WO2013107492A1

WO2013107492A1 - Fuel cell system

Info

Publication number: WO2013107492A1
Application number: PCT/EP2012/005370
Authority: WO
Inventors: Cosimo Mazzota
Original assignee: Daimler Ag
Priority date: 2012-01-21
Filing date: 2012-12-22
Publication date: 2013-07-25
Also published as: DE102012001155A1

Abstract

The invention relates to a fuel cell system (1) comprising at least one fuel cell (3), which has a cathode space (5) and an anode space (4), wherein an outgoing line (15) for waste gas and/or water out of the anode space (4) of the fuel cell (3) is divided into two flow branches (16, 17), wherein one of the flow branches (16) is connected to the output of the cathode space (5) and one of the flow branches (17) is connected to the input of the cathode space (5). The invention is characterized in that both flow branches (16, 17) have a continuously open cross section through which a flow can pass.

Description

The fuel cell system

The invention relates to a fuel cell system with at least one fuel cell according to the manner defined in greater detail in the preamble of claim 1. In addition, a preferred use of the invention is given. ^'

Fuel cell systems are known from the general state of the art. They use fuel cells, such as fuel cells in PEM fuel cell technology, to provide electrical power from oxygen and hydrogen. One of the problems with fuel cells is the removal of unconsumed hydrogen from the area of the anode compartment. This one will

typically with a small amount of fuel cell resulting

Product water discharged from the anode compartment. In a so-called near-dead-end design of the fuel cell, this is a continuous stream of a comparatively small amount of water and hydrogen. At a

alternative construction with a so-called anode recirculation, the exhaust gas is returned to the anode compartment. In the anode recirculation, water and inert gas, which has diffused through the membranes of the fuel cell into the anode space, also accumulate over time. In order to maintain the hydrogen concentration at such a high level that the fuel cell continues to work well, it is also necessary here, for example from time to time or depending on the amount of water and / or hydrogen concentration, to drain water and / or gas from the anode recirculation. This gas also contains a certain amount of residual hydrogen.

From WO 2008/052578 A1 a structure is known in which a combined discharge of water and gas from an anode recirculation is described. For that will be a water separator is used, which has a valve device with a

Drain line is connected. The valve device is opened until first the water and then the desired amount of gas has flowed through the discharge line. In this case, the discharge line preferably opens into the cathode inlet, that is to say the supply air flow flowing to a cathode space of the fuel cell. Optionally, it can also be in the cathode output, so one flowing from the fuel cell

Cathode exhaust flow open.

Both approaches have advantages and disadvantages known from the general state of the art. The discharge of the exhaust gas in the area of the

Cathode space effluent exhaust has the advantage that it is very easy.

is to implement. The disadvantage is that it is undesirably high

Hydrogen emissions may occur in the exhaust gas, since the exhaust gas from the anode compartment will always contain at least a certain residual amount of hydrogen. The delivery of water and / or gas to the cathode inlet has the decisive advantage that any residual hydrogen is reacted at the cathode catalyst. As a result, no hydrogen emissions can occur. The disadvantage is that an additional degradation of the. By the addition of hydrogen into the cathode compartment

Electrocatalyst in the cathode compartment results. The catalyst is loaded with it and the fuel cell ages faster. In addition, heat is generated in this process, which is not desirable in regular operation of the fuel cell. Rather, this additional heat stresses the cooling system of the fuel cell and must be expensively dissipated.

In order to ideally meet this combination of advantages and disadvantages of the two possibilities, it is known from US 2001/0048837 A1 that a division of the discharge line into two flow branches can take place. Each of the flow branches has its own valve device. Depending on the situation, especially depending on

Driving speed of the equipped with the fuel cell system vehicle, the power output from the fuel cell and the water level

separated water, then each one or the other valve is opened, so that the exhaust gas is discharged once in the cathode input and once in the cathode output, depending on which situation exists and in which situation outweigh the benefits or the disadvantages are more tolerable. The structure is comparatively complex, needed for each individual

Flow branch its own valve and requires a control, which must allow reliable predictions about the effect of the advantages and disadvantages, so as to decide whether the one or the other solution is the better in the particular situation.

From the further general state of the art in the form of DE 10 2009 057 573 A1, it is also known to provide a similar construction so as to meter hydrogen-containing offgas or hydrogen into the region of the cathode feed for heating the fuel cell in a cold start. The fuel cell is heated up faster.

The object of the present invention is now to prevent the aforementioned disadvantages of the prior art and to provide a fuel cell system, which is simple and efficient.

