FR2887371A1 - Electrical energy producing system for propulsion of motor vehicle, has fuel cell device with stack of individual cells and reformer device associated to burner, and oxygenation device oxygenating airflow supplying fuel cell device - Google Patents

Abstract

The system has condensers mounted downstream of a fuel cell device (1) which is supplied by a compressed airflow and by a flow of a hydrogen gas or hydrogen-rich gas, where a part of gas not utilized in the fuel cell device is provided to an expansion turbine (24). The fuel cell device has a stack of individual cells assembled in series and a reformer device (2) associated to a burner (3). An oxygenation device (4) mounted in a compressed air supply conduit oxygenates the compressed airflow supplying the fuel cell device. An independent claim is also included for producing electrical energy using a fuel cell device for a motor vehicle.

Description

2887371 1

  The present invention relates to the production of electrical energy by means of a fuel cell device which can be used in particular for the production of electrical energy by means of a fuel cell device which can be used in particular for the propulsion of a motor vehicle using one or more electric motors.

  Fuel cell devices which can be of different types allow the production of electrical energy for example from the consumption of hydrogen or a gas rich in hydrogen and oxygen or air. Hydrogen can for example be stored on board the vehicle. Alternatively, the hydrogen can be produced in the vehicle itself using a reformer device supplied with hydrogenated fuel such as gasoline, gas oil, ethanol, etc. Such a fuel cell generally uses as oxygen-rich gas, the outside air which contains, as is known, 21% oxygen. This air can then feed the cathode portion of the fuel cell and also serve, if necessary, the various reforming reactions for the production of hydrogen.

  A fuel cell is generally comprised of a plurality of electrochemical unit cells connected in series. The difficulties encountered during the implementation of such devices reside in the dimensions of the assembly of these cells. Indeed, to obtain the desired electrical energy, the volume and mass of the cell assembly of the fuel cell and the resulting cost, are sometimes prohibitive.

  To improve the overall efficiency of an electric power generation system comprising a fuel cell, a turbocharger is generally provided capable of raising the air pressure at the inlet of the reformer and the fuel cell. . A turbine mounted on the same shaft as the compressor can receive unburned or unused gases from a burner associated with the reformer or the cathode compartment 2847371 2 of the fuel cell. These gases, by relaxing in the turbine, allow the drive of the compressor.

  The present invention aims to further improve the performance of such a system.

  The invention also aims to facilitate the evacuation of the heat produced in the fuel cell.

  Another object of the invention is to provide an assembly of individual cells for a fuel cell which is particularly compact and therefore of a reduced cost while maintaining an acceptable level of efficiency.

  Another object of the invention is to reduce the duration of the start-up period of the system by increasing the temperature of the gases at the outlet of the burner associated with a reformer device.

  In one embodiment, the electrical energy production system, in particular for a motor vehicle, comprises a fuel cell device powered by a flow of compressed air and by a stream of hydrogen or a gas rich in hydrogen. . The system comprises a device mounted in the compressed air supply line, for the oxygen enrichment of the supply air.

  In a preferred embodiment, the oxygen enrichment device comprises a selective membrane device and means for establishing a pressure gradient, such as for example a vacuum pump mounted downstream of the enrichment device. .

  The efficiency of the fuel cell can thus be improved or the dimensions of the battery reduced for the same efficiency.

  Advantageously, the system comprises a compressor device for raising the pressure of the air supplying the various members. In this case, the vacuum pump and the enrichment device are mounted upstream of the compressor.

  The system can use hydrogen contained in a tank on the vehicle. However, the system preferably comprises a reformer device for producing a hydrogen-rich gas from a hydrocarbon fuel.

  A burner can then be associated with the reformer device.

  In an advantageous embodiment, a portion of the unused gases in the fuel cell is fed to an expansion turbine mechanically coupled to the compressor device.

  The enrichment device may for example comprise a hollow body separated by the selective membrane between an oxygen enriched permeate zone and an oxygen depleted retentate zone.

  In one embodiment, the enrichment device comprises a plurality of selectively permeable microporous fibers through which the compressed air to be enriched is circulated.

