FR2883669A1 - Electricity generating system for motor vehicle, has humidifying membrane to transfer part of water vapor contained in cathodic residual gas towards air flow supplying reformer without changing phase - Google Patents

Abstract

The system has a fuel cell (3) including a cathode (5) having a cathodic exhaust port (6) through which cathodic exhaust gas is discharged into a cathodic exhaust pipe (7). The fuel cell has an anode (4) with an anodic exhaust port (8) through which anodic exhaust gas is discharged in an anodic exhaust pipe (9) towards a burner (10). A humidifying membrane (11) transfers a part of water vapor contained in the cathodic exhaust gas towards air flow supplying a reformer (2) without changing phase.

Description

Water recovery device in a water plant

  The invention relates to a power generation installation on board a motor vehicle, of the type comprising a fuel cell.

  The invention relates more particularly to an installation for producing electricity on board a motor vehicle, comprising a reformer, a fuel cell consisting of an anode and a cathode, said battery comprising at least one orifice of evacuation of cathodic residual gases which consist in particular of air and water vapor, and which are discharged into a cathodic evacuation pipe, and at least one anode residual gas outlet, which are discharged into a pipe anode discharge to a burner, said installation further comprising a means for humidifying the gases.

  Fuel cells are used in particular to provide electrical energy necessary for the propulsion of motor vehicles. The fuel cell is then embarked on board the vehicle.

  A fuel cell consists mainly of two electrodes, anode and a cathode, which are separated by an electrolyte. This type of cell allows the direct conversion into electrical energy of the energy produced by the following oxidation-reduction reactions: an oxidation reaction of a fuel, or fuel, which feeds the anode continuously; and a reduction reaction of an oxidant which feeds the cathode continuously.

  The fuel cells used to supply electrical energy in motor vehicles are generally of the solid electrolyte type, in particular with an electrolyte formed by a polymer membrane. Such a cell uses in particular hydrogen (H2) and oxygen (02) as fuel and oxidant respectively.

  Unlike thermal engines which reject with io the exhaust gas a significant amount of polluting substances, the fuel cell offers the particular advantage of rejecting mainly water that is produced by the reduction reaction at the cathode.

  The cell also rejects a portion of the unreacted oxidant as cathodic evacuation gas and eventually rejects a portion of the unreacted fuel as anode exhaust gas. In the latter case, the fuel is usually burned before being released into the atmosphere as water vapor.

  In addition, the oxidant of a battery of the type described above may be ambient air whose oxygen (02) is reduced.

  The oxidant is generally moistened before being injected at the cathode so that the membrane of polymeric material is not damaged, for example by dewatering. This humidification operation is also applied to the fuel when the latter leaves the anode via an anode outlet.

  The water required for humidification of the membrane is generally recovered at the cell outlet, and more particularly in the cathodic discharge gases which comprise water, in liquid or vapor form, which is produced by the reduction reaction of the oxidant at the cathode.

  The water recovery at the outlet of the cathode has the advantage of not having to frequently renew the water reserves of the vehicle. In addition, if enough water can be recovered to humidify the membrane, it is not necessary that the vehicle is equipped with a water tank of large volume.

  In order to recover the water produced at the cathode, it is known to arrange a condenser in the cathodic evacuation gas stream. For optimum operation of the fuel cell which is supplied with oxidant and fuel at atmospheric pressure, this type of condenser generally requires a cold source whose temperature must be maintained at between 20 and 30 ° C.

  This solution is not applicable because motor vehicles are generally designed to operate in an environment whose temperature is likely to vary between -20 C and 45 C. The use of a condenser therefore requires the use of an expensive air conditioning device that is not available on all vehicle models.

  It is therefore known to increase the pressure of the oxidant in the cathode circuit while maintaining the condenser. Indeed, by increasing the pressure of the exhaust gas containing water vapor, the dew point temperature of the water vapor is also increased. The dew point temperature is the temperature at which the water vapor condenses. A mist of condensation is deposited on the surfaces whose temperature is lower than the dew point temperature.

  Thus, when the exhaust gas is injected into the condenser, for example at a pressure of 4 bar, the cold source of the condenser must then be maintained at a temperature of approximately 60 ° C. in order to operate optimally.

  It is much easier to keep the cold source of the condenser at a temperature greater than the ambient temperature.

