DE102012221461A1 - Fuel cell system and method for operating a fuel cell system - Google Patents

Abstract

The present invention relates to a fuel cell system (1) with a fuel cell stack. In order to achieve a particularly effective replacement of a desulfurization device (10) and to protect the fuel cell system (1) from damage caused by substances containing sulfur, the fuel cell system (1) comprises - at least one fuel cell (2); - An anode gas guide (9) for supplying anode gas to the fuel cell (2); A cathode gas guide (15) for supplying cathode gas to the fuel cell (2); and - a desulfurization device (10) for removing sulfur-containing substances from the anode gas, wherein - a sulfur sensor (36) is provided for detecting the sulfur content of the supplied anode gas. The present invention further relates to a method for operating a fuel cell system (1) and the use of such a fuel cell system (1).

Description

The present invention relates to a fuel cell system and a method of operating a fuel cell system.

State of the art

Cogeneration is playing an increasingly important role in the energy market because of its potential to reduce CO ₂ emissions for the provision of electricity and heat. Here, fuel cell systems based on ceramic cells (SOFC), which are operated at high temperature (for example, 650-1000 ° C), because of their high electrical efficiency (about up to 60%) are particularly interesting. These plants are often operated with natural gas from the natural gas grid. Important challenges are the achievement of the highest possible electrical efficiency combined with a high cell life.

In the document US 6,682,836 B2 a method for operating a fuel cell system is described. In this method, a control system is used to direct the educts in a controlled manner in the fuel cell, so as to be able to influence the combustion process. For this purpose, the exhaust gas of the fuel cell is examined, for example, by means of a lambda probe, or the characteristic parameters relating to the hydrogen concentration are measured by means of a sensor.

In the document DE 10 2010 001 011 A1 a method for operating a cogeneration plant is described. In such a method, a first portion of a fuel in a fuel cell is converted to generate electric power and a second portion of the fuel in an afterburner is eliminated to generate heat.

Disclosure of the invention

• – wenigstens eine Brennstoffzelle;
• – eine Anodengasführung zum Zuführen von Anodengas zu der Brennstoffzelle;
• – eine Kathodengasführung zum Zuführen von Kathodengas zu der Brennstoffzelle; und
• – eine Entschwefelungsvorrichtung zum Entfernen von schwefelhaltigen Substanzen aus dem Anodengas, wobei
• – ein Schwefelsensor zur Erfassung des Schwefelgehaltes des zugeführten Anodengases vorgesehen ist.

The subject of the present invention is a fuel cell system with a fuel cell stack comprising

• - at least one fuel cell;
• An anode gas guide for supplying anode gas to the fuel cell;
• A cathode gas guide for supplying cathode gas to the fuel cell; and
• - A desulfurization device for removing sulfur-containing substances from the anode gas, wherein
• - A sulfur sensor is provided for detecting the sulfur content of the supplied anode gas.

Such a fuel cell system may thus comprise as a central unit a fuel cell stack which has at least one fuel cell. In particular, the fuel cell stack may have a plurality of fuel cells, which may be planar and / or tubular. The term fuel cell stack should not be understood to be limiting in that the fuel cells are stacked.

The fuel cells are not limited in their execution and can be freely selected, for example, with respect to the type and material of the anode or cathode, with respect to the type and material of the electrolyte and with respect to the anode and cathode gas. For example, the fuel cells may be designed as solid oxide fuel cells. In this case, an electrolyte can be arranged between the anode and the cathode in a manner known per se.

Furthermore, the fuel cell system may expediently comprise a connection or an interface for connecting an anode gas source and a connection or an interface for connecting a cathode gas source. The type of gas source is not limiting. For example, the anode gas source may be a source of natural gas, LPG, hydrogen, or a hydrogen-containing gas, whereas the cathode gas source may be, for example, a source of oxygen or an oxygen-containing gas, such as air. The anode gas source and the cathode gas source are connected to the anode or to the cathode in such a way, for example via a suitable anode gas guide or cathode gas guide, so that anode gas or cathode gas to the anode or to the cathode is feasible. Consequently, for the purposes of the present invention, anode gas may be, in particular, the gas guided to the anode, whereas cathode gas may be, in particular, the gas conducted to the cathode.

In particular, the fuel cell system may include a reformer for processing anode gas. This embodiment is particularly advantageous for the use of a fuel cell, which works with natural gas as the anode gas. Here, under certain circumstances, the hydrocarbon compounds contained in the natural gas at the anode, for example, a high-temperature fuel cell can not be or only partially reactive. However, they can be converted by a reforming reaction into, for example, hydrogen and carbon monoxide. Such reforming can take place in addition to a reaction on the catalytic anode surface, in particular in the arranged before the anode input reformer or pre-reformer.

For example, since natural gas often comprises sulfur-containing substances or sulfur compounds are added thereto as odorants in the natural gas network, the fuel cell system may comprise a desulfurization device for removing sulfur or sulfur-containing substances from the anode gas. In the context of the present invention, sulfur-containing substances may in particular be pure sulfur or substances which at least partially comprise sulfur and / or sulfur compounds.

By means of such a desulphurisation device, sulfur-containing substances can therefore be removed from the anode gas stream and it can thus be prevented that such sulfur-containing substances enter the reformer or the fuel cell or into the fuel cell stack, where they could cause damage to these components.

A desulphurisation device may be based in particular on physical and / or chemical adsorption processes. It can also be designed as a cartridge or as a replaceable component, which is often not designed, for example, due to volume requirements of the fuel cell system for the entire life of the fuel cell system, but can be configured as a replacement element for defined intervals.

For example, in order to make an exchange of such devices particularly efficient, a sulfur sensor for detecting the sulfur content of the supplied anode gas is provided. As a result, the sulfur content of the anode gas can be determined and thus the sulfur loading of a desulphurisation device can be determined in the same way. For the purposes of the present invention, the sulfur content may be understood in particular to mean the concentration of sulfur or of substances containing sulfur, in particular in the anode gas. In this case, the sulfur content in the anode gas can also be indirectly determined by measuring the sulfur content in the anode exhaust gas in a way which is obvious to the person skilled in the art.

