FR2872960A1 - Cooling system for fuel cell, has deionization reservoir disposed in heat transfer fluid circulation path and having anode and cathode electrodes that are immersed in circulating heat transfer fluid to traverse reservoir to de-ionize fluid - Google Patents

Abstract

The system has a deionization reservoir (5) disposed in a heat transfer fluid circulation path (1) and including anode and cathode electrodes (6, 7) that are immersed in a circulating heat transfer fluid (8) to traverse the reservoir to de-ionize the fluid. Hydrogen and oxygen recovering ends are formed at respective ends of electrodes, and conduits and non return valves are coupled to fuel cell supply circuits.

Description

The present invention relates to a cooling system for a battery

combustible.

  A fuel cell is an electrochemical device that converts chemical energy into electrical energy from a fuel, usually hydrogen, and an oxidant, oxygen, or an oxygen-containing gas such as the air.

  A fuel cell comprises two anodic and cathodic porous electrodes each comprising an active layer which are the seat of the respectively anodic and cathodic reactions: Anodic reaction: H2 - * 2e- + 2H + Cathode reaction: 02 + 2H + + 2e- - * H2O These anodic and cathodic reactions induce a global reaction leading to the only formation of water accompanied by a release of heat and production of electricity.

  A fuel cell, consisting of a stack of cells in series, can generate voltages and power required and can be used to provide electrical power to any device such as for example a computer, a mobile phone but it can be also used to provide traction for a motor vehicle and / or supply electrical devices contained in a vehicle.

  Structurally, a fuel cell cell mainly comprises an electrolyte which is sandwiched between the respectively anodic and cathodic porous electrodes and which provides the proton transfer between these electrodes.

  For this purpose, the electrolyte may for example be a solid polymer electrolyte, the resulting cell being of the PCESP type (polymeric solid electrolyte fuel cell) or more particularly a proton exchange membrane, the resulting cell being a PCMEP type cell. (proton exchange membrane fuel cell), the latter type of fuel cell being particularly interesting for automotive traction provided that it ensures the membrane a certain humidity.

  The electrolyte may be a polymer membrane with a thickness of 15 to 200 m.

  The electrode-electrolyte-electrode assembly is itself interposed between two bipolar plates mainly ensuring the collection of the current and also generally the distribution of the reactive gases.

  Since the overall reaction of the fuel cell is exothermic, the bipolar plates also provide for the distribution of a coolant intended to cool the cell and to maintain the core of the cell at a temperature of less than 90 ° C since beyond this temperature the performance of current batteries are reduced.

  Among the heat transfer fluids used, deionized water has many of the properties required for heat transfer fluids, namely a high electrical resistivity of the order of 18 MS2.cm, a specific heat, a thermal conductivity, as well as a low viscosity and an ignition temperature above 90 C.

  However, the strong corrosivity of the deionized water leads to the presence, over time, of organic and inorganic ions from the tearing of metal particles and / or polymers of the materials in contact with the fluid in the cooling circuit. .

  However, it is preferable that a coolant has a low conductivity, preferably less than 5 cm.sup.-1, to avoid current leakage and short circuits.

  Another disadvantage of deionized water is that the water freezes at 0 C which prevents its use in cold environments.

  This disadvantage, however, is easily solved by the addition or use of heat transfer fluids known in the automotive field which remain in liquid form at temperatures below 0 C.

  For example, it is known to add to the deionized water one or more known antifreezes such as ethylene glycol and / or propylene glycol.

  However, this type of addition leads to the increase in the conductivity of the coolant due to the presence of pH stabilizers and salt-based corrosion inhibitors normally used in such additives.

  In addition, the glycols decompose to form glycolic, glyoxylic and formic acids which, on the one hand, accelerate the corrosion processes of components of the cooling system, and on the other hand contribute to the increase of the conductivity of the heat transfer fluid. .

  There are ion-exchange resin-based filters that are used to maintain low electrical conductivity by retaining the ions produced and released.

  The major disadvantage of the use of these filters is the need to regularly replace the resins to ensure low conductivity.

  To increase the life of the resins, their dimensions can be increased with consequent increased bulk of the filtration system.

  The other solutions currently developed consist of the use of hydrocarbon, silicone or perfluorinated heat transfer fluids.

  However, hydrocarbon and silicone fluids are often flammable and / or incompatible with the materials commonly used for joints, pipes and tubes such as silicone, EPDM.

  Also, the high costs of fluoridated fluids reserve them rather for military and space applications and environmental constraints restrict the use of many fluorinated products.

  In this context, the invention aims a cooling system meeting the needs described above and to overcome the aforementioned drawbacks.

