WO2001095415A2

WO2001095415A2 - Fuel cell system and method for starting up a fuel cell system

Info

Publication number: WO2001095415A2
Application number: PCT/DE2001/002111
Authority: WO
Inventors: Wolfgang Herdeg; Holger Klos; Martin Sattler; Franz Reichenbach; Sabine Hess; Hans-Dieter Wilhelm; Jürgen HABRICH; Karl Eck; Markus Keutz; Thomas Zapp
Original assignee: Vodafone Ag
Priority date: 2000-06-05
Filing date: 2001-06-05
Publication date: 2001-12-13
Also published as: DE10028331A1; EP1290745A2; WO2001095415A3; DE10028331C2

Abstract

The invention relates to a fuel cell system comprising a fuel cell, which has an anode part with a supply and drain line for a fuel, a cathode part with a supply and drain line for an oxidation agent, and a membrane. The invention is also provided with a device, which is connected to the fuel cell via the fuel supply line, for producing/preparing the fuel. A sensor element for determining the concentration and a valve, which is connected to a bypass line that circumvents the fuel cell, are located in the fuel supply line. A fuel-precursor tank is connected to the device for producing/preparing the fuel via a fuel-precursor supply line, whereby at least one transport device is provided in said supply line. The transport devices are electrically connected to a battery in such a way that said devices are driven by the battery during the start-up phase of the fuel cell system.

Description

Fuel cell system and method for starting up a fuel cell system

description

The present invention relates to a fuel cell system and a method for starting up such a fuel cell system.

Fuel cells have been known for a long time and have become significantly more important, particularly in the automotive industry.

A chemical reaction generates electricity in a fuel cell. This turns a fuel and an oxidant into electrical energy and water

Reaction products converted. A fuel cell essentially consists of an anode part, a membrane and a cathode part. The membrane is made of porous, electrically conductive material and is arranged between the anode and the cathode in order to exchange ions. The fuel is supplied on the anode side, while the oxidant is supplied on the cathode side. Protons or hydrogen ions are generated at the anode by catalytic reactions and move through the membrane to the cathode. At the cathode, the hydrogen ions react with the oxygen and water is formed. The electrons released during the reaction can be conducted as electrical current through a consumer, for example the electric motor of an automobile.

For example, hydrogen as fuel and oxygen or air as oxidizing agent are used as gaseous reactants for the fuel cell. If you want to operate the fuel cell with a readily available or storable fuel such as natural gas, methanol or the like, you first have to convert the hydrocarbon into a hydrogen-rich gas. In particular, when such fuel cells are used in vehicles, there is a desire for them to be ready for use as quickly as possible, ie for all components to be brought to operating temperature as quickly as possible and to achieve their full performance.

It is therefore an object of the present invention to provide a fuel cell system which, after starting, can be used as quickly as possible and yet in a reliable manner. The start-up phase or start-up phase should be kept as short as possible. Furthermore, a method for starting up such a fuel cell is to be provided.

The object is achieved according to the first aspect of the invention by a fuel cell system, with a fuel cell having an anode part with a feed line and a discharge line for a fuel, a cathode part with a feed line and a discharge line for an oxidizing agent and a membrane, with a device for generating / processing the fuel, which is connected to the fuel cell via the fuel feed line, wherein a sensor element for determining the concentration and a valve, which is connected to a bypass line bypassing the fuel cell, are provided in the fuel feed line, with a delivery device and a valve are arranged in the oxidant feed line, the

Valve is connected to a bypass line bypassing the fuel cell, a fuel tank, which is connected via a fuel feed line to the device for producing / processing the fuel, at least one delivery device being provided in the fuel feed line, and to an additional electrical power source, in particular a battery, which is electrically connected to the conveyor devices so that they are driven or can be driven by the power source during the starting phase of the fuel cell system.

With a fuel cell system according to the invention designed in this way, it becomes possible to quickly make the individual elements and components operational when it is started, so that the starting phase or start-up phase of the fuel cell system can be kept very short.

A basic idea of the present invention is that those components of the fuel cell system that are absolutely necessary for starting up the fuel cell system are initially driven by an additional electrical power source during the starting phase. For example, a battery, in particular one, can be used as an additional electrical power source rechargeable battery, also a capacitor can be used. It is particularly recommended to use capacitors with excessive storage density compared to conventional capacitors, which are also called "ultracaps" and can withstand an extremely high number of cycles (loading and unloading). The energy required by the individual components during the starting phase of the fuel cell system can be provided immediately via the additional electrical power source. The power requirement for the electrical power source should be as small as possible. During normal operation of the fuel cell system, the individual electrical consumers of the fuel cell system are then supplied via the fuel cell itself, the additional electrical power source being recharged via the fuel cell. The energy supply for the thermal consumers is realized through the use of fuel.

During the start-up phase of the fuel cell system, various aspects have to be taken into account, which have to run at the same time or at short intervals if possible. Some of these aspects are explained in more detail in the further course of the description.

If the fuel cell is to be operated, for example, with hydrogen as fuel, the hydrogen must first be produced or processed, for example, from a liquid or gaseous fuel consisting of hydrocarbons, such as methanol, methane, gasoline, natural gas, coal gas, biogas or the like. This production or processing of the fuel takes place in the device for generating / processing the fuel. For this purpose, the fuel is fed into the fuel tank via a fuel feed line

Device fed. At least one delivery device is provided in the fuel supply line to support the feed. This conveying device or these conveying devices, which can be designed when using liquid fuel as a pump or the like, usually initially convey the fuel into an intermediate tank, from which the device for

Generation / preparation of the fuel is supplied. During startup of the fuel cell system, it is therefore necessary for the at least one delivery device, for example a fuel injection pump, to be driven via the additional electrical power source. The conveyor is advantageously designed such that only a small electrical power is required.

