EP4315463A1

EP4315463A1 - System and method for cooling a fuel cell

Info

Publication number: EP4315463A1
Application number: EP22716234.4A
Authority: EP
Inventors: Pascal SMAGUE; Jules SERY; Mickael LOSZKA
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2021-03-31
Filing date: 2022-03-18
Publication date: 2024-02-07
Also published as: FR3121554A1; KR20230163448A; JP2024514410A; FR3121554B1; WO2022207364A1

Abstract

The present invention relates to a system and method for cooling a fuel cell (1), using three circuits (c1, c2, c3) with a single radiator (6) and a single thermostat (3), wherein one of the circuits is a closed circuit according to the Rankine cycle for recovering the heat released by the fuel cell (1).

Description

SYSTEM AND METHOD FOR COOLING A FUEL CELL

Technical area

The present invention relates to the field of cooling a fuel cell, in particular an on-board fuel cell, in particular in a vehicle.

Much work is currently devoted to the development of fuel cells as sources of electrical energy for power supply, both for stationary applications and for on-board applications, in particular for vehicles driven by electrical machines. Indeed, the environmental advantages of fuel cells (high electrical and energy yields, very low emissions of harmful gases, low noise pollution, localized production, etc.) are assets that are becoming important, in particular for the field of transport.

A fuel cell transforms chemical energy into electrical energy. In the case of a hydrogen/oxygen fuel cell, the chemical reaction implemented is a combustion of hydrogen in oxygen, the reaction of which can be written by the equation:

1

H ₂ + — 0 ₂ ® H ₂ O

Within a fuel cell, the electrochemical oxidation of hydrogen is carried out at the level of an anode made of a conductive catalytic material, while the electrochemical reduction of oxygen occurs at the level of a cathode. generally made of the same catalytic material. In addition, the anodic and cathodic compartments are separated by an electrolyte allowing the exchange of protons or ions.

For motor vehicles, the fuel cells which currently prove to be the most promising are so-called proton exchange membrane cells, operating from a source of hydrogen coming either from a bottle on board the vehicle, or from a unit producing hydrogen directly in the vehicle. Thus, hydrogen can be produced directly using a reformer operating with an appropriate fuel, such as methanol, gasoline, diesel fuel, etc. In a motor vehicle of the aforementioned type, it is not only necessary to cool the electric motor ensuring the propulsion of the vehicle as well as the power control of said motor, its battery possibly if it is equipped with one, but also the fuel cell itself since this last is generating thermal losses linked to the chemical reactions taking place at the electrodes, and to ohmic losses at the membrane.

The heat generated by the fuel cell is generally waste energy, which could be interesting to recover to increase the overall efficiency of the system.

These problems related to the management of the cooling of the fuel cell are particularly constrained for on-board applications, in particular within vehicles. Indeed, the sizing of the cooling and heat recovery system must be adjusted to the available space.

Prior technique

As it is widely known, the Rankine cycle is a thermodynamic cycle by which heat from an external heat source is transmitted to a closed circuit which contains a fluid, called working fluid or heat transfer fluid. When this cycle uses an organic fluid, it is called the organic Rankine cycle or ORC. This type of cycle generally breaks down into a step during which the working fluid used in liquid form is compressed isentropically, followed by a step where this compressed liquid fluid is heated and vaporized in contact with a heat source. This vapor is then expanded, during another stage, in an isentropic manner in an expansion machine, then, in a final stage, this expanded vapor is cooled and condensed in contact with a cold source. To carry out these different steps, the circuit generally comprises a compressor pump to circulate and compress the fluid in liquid form, an evaporator which is swept by a hot fluid to achieve at least partial vaporization of the compressed fluid, an expansion machine to expand superheated steam, such as a turbine, which transforms the energy of this steam into another energy, such as mechanical or electrical energy, and a condenser through which the heat contained in the steam is transferred to a cold source, generally the outside air which sweeps this condenser or a liquid loop at low temperature, to transform this vapor into a fluid in liquid form.

In the field of fuel cells, the conventional Rankine cycles can consist of the insertion of a heat transfer fluid loop for the valuation of the heat losses of the fuel cells, this recovery can be carried out in particular on the cooling circuit of the fuel cell. Under these conditions, the recovery must be controlled in particular under cold fuel cell conditions (in temperature rise) so as not to penalize the rise in temperature of the fuel cell, which could harm its efficiency. Once the fuel cell has reached the ideal operating temperature, the thermostat located downstream of the Rankine circuit exchanger sends the excess calories from the cooling circuit not removed by the Rankine cycle back to the radiator.

