Method and device for operating fuel cells

Abstract

A system and method for operating a fuel-cell system, which is attached to at least one further component via a cooling and/or lubricating circuit. A water-based, oil-free coolant and lubricant is used, and a flushing procedure for the fuel cell is initiated when a contamination of the fuel cell by the water-based, oil-free coolant and lubricant is detected.

Claims

1. A method for operating a fuel-cell system, the method comprising: connecting the fuel-cell system to a compressor using a cooling and lubricating circuit that uses a water-based, oil-free coolant and lubricant to lubricate the compressor; lubricating a bearing point with the water-based, oil-free coolant and lubricant, the bearing point being a connection between the compressor and a drive motor; detecting whether the water-based, oil free coolant and lubricant, that lubricated the bearing point, has contaminated at least one fuel cell of the fuel-cell system; and initiating, upon detection that the water-based, oil free coolant and lubricant has contaminated the at least one fuel cell, a flushing sequence to remove the water-based, oil free coolant and lubricant from the at least one fuel cell.

2. The method of claim 1, wherein the water-based, oil-free coolant and lubricant contains water-soluble additives.

3. The method of claim 1, wherein the fuel-cell system is attached to auxiliary assemblies of a vehicle.

4. The method of claim 3, wherein the fuel-cell system and the attached auxiliary assemblies have a shared cooling-lubricant circuit.

5. The method of claim 1, wherein the flushing sequence is performed using additional water to the water-based, oil-free coolant and lubricant.

6. The method of claim 1, wherein: detection of the contamination includes detecting a power drop by conducting measurements including at least one from the group consisting of current measurement, impedance measurement, exhaust gas measurements on the anode side, exhaust gas measurements on the cathode side and cyclic voltammetry.

7. The method of claim 1, wherein the flushing sequence is performed by introducing additional moisture from a humidifier via an air supply line.

8. The method of claim 1, wherein: the flushing sequence is performed by multiple repetitions of the flushing sequence and/or by single or multiple combination of different methods of flushing; and the flushing sequence is terminated using a drying process.

9. The method of claim 1, further comprising cooling the at least one fuel cell with the water-based, oil free coolant and lubricant.

Description

DRAWINGS

(1) Embodiments are described by way of example below with reference to the drawings.

(2) FIG. 1 illustrates a schematic view of a fuel-cell system, in accordance with embodiments.

(3) FIG. 2 illustrates a sectional view of a conventional fuel cell.

DESCRIPTION

(4) FIG. 1 illustrates a fuel-cell system in accordance with embodiments, in which an air supply occurs via a compressor having electric motor attached via a bearing. A cooling-lubricating circuit for the combination of the heat exchanger of the fuel cell air supply and the electric motor windings of the compressor is illustrated. The illustration of the switching valves is omitted for reasons of comprehensibility. Further components which the same lubricating and cooling circuit could use are also not illustrated. Although embodiments are exemplary, separate cooling/lubricating circuits may also be integrated in the system.

(5) The fuel cell 20 is connected via an inflow 3 to a heat exchanger 11. The heat exchanger 11 is connected via an inflow 2 of heat exchanger 11 to an air compressor 10. The air compressor 10 is operatively connected via a bearing 41 to a drive motor 10′. On the side of the inflow to the fuel cell 3, a humidifier 12 is located, which is attached via an inflow of the humidifier on the inlet side 5′ to the inflow of the fuel cell 20 and has a further attachment 6′ as the inflow to the hydrogen feed 6. On the outlet side, the fuel cell 20 has a hydrogen exhaust gas 7. In addition, an outflow 4 is provided, which is connected via a pressure regulating valve 14 to a condenser 13. The condenser 13 has a discharge 8, and also an inflow to the humidifier on the outlet side 5.

(6) The fuel-cell system additionally has a regulator unit 30, which is operatively connected via a connection 31 to an energy accumulator. Furthermore, the regulator unit 30 may be operatively connected to the controller of the vehicle itself via further signal connections. The regulator unit 30 may have operative connections to the different assemblies of the fuel-cell system.

(7) Thus, there is a control connection 33 for the drive motor 10′, a connection 34 for measuring/detecting and controlling the air mass flow, a connection 35 for analyzing a sensor signal, sensor signal connections 36, 37 for CO.sub.2 analysis, and also the connection 38 to analyze the current of the fuel cell 20 and a connection 39 to analyze the voltage. The arrangement of the measurement and control signals is exemplary and may vary in the number and position. The control unit 30 does not have to be part of the fuel-cell system, but rather may be integrated in further control units located in the vehicle.

(8) The cooling and lubricating circuit is illustrated by way of example by dashed lines in the upper part of FIG. 1. Using pump unit 40, the process medium is distributed via fluid lines 42 to the various components, such as, for example, the heat exchanger 11, the drive motor 10′ and also the bearing 41.

