AT520976B1 - Heat exchanger for a fuel cell system and method for operating a fuel cell system - Google Patents

Abstract

The invention relates to a heat exchanger (1) for a fuel cell system (100), in particular a SOFC system operated with a liquid fuel, with a plurality of heat transfer elements (2), thermal energy between a system exhaust pipe (3) and a through the heat exchanger (1) Anode supply line (4) of a fuel cell system (100) is transferable, comprising an evaporation area (5), an overheating area (6) and a reforming area (7) which are flow-connected to one another, the heat transfer elements (2) at least partially comprising a catalytic material, wherein the heat transfer elements (2) have a catalytic material on the side through which system exhaust gas can flow. The invention further relates to the use of such a heat exchanger (1) and a fuel cell system (100) with such a heat exchanger (1). The invention further relates to a method for operating a fuel cell system (100), in particular an SOFC system, with such a heat exchanger (1).

Description

HEAT EXCHANGER FOR A FUEL CELL SYSTEM AND METHOD FOR OPERATING A FUEL CELL SYSTEM The invention relates to heat exchangers for a fuel cell system, in particular a SOFC system operated with a liquid fuel, with a plurality of heat transfer elements, whereby thermal energy between a fuel supply system and an anode exhaust gas line through the heat exchanger is transferable, comprising an evaporation area, an overheating area and a reforming area, which are flow-connected to one another, the heat transfer elements of a heat exchanger of the type mentioned at least partially comprising a catalytic material.

The invention further relates to the use of such a heat exchanger.

The invention further relates to a fuel cell system, in particular SOFC system, with such a heat exchanger, comprising a fuel cell stack with an anode section and a cathode section.

The invention further relates to a method for operating a fuel cell system, in particular an SOFC system.

[0005] Heat exchangers for fuel cell systems are known from the prior art. These are arranged at different locations in a fuel cell system, such as in an anode supply line. Fuel is conducted via the anode feed line to an anode section of the fuel cell system. If a liquid fuel such as diesel or ethanol is used, it must be evaporated and reformed beforehand so that the synthesis gas or hydrogen-rich gas required for the reaction in the fuel cell stack is generated. In order to be able to generate the temperatures required for this, it is known to use several heat exchangers, by means of which heat from system exhaust gas can be transferred to the fuel.

[0006] For example, DE 102007018264 A1 and WO 02085777 A2 show heat exchangers with a catalytic material.

In particular, when using a fuel cell system in a vehicle, it is an aim to keep the number of components of the same as low as possible. Consequently, solutions known from the prior art attempt to combine individual components in a common component.

For example, it is known from DE ° 10 ° 2011 ° 088 ° 566 ° A1 to couple a reformer of a fuel cell system at least in a heat-transferring manner with a heating jacket. Such a reformer is designed to carry out a partial catalytic reaction, which is why it also includes a mixing space for adding air. Thus, the goal of reducing the number of components while simultaneously reducing a component size and effective operation of the fuel cell system is not achieved by such a fuel cell system.

[0009] This is where the invention comes in. The object of the invention is to provide a heat exchanger of the type mentioned at the outset, with which a fuel cell system can be operated efficiently with as few components as possible.

It is also an aim to specify the use of such a heat exchanger.

[0011] It is also an aim to provide an improved fuel cell system.

Another goal is to provide a method of the type mentioned, with which a fuel cell system can be operated with few components and efficiently.

[0013] The object is achieved according to the invention in that the heat transfer element / 15

AT 520 976 B1 2020-04-15 Austrian patent office elements on the side through which system exhaust gas can flow have a catalytic material.

An advantage achieved in this way can be seen in particular in the fact that, through the integral design of an evaporator, superheater and reformer as the heat exchanger according to the invention, in combination with the catalytic material, only a single element is required which combines the three elements mentioned. In addition, it is possible in the heat exchanger according to the invention to process liquid fuel directly in it, without a separate evaporator and / or heat exchanger being necessary for this in the anode feed line upstream thereof. The catalytic material of the heat transfer elements allows a process of steam reforming with simultaneous heat transfer from a warm to a cold side of the heat exchanger. Furthermore, the solution according to the invention makes it possible to optimize the installation space optimization of the heat exchanger and consequently also of a fuel cell system with such a heat exchanger in such a way that the areas for heat exchange are still large enough to enable steam reforming or to be carried out efficiently. Steam reforming requires a high heat transfer and consequently a large area for carrying out the chemical reaction. This is made possible by the design of the heat exchanger according to the invention in contrast to solutions known from the prior art.

