WO2018108545A1

WO2018108545A1 - Mixing device and fuel cell comprising such a mixing device

Info

Publication number: WO2018108545A1
Application number: PCT/EP2017/080952
Authority: WO
Inventors: Stefan Loesch
Original assignee: Robert Bosch Gmbh
Priority date: 2016-12-12
Filing date: 2017-11-30
Publication date: 2018-06-21
Also published as: DE102016224652A1

Abstract

The invention relates to a mixing device for a fuel cell system for combining a flush gas of an anode space with an exhaust gas of a cathode space of at least one fuel cell, comprising an exhaust line for removing an exhaust gas from the cathode space of the at least one fuel cell and a flush line that can be closed by a valve and connects the anode space of the at least one fuel cell to the exhaust line in a fluid-guiding manner, a mixing element being couplable to the flush line in order to distribute the flush gas into the exhaust line. The invention also relates to a fuel cell system comprising such a mixing device.

Description

Description title

Mixing device and a fuel cell with such a mixing device

The invention relates to a mixing device for a fuel cell system according to the preamble of claim 1 for merging a purge gas at least one anode compartment with an exhaust gas at least one cathode compartment of a fuel cell, and a fuel cell system.

State of the art

To reduce carbon dioxide emissions, vehicles are increasingly being equipped with electrically powered drive systems. The electrical energy required for this purpose is usually obtained from an electrochemical storage. Alternatively, the electrical energy may be generated by a fuel cell system according to the prior art. One

Fuel cell system mainly consists of a variety of

Fuel cells, a hydrogen supply, an air supply and a control unit. In a fuel cell, hydrogen is supplied to an anode side or an anode space, and air to a cathode side or to a cathode space. Both parts of the fuel cell are separated by a membrane which is permeable to protons. Thus, in a reaction of hydrogen and oxygen to water electrical energy can be generated. During the operation of such a fuel cell system, undesirable processes also occur. For example, water also diffuses into the anode compartment and thereby reduces the efficiency of the fuel cell. Thus, rinsing operations of the anode compartment and the cathode compartment are necessary to ensure the performance of the fuel cell. For this purpose, corresponding valves can be opened and the respective spaces of the fuel cell can be flushed with hydrogen or oxygen. From DE 1 1 2006 003 069 T5 a fuel cell system with a fuel cell for generating electrical energy is known. After each operation of the fuel cell, rinsing with hydrogen and oxygen occurs to reduce the moisture content within the fuel cell. The purge gas is treated prior to feeding into the exhaust pipe and then introduced via a T-piece in an exhaust stream. Nevertheless, a small amount of hydrogen can be added to each flushing process

Exhaust gas reach the fuel cell system. As a result, locally the hydrogen concentration can rise in such a way that a gas mixture capable of detonating forms.

Disclosure of the invention

The object of the invention is to propose a mixing device for a fuel cell system, which eliminates the disadvantages mentioned and prevents the formation of an ignitable hydrogen-air mixture in an exhaust pipe of a fuel cell system. Furthermore, it is an object of the invention to provide a fuel cell system with such a mixing device.

This object is achieved by a mixing device for a fuel cell system having the features of claim 1 and by a fuel cell system having the features of claim 12.

A mixing device for a fuel cell system for merging a purge gas of an anode compartment with an exhaust gas of a cathode compartment of at least one fuel cell has an exhaust pipe for discharging an exhaust gas from the cathode compartment of the at least one fuel cell and a purge line closable by a valve, which includes the anode compartment of the at least one fuel cell the exhaust pipe fluidly connects. According to the invention, a mixing element for distributing the purge gas within the exhaust gas line can be coupled to the purge line.

As a result, the purge gas from the anode compartment is not guided directly into the exhaust pipe during a purge operation. The purge gas is preferably hydrogen. By means of the mixing element according to the invention, the purge gas is passed in a controlled manner into the exhaust gas line, so that the purge gas and the exhaust gas can slowly mix with one another. In particular, this results in an effective dilution of the hydrogen contained in the purge gas, so that the hydrogen concentration in the exhaust pipe is always below the

Concentration of a detonable mixture remains. This means that a small volume flow, which usually contains hydrogen, over the

