AT520156B1 - Method for cooling a fuel cell stack with partially reformed fuel - Google Patents

Abstract

The present invention relates to a method for cooling a fuel cell stack (10) in a fuel cell system (100a; 100b), the fuel cell stack (10) having an anode section (11) and a cathode section (12) and a reformer in the fuel cell system (100a; 100b) (20) is arranged for reforming fuel for the anode section (11), fuel being partially reformed in the reformer (20) and the partially reformed fuel being supplied to the anode section (11) for cooling the fuel cell stack (10). The invention also relates to a fuel cell system (100a; 100b), a control unit (1), a memory unit (2), a computer program product (3) and a vehicle (1000).

Description

description

METHOD OF COOLING A FUEL CELL STACK WITH PARTIALLY REFORMED FUEL

The present invention relates to a method for cooling a fuel cell stack in a fuel cell system. The invention further relates to a computer program product, a storage unit with a computer program product stored thereon, a control unit for carrying out a method for cooling a fuel cell stack, a fuel cell system and a vehicle with a fuel cell system.

Various fuel cell systems are known in the prior art. One of them is a so-called SOFC system with a solid oxide fuel cell. SOFC systems are used in particular for stationary applications. In recent years, however, SOFC systems have also increasingly been developed for mobile use. SOFC systems or correspondingly configured fuel cell systems generally have at least one fuel cell stack with at least one anode section and at least one cathode section. When using such a fuel cell system, care must be taken that the anode section does not come into contact with oxygen for too long at high temperatures, for example at temperatures above 400 ° C. If this is the case, reoxidation can take place on the anode section, which can lead to immediate breakage of the electrolyte and / or to continuous degradation of the anode material.

Nevertheless, there are fuel cell systems in the prior art in which the anode section, for example, when the fuel cell system is switched off at temperatures of over 400 ° C. with oxygen or a fluid, e.g. B. is purged with air to cool the fuel cell stack as quickly as possible. Various methods and systems for cooling the fuel cell stack emerge from US 2011/123884 A1, US 2009/253007 A1, WO 2005/101556 A1 and WO 2008/001119 A2. In addition to the above-mentioned problem with regard to purging the anode section with oxygen-containing gas at excessively high temperatures, such a procedure has a further problem. In the case of a flushing process in question, a fan is usually operated by a supply battery of the fuel cell system, which blows ambient air into the anode section. This can severely discharge the supply battery. This means that either a sufficiently large supply battery would have to be installed or the supply battery would have to be charged correspondingly frequently in a mobile application. However, both should be prevented or minimized as far as possible. Correspondingly, as many power-consuming components of the fuel cell system as possible should be switched off during the switch-off process in order to keep the power consumption of the supply battery correspondingly low.

A method for cooling a reformer of a fuel cell system is disclosed in US 4965143 A, for example.

[0005] The object of the present invention is to at least partially take account of the problems described above. In particular, the object of the present invention is to provide a method for cooling a fuel cell stack, a computer program product, a memory unit, a control unit, a fuel cell system and a vehicle with a fuel cell system, through which or in which at least one component of a fuel cell system, in particular a fuel cell stack, can be cooled in a power-saving and safe manner, wherein an anode section of the fuel cell stack can be protected from damage and / or destruction.

[0006] The above object is achieved by the patent claims. In particular, the above object is achieved by the method according to claim 1, the computer program product according to claim 10, the storage unit according to claim 11, the control unit according to claim 12, the fuel cell system according to claim 13 and the vehicle according to claim

Proverb 14 solved. Further advantages of the invention emerge from the dependent claims, the description and the drawings. Features and details that are described in connection with the method naturally also apply in connection with the computer program product according to the invention, the memory unit according to the invention, the control unit according to the invention, the fuel cell system according to the invention, the vehicle according to the invention and vice versa, so that with regard to the disclosure to the individual Aspects of the invention are always referred to alternately or can be.

