DE102016223436A1 - Apparatus and method for operating a fuel cell system - Google Patents

Abstract

The invention relates to a method for operating a fuel cell system (1) with a fuel (27), which fuel cell system (1) at least one high-temperature fuel cell (10) having at least one in a cathode chamber (12) arranged cathode (11), with at least one in a Anodes (13) arranged anode space (14) and with a between cathode space (12) and anode space (14) existing electrolyte (15), wherein in an anode gas cycle (20) from the anode space (14) of at least one high-temperature fuel cell (10) recycled Anode exhaust gas (25) is mixed with fuel (27) and supplied as anode gas (30) with at least one gas conveyor (50) to an anode gas heat exchanger (70) in which the anode gas (31) is thermostated, wherein further in at least one reforming unit (60, 61) in the anode gas circuit (20) of the fuel (27) is reformed. The at least one reforming unit (60, 61, 62, 63) is disposed in a hot circulation section (210) of the anode gas loop (20) in which an anode gas temperature (200) is above that required in the reforming unit (60, 61, 62, 63) Equilibrium temperature is reached and the at least one gas conveyor (50) in a cool circuit section (220) of the Anodengaskreislaufs (20) is arranged, in which an anode gas temperature (200) below that in the hot circuit section (210) is reached.

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 disposed in a cathode compartment cathode, at least one arranged in an anode compartment anode and an existing between the cathode compartment and anode compartment electrolyte, wherein in an anode gas circulation from the anode space of the at least one high-temperature fuel cell recycled anode exhaust gas mixed with fuel and this mixture is fed as an anode gas with at least one gas conveyor an anode gas heat exchanger in which the anode gas is thermostated, wherein further reformed in at least one reforming unit in the anode gas cycle of the fuel. Likewise, devices for operating a fuel cell system with a fuel are specified in the context of the invention.

By a high-temperature fuel cell, the person skilled in the art understands, for example, a molten carbonate fuel cell (MCFC) which operates at operating temperatures of approximately from 580 ° C to 675 ° C. The electrolyte used in this type of fuel cell is usually an alkali metal carbonate mixed melt of lithium and potassium carbonate. Similarly, Solid Oxide Fuel Cells (SOFCs) are high temperature fuel cells. Solid oxide fuel cells are operated at operating temperatures of about 650 ° C to 1000 ° C.

The electrolyte of this cell type consists of a solid ceramic material capable of conducting oxygen ions but insulating for electrons. On both sides of the electrolyte layer are the electrodes, cathode and anode attached. 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 low energy, which, however, only works at the aforementioned high temperatures. The remote from the electrolyte, the outer side of the cathode is surrounded by air, the outer anode side of fuel gas. Unused air and unused fuel gas and combustion products are extracted.

Fuel cell systems, which are used in particular as auxiliary power supply devices in motor vehicles or as stationary systems or "stationary power plants", and which usually comprise at least one fuel cell for generating electric current from cathode air and reformate gas, are already known from the prior art. Such a fuel cell is usually composed of a plurality of individual fuel cell elements, which are stacked on each other and are referred to as a fuel cell stack.

For producing reformate gas, such fuel cell systems are equipped with a reformer which generates the reformate gas from a fuel, usually a hydrocarbon such as diesel or natural gas, and from reformer air and / or 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 sucks in ambient air by means of an air conveyor from an environment of the fuel cell system and subdivides these, for example, into reformer air and cathode air. The reformer air can then be supplied to the reformer via a reformer air line, while the cathode air can be supplied via a cathode air line to a cathode side of the at least one fuel cell.

Usually, in such a fuel cell system, it is provided to guide anode gas of an anode side of the at least one fuel cell in the direction of the reformer by means of a recirculation line so as to be able to recycle anode exhaust gas from the respective fuel cell to the reformer. For driving the anode exhaust gas, a gas delivery device for conveying hot anode exhaust gas is usually arranged in the recirculation line, wherein a recirculation pump or an anode gas blower is usually used for this purpose.

Furthermore, various variants of the fuel supply to the anode of a fuel cell are already known. Usually, the gas delivery device is arranged in an anode gas circulation upstream of the reformer. Thus, the Anodenzugas, so the mixture of recycled anode exhaust gas and fed fuel, further mixed in the gas conveyor and fed from this the downstream reformer. It is necessary to achieve high anode inlet temperatures in order to prevent the formation of thermal stresses in the fuel cell or in a fuel cell stack. Conversely, in the gas conveying device required for the recirculation of the anode gas, it should be noted that the inlet temperature of the anode gas into the gas conveying device does not become too high to prevent damage and to ensure proper operation of the gas conveying device.

A disadvantage of the fuel cell systems known hitherto is that the hot anode gas is cooled or the gas delivery device for safe operation of the gas delivery device must be cooled separately and thus the anode gas, which is mixed with a fuel and fed to the reformer as Anodenzugas too cold for the reforming. Why the anode gas must be reheated before the reformer or the reformer must be heated with an external heater, which is complicated and energetically unfavorable.