(9) In the case of an operationally-ready fuel-cell system, in the event of a power demand, for example, by actuating a gas pedal, and by way of the signaling 32 to the regulator unit 30, ambient air 1 is accordingly suctioned in by the compressor 10, compressed, and delivered by the cooler/heat exchanger 11 to the fuel cell 20 having integrated cooling and heating system. The compressor 10 is driven by the electric motor 10′ via conventional roller or friction bearings 41 having bearing lubrication. The oil-free, water-soluble lubricant is delivered in this illustration by a pump unit having cooler 40 through lines 42 to the heat exchanger 11, through the bearing point 41 and the winding heads of the electric motor 10′.

(10) It is also possible to lubricate and cool conventional turbochargers, as are also used in vehicles driven by internal combustion engines, using a bearing lubricant having an aqueous or aqueous-glycol, oil-free basis, and to achieve a complete regeneration of the fuel cell by flushing after the establishment of a power drop due to contamination or blockage of active surfaces, caused by leaks in the compressor or turbocharger.

(11) The use of conventional turbochargers as air compressors 10 for fuel cells is simple and inexpensive, wherein a lubricant on an oil-free basis is used instead of oil, more precisely: a coolant and lubricant on an aqueous basis or aqueous-glycol basis. The aqueous lubricant for the turbocharger bearing lubrication may be optionally combined or used as a transmission lubricant in vehicles, as a coolant in the overall vehicle system, as a coolant of the fuel cell, as a bearing lubricant exclusively in the compressor, or as a coolant for electric motors, also having the power electronics thereof and the batteries.

(12) The lubricant and coolant used preferably has a composition in this case of: 5 to 90 wt.-% water, in particular 10, 20, or 40 to 80 wt.-% water and/or 0 to 70 wt.-% alcohol, in particular 5 to 70 wt.-% alcohol or in particular 10 to 50 wt.-% alcohol and/or 0 to 20 wt.-% additives of other types. The additives are, for example, corrosion protection agents, stabilizers, defoaming agents, etc., wherein all additives are water-soluble, however.

(13) The fuel cell 20 is supplied approximately at the same time with hydrogen via the hydrogen feed 6. On the exhaust gas side 7, in the fuel cell 20 on the hydrogen side, the medium is either recirculated into the hydrogen feed 6, which is not illustrated in the figure, and/or supplied to the condenser 13. Also on the exhaust gas side, on the air side, the enriched air having water is supplied corresponding to the outflow 4 via the pressure regulating valve 14 to the condenser 13. The water obtained is either supplied to an external use corresponding to the discharge 8, or supplied to the humidifier 12 via the inflow line of the humidifier outlet side 5.

(14) The humidifier 12 ensures via the inflow humidifier inlet side 5′ that on the air side, the proportion of moisture in the inflow of the fuel cell 3 is sufficiently high that no drying out of the fuel cell membrane occurs. Via the inflow line of hydrogen 6′, moisture may additionally also be supplied to the hydrogen side.

(15) If the water-based lubricant enters the fuel cell in the event of leaks in the bearing 41, this fuel cell is “contaminated”, but is not damaged, since the fuel cell may be completely regenerated and cleaned again using flushing procedures.

(16) The method is not restricted to PEMFC fuel cells, since other fuel cells (for example, AFC=alkaline fuel cell or DMFC=direct methanol fuel cell) also use air.

(17) The water contained in the lubricant alone would not make a flushing procedure necessary, if the lubricant should enter the fuel cell as a result of leaks. However, a flushing procedure is certainly necessary if the glycol possibly contained in the lubricant or another additive contained in the lubricant (for example, defoaming agent, corrosion protection agent, etc.) enters the fuel cell.

(18) Since speed-dependent, load-dependent, pressure-dependent, and/or temperature-dependent leaks may occur in the compressor in the direction of the air delivery side and further in the direction of the fuel cell, a power drop is recognizable in the case of a contamination of active catalyst surfaces in the fuel cell. These power drops due to contaminations may be detected by current-voltage measurement, impedance or harmonic distortion analyses, exhaust gas measurements on the anode and/or cathode side, and by cyclic voltammetry.

(19) The flushing procedures set forth in following examples 1-9 generate more water in the fuel cell than is provided by normal operation, whereby the contaminations and impurities of the fuel cell are flushed out more rapidly.

(20) Depending on the flushing procedure or the duration thereof, the fuel cell regenerates, i.e., an existing lubricant film on the active surfaces of the fuel cell dissolves in water and may be blown out using air or using the fuel or humidified air.

(21) Depending on the intensity of the contamination and the operating state of the fuel cell 20, different measures may be used for flushing in accordance with embodiments.