According to the invention, all areas of the heat exchanger can be coated catalytically on one side through which the system exhaust gas flows, or only some of them. It is expedient if at least the heat transfer elements of the reforming area are catalytically coated both on the side through which the fuel flows and on the side through which the system exhaust gas flows. The catalytic material arranged on the system exhaust side of the heat transfer elements makes it possible, on the one hand, to completely catalytically burn the system exhaust gas, which has not yet been completely burned in the fuel cell stack, in the heat exchanger, and on the other hand to generate sufficient heat, which further improves heat transfer. Due to the possible saving of the afterburner in a fuel cell system with a heat exchanger according to the invention, the number of components is further reduced and the compactness of the fuel cell system is increased. A heat exchanger designed in this way thus comprises not only an evaporation area, an overheating area and a reforming area, but also an afterburner area.

The fact that the heat exchanger according to the invention comprises an evaporator, a superheater and a reformer is to be understood in the context of the invention in particular that these are arranged within a common box or comprise a common shell or closed off to the outside by a common jacket are. In any case, these are jointly closed off from one environment. The heat transfer elements are arranged distributed over an entire volume of the heat exchanger. In the context of the invention, the fact that the heat exchanger can be arranged in a fuel cell system and / or can be flow-connected with lines of the same means that it is designed for arrangement in a fuel cell system and for the corresponding heat exchange.

It is also advantageous that all processes that can be carried out in the heat exchanger (evaporation, overheating, reforming) can be carried out or are carried out by steam reforming. Consequently, the heat exchanger is in particular free of and / or without a mixing chamber. It is not necessary to add air, especially oxygen. The evaporation area, the overheating area and the reforming area of the heat exchanger are directly fluidly connected to one another. It is favorable if each of the areas with the exception of the fluid connection is self-contained. The fuel can flow through the heat exchanger.

In the context of the invention, a heat exchanger is understood to mean a heat exchanger which is basically based on the cocurrent principle, countercurrent principle or cross-flow principle

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AT 520 976 B1 2020-04-15 Austrian patent office zip can be operated. In the context of the invention, the heat exchanger transfers thermal energy from a first fluid, in particular system exhaust gas, to a second fluid, in particular fuel or fuel, preferably a water-fuel mixture. In the context of the invention, the fluids can be gaseous or liquid or partly gaseous or partly liquid. The second fluid, in particular a water-containing fuel, is preferably liquid upstream of the heat exchanger and the system exhaust gas is gaseous. The anode supply line or the fuel and the system exhaust line or the system exhaust gas are therefore coupled to one another in a heat-transferring manner.

According to a first aspect of the present invention, a heat exchanger for a fuel cell system, in particular for an SOFC system (SOFC stands for “solid oxide fuel cell” or solid oxide fuel cell), is provided. Such a fuel cell system is operated in particular with liquid fuel, particularly preferably with a liquid fuel-water mixture such as an ethanol-water mixture. Nevertheless, it can also be favorable if the heat exchanger according to the invention is used in a motor arrangement of an internal combustion engine or is made available for this purpose. In particular, this can be provided for use in an EGR line and / or in an exhaust line or for heat transfer between an EGR line and an exhaust line.

In the case of a heat exchanger according to the invention, the heat transfer elements of the reforming area and / or of the superheating area in particular comprise a catalytic material, so that a catalytic reaction necessary for a reforming process can be carried out. The heat transfer elements are particularly preferably coated with a catalytic material. It is advantageous if the evaporation area is made smaller than the reforming area, that is to say the evaporation area also comprises fewer heat transfer elements than the reforming area. Its volume is preferably also smaller than the volume of the reforming area. The evaporation area is fluidly connected to the overheating area and the overheating area is fluidly connected to the reforming area.