By means of such a sulfur sensor, it can thus be advantageously determined which concentration of sulfur-containing substances is actually present in the anode gas or which amount of sulfur-containing substances has already been removed from the anode gas by the desulphurisation device. This can be reacted to the fact that the sulfur content of the gas is different at different locations and also varies over time. It can thus be defined and determined in advance and in advance when a desulphurisation device should be replaced or when a sulfur breakthrough that is detrimental to the fuel cell system can be expected.

This can be prevented on the one hand that the desulfurization device or the cartridge must be oversized and / or replaced before a maximum load is reached. Rather, the change intervals can be performed as needed, so that the cartridges used can be used optimally. This can save costs. Furthermore, damage to the fuel cell system can be prevented even at unexpectedly high concentration, such as a shock odorization of sulfur or sulfur-containing substances. Thus, the system is protected from damage by unexpectedly high sulfur concentrations in the anode gas used, such as natural gas used.

Within the scope of an embodiment, the sulfur sensor can be based on a chemical and / or electrochemical reaction. In particular, the sulfur sensor may be based on a reaction of the anode gas with oxygen. The strength of the reaction may decrease depending on the sulfur content. Furthermore, in this embodiment, the sulfur sensor may comprise at least one catalyst poisonable by a sulfur-containing substance. In this case, the sulfur content can be determined from the decrease in the strength of the reaction, which can be measured, for example, electrically and / or thermally. In this embodiment, a determination of the sulfur content can thus be based in particular on influencing or poisoning of the sulfur sensor. In this case, the influence or poisoning is caused by the presence of sulfur-containing substances and is particularly dependent on the content of sulfur-containing compounds, ie of their concentration. Thus, by influencing the operation of a sulfur sensor, ie in particular by influencing or decreasing the strength of a chemical and / or electrochemical reaction of the sulfur sensor on the content of sulfur-containing substances in the anode gas can be concluded.

In the context of a further embodiment, the sulfur sensor may be formed as a catalytic and / or electrochemical sensor, in particular wherein the sulfur sensor may include or may be a combustion catalyst, a fuel cell or a lambda probe. Such sulfur sensors can be formed particularly inexpensive and can in particular with respect to sulfur or sulfur-containing substances to be particularly sensitive and selective. In addition, such sulfur sensors are particularly long-term stability and work safely even at high temperatures. Furthermore, it may be possible to control such sulfur sensors by control units or peripherals already present in a fuel cell system or to be able to evaluate the determined data. As a result, such sulfur sensors can be integrated into existing fuel cell systems in a particularly cost-effective and simple manner.

In this case, such sulfur sensors can also be based on a particularly advantageous measurement method. In detail, the evaluation, for example, in this embodiment based on that the sulfur sensor is poisoned by sulfur-containing substances and thus no longer works as desired. Consequently, in this embodiment of the sulfur sensor in particular a deviation from a standardized and defined operation for sulfur determination can serve. For example, in the case of a combustion catalyst, the oxidation of the anode gas may serve to determine sulfur. In this case, for the oxidation of the anode gas in particular the supply of cathode gas as an oxygen source for burning the anode gas or anode exhaust gas be advantageous because in a fuel cell system usually a precisely controlled control of the cathode gas supply is provided anyway. With regard to an electrochemical sensor, which may be a fuel cell in particular, it may also be poisoned by substances containing sulfur, which may be detectable, for example, due to a reduced generation of electrical energy. Furthermore, a lambda probe can work by a sulfur poisoning with reduced power. Thus, the sulfur sensor can detect the concentration of sulfur-containing substances in particular via sulfur poisoning and thus a limited reaction with the anode gas.

In a further embodiment, the catalyst of the sulfur sensor nickel, palladium, platinum or mixtures thereof may comprise or consist of the aforementioned materials. In particular, as a catalytic sensor sulfur-containing substances or sulfur can be detected and detected particularly sensitive and selective. For example, the sulfur sensor in this embodiment, in addition to the anode gas, an oxygen-containing gas, such as the cathode gas, such as air, are supplied to catalytically oxidize the anode gas and related to the catalytic oxidation parameters for determining the concentration of sulfur or sulfur-containing substances to be able to. In this case, such materials can also be poisoned by sulfur-containing substances for a good evaluation in a suitable manner. Furthermore, such materials are usually already present in a fuel cell system anyway, so that a fuel cell system in this embodiment can be designed in a particularly cost-effective manner.

• – in der Anodengasführung und/oder
• – in einer Anodenabgasführung zum Abführen von Anodenabgas von der Brennstoffzelle und/oder
• – in einer von der Anodengasführung und/oder von der Anodenabgasführung abzweigenden Sensorführung

angeordnet sein. In the context of a further embodiment, the sulfur sensor

• - in the anode gas guide and / or
• In an anode exhaust gas duct for discharging anode exhaust gas from the fuel cell and / or
• In a sensor guide branching off from the anode gas guide and / or from the anode exhaust gas guide

be arranged.

In this embodiment, the sulfur sensor can be arranged particularly favorable in order to detect a concentration of sulfur-containing substances in the anode gas or anode exhaust gas safely and accurately. When arranging the sulfur sensor in an anode gas guide or anode exhaust gas, the sulfur sensor with a particularly simple structure with the anode gas or with the anode exhaust gas comes into contact to determine the content of sulfur-containing substances. In an arrangement in a sensor guide, the sulfur sensor can be tempered independently. In addition, under defined conditions oxygen-containing gas can be passed to the sulfur sensor in a particularly simple manner, for example, to provide oxygen for an oxidation of the anode gas. This can be realized for example by a suitable cathode gas guide or cathode exhaust gas guide, which can lead to the sensor guide.

