Fuel cell system with increasing hydrogen content

Abstract

The present invention relates to a fuel cell system (100), in particular a solid oxide fuel cell system. Furthermore, the invention relates to a corresponding method for the optimized operation of a fuel cell system (100), a computer program product, a computer-readable data carrier, a control unit (FCCU), and a system (200).

Description

[0001] The invention relates to a method having the features of the independent method claim, a fuel cell system having the features of the independent device claim, a computer program product having the features of the independent patent claim relating to a computer program product, a computer-readable data carrier having the features of the independent patent claim relating to a computer-readable data carrier, a control unit having the features of the independent patent claim relating to a control unit, and a system having the features of the independent patent claim relating to a system.

[0002] Fuel cell systems, in particular solid oxide fuel cells, are known, comprising at least one fuel cell unit having an anode and a cathode, as well as an electrolyte located therebetween. A fuel gas, for example hydrogen or a gas comprising hydrogen (e.g. ammonia), can be supplied from the anode, and a further substance comprising oxygen, e.g. air, can be supplied from the cathode. The anode and cathode can be gas-permeable. The electrolyte represents an interface at which (separate) a reduction and an oxidation of a redox reaction take place. The redox reaction can comprise a reaction of oxygen with the fuel gas, e.g. hydrogen. There can be an excess of oxygen on the cathode side, while there can be a deficiency of oxygen on the anode side, since the oxygen reacts directly with hydrogen there.Due to the resulting concentration gradient, oxygen diffuses from the cathode to the anode. Since the electrolyte in between is permeable only to oxygen ions, the oxygen absorbs electrons there. The resulting oxygen ions react with hydrogen ions on the anode side, which release electrons. During the exothermic reaction, an electron flow between the anode and cathode can be used externally as electrical power (current and / or voltage). Furthermore, fuel cell systems can comprise a stack of the fuel cell units described above.

[0003] However, devices and methods known from the prior art have disadvantages. For example, the electrical and / or thermal performance as well as the efficiency can be optimized. In particular, the fuel utilization may be inadequate. Deposits, in particular carbon deposits, resulting from the fuel can affect performance, longevity and / or freedom from faults. Furthermore, diffusion losses and / or polarization losses can affect performance, efficiency, costs, longevity and / or freedom from faults. The cell voltage, in particular the Nernst voltage, may be inadequate, which can particularly reduce the performance of a cell or stack. The control and / or regulation of known devices may be inadequate. A changed proportion of hydrogen, in particular in the anode path, may be taken into account only inadequately or not at all.Appropriate control and / or regulation cannot be provided or can be improved.

[0004] It is therefore an object of the present invention to at least partially overcome at least one of the disadvantages described above. In particular, it is an object of the invention to provide an optimized fuel cell system and a method which optimize performance, efficiency, longevity, freedom from faults and / or costs. In particular, it can be an object of the invention to provide optimized operation as a function of a (particularly increasing) hydrogen content in the anode path. Furthermore, it can be an object of the invention to provide optimized fuel utilization of the fuel cell system and / or the fuel cell unit. In particular, a comparison can be made with operation using (pure) natural gas and / or methane.

[0005] The above object is achieved by a method having the features of the independent method claim, a fuel cell system having the features of the independent device claim, a computer program product having the features of the independent patent claim relating to a computer program product, a computer-readable data carrier having the features of the independent patent claim relating to a computer-readable data carrier, a control unit having the features of the independent patent claim relating to a control unit, and a system having the features of the independent patent claim relating to a system. Further features and details of the invention emerge from the subclaims, the description, and the drawings.Features and details described in connection with the method according to the invention naturally also apply in connection with the fuel cell system according to the invention and / or in connection with the computer program product according to the invention and / or in connection with the computer-readable data carrier according to the invention and / or in connection with the control unit according to the invention and / or in connection with the system according to the invention and vice versa, so that with regard to the disclosure of the individual aspects of the invention, reference is or can always be made to each other. In particular, advantages described in the context of the first, second, third, fourth, fifth and / or sixth aspect also apply to the first, second, third, fourth, fifth and / or sixth aspect.

[0006] The above object is achieved according to a first aspect by a method for operating a fuel cell system, in particular a solid oxide fuel cell system, the fuel cell system comprising - at least one fuel cell unit for energy generation, comprising ◯ an anode path comprising ▪ an anode input for receiving an anode input current and ▪ an anode output for outputting an anode output current, and - a cathode path, comprising ▪ a cathode input for receiving a cathode input current and ▪ a cathode output for outputting a cathode output current, - a control unit for controlling and / or regulating the fuel cell system, - comprising the method ◯ Control of the fuel cell system by the control unit to adjust a proportion of hydrogen in the anode input current, ◯ Control of the fuel cell system by the control unit in order to set at least one, in particular at least two, preferably (exactly) three, of the following setpoint values ​​for optimized operation depending on the proportion of hydrogen in the anode input current: ▪ a target oxygen-carbon ratio, ▪ a target fuel utilization of the fuel cell system, ▪ a target fuel utilization of a fuel cell unit of the fuel cell system, ▪ a target current generated by the fuel cell unit.

[0007] In this case, operation and / or control can comprise control and / or regulation, wherein preferably a control unit (see below) is used. The described actions or features of the method can be carried out in the order shown and in particular can be carried out repeatedly. Preferably, the method can be used to control and / or regulate a fuel cell system according to the second aspect. In this case, a control unit according to the fifth aspect can particularly preferably be used for control and / or regulation. In this case, the control unit can carry out the corresponding actions or features and / or carry out control, in particular insofar as technically expedient, in order to preferably implement the actions.

[0008] The fuel cell system can have a recirculation unit for at least partially returning the anode output stream to the anode input stream. Controlling the fuel cell system to absorb water vapor contained in the anode output stream through a heat exchanger of the recirculation unit can comprise absorbing the anode output stream (in its entirety), which in particular comprises water vapor that has arisen, in particular, inside the fuel cell unit. The water vapor can be (at least partially) condensed by the recirculation unit for regulating and / or controlling the anode input stream of the fuel cell unit. This can be carried out, in particular, in the heat exchanger of the recirculation unit. Within the scope of the invention, the control unit can initiate or start the inflow of substances into the fuel cell system.

[0009] Optimized operation can realize the advantages according to the invention. This can include optimizing the (electrical) efficiency, wherein in particular the efficiency is increased and / or a drop can be prevented or reduced. This can further include optimizing the fuel utilization of the fuel cell system and / or the fuel cell unit, wherein in particular the fuel utilization of the fuel cell system and / or the fuel cell unit is increased and / or a drop can be prevented or reduced. This can further include optimizing an oxygen-carbon ratio of the fuel cell system, wherein in particular the oxygen-carbon ratio of the fuel cell system is increased and / or a drop can be prevented or reduced. It can be provided that optimized operation (in particular only oronly) by controlling and / or regulating the fuel cell system by the control unit.

[0010] In this case, the control of the fuel cell system by the control unit to adjust a proportion of hydrogen in the anode input stream can in particular comprise adjusting a specific percentage of hydrogen, in particular in a mixture (or in the corresponding volume flows). The mixture can comprise a fuel and hydrogen. Preferably, control and / or regulation can be optimized with differently adjusted proportions of hydrogen in the anode input stream, preferably with an increasing proportion of hydrogen. The anode input stream can be supplied to the anode at the anode inlet. This preferably comprises the volume flow of the mixture and / or a recirculating volume flow. An increasing proportion (in particular molar proportion) of hydrogen, in particular at the anode inlet or in the anode input stream, can advantageously prevent fuel depletion, thus in particular a decrease in efficiency.

[0011] The control of the fuel cell system by the control unit may comprise setting at least one, in particular two, in particular (exactly) three, of the following setpoint values ​​for optimized operation, in particular depending on the proportion of hydrogen in the anode input current: - a target oxygen-carbon ratio, - a target fuel utilization of the fuel cell system, - a target fuel utilization of a fuel cell unit of the fuel cell system, - a target current generated by the fuel cell unit.

[0012] The target values ​​can be calculated and / or specified by the control unit. Corresponding actual values ​​can be measured by corresponding sensors and / or calculated or simulated (model-based). The control unit can control and / or regulate the sensors and / or actuators, for example via a data connection, via which actual values ​​in particular can also be transmitted to the control unit, whereby, for example, the sensors can determine measured values ​​and / or actuators can adjust the fuel cell system. Particularly preferably, it can be provided to specify one, in particular two, preferably (exactly) three, of the above-mentioned target values, and to calculate and / or monitor the remaining one (or values) (in particular based on actual values). Preferably, two or three of the above (four) target values ​​can be set, while in particular the remaining ones are calculated.It may be provided to set (only) one setpoint for the target fuel utilization of the fuel cell system or fuel cell unit. Particularly preferably, two or three of the following setpoints can be set: - a target oxygen-carbon ratio, - a target fuel utilization of the fuel cell system, - a target fuel utilization of a fuel cell unit of the fuel cell system - a target current generated by the fuel cell unit.

[0013] Alternatively or additionally, it may be provided that the control of the fuel cell system by the control unit comprises setting, in particular depending on the proportion of hydrogen in the anode input current, a target hydrogen concentration at the anode output (or at the outlet of the stack).

[0014] Preferably, the remaining value (or values) can be calculated (see below). It may be provided that formulas and / or equations for specific values, e.g., fuel utilization, can also be used to calculate corresponding actual values ​​and / or target values, e.g., actual fuel utilization and / or target fuel utilization.

[0015] The oxygen-carbon ratio can comprise the ratio between oxygen (atoms) and carbon (atoms), in particular at the anode inlet, for example upstream of the fuel cell unit and downstream of the recirculation fan. The oxygen-carbon ratio can be used as an indicator of coking. Accordingly, the risk of coking of the fuel cell system, in particular of the fuel cell unit and / or the anode path, can advantageously be lower with a larger value. Preferably, in particular by controlling and / or regulating, the oxygen-carbon ratio can have a value greater than 20, in particular greater than 10, preferably greater than 6, particularly preferably greater than 4, advantageously greater than 3, ideally greater than 2.3.By controlling and / or regulating, in particular adjusting, the oxygen-carbon ratio, the durability and / or efficiency of the fuel cell system can be optimized. The oxygen-carbon ratio (hereinafter: OC) can be defined and / or calculated using (Equation 1): OC=OCFuel+FUStk−FUSysFUstk−1∗ΓOC

[0016] FU stands for Stk for the fuel utilization of a fuel cell unit of the fuel cell system and FU Sys for the fuel utilization of the fuel cell system. Γ OC stands for a fuel coefficient. OC Brennstoff also represents an oxygen-carbon ratio in the fuel, especially when oxygen, such as CO2, is present in the fuel (e.g., in natural gas). The oxygen-carbon ratio in the fuel can be identical to an oxygen-carbon ratio in the mixture OC Gemisch, especially since hydrogen (as a further component) has no oxygen and no carbon. The oxygen-carbon ratio in the fuel can be a fixed parameter, which preferably depends exclusively on the fuel composition. The fuel coefficient can in particular depend (only) on the fuel composition or the mixture composition, preferably on a (molar) fraction (hereinafter: x i,Brennstoff ) which the fuel in the mixture has (e.g. in percent such as 80%). Γ OC be defined and / or calculable by: ΓOC=∑ixi,fuel∗γie−2∗∑ixi,fuel∗γiC

[0017] Here, γ ie - have a number of electrons that can be released by component i during one, especially half, electrochemical reaction. γ iCa number of carbon atoms in the fuel (e.g. γ iC = 1 for CH4).

[0018] It can therefore be particularly preferably provided (in particular as operating strategy a) that the control of the fuel cell system, in particular depending on the proportion of hydrogen in the anode input current, by setting the values ​​of FU Stk and OC, in particular about the target fuel utilization of a fuel cell unit of the fuel cell system (hereinafter: FU Stk , soll ) and the target oxygen-carbon ratio (hereinafter: OC soll ), preferably using the values ​​OC or OC soll , particularly depending on the proportion of hydrogen.

[0019] Alternatively or additionally, it may be particularly preferably provided (in particular as operating strategy b) that the control of the fuel cell system, in particular depending on the proportion of hydrogen in the anode input current, is carried out by setting the values ​​of FU Sys and FU Stk , in particular the values ​​of a target fuel utilization of the fuel cell system (hereinafter: FU Sys , soll ) and FU Stk , soll , preferably the values ​​OC or an actual value of the oxygen-carbon ratio OC ist are determined, calculated and / or monitored by the control unit (e.g. depending on actual values), preferably OC soll is not used as a setpoint, but is (only) monitored. It may be provided that monitoring of OC or OC istby the control unit, whereby in particular if a threshold value for OC is exceeded, an alarm is triggered, the fuel cell system is switched off and / or the target current is reduced (hereinafter: I soll) occurs.

[0020] It can be provided within the scope of the invention that methane is used as fuel, in particular with x CH4 = 100%, which is used as a reference value, especially in the comparison tables (see below).