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

The first object according to the invention relates to a method for operating a generic fuel cell system with a fuel comprising fuel cell system at least one high-temperature fuel cell with at least one arranged in a cathode compartment cathode, at least one arranged in an anode compartment anode and an existing between the cathode compartment and anode compartment electrolyte in an anode gas cycle from the anode compartment of the at least one high-temperature fuel cell recycled anode exhaust gas mixed with fuel and is supplied as Anodenzugas with at least one gas conveyor an anode gas heat exchanger in which the anode gas is thermostated, wherein further reformed in at least one reforming unit in the Anodengaskreislauf the fuel, is achieved in that the at least one reforming unit is arranged in a hot circulation section of the anode gas cycle is in which hot cycle section in fuel cell operation, an anode gas temperature above the equilibrium temperature required in the reforming unit is reached, and the at least one gas conveyor is arranged in a cool circuit section of the Anodengaskreislaufs in which cool circuit section in fuel cell operation reaches an anode gas temperature below the prevailing in the hot circuit section temperature becomes.

With the method according to the invention, the target conflicts usually occurring in an anode recirculation, namely to prevent or reduce thermoelectric voltages in the fuel cells as possible, and at the same time keep the Anodengaseintrittstemperatur in a gas conveying device, such as an anode gas blower, as low as possible To save material of the gas conveyor and to achieve a higher flow rate or greater delivery efficiency, be solved together. Furthermore, it is ensured for the reformer use that required for the reforming operating temperatures of at least 500 ° C are achieved without external heating, since the reformer is placed in a hot cycle section in which the required for the reforming equilibrium temperature of about 470 ° C is exceeded , Thus, advantageously, the desired anode gas composition for the anode reaction in the anode compartment of the high-temperature fuel cell is achieved without having to externally heat the reformer.

Advantageous further refinements and developments of the invention are set forth in the subclaims and the description.

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

Steam reforming is a process for the production of synthesis gas or reformate gas, a mixture of carbon monoxide and hydrogen from carbonaceous energy sources such as natural gas, light gasoline, methanol, biogas or biomass. Steam reforming is an all-thermal process in which methane and water vapor are converted to carbon monoxide and hydrogen, and runs according to the following equation: CH ₄ + H ₂ O⇆CO + 3H ₂

In order to increase the hydrogen yield, the resulting carbon monoxide can be converted into carbon dioxide and further hydrogen in a further reaction, the water gas shift reaction: CO + H ₂ O ⇆ CO ₂ + H ₂

For this purpose, hot steam is mixed with the gas to be reformed (for example natural gas) or with vaporized liquid (for example mineral spirits) and reacted with constant supply of energy to a heterogeneous catalyst in the gas phase.

It may be particularly useful in a method according to the invention that the anode gas temperature in the hot cycle section of the anode gas cycle, in which the at least a reforming unit is arranged, at least 500 ° C, preferably at least 550 ° C, more preferably at least 600 ° C, is. In this process variant, the anode gas temperature in the hot cycle section is sufficient to heat the reforming unit arranged there and to ensure the required temperature for the reforming of the fuel.

Also advantageous in a method according to the invention may be that the anode gas temperature in the cool circulation section of the anode gas circulation, in which the at least one gas conveyor is arranged at most 470 ° C, preferably at most 450 ° C, more preferably at most 400 ° C. In particular, if the gas delivery device is, for example, an anode gas blower, the efficiency of the blower is increased at the comparatively lower temperatures in the cool circulation section of the anode gas circulation. As the temperature decreases, the density of the gas increases and less fan power is needed to deliver the same mass flow. The service life of the gas conveyor is thereby advantageously extended.

In a preferred variant, in a method according to the invention, the at least one reforming unit may include a reformer located in the anode gas loop in the recirculation line downstream of the anode gas heat exchanger and upstream of the gas conveyor, wherein the fuel to be reformed is the hot anode exhaust gas in the anode gas drain upstream of the anode gas heat exchanger and / or the Anodenrecyclegas in the recirculation line is supplied before the reformer or be.

In this variant, the otherwise necessary long recirculation path of the anode gas circulation can be saved by the reformer is arranged directly after the anode gas heat exchanger or immediately downstream of 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 pipe. The reformer is advantageously no longer additionally heated in this variant. In addition, the gas delivery device, such as the anode fan, is also located 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 before the anode gas heat exchanger. Advantageously, a good mixing with anode exhaust gas is made possible by this comparatively early addition of the fuel into the anode gas circulation upstream of the reformer via the line to the reformer. However, with this type of admixture, part of the fuel also flows into the exhaust gas line and thus does not reach the reformer.

Alternatively or in addition to the admixture of the fuel in the anode gas discharge, the fuel may also be supplied to the anode recycle gas in the recirculation line prior to the reformer. Advantageously, the entire admixed fuel thus enters the reformer. However, it should be noted that the reformer inlet temperature of the anode gas due to the admixture of the cooler natural gas so slightly lower.