With regard to the sensor guidance, a suitable volume of anode gas can furthermore be supplied to the sulfur sensor, but without substantially influencing the flow of anode gas. As a result, for example, when the anode gas stream is divisible by valves in a flowing through the sensor guide partial flow and a partial stream flowing to the anode, for a fuel cell always as desired and work with a suitable anode gas flow, on the other hand, however, the sulfur sensor always the same and constant volume of anode gas are supplied, so that the measurement conditions can always be constant. In this embodiment, in particular, the guided through the sensor guide anode gas flow and guided to the anode anode gas flow can be independently adjustable. A branching off of the anode gas guide can equally well Branches of the arranged in the anode gas guide desulfurization include.

In the context of a further embodiment, the anode gas guide and / or the anode exhaust gas guide and / or the sensor guide may have an inner coating, wherein the inner coating comprises the catalyst of the sulfur sensor. This is a particularly simple and effective embodiment in order to be able to measure the sulfur content in the anode gas or in the anode exhaust gas. In detail, the catalyst can be applied by a conventional coating method, for example, to the inner surface of a gas guide, such as a pipe, which can save costs and be easy to manufacture. In addition, the catalyst can be brought into contact with the anode gas in a particularly simple manner by simply flowing through the gas guide, wherein the catalyst further has a particularly large surface and thus can be particularly active.

In the context of a further embodiment, the sulfur sensor in gas-conducting connection, in particular in direct gas-conducting connection, is arranged with the desulfurization device. In this embodiment, the concentration to be detected can be determined particularly accurately. Because of the particular direct and immediate gas-conducting connection between desulfurization and sulfur sensor, the sulfur sensor can directly measure the gas flow through the desulfurization and thus always provide correct and reliable data that are directly related to the work of the desulfurization. A gas-conducting connection can be realized for example by a gas guide, such as a pipe, or in any other way known in the art.

In another embodiment, the desulfurization device may have a certain flow path for the anode gas and may branch the sensor guide from the desulfurization device at a location that is within a range of 50 to 90% of the anode gas flow path, or the sulfur sensor may be located at one location can be arranged, which lies in a range of 50 to 90% of the flow path for the anode gas. In this embodiment, a particularly accurate detection of the content of sulfur-containing substances is possible because essentially only one sulfur breakthrough needs to be detected here. In detail, no sulfur is detected as long as the desulfurization device operates upstream of the branch or sulfur sensor as desired. However, if the desulfurization device or the region arranged in an initial region only works to a limited extent, for instance due to a high degree of loading, and thereby allows substances containing sulfur to pass through, this can be determined by the sulfur sensor. It may be particularly advantageous that the sulfur sensor is arranged at one point or the sensor guide branches from a point downstream of the flow direction of the anode gas still has a residual capacity of unloaded and thus properly operating desulfurization, whereby an exchange of the desulfurization not becomes immediately necessary. In this case, the further possible running time can be formed in particular depending on the exact arrangement of the branch of the sensor guide or the sulfur sensor. For example, a suitable location for the sulfur sensor or for the diversion of the sensor guide in the last third of the desulfurization in the direction of flow of the anode gas. For example, such a location in the direction of flow of the anode gas may be located at a position of 75% to 90% of the flow path of the desulfurization device, thus still providing a range of> 10% to <25% of the flow distance downstream of the sulfur sensor or branch. However, these values are purely exemplary and may depend on the anticipated sulfur loading of the anode gas and the desired lead time to failure of the desulfurization device. The above values may, for example, be valid for a change interval of the desulphurisation device of two years and a lead time of 2 to 3 months. In this case, the flow path can mean, in particular, the path through which the anode gas flows.

• – ein Temperatursensor zum Ermitteln der Temperatur des Schwefelsensors und/oder des Sensorabgases vorgesehen sein, und kann der Schwefelgehalt aus einer Abnahme der Temperatur des Schwefelsensors und/oder des Sensorabgases ermittelbar sein, und/oder kann
• – eine Spannungs- und/oder Strom- und/oder Widerstandsmessvorrichtung zum Ermitteln von Strom, Widerstand und/oder Spannung des Schwefelsensors vorgesehen sein, wobei der Schwefelgehalt aus einer Veränderung der Spannung und/oder des Stroms und/oder des Widerstands des Schwefelsensors ermittelbar ist.

Within the scope of a further embodiment

• A temperature sensor for determining the temperature of the sulfur sensor and / or the sensor exhaust gas can be provided, and the sulfur content can be determined from a decrease in the temperature of the sulfur sensor and / or the sensor exhaust gas, and / or can
• A voltage and / or current and / or resistance measuring device can be provided for determining the current, resistance and / or voltage of the sulfur sensor, wherein the sulfur content can be determined from a change in the voltage and / or the current and / or the resistance of the sulfur sensor ,

In this embodiment, a detection of the content of sulfur-containing substances can be evaluated in a particularly advantageous manner. In detail, a temperature sensor as well as a voltage and / or current and / or resistance measuring device are inexpensive in one Fuel cell system can be implemented. Furthermore, even small changes in the temperature or current, resistance or voltage can be detected by such measuring methods, so that a sulfur sensor in this embodiment can be particularly sensitive.

A temperature sensor may be advantageous in particular when using a combustion catalyst in a sulfur sensor, since a temperature increase is achieved here by combustion of the anode gas and / or anode exhaust gas, which can be detected in a simple manner. It can be determined by a decreasing temperature, a decreasing reactivity of the catalyst. If the reactivity of the catalyst decreases, this can be traced back to the poisoning of the catalyst and thus to the poisoning-related sulfur-containing substances in the anode gas. Determining the temperature of the sulfur sensor may mean, for example, determining the temperature of a sensor housing or the catalytic surface itself. A temperature sensor can also be arranged with little effort and require little peripheral for a suitable evaluation.

With regard to a voltage and / or current and / or resistance measuring device, this can be advantageous, in particular, for an electrochemical sulfur sensor, such as a fuel cell, since a voltage or a current can be generated here, for example, by utilizing the anode gas or the anode exhaust gas the fuel cell has an internal resistance, which parameters can be advantageously determined, since both the internal resistance of the fuel cell, as well as the generated voltage or the generated current is dependent on a poisoning by sulfur-containing substances.