[0021] The fuel utilization of the fuel cell system can be defined and / or calculated as (Equation 2): FUSys=I∗nc∗60∗VNorm∑ixi,fuel∗γie−∗V˙mixture

[0022] Here, I stands for a current, in particular a current intensity. n c can be a number of fuel cell units. V Norm stands for a standard volume, and V̇ H2in represents a volume flow of hydrogen.

[0023] It may be provided to use in equation 2 a volume flow of mixture (hereinafter: V̇ Gemisch ), especially instead of V̇ H2in , since the mixture may contain other hydrogen-containing compounds in addition to (pure) hydrogen. FUSys=I∗nc∗60∗VNorm∑ixi,fuel∗γie−∗V˙mixture

[0024] The volume flow of the mixture can be the sum of the volume flow of hydrogen and the volume flow of fuel (hereinafter: V̇ Brennstoff ) include.

[0025] A target fuel utilization of the fuel cell system can have a corresponding target value.

[0026] Alternatively or additionally, the fuel utilization of the fuel cell system can be defined and / or calculated as (Equation 3): OFUSys=FUStk−(OC−OCfuel)∗(FUStk−1)ΓOC

[0027] Accordingly, it can preferably be provided to adjust the fuel utilization of the fuel cell system by controlling and / or regulating the volume flow of hydrogen, fuel and / or mixture. In particular, the control unit can control and / or regulate a hydrogen valve, a hydrogen flow controller, a fuel valve, a fuel flow controller, a mixture valve and / or a mixture flow controller. A target value for the fuel utilization can therefore be specified, e.g., by a user and / or the control unit, whereupon the control unit preferably determines a (target value for the) volume flow of hydrogen (hereinafter: V̇ H2in,soll), fuel and / or mixture. Depending on the (setpoint for the) volume flow of hydrogen, fuel and / or mixture, the control unit can then determine a control value for the hydrogen valve, a hydrogen flow controller, a fuel valve, a fuel flow controller, a mixture valve and / or a mixture flow controller. The hydrogen valve, the hydrogen flow controller, the fuel valve, the fuel flow controller, the mixture valve and / or the mixture flow controller can then be adjusted by the control unit, e.g., by controlling it with the control value.

[0028] Within the scope of the invention, it can be provided that (particularly as an assumption) the (electrical) efficiency, in particular the net electrical efficiency, especially relative to a constant chemical power inflow (in particular LHV of the fuel inflow), is directly proportional to the fuel utilization of the fuel cell system. Accordingly, the efficiency and / or effectiveness can be optimized and / or adjusted depending on the fuel utilization of the fuel cell system.

[0029] In this case, I can in particular be a current drawn and / or generated by the fuel cell unit. This can be specified as a target current, in particular by the control unit, in particular as a function of a load operated by the fuel cell system. The current intensity can represent a manipulated variable (from the perspective of the control unit). A corresponding target value can comprise a (required) electrical power, a current and / or a voltage, in particular of the inverter or at the (AC) output of the fuel cell system. The control unit can have an (internal) controller that calculates the appropriate manipulated variable in order to set the target value. It is conceivable that the control unit, for example via a data connection, controls an inverter in order to produce, in particular to "draw" a (target) current specified by the control unit. c for example n c= 1 for a fuel cell unit or n c = 100 for a fuel cell system comprising (a stack of) 100 fuel cell units. Where V Norm in particular 22.41 NL mol -1 at 0 °C and 1013.15 m bar. V̇ H2in The (incoming or adjustable) volume flow of hydrogen can be adjusted, in particular, by a hydrogen flow regulator, which can preferably be controlled by a control unit. Accordingly, for example, the hydrogen flow regulator can be adjusted by the control unit and / or the hydrogen valve can be opened, for example, proactively to start operation of the fuel cell system.

[0030] The fuel utilization of a fuel cell unit of the fuel cell system (or the “stack”) can be defined and / or calculated as (Equation 4): FUStk=I∗nc∗60∗VNorm∑ixi,fuel∗kie−∗V˙mixture

[0031] V̇ Gemisch the (incoming or adjustable) volume flow of mixture at the anode inlet, especially in NL min -1 , which can be adjusted in particular as a function of a mixture flow controller, a mixture valve and / or a recirculation rate.

[0032] A target fuel utilization of a fuel cell unit of the fuel cell system can have a corresponding target value.

[0033] Particularly preferably, it can be provided that by controlling and / or regulating the fuel cell system (always) a combination (in particular “size triples”) of FU Sys , FU Stk , and OC can be adjusted, particularly independently of a specific operating strategy. Within the scope of the invention, it can be assumed (for simplification) that no water condensation occurs in the anode circuit.

[0034] It may be provided to use in equation 4 above an (incoming or adjustable) volume flow of mixture at the anode inlet, wherein in particular alternatively V̇ H2 An in can be used, especially when (pure) hydrogen is used.

[0035] Within the scope of the invention, a volume flow, in particular designated by a point above a V (e.g. V̇ H2 An in ), a volume flow rate, in particular a volume that passes per unit of time, for example a cross-sectional area of ​​a pipe.

[0036] Accordingly, it can preferably be provided to control the fuel utilization of a fuel cell unit of the fuel cell system by controlling and / or regulating the volume flow of hydrogen V̇ H2in , of fuel, of mixture and / or of the volume flow of hydrogen at the anode inlet V̇ H2 An inIn particular, the control unit can control and / or regulate a hydrogen valve, a hydrogen flow regulator and / or a recirculation fan. A target value for the fuel utilization of a fuel cell unit of the fuel cell system can therefore be specified, e.g., by a user and / or the control unit, whereupon the control unit preferably sets a (target value for the) volume flow of hydrogen V̇ H2in,soll , of fuel, of mixture and / or for the volume flow of hydrogen at the anode inlet V̇ H2 An inDepending on this, the control unit can then determine a control value for the hydrogen valve, the hydrogen flow controller, the fuel valve, the fuel flow controller, the mixture valve, the mixture flow controller, and / or the recirculation fan. The hydrogen valve, the hydrogen flow controller, the fuel valve, the fuel flow controller, the mixture valve, the mixture flow controller, and / or the recirculation fan can then be adjusted by the control unit, e.g., by controlling it with the control value.

[0037] Within the scope of the invention, it may be advantageous that the control of the fuel cell system for adjusting a proportion of hydrogen in the anode input current has at least one of the following features: - controlling, by the control unit, a hydrogen flow controller of the fuel cell system to adjust the volume flow of hydrogen, in particular to adjust the proportion of hydrogen in the anode input stream, - Controlling, by the control unit, a fuel flow controller of the fuel cell system to adjust the volume flow of fuel, in particular to adjust the proportion of fuel in the anode input stream.

[0038] Adjustment, particularly within the scope of the invention, may include increasing, maintaining constant, and / or decreasing. Preferably, one, two, or three setpoints can be kept constant, while the others can be changed and / or adjusted.

[0039] It can be provided that the volume flow of hydrogen is adjusted and the volume flow of fuel is kept constant, in order to adjust in particular the proportion of fuel in the anode input stream, for example in the mixture flow controller. It can also be provided that the volume flow of fuel is adjusted and the volume flow of hydrogen is kept constant, in order to adjust in particular the proportion of fuel in the anode input stream. This can (in each case) enable efficient and / or precise, in particular precisely predictable, adjustment, e.g. without readjustment (in particular "readjustment"). Alternatively or additionally, it can also be provided to change both volume flows simultaneously. This can enable particularly rapid adjustment.It may be particularly preferred that the volume flow of fuel, in particular at the mixture flow controller, be kept constant or reduced, with a high volume flow of fuel preferably being set (simultaneously) at the anode inlet. This advantageously prevents and / or reduces fuel depletion at the anode. This can be achieved, in particular, by the recirculation unit, in particular by adjusting the recirculation fan.

[0040] The fuel can be natural gas (C x H 2x+2, in particular comprising oxygen and / or carbon dioxide), methane (CH4), biogas (in particular comprising natural gas with a comparatively large proportion of CO2), a mixture of hydrogen and one of the aforementioned compounds and / or pure hydrogen (H2). It can be provided to operate the fuel cell system with pure hydrogen. It can be provided to operate the fuel cell system with pure fuel. Preferably, it can be provided to operate the fuel cell system with a mixture of (pure) hydrogen and fuel, wherein the proportion of hydrogen particularly preferably changes, for example increases. The (increasing) addition of hydrogen to the fuel can increase the proportion of H atoms in the fuel or in the mixture, in particular compared to a reference case in which pure fuel is used, for example natural gas or methane.It can be envisaged that at a constant chemical power inflow (in particular, the LHV of the fuel inflow), approximately the same net electrical power can be generated, particularly regardless of the hydrogen admixture rate. The percentage of carbon atoms in the system can decrease as more and more hydrogen is added. Since the generated electrical power can be roughly proportional to the oxygen atoms in the system and / or to the volumetric flow of oxygen, the oxygen-to-carbon ratio in the system (tends to) decrease with increasing hydrogen admixture and constant fuel supply.

[0041] Within the scope of the invention, it is conceivable that the control of the fuel cell system has at least one of the following features: - controlling, by the control unit, a mixture valve of the fuel cell system to introduce a volume flow of mixture, comprising the volume flow of hydrogen and the volume flow of fuel, into the anode path, - Controlling, by the control unit, a mixture flow controller of the fuel cell system to adjust the volume flow of mixture, - Controlling, by the control unit, the recirculation unit, in particular a recirculation fan of the recirculation unit, in order to set a recirculating volume flow, - controlling, by the control unit, an anode path drain valve of the recirculation unit, in particular a heat exchanger, and / or an anode path heat exchanger of the recirculation unit, in order to adjust a volume flow of condensed water vapor, - controlling, by the control unit, an inverter of the fuel cell system in order to adjust a current of the fuel cell system, wherein in particular a current control value of the inverter is adjusted by the control unit as a function of a current setpoint, - wherein the setpoints are set in particular as a function of the (above-described) control of the mixture valve, the mixture flow controller, the recirculation unit, in particular a recirculation fan, an anode path drain valve of the recirculation unit, in particular a heat exchanger, an anode path heat exchanger of the recirculation unit and / or the inverter.

[0042] It may be provided to distinguish between the following three cases when controlling and / or regulating: use of pure fuel, use of fuel mixed with hydrogen, use of pure hydrogen.

[0043] By controlling, in particular by admixing hydrogen, at least one, in particular all, of the following advantages can be realized (equally): - Maximizing the fuel utilization of the fuel cell system (hereinafter: FU Sys,max ), especially FU Sys = FU Sys,max , - Prevention of a fuel shortage in the fuel cell unit, in particular by setting a (too high) maximum value of the fuel utilization of a fuel cell unit of the fuel cell system (hereinafter: FU Stk,max ) is not undercut, especially FU Stk < FU Stk,max , - Protection against (excessive) carbon deposition (e.g. coking), in particular in the anode path and / or the fuel cell unit, wherein preferably the oxygen-carbon ratio has a minimum oxygen-carbon ratio (hereinafter: OC min), in particular OC > OC min and / or - Avoidance of (too) high oxygen-carbon ratio (which could in particular lead to [comparatively] reduced efficiency), preferably by adjusting the oxygen-carbon ratio to the target value of the oxygen-carbon ratio, preferably avoiding exceeding the target value OC > OC soll is prevented. Pure fuel

[0044] Headings can only serve to structure the text and do not restrict the wording and / or features.

[0045] Within the scope of the invention, especially if the anode input stream does not (yet) contain any hydrogen, the following relationships may apply. This may (also) apply in particular to a mixture of hydrogen with biogas and / or methane.

[0046] It can be provided within the scope of the invention that the volume flow of mixture is dependent on FU Stk , soll , OC Soll and i Stk , I or I soll is defined and / or adjustable (equation 5): V˙Mixture=ƒ11(FUStk,soll, OCSoll, ISoll)

[0047] In particular, this can be assumed to be true regardless of water condensation in the anode path.

[0048] This can f 11 be defined and / or calculable by (Equation 5.1): V˙Mixture=iStk∗nc∗ΓΦ(OCSoll−OCFuel+(ΓΦ−OCSoll+OCFuel)∗FUStk,Soll)∗F∗Ke−

[0049] Within the scope of the invention, the following may apply: KC=∑ixi,fuel∗kiC Ke−=∑ixi,fuel∗kie− KO=∑ixi,fuel∗kiO

[0050] Here, x i,Brennstoff the (molar) fraction of the fuel. Here, k iCthe number of (bonded) carbon atoms in the fuel (molecule). K C specify the total number. k can be ie - the number of (bound) electrons in the fuel (molecule). K e - specify the total number. For example, the following applies: for CH4: k ie - = 8 for H2: k ie - = 2 for CO: k ie - = 2 for C2H6: k ie - = 14 for C3H8: k ie - = 20 for C4H10: k ie - = 26

[0051] In this case, k iO the number of (bound) oxygen in the fuel (molecule). K O specify the total number.

[0052] Here, F can be the Faraday constant. It can specify the electrical charge of one mole of singly charged ions in the unit coulomb (C).

[0053] This can OCFuel=KOKC apply. ΓΦ=Ke−2∗KC apply. Here I = i Stk * n c apply, and in particular the (above-mentioned) current. n c the number of fuel cell units. Stk the power of a fuel cell unit.

