Method and apparatus for separating water from a water-containing gas stream, anode subsystem for a fuel cell system

Abstract

The invention relates to a method for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem (13) for supplying a fuel cell stack (14) with hydrogen, using a water separator (1), comprising the steps: - Introducing the gas flow into a cavity (2) of the water separator (1) so that the gas flow is slowed down and water contained in the gas flow rains off, - Guiding the gas flow along at least one surface area (7) of a ceiling (4) bounding the cavity (2), wherein the surface area (7) has a machining (5) and / or coating (6) influencing the contact angle, such that the contact angles differ in at least two adjacent surface areas (7) of the ceiling (4) and water droplets (3) condensing on the ceiling (4) accumulate and drip off at the boundary between the two surface areas (7), and - Discharge of the gas flow from the cavity (2). The invention further relates to a device (10) for separating water from a water-containing gas stream and an anode subsystem (13) for a fuel cell system with a device (10) according to the invention.

Description

[0001] The invention relates to a method and a device for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem for supplying a fuel cell stack with hydrogen. The invention therefore further relates to an anode subsystem for a fuel cell system comprising a device according to the invention. State of the art

[0002] Polymer electrolyte membrane (PEM) fuel cells convert hydrogen into electrical energy, heat, and water with the help of oxygen. The hydrogen is fed to an anode of the PEM fuel cell, and the oxygen to a cathode, which is separated from the anode by a polymer electrolyte membrane. Ambient air typically serves as the oxygen source. In practice, to increase electrical output, several fuel cells are stacked together to form a fuel cell stack. The fuel cell stack is crisscrossed by supply channels through which the individual fuel cells are supplied with hydrogen and air. The depleted anode gas and the depleted moist air escaping from the fuel cells are removed via exhaust channels.

[0003] A systemic approach has been established in which depleted anode gas is actively recirculated using a gas delivery unit and / or passively recirculated, as this still contains residual hydrogen. The recirculated anode gas also contains product water, which is transferred from the cathode side to the anode side through diffusion processes. Before the recirculated anode gas enters the fuel cell stack, the product water must be separated from the gas stream and removed. Separation is typically achieved using a water separator, which, in addition to its separation function, also performs a storage function. This means that the separated water is collected in a storage volume of the water separator. Only when the storage volume is full is a drain valve opened, through which the storage volume can be emptied.

[0004] In fuel cell systems, so-called "sedimenters" are often used as water separators, which separate the water using the principle of sedimentation. The gas stream containing the product water is fed into a cavity of the water separator, which slows the gas flow. This slows the flow. This slows the flow and separates the liquid phase from the gas phase, causing the liquid phase to fall or rain down under the force of gravity. In this way, separation efficiencies of 85% and more can be achieved. In practice, however, it has been shown that water droplets settle in the ceiling area of ​​the water separator and do not rain down, but are carried along by the gas flow towards the outlet of the water separator. This means that this water is not separated, thereby reducing the separation efficiency of the water separator.

[0005] The present invention is concerned with the task of optimizing the separation efficiency of a water separator, in particular when used in an anode subsystem of a fuel cell system.

[0006] To achieve this objective, the method having the features of claim 1 and the device having the features of claim 6 are proposed. Advantageous further developments of the invention can be found in the respective subclaims. Furthermore, an anode subsystem for a fuel cell system having a device according to the invention is specified. Disclosure of the invention

[0007] A method is proposed for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem for supplying a fuel cell stack with hydrogen, using a water separator, comprising the steps: - introducing the gas flow into a cavity of the water separator so that the gas flow is slowed down and water contained in the gas flow rains down, - guiding the gas flow along at least one surface area of ​​a ceiling delimiting the cavity, wherein the surface area has a processing and / or coating influencing the contact angle, so that the contact angles differ in at least two adjacent surface areas of the ceiling and water droplets precipitating on the ceiling accumulate and drip off at the boundary between the two surface areas, and - Discharge of the gas stream from the cavity.

