WO2009083118A1

WO2009083118A1 - Supply system for at least one fuel cell stack, method and jet pump in the supply system

Info

Publication number: WO2009083118A1
Application number: PCT/EP2008/010630
Authority: WO
Inventors: Matthias Jesse; Cosimo S. Mazzotta; Klaus Scherbacher; Thomas Baur; Thomas Winkeler
Original assignee: Daimler Ag; Ford Global Technologies, Llc
Priority date: 2008-01-02
Filing date: 2008-12-15
Publication date: 2009-07-09
Also published as: DE102008003034A1

Abstract

The object of the invention is further to improve the fitness for everyday use of a fuel cell system. To this end, a supply system 5 is provided for at least one fuel cell stack 2, having at least one media line 8 for feeding and/or removing media into, inside or from the fuel cell stack 2, having at least one functional element 19, the functional element 19 being connected for flow purposes at an end region of the media line 8 and being designed to modify the flow state of the medium being conveyed, and having a heating device 9 for heating the functional element 19 and optionally the media line 8, the heating device 9 being arranged and/or designed to transfer the heating energy to the functional element 19 in a manner concentrated locally onto the end region of the media line and/or independently of and/or parallel to the media line 8.

Description

SUPPLY SYSTEM FOR AT LEAST ONE FUEL CELL STACK, METHOD AND JET

PUMP IN THE SUPPLY SYSTEM

The invention relates to a supply system for at least one fuel cell stack, having at least one media line for feeding and/or removing media into or from the fuel cell stack, having at least one functional element, the functional element being connected for flow purposes in an end region of the media line and being designed to modify the flow state of the medium being conveyed, and having a heating device for heating the functional element and optionally the media line, and to a control method and to a jet pump for the supply system.

The purpose of fuel cell systems is to generate electrical energy on the basis of an electrochemical process, a fuel, often hydrogen, being used, together with an oxidizing agent, often ambient air, to convert chemical energy into electrical energy. An important field of application of such fuel cell systems relates to the generation of driving energy for vehicles, which may thus be operated independently of fossil fuels.

Although the underlying electrochemical process has long been known, it is a technical challenge to design fuel cell systems such that they perform their task robustly and reliably in everyday life.

For example, water management in the fuel cell systems is very important, since on the one hand the electrode membrane dividing the electrode areas has always to be kept sufficiently moist when in operation in order to prevent premature wear, while on the other hand water is formed during the electrochemical reaction which has to be removed. To control the water balance, it is conventional on the one hand to provide dehumidifying means for draining away the water formed and humidifying means for moistening the membrane.

Publication DE 10013687 A1 relates to a fuel cell system having a fuel cell unit and an installation for humidifying process gases, wherein water-conveying media lines of the fuel cell unit are provided at least in part as heatable media lines. According to the above publication this construction has the advantage that the process water part of the water balance may be kept liquid in the media lines irrespective of ambient conditions and the risk of blockage of media lines and/or of valves and pumps arranged in the media lines as a result of water freeze-out is avoided.

The object of the invention is further to improve the fitness for everyday use of a fuel cell system.

This object is achieved with a supply system for at least one fuel cell stack having the features of claim 1 , with a method for controlling the supply system having the features of claim 12, and with a jet pump having the features of c laim 15. Preferred or advantageous embodiments of the invention are disclosed by the subclaims, the following description and the attached figures.

According to the invention, a supply system is proposed which is suitable and/or designed for supplying at least one fuel cell stack. The at least one fuel cell stack and the supply system preferably form a fuel cell system which is designed to supply energy to a drive train in a vehicle. The fuel cell stack comprises a plurality of fuel cells, preferably over 100, which each have a cathode and an anode area, these being separated from one another by an electrode membrane, in particular a proton exchange membrane.

To feed and/or remove media, in particular process water, oxidizing agent gases or fuel gas, into, inside or from the fuel cell stack, the supply system comprises at least one media line, these preferably taking the form of pipes with or without bends.

The supply system comprises at least one functional element, which is preferably connected for flow purposes directly in an end region of the media line and is designed to modify the flow state of the medium being conveyed. The flow state is modified in particular by switching, mixing, throttling and/or with regard to the flow rate or the density distribution of the medium.

In addition, the supply system comprises a heating device, which is provided for heating the functional element and optionally the media line.