According to the invention this object is achieved by the features in the characterizing part of claim 1. Advantageous embodiments and further developments thereof are specified in the dependent subclaims. A particularly preferred use of the fuel cell system according to the invention is further specified in claim 12.

The solution according to the invention provides, in a simple and very efficient design, for diverting the discharge for exhaust gas and / or water from the anode compartment into two flow branches as in the prior art. One of the flow branches is connected to the inlet of the cathode compartment and one to the outlet of the cathode compartment. In the solution according to the invention, however, it is provided that both flow branches have a constantly open flow-through cross-section. The inventor has in fact recognized that it is sufficient to reduce the aforementioned disadvantages when the volume flow is reduced. An elaborate switching of the volume flow via corresponding valves once on the input of the cathode compartment and once on the output of the cathode compartment is therefore not necessary. Rather, it is sufficient to divide the volume flow into two partial streams via a simple division of the flow branches and their constantly open flow connection once to the cathode compartment and once to the anode compartment. Each of the partial flows is then smaller than the total volume flow, so that even the disadvantages described above can be significantly minimized. The fuel cell gets so a longer Life and the amount of any critical hydrogen emissions is reduced. The structure is very simple and efficient, since it manages without additional valves and without a control, which for example, the performance of the fuel cell system or, if this has been installed in a vehicle, detect the driving situation and must take into account in the control.

In a particularly favorable and advantageous embodiment of the fuel cell system according to the invention, it may further be provided that the two

Flow branches have different pressure losses. Such an embodiment of the two flow branches so that they have different pressure losses, for example due to different pipe diameters and / or

Line lengths, can very easily and efficiently accomplish a fixed predetermined by the construction division of the volume flows on the output of the cathode compartment on the one hand and on the input of the cathode compartment on the other.

Additionally or alternatively, could also in at least one of the two

Flow branches may be provided a flow aperture or throttle.

In a further very favorable embodiment of this, it is further provided that the pressure losses of the two flow branches are designed so that adjusts a distribution of the volume flow, so that 40 to 60%, preferably about 50%, of the total volume flow through the with the input connected to the cathode compartment

Flow branch flow. This division has the particular advantage that the hydrogen emission values in the exhaust gas thus always below the legal

Requirements remain.

The fuel cell system according to the invention can be designed as a fuel cell system, which is equipped with a so-called near-dead-end fuel cell. Such a fuel cell typically has a cascaded area distribution within the anode space, so as to implement a maximum of the supplied hydrogen in the anode space. However, in order to be able to remove product water arising in the area of the anode space and to be able to ensure complete supply of the area of the anode space with hydrogen, a certain excess of hydrogen is necessary in the operation of such a near-dead-end fuel cell. This excess then passes to the environment together with the product water produced in the anode compartment. He can in the sense of Invention are divided into the air flow to the inlet of the cathode compartment and the exhaust air flow from the cathode compartment.

In a particularly preferred embodiment of the fuel cell system, however, it is provided that exhaust gas and / or water are recirculated via a recirculation line from an output of the anode compartment to an input of the anode compartment, wherein the derivative branches off from the recirculation line. The fuel cell system according to the invention can thus be constructed not only with a near-dead-end fuel cell, but in particular also with the very common design with an anode recirculation. In such an anode recirculation, a continuous or a discontinuous outflow of water and / or gas is necessary. Since this gas can also contain hydrogen, essentially the same apply here

Conditions.

The fuel cell system according to the invention can be constructed very simply. It may dispense with additional valves and a complex and trouble-prone control electronics with appropriate sensors for detecting, for example, the power state of the fuel cell system. It can therefore be implemented robust accordingly. It is therefore particularly suitable for use in a vehicle where electrical drive power is provided by the fuel cell system.

Further advantageous embodiments of the fuel cell system according to the invention also emerge from the remaining dependent subclaims and become clear from the exemplary embodiments, which are described in more detail below with reference to the figures.

Showing:

Fig. 1 is a principle indicated fuel cell system in a first

Embodiment according to the invention in a vehicle; and

Fig. 2 is a principle indicated fuel cell system in a second

Embodiment according to the invention in a vehicle.

In the representation of FIG. 1, a fuel cell system 1 in an indicated vehicle 2 can be seen purely by way of example and in a very highly schematic manner. The Fuel cell system 1 essentially has a fuel cell 3, which in turn has an anode compartment 4 and a cathode compartment 5. The fuel cell 3 should be designed as a stack of PEM fuel cells. The cathode compartment 5 of the fuel cell 3 is supplied via an air conveyor 6 with air as an oxygen supplier. The air passes through an air supply line 7 to the input of the cathode compartment 5. The exhaust air from the cathode compartment 5 passes through an exhaust duct 8 in the embodiment shown here directly into the environment. Here, in principle, a post-processing, such as an afterburner, a turbine and / or the like could be arranged.

