DE102016223436B4 - Device and method for operating a fuel cell system - Google Patents

Abstract

Method for operating a fuel cell system (1) with a fuel (27), which fuel cell system (1) has at least one high-temperature fuel cell (10) with at least one cathode (11) arranged in a cathode chamber (12), with at least one cathode (11) arranged in an anode chamber (14) arranged anode (13) and with an electrolyte (15) present between the cathode compartment (12) and the anode compartment (14), wherein in an anode gas circuit (20) from the anode compartment (14) of the at least one high-temperature fuel cell (10) recirculated anode waste gas (25) mixed with fuel (27) and fed as anode feed gas (30) with at least one gas conveying device (50) to an anode gas heat exchanger (70), in which the anode feed gas (30) is thermostated, with further in at least one reforming unit (60, 61) in the anode gas circuit (20) the fuel (27) is reformed, characterized in that the at least one reforming unit (60, 61, 62, 63) is arranged in a hot circuit section (210) of the anode gas circuit (20), in which hot circuit section (210) during fuel cell operation, an anode gas temperature (200) above the equilibrium temperature required in the reforming unit (60, 61, 62, 63) is reached, and the at least one gas delivery device (50) is arranged in a cool circuit section (220) of the anode gas circuit (20), in which cool circuit section (220) in fuel cell operation an anode gas temperature (200) below the anode gas temperature (200) prevailing in the hot circuit section (210) is reached, wherein the at least one reforming unit (60) comprises a catalytic reformer heat exchanger (62) in which the fuel ( 27) is reformed, with the reformer heat exchanger (62) being combined with the anode gas heat exchanger (70) to form a common component and being arranged in an anode feed gas line (31) upstream of the anode chamber (14), with a cold heat exchanger side (71) and/or a hot heat exchanger side (72) is or are coupled to the reformer heat exchanger (62) and fuel (27) to be reformed hot anode waste gas (22) in an anode gas discharge line (21) on the hot heat exchanger side (72) before the anode gas heat exchanger (70) and/or the recirculated anode exhaust gas (25) in a recirculation line (24) on the cold heat exchanger side (71) before the anode gas heat exchanger (70) is or are supplied.

Description

The invention relates to a method for operating a fuel cell system with a fuel, which fuel cell system comprises at least one high-temperature fuel cell with at least one cathode arranged in a cathode compartment, with at least one anode arranged in an anode compartment and with an electrolyte present between the cathode compartment and the anode compartment, with an anode gas circuit anode exhaust gas recirculated from the anode chamber of the at least one high-temperature fuel cell is mixed with fuel and this mixture is fed as anode feed gas with at least one gas delivery device to an anode gas heat exchanger, in which the anode feed gas is thermostated, the fuel also being reformed in at least one reforming unit in the anode gas circuit. Devices for operating a fuel cell system with a fuel are also specified within the scope of the invention.

Those skilled in the art understand a high-temperature fuel cell to mean, for example, a molten carbonate fuel cell (MCFC), which operates at operating temperatures of approximately 580° C. to 675° C. In this type of fuel cell, an alkali carbonate mixed melt of lithium and potassium carbonate is usually used as the electrolyte. Solid oxide fuel cells (SOFC) are also high-temperature fuel cells. Solid oxide fuel cells operate at operating temperatures of about 650°C to 1000°C.

The electrolyte of this type of cell consists of a solid ceramic material that is able to conduct oxygen ions but has an insulating effect on electrons. The electrodes, cathode and anode, are attached to both sides of the electrolyte layer. They are gas-permeable electrical conductors. The oxygen-ion-conducting electrolyte is provided, for example, as a thin membrane in order to be able to transport the oxygen ions with little energy, but this only works at the high temperatures mentioned. The outer side of the cathode facing away from the electrolyte is surrounded by air, the outer anode side by fuel gas. Unused air and fuel gas as well as combustion products are extracted.

Fuel cell systems, which are used in particular as an auxiliary power supply device in motor vehicles or as stationary systems or "stationary power plants", and which usually include at least one fuel cell for generating electricity from cathode air and reformate gas, are already known from the prior art. A fuel cell of this type is usually composed of a large number of individual fuel cell elements which are stacked on top of one another and are referred to as fuel cell stacks.

To generate reformate gas, such fuel cell systems are equipped with a reformer that generates the reformate gas from a fuel, usually a hydrocarbon such as diesel or natural gas, and from reformer air and/or from water vapor. The reformate gas then contains hydrogen gas and carbon monoxide. The fuel cell system can also be equipped with an air supply device, which draws in ambient air from an area surrounding the fuel cell system by means of an air conveying device and divides it into reformer air and cathode air, for example. The reformer air can then be fed to the reformer via a reformer air line, while the cathode air can be fed to a cathode side of the at least one fuel cell via a cathode air line.

In a fuel cell system of this type, it is usually provided to conduct anode gas from an anode side of the at least one fuel cell in the direction of the reformer with the aid of a recirculation line, in order to be able to return anode waste gas from the respective fuel cell to the reformer. To drive the anode waste gas, a gas conveying device for conveying hot anode waste gas is usually arranged in the recirculation line, with a recirculation pump or an anode gas blower usually being used for this purpose.