It is expedient if the anode supply line is in fluid communication with the evaporation region, fuel, in particular a fuel / water mixture, being able to be conducted to an anode section of the fuel cell system via the anode supply line connected to a cold side of the heat exchanger. Liquid fuel can be conducted to a part of the anode feed line which forms a fuel feed line and to the evaporation area, where it is converted into a gas. The fuel is therefore conducted over the cold side of the heat exchanger, which can be vaporized in particular by heat from system exhaust gas. The fuel flows in the direction of flow in the anode feed line first into the evaporation area, then into the overheating area and finally into the reforming area before it can be conducted downstream of the heat exchanger in the direction of the anode gate.

It is advantageous if a system exhaust gas line for supplying system exhaust gas of the fuel cell system to the overheating area and / or to the reforming area is provided, wherein the completely exhausted system exhaust gas can be guided over the warm side of the heat exchanger. The catalytic material of the reforming area can in particular be brought to a predetermined operating temperature or activation temperature by means of warm or hot system exhaust gas. The catalytic material enables chemical reactions to convert the fuel from around 450 ° C in the reforming area of the heat exchanger. The heat of the system exhaust gas is transferred through the heat transfer elements to the gaseous fuel in the reforming area. Since the reforming area and / or the overheating area requires higher temperatures than the evaporation area, a downstream flow direction of the system exhaust gas is in particular as follows: reforming area, overheating area, evaporation area. In the context of the invention, system exhaust gas is understood to mean in particular anode exhaust gas and cathode exhaust gas. In a fuel cell system with a heat exchanger according to the invention, anode exhaust gas is downstream of a fuel cell stack with the addition of

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Cathode exhaust gas (air) in particular burned completely in an afterburner. The system exhaust gas is then fed downstream of the afterburner to the heat exchanger according to the invention, the heat of the same being used almost completely for the processes in the heat exchanger before cooled system exhaust gas is released to the environment downstream of the heat exchanger.

In principle, it can also be advantageous if system exhaust gas which is not completely burned can be passed over the warm side of the heat exchanger via the system exhaust line for supplying system exhaust gas from the fuel cell system to the overheating region and / or to the reforming region. That is to say, in a fuel cell system with the heat exchanger according to the invention, the system exhaust gas which is combined downstream of a fuel cell stack from anode exhaust gas and cathode exhaust gas is in particular fed directly to the heat exchanger. There is therefore no need for a catalytic afterburner. The heat transfer elements therefore have a catalytic material on the side through which the system exhaust gas flows or can be flowed through, or are coated with a catalytic material. All areas of the heat exchanger can be catalytically coated on one side through which the system exhaust gas flows, or only some of them. It is expedient if at least the heat transfer elements of the reforming area are catalytically coated both on the side through which the fuel flows and on the side through which the system exhaust gas flows. The catalytic material arranged on the system exhaust side of the heat transfer elements makes it possible, on the one hand, to completely catalytically burn the system exhaust gas, which has not yet been completely burned in the fuel cell stack, in the heat exchanger, and on the other hand to generate sufficient heat, which further improves heat transfer. Due to the possible saving of the afterburner in a fuel cell system with a heat exchanger according to the invention, the number of components is further reduced and the compactness of the fuel cell system is increased. A heat exchanger designed in this way thus comprises not only an evaporation area, an overheating area and a reforming area, but also an afterburner area.

[0024] It is advantageous if the overheating area and the reforming area are designed as a common area. This means that the fuel can be overheated and reformed in one step or at least very quickly in succession. The overheating area and the reforming area are not spatially separated. In contrast to this, the evaporation area is separated from the overheating area and / or reforming area in such a way that the fuel first passes the evaporation area in the flow direction and then enters the overheating area and / or reforming area in gaseous form. In the overheating area, the gaseous fuel can be heated to a temperature of approximately 300 ° C. to approximately 400 ° C. or more by heat transfer from the system exhaust gas and can therefore be preconditioned for reforming. By designing the overheating area and the reforming area as a common area, the overheated and preconditioned gas can be used and reformed directly in the reformer.