It is proposed according to the invention that the heating device be arranged and/or designed in such a way that the heating energy is transferred to the functional element in a manner concentrated locally onto the end region of the media line and/or independently of and/or parallel, in particular substantially or predominantly parallel, to the media line.

One concept behind the invention is to heat just the area of the functional element rather than the entire media line and thus to transfer the thermal energy from the heating device primarily, for the most part, to a considerable extent and/or solely to the functional element instead of to the media line. In particular, at least a major part of the thermal energy transferred to the functional element is introduced into the functional element without being transferred via the media line.

With this inventive development it is ensured that the supply system can be thawed in relevant areas by the heating device even in cold operating states, in particular in frozen states, without the entire media line being heated. This procedure results in a marked saving in the energy required for heating. If one thinks that in particular in a mobile fuel cell system in a vehicle only limited amounts of stored energy are available prior to startup of the fuel cell system, the advantage is achieved that the energy resources of the storage means are conserved. In addition it is possible to carry out thawing of the relevant areas more quickly, such that fitness for use under freezing conditions may be increased markedly.

In a preferred embodiment of the invention, the functional element takes the form of a component critical with regard to freezing and preferably is embodied as a nozzle, valve or throttle. In particular, the components critical with regard to freezing have flow areas for the medium which are distinguished by a small cross-section, in particular a smaller cross-section than the media line. In a particularly preferred embodiment of the invention, the functional element takes the form of a motive nozzle in a jet pump or momentum exchanger, in particular a jet pump for accelerating or compressing the fuel for the fuel cell stack.

The jet pump is inserted in the supply system in order to accelerate a gas recirculated in an anode circuit by means of motive gas fed through the motive nozzle, in particular in the form of hydrogen from a storage tank or from a reformer, by way of momentum transfer.

In a preferred further development of the invention, the supply system comprises the jet pump, as has just been described, the heating device being incorporated into a housing of the jet pump. Preferably, this housing comprises a port for the media line. In this further development, the transfer of heating energy from the heating device to the functional element takes place inside the housing and independently of the media line.

In a particularly preferred structural embodiment, the jet pump comprises a main body, which is preferably of one piece construction and which bears or forms the functional element, the heating device being incorporated into the main body, such that the heating energy is transferred via the main body to the functional element.

In a particularly preferred configuration, the motive nozzle for fresh hydrogen and the main flow nozzle for recirculated hydrogen are incorporated into the main body.

It is additionally preferable for the heating device to be fixed detachably in the main body, i.e. to be of plug-in or screw-in construction, for example.

In a particularly preferred embodiment of the invention, the heating device takes the form of an electric heater, which is in thermal contact with the functional element. Preferably, the thermal contact is such that a majority of the transferred heating power flows from the heating device to the functional element independently of the media line.

In a modification of the invention, the heating device takes the form of an electrochemical heater, wherein the heating energy is generated by a catalyst and the medium being conveyed, in particular hydrogen. In a preferred embodiment, the heating device takes the form of a coating on the functional element and/or of a catalytic reaction layer. Further alternatives for configuring the heating device are IR/NIR radiation emitters. In order to make the heating device intrinsically safe, i.e. to ensure that it may for example continue to be operated in the event of a fault without this resulting in disadvantageous consequential damage, provision is preferably made for the heating device to be gas- insulated from the medium being conveyed.

In a further development of the invention, the supply system comprises an open-loop control device for actuating the heating device, which is or may be coupled for signalling purposes to a temperature sensor and/or a fuel cell stack operation detector.

This further development of the invention enables implementation of a method for controlling the supply system according to claim 12, which constitutes a further subject matter of the invention.

In the method according to the invention, the heating device is controlled, in particular by open-loop or closed-loop control, in dependence on temperature and/or on the operating state of the fuel cell stack or of the fuel cell system.

Temperature-dependent open-loop control here proceeds for example optionally by means of evaluation of a local temperature in the area of the functional element, an overall temperature of the fuel cell stack and/or an external temperature, i.e. an outside temperature.

In a first possible mode of operation of the method according to the invention, the heating device is activated to de-ice the functional element and/or during the start phase of the fuel cell stack. In this mode of operation, it is possible, owing to the particular structural configuration of the supply system, to manage with very low heating energies, for example less than 100 watt, preferably less than 50 watt, heating power.