Furthermore, various variants of the fuel supply to the anode of a fuel cell are already known. The gas conveying device is usually arranged in an anode gas circuit upstream of the reformer. Thus, the anode feed gas, ie the mixture of recirculated anode waste gas and fuel fed in, is further mixed in the gas conveying device and fed from it to the downstream reformer. It is necessary to achieve high anode inlet temperatures in order to prevent thermal stresses from developing in the fuel cell or in a fuel cell stack. Conversely, in the case of the gas delivery device required for the recirculation of the anode gas, it must be ensured that the inlet temperature of the anode gas into the gas delivery device does not become too high, in order to prevent damage and to ensure proper operation of the gas delivery device.

US 2011/0 111 314 A1 relates to a method according to the preamble of claim 1.

The disadvantage of the previously known fuel cell systems is that, for reliable operation of the gas delivery device, the hot anode gas has to be cooled or the gas delivery device has to be cooled separately, and the anode gas, which is mixed with a fuel and fed to the reformer as anode feed gas, is therefore too cold for the reformation is. This is why the anode feed gas has to be reheated before the reformer or the reformer has to be heated with an external heater, which is costly and energetically unfavorable.

It is therefore the object of the present invention to specify a method for operating a fuel cell system with a fuel which avoids the disadvantages of the prior art described and in which proper and energy-optimized operation of the fuel cell system is ensured. Furthermore, it is the object of the present invention to provide corresponding devices for operating such a fuel cell system with one fuel.

The first-mentioned object of the invention relates to a method for operating a generic fuel cell system with a fuel, which fuel cell system comprises at least one high-temperature fuel cell with at least one cathode arranged in a cathode compartment, with at least one anode arranged in an anode compartment and with an electrolyte present between the cathode compartment and the anode compartment, wherein mixed with fuel in an anode gas circuit from the anode space of the at least one high-temperature fuel cell and fed as anode feed gas with at least one gas delivery device to an anode gas heat exchanger, in which the anode feed gas is thermostated, with the fuel also being reformed in at least one reforming unit in the anode gas circuit, is thereby solved that the at least one reforming unit is arranged in a hot circuit section of the anode gas circuit, in which hot circuit section an anode gas temperature above the equilibrium temperature required in the reforming unit is reached during fuel cell operation, and the at least one gas conveying device is arranged in a cool circuit section of the anode gas circuit, in which cooling Circuit section in fuel cell operation, an anode gas temperature below the temperature prevailing in the hot circuit section is reached, the at least one reforming unit comprising a catalytic reformer heat exchanger in which the fuel is reformed, the reformer heat exchanger being combined with the anode gas heat exchanger to form a common component and in an anode feed gas line in front of the anode chamber is arranged, wherein a cold heat exchanger side and/or a hot heat exchanger side is/are coupled to the reformer heat exchanger and fuel to be reformed is hot anode exhaust gas in an anode gas discharge line on the hot heat exchanger side upstream of the anode gas heat exchanger and/or the recirculated anode exhaust gas in a recirculation line on the cold heat exchanger side is or are supplied before the anode gas heat exchanger.

With the method according to the invention, the conflicting goals that usually occur with anode recirculation, namely ensuring the highest possible anode inlet temperatures in the fuel cells in order to prevent or reduce thermal stresses and at the same time keep the anode gas inlet temperature in a gas conveying device, for example an anode gas blower, as low as possible in order to To protect the material of the gas conveying device and to achieve a higher conveying capacity or greater conveying efficiency, be solved together. Furthermore, when using the reformer, it is ensured that the operating temperatures of at least 500°C required for reforming are achieved without external heating, since the reformer is arranged in a hot circuit section in which the equilibrium temperature of around 470°C required for reforming is exceeded . The desired anode gas composition for the anode reaction in the anode compartment of the high-temperature fuel cell is thus advantageously achieved without having to heat the reformer externally.

Described subclaims and the description.

Particularly advantageously, a reformate gas as a mixture of carbon monoxide and hydrogen can be produced in a method according to the invention in the at least one reforming unit by endothermic steam reforming from a carbonaceous mixture containing the fuel and the recirculated anode waste gas.

Steam reforming is a process for producing synthesis gas or reformate gas, a mixture of carbon monoxide and hydrogen from carbonaceous energy carriers such as natural gas, light petroleum, methanol, biogas or biomass. Steam reforming is an allothermal process that converts methane and water vapor to form carbon monoxide and hydrogen, and works according to the following equation: CH ₄ + H ₂ O ▼ CO + 3 H ₂

To increase the hydrogen yield, the resulting carbon monoxide can be converted into carbon dioxide and additional hydrogen in a further reaction, the water-gas shift reaction: CO + _H2O ▼ _CO2 + _H2

To do this, hot water vapor is mixed with the gas to be reformed (e.g. natural gas) or with vaporized liquid (e.g. light petrol) and reacted in the gas phase over a heterogeneous catalyst with a constant supply of energy.

In a method according to the invention, it can be particularly expedient for the anode gas temperature in the hot circuit section of the anode gas circuit, in which the at least one reforming unit is arranged, to be at least 500° C., preferably at least 550° C., particularly preferably at least 600° C. In this process variant, the anode gas temperature in the hot circuit section is sufficient to heat the reforming unit arranged there and to ensure the required temperature for reforming the fuel.

It can also be advantageous in a method according to the invention that the anode gas temperature in the cool circuit section of the anode gas circuit, in which the at least one gas conveying device is arranged, is at most 470° C., preferably at most 450° C., particularly preferably at most 400° C. In particular when the gas delivery device is an anode gas fan, for example, the efficiency of the fan is increased at the comparatively lower temperatures in the cool circuit section of the anode gas circuit. As the temperature decreases, the density of the gas increases and less fan power is required to convey the same mass flow. This advantageously lengthens the service life of the gas conveying device.

