Fuel cell system for generating electric energy
Patent Information
- Application Number
- EP2023772082
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-08-09
- Filing Date
- 2023-08-08
- Publication Date
- 2025-02-26
AI Technical Summary
Recirculation of anode exhaust gas in fuel cell systems using hydrogen reduces efficiency due to water content, leading to a drop in Nernst voltage, and existing solutions require complex and costly external cooling circuits for condensation.
A fuel cell system with a dividing section to separate anode exhaust gas into recirculation and outlet streams, utilizing a capacitor device in heat-transferring contact with the cathode supply section to cool and condense the recirculation gas without an external cooling circuit, allowing for efficient separation and reuse of the anode recirculation gas.
This approach increases efficiency by eliminating the need for external cooling, reducing complexity and cost, while maintaining high performance by ensuring the anode recirculation gas is dry, thus avoiding efficiency losses associated with undried gas recirculation.
Smart Images
Figure 1.1
Abstract
Description
[0001] Fuel cell system for generating electrical energy
[0002] The present invention relates to a fuel cell system for generating electrical energy and a method for recirculating anode exhaust gas in such a fuel cell system.
[0003] It is well known that fuel cell systems are used to generate electrical energy. For this purpose, these fuel cell systems are typically equipped with fuel cell stacks in which a large number of individual fuel cells are stacked, each with an anode section and a cathode section. To generate electrical energy, fuel gas and usually ambient air are fed into the fuel cell stack, where a chemical conversion of these gases can take place, generating electrical energy.
[0004] In conventional fuel cell systems, either hydrogen or natural gas is typically used as fuel gas. Furthermore, it is known that a portion of the fuel gas that is not converted during the conversion in the fuel cell stack is fed back into the fuel cell stack as recirculation gas for a further cycle to increase the efficiency of fuel gas utilization.
[0005] A disadvantage of the known solutions is that recirculation can reduce operational efficiency, particularly when hydrogen is used as the fuel gas. If hydrogen is fed to a fuel cell stack, this hydrogen is converted in the anode section into a mixture of water and a residual hydrogen in the anode exhaust gas. When this gas mixture is recirculated, the water it contains can cause the Nernst voltage to drop significantly. The drop in the Nernst voltage for the fuel cell stack leads to a reduction in efficiency, which usually compensates for the increase in efficiency due to recirculation. In other words, when a fuel cell system is operated with hydrogen, recirculation does not lead to the desired increase in efficiency, or only to a reduced extent.
[0006] While it is already known in principle that recirculation can utilize cooling of the anode exhaust gas to condense some of the water it contains and to separate this condensate, these designs are very complex and laborious. In particular, they rely on the use of an external cooling circuit, which, with an external heat sink, is capable of supplying coolant to the recirculation line to condense the vaporous water in the anode exhaust gas. Adding an additional cooling circuit and the corresponding peripherals leads to an undesirable increase in the complexity and cost of a fuel cell system.
[0007] The object of the present invention is to at least partially remedy the disadvantages described above. In particular, the object of the present invention is to provide a cost-effective and simple way to remove condensate even when operating with hydrogen in a fuel cell system.
[0008] The above object is achieved by a fuel cell system having the features of claim 1 and a method having the features of claim 12. Further features and details of the invention emerge from the subclaims, the description, and the drawings. Features and details described in connection with the fuel cell system according to the invention naturally also apply in connection with the method according to the invention, and vice versa, so that reciprocal reference is and can always be made to the individual aspects of the invention with regard to the disclosure.
[0009] According to the invention, a fuel cell system for generating electrical energy is proposed. This system comprises a fuel cell stack with an anode section and a cathode section. The anode section is equipped with an anode feed section for supplying anode feed gas and an anode discharge section for discharging anode exhaust gas. Similarly, the cathode section is equipped with a cathode feed section for supplying cathode feed gas and a cathode discharge section for discharging cathode exhaust gas. A dividing section is provided in the anode discharge section, which allows the anode exhaust gas to be divided between an anode recirculation section for recirculation as anode recirculation gas and an anode outlet section for discharge to the environment as anode outlet gas.A fuel cell system according to the invention is characterized in that a condenser device is arranged in the anode discharge section or the anode recirculation section in heat-transferring contact with the cathode supply section. This serves to cool the anode exhaust gas or the anode recirculation gas by heating the cathode supply gas. Downstream of this condenser device, a water outlet is provided for discharging the condensed water condensed in the condenser device. Further downstream of the water outlet is a mixing section arranged for mixing the anode recirculation gas with the fuel gas and for supplying it as anode supply gas to the anode supply section.
