Fuel cell system for generating electrical energy

Abstract

The present invention relates to a 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) having an anode supply section (122) for supplying an anode supply gas (AZG) and an anode discharge section (124) for discharging an anode exhaust gas (AAG), the cathode section (130) having a cathode supply section (132) for supplying a cathode supply gas (KZG) and a cathode discharge section (134) for discharging a cathode exhaust gas (KAG), the anode discharge section (124) having an anode recirculation section (140) for recirculating the anode exhaust gas (AAG) as an anode recirculation gas (ARG) and an anode discharge gas (AUG). anode exhaust gas (AAG) or anode recirculation gas (ARG) for cooling the anode exhaust gas (AAG) or anode recirculation gas (ARG) by heating the cathode supply gas (KZG); a condenser (126) is disposed in heat transfer contact with the cathode supply section (132) in the anode discharge section (124) or the anode recirculation section (140); a water discharge section (128) is disposed downstream of the condenser (126) for discharging condensed water (KW) condensed in the condenser (126); and a mixing section (123) is disposed downstream of the water discharge section (128) for mixing the combustion gas (BRG) and the anode recirculation gas (ARG) and for supplying the anode supply gas (AZG) to the anode supply section (122).

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system for producing electrical energy and to a method for recycling anode exhaust gas in such a fuel cell system. [Background technology]

[0002] It is known to use fuel cell systems for the production of electrical energy. To this end, such fuel cell systems typically comprise a fuel cell stack, in which a number of individual fuel cells, each having an anode region and a cathode region, are arranged in a stack. To produce electrical energy, fuel gases and usually ambient air are supplied to the fuel cell stack, where they can undergo chemical conversion while producing electrical energy.

[0003] In known fuel cell systems, hydrogen or natural gas is usually used as the fuel gas, and in addition, in order to improve the efficiency of fuel gas utilization, it is also known that a portion of the fuel gas that is not converted in the fuel cell stack during conversion is supplied again to the fuel cell stack for the next cycle as a recycle gas.

[0004] A drawback of known solutions is that recirculation can reduce efficiency during operation, especially when hydrogen is used as the fuel gas. When hydrogen is supplied to a fuel cell stack, it is converted in the anode region into a mixture of water and residual hydrogen that remains in the anode exhaust gas. When this mixture is recirculated, the water contained therein can significantly reduce the Nernst voltage. For a fuel cell stack, a decrease in Nernst voltage leads to a decrease in efficiency, which usually offsets the efficiency gains achieved by 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] Although it is already known in principle that cooling of the anode exhaust gas during recirculation can be used to condense a portion of the water contained therein and to separate this condensed water, such designs are very complex and expensive. In particular, such designs rely on the use of an external cooling circuit that can deliver coolant to the recirculation piping via an external heat sink to induce condensation of the water vapor in the anode exhaust gas. The addition of an additional cooling circuit and the corresponding peripheral equipment undesirably increases the complexity and cost of the fuel cell system. Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to at least partially eliminate the above-mentioned disadvantages, and in particular to provide a cost-effective and simple method for draining condensed water from a fuel cell system, even when operating on hydrogen. [Means for solving the problem]

[0007] The above-mentioned problem is solved 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 will become apparent from the dependent claims, the detailed description and the drawings, whereby features and details described in the context of the fuel cell system according to the invention naturally also apply in the context of the method according to the invention and vice versa, so that cross-reference is always made or can be made to the disclosure of the individual inventive aspects.

[0008] According to the present invention, a fuel cell system for generating electrical energy is proposed. It comprises a fuel cell stack with an anode section and a cathode section. The anode section comprises an anode supply section for supplying an anode supply gas and an anode discharge section for discharging an anode exhaust gas. Similarly, the cathode section comprises a cathode supply section for supplying a cathode supply gas and a cathode discharge section for discharging the cathode exhaust gas. The anode discharge section is provided with a division section that allows the anode exhaust gas to be divided into an anode recirculation section for recirculation as an anode recirculation gas and an anode discharge section for discharge to the environment as an anode discharge gas. The fuel cell system according to the present invention is characterized in that a condenser is arranged in the anode discharge section or the anode recirculation section in heat-conducting 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 the condenser, a water discharge section is provided for discharging condensed water condensed in the condenser. Further downstream from the water discharge is a mixing zone for mixing the combustion gas and the anode recirculated gas and supplying them to the anode supply zone as anode feed gas.

