Collection line for electrolysis

Abstract

The invention relates to an electrochemical cell (1) for electrolysis, the electrochemical cell (1) comprising opposite main surfaces (2) and discharge channels (3) arranged between the main surfaces (2) for discharging an electrolysis product, the discharge channels (3) opening out into a collecting channel portion (4), the collecting channel portion (4) extending from one main surface (2) to the other main surface (2) of the electrochemical cell (1) and forming an opening (5) in a perpendicular direction to the main surfaces (2) with a circumferential line (6), the discharge channels (3) opening out into the collecting channel portion (4) approximately tangentially to the circumferential line (6). The invention further relates to an electrolyser (9) comprising a plurality of stacked electrochemical cells (1) and to an electrolysis method.

Description

Description JUEL Collecting line for electrolysis TECHNICAL FIELD

[0001] The invention relates to an electrochemical cell for electrolysis, an electrolyzer and a method for operating an electrolyzer. BACKGROUND D

[0002] Process equipment plays a central role in industrial production and energy generation. They exhibit a number of characteristics that determine their performance and efficiency. The design and arrangement of internal channels, in particular, plays a crucial role. Many of these equipments contain a multitude of such internal channels, which serve to discharge a mixture or a pure liquid and gas phase into a collecting channel.

[0003] These devices are found in a wide range of applications, including water electrolysis stacks, galvanic cells of all kinds, fuel cell stacks, redox flow battery stacks, plate heat exchangers, specialized chemical reactors, and more. They all feature a specific flow pattern that allows the fluid to flow from the channels running in the plane of the individual cells into a collecting channel perpendicular to them. This collecting channel thus connects the individual channels to one another.

[0004] This collecting channel is also called a manifold. In the case of proton exchange membrane (PEM) electrolyzers, a gas-liquid mixture is discharged through the manifold. Generally, in such systems, the goal is to achieve the finest possible distribution of the gas in the liquid until the targeted and monitored separation of the gas and liquid phases in a separator. Specific focus on a finely dispersed distribution aims to avoid larger stationary gas cushions in the manifold.

[0005] The occurrence of such gas pockets can lead to a variety of negative effects. These include, among others, the local drying out of electrochemical components, inadequate cooling, embrittlement, and corrosion. Furthermore, gas pockets lead to a higher categorization within the assessment of individual pressure equipment according to the Pressure Equipment Directive. In combination with failing safety measures, they can even lead to property damage and personal injury. In the case of vertically stacked stacks, the risk of stationary gas pockets within the manifold is greatly reduced due to its vertical orientation and the associated natural buoyancy of the gas in the main flow direction. However, the problem of gas pockets in horizontally arranged manifolds or transitions from vertical to horizontal remains.

[0007] One possible solution to this problem is to increase the water flow. However, this would lead to a significant increase in the size of the pumps, causing unnecessary economic expenditure and energy consumption, and thus reducing the efficiency of the system. Increasing the water flow reduces the gas volume fraction and increases the flow velocity, resulting in a more finely dispersed gas. In some cases, this solution may encounter design limitations.

[0008] An alternative solution is to reduce the flow cross-section at the beginning of the collecting channel, especially in the area of ​​low mass flows. However, this approach can lead to increased pressure losses, which in turn can reduce the efficiency of the system. Furthermore, the implementation of this approach is very complex from a manufacturing perspective. For example, stacked parts of a vessel require different geometries. must be manufactured individually instead of being mass-produced, which slows down the production process and increases costs.

[0009] The challenges become even greater when one considers the ever-increasing power densities and efficiency requirements of modern industry. In particular, water electrolysis, which has the potential to make a significant contribution to combating global warming, is reaching the limits of what is realistically feasible. Increasing power density and efficiency is essential to achieving climate protection goals. However, the technical and economic challenges associated with implementing these improvements pose significant obstacles. SUMMARY OF THE INVENTION

[0010] The object of the invention is to provide an electrochemical cell that prevents or at least reduces phase separation during electrolysis. Furthermore, the object of the invention is to provide a corresponding electrolyzer. Finally, the object of the invention is to provide an improved method for operating an electrolyzer.

[0011] The problem addressed to an electrochemical cell is solved by an electrochemical cell for electrolysis, the electrochemical cell comprising opposing main surfaces and discharge channels arranged between the main surfaces for discharging an electrolysis product. The discharge channels open into a collecting channel section, wherein the collecting channel section extends from one main surface to the other main surface of the electrochemical cell and represents an opening perpendicular to the main surfaces with a circumferential line. According to the invention, the discharge channels open into the collecting channel section approximately tangentially to the circumferential line.

