Fuel cell device, fuel cell system and method

Abstract

The invention is based on a fuel cell device, in particular an SOFC fuel cell, with at least one reaction unit (10) which is designed to generate electrical energy from a process gas (12), for example natural gas, and an oxygen-containing process air (14), in particular ambient air, in a chemical reaction, with at least one process air supply unit (16) which is designed to supply at least the process air (14) to the reaction unit (10), with at least one exhaust gas unit (18) which is designed to discharge an exhaust gas (20) generated by the reaction unit (10). A heat exchanger unit (22) is proposed which is designed to transfer thermal energy of the exhaust gas (20) to the process air (14) at least during a start-up process, at least when the ambient temperature falls below a critical level.

Description

State of the art

[0001] A fuel cell device, in particular an SOFC fuel cell, has already been proposed, comprising at least one reaction unit which is designed to generate electrical energy from a process gas, for example natural gas, and an oxygen-containing process air, in particular ambient air, in a chemical reaction, comprising at least one process air supply unit which is designed to supply at least the process air to the reaction unit, and comprising at least one exhaust gas unit which is designed to discharge an exhaust gas generated by the reaction unit. Disclosure of the invention

[0002] The invention is based on a fuel cell device, in particular SOFC fuel cell, with at least one reaction unit which is designed to generate electrical energy from a process gas, for example natural gas, and an oxygen-containing process air, in particular ambient air, in a chemical reaction, with at least one process air supply unit which is designed to supply at least the process air to the reaction unit, with at least one exhaust gas unit which is designed to discharge an exhaust gas generated by the reaction unit.

[0003] A heat exchanger unit is proposed which is designed to transfer thermal energy of the exhaust gas to the process air at least during a start-up process, at least when a critical ambient temperature is undershot.

[0004] The inventive design of the fuel cell device advantageously enables a particularly high level of efficiency to be provided, since, in particular, the thermal energy in the exhaust gas stream is used to preheat the process air, at least during the start-up process, and thus no additional energy needs to be used to heat the process air. Advantageously, a low-cost design can be provided, since, in particular, an additional heating unit for preheating the process air can be dispensed with. Advantageously, a high level of operational reliability can be provided, since, in particular, the preheating of the process air ensures reliable operation of the fuel cell even when the ambient temperature falls below the critical level.

[0005] The fuel cell device is preferably designed as a solid oxide fuel cell, in particular SOFC (Solid Oxide Fuel Cell). Preferably, a plurality of fuel cell devices are connected as a fuel cell stack. Preferably, the fuel cell device has at least one reaction unit. It is conceivable for the fuel cell device to have a plurality of reaction units, in particular connected in parallel with regard to a process gas and process air supply. Preferably, the reaction unit is designed as a fuel cell. Preferably, the at least one reaction unit of the fuel cell device is designed to generate electrical energy and thermal energy. Preferably, the reaction unit is designed to generate the electrical energy by cold combustion, in particular oxidation, of the process gas in a redox reaction.The reaction unit preferably has at least one anode, at least one cathode, and at least one membrane, in particular separating a cathode chamber and an anode chamber. It is conceivable for the reaction unit to have a reformer unit designed to reform hydrogen from the fuel for the chemical reaction to generate energy. The reformer unit could be connected upstream of the anode chamber. The process gas is preferably in the form of a fluidic fuel, in particular natural gas. Alternatively, the process gas could also be in the form of hydrogen or a comparable fuel. A “process gas” is to be understood in particular as a fluidic fuel designed to carry out at least one redox reaction with oxygen. “Process air” is to be understood in particular as oxygen-containing ambient air."Configured" should be understood in particular as specifically programmed, designed, and / or equipped. The fact that an object is configured for a specific function should be understood in particular as meaning that the object fulfills and / or executes this specific function in at least one application and / or operating state.

[0006] The process air supply unit is preferably designed to supply the process air to the reaction unit, in particular continuously. The process air supply unit preferably has at least one air filter, in particular an air particle filter. In particular, the air filter is designed to filter particles from the process air. The process air supply unit preferably has at least one compressor which generates a process air flow for a continuous supply of process air to the reaction unit. The process air supply unit preferably has at least one process air supply element. The process air supply element could, for example, be designed as a pipe or a shaft or the like. The process air supply element preferably forms at least one process air supply channel.Preferably, the process air supply element is configured to fluidically connect the reaction unit to the air filter and / or the compressor. Preferably, the process air supply unit is configured to conduct the process air. Preferably, the process air supply unit is fluidically connected to the heat exchanger unit.

