WO2013045044A1

WO2013045044A1 - Anode circuit and method for preparing a restart

Info

Publication number: WO2013045044A1
Application number: PCT/EP2012/003914
Authority: WO
Inventors: Thomas Baur; Oliver Harr; Philipp Hausmann; Matthias Jesse; Wilfried Marx; Cosimo Mazzotta; Klaus Scherrbacher; Christian Schmidt
Original assignee: Daimler Ag
Priority date: 2011-10-01
Filing date: 2012-09-20
Publication date: 2013-04-04
Also published as: DE102011114719A1

Abstract

The invention relates to a method for preparing a fuel cell (3) of a fuel cell system (1) for a restart, said fuel cell system (1) comprising an anode circuit including a recirculation line (11) and an anode gas supply line (10). The recirculation line (10) and the anode recirculation line (11) are joined by means of at least one gas jet pump (9). In said method, a purge gas flows through at least one anode chamber (4) of the fuel cell (3). The invention is characterized in that the purge gas is fed from a purge gas source (15) in the area of the gas jet pump (9) in such a way that the purge gas forms the propellant gas stream of the gas jet pump (9). The invention further relates to an anode circuit which is used to carry out the disclosed method.

Description

Anode circuit and method for preparing to restart

The invention relates to an anode circuit for a fuel cell system according to the closer defined in the preamble of claim 1. Art Furthermore, the invention relates to a method for preparing a fuel cell of a fuel cell system to a restart, according to the closer defined in the preamble of claim 4.

From the general state of the art are fuel cell systems with

Fuel cells, for example in PE fuel cell technology, well known. In such fuel cell systems so-called anode circuits or

Anode loops very common. They consist of a recirculation line, which recirculates exhaust gas from an anode compartment of the fuel cell to an anode gas supply line. Through this, the recirculated exhaust gas is then passed together with fresh fuel for the fuel cell back into the anode compartment. To compensate for pressure losses in the anode chamber itself and in the recirculation line, has such

Anodenkreislauf typically a recirculation conveyor on. Both blowers and gas jet pumps or the combination thereof are known from the prior art. In particular, the use of a gas jet pump as

Recirculation conveyor has the decisive advantage that it can be operated with the typically pressurized fuel, for example hydrogen from a compressed gas storage. The recirculation of the exhaust gas can be done comparatively energy-saving. The fresh fuel as a propellant stream flows to a chamber with the recirculated exhaust gas, which is typically followed by a venturi. By exchanging pulses between the propellant gas stream and the exhaust gas and / or the negative pressure built up in the region of the venturi tube, the anode exhaust gas is then conveyed through the propellant gas stream and fed via the anode gas supply line to the anode chamber.

CONFIRMATION COPY Furthermore, inert gases and water accumulate over time in such an anode circuit over time. The hydrogen concentration drops thereby. To the

counteract, an anode circuit typically has a drain line with a shutter or a drain valve. About the drain line, for example, from time to time or as a function of a hydrogen or nitrogen concentration in the anode circuit gas and possibly water drained so as to

Raise hydrogen concentration in the anode circuit again and the

Improve performance of the fuel cell. In each case, a drain line for the gas and a drain line for the water can be provided. It is also possible to provide only one discharge line, which then preferably branches off in the region of a water separator from the recirculation line, in order to discharge the water from the anode circulation first and, if necessary, the gas when it is discharged.

A problem with fuel cells, especially PEM fuel cells, is the start of the fuel cell or the fuel cell system. This is especially true if the start must be done at temperatures below freezing. Since liquid product water is generated during operation in the area of the fuel cell and the fuel cell system, it can be heated at temperatures below that

Freezing freeze and block essential functionalities of the fuel cell and the fuel cell system. In particular, the freezing of the fuel cell itself is critical to a successful restart. It is known from the general state of the art that a fuel cell which is as dry as possible has a better starting capability. Therefore, the fuel cell can be purged when switching off the system with air from an air conveyor to water from the

Remove flow channels. This is according to DE 10 2006 046 104 A1

For example, on the anode side of the fuel cell possible in order to prepare them as best as possible for a later restart. A comparable structure is also described in US 2010/0151291 A1. In both cases, the air conveyor of the fuel cell is used to rinse the anode side.

DE 103 08 473 A1 describes the purging of the fuel cell with air from a compressed air source in order to realize this without the operation of the air conveyor. DE 11 204 001 726 T5 also describes the possibility of using nitrogen for this purpose. The object of the present invention is now to provide an anode circuit of a fuel cell system or a method for preparing a fuel cell system with such an anode circuit to a resistance, which avoids the disadvantages mentioned above.