In the context of a further embodiment, the sulfur sensor can be arranged in gas-conducting connection to the cathode gas guide and / or a cathode exhaust gas guide for discharging cathode exhaust gas from the fuel cell and / or an air supply. In this embodiment, in particular for the provision of a combustion catalyst in a particularly simple and cost-effective manner, oxygen can be supplied to the sulfur sensor in order to oxidize or burn anode gas or anode exhaust gas. By using a cathode gas guide or cathode exhaust gas guide, it is thus possible to use a stream of oxygen-containing gas which is regulated anyway by the fuel cell system, which thus allows particularly simple control behavior. With respect to a particular own and thus separated from the cathode gas guide or cathode exhaust gas supply air this can be controlled particularly freely and independently of a cathode gas flow or cathode exhaust gas flow.

In the context of a further embodiment, the sulfur sensor can be heated by a thermal coupling to a heatable part of the fuel cell system by the heat generated during operation of the fuel cell system waste heat. In this embodiment, on the one hand, a particularly simple and energy-saving heating of the sulfur sensor may be possible. In addition, the sulfur sensor, for example, in the case of using a catalytic sulfur sensor, be particularly active and also sensitive. In this embodiment, the sulfur sensor can in particular be thermally coupled thermally to a part of the so-called hot box, ie the heated or heatable part of the fuel cell system. Thereby, heating of the sulfur sensor can be made possible by a part of the fuel cell system, which can be suitably temperature-controlled already by the operation of the fuel cell system. Thus, it is possible in particular to resort to a temperature source regulated in any case, so that heating of the sulfur sensor can be possible in a particularly simple and cost-effective manner.

In the context of a further embodiment, the sulfur sensor can be integrated into a heat exchanger, into a reformer, and / or into an afterburner. These can be particularly suitable positions in order to heat the sulfur sensor through components of the fuel cell system that are usually thermally precisely controlled anyway, since a very precise temperature control usually takes place here.

In the context of a further embodiment, a sulfur loading of the desulfurization device can be determined as a function of the sulfur content determined by the sulfur sensor, in particular if a warning message, in particular for renewing the desulfurization device, can be output when a predetermined sulfur loading threshold is exceeded. In this embodiment, it is therefore possible to conclude the loading of the desulphurisation device by evaluating the data determined by the sulfur sensor. In the event that the loading of the desulphurisation device exceeds a predetermined limit value, the desulphurisation device can be renewed after the issuing of a warning. Renewing the desulfurization can in a non-limiting way, a regeneration, ie in particular a removal of the deposited sulfur-containing substances, mean, or even a replacement of the desulfurization or the active part of the desulfurization device, in particular a desulphurisation cartridge.

Within the scope of an embodiment, the fuel cell system may have a control unit for evaluating the sulfur content data determined by the sulfur sensor. In this embodiment, it can be ensured with particular advantage that the concentration of sulfur-containing substances contained in the anode gas, as determined by the sulfur sensor, can be evaluated with respect to the desulphurisation power of the desulphurisation device and, if appropriate, a warning or a sign can be issued in order to obtain an almost complete charge or one Sulfur breakthrough to renew the desulfurization or shut down the fuel cell system.

With regard to further advantages and technical features of the fuel cell system according to the invention, reference is hereby explicitly made to the explanations in connection with the method according to the invention, the figures, as well as to the description of the figures.

• a) Führen eines Anodengases zu der Anode einer Brennstoffzelle;
• b) Führen eines Kathodengases zu der Kathode einer Brennstoffzelle;
• c) Entfernen von schwefelhaltigen Substanzen aus dem Anodengas durch eine Entschwefelungsvorrichtung, und
• d) Ermitteln der Konzentration an schwefelhaltigen Substanzen in dem Anodengas durch einen Schwefelsensor.

The present invention furthermore relates to a method for operating a fuel cell system, in particular a fuel cell system according to the invention, comprising the method steps:

• a) passing an anode gas to the anode of a fuel cell;
• b) passing a cathode gas to the cathode of a fuel cell;
• c) removing sulfur-containing substances from the anode gas through a desulfurization device, and
• d) Determining the concentration of sulfur-containing substances in the anode gas by a sulfur sensor.

By the method described above, it is possible to determine which concentration of sulfur or of sulfur-containing substances is actually present in the anode gas or has occurred summarily over a defined period of time. This can be reacted to the fact that the sulfur content of the gas is different at different locations and also varies over time. It can thus be defined and determined in advance and in advance when a desulphurisation device should be replaced or when a sulfur breakthrough that is detrimental to the fuel cell system can be expected.

In one embodiment, the sulfur content can be determined by sulfur poisoning of the sulfur sensor. This is a particularly simple, reliable and accurate way of determining the concentration of sulfur-containing substances.

With regard to further advantages and technical features of the method according to the invention, reference is hereby explicitly made to the explanations in connection with the fuel cell system according to the invention, the figures, as well as to the description of the figures.

The present invention further provides the use of a fuel cell system, which may be configured as described above, in combined heat and power plants or combined heat and power plants. Combined heat and power plants can be in particular plants, which provides useful heat, for example for heating purposes or for production processes, in particular with the simultaneous production of electrical energy. Such a system can thus produce a decoupling of useful heat in power generation by means of fuels. In particular, use in fuel cell heaters, combined heat and power or combined heat and power plants (CHP) of different power class, such as ≥ 0.5 to over 1000 kW, may be possible.

Further advantages and advantageous embodiments of the subject invention are illustrated by the drawings and explained in the following description. It should be noted that the drawings have only descriptive character and are not intended to limit the invention in any way. Show it

1 a schematic representation of an embodiment of a fuel cell system;

2 a schematic representation of an embodiment of an arrangement of desulfurization and sulfur sensor;

3 a schematic representation of the embodiment 2 ;

4 a schematic representation of the measured values of a sulfur sensor over time;

5 a schematic representation of another embodiment of an arrangement of a sulfur sensor;

6 a schematic representation of the measured values of the sulfur sensor

5 over time;

7 a schematic representation of another embodiment of an arrangement of a sulfur sensor; and

8th a schematic representation of another embodiment of an arrangement of a sulfur sensor.

