DE102017221983A1 - Variable fiber density humidifier for a fuel cell system, fuel cell system, and vehicle having such - Google Patents

Abstract

A humidifier (39) for a fuel cell system (100), comprising a housing (391) having a first channel (392) for a first gas stream (394) and a second channel (393) for a second gas stream (395) A humidifier section (B) in which the first channel (392) and the second channel (393) are separated by a water vapor permeable array of hollow fiber membranes (396), the first gas stream (394) bypassing the hollow fiber membranes (396) and the second gas stream (395) traversing the hollow fiber membranes (396) to optimize the water transfer capability, it is proposed that the density of the arrangement of at least a part of the hollow fiber membranes (396) in the flow direction of the second gas flow (395) is not constant. In addition, a fuel cell system and a Vehicle revealed.

Description

The invention relates to a humidifier for a fuel cell system, comprising a housing having a first channel for a first gas stream and a second channel for a second gas stream, a humidifier, in which the first channel and the second channel separated by a water vapor permeable arrangement of hollow fiber membranes are, wherein the first gas stream flows around the hollow fiber membranes and the second gas stream flows through the hollow fiber membranes, a fuel cell system and a vehicle.

Fuel cells use the chemical transformation of a fuel with oxygen to water to generate electrical energy. For this purpose, fuel cells contain as a core component the so-called membrane electrode assembly (MEA for membrane electrode assembly), which is a microstructure of an ion-conducting (usually proton-conducting) membrane and in each case on both sides of the membrane arranged catalytic electrode (anode and cathode). The latter mostly comprise supported noble metals, in particular platinum. In addition, gas diffusion layers (GDL) can be arranged on both sides of the membrane-electrode arrangement on the sides of the electrodes facing away from the membrane.

As a rule, the fuel cell is formed by a multiplicity of stacked MEAs whose electrical powers add up. As a rule, bipolar plates (also called flow field plates or separator plates) are arranged between the individual membrane electrode assemblies, which ensure that the individual cells are supplied with the operating media, ie the reactants, and are usually also used for cooling. In addition, the bipolar plates provide an electrically conductive contact to the membrane-electrode assemblies.

During operation of the fuel cell, the fuel (anode operating medium), in particular hydrogen, is supplied to the anode via a flux field of the bipolar plate and electrochemically oxidized to protons with release of electrons (H ₂ → 2 H ⁺ + 2 e ^- ). About the electrolyte or the membrane, which gas-tight and electrically isolated from each other, the reaction chambers, a transport of protons from the anode compartment into the cathode compartment. The electrons provided at the anode are supplied to the cathode via an electrical line.

The cathode is supplied during operation of the fuel cell, oxygen or an oxygen-containing gas mixture (for example air) as a cathode operating medium, so that a reduction of O ₂ to O ^2- with absorption of the electrons takes place ½ O ₂ + 2 e ^- → O ^2-). At the same time, the oxygen anions in the cathode compartment react with the protons transported via the membrane to form water (O ^2- + 2 H ⁺ → H ₂ O).

In order to supply a fuel cell stack with the operating media, this has an anode supply and a cathode supply. The anode supply includes an anode supply path for supplying the anode operating medium into the anode chambers of the fuel cell and an anode exhaust gas path for discharging an anode exhaust gas out of the anode chambers. In addition, a recirculation line is arranged in the anode supply in order to feed unused and discharged from the fuel cell stack hydrogen in the stack again. The cathode supply includes a cathode supply path for supplying the cathode operating medium into the cathode chambers of the fuel cell and a cathode exhaust path for discharging a cathode exhaust gas out of the cathode compartments.

The operating media are usually conditioned in several ways before being supplied to the fuel cell. For this purpose, service media supplies often include a humidifier to increase the humidity of the operating gases since many polymer electrolyte membranes of fuel cells must be kept moist for proper function.

Membrane humidifiers are widely used in which the operating medium to be humidified absorbs the moisture of a moist gas via water-vapor-permeable membranes. As the wet gas, the cathode or anode exhaust gas is often used because they have a relatively high humidity due to the fuel cell reaction. Such humidifiers can be used to realize high power densities of the fuel cell stack. As membranes hollow fiber membranes are often used, which have a tube-like geometry.