[0007] The exhaust gas unit is preferably designed to direct the exhaust gas away from the reaction unit. In particular, the exhaust gas is designed at least as the oxidized process gas. The exhaust gas unit is preferably designed to generate an exhaust gas stream. The exhaust gas stream is preferably designed as the flowing exhaust gas, in particular at least one moved through the compressor. The exhaust gas preferably comprises the thermal energy generated by the redox reaction in the reaction unit. In particular, the thermal energy introduced into the reaction unit by the redox reaction is designed as waste heat. Alternatively or in addition to the compressor of the process air supply unit, the exhaust gas unit could comprise the compressor or a further compressor. The exhaust gas unit preferably comprises at least one exhaust gas element. The exhaust gas element is preferably designed as an exhaust pipe or an exhaust gas shaft or the like.The exhaust element preferably forms at least one exhaust channel. The exhaust unit is preferably configured to fluidically connect the reaction unit to the heat exchanger unit. "Heat energy" is understood to mean, in particular, thermal energy, which is expressed as a temperature difference relative to a fluid or solid body to which the thermal energy is to be transferred and / or relative to an ambient temperature.

[0008] The heat exchanger unit is preferably configured to transfer the thermal energy of the exhaust gas stream to the process air stream of the fuel cell device in at least one operating state, in particular at least during the start-up process and when the temperature falls below the critical ambient temperature. It is conceivable for the heat exchanger unit to be designed to be connectable to at least one further process air stream of a further fuel cell device, in particular of the fuel cell stack. For example, during extended standby operation of a further fuel cell device, the heat exchanger unit could be configured to preheat the process air of the further fuel cell device using the thermal energy of the exhaust gas stream of the fuel cell device operating in regular mode.

[0009] A “start-up process” is to be understood in particular as at least one operating state in which the reaction unit at least substantially has an operating temperature, in particular less than 100°C, preferably less than 75°C. In particular, the start-up process follows a deactivated state of the fuel cell device and / or a standby mode and / or cleaning / maintenance mode and / or a comparable mode in which at least the temperature of the reaction unit is reduced compared to normal operation. A “normal operation” is to be understood in particular as at least one operating state in which the reaction unit at least substantially has an operating temperature, in particular at least 100°C, preferably at least 200°C.In this context, “at least substantially” should be understood to mean that a deviation from a predetermined value deviates in particular by less than 25%, preferably less than 10% and particularly preferably less than 5% of the predetermined value.

[0010] The critical ambient temperature is preferably -5°Celsius. It is conceivable that the critical ambient temperature depends on the process gas and / or the design of the fuel cell device and / or other influencing factors. The person skilled in the art will therefore determine the critical ambient temperature on a case-by-case basis. The critical ambient temperature is, in particular, at most 5°C, preferably at most 0°C, preferably between -5°C and, for example, -10°C. A "critical ambient temperature" is understood to mean, in particular, an ambient air temperature below which process air must be preheated to ensure reliable operation of the fuel cell device.

[0011] The fuel cell device preferably has at least one temperature sensor. The temperature sensor is preferably configured at least to determine an ambient air temperature, in particular a process air temperature. The temperature sensor could be configured as a temperature sensor. Alternatively or additionally, the temperature sensor could also be configured to receive external temperature measurement data. The fuel cell device preferably has at least one further temperature sensor configured to determine the temperature in the reaction unit. The further temperature sensor is preferably configured as a temperature sensor.The fuel cell device preferably has at least one control and / or regulating unit configured to control and / or regulate the fuel cell device, in particular as a function of sensor measurement data from the at least one temperature sensor and / or the at least one further temperature sensor. A "control and / or regulating unit" is understood to mean, in particular, a unit with at least one control electronics unit. A "control electronics unit" is understood to mean, in particular, a unit with a processor unit and a memory unit, as well as with an operating program stored in the memory unit.