1 shows a schematic representation of an embodiment of a fuel cell system 1 , Such a fuel cell system 1 can be used, for example, in combined heat and power plants, or in cogeneration plants, or in motor vehicles.

The fuel cell system 1 includes according to 1 a fuel cell stack with at least one fuel cell 2 , such as a solid oxide fuel cell, with an anode 3 and a cathode 4 , Between the anode 3 and the cathode 4 is an electrolyte 5 arranged, wherein in the fuel cell 2 Anodic gas and cathode gas are electrochemically converted into electricity and heat. Conveniently, the fuel cell system includes 1 Further, an electrical connection, not shown, for tapping electrical energy from the fuel cell 2 or from a plurality of fuel cells 2 formed fuel cell stack.

The fuel cell system 1 may further comprise an anode circuit, such as with a suitable gas delivery unit, and heat exchangers for recirculating anode exhaust gas.

Furthermore, the fuel cell system 1 depending on the desired fuel gas used, a reformer 6 to carry out a reforming reaction and for the treatment of anode gas.

The fuel cell system 1 may further include a port for connecting an anode gas source 7 or for removing anode gas from the anode gas source 7 having an anode gas inlet 8th the fuel cell 2 by an anode gas guide 9 is fluidically connected. Conveniently, the anode gas while the reformer 6 run through. In the anode gas guide 9 can be about a desulfurization device 10 as later in detail with reference to the 2 to 8th is explained, and a suitable gas delivery unit 11 , such as a compressor, and a valve 12 be provided. The desulphurisation device 10 For example, it can be interchangeable and designed as a cartridge. In addition, a water entry device, such as an evaporator 47 , be provided.

Furthermore, the fuel cell system 1 a port for connecting a cathode gas source 13 or for removing cathode gas from the cathode gas source 13 exhibit. The cathode gas can be about with a suitable gas delivery unit 14 , such as a compressor, in a cathode or a gas guide 15 be encouraged. The cathode gas guide 15 can also be equipped with a cathode gas inlet 16 the fuel cell 2 be connected. In the cathode gas guide 15 can one or a plurality of heat exchangers 48 be arranged, for example, preheat by an interaction with the fuel cell exhaust gas, the cathode gas.

There may also be another cathode gas path 17 , for example with another gas delivery unit 18 Be provided with a valve 19 from the cathode gas guide 15 branches. The cathode gas path 17 can, for example, for a startup of the fuel cell system 1 be used and / or cathode gas, such as a water entry device or an evaporator 47 , in the reformer 6 for a reforming reaction.

One with a cathode exhaust outlet 20 connected cathode exhaust gas guide 21 can, for example via heat exchanger for preheating the cathode gas, as indicated by the arrow 22 is hinted at, with an afterburner 23 be connected so that cathode exhaust gas to the afterburner 23 is feasible. Through the afterburner 23 can be made using the from the cathode 4 effluent cathode exhaust gas are oxidized as oxidizing agent contained in the anode exhaust gas, for example, such as carbon monoxide (CO) to carbon dioxide (CO ₂ ) or hydrogen (H ₂ ) to water. For this purpose, anode exhaust gas from an anode exhaust gas outlet 24 by an anode exhaust gas guide 25 for example, by providing appropriate valves to the afterburner 23 feasible.

The afterburner 23 For example, with the reformer 6 be connected. In addition, downstream of the afterburner 23 an exhaust pipe 26 be provided, which in particular thermally connected to the heat exchanger 48 or the evaporator 47 , with an exit 27 may be connected, wherein the exhaust pipe 26 Part of the anode exhaust gas duct 25 or and / or the cathode exhaust gas guide 21 can be. Upstream of the exit 27 of the fuel cell system 1 can be another heat exchanger 28 be provided, which may be connected to a device for heat utilization.

In addition, a condensation device, not shown, may be provided, which condense water and a conveyor 29 a water entry device 30 can supply. This can also be from a source of water 31 , about a valve 32 , Water are supplied. The water entry device 30 can then, for example by a conveyor 33 and by a water guide 34 , Water of the anode gas guide 9 respectively.

Furthermore, with 35 an embodiment of the so-called hot box, ie the hot or heatable part of the fuel cell system 1 designated.

In the following, in particular, the desulfurization device will be described in detail 10 or explained with this related components.

An embodiment of the fuel cell system 1 is in 2 shown. In 2 is first in the anode gas guide 9 arranged desulfurization device 10 for removing sulfur-containing substances from the anode gas shown. Further is 2 to deduce that a sensor for detecting the sulfur content of the supplied anode gas, hereinafter referred to as sulfur sensor 36 is designated, is provided. In this case, the sulfur sensor 36 be designed as a catalytic sensor and / or as an electrochemical sensor. In particular, the sulfur sensor 36 a combustion catalyst, a fuel cell or a lambda probe, as will be explained in detail later.

Thus, the sulfur sensor can 36 based on a chemical and / or electrochemical reaction, in particular of the anode gas with oxygen, wherein the strength of the reaction as a function of the sulfur content decreases, in particular wherein the sulfur sensor 36 comprises at least one catalyst which can be poisoned by a sulfur-containing substance, in particular wherein the sulfur content can be determined from the decrease in the strength of the reaction, in particular which, for example, electrically and / or thermally, is measurable. Thus, determination of the sulfur content may be made especially by sulfur poisoning of the sulfur sensor 36 be determinable.

In the embodiment as a catalytic sulfur sensor 36 or as a combustion catalyst, for example, this can serve in particular to oxidize anode gas, wherein the catalyst loses activity by sulfur loading of the anode gas. By detecting specific parameters of this reaction, the poisoning can be tracked and thus for the sulfur content in the anode gas and also for the loading of the desulphurisation device 10 getting closed. For example, the sulfur sensor 36 Nickel, palladium, platinum or mixtures thereof. Furthermore, the catalyst of the sulfur sensor 36 be arranged in this embodiment in a combustion chamber and / or limit this, in which the supplied fuel gas or anode gas is reacted with oxygen-containing gas, such as the cathode gas or cathode exhaust gas, for example air.