In one variant, in a method the at least one reforming unit can comprise a reformer which is arranged in the anode gas circuit in the recirculation line downstream after the anode gas heat exchanger and upstream before the gas conveying device, with the fuel to be reformed being the hot anode waste gas in the anode gas discharge line before the anode gas heat exchanger and/or is or are fed to the anode recycle gas in the recirculation line before the reformer.

In this variant, the otherwise necessary long recirculation section of the anode gas circuit can be saved by arranging the reformer directly after the anode gas heat exchanger or immediately downstream after a T-shaped branching of the anode exhaust gas line on the one hand in the anode gas supply line and on the other hand in the exhaust gas line. In this variant, the reformer is advantageously no longer additionally heated. In addition, the gas conveying device, for example the anode fan, is also arranged downstream of the reformer. The supply of fuel - preferably natural gas is used as fuel - takes place, for example, the hot anode exhaust gas in the anode gas discharge line before the anode gas heat exchanger. This comparatively early admixture of the fuel into the anode gas circuit upstream in front of the reformer via the line section to the reformer advantageously enables thorough mixing with the anode waste gas. However, with this type of admixture, part of the fuel also flows into the exhaust pipe and does not reach the reformer.

As an alternative or in addition to the admixing of the fuel in the anode gas discharge line, the fuel can also be fed to the anode recycle gas in the recirculation line upstream of the reformer. The entire admixed fuel thus advantageously reaches the reformer. However, it should be noted that the reformer inlet temperature of the anode train gas is somewhat lower due to the admixture of the cooler natural gas.

Another advantage of this variant of the process is that the heat losses associated with it can also be significantly reduced by eliminating the reformer heating. The heat that remains as a result is available on the cathode side for preheating the air. This results in a higher cathode inlet temperature, which is an essential variable in the thermal management of a fuel cell system.

The temperature level in the recirculation line of the anode gas is lower with temperatures below 300° C., for example, so the heat losses are also lower. The lower inlet temperature level at the gas conveying device or at the anode gas fan leads to a higher efficiency of the fan. In addition, as a result, less cooling capacity is required for the anode gas fan and its thermal stress is reduced, which allows longer, trouble-free operation of the gas conveying device.

Due to the higher reformer inlet temperature, no additional external reformer heating or pipes or controllable throttle valves are required. The entry temperature of the anode feed gas into the reformer is higher and sufficient to reach the equilibrium temperature. Due to the lack of reformer heating the temperature level in the anode circuit drops. Although this can lead to lower anode gas inlet temperatures, which under certain circumstances can be critical for the high-temperature fuel cell due to thermal stresses, this effect is compensated for by the reduced heat losses in the recirculation line.

The variant of the method according to the invention differs from the variants mentioned above in that the reforming unit and the anode gas heat exchanger are combined to form a common component. This achieves a higher reformer inlet temperature. At the same time, both paths of the anode gas heat exchanger, ie the cold heat exchanger side and the hot heat exchanger side, can be designed as reformers, which means that more reformer surface is available and the combination component can be made smaller. However, either only the path of the cold heat exchanger side or only the path of the hot heat exchanger side can be designed in a reforming manner or be coupled to the reformer heat exchanger.

The anode gas inlet temperature in the gas conveying device is lower, with the previously described advantages of less wear and tear as well as higher conveying efficiency and a lower cooling capacity required. Furthermore, due to the lower pressure loss that occurs, the required drive power of the gas conveying device is lower. The recirculation line can be made comparatively short and the temperature of the medium flowing in it is low, which advantageously results in only low waste heat losses via the recirculation line.

In a development, in a method variant, the catalytic reformer heat exchanger can be integrated in the anode gas heat exchanger, with the cold heat exchanger side and/or the hot heat exchanger side being designed to reform the fuel catalytically.

In a further alternative embodiment, the at least one reforming unit in a method according to the invention can comprise at least one catalytic reformer anode which is arranged in the anode space of the high-temperature fuel cell, the fuel being fed to the recirculation line of the anode gas cycle and being reformed in the anode space. A reformer can advantageously be omitted in this variant of the method according to the invention. Due to the catalytic activity of a catalytic reformer anode, the anode feed gas can also be reformed completely in the anode compartment of the high-temperature fuel cell.

In a preferred development of the invention, the anode of the high-temperature fuel cell can be designed as a catalytic reformer anode in a method. Due to the catalytic activity of the fuel cell anode, the reforming can also take place completely at the anode of the high-temperature fuel cell. It should be noted that due to the endothermic reforming reaction, high thermal stresses can occur at the anode. Furthermore, fuel contaminants such as sulfur can impair the catalytic activity of the reformer anode. Through the use of particularly robust reformer anodes, which are largely inert to catalyst poisons in the anode feed gas or the fuel, a sufficient service life for the operation of the high-temperature fuel cell can also be ensured in this process variant.

In a method according to the invention, a plurality of reforming units of the same or different design can expediently be arranged in each case in hot circuit sections of the anode gas circuit. For example, within the scope of the method according to the invention, a reformer, a catalytic reformer heat exchanger and/or a catalytic reformer anode, which is arranged in the anode chamber of the high-temperature fuel cell, can be used together in the anode circuit and each have a reforming effect.

