WO2022008255A1

WO2022008255A1 - Humidification system for a fuel cell system

Info

Publication number: WO2022008255A1
Application number: PCT/EP2021/067284
Authority: WO
Inventors: Jan Hendrik OHS; Stefan Schoenbauer; Manuel Schneiter
Original assignee: Robert Bosch Gmbh
Priority date: 2020-07-07
Filing date: 2021-06-24
Publication date: 2022-01-13
Also published as: DE102020208492A1

Abstract

The present invention relates to a humidification system (100) for a fuel cell system (200). The humidification system (100) comprises: a humidifier (101) for humidifying air to be supplied to the fuel cell system (200); a primary line (103) and a secondary line (105). The primary line (103) is configured to convey air to the humidifier (101). The secondary line (105) is configured to convey air around the humidifier (101). The humidification system (100) is configured to apply, to the fuel cell system (200), a first air flow quantity of a first relative air humidity from the primary line (103), and a second air flow quantity of a second relative air humidity that is different from the first air humidity from the secondary line (105). The proposed invention also relates to a fuel cell system (200).

Description

description

title

Humidification system for a fuel cell system

State of the art

Fuel cell systems use oxygen to convert hydrogen into electrical energy while generating waste heat and water. To this end, fuel cell systems include at least one fuel cell stack made up of a number of fuel cells with an anode that is supplied with hydrogen, a cathode that is supplied with air and a polymer electrolyte membrane arranged between the anode and the cathode.

Within a membrane electrode assembly (MEA) of a fuel cell, partial electrochemical reactions of hydrogen and oxygen take place separately through a membrane. The reactions take place within a catalyst layer on a so-called active area of the MEA.

The reaction gases hydrogen and oxygen, which is provided by the air supplied, as well as cooling liquid are fed into a respective fuel cell via a so-called bipolar plate (BPP) and distributed evenly over the active surface.

In order to increase the performance of a fuel cell, a repeating unit consisting of MEA and BPP is stacked in series to form a fuel cell stack.

In order to create optimal operating conditions for a fuel cell, it is necessary for the MEA to be sufficiently well moistened under as many operating conditions as possible, since areas that are too dry one Increase membrane proton resistance and promote aging due to pitting. Furthermore, areas that are too humid lead to a loss of liquid water and thus to a blockage of gas diffusion paths, which can lead to significant mass transport losses.

A countercurrent humidifier is generally used to humidify air supplied to a fuel cell system. A counter-current humidifier consists of thin or fine capillary tubes. Highly humidified exhaust air from the fuel cell system flows inside the tubes, while unhumidified supply air from the environment flows around the tubes, so that the supply air absorbs moisture from the outlet.

Disclosure of Invention

As part of the presented invention, a humidification system and a fuel cell system are presented with the features of the respective independent patent claims. Further features and details of the invention result from the respective dependent claims, the description and the drawings. Features and details that are described in connection with the humidification system according to the invention naturally also apply in connection with the fuel cell system according to the invention and vice versa, so that the disclosure of the individual aspects of the invention is always referred to or can be referred to alternately.

The invention presented serves to enable robust operation of a fuel cell system. In particular, the presented invention serves to prevent a fuel cell from drying out in certain areas or flooding in certain areas with water.

A humidification system for a fuel cell system is thus presented. The humidification system includes a humidifier for humidifying air to be supplied to the fuel cell system, a primary line and a secondary line. The primary line is configured to direct air into the humidifier. The secondary line is configured to draw air around the humidifier to guide around. The humidification system is configured to supply the fuel cell system with a first quantity of air or with primary air from the primary line, which has a first relative humidity, and with a second quantity of air or secondary air from the secondary line, which has a second relative humidity different from the first relative humidity , to irrigate.

In the context of the present invention, humidity or moisture is to be understood as relative humidity.

The humidification system presented serves in particular to reduce or narrow a humidity range in a so-called “cross-flow design” by supplying air with lower humidity to a lower region of a respective fuel cell than to an upper region.

In order to adjust areas in a fuel cell system that are flown through with air of different humidity levels, the humidification system presented comprises two lines, a primary line and a secondary line, which flow through the fuel cell system with air of different humidity levels.

Since the primary line is configured to conduct incoming air, in particular ambient air, into the humidifier of the humidification system presented, the air flowing through the primary line is humidified by the humidifier.

Since the secondary line is configured to conduct incoming air, in particular ambient air, around the humidifier of the humidification system presented or past the humidifier, air flowing through the secondary line is not humidified by the humidifier. Accordingly, the secondary line forms a humidifier bypass.