It can, as in 3 is shown, further a temperature sensor 41 for determining the temperature of the sulfur sensor 36 and / or the sensor exhaust gas, wherein the sulfur content from a decrease in the temperature of the sulfur sensor 36 and / or the sensor exhaust gas, which is a measure of the oxidation of the anode gas, can be determined. Additionally or alternatively, further depending on the configuration of the sulfur sensor 36 a voltage and / or current and / or resistance measuring device for determining current, resistance or voltage of the sulfur sensor 36 be provided, wherein the sulfur content of a change in the voltage and / or the current and / or the resistance of the sulfur sensor 36 can be determined, as will be explained later.

Furthermore, the sulfur sensor 36 to a portion of the fuel cell system 1 , which is thermally controlled anyway, such as by thermal coupling to the hot box 35 be thermally coupled. In other words, the sulfur sensor 36 by a thermal coupling to a heatable part of the fuel cell system 1 during operation of the fuel cell system 1 be generated heat recoverable. Suitable positions for the sulfur sensor 36 include a heat exchanger 47 , a reformer 6 , and / or in an afterburner 23 into which the sulfur sensor 36 can be integrated.

The sulfur sensor 36 may also be in the anode gas guide 9 and / or in the anode exhaust gas duct 25 to remove anode exhaust gas from the fuel cell 2 and / or in one of the anode gas guide 9 and / or the anode exhaust gas guide 25 branching sensor guide 37 be arranged. In this case, the sulfur sensor 36 in gas-conducting connection, in particular in direct gas-conducting connection, with the desulphurisation device 10 be arranged.

According to 2 is the sulfur sensor 36 in the of the anode gas guide 9 branching and in particular to the anode gas guide 9 Parallel guided sensor guidance 37 arranged. That through the sensor guide 37 Guided anode gas can, for example, in the afterburner 23 or in an output of the fuel cell system 1 be directed. For example, the anode gas supply 9 and / or the anode exhaust gas guide 25 and / or the sensor guide 37 according to 2 a Internal coating, wherein the inner coating, the catalyst of the sulfur sensor 36 includes.

In this case, the desulfurization 10 have a certain flow path for the anode gas and can the sensor guide 37 from the desulfurization device 10 branch off at a location that is in a range of 50 is up to 90% of the flow distance for the anode gas, or may be the sulfur sensor 36 be arranged in a place that is in a range of 50 Up to 90% of the river route for the anode gas lies. For example, the sensor guide 37 approximately after ¾ run length of the desulphurisation device 10 branch off, or can the sulfur sensor 36 even after about ¾ run length of the desulfurization device 10 be arranged. The branch or the sulfur sensor 36 itself can also be between two particularly identical desulphurisation devices 10 be arranged so that when replacing the desulfurization 10 in front of the sulfur sensor 36 , or upstream of the sulfur sensor 36 , can be removed. The desulphurisation device 10 after the sulfur sensor 36 or downstream of the sulfur sensor 36 may be retained, for example, or upstream of the sulfur sensor 36 positioned and through a new desulfurization device 10 be replaced.

Preferably, the desulfurization device 10 before and after the branch or the sulfur sensor 36 be configured identically. Thus, for example, are several different sorbents for the sulfur-containing substances in the desulfurization 10 provided, they may preferably all before and after the branch to the sulfur sensor 36 or the sulfur sensor 36 be provided for yourself.

The sulfur sensor 36 or the sensor guide 37 can, for example, on the inside of a heat exchanger, such as the heat exchanger 48 , Which is traversed by air or exhaust gas, or in an air or exhaust gas flow-through conduit, may be arranged approximately as a tube, wherein the anode gas, the sensor guide 37 or the sulfur sensor 36 flows through. For example, the sulfur sensor 36 in gas-conducting connection to the cathode gas guide and / or the cathode exhaust gas guide 21 for discharging cathode exhaust gas from the fuel cell 2 and / or an air supply.

Preferably, for the sulfur sensor 36 a position can be selected which is either kept at a constant temperature by the system control, such as at the identical operating point of the system, or whose temperature is already measured by the system. Includes the sulfur sensor 36 a catalyst, so is for example the sensor guide 37 coated with catalyst inside, it can with simultaneous supply of anode gas and the presence of an oxygen-containing gas stream or air flow approximately in the sensor guide 37 a combustion and thus a temperature increase can be determined. For this purpose, for example, the sensor guide 37 flowed through with cathode air or exhaust gas. Preferably, the same catalyst is used, which is also used in the reformer 6 or in the fuel cell 2 can be used, namely in particular nickel, or palladium, platinum or mixtures thereof.

Specific installation options for sensor guidance 37 or for the sulfur sensor 36 For example, they may include: the outer wall of the reformer 6 , the inner wall of the combustion chamber of the afterburner 23 , the inside of the wall of the fuel cell 2 surrounding hotbox 35 , or the inside of a heat exchanger 28 . 48 for example for air preheating or for cathode gas preheating.

The sulfur sensor 36 For example, in a steady-state state of the system, ie when all temperatures are constant, they can work particularly advantageously. In the design of the areas before and after the branch or the sulfur sensor 36 even according to 2 In particular, it can be ensured with regard to the positioning that there is enough time between the detection and a breakthrough so as to perform a stop and / or a start procedure. Due to the lifetime of the desulfurization device 10 usually at least a few months, this is not a limitation.