The above-mentioned object of the present invention, to provide corresponding devices for operating a generic fuel cell system with a fuel, which fuel cell system has at least one high-temperature fuel cell with at least one cathode arranged in a cathode compartment, with at least one anode arranged in an anode compartment and with an existing one between the cathode compartment and the anode compartment Electrolytes, wherein a fuel supply line for adding fuel to the anode gas opens into an anode gas circuit for returning anode exhaust gas from the anode chamber, wherein at least one gas conveying device for conveying the mixture as anode feed gas into an anode gas heat exchanger, which is connected into the anode gas circuit, is provided, and which Fuel cell system further comprises at least one reforming unit for reforming the fuel in the anode gas circuit, is solved by a device, in which device the at least one reforming unit is arranged in a hot circuit section of the anode gas circuit, in which hot circuit section during operation of the fuel cell system an anode gas temperature is above that in the reforming unit required equilibrium temperature is set and the at least one gas conveying device is arranged in a cool circuit section of the anode gas circuit, in which cool circuit section an anode gas temperature is set during operation of the fuel cell system below the anode gas temperature prevailing in the hot circuit section, wherein the at least one reforming unit comprises a catalytic reformer heat exchanger, wherein the reformer heat exchanger is combined with the anode gas heat exchanger or is integrated into this and in one

Anode feed gas line is arranged upstream of the anode chamber, with a cold heat exchanger side and/or a hot heat exchanger side being designed to be catalytically reforming or coupled to the reformer heat exchanger and the fuel supply line opening into an anode gas discharge line upstream of the anode gas heat exchanger and/or into a recirculation line upstream of the reformer heat exchanger.

The advantages and effects mentioned above for the different methods according to the invention also apply analogously to the corresponding devices for operating a generic fuel cell system with one fuel.

In a device according to the invention, the at least one reforming unit can advantageously be designed for endothermic steam reforming, with the anode gas temperature in the hot circuit section of the anode gas circuit in which the at least one reforming unit is arranged being at least 500° C., preferably at least 550° C., particularly preferably at least 600°C.

In a device, at least one reforming unit can expediently comprise a reformer, which is arranged in the anode gas circuit in the recirculation line downstream after the anode gas heat exchanger and upstream before the gas conveying device, with the fuel feed line opening into the anode gas discharge line before the anode gas heat exchanger and/or into the recirculation line before the reformer.

In one variant, the at least one reforming unit in a device can comprise at least one catalytic reformer anode, which is arranged in the anode chamber of the high-temperature fuel cell, with the anode of the high-temperature fuel cell preferably being designed as a catalytic reformer anode, with the fuel supply line opening into the recirculation line of the anode gas circuit.

According to the invention, different variants of the anode gas circuit or different configurations of the arrangement of reforming unit/gas conveying device/anode gas heat exchanger are possible, as is also explained in the following description of the figures.

In principle, at least one reforming unit is provided in all variants of both the method and the device for operating the generic fuel cell system, which can also be combined with other components, for example as a catalytic reformer heat exchanger or as a catalytic reformer anode. A reforming unit is necessary to ensure the desired anode gas composition or to prevent uncontrolled reforming from occurring in the fuel cell, which due to its endothermic character could lead to thermal stresses and thus damage to the fuel cell.

• - 1 ein Brennstoffzellensystem gemäß dem bekannten Stand der Technik, bei dem in einem Anodengaskreislauf stromaufwärts eines Reformers eine Gasfördereinrichtung angeordnet ist;
• - 2 in einer Detailansicht von 1 den Anodengaskreislauf gemäß dem Stand der Technik;
• - 3 den Anodengaskreislauf eines Brennstoffzellensystems gemäß einer ersten Variante, wobei die Reformierungseinheit einen Reformer umfasst, der im Anodengaskreislauf in der Rezirkulationsleitung stromabwärts nach einem Anodengaswärmeübertrager sowie stromaufwärts vor einer Gasfördereinrichtung angeordnet ist, wobei der zu reformierende Brennstoff dem heißen Anodenabgas in der Anodenabgasleitung vor dem Anodengaswärmeübertrager zugeführt wird;
• - 4 den Anodengaskreislauf eines Brennstoffzellensystems gemäß einer zweiten Variante, wobei ein Reformer im Anodengaskreislauf in der Rezirkulationsleitung stromabwärts nach einem Anodengaswärmeübertrager sowie stromaufwärts vor einer Gasfördereinrichtung angeordnet ist, wobei der zu reformierende Brennstoff dem rückgeführten Anodenabgas in der Rezirkulationsleitung vor dem Reformer zugeführt wird;
• - 5 den Anodengaskreislauf eines Brennstoffzellensystems gemäß einer dritten Variante, wobei die Reformierungseinheit einen katalytischen Reformerwärmeübertrager umfasst, in dem der Brennstoff reformiert wird, wobei der Reformerwärmeübertrager mit dem Anodengaswärmeübertrager kombiniert oder in diesen integriert ist;
• - 6 den Anodengaskreislauf eines Brennstoffzellensystems gemäß einer vierten Variante, wobei die Reformierungseinheit eine katalytische Reformeranode umfasst, die im Anodenraum der Hochtemperaturbrennstoffzelle angeordnet ist;
• - 7 den in 3 dargestellten Anodengaskreislauf eines Brennstoffzellensystems während des Anfahrens des Brennstoffzellensystems.