In an advantageous embodiment, the intermediate tank can be higher than various heating devices of the fuel production and processing system, which are in the further course of the description will be explained in more detail and are designed for example as a burner or the like. These heating devices are used to supply thermal energy to various thermal consumers. In such a case, the fuel can be transported by means of the hydrostatic pressure. A separate conveying device can then be dispensed with and only a corresponding valve for controlling the inflow is required. With such a configuration, the heating devices could be ignited electrically and the system could be brought up thermally.

The fuel gas leaving the device for generating / processing the fuel is fed into the fuel cell via the fuel feed line. If the fuel cell is operated with hydrogen and this is generated from one of the fuels already mentioned as a hydrogen-rich gas, essentially hydrogen and carbon dioxide are generated during the conversion process. Furthermore, substances which are harmful to the fuel cell, such as carbon monoxide or the like, also arise and must be removed before the fuel enters the fuel cell. From a certain concentration, such harmful substances result in the power output by the fuel cell being reduced and the efficiency of the fuel cell being greatly reduced.

The sensor element for determining the concentration of harmful substances in the fuel and the bypass line bypassing the fuel cell, which is connected to the fuel supply line via the valve, can prevent harmful substances from accidentally entering the fuel cell. Basically that is

Invention is not limited to the detection of certain substances.

After the fuel has escaped from the device for generating / processing the fuel, it flows through the sensor element for determining the concentration, through which the respective concentration of harmful substances in the

Fuel can be detected and measured. If the concentration of a harmful substance in the fuel exceeds a predetermined limit value, the gas flow of the fuel is not directed into the fuel cell via a corresponding position of the valve, but instead bypasses the fuel cell via the bypass line. The consequence of this is that the fuel cell cannot be poisoned by the substances in the gas stream. As long as the sensor element measures a concentration of the harmful substances that exceeds the limit value, the gas flow is guided past the fuel cell. Only at the moment when the concentration of harmful substances falls below a permissible limit value is the gas stream introduced into the fuel cell, so that the required electrical power can then be supplied by the fuel cell.

Another aspect that must be considered when starting the fuel cell system is the supply of the oxidizing agent. The oxidizing agent, for example oxygen or air, is fed to the fuel cell via the oxidizing agent feed line. For this purpose, a suitable conveying device is provided in the oxidant feed line. This conveying device can be designed, for example, but not exclusively, as a pump, compressor or blower, and here in particular as a regulated blower.

The oxidizing agent is sucked into the oxidizing agent feed line via the conveying device. In order to avoid damage to the fuel cell, it is necessary for the oxidizing agent to be moistened when it enters the fuel cell. During the operation of the fuel cell, this moistening of the oxidizing agent can be carried out, for example, by means of water formed in the fuel cell. However, such water is not yet available during the start-up phase of the fuel cell. The one entering the fuel cell

Oxidant stream would thus enter the fuel cell dry during the starting phase, which would lead to the fuel cell drying out for a short time.

To avoid such drying out of the fuel cell, this is in the

Oxidizing agent supply valve is provided, which is connected to a bypass line bypassing the fuel cell. During the start-up phase of the fuel cell system, the valve is switched in such a way that the oxidant gas stream is not directed into the fuel cell, but rather bypasses it. The oxidant gas stream directed past the fuel cell can then take on further functions in the fuel cell system, as will be explained in more detail in the further course of the description. It is therefore necessary that the conveyor device located in the oxidant feed line is already driven by the additional electrical power source during the starting phase of the fuel cell system. During normal operation of the fuel cell system, the delivery device can then be driven via the power generated by the fuel cell itself. The conveyor in the oxidant supply line, for example a compressor, should be controlled in such a way that it starts to demand power as late as possible.

The fuel cell system designed according to the invention ensures that those which are absolutely necessary for the startup process of the fuel cell system

Components can be actuated immediately, so that the starting phase, that is, the phase until the fuel cell can supply the electrical current required for the operation of a consumer, can be kept very short, without causing damage to the fuel cell or individual components of the burner - can come.

Advantageous embodiments of the fuel cell system result from the subclaims.

Two delivery devices can advantageously be provided in the fuel feed line. One of these delivery devices can be designed, for example, as a fuel pump. The fuel is pumped out of the fuel tank via this fuel pump and passed into the device for generating / processing the fuel. The conveyor device which is also provided can be designed as a double pump, i.e. be prepared for the simultaneous promotion of two media. such

Double pumps have the task, for example, of mixing the pure fuel pumped out of the fuel tank with another medium, for example water or the like, before entering the device for generating / processing the fuel. This fuel mixture generated in the double pump is then either temporarily stored in an intermediate tank, or is fed directly into the device for producing / processing the fuel. Since the supply of fuel or the fuel mixture is already required in the starting phase of the fuel cell system, both delivery devices are preferably driven via the additional electrical power source during the starting phase of the fuel cell system.

In another embodiment, it can be provided that the intermediate tank is always filled and the fuel mixture is conveyed out of the intermediate tank. This can be done, for example, without or with a corresponding conveyor device which can be connected to the electrical power source.

The valves for the bypass lines can preferably be designed as three-way valves. Such valves allow easy and accurate control of the Gas streams. Three-way valves can usually be controlled quickly, so that they can be opened or closed without delay. In this way, if a value exceeding the permissible limit value for harmful substances is measured in the sensor element for determining the concentration, this information can be quickly implemented, for example via a corresponding computer, a control and control device or the like, so that poisoning of the fuel cell by harmful Substances or their drying out is prevented. The drives required to actuate the valves can also be driven via the additional electrical power source during the starting phase of the fuel cell system.

