FUEL CELL SYSTEM FOR ELECTRICAL ENERGY GENERATION

Description

[0001] 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.

[0002] Fuel cell systems are known to be used to generate electrical energy. For this purpose, these fuel cell systems are typically equipped with fuel cell stacks in which a plurality 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 to generate electrical energy.

[0003] In conventional fuel cell systems, either hydrogen or natural gas is typically used as the 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.

[0004] A disadvantage of the known solutions is that recirculation can reduce efficiency during operation, 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 contained in it 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 through 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.

[0005] 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 require 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.

[0006] Further fuel cell systems with an anode recirculation line are known, for example, from US 2008 / 187789 A1 A1, US 2007 / 017368 A1 and WO 2021199103 A1.

[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 14. 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 with regard to the disclosure of the individual aspects of the invention, reference is always made to each other.

[0009] According to the invention, a fuel cell system is proposed for generating electrical energy. Such a fuel cell 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. Furthermore, the anode feed section transitions into an anode recirculation section for recirculating the anode exhaust gas as anode recirculation gas to the anode feed section. The cathode section also has a cathode feed section for supplying cathode feed gas and a cathode discharge section for discharging cathode exhaust gas. A fuel cell system according to the invention is characterized in that an active cooling device for cooling the anode recirculation gas is arranged in the anode recirculation section.Downstream of the active cooling device, a water outlet is arranged for discharging the condensed water condensed in the active cooling device. Further downstream of the water outlet, a mixing section is arranged for mixing the anode recirculation gas with fuel gas and feeding it as anode feed gas into the anode feed section.

[0010] The core concept of the invention is to ensure the recirculation of anode exhaust gas as anode recirculation gas. The anode recirculation gas is recirculated in a dry manner, namely by passing it through an active cooling device. In this active cooling device, the temperature of the anode recirculation gas is brought below the boiling point of water, i.e., depending on the pressure situation and partial pressure, which depends on the composition of the gas, below approximately 100 °C. This causes the water vapor contained in the anode recirculation gas to condense and form as liquid condensate.

[0011] Downstream of the active cooling device, a separator serves 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.

[0012] 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 active cooling device is provided in accordance with the invention. According to the invention, the condensation process in this active cooling device occurs free from the influence of external cooling sources, in particular free from an external cooling circuit of the fuel cell system.

[0013] 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.

[0014] According to the invention, the integration of the condensation function using the active cooling device achieves the desired condensation of condensate in the anode recirculation 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 existing solutions, this drying step and the associated efficiency increase in the operation of the fuel cell system are achieved without the need for additional complex components.

[0015] 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.

[0016] In the solution according to the invention for the fuel cell system, a separate external cooling circuit is no longer used, but rather an active cooling device. In the context of the present invention, an active cooling device is understood to mean the active generation of cold and thus the active generation of a heat sink. Thermally activated and / or electrically activated heat sinks are particularly conceivable. A thermally activated heat sink can, for example, be an absorption heat pump. The use of electric compressors and the corresponding cold generated by changing the pressure via a refrigerant can also be used here as an electrically activated cooling device. Of course, other active cooling devices are also conceivable, which generate the desired heat sink on site without having to resort to a separate external cooling circuit.

[0017] Key advantages of a fuel cell system according to the invention stem, in particular, from the fact that active cooling enables a maximum recirculation rate of up to 100% of the anode exhaust gas as anode recirculation gas. In other words, it is possible to design the anode section as a so-called dead end, since the anode exhaust gas discharged there is 100% and thus completely fed back into the anode feed gas as anode recirculation gas. This allows the complexity of the overall fuel cell system to be further reduced and, in particular, the effort required for exhaust gas aftertreatment to be essentially eliminated.In known solutions, the collected exhaust gas from the fuel cell system usually has to be post-treated, for example using an oxidation catalyst, in order to oxidize any residual fuel gas in the anode exhaust gas and thus combust it in a targeted manner before the mixed exhaust gas is released into the environment. Because the inventive design of a fuel cell system now allows a recirculation rate of 100% of the anode exhaust gas, this anode exhaust gas is no longer released into the environment at all. Post-treatment of the anode exhaust gas, which is no longer released into the environment, is therefore also no longer necessary. Finally, it should be noted that the mixing section, for example in the form of an injector device, can also operate with less pressure on the primary side and can therefore be designed smaller and more cost-effectively.