Further details, features and advantages of the invention result from the following explanation of non-limiting exemplary embodiments which are each shown schematically in the drawings. The following statements relating to the descriptions of the figures relate both to methods and to devices for operating a fuel cell system. The drawings show in representations as a simplified process flow diagram:

• - 1 a fuel cell system according to the known prior art, in which a gas delivery device is arranged in an anode gas circuit upstream of a reformer;
• - 2 in a detailed view of 1 the anode gas circuit according to the prior art;
• - 3 the anode gas circuit of a fuel cell system according to a first variant, the reforming unit comprising a reformer which is arranged in the anode gas circuit in the recirculation line downstream after an anode gas heat exchanger and upstream before a gas conveying device, the fuel to be reformed being fed to the hot anode exhaust gas in the anode exhaust gas line before the anode gas heat exchanger ;
• - 4 the anode gas circuit of a fuel cell system according to a second variant, wherein a reformer is arranged in the anode gas circuit in the recirculation line downstream of an anode gas heat exchanger and upstream of a gas delivery device, wherein the to be reformed fuel is added to the recirculated anode off-gas in the recirculation line before the reformer;
• - 5 the anode gas circuit of a fuel cell system according to a third variant, wherein the reforming unit comprises a catalytic reformer heat exchanger in which the fuel is reformed, wherein the reformer heat exchanger is combined with the anode gas heat exchanger or is integrated into it;
• - 6 the anode gas circuit of a fuel cell system according to a fourth variant, the reforming unit comprising a catalytic reformer anode which is arranged in the anode chamber of the high-temperature fuel cell;
• - 7 the in 3 illustrated anode gas circuit of a fuel cell system during start-up of the fuel cell system.

An example is in 1 a known fuel cell system 1 with a so-called solid oxide fuel cell 10 (English: Solid Oxide Fuel Cell, SOFC) is shown. This is a high-temperature fuel cell 10 that is operated at operating temperatures of approximately 650.degree. C. to 1000.degree. The electrolyte 15 of this type of cell consists of a solid ceramic material which is able to conduct oxygen ions but has an insulating effect on electrons. Electrodes, cathode 11 and anode 13, are attached to both sides of the electrolyte layer 15 . They are gas-permeable electrical conductors. The oxygen-ion-conducting electrolyte 15 is provided, for example, as a thin membrane in order to be able to transport the oxygen ions with little energy. It only works at the prevailing high temperatures. The outer side of the cathode 11 facing away from the electrolyte is surrounded by air, and the outer anode side 13 by fuel gas. Unused air and fuel gas as well as combustion products are extracted.

Solid oxide fuel cells 10 are galvanic cells for continuous electrochemical power generation, which are usually operated as fuel cell stacks, so-called SOFC stacks, ie as a combination of several high-temperature fuel cells 10 . For a better overview, in 1 only a single high temperature fuel cell 10 is illustrated. The function of every galvanic cell and every electrochemical reaction in general is based on a redox reaction, in which reduction and oxidation take place separately, namely at the interface between the electrode and the electrolyte. In the solid oxide fuel cell 10, this redox reaction is a reaction of oxygen with the fuel, which can be hydrogen, but here also contains carbon monoxide, for example. On the cathode side 12 there is an excess of oxygen, while on the anode side 14 there is a lack of oxygen because the oxygen present reacts immediately with the hydrogen present, for example. Owing to this concentration gradient, oxygen 19 diffuses from the cathode 11 through the electrolyte 15 to the anode 13. However, the electrolyte 15 in between is only permeable to oxygen ions.

Once the oxygen molecule has reached the interface between the cathode and the electrolyte, it accepts two electrons, becoming an ion and can penetrate the barrier. Arrived at the boundary to the anode 13, it reacts catalytically with the fuel gas, giving off heat and the corresponding combustion products, and again gives off two electrons to the anode. The prerequisite for this is a current flow - the actual purpose of the high-temperature fuel cell - whereby the current flow can be used for other purposes.

According to the 1 In the variant shown, an anode gas circuit 20 is provided, which is also described in detail in 2 is shown. In the anode gas cycle 20, the high -temperature fuel cell 10 in an anode emission line 21 Hot anode exhaust gas 22 is promoted to an anodegas heat transformer 70, whereby the anodeling exhaust gas 22 in anode gas heat transfer, which is preferably operated in the counter -current, is somewhat cooled and in the anodeling 21 Gas heat exchanger 70 as hot anode exhaust gas 23 leaves again. Part of the hot anode waste gas 23 enters a recirculation line 24 at a circuit branch that is T-shaped here and is returned there as anode recycle gas 25 or as recirculated anode waste gas 25 in the anode gas circuit 20 and with fresh fuel 27 from a fuel supply line 26, which is fed into the anode gas circuit 20 flows, mixed.

The mixture of recirculated anode waste gas 25 and fresh fuel 27, the anode feed gas 29, is now fed in an anode gas supply line 28 with a gas conveying device 50, which is designed here as an anode gas blower 50, to a reforming unit 60 with a reformer 61 that follows upstream of the anode gas blower 50. Furthermore, a water vapor line which is fed by an evaporator 90 and with which water vapor 91 can be injected opens into the anode gas feed line 28 . After the reforming step in the reformer 61, the anode feed gas 29 leaves this as reformed anode feed gas 30 and arrives in an anode feed gas line 31 in the anode gas heat exchanger 70, is absorbed in this heats and is supplied to the anode compartment 14 as hot anode feed gas 32 . Part of the hot anode waste gas 23 is not recirculated, but is discharged from the anode gas circuit 20 in a waste gas line 33 and leaves it as waste gas 34.