In a further embodiment, the device for generating / processing the fuel can have a number of reactor elements, individual reactor elements being designed as heat sinks, each of which is thermally connected to a heating device. The heating device in turn is preferably connected to the fuel supply line or the electrical power source for energy supply in order to enable the system to be started up thermally.

The individual reactor elements of the arrangement for generating / processing the fuel are connected to one another via corresponding lines, so that the fuel can flow through the individual reactor elements during its generation or processing.

Exothermic reactions take place in some of the reactor elements, which means that heat is released. These reactor elements are called heat sources in the following.

In contrast, heat is required in other reactor elements. These reactor elements are referred to below as heat sinks. A reactor element functioning as a heat sink can be designed, for example, as an evaporator. Such an evaporator is required, for example, if hydrogen is to be reformed from methanol, natural gas or the like. Another heat sink is a reformer which is connected downstream of the evaporator and in which the fuel used as the starting material is reformed to hydrogen with water vapor.

The reactor elements functioning as a heat source can be designed, for example, as selective oxidation. This reactor element is required if the

Hydrogen is processed by the partial oxidation process. Here, the gas is first cleaned in a shift reactor by means of a homogeneous water gas reaction and finely cleaned in the subsequent stage - the selective oxidation. The reactor elements designed as heat sinks are connected to a heating device, via which they can be brought to their required operating temperature. The heating devices can be designed, for example, but not exclusively, as burners, in particular as catalytic burners, or as electrical heating elements.

If the heating device is designed as an electrical heating element, the required electrical energy can be provided by the additional electrical power source during the starting phase of the fuel cell system. The electrical heating device can be designed, for example, as a heating wire, heating coil or the like.

If the heating device is designed as a burner, in particular as a catalytic burner, it is expediently connected to the fuel supply line for energy supply. The heating device can thus be supplied with fuel as long as necessary during the starting phase of the fuel cell system. The fuel can be drawn from the fuel tank in the fuel line by means of the delivery device and made available to the heating devices designed as burners in the fuel production. Suitable metering devices can optionally be provided between the conveying device and the heating devices.

In another embodiment, it is possible, for example, to arrange the heating devices lower than the fuel tank so that the fuel is transported via the hydrostatic pressure and a special delivery device can be dispensed with. The heaters are preferably ignited electrically.

Furthermore, a bypass line can be provided for temporarily bypassing the conveyor. With normal arrangement of the elements, the fuel can then be transported during normal operation on the basis of the hydrostatic principle solely on the basis of the hydrostatic pressure. If there is an increased fuel requirement, the fuel can be passed or pumped via the delivery device by providing appropriate valves.

For the temperature control of the reactor elements, an electrically operated conveying device can advantageously be provided, which is arranged in a flow circuit for a heating / cooling medium passing through the reactor elements and for the power supply the additional electrical power source is connected. This conveyor device can thus also be driven via the electrical power source during the starting phase of the fuel cell system. The flow circuit of the heating / cooling medium, which is designed, for example, as a closed flow circuit, ensures that heat is transported between the individual reactor elements. The heat released in the reactor elements functioning as a heat source can thus be used to additionally heat the reactor elements designed as a heat sink. As a result, the thermal energy generated by the reactor elements acting as a heat source is not lost.

Depending on the use of a heating / cooling medium flowing through the flow circuit, the conveying device can advantageously be designed as a pump or blower. An especially advantageous heating / cooling medium is, for example, an oil, and here in particular a highly heat-resistant oil. The flow rate and the throughput of the heating / cooling medium in the

Effectively influence the flow circuit and thus regulate the heat exchange.

In a further embodiment, the sensor element can be designed to determine the concentration of carbon monoxide in a gas stream, in particular in the fuel stream. As has already been described in detail above, these are:

Carbon monoxide is a very harmful gas for the fuel cell, which can arise from the reforming of hydrogen from hydrocarbons. The presence of carbon monoxide in the fuel can be detected at an early stage via a correspondingly designed sensor element, so that suitable measures can be taken, such as switching the valve and bypassing the gas flow via the bypass line past the fuel cell.

The sensor element for determining the concentration can advantageously be designed as an infrared spectrometer. Infrared spectrometry measures molecular vibrations and rotations by absorbing radiation in the infrared region of the electromagnetic spectrum. In another embodiment, the sensor element for determining the concentration can be designed as a sensor element for measuring the nuclear magnetic resonance of a substance. However, the invention is not limited to the two examples mentioned, so that other configurations of the sensor element for determining the concentration are also possible. The oxidant discharge line can advantageously be connected to a filter, in particular an activated carbon filter, which in turn has a connecting line to the fuel tank. As will be explained in more detail below, the oxidant, for example an air stream, which bypasses the fuel cell during the starting phase of the fuel cell system can be used to clean and regenerate the filter, which performs various functions.

When a fuel tank is filled with fuel that is to be converted into fuel for operating the fuel cell, and also when the fuel tank is vented, hydrocarbons are generally released. Since hydrocarbons are harmful to the environment and can also cause damage in the fuel cell system, they must be bound in a suitable manner. This is usually done via the filter element, for example the activated carbon filter. However, this filter element must be regenerated from time to time to ensure the functionality. If timely regeneration is neglected, the hydrocarbons can reach the atmosphere unhindered through the filter element.

To regenerate the filter element, the oxidant gas stream is introduced into it or passed through it. During the starting phase of the fuel cell system, the oxidant stream is used for this purpose, which is bypassed the fuel cell via the bypass line. During normal operation of the fuel cell, the oxidant gas stream is used for this purpose, which is derived from the fuel cell via the corresponding discharge line. The actual regeneration of the filter element takes place in that the oxidant gas stream entrains the hydrocarbon molecules located in the filter element.