In the context of the invention, the heat exchanger can be designed as desired, for example as a tube bundle heat exchanger. However, this is expediently designed as a plate heat exchanger. The heat transfer elements are thus designed as plates or bundles of plates, the plates or bundles of plates of the reforming area comprising a catalytic material or being coated with a catalytic material. A heat exchanger designed as a plate heat exchanger is particularly advantageous if the plates have a small thickness in the range from approximately 1 mm to 2 mm, in particular approximately 1.2 mm to 1.5 mm, particularly preferably approximately 1.3 mm . Due to the thin wall thickness and a large area of the plates (in the range of approximately 200 mm by 80 mm), a large heat transfer is possible. The evaporation area can comprise, for example, approximately 24 plates, whereas a common area for overheating and reforming can comprise approximately 30 plates, these being at least partially catalytic

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AT 520 976 B1 2020-04-15 Austrian patent office are coated or comprise a catalytic material. In principle, however, more or fewer plates can also be provided. A number of the plates depends on a given installation space and / or pressure loss requirements. The plates of the plate-shaped heat exchanger are connected to one another in a force-locking or material-locking manner in such a way that in each case the fuel flows and then the system exhaust gas flows in successive gaps between individual plates. The plates are advantageously each formed with a profile or profiled, so that an area for heat transfer is further increased. It is advantageous if the plates, which are arranged in the reforming area, are coated with a catalytic material. One side of each of the plates is coated catalytically, the coated side of two successive plates being aligned with one another, so that the gaseous and superheated fuel flows between these plates and is reformed. In principle, however, it can also be provided that only every second plate is coated catalytically. The plates of the plate heat exchanger can also be coated at least partially on both sides, so that even those areas in which the system exhaust gas flows are designed for catalytic reforming. This is particularly advantageous if the system exhaust gas is fed directly downstream of a fuel cell stack to the heat exchanger via the system exhaust gas line without being completely burned in an afterburner. Such a heat exchanger then takes on the function of an afterburner or also contains this component.

It is advantageous if the catalytic coating is designed as a catalytic fabric or a catalytically coated, in particular metallic, grid. It is particularly expedient if the heat transfer elements of the reforming area are coated with the catalytic fabric or the catalytically coated grid. The catalytic coating is designed to reform the vaporized and possibly overheated fuel. If the reforming area and the overheating area are integrally formed, the vaporized fuel is overheated and reformed approximately simultaneously. The reforming is advantageously carried out by steam reforming without the addition of air or steam. In particular, if a water-containing fuel such as an ethanol-water mixture is used, no separate supply of (water) steam is necessary. The amount of steam required for steam reforming is already provided by the vaporized fuel itself. In particular, it can be provided within the scope of the invention that the catalytic coating is designed as a catalytically coated metallic grid. This is inserted between two plate-shaped heat transfer elements, after which they are connected to one another in particular in a force-locking manner in such a way that the sides of the plates which are arranged in relation to one another are coated with the grid. The fuel to be reformed is then passed between these two plates. The advantage of using a catalytically coated metallic grid is that it has a low thermal mass and consequently can be heated to the predetermined temperature required to activate the catalytic reactions in a short time. If, as an alternative or in addition, a catalytic coating is also provided on that side of the heat transfer elements around which the system exhaust gas flows, this is designed accordingly as described above.

It is particularly expedient if the reforming area is designed and arranged to carry out steam reforming. So there is an endothermic reaction. According to the invention, the energy required for this is provided via the system exhaust gas, which is coupled to the reforming area for heat transfer.

In addition, however, it can also be advantageous if a supply line of air to the evaporation area or superheating area is provided. In particular, air upstream of the evaporation area can be mixed with the fuel. Alternatively, it can also be provided that the fuel and the air are fed separately to the evaporation area of the heat exchanger. It may also be advantageous if the air is fed to the superheating area downstream of the evaporation area. In the air

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AT 520 976 B1 2020-04-15 Austrian patent office is understood in the context of the invention to be an oxygen-containing fluid, in particular an oxygen-containing gas, particularly preferably ambient air. This makes it possible, optionally in addition to or as an alternative to steam reforming, to carry out a catalytic partial oxidation. This is particularly advantageous in a starting phase of the fuel cell system, in which a fuel cell stack is still cold and has to be heated. By supplying air during, in particular exclusively, a starting phase of the fuel cell system, the fuel cell stack can thus be warmed up by catalytic partial oxidation. When this has reached a predetermined temperature, the supply of air is switched off again, in particular by means of a valve. In addition, the air supply prevents or at least greatly reduces soot formation in the heat exchanger, in particular in the overheating area, during a starting phase of the fuel cell system in which the heat exchanger according to the invention can be arranged. It has been found that the supply of an oxygen-containing fluid to the evaporation process of the water-fuel mixture prevents or at least greatly reduces soot formation during an, in particular exclusive, starting phase of a fuel cell system. Since the formation of soot occurs in particular only when the water / fuel mixture overheats, for example from 200 ° C., in particular from 300 ° C. or more, the air is preferably only fed to the heat exchanger downstream of the evaporation area.