According to a first aspect of the present invention, a method for cooling a fuel cell stack in a fuel cell system is provided, wherein the fuel cell stack has an anode section and a cathode section and a reformer for reforming fuel for the anode section is arranged in the fuel cell system. According to the invention, fuel is only partially reformed in the reformer and the partially reformed fuel is then fed to the anode section to cool the anode section and thus also the fuel cell stack.

The only partially reformed fuel can be converted at the anode section as part of a particularly effective endothermic reaction. As a result, the anode section or the fuel cell stack are correspondingly cooled. Cooling by means of the only partially reformed fuel is a particularly easy-to-use and energy-saving measure, since basically no additional devices are required. In addition, the reduced environment protects the anode section from oxidation. Because the anode section is not exposed to air at high temperatures of, for example, over 400 ° C, in particular over 300 ° C, but at least initially only or mainly with the partially reformed fuel, the problem mentioned in the introduction to the description can be adequately taken into account will. The anode section is in particular acted upon with reformed or only partially reformed fuel which is essentially, in particular completely, free of oxygen. Damage or destruction by oxygen in the anode section at excessively high temperatures can thereby be prevented. In addition, it is advantageous that, in a method according to the invention, the operation of a fan, which is operated to flush the anode section with air, can be dispensed with at least temporarily, since the anode section is actively cooled. By doing without, electricity can be saved and the state of charge of a supply battery of the fuel cell system can be kept correspondingly high. This is particularly advantageous in the case of mobile use of the fuel cell system or the proposed method. As a result of the power-saving operation of the fuel cell system, a supply battery of the fuel cell system can still be protected from undesired deep discharge using the present method. The method therefore also serves to protect the fuel cell system. It is also advantageous that the method according to the invention results in active cooling, which is why a cathode fan can be dispensed with. It is advantageous if the fuel, which comprises methane, is at least partially reformed in the reformer in such a way that methane at least partially flows out of the reformer and is introduced into the fuel cell stack. However, the method according to the invention can also be used in combination with a cathode blower. For example, the fuel cell stack can be cooled according to the invention in a first step and cooled with the cathode fan in a second step.

The inventive method is also advantageous in order to prevent soot formation on the anode or in the anode section. For this purpose, a temperature of the reformer is changed in such a way that a temperature of the fuel cell stack is lowered in a short time by partially reformed fuel. In a further step, the fuel cell stack, in particular the anode section, is flushed with completely reformed fuel.

Under partially reformed fuel is to be understood in the context of the invention that not all of the fuel is reformed, but a predetermined proportion of fuel emerges unreformed from the reformer. Methane in particular is used as fuel. Partial reforming of the fuel can be achieved in particular by maintaining a predetermined

th reformer temperature can be reached. In principle, the degree of reforming of the fuel seems to be dependent on the reformer temperature, whereby the higher the reformer temperature, the more fuel is reformed. Consequently, with only partial reforming, the reformer temperature is kept at a constant low value, for example in the range from approximately 500 ° C. to 600 ° C.

The only partially reformed fuel is then reformed further at the anode section. This conversion takes place as part of a particularly effective endothermic reaction. The anode section has a warmer temperature than the partially reformed fuel, which is why it is cooled due to the endothermic reforming reaction. Provision can be made for the fuel cell stack to be cooled using the method according to the invention to a predetermined temperature, in particular approximately 300 ° C. or less, from which oxygen can be introduced without the fuel cell stack being damaged.

The method according to the invention is particularly preferably used in a shutdown process of a fuel cell system in which no electricity is generated.

In the present case, the cooling of the fuel cell stack is to be understood as meaning at least partial cooling of the fuel cell stack or at least partial cooling of the fuel cell system. According to the invention, in particular the anode section is cooled. This can of course also affect other components of the fuel cell system.

[0014] The proposed fuel cell system has at least one fuel cell stack. That is to say, the fuel cell system can also have several fuel cell stacks. The fuel cell stack is therefore to be understood as at least one fuel cell stack. The fuel is preferably to be understood as meaning pure fuel or a fuel mixture with pure fuel, air, another oxygen-containing fluid, water and / or another water-containing fluid. The fuel is preferably a hydrocarbon fuel.