[0012] Furthermore, it is proposed that the heat exchanger unit is configured to transfer the thermal energy of an exhaust gas stream to water, in particular heating water, of a water circuit, at least during normal operation. A high degree of efficiency can advantageously be provided since, in particular, the thermal energy in the exhaust gas stream can be utilized by transferring the thermal energy to the water in the water circuit. Preferably, the heat exchanger unit is configured to transfer the thermal energy, in particular waste heat, of the exhaust gas stream to the water in the water circuit. For example, the heat exchanger unit could be designed as a single heat exchanger that is fluidly connected, in particular switchably, either to the water circuit or to the process air supply unit. For example, the heat exchanger unit could be configured to be switched back and forth between the water circuit and the process air supply unit.In particular, the water circuit is designed as an external water circuit, in particular a customer water network. The water circuit preferably has at least one consumer and / or a water reservoir. It is conceivable that the water circuit is contained in a higher-level system, in particular a fuel cell system, comprising at least the fuel cell device. Alternatively, the heat exchanger unit could also be configured to transfer the waste heat to a comparable fluid and / or solid.

[0013] It is further proposed that the heat exchanger unit have at least a first heat exchanger which is designed to transfer the thermal energy of the exhaust gas flow to the process air and at least a second heat exchanger which is designed to transfer the thermal energy of the exhaust gas flow to water in a water circuit. A particularly high level of efficiency can advantageously be provided since, in particular, the two heat exchangers of the heat exchanger unit allow each heat exchanger to be individually designed and the best possible heat transfer can thus be achieved. Preferably, the first heat exchanger is designed as a gas-to-gas heat exchanger. Preferably, the second heat exchanger is designed as a gas-to-liquid heat exchanger. Preferably, the first heat exchanger of the heat exchanger unit and the second heat exchanger of the heat exchanger unit are arranged without contact with one another.Alternatively, the first heat exchanger and the second heat exchanger could also be formed as a single piece. Preferably, the first heat exchanger is at least thermally decoupled from the second heat exchanger. For example, the heat exchanger unit could have a heat exchanger, in particular a two-part heat exchanger, with two functional areas, wherein the first functional area of the heat exchanger unit could be configured to transfer the thermal energy of the exhaust gas flow to the process air and the second functional area of the heat exchanger unit could be configured to transfer the thermal energy of the exhaust gas flow to the water in the water circuit. “Single piece” should be understood to mean, in particular, materially connected, for example by a welding process and / or adhesive process, etc., and particularly advantageously, integrally formed, such as by production from a single casting and / or by production using a single-component or multi-component injection molding process.

[0014] Furthermore, it is proposed that the heat exchanger unit comprise a distribution unit configured to supply the exhaust gas stream to the first heat exchanger of the heat exchanger unit and to the second heat exchanger of the heat exchanger unit. Advantageously, a high degree of flexibility can be provided, since, in particular, the distribution unit can be switched over when preheating of the process air is required or not. Advantageously, a high degree of efficiency can be provided, since, in particular, the thermal energy from the exhaust gas stream is only used to preheat the process air during the start-up process and can be switched over as soon as the process air no longer requires preheating. Preferably, the distribution unit is configured to continuously adjust the supply of the exhaust gas stream to the first heat exchanger and to the second heat exchanger of the heat exchanger unit.For example, the distribution unit could have at least one, preferably electronically controllable, multi-way valve, in particular a two-way valve. Alternatively, the distribution unit could have a first throttle valve configured to control the exhaust gas flow into the first heat exchanger. Alternatively, the distribution unit could have a second throttle valve configured to control the exhaust gas flow into the second heat exchanger. It is conceivable that the distribution unit is configured to adjust an inflow of the exhaust gas flow to the first heat exchanger and the second heat exchanger depending on at least one sensor signal from the temperature sensor, in particular the ambient temperature.

[0015] Furthermore, it is proposed that the distribution unit have at least one control flap which has a plurality of positions which are designed to supply at least a portion of the exhaust gas flow to the first heat exchanger and the second heat exchanger. Advantageously, a high degree of flexibility can be provided since, particularly at very cold temperatures, even in normal operation, a portion of the exhaust gas flow can be used to preheat the process gas and the remaining portion of the exhaust gas flow can be used to transfer the thermal energy of the exhaust gas flow to the water. The portion of the exhaust gas flow is preferably designed as a percentage between 0% and 100%. The control flap could, for example, have five positions with the portions of the exhaust gas flow to the first heat exchanger of the heat exchanger unit of 0%, 25%, 50%, 75% and 100%.Preferably, the at least one position is configured as at least one detent or at least one adjustable angle or the like. The aforementioned positions of the control flap are exemplary and could have more or fewer positions with different components that would be deemed appropriate by those skilled in the art.