A pressure measuring device 40, for example a Venturi tube 40, is installed in the recirculation line 24 in order to measure the flow in the anode gas circuit 20 by means of differential pressure measurement. This pressure gauge 40 is optional and can also be omitted. Natural gas (NG) is fed into the anode gas circuit 20 as the fuel 27 here. The anode gas recirculation is maintained with the anode gas blower 50 arranged upstream of the reformer 61 . The anode gas heat exchanger 70 is arranged between the reformer 61 and the anode space 14 . As in 2 as can be seen, the path of the anode feed gas 30, 32 to be heated, which is supplied to the anode chamber 14, forms a cold heat exchanger side 71, which flows from the hot anode exhaust gas 22, 23 that flows in the anode exhaust gas line 21 from the anode chamber 14 and a hot heat exchanger side 72 of the anode gas heat exchanger 70 forms, is heated.

in the in 1 In the variant shown, the reformer 61 is heated by hot exhaust gas 86 from the burner, which comes from a catalytic afterburner 80 or from a burner 85 as exhaust gas. Further are in 1 a supply air line 35 for supplying supply air 36 by means of an air blower 37 together with an air preheater 38 and corresponding valves 45, for example throttle valves 45, in the lines. The gas delivery device 50 or the anode gas blower 50 is provided with a cooling device 51 which serves to cool the bearing and motor of the gas delivery device 50 . Due to the cooling 51 required for the operation of the anode gas fan 50, however, there is a significant cooling of the anode recirculation gas between the entry and exit of the anode gas fan 50. This cooling in the anode gas feed line 28 to a temperature here of around 400° C. causes the temperature to fall below that in the upstream the anode gas blower 50 downstream reformer 61 at least required equilibrium temperature of about 470 ° C to start the reforming reaction.

For this reason, or in order to substitute the reforming reaction temperature of at least 500° C. required on the input side at the reformer 61 , the reformer 61 must also be heated with burner exhaust gas 86 , which then leaves the system 1 as cooled burner exhaust gas 87 . Another disadvantage of the 1 and 2 The process variant shown results - in addition to the anode gas cooling required for the operation of the anode gas fan 50 and the subsequent additional heating of the reformer 61 - due to additional heat losses 100 in the comparatively long recirculation line 24 between the anode gas heat exchanger 70 and the anode gas fan 50.

3 illustrates the anode gas circuit 20 of a fuel cell system 1 according to a first variant, the reforming unit 60 comprising a reformer 61 which is arranged in the anode gas circuit 20 in the recirculation line 24 downstream after an anode gas heat exchanger 70 and upstream before a gas conveying device 50. The fuel 26 to be reformed is fed to the hot anode exhaust gas 22 in the anode exhaust gas line 21 before the anode gas heat exchanger 70 . The fuel supply is symbolized by an arrow 27 . The anode gas temperature 200 in a hot circuit section 210 of the anode gas circuit 20, in which the reforming unit 60 is arranged, is 560° C. here, for example.

The anode gas temperature 200 in a cool circuit section 220 of the anode gas circuit 20, which follows the hot circuit section 210 in the downstream direction and in which the gas conveying device 50 is arranged, is at most 470° C. here. The anode gas temperature 200 after the anode gas blower 50 is 270° C. here and is further cooled in the anode gas feed line 31, which is why the anode feed gas 30 has an anode gas temperature 200 of around 250° C. on the cold heat exchanger side 71 before the anode gas heat exchanger 70. The anode feed gas 32 is heated as it passes through the comparatively cold heat exchanger side 71 and has an anode gas temperature 200 of 700° C. after the anode gas heat exchanger 70 , at which the heated anode feed gas 32 reaches the anode space 14 . When the anode gas emerges from the anode chamber of the high-temperature fuel cell 10, the anode gas temperature 200 in the anode exhaust gas line 21 is approximately 820° C. here. The anode feed gas 29, which enters the anode gas heat exchanger 70 here with an anode gas temperature 200 of around 800° C., thus forms its hot heat exchanger side 72.

After passing through the comparatively hot heat exchanger side 72 of the anode gas heat exchanger 70, the anode gas temperature 200 of the anode feed gas 29 upstream of the reformer 60 is approximately 560° C. here. As in here 3 illustrated, no additional heating of the reforming unit 60 is required in this device of a fuel cell system 1 .

4 shows the anode gas circuit 20 of a fuel cell system 1 according to a second variant, the reforming unit 60 comprising a reformer 61 which is arranged here in the anode gas circuit 20 in the recirculation line 24 downstream after an anode gas heat exchanger 70 and upstream before a gas conveying device 50. The reformer 61 is therefore arranged in the anode gas circuit 20 between the upstream anode gas heat exchanger 70 and the downstream gas conveying device 50 . Deviating from the in 3 shown variant is here in 4 the fuel 26 to be reformed is fed to the recirculated anode waste gas 29 in the recirculation line 24 directly before the reformer 61 . The fuel supply is symbolized by an arrow 27 .

5 illustrates the anode gas circuit 20 of a fuel cell system 1 according to a third variant, the reforming unit 60 here comprising a catalytic reformer heat exchanger 62 in which the fuel is reformed, the reformer heat exchanger 62 being combined with the anode gas heat exchanger 70 or integrated into it. According to the previous illustrations 3 or. 4 it is also at the in 5 shown variant possible to provide the fuel supply 27 with fuel 26 to be reformed either in the anode exhaust gas line 21 before the anode gas heat exchanger 70, wherein the fuel 26 is the hot anode exhaust gas 22 is supplied. Or the fuel feed 27 is arranged in such a way that the fuel 26 is mixed into the anode feed gas line 31 just before the gas conveying device 50 . This alternative variant of the fuel supply 27 is in 5 drawn in dashed. It is also possible to implement the fuel supply 27 at a number of points in the fuel cell system 1 .