  For this purpose, the cooling system for a fuel cell comprising means for circulating and cooling an aqueous heat-transfer fluid making it possible to ensure continuous cooling of said stack is essentially characterized in that it further comprises a deionization tank 5 disposed in the circulation line 1 of the coolant and comprising at least two respectively anodic electrode 6 and cathode 7 to which a potential is applied and which are immersed in the coolant 8 flowing through the deionization tank 5 so to ensure the deionization of the coolant 8.

  Advantageously, the system of the invention also comprises recovery means 13, 14 of the hydrogen and oxygen formed at the respectively cathodic electrode 7 and anode 6 and circulation means 11, 12, 15, 16 of hydrogen and oxygen from the deionization tank 5 to the respective fuel supply circuits 18 and oxidant 17 of the fuel cell 2.

  For this purpose, the system can provide that two suitable conduits 11, 12 cover at their respective ends 13, 14 at least partially the respectively anodic electrode 6 and cathodic electrode 7 and that each of the conduits 11, 12 comprises at least a simple anti-condensation valve. 15, 16 or a pump 15, 16 according to the pressure of the fluids in the lines for conveying hydrogen and oxygen to the respective fuel supply circuits 18 and oxidant 17 of the fuel cell 2.

  Preferably, the system of the invention comprises a residual particles and ions retention filter 10, 24 which is arranged in the circulation line 1 of the coolant at a place where the heat transfer fluid 8 which passes through it has already undergone the deionization operation in the deionization tank 5.

  It can thus be provided that a filter 24 is placed in the deionization tank 5 at the outlet of the heat transfer fluid.

  Alternatively, a filter 10 may be provided in the fluid circulation line 1 downstream of the deionization tank (5).

  Very advantageously, the system of the invention also comprises means 19,20,22 for conveying the water produced in the fuel cell 2 to the deionization tank 5 in order to compensate for the water deficit in the reservoir deionization 5, from the production of hydrogen and oxygen at the respectively cathodic electrode 7 and anodic 6.

  In this sense, a water / gas separator 20 can be arranged at the outlet of the fuel cell 2 and thus the water produced by the cell 2 can flow to the deionization tank 5.

  According to the invention, it can be provided that the potential applied to the electrodes 6, 7 is at least derived from a converter 9a supplied by the fuel cell 2.

  It is also possible to provide that a portion of the potential applied to the electrodes 6, 7 comes from a battery 23.

  Also, the coolant 8 used may be deionized water or a mixture of deionized water and antifreeze commonly used.

  Finally, it can be provided that the cooling means 3 of the coolant is a heat exchanger 3 which is disposed downstream of the deionization tank 5.

  The invention will be better understood and other objects, advantages and characteristics thereof will appear more clearly on reading the description which follows and which is made with reference to the accompanying drawings which show non-limiting examples of embodiment of the method and of the device of the invention and in which: - Figure 1 is a block diagram functional system of the invention according to a first embodiment; FIG. 2 is a functional block diagram of the system of the invention according to a second embodiment; and FIG. 3 is a functional block diagram of a portion of the system of the invention according to a third embodiment.

  Referring to Figure 1, the cooling system of the invention comprises a circulation line 1 of the aqueous heat transfer fluid including the fuel cell 2 and more particularly the bipolar plates of the fuel cell which are not shown.

  This circulation line 1 comprises a pump 4 and a heat exchanger 3 adapted to cool the aqueous heat transfer fluid before its circulation within the stack 2.

  According to the invention, the cooling system comprises a deionization tank 5 which is also arranged in the circulation line 1 upstream of the heat exchanger 3 and which comprises two respectively anodic electrode 6 and cathode electrode 7 immersed in the heat transfer fluid 8 through the deionization tank.

  In the case of a traction application of a motor vehicle, the fuel cell 2 supplies the motor 9 of the vehicle and the two electrodes are also electrically powered by the fuel cell 2 via a converter 9a.

  Thus, when the heat transfer fluid 8 passes through the deionization tank 5 containing the two electrodes 6, 7 in operation, the anions and cations contained in the fluid accumulate around the respectively anodic electrode 6 and cathodic electrode 7 by electrical attraction.

  The fluid at the outlet of the deionization tank 5 is thus depleted of ions, its electrical conductivity therefore remains low enough to prevent current leakage and / or short circuits.

  According to the embodiment presented in this figure, there is provided a filter the addition of the filter is optimal retention of particles and residual ions 10 disposed in the circulation line 1 downstream of the deionization tank 5 and upstream of the exchanger 3.

  This filter makes it possible to recover the ions and the neutral particles remaining in the fluid 8 after passing through the deionization tank 5.

  According to the invention, the cooling system also comprises two ducts 11, 12 whose respective ends 13, 14 cover at least partly the respectively anodic electrode 6 and cathodic electrode 7 and each of which is arranged a pump at least a single valve anti -return 15, 16 or a pump 15, 16 according to the pressure of the fluids in the lines, allowing the circulation, through the conduits 11, 12, of the gases emitted respectively by the anodic electrode 6 and the cathode electrode 7, namely the oxygen and hydrogen.