[0016] Furthermore, it is proposed that the distributor unit have a control flap which has precisely two positions which are designed to connect the exhaust gas flow either to the first heat exchanger of the heat exchanger unit or to the second heat exchanger of the heat exchanger unit. Advantageously, low complexity can be provided since, in particular, only two positions of the control flap are provided. Preferably, a first opening surface to the first heat exchanger of the heat exchanger unit is completely closed in a first position. Preferably, a second opening surface to the second heat exchanger of the heat exchanger unit is completely closed in a second position. Preferably, the control flap is designed to be rotated, preferably pivoted, about an axis of rotation. In particular, the axis of rotation is arranged at least substantially perpendicular to a flow direction of the exhaust gas flow.

[0017] Furthermore, a fuel cell system, in particular a prefab fuel cell system, with at least one fuel cell is proposed. Advantageously, a particularly high level of efficiency can be achieved because, in particular, the thermal energy in the exhaust gas stream is used to preheat the process air, at least during the start-up process, when the ambient temperature falls below the critical level, thus eliminating the need for additional energy to heat the process air. Preferably, the prefab fuel cell system comprises at least the water circuit. Preferably, the prefab fuel cell system comprises at least one water reservoir. Preferably, the prefab fuel cell system comprises at least one fuel cell device. In particular, the fuel cell system comprises further components deemed appropriate by those skilled in the art, such as piping elements, seals, valves, pumps, and / or the like.

[0018] In addition, it is proposed that at least the process air is preheated by the exhaust gas flow, at least during the start-up process, at least when the ambient temperature falls below the critical level. A particularly high level of efficiency can advantageously be achieved because the thermal energy in the exhaust gas flow is used to preheat the process air, at least during the start-up process, and thus no additional energy needs to be used to heat the process air. Preferably, the exhaust gas flow is directed into the first heat exchanger of the heat exchanger unit when the ambient temperature falls below the critical level. Preferably, the exhaust gas flow is directed into the first heat exchanger of the heat exchanger unit by moving the control flap to the second position.Preferably, the process air is preheated by transferring the thermal energy, in particular waste heat, of the exhaust gas stream in the heat exchanger unit to the process air, in particular along a temperature gradient. In particular, the exhaust gas stream is at least partially connected to the first heat exchanger, at least depending on the ambient temperature and / or a temperature in the reaction unit, thereby preheating the process air.

[0019] It is also proposed that, at least during normal operation, at least the water from the water circuit is heated by the exhaust gas stream. A particularly high level of efficiency can advantageously be achieved since, in particular, the thermal energy of the exhaust gas stream is only used to preheat the process air when it needs to be heated. Preferably, during normal operation, at least a portion of the exhaust gas stream is fed into the second heat exchanger of the heat exchanger unit. Preferably, the water in the water circuit is preheated by transferring the thermal energy, in particular waste heat, of the exhaust gas stream to the water in the heat exchanger unit, in particular along the temperature gradient. Preferably, the exhaust gas stream is at least partially fed to the second heat exchanger when the operating temperature in the reaction unit is reached and / or when the critical ambient temperature is exceeded.

[0020] In addition, it is proposed that, depending on an ambient temperature, in particular a process air temperature, the exhaust gas flow is connected to a first heat exchanger, in which the thermal energy is transferred from the exhaust gas flow to the process air, and / or to a second heat exchanger of the heat exchanger unit, in which the thermal energy is transferred from the exhaust gas flow to the water of the water circuit, in particular by selecting from several positions of the control flap. Advantageously, a high level of flexibility can be provided since, particularly at very cold temperatures, even in normal operation, a portion of the exhaust gas flow can be used to preheat the process gas and the remaining portion of the exhaust gas flow can be used to transfer the thermal energy of the exhaust gas flow to the water.During normal operation, a portion of the exhaust gas flow, for example 25%, is preferably directed into the first heat exchanger of the heat exchanger unit, and a further portion of the exhaust gas flow, for example 75%, is directed into the second heat exchanger of the heat exchanger unit. It is conceivable that the portion is selected from several positions, in particular temperature-dependent. Preferably, the control flap is switched to a further position, at least when the temperature falls below the critical temperature.

