DE102021204734A1 - Fuel cell and method for operating the fuel cell - Google Patents

Abstract

The invention is based on a method (56) for operating a fuel cell (10), in particular a solid oxide fuel cell, which comprises at least one fuel cell and/or electrolyzer unit (12) with at least one anode, with recirculated material in the form of anode waste gas in at least one recirculation module ( 18) is recycled from an anode gas outlet (14) of the fuel cell and/or electrolyzer unit (12) to an anode gas inlet (16) of the fuel cell and/or electrolyzer unit (12). It is proposed that in at least one operating state in the recirculation module ( 18) a fluid, in particular water, is expanded, preferably evaporated, by means of at least one expansion unit (32).

Description

State of the art

A method for operating a fuel cell has already been proposed, which comprises at least one fuel cell and/or electrolyzer unit with at least one anode, with recirculated material in the form of anode waste gas being passed in at least one recirculation module from an anode gas outlet of the fuel cell and/or electrolyzer unit to an anode gas inlet of the Fuel cell and / or electrolyzer unit is recycled.

Disclosure of Invention

The invention is based on a method for operating a fuel cell, in particular a solid oxide fuel cell, which comprises at least one fuel cell and/or electrolyzer unit with at least one anode, with recirculated material formed as anode waste gas in at least one recirculation module from an anode gas outlet of the fuel cell and/or electrolyzer unit is recycled to an anode gas inlet of the fuel cell and/or electrolyzer unit.

It is proposed that in at least one operating state in the recirculation module a fluid, in particular water, is overheated by means of at least one expansion unit. Due to the configuration of the method according to the invention, the anode waste gas can be recycled in a particularly advantageous manner. As a result of the configuration according to the invention, the fuel cell can advantageously be operated with little or no mechanical energy supply for recycling anode waste gas, in particular depending on the requirement for dynamic system behavior. In particular, as a result of the configuration according to the invention, a volume flow of anode waste gas to be conveyed can advantageously be operated without or only with little mechanical energy supply. As a result, a fuel cell with an advantageously high, in particular electrical, efficiency can be provided. The fuel cell is preferably designed as a stationary fuel cell, for example as a heating module. Alternatively, the fuel cell can be designed as a mobile fuel cell, for example in a vehicle. In principle, the method can also be used for alternative applications in which a hot medium is to be pumped. The solid oxide fuel cell is preferably a “solid oxide fuel cell”. Heat and power utilization is particularly preferably integrated into available heat flows of the fuel cell, in particular the solid oxide fuel cell. A “fuel cell and/or electrolyzer unit” should preferably be understood to mean at least a part, in particular a subassembly, of a fuel cell, in particular a solid oxide fuel cell, in particular a planar one, and/or an electrolyzer, in particular a high-temperature electrolyzer, in particular for stationary or mobile applications . In particular, the fuel cell and/or electrolyzer unit, in particular metal-supported, can also include the entire fuel cell, in particular the entire solid oxide fuel cell, the entire electrolyzer, in particular the entire high-temperature electrolyzer, a stack of fuel cells and/or electrolyzers and/or a combination of several stacks of fuel cells and / or include electrolysers. Preferably, the at least one preferably supported, in particular metal-supported, fuel cell and/or electrolyzer unit is provided to burn a fuel with supply of an oxidant in a combustion process to generate electrical energy. Alternatively or additionally, the at least one fuel cell and/or electrolyzer unit is provided for dividing a fluid into at least two components in a separation process with the supply of electrical energy. The at least one fuel cell and/or electrolyzer unit preferably comprises at least one electrode unit. The at least one electrode unit preferably comprises the at least one anode. The at least one anode preferably has or forms a functional layer designed as an electrode layer. The at least one electrode unit preferably comprises at least one cathode. The at least one cathode preferably has or forms a functional layer designed as an electrode layer. The at least one anode and the at least one cathode are preferably directly involved in the combustion process and/or separation process carried out by means of the at least one fuel cell and/or electrolyzer unit. The at least one cathode and the at least one anode are particularly preferably provided for use as a cathode-anode pair. The at least one electrode unit preferably comprises at least one separating element, in particular a functional layer designed as an electrolyte layer. The separating element is preferably arranged between the at least one anode and the at least one cathode. Preferably, the at least one anode and/or the at least one cathode is designed as an oxidant electrode, in particular for contact with an oxidant and/or a cleavage product. At least the at least one anode and/or the at least one cathode is preferably designed as a fuel electrode, in particular for contact with a fuel, in particular a fuel gas, and/or another fission product. Under an "Ano denabgas” should preferably be understood to mean a gas mixture which exits from the at least one fuel cell and/or electrolyzer unit, in particular at the anode gas outlet, after completion of a combustion process and/or separation process at the at least one anode. A “recirculate” is to be understood in particular as a gas mixture which is returned to a combustion process and/or separation process in the at least one fuel cell and/or electrolyzer unit after a combustion process and/or separation process. The recirculated material preferably contains fuel gas, in particular methane, which was not combusted in the at least one fuel cell and/or electrolyzer unit. The recirculated material preferably contains water. The recirculated material preferably contains carbon dioxide. Preferably, water and carbon dioxide are reaction products of the combustion process. An “anode gas inlet” is to be understood in particular as an inlet opening into a reaction chamber of the at least one anode. An “anode gas outlet” is to be understood in particular as an outlet opening from the reaction chamber of the at least one anode. A “return module” should preferably be understood to mean a module that is intended to feed recirculated material removed from the at least one fuel cell and/or electrolyzer unit back to the at least one fuel cell and/or electrolyzer unit. The return module is preferably designed as a fluid-technical line system which comprises a plurality of fluid-technical components and/or assemblies. An "operating state" should preferably be understood to mean a state in which the at least one fuel cell and/or electrolyzer unit is operated for a combustion process and/or a separation process and the at least one recirculation module recirculates from the anode gas outlet of the at least one fuel cell and/or Electrolyzer unit to the anode gas inlet of the at least one fuel cell and / or electrolyzer unit returns. The fluid is preferably in the form of water, in particular steam. Alternatively, the fluid can also be in the form of a fuel, in particular methanol. The at least one expansion unit preferably expands the fluid. The at least one expansion unit is preferably designed as an evaporator. The at least one expansion unit particularly preferably evaporates the fluid. The at least one expansion unit preferably overheats the fluid, in particular water. “Overheating” should preferably be understood to mean that a temperature of the water is increased above the boiling temperature of the water at a corresponding pressure. The water is preferably converted from a liquid to a gaseous state in the expansion unit designed as an evaporator. The water superheated by means of the expansion unit configured as an evaporator is preferably configured as superheated steam in at least one operating state. “Superheated steam” should preferably be understood to mean a state of water, in particular water vapor, in which water, in particular water vapor, has a temperature above the boiling point of water. Alternatively, however, it is conceivable that water expands in the at least one expansion unit, but is not overheated and wet steam is therefore present.