[0008] The accumulation of water droplets promotes dripping. During the accumulation process, several small water droplets merge into a single large one, which – once it reaches a certain size – falls from the ceiling under the force of gravity. This means that the separation efficiency increases and fewer water droplets adhere to the ceiling, which are then entrained by the gas flow passing through the cavity.

[0009] The accumulation of water droplets is supported in this case by the fact that the cover has different contact angles in at least two adjacent surface areas. Preferably, the contact angle is <90° in a first surface area and >90° in an adjacent further surface area. To achieve the desired contact angles, at least one surface area has a treatment and / or coating that influences the contact angle.

[0010] In the first surface area, where the contact angle is < 90°, the falling water droplets spread out across the surface. At the boundary of the surface area, where the contact angle is > 90°, the water contracts and forms a droplet that can more easily detach from the ceiling and rain down.

[0011] If the surface of the water separator cover is not already hydrophilic, the contact angle in at least one surface area of ​​the cover can be specifically reduced and thus made hydrophilic (contact angle < 90°) through the proposed processing and / or coating. The wettability of the surface area increases accordingly.

[0012] If the surface of the water separator's cover is not already hydrophobic, the contact angle in at least one surface area of ​​the cover can be specifically increased and thus made hydrophobic (contact angle > 90°) through the proposed processing and / or coating. This reduces the wettability of the surface area. This not only makes it easier for the water droplets that have settled on the cover to loosen and drip off, but also reduces the number of water droplets that settle on the cover altogether. This ultimately further improves the separation efficiency of the water separator.

[0013] According to a preferred embodiment of the invention, the processing and / or coating of at least one surface area, which influences the contact angle, specifies at least one movement path for the accumulating water droplets. For this purpose, certain surface areas can be processed and / or coated differently so that they exhibit different contact angles. Specifying a direction of movement supports the accumulation of the water droplets. Furthermore, the water droplets can be directed into a central area of ​​the cavity so that they land safely in a storage volume of the water separator upon dripping.

[0014] Furthermore, it is proposed that the gas flow be guided along the at least one surface area in a flow direction that is angled to the at least one movement path. This means that the accumulating water droplets and the gas flow move in different directions. This measure supports the separation of the water from the gas flow. Furthermore, the risk of the water droplets precipitating on the ceiling being entrained by the gas flow is reduced.

[0015] It is further proposed that the gas flow be swirled within the cavity. The swirling of the gas flow contributes to the detachment of the water droplets from the ceiling and raining down. The swirling can be achieved by introducing the gas flow into the cavity via an inlet arranged substantially tangentially with respect to the cavity's footprint. Alternatively or additionally, at least one flow-guiding element, for example in the form of a baffle, a vane, and / or a wing, can be arranged within the cavity.

[0016] According to an advantageous embodiment of the invention, an installation component with defined surface properties is used to form the coating that influences the contact angle of at least one surface area of ​​the ceiling. The surface properties of the installation component can be used to set a contact angle of < 90° or > 90°, as required. The installation component can be easily integrated, thus simplifying the production of the water separator. This applies in particular if the alternatively or additionally proposed processing of at least one surface area of ​​the ceiling can be omitted. The installation component can also be subsequently integrated into the water separator, so that existing water separators can also be retrofitted with a corresponding installation component. The installation component is preferably self-adhesive, thus further simplifying production.

[0017] Furthermore, a device for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem for supplying a fuel cell stack with hydrogen, is proposed. The device comprises a water separator with a cavity defined by a cover having, in at least one surface region, a treatment and / or coating that influences the contact angle, such that the contact angles differ in at least two adjacent surface regions of the cover.

[0018] The proposed device is particularly suitable for carrying out the previously described method according to the invention, so that the same advantages can be achieved with it. In particular, the separation efficiency of the water separator can be improved, since the accumulating water droplets detach more easily from the ceiling and then rain down. At the same time, the risk of water droplets precipitating on the ceiling being entrained by the gas flow guided along the ceiling and carried out of the water separator is reduced. In particular, it prevents water droplets carried by the gas flow from entering a downstream gas delivery unit or even the fuel cell stack.