[0009] The central idea of the present invention is to ensure the recirculation of the anode exhaust gas. This recirculation is carried out in a divided manner, whereby a portion of the anode exhaust gas is recirculated as anode recirculation gas by a divided section. The remaining residue of the anode exhaust gas is discharged to the environment as anode discharge gas. This anode discharge gas can also be subjected to aftertreatment, as will be explained later. In particular, the anode discharge gas is combined with the cathode exhaust gas.

[0010] The anode recirculation gas is recycled in dry form, i.e., by passing through a condenser. In this condenser, the temperature of the anode exhaust gas or anode recirculation gas is lowered below the boiling point of water, i.e., below approximately 100°C, depending on the pressure conditions and the partial pressure, which depends on the gas composition. This causes the water vapor contained in the anode recirculation gas to condense and appear as liquid condensate. It should be noted here that, depending on the positioning of the dividing section, the condenser can be located not only before the dividing section in the anode discharge section, but also after the dividing section in the anode recirculation section. In both cases, the advantages of the present invention can be realized.

[0011] A separator is provided downstream of the condenser as a water discharge, where the condensed components, and therefore the condensed water, are separated from the gaseous components of the anode recirculation gas. The liquid condensate can then be removed from the system and, for example, discharged to the environment. The remaining anode recirculation gas, also referred to as dry anode recirculation gas, can be supplied to a mixing zone in this dry state. In this mixing zone, which can be configured, for example, as an ejector device, a mixing chamber, or similar, the combustion gas supplied from the combustion gas source and the anode recirculation gas are mixed. Depending on how much anode recirculation gas is available, the remaining required amount of combustion gas can be mixed accordingly. The mixture of combustion gas and anode recirculation gas is then supplied back to the anode zone of the fuel cell stack as anode feed gas.

[0012] The central idea of the present invention is that an external cold air source and a separate external cold air circuit are not required, particularly for condensing the condensate from the anode recirculation gas or the anode exhaust gas. Instead, the condenser is configured in a manner according to the present invention to be in heat-conducting contact with the cathode supply area. Since such a fuel cell system operates using air as the cathode supply gas for the cathode area, air is drawn in from the surroundings. This can be achieved, for example, by a fan device. The drawn-in air has an ambient temperature that can range from -20°C to 50°C or even higher, depending on the temperature situation. It is crucial here that even under very high operating temperatures, such as in desert regions, the ambient air does not exceed the boiling temperature of water, which is typically 100°C. In other words, even under high ambient temperatures, the supplied ambient air is sufficient as a heat sink, thereby providing a cooling output for the anode exhaust gas or anode recirculation gas at the lowest available temperature, which allows cooling below the condensation temperature of the water. As is clear from the above description, the supply of ambient air as the cathode supply gas alone provides a secondary function: a cooling source, which can also be called a heat sink. This heat sink serves as a condenser that removes heat energy from the anode exhaust gas that is recycled as the anode recirculation gas, in an amount such that the temperature of the anode exhaust gas or anode recirculation gas is lower than the boiling point of water. This condensation process, according to the present invention, is carried out without the action of an external cooling source, in particular without a cooling circuit external to the fuel cell system.

[0013] It should also be noted that in complex fuel cell systems, cooling circuits may of course be provided at other locations to allow the desired temperature regulation process to be carried out. In particular, in the case of a fuel cell system configured as an SOFC system, due to the expected extremely high temperatures, for example, a portion of the fuel cell stack may be configured with an external cooling device. However, in the present invention, such an external cooling source is not utilized for the condensation function of the anode recirculation gas or the anode exhaust gas.

[0014] According to the present invention, the integration of the condensation function into the cathode supply section results in the desired condensation of condensed water in the anode recirculation gas or anode exhaust gas. The dry anode recirculation gas is then mixed with the combustion gas, realizing the correspondingly desired efficiency increase due to the recirculation without the expense of a lower Nernst voltage, which occurs in the case of undried anode recirculation gas. Compared to known solutions, this drying step and the associated efficiency increase are realized without additional complex components during operation of the fuel cell system, specifically by a condensation device configured as a gas-gas heat exchanger alone.

[0015] In addition to the resulting increased efficiency, it is even possible to use a smaller ejector, since the unwanted condensate is separated and therefore a correspondingly smaller volumetric flow rate has to be mixed into the combustion gases.