[0018] It is envisaged that in a fuel cell system according to the invention, the active cooling device comprises a thermally activated cooling device, in particular comprising an absorption heat pump. The active cooling device is in heat-transferring contact with the cathode discharge section and is equipped for thermal activation using the heat contained in the cathode exhaust gas. As already explained in the introduction, a thermally activated cooling device is one possible embodiment of an active cooling device according to the invention. In this embodiment, heat provided by the fuel cell system itself is also used for the thermal activation. During the conversion of the individual gases in the fuel cell stack, a large amount of heat is generated as a by-product. This generated heat heats the anode exhaust gas and the cathode exhaust gas accordingly.The heat present in the cathode exhaust gas can now be used, at least in part, for the thermal activation of such a cooling device. A thermally activated cooling device therefore means that hot cathode exhaust gas is used as energy within this thermally activated cooling device, is cooled in the process, and thus provides a heat sink. To use this thermal energy for cooling, an absorption heat pump is usually provided in a thermally activated cooling device, making it possible to specifically create a heat sink for the anode exhaust gas as the anode recirculation gas through absorption and desorption processes. This clearly shows how such an active cooling device requires neither external energy nor an external cooling circuit.Apart from a possibly necessary circulation pump for the coolant between the absorption section and the desorption section of such a thermally activated cooling device, no external energy supply and in particular no supply of an external cooled coolant is necessary.

[0019] Alternatively or additionally, it is conceivable for the active cooling device in a fuel cell system according to the invention to have an electrically activated cooling device. This can be provided in addition to or as an alternative to a thermally activated cooling device. This can, in particular, be a refrigeration cycle machine that forms a conventional heat pump with the aid of a compressor. In this way, it is possible to provide the desired heat sink by introducing electrical energy directly at the active cooling device and, accordingly, to provide the condensation function for the condensate in the anode recirculation gas.

[0020] Further advantages can be achieved if, in a fuel cell system according to the invention, the anode recirculation section has a condenser device in heat-transfer contact with a cathode feed section. This serves to cool the anode recirculation gas by heating the cathode feed gas. A further water outlet for discharging the condensed water condensed in the condenser device is arranged downstream of the condenser device and upstream of the active cooling device. In other words, this embodiment now enables two-stage cooling and thus also two-stage condensation. This means that the anode exhaust gas leaves the anode section at a high outlet temperature and is heated over several steps to the desired temperature, at which it is admixed with the fuel gas as anode recirculation gas.Here, two cooling steps and two condensing steps are implemented, so that in a first step the still hot anode exhaust gas is cooled via the ambient air, whereby the ambient air can have different ambient air temperatures in different regions. Particularly in hot regions, the ambient air sucked in as cathode feed gas can therefore also be 50° Celsius or more, which limits the cooling effect on the hot anode exhaust gas. Since the volume flow of air as cathode feed gas can only be flexibly varied to a limited extent, an active cooling device according to the invention can now be arranged downstream of this cooling and condensing process. However, this active cooling device can be designed to be smaller and more compact than the general solution, since pre-condensation has already been provided by the condenser device.The cooling water discharged from the two water outlets through the corresponding separators in the water outlets can be discharged separately into the environment or can be combined and discharged together.

[0021] Furthermore, it can be advantageous if, in a fuel cell system according to the invention, the cathode discharge section is designed free of a catalyst device and / or a burner. As already explained, a fuel cell system according to the invention serves, in particular, to completely recirculate the anode exhaust gas as anode recirculation gas. This means that no anode exhaust gas needs to be discharged to the environment, and thus post-treatment of any residual fuel present in this anode exhaust gas is not necessary. Rather, only the cathode exhaust gas is released into the environment, which, however, is free of fuel in a functioning fuel cell. The omission of a catalyst device and / or a burner leads to a smaller, lighter, and cheaper design of the entire fuel cell system.

[0022] Furthermore, it can be advantageous if, in a fuel cell system according to the invention, the anode discharge section and the anode recirculation section are designed free of a dividing section for complete or essentially complete recirculation of the anode exhaust gas as anode recirculation gas. As already explained, this is only possible through the use of an active cooling device and entails further advantages, such as the possibility of dispensing with a catalyst device as described in the previous paragraph. This means that no exhaust gases are discharged to the environment on the anode side and, therefore, no aftertreatment is necessary. By dispensing with such a dividing section, it is now also possible to design the overall fuel cell system without such a component, thus being simpler, more cost-effective, and smaller.

