Device for humidifying a gas stream, air system for supplying a fuel cell stack with air

Abstract

The invention relates to a device for humidifying a gas stream, preferably air, comprising a semipermeable membrane (1) through which water vapor and heat can be transported. According to the invention, the membrane (1) is folded in a lamellar fashion into a plurality of membrane lamellae, which are arranged in a star-shaped fanning within a housing (2). They separate a radially outer gas space (3) from a radially inner gas space (4). The invention further relates to an air system for supplying air to at least one fuel cell stack, comprising a device according to one of the claims according to the invention, wherein the inner gas space (4) is assigned to a cold, dry air stream and the outer gas space (3) is assigned to a warm, moist air stream.

Description

[0001] The present invention relates to a device for humidifying a gas stream, preferably air, having the features of the preamble of claim 1. Furthermore, the invention relates to an air system for supplying air to at least one fuel cell stack, comprising the device according to the invention. State of the art

[0002] A PEM fuel cell electrochemically converts hydrogen and oxygen into electrical energy, heat, and water. The main component of a PEM fuel cell is the membrane-electrode assembly. This comprises a proton electrolyte membrane arranged between an anode and a cathode. To operate the fuel cell, hydrogen is supplied to the anode side and oxygen to the cathode side in the form of air. For efficient operation, the proton electrolyte membrane must be kept permanently and comprehensively moist. Without humidification, the membrane begins to dry out on the cathode side at cell temperatures above approximately 60°C. The decisive factor is the supplied air, which dries out the cathode electrode at temperatures above 60°C faster than product water can be replenished through the electrochemical reaction.The consequences of localized drying of the membrane are reduced efficiency of the energy conversion process, reduced fuel cell lifetime, and localized damage to the proton electrolyte membrane. Conversely, with sufficient humidification, a higher process temperature can be selected and a smaller fuel cell cooling circuit can be designed.

[0003] To ensure sufficient humidification of the membrane at all times and prevent drying out, external air humidification in the form of a separate humidification component, the humidifier, can be used. This supplies the supply air stream with water taken from the exhaust air exiting the cathode side. Water transport typically occurs via a membrane or hollow fibers. The moist exhaust air stream is guided along one side of the membrane or hollow fibers, with the exhaust air stream transferring the water it contains to the drier supply air stream guided on the opposite side of the membrane or within the hollow fibers. The effectiveness of this transport process depends essentially on the size of the available transport surface - in the case of the membrane, on the membrane surface.

[0004] The biggest disadvantage of external humidification is the relatively large installation space required. Furthermore, the membrane is subject to aging during operation, which reduces the efficiency of the humidifier over its life cycle. If the humidifier can no longer deliver the required humidification capacity, it typically has to be completely replaced, which is expensive and time-consuming.

[0005] The present invention is therefore concerned with the task of optimizing the ratio of the available membrane surface area in a humidifier to the required installation space. To achieve this task, the device with the features of claim 1 is proposed. Advantageous further developments of the invention can be found in the subclaims. Furthermore, an air system with a device according to the invention is specified. Disclosure of the invention

[0006] Proposed is a device for humidifying a gas stream, preferably air, comprising a semipermeable membrane through which water vapor and heat can be transported. According to the invention, the membrane is folded lamellarly into a plurality of membrane lamellae, which are arranged in a star-shaped fan-out within a housing. They separate a radially outer gas space from a radially inner gas space.

[0007] Folding the membrane significantly increases the surface area available for water transport. The star-shaped fan-out improves the humidifier's flow characteristics while simultaneously requiring minimal space.

[0008] In a further development of the invention, it is proposed to arrange the membrane around an inlet pipe that can be supplied with the gas stream to be humidified or with a humid gas stream and is in fluid communication with the inner gas space. In a preferred embodiment of the invention, the gas to be humidified is guided via the inlet pipe, and the spatial connection to the inner gas space is established via an opening at a downstream end of the inlet pipe. This preferred embodiment stabilizes the star-shaped fanning of the membrane and fixes it in place.