Example 1

(22) Additional moisture is supplied through the channels 51 of the cathode side 57 bipolar plate 53 from the humidifier 12 via the supply line 5′ of the air supply line 3. The accumulated, water-soluble lubricant is thus diluted in the channels 51, dissolved out of the membrane 56 and the gas distributor layer 52, and then continuously blown out, until the measurement results show cleaning of the fuel cell 20.

Example 2

(23) The pressure in the channels 51 of the fuel cell 20 is raised via a pressure regulator 14 on the cathode side 57, whereby the percentage proportion of the ambient humidity increases at constant moisture supply and the flushing procedure results.

Example 3

(24) The method requires a decrease of the air lambda value on the cathode side 57, which means that more moisture is present in the airstream. This has the result that the resulting product water on the active layers of the membrane 56 forms a higher relative ambient humidity or also results in aerosol formation and up to liquid water droplet formation in the cathode-side channels 51 of the fuel cell 20 or in the outlet region of the cathode air and thus allows the flushing procedure.

Example 4

(25) By cooling humidified cathode air by way of an external cooling device, which is not illustrated in the figure, the fuel cell 20 is flushed during operation or also during the shutdown procedures on the bipolar plates 53. This has the result that the resulting product water on the active layers of the membrane 56 forms a higher relative ambient humidity or also results in aerosol formation up to liquid water droplet formation in the cathode side 57 channels 51 of the fuel cell or in the outlet region of the cathode air and thus allows the flushing procedure.

Example 5

(26) The flushing procedure is also triggered by electrical power reduction at the fuel cell 20, since thus the ratio of air to the quantities of water still present in the fuel cell 20 is temporarily changed in such a manner that a brief moisture excess arises on the cathode side 57, which allows the flushing procedure.

Example 6

(27) Additional moisture is supplied from the humidifier 12 via the supply line 6′ of the hydrogen supply line 6 and the channels 55 in the bipolar plate 53. The moisture is transferred from the anode side 58 to the cathode side 57 via the gas distributor layer 52′ and the membrane 56 of the fuel cell 20. The water-soluble lubricant is thus diluted and dissolved from the membrane 56 and the gas distributor layer 52 and may be blown out from the air side using the introduced air.

Example 7

(28) The fuel cell is cleaned by direct introduction of liquid water to flush the cathode circuit 57 with electrically deactivated fuel cell and subsequent blowing out.

Example 8

(29) By introducing warm, moist air on the cathode side 57 with electrically deactivated and cold fuel cell, condensation is triggered, which in turn causes dilution and dissolving of the lubricant on the membrane 56 and the gas distributor layer 52 and may subsequently be blown out.

Example 9

(30) By combining decreased pressure by way of the pressure regulator 14 with increased ambient humidity from the humidifier 12 in the supply line 3, dissolving and blowing out of contaminants on the membrane is also achieved.

(31) The flushing procedures described as examples may be carried out multiple times in succession, or chronologically superimposed and/or successively in combined form.

(32) Offset in time from the flushing procedure, in all mentioned examples, possibilities for washing out existing lubricant films and liquid water, droplet, or aerosol formation resulting therefrom, the blowing out process or drying process may be carried out, wherein either the moisture is reduced, or the pressure and the temperature are adapted to the required operating state, or the amount of air is increased depending on the flushing procedure, so that the membrane 56 is also dried up to a drying state which does not damage the membrane. The drying process may already be initiated during the flushing procedures, but is always carried out as a final process after the flushing procedures.

(33) The contaminated condensate which is obtained during the flushing procedures in the condenser 13 is supplied via the discharge 8 to an external use.

(34) The term “coupled” or “connected” may be used herein to refer to any type of relationship, direct or indirect, between the components in question, and may apply to electrical, mechanical, fluid, optical, electromagnetic, electromechanical or other connections. In addition, the terms “first,” “second,” etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated.

(35) Those skilled in the art will appreciate from the foregoing description that the broad techniques of the embodiments may be implemented in a variety of forms. Therefore, while the embodiments have been described in connection with particular examples thereof, the true scope of the embodiments should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.

LIST OF REFERENCE SIGNS

(36) 1 supply of ambient air 2 inflow to heat exchanger 3 inflow to fuel cell 4 outflow 5 inflow to humidifier outlet side 5′ inflow to humidifier inlet side 6 hydrogen feed 6′ inflow of humidifier hydrogen 7 hydrogen exhaust gas 10 air compressor 10′ drive motor 11 heat exchanger 12 humidifier 13 condenser 14 pressure regulating valve 20 fuel cell having cooling-heating system 30 regulator unit 31 connection to energy accumulator 32 signal of gas pedal 33 controller of drive motor 34 air mass flow 35 sensor 36 sensor CO.sub.2 37 sensor CO.sub.2 38 signal current 39 voltage 40 pump unit 41 bearing 42 lines 51 channels 52 gas distributor layer 53 bipolar plate 54 sealing end fittings 55 channels 56 membrane-electrode unit (MEA) 57 cathode side 58 anode side