The anode chamber 4 of the fuel cell 3, hydrogen is supplied from a compressed gas storage 9. This passes through a pressure control device 10 and a recirculation conveyor 11 explained in more detail later to the entrance of the anode compartment 4. Exhaust gas from the anode compartment 4 arrives in the recirculation conveyor shown in FIG

Embodiment of the fuel cell system 1 via a recirculation line 12 back into the region of the recirculation conveyor 11 and can be supplied from there together with fresh hydrogen from the compressed gas storage 9 to the anode compartment 4 again. This structure of a so-called anode recirculation is known from the general state of the art. In order to compensate for the pressure losses which have occurred in the anode chamber 4 and in the recirculation line 12, it is necessary to provide the recirculation conveyor 11. This can be either as

Recirculation fan and / or as one or more gas jet pumps

or ejectors be formed. This is for the present invention of minor importance, so it will not be discussed further.

In the area of the recirculation line 12, a water separator 13 is now arranged. This is connected via a drain valve 14 with a discharge line 15. In the area of the anode recirculation, water and inert gas, which has diffused through the membranes of the fuel cell 3, accumulate over time. To the

To maintain hydrogen concentration in the anode recirculation, it is necessary to discharge water and / or gas from the anode recirculation from time to time. Purely by way of example, the water separator 13 with the valve device 14 is formed for this purpose. This construction makes it possible to simultaneously realize the discharge of water and gas via the water separator 13 as set forth in the prior art described in the introduction. Comparable structures, which dissipate water and gas separately, are known from the general state of the art. These too would be analogously conceivable for the structure of the fuel cell system 1 described here.

The core of the construction shown here is now that the discharge line 15 is divided into two flow branches 16, 17. The first flow branch 16 opens into the exhaust air line 8, the second flow branch 17 opens into the supply air line 7. The first flow branch 16 is thus connected to the output of the cathode chamber 5 and allows a portion of the discharged via the exhaust duct 15 volume flow in the exhaust air flow Inject fuel cell 3. Another part passes via the second flow branch 17 into the supply air flowing to the fuel cell 3. Since there is always also a quantity of residual hydrogen in the gas located in the discharge line 15, at least part of the residual hydrogen, namely the part which flows via the second flow branch 17, can be correspondingly reacted together with oxygen in the region of the cathode space 5 on the local catalyst become. The hydrogen emissions to the environment are thus reduced. The discharged in the region of the exhaust duct 8 residual hydrogen is then typically diluted so much that even here no danger from the hydrogen more.

In order to prevent that compressed air flows into the region of the second flow branch 17 via the air conveying device 6, in the region of the second

Flow branch 17, and here in particular in the immediate vicinity of its confluence with the supply air line 7 a backflow 21 may be provided. Another such Rückströmsicherung 21 may also in the region of the first

Flow branch 16, here also preferably be provided as close to its confluence with the exhaust duct 8. The one, or if available both,

Rückströmsicherungen 16 should be as close to the confluence with the supply air line 7 and exhaust duct 8 arranged to get in the supply air line 7 and possibly the exhaust duct 8 no unnecessary air traps, which is undesirable in particular in the supply air line 7 in terms of control of the air supply is.

The pressure losses in the two flow branches 16, 17 can be adjusted for example by the line lengths and line cross sections so that a desired structurally fixed division of the present in the derivative 15

Volumetric flow to the two flow branches 16, 17 takes place. It's the same possible to make this adjustment of the partial volume flows via appropriate fixed orifices or throttling points 18, 19.

In order to prevent water from passing via the flow branches 16, 17 but in particular via the flow branch 17 into the cathode space 5, it can also be provided that the flow branches 16, 17 and here in particular the

Flow branch 17 branches off from the discharge line 15 as vertically as possible and upwards. In particular, in combination with a slightly larger diameter of the flow branches 16, 17, but in particular of the flow branch 17, compared to the diameter of the discharge line 15, it is achieved that the water largely enters the exhaust air line 8 and not into the supply air line 7.