Purge line and the mixing element into a larger volume flow,

preferably in the exhaust pipe of the fuel cell itself or in a

Exhaust pipe of a whole fuel cell system is initiated. Through this

Measure the risk of explosion of the fuel cell system can be significantly reduced. The exhaust pipe can be designed here as a pipe and be connected directly to the cathode space of at least one fuel cell. In particular, it carries the water or the water vapor as the reaction product of the fuel cell. The exhaust pipe basically carries air and thus

Oxygen from the environment and may additionally comprise air or oxygen from an oxygen supply unit. The cathode compartment can also be subjected to a rinsing process, for example by one

Prevent freezing of the cathode compartment. Here, the exhaust gas of the cathode compartment may also be a purge gas of the cathode compartment, which consists largely of purge air or oxygen. Advantageously, the exhaust pipe is multi-part and includes an orifice area, which the protruding purge line and a arranged on the purge line

Has mixing element. As a result, for example, the mixing element or the flushing line can be easily replaced. Individual parts of the

Exhaust pipe can be positively inserted into one another, welded, glued or connected to each other via screw or flange connections. The components may for example consist of a metal, a plastic, a technical ceramic or the like. Alternatively, the purge line may be integral with the exhaust pipe and project through a wall of the exhaust pipe and open into the exhaust pipe. It is advantageous if the flushing line is connected by gluing, welding or soldering to the exhaust pipe. Alternatively, the purge line can also be passed through an opening in the exhaust pipe and connected there non-positively or positively with the exhaust pipe. For example, the purge line be elastic and have a slight oversize relative to the opening in the wall of the exhaust pipe, so that the purge line can be force-fit and gas-tight pressed into the opening. Within the

Mouth region of the exhaust pipe, the purge line may be preferably angled so that it is aligned parallel to the course of the exhaust pipe.

In a preferred embodiment of the invention

Mixing device has the mixing element at least two openings for distributing the purge gas. By this measure, the merging or the distribution or mixing of the purge gas with the exhaust gas is throttled or slowed down by the at least two openings and there is a distribution of the volume flows to the openings attached to different areas of the mixing element. The mixing element can

For example, be designed as an end cap with at least two openings, which can be connected end to end with the purge line. Due to the number and size of the openings, the volume flow of purge gas can be defined. Preferably, the mixing element has a portion or a region with openings, which can be designed as bores, perforations, slots and the like, as well as a section for fastening the mixing element to the flushing line. Alternatively or additionally, the

Mixing element have a portion which is porous.

For example, the walls of the mixing element may consist of a coarsely sintered material or an open-pored foam. The openings can also be made microporous or macroporous. In addition, the mixing element may comprise holding elements which slippage within the

Prevent exhaust pipe or allow a connection of the mixing element with the exhaust pipe.

According to a further embodiment of the invention

Mixing device, the mixing element has an elongated extent along the

Exhaust pipe on. As a result, the merging or mixing of both gases is spatially distributed, so locally no excessive hydrogen concentration. Advantageously, the mixing element is tubular and closed at the ends. As a mixing element, however, may also have any other shape. In particular, the perforations or holes can be radially out The mixing element protrude into the exhaust pipe and be directed so that the purge gas when leaving or when crossing a mixing element wall, a direction or a twist is experienced. Advantageously, the purge gas is passed in the form of a plurality of turbulent flows in the exhaust pipe. This can increase the mixing efficiency.

In a further exemplary embodiment of the mixing device according to the invention, the at least two openings for distributing the flushing gas are arranged along a wall of the mixing element. As a result, the mixing element can be produced particularly easily. The arrangement of the openings or

Perforation can be carried out uniformly or non-uniformly along an example, tubular wall of the mixing element.

According to a further embodiment of the invention

Mixing device is a distribution element connected to the purge line in such a way that the distribution element connects the purge line with the exhaust pipe with at least two spaced Verteilarmen. Alternatively, the distribution element can be connected to the purge line within the exhaust pipe. As a result, the volume flow of the purge line in several smaller

Volume flows are shared. This can be especially the mixing of the

Purify purge gas with the exhaust gas of the cathode compartment.

In a further preferred embodiment of the mixing device according to the invention, the at least two distribution arms of the distribution element within the exhaust pipe can each be connected to a mixing element. By this measure, the already distributed volume flows can be additionally scattered and distributed efficiently.