It is expedient if an electrical heating device is provided. This means that the heat exchanger comprises an electrical heating device. In principle, however, the heating device can also be non-electrical. This is especially designed for heating the fuel or fuel-water mixture, particularly preferably the heating device is designed and arranged exclusively for heating, evaporating and / or reforming the fuel or fuel-water mixture during a warm-up phase of the fuel cell system. During a start-up phase or a warm-up phase of the fuel cell system, there is still no or not enough or not enough warm system exhaust gas to transfer the required heat to the heat exchanger. In the case of a heating operation, the electrical heating device can be in operation for a period of approximately 2 minutes to 10 minutes, for example. It is advantageous if the heating device is arranged in a section through the heat exchanger between the evaporation area and the reforming area and / or overheating area. Electrical support for evaporation and reforming can in principle be carried out in an external component, but integration of this function is desirable for reasons of space. As soon as the fuel cell system has reached an operating temperature, the heating device is switched off again.

A heat exchanger according to the invention is advantageously used for evaporating, overheating and reforming a liquid fuel in a SOFC system.

According to a further aspect of the present invention, a fuel cell system with a heat exchanger as shown in detail above is provided. The fuel cell system furthermore has a fuel cell stack with an anode section and a cathode section as well as a starting burner, an afterburner and at least one further heat exchanger. It is also expedient if the fuel cell system has a plurality of valves for controlling various lines and a blower for conveying the cathode supply air to the cathode section. The at least one further heat exchanger is arranged with a cold side in a cathode supply line downstream of the fan in order to raise the air which is supplied to the cathode section to a temperature which is correspondingly necessary for this. The fuel cell system according to the invention is used in particular in a motor vehicle.

The further goal is achieved if a method of the type mentioned at the beginning comprises the following steps:

Directing a liquid fuel, in particular a liquid fuel-water mixture, in the direction of a heat exchanger according to the invention arranged in an anode supply line,

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Evaporation, overheating and reforming of the fuel in the heat exchanger, the heat exchanger being heated via, in particular completely burned, system exhaust gas, heat being transferred from the system exhaust gas carried in a system exhaust gas line to the fuel, system exhaust gas being conducted via heat transfer elements comprising catalytic material,

- Feeding the vaporized, superheated and reformed fuel to an anode section of the fuel cell system.

An advantage achieved in this way can be seen in particular in the fact that the fuel is evaporated efficiently and in a single component, overheated and completely reformed by the steps of the method according to the invention, so that it subsequently becomes synthesis gas for the fuel cell stack, more precisely for the anode section can be directed. In the context of the invention, a reformed fuel is to be understood as synthesis gas that can be used in the fuel cell stack. Due to the heat transfer from the system exhaust gas to an evaporation area, overheating area and reforming area, the entire waste heat of the system exhaust gas is used to heat a single component. The heat of the system exhaust gas is advantageously transferred in the following order to carry out the processes taking place in the heat exchanger: overheating and / or reforming of the vaporized fuel or vaporized water-fuel mixture and vaporization of the fuel or water-fuel mixture.

The other advantages and functions associated with the functioning of the heat exchanger are the same as those described in detail above with reference to the heat exchanger according to the invention and the fuel cell system according to the invention.

It is further advantageous if the fuel is steam-reformed in the heat exchanger, the heat exchanger comprising a catalytic material. In particular, no air supply is necessary or provided. Thermally conductive elements, for example plates, are particularly preferably coated with a catalytic material.

Basically, the heat and the system exhaust gas can flow through the heat exchanger in the direct current principle or in the cross flow principle. A particularly efficient heat transfer from the system exhaust gas to the fuel is achieved, however, if the fuel and system exhaust gas flow through the heat exchanger in the counterflow principle. The fuel or vaporized or overheated fuel is therefore flowed past the system exhaust gas in the opposite area of the heat exchanger, heat being transferred from the system exhaust gas to the (vaporized and overheated) fuel and / or the catalytic material of the reforming area.