[0010] The core concept of the invention is to ensure the recirculation of anode exhaust gas. This recirculation takes place in a split manner, so that, with the help of the splitting section, a portion of the anode exhaust gas is recirculated as anode recirculation gas. The remaining anode exhaust gas is discharged into the environment as anode outlet gas. This anode outlet gas can also be post-treated, as will be explained later. In particular, the anode outlet gas is combined with the cathode exhaust gas.
[0011] The anode recirculation gas is recirculated in a dry manner, namely by passing it through a condenser device. In this condenser device, the temperature of the anode exhaust gas or the anode recirculation gas is brought below the boiling point of water, i.e., depending on the pressure situation and a partial pressure dependent on the gas composition, below approximately 100 °C. This causes the water vapor contained in the anode recirculation gas to condense and form as liquid condensate. It should be noted here that, depending on the positioning of the dividing section, the condenser device can be arranged either upstream of this dividing section in the anode discharge section or downstream of this dividing section in the anode recirculation section. In both cases, the advantages of the invention can be achieved.
[0012] Downstream of the condenser device, a separator is provided as a water outlet, in which the condensed components, and thus the condensate, are separated from the gaseous components of the anode recirculation gas. This allows the liquid condensate to be removed from the system and, for example, released into the environment. The remaining anode recirculation gas can also be referred to as dried anode recirculation gas and, in this dried state, is fed to a mixing section. In this mixing section, which can be designed, for example, as an ejector device, a mixing chamber, or in a similar manner, the anode recirculation gas is mixed with a fuel gas supplied from a fuel gas source. Depending on the amount of anode recirculation gas available, the required remaining amount of fuel gas can be added accordingly.The mixed gas of fuel gas and anode recirculation gas is then fed back to the anode section of the fuel cell stack as anode feed gas.
[0013] The core concept of the invention is based, among other things, on the fact that no external cooling source or separate external cooling circuit is necessary for condensing the condensate in the anode recirculation gas or in the anode exhaust gas. Rather, the condenser device is designed according to the invention in heat-transferring contact with the cathode supply section. Since such a fuel cell system is operated with air as the cathode supply gas for the cathode section, air is drawn in from the environment. This drawing in can be achieved, for example, with a blower device. The drawn-in air has a corresponding ambient temperature, which, depending on the temperature situation, can range from -20 °C to 50 °C or even more. It is crucial that even in very hot operating conditions, for example in desert areas, the ambient air does not exceed the boiling point of water, usually 100 °C.In other words, even at a hot ambient temperature, the supplied ambient air is sufficient as a heat sink to provide the coldest available temperature, providing cooling capacity for the anode exhaust gas or the anode recirculation gas, allowing it to cool below the condensation temperature of water. As can be seen from the previous explanation, simply by supplying ambient air as the cathode supply gas, a cooling source is provided as a secondary function, which can also be referred to as a heat sink. This heat sink serves to extract enough heat energy from the recirculated anode exhaust gas, as the anode recirculation gas, in the condenser device, that the temperature of the anode exhaust gas or the anode recirculation gas drops below the boiling point of water.According to the invention, this condensation process takes place free from the influence of external cooling sources, in particular free from an external cooling circuit of the fuel cell system.
[0014] It should also be noted that, of course, cooling circuits can be provided at other locations in a complex fuel cell system to enable desired temperature control processes. Particularly in fuel cell systems designed as SOFC systems, very high temperatures are to be expected, so that, for example, parts of the fuel cell stack can be designed with an external cooling device. However, according to the invention, even such an existing external cooling source is not used for the condensing function of the anode recirculation gas and the anode exhaust gas.
[0015] According to the invention, the integration of the condensation function into the cathode feed section achieves the desired condensation of condensate in the anode recirculation gas or in the anode exhaust gas. Dried anode recirculation gas is thus mixed with the fuel gas, thus achieving the desired efficiency increase through recirculation without incurring a reduced Nernst voltage in undried anode recirculation gas. Compared to known solutions, this drying step and the associated increase in efficiency during operation of the fuel cell system are achieved without additional complex components, in particular exclusively through a condenser device designed as a gas-to-gas heat exchanger.