The fuel cell system is preferably an SOFC system, i.e. a fuel cell system with at least one solid oxide fuel cell. The method is therefore provided in particular for cooling a fuel cell stack in an SOFC system. The partial reforming of the fuel is preferably to be understood as the partial conversion of the fuel into a synthesis gas in the context of steam reforming. If methane is used as fuel, for example, methane and water are converted into carbon monoxide and hydrogen as part of the reforming process. With partial reforming, the fuel is not completely converted. For example, only less than 90%, in particular only less than 70% of the fuel is converted or reformed.

According to a development of the present invention, in a method, the fuel in the reformer is partially reformed during a shutdown process of the fuel cell system and the partially reformed fuel is fed to the anode section during the shutdown process. The cooling of the fuel cell stack is particularly advantageous for the switching off process of the fuel cell system. A switch-off process is understood to mean a process in which the fuel cell system is put into a state in which it no longer generates electricity. The present method allows the fuel cell stack to be cooled down quickly during the switch-off process, while the anode section is protected from undesired oxidation due to the reduced environment. The partially reformed fuel is preferably supplied to the anode section over a predetermined period of time, in particular over a predefined initial period of the switch-off process. However, the method according to the invention is not restricted to being carried out only during a switch-off process of the fuel cell system. In principle, the method can always be carried out when the fuel cell stack or components of the fuel cell system adjoining it are to be cooled.

[0017] In a method according to the invention, it is also possible that in the combustion

fuel cell system an evaporator for evaporating the fuel is arranged upstream of the reformer, the fuel being evaporated by the evaporator, in particular during the switching-off process of the fuel cell system, and the evaporated fuel being fed to the reformer. The evaporator can therefore continue to operate during the switch-off process. As a result, the fuel can be reformed efficiently and in an energy-saving manner. The evaporator can be understood to mean a heat exchanger by means of which the fuel is heated by means of exhaust gas from the fuel cell stack or an exhaust gas burner of the fuel cell system and thereby evaporated. The reformer and thus also the evaporator are in particular arranged upstream of the fuel cell stack.

It can be of further advantage that, in a method according to the present invention, downstream of the anode section, an exhaust gas burner for burning anode exhaust gas and / or cathode exhaust gas is arranged, which is in thermal active connection with the reformer, the reformer being opened by means of the exhaust gas burner a predefined target temperature is maintained at which only a predefined part of the fuel is reformed. Temperature control of the reformer by means of the exhaust gas burner can be implemented easily and inexpensively, since no separate auxiliary devices are required. For effective heat transport from the exhaust gas burner to the reformer, the exhaust gas burner can be arranged in a ring around the reformer. However, all other arrangements from the reformer to the exhaust gas burner are also conceivable. It is always advantageous that these are arranged with respect to one another in such a way that heat is effectively transported or can be transported between them. As a result of the direct or essentially direct thermal operative connection between the reformer and the exhaust gas burner, the reformer can be kept reliably and uniformly at a desired or predefined temperature. As a result, the desired partial reforming of the fuel is possible in a correspondingly reliable manner. Heat is transferred from the flue gas burner to the reformer either through thermal convection, thermal conduction or through thermal radiation. The exhaust gas burner and the reformer are each designed and arranged in such a way that a corresponding heat transfer can take place. A reformer temperature can be changed by supplying air to the reformer or by supplying heat from the starter burner to the reformer. It can also be provided that the fuel which leaves the anode area is sufficiently warm to keep the reformer at a predetermined temperature or a predetermined temperature range. If the reformer is to be cooled, cold air can be supplied to the exhaust gas burner via the starter burner or via the cathode area.

In addition, it can be advantageous that in one method the fuel in the reformer is partially reformed during a shutdown of the fuel cell system and the partially reformed fuel is supplied to the anode section during the shutdown process, the exhaust gas burner less or more oxygen during the shutdown process is supplied than during normal operation and / or during a starting process of the fuel cell system.