In a further possible mode of operation of the method according to the invention, the heating device is activated to prevent condensate and/or during a cooling-down phase of the fuel cell stack. Because the heating device is switched on during operation or during the cooling-down phase of the fuel cell stack, the dew point at the motive nozzle is shifted, such that no or less condensate is formed on the motive nozzle. The supply system, in particular the heating device may also optionally be used advantageously during operation of the fuel cell stack to thaw ice particles during operation or to evaporate water after operation. In the various modes of operation, the heating device may be operated at various heating powers.

The invention further provides a jet pump having the features of claim 15 optionally in conjunction with any desired features of the above-described jet pump.

Further features, advantages and effects of the invention are revealed by the following f igures showing a preferred exemplary embodiment of the invention. In the figures: Figure 1 shows a schematic block diagram of a supply system as an exemplary embodiment of the invention;

Figure 2 is a schematic representation of a portion of the motive jet pump of Figure 1.

Figure 1 shows a fuel cell system 1 as is used for example in vehicles for supplying electrical energy to the drive train. The fuel cell system 1 comprises at least one fuel cell stack 2 with a plurality of fuel cells, which each comprise an anode area 3 and a cathode area 4, as are summarized schematically in Figure 1.

To supply the anode area 3 with hydrogen, the fuel cell system 1 comprises a supply system 5, which conveys unused hydrogen from a tank 6 via a pump device 7 into the anode area 3. The hydrogen which has been partially used after the electrochemical reaction is fed back from the anode area 3 via a recirculation arrangement 8 to the pump device 7, mixed therein with fresh or unused hydrogen from the tank 6 and passed back into the anode area 3.

To ensure robust, trouble-free operating behaviour of the fuel cell system 1 , a heating device 9 is incorporated into the pump device 7, said heating device being designed and/or arranged to heat locally and/or selectively components in the pump device 7 which are critical with regard to freezing. By incorporating the heating device 9 into the pump device 7, it is possible to warm up or de-ice these components which are critical with regard to freezing with only very low energy input. For open-loop control of the heating device 9, the latter is connected to an open-loop control device 10, which controls the heating device 9 on the basis of temperature and/or operating mode. The open-loop control device 10 is connected to a first temperature sensor 11 , which records the temperature in the pump device 7 or in the area of the pump device 7. Alternatively or in addition, the open-loop control device 10 is connected to a second temperature sensor 12, which records the outside temperature. Optionally, the open-loop control device 10 is connected for signalling purposes to an operating mode detector 13, which supplies a signal to the open-loop control device 10 as a function of the operating mode, in particular with regard to a start phase or a cooling-down phase of the fuel cell system 1.

On the basis of the input signals from the first temperature sensor 11 , the second temperature sensor 12 or the operating mode detector 13, the heating device 9 is activated for example in the start phase at temperatures of below 0° C. Alternatively or in addition, the heating device 9 is activated during a cooling-down phase of the fuel cell system 1 or of the fuel cell stack 2, in order to shift the dew point in the area of the pump device 7 and stop water from condensing out. In a further possible mode of operation, the pump device 7 is heated in order to evaporate condensate which arises.

Figure 2 shows the pump device 7 in a highly schematic cross-sectional representation, not to scale, in the mixing area for the recirculated hydrogen gas 14 and the fresh hydrogen gas 15 fed in from the tank 6. The pump device 7 takes the form of a momentum exchanger, wherein in the acceleration stage shown the recirculated hydrogen gas 14 is accelerated by the fed-in hydrogen gas 15 acting as motive gas by way of momentum transfer.

The pump device 7 comprises a main body 16, in which a cone 17 for guiding the recirculated hydrogen gas 14 is introduced. On the wall side and parallel to the longitudinal extension of the cone 17, individual bores 18 are introduced, which act as motive nozzles 19. The motive nozzles 19 are preferably distributed regularly around the cone 17 in the circumferential direction.

At low temperatures in particular, the motive nozzles 19 are components critical with regard to freezing due to their small clear diameters. In order to ensure operating reliability of the pump device 7 even at low temperatures, the heating device 9 is incorporated therein, the latter taking the form of a pin-shaped electric heater, which is screwed or plugged into the main body 16 in the immediate vicinity of the motive nozzle 19. Due to the physical proximity of heating devices 9 and motive nozzle 19 it is possible, even at low temperatures, to thaw the motive nozzle 19 within a few seconds, in particular in under 10 seconds with a heating power of less than 50 watt.