  The selective membrane (s) may be selected appropriately. They may for example comprise a copolymer of perfluoro-2,2-dimethyl-1,3-dioxole and tetrafluoroethylene.

  According to a more general aspect, the invention relates to a method of producing electrical energy by means of a fuel cell device powered by a flow of compressed air and by a flow of a gas allowing the production of electricity. electricity, such as hydrogen or a hydrogen-rich gas, in particular for a motor vehicle, comprising a preliminary step of oxygen enrichment of the air supplying the fuel cell.

  Oxygen enrichment is preferably accomplished by forcing a flow of air through one or more selective permeable membranes.

  The invention will be better understood on reading the detailed description of an embodiment given by way of example and illustrated by the appended drawing which shows schematically the general architecture of an electrical production system according to the invention.

  As illustrated in the figure, the electric power generation system comprises a fuel cell device 1, consisting of a stack of individual cells connected in series and not shown precisely in the figure. The system further comprises a reformer device 2 associated with a burner 3. Finally, the system 2887371 4 also includes a device 4 for oxygen enrichment of the supply air.

  In the illustrated example, the entire electrical energy production system is mounted in a motor vehicle. A fuel tank 5, for example gasoline or gas oil, allows the hydrogenated fuel supply of the reformer 2 through a pipe 6 and the burner 3 through a pipe 7. A water tank 8 allows the supply of fuel. reformer water 2 through line 9.

  Oxygen-enriched compressed air is fed to the reformer 2 via the pipe 10 and to the burner 3 via the pipe 11. For this purpose, an outside air flow, shown diagrammatically by the arrow 12, is fed to the device. oxygen enrichment referenced 4 as a whole.

  Oxygen air enrichment devices developed for medical applications, as described for example in US Pat. No. 6,126,721, are generally known. Such breathing aids may for example be used for example. understand selectively permeable membrane systems. Such membrane systems may for example comprise a plurality of hollow fibers coated with a suitable substrate which makes it possible to obtain the character of selective permeability desired. As described for example in US Pat. No. 6,126,721 to which reference may be made, a tubular body having a plurality of hollow fibers in communication with an inlet plenum for outside air and an exit plenum for air depleted of oxygen. The oxygen enriched air constituting the permeate, which has passed through the wall of the various hollow fibers, is then recovered on an outlet orifice.

  The electric power generation system illustrated in the attached figure is based on the same principle. A chamber 13 having one or more selectively permeable membranes generally noted 14 is mounted in the air supply line. The chamber 13 receives the outside air 12 while at the outlet 15 the permeate is air enriched with oxygen. The retentate is nitrogen-enriched and oxygen-depleted air and is discharged through line 16. To improve the operating performance of the membrane chamber 13, a vacuum pump 17 is mounted downstream of the chamber. membrane chamber 13. The vacuum pump is driven by an electric motor 18 and creates a vacuum on the outlet 15 of the membrane chamber 13. It is thus possible to obtain an oxygen-enriched air up to about 31% d 'oxygen. The establishment of a pressure gradient on either side of the chamber 13 can also be achieved by means other than the vacuum pump 17, for example by arranging a blower or any other compression device, upstream of the room 13.

  The nature of the selective membranes and the coatings which they comprise, generally consisting of polymeric materials which equip these membranes, is conventional in the field of selectively permeable membranes.

  Excellent results can be obtained for example using a copolymer of perfluoro 2,2-dimethyl 1,3-dioxole and tetrafluoroethylene. Other examples are mentioned in particular in US Pat. No. 6,126,721.

  The oxygen-enriched air thus produced is then fed to a first compression stage comprising a compressor 19 driven by an electric motor 20. At the outlet of the compressor 19, the compressed air enriched with oxygen passes through a heat exchanger 21 where it undergoes a decrease in temperature before being brought to the inlet of a turbocharger comprising a compressor 22 mounted on the same mechanical shaft 23 as a turbine 24. The air enriched in oxygen having thus undergone a second compression is brought, as it has been said previously, by the line 10 at the inlet of the reformer 2 and by the pipe 11 at the inlet of the burner 3. In addition, this oxygen-enriched air supplies the cathode compartment 25 of the fuel cell 1 with the pipe 26 after being cooled in a heat exchanger 27.