According to a further embodiment of the invention

Mixing device is in the mouth region of the purge line in the

Exhaust pipe arranged a sensor for measuring a hydrogen concentration. As an additional security measure can thereby the

Concentration of the hydrogen to be monitored within the exhaust pipe. A corresponding sensor may be, for example, a hydrogen microsensor, which can be monitored and read by a measuring electronics. As a result, for example, a warning signal for the operator of

Fuel cell system to be generated.

In a further exemplary embodiment of the mixing device according to the invention, the valve can be regulated as a function of the measured hydrogen concentration. If the concentration of hydrogen reaches or exceeds a defined limit, the valve can automatically be triggered based on an output of the measuring electronics and the flushing line can be closed so that the flushing process is interrupted. As a result, any inflow of the purge gas is prevented in the exhaust pipe.

According to one embodiment of the mixing device according to the invention, the volume flow of the purge gas to the exhaust gas can be controlled by the valve.

As a result, as an alternative or in addition to the measures already mentioned, the volume flow of the purge gas can be controlled by a controllable valve. In particular, as a result, the volume flow through the purge line can be additionally reduced if necessary.

In a further embodiment of the mixing device according to the invention, the mixing element is at least partially elastic.

This allows the mixing element in the event of freezing through the

Extend the pressure of the purge gas and thus loosen or break up any possible ice formation. Thus, a gas transport after a complete or

gastight freezing of the mixing element are made possible again.

Advantageously, the mixing element consists of a plastic, elastomer,

Silicone or another elastic material that fits at a

can expand applied pressure.

According to a preferred embodiment of the mixing device according to the invention, the mixing element is positively or cohesively with the

Flushing line connectable. Preferably, the mixing element can be glued, soldered or welded to the flushing line. In particular, in an elastic embodiment of the mixing element, it may be advantageous to be able to change this at certain intervals, so that a

positive connection can make this possible. For example, hereby the elastic mixing element are placed on the end of the flushing line. For secure fixation of the mixing element and a clamp can be attached, which presses the mixing element radially against a wall of the purge line. Alternatively, the mixing element may also be an integral end-side component of the flushing line.

A fuel cell system according to the invention has at least one

A fuel cell having an anode space which is separated by a membrane from a cathode space, a fuel supply of the at least one fuel cell, an oxygen supply of the at least one fuel cell and a mixing device, which controls merging a purge gas of an anode compartment with an exhaust gas of a cathode compartment. As a result, an unwanted explosion or fire hazard by ensuring a fast below the lower ignition limit of a hydrogen-air mixture achieved in that a hydrogen-containing gas such

For example, a purge gas of an anode chamber is spatially distributed in an oxygen-containing exhaust stream of a cathode chamber is initiated. This goal can be achieved both by a slow introduction of the hydrogen-containing gas with a low volume flow into an exhaust pipe and by introducing the hydrogen-containing gas through distributed openings. By introducing the purge gas through the area distributed openings local hydrogen concentrations can be prevented because the hydrogen-containing gas is not supplied from a single opening of the purge line in the exhaust pipe.

Such a fuel cell system may be particularly advantageous in application in which a special attention to fire and

Explosion protection is laid, such as when used underground.

Other advantageous embodiments are the subject of further

Dependent claims.

The following are based on highly simplified schematic

Representations preferred embodiments of the invention explained in more detail. FIG. 1 shows a schematic representation of the invention

Fuel cell system.

FIG. 2 shows a further simplified section of the fuel cell system according to the invention from FIG. 1 with a fuel cell.

FIG. 3 shows a schematic representation of the invention

Mixing device according to a first embodiment.

FIG. 4 shows a schematic representation of the invention

Mixing device according to a second embodiment. In the figures, the same structural elements each have the same

Reference numbers on.

1 shows a schematic representation of a fuel cell system 1 according to the invention. The fuel cell system 1 according to the exemplary embodiment has a large number of fuel cells 2, which are designed in the form of a so-called fuel cell stack 2. The fuel cell stack 2 generates in a chemical reaction of hydrogen and oxygen electrical energy and water as a reaction product. For the sake of clarity, components for the generation and the conduction of the electrical energy such as anodes, cathodes or electrical conductors are not shown. The fuel cells 2 are connected via fuel lines 4 with a fuel supply 6.