[0054] It can be provided within the scope of the invention that the recirculating volume flow (hereinafter: V̇ recy ) depending on FU Stk , soll , OC Soll and i Stk , I or I soll is defined and / or adjustable (equation 6): V˙recy=ƒ12(FUStk,soll, OCSoll, ISoll)

[0055] Accordingly, V̇ recy depending on FU Stk , soll , OC Soll and / or I soll be adjusted, preferably depending on FU Stk , soll , OC Soll and I soll (analogous for the equations below).

[0056] This can f12 be defined and / or calculable by (equation 6.1): V˙recy=iStk∗nc∗ΓΦ∗((1+KΔAn)∗OCSoll+(ΓΦ−OCSoll)∗FUStk,Soll)((OCSoll+(ΓΦ−OCSoll)∗FUStk,Soll)∗F∗Ke−)∗(ΓΦ−OCSoll)∗FUStk,Soll

[0057] It can be defined and / or calculable within the scope of the invention (equation 6.2): KΔAn=∑ixi,fuel∗kiΔAn

[0058] In this case, k iΔAn the number of pairs of hydrogen atoms (or the number of H2 molecules) which react (chemically) in particular in the fuel cell unit to form water or an increase in molecules within a flow (e.g. during flow through the fuel cell unit, in particular the anode), in particular due to steam reforming of the molecules.

[0059] Within the scope of the invention, it can be provided that the volume flow of condensed water vapor is not present and / or is equal to 0.

[0060] In this case, a control, in particular by a control unit, of the recirculation unit can adjust a proportion of the anode output current which is (re)circulated into the anode input current.

[0061] Within the scope of the invention, the control unit can, in particular depending on the desired (above) setpoints, V̇ Gemisch , V̇ recy , and / or the volume flow of condensed water vapor (hereinafter: V̇ Cond ). The setpoints FU Stk , soll , I soll and / or OC soll used (specified). It can be provided that V̇ Cond is not adjusted, or cannot be adjusted, especially if no hydrogen is added or the volume flow of hydrogen is 0. FU is preferred Stk , soll not used as a setpoint, but preferably only monitored. Fuel & proportion of hydrogen

[0062] Within the scope of the invention, especially if at least a portion of hydrogen is included in the anode input stream, the following relationships may apply. This may apply in particular to a mixture of hydrogen with biogas and / or methane.

[0063] It can be provided within the scope of the invention that the volume flow of mixture is dependent on FU Sys , soll and i Stk , I or I soll is defined and / or adjustable (equation 8): V˙Mixture=ƒ21(FUStys,soll, ISoll)

[0064] This can be especially true (as an assumption) regardless of any condensation of water in the anode path. 21 = f 31 apply.

[0065] It can be provided within the scope of the invention that the recirculating volume flow depends on FU Sys , soll , FU Stk , soll , and i Stk, I or I soll is defined and / or adjustable (equation 9): V˙recy=ƒ22(FUSys,soll, FUStk,soll, ISoll)

[0066] This can f 22 be defined and / or calculable by (Equation 9.1): V˙recy=iStk∗ncF∗FSys,soll∗Ke−+(1+FUStk,soll−FUSys,sollFUSys,soll∗(FUStk,soll−1)∗(1+KΔAn))−V˙Cond1−FUStk,soll−FUSys,sollFUSys,soll∗(FUStk,soll−1)

[0067] Alternatively, the following may apply, especially if the recirculation fan is arranged differently, preferably between the anode path heat exchanger and the heat exchanger: V˙recy=iStk∗ncF∗FSys,soll∗Ke−∗FUStk,soll−FUSys,sollFUSys,soll∗(FUStk,soll−1)∗(2+KΔAn)1−FUStk,soll−FUSys,sollFUSys,soll∗(FUStk,soll−1)+V˙Cond

[0068] It can be provided within the scope of the invention that the volume flow of condensed water vapor is dependent on OC soll , FU Stk , soll , and i Stk, I or I soll is defined and / or adjustable (equation 10): V˙Cond=ƒ22(FUStk,soll, OCSoll, ISoll)

[0069] In this case, especially if there is no condensation (of water vapor), V̇ Cond = 0 apply.

[0070] This can f 23 be defined and / or calculable by (equation 10.1): V˙Cond=V˙recy=(FUStk,soll−FUStk,soll)∗iStk∗nc2∗F∗FUStk,soll∗(FUStk,soll−1)+(OCFuel−OCSoll)∗iStk∗nc∗KCF∗FSys,soll∗Ke−

[0071] In this case, a control, in particular by a control unit, of the recirculation unit can adjust a proportion of the anode output current which is (re)circulated into the anode input current.

[0072] Within the scope of the invention, the control unit can, in particular depending on the desired (above) setpoints, V̇ Gemisch , V̇ recy , and / or V̇ CondThe setpoints FU Sys , soll , FU Stk , soll and OC soll (especially if condensation of water in the anode path is assumed) may be used (specified). It may be provided that OC soll is not specified, especially if no condensation is assumed. Pure hydrogen

[0073] Within the scope of the invention, in particular if at least only hydrogen is included in the anode input stream, the following relationships may apply.

[0074] It can be provided within the scope of the invention that the volume flow of mixture is dependent on FU Sys , soll and i Stk , I or I soll is defined and / or adjustable (equation 11): V˙Mixture=ƒ31(FUSys,set, ISet)

[0075] In particular, this can be assumed to be true regardless of water condensation in the anode path.

[0076] In this case, t 31 be defined and / or calculable by (equation 11.1): V˙mixture=iStk∗ncFSys,soll∗F∗Ke−

[0077] It can be provided within the scope of the invention that the recirculating volume flow depends on FU Sys , soll , FU Stk , soll , and i Stk , I or I soll is defined and / or adjustable (equation 12): V˙recy=ƒ32(FUSys,soll, FUStk,soll, ISoll)

[0078] This can f 32 be defined and / or calculable by (Equation 12.1): V˙recy=iStk∗ncF∗FSys,soll∗Ke−−V˙Cond1−FUStk,soll−FUSys,sollFUSys,soll∗(FUStk,soll−1)

[0079] It can be provided within the scope of the invention that the volume flow of condensed water vapor is dependent on OC soll , FU Stk , soll , and i Stk , I or I soll is defined and / or adjustable (equation 13): V˙Cond=ƒ33(FUStk,soll, FUSys,soll, xStk,soll)

[0080] In this case, especially if there is no condensation (of water vapor), V̇ Cond = 0 apply.

[0081] Here, x Stk,soll in particular have at least one of the following features: - Molar fraction of hydrogen at the anode inlet, - Molar fraction of water at the anode inlet, - Molar fraction of hydrogen at the anode outlet, - Molar fraction of water at the anode outlet, - Humidity of the anode input stream, in particular of water vapor and / or - Humidity of the anode output stream, in particular water vapor contained in the anode output stream.

[0082] For example, f 33 be defined and / or calculable by (Equation 13.1): V˙Cond=FUStk−FUSysFUSys∗(FUStk−1)∗I∗nc∗60∗VNorm2∗F∗1−pSatpNorm∗FUSys1−pSatpNorm

[0083] Equation 13.1 can apply, especially if x Stk,Soll the humidity of the anode input current or anode output current. V Norm comprise a standard volume which in particular is 22.41 NL mol -1 at 0°C and 1013.15m bar. Here, p Norm have a standard pressure, which can be in particular 1013 hPa (1013 mbar). sat have a saturation vapor pressure, especially of water vapor in the recirculation unit, e.g., after the heat exchanger. This can be determined, for example, by a (pressure) sensor.

[0084] In this case, a control, in particular by a control unit, of the recirculation unit can adjust a proportion of the anode output current which is (re)circulated into the anode input current.

[0085] Within the scope of the invention, the control unit can be used for controlling and / or regulating, in particular depending on the desired (above) setpoints, V̇ Gemisch , V̇ recy , and / or V̇ Cond , can be set. The setpoints FU Sys, soll and FU Stk, soll be used (default). X can also be used Stk, soll be used as a target value.

[0086] Within the scope of the invention, it can be provided that the control unit sets a recirculation rate of the recirculation unit in order to control and / or regulate the recirculating volume flow, in particular as a function of the recirculation rate. Alternatively or additionally, the recirculating volume flow can be controlled and / or regulated by the control unit adjusting a cathode path valve, whereby preferably a certain portion of the cathode input stream is diverted in order to cool the cathode output stream. The control unit can set a control value for the cathode path valve for this purpose. The tapped cathode input stream can be provided to the heat exchanger (of the recirculation unit) in order to cool the absorbed anode output stream, in particular a contained water vapor, by the tapped cathode input stream.The extracted portion, which is fed to the heat exchanger of the recirculation unit, can be used to cool the anode output stream and / or the water vapor. This allows the water vapor to condense (at least partially).

[0087] The absorbed water vapor can be fed to the anode input stream through the heat exchanger, in particular subsequently, in particular by feeding it to an anode path connection point. The absorbed water vapor can be removed through the heat exchanger, in particular subsequently, in particular by removing it via an anode path outlet. This allows the humidity of the anode input stream to be influenced, preferably reduced. In this way, the recirculation unit can influence the humidity of the anode input stream or enable the humidity of the anode input stream to be adjusted.

[0088] A recirculation rate (hereinafter: r) can be defined and / or calculated by: r=V˙loopV˙An out

[0089] In particular, the recirculation rate can have a value in the range r = [0,1]. V̇ An out a volume flow at the anode outlet, especially in NL min -1 , include. Accordingly, the anode output current can have a volume flow at the anode outlet, in particular be characterized by this. V̇ loop a returned volume flow, especially in NL min -1 , which can correspond in particular to the volume flow directed toward the anode path heat exchanger. In other words, it can be provided that the returned volume flow is not directed into a burner.

[0090] The following relationship can be defined and / or calculated: FUStk=(1−r)∗FUSys1−r∗FUSys

[0091] The following relationship can be defined and / or calculated, especially by rearranging (equation 14): r=FUStk−FUSysFUSys∗(FUStk−1)

[0092] In this case, Equation 14 can be valid even under and / or despite consideration of water condensation (condensation of water vapor) in the anode path. In other words, it can be provided that even the condensation of water vapor in the heat exchanger does not affect the validity of Equation 14. This can be taken into account by the control unit during control and / or regulation, in particular during calculation.

[0093] The taking of a certain share (hereinafter: r div ) of the cathode input current through the recirculation unit can be described as follows. The following relationship can be defined and / or calculated: rdiv=V˙Air heat exchanger inV˙An air filter out

[0094] V̇ Air Wärmetauseher in the (incoming or adjustable) volume flow of air at the inlet of the heat exchanger, especially in NL min -1 , which can be controlled and / or regulated in particular by adjusting the cathode path valve by the control unit, in particular by controlling and / or specifying a control value for the cathode path valve. In this case, V̇ Air Luftritter out the (outgoing or adjustable) volume flow of air at an outlet of the air filter, especially in NL min -1 , which can be controlled and / or regulated in particular by adjusting the air filter (e.g. via an actuator) by the control unit.

[0095] During operation, the fuel cell system can supply a current. The current can be adjusted, in particular, depending on the volume flow of oxygen. The control unit can adjust the volume flow of oxygen and / or the current accordingly, for example, by controlling and / or regulating an air supply unit, a cathode path valve, and / or an air blower.

[0096] Tables 1-5 below can be used for explanation or comparison. The explanations for the tables below can, of course, also apply to the corresponding features described elsewhere, and vice versa.

[0097] Table 2 can be used for the following explanations, especially for illustration purposes.

[0098] Within the scope of the invention, it can be provided that the control of the fuel cell system has at least one, preferably all, of the following features: - Determining, by the control unit, a target fuel utilization of a fuel cell unit of the fuel cell system as a function of the proportion of hydrogen in the anode input current, wherein in particular an increase, in particular a linear increase, of the target fuel utilization is determined with an increasing proportion of hydrogen in the anode input current, wherein in particular the target fuel utilization is proportional to the proportion of hydrogen, - Setting, by the control unit, a fuel utilization of a fuel cell unit of the fuel cell system depending on the target fuel utilization of a fuel cell unit of the fuel cell system and / or - Controlling and / or regulating, by the control unit, the fuel cell system to keep the oxygen-carbon ratio constant.

[0099] It can be provided that by adjusting and / or controlling and / or regulating the fuel utilization of the fuel cell system does not decrease or does not decrease as much as the proportion of hydrogen in the anode input current increases.

[0100] Table 3 can be used for the following explanations, especially for illustration purposes.

[0101] It is further conceivable that the control of the fuel cell system has at least one, preferably all, of the following features: - Controlling and / or regulating, by the control unit, the fuel cell system in order to keep a fuel utilization of the fuel cell system and a fuel utilization of a fuel cell unit of the fuel cell system constant, whereby the oxygen-carbon ratio preferably increases with increasing proportion of hydrogen in the anode input stream.

[0102] This can prevent and / or reduce, in particular, a (significant) drop in the (electrical) efficiency. Within the scope of the invention, FU Sys proportional to the electrical efficiency. Therefore, by keeping or increasing the FU Sys the electrical efficiency can be improved.