Correspondingly, the humidity of the air provided by the primary line, ie primary air, differs from the humidity of the air provided by the secondary line, ie secondary air. In particular, the Primary air is more humid or the humidity of the primary air is higher than the humidity of the secondary air.

By generating two differently humid air flows in the form of primary air and secondary air, it is possible to flow a fuel cell system selectively or in certain areas with particularly humid or particularly dry air and, as a result, to change the operating conditions in the respective areas of the fuel cell system, in particular respective areas a respective fuel cell.

Provision can be made for the primary line and the secondary line to lead separately from one another to at least one supply connection of the fuel cell system.

In order to prevent primary air and secondary air from mixing, the primary line and the secondary line can also be continued in the area behind the humidifier of the humidification system presented. When using a short supply connection with a length of less than 500 mm, for example, primary air and secondary air are only mixed to a limited extent in the supply connection, so that there are still different humidities locally, but there is a smooth transition of the humidities and no step between the respective humidities are. A moisture jump can also be smoothed out by a membrane that is permeable to water vapor.

Alternatively, a supply connection configured for connecting to the primary line and the secondary line can also be used, which is particularly long, in particular with a length of more than 500 mm, and possibly has a separation into two gas channels in its interior.

Provision can be made for the primary line and the secondary line to be configured to be connected to a common supply connection for supplying the fuel cell system with air. In order to be connected to a common service port, the primary line and the secondary line may converge in a connector for connection to the service port. A partition, such as a wall or a membrane permeable to water vapor, can be arranged in the connecting piece in order to prevent or regulate the mixing of primary air and secondary air.

It can furthermore be provided that the primary line is configured to be connected to a primary connection of the fuel cell system and the secondary line is configured to be connected to a secondary connection of the fuel cell system in order to supply the fuel cell system with air.

In order to be connected to separate supply connections of a fuel cell system, the primary line and the secondary line can each have a connecting piece at their end. The fitting may be configured to provide flow dynamics in the corresponding supply port, to create, for example, turbulent flow or laminar flow in the corresponding supply port. For this purpose, the connection piece can be configured, for example, in a linear or radially curved manner.

Provision can furthermore be made for the humidifier to be configured to be arranged at the respective supply connections of the fuel cell system and to supply the supply connections with air via a multiplicity of integrated primary air lines.

By arranging the humidifier on respective supply connections, the supply connections can act as air lines and transport primary air and/or secondary air.

It can be provided that the cross section and/or the number of the respective primary air lines of the plurality of primary air lines are selected such that a predetermined flow pattern is established in the fuel cell system. Depending on the design of the humidifier, the capillary tubes present in the humidifier can be designed in such a way that a predetermined humidification pattern is established in the air lines. For example, a number of first capillary tubes can be made particularly thick in order to generate a high level of moisture ingress into the air flowing around the first capillary tubes, while a number of second capillary tubes can be made particularly thin in order to generate a low or, compared to the first capillary tube, less moisture ingress .

Provision can furthermore be made for the humidification system to comprise a mixing chamber for mixing air flowing out of the primary line and the secondary line.

In order to generate not only a primary air flow and a secondary air flow, but at least one additional air flow, a mixing chamber can be used, into which primary air and secondary air are introduced and from which a mixed form, i.e. tertiary air, is discharged. Accordingly, only tertiary air or primary air, secondary air and tertiary air can flow through a fuel cell system.

A humidity of the tertiary air changes depending on a ratio of primary air and secondary air introduced into the mixing chamber. Accordingly, provision can be made for the ratio to be dynamically adjusted, for example by at least partially closing the primary line and/or the secondary line, for example as a function of a state of the fuel cell system to which flow is to be applied.

It can furthermore be provided that the primary line, the secondary air line and the mixing chamber are each configured to be connected to a supply connection of the fuel cell system.

By using three separate connections, humidification of a fuel cell system can be adjusted very finely using three different air flows. It can be provided that respective connections are partially and / or temporarily closed in order to adjust the distribution of humidification in the fuel cell system.

It can also be provided that the humidifier is constructed according to the cross-flow principle, that a large number of primary lines are arranged on the humidifier, and that the humidifier is configured to flow respective primary lines with respective streams of primary air whose relative humidity differs from one another.

By using a humidifier constructed according to the cross-flow principle, a humidity gradient forms at the outlet of the humidifier over its length. If the air flowing out of the humidifier is taken off via a number of primary lines, such as pipes, which are arranged next to one another on the humidifier, a large number of primary air flows with different levels of humidity are available for separate supply to a fuel cell system. Provision can be made for only one primary line or a selection of primary lines to be connected to a fuel cell system, for example by setting a directional control valve or a flap control accordingly.

