and oxygen as product gases, wherein the product gas is supplied to the gas separator (3) as a phase mixture consisting of water and product gas, wherein water is separated from the product gas in the gas separator, and wherein in shutdown operation the electrolysis current is stopped and a safety shutdown is initiated, characterized in that Only due to the height difference (ΔH) is water automatically driven from the gas separator (3) through the return line (9) into the electrolysis module (3), wherein water flows through the feed pump (13) arranged without current and the electrolysis module (3) is filled, wherein rapid filling is ensured in the without current state.

10. The method according to claim 9, wherein the filling with water is carried out automatically until the water levels in the gas separator (3) and the electrolysis module (3) are equalized.

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