It is advantageous if the evaporation area of the heat exchanger flows through downstream of a reforming area of the heat exchanger from the system exhaust gas, wherein the reforming area flows through upstream of an overheating area of the heat exchanger from the system exhaust gas. With this arrangement of the elements or the order in which they flow through, heat is transferred particularly efficiently. This means that the necessary and predetermined temperatures which are required for the respective processes (evaporation, overheating, reforming) are reached in a short period of time.

It is particularly advantageous if the fuel flows through an evaporation region of the heat exchanger upstream of an overheating region of the heat exchanger, wherein the fuel flows through a reforming region of the heat exchanger downstream of the overheating region in order to further optimize the heat transfer.

It is expedient if air is passed via a cathode supply line to a cathode section of the fuel cell system. In the context of the invention, air is understood to mean, in particular, ambient air, although air can also consist of a larger part of oxygen or pure oxygen. Downstream of the fuel cell stack, anode exhaust gas and cathode exhaust gas are mixed to form the system exhaust gas, through which the

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AT 520 976 B1 2020-04-15 Austrian patent office the necessary heat for the evaporation process, overheating process and reforming process is provided.

Further advantages, features and effects result from the exemplary embodiments shown below. In the drawings, to which reference is made, show:

1 shows a heat exchanger according to the invention;

[0043] FIG. 2 is a block diagram to show a fuel cell system according to the invention in accordance with an embodiment of the invention;

3 shows a block diagram to illustrate a further fuel cell system according to the invention in accordance with an embodiment according to the invention.

1 shows a heat exchanger 1 according to the invention. This comprises a plurality of heat transfer elements 2, an evaporation area 5, an overheating area 6 and a reforming area 7. Furthermore, the heat exchanger 1 designed as a plate heat exchanger has a cold side 8 and a warm side 9. The cold side 8 of the heat exchanger 1 can be arranged in an anode supply line 4, and heat from system exhaust gas can be transferred to an aqueous fuel carried in the anode supply line 4 via a system exhaust gas line 3. The heat exchanger 1 is designed as a plate heat exchanger and comprises a plurality of plate-shaped heat transfer elements 2, some of which comprise a catalytic material. Both the evaporation area 5, the overheating area 6 and the reforming area 7 comprise heat transfer element 2, these areas being connected to one another in terms of flow. The heat exchanger 1 is designed to gradually evaporate, overheat and reform a fuel-water mixture, the thermal energy required for this being transmitted by the system exhaust gas. Since the heat exchanger 1 can be made compact due to the integral design of the three areas mentioned above, the size of an entire fuel cell system 100 is subsequently reduced. The heat exchanger 1 can in principle be designed for heat transfer in the cocurrent principle, countercurrent principle or cross-flow principle. The direction of flow of the fuel in the anode supply line 4 is always the same: in the direction of flow of the fuel first into the evaporation area 5, then into the overheating area 6 and finally into the reforming area 7. The heat exchanger 1 shown in FIG. 1 is operated in the counterflow principle. If this is to be operated according to the direct current principle or the cross-flow principle, a routing of the system exhaust gas line 3 or a flow sequence of the areas of the system exhaust gas is accordingly adapted.

2 shows a block diagram to illustrate a fuel cell system (100) according to the invention in accordance with an embodiment according to the invention. In addition to the heat exchanger 1, this further comprises a fuel cell stack 120 with an anode section 110 and a cathode section 130. In addition, a start burner 140, an afterburner 150, a further heat exchanger 160 and a fuel source 170 and an air source 180 are provided. The elements mentioned are connected to one another via an anode supply line 4, a cathode supply line 12 and a system exhaust gas line 3. Various valves 13 are provided for switching these lines 3, 4, 12. To supply air to the cathode section 130, a cathode fan 200 is provided, which is arranged in the cathode supply line 12 in the flow direction of the air downstream of the air source 180 and upstream of the further heat exchanger 160. The further heat exchanger 160 is arranged with its cold side in the cathode supply line 12 and is designed to heat the air which is supplied to the cathode section 130. A warm side of the further heat exchanger 160 is flowed through by the system exhaust gas upstream of the heat exchanger 1.