As a result, the reformer temperature can be regulated in a simple manner and it can be ensured that the fuel in the reformer is only partially and not completely reformed to a predefined extent. Whether less or more oxygen is supplied to the exhaust gas burner during the switch-off process than during normal operation and / or during a starting process of the fuel cell system depends on a desired reformer temperature and / or a maximum operating temperature of the reformer. Alternatively or at the same time, air can be supplied to the reformer in order to generate an exothermic reaction so that a temperature on the reformer can be regulated autonomously. When air is supplied to the reformer, catalytic partial oxidation takes place. It can also be provided that heat is passed from the starter burner to the reformer in order to regulate a temperature of the reformer. During the switch-off process, the exhaust gas burner is preferably not only supplied with less oxygen, but rather no oxygen at all, so that only the residual heat of the exhaust gas burner is used in a controlled manner, if possible. As a result, energy resources in the fuel cell system can be used or saved efficiently. It is therefore always advantageous

when the gas for purging and / or cooling the anode section is free of oxygen or substantially free of oxygen. Any oxygen present would namely combine with the anode material, as a result of which the anode is oxidized. Oxidation of the anode section should, however, be avoided.

In experiments within the scope of the present invention it has also been found that it can be advantageous if in the fuel cell system upstream of the reformer an evaporator for evaporating the fuel and a separate fuel inlet for supplying the evaporator, in particular for preferably direct injection , of fuel are arranged in the reformer, wherein the fuel for partially reforming the fuel in the reformer is supplied to the reformer through the fuel inlet. The evaporator can also be arranged upstream of the afterburner or upstream of the fuel cell stack. The fuel is preferably injected into the reformer, for which purpose the fuel inlet is designed in particular as a fuel injector. However, the fuel can also be sprayed or pumped into the reformer, for which purpose the fuel inlet is designed for the introduction of gaseous fuel. Particularly preferably, however, the fuel is injected directly into the reformer by a fuel injector. Direct injection of the fuel by means of the fuel injector means that further operation of the evaporator can be dispensed with. This saves the energy required to operate the evaporator. The fuel cell system can thus be operated efficiently. However, it is advantageous to use the evaporator when the fuel cell system is operating below about 300 ° C., in particular when it is switched off. Furthermore, the fuel can already be atomized and injected into the reformer through the fuel inlet or the fuel injector. This enables the reforming process to be carried out efficiently. The described injection process by means of the fuel inlet is preferably carried out during the switch-off process of the fuel cell system.

In addition, it can be advantageous that, in a method according to the invention, a temperature in the fuel cell system, in particular a temperature on the fuel cell stack, is determined, the anode section being flushed with oxygen-containing gas as soon as the determined temperature is below a predefined threshold value, in particular below 400 ° C, preferably below 300 ° C. These threshold values are particularly relevant for solid oxide fuel cells. As a result, the cooling process according to the invention, in which the partially reformed fuel is used, can be combined in a simple and safe manner with a conventional cooling process in which oxygen-containing fluid is used as a flushing or coolant. In the context of the present invention, it was recognized that the anode section can be rinsed relatively safely with oxygen-containing fluid, for example air, and thus cooled accordingly at temperatures below approx. 300 ° C, if carbon monoxide forms or would form nickel carbonyl. In the context of the invention it has been found that in solid oxide fuel cells which comprise metal, more oxidation can be tolerated or a threshold value can be higher than in the case of technologically different fuel cells. Basically, a temperature range in which oxidation occurs without mechanical damage or loss of performance appears to be between about 300 ° C and 500 ° C. However, this temperature range is dependent on the design of the fuel cell stack.