On light or heavy vehicles, the increase in cooling needs and the different levels of regulation temperature, namely at high temperature (HT) from 80 to 100°C for the fuel cell and at low temperature (BT) from 30 to 60°C for the electrical machine, the batteries, the electrical components and the fuel cell power supply, require the use of several dedicated and separate cooling circuits as well as the implementation of several radiators to evacuate the calories of each circuit on the front of the vehicle. With the increasing complexity of vehicles and the addition of functions requiring cooling, the space available to house the radiators on the front panel is very limited, and requires the optimization of the available space. Very often a high temperature radiator and a low temperature radiator are thus placed in cascade one in front of the other or one next to the other with masking effects, which affects their efficiency and leaves little possibility increase in useful cooling power necessary in the event of the addition of a low temperature ORC which requires cooling on its condenser.

Patent application CN 111911254 proposes a cooling device with a shared single air radiator for cooling the ORC system and the fuel cell. This system requires both three and four way valves to allow the use of the radiator for either cooling function. Such a construction is therefore complex, with numerous actuators. In addition, the ORC cycle evaporator is placed downstream of one of the valves, which imposes a specific control for the passage of the coolant in the evaporator.

Patent application CN 110911711 concerns the coupling of a fuel cell air compressor with an ORC turbine, so as to limit the energy required for the air compressor. A single radiator is used for this system, however in this system, the ORC loop is used as a transfer loop, which requires specific integration and does not make it possible to cool the fuel cell without going through the ORC loop. Patent application JP 2009283178 concerns the coupling of an ORC system with a fuel cell for a vehicle. This coupling requires two independent radiators: one for the fuel cell and one for the ORC cycle.

In addition, several patent applications (US2016156083, US2010291455) also deal with the coupling of an ORC system with a fuel cell to recover the thermal losses of the fuel cell into electricity either on the exhaust part of the fuel cell or on the cooling part. Most of the patents relate to fuel cells typed at high temperatures (for example SOFC from the English "Solid Oxide Fuel Cell" which can be translated by solid oxide fuel cell and MCFC from the English "Molten Carbonate Fuel Cell" which can be translated as molten carbonate fuel cell) for stationary applications and therefore do not specifically address the coupling of the fuel cell cooling system and the ORC system for space saving purposes. The systems described in these patent applications cannot be used for an on-board fuel cell.

In addition, patent US10577984 relates to a solution for transferring thermal energy from a hot source (a combustion engine or another converter) to a cooling system which notably comprises an air radiator via an energy recovery system. lost thermal energy: an ORC system. In this patent, the air radiator is shared between the energy converter, here the thermal engine, and the ORC system which must be cooled at low temperature. In this patent, several architectures of cooling circuits are proposed. An elementary circuit in which only the ORC circuit is connected to the radiator (figure 1 of this patent). In this configuration, the ORC system must be able to capture all the thermal power from the engine and transfer it to the low temperature radiator via the ORC condenser. Moreover, it does not allow engine cooling in the event of failure of the ORC. The evaporator is placed on a branch of the cooling circuit of the energy converter parallel to a branch equipped with a three-way valve allowing thermostatic regulation. A pump ensures the circulation of the heat transfer fluid between the motor to be cooled and the ORC evaporator. The ORC condenser circuit is connected to the radiator but no circulation pump is used. Other architectures are proposed with one or more three-way valves (thermostated) and several pumps to allow, depending on the case, to transfer the heat from the engine to the radiator via the ORC or directly to the radiator without going through the ORC cycle. when the maximum exchange capacities of the radiator via the ORC are reached. Under these conditions, the temperature of the cooling fluid arriving at the radiator increases, which improves its exchange capacity. The performance of the ORC is then degraded because the temperature of its cold source increases. In the architectures proposed in Figures 2 and 3 of this patent, the ORC evaporator is positioned on a parallel branch and upstream of the three-way valve (thermostat), which makes it possible to offload the heat engine to the radiator in the event of thermal overload that cannot be recovered by it. In these cases, it is specified that the hot water from the engine returned to the radiator mixes with the cold water at the junction, which causes the cooling water of the ORC circuit to heat up and therefore a degradation in performance. of this one.