[0103] Table 4 can be used for the following explanations, especially for illustration purposes.

[0104] It is also conceivable that the control of the fuel cell system has at least one, preferably all, of the following features: - Determining, by the control unit, a target fuel utilization of a fuel cell unit of the fuel cell system as a function of the proportion of hydrogen in the anode input current, wherein in particular an increase, in particular a linear increase, of the target fuel utilization is determined with an increasing proportion of hydrogen in the anode input current, wherein in particular the target fuel utilization is proportional to the proportion of hydrogen, - Setting, by the control unit, a fuel utilization of a fuel cell unit of a fuel cell system depending on the target fuel utilization of a fuel cell unit of the fuel cell system and / or - Controlling and / or regulating, by the control unit, the fuel cell system in order to keep a fuel utilization of the fuel cell system constant, whereby preferably the oxygen-carbon ratio increases with increasing proportion of hydrogen in the anode input stream.

[0105] Table 5 can be used for the following explanations, especially for illustration purposes.

[0106] Within the scope of the invention, it is optionally possible for the control of the fuel cell system to have at least one, preferably all, of the following features: - Determining, by the control unit, a target fuel utilization of the fuel cell system as a function of the proportion of hydrogen in the anode input current, wherein in particular an increase, in particular a linear increase, of the target fuel utilization is determined with an increasing proportion of hydrogen in the anode input current, wherein in particular the target fuel utilization is proportional to the proportion of hydrogen, - Setting, by the control unit, a fuel utilization of the fuel cell system depending on the target fuel utilization of the fuel cell system, - Determining, by the control unit, a target fuel utilization of a fuel cell unit of the fuel cell system as a function of the proportion of hydrogen in the anode input current, wherein in particular an increase, in particular a linear increase, of the target fuel utilization is determined with an increasing proportion of hydrogen in the anode input current, wherein in particular the target fuel utilization is proportional to the proportion of hydrogen and / or - Setting, by the control unit, a fuel utilization of a fuel cell unit of the fuel cell system depending on the target fuel utilization of a fuel cell unit of the fuel cell system - wherein, in particular, by adjusting a fuel utilization of the fuel cell system and / or adjusting a fuel utilization of a fuel cell unit of the fuel cell system, the oxygen-carbon ratio increases with increasing proportion of hydrogen in the anode input stream.

[0107] All steps can be carried out in parallel, sequentially, and / or interdependently. This can preferably be achieved by Stk , FU Sys and / or OC optimized.

[0108] The above object is achieved according to a second aspect by a fuel cell system according to the invention, in particular a solid oxide fuel cell system, comprising - at least one fuel cell unit for energy generation, comprising ◯ an anode path comprising ▪ an anode input for receiving an anode input current and ▪ an anode output for outputting an anode output current, and ◯ a cathode path comprising ▪ a cathode input for receiving a cathode input current and ▪ a cathode output for outputting a cathode output current, - a control unit for controlling and / or regulating the fuel cell system, - wherein the fuel cell system is configured to implement the method according to the first aspect.

[0109] The fuel cell unit can comprise one or more fuel cells, which can be arranged in a stack (e.g., a "stack"). Each fuel cell can comprise an anode and / or a cathode, with the anode being connected to the anode path and / or the cathode being connected to the cathode path. The fuel cell unit(s) can preferably comprise solid oxide fuel cells. The fuel cell system or fuel cell unit can be used to generate energy, in particular by generating thermal and / or electrical energy or power. Thus, a current and / or voltage can be utilized, for example, for external devices. The fuel cell system preferably comprises an inverter, in particular a DC / AC converter. This can preferably be tapped via an anode electrode connected to the anode and a cathode electrode connected to the cathode.

[0110] The anode path can guide a material flow, in particular toward an anode inlet (see below). The anode path can also, at least partially, comprise a material flow from the anode outlet. The anode path can comprise, in particular guide, the anode inlet current and / or the anode outlet current.

[0111] The anode input stream can (essentially) comprise the material flow from a hydrogen tank (in particular the inlet into the system) to an anode inlet.

[0112] The anode inlet can be configured to receive an anode input current and, in particular, to lead into the interior of the fuel cell unit.

[0113] The anode outlet can be configured to output an anode output current, in particular from the interior of the fuel cell unit. The anode output current comprises at least partially water, in particular water vapor.

[0114] The cathode path can guide a material flow, in particular toward a cathode inlet (see below). The cathode path can also, at least partially, comprise a material flow from the cathode outlet. The cathode path can comprise, in particular guide, the cathode inlet current and / or the cathode outlet current.

[0115] The cathode input stream can (essentially) comprise the material flow from an air supply unit (in particular inlet for air into the system) to a cathode inlet.

[0116] The cathode inlet can be configured to receive a cathode input current and, in particular, to lead into the interior of the fuel cell unit.

[0117] The cathode output may be configured to output a cathode output current, and in particular may lead from the interior of the fuel cell unit.

[0118] The fuel cell unit can comprise an electrolyte, in particular in the form of a membrane, along the sides of which the cathode path and the anode path or the corresponding material flows are guided, in order to preferably enable an (exothermic) redox reaction.

[0119] Unless otherwise stated, transport between different components of the fuel cell unit can be achieved through connecting units, such as pipes. This can enable a flow of materials to operate the fuel cell system.

[0120] The fuel cell system can have a recirculation unit for at least partially returning the anode output stream to the anode input stream. The recirculation unit can be encompassed by the anode path, in particular forming part of the anode path. Preferably, the recirculation unit can be configured to regulate and / or control the humidity of the anode input stream and / or a portion of the anode output stream that is fed back to the anode input stream. The recirculation unit comprises a heat exchanger connected (directly or at least indirectly) to the anode output. The heat exchanger can thereby absorb the anode output stream completely or at least partially and then feed it to the anode input stream, in particular at an anode path connection point.This can be achieved via a recirculation path, which in particular leads from a (second) inlet of the anode path heat exchanger to a (second) outlet of the anode path heat exchanger. The heat exchanger can absorb water vapor contained in the anode output stream and then feed it to the anode input stream, in particular at an anode path connection point. Alternatively or additionally, the (condensed) water vapor can be removed, for example, via an anode path outlet. This can create a cycle in which (at least partially) the anode output stream is fed back into the anode input stream (in particular, feedback).The recirculation unit can be configured to tap a specific portion of the cathode input stream and provide it to the heat exchanger in order to cool the anode output stream, in particular the water vapor contained therein, using the specific portion of the tapped cathode input stream, for example, through heat transfer. In particular, the cathode input stream or the tapped specific portion thereof has a lower temperature than the anode output stream or the water vapor. Thus, the temperature can be influenced, in particular reduced, in particular before the absorbed anode output stream or water vapor is supplied to the anode input stream, in particular via the anode path connection point. As a result, the saturation vapor temperature can be influenced, in particular reduced.This allows the humidity of the anode input current to be controlled and / or regulated, preferably influenced, in particular reduced. This can realize the aforementioned advantages, in particular, increasing the performance of the fuel cell system.

[0121] The heat exchanger, the anode path heat exchanger, and / or the cathode path heat exchanger can each have a first inlet connected to a first outlet and a second inlet connected to a second outlet. Preferably, no material or material flow can occur between the first inlet / outlet and the second inlet / outlet. Preferably, only (thermal) energy can be exchanged. Thus, it can be provided that a respective volume flow does not change when passing through a heat exchanger, anode path heat exchanger, and / or cathode path heat exchanger.

[0122] The anode path connection point can be located between the hydrogen flow controller and the recirculation blower. This can be advantageous to allow the recirculation blower and / or the anode path heat exchanger to influence the flow, particularly after mixing and / or before reaching the anode inlet. Thus, the flow rate can be varied by the recirculation blower. Heat can also be removed and / or added by the anode path heat exchanger.

[0123] This results in the same advantages with regard to a fuel cell system according to the invention as have already been described with regard to a method according to the invention according to the first aspect.

[0124] It is also conceivable that the recirculation unit has a temperature sensor for detecting an actual temperature, in particular an actual saturation vapor temperature, of the water vapor, which is used for regulating and / or controlling the humidity of the anode input stream, wherein the temperature sensor is arranged on the heat exchanger, in particular on an outlet of the heat exchanger.

[0125] The temperature sensor can be arranged shortly after and / or within the heat exchanger. It can be arranged shortly after the heat exchanger, in particular shortly after the first feeder. This can be advantageous in order to enable precise measurement and / or to prevent the temperature sensor from being exposed to excessive temperatures (in particular due to a temperature gradient from the first receptacle to the first feeder of the heat exchanger). A temperature sensor with lower temperature resistance can be selected and / or wear can be reduced. The actual temperature, in particular the actual saturation vapor temperature, of the steam can be transmitted to the control unit, preferably to be taken into account during control and / or regulation, in particular during calculation.

[0126] Alternatively or additionally, the temperature sensor can detect a pressure, an actual pressure, and / or an actual saturation vapor pressure. This can be transmitted to the control unit, particularly analogously to the above explanations, to be preferably taken into account during control and / or regulation, particularly during calculation.

[0127] A high-temperature region can be provided, which in particular includes the fuel cell unit, the cathode path heat exchanger, the anode path heat exchanger, the burner, the cathode inlet, the cathode outlet, the anode inlet, and / or the anode outlet. The temperature in the high-temperature region can be (relatively) high; for this purpose, it can, in particular, be thermally insulated.

[0128] Within the scope of the invention, it is optionally possible for the heat exchanger to have at least one, preferably all, of the following features: - a condensate separator for at least partially condensing the water vapor in order to cool the anode output stream and / or reduce the humidity, - an anode path drain connected to the heat exchanger, in particular the condensate separator, for discharging a volume flow of condensed water vapor, - a first receptacle for (at least partially) receiving the anode output stream, in particular water vapor contained in the anode output stream, - a first feeder for feeding the absorbed water vapor to the anode input stream, - a second receptacle for tapping the specific portion of the cathode input current, wherein in particular the second receptacle is connected to a cathode path valve and / or - a second feeder for at least partially returning the determined portion of the cathode input current to the cathode path, in particular to the cathode input current via a cathode path connection point.

[0129] The condensate separator can be arranged in the heat exchanger. The condensate separator can cool the anode output stream, preferably by heat removal, in particular by heat exchange or cooling. The water vapor at least partially contained in the anode output stream can be at least partially condensed in the condensate separator through condensation. Humidity, moisture, and / or water vapor can be removed from the anode output stream in the heat exchanger, in particular in the condensate separator, in particular through condensation.

[0130] The resulting condensate can then be removed from the fuel cell system, for example via an anode path drain, which is preferably connected to the heat exchanger, in particular to the condensate separator. Accordingly, the anode path drain can be configured to drain a volume flow of condensed water vapor, which can preferably be adjusted by the control unit via an anode path drain valve. The volume flow of condensed water vapor can be detected by a volume flow sensor for condensed water vapor. The volume flow sensor can be arranged in or downstream of the heat exchanger, in particular in a connecting section between the heat exchanger and the anode path drain. Alternatively or additionally, the volume flow sensor for condensed water vapor can be arranged on or in the anode path drain.The result of the detection can be transmitted to a control unit to be used preferably in controlling and / or regulating, in particular in calculating.

[0131] The heat exchanger may have a first receptacle for (at least partially) receiving the anode output stream, in particular water (vapor) and / or hydrogen contained in the anode output stream.

[0132] The heat exchanger may have a first feeder for feeding the absorbed water vapor to the anode input stream. The first feeder may be connected, in particular directly, to the first feeder.

[0133] The heat exchanger may have a second receptacle for tapping the specific portion of the cathode input current, wherein in particular the second receptacle is connected to a cathode path valve.

[0134] The heat exchanger can have a second feeder for at least partially returning the specific portion of the cathode input stream to the cathode path, in particular to the cathode input stream, via a cathode path connection point. The second receptacle can be connected to the second feeder, in particular directly. Thus, the cathode input stream can flow at least partially through the heat exchanger. Provision can be made for the remaining portion of the cathode input stream to flow (without detour) through the cathode path valve, in particular toward the cathode inlet. Preferably, heat exchange (only) takes place in the heat exchanger between the first receptacle / feeder and the second receptacle / feeder. Preferably, no medium, in particular no gas and / or liquid, is exchanged. As a result, the saturation vapor temperature and / or humidity can be influenced (solely) by cooling.

[0135] The cathode path connection point can be designed as a T-piece, Y-splitter, and / or component (e.g., a pipe) with three openings, in particular two inlets (e.g., connected to the outlet of the cathode path valve and the, in particular, second, feeder from the heat exchanger) and one outlet (e.g., toward the cathode inlet). The cathode path connection point preferably recombines the cathode inlet stream, which in particular was tapped at least partially by the cathode path valve, while the remaining portion flows directly from the cathode path valve to the cathode path connection point. The volume flow of the cathode inlet stream upstream of the cathode path valve can preferably correspond to the volume flow downstream of the cathode path connection point, in particular since only heat is exchanged in the heat exchanger and preferably no medium (“volume-preserving”).