Furthermore, it is proposed that a liquid fluid, in particular liquid water, be separated from the recirculated material discharged in the return module, in particular by means of a condenser. As a result of this configuration, the recirculated material that has been removed can advantageously be simply cooled and a liquid fluid can be separated from the recirculated material. As a result, a working medium for a combined heat and power generation can advantageously be provided, which is already part of a substance composition of the recirculated material. A “discharged recirculate” should preferably be understood to mean recirculate which emerges from the anode gas outlet. The liquid fluid is preferably fed into the at least one expansion unit in at least one operating state. The liquid water is preferably fed into the expansion unit designed as an evaporator in at least one operating state. The liquid fluid is preferably conveyed from the condenser into the at least one expansion unit via a geodetic pressure difference without the supply of mechanical energy.

Furthermore, it is proposed that the expansion unit is operated with residual heat from at least one functional unit, in particular residual heat from the at least one fuel cell and/or electrolyzer unit. An advantageously efficient use of residual heat can be achieved with this configuration. As a result, an additional mechanical and/or electrical energy input for operating the feedback module can advantageously be dispensed with. The expansion unit preferably transfers heat from the residual heat of the fuel cell and/or electrolyzer unit to the fluid, in particular liquid, located in the expansion unit. As a result, thermal energy can be supplied to the liquid fluid and it can thereby be heated, preferably evaporated. A “functional unit” can be understood to mean a unit that performs a specific function in at least one operating state and emits heat in the process. The at least one functional unit is preferably designed as a heat source. Under "Residual heat" should preferably be understood as heat that is excessive in a process of the at least one functional unit and/or is intended to be given off to an environment. The at least one functional unit is preferably necessary for the operation of the fuel cell. The at least one functional unit is preferably part of the fuel cell. In principle, the at least one functional unit can be designed as the at least one fuel cell and/or electrolyzer unit, as an adjacent fuel cell and/or electrolyzer unit, as a heat exchanger, as a reformer or as another module with a heat output that a person skilled in the art deems suitable . It is conceivable that a cross-exchange of residual heat takes place between a number of fuel cell and/or electrolyzer units or a number of fuel cells. Alternatively, the at least one functional unit can also be designed as an external unit that can be operated independently of the fuel cell. The residual heat is particularly preferably in the form of exhaust gas heat from the at least one fuel cell and/or electrolyzer unit. The expansion unit is preferably operated with exhaust gas heat from the at least one fuel cell and/or electrolyzer unit. As a result, exhaust gas heat from the at least one fuel cell and/or electrolyzer unit can be advantageously reduced. Furthermore, an advantageously efficient use of energy can take place.