Summary of the invention

The aim of the invention is to cool and recover the heat of a fuel cell, with a reduced size (to facilitate its use on board, if necessary), and a simple construction. For this, the present invention relates to a system and a process for cooling a fuel cell using three circuits with a single radiator and a single thermostat, and one of the circuits being a closed circuit according to the Rankine cycle to recover the heat emitted by the fuel cell. The single heat sink and single thermostat simplify the number of components, reducing the system footprint.

The invention relates to a system for cooling a fuel cell, in particular a fuel cell able to be embarked in a vehicle, preferably a fuel cell of the proton exchange membrane type, or a solid oxide fuel cell or a molten carbonate fuel cell, said cooling system comprising three closed thermal fluid circulation circuits, a first circuit comprising at least one fuel cell, an evaporator, a first pump, a single thermostat and a heat exchanger, a second circuit comprising at least one condenser, a second pump and a heat exchanger connected in series, and a third circuit, according to the Rankine cycle, comprising at least said evaporator, said condenser, a turbine and a third pump connected in series. In this cooling system:

- a single and unique cooling fluid circulates in said first and second circuits, and a working fluid circulates in said third circuit,

- said heat exchanger of said first circuit and said heat exchanger of said second circuit are a single and unique heat exchanger, - said evaporator being configured so that said cooling fluid of said first circuit exchanges heat with said working fluid of said third circuit, and

- the condenser being configured so that said cooling fluid of said second circuit exchanges heat with said working fluid of said third circuit.

According to one embodiment, said first circuit comprises an air heater, preferably in series or in parallel with said evaporator.

In accordance with an implementation of the invention, said second circuit comprises at least one element to be cooled, preferably chosen an electric battery, preferably an electric battery connected to said fuel cell, an electric machine connected to said fuel cell, a supply of pure air or oxygen to said fuel cell, an evacuation of moist air from said fuel cell.

According to one embodiment, said third circuit comprises at least one element to be cooled, preferably a supply of pure air or oxygen to said fuel cell and/or an evacuation of humid air from said fuel cell.

According to one aspect, said thermostat is a three-way thermostat.

As a variant, said thermostat is a two-way thermostat, and said second circuit comprises a stopper valve with a non-return valve limiting circulation in one direction only.

Furthermore, the invention relates to a method for cooling a fuel cell implementing the system according to one of the preceding characteristics. For this method, a step of raising the temperature of said fuel cell is implemented, during which said thermostat is closed, and said first pump is activated.

According to one embodiment of the invention, during the step of raising the temperature of said fuel cell, said second pump is also activated.

The invention also relates to a method for cooling a fuel cell using the cooling system according to one of the preceding characteristics. For this method, an energy recovery step is implemented, during which said thermostat is closed and said first, second and third pumps are activated.

Furthermore, the invention relates to a method for cooling a fuel cell using the cooling system according to one of the preceding characteristics. For In this method, a step of operation with full charge of said fuel cell is implemented, during which said thermostat is opened and said first and second pumps are activated.

Furthermore, the invention relates to a vehicle, in particular a motor vehicle or heavy goods vehicle, comprising a fuel cell supplying power to at least one electric machine, and a cooling system according to one of the preceding characteristics, in which said heat exchanger is arranged near an air inlet.

Other characteristics and advantages of the system and of the method according to the invention will appear on reading the following description of non-limiting examples of embodiments, with reference to the appended figures and described below.

List of Figures

FIG. 1 illustrates a fuel cell cooling system according to a first embodiment of the invention.

FIG. 2 illustrates a fuel cell cooling system according to a second embodiment of the invention.

FIG. 3 illustrates a fuel cell cooling system according to a third embodiment of the invention. FIG. 4 illustrates a fuel cell cooling system according to a fourth embodiment of the invention.

FIG. 5 illustrates a fuel cell cooling system according to a fifth embodiment of the invention.

FIG. 6 illustrates a fuel cell cooling system according to a sixth embodiment of the invention.

FIG. 7 illustrates a fuel cell cooling system according to the fourth embodiment during a fuel cell temperature rise step. FIG. 8 illustrates a fuel cell cooling system according to the fifth embodiment during a fuel cell temperature rise step.

FIG. 9 illustrates a fuel cell cooling system according to the fourth embodiment during an energy recovery step.

FIG. 10 illustrates a fuel cell cooling system according to the fourth embodiment during a high load/full load operating stage of the fuel cell.