The prerequisite for effective water transfer behavior during humidification is the bilateral overflow of the membranes over their entire surface.

Since the size of the humidifier can exceed the hose or pipe diameter of incoming and outgoing lines to the humidifier many times, usually funnel-shaped connecting elements, so-called housing cover or ports are used. This is due to space and Packagerestriktionen as possible to save space. These restrictions in the design of the housing cover, for example, lead to flow separation or turbulences in the humidifier, which has a direct effect on the flow of the hollow fiber bundle of a humidifier and the resulting flow. An uneven flow or flow through the hollow fibers leads to a lower overall efficiency of water transfer in the humidifier. Deflections in the upstream and downstream ducts to the humidifier lead to further inhomogeneities in the flow of the gases.

A uniform flow through the humidifier is desirable both fresh air and exhaust air side, in order to achieve the highest possible water transfer capacity with the same humidifier volume.

Thus, CFD (Computational Fluid Dynamics Computational Fluid Dynamics) simulations and adaptation of the design of the inlet and outlet cover, the flow of the package of hollow fiber membranes is made as homogeneous as possible. The covers are constructed very expensive for a homogeneous flow of the fiber package to take as little space to complete.

Another approach to achieve the highest possible water transmission capacity is in the DE 10 2005 028 718 A1 discloses a hollow fiber assembly of a humidifier for a variable fiber density fuel cell which is intended to balance flow inhomogeneities.

In the DE 10 2013 017 375 A1 describes a humidifier with hollow fiber membranes for a fuel cell, are provided in the spacers between the hollow fibers to produce a constant packing density.

DE 10 2012 206 227 A1 discloses a membrane humidifier for a fuel cell with a glass fiber paper as a diffusion medium.

The object of the invention is to at least partially overcome the disadvantages of the prior art and to provide a humidifier for a fuel cell system in which the water transmission capability is optimized.

This object is achieved by a humidifier, a fuel cell system having the humidifier and a vehicle with the fuel cell system having the features of the independent claims.

Advantageous embodiments of the invention are characterized in the subclaims.

According to the invention, a humidifier for a fuel cell system is provided, which has a housing with a first channel for a first gas stream and with a second channel for a second gas stream. In addition, a humidifier area is provided, in which the first channel and the second channel are separated from one another by a water-vapor-permeable arrangement of hollow-fiber membranes. The first gas stream flows around the hollow-fiber membranes and the second gas stream flows through the hollow-fiber membranes, wherein the density of the arrangement of at least part of the hollow-fiber membranes is not constant in the direction of flow of the second gas stream.

The first and second gas streams are the cathode gas for the fuel cell reaction and the cathode exhaust gas, between which a moisture exchange is to be effected.

The invention relates to a variable density of the arrangement of the hollow-fiber membranes (number of hollow-fiber membranes per unit volume). A higher density leads on the side surrounding the hollow fiber membrane (shell side) to a higher flow resistance, a low density corresponding to a lower flow resistance. The arrangement of the hollow-fiber membranes is preferably designed so that in the areas which are flown through more than other areas due to the flow guide, the density is increased in order to increase the flow resistance at this point and to direct a portion of the gas stream in areas with less flow , As a result, a uniform overflow of the hollow-fiber membrane is advantageously achieved.

According to the invention, it is therefore provided to adjust the density of the arrangement of the hollow-fiber membranes by varying the space / volume available for the arrangement along the flow direction of the second gas flow.

The variation of the density can be orthogonal to the orientation of the hollow fiber membranes in one or two spatial directions.

In a preferred embodiment of the humidifier, the density decreases from a first end of the hollow fiber membranes to the second end of the hollow fiber membranes, which may be in one or two spatial directions, i. the arrangement of the hollow fiber membranes is simply expanded or narrowed.

The density of the arrangement of the hollow-fiber membranes can be varied continuously or discontinuously along the flow direction of the second gas stream, in order to be advantageous for differently designed humidifier to be suitable. Thus, for example, the arrangement of the hollow-fiber membranes in the middle can be the densest and widen to the two ends or vice versa.