[0016] In a fuel cell system according to the invention, it may be advantageous if the anode discharge area has an anode discharge heat exchanger in heat transfer contact with the anode supply area for heat transfer from the anode exhaust gas to the anode supply gas. This allows for even greater efficiency in terms of temperature. In this way, in conjunction with various other possible heat exchangers, which will be described later, a heat exchange system, also known as a temperature regulation system, is provided together with the condenser, making it possible to reuse as much residual heat as possible from the anode exhaust gas and / or the cathode exhaust gas for other functions, such as condensation or the supply and conditioning of the anode supply gas and / or cathode supply gas. This embodiment therefore offers the possibility of cooling the hot anode exhaust gas and utilizing its energy to heat the anode supply gas as it is fed to the anode area. As a side effect, this allows the condenser to assume a correspondingly lower input temperature, since the anode exhaust gas arrives at the condenser already pre-cooled, resulting in a correspondingly lower required condensation power. In other words, it is thus possible to equip the condenser with the desired condensing function even with a relatively small amount of air or a relatively small design shape and design volume.

[0017] In the fuel cell system according to the present invention, it is also advantageous if the mixing section is configured as an ejector device, with a fuel supply of combustion gas at the primary connection of the ejector device and an anode recirculation section at the secondary connection of the ejector device. Using an ejector device instead of a conventional fan device for the mixing section offers many advantages. On the one hand, rotating components and, accordingly, wear parts are eliminated. On the other hand, mixing and delivery are preferably combined in a common component, so that a separate delivery device is not required in the anode supply section, especially when a combustion gas source with a high delivery pressure is available. Instead, it is sufficient to apply the appropriate combustion gas with the desired prepressure to the primary connection of the ejector device, and the corresponding suction action at the secondary connection of the ejector device draws in the dry anode recirculation gas for mixing. This results in an improved overall efficiency for the fuel cell system according to the present invention, and in particular improved wear resistance.

[0018] In the fuel cell system according to the present invention, the cathode discharge section also preferably has a catalytic device connected in fluid communication with the anode discharge section, which is provided for catalytic after-treatment of the anode discharge 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 separation section and discharged to the environment. As also already explained, the anode exhaust gas contains residual components of combustion gases, such as hydrogen and ammonia. To ensure that this hydrogen does not reach the environment in pure form, catalytic after-treatment can be performed in such a catalytic device. To provide a sufficiently high oxygen fraction for such catalytic after-treatment, mixing with the cathode exhaust gas is preferably intended within or before this catalytic device. The purpose of such catalytic after-treatment is, in particular, to minimize or even completely consume the combustion gas content in the anode discharge gas. This leads to increased safety and, especially if heat is generated in this manner, also leads to increased efficiency. This is particularly the case if the heat generated in such a catalytic converter, for example configured as an oxidation catalyst, is fed back to the fuel cell system via a heat exchanger at another point. If the fuel cell system is powered by ammonia, it may be advantageous to additionally provide an aftertreatment unit that also converts the last residues of ammonia.

[0019] Another advantage of the fuel cell system according to the present invention is realized when the cathode supply section includes a cathode supply heat exchanger in heat transfer contact with the cathode discharge section for heat transfer from the cathode exhaust gas to the cathode supply gas. Preconditioning the cathode supply gas so that it enters the cathode section at as high a temperature as possible, and thus particularly close to the operating temperature of the fuel cell stack, similar to preheating the anode supply gas, further improves the efficiency of the fuel cell system during operation. Because the cathode exhaust gas is at a correspondingly high operating temperature as a result of the chemical reactions within the fuel cell stack, this high temperature can be utilized to partially release it into the cathode supply gas. This corresponds to preconditioning in the form of preheating the cathode exhaust gas to the cathode supply gas. Such recovery of the heat contained in the cathode exhaust gas further improves efficiency and avoids heat loss through the cathode exhaust gas. This cathode feed heat exchanger is preferably located immediately upstream before the cathode section and accordingly upstream of the catalyst device in the cathode discharge section and after the condenser in the cathode feed section.

[0020] Further advantages can be obtained if in the fuel cell system according to the invention the dividing section is arranged in one of the following positions: upstream of the condenser, downstream of the condenser and downstream of the water discharge; - Downstream of the condenser and upstream of the water discharge.

[0021] The above list includes three different positions that preferably cannot be occupied simultaneously. If the split occurs upstream of the condenser, the subsequent condensation process and the discharge of condensed water only need to be performed for the anode recirculation gas that is actually recycled. However, it may be advantageous to pass the entire anode exhaust gas through the condenser and also through the water discharge section. This not only cools the entire anode exhaust gas, but also removes water, due to the subsequent placement of the split section. In particular, if a higher preconditioning power is required for the air than for the cathode feed gas, it may be advantageous to utilize the residual heat of the entire volumetric flow of the anode exhaust gas for this preheating. This is because the entire anode exhaust gas, not just the correspondingly separated anode recirculation gas, is passed through the condenser. Since a correspondingly large amount of condensed water is generated in such a case, it is additionally preferable to place this split section downstream of the water discharge section, rather than between the condenser and the water discharge section. This allows for maximum thermal efficiency for the cathode supply gas, while at the same time allowing the relatively large amount of condensed water that is generated to be separated from the anode recirculation gas before being fed to the separation section and then to the mixing section.