FIG. 11 illustrates a fuel cell cooling system according to the fifth embodiment during a high load/full load operation stage of the fuel cell.

Description of embodiments

The present invention relates to a cooling system for a fuel cell, preferably a fuel cell for an on-board application.

The cooling system includes three closed thermal fluid circulation circuits:

- a first circuit which comprises at least one fuel cell (for its cooling), an evaporator, a first pump, a single thermostat (single thermostat of the cooling system), and a heat exchanger,

- a second circuit which comprises, in series, at least one condenser, a second pump and a heat exchanger, which is separated from the first circuit by the thermostat of the cooling system and operates at a temperature lower than that of the first circuit.

- a third circuit according to the Rankine cycle, which includes, in series, at least an evaporator, a turbine, a condenser, and a third pump, this third circuit allows the recovery of energy and its valorization in the form of work.

According to the invention, a single and unique cooling fluid circulates in the liquid state in the first and second circuits, and a working fluid circulates in the third circuit alternately in the liquid state or in the gaseous state according to the zones of the circuit In addition, the heat exchanger of the first circuit and the heat exchanger of the second circuit are a single and unique heat exchanger. Thus, a single heat exchanger (if applicable a radiator) is used by the cooling system, which makes it possible to limit the size of the system.

Furthermore, within the evaporator, the cooling fluid of the first circuit exchanges heat with the working fluid of the third circuit, and within the condenser, the cooling fluid of the second circuit exchanges heat with the working fluid of the third circuit. third circuit work. Thus, the cooling of the fuel cell heats the cooling fluid, which heats the working fluid of the third circuit, this heat being used in the turbine of the third circuit to generate energy, for example electrical energy.

The single thermostat of the system according to the invention makes it possible to simplify the number of components, also reducing the bulk of the system while ensuring the functionality of regulating the temperature of the circuit. Thus, a cooling system of a fuel cell integrating a Rankine cycle is achieved in a simple manner.

Within each circuit, the components are connected by pipes adapted to the fluid used and to their operating conditions (in particular temperature and pressure).

Advantageously, the fuel cell can be a low-temperature fuel cell, for example a proton-exchange polymer membrane (PEM) fuel cell. This type of fuel cell is currently the most suitable for mobile applications, in particular because of its cost. Alternatively, the fuel cell can be a high temperature fuel cell, for example SOFC from the English “Solid Oxide Fuel Cell” which can be translated as solid oxide fuel cell or MCFC from the English “Molten Carbonate Fuel Cell”. which can be translated as molten carbonate fuel cell.

According to one embodiment of the invention, the first circuit can comprise a heater. This embodiment is particularly suitable for a fuel cell on board a vehicle. Indeed, the air heater can be used in particular for heating the passenger compartment of the vehicle, while allowing the heat to be evacuated from the fuel cell. In addition, the first circuit may further comprise a bypass of the air heater, in particular when the passenger compartment of the vehicle does not need to be heated.

According to an implementation of this embodiment, the air heater can be mounted in series with the evaporator. Preferably, the unit heater is the first element crossed by the cooling fluid at the outlet of the fuel cell.

Alternatively, the air heater can be mounted in parallel with the evaporator.

In accordance with one implementation of the invention, the second circuit may comprise at least one additional element to be cooled. Preferably, the additional element to be cooled is linked to the fuel cell: for example an electric battery connected to the fuel cell, an electric machine powered by the fuel cell, a supply of air or pure oxygen to the fuel cell fuel, and a water drain from the fuel cell, or any other element. Cooling the air or pure oxygen supply to the fuel cell can cool the compressed oxygen used within the fuel cell. Moisture-saturated air escaping from the fuel cell can also be cooled. Thus, the cooling system makes it possible to cool the fuel cell as well as other elements of the vehicle's powertrain, moreover in a compact way.

In accordance with one implementation of the invention, the third circuit may comprise at least one additional element to be cooled. Preferably, the element to be cooled is linked to the fuel cell: a supply of air or pure oxygen to the fuel cell, and an evacuation of moist air from the fuel cell. The cooling of the compressed air or pure oxygen supply of the fuel cell can also be carried out by this additional exchanger in the ORC loop. The humid air produced at the exhaust of the fuel cell can also be cooled. Thus, the cooling system makes it possible to cool the fuel cell, its compressed air supply as well as its humid air exhaust, in a more compact manner.

