The invention relates to a fuel cell system comprising at least one fuel cell.
A generic fuel cell system is described in German patent document DE 10 2007 003 144 A1. The fuel system comprises an exchanging device, which combines the two functions “cooling” and humidification“. The exchanging device, referred to as a function unit in that document, permits a material flow from the used air of the fuel cell to the intake air to the fuel cell, while a heat exchange from the intake air heated by a compression device to the comparatively cool exhaust air likewise takes place.
German patent document DE 101 15 336 A1 discloses a fuel cell system, though not one with a device which is formed comparable to the function unit or the exchanging device of the above-mentioned document. DE 101 15 336 A1, however, concerns the handling of hydrogen-containing exhaust gas, which has to be emitted from time to time from the region of the anode cycle with a cycle guidance of the anode gases. The hydrogen-containing gas is introduced into the region of the intake air to the cathode region of the fuel cell so that this reacts together with the oxygen of the intake air at a catalyst, particularly at the catalyst that is present in any case in the region of the cathode.
This dosing of hydrogen-containing exhaust gas from the anode region of the fuel cell has a negative effect on the conditioning of the intake air to the cathode region of the fuel cell with regard to the temperature developed during the reaction. If the reaction is additionally permitted in the region of the catalyst at the cells themselves, a quicker ageing of the fuel cells is effected. The construction thus has the disadvantage that it is very restricted in its use, particularly also with regard to the convertible amount of hydrogen-containing exhaust gas, in order to avoid the above-mentioned disadvantages from becoming too large. The use is thus afflicted with decisive disadvantages and, due to the restriction of the hydrogen-containing exhaust gas with regard to amount, in order to minimize the disadvantages, is restricted to the use in a construction with an anode recirculation cycle.
Exemplary embodiments of the present invention provide an improved fuel cell system in that a conversion of hydrogen-containing exhaust gases is enabled, which can beneficially be used in a fuel cell system, and which avoids the above-mentioned disadvantages.
By the arrangement of catalytic material in the intake air side of the exchanging device, the exhaust gas from the anode region is converted in the exchanging device. This has the advantage that a special catalyst can be used in the exchanging device, and a reaction of hydrogen and oxygen in the cathode region is thus omitted. The negative influences on the ageing of the fuel cell can thereby be avoided. The conditioning of the intake air to the cathode region of the fuel cell additionally takes place in the exchanging device. The supply of exhaust gas from the anode region into the exchanging device thus has no or no non-correctable influence on the intake air flowing from the exchanging device to the cathode region of the fuel cell. In the region of the catalytic material the temperature of the intake air is increased, as it is, however, first cooled in the region of the exchanging device before it continues to flow to the cathode region, it has no negative influence on the intake air. Rather, the heat will further heat the used air flow cooling the intake air. This can have a decisive advantage, if, for example, the heat from the used air flow shall be used in a different manner, or if a discharge of liquid water with the used air flow from the fuel cell system shall be prevented.
Additionally, a certain amount of water or water vapor results with the conversion of the hydrogen-containing exhaust gas in the region of the catalytic material in the exchanging device. This provides, together with the water vapor transferred from the used air flow to the intake air flow through the exchanging device, a humidification of the fuel cell or of polymer electrolyte membranes (PE membranes) typically used in such a fuel cell, which separate the cathode region from the anode region and provide the function of the fuel cell in a known manner.
In a particularly favorable arrangement of the fuel cell system according to the invention, the supply of exhaust gas from the anode region takes place in a controlled and/or regulated manner. Particularly with the use of a fuel cell system with a recirculation of anode exhaust gas, the temporal and/or the quantitative supply of exhaust gas from the anode region into the intake air side of the exchanging device can be controlled or regulated within certain limits. Thereby, the supply of the exhaust gas into the exchanging device can be delayed at an unfavorable time, where, for example, no sufficient used air flow is available for cooling the resulting heat. Unfavorable operating states can thus be avoided and an improved operating guidance can be realized for the fuel cell system.