The filter can advantageously also be connected to the heating device or devices in the device for generating / processing the fuel. In this way, the oxidant stream, after flowing through the filter and desorbing and entraining the hydrocarbons, can be used in the production of the fuel. The heating devices, which are in particular designed as burners, are supplied with the fuel absorbed or the hydrocarbons absorbed when the filter is being regulated, as a result of which, among other things, the gas treatment process within the device for generating / processing the fuel is brought to the corresponding operating temperature when the fuel cell system is started up becomes. In a further embodiment, an arrangement for heating / cooling the fuel cell via a heating / cooling medium can be provided, which has a heating device which is connected to the fuel supply line or the additional electrical power source. With such an arrangement, the fuel cell can be quickly and easily heated to the ideal temperature range during the starting phase. Heat is usually generated in the fuel cell during operation, which causes it to heat up. After the operating temperature has been reached, the excess heat loss generated in a fuel cell must be dissipated. However, the heating phase of the fuel cell until the ideal operating temperature is reached takes a certain amount of time, which is particularly disadvantageous for a faster start of the fuel cell. By means of the heating device provided in the arrangement, the fuel cell can be preheated during the starting phase and thus accelerated to the ideal operating temperature. This means that the fuel cell is fully operational in a very short time.

If the heating device is designed as a burner, in particular as a catalytic burner, it should expediently be connected to the fuel feed line for its energy supply. In this way, the heating device can be supplied with fuel via the delivery device. If the heating device is designed as an electrical heating device, it is preferably connected to the additional electrical power source.

A conveyor for the heating / cooling medium, which is connected to the additional electrical power source, can preferably be provided in the arrangement for heating / cooling the fuel cell.

In an advantageous embodiment, the arrangement for heating / cooling the fuel cell has a flow line for the heating / cooling medium, which is connected to the fuel cell in such a way that an indirect thermal exchange takes place or takes place between the fuel cell and the heating / cooling medium in the flow line can. For this purpose, the flow line can penetrate the fuel cell, for example, at least in some areas. When the heating / cooling medium flows through the flow line, heat is exchanged between the heating / cooling medium and the fuel cell.

During the starting phase of the fuel cell system, the heating / cooling medium in the flow line is heated via the heating device. The heated heating / cooling medium enters the fuel cell, where it stores the stored heat releases the fuel cell and heats it up. During normal operation of the fuel cell, the heat loss generated in it is transported away via the heating / cooling medium.

Depending on the type of heating / cooling medium used, whether liquid or gaseous, the delivery device can be designed as a pump, blower or the like.

Since heating the fuel cell to the ideal operating temperature as quickly as possible is also advantageous for the rapid start of the fuel cell system, the conveying device is preferably connected to the additional electrical power source, so that it can also be operated immediately when the fuel cell system is started.

According to the second aspect of the present invention, a method for starting up a fuel cell system according to the invention as described above is provided, which is characterized according to the invention by the following steps:

a) during the start-up phase, suction of oxidizing agent into the oxidizing agent supply line via the delivery device operated by the additional electrical power source and bypassing the oxidizing agent by appropriate position of the valve via the bypass line past the fuel cell,

b) introducing fuel from a fuel tank via the at least one delivery device operated in the by the additional electrical power source

Fuel supply line or via a bypass line in the device for generating / processing fuel, measuring the pollutant concentrations of the fuel leaving this device by means of the sensor element for determining the concentration and bypassing the fuel by appropriate position of the valve via the bypass line past the fuel cell as long as the fuel for the Fuel cell has harmful concentrations of pollutants, the operation of the individual conveying devices being carried out during the starting phase of the fuel cell system via the additional electrical power source and during normal operation of the fuel cell system via the fuel cell itself.

The method according to the invention makes it possible in a simple manner to start the fuel cell system without causing damage to the fuel cell or individual components of the fuel cell system can come, and the start phase of the fuel cell system is kept very short. Regarding the advantages, effects, effects and the mode of operation of the method according to the invention, reference is made in full to the above statements regarding the fuel cell system according to the invention and reference is hereby made. Preferred embodiments of the method result from the subclaims.

Advantageously, in the starting phase of the fuel cell system, fuel can be introduced into the heating device or heating devices for the reactor elements in the device for generating / processing the fuel via the at least one delivery device in the fuel supply line or the bypass line operated by the additional electrical power source, or the heating device or Heating devices can be operated via the additional electrical power source in order to supply the reactor elements with the thermal energy required for the operation of the device for generating / processing the fuel.

In a further embodiment, in the start-up phase of the fuel cell system, a delivery device for a heating / cooling medium provided in the device for generating / processing the fuel can be driven to control the temperature of the reactor elements via the electrical power source.

In the start-up phase of the fuel cell system, the oxidizing agent bypassing the fuel cell can preferably be introduced into the filter connected to the fuel tank, in particular the activated carbon filter, in order to rinse it and then to add the oxidizing agent enriched in this way with fuel into the heating device or devices to generate / prepare the fuel and use it there for combustion, thereby bringing the reactor elements to temperature.

In a further embodiment, in the starting phase of the fuel cell system, fuel can be introduced into the heating device provided in the arrangement for heating / cooling the fuel cell via the at least one conveying device in the fuel supply line, or the heating device is supplied via the additional electrical power source operated to bring the fuel cell to the required operating temperature. Preferably, a fuel cell system as described above or a method as described above for starting a fuel cell system in or for a vehicle, in particular a vehicle with an electric traction drive, can be used. Due to the rapid development of fuel cell technology in the vehicle sector, such use currently offers particularly good applications. However, other possible uses are also conceivable. These include fuel cells for mobile devices such as computers or the like up to power plants. Here, fuel cell technology is particularly suitable for the decentralized energy supply of houses, industrial plants or the like.