The system can include several types of heat exchangers. The air heater (if applicable) and the heat exchanger (the radiator), can be exchangers of the liquid/air type. The exchangers in the fuel cell, in the electrical machine (if applicable) and the batteries (if applicable) can be conduction exchangers between a hot body and a liquid circuit. The evaporator and the condenser can be exchangers of the liquid/liquid type.

According to one aspect of the invention, the single thermostat can be a three-way thermostat, having an input downstream of the cooling of the fuel cell, a first output connected to the heat exchanger (radiator), and a second output connected to a branch of the second circuit downstream of the condenser.

Alternatively, the single thermostat can be a two-way thermostat, having an inlet downstream of the fuel cell cooling, and an outlet connected to the heat exchanger. For this embodiment, a branch of the second circuit connected to the heat exchanger may comprise a valve limiting circulation in one direction in this branch of the second circuit, to prevent the cooling fluid downstream of the fuel cell from entering in this branch of the second circuit. This one-way flow-limiting valve can be a pilot-operated plug valve that opens or closes electrically on demand, which includes a check valve (passes in one direction only by means of a pressure differential).

According to an exemplary embodiment, the coolant may comprise a mixture of ethylene glycol and water, for example up to 30 to 40% to allow frost resistance down to -20/-30°C. The coolant may further comprise an anti-corrosion additive. Alternatively, the cooling liquid can be of any type suitable for the temperatures used by the fuel cell.

According to one implementation of the invention, the second circuit can comprise a temperature sensor for measuring the temperature of the cooling fluid entering the heat exchanger. This temperature measurement allows the monitoring of the temperature in the second circuit, and thus allows the control of the recovery by the ORC (the third circuit). Beyond a certain temperature threshold measured by this temperature sensor, and corresponding to the opening of the thermostat, recovery can be stopped by the ORC by deactivating the third, because this means that the hot fluid of the first circuit has mixed with the cold fluid from the second circuit, and that the cooling of the ORC could be insufficient to justify continuing the recovery. Figure 1 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a first embodiment of the invention. In this figure, the solid lines represent the pipes, and the arrows illustrate the air (or any other gas) coming to exchange heat in the heat exchanger 6, for example a radiator. The cooling system comprises a first circuit c1 (dotted lines), a second circuit c2 (broken line formed by an alternation of a dash and two dots) and a third circuit c3 (continuous line formed by an alternation of a dot dash). The first circuit c1 allows the cooling of the fuel cell 1. For this, it comprises a first pump 2, the fuel cell 1, a three-way thermostat 3, a heat exchanger 6 (radiator) and an evaporator 5, and pipes for connecting the various components, in particular by forming two parallel branches downstream of the cooling of the fuel cell: one comprising the evaporator 5, and one comprising the thermostat 3 and the heat exchanger 6. The second circuit c2 comprises , in series and connected by pipes, a second pump 7 and a condenser 8. In addition, the second circuit c2 comprises a temperature sensor 15 upstream of the heat exchanger 6. The third circuit c3 is a closed circuit according to the Rankine cycle, comprises in series and connected by pipes, an evaporator 5, a turbine 12, a condenser 8 and a third pump 11. The first and second circuits c1 and c2 share a single cooling fluid. The evaporator 5 of the first circuit c1 corresponds to the evaporator 5 of the third circuit c3, in which the cooling fluid of the first circuit c1 exchanges heat with the working fluid of the third circuit c3. The condenser 8 of the second circuit c2 corresponds to the condenser 8 of the third circuit c3, within which the cooling fluid of the second circuit c2 exchanges heat with the working fluid of the third circuit c3.

Figure 2 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a second embodiment of the invention. Only the elements different from the first embodiment are described. For this embodiment, the first circuit c1 further comprises a heater 4. The heater 4 is placed on the branch of the first circuit c1 which includes the evaporator 5, the heater 4 being arranged between the fuel cell 1 and the evaporator 5. In addition, the second circuit c2 comprises two additional elements to be cooled 9, 10, for example an electric battery connected to the fuel cell 1, and/or an electric machine connected to the fuel cell 1, and /or an oxygen or air supply to the fuel cell 1 , and/or a water discharge from the fuel cell 1 . The two additional elements 9, 10 to be cooled are placed in series, downstream of the condenser 8. FIG. 3 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a third embodiment of the invention. Only the elements different from the first embodiment are described. For this embodiment, the first circuit c1 further comprises a heater 4. The heater 4 is placed on the branch of the first circuit c1 which includes the evaporator 5, the heater 4 being arranged between the fuel cell 1 and the evaporator 5. In addition, the second circuit c2 comprises an additional element 9 to be cooled, for example an electric battery connected to the fuel cell 1, an electric machine connected to the fuel cell 1, an oxygen supply or air from the fuel cell 1 , and/or a water drain from the fuel cell 1 . The additional element to be cooled 9 is in series downstream of the condenser 8. In addition, the third circuit c3 comprises an additional element to be cooled 14, for example an air or oxygen supply to the fuel cell 1, and/or a evacuation of moist air from the fuel cell 1. The element to be cooled 14 is in series upstream of the evaporator 5.