In addition, it is proposed that the expanded, in particular evaporated, fluid from the expansion unit is used in at least one operating state as a propellant gas for a jet pump that conveys dry recirculated material and/or fuel gas. With this configuration, a combined heat and power generation can be used particularly advantageously for returning the recirculated material. Furthermore, this configuration can advantageously ensure that the water contained in the discharged recirculated material serves as the working medium for the propellant gas. As a result, an additional supply of substances can advantageously be dispensed with. Furthermore, an advantageously robust and low-maintenance delivery of the dry recirculated material and/or the fuel gas can be achieved with this configuration, since the jet pump has at least essentially no moving elements. A "jet pump" should preferably be understood to mean a pump in which a pumping effect is generated by a fluid jet, which is formed in particular from the propellant gas, the fluid jet through an exchange of momentum another medium, in particular as dry recirculated material and/or fuel gas is formed, sucks in, accelerates and compresses. “Dry recirculated material” should preferably be understood to mean discharged recirculated material without any water content. Preferably, the dry recirculated material, which is conveyed by the jet pump, at least partially forms a suction gas. The suction gas is preferably sucked in by the jet pump. Fuel gas is preferably supplied to the jet pump at least at times. Preferably the fuel gas is part of the suction gas.

Furthermore, it is proposed that in at least one operating state, recirculated material to be returned is heated in a heat exchanger by means of the heat from removed recirculated material. An advantageous heat exchange between the discharged recirculated material and the recirculated material to be returned can be achieved with this configuration. As a result, heat from the recirculated material removed can be used in an advantageous, energy-efficient manner. The recirculated material removed preferably has a higher temperature than the recirculated material to be returned. A “recirculated material to be returned” should preferably be understood to mean recirculated material which is fed to the anode gas inlet by means of the recirculation module. The recirculated material to be returned preferably contains fuel gas which was admixed with the dry recirculated material.

Furthermore, the invention is based on a fuel cell, in particular the aforementioned fuel cell, for carrying out the method according to the invention, with the at least one fuel cell and/or electrolyzer unit, which has at least one anode, and with the at least one recirculation module for recycling as anode waste gas trained recirculation. It is proposed that the recirculation module comprises at least one expansion unit, which is designed in particular as an evaporator and is provided for expanding, preferably evaporating, a fluid, in particular water. Due to the configuration of the fuel cell according to the invention, anode waste gas can advantageously be recycled in an energy-efficient manner. As a result, a fuel cell with an advantageously high, in particular electrical, efficiency can be provided. The at least one expansion unit is preferably designed as a heat exchanger. The at least one expansion unit is preferably coupled to an exhaust gas line of the at least one fuel cell and/or electrolyzer unit for heat transfer. The at least one expansion unit is preferably provided for evaporating the fluid, in particular water.

In addition, it is proposed that the recirculation module comprises at least one heat exchanger which is provided for the purpose of transferring heat from recirculated material that has been removed to recirculated material and/or fuel gas that is to be returned. With this configuration, an advantageous heat exchange between the discharged recirculate and the recirculate to be returned. As a result, heat from the discharged recirculation can be used in an energy-efficient manner. Furthermore, the recirculated material to be returned and/or the fuel gas can be advantageously heated in an energy-efficient manner.

Furthermore, it is proposed that the recirculation module has at least one condenser, which is provided for separating liquid water from the recirculated material that is discharged. As a result of this configuration, the recirculated material that is removed can advantageously be simply cooled and liquid water can be separated from the recirculated material. As a result, a working medium for a combined heat and power generation can advantageously be provided, which is already part of a substance composition of the recirculated material.

Furthermore, it is proposed that the condenser is arranged geodetically higher than the at least one expansion unit. This configuration makes it possible to feed liquid fluid, in particular liquid water, which has been separated in the condenser into the expansion unit without mechanical energy supply. As a result, an advantageously high degree of efficiency of the fuel cell can be achieved. By “geodesically higher” it is preferably to be understood that the expansion unit is spaced gravitationally from the condenser, wherein the expansion unit is preferably closer to a point at which the gravitational direction is aligned than the condenser. In at least one operating state, the liquid fluid preferably flows into the expansion unit automatically due to gravitational forces.

In addition, it is proposed that the recirculation module comprises at least one check valve, which is arranged fluidically between the condenser and the expansion unit. As a result of this configuration, the fluid in the at least one expansion unit can advantageously be superheated in a defined manner. As a result, an advantageously automatic heat-power coupling can be achieved which, in particular, does not require any external influence. "Fluidically" should preferably be understood to mean a connection property in which at least two components or assemblies are coupled to one another in such a way that a fluid, in particular recirculated material and/or fuel gas, can be exchanged between them, in particular without loss of fluid.