[0012] The invention addresses the problem to be solved by a specific adaptation of the channel geometry at the transition of the discharge channels of each electrochemical cell into the collecting channel. The invention provides that the discharge channels flow approximately tangentially into the collecting channel. If a specific flow rate is exceeded, which depends on the geometry of the collecting channel and the phase fraction of the mixture, a type of vortex flow is formed due to the resulting momentum input.

[0013] This refers to a flow that, in addition to the axial (i.e., in the direction of the main axis of the collecting channel), also has a tangential (i.e., perpendicular to the main axis of the collecting channel and parallel to the inner wall of the collecting channel) velocity component. This vortex flow prevents gas from accumulating in the upper region of the collecting channel due to gravity. Due to the formation of a vortex flow, the mixture is mixed in a finely dispersive manner, thus avoiding gas cushions and their negative effects.

[0014] In an advantageous embodiment of the invention, the circumference of the collecting channel section is circular. Due to the circular geometry, a medium (liquid, gas) moves with less resistance. This promotes the formation of vortices around the entire periphery of the collecting channel section, which can lead to a stronger and more uniform vortex flow. Furthermore, circular shapes are often simpler and more cost-effective to manufacture, as standardized manufacturing processes and tools can be used. Finally, circular structures generally exhibit greater structural integrity, which can increase the longevity and reliability of the collecting channel section.

[0015] In a further advantageous embodiment of the invention, the discharge channels open into the collecting channel section at least over a portion of the circumferential line of the collecting channel section, evenly distributed. This can have several advantages. For example, a uniform distribution can contribute to creating a more uniform flow within the collecting channel. This can lead to more efficient flow dynamics. In particular, this can lead to a more uniform distribution of the flowing medium and to a homogeneous mixture in the collecting channel. Generally, evenly distributed discharge channels ensure the formation and maintenance of a stable vortex flow in the collecting channel.

[0016] These positive effects are advantageously further enhanced if the discharge channels flow into the collecting channel section evenly distributed over the entire circumference of the collecting channel section.

[0017] Advantageously, the electrochemical cell comprises a membrane electrode assembly having an ion-conducting polymer membrane layer flanked by electrodes and a gas diffusion layer arranged on an anode side of the membrane electrode assembly, wherein the discharge channels connect the gas diffusion layer to the collection channel section.

[0018] An ion-conducting polymer membrane layer, often referred to as a proton exchange membrane (PEM), reliably meets the basic requirements, such as proton transport from the anode to the cathode side and the spatial separation of hydrogen and oxygen produced during electrolysis. An anion exchange membrane (AEM) functions analogously in AEM electrolyzers. Potentially dangerous mixing of the two gases is avoided, and because the membrane forms a physical barrier between the electrodes, it can contribute to the production of high-purity hydrogen. Furthermore, unlike other types of electrolysis, such as alkaline electrolysis, PEM electrolysis can be operated at lower temperatures and pressures, resulting in higher overall efficiency and lower operating costs. The invention is also suitable for use in alkaline or AEM electrolyzers to prevent phase separation and its negative consequences.

[0019] By directly incorporating the removal channels into the individual cells as a link between the gas diffusion layers and the collection channel, the gases (hydrogen and oxygen) generated during electrolysis can be efficiently removed. This can help prevent the gases from blocking active sites on the electrode, which can improve the performance and efficiency of the electrochemical cell. Furthermore, by removing the gases directly from the gas diffusion layer, Excessive pressure build-up in the electrochemical cell can be avoided, which can contribute to improved safety and longevity of the electrochemical cell. The electrochemical cell according to the invention is particularly advantageous for an anode-side collecting channel section. In common polymer electrolyte membrane water electrolyzers (PEMWE), the gases generated by electrolysis, hydrogen (H2) and oxygen (O2), are usually separated by a polymer electrolyte membrane. However, aging phenomena or unusual stresses such as unexpected or high differential pressures can cause holes or cracks in the membrane. These can allow a higher gas permeation than normal, particularly during prolonged differential pressure operation. Oxygen that has transferred to the hydrogen side can be removed relatively easily by the cathode, which usually contains platinum. Furthermore, the hydrogen gas flow is twice as high as the oxygen gas flow. Consequently, such a transfer is considered less critical.Of particular importance, however, is the passage of hydrogen to the oxygen side of the membrane. A high level of hydrogen passage is particularly problematic in areas with low oxygen flow in the oxygen collection channel. This can create an ignitable gas mixture that can potentially ignite on the dry surface of the anodic collection channel, especially if surface inhomogeneities or catalytic particles are present that adhere locally to the surface.