[0016] As a result, in addition to the increase in efficiency, even a smaller ejector can be used, since the separation of the unwanted condensate means that correspondingly lower volume flows have to be added to the fuel gas.
[0017] It can be advantageous if, in a fuel cell system according to the invention, the anode discharge section has an anode discharge heat exchanger in heat-transferring contact with the anode supply section for heat transfer from the anode exhaust gas to the anode supply gas. This enables a further increase in efficiency from a temperature perspective. In conjunction with the other possible different heat exchangers explained later, a heat exchanger system is thus created together with the condenser device, which can also be called a temperature control system. This allows the largest possible proportion of residual heat in the anode exhaust gas and the cathode exhaust gas to be recycled and used for other functions, such as condensing, but also supplying and conditioning the anode supply gas and the cathode supply gas.This embodiment provides the possibility of cooling the hot anode exhaust gas and using this energy to heat the anode feed gas as it is guided to the anode section. As a side effect, this results in the anode exhaust gas arriving at the condenser device already pre-cooled, so that lower inlet temperatures at the condenser device can be assumed and the required condenser power is correspondingly lower. In other words, this makes it possible to equip the condenser device with the desired condensation function even with lower air flows, but also with smaller designs and volumes.
[0018] It can also be advantageous if, in a fuel cell system according to the invention, the mixing section is designed as an ejector device, with a fuel supply of fuel gas at a primary connection of the ejector device and the anode recirculation section at the secondary connection of the ejector device. The use of an ejector device as an alternative to conventional blower devices for the mixing section brings many advantages. Firstly, rotating components and corresponding wear parts are dispensed with. Secondly, mixing and conveying are preferably combined in a common component, so that a separate conveying device in the anode supply section is no longer necessary, particularly when a fuel gas source with a high delivery pressure is available.Rather, it is sufficient to apply the corresponding fuel gas at the desired pre-pressure to the primary connection of the ejector device, so that the resulting suction effect at the secondary connection of the ejector device draws in the dried anode recirculation gas for mixing. The overall efficiency of a fuel cell system according to the invention is thus further increased and, in particular, wear resistance is improved.
[0019] It is also advantageous if, in a fuel cell system according to the invention, the cathode discharge section has a catalyst device that is fluidly connected to the anode outlet section and is provided for catalytic aftertreatment of the anode outlet gas and the cathode exhaust gas. As already explained, a portion of the anode exhaust gas is separated from the anode recirculation gas in the dividing section and is to be released into the environment. As also already explained, the anode exhaust gas contains a residual component of fuel gas, for example, hydrogen or ammonia. To ensure that this hydrogen does not escape into the environment in pure form, catalytic aftertreatment can take place in such a catalyst device.In order to provide a sufficiently large proportion of oxygen for this catalytic aftertreatment, mixing with the cathode exhaust gas is preferably provided in or upstream of this catalyst device. The aim of this catalytic aftertreatment is, in particular, to reduce the fuel gas content in the anode outlet gas to a minimum or even to use it up completely. This increases safety and can, particularly if heat is generated in this way, further increase efficiency. This applies in particular if the heat generated by this catalyst device, which is designed, for example, as an oxidative catalyst, is returned to the fuel cell system at another location via heat exchangers. If the fuel cell system is operated with ammonia, it can be advantageous to additionally provide an aftertreatment unit which converts even the last traces of ammonia.
[0020] A further advantage can be achieved if, in a fuel cell system according to the invention, the cathode supply section has a cathode supply heat exchanger in heat-transferring contact with the cathode discharge section for heat transfer from the cathode exhaust gas to the cathode supply gas. Similar to preheating the anode supply gas, the efficiency of the fuel cell system's operation is further increased if the cathode supply gas is also preconditioned to enter the cathode section at the highest possible temperature, and thus, in particular, close to the operating temperature of the fuel cell stack. Since the cathode exhaust gas has been brought to a correspondingly high load temperature as a result of the chemical reaction within the fuel cell stack, this high temperature can be used to partially transfer heat to the cathode supply gas.This corresponds to preconditioning in the form of preheating the cathode exhaust gas to the cathode feed gas. This recovery of the heat contained in the cathode exhaust gas further increases efficiency and avoids heat loss through the cathode exhaust gas. This cathode feed heat exchanger is preferably arranged directly upstream of the cathode section, and thus upstream of a catalyst device in the cathode discharge section, and downstream of the condenser device in the cathode feed section.