[0136] The cathode path valve can be arranged between the air supply unit and the cathode path connection point, in particular connected to them. The cathode path valve can have a three-way valve. In particular, by adjusting the valve, a specific portion of the cathode input current can be tapped, while the remaining portion preferably flows directly to the cathode path connection point. Thus, in particular in a first end position, the entire flow can be directed directly to the cathode path connection point by adjusting it. In particular in a second end position, the entire flow can be directed via the heat exchanger to the cathode path connection point by adjusting it. In an intermediate position of the cathode path valve, a specific (e.g., percentage) portion can be supplied to the heat exchanger, preferably to enable cooling.Preferably, the cathode input stream has a lower temperature than the anode output stream. This allows the cathode input stream to cool the anode output stream (reduce its temperature), particularly by transferring heat. For example, the temperature of the anode output stream can be cooled by the heat exchanger from approximately 250°C to 40°C.

[0137] This results in the same advantages with regard to a fuel cell system according to the invention as have already been described with regard to a method according to the invention according to the first aspect.

[0138] Furthermore, it can be provided within the scope of the invention that the anode path has at least one of the following features: - a hydrogen tank comprising hydrogen, ammonia and / or a chemical compound comprising hydrogen, - a fuel tank comprising a fuel, in particular natural gas, methane, biogas and / or a mixture thereof with hydrogen, - a mixture valve, - a hydrogen valve, - a fuel valve, - a mixture flow controller, in particular for adjusting a volume flow of mixture in the anode input stream, - a hydrogen flow regulator, in particular for adjusting a volume flow of hydrogen in the anode input stream, - a fuel flow regulator, in particular for adjusting a volume flow of fuel in the anode input stream, - a recirculation fan, in particular for setting a recirculating volume flow, - an anode path heat exchanger, in which in particular the anode input stream is heated by the anode output stream and / or the anode output stream is cooled by the anode input stream, wherein preferably the anode input stream is received via a first inlet of the anode path heat exchanger and is supplied to the anode inlet via a first outlet of the anode path heat exchanger, wherein preferably the anode output stream is received via a second inlet of the anode path heat exchanger and is supplied to the heat exchanger via a second outlet of the anode path heat exchanger, - a recirculation path, a heat exchanger, a temperature sensor, and / or an anode path connection point of the recirculation unit and / or - an anode path drain connected to the heat exchanger to allow a volume flow of condensed water vapor from the anode path.

[0139] The hydrogen tank can comprise a container and / or a supply line. This allows hydrogen, ammonia, and / or a chemical compound comprising hydrogen to be provided. These can then be introduced into the anode path through the hydrogen tank.

[0140] The fuel tank can include a container and / or a supply line. This allows fuel (see above) to be provided. This fuel can then be introduced into the anode path through the fuel tank.

[0141] The hydrogen valve can be used for connecting and / or disconnecting, especially between the hydrogen tank and the hydrogen flow regulator. This allows you to adjust whether a medium (such as those mentioned above) can even enter the anode path.

[0142] The fuel valve can be used for connecting and / or disconnecting, particularly between the fuel tank and the mixture flow regulator. This allows adjustment of whether fuel can even enter the anode path.

[0143] The mixture valve can be used for connecting and / or disconnecting. It can preferably be connected to the fuel valve (particularly its outlet) and the hydrogen valve (particularly its outlet). It can thus be adjusted whether the mixture of fuel and hydrogen is introduced into the anode path or passed on.

[0144] The hydrogen flow controller can be used to adjust a volume flow of hydrogen (particularly at the system inlet), in particular by being controlled by a control unit, for example, by the control unit adjusting a valve of the hydrogen flow controller. The volume flow of hydrogen can have a mass and / or a volume, in particular per unit of time. In other words, the amount of hydrogen per unit of time can be adjusted.

[0145] The fuel flow controller can be used to adjust a volume flow of fuel (particularly at the system inlet), in particular by being controlled by a control unit, for example, by the control unit adjusting a valve of the fuel flow controller. The volume flow of fuel can have a mass and / or a volume, in particular per unit of time. In other words, the amount of fuel per unit of time can be adjusted.

[0146] The mixture flow controller can be used to adjust a volume flow of the mixture (particularly in the anode path), in particular by being controlled by a control unit, for example, by the control unit adjusting a valve of the mixture flow controller. The volume flow of the mixture can have a mass and / or a volume, in particular per unit of time. In other words, the amount of mixture per unit of time can be adjusted.

[0147] It may be provided that control and / or adjustment comprises only two of the following components: - Hydrogen flow regulator - Fuel flow regulator - Mixture flow regulator

[0148] This can simplify control and / or regulation, in particular calculation by the control unit.

[0149] Controlling and / or adjusting another (third) component can increase the degrees of freedom.

[0150] The recirculation fan can adjust the flow rate of the anode input flow. A recirculation sensor can be arranged before, on, in, and / or after the recirculation fan, which can be configured, in particular, to measure a recirculating volume flow. The measured value can be transmitted, in particular, to the control unit, preferably to be taken into account during control and / or regulation, in particular during calculation.

[0151] The recirculating volume flow can comprise the sum of the volume flow of mixture and the anode output flow (in particular minus the volume flow of condensed water vapor and / or minus a portion flowing to the (after-)burner, in particular if present). The anode input flow can comprise or comprise (in particular at the anode inlet and / or exclusively) the recirculating volume flow. In particular, the anode input flow can initially comprise (only) the volume flow of mixture at the mixture flow controller. The anode input flow can (subsequently), due to what is supplied from the heat exchanger, comprise the volume flow of mixture and (at least partially) the anode output flow, wherein in particular the anode output flow can be reduced by a volume flow of condensed water vapor (outflow from the anode path).Thus, the anode inlet flow may change during transport from the hydrogen tank to the anode inlet, particularly with regard to humidity (preferably reduced by recirculation), volume flow (particularly increase), temperature (particularly increase) and / or pressure.

[0152] In this case, the anode path heat exchanger can preferably (only) provide an exchange of heat, in particular from the anode output stream to the anode input stream or the recirculating volume flow, the temperature of which preferably increases in order to advantageously already have a higher temperature at the anode inlet, wherein the temperature of the anode output stream is advantageously reduced before it is fed to the heat exchanger.

[0153] A reformer can be provided in the anode path, particularly between the anode path heat exchanger and the anode inlet. This can advantageously convert alkanes into hydrocarbons and hydrogen (at least partially). This can increase the proportion of hydrogen usable in the fuel cell unit.

[0154] With regard to the present invention, it is conceivable that the cathode path has at least one of the following features: - an air supply unit for introducing the cathode input current into the cathode path, - a cathode path connection point, via which air tapped by the cathode path valve can be at least partially returned to the cathode path, - an air blower, in particular for adjusting a flow rate of the cathode input current, - a cathode path heat exchanger, in which in particular the cathode input stream is heated by the cathode output stream and / or the cathode output stream is cooled by the cathode input stream, wherein preferably the cathode input stream is received via a first inlet of the cathode path heat exchanger and is supplied to the cathode inlet via a first outlet of the cathode path heat exchanger, - a burner connected to the cathode output and / or the anode output, in particular to at least partially burn the cathode output current and / or the anode output current and / or - an air outlet connected to the cathode outlet, in particular the burner, for at least partially removing air from the fuel cell system.

[0155] An air supply unit can be configured to introduce the cathode input stream into the cathode path. The air supply unit can comprise an oxygen tank, an air tank, a filter, in particular an oxygen filter or air filter, and / or an intake device, for example, for intake of air. Accordingly, the cathode input stream, which is preferably introduced into the cathode path, can comprise oxygen and / or air.

[0156] The cathode path connection point can be configured to allow a previously tapped portion of the cathode input current and / or the air to flow back into the cathode input current by recirculating it. Accordingly, a portion of the cathode input current can preferably be tapped to cool the anode output current. The extent of cooling can be adjusted by controlling and / or regulating the tapped portion. The cathode path connection point is preferably arranged between the cathode path valve and the air blower. Preferably, the volume flow downstream of the cathode path connection point corresponds to the volume flow at or downstream of the air supply unit.

[0157] In this case, an air blower, in particular for controlling and / or regulating a flow rate (and / or a volume flow or a quantity) of the (in particular recombined) cathode input stream, can be provided, which is preferably arranged between the cathode connection point and the cathode path heat exchanger.

[0158] In this case, the cathode path heat exchanger can preferably (only) provide an exchange of heat, in particular from the cathode output stream to the cathode input stream, the temperature of which preferably increases in order to advantageously already have a higher temperature at the cathode inlet, wherein the temperature of the cathode output stream is advantageously reduced before it is fed to the cathode path heat exchanger.

[0159] The burner can preferably be arranged between the cathode outlet and the cathode path heat exchanger. It can be provided that the anode output current is at least partially fed to the burner. The cathode output current and / or the anode output current can be combusted, in particular partially, by the burner. In particular, air, oxygen, ammonia and / or (flammable) chemical compounds, in particular comprising hydrogen, can be combusted. It can also be provided that at least one additional substance is fed to the burner, in particular to enable improved combustion. The burner can preferably be controlled and / or regulated by the control unit. In particular, adjustment of the temperature, the proportion of the anode output current and / or the supply of additional substances can be enabled.

[0160] The air outlet can guide the cathode output stream, in particular air, out of the cathode path or allow it to escape. The air outlet can be connected to the cathode path heat exchanger, in particular to its outlet. If a burner is provided, its combustion products can be expelled via the air outlet. The anode output stream can also be expelled, at least partially, via the air outlet after being fed to the burner, in particular after combustion.

[0161] The above object is further achieved according to a third aspect by a computer program product according to the invention, comprising instructions which, when the computer program product is executed by a computer, cause the computer to implement the method according to the first aspect.

[0162] This results in the same advantages with regard to a computer program product according to the invention as have already been described with regard to a method according to the invention according to the first aspect and / or a fuel cell system according to the invention according to the second aspect.

[0163] The above object is further achieved according to a fourth aspect by a computer-readable data carrier according to the invention, in which instructions are stored which, when executed by a computer, cause the computer to carry out the method according to the first aspect.

[0164] This results in the same advantages with regard to a computer-readable data carrier according to the invention as have already been described with regard to a method according to the invention according to the first aspect and / or a fuel cell system according to the invention according to the second aspect and / or a computer program product according to the invention according to the third aspect.

[0165] The above object is further achieved according to a fifth aspect by a control unit according to the invention, comprising a computing unit and a memory unit in which instructions are stored which, when at least partially executed by the computing unit, carry out a method according to the first aspect.

[0166] In this case, it can be provided that the control unit, in particular the computing unit, carries out and / or initiates the method steps, for example by controlling the fuel cell system and / or its (above) components. The control unit can send control signals to corresponding actuators of the fuel cell system in order to adjust them. The control unit can also receive sensor signals from sensors of the fuel cell system, for example a temperature sensor, which are taken into account in particular during control and / or regulation. Based on these signals, for example, target values ​​can be calculated.

[0167] The control unit can be connected to the mixture valve, hydrogen valve, fuel valve, mixture flow controller, hydrogen flow controller, fuel flow controller, recirculation blower, recirculation unit, temperature sensor, air supply unit, anode path heat exchanger, anode path drain valve, cathode path valve, air blower, burner, and / or air outlet, preferably via a data connection, for controlling and / or regulating purposes. The aforementioned components can each have an actuator that can be controlled by the control unit, for example, for adjusting a valve, controlling a sensor, and / or transmitting data (e.g., acquired sensor data). Furthermore, the aforementioned components can each have a sensor that is designed to detect temperature, pressure, volume flow, and / or other relevant parameters.The recorded results can be forwarded to the control unit, in particular via a data connection, in order to be taken into account preferably in a control and / or regulation, in particular calculation.

[0168] This results in the same advantages with regard to a control unit according to the invention as have already been described with regard to a method according to the invention according to the first aspect and / or a fuel cell system according to the invention according to the second aspect and / or a computer program product according to the invention according to the third aspect and / or a computer-readable data carrier according to the invention according to the fourth aspect.

[0169] The above object is further achieved according to a sixth aspect by a system according to the invention, comprising a fuel cell system according to the second aspect and / or a control unit according to the fifth aspect.

[0170] A system may comprise a (residential) building, an industrial building, a power plant, a storage facility, a vehicle, a ship, an aircraft, or another system with, in particular, increased energy requirements. It may be particularly preferred to provide a (substantially) stationary (immobile) application of the fuel cell system.

[0171] This results in the same advantages with regard to a system according to the invention as have already been described with regard to a method according to the invention according to the first aspect and / or a fuel cell system according to the invention according to the second aspect and / or a computer program product according to the invention according to the third aspect and / or a computer-readable data carrier according to the invention according to the fourth aspect and / or a control unit according to the invention according to the fifth aspect.

[0172] Further advantages, features, and details of the invention will become apparent from the following description, in which several embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description may be essential to the invention individually or in any combination. These schematically show: Fig. 1 a fuel cell system, Fig. 2 a system and Fig. 3 a procedure.