[0022] It is also advantageous if a cathode exhaust heat exchanger for transferring heat from the cathode exhaust gas to the anode supply gas is arranged in the anode supply section, preferably downstream of the anode supply heat exchanger. This allows the heat contained in the cathode exhaust gas to be transferred to the anode supply gas, either additionally or alternatively. In addition, in combination with the anode supply heat exchanger, this allows for a correspondingly improved preheating function, or, in other words, for the anode supply gas to be heated to a higher temperature. As already mentioned, a fuel cell system according to the present invention can be equipped with a heat exchanger system at multiple locations throughout the heat exchange function. Naturally, the individual heat exchangers of this heat exchange system can be controlled via valves, which allows, in particular, for flexible activation or deactivation of various parts of such a heat exchange system depending on the operating situation. This allows for precise and flexible adaptation to various operating situations and always achieving the maximum temperature difference.

[0023] It may also be advantageous if a cathode supply heat exchanger is arranged in the cathode supply section of the fuel cell system according to the invention for heat transfer from the cathode exhaust gas to the cathode supply gas. This can be considered as an alternative or in addition to the other heat exchangers mentioned above, and it should be noted that valves are preferably capable of activating and deactivating the various heat exchangers. In this case, too, the residual heat of the cathode exhaust gas can be utilized by heat transfer to ensure preconditioning in the form of pre-temperature adjustment of the cathode supply gas, thereby further improving the operating efficiency of the fuel cell system.

[0024] In addition, in the fuel cell system according to the present invention, it may be preferable to arrange a control valve in the anode supply section upstream of the mixing section for controlling the volumetric flow rate of the combustion gas through the mixing section. This allows the amount and pressure of the fuel gas to be controlled in a controlled manner, particularly from a pressure-biased combustion gas source. Depending on the divided amount of the anode recirculation gas, a correspondingly adapted amount of combustion gas can be added, so that the desired composition and the desired volumetric flow rate of the anode supply gas are always actually provided in the anode section. Therefore, the control valve is preferably a quantitatively controllable control valve, in order to be able to adapt appropriately to various operating conditions of the fuel cell system.

[0025] In addition, in the fuel cell system according to the invention, it is preferred that the anode discharge area be configured without an external cooling circuit. As already explained, the central idea of the invention is to provide such a condensation function as efficiently as possible and without additional complexity. The configuration of the anode discharge area without an external cooling circuit represents precisely such reduced complexity, since the condensation function is essentially ensured only by the heat sink provided by the ambient air supplied as cathode supply gas.

[0026] It is also preferred in the fuel cell system according to the invention if a cathode mixing section, particularly in the form of an ejector device, is arranged in the cathode supply section. A secondary connection to such an ejector device is fluidly connected to a cathode recirculation section for the recirculation of a portion of the cathode exhaust gas as cathode recirculation gas. In combination with the recirculation to the anode section, this can also be called double recirculation. This allows the cathode exhaust gas and the residual oxygen contained therein to be fed back to the cathode section in a mixture with the cathode supply gas.

[0027] The subject of the invention is also a method for recycling an anode exhaust gas as an anode recycle gas in a fuel cell system according to the invention, comprising the following steps: - at least a portion of the anode exhaust gas is split into the anode recirculation zone as anode recirculation gas; - the anode recirculation gas is cooled below the boiling temperature of water by heat transfer to the cathode supply gas; - the condensed water is separated from the anode recirculation gas; The dry anode recirculation gas is mixed with the combustion gas to form the anode feed gas.

[0028] The method according to the invention, when applied in the fuel cell system according to the invention, provides the same advantages as those explained in detail in relation to the fuel cell system according to the invention. [Brief explanation of the drawings]

[0029] Other advantages, features and specific features of the invention will become apparent from the following description of an embodiment of the invention, which is given with reference to the drawings, in which:

[0030] [Figure 1] 1 is an embodiment of a fuel cell system according to the present invention. [Figure 2] 3 is another embodiment of a fuel cell system according to the present invention. [Figure 3] 3 is another embodiment of a fuel cell system according to the present invention. [Figure 4] 3 is another embodiment of a fuel cell system according to the present invention. [Figure 5] 3 is another embodiment of a fuel cell system according to the present invention. [Figure 6] 3 is another embodiment of a fuel cell system according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0031] 1, a fuel cell system 100 for generating electrical energy is shown schematically. Illustrated here is a fuel cell stack 110 having an anode section 120 and a cathode section 130. Naturally, the fuel cell stack 110 includes a number of individual fuel cells, each having a correspondingly large number of individual anode sections 120 and cathode sections 130, stacked one above the other. For convenience, the stack as a whole will be referred to herein as an anode supply section 122, an anode discharge section 124, a cathode supply section 132, and a cathode discharge section 134.