3 shows a preferred embodiment of the fuel cell system 100, wherein the heat exchanger 1 is flowed through in the counterflow principle.

[0048] In a method according to the invention for operating a fuel cell system

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100 in accordance with FIG. 3, a liquid water-fuel mixture is guided from the fuel source 170 through the fuel pump 210 and a valve 13a in the open position in the anode supply line 4 in the direction of the heat exchanger 1 in regular operation. In the heat exchanger 1, the water-fuel mixture is completely evaporated in the evaporation area 5 in a first step, this having a temperature of over 100 ° C., preferably over 110 ° C., in particular about 120 ° C., when it emerges from the evaporation area 5 . In a second step, the temperature of the now gaseous water-fuel mixture step in the overheating area 6 is completely reformed to approximately 200 ° C. or 300 ° C. and in a third step in the reforming area 7. In the overheating area 6, the gaseous water-fuel mixture is thus preconditioned for use in the reforming area. The thermal energy required for these processes in the heat exchanger 1 is transferred via the heat transfer elements 2 by means of the system exhaust gas in the system exhaust gas line 3. The water-fuel mixture now present as synthesis gas is conducted downstream of the heat exchanger 1 in the anode supply line 4 to the fuel cell stack 120, more precisely to the anode section 110.

Downstream of the fuel cell stack 120, the anode exhaust gas and the cathode exhaust gas are combined to form the system exhaust gas, the anode exhaust gas being burned in a catalytic afterburner 150 with admixture of the cathode exhaust gas. Downstream of the afterburner 150, the now completely burned system exhaust gas is conducted in the system exhaust line 3 in the direction of the further heat exchanger 160. Via the further heat exchanger 160, thermal energy is transferred from the system exhaust gas to the air, which is supplied to the cathode section 130 in the cathode supply line. The heat exchanger 1, to which the system exhaust gas is fed, is arranged downstream of the further heat exchanger 160. The heat exchanger 1 is flowed through according to FIG. 3 in the counterflow principle, which is why heat is first transferred to the reforming area 7. 3, the reforming area 7 and the overheating area 6 are essentially designed as a common area. This means that the two steps of overheating and reforming in the heat exchanger 1 take place essentially simultaneously or with a very short time interval from one another. Downstream of the reforming area 7 or overheating area 6, the system exhaust gas is fed to the evaporation area 5 connected to the flow. The remaining heat from the system exhaust gas is used to evaporate the water-fuel mixture. The now cooled system exhaust gas is discharged downstream of the heat exchanger 1 into the environment 220.

Before the regular operation of the fuel cell system 100 described above, this and / or the elements arranged therein must generally be heated to a predetermined temperature. For this purpose, the fuel cell system 100 comprises a start burner 140. This is arranged in a partial line 14 of the fuel cell system 100. Fuel from the fuel source 170 and air from the air source 180 are fed to the starting burner 140 via two subsections 14a, 14b of the sub-line 14. The first section 14a separates from the anode supply line 4 downstream of the fuel source 170, a valve 13b being arranged in the first section. The second section 14b separates from the cathode supply line 12 downstream of the air source 180, the first section 14a and the second section 14b being brought together upstream of the starting burner 140. In the start burner 140, the fuel is consequently burned while supplying air to a hot gas. The gas is fed downstream of the start burner 140 during a warm-up phase of the fuel cell system 100 in the flow direction first to the further heat exchanger 160 and then to the heat exchanger 1, the heat of the gas being transferred to the latter. As soon as the fuel cell system 100 or the individual elements thereof have reached the predetermined operating temperature, the heat transfer to the heat exchangers 1, 160 takes place via the system exhaust gas, as described above.

Furthermore, it is advantageous if a supply line 10 of air to the evaporation area 5 or overheating area 6 is provided. According to FIGS. 2 and 3, air or an oxygen-containing fluid can be supplied to the evaporation region 5 via the supply line 10 in order to be able to

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Heating operation of the fuel cell system 100 to heat the fuel cell stack 120 via a catalytic partial oxidation. As soon as the fuel cell system 100 has reached an operating temperature, the air supply can be adjusted via a valve, not shown.