  The anode compartment 28 of the fuel cell 1 receives meanwhile through the pipe 29, the hydrogen-rich gas that has been produced in the reformer 2. A condenser 30 removes the water vapor remaining in the gas rich in water. hydrogen produced by the reformer 2.

  The hydrogen not consumed in the fuel cell 1 and from the anode compartment 28 through the outlet pipe 31 passes through a condenser 32 before being returned via the pipe 33 to the burner 3 where it participates in the generation of energy thermal.

  The compressed air that has not been used in the fuel cell 1 leaves via the pipe 34, passes through a condenser 35 before being led through the pipe 36 to the inlet of the turbine 24, which allows the The relaxed air then escapes through the exhaust pipe 37.

  A heat exchanger 38 allows the recovery of a portion of the thermal energy generated by the burner 3 and maintains the temperature of the reformer 2. The gases from the burner 3 pass through the heat exchanger 38 and are then fed through the pipe 39 at the inlet of the turbine 24.

  Thanks to the oxygen enrichment of the compressed air supplying the fuel cell, it is possible to obtain a significant increase in the overall efficiency of the electric power generation system. Alternatively, if the efficiency of the fuel cell is kept constant, it is possible to reduce the volume and mass of the stack of fuel cell units thus reducing the overall size and cost of the assembly. of the energy production system.

  The increase in the oxygen richness of the gas supplying the fuel cell makes it possible to reach more quickly the temperature necessary for the recovery of the liquid water in the condensers mounted downstream of the fuel cell. This end of condensation temperature is indeed higher at stoichiometric level given the reduction in the amount of inert gas to be cooled. This results in better thermal management of the system.

  Furthermore, the increase in oxygen richness of the gas supplying the burner makes it possible to increase the temperature of the gases at the outlet of the burner 3, resulting in a greater quantity of energy recovered on the turbine 24 and a reduction in the duration of the start phase of the burner, which allows to obtain more quickly the desired production of electrical energy by the entire system.

Claims (2)

8 claims   An electric power generating system of the type comprising a fuel cell device (1) supplied with a flow of compressed air and a flow of a gas such as hydrogen or a gas rich in hydrogen, in particular for a motor vehicle, characterized in that it comprises a device (4) for enriching the oxygen supply air, mounted in the compressed air supply line.   An electric power generation system according to claim 1, wherein the oxygen enrichment device comprises a permselective membrane (14), and a means for establishing a pressure gradient, such as a vacuum pump. (17) being mounted downstream of the enrichment device.   3. System of claim 2, in enrichment (13) compressor (19, 22).   4. System of claim 3, production of electrical energy according to which the vacuum pump (17) and the device are mounted upstream of an electric power generation device according to la comprising a reformer device (2) for producing the hydrogen-rich gas from a hydrocarbon fuel.   Electric power generation system according to claim 4, comprising a burner (3) associated with the reformer device (2).   An electric power generating system according to claims 4 or 5, wherein a portion of the unused gases in the fuel cell is supplied to an expansion turbine (24) mechanically coupled to the compressor device (22).   The electric power generation system according to one of claims 2 to 6, wherein the enrichment device comprises a hollow body separated by the selective membrane between an oxygen enriched permeate zone and a retentate zone depleted in oxygen. oxygen.   The electric power generation system according to one of claims 2 to 7, wherein the enrichment device comprises a plurality of selectively permeable microporous fibers through which the compressed air to be enriched is circulated.   The electric power generating system according to one of claims 2 to 8, wherein the at least one selective membrane comprises a copolymer of perfluoro-2,2-dimethyl-1,3-dioxole and tetrafluoroethylene.   10. A method of producing electrical energy by means of a fuel cell device powered by a flow of compressed air and by a flow of hydrogen or a gas rich in hydrogen, in particular for a motor vehicle, characterized by the fact that it comprises a preliminary stage of oxygen enrichment of the air supplying the fuel cell.   The method of claim 10, wherein the oxygen enrichment is accomplished by forcing a flow of air through one or more selective porous membranes.