[0032] During operation of the fuel cell system 100, combustion gas BRG is supplied from a fuel source (not shown in detail). This combustion gas is mixed with anode recirculation gas ARG, which will be described later, to form anode supply gas AZG, and an ejector device is used as the mixing zone 123. The ejector device serves to suck in the anode recirculation gas ARG and mix it with the combustion gas BRG.

[0033] The anode supply gas AZG is then fed to the anode section 120 in the anode supply section 122, where it is allowed to react with the cathode supply gas KZG in the form of air LU. During this chemical reaction, heat is generated in addition to the electrical energy that is intended to be generated during operation of the fuel cell system 100, thereby heating the anode exhaust gas AAG and the cathode exhaust gas KAG. The hot anode exhaust gas AAG is then fed to the separation section 125, where it is split into an anode recirculation gas ARG in the anode recirculation section 140 and an anode discharge gas AUG in the anode discharge section 150. The discharge sections may be flexibly controllable, which in particular allows for adaptation of the volumetric ratio between the anode recirculation gas ARG and the anode discharge gas AUG.

[0034] The still hot anode recirculation gas ARG is then guided through a condenser 126, which exchanges heat with the supplied air LU. Since the air LU is drawn in from the surroundings and has a corresponding ambient temperature, it has a temperature below the boiling point of water, even under very high ambient conditions. This allows the anode exhaust gas AAG, serving as the anode recirculation gas ARG, to be cooled below its boiling point, so that the water present therein condenses as condensed water KW, which is then present in the further guided anode recirculation gas ARG. This mixture of condensed water KW and dry anode recirculation gas ARG is then passed through a separator in the form of a water outlet 128, which separates the condensed water KW and allows it to be discharged to the surroundings. The remaining dry anode recirculation gas ARG is then supplied to an ejector device serving as a mixing section 123, whereby the residual combustion gas remaining in the anode recirculation gas ARG is mixed with fresh fuel gas BRG and supplied again to the anode section 120 as anode supply gas AZG.

[0035] The cathode exhaust gas KAG also has a correspondingly high temperature and is after-treated before being released into the environment. In the simplest embodiment shown in FIG. 1, the after-treatment is provided by a catalytic device 136, in which the mixture of the cathode exhaust gas KAG and the anode discharge gas AUG is catalytically after-treated together. The purpose of such catalytic after-treatment is, in particular, to reduce the volume fraction of the combustion gas BRG remaining in the anode discharge gas AUG, thereby enabling the mixture of the anode discharge gas AUG and the cathode discharge gas KAG to be released into the environment as safely as possible.

[0036] 2 shows a development of the embodiment of FIG. 1, in which various additional components are integrated, which can be used by way of example alone or in combination. One such additional component is an anode supply heat exchanger 121, which allows pre-cooling of the anode exhaust gas AAG, which subsequently requires a lower cooling power in the condenser 126. This pre-cooling is achieved by heat transfer from the hot anode exhaust gas AAG to the anode supply gas AZG to be pre-conditioned, whereby this pre-cooling simultaneously has a positive effect on the anode supply gas, which can further improve the efficiency of operation of the fuel cell system 100.

[0037] 2 is an air-heat exchanger 190, which is arranged downstream of the cathode supply section 132 and downstream of the condenser 126. As a result, the cathode supply gas KZG, which has already been heated by the condenser 126, is further heated by the residual heat of the gas mixture present there after the catalytic device 136, so that a correspondingly higher inlet temperature of the cathode supply gas KZG is achieved in the cathode section 130.

[0038] 1 is the position of the dividing section 125 in FIG. 2. The dividing section is now located downstream of the water discharge section 128, so that the condensation and water discharge functions are accordingly performed on the entire anode exhaust gas AAG. This allows for maximum heat recovery from the anode exhaust gas, but the trade-off is that a correspondingly large condenser 126 is required in order to allow a correspondingly large amount of air LU to be drawn in and passed through for cooling. Here, the condensed water KW is completely separated from the entire dry anode exhaust gas AAG, so that only the dry anode exhaust gas is transported further in the fuel cell system 100 as anode recirculation gas ARG and anode discharge gas AUG.