Furthermore, it is proposed that the recirculation module comprises at least one jet pump which is fluidically connected to the expansion unit, is connected downstream of the expansion unit and is intended to convey recirculated material and/or fuel gas to be recirculated. With this configuration, a combined heat and power generation can be used particularly advantageously for returning the recirculated material. Furthermore, an advantageously robust and low-maintenance delivery of the dry recirculated material and/or the fuel gas can be achieved with this configuration, since the jet pump has at least essentially no moving elements. The jet pump is preferably designed as an ejector. The jet pump is preferably provided to generate a negative pressure for sucking in the suction gas. The jet pump is preferably provided to convey the suction gas together with the propellant gas.

It is also proposed that the jet pump is fluidly connected to the condenser. As a result of this configuration, dry recirculated material and/or, in particular fresh, fuel gas can advantageously be drawn in easily and efficiently by the jet pump. Preferably, a suction area of the jet pump is fluidly connected to the condenser.

The method according to the invention and the fuel cell according to the invention should not be limited to the application and embodiment described above. In particular, the method according to the invention and the fuel cell according to the invention can have a number of individual elements, components and units as well as method steps that differs from a number specified here in order to fulfill a function described herein. In addition, in the value ranges specified in this disclosure, values lying within the specified limits should also be considered disclosed and can be used as desired.

character list

Further advantages result from the following description of the drawing. In the drawings an embodiment of the invention is shown. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into further meaningful combinations.

• 1 eine erfindungsgemäße Brennstoffzelle in einer schematischen Darstellung und
• 2 ein erfindungsgemäßes Verfahren zum Betrieb der Brennstoffzelle in einer schematischen Darstellung.

Show it:

• 1 a fuel cell according to the invention in a schematic representation and
• 2 an inventive method for operating the fuel cell in a schematic representation.

Description of the embodiment

In the 1 a fuel cell 10 according to the invention is shown. In the present case, the fuel cell 10 is designed as a stationary fuel cell, for example as a heating module. Alternatively, the fuel cell 10 can also be designed as a mobile fuel cell, for example in a vehicle. In the present case, the fuel cell 10 is designed as a solid oxide fuel cell. The solid oxide fuel cell is also known as "Solid Oxide Fuel Cell". A thermal power utilization is integrated into available heat flows of the fuel cell 10 . The use of heat and power integrated into the fuel cell 10 manages with waste heat from the fuel cell 10 .

The fuel cell 10 includes a fuel cell and/or electrolyzer unit 12. The fuel cell and/or electrolyzer unit 12 is intended to burn a fuel with supply of an oxidant in a combustion process to generate electrical energy. The fuel is in the form of a fuel gas. In the present case, the fuel cell and/or electrolyzer unit 12 has an anode that is not shown in detail. In the present case, the fuel cell and/or electrolyzer unit 12 comprises an electrode unit that is not shown in detail. In the present case, the electrode unit comprises the anode. The anode has or forms a functional layer designed as an electrode layer. In the present case, the electrode unit comprises a cathode. The cathode has or forms a functional layer designed as an electrode layer. The anode and the cathode are directly involved in the combustion process carried out by means of the fuel cell and/or electrolyzer unit 12 . The cathode and anode are intended for use as a cathode-anode pair. In the present case, the electrode unit comprises a separating element, which is designed in particular as a functional layer designed as an electrolyte layer. The separator is arranged between the anode and the cathode. The cathode is designed as an oxidant electrode, in particular for contact with an oxidant and/or a cleavage product. The anode is designed as a fuel electrode, in particular for contact with a fuel, in particular a fuel gas, and/or another fission product. The fuel cell and/or electrolyzer unit 12 has an anode gas outlet 14 . The fuel cell and/or electrolyzer unit 12 has an anode gas inlet 16 .

The fuel cell 10 includes a return module 18 for recycling formed as anode waste gas recirculated. The recirculation module 18 is provided for returning recirculated material from the fuel cell and/or electrolyzer unit 12 to the fuel cell and/or electrolyzer unit 12 without additional mechanical energy supply to the fuel cell 10 . The recirculation module is provided to automatically convey recirculated material from the fuel cell and/or electrolyzer unit 12 back to the fuel cell and/or electrolyzer unit 12 by means of heat and power coupling, in particular without supplying energy to the fuel cell 10 . An electrical efficiency of the fuel cell 10 is largely determined by the use of fuel gas. A recycling of anode waste gas offers the possibility to increase the use of fuel gas in the fuel cell. In order to create favorable reaction conditions, it is necessary to circulate a gas at a temperature of approx. 600° C. on one side of the anode, the anode waste gas. The feedback module 18 is designed as a fluidic line system. The recirculation module 18 is provided for the purpose of feeding anode waste gas discharged from the fuel cell and/or electrolyzer unit 12 back to the fuel cell and/or electrolyzer unit 12 as recirculation. The return module 18 is intended to convey recirculated material from the anode gas outlet 14 to the anode gas inlet 16 . The anode waste gas emerges from the fuel cell and/or electrolyzer unit 12 , in particular at the anode gas outlet 14 , after the end of a combustion process at the anode. The anode waste gas is designed as a recirculate. The recirculated material is returned to the combustion process in the fuel cell and/or electrolyzer unit 12 after a combustion process. The recirculated gas contains fuel gas that was not burned in the at least one fuel cell and/or electrolyzer unit 12 in the combustion process. In the present case, the fuel gas is methane. The recirculation contains water. The recirculate contains carbon dioxide. Water and carbon dioxide are reaction products of the combustion process.