A further advantage of this method variant is that the heat losses associated therewith can be significantly reduced by eliminating the reformer heating. The remaining heat is available for preheating the cathode side. This results in a higher cathode inlet temperature, which is an important factor in the thermal management of a fuel cell system.

The temperature level in the recirculation line of the anode gas is lower with temperatures, for example, below 300 ° C, so that the heat losses are lower. The lower inlet temperature level at the gas conveyor or at the anode gas blower leads to a higher efficiency of the blower. In addition, it is necessary for the anode gas blower less cooling power and its thermal stress is reduced, allowing a longer, trouble-free operation of the gas conveyor.

Due to the higher reformer inlet temperature, no additional external reformer heating or pipelines or controllable throttle valves are necessary. The inlet temperature of the anode 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. While this may result in lower anode gas inlet temperatures, which may be critical due to thermal stresses for the high temperature fuel cell, this effect is offset by the reduced heat losses in the recirculation line.

In a further advantageous variant, in a method according to the invention, the at least one reforming unit comprise a catalytic reformer heat exchanger in which the fuel is reformed, the reformer heat exchanger is combined with the anode gas heat exchanger and arranged in the Anodenzugasleitung before the anode compartment, wherein the cold heat exchanger side and / or the hot heat exchanger side with the reformer heat exchanger and the fuel to be reformed is supplied to the hot anode exhaust gas in the anode gas exhaust on the hot heat exchanger side upstream of the anode gas heat exchanger and / or the anode recycle gas in the recirculation line on the cold heat exchanger side upstream of the anode gas heat exchanger.

This variant of the method differs from the previously mentioned variants in that the reforming unit and anode gas heat exchangers are combined to form a common component. As a result, a higher reformer inlet temperature is achieved. At the same time both paths of the Anodengaswärmeübertragers, so the cold heat exchanger side and the hot heat exchanger side can be performed as a reformer, creating 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 each be designed to be reforming or coupled to the reformer heat exchanger.

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

In an advantageous development of the invention, the catalytic reformer heat exchanger can be integrated in the anode gas heat exchanger in a variant of the method, wherein the cold heat exchanger side and / or the hot heat exchanger side is or are formed catalytically reforming the fuel.

In a further alternative embodiment, in a method according to the invention, the at least one reforming unit comprise at least one catalytic reformer anode which is arranged in the anode chamber of the high-temperature fuel cell, wherein the fuel is supplied to the recirculation line of the anode gas cycle and reformed in the anode chamber. Advantageously, a reformer can be omitted in this variant of the method according to the invention. Due to the catalytic activity of a catalytic reformer anode, the reforming of the anode gas can also take place completely in the anode space of the high-temperature fuel cell.

In a preferred embodiment of the invention, in one method, the anode of the high temperature fuel cell may be formed as a catalytic reformer anode. 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 affect the catalytic activity of the reformer anode. Through the use of particularly robust reformer anodes, which are largely inert to catalyst poisons of anode gas or the fuel, sufficient service life for the operation of the high-temperature fuel cell can be ensured in this process variant.

Suitably, in a method according to the invention, a plurality of reforming units of the same or different design can be arranged in each case in hot circulation sections of the anode gas cycle. For example, in the context 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, are used together in the anode circuit and each have a reforming effect.

The aforementioned object of the present invention to provide corresponding devices for operating a generic fuel cell system with a fuel, which fuel cell system at least one high-temperature fuel cell with at least one arranged in a cathode compartment cathode, with at least one arranged in an anode compartment anode and with an existing between cathode compartment and anode compartment Electrolyte comprises, wherein in a Anodengaskreislauf for returning anode exhaust gas from the anode compartment opens a fuel supply for admixing fuel to the anode gas, wherein at least one gas conveying means for conveying the mixture as anode gas into an anode gas heat exchanger, which is connected in the anode gas circuit is provided, and which Fuel cell system further comprises at least one reforming unit for reforming the fuel in the Anodengaskreislauf is dissolved by a device st, in which device the at least one reforming unit in a hot cycle section the anode cycle gas is arranged in which hot cycle section during operation of the fuel cell system is set an anode gas temperature above the equilibrium temperature required in the reforming and the at least one gas conveyor is arranged in a cool circuit section of the anode gas circulation, in which cool circuit section during operation of the fuel cell system an anode gas temperature below the is set in the hot cycle section prevailing anode gas temperature.

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

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

Expediently, in a device according to the invention, at least one reforming unit may comprise a reformer which is arranged in the anode gas circulation in the recirculation line downstream of the anode gas heat exchanger and upstream of the gas conveyor, the fuel feed into the anode gas discharge before the anode gas heat exchanger and / or into the recirculation line before the reformer ,

In a further embodiment variant of the invention, in a device the at least one reforming unit may comprise a catalytic reformer heat exchanger, wherein the reformer heat exchanger is combined with or integrated into the anode gas heat exchanger and located in the anode gas line upstream of the anode space, the cold heat exchanger side and / or the hot one Heat exchanger side formed catalytically reforming or is coupled to the reformer heat exchanger or are and the fuel supply into the Anodengasableitung before the anode gas heat exchanger and / or in the recirculation line before the reformer heat exchanger opens.