The present invention is preferably used in connection with fuel cells with polymer membranes (PEM). These fuel cells have a high electrical efficiency, cause only minimal emissions, have an optimal part-load behavior and are essentially free of mechanical

Wear.

The invention will now be explained in more detail using an exemplary embodiment with reference to the accompanying drawings. The sole FIGURE shows a schematic view of a fuel cell system according to the invention.

In the figure, a fuel cell system 10 is shown, which is used to operate an electric drive for a vehicle.

The fuel cell system 10 has a fuel cell 11 with an anode part 12, a cathode part 14 and a membrane 13. The anode part 12 is connected to a feed line 15 and a discharge line 16 for a fuel, in the present case hydrogen. The cathode part 14 is connected to a feed line 17 and a discharge line 18 for an oxidizing agent, in the present case oxygen or air.

In the supply line 17 for the oxidizing agent there is a filter 20, an oxidizing agent mass sensor 21, a conveying device 22 designed as a regulated fan, a residual moisture transmitter 23, a three-way valve 24 and an arrangement 40 for heating / cooling the fuel cell 1 1 belonging heat sink 43, which takes over the function of a heat exchanger, is provided. The fan 22 is connected via an electrical connection 76 to an additional electrical power source 75 designed as a rechargeable battery and provided for the fuel cell 11. A water separator 26 is provided in the discharge line 18 for the oxidizing agent and is connected to a line 27 for discharging water. Furthermore, a pressure regulator 28 and part of the residual moisture exchanger 23 are provided in the discharge line 18.

The three-way valve 24 provided in the supply line 17 is connected to the oxidant discharge line 18 via a bypass line 25.

Finally, a check valve 29 is also provided in the oxidant discharge line 18. The oxidant discharge 18 opens into a filter element 57, in the present case an activated carbon filter.

During the operation of the fuel cell system 10, the ambient air used as the oxidizing agent is sucked in via the particle filter 20 by the regulated fan 22. The entering air mass is determined in front of the blower 22 with the air mass sensor 21. After passing through the residual moisture exchanger 23, the air mass flows through the three-way valve 24.

During the starting phase of the fuel cell system 10, no water is produced in the fuel cell 11 yet, so that the oxidant stream entering the fuel cell 11 is very dry. Such a dry oxidant flow would lead to the fuel cell 11 drying out. For this reason, in the starting phase of the fuel cell system 10, the three-way valve 24 is switched in such a way that the oxidant flow is passed via the bypass line 25 past the fuel cell 11 directly into the oxidant discharge line 18. In this way, the dry stream of oxidant cannot enter the fuel cell 11. The oxidant stream is passed through the oxidant discharge line 18 into the filter element 57 in order to rinse and regenerate it, as will be explained in more detail in the further course of the description.

Since the fuel cell 11 still does not produce sufficient power during the starting phase of the fuel cell system 10, the blower 22 and any control devices (not shown) of the valve 24 are driven by the battery 75. During normal operation of the fuel cell 11, the blower

22 and the corresponding control devices of the valve 24 are supplied with electrical current via the fuel cell 11, the battery 75 simultaneously again is charged. In this phase, the blower 22 is operated only with low power in the so-called power saving mode.

During normal operation of the fuel cell 11, in addition to heat, water is also produced, which is derived in the form of water vapor in the exhaust gas stream of the cathode part 14 via the discharge line 18. In order to be able to convert this gaseous water into the liquid state so that it is available for other processes in which water is required (for example the moistening of the oxidizing agent), the oxidizing agent containing the water vapor flows through after it has left the fuel cell 11 first the water separator 26, in which a portion of the water vapor already condenses into liquid water. The water condensed out in this way is discharged via line 27.

After exiting the water separator 26, the remaining exhaust gas stream of the oxidizing agent is expanded in the pressure regulator 28. This reduces the moisture content in the exhaust gas flow. The remaining moisture is then extracted from the gas stream by the residual moisture exchanger 23. The moisture extracted from the oxidizing agent in the residual moisture exchanger 23 is used to suitably moisten the oxidizing agent that is originally dry to the fuel cell 11 via the oxidizing agent feed line 17 and is dry. In order to bring the oxidizing agent to a suitable temperature before entering the fuel cell, the heat exchanger 43 is provided, which will be explained in more detail in the further course of the description.

A device 80 for generating / processing the fuel is also provided for generating or processing the fuel. The device 80 has a number of reactor elements which, in the present exemplary embodiment, are designed as evaporators 81, reformer 82, shift reactor 83 and partial oxidation 84. These reactor elements are connected to a fuel feed line 63 on the inlet side of the device 80 and to the fuel feed line 15 on their outlet side.

Two of the reactor elements, namely the evaporator 81 and the reformer 82, are designed as so-called heat sinks, which means that heat is required in them for operation. For this reason, the evaporator 81 and the reformer 82 are coupled to heating devices 85, 86 designed as catalytic burners. The required heat is supplied to the reactor elements during operation of the device 80 via the heating devices 85, 86. A flow circuit 88 is also provided for temperature control of the individual reactor elements conveyor 87 designed as a pump. The heating / cooling medium flowing through the flow circuit 88 absorbs the heat released in the reactor elements designed as heat sources and transports it to the reactor elements designed as a heat sink, where the heat is then transferred. The conveyor 87 regulates the flow rate and thus the flow rate of the heating / cooling medium. The conveyor 87 is connected to the additional electrical power source 75 via an electrical connection 89.

If the heat gain from the partial oxidation 83 is too small to be practically usable, the operation of the conveyor 87 during the start phase of the fuel cell system 10 can be dispensed with better, since the operation of the conveyor 87 also consumes energy.