[0009] In a further development of the aforementioned embodiment, it is proposed that the housing have an end-face access for the inlet pipe, through which a gas stream flowing in the inner gas chamber can also be discharged. This ensures that the gas entering the inner gas chamber at the end of the inlet pipe flows along the entire length of the membrane before exiting the humidifier through the housing. This ensures that a maximum membrane surface is utilized for water transport.

[0010] In a modification of the aforementioned embodiment, it is proposed that the inlet pipe be divided into an inlet and an outlet channel via an internal division, wherein both the inlet channel and the outlet channel are in fluid communication with the inner gas space. Preferably, the inlet channel connects to the inner gas space through an opening at the downstream end of the inlet pipe, while the inlet of the gas leaving the inner gas space into the outlet channel is arranged upstream. The inlet into the outlet channel is positioned such that the gas entering the inner gas space at the end of the inlet pipe flows along the entire length of the membrane before entering the outlet channel and leaving the humidifier. This ensures that a maximum membrane surface is utilized for water transport.

[0011] It is further proposed that a spacer be arranged between the inlet pipe and the membrane. This spacer holds the individual membrane lamellae in position and stabilizes the star-shaped fanning of the membrane within the housing, particularly with regard to collapse due to pressure drop. Since the distance between two membrane lamellae within the star-shaped fanning is much smaller on the inside than on the outside, proper operation of the humidifier imposes requirements on operating parameters such as volume flow and maximum tolerable pressure reduction. These requirements can be influenced constructively through the design of the spacer, which provides this preferred embodiment with a further advantage.

[0012] Furthermore, it is proposed that an inlet and an outlet be guided through the housing. These outlets are arranged at an axial distance from each other at the level of the membrane and are each in fluid communication with the outer gas space. Preferably, the axial distance is selected such that a fluid entering the outer gas space via the inlet must flow a maximum distance along the membrane before reaching the outlet.

[0013] The advantage of this configuration compared to, for example, a front-end introduction of the fluid into the outer gas space is that no components that reproduce the complex edge structure of the membrane need to be installed at the front ends of the membrane, thus reducing manufacturing costs. In a preferred embodiment of the invention, the water-releasing gas is guided via the inlet and outlet of the housing.

[0014] In a further development of the previous embodiment, it is proposed that the membrane rests circumferentially against an inner circumferential surface of the housing, which has a circumferential recess at the level of the inlet and outlet, connecting the spaces formed between the membrane lamellae. This embodiment has the advantage that, except in the recesses, no flow develops transversely to the lamella direction. This increases the efficiency of water transport. The fluid entering the outer gas space is distributed over the entire circumference of the membrane via the recesses, so that the entire membrane surface is used for humidification.

[0015] In a further development of the previous embodiment, it is proposed that, to seal the inner gas space from the outer gas space, adjacent membrane lamellae are glued together at at least one end face. This preferred embodiment achieves a seal at the end faces of the membrane without the need for a separate seal and / or additional components, which, due to the lamella-shaped folding of the membrane, would have to follow a complex shape and would therefore be complex to manufacture.

[0016] Alternatively or additionally, it is proposed that at least one seal be arranged between the diaphragm fins and an inner end face of the housing to seal the inner gas space from the outer gas space. A seal installed separately on the housing eliminates the need for the diaphragm fins to rest against the inner peripheral surface of the housing, thus allowing more design flexibility in the housing layout. Furthermore, an end face seal simultaneously stabilizes the star-shaped diaphragm fins.

[0017] It is further proposed that the housing can be opened via a movably hinged and / or removable cover so that the membrane can be replaced. This preferred embodiment offers the advantage that when signs of aging appear on the membrane, only the membrane can be replaced, not the entire humidifier. This reduces maintenance effort and increases the humidifier's range of applications.