In addition, a dilution chamber 20 is provided in the region of the connection of the flow branch 16 to the exhaust air line 8. This consists for example of an increase in volume in the region of the exhaust duct 8 or in the region of

Flow branch 16, which is connected to the exhaust duct 8. In this area then flows in addition to the exhaust air from the exhaust duct 8, the gas from the drain line 15 a. This is diluted accordingly. In particular, in the case of a discontinuous discharge of gas via the flow branch 16, such a dilution chamber 20 has the decisive advantage that it prevents the occurrence of high

Equalizes hydrogen concentrations in the exhaust air and ensures a uniformly high dilution of the released hydrogen. High emissions of undiluted hydrogen, which suddenly reach the environment, can thus be prevented. Hydrogen sensors, which respond from certain hydrogen concentrations in the exhaust air and indicate a safety-critical problem, can continue to be set sufficiently sensitive and still do not respond to each discharge of gas in the exhaust duct 8. In addition to this, a dilution chamber 20 would also be conceivable in the junction between the flow branch 17 and the supply air line 7.

In addition to the structure of a fuel cell system 1 with a fuel cell 3 with anode recirculation described in Figure 1, it is of course also conceivable to realize this structure in a fuel cell 3 without anode recirculation. Such a fuel cell 3 will typically be designed as a so-called near-dead-end fuel cell. Such a can be seen in the illustration of FIG. One and only The difference is that the anode recirculation is absent.

Typically, the area present in the anode space 4 is formed in a cascade, so that the hydrogen introduced into the anode space 4 is largely converted. Only a small amount of residual hydrogen, typically about 3 - 5%, leave the anode compartment 4 together with resulting product water. These are derived analogously to the illustration in Figure 1 via the derivative 15, which then in two

Flow branches is divided. The drain valve 14 and the water separator 13 can be dispensed with here, otherwise the functionality of the fuel cell system 1 shown in FIG. 2 is essentially the same as that of the one already described above

described embodiment. In principle, the use of a dilution chamber 20 would also be conceivable here.

Claims

claims

1. A fuel cell system (1) having at least one fuel cell (3) which has a cathode space (5) and an anode space (4), wherein a discharge (15) for exhaust gas and / or water from the anode space (4) of the fuel cell (3 ) is divided into two flow branches (16, 17), wherein one of the flow branches (16) with the output of the cathode space (5) and one of the flow branches (17) is connected to the input of the cathode space (5),

characterized in that

Both flow branches (16, 17) has a constantly open through-flow

Have cross-section.

2. Fuel cell system (1) according to claim 1,

characterized in that

the two flow branches (16, 17) have different pressure losses.

3. Fuel cell system (1) according to claim 1 or 2,

characterized in that

at least one of the two flow branches (16, 17) has a flow aperture (18, 19).

4. Fuel cell system (1) according to claim 3 or 4,

characterized in that

the pressure losses of the two flow branches (16, 17) are designed so that a division of the partial volume flows is such that 40 to 60%, preferably about 50%, of the total volume flow through the with the input of the

Cathode space (5) connected flow branch (17) flow.

5. Fuel cell system (1) according to one of claims 1 to 4, characterized in that

a valve device (14) for influencing the volume flow of exhaust gas and / or water in a discharge line (15) before the branching into the two

Flow branches (16, 17) is arranged.

6. Fuel cell system (1) according to one of claims 1 to 5,

characterized in that

at least one of the flow branches (16, 17) has a dilution chamber (20) before it is connected to the outlet or inlet of the cathode compartment (5) or in the region of the connection to the outlet or inlet of the cathode compartment (5).

7. Fuel cell system (1) according to one of claims 1 to 6,

characterized in that

Exhaust gas and / or water via a recirculation line (12) from an output of the anode chamber (4) is returned to an input of the anode chamber (4), wherein a derivative (15) before the branching into the two flow branches (16, 17) of the Recirculation line (12) branches off.

8. Fuel cell system (1) according to claim 7,

characterized in that

in the region of the branch a water separator (13) is provided.

9. Fuel cell system (1) according to one of claims 1 to 8,

characterized in that

at least one of the flow branches (16, 17), in particular that with the

Entrance of the cathode compartment (5) connected flow branch (17), a

Backflow (21), which can be flowed through only in the direction of the cathode side.

10. Fuel cell system (1) according to one of claims 1 to 9,

characterized in that

the flow branch (17), which is connected to the input of the cathode chamber (5), in the region of the branch a larger permeable Cross section as a derivative (15) before branching into the two

Has flow branches (16, 17).

11. Fuel cell system (1) according to one of claims 1 to 10,

characterized in that

the flow branch (17) connected to the inlet of the cathode space (5) branches off approximately vertically, in particular in the intended use vertically upward, from a discharge (15) before the branch into the two flow branches (16, 17).

12. Use of a fuel cell system according to one of claims 1 to 1 1, for the provision of electrical drive energy in a vehicle (2).