In 3 is a further illustration of the embodiment 2 shown. It is the sulfur sensor 36 represented by which or along which a stream of oxygen-containing gas, by the arrow 38 is characterized and serves for an oxidation of the anode gas flows. This can be about a cathode gas stream, cathode exhaust stream or burner exhaust stream of the afterburner 23 be, or from the cathode gas stream, cathode exhaust stream or burner exhaust stream, by the arrow 39 is indicated, branch off. In addition, the potentially sulfur-containing substances comprising anode gas flow flows through the sulfur sensor 36 or along it, for example through the sensor guide 37 , The sulfur sensor 36 can be a temperature sensor or temperature sensor 41 have, with the temperature of the sensor exhaust gas and the sulfur sensor 36 even, like those in one Combustion chamber of the sulfur sensor 36 prevailing temperature, can be determined. The temperature sensor 41 thus measures the temperature increase caused by the catalytic oxidation of the anode gas, especially if a catalytic sulfur sensor 36 is used. For this purpose, for example, a gas-conducting compound of the sulfur sensor 36 be provided to the anode gas or an oxygen-containing gas, or both gases can flow through a common tube.

By a temperature measurement can on the aging state of the desulfurization 10 getting closed. This is in 4 shown. In 4 a diagram is shown in which the determined temperature (T) is plotted qualitatively against the time (t). It can be seen that until a time a), at which a full or almost full load of the part of the desulfurization 10 is present, the upstream of the sulfur sensor 36 or a branch to the sensor guide 37 the temperature is slowly decreasing due to a slight degradation under normal conditions. From the point a), which is typically in a range of 2 Years, there is a stronger degradation caused by a sulfur breakthrough triggered by an increasing poisoning of the catalyst instead.

This temperature measurement can be evaluated in a control unit. In this case, the increase in the temperature over time can be determined in the control, in particular in the event that the system control regulates the temperature in the vicinity of the sulfur sensor 36 keeps constant. Instead of the absolute temperature, the temperature difference to the environment or to an incoming gas, such as air, can be measured. If a predetermined limit or a predetermined slope is exceeded, a warning can be issued, which is visible for example by the user or via a communication interface by the maintenance personnel, thereby replacing the desulfurization 10 , such as a cartridge, can be arranged.

In 5 is a further embodiment of the fuel cell system according to the invention 1 shown. In this embodiment, as a sulfur sensor 36 a lambda probe 42 Find use. Purely exemplary for the use of a lambda probe 42 as a sulfur sensor 36 this may be in the exhaust path after the cathode 4 or after the afterburner 23 be used. Again, the gas to be tested on the lambda probe 42 or the sulfur sensor 36 or in the sensor guide 37 where also the degradation of the sulfur sensor 36 or the lambda probe 42 can be measured. This can also be a stream 38 be supplied to oxygen-containing gas. The measurement can be based on the speed of the degradation of the lambda probe 42 , as in 6 shown, done. In 6 is the signal S of the lambda probe 42 along the time t shown as curve A, which indicates a significantly increasing degradation from a point a).

Alternatively, two lambda probes 42 . 43 be used, with a lambda probe 43 in this case can serve as a reference and the corresponding signals, illustrated by the curve A for the lambda probe 42 and the curve B for the reference lambda probe 43 to be compared, as in 6 is shown. This may be particularly interesting in systems where a lambda probe 43 anyway for Luftmassenstrom- and thus used for temperature control. By the thermal coupling to a hot or heatable part of the fuel cell system 2 or the hotbox 35 or by an arrangement in a hot area can on the in the lambda probe 42 . 43 otherwise usual heating can be omitted, whereby costs can be saved.

In 7 is another embodiment of the present fuel cell system 1 shown. According to the embodiment according to 7 can the sulfur sensor 36 as a fuel cell 44 , such as a SOFC fuel cell, for example, with a tubular, with external cathode and internal anode equipped fuel cell 44 be educated. In this case, by a voltage measuring device 45 measured voltage serve as an indicator of the sulfur content of the anode gas. To avoid coking, air can also be metered into the interior anode, for example, here.

Alternatively, in the embodiment according to 8th when using a fuel cell 44 as a sulfur sensor 36 a current flow, for example via a resistor 49 , can be produced, wherein on the anode side product water can arise. The fuel cell 44 For example, it may be a medium temperature SOFC fuel cell. Due to the current flow is on the anode of the fuel cell 44 Produces water, which is why it can be dispensed with the supply of air to the anode and the input side 46 can be closed. The sulfur sensor 36 can also be adapted in its configuration, the power-generating cells in the fuel cell stack and there, for example, outside of the pantograph plates (in planar stacks) or outside of the pantograph (in tubular stacks) can be arranged.

Also when using a fuel cell 44 as a sulfur sensor 36 can the through Degradation caused by sulfur-containing substances serve as a measure of the sulfur content of the anode gas, such as measurable by the current flow or the voltage, as described above, or by measuring a resistance of the sulfur sensor 36 ,

The sulfur sensor 36 In particular, it can be easily accessible and with the desulphurisation device 10 be changeable. Alternatively, several sulfur sensors can be used 36 be installed at the beginning, which are used successively for measurement. When the outputs are merged, a common temperature measuring point is sufficient. The unused inputs are then closed.

• a) Führen eines Anodengases zu der Anode 3 einer Brennstoffzelle 2;
• b) Führen eines Kathodengases zu der Kathode 4 einer Brennstoffzelle 2;
• c) Entfernen von schwefelhaltigen Substanzen aus dem Anodengas durch eine Entschwefelungsvorrichtung 10, und
• d) Ermitteln der Konzentration an schwefelhaltigen Substanzen in dem Anodengas durch einen Schwefelsensor 36.

A method of controlling such a fuel cell system 1 can include the following process steps:

• a) Passing an anode gas to the anode 3 a fuel cell 2 ;
• b) passing a cathode gas to the cathode 4 a fuel cell 2 ;
• c) removing sulfur-containing substances from the anode gas through a desulfurization device 10 , and
• d) Determining the concentration of sulfur-containing substances in the anode gas by a sulfur sensor 36 ,

In particular, the sulfur content may be due to sulfur poisoning of the sulfur sensor 36 be determined.