Furthermore, it can be advantageous that, in a method according to the invention, a water content is determined in and / or on the anode section, and the predefined threshold value is established as a function of the determined water content. In the context of the present invention, it was found that purging or cooling with air, depending on the water content in and / or on the anode section or a moisture content in and / or on the anode section, can also be advantageous at temperatures above 300 ° C. Basically, it must be ensured, as far as possible, that the decomposition of carbon from unburned fuel in the fuel cell system is prevented. This is better possible at higher temperatures, for example above 300 ° C., than at lower temperatures. In experiments within the scope of the present invention it has been found that the risk of carbon decomposition depends largely on a water

content or a moisture content in the anode section, for example in anode channels, depends. Accordingly, taking into account the water content in and / or on the anode section, as a kind of compromise, flushing of the anode section with oxygen-containing fluid can be started at temperatures above 300 ° C in order to prevent or at least to prevent damage or destruction of the anode section or the fuel cell stack to reduce. In order to prevent soot formation, especially at temperatures below 300 ° C, a ratio between carbon, especially carbon monoxide, and water is crucial. According to the invention, the threshold value can be set dynamically. That is, the threshold value can be set differently for different operating states of the fuel cell system. As a result, the fuel cell system can be operated particularly reliably and safely.

In a further embodiment of the present invention, it is possible that methane is used as fuel in a method. Methane has proven to be an advantageous starting material for the cooling process according to the invention in various experiments within the scope of the present invention. However, the invention is not limited to methane. In addition to methane, fuels such as ethanol or diesel can also be used.

According to a further aspect of the present invention, a computer program product for cooling a fuel cell stack in a fuel cell system is provided. A computer program product according to the invention thus has the same advantages as have been described in detail with reference to the method according to the invention. The computer program product is configured and designed to carry out a method as described in detail above. The computer program product can be implemented as computer-readable instruction code in any suitable programming language such as, for example, JAVA, C ++, etc. The computer program product can be stored on a computer-readable storage unit (data disc, removable drive, volatile or non-volatile memory, built-in memory / processor, etc.). The instruction code can program a computer or other programmable device such as a control unit to perform the desired functions. Furthermore, the computer program product can be made available or be in a network such as the Internet, from which it can be downloaded by a user if necessary. The computer program product can be used both by means of a computer program, i. software, as well as by means of one or more special electronic circuits, i.e. in hardware, or in any hybrid form, i.e. by means of software components and hardware components.

According to a further aspect of the present invention, a memory unit is provided on which a computer program product as described above is stored. In addition, a control unit for a fuel cell system is provided, the control unit being configured and designed, in particular by means of a computer program product as described above, to carry out the method described above. The memory unit according to the invention and the control unit according to the invention thus bring the same advantages as have been described in detail above. The control unit can be designed in the form of a vehicle control device.

Furthermore, a fuel cell system is provided which has a fuel cell stack with an anode section and a cathode section, a reformer for reforming fuel, a fluid-communicating connection being configured between the reformer and the anode section, an exhaust gas burner for burning anode exhaust gas and / or Cathode exhaust gas, and a control unit as described above for performing the method described above. The fuel cell system is preferably designed as an SOFC system. The fuel cell system is also designed for use in mobile use.

According to a further aspect of the present invention, a vehicle with a fuel cell system as described above is provided. That also brings

a vehicle according to the invention has the advantages described above. The vehicle preferably has a drive device for driving or accelerating the vehicle, the fuel cell system being arranged and configured for a power supply to the drive device. The vehicle is preferably to be understood as a motor vehicle such as a passenger vehicle or a truck. However, the invention is not limited to this. Thus, the vehicle can be understood to mean not only a road vehicle, but also a rail vehicle, a watercraft or an aircraft. The vehicle can even be understood as a robot which is supplied with energy or electricity by the fuel cell system in question.

Further measures improving the invention emerge from the following description of various exemplary embodiments of the invention, which are shown schematically in the figures. They each show schematically:

FIG. 1 shows a block diagram to illustrate a fuel cell system with a control unit according to a first embodiment of the present invention, the control unit having a memory unit and a computer program product stored thereon,

FIG. 2 shows a block diagram to show a fuel cell system according to a second embodiment of the present invention,

FIG. 3 shows a flowchart for explaining a method according to an embodiment of the invention, and

Fig. 4 shows a vehicle with a fuel cell system according to the first embodiment of the present invention.