[0021] Further advantages can be achieved if, in a fuel cell system according to the invention, the dividing section is arranged at one of the following positions:
[0022] - Upstream of the condenser device,
[0023] - Downstream of the condenser device and downstream of the water outlet,
[0024] - Downstream of the condenser device and upstream of the water outlet.
[0025] The above list represents three different positions, which preferably cannot be occupied simultaneously. If the splitting takes place upstream of the condenser device, the subsequent condensation process, as well as the removal of condensate water, only needs to be carried out for the actually recirculated anode recirculation gas. However, it can also be advantageous to route the entire anode exhaust gas through the condenser device and even through the water outlet, so that the subsequent arrangement of the splitting section not only cools the entire anode exhaust gas but also removes the water.Particularly when a higher preconditioning power is required for the air than the cathode feed gas, it can be advantageous to use the residual heat of the entire volume flow of anode exhaust gas for this preheating as well, by accordingly passing not only the separated anode recirculation gas, but the entire anode exhaust gas through the condenser device. Since in such a case, correspondingly larger quantities of condensate are also produced, it is also advantageous if this dividing section is not only located between the condenser device and the water outlet, but preferably downstream of the water outlet. This allows a maximum heating effect to be achieved for the cathode feed gas and, at the same time, the larger amount of condensate produced can be separated from the anode recirculation gas before it is fed to the dividing section and later to the mixing section.
[0026] It is also advantageous if, in a fuel cell system according to the invention, a cathode discharge heat exchanger is arranged in the anode feed section, preferably downstream of an anode feed heat exchanger, for heat transfer from the cathode exhaust gas to the anode feed gas. This allows heat contained in the cathode exhaust gas to be additionally or alternatively transferred to the anode feed gas. Furthermore, in combination with an anode feed heat exchanger, this allows the corresponding preheating functionality to be further increased or, in other words, the anode feed gas to be brought to an even higher temperature. As shown, the system of heat exchangers in a fuel cell system according to the invention can now be equipped with heat exchanger functions at a variety of positions.Of course, individual heat exchangers in this heat exchanger system can be controlled via valves, allowing different parts of the heat exchanger system to be activated or deactivated flexibly depending on the operating situation. This allows for targeted and flexible responses to different operating situations and always achieves maximum temperature efficiency.
[0027] It may also be advantageous if, in a fuel cell system according to the invention, a cathode supply heat exchanger is arranged in the cathode supply section for heat transfer from the cathode exhaust gas to the cathode supply gas. This is also conceivable as an alternative, but also in addition to the other heat exchangers mentioned, whereby it should be noted that valves can preferably activate and deactivate the various heat exchangers. Here, too, it is possible to utilize residual heat from the cathode exhaust gas through the heat transfer in order to ensure preconditioning in the form of pre-tempering the cathode supply gas and thus further increase the operating efficiency of the fuel cell system.
[0028] Furthermore, it can be advantageous if, in a fuel cell system according to the invention, a control valve for controlling the volume flow of fuel gas through the mixing section is arranged in the anode feed section upstream of the mixing section. This makes it possible to regulate the quantity and pressure of the fuel gas in a controlled manner, particularly from a pressurized fuel gas source. Depending on the distributed quantity of anode recirculation gas, a correspondingly adjusted quantity of fuel gas can then be added, so that the desired composition and the desired volume flow of anode feed gas are always actually made available to the anode section. This control valve is therefore preferably a quantitatively controllable control valve in order to be able to respond flexibly to a wide variety of operating situations of the fuel cell system.
[0029] Furthermore, it is advantageous if, in a fuel cell system according to the invention, the anode discharge section is designed free of an external cooling circuit. As already explained, the core idea of the present invention is to provide this condensation function as efficiently as possible and without additional complexity. The design of the anode discharge section free of external cooling circuits represents precisely this reduced complexity, since the condensation function is ensured essentially exclusively by the heat sink, which is provided by the ambient air supplied as the cathode supply gas.