This object is achieved by an anode circuit with the features in the characterizing part of claim 1. In addition, a method with the features in the characterizing part of claim 4 solves this problem. Advantageous embodiments of the anode circuit and / or of the method result from the remaining dependent claims.

In the anode circuit according to the invention, it is provided that the

Gas jet pump switchable either with a fuel source or a purge gas source is connected as a propellant gas stream source. The gas jet pump can take over the promotion of the anode exhaust gas in regular operation, either alone or in addition to an anode recirculation fan. It is connected to the fuel source and the fresh fuel supplied to the anode compartment serves as a propellant gas stream for the gas jet pump. In addition, it is switchably connected to a purge gas source such as an air source, a nitrogen source or the like. So can

For example, for preparing a possible later restart instead of the fuel purge gas can be metered as a propellant gas stream through the gas jet pump in the anode circuit. The design offers the possibility of flushing both the anode compartment and the entire circuit of the anode recirculation with the purge gas, so as to dry this area, moisture and any water present

blow. In this case, the gas jet pump is actively operated by the purge gas, so that not only the anode chamber itself, but also the recirculation line is flushed accordingly.

In the method according to the invention, it is accordingly provided that the fuel cell is prepared for a restart by flowing through a purge gas. The supply of the purge gas takes place according to the invention from a purge gas source in the region of the gas jet pump, in such a way that the purge gas forms the propellant gas stream of the gas jet pump. The inventive method thus allows the flushing of the anode compartment as well as the flushing of the

Recirculation line and the anode gas supply line. This will be a safe drying or blowing out liquid water from the entire anode circuit, so that the fuel cell on the anode side is ideally prepared for a later restart. The method according to the invention can be carried out either when the fuel cell system is switched off or else in a separate procedure which prepares the fuel cell system for a restart. For example, such a procedure may be temperature controlled during standstill of the

Fuel cell system done. The fuel cell system is, if the temperature falls below a predetermined threshold and must therefore be expected to restart at temperatures below freezing point, woken up briefly and prepared for re-start with a suitable procedure. In this case, the inventive method can be used to dry the anode side accordingly.

According to an advantageous embodiment of the method according to the invention can be used as the purge gas source, a compressed gas storage. Such a compressed gas storage, in particular when it is filled with the compressed gas during operation of the fuel cell system, represents a very simple and inexpensive flushing gas source.

For example, the compressed gas container may be formed as a compressed air reservoir. This is filled during normal operation of the fuel cell by the compressor with compressed air and can then be used in the inventive method as a purge gas source. The advantage is given in particular if the method is carried out independently of the operation of the fuel cell system. In this case, it is particularly advantageous if the purge gas source, the purge gas without additional

Provide energy costs, as is the case with a compressed gas storage. In this case, only energy for driving the corresponding valves is necessary.

In an alternative embodiment of the method according to the invention can as

Purge gas source an air conveyor can be used. This can be the

Be air delivery of the fuel cell system, which then, for example, at a reduced speed, to save energy, can be operated. In particular, however, this may also be a separate air conveying device, which is used exclusively for this method and optionally a start of the fuel cell system. Such an air conveyor can in particular as

Niedervoltluftfördereinrichtung be formed, for example on the basis of a 12 or 24 V system. The construction also has, especially if the procedure is performed independently of the shutdown of the fuel cell system, the

decisive advantage that energy is only needed from a typical already existing on-board battery. In addition, the use of high voltages in the normally unattended fuel cell system is avoided. This is a decisive advantage for safety reasons.

In a further very favorable and advantageous embodiment of the method according to the invention, it can also be provided that a valve device is alternately opened and closed alternately in a discharge line connected to the recirculation line during the supply of the purge gas. In addition to the principle conceivable permanent opening of the valve device, this pulsed operation is of particular advantage. It allows good functionality of the gas jet pump whenever the valve device is closed, since then an immediate recirculation of the gas flow in the recirculation line can take place. Only if the

Valve device is opened, the gas flow is blown off. Another advantage is that, in the phases in which the valve device is closed, a higher pressure is built up, which is then degraded again in the phases in which the valve device is open. Due to these pressure fluctuations between low and high pressure, it is very well possible to remove liquid water from the area of

Anodenraums and the recirculation line to blow out. The removal of liquid water is significantly better than with constantly open valve device and constant pressure gradient.

