Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04007—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids related to heat exchange
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
  • H01M8/04082—Arrangements for control of reactant parameters, e.g. pressure or concentration
  • H01M8/04089—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants
  • H01M8/04097—Arrangements for control of reactant parameters, e.g. pressure or concentration of gaseous reactants with recycling of the reactants
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M8/00—Fuel cells; Manufacture thereof
  • H01M8/10—Fuel cells with solid electrolytes
  • H01M2008/1095—Fuel cells with polymeric electrolytes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• the invention relates to a method of operating a fuel cell system according to the preamble of claim 1 and a fuel cell system for carrying out this method.
• a generally gaseous fuel e.g. hydrogen
• an oxidizing agent are supplied to at least one fuel cell, the fuel being electrochemically oxidized in the fuel cell.
• the chemical energy released in this way is made available by the fuel cell as usable electrical energy.
• Fuel cells with a proton exchange membrane are used particularly frequently, especially in automotive technology. With such cells it is additionally necessary to ensure sufficient humidification of the proton exchange membrane, in order to ensure optimum proton transport between the anode and cathode compartments.
• the fundamental operating parameters of such fuel cell systems are thus on the one hand the recirculation rate of unused fuel gas and on the other hand the moisture content of the in- and outflowing gases.
• the object is achieved by a method as claimed in claim 1 and a fuel cell system as claimed in claim 10.
• the partial pressure of the fuel gas in a fuel gas feed line leading to the fuel cell, and/or the partial pressure of the fuel gas in an exhaust gas discharge line of the fuel cell are measured in each case by means of a fuel gas sensor.
• a fuel gas sensor advantageously provides a further parameter for monitoring the operating state of the fuel cell.
• measurement of the reactants of the cell reaction allows more direct monitoring of the state of the cell and its material conversion.
• the flow rate of the gas in the respective line is additionally determined, such that the in each case in- or outflowing fuel gas quantity can be established from the combination of gas flow and fuel gas partial pressure.
• This may supply information about the current stoichiometry of the cell reaction. For example, it may be identified whether fuel gas and oxidizing gas are being supplied in the correct quantity ratio corresponding to the cell reaction.
• the actual fuel gas consumption of the fuel cell is additionally determined from the difference between the in- and outflowing fuel gas quantities. From these consumption values it is possible to obtain further information about the operating state of the fuel cell.
• the efficiency of the cell may be determined from the ratio between the output electrical energy and the gas used. Discrepancies between consumption and energy output allow conclusions to be drawn about gas losses in the system.
• the fuel cell's fuel gas consumption determined in this way is used as an input quantity for a control unit, which is used to control fuel gas supply and to control fuel gas recirculation to the fuel cell.
• a control unit which is used to control fuel gas supply and to control fuel gas recirculation to the fuel cell.
• the control unit may initiate the necessary countermeasures, such as for example an increase in the quantity of fuel gas supplied or an increase in the fuel gas recirculation rate.
• still further fuel cell operating parameters may be made available to this control unit, in particular the temperature of the exhaust gas flowing out of the fuel cell and the water content of this exhaust gas. This allows still more sensitive control and targeted optimization of operation of the fuel cell.
• a malfunction warning is generated. In this way, the operator of the fuel cell system may be alerted to critical malfunctions or to operating states in which there is a risk of damage to the fuel cell system.
• the values of the measured operating parameters such as fuel partial pressure, the quantity of supplied or discharged gas and the temperature or humidity of the discharged gas in the exhaust gas line are stored in a memory means. This allows subsequent diagnostic analysis of the operating state of the fuel cell and thus evaluation over an extended period. Furthermore, fuel cell system consumption data may for example be recorded over an extended period, so as to be available to the operator of the fuel cell system at a later date.
• a fuel cell system according to the invention as claimed in claim 12 is used.
• This fuel cell system consists of at least one fuel cell having a fuel gas feed line and an exhaust gas discharge line and comprises at least one fuel gas sensor in one of said lines.
• a fuel gas sensor is arranged in the fuel gas feed line downstream of the fuel gas recirculation point in the direction of flow.
• the fuel gas recirculation point is in this case the point at which the unburned fuel gas is fed back by a fuel gas recirculation means from the exhaust gas discharge line into the fuel gas feed line.
• the fuel gas partial pressure is thus determined at a point of the fuel gas feed line at which it corresponds to the fuel gas partial pressure of the gas flowing into the anode compartment.
• the measured values from the sensor may serve directly as an indication of the fuel gas quantity supplied to the fuel cell.
• a further fuel gas sensor may be arranged in the fuel gas feed line, this further fuel gas sensor measuring the fuel gas partial pressure upstream of the fuel gas recirculation point. From the difference between the measured values from the fuel gas sensors upstream and downstream of the fuel gas recirculation point, it is thus possible to determine the precise quantity of fuel gas recirculated by the fuel gas recirculation system.
• the sensors may thus be used for direct determination of the efficiency of the fuel gas recirculation system.
• an evaluation unit is provided for recording the data from the fuel gas sensors.
• the evaluation unit may advantageously be designed both for diagnosing and monitoring the operating state of the fuel cell system and for controlling further actuators in the system.
• a controllable valve is provided in the fuel gas feed line, said valve being controllable by the evaluation unit.
• fuel gas supply in the fuel cell system may be optimally regulated on the basis of the data collected by the fuel gas sensors.
• the fuel gas recirculation means is designed to be controllable by the evaluation unit. This allows fuel gas recirculation to be optimized on the basis of the data collected by the fuel gas sensors.
• a fuel cell system designated overall as 10 consists of at least one fuel cell 12 with an anode compartment 14 and a cathode compartment 16, the two compartments being separated from one another by a membrane 18.
• the fuel gas is supplied from a tank 20 via a fuel gas feed line 22 to the fuel cell, a controllable valve 24 being provided in the feed line 22 for controlling fuel gas flow between tank and fuel cell.
• fuel gas sensors 30, 30' are mounted in the feed line 22 and in the discharge line 26, these determining the partial pressure of the fuel gas and the gas flow in the respective line and communicating the values to a control unit 32.
• the control unit 32 can then control the opening state of the valve 24 and the activity of the recirculation means 28.
• valve 24 is opened further by the control unit 32, such that a greater quantity of fuel gas is made available to the fuel cell system.
• control unit 32 may close the controllable valve 24 further, in order to make a smaller quantity of fuel gas available to the fuel cell, since too much fuel gas was clearly being supplied. Furthermore, in this instance of the control device 32, it is possible to increase the activity of the fuel gas recirculation system 28, in order to prevent fuel gas from being lost via the discharge line 26 and thus into the ambient air. As a result of achieving optimum recirculation in this way, the energy efficiency of the fuel cell system is increased overall.
• control device 32 communicates both the measured data from the sensors 30, 30' and the operating states of the recirculation means 28 and of the controllable valve 24 to a memory means 34. In the context of servicing such a fuel cell system, these data may be read out of the memory means 34 again and analyzed over an extended period.
• a suitable signaling device 36 is provided, which is activated by the control means 32 if the value of one of the operating parameters of the fuel cell system exceeds or falls below a predetermined limit value, and so alerts the operator of the fuel cell system to a system malfunction.

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• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Sustainable Energy (AREA)
• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Fuel Cell (AREA)

Applications Claiming Priority (2)

Publications (2)

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Cited By (1)

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• 2008
  • 2008-05-19 DE DE102008024227A patent/DE102008024227A1/de not_active Withdrawn
• 2009
  • 2009-05-05 WO PCT/EP2009/003203 patent/WO2009141054A2/en not_active Ceased

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