Elements with the same function and mode of operation are each provided with the same reference numerals in FIGS. 1 to 4.

In Fig. 1, a fuel cell system 100a is shown schematically in the form of an SOFC system according to a first embodiment. The fuel cell system 100a has a fuel cell stack 10 with an anode section 11 and a cathode section 12. The fuel cell system 100a also has a reformer 20 for reforming fuel, in the present case liquid fuel. A fluid-communicating connection through which at least partially reformed fuel can be conducted from the reformer 20 to the anode section 11 is configured between the reformer 20 and the anode section 11. The fuel cell system 100a also has an exhaust gas burner 30 for burning anode exhaust gas and / or cathode exhaust gas. The exhaust gas burner 30 is in the present case arranged in a ring around the reformer 20.

An evaporator 40 for evaporating the fuel is arranged upstream of the reformer 20. That is to say, evaporated fuel can be conducted to the reformer 20 via the evaporator 40. A fuel tank 80, through which the evaporator 40 can be supplied with fuel, is arranged upstream of the evaporator 40. This can be done via a first fuel pump P1. The fuel cell system 100a furthermore has a starting burner 50 for a starting process of the fuel cell system 100a. Alternatively, the exhaust gas burner 30 itself can also be used as a starter burner. The starting burner 50 is in a fluid-communicating connection both with the fuel tank 80 and with the exhaust gas burner 30. Fuel from the fuel tank 80 can be fed to the starting burner 50 via a second fuel pump P2. When the fuel cell system 100a is started, the exhaust gas burner 30 and thus also the reformer 20 can be brought to the desired temperature by means of burned fuel in the starting burner 50. For the combustion in the starting burner 50, air or another oxygen-containing fluid can be supplied to it. This can be implemented by a fan 70 of the fuel cell system 100a. The fan 70 is also arranged and configured for transporting oxygen to the cathode section 12 of the fuel cell stack 10. By appropriately setting a valve V1, the air can be conveyed by the blower 70 to the starting burner 50 and / or to the cathode section 12

will.

Another valve V2 is provided, via the position of which air is conveyed to the reformer 20 by the fan 70. By supplying air to the reformer 20, an exothermic reaction can take place there, which releases heat and thereby increases or regulates a reformer temperature. According to FIG. 1, conveyed by the same fan 70 as the air which is conveyed by this to the starting burner 50 and / or to the cathode section 12. For this purpose, the line downstream of the fan 70 is divided into three partial lines, the further valve V2 being arranged in a first partial line and the valve V1 being arranged in a second partial line. In principle, however, two or more fans 70 can also be provided, which convey air into one line each. 1 also shows that air is fed to a line via a position of the further valve V2 upstream of the reformer 20 and downstream of the evaporator 40. However, it can also be provided that this air is introduced or injected into the reformer 20 directly or via its own line.

The fuel cell system 100a according to FIG. 1 also has a heat exchanger 60 which is arranged downstream of the exhaust gas burner 30 and upstream of the cathode section 12 for heating the air or a corresponding cathode feed gas by means of exhaust gas from the exhaust gas burner 30. A cathode gas supply line and an exhaust gas burner exhaust line are fluidly arranged separately from one another. The burned exhaust gas from the exhaust gas burner 30 is conducted via the heat exchanger 60 to the evaporator 40 and from there out of the fuel cell system 100a. However, it can also be provided that the burned exhaust gas from the exhaust gas burner 30 is first passed to the evaporator 40 and then to the heat exchanger 60 before it is passed out of the fuel cell system 100a (not shown in FIG. 1). Such an interchanging of the evaporator 40 with the heat exchanger 60 in a representation according to FIG. 1 or FIG. 2 is possible in principle in all embodiment variants according to the invention.

The fuel cell system 100a shown in FIG. 1 also has a control unit 1. A memory unit 2 on which a computer program product 3 is stored is installed in the control unit 1. The control unit 1 and the computer program product 3 are configured to carry out a method which will be explained later with reference to FIG. 3.