According to a particularly preferred embodiment of the humidifier, the hollow-fiber membranes are arranged in at least one bundle, which is present in the housing of the humidifier, so that advantageously the packaging of the humidifier is facilitated.

If at least two bundles are provided in the humidifier, they may be designed identically and / or differently with regard to the density of the arrangement of the hollow-fiber membranes. Advantageously, almost any density gradients or other density profiles can be designed with these bundles in order to optimize the water exchange between the two gas streams by optimizing the flow behavior.

The bundles can be arranged in a plane next to each other or in addition to each other, so that the desired density profiles are limited only by the available space.

With regard to the configuration of the density in the at least one bundle, reference is made to the preceding statements with regard to the arrangement of the hollow-fiber membranes.

The bundles are preferably provided with means defining the shape and thus the density of the bundle (s). These means may be, for example, yarn, nets, perforated films / sheets, or rigid solid support structures within the bundle. The means advantageously facilitate the adjustment of the density of the arrangement of the hollow-fiber membranes during assembly.

In particular, when bundles have a more complex density profile along the fiber direction, the means are to be used particularly advantageously.

As an aid, stencil-like or screened holders can also serve to join the assemblies. The brackets are filled with the required number of hollow fiber membranes for the corresponding density and then preferably fixed. The brackets remain in the bundle, and one or more means may be provided along the hollow fiber membranes to ensure retention of the defined density in all areas of the array.

The means are preferably designed and introduced into the bundle or bundles so that they can remain in the respective bundle without noticeably influencing the flow.

It is also provided to select the means such that they can be at least partially removed from the bundle or bundles after their completion. This can be done for example by dissolving in suitable solvents. Thus, advantageously a possibly given flow resistance can at least be reduced.

After design or formation of the respective bundle, this is preferably additionally held in the desired shape by means of a fixing means. Suitable fixatives are known to those skilled in principle. For example, an epoxy resin can be used with which at least the ends of the hollow fiber membranes are fixed.

The humidifier has preferably arranged on the housing housing cover for the inlet and outlet of the first gas stream and for the inlet and outlet of the second gas stream, in particular the housing cover for the entry of the gas streams are formed and arranged such that the arrangement of Hollow fiber membranes in the flow area of at least the gas flow, which flows around the hollow fiber membranes, their greatest density, since the back pressure is highest here.

As a result, a uniform overflow of the hollow fiber membrane surface is advantageously achieved, the cost of construction and the required space for the housing cover is reduced.

The invention also relates to a fuel cell system with the above-described humidifier and a vehicle which is provided with the humidifier and / or fuel cell system.

Further preferred embodiments of the invention will become apparent from the remaining, mentioned in the dependent claims characteristics. The various embodiments of the invention mentioned in this application are, unless otherwise stated in the individual case, advantageously combinable with one another.

• 1 ein Blockschaltbild eines Brennstoffzellensystems gemäß einer bevorzugten Ausgestaltung;
• 2 eine geschnittene Ansicht eines erfindungsgemäßen Befeuchters; und
• 3 eine geschnittene Ansicht des Befeuchters gemäß 2 entlang der in 2 gezeigten Schnittlinie A - A.

The invention will be explained below in embodiments with reference to the accompanying drawings. Show it:

• 1 a block diagram of a fuel cell system according to a preferred embodiment;
• 2 a sectional view of a humidifier according to the invention; and
• 3 a sectional view of the humidifier according to 2 along the in 2 shown section line A - A ,

1 shows a total of 100 designated fuel cell system according to the present invention. The fuel cell system 100 is part of a not further illustrated vehicle, in particular an electric vehicle having an electric traction motor, by the fuel cell system 100 is supplied with electrical energy.

The fuel cell system 100 comprises as a core component a fuel cell stack 10 containing a plurality of stacked single cells 11 having alternately stacked membrane-electrode assemblies (MEAs) 14 and bipolar plates 15 be formed between which optional gas diffusion layers are arranged. Every single cell 11 thus includes one MEA each 14 , which has an ion-conducting polymer electrolyte membrane, not shown here, as well as on both sides arranged thereon catalytic electrodes, namely an anode and a cathode, which catalyze the respective partial reaction of the fuel cell reaction and in particular can be formed as coatings on the membrane. Between a bipolar plate 15 and the anode thus becomes an anode compartment 12 formed and between the cathode and the next bipolar plate 15 the cathode compartment 13 ,

To the fuel cell stack 10 to supply with the operating media, the fuel cell system 100 on the one hand, an anode supply 20 and on the other hand, a cathode supply 30 on.