  According to the invention, the oxygen and the hydrogen recovered at the respectively anodic electrode 6 and cathode 7 are conveyed in the respective ducts 11, 12 to the fuel supply lines 17 and fuel 18 of the battery fuel.

  By this system, the phenomena of overpressure in the tank 5 are avoided and the fuel and fuel supply of the fuel cell are enriched respectively in hydrogen and oxygen.

  The production of hydrogen and oxygen at the respectively cathodic and anodic electrodes causes consumption of the water contained in the coolant.

  To compensate for this consumption of water, the system of the invention provides that part of the water produced by the cell is recovered and then added to the deionization tank.

  For this, a mixture of water and gas is recovered at the outlet of the fuel cell 2 and transported via a conduit 19 to a water / gas separator 20 from which the gas 21 and the water which is supplied by via a conduit 22 to the deionization tank 5.

  With reference to FIG. 2, the cooling system of the invention according to a second embodiment provides that the respectively anodic electrode 6 and cathode electrode 7 are powered by a secondary battery 23.

  With reference to FIG. 3, in the cooling system of the invention according to a third embodiment, the retention filter for the residual particles and ions 10 is disposed in the deionization tank 5, which makes it possible to reduce the bulk of the Cooling system.

  The system of the invention is not limited to the embodiments described above.

  For example, it is possible to provide, in the system of the invention, a deionization tank containing more than two electrodes.

  Of course, although the cooling systems represented in FIGS. 1 to 3 relate to fuel cell systems used in the automotive field, it is possible to provide for the use of the cooling system for fuel cells applied to another domain. .

2872960 10

Claims (13)

  A cooling system for a fuel cell comprising means for circulating and cooling an aqueous heat transfer fluid for cooling said cell, characterized in that it further comprises a deionization tank (5). disposed in the circulation line (1) of the coolant and comprising at least two electrodes respectively anode (6) and cathodic (7) to which a potential is applied and which are immersed in the coolant (8) flowing through the reservoir of deionization (5) so as to ensure the deionization of the coolant (8).   2. System according to claim 1, characterized in that it comprises recovery means (13, 14) of hydrogen and oxygen formed at the respectively cathodic electrode (7) and anodic (6) and means for circulating (11, 12, 15, 16) hydrogen and oxygen from the deionization tank (5) to the respective fuel (18) and oxidizer (17) feed circuits of the fuel cell (2).   3. System according to claim 2, characterized in that two ducts (11, 12) suitable cover at their respective ends (13, 14) at least partially respectively the electrodes respectively anode (6) and cathode (7) and in that each conduits (11, 12) comprise at least a single non-return valve 15, 16 or a pump (15, 16) according to the pressure of the fluids in the lines for conveying the hydrogen and the oxygen to the circulating circuits. respective fuel supply (18) and oxidant (17) of the fuel cell (2).   4. System according to any one of the preceding claims, characterized in that it comprises a residual particle and ion retention filter (10, 24) which is arranged in the circulation line (1) of the heat transfer fluid to a where the heat transfer fluid (8) passing through it has already undergone the deionization operation in the deionization tank (5).   5. System according to claim 4, characterized in that the filter (24) is disposed in the deionization tank (5) at the outlet of the heat transfer fluid.   6. System according to claim 4, characterized in that the filter (10) is disposed in the fluid flow line (1) downstream of the deionization tank (5).   7. System according to any one of the preceding claims, characterized in that it comprises means (19, 20, 22) for conveying the water produced in the fuel cell (2) to the deionization tank. (5) in order to compensate for the water deficit in the deionization tank (5) resulting from the production of hydrogen and oxygen at the respectively cathodic (7) and anodic (6) electrodes.   8. System according to claim 7, characterized in that it comprises a water / gas separator (20) disposed at the outlet of the fuel cell (2) through which water, produced by the battery (2), flows until to the deionization tank (5).   9. System according to any one of the preceding claims, characterized in that the potential applied to the electrodes (6, 7) is at least derived from a converter (9a) fed by the fuel cell (2).   10. System according to any one of the preceding claims, characterized in that at least a portion of the potential applied to the electrodes (6, 7) is derived from a battery (23).   11. System according to any one of the preceding claims, characterized in that the coolant (8) is deionized water.   12. System according to any one of claims 1 to 10, characterized in that the coolant (8) comprises deionized water and at least one commonly used antifreeze.   13. System according to any one of the preceding claims, characterized in that the cooling means (3) of the coolant is a heat exchanger (3) which is disposed downstream of the deionization tank (5).