[0021] The fuel cell device according to the invention, the fuel cell system according to the invention, and the method according to the invention are not intended to be limited to the application and embodiment described above. In particular, the fuel cell device according to the invention, the fuel cell system according to the invention, and the method according to the invention may have a number of individual elements, components, units, and method steps that differs from the number stated herein to fulfill a functionality described herein. Furthermore, in the value ranges specified in this disclosure, values within the stated limits are also to be considered disclosed and can be used arbitrarily. drawing

[0022] Further advantages will become apparent from the following description of the drawings. The drawings illustrate an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. Those skilled in the art will also expediently consider the features individually and combine them into useful further combinations.

[0023] They show: Fig. 1 a fuel cell device with the heat exchanger unit and Fig. 2 a schematic flow diagram of a method for operating the fuel cell device.

[0024] The Fig. 1 shows a fuel cell system 44. The fuel cell system 44 is designed as a prefab fuel cell system. The fuel cell system 44 has a fuel cell device. It is conceivable for the fuel cell system to have multiple fuel cell devices. The fuel cell devices are connected in parallel with respect to a process gas supply and a process air supply. The fuel cell device is designed as an SOFC fuel cell. The fuel cell device has a reaction unit 10. The reaction unit 10 is configured to generate electrical energy from a process gas 12 and an oxygen-containing process air 14 in a chemical reaction. The reaction unit 10 has an anode. The reaction unit 10 has a cathode. The reaction unit 10 has a membrane configured to separate a cathode chamber and an anode chamber.The process air 14 is located in the cathode chamber. The process gas 12 is located in the anode chamber. The process gas 12 is in the form of natural gas. The process gas 12 could also be in the form of hydrogen or a comparable fuel gas. The process air 14 is in the form of ambient air. The chemical reaction is in the form of a redox reaction.

[0025] The fuel cell device has a process air supply unit 16. The process air supply unit 16 is configured to supply the process air 14 to the reaction unit 10. The process air supply unit 16 has a process air supply channel. The process air supply channel is formed by a process air supply element. The process air supply element is designed as a tube. The process air supply unit 16 has a compressor 48. The compressor 48 is configured to continuously supply the process air 14 to the reaction unit 10. The process air supply unit 16 has an air filter 46. The air filter 46 is designed as an air particle filter. The process air supply element is configured to fluidically connect the compressor 48 and the air filter 46 and the reaction unit 10. The process air supply unit 16 has a temperature sensor 50.For example, the temperature sensor 50 could be designed as an NTC temperature sensor (negative temperature coefficient temperature sensor) or a PTC temperature sensor (positive temperature coefficient temperature sensor) or a comparable temperature measuring device. The temperature sensor 50 is configured to measure a temperature of the process air 14. The temperature sensor 50 is arranged at an inlet of the process air supply unit 16. Alternatively, the temperature sensor 50 could also be configured to receive an external temperature measurement signal from an external temperature measurement unit or a weather report or the like. The reaction unit 10 has a further temperature sensor 54. The further temperature sensor 54 is structurally identical to the temperature sensor 50. The further temperature sensor 54 is arranged at an exhaust gas outlet of the reaction unit 10.The further temperature sensor 54 is configured to determine a process temperature in the reaction unit 10.

[0026] The fuel cell device has an exhaust gas unit 18. The exhaust gas unit 18 is configured to discharge an exhaust gas 20 generated by the reaction unit 10. The exhaust gas unit 18 has an exhaust gas element. The exhaust gas element is designed as an exhaust pipe. The exhaust gas element forms an exhaust gas duct. The fuel cell device has a heat exchanger unit 22. The exhaust gas element is configured to fluidically connect the reaction unit 10 to the heat exchanger unit 22. The heat exchanger unit 22 is configured to transfer thermal energy of the exhaust gas 20 to the process air 14 during a start-up process. The heat exchanger unit 22 is configured to transfer the thermal energy of the exhaust gas 20 to the process air 14 when the ambient temperature falls below a critical level. In this exemplary embodiment, the critical ambient temperature is -5°C.The heat exchanger unit 22 is configured to transfer thermal energy from an exhaust gas stream 24 to water in a water circuit 26 during normal operation. The water could be configured as heating water. The water could be configured as drinking water. It is conceivable that the heat exchanger unit 22 is configured to transfer the thermal energy to a comparable heat storage device and / or heat consumer during normal operation.