In an alternative variant of the invention, in a device the at least one reforming unit may comprise at least one catalytic reformer anode which is arranged in the anode chamber of the high-temperature fuel cell, wherein the anode of the high-temperature fuel cell is preferably designed as a catalytic reformer anode, wherein the fuel feed line opens into the recirculation line of the anode gas cycle.

According to the invention, different variants of the anode gas circulation or different embodiments of the arrangement of reforming unit / gas delivery means / anode gas heat exchangers are thus possible, as is also carried out 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 apparatus for operating the generic fuel cell system, which, however, can also be combined with other components 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 it in the fuel cell to an uncontrolled reforming, which could lead to thermal stresses and thus damage the fuel cell due to their endothermic nature.

Further details, features and advantages of the invention will become apparent from the following description of the drawings in each case schematically illustrated, non-limiting embodiments. The following explanations regarding the description of the figures relate to processes as well as devices for operating a fuel cell system. In the drawings, in each case representations as a simplified process flow diagram:

1 a fuel cell system according to the known state of the art, wherein in a Anodengaskreislauf upstream of a reformer, a gas conveying device is arranged;

2 in a detail view of 1 the anode gas cycle according to the prior art;

3 the anode gas cycle of a fuel cell system according to a first variant of the invention, wherein the reforming unit comprises a reformer which is arranged in the Anodengaskreislauf in the recirculation downstream of an anode gas heat exchanger and upstream of a gas conveyor, wherein the fuel to be reformed the hot anode exhaust gas in the anode exhaust gas upstream of the anode gas heat exchanger is supplied;

4 the anode gas cycle of a fuel cell system according to a second variant of the invention, wherein a reformer in the Anodengaskreislauf in the recirculation line is arranged downstream of an anode gas heat exchanger and upstream of a gas conveyor, wherein the fuel to be reformed is supplied to the recycled anode exhaust gas in the recirculation line before the reformer;

5 the anode gas cycle of a fuel cell system according to a third variant of the invention, wherein the reforming unit comprises a catalytic reformer heat exchanger in which the fuel is reformed, wherein the reformer heat exchanger is combined with or integrated into the anode gas heat exchanger;

6 the anode gas cycle of a fuel cell system according to a fourth variant of the invention, wherein the reforming unit comprises a catalytic reformer anode, which is arranged in the anode chamber of the high-temperature fuel cell;

7 the in 3 illustrated Anodengaskreislauf a fuel cell system according to the invention during startup of the fuel cell system.

Exemplary is in 1 a known fuel cell system 1 with a so-called solid oxide fuel cell 10 (Solid Oxide Fuel Cell, SOFC). This is a high-temperature fuel cell 10 , which is operated at operating temperatures of about 650 ° C to 1000 ° C. The electrolyte 15 This type of cell consists of a solid ceramic material that is capable of conducting oxygen ions but is insulating for electrons. On both sides of the electrolyte layer 15 are the electrodes, cathode 11 and anode 13 , appropriate. 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 low energy. It works only at the prevailing high temperatures. The electrolyte side facing away from the outer side of the cathode 11 is surrounded by air, the outer anode side 13 of fuel gas. Unused air and unused fuel gas and combustion products are extracted.

solid oxide fuel cells 10 are galvanic cells for continuous electrochemical power generation, usually as a fuel cell stack, so-called SOFC stacks, so as the interconnection of several high-temperature fuel cells 10 , operate. For a better overview, see 1 only a single high-temperature fuel cell 10 illustrated. The function of each galvanic cell and of each electrochemical reaction in general is based on a redox reaction in which reduction and oxidation occur spatially separated, namely at the interface between the electrode and the electrolyte. In the solid oxide fuel cell 10 For example, this redox reaction is a reaction of oxygen with the fuel, which may be hydrogen, but here also includes carbon monoxide, for example. On the cathode side 12 oxygen surplus prevails while on the anode side 14 Lack of oxygen prevails, because the existing oxygen reacts with the existing hydrogen, for example. Oxygen diffuses through this concentration gradient 19 from the cathode 11 through the electrolyte 15 to the anode 13 , The electrolyte 15 in between, however, is only permeable to oxygen ions.

When the oxygen molecule reaches the interface between the cathode and the electrolyte, it absorbs two electrons, becoming an ion and penetrating the barrier. At the border to the anode 13 arrived, it reacts catalytically with the fuel gas with the release of heat and the corresponding combustion products, and again gives 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 elsewhere.

According to the in 1 shown variant is an anode gas cycle 20 provided in detail also in 2 is shown. In the anode gas cycle 20 gets out of the anode compartment 14 the high-temperature fuel cell 10 in an anode exhaust gas line 21 hot anode exhaust 22 to an anode gas heat exchanger 70 promoted, wherein the supplied anode exhaust gas 22 in the anode gas heat exchanger 70 which is preferably operated in countercurrent, is cooled slightly and in the anode exhaust gas line 21 the anode gas heat exchanger 70 as hot anode exhaust gas 23 leaves again. Part of the hot anode exhaust 23 arrives at a here T-shaped circuit branching in a recirculation line 24 and is used as an anode recycle 25 or as recycled anode exhaust gas 25 in the anode gas cycle 20 returned and with fresh fuel 27 that from a fuel supply 26 that enter the anode gas cycle 20 opens, mixed.