The inventive structure of the anode circuit and the method for

Preparing the fuel cell for a restart is preferably suitable for fuel cells or fuel cell systems, which often have to be turned off and restarted. This is especially true if occasionally temperatures below freezing also occur for the restart. In these

Systems of the anode circuit according to the invention and the method carried out according to the invention can play its particular advantages. Fuel cells which are exposed to such conditions are frequently used in vehicles, for example motor vehicles on land or in water vehicles. In particular, here is the preferred use of the invention

Anode circuit and the procedure for preparing the restart of the

Fuel cell. Further advantageous embodiments of the anode circuit according to the invention and of the method for preparing a fuel cell of a fuel cell system to a restart can be found in the remaining dependent claims and will be apparent from the embodiment, which below

Referring to the figure is described in more detail.

The sole attached figure shows a relevant to the explanation of the invention

Detail of a fuel cell system in a vehicle.

In the single attached figure, a detail of a fuel cell system 1 is shown in a vehicle 2 indicated in principle. There is one

To recognize fuel cell 3, which should be constructed as a stack of PEM fuel cells, as a so-called fuel cell stack. The fuel cell 3 has an anode compartment 4 and a cathode compartment 5. The cathode compartment 5 of the fuel cell 3 is fed in a manner known per se via an air conveyor 6 air as an oxygen supplier. Unused exhaust air passes to the cathode compartment 5 of the fuel cell 3 from the fuel cell system 1. The anode compartment 4 of the fuel cell 3, hydrogen is supplied from a compressed gas storage 7. Of the

Wasserstroff flows through a shut-off and pressure control device 8 to a

Gas jet pump 9. After the gas jet pump 9, the hydrogen passes via an anode gas supply line 10 into the anode compartment 4. From the exit of the anode compartment 4 exhaust gas is recirculated via a recirculation line 11 into the region of the gas jet pump 9. This structure is also referred to as an anode circuit or anode loop. The gas jet pump 9 is driven in the regular operation of the fresh hydrogen as a propellant gas stream and by pulse exchange and / or negative pressure effects of the exhaust gas flow from the recirculation line 11 is conveyed and mixed with the fresh hydrogen through the anode gas supply line 10 into the anode compartment 4 of the fuel cell. 3

In the anode circuit, water and nitrogen, which diffuses through the membranes of the fuel cell 3 from the cathode compartment 5 into the anode compartment 4, accumulates over time. This causes the hydrogen concentration in the

Anodenkreislauf drops and therefore this nitrogen, ideally together with resulting product water, from time to time or depending on the nitrogen or Hydrogen concentration must be drained. In the illustrated here

Embodiment serves to a drain line 12 with a drain valve 13. These are connected by means of a water separator 14 with the recirculation line 11. As a result, liquid water is separated in the exhaust gas stream and collects in the water separator 14. After the valve device 14, for example in

Depending on the amount of water collected has been opened, the water first flows through the drain line 12 from. Thereafter, a certain amount of gas still flows with, for example, until the valve device time-controlled and / or in dependence on the hydrogen or nitrogen concentration in the recirculation line 11 is closed again. In principle, it would also be conceivable to divide this structure, referred to as a combined drain / purge, so that exclusively water is drained via a drain line as the drain line and only gas is discharged via a purge line as a drain line.

In order to be able to ideally prepare the fuel cell system 1 for a later upcoming restart, it is crucial that in particular the anode side of the fuel cell system is comparatively dry. For this, the anode side of the fuel cell system 1 is purged with a purge gas to expel water and moist residual gases from the anode side. In the structure of the illustrated here

The purge gas source 15 can be connected via a suitable valve means 16 so with the gas jet pump 9, that the purge gas serves as a propellant gas stream and both the anode chamber 4 of the fuel cell 3 and the region of the anode gas supply line 10 and the

Circulation line 11 flushed through accordingly. Ideally, this is the

Valve device 13 is opened. This may either be continuous or periodic so that the valve means is closed over time for a certain time and then opened again for a certain time. As already explained above, the flow through the entire recirculation line 11 and the discharge of

Moisture and water are improved.

The structure is very simple and efficient and allows the preparation of the fuel cell 3 for an efficient restart either immediately when the engine shuts off

Fuel cell system or in a separate process routine for the preparation of the restart, which can be started, for example, depending on the ambient temperature when needed at standstill of the fuel cell system 1. In particular, air or stored nitrogen is suitable as purge gas, wherein the use of air due to unrestricted availability in the environment of the fuel cell system 1 is to be preferred.