[0018] Furthermore, an air system for supplying air to at least one fuel cell stack is proposed, comprising a device according to the invention, wherein preferably the inner gas space is assigned to a supply air flow and the outer gas space is assigned to an exhaust air flow.

[0019] Preferred embodiments of the invention are explained in more detail below with reference to the figures. These show: Fig. 1 a longitudinal section through a first preferred embodiment of a device according to the invention, Fig. 2 a longitudinal section through a second preferred embodiment of a device according to the invention Fig. 3 a simplified perspective view of a lamellar folded and star-shaped fanned-out membrane for a device according to the invention and Fig. 4 a simplified cross-section through a device according to the invention. Detailed description of the characters

[0020] The Fig. The device shown in Figure 1 for humidifying a gas stream comprises a membrane 1 folded in a lamella-like manner to form a plurality of membrane lamellae, which are arranged in a star-shaped fan-out (see, for example, Fig. 4) is accommodated within a housing 2. The membrane 1 rests circumferentially on an inner circumferential surface 12 of the housing 2. It separates an inner gas space 4 from an outer gas space 3 (see example Fig. 4). An inlet pipe 5 leads through a frontal access 6 to the housing 2 into the housing 2, around which the membrane 1 is placed. In Fig. 1, the front access 6 to the housing 2 is arranged in a removable cover 16. A gas stream to be humidified is introduced into the housing 2 of the humidifier through the inlet pipe 5. The gas stream to be humidified enters the inner gas chamber 4 through inlet openings 17 provided for this purpose at the downstream end of the inlet pipe 5 and flows in an axial direction along the membrane lamellae. A water-transporting gas stream is introduced into the housing 2 via an inlet 10. This gas stream is distributed circumferentially around the membrane 1 via a recess 13 arranged at the level of the inlet, enters the outer gas chamber 3 and flows in an axial direction along the membrane lamellae. Water is transported through the membrane 1 from the outer gas chamber 3 to the inner gas chamber 4.To seal the outer gas space 3 from the inner gas space 4, adjacent membrane lamellae are glued together at their front edges (see . Fig. 3).

[0021] The gas flow in the outer gas chamber 3 leaves the housing 2 via an outlet 11. The gas flows from the outer gas chamber 3 into a further recess 13 arranged at the level of the outlet 11 and from there leaves the housing 2 via the outlet 11. The gas flow in the inner gas chamber 4 leaves the housing 2 via the front inlet 6.

[0022] A further preferred embodiment of a device according to the invention for humidifying a gas stream is described in Fig. 2. This also has a lamellar folded membrane 1, which is arranged in a star-shaped fan-out within a housing 2. The membrane 1 lies circumferentially against an inner circumferential surface 12 of the housing 2 and separates an inner gas space 4 from an outer gas space 3 (see example Fig. 4). An inlet pipe 5 leads into the housing 2 through a frontal access 6 to the housing 2. A spacer 9 is arranged around the inlet pipe 5, on which the membrane 1 is mounted. Fig. 2, the front access 6 to the housing 2 is also arranged in a removable cover 16. The inlet pipe 5 is internally divided into an inlet channel 7 and an outlet channel 8. A gas stream to be humidified is introduced into the housing 2 of the humidifier through the inlet channel 7. The gas stream to be humidified enters the inner gas chamber 4 through inlet openings 17 provided for this purpose at the downstream end of the inlet pipe 5 and flows in the axial direction along the membrane lamellae. A water-transporting gas stream is introduced into the housing 2 via an inlet 10. This gas stream is distributed circumferentially around the membrane 1 via a recess 13 arranged at the level of the inlet 10, enters the outer gas chamber 3 and flows in the axial direction along the membrane lamellae. In this case, water is transported through the membrane 1 from the outer gas chamber 3 to the inner gas chamber 4. Unlike in the Fig. 1, seals 14 are applied to the inner end faces 15 of the housing for the end-face sealing of the outer gas space 3 from the inner gas space 4.