[0030] It is also advantageous if, in a fuel cell system according to the invention, a cathode mixing section, particularly in the form of an ejector device, is arranged in the cathode supply section. A cathode recirculation section is fluidly connected to this ejector device at the secondary connection, for recirculating a portion of the cathode exhaust gas as cathode recirculation gas. In combination with the recirculation to the anode section, this can also be referred to as double recirculation. This makes it possible to also feed the cathode exhaust gas and the residual oxygen contained therein back to the cathode section as an admixture with the cathode supply gas.
[0031] The present invention also relates to a method for recirculating anode exhaust gas in a fuel cell system according to the invention as anode recirculation gas, comprising the following steps:
[0032] - Distributing at least a portion of the anode exhaust gas as anode recirculation gas to the anode recirculation section, - Cooling the anode recirculation gas by heat transfer to the cathode feed gas below the boiling temperature of water,
[0033] - Separation of the condensed condensate from the anode recirculation gas,
[0034] - Mixing the dried anode recirculation gas with a fuel gas to form anode feed gas.
[0035] A method according to the invention, when used in a fuel cell system according to the invention, brings with it the same advantages as have been explained in detail with reference to a fuel cell system according to the invention.
[0036] Further advantages, features, and details of the invention will become apparent from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. They show schematically:
[0037] Fig. 1 shows an embodiment of a fuel cell system according to the invention,
[0038] Fig. 2 shows a further embodiment of a fuel cell system according to the invention,
[0039] Fig. 3 shows a further embodiment of a fuel cell system according to the invention,
[0040] Fig. 4 shows a further embodiment of a fuel cell system according to the invention,
[0041] Fig. 5 shows a further embodiment of a fuel cell system according to the invention,
[0042] Fig. 6 shows a further embodiment of a fuel cell system according to the invention.
[0043] Figure 1 schematically illustrates a fuel cell system 100 for generating electrical energy. A fuel cell stack 110 is schematically illustrated here, which has an anode section 120 and a cathode section 130. Of course, a plurality of individual fuel cells are stacked one above the other in this fuel cell stack 110, which correspondingly have a plurality of individual anode sections 120 and cathode sections 130. For the sake of simplicity, the entire stack is illustrated here with an anode supply section 122, an anode discharge section 124, a cathode supply section 132, and a cathode discharge section 134.
[0044] During operation of the fuel cell system 100, fuel gas BRG is supplied from a fuel source (not shown in detail). This fuel gas BRG is mixed with the anode recirculation gas ARG (explained later) to form the anode feed gas AZG. An ejector device serves as the mixing section 123. This ejector device serves to draw in the anode recirculation gas ARG and also to mix it with the fuel gas BRG.
[0045] The anode feed gas AZG is then fed to the anode section 120 in the anode feed section 122, where it can be reacted with the cathode feed gas KZG in the form of air LU. This chemical reaction generates not only the electrical energy intended to be generated during operation by the fuel cell system 100, but also heat, which heats the anode exhaust gas AAG and the cathode exhaust gas KAG. The hot anode exhaust gas AAG is then fed to a splitting section 125, where it is split into an anode recirculation gas ARG in an anode recirculation section 140 and an anode outlet gas AUG in an anode outlet section 150. The outlet section can also be flexibly controlled, making it possible, in particular, to adjust the volume fractions between the anode recirculation gas ARG and the anode outlet gas AUG.
[0046] As the still-hot anode recirculation gas ARG is passed on, it is now passed through a condenser device 126, which acts as a heat exchanger with the supplied air LU. The air LU is taken from the environment and is at ambient temperature, so that even in very hot ambient conditions, it remains below the boiling point of water. This makes it possible to cool the anode exhaust gas AAG, here as anode recirculation gas ARG, below this boiling point, so that the water components it contains condense and are present as condensate KW in the continued anode recirculation gas ARG. This mixture of condensate KW and dried anode recirculation gas ARG is passed through a separator in the form of a water outlet 128, so that the condensate KW can be separated and discharged to the environment.The remaining dried anode recirculation gas ARG is now fed to the ejector device as a mixing section 123, so that the remaining amount of fuel in the anode recirculation gas ARG is mixed with new fuel gas BRG and in turn fed to the anode section 120 as anode feed gas AZG.