Provision can furthermore be made for the primary air line to be configured to flow air through a hot region of the fuel cell system and for the secondary air line to be configured to flow air through a cold region of the fuel cell system.

By selectively flowing primary air into a hot area, i.e. an area with a higher temperature than a cold area, a cooling effect and a humidification effect is achieved due to the high moisture input, which in combination with a selective supply of a cold area with secondary air results in a homogeneous heat and moisture distribution in a corresponding fuel cell system.

In a second aspect, the presented invention relates to a fuel cell system with a possible embodiment of the presented humidification system. It can be provided that the fuel cell system comprises a primary connection for connection to the primary line and a secondary connection for connection to the secondary line, and that the primary connection and the secondary connection are designed as a collecting line with a membrane permeable to water vapor.

In order to achieve a gradual transition between the primary air and the secondary air or to avoid a gradual transition of the various moisture inputs into the fuel cell system, a water vapor-permeable membrane is suitable, which leads to a controlled and only partial mixing of primary air and secondary air.

Provision can furthermore be made for the fuel cell system to comprise a plurality of outlet lines for blowing out air heated by the fuel cell system, the outlet lines comprising a number of primary outlets and a number of secondary outlets, and only the number of primary outlets being fluidly connected to the humidifier.

Due to the first and second outlet lines, the humidifier causes a lower pressure loss at a low flow rate, with a total water content being slightly smaller than when using a central outlet line due to the higher temperature level.

Show it:

FIG. 1 shows a possible embodiment of the humidification system according to the invention,

FIG. 2 shows a possible embodiment of the fuel cell system according to the invention,

FIG. 3 shows a possible embodiment of a humidifier of the humidifying system according to the invention. A humidification system 100 is shown in FIG. The humidification system comprises a humidifier 101 for humidifying air, a primary line 103 and a secondary line 105.

The primary line 103 is connected to the humidifier 101 so that air flowing into the primary line is guided into the humidifier 101 and humidified there.

The secondary line 105 goes around the humidifier 101 so that air flowing into the secondary line is not humidified by the humidifier.

After the humidifier 101, the primary line 103 and the secondary line 105 run separately from one another to an optional mixing chamber 107. Accordingly, primary air humidified through the primary line and secondary air that is not humidified or is dry relative to the primary air is blown into the mixing chamber 107 through the secondary line.

A mixture of primary air and secondary air is produced in the mixing chamber 107, which is referred to below as tertiary air.

In order to supply air to a fuel cell system, an outlet of the primary line, an outlet of the secondary line and an outlet of the mixing chamber are connected to respective supply connections of the fuel cell system, so that the fuel cell system is supplied with primary air, secondary air and tertiary air.

The configuration of the supply connections of the fuel cell system allows air to flow through selected areas of the fuel cell system, as is shown in detail in FIG.

Figure 2 shows a fuel cell system 200 with a primary connection 201, which is supplied with primary air through the primary line 103, as shown in Figure 1, and a secondary connection 203, which is supplied with secondary air through the secondary line 105, as shown in Figure 1 is supplied. Accordingly, more humid air flows through the primary connection 201 than through the secondary connection 203.

Furthermore, the fuel cell system 200 includes a bipolar plate 205. In the present case, the bipolar plate 205 is supplied with operating media in a so-called cross-flow specification, so that hydrogen flows from a hydrogen inlet 207 to a hydrogen outlet 209 and coolant from a coolant inlet 211 to a coolant outlet 213. Due to the cross-flow specification, a rather warm/hot area results in the upper part of the bipolar plate 205, as indicated by a first arrow 215, while a lower area, as indicated by a second arrow 217, is rather cool.

In order to prevent areas of the fuel cell system 200 from drying out or being flooded in some areas, moist primary air from the primary connection 201 flows through the warm area, whereas dry secondary air from the secondary connection 203 flows through the cold area. Accordingly, the wetter primary air humidifies the warm area to a greater extent than the drier secondary air, which has a dehumidifying effect, in the cold area.

Due to the fact that only the warm area is humidified with air that was humidified by the humidifier 101, a humid area of the fuel cell system 200 narrows compared to a structure without the humidification system 100. Accordingly, the water consumption of the fuel cell system is reduced compared to a fuel cell system without the humidification system 100.

The fuel cell system further includes a primary outlet 219 that is connected to the humidifier 101 to supply moist exhaust air from the fuel cell system 200 to the humidifier 101, and a secondary outlet 221 that discharges used air to an environment. The primary outlet 219 and the secondary outlet 221 can optionally be formed in a common outlet tube 223 which is divided into two areas by a water vapor permeable membrane 225 . Of course, the fuel cell system 200 can also be configured in a so-called co-flow or counter-flow specification.