As purge gas source 15 different purge gas sources can be used. The purge gas source 15 may preferably supply air as purge gas. It may be in the simplest embodiment, the air conveyor 6 of the fuel cell system 1, which is connected via suitable line elements and valves so that at least a partial gas flow of the normal air supply device 6 provides the propellant gas stream for the gas jet pump 9. Preferably, another partial gas flow of the air supply device 6 can then flush through the cathode compartment 5 of the fuel cell 3.

Alternatively, it would also be possible to use a compressed gas storage as purge gas source 15. This could in principle be filled with air or with nitrogen, which is then supplied externally. Alternatively, it would also be conceivable and particularly efficient possible to fill the compressed gas storage with air, which during operation of the fuel cell system 1 via the air conveyor 6 in the

Compressed gas storage is promoted. The structure would have the advantage that it is very energy efficient when flushing the anode side. As a compressed gas storage can either a conventional compressed gas storage, as it is known from the field of air pressure technology, are used. It would also be conceivable to use an already existing volume on board the vehicle as compressed gas storage, for example a spare wheel, in which case the filling during operation would be crucial, since otherwise there is the danger that the spare wheel will not be usable if necessary.

Another option would be a separate secondary fan or a

Secondary compressor. Such could for example be held specifically for the purpose mentioned. However, it would also be conceivable to use an already existing compressor, e.g. the compressor of a compressed air system, the compressor of a tire pressure system, the compressor of a system which replaces a spare tire (Tire-fit) or the like.

This could then be used either for filling a memory, or directly for purging the anode side of the fuel cell 3. In particular, a such own secondary fan, for example, be constructed as a 12 V blower. This can then, without the high-voltage energy must be activated in the fuel cell system 1, for example, operated from the on-board battery for the already existing electrical system. This is also a comparatively energy-efficient operation for purging the anode side of the fuel cell system 1 is possible. In addition, the application of voltage to the high-voltage circuit in the

Unattended operation prevents what constitutes a security advantage. In order not to have to hold such a separate secondary air blower exclusively for this purpose, this can also be used elsewhere, for example for air supply of the fuel cell system 1 in the start case, as a fan, for example, in the context of stationary air conditioning of the vehicle 2 or the like.

Claims

claims

1. anode circuit of a fuel cell system (1) with a

Anoderezirkulationsleitung (11), which connects the output of an anode chamber (4) of a fuel cell (3) with an anode gas supply line (10), wherein in the region of the compound, a gas jet pump (9) is arranged,

characterized in that

the gas jet pump (9) is switchably connected to either a fuel source (7) or a purge gas source (15) as a propellant gas source.

2. Anodenkreislauf according to claim 1,

characterized in that

from the recirculation line (11) branches off at least one drain line (12) with a drain valve (13).

3. anode circuit according to claim 2,

characterized in that

the branch is provided in the region of a water separator (14).

4. A method for preparing a fuel cell (3) of a fuel cell system (1) on a restart, wherein the fuel cell system (1) a

Anodenkreislauf with a recirculation line (11) and an anode gas supply line (10), and wherein the recirculation line (10) and the

Anoderezirkulationsleitung (11) are merged by means of at least one gas jet pump (9), wherein at least one anode space (4) of the

Fuel cell (3) is flowed through with a purge gas,

characterized in that the supply of the purge gas from a purge gas source (15) in the region of

Gas jet pump (9) takes place so that the purge gas, the propellant gas flow of the

Gas jet pump (9) forms.

5. The method according to claim 4,

characterized in that

As purge gas source (15) a compressed gas storage is used.

6. The method according to claim 5,

characterized in that

is stored in the compressed gas storage gas during operation of the fuel cell system (1).

7. The method according to claim 4,

characterized in that

As purge gas source, an air conveyor is used.

8. The method according to claim 7,

characterized in that

as an air conveying device, a specially used for providing the purge gas air conveying device next to the air conveying device (6) of the fuel cell (3) is used.

9. The method according to any one of claims 4 to 8,

characterized in that

a valve device (13) is continuously opened in a discharge line (12) connected to the recirculation line (11) during the supply of the purge gas.

10. The method according to any one of claims 4 to 8,

characterized in that

a valve device (13) is alternately opened and closed alternately in a discharge line (12) connected to the recirculation line (11) during the supply of the purge gas.