The mixture of recycled anode exhaust gas 25 and fresh fuel 27 , the anodic gas 29 , will now be in an anode gas supply line 28 with a gas conveyor 50 , here as an anode gas blower 50 is executed, one upstream of the anode gas blower 50 subsequent reforming unit 60 with a reformer 61 fed. Further, it flows into the anode gas supply line 28 a steam line coming from an evaporator 90 is fed and with the water vapor 91 can be injected. The anodic gas 29 leaves after the reforming step in the reformer 61 this as a reformed anode gas 30 and enters an anode gas line 31 in the anode gas heat exchanger 70 , is heated in this and called hot anode gas 32 the anode compartment 14 fed. Part of the hot anode exhaust 23 is not returned, but in an exhaust pipe 33 from the anode gas cycle 20 discharged and leaves this as exhaust 34 ,

In the recirculation line 24 here is a pressure gauge 40 For example, a Venturi tube 40 , installed to measure the flow in the anode gas cycle by means of differential pressure measurement 20 to eat. This pressure gauge 40 is optional and can be omitted. As fuel 27 Here is natural gas (English: Natural Gas, NG) in the anode gas cycle 20 fed. With the upstream of the reformer 61 arranged anode gas blower 50 the anode gas recirculation is maintained. The anode gas heat exchanger 70 is between reformers 61 and anode compartment 14 arranged. As in 2 the path of the anode gas to be heated forms visible 30 . 32 that the anode room 14 is supplied, thereby forming a cold heat exchanger side 71 that from the hot anode exhaust 22 . 23 in that in the anode exhaust gas line 21 from the anode compartment 14 coming streams and a hot heat exchanger side 72 the anode gas heat exchanger 70 forms, is heated.

In the in 1 variant shown is the reformer 61 through hot burner exhaust 86 heated, as exhaust gas from a catalytic afterburner 80 or from a burner 85 comes. Furthermore are in 1 an air supply line 35 for supplying supply air 36 by means of an air blower 37 including air preheater 38 as well as appropriate valves 45 , For example, throttle valves 45 , referred to in the lines. The gas conveyor 50 or the anode gas blower 50 is with a cooling device 51 provided for cooling the bearing and motor of the gas conveyor 50 serves. Due to the operation of the anode gas blower 50 necessary cooling 51 However, there is a significant cooling of the anode recirculation gas between inlet and outlet of the anode gas blower 50 , This cooling in the anode gas supply line 28 to a temperature here of around 400 ° C, however, causes a shortfall in the upstream of the anode gas blower 50 subsequent reformer 61 At least required equilibrium temperature of about 470 ° C to start the Refomierungsreaktion.

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

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

The anode gas temperature 200 in a cool cycle section 220 of the anode gas cycle 20 , the hot circuit section 210 downstream in the downstream direction and in which the gas conveyor 50 is arranged here is at most 470 ° C. The anode gas temperature 200 after the anode gas blower 50 here is 270 ° C and is in the anode gas supply line 31 cooled down further, which is why the Anodenzugas 30 before the anode gas heat exchanger 70 on the cold heat exchanger side 71 an anode gas temperature 200 of about 250 ° C has. The anodic gas 32 when passing the comparatively cold heat exchanger side 71 heated and points to the anode gas heat exchanger 70 an anode gas temperature 200 from 700 ° C, with which the heated anode gas 32 in the anode compartment 14 arrives. At exit of the anode gas from the anode compartment of the high-temperature fuel cell 10 is the anode gas temperature 200 in the anode exhaust gas line 21 here about 820 ° C. The anodic gas 29 , which here with an anode gas temperature 200 of about 800 ° C in the anode gas heat exchanger 70 reaches, thus forming its hot heat exchanger side 72 ,

After passing the comparatively hot heat exchanger side 72 the anode gas heat exchanger 70 is the anode gas temperature 200 of the anode bug 29 before the reformer 60 here about 560 ° C. Like here in 3 is illustrated in this device according to the invention of a fuel cell system 1 no additional heating of the reforming unit 60 required.

4 shows the anode gas cycle 20 a fuel cell system 1 according to a second variant of the invention, wherein the reforming unit 60 a reformer 61 includes, here in the anode gas cycle 20 in the recirculation line 24 downstream to an anode gas heat exchanger 70 and upstream of a gas conveyor 50 is arranged. The reformer 61 is So in the anode gas cycle 20 between the upstream anode gas heat exchanger 70 and the downstream gas conveyor 50 arranged. Notwithstanding the in 3 variant shown here in 4 the fuel to be reformed 26 the recycled anode exhaust gas 29 in the recirculation line 24 right in front of the reformer 61 fed. The fuel supply is indicated by an arrow 27 symbolizes.