It is particularly advantageous here at the in 5 Variant shown that in the catalytic reformer heat exchanger 62, the reforming unit 60 and the anode gas heat exchanger 70 are combined to form a common component. The reformer heat exchanger 62 is arranged in the hot circuit section 210 of the anode gas circuit. The anode gas temperature 200 in the hot circuit section 210 of the anode gas circuit 20, in which the reformer heat exchanger 62 is arranged, is 800° C. here, for example. The anode gas temperature 200 in a cool circuit section 220 of the anode gas circuit 20, which follows the hot circuit section 210 in the downstream direction and in which the gas conveying device 50 is arranged, is at most 450° C. here.

The anode gas temperature 200 after the anode gas blower 50 is 270° C. here and is further cooled in the anode gas feed line 31, which is why the anode feed gas 30 has an anode gas temperature 200 of around 250° C. on the cold heat exchanger side 71 before the anode gas heat exchanger 70. The anode feed gas 32 is heated as it passes through the comparatively cold heat exchanger side 71 and has an anode gas temperature 200 of 700° C. after the anode gas heat exchanger 70 , at which the heated anode feed gas 32 reaches the anode space 14 . When the anode gas emerges from the anode chamber of the high-temperature fuel cell 10, the anode gas temperature 200 in the anode exhaust gas line 21 is approximately 820° C. here. The anode feed gas 29, which enters the anode gas heat exchanger 70 here with an anode gas temperature 200 of around 800° C., thus forms its hot heat exchanger side 72.

After passing through the comparatively hot heat exchanger side 72 of the reformer heat exchanger 62, the anode gas temperature 200 of the anode feed gas 29 downstream of the reformer 60 is approximately 470° C. here. As in 5 illustrated, no additional heating of the reforming unit 60 is required in this device of a fuel cell system 1 either.

6 shows the anode gas circuit 20 of a fuel cell system 1 according to a fourth variant, the reforming unit 60 comprising a catalytic reformer anode 63 which is arranged in the anode space 14 of the high-temperature fuel cell 10 . The fuel 27 is fed to the anode gas circuit 20 or the recirculation line 24 before the anode gas blower 50 . The anode gas fan 50 is located in a cool circuit section 220 of the anode gas circuit 20.

The temperature 200 of the anode feed gas 29 before the anode gas fan 50 is approximately 340° C. and drops to a temperature 200 of approximately 300° C. after the anode gas fan 50 . The anode feed gas 30 thus enters the anode gas heat exchanger 70 at around 300° C. on the cold heat exchanger side 71 . The anode feed gas 32 is heated as it passes through the comparatively cold heat exchanger side 71 and, downstream from the anode gas heat exchanger 70 , has an anode gas temperature 200 of approximately 780° C., for example, at which the heated anode feed gas 32 reaches the anode space 14 . The reforming takes place at the catalytic reformer anode 63. When the reformed anode gas exits the anode chamber 14 of the high-temperature fuel cell 10, the anode gas temperature 200 in the anode exhaust gas line 21 is about 820° C. here, for example.

The anode chamber 14, together with the catalytic reformer anode 63 arranged therein, is located in the hot circuit section 210 of the anode gas circuit 20. The hot anode waste gas 22, which enters the anode gas heat exchanger 70 here with an anode gas temperature 200 of around 800° C., thus forms its hot heat exchanger side 72 Passing through the comparatively hot heat exchanger side 72 of the anode gas heat exchanger 70, the anode gas temperature 200 of the anode exhaust gas 23 or of the anode recycle gas 25 is approximately 360° C. here. As in 6 illustrated, no additional heating of the reforming unit 60 is required in this device of a fuel cell system 1 either.

7 shows the in 3 illustrated anode gas circuit 20 of a fuel cell system 1 during the start-up of the fuel cell system 1. In certain operating phases of the fuel cell system 1, it may be necessary to supply water vapor externally to the system 1, since the anode gas recirculation, for example, in start-up, standby or part-load operation or insufficient water vapor is returned.

In order to prevent this, water vapor previously had to be generated in an evaporator heat exchanger and, if necessary, fed to the system, which, however, results in additional investment and operating costs as well as undesirable pressure losses due to the large number of conditioning devices required.

In 7 An alternative embodiment is therefore shown, with a water injection 110 being provided here, with the water 111, preferably under pressure, being injected through an injection nozzle into the anode gas stream and being vaporized directly in the process. The water 111 is injected here at a temperature 200 of around 95° C. into the anode feed gas line 32 after the anode gas heat exchanger 70, the anode feed gas 32 having an anode gas temperature 200 of about 140° C. and being cooled to about 100° C. by the water 111 that is injected , before the anode gas 32 enters the anode chamber 14. In contrast to the previously known state of the art, in which water vapor is supplied to the system, the spraying or injecting of water is much easier and cheaper to implement in terms of apparatus.