[0039] FIG. 3 also shows additional components, which can further increase the efficiency of the fuel cell system 100. On the one hand, a cathode supply heat exchanger 131 is additionally provided, which allows heat recovery from the hot cathode exhaust gas KAG to the cathode supply gas KZG. The cathode supply gas KZG is thus supplied with heat at three points: the condenser 126, the air heat exchanger 190, and finally, as the final heat transfer, the cathode supply heat exchanger 131. FIG. 3 also shows an embodiment in which the dividing section 125 is provided downstream of the condenser 126 but upstream of the water discharge 128. This allows the corresponding advantages of heat recovery from the anode exhaust gas AAG to be fully applied to the air LU in the condenser 126. However, since the water discharge section 128 and separator function need only be provided here for the anode recirculation gas ARG that is actually desired, the separator of the water discharge section 128 may accordingly be configured smaller than in the embodiment of FIG. 2.

[0040] 4 also shows another subcomponent that can be applied in the fuel cell system 100 according to the invention. Here, part of the temperature of the cathode exhaust gas KAG is used solely for additional heating of the anode supply gas AZG, since the cathode exhaust heat exchanger 133 is arranged in heat-conducting contact with the anode supply section 122. This option therefore aims to inject as high a temperature effect as possible into the anode supply gas AZG.

[0041] 5 also shows further components with which the fuel cell system 100 can be further developed. On the one hand, these are the cathode recirculation fan 171 and the cathode dividing section 137, which allow a portion of the cathode exhaust gas KAG to be divided into the cathode recirculation section 170. This divided portion of the cathode exhaust gas KAG can then be supplied as cathode recirculation gas KRG to an ejector device, here the cathode mixing section 135, ensuring cathode recirculation. In this way, a variable recirculation rate is possible at the cathode, and even higher recirculation rates can be set during partial load operation. The variable cathode exhaust gas KAG is supplied to the catalytic device 136 in the manner already described several times.

[0042] 5 also shows a control valve 160 in the combustion gas supply for the combustion gas BRG, which is particularly configured to be quantitatively controllable so that different volumetric flow rates of the combustion gas BRG can be adjusted and different amounts of combustion gas actually mixed into the anode recirculation gas ARG for different operating conditions.

[0043] FIG. 6 shows another embodiment of a fuel cell system 100 according to the invention, in which most of the components shown correspond to those shown in FIG. 5. Here, an aftertreatment unit 191 is additionally provided, arranged downstream of the air / heat exchanger 190. The aftertreatment unit 191 is particularly preferred when operating the fuel cell system 100 with ammonia, in which case it reconverts a small amount of ammonia before the exhaust gas is released into the atmosphere. For this purpose, the aftertreatment unit 191 may be configured as an ammonia slip catalyst (ASC) operating at temperatures between 200°C and 500°C. It may also be preferable to provide purge and / or bypass valves (not shown in FIG. 6) for discharging hydrogen and / or ammonia in the event of a leak. Corresponding valves may be provided in either embodiment.

[0044] In this case, the individual components of the system, in particular consisting of a number of heat exchangers, can be freely combined with one another and, in particular, can be freely switchable via a control valve system in order to be able to adapt as flexibly as possible to the various operating conditions of the fuel cell system 100.

[0045] More specifically, the additional components of the embodiment of fuel cell system 100 shown in FIG. 2, i.e., anode supply heat exchanger 121 and / or air heat exchanger 190, may be combined in a complementary manner with the system components of the embodiment of fuel cell system 100 shown in FIG. 1, 3, 4 or 5, with the same positioning relative to division section 125.

[0046] Furthermore, the additional components of the embodiment of fuel cell system 100 shown in FIG. 3, namely cathode supply heat exchanger 131, can also be combined in a complementary manner with the system components of the embodiments of fuel cell system 100 shown in FIGS. 1, 2, 4 or 5.

[0047] Additionally, the additional components of the embodiment of fuel cell system 100 shown in FIG. 4, namely cathode exhaust heat exchanger 133, may be combined in a complementary manner with the system components of the embodiment of fuel cell system 100 shown in FIGS. 1, 2, 3 or 5.

[0048] Similarly, additional components of the embodiment of fuel cell system 100 shown in Figures 5 and / or 6, i.e., cathode recirculation section 170, can be combined with cathode recirculation fan 171 and cathode split section 137, and / or aftertreatment unit 191 and / or control valve 160, can also be combined in a complementary manner with system components of the embodiment of fuel cell system 100 shown in Figures 1, 2, 3 or 4.