5 illustrates the anode gas cycle 20 a fuel cell system 1 according to a third variant of the invention, wherein the reforming unit 60 here a catalytic reformer heat exchanger 62 in which the fuel is reformed, wherein the reformer heat exchanger 62 with the anode gas heat exchanger 70 combined or integrated into it. According to the previous pictures 3 respectively. 4 it is also at the in 5 variant shown possible, the fuel supply 27 with fuel to be reformed 26 optionally in the anode exhaust gas line 21 before the anode gas heat exchanger 70 to provide, the fuel 26 while the hot anode exhaust gas 22 is supplied. Or it will be the fuel supply 27 so arranged that the fuel 26 just before the gas conveyor 50 into the anode gas line 31 is mixed. This alternative variant of the fuel supply 27 is in 5 drawn in dashed lines. It is also possible within the scope of the invention, the fuel supply 27 in several places of the fuel cell system 1 to realize.

Particularly advantageous here is at the in 5 shown variant that in the catalytic reformer heat exchanger 62 the reforming unit 60 and the anode gas heat exchanger 70 combined into a common component. The reformer heat exchanger 62 is in the hot circulation section 210 of the anode gas cycle arranged. The anode gas temperature 200 in the hot circulation section 210 of the anode gas cycle 20 in which the reformer heat exchanger 62 is arranged here is for example 800 ° C. The anode gas temperature 200 in a cool cycle section 220 of the anode gas cycle 20 , the hot circuit section 210 downstream in the downstream direction and in which the gas conveyor 50 is arranged here is at most 450 ° C.

The anode gas temperature 200 after the anode gas blower 50 here is 270 ° C and is in the anode gas supply line 31 cooled down further, which is why the Anodenzugas 30 before the anode gas heat exchanger 70 on the cold heat exchanger side 71 an anode gas temperature 200 of about 250 ° C has. The anodic gas 32 when passing the comparatively cold heat exchanger side 71 heated and points to the anode gas heat exchanger 70 an anode gas temperature 200 from 700 ° C, with which the heated anode gas 32 in the anode compartment 14 arrives. At exit of the anode gas from the anode compartment of the high-temperature fuel cell 10 is the anode gas temperature 200 in the anode exhaust gas line 21 here about 820 ° C. The anodic gas 29 , which here with an anode gas temperature 200 of about 800 ° C in the anode gas heat exchanger 70 reaches, thus forming its hot heat exchanger side 72 ,

After passing the comparatively hot heat exchanger side 72 the Reformerwärmeübertragers 62 is the anode gas temperature 200 of the anode bug 29 after the reformer 60 here about 470 ° C. As in 5 is illustrated in this device according to the invention of a fuel cell system 1 also no additional heating of the reforming unit 60 required.

6 shows the anode gas cycle 20 a fuel cell system 1 according to a fourth variant of the invention, wherein the reforming unit 60 a catalytic reformer anode 63 includes that in the anode compartment 14 the high-temperature fuel cell 10 is arranged. The fuel 27 is doing the anode gas cycle 20 or the recirculation line 24 before the anode gas blower 50 fed. The anode gas blower 50 is located in a cool cycle section 220 of the anode gas cycle 20 ,

The temperature 200 of the anode gas 29 before the anode gas blower 50 is about 340 ° C and drops after the anode gas blower 50 to a temperature 200 of about 300 ° C. The anodic gas 30 thus occurs at the cold heat exchanger side 71 in the anode gas heat exchanger 70 at around 300 ° C. The anodic gas 32 when passing the comparatively cold heat exchanger side 71 heated and points to the anode gas heat exchanger 70 an anode gas temperature 200 For example, from about 780 ° C, with which the heated Anodenzugas 32 in the anode compartment 14 arrives. The reforming takes place at the catalytic reformer anode 63 , Upon exit of the reformed anode gas from the anode compartment 14 the high-temperature fuel cell 10 is the anode gas temperature 200 in the anode exhaust gas line 21 here for example about 820 ° C.

The anode compartment 14 including the catalytic reformer anode disposed therein 63 is in the hot circulation section 210 of the anode gas cycle 20 , The hot anode exhaust 22 , which here with an anode gas temperature 200 of about 800 ° C in the anode gas heat exchanger 70 reaches, thus forming its hot heat exchanger side 72 , After passing the comparatively hot heat exchanger side 72 the anode gas heat exchanger 70 is the anode gas temperature 200 of the anode exhaust gas 23 or the anode recycle gas 25 here about 360 ° C. As in 6 is illustrated in this device according to the invention of a fuel cell system 1 also no additional heating of the reforming unit 60 required.

7 shows the in 3 shown anode gas cycle 20 a fuel cell system according to the invention 1 during startup of the fuel cell system 1 , In certain operating phases of the fuel cell system according to the invention 1 It may be necessary to add external water vapor to the system 1 supply, as returned by the anode gas recirculation, for example, in the start-up, standby or part-load operation no or not enough water vapor.