The recirculation module 18 includes a heat exchanger 20. The heat exchanger 20 is fluidically connected to the anode gas outlet 14 via a first line element 22 of the recirculation module 18. The heat exchanger 20 is intended to cool the recirculated material that has been discharged.

The recirculation module 18 includes a condenser 24. The condenser 24 is fluidically connected to the heat exchanger 20 via a second line element 26 of the recirculation module 18. The first line element 22 and the second line element 26 are fluidically connected to one another via the heat exchanger 20 . The condenser 24 is provided to a liquid fluid, esp special liquid water to separate from the discharged recirculate.

The return module 18 includes a check valve 28. The check valve 28 is fluidically connected to the condenser 24 via a third line element 30 of the return module 18.

The recirculation module 18 includes an expansion unit 32. In the present case, the expansion unit 32 is designed as an evaporator. The expansion unit 32 is fluidically connected to the check valve 28 via a fourth line element 34 of the recirculation module 18 . The check valve 28 is fluidly disposed between the condenser 24 and the expansion unit 32 . The check valve 28 is provided to block fluid flow from the expansion unit 32 to the condenser 24 . The check valve 28 is provided to allow a fluid flow from the condenser 24 to the expansion unit 32 above a defined pressure threshold in the third line element 30 . The condenser 24 is arranged geodetically higher than the expansion unit 32 . The expansion unit 32 is intended to expand a fluid, in particular water. The expansion unit 32 is intended to evaporate water. The expansion unit 32 is designed to superheat water. The expansion unit 32 is designed as a heat exchanger. The expansion unit 32 is coupled to an exhaust gas line 36 of the fuel cell and/or electrolyzer unit 12 for heat transfer. The exhaust line 36 is intended to introduce residual heat from an exhaust gas of the fuel cell and/or electrolyzer unit 12 into the expansion unit 32 .

The recirculation module 18 includes a jet pump 38 . The jet pump 38 is fluidically connected to the expansion unit 32 . The jet pump 38 is connected downstream of the expansion unit 32 . The jet pump 38 is fluidically connected to the expansion unit 32 via a fifth line element 40 of the recirculation module 18 . The jet pump 38 is connected downstream of the expansion unit 32 in terms of fluid technology. The expansion unit 32 is intended to provide a propellant gas for the jet pump 38 . The jet pump 38 is intended to convey recirculated material and/or fuel gas to be returned. The jet pump 38 is designed as an ejector. The jet pump 38 is provided to generate a negative pressure for suction of a suction gas. The jet pump 38 is intended to convey the suction gas together with the propellant gas.

The jet pump 38 is fluidically connected to the condenser 24 . The jet pump 38 is fluidically connected to the condenser 24 via a sixth line element 42 of the recirculation module 18 . A suction area 44 of the jet pump 38 is fluidically connected to the condenser 24 .

The recirculation module 18 includes a fuel gas connection element 46. The fuel gas connection element 46 is provided for supplying fresh fuel gas to the sixth line element 42. The fuel gas connection element 46 is connected to a fuel gas reservoir, not shown in detail, or to a gas line 48, in particular an external gas line. The recirculation module 18 includes a control valve 50 which is provided for controlling a supply of fresh fuel gas. The control valve 50 is fluidly arranged between the fuel gas connection element 46 and the jet pump 38 .

The jet pump 38 is fluidically connected to the heat exchanger 20 via a seventh line element 52 of the recirculation module 18 . The heat exchanger 20 is intended to heat recirculated material to be returned. The heat exchanger 20 is provided for the purpose of transferring heat from recirculated material that has been removed to recirculated material and/or fuel gas that is to be returned. The heat exchanger 20 is fluidically connected to the anode gas inlet 16 via an eighth line element 54 of the recirculation module 18 . The seventh line element 52 and the eighth line element 54 are fluidically connected to one another via the heat exchanger 20 . The first line element 22 and the eighth line element 54 are not fluidically connected to one another via the heat exchanger 20 .