In Fig. 2, a fuel cell system 100b is shown according to a second embodiment. The fuel cell system 100b according to the second embodiment has a fuel inlet 90, which is designed here as a fuel injector, for injecting, in particular for direct injection, fuel into the reformer 20. It can also be advantageous if the fuel is introduced into the reformer 20 via an evaporator (not shown) in order to evaporate it in an energy-saving manner before it is introduced into the reformer 20. The fuel can also already be present in gaseous form in the fuel inlet 90. The rest of the structure essentially corresponds to the structure of the fuel cell system 100a according to the first embodiment.

With reference to FIG. 3, a method for cooling a fuel cell stack 10 in a fuel cell system 100a, 100b as described above is then explained.

In a first step S1, a switch-off process of the fuel cell system 100a, 100b is first activated.

In a second step S2 the reformer 20 fuel or a fuel mixture is supplied. In the case of a fuel cell system 100a according to the first embodiment, this can take place via the evaporator 40, or in the case of a fuel cell system 100b according to the second embodiment via the fuel inlet 90. It should be pointed out here that, even in the case of a fuel cell system 100b according to the second embodiment, the fuel can be introduced into the reformer 20 additionally or completely via the evaporator 40 during the switch-off process. A temperature of the reformer 20 can be regulated via an amount of fuel in the exhaust gas burner 30 or via a supply of air to the reformer 20. If air is fed to the reformer, catalytic partial oxidation takes place there,

which generates heat. Such a supply of air is regulated via a position of the further valve V2. A quantity of the supplied air can in particular be adjusted continuously by means of the further valve V2, wherein the further valve V2 can also completely prevent the supply of air.

In a third step S3, the fuel introduced into the reformer 20 is only partially reformed during the switch-off process. Here, the reformer 20 can be kept at a predefined target temperature by means of the exhaust gas burner 30 or by supplying air, at which only the desired part of the fuel is reformed. It can also be provided that the exhaust gas burner 30 is supplied with heat from the starter burner 50. The exhaust gas burner 30 is fed less (or no) oxygen than during normal operation and / or during a starting process of the fuel cell system 100a, 100b. The amount of air and thus also the amount of oxygen supplied to the exhaust gas burner 30 is basically regulated by the temperature of the reformer 20 in order to achieve a desired lambda value.

Then, in a fourth step S4, the partially reformed fuel is fed to the anode section 11. Exhaust gas is then at least partially fed to the exhaust gas burner 30. In a fifth step S5, a temperature of the fuel cell stack 10 is determined. As soon as the determined temperature is below a predefined threshold value, for example below 400 ° C or below 300 ° C, the reforming of the fuel is ended immediately or after a predetermined period of time in accordance with a sixth step S6 and the anode section 11 is terminated in accordance with a seventh step S7 oxygen-containing gas, especially with air. In an embodiment not shown, a water content in and / or on the anode section 11 can be determined and the predefined threshold value can be determined as a function of the determined water content.

The steps shown in FIG. 3 can be carried out one after the other and / or at least partially with one another. In addition, not all of the steps shown in FIG. 3 are necessary for carrying out the method according to the invention. For example, step S1 can be dispensed with if the method is not to be carried out as part of a shutdown process of a fuel cell system 100a, 100b.

In Fig. 4, a vehicle 1000 with a fuel cell system 100 according to the first embodiment 100a is shown. As can be seen in FIG. 4, the fuel cell system 100a is controlled by a control unit 1, which is part of an on-board computer of the vehicle 1000. The control unit 1 can, as shown in FIG. 4, be provided separately from the fuel cell system 100a, or it can be at least partially part of a fuel cell system 100a, 100b.

In addition to the illustrated embodiments, the invention also allows further design principles. That is to say, the invention is not restricted to the exemplary embodiments shown.