Figure 4 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a fourth embodiment of the invention. Only the elements different from the first embodiment are described. In this embodiment, the only thermostat 3 is a two-way thermostat 3 (one input/one output). For this embodiment, the second circuit c2 further comprises a valve 13 limiting the flow in one direction to prevent the passage of fluid from the first thermostat in the second circuit in the opposite direction to that in the second circuit.

Figure 5 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a fifth embodiment of the invention. Only the elements different from the fourth embodiment are described. For this embodiment, the first circuit c1 further comprises a heater 4. The heater 4 is placed on the branch of the first circuit c1 which includes the evaporator 5, the heater 4 being arranged between the fuel cell 1 and the evaporator 5. In addition, the second circuit c2 comprises two additional elements to be cooled 9, 10, for example an electric battery connected to the fuel cell 1, and/or an electric machine connected to the fuel cell 1, and /or an oxygen or air supply to the fuel cell 1 , and/or a water discharge from the fuel cell 1 . The two additional elements 9, 10 to be cooled are placed in series, downstream of the condenser 8.

FIG. 6 illustrates, schematically and in a non-limiting way, a cooling system of a fuel cell according to a sixth embodiment of the invention. Only the elements different from the fourth embodiment are described. For this embodiment, the first circuit c1 further comprises a heater 4. The heater 4 is placed on the branch of the first circuit c1 which includes the evaporator 5, the heater 4 being arranged between the fuel cell 1 and the evaporator 5. In addition, the second circuit c2 comprises an additional element to be cooled 9, for example an electric battery connected to the fuel cell 1, and/or an electric machine connected to the fuel cell 1, and/or an air oxygen supply from the fuel cell 1, and/or a water discharge from the fuel cell 1. The additional element to be cooled 9 is in series downstream of the condenser 8. In addition, the third circuit c3 comprises an additional element to be cooled 14, for example an air oxygen supply to the fuel cell 1, and/or a water discharge from the fuel cell 1. The element to be cooled 14 is in series upstream of the evaporator 5.

Furthermore, the invention relates to a method for cooling a fuel cell, this method of cooling implementing the cooling system according to any one of the variants or combinations of variants described previously. The method can implement at least one of the following three steps:

- a fuel cell temperature rise step (that is to say when the fuel cell has not reached its optimum operating temperature), during which the thermostat remains closed, and the first pump is activated and the third pump is deactivated, thus the first circuit is activated while the third circuit is deactivated. Thus the heat generated by the fuel cell is conserved for its rise in temperature. According to one embodiment of this step, the second pump can also be activated if an additional element to be cooled belongs to the second circuit (for example an electric machine). For this operation, the heat exchanger is used to cool additional elements to be cooled. Alternatively (especially if the second circuit does not include additional elements to be cooled), the second pump can be deactivated.

- an energy recovery step when the fuel cell is at its operating temperature, during which the thermostat remains closed, and the three pumps are activated. Thus, the three circuits are activated, and heat is recovered by transforming it into energy by means of the Rankine cycle of the third circuit. For this step, the fuel cell is then cooled indirectly by the heat exchanger via the Rankine cycle which captures the heat at high temperature from the first circuit and returns it at low temperature to the heat exchanger via the condenser of the second circuit. The thermostat remains closed since the temperature of the fuel cell is regulated by the third circuit. This step can remain activated as long as the capacity of the third circuit to recover the heat from the fuel cell is sufficient, and the cooling capacity of the heat exchanger is sufficient to evacuate the heat from the third circuit at low temperature.