In a further particularly favorable arrangement of the fuel cell system according to the invention, a fuel, particularly hydrogen, can be supplied to the exchanging device on the intake air side. By this supply of an optional fuel, particularly of the hydrogen present in any case in the fuel cell system, a further flexibilization of the fuel cell system can be achieved. Such a supply of further fuel into the region on the intake air side of the exchanging device, and thus into the region of the catalytic material, can always take place if a higher humidity amount is required, as the supplied fuel reacts with the oxygen to water vapor. Such an optional supply can additionally take place when a larger heat amount is required in the used air flow, for example with a use of the exhaust heat, or for the evaporation of a larger amount of liquid water in the used air flow, which shall not leave the system in liquid form.
In a particularly favorable and advantageous further development of the fuel cell system according to the invention, the intake air is supplied via a compressor arranged downstream of the exchanging device, wherein the compressor can be driven by a turbine at least in a supporting manner, through the used air downstream of the exchanging device is passed. This construction with a turbine, which drives the compressor at least in a supporting manner in the manner of a turbocharger customary with internal combustion engines, permits use of the used heat in the used air flow together with the remaining pressure energy. If additional heat is now introduced into the used air flow by the construction of the fuel cell system according to the invention, this can again be converted back to mechanical energy, so that the fuel cell system altogether has less parasitic energy usage, and thus permits a higher efficiency.
The fuel cell system according to the invention thus provides a simple, compact and thus cost-efficient construction, with an ideal arrangement for the life span and the efficiency that can be achieved. The fuel cell system according to the invention is thus particularly suitable for the use in a means of transport, and here for the generation of power for the drive and/or electrical auxiliary users in the means of transport. A means of transport in the sense of the invention present can be any type of means of transport on land, on water or in the air, wherein a particular attention is certainly in the use of these fuel cell systems for motor vehicle without rails, without the use of a fuel cell system according to the invention being restricted hereby.
Further advantageous arrangements of the fuel cell system will become clear by means of the exemplary embodiments, which are described in more detail in the following with reference to the figures.
It shows thereby:
The depiction in the following figures only shows the components necessary for the understanding of the invention of the rather complex fuel cell system per se present here in a highly schematized depiction. It should be understood for the fuel cell system that further components, as for example a cooling cycle and the like are also provided in the fuel cell system, even though these are not illustrated in the figures.
In
Hydrogen from a hydrogen storage device 7, for example, a pressure gas store and/or a hydride store, is supplied to the anode region 4 in the exemplary embodiment shown here. It would also be possible to supply the fuel cell 2 with a hydrogen-containing gas, which is for example generated from hydrocarbon-containing start materials in the region of the fuel cell system.
In the exemplary embodiment of
The intake air flowing from the compressor 6 to the cathode region 3 flows through an exchanging device 12 in the construction of the fuel cell system 1 according to
It has proved to be particularly advantageous to construct the exchanging device 12 in the form of a honeycomb body, as is, for example, customary with exhaust gas catalysts of motor vehicles. A corresponding arrangement of the honeycomb body provides that the intake air flow and the used air flow flow in different adjacent channels of the honeycomb body. Any type of flow-through is thereby basically possible, for example, a co-current flow guidance or a cross flow guidance of the two material flows. It has, however, shown to be particularly suitable to guide the material flows through the exchanging device 12 in a counterflow or a flow guide with a high counterflow part. A heat exchange of the hot intake air flow to the cold used air flow of the cathode region 13 results now in the exchanging device 12. By means of a counterflow guidance the coldest used air flow is in heat-conductive contact with the part of the intake air flow that is already cooled the most, while the used air flow that is already heated to a large extent cools the intake air flow which is still very hot during the inflow into the exchanging device 12. A very good cooling of the intake air flow is achieved. The material of the exchanging device, for example temperature-resistant membranes, porous ceramics, zeolites or the like, permits a passage of water vapor from the very humid used air flow of the cathode region 3, which entrains the product water resulting in the fuel cell 2, into the region of the very dry intake air flow to the cathode region 3. The intake air flow is humidified correspondingly thereby, which has a positive effect on the function and the life span of the PE membranes 5 in the region of the fuel cell 2. Thus is the construction and the function of the exchanging device 12 also already known from DE 10 2007 003 144 A1 already mentioned at the outset.