[0023] It is also advantageous if, in a fuel cell system according to the invention, a drain valve is arranged in the anode recirculation section downstream of the active cooling device and downstream of the water outlet, for the controlled discharge of at least a portion of the recirculation gas. Because a complete recirculation rate for the anode exhaust gas is preferably provided in a fuel cell system according to the invention, this complete recirculation may be undesirable for the fuel cell system in special situations. To provide control flexibility, at least a qualitative, preferably a quantitative, portion of the recirculation gas can be discharged to the environment using a drain valve.Since the anode recirculation gas typically still contains residual amounts of fuel, a catalyst device can preferably be integrated into such a discharge valve in order to catalytically treat the anode exhaust gas as anode recirculation gas in such a special case and thus oxidize the residual fuel. In particular, the discharge valve is provided and designed exclusively for the controlled discharge of at least a portion of the recirculation gas. As a result, no heat transfer of any kind occurs, nor is a permanent distribution created. If the hydrogen is at least nearly pure, such a discharge valve is generally not provided.

[0024] 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, together with the active cooling device, a heat exchanger system is created, 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 opportunity to cool the hot anode exhaust gas and use 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 active cooling device already pre-cooled, so that lower inlet temperatures can be assumed at the active cooling device, and the required cooling capacity is correspondingly lower.

[0025] 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.

[0026] 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 prevents heat loss through the cathode exhaust gas.

[0027] 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 enhanced 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 exchange system can be controlled via valves, allowing different parts of this heat exchange system to be flexibly activated or deactivated depending on the operating situation. This allows for targeted and flexible responses to different operating situations and always achieves maximum temperature efficiency.

[0028] 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, although 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 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.

[0029] 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.

[0030] 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. Designing the anode discharge section free of external cooling circuits precisely represents this reduced complexity, since the condensation function is ensured at least partially by the heat sink of the active cooling device.

[0031] 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.

[0032] In principle, it can also be advantageous within the scope of the invention if regenerative adsorption is provided. In this case, water contained in the steam is regeneratively separated, for which purpose, for example, silicone gel pads can be provided. In particular, regenerative separation elements such as silicone gel pads are arranged in the active cooling device.

[0033] A further subject of the present invention is a method for recirculating an anode exhaust gas in a fuel cell system according to the invention as anode recirculation gas, comprising the following steps: Cooling the anode recirculation gas by active cooling using the active cooling device below the boiling temperature of water, separating the condensed condensate from the anode recirculation gas, mixing the dried recirculation gas with a fuel gas to form anode feed gas.

[0034] The use of a method according to the invention 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.

[0035] 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: Fig. 1 shows an embodiment of a fuel cell system according to the invention, Fig. 2 shows a further embodiment of a fuel cell system according to the invention, Fig. 3 shows a further embodiment of a fuel cell system according to the invention, Fig. 4a shows a further embodiment of a fuel cell system according to the invention, Fig. 4b shows a further embodiment of a fuel cell system according to the invention, Fig. 5 shows a further embodiment of a fuel cell system according to the invention, Fig. 6 shows a further embodiment of a fuel cell system according to the invention, Fig. 7 shows a further embodiment of a fuel cell system according to the invention.

[0036] In Figure 1A fuel cell system 100 is schematically shown, which has a fuel cell stack 110 with an anode section 120 and a cathode section 130. The anode section is supplied with anode supply gas AZG via an anode supply section 122, and the anode exhaust gas AAG is discharged via the anode discharge section 124. Similarly, the cathode section 130 is supplied with cathode supply gas KZG, here in the form of air LU, via a cathode supply section 132, and the cathode exhaust gas KAG is discharged via the cathode discharge section 134. As in the Figure 1As can be clearly seen, the anode section here is a so-called dead-end design, since the anode exhaust gas AAG is also 100% and thus completely recirculated as anode recirculation gas ARG. This is achieved structurally by the anode discharge section 124 merging into the anode recirculation section 140. In order to provide the desired drying for this recirculation of the anode exhaust gas AAG, an active cooling device 180 is arranged further along the anode recirculation section 140, which actively provides a heat sink for cooling the anode recirculation gas ARG at this point and thus free of external cooling connections. The cooling function is designed as a condensation function, so that the anode recirculation gas ARG is cooled below the boiling point of water, depending on the partial pressure, simplified, for example, 100 degrees Celsius.The cooled anode circulation gas ARG is thus condensed with respect to its water content, and the now liquefied condensate KW is discharged from the anode recirculation section 140 via a separator into the water outlet 128. The dried anode recirculation gas ARG is fed to an injector device as a mixing section 123 and mixed there with fuel gas BRG. This mixed gas is then fed back to the anode section 120 as anode feed gas AZG. It is clearly evident here that the 100% recirculation rate allows maximum efficiency in the use of the fuel gas BRG, even from the anode exhaust gas AAG.The otherwise increasing reduction in the Nernst voltage due to the water loading of the anode recirculation gas ARG can be avoided or at least reduced here, since the water contained can be at least partially condensed out and separated via the water outlet 128 in a cost-effective and simple manner using an active cooling device 180.