[0021] The object directed to an electrolyzer is achieved by an electrolyzer comprising several stacked electrochemical cells according to the invention, wherein these electrochemical cells are arranged in alignment so that the collecting channel sections form a continuous collecting channel running in the stacking direction. Preferably, the collecting channel begins where, in the flow direction, the first discharge channel flows into the collecting channel. Avoiding "dead volume" promotes the formation of a vortex flow. "Dead volume" refers to areas where the fluid is stagnant or moving very slowly.

[0022] Avoiding dead volume promotes the formation of this vortex flow for several reasons. First, the fluid can flow unhindered through the collecting channel, promoting a more uniform and efficient flow, thus leading to improved flow dynamics. Second, with no dead volume, the energy of the incoming fluid is distributed more evenly across the entire cross-section of the collecting channel. This promotes efficient energy distribution. Third, stagnation zones are prevented, where the fluid flows slowly or not at all, thus hindering the formation of vortex flows.

[0023] The object directed to a method for operating an electrolyzer is achieved by an electrolysis process in which water (H2O) is supplied as a reactant and hydrogen (H2) and oxygen (O2) are produced as product gases, wherein on the anode side the oxygen product gas, which also contains hydrogen as a foreign gas, is introduced in a product stream into an anode-side collecting channel and transported away via this, characterized in that the product stream is introduced into the collecting channel approximately tangentially to a circumferential line of the collecting channel, so that a vortex flow is created and a uniform areal wetting of the inner surface in the collecting channel is effected.

[0024] It is advantageous if the oxygen product gas is introduced into the collecting channel at various points along the circumference. The oxygen product gas is already supplied to the collecting channel in several product streams anyway. Distributing these product streams along the circumference rather than at a single point promotes a homogeneous and stable vortex flow in the collecting channel.

[0025] No additional components or sensors are required. All individual cells can still be manufactured identically. The design of the already The required channels can be designed to optimally utilize inertial forces to ensure safe operation without incurring additional costs. Efficiency losses and increased CAPEX due to oversized pumps are avoided without compromising functionality. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] FIG 1 shows a section of a cell frame according to the prior art with layers, FIG 2 shows a further section of the cell frame of FIG 1,

[0028] FIG 3 shows a schematic representation of a part of the cell frame of an electrochemical cell according to the invention and

[0029] FIG 4 shows a schematic representation of a channel system with collection channel and discharge channels of an electrolyzer according to the invention. DESCRIPTION OF THE EMBODIMENT

[0030] FIG. 1 shows a section through a cell frame 17 according to the prior art for an electrochemical cell 1, in particular an electrolysis cell or a fuel cell. In the present example, the inner profile of the cell frame 17 is stepped, but other designs are also possible. Arranged in the cell frame 17 are a first gas diffusion layer 8, a second gas diffusion layer 9, and a membrane-electrode unit 7 between them. The membrane-electrode unit 7 comprises an ion-conducting polymer membrane layer flanked by electrodes. The polymer membrane layer and electrodes, as well as any seals, are not shown in FIG. 1, since they are not relevant to understanding the invention.Relevant, however, are the anode side 14 and the cathode side 15 of the membrane electrode assembly 7 as well as the collecting channel section 4, which represents a breakthrough over the entire thickness of the cell frame 17, as well as a discharge channel 3, which connects the first gas diffusion layer 8 on the anode side 14 with the collecting channel section 4.

[0031] FIG. 2 shows a view of a section along the line AA in FIG. 1. The section runs in particular longitudinally through the discharge channel 3 and transversely to the collecting channel section 4. According to the prior art, the collecting channel section 4 has a space-optimized, essentially rectangular shape with rounded corners, and the discharge channel 3 opens essentially vertically into this collecting channel section 4.

[0032] FIG 3 is a highly simplified schematic representation of a section of an electrochemical cell 1, in particular of a part of the cell frame 17 of the electrochemical cell 1 according to the invention. The electrochemical cell 1 according to the invention comprises opposing main surfaces 2. Discharge channels 3 for discharging an electrolysis product are arranged between the main surfaces 2 of the electrochemical cell 1 and open into a collecting channel section 4. The collecting channel section 4 extends from one main surface 2 to the other main surface 2 of the electrochemical cell 1 and represents an opening 5 in a direction perpendicular to the main surfaces 2 with a circular circumferential line 6. In other words, in an electrochemical cell 1, the collecting channel section 4 extends continuously from the anode side 14 to the cathode side 15 of the electrochemical cell 1. The collecting channel section 4 is open on both sides.This makes it possible to stack a large number of identical electrochemical cells 1 axially and to connect them hydraulically in parallel and electrically in series.