[0173] Fig. 1 shows an example of an anode path 10, as may be provided in particular in a fuel cell system 100. The anode path 10 may be configured to supply an anode input current A to the anode input 16 of a fuel cell unit 101. in This can achieve a volume flow of mixture V̇ Gemisch which in turn has a volume flow of fuel V̇Brennstoff and a volume flow of hydrogen V̇ H2in The proportion of fuel x i,Brennstoff and / or hydrogen x H2 can be adjusted. Fuel can be fed to a mixture valve 12 via a fuel tank 11.2, a fuel valve 12.2 and / or a fuel flow regulator 13.2. Hydrogen can be fed to a mixture valve 12 via a hydrogen tank 11.1, a hydrogen valve 12.1 and / or a hydrogen flow regulator 13.1. The mixture valve 12 can control the volume flow of mixture V̇ Gemisch open and / or closed. This is equipped with a mixture flow regulator 13 for adjusting the volume flow of mixture V̇ Gemisch The mixing ratio can be adjusted, for example, via the fuel valve 12.2 and / or the hydrogen valve 12.1. The fuel or the volume flow of fuel V̇ Brennstoff can be an oxygen-carbon ratio in the fuel OCBrennstoff and a fuel coefficient Γ OC The mixture or the volume flow of mixture V̇ Gemisch can contain a proportion of fuel in the mixture x i,Brennstoff and / or a proportion of hydrogen in the mixture x H2 . In particular, if no change occurs, the anode input current A in a (in particular the same or a comparable) proportion of fuel x i,Brennstoff and / or a proportion of hydrogen x H2 The anode input current A in can have, in particular upstream of the anode inlet 16, an oxygen-carbon ratio OC, which can be adjusted in particular by the control unit FCCU. For this purpose, the control unit FCCU can set a target value for an oxygen-carbon ratio OC soll determine and adjust in particular by controlling the fuel cell system.

[0174] Furthermore, a recirculation fan 14 can be used to increase the recirculating volume flow V̇ recyat this point on the anode path 10. For this purpose, the recirculation fan 14 can be controlled by a control unit FCCU. The volume flow can then be guided via an anode path heat exchanger 15, which in particular enables heating. The anode path 10 can then be connected to the anode inlet 16. In this case, the volume flow can be introduced into the anode inlet 16. Within the fuel cell unit 101, the volume flow is guided from the anode inlet 16 to an anode outlet 17. A connection to the anode path heat exchanger 15 can be provided from the anode outlet 17, wherein the volume flow is guided, for example, via a recirculation path 18.1 through the anode path heat exchanger 15 to a heat exchanger 18.2. A recirculation unit 18 can have a recirculation path 18.1, in particular as an “input”, a heat exchanger 18.2, and an anode path connection point 18.4.An output of heat exchanger 18.2 can therefore be connected to an inlet of heat exchanger 18.2. The volume flow can be fed back to the anode path 10 at the anode path connection point 18.4 via heat exchanger 18.2.

[0175] The cathode path 20 can have an air supply unit 21 (as a "starting point"), via which air can be introduced into the cathode path 20. The corresponding volume flow can then be directed via a cathode path valve 22, where, in particular, a portion of the volume flow can be diverted to feed it to the heat exchanger 18.2. The tapped portion can be returned at a cathode path connection point 23. An air blower 24 can then adjust the volume flow. This can then be directed via a cathode path heat exchanger 25 before being fed into the fuel cell unit 101 via a cathode inlet 26. Inside the fuel cell unit 101, the volume flow can be transported from the cathode inlet 26 to a cathode outlet 27.A corresponding reaction can take place inside the fuel cell unit 101 in order to advantageously generate energy, in particular current and / or voltage.

[0176] At the cathode path valve 22, a certain proportion r div the cathode input current K in The cathode input current K in can extend from the air supply unit 21 to the cathode inlet 26 and, in particular, can be changed along the way (e.g., by tapping and / or changing the temperature). A cathode output current K out leaves the fuel cell unit 101 via a cathode outlet 27. The cathode output current K out a burner 28. The anode output current A out can be fed, in particular partially, to the burner 28. In this case, a recirculation rate r can be provided which determines the proportion of the anode output current A out, in particular a volume flow V̇ An,out at the anode outlet 17, which is fed to the recirculation unit 18. Combustion can take place in the burner 28. This can be used for material conversion and / or to increase the temperature. An outlet of the burner 28 can be connected to the cathode path heat exchanger 25. This allows, in particular, the cathode input current K in be tempered, in particular heated, preferably (at least partially) by the cathode output current K out .

[0177] The reaction in the fuel cell unit 101 can generate a current I and / or a voltage. An inverter 40 can be used to generate an alternating current from direct current, in particular the current I. The resulting (waste) heat can also be utilized. The fuel cell unit 101 can comprise a stack of fuel cells.

[0178] The specific proportion r div the cathode input current K in can be fed to the heat exchanger 18.2 to cool 131 the anode output stream A out , especially the water vapor contained therein. This allows the humidity x H2O, Ain the anode input current A in changed, especially reduced. For this purpose, recording an actual temperature t ist , in particular an actual saturation steam temperature t sat, ist , which can preferably be carried out by a temperature sensor 18.3, in particular included in the recirculation unit 18. The actual saturation steam temperature t sat, ist can be determined depending on a saturation steam temperature t sat be determined, in particular they essentially correspond to this. The saturation steam temperature t sat , and in particular a saturation vapor pressure p sat, prevail in a section between heat exchanger 18.2 and anode path connection point 18.4. Preferably, the temperature sensor 18.3 can be arranged in this area to detect the actual temperature t ist , in particular an actual saturation steam temperature t sat, ist , to enable. The anode input current A in can, especially initially, (only) determine the volume flow of mixture V̇ Gemisch At the anode path connection point 18.4, an additional volume flow can be supplied. The anode output current A out (at least partially). Accordingly, a recirculating volume flow V̇ recy the volume flow of mixture V̇ Gemisch and the (returned) anode output current A out The recirculating volume flow V̇ recy can be introduced again into the anode input 16. It could also be formulated so that the anode input current A inthen the recirculating volume flow V̇ recy or is converted to it, especially after the recirculating volume flow V̇ recy has passed the anode path heat exchanger 15 (e.g. to increase the temperature).

[0179] A volume flow V̇ Cond of condensed water vapor, which is produced in particular during the cooling of water vapor in the heat exchanger 18.2, can be removed, and in particular leave the fuel cell system 100. This can be adjusted via an anode path drain valve 19.1. An air outlet 29 can also be provided, which is connected in particular to the cathode path heat exchanger 25. Via this, (excess) air from the cathode path or the cathode output stream K outA high-temperature region 102 can be provided, which in particular comprises the fuel cell unit 101, the cathode path heat exchanger 25, the anode path heat exchanger 15, the burner 28, the cathode inlet 26, the cathode outlet 27, the anode inlet 16 and / or the anode outlet 17. In the high-temperature region 102, the temperature can be (relatively) high; for this purpose, it can in particular be thermally insulated. The fuel cell unit of the fuel cell system 101 can have a fuel utilization FU Stk This can in particular include a quantification of the proportion of the fuel or mixture used, in particular with respect to the fuel cell unit 101. The fuel cell system 100 can have a fuel utilization FU Sys This may, in particular, include a quantification of the proportion of the (efficiently) used fuel or mixture, in particular with respect to the fuel cell system 100.

[0180] The fuel cell system 100 can comprise a control unit FCCU and / or be connected to it, in particular via a data connection. The control unit FCCU can, for example, provide a control value r div,SW for the cathode path valve 22. This can be transmitted, in particular via a data connection, to the cathode path valve 22, in particular to an actuator, in order to adjust the cathode path valve 22, in particular to set a certain proportion r div the cathode input current K in Depending on the specific proportion r div the cathode input current K in can be a cooling, in particular a cooling capacity, of (or for) the water vapor / s or the anode output current A out Preferably, the control unit FCCU can be adjusted depending on the proportion of hydrogen x H2 in the anode input current A in, set at least one, in particular two, of the following setpoints for optimized operation: - a target oxygen-carbon ratio OC soll , - a target fuel utilization FU Sys, soll of the fuel cell system 100, - a target fuel utilization FU Stk, soll a fuel cell unit 101 of the fuel cell system 100 and / or - a target current I soll which is generated by the fuel cell unit 101.

[0181] This can be done by controlling 120 the fuel cell system 100. The control unit FCCU can be connected, in particular via a data connection, to the anode path drain valve 19.1. The control unit FCCU can thus control the volume flow of condensed water vapor V̇ CondThe control unit FCCU can be connected, in particular via a data connection, to the recirculation fan 14. The control unit FCCU can thus control the recirculating volume flow V̇ recy control and / or regulate. The control unit FCCU can be connected, in particular via a data connection, to the mixture flow controller 13. The control unit FCCU can thus control the volume flow of mixture V̇ Gemisch control and / or regulate. This allows the above setpoints to be set by the FCCU control unit. For this purpose, the different operating modes (see below and above) can be provided, which are shown in Tables 1 - 5.

[0182] Fig. Figure 2 shows a system 200 with a fuel cell system 100, which can be controlled by a control unit FCCU. The control unit FCCU can have a computing unit CU and a memory unit MU.

[0183] Fig. 3 shows a method for operating a fuel cell system 100, in particular a solid oxide fuel cell system, such as Fig. 1.

[0184] The procedure can include: - Control 110 of the fuel cell system 100 by the control unit FCCU to adjust a proportion of hydrogen x H2 in the anode input current A in , - Control 120 of the fuel cell system 100 by the control unit FCCU in order to, depending on the proportion of hydrogen x H2 in the anode input current A in to set at least one, in particular two, of the following setpoints for optimized operation: ◯ a target oxygen-carbon ratio OC soll , ◯ a target fuel utilization FU Sys, soll of the fuel cell system 100, ◯ a target fuel utilization FU Stk, solla fuel cell unit 101 of the fuel cell system 100 and / or ◯ a target current I soll , which is generated by the fuel cell unit 101.

[0185] Furthermore, it can be provided that the control 110 of the fuel cell system 100 for setting a proportion of hydrogen x H2 in the anode input current A in has at least one of the following features: - Control 111, by the control unit FCCU, of a hydrogen flow controller 13.1 of the fuel cell system 100, in order to control the volume flow of hydrogen V̇ H2in to adjust in particular the proportion of hydrogen x H2 in the anode input current A in to stop and / or - Control 112, by the control unit FCCU, of a fuel flow controller 13.2 of the fuel cell system 100, in order to control the volume flow of fuel V̇ Brennstoff to adjust in particular the proportion xBrennstoff of fuel in the anode input current A in to set.

[0186] Furthermore, it can be provided that the control 120 of the fuel cell system 100 has at least one of the following features: - Control 121, by the control unit FCCU, of a mixture valve 12 of the fuel cell system 100 to achieve a volume flow of mixture V̇ Gemisch , comprising the volume flow of hydrogen V H2in and the volume flow of fuel V̇ Brennstoff , to be introduced into the anode path 10, - Control 122, by the control unit FCCU, of a mixture flow controller 13 of the fuel cell system 100 to control the volume flow of mixture V̇ Gemisch to set, - Control 123, by the control unit FCCU, of the recirculation unit 18, in particular a recirculation fan 14 of the recirculation unit 18, in order to generate a recirculating volume flow V̇ recy to set, - Controlling 124, by the control unit FCCU, an anode path drain valve 19.1 of the recirculation unit 18, in particular a heat exchanger 18.2, and / or an anode path heat exchanger 15 of the recirculation unit 18, in order to achieve a volume flow of condensed water vapor V̇ Cond to stop and / or - Control 125, by the control unit FCCU, of an inverter 40 of the fuel cell system 100 in order to set a current I of the fuel cell system 100, wherein in particular a current control value I Steilwert of the inverter 40 depending on a current setpoint I soll is set by the control unit FCCU, - wherein the setpoints are set in particular as a function of the control 121, 122, 123, 124, 125 of the mixture valve 12, the mixture flow controller 13, the recirculation unit 18, in particular a recirculation fan 14, an anode path drain valve 19.1 of the recirculation unit 18, in particular a heat exchanger 18.2, an anode path heat exchanger 15 of the recirculation unit 18 and / or the inverter 40.

[0187] Furthermore, it can be provided that the control 120 of the fuel cell system 100 has at least one, preferably all, of the following features: - Determining 126, by the control unit FCCU, a target fuel utilization FU Stk, soll a fuel cell unit 101 of the fuel cell system depending on the proportion of hydrogen x H2 in the anode input current A in , wherein in particular an increase, in particular a linear increase, of the target fuel utilization FUStk, soll with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Stk, soll proportional to the proportion of hydrogen x H2 is, - Setting 127, by the control unit FCCU, a fuel utilization FU Stk a fuel cell unit 101 of the fuel cell system depending on the target fuel utilization of a fuel cell unit 101 of the fuel cell system FU Stk, soll and / or - Controlling and / or regulating 128, by the control unit FCCU, the fuel cell system 100 to keep the oxygen-carbon ratio OC constant.