The heating device 9 thus enables thawing of ice particles prior to operation, thawing of ice particles during operation, evaporation of water after operation and shifting of the dew point at the motive nozzle, such that no or little condensate is present on the motive nozzle 19. A further advantage of the heating concept illustrated in Figure 2 is that the heating device 9 is spatially separated from the medium hydrogen being conveyed, such that the heating device 9 is intrinsically safe, i.e. it may continue to be operated, such as for example in the event of a fault, without this leading to consequential damage.

In modified embodiments the local heating of the motive nozzles 19 is brought about by other types of heating devices, for instance a similar effect is achieved for example by applying a catalytic reaction layer to the walls of the motive nozzles, such that heating is implemented by way of the heat which arises upon chemical or physical effects in a manner similar to a catalytic burner or a hybrid hydrogen reservoir. Further options for the heating device 9 are IR/NIR radiation emitters.

Claims

Patent Claims

1. A supply system (5) for at least one fuel cell stack (2) ,

having at least one media line (8) for feeding and/or removing media into, inside or from the fuel cell stack (2), having at least one functional element (19), the functional element (19) being connected for flow purposes at an end region of the media line (8) and being designed to modify the flow state of the medium being conveyed, and having a heating device (9) for heating the functional element (19) and optionally the media line (8), characterized in that the heating device (9) is arranged and/or designed so as to transfer the heating energy to the functional element (19) in a manner concentrated locally onto the end region of the media line and/or independently of and/or parallel to the media line (8).

2. The supply system (5) as claimed in claim 1 , characterized in that the functional element (19) takes the form of a component critical with regard to freezing.

3. The supply system (5) as claimed in claim 1 or 2, characterized in that the functional element (19) takes the form of a nozzle, valve or throttle.

4. The supply system (5) as claimed in one of the preceding claims, characterized in that the functional element takes the form of a motive nozzle (19) in a jet pump (7) for accelerating or compressing the fuel.

5. The supply system (5) as claimed in one of the preceding claims, characterized by a or the jet pump (7), the heating device (9) being incorporated into the housing of the jet pump (7).

6. The supply system (5) as claimed in claim 5, characterized in that the heating device (9) is incorporated into a main body (16) of the jet pump (7), which bears or forms the functional element (19).

7. The supply system (5) as claimed in claim 6, characterized in that the motive nozzle (19) and a main flow nozzle (17) are incorporated into the main body.

8. The supply system (5) as claimed in one of the preceding claims, characterized in that the heating device (9) takes the form of an electric heater.

9. The supply system (5) as claimed in one of preceding cairns 1 to 8, characterized in that the heating device (9) takes the form of a chemical heater, preferably of a coating on the functional element, in particular of a catalytic reaction layer.

10. The supply system (5) as claimed in one of the preceding claims, characterized in that the heating device (9) is gas-insulated from the medium being conveyed.

11. The supply system (5) as claimed in one of the preceding claims, characterized by an open-loop control device (10) for actuating the heating device (9) and a temperature sensor (11 , 12) and/or a fuel cell stack operating mode detector (13), which is or are coupled to the open-loop control device (10) for signalling purposes.

12. A method for controlling the supply system (5) as claimed in one of the preceding claims, characterized in that the heating device (9) is open-loop controlled in dependence on temperature and/or in dependence on the operating state of the fuel cell stack (2).

13. The method as claimed in claim 12, characterized in that the heating device (9) is activated to de-ice the functional element (19) and/or during the start phase of the fuel cell stack (2).

14. The method as claimed in one of the preceding claims, characterized in that the heating device (9) is activated to prevent condensate and/or during a cooling-down phase of the fuel cell stack (2).

15. A jet pump (7) for connection to at least one media line, in particular for the supply system as claimed in one of the preceding claims, having at least one or the functional element (19), the functional element (19) being designed to modify the flow state of the medium being conveyed in the jet pump (7), characterized by an incorporated or the heating device (9), the heating device (9) being designed and/or arranged to transfer heating energy to the functional element (19).