The anode supply 20 includes an anode supply path 21 which feeds an anode operating medium (the fuel), for example hydrogen, to the fuel cell stack 10 serves. The anode supply path 21 connects a fuel storage 23 with an anode inlet of the fuel cell stack 10 , The anode supply 20 further includes an anode exhaust path 22 containing the anode exhaust gas from the fuel cell stack 10 dissipates. The anode operating pressure is via an actuating means 24 in the anode supply path 21 set. There is also a fuel recirculation line 25 provided, which the anode exhaust path 22 with the anode supply path 21 combines.

The cathode supply 30 includes a cathode supply path 31 for supplying an oxygen-containing cathode operating medium, in particular air, and a cathode exhaust gas path 32 which removes the cathode exhaust gas from the fuel cell stack 10 dissipates. For conveying and compressing the cathode operating medium is in the cathode supply path 31 a compressor 33 arranged here as a mainly electric motor driven compressor 33 is designed, the drive via a with a corresponding power electronics 35 equipped electric motor 34 he follows. The compressor 33 may also be through a in the cathode exhaust path 32 arranged turbine 36 (optionally with variable turbine geometry) are supported by a common shaft (not shown) driven.

The cathode supply 30 may also according to the illustrated embodiment, a wastegate line 37 having the cathode supply line 31 with the cathode exhaust gas line 32 connects, so a bypass of the fuel cell stack 10 represents.

One in the wastegate pipe 37 arranged adjusting means 38 serves to control the amount of the fuel cell stack 10 immediate cathode operating medium. All adjusting means 24 . 26 . 38 of the fuel cell system 100 can be designed as controllable or non-controllable valves or flaps. Corresponding further actuating means can be in the lines 21 . 22 . 31 and 32 be arranged to the fuel cell stack 10 isolate from the environment.

The fuel cell system 100 further comprises a humidifier according to the invention 39 on. The humidifier 39 on the one hand is in the cathode supply path 31 arranged to be flowed through by the cathode operating gas. On the other hand, the humidifier 39 so in the cathode exhaust path 32 arranged to be flowed through by the cathode exhaust gas. Alternatively or additionally, the humidifier 39 in the anode supply 20 , in particular between the anode supply path 21 and the anode exhaust path 22 , be arranged (not shown).

Various other details of the anode and cathode supply 20 . 30 are in the simplified 1 not shown for reasons of clarity.

2 shows a humidifier 39 , the one housing 391 with a first channel 392 for a cathode operating gas stream as the first gas stream 394 which, in the illustration of the 2 runs from top to bottom. The first channel 392 has a housing cover 3910 for gas supply and a housing cover 3911 for gas discharge, over which the first channel 392 in the cathode supply path 31 of the fuel cell system 100 is integrated.

The housing 391 has a second channel 393 for a cathode exhaust stream as the second gas stream 395 on, in the presentation of the 2 from left to right. The second channel 393 has a housing cover 3912 for gas supply and a housing cover 3913 for gas discharge 3913 on, over which the second channel 393 in the cathode exhaust path 32 of the fuel cell system 100 is integrated. The housing 391 has a humidifier area B on, in which the first channel 392 and the second channel 393 by an arrangement of a plurality of water vapor permeable hollow fiber membranes 396 are separated from each other. A dry cathode exhaust stream occurs as a dry first gas stream 394 through the housing cover 3910 in the first channel 392 and flows around the hollow fiber membranes 396 , A dry cathode operating gas stream occurs as a wet second gas stream 395 through the housing cover 3912 in the second channel 393 one in the humidifier area B through the hollow fiber membranes 396 is formed. In the humidifier area B gives the moist second gas stream 395 through the water vapor permeable hollow fiber membranes 396 Moisture to the dry first gas stream 394 from. A moist first gas stream 394 then leaves the first channel 392 of the humidifier 39 and a dry second gas stream 395 leaves the second channel 393 of the humidifier 39 , The hollow fiber membranes 396 are arranged such that their highest density in the region of entry of the first gas stream 394 is provided, which then partially to the flared portion of the hollow fiber membranes 396 Redirected with a lower density.