In the exemplary embodiment present here, the exchanging device 12 additionally has a catalytic material in addition to its construction according to the state of the art. This catalytic material, which shall be symbolized in the depiction by the region 13, serves for the reaction of hydrogen with the oxygen in the intake air. The hydrogen thereby comes from the recirculation line 9 around the anode region 2 of the fuel cell 2. It is, as already mentioned, discharged from time to time via the discharge valve 11. This hydrogen-containing exhaust gas, which is also called purge gas, now reaches the exchanging device 12 on the used air side. The exhaust gas or the hydrogen contained in the exhaust gas can react there with a part of the residual oxygen in the used air in the region of catalytic material 13. Heat and water in the form of water vapor result. The water vapor is particularly advantageous here, as it supports the humidification of the intake air flow and thus the humidification of the cathode region of the fuel cell. The resulting heat is not desired in the region of the intake air. By means of the construction of the exchanging device 12, it can, however, be transferred directly to the used air flow from the cathode region 3 of the fuel cell 2 and increases its temperature compared to an exchanging device 12 without the catalytic material and the supply of exhaust gas from the anode region in addition. This, however, does not pose a disadvantage with the emission of the used air to the environment, as a comparatively warm used air is desired in order to discharge the water still contained in the used air to the environment in the form of water vapor and thus to prevent the discharge of liquid water together with the used air.
The catalytic material 13 can be introduced on the intake air side into the exchanging device 12, for example, in the form of a ballasting of catalytically active parts. It is, however, particularly advantageous if the exchanging device 12 is coated with the catalytic material 13 in its region on the intake air side. It is thereby basically possible to coat the entire surface of the exchanging device 12 on the intake air side with the catalytic material 13. It thereby only has to be observed that the coating with the catalytic material does not hinder the transfer of the water vapor from the used air to the intake air. This can, however, be achieved by a corresponding pore size or the like in the coating with catalytic material 13. Alternatively, the catalytic material 13 can be arranged only in the intake air side region of the exchanging device 12, that is, in the region in which the intake air flows from the compressor 6 into the exchanging device 12. The region is thereby meant to be a certain section of the intake air side of the exchanging device 12, for example a region of about 1/8 to 1/4 of the exchanging surface of the exchanging device 12. With such a construction it would then be possible that a material exchange between the two flows can be omitted in the region of the catalytic material 13. The remaining region of the exchange surface would be sufficient to transfer a correspondingly high amount of water vapor from the used air to the intake air. The region with the catalytic material 13 would then only serve for the catalytic reaction of the hydrogen present in the exhaust gas of the anode region 4 and for the transfer of the heat resulting thereby to the used air flow flowing from the exchanging device 12.
Additionally, a further fuel can be supplied to the exchanging device 12 on the used air side. This could be hydrogen with the hydrogen present in the fuel cell system 1 in any case. It is, however, also conceivable to supply a hydrocarbon or the like, if this would be available in the fuel cell system 1. The supply of the additional hydrogen takes place in the exemplary embodiment of the fuel cell system 1 shown here from the region of the water storage device 7 via a dosing device 14 and a corresponding guidance element 15. The optional hydrogen can, as also the exhaust gas from the anode region 4, be introduced either into the feed line of the intake air in front of the exchanging device 12, as is indicated in principle by
The construction of the fuel cell system 1 according to
The second difference of the fuel cell system 1 of
A particular advantage now results in that the exhaust heat present in the used air can now be used via the turbine 16. The heating with the catalytic reaction of exhaust gas from the anode region with oxygen in the intake air flow perceived as very problematic up to now can be used in a beneficial manner with this construction, as the heat transferred to the used air can now be used in the turbine 16 and be converted to mechanical energy.
The construction of the fuel cell system according to
It shall finally be noted that the fuel cell system 1 according to the arrangement of
Number | Date | Country | Kind |
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10 2009 009 674.4 | Feb 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/000474 | 1/27/2010 | WO | 00 | 9/29/2011 |