Furthermore, the fuel cell system 10 has a fuel tank 55 for holding a fuel consisting of hydrocarbons, such as methanol, natural gas, gasoline or the like, from which hydrogen is produced in the device 80 for generating / processing the fuel. The fuel tank 55 is connected via a tank protection valve 56 to the filter element 57 designed as an activated carbon filter. Furthermore, the fuel tank 55 is connected via the fuel line 63 to the device 80 for generating / processing the fuel. In addition, two delivery devices are provided in the fuel line 63, which are designed as a fuel pump 58 and as a double pump 60. The double pump 60 is not only connected to the fuel tank 55 on the suction side, but also to a water tank 62. The fuel pump 58 and the double pump 60 are connected to the additional electrical power source 75 via corresponding electrical connections 77, 78. There is an additional fuel filter 59 between the fuel pump 58 and the double pump 60. Finally, an intermediate tank 61 is connected downstream of the double pump 60 in the fuel feed line 63.

It is possible to dispense with the fuel pump 58 if the double pump 60 takes over its work.

The heating devices 85, 86 of the device 80 for generating / processing the fuel, which are designed as burners, are connected to the fuel supply line 63 via a corresponding line 64. The line 64 is connected to the fuel line 63 in the flow direction after the fuel pump 58. The individual heating devices 85, 86 are connected to the line via corresponding branch lines 69, 70 Line 64 connected. Corresponding metering devices 66, 67 are provided in the branch lines 69, 70 for supplying a precisely defined amount of fuel to the heating devices 85, 86.

The filter element 57 is connected to a divider 71 via a feed line 72. Two lines 73, 74 come out of the divider 71, each of which is connected to the heating devices 85, 86, so that the filter element 57 is connected to the heating devices 85, 86.

A sensor element 90 for determining the concentration of pollutants, in the present case a sensor element for determining the concentration of carbon monoxide in the fuel, is provided in the feed line 15 for the fuel, which adjoins this on the outlet side of the device 80 for generating / processing the fuel , Furthermore, a three-way valve 91 is arranged in the feed line 15, which is connected to a bypass line 92 bypassing the fuel cell 11. Finally, a heat sink 44 is provided in the feed line 15, which is designed in the form of a heat exchanger. The heat sink 44 is part of the arrangement 40 for heating / cooling the fuel cell 11.

When the fuel cell system 10 is started, the hydrogen must be generated or processed as quickly as possible in the device 80. For this purpose, the fuel is pumped out of the fuel tank 55 via the fuel pump 58 and pumped into the double pump 60 through the fuel filter 59. In the double pump 60, the fuel is mixed with water taken from the water tank 62. This mixture is then temporarily stored in the intermediate tank 61 before it is introduced into the device 80 for generating / processing the fuel. In order to be able to carry out these functions reliably during the starting phase of the fuel cell system 10, the fuel pump 58 and the double pump 60 are connected to the additional electrical power source 75. In this way, they can already be operated reliably before the fuel cell 11 has reached its operational capability and can supply electrical current. The fuel mixture entering device 80 is reformed therein to produce hydrogen. The components required for this, such as the conveying device 87 or the heating devices 85, 86, if they are designed as electrical heating devices, are likewise operated via the additional electrical power source 75 during the starting phase of the fuel cell system 10. In normal operation of the fuel cell system, operation takes place via the fuel cell 11. If the heating devices 85, 86 are designed as burners, as in the case shown in the figure, they are operated on the one hand by means of the fuel removed from the fuel tank 55. For this purpose, a partial flow of the fuel is pumped via the fuel pump 58 into the branch line 64 and via this into the lines 69, 70. The quantity of fuel required for the heating devices 85, 86 is set in the metering devices 66, 67 and this is then fed into the heating devices 85, 86. The heating devices 85, 86 driven in this way can now supply the reactor elements 81, 82 which act as a heat sink with the heat required for operation.

In addition, the heating devices 85, 86 are also supplied via the filter element 57. The oxidizing agent bypassed the fuel cell 11 during the starting phase of the fuel cell system 10 is conducted into the filter element 57 through the oxidizing agent discharge line 18 and through it.

As a result, the hydrocarbons located in the filter element 57 are entrained by the oxidizing agent. The oxidant enriched in this way with fuel is passed on via the feed line 72 to the divider 71, where it is divided between the two lines 73, 74 and is then made available to the heating devices 85, 86 for combustion. On the one hand, the filter element 57 can be regenerated, on the other hand the fuel in the filter element 57 can be used to operate the heating devices 85, 86.

It is already in the start phase of the fuel pump 58 and the blower 22, both of which are driven by the additional electrical power source 75

Fuel cell system 10 possible to supply the necessary heating devices for generating / processing the fuel with energy. In this way, the starting phase of the fuel cell system 10 can be shortened considerably.

In particular during the starting phase of the fuel cell system 10, it can happen that the fuel leaving the device 80 has a concentration of certain substances that are harmful to the fuel cell 11. One such substance is carbon monoxide. In order to prevent carbon monoxide from entering the fuel cell 11, in particular during the starting phase of the fuel cell system 10, the fuel emerging from the device 80 and flowing through the feed line 15 is examined with the aid of the sensor element 90. If the sensor element 90 measures a concentration of carbon monoxide that exceeds a predetermined limit value, the three-way valve 91 switched in such a way that the fuel does not enter the fuel cell 11 via the feed line 15, but rather is led past the latter via the bypass line 92. For this purpose, the bypass line 92 is advantageously connected to the fuel line 16 from the anode part 12. The fuel that bypasses the fuel cell 11 in this way can either be derived from the fuel cell system 10 or used further. To further utilize the fuel, it can be fed into the heating devices 85, 86, for example via corresponding lines, dividers or the like, and used there to generate heat. It is also conceivable to introduce the fuel again into the device 80 for producing / processing the fuel and to subject it to a renewed reforming process.