[0027] The heat exchanger unit 22 has a first heat exchanger 28. The first heat exchanger 28 is designed to transfer the thermal energy of the exhaust gas stream 24 to the process air 14. The first heat exchanger 28 is designed as a gas-gas heat exchanger. The first heat exchanger 28 is designed as a heat exchanger according to the cross-flow principle. The heat exchanger unit 22 has a second heat exchanger 30. The second heat exchanger 30 is designed to transfer the thermal energy of the exhaust gas stream 24 to the water of the water circuit 26. The second heat exchanger 30 is designed as a gas-liquid heat exchanger. The second heat exchanger 30 is designed as a heat exchanger according to the cross-flow principle. The first heat exchanger 28 is arranged at a distance from the second heat exchanger 30. The first heat exchanger 28 and the second heat exchanger 30 are arranged thermally decoupled from each other.Alternatively, the heat exchanger unit 22 could also be designed as a heat exchanger with two functional areas.

[0028] The heat exchanger unit 22 has a distribution unit 32. The distribution unit 32 is configured to feed the exhaust gas stream 24 to the first heat exchanger 28 of the heat exchanger unit 22. The distribution unit 32 is configured to feed the exhaust gas stream 24 to the second heat exchanger 30 of the heat exchanger unit 22. The distribution unit 32 has a control flap 34. The control flap 34 has exactly two positions 36. The two positions 36 are configured to connect the exhaust gas stream 24 either to the first heat exchanger 28 of the heat exchanger unit 22 or to the second heat exchanger 30 of the heat exchanger unit 22. The control flap 34 has a first position. In the first position, an opening to the second heat exchanger 30 is completely closed. The reaction unit 10 is connected to the first heat exchanger 28. The control flap 34 has a second position.In the second position, an opening to the first heat exchanger 28 is completely closed. The reaction unit 10 is connected to the second heat exchanger 30. The control flap 34 is configured to be pivoted about a rotation axis. The rotation axis is arranged perpendicular to a flow direction of the exhaust gas flow 24. The control flap 34 can also have multiple positions 36. The positions 36 could each be configured to supply a portion of the exhaust gas flow 24 to the first heat exchanger 28 and the second heat exchanger 30. The . Fig. 1 shows five positions 36 by way of example. However, a person skilled in the art can also provide more or fewer than five positions if necessary. The positions 36 are designed as detents. The detents could be designed as a proportion of 0%, 25%, 50%, 75%, 100%. The positions are designed as force-locking and / or positive-locking detents. The fuel cell device has a control and / or regulating unit 52. The control and / or regulating unit 52 is configured to adjust the position 36 of the control flap 34 depending on a sensor signal from the temperature sensor 50.

[0029] The Fig. 2 shows a schematic flow diagram of a method for operating the fuel cell device.

[0030] In at least one method step 38, the process air 14 is preheated by the exhaust gas stream 24 during the start-up process if the temperature falls below the critical ambient temperature. For this purpose, the exhaust gas stream 24 is directed from the distribution unit 32 into the first heat exchanger 28. It is conceivable that only a portion of the exhaust gas stream 24 is directed into the first heat exchanger 28. The remaining portion of the exhaust gas stream 24 could be directed into the second heat exchanger 30. It is conceivable that at least a portion of the exhaust gas stream 24 is directed into the first heat exchanger 28 if the temperature falls below the critical ambient temperature during normal operation. It is conceivable that the exhaust gas stream 24 is directed from the distribution unit 32 into the second heat exchanger 30 if the temperature falls below the critical ambient temperature.

[0031] In at least one further method step 40, during normal operation, at least the water from the water circuit 26 is heated by the exhaust gas stream 24. For this purpose, the exhaust gas stream 24 is directed from the distribution unit 32 into the second heat exchanger 30. It is conceivable that only a portion of the exhaust gas stream 24 is directed into the second heat exchanger 30 to heat the water from the water circuit 26. The remaining portion of the exhaust gas stream 24 could be directed into the first heat exchanger 28, thereby heating the process air 14. Above the critical ambient temperature, the exhaust gas stream 24 is fed to the second heat exchanger 30.