[0037] The Figure 2 shows a further development of the embodiment of the Figure 1 . Additional heat transfer systems are provided here to complement the active cooling device 180 and thus further increase the efficiency of the overall system. The individual components of this additional temperature control system can, of course, be freely combined with one another, provided this is technically feasible.

[0038] So in the Figure 2An anode supply heat exchanger 121 is shown, which is capable of ensuring heat exchange from the hot anode exhaust gas AAG to the anode supply gas AZG to be heated. This allows the anode supply gas AZG to be conditioned and preheated to have a desired higher inlet temperature into the anode section 120. At the same time, the anode exhaust gas AAG is precooled here, so that the necessary cooling capacity, particularly at the active cooling device 180, is further reduced. The dimensions of the active cooling device 180 can be correspondingly smaller.

[0039] In order to provide further pre-cooling, in particular partial condensation, a condenser device 126 is also integrated into the cathode feed section 132. Heat exchange takes place there between the anode exhaust gas AAG and the air LU supplied as cathode feed gas KZG. The air is thus drawn in from the environment and warmed up by heat transfer from the hot anode exhaust gas AAG. In the same way, in particular in combination with the anode feed heat exchanger 121 already explained, a first condensation step is already generated here, the anode exhaust gas AAG here as anode recirculation gas ARG, i.e., cooled to a temperature of less than 100° Celsius. Thus, at least some of the water from the anode recirculation gas ARG condenses and is expelled as condensate KW via a separate water outlet 128.The active cooling device 180 is located downstream, enabling even further cooling and thus even more intensive drying of the anode recirculation gas. The effect according to the invention is further enhanced by the three-stage cooling of the anode exhaust gas as anode recirculation gas (ARG).

[0040] Furthermore, the Figure 2also an additional detailed design of the activity of the active cooling device 180. This is designed here as a thermally activated cooling device 180. The thermal activation is provided by the fuel cell system itself, since hot cathode exhaust gas KAG is also conducted from the cathode discharge section 134 to the activation area of ​​the active cooling device 180. As already indicated, such a thermally activated cooling device 180 can be designed, for example, as an absorption heat pump, wherein the necessary heat activation is provided here by the increased temperature of the cathode exhaust gas KAG. Since the cathode exhaust gas KAG also usually has a very high temperature and the cathode feed gas KZG can also be preconditioned to an elevated temperature, in the embodiment of the Figure 2An additional air heat exchanger 190 is provided in the overall temperature control system of the fuel cell system 100. This allows the very hot cathode exhaust gas KAG to be used in a first step for preconditioning the cathode supply gas KZG, and then the remaining residual heat for the thermal activation of the active cooling device. Conversely, for the supplied air LU as the cathode supply gas KZG, this means that two heating stages are provided, namely by the compensator device 126 and the aforementioned air heat exchanger 190.

[0041] The Figure 3 forms the embodiment of the Figures 1 and 2also further. Here, too, additional components have been added, which can be used individually or in combination with the other components of the temperature control system. One of these components is a cathode feed heat exchanger 131, which is used here as a third heating stage for heating the cathode feed gas 132. In addition, a drain valve 129 is provided, which provides additional flexibility due to the 100% recirculation rate of the anode exhaust gas. In special situations where the amount of anode recirculation gas ARG is greater than required, such a drain valve 129, also referred to as a blowout valve, can provide a drain function for part or all of the anode recirculation gas ARG.

[0042] Also the Figure 4ashows further components of a temperature control system, here in particular with regard to additional temperature control of the anode supply gas AZG with the heated cathode exhaust gas KAG. For this purpose, a cathode exhaust heat exchanger 133 is arranged in the anode supply section 122 to ensure the aforementioned heat transfer.