- a phase of high load / full load of the fuel cell, during which the thermostat opens, and during which the first pump and the second pump are activated, and the third pump is deactivated. Thus, the first circuit is activated, and the heat exchanger allows the direct cooling of the fuel cell. When the cooling capacities of the heat exchanger are reached or the recovery capacities of the ORC cycle turbine are saturated, the thermostat opens with the rise in temperature at the outlet of the fuel cell. Under these conditions, the first and second circuits hitherto separated are mixed. The operating conditions of this stage are achieved when the energy converter operates at high load and the heat to be evacuated becomes too great. If an additional element to be cooled (for example an electric machine, a battery) is present on the second circuit, the second pump is also activated to provide degraded cooling at high temperature to its elements. If these elements are not present on the second circuit, the second pump can be deactivated.

For these steps, the opening and closing of the thermostat are carried out automatically according to the temperature of the cooling fluid leaving the fuel cell.

FIG. 7 represents, schematically and in a non-limiting manner, the step of raising the temperature of the fuel cell for the fourth embodiment of the invention (FIG. 4) with, in addition, the presence of the heater 4 within of the first circuit. In this figure, the bold black lines represent the pipes in which a fluid circulates, and the thin gray lines represent the pipes without fluid circulation. For this embodiment, only the first pump 2 is activated and the thermostat 3 is closed, the cooling fluid then circulates successively in the fuel cell 1, the unit heater 4, the evaporator 5, and the first pump 2. Further, valve 13 is closed.

FIG. 8 represents, schematically and in a non-limiting manner, the step of raising the temperature of the fuel cell for the fifth embodiment of the invention (FIG. 5). In this figure, the bold black lines represent the pipes in which a fluid circulates, and the thin gray lines represent the pipes without fluid circulation. For this embodiment, only the first and second pumps 2 and 7 are activated and the thermostat 3 is closed; in the first circuit, the cooling fluid then circulates successively in the fuel cell 1, the unit heater 4, the evaporator 5, and the first pump 2, and in the second circuit, the cooling fluid then circulates successively in the heat exchanger 6, the second pump 7, the condenser 8, the additional elements to be cooled 9 and 10. For this operation, the valve 13 is open.

FIG. 9 represents, schematically and in a non-limiting manner, the energy recovery step for the fourth embodiment of the invention (FIG. 4) with, in addition, the presence of the heater 4 within the first circuit. In this figure, the bold black lines represent the pipes in which a fluid circulates, and the thin gray lines represent the pipes without fluid circulation. For this embodiment, the three pumps 2, 7 and 11 are activated, and the thermostat is closed: the three circuits are active. Furthermore, valve 13 is open. In the first circuit, the cooling fluid then circulates successively in the fuel cell 1, the unit heater 4, the evaporator 5, and the first pump 2. In the second circuit, the cooling fluid circulates successively in the heat exchanger 6, in the second pump 7 and in the condenser 8 and the valve 13. In the third circuit, the working fluid circulates successively in the third pump 11, in the evaporator 5, in the turbine 12 and in the condenser 8.

The fifth embodiment of Figure 5 operates in a similar way for this energy recovery step, with activation of the three pumps.

FIG. 10 represents, schematically and in a non-limiting manner, the step of high load/full load of the fuel cell for the fourth embodiment of the invention (FIG. 4) with, in addition, the presence of the heater 4 In this figure, the bold black lines represent the pipes in which a fluid circulates, and the thin gray lines represent the pipes without fluid circulation. For this embodiment, only the first pump 2 is activated and the thermostat 3 is open, the cooling fluid then circulates in the first pump 2 and the fuel cell 1, then in a first branch comprising the heater 4, the evaporator 5, and in parallel with the first branch in a second branch which comprises the thermostat 3 and the heat exchanger 6. In addition, the valve 13 is closed.

FIG. 11 represents, schematically and in a non-limiting manner, the high charge/full charge stage of the fuel cell for the fifth embodiment (FIG. 5). In this figure, the bold black lines represent the pipes in which a fluid circulates, and the thin gray lines represent the pipes without fluid circulation. For this embodiment, only the first pump 2 and the second pump 7 are activated and thermostat 3 is open. In addition, valve 13 is open but imposes the direction of fluid circulation. In the first circuit, the cooling fluid then circulates in the first pump 2 and the fuel cell 1, then in a first branch comprising the heater 4, the evaporator 5, and in parallel with the first branch in a second branch which comprises the thermostat 3 and the heat exchanger 6. In the second circuit, the cooling fluid then circulates successively through the heat exchanger 6, the second pump 7, the condenser 8, the additional elements to be cooled 9 and 10 For this step, the cooling fluid of the first circuit is mixed with the cooling fluid of the second circuit at the inlet of the heat exchanger 6. At the outlet of the heat exchanger 6, the cooling fluid is separated into two portions , one for the first circuit and the other for the second circuit.