A measurement need not be made continuously, but may at certain intervals or at certain operating points in which the ambient temperature of the sulfur sensor 36 or the air flow in the surrounding space, for example, is sufficiently known to be measured. In this case, in the event that a sulfur breakthrough is detected or is expected and thus the desulfurization should be replaced, a warning will be issued.

The supply of the gas to be measured to the sulfur sensor 36 can be equipped with a mechanical or electronic flow limiter, for example, so that even with fluctuating gas pressure always the same amount of gas flows and thus prevail constant measuring conditions.

Furthermore, several sulfur sensors 36 be built in, which are used sequentially in the event that the sulfur sensors 36 successively poisoned by sulfur-containing substances. If the corresponding outputs are merged, a common measurement position, such as temperature measurement position, may be sufficient.

For units with a peak boiler for heat generation, the sulfur sensor can 36 continue to be installed in this burner in the hot exhaust stream near the burner.

The above-described arrangement of the sulfur sensor 36 can in principle also be used analogously to the detection of other pollutants, such as for the detection of alkali. In principle, it is also possible to use it in the air and / or gas path, ie in the cathode gas path and / or in the anode gas path.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6682836 B2 [0003]
• DE 102010001011 A1 [0004]

Claims (15)

Fuel cell system with a fuel cell stack, comprising - at least one fuel cell ( 2 ); An anode gas guide ( 9 ) for supplying anode gas to the fuel cell ( 2 ); A cathode gas guide ( 15 ) for supplying cathode gas to the fuel cell ( 2 ); and a desulphurisation device ( 10 ) for removing sulfur-containing substances from the anode gas, wherein - a sulfur sensor ( 36 ) is provided for detecting the sulfur content of the supplied anode gas. Fuel cell system according to claim 1, wherein the sulfur sensor ( 36 ) based on a chemical and / or electrochemical reaction, wherein the strength of the reaction as a function of the sulfur content decreases, in particular wherein the sulfur sensor ( 36 ) comprises at least one catalyst poisonable by a sulfur-containing substance, in particular wherein the sulfur content can be determined from the decrease in the strength of the reaction, in particular which, for example, electrically and / or thermally, is measurable. Fuel cell system according to claim 1 or 2, wherein the sulfur sensor ( 36 ) is designed as a catalytic and / or electrochemical sensor, in particular wherein the sulfur sensor ( 36 ) comprises a combustion catalyst, a fuel cell or a lambda probe. Fuel cell system according to claim 3, wherein the catalyst of the sulfur sensor ( 36 ) Comprises nickel, palladium, platinum or mixtures thereof. Fuel cell system according to one of claims 1 to 4, wherein the sulfur sensor ( 36 ) - in the anode gas guide ( 9 ) and / or - in an anode exhaust gas duct ( 25 ) for discharging anode exhaust gas from the fuel cell ( 2 ) and / or - in one of the anode gas guide ( 9 ) and / or from the anode exhaust gas duct ( 25 ) branching sensor guide ( 37 ) is arranged. Fuel cell system according to one of claims 1 to 5, wherein the anode gas guide ( 9 ) and / or the anode exhaust gas duct ( 25 ) and / or the sensor guide ( 37 ) has an inner coating, wherein the inner coating of the catalyst of the sulfur sensor ( 36 ). Fuel cell system according to one of claims 1 to 6, wherein the sulfur sensor ( 36 ) in gas-conducting connection, in particular in direct gas-conducting connection, with the desulphurisation device ( 10 ) is arranged. Fuel cell system according to one of claims 1 to 7, wherein the desulfurization device ( 10 ) has a certain flow path for the anode gas and wherein the sensor guide ( 37 ) from the desulfurization device ( 10 ) branches off at a point which is in a range from where the sulfur sensor ( 36 ) is disposed at a position which is in a range of Fuel cell system according to one of claims 1 to 8, wherein - a temperature sensor ( 41 ) for determining the temperature of the sulfur sensor ( 36 ) and / or the sensor exhaust gas is provided, and wherein the sulfur content from a decrease in the temperature of the sulfur sensor ( 36 ) and / or the sensor exhaust gas can be determined, and / or wherein - a voltage and / or current and / or resistance measuring device for determining the current, resistance and / or voltage of the sulfur sensor ( 36 ), wherein the sulfur content from a change in the voltage and / or the current and / or the resistance of the sulfur sensor ( 36 ) can be determined. Fuel cell system according to one of claims 1 to 9, wherein the sulfur sensor ( 36 ) in gas-conducting connection to the cathode gas guide ( 15 ) and / or a cathode exhaust gas duct ( 21 ) for discharging cathode exhaust gas from the fuel cell ( 2 ) and / or an air supply is arranged. Fuel cell system according to one of claims 1 to 10, wherein the sulfur sensor ( 36 ) by a thermal coupling to a heatable part of the fuel cell system ( 1 ) during operation of the fuel cell system ( 1 ) Waste heat can be heated. Fuel cell system according to one of claims 1 to 11, wherein the sulfur sensor ( 36 ) in a heat exchanger ( 28 . 48 ), into a reformer ( 6 ), and / or in an afterburner ( 23 ) is integrated. Fuel cell system according to one of claims 1 to 12, wherein a sulfur loading of the desulfurization device ( 10 ) as a function of the sulfur sensor ( 36 ) is determined, in particular wherein when exceeding a predetermined threshold value of sulfur loading a warning, in particular for renewing the desulfurization ( 10 ), is dispensable. Method for operating a fuel cell system ( 1 ), comprising the method steps: a) passing an anode gas to the anode ( 3 ) a fuel cell ( 2 ); b) passing a cathode gas to the cathode ( 4 ) a fuel cell ( 2 ); c) removing sulfur-containing substances from the anode gas through a desulphurisation device ( 10 ), and d) determining the concentration of sulfur-containing substances in the anode gas by a sulfur sensor ( 36 ), in particular wherein the sulfur content is due to sulfur poisoning of the sulfur sensor ( 36 ) is determined. Use of a fuel cell system ( 1 ) according to one of claims 1 to 10 in combined heat and power plants or combined heat and power plants.

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