In order to prevent carbon monoxide from penetrating into the anode space 12 of the fuel cell 11 via the fuel line 16, a corresponding valve, in particular a check valve 93, is provided in the fuel line 16 at the outlet of the fuel cell 11.

As soon as the concentration of carbon monoxide in the fuel flow has fallen below a certain limit, the valve 91 is switched over in such a way that the fuel can now enter the fuel cell 11 via the feed line 15. If the valve 91 by electrical actuators, such as those in

With regard to the three-way valve 24 that has been described, these control devices can be connected to the additional electrical power source 75 in order to enable operation at the start of the fuel cell system 10.

The fuel cell system 10 furthermore has an arrangement 40 for heating / cooling the fuel cell 1 1. The arrangement 40 has a flow line 45 designed as a closed heating / cooling circuit, which is preferably supplied by a liquid heating / cooling medium, for example water, oil or the like - the same is flowing through. For heating / cooling the fuel cell 11 is part of the

Flow line 46 connected to the fuel cell 11 such that a thermal exchange between the fuel cell 11 and the heating / cooling medium takes place or can take place in the flow line 45, 46. For this purpose, the fuel cell 11 is penetrated by the partial area 46 of the flow line 45. In this partial area 46, the flow line 45 is preferably designed as a coil. In the flow line 45 a pump 49 is also provided, via which the flow rate of the heating / cooling medium is set and regulated.

Furthermore, a cooling device 42 is provided with which the heat loss generated during operation of the fuel cell 11 can be dissipated.

A heating element 41 is provided in the flow line 45 and is connected to a heating device 48. Furthermore, an additional flow line 47 branches off from the flow line 45 behind the fuel cell 1 1, which flows back into the flow line 45 behind the heat sink 44 and in which the heat sink 43 designed as a heat exchanger is arranged, which is connected in this way parallel to the heat sink 44 ,

During the starting phase of the fuel cell system 10, the heating element 41 is supplied with heat via the heating device 48. If the heating device 48 is designed as an electrical heating device, it is preferably connected to the additional electrical power source 75 for this purpose. However, if the heating device 48 is designed as a burner or the like, as in the case shown, it is preferably connected to the line 64 via a branch line 68 and a corresponding metering device 65 and via this to the fuel line 63. Similar to the heating devices 85, 86, the heating device 48 is thus supplied with fuel. The heat generated in the heating device 48 and thus in the heating element 41 is used to heat the heating / cooling medium flowing through the flow line 45. The heating / cooling medium heated in this way is pumped into the fuel cell 11 via the conveying device 49, where it releases the heat to the fuel cell 11 and thus heats it up. At the same time, the heated heating / cooling medium is conducted via the flow line 47 into the heat sinks 43, 44, where it releases its heat to the oxidizing agent or the fuel supplied. In this way, both the oxidizing agent and the

Fuel are heated to a suitable temperature before entering the fuel cell 11.

Since the fastest possible heating of the fuel cell 11 in the starting phase of the fuel cell system 10 is advantageous, this rapid heating preferably takes place in that the conveyor device 49 is connected to the additional electrical power source 75 via an electrical connection 50 and in that the heating direction 48 fuel is made available via the fuel pump 58 connected to the additional electrical power source 75.

In normal operation of the fuel cell 11, i. H. if this produces sufficient heat loss, the heating element 41 and the heating device 48 can be switched off. The waste heat produced by the fuel cell 11 is then used to heat the fuel or the oxidizing agent via the heat sinks 43, 44. The excess heat loss of the fuel cell 11 is dissipated via the cooling device 42.

The additional electrical power source 75, which is not required during normal operation of fuel cell 11 and which can be designed, for example, as an on-board electrical system battery when fuel cell system 10 is used in a vehicle, is recharged via fuel cell 11 during normal operation thereof.

LIST OF REFERENCES

10 fuel cell system

11 = fuel cell

12 = anode part

13 = membrane

14 = cathode part

15 = fuel supply

16 = fuel discharge

17 = oxidant supply

18 - = oxidant discharge

0 - = filter

21 = oxidant mass sensor

22 = conveyor

23 = residual moisture exchanger 4 = valve (three-way valve) 5 = bypass line 6 = water separator 7 = line 8 = pressure regulator 9 =: check valve

0 = arrangement for heating / cooling the fuel cell 1 = heating element 2 = cooling device 3 = heat sink (heat exchanger) 4 = heat sink (heat exchanger) 5 = flow line 6 = partial area of the flow line 7 = flow line 8 = heating device

49 = conveyor

50 = electrical connection

55 = fuel tank

56 = tank protection valve = Activated carbon filter

= Fuel pump

= Fuel filter

= Double pump

= Intermediate tank

= Water tank

= Fuel supply

= Line

= Dosing device

= Branch line

= Divider

= Supply line

= Line

= electrical power source (battery)

= electrical connection

= Device for generating / processing fuel

= Evaporator

= Reformer

= Shift reactor

= partial oxidation

= Heating device

= Conveyor

= Flow circuit

- = electrical connection

- = concentration sensor

= Valve (three-way valve)

= Bypass line

= Check valve

Claims

claims

1. Fuel cell system, with a fuel cell (11) having an anode part (12) with a feed line (15) and a discharge line (16) for a fuel, one

Has cathode part (14) with a feed line (17) and a discharge line (18) for an oxidizing agent and a membrane (13), with a device (80) for generating / processing the fuel, which via the fuel feed line (15) to the fuel cell (11), a sensor element (90) for determining the concentration and a valve (91), which is connected to a bypass line (92) that bypasses the fuel cell (11), are provided in the fuel feed line (15) with a delivery device ( 22) and a valve (24) which are arranged in the oxidant feed line (17), the valve (24) being connected to a bypass line (25) bypassing the fuel cell (11), furthermore to a fuel tank (55), the one about a fuel supply

(63) is connected to the device (80) for producing / processing the fuel, at least one delivery device (58, 60) being provided in the fuel feed line (63), and to an additional electrical power source (75) connected to the delivery devices (22; 58, 60) is electrically connected so that they can be driven via the power source (75) during the starting phase of the fuel cell system (10).