The fuel supply 6 leads gaseous hydrogen to each individual fuel cell 8 in the fuel cell stack 2. The fuel supply 6 here is a cryogenic hydrogen tank with a not shown

Heating device, the cryogenic hydrogen into a gaseous

Physical state transferred. About corresponding oxygen lines 10, the fuel cell 2 with a

Oxygen supply 12 connected, which supplies the fuel cell 2 with gaseous oxygen. The oxygen supply 12 is according to the

Embodiment of a cryogenic oxygen tank. The cryogenic oxygen is converted into a gaseous state via a heater, not shown

Physical state transferred and passed into the fuel cell 2. Alternatively, you can the oxygen supply 12 also in the form of an air compressor or

Compressor designed to filter the air and pressurized the

Fuel cell 2 supplies.

In the fuel cell 2, the reaction product water is passed, depending on the nature of the fuel cell 2 in liquid or gaseous form through an exhaust pipe 14 from the fuel cell system 1.

So that the fuel cells 2 can maintain their efficiency, a purge line 18 which can be regulated via a valve 16 connects the fuel cells 2 to the exhaust gas line 14. The exhaust gas line 14, the valve 16 and the purge line 18 are parts of a mixing device 20 according to the invention, which is described in more detail in the further figures is described.

FIG. 2 shows a further simplified section of the fuel cell system 1 from FIG. For the sake of clarity, only one fuel cell 8 of the fuel cell stack 2 from FIG. 1 with an exhaust gas line 14 and a purge line 18 is shown.

The individual fuel cell 8 consists of an anode chamber 22 and a cathode chamber 24 which are separated from each other by a partially permeable membrane 26. The membrane 26 is for protons such as

Hydrogen protons permeable.

The cathode chamber 24 has a cathode, not shown, which is supplied via an oxygen line 10 with gaseous oxygen. the

Cathode space 24 may alternatively be supplied to ambient air. The anode chamber 22 has an anode, not shown, which is supplied via a fuel line 4 and hydrogen line 4 with gaseous hydrogen.

During operation of the fuel cell 8, water is formed in the cathode space 24, which is conducted together with residual oxygen into the exhaust gas line 14. The remaining oxygen can in this case from the reaction to

Energy generation must be left over. The exhaust pipe 14 is here tubular and directly fluidly connected to each cathode compartment 24. The exhaust pipe 14 is open towards an environment.

In addition to the desired reaction, undesirable processes occur, which require appropriate remedial measures. For example, water diffuses into the anode compartment 22 and must be discharged there regularly. Likewise, nitrogen from the air can pass through the membrane 26 from the cathode space 24 to the anode space 22 and must be drained from there. For the discharge of undesirable substances or gases, the purge line 18 connects the anode chamber 22 with the exhaust pipe 14 of the cathode chamber 24. The valve 16 is connected to the purge line 18 and can be operated manually or electrically, whereby the purge line 18 can be closed or opened. In a rinsing process, the valve 16 is opened and the anode chamber 22 is acted upon by hydrogen via the line 4, so that hydrogen together with undesirable substances or gases are passed through the purge line 18 into the exhaust pipe.

The purge line 18 in this case opens into the exhaust pipe 14 and there passes into a mixing element 28, through which the purge gas can mix slowly and in a controlled manner with the exhaust gas in the exhaust pipe 14.

Figure 3 apparently a schematic representation of the mixing device 20 according to the invention according to a first embodiment. The

Mixing device 20 has an exhaust pipe 14, which may also be a portion of the exhaust pipe 14. The section can thus also be used in the exhaust pipe 14.

Into the exhaust pipe 14 protrudes through a wall 15 of the exhaust pipe 14 the

Rinse line 18 into it. The purge line 18 is executed rohrformig according to the embodiment and is cohesively connected to the wall 15 of the exhaust pipe 14.

The purge line 18 is bent within the exhaust pipe 14 at an angle of 90 ° and points away from the fuel cell 8 in the direction of

Exhaust pipe port 30 which is connected to the ambient air. ends the purge line 18 is open. The mixing element 28 is non-positively connected to the purge line 18. According to the embodiment, this is

Mixing element 28 designed as a resilient end cap, which can be pulled on the end of the purge line 18. For this purpose, the mixing element 28 has a cylindrical shape which is open on one side. The opposite end of the

Mixing element 28 is provided with a plurality of openings 32. In a flushing thus purge gas passes through the purge line 18 in the

Mixing element 28 and there can flow through the openings 32 in the exhaust pipe 14. On the one hand, the openings 32 distribute the purge gas in the exhaust gas line 14 when flowing through, and on the other hand reduce an outlet cross section of the purge gas, so that mixing or distribution of the purge gas with the exhaust stream does not occur abruptly, but is delayed.