  However, such a solution requires a pressurization of all fuel cell fuel supply circuits under penalty of degradation of the latter. It is therefore necessary to use a significant part of the energy supplied by the battery to compress the oxidizer and fuel circuits to the detriment of the efficiency of the fuel cell.

  To solve these problems, the invention proposes an installation for producing electricity on board a motor vehicle of the type described above, characterized in that said humidifying means performs a transfer of water vapor between a stream coming from the fuel cell and a flow supplying the reformer without changing phase.

  Such a water recuperator in the form of a humidification membrane makes it possible to avoid the use of liquid water recuperators while reducing the size of the cooling circuit. Indeed, the fact of not changing phase and performing a transfer of water vapor allows on the one hand to reduce the amount of calories to be removed by the cooling circuit and on the other hand to reduce the pressure of system operation.

  According to other characteristics of the power generation installation: the gas humidification means is a humidification membrane making it possible to reduce the operating pressure of the installation; the installation comprises a compression means; 5 which feeds the cathode on the one hand and the reformer via the humidifying means on the other hand, the humidification means is inserted in the cathodic evacuation pipe, the humidification means exchange the water vapor between the flow from the cathodic residual gas outlet and the air flow fed to the reformer, which is derived from the compression means, the humidification means is inserted in the duct anodic evacuation, and - the humidification means exchange of water vapor between the flow from the anode residual gas outlet and the air flow fed to the reformer, which is derived from the compression means .

  Other characteristics and advantages of the invention will appear during the reading of the detailed description of an embodiment taken by way of non-limiting example, for the understanding of which reference will be made to the appended figures for which: FIG. 1 is a diagrammatic representation of the electricity generation installation produced according to a first embodiment, and FIG. 2 is a schematic representation of the electricity production installation produced according to a second embodiment. .

  There is shown in Figure 1 a power generation facility 1 which is here on board a motor vehicle. The installation 1 mainly comprises a fuel cell 3, the electrolyte of which is here a polymer membrane 13. The fuel cell 3 comprises an anode 4 and a cathode 5. The cathode 5 is continuously supplied with an oxidant which is here the air. The anode 4 is fed continuously with a fuel which is here mainly hydrogen (H2). The oxidizer and fuel flow rates are here regulated according to the electrical power required for the automobile vehicle.

  The fuel cell 3 comprises a first cathode circuit of oxidant, and is traversed by a second anode circuit of fuel.

  The cathode circuit includes in particular a cathode supply line 14 which is connected to a cathode supply port 15 for supplying the cathode 15 with air. The cathode 5 comprises a cathode evacuation orifice 6 through which the cathodic evacuation gases, or residual gases, that is to say not having been consumed by the cathode 5, are evacuated in an evacuation pipe cathode 7.

  The cathodic evacuation pipe 7 is connected to a humidification membrane 11. The cathodic supply pipe 14 receives the compressed air coming from a compression means 12 and includes a bypass 16 which supplies compressed air to the membrane. humidification 11.

  The compression means 12 is intended to compress the oxidant in the direction of the cathode and to supply a reformer 2 with humidified gas, via the humidification membrane 11.

  The humidifying membrane 11 is intended to transfer a portion of the water vapor contained in the cathodic evacuation gases to the air stream fed to the reformer 2.

  After passing through the humidification membrane 11, the cathodic evacuation gases are then expelled into the atmosphere via a gas expulsion pipe 17.

  The anode circuit comprises in particular a tank 18 containing a conventional fuel which is gasoline here and which is located upstream of the anode 4. The gasoline is guided by a pipe for conveying gasoline 19 from the tank 18 to reformer 2 which is intended to extract hydrogen (H2) from gasoline.

  The reformer 2 rejects a reformate containing hydrogen (H2) in an anode feed pipe 20 which is connected to an anode feed port 21 which opens at the anode 4 of the fuel cell 3.

  After consumption of a portion of the hydrogen (H2), the residual fuel is injected here via an anodic discharge pipe 9 into a burner 10 in order to be burned. The resulting exhaust gases from this operation are then discharged through an exhaust port 22 of the burner 10 into an exhaust pipe 23 of the burner 10.

  According to the second embodiment of the invention shown in FIG. 2, in which the same members have the same references, the humidification membrane 11 is here interposed in the exhaust manifold 23 of the burner 10. In this embodiment of FIG. embodiment, the anodic flow is used to transfer the water vapor it contains to the feed stream of the reformer 2.