[0049] The above description of the various embodiments describes the present invention by way of example only. (Other possible items) (Item 1) A fuel cell system (100) for generating electrical energy, comprising a fuel cell stack (110) having an anode section (120) and a cathode section (130), the anode section (120) having an anode supply section (122) for supplying an anode supply gas (AZG) and an anode discharge section (124) for discharging an anode exhaust gas (AAG), the cathode section (130) having a cathode supply section (132) for supplying a cathode supply gas (KZG) and a cathode discharge section (134) for discharging a cathode exhaust gas (KAG), the anode discharge section (124) having an anode recirculation section (140) for recirculating the anode exhaust gas (AAG) as an anode recirculation gas (ARG) and an anode discharge section (140) for discharging the anode exhaust gas (AAG) to the environment as an anode discharge gas (AUG). anode exhaust gas (AAG) or anode recirculation gas (ARG) by heating a cathode supply gas (KZG); a condenser (126) for cooling an anode exhaust gas (AAG) or an anode recirculation gas (ARG) by heating a cathode supply gas (KZG) is disposed in heat transfer contact with the cathode supply section (132), a water discharge section (128) is disposed downstream of the condenser (126) for discharging condensed water (KW) condensed in the condenser (126); and a mixing section (123) is disposed downstream of the water discharge section (128) for mixing a combustion gas (BRG) and an anode recirculation gas (ARG) and for supplying an anode supply gas (AZG) to the anode supply section (122). (Item 2) 2. The fuel cell system (100) of claim 1, wherein the anode discharge section (124) has an anode supply heat exchanger (121) in thermal conduction contact with the anode supply section (122) for heat transfer from an anode exhaust gas (AAG) to an anode supply gas (AZG). (Item 3) 3. The fuel cell system (100) according to item 1 or 2, wherein the mixing section (123) is configured as an ejector device, has a fuel supply of combustion gas (BRG) at a primary connection of the ejector device, and has the anode recirculation section (140) at a secondary connection of the ejector device. (Item 4) 4. The fuel cell system (100) according to any one of items 1 to 3, wherein the cathode discharge area (134) has a catalytic device (136) connected in fluid communication with the anode discharge area (150) for catalytic post-treatment of an anode discharge gas (AUG) and a cathode exhaust gas (KAG). (Item 5) 5. The fuel cell system (100) according to any one of claims 1 to 4, wherein the cathode supply section (132) comprises a cathode supply heat exchanger (131) in heat transfer contact with the cathode discharge section (134) for heat transfer from a cathode exhaust gas (KAG) to a cathode supply gas (KZG). (Item 6) The divided areas (125) are located at the following positions: upstream of the condenser (126); downstream of the condenser (126) and downstream of the water discharge section (128); downstream of the condenser (126) and upstream of the water discharge section (128); 6. The fuel cell system (100) according to any one of items 1 to 5, wherein the fuel cell system (100) is disposed in any one of the following locations: (Item 7) 7. The fuel cell system (100) according to any one of items 1 to 6, wherein a cathode exhaust heat exchanger (133) for heat transfer from cathode exhaust gas (KAG) to anode supply gas (AZG) is arranged in the anode supply section (122), preferably downstream of the anode supply heat exchanger (121). (Item 8) 8. The fuel cell system (100) according to any one of items 1 to 7, wherein a cathode supply heat exchanger (131) for transferring heat from a cathode exhaust gas (KAG) to a cathode supply gas (KZG) is arranged in the cathode supply zone (132). (Item 9) 9. The fuel cell system (100) according to any one of items 1 to 8, wherein a control valve (160) is disposed in the anode supply zone (122) upstream of the mixing zone (125) for controlling the volumetric flow rate of the combustion gas (BRG) passing through the mixing zone (125). (Item 10) 10. The fuel cell system (100) of any one of items 1 to 9, wherein the anode discharge area (124) is configured without an external cooling circuit. (Item 11) 11. The fuel cell system (100) according to any one of items 1 to 10, wherein a cathode mixing section (135), in particular in the form of an ejector device, is arranged in the cathode supply section (132), at a secondary connection of which a cathode recirculation section (170) for the recirculation of a portion of the cathode exhaust gas (KAG) as cathode recirculation gas (KRG) is connected in fluid communication. (Item 12) 12. A method for recycling an anode exhaust gas (AAG) as an anode recirculation gas (ARG) in a fuel cell system (100) according to any one of items 1 to 11, comprising the steps of: splitting at least a portion of the anode exhaust gas (AAG) into said anode recirculation zone (140) as an anode recirculation gas (ARG); cooling the anode recirculation gas (ARG) below the boiling temperature of water by heat transfer to the cathode supply gas (KZG); Separation of condensed water (KW) from anode recirculation gas (ARG); The dry anode recirculation gas (ARG) is mixed with the combustion gas (BRG) to form the anode feed gas (AZG); A method comprising: [Explanation of symbols]