[0188] Furthermore, it can be provided that the control 120 of the fuel cell system 100 has at least one, preferably all, of the following features: - Control and / or regulation 130, by the control unit FCCU, of the fuel cell system 100, in order to achieve a fuel utilization FU Sys of the fuel cell system 100 and a fuel utilization FU Stk a fuel cell unit 101 of the fuel cell system, whereby the oxygen-carbon ratio OC preferably increases with increasing proportion of hydrogen x H2 in the anode input current A in increases.

[0189] Furthermore, it can be provided that the control 120 of the fuel cell system 100 has at least one, preferably all, of the following features: - Determining 140, by the control unit FCCU, a target fuel utilization FU Stk , soll a fuel cell unit 101 of the fuel cell system depending on the proportion of hydrogen x H2 in the anode input current A in, wherein in particular an increase, in particular a linear increase, of the target fuel utilization FU Stk, soll with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Stk, soll proportional to the proportion of hydrogen x H2 is, - Setting 141, by the control unit FCCU, a fuel utilization FU Stk a fuel cell unit 101 of the fuel cell system depending on the target fuel utilization of a fuel cell unit 101 of the fuel cell system FU Stk, soll and / or - Control and / or regulation 142, by the control unit FCCU, of the fuel cell system 100, in order to achieve a fuel utilization FU Sys of the fuel cell system 100 constant, whereby preferably the oxygen-carbon ratio OC increases with increasing proportion of hydrogen x H2 in the anode input current Ain increases.

[0190] Furthermore, it can be provided that the control 120 of the fuel cell system 100 has at least one, preferably all, of the following features: - Determine 150, by the control unit FCCU, a target fuel utilization FU Sys, soll of the fuel cell system 100 depending on the proportion of hydrogen x H2 in the anode input current A in , wherein in particular an increase, in particular a linear increase, of the target fuel utilization FU Sys, soll with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Sys, soll proportional to the proportion of hydrogen x H2 is, - Setting 151, by the control unit FCCU, a fuel utilization FU Sysof the fuel cell system 100 depending on the target fuel utilization of the fuel cell system FU Sys, soll , - Determining 152, by the control unit FCCU, a target fuel utilization FU Stk, soll a fuel cell unit 101 of the fuel cell system depending on the proportion of hydrogen x H2 in the anode input current A in , wherein in particular an increase, in particular a linear increase, of the target fuel utilization FU Stk, soll with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Stk, soll proportional to the proportion of hydrogen x H2 is and / or - Setting 153, by the control unit FCCU, a fuel utilization FU Stka fuel cell unit 101 of the fuel cell system depending on the target fuel utilization of a fuel cell unit 101 of the fuel cell system FU Stk, soll , - in particular by setting 151 a fuel utilization FU Sys of the fuel cell system 100 and / or setting 153 a fuel utilization FU Stk a fuel cell unit 101 of the fuel cell system, the oxygen-carbon ratio OC with increasing proportion of hydrogen x H2 in the anode input current A in increases.

[0191] In the following figures and / or tables, identical reference numerals are used for the same technical features, even for different embodiments. In this case, x CH4 and / or x H2 (molar) proportions, in particular at the mixture valve 12 and / or mixture flow regulator 13. Table 1 [0,1] [0,1] - [0,1] [0,1] - 100 % CH4 1,00 0,00 4,00 0,65 0,86 2,40 10 % H2 0,90 0,10 4,11 0,65 0,85 2,40 20 % H2 0,80 0,20 4,25 0,65 0,85 2,40 30 % H2 0,70 0,30 4,43 0,65 0,84 2,40 40 % H2 0,60 0,40 4,67 0,65 0,83 2,40 50 % H2 0,50 0,50 5,00 0,65 0,82 2,40 60 % H2 0,40 0,60 5,50 0,65 0,80 2,40 70 % H2 0,30 0,70 6,33 0,65 0,78 2,40 80 % H2 0,20 0,80 8,00 0,65 0,76 2,40 90 % H2 0,10 0,90 13,00 0,65 0,71 2,40

[0192] Table 1 shows the respective (actual) values ​​for FU Stk , FU Sys and OC. The fuel utilization FU Stk a fuel cell unit of the fuel cell system, the fuel utilization FU Sys of the system and the oxygen-carbon ratio OC can be adjusted in particular by controlling and / or regulating the control unit FCCU. In this case, the fuel efficiency FU can be adjusted (see Table 1). Stk a fuel cell unit and the oxygen-carbon ratio OC, in particular by controlling and / or regulating by the control unit FCCU, while preferably the fuel utilization FU Sys of the system is not controlled and / or regulated. These values ​​can still vary depending on the proportion of hydrogen x H2 , of methane x CH4 and / or the fuel coefficient Γ OCare or are indicated. Methane can be used as a fuel, in particular by way of example. As can be seen here, (without inventive control and / or regulation) FU Stk and OC are the same, while FU Sys with increasing proportion of hydrogen x H2 This may be due to a lack of control and / or regulation. In particular, FU Sys be proportional to the electrical efficiency.

[0193] Table 2 shows (based on Table 1) the respective (actual) values ​​for FU Stk , FU Sys and OC. The fuel utilization FU Stk a fuel cell unit of the fuel cell system, the fuel utilization FU Sys of the system and the oxygen-carbon ratio OC can be adjusted in particular by controlling and / or regulating the FCCU control unit, which was done in this case. In particular, FU Stkproportional, in particular linearly proportional, to the proportion of hydrogen x H2 be increased, preferably keeping OC constant. These values ​​can be further varied depending on the proportion of hydrogen x R2 , of methane x CH4 and / or the fuel coefficient Γ OC Methane can be used as a fuel, particularly as an example. With increasing proportion of hydrogen x H2 , preferably due to the method according to the invention, in particular the control, FU Stk and FU Sys does not decrease as much (especially in comparison to Table 1), while OC remains the same. In comparison, FU Stk increase. Since FU Sys can be proportional to the electrical efficiency, this is higher, especially with a higher proportion of hydrogen x H2 . Table 3 x CH4 x H2 T OC IT WAS Stk IT WAS Sys OC [0,1] [0,1] - [0,1] [0,1] - 100 % CH4 1,00 0,00 4,00 0,65 0,86 2,40 10 % H2 0,90 0,10 4,11 0,65 0,86 2,47 20 % H2 0,80 0,20 4,25 0,65 0,86 2,55 30 % H2 0,70 0,30 4,43 0,65 0,86 2,66 40 % H2 0,60 0,40 4,67 0,65 0,86 2,80 50 % H2 0,50 0,50 5,00 0,65 0,86 3,00 60 % H2 0,40 0,60 5,50 0,65 0,86 3,30 70 % H2 0,30 0,70 6,33 0,65 0,86 3,80 80 % H2 0,20 0,80 8,00 0,65 0,86 4,80 90 % H2 0,10 0,90 13,00 0,65 0,86 7,80

[0194] Table 3 shows the respective (actual) values ​​for FU Stk , FU Sys and OC. The fuel utilization FU Stk a fuel cell unit of the fuel cell system, the fuel utilization FU Sys The system's oxygen-carbon ratio (OC) can be adjusted, in particular, by controlling and / or regulating the FCCU, which was done in this case. The FCCU can be used to control and / or regulate the fuel efficiency (FU). Sys of the fuel cell system and fuel utilization FU Stk a fuel cell unit of the fuel cell system constant, whereby the oxygen-carbon ratio OC preferably increases with increasing proportion of hydrogen x H2 in the anode input current A in With increasing proportion of hydrogen x H2advantageously, OC (safe) can be increased to higher values, which can prevent and / or reduce coking. Especially compared to other operating strategies (e.g. Table 2), this can lead to FU Sys kept constant or reduced to a lesser extent, whereby the electrical efficiency is advantageously optimized, in particular there is less or no drop. Table 4 x CH4 x H2 C OC IT WAS Stk IT WAS Sys OC [0,1] [0,1] - [0,1] [0,1] - 100 % CH4 1,00 0,00 4,00 0,65 0,86 2,40 10 % H2 0,90 0,10 4,11 0,66 0,86 2,44 20 % H2 0,80 0,20 4,25 0,66 0,86 2,49 30 % H2 0,70 0,30 4,43 0,67 0,86 2,57 40 % H2 0,60 0,40 4,67 0,67 0,86 2,67 50 % H2 0,50 0,50 5,00 0,68 0,86 2,83 60 % H2 0,40 0,60 5,50 0,68 0,86 3,07 70 % H2 0,30 0,70 6,33 0,69 0,86 3,48 80 % H2 0,20 0,80 8,00 0,69 0,86 4,33 90 % H2 0,10 0,90 13,00 0,70 0,86 6,93

[0195] Table 4 shows the respective (actual) values ​​for FU Stk , FU Sys and OC. The fuel utilization FU Stk a fuel cell unit of the fuel cell system, the fuel utilization FU Sys The system's oxygen-carbon ratio (OC) can be adjusted, in particular, by controlling and / or regulating the FCCU control unit, which was done in this case. The FCCU control unit can determine a target fuel utilization (FU)Stk, soll a fuel cell unit of the fuel cell system depending on the proportion of hydrogen x H2 in the anode input current A in be carried out, whereby in particular an increase, in particular a linear increase, of the target fuel utilization FU Stk, soll with increasing proportion of hydrogen x H2 , especially in the anode input current A in , for example at the mixture valve 12 and / or mixture flow controller 13, wherein in particular the target fuel utilization FU Stk, soll proportional to the proportion of hydrogen x H2 Furthermore, the control unit FCCU can adjust the fuel utilization FU Stk depending on the target fuel utilization FU Stk, soll a fuel cell unit of the fuel cell system. In addition, the fuel cell system can be controlled and / or regulated by the control unit FCCU in order to ensure fuel utilization FUSys of the fuel cell system constant, whereby the oxygen-carbon ratio OC preferably increases with increasing proportion of hydrogen x H2 , especially in the anode input current A in , for example, at the mixture valve 12 and / or mixture flow controller 13. In other words, the advantages or the procedure of Table 2 and Table 3 can be combined. This can accordingly offer the same advantages (see above). Thus, with increasing proportion of hydrogen x H2 advantageously, OC (safe) can be increased to higher values, which can prevent and / or reduce coking. Especially compared to other operating strategies (e.g. Table 2), this can lead to FU Syskept constant or reduced to a lesser extent, which advantageously optimizes the electrical efficiency, in particular, resulting in a lesser or no drop. This can also be advantageous because the oxygen-carbon ratio (OC) increases less, especially compared to Table 3. A very high OC can (theoretically) have a lower cell voltage due to a lower Nernst voltage, since the high water vapor molar fraction, in particular, can lower the Nernst voltage. This could have a negative effect on the electrical efficiency. Thus, it may be advisable not to increase OC too much. Table 5 x CH4 x H2 C OC IT WAS Stk IT WAS Sys OC [0,1] [0,1] - [0,1] [0,1] - 100 % CH4 1,00 0,00 4,00 0,65 0,86 2,40 10 % H2 0,90 0,10 4,11 0,66 0,86 2,49 20 % H2 0,80 0,20 4,25 0,66 0,87 2,61 30 % H2 0,70 0,30 4,43 0,67 0,87 2,75 40 % H2 0,60 0,40 4,67 0,67 0,88 2,93 50 % H2 0,50 0,50 5,00 0,68 0,88 3,17 60 % H2 0,40 0,60 5,50 0,68 0,89 3,53 70 % H2 0,30 0,70 6,33 0,69 0,89 4,12 80 % H2 0,20 0,80 8,00 0,69 0,90 5,27 90 % H2 0,10 0,90 13,00 0,70 0,90 8,67

[0196] Table 5 shows the respective (actual) values ​​for FU Stk , FU Sys and OC. The fuel utilization FU Stk a fuel cell unit of the fuel cell system, the fuel utilization FU SysThe system's oxygen-carbon ratio (OC) can be adjusted, in particular, by controlling and / or regulating the FCCU control unit, which was done in this case. The FCCU control unit can determine a target fuel utilization (FU) Sys, soll of the fuel cell system depending on the proportion of hydrogen x H2 in the anode input current A in be carried out, whereby in particular an increase, in particular a linear increase, of the target fuel utilization FU Sys, soll with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Sys, soll proportional to the proportion of hydrogen x H2 Furthermore, the control unit FCCU can adjust the fuel utilization FU Sys depending on the target fuel utilization of the fuel cell system FU Sys, soll, can be carried out. This can consequently result in the (actual) values ​​shown in Table 5. Furthermore, in particular subsequently or in parallel, a (corresponding) determination by the control unit FCCU of a target fuel utilization FU Stk, soll of the fuel cell unit depending on the proportion of hydrogen x H2 in the anode input current A in be carried out, whereby in particular an increase, in particular a linear increase, of the target fuel utilization FU Stk, soll a fuel cell unit of the fuel cell system with increasing proportion of hydrogen x H2 in the anode input current A in is determined, whereby in particular the target fuel utilization FU Stk, soll proportional to the proportion of hydrogen x H2 Furthermore, a (corresponding) setting, by the control unit FCCU, of a fuel utilization FU Stkdepending on the target fuel utilization of a fuel cell unit of the fuel cell system FU Stk, soll be carried out, in particular by setting a fuel utilization FU Sys of the fuel cell system and / or setting a fuel utilization FU Stk a fuel cell unit of the fuel cell system, the oxygen-carbon ratio OC with increasing proportion of hydrogen x H2 in the anode input current A in In other words, FU Sys and FU Stk proportional to the proportion of hydrogen x H2 The results can show an improvement in FU Sys and FU Stk , especially in comparison to the operating strategies presented above (see Tables 1 -a 4). In particular, by increasing FU SysThis can lead to a reduced release of heat in the (after)burner, which can result in less heat to maintain the fuel cell system at (operating) temperature. However, this can be advantageously offset by the lower heat demand with increasing hydrogen content x H2 It may also be intended to reduce, in particular to relax, the temperature limits of the fuel cell unit (“stack temperature limits”), which can be achieved, for example, by lowering the cathode inlet temperature if the proportion of hydrogen x H2 This can be advantageous because a reduction in the reforming activity of the alkanes can occur when the proportion of hydrogen x H2 increases.