[0033] According to the invention, discharge channels 3 are arranged in the cell frame 17 on the anode side 14, where they open tangentially into the collecting channel section 4. The vortex flow 16 resulting from the tangential inflow is indicated. For the cathode side 15, another such collecting channel section with corresponding discharge channels can be provided in the cell frame 17, but this is not shown in FIG. 3. This additional collecting channel section can, but need not, have tangential discharge channels for the corresponding product gas opening into it.

[0034] FIG. 4 shows a schematic representation of a product channel system for the anode side 14 of an electrolyzer 10 according to the invention with discharge channels 3 of the first four ("1", "2", "3", and "4") and the last electrochemical cells 1 designated "n". The channel system of the cathode side 15 is omitted for reasons of clarity.

[0035] The electrochemical cells 1 are arranged in alignment, so that the collecting channel sections 4 form a continuous collecting channel 12 running in the stacking direction 11 (y-direction). Figure 4 shows the vortex flow 16 generated by the almost tangential inflow of the product gas into the collecting channel 12. The collecting channel 12 begins where, in the flow direction 13 of the product flow in the collecting channel 12, the first discharge channel 3 or a group of first discharge channels 3 flows into it. REFERENCE NUMBER LIST 1 electrochemical cell 2 Main area 3 discharge channel 4 Collecting channel section 5 Breakthrough 6 circumference line 7 Membrane electrode assembly with an ion-conducting polymer membrane layer flanked by electrodes 8 first gas diffusion layer 9 second gas diffusion layer 10 Electrolyzer 11 Stacking direction 12 Collecting channel 13 Flow direction of a product stream 14 Anode side 15 Cathode side 16 Vortex flow 17 cell frames

Claims

Claims What is claimed: 1 . An electrochemical cell (1 ) for electrolysis, the electrochemical cell (1 ) comprising opposite main surfaces (2) and discharge channels (3) arranged between the main surfaces (2) for discharging an electrolysis product, wherein the discharge channels (3) open into a collecting channel section (4), wherein the collecting channel section (4) extends from one main surface (2) to the other main surface (2) of the electrochemical cell (1 ) and represents an opening (5) in the direction perpendicular to the main surfaces (2) with a circumferential line (6), characterized in that the discharge channels (3) open into the collecting channel section (4) approximately tangentially to the circumferential line (6).

2. The electrochemical cell (1) according to claim 1, wherein the circumferential line (6) of the collecting channel section (4) is circular.

3. The electrochemical cell (1) according to one of claims 1 or 2, wherein the discharge channels (3) open into the collecting channel section (4) in a uniformly distributed manner at least over part of the circumferential line (6) of the collecting channel section (4).

4. The electrochemical cell (1) according to claim 3, wherein the discharge channels (3) open into the collecting channel section (4) in a uniformly distributed manner over the entire circumferential line (6) of the collecting channel section (4).

5. The electrochemical cell (1) according to one of the preceding claims, comprising a membrane electrode unit (7) and a first gas diffusion layer (8) arranged on an anode side (14) of the membrane electrode unit (7), wherein the discharge channels (3) connect the first gas diffusion layer (8) to the collecting channel section (4).

6. An electrolyzer (10) comprising a plurality of stacked electrochemical cells (1) according to one of the preceding claims, wherein the cells are arranged in alignment such that the collecting channel sections (4) form a continuous collecting channel (12) extending in the stacking direction (11).

7. The electrolyzer (10) according to claim 6, wherein the collecting channel (12) begins where, in the flow direction (13) of a product stream in the collecting channel (12), the first discharge channel (3) opens into the collecting channel (12).

8. Electrolysis process in which water (H2O) is supplied as a reactant and hydrogen (H2) and oxygen (O2) are produced as product gases, wherein on the anode side the oxygen product gas, which also contains hydrogen as a foreign gas, is introduced in a product stream into an anode-side collecting channel (12) and transported away via this, characterized in that the product stream is introduced into the collecting channel (12) approximately tangentially to a circumferential line (6) of the collecting channel (12) so that a vortex flow (16) is created and a uniform surface wetting is effected in the collecting channel (12).

9. Electrolysis process according to claim 8, wherein the oxygen product gas is introduced into the collecting channel (12) at different points on the circumferential line (6).

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