[0019] The proposed coating and / or treatment of at least one surface area preferably makes it hydrophilic (contact angle < 90°) or hydrophobic (contact angle > 90°), depending on the properties of the adjacent surface of the ceiling. If the adjacent surface area is neither clearly hydrophilic nor clearly hydrophobic, the adjacent surface area can also have a coating and / or treatment that influences the contact angle.

[0020] Preferably, the processing and / or coating of the at least one surface region that influences the contact angle forms at least one movement path for the accumulating water droplets. The accumulating water droplets can be directed in a targeted manner via the at least one movement path, for example, into a central region of the cavity, where the then raining water droplets are reliably collected. The at least one movement path preferably runs at an angle to the flow direction of the gas flow along the ceiling. This means that the accumulating water droplets and the gas flow move in different directions. This facilitates the separation of the water from the gas flow, and the water droplets that settle on the ceiling cannot be easily swept away by the gas flow.

[0021] Furthermore, it is proposed that the cavity have an inlet arranged essentially tangentially with respect to the cavity's floor plan. With such an inlet arrangement, turbulence in the gas flow is created within the cavity. This turbulence supports the precipitation of the accumulating water droplets that settle on the ceiling. Alternatively or additionally, it is proposed that at least one flow-guiding element be arranged within the cavity to turbulence the gas flow.

[0022] In a further development of the invention, it is proposed that the coating influencing the contact angle be a preferably self-adhesive, built-in component with defined surface properties. The built-in component can be retrofitted, thus simplifying the manufacture of a device according to the invention. This applies particularly to a self-adhesive built-in component. Furthermore, the built-in component enables the retrofitting of existing water separators.

[0023] Since the preferred application of the invention is an anode subsystem for supplying a fuel cell stack with hydrogen, an anode subsystem for a fuel cell system comprising a device according to the invention is further proposed. Since the separation efficiency of the device is improved, the ingress of water into the fuel cell stack can be minimized.

[0024] If the anode subsystem has a gas conveying unit downstream of the water separator, this is also protected from the ingress of water.

[0025] The invention and its advantages are described in more detail below with reference to the accompanying drawings. These show: Fig. 1 a schematic longitudinal section through a fuel cell stack with an anode subsystem, Fig. 2 a plan view of a ceiling defining a cavity of a water separator of a first device according to the invention for separating water from a gas stream, Fig. 3 is a plan view of a cover defining a cavity of a water separator of a second device according to the invention for separating water from a gas stream, and Fig. 4 a plan view of a ceiling which defines a cavity of a water separator of a third device according to the invention for separating water from a gas stream. Detailed description of the drawings

[0026] Fig. 1 shows a fuel cell stack 14 comprising a plurality of fuel cells 15 arranged one above the other. To supply each fuel cell 15 with hydrogen, the fuel cell stack 14 is traversed by a supply channel 16. A disposal channel 17 traversing the fuel cell stack 14 serves to remove depleted anode gas. Since this still contains hydrogen, it is recirculated via an anode subsystem 13, i.e., fed back to the fuel cells 15. The anode subsystem 13 comprises a gas delivery unit 18 for this purpose. Since recirculated anode gas contains water that has passed from the cathode side to the anode side through diffusion processes, the anode subsystem 13 additionally comprises a device 10 for separating water from the anode gas stream. This is intended to prevent water from entering the gas delivery unit 18 and / or the fuel cell stack 14.The device 10 for separating water can be designed in particular according to the following with reference to the . Fig. 2 to 4 described preferred embodiments of a device 10 according to the invention.