FIG. 3 shows a humidifier 300 which is constructed according to a cross-flow principle. Moist air discharged from a fuel cell stack is conducted into the humidifier 300 through first inlets, as indicated by arrows 301 , and conducted as exhaust air out of the humidifier 300 through first outlets, as indicated by arrows 303 .

Ambient dry air is routed through primary lines, as indicated by arrows 305, into the humidifier 300 and through other primary lines, as indicated by arrows 307, as primary air to the fuel cell stack.

A curve 309 schematically shows a distribution of a relative humidity of primary air flowing through the further primary lines. Accordingly, primary ducts located at an upper edge of the humidifier 300 conduct primary air that is particularly moist, while primary ducts located at a lower edge of the humidifier conduct relatively dry primary air.

The distribution of the relative air humidity in the various primary lines can be used to flow selected areas of a fuel cell system with an exactly specified air humidity in order to provide a specific cooling capacity or a specific humidification capacity for a respective selected area.

Claims

Expectations

1. humidification system (100) for a fuel cell system (200), wherein the humidification system (100) comprises:

- a humidifier (101, 300) for humidifying the

Fuel cell system (200) to be supplied air,

- a primary line (103), and

- a secondary duct (105), the primary duct (103) being configured to direct air into the humidifier (101), the secondary duct (105) being configured to direct air around the humidifier (101), and wherein the humidification system (100) is configured to supply the fuel cell system (200) with a first amount of air from the primary line (103), which has a first relative humidity, and with a second amount of air from the secondary line (105), which has a second, different from the first Humidity has different relative humidity to flow.

2. humidification system (100) according to claim 1, characterized in that the primary line (103) and the secondary line (105) lead separately to at least one supply connection (201, 203) of the fuel cell system (200).

3. Humidification system (100) according to claim 1 or 2, characterized in that the primary line (103) and the secondary line (105) are configured to be connected to a common supply connection for supplying the fuel cell system (200) with air.

4. Humidification system (100) according to claim 1 or 2, characterized in that the primary line (103) is configured to be connected to a primary connection (201) of the fuel cell system (200) and the secondary line (105) is configured to be connected to a secondary connection ( 203) of the fuel cell system (200) for supplying the fuel cell system (200) with air.

5. Humidification system (100) according to one of the preceding claims, characterized in that the humidifier (101, 300) is configured to be arranged at respective supply connections (201, 203) of the fuel cell system (200) and the supply connections (201, 203 ) via a large number of integrated primary air lines (103) with air.

6. Humidification system (100) according to claim 5, characterized in that the respective primary air lines (103) of the plurality of primary air lines (103) are selected in terms of their cross section and/or their number such that a predetermined flow pattern is set in the fuel cell system (200).

7. humidification system (100) according to any one of the preceding claims, characterized in that the humidification system (100) comprises a mixing chamber (107) for mixing from the primary line (103) and the secondary line (105) flowing air.

8. Humidification system (100) according to claim 7, characterized in that the primary line (103), the secondary air line (105) and the mixing chamber (107) are each configured to be connected to a supply connection (201, 203) of the fuel cell system (200). to become.

9. humidification system (100) according to any one of the preceding claims, characterized in that the humidifier (300) is constructed according to the cross-flow principle, that a plurality of primary lines (105) are arranged on the humidifier (300), and that the humidifier (300) to is configured to flow respective primary lines (105) with respective flows of primary air whose relative humidity differs from one another.

10. humidification system (100) according to any one of the preceding claims, characterized in that the primary air line (103) is configured to flow a hot area of the fuel cell system (200) with air and the secondary air line (105) is configured to a cold area of the fuel cell system (200) to flow with air.

11. Fuel cell system (200) with a humidification system (100) according to any one of claims 1 to 10.

12. Fuel cell system (200) according to claim 11, characterized in that the fuel cell system (200) comprises a primary connection (201) for connecting to the primary line (103) and a secondary connection (203) for connecting to the secondary line (105), and that the primary connection (201) and the secondary connection (203) are designed as a collecting line (223) with a membrane (225) permeable to water vapor.

13. Fuel cell system (200) according to claim 11 or 12, characterized in that the fuel cell system (200) comprises a plurality of outlet lines (219, 221) for blowing out air heated by the fuel cell system (200), the outlet lines (219, 221) having a A number of primary outlets (219) and a number of secondary outlets (221), only the number of primary outlets (219) being fluidly connected to the humidifier (101).