In the 2 a method 56 for operating the fuel cell 10 is shown. The fuel cell 10 is used to carry out the method 56 . The recirculation module 18 returns recirculated material from the anode gas outlet 14 of the fuel cell and/or electrolyzer unit 12 to the anode gas inlet 16 of the fuel cell and/or electrolyzer unit 12 . Recirculate formed as anode waste gas is recycled in the recirculation module 18 from the anode gas outlet 14 of the fuel cell and/or electrolyzer unit 12 to the anode gas inlet 16 of the fuel cell and/or electrolyzer unit 12 .

In a cooling process step 58 of the process 56, the recirculated material removed is cooled. In the present case, the recirculated material removed has a temperature of approximately 600° C. at the anode gas outlet 14 . In the present case, the discharged recirculate has a pressure of approximately 1 bar at the anode gas outlet 14 . In the present case, the discharged recirculated material has a temperature of approx. 600° C. in the first line element 22 on. In the present case, the discharged recirculate has a pressure of approximately 1 bar in the first line element 22 . The recirculated material removed is cooled by the heat exchanger 20 . In the present case, the heat exchanger 20 transfers a heat of 2300 W. The discharged recirculate has a temperature in the second line element 26 which is above a dew point. In the present case, the discharged recirculate has a temperature of approx. 140° C. in the second line element 26 . In the present case, the discharged recirculate has a pressure of approximately 1 bar in the second line element 26 . The discharged recirculate has a lower pressure than the recirculate to be returned.

In a condensation process step 60 of the process 56, a liquid fluid, which is liquid water in the present case, is separated from the recirculated material that is removed. In the condenser 24, the discharged recirculate is further cooled until a temperature is reached which leads to the condensing out of an appreciable proportion of water. The discharged recirculated material is cooled to well below 100 °C. In the return module 18, liquid water is separated from the discharged recirculated material by means of the condenser 24. The liquid water is formed as a condensate. In the present case, the condenser 24 transfers heat of approximately 2000 W. The liquid water flows, in particular automatically, into the third line element 30. The liquid water has a temperature below the boiling point of water. In the present case, the liquid water has a temperature of approximately 69° C. in the third line element 30 . In the present case, the liquid water in the third line element 30 has a pressure of approximately 1 bar. In the condensation process step 60, the recirculated material removed is divided into liquid fluid, in particular liquid water, and dry recirculated material. The dry recirculated material is fed into the sixth line element 42 . In the present case, the dry recirculated material has a temperature of approx. 69° C. in the sixth line element 42 . In the present case, the dry recirculated fluid has a pressure of approximately 1 bar in the sixth line element 42 .

In a feeding process step 62 of the process 56 the liquid fluid, in particular the liquid water, is fed into the expansion unit 32 . The liquid water is fed into the expansion unit 32 in at least one operating state. The liquid water is conveyed from the condenser 24 into the expansion unit 32 via a geodetic pressure difference without the supply of mechanical energy. Execution of the feeding method step 62 depends on an amount of water in the third line element 30. The liquid water runs in batches through the check valve 28 into the expansion unit 32.

In an evaporation method step 64 of the method 56 the liquid fluid, in particular the liquid water, is heated in the expansion unit 32 . The expansion unit 32 is operated with residual heat from at least one functional unit. In the present case, the functional unit is designed as the fuel cell and/or electrolyzer unit 12 . In the present case, the expansion unit 32 is operated with residual heat, in particular exhaust gas heat, from the fuel cell and/or electrolyzer unit 12 . The expansion unit 32 transfers heat from the residual heat of the fuel cell and/or electrolyzer unit 12 to the water located in the expansion unit 32 . In the present case, the expansion unit 32 transfers a heat of 1800 W. As a result, the liquid fluid, in particular the liquid water, can be heated. The exhaust pipe 36 has a section 66 upstream of the expansion unit 32 and a section 68 downstream of the expansion unit 32 . In the present case, the exhaust gas has a temperature of approximately 236° C. in the upstream section 66 of the exhaust gas line 36 . In the present case, the exhaust gas has a pressure of approximately 1 bar in the upstream section 66 of the exhaust gas line 36 . In the present case, the exhaust gas has a temperature of approximately 172° C. in the downstream section 68 of the exhaust gas line 36 . In the present case, the exhaust gas has a pressure of approximately 1 bar in the downstream section 68 of the exhaust gas line 36 . The exhaust gas is gaseous both in the upstream section 66 and in the downstream section 68 . In at least one operating state, a fluid is expanded in the return module 18 by means of the expansion unit 32 . In the present case, the fluid is water. Alternatively, however, other fluids that appear suitable to those skilled in the art, such as methanol, could also be used. In the present case, water is evaporated by means of the expansion unit 32 in the at least one operating state in the recirculation module 18 . In the present case, in the at least one operating state, water in the recirculation module 18 is superheated by means of the expansion unit 32 . The water superheated by means of the expansion unit 32 is in the form of superheated steam in at least one operating state. In the present case, the superheated steam has a temperature of approximately 230° C. in the fifth line element 40 . In the present case, the superheated steam has a pressure of approximately 4 bar in the fifth line element 40 . The liquid water evaporates in the expansion unit 32 . A resulting increase in pressure closes the non-return valve 28 and the superheated water enters the jet pump 38 under pressure as propellant gas. A vaporization energy of Expansion unit 32 is taken from the exhaust gas. In principle, it would be conceivable that the evaporation energy does not lead to sufficient superheating of the vapor and that droplets form in the jet pump 38 . Such an operating behavior can be avoided, for example, by the heat exchanger 20 being pulled so far over the jet pump 38 that the steam is sufficiently overheated before exiting from a nozzle of the jet pump 38 . In principle, it would also be possible for the liquid fluid, in particular liquid water, to be heated and expanded in the expansion unit 32 but not overheated. In this case, wet steam would enter the jet pump 38 as the propellant gas.