Claims

[1] Method for operating a fuel cell system (100), in particular a solid oxide fuel cell system, the fuel cell system (100) comprising - at least one fuel cell unit (101) for generating energy, comprising ◯ an anode path (10) comprising ▪ an anode input (16) for receiving an anode input current (A in ) and ▪ an anode output (17) for outputting an anode output current (A out ), and ◯ a cathode path (20) comprising ▪ a cathode input (26) for receiving a cathode input current (K in ) and ▪ a cathode output (27) for outputting a cathode output current (K out ), - a control unit (FCCU) for controlling and / or regulating the fuel cell system (100), - comprising the method o Controlling (110) the fuel cell system (100) by the control unit (FCCU) to adjust a proportion of hydrogen (x H2 ) in the anode input current (A in ), o Controlling (120) the fuel cell system (100) by the control unit (FCCU) in order to determine, depending on the proportion of hydrogen (x H2 ) in the anode input current (A in ), at least one, in particular at least two, of the following setpoints for optimized operation: ▪ a target oxygen-carbon ratio (OC soll ), ▪ a target fuel utilization (FU Sys, soll ) of the fuel cell system (100), ▪ a target fuel utilization (FU Stk, soll ) a fuel cell unit (101) of the fuel cell system (100), ▪ a target current (I soll ) generated by the fuel cell unit (101). [2] Method according to claim 1, characterized bythat the control (110) of the fuel cell system (100) for adjusting a proportion of hydrogen (x H2 ) in the anode input current (A in ) has at least one of the following features: - controlling (111), by the control unit (FCCU), a hydrogen flow controller (13.1) of the fuel cell system (100) to control the volume flow of hydrogen V̇ H2in to adjust in particular the proportion of hydrogen (x H2 ) in the anode input current (A in ) and / or - controlling (112), by the control unit (FCCU), a fuel flow controller (13.2) of the fuel cell system (100) to control the volume flow of fuel V̇ Brennstoff to adjust in particular the proportion (x Brennstoff ) of fuel in the anode input current (A in ) to set. [3] Method according to one of the preceding claims, characterized bythat the control (120) of the fuel cell system (100) has at least one of the following features: - controlling (121), by the control unit (FCCU), a mixture valve (12) of the fuel cell system (100) to achieve a volume flow of mixture (V̇ Gemisch ), comprising the volume flow of hydrogen (V̇ H2in ) and the volume flow of fuel (V̇ Brennstoff ), into the anode path (10), - controlling (122), by the control unit (FCCU), a mixture flow controller (13) of the fuel cell system (100) in order to control the volume flow of mixture (V̇ Gemisch ), - controlling (123), by the control unit (FCCU), a recirculation unit (18) which is designed to at least partially recirculate the anode output current (A out ) to the anode input current (A in), in particular a recirculation fan (14) of the recirculation unit (18), in order to generate a recirculating volume flow V̇ recy to set, - controlling (124), by the control unit (FCCU), an anode path drain valve (19.1) of the recirculation unit (18), in particular a heat exchanger (18.2), and / or an anode path heat exchanger (15) of the recirculation unit (18), in order to achieve a volume flow of condensed water vapor V̇ Cond to stop and / or - controlling (125), by the control unit (FCCU), an inverter (40) of the fuel cell system (100) in order to set a current (I) of the fuel cell system (100), wherein in particular a current control value (I Stellwert ) of the inverter (40) depending on a current setpoint (I soll ) is set by the control unit (FCCU), - wherein the setpoints are set in particular as a function of the control (121, 122, 123, 124, 125) of the mixture valve (12), the mixture flow controller (13), the recirculation unit (18), in particular a recirculation fan (14), an anode path drain valve (19.1) of the recirculation unit (18), in particular a heat exchanger (18.2), an anode path heat exchanger (15) of the recirculation unit (18) and / or the inverter (40). [4] Method according to one of the preceding claims, characterized by that the control (120) of the fuel cell system (100) has at least one, preferably all, of the following features: - Determining (126), by the control unit (FCCU), a target fuel utilization (FU Stk, soll ) of a fuel cell unit (101) of the fuel cell system (100) depending on the proportion of hydrogen (x H2 ) in the anode input current (A in), wherein in particular an increase, in particular a linear increase, of the target fuel utilization (FU Stk, soll ) with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ), whereby in particular the target fuel utilization (FU Stk, soll ) proportional to the proportion of hydrogen (x H2 ) is, - Setting (127), by the control unit (FCCU), a fuel utilization (FU Stk ) of a fuel cell unit (101) of the fuel cell system (100) depending on the target fuel utilization of a fuel cell unit of the fuel cell system (FU Stk, soll ) and / or - controlling and / or regulating (128), by the control unit (FCCU), the fuel cell system (100) to keep the oxygen-carbon ratio (OC) constant. [5] Method according to one of the preceding claims, characterized bythat the control (120) of the fuel cell system (100) has at least one, preferably all, of the following features: - controlling and / or regulating (130), by the control unit (FCCU), the fuel cell system (100) in order to achieve a fuel utilization (FU Sys ) of the fuel cell system (100) and a fuel utilization (FU Stk ) of a fuel cell unit (101) of the fuel cell system (100) constant, whereby preferably the oxygen-carbon ratio (OC) increases with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ) increases. [6] Method according to one of the preceding claims, characterized by that the control (120) of the fuel cell system (100) has at least one, preferably all, of the following features: - Determining (140), by the control unit (FCCU), a target fuel utilization (FU Stk, soll) of a fuel cell unit (101) of the fuel cell system (100) depending on the proportion of hydrogen (x H2 ) in the anode input current (A in ), wherein in particular an increase, in particular a linear increase, of the target fuel utilization (FU Stk, soll ) with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ), whereby in particular the target fuel utilization (FU Stk, soll ) proportional to the proportion of hydrogen (x H2 ) is, - Setting (141), by the control unit (FCCU), a fuel utilization (FU Stk ) of a fuel cell unit (101) of the fuel cell system (100) depending on the target fuel utilization of a fuel cell unit of the fuel cell system (FU Stk, soll ) and / or - controlling and / or regulating (142), by the control unit (FCCU), the fuel cell system (100) in order to achieve a fuel utilization (FU Sys) of the fuel cell system (100) constant, whereby preferably the oxygen-carbon ratio (OC) increases with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ) increases. [7] Method according to one of the preceding claims, characterized by that the control (120) of the fuel cell system (100) has at least one, preferably all, of the following features: - Determining (150), by the control unit (FCCU), a target fuel utilization (FU Sys, soll ) of the fuel cell system (100) depending on the proportion of hydrogen (x H2 ) in the anode input current (A in ), wherein in particular an increase, in particular a linear increase, of the target fuel utilization (FU Sys, soll ) with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ), whereby in particular the target fuel utilization (FU Sys, soll) of the fuel cell system proportional to the proportion of hydrogen (x H2 ) is, - Setting (151), by the control unit (FCCU), a fuel utilization (FU Sys ) of the fuel cell system (100) depending on the target fuel utilization (FU Sys, soll ) of the fuel cell system, - Determining (152), by the control unit (FCCU), a target fuel utilization (FU Stk, soll ) of a fuel cell unit (101) of the fuel cell system (100) depending on the proportion of hydrogen (x H2 ) in the anode input current (A in ), wherein in particular an increase, in particular a linear increase, of the target fuel utilization (FU Stk, soll ) with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ), whereby in particular the target fuel utilization (FU Stk, soll ) proportional to the proportion of hydrogen (x H2 ) and / or - Setting (153), by the control unit (FCCU), a fuel utilization (FU Stk ) of a fuel cell unit (101) of the fuel cell system (100) depending on the target fuel utilization (FU Stk, soll ) a fuel cell unit of the fuel cell system, - wherein in particular by setting (151) a fuel utilization (FU Sys ) of the fuel cell system (100) and / or setting (153) a fuel utilization (FU Stk ) of a fuel cell unit (101) of the fuel cell system (100), the oxygen-carbon ratio (OC) with increasing proportion of hydrogen (x H2 ) in the anode input current (A in ) increases. [8] Fuel cell system (100), in particular solid oxide fuel cell system, comprising - at least one fuel cell unit (101) for generating energy, comprising o an anode path (10) comprising ▪ an anode input (16) for receiving an anode input current (A in ) and ▪ an anode output (17) for outputting an anode output current (A out ), and ◯ a cathode path (20) comprising ▪ a cathode input (26) for receiving a cathode input current (K in ) and ▪ a cathode output (27) for outputting a cathode output current (K out ), - a control unit (FCCU) for controlling and / or regulating the fuel cell system (100), - wherein the fuel cell system (100) is configured to implement the method according to one of the preceding claims. [9] Fuel cell system (100) according to one of the preceding claims, characterized by that the anode path (10) has at least one of the following features: - a hydrogen tank (11.1) comprising hydrogen, ammonia and / or a chemical compound comprising hydrogen, - a fuel tank (11.2) comprising a fuel, in particular natural gas, methane, biogas and / or a mixture thereof with hydrogen, - a mixture valve (12), - a hydrogen valve (12.1), - a fuel valve (12.2), - a mixture flow controller (13), in particular for adjusting a volume flow of mixture V̇ Gemisch in the anode input current (A in ), - a hydrogen flow controller (13.1), in particular for adjusting a volume flow of hydrogen V̇ H2in in the anode input current (A in ), - a fuel flow regulator (13.2), in particular for adjusting a volume flow of fuel V̇ Brennstoff in the anode input current (A in ), - a recirculation fan (14), in particular for setting a recirculating volume flow (V̇ recy ), - an anode path heat exchanger (15), in which in particular the anode input current (A in ) by the anode output current (A out ) is heated and / or the anode output current (A out ) by the anode input current (A in ), wherein preferably the anode input current (A in ) is received via a first inlet of the anode path heat exchanger (15) and is fed to the anode inlet (16) via a first outlet of the anode path heat exchanger (15), wherein preferably the anode output current (A out ) is taken up via a second inlet of the anode path heat exchanger (15) and is fed to the heat exchanger (18.2) via a second outlet of the anode path heat exchanger (15), - a recirculation unit (18) for at least partially recirculating the anode output current (A out ) to the anode input current (A in ), - a recirculation path (18.1), a heat exchanger (18.2), a temperature sensor (18.3), and / or an anode path connection point (18.4) of the recirculation unit (18) and / or - an anode path outlet (19) connected to the heat exchanger (18.2) to provide a volume flow of condensed water vapor (V̇ Cond ) from the anode path (10). [10] Fuel cell system (100) according to one of the preceding claims, characterized by that the cathode path (20) has at least one of the following features: - an air supply unit (21) for introducing the cathode input current (K in ) into the cathode path (20), - a cathode path connection point (23), via which a return of air tapped by the cathode path valve (22) into the cathode path (20) is at least partially made possible, - an air blower (24), in particular for adjusting a flow rate and / or a volume flow of the cathode input current (K in ), - a cathode path heat exchanger (25), in which in particular the cathode input current (K in ) by the cathode output current (K out ) is heated and / or the cathode output current (K out ) by the cathode input current (K in ), wherein preferably the cathode input current (K in ) is received via a first inlet of the cathode path heat exchanger (25) and is fed to the cathode inlet (26) via a first outlet of the cathode path heat exchanger (25), - a burner (28) which is connected to the cathode output (27) and / or the anode output (17), in particular to control the cathode output current (K out ) and / or the anode output current (A out ) at least partially incinerate, and / or - an air outlet (29) connected to the cathode outlet (27), in particular the burner (28), in order to at least partially discharge air from the fuel cell system. [11] A computer program product comprising instructions which, when the computer program product is executed by a computer, cause the computer to implement the method according to any one of the preceding claims 1 to 7. [12] Computer-readable data carrier in which instructions are stored which, when executed by a computer, cause the computer to carry out the method according to one of the preceding claims 1 to 7. [13] Control unit (FCCU), comprising a computing unit (CU) and a memory unit (MU) in which instructions are stored which, when at least partially executed by the computing unit (CU), carry out a method according to one of the preceding claims 1 to 7. [14] System (200) comprising a fuel cell system (100) according to one of the preceding claims 8 to 10 and / or a control unit (FCCU) according to the preceding claim.

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