In 3 is a cross section of the humidifier 39 according to 2 shown along the line AA. In this illustration, it can be seen that the hollow fiber membranes 396 in a variety of bundles 397 are arranged, whose density is freely adjustable ..

LIST OF REFERENCE NUMBERS

100

The fuel cell system

10

fuel cell stack

11

single cell

12

anode chamber

13

cathode space

14

Membrane electrode assembly (MEA)

15

Bipolar plate (separator plate, flow field plate)

20

anode supply

21

Anode supply path

22

Anode exhaust gas path

23

fuel tank

24

actuating means

25

Brennstoffrezirkulationsleitung

30

cathode supply

31

Cathode supply path

32

Cathode exhaust path

33

compressor

34

electric motor

35

power electronics

36

turbine

37

Waste gate line

38

actuating means

39

humidifier

391

casing

392

first channel

393

second channel

394

first gas flow (dry) in front of the humidifier

394

first gas flow (moist) after the humidifier

395

second gas flow (humid) in front of the humidifier

395

second gas flow (dry) after the humidifier

396

Hollow fiber membrane

397

bunch

3910

first housing cover

3911

first housing cover

3912

second housing cover

3913

second housing cover

B

Befeuchterbereich

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102005028718 A1 [0013]
• DE 102013017375 A1 [0014]
• DE 102012206227 A1 [0015]

Claims (9)

A humidifier (39) for a fuel cell system (100), comprising a housing (391) having a first channel (392) for a first gas stream (394) and a second channel (393) for a second gas stream (395), a humidifier area (39) B) in which the first channel (392) and the second channel (393) are separated by a water vapor permeable arrangement of hollow fiber membranes (396), wherein the first gas stream (394) flows around the hollow fiber membranes (396) and the second gas stream (395) ) flows through the hollow fiber membranes (396), characterized in that the density of the arrangement of at least a portion of the hollow fiber membranes (396) in the flow direction of the second gas stream (395) is not constant. Humidifier (39) after Claim 1 , characterized in that the density of the arrangement of the hollow fiber membranes (396) is adjusted by varying the volume occupied by the arrangement of the hollow fiber membranes (396) along the flow direction of the second gas flow (395). Humidifier (39) after Claim 1 or 2 , characterized in that the density of the arrangement of the hollow-fiber membranes (396) varies continuously or discontinuously along the flow direction of the second gas flow (395), and / or that the density of the arrangement of the hollow-fiber membranes (396) along the flow direction of the first gas flow (396) 394) varies continuously or discontinuously, preferably decreases. Humidifier (39) according to one of Claims 1 to 3 , characterized in that the hollow fiber membranes (396) are present in at least one bundle (397) in the housing (391). Humidifier (39) after Claim 4 , characterized in that at least two bundles (397) are provided, which are identical and / or designed differently with regard to the density of the arrangement of the hollow-fiber membranes (396). A humidifier (39) according to any one of the preceding claims, characterized in that the bundle (s) (397) comprise means defining the shape of the bundle or bundles (397) and optionally the shape of the bundle or bundles (397) with a fixing agent is fixed. Humidifier (39) according to one of the preceding claims, characterized in that the humidifier (39) on the housing (391) arranged housing cover (3910, 3911, 3912, 3913) for the inlet and outlet of the first gas stream (394) and for the Inlet and outlet of the second gas stream (395), wherein at least the housing cover (3910) for the entry of the first gas stream (394) is formed and arranged such that the density of the arrangement of the hollow fiber membranes (396) in the flow area (394, 395 ) is higher with a larger back pressure than in the area of a smaller back pressure. Fuel cell system (100) a humidifier (39) according to one of Claims 1 to 7 having. Vehicle with a humidifier (39) according to one of Claims 1 to 7 and / or with a fuel cell system (100) Claim 8 ,

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