2. Fuel cell system according to claim 1, characterized in that the additional electrical power source (75) as rechargeable

Battery or as a capacitor, in particular as a capacitor with excessive storage density ("Ultracap") is formed.

3. Fuel cell system according to one of claims 1 to 2, characterized in that two delivery devices (58, 60) are provided in the fuel feed line (63).

4. Fuel cell system according to one of claims 1 to 3, characterized in that the valves (24, 91) are designed as three-way valves.

5. Fuel cell system according to one of claims 1 to 4, characterized in that the device (80) for generating / processing the fuel has a number of reactor elements (81, 82, 83, 84), wherein individual reactor elements (81, 82) as Heat sinks are formed, each of which is thermally connected to a heating device (85, 86), which in turn is connected to the fuel supply line (63) or the electrical power source (75) for energy supply.

6. Fuel cell system according to claim 5, characterized in that for the temperature control of the reactor elements (81, 82, 83, 84) a conveyor (87) is provided, which in a through the reactor elements (81, 83, 84) continuous flow circuit (88) for a heating / cooling medium is arranged and which is connected to the electrical power source (75).

7. Fuel cell system according to one of claims 1 to 6, characterized in that the sensor element (90) is designed to determine the concentration of carbon monoxide in a gas stream, in particular in the fuel stream.

8. Fuel cell system according to one of claims 1 to 7, characterized in that the oxidant discharge line (18) is connected to a filter, in particular an activated carbon filter (57), which in turn is connected via a line to the

Fuel tank (55) is connected.

9. Fuel cell system according to claim 8, characterized in that the filter (57) is connected via a further line to at least one heating device (85, 86) of the device (80) for producing / processing the fuel.

10. Fuel cell system according to one of claims 1 to 9, characterized in that an arrangement (40) for heating / cooling the fuel cell (11) via a heating / cooling medium is provided, which has a heating device (48) which with the fuel supply line ( 63) or the additional electrical

Power source (75) is connected.

11. Fuel cell system according to claim 10, characterized in that in the arrangement (40) for heating / cooling the fuel cell (11)

Delivery device (49) for the heating / cooling medium is provided, which is connected to the additional electrical power source (75).

12. A method for starting up a fuel cell system according to one of claims 1 to 11, characterized by the following steps: a) During the starting phase, suction of oxidizing agents via the conveying device operated by the additional electrical power source into the oxidizing agent supply line and bypassing the oxidizing agent by the corresponding position of the Valve over the bypass line past the fuel cell, b) introducing fuel from a fuel tank via the at least one delivery device in the fuel supply line operated by the additional electrical power source or via a bypass line into the device for generating / processing fuel, c) measuring the pollutant concentration of the fuel leaving this device by means of the sensor element for determining the concentration and bypassing the fuel by appropriate position of the valve via the bypass line past the fuel cell , as long as the fuel for the fuel cell has harmful concentrations of pollutants, the operation of the individual conveying devices being carried out during the starting phase of the fuel cell system via the additional electrical power source and during normal operation of the fuel cell system via the fuel cell itself.

13. The method according to claim 12, characterized in that in the starting phase of the fuel cell system via the operated by the additional electrical power source at least one conveyor in the fuel supply line fuel in the heating device or

Heating devices for the reactor elements in the device for producing / processing the fuel is introduced, or that the heating device or heating devices is / are operated via the additional electrical power source, in order to supply the reactor elements with the thermal energy required for the operation of the device for producing / processing the fuel ,

14. The method according to claim 12 or 13, characterized in that in the starting phase of the fuel cell system in the device for

Generating / processing the fuel provided for a heating / cooling medium for temperature control of the reactor elements is driven by the electrical power source.

15. The method according to any one of claims 12 to 14, characterized in that in the starting phase of the fuel cell system, the bypassing the fuel cell oxidant is introduced into the filter connected to the fuel tank, in particular an activated carbon filter, to regenerate it, and. that the fueled in this way

Oxidizing agent is then fed into the heating device or heating devices of the device for generating / processing the fuel and is used for combustion in order to bring the reactor elements to temperature.

16. The method according to any one of claims 12 to 15, characterized in that in the starting phase of the fuel cell system via the operated by the additional electrical power source at least one delivery device in the fuel supply line fuel in the in the arrangement for

Heating / cooling of the fuel cell provided heating device is initiated, or that the heating device via the additional electrical Power source is operated to bring the fuel cell to the required operating temperature.

17. Vehicle with a fuel cell system according to one of claims 1 to 11

The fuel cell system has a fuel cell which has an anode part with a feed line and a discharge line for a fuel, a cathode part with a feed line and a discharge line for an oxidizing agent and a membrane. Furthermore, a device for producing / processing the fuel is provided, which is connected to the fuel cell via the fuel feed line, a sensor element for determining the concentration and a valve being connected to a bypass line bypassing the fuel cell are provided in the fuel feed line. A conveying device and a valve are arranged in the oxidant feed line, the valve having a bypassing the fuel cell

Bypass line is connected. A fuel tank is connected to the device for producing / processing the fuel via a fuel feed line, at least one delivery device being provided in the fuel feed line. The conveyors are electrically connected to a battery so that they are driven by the battery during the starting phase of the fuel cell system.