[0023] The gas flow in the outer gas space 3 leaves the housing 2 via an outlet 11. The gas flows from the outer gas space 3 into a recess 13 arranged at the level of the outlet 11 and from there leaves the housing 2 via the outlet 11. The gas flow in the inner gas space 4 leaves the inner gas space 4 via outlet openings 18 arranged at the upstream end of the inlet pipe 5, via which it enters the outlet channel 8 of the inlet pipe 5 and is discharged from the housing 2.

[0024] In the described embodiments, the humidifier is operated in a cocurrent configuration, meaning that both gas streams have the same flow direction. To operate the humidifier in a countercurrent configuration, the inlet 10 and outlet 11 can be interchanged.

[0025] Fig. 3 shows, by way of example, a lamella-shaped folded and star-shaped fanned-out membrane 1, which is placed around an inlet pipe 5. It separates a radially outer gas space 3 from a radially inner gas space 4. To seal the outer gas space 3 from the inner gas space 4, adjacent membrane lamellas are bonded together at their end faces via an adhesive bond 19.

[0026] Fig.Figure 4 shows, by way of example, a lamellar-folded and star-shaped membrane 1 in a housing 2, which is placed around an inlet pipe 5. It separates a radially outer gas space 3 from a radially inner gas space 4.

Claims

[1] Device for humidifying a gas stream, preferably air, comprising a semipermeable membrane (1) through which water vapor and heat can be transported, characterized by , that the membrane (1) is folded in a lamellar manner into a plurality of membrane lamellae which are arranged in a star-shaped fanning within a housing (2) and thereby separate an outer gas space (3) in the radial direction from an inner gas space (4) in the radial direction. [2] Device according to any one of the preceding claims, characterized by , that the membrane (1) is arranged around an inlet pipe (5) which can be supplied with the gas stream to be humidified or with a moist gas stream and is in fluidic communication with the inner gas space (4). [3] Device according to claim 2, characterized by , that the housing (2) has an end-face access (6) for the inlet pipe (5), through which an additional gas flow in the inner gas space (4) can be discharged. [4] Device according to claim 2, characterized by , that the inlet pipe (5) is divided by an internal division into an inlet (7) and an outlet channel (8), wherein both the inlet channel (7) and the outlet channel (8) are in fluidal connection with the inner gas space (4). [5] Device according to any one of the preceding claims 2 to 4, characterized by , that a spacer (9) is arranged between the inlet pipe (5) and the membrane (1), which holds the individual membrane lamellae in position and stabilizes the star-shaped fanning of the membrane (1) within the housing (2), in particular with regard to a collapse caused by pressure drop. [6] Device according to any one of the preceding claims, characterized by, that an inlet (10) and an outlet (11) are guided through the housing (2), which are arranged at an axial distance from each other in the axial direction at the level of the membrane (1) and are each in fluidal communication with the outer gas space (3). [7] Device according to claim 6, characterized by , that the membrane (1) is circumferentially abutted an inner circumferential surface (12) of the housing (2), which has a circumferentially circumferential recess (13) at the level of the inlet (10) and the outlet (11), which connects the spaces formed between the membrane lamellae. [8] Device according to claim 7, characterized by , that to seal the inner gas space (4) from the outer gas space (3), adjacent membrane lamellae are bonded together at at least one end face. [9] Device according to any one of the preceding claims, characterized by, that at least one seal (14) is arranged between the membrane lamellae and an inner end face (15) of the housing (2) to seal the inner gas space (4) from the outer gas space (3). [10] Device according to any one of the preceding claims, characterized by , that the housing (2) can be opened via a movable hinge and / or removable cover (16) so that the membrane (1) can be replaced. [11] Air system for supplying air to at least one fuel cell stack, comprising a device according to one of the preceding claims, wherein the inner gas space (4) is assigned to an air supply flow and the outer gas space (3) is assigned to an exhaust air flow.

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