Claims (17)

1. Heat exchanger (1) for a fuel cell system (100), in particular a SOFC system operated with a liquid fuel, with a plurality of heat transfer elements (2), thermal energy between a system exhaust gas line (3) and an anode supply line () through the heat exchanger (1) 4) of a fuel cell system (100) is transferable, comprising an evaporation area (5), an overheating area (6) and a reforming area (7) which are flow-connected to one another, the heat transfer elements (2) at least partially comprising a catalytic material, characterized in that that the heat transfer elements (2) have a catalytic material on the side through which system exhaust gas can flow. 2. Heat exchanger (1) according to claim 1, characterized in that the anode supply line (4) is connected to the evaporation region (5) by flow, fuel via the anode supply line (4) connected to a cold side (8) of the heat exchanger (1), in particular a fuel-water mixture, which can be guided to an anode section (110) of the fuel cell system (100). 3. Heat exchanger (1) according to claim 1 or 2, characterized in that the system exhaust gas line (3) for supplying system exhaust gas of the fuel cell system (100) to the overheating area (6) and / or to the reforming area (7) is provided, which in particular completely burned system exhaust gas can be conducted over a warm side (9) of the heat exchanger (1). 4. Heat exchanger (1) according to one of claims 1 to 3, characterized in that the overheating area (6) and the reforming area (7) are designed as a common area. 5. Heat exchanger (1) according to one of claims 1 to 4, characterized in that the heat exchanger (1) is designed as a plate heat exchanger. 6. Heat exchanger (1) according to one of claims 1 to 5, characterized in that the catalytic coating is designed as a catalytic fabric or catalytically coated, in particular metallic, grid. 7. Heat exchanger (1) according to one of claims 1 to 6, characterized in that the reforming area (7) is designed and arranged to carry out a steam reforming. 8. Heat exchanger (1) according to one of claims 1 to 7, characterized in that a supply line (10) of air to the evaporation area (5) or overheating area (6) is provided. 9. Heat exchanger (1) according to one of claims 1 to 8, characterized in that an electrical heating device is provided. 10. Use of a heat exchanger (1) according to one of claims 1 to 9 for evaporating, overheating and reforming a liquid fuel in a SOFC system. 11. Fuel cell system, in particular SOFC system, with a heat exchanger (1) according to one of claims 1 to 9, comprising a fuel cell stack (120) with an anode section (110) and a cathode section (130), characterized in that a starting burner ( 140), an afterburner (150) and at least one further heat exchanger (160) are provided. 12. A method for operating a fuel cell system, in particular an SOFC system, comprising the steps: Directing a liquid fuel, in particular a liquid fuel-water mixture, in the direction of a heat exchanger (1) arranged in an anode supply line (4) according to one of claims 1 to 10, 11/15 AT 520 976 B1 2020-04-15 Austrian patent office - Evaporation, overheating and reforming of the fuel in the heat exchanger (1), the heat exchanger (1) being heated via, in particular completely burned, system exhaust gas, heat being transferred from the system exhaust gas conducted in a system exhaust gas line (3) to the fuel, system exhaust gas being transferred heat transfer elements (2) having catalytic material is guided, - Feeding the vaporized, superheated and reformed fuel to an anode section (110) of the fuel cell system (100). 13. The method according to claim 12, characterized in that the fuel in the heat exchanger (1) is steam reformed, the heat exchanger (1) comprising a catalytic material. 14. The method according to claim 12 or 13, characterized in that the heat exchanger (1) is flowed through by the fuel and the system exhaust gas in the countercurrent principle. 15. The method according to any one of claims 12 to 14, characterized in that an evaporation area (5) of the heat exchanger (1) downstream of a reforming area (7) of the heat exchanger (1) is flowed through by the system exhaust gas, wherein the reforming area (7) upstream of an overheating area (6) of the heat exchanger (1) is flowed through by the system exhaust gas. 16. The method according to any one of claims 12 to 15, characterized in that an evaporation area (5) of the heat exchanger (1) upstream of an overheating area (6) of the heat exchanger (1) is flowed through by the fuel, wherein a reforming area (7) of the heat exchanger ( 1) the fuel flows through downstream of the overheating region (6). 17. The method according to any one of claims 12 to 16, characterized in that air is passed via a cathode supply line (12) to a cathode section (130) of the fuel cell system (110).