In the case of frozen openings 32, the mixing element 28, which is designed to be elastic in this case, can buckle convexly in the direction of the exhaust gas line orifice 30 by means of a pressure of the purge gas and thus mechanically dissolve ice formation. Due to the loosened ice layer, the purge gas can enter the exhaust pipe 14 again.

FIG. 4 discloses a schematic representation of the mixing device 20 according to the invention in accordance with a second exemplary embodiment. Analogous to the first embodiment of the mixing device 20 according to the invention, the purge line 18 extends into the exhaust pipe 14 and has a curvature. Following the curve towards the

Exhaust line opening 30, a mixing element 28 is arranged at the end of the purge line 18.

According to the embodiment, the mixing element 28 is cylindrical and made of a stainless steel. The mixing element 28 extends in the direction of the exhaust pipe mouth 30 and is configured at the end as integral with the flushing pipe, also made of stainless steel. A lateral surface of the

Mixing element 28 is made of an open-pore stainless steel foam 32, so that the purge gas can be fed into the exhaust pipe 14 through a plurality of pores 32 which serve as openings 32. According to the In the exemplary embodiment, the mixing device 20 has a hydrogen sensor 34, which can measure a hydrogen concentration in the region of the mixing element 28. A measuring electronics 36 can read out and evaluate the hydrogen sensor. Depending on defined limits, the measuring electronics 36 can close or open the electric valve 16 automatically.

Claims

claims

1 . Mixing device (20) for a fuel cell system (1) for

Merging a purge gas of an anode chamber (22) with an exhaust gas of a cathode compartment (24) at least one fuel cell (8), with an exhaust pipe (14) for discharging an exhaust gas from the cathode compartment (24) of the at least one fuel cell (8) and with a through a valve (16) closable flushing line (18), the anode space (22) of the at least one fuel cell (8) fluidly connected to the exhaust pipe (14), characterized in that a mixing element (28) for distributing the

Purge gas within the exhaust pipe (14) with the purge line (18) can be coupled.

2. Mixing device according to claim 1, wherein the mixing element (28) has at least two openings (32) for distributing the purge gas in the exhaust pipe (14).

3. A mixing device according to claim 1 or 2, wherein the mixing element (28) is tubular and has an elongated extent along the exhaust pipe (14).

4. Mixing device according to one of claims 1 to 3, wherein the at least two openings (32) for distributing the purge gas along a wall of the mixing element (28) are arranged.

5. Mixing device according to one of claims 1 to 4, wherein a distribution element to the purge line (18) is connectable, which is connectable with at least two spaced Verteilarmen with the exhaust pipe (14) or to the purge line (18) within the exhaust pipe (14 ) is connectable.

6. Mixing device according to one of claims 1 to 5, wherein the at least two Verteilarme of the distribution element within the exhaust pipe (14) in each case with a mixing element (28) are connectable.

7. Mixing device according to one of claims 1 to 6, wherein in one

Mouth region of the purge line (18) in the exhaust pipe (14), a sensor (34) is arranged for measuring a hydrogen concentration.

8. Mixing device according to one of claims 1 to 7, wherein the valve (16) is controllable depending on the hydrogen concentration.

9. Mixing device according to one of claims 1 to 8, wherein the volume flow of purge gas to the exhaust pipe (14) through the valve (16) is controllable.

10. Mixing device according to one of claims 1 to 9, wherein the

Mixing element (28) is performed at least partially elastic.

1 mixing device according to one of claims 1 to 10, wherein the

Mixing element (28) form-fitting or cohesively with the purge line (18) is connectable.

12. Fuel cell system (1) comprising:

at least one fuel cell (8) having an anode space (22) separated by a membrane (26) from a cathode space (24),

a fuel supply (6) of the at least one fuel cell (8),

- An oxygen supply (12) of the at least one fuel cell (8) and

- A mixing device (20) according to any one of the preceding claims, for the controlled merging of a purge gas of an anode chamber (22) with an exhaust gas of a cathode chamber (24).