To prevent this, steam had previously been generated in an evaporator heat exchanger and possibly fed to the system, which, however, results in additional investment and operating costs and undesirable pressure losses due to the required number of conditioning devices.

In 7 Therefore, an alternative embodiment is shown, in which case a water injection 110 is provided with the water 111 , preferably under pressure, is injected through an injection nozzle into the anode gas stream and thereby directly evaporated. The water 111 is here with a temperature 200 of about 95 ° C in the Anodenzugasleitung 32 after the anode gas heat exchanger 70 injected, wherein the Anodenzugas 32 about an anode gas temperature 200 from 140 ° C and through the injected water 111 is cooled to about 100 ° C, before the anode gas 32 in the anode compartment 14 arrives. In contrast to the previously known state of the art, in which steam is supplied to the system, the spraying or injection of water is technically much easier and cheaper to accomplish.

Claims (15)

Method for operating a fuel cell system ( 1 ) with a fuel ( 27 ), which fuel cell system ( 1 ) at least one high-temperature fuel cell ( 10 ) with at least one in a cathode compartment ( 12 ) arranged cathode ( 11 ), with at least one in an anode compartment ( 14 ) arranged anode ( 13 ) and with a between cathode space ( 12 ) and anode space ( 14 ) existing electrolytes ( 15 ), wherein in an anode gas cycle ( 20 ) from the anode compartment ( 14 ) of the at least one high-temperature fuel cell ( 10 ) recycled anode exhaust gas ( 25 ) with fuel ( 27 ) and used as anodine gas ( 30 ) with at least one gas delivery device ( 50 ) an anode gas heat exchanger ( 70 ), in which the anode gas ( 31 ) is thermostatically, wherein further in at least one reforming unit ( 60 . 61 ) in the anode gas cycle ( 20 ) the fuel ( 27 ), characterized in that the at least one reforming unit ( 60 . 61 . 62 . 63 ) in a hot cycle section ( 210 ) of the anode gas cycle ( 20 ) is arranged in which hot cycle section ( 210 ) in fuel cell operation, an anode gas temperature ( 200 ) above that in the reforming unit ( 60 . 61 . 62 . 63 ) is reached, and the at least one gas conveying device ( 50 ) in a cool circulation section ( 220 ) of the anode gas cycle ( 20 ) is arranged in which cool cycle section ( 220 ) in fuel cell operation, an anode gas temperature ( 200 ) below the one in the hot circulation section ( 210 ) prevailing anode gas temperature ( 200 ) is achieved. Method according to claim 1, characterized in that in the at least one reforming unit ( 60 . 61 . 62 . 63 ) by an endothermic steam reforming of a carbonaceous mixture containing the fuel ( 27 ) and the recycled anode exhaust gas ( 25 ) a reformate gas is produced as a mixture of carbon monoxide and hydrogen. Method according to claim 1 or 2, characterized in that the anode gas temperature ( 200 ) in the hot circulation section ( 210 ) of the anode gas cycle ( 20 ) in which the at least one reforming unit ( 60 . 61 . 62 . 63 ), at least 500 ° C, preferably at least 550 ° C, more preferably at least 600 ° C, is. Method according to one of claims 1 to 3, characterized in that the anode gas temperature ( 200 ) in the cool circulation section ( 220 ) of the anode gas cycle ( 20 ), in which the at least one gas conveying device ( 50 ), at most 470 ° C, preferably at most 450 ° C, more preferably at most 400 ° C, is. Method according to one of claims 1 to 4, characterized in that the at least one reforming unit ( 60 ) a reformer ( 61 ), which in the Anodengaskreislauf ( 20 ) in the recirculation line ( 24 ) downstream of the anode gas heat exchanger ( 70 ) and upstream of the gas conveyor ( 50 ), wherein the fuel to be reformed ( 27 ) the hot anode exhaust gas ( 22 ) in the anode gas discharge ( 21 ) in front of the anode gas heat exchanger ( 70 ) and / or the anode recycle ( 25 ) in the recirculation line ( 24 ) before the reformer ( 61 ) is supplied. Method according to one of claims 1 to 4, characterized, in that the at least one Reforming unit ( 60 ) a catalytic reformer heat exchanger ( 62 ), in which the fuel ( 27 ), the reformer heat exchanger ( 62 ) with the anode gas heat exchanger ( 70 ) and in the anode gas line ( 31 ) in front of the anode compartment ( 14 ), wherein the cold heat exchanger side ( 71 ) and / or the hot heat exchanger side ( 72 ) with the reformer heat exchanger ( 62 ) and the fuel to be reformed ( 27 ) the hot anode exhaust gas ( 22 ) in the anode gas discharge ( 21 ) on the hot heat exchanger side ( 72 ) in front of the anode gas heat exchanger ( 70 ) and / or the anode recycle ( 25 ) in the recirculation line ( 24 ) on the cold heat exchanger side ( 71 ) in front of the anode gas heat exchanger ( 70 ) is supplied. A method according to claim 6, characterized in that the catalytic reformer heat exchanger ( 62 ) in the anode gas heat exchanger ( 70 ), wherein the cold heat exchanger side ( 71 ) and / or the hot heat exchanger side ( 72 ) the fuel ( 27 ) is formed catalytically reforming or are. Method according to one of claims 1 to 7, characterized in that the at least one reforming unit ( 60 ) at least one catalytic reformer anode ( 63 ), which in the anode compartment ( 14 ) of the high-temperature fuel cell ( 10 ), wherein the fuel ( 27 ) of the recirculation line ( 24 ) of the anode gas cycle ( 20 ) and in the anode compartment ( 14 ) is reformed. Method according to claim 8, characterized in that the anode ( 13 ) of the high-temperature fuel cell ( 10 ) as a catalytic reformer anode ( 63 ) is trained. Method according to one of claims 1 to 9, characterized in that several reforming units ( 60 . 61 . 62 . 63 ) of the same or different design in each case in hot circulation sections ( 210 ) of the anode gas cycle ( 20 ) are arranged. Device for operating a fuel cell system ( 1 ) with a fuel ( 27 ), which fuel cell system ( 1 ) at least one high-temperature fuel cell ( 10 ) with at least one in a cathode compartment ( 12 ) arranged cathode ( 11 ), with at least one in an anode compartment ( 14 ) arranged anode ( 13 ) and with a between cathode space ( 12 ) and anode space ( 14 ) existing electrolytes ( 15 ), wherein in an anode gas cycle ( 20 ) for recycling anode exhaust gas ( 25 ) from the anode compartment ( 14 ) a fuel supply line ( 26 ) for admixing fuel ( 27 ) to the anode gas ( 25 ), wherein at least one gas conveying device ( 50 ) for conveying the mixture as anode gas ( 30 ) in an anode gas heat exchanger ( 70 ) which enters the anode gas cycle ( 20 ), it is provided which fuel cell system ( 1 ) at least one reforming unit ( 60 . 61 ) for reforming the fuel ( 27 ) in the anode gas cycle, characterized in that the at least one reforming unit ( 60 . 61 . 62 . 63 ) in a hot cycle section ( 210 ) of the anode gas cycle ( 20 ) is arranged in which hot cycle section ( 210 ) during operation of the fuel cell system ( 1 ) an anode gas temperature ( 200 ) above that in the reforming unit ( 60 . 61 . 62 . 63 ) is set to the required equilibrium temperature and the at least one gas delivery device ( 50 ) in a cool circulation section ( 220 ) of the anode gas cycle ( 20 ) is arranged in which cool cycle section ( 220 ) during operation of the fuel cell system ( 1 ) an anode gas temperature ( 200 ) below the one in the hot circulation section ( 210 ) prevailing anode gas temperature ( 200 ) is set. Apparatus according to claim 11, characterized in that the at least one reforming unit ( 60 . 61 . 62 . 63 ) is designed for an endothermic steam reforming, wherein the anode gas temperature ( 200 ) in the hot circulation section ( 210 ) of the anode gas cycle ( 20 ) in which the at least one reforming unit ( 60 . 61 . 62 . 63 ), at least 500 ° C, preferably at least 550 ° C, more preferably at least 600 ° C, is. Apparatus according to claim 11 or 12, characterized in that at least one reforming unit ( 60 ) a reformer ( 61 ), which in the Anodengaskreislauf ( 20 ) in the recirculation line ( 24 ) downstream of the anode gas heat exchanger ( 70 ) and upstream of the gas conveyor ( 50 ), wherein the fuel supply line ( 26 ) into the anode gas discharge ( 21 ) before the Anodengaswärmeübertrager ( 70 ) and / or in the recirculation line ( 24 ) before the reformer ( 61 ) opens. Device according to one of claims 11 to 12, characterized in that the at least one reforming unit ( 60 ) a catalytic reformer heat exchanger ( 62 ), wherein the reformer heat exchanger ( 62 ) with the anode gas heat exchanger ( 70 ) is combined or integrated into it and in the Anodenzugasleitung ( 31 ) in front of the anode compartment ( 14 ), wherein the cold heat exchanger side ( 71 ) and / or the hot heat exchanger side ( 72 ) formed catalytically reforming or with the reformer heat exchanger ( 62 ) is coupled and / or the fuel supply ( 26 ) into the anode gas discharge ( 21 ) in front of the anode gas heat exchanger ( 70 ) and / or in the recirculation line ( 24 ) before the reformer heat exchanger ( 62 ) opens. Device according to one of claims 11 to 12, characterized in that the at least one reforming unit ( 60 ) at least one catalytic reformer anode ( 63 ), which in the anode compartment ( 14 ) of the high-temperature fuel cell ( 10 ), wherein preferably the anode ( 13 ) of the high-temperature fuel cell ( 10 ) as a catalytic reformer anode ( 63 ), wherein the fuel supply line ( 26 ) in the recirculation line ( 24 ) of the anode gas cycle ( 20 ) opens.

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