When the condensate is conveyed, in particular from the third line element 30 to the jet pump 38, no mechanical energy is consumed. A promotion of the condensate pulsates due to the principle.

In a conveying method step 70 of the method 56, the jet pump 38 is operated. The expanded, in particular vaporized, fluid, in particular steam, from the expansion unit 32 is used in at least one operating state as a propellant gas for the jet pump 38, which conveys dry recirculated material and/or fuel gas. Superheated steam from the expansion unit 32 is used as propellant gas for the jet pump 38 in at least one operating state. The propellant gas is fed to the jet pump 38 via the fifth line element 40 via a pressure difference. The jet pump 38 conveys the dry recirculated material and/or fresh fuel gas. The jet pump 38 draws in the suction gas, which is designed in particular as dry recirculated material and/or fuel gas. The dry recirculated material, which is conveyed by the jet pump 38, at least partially forms the suction gas. In the present case, the recirculated material to be returned has a temperature of approximately 110° C. in the seventh line element 52 . In the present case, the recirculated material to be returned has a pressure of approximately 1.075 bar in the seventh line element 52 .

Fresh fuel gas is supplied to the recirculation module 18 in a fuel gas supply method step 72 . Fresh fuel gas is fluidly fed to the dry recirculate upstream of the jet pump 38 . The fuel gas is fed to the dry recirculated material in the sixth line element 42 . The fuel gas is fed to the dry recirculate fluidically between the condenser 24 and the jet pump 38 . In this case, the pressure is advantageously particularly low. Combustion gas is supplied to the jet pump 38 at least at times. The fuel gas supply process step 72 is independent of other process steps of the process 56. The fuel gas is part of the suction gas. In the present case, the fresh fuel gas has a temperature of approximately 45° C. in the fuel gas connection element 46 . In the present case, the fresh fuel gas has a pressure of approximately 1 bar in the fuel gas connection element 46 .

In a heating process step 74 of the process 56, the recirculate to be returned is heated. In at least one operating state, recirculated material to be returned is heated in the heat exchanger 20 by means of the heat of the recirculated material that is removed. A counterflow to the first line element 22 is conducted in the eighth line element 54 . The discharged recirculate has a higher temperature than the recirculate to be returned. The recirculated material to be returned contains fresh fuel gas, which is mixed with the dry recirculated material. In the present case, the recirculated material to be returned has a temperature of approximately 500° C. in the eighth line element 54 . In the present case, the recirculated material to be returned has a pressure of approximately 1.075 bar in the eighth line element 54 .

The one in the 2 The sequence of process steps 58, 60, 62, 64, 70, 72, 74 of process 56 shown is to be understood as a sequence of the conveyed recirculate in the return module 18, with process steps 58, 60, 62, 64, 70, 72, 74 can in principle also be carried out simultaneously and/or continuously.

Basically, in an alternative configuration of the fuel cell 10 according to the invention, it would be conceivable for the recirculation module 18 to include a small pump, in particular a feed pump, instead of the check valve 28, which continuously delivers the liquid fluid, in particular the liquid water, into the expansion unit 32. As a result, a pulsation can advantageously be avoided. In this case, little mechanical or electrical energy would be required to operate the pump, which, however, would have a comparatively small effect on the overall efficiency of the fuel cell 10 due to the small volume of the liquid water.