REFERENCE LIST

10 11 12 20 30 40 50 60 70 80 90

100a,

1000

P1

P2

V1 V2

Control unit storage unit computer program product

Fuel cell stack Anode section Cathode section Reformer Exhaust gas burner Evaporator Start burner Heat exchanger Fan Fuel tank Fuel inlet

100b fuel cell system vehicle

first fuel pump second fuel pump

Valve valve

AT 520 156 B1 2020-11-15

Claims (14)

Claims 1. A method for cooling a fuel cell stack (10) in a fuel cell system (100a; 100b), the fuel cell stack (10) having an anode section (11) and a cathode section (12) and a reformer (20) in the fuel cell system (100a; 100b) for reforming fuel is arranged for the anode section (11), characterized in that fuel is partially reformed in the reformer (20) and the partially reformed fuel is fed to the anode section (11) for cooling the fuel cell stack (10). 2. The method according to claim 1, characterized in that the fuel in the reformer (20) is partially reformed during a shutdown process of the fuel cell system (100a; 100b) and the partially reformed fuel is fed to the anode section (11) during the shutdown process. 3. The method according to any one of the preceding claims, characterized in that an evaporator (40) for evaporating the fuel is arranged in the fuel cell system (100a) upstream of the reformer (20), the fuel, in particular during the switch-off process of the fuel cell system (100a) , is evaporated by the evaporator (40) and the evaporated fuel is fed to the reformer (20). 4. The method according to any one of the preceding claims, characterized in that downstream of the anode section (11) an exhaust gas burner (30) for burning anode exhaust gas and / or cathode exhaust gas is arranged, which is in thermal active connection with the reformer (20), the reformer (20) is kept at a predefined target temperature by means of the exhaust gas burner (30), at which only a predefined part of the fuel is reformed. 5. The method according to claim 4, characterized in that the fuel in the reformer (20) is partially reformed during a shutdown process of the fuel cell system (100a; 100b) and the partially reformed fuel is supplied to the anode section (11) during the shutdown process, the exhaust gas burner (30) being supplied with less oxygen than during the shutdown process during normal operation and / or during a starting process of the fuel cell system (100a; 100b). 6. The method according to any one of the preceding claims, characterized in that In the fuel cell system (100b) upstream of the reformer (20) an evaporator (40) for evaporating the fuel and a fuel inlet (90) arranged separately from the evaporator (40) for feeding, in particular for injecting, fuel into the reformer (20) are arranged are, wherein the fuel for the partial reforming of the fuel in the reformer (20) is fed through the fuel inlet (90) to the reformer (20). 7. The method according to any one of the preceding claims, characterized in that a temperature in the fuel cell system (100a; 100b), in particular a temperature on the fuel cell stack (10), is determined, the anode section (11) being flushed with oxygen-containing gas as soon as the determined Temperature is below a predefined threshold value, in particular below 400 ° C, preferably below 300 ° C. 8. The method according to claim 7, characterized in that a water content is determined in and / or on the anode section (11), and the predefined threshold value is established as a function of the determined water content. 9. The method according to any one of the preceding claims, characterized in that methane is used as fuel. 10. Computer program product (3) for cooling a fuel cell stack (20) in a fuel cell system (100a; 100b), wherein the computer program product (3) is configured and designed to carry out a method according to one of the preceding claims. 11. Storage unit (2) on which a computer program product (2) according to claim (10) is stored. 12. Control unit (1) for a fuel cell system (100a; 100b), wherein the control unit (1), in particular by means of a computer program product (3) according to claim 10, is configured and designed to carry out a method according to one of claims 1 to 9. 13. Fuel cell system (100a; 100b) with a fuel cell stack (10) which has an anode section (11) and a cathode section (12), a reformer (20) for reforming fuel, wherein between the reformer (20) and the anode section ( 11) a fluid-communicating connection is configured, an exhaust gas burner (30) for burning anode exhaust gas and / or cathode exhaust gas, and a control unit (1) according to claim 12 for performing a method according to one of claims 1 to 9. 14. Vehicle (1000) with a fuel cell system (100a; 100b) according to claim 13. In addition 3 sheets of drawings