  As for the first embodiment, the humidified compressed air 3o coming from the membrane 11 arrives in the reformer 2 via a supply pipe 24. The humidified compressed air mixes with the fuel in the pipe 19 before feeding the reformer 2.

  We will now describe the operation of such an installation 1, and in particular the operation of the humidification device 5.

  In the anode circuit, the gasoline is conducted in the reformer 2 by the fuel delivery pipe 19. The product of the reforming operation is called reformate.

  The reformate consists mainly of hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2) and water (H2O). The reformate is the fuel that feeds the anode inlet 21 through the anode feed line 20.

  In the cathode circuit, the atmospheric air is first compressed in the compression means 12 and is then admitted into the cathode supply line 14. The compressed air is then introduced to the cathode 5 through the orifice of the cathode. cathodic power supply 15.

  The fuel cell 3 is thus fueled with fuel and oxidant. Oxidation reactions at the anode 4 and reduction at the cathode 5 then allow the production of electrical energy.

  When the fuel is in contact with the anode 4, 70% to 95% of the hydrogen (H2) is oxidized here. The remainder of the fuel is discharged as anode exhaust gas to the burner 10 via the anode discharge manifold 9. According to the embodiment of FIG. 1, these gases are discharged into the atmosphere after their passage through the burner 10, which makes it possible to recover the energy of the gases that are not consumed. According to the embodiment of FIG. 2, the anodic evacuation gases first pass into the burner 10 and then into the humidification membrane 11, which transfers moisture from these gases to the flow of the gas supplying the reformer.

  When the air is in contact with the cathode 5, a portion of the oxygen (02) contained in the air is reduced to water. The surplus air and water are then discharged in the form of cathodic evacuation gas via the cathodic evacuation pipe 7. The water is present in the cathodic evacuation gases in the form of a liquid and in the form of a vapor . The cathodic evacuation gases here have a temperature of about 70.degree. C. According to the embodiment of FIG. 1, these gases are discharged in the direction of the humidifying membrane 11. According to the embodiment of the FIG. 2, the cathodic evacuation gases are directly discharged into the atmosphere or recycled to recover the liquid water they contain, for example.

  Such an installation 1 using a humidification membrane 11 makes it possible to transfer the water coming from the cell 3 to the reformer without changing state, while the liquid water recuperators require switching from a gaseous phase to a phase liquid then to a vaporization phase upstream of the reformer.

  This architecture also makes it possible to reduce the water balance stress of the installation. The water supply of the reformer 2 is done by decreasing the thermal power evacuation and decreasing the operating pressure of the fuel cell system since the need for recovery of water in liquid form decreases.

Claims (7)

  1. Electricity production plant (1) on board a motor vehicle, comprising a reformer (2), a fuel cell (3) consisting of an anode (4) and a cathode (5), said battery (3) having at least one discharge port of the residual cathodic gases (6) which consist in particular of air and water vapor, and which are discharged into a cathodic evacuation pipe (7), and at least one anode residual gas outlet (8), which is discharged into an anode discharge pipe (9) to a burner (10), said installation further comprising a gas humidification means (11). ), characterized in that said humidifying means (11) performs a transfer of water vapor between a stream from the fuel cell (3) and a flow supplying the reformer (2) without changing phase.   2. Electricity generation plant (1) according to the preceding claim, characterized in that the gas humidification means (11) is a humidification membrane for reducing the operating pressure of the installation (1) .   3. Power generation plant (1) according to one of claims 1 or 2, characterized in that it comprises a gas compression means (12) which feeds on the one hand the cathode (5) and on the other hand the reformer (2) via the humidifying means (11).   4. Electricity generation plant (1) according to one of the preceding claims, characterized in that the humidifying means (11) is interposed in the cathodic discharge pipe (7).   5. Electricity generation plant (1) according to claim 4, characterized in that the humidifying means (11) exchanges water vapor between the flow from the cathodic residual gas discharge orifice. (6) and the air stream feeding the reformer (2), which is derived from the compression means (12).   6. Electricity generation plant (1) according to one of claims 1 to 3, characterized in that the humidifying means (11) is interposed in the anode evacuation pipe (9).   7. Electricity generation plant (1) according to claim 6, characterized in that the humidifying means (11) exchanges water vapor between the flow from the anode residual gas discharge orifice. (6) and the air stream feeding the reformer (2), which is derived from the compression means (12).