Furthermore, in an alternative configuration of the fuel cell 10 according to the invention, it would basically be conceivable for the recirculation module 18 to comprise a further expansion unit, which is designed in particular as a further evaporator, and a further non-return valve. The check valve 28 and the expansion unit 32 form a first condensate path and the additional check valve and the additional expansion unit form a second condensate path. The first condensate path is formed separately from the second condensate path. In the first condensate path and in the second condensate path, the condensate is expanded, in particular overheated, independently of one another. By installing suitable valves, both expansion units or both condensate paths can alternate. As a result, a pulsation can advantageously be avoided.

In principle, other conceptual configurations of feedback modules would also be conceivable, which are listed in the following paragraph. However, these other configurations of feedback modules cannot do without a mechanical energy supply, which would reduce the overall efficiency of the fuel cell 10 .

Basically, it would be conceivable that an alternative recirculation module includes a low-temperature fan with an upstream heat exchanger and a downstream heat exchanger for temporary cooling. However, a complex structure with several heat exchangers, pipelines and a mechanical blower, which is also subject to regular maintenance, is disadvantageous. Furthermore, it would be fundamentally conceivable for an alternative recirculation module to include a jet pump, in particular a “jet pump”, which is fed with fresh fuel gas as the propellant gas. Here, the necessary kinetic energy comes from an overpressure of the fuel gas that is fed in. The efficiency of the flow pump is disadvantageous, in particular because in a stationary fuel cell, methane from a natural gas network is usually used as the energy carrier, which, in contrast to fuel gases, would have to be compressed from pressure accumulators to operate the jet pump, which means that additional compression energy must be provided. In addition, with a stationary fuel cell there is the option of operating with hydrogen or a mixture of hydrogen and methane. In this case, however, operation of the jet pump is difficult, since the density of hydrogen is low and can only provide a manageable impulse for accelerating the suction gas. It would also be conceivable in principle for an alternative recirculation module to include a high-temperature fan. Because of temperature-related stresses on the material, however, the production of a high-temperature blower involves considerable effort. In addition, conveying hot gas is counterproductive in terms of energy, because the power required is proportional to the volume conveyed and thus proportional to the absolute temperature of the medium.

Claims (12)

Method (56) for operating a fuel cell (10), in particular a solid oxide fuel cell, which comprises at least one fuel cell and/or electrolyser unit (12) with at least one anode, with recirculated material formed as anode waste gas in at least one recirculation module (18) from an anode gas outlet ( 14) of the fuel cell and/or electrolyzer unit (12) to an anode gas inlet (16) of the fuel cell and/or electrolyzer unit (12) is recycled, characterized in that in at least one operating state in the return module (18) a fluid, in particular water , is expanded, preferably vaporized, by means of at least one expansion unit (32). Method (56) according to claim 1 , characterized in that in the recirculation module (18) a liquid fluid, in particular liquid water, is separated from discharged recirculated material, in particular by means of a condenser (24). Method (56) according to claim 1 or 2 , characterized in that the expansion unit (32) is operated with residual heat from at least one functional unit, in particular residual heat from the at least one fuel cell and/or electrolyzer unit (12). Method (56) according to one of the preceding claims, characterized in that the expanded, in particular evaporated, fluid from the expansion unit (32) is used in at least one operating state as a propellant gas for a jet pump (38) which conveys dry recirculated material and/or fuel gas becomes. Method (56) according to one of the preceding claims, characterized in that in at least one operating state recirculated material to be returned is heated in a heat exchanger (20) by means of the heat from removed recirculated material. Fuel cell (10), in particular solid oxide fuel cell, for carrying out a method (56) according to one of the preceding claims, with at least one fuel cell and/or electrolyzer unit (12) which has at least one anode, and at least one return module (18) for recycling recirculated material designed as anode waste gas, characterized in that the recirculation module (18) comprises at least one expansion unit (32), which is designed in particular as an evaporator and is provided for expanding, preferably evaporating, a fluid, in particular water. Fuel cell (10) after claim 6 , characterized in that the recirculation module (18) comprises at least one heat exchanger (20) which is intended to remove heat from led recirculate to transfer recirculate to be returned and / or fuel gas. Fuel cell (10) after claim 6 or 7 , characterized in that the recirculation module (18) has at least one condenser (24) which is intended to separate a liquid fluid, in particular liquid water, from the discharged recirculated material. Fuel cell (10) after claim 8 , characterized in that the condenser (24) is arranged geodetically higher than the at least one expansion unit (32). Fuel cell (10) after claim 8 , characterized in that the recirculation module (18) comprises at least one check valve (28) which is fluidly arranged between the condenser (24) and the expansion unit (32). Fuel cell (10) according to one of Claims 6 until 10 , characterized in that the recirculation module (18) comprises at least one jet pump (38) which is fluidically connected to the expansion unit (32), the expansion unit (32) is connected downstream and is intended to promote recirculated recirculate and / or fuel gas. Fuel cell (10) after claim 11 , characterized in that the jet pump (38) is fluidly connected to the condenser (24).

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