Claims (9)

Method for operating a fuel cell system (1) with a fuel (27), which fuel cell system (1) has at least one high-temperature fuel cell (10) with at least one cathode (11) arranged in a cathode chamber (12), with at least one cathode (11) arranged in an anode chamber (14) arranged anode (13) and with an electrolyte (15) present between the cathode compartment (12) and the anode compartment (14), wherein in an anode gas circuit (20) from the anode compartment (14) of the at least one high-temperature fuel cell (10) recirculated anode waste gas (25) mixed with fuel (27) and fed as anode feed gas (30) with at least one gas conveying device (50) to an anode gas heat exchanger (70), in which the anode feed gas (30) is thermostated, with further in at least one reforming unit (60, 61) in the anode gas circuit (20) the fuel (27) is reformed, characterized in that the at least one reforming unit (60, 61, 62, 63) is arranged in a hot circuit section (210) of the anode gas circuit (20), in which hot circuit section (210) during fuel cell operation, an anode gas temperature (200) above the equilibrium temperature required in the reforming unit (60, 61, 62, 63) is reached, and the at least one gas delivery device (50) is arranged in a cool circuit section (220) of the anode gas circuit (20), in which cool circuit section (220) in fuel cell operation an anode gas temperature (200) below the anode gas temperature (200) prevailing in the hot circuit section (210) is reached, wherein the at least one reforming unit (60) comprises a catalytic reformer heat exchanger (62) in which the fuel ( 27) is reformed, with the reformer heat exchanger (62) being combined with the anode gas heat exchanger (70) to form a common component and being arranged in an anode feed gas line (31) upstream of the anode chamber (14), with a cold heat exchanger side (71) and/or a hot heat exchanger side (72) is or are coupled to the reformer heat exchanger (62) and fuel (27) to be reformed hot anode waste gas (22) in an anode gas discharge line (21) on the hot heat exchanger side (72) before the anode gas heat exchanger (70) and/or the recirculated anode exhaust gas (25) in a recirculation line (24) on the cold heat exchanger side (71) before the anode gas heat exchanger (70) is or are supplied. procedure after claim 1 , characterized in that in the at least one reforming unit (60, 61, 62, 63) a reformate gas as a mixture of carbon monoxide and hydrogen is produced by endothermic steam reforming from a carbon-containing mixture containing the fuel (27) and the recirculated anode waste gas (25). . procedure after claim 1 or 2 , characterized in that the anode gas temperature (200) in the hot circuit section (210) of the anode gas circuit (20), in which the at least one reforming unit (60, 61, 62, 63) is arranged, at least 500° C., preferably at least 550° C., particularly preferably at least 600° C , amounts to. Procedure according to one of Claims 1 until 3 , characterized in that the anode gas temperature (200) in the cool circuit section (220) of the anode gas circuit (20), in which the at least one gas conveying device (50) is arranged, is at most 470°C, preferably at most 450°C, particularly preferably at most 400° C, is. Procedure according to one of Claims 1 until 4 , characterized in that the at least one reforming unit (60) comprises at least one catalytic reformer anode (63) which is arranged in the anode chamber (14) of the high-temperature fuel cell (10), the fuel (27) of the recirculation line (24) of the anode gas circuit (20 ) is supplied and reformed in the anode compartment (14). procedure after claim 5 , characterized in that the anode (13) of the high-temperature fuel cell (10) is designed as a catalytic reformer anode (63). Procedure according to one of Claims 1 until 6 , characterized in that a plurality of reforming units (60, 61, 62, 63) of the same or different design are each arranged in hot circuit sections (210) of the anode gas circuit (20). Device for operating a fuel cell system (1) with a fuel (27), which fuel cell system (1) has at least one high-temperature fuel cell (10) with at least one cathode (11) arranged in a cathode chamber (12), with at least one cathode (11) arranged in an anode chamber (14) arranged anode (13) and with an electrolyte (15) present between the cathode compartment (12) and the anode compartment (14), wherein a fuel feed line (26) for adding fuel (27) to the recirculated anode gas (25), at least one gas conveying device (50) being provided for conveying the mixture as anode feed gas (30) into an anode gas heat exchanger (70), which is connected into the anode gas circuit (20). , which fuel cell system (1) further comprises at least one reforming unit (60, 61) for reforming the fuel (27) in the anode gas circuit, characterized in that the at least one reforming unit (60, 61, 62, 63) in a hot circuit section (210) of the anode gas circuit (20), in which hot circuit section (210) an anode gas temperature (200) above the equilibrium temperature required in the reforming unit (60, 61, 62, 63) is set during operation of the fuel cell system (1), and the at least one gas conveying device (50) is arranged in a cool circuit section (220) of the anode gas circuit (20), in which cool circuit section (220) during operation of the fuel cell system (1) an anode gas temperature (200) below the anode gas temperature (200) prevailing in the hot circuit section (210) is set, wherein the at least one reforming unit (60) comprises a catalytic reformer heat exchanger (62), wherein the reformer heat exchanger (62) is combined with the anode gas heat exchanger (70) to form a common component or is integrated into it and in an anode feed gas line (31) upstream of the anode space (14), wherein a cold heat exchanger side (71) and/or a hot heat exchanger side (72) is/are designed to be catalytically reforming or is/are coupled to the reformer heat exchanger (62) and the fuel supply line (26) leads into an anode gas discharge line (21) before the anode gas heat exchanger (70) and/or in a recirculation line (24) before the reformer heat exchanger (62). device after claim 8 , characterized in that the at least one reforming unit (60, 61, 62, 63) is designed for endothermic steam reforming, the anode gas temperature (200) in the hot circuit section (210) of the anode gas circuit (20) in which the at least one reforming unit ( 60, 61, 62, 63) is at least 500°C, preferably at least 550°C, particularly preferably at least 600°C.

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