[0050] 100 Fuel Cell System 110 Fuel Cell Stack 120 Anode Section 121 Anode supply heat exchanger 122 Anode Supply Area 123 Mixed area 124 Anode Discharge Area 125 Division area 126 Condenser 128 Water discharge part 130 cathode area 131 Cathode supply heat exchanger 132 cathode supply area 133 Cathode exhaust heat exchanger 134 Cathode Discharge Area 135 Cathode Mixing Area 136 Catalytic Converter 137 Cathode division area 140 Anode Recirculation Zone 150 Anode Discharge Area 160 Control Valve 170 cathode recirculation zone 171 Cathode recirculation fan 190 Air and Heat Exchanger 191 Aftertreatment Unit AZG Anode supply gas AAG Anode exhaust gas AUG Anode Emission Gas ARG Anode recirculation gas KZG cathode supply gas KAG cathode exhaust gas KRG cathode recirculation gas BRG Combustion Gas LU Air KW condensate

Claims

1. A fuel cell system for generating electrical energy, comprising a fuel cell stack having an anode area and a cathode area, the anode area having an anode supply area for supplying an anode supply gas and an anode discharge area for discharging an anode exhaust gas, the cathode area having a cathode supply area for supplying a cathode supply gas and a cathode discharge area for discharging the cathode exhaust gas, the anode discharge area having an anode recirculation area for recirculating the anode exhaust gas as an anode recirculation gas and an anode discharge area for discharging the anode exhaust gas to the environment as an anode discharge gas. a condenser for cooling anode exhaust gas or anode recirculation gas by heating a cathode supply gas, disposed in heat transfer contact with the cathode supply section in the anode discharge section or the anode recirculation section; a water discharge section for discharging condensed water condensed in the condenser, disposed downstream of the condenser; and a mixing section for mixing the combustion gas and the anode recirculation gas and for supplying the anode supply gas to the anode supply section, disposed downstream of the water discharge section.

2. 10. The fuel cell system of claim 1, wherein the anode exhaust section includes an anode supply heat exchanger in heat conductive contact with the anode supply section for heat transfer from the anode exhaust gas to the anode supply gas.

3. 2. The fuel cell system of claim 1, wherein the mixing zone is configured as an ejector device having a fuel supply of combustion gas at a primary connection of the ejector device and the anode recirculation zone at a secondary connection of the ejector device.

4. 10. The fuel cell system of claim 1, wherein the cathode discharge area includes a catalytic device connected in fluid communication with the anode discharge area for catalytic after-treatment of the anode discharge gas and the cathode exhaust gas.

5. 10. The fuel cell system of claim 1, wherein the cathode supply section comprises a cathode supply heat exchanger in heat transfer contact with the cathode discharge section for heat transfer from cathode exhaust gas to cathode supply gas.

6. The divided areas are located at the following positions: upstream of the condenser; downstream of the condenser and downstream of the water discharge section; downstream of the condenser and upstream of the water discharge section; 10. The fuel cell system of claim 1, wherein the fuel cell system is disposed in any one of the following locations:

7. 2. The fuel cell system of claim 1, wherein a cathode exhaust heat exchanger is disposed in the anode supply section, preferably downstream of the anode supply heat exchanger, for transferring heat from the cathode exhaust gas to the anode supply gas.

8. 10. The fuel cell system of claim 1, wherein a cathode supply heat exchanger is disposed in the cathode supply area for transferring heat from the cathode exhaust gas to the cathode supply gas.

9. 10. The fuel cell system of claim 1, wherein a control valve is disposed in the anode supply section upstream of the mixing section for controlling a volumetric flow rate of combustion gases through the mixing section.

10. 10. The fuel cell system of claim 1, wherein the anode exhaust area is configured without an external cooling circuit.

11. 2. The fuel cell system according to claim 1, wherein a cathode mixing section, in particular in the form of an ejector device, is arranged in the cathode supply section, the secondary connection of which is connected in fluid communication with a cathode recirculation section for the recirculation of a portion of the cathode exhaust gas as cathode recirculation gas.

12. 12. A method for recycling an anode exhaust gas as an anode recirculation gas in a fuel cell system according to claim 1, comprising the steps of: at least a portion of the anode exhaust gas is split into the anode recirculation zone as an anode recirculation gas; cooling the anode recirculation gas below the boiling temperature of water by heat transfer to the cathode feed gas; Separating condensed water from the anode recycle gas; mixing the dried anode recirculation gas with the combustion gas to form the anode feed gas; A method comprising:

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