[0032] In at least one method step 42, the exhaust gas stream 24 is proportionally added to the first heat exchanger 28 depending on an ambient temperature. In the first heat exchanger 28, the thermal energy from the exhaust gas stream 24 is transferred to the process air 14. The exhaust gas stream 24 is proportionally added to the second heat exchanger 30 of the heat exchanger unit 22 depending on the ambient temperature. In the second heat exchanger 30, the thermal energy from the exhaust gas stream 24 is transferred to the water of the water circuit 26. The exhaust gas stream 24 is directed to the first heat exchanger 28 and / or the second heat exchanger 30 by selecting a position 36 from several positions 36 of the control flap 34. The lower the ambient temperature, the greater the proportion of the exhaust gas stream 24 that is fed to the first heat exchanger 28. For this purpose, an ambient temperature is determined by the temperature sensor 50.It is conceivable that the proportion of the exhaust gas flow 24 that is directed into the first heat exchanger 28 is additionally adjusted depending on a further temperature of the further temperature sensor 54, for example, the temperature in the reaction unit 10. When the critical ambient temperature is exceeded, the control flap 34 is switched, whereby the exhaust gas flow is at least partially diverted to the second heat exchanger 30.

Claims

[1] Fuel cell device, in particular SOFC fuel cell, with at least one reaction unit (10) which is designed to generate electrical energy from a process gas (12), for example natural gas, and an oxygen-containing process air (14), in particular ambient air, in a chemical reaction, with at least one process air supply unit (16) which is designed to supply at least the process air (14) to the reaction unit (10), with at least one exhaust gas unit (18) which is designed to discharge an exhaust gas (20) generated by the reaction unit (10), characterized by a heat exchanger unit (22) which is designed to transfer thermal energy of the exhaust gas (20) to the process air (14) at least during a start-up process, at least when a critical ambient temperature is undershot. [2] Fuel cell device according to claim 1, characterized bythat the heat exchanger unit (22) is designed to transfer the thermal energy of an exhaust gas stream (24) to water, in particular heating water of a water circuit (26), at least in a control operation. [3] Fuel cell device according to claim 1 or 2, characterized by that the heat exchanger unit (22) has at least one first heat exchanger (28) which is designed to transfer the thermal energy of the exhaust gas flow (24) to the process air (14) and at least one second heat exchanger (30) which is designed to transfer the thermal energy of the exhaust gas flow (24) to a water of a water circuit (26). [4] Fuel cell device according to one of the preceding claims, characterized bythat the heat exchanger unit (22) has a distributor unit (32) which is designed to supply the exhaust gas flow (24) to a first heat exchanger (28) of the heat exchanger unit (22) and to a second heat exchanger (30) of the heat exchanger unit (22). [5] Fuel cell device according to claim 4, characterized by in that the distributor unit (32) has at least one control flap (34) which has a plurality of positions (36) which are designed to supply at least a portion of the exhaust gas flow (24) to the first heat exchanger (28) and the second heat exchanger (30). [6] Fuel cell device according to claim 4, characterized by in that the distributor unit (32) has a control flap (34) which has exactly two positions (36) which are designed to connect the exhaust gas flow (24) either to the first heat exchanger (28) of the heat exchanger unit (22) or to the second heat exchanger (30) of the heat exchanger unit (22). [7] Fuel cell system, in particular prefab, with at least one fuel cell according to one of the preceding claims. [8] Method for starting the fuel cell device according to one of the preceding claims, characterized by that at least during the start-up process at least the process air (14) is preheated by the exhaust gas flow (24), at least when the critical ambient temperature is undershot. [9] Method for operating the fuel cell device according to one of the preceding claims, characterized by that at least during normal operation at least the water from the water circuit (26) is heated by the exhaust gas stream (24). [10] Method according to claim 8 or 9, characterized bythat depending on an ambient temperature, in particular a process air temperature, the exhaust gas flow (24) is connected to a first heat exchanger (28), in which the thermal energy is transferred from the exhaust gas flow (24) to the process air (14), and / or to a second heat exchanger (30) of the heat exchanger unit (22), in which the thermal energy is transferred from the exhaust gas flow (24) to a water of a water circuit (26), in particular by a selection from a plurality of positions (36) of the control flap (34).

Images