[0027] The Fig. The preferred embodiment of a device 10 according to the invention for separating water, shown in Figure 2, comprises a water separator 1 having a cavity 2 with an inlet 11 and an outlet 12. The water-containing anode gas stream is guided into the cavity 2 via the inlet 11. Since the inlet 11 is arranged essentially tangentially with respect to the layout of the cavity 2, the anode gas stream is swirled. The cavity 2 is delimited by a ceiling 4, on which water droplets 3 are deposited as the water-containing anode gas stream is guided. These droplets can be entrained by the gas stream in the direction of the outlet 12 of the cavity 2 (see arrow in the Fig. 2), so that the separation efficiency of the water separator 1 deteriorates. To prevent this, the ceiling 4 has a treatment 5 in at least one surface area 7 that influences the contact angle of water. This means that the contact angles differ in at least two adjacent surface areas of the ceiling 4. A first surface area 7 is preferably hydrophilic or is made hydrophilic by the coating 5 (contact angle < 90°). At least one further surface area 7 adjacent to this, in contrast, is hydrophobic or is made hydrophobic by the coating 5 (contact angle > 90°). This means that easily and difficultly wettable surface areas are adjacent to one another, which leads to water droplets 3 accumulating and raining down from the ceiling 4 more easily.

[0028] In the Fig. In the device 10 for separating water shown in Figure 3, the surface area 7 does not have a treatment 5, but rather a coating 6, for example in the form of a self-adhesive built-in component with defined surface properties. This has essentially the same effect as the coating 5 of the device 10 of Figure 3. Fig. 2. This means that a surface area 7 is created which has a different contact angle than at least one adjacent further surface area, so that the accumulation of water droplets 3 and the raining of the water droplets 3 is promoted.

[0029] As exemplified in the Fig.As shown in Figure 4, the coating 6 can form movement paths 8 for the accumulating water droplets 3, so that they move in a specific direction, in particular away from the outlet 12. The movement paths 8 are preferably arranged at an angle to a flow direction of the anode gas stream, so that the water droplets 3 are deflected in a targeted manner. This reduces the risk of them being entrained by the anode gas stream.

Claims

[1] Method for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem (13) for supplying a fuel cell stack (14) with hydrogen, using a water separator (1), comprising the steps: - introducing the gas flow into a cavity (2) of the water separator (1) so that the gas flow is delayed and water contained in the gas flow rains down, - guiding the gas flow along at least one surface region (7) of a ceiling (4) delimiting the cavity (2), wherein the surface region (7) has a processing (5) and / or coating (6) influencing the contact angle, so that the contact angles differ in at least two adjacent surface regions (7) of the ceiling (4) and water drops (3) precipitating on the ceiling (4) accumulate and drip off at the boundary between the two surface regions (7), and - Discharge of the gas stream from the cavity (2). [2] Method according to claim 1, characterized by that by the processing (5) and / or coating (6) of the at least one surface area (7) influencing the contact angle, at least one movement path (8) for the accumulating water drops (3) is specified. [3] Method according to claim 2, characterized bythat the gas flow is guided along the at least one surface region (7) in a flow direction (9) which is at an angle to the at least one movement path (8). [4] Method according to one of the preceding claims, characterized by that the gas flow is swirled within the cavity (2). [5] Method according to one of the preceding claims, characterized by that a preferably self-adhesive installation component with defined surface properties is used to form the coating (6) influencing the contact angle of at least one surface area (7) of the ceiling (4). [6] Device (10) for separating water from a water-containing gas stream, in particular from a water-containing anode gas stream in an anode circuit of an anode subsystem (13) for supplying a fuel cell stack (14) with hydrogen, comprising a water separator (1) with a cavity (2) which is delimited by a cover (4) which has, in at least one surface area (7), a processing (5) and / or coating (6) which influences the contact angle, so that the contact angles differ in at least two adjacent surface areas (7) of the cover (4). [7] Device (10) according to claim 6, characterized bythat the processing (5) and / or coating (6) of the at least one surface region (7) influencing the contact angle forms at least one movement path (8) for the accumulating water droplets (3), wherein preferably the at least one movement path (8) runs at an angle to the flow direction (9) of the gas flow along the ceiling (4). [8] Device (10) according to claim 6 or 7, characterized by that the cavity (10) has an inlet (11) arranged substantially tangentially with respect to the floor plan of the cavity and / or at least one flow-guiding element is arranged in the cavity (2). [9] Device (10) according to one of claims 6 to 8, characterized by that the coating (6) influencing the contact angle is a preferably self-adhesive, built-in component with defined surface properties. [10] Anode subsystem (13) for a fuel cell system comprising a device (10) according to any one of claims 6 to 9.

Images