[0047] The cathode exhaust gas KAG also has a correspondingly high temperature and is post-treated before being released to the environment. In the simplest version shown in Figure 1, a catalyst device 136 is provided as post-treatment, in which a mixture of cathode exhaust gas KAG and anode outlet gas AUG is jointly catalytically post-treated. The aim of this catalytic post-treatment is, in particular, to reduce the volume fraction of remaining fuel gas BRG in the anode outlet gas AUG in order to enable the safest possible release of this mixed gas consisting of anode outlet gas AUG and cathode exhaust gas KAG to the environment.
[0048] Figure 2 shows a further development of the embodiment of Figure 1, wherein various additional components are integrated here by way of example, which can be used individually or in combination. One of these additional components is an anode supply heat exchanger 121. This allows the anode exhaust gas AAG to be pre-cooled, in order to subsequently require less cooling power at the condenser device 126. This pre-cooling occurs through the heat transfer from the hot anode exhaust gas AAG to the anode supply gas AZG to be preconditioned, so that this pre-cooling simultaneously has a positive effect on the anode supply gas, whereby the operating efficiency of the fuel cell system 100 can be further increased.
[0049] Another additional component in Figure 2 is the air heat exchanger 190, which is arranged downstream in the cathode supply section 132, downstream of the condenser device 126. Thus, the cathode supply gas KZG, which has already been heated by the condenser device 126, is further heated by residual heat from the mixed gas present after the catalyst device 136, and a correspondingly higher inlet temperature for the cathode supply gas KZG is achieved at the cathode section 130.
[0050] A third distinction from Figure 1 is shown in Figure 2 by the position of the dividing section 125. Here, this is arranged downstream of the water outlet 128, so that the entire anode exhaust gas AAG is subjected to both the condensation function and the water outlet function. This allows for maximum heat recovery from the anode exhaust gas, but conversely requires a correspondingly larger condenser device 126 in order to be able to draw in and discharge correspondingly larger quantities of air LU for cooling. Because the condensate water KW is now also completely separated from the entire dried anode exhaust gas AAG, only the dried anode exhaust gas is further conveyed as anode recirculation gas ARG and as anode outlet gas AUG in the fuel cell system 100.
[0051] Figure 3 also shows additional components that can further increase the efficiency of the fuel cell system 100. Firstly, a cathode supply heat exchanger 131 is additionally provided, which allows heat recovery from the hot cathode exhaust gas KAG in the cathode supply gas KZG. Thus, the cathode supply gas KZG is supplied with heat at three points, namely in the condenser device 126, in the air heat exchanger 190, and finally, as the last heat transfer point, in the cathode supply heat exchanger 131. Figure 3 also shows a variant in which the dividing section 125 is now provided downstream of the condenser device 126, but upstream of the water outlet 128. This allows the corresponding advantages of heat recovery from the anode exhaust gas AAG to be fully supplied to the air LU in the condenser device 126.However, the water outlet 128 and the separator effect only need to be provided for the actually desired anode recirculation gas ARG, so that the separator of the water outlet 128 can be made smaller than would be the case in the variant of Figure 2.
[0052] Figure 4 also shows further subcomponents that can be used in a fuel cell system 100 according to the invention. Here, a portion of the temperature of the cathode exhaust gas KAG is used for additional heating of the anode feed gas AZG by providing a cathode exhaust heat exchanger 133 in heat-transferring contact with the anode feed section 122. With this option, it is therefore intended to introduce the highest possible temperature effect into the anode feed gas AZG.
[0053] Figure 5 also shows further components with which the fuel cell system 100 can be further developed. Firstly, these are a cathode recirculation blower 171 and a cathode dividing section 137, which allow a portion of the cathode exhaust gas KAG to be divided into a cathode recirculation section 170. This divided portion of the cathode exhaust gas KAG can thus be fed as cathode recirculation gas KRG to an ejector device as a cathode mixing section 135, ensuring cathode recirculation. This allows a variable recirculation proportion at the cathode, with higher recirculation rates being adjustable under partial load operation. The remaining cathode exhaust gas KAG is fed to the catalyst device 136 in the manner already explained several times.
[0054] Also shown in Figure 5 is a control valve 160 in the fuel gas supply for the fuel gas BRG. This is designed in particular to be quantitatively controllable so that different volume flows of fuel gas BRG can be set and different amounts of fuel gas can actually be mixed into the anode recirculation gas ARG for different operating situations.
[0055] Figure 6 shows a further embodiment of a fuel cell system 100 according to the invention, most of the elements shown correspond to those in Figure 5. Here, an aftertreatment unit 191 is additionally provided, which is arranged downstream of the air heat exchanger 190. The aftertreatment unit 191 is particularly advantageous when the fuel cell system 100 is operated with ammonia, in order to convert traces of ammonia again before the exhaust gas is released into the environment. The aftertreatment unit 191 can for this purpose be designed, for example, as an ammonia slip catalyst (ASC), which operates at temperatures between 200 °C and 500 °C. It can also be advantageous if a purge valve and / or bypass valve (not shown in Figure 6) is provided to discharge hydrogen and / or ammonia in the event of a leak. A corresponding valve can be provided in all embodiments.
[0056] The individual components, in particular of the system comprising a plurality of heat exchangers, can be freely combined with one another and, in particular, can be freely switchable via control valve systems in order to be able to react as flexibly as possible to a wide variety of operating situations of the fuel cell system 100.
[0057] Explained more explicitly, the additional components of the embodiment of the fuel cell system 100 shown in Fig. 2, ie the anode supply heat exchanger 121 and / or the air heat exchanger 190 in the same positioning to the dividing section 125 can also be combined with the system components of the embodiments of the fuel cell system 100 from Figures 1, 3, 4 or 5.
[0058] Furthermore, the additional component of the embodiment of the fuel cell system 100 shown in Fig. 3, ie the cathode supply heat exchanger 131, can also be additionally combined with the system components of the embodiments of the fuel cell system 100 from Figs. 1, 2, 4 or 5.
[0059] Furthermore, the additional component of the embodiment of the fuel cell system 100 shown in Fig. 4, ie the cathode discharge heat exchanger 133, can also be combined with the system components of the embodiments of the fuel cell system 100 from Figs. 1, 2, 3 or 5.
[0060] Likewise, the additional components of the embodiment of the fuel cell system 100 shown in Fig. 5 and or Fig. 6, ie the cathode recirculation section 170 with the cathode recirculation fan 171 and the cathode dividing section 137 and / or the aftertreatment unit 191 and / or the control valve 160 can be additionally combined with the system components of the embodiments of the fuel cell system 100 from Figures 1, 2, 3 or 4.
[0061] The above explanation of the embodiments describes the present invention exclusively by way of examples. List of reference symbols
[0062] 100 fuel cell system
[0063] 110 fuel cell stacks
[0064] 120 anode section
[0065] 121 Anode supply heat exchanger
[0066] 122 Anode feed section
[0067] 123 mixing section
[0068] 124 Anode discharge section
[0069] 125 dividing section
[0070] 126 Capacitor device
[0071] 128 Water outlet
[0072] 130 Cathode section
[0073] 131 Cathode supply heat exchanger
[0074] 132 Cathode feed section
[0075] 133 Cathode discharge heat exchanger
[0076] 134 Cathode discharge section
[0077] 135 Cathode mixing section
[0078] 136 Catalyst device
[0079] 137 Cathode dividing section
[0080] 140 Anode recirculation section
[0081] 150 anode outlet section
[0082] 160 Control valve
[0083] 170 Cathode recirculation section
[0084] 171 Cathode recirculation blower
[0085] 190 air heat exchangers
[0086] 191 Aftertreatment unit
[0087] AZG anode feed gas
[0088] AAG anode exhaust gas
[0089] AUG anode outlet gas
[0090] ARG anode recirculation gas
[0091] KZG cathode feed gas
[0092] KAG cathode exhaust gas
[0093] KRG cathode recirculation gas BRG fuel gas
[0094] LU Air
[0095] KW condensate
Claims
Patent claims Fuel cell system (100) for generating electrical energy, comprising a fuel cell stack (110) with an anode section (120) and a cathode section (130), the anode section (120) comprising an anode feed section (122) for feeding anode feed gas (AZG) and an anode discharge section (124) for discharging anode exhaust gas (AAG), the cathode section (130) comprising a cathode feed section (132) for feeding cathode feed gas (KZG) and a cathode discharge section (134) for discharging cathode exhaust gas (KAG), wherein the anode discharge section (124) has a dividing section (125) for dividing the anode exhaust gas (AAG) to an anode recirculation section (140) for Recirculation as anode recirculation gas (ARG) and an anode outlet section (150) for outlet to the environment as anode outlet gas (AUG), characterized inthat in the anode discharge section (124) or in the anode recirculation section (140) a condenser device (126) is arranged in heat-transferring contact with the cathode feed section (132) for cooling the anode exhaust gas (AAG) or the anode recirculation gas (ARG) by heating the cathode feed gas (KZG), wherein downstream of the condenser device (126) a water outlet (128) is arranged for an outlet of the condensate water (KW) condensed in the condenser device (126), wherein downstream of the water outlet (128) a mixing section (123) is arranged for mixing the anode recirculation gas (ARG) with fuel gas (BRG) and for feeding it as anode feed gas (AZG) into the anode feed section (122). Fuel cell system (100) according to claim 1, characterized inthat the anode discharge section (124) has an anode supply heat exchanger (121) in heat-transferring contact with the anode supply section (122) for heat transfer from the anode exhaust gas (AAG) to the anode supply gas (AZG). Fuel cell system (100) according to one of the preceding claims, characterized in that the mixing section (123) is designed as, The ejector device is configured with a fuel supply of fuel gas (BRG) at a primary connection of the ejector device and the anode recirculation section (140) at the secondary connection of the ejector device. The fuel cell system (100) according to one of the preceding claims, characterized in that the cathode discharge section (134) has a catalyst device (136) fluidly connected to the anode outlet section (150) for catalytic aftertreatment of the anode outlet gas (AUG) and the cathode exhaust gas (KAG). Fuel cell system (100) according to one of the preceding claims, characterized in that the cathode supply section (132) has a cathode supply heat exchanger (131) in heat-transferring contact with the cathode discharge section (134) for heat transfer from the cathode exhaust gas (KAG) to the cathode supply gas (KZG).Fuel cell system (100) according to one of the preceding claims, characterized in that the dividing section (125) is arranged at one of the following positions:. - upstream of the capacitor device (126), - downstream of the condenser device (126) and downstream of the water outlet (128), - Downstream of the condenser device (126) and upstream of the water outlet (128). Fuel cell system (100) according to one of the preceding claims, characterized in that in the anode supply section (122), preferably downstream of an anode supply heat exchanger (121), a cathode exhaust heat exchanger (133) is arranged for heat transfer from the cathode exhaust gas (KAG) to the anode supply gas (AZG). Fuel cell system (100) according to one of the preceding claims, characterized in that in the cathode supply section (132) a A cathode supply heat exchanger (131) is arranged for heat transfer from the cathode exhaust gas (KAG) to the cathode supply gas (KZG). The fuel cell system (100) according to one of the preceding claims, characterized in that a control valve (160) for controlling the volume flow of fuel gas (BRG) through the mixing section (125) is arranged in the anode supply section (122) upstream of the mixing section (125). The fuel cell system (100) according to one of the preceding claims, characterized in that the anode discharge section (124) is designed to be free of an external cooling circuit.Fuel cell system (100) according to one of the preceding claims, characterized in that a cathode mixing section (135), in particular in the form of an ejector device, is arranged in the cathode supply section (132), to whose secondary connection a cathode recirculation section (170) is fluidly connected for recirculating a portion of the cathode exhaust gas (KAG) as cathode recirculation gas (KRG). A method for recirculating anode exhaust gas (AAG) in a fuel cell system (100) having the features of one of claims 1 to 11, as anode recirculation gas (ARG), comprising the following steps: - dividing at least a portion of the anode exhaust gas (AAG) as anode recirculation gas (ARG) to the anode recirculation section (140), - Cooling of the anode recirculation gas (ARG) by heat transfer to the cathode feed gas (KZG) below the boiling temperature of water, - Separation of the condensed condensate (KW) from the anode recirculation gas (ARG), Mixing the dried anode recirculation gas (ARG) with a fuel gas (BRG) to form anode feed gas (AZG).