Furthermore, the invention relates to a vehicle, in particular an automobile road vehicle or heavy goods vehicle (or also a bus, a boat, an airplane, a hovercraft, an amphibious vehicle, etc.), comprising a fuel cell supplying at least one electric machine, and a cooling system according to any one of the variants or combinations of variants described above. For this embodiment, the heat exchanger is arranged close to an air inlet: in other words, the heat exchanger is a vehicle radiator. The vehicle can implement one of the steps of the method according to any one of the variants or combinations of variants described previously.

Alternatively, the invention also relates to a fuel cell for a stationary system, the fuel cell being equipped with a cooling system according to any one of the preceding characteristics. The fuel cell can implement one of the steps of the method according to any one of the variants or combinations of variants described previously.

Claims

1. System for cooling a fuel cell (1), in particular a fuel cell able to be embarked in a vehicle, preferably a fuel cell of the proton exchange membrane type, or a solid oxide fuel cell or a molten carbonate fuel cell, said cooling system comprising three closed circuits (c1, c2, c3) for circulating thermal fluid, a first circuit (c1) comprising at least one fuel cell (1), an evaporator (5 ), a first pump (2), a single thermostat (3) and a heat exchanger (6), a second circuit (c2) comprising at least one condenser (8), a second pump (7) and a heat exchanger (6) connected in series, and a third circuit (c3), according to the Rankine cycle, comprising at least said evaporator (5), a turbine (12), said condenser (8), and a third pump (11) connected in series, characterized in that:

- a single and unique cooling fluid circulates in said first (c1) and second (c2) circuits, and a working fluid circulates in said third circuit (c3),

- said heat exchanger (6) of said first circuit (c1) and said heat exchanger (6) of said second circuit (c2) are a single and unique heat exchanger (6),

- said evaporator (5) being configured so that said cooling fluid of said first circuit (c1) exchanges heat with said working fluid of said third circuit (c3), and

- the condenser (8) being configured so that said cooling fluid of said second circuit (c2) exchanges heat with said working fluid of said third circuit (c3).

2. Cooling system according to claim 1, wherein said first circuit (c1) comprises a heater (4), preferably in series or in parallel with said evaporator (5).

3. Cooling system according to one of the preceding claims, wherein said second circuit (c2) comprises at least one element to be cooled (9, 10), preferably chosen an electric battery, preferably an electric battery connected to said battery. fuel (1), an electrical machine connected to said fuel cell (1), a supply of pure air or oxygen to said fuel cell (1), an evacuation of humid air from said fuel cell (1).

4. Cooling system according to one of the preceding claims, wherein said third circuit (c3) comprises at least one element to be cooled (14), preferably a supply of pure air or oxygen to said fuel cell (1) and/or an evacuation of moist air from said fuel cell (1).

5. Cooling system according to one of the preceding claims, wherein said thermostat (3) is a three-way thermostat.

6. Cooling system according to one of claims 1 to 4, wherein said thermostat (3) is a two-way thermostat, and said second circuit comprises a plug valve with check valve (13) limiting circulation in one direction. unique.

7. Method for cooling a fuel cell implementing the system according to one of the preceding claims, characterized in that a step of raising the temperature of said fuel cell (1) is implemented, during which said thermostat (3) is closed, and said first pump (2) is activated.

8. Cooling method according to claim 7, wherein during the step of raising the temperature of said fuel cell (1), said second pump (7) is also activated.

9. A process for cooling a fuel cell using the cooling system according to one of claims 1 to 6, characterized in that an energy recovery step is implemented, during which said thermostat (3) and said first (2), second (7) and third (11) pumps are activated.

10. A method of cooling a fuel cell using the cooling system according to one of claims 1 to 6, characterized in that a step of operating at full load of said fuel cell is implemented ( 1), during which said thermostat (3) is opened and said first (2) and second (7) pumps are activated.

11. Vehicle, in particular motor vehicle or heavy goods vehicle, comprising a fuel cell (1) supplying at least one electric machine, and a cooling system according to one of claims 1 to 6, in which said heat exchanger (6) is arranged near an air inlet.