[0043] The Figure 4b shows a fuel cell system 100 which is largely similar to that of Figure 4a corresponds. In the Fig. 4ba cathode exhaust heat exchanger 133 is arranged with the cold side downstream of the anode supply heat exchanger 121. The hot andean exhaust gas AAG is thus passed through a warm side of the anode supply heat exchanger 121, whereby the anode supply gas AZG is further brought to operating temperature. The cathode exhaust gas KAG is passed through the warm side of the cathode exhaust heat exchanger 133, whereby the anode supply gas AZG is first heated by the cathode exhaust gas KAG in the cathode exhaust heat exchanger 133 and then by the anode exhaust gas AAG in the anode supply heat exchanger 121. In the embodiment according to the Figure 4a In contrast, the anode feed gas AZG is first heated by the anode exhaust gas AAG in the anode feed heat exchanger 121 and then by the cathode exhaust gas KAG in the cathode exhaust heat exchanger 133.

[0044] In the Figure 5Further components are also shown 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.

[0045] Also in the Figure 5A control valve 160 is shown 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.

[0046] In the Figure 6 A further component is shown with which the fuel cell system 100 can be further developed. Thus, in the embodiment of the Figure 6In the overall temperature control system of the fuel cell system 100, an additional air heat exchanger 192 is added, which utilizes residual heat from the cathode exhaust gas KAG before its discharge into the environment in a further step for preconditioning the cathode feed gas KZG. Conversely, for the supplied air LU as the cathode feed gas KZG, this means that three heating stages are provided, namely by the condenser device 126, the air heat exchanger 192, and the air heat exchanger 190.

[0047] The Figure 7shows another fuel cell system 100. Those elements that have the same reference numerals as in the previous embodiments correspond to these and will not be described further. Here, a drain valve 195 is provided, via which anode exhaust gas AAG can be drained from the anode recirculation section 140. The dashed representation of the drain valve 195 shows another possible arrangement thereof. The drain valve 195 may be necessary if a fuel such as hydrogen or ammonia contains impurities such as nitrogen or carbon dioxide in order to prevent an enrichment of the inert and non-condensable gases in the anode path. The drain valve 195 can be opened periodically, or drainage can also occur continuously. In order to chemically convert anode exhaust gas, an exhaust gas conversion device 194 is provided, which is designed, for example, as an oxidation catalyst.In addition, an aftertreatment unit 193 is provided, which is arranged downstream of the air heat exchanger 190. The aftertreatment unit 193 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. For this purpose, the aftertreatment unit 193 can be designed, for example, as an ammonia slip catalyst (ASC), which operates at temperatures between 200°C and 500°C.

[0048] 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.

[0049] In this sense, further alternative features and feature combinations are explicitly proposed below.

[0050] Thus, the component of the ejector device can be used as a cathode mixing section 135 from the Fig. 5 shown embodiment of the fuel cell system 100 also with the embodiments of the fuel cell system 100 of Fig. 6 combined, which includes the component of the further air heat exchanger 192.

[0051] Furthermore, in an embodiment which comprises the said components of the ejector device as a cathode mixing section 135 from Fig. 5 and the further air heat exchanger 192 from Fig. 6 comprises, the cooling device 180 can be supported by a water cooling system, which can optionally be used by a system environment of the application of the fuel cell system 100.

[0052] Furthermore, in an embodiment which comprises said component of the further air heat exchanger 192 Fig. 6 instead of the ejector device from Fig. 5 a blower can be used as cathode mixing section 135.

[0053] Alternatively, in an embodiment which comprises the said component of the further air heat exchanger 192 Fig. 6 and in which, instead of the ejector device, Fig. 5 said fan is used as the cathode mixing section 135, the cooling device 180 is supported by said water cooling, which may be usable by a system environment of the application of the fuel cell system 100.

[0054] The above explanation of the embodiments describes the present invention exclusively by way of examples. List of reference symbols

[0055] 100 Fuel cell system 110 Fuel cell stack 120 Anode section 121 Anode feed heat exchanger 122 Anode feed section 123 Mixing section 124 Anode discharge section 126 Condenser device 128 Water outlet 129 Drain valve 130 Cathode section 131 Cathode feed heat exchanger 132 Cathode feed section 133 Cathode discharge heat exchanger 134 Cathode discharge section 135 Cathode mixing section 140 Anode recirculation section 160 Control valve 170 Cathode recirculation section 171 Cathode recirculation fan 180 Active cooling device 190 Air heat exchanger 192Air heat exchanger 193Aftertreatment unit 194Exhaust gas conversion device 195Drain valve AZGAnode feed gas AAGAnode exhaust gas ARGAnode recirculation gas KZGcathode feed gas KAGcathode exhaust gas KRGcathode recirculation gas BRGFuel gas LUAir KWCondensate water

Claims

1. Fuel cell system (100) for generating electrical energy, having a fuel cell stack (110) with an anode section (120) and a cathode section (130), the anode section (120) having an anode supply section (122) for supplying anode supply gas (AZG) and an anode discharge section (124) for discharging anode exhaust gas (AAG), wherein the anode discharge section (124) merges into an anode recirculation section (140) for recirculating the anode exhaust gas (AAG) as anode recirculation gas (ARG) to the anode supply section (122), the cathode section (130) comprising a cathode supply section (132) for supplying cathode supply gas (KZG) and a cathode discharge section (134) for discharging cathode exhaust gas (KAG), wherein an active cooling device (180) for cooling the anode recirculation gas (ARG) is arranged in the anode recirculation section (140), wherein a water outlet (128) for an outlet of the condensed water (KW) condensed in the active cooling device (180) is arranged downstream of the active cooling device (180), wherein a mixing section (123) is arranged downstream of the water outlet (128) for mixing the anode recirculation gas (ARG) with fuel gas (BRG) and for supplying it as anode feed gas (AZG) into the anode feed section (122), characterized in that the active cooling device (180) comprises a thermally activated cooling device, in particular comprising an absorption heat pump, the active cooling device (180) being arranged in heat-transferring contact with the cathode discharge section (134) for thermal activation by means of the heat contained in the cathode exhaust gas (KAG).

2. Fuel cell system (100) according to one of the preceding claims, characterized in that the active cooling device (180) comprises an electrically activated cooling device.

3. Fuel cell system (100) according to one of the preceding claims, characterized in that the anode recirculation section (140) comprises a condenser device (126) in heat-transferring contact with the cathode supply section (132) for cooling the anode recirculation gas (ARG) by heating the cathode supply gas (KZG), wherein a water outlet (128) for an outlet of the condensed water (KW) condensed in the condenser device (126) is arranged downstream of the condenser device (126) and upstream of the active cooling device (180).

4. Fuel cell system (100) according to one of the preceding claims, characterized in that the cathode discharge section (134) is formed free of a catalyst device and / or a burner.

5. Fuel cell system (100) according to one of the preceding claims, characterized in that the anode discharge section (124) and the anode recirculation section (140) are formed free of a splitting section for a complete or substantially complete recirculation of the anode exhaust gas (AAG) as anode recirculation gas (RZG).

6. Fuel cell system (100) according to one of the preceding claims, characterized in that a discharge valve (129) is arranged in the anode recirculation section (140) downstream of the active cooling device (180) and downstream of the water outlet (128) for a controlled discharge of at least a part of the recirculation gas (RZG).

7. Fuel cell system (100) according to one of the preceding claims, characterized in that the anode feed section (124) comprises an anode feed heat exchanger (121) in heat-transferring contact with the anode feed section (122) for heat transfer from the anode exhaust gas (AAG) to the anode feed gas (AZG).

8. Fuel cell system (100) according to one of the preceding claims, characterized in that the mixing section (123) is designed as an ejector device 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.

9. Fuel cell system (100) according to one of the preceding claims, characterized in that the cathode supply section (132) comprises 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).

10. Fuel cell system (100) according to one of the preceding claims, characterized in that a cathode removal heat exchanger (133) is arranged in the anode feed section (122), preferably downstream of an anode feed heat exchanger (121), for a heat transfer from the cathode exhaust gas (KAG) to the anode feed gas (AZG).

11. 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 (123) is arranged in the anode feed section (122) upstream of the mixing section (123).

12. Fuel cell system (100) according to one of the preceding claims, characterized in that the anode feed-off section (122) is formed free of an external cooling circuit.

13. 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 feed section (132), to the secondary connection of which a cathode recirculation section (170) is connected in a fluid-communicating manner for recirculation of a part of the cathode exhaust gas (KZG) as cathode recirculation gas (KRG).

14. Method for a recirculation of anode exhaust gas (AZG) in a fuel cell system (100) having the features of any one of claims 1 to 13, as anode recirculation gas (ARG), comprising the following steps: - cooling the anode recirculation gas (ARG) by active cooling by means of the active cooling device (180) below the boiling temperature of water, - separating the condensed water (KW) from the anode recirculation gas (ARG), - mixing the dried anode recirculation gas (